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Sample records for density sintered silicon

  1. Sintering of nano crystalline o silicon carbide doping with

    Indian Academy of Sciences (India)

    Sinterable silicon carbide powders were prepared by attrition milling and chemical processing of an acheson type -SiC. Pressureless sintering of these powders was achieved by addition of aluminium nitride together with carbon. Nearly 99% sintered density was obtained. The mechanism of sintering was studied by ...

  2. Mechanical characteristics of microwave sintered silicon carbide

    Indian Academy of Sciences (India)

    In firing of products by conventionally sintered process, SiC grain gets oxidized producing SiO2 (∼ 32 wt%) and deteriorates the quality of the product substantially. Partially sintered silicon carbide by such a method is a useful material for a varieties of applications ranging from kiln furniture to membrane material.

  3. Sintered ceramics having controlled density and porosity

    International Nuclear Information System (INIS)

    Brassfield, H.C.; DeHollander, W.R.; Nivas, Y.

    1980-01-01

    A new method was developed for sintering ceramic uranium dioxide powders, in which ammonium oxalate is admixed with the powder prior to being pressed into a cylindrical green body, so that the end-point density of the final nuclear-reactor fuel product can be controlled. When the green body is heated, the ammonium oxalate decomposes and leaves discrete porosity in the sintered body, which corresponds to the ammonium oxalate regions in the green body. Thus the end-point density of the sintered body is a function of the amount of ammonium oxalate added. The final density of the sintered product is about 90-97% of the theoretical. The addition of ammonium oxalate also allows control of the pore size and distribution throughout the fuel. The process leaves substantially no impurities in the sintered strucuture. (DN)

  4. Mechanical characteristics of microwave sintered silicon carbide

    Indian Academy of Sciences (India)

    Unknown

    sintered process, SiC grain gets oxidized producing SiO2 (∼ 32 wt%) and deteriorates the quality of the product substantially. Partially sintered .... product, could be due to oxidation of SiC, e.g. 50% weight gain of a green SiC sample ... because, the charging current is 90° advanced in phase, ideally, with respect to the ...

  5. Non-pressurized sintered silicon carbide with titanium carbide reinforcement

    International Nuclear Information System (INIS)

    Adler, J.

    1992-01-01

    A non-pressurized compression of SiC-TiC composite materials can be achieved via liquid phase sintering by the application of oxidic additives. Materials with TiC proportions up to 40% by volume of TiC and densities of 97 to 98% TD were produced at sintering temperatures around 1875 C. With SiC sintered in the liquid phase an increase of toughness at fracture of 80% compared with conventionally non-pressurized sintered SiC was achieved with B/C additive. No further increase could be achieved by the addition of TiC particles. However, the oxidation resistance at 1200 C was worsened. (orig.) [de

  6. Effects of Sintering Temperature on the Density And Porosity of ...

    African Journals Online (AJOL)

    Effects of sintering temperature on the density and porosity of sodium chloride preforms for alu- minium foam manufacturing have been investigated. Cold pressed salt preforms were sintered at 30, 760 and 790 and di erent times ranging between 6- 18 hours in a carbolite furnace at a heating rate of 5/minute. The Results of ...

  7. Comparative Evaluations and Microstructure: Mechanical Property Relations of Sintered Silicon Carbide Consolidated by Various Techniques

    Science.gov (United States)

    Barick, Prasenjit; Chatterjee, Arya; Majumdar, Bhaskar; Saha, Bhaskar Prasad; Mitra, Rahul

    2018-04-01

    A comparative evaluation between pressureless or self-sintered silicon carbide (SSiC), hot-pressed silicon carbide (HP-SiC), and spark plasma-sintered silicon carbide (SPS-SiC) has been carried out with emphasis on examination of their microstructures and mechanical properties. The effect of sample dimensions on density and properties of SPS-SiC has been also examined. Elastic modulus, flexural strength, and fracture toughness measured by indentation or testing of single-edge notched beam specimens have been found to follow the following trend, HP-SiC > SSiC > SPS-SiC. The SPS-SiC samples have shown size-dependent densification and mechanical properties, with the smaller sample exhibiting superior properties. The mechanical properties of sintered SiC samples appear to be influenced by relative density, grain size, and morphology, as well as the existence of intergranular glassy phase. Studies of fracture surface morphologies have revealed the mechanism of failure to be transgranular in SSiC or HP-SiC, and intergranular in case of SPS-SiC, indicating the dominating influence of grain size and α-SiC formation with high aspect ratio.

  8. Low density, variation in sintered density and high nitrogen in uranium dioxide

    International Nuclear Information System (INIS)

    Balakrishna, Palanki; Murty, B.N.; Anuradha, M.; Nageshwara Rao, P.; Jayaraj, R.N.; Ganguly, C.

    2000-01-01

    Low sintered density and density variation in sintered UO 2 were found to have been caused by non uniformity in the granule feed characteristics to the compacting press. The nitrogen impurity content of sintered UO 2 was found to be sintering furnace related and associated with low sintered density pellets. The problems of low density, variation in sintered density and high nitrogen could be solved by the replacement of the prevailing four punch precompaction by a single punch process; by the introduction of a vibro-sieve for the separation of fine particles from the press feed granules; by innovation in the powder feed shoe design for simultaneous and uniform dispensing of powder in all the die holes; by increasing the final compaction pressure and by modifying the gas flows and preheat temperature in the sintering furnace. (author)

  9. Sintering of nano crystalline α silicon carbide by doping with boron ...

    Indian Academy of Sciences (India)

    Unknown

    tions, they concluded that either reaction sintering or liquid phase .... α-6H silicon carbide single crystal by three different laboratories ... silicon carbide particles by the overall reaction .... layer displacement is likely to occur in such a manner as.

  10. Manufacture of sintered bricks of high density from beryllium oxide

    International Nuclear Information System (INIS)

    Pointud, R.; Rispal, Ch.; Le Garec, M.

    1959-01-01

    Beryllium oxide bricks of nuclear purity 100 x 100 x 50 and 100 x 100 x 100 mm of very high density (between 2.85 and 3.00) are manufactured by sintering under pressure in graphite moulds at temperatures between 1,750 and 1,850 deg. C, and under a pressure of 150 kg/cm 2 . The physico-chemical state of the saw material is of considerable importance with regard to the success of the sintering operation. In addition, a study of the sintering of a BeO mixture with 3 to 5 per cent of boron introduced in the form of boric acid, boron carbide or elementary boron shows that high densities can only be obtained by sintering under pressure. For technical reasons of manufacture, only the mixture based on boron carbide is used. The sintering is carried out in graphite moulds at 1500 deg. C under 150 kg/cm 2 pressure, and bricks can be obtained with density between 2,85 and 2,90. Laboratory studies and the industrial manufacture of various sinters are described in detail. (author) [fr

  11. Sintering of nano crystalline α silicon carbide by doping with boron ...

    Indian Academy of Sciences (India)

    Sinterable nano silicon carbide powders of mean particle size (37 nm) were prepared by attrition milling and chemical processing of an acheson type alpha silicon carbide having mean particle size of 0.39 m (390 nm). Pressureless sintering of these powders was achieved by addition of boron carbide of 0.5 wt% together ...

  12. The influence of processing conditions on the microstructure and the mechanical properties of reaction sintered silicon nitride

    International Nuclear Information System (INIS)

    Heinrich, J.

    1979-09-01

    The microstructure of reaction sintered silicon nitride (RBSN) was changed in a wide range of varying green density, grain size of the silicon starting powder, nitriding conditions, and by introducing artificial pores. The influence of single microstructural parameters on mechanical properties like room temperature strength, creep behaviour, and resistance to thermal shock has been investigated. The essential factors influencing these properties were found to be total porosity, pore size distribution, and the fractions of α- and β-Si 3 N 4 . In view of high temperature engineering applications of RBSN possibilities to optimize the material's properties by controlled processing are discussed. (orig.) [de

  13. Implementation Challenges for Sintered Silicon Carbide Fiber Bonded Ceramic Materials for High Temperature Applications

    Science.gov (United States)

    Singh, M.

    2011-01-01

    During the last decades, a number of fiber reinforced ceramic composites have been developed and tested for various aerospace and ground based applications. However, a number of challenges still remain slowing the wide scale implementation of these materials. In addition to continuous fiber reinforced composites, other innovative materials have been developed including the fibrous monoliths and sintered fiber bonded ceramics. The sintered silicon carbide fiber bonded ceramics have been fabricated by the hot pressing and sintering of silicon carbide fibers. However, in this system reliable property database as well as various issues related to thermomechanical performance, integration, and fabrication of large and complex shape components has yet to be addressed. In this presentation, thermomechanical properties of sintered silicon carbide fiber bonded ceramics (as fabricated and joined) will be presented. In addition, critical need for manufacturing and integration technologies in successful implementation of these materials will be discussed.

  14. Effects of sintering temperature on the density and porosity

    African Journals Online (AJOL)

    2013-03-01

    bonding) between the salt beads at all the temperatures in which sintering was performed. .... and the sintering of some covalent solids and low- stability ceramics. The entire sintering process is gen- erally considered to occur in ...

  15. Microstructure and properties of sintered silicon carbides fabricated by different methods

    International Nuclear Information System (INIS)

    Maruyama, Tadashi; Kitamura, Hideya; Iseki, Takayoshi

    1986-01-01

    Studies were made of effects of fabrication methods on the properties and microstructure of sintered silicon carbides. The specimens used in this investigation were three kinds of commercially available SiC bodies which were fabricated by reaction bonding, pressureless sintering and hot-pressing. The hot-pressed SiC contained a small amount of BeO. Measurements were carried out on density, the polytype by X-ray diffraction method and 4-point bend strength. Microstructural observation was also carried out using an optical microscope, a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The results of density measurement showed that the open porosities of three specimens were negligibly small and that the density of the hot pressed SiC had nearly the theoretical density. The measurement of 4-point bend strength indicated that the reaction bonded SiC had the highest value and the hot-pressed SiC the lowest. The analysis of the polytype indicated that all the specimens consisted mainly of α-SiC of 6 H type. In the reaction bonded SiC, about 11 % of 3 C type (β-SiC) and 9 % of free Si were recognized. The average grain diameter and fracture mode of each specimen were determined from observation with an optical microscope and SEM. In the hot-pressed SiC, the fracture occurred mainly at grain boundaries, whereas it occurred mostly in grains in the reaction bonded and pressureless sintered SiC. A lot of stacking faults were observed in all the specimens with a TEM. In addition, small closed pores were often recognized in the pressureless sintered SiC. In the hot-pressed SiC, a contrast originated from strain field within grains was observed, and dislocations near grain boundaries were a characteristic feature of this material. Small short partial dislocations accompanied by stacking fault were often observed in the reaction bonded SiC. (author)

  16. Density determination of sintered ceramic nuclear fuel materials

    International Nuclear Information System (INIS)

    Landspersky, H.; Medek, J.

    1980-01-01

    The feasibility was tested of using solids for pycnometric determination of the density of uranium dioxide-based sintered ceramic fuel materials manufactured by the sol-gel method in the shape of spherical particles of 0.7 to 1.0 mm in size and of particles smaller than 200 μm. For fine particles, this is the only usable method of determining their density which is a very important parameter of the fine fraction when it is employed for the manufacture of fuel elements by vibration compacting. The method consists in compacting a mixture of pycnometric material and dispersed particles of uranium dioxide, determining the size and weight of the compact, and in calculating the density of the material measured from the weight of the oxide sample in the mixture. (author)

  17. Influence of Various Process Parameters on the Density of Sintered Aluminium Alloys

    Directory of Open Access Journals (Sweden)

    Mateusz Laska

    2012-01-01

    Full Text Available This paper presents the results of density measurements carried out on Alumix sintered parts. ECKA Alumix aluminium powders were used because of their wide application in the powder metallurgy industry. The compacts were produced using a wide range of compaction pressures for three different chemical compositions. The compacts were then sintered under a pure dry nitrogen atmosphere at three different temperatures. The heating and cooling rates were the same throughout the entire test. The results showed that the green density increases with compaction pressure, but that sintered density is independent of green density (compaction pressure for each sintering temperature.

  18. Corrosion of high-density sintered tungsten alloys. Part 2

    International Nuclear Information System (INIS)

    Batten, J.J.; Moore, B.T.

    1988-12-01

    The behaviour of four high-density sintered tungsten alloys has been evluated and compared with that of pure tungsten. Rates of corrosion during the cyclic humidity and the salt mist tests were ascertained from weight loss measurements. Insight into the corrosion mechanism was gained from the nature of the corrosion products and an examination of the corroded surfaces. In the tests, the alloy 95% W, 2.5% Ni, 1.5% Fe was the most corrosion resistant. The data showed that copper as an alloying element accelerates corrosion of tungsten alloys. Both attack on the tungsten particles and the binder phase were observed together with tungsten grain loss. 6 refs., 3 tabs.,

  19. Preparation of silicon carbide/carbon fiber composites through high-temperature spark plasma sintering

    Directory of Open Access Journals (Sweden)

    Ehsan Ghasali

    2017-12-01

    Full Text Available This study discusses the potentials of spark plasma sintering (SPS integrated with high temperature process that can enable sintering of SiC/Cf composites without any sintering aids. The random distribution of carbon fibers was obtained through mixing composite components in ethanol by using a shaker mill for 10 min. The corresponding sintering process was carried out at 1900 and 2200 °C with 50 MPa pressure applied at maximum temperature. The results showed that 89 ± 0.9 and 97 ± 0.8% of the theoretical density can be obtained for sintering temperatures of 1900 and 2200 °C, respectively. The densification curves were plotted to monitor sintering behavior with punch displacement changes. The appropriate bonding between SiC particles and carbon fibers was detected using FE-SEM for sample which was sintered at 2200 °C. The clear maximum in hardness (2992 ± 33 Vickers, bending strength (427 ± 26 MPa and fracture toughness (4.2 ± 0.3 MPa m1/2 were identified for sample sintered at 2200 °C. XRD investigations supposed that SiC and carbon were the only crystalline phases in both sintered samples.

  20. Some new aspects of microstructural development during sintering of silicon nitride

    International Nuclear Information System (INIS)

    Feuer, H.; Woetting, G.; Gugel, E.

    1994-01-01

    The mechanical properties of silicon nitride ceramics strongly depend on their microstructure. However, there is still a lively discussion about the parameters controlling the microstructural development. The current research was stimulated by the observation that a bimodal grain-size distribution in dense silicon nitride has a very beneficial effect on the mechanical properties, especially on the fracture toughness. This paper is focused on the relationship between the α-β-transformation and the densification of silicon nitride powders with different characteristics and sintering additives. Effects of β-grains originally present in the silicon nitride powder, of added β-silicon nitride seeds and of β-crystals formed by the α/β-transformation on the resulting microstructure and on the properties are discussed. The results are summarised in a model describing prerequisites and processing conditions, which are necessary to achieve a bimodal microstructure, i. e. a self-reinforced silicon nitride ceramic. (orig.)

  1. Study of nano-metric silicon carbide powder sintering. Application to fibers processing

    International Nuclear Information System (INIS)

    Malinge, A.

    2011-01-01

    Silicon carbide ceramic matrix composites (SiCf/SiCm) are of interest for high temperature applications in aerospace or nuclear components for their relatively high thermal conductivity and low activation under neutron irradiation. While most of silicon carbide fibers are obtained through the pyrolysis of a poly-carbo-silane precursor, sintering of silicon carbide nano-powders seems to be a promising route to explore. For this reason, pressureless sintering of SiC has been studied. Following the identification of appropriate sintering aids for the densification, optimization of the microstructure has been achieved through (i) the analysis of the influence of operating parameters and (ii) the control of the SiC β a SiC α phase transition. Green fibers have been obtained by two different processes involving the extrusion of SiC powder dispersion in polymer solution or the coagulation of a water-soluble polymer containing ceramic particles. Sintering of these green fibers led to fibers of around fifty microns in diameter. (author) [fr

  2. Densification of silicon and zirconium carbides by a new process: spark plasma sintering

    International Nuclear Information System (INIS)

    Guillard, F.

    2006-12-01

    Materials research for suitable utilization in 4. generation nuclear plants needs new ways to densify testing components. Two carbides, silicon and zirconium carbide seems to be the most suitable choice due to their mechanical, thermal and neutron-transparency properties against next nuclear plant specifications. Nevertheless one main difficulty remains, which is densifying them even at high temperature. Spark Plasma Sintering a new metal-, ceramic- and composite-sintering process has been used to densify both SiC and ZrC. Understanding bases of mass transport mechanisms in SPS have been studied. Composites and interfaces have been processed and analyzed. This manuscript reports original results on SiC and ZrC ceramics sintered with commercial powder started, without additives. (author)

  3. X-ray powder diffraction analysis of liquid-phase-sintered silicon carbide ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Ortiz, A.L.; Sanchez-Bajo, F. [Universidad de Extremadura, Badajoz (Spain). Dept. de Electronica e Ingenieria Electromecanica; Cumbrera, F.L. [Universidad de Extremadura, Badajoz (Spain). Dept. de Fisica

    2002-07-01

    In an attempt to gain a comprehensive understanding of the microstructural evolution in liquid-phase-sintered silicon carbide ceramics, the effect of the starting {beta}-SiC powder has been studied. Pellets of two different {beta}-SiC starting powders were sintered with simultaneous additions of Al{sub 2}O{sub 3} and Y{sub 2}O{sub 3} at 1950 C for 1 hour in flowing argon atmosphere. Here we have used X-ray diffraction to obtain the relative abundance of the resulting SiC polytypes after sintering. The significant influence of the defects concentration on the {beta} to {alpha} transformation rate has been determined using the Rietveld method. (orig.)

  4. Strength evaluation test of pressureless-sintered silicon nitride at room temperature

    Science.gov (United States)

    Matsusue, K.; Takahara, K.; Hashimoto, R.

    1984-01-01

    In order to study strength characteristics at room temperature and the strength evaluating method of ceramic materials, the following tests were conducted on pressureless sintered silicon nitride specimens: bending tests, the three tensile tests of rectangular plates, holed plates, and notched plates, and spin tests of centrally holed disks. The relationship between the mean strength of specimens and the effective volume of specimens are examined using Weibull's theory. The effect of surface grinding on the strength of specimens is discussed.

  5. High-density oxidized porous silicon

    International Nuclear Information System (INIS)

    Gharbi, Ahmed; Souifi, Abdelkader; Remaki, Boudjemaa; Halimaoui, Aomar; Bensahel, Daniel

    2012-01-01

    We have studied oxidized porous silicon (OPS) properties using Fourier transform infraRed (FTIR) spectroscopy and capacitance–voltage C–V measurements. We report the first experimental determination of the optimum porosity allowing the elaboration of high-density OPS insulators. This is an important contribution to the research of thick integrated electrical insulators on porous silicon based on an optimized process ensuring dielectric quality (complete oxidation) and mechanical and chemical reliability (no residual pores or silicon crystallites). Through the measurement of the refractive indexes of the porous silicon (PS) layer before and after oxidation, one can determine the structural composition of the OPS material in silicon, air and silica. We have experimentally demonstrated that a porosity approaching 56% of the as-prepared PS layer is required to ensure a complete oxidation of PS without residual silicon crystallites and with minimum porosity. The effective dielectric constant values of OPS materials determined from capacitance–voltage C–V measurements are discussed and compared to FTIR results predictions. (paper)

  6. Improved reaction sintered silicon nitride. [protective coatings to improve oxidation resistance

    Science.gov (United States)

    Baumgartner, H. R.

    1978-01-01

    Processing treatments were applied to as-nitrided reaction sintered silicon nitride (RSSN) with the purposes of improving strength after processing to above 350 MN/m2 and improving strength after oxidation exposure. The experimental approaches are divided into three broad classifications: sintering of surface-applied powders; impregnation of solution followed by further thermal processing; and infiltration of molten silicon and subsequent carburization or nitridation of the silicon. The impregnation of RSSN with solutions of aluminum nitrate and zirconyl chloride, followed by heating at 1400-1500 C in a nitrogen atmosphere containing silicon monoxide, improved RSSN strength and oxidation resistance. The room temperature bend strength of RSSN was increased nearly fifty percent above the untreated strength with mean absolute strengths up to 420 MN/m2. Strengths of treated samples that were measured after a 12 hour oxidation exposure in air were up to 90 percent of the original as-nitrided strength, as compared to retained strengths in the range of 35 to 60 percent for untreated RSSN after the same oxidation exposure.

  7. Study on factors affecting sintering density of Gd2O3-UO2 pellets

    International Nuclear Information System (INIS)

    Zhu Shuming; Zou Congpei; Yang Jing; Yang Youqing; Mei Xiaohui

    1996-02-01

    The sintered density of Gd 2 O 3 -UO 2 burnable poison fuel pellets is an important quality index and is one of main QC items. Therefore, the efforts were made to investigate the factors affecting the sintered density of Gd 2 O 3 -UO 2 , that is, the influences of pre-treatment of Gd 2 O 3 powder, additives, mixing methods and time, sintering atmosphere, sintering temperature and time on the final density of Gd 2 O 3 UO 2 pellets contained 0, 3%, 7% and 10% (mass percentage) Gd 2 O 3 . The results show: the pre-treatment is useful for improving the distribution of Gd 2 O 3 ; the additive of ammonium oxalate will effectively adjust the density of pellets; 1750 degree C is the suitable sintering temperature. The proper process parameters have been obtained, and the Gd 2 O 3 -UO 2 pellets prepared for in-pile irradiation test meet the design requirements for the density (93.5%∼96.5% of T.D.), homogeneity, microstructure, etc. (8 refs., 3 figs., 8 tabs.)

  8. Optimization of the sintering atmosphere for high-density hydroxyapatite–carbon nanotube composites

    Science.gov (United States)

    White, Ashley A.; Kinloch, Ian A.; Windle, Alan H.; Best, Serena M.

    2010-01-01

    Hydroxyapatite–carbon nanotube (HA–CNT) composites have the potential for improved mechanical properties over HA for use in bone graft applications. Finding an appropriate sintering atmosphere for this composite presents a dilemma, as HA requires water in the sintering atmosphere to remain phase pure and well hydroxylated, yet CNTs oxidize at the high temperatures required for sintering. The purpose of this study was to optimize the atmosphere for sintering these composites. While the reaction between carbon and water to form carbon monoxide and hydrogen at high temperatures (known as the ‘water–gas reaction’) would seem to present a problem for sintering these composites, Le Chatelier's principle suggests this reaction can be suppressed by increasing the concentration of carbon monoxide and hydrogen relative to the concentration of carbon and water, so as to retain the CNTs and keep the HA's structure intact. Eight sintering atmospheres were investigated, including standard atmospheres (such as air and wet Ar), as well as atmospheres based on the water–gas reaction. It was found that sintering in an atmosphere of carbon monoxide and hydrogen, with a small amount of water added, resulted in an optimal combination of phase purity, hydroxylation, CNT retention and density. PMID:20573629

  9. Hot-pressed silicon nitride with various lanthanide oxides as sintering additives

    Science.gov (United States)

    Ueno, K.; Toibana, Y.

    1984-01-01

    The effects of addition of various lanthanide oxides and their mixture with Y2O3 on the sintering of Si3N4 were investigated. The addition of simple and mixed lanthanide oxides promoted the densification of Si3N4 in hot-pressing at 1800 C under 300-400kg/ centimeters squared for 60 min. The crystallization of yttrium and lanthanide-silicon oxynitrides which was observed inn the sintered body containing yttrium-lanthanide mixed oxides as additives led to the formation of a highly refractory Si3N4 ceramic having a bending strength of 82 and 84 kg/millimeters squared at room temperature and 1300 C respectively. In a Y2O3+La2O3 system, a higher molar ratio of La2O3 to Y2O3 gave a higher hardness and strength at high temperatures. It was found that 90 min was an optimum sintering time for the highest strength.

  10. Reaction sintering of two-dimensional silicon carbide fiber-reinforced silicon carbide composite by sheet stacking method

    International Nuclear Information System (INIS)

    Yoshida, Katsumi; Mukai, Hideki; Imai, Masamitsu; Hashimoto, Kazuaki; Toda, Yoshitomo; Hyuga, Hideki; Kondo, Naoki; Kita, Hideki; Yano, Toyohiko

    2007-01-01

    Two-dimensionally plain woven SiC fiber-reinforced SiC composite has been developed by reaction sintering using a sheet stacking method in order to further increase mechanical and thermal properties of the composite and to obtain flexibility of manufacturing process of 2D woven SiC/SiC composites which can be applied to the fabrication of larger parts. In addition, sinterability and mechanical properties of the composite were investigated. In this study, relative density of the composites was about 90-93% and a dense composite could be obtained by reaction sintering using the sheet stacking method. The bulk density and maximum bending strength of SiC/SiC composite with a C/SiC weight ratio of 0.6 were higher than that of the composite with C/SiC ratios of 0.5 or 0.7. The values were 2.9 g/cm 3 and 200 MPa, respectively. However, the composites obtained in this study fractured in almost brittle manner due to the lower fiber volume fraction

  11. Development of nano-structured silicon carbide ceramics: from synthesis of the powder to sintered ceramics

    International Nuclear Information System (INIS)

    Reau, A.

    2008-12-01

    The materials used inside future nuclear reactors will be subjected to very high temperature and neutrons flux. Silicon carbide, in the form of SiC f /SiC nano-structured composite is potentially interesting for this type of application. It is again necessary to verify the contribution of nano-structure on the behaviour of this material under irradiation. To verify the feasibility and determine the properties of the matrix, it was envisaged to produce it by powder metallurgy from SiC nanoparticles. The objective is to obtain a fully dense nano-structured SiC ceramic without additives. For that, a parametric study of the phases of synthesis and agglomeration was carried out, the objective of which is to determine the active mechanisms and the influence of the key parameters. Thus, studying the nano-powder synthesis by laser pyrolysis allowed to produce, with high production rates, homogeneous batches of SiC nanoparticles whose size can be adjusted between 15 and 90 nm. These powders have been densified by an innovating method: Spark Plasma Sintering (SPS). The study and the optimization of the key parameters allowed the densification of silicon carbide ceramic without sintering aids while preserving the nano-structure of material. The thermal and mechanical properties of final materials were studied in order to determine the influence of the microstructure on their properties. (author)

  12. High-temperature effect of hydrogen on sintered alpha-silicon carbide

    Science.gov (United States)

    Hallum, G. W.; Herbell, T. P.

    1986-01-01

    Sintered alpha-silicon carbide was exposed to pure, dry hydrogen at high temperatures for times up to 500 hr. Weight loss and corrosion were seen after 50 hr at temperatures as low as 1000 C. Corrosion of SiC by hydrogen produced grain boundary deterioration at 1100 C and a mixture of grain and grain boundary deterioration at 1300 C. Statistically significant strength reductions were seen in samples exposed to hydrogen for times greater than 50 hr and temperatures above 1100 C. Critical fracture origins were identified by fractography as either general grain boundary corrision at 1100 C or as corrosion pits at 1300 C. A maximum strength decrease of approximately 33 percent was seen at 1100 and 1300 C after 500 hr exposure to hydrogen. A computer assisted thermodynamic program was also used to predict possible reaction species of SiC and hydrogen.

  13. Compressive deformation of liquid phase-sintered porous silicon carbide ceramics

    Directory of Open Access Journals (Sweden)

    Taro Shimonosono

    2014-12-01

    Full Text Available Porous silicon carbide ceramics were fabricated by liquid phase sintering with 1 wt% Al2O3–1 wt% Y2O3 additives during hot-pressing at 1400–1900 °C. The longitudinal strain at compressive fracture increased at a higher porosity and was larger than the lateral strain. The compressive Young's modulus and the strain at fracture depended on the measured direction, and increased with the decreased specific surface area due to the formation of grain boundary. However, the compressive strength and the fracture energy were not sensitive to the measured direction. The compressive strength of a porous SiC compact increased with increasing grain boundary area. According to the theoretical modeling of the strength–grain boundary area relation, it is interpreted that the grain boundary of a porous SiC compact is fractured by shear deformation rather than by compressive deformation.

  14. Process for obtaining sintered conglomerates with a high density of rare earth oxides and actinides

    International Nuclear Information System (INIS)

    Pasto, A.E.

    1974-01-01

    The invention concerns a method to produce agglomerates of actinide and rare earth oxides possessing a cubic-monoclinic transformation in order to obtain high densities close to the theoretical density, and the articles produced by the method. The process is based on the use of a rare earth or actinide oxide, in particular Eu 2 O 3 , with a cubic-monoclinic phase transformation, the oxide being sintered by hot compression at a temperature 50 deg C to 100 deg C above the transformation temperature. The sintered agglomerates obtained can have a purity of at least 99.9% and a density of practically 100%. These agglomerates are suitable in particular for the formation of nuclear reactor control rods [fr

  15. Process for the production of metal nitride sintered bodies and resultant silicon nitride and aluminum nitride sintered bodies

    Science.gov (United States)

    Yajima, S.; Omori, M.; Hayashi, J.; Kayano, H.; Hamano, M.

    1983-01-01

    A process for the manufacture of metal nitride sintered bodies, in particular, a process in which a mixture of metal nitrite powders is shaped and heated together with a binding agent is described. Of the metal nitrides Si3N4 and AIN were used especially frequently because of their excellent properties at high temperatures. The goal is to produce a process for metal nitride sintered bodies with high strength, high corrosion resistance, thermal shock resistance, thermal shock resistance, and avoidance of previously known faults.

  16. Microstructural Evaluation of Inductively Sintered Aluminum Matrix Nanocomposites Reinforced with Silicon Carbide and/or Graphene Nanoplatelets for Tribological Applications

    Science.gov (United States)

    Islam, Mohammad; Khalid, Yasir; Ahmad, Iftikhar; Almajid, Abdulhakim A.; Achour, Amine; Dunn, Theresa J.; Akram, Aftab; Anwar, Saqib

    2018-04-01

    Silicon carbide (SiC) nanoparticles (NP) and/or graphene nanoplatelets (GNP) were incorporated into the aluminum matrix through colloidal dispersion and mixing of the powders, followed by consolidation using a high-frequency induction heat sintering process. All the nanocomposite samples exhibited high densification (> 96 pct) with a maximum increase in Vickers microhardness by 92 pct relative to that of pure aluminum. The tribological properties of the samples were determined at the normal frictional forces of 10 and 50 N. At relatively low load of 10 N, the adhesive wear was found to be the predominant wear mechanism, whereas in the case of a 50 N normal load, there was significant contribution from abrasive wear possibly by hard SiC NP. From wear tests, the values for the coefficient of friction (COF) and the normalized wear rate were determined. The improvement in hardness and wear resistance may be attributed to multiple factors, including high relative density, uniform SiC and GNP dispersion in the aluminum matrix, grain refinement through GNP pinning, as well as inhibition of dislocation movement by SiC NP. The nanocomposite sample containing 10 SiC and 0.5 GNP (by wt pct) yielded the maximum wear resistance at 10 N normal load. Microstructural characterization of the nanocomposite surfaces and wear debris was performed using scanning electron microscope (SEM) and transmission electron microscope (TEM). The synergistic effect of the GNP and SiC nanostructures accounts for superior wear resistance in the aluminum matrix nanocomposites.

  17. Effect of agglomerate strength on sintered density for yttria powders containing agglomerates of monosize spheres

    International Nuclear Information System (INIS)

    Ciftcioglu, M.; Akine, M.; Burkhart, L.

    1987-01-01

    The effect of agglomerate strength on sintered density was determined for several yttria powders made by intentionally agglomerating 0.1-μm, monodisperse yttriuim hydrocarbonate precursor spheres and calcining separate portions of the precursor at different temperatures to vary the strength of the intraaglomeate bonds. In this way, the effects of differences in particle morphology and other characteristics among the powders were minimized and the effect of agglomerate strength could be seen more clearly

  18. Reaction sintering of a clay-containing silicon nitride bonded silicon carbide refractory

    International Nuclear Information System (INIS)

    Swenser, S.P.; Cheng, Y.B.

    1998-01-01

    Aspects of the reaction sequence for the reaction bonding of a cast refractory, which in the green state was composed of 79 wt-% SiC grit, 16 wt-% Si powder and 5 wt-% clay were established. As it was fired up to 1600 deg C in flowing N 2 (g), weight gains were noted and phase evolution was monitored by X-ray diffraction. However, details of the reaction sequence were not determined directly from this material because several reaction-bonding processes occurred simultaneously. Reaction features were ascertained by contrasting the weight changes and phase evolution in the refractory with those observed during reaction-bonding of (a) Si and clay without the SiC and (b) SiC and clay without the Si. In addition to silicon nitridation and the development of sialon phases by silicothermal and carbothermal reduction-nitridation processes, indirect evidence suggested that α-Si 3 N 4 formed by the carbothermal reduction-nitridation (CRN) of SiO(g). Copyright (1998) Australasian Ceramic Society

  19. Microwave sintering of hydroxyapatite-based composites

    International Nuclear Information System (INIS)

    Fang, Y.; Roy, D.M.; Cheng, J.; Roy, R.; Agrawal, D.K.

    1993-01-01

    Composites of hydroxyapatite/partially stabilized zirconia (HAp/PSZ) and hydroxyapatite/silicon carbide whiskers (HAp/SiC) were sintered at 1100-1200 degrees C by microwave at 2.45 GHz. Characterization of the sintered composites was carried out by density, microstructure, phase composition, and fracture toughness measurements. The results show that although not yet fully densified, a much higher sintered density in the HAp/PSZ composite was achieved by microwave sintering than by conventional sintering at the same temperature. A relative density of 93% was achieved by 20 min. microwave processing at 1200 degrees C. Comparatively, 2 h conventional sintering of the same material at 1200 degrees C led to only 75.5% relative density. K IC of this microwave sintered HAp/PSZ of 93% density was found to be 3.88 MPa√m, which is 250% of the value for pure HAp of the same density. A further increase in K IC could be expected if full or nearly full densification was achieved. Sintering of PSZ particles in the HAp/PSZ composite was also observed in the microwave processed sample. Microwave sintering of HAp/SiC was not successful in the current study due to the oxidation of SiC in air at high temperature. 8 refs., 4 figs., 1 tab

  20. Density of oxidation-induced stacking faults in damaged silicon

    NARCIS (Netherlands)

    Kuper, F.G.; Hosson, J.Th.M. De; Verwey, J.F.

    1986-01-01

    A model for the relation between density and length of oxidation-induced stacking faults on damaged silicon surfaces is proposed, based on interactions of stacking faults with dislocations and neighboring stacking faults. The model agrees with experiments.

  1. The effects of surface finish and grain size on the strength of sintered silicon carbide

    Science.gov (United States)

    You, Y. H.; Kim, Y. W.; Lee, J. G.; Kim, C. H.

    1985-01-01

    The effects of surface treatment and microstructure, especially abnormal grain growth, on the strength of sintered SiC were studied. The surfaces of sintered SiC were treated with 400, 800 and 1200 grit diamond wheels. Grain growth was induced by increasing the sintering times at 2050 C. The beta to alpha transformation occurred during the sintering of beta-phase starting materials and was often accompanied by abnormal grain growth. The overall strength distributions were established using Weibull statistics. The strength of the sintered SiC is limited by extrinsic surface flaws in normal-sintered specimens. The finer the surface finish and grain size, the higher the strength. But the strength of abnormal sintering specimens is limited by the abnormally grown large tabular grains. The Weibull modulus increases with decreasing grain size and decreasing grit size for grinding.

  2. Amorphous silicon rich silicon nitride optical waveguides for high density integrated optics

    DEFF Research Database (Denmark)

    Philipp, Hugh T.; Andersen, Karin Nordström; Svendsen, Winnie Edith

    2004-01-01

    Amorphous silicon rich silicon nitride optical waveguides clad in silica are presented as a high-index contrast platform for high density integrated optics. Performance of different cross-sectional geometries have been measured and are presented with regards to bending loss and insertion loss...

  3. Flash sintering of ceramic materials

    Science.gov (United States)

    Dancer, C. E. J.

    2016-10-01

    During flash sintering, ceramic materials can sinter to high density in a matter of seconds while subjected to electric field and elevated temperature. This process, which occurs at lower furnace temperatures and in shorter times than both conventional ceramic sintering and field-assisted methods such as spark plasma sintering, has the potential to radically reduce the power consumption required for the densification of ceramic materials. This paper reviews the experimental work on flash sintering methods carried out to date, and compares the properties of the materials obtained to those produced by conventional sintering. The flash sintering process is described for oxides of zirconium, yttrium, aluminium, tin, zinc, and titanium; silicon and boron carbide, zirconium diboride, materials for solid oxide fuel applications, ferroelectric materials, and composite materials. While experimental observations have been made on a wide range of materials, understanding of the underlying mechanisms responsible for the onset and latter stages of flash sintering is still elusive. Elements of the proposed theories to explain the observed behaviour include extensive Joule heating throughout the material causing thermal runaway, arrested by the current limitation in the power supply, and the formation of defect avalanches which rapidly and dramatically increase the sample conductivity. Undoubtedly, the flash sintering process is affected by the electric field strength, furnace temperature and current density limit, but also by microstructural features such as the presence of second phase particles or dopants and the particle size in the starting material. While further experimental work and modelling is still required to attain a full understanding capable of predicting the success of the flash sintering process in different materials, the technique non-etheless holds great potential for exceptional control of the ceramic sintering process.

  4. Selective Laser Sintering of PA2200: Effects of print parameters on density, accuracy, and surface roughness

    Energy Technology Data Exchange (ETDEWEB)

    Bajric, Sendin [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-06-12

    Additive manufacturing needs a broader selection of materials for part production. In order for the Los Alamos National Laboratory (LANL) to investigate new materials for selective laser sintering (SLS), this paper reviews research on the effect of print parameters on part density, accuracy, and surface roughness of polyamide 12 (PA12, PA2200). The literature review serves to enhance the understanding of how changing the laser powder, scan speed, etc. will affect the mechanical properties of a commercial powder. By doing so, this understanding will help the investigation of new materials for SLS.

  5. Silicon surface barrier detectors used for liquid hydrogen density measurement

    Science.gov (United States)

    James, D. T.; Milam, J. K.; Winslett, H. B.

    1968-01-01

    Multichannel system employing a radioisotope radiation source, strontium-90, radiation detector, and a silicon surface barrier detector, measures the local density of liquid hydrogen at various levels in a storage tank. The instrument contains electronic equipment for collecting the density information, and a data handling system for processing this information.

  6. Clathrates and beyond: Low-density allotropy in crystalline silicon

    Energy Technology Data Exchange (ETDEWEB)

    Beekman, Matt [Department of Physics, California Polytechnic State University, San Luis Obispo, California 93407 (United States); Wei, Kaya; Nolas, George S., E-mail: gnolas@usf.edu [Department of Physics, University of South Florida, Tampa, Florida 33620 (United States)

    2016-12-15

    In its common, thermodynamically stable state, silicon adopts the same crystal structure as diamond. Although only a few alternative allotropic structures have been discovered and studied over the past six decades, advanced methods for structure prediction have recently suggested a remarkably rich low-density phase space that has only begun to be explored. The electronic properties of these low-density allotropes of silicon, predicted by first-principles calculations, indicate that these materials could offer a pathway to improving performance and reducing cost in a variety of electronic and energy-related applications. In this focus review, we provide an introduction and overview of recent theoretical and experimental results related to low-density allotropes of silicon, highlighting the significant potential these materials may have for technological applications, provided substantial challenges to their experimental preparation can be overcome.

  7. Influence of alloying elements and density on aqueous corrosion behaviour of some sintered low alloy steels

    International Nuclear Information System (INIS)

    Kandavel, T.K.; Chandramouli, R.; Karthikeyan, P.

    2012-01-01

    Highlights: ► Corrosion of low alloy P/M steels under HCl acid pickling environment has been studied. ► Influence of density, strain and alloying elements on the rate of corrosion of the steels has been investigated. ► Residual porosity has significant effect on acid corrosion. ► Addition of the alloying elements Cu, Mo and Ti reduces the corrosion rate significantly. ► Carbide forming elements Mo and Ti improve further the resistance of the steels to aqueous corrosion. -- Abstract: Low alloy steels produced through powder metallurgy route of sintering followed by forging are promising candidate materials for high strength small components. Porosity in such steels poses a real challenge during acid pickling treatment, which is one of the processing steps during manufacturing. The present research work attempts to investigate the mechanism underlying the acid corrosion behaviour of some sintered low alloy steels under induced acid pickling conditions. Sintered-forged low alloy steel samples containing molybdenum (Mo), copper (Cu) and titanium (Ti) were subjected to aqueous corrosion attack by immersing the samples in 18% HCl (Hydrochloric acid) solution for 25 h. Sample weight loss and Fe (Iron) loss were estimated for the corroded samples. The morphology of the corroded surfaces was studied through metallography and scanning electron microscopy. Higher porosity alloys underwent enhanced corrosion rates. Both corrosion rate and iron loss are found to decrease linearly with reduction in porosity in all cases of the alloys. The alloying elements Mo, Ti and Cu, when added in combination, have played a complementary role in the reduction of corrosion rate by almost one order of magnitude compared to unalloyed steel. Presence of carbides of the carbide forming elements Mo and Ti played a positive role on the corrosion behaviour of the low alloy steels.

  8. Influence of the initial grain size of silicon on microstructure and mechanical properties of reaction-sintered silicon nitride

    International Nuclear Information System (INIS)

    Heinrich, J.

    1977-01-01

    The influence of the initial grain size of the silicon powder on the microstructure and the resulting mechanical properties are studied. The smaller the grain size of the silicon powders used, the higher will be the degree of reaction at the beginning of the nitridation reaction and the higher the amount of α-modification in the fully nitridated samples. Moreover, the nitrification time can be considerably shortened when fine-grained silicon powders ( [de

  9. Microstructural designs of spark-plasma sintered silicon carbide ceramic scaffolds

    Energy Technology Data Exchange (ETDEWEB)

    Roman-Manso, B.; Pablos, A. de; Belmonte, M.; Osendi, M. I.; Miranzo, P.

    2014-04-01

    Concentrated ceramic inks based on (SiC) powders, with different amounts of Y{sub 2}O{sub 3} and Al{sub 2}O{sub 3} as sintering aids, are developed for the adequate production of SiC scaffolds, with different patterned morphologies, by the Robocasting technique. The densification of the as-produced 3D structures, previously heat treated in air at 600 degree centigrade for the organics burn-out, is achieved with a Spark Plasma Sintering (SPS) furnace. The effects of the amount of sintering additives (7 - 20 wt. %) and the size of the SiC powders (50 nm and 0.5 {mu}m) on the processing of the inks, microstructure, hardness and elastic modulus of the sintered scaffolds, are studied. The use of nano-sized (SiC) powders significantly restricts the attainable maximum solids volume fraction of the ink (0.32 compared to 0.44 of the submicron-sized powders-based ink), involving a much larger porosity of the green ceramic bodies. Furthermore, reduced amounts of additives improve the mechanical properties of the ceramic skeleton; particularly, the stiffness. The grain size and specific surface area of the starting powders, the ink solids content, green porosity, amount of sintering additives and SPS temperatures are the main parameters to be taken into account for the production of these SiC cellular ceramics. (Author)

  10. X-ray electron charge density distribution in silicon

    International Nuclear Information System (INIS)

    Pietsch, U.

    1986-01-01

    During the last two years new highly accurate X-ray structure amplitudes for silicon have been published. Also the scattering phases of some 'forbidden' reflections have been determined using the X-ray three-beam case. This allows the construction of most precise valence and difference electron density plots and the comparison with those calculated on the basis of the Aldret-Hart X-ray pendelloesung data or theoretically. The density plots are discussed in details of both, the bond and the atomic site. The contributions of various Fourier components and the influence of different temperature factors on the difference density are studied. (author)

  11. Densification of silicon and zirconium carbides by a new process: spark plasma sintering; Densification des carbures de silicium et de zirconium par un procede innovant: le spark plasma sintering

    Energy Technology Data Exchange (ETDEWEB)

    Guillard, F

    2006-12-15

    Materials research for suitable utilization in 4. generation nuclear plants needs new ways to densify testing components. Two carbides, silicon and zirconium carbide seems to be the most suitable choice due to their mechanical, thermal and neutron-transparency properties against next nuclear plant specifications. Nevertheless one main difficulty remains, which is densifying them even at high temperature. Spark Plasma Sintering a new metal-, ceramic- and composite-sintering process has been used to densify both SiC and ZrC. Understanding bases of mass transport mechanisms in SPS have been studied. Composites and interfaces have been processed and analyzed. This manuscript reports original results on SiC and ZrC ceramics sintered with commercial powder started, without additives. (author)

  12. Controlling growth density and patterning of single crystalline silicon nanowires

    International Nuclear Information System (INIS)

    Chang, Tung-Hao; Chang, Yu-Cheng; Liu, Fu-Ken; Chu, Tieh-Chi

    2010-01-01

    This study examines the usage of well-patterned Au nanoparticles (NPs) as a catalyst for one-dimensional growth of single crystalline Si nanowires (NWs) through the vapor-liquid-solid (VLS) mechanism. The study reports the fabrication of monolayer Au NPs through the self-assembly of Au NPs on a 3-aminopropyltrimethoxysilane (APTMS)-modified silicon substrate. Results indicate that the spin coating time of Au NPs plays a crucial role in determining the density of Au NPs on the surface of the silicon substrate and the later catalysis growth of Si NWs. The experiments in this study employed optical lithography to pattern Au NPs, treating them as a catalyst for Si NW growth. The patterned Si NW structures easily produced and controlled Si NW density. This approach may be useful for further studies on single crystalline Si NW-based nanodevices and their properties.

  13. Improved critical current densities in bulk FeSe superconductor using ball milled powders and high temperature sintering

    Energy Technology Data Exchange (ETDEWEB)

    Muralidhar, M.; Furutani, K.; Murakami, M. [Graduate School of Science and Engineering, Superconducting Materials Laboratory, Shibaura Institute of Technology, Tokyo (Japan); Kumar, Dinesh; Rao, M.S. Ramachandra [Department of Physics, Nano Functional Materials Technology Centre and Materials Science Research Centre, Indian Institute of Technology Madras, Chennai (India); Koblischka, M.R. [Institute of Experimental Physics, Saarland University, Saarbruecken (Germany)

    2016-12-15

    The present study is investigating the effect of high temperature sintering combined with ball milled powders for the preparation of FeSe material via solid state sintering technique. The commercial powders of Fe (99.9% purity) and Se (99.9% purity) were mixed in a nominal ratio Fe:Se = 1:1 and thoroughly ground and ball-milled in a glove box during 6 h. Then, the powder mixture was pressed into pellets of 5 mm in diameter and 2 mm thickness using an uniaxial pressure of 100 MPa. The samples were sealed in quartz tubes and sintered at 600 C for 24 h. Then, the pellets were again thoroughly ground and ball-milled in the glove box and pressed into pellets, and the final sintering was performed at two different temperatures, namely at 900 C for 24 h and at 950 C for 24 h. X-ray diffraction results confirmed that both samples showed mainly of the β-FeSe with tetragonal structure. The temperature dependence of magnetization (M-T) curves revealed a sharp superconducting transition T{sub c,} {sub onset} = 8.16 K for the sample sintered at 900 C. Further, scanning electron microscopy observations proved that samples sintered at 900 C show a platelike grain structure with high density. As a result, improved irreversibility fields around 5 T and the critical current density (J{sub c}) values of 6252 A cm{sup -2} at 5 K and self-field are obtained. Furthermore, the normalized volume pinning force versus the reduced field plots indicated a peak position at 0.4 for the sample sintered at 900 C. Improved flux pinning and the high J{sub c} values are attributed to the textured microstructure of the material, produced by a combination of high temperature sintering and ball milling. (copyright 2016 The Authors. Phys. Status Solidi A published by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. Effect of Sintering Atmosphere and Solution Treatment on Density, Microstructure and Tensile Properties of Duplex Stainless Steels Developed from Pre-alloyed Powders

    Science.gov (United States)

    Murali, Arun Prasad; Mahendran, Sudhahar; Ramajayam, Mariappan; Ganesan, Dharmalingam; Chinnaraj, Raj Kumar

    2017-10-01

    In this research, Powder Metallurgy (P/M) of Duplex Stainless Steels (DSS) of different compositions were prepared through pre-alloyed powders and elemental powders with and without addition of copper. The powder mix was developed by pot mill for 12 h to obtain the homogeneous mixture of pre-alloyed powder with elemental compositions. Cylindrical green compacts with the dimensions of 30 mm diameter and 12 mm height were compacted through universal testing machine at a pressure level of 560 ± 10 MPa. These green compacts were sintered at 1350 °C for 2 h in hydrogen and argon atmospheres. Some of the sintered stainless steel preforms were solution treated at 1050 °C followed by water quenching. The sintered as well as solution treated samples were analysed by metallography examination, Scanning Electron Microscopy and evaluation of mechanical properties. Ferrite content of sintered and solution treated DSS were measured by Fischer Ferritoscope. It is inferred that the hydrogen sintered DSS depicted better density (94% theoretical density) and tensile strength (695 MPa) than the argon sintered steels. Similarly the microstructure of solution treated DSS revealed existence of more volume of ferrite grains than its sintered condition. Solution treated hydrogen sintered DSS A (50 wt% 316L + 50 wt% 430L) exhibited higher tensile strength of 716 MPa and elongation of 17%, which are 10-13% increment than the sintered stainless steels.

  15. Sintering of nonstoichiometric UO2

    International Nuclear Information System (INIS)

    Susnik, D.; Holc, J.

    1983-01-01

    Activated sintering of UO 2 pellets at 1100 deg C is described. In CO 2 atmosphere is UO 2 is nonstoichiometric and pellets from active UO 2 powders sinter at 900 deg C to high density. At 1100 deg C the final sintered density is practically achieved at heating on sintering temperature. After reduction and cooling in H 2 atmosphere which is followed sintering in CO 2 the structure is identical to the structured UO 2 pellets sintered at high temperature in H 2 . Density of activated sintered UO 2 pellets is stable, even after additional sintering at 1800 deg C. (author)

  16. Spark plasma sintering of SiC and ZrC

    Energy Technology Data Exchange (ETDEWEB)

    Guillard, F.; Galy, J. [CEMES-CNRS, 29 rue Jeanne Marvig BP94347 31055 Toulouse Cx 4 (France); Allemand, A. [CEA Saclay, DRT/DTEN/S3ME/LTMEx, 91191 Gif-sur-Yvette (France)

    2005-07-01

    Spark plasma sintering a relative new technique allows sintering material powders in a reduced time compared to formal process of densification. In order to analyse densification mechanisms and to compare with hot isostatic pressing technique, pellets of silicon carbide and zirconium carbide were sintered by HIP and by SPS from 1750 to 1950 deg. C, with different pressures (50 to 75 MPa) and various holding times (0 to 10 min). Their densities were determined and their microstructures were SEM analysed. (authors)

  17. Microstructural designs of spark-plasma sintered silicon carbide ceramic scaffolds

    Directory of Open Access Journals (Sweden)

    Román-Manso, B.

    2014-04-01

    Full Text Available Concentrated ceramic inks based on β-SiC powders, with different amounts of Y2O3 and Al2O3 as sintering aids, are developed for the adequate production of SiC scaffolds, with different patterned morphologies, by the Robocasting technique. The densifi cation of the as-produced 3D structures, previously heat treated in air at 600 ºC for the organics burn-out, is achieved with a Spark Plasma Sintering (SPS furnace. The effects of the amount of sintering additives (7 - 20 wt. % and the size of the SiC powders (50 nm and 0.5 μm on the processing of the inks, microstructure, hardness and elastic modulus of the sintered scaffolds, are studied. The use of nano-sized β-SiC powders significantly restricts the attainable maximum solids volume fraction of the ink (0.32 compared to 0.44 of the submicron-sized powders-based ink, involving a much larger porosity of the green ceramic bodies. Furthermore, reduced amounts of additives improve the mechanical properties of the ceramic skeleton; particularly, the stiffness. The grain size and specific surface area of the starting powders, the ink solids content, green porosity, amount of sintering additives and SPS temperatures are the main parameters to be taken into account for the production of these SiC cellular ceramics.Se han fabricado andamiajes de carburo de silicio (SiC usando la técnica de “Robocasting”, a partir de tintas cerámicas conteniendo β-SiC y distintas cantidades de Y2O3 and Al2O3, como aditivos de sinterización. La densificación de las estructuras tridimensionales, previamente calcinadas a 600 ºC para eliminar los aditivos orgánicos, se realizó en un horno de “Spark Plasma Sintering” (SPS. Se analizó el efecto de la cantidad de aditivos de sinterización (7-20 % en peso y del tamaño de partícula inicial del polvo de SiC (50 nm y 0.5 μm en el procesado de las tintas, en la microestructura, la dureza y el módulo elástico de las estructuras sinterizadas. El uso de polvo

  18. Investigations on the conditions for obtaining high density boron carbide by sintering

    International Nuclear Information System (INIS)

    Kislyj, P.S.; Grabtschuk, B.L.

    1975-01-01

    The results of investigations on kinetics of condensation and mechanisms of mass transfer in the process of sintering of technical, chemically pure and synthesized boron carbide are generalized. Laws on boron carbide densification depending upon temperature, time of isothermic endurance, thermal speed, size of powder particles and variable composition in homogeneity are determined. From the results obtained on condensation kinetics and special experiments on studying the changes in properties after heating under different conditions, the role of dislocation and diffusion processes in mass transfer during boron carbide sintering is exposed. The properties of sintered boron carbide are 15-20% lower than the properties of high-pressed one, that is conditioned by intercrystallite distortion of the first one and transcrystallite of the second one

  19. Effect of hot isostatic pressing on the properties of sintered alpha silicon carbide

    Science.gov (United States)

    Watson, G. K.; Moore, T. J.; Millard, M. L.

    1985-01-01

    Two lots of alpha silicon carbide were isostatically hot-pressed under 138 MPa for 2 h in Ar at temperatures up to 2200 C. Nearly theoretically dense specimens resulted. Hot isostatic pressing increased both room-temperature strength and 1200 C strength, and resulted in improved reliability. One lot of material which was pressed at 2200 C showed increases of about 20 percent in room-temperature strength and about 50 percent in 1200 C flexural strength; the Weibull modulus improved about 100 percent.

  20. Sintering and densification; new techniques: sinter forging

    International Nuclear Information System (INIS)

    Winnubst, A.J.A.

    1998-01-01

    In this chapter pressure assisted sintering methods will be described. Attention will mainly be paid to sinter forging as a die-wall free uniaxial pressure sintering technique, where large creep strains are possible. Sinter forging is an effective tool to reduce sintering temperature and time and to obtain a nearly theoretically dense ceramic. In this way grain size in tetragonal zirconia ceramics can be reduced down to 100 nm. Another important phenomenon is the reduction of the number density and size of cracks and flaws resulting in higher strength and improved reliability, which is of utmost importance for engineering ceramics. The creep deformation during sinter forging causes a rearrangement of the grains resulting in a reduction of interatomic spaces between grains, while grain boundary (glassy) phases can be removed. The toughness and in some cases the wear resistance is enhanced after sinter forging as a result of the grain-boundary-morphology improvement. (orig.)

  1. Density functional study of the bonding in small silicon clusters

    International Nuclear Information System (INIS)

    Fournier, R.; Sinnott, S.B.; DePristo, A.E.

    1992-01-01

    We report the ground electronic state, equilibrium geometry, vibrational frequencies, and binding energy for various isomers of Si n (n = 2--8) obtained with the linear combination of atomic orbitals-density functional method. We used both a local density approximation approach and one with gradient corrections. Our local density approximation results concerning the relative stability of electronic states and isomers are in agreement with Hartree--Fock and Moller--Plesset (MP2) calculations [K. Raghavachari and C. M. Rohlfing, J. Chem. Phys. 89, 2219 (1988)]. The binding energies calculated with the gradient corrected functional are in good agreement with experiment (Si 2 and Si 3 ) and with the best theoretical estimates. Our analysis of the bonding reveals two limiting modes of bonding and classes of silicon clusters. One class of clusters is characterized by relatively large s atomic populations and a large number of weak bonds, while the other class of clusters is characterized by relatively small s atomic populations and a small number of strong bonds

  2. High-Current-Density Vertical-Tunneling Transistors from Graphene/Highly Doped Silicon Heterostructures.

    Science.gov (United States)

    Liu, Yuan; Sheng, Jiming; Wu, Hao; He, Qiyuan; Cheng, Hung-Chieh; Shakir, Muhammad Imran; Huang, Yu; Duan, Xiangfeng

    2016-06-01

    Scalable fabrication of vertical-tunneling transistors is presented based on heterostructures formed between graphene, highly doped silicon, and its native oxide. Benefiting from the large density of states of highly doped silicon, the tunneling transistors can deliver a current density over 20 A cm(-2) . This study demonstrates that the interfacial native oxide plays a crucial role in governing the carrier transport in graphene-silicon heterostructures. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Density control of dodecamanganese clusters anchored on silicon(100).

    Science.gov (United States)

    Condorelli, Guglielmo G; Motta, Alessandro; Favazza, Maria; Nativo, Paola; Fragalà, Ignazio L; Gatteschi, Dante

    2006-04-24

    A synthetic strategy to control the density of Mn12 clusters anchored on silicon(100) was investigated. Diluted monolayers suitable for Mn12 anchoring were prepared by Si-grafting mixtures of the methyl 10-undecylenoate precursor ligand with 1-decene spectator spacers. Different ratios of these mixtures were tested. The grafted surfaces were hydrolyzed to reveal the carboxylic groups available for the subsequent exchange with the [Mn12O12(OAc)16(H2O)4]4 H2O2 AcOH cluster. Modified surfaces were analyzed by attenuated total reflection (ATR)-FTIR spectroscopy, X-ray photoemission spectroscopy (XPS), and AFM imaging. Results of XPS and ATR-FTIR spectroscopy show that the surface mole ratio between grafted ester and decene is higher than in the source solution. The surface density of the Mn12 cluster is, in turn, strictly proportional to the ester mole fraction. Well-resolved and isolated clusters were observed by AFM, using a diluted ester/decene 1:1 solution.

  4. Engineering the size and density of silicon agglomerates by controlling the initial surface carbonated contamination

    Energy Technology Data Exchange (ETDEWEB)

    Borowik, Ł., E-mail: Lukasz.Borowik@cea.fr [CEA, LETI, MINATEC Campus, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France); Chevalier, N.; Mariolle, D.; Martinez, E.; Bertin, F.; Chabli, A.; Barbé, J.-C. [CEA, LETI, MINATEC Campus, 17 rue des Martyrs, 38054 Grenoble Cedex 9 (France)

    2013-04-01

    Actually, thermally induced thin-films dewetting silicon in the silicon-on-insulator is a way to obtain silicon agglomerates with a size and a density fixed by the silicon film thickness. In this paper we report a new method to monitor both the size and the density of the Si agglomerates thanks to the deposition of a carbon-like layer. We show that using a 5-nm thick layer of silicon and additional ≤1-nm carbonated layer; we obtain agglomerates sizes ranging from 35 nm to 60 nm with respectively an agglomerate density ranging from 38 μm{sup −2} to 18 μm{sup −2}. Additionally, for the case of strained silicon films an alternative dewetting mechanism can be induced by monitoring the chemical composition of the sample surface.

  5. Broadband infrared photoluminescence in silicon nanowires with high density stacking faults.

    Science.gov (United States)

    Li, Yang; Liu, Zhihong; Lu, Xiaoxiang; Su, Zhihua; Wang, Yanan; Liu, Rui; Wang, Dunwei; Jian, Jie; Lee, Joon Hwan; Wang, Haiyan; Yu, Qingkai; Bao, Jiming

    2015-02-07

    Making silicon an efficient light-emitting material is an important goal of silicon photonics. Here we report the observation of broadband sub-bandgap photoluminescence in silicon nanowires with a high density of stacking faults. The photoluminescence becomes stronger and exhibits a blue shift under higher laser powers. The super-linear dependence on excitation intensity indicates a strong competition between radiative and defect-related non-radiative channels, and the spectral blue shift is ascribed to the band filling effect in the heterostructures of wurtzite silicon and cubic silicon created by stacking faults.

  6. Silicon micromachining using a high-density plasma source

    International Nuclear Information System (INIS)

    McAuley, S.A.; Ashraf, H.; Atabo, L.; Chambers, A.; Hall, S.; Hopkins, J.; Nicholls, G.

    2001-01-01

    Dry etching of Si is critical in satisfying the demands of the micromachining industry. The micro-electro-mechanical systems (MEMS) community requires etches capable of high aspect ratios, vertical profiles, good feature size control and etch uniformity along with high throughput to satisfy production requirements. Surface technology systems' (STS's) high-density inductively coupled plasma (ICP) etch tool enables a wide range of applications to be realized whilst optimizing the above parameters. Components manufactured from Si using an STS ICP include accelerometers and gyroscopes for military, automotive and domestic applications. STS's advanced silicon etch (ASE TM ) has also allowed the first generation of MEMS-based optical switches and attenuators to reach the marketplace. In addition, a specialized application for fabricating the next generation photolithography exposure masks has been optimized for 200 mm diameter wafers, to depths of ∼750 μm. Where the profile is not critical, etch rates of greater than 8 μm min -1 have been realized to replace previous methods such as wet etching. This is also the case for printer applications. Specialized applications that require etching down to pyrex or oxide often result in the loss of feature size control at the interface; this is an industry wide problem. STS have developed a technique to address this. The rapid progression of the industry has led to development of the STS ICP etch tool, as well as the process. (author)

  7. Performance of conversion efficiency of a crystalline silicon solar cell with base doping density

    Directory of Open Access Journals (Sweden)

    Gokhan Sahin

    Full Text Available In this study, we investigate theoretically the electrical parameters of a crystalline silicon solar cell in steady state. Based on a one-dimensional modeling of the cell, the short circuit current density, the open circuit voltage, the shunt and series resistances and the conversion efficiency are calculated, taking into account the base doping density. Either the I-V characteristic, series resistance, shunt resistance and conversion efficiency are determined and studied versus base doping density. The effects applied of base doping density on these parameters have been studied. The aim of this work is to show how short circuit current density, open circuit voltage and parasitic resistances are related to the base doping density and to exhibit the role played by those parasitic resistances on the conversion efficiency of the crystalline silicon solar. Keywords: Crystalline silicon solar cell, Base doping density, Series resistance, Shunt resistance, Conversion efficiency

  8. Effect of Current Density on Thermal and Optical Properties of p-Type Porous Silicon

    International Nuclear Information System (INIS)

    Kasra Behzad; Wan Mahmood Mat Yunus; Zainal Abidin Talib; Azmi Zakaria; Afarin Bahrami

    2011-01-01

    The different parameters of the porous silicon (PSi) can be tuned by changing some parameters in preparation process. We have chosen the anodization as formation method, so the related parameters should be changed. In this study the porous silicon (PSi) layers were formed on p-type Si wafer. The samples were anodized electrically in a fixed etching time under some different current densities. The structural and optical properties of porous silicon (PSi) on silicon (Si) substrates were investigated using photoluminescence (PL) and Photoacoustic Spectroscopy (PAS). (author)

  9. 3D Mapping Of Density And Crack Propagation Through Sintering Of Catalysis Tablets By X-Ray Tomography

    DEFF Research Database (Denmark)

    Jacobsen, Hjalte Sylvest; Puig-Molina, A.; Dalskov, N.

    2016-01-01

    sintering of the rejected tabletized support material are studied by 3D X-ray tomography. This is a powerful technique, which due to its nondestructive nature is suitable to study the development of internal cracks in the tablets during sintering. Cracks could be identified in the green tablet (before...... properly, cracks may arise and propagate during the sintering of the tablets. This can lead to weak sintered tablets that get rejected in the quality control. For this work, crack-containing samples of rejected tabletized support were provided. The formation, growth and closure of internal cracks during...

  10. The role of the bimodal distribution of ultra-fine silicon phase and nano-scale V-phase (AlSi2Sc2) on spark plasma sintered hypereutectic Al–Si–Sc alloys

    International Nuclear Information System (INIS)

    Raghukiran, Nadimpalli; Kumar, Ravi

    2016-01-01

    Hypereutectic Al–Si and Al–Si–Sc alloys were spark plasma sintered from corresponding gas-atomized powders. The microstructures of the Al–Si and Al–Si–Sc alloys possessed remarkably refined silicon particles in the size range of 0.38–3.5 µm and 0.35–1.16 µm respectively in contrast to the silicon particles of size greater than 100 µm typically found in conventionally cast alloys. All the sintered alloys exhibited significant ductility of as high as 85% compressive strain without failure even with the presence of relatively higher weight fraction of the brittle silicon phase. Moreover, the Al–Si–Sc alloys have shown appreciable improvement in the compressive strength over their binary counterparts due to the presence of intermetallic compound AlSi 2 Sc 2 of size 10–20 nm distributed uniformly in the matrix of those alloys. The dry sliding pin-on-disc wear tests showed improvement in the wear performance of the sintered alloys with increase in silicon content in the alloys. Further, the Al–Si–Sc ternary alloys with relatively lesser silicon content exhibited appreciable improvement in the wear resistance over their binary counterparts. The Al–Si–Sc alloys with bimodal distribution of the strengthening phases consisting of ultra-fine (sub-micron size) silicon particles and the nano-scale AlSi 2 Sc 2 improved the strength and wear properties of the alloys while retaining significant amount of ductility.

  11. Influence of high sintering pressure on the microhardness and wear resistance of diamond powder and silicon carbide-based composites

    Directory of Open Access Journals (Sweden)

    Osipov Oleksandr Sergueevitch

    2004-01-01

    Full Text Available The work reported on here involved the development of several samples of "diamond-SiC" composite produced under sintering pressures of up to 9.0 GPa at temperatures of up to 1973 7K. The average size of the diamond micropowder crystals used was 40/28 µm. The sintering process was carried out in a 2500-ton hydraulic press equipped with an anvil-type high-pressure device having a toroidal work surface and a central concavity diameter of 20 mm. The microhardness and wear resistance of the samples were found to be dependent on the sintering pressure. The experimental results indicated that the maximum microhardness and minimum wear resistance coefficients of each compact were attained when the pressure applied during sintering exceeded 6.5 GPa. Based on the established values of pressure, this study served to identify the types of devices applicable for the manufacture of composite material inserts for a variety of rock drilling applications.

  12. Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon

    International Nuclear Information System (INIS)

    Astakhov, Oleksandr; Carius, Reinhard; Finger, Friedhelm; Petrusenko, Yuri; Borysenko, Valery; Barankov, Dmytro

    2009-01-01

    The influence of dangling-bond defects and the position of the Fermi level on the charge carrier transport properties in undoped and phosphorous doped thin-film silicon with structure compositions all the way from highly crystalline to amorphous is investigated. The dangling-bond density is varied reproducibly over several orders of magnitude by electron bombardment and subsequent annealing. The defects are investigated by electron-spin-resonance and photoconductivity spectroscopies. Comparing intrinsic amorphous and microcrystalline silicon, it is found that the relationship between defect density and photoconductivity is different in both undoped materials, while a similar strong influence of the position of the Fermi level on photoconductivity via the charge carrier lifetime is found in the doped materials. The latter allows a quantitative determination of the value of the transport gap energy in microcrystalline silicon. The photoconductivity in intrinsic microcrystalline silicon is, on one hand, considerably less affected by the bombardment but, on the other hand, does not generally recover with annealing of the defects and is independent from the spin density which itself can be annealed back to the as-deposited level. For amorphous silicon and material prepared close to the crystalline growth regime, the results for nonequilibrium transport fit perfectly to a recombination model based on direct capture into neutral dangling bonds over a wide range of defect densities. For the heterogeneous microcrystalline silicon, this model fails completely. The application of photoconductivity spectroscopy in the constant photocurrent mode (CPM) is explored for the entire structure composition range over a wide variation in defect densities. For amorphous silicon previously reported linear correlation between the spin density and the subgap absorption is confirmed for defect densities below 10 18 cm -3 . Beyond this defect level, a sublinear relation is found i.e., not

  13. Ultrahigh capacitance density for multiple ALD-grown MIM capacitor stacks in 3-D silicon

    NARCIS (Netherlands)

    Klootwijk, J.H.; Jinesh, K.B.; Dekkers, W.; Verhoeven, J.F.C.; Heuvel, van den F.C.; Kim, H.-D.; Blin, D.; Verheijen, M.A.; Weemaes, R.G.R.; Kaiser, M.; Ruigrok, J.J.M.; Roozeboom, F.

    2008-01-01

    "Trench" capacitors containing multiple metal-insulator-metal (MIM) layer stacks are realized by atomic-layer deposition (ALD), yielding an ultrahigh capacitance density of 440 nF/mm2 at a breakdown voltage VBD > 6 V. This capacitance density on silicon is at least 10 times higher than the values

  14. Effect of sintering temperature on structure of C-B4C-SiC composites with silicon additive

    International Nuclear Information System (INIS)

    Wu Lijun; Academia Sinica, Shenyang; Huang Qizhong; Yang Qiaoqin; Zhao Lihu; Xu Zhongyu

    1996-01-01

    Carbon materials possess good electric conductivity, heat conductivity, corrosion-resistance, self-lubrication and hot-shocking resistance, and are easily machined. However, they have low mechanical strength, and are easily oxidized in air at high temperature. On the contrary, ceramic materials have high mechanical strength and hardness, and have good wear-resistance and oxidation-resistance. However, they have the shortages of poor thermal-shock resistance lubrication, and are difficult to machine. Therefore, carbon/ceramic composites with the advantages of both carbon and ceramic materials have been widely studied in the recent years. Huang prepared C-B 4 C-SiC composites with the free sintering method and the hot pressing method, and studied the effects of Si, Al, Al 2 O 3 , Ni and Ti additives on the properties of the composites. The results showed that these additives could improve the properties of the composites. Zhao et al. studies the structure of C-B 4 C-SiC composites with Si additive sintered at 2,000 C and found two c-center monoclinic phases. In this paper, the authors discussed the effect of the sintering temperature on the structure of C-B 4 C-SiC composites with Si additive by means of transmission electron microscope (TEM) and x-ray diffractometer (XRD)

  15. Elaboration of silicon carbides nano particles (SiC): from the powder synthesis to the sintered ceramic

    International Nuclear Information System (INIS)

    Reau, A.

    2008-01-01

    Materials for the reactor cores of the fourth generation will need materials supporting high temperatures with fast neutrons flux. SiC f /SiC ceramics are proposed. One of the possible elaboration process is to fill SiC fiber piece with nano particles SiC powder and to strengthen by sintering. The aim of this thesis is to obtain a nano structured SiC ceramic as a reference for the SiC f /SiC composite development and to study the influence of the fabrication parameters. (A.L.B.)

  16. Manufacture of sintered bricks of high density from beryllium oxide; Fabrication de frittes de forte densite a base d'oxyde de beryllium

    Energy Technology Data Exchange (ETDEWEB)

    Pointud, R; Rispal, Ch; Le Garec, M [Commissariat a l' Energie Atomique, Saclay (France).Centre d' Etudes Nucleaires

    1959-07-01

    Beryllium oxide bricks of nuclear purity 100 x 100 x 50 and 100 x 100 x 100 mm of very high density (between 2.85 and 3.00) are manufactured by sintering under pressure in graphite moulds at temperatures between 1,750 and 1,850 deg. C, and under a pressure of 150 kg/cm{sup 2}. The physico-chemical state of the saw material is of considerable importance with regard to the success of the sintering operation. In addition, a study of the sintering of a BeO mixture with 3 to 5 per cent of boron introduced in the form of boric acid, boron carbide or elementary boron shows that high densities can only be obtained by sintering under pressure. For technical reasons of manufacture, only the mixture based on boron carbide is used. The sintering is carried out in graphite moulds at 1500 deg. C under 150 kg/cm{sup 2} pressure, and bricks can be obtained with density between 2,85 and 2,90. Laboratory studies and the industrial manufacture of various sinters are described in detail. (author) [French] La fabrication de briques d'oxyde de beryllium de purete nucleaire de 100 x 100 x 50 et de 100 x 100 x 100 mm de densite tres elevee (comprise entre 2.85 et 3.00) est realisee par frittage sous charge dans des moules en graphite entre 1750 et 1850 deg. C, sous 150 kg/cm{sup 2} de pression. L'etat physico-chimique de la matiere premiere a une importance considerable quant au succes de l'operation de frittage. Par ailleurs, l'etude du frittage du mixte BeO a 3 et 5 pour cent de bore element introduit sous forme d'anhydride borique, soit de carbure de bore ou de bore element, montre que seul le frittage sous charge permet d'obtenir des densites elevees. Pour des raisons techniques de fabrication seul le mixte a base de carbure de bore est retenu. Le frittage s'opere dans des moules de graphite a 1500 deg. C sous 150 kg/cm{sup 2} de pression et permet d'obtenir des briques de densite comprise entre 2.85 et 2.90. Les etudes de laboratoire et la fabrication industrielle des differents

  17. Ultrahigh-density trench cpacitors in silicon and their application to integrated DC-DC conversion

    NARCIS (Netherlands)

    Roozeboom, F.; Bergveld, H.J.; Nowak, K.; Le Cornec, F.; Guiraud, L.; Bunel, C.; Iochem, S.; Ferreira, J.; Ledain, S.; Pieraerts, E.; Pommier, M.

    2009-01-01

    This paper addresses silicon-based integration of passive components applied to 3D integration with dies of other technologies within one package. Particularly, the development of high-density trench capacitors has enabled the realization of small-formfactor DC-DC converters. As illustration, an

  18. VV and VO2 defects in silicon studied with hybrid density functional theory

    KAUST Repository

    Christopoulos, Stavros Richard G; Wang, Hao; Chroneos, Alexander I.; Londos, Charalampos A.; Sgourou, Efstratia N.; Schwingenschlö gl, Udo

    2014-01-01

    The formation of VO (A-center), VV and VO2 defects in irradiated Czochralski-grown silicon (Si) is of technological importance. Recent theoretical studies have examined the formation and charge states of the A-center in detail. Here we use density

  19. Guidelines for etching silicon MEMS structures using fluorine high-density plasmas at cryogenic temperatures

    NARCIS (Netherlands)

    de Boer, Meint J.; Gardeniers, Johannes G.E.; Jansen, Henricus V.; Gilde, M.J.; Roelofs, Gerard; Sasserath, Jay N.; Elwenspoek, Michael Curt

    This paper presents guidelines for the deep reactive ion etching (DRIE) of silicon MEMS structures, employing SF6/O2-based high-density plasmas at cryogenic temperatures. Procedures of how to tune the equipment for optimal results with respect to etch rate and profile control are described. Profile

  20. Effect of sintering in a hydrogen atmosphere on the density and coercivity of (Sm,Zr)(Co,Cu,Fe)Z permanent magnets

    Science.gov (United States)

    Burkhanov, G. S.; Dormidontov, N. A.; Kolchugina, N. B.; Dormidontov, A. G.

    2018-04-01

    The effect of heat treatments in manufacturing (Sm,Zr)(Co,Cu,Fe)Z-based permanent magnets sintered in a hydrogen atmosphere on their properties has been studied. It was shown that the dynamics of the magnetic hardening of the studied magnets during heat treatments, in whole, corresponds to available concepts of phase transformations in five-component precipitation-hardened SmCo-based alloys. Peculiarities of the studied compositions consist in the fact that the coercive force magnitude of magnets quenched from the isothermal aging temperature is higher by an order of magnitude than those available in the literature. It was noted that, in using the selected manufacturing procedure, the increase in the density of samples does not finish at the sintering stage but continues in the course of solid-solution heat treatment.

  1. Boric oxide or boric acid sintering aid for sintering ceramics

    International Nuclear Information System (INIS)

    Lawler, H.A.

    1979-01-01

    The invention described relates to the use of liquid sintering aid in processes involving sintering of ceramic materials to produce dense, hard articles having industrial uses. Although the invention is specifically discussed in regard to compositions containing silicon carbide as the ceramic material, other sinterable carbides, for example, titanium carbide, may be utilized as the ceramic material. A liquid sintering aid for densifying ceramic material is selected from solutions of H 3 BO 3 , B 2 O 3 and mixtures of these solutions. In sintering ceramic articles, e.g. silicon carbide, a shaped green body is formed from a particulate ceramic material and a resin binder, and the green body is baked at a temperature of 500 to 1000 0 C to form a porous body. The liquid sintering aid of B 2 O 3 and/or H 3 BO 3 is then dispersed through the porous body and the treated body is sintered at a temperature of 1900 to 2200 0 C to produce the sintered ceramic article. (U.K.)

  2. Sintering of beryllium oxide

    International Nuclear Information System (INIS)

    Caillat, R.; Pointud, R.

    1955-01-01

    This study had for origin to find a process permitting to manufacture bricks of beryllium oxide of pure nuclear grade, with a density as elevated as possible and with standardized shape. The sintering under load was the technique kept for the manufacture of the bricks. Because of the important toxicity of the beryllium oxide, the general features for the preliminary study of the sintering, have been determined while using alumina. The obtained results will be able to act as general indication for ulterior studies with sintering under load. (M.B.) [fr

  3. Hierarchical columnar silicon anode structures for high energy density lithium sulfur batteries

    Science.gov (United States)

    Piwko, Markus; Kuntze, Thomas; Winkler, Sebastian; Straach, Steffen; Härtel, Paul; Althues, Holger; Kaskel, Stefan

    2017-05-01

    Silicon is a promising anode material for next generation lithium secondary batteries. To significantly increase the energy density of state of the art batteries with silicon, new concepts have to be developed and electrode structuring will become a key technology. Structuring is essential to reduce the macroscopic and microscopic electrode deformation, caused by the volume change during cycling. We report pulsed laser structuring for the generation of hierarchical columnar silicon films with outstanding high areal capacities up to 7.5 mAh cm-2 and good capacity retention. Unstructured columnar electrodes form a micron-sized block structure during the first cycle to compensate the volume expansion leading to macroscopic electrode deformation. At increased silicon loading, without additional structuring, pronounced distortion and the formation of cracks through the current collector causes cell failure. Pulsed laser ablation instead is demonstrated to avoid macroscopic electrode deformation by initial formation of the block structure. A full cell with lithiated silicon versus a carbon-sulfur cathode is assembled with only 15% overbalanced anode and low electrolyte amount (8 μl mgsulfur-1). While the capacity retention over 50 cycles is identical to a cell with high excess lithium anode, the volumetric energy density could be increased by 30%.

  4. Microstructure and mechanical properties of thermoelectric nanostructured n-type silicon-germanium alloys synthesized employing spark plasma sintering

    Energy Technology Data Exchange (ETDEWEB)

    Bathula, Sivaiah [CSIR-Network of Institutes for Solar Energy, CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012 (India); Department of Applied Physics, Delhi Technological University, Delhi (India); Gahtori, Bhasker; Tripathy, S. K.; Tyagi, Kriti; Srivastava, A. K.; Dhar, Ajay, E-mail: adhar@nplindia.org [CSIR-Network of Institutes for Solar Energy, CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012 (India); Jayasimhadri, M. [Department of Applied Physics, Delhi Technological University, Delhi (India)

    2014-08-11

    Owing to their high thermoelectric (TE) figure-of-merit, nanostructured Si{sub 80}Ge{sub 20} alloys are evolving as a potential replacement for their bulk counterparts in designing efficient radio-isotope TE generators. However, as the mechanical properties of these alloys are equally important in order to avoid in-service catastrophic failure of their TE modules, we report the strength, hardness, fracture toughness, and thermal shock resistance of nanostructured n-type Si{sub 80}Ge{sub 20} alloys synthesized employing spark plasma sintering of mechanically alloyed nanopowders of its constituent elements. These mechanical properties show a significant enhancement, which has been correlated with the microstructural features at nano-scale, delineated by transmission electron microscopy.

  5. Preparation of high density (Th, U)O2 pellets by sol-gel microsphere pelletization and 1300 C air sintering

    International Nuclear Information System (INIS)

    Yamagishi, Shigeru; Takahashi, Yoshihisa

    1994-01-01

    The fabrication of high density (Th, U)O 2 pellets by the sol-gel microsphere pelletization (SGMP) process was studied. To prepare source ThO 2 -UO 3 microspheres, isopropyl alcohol was substituted for the water in gel and thereafter removed by evacuating and subsequently by heating at 200 C in air. After humidifying the microspheres up to the moisture content ranging 10-21%, they were compacted into a pellet under 150-500 MPa and sintered in air at 1300 C. Even at the relatively low temperature, the maximum density reached 98% TD or higher for the U/(Th+U) ratios of 5-20 mol%. Such high density products survived as firm pellets with a similarly high density of 99% TD during the reduction into (Th, U)O 2 in Ar-4% H 2 at 1300 C. ((orig.))

  6. Effects of Ceramic Density and Sintering Temperature on the Mechanical Properties of a Novel Polymer-Infiltrated Ceramic-Network Zirconia Dental Restorative (Filling) Material.

    Science.gov (United States)

    Li, Weiyan; Sun, Jian

    2018-05-10

    BACKGROUND Polymer-infiltrated ceramic-network (PICN) dental material is a new and practical development in orthodontics. Sintering is the process of forming a stable solid mass from a powder by heating without melting. The aim of this study was to evaluate the effects of sintering temperature on the mechanical properties of a PICN zirconia dental material. MATERIAL AND METHODS A dense zirconia ceramic and four PICN zirconia dental materials, with varying porosities, were sintered at three different temperatures; 12 PICN zirconia dental materials based on these porous ceramics were prepared, as well as a pure polymer. After the specimen preparation, flexural strength and elastic modulus values were measured using the three-point bending test, and fracture toughness were determined by the single-edge notched beam (SENB) method. The Vickers hardness test method was used with an indentation strength (IS) test. Scanning electron microscopy (SEM) was used to examine the microstructure of the ceramic surface and the fracture surface. RESULTS Mechanical properties of the PICN dental materials, including flexural strength, elastic modulus, fracture toughness, and hardness, were more similar to the properties of natural teeth when compared with traditional dental ceramic materials, and were affected by the density and sintering temperature. SEM showed that the porous ceramic network became cohesive and that the length of cracks in the PICN dental material was reduced. CONCLUSIONS PICN zirconia dental materials were characterized by similar mechanical properties to natural dental tissues, but further studies are required continue to improve the similarities with natural human enamel and dentin.

  7. Pressureless sintering of whisker-toughened ceramic composites

    Science.gov (United States)

    Tiegs, T.N.

    1993-05-04

    A pressureless sintering method is disclosed for use in the production of whisker-toughened ceramic composites wherein the sintered density of composites containing up to about 20 vol. % SiC whiskers is improved by reducing the average aspect ratio of the whiskers to from about 10 to about 20. Sintering aids further improve the density, permitting the production of composites containing 20 vol. % SiC with sintered densities of 94% or better of theoretical density by a pressureless sintering method.

  8. Optimization of Gas Composition Used in Plasma Chemical Vaporization Machining for Figuring of Reaction-Sintered Silicon Carbide with Low Surface Roughness.

    Science.gov (United States)

    Sun, Rongyan; Yang, Xu; Ohkubo, Yuji; Endo, Katsuyoshi; Yamamura, Kazuya

    2018-02-05

    In recent years, reaction-sintered silicon carbide (RS-SiC) has been of interest in many engineering fields because of its excellent properties, such as its light weight, high rigidity, high heat conductance and low coefficient of thermal expansion. However, RS-SiC is difficult to machine owing to its high hardness and chemical inertness and because it contains multiple components. To overcome the problem of the poor machinability of RS-SiC in conventional machining, the application of atmospheric-pressure plasma chemical vaporization machining (AP-PCVM) to RS-SiC was proposed. As a highly efficient and damage-free figuring technique, AP-PCVM has been widely applied for the figuring of single-component materials, such as Si, SiC, quartz crystal wafers, and so forth. However, it has not been applied to RS-SiC since it is composed of multiple components. In this study, we investigated the AP-PCVM etching characteristics for RS-SiC by optimizing the gas composition. It was found that the different etching rates of the different components led to a large surface roughness. A smooth surface was obtained by applying the optimum gas composition, for which the etching rate of the Si component was equal to that of the SiC component.

  9. Investigation of the silicon ion density during molecular beam epitaxy growth

    Science.gov (United States)

    Eifler, G.; Kasper, E.; Ashurov, Kh.; Morozov, S.

    2002-05-01

    Ions impinging on a surface during molecular beam epitaxy influence the growth and the properties of the growing layer, for example, suppression of dopant segregation and the generation of crystal defects. The silicon electron gun in the molecular beam epitaxy (MBE) equipment is used as a source for silicon ions. To use the effect of ion bombardment the mechanism of generation and distribution of ions was investigated. A monitoring system was developed and attached at the substrate position in the MBE growth chamber to measure the ion and electron densities towards the substrate. A negative voltage was applied to the substrate to modify the ion energy and density. Furthermore the current caused by charge carriers impinging on the substrate was measured and compared with the results of the monitoring system. The electron and ion densities were measured by varying the emission current of the e-gun achieving silicon growth rates between 0.07 and 0.45 nm/s and by changing the voltage applied to the substrate between 0 to -1000 V. The dependencies of ion and electron densities were shown and discussed within the framework of a simple model. The charged carrier densities measured with the monitoring system enable to separate the ion part of the substrate current and show its correlation to the generation rate. Comparing the ion density on the whole substrate and in the center gives a hint to the ion beam focusing effect. The maximum ion and electron current densities obtained were 0.40 and 0.61 μA/cm2, respectively.

  10. Investigation of the silicon ion density during molecular beam epitaxy growth

    CERN Document Server

    Eifler, G; Ashurov, K; Morozov, S

    2002-01-01

    Ions impinging on a surface during molecular beam epitaxy influence the growth and the properties of the growing layer, for example, suppression of dopant segregation and the generation of crystal defects. The silicon electron gun in the molecular beam epitaxy (MBE) equipment is used as a source for silicon ions. To use the effect of ion bombardment the mechanism of generation and distribution of ions was investigated. A monitoring system was developed and attached at the substrate position in the MBE growth chamber to measure the ion and electron densities towards the substrate. A negative voltage was applied to the substrate to modify the ion energy and density. Furthermore the current caused by charge carriers impinging on the substrate was measured and compared with the results of the monitoring system. The electron and ion densities were measured by varying the emission current of the e-gun achieving silicon growth rates between 0.07 and 0.45 nm/s and by changing the voltage applied to the substrate betw...

  11. Reduction in Recombination Current Density in Boron Doped Silicon Using Atomic Hydrogen

    Science.gov (United States)

    Young, Matthew Garett

    The solar industry has grown immensely in recent years and has reached a point where solar energy has now become inexpensive enough that it is starting to emerge as a mainstream electrical generation source. However, recent economic analysis has suggested that for solar to become a truly wide spread source of electricity, the costs still need to plummet by a factor of 8x. This demands new and innovative concepts to help lower such cost. In pursuit of this goal, this dissertation examines the use of atomic hydrogen to lessen the recombination current density in the boron doped region of n-type silicon solar cells. This required the development of a boron diffusion process that maintained the bulk lifetime of n-type silicon such that the recombination current density could be extracted by photoconductance spectroscopy. It is demonstrated that by hydrogenating boron diffusions, the majority carrier concentration can be controlled. By using symmetrically diffused test structures with quinhydrone-methanol surface passivation the recombination current density of a hydrogenated boron profile is shown to be less than that of a standard boron profile, by as much as 30%. This is then applied to a modified industrial silicon solar cell process to demonstrate an efficiency enhancement of 0.4%.

  12. A-centers in silicon studied with hybrid density functional theory

    KAUST Repository

    Wang, Hao; Chroneos, Alexander; Londos, C. A.; Schwingenschlö gl, Udo; Sgourou, E. N.

    2013-01-01

    Density functional theory employing hybrid functional is used to gain fundamental insight into the interaction of vacancies with oxygen interstitials to form defects known as A-centers in silicon. We calculate the formation energy of the defect with respect to the Fermi energy for all possible charge states. It is found that the neutral and doubly negatively charged A-centers dominate. The findings are analyzed in terms of the density of states and discussed in view of previous experimental and theoretical studies.

  13. G-centers in irradiated silicon revisited: A screened hybrid density functional theory approach

    KAUST Repository

    Wang, H.

    2014-05-13

    Electronic structure calculations employing screened hybrid density functional theory are used to gain fundamental insight into the interaction of carbon interstitial (Ci) and substitutional (Cs) atoms forming the CiCs defect known as G-center in silicon (Si). The G-center is one of the most important radiation related defects in Czochralski grown Si. We systematically investigate the density of states and formation energy for different types of CiCs defects with respect to the Fermi energy for all possible charge states. Prevalence of the neutral state for the C-type defect is established.

  14. Determination of density of band-gap states of hydrogenated amorphous silicon suboxide thin films

    International Nuclear Information System (INIS)

    Bacioglu, A.

    2005-01-01

    Variation of density of gap states of PECVD silicon suboxide films with different oxygen concentrations was evaluated through electrical and optical measurements. Optical transmission and constant photocurrent method (CPM) were used to determine absorption coefficient as a function of photon energy. From these measurements the localized density of states between the valance band mobility edge and Fermi level has been determined. To determine the variation of conduction band edge, steady state photoconductivity (SSPC), photoconductivity response time (PCRT) and transient photoconductivity (TPC) measurements were utilized. Results indicate that the conduction and valance band edges, both, widen monotonically with oxygen content

  15. A-centers in silicon studied with hybrid density functional theory

    KAUST Repository

    Wang, Hao

    2013-07-29

    Density functional theory employing hybrid functional is used to gain fundamental insight into the interaction of vacancies with oxygen interstitials to form defects known as A-centers in silicon. We calculate the formation energy of the defect with respect to the Fermi energy for all possible charge states. It is found that the neutral and doubly negatively charged A-centers dominate. The findings are analyzed in terms of the density of states and discussed in view of previous experimental and theoretical studies.

  16. Influence of sintering atmospheres on the aluminium sintering characteristics

    International Nuclear Information System (INIS)

    Mintzer, S.; Bermudez Belkys, S.

    1993-01-01

    This paper describes the aluminium powder (Al) cool compacted (at 95% from theoretical density) which was sintered at 903 K during 4 hours at different atmospheres; oxidizing (air), inert Argon (Ar), Nitrogen (N) and high vacuum. The results obtained show: a) porosity measurements; greater porosity when sintering in Ar and air. b) Metallographic and Scanning observations: many fine pores (< 1 μm) and pore lines distributed at random, at air sintering and greater pores distributed preferentially near the surface, in Ar and N atmospheres. c) Dimensional changes: tendency to contraction of the samples at N and vacuum sintering and expansion in Ar or air. d) Mechanical properties: greater strength and fluence stresses at air and N sintering. The analysis of the results is performed considering sintering modes in presence of an oxide layer and dropped inert gases. (Author)

  17. Data on the impact of increasing the W amount on the mass density and compressive properties of Ni-W alloys processed by spark plasma sintering.

    Science.gov (United States)

    Sadat, T; Hocini, A; Lilensten, L; Faurie, D; Tingaud, D; Dirras, G

    2016-06-01

    Bulk Ni-W alloys having composite-like microstructures are processed by spark plasma sintering (SPS) route of Ni and W powder blends as reported in a recent study of Sadat et al. (2016) (DOI of original article: doi:10.1016/j.matdes.2015.10.083) [1]. The present dataset deals with determination of mass density and evaluation of room temperature compressive mechanical properties as function of the amount of W (%wt. basis). The presented data concern: (i) measurement of the mass of each investigated Ni-W alloy which is subsequently used to compute the mass density of the alloy and (ii) the raw (stress (MPa) and strain ([Formula: see text])) data, which can be subsequently used for stress/ strain plots.

  18. Kinetics of sintering of uranium dioxide

    International Nuclear Information System (INIS)

    Soni, N.C.; Moorthy, V.K.

    1978-01-01

    The kinetics of sintering of UO 2 powders derived from ADU route and calcined at different temperatures was studied. The activation energy for sintering was found to depend on the calcination temperature, the density chosen and the sintering temperature range. The motive force for sintering is the excess free energy in the particle system. This exists in the powder compact in the form of surface energy and the excess lattice energy due to defects. The defects which can be eliminated at the operating temperature are responsible for the mobility and hence sintering. This concept of the motive force for sintering has been used to explain the difference in the activation energies observed in the present study. This would also explain phenomena such as attainment of limiting density, presence of optimum sintering temperature and the influence of calcination treatments on the sintering behaviour of powders. (author)

  19. Self-assisted GaAs nanowires with selectable number density on Silicon without oxide layer

    International Nuclear Information System (INIS)

    Bietti, S; Somaschini, C; Esposito, L; Sanguinetti, S; Frigeri, C; Fedorov, A; Geelhaar, L

    2014-01-01

    We present the growth of self-assisted GaAs nanowires (NWs) with selectable number density on bare Si(1 1 1), not covered by the silicon oxide. We determine the number density of the NWs by initially self-assembling GaAs islands on whose top a single NW is nucleated. The number density of the initial GaAs base islands can be tuned by droplet epitaxy and the same degree of control is then transferred to the NWs. This procedure is completely performed during a single growth in an ultra-high vacuum environment and requires neither an oxide layer covering the substrate, nor any pre-patterning technique. (paper)

  20. Ultrathin silicon dioxide layers with a low leakage current density formed by chemical oxidation of Si

    Science.gov (United States)

    Asuha,; Kobayashi, Takuya; Maida, Osamu; Inoue, Morio; Takahashi, Masao; Todokoro, Yoshihiro; Kobayashi, Hikaru

    2002-10-01

    Chemical oxidation of Si by use of azeotrope of nitric acid and water can form 1.4-nm-thick silicon dioxide layers with a leakage current density as low as those of thermally grown SiO2 layers. The capacitance-voltage (C-V) curves for these ultrathin chemical SiO2 layers have been measured due to the low leakage current density. The leakage current density is further decreased to approx1/5 (cf. 0.4 A/cm2 at the forward gate bias of 1 V) by post-metallization annealing at 200 degC in hydrogen. Photoelectron spectroscopy and C-V measurements show that this decrease results from (i) increase in the energy discontinuity at the Si/SiO2 interface, and (ii) elimination of Si/SiO2 interface states and SiO2 gap states.

  1. Evaluation of sintering effects on SiC-incorporated UO2 kernels under Ar and Ar–4%H2 environments

    International Nuclear Information System (INIS)

    Silva, Chinthaka M.; Lindemer, Terrence B.; Hunt, Rodney D.; Collins, Jack L.; Terrani, Kurt A.; Snead, Lance L.

    2013-01-01

    Silicon carbide (SiC) is suggested as an oxygen getter in UO 2 kernels used for tristructural isotropic (TRISO) particle fuels and to prevent kernel migration during irradiation. Scanning electron microscopy and X-ray diffractometry analyses performed on sintered kernels verified that an internal gelation process can be used to incorporate SiC in UO 2 fuel kernels. Even though the presence of UC in either argon (Ar) or Ar–4%H 2 sintered samples suggested a lowering of the SiC up to 3.5–1.4 mol%, respectively, the presence of other silicon-related chemical phases indicates the preservation of silicon in the kernels during sintering process. UC formation was presumed to occur by two reactions. The first was by the reaction of SiC with its protective SiO 2 oxide layer on SiC grains to produce volatile SiO and free carbon that subsequently reacted with UO 2 to form UC. The second process was direct UO 2 reaction with SiC grains to form SiO, CO, and UC. A slightly higher density and UC content were observed in the sample sintered in Ar–4%H 2 , but both atmospheres produced kernels with ∼95% of theoretical density. It is suggested that incorporating CO in the sintering gas could prevent UC formation and preserve the initial SiC content

  2. VV and VO2 defects in silicon studied with hybrid density functional theory

    KAUST Repository

    Christopoulos, Stavros Richard G

    2014-12-07

    The formation of VO (A-center), VV and VO2 defects in irradiated Czochralski-grown silicon (Si) is of technological importance. Recent theoretical studies have examined the formation and charge states of the A-center in detail. Here we use density functional theory employing hybrid functionals to analyze the formation of VV and VO2 defects. The formation energy as a function of the Fermi energy is calculated for all possible charge states. For the VV and VO2 defects double negatively charged and neutral states dominate, respectively.

  3. Dependence of the saturated light-induced defect density on macroscopic properties of hydrogenated amorphous silicon

    OpenAIRE

    Park, H. R.; Liu, J. Z.; Roca i Cabarrocas, P.; Maruyama, A.; Isomura, M.; Wagner, S.; Abelson, J. R.; Finger, F.

    2008-01-01

    We report a study of the saturated light-induced defect density Ns,sat in 37 hydrogenated (and in part fluorinated) amorphous silicon [a-Si:H(F)] films grown in six different reactors under widely different conditions. Ns,sat was attained by exposing the films to light from a krypton ion laser (λ=647.1 nm). Ns,sat is determined by the constant photocurrent method and lies between 5×1016 and 2×1017 cm−3. Ns,sat drops with decreasing optical gap Eopt and hydrogen content cH, but is not correlat...

  4. Spontaneous layering of porous silicon layers formed at high current densities

    Energy Technology Data Exchange (ETDEWEB)

    Parkhutik, Vitali; Curiel-Esparza, Jorge; Millan, Mari-Carmen [R and D Center MTM, Technical University of Valencia, Valencia (Spain); Albella, Jose [Institute of Materials Science (ICMM CSIC) Madrid (Spain)

    2005-06-01

    We report here a curious effect of spontaneous fracturing of the silicon layers formed in galvanostatic conditions at medium and high current densities. Instead of formation of homogeneous p-Si layer as at low currents, a stack of thin layers is formed. Each layer is nearly separated from others and possesses rather flat interfaces. The effects is observed using p{sup +}-Si wafers for the p-Si formation and starts being noticeable at above 100 mA/cm{sup 2}. We interpret these results in terms of the porous silicon growth model where generation of dynamic mechanical stress during the p-Si growth causes sharp changes in Si dissolution mechanism from anisotropic etching of individual needle-like pores in silicon to their branching and isotropic etching. At this moment p-Si layer loses its adhesion to the surface of Si wafer and another p-Si layer starts growing. One of the mechanisms triggering on the separation of p-Si layers from one another is a fluctuation of local anodic current in the pore bottoms associated with gas bubble evolution during the p-Si formation. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  5. Method of sintering ceramic materials

    Science.gov (United States)

    Holcombe, Cressie E.; Dykes, Norman L.

    1992-01-01

    A method for sintering ceramic materials is described. A ceramic article is coated with layers of protective coatings such as boron nitride, graphite foil, and niobium. The coated ceramic article is embedded in a container containing refractory metal oxide granules and placed within a microwave oven. The ceramic article is heated by microwave energy to a temperature sufficient to sinter the ceramic article to form a densified ceramic article having a density equal to or greater than 90% of theoretical density.

  6. Contribution to the densification study of silicon and zirconium carbides by an innovating process: the Spark Plasma Sintering; Contribution a l'etude de la densification des carbures de silicium et de zirconium par un procede innovant: le spark plasma sintering

    Energy Technology Data Exchange (ETDEWEB)

    Allemand, A. [CEA Saclay, Dept. des Materiaux pour le Nucleaire (DEN/DMN/SRMA/LTMEx), 91 - Gif-sur-Yvette (France); Guillard, F.; Galy, J. [Centre d' Elaboration de Materiaux et d' Etudes Structurales (CEMES-CNRS), 31 - Toulouse (France)

    2007-07-01

    In the framework of the CPR ISMIR, the works presented here take up the results of the thesis of F. Guillard defended on december 2006. This thesis has dealt with the Spark Plasma Sintering (SPS) technique and more particularly have been studied: 1)the {beta}SiC and ZrC sintering 2)the modelling of ZrC sintering by the SPS technique and 3)the studies of the carbides/oxides interfaces carried out by SPS. Concerning the {beta}SiC and ZrC sintering: the two carbides have been sintered between 1450 and 1950 C with times periods of 10 minutes and pressures between 50 and 150 MPa. These experiments have shown that the way to apply the pressure is of major importance. Moreover, 92% of densification can be reached after 5 minutes in 1850 C for SiC. For ZrC, 95% of densification is reached as soon as 5 minutes in 1750 C. Different correlations between grains size, density and the way to apply pressure are presented. For the SPS modelling of ZrC, two existing models, taking into account the diffusion laws, are used to try to model the SPS. The results are presented and discussed. At last, the SPS allows to make interfaces starting from powders or materials previously sintered. The SiC/ZrC and ZrO{sub 2}/SiC interfaces have been studied. A microstructural study is presented as well as a technique which allows the assembling with no cracks of SiC and ZrC. (O.M.)

  7. Sintering of Synroc D

    International Nuclear Information System (INIS)

    Robinson, G.

    1982-01-01

    Sintering has been investigated as a method for the mineralization and densification of high-level nuclear defense waste powder. Studies have been conducted on Synroc D composite powder LS04. Optimal densification has been found to be highly dependent on the characteristics of the starting material. Powder subjected to milling, which was believed to reduce the level of agglomeration and possibly particle size, was found to densify better than powder not subjected to this milling. Densities of greater than 95% of theoretical could be achieved for samples sintered at 1150 to 1200 0 C. Mineralogy was found to be as expected for Synroc D for samples sintered in a CO 2 /CO atmosphere where the Fe +2 /Fe +3 ratio was maintained at 1.0 to 5.75. In a more oxidizing, pure CO 2 atmosphere a new phase, not previously identified in Synroc D, was found

  8. Effect of grain alignment on interface trap density of thermally oxidized aligned-crystalline silicon films

    Science.gov (United States)

    Choi, Woong; Lee, Jung-Kun; Findikoglu, Alp T.

    2006-12-01

    The authors report studies of the effect of grain alignment on interface trap density of thermally oxidized aligned-crystalline silicon (ACSi) films by means of capacitance-voltage (C-V) measurements. C-V curves were measured on metal-oxide-semiconductor (MOS) capacitors fabricated on ⟨001⟩-oriented ACSi films on polycrystalline substrates. From high-frequency C-V curves, the authors calculated a decrease of interface trap density from 2×1012to1×1011cm-2eV-1 as the grain mosaic spread in ACSi films improved from 13.7° to 6.5°. These results demonstrate the effectiveness of grain alignment as a process technique to achieve significantly enhanced performance in small-grained (⩽1μm ) polycrystalline Si MOS-type devices.

  9. Doping strategies to control A-centres in silicon: Insights from hybrid density functional theory

    KAUST Repository

    Wang, Hao; Chroneos, Alexander I.; Londos, Charalampos A.; Sgourou, Efstratia N.; Schwingenschlö gl, Udo

    2014-01-01

    Hybrid density functional theory is used to gain insights into the interaction of intrinsic vacancies (V) and oxygen-vacancy pairs (VO, known as A-centres) with the dopants (D) germanium (Ge), tin (Sn), and lead (Pb) in silicon (Si). We determine the structures as well as binding and formation energies of the DVO and DV complexes. The results are discussed in terms of the density of states and in view of the potential of isovalent doping to control A-centres in Si. We argue that doping with Sn is the most efficient isovalent doping strategy to suppress A-centres by the formation of SnVO complexes, as these are charge neutral and strongly bound. © 2014 the Owner Societies.

  10. Effect of Current Density on Optical Properties of Anisotropic Photoelectrochemical Etched Silicon (110)

    Science.gov (United States)

    Amirhoseiny, M.; Hassan, Z.; Ng, S. S.

    2012-08-01

    Photoelectrochemical etched Si layers were prepared on n-type (110) oriented silicon wafer. The photoluminescence (PL), Fourier transformed infrared (FTIR) absorption and Raman spectroscopies of etched Si (110) at two different current densities were studied. Both samples showed PL peak in the visible spectral range situated from 650 nm to 750 nm. The corresponding changes in Raman spectra at different current density are discussed. The blue shift in the PL and Raman peaks is consequent of the quantum confinement effect and defect states of surface Si nanocrystallites complexes and hydrogen atoms of the photoelectrochemical etched Si (110) samples. The attenuated total reflection (ATR) results show both hydrogen and oxygen related IR modes in the samples which can be used to explain the PL effect.

  11. Extraction of the defect density of states in microcrystalline silicon from experimental results and simulation studies

    International Nuclear Information System (INIS)

    Tibermacine, T.; Ledra, M.; Ouhabab, N.; Merazga, A.

    2015-01-01

    The constant photocurrent method in the ac-mode (ac-CPM) is used to determine the defect density of states (DOS) in hydrogenated microcrystalline silicon (μc-Si:H) prepared by very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD). The absorption coefficient spectrum (ac-α(hv)), is measured under ac-CPM conditions at 60 Hz. The measured ac-α(hv) is converted by the CPM spectroscopy into a DOS distribution covering a portion in the lower energy range of occupied states. We have found that the density of valence band-tail states falls exponentially towards the gap with a typical band-tail width of 63 meV. Independently, computer simulations of the ac-CPM are developed using a DOS model that is consistent with the measured ac-α(hv) in the present work and a previously measured transient photocurrent (TPC) for the same material. The DOS distribution model suggested by the measurements in the lower and in the upper part of the energy-gap, as well as by the numerical modelling in the middle part of the energy-gap, coincide reasonably well with the real DOS distribution in hydrogenated microcrystalline silicon because the computed ac-α(hv) is found to agree satisfactorily with the measured ac-α(hv). (paper)

  12. Development of nano-structured silicon carbide ceramics: from synthesis of the powder to sintered ceramics; Elaboration de ceramiques nanostructurees en carbure de silicium: de la synthese de la poudre a la ceramique frittee

    Energy Technology Data Exchange (ETDEWEB)

    Reau, A.

    2008-12-15

    The materials used inside future nuclear reactors will be subjected to very high temperature and neutrons flux. Silicon carbide, in the form of SiC{sub f}/SiC nano-structured composite is potentially interesting for this type of application. It is again necessary to verify the contribution of nano-structure on the behaviour of this material under irradiation. To verify the feasibility and determine the properties of the matrix, it was envisaged to produce it by powder metallurgy from SiC nanoparticles. The objective is to obtain a fully dense nano-structured SiC ceramic without additives. For that, a parametric study of the phases of synthesis and agglomeration was carried out, the objective of which is to determine the active mechanisms and the influence of the key parameters. Thus, studying the nano-powder synthesis by laser pyrolysis allowed to produce, with high production rates, homogeneous batches of SiC nanoparticles whose size can be adjusted between 15 and 90 nm. These powders have been densified by an innovating method: Spark Plasma Sintering (SPS). The study and the optimization of the key parameters allowed the densification of silicon carbide ceramic without sintering aids while preserving the nano-structure of material. The thermal and mechanical properties of final materials were studied in order to determine the influence of the microstructure on their properties. (author)

  13. Electromagnetic local density of states in graphene-covered porous silicon carbide

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Ting [Department of Physics, Nanchang University, Nanchang 330031 (China); Wang, Tong-Biao, E-mail: tbwang@ncu.edu.cn [Department of Physics, Nanchang University, Nanchang 330031 (China); Liao, Qing-Hua; Liu, Jiang-Tao; Yu, Tian-Bao [Department of Physics, Nanchang University, Nanchang 330031 (China); Liu, Nian-Hua [Institute for Advanced Study, Nanchang University, Nanchang 330031 (China)

    2017-06-21

    Surface phonon polariton supported by silicon carbide (SiC) can be strongly coupled with graphene plasmon in the graphene-covered SiC bulk. The spectrum of the electromagnetic local density of states exhibits two peaks whose positions can be tuned by the chemical potential of graphene. In this work, we study the electromagnetic local density of states in the proximity of a graphene-covered SiC with periodic hole arrays. The well-known peak from the coupling of surface polariton supported by SiC and graphene plasmon splits into two. With increased volume ratio of holes, one of the split peak shifts towards high frequencies, whereas the other moves towards low frequencies. The dependence of split-peak positions on the chemical potential and permittivity of filling materials in the holes are also investigated. This study offers another method of modulating the electromagnetic local density of states. - Highlights: • The electromagnetic local density of states in the proximity of graphene-covered anisotropic SiC is firstly studied. • The peak from resonance of surface phonon polaritons in the EM-LDOS spectrum can be split into two. • The split peaks can be tuned by chemical potential, filling factor, and filling materials. • Our results provide a new method to modulate the EM-LDOS.

  14. Discrimination symbol applying method for sintered nuclear fuel product

    International Nuclear Information System (INIS)

    Ishizaki, Jin

    1998-01-01

    The present invention provides a symbol applying method for applying discrimination information such as an enrichment degree on the end face of a sintered nuclear product. Namely, discrimination symbols of information of powders are applied by a sintering aid to the end face of a molded member formed by molding nuclear fuel powders under pressure. Then, the molded product is sintered. The sintering aid comprises aluminum oxide, a mixture of aluminum oxide and silicon dioxide, aluminum hydride or aluminum stearate alone or in admixture. As an applying means of the sintering aid, discrimination symbols of information of powders are drawn by an isostearic acid on the end face of the molded product, and the sintering aid is sprayed thereto, or the sintering aid is applied directly, or the sintering aid is suspended in isostearic acid, and the suspension is applied with a brush. As a result, visible discrimination information can be applied to the sintered member easily. (N.H.)

  15. Low-density silicon thin films for lithium-ion battery anodes

    Energy Technology Data Exchange (ETDEWEB)

    Demirkan, M.T., E-mail: tmdemirkan@ualr.edu [Department of Physics and Astronomy, University of Arkansas at Little Rock, Little Rock, AR 72204 (United States); Department of Materials Science and Engineering, Gebze Technical University, Kocaeli (Turkey); Trahey, L. [Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Karabacak, T. [Department of Physics and Astronomy, University of Arkansas at Little Rock, Little Rock, AR 72204 (United States)

    2016-02-01

    Density of sputter deposited silicon (Si) thin films was changed by a simple working gas pressure control process, and its effects on the cycling performance of Si films in Li-ion batteries as anodes was investigated. Higher gas pressure results in reduced film densities due to a shadowing effect originating from lower mean free path of sputter atoms, which leads to a wider angular distribution of the incoming flux and formation of a porous film microstructure. Si thin film anodes of different densities ranging from 2.27 g/cm{sup 3} (film porosity ~ 3%) down to 1.64 g/cm{sup 3} (~ 30% porosity) were fabricated by magnetron sputtering at argon pressures varying from 0.2 Pa to 2.6 Pa, respectively. High density Si thin film anodes of 2.27 g/cm{sup 3} suffered from an unstable cycling behavior during charging/discharging depicted by a continuous reduction in specific down to ~ 830 mAh/g at the 100th cycle. Electrochemical properties of lower density films with 1.99 g/cm{sup 3} (~ 15% porosity) and 1.77 g/cm{sup 3} (~ 24% porosity) got worse resulting in only ~ 100 mAh/g capacity at 100th cycle. On the other hand, as the density of anode was further reduced down to about 1.64 g/cm{sup 3} (~ 30% porosity), cycling stability and capacity retention significantly improved resulting in specific capacity values ~ 650 mAh/g at 100th cycle with coulombic efficiencies of > 98%. Enhancement in our low density Si film anodes are believed to mainly originate from the availability of voids for volumetric expansion during lithiation and resulting compliant behavior that provides superior mechanical and electrochemical stability. - Highlights: • Low density Si thin films were studied as Li-ion battery anodes. • Low density Si films were fabricated by magnetron sputter deposition. • Density of Si films reduced down to as low as ~ 1.64 g/cm{sup 3} with a porosity of ~ 30% • Low density Si films presented superior mechanical properties during cycling.

  16. Effect of argon implantation on solid-state dewetting: control of size and surface density of silicon nanocrystals.

    Science.gov (United States)

    Almadori, Y; Borowik, Ł; Chevalier, N; Barbé, J-C

    2017-01-27

    Thermally induced solid-state dewetting of ultra-thin films on insulators is a process of prime interest, since it is capable of easily forming nanocrystals. If no particular treatment is performed to the film prior to the solid-state dewetting, it is already known that the size, the shape and the density of nanocrystals is governed by the initial film thickness. In this paper, we report a novel approach to control the size and the surface density of silicon nanocrystals based on an argon-implantation preliminary surface treatment. Using 7.5 nm thin layers of silicon, we show that increasing the implantation dose tends to form smaller silicon nanocrystals with diameter and height lower than 50 nm and 30 nm, respectively. Concomitantly, the surface density is increased by a factor greater than 20, going from 5 μm -2 to values over 100 μm -2 .

  17. High density micro-pyramids with silicon nanowire array for photovoltaic applications

    International Nuclear Information System (INIS)

    Rahman, Tasmiat; Navarro-Cía, Miguel; Fobelets, Kristel

    2014-01-01

    We use a metal assisted chemical etch process to fabricate silicon nanowire arrays (SiNWAs) onto a dense periodic array of pyramids that are formed using an alkaline etch masked with an oxide layer. The hybrid micro-nano structure acts as an anti-reflective coating with experimental reflectivity below 1% over the visible and near-infrared spectral regions. This represents an improvement of up to 11 and 14 times compared to the pyramid array and SiNWAs on bulk, respectively. In addition to the experimental work, we optically simulate the hybrid structure using a commercial finite difference time domain package. The results of the optical simulations support our experimental work, illustrating a reduced reflectivity in the hybrid structure. The nanowire array increases the absorbed carrier density within the pyramid by providing a guided transition of the refractive index along the light path from air into the silicon. Furthermore, electrical simulations which take into account surface and Auger recombination show an efficiency increase for the hybrid structure of 56% over bulk, 11% over pyramid array and 8.5% over SiNWAs. (paper)

  18. Dielectronic recombination data for dynamic finite-density plasmas. XV. The silicon isoelectronic sequence

    Science.gov (United States)

    Kaur, Jagjit; Gorczyca, T. W.; Badnell, N. R.

    2018-02-01

    Context. We aim to present a comprehensive theoretical investigation of dielectronic recombination (DR) of the silicon-like isoelectronic sequence and provide DR and radiative recombination (RR) data that can be used within a generalized collisional-radiative modelling framework. Aims: Total and final-state level-resolved DR and RR rate coefficients for the ground and metastable initial levels of 16 ions between P+ and Zn16+ are determined. Methods: We carried out multi-configurational Breit-Pauli DR calculations for silicon-like ions in the independent processes, isolated resonance, distorted wave approximation. Both Δnc = 0 and Δnc = 1 core excitations are included using LS and intermediate coupling schemes. Results: Results are presented for a selected number of ions and compared to all other existing theoretical and experimental data. The total dielectronic and radiative recombination rate coefficients for the ground state are presented in tabulated form for easy implementation into spectral modelling codes. These data can also be accessed from the Atomic Data and Analysis Structure (ADAS) OPEN-ADAS database. This work is a part of an assembly of a dielectronic recombination database for the modelling of dynamic finite-density plasmas.

  19. Study of the photo-detection efficiency of FBK High-Density silicon photomultipliers

    International Nuclear Information System (INIS)

    Zappalà, G.; Regazzoni, V.; Acerbi, F.; Ferri, A.; Gola, A.; Paternoster, G.; Zorzi, N.; Piemonte, C.

    2016-01-01

    This work presents a study of the factors contributing to the Photo-Detection Efficiency of Silicon Photomultipliers (SiPMs): Quantum Efficiency, Triggering Probability and Fill Factor. Two different SiPM High-Density technologies are tested, NUV-HD, based on n-on-p junction, and RGB-HD, based on p-on-n junction, developed at FBK, Trento. The quantum efficiency was measured on photodiodes produced along with the SiPMs. The triggering probability, as a function of wavelength and bias voltage, was measured on circular Single Photon Avalanche Diodes (SPADs) with 100% fill factor. Square SPADs, having the same layout of single SiPM cells, were studied to measure the effective fill factor and compare it to the nominal value. The comparison of the circular and square SPADs allows to get the transition region size between the effective active area of the cell and the one defined by the layout.

  20. Threshold defect production in silicon determined by density functional theory molecular dynamics simulations

    International Nuclear Information System (INIS)

    Holmstroem, E.; Kuronen, A.; Nordlund, K.

    2008-01-01

    We studied threshold displacement energies for creating stable Frenkel pairs in silicon using density functional theory molecular dynamics simulations. The average threshold energy over all lattice directions was found to be 36±2 STAT ±2 SYST eV, and thresholds in the directions and were found to be 20±2 SYST eV and 12.5±1.5 SYST eV, respectively. Moreover, we found that in most studied lattice directions, a bond defect complex is formed with a lower threshold than a Frenkel pair. The average threshold energy for producing either a bond defect or a Frenkel pair was found to be 24±1 STAT ±2 SYST eV

  1. Broadband enhancement of local density of states using silicon-compatible hyperbolic metamaterials

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yu; Inampudi, Sandeep; Capretti, Antonio [Department of Electrical and Computer Engineering and Photonics Center, Boston University, 8 Saint Mary' s Street Boston, Massachusetts 02215 (United States); Sugimoto, Hiroshi [Department of Electrical and Computer Engineering and Photonics Center, Boston University, 8 Saint Mary' s Street Boston, Massachusetts 02215 (United States); Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501 (Japan); Fujii, Minoru [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501 (Japan); Dal Negro, Luca, E-mail: dalnegro@bu.edu [Department of Electrical and Computer Engineering and Photonics Center, Boston University, 8 Saint Mary' s Street Boston, Massachusetts 02215 (United States); Division of Materials Science and Engineering, Boston University, 15 Saint Mary' s Street, Brookline, Massachusetts 02446 (United States)

    2015-06-15

    Light emitting silicon quantum dots by colloidal synthesis were uniformly spin-coated into a 20 nm-thick film and deposited atop a hyperbolic metamaterial of alternating TiN and SiO{sub 2} sub-wavelength layers. Using steady-state and time-resolved photoluminescence spectroscopy as a function of the emission wavelength in partnership with rigorous electromagnetic modeling of dipolar emission, we demonstrate enhanced Local Density of States and coupling to high-k modes in a broad spectral range. These findings provide an alternative approach for the engineering of novel Si-compatible broadband sources that leverage the control of radiative transitions in hyperbolic metamaterials and the flexibility of the widespread Si platform.

  2. Density gradient in SiO 2 films on silicon as revealed by positron annihilation spectroscopy

    Science.gov (United States)

    Revesz, A. G.; Anwand, W.; Brauer, G.; Hughes, H. L.; Skorupa, W.

    2002-06-01

    Positron annihilation spectroscopy of thermally grown and deposited SiO 2 films on silicon shows in a non-destructive manner that these films have a gradient in their density. The gradient is most pronounced for the oxide grown in dry oxygen. Oxidation in water-containing ambient results in an oxide with reduced gradient, similarly to the gradient in the deposited oxide. These observations are in accordance with earlier optical and other studies using stepwise etching or a set of samples of varying thickness. The effective oxygen charge, which is very likely one of the reasons for the difference in the W parameters of silica glass and quartz crystal, could be even higher at some localized configurations in the SiO 2 films resulting in increased positron trapping.

  3. Ab initio density functional theory investigation of Li-intercalated silicon carbide nanotube bundles

    International Nuclear Information System (INIS)

    Moradian, Rostam; Behzad, Somayeh; Chegel, Raad

    2009-01-01

    We present the results of ab initio density functional theory calculations on the energetic, and geometric and electronic structure of Li-intercalated (6,6) silicon carbide nanotube (SiCNT) bundles. Our results show that intercalation of lithium leads to the significant changes in the geometrical structure. The most prominent effect of Li intercalation on the electronic band structure is a shift of the Fermi energy which occurs as a result of charge transfer from lithium to the SiCNTs. All the Li-intercalated (6,6) SiCNT bundles are predicted to be metallic representing a substantial change in electronic properties relative to the undoped bundle, which is a wide band gap semiconductor. Both inside of the nanotube and the interstitial space are susceptible for intercalation. The present calculations suggest that the SiCNT bundle is a promising candidate for the anode material in battery applications.

  4. Ab initio density functional theory investigation of structural and electronic properties of silicon carbide nanotube bundles

    Science.gov (United States)

    Moradian, Rostam; Behzad, Somayeh; Chegel, Raad

    2008-10-01

    By using ab initio density functional theory the structural and electronic properties of isolated and bundled (8,0) and (6,6) silicon carbide nanotubes (SiCNTs) are investigated. Our results show that for such small diameter nanotubes the inter-tube interaction causes a very small radial deformation, while band splitting and reduction of the semiconducting energy band gap are significant. We compared the equilibrium interaction energy and inter-tube separation distance of (8,0) SiCNT bundle with (10,0) carbon nanotube (CNT) bundle where they have the same radius. We found that there is a larger inter-tube separation and weaker inter-tube interaction in the (8,0) SiCNT bundle with respect to (10,0) CNT bundle, although they have the same radius.

  5. Ab initio density functional theory investigation of Li-intercalated silicon carbide nanotube bundles

    Science.gov (United States)

    Moradian, Rostam; Behzad, Somayeh; Chegel, Raad

    2009-06-01

    We present the results of ab initio density functional theory calculations on the energetic, and geometric and electronic structure of Li-intercalated ( 6,6) silicon carbide nanotube (SiCNT) bundles. Our results show that intercalation of lithium leads to the significant changes in the geometrical structure. The most prominent effect of Li intercalation on the electronic band structure is a shift of the Fermi energy which occurs as a result of charge transfer from lithium to the SiCNTs. All the Li-intercalated ( 6,6) SiCNT bundles are predicted to be metallic representing a substantial change in electronic properties relative to the undoped bundle, which is a wide band gap semiconductor. Both inside of the nanotube and the interstitial space are susceptible for intercalation. The present calculations suggest that the SiCNT bundle is a promising candidate for the anode material in battery applications.

  6. Ab initio density functional theory investigation of structural and electronic properties of silicon carbide nanotube bundles

    International Nuclear Information System (INIS)

    Moradian, Rostam; Behzad, Somayeh; Chegel, Raad

    2008-01-01

    By using ab initio density functional theory the structural and electronic properties of isolated and bundled (8,0) and (6,6) silicon carbide nanotubes (SiCNTs) are investigated. Our results show that for such small diameter nanotubes the inter-tube interaction causes a very small radial deformation, while band splitting and reduction of the semiconducting energy band gap are significant. We compared the equilibrium interaction energy and inter-tube separation distance of (8,0) SiCNT bundle with (10,0) carbon nanotube (CNT) bundle where they have the same radius. We found that there is a larger inter-tube separation and weaker inter-tube interaction in the (8,0) SiCNT bundle with respect to (10,0) CNT bundle, although they have the same radius

  7. Ab initio density functional theory investigation of Li-intercalated silicon carbide nanotube bundles

    Energy Technology Data Exchange (ETDEWEB)

    Moradian, Rostam [Physics Department, Faculty of Science, Razi University, Kermanshah (Iran, Islamic Republic of); Nano Science and Technology Research Center, Razi University, Kermanshah (Iran, Islamic Republic of); Computational Physical Science Research Laboratory, Department of Nano Science, Institute for Studies in Theoretical Physics and Mathematics (IPM), PO Box 19395-5531, Tehran (Iran, Islamic Republic of)], E-mail: moradian.rostam@gmail.com; Behzad, Somayeh; Chegel, Raad [Physics Department, Faculty of Science, Razi University, Kermanshah (Iran, Islamic Republic of)

    2009-06-15

    We present the results of ab initio density functional theory calculations on the energetic, and geometric and electronic structure of Li-intercalated (6,6) silicon carbide nanotube (SiCNT) bundles. Our results show that intercalation of lithium leads to the significant changes in the geometrical structure. The most prominent effect of Li intercalation on the electronic band structure is a shift of the Fermi energy which occurs as a result of charge transfer from lithium to the SiCNTs. All the Li-intercalated (6,6) SiCNT bundles are predicted to be metallic representing a substantial change in electronic properties relative to the undoped bundle, which is a wide band gap semiconductor. Both inside of the nanotube and the interstitial space are susceptible for intercalation. The present calculations suggest that the SiCNT bundle is a promising candidate for the anode material in battery applications.

  8. Responsivity Dependent Anodization Current Density of Nanoporous Silicon Based MSM Photodetector

    Directory of Open Access Journals (Sweden)

    Batool Eneaze B. Al-Jumaili

    2016-01-01

    Full Text Available Achieving a cheap and ultrafast metal-semiconductor-metal (MSM photodetector (PD for very high-speed communications is ever-demanding. We report the influence of anodization current density variation on the response of nanoporous silicon (NPSi based MSM PD with platinum (Pt contact electrodes. Such NPSi samples are grown from n-type Si (100 wafer using photoelectrochemical etching with three different anodization current densities. FESEM images of as-prepared samples revealed the existence of discrete pores with spherical and square-like shapes. XRD pattern displayed the growth of nanocrystals with (311 lattice orientation. The nanocrystallite sizes obtained using Scherrer formula are found to be between 20.8 nm and 28.6 nm. The observed rectifying behavior in the I-V characteristics is ascribed to the Pt/PSi/n-Si Schottky barrier formation, where the barrier height at the Pt/PSi interface is estimated to be 0.69 eV. Furthermore, this Pt/PSi/Pt MSM PD achieved maximum responsivity of 0.17 A/W and quantum efficiency as much as 39.3%. The photoresponse of this NPSi based MSM PD demonstrated excellent repeatability, fast response, and enhanced saturation current with increasing anodization current density.

  9. Agglomeration of amorphous silicon film with high energy density excimer laser irradiation

    International Nuclear Information System (INIS)

    He Ming; Ishihara, Ryoichi; Metselaar, Wim; Beenakker, Kees

    2007-01-01

    In this paper, agglomeration phenomena of amorphous Si (α-Si) films due to high energy density excimer laser irradiation are systematically investigated. The agglomeration, which creates holes or breaks the continuous Si film up into spherical beads, is a type of serious damage. Therefore, it determines an upper energy limit for excimer laser crystallization. It is speculated that the agglomeration is caused by the boiling of molten Si. During this process, outbursts of heterogeneously nucleated vapor bubbles are promoted by the poor wetting property of molten silicon on the SiO 2 layer underneath. The onset of the agglomeration is defined by extrapolating the hole density as a function of the energy density of the laser pulse. A SiO 2 capping layer (CL) is introduced on top of the α-Si film to investigate its influence on the agglomeration. It is found that effects of the CL depend on its thickness. The CL with a thickness less than 300 nm can be used to suppress the agglomeration. A thin CL acts as a confining layer and puts a constraint on bubble burst, and hence suppresses the agglomeration

  10. First-principles equation-of-state table of silicon and its effects on high-energy-density plasma simulations

    Science.gov (United States)

    Hu, S. X.; Gao, R.; Ding, Y.; Collins, L. A.; Kress, J. D.

    2017-04-01

    Using density-functional theory-based molecular-dynamics simulations, we have investigated the equation of state for silicon in a wide range of plasma density and temperature conditions of ρ =0.001 -500 g /c m3 and T =2000 -108K . With these calculations, we have established a first-principles equation-of-state (FPEOS) table of silicon for high-energy-density (HED) plasma simulations. When compared with the widely used SESAME-EOS model (Table 3810), we find that the FPEOS-predicted Hugoniot is ˜20% softer; for off-Hugoniot plasma conditions, the pressure and internal energy in FPEOS are lower than those of SESAME EOS for temperatures above T ≈ 1-10 eV (depending on density), while the former becomes higher in the low-T regime. The pressure difference between FPEOS and SESAME 3810 can reach to ˜50%, especially in the warm-dense-matter regime. Implementing the FPEOS table of silicon into our hydrocodes, we have studied its effects on Si-target implosions. When compared with the one-dimensional radiation-hydrodynamics simulation using the SESAME 3810 EOS model, the FPEOS simulation showed that (1) the shock speed in silicon is ˜10% slower; (2) the peak density of an in-flight Si shell during implosion is ˜20% higher than the SESAME 3810 simulation; (3) the maximum density reached in the FPEOS simulation is ˜40% higher at the peak compression; and (4) the final areal density and neutron yield are, respectively, ˜30% and ˜70% higher predicted by FPEOS versus the traditional simulation using SESAME 3810. All of these features can be attributed to the larger compressibility of silicon predicted by FPEOS. These results indicate that an accurate EOS table, like the FPEOS presented here, could be essential for the precise design of targets for HED experiments.

  11. Human islet viability and function is maintained during high density shipment in silicone rubber membrane vessels

    Science.gov (United States)

    Kitzmann, Jennifer P; Pepper, Andrew R; Lopez, Boris G; Pawlick, Rena; Kin, Tatsuya; O’Gorman, Doug; Mueller, Kathryn R; Gruessner, Angelika C; Avgoustiniatos, Efstathios S; Karatzas, Theodore; Szot, Greg L; Posselt, Andrew M; Stock, Peter G; Wilson, John R; Shapiro, AM; Papas, Klearchos K

    2014-01-01

    The shipment of human islets from processing centers to distant laboratories is beneficial for both research and clinical applications. The maintenance of islet viability and function in transit is critically important. Gas-permeable silicone rubber membrane (SRM) vessels reduce the risk of hypoxia-induced death or dysfunction during high-density islet culture or shipment. SRM vessels may offer additional advantages: they are cost-effective (fewer flasks, less labor needed), safer (lower contamination risk), and simpler (culture vessel can also be used for shipment). Human islets(IE) were isolated from two manufacturing centers and shipped in 10cm2 surface area SRM vessels in temperature and pressure controlled containers to a distant center following at least two days of culture (n = 6). Three conditions were examined: low density (LD), high density (HD), and a micro centrifuge tube negative control (NC). LD was designed to mimic the standard culture density for human islet preparations (200 IE/cm2), while HD was designed to have a 20-fold higher tissue density, which would enable the culture of an entire human isolation in 1–3 vessels. Upon receipt, islets were assessed for viability, measured by oxygen consumption rate normalized to DNA content (OCR/DNA), and quantity, measured by DNA, and, when possible, potency and function with dynamic glucose-stimulated insulin secretion (GSIS) measurements and transplants in immunodeficient B6 rag mice. Post-shipment OCR/DNA was not reduced in HD versus LD, and was substantially reduced in the NC condition. HD islets exhibited normal function post-shipment. Based on the data we conclude that entire islet isolations (up to 400,000 IE) may be shipped using a single, larger SRM vessel with no negative effect on viability and ex vivo and in vivo function. PMID:25131090

  12. Strain-enhanced sintering of iron powders

    Energy Technology Data Exchange (ETDEWEB)

    Amador, D.R.; Torralba, J.M. [Universidad Carlos III de Madrid, Departamento de Ciencias de Materiales e Ingenieria Metalurgica, Leganes, Madrid (Spain); Monge, M.A.; Pareja, R. [Universidad Carlos III de Madrid, Departamento de Fisica, Madrid (Spain)

    2005-02-01

    Sintering of ball-milled and un-milled Fe powders has been investigated using dilatometry, X-ray, density, and positron annihilation techniques. A considerable sintering enhancement is found in milled powders showing apparent activation energies that range between 0.44 and 0.80 eV/at. The positron annihilation results, combined with the evolution of the shrinkage rate with sintering temperature, indicate generation of lattice defects during the sintering process of milled and un-milled powders. The sintering enhancement is attributed to pipe diffusion along the core of moving dislocations in the presence of the vacancy excess produced by plastic deformation. Positron annihilation results do not reveal the presence of sintering-induced defects in un-milled powders sintered above 1200 K, the apparent activation energy being in good agreement with that for grain-boundary diffusion in {gamma}-Fe. (orig.)

  13. Spatially resolved determination of the short-circuit current density of silicon solar cells via lock-in thermography

    International Nuclear Information System (INIS)

    Fertig, Fabian; Greulich, Johannes; Rein, Stefan

    2014-01-01

    We present a spatially resolved method to determine the short-circuit current density of crystalline silicon solar cells by means of lock-in thermography. The method utilizes the property of crystalline silicon solar cells that the short-circuit current does not differ significantly from the illuminated current under moderate reverse bias. Since lock-in thermography images locally dissipated power density, this information is exploited to extract values of spatially resolved current density under short-circuit conditions. In order to obtain an accurate result, one or two illuminated lock-in thermography images and one dark lock-in thermography image need to be recorded. The method can be simplified in a way that only one image is required to generate a meaningful short-circuit current density map. The proposed method is theoretically motivated, and experimentally validated for monochromatic illumination in comparison to the reference method of light-beam induced current.

  14. Evaluation of sintering effects on SiC-incorporated UO{sub 2} kernels under Ar and Ar–4%H{sub 2} environments

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Chinthaka M., E-mail: silvagw@ornl.gov [Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee TN 37831-6223 (United States); Materials Science and Engineering, The University of Tennessee Knoxville, TN 37996-2100, United States. (United States); Lindemer, Terrence B.; Hunt, Rodney D.; Collins, Jack L.; Terrani, Kurt A.; Snead, Lance L. [Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee TN 37831-6223 (United States)

    2013-11-15

    Silicon carbide (SiC) is suggested as an oxygen getter in UO{sub 2} kernels used for tristructural isotropic (TRISO) particle fuels and to prevent kernel migration during irradiation. Scanning electron microscopy and X-ray diffractometry analyses performed on sintered kernels verified that an internal gelation process can be used to incorporate SiC in UO{sub 2} fuel kernels. Even though the presence of UC in either argon (Ar) or Ar–4%H{sub 2} sintered samples suggested a lowering of the SiC up to 3.5–1.4 mol%, respectively, the presence of other silicon-related chemical phases indicates the preservation of silicon in the kernels during sintering process. UC formation was presumed to occur by two reactions. The first was by the reaction of SiC with its protective SiO{sub 2} oxide layer on SiC grains to produce volatile SiO and free carbon that subsequently reacted with UO{sub 2} to form UC. The second process was direct UO{sub 2} reaction with SiC grains to form SiO, CO, and UC. A slightly higher density and UC content were observed in the sample sintered in Ar–4%H{sub 2}, but both atmospheres produced kernels with ∼95% of theoretical density. It is suggested that incorporating CO in the sintering gas could prevent UC formation and preserve the initial SiC content.

  15. Indentation fatigue in silicon nitride, alumina and silicon carbide ...

    Indian Academy of Sciences (India)

    Repeated indentation fatigue (RIF) experiments conducted on the same spot of different structural ceramics viz. a hot pressed silicon nitride (HPSN), sintered alumina of two different grain sizes viz. 1 m and 25 m, and a sintered silicon carbide (SSiC) are reported. The RIF experiments were conducted using a Vicker's ...

  16. RF plasma cleaning of silicon substrates with high-density polyethylene contamination

    Science.gov (United States)

    Cagomoc, Charisse Marie D.; De Leon, Mark Jeffry D.; Ebuen, Anna Sophia M.; Gilos, Marlo Nicole R.; Vasquez, Magdaleno R., Jr.

    2018-01-01

    Upon contact with a polymeric material, microparticles from the polymer may adhere to a silicon (Si) substrate during device processing. The adhesion contaminates the surface and, in turn, leads to defects in the fabricated Si-based microelectronic devices. In this study, Si substrates with artificially induced high-density polyethylene (HDPE) contamination was exposed to 13.56 MHz radio frequency (RF) plasma utilizing argon and oxygen gas admixtures at a power density of 5.6 W/cm2 and a working pressure of 110 Pa for up to 6 min of treatment. Optical microscopy studies revealed the removal of up to 74% of the polymer contamination upon plasma exposure. Surface free energy (SFE) increased owing to the removal of contaminants as well as the formation of polar groups on the Si surface after plasma treatment. Atomic force microscopy scans showed a decrease in surface roughness from 12.25 nm for contaminated samples to 0.77 nm after plasma cleaning. The smoothening effect can be attributed to the removal of HDPE particles from the surface. In addition, scanning electron microscope images showed that there was a decrease in the amount of HDPE contaminants adhering onto the surface after plasma exposure.

  17. Hydrogen, oxygen and hydroxyl on porous silicon surface: A joint density-functional perturbation theory and infrared spectroscopy approach

    International Nuclear Information System (INIS)

    Alfaro, Pedro; Palavicini, Alessio; Wang, Chumin

    2014-01-01

    Based on the density functional perturbation theory (DFPT), infrared absorption spectra of porous silicon are calculated by using an ordered pore model, in which columns of silicon atoms are removed along the [001] direction and dangling bonds are initially saturated with hydrogen atoms. When these atoms on the pore surface are gradually replaced by oxygen ones, the ab-initio infrared absorption spectra reveal oxygen, hydroxyl, and coupled hydrogen–oxygen vibrational modes. In a parallel way, freestanding porous silicon samples were prepared by using electrochemical etching and they were further thermally oxidized in a dry oxygen ambient. Fourier transform infrared spectroscopy was used to investigate the surface modifications caused by oxygen adsorption. In particular, the predicted hydroxyl and oxygen bound to the silicon pore surface are confirmed. Finally, a global analysis of measured transmittance spectra has been performed by means of a combined DFPT and thin-film optics approach. - Highlights: • The density functional perturbation theory is used to study infrared absorption. • An ordered pore model is used to investigate the oxidation in porous silicon (PSi). • Infrared transmittance spectra of oxidized PSi freestanding samples are measured

  18. Modeling of sintering of functionally gradated materials

    International Nuclear Information System (INIS)

    Gasik, M.; Zhang, B.

    2001-01-01

    The functionally gradated materials (FGMs) are distinguished from isotropic materials by gradients of composition, phase distribution, porosity, and related properties. For FGMs made by powder metallurgy, sintering control is one of the most important factors. In this study sintering process of FGMs is modeled and simulated with a computer. A new modeling approach was used to formulate equation systems and the model for sintering of gradated hard metals, coupled with heat transfer and grain growth. A FEM module was developed to simulate FGM sintering in conventional, microwave and hybrid conditions, to calculate density, stress and temperature distribution. Behavior of gradated WC-Co hardmetal plate and cone specimens was simulated for various conditions, such as mean particle size, green density distribution and cobalt gradation parameter. The results show that the deformation behavior and stress history of graded powder compacts during heating, sintering and cooling could be predicted for optimization of sintering process. (author)

  19. Oxygen-promoted catalyst sintering influences number density, alignment, and wall number of vertically aligned carbon nanotubes.

    Science.gov (United States)

    Shi, Wenbo; Li, Jinjing; Polsen, Erik S; Oliver, C Ryan; Zhao, Yikun; Meshot, Eric R; Barclay, Michael; Fairbrother, D Howard; Hart, A John; Plata, Desiree L

    2017-04-20

    A lack of synthetic control and reproducibility during vertically aligned carbon nanotube (CNT) synthesis has stifled many promising applications of organic nanomaterials. Oxygen-containing species are particularly precarious in that they have both beneficial and deleterious effects and are notoriously difficult to control. Here, we demonstrated diatomic oxygen's ability, independent of water, to tune oxide-supported catalyst thin film dewetting and influence nanoscale (diameter and wall number) and macro-scale (alignment and density) properties for as-grown vertically aligned CNTs. In particular, single- or few-walled CNT forests were achieved at very low oxygen loading, with single-to-multi-walled CNT diameters ranging from 4.8 ± 1.3 nm to 6.4 ± 1.1 nm over 0-800 ppm O 2 , and an expected variation in alignment, where both were related to the annealed catalyst morphology. Morphological differences were not the result of subsurface diffusion, but instead occurred via Ostwald ripening under several hundred ppm O 2 , and this effect was mitigated by high H 2 concentrations and not due to water vapor (as confirmed in O 2 -free water addition experiments), supporting the importance of O 2 specifically. Further characterization of the interface between the Fe catalyst and Al 2 O 3 support revealed that either oxygen-deficit metal oxide or oxygen-adsorption on metals could be functional mechanisms for the observed catalyst nanoparticle evolution. Taken as a whole, our results suggest that the impacts of O 2 and H 2 on the catalyst evolution have been underappreciated and underleveraged in CNT synthesis, and these could present a route toward facile manipulation of CNT forest morphology through control of the reactive gaseous atmosphere alone.

  20. Growth of High-Density Zinc Oxide Nanorods on Porous Silicon by Thermal Evaporation

    Directory of Open Access Journals (Sweden)

    Nurul Izni Rusli

    2012-12-01

    Full Text Available The formation of high-density zinc oxide (ZnO nanorods on porous silicon (PS substrates at growth temperatures of 600–1000 °C by a simple thermal evaporation of zinc (Zn powder in the presence of oxygen (O2 gas was systematically investigated. The high-density growth of ZnO nanorods with (0002 orientation over a large area was attributed to the rough surface of PS, which provides appropriate planes to promote deposition of Zn or ZnOx seeds as nucleation sites for the subsequent growth of ZnO nanorods. The geometrical morphologies of ZnO nanorods are determined by the ZnOx seed structures, i.e., cluster or layer structures. The flower-like hexagonal-faceted ZnO nanorods grown at 600 °C seem to be generated from the sparsely distributed ZnOx nanoclusters. Vertically aligned hexagonal-faceted ZnO nanorods grown at 800 °C may be inferred from the formation of dense arrays of ZnOx clusters. The formation of disordered ZnO nanorods formed at 1000 °C may due to the formation of a ZnOx seed layer. The growth mechanism involved has been described by a combination of self-catalyzed vapor-liquid-solid (VLS and vapor-solid (VS mechanism. The results suggest that for a more precise study on the growth of ZnO nanostructures involving the introduction of seeds, the initial seed structures must be taken into account given their significant effects.

  1. Sintering of a class F fly ash

    Energy Technology Data Exchange (ETDEWEB)

    Joseph J. Biernacki; Anil K. Vazrala; H. Wayne Leimer [Tennessee Technological University, Cookeville, TN (United States). Department of Chemical Engineering

    2008-05-15

    The sinterability of a class F fly ash was investigated as a function of processing conditions including sintering temperature (1050-1200{sup o}C) and sintering time (0-90 min). Density, shrinkage, splitting tensile strength, water absorption and residual loss on ignition (RLOI) were evaluated as measures of sintering efficiency. Scanning electron microscopy (SEM), X-ray microanalysis and X-ray diffraction was used to examine microstructure and phase development due to processing. The results show that premature densification can inhibit complete carbon removal and that carbon combustion is influenced by both internal and external mass transfer conditions. 18 refs., 10 figs., 1 tab.

  2. Sintered-to-size FBR fuel

    International Nuclear Information System (INIS)

    Rasmussen, D.E.; Schaus, P.S.

    1984-04-01

    Fabrication of sintered-to-size PuO 2 -UO 2 fuel pellets was completed for testing of proposed FBR product specifications. Approximately 6000 pellets were fabricated to two nominal diameters and two densities by cold pressing and sintering to size. Process control and correlation between test and production batches are discussed

  3. Investigation of charges carrier density in phosphorus and boron doped SiNx:H layers for crystalline silicon solar cells

    International Nuclear Information System (INIS)

    Paviet-Salomon, B.; Gall, S.; Slaoui, A.

    2013-01-01

    Highlights: ► We investigate the properties of phosphorus and boron-doped silicon nitride films. ► Phosphorus-doped layers yield higher lifetimes than undoped ones. ► The fixed charges density decreases when increasing the films phosphorus content. ► Boron-doped films feature very low lifetimes. ► These doped layers are of particular interest for crystalline silicon solar cells. -- Abstract: Dielectric layers are of major importance in crystalline silicon solar cells processing, especially as anti-reflection coatings and for surface passivation purposes. In this paper we investigate the fixed charge densities (Q fix ) and the effective lifetimes (τ eff ) of phosphorus (P) and boron (B) doped silicon nitride layers deposited by plasma-enhanced chemical vapour deposition. P-doped layers exhibit a higher τ eff than standard undoped layers. In contrast, B-doped layers exhibit lower τ eff . A strong Q fix decrease is to be seen when increasing the P content within the film. Based on numerical simulations we also demonstrate that the passivation obtained with P- and B-doped layers are limited by the interface states rather than by the fixed charges

  4. SnO2*CoO ceramic obtained by microwave sintering

    International Nuclear Information System (INIS)

    Bordignon, M.A.N; Moura, F.; Zaghete, M.A.; Varela, J.A.; Perazolli, L.

    2009-01-01

    This work consists in the sintering study of CoO doped SnO 2 using microwave sintering oven and silicon carbide as a susceptor. The powders were obtained by dry oxides mixture and conformed in cylindrical shapes with 6mmx8mm and green density to 60%. Then the compacts were sintering up to 1.050 deg C, using heating rate of 50 deg C/min and isotherm up to 30min. The densities obtained were above 95% for both techniques. It was observed that occurred a temperature reducing of 400 deg C and time reducing of 210min to obtain the same densities, when was used the microwave oven without the phenomena of thermal runaway. So the sintered compacts were accomplished using DRX and SEM. It was made the electrical characterization (current x voltage) and it was found to have great potential in the production of dense ceramic-based SnO 2 with low resistivity to obtain electro-ceramic devices. (author)

  5. In-situ determination of electronic surface and volume defect density of amorphous silicon (a-Si:H) and silicon alloys

    International Nuclear Information System (INIS)

    Siebke, F.

    1992-07-01

    The density of localized gap states in the bulk and in the near-surface region of amorphous hydrogenated silicon (a-Si:H) was measured for non oxidized undoped, B-doped and P-doped samples as well as for films with low carbon (C) and germanium (Ge) content. Also the influence of light soaking on the bulk and surface density of states was investigated. The samples were prepared by rf glow discharge in an UHV-system at substrate temperatures between 100degC and 400degC and transferred to the analysis chamber by a vacuum lock. We combined the constant photocurrent method (CPM) and the total-yield photoelectron spectroscopy (TY) to obtain in-situ information about the defect densities. While the first method yields information about the density of states in the bulk, the other method obtains the density of occupied states in the near-surface region. The mean information depth of the TY-measurements is limited by the escape lenght of photoelectrons and can be estimated to 5 nm. In addition to the defect density the position of the Fermi energy was determined for the bulk by dark conductivity measurements and at the surface using a calibrated Kelvin probe. (orig.)

  6. Solid-state sintering of tungsten heavy alloys

    International Nuclear Information System (INIS)

    Gurwell, W.E.

    1994-10-01

    Solid-state sintering is a technologically important step in the fabrication of tungsten heavy alloys. This work addresses practical variables affecting the sinterability: powder particle size, powder mixing, and sintering temperature and time. Compositions containing 1 to 10 micrometer (μM) tungsten (W) powders can be fully densified at temperatures near the matrix solidus. Blending with an intensifier bar provided good dispersion of elemental powders and good as-sintered mechanical properties under adequate sintering conditions. Additional ball milling increases powder bulk density which primarily benefits mold and die filling. Although fine, 1 μm W powder blends have high sinterability, higher as-sintered ductilities are reached in shorter sintering times with coarser, 5 μm W powder blends; 10μm W powder blends promise the highest as-sintered ductilities due to their coarse microstructural W

  7. A New Method for Simulating Power Flow Density Focused by a Silicon Lens Antenna Irradiated with Linearly Polarized THz Wave

    Directory of Open Access Journals (Sweden)

    Catur Apriono

    2015-08-01

    Full Text Available A terahertz system uses dielectric lens antennas for focusing and collimating beams of terahertz wave radiation. Linearly polarized terahertz wave radiation has been widely applied in the terahertz system. Therefore, an accurate method for analyzing the power flow density in the dielectric lens antenna irradiated with the linearly polarized terahertz wave radiation is important to design the terahertz systems. In optics, ray-tracing method has been used to calculate the power flow density by a number density of rays. In this study, we propose a method of ray-tracing combined with Fresnel’s transmission, including transmittance and polarization of the terahertz wave radiation to calculate power flow density in a Silicon lens antenna. We compare power flow density calculated by the proposed method with the regular ray-tracing method. When the Silicon lens antenna is irradiated with linearly polarized terahertz wave radiation, the proposed method calculates the power flow density more accurately than the regular ray-tracing.

  8. Ab initio density functional theory investigation of structural and electronic properties of double-walled silicon carbide nanotubes

    Science.gov (United States)

    Moradian, Rostam; Behzad, Somayeh; Chegel, Raad

    2009-12-01

    By using ab initio density functional theory, the structural and electronic properties of (n,n)@(11,11) double-walled silicon carbide nanotubes (SiCNTs) are investigated. Our calculations reveal the existence of an energetically favorable double-walled nanotube whose interwall distance is about 4.3 Å. Interwall spacing and curvature difference are found to be essential for the electronic states around the Fermi level.

  9. Influence of sintering temperature on mechanical properties of spark plasma sintered pre-alloyed Ti-6Al-4 V powder

    Energy Technology Data Exchange (ETDEWEB)

    Muthuchamy, A.; Patel, Paridh; Rajadurai, M. [VIT Univ., Vellore, Tamil Nadu (India); Chaurisiya, Jitendar K. [NIT, Suratkal (India); Annamalai, A. Raja [VIT Univ., Vellore, Tamil Nadu (India). Centre for Innovative Manufacturing Research

    2018-04-01

    Spark plasma sintering provides faster heating that can create fully, or near fully, dense samples without significant grain growth. In this study, pre-alloyed Ti-6Al-4 V powder compact samples produced through field assisted sintering in a spark plasma sintering machine are compared as a function of consolidation temperature. The effect of sintering temperature on the densification mechanism, microstructural evolution and mechanical properties of spark plasma sintered Ti-6Al-4 V alloy compacts was investigated in detail. The compact, sintered at 1100 C, exhibited near net density, highest hardness and strength as compared to the other compacts processed at a temperature lower than 1100 C.

  10. Sintering of dioxide pellets in an oxidizing atmosphere (CO2)

    International Nuclear Information System (INIS)

    Santos, G.R.T.

    1992-01-01

    This work consists in the study of the sintering process of U O 2 pellets in an oxidizing atmosphere. Sintering tests were performed in an CO 2 atmosphere and the influence of temperature and time on the pellets density and microstructure were verified. The results obtained were compared to those from the conventional sintering process and its efficiency was confirmed. (author)

  11. Two steps sintering alumina doped with niobia

    International Nuclear Information System (INIS)

    Gomes, L.B.; Hatzfeld, J.; Heck, M.; Pokorny, A.; Bergmann, C.P.

    2014-01-01

    In this work, high surface area commercial alumina was doped with niobia and sintered in two steps in order to obtain dense materials with lower processing temperatures. The powders were milled and uniaxially pressed (200 MPa). The first step of sintering took place at 1100°C for 3, 6, 9 and 12 hours, followed by the second step at 1350°C for 3 hours. The relative density, porosity and water absorption of the samples were determined by the Archimedes method. The crystalline phases were analyzed by X-ray Diffraction (XRD) and the morphology of the samples after sintering, evaluated by Scanning Electron Microscopy (SEM). The results indicate that the use of niobia combined with the two steps sintering promotes an increase in the density of the material, even at lower sintering temperatures. (author)

  12. Structural, electronic, and vibrational properties of high-density amorphous silicon: a first-principles molecular-dynamics study.

    Science.gov (United States)

    Morishita, Tetsuya

    2009-05-21

    We report a first-principles study of the structural, electronic, and dynamical properties of high-density amorphous (HDA) silicon, which was found to be formed by pressurizing low-density amorphous (LDA) silicon (a normal amorphous Si) [T. Morishita, Phys. Rev. Lett. 93, 055503 (2004); P. F. McMillan, M. Wilson, D. Daisenberger, and D. Machon, Nature Mater. 4, 680 (2005)]. Striking structural differences between HDA and LDA are revealed. The LDA structure holds a tetrahedral network, while the HDA structure contains a highly distorted tetrahedral network. The fifth neighboring atom in HDA tends to be located at an interstitial position of a distorted tetrahedron composed of the first four neighboring atoms. Consequently, the coordination number of HDA is calculated to be approximately 5 unlike that of LDA. The electronic density of state (EDOS) shows that HDA is metallic, which is consistent with a recent experimental measurement of the electronic resistance of HDA Si. We find from local EDOS that highly distorted tetrahedral configurations enhance the metallic nature of HDA. The vibrational density of state (VDOS) also reflects the structural differences between HDA and LDA. Some of the characteristic vibrational modes of LDA are dematerialized in HDA, indicating the degradation of covalent bonds. The overall profile of the VDOS for HDA is found to be an intermediate between that for LDA and liquid Si under pressure (high-density liquid Si).

  13. Electronic and Optical Properties of Small Hydrogenated Silicon Quantum Dots Using Time-Dependent Density Functional Theory

    Directory of Open Access Journals (Sweden)

    Muhammad Mus-’ab Anas

    2015-01-01

    Full Text Available This paper presents a systematic study of the absorption spectrum of various sizes of small hydrogenated silicon quantum dots of quasi-spherical symmetry using the time-dependent density functional theory (TDDFT. In this study, real-time and real-space implementation of TDDFT involving full propagation of the time-dependent Kohn-Sham equations were used. The experimental results for SiH4 and Si5H12 showed good agreement with other earlier calculations and experimental data. Then these calculations were extended to study larger hydrogenated silicon quantum dots with diameter up to 1.6 nm. It was found that, for small quantum dots, the absorption spectrum is atomic-like while, for relatively larger (1.6 nm structure, it shows bulk-like behavior with continuous plateau with noticeable peak. This paper also studied the absorption coefficient of silicon quantum dots as a function of their size. Precisely, the dependence of dot size on the absorption threshold is elucidated. It was found that the silicon quantum dots exhibit direct transition of electron from HOMO to LUMO states; hence this theoretical contribution can be very valuable in discerning the microscopic processes for the future realization of optoelectronic devices.

  14. Silicon photonics integrated circuits: a manufacturing platform for high density, low power optical I/O's.

    Science.gov (United States)

    Absil, Philippe P; Verheyen, Peter; De Heyn, Peter; Pantouvaki, Marianna; Lepage, Guy; De Coster, Jeroen; Van Campenhout, Joris

    2015-04-06

    Silicon photonics integrated circuits are considered to enable future computing systems with optical input-outputs co-packaged with CMOS chips to circumvent the limitations of electrical interfaces. In this paper we present the recent progress made to enable dense multiplexing by exploiting the integration advantage of silicon photonics integrated circuits. We also discuss the manufacturability of such circuits, a key factor for a wide adoption of this technology.

  15. Sintering studies on iron-carbon-copper compacts

    Directory of Open Access Journals (Sweden)

    Perianayagam Philomen-D-Anand Raj

    2016-01-01

    Full Text Available Sintered Iron-Carbon-Copper parts are among the most widely used powder metallurgy product in automobile. In this paper, studies have been carried out to find out the sintering characteristics of iron-carbon-copper compacts when sintered in nitrogen atmosphere. The effects of various processing parameters on the sintering characteristics were studied. The various processing parameters considered were compaction pressure, green density and sintering temperature. The sintering characteristics determined were sintered density, porosity, dimensional change, micro hardness and radial crush strength. The results obtained have been discussed on the basis of micro structural observations. The characteristics of SEM fractography were also used to determine the mechanism of fracture. The fracture energy is strongly dependent on density of the compact.

  16. Composites comprising silicon carbide fibers dispersed in magnesia-aluminate matrix and fabrication thereof and of other composites by sinter forging

    Science.gov (United States)

    Panda, Prakash C.; Seydel, Edgar R.; Raj, Rishi

    1989-10-03

    A novel ceramic-ceramic composite of a uniform dispersion of silicon carbide fibers in a matrix of MgO.multidot.nAl.sub.2 O.sub.3 wherein n ranges from about 1 to about 4.5, said composite comprising by volume from 1 to 50% silicon carbide fibers and from 99 to 50% MgO.multidot.nAl.sub.2 O.sub.3. The composite is readily fabricated by forming a powder comprising a uniform dispersion of silicon carbide fibers in poorly crystalline phase comprising MgO and Al.sub.2 O.sub.3 in a mole ratio of n and either (a) hot pressing or preferably (b) cold pressing to form a preform and then forging utilizing a temperature in the range of 1100.degree. C. to 1900.degree. C. and a strain rate ranging from about 10.sup.-5 seconds .sup.-1 to about 1 seconds .sup.-1 so that surfaces cracks do not appear to obtain a shear deformation greater than 30%.

  17. Field assisted sintering of refractory carbide ceramics and fiber reinforced ceramic matrix composites

    Science.gov (United States)

    Gephart, Sean

    The sintering behaviors of silicon carbide (SiC) and boron carbide (B4C) based materials were investigated using an emerging sintering technology known as field assisted sintering technology (FAST), also known as spark plasma sintering (SPS) and pulse electric current sintering (PECS). Sintering by FAST utilizes high density electric current, uniaxial pressure, and relatively high heating rate compared to conventional sintering techniques. This effort investigated issues of scaling from laboratory FAST system (25 ton capacity) to industrial FAST system (250 ton capacity), as well as exploring the difference in sintering behavior of single phase B4C and SiC using FAST and conventional sintering techniques including hot-pressing (HP) and pressure-less sintering (PL). Materials were analyzed for mechanical and bulk properties, including characterization of density, hardness, fracture toughness, fracture (bend) strength, elastic modulus and microstructure. A parallel investigation was conducted in the development of ceramic matrix composites (CMC) using SiC powder impregnation of fiber compacts followed by FAST sintering. The FAST technique was used to sinter several B4C and SiC materials to near theoretical density. Preliminary efforts established optimized sintering temperatures using the smaller 25 ton laboratory unit, targeting a sample size of 40 mm diameter and 8 mm thickness. Then the same B4C and SiC materials were sintered by the larger 250 ton industrial FAST system, a HP system, and PL sintering system with a targeted dense material geometry of 4 x 4 x 0.315 inches3 (101.6 x 101.6 x 8 mm3). The resulting samples were studied to determine if the sintering dynamics and/or the resulting material properties were influenced by the sintering technique employed. This study determined that FAST sintered ceramic materials resulted in consistently higher averaged values for mechanical properties as well as smaller grain size when compared to conventionally sintered

  18. Factors Affecting the Sintering of UO2 Pellets

    International Nuclear Information System (INIS)

    El-Hakim, E.; Afifi, Y.K.

    1999-01-01

    Sintering of UO 2 pellets is affected by many parameters such as; UO 2 powder parameters, the conditions followed for preparing the green UO 2 pellets and the sintering scheme(heating and cooling rate, soaking time and temperature). The aim of this work is to study the effect of some these parameters on the characteristics of the sintered UO 2 pellets were qualified according to the technical specifications of Candu fuel. Pressed green pellets at different pressing force (15 to 50 k N) were sintered at 1650 ±20 degree for two hours to study the effect of pressing force on the sintered pellets characteristics; visual inspection, pellet dimensions, density and shrinkage ratio. Compacted green pellets at a pressing force of 48 k N were sintered at different sintering temperature (1600± 20 degree, 1650 ±20 degree, 1700± 20 degree) for two hours to study the effect of sintering temperature on the sintered pellets characteristics. The effect of the heating rate (200,300 and 400 degree per hour) on the sintered pellets characteristics was also investigated. It was found that the pressing force used to compact the green pellets had an effect on the density of the sintered pellets. Pellets pressed at 15 k N have a density of 10.3 g/cm 3 while, those pressed at 50 k N have a density of 10.6 g/cm 3. It was observed that increasing the heating rate to 400 degree /h lead to cracked pellets

  19. Design of experiment approach for sintering study of nanocrystalline SiC fabricated using plasma pressure compaction

    Directory of Open Access Journals (Sweden)

    Bothara M.G.

    2009-01-01

    Full Text Available Plasma pressure compaction (P2C is a novel sintering technique that enables the consolidation of silicon carbide with a nanoscale microstructure at a relatively low temperature. To achieve a high final density with optimized mechanical properties, the effects of various sintering factors pertaining to the temperature-time profile and pressure were characterized. This paper reports a design of experiment approach used to optimize the processing for a 100 nm SiC powder focused on four sintering factors: temperature, time, pressure, and heating rate. Response variables included the density and mechanical properties. A L9 orthogonal array approach that includes the signal-to-noise (S/N ratio and analysis of variance (ANOVA was employed to optimize the processing factors. All of the sintering factors have significant effect on the density and mechanical properties. A final density of 98.1% was achieved with a temperature of 1600°C, hold time of 30 min, pressure of 50 MPa, and heating rate of 100°C/min. The hardness reached 18.4 GPa with a fracture toughness of 4.6 MPa√m, and these are comparable to reports from prior studies using higher consolidation temperatures.

  20. Titanium Powder Sintering in a Graphite Furnace and Mechanical Properties of Sintered Parts

    Directory of Open Access Journals (Sweden)

    Changzhou Yu

    2017-02-01

    Full Text Available Recent accreditation of titanium powder products for commercial aircraft applications marks a milestone in titanium powder metallurgy. Currently, powder metallurgical titanium production primarily relies on vacuum sintering. This work reported on the feasibility of powder sintering in a non-vacuum furnace and the tensile properties of the as-sintered Ti. Specifically, we investigated atmospheric sintering of commercially pure (C.P. titanium in a graphite furnace backfilled with argon and studied the effects of common contaminants (C, O, N on sintering densification of titanium. It is found that on the surface of the as-sintered titanium, a severely contaminated porous scale was formed and identified as titanium oxycarbonitride. Despite the porous surface, the sintered density in the sample interiors increased with increasing sintering temperature and holding time. Tensile specimens cut from different positions within a large sintered cylinder reveal different tensile properties, strongly dependent on the impurity level mainly carbon and oxygen. Depending on where the specimen is taken from the sintered compact, ultimate tensile strength varied from 300 to 580 MPa. An average tensile elongation of 5% to 7% was observed. Largely depending on the interstitial contents, the fracture modes from typical brittle intergranular fracture to typical ductile fracture.

  1. First-principle study of quantum confinement effect on small sized silicon quantum dots using density-functional theory

    International Nuclear Information System (INIS)

    Anas, M. M.; Othman, A. P.; Gopir, G.

    2014-01-01

    Density functional theory (DFT), as a first-principle approach has successfully been implemented to study nanoscale material. Here, DFT by numerical basis-set was used to study the quantum confinement effect as well as electronic properties of silicon quantum dots (Si-QDs) in ground state condition. Selection of quantum dot models were studied intensively before choosing the right structure for simulation. Next, the computational result were used to examine and deduce the electronic properties and its density of state (DOS) for 14 spherical Si-QDs ranging in size up to ∼ 2 nm in diameter. The energy gap was also deduced from the HOMO-LUMO results. The atomistic model of each silicon QDs was constructed by repeating its crystal unit cell of face-centered cubic (FCC) structure, and reconstructed until the spherical shape obtained. The core structure shows tetrahedral (T d ) symmetry structure. It was found that the model need to be passivated, and hence it was noticed that the confinement effect was more pronounced. The model was optimized using Quasi-Newton method for each size of Si-QDs to get relaxed structure before it was simulated. In this model the exchange-correlation potential (V xc ) of the electrons was treated by Local Density Approximation (LDA) functional and Perdew-Zunger (PZ) functional

  2. Surface chemistry and density distribution influence on visible luminescence of silicon quantum dots: an experimental and theoretical approach.

    Science.gov (United States)

    Dutt, Ateet; Matsumoto, Yasuhiro; Santana-Rodríguez, G; Ramos, Estrella; Monroy, B Marel; Santoyo Salazar, J

    2017-01-04

    The impact of the surface reconstruction of the density distribution and photoluminescence of silicon quantum dots (QDs) embedded in a silicon oxide matrix (SiO x ) has been studied. Annealing treatments carried out on the as-deposited samples provoked the effusion of hydrogen species. Moreover, depending on the surrounding density and coalescence of QDs, they resulted in a change in the average size of the particles depending on the initial local environment. The shift in the luminescence spectra all over the visible region (blue, green and red) shows a strong dependence on the resultant change in the size and/or the passivation environment of QDs. Density functional theoretical (DFT) calculations support this fact and explain the possible electronic transitions (HOMO-LUMO gap) involved. Passivation in the presence of oxygen species lowers the band gap of Si 29 and Si 35 nanoclusters up to 1.7 eV, whereas, surface passivation in the environment of hydrogen species increases the band gap up to 4.4 eV. These results show a good agreement with the quantum confinement model described in this work and explain the shift in the luminescence all over the visible region. The results reported here offer vital insight into the mechanism of emission from silicon quantum dots which has been one of the most debated topics in the last two decades. QDs with multiple size distribution in different local environments (band gap) observed in this work could be used for the fabrication of light emission diodes (LEDs) or shift-conversion thin films in third generation efficient tandem solar cells for the maximum absorption of the solar spectrum in different wavelength regions.

  3. Silicon nanodot layers for photovoltaic application: size/density control and electrical properties

    Czech Academy of Sciences Publication Activity Database

    Stegemann, B.; Čermák, Jan; Rezek, Bohuslav; Kočka, Jan; Schmidt, M.

    2014-01-01

    Roč. 228, 4-5 (2014), 543-556 ISSN 0942-9352 R&D Projects: GA MŠk(CZ) LM2011026 Institutional support: RVO:68378271 Keywords : silicon nanodots * Kelvin probe force microscopy * current-sensing AFM * photovoltaic s Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.356, year: 2014

  4. Studies on the sintering of copper powder compacts

    International Nuclear Information System (INIS)

    Elmasry, M.A.A.; Abadir, M.F.; Mahdy, A.N.; Elkinawy, W.S.

    1995-01-01

    Solid state sintering behavior of cylindrical compacts, (1 cm diameter and 1 cm height), made of copper powder was studied within a range of compacting pressure of 75 up to 300 MPa, sintering temperature of 600 up to to 900 degree C, and sintering time of 5 up to 60 min in a reducing atmosphere composed of H2 and N 2 gases with a volumetric ratio 3:1. The green and the sintered densities were found to to increase with the compacting pressure. Higher sintering temperature, and time favour increased sintered density. probable mechanisms during the initial stage of sintering were disclosed. It was found that low pressures cause dilation of closed pores, and vice versa. At low pressures and temperatures the surface diffusion mechanism is favoured, While high temperatures favour lattice diffusion mechanism. at high pressures, the lattice diffusion mechanism is suppressed while surface diffusion predominates. Density and hence shrinkage were also found to increase with the increase of sintering time, While its rate increases with the increase of sintering temperature. the influence of sintering conditions on the hardness of the compacts was studied. An increase in hardness, When higher compacting pressures and higher sintering temperatures were adopted, has bee obtained. 11 figs

  5. A study on some properties of sintered stainless steel powder compacts with sintering conditions

    International Nuclear Information System (INIS)

    Lee, Bang Sik; Kim, Kwan Hyu; Lee, Doh Jae; Choi, Dap Chun

    1986-01-01

    Sintered specimens for the mechanical and corrosion tests were prepared from 316L, 410L and 434L stainless steel powder compacts with green densities in the range of 6.2∼7.0g/cm 3 . The experimental variables studied were green density, sintering atmosphere, temperature and time, type of lubricant used and cooling rate after sintering operation. Mechanical properties of green compacts and sintered specimens were evaluated. The corrosion tests were performed by potentiodynamic anodic polarization technique. Mechanical properties were very sensitive to the sintering atmosphere; sintering in dissociated ammonia resulted in the strengthing but embrittlement of sintered 316L, 410L and 434L strainless steel powder compacts. Their corrosion resistance was also decreased. The tensile strength was increased with increases in sintering time and temperature while the decreases in the yield strength were observed. The tensile properties of green compacts were shown to closely related to the green density. Addition of 1% acrawax as a lubricant was appeared to be most effective for the improvement of green strength. (Author)

  6. The influence of powder composition and sintering temperature on transformation kinetics, structure and mechanical properties of hot-pressed silicon nitride

    International Nuclear Information System (INIS)

    Knoch, H.; Ziegler, G.

    1977-01-01

    The strength at room temperature of hot-pressed silicon nitride is strongly dependent on the structure which in turn depends on powder composition and process parameters. Connections between production conditions (MgO content, pressing temperature, pressing time), structure (α/β content and morphology), and the properties at room temperature are discussed. The growth of oblong β grains - as a direct result of phase transition from α- to β-Si 3 N 4 - results in microstructural meshing and thus in a higher strength. Optimum mechanical properties are achieved after full phase transformation and with a microstructure as fine as possible. The direct connection between strength and transformed β fraction indicates a possible way for a relatively fast determination of optimum properties for a given initial powder. (orig.) [de

  7. Low threading dislocation density aluminum nitride on silicon carbide through the use of reduced temperature interlayers

    KAUST Repository

    Foronda, Humberto M.; Wu, Feng; Zollner, Christian; Alif, Muhammad Esmed; Saifaddin, Burhan; Almogbel, Abdullah; Iza, Michael; Nakamura, Shuji; DenBaars, Steven P.; Speck, James S.

    2017-01-01

    temperature on the AlN crystal quality, defect density, and surface morphology. The crystal quality was characterized using omega rocking curve scans and the threading dislocation density was determined by plan view transmission electron microscopy. The growth

  8. The Development of High-Density Vertical Silicon Nanowires and Their Application in a Heterojunction Diode

    Directory of Open Access Journals (Sweden)

    Wen-Chung Chang

    2016-06-01

    Full Text Available Vertically aligned p-type silicon nanowire (SiNW arrays were fabricated through metal-assisted chemical etching (MACE of Si wafers. An indium tin oxide/indium zinc oxide/silicon nanowire (ITO/IZO/SiNW heterojunction diode was formed by depositing ITO and IZO thin films on the vertically aligned SiNW arrays. The structural and electrical properties of the resulting ITO/IZO/SiNW heterojunction diode were characterized by field emission scanning electron microscopy (FE-SEM, X-ray diffraction (XRD, and current−voltage (I−V measurements. Nonlinear and rectifying I−V properties confirmed that a heterojunction diode was successfully formed in the ITO/IZO/SiNW structure. The diode had a well-defined rectifying behavior, with a rectification ratio of 550.7 at 3 V and a turn-on voltage of 2.53 V under dark conditions.

  9. Effects of Preform Density on Structure and Property of C/C-SiC Composites Fabricated by Gaseous Silicon Infiltration

    Directory of Open Access Journals (Sweden)

    CAO Yu

    2016-07-01

    Full Text Available The 3-D needled C/C preforms with different densities deposited by chemical vapor infiltration (CVI method were used to fabricate C/C-SiC composites by gaseous silicon infiltration (GSI. The porosity and CVI C thickness of the preforms were studied, and the effects of preform density on the mechanical and thermal properties of C/C-SiC composites were analyzed. The results show that with the increase of preform density, the preform porosity decreases and the CVI C thickness increases from several hundred nanometers to several microns. For the C/C-SiC composites, as the preform density increases, the residual C content increases while the density and residual Si content decreases. The SiC content first keeps at a high level of about 40% (volume fraction, which then quickly reduces. Meanwhile, the mechanical properties increase to the highest values when the preform density is 1.085g/cm3, with the flexure strength up to 308.31MP and fracture toughness up to 11.36MPa·m1/2, which then decrease as the preform density further increases. The thermal conductivity and CTE of the composites, however, decrease with the increase of preform density. It is found that when the preform porosity is too high, sufficient infiltration channels lead to more residual Si, and thinner CVI C thickness results in the severe corrosion of the reinforcing fibers by Si and lower mechanical properties. When the preform porosity is relatively low, the contents of Si and SiC quickly reduce since the infiltration channels are rapidly blocked, resulting in the formation of large closed pores and not high mechanical properties.

  10. Improving NASICON Sinterability through Crystallization under High Frequency Electrical Fields

    Directory of Open Access Journals (Sweden)

    Ilya eLisenker

    2016-03-01

    Full Text Available The effect of high frequency (HF electric fields on the crystallization and sintering rates of a lithium aluminum germanium phosphate (LAGP ion conducting ceramic was investigated. LAGP with the nominal composition Li1.5Al0.5Ge1.5(PO43 was crystallized and sintered, both conventionally and under effect of electrical field. Electrical field application, of 300V/cm at 1MHz, produced up to a 40% improvement in sintering rate of LAGP that was crystallized and sintered under the HF field. Heat sink effect of the electrodes appears to arrest thermal runaway and subsequent flash behavior. Sintered pellets were characterized using XRD, SEM, TEM and EIS to compare conventionally and field sintered processes. The as-sintered structure appears largely unaffected by the field as the sintering curves tend to converge beyond initial stages of sintering. Differences in densities and microstructure after 1 hour of sintering were minor with measured sintering strains of 31% vs. 26% with and without field, respectively . Ionic conductivity of the sintered pellets was evaluated and no deterioration due to the use of HF field was noted, though capacitance of grain boundaries due to secondary phases was significantly increased.

  11. Hydrothermal Cold Sintering

    Science.gov (United States)

    Kang, Xiaoyu

    C, respectively. Process variables were defined and effects of individual parameters were studied systematically through control variable method with Li2MoO4-water system. Crystalline structure, fractured surface morphology and chemical bonding information of the cold sintered pellets were studied with X-ray diffraction (XRD), field effect scanning electron microscopy (FE-SEM) and Raman spectroscopy, etc. Densification mechanism studies were conducted on ZnO. Through comparison experiments, it was found that the Zn2+ concentration in the solution is critical for densification, while dissolution of grains only serves as a means to the former. Through pressure dependent studies, a critical value was found, which correlated well with the hydrostatic pressure keeping liquid water from thermal expansion. These results confirmed establishment of hydrothermal condition that would be important for mass transport in densification. Densification rate variations with process time was estimated and similar time dependence to Kingery's model was found. The densification process was proposed to be consist of three consecutive stages, which are quick initial compaction, grain rearrangement and dissolution-reprecipitation events. Binary metal oxides with different acidities were subjected to cold sintering with various aqueous solutions in establishing a criteria for material selection. It was found that in general materials with high solubility at around neutral pH, high dissolution kinetics and similar free energy to their hydroxides or hydrates at ambient would be more likely for full densification with high phase purity. The anions in solution should also be wisely selected to avoid stable compound or complex formation. To extend the applicable material list for full densification, non-aqueous solvent of dimethyl sulfoxide (DMSO) based solution was studied for cold sintering. Both improvement of pellet density and suppression of hydroxide formation were achieved for MnO by using DMSO

  12. Optical excitation and electron relaxation dynamics at semiconductor surfaces: a combined approach of density functional and density matrix theory applied to the silicon (001) surface

    Energy Technology Data Exchange (ETDEWEB)

    Buecking, N

    2007-11-05

    In this work a new theoretical formalism is introduced in order to simulate the phononinduced relaxation of a non-equilibrium distribution to equilibrium at a semiconductor surface numerically. The non-equilibrium distribution is effected by an optical excitation. The approach in this thesis is to link two conventional, but approved methods to a new, more global description: while semiconductor surfaces can be investigated accurately by density-functional theory, the dynamical processes in semiconductor heterostructures are successfully described by density matrix theory. In this work, the parameters for density-matrix theory are determined from the results of density-functional calculations. This work is organized in two parts. In Part I, the general fundamentals of the theory are elaborated, covering the fundamentals of canonical quantizations as well as the theory of density-functional and density-matrix theory in 2{sup nd} order Born approximation. While the formalism of density functional theory for structure investigation has been established for a long time and many different codes exist, the requirements for density matrix formalism concerning the geometry and the number of implemented bands exceed the usual possibilities of the existing code in this field. A special attention is therefore attributed to the development of extensions to existing formulations of this theory, where geometrical and fundamental symmetries of the structure and the equations are used. In Part II, the newly developed formalism is applied to a silicon (001)surface in a 2 x 1 reconstruction. As first step, density-functional calculations using the LDA functional are completed, from which the Kohn-Sham-wave functions and eigenvalues are used to calculate interaction matrix elements for the electron-phonon-coupling an the optical excitation. These matrix elements are determined for the optical transitions from valence to conduction bands and for electron-phonon processes inside the

  13. On the sintering kinetics in UO2

    International Nuclear Information System (INIS)

    Marajofsky, A.

    1998-01-01

    The fabrication process of UO 2 pellets from powders involve pressing and a sintering anneal at high temperature (1650 deg. C to 1750 deg. C) during two or more hours in a hydrogen atmosphere. An alternative method is the oxidative sintering, made at lower temperature (1000 deg. C to 1300 deg. C) in a CO 2 or CO/CO 2 atmosphere. The sintering phenomena consist in the densification of the material by a thermal treatment below the fusion point. For a compact made by pressing a powder, sintering is the process of annulation of the porosity present in the compact or pellet. Several theories describe the sintering phenomena dividing it in three stages, initial, intermediate and final: in all of them the densification is a continuous growing function of time. Nevertheless it has been experimentally reported that a reduction of the density occurs in the third step of the sintering. The phenomena has been called solarization. Solarization has been attributed to the effect of the evolved gases from additives or to the CO 2 atmosphere in oxidative sintering. Thus, it is convenient to distinguish between solarization in oxidative or reducing conditions. Reducing solarization is a consequence of the tendency towards equilibrium of intergranular pores. In oxidative sintering it occurs in the reducing anneal after the sintering and is due to the change in the lattice parameter. This work shows examples of both types of solarization and qualitative interpretation of this phenomena. Both situations show the need of strict control of the sintering and powder production conditions. (author)

  14. Short-circuit current density imaging of crystalline silicon solar cells via lock-in thermography: Robustness and simplifications

    International Nuclear Information System (INIS)

    Fertig, Fabian; Greulich, Johannes; Rein, Stefan

    2014-01-01

    Spatially resolved determination of solar cell parameters is beneficial for loss analysis and optimization of conversion efficiency. One key parameter that has been challenging to access by an imaging technique on solar cell level is short-circuit current density. This work discusses the robustness of a recently suggested approach to determine short-circuit current density spatially resolved based on a series of lock-in thermography images and options for a simplified image acquisition procedure. For an accurate result, one or two emissivity-corrected illuminated lock-in thermography images and one dark lock-in thermography image have to be recorded. The dark lock-in thermography image can be omitted if local shunts are negligible. Furthermore, it is shown that omitting the correction of lock-in thermography images for local emissivity variations only leads to minor distortions for standard silicon solar cells. Hence, adequate acquisition of one image only is sufficient to generate a meaningful map of short-circuit current density. Beyond that, this work illustrates the underlying physics of the recently proposed method and demonstrates its robustness concerning varying excitation conditions and locally increased series resistance. Experimentally gained short-circuit current density images are validated for monochromatic illumination in comparison to the reference method of light-beam induced current

  15. Microwave sintering of zirconia toughened alumina at 28GHz

    International Nuclear Information System (INIS)

    Samandi, M.; Ji, H.; Miyake, S.

    1998-01-01

    Microwave radiation from a 10 kW, CW gyrotron operating at 28 GHz was employed to sinter 10% zirconia toughened alumina (ZTA) ceramic samples. It has been established that the use of millimetre wave radiation circumvents the difficulties encountered during the sintering of ceramics, i e. formation of hot spot, by radiation at industrially permissible frequency of 2.45GHz. Further, careful density measurement and microstructural characterisation of mm- wave and conventionally sintered samples by XRD, SEM and TEM has unequivocally demonstrated the effectiveness of mm-wave radiation for obtaining high density ceramics at lower sintering temperatures. Copyright (1998) Australasian Ceramic Society

  16. Quantum information density scaling and qubit operation time constraints of CMOS silicon-based quantum computer architectures

    Science.gov (United States)

    Rotta, Davide; Sebastiano, Fabio; Charbon, Edoardo; Prati, Enrico

    2017-06-01

    range of a silicon complementary metal-oxide-semiconductor quantum processor to be within 1 and 100 GHz. Such constraint limits the feasibility of fault-tolerant quantum information processing with complementary metal-oxide-semiconductor technology only to the most advanced nodes. The compatibility with classical complementary metal-oxide-semiconductor control circuitry is discussed, focusing on the cryogenic complementary metal-oxide-semiconductor operation required to bring the classical controller as close as possible to the quantum processor and to enable interfacing thousands of qubits on the same chip via time-division, frequency-division, and space-division multiplexing. The operation time range prospected for cryogenic control electronics is found to be compatible with the operation time expected for qubits. By combining the forecast of the development of scaled technology nodes with operation time and classical circuitry constraints, we derive a maximum quantum information density for logical qubits of 2.8 and 4 Mqb/cm2 for the 10 and 7-nm technology nodes, respectively, for the Steane code. The density is one and two orders of magnitude less for surface codes and for concatenated codes, respectively. Such values provide a benchmark for the development of fault-tolerant quantum algorithms by circuital quantum information based on silicon platforms and a guideline for other technologies in general.

  17. Determination of silicone rubber and low-density polyethylene diffusion and polymer/water partition coefficients for emerging contaminants.

    Science.gov (United States)

    Pintado-Herrera, Marina G; Lara-Martín, Pablo A; González-Mazo, Eduardo; Allan, Ian J

    2016-09-01

    There is a growing interest in assessing the concentration and distribution of new nonregulated organic compounds (emerging contaminants) in the environment. The measurement of freely dissolved concentrations using conventional approaches is challenging because of the low concentrations that may be encountered and their temporally variable emissions. Absorption-based passive sampling enables the estimation of freely dissolved concentrations of hydrophobic contaminants of emerging concern in water. In the present study, calibration was undertaken for 2 polymers, low-density polyethylene (LDPE) and silicone rubber for 11 fragrances, 5 endocrine-disrupting compounds, 7 ultraviolet (UV) filters, and 8 organophosphate flame retardant compounds. Batch experiments were performed to estimate contaminant diffusion coefficients in the polymers (Dp ), which in general decreased with increasing molecular weight. The values for fragrances, endocrine-disrupting compounds, and UV filters were in ranges similar to those previously reported for polycyclic aromatic hydrocarbons, but were 1 order of magnitude lower for organophosphate flame retardant compounds. Silicone rubber had higher Dp values than LDPE and was therefore selected for further experiments to calculate polymer/water partition coefficients (KPW ). The authors observed a positive correlation between log KPW and log octanol/water partition coefficient values. Field testing of silicone rubber passive samplers was undertaken though exposure in the River Alna (Norway) for an exposure time of 21 d to estimate freely dissolved concentration. Some fragrances and UV filters were predominant over other emerging and regulated contaminants, at levels up to 1600 ng L(-1) for galaxolide and 448 ng L(-1) for octocrylene. Environ Toxicol Chem 2016;35:2162-2172. © 2016 SETAC. © 2016 SETAC.

  18. G-centers in irradiated silicon revisited: A screened hybrid density functional theory approach

    KAUST Repository

    Wang, H.; Chroneos, A.; Londos, C. A.; Sgourou, E. N.; Schwingenschlö gl, Udo

    2014-01-01

    Electronic structure calculations employing screened hybrid density functional theory are used to gain fundamental insight into the interaction of carbon interstitial (Ci) and substitutional (Cs) atoms forming the CiCs defect known as G

  19. Chemically and Thermally Stable High Energy Density Silicone Composites, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — Thermal energy storage systems with 300 -- 1000 kJ/kg energy density through either phase changes or chemical heat absorption are sought by NASA. This proposed...

  20. Effect of etching current density on microstructure and NH3-sensing properties of porous silicon with intermediate-sized pores

    International Nuclear Information System (INIS)

    Li, Mingda; Hu, Ming; Zeng, Peng; Ma, Shuangyun; Yan, Wenjun; Qin, Yuxiang

    2013-01-01

    In this work, porous silicon with intermediate-sized pores (intermediate–PS) was prepared by using galvanostatic electrochemical etching method and the effect toward sensing response characteristics of NH 3 gas was also studied. The morphology and surface chemical bonds of intermediate–PS were characterized by using field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscopy (FTIR), respectively. The results showed the intermediate–PS microstructure can be significantly modulated by the etching current density. Moreover, the freshly prepared intermediate–PS surface could achieve reliable passivation after storage in ethanol. Furthermore, the gas-sensing measurements of the intermediate–PS sensors were carried out versus different concentrations of NH 3 . The PS sensor exhibited good NH 3 -sensing performances at room temperature owing to its unique microstructure features, including large specific surface area and highly ordered pore channels. In addition, the conceivable pore formation mechanism as well as gas sensing mechanism was also discussed

  1. Ab initio density functional theory investigation of crystalline bundles of polygonized single-walled silicon carbide nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Moradian, Rostam; Behzad, Somayeh; Chegel, Raad [Physics Department, Faculty of Science, Razi University, Kermanshah (Iran, Islamic Republic of)], E-mail: moradian.rostam@gmail.com

    2008-11-19

    By using ab initio density functional theory, the structural characterizations and electronic properties of two large-diameter (13, 13) and (14, 14) armchair silicon carbide nanotube (SiCNT) bundles are investigated. Full structural optimizations show that the cross sections of these large-diameter SiCNTs in the bundles have a nearly hexagonal shape. The effects of inter-tube coupling on the electronic dispersions of large-diameter SiCNT bundles are demonstrated. By comparing the band structures of the triangular lattices of (14, 14) SiCNTs with nearly hexagonal and circular cross sections we found that the polygonization of the tubes in the bundle leads to a further dispersion of the occupied bands and an increase in the bandgap by 0.18 eV.

  2. Ab initio density functional theory investigation of crystalline bundles of polygonized single-walled silicon carbide nanotubes

    International Nuclear Information System (INIS)

    Moradian, Rostam; Behzad, Somayeh; Chegel, Raad

    2008-01-01

    By using ab initio density functional theory, the structural characterizations and electronic properties of two large-diameter (13, 13) and (14, 14) armchair silicon carbide nanotube (SiCNT) bundles are investigated. Full structural optimizations show that the cross sections of these large-diameter SiCNTs in the bundles have a nearly hexagonal shape. The effects of inter-tube coupling on the electronic dispersions of large-diameter SiCNT bundles are demonstrated. By comparing the band structures of the triangular lattices of (14, 14) SiCNTs with nearly hexagonal and circular cross sections we found that the polygonization of the tubes in the bundle leads to a further dispersion of the occupied bands and an increase in the bandgap by 0.18 eV.

  3. Ab initio density functional theory investigation of crystalline bundles of polygonized single-walled silicon carbide nanotubes

    Science.gov (United States)

    Moradian, Rostam; Behzad, Somayeh; Chegel, Raad

    2008-11-01

    By using ab initio density functional theory, the structural characterizations and electronic properties of two large-diameter (13, 13) and (14, 14) armchair silicon carbide nanotube (SiCNT) bundles are investigated. Full structural optimizations show that the cross sections of these large-diameter SiCNTs in the bundles have a nearly hexagonal shape. The effects of inter-tube coupling on the electronic dispersions of large-diameter SiCNT bundles are demonstrated. By comparing the band structures of the triangular lattices of (14, 14) SiCNTs with nearly hexagonal and circular cross sections we found that the polygonization of the tubes in the bundle leads to a further dispersion of the occupied bands and an increase in the bandgap by 0.18 eV.

  4. Low threading dislocation density aluminum nitride on silicon carbide through the use of reduced temperature interlayers

    KAUST Repository

    Foronda, Humberto M.

    2017-11-23

    In this work, reduced threading dislocation density AlN on (0 0 0 1) 6H-SiC was realized through the use of reduced temperature AlN interlayers in the metalorganic chemical vapor deposition growth. We explored the dependence of the interlayer growth temperature on the AlN crystal quality, defect density, and surface morphology. The crystal quality was characterized using omega rocking curve scans and the threading dislocation density was determined by plan view transmission electron microscopy. The growth resulted in a threading dislocation density of 7 × 108 cm−2 indicating a significant reduction in the defect density of AlN in comparison to direct growth of AlN on SiC (∼1010 cm−2). Atomic force microscopy images demonstrated a clear step-terrace morphology that is consistent with step flow growth at high temperature. Reducing the interlayer growth temperature increased the TD inclination and thus enhanced TD-TD interactions. The TDD was decreased via fusion and annihilation reactions.

  5. HAp physical investigation - the effect of sintering temperature

    International Nuclear Information System (INIS)

    Mohd Reusmaazran Yusof; Idris Besar; Rusnah Mustaffa; Cik Rohaida Che Hak

    2004-01-01

    The paper presents the effect of sintering temperature on the physical properties of porous hydroxyapatite (HAp). In this study, the HAp was prepared using polymeric sponge techniques with different binder concentration. The sintering process was carried out in air for temperature ranging from 1200 degree C to 1600 degree C. Different physical properties namely density and porosity were observed at different sintering temperatures. The HAp prepared with higher PVP binder showed a slightly decreased in apparent density with increasing sintering temperature, while those HAp prepared with lower PVP showed a slightly increase in apparent density with increasing sintering temperature. The total porosity was found to be approximately constant in the whole sintering temperature range. However, closed porosity decreases with increasing sintering temperature for HAp prepared by lower binder concentration. On the other hand, the HAp prepared by higher binder concentration HAp showed increasing closed porosity with increasing sintering temperature. Other features such as the influence of sintering temperatures on grain and strut also be presented in this paper. (Author)

  6. Matrix density effects on the mechanical properties of SiC fiber-reinforced silicon nitride matrix properties

    Science.gov (United States)

    Bhatt, Ramakrishna T.; Kiser, Lames D.

    1990-01-01

    The room temperature mechanical properties were measured for SiC fiber reinforced reaction-bonded silicon nitride composites (SiC/RBSN) of different densities. The composites consisted of approx. 30 vol percent uniaxially aligned 142 micron diameter SiC fibers (Textron SCS-6) in a reaction-bonded Si3N4 matrix. The composite density was varied by changing the consolidation pressure during RBSN processing and by hot isostatically pressing the SiC/RBSN composites. Results indicate that as the consolidation pressure was increased from 27 to 138 MPa, the average pore size of the nitrided composites decreased from 0.04 to 0.02 microns and the composite density increased from 2.07 to 2.45 gm/cc. Nonetheless, these improvements resulted in only small increases in the first matrix cracking stress, primary elastic modulus, and ultimate tensile strength values of the composites. In contrast, HIP consolidation of SiC/RBSN resulted in a fully dense material whose first matrix cracking stress and elastic modulus were approx. 15 and 50 percent higher, respectively, and ultimate tensile strength values were approx. 40 percent lower than those for unHIPed SiC/RBSN composites. The modulus behavior for all specimens can be explained by simple rule-of-mixture theory. Also, the loss in ultimate strength for the HIPed composites appears to be related to a degradation in fiber strength at the HIP temperature. However, the density effect on matrix fracture strength was much less than would be expected based on typical monolithic Si3N4 behavior, suggesting that composite theory is indeed operating. Possible practical implications of these observations are discussed.

  7. High-rate synthesis of microcrystalline silicon films using high-density SiH4/H2 microwave plasma

    International Nuclear Information System (INIS)

    Jia, Haijun; Saha, Jhantu K.; Ohse, Naoyuki; Shirai, Hajime

    2007-01-01

    A high electron density (> 10 11 cm -3 ) and low electron temperature (1-2 eV) plasma is produced by using a microwave plasma source utilizing a spoke antenna, and is applied for the high-rate synthesis of high quality microcrystalline silicon (μc-Si) films. A very fast deposition rate of ∼ 65 A/s is achieved at a substrate temperature of 150 deg. C with a high Raman crystallinity and a low defect density of (1-2) x 10 16 cm -3 . Optical emission spectroscopy measurements reveal that emission intensity of SiH and intensity ratio of H α /SiH are good monitors for film deposition rate and film crystallinity, respectively. A high flux of film deposition precursor and atomic hydrogen under a moderate substrate temperature condition is effective for the fast deposition of highly crystallized μc-Si films without creating additional defects as well as for the improvement of film homogeneity

  8. Correlation of film density and wet etch rate in hydrofluoric acid of plasma enhanced atomic layer deposited silicon nitride

    Energy Technology Data Exchange (ETDEWEB)

    Provine, J., E-mail: jprovine@stanford.edu; Schindler, Peter; Kim, Yongmin; Walch, Steve P.; Kim, Hyo Jin [Department of Mechanical Engineering, Stanford University, Stanford, California 94305 (United States); Kim, Ki-Hyun [Manufacturing Technology Center, Samsung Electronics, Suwon, Gyeonggi-Do (Korea, Republic of); Prinz, Fritz B. [Department of Mechanical Engineering, Stanford University, Stanford, California 94305 (United States); Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States)

    2016-06-15

    The continued scaling in transistors and memory elements has necessitated the development of atomic layer deposition (ALD) of silicon nitride (SiN{sub x}), particularly for use a low k dielectric spacer. One of the key material properties needed for SiN{sub x} films is a low wet etch rate (WER) in hydrofluoric (HF) acid. In this work, we report on the evaluation of multiple precursors for plasma enhanced atomic layer deposition (PEALD) of SiN{sub x} and evaluate the film’s WER in 100:1 dilutions of HF in H{sub 2}O. The remote plasma capability available in PEALD, enabled controlling the density of the SiN{sub x} film. Namely, prolonged plasma exposure made films denser which corresponded to lower WER in a systematic fashion. We determined that there is a strong correlation between WER and the density of the film that extends across multiple precursors, PEALD reactors, and a variety of process conditions. Limiting all steps in the deposition to a maximum temperature of 350 °C, it was shown to be possible to achieve a WER in PEALD SiN{sub x} of 6.1 Å/min, which is similar to WER of SiN{sub x} from LPCVD reactions at 850 °C.

  9. Translucence in dental prosthesis based on zirconia ceramics: effect of the sintering parameters

    International Nuclear Information System (INIS)

    Santos, C.

    2011-01-01

    In this work the translucence of Zirconia dental ceramics was evaluated as function of sintering conditions (temperature and isothermal holding time). Samples with 15x15x1mm, were sintered at 1450 to 1600 deg C, with holding of 2h or 4h. Sintered samples were characterized by relative density, crystalline phases and microstructural aspects. Full density was obtained in samples sintered at 1530 and 1600 deg C, which presented higher grain sizes. Na increasing of translucence was observed in samples sintered at 1530 and 1600, correlating these properties with increasing of density and grain size of the samples. (author)

  10. Sintering, microstructural and dilatometric studies of combustion synthesized Synroc phases

    International Nuclear Information System (INIS)

    Muthuraman, M.; Patil, K.C.; Senbagaraman, S.; Umarji, A.M.

    1996-01-01

    Sintering, microstructure, and linear thermal expansion properties of Synroc-B and constituent phases, viz. perovskite CaTiO 3 , zirconolite ZrTi 2 O 7 , hollandite (ideal formula BaAl2Ti 6 O 16 ) have been investigated. Synroc-B powder when pelletized and sintered at 1250 C for 2 h achieved >95% theoretical density. Sintered Synroc-B has a linear thermal expansion coefficient α of 8.72 x 10 -6 K -1 and Vicker's microhardness 9.88 GPa. The linear thermal expansion curves did not show any hysteresis indicating the absence of microcracking in the sintered bodies

  11. On the Control of the Fixed Charge Densities in Al2O3-Based Silicon Surface Passivation Schemes.

    Science.gov (United States)

    Simon, Daniel K; Jordan, Paul M; Mikolajick, Thomas; Dirnstorfer, Ingo

    2015-12-30

    A controlled field-effect passivation by a well-defined density of fixed charges is crucial for modern solar cell surface passivation schemes. Al2O3 nanolayers grown by atomic layer deposition contain negative fixed charges. Electrical measurements on slant-etched layers reveal that these charges are located within a 1 nm distance to the interface with the Si substrate. When inserting additional interface layers, the fixed charge density can be continuously adjusted from 3.5 × 10(12) cm(-2) (negative polarity) to 0.0 and up to 4.0 × 10(12) cm(-2) (positive polarity). A HfO2 interface layer of one or more monolayers reduces the negative fixed charges in Al2O3 to zero. The role of HfO2 is described as an inert spacer controlling the distance between Al2O3 and the Si substrate. It is suggested that this spacer alters the nonstoichiometric initial Al2O3 growth regime, which is responsible for the charge formation. On the basis of this charge-free HfO2/Al2O3 stack, negative or positive fixed charges can be formed by introducing additional thin Al2O3 or SiO2 layers between the Si substrate and this HfO2/Al2O3 capping layer. All stacks provide very good passivation of the silicon surface. The measured effective carrier lifetimes are between 1 and 30 ms. This charge control in Al2O3 nanolayers allows the construction of zero-fixed-charge passivation layers as well as layers with tailored fixed charge densities for future solar cell concepts and other field-effect based devices.

  12. Defects influence on short circuit current density in p-i-n silicon solar cell

    International Nuclear Information System (INIS)

    Wagah F Mohamad; Alhan M Mustafa

    2006-01-01

    The admittance analysis method has been used to calculate the collection efficiency and the short circuit current density in a-Si:H p-i-n solar cell, as a function of the thickness of i-layer. Its is evident that the results of the short circuit current can be used to determine the optimal thickness of the i-layer of a cell, and it will be more accurate in comparison with the previous studies using a constant generation rate or an empirical exponential function for the generation of charge carriers throughout the i-layer

  13. Spark plasma sintering of α-Si3N4 ceramics with Al2O3 and Y2O3 as additives and its morphology transformation

    International Nuclear Information System (INIS)

    Ceja-Cardenas, L.; Lemus-Ruiz, J.; Jaramillo-Vigueras, D.; Torre, S.D. de la

    2010-01-01

    The spark plasma sintering SPS technique has been used to densify pure α-Si 3 N 4 commercial powder, having Y 2 O 3 and Al 2 O 3 additions; from 0, 2.5 and 5.0 wt% to 0, 1.5 and 3 wt%, respectively. Such powder admixtures were previously spray-dried at 160 o C in such a way that powder was thoroughly homogenized. Set sintering treatment included: 0-20 min holding time and 38 MPa axial load, sintering temperature of 1500 o C and heating rate of 300 o C/min. The maximum relative density developed on studied specimens ranged from 99.4 to 99.8% and could only be attained once the β-phase nucleated from the α-silicon nitride matrix. Obtained Si 3 N 4 composites combine both α- and β-phases. The later phase becomes evident trough the rod-like geometry, which forms throughout the presence of a liquid face. The largest hardness value developed (1588 Hv (20kgf) ) on studied ceramics (3M-series - 3 min) matched close to the corresponding counterpart found in literature (1600 Hv), the former developed in much shorter sintering times. Using X-ray diffraction XRD and scanning electron microscope SEM analyses, the two major phases of Si 3 N 4 were identified in the resultant microstructures. The morphology evolution of Si 3 N 4 particles as occurred upon SPS-sintering is analyzed.

  14. Effect of sintering temperature on physical, structural and optical properties of wollastonite based glass-ceramic derived from waste soda lime silica glasses

    Directory of Open Access Journals (Sweden)

    Karima Amer Almasri

    Full Text Available The impact of different sintering temperatures on physical, optical and structural properties of wollastonite (CaSiO3 based glass-ceramics were investigated for its potential application as a building material. Wollastonite based glass-ceramics was provided by a conventional melt-quenching method and followed by a controlled sintering process. In this work, soda lime silica glass waste was utilized as a source of silicon. The chemical composition and physical properties of glass were characterized by using Energy Dispersive X-ray Fluorescence (EDXRF and Archimedes principle. The Archimedes measurement results show that the density increased with the increasing of sintering temperature. The generation of CaSiO3, morphology, size and crystal phase with increasing the heat-treatment temperature were examined by field emission scanning electron microscopy (FESEM, Fourier transforms infrared reflection spectroscopy (FTIR, and X-ray diffraction (XRD. The average calculated crystal size gained from XRD was found to be in the range 60 nm. The FESEM results show a uniform distribution of particles and the morphology of the wollastonite crystal is in relict shapes. The appearance of CaO, SiO2, and Ca-O-Si bands disclosed from FTIR which showed the formation of CaSiO3 crystal phase. In addition to the calculation of the energy band gap which found to be increased with increasing sintering temperature. Keywords: Soda lime silica glass, Wollastonite, Sintering, Structural properties, Optical properties

  15. State density of valence-band tail and photoconductivity amorphous hydrogenated silicon

    International Nuclear Information System (INIS)

    Golikova, O.A.; Domashevskaya, Eh.P.; Mezdrogina, M.M.; Sorokina, K.L.; Terekhov, V.A.; Trostyanskij, S.N.

    1991-01-01

    Relation between photoconductivity and g(ε) mobility gap within the range adjoining to the top (mobility end) of valent zone (VZ tail) in a-Si:H film is studied. Stationary photoconductivity within spectral maximum range (χ=0.63μm) at Φ=10 17 photxcm -2 s -1 flow is measured. Density of g(ε) states are controlled using ultrasoft X-ray emission spectroscopy. It is shown, that correlation between photoconductivity and width of VZ tail may reflect the fact of their similar dependence o film heterogeneity: at the increase of share of microholes there occur both expansion of VZ tail and growth of number of respective hydrogen complexes and torn relations which results in drop of photoconductivity

  16. Sintering of uranium dioxide pellets (UO2) in an oxidizing atmosphere (C O2)

    International Nuclear Information System (INIS)

    Santos, G.R.T.

    1992-01-01

    This work consists in the study of the sintering process of U O 2 pellets in an oxidizing atmosphere. Sintering tests were performed in an CO 2 atmosphere and the influence of temperature and time on the pellets density and microstructure were verified. The results obtained were compared to those from the conventional sintering process and its efficiency was confirmed. (author)

  17. Microstructure evolution of SiC sintered bodies activated by boron and carbon

    International Nuclear Information System (INIS)

    Gubernat, A.; Stobierski, L.

    2003-01-01

    Investigation on the role of sintering aids on densification of silicon carbide indicate that boron and carbon modify mass transport mechanisms. It leads to changes of microstructure of polycrystalline silicon carbide. In the present work the influence of varying proportions of sintering aids on the material microstructure was studied. The microstructural changes were related to the changes of the selected properties of the resulting materials. (author)

  18. Microstructure and properties of TiC-high manganese steel cermet prepared by different sintering processes

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhi; Lin, Tao, E-mail: lintao@ustb.edu.cn; He, Xinbo; Shao, Huiping; Zheng, Jianshu; Qu, Xuanhui

    2015-11-25

    In the paper, the TiC −50 wt.% high manganese steel cermet was made with different sintering processes including vacuum sintering, hot pressing, microwave sintering and spark plasma sintering (SPS). The microstructure, porosity and fracture morphology of the samples were analyzed with scanning electron microscopy (SEM). Phase analysis was carried out using X-ray diffraction (XRD). The density, hardness, transverse rupture strength (TRS) and wear resistance were investigated for the effect of the sintering processes. The results showed that the core–shell structure was not clearly observed for the TiC particles in microstructures and the high manganese steel matrix is BCC structure. Hot pressing, microwave sintering and SPS are useful processes for densification of the cermet. Nearly full density and higher hardness can be reached by these three processes at a lower sintering temperature and in a shorter sintering time. However, higher TRS can be reached by means of alloying completely in a longer sintering time, for example vacuum sintering. Pre-sintering in a long sintering time at a lower sintering temperature is also useful for improving the TRS. Finally, vacuum sintering is an effective process for producing this composite with the lowest cost in the mass production. - Highlights: • TiC-high manganese steel cermets were prepared by four sintering processes. • The core–shell structure was not clearly observed for the TiC particles in microstructures. • Th high manganese steel matrix is BCC structure instead of FCC structure. • Pre-sintering before microwave sintering is also useful for improving the TRS. • Vacuum sintering can be effective way for prepare this cermet in mass production.

  19. Process parameter influence on Electro-sinter-forging (ESF) of titanium discs

    DEFF Research Database (Denmark)

    Cannella, Emanuele; Nielsen, Chris Valentin; Bay, Niels

    Electro-sinter-forging (ESF) is an innovative sintering process based on the principle of electrical Joule heating. The electrical current is flowing through the powder compact, which is under mechanical pressure. As compared to conventional sintering [1] and spark plasma sintering [2], the main...... advantages are the decreased sintering time and high relative density [3]. Near net-shape components can be manufactured and post-removal processing is limited to surface polishing. The present work is focused on analysing the influence of the main process parameters, namely compacting pressure, sintering...... time and electrical current density, on the final density of a disc sample made from commercially pure titanium powder. The maximum achieved relative density was 94% of the bulk density of pure titanium. The density estimation was carried out by using both Archimedes’ and 3D scanning....

  20. Densification of LSGM electrolytes using activated microwave sintering

    Science.gov (United States)

    Kesapragada, S. V.; Bhaduri, S. B.; Bhaduri, S.; Singh, P.

    Lanthanum gallate doped with alkaline rare earths (LSGM) powders were densified using an activated microwave sintering process for developing a dense stable electrolyte layer for applications in intermediate temperature-solid oxide fuel cells (IT-SOFCs). Due to heat generation in situ, the process of sintering gets activated with faster kinetics compared to a conventional sintering process. The effect of various microwave process parameters on the microstructure and phase formation was studied. The sintered pellets were characterized using scanning electron microscopy-energy dispersive analysis (SEM-EDAX), and X-ray diffraction (XRD). The density of LSGM pellets microwave sintered at 1350 °C for 20 min is greater than 95% theoretical density with a fine grained microstructure (˜2-3 μm) and without the presence of other phase(s).

  1. Measurement and model on thermal properties of sintered diamond composites

    International Nuclear Information System (INIS)

    Moussa, Tala; Garnier, Bertrand; Peerhossaini, Hassan

    2013-01-01

    Highlights: ► Thermal properties of sintered diamond used for grinding is studied. ► Flash method with infrared temperature measurement is used to investigate. ► Thermal conductivity increases with the amount of diamond. ► It is very sensitive to binder conductivity. ► Results agree with models assuming imperfect contact between matrix and particles. - Abstract: A prelude to the thermal management of grinding processes is measurement of the thermal properties of working materials. Indeed, tool materials must be chosen not only for their mechanical properties (abrasion performance, lifetime…) but also for thermal concerns (thermal conductivity) for efficient cooling that avoids excessive temperatures in the tool and workpiece. Sintered diamond is currently used for grinding tools since it yields higher performances and longer lifetimes than conventional materials (mineral or silicon carbide abrasives), but its thermal properties are not yet well known. Here the thermal conductivity, heat capacity and density of sintered diamond are measured as functions of the diamond content in composites and for two types of metallic binders: hard tungsten-based and soft cobalt-based binders. The measurement technique for thermal conductivity is derived from the flash method. After pulse heating, the temperature of the rear of the sample is measured with a noncontact method (infrared camera). A parameter estimation method associated with a three-layer nonstationary thermal model is used to obtain sample thermal conductivity, heat transfer coefficient and absorbed energy. With the hard metallic binder, the thermal conductivity of sintered diamond increased by up to 64% for a diamond content increasing from 0 to 25%. The increase is much less for the soft binder: 35% for diamond volumes up to 25%. In addition, experimental data were found that were far below the value predicted by conventional analytical models for effective thermal conductivity. A possible explanation

  2. Science of sintering

    International Nuclear Information System (INIS)

    Kuczynski, G.

    1977-01-01

    Although the methods of integration of materials by sintering, have been used since the early history of humanity, the actual understanding of the process involved came only in the last three decades. As in the most human endeavors, the art preceded theory. The comprehension of the elementary processes occuring during sintering comes from the studies of model system. Although the elementary processes occuring during sintering are today quite well understood, the problem of shrinkage of a powder compact which was at the origin of Sintering Science is still far from solved. This is due to the complexity of the internal geometry of the compacts. The recent attempts to apply statistics to this problem, seem to offer some promise

  3. Uranium dioxide. Sintering test

    International Nuclear Information System (INIS)

    Anon.

    Description of a sintering method and of the equipment devoted to uranium dioxide powder caracterization and comparison between different samples. Determination of the curve giving specific volume versus pressure and micrographic examination of a pellet at medium pressure [fr

  4. Kinetics of UO2 sintering

    International Nuclear Information System (INIS)

    Ristic, M.M.

    1962-01-01

    Detailed conclusions related to the UO 2 sintering can be drawn from investigating the kinetics of the sintering process. This report gives an thorough analysis of the the data concerned with sintering available in the literature taking into account the Jander and Arrhenius laws. This analysis completes the study of influence of the O/U ratio and the atmosphere on the sintering. Results presented are fundamentals of future theoretical and experimental work related to characterisation of the UO 2 sintering process

  5. Ir-based refractory superalloys by pulse electric current sintering (PECS) process (II prealloyed powder)

    Science.gov (United States)

    Huang, C.; Yamabe-Mitarai, Y.; Harada, H.

    2002-02-01

    Five prealloyed powder samples prepared from binary Ir-based refractory superalloys were sintered at 1800 °C for 4 h by Pulse Electric Current Sintering (PECS). No metal loss was observed during sintering. The relative densities of the sintered specimens all exceeded 90% T.D. The best one was Ir-13% Hf with the density of 97.82% T.D. Phases detected in sintered samples were in accordance with the phase diagram as expected. Fractured surfaces were observed in two samples (Ir-13% Hf and Ir-15% Zr). Some improvements obtained by using prealloyed powders instead of elemental powders, which were investigated in the previous studies, were presented.

  6. Effect of sintering process parameters on the properties of 3Y-PSZ ceramics

    International Nuclear Information System (INIS)

    Chu, H L; Chen, R S; Wang, C L; Hwang, W S; Lee, H E; Sie, Y Y; Wang, M C

    2013-01-01

    The effect of sintering process parameters on the properties of 3 mol% yttria partially stability zirconia (3Y-PSZ) ceramics has been investigated. The relative density of the sintered pellet rapidly increases from 70.5 to 93.6% with rose temperature from 1473 to 1573 K. In addition, the relative density only slightly increases from 94.9 to 96.6 %, when rose sintered temperature from 1573 to 1773 K. This result shows that no significant influence on the densification behavior when sintering at 1573 to 1773 K for 2 h. The Vickers hardness and toughness also increase with the sintered temperature

  7. Microwave sintering of nano size powder β-TCP bioceramics

    Directory of Open Access Journals (Sweden)

    Mirhadi B.

    2014-01-01

    Full Text Available A nano sized beta tricalcium phosphate (β-TCP powder was conventional sintered (CS and microwave sintered (MW, in order to obtain dense β-TCP ceramics. In this work the effect of microwave sintering conditions on the microstructure, phase composition and mechanical properties of materials based on tricalcium phosphate (TCP was investigated by SEM (scanning electron microscopyand XRD(X-ray diffraction and then compared with conventional sintered samples. Nano-size β-TCP powders with average grain size of 80 nm were prepared by the wet chemical precipitation method with calcium nitrate and diammonium hydrogen phosphate as calcium and phosphorus precursors, respectively. The precipitation process employed was also found to be suitable for the production of submicrometre β-TCP powder in situ. The β-TCP samples microwave (MW sintered for 15 min at 1100°C, with average grain size of 3μm, showed better densification, higher density and certainly higher hardness than samples conventionally sintered for 2 h at the same temperature. By comparing sintered and MW sintered β-TCP samples, it was concluded that MW sintered β-TCP samples have superior mechanical properties.

  8. Properties, structure and machnining capabilities sintered corundum abrasives

    Directory of Open Access Journals (Sweden)

    Cz.J. Niżankowski

    2010-07-01

    Full Text Available The diversity of sintered corundum abrasives used in both bonded and in the embankment of abrasive tools currently poses substantialproblems for their choice of technology to specific tasks. Therefore performed a comparative study of ownership structures and capacitiesof elected representatives machnining sintered corundum abrasives of different generations, and this is normal sintered alumina,submicrocrystalline alumina sintered and nanocrystalline alumina sintered. Were studied some properties of a set of abrasive particles,physicochemical properties and structural and mechanical and technological properties. The studies used the method of microscopicmeasurement to determine the shape of abrasive particles, the pycnometer to determine the density of abrasive, a spectrometer todetermine the chemical composition of the magnetic analyzer for determining the magnetic fraction, scanning electron microscope toanalysis of abrasive grains and a special position to designate the machining capacity abrasive grains. The results showed a significantincrease in machining capacity sintered corundum abrasives with increasing degree of fragmentation of the crystallites sintered corundum abrasives and distinctive bands in the emerging microchip. The originality of the development provides a comparative summary ofproperties of sintered corundum abrasives of different generations and functions obtained by the author making the change in value indexof machininhcapacity grit from cutting speeds for different generations of sintered corundum.

  9. The behaviour of doped elements in tungsten sintering

    International Nuclear Information System (INIS)

    Scheiner, L.

    1975-01-01

    The lecture deals with the occurrence of bubbles in the sintering of doped tungsten. The doping of tungsten normally takes place by the addition of K, Al and Si compounds. A part of the doping substances disappears with sintering which can easily be proved by chemical analyses. In the process described here, the evaporation is non-destructively observed during sintering with an absorption spectrometer. Temperature, absorption slope and sintering resistance are recorded. The evaluation of the absorption curves gives a diffusion equation. The discussion of the curves resulted so far in that a doped substance compound sets free the single elements of the compound at high temperature. Aluminium and silicon diffuse out. In the case of aluminium, the activation energy can be determined. (GSC/LH) [de

  10. Investigation of carrier density and mobility in microcrystalline silicon alloys using Hall effect and thermopower measurements; Untersuchung der Ladungstraegerkonzentration und -beweglichkeit in mikrokristallinen Siliziumlegierungen mit Hall-Effekt und Thermokraft

    Energy Technology Data Exchange (ETDEWEB)

    Sellmer, Christian

    2012-08-31

    The electronic properties of amorphous and microcrystalline silicon layers in thin-film solar cells significantly affect the efficiency of solar cells. An important property of the individual layer is the electronic transport, which is described by the variables conductivity, photoconductivity, mobility, and carrier concentration. In the past, individual characterization methods were typically used to determine the electronic properties. Using the combination of Hall effect, conductivity, and thermoelectric power measurements additional variables can be derived, such as the effective density of states at the valence and conduction band edge, making a more detailed description of the material possible. To systematically study the electronic properties - in particular carrier mobility and carrier concentration - various series of silicon films are prepared for this work including microcrystalline silicon layers of different doping and crystallinity and a series of silicon films where the Fermi level is moved by irradiation with high energy electrons on one and the same sample. The results show that the transition from amorphous to microcrystalline transport is relatively abrupt. If the electron transport takes place in only amorphous regions, it is marked by the sign anomaly of the Hall effect. If a continuous crystalline path exists, the electronic properties are dominated by the crystalline volume fraction. The results of the measurements of silicon layers are compared with those of microcrystalline silicon carbide samples. Silicon carbide is especially interesting for future applications in thin-film solar cells due to high transparency and high conductivity. It is shown that the effective density of states at the valence and conduction band edge as a function of temperature in p- and n-type microcrystalline silicon and silicon carbide samples largely coincide with those of crystalline silicon or silicon carbide. A square root shaped profile of the density of

  11. Uranium dioxide sintering Kinetics and mechanisms under controlled oxygen potentials

    International Nuclear Information System (INIS)

    Freitas, C.T. de.

    1980-06-01

    The initial, intermediate, and final sintering stages of uranium dioxide were investigated as a function of stoichiometry and temperature by following the kinetics of the sintering reaction. Stoichiometry was controlled by means of the oxygen potential of the sintering atmosphere, which was measured continuously by solid-state oxygen sensors. Included in the kinetic study were microspheres originated from UO 2 gels and UO 2 pellets produced by isostatic pressing ceramic grade powders. The microspheres sintering behavior was examined using hot-stage microscopy and a specially designed high-temperature, controlled atmosphere furnace. This same furnace was employed as part of an optical dilatometer, which was utilized in the UO 2 pellet sintering investigations. For controlling the deviations from stoichiometry during heat treatment, the oxygen partial pressure in the sintering atmosphere was varied by passing the gas through a Cu-Ti-Cu oxygen trap. The trap temperature determined the oxygen partial pressure of the outflowing mixture. Dry hydrogen was also used in some of the UO sub(2+x) sintering experiments. The determination of diametrial shrinkages and sintering indices was made utilizing high-speed microcinematography and ultra-microbalance techniques. It was observed that the oxygen potential has a substantial influence on the kinetics of the three sintering stages. The control of the sintering atmosphere oxygen partial pressure led to very fast densification of UO sub(2+x). Values in the interval 95.0 to 99.5% of theoretical density were reached in less than one minute. Uranium volume diffusion is the dominant mechanism in the initial and intermediate sintering stages. For the final stage, uranium grain boundary diffusion was found to be the main sintering mechanism. (Author) [pt

  12. Improvement of mechanical strength of sintered Mo alloyed steel by optimization of sintering and cold-forging processes with densification

    Science.gov (United States)

    Kamakoshi, Y.; Shohji, I.; Inoue, Y.; Fukuda, S.

    2017-10-01

    Powder metallurgy (P/M) materials have been expected to be spread in automotive industry. Generally, since sintered materials using P/M ones contain many pores and voids, mechanical properties of them are inferior to those of conventional wrought materials. To improve mechanical properties of the sintered materials, densification is effective. The aim of this study is to improve mechanical strength of sintered Mo-alloyed steel by optimizing conditions in sintering and cold-forging processes. Mo-alloyed steel powder was compacted. Then, pre-sintering (PS) using a vacuum sintering furnace was conducted. Subsequently, coldforging (CF) by a backward extrusion method was conducted to the pre-sintered specimen. Moreover, the cold-forged specimen was heat treated by carburizing, tempering and quenching (CQT). Afterwards, mechanical properties were investigated. As a result, it was found that the density of the PS specimen is required to be more than 7.4 Mg/m3 to strengthen the specimen by heat treatment after CF. Furthermore, density and the microstructure of the PS specimen are most important factors to make the high density and strength material by CF. At the CF load of 1200 kN, the maximum density ratio reached approximately 99% by the use of the PS specimen with proper density and microstructure. At the CF load of 900 kN, although density ratio was high like more than 97.8%, transverse rupture strength decreased sharply. Since densification caused high shear stress and stress concentration in the surface layer, microcracks occurred by the damages of inter-particle sintered connection of the surface layer. On the contrary, in case of the CF load of 1200 kN, ultra-densification of the surface layer occurred by a sufficient plastic flow. Such sufficient compressed specimens regenerated the sintered connections by high temperature heat treatment and thus the high strength densified material was obtained. These processes can be applicable to near net shape manufacturing

  13. Liquid phase sintered superconducting cermet

    International Nuclear Information System (INIS)

    Ray, S.P.

    1990-01-01

    This patent describes a method of making a superconducting cermet having superconducting properties with improved bulk density, low porosity and in situ stabilization. It comprises: forming a structure of a superconducting ceramic material having the formula RM 2 Cu 3 O (6.5 + x) wherein R is one or more rare earth elements capable of reacting to form a superconducting ceramic, M is one or more alkaline earth metal elements selected from barium and strontium capable of reacting to form a superconducting ceramic, x is greater than 0 and less than 0.5; and a precious metal compound in solid form selected from the class consisting of oxides, sulfides and halides of silver; and liquid phase sintering the mixture at a temperature wherein the precious metal of the precious metal compound is molten and below the melting point of the ceramic material. The liquid phase sintering is carried out for a time less than 36 hours but sufficient to improve the bulk density of the cermet

  14. Spark plasma sintering of tantalum carbide

    International Nuclear Information System (INIS)

    Khaleghi, Evan; Lin, Yen-Shan; Meyers, Marc A.; Olevsky, Eugene A.

    2010-01-01

    A tantalum carbide powder was consolidated by spark plasma sintering. The specimens were processed under various temperature and pressure conditions and characterized in terms of relative density, grain size, rupture strength and hardness. The results are compared to hot pressing conducted under similar settings. It is shown that high densification is accompanied by substantial grain growth. Carbon nanotubes were added to mitigate grain growth; however, while increasing specimens' rupture strength and final density, they had little effect on grain growth.

  15. Electro sinter forging of titanium disks

    DEFF Research Database (Denmark)

    Cannella, Emanuele; Nielsen, Chris Valentin; Bay, Niels Oluf

    by measuring the electrical resistance during the sintering process [5], since low electrical resistance corresponds to high density. It is, however, necessary to be aware that increased temperature, on the other hand, increases the resistance. SEM micrographs and Computed Tomography (CT) are carried out......Electro sinter forging (ESF) is a new sintering process based on the principle of electrical Joule heating. In the present work, middle frequency direct current (MFDC) was flowing through the powder compact, which was under mechanical pressure. The main parameters are the high electrical current......, up to 10 kA, and the low voltage, 1-2 V, resulting in heat generation in the powder. Figure 1 shows the experimental setup. The punches were made of a conductive material; namely a copper alloy. The die, which has to be electrically insulating, was made of alumina. The ESF process takes 3-4s...

  16. Sintered cobalt-rare earth intermetallic product

    International Nuclear Information System (INIS)

    Benz, M.G.

    1975-01-01

    This patent describes a sintered product having substantially stable permanent magnet properties in air at room temperature. It comprises compacted particulate cobalt--rare earth alloy consisting essentially of a Co 5 R intermetallic phase and a CoR intermetallic phase which is richer in rare earth metal content than the Co 5 R phase, where R is a rare earth metal. The Co 5 R intermetallic phase is present in an amount of at least 65 percent by weight of the sintered product and the CoR intermetallic phase which is richer in rare earth metal content than the Co 5 R phase is present in a positive amount having a value ranging up to about 35 percent by weight of the product. The sintered product has a density of at least 87 percent and has pores which are substantially noninterconnecting and wherein the component grains have an average size less than 30 microns

  17. Method of manufacturing sintered nuclear fuel

    International Nuclear Information System (INIS)

    Watarumi, Kazutoshi.

    1984-01-01

    Purpose: To obtain composite pellets with an improved strength. Method: A core mainly composed of fuel materials is previously prepared, embedded into the central portion of a pellet, silted therearound with cladding material, and then pressmolded and sintered. For instance, a rugby-ball like core body with the maximum outer diameter of 6 mm and the height of 6 mm is made by compressive molding with uranium dioxide powder, then coating material comprising the same powder incorporated with 0.1 % by weight of SiC fibers is filled around the core body, which is molded into a composite pellet by means of pressing and then sintered at 1600 0 C, to obtain a sintered pellet of 93.5 % theoretical density. As the result of the compression test for the pellet, it showed a strength greater by 15 % than that of the similar mono-layer pellet. (Kamimura, M.)

  18. A study on the development of silicon carbide materials for nuclear application

    International Nuclear Information System (INIS)

    Won, Dong Yeon; Kim, Chan Jung; Lee, Jae Choon; Kim, Joon Hyung; Lim, Kyung Soo; Kim, Ki Baik

    1987-12-01

    Silicon carbide was synthesized by reaction sintering process from carbon and silicon powders as starting materials. The effects of two processing parameters, i.e., heat treatment time and temperature, were examined (to characterize the reaction sintering process) in terms of the degree of reaction and phase developed during heat treatment. The final products after reaction of silicon and carbon powders were identified as β-SiC having ZnS crystal structure. Sintering of cordierite ceramics which was used as an high temperature inorganic binder to fabricate ceramically bound silicon carbide, and phase identification of the sintered ceramics by X-ray powder diffraction techniques. (Author)

  19. Sintering Theory and Practice

    Science.gov (United States)

    German, Randall M.

    1996-01-01

    Although sintering is an essential process in the manufacture of ceramics and certain metals, as well as several other industrial operations, until now, no single book has treated both the background theory and the practical application of this complex and often delicate procedure. In Sintering Theory and Practice, leading researcher and materials engineer Randall M. German presents a comprehensive treatment of this subject that will be of great use to manufacturers and scientists alike. This practical guide to sintering considers the fact that while the bonding process improves strength and other engineering properties of the compacted material, inappropriate methods of control may lead to cracking, distortion, and other defects. It provides a working knowledge of sintering, and shows how to avoid problems while accounting for variables such as particle size, maximum temperature, time at that temperature, and other problems that may cause changes in processing. The book describes the fundamental atomic events that govern the transformation from particles to solid, covers all forms of the sintering process, and provides a summary of many actual production cycles. Building from the ground up, it begins with definitions and progresses to measurement techniques, easing the transition, especially for students, into advanced topics such as single-phase solid-state sintering, microstructure changes, the complications of mixed particles, and pressure-assisted sintering. German draws on some six thousand references to provide a coherent and lucid treatment of the subject, making scientific principles and practical applications accessible to both students and professionals. In the process, he also points out and avoids the pitfalls found in various competing theories, concepts, and mathematical disputes within the field. A unique opportunity to discover what sintering is all about--both in theory and in practice What is sintering? We see the end product of this thermal

  20. Sintered cobalt-rare earth intermetallic product

    International Nuclear Information System (INIS)

    Benz, M.C.

    1975-01-01

    A process is described for preparing novel sintered cobalt--rare earth intermetallic products which can be magnetized to form permanent magnets having stable improved magnetic properties. A cobalt--rare earth metal alloy is formed having a composition which at sintering temperature falls outside the composition covered by the single Co 5 R intermetallic phase on the rare earth richer side. The alloy contains a major amount of the Co 5 R intermetallic phase and a second solid CoR phase which is richer in rare earth metal content than the Co 5 R phase. The specific cobalt and rare earth metal content of the alloy is substantially the same as that desired in the sintered product. The alloy, in particulate form, is pressed into compacts and sintered to the desired density. The sintered product is comprised of a major amount of the Co 5 R solid intermetallic phase and up to about 35 percent of the product of the second solid CoR intermetallic phase which is richer in rare earth metal content than the Co 5 R phase

  1. Synthesis, Sintering, and Electrical Properties of BaCe0.9−xZrxY0.1O3−δ

    DEFF Research Database (Denmark)

    Ricote, S.; Caboche, G.; Estournes, C.

    2008-01-01

    BaCe0.9-xZrxY0.1O3-delta powders were synthesized by a solid-state reaction. Different contents of cerium and zirconium were studied. Pellets were sintered using either conventional sintering in air at 1700 degrees C or the Spark Plasma Sintering (SPS) technique. The density of the samples sintered...

  2. Predicting sintering deformation of ceramic film constrained by rigid substrate using anisotropic constitutive law

    International Nuclear Information System (INIS)

    Li Fan; Pan Jingzhe; Guillon, Olivier; Cocks, Alan

    2010-01-01

    Sintering of ceramic films on a solid substrate is an important technology for fabricating a range of products, including solid oxide fuel cells, micro-electronic PZT films and protective coatings. There is clear evidence that the constrained sintering process is anisotropic in nature. This paper presents a study of the constrained sintering deformation using an anisotropic constitutive law. The state of the material is described using the sintering strains rather than the relative density. In the limiting case of free sintering, the constitutive law reduces to a conventional isotropic constitutive law. The anisotropic constitutive law is used to calculate sintering deformation of a constrained film bonded to a rigid substrate and the compressive stress required in a sinter-forging experiment to achieve zero lateral shrinkage. The results are compared with experimental data in the literature. It is shown that the anisotropic constitutive law can capture the behaviour of the materials observed in the sintering experiments.

  3. Morphological analysis and modelling of sintering and of sintered materials

    International Nuclear Information System (INIS)

    Jernot, Jean-Paul

    1982-01-01

    This research thesis addresses the study of solid phase sintering of metallic powders, and aims at describing as precisely as possible the different involved matter transport mechanisms, first by using a thermodynamic approach to sintering. Sintering diagrams are also used to determine prevailing mechanisms. The microstructure of sintered materials has been studied by using image quantitative analysis, thus by using a morphological approach to sintering. Morphological parameters allow, on the one hand, the evolution of powders during sintering to be followed, and, on the other hand, sintered products to be correctly characterised. Moreover, the author reports the study of the evolution of some physical properties of sintered materials with respect to their microstructure parameters. This leads to the development of a modelling of the behaviour of these materials [fr

  4. Microstructure evolution during pressureless sintering of bulk oxide ceramics

    Directory of Open Access Journals (Sweden)

    Karel Maca

    2009-06-01

    Full Text Available The author’s experience concerning the infl uence of the choice of different pressureless heating schedules on the fi nal microstructure of oxide ceramic materials is summarized in the paper. Alumina, ceria, strontium titanate, as well as tetragonal (3 mol% Y2O3 and cubic (8 mol% Y2O3 zirconia were cold isostatically pressed or injection moulded and pressureless sintered with different heating schedules – namely with Constant-Rate of Heating with different dwell temperatures (CRH, with Rate-Controlled Sintering (RCS and with Two-Step Sintering (TSS. It was examined whether some of these three sintering schedules, with the same fi nal density achieved, can lead to a decrease of the grain size of sintered ceramics. The results showed that only TSS (and only for selected materials brought significant decrease of the grain size.

  5. Sintering with a chemical reaction as applied to uranium monocarbide

    International Nuclear Information System (INIS)

    Accary, A.; Caillat, R.

    1960-01-01

    The present paper provides a survey of different investigations whose aim was the preparation and fabrication of uranium monocarbide for nuclear use. If a chemical reaction takes place in the sample during the sintering operation, it may be expected that the atom rearrangements involved in this reaction should favour the sintering process and thereby lower the temperature needed to yield a body of a given density. With this hypothesis in mind, the following methods have been studied: - Sintering of U-C mixtures; - Sintering of UO 2 -C mixtures; - Hot pressing of U-C mixtures; - Extrusion of U-C mixtures. To generalize our result, it could be said that a chemical reaction does not lead to high densification, if one depends on a simple contact between discrete particles. On the contrary, a chemical reaction can help sintering if, as our hot pressing experiments shows, the densification can be achieved prior to the reaction. (author) [fr

  6. Preliminary investigation of liquid phase sintering in ferrous systems

    International Nuclear Information System (INIS)

    Klein, J.

    1975-04-01

    Liquid phase sintering was utilized to achieve, by a simple compaction and sintering procedure involving short times and moderate temperatures, a virtually full dense high carbon Fe:C alloy and high boron Fe:B alloy. Parameters such as powder characteristics and mixing, compacting pressure, heating program and the liquid phase fraction were found to influence the sintered density. The response of the Fe:C alloy to a heat treatment is reported along with preliminary experiments in the iron base ternary system Fe:W:C. Residual porosities observed in microstructures of certain liquid phase sintered compacts were accounted for by a proposed capillary flow of the liquid phase and a local densification competing against an overall densification. Some general recommendations are made for liquid phase sintering of powder aggregates. 15 fig., 7 tables

  7. Sol-gel bonding of silicon wafers

    International Nuclear Information System (INIS)

    Barbe, C.J.; Cassidy, D.J.; Triani, G.; Latella, B.A.; Mitchell, D.R.G.; Finnie, K.S.; Short, K.; Bartlett, J.R.; Woolfrey, J.L.; Collins, G.A.

    2005-01-01

    Sol-gel bonds have been produced between smooth, clean silicon substrates by spin-coating solutions containing partially hydrolysed silicon alkoxides. The two coated substrates were assembled and the resulting sandwich fired at temperatures ranging from 60 to 600 deg. C. The sol-gel coatings were characterised using attenuated total reflectance Fourier transform infrared spectroscopy, ellipsometry, and atomic force microscopy, while the corresponding bonded specimens were investigated using scanning electron microscopy and cross-sectional transmission electron microscopy. Mechanical properties were characterised using both microindentation and tensile testing. Bonding of silicon wafers has been successfully achieved at temperatures as low as 60 deg. C. At 300 deg. C, the interfacial fracture energy was 1.55 J/m 2 . At 600 deg. C, sol-gel bonding provided superior interfacial fracture energy over classical hydrophilic bonding (3.4 J/m 2 vs. 1.5 J/m 2 ). The increase in the interfacial fracture energy is related to the increase in film density due to the sintering of the sol-gel interface with increasing temperature. The superior interfacial fracture energy obtained by sol-gel bonding at low temperature is due to the formation of an interfacial layer, which chemically bonds the two sol-gel coatings on each wafer. Application of a tensile stress on the resulting bond leads to fracture of the samples at the silicon/sol-gel interface

  8. Sintered bentonite ceramics for the immobilization of cesium- and strontium-bearing radioactive waste

    Science.gov (United States)

    Ortega, Luis Humberto

    The Advanced Fuel Cycle Initiative (AFCI) is a Department of Energy (DOE) program, that has been investigating technologies to improve fuel cycle sustainability and proliferation resistance. One of the program's goals is to reduce the amount of radioactive waste requiring repository disposal. Cesium and strontium are two primary heat sources during the first 300 years of spent nuclear fuel's decay, specifically isotopes Cs-137 and Sr-90. Removal of these isotopes from spent nuclear fuel will reduce the activity of the bulk spent fuel, reducing the heat given off by the waste. Once the cesium and strontium are separated from the bulk of the spent nuclear fuel, the isotopes must be immobilized. This study is focused on a method to immobilize a cesium- and strontium-bearing radioactive liquid waste stream. While there are various schemes to remove these isotopes from spent fuel, this study has focused on a nitric acid based liquid waste. The waste liquid was mixed with the bentonite, dried then sintered. To be effective sintering temperatures from 1100 to 1200°C were required, and waste concentrations must be at least 25 wt%. The product is a leach resistant ceramic solid with the waste elements embedded within alumino-silicates and a silicon rich phase. The cesium is primarily incorporated into pollucite and the strontium into a monoclinic feldspar. The simulated waste was prepared from nitrate salts of stable ions. These ions were limited to cesium, strontium, barium and rubidium. Barium and rubidium will be co-extracted during separation due to similar chemical properties to cesium and strontium. The waste liquid was added to the bentonite clay incrementally with drying steps between each addition. The dry powder was pressed and then sintered at various temperatures. The maximum loading tested is 32 wt. percent waste, which refers to 13.9 wt. percent cesium, 12.2 wt. percent barium, 4.1 wt. percent strontium, and 2.0 wt. percent rubidium. Lower loadings of waste

  9. Sintering of composite

    International Nuclear Information System (INIS)

    Bordia, R.K.; Scherer, G.W.

    1988-01-01

    Several constitutive laws have been used in the literature to predict the response of sintering bodies under external and internal stress fields. These analyses are based on the assumptions of linear and isotropic behavior. The authors provide a critical examination of these equations and show that some of the available constitutive laws predict a negative Poisson's ratio. These laws have been used to analyze sintering of ceramic matrix composites with rigid inclusions and predict large values of the internal stresses and significant retardation of the densification of composites. Since a negative value of Poisson's ratio has never been observed in sinter - forging experiments, the authors conclude that either the stresses are small (as predicted by the constitutive laws with positive Poisson's ratio) or the basic assumption of linearity and isotropy used in all the analyses is incorrect. Finally, the authors discuss some phenomena that could be important in understanding the densification of ceramic matrix composites

  10. Evaluation of Sintering Behavior of Premix Al-Zn-Mg-Cu Alloy Powder

    Directory of Open Access Journals (Sweden)

    Haris Rudianto

    2015-01-01

    Full Text Available Sintering of light aluminium alloys powder has been investigated as a way to substitute steels in automotive and aerospace industries. Premix Al-5.5Zn-2.5Mg-0.5Cu composite powder called Alumix 431D was analyzed in this research. Sintering was carried out under ultra high purity nitrogen gas and before reaching sintering temperature, green samples were delubricated at 400°C for 30 min. The powder possesses high sinterability by reaching 96% relative density at 580°C sintering temperature. Formation of liquid phase seems to support achieving high sintering density. Optimum mechanical properties also were obtained under those conditions. T6 heat treatment was done to improve the mechanical properties by formation of precipitation strengthening, and MgZn2 appears to be dominant strengthening precipitate. X-ray diffraction, optical microscopy, and SEM-EDS were used to characterize powder, and sintered and heat treated samples.

  11. The influence of green microstructure and sintering parameters on precipitation process during copper-nickel-zinc ferrites sintering

    International Nuclear Information System (INIS)

    Barba, A.; Clausell, C.; Jarque, J. C.; Monzo, M.

    2014-01-01

    Microstructural changes that occur during heat treatment of copper-nickel-zinc ferrites have been studied. The process of precipitation of the two types of crystals that occur during the sintering process has been analyzed. It is found that this process depends on dry relative density of the press specimens and on the following sintering parameters: sintering temperature, sintering time and cooling rate of the thermal cycle. Crystal precipitates characterization have been done by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). These techniques have allowed to determine the nature of these crystals, which in this case correspond to zinc and copper oxides. It has been used two chemical reactions to explain the bulk precipitation and subsequent re-dissolution of these crystal precipitates during sintering. (Author)

  12. Process parameter influence on Electro-sinter-forging (ESF) of titanium discs

    DEFF Research Database (Denmark)

    Cannella, Emanuele; Nielsen, Chris Valentin; Bay, Niels

    Electro-sinter-forging (ESF) is a sintering process based on the resistance heating principle, which makes it faster than conventional sintering. The process is investigated as a function of the main process parameters, namely compacting pressure, electrical current density and sintering time....... The present work is focused on analysing the influence of these process parameters on the final density of a disc sample made from commercially pure titanium powder. Applying the design of experiments (DoE) approach, the electrical current was seen to be of largest influence. The maximum obtained density...

  13. SnO{sub 2}{sup *}CoO ceramic obtained by microwave sintering; Ceramicas de SnO{sub 2} {sup *}CoO obtidas por sinterizacao microondas

    Energy Technology Data Exchange (ETDEWEB)

    Bordignon, M.A.N; Moura, F.; Zaghete, M.A.; Varela, J.A.; Perazolli, L. [Universidade Estadual Paulista (UNESP), Araraquara, SP (Brazil). Chemistry Institute. Dept. de Biochemistry and Technological Chemistryl

    2009-07-01

    This work consists in the sintering study of CoO doped SnO{sub 2} using microwave sintering oven and silicon carbide as a susceptor. The powders were obtained by dry oxides mixture and conformed in cylindrical shapes with 6mmx8mm and green density to 60%. Then the compacts were sintering up to 1.050 deg C, using heating rate of 50 deg C/min and isotherm up to 30min. The densities obtained were above 95% for both techniques. It was observed that occurred a temperature reducing of 400 deg C and time reducing of 210min to obtain the same densities, when was used the microwave oven without the phenomena of thermal runaway. So the sintered compacts were accomplished using DRX and SEM. It was made the electrical characterization (current x voltage) and it was found to have great potential in the production of dense ceramic-based SnO{sub 2} with low resistivity to obtain electro-ceramic devices. (author)

  14. The sintering behavior of close-packed spheres

    DEFF Research Database (Denmark)

    Bjørk, Rasmus; Tikare, V.; Frandsen, Henrik Lund

    2012-01-01

    The sintering behavior of close-packed spheres is investigated using a numerical model. The investigated systems are the body-centered cubic (bcc), face-centered cubic (fcc) and hexagonal close-packed spheres (hcp). The sintering behavior is found to be ideal, with no grain growth until full dens...... density is reached for all systems. During sintering, the grains change shape from spherical to tetrakaidecahedron, similar to the geometry analyzed by Coble [R.L. Coble, J. Appl. Phys. 32 (1961) 787]....

  15. Low temperature spark plasma sintering of YIG powders

    International Nuclear Information System (INIS)

    Fernandez-Garcia, L.; Suarez, M.; Menendez, J.L.

    2010-01-01

    A transition from a low to a high spin state in the magnetization saturation between 1000 and 1100 o C calcination temperature is observed in YIG powders prepared by oxides mixture. Spark plasma sintering of these powders between 900 and 950 o C leads to dense samples with minimal formation of YFeO 3 , opening the way to co-sintering of YIG with metals or metallic alloys. The optical properties depend on the sintering stage: low (high) density samples show poor (bulk) optical absorption.

  16. Quartz crystal reinforced quartz glass by spark plasma sintering

    International Nuclear Information System (INIS)

    Torikai, D.; Barazani, B.; Ono, E.; Santos, M.F.M.; Suzuki, C.K.

    2011-01-01

    The Spark Plasma Sintering presents fast processing time when compared to conventional sintering techniques. This allows to control the grain growth during sintering as well as the diffusion rate of a multi-material compounds, and make possible obtainment of functionally graded materials and nanostructured compounds. Powders of high purity silica glass and crystalline silica were sintered in a SPS equipment at temperatures around 1350° C, i.e., above the softening temperature of silica glass and below the melting temperature of quartz crystal. As a result, glass ceramics with pure silica glass matrix reinforced with crystalline alpha-quartz grains were fabricated at almost any desired range of composition, as well as controlled size of the crystalline reinforcement. X-ray diffraction and density measurements showed the possibility to manufacture a well controlled density and crystallinity glass-ceramic materials. (author)

  17. Improving NASICON Sinterability through Crystallization under High-Frequency Electrical Fields

    Energy Technology Data Exchange (ETDEWEB)

    Lisenker, Ilya; Stoldt, Conrad R., E-mail: stoldt@colorado.edu [Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO (United States)

    2016-03-31

    The effect of high-frequency (HF) electric fields on the crystallization and sintering rates of a lithium aluminum germanium phosphate (LAGP) ion conducting ceramic was investigated. LAGP with the nominal composition Li{sub 1.5}Al{sub 0.5}Ge{sub 1.5}(PO{sub 4}){sub 3} was crystallized and sintered, both conventionally and under effect of electrical field. Electrical field application, of 300 V/cm at 1 MHz, produced up to a 40% improvement in sintering rate of LAGP that was crystallized and sintered under the HF field. Heat sink effect of the electrodes appears to arrest thermal runaway and subsequent flash behavior. Sintered pellets were characterized using X-ray diffraction, scanning electron microscope, TEM, and electrochemical impedance spectroscopy to compare conventionally and field-sintered processes. The as-sintered structure appears largely unaffected by the field as the sintering curves tend to converge beyond initial stages of sintering. Differences in densities and microstructure after 1 h of sintering were minor with measured sintering strains of 31 vs. 26% with and without field, respectively. Ionic conductivity of the sintered pellets was evaluated, and no deterioration due to the use of HF field was noted, though capacitance of grain boundaries due to secondary phases was significantly increased.

  18. Numerical analysis of thermal stress and dislocation density distributions in large size multi-crystalline silicon ingots during the seeded growth process

    Science.gov (United States)

    Nguyen, Thi Hoai Thu; Chen, Jyh-Chen; Hu, Chieh; Chen, Chun-Hung; Huang, Yen-Hao; Lin, Huang-Wei; Yu, Andy; Hsu, Bruce

    2017-06-01

    In this study, a global transient numerical simulation of silicon growth from the beginning of the solidification process until the end of the cooling process is carried out modeling the growth of an 800 kg ingot in an industrial seeded directional solidification furnace. The standard furnace is modified by the addition of insulating blocks in the hot zone. The simulation results show that there is a significant decrease in the thermal stress and dislocation density in the modified model as compared to the standard one (a maximal decrease of 23% and 75% along the center line of ingot for thermal stress and dislocation density, respectively). This modification reduces the heating power consumption for solidification of the silicon melt by about 17% and shortens the growth time by about 2.5 h. Moreover, it is found that adjusting the operating conditions of modified model to obtain the lower growth rate during the early stages of the solidification process can lower dislocation density and total heater power.

  19. Process for preparing sintered uranium dioxide nuclear fuel

    International Nuclear Information System (INIS)

    Carter, R.E.

    1975-01-01

    Uranium dioxide is prepared for use as fuel in nuclear reactors by sintering it to the desired density at a temperature less than 1300 0 C in a chemically controlled gas atmosphere comprised of at least two gases which in equilibrium provide an oxygen partial pressure sufficient to maintain the uranium dioxide composition at an oxygen/uranium ratio of at least 2.005 at the sintering temperature. 7 Claims, No Drawings

  20. The dimensional accuracy of the sintered billets

    Directory of Open Access Journals (Sweden)

    Чингиз Ариф оглы Алиев

    2016-01-01

    Full Text Available The article presents the results of assessing the impact of the behaviour stability of the components included in the compositions and process parameters of their production, on the dimensional accuracy of workpieces. It was found that by increasing the amount of oxide in the composition is greater compaction of the sintered billet in the process of heat treatment. This also increases the density of all components of the composition

  1. Low temperature sintering of hyperstoichiometric uranium dioxide

    International Nuclear Information System (INIS)

    Chevrel, H.

    1991-12-01

    In the lattice of uranium dioxide with hyperstoichiometric oxygen content (UO 2+x ), each additional oxygen atoms is introduced by shifting two anions from normal sites to interstitial ones, thereby creating two oxygen vacancies. The point defects then combine to form complex defects comprising several interstitials and vacancies. The group of anions (3x) in the interstitial position participate in equilibria promoting the creation of uranium vacancies thereby considerably increasing uranium self-diffusion. However, uranium grain boundaries diffusion governs densification during the first two stages of sintering of uranium dioxide with hyperstoichiometric oxygen content, i.e., up to 93% of the theoretical density. Surface diffusion and evaporation-condensation, which are considerably accentuated by the hyperstoichiometric deviation, play an active role during sintering by promoting crystalline growth during the second and third stages of sintering. U 8 O 8 can be added to adjust the stoichiometry and to form a finely porous structure and thus increase the pore area subjected to surface phenomena. The composition with an O/U ratio equal to 2.25 is found to densify the best, despite a linear growth in sintering activation energy with hyperstoichiometric oxygen content, increasing from 300 kj.mol -1 for UO 2.10 to 440 kJ.mol -1 for UO 2.25 . Seeds can be introduced to obtain original microstructures, for example the presence of large grains in small-grain matrix

  2. Comparison of Ti(C,N)-based cermets processed by hot-pressing sintering and conventional pressureless sintering

    International Nuclear Information System (INIS)

    Xu, Qingzhong; Ai, Xing; Zhao, Jun; Qin, Weizhen; Wang, Yintao; Gong, Feng

    2015-01-01

    Highlights: • The HP sintered Ti(C,N)-based cermets exhibit high hardness with fine grain size. • The PLS sintered cermets possess high mechanical properties with low porosity. • The applied pressure can rearrange particles and contribute to grain refinement. • The heating rate can greatly affect the solid and liquid phase sintering of cermets. - Abstract: A suitable sintering method is important to obtain the Ti(C,N)-based cermets with superior properties. In this paper, Ti(C,N)-based cermets were fabricated by hot-pressing sintering (HP) and conventional pressureless sintering (PLS) technology, respectively, to investigate the influence of different sintering methods on the microstructure and mechanical properties of cermets materials. The microstructure, fracture morphology, indention cracks and phase composition were observed and detected using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The transverse rupture strength (TRS), Vickers hardness (HV) and fracture toughness (K IC ) were also measured. The results reveal that all of the Ti(C,N)-based cermets exhibit core–rim microstructures with black cores, white cores and grey rims embedded into metal binder phases. The grain size of the samples fabricated by HP is much finer and the structure is more compact than those fabricated by PLS, while there exist pores in the HP sintered samples. The sintering process has no influence on the phase composition of cermets, but affects the phase content and crystallinity. The samples fabricated by PLS present higher transverse rupture strength, fracture toughness and density than samples fabricated by HP. However, the HP sintered samples possess a higher hardness

  3. Improved microstructure and thermoelectric properties of iodine doped indium selenide as a function of sintering temperature

    Science.gov (United States)

    Dhama, Pallavi; Kumar, Aparabal; Banerji, P.

    2018-04-01

    In this paper, we explored the effect of sintering temperature on the microstructure, thermal and electrical properties of iodine doped indium selenide in the temperature range 300 - 700 K. Samples were prepared by a collaborative process of vacuum melting, ball milling and spark plasma sintering at 570 K, 630 K and 690 K. Single phase samples were obtained at higher sintering temperature as InSe is stable only at lower temperature. With increasing sintering temperature, densities of the samples were found to improve with larger grain size formation. Negative values of Seebeck coefficient were observed which indicates n-type carrier transport. Seebeck coefficient increases with sintering temperature and found to be the highest for the sample sintered at 690 K. Thermal conductivity found to be lower in the samples sintered at lower temperatures. The maximum thermoelectric figure of merit found to be ˜ 1 at 700 K due to the enhanced power factor as a result of improved microstructure.

  4. Elaboration of silicon carbides nano particles (SiC): from the powder synthesis to the sintered ceramic; Elaboration de ceramiques nanostructurees en carbure de silicium (SiC): de la synthese de poudre a la ceramique frittee

    Energy Technology Data Exchange (ETDEWEB)

    Reau, A. [CEA Saclay, Dept. des Materiaux pour le Nucleaire (DEN/DANS/DMN/SRMA), 91 - Gif-sur-Yvette (France)

    2008-07-01

    Materials for the reactor cores of the fourth generation will need materials supporting high temperatures with fast neutrons flux. SiC{sub f}/SiC ceramics are proposed. One of the possible elaboration process is to fill SiC fiber piece with nano particles SiC powder and to strengthen by sintering. The aim of this thesis is to obtain a nano structured SiC ceramic as a reference for the SiC{sub f}/SiC composite development and to study the influence of the fabrication parameters. (A.L.B.)

  5. Indentation fatigue in silicon nitride, alumina and silicon carbide ...

    Indian Academy of Sciences (India)

    Unknown

    carbide ceramics. A K MUKHOPADHYAY. Central Glass and Ceramic Research Institute, Kolkata 700 032, India. Abstract. Repeated indentation fatigue (RIF) experiments conducted on the same spot of different structural ceramics viz. a hot pressed silicon nitride (HPSN), sintered alumina of two different grain sizes viz.

  6. Spark Plasma Sintering of Ultracapacitors

    Energy Technology Data Exchange (ETDEWEB)

    Hill, Curtis W. [CK Technologies, Camirillo, CA (United States); Boatner, Lynn A. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Tucker, Dennis [NASA Johnson Space Center, Houston, TX (United States); Kolopus, James A. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Cheng, Zhongyang [Auburn Univ., AL (United States)

    2016-01-01

    A solid-state ultracapacitor module to replace standard electrochemical batteries would achieve major performance gains and mass/volume reduction. This report summarizes a project to evaluate an alternative sintering process to produce a solid-state ultracapacitor to overcome the limitations of both the electrochemical batteries presently in use on spacecraft and of currently available electrochemical ultracapacitors. It will provide a robust energy storage device with higher reliability, wider working temperature range, longer lifetime, and less weight and volume than electrochemical batteries. As modern electronics decrease in size, more efficient and robust remote power is needed. Current state-of-the-art rechargeable batteries cannot be rapidly charged, contain harmful chemicals, and suffer from early wear-out mechanisms. Solid-state ultracapacitors are recyclable energy storage devices that offer the promise of higher power and a greater number of charge/discharge cycles than current rechargeable batteries. In addition, the theoretical energy density when compared to current electrochemical batteries indicates that a significant weight savings is possible. This is a project to develop a very high density solid-state ultracapacitor with giant permittivity and acceptable dielectric loss to overcome the energy-density barrier such that it will be a suitable replacement for batteries.

  7. Ferritic oxide dispersion strengthened alloys by spark plasma sintering

    Energy Technology Data Exchange (ETDEWEB)

    Allahar, Kerry N., E-mail: KerryAllahar@boisestate.edu [Materials and Science Engineering Department, Boise State University, 1910 University Blvd., Boise, ID 83725 (United States); Center for Advanced Energy Studies, 995 University Blvd., Idaho Falls, ID 83401 (United States); Burns, Jatuporn [Materials and Science Engineering Department, Boise State University, 1910 University Blvd., Boise, ID 83725 (United States); Center for Advanced Energy Studies, 995 University Blvd., Idaho Falls, ID 83401 (United States); Jaques, Brian [Materials and Science Engineering Department, Boise State University, 1910 University Blvd., Boise, ID 83725 (United States); Wu, Y.Q. [Materials and Science Engineering Department, Boise State University, 1910 University Blvd., Boise, ID 83725 (United States); Center for Advanced Energy Studies, 995 University Blvd., Idaho Falls, ID 83401 (United States); Charit, Indrajit [Department of Chemical and Materials Engineering, University of Idaho, McClure Hall Room 405D, Moscow, ID 83844 (United States); Cole, James [Idaho National Laboratory, Idaho Falls, ID 83401 (United States); Butt, Darryl P. [Materials and Science Engineering Department, Boise State University, 1910 University Blvd., Boise, ID 83725 (United States); Center for Advanced Energy Studies, 995 University Blvd., Idaho Falls, ID 83401 (United States)

    2013-11-15

    Spark plasma sintering (SPS) was used to consolidate a Fe–16Cr–3Al (wt.%) powder that was mechanically alloyed with Y{sub 2}O{sub 3} and Ti powders to produce 0.5 Y{sub 2}O{sub 3} and 0.5 Y{sub 2}O{sub 3}–1Ti powders. The effects of mechanical alloying and sintering conditions on the microstructure, relative density and hardness of the sintered oxide dispersion strengthened (ODS) alloys are presented. Scanning electron microscopy indicated a mixed fine-grain and coarse-grain microstructure that was attributed to recrystallization and grain growth during sintering. Analysis of the transmission electron microscopy (TEM) and atom probe tomography (APT) data identified Y–O and Y–O–Ti nanoclusters. Elemental ratios of these nanoclusters were consistent with that observed in hot-extruded ODS alloys. The influence of Ti was to refine the grains as well as the nanoclusters with there being greater number density and smaller sizes of the Y–O–Ti nanoclusters as compared to the Y–O nanoclusters. This resulted in the Ti-containing samples being harder than the Ti-free alloys. The hardness of the alloys with the Y–O–Ti nanoclusters was insensitive to sintering time while smaller hardness values were associated with longer sintering times for the alloys with the Y–O nanoclusters. Pressures greater than 80 MPa are recommended for improved densification as higher sintering temperatures and longer sintering times at 80 MPa did not improve the relative density beyond 97.5%.

  8. Sintering and microstructure evolution in columnar thermal barrier coatings

    International Nuclear Information System (INIS)

    Krishnamurthy, Ramanathan; Srolovitz, David J.

    2009-01-01

    Sintering of thermal barrier coatings changes their key properties, such as thermal conductivity and thermal shock resistance, thus adversely impacting their reliability. We present a novel modeling approach to study the evolution of coating structure during sintering. We model the sintering of individual columns using a thermodynamic principle, and incorporate the center-to-center approach rates for the columns calculated using this principle in a larger scale discrete dynamics model for the evolution of a large number of columns. Surface energies, grain boundary energies and strain energies associated with the deformation of the columns are all included in this framework, while sintering is assumed to occur by the concerted action of surface and grain boundary diffusion. Two sets of initial conditions corresponding to different extents of pre-sintering among neighboring columns are considered. When the extent of pre-sintering is small, we observe that small clusters containing 5-20 columns are formed. In contrast, where a larger amount of pre-sintering exists, we observe, especially at large column densities, that clusters containing 50-100 columns separated by large inter-cluster pores/channels that appear to organize themselves into a network are formed. These observations are in good agreement with recently published experimental observations. We also explain how these results can explain the development of a 'mud-crack'-like pattern

  9. Spark plasma sintering of titanium aluminide intermetallics and its composites

    Science.gov (United States)

    Aldoshan, Abdelhakim Ahmed

    Titanium aluminide intermetallics are a distinct class of engineering materials having unique properties over conventional titanium alloys. gamma-TiAl compound possesses competitive physical and mechanical properties at elevated temperature applications compared to Ni-based superalloys. gamma-TiAl composite materials exhibit high melting point, low density, high strength and excellent corrosion resistance. Spark plasma sintering (SPS) is one of the powder metallurgy techniques where powder mixture undergoes simultaneous application of uniaxial pressure and pulsed direct current. Unlike other sintering techniques such as hot iso-static pressing and hot pressing, SPS compacts the materials in shorter time (< 10 min) with a lower temperature and leads to highly dense products. Reactive synthesis of titanium aluminide intermetallics is carried out using SPS. Reactive sintering takes place between liquid aluminum and solid titanium. In this work, reactive sintering through SPS was used to fabricate fully densified gamma-TiAl and titanium aluminide composites starting from elemental powders at different sintering temperatures. It was observed that sintering temperature played significant role in the densification of titanium aluminide composites. gamma-TiAl was the predominate phase at different temperatures. The effect of increasing sintering temperature on microhardness, microstructure, yield strength and wear behavior of titanium aluminide was studied. Addition of graphene nanoplatelets to titanium aluminide matrix resulted in change in microhardness. In Ti-Al-graphene composites, a noticeable decrease in coefficient of friction was observed due to the influence of self-lubrication caused by graphene.

  10. Analysis of defect structure in silicon. Effect of grain boundary density on carrier mobility in UCP material

    Science.gov (United States)

    Dunn, J.; Stringfellow, G. B.; Natesh, R.

    1982-01-01

    The relationships between hole mobility and grain boundary density were studied. Mobility was measured using the van der Pauw technique, and grain boundary density was measured using a quantitative microscopy technique. Mobility was found to decrease with increasing grain boundary density.

  11. Silicon nitride-fabrication, forming and properties

    International Nuclear Information System (INIS)

    Yehezkel, O.

    1983-01-01

    This article, which is a literature survey of the recent years, includes description of several methods for the formation of silicone nitride, and five methods of forming: Reaction-bonded silicon nitride, sintering, hot pressing, hot isostatic pressing and chemical vapour deposition. Herein are also included data about mechanical and physical properties of silicon nitride and the relationship between the forming method and the properties. (author)

  12. Optical characterization of nanocrystals in silicon rich oxide superlattices and porous silicon

    International Nuclear Information System (INIS)

    Agocs, E.; Petrik, P.; Milita, S.; Vanzetti, L.; Gardelis, S.; Nassiopoulou, A.G.; Pucker, G.; Balboni, R.; Fried, M.

    2011-01-01

    We propose to analyze ellipsometry data by using effective medium approximation (EMA) models. Thanks to EMA, having nanocrystalline reference dielectric functions and generalized critical point (GCP) model the physical parameters of two series of samples containing silicon nanocrystals, i.e. silicon rich oxide (SRO) superlattices and porous silicon layers (PSL), have been determined. The superlattices, consisting of ten SRO/SiO 2 layer pairs, have been prepared using plasma enhanced chemical vapor deposition. The porous silicon layers have been prepared using short monopulses of anodization current in the transition regime between porous silicon formation and electropolishing, in a mixture of hydrofluoric acid and ethanol. The optical modeling of both structures is similar. The effective dielectric function of the layer is calculated by EMA using nanocrystalline components (nc-Si and GCP) in a dielectric matrix (SRO) or voids (PSL). We discuss the two major problems occurring when modeling such structures: (1) the modeling of the vertically non-uniform layer structures (including the interface properties like nanoroughness at the layer boundaries) and (2) the parameterization of the dielectric function of nanocrystals. We used several techniques to reduce the large number of fit parameters of the GCP models. The obtained results are in good agreement with those obtained by X-ray diffraction and electron microscopy. We investigated the correlation of the broadening parameter and characteristic EMA components with the nanocrystal size and the sample preparation conditions, such as the annealing temperatures of the SRO superlattices and the anodization current density of the porous silicon samples. We found that the broadening parameter is a sensitive measure of the nanocrystallinity of the samples, even in cases, where the nanocrystals are too small to be visible for X-ray scattering. Major processes like sintering, phase separation, and intermixing have been

  13. Preparation of Nd–Fe–B sintered magnets from HDDR-processed powder

    Energy Technology Data Exchange (ETDEWEB)

    Takagi, Kenta, E-mail: k-takagi@aist.go.jp [Green Innovative Magnetic Materials Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Nagoya 463-8560 (Japan); Akada, Misaho [Magnetic Materials R& D Center, Research Associations of Magnetic Materials for High-Efficiency Motors (MagHEM), Nagoya 463-8560 (Japan); Soda, Rikio; Ozaki, Kimihiro [Green Innovative Magnetic Materials Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Nagoya 463-8560 (Japan)

    2015-11-01

    The electric-current sintering technique was used to fully densify hydrogenation–disproportionation–desorption–recombination (HDDR)-processed Nd–Fe–B powder at temperatures below the grain growth temperature in order to produce high-coercive bulk magnets. However, the sintered magnets exhibited anomalous coercivity reduction that depended on sintered density. Reheating examination of the sintered magnets revealed that the reduced coercivity was increased in proportion to the heating temperature, resulting in complete recovery of coercivity. As a result, the combination of electric-current sintering and post-annealing produced sintered magnets with a coercivity of 15 kOe. Scanning and transmission electron microscopy revealed no evidence that associated the anomalous coercivity reduction and recovery with grain boundary morphology. On the other hand, various HDDR powders with different particle sizes were sintered, and finer powders yielded lower coercivity after sintering, implying that the anomalous coercivity reduction was associated with particle surface oxides of the raw powder. - Highlights: • We conduct a sintering of HDDR-processed Nd–Fe–B powder without coercivity reduction. • Rapid current sintering allows densification of this powder without grain growth. • However, the sintered magnets show an anomalous coercivity reduction phenomenon. • It is found that post-annealing completely recovers the reduced coercivity. • The anomalous coercivity reduction would be due to surface oxide of the raw powder.

  14. Electrical and microstructural properties of microwave sintered SnO{sub 2}-based varistors

    Energy Technology Data Exchange (ETDEWEB)

    Furtado, P.S.; Oliveira, M.M.; Vasconcelos, J.S.; Rangel, J.H.G., E-mail: periclesft@ifma.edu.br, E-mail: marcelo@ifma.edu.br, E-mail: jomar@ifma.edu.br, E-mail: hiltonrangel@ifma.edu.br [IFMA-DAQ- PPGEM, S. Luis, MA (Brazil); Longo, E., E-mail: elson@iq.unesp.br [CMDMC, LIEC, Instituto de Quimica, UNESP, Araraquara, SP (Brazil); Sousa, V.C. de, E-mail: vania.sousa@ufrgs.br [DEMAT, Universidade Federal do Rio Grande do Sul - UFRGS, Porto Alegre, RS (Brazil)

    2012-04-15

    An investigation was made of the microstructural and electrical properties of SnO{sub 2} -based varistors microwave sintered at 1200 deg C, applying a heating rate of 120 deg C/min and treatment times of 10, 20, 30, 40, 50 and 60 min. The system used in this study was (98.95-X)%SnO{sub 2}.1.0%CoO.0.05%Cr{sub 2}O{sub 3}.X%Ta{sub 2}O{sub 5}, where X corresponds to 0.05 and 0.065 mol%. Sintering was carried out in a domestic microwave oven (2.45 GHz) fitted for lab use. Silicon carbide was placed in a refractory vessel to form a heating chamber surrounding the sample holder. The pellets were examined by scanning electron microscopy, X-ray diffractometry, direct current measurements and impedance spectroscopy. The parameters of density, medium grain size, coefficient of nonlinearity, breakdown electrical field, leakage current, and height and width of the potential barrier were analyzed. (author)

  15. Grain-growth law during Stage 1 sintering of materials

    International Nuclear Information System (INIS)

    He Zeming; Ma, J.

    2002-01-01

    This work investigates the grain-growth behaviour of powder compact during Stage 1 sintering (<90{%} theoretical density). It is widely accepted that grain size is an important state variable in the constitutive modelling in material sintering. However, it is noted that all the existing grain-growth laws proposed in the literature do not incorporate the effect of externally applied stress independently. In this work, a grain-growth law with externally applied stress as a variable was proposed. Alumina powders were forge-sintered at different applied stresses to examine the proposed grain-growth relationship. The proposed grain-growth law was then applied to model the grain-growth process on the sinter forging of tool steel. It is shown that the present proposed grain-growth law provides a good description on the experimental results. (author)

  16. Sintered stabilized zirconia microstructure and conductivity

    International Nuclear Information System (INIS)

    Bernard, Herve.

    1981-04-01

    The elaboration of a stabilized zirconia powder which sinters at 1300 0 C and the influence of the sintered polycristal microstructure on its ionic conductivity have been studied. Among three investigated powder preparation processes, coprecipitation in an ammoniacal solution was chosen. After sintering at 1300 0 C, the pellet density was higher than 93% of the theoretical density. It even approached up to 98% TD with addition of less than 0,5 mole % Al 2 O 3 to the initial powder. The overall electrolyte conductivity and the inter and intragranular contributions have been determined by complex impedance spectroscopy. ZrO 2 -Y 2 O 3 solid solution conductivity was scarcely improved by Y 2 O 3 exchange with Yb 2 O 3 or Gd 2 O 3 . This conductivity greatly increases with grain size, its improvement with decreasing porosity, which has been quantified, is less sensible. Moreover, two original properties were noticed: small amounts of Al 2 O 3 and quenching greatly enhanced the overall conductivity. At temperatures below 500 0 C, grain boundaries only insured a partial migration of conductive ions. A parallel type electrical equivalent circuit suited well with this blocking effect [fr

  17. Sintering of Spherical Particles of Equal and Different Size Arranged in a Body Centered Cubic Structure

    DEFF Research Database (Denmark)

    Redanz, Pia; McMeeking, R. M.

    2003-01-01

    Solid-state sintering of a bcc structure of spherical particles has been studied numerically by use of simple shape parameters to describe the state of the unit cell. Both free and pressure-assisted sintering of particles of equal and different sizes for various ratios of boundary and surface dif......, different dihedral angles and the evolution of relative density and sintering stresses are studied....

  18. The effect of various sintering temperature on used refractory towards its physical properties

    Science.gov (United States)

    Sudibyo; Wulandari, Y. R.; Amin, M.; Azhar

    2018-01-01

    The used magnesia refractory from the kiln of cement industry was successfully recycled to new refractory using Kaolin as an adhesive. In this work, the temperatures of sintering were varied from 1000°C to 1500°C. The result shows that the increment temperature effects in sintering process will enhance refractory physical properties such as bulk density, cold crushing strength or pressure strength and thermal conductivity. Meanwhile, the porosity was decreased as the increase of the sintering temperature.

  19. Low sintering temperature glass waste forms for sequestering radioactive iodine

    Science.gov (United States)

    Nenoff, Tina M.; Krumhansl, James L.; Garino, Terry J.; Ockwig, Nathan W.

    2012-09-11

    Materials and methods of making low-sintering-temperature glass waste forms that sequester radioactive iodine in a strong and durable structure. First, the iodine is captured by an adsorbant, which forms an iodine-loaded material, e.g., AgI, AgI-zeolite, AgI-mordenite, Ag-silica aerogel, ZnI.sub.2, CuI, or Bi.sub.5O.sub.7I. Next, particles of the iodine-loaded material are mixed with powdered frits of low-sintering-temperature glasses (comprising various oxides of Si, B, Bi, Pb, and Zn), and then sintered at a relatively low temperature, ranging from 425.degree. C. to 550.degree. C. The sintering converts the mixed powders into a solid block of a glassy waste form, having low iodine leaching rates. The vitrified glassy waste form can contain as much as 60 wt % AgI. A preferred glass, having a sintering temperature of 500.degree. C. (below the silver iodide sublimation temperature of 500.degree. C.) was identified that contains oxides of boron, bismuth, and zinc, while containing essentially no lead or silicon.

  20. 3Y-TZP/Si2N2O composite obtained by pressureless sintering

    International Nuclear Information System (INIS)

    Santos, Carlos Augusto Xavier

    2006-01-01

    Zirconia 3YTZP presents excellent properties at room temperature. These properties decrease as the temperature increases because high temperature acts negatively over the stress induced transformation toughening in the matrix. The addition of Si 3 N 4 and SiC in a Y-TZP matrix is very interesting because leads to formation of silicon oxynitride and it increases the mechanical properties like toughness and hardness. Certainly the mechanical properties increment is limited by several difficulties which have appeared during processing and heating of these materials. This paper studies the Y-TZP/Si 2 N 2 0 pressureless sintered composite, under different temperatures, showing the behavior of 20 vol %Si 3 N 4 -SiC when added in YTZP matrix and heated under no pressure system. Al 2 O 3 and Y 2 O 3 were used as sintering aids. The mixture was milled and molded by cold isostatic pressure. Samples were heated at 1500 deg, 1600 deg and 17000 deg C x 2h without pressure under atmospheric conditions using Si 3 N 4 bed-powder. Samples were characterized by XRD and density, hardness, toughness, bending strength were measured. The structure of the material was observed in SEMITEM/EPMA to verify the distribution and composition of the materials in the composite and the contact between filler surface and the matrix. The formation of SiON 2 was observed in the sintered material due to reaction between both nitride and carbide with Y - TZP matrix. Furthermore the material showed an increment of both hardness and toughness as temperature increases. The samples presented considerable resistance to oxidation below 1000 deg C. (author)

  1. Effect Of Compaction Pressure And Sintering Temperature On The Liquid Phase Sintering Behavior Of Al-Cu-Zn Alloy

    Directory of Open Access Journals (Sweden)

    Lee S.H.

    2015-06-01

    Full Text Available The liquid phase sintering characteristics of Al-Cu-Zn alloy were investigated with respect to various powder metallurgy processing conditions. Powders of each alloying elements were blended to form Al-6Cu-5Zn composition and compacted with pressures of 200, 400, and 600 MPa. The sintering process was performed at various temperatures of 410, 560, and 615°C in N2 gas atmosphere. Density and micro-Vickers hardness measurements were conducted at different processing stages, and transverse rupture strength of sintered materials was examined for each condition, respectively. The microstructure was characterized using optical microscope and scanning electron microscopy. The effect of Zn addition on the liquid phase sintering behavior during P/M process of the Al-Cu-Zn alloy was also discussed in detail.

  2. Liquid phase sintered SiC. Processing and transformation controlled microstructure tailoring

    Directory of Open Access Journals (Sweden)

    V.A. Izhevskyi

    2000-10-01

    Full Text Available Microstructure development and phase formation processes during sintering of silicon carbide based materials with AlN-Y2O3, AlN-Yb2O3, and AlN-La2O3 sintering additives were investigated. Densification of the materials occurred by liquid-phase sintering mechanism. Proportion of alpha- and beta-SiC powders in the initial mixtures was a variable parameter, while the molar ratio of AlN/RE2O3, and the total amount of additives (10 vol. % were kept constant. Shrinkage behavior during sintering in interrelation with the starting composition of the material and the sintering atmosphere was investigated by high temperature dilatometry. Kinetics of b-SiC to a-SiC phase transformation during post-sintering heat treatment at temperatures 1900-1950 °C was studied, the degree of phase transformation being determined by quantitative x-ray analysis using internal standard technique. Evolution of microstructure resulting from beta-SiC to alpha-SiC transformation was followed up by scanning electron microscopy on polished and chemically etched samples. Transformation-controlled grain growth mechanism similar to the one observed for silicon nitride based ceramics was established. Possibility of in-situ platelet reinforced dense SiC-based ceramics fabrication with improved mechanical properties by means of sintering was shown.

  3. Influence of van der Waals forces on the adsorption structure of benzene on silicon studied using density functional theory

    DEFF Research Database (Denmark)

    Johnston, Karen; Kleis, Jesper; Lundqvist, Bengt

    2008-01-01

    Two different adsorption configurations of benzene on the Si(001)-(2×1) surface, the tight-bridge and butterfly structures, were studied using density functional theory. Several exchange and correlation functionals were used, including the recently developed van der Waals density functional (vd...

  4. Sintering and microstructure of ZnO varistor

    International Nuclear Information System (INIS)

    Leite, E.R.; Longo, E.; Varela, J.A.

    1987-01-01

    The sintering and microstructure of ZnO-Bi 2 O 3 (ZB) and ZuO-Sb 2 O 3 -CoO-Bi 2 O 3 (ZSCB) varistors in several temperatures, for one hour in dry air temperature were studied. The compounds were analyzed by scanning electron microscopy, X-ray diffraction, differential thermal analysis and the density and porosity were determined by mercury picnometry. The experimental results showed that the ZB and ZSCB system sinters by liquid means and that liquid will control the density and grain growth mechanisms. (E.G.) [pt

  5. Interactions of structural defects with metallic impurities in multicrystalline silicon

    International Nuclear Information System (INIS)

    McHugo, S.A.; Thompson, A.C.; Hieslmair, H.

    1997-01-01

    Multicrystalline silicon is one of the most promising materials for terrestrial solar cells. It is critical to getter impurities from the material as well as inhibit contamination during growth and processing. Standard processing steps such as, phosphorus in-diffusion for p-n junction formation and aluminum sintering for backside ohmic contact fabrication, intrinsically possess gettering capabilities. These processes have been shown to improve L n values in regions of multicrystalline silicon with low structural defect densities but not in highly dislocated regions. Recent Deep Level Transient Spectroscopy (DLTS) results indirectly reveal higher concentrations of iron in highly dislocated regions while further work suggests that the release of impurities from structural defects, such as dislocations, is the rate limiting step for gettering in multicrystalline silicon. The work presented here directly demonstrates the relationship between metal impurities, structural defects and solar cell performance in multicrystalline silicon. Edge-defined Film-fed Growth (EFG) multicrystalline silicon in the as-grown state and after full solar cell processing was used in this study. Standard solar cell processing steps were carried out at ASE Americas Inc. Metal impurity concentrations and distributions were determined by use of the x-ray fluorescence microprobe (beamline 10.3.1) at the Advanced Light Source, Lawrence Berkeley National Laboratory. The sample was at atmosphere so only elements with Z greater than silicon could be detected, which includes all metal impurities of interest. Structural defect densities were determined by preferential etching and surface analysis using a Scanning Electron Microscope (SEM) in secondary electron mode. Mapped areas were exactly relocated between the XRF and SEM to allow for direct comparison of impurity and structural defect distributions

  6. Mechanisms of sintering

    International Nuclear Information System (INIS)

    Mohan, Ashok; Soni, N.C.; Moorthy, V.K.

    1980-01-01

    The basic mechanisms by which the material moves during sintering have not only held a strange fascination but are also very important in determining the properties of the end product. Kuczynski's exponent method has been subsequently refined by several schools to make it increasingly reliable. There is now a fairly good understanding of mechanisms in some of the materials. However in others the issue is complicated by their basic nature. The problems of ambiguity in criterion and that of more than one mechanism being simultaneously operative have been tackled with dexterity by Ashby for drawing sintering mechanism diagrams. The method has been modified to give Relative Contribution Diagrams (RCD). These yield additional information and have been used for analysis. The main criticism against this is that it uses a very large number of rate equations and material properties, which can communicate their inaccuracies to the diagram. A case study of UO 2 was undertaken and it has been shown quantitatively that inaccuracies in a smaller number of properties only affect the diagrams to any significant extent. (auth.)

  7. Effect of Power Characteristics on the Densification of Sintered Alumina

    International Nuclear Information System (INIS)

    Al-Sarraj, Z.S.A.; Noor, S.S.

    2011-01-01

    The effect of particle size distribution, soaking time and sintering temperatures on the densification behaviors of α-Al 2 O 3 was investigated. Two different average particle sizes of 36 and 45μ were examined as a variable to analyze the difference in density, radial and axial shrinkage, densification, and microstructure developments. Conventional powder technology route was used to prepare disc-shaped green pellets sintered at 1200-1600 0 C for different periods. Density measurements for both green and sintered compacts allow for the refinement of processing parameters to obtain dense sintered bodies. Compacts with particle size of 36 μm were noticed to attain higher relative densities as compared with those of 45μm. Densification parameter (ΔP) calculations clearly reveals the presence of definite temperatures and times in which limited densification retardation occurred, which permits the suggesting of suitable sintering schemes for this material. Scanning electron micrographs analysis revealed a pore structure assist the observed behaviours for the different schemes. (author)

  8. Room temperature photoluminescence spectrum modeling of hydrogenated amorphous silicon carbide thin films by a joint density of tail states approach and its application to plasma deposited hydrogenated amorphous silicon carbide thin films

    International Nuclear Information System (INIS)

    Sel, Kıvanç; Güneş, İbrahim

    2012-01-01

    Room temperature photoluminescence (PL) spectrum of hydrogenated amorphous silicon carbide (a-SiC x :H) thin films was modeled by a joint density of tail states approach. In the frame of these analyses, the density of tail states was defined in terms of empirical Gaussian functions for conduction and valance bands. The PL spectrum was represented in terms of an integral of joint density of states functions and Fermi distribution function. The analyses were performed for various values of energy band gap, Fermi energy and disorder parameter, which is a parameter that represents the width of the energy band tails. Finally, the model was applied to the measured room temperature PL spectra of a-SiC x :H thin films deposited by plasma enhanced chemical vapor deposition system, with various carbon contents, which were determined by X-ray photoelectron spectroscopy measurements. The energy band gap and disorder parameters of the conduction and valance band tails were determined and compared with the optical energies and Urbach energies, obtained by UV–Visible transmittance measurements. As a result of the analyses, it was observed that the proposed model sufficiently represents the room temperature PL spectra of a-SiC x :H thin films. - Highlights: ► Photoluminescence spectra (PL) of the films were modeled. ► In the model, joint density of tail states and Fermi distribution function are used. ► Various values of energy band gap, Fermi energy and disorder parameter are applied. ► The model was applied to the measured PL of the films. ► The proposed model represented the room temperature PL spectrum of the films.

  9. Study of the changes of uranium dioxide properties resulting from sintering; Izucavanje procesa sinterovanja urandioksida sa gledista promene karakteristicnih osobina

    Energy Technology Data Exchange (ETDEWEB)

    Ristic, M M [Institute of Nuclear Sciences Vinca, Laboratorija za reaktorske materijale, Beograd (Serbia and Montenegro)

    1962-12-15

    Uranium dioxide powder used for studying the sintering process having grain size 63 {mu}. Sintering was performed in the temperature interval from 1000 - 1300 deg C in argon atmosphere. The O/U ratio of the used uranium dioxide was 2.07. Densities obtained by sintering under the mentioned conditions were not higher than 91% TG (theoretical density). This showed that the mentioned conditions were optimal, but the uranium dioxide obtained could be used for studying the radiation damage of fuel.

  10. Laser sintering of copper nanoparticles

    International Nuclear Information System (INIS)

    Zenou, Michael; Saar, Amir; Ermak, Oleg; Kotler, Zvi

    2014-01-01

    Copper nanoparticle (NP) inks serve as an attractive potential replacement to silver NP inks in functional printing applications. However their tendency to rapidly oxidize has so far limited their wider use. In this work we have studied the conditions for laser sintering of Cu-NP inks in ambient conditions while avoiding oxidation. We have determined the regime for stable, low-resistivity copper (< ×3 bulk resistivity value) generation in terms of laser irradiance and exposure duration and have indicated the limits on fast processing. The role of pre-drying conditions on sintering outcome has also been studied. A method, based on spectral reflectivity measurements, was used for non-contact monitoring of the sintering process evolution. It also indicates preferred spectral regions for sintering. Finally, we illustrated how selective laser sintering can generate high-quality, fine line (<5 µm wide) and dense copper circuits. (paper)

  11. Silver-capped silicon nanopillar platforms for adsorption studies of folic acid using surface enhanced Raman spectroscopy and density functional theory

    DEFF Research Database (Denmark)

    Castillo, Jaime; Rindzevicius, Tomas; Wu, Kaiyu

    2015-01-01

    The study of the interactions of folic acid (FA) with surface enhanced Raman scattering substrates is relevant for understanding its adsorption mechanismand for fabricating analytical devices for detection ofmalignant cells over-expressing folate receptors. This paper presents a study of the adso......The study of the interactions of folic acid (FA) with surface enhanced Raman scattering substrates is relevant for understanding its adsorption mechanismand for fabricating analytical devices for detection ofmalignant cells over-expressing folate receptors. This paper presents a study...... of the adsorption of FA on silver-capped silicon nanopillar substrates employing surface enhanced Raman scattering spectroscopy and density functional theory calculations. The experimentally observed vibrations from free FA and FA bound to the Ag surface display different vibrational spectra indicating chemical...

  12. Valence band structure and density of states effective mass model of biaxial tensile strained silicon based on k · p theory

    International Nuclear Information System (INIS)

    Kuang Qian-Wei; Liu Hong-Xia; Wang Shu-Long; Qin Shan-Shan; Wang Zhi-Lin

    2011-01-01

    After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k · p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states (DOS) effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal—oxide semiconductor field effect transistor (MOSFET). It also a provides valuable reference for biaxial tensile strained silicon MOSFET design. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  13. Effects of inter-tube coupling on the electro-optical properties of silicon carbide nanotube bundles studied by density functional theory

    Science.gov (United States)

    Behzad, Somayeh

    2015-09-01

    The electronic and optical properties of bundled armchair and zigzag silicon carbide nanotubes (SiCNTs) are investigated by using density functional theory. The effects of inter-tube coupling on the electronic dispersions of SiCNT bundles are demonstrated. It was found that the band structure of (6, 0) SiCNT bundle shows metallic feature. The calculated dielectric functions of the armchair and zigzag bundles are similar to that of the isolated tubes, except for the appearance of broadened peaks, small shifts of peak positions about 0.1 eV and increasing of peak intensities. For (6, 0) SiCNT with smaller radius, by considering interband and interaband transitions, the band structure coupling causes an extra peak at low energies.

  14. Joining of porous silicon carbide bodies

    Science.gov (United States)

    Bates, Carl H.; Couhig, John T.; Pelletier, Paul J.

    1990-05-01

    A method of joining two porous bodies of silicon carbide is disclosed. It entails utilizing an aqueous slip of a similar silicon carbide as was used to form the porous bodies, including the sintering aids, and a binder to initially join the porous bodies together. Then the composite structure is subjected to cold isostatic pressing to form a joint having good handling strength. Then the composite structure is subjected to pressureless sintering to form the final strong bond. Optionally, after the sintering the structure is subjected to hot isostatic pressing to further improve the joint and densify the structure. The result is a composite structure in which the joint is almost indistinguishable from the silicon carbide pieces which it joins.

  15. Study of spectral properties of bis(1,10-phenanthroline) silicon hexacoordinated complexes by density functional theory

    Science.gov (United States)

    Irgibaeva, Irina; Aldongarov, Anuar; Barashkov, Nikolay; Schmedake, Thomas

    Applying ab initio method the structures and UV-vis spectra of silicon hexacoordinated compound [Si(phen)2(OMe)2]I2 and it's nitrate [Si(phen)2(OMe)2](NO3)2 were calculated. On the ground of comparison of theoretical and experimental data (1H NMR and electronic absorption spectra) it was shown that the theoretical method B3LYP/LanL2DZ we have used describes bis(1,10-phenanthroline) silicon complexes reasonably well. On the basis of TDDFT calculations at B3LYP/LanL2DZ level it is predicted that [Si(phen)2(OMe)2]I2 compound has charge transfer band in UV-vis spectrum at 557 nm which is associated with electron transfer from I- to phen ligand while [Si(phen)2(OMe)2](NO3)2 doesn't have one. The absence of this band in the observed spectrum of the [Si(phen)2(OMe)2]I2 complex methanol solution (10-5 M) is explained by the dissociation of the complex into ions [Si(phen)2(OMe)2]2+ and 2I-. We assume that this charge transfer band corresponds to peak at 400 nm in UV-vis spectrum of [Si(phen)2(OMe)2]I2 thin film. The missing of such bands in UV-vis spectrum of nitrate [Si(phen)2(OMe)2](NO3)2 film is explained by n rarr p* nature of these transitions. Significant error in prediction of charge transfer band energy is due to failure of TDDFT method to yield underestimated charge transfer electronic energies.

  16. Forging loads, deformation modes and fracture in axi-symmetrric closed die cold forging of sintered aluminium powder compacts

    International Nuclear Information System (INIS)

    Butt, M.A.; Ali, L.

    2003-01-01

    An experimental investigation into closed-die cold forging of sintered aluminium powder rod- shaped compacts was carried out. Axi-symmetric components were forged from sintered powder preforms with different initial diameter to height ratios. Different compaction pressures, sintering and lubrication conditions were used as variables during the investigations. Detailed observations were made on green/sintered density, compaction defects, forging loads, deformation modes and on the onset of fracture during progressive forging of sintered powder compacts. Experimental results obtained during the investigations have been presented and discussed in detail. (author)

  17. Cermet sintering on the oase of molybdenum, nickel, aluminium oxide in dry and wet hydrogen medium

    International Nuclear Information System (INIS)

    Fedotov, A.V.; Lutskaya, E.Eh.

    1985-01-01

    Cermet sintering on the base of molybdenum, nickel and aluminium oxide in dry and wer hydrogen medium is studied. It is stated that presence of water vapours permits to decrease sintering temperature of molybdenum containing cermets and to prepare dense nickeliferous cermets. Cermet density can he rather high at final stages of sintering that is probably conditioned by decrease of growth rate of corundum crystals. Pressing pressure activates cermet siptering at intermediate stages and it is low effective at finite stages of condensation. Constancy of relative reduction of void volume is preserved only at final stages of sintering

  18. Effect of boric acid sintering aid on densification of barium ferrite

    Indian Academy of Sciences (India)

    Unknown

    Physical properties like density and porosity have been studied for all compositions. The phase identification and microstructural investigation on the fractured surface have been carried out to understand the effect of sintering aid on the densification characteristics. Keywords. Barium ferrite; sintering aid; densification. 1.

  19. Qualitative relations between the kinetics of sintering in hydrogen and the observed microstructures of uranium dioxide

    International Nuclear Information System (INIS)

    Francois, B.; Delmas, R.; Caillat, F.; Lacombe, P.

    1975-01-01

    The microscopic study of uranium dioxide sintered in hydrogen, together with density measurements, shows on the one hand that the large scale appearance of pores trapped at the grain boundaries in the course of sintering has the effect of practically stopping densification, and on the other hand that this particular microstructure is stable over a wide range of time and temperature. (author)

  20. Sintering of bi-layered porous structures: Stress development and shape evolution

    DEFF Research Database (Denmark)

    Ni, De Wei; Esposito, Vincenzo; Ramousse, Severine

    viscosity of layers was determined as a function of temperature and density using a vertical sintering approach. The distortion in the bi-layer configurations was experimentally recorded and compared with the analytical calculations. The sintering mismatch stress was calculated from both the camber...... development and linear strain rate mismatch, which showed a good agreement....

  1. Analysis of the properties of silicon nitride based ceramic (Si_3N_4) cutting tool using different addictive

    International Nuclear Information System (INIS)

    Pereira, Joaquim Lopes; Souza, Jose Vitor Candido de; Raymundo, Emerson Augusto; Silva, Oliverio Macedo Moreira

    2013-01-01

    The constant search for new materials is part of the scientific and technological development of the industries. Ceramic been presenting important developments in terms of scientific and technological development, highlighting the predominance of covalent ceramics, which has important applications where abrasion resistance and hardness are required. Between covalent materials, several research papers in search of property improvements and cost reduction. However the production of ceramics of silicon nitride (Si_3N_4) with a reduced cost is possible only if used methods and different additives. The aim of this work is the development of compositions based on silicon nitride (Si_3N_4) using different additives such as Y_2O_3, CeO_2, Al_2O_3 , and CTR_2O_3 in varying amounts. For the development of ceramics, the mixtures were homogenized, dried, compacted and sintered using the sintering process of 1850°C for 1 hour, with a heating rate of 25°C/min. The characterizations were performed as a function of relative density by Archimedes method, the mass loss measured before and after sintering, phase analysis by X-ray diffraction, microstructure by scanning electron microscopy (SEM), and hardness and fracture toughness indentation method. The results showed relative density 97-98, Vickers hardness 17-19 GPa, fracture toughness from 5.6 to 6.8 MPa.m"1"/"2. The different phases were obtained depending on the types of additives used. The obtained results are promising for tribological applications. (author)

  2. Microwave-assisted sintering of non-stoichiometric strontium bismuth niobate ceramic: Structural and dielectric properties

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Rajveer [Department of Physics and Astrophysics, University of Delhi, New Delhi 110007 (India); Department of Physics, Atmaram Sanatan Dharma College, University of Delhi, Dhaula Kuan, New Delhi 110021 (India); Luthra, Vandna [Department of Physics, Gargi College, University of Delhi, Siri Fort Road, New Delhi 110049 (India); Tandon, R.P., E-mail: ram_tandon@hotmail.com [Department of Physics and Astrophysics, University of Delhi, New Delhi 110007 (India)

    2016-11-01

    In recent years the microwave sintering has been utilized for the synthesis of materials in enhancement of the properties. In this paper strontium bismuth niobate (Sr{sub 0.8}Bi{sub 2.2}Nb{sub 2}O{sub 9}:SBN) bulk ceramic has been synthesized by microwave reactive sintering and conventional heating techniques. A relative density of 99.6% has been achieved for microwave sintered SBN, which is higher than that of (98.81%) conventionally sintered SBN. The phase formation of SBN synthesized by both processes has been confirmed by X-ray diffraction (XRD). The surface morphology of SBN was observed by scanning electron microscopy (SEM). The microstructure was found to be more uniform in case of SBN sintered by microwave sintering. The dielectric properties of SBN were studied as a function of frequency in the temperature range of 30–500 °C. Both the samples synthesized by two different processes were found to follow Curie–Weiss law above the transition temperature. The Curie temperature was found to be higher for microwave sintered SBN. The dielectric constant and the transition temperature were observed to be higher for SBN ceramic synthesized by microwave sintering technique. The ac and dc activation energy values were also found to be higher for microwave sintered SBN as compared to conventional sintering technique.

  3. SINTERING EFFECTS ON THE DENSIFICATION OF NANOCRYSTALLINE HYDROXYAPATITE

    Directory of Open Access Journals (Sweden)

    M. Amiriyan

    2011-06-01

    Full Text Available The effects of sintering profiles on the densification behaviour of synthesized nanocrystalline hydroxyapatite (HA powder were investigated in terms of phase stability and mechanical properties. A wet chemical precipitation method was successfully employed to synthesize a high purity and single phase HA powder. Green HA compacts were prepared and subjected to sintering in air atmosphere over a temperature range of 700° C to 1300° C. In this study two different holding times were compared, i.e. 1 minute versus the standard 120 minutes. The results revealed that the 1 minute holding time sintering profile was indeed effective in producing a HA body with high density of 98% theoretical when sintered at 1200° C. High mechanical properties such as fracture toughness of 1.41 MPa.m1/2 and hardness of 9.5 GPa were also measured for HA samples sintered under this profile. Additionally, XRD analysis indicated that decomposition of the HA phase during sintering at high temperatures was suppressed.

  4. Investigation of the Sintering Process Using Non-Contact Electromagnetic Acoustic Transducers

    International Nuclear Information System (INIS)

    James C. Foley; David K. Rehbein; Daniel J. Barnard

    2001-01-01

    In-situ characterizations of green state part density and sintering state have long been desired in the powder metal community. Recent advances in non-contact electromagnetic acoustic transducer (EMAT) technology have enabled in-situ monitoring of acoustic amplitude and velocity as sintering proceeds. Samples were made from elemental powders of Al (99.99%), Al (99.7%), Ag, (99.99%), Cu (99.99%) and Fe (99.9%). The powders were pressed in a uniaxial die and examined with acoustic waves for changes in velocity and amplitude during sintering for the samples containing Al, Ag, and Cu. The changes in acoustic properties were correlated with sample microstructures and mechanical properties. Evolution of a series of reverberating echoes during sintering is shown to provide information on the state of sintering, and changes in sintering kinetics as well as having the potential for detection of interior flaws

  5. Preparation of Ti3Al intermetallic compound by spark plasma sintering

    Science.gov (United States)

    Ito, Tsutomu; Fukui, Takahiro

    2018-04-01

    Sintered compacts of single phase Ti3Al intermetallic compound, which have excellent potential as refractory materials, were prepared by spark plasma sintering (SPS). A raw powder of Ti3Al intermetallic compound with an average powder diameter of 176 ± 56 μm was used in this study; this large powder diameter is disadvantageous for sintering because of the small surface area. The samples were prepared at sintering temperatures (Ts) of 1088, 1203, and 1323 K, sintering stresses (σs) of 16, 32, and 48 MPa, and a sintering time (ts) of 10 min. The calculated relative densities based on the apparent density of Ti3Al provided by the supplier were approximately 100% under all sintering conditions. From the experimental results, it was evident that SPS is an effective technique for dense sintering of Ti3Al intermetallic compounds in a short time interval. In this report, the sintering characteristics of Ti3Al intermetallic compacts are briefly discussed and compared with those of pure titanium compacts.

  6. Ab initio quasi-particle approximation bandgaps of silicon nanowires calculated at density functional theory/local density approximation computational effort

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, M., E-mail: ribeiro.jr@oorbit.com.br [Office of Operational Research for Business Intelligence and Technology, Principal Office, Buffalo, Wyoming 82834 (United States)

    2015-06-21

    Ab initio calculations of hydrogen-passivated Si nanowires were performed using density functional theory within LDA-1/2, to account for the excited states properties. A range of diameters was calculated to draw conclusions about the ability of the method to correctly describe the main trends of bandgap, quantum confinement, and self-energy corrections versus the diameter of the nanowire. Bandgaps are predicted with excellent accuracy if compared with other theoretical results like GW, and with the experiment as well, but with a low computational cost.

  7. Ab initio quasi-particle approximation bandgaps of silicon nanowires calculated at density functional theory/local density approximation computational effort

    International Nuclear Information System (INIS)

    Ribeiro, M.

    2015-01-01

    Ab initio calculations of hydrogen-passivated Si nanowires were performed using density functional theory within LDA-1/2, to account for the excited states properties. A range of diameters was calculated to draw conclusions about the ability of the method to correctly describe the main trends of bandgap, quantum confinement, and self-energy corrections versus the diameter of the nanowire. Bandgaps are predicted with excellent accuracy if compared with other theoretical results like GW, and with the experiment as well, but with a low computational cost

  8. Low temperature sintering of fluorapatite glass-ceramics

    Science.gov (United States)

    Denry, Isabelle; Holloway, Julie A.

    2014-01-01

    Fluorapatite glass-ceramics have been shown to be excellent candidates as scaffold materials for bone grafts, however, scaffold production by sintering is hindered by concurrent crystallization of the glass. Our goal was to investigate the effect of Ca/Al ratio on the sintering behavior of Nb-doped fluorapatite-based glasses in the SiO2-Al2O3-P2O5-MgO-Na2O-K2O-CaO-CaF2 system. Glass compositions with Ca/Al ratio of 1 (A), 2 (B), 4 (C) and 19 (D) were prepared by twice melting at 1525°C for 3h. Glasses were either cast as cylindrical ingots or ground into powders. Disc-shaped specimens were prepared by either sectioning from the ingots or powder-compacting in a mold, followed by heat treatment at temperatures ranging between 700 and 1050°C for 1h. The density was measured on both sintered specimens and heat treated discs as controls. The degree of sintering was determined from these measurements. XRD showed that fluorapatite crystallized in all glass-ceramics. A high degree of sintering was achieved at 775°C for glass-ceramic D (98.99±0.04%), and 900°C for glass-ceramic C (91.31±0.10). Glass-ceramics A or B were only partially sintered at 1000°C (63.6±0.8% and 74.1±1.5%, respectively). SEM revealed a unique microstructure of micron-sized spherulitic fluorapatite crystals in glass-ceramics C and D. Increasing the Ca/Al ratio promoted low temperature sintering of fluorapatite glass-ceramics, which are traditionally difficult to sinter. PMID:24252652

  9. Low temperature sintering of fluorapatite glass-ceramics.

    Science.gov (United States)

    Denry, Isabelle; Holloway, Julie A

    2014-02-01

    Fluorapatite glass-ceramics have been shown to be excellent candidates as scaffold materials for bone grafts, however, scaffold production by sintering is hindered by concurrent crystallization of the glass. Objective, our goal was to investigate the effect of Ca/Al ratio on the sintering behavior of Nb-doped fluorapatite-based glasses in the SiO2-Al2O3-P2O5-MgO-Na2O-K2O-CaO-CaF2 system. Methods, glass compositions with Ca/Al ratio of 1 (A), 2 (B), 4 (C) and 19 (D) were prepared by twice melting at 1525°C for 3h. Glasses were either cast as cylindrical ingots or ground into powders. Disk-shaped specimens were prepared by either sectioning from the ingots or powder-compacting in a mold, followed by heat treatment at temperatures ranging between 700 and 1050°C for 1h. The density was measured on both sintered specimens and heat treated discs as controls. The degree of sintering was determined from these measurements. Results and Significance XRD showed that fluorapatite crystallized in all glass-ceramics. A high degree of sintering was achieved at 775°C for glass-ceramic D (98.99±0.04%), and 900°C for glass-ceramic C (91.31±0.10). Glass-ceramics A or B were only partially sintered at 1000°C (63.6±0.8% and 74.1±1.5%, respectively). SEM revealed a unique microstructure of micron-sized spherulitic fluorapatite crystals in glass-ceramics C and D. Increasing the Ca/Al ratio promoted low temperature sintering of fluorapatite glass-ceramics, which are traditionally difficult to sinter. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  10. Production of pure sintered alumina

    International Nuclear Information System (INIS)

    Rocha, J.C. da; Huebner, H.W.

    1982-01-01

    With the aim of optimizing the sintering parameters, the strength of a large number of alumina samples was determined which were produced under widely varying sintering conditions and with different amounts of MgO content. The strength as a function of sintering time or temperature was found to go through a maximum. With increasing time, this maximum is shifted to lower temperatures, and with decreasing temperature to longer times. Data pairs of sintering times and temperatures which yeld the strength maximum were determined. The value of the strength at the maximum remains unchanged. The strength is high (= 400 MN/m 2 , at a grain size of 3 um and a porosity of 2 per cent) and comparable to foreign aluminas produced for commercial purposes, or even higher. The increase in the sintering time from 1 h to 16 h permits a reduction of the sintering temperature from 1600 to 1450 0 C without losing strength. The practical importance of this fact for a production of sintered alumina on a large scale is emphasized. (Author) [pt

  11. The Influence of Spark Plasma Sintering Temperature on the Microstructure and the Thermoelectric Properties of Al, Ga dually-doped ZnO

    DEFF Research Database (Denmark)

    Han, Li; Le, Thanh Hung; Van Nong, Ngo

    2012-01-01

    Al, Ga dually-doped ZnO was prepared by spark plasma sintering with different sintering temperatures. The microstructural evolution and thermoelectric properties of the samples were investigated in detail. The samples with a sintering temperature above 1223K obtained higher relative densities...

  12. Extension of the master sintering curve for constant heating rate modeling

    Science.gov (United States)

    McCoy, Tammy Michelle

    The purpose of this work is to extend the functionality of the Master Sintering Curve (MSC) such that it can be used as a practical tool for predicting sintering schemes that combine both a constant heating rate and an isothermal hold. Rather than just being able to predict a final density for the object of interest, the extension to the MSC will actually be able to model a sintering run from start to finish. Because the Johnson model does not incorporate this capability, the work presented is an extension of what has already been shown in literature to be a valuable resource in many sintering situations. A predicted sintering curve that incorporates a combination of constant heating rate and an isothermal hold is more indicative of what is found in real-life sintering operations. This research offers the possibility of predicting the sintering schedule for a material, thereby having advanced information about the extent of sintering, the time schedule for sintering, and the sintering temperature with a high degree of accuracy and repeatability. The research conducted in this thesis focuses on the development of a working model for predicting the sintering schedules of several stabilized zirconia powders having the compositions YSZ (HSY8), 10Sc1CeSZ, 10Sc1YSZ, and 11ScSZ1A. The compositions of the four powders are first verified using x-ray diffraction (XRD) and the particle size and surface area are verified using a particle size analyzer and BET analysis, respectively. The sintering studies were conducted on powder compacts using a double pushrod dilatometer. Density measurements are obtained both geometrically and using the Archimedes method. Each of the four powders is pressed into ¼" diameter pellets using a manual press with no additives, such as a binder or lubricant. Using a double push-rod dilatometer, shrinkage data for the pellets is obtained over several different heating rates. The shrinkage data is then converted to reflect the change in relative

  13. SEM hot stage sintering of UO2

    International Nuclear Information System (INIS)

    Miller, D.J.

    1976-06-01

    The sintering of hyperstoichiometric uranium dioxide powder compacts, in the hot stage of a scanning electron microscope, was continuously monitored using 16 mm time lapse movies. From alumina microspheres placed on the surface of the compacts, shrinkage measurements were obtained. Converting shrinkage measurements into densification profiles indicates that a maximum densification rate is reached at a critical density, independent of the constant heating rates. At temperatures above 1350 0 C, the movement of the reference microspheres made shrinkage measurements impossible. It is believed the evolution of UO 3 gas from hyperstoichiometric UO 2 is the cause of this limitation

  14. Powder densification maps in Selective Laser Sintering

    International Nuclear Information System (INIS)

    Bourell, D.; Wohlert, M.; Harlan, N.; Beaman, J.; Das, S.

    2002-01-01

    Selective Laser Sintering (SLS) is a manufacturing process in which a part is produced without the need for part-specific tooling. It competes effectively with other manufacturing processes when part geometry is complex and the production run is not large. Traditionally, this was limited to prototype production, although tooling applications are now appearing. This paper describes several applications of powder densification maps to advance solutions in direct SLS of metallic and ceramic powders. Time-dependent plasticity issues arise in pre-processing of powder to make it suitable for SLS and in post-processing of SLS parts to obtain desired density. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

  15. An investigation on preparation of CIGS targets by sintering process

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Ning, E-mail: zhn98@126.co [Department of Mechanical Engineering, Tsinghua University, Beijing 100084 (China); Zhuang Daming; Zhang Gong [Department of Mechanical Engineering, Tsinghua University, Beijing 100084 (China)

    2010-01-15

    Pressureless sintering process was used to fabricate CIGS targets with Cu{sub 2}Se, In{sub 2}Se{sub 3}, and Ga{sub 2}Se{sub 3} as raw powders mixed according to the stoichiometry of CuIn{sub 0.72}Ga{sub 0.28}Se{sub 2} (CIGS). The results showed that only CuIn{sub 0.7}Ga{sub 0.3}Se{sub 2} phase can be detected in the sintered targets. The pores in sintered specimen become smaller and distribute more homogeneously under the conditions of finer powders and higher cold pressure. Both mass loss caused by the formation of volatile phase relating to Ga and volume expansion occur during the sintering process, which result in the decrease of density. The tendency of anti-densification becomes stronger under the conditions of coarser powders and higher cold pressure. The sintering process and causes for anti-densification were discussed. Finally, a hot pressing process was carried out, which was proved to be fairly effective to increase the density of CIGS target. The fabricated target can be used for magnetron-sputtering deposition of CIGS absorbers.

  16. Processing and Properties of Distaloy Sa Sintered Alloys with Boron and Carbon

    Directory of Open Access Journals (Sweden)

    Karwan-Baczewska J.

    2015-04-01

    Full Text Available Prealloyed iron-based powders, manufactured in Höganäs Company, are used in the automotive parts industry. The properties and life time of such sintered parts depend, first of all, on their chemical composition, the production method of the prealloyed powder as well as on the technology of their consolidation and sintering. One of simpler and conventional methods aimed at increasing the density in sintered products is the process of activated sintering, performed, for example, by adding boron as elementary boron powder. Under this research project obtained were novel sintered materials, based on prealloyed and diffusion bonded powder, type: Distaloy SA, with the following chemical composition: Fe-1.75% Ni-1.5%Cu- 0.5%Mo with carbon (0.55%; 0.75% and boron (0.2%, 0.4% and 0.6%. Distaloy SA samples alloyed with carbon and boron were manufactured by mixing powders in a Turbula mixer, then compressed using a hydraulic press under a pressure of 600 MPa and sintered in a tube furnace at 1473 K, for a 60 minute time, in the hydrogen atmosphere. After the sintering process, there were performed density and porosity measurements as well as hardness tests and mechanical properties were carried out, too. Eventually, analyzed was the effect of boron upon density, hardness and mechanical properties of novel sintered construction parts made from Distaloy SA powder.

  17. High-current-density electrodeposition using pulsed and constant currents to produce thick CoPt magnetic films on silicon substrates

    Science.gov (United States)

    Ewing, Jacob; Wang, Yuzheng; Arnold, David P.

    2018-05-01

    This paper investigates methods for electroplating thick (>20 μm), high-coercivity CoPt films using high current densities (up to 1 A/cm2) and elevated bath temperatures (70 °C). Correlations are made tying current-density and temperature process parameters with plating rate, elemental ratio and magnetic properties of the deposited CoPt films. It also investigates how pulsed currents can increase the plating rate and film to substrate adhesion. Using 500 mA/cm2 and constant current, high-quality, dense CoPt films were successfully electroplated up to 20 μm thick in 1 hr on silicon substrates (0.35 μm/min plating rate). After standard thermal treatment (675°C, 30 min) to achieve the ordered L10 crystalline phase, strong magnetic properties were measured: coercivities up 850 kA/m, remanences >0.5 T, and maximum energy products up to 46 kJ/m3.

  18. Impact of hydrogen dilution on optical properties of intrinsic hydrogenated amorphous silicon films prepared by high density plasma chemical vapor deposition for solar cell applications

    Science.gov (United States)

    Chen, Huai-Yi; Lee, Yao-Jen; Chang, Chien-Pin; Koo, Horng-Show; Lai, Chiung-Hui

    2013-01-01

    P-i-n single-junction hydrogenated amorphous silicon (a-Si:H) thin film solar cells were successfully fabricated in this study on a glass substrate by high density plasma chemical vapor deposition (HDP-CVD) at low power of 50 W, low temperature of 200°C and various hydrogen dilution ratios (R). The open circuit voltage (Voc ), short circuit current density (Jsc ), fill factor (FF) and conversion efficiency (η) of the solar cell as well as the refractive index (n) and absorption coefficient (α) of the i-layer at 600 nm wavelength rise with increasing R until an abrupt drop at high hydrogen dilution, i.e. R > 0.95. However, the optical energy bandgap (Eg ) of the i-layer decreases with the R increase. Voc and α are inversely correlated with Eg . The hydrogen content affects the i-layer and p/i interface quality of the a-Si:H thin film solar cell with an optimal value of R = 0.95, which corresponds to solar cell conversion efficiency of 3.85%. The proposed a-Si:H thin film solar cell is expected to be improved in performance.

  19. Improved porous silicon (P-Si) microarray based PSA (prostate specific antigen) immunoassay by optimized surface density of the capture antibody

    Science.gov (United States)

    Lee, SangWook; Kim, Soyoun; Malm, Johan; Jeong, Ok Chan; Lilja, Hans; Laurell, Thomas

    2014-01-01

    Enriching the surface density of immobilized capture antibodies enhances the detection signal of antibody sandwich microarrays. In this study, we improved the detection sensitivity of our previously developed P-Si (porous silicon) antibody microarray by optimizing concentrations of the capturing antibody. We investigated immunoassays using a P-Si microarray at three different capture antibody (PSA - prostate specific antigen) concentrations, analyzing the influence of the antibody density on the assay detection sensitivity. The LOD (limit of detection) for PSA was 2.5ngmL−1, 80pgmL−1, and 800fgmL−1 when arraying the PSA antibody, H117 at the concentration 15µgmL−1, 35µgmL−1 and 154µgmL−1, respectively. We further investigated PSA spiked into human female serum in the range of 800fgmL−1 to 500ngmL−1. The microarray showed a LOD of 800fgmL−1 and a dynamic range of 800 fgmL−1 to 80ngmL−1 in serum spiked samples. PMID:24016590

  20. Spark plasma sintering and porosity studies of uranium nitride

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Kyle D., E-mail: kylej@kth.se; Wallenius, Janne; Jolkkonen, Mikael; Claisse, Antoine

    2016-05-15

    In this study, a number of samples of UN sintered by the SPS method have been fabricated, and highly pure samples ranging in density from 68% to 99.8%TD – corresponding to an absolute density of 14.25 g/cm{sup 3} out of a theoretical density of 14.28 g/cm{sup 3} – have been fabricated. By careful adjustment of the sintering parameters of temperature and applied pressure, the production of pellets of specific porosity may now be achieved between these ranges. The pore closure behaviour of the material has also been documented and compared to previous studies of similar materials, which demonstrates that full pore closure using these methods occurs near 97.5% of relative density. - Highlights: • UN pellets are fabricated over a wide array of densities using the SPS method. • The sintereing parameters necessary to produce pellets over a wide array of density space are charted. • Pellets of extremely high density (99.9% of TD, absolute density of 14.25 g/cm{sup 3}) are fabricated. • Full-closure of the porosity in this material is obtained at around 2.5% of total porosity.

  1. Sinterability and microstructure evolution during sintering of ferrous powder mixtures

    Directory of Open Access Journals (Sweden)

    Kétner Bendo Demétrio

    2013-01-01

    Full Text Available The present work is focused on ferrous powder metallurgy and presents some results of a development of a suitable masteralloy for use as an additive to iron powder for the production of sintered steels. The masteralloy was produced by melting a powder mixture containing approximately Fe + 20% Ni + 20% Mn + 20% Si + 1% C (wt%, in order to obtain a cast billet that was converted into fine powder by crushing and milling. It was observed presence of SiC in the masteralloy after melting that is undesirable in the alloy. Si element should be introduced by using ferrosilicon. Sintered alloys with distinct contents of alloying elements were prepared by mixing the masteralloy powder to plain iron powder. Samples were produced by die compaction of the powder mixtures and sintering at 1200 °C in a differential dilatometer in order to record their linear dimensional behaviour during heating up and isothermal sintering, aiming at studying the sinterability of the compacts. Microstructure development during sintering was studied by SEM, XRD and microprobe analyses.

  2. Development of synthetic graphite resistive elements for sintering furnace

    International Nuclear Information System (INIS)

    Otani, C.; Rezende, Mirabel C.; Polidoro, H.A.; Otani, S.

    1987-01-01

    The synthetic graphites have been produced using lignin coke, natural graphite and phenolic resin. The bulk density, porosity, flexural strength and eletrical resistivity measurements have been performed on specimens at about 2400 0 C. The performance of these materials, as heating elements, was evaluated in a sintering furnace prototype. This paper reports the fabrication process and the experimental results. (Author) [pt

  3. Damage radiation alpha effects in sintered waste form

    International Nuclear Information System (INIS)

    Messi de Bernasconi, Norma B.; Prado, Miguel O.; Bevilacqua, Arturo M.; Arribere, Maria; Heredia, Arturo D.; Sanfilippo, Miguel

    1999-01-01

    We have subjected the borosilicate glass to thermal neutron irradiation in a reactor, with an accumulated fluence equivalent to approximately E3, E4, E5, y E6 years of waste disposal. We considered the following potential effects of accumulated alpha decay: a) Changes in the density; b) Changes in the dissolution rates; c) Changes in the microstructure of the sintered glass. (author)

  4. Al2O3-TiC Composite Prepared by Spark Plasma Sintering Process: Evaluation of Mechanical and Tribological Properties

    Science.gov (United States)

    Kumar, Rohit; Chaubey, A. K.; Bathula, Sivaiah; Prashanth, K. G.; Dhar, Ajay

    2018-03-01

    Al2O3-10TiC composites were synthesized by spark plasma sintering (SPS) process. Microstructural and mechanical properties of the composite reveal homogeneous distribution of the fine TiC particles in the matrix. The samples were produced with different sintering temperature, and it shows that the hardness and density gradually increases with increasing sintering temperature. Abrasion wear test result reveals that the composite sintered at 1500 °C shows high abrasion resistance (wt. loss 0.016 g) and the lowest abrasion resistance was observed for the composite sample sintered at 1100 °C (wt. loss 1.459 g). The profilometry surface roughness study shows that sample sintered at 1100 °C shows maximum roughness ( R a = 6.53 µm) compared to the sample sintered at 1500 °C ( R a = 0.66 µm) corroborating the abrasion wear test results.

  5. Oxygen defect processes in silicon and silicon germanium

    KAUST Repository

    Chroneos, A.; Sgourou, E. N.; Londos, C. A.; Schwingenschlö gl, Udo

    2015-01-01

    Silicon and silicon germanium are the archetypical elemental and alloy semiconductor materials for nanoelectronic, sensor, and photovoltaic applications. The investigation of radiation induced defects involving oxygen, carbon, and intrinsic defects is important for the improvement of devices as these defects can have a deleterious impact on the properties of silicon and silicon germanium. In the present review, we mainly focus on oxygen-related defects and the impact of isovalent doping on their properties in silicon and silicon germanium. The efficacy of the isovalent doping strategies to constrain the oxygen-related defects is discussed in view of recent infrared spectroscopy and density functional theory studies.

  6. Oxygen defect processes in silicon and silicon germanium

    KAUST Repository

    Chroneos, A.

    2015-06-18

    Silicon and silicon germanium are the archetypical elemental and alloy semiconductor materials for nanoelectronic, sensor, and photovoltaic applications. The investigation of radiation induced defects involving oxygen, carbon, and intrinsic defects is important for the improvement of devices as these defects can have a deleterious impact on the properties of silicon and silicon germanium. In the present review, we mainly focus on oxygen-related defects and the impact of isovalent doping on their properties in silicon and silicon germanium. The efficacy of the isovalent doping strategies to constrain the oxygen-related defects is discussed in view of recent infrared spectroscopy and density functional theory studies.

  7. Ultra-thin silicon oxide layers on crystalline silicon wafers: Comparison of advanced oxidation techniques with respect to chemically abrupt SiO{sub 2}/Si interfaces with low defect densities

    Energy Technology Data Exchange (ETDEWEB)

    Stegemann, Bert, E-mail: bert.stegemann@htw-berlin.de [HTW Berlin - University of Applied Sciences, 12459 Berlin (Germany); Gad, Karim M. [University of Freiburg, Department of Microsystems Engineering - IMTEK, 79110 Freiburg (Germany); Balamou, Patrice [HTW Berlin - University of Applied Sciences, 12459 Berlin (Germany); Helmholtz Center Berlin for Materials and Energy (HZB), 12489 Berlin (Germany); Sixtensson, Daniel [Helmholtz Center Berlin for Materials and Energy (HZB), 12489 Berlin (Germany); Vössing, Daniel; Kasemann, Martin [University of Freiburg, Department of Microsystems Engineering - IMTEK, 79110 Freiburg (Germany); Angermann, Heike [Helmholtz Center Berlin for Materials and Energy (HZB), 12489 Berlin (Germany)

    2017-02-15

    Highlights: • Fabrication of ultrathin SiO{sub 2} tunnel layers on c-Si. • Correlation of electronic and chemical SiO{sub 2}/Si interface properties revealed by XPS/SPV. • Chemically abrupt SiO{sub 2}/Si interfaces generate less interface defect states considerable. - Abstract: Six advanced oxidation techniques were analyzed, evaluated and compared with respect to the preparation of high-quality ultra-thin oxide layers on crystalline silicon. The resulting electronic and chemical SiO{sub 2}/Si interface properties were determined by a combined x-ray photoemission (XPS) and surface photovoltage (SPV) investigation. Depending on the oxidation technique, chemically abrupt SiO{sub 2}/Si interfaces with low densities of interface states were fabricated on c-Si either at low temperatures, at short times, or in wet-chemical environment, resulting in each case in excellent interface passivation. Moreover, the beneficial effect of a subsequent forming gas annealing (FGA) step for the passivation of the SiO{sub 2}/Si interface of ultra-thin oxide layers has been proven. Chemically abrupt SiO{sub 2}/Si interfaces have been shown to generate less interface defect states.

  8. Compressive creep of silicon nitride

    International Nuclear Information System (INIS)

    Silva, C.R.M. da; Melo, F.C.L. de; Cairo, C.A.; Piorino Neto, F.

    1990-01-01

    Silicon nitride samples were formed by pressureless sintering process, using neodymium oxide and a mixture of neodymium oxide and yttrio oxide as sintering aids. The short term compressive creep behaviour was evaluated over a stress range of 50-300 MPa and temperature range 1200 - 1350 0 C. Post-sintering heat treatments in nitrogen with a stepwise decremental variation of temperature were performed in some samples and microstructural analysis by X-ray diffraction and transmission electron microscopy showed that the secondary crystalline phase which form from the remnant glass are dependent upon composition and percentage of aditives. Stress exponent values near to unity were obtained for materials with low glass content suggesting grain boundary diffusion accommodation processes. Cavitation will thereby become prevalent with increase in stress, temperature and decrease in the degree of crystallization of the grain boundary phase. (author) [pt

  9. Lanthanide (Nd, Gd) compounds with garnet and monazite structures. Powders synthesis by “wet” chemistry to sintering ceramics by Spark Plasma Sintering

    Energy Technology Data Exchange (ETDEWEB)

    Potanina, Ekaterina, E-mail: ekaterina.potanina@list.ru [Department of Solid State Chemistry, Lobachevsky State University of Nizhni Novgorod, National Research University, 23 Prospekt Gagarina, BLDG 2, 603950 Nizhny Novgorod (Russian Federation); Golovkina, Ludmila, E-mail: golovkina_lyudmila@mail.ru [Department of Solid State Chemistry, Lobachevsky State University of Nizhni Novgorod, National Research University, 23 Prospekt Gagarina, BLDG 2, 603950 Nizhny Novgorod (Russian Federation); Orlova, Albina, E-mail: albina.orlova@inbox.ru [Department of Solid State Chemistry, Lobachevsky State University of Nizhni Novgorod, National Research University, 23 Prospekt Gagarina, BLDG 2, 603950 Nizhny Novgorod (Russian Federation); Nokhrin, Aleksey, E-mail: nokhrin@nifti.unn.ru [Research Institute of Physics and Technology, Lobachevsky State University of Nizhni Novgorod, National Research University, 23 Prospekt Gagarina, BLDG 3, 603950 Nizhny Novgorod (Russian Federation); Boldin, Maksim, E-mail: boldin@nifti.unn.ru [Research Institute of Physics and Technology, Lobachevsky State University of Nizhni Novgorod, National Research University, 23 Prospekt Gagarina, BLDG 3, 603950 Nizhny Novgorod (Russian Federation); Sakharov, Nikita, E-mail: nvsaharov@nifti.unn.ru [Research Institute of Physics and Technology, Lobachevsky State University of Nizhni Novgorod, National Research University, 23 Prospekt Gagarina, BLDG 3, 603950 Nizhny Novgorod (Russian Federation)

    2016-05-15

    Complex oxide Y{sub 2.5}Nd{sub 0.5}Al{sub 5}O{sub 12} with garnet structure and phosphates NdPO{sub 4} and GdPO{sub 4} with monazite structure were obtained by using precipitation methods. Ceramics Y{sub 2.5}Nd{sub 0.5}Al{sub 5}O{sub 12} and NdPO{sub 4} were processed by Spark Plasma Sintering (SPS). Relative density more 98%, sintering time did not exceed 8 min, sintering temperature 1330–1390 °C. Leaching rates of elements from ceramics were 10{sup −6}–10{sup −7} g/(cm{sup 2} d). The process of ceramics sintering has two-stage character: the first step of sintering-compaction process is related to the plastic flow of the material, the second step–to the process of grain boundary diffusion and grain growth. - Highlights: • Powders were obtained by precipitation (sol–gel) method. • Ceramics were sintering by Spark Plasma Sintering method (ρ{sub rel} > 98%); shrinkage time does not exceed 8 min. • The process of ceramics sintering has two-stage character.

  10. The influence of carrier density and doping type on lithium insertion and extraction processes at silicon surfaces

    International Nuclear Information System (INIS)

    McSweeney, W.; Lotty, O.; Glynn, C.; Geaney, H.; Holmes, J.D.; O’Dwyer, C.

    2014-01-01

    The Li + insertion and extraction characteristics at n-type and p-type Si(100) electrodes with different carrier density and doping type are investigated by cyclic voltammetry and constant current measurements. The insertion and extraction potentials are demonstrated to vary with cycling and the occurrence of an activation effect is shown in n-type electrodes where the charge capacity and voltammetric currents are found to be much higher than p-type electrodes. A rate-dependent redox process influenced by the surface region electronic density, which influences the magnitude of cyclic voltammetry current is found at Si(100) surface regions during Li insertion and extraction. At p-type Si(100) surface regions, a thin, uniform film forms at lower currents, while also showing a consistently high (>70%) Coulombic efficiency for Li extraction. The p-type Si(100) surface region does not undergo crack formation after deintercalation and the amorphization was demonstrated using transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and Raman scattering demonstrate that highly doped n-type Si(100) retains Li as a silicide and converts to an amorphous phase as a two-step phase conversion process. The findings show the succinct dependence of Li insertion and extraction processes for uniformly doped Si(100) single crystals and how the doping type and its effect on the semiconductor-solution interface dominate Li insertion and extraction, composition, crystallinity changes and charge capacity

  11. Influence of the flux density on the radiation damage of bipolar silicon transistors by protons and electrons

    International Nuclear Information System (INIS)

    Bannikov, Y.; Gorin, B.; Kozhevnikov, V.; Mikhnovich, V.; Gusev, L.

    1981-01-01

    It was found experimentally that the radiation damage of bipolar n-p-n transistors increased by a factor of 8--12 when the proton flux density was reduced from 4.07 x 10 10 to 2.5 x 10 7 cm -2 sec -1 . In the case of p-n-p transistors the effect was opposite: there was a reduction in the radiation damage by a factor of 2--3 when the dose rate was lowered between the same limits. A similar effect was observed for electrons but at dose rates three orders of magnitude greater. The results were attributed to the dependences of the radiation defect-forming reactions on the charge state of defects which was influenced by the formation of disordered regions in the case of proton irradiation

  12. Corrosion behaviour of sintered duplex stainless steels

    Energy Technology Data Exchange (ETDEWEB)

    Utrilla, M. Victoria; Urena, Alejandro; Otero, Enrique; Munez, Claudio Jose [Escuela Superior de Ciencias Experimentales y Tecnologia, Universidad Rey Juan Carlos, C/ Tulipan s/n, 28933 Mostoles, Madrid (Spain)

    2004-07-01

    Duplex austenite-ferrite stainless steels were prepared by mixing austenitic (316L) and ferritic (434L) atomized powders. Although different 316L/434L ratios were prepared, present work centred its study on 50% ferrite - 50% austenite sintered steel. The powders were mixed and pressed at 700 MPa and sintered at 1250 deg. C for 30 min in vacuum. The cooling rate was 5 deg. C/min. Solution treatment was carried out to homogenize the microstructure at 1100 deg. C during 20 min. A microstructural study of the material in solution was performed, evaluating the microstructure, proportion and shape of porosity, and ferrite percentage. This last was measured by two methods, quantitative metallography and Fischer ferrito-metry. The materials were heat treated in the range of 700 to 1000 deg. C, for 10, 30 and 60 min and water quenched, to study the microstructural changes and the influence on the intergranular corrosion resistance. The method used to evaluate the sensitization to the intergranular corrosion was the electrochemical potentio-kinetic reactivation procedure (EPR). The test solution was 0.5 M H{sub 2}SO{sub 4} + 0,01 M KSCN at 30 deg. C. The criterion used to evaluate the sensitization was the ratio between the maximum reactivation density (Ir) and the maximum activation density (Ia). The results of the electrochemical tests were discussed in relation with the microstructures observed at the different heat treatments. (authors)

  13. Solidification of high level liquid waste (HLLW) into ceramics by sintering process

    International Nuclear Information System (INIS)

    Masuda, Sumio; Oguino, Naohiko; Tsunoda, Naomi; O-oka, Kazuo; Ohta, Takao.

    1979-01-01

    One of the alternatives to vitrified solid which is acceptable and well characterized for storing radioactive HLLW with desirable long-term stability is ceramics. On the other hand, the solidification process of highly radioactive wastes should be simple and suitable for continuous production. On the above described basis, the authors have made preliminary study on the production of sintered ceramics by the addition of several oxides to HLLW. The simulated waste and additive oxides were pressed in a mold to make the preforms of 50 mm diameter and 10 to 15 mm thick. The preforms were then normally sintered at temperature from 1000 to 1400 deg C for 2 to 4 hours. The characterization of the sintered solids revealed the following facts. (1) X-ray diffraction analysis showed that the expected crystals were formed by normal-sintering as well as by hot-pressing. (2) The bulk density of the ceramics by normal-sintering was around 90 to 95% of the assumed theoretical values. (3) The leach-rate of the solids was affected by the bulk density. (4) Other properties of the solids, such as thermal expansion or thermal conductivity, are dominantly determined by those of main crystals in the solids. Sintering process is generally simple and productive as far as normal sintering is concerned. However, hot-pressing is an intermittent and time consuming process. From this fact, the authors intended to adopt the normal sintering process for the ceramic solidification of high level liquid wastes. (Wakatsuki, Y.)

  14. Sintering and annealing effects on undoped yttria transparent ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Letue, Laetitia; Petit, Johan, E-mail: johan.petit@onera.fr; Ritti, Marie-Hélène; Lalanne, Sylvie; Landais, Stéphane

    2017-06-15

    Transparent yttrium oxide (Y{sub 2}O{sub 3}) ceramics were processed by several densifications steps without any doping species. The green bodies were obtained by the aqueous way and sintered at high temperature under vacuum and then under high pressure. We studied the effects of different sintering cycles and air annealing at different steps of the process on the density and the grain growth. We also focused on the reaction between yttria ceramics and BN-coated graphite crucible which occurs during HIP. We noted that a low heating rate and two annealing steps are necessary to improve our samples’ transparency. - Highlights: • The quality of transparent ceramics is compared with the tested process parameters. • Air annealing is critical when using a carbon environment in the process. • Intra-granular pores, and so the final transparency, are directly linked to the sintering heating rates.

  15. Immobilization of high-level wastes into sintered glass: 1

    International Nuclear Information System (INIS)

    Russo, D.O.; Messi de Bernasconi, N.; Audero, M.A.

    1987-01-01

    In order to immobilize the high-level radioactive wastes from fuel elements reprocessing, borosilicate glass was adopted. Sintering experiments are described with the variety VG 98/12 (SiO 2 , TiO 2 , Al 2 O 3 , B 2 O 3 , MgO, CaO and Na 2 O) (which does not present devitrification problems) mixed with simulated calcinated wastes. The hot pressing line (sintering under pressure) was explored in two variants 1: In can; 2: In graphite matrix with sintered pellet extraction. With scanning electron microscopy it is observed that the simulated wastes do not disolve in the vitreous matrix, but they remain dispersed in the same. The results obtained point out that the leaching velocities are independent from the density and from the matrix type employed, as well as from the fact that the wastes do no dissolve in the matrix. (M.E.L.) [es

  16. Consolidation of copper and aluminium powders by spark plasma sintering

    Science.gov (United States)

    Saiprasad, M.; Atchayakumar, R.; Thiruppathi, K.; Raghuraman, S.

    2016-09-01

    Processing in the powder metallurgy route has emerged as an economical process for the production of near net shaped components with a wide range of desired mechanical properties suitable for various applications of industrial needs. This research work was conducted with an objective of studying the improvisation of density and hardness of Copper-Aluminium alloy prepared by spark plasma sintering. Cu-Al alloy with a composition of 95% copper and 5% aluminium was prepared by SPS process. SPS is a low voltage, DC pulse current activated, pressure-assisted sintering, which enables sintering at lower temperatures and shorter durations. The combination offered by Cu-Al alloy of high strength and high corrosion resistance results their applications under a wide variety of conditions. The density and hardness of the prepared sample were measured by conducting appropriate tests. Apparently, the values of hardness and density of the specimen prepared by SPS seemed to be better than that of conventional sintering. The experimental procedure, testing methodologies and analysis are presented.

  17. An Evaluation of the Gap Sizes of 3-Unit Fixed Dental Prostheses Milled from Sintering Metal Blocks

    OpenAIRE

    Jung, Jae-Kwan

    2017-01-01

    This study assessed the clinical acceptability of sintering metal-fabricated 3-unit fixed dental prostheses (FDPs) based on gap sizes. Ten specimens were prepared on research models by milling sintering metal blocks or by the lost-wax technique (LWC group). Gap sizes were assessed at 12 points per abutment (premolar and molar), 24 points per specimen (480 points in a total in 20 specimens). The measured points were categorized as marginal, axial wall, and occlusal for assessment in a silicone...

  18. Investigation of control conditions of uranium dioxide pellets sinterability through microspheres

    International Nuclear Information System (INIS)

    Assis, Gino de.

    1996-01-01

    Promotion or inhibition of ceramic powders sinterability, the decisive question in ceramic processing is approached in this dissertation. Each high density microsphere has been considered as a solid inclusion in a low density microspheres matrix, generating big pores. Such pores make it difficult for the pellets density due the fact that they are difficult to be eliminated. A master mixture, allowing the pellet densification in the projected range has been reached. Batches of microspheres have been observed sometimes with high apparent density and sometimes with low apparent density. This apparent density variation was attributed to changing the oxygen partial pressure during calcination under air atmosphere. It is evident that the control of the apparent density of the microspheres needs a further research in order to adjust the sinterability of the microspheres on the desired level.It was demonstrated that the produced microspheres do not have impurities levels that can promote its sinterability or avoid their use in nuclear area

  19. Application of Silicon Nitride (Si3N4 Ceramics in Ball Bearing

    Directory of Open Access Journals (Sweden)

    Wijianto Wijianto

    2016-08-01

    operation up to 1000°C, greater thermal shock resistance, lower density and low thermal expansion. This properties gives some benefit for ball bearing material such as higher running speed, reduce vibration of the shaft, will improve the life time and maintenance cost, lower heat generated, less energy consumption, lower wear rate, reducing noise level and reduce of using lubricant. The sintering methods are used to produce ball bearing from silicon nitride. Some techniques can be applied to increase ceramics strength which are reduce porosity, reduce grain size, reduce surface flaw and proof stressing. The surface finishing of the ceramic bearing is very important because silicon nitride as a brittle material, its strength is limited to the flaw sizes especially the flaw at the surface.

  20. Performance potential of low-defect density silicon thin-film solar cells obtained by electron beam evaporation and laser crystallisation

    Directory of Open Access Journals (Sweden)

    Kim K. H.

    2013-01-01

    Full Text Available A few microns thick silicon films on glass coated with a dielectric intermediate layer can be crystallised by a single pass of a line-focused diode laser beam. Under favorable process conditions relatively large linear grains with low defect density are formed. Most grain boundaries are defect-free low-energy twin-boundaries. Boron-doped laser crystallised films are processed into solar cells by diffusing an emitter from a phosphorous spin-on-dopant source, measuring up to 539 mV open-circuit voltage prior to metallisation. After applying a point-contact metallisation the best cell achieves 7.8% energy conversion efficiency, open-circuit voltage of 526 mV and short-circuit current of 26 mA/cm2. The efficiency is significantly limited by a low fill-factor of 56% due to the simplified metallisation approach. The internal quantum efficiency of laser crystallised cells is consistent with low front surface recombination. By improving cell metallisation and enhancing light-trapping the efficiencies of above 13% can be achieved.

  1. Micro-architecture embedding ultra-thin interlayer to bond diamond and silicon via direct fusion

    Science.gov (United States)

    Kim, Jong Cheol; Kim, Jongsik; Xin, Yan; Lee, Jinhyung; Kim, Young-Gyun; Subhash, Ghatu; Singh, Rajiv K.; Arjunan, Arul C.; Lee, Haigun

    2018-05-01

    The continuous demand on miniaturized electronic circuits bearing high power density illuminates the need to modify the silicon-on-insulator-based chip architecture. This is because of the low thermal conductivity of the few hundred nanometer-thick insulator present between the silicon substrate and active layers. The thick insulator is notorious for releasing the heat generated from the active layers during the operation of devices, leading to degradation in their performance and thus reducing their lifetime. To avoid the heat accumulation, we propose a method to fabricate the silicon-on-diamond (SOD) microstructure featured by an exceptionally thin silicon oxycarbide interlayer (˜3 nm). While exploiting the diamond as an insulator, we employ spark plasma sintering to render the silicon directly fused to the diamond. Notably, this process can manufacture the SOD microarchitecture via a simple/rapid way and incorporates the ultra-thin interlayer for minute thermal resistance. The method invented herein expects to minimize the thermal interfacial resistance of the devices and is thus deemed as a breakthrough appealing to the current chip industry.

  2. Structure and characteristics of functional powder composite materials obtained by spark plasma sintering

    Science.gov (United States)

    Oglezneva, S. A.; Kachenyuk, M. N.; Kulmeteva, V. B.; Ogleznev, N. B.

    2017-07-01

    The article describes the results of spark plasma sintering of ceramic materials based on titanium carbide, titanium carbosilicide, ceramic composite materials based on zirconium oxide, strengthened by carbon nanostructures and composite materials of electrotechnical purpose based on copper with addition of carbon structures and titanium carbosilicide. The research shows that the spark plasma sintering can achieve relative density of the material up to 98%. The effect of sintering temperature on the phase composition, density and porosity of the final product has been studied. It was found that with addition of carbon nanostructures the relative density and hardness decrease, but the fracture strength of ZrO2 increases up to times 2. The relative erosion resistance of the electrodes made of composite copper-based powder materials, obtained by spark plasma sintering during electroerosion treatment of tool steel exceeds that parameter of pure copper up to times 15.

  3. K- and L-edge X-ray absorption spectrum calculations of closed-shell carbon, silicon, germanium, and sulfur compounds using damped four-component density functional response theory.

    Science.gov (United States)

    Fransson, Thomas; Burdakova, Daria; Norman, Patrick

    2016-05-21

    X-ray absorption spectra of carbon, silicon, germanium, and sulfur compounds have been investigated by means of damped four-component density functional response theory. It is demonstrated that a reliable description of relativistic effects is obtained at both K- and L-edges. Notably, an excellent agreement with experimental results is obtained for L2,3-spectra-with spin-orbit effects well accounted for-also in cases when the experimental intensity ratio deviates from the statistical one of 2 : 1. The theoretical results are consistent with calculations using standard response theory as well as recently reported real-time propagation methods in time-dependent density functional theory, and the virtues of different approaches are discussed. As compared to silane and silicon tetrachloride, an anomalous error in the absolute energy is reported for the L2,3-spectrum of silicon tetrafluoride, amounting to an additional spectral shift of ∼1 eV. This anomaly is also observed for other exchange-correlation functionals, but it is seen neither at other silicon edges nor at the carbon K-edge of fluorine derivatives of ethene. Considering the series of molecules SiH4-XFX with X = 1, 2, 3, 4, a gradual divergence from interpolated experimental ionization potentials is observed at the level of Kohn-Sham density functional theory (DFT), and to a smaller extent with the use of Hartree-Fock. This anomalous error is thus attributed partly to difficulties in correctly emulating the electronic structure effects imposed by the very electronegative fluorines, and partly due to inconsistencies in the spurious electron self-repulsion in DFT. Substitution with one, or possibly two, fluorine atoms is estimated to yield small enough errors to allow for reliable interpretations and predictions of L2,3-spectra of more complex and extended silicon-based systems.

  4. The effect of lanthanum boride on the sintering, sintered microstructure and mechanical properties of titanium and titanium alloys

    International Nuclear Information System (INIS)

    Yang, Y.F.; Luo, S.D.; Qian, M.

    2014-01-01

    An addition of ≤0.5 wt% lanthanum boride (LaB 6 ) to powder metallurgy commercially pure Ti (CP-Ti), Ti–6Al–4V and Ti–10V–2Fe–3Al (all in wt%) resulted in improved sintered density, substantial microstructural refinement, and noticeably increased tensile elongation. The addition of LaB 6 led to scavenging of both oxygen (O) and chlorine (Cl) from the titanium powder during sintering, evidenced by the formation of La 2 O 3 and LaCl x O y . The pinning effect of La 2 O 3 , LaCl x O y and TiB inhibited prior-β grain growth and resulted in subsequent smaller α-laths. The formation of nearly equiaxed α-Ti phase is partially attributed to the nucleation effect of α-Ti on TiB. The improved sintered density was caused by B from LaB 6 rather than La, while excessive formation of La 2 O 3 and TiB with an addition of >0.5 wt% LaB 6 resulted in a noticeable decrease in sintered density. The improved tensile elongation with an addition of ≤0.5 wt% LaB 6 was mainly attributed to the scavenging of oxygen by LaB 6 , partially assisted by the improved sintered density. However, an addition of >0.5 wt% LaB 6 led to the formation of large La 2 O 3 aggregates and more brittle TiB whiskers and therefore decreased tensile elongation. Balanced scavenging of O is thus important. The optimal addition of LaB 6 was 0.5 wt% but this may change depending on the powder size of the LaB 6 to be used

  5. Superior sinterability of nano-crystalline gadolinium doped ceria powders synthesized by co-precipitation method

    International Nuclear Information System (INIS)

    Hari Prasad, D.; Kim, H.-R.; Park, J.-S.; Son, J.-W.; Kim, B.-K.; Lee, H.-W.; Lee, J.-H.

    2010-01-01

    Reduced sintering temperature of doped ceria can greatly simplify the fabrication process of solid oxide fuel cells (SOFCs) by utilizing the co-firing of all cell components with a single step. In the present study, nano-crystalline gadolinium doped ceria (GDC) powders of high sinterability at lower sintering temperature has been synthesized by co-precipitation at room temperature. The successful synthesis of nano-crystalline GDC was confirmed by XRD, TEM and Raman spectroscopy analysis. Dilatometry studies showed that GDC prepared by this method can be fully densified (97% relative density) at a sintering temperature of 950 o C which is fairly lower than ever before. It has also been found that the sintered samples have a higher ionic conductivity of 1.64 x 10 -2 S cm -1 at 600 o C which is suitable for the intermediate temperature SOFC application.

  6. Microstructure and thermal properties of Cu-SiC composite materials depending on the sintering technique

    Directory of Open Access Journals (Sweden)

    Chmielewski Marcin

    2017-01-01

    Full Text Available The presented paper investigates the relationship between the microstructure and thermal properties of copper-silicon carbide composites obtained through hot pressing (HP and spark plasma sintering (SPS techniques. The microstructural analysis showed a better densification in the case of composites sintered in the SPS process. TEM investigations revealed the presence of silicon in the area of metallic matrix in the region close to metal-ceramic boundary. It is the product of silicon dissolving process in copper occurring at an elevated temperature. The Cu-SiC interface is significantly defected in composites obtained through the hot pressing method, which has a major influence on the thermal conductivity of materials.

  7. Silicone metalization

    Energy Technology Data Exchange (ETDEWEB)

    Maghribi, Mariam N. (Livermore, CA); Krulevitch, Peter (Pleasanton, CA); Hamilton, Julie (Tracy, CA)

    2008-12-09

    A system for providing metal features on silicone comprising providing a silicone layer on a matrix and providing a metal layer on the silicone layer. An electronic apparatus can be produced by the system. The electronic apparatus comprises a silicone body and metal features on the silicone body that provide an electronic device.

  8. Sintering Behavior of Spark Plasma Sintered SiC with Si-SiC Composite Nanoparticles Prepared by Thermal DC Plasma Process

    Science.gov (United States)

    Yu, Yeon-Tae; Naik, Gautam Kumar; Lim, Young-Bin; Yoon, Jeong-Mo

    2017-11-01

    The Si-coated SiC (Si-SiC) composite nanoparticle was prepared by non-transferred arc thermal plasma processing of solid-state synthesized SiC powder and was used as a sintering additive for SiC ceramic formation. Sintered SiC pellet was prepared by spark plasma sintering (SPS) process, and the effect of nano-sized Si-SiC composite particles on the sintering behavior of micron-sized SiC powder was investigated. The mixing ratio of Si-SiC composite nanoparticle to micron-sized SiC was optimized to 10 wt%. Vicker's hardness and relative density was increased with increasing sintering temperature and holding time. The relative density and Vicker's hardness was further increased by reaction bonding using additional activated carbon to the mixture of micron-sized SiC and nano-sized Si-SiC. The maximum relative density (97.1%) and Vicker's hardness (31.4 GPa) were recorded at 1800 °C sintering temperature for 1 min holding time, when 0.2 wt% additional activated carbon was added to the mixture of SiC/Si-SiC.

  9. Sintering Behavior of Spark Plasma Sintered SiC with Si-SiC Composite Nanoparticles Prepared by Thermal DC Plasma Process.

    Science.gov (United States)

    Yu, Yeon-Tae; Naik, Gautam Kumar; Lim, Young-Bin; Yoon, Jeong-Mo

    2017-11-25

    The Si-coated SiC (Si-SiC) composite nanoparticle was prepared by non-transferred arc thermal plasma processing of solid-state synthesized SiC powder and was used as a sintering additive for SiC ceramic formation. Sintered SiC pellet was prepared by spark plasma sintering (SPS) process, and the effect of nano-sized Si-SiC composite particles on the sintering behavior of micron-sized SiC powder was investigated. The mixing ratio of Si-SiC composite nanoparticle to micron-sized SiC was optimized to 10 wt%. Vicker's hardness and relative density was increased with increasing sintering temperature and holding time. The relative density and Vicker's hardness was further increased by reaction bonding using additional activated carbon to the mixture of micron-sized SiC and nano-sized Si-SiC. The maximum relative density (97.1%) and Vicker's hardness (31.4 GPa) were recorded at 1800 °C sintering temperature for 1 min holding time, when 0.2 wt% additional activated carbon was added to the mixture of SiC/Si-SiC.

  10. Sintering diagrams of UO2

    International Nuclear Information System (INIS)

    Mohan, A.; Soni, N.C.; Moorthy, V.K.

    1979-01-01

    Ashby's method (see Acta Met., vol. 22, p. 275, 1974) of constructing sintering diagrams has been modified to obtain contribution diagrams directly from the computer. The interplay of sintering variables and mechanisms are studied and the factors that affect the participation of mechanisms in UO 2 are determined. By studying the physical properties, it emerges that the order of inaccuracies is small in most cases and do not affect the diagrams. On the other hand, even a 10% error in activation energies, which is quite plausible, would make a significant difference to the diagram. The main criticism of Ashby's approach is that the numerous properties and equations used, communicate their inaccuracies to the diagrams and make them unreliable. The present study has considerably reduced the number of factors that need to be refined to make the sintering diagrams more meaningful. (Auth.)

  11. The pressureless sintering and mechanical properties of AlON ceramic

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, N., E-mail: zhangning5832@163.com [Key Lab. of Advanced Materials and Manufacturing Technology of Liaoning Province, Shenyang University, Shenyang, Liaoning 110044 (China); Liang, B.; Wang, X.Y.; Kan, H.M.; Zhu, K.W. [Key Lab. of Advanced Materials and Manufacturing Technology of Liaoning Province, Shenyang University, Shenyang, Liaoning 110044 (China); Zhao, X.J. [Department of Materials Science and Engineering, School of Materials and Metallurgy, Northeastern University, Shenyang, Liaoning 110004 (China)

    2011-07-25

    Highlights: {yields} A one-step pressureless sintering process was proposed, which is simple and viable. {yields} Cheap and easily available {alpha}-Al{sub 2}O{sub 3} and aluminum powders were chosen as raw materials substituting for expensive AlN ultrafine powders. {yields} The sintering temperature of AlON ceramic was reduced by 50 deg. C and the flexural strength was enhanced by 29.4%. - Abstract: Aluminum oxynitride (AlON) ceramic was synthesized by one-step pressureless sintering technology using low cost and easily available {alpha}-Al{sub 2}O{sub 3} and aluminum powders as raw materials. The sintering temperature was reduced because aluminum powders were nitridized into high activity AlN under the flowing nitrogen atmosphere. The curves of thermal analysis, microstructure and atomic distribution were investigated. The influence of sintering temperatures on phase composition, sintering densification and flexural strength was also explored. The experimental results showed that {alpha}-Al{sub 2}O{sub 3} and aluminum powders were acceptable substitutes for more expensive AlN ultrafine powders. Under the optimum sintering process at 1750 deg. C for 2 h, the sintered density and flexural strength of AlON ceramic were higher, 3.62 g/cm{sup 3} and 321 MPa, respectively. The sintering temperature was decreased by 50 deg. C because newly formed high activity AlN in situ reacted with Al{sub 2}O{sub 3} into Al{sub 23}O{sub 27}N{sub 5}, enhancing flexural strength by 29.4%. However, the sintering temperature could not be too high because grain growth and displacement of oxygen atoms from AlON ceramics by nitrogen atoms caused a decline in sintering densification and flexural strength.

  12. Two step sintering of zirconia-escandia-ceria

    International Nuclear Information System (INIS)

    Grosso, R.L.; Muccillo, E.N.S.

    2011-01-01

    Recent reports show that the ceramic system based on zirconia-scandia-ceria is a good candidate to act as solid electrolyte in solid oxide fuel cells operating at intermediate temperatures (600-800 °C). In this work, commercial ZrO_2 containing 10 mol% scandium oxide and 1 mol% cerium oxide was sintered by the two stage method. This technique was proposed to in order to obtain ceramic materials with high density along with fine grain sizes, because it avoids the grain growth occurring in the last stage of sintering. A number of experimental conditions were fully exploited by varying the dwell temperature (T_2) and the dwell time. The peak temperature (T_1) was chosen from linear shrinkage results. High (>98%) density values were obtained using this method. The medium grain size was evaluated for selected sintered samples. X-ray diffraction patterns reveal a secondary (rhombohedral) phase in sintered samples. The intensity of the secondary phase is a function of T_1 being small for relatively higher peak temperatures. (author)

  13. Phosphorus containing sintered alloys (review)

    International Nuclear Information System (INIS)

    Muchnik, S.V.

    1984-01-01

    Phosphorus additives are considered for their effect on the properties of sintered alloys of different applications: structural, antifriction, friction, magnetic, hard, superhard, heavy etc. Data are presented on compositions and properties of phosphorus-containing materials produced by the powder metallurgy method. Phosphorus is shown to be an effective activator of sintering in some cases. When its concentration in the material is optimal it imparts the material such properties as strength, viscosity, hardness, wear resistance. Problems concerning powder metallurgy of amorphous phosphorus-containing alloys are reported

  14. Recycling of mill scale in sintering process

    Directory of Open Access Journals (Sweden)

    El-Hussiny N.A.

    2011-01-01

    Full Text Available This investigation deals with the effect of replacing some amount of Baharia high barite iron ore concentrate by mill scale waste which was characterized by high iron oxide content on the parameters of the sintering process., and investigation the effect of different amount of coke breeze added on sintering process parameters when using 5% mill scale waste with 95% iron ore concentrate. The results of this work show that, replacement of iron ore concentrate with mill scale increases the amount of ready made sinter, sinter strength and productivity of the sinter machine and productivity at blast furnace yard. Also, the increase of coke breeze leads to an increase the ready made sinter and productivity of the sintering machine at blast furnace yard. The productivity of the sintering machine after 5% decreased slightly due to the decrease of vertical velocity.

  15. Stress-dislocation interaction mechanism in low-temperature thermo-compression sintering of Ag NPs

    Science.gov (United States)

    Wang, Fuliang; Tang, Zikai; He, Hu

    2018-04-01

    The sintering of metal nanoparticles (NPs) has been widely studied in the field of nanotechnology, and low-temperature sintering has become the industry standard. In this study, a molecular dynamics (MD) model was established to study the sintering behaviour of silver NPs during low-temperature thermo-compression. Primarily, we studied the sintering process, in which the ratio of neck radius to particle radius (x/r) changes. Under a uniaxial pressure, the maximum ratio in the temperature range 420-425 K was 1. According to the change of x/r, the process can be broken down into three stages: the neck-formation stage, neck-growth stage, and neck-stability stage. In addition, the relationship between potential energy, internal stress, and dislocation density during sintering is discussed. The results showed that cycling internal stress played an important role in sintering. Under the uniaxial pressure, the stress-dislocation interaction was found to be the major mechanism for thermo-compression sintering because the plastic deformation product dislocation intensified the diffusion of atoms. Also, the displacement vector, the mean square displacement, and the changing crystal structure during sintering were studied.

  16. Stress-dislocation interaction mechanism in low-temperature thermo-compression sintering of Ag NPs

    Directory of Open Access Journals (Sweden)

    Fuliang Wang

    2018-04-01

    Full Text Available The sintering of metal nanoparticles (NPs has been widely studied in the field of nanotechnology, and low-temperature sintering has become the industry standard. In this study, a molecular dynamics (MD model was established to study the sintering behaviour of silver NPs during low-temperature thermo-compression. Primarily, we studied the sintering process, in which the ratio of neck radius to particle radius (x/r changes. Under a uniaxial pressure, the maximum ratio in the temperature range 420–425 K was 1. According to the change of x/r, the process can be broken down into three stages: the neck-formation stage, neck-growth stage, and neck-stability stage. In addition, the relationship between potential energy, internal stress, and dislocation density during sintering is discussed. The results showed that cycling internal stress played an important role in sintering. Under the uniaxial pressure, the stress-dislocation interaction was found to be the major mechanism for thermo-compression sintering because the plastic deformation product dislocation intensified the diffusion of atoms. Also, the displacement vector, the mean square displacement, and the changing crystal structure during sintering were studied.

  17. Microstructure and superconducting properties of Bi-2223/Ag tapes fabricated in the two-step sintering process

    International Nuclear Information System (INIS)

    Lu, X.Y.; Nagata, A.; Sugawara, K.

    2008-01-01

    The microstructure and superconducting properties of Bi-2223/Ag tapes fabricated in the two-step sintering process were investigated. The tapes were then subjected to two heat treatments with an intermediate rolling. All the tapes were sintered at 835 deg. C for 24 h at initial sintering stage. A two-step sintering procedure was then used in the final sintering stage. In the first step, the tapes are sintered at 840-865 deg. C for 1 h. In the second step, they were sintered at 835 deg. C for 120 h. The results show that the first step sintering temperature has significant influence on the microstructure and the critical current density J c . The observed microstructures are consistent well with the different J c performances of the tapes first-step-sintered at different temperatures. The tape first-step-sintered at 850 deg. C, which has small secondary phases, stronger c-axis grain alignment, higher proportion of Bi-2223 phase, and no cracks, exhibits the highest J c value

  18. Effect of the sintering temperature and time on phase assemblage and electrical conductivity of zirconia-scandia-ceria

    International Nuclear Information System (INIS)

    Grosso, R.L.; Muccillo, E.N.S.

    2012-01-01

    ZrO 2 -based solid electrolytes have been extensively studied over the last decades for application in solid oxide fuel cells (SOFCs). Zirconia containing scandia and ceria solid electrolyte is a potential candidate in SOFCs operating at intermediate temperatures (600 - 800 deg C). In this work, commercial ZrO 2 containing 10 mol% Sc 2 O 3 and 1 mol% CeO 2 was sintered by the conventional and two-step methods. Several sintering conditions were evaluated by varying the temperature as well as the residence time. High values of sintered density (> 98%) were obtained. A careful selection of the sintering conditions is necessary in order to obtain a single cubic phase, as revealed by X-ray diffraction results. The grain growth can be controlled in specimens sintered by the two-step method. The electrical conductivity show similar behavior for the grain component independent on the sintering method. (author)

  19. Master Sintering Surface: A practical approach to its construction and utilization for Spark Plasma Sintering prediction

    Directory of Open Access Journals (Sweden)

    Pouchly V.

    2012-01-01

    Full Text Available The sintering is a complex thermally activated process, thus any prediction of sintering behaviour is very welcome not only for industrial purposes. Presented paper shows the possibility of densification prediction based on concept of Master Sintering Surface (MSS for pressure assisted Spark Plasma Sintering (SPS. User friendly software for evaluation of the MSS is presented. The concept was used for densification prediction of alumina ceramics sintered by SPS.

  20. Optimization of process parameters for spark plasma sintering of nano structured SAF 2205 composite

    Directory of Open Access Journals (Sweden)

    Samuel Ranti Oke

    2018-04-01

    Full Text Available This research optimized spark plasma sintering (SPS process parameters in terms of sintering temperature, holding time and heating rate for the development of a nano-structured duplex stainless steel (SAF 2205 grade reinforced with titanium nitride (TiN. The mixed powders were sintered using an automated spark plasma sintering machine (model HHPD-25, FCT GmbH, Germany. Characterization was performed using X-ray diffraction and scanning electron microscopy. Density and hardness of the composites were investigated. The XRD result showed the formation of FeN0.068. SEM/EDS revealed the presence of nano ranged particles of TiN segregated at the grain boundaries of the duplex matrix. A decrease in hardness and densification was observed when sintering temperature and heating rate were 1200 °C and 150 °C/min respectively. The optimum properties were obtained in composites sintered at 1150 °C for 15 min and 100 °C/min. The composite grades irrespective of the process parameters exhibited similar shrinkage behavior, which is characterized by three distinctive peaks, which is an indication of good densification phenomena. Keywords: Spark plasma sintering, Duplex stainless steel (SAF 2205, Titanium nitride (TiN, Microstructure, Density, Hardness

  1. Debinding and Sintering of an Injection-Moulded Hypereutectic Al–Si Alloy

    Directory of Open Access Journals (Sweden)

    Jiaqi Ni

    2018-05-01

    Full Text Available Hypereutectic Al–Si (20 wt.% alloy parts were fabricated by employing a powder injection moulding (PIM technique with a developed multi-component binder system composed of high-density polyethylene (35 wt.%, carnauba wax (62 wt.% and stearic acid (3 wt.%. The feedstocks contained 83 wt.% metal powders. The debinding process was carried out by a combination of solvent extraction and thermal decomposition. The effects of solvent debinding variables such as kind of solvents, debinding temperatures and time, and the bulk surface area to volume ratios on the debinding process were investigated. Thermal debinding and the subsequent sintering process were carried out in a heating sequence under a nitrogen atmosphere. The influences of sintering temperature and sintering time on the mechanical properties and structure were considered. Under the optimal sintering condition, sintering at 550 °C for 3 h, the final sintering parts were free of distortion and exhibited good mechanical properties. Relative sintered density, Brinell hardness, and tensile strength were ~95.5%, 58 HBW and ~154, respectively.

  2. Debinding and Sintering of an Injection-Moulded Hypereutectic Al⁻Si Alloy.

    Science.gov (United States)

    Ni, Jiaqi; Yu, Muhuo; Han, Keqing

    2018-05-16

    Hypereutectic Al⁻Si (20 wt.%) alloy parts were fabricated by employing a powder injection moulding (PIM) technique with a developed multi-component binder system composed of high-density polyethylene (35 wt.%), carnauba wax (62 wt.%) and stearic acid (3 wt.%). The feedstocks contained 83 wt.% metal powders. The debinding process was carried out by a combination of solvent extraction and thermal decomposition. The effects of solvent debinding variables such as kind of solvents, debinding temperatures and time, and the bulk surface area to volume ratios on the debinding process were investigated. Thermal debinding and the subsequent sintering process were carried out in a heating sequence under a nitrogen atmosphere. The influences of sintering temperature and sintering time on the mechanical properties and structure were considered. Under the optimal sintering condition, sintering at 550 °C for 3 h, the final sintering parts were free of distortion and exhibited good mechanical properties. Relative sintered density, Brinell hardness, and tensile strength were ~95.5%, 58 HBW and ~154, respectively.

  3. Borax as flux on sintering of iron Ancor Steel 1000® under glow discharge

    Science.gov (United States)

    Ariza Suarez, H. G.; Sarmiento Santos, A.; Ortiz Otálora, C. A.

    2016-02-01

    This work studies the flux effect of borax (di sodium tetraborate decahydrate) on sintering of iron Ancor Steel 1000® in abnormal glow discharge. The incidence of the percentage by weight of borax and the sintering temperature in the process were observed. Samples of powder metallurgical iron were prepared with proportions of 0.50%, 2.0%, 4.0% and 6.0% by weight of borax using the procedures of powder metallurgy. The samples were sintered at 800 and 1100°C for 30min, by glow discharge at low pressure in a reducing atmosphere composed of 20% H2+80% Ar. The samples in compact green-state were analyzed by TGA-DSC to determine the fusion process and mass loss during sintering. The analysis of microhardness and density, shows that at a sintering temperature of 800°C the sample density decreases and the sample microhardness increases with respect to sintered samples without borax. Sintered samples were analysed by DRX showing the absence of precipitates.

  4. Lanthana-bearing nanostructured ferritic steels via spark plasma sintering

    Energy Technology Data Exchange (ETDEWEB)

    Pasebani, Somayeh [Department of Chemical and Materials Engineering, University of Idaho, Moscow, ID 83844 (United States); Center for Advanced Energy Studies, Idaho Falls, ID 83401 (United States); Charit, Indrajit, E-mail: icharit@uidaho.edu [Department of Chemical and Materials Engineering, University of Idaho, Moscow, ID 83844 (United States); Center for Advanced Energy Studies, Idaho Falls, ID 83401 (United States); Wu, Yaqiao; Burns, Jatuporn; Allahar, Kerry N.; Butt, Darryl P. [Department of Materials Science and Engineering, Boise State University, Boise, ID 83725 (United States); Center for Advanced Energy Studies, Idaho Falls, ID 83401 (United States); Cole, James I. [Idaho National Laboratory, Idaho Falls, ID 83401 (United States); Center for Advanced Energy Studies, Idaho Falls, ID 83401 (United States); Alsagabi, Sultan F. [Department of Chemical and Materials Engineering, University of Idaho, Moscow, ID 83844 (United States); Center for Advanced Energy Studies, Idaho Falls, ID 83401 (United States)

    2016-03-15

    A lanthana-containing nanostructured ferritic steel (NFS) was processed via mechanical alloying (MA) of Fe-14Cr-1Ti-0.3Mo-0.5La{sub 2}O{sub 3} (wt.%) and consolidated via spark plasma sintering (SPS). In order to study the consolidation behavior via SPS, sintering temperature and dwell time were correlated with microstructure, density, microhardness and shear yield strength of the sintered specimens. A bimodal grain size distribution including both micron-sized and nano-sized grains was observed in the microstructure of specimens sintered at 850, 950 and1050 °C for 45 min. Significant densification occurred at temperatures greater than 950 °C with a relative density higher than 98%. A variety of nanoparticles, some enriched in Fe and Cr oxides and copious nanoparticles smaller than 10 nm with faceted morphology and enriched in La and Ti oxides were observed. After SPS at 950 °C, the number density of Cr–Ti–La–O-enriched nanoclusters with an average radius of 1.5 nm was estimated to be 1.2 × 10{sup 24} m{sup −3}. The La + Ti:O ratio was close to 1 after SPS at 950 and 1050 °C; however, the number density of nanoclusters decreased at 1050 °C. With SPS above 950 °C, the density improved but the microhardness and shear yield strength decreased due to partial coarsening of the grains and nanoparticles.

  5. SINTERING OF NASCENT CALCIUM OXIDE

    Science.gov (United States)

    The paper discusses the measurement of the sintering rate of CaO in a nitrogen atmosphere at temperatures of 700-1100 C. CaO prepared from ultrapure CaCO3 was compared with an impure CaO derived from limestone. Both materials yielded an initial surface area of 104 sq m/g. The rat...

  6. The evaluation of different environments in ultra-high frequency induction sintered powder metal compacts

    International Nuclear Information System (INIS)

    Cavdar, P. S.; Cavdar, U.

    2015-01-01

    The application of the iron based Powder Metal (PM) compacts in Ultra-High Frequency Induction Sintering (UHFIS) was reviewed for different environments. The three different environments: atmosphere, argon and vacuum were applied to the PM compacts. Iron based PM compacts were sintered at 1120 degree centigrade for a total of 550 seconds by using induction sintering machines with 2.8 kW power and 900 kHz frequency. Micro structural properties, densities, roughness and micro hardness values were obtained for all environments. The results were compared with each other. (Author)

  7. Influences of chemical packing and the chemical composition in porcelain sintering: from theory to practice

    International Nuclear Information System (INIS)

    Conceicao, E.S.; Gouvea, D.; Romano, R.C.O.; Pileggi, R.G.

    2011-01-01

    Studies have been conducted using the size distribution particles as a tool to obtain maximum packing in porcelain bodies. However, little attention has been given for the maximum size of particles and its effect in the sintering. While some particles are relatively large (63 μ m) for some oxides in the porcelain composition, they could compromise the sintering if a liquid phase is formed during heat processing. In this work, a comparative analysis showed that compositions with a maximum green packing density does not always lead to a maximum final densification in sintering if there is no control of the maximum size of the particles. (author)

  8. Some aspects of barreling in sintered plain carbon steel powder metallurgy preforms during cold upsetting

    Directory of Open Access Journals (Sweden)

    Sumesh Narayan

    2012-04-01

    Full Text Available The present research establishes a relationship of bulged diameter with densification and hydrostatic stress in forming of sintered iron (Fe powder metallurgy preforms cold upset under two different frictional conditions, namely, nil/no and graphite lubricant condition. Sintered plain carbon steel cylindrical preforms with carbon (C contents of 0, 0.35, 0.75 and 1.1% with constant initial theoretical density of 84% and aspect ratio of 0.4 and 0.6 were prepared using a suitable die-set assembly on a 1 MN capacity hydraulic press and sintered for 90 minutes at 1200 °C. Each sintered preform was cold upset under two different frictional constraints. It is seen that the degree of bulging reduces with reducing frictional constraints at the die contact surface. Further, it is found that the bulging ratio changed as a function of relative density and hydrostatic stress, respectively, according to the power law equations.

  9. Properties and sinterability of wet and dry attrition-milled OREOXed powder

    International Nuclear Information System (INIS)

    Lee, J. W.; Kim, J. H.; Kim, W. K.; Park, K. I.; Lee, J. W.

    2001-01-01

    The powder properties and sinterability were investigated with the powder prepared by wet and dry attrition milling of OREOX-treated powder. The OREOX-treated powder was prepared from the simulated spent fuel. Powder having less than 1 μm of average particle size could be obtained by dry milling, but not be obtained by wet milling. Thus, specific surface area of dry milled powder was higher than that of wet milled powder. With increasing of milling time, dry milled powder formed dense agglomerate while wet milled powder showed loose agglomerate. The pellets with higher than 95% T.D. of sintered density and larger than 7 μm of grain size were made with the milled powder regardless of milling method. The milling time in wet milling has greatly improved the sinterability. The pellets produced with dry milled powder have higher sintered density and larger grain size

  10. Effect of two-stage sintering process on microstructure and mechanical properties of ODS tungsten heavy alloy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Kyong H. [Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusong-dong, Yusong-gu, Taejon 305-701 (Korea, Republic of); Cha, Seung I. [International Center for Young Scientists, National Institute for Materials Science 1-1, Namiki, Tsukuba 305-0044 (Japan); Ryu, Ho J. [DUPIC, Korea Atomic Energy Research Institute, 150 Deokjin-dong, Yusong-gu, Taejon 305-353 (Korea, Republic of); Hong, Soon H. [Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1 Kusong-dong, Yusong-gu, Taejon 305-701 (Korea, Republic of)], E-mail: shhong@kaist.ac.kr

    2007-06-15

    Oxide dispersion strengthened (ODS) tungsten heavy alloys have been considered as promising candidates for advanced kinetic energy penetrator due to their characteristic fracture mode compared to conventional tungsten heavy alloy. In order to obtain high relative density, the ODS tungsten heavy alloy needs to be sintered at higher temperature for longer time, however, induces growth of tungsten grains. Therefore, it is very difficult to obtain controlled microstructure of ODS tungsten heavy alloy having fine tungsten grains with full densification. In this study, two-stage sintering process, consisted of primary solid-state sintering and followed by secondary liquid phase sintering, was introduced for ODS tungsten heavy alloys. The mechanically alloyed 94W-4.56Ni-1.14Fe-0.3Y{sub 2}O{sub 3} powders are solid-state sintered at 1300-1450 deg. C for 1 h in hydrogen atmosphere, and followed by liquid phase sintering temperature at 1465-1485 deg. C for 0-60 min. The microstructure of ODS tungsten heavy alloys showed high relative density above 97%, with contiguous tungsten grains after primary solid-state sintering. The microstructure of solid-state sintered ODS tungsten heavy alloy was changed into spherical tungsten grains embedded in W-Ni-Fe matrix during secondary liquid phase sintering. The two-stage sintered ODS tungsten heavy alloy from mechanically alloyed powders showed finer microstructure and higher mechanical properties than conventional liquid phase sintered alloy. The mechanical properties of ODS tungsten heavy alloys are dependent on the microstructural parameters such as tungsten grain size, matrix volume fraction and tungsten/tungsten contiguity, which can be controlled through the two-stage sintering process.

  11. Influence of spark plasma sintering conditions on the sintering and functional properties of an ultra-fine grained 316L stainless steel obtained from ball-milled powder

    Energy Technology Data Exchange (ETDEWEB)

    Keller, C., E-mail: clement.keller@insa-rouen.fr [Groupe de Physique des Matériaux, CNRS-UMR 6634, Université de Rouen, INSA de Rouen, Avenue de l' Université, 76800 Saint-Etienne du Rouvray (France); Tabalaiev, K.; Marnier, G. [Groupe de Physique des Matériaux, CNRS-UMR 6634, Université de Rouen, INSA de Rouen, Avenue de l' Université, 76800 Saint-Etienne du Rouvray (France); Noudem, J. [Laboratoire de Cristallographie des Matériaux, CNRS-UMR 6508, Université de Caen, ENSICAEN, 7 bd du Maréchal Juin, 14050 Caen (France); Sauvage, X. [Groupe de Physique des Matériaux, CNRS-UMR 6634, Université de Rouen, INSA de Rouen, Avenue de l' Université, 76800 Saint-Etienne du Rouvray (France); Hug, E. [Laboratoire de Cristallographie des Matériaux, CNRS-UMR 6508, Université de Caen, ENSICAEN, 7 bd du Maréchal Juin, 14050 Caen (France)

    2016-05-17

    In this work, 316L samples with submicrometric grain size were sintered by spark plasma sintering. To this aim, 316L powder was first ball-milled with different conditions to obtain nanostructured powder. The process control agent quantity and milling time were varied to check their influence on the crystallite size of milled powder. Samples were then sintered by spark plasma sintering using different sets of sintering parameters (temperature, dwell time and pressure). For each sample, grain size and density were systematically measured in order to investigate the influence of the sintering process on these two key microstructure parameters. Results show that suitable ball-milling and subsequent sintering can be employed to obtain austenitic stainless steel samples with grain sizes in the nanometer range with porosity lower than 3%. However, ball-milling and subsequent sintering enhance chromium carbides formation at the sample surface in addition to intragranular and intergranular oxides in the sample as revealed by X-ray diffraction and transmission electron microscopy. It has been shown that using Boron nitride together with graphite foils to protect the mold from powder welding prevent such carbide formation. For mechanical properties, results show that the grain size refinement strongly increases the hardness of the samples without deviation from Hall-Petch relationship despite the oxides formation. For corrosion resistance, grain sizes lower than a few micrometers involve a strong decrease in the pitting potential and a strong increase in passivation current. As a consequence, spark plasma sintering can be considered as a promising tool for ultra-fine grained austenitic stainless steel.

  12. Modeling the microstructural evolution during constrained sintering

    DEFF Research Database (Denmark)

    Bjørk, Rasmus; Frandsen, Henrik Lund; Tikare, V.

    A numerical model able to simulate solid state constrained sintering of a powder compact is presented. The model couples an existing kinetic Monte Carlo (kMC) model for free sintering with a finite element (FE) method for calculating stresses on a microstructural level. The microstructural response...... to the stress field as well as the FE calculation of the stress field from the microstructural evolution is discussed. The sintering behavior of two powder compacts constrained by a rigid substrate is simulated and compared to free sintering of the same samples. Constrained sintering result in a larger number...

  13. Colloidal characterization of silicon nitride and silicon carbide

    Science.gov (United States)

    Feke, Donald L.

    1986-01-01

    The colloidal behavior of aqueous ceramic slips strongly affects the forming and sintering behavior and the ultimate mechanical strength of the final ceramic product. The colloidal behavior of these materials, which is dominated by electrical interactions between the particles, is complex due to the strong interaction of the solids with the processing fluids. A surface titration methodology, modified to account for this interaction, was developed and used to provide fundamental insights into the interfacial chemistry of these systems. Various powder pretreatment strategies were explored to differentiate between true surface chemistry and artifacts due to exposure history. The colloidal behavior of both silicon nitride and carbide is dominated by silanol groups on the powder surfaces. However, the colloid chemistry of silicon nitride is apparently influenced by an additional amine group. With the proper powder treatments, silicon nitride and carbide powder can be made to appear colloidally equivalent. The impact of these results on processing control will be discussed.

  14. Microwave combustion and sintering without isostatic pressure

    International Nuclear Information System (INIS)

    Ebadian, M.A.

    1998-01-01

    In recent years interest has grown rapidly in the application of microwave energy to the processing of ceramics, composites, polymers, and other materials. Advances in the understanding of microwave/materials interactions will facilitate the production of new ceramic materials with superior mechanical properties. One application of particular interest is the use of microwave energy for the mobilization of uranium for subsequent redeposition. Phase III (FY98) will focus on the microwave assisted chemical vapor infiltration tests for mobilization and redeposition of radioactive species in the mixed sludge waste. Uranium hexachloride and uranium (IV) borohydride are volatile compounds for which the chemical vapor infiltration procedure might be developed for the separation of uranium. Microwave heating characterized by an inverse temperature profile within a preformed ceramic matrix will be utilized for CVI using a carrier gas. Matrix deposition is expected to commence from the inside of the sample where the highest temperature is present. The preform matrix materials, which include aluminosilicate based ceramics and silicon carbide based ceramics, are all amenable to extreme volume reduction, densification, and vitrification. Important parameters of microwave sintering such as frequency, power requirement, soaking temperature, and holding time will be investigated to optimize process conditions for the volatilization of uranyl species using a reactive carrier gas in a microwave chamber

  15. Rapid immobilization of simulated radioactive soil waste by microwave sintering.

    Science.gov (United States)

    Zhang, Shuai; Shu, Xiaoyan; Chen, Shunzhang; Yang, Huimin; Hou, Chenxi; Mao, Xueli; Chi, Fangting; Song, Mianxin; Lu, Xirui

    2017-09-05

    A rapid and efficient method is particularly necessary in the timely disposal of seriously radioactive contaminated soil. In this paper, a series of simulated radioactive soil waste containing different contents of neodymium oxide (3-25wt.%) has been successfully vitrified by microwave sintering at 1300°C for 30min. The microstructures, morphology, element distribution, density and chemical durability of as obtained vitrified forms have been analyzed. The results show that the amorphous structure, homogeneous element distribution, and regular density improvement are well kept, except slight cracks emerge on the magnified surface for the 25wt.% Nd 2 O 3 -containing sample. Moreover, all the vitrified forms exhibit excellent chemical durability, and the leaching rates of Nd are kept as ∼10 -4 -10 -6 g/(m 2 day) within 42days. This demonstrates a potential application of microwave sintering in radioactive contaminated soil disposal. Copyright © 2017 Elsevier B.V. All rights reserved.

  16. Strain rate dependency of laser sintered polyamide 12

    Directory of Open Access Journals (Sweden)

    Cook J.E.T.

    2015-01-01

    Full Text Available Parts processed by Additive Manufacturing can now be found across a wide range of applications, such as those in the aerospace and automotive industry in which the mechanical response must be optimised. Many of these applications are subjected to high rate or impact loading, yet it is believed that there is no prior research on the strain rate dependence in these materials. This research investigates the effect of strain rate and laser energy density on laser sintered polyamide 12. In the study presented here, parts produced using four different laser sintered energy densities were exposed to uniaxial compression tests at strain rates ranging from 10−3 to 10+3 s−1 at room temperature, and the dependence on these parameters is presented.

  17. Microwave synthesis and sintering characteristics of CaCu 3 Ti 4 O 12

    Indian Academy of Sciences (India)

    CaCu3Ti4O12 (CCTO) was synthesized and sintered by microwave processing at 2.45 GHz, 1.1 kW. The optimum calcination temperature using microwave heating was determined to be 950°C for 20 min to obtain cubic CCTO powders. The microwave processed powders were sintered to 94% density at 1000°C/60 min.

  18. Formation of solid solution during mutual diffusion of tungsten and molybdenum in the process of sintering

    International Nuclear Information System (INIS)

    Timofeeva, A.A.; Bulat, I.B.; Voronin, Yu.V.; Fedoseev, G.K.; Karasev, V.M.

    1984-01-01

    A process of a solid solution homogenization during sintering of W-15Mo and W-5Mo alloys is studied by the methods of density measurements, analysis of the X-ray lines physical broadening and determination of crystalline lattice constant. Study of the process of solid solution formation under conditions of powder composite sintering is shown to be conducted with account of peculiarities of tungsten and molybdenum mutual diffusion in the investigated temperature range of concentrations

  19. Effect of impurities on sintering and conductivity of yttria-stabilized zirconia

    NARCIS (Netherlands)

    Verkerk, M.J.; Winnubst, Aloysius J.A.; Burggraaf, A.J.

    1982-01-01

    The effect of low concentrations of Fe2O3, Al2O3 and Bi2O3 on the sintering behaviour of (ZrO2)0.83 (YO1.5)0.17, made by alkoxide synthesis, has been investigated. The best results are achieved with Bi2O3 as a sinter agent and a relative density of 95% is obtained at 1200 K. The effects of these

  20. Synergistic effect of carbon nanotube as sintering aid and toughening agent in spark plasma sintered molybdenum disilicide-hafnium carbide composite

    Energy Technology Data Exchange (ETDEWEB)

    Mukherjee, Biswajyoti; Asiq Rahman, O.S.; Sribalaji, M [Materials Science and Engineering, Indian Institute of Technology Patna, Bihta Kanpa Road, Bihta, Patna, Bihar 801103 (India); Bakshi, Srinivasa Rao [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Keshri, Anup Kumar, E-mail: anup@iitp.ac.in [Materials Science and Engineering, Indian Institute of Technology Patna, Bihta Kanpa Road, Bihta, Patna, Bihar 801103 (India)

    2016-12-15

    Hafnium carbide (HfC) along with sintering aids was consolidated at a relatively lower temperature i.e. 1600 °C (i.e. T=~0.41 T{sub m}) under a uniaxial load of 50 MPa by spark plasma sintering. Two different sintering aids such as molybdenum disilicide (MoSi{sub 2}) and carbon nanotube (CNT) were added to enhance the densification and lower the extent of grain growth in the sintered pellets. Density of the sintered pellet increased from 96.0±0.8% in HfC +5 wt% MoSi{sub 2} (HM) to 99.0±0.5% with the addition of 2 wt% CNT in HfC+5 wt% MoSi{sub 2} (HMC) at sintering temperature of 1600 °C. Further, the extent of grain growth drastically reduced from 204% in HM to 50% in HMC. Analysis of linear shrinkage during densification revealed that CNT addition increased densification rate and decreased the time required to reach the density of 99.0±0.5% at 1600 °C. Increased densification and lower degree of grain growth could be due to the synergistic effect offered by the CNT, which are as follows: (i) Lubrication effect of CNT, (ii) Lower activation energy for grain boundary diffusion (iii) Reduction in liquid phase sintering temperature and (iv) Grain boundary pinning. Fracture toughness of the sintered HM and HMC composite was obtained using indentation technique. By the addition of 2 wt% CNT in HM, drastic increase of 91% in fracture toughness was seen. This significant improvement in fracture toughness was due to the enhanced densification and relatively lower grain size of HMC. Also crack bridging, crack deflection, crack arrest, CNT and graphene sheet pull-out and swording played major role in toughening of HMC pellet.

  1. Vacuum Pressureless Sintering of Ti-6Al-4V Alloy with Full Densification and Forged-Like Mechanical Properties

    Science.gov (United States)

    Zhang, Ce; Lu, Boxin; Wang, Haiying; Guo, Zhimeng; Paley, Vladislav; Volinsky, Alex A.

    2018-01-01

    Ti-6Al-4V ingots with a nearly 100% density, fine and homogeneous basket-weave microstructure, and better comprehensive mechanical properties (UTS = 935 MPa, Y.S. = 865 MPa, El. = 15.8%), have been manufactured by vacuum pressureless sintering of blended elemental powders. Coarse TiH2 powder, Al powder (2, 20 μm), V powder, and Al-V master alloy powder were used as raw materials to produce different powder mixtures ( D 50 = 10 μm). Then, the compacts made by cold isostatic pressing were consolidated by different sintering curves. A detailed investigation of different as-sintered samples revealed that a higher density can be obtained by generating transient molten Al in the sintering process. Coarse Al powder and a rapid heating rate under the melting point of Al contribute to molten Al formation. The presence of temporary liquid phase changes the sintering mechanism, accelerating the sintering neck formation, improving sinterability of the powder mixtures. Density of 99.5% was achieved at 1150 °C, which is markedly lower than the sintering temperatures reported for conventional blended elemental powder metallurgy routes. In addition, low interstitial content, especially for oxygen (0.17 wt.%), is obtained by strict process control.

  2. Porous silicon gettering

    Energy Technology Data Exchange (ETDEWEB)

    Tsuo, Y.S.; Menna, P.; Pitts, J.R. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1996-05-01

    The authors have studied a novel extrinsic gettering method that uses the large surface areas produced by a porous-silicon etch as gettering sites. The annealing step of the gettering used a high-flux solar furnace. They found that a high density of photons during annealing enhanced the impurity diffusion to the gettering sites. The authors used metallurgical-grade Si (MG-Si) prepared by directional solidification casing as the starting material. They propose to use porous-silicon-gettered MG-Si as a low-cost epitaxial substrate for polycrystalline silicon thin-film growth.

  3. Sinterization of manganese ore tailings under natural air

    Energy Technology Data Exchange (ETDEWEB)

    Lima, M.M.F.; Souza, L.G.P.R.M.F. [Universidade Federal de Ouro Preto (UFOP), MG (Brazil)

    2014-07-01

    The manganese ore has wide application in metallurgy. However, from each of three hundred concentrations found, only one can be seen as a deposit. The aim of this study was to obtain and characterize a sinter from manganese ore tailing. The tailing was milled, classified (<400 ⧣) and calcinated (800°C - 3600s). The mixture had 12% moisture, 7 and 9% of activated charcoal. After homogenization, the sintering were carried out at 1140, 1145 and 1150°C during 1800, 7200 and 14400s at natural air. The sintered products were characterized by EDS analysis, BET surface area, apparent density, X-rays diffraction and SEM/EDS. The mass loss was approximately 14% and 16% in the calcination and sintering, respectively, due to the elimination of volatile products and water. The main phases characterized: SiO2, silicate with high content of manganese in the matrix and other silicates with different proportions of Ti, Na, Mn, Mg and Ca. (author)

  4. Conventional and two step sintering of PZT-PCN ceramics

    Science.gov (United States)

    Keshavarzi, Mostafa; Rahmani, Hooman; Nemati, Ali; Hashemi, Mahdieh

    2018-02-01

    In this study, PZT-PCN ceramic was made via sol-gel seeding method and effects of conventional sintering (CS) as well as two-step sintering (TSS) were investigated on microstructure, phase formation, density, dielectric and piezoelectric properties. First, high quality powder was achieved by seeding method in which the mixture of Co3O4 and Nb2O5 powder was added to the prepared PZT sol to form PZT-PCN gel. After drying and calcination, pyrochlore free PZT-PCN powder was synthesized. Second, CS and TSS were applied to achieve dense ceramic. The optimum temperature used for 2 h of conventional sintering was obtained at 1150 °C; finally, undesired ZrO2 phase formed in CS procedure was removed successfully with TSS procedure and dielectric and piezoelectric properties were improved compared to the CS procedure. The best electrical properties obtained for the sample sintered by TSS in the initial temperature of T 1 = 1200 °C and secondary temperature of T 2 = 1000 °C for 12 h.

  5. High-level radioactive waste fixation in sintered vitreous matrix

    International Nuclear Information System (INIS)

    Russo, D.O.; Messi de Bernasconi, N.; Audero, M.A.

    1987-01-01

    The safe storage of high-level wastes from fuel elements reprocessing includes, as a first step, the fixation of the same in materials having a good resistance to the leaching in aqueous medium, such as borosilicate glass. As an alternative to the usual method of the molten glasses, a procedure for the sintering of a powdered glass and waste mixture at lower temperatures (600-700 deg C) has been developed, which minimizes the volatilization of active compounds during the process. Two glasses matrices of different composition and characteristics were used, to which the simulated wastes were added in the ratio of a 10% in weight of oxides. Two sintering techniques were employed 1: cold pressing and further sintering; 2: hot pressing and sintering under pressure. The densities were measured, the microstructure of the samples was analyzed and leaching essays were made in distilled water. The pellet's microstructure was observed by means of optical microscopy, by reflection in polished samples and by transparency in thin slices. The presence of crystalline compounds was analyzed by means of x rays and electron microprobe. The results have shown the convenience to continue with hot pressing essays, because a denser product with a higher resistance to the leaching is thus obtained. (M.E.L.) [es

  6. Coal fly ash utilization: Low temperature sintering of wall tiles

    International Nuclear Information System (INIS)

    Chandra, Navin; Sharma, Priya; Pashkov, G.L.; Voskresenskaya, E.N.; Amritphale, S.S.; Baghel, Narendra S.

    2008-01-01

    We present here a study of the sintering of fly ash and its mixture with low alkali pyrophyllite in the presence of sodium hexa meta phosphate (SHMP), a complex activator of sintering, for the purpose of wall tile manufacturing. The sintering of fly ash with SHMP in the temperature range 925-1050 deg. C produces tiles with low impact strength; however, the incremental addition of low alkali pyrophyllite improves impact strength. The impact strength of composites with ≥40% (w/w) pyrophyllite in the fly ash-pyrophyllite mix satisfies the acceptable limit (19.6 J/m) set by the Indian Standards Institute for wall tiles. Increasing the pyrophyllite content results in an increase in the apparent density of tiles, while shrinkage and water absorption decrease. The strength of fly ash tiles is attributed to the formation of a silicophosphate phase; in pyrophyllite rich tiles, it is attributed to the formation of a tridymite-structured T-AlPO 4 phase. Scanning electron micrographs show that the reinforcing rod shaped T-AlPO 4 crystals become more prominent as the pyrophyllite content increases in the sintered tiles

  7. The influence of sintering temperature on microstructure and mechanical properties of Ni-Al intermetallics fabricated by SPS

    Energy Technology Data Exchange (ETDEWEB)

    Thömmes, A., E-mail: thoemmes.alexander@gmail.com; Shevtsova, L. I., E-mail: edeliya2010@mail.ru; Laptev, I. S., E-mail: ilya-laptev-nstu@mail.ru; Mul, D. O., E-mail: ddariol@yandex.ru [Novosibirsk State Technical University, Novosibirsk, 630073 (Russian Federation); Mali, V. I., E-mail: vmali@mail.ru; Anisimov, A. G., E-mail: anis@hydro.nsc.ru [Lavrentyev Institute of Hydrodynamics SB RAS, Novosibirsk, 630090 (Russian Federation)

    2015-10-27

    In the present study PN85Yu15 was used as elemental powder to produce a sintered compound with Ni3Al as main phase. The Spark Plasma Sintering (SPS) technique is used to compact the powders. The powder was sintered in a temperature range between 1000°C and 1150°C to observe the influence of the sintering temperature on the microstructure and the mechanical properties. The microstructure was observed with optical microscope (OM), the phase composition was characterized by X-ray diffraction (XRD) technique. Density and microhardness were observed and compared the values with the results of other researchers. The compressive-, density- and microhardness tests show as clear result that with increasing the sintering temperature nearly all properties become better and also the microstructure studies show that porous places become less.

  8. Effect of microstructure changes on magnetic properties of spark plasma sintered Nd-Fe-B powders

    Directory of Open Access Journals (Sweden)

    Michalski B.

    2013-01-01

    Full Text Available In this study the SPS method was applied for low RE content (8,5% at. and high RE content (13,5 % at. MQ powders. The powders were sintered in a wide range of temperature, for 5 min., under pressure of 35 MPa. The low RE content grade, densified reluctantly and gained the density close to the theoretical value only for 850 °C. The coercivity decreased gradually with increasing sintering temperature. On the other hand, the densification of the higher RE content grade powder occurred much easier and the coercivity, close to the theoretical value, was achieved already at 650 °C. The coercivity of this material also decreased with increasing sintering temperature. Microstructural studies revealed that the SPS sintering process leads to partial decomposition of the Nd2Fe14B phase. The proportion of the RE-rich and iron phases increases parallel to the increasing sintering temperature. On the basis of the current results one can conclude that fabrication of high density MQ powders based magnets by the SPS method is possible, however the powders having higher RE content should be used for this purpose and the sintering temperature as low as possible, related to density, should be kept.

  9. Development and evaluation of die materials for use in the growth of silicon ribbons by the inverted ribbon growth process, task 2. LSSA project

    Science.gov (United States)

    Duffy, M. T.; Berkman, S.; Moss, H. S.; Cullen, G. W.

    1978-01-01

    The results of emission spectroscopic analysis indicate that molten silicon can remain in contact with hot-pressed Si3N4 (99.2 percent theoretical density) for prolonged periods without attaining the impurity content level of the nitride. Although MgO was used as binder, Mg was not found present in the silicon sessile drop in quantities much above the level initially present in the silicon source material. Preliminary experiments with EFG-type dies coated with CVD Si3N4 or CVD SiOxNy indicate that capillary rise does not occur readily in these dies. The same was found to be true of hot-pressed and reaction-sintered Si3N4 obtained commercially. However, when dies were formed by depositing CVD layers on shaped silicon slabs, a column of molten silicon was maintained in each CVD die while being heated in contact with a crucible of molten silicon. Preliminary wetting of dies appears necessary for EFG growth. Several ribbon growth experiments were performed from V-shaped dies.

  10. Sintering of solution-based nano-particles by a UV laser pulse train

    Science.gov (United States)

    Zhang, Jie; Li, Ming; Morimoto, Kiyoshi

    2011-03-01

    Sintering of palladium (Pd) and silicon (Si) nano-particles (NPs) by a 266nm laser pulse train on ink-printed films was investigated. Organic Pd-ink, and organic Si-ink were used as precursors. A high repetition rate DPSS laser (up to 300 kHz, 25ns, 266nm, Coherent AVIA series), which produces a ns pulse train with 3.3 μs -33.3 μs interval of pulse-topulse, was used as the heating source. Highly electrically conductive Pd (Resistivity=~150μΩ.cm) thin film on PET substrate and semi-conductive Si (Resistivity=~23kΩ.cm) thin film on glass substrate were successfully obtained with this laser pulse train sintering process. The sintered films were characterized by AFM, SEM, TEM and Raman spectroscopy, respectively. The pulse train heating process was also numerically simulated.

  11. Determining the solubility parameter and the cross-link density of medical grade silicones: effect of increasing the range of swelling liquids.

    Science.gov (United States)

    Mahomed, Aziza; Kocharian, Areg

    2015-01-01

    Four samples of four medical grade silicones were swollen in six "good" liquids (i.e. those with a good swelling ability, in which silicones swell appreciably) at 25°C, until they reached constant mass (i.e. equilibrium). The volume fraction, ϕ, of the silicone in the swollen sample was calculated for each grade of silicone. Using a combination of the six ϕ values obtained in this study and four of those obtained in a previous study, for each silicone grade, ϕ was plotted against δl, the liquid solubility parameter for the ten liquids used. Using a curve fitting technique a second-order polynomial was plotted through the data points; the minimum in this polynomial provided a value for δp (the polymer solubility parameter). Furthermore, the results showed that the δp values obtained in this study (using ten liquids) were slightly but significantly greater (pliquids), for grade C6-165 only. Similarly, the χ and υ values obtained in the two studies were only significantly different (p<0.05) from each other, for grade C6-165.

  12. Study of the sintering process and the formation of a (Th, U) O2 solid solution

    International Nuclear Information System (INIS)

    Tomasi, Roberto

    1979-01-01

    The effect of some variables in the (Th, U) O 2 sintering process and solid solution formation was studied. ThO 2 , U 3 O 8 and UO 2 powder were prepared. The ThO 2 powders were obtained by calcination of thorium at 500 and 750 deg C; the U 3 O 8 powders were derived from the calcination of ADU at 660 and 750 deg C; the UO 2 powder were prepared from ADU and from ATCU. The different characteristics of these materials were determined by measurements of surface area, by scanning electron microscopy, tap density tests, X-ray diffractometry and by measurements of the O/U ratios. The oxide mixtures were chosen in order to produce a final composition with 10 w/o of UO 2 . A mixture of thorium oxalate and ADU was also prepared by calcining these salts in air at 700 deg C, in order to obtain certain amount of solid solution prior to sintering. The sintering operations were developed in an argon atmosphere at temperatures between 1400 and 1700 deg C, during interval varying from 1 to 4 hours. The effect of the mixture characteristics on the sintering process and solid solution formation were studied considering the results of densification, microstructure development and X-ray diffractometry. The ThO 2 powder characteristics have a main effect on the mixtures compactability and sinterability, the higher calcining temperatures increasing the green density, but decreasing the final density of the sintered pellets. In the sintering of mixtures containing U 3 O 3 , this oxide is reduced to UO 2 and it is possible to obtain pellets with density and microstructures similar to those produced from mixtures containing UO 2 . But if oxygen in excess is present during sintering, the process is affected, occurring exaggerated grain growth. The densification results were related to the Coble's kinetics equation for second stage of sintering, valid for bulk diffusion, grain boundary acting as vacancy sinks. The sintering activation energy is independent from the powder starting

  13. Enhanced proton conductivity of yttrium-doped barium zirconate with sinterability in protonic ceramic fuel cells

    International Nuclear Information System (INIS)

    Park, Ka-Young; Seo, Yongho; Kim, Ki Buem; Song, Sun-Ju; Park, Byoungnam; Park, Jun-Young

    2015-01-01

    Highlights: • Report effects of ceramic processing methods on the electrical conductivity of BZY. • Present effects of sintering aids on the conductivity and density of BZY. • CuO is the most effective sintering aid for the BZY. • Polymer gelation is the most effective method in terms of conductivity of BZY. • Grain boundary conductivity of the polymer gelation BZY is higher than others. - Abstract: In this study, we report the effects of various ceramic processing methods with different sintering aids on the relative density, crystallinity, microstructure, and electrical conductivity of proton conducting BaZr 0.85 Y 0.15 O 3−δ (BZY) pellets in details. First, the BZY ceramic pellets are fabricated by the solid-state reactive sintering by adding diverse sintering aids including CuO, NiO, ZnO, SnO, MgO, and Al 2 O 3 . Among these, CuO is found to be the most effective sintering aid in terms of the sintering temperature and total conductivity. However, transition metals as sintering aids have detrimental effects on the electrical conductivity of the BZY electrolytes. Second, the BZY electrolytes have been synthesized by four different methods: the solid-state, combustion, hydrothermal, and polymer gelation methods. The BZY pellets synthesized by the polymer gelation method exhibit dense microstructure with a high relative density of 95.3%. Moreover, the electrical conductivity of the BZY pellets synthesized by the polymer gelation method is higher than those prepared by the solid-state methods under the same test conditions: 1.28 × 10 −2 S cm −1 (by the polymer gelation method) vs. 0.53 × 10 −2 S cm −1 by the solid-state method at 600 °C in wet 5% H 2 in Ar

  14. Microwave sintering of ceramic materials

    Science.gov (United States)

    Karayannis, V. G.

    2016-11-01

    In the present study, the potential of microwave irradiation as an innovative energy- efficient alternative to conventional heating technologies in ceramic manufacturing is reviewed, addressing the advantages/disadvantages, while also commenting on future applications of possible commercial interest. Ceramic materials have been extensively studied and used due to several advantages they exhibit. Sintering ceramics using microwave radiation, a novel technology widely employed in various fields, can be an efficient, economic and environmentally-friendlier approach, to improve the consolidation efficiency and reduce the processing cycle-time, in order to attain substantial energy and cost savings. Microwave sintering provides efficient internal heating, as energy is supplied directly and penetrates the material. Since energy transfer occurs at a molecular level, heat is generated throughout the material, thus avoiding significant temperature gradients between the surface and the interior, which are frequently encountered at high heating rates upon conventional sintering. Thus, rapid, volumetric and uniform heating of various raw materials and secondary resources for ceramic production is possible, with limited grain coarsening, leading to accelerated densification, and uniform and fine-grained microstructures, with enhanced mechanical performance. This is particularly important for manufacturing large-size ceramic products of quality, and also for specialty ceramic materials such as bioceramics and electroceramics. Critical parameters for the process optimization, including the electromagnetic field distribution, microwave-material interaction, heat transfer mechanisms and material transformations, should be taken into consideration.

  15. Effects of sintering atmosphere on the physical and mechanical properties of modified BOF slag glass

    Science.gov (United States)

    Dai, Wen-bin; Li, Yu; Cang, Da-qiang; Zhou, Yuan-yuan; Fan, Yong

    2014-05-01

    This study proposes an efficient way to utilize all the chemical components of the basic oxygen furnace (BOF) slag to prepare high value-added glass-ceramics. A molten modified BOF slag was converted from the melting BOF slag by reducing it and separating out iron component in it, and the modified BOF slag was then quenched in water to form glasses with different basicities. The glasses were subsequently sintered in the temperature range of 600-1000°C in air or nitrogen atmosphere for 1 h. The effects of different atmospheres on the physical and mechanical properties of sintered samples were studied by using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) and by conducting experiment on evaluating the sintering shrinkage, water absorption and bulk density. It is found that the kinetics of the sintering process is significantly affected by sintering atmosphere. In particular, compared with sintering in air atmosphere, sintering in N2 atmosphere promotes the synergistic growth of pyroxene and melilite crystalline phases, which can contribute to better mechanical properties and denser microstructure.

  16. Nd:YAG transparent ceramics fabricated by direct cold isostatic pressing and vacuum sintering

    Science.gov (United States)

    Ge, Lin; Li, Jiang; Zhou, Zhiwei; Liu, Binglong; Xie, Tengfei; Liu, Jing; Kou, Huamin; Shi, Yun; Pan, Yubai; Guo, Jingkun

    2015-12-01

    The sintering behavior of neodymium doped yttrium aluminum garnet (Nd:YAG) ceramics was investigated on the basis of densification trajectory, microstructure evolution and transmittance. Nd:YAG ceramics with in-line transmittance of 83.9% at 1064 nm and 82.5% at 400 nm were obtained by direct cold isostatic pressing (CIP) at 250 MPa and solid-state reactive sintering at 1790 °C for 30 h under vacuum. Compared with the porosity and the average pore diameter of the sample from uniaxial dry-pressing followed by CIP, those from direct CIP are much smaller. The samples pressed at 250 MPa were sintered from 1500 °C to 1750 °C for 0.5-20 h to study their sintering behavior. At the temperature higher than 1500 °C, pure YAG phase is formed, followed by the densification and grain growth process. The relative density and the grain size increase with the increase of sintering time and temperature, and the sintering behavior is more sensitive to temperature than holding time. The mechanism controlling densification and grain growth at sintering temperature of 1550 °C is grain boundary diffusion.

  17. Sintering of micro-trusses created by extrusion-3D-printing of lunar regolith inks

    Science.gov (United States)

    Taylor, Shannon L.; Jakus, Adam E.; Koube, Katie D.; Ibeh, Amaka J.; Geisendorfer, Nicholas R.; Shah, Ramille N.; Dunand, David C.

    2018-02-01

    The development of in situ fabrication methods for the infrastructure required to support human life on the Moon is necessary due to the prohibitive cost of transporting large quantities of materials from the Earth. Cellular structures, consisting of a regular network (truss) of micro-struts with ∼500 μm diameters, suitable for bricks, blocks, panels, and other load-bearing structural elements for habitats and other infrastructure are created by direct-extrusion 3D-printing of liquid inks containing JSC-1A lunar regolith simulant powders, followed by sintering. The effects of sintering time, temperature, and atmosphere (air or hydrogen) on the microstructures, mechanical properties, and magnetic properties of the sintered lunar regolith micro-trusses are investigated. The air-sintered micro-trusses have higher relative densities, linear shrinkages, and peak compressive strengths, due to the improved sintering of the struts within the micro-trusses achieved by a liquid or glassy phase. Whereas the hydrogen-sintered micro-trusses show no liquid-phase sintering or glassy phase, they contain metallic iron 0.1-2 μm particles from the reduction of ilmenite, which allows them to be lifted with magnets.

  18. Synthesis of High Purity Sinterable Silicon Carbide Powder

    Science.gov (United States)

    1989-11-01

    10 G-500 TORCH 50 kW (Max) : kW (Derated) BTU/HR (Derated) RE, E-500 »CTOR/AFTERCOOLEP B70" .0X 72" T/T ISO M BTU/HR Copper B-500 DUST...Fourth and Canal Streets Post Office Box 27003 Richmond, VA 23219 137. Stephen C. Danforth Rutgers University Bowser Road Post Office Box 909

  19. Interfacial barrier height modification of indium tin oxide/a-Si:H(p) via control of density of interstitial oxygen for silicon heterojunction solar cell application

    Energy Technology Data Exchange (ETDEWEB)

    Ahn, Shihyun; Kim, Sunbo; Dao, Vinh Ai; Lee, Seungho; Iftiquar, S.M. [College of Information and Communication Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Gyeonggi-do 400-746 (Korea, Republic of); Kim, Doyoung [School of Electricity and Electronics, Ulsan College, Ulsan, 680-749 (Korea, Republic of); Hussain, Shahzada Qamar [Department of Energy Science, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Gyeonggi-do 400-746 (Korea, Republic of); Park, Hyeongsik; Lee, Jaehyeong [College of Information and Communication Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Gyeonggi-do 400-746 (Korea, Republic of); Lee, Youngseok [Department of Energy Science, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Gyeonggi-do 400-746 (Korea, Republic of); Cho, Jaehyun [College of Information and Communication Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Gyeonggi-do 400-746 (Korea, Republic of); Kim, Sangho [Department of Energy Science, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Gyeonggi-do 400-746 (Korea, Republic of); Yi, Junsin, E-mail: yi@yurim.skku.ac.kr [College of Information and Communication Engineering, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Gyeonggi-do 400-746 (Korea, Republic of); Department of Energy Science, Sungkyunkwan University, 300 Chunchun-dong, Jangan-gu, Suwon, Gyeonggi-do 400-746 (Korea, Republic of)

    2013-11-01

    An indium tin oxide (ITO) film with low carrier concentration (n), high mobility (μ) and high work function (Φ{sub ITO}) is a beneficial material for the front electrode in heterojunction silicon (HJ) solar cells due to its low free-carrier absorption in the near-infrared wavelength and low Schottky barrier height at the ITO/emitter-layer front contact. This low free-carrier absorption as well as the low Schottky barrier height increase the open-circuit voltage (V{sub oc}) and the short-circuit current density (J{sub sc}), which in turn increases the overall cell efficiency (η). Hence, ITO films with lower n, higher μ and higher Φ{sub ITO} were prepared by controlling the density of the interstitial oxygen [O{sub i}] in the films and used as anti-reflection electrodes in HJ solar cells. With increasing [O{sub i}] in the ITO, the preferential orientation of the (222) crystalline plane became more dominant. The Φ{sub ITO} and μ increased from 4.87 eV and 38.9 cm{sup 2} V{sup −1} s{sup −1} to 5.04 eV and 48.79 cm{sup 2} V{sup −1} s{sup −1}, respectively, whereas n decreased from 4.7 × 10{sup 20} cm{sup −3} to 2.8 × 10{sup 20} cm{sup −3}. We attribute these changes to the chemisorbed oxygen into the ITO films, while the decrease of n is due to the ability of interstitial oxygen to capture electron, and the increase of μ is due to the reduction in free-carrier scattering. These ITO films were used to fabricate HJ solar cells. As [O{sub i}] in the ITO film increased, the device performance improved and the best cell performance was obtained with V{sub oc} of 714 mV, J{sub sc} 34.79 mA/cm{sup 2} and η of 17.82%. By computer simulation, we found that the higher Φ{sub ITO} and μ but lower n were responsible for the enhanced cell performance. The cell performance, however, deteriorated due to poor film properties when [O{sub i}] exceeded concentration limit from 3.2 × 10{sup 20} cm{sup −3}. - Highlights: • The carrier concentration (n) decreases

  20. Sintering of Si C by hot-pressing with addition of Al2O3 and concentrate of rare earths

    International Nuclear Information System (INIS)

    Hwang, M.K.; Silva, C.R.M.

    2004-01-01

    Silicon carbide (SiC) has essentially covalent bonds (∼88%). The high covalency bond is responsible for the good mechanical properties, although it induces a low self diffusion coefficient, making densification more difficult. For a successful densification is necessary to apply pressure on the samples, and/or the addition of sintering additives, which improves the densification. In this SiC samples with alumina (Al2O3) and concentrate of rare earth (CRE) addition were sintered by hot pressing in argon atmospheric at 20 MPa of pressure, heating rate of 20 deg C/min up to 1800 deg C and a dwell time of 1 h. Initially the CRE was calcined at 1000 deg C during 1 h. After that, three mixtures were prepared with distinct concentrations in high energy mill and the samples were sintered. The aim of this work is to improve SiC densification by the liquid phase formation during sintering owing to the additives reactions between itself. The pressure intensify the driving force for densification, taking the liquid phase to drain easier through the grain boundaries, making possible best accommodation and rearrangement of the grains. The application of the pressure on the samples during sintering contributes to improve densification and becomes possible sintering in lower temperature than conventional one. The phases of the sintered samples were analyzed by X-ray diffraction and the morphology were verified by scanning electron microscopy. (author)

  1. On the Mechanism of Microwave Flash Sintering of Ceramics

    Directory of Open Access Journals (Sweden)

    Yury V. Bykov

    2016-08-01

    Full Text Available The results of a study of ultra-rapid (flash sintering of oxide ceramic materials under microwave heating with high absorbed power per unit volume of material (10–500 W/cm3 are presented. Ceramic samples of various compositions—Al2O3; Y2O3; MgAl2O4; and Yb(LaO2O3—were sintered using a 24 GHz gyrotron system to a density above 0.98–0.99 of the theoretical value in 0.5–5 min without isothermal hold. An analysis of the experimental data (microwave power; heating and cooling rates along with microstructure characterization provided an insight into the mechanism of flash sintering. Flash sintering occurs when the processing conditions—including the temperature of the sample; the properties of thermal insulation; and the intensity of microwave radiation—facilitate the development of thermal runaway due to an Arrhenius-type dependency of the material’s effective conductivity on temperature. The proper control over the thermal runaway effect is provided by fast regulation of the microwave power. The elevated concentration of defects and impurities in the boundary regions of the grains leads to localized preferential absorption of microwave radiation and results in grain boundary softening/pre-melting. The rapid densification of the granular medium with a reduced viscosity of the grain boundary phase occurs via rotation and sliding of the grains which accommodate their shape due to fast diffusion mass transport through the (quasi-liquid phase. The same mechanism based on a thermal runaway under volumetric heating can be relevant for the effect of flash sintering of various oxide ceramics under a dc/ac voltage applied to the sample.

  2. Spark plasma sintering and microwave electromagnetic properties of MnFe{sub 2}O{sub 4} ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Penchal Reddy, M., E-mail: drlpenchal@gmail.com [Center for Advanced Materials, Qatar University, Doha 2713 (Qatar); Mohamed, A.M.A. [Center for Advanced Materials, Qatar University, Doha 2713 (Qatar); Department of Metallurgical and Materials Engineering, Faculty of Petroleum and Mining Engineering, Suez University, Suez 4372 (Egypt); Venkata Ramana, M. [Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan (China); Zhou, X.B.; Huang, Q. [Division of Functional Materials and Nanodevices, Ningbo Institute of Materials Technology and Engineering, Ningbo 315201 (China)

    2015-12-01

    MnFe{sub 2}O{sub 4} ferrite powder was synthesized by a facile one-pot hydrothermal route and then consolidated into dense nanostructured compacts by the spark plasma sintering (SPS) technique. The effect of sintering temperature, on densification, morphology, magnetic and microwave absorption properties was examined. Spark plasma sintering resulted in uniform microstructure, as well as maximum relative density of 98%. The magnetic analysis indicated that the MnFe{sub 2}O{sub 4} ferrite nanoparticles showed ferrimagnetic behavior. Moreover, the dielectric loss and magnetic loss properties of MnFe{sub 2}O{sub 4} ferrite nanoparticles were both enhanced due to its better dipole polarization, interfacial polarization and shape anisotropy. It is believed that such spark plasma sintered ceramic material will be applied widely in microwave absorbing area. - Highlights: • Successful synthesis of dense MnFe{sub 2}O{sub 4} ceramics using spark plasma sintering. • Lower temperature and shorter sintering time, compared to conventional methods. • Optimal sintering condition was achieved. • The magnetic properties of the sintered samples are sensitive to the density and microstructure.

  3. Effects of silicon carbide on the phase developments in mullite-carbon ceramic composite

    Directory of Open Access Journals (Sweden)

    Fatai Olufemi ARAMIDE

    2017-12-01

    Full Text Available The effects of the addition of silicon carbide and sintering temperatures on the phases developed, in sintered ceramic composite produced from kaolin and graphite was investigated. The kaolin and graphite of known mineralogical composition were thoroughly blended with 4 and 8 vol % silicon carbide. From the homogeneous mixture of kaolin, graphite and silicon carbide, standard samples were prepared via uniaxial compaction. The test samples produced were subjected to firing (sintering at 1300°C, 1400°C and 1500°C. The sintered samples were characterized for the developed phases using x‐ray diffractometry analysis, microstructural morphology using ultra‐high resolution field emission scanning electron microscope (UHRFEGSEM. It was observed that microstructural morphology of the samples revealed the evolution of mullite, cristobalite and microcline. The kaolinite content of the raw kaolin undergoes transformation into mullite and excess silica, the mullite and the silica phases contents increased with increased sintering temperature. It is also generally observed that the graphite content progressively reduced linearly with increased sintering temperature. It is concluded that silicon carbide acts as anti-oxidant for the graphite, this anti-oxidant effect was more effective at 4 vol % silicon carbide.

  4. Effect of bioglass additions on the sintering of Y-TZP bioceramics

    Energy Technology Data Exchange (ETDEWEB)

    Habibe, A.F.; Maeda, L.D.; Souza, R.C.; Barboza, M.J.R.; Daguano, J.K.M.F. [USP-EEL, Universidade de Sao Paulo, Escola de Engenharia de Lorena, Polo Urbo-Industrial, Gleba AI6, s/n, P.O. Box 116, CEP 12600-970, Lorena-SP (Brazil); Rogero, S.O. [IPEN/CNEN-SP, Instituto de Pesquisas Energeticas e Nucleares, Av. Prof. Lineu Prestes, 2242, Sao Paulo-SP, CEP 05508-900 (Brazil); Santos, C., E-mail: claudinei@demar.eel.usp.br [USP-EEL, Universidade de Sao Paulo, Escola de Engenharia de Lorena, Polo Urbo-Industrial, Gleba AI6, s/n, P.O. Box 116, CEP 12600-970, Lorena-SP (Brazil)

    2009-08-01

    The objective of this work was to evaluate the influence of bioglass additions on the sintering and mechanical properties of yttria-stabilized zirconia ceramics, Y-TZP. Samples containing different bioglass additions, varying between 0 and 30 wt.%, were cold uniaxial pressed at 80 MPa and sintered in air at 1200 deg. C or 1300 deg. C for 120 min. Sintered samples were characterized by X-ray Diffractometry and Scanning Electron Microscopy. Hardness and fracture toughness were determined using Vickers indentation method. As a preliminary biological evaluation, in vitro cytotoxicity tests by Neutral Red Uptake method (using mouse connective tissue cells, NCTC clone L929 from ATCC bank) were realized to determine the cytotoxicity level of ZrO{sub 2}-bioglass ceramics. The increasing of bioglass amount leads to the decreasing of relative density due to martensitic (tetragonal-monoclinic) transformation during cooling of the sintered samples. Y-TZP samples sintered at 1300 deg. C containing 5 wt.% of bioglass presented the best results, with high relative density, hardness and fracture toughness of 11.3 GPa and 6.1 MPa m{sup 1/2}, respectively. Furthermore, the un-cytotoxic behavior was observed in all sintering conditions and bioglass amounts used in this study.

  5. Effect of Sintering Temperature on the Properties of Aluminium-Aluminium Oxide Composite Materials

    Directory of Open Access Journals (Sweden)

    Dewan Muhammad Nuruzzaman

    2016-12-01

    Full Text Available In this study, aluminium-aluminium oxide (Al-Al2O3 metal matrix composites of different weight percentage reinforcements of aluminium oxide were processed at different sintering temperatures. In order to prepare these composite specimens, conventional powder metallurgy (PM method was used. Three types specimens of different compositions such as 95%Al+5%Al2O3, 90%Al+10%Al2O3 and 85%Al+15%Al2O3 were prepared under 20 Ton compaction load. Then, all the specimens were sintered in a furnace at two different temperatures 550oC and 580oC. In each sintering process, two different heating cycles were used. After the sintering process, it was observed that undistorted flat specimens were successfully prepared for all the compositions. The effects of sintering temperature and weight fraction of aluminium oxide particulates on the density, hardness and microstructure of Al-Al2O3 composites were observed. It was found that density and hardness of the composite specimens were significantly influenced by sintering temperature and percentage aluminium oxide reinforcement. Furthermore, optical microscopy revealed that almost uniform distribution of aluminium oxide reinforcement within the aluminium matrix was achieved.

  6. Microstructural evaluation of the NbC-20Ni cemented carbides during sintering

    International Nuclear Information System (INIS)

    Rodrigues, D.; Cannizza, E.

    2016-01-01

    Full text: Fine carbides in a metallic matrix (binder) form the microstructure of the cemented carbides. Grain size and binder content are the main variables to adjust hardness and toughness. These products are produced by Powder Metallurgy, and traditional route involves mixing carbides with binder by high energy milling, pressing and sintering. During sintering, a liquid phase promotes densification, and a final relative density higher than 99% is expected. Sintering is carried out at high temperatures, and dissolution of the carbides changes the chemical composition of the binder. To control grain growth of the main carbide, which reduces hardness, small quantities of secondary carbides are used. These additives limit dissolution and precipitation of the main carbides reducing the final grain size. This paper focused the structural and chemical evolution during sintering using NbC-20Ni cermets. Mixtures of very fine NbC carbides and carbonyl Ni powders were produce by intense milling. These mixtures were pressed using uniaxial pressures from 50 to 200MPa. Shrinkage was evaluated using dilatometric measurements under an atmosphere of dynamic argon. Samples were also sintered under vacuum in high temperature industrial furnace. The sintered samples were characterized in terms of density hardness, toughness and microstructure. DRX was the main tool used to evaluate the structural evolution of the binder. In situ chemical analysis helped to understand the dissolution mechanisms. (author)

  7. Effects of Admixed Titanium on Densification of 316L Stainless Steel Powder during Sintering

    Directory of Open Access Journals (Sweden)

    Aslam Muhammad

    2014-07-01

    Full Text Available Effects of admixed titanium on powder water atomized (PWA and powder gas atomized (PGA 316L stainless steel (SS have been investigated in terms of densification. PGA and PWA powders, having different shapes and sizes, were cold pressed and sintered in argon atmosphere at 1300°C. The admixed titanium compacts of PGA and PWA have shown significant effect on densification through formation of intermetallic compound and reducing porosity during sintering process. PWA, having particle size 8 μm, blended with 1wt% titanium has exhibited higher sintered density and shrinkage as compared to gas atomized powder compacts. Improved densification of titanium blended PGA and PWA 316L SS at sintering temperature 1300°C is probably due to enhanced diffusion kinetics resulting from stresses induced by concentration gradient in powder compacts.

  8. Material Evaluation and Process Optimization of CNT-Coated Polymer Powders for Selective Laser Sintering

    Directory of Open Access Journals (Sweden)

    Shangqin Yuan

    2016-10-01

    Full Text Available Multi-walled carbon nanotubes (CNTs as nano-reinforcements were introduced to facilitate the laser sintering process and enhance the thermal and mechanical properties of polymeric composites. A dual experimental-theoretical method was proposed to evaluate the processability and predict the process parameters of newly developed CNT-coated polyamide 12 (CNTs/PA12 powders. The thermal conductivity, melt viscosity, phase transition and temperature-dependent density and heat capacity of PA12 and CNTs/PA12 powders were characterized for material evaluation. The composite powders exhibited improved heat conduction and heat absorption compared with virgin polymer powders, and the stable sintering range of composite powders was extended and found to be favourable for the sintering process. The microstructures of sintered composites revealed that the CNTs remained at the powder boundaries and formed network architectures, which instantaneously induced the significant enhancements in tensile strength, elongation at break and toughness without sacrificing tensile modulus.

  9. Microstructure and properties of gravity sintered 316l stainless steel powder with nickel boride addition

    Directory of Open Access Journals (Sweden)

    Božić Dušan

    2016-01-01

    Full Text Available The present work demonstrates a procedure for synthesis of stainless steel powder by gravity sintering method. As an additive to the basic powder, NiB powder was added in the amount of 0.2 - 1.0 wt.%. Gravity sintering was done in vacuum, at the temperatures of 1100°C-1250°C, in the course of 3 - 60 min, using ceramic mould. Structural characterization was conducted by XRD, and microstructural analysis by optical and scanning electron microscope (SEM. Mechanical properties were investigated by tensile tests with steel rings. Density and permeability were determined by standard techniques for porous samples. Gravity sintered stainless steel with NiB addition had more superior mechanical and physico-chemical properties compared to stainless steel obtained by standard powder metallurgy procedures - pressing and sintering. [Projekat Ministarstva nauke Republike Srbije, br. 172005

  10. The role of the native oxide shell on the microwave sintering of copper metal powder compacts

    International Nuclear Information System (INIS)

    Mahmoud, Morsi M.; Link, Guido; Thumm, Manfred

    2015-01-01

    Highlights: • Thin oxide native layer had a critical role on microwave sintering of copper. • Explain why microwaves interact with copper powder differently than its bulk. • Abnormal expansion in copper is due to the plastic deformation and crack formation. • In-situ setup gives important insight about the microwave sintering of metals. • Microwave sintering is a promising candidate technology in powder metallurgy. - Abstract: Successful microwave sintering of several metal powders had been reported by many researchers with remarkable improvements in the materials properties and/or in the overall process. However, the concept behind microwave heating of metal powders has not been fully understood till now, as it is well known that bulk metals reflect microwaves. The progress of microwave sintering of copper metal powder compacts was investigated via combining both in-situ electrical resistivity and dilatometry measurements that give important information about microstructural changes with respect to the inter-particle electrical contacts during sintering. The sintering behavior of copper metal powders was depending on the type of the gas used, particle size, the initial green density, the soaking sintering time and the thin oxide layer on the particles surfaces. The thin copper oxide native layer (ceramics) that thermodynamically formed on the particles surfaces under normal handling and ambient environmental conditions had a very critical and important role in the microwave absorption and interaction, the sintering behavior and the microstructural changes. This finding could help to have a fundamental understanding of why MW’s interact with copper metal powder in a different way than its bulk at room temperature, i.e. why a given metal powder could be heated using microwaves while its bulk reflects it

  11. Production of sintered alumina from powder; optimization of the sinterized parameters for the maximum mechanical resistence

    International Nuclear Information System (INIS)

    Rocha, J.C. da.

    1981-02-01

    Pure, sinterized alumina and the optimization of the parameters of sinterization in order to obtain the highest mechanical resistence are discussed. Test materials are sinterized from a fine powder of pure alumina (Al 2 O 3 ), α phase, at different temperatures and times, in air. The microstructures are analysed concerning porosity and grain size. Depending on the temperature or the time of sinterization, there is a maximum for the mechanical resistence. (A.R.H.) [pt

  12. Mineralogy and microstructure of sintered lignite coal fly ash

    Energy Technology Data Exchange (ETDEWEB)

    Marina Ilic; Christopher Cheeseman; Christopher Sollars; Jonathan Knight [Faculty of Technology and Metallurgy, Belgrade (Yugoslavia)

    2003-02-01

    Lignite coal fly ash from the 'Nikola Tesla' power plant in Yugoslavia has been characterised, milled, compacted and sintered to form monolithic ceramic materials. The effect of firing at temperatures between 1130 and 1190{sup o}C on the density, water accessible porosity, mineralogy and microstructure of sintered samples is reported. This class C fly ash has an initial average particle size of 82 {mu}m and contains siliceous glass together with the crystalline phases quartz, anorthite, gehlenite, hematite and mullite. Milling the ash to an average particle size of 5.6 m, compacting and firing at 1170{sup o}C for 1 h produces materials with densities similar to clay-based ceramics that exhibit low water absorption. Sintering reduces the amount of glass, quartz, gehlenite and anhydrite, but increases formation of anorthite, mullite, hematite and cristobalite. SEM confirms the formation of a dense ceramic at 1170{sup o}C and indicates that pyroplastic effects cause pore formation and bloating at 1190{sup o}C. 23 refs., 6 figs., 2 tabs.

  13. Photovoltaic characteristics of porous silicon /(n+ - p) silicon solar cells

    International Nuclear Information System (INIS)

    Dzhafarov, T.D.; Aslanov, S.S.; Ragimov, S.H.; Sadigov, M.S.; Nabiyeva, A.F.; Yuksel, Aydin S.

    2012-01-01

    Full text : The purpose of this work is to improve the photovoltaic parameters of the screen-printed silicon solar cells by formation the nano-porous silicon film on the frontal surface of the cell. The photovoltaic characteristics of two type silicon solar cells with and without porous silicon layer were measured and compared. A remarkable increment of short-circuit current density and the efficiency by 48 percent and 20 percent, respectively, have been achieved for PS/(n + - pSi) solar cell comparing to (n + - p)Si solar cell without PS layer

  14. Alternative sintering methods compared to conventional thermal sintering for inkjet printed silver nanoparticle ink

    NARCIS (Netherlands)

    Niittynen, J.; Abbel, R.; Mäntysalo, M.; Perelaer, J.; Schubert, U.S.; Lupo, D.

    2014-01-01

    In this contribution several alternative sintering methods are compared to traditional thermal sintering as high temperature and long process time of thermal sintering are increasing the costs of inkjet-printing and preventing the use of this technology in large scale manufacturing. Alternative

  15. Engineering piezoresistivity using biaxially strained silicon

    DEFF Research Database (Denmark)

    Pedersen, Jesper Goor; Richter, Jacob; Brandbyge, Mads

    2008-01-01

    of the piezocoefficient on temperature and dopant density is altered qualitatively for strained silicon. In particular, we find that a vanishing temperature coefficient may result for silicon with grown-in biaxial tensile strain. These results suggest that strained silicon may be used to engineer the iezoresistivity...

  16. The influence of the milling environment on the sintered structure of a W-Cu composite

    International Nuclear Information System (INIS)

    Costa, F.A.; Gomes, U.U.; Acchar, W.; Ambrozio Filho, F.; Silva, A.G.P.; Lima, S.J.G.

    2009-01-01

    This work reports an investigation about the influence of the environment of milling on the characteristics of the powders and on the structure and density of sintered samples made of these powders. Mixtures of composition W-30wt%Cu were milled for 51 hours in a high energy planetary mill in dry and wet (cyclohexane) conditions. The milled powders have composite particles. The powders were pressed and sintered at 1050 deg, 1150 deg and 1200 deg C under flowing hydrogen. The isothermal times were 0 minutes for the first two temperatures and 60 minutes for the latter. The samples reached around 95% of relative density. The powders were characterized by means of XRD and SEM. The sintered samples were characterized by means of SEM, optical microscopy and density measurement. (author)

  17. Sintering of cermets on the base of corundum and molybdenum

    International Nuclear Information System (INIS)

    Fedotov, A.V.

    1987-01-01

    Liquid-phase sintering of cermets has been studied to develop rational technology allowing to produce a dense material at lower temperatures. Molybdenum of the MPCh mark with the specific surface ranged from 1900 to 4000 cm 2 /g and the corundum powder of the VK-94-1 mark with the specific surface of 6000 cm 2 /g containing upto 10% of the glass-phase have been used as initial materials. It is shown that application of the VK-94-1 ceramics powder for molybdenum content cermets allows to decrease the temperature of dense material production (∼ upto 100 deg C). To produce dense materials, it is necessary to restrict the initial porosity of compaction and to correspond it to the sintering conditions. The increase of molybdenum dispersion allows to produce material with the more homogeneous structure, higher density and strength. Molybdenum presence decreases recrystallization of corundum crystals and causes structure production resistant to high-temperature heating

  18. Silicon detectors

    International Nuclear Information System (INIS)

    Klanner, R.

    1984-08-01

    The status and recent progress of silicon detectors for high energy physics is reviewed. Emphasis is put on detectors with high spatial resolution and the use of silicon detectors in calorimeters. (orig.)

  19. Nitrogen implantation into silicon at 700-1100 deg C

    International Nuclear Information System (INIS)

    Kachurin, G.A.; Tyschenko, I.E.; Popov, V.P.; Tijs, S.A.; Plotnikov, A.E.

    1989-01-01

    Nitrogen ions 130-140 kW potential accelerated were implanted in silicon heated up to Ti=700-1100 deg C. Densities of ion current were 1-5 mcA/cm 2 , doses did not exceed 5x10 17 cm -2 . Initial stages of nitride formation in buried layers are investigated by means of Rutherford backscattering, layer-by-layer Augerspctroscopy and electron microscopy. It is determind, that Ti growth from 700 up to 900 deg C is accompanied by essential reduction of defectiveness of silicon near-the-surface layer at nitrogen retention within the limits of the calculation profile of ion ranges. At Ti=900 deg C nitrogen is rather mobile and at ∼5x10 16 cm -2 dose it is drown to α-Si 3 N 4 crystalling extraction in R p range. Beginning from Ti ≅1000 deg C nitrogen is not retained in the furied layer and diffuses to the surface. No essenstial losses of nitrogen due to evaporation or inside diffusion are observed. It is noted, that critical Ti, when nitrogen is accumulated in the buried layer, correspond to critical temperatures, when light ions introduce essential structure distortions. Conclusion is made, that irradition-introduced distortions of structure represent centres of initiation and growth of nitride phase. At 1150 deg C additional annaling during 3 hs nitrogen, occurring outside the stable extraction, is redistributed between th surface and furied layers, sintering in narrow concentration peaks

  20. Studies of ZrO2-Y2O3 ceramics properties sintered in conventional and microwave oven

    International Nuclear Information System (INIS)

    Gelfuso, M.V.; Capistrano, D.; Thomazini, D.; Grzebielucka, E.C.; Chinelatto, A.L.; Chinelatto, A.S.A.

    2009-01-01

    The ceramic materials processing with nano grain size has developed materials with new properties or improves some of its existing properties. To obtain ceramics with nano grain size, besides that to obtaining nanometric powders, a major goal is to keep the grains size after sintering. Contributing in this line of research, this study aimed to sinter zirconia-Yttria powders through two processes: conventional and microwave sintering. Zirconia stabilized with Yttria powders were obtained by chemical route based on Pechini method. Cylindrical samples were sintered between 1300 to 1500 deg C between 10 and 40 minutes. The samples were characterized by Xray diffraction, Scanning Electron Microscopy and apparent density. It was observed that the final microstructure is influenced by both methods of sintering as the curve of firing used. (author)

  1. Implementation of a spark plasma sintering facility in a hermetic glovebox for compaction of toxic, radiotoxic, and air sensitive materials

    Energy Technology Data Exchange (ETDEWEB)

    Tyrpekl, V., E-mail: vaclav.tyrpekl@ec.europa.eu, E-mail: vaclav.tyrpekl@gmail.com; Berkmann, C.; Holzhäuser, M.; Köpp, F.; Cologna, M.; Somers, J. [European Commission, Joint Research Centre (JRC), Institute for Transuranium Elements (ITU), Postfach 2340, 76125 Karlsruhe (Germany); Wangle, T. [European Commission, Joint Research Centre (JRC), Institute for Transuranium Elements (ITU), Postfach 2340, 76125 Karlsruhe (Germany); Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Břehová 7, Praha 1, 115 19 (Czech Republic)

    2015-02-15

    Spark plasma sintering (SPS) is a rapidly developing method for densification of powders into compacts. It belongs to the so-called “field assisted sintering techniques” that enable rapid sintering at much lower temperatures than the classical approaches of pressureless sintering of green pellets or hot isostatic pressing. In this paper, we report the successful integration of a SPS device into a hermetic glovebox for the handling of highly radioactive material containing radioisotopes of U, Th, Pu, Np, and Am. The glovebox implantation has been facilitated by the replacement of the hydraulic system to apply pressure with a compact electromechanical unit. The facility has been successfully tested using UO{sub 2} powder. Pellets with 97% of the theoretical density were obtained at 1000 °C for 5 min, significantly lower than the ∼1600 °C for 5-10 h used in conventional pellet sintering.

  2. Room-temperature saturated ferroelectric polarization in BiFeO3 ceramics synthesized by rapid liquid phase sintering

    International Nuclear Information System (INIS)

    Wang, Y.P.; Zhou, L.; Zhang, M.F.; Chen, X.Y.; Liu, J.-M.; Liu, Z.G.

    2004-01-01

    Single-phased ferroelectromagnet BiFeO 3 ceramics with high resistivity were synthesized by a rapid liquid phase sintering technique. Saturated ferroelectric hysteresis loops were observed at room temperature in the ceramics sintered at 880 deg. C for 450 s. The spontaneous polarization, remnant polarization, and the coercive field are 8.9 μC/cm 2 , 4.0 μC/cm 2 , and 39 kV/cm, respectively, under an applied field of 100 kV/cm. It is proposed that the formation of Fe 2+ and an oxygen deficiency leading to the higher leakage can be greatly suppressed by the very high heating rate, short sintering period, and liquid phase sintering technique. The latter was also found effective in increasing the density of the ceramics. The sintering technique developed in this work is expected to be useful in synthesizing other ceramics from multivalent or volatile starting materials

  3. The effect of lanthanum boride on the sintering, sintered microstructure and mechanical properties of titanium and titanium alloys

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Y.F. [RMIT University, Centre for Additive Manufacturing, School of Aerospace, Mechanical and Manufacturing Engineering, GPO Box 2476, Melbourne VIC 3001 (Australia); Luo, S.D. [The University of Queensland, School of Mechanical and Mining Engineering, Brisbane, QLD 4072 (Australia); Qian, M., E-mail: ma.qian@rmit.edu.au [RMIT University, Centre for Additive Manufacturing, School of Aerospace, Mechanical and Manufacturing Engineering, GPO Box 2476, Melbourne VIC 3001 (Australia)

    2014-11-17

    An addition of ≤0.5 wt% lanthanum boride (LaB{sub 6}) to powder metallurgy commercially pure Ti (CP-Ti), Ti–6Al–4V and Ti–10V–2Fe–3Al (all in wt%) resulted in improved sintered density, substantial microstructural refinement, and noticeably increased tensile elongation. The addition of LaB{sub 6} led to scavenging of both oxygen (O) and chlorine (Cl) from the titanium powder during sintering, evidenced by the formation of La{sub 2}O{sub 3} and LaCl{sub x}O{sub y}. The pinning effect of La{sub 2}O{sub 3}, LaCl{sub x}O{sub y} and TiB inhibited prior-β grain growth and resulted in subsequent smaller α-laths. The formation of nearly equiaxed α-Ti phase is partially attributed to the nucleation effect of α-Ti on TiB. The improved sintered density was caused by B from LaB{sub 6} rather than La, while excessive formation of La{sub 2}O{sub 3} and TiB with an addition of >0.5 wt% LaB{sub 6} resulted in a noticeable decrease in sintered density. The improved tensile elongation with an addition of ≤0.5 wt% LaB{sub 6} was mainly attributed to the scavenging of oxygen by LaB{sub 6}, partially assisted by the improved sintered density. However, an addition of >0.5 wt% LaB{sub 6} led to the formation of large La{sub 2}O{sub 3} aggregates and more brittle TiB whiskers and therefore decreased tensile elongation. Balanced scavenging of O is thus important. The optimal addition of LaB{sub 6} was 0.5 wt% but this may change depending on the powder size of the LaB{sub 6} to be used.

  4. Characterization and properties of sintered WC–Co and WC–Ni–Fe hard metal alloys

    International Nuclear Information System (INIS)

    Chang, Shih-Hsien; Chen, Song-Ling

    2014-01-01

    Highlights: • WC–Ni–Fe alloy sintered at 1400 °C had the highest hardness (HRA 85.3 ± 0.5). • The optimal WC–Ni–Fe sintered alloy possessed the highest TRS value (2524.5 ± 1.0 MPa). • The fracture toughness of the sintered WC–Ni–Fe alloys is mainly provided by the Ni–Fe binders. • WC–Ni–Fe sintered alloy possessed the highest fracture toughness of K IC (15.1 MPa m 1/2 ). • The WC–Ni–Fe sintered alloy had the much better corrosion resistance in 0.15 M HCl solution. -- Abstract: The aim of this study is to explore two different tungsten carbide binders (Co and Ni–Fe) and then impose various sintering temperature treatments. Experimental results show that the optimal sintering temperatures for WC–Co and WC–Ni–Fe hard metal alloys are 1350 °C and 1400 °C for 1 h, respectively. Meanwhile, the WC–Co and WC–Ni–Fe alloys undergo a well liquid-phase sintering and, thus, exhibit excellent mechanical properties. In addition, the sintered WC–Co and WC–Ni–Fe alloys show that when the relative density reached 99.76% and 99.68%, the hardness was enhanced to HRA 84.4 ± 0.5 and 85.3 ± 0.5, and the TRS increased to 2471.2 ± 1.0 and 2524.5 ± 1.0 MPa, respectively. Moreover, the corrosion test results show that the WC–Ni–Fe alloy sintered at 1400 °C had the lowest corrosion current (I corr ) of 1.11 × 10 −5 A cm −2 and the highest polarization resistance (R p ) of 2464.61 Ω cm 2 in 0.15 M HCl solution. Simultaneously, the fracture toughness of K IC increased to 15.1 MPa m 1/2 . Compared with sintered WC–Co alloys, the sintered WC–Ni–Fe hard metal alloys possessed much better corrosion resistance and mechanical properties

  5. Optimization of time–temperature schedule for nitridation of silicon ...

    Indian Academy of Sciences (India)

    pact was optimized by kinetic study of the reaction, 3Si + 2N2 = Si3N4 at four different temperatures (1250°C,. 1300°C, 1350°C and 1400°C). ... Reaction sintered silicon nitride; nitridation; reaction kinetics. 1. Introduction. Formation of ..... cation of silica layer resulted in active oxidation of silicon at high temperature to ...

  6. A finite difference model of the iron ore sinter process

    OpenAIRE

    Muller, J.; de Vries, T.L.; Dippenaar, B.A.; Vreugdenburg, J.C.

    2015-01-01

    Iron ore fines are agglomerated to produce sinter, which is an important feed material for blast furnaces worldwide. A model of the iron ore sintering process has been developed with the objective of being representative of the sinter pot test, the standard laboratory process in which the behaviour of specific sinter feed mixtures is evaluated. The model aims to predict sinter quality, including chemical quality and physical strength, as well as key sinter process performance parameters such ...

  7. Silicon epitaxy on textured double layer porous silicon by LPCVD

    International Nuclear Information System (INIS)

    Cai Hong; Shen Honglie; Zhang Lei; Huang Haibin; Lu Linfeng; Tang Zhengxia; Shen Jiancang

    2010-01-01

    Epitaxial silicon thin film on textured double layer porous silicon (DLPS) was demonstrated. The textured DLPS was formed by electrochemical etching using two different current densities on the silicon wafer that are randomly textured with upright pyramids. Silicon thin films were then grown on the annealed DLPS, using low-pressure chemical vapor deposition (LPCVD). The reflectance of the DLPS and the grown silicon thin films were studied by a spectrophotometer. The crystallinity and topography of the grown silicon thin films were studied by Raman spectroscopy and SEM. The reflectance results show that the reflectance of the silicon wafer decreases from 24.7% to 11.7% after texturing, and after the deposition of silicon thin film the surface reflectance is about 13.8%. SEM images show that the epitaxial silicon film on textured DLPS exhibits random pyramids. The Raman spectrum peaks near 521 cm -1 have a width of 7.8 cm -1 , which reveals the high crystalline quality of the silicon epitaxy.

  8. Sintering of powders obtained by mechanical alloying of Cu-1.2 Al w%, Cu-2.3 Ti w% and Cu-2.7 V w%

    International Nuclear Information System (INIS)

    Rivas, C; Sepulveda, A; Zuniga, A; Donoso, E; Palma, R

    2008-01-01

    This work studies the effect of compacting pressure, temperature and sintering time on density and microstructure after sintering mechanically alloyed powders of Cu-1.2 Al w%, Cu- 2.3 Ti w% and Cu-2.7 V w%. The alloys were manufactured from elementary powders of Cu, Ti, Al and V, by reactive milling. The powders were compacted and sintered under reducer atmosphere. For each alloy, the final density and resulting microstructure of 8 different compacting and sintering conditions were studied, where the following parameters were considered: (1) Compacting pressure (200 MPa and 400 MPa), (2) Sintering temperature (850 o C and 950 o C), (3) Sintering time (1h and 4h). Adjustments were made using lineal regression to describe the effect of the variation of pressure, temperature and time on the density of the materials obtained, and the morphology of the residual porosity was described by observation under an optic microscope. The final maximum density obtained was, in ascending order: Cu-V, 66% of the theoretical density, TD; Cu-Ti, 65% TD and Cu-Al, 77% TD. The reactive milling process produced flake-shaped particles, hardened by deformation, which made the alloys have a final density that was much less than the sintered pure copper (density 87% TD). This is because the hardened powder resists deformation during compacting, which creates less points of contact between particles, slows down sintering, and yields a lower density. The alloying element influenced the size of the particle obtained during the milling, which is attributed to the different milling mediums (toluene for Ti and V, methanol for Al) and to the different hardness of each ceramic when forming in the copper during milling. The bigger the particle size, the greater the green density, the lesser the densification, and the greater the final density, in accordance with the theory. For the three alloys, the increased compacting pressure gives greater green density, greater densification and a final greater

  9. Processing of pure titanium containing titanium-based reinforcing ceramics additives using spark plasma sintering

    Directory of Open Access Journals (Sweden)

    Mondiu Olayinka DUROWOJU

    2017-06-01

    Full Text Available The densification behaviour, microstructural changes and hardness characteristics during spark plasma sintering of CP-Ti reinforced with TiC, TiN, TiCN and TiB2 were investigated. Commercially pure Ti powders were dry mixed with varied amounts (2.5 and 5 wt. % of the ceramic additives using a T2F Turbula mixer for 5 h and at a speed of 49 rpm. The blended composite powders were then sintered using spark plasma sintering system (model HHPD-25 from FCT Germany at a heating rate of 100oC min-1, dwell time of 5 min and sintering temperature of 950ºC. The sintering of CP-Ti was used as a base study to select the proper spark plasma sintering temperature for full density. Densification was monitored through analysis of the recorded punch displacement and the measured density of the sintered samples using Archimedes method. High densities ranging from 97.8% for 5% TiB2 addition to 99.6% for 5% TiCN addition were achieved at a relatively low temperature of 950°C. Microstructural analyses show a uniform distribution of the additives and finer structure showing their inhibitive effect on grain growth. An improved hardness was observed in all the cases with highest values obtained with TiCN as a result of the combined effect of TiC and TiN. A change in the fracture mode from trans granular to intergranular was also observed.

  10. Sintering characteristics of nano-ceramic coatings

    NARCIS (Netherlands)

    de Hosson, J.T.M.; Popma, R.

    2003-01-01

    This paper concentrates on sintering characteristics of nano-sized ceramic SiO2 particles. The sintering process is studied as a function of temperature using a conventional furnace and using a laser beam. The underlying idea is to combine the nanoceramic sol-gel concept with inkjet technology and

  11. Thermally stable sintered porous metal articles

    International Nuclear Information System (INIS)

    Gombach, A.L.; Thellmann, E.L.

    1980-01-01

    A sintered porous metal article is provided which is essentially thermally stable at elevated temperatures. In addition, a method for producing such an article is also provided which method comprises preparing a blend of base metal particles and active dispersoid particles, forming the mixture into an article of the desired shape, and heating the so-formed article at sintering temperatures

  12. Sintering of ultra high molecular weight polyethylene

    Indian Academy of Sciences (India)

    Abstract. Ultra high molecular weight polyethylene (UHMWPE) is a high performance polymer having low coefficient of friction, good abrasion resistance, good chemical ... In this study, we report our results on compaction and sintering behaviour of two grades of UHMWPE with reference to the powder morphology, sintering ...

  13. Recrystallization and embrittlement of sintered tungsten

    International Nuclear Information System (INIS)

    Bega, N.D.; Babak, A.V.; Uskov, E.I.

    1982-01-01

    The recrystallization of sintered tungsten with a cellular structure of deformation is studied as related to its embrittlement. It is stated that in case of preliminary recrystallization the sintered tungsten crack resistance does not depend on the testing temperature. The tungsten crack resistance is shown to lower with an increase of the structure tendency to primary recrystallization [ru

  14. Master sintering curves of two different alumina powder compacts

    Directory of Open Access Journals (Sweden)

    Vaclav Pouchly

    2009-12-01

    Full Text Available Concept of Master Sintering Curve is a strong tool for optimizing sintering schedule. The sintering behaviour can be predicted, and sintering activation energy can be calculated with the help of few dilatometric measurements. In this paper an automatic procedure was used to calculate Master Sintering Curves of two different alumina compacts. The sintering activation energies were determined as 640 kJ/mol for alumina with particle size of 240 nm, respective 770 kJ/mol for alumina with particle size of 110 nm. The possibility to predict sintering behaviour with the help of Master Sintering Curve was verified.

  15. Synthesis and characterization of aluminium–alumina micro- and nano-composites by spark plasma sintering

    International Nuclear Information System (INIS)

    Dash, K.; Chaira, D.; Ray, B.C.

    2013-01-01

    Graphical abstract: The evolution of microstructure by varying the particle size of reinforcement in the matrix employing spark plasma sintering has been demonstrated here in Al–Al 2 O 3 system. An emphasis has been laid on varying the reinforcement particle size and evaluating the microstructural morphologies and their implications on mechanical performance of the composites. Nanocomposites of 0.5, 1, 3, 5, 7 volume % alumina (average size 2 O 3 micro- and nano-composites fabricated by spark plasma sintering. • Better matrix-reinforcement integrity in nanocomposites than microcomposites. • Spark plasma sintering method results in higher density and hardness values. • High density and hardness values of nanocomposites than microcomposites. • High dislocation density in spark plasma sintered Al–Al 2 O 3 composites. - Abstract: In the present study, an emphasis has been laid on evaluation of the microstructural morphologies and their implications on mechanical performance of the composites by varying the reinforcement particle size. Nanocomposites of 0.5, 1, 3, 5, 7 volume % alumina (average size 2 O 3 nancomposites respectively. Spark plasma sintering imparts enhanced densification and matrix-reinforcement proximity which have been corroborated with the experimental results

  16. Ageing sintered silver: Relationship between tensile behavior, mechanical properties and the nanoporous structure evolution

    Energy Technology Data Exchange (ETDEWEB)

    Gadaud, Pascal; Caccuri, Vincenzo; Bertheau, Denis [Institut Pprime, Dept. Phys. Mech. Mat., UPR CNRS 3346, ENSMA, Université de Poitiers, 1 av. Clément Ader, Téléport 2, 86961 Futuroscope – Chasseneuil (France); Carr, James [HMXIF, Materials Science Centre, The University of Manchester, M13 9PL (United Kingdom); Milhet, Xavier, E-mail: xavier.milhet@ensma.fr [Institut Pprime, Dept. Phys. Mech. Mat., UPR CNRS 3346, ENSMA, Université de Poitiers, 1 av. Clément Ader, Téléport 2, 86961 Futuroscope – Chasseneuil (France)

    2016-07-04

    Silver pastes sintering is a potential candidate for die bonding in power electronic modules. The joints, obtained by sintering, exhibit a significant pore fraction thus reducing the density of the material compared to bulk silver. This was shown to alter drastically the mechanical properties (Young's modulus, yield strength and ultimate tensile stress) at room temperature. While careful analysis of the microstructure has been reported for the as-sintered material, little is known about its quantitative evolution (pores and grains) during thermal ageing. To address this issue, sintered bulk specimens and sintered joints were aged either under isothermal conditions (125 °C up to 1500 h) or under thermal cycling (between −40 °C/+125 °C with 30 min dwell time at each temperature for 2400 cycles). Under these conditions, it is shown that the density of the material does not change but the sub-micron porosity evolves towards a broader size distribution, consistent with Oswald ripening. It is also shown that only the step at 125 °C during the non-isothermal ageing is responsible for the microstructure evolution: isothermal ageing at high temperature can be regarded as a useful tool to perform accelerated ageing tests. Tensile properties are investigated as both a function of ageing time and a function of density. It is shown that the elastic properties do not evolve with the ageing time unlike the plastic properties. This is discussed as a function of the material microstructure evolution.

  17. The Influence of Sintering Temperature of Reactive Sintered (Ti, MoC-Ni Cermets

    Directory of Open Access Journals (Sweden)

    Marek Jõeleht

    2015-09-01

    Full Text Available Titanium-molybdenum carbide nickel cermets ((Ti, MoC-Ni were produced using high energy milling and reactive sintering process. Compared to conventional TiC-NiMo cermet sintering the parameters for reactive sintered cermets vary since additional processes are present such as carbide synthesis. Therefore, it is essential to acquire information about the suitable sintering regime for reactive sintered cermets. One of the key parameters is the final sintering temperature when the liquid binder Ni forms the final matrix and vacancies inside the material are removed. The influence of the final sintering temperature is analyzed by scanning electron microscopy. Mechanical properties of the material are characterized by transverse rupture strength, hardness and fracture toughness.DOI: http://dx.doi.org/10.5755/j01.ms.21.3.7179

  18. Dielectric Properties of Sol-Gel Derived Barium Strontium Titanate and Microwave Sintering of Ceramics

    Science.gov (United States)

    Selmi, Fathi A.

    This thesis consists of two areas of research: (1) sol-gel processing of Ba_{rm 1-x}Sr_{rm x} TiO_3 ceramics and their dielectric properties measurement; and (2) microwave versus conventional sintering of ceramics such as Al_2 O_3, Ba_{ rm 1-x}Sr_{rm x}TiO_3, Sb-doped SnO _2 and YBa_2Cu _3O_7. Sol-gel powders of BaTiO_3, SrTiO_3, and their solid solutions were synthesized by the hydrolysis of titanium isopropoxide and Ba and Sr methoxyethoxides. The loss tangent and dielectric constant of both sol-gel and conventionally prepared and sintered Ba_{rm 1-x}Sr _{rm x}TiO _3 ceramics were investigated at high frequencies. The sol-gel prepared ceramics showed higher dielectric constant and lower loss compared to those prepared conventionally. Ba _{rm 1-x}Sr _{rm x}TiO_3 ceramics were tunable with applied bias, indicating the potential use of this material for phase shifter applications. Porous Ba_{0.65}Sr _{0.35}TiO_3 was also investigated to lower the dielectric constant. Microwave sintering of alpha -Al_2O_3 and SrTiO_3 was investigated using an ordinary kitchen microwave oven (2.45 GHz; 600 Watts). The use of microwaves with good insulation of alpha -Al_2O_3 and SrTiO_3 samples resulted in their rapid sintering with good final densities of 96 and 98% of the theoretical density, respectively. A comparison of grain size for conventionally and microwave sintered SrTiO_3 samples did not show a noticeable difference. However, the grain size of microwave sintered alpha-Al_2O _3 was found to be larger than that of conventionally sintered sample. These results show that rapid sintering of ceramics can be achieved by using microwave radiation. The sintering behavior of coprecipitated Sb-doped SnO_2 was investigated using microwave power absorption. With microwave power, samples were sintered at 1450^circC for 20 minutes and showed a density as high as 99.9% of theoretical. However, samples fired in a conventional electric furnace at the same temperature for 4 hours showed only

  19. Marginal Accuracy and Internal Fit of 3-D Printing Laser-Sintered Co-Cr Alloy Copings.

    Science.gov (United States)

    Kim, Myung-Joo; Choi, Yun-Jung; Kim, Seong-Kyun; Heo, Seong-Joo; Koak, Jai-Young

    2017-01-23

    Laser sintered technology has been introduced for clinical use and can be utilized more widely, accompanied by the digitalization of dentistry and the development of direct oral scanning devices. This study was performed with the aim of comparing the marginal accuracy and internal fit of Co-Cr alloy copings fabricated by casting, CAD/CAM (Computer-aided design/Computer-assisted manufacture) milled, and 3-D laser sintered techniques. A total of 36 Co-Cr alloy crown-copings were fabricated from an implant abutment. The marginal and internal fit were evaluated by measuring the weight of the silicone material, the vertical marginal discrepancy using a microscope, and the internal gap in the sectioned specimens. The data were statistically analyzed by One-way ANOVA (analysis of variance), a Scheffe's test, and Pearson's correlation at the significance level of p = 0.05, using statistics software. The silicone weight was significantly low in the casting group. The 3-D laser sintered group showed the highest vertical discrepancy, and marginal-, occlusal-, and average- internal gaps ( p marginal discrepancy and the internal gap variables ( r = 0.654), except for the silicone weight. In this study, the 3-D laser sintered group achieved clinically acceptable marginal accuracy and internal fit.

  20. Marginal Accuracy and Internal Fit of 3-D Printing Laser-Sintered Co-Cr Alloy Copings

    Directory of Open Access Journals (Sweden)

    Myung-Joo Kim

    2017-01-01

    Full Text Available Laser sintered technology has been introduced for clinical use and can be utilized more widely, accompanied by the digitalization of dentistry and the development of direct oral scanning devices. This study was performed with the aim of comparing the marginal accuracy and internal fit of Co-Cr alloy copings fabricated by casting, CAD/CAM (Computer-aided design/Computer-assisted manufacture milled, and 3-D laser sintered techniques. A total of 36 Co-Cr alloy crown-copings were fabricated from an implant abutment. The marginal and internal fit were evaluated by measuring the weight of the silicone material, the vertical marginal discrepancy using a microscope, and the internal gap in the sectioned specimens. The data were statistically analyzed by One-way ANOVA (analysis of variance, a Scheffe’s test, and Pearson’s correlation at the significance level of p = 0.05, using statistics software. The silicone weight was significantly low in the casting group. The 3-D laser sintered group showed the highest vertical discrepancy, and marginal-, occlusal-, and average- internal gaps (p < 0.05. The CAD/CAM milled group revealed a significantly high axial internal gap. There are moderate correlations between the vertical marginal discrepancy and the internal gap variables (r = 0.654, except for the silicone weight. In this study, the 3-D laser sintered group achieved clinically acceptable marginal accuracy and internal fit.

  1. Study on the process of sintering matrix metallic Fe-Cu-25%Nb and Fe-Cu-25%Co during hot pressing

    International Nuclear Information System (INIS)

    Batista, A.C.; Oliveira, H.C.P.; Souza, M.H.; Assis, P.S.

    2016-01-01

    The sintering process promotes densification and the evolution of the microstructure of the material, with consequent significant increase in hardness and mechanical strength. However, few studies show the influence of pressure and temperature during sintering by hot pressing. In this sense, this work aims to evaluate the microstructural changes and properties with the variation of pressure and temperature and the type suffered by sintering metal powders during sintering by hot pressing. For this, two samples were studied by changing the sintering parameters: 25% Fe-50% Cu-25% Nb and 25% Fe-50% Cu-25% Co. Samples were analyzed by SEM / EDS in order to check the morphology and the presence of pores, as well as the interaction between the metallic constituents of each sample by the EDS analysis in line. They also determined the relative density, porosity and Vickers hardness (HV5). At the end of the study it was concluded that niobium alloy composite element by sintering activated suffered together with the liquid phase sintering. For cobalt alloys were observed by liquid phase sintering. The increase in the severity of the sintering conditions (temperature and pressure) led to an improvement in physical and mechanical properties of the alloys, which indicates that these parameters are directly related to the mechanisms of diffusion in the sintering process, improving the properties and diffusivity between elements. (author)

  2. Effect of sintering on structure and mechanical properties of alumina-15 vol% zirconia nanocomposite compacts

    International Nuclear Information System (INIS)

    Maneshian, Mohammad H.; Banerjee, Malay K.

    2010-01-01

    The sintering and densification behavior of high energy ball milled (HEBM-ed) alumina-15 vol% zirconia nanocomposite were carried out and the probable tetragonal to monoclinic phase transformation of ZrO 2 during sintering was investigated. Evolution of microstructure resulting from sintering was followed up by means of scanning electron microscopy (SEM) on polished samples, and the degree of phase transformation was determined by quantitative X-ray analysis (XRD). Moreover, synergetic effect of milling time and dopant composition on properties such as relative density, hardness, and fracture toughness was studied. The results have shown that mechanical properties of the composites were strongly dependent on the dopant content, structure and the fraction of tetragonal to monoclinic induced by HEBM and subsequent sintering. The extent of retention of t-ZrO 2 depends on the balance of magnitude of the strain energy arising from HEBM and releasing from sintering. In fact, compacts with aggressive HEBM history showed improved fracture toughness. Also it is shown the homogeneous microstructure obtained by HEBM and subsequent sintering promotes better densification.

  3. The effect of the atmosphere and the role of pore filling on the sintering of aluminium

    International Nuclear Information System (INIS)

    Schaffer, G.B.; Hall, B.J.; Bonner, S.J.; Huo, S.H.; Sercombe, T.B.

    2006-01-01

    Alloys of Al-3.8Cu-1Mg-0.7Si, Al-4Cu-0.6Si-0.1Mg, Al-4Cu-1.2Mg and Al-1.9Mg-1.9Si were made using air atomised powder and conventional press-and-sinter powder metallurgy techniques. These were sintered under nitrogen with a controlled water content which varied from 3 to 630 ppm (a dew point of -69 to -25 deg. C), nitrogen-5%hydrogen, argon and argon-5%hydrogen, all at atmospheric pressure, or a vacuum of -2 torr. Dry nitrogen is the most efficacious atmosphere. Vacuum is more effective than argon while hydrogen, and thus water, is extremely prejudicial to sintered density. The minimum dew point for optimum sintering is -60 deg. C (10.5 ppm H 2 O). The key feature in the beneficial effect of nitrogen is the formation of aluminium nitride. This reduces the pressure in the pore spaces relative to the external atmosphere, which induces pore filling at grain sizes that are smaller than those required for sintering in inert atmospheres. It is suggested that pore filling is an important densification mechanism during the sintering of aluminium

  4. Fabrication of Bi2223 bulks with high critical current properties sintered in Ag tubes

    Energy Technology Data Exchange (ETDEWEB)

    Takeda, Yasuaki, E-mail: ytakeda@g.ecc.u-tokyo.ac.jp [Department of Applied Chemistry, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Shimoyama, Jun-ichi; Motoki, Takanori [Department of Physics and Mathematics, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258 (Japan); Kishio, Kohji [Department of Applied Chemistry, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Nakashima, Takayoshi; Kagiyama, Tomohiro; Kobayashi, Shin-ichi; Hayashi, Kazuhiko [Sumitomo Electric Industries, Ltd. 1-1-3 Shimaya, Konohana-ku, Osaka 554-0024 (Japan)

    2017-03-15

    Highlights: • Fabrication conditions of Bi2223 bulks was reconsidered in terms of high J{sub c}. • Pressure of uniaxial pressing and heat treatment conditions were investigated. • The best sample showed higher J{sub c} than that of practically used Bi2223 bulks. - Abstract: Randomly grain oriented Bi2223 sintered bulks are one of the representative superconducting materials having weak-link problem due to very short coherence length particularly along the c-axis, resulting in poor intergrain J{sub c} properties. In our previous studies, sintering and/or post-annealing under moderately reducing atmospheres were found to be effective for improving grain coupling in Bi2223 sintered bulks. Further optimizations of the synthesis process for Bi2223 sintered bulks were attempted in the present study to enhance their intergrain J{sub c}. Effects of applied pressure of uniaxial pressing and sintering conditions on microstructure and superconducting properties have been systematically investigated. The best sample showed intergrain J{sub c} of 2.0 kA cm{sup −2} at 77 K and 8.2 kA cm{sup −2} at 20 K, while its relative density was low ∼65%. These values are quite high as for a randomly oriented sintered bulk of cuprate superconductors.

  5. Silicon microphotonic waveguides

    International Nuclear Information System (INIS)

    Ta'eed, V.; Steel, M.J.; Grillet, C.; Eggleton, B.; Du, J.; Glasscock, J.; Savvides, N.

    2004-01-01

    Full text: Silicon microphotonic devices have been drawing increasing attention in the past few years. The high index-difference between silicon and its oxide (Δn = 2) suggests a potential for high-density integration of optical functions on to a photonic chip. Additionally, it has been shown that silicon exhibits strong Raman nonlinearity, a necessary property as light interaction can occur only by means of nonlinearities in the propagation medium. The small dimensions of silicon waveguides require the design of efficient tapers to couple light to them. We have used the beam propagation method (RSoft BeamPROP) to understand the principles and design of an inverse-taper mode-converter as implemented in several recent papers. We report on progress in the design and fabrication of silicon-based waveguides. Preliminary work has been conducted by patterning silicon-on-insulator (SOI) wafers using optical lithography and reactive ion etching. Thus far, only rib waveguides have been designed, as single-mode ridge-waveguides are beyond the capabilities of conventional optical lithography. We have recently moved to electron beam lithography as the higher resolutions permitted will provide the flexibility to begin fabricating sub-micron waveguides

  6. Influence of size and volume fraction of SiC particulates on properties of ex situ reinforced Al-4.5Cu-3Mg metal matrix composite prepared by direct metal laser sintering process

    Energy Technology Data Exchange (ETDEWEB)

    Ghosh, Subrata Kumar [Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Midnapore (West), Kharagpur 721302, West Bengal (India); Saha, Partha, E-mail: psaha@mech.iitkgp.ernet.in [Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Midnapore (West), Kharagpur 721302, West Bengal (India); Kishore, Shyam [Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Midnapore (West), Kharagpur 721302, West Bengal (India)

    2010-07-15

    Direct metal laser sintering (DMLS) process has a great potential to prepare metal matrix composites (MMCs) in fabrication of arbitrary shaped jobs through rapid manufacturing. In the present work, silicon carbide particulates reinforced aluminium based metal matrix composite was developed by direct metal laser sintering process. Influences of SiC particulate (SiCp) on density, porosity and microhardness of the composite were investigated. It shows that SiCp having 300 mesh size provides higher density and lower porosity because of lower clustering effect. Higher microhardness was achieved at 1200 mesh of reinforcement because of lower grain size. Microhardness increases with increase of volume fraction of SiCp and higher value was achieved at high reinforcement content of 30 vol.%. Microstructure was studied through scanning electron microscopy (SEM) and X-ray elemental mapping. Interfacial microstructure was also investigated and cracks were found in number of cases due to difference between co-efficient of thermal expansion of matrix alloy and SiCp.

  7. Influence of size and volume fraction of SiC particulates on properties of ex situ reinforced Al-4.5Cu-3Mg metal matrix composite prepared by direct metal laser sintering process

    International Nuclear Information System (INIS)

    Ghosh, Subrata Kumar; Saha, Partha; Kishore, Shyam

    2010-01-01

    Direct metal laser sintering (DMLS) process has a great potential to prepare metal matrix composites (MMCs) in fabrication of arbitrary shaped jobs through rapid manufacturing. In the present work, silicon carbide particulates reinforced aluminium based metal matrix composite was developed by direct metal laser sintering process. Influences of SiC particulate (SiCp) on density, porosity and microhardness of the composite were investigated. It shows that SiCp having 300 mesh size provides higher density and lower porosity because of lower clustering effect. Higher microhardness was achieved at 1200 mesh of reinforcement because of lower grain size. Microhardness increases with increase of volume fraction of SiCp and higher value was achieved at high reinforcement content of 30 vol.%. Microstructure was studied through scanning electron microscopy (SEM) and X-ray elemental mapping. Interfacial microstructure was also investigated and cracks were found in number of cases due to difference between co-efficient of thermal expansion of matrix alloy and SiCp.

  8. Sinterization of manganese ore tailings under argon atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Valduga, M.M.F.; Lima, F.; Lima, R.M.F. [Universidade Federal de Ouro Preto (UFOP), MG (Brazil)

    2014-07-01

    Manganese is an element widely used in Metallurgy, however the Brazilian reserves has low grade. The aim of this work was to obtain and characterize the sinters from manganese ore tailings. The fines (less than 400⧣) were calcinated (800°C - 3600s) and homogenized with activated charcoal (7 and 10%) and CaO (5 and 10%). The sintering were carried out at 1135, 1140 and 1145°C during 7200 and 14400s under argon atmosphere. The sintered products were characterized by EDS analysis, BET surface area, apparent density, X-rays diffraction and SEM/EDS. The surface area was 0.03m2/g. The alkali element present (potassium) justified the low melting point of waste (1140°C). Due to the chemical complexity of the tailings, several phases were characterized in the products: pores, silicates with high content of manganese in the matrix, other silicates with different proportions of Al, Mn, Mg and Ca, pure Fe, SiO2, etc. (author)

  9. Sintering mechanism of blast furnace slag-kaolin ceramics

    International Nuclear Information System (INIS)

    Mostafa, Nasser Y.; Shaltout, Abdallah A.; Abdel-Aal, Mohamed S.; El-maghraby, A.

    2010-01-01

    A general ceramics processing scheme by cold uniaxial pressing and conventional sintering process have been used to prepare ceramics from mixtures of blast furnace slag (BFS) and kaolin (10%, 30% and 50% kaolin). The properties of the ceramics were studied by measuring linear shrinkage, bulk density, apparent porosity and mechanical properties of samples heated at temperatures from 800 o C to 1100 o C. The formed crystalline phases were characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). Slag melt formed at relatively low temperatures (800-900 o C) modified the sintering process to liquid phase sintering mechanism. Combination of BFS with 10% kaolin gave the highest mechanical properties, densification and shrinkage at relatively low firing temperatures. The crystalline phases were identified as gehlenite (Ca 2 Al 2 SiO 7 ) in both BFS and BFS with 10% kaolin samples. Anorthite (CaAl 2 Si 2 O 8 ) phase increased with increasing kaolin contents. In the case of kaolin-rich mixtures (30% and 50% kaolin), increased expansion took place during firing at temperatures in the range 800-1000 o C. This effect could be attributed to the entrapment of released gases.

  10. Investigation of the sinterability of ZrO_2 (Y_2O3_)-bioglass dental ceramics by dilatometry

    International Nuclear Information System (INIS)

    Bicalho, Luiz de Araujo; Barboza, Miguel Ribeiro Justino; Santos, Claudinei dos; Habibe, Alexandre Fernandes; Magnago, Roberto de Oliveira

    2013-01-01

    The objective of this work is to study by dilatometry, the liquid phase sintering of ZrO_2 ceramics using bioglass as sintering additive. Y_2 O_3 - stabilized ZrO_2 powders were mixed with 3, 5 and 10 wt% of bioglass with the composition based on 3CaOP_2 O_5 -MgO-SiO_2 system. Specimens were prepared by cold uniaxial pressing under 80MPa and the green relative density was determined. The sintering behavior was studied by measuring the linear shrinkage of samples in a dilatometer in relation to the temperature. The heating and cooling rates used in this study were 10 deg C/min and the maximum sintering temperatures was 1300 deg C with a 120 min isothermal holding time. The results of the shrinkage and shrinkage rates in regard of the sintering temperature and time were related to the amount of bioglass added. The sintered samples were characterized by X-ray diffraction analysis and their relative density. SEM micrographs indicates similar microstructure, and an increase of bioglass content leads to increasing of monoclinic ZrO_2 phase content. The dilatometry results indicate a reduction of the temperature where a maximum shrinkage rate occurs, as function of bioglass increasing. Furthermore, the use of liquid phase reduces the maximum sintering temperature of 1447 deg C to 1250-1280 deg C. (author)

  11. Matrix Structure Evolution and Nanoreinforcement Distribution in Mechanically Milled and Spark Plasma Sintered Al-SiC Nanocomposites.

    Science.gov (United States)

    Saheb, Nouari; Aliyu, Ismaila Kayode; Hassan, Syed Fida; Al-Aqeeli, Nasser

    2014-09-19

    Development of homogenous metal matrix nanocomposites with uniform distribution of nanoreinforcement, preserved matrix nanostructure features, and improved properties, was possible by means of innovative processing techniques. In this work, Al-SiC nanocomposites were synthesized by mechanical milling and consolidated through spark plasma sintering. Field Emission Scanning Electron Microscope (FE-SEM) with Energy Dispersive X-ray Spectroscopy (EDS) facility was used for the characterization of the extent of SiC particles' distribution in the mechanically milled powders and spark plasma sintered samples. The change of the matrix crystallite size and lattice strain during milling and sintering was followed through X-ray diffraction (XRD). The density and hardness of the developed materials were evaluated as function of SiC content at fixed sintering conditions using a densimeter and a digital microhardness tester, respectively. It was found that milling for 24 h led to uniform distribution of SiC nanoreinforcement, reduced particle size and crystallite size of the aluminum matrix, and increased lattice strain. The presence and amount of SiC reinforcement enhanced the milling effect. The uniform distribution of SiC achieved by mechanical milling was maintained in sintered samples. Sintering led to the increase in the crystallite size of the aluminum matrix; however, it remained less than 100 nm in the composite containing 10 wt.% SiC. Density and hardness of sintered nanocomposites were reported and compared with those published in the literature.

  12. Effect of process parameters on surface oxides on chromium-alloyed steel powder during sintering

    International Nuclear Information System (INIS)

    Chasoglou, D.; Hryha, E.; Nyborg, L.

    2013-01-01

    The use of chromium in the PM steel industry today puts high demands on the choice and control of the atmosphere during the sintering process due to its high affinity to oxygen. Particular attention is required in order to control the surface chemistry of the powder which in turn is the key factor for the successful sintering and production of PM parts. Different atmosphere compositions, heating rates and green densities were employed while performing sintering trials on water atomized steel powder pre-alloyed with 3 wt.% Cr in order to evaluate the effect on surface chemical reactions. Fracture surfaces of sintered samples were examined using high resolution scanning electron microscopy combined with X-ray microanalysis. The investigation was complemented with thermogravimetric (TG) studies. Reaction products in particulate form containing strong-oxide forming elements such as Cr, Si and Mn were formed during sintering for all conditions. Processing in vacuum results in intensive inter-particle neck development during the heating stage and consequently in the excessive enclosure of surface oxide which is reflected in less good final mechanical properties. Enhanced oxide reduction was observed in samples processed in hydrogen-containing atmospheres independent of the actual content in the range of 3–10 vol.%. An optimum heating rate was required for balancing reduction/oxidation processes. A simple model for the enclosure and growth of oxide inclusions during the sinter-neck development is proposed. The obtained results show that significant reduction of the oxygen content can be achieved by adjusting the atmosphere purity/composition. - Highlights: ► A local atmosphere microclimate is very important for sintering of PM steels. ► High risk of surface oxide enclosure between 800 and 1000 °C. ► Coalescence and agglomeration of enclosed oxides take place during sintering. ► The effect of different process parameters on the oxide reduction is examined. ► A

  13. Microstructural development and mechanical properties of iron based cermets processed by pressureless and spark plasma sintering

    International Nuclear Information System (INIS)

    Alvaredo, P.; Gordo, E.; Van der Biest, O.; Vanmeensel, K.

    2012-01-01

    Highlights: ► Processing of Fe-based cermets by pressureless sintering and spark plasma sintering. ► Influence of carbon content on the sintering mechanism and hardness. ► The cermet phase diagram was calculated and permits to explain the microstructure. ► SPS provides ferritic matrix and different carbide distribution than CPS samples. ► Pressureless sintered samples contain retained austenite at room temperature. - Abstract: Iron-based cermets are an interesting class of metal-ceramic composites in which properties and the factors influencing them are to be explored. In this work the metal matrix contains Cr, W, Mo and V as alloying elements, and the hard phase is constituted by 50 vol% of titanium carbonitride (TiCN) particles. The work studies the influence of the C content and the processing method on the sinterability, microstructure and hardness of the developed cermet materials. For that purpose, cermet samples with different C content in the matrix (0 wt%, 0.25 wt%, 0.5 wt%, 1.0 wt%) were prepared by conventional pressureless sintering (CPS) and, in order to achieve finer microstructures and to reduce the sintering time, by spark plasma sintering (SPS). The density and hardness (HV30) of the processed materials was evaluated, while their phase composition and microstructure was characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The equilibrium phase diagram of the composite material was calculated by ThermoCalc software in order to elucidate the influence of the carbon content on the obtained phases and developed microstructures.

  14. Underwater explosive compaction-sintering of tungsten-copper coating on a copper surface

    Science.gov (United States)

    Chen, Xiang; Li, Xiaojie; Yan, Honghao; Wang, Xiaohong; Chen, Saiwei

    2018-01-01

    This study investigated underwater explosive compaction-sintering for coating a high-density tungsten-copper composite on a copper surface. First, 50% W-50% Cu tungsten-copper composite powder was prepared by mechanical alloying. The composite powder was pre-compacted and sintered by hydrogen. Underwater explosive compaction was carried out. Finally, a high-density tungsten-copper coating was obtained by diffusion sintering of the specimen after explosive compaction. A simulation of the underwater explosive compaction process showed that the peak value of the pressure in the coating was between 3.0 and 4.8 GPa. The hardness values of the tungsten-copper layer and the copper substrate were in the range of 87-133 and 49 HV, respectively. The bonding strength between the coating and the substrate was approximately 100-105 MPa.

  15. Origin of unusual sintering phenomena in compacts of chloride-derived 3Y-TZP nanopowders

    Directory of Open Access Journals (Sweden)

    Sweeney Sean M.

    2014-01-01

    Full Text Available After evaluating three alternative possibilities, the present study shows that seemingly minor amounts (at least as low as 0.06 wt% of chlorine impurities are responsible for the poor sintering behavior observed in chloride-derived 3 mol% yttria stabilized zirconia (3Y-TZP nanopowders. Models and quantitative estimates are used to explain the role of evolved HCl and ZrCl4 gases in such anomalous behaviors as reduced sintered densities for higher green densities, de-densification, improved sintering in nitrogen over oxygen, and formation of a dense shell microstructure. Two solutions to problematic residual chlorides are compared: 1 a thermal treatment composed of an extended hold at 1000°C to allow HCl gas removal before the onset of closed porosity, and 2 a chemical treatment performed by washing bisque-fired samples at room temperature using a concentrated ammonium hydroxide solution to remove chlorides. The thermal treatment was found to be superior.

  16. Spark Plasma Co-Sintering of Mechanically Milled Tool Steel and High Speed Steel Powders.

    Science.gov (United States)

    Pellizzari, Massimo; Fedrizzi, Anna; Zadra, Mario

    2016-06-16

    Hot work tool steel (AISI H13) and high speed steel (AISI M3:2) powders were successfully co-sintered to produce hybrid tool steels that have properties and microstructures that can be modulated for specific applications. To promote co-sintering, which is made difficult by the various densification kinetics of the two steels, the particle sizes and structures were refined by mechanical milling (MM). Near full density samples (>99.5%) showing very fine and homogeneous microstructure were obtained using spark plasma sintering (SPS). The density of the blends (20, 40, 60, 80 wt % H13) was in agreement with the linear rule of mixtures. Their hardness showed a positive deviation, which could be ascribed to the strengthening effect of the secondary particles altering the stress distribution during indentation. A toughening of the M3:2-rich blends could be explained in view of the crack deviation and crack arrest exerted by the H13 particles.

  17. Composite materials and bodies including silicon carbide and titanium diboride and methods of forming same

    Science.gov (United States)

    Lillo, Thomas M.; Chu, Henry S.; Harrison, William M.; Bailey, Derek

    2013-01-22

    Methods of forming composite materials include coating particles of titanium dioxide with a substance including boron (e.g., boron carbide) and a substance including carbon, and reacting the titanium dioxide with the substance including boron and the substance including carbon to form titanium diboride. The methods may be used to form ceramic composite bodies and materials, such as, for example, a ceramic composite body or material including silicon carbide and titanium diboride. Such bodies and materials may be used as armor bodies and armor materials. Such methods may include forming a green body and sintering the green body to a desirable final density. Green bodies formed in accordance with such methods may include particles comprising titanium dioxide and a coating at least partially covering exterior surfaces thereof, the coating comprising a substance including boron (e.g., boron carbide) and a substance including carbon.

  18. Microstructure and Mechanical Properties of Highly Alloyed FeCrMoVC Steel Fabricated by Spark Plasma Sintering

    Science.gov (United States)

    Oh, Seung-Jin; Jun, Joong-Hwan; Lee, Min-Ha; Shon, In-Jin; Lee, Seok-Jae

    2018-05-01

    In this study, we successfully fabricated highly alloyed FeCrMoVC specimens within 2 min by using the spark plasma sintering (SPS) method. The densities of the sintered specimens were almost identical to their theoretical values. Fine (Mo, V)-rich carbides with lamellar structure were precipitated along the grain boundaries of the as-sintered specimen, whereas relatively large carbides were formed additionally in the transgranular region during the tempering treatment. Compared with the specimen produced by a conventional casting method, the FeCrMoVC specimens from SPS showed smaller grain size with finer carbides and higher hardness values.

  19. Pressureless sintering of dense Si3N4 and Si3N4/SiC composites with nitrate additives

    International Nuclear Information System (INIS)

    Kim, J.Y.; Iseki, Takayoshi; Yano, Toyohiko

    1996-01-01

    The effect of aluminum and yttrium nitrate additives on the densification of monolithic Si 3 N 4 and a Si 3 N 4 /SiC composite by pressureless sintering was compared with that of oxide additives. The surfaces of Si 3 N 4 particles milled with aluminum and yttrium nitrates, which were added as methanol solutions, were coated with a different layer containing Al and Y from that of Si 3 N 4 particles milled with oxide additives. Monolithic Si 3 N 4 could be sintered to 94% of theoretical density (TD) at 1,500 C with nitrate additives. The sintering temperature was about 100 C lower than the case with oxide additives. After pressureless sintering at 1,750 C for 2 h in N 2 , the bulk density of a Si 3 N 4 /20 wt% SiC composite reached 95% TD with nitrate additives

  20. Melting and Sintering of Ashes

    DEFF Research Database (Denmark)

    Hansen, Lone Aslaug

    1997-01-01

    -1300°C, and a trend of higher fusion temperatures with increasing contents of Al-silicates and quartz was found.c) Fly ashes, bottom ashes and deposits from coal/straw co-firing were all found to consist mainly of metal-alumina and alumina-silicates. These ashes all melt in the temperature range 1000......The thesis contains an experimental study of the fusion and sintering of ashes collected during straw and coal/straw co-firing.A laboratory technique for quantitative determination of ash fusion has been developed based on Simultaneous Thermal Analysis (STA). By means of this method the fraction......, the biggest deviations being found for salt rich (i.e. straw derived) ashes.A simple model assuming proportionality between fly ash fusion and deposit formation was found to be capable of ranking deposition rates for the different straw derived fly ashes, whereas for the fly ashes from coal/straw co-firing...

  1. Thermodynamics and mechanisms of sintering

    International Nuclear Information System (INIS)

    Pask, J.A.

    1978-10-01

    A phenomenological overview and exploration of the thermodynamic and geometric factors play a role in the process of densification of model compact systems consisting of crystalline spheres of uniform size in regular and irregular packing that form grain boundaries at every contact point. A further assumption is the presence of isotropic surface and grain boundary energies. Although such systems are unrealistic in comparison with normal powder compacts, their potential sintering behavior can be analyzed and provided with a limiting set of behavior conditions which can be looked upon as one boundary condition. This approach is logically realistic since it is easier to understand and provide a basis for understanding the more complex real powder systems

  2. Fabrication and microstructure of CNTs activated sintered W–Nb alloys

    International Nuclear Information System (INIS)

    Sha, J.J.; Hao, X.N.; Li, J.; Wang, Z.

    2014-01-01

    . (iv) The micro-hardness is varied from 4.84 to 6.07 GPa for the CNTs activated sintered W–Nb alloys, which is much higher than that of pure W specimen. The high micro-hardness could be attributed to the increased density and reduced grain size

  3. Processing development for ceramic structural components: the influence of a presintering of silicon on the final properties of reaction bonded silicon nitride. Final technical report

    Energy Technology Data Exchange (ETDEWEB)

    1982-03-01

    The influence of a presintering of silicon on the final properties of reaction bonded silicon nitride has been studied using scanning electron and optical microscopy, x-ray diffraction analysis, 4 pt. bend test, and mecury intrusion porosimetry. It has been shown that presintering at 1050/sup 0/C will not affect the final nitrided properties. At 1200/sup 0/C, the oxide layer is removed, promoting the formation of B-phase silicon nitride. Presintering at 1200/sup 0/C also results in compact weight loss due to the volatilization of silicon, and the formation of large pores which severely reduce nitrided strength. The development of the structure of sintered silicon compacts appears to involve a temperature gradient, with greater sintering observed near the surface.

  4. Role of Cu During Sintering of Fe0.96Cu0.04 Nanoparticles

    Science.gov (United States)

    Sivaprahasam, D.; Sriramamurthy, A. M.; Bysakh, S.; Sundararajan, G.; Chattopadhyay, K.

    2018-04-01

    Nanoparticle agglomerates of passivated Fe ( n-Fe) and Fe0.96Cu0.04 ( n-Fe0.96Cu0.04), synthesized through the levitational gas condensation (LGC) process, were compacted and sintered using the conventional powder metallurgy method. The n-Fe0.96Cu0.04 agglomerates produced lower green density than n-Fe, and when compacted under pressure beyond 200 MPa, they underwent lateral cracking during ejection attributed to the presence of a passive oxide layer. Sintering under dynamic hydrogen atmosphere can produce a higher density of compact in n-Fe0.96Cu0.04 in comparison to n-Fe. Both the results of dilatometry and thermogravimetric (TG) measurements of the samples under flowing hydrogen revealed enhancement of the sintering process as soon as the reduction of oxide layers could be accomplished. The shrinkage rate of n-Fe0.96Cu0.04 reached a value three times higher than n-Fe at a low temperature of 723 K (450 °C) during heating. This enhanced shrinkage rate was the manifestation of accumulation of Cu at the surface of the particles. The formation of a thin-surface melted layer enriched with copper during heating to isothermal holding facilitated as a medium of transport for diffusion of the elements. The compacts produced by sintering at 773 K (500 °C), with relative density 82 pct, were found to be unstable and oxidized instantly when exposed to ambient atmosphere. The stable compacts of density more than 92 pct with 300- to 450-nm grain size could only be produced when sintering was carried out at 973 K (700 °C) and beyond. The 0.22 wt pct residual oxygen obtained in the sintered compact is similar to what is used for conventional ferrous powder metallurgy products.

  5. A new UO2 sintering technology for the recycling of defective fuel pellets

    International Nuclear Information System (INIS)

    Song, K. W.; Kim, K. S.; Jeong, Y. H.

    1998-01-01

    A new UO 2 sintering technology to recycle defective UO 2 pellets has been developed. The defective UO 2 pellets were oxidized in an air to produce U 3 O 8 powder, and the U 3 O 8 powder was mixed with fresh AUC-UO 2 powder in the range of 10 to 100 wt%. Nb 2 O 5 and TiO 2 are added to the mixed powder. The mixed powder was pressed and sintered at 1680 deg C for 4 hours in hydrogen. The density of UO 2 pellets without sintering agents decreased linearly with the U 3 O 8 content at the rate of 0.2 %TD per 1 wt% U 3 O 8 , and the density was below 93.5 %TD at the U 3 O 8 contents above 10 wt%. However, the mixed UO 2 and U 3 O 8 powder containing Nb 2 O 5 (≥0.3 wt%) and TiO 2 (≥0.1 wt%) yielded a sintered density above 94 %TD in all ranges of U 3 O 8 contents. It was found that higher mixing ratios of U 3 O 8 to UO 2 powder did not affect the grain size of UO 2 pellets under the addition of Nb 2 O 5 , but decreased the grain size of UO 2 pellets under the addition of TiO 2 . The doped UO 2 pellets have grain sizes larger than 20 μm, and have small density gain after re-sintering test, owing to large pores. Therefore, the sintering agents such as Nb 2 O 5 and TiO 2 can make highly densified UO 2 pellets from the powder comprising a large amount of U 3 O 8 powder

  6. Science of sintering and its future

    International Nuclear Information System (INIS)

    Ristic, M.M.

    1975-01-01

    Some new books published by M.Yu. Baljshin, V.A. Ivensen, V.V. Skorohod and others are characterized by the wish to give a complete approach to the problems of sintering theory. Bearing just this in mind while writing the book ''An Essay on the Generalization of Sintering Theory'' (G.V.Samsonov, M.M. Ristic with the collaborators) an idea was born: to ask the most eminent scientists in this field to present their own opinions on the theme ''The Science of Sintering and Modern Views on its Future''. There were formed 18 questions, given in the appendix to be answered. The received answers were presented in 10 chapters of this book. The fourth part of the book consists of papers of eminent scientists engaged in the field of sintering science (some of which were published here for the first time). This material is published in the book with the consent of the authors and these original contributions provide a more profound knowledge of sintering. The initial idea, that the book should have a monograph character and in which the answers would serve as some data on the latest notions of the science of sintering, was somewhat changed since the original opinions of individual scientists are given in the book and these, are sometimes very contradictory. This, in fact, gives the book a special charm because the unsolved problems in the science of sintering are most evidently stressed in this way

  7. Sintering and microstructure of ice: a review

    International Nuclear Information System (INIS)

    Blackford, Jane R

    2007-01-01

    Sintering of ice is driven by the thermodynamic requirement to decrease surface energy. The structural morphology of ice in nature has many forms-from snowflakes to glaciers. These forms and their evolution depend critically on the balance between the thermodynamic and kinetic factors involved. Ice is a crystalline material so scientific understanding and approaches from more conventional materials can be applied to ice. The early models of solid state ice sintering are based on power law models originally developed in metallurgy. For pressure sintering of ice, these are based on work on hot isostatic pressing of metals and ceramics. Recent advances in recognizing the grain boundary groove geometry between sintering ice particles require models that use new approaches in materials science. The newer models of sintering in materials science are beginning to incorporate more realistic processing conditions and microstructural complexity, and so there is much to be gained from applying these to ice in the future. The vapour pressure of ice is high, which causes it to sublime readily. The main mechanism for isothermal sintering of ice particles is by vapour diffusion; however other transport mechanisms certainly contribute. Plastic deformation with power law creep combined with recrystallization become important mechanisms in sintering with external pressure. Modern experimental techniques, low temperature scanning electron microscopy and x-ray tomography, are providing new insights into the evolution of microstructures in ice. Sintering in the presence of a small volume fraction of the liquid phase causes much higher bond growth rates. This may be important in natural snow which contains impurities that form a liquid phase. Knowledge of ice microstructure and sintering is beneficial in understanding mechanical behaviour in ice friction and the stability of snow slopes prone to avalanches. (topical review)

  8. Instrumentation for thermal diffusivity determination of sintered materials

    International Nuclear Information System (INIS)

    Turquetti Filho, R.

    1990-01-01

    A new procedure to measure the sinterized materials thermal diffusivity, using the heat pulse method was developed in this work. The experimental data were performed at room temperature with UO sub(2), ThO sub(2), and Al sub(2)O sub(3) samples with 94%, 95%, and 96% of theoretical densities, respectively. Nondimensional root mean square deviation for theoretical function fitting was found to be on the order, of 10 sup(-3). The total error associated with the measurements for thermal diffusivity was ± 5%. (author)

  9. The Properties of Sintered Calcium Phosphate with [Ca]/[P] = 1.50

    Directory of Open Access Journals (Sweden)

    Moo-Chin Wang

    2012-10-01

    Full Text Available In order to obtain the properties of the sintered as-dried calcium phosphate with [Ca]/[P] = 1.50, the characteristics of sintered pellets have been investigated using X-ray diffraction (XRD, inductively coupled plasma-mass spectrometry (ICP-MS, Fourier-transform infrared (FT-IR spectra, Vickers hardness indentation and scanning electron microscopy (SEM. When the pellet samples were sintered between 700 °C and 1200 °C for 4 h, the hydroxyapatite (Ca10(PO46(OH2, HA still maintained the major phase, accompanied with the rhenanite (NaCaPO4 as the secondary phase and β-tricalcium phosphate (β-Ca3(PO42, β-TCP as the minor phases. In addition, the HA partially transformed to α-tricalcium phosphate (α-Ca3(PO42, α-TCP and tetracalcium phosphate (Ca4(PO42O, TTCP, when the pellet samples were sintered at 1300 °C and 1400 °C, respectively, for 4 h. The maximum density and Vickers Hardness (HV of sintered pellet samples were 2.85 g/cm3 (90.18% theoretical density (T.D. and 407, which appeared at 1200 °C and 900 °C, respectively.

  10. Study on the characteristics and sinterability of DUPIC powder by using simulated fuel

    International Nuclear Information System (INIS)

    Lee, Jae-Won; Lee, Jung-Won; Kim, Jong-Ho; Yim, Sung-Paal; Lee, Young-Woo; Yang, Myung-Seung

    2002-01-01

    The sinterability of the OREOX (oxidation and reduction of oxide fuels) powder was investigated in terms of the number of the OREOX cycles and milling time using simulated spent fuel of an equivalent burnup of 35,000 MWD/MTU. Wet milled powder was prepared and sintered to compare the morphology and sinterability with the dry milled powder. Powders having a medium particle size of less than 1μm were obtained by dry milling of OREOX powders regardless of the number of cycles. The specific surface area of the simulated DUPIC powder was governed by the number of OREOX cycles rather than by milling time. The sound pellets with a sintered density of higher than 95% TD and average grain size of larger than 8μm were obtained with the dry milled powder after 1 cycle of OREOX treatment. The powders prepared by dry milling for a short time and wet milling for a long time after 3 cycles of OREOX treatment also produced pellets with a sintered density of higher than 95% TD and average grain size of larger than 8μm. (author)

  11. Laser sintering of ceramics of Y2O3 pure e doped

    International Nuclear Information System (INIS)

    Oliveira, T.C. de; Goncalves, R.S.; Silva, R.S. da

    2012-01-01

    The Yttria (Y 2 O 3 ) is one of the most promising materials for refractory and optical applications due mainly to its high corrosion resistance, wide range of optical transmission and high melting point. However, due to its high melting point, ceramic bodies to obtain high density Y 2 O 3 high temperatures and require special sintering. Recently it has been proposed in the literature a new method of sintering in which a CO 2 laser, in continuous mode, is employed as the primary source of heat during sintering. Irradiation with laser light produces heating surface at elevated temperatures in a time interval of a few seconds, allowing to obtain dense ceramic bodies at elevated temperatures and with different properties from those sintered by conventional methods. In this paper, Y 2 O 3 powders of pure and doped with Mn, Ca and Zn were synthesized by the polymeric precursors and after calcination at 600 ° C/4h showed single phase. For the production and characterization of the samples used techniques DTA / TG, XRD Dilatometry, SEM and Radioluminescence. The sintered ceramics had a high relative density and strong dependence on the dopant used, which accelerate the densification process. Measures Radioluminescence showed characteristic peaks of Y 2 O 3 and dependence on the dopant used. (author)

  12. Transparent Lu 2 O 3 :Eu ceramics by sinter and HIP optimization

    Science.gov (United States)

    Seeley, Z. M.; Kuntz, J. D.; Cherepy, N. J.; Payne, S. A.

    2011-09-01

    Evolution of porosity and microstructure was observed during densification of lutetium oxide ceramics doped with europium (Lu 2O 3:Eu) fabricated via vacuum sintering and hot isostatic pressing (HIP'ing). Nano-scale starting powder was uniaxially pressed and sintered under high vacuum at temperatures between 1575 and 1850 °C to obtain densities ranging between 94% and 99%, respectively. Sintered compacts were then subjected to 200 MPa argon gas at 1850 °C to reach full density. Vacuum sintering above 1650 °C led to rapid grain growth prior to densification, rendering the pores immobile. Sintering between 1600 and 1650 °C resulted in closed porosity yet a fine grain size to allow the pores to remain mobile during the subsequent HIP'ing step, resulting in a fully-dense highly transparent ceramic without the need for subsequent air anneal. Light yield performance was measured and Lu 2O 3:Eu showed ˜4 times higher light yield than commercially used scintillating glass indicating that this material has the potential to improve the performance of high energy radiography devices.

  13. Spark Plasma Sintering and Densification Mechanisms of Antimony-Doped Tin Oxide Nanoceramics

    Directory of Open Access Journals (Sweden)

    Junyan Wu

    2013-01-01

    Full Text Available Densification of antimony-doped tin oxide (ATO ceramics without sintering aids is very difficult, due to the volatilization of SnO2, formation of deleterious phases above 1000°C, and poor sintering ability of ATO particles. In this paper, monodispersed ATO nanoparticles were synthesized via sol-gel method, and then ATO nanoceramics with high density were prepared by spark plasma sintering (SPS technology using the as-synthesized ATO nanoparticles without the addition of sintering aids. The effect of Sb doping content on the densification was investigated, and the densification mechanisms were explored. The results suggest that ATO nanoparticles derived from sol-gel method show good crystallinity with a crystal size of 5–20 nm and Sb is incorporated into the SnO2 crystal structure. When the SPS sintering temperature is 1000°C and the Sb doping content is 5 at.%, the density of ATO nanoceramics reaches a maximum value of 99.2%. Densification mechanisms are explored in detail.

  14. Structure and strength of aluminum with sub-micrometer/micrometer grain size prepared by spark plasma sintering

    DEFF Research Database (Denmark)

    Le, G.M.; Godfrey, A.; Hansen, Niels

    2013-01-01

    A spark plasma sintering (SPS) technique has been applied to prepare fully dense Al samples from Al powder. By applying a sintering temperature of 600°C and a loading pressure of 50MPa, fully recrystallized samples of nearly 100% density with average grain sizes of 5.2μm, 1.3μm and 0.8μm have bee...... strengthening. © 2013 Elsevier Ltd....

  15. Design of sintering-stable heterogeneous catalysts

    DEFF Research Database (Denmark)

    Gallas-Hulin, Agata

    One of the major issues in the use of metal nanoparticles in heterogeneous catalysis is sintering. Sintering occurs at elevated temperatures because of increased mobility of nanoparticles, leading to their agglomeration and, as a consequence, to the deactivation of the catalyst. It is an emerging...... problem especially for the noble metals-based catalysis. These metals being expensive and scarce, it is worth developing catalyst systems which preserve their activity over time. Encapsulation of nanoparticles inside zeolites is one of the ways to prevent sintering. Entrapment of nanoparticles inside...

  16. Solidification of HLLW into sintered ceramics

    International Nuclear Information System (INIS)

    O-Oka, K.; Ohta, T.; Masuda, S.; Tsunoda, N.

    1979-01-01

    Simulated HLLW from the PNC reprocessing plant at Tokai was solidified into sintered ceramics by normal sintering or hot-pressing with addition of some oxides. Among various ceramic products obtained so far, the most preferable was nepheline-type sintered solids formed with addition of SiO 2 and Al 2 O 3 to the simulated waste calcine. The solid shows advantageous properties in leach rate and mechanical strength, which suggest that the ceramic solids were prepared with additions of ZrO 2 or MnO 2 , and some of them showed good characteristics

  17. Effect of rigid inclusions on sintering

    International Nuclear Information System (INIS)

    Rahaman, M.N.; De Jonghe, L.C.

    1988-01-01

    The predictions of recent theoretical studies on the effect of inert, rigid inclusions on the sintering of ceramic powder matrices are examined and compared with experimental data. The densification of glass matrix composites with inclusion volume fractions of ≤0.15 can be adequately explained by Scherer's theory for viscous sintering with rigid inclusions. Inclusions cause a vast reduction in the densification rates of polycrystalline matrix composites even at low inclusion volume fractions. Models put forward to explain the sintering of polycrystalline matrix composites are discussed

  18. Immobilization of Uranium Silicides in Sintered Glass

    International Nuclear Information System (INIS)

    Mateos, P.; Russo, D.O.; Heredia, A.D.; Sanfilippo, M.

    2003-01-01

    High activity nuclear spent fuels vitrification by fusion is a well known technology which has industrial scale in France, England, Japan, EEUU. Borosilicates glasses are used in this process.Sintered glasses are an alternative to the immobilization task in which there is also a wide experience around the world.The available technics are: cold pressing and sintering , hot-pressing and hot isostatic pressing.This work compares Borosilicates and Iron silicates sintered glasses behaviour when different ammounts of nuclear simulated waste is added

  19. Characterization and sintering of ATR aluminia from niobium

    International Nuclear Information System (INIS)

    Shibuya, N.H.

    1987-01-01

    The characterization of resultante slag from Aluminothermic Reduction (ATR) process to obtain metallic niobium is presented. The slag was characterized for concentration and phases of aluminia by X-ray diffractometry. The results show that 70% of the slag is constituted by α aluminia. The lixiviation and calcination of the slag increased the α aluminia concentration to 95%, the slag was used for producing samples to be burning in three furnaces: electrical resistance furnace in the air, and two furnaces in the vacuum. The burned samples were characterized by microscopy, ultrasonic analysis, density measurements and X-ray diffractometry. The sintering in the vacuum is possible because the samples burned in vacuum presented major density. The formation of NbO 2 and mullite was observed, by X-ray diffractometry. The data from optical microscopy, density measurements and X-ray diffractometry show high porosity. (M.C.K.) [pt

  20. Process Developed for Generating Ceramic Interconnects With Low Sintering Temperatures for Solid Oxide Fuel Cells

    Science.gov (United States)

    Zhong, Zhi-Min; Goldsby, Jon C.

    2005-01-01

    Solid oxide fuel cells (SOFCs) have been considered as premium future power generation devices because they have demonstrated high energy-conversion efficiency, high power density, and extremely low pollution, and have the flexibility of using hydrocarbon fuel. The Solid-State Energy Conversion Alliance (SECA) initiative, supported by the U.S. Department of Energy and private industries, is leading the development and commercialization of SOFCs for low-cost stationary and automotive markets. The targeted power density for the initiative is rather low, so that the SECA SOFC can be operated at a relatively low temperature (approx. 700 C) and inexpensive metallic interconnects can be utilized in the SOFC stack. As only NASA can, the agency is investigating SOFCs for aerospace applications. Considerable high power density is required for the applications. As a result, the NASA SOFC will be operated at a high temperature (approx. 900 C) and ceramic interconnects will be employed. Lanthanum chromite-based materials have emerged as a leading candidate for the ceramic interconnects. The interconnects are expected to co-sinter with zirconia electrolyte to mitigate the interface electric resistance and to simplify the processing procedure. Lanthanum chromites made by the traditional method are sintered at 1500 C or above. They react with zirconia electrolytes (which typically sinter between 1300 and 1400 C) at the sintering temperature of lanthanum chromites. It has been envisioned that lanthanum chromites with lower sintering temperatures can be co-fired with zirconia electrolyte. Nonstoichiometric lanthanum chromites can be sintered at lower temperatures, but they are unstable and react with zirconia electrolyte during co-sintering. NASA Glenn Research Center s Ceramics Branch investigated a glycine nitrate process to generate fine powder of the lanthanum-chromite-based materials. By simultaneously doping calcium on the lanthanum site, and cobalt and aluminum on the

  1. Sintering of MnCo2O4 coatings prepared by electrophoretic deposition

    DEFF Research Database (Denmark)

    Bobruk, M.; Molin, Sebastian; Chen, Ming

    2018-01-01

    Sintering of MnCo2O4 coatings prepared by electrophoretic deposition on steel substrates has been studied in air and in reducing-oxidizing atmosphere. Effect of temperature and pO2 on the resulting coating density was evaluated from scanning electron microscopy images of polished cross sections...

  2. Sintering of a freeze-dried 10 mol% Y2O3-stabilized zirconia

    International Nuclear Information System (INIS)

    Rakotoson, A.; Paulus, M.

    1983-01-01

    After presenting the results of freeze drying a sulfate solution, the authors describe a preparation process in which the freeze-drying technique by addition of a suspension of stabilized zirconia in the liquid solution before freeze-drying. This process breaks the polymeric chains, increases the green density of the compact, and decreases the sintering temperature. The mechanisms involved are discussed

  3. The First Static and Dynamic Analysis of 3-D Printed Sintered Ceramics for Body Armor Applications

    Science.gov (United States)

    2016-09-01

    hardness , and fracture strength) and semi-infinite penetration performance of 3-D printed sintered alumina. These results are compared with traditionally...parameters (including density, hardness , and fracture strength), semi-infinite penetration performance, and the fracture profile following impact of 3...of advanced ceramics differs mostly in terms of the initial green part formation when compared with a traditional manufacturing process. The

  4. Analytical and experimental evaluation of joining silicon carbide to silicon carbide and silicon nitride to silicon nitride for advanced heat engine applications Phase 2. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Sundberg, G.J.; Vartabedian, A.M.; Wade, J.A.; White, C.S. [Norton Co., Northboro, MA (United States). Advanced Ceramics Div.

    1994-10-01

    The purpose of joining, Phase 2 was to develop joining technologies for HIP`ed Si{sub 3}N{sub 4} with 4wt% Y{sub 2}O{sub 3} (NCX-5101) and for a siliconized SiC (NT230) for various geometries including: butt joins, curved joins and shaft to disk joins. In addition, more extensive mechanical characterization of silicon nitride joins to enhance the predictive capabilities of the analytical/numerical models for structural components in advanced heat engines was provided. Mechanical evaluation were performed by: flexure strength at 22 C and 1,370 C, stress rupture at 1,370 C, high temperature creep, 22 C tensile testing and spin tests. While the silicon nitride joins were produced with sufficient integrity for many applications, the lower join strength would limit its use in the more severe structural applications. Thus, the silicon carbide join quality was deemed unsatisfactory to advance to more complex, curved geometries. The silicon carbide joining methods covered within this contract, although not entirely successful, have emphasized the need to focus future efforts upon ways to obtain a homogeneous, well sintered parent/join interface prior to siliconization. In conclusion, the improved definition of the silicon carbide joining problem obtained by efforts during this contract have provided avenues for future work that could successfully obtain heat engine quality joins.

  5. Corrosion of high-density sintered tungsten alloys. Part 1

    International Nuclear Information System (INIS)

    Batten, J.J.; McDonald, I.G.; Moore, B.T.; Silva, V.M.

    1988-10-01

    The corrosion behaviour of four tungsten alloys has been evaluated through weight loss measurements after total immersion in both distilled water insight into the mechanism of corrosion was afforded by an examination of the and 5% sodium chloride solutions. Some insight the mechanism of corrosion was afforded by using the Scanning Electron Microscopy and through an analysis of the corrosion products. Pure tungsten and all the alloys studied underwent corrosion during the tests, and in each case the rare of corrosion in sodium chloride solution was markedly less than that in distilled water. A 95% W, 3.5% Ni, 1.5% Fe alloy was found to be the most corrosion resistant of the alloys under the experimental conditions. Examination of the data shows that for each of the tests, copper as an alloying element accelerates corrosion of tungsten alloys. 9 refs., 7 tabs., 12 figs

  6. Corrosion of high-density sintered tungsten alloys

    International Nuclear Information System (INIS)

    Batten, J.J.; Moore, B.T.

    1989-01-01

    In comparative corrosion tests, the corrosion resistance of an Australian tungsten alloy (95% W, 3.5% Ni, 1.5% Fe) was found to be superior to three other tungsten alloys and, under certain conditions, even more corrosion-resistant than pure tungsten. Corrosion resistance was evaluated after immersion in both distilled water and 5% sodium chloride solutions, and in cyclic humidity and salt mist environments. For all but the Australian alloy, the rate of corrosion in sodium chloride solution was markedly less than that in distilated water. In all cases, alloys containing copper had the greatest corrosion rates. Corrosion mechanisms were investigated using a scanning electron microscope, analysis of corrosion products and galvanic corrosion studies. For the alloys, corrosion was attributed primarily to a galvanic reaction. Whether the tungsten or binder phase of the alloy became anodic, and thus was attacked preferentially, depended upon alloy composition and corrosion environment. 16 refs., 4 tabs., 4 figs

  7. Tin - an unlikely ally for silicon field effect transistors?

    KAUST Repository

    Hussain, Aftab M.; Fahad, Hossain M.; Singh, Nirpendra; Sevilla, Galo T.; Schwingenschlö gl, Udo; Hussain, Muhammad Mustafa

    2014-01-01

    We explore the effectiveness of tin (Sn), by alloying it with silicon, to use SiSn as a channel material to extend the performance of silicon based complementary metal oxide semiconductors. Our density functional theory based simulation shows

  8. Two-dimensional simulation of sintering process

    International Nuclear Information System (INIS)

    Vasconcelos, Vanderley de; Pinto, Lucio Carlos Martins; Vasconcelos, Wander L.

    1996-01-01

    The results of two-dimensional simulations are directly applied to systems in which one of the dimensions is much smaller than the others, and to sections of three dimensional models. Moreover, these simulations are the first step of the analysis of more complex three-dimensional systems. In this work, two basic features of the sintering process are studied: the types of particle size distributions related to the powder production processes and the evolution of geometric parameters of the resultant microstructures during the solid-state sintering. Random packing of equal spheres is considered in the sintering simulation. The packing algorithm does not take into account the interactive forces between the particles. The used sintering algorithm causes the densification of the particle set. (author)

  9. SINTERED REFRACTORY TUNGSTEN ALLOYS. Gesinterte hochschmelzende wolframlegierungen

    Energy Technology Data Exchange (ETDEWEB)

    Kieffer, R.; Sedlatschek, K.; Braun, H.

    1971-12-15

    Dependence of the melting point of the refractory metals on their positions in the periodic system - alloys of tungsten with other refractory metals - sintering of the alloys - processing of the alloys - technological properties.

  10. U3O8 microspheres sintering kinetics

    International Nuclear Information System (INIS)

    Godoy, A.L.E.

    1986-01-01

    U 3 O 8 microspheres sintering kinetics was determined using a hot-stage optical microscopy apparatus, able to reach temperature up to 1350 0 C in controlled atmospheres. The sintered material had its microstructure analysed by optical and electron microscopy. The microspheres were characterized initialy utilizing X-ray diffractometry and thermogravimetry. The equation which describes the microspheres shrinkage in function of the time was obtained using finite difference analysis X-ray diffractometry indicated hexagonal structure for the microspheres main starting material, ammonium diuranate thermogravimetric analysis showed reduction of this material to U 3 O 8 at 600 0 C. Ceramography results showed 5 hours sintered microspheres grain sizes G vary with the temperature. Sintered U 3 O 8 micrographs compared with published results for UO 2 , indicate similar homogeneity microstructural characteristics and suggest the processed micorspheres to be potentially useful as nuclear fuels. (Author) [pt

  11. Studies on the synthesis of nanocrystalline Y{sub 2}O{sub 3} and ThO{sub 2} through volume combustion and their sintering

    Energy Technology Data Exchange (ETDEWEB)

    Sanjay Kumar, D. [Fuel Chemistry Division, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Ananthasivan, K., E-mail: asivan@igcar.gov.in [Fuel Chemistry Division, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Venkata Krishnan, R. [Fuel Chemistry Division, Chemistry Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Amirthapandian, S. [Material Physics Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India); Dasgupta, Arup [Microscopy and Thermo-Physical Property Division, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102, Tamil Nadu (India)

    2016-10-15

    Volume combustion was observed in the auto-ignition of the citrate gels containing the nitrates of yttrium/thorium for the first time in mixture with a fuel (citric acid) to oxidant (Y{sup 3+} or Th{sup 4+} nitrate) ratio close to that demanded by the stoichiometry. These nanocrystalline powders were characterized for their bulk density, specific surface area, particle size distribution, carbon residue and X-ray crystallite size and were sintered by both the conventional and the two-step method. The maximum relative sintered density of Y{sub 2}O{sub 3} was 98.9% TD. The sintered density of thoria (97.8% TD) is the highest among the values reported so far, for nanocrystalline ThO{sub 2}. Characterization of the pellets and powders by using scanning electron microscopy and transmission electron microscopy reaffirmed nanocrystallinity and that the sintered pellets comprised faceted sintered grains. The two-step sintering was found to restrict “runaway” sintering. - Highlights: • Scaled-up synthesis of nanocrystalline Y{sub 2}O{sub 3} and ThO{sub 2} using citrate gel-combustion method. • VCR was observed at a fuel to nitrate ratio (R) of 0.125 and 0.17 in mixtures containing Th(NO{sub 3}){sub 4} and Y(NO{sub 3}){sub 3} respectively. • The calcined powders were compacted and sintered by using a novel two-step sintering method. • Sintered densities as high as 97.8% T.D. (ThO{sub 2}, T{sub H} = 0.48) and 98.9% T.D. (Y{sub 2}O{sub 3}, T{sub H} = 0.61) were obtained.

  12. Techniques for ceramic sintering using microwave energy

    International Nuclear Information System (INIS)

    Kimrey, H.D.; Janney, M.A.; Becher, P.F.

    1987-01-01

    The use of microwave energy for ceramic sintering offers exciting new possibilities for materials processing. Based on experience gathered in microwave processing associated with the heating of fusion plasmas, we have developed hardware and methods for uniformly heating ceramic parts of large volume and irregular shape to temperatures in excess of 1600 0 C, in vacuum or pressurized atmosphere. Microwave processing at 28 GHz yields enhanced densification rates with a corresponding reduction in sintering temperatures. 6 refs

  13. High density microelectronics package using low temperature cofirable ceramics

    International Nuclear Information System (INIS)

    Fu, S.-L.; Hsi, C.-S.; Chen, L.-S.; Lin, W. K.

    1997-01-01

    Low Temperature Cofired Ceramics (LTCC) is a relative new thick film process and has many engineering and manufacturing advantages over both the sequential thick film process and high temperature cofired ceramic modules. Because of low firing temperature, low sheet resistance metal conductors, commercial thick film resistors, and thick film capacitors can be buried in or printed on the substrates. A 3-D multilayer ceramic substrate can be prepared via laminating and co-firing process. The packing density of the LTCC substrates can be increased by this 3-D packing technology. At Kaohsiung Polytechnic Institute (KPI), a LTCC substrate system has been developed for high density packaging applications, which had buried surface capacitors and resistors. The developed cordierite-glass ceramic substrate, which has similar thermal expansion as silicon chip, is a promising material for microelectronic packaging. When the substrates were sintered at temperatures between 850-900 degree centigrade, a relative density higher than 96 % can be obtained. The substrate had a dielectric constant between 5.5 and 6.5. Ruthenium-based resistor pastes were used for resistors purposes. The resistors fabricated in/on the LTCC substrates were strongly depended on the microstructures developed in the resistor films. Surface resistors were laser trimmed in order to obtain specific values for the resistors. Material with composition Pb(Fe 2/3 W 1/3 ) x (Fe l/2 Nb l/2 ) y Ti 2 O 3 was used as dielectric material of the capacitor in the substrate. The material can be sintered at temperatures between 850-930 degree centigrade, and has dielectric constant as high as 26000. After cofiring, good adhesion between dielectric and substrate layers was obtained. Combing the buried resistors and capacitors together with the lamination of LTCC layer, a 3-dimensional multilayered ceramic package was fabricated. (author)

  14. High density microelectronics package using low temperature cofirable ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Fu, S -L; Hsi, C -S; Chen, L -S; Lin, W K [Kaoshiung Polytechnic Institute Ta-Hsu, Kaoshiung (China)

    1998-12-31

    Low Temperature Cofired Ceramics (LTCC) is a relative new thick film process and has many engineering and manufacturing advantages over both the sequential thick film process and high temperature cofired ceramic modules. Because of low firing temperature, low sheet resistance metal conductors, commercial thick film resistors, and thick film capacitors can be buried in or printed on the substrates. A 3-D multilayer ceramic substrate can be prepared via laminating and co-firing process. The packing density of the LTCC substrates can be increased by this 3-D packing technology. At Kaohsiung Polytechnic Institute (KPI), a LTCC substrate system has been developed for high density packaging applications, which had buried surface capacitors and resistors. The developed cordierite-glass ceramic substrate, which has similar thermal expansion as silicon chip, is a promising material for microelectronic packaging. When the substrates were sintered at temperatures between 850-900 degree centigrade, a relative density higher than 96 % can be obtained. The substrate had a dielectric constant between 5.5 and 6.5. Ruthenium-based resistor pastes were used for resistors purposes. The resistors fabricated in/on the LTCC substrates were strongly depended on the microstructures developed in the resistor films. Surface resistors were laser trimmed in order to obtain specific values for the resistors. Material with composition Pb(Fe{sub 2/3}W{sub 1/3}){sub x}(Fe{sub l/2}Nb{sub l/2}){sub y}Ti{sub 2}O{sub 3} was used as dielectric material of the capacitor in the substrate. The material can be sintered at temperatures between 850-930 degree centigrade, and has dielectric constant as high as 26000. After cofiring, good adhesion between dielectric and substrate layers was obtained. Combing the buried resistors and capacitors together with the lamination of LTCC layer, a 3-dimensional multilayered ceramic package was fabricated. (author)

  15. Preparation and sintering of Zr(C,N,O) phases

    International Nuclear Information System (INIS)

    Tamborenea, S.; Mazzoni, A.D.; Aglietti, E.F.

    2003-01-01

    The Zr(C,O,N) compounds form a great mono-phase zone belonging to the pseudoternary ZrO-ZrN-ZrC system.Theses phases have cubic crystalline structure with a o parameter depending on the C, O 2 and N 2 content.These phases have many potential applications in the manufacture of ceramic pieces utilizable as electronic conductors.The Zr (C,O,N) phases can be obtained from ZrO 2 by carbonitriding reactions: that is carbothermal reduction and simultaneous nitriding.In this work a series of experiences of carbonitriding of zirconia under different conditions (temperatures between 1400 and 1600degC, times of 120 min, carbon content between 20 and 40%) in order to obtain suitable powders to be sintered.The XRD analysis shows the Zr(C,O,N) as the main products and β -ZrON as the only secondary product in proportions depending on the obtaining conditions.The variables employed were the C content and the reaction temperature.The Zr(C,O,N) content varies between 40 and 90% and tends to increase with the temperature and the carbon content whereas the β -ZrON phase varies between the 40 and 10 % decreasing its proportion with temperature and the carbon content.The oxidation resistance of these phases was studied by DTA-TG tests in air.Results show complete oxidation reaction at ∼500degC in air.The sintering of these materials was made on disks obtained by pressing of powders of Zr(C,N,O) contents higher than 90%.Sintering was performed in nitrogen atmosphere and temperatures between 1450 and 1620degC.Disks were characterized by pycnometry and Hg volumeter.The densities obtained were between 5 and 6,6g/cm 3 with a tendency to increase with the Zr(C,N,O) phase content, the temperature and the sintering time.Sintered disks were characterized by dilatometry in N 2

  16. Improvement of conditions for ceramics sintering on the base of lead zirconate-titanate

    International Nuclear Information System (INIS)

    Glinchuk, M.D.; Kim, P.V.; Bykov, I.P.; Lyashchenko, A.B.

    1989-01-01

    Lead zirconate-titanate powders of different graininess are studied for their phase composition. The finest grains of the powder consist of lead zirconate-titanate with the rhombohedral structure. Grains of 3-5 μm size are a mixture of lead zirconate-titanate and lead titanate, the latter exceeding 50% (by weight) causes the effect of anomalous expansion in the process of sintering. Control of the technological parameters of the synthesis permits producing powder with favourable correlation of the above phases and grain sizes. Sintering of such a powder induces no effect of the anomalous expansion with an increased density of the product attained

  17. Structural Integration of Silicon Solar Cells and Lithium-ion Batteries Using Printed Electronics

    Science.gov (United States)

    Kang, Jin Sung

    Inkjet printing of electrode using copper nanoparticle ink is presented. Electrode was printed on a flexible glass epoxy composite substrate using drop on demand piezoelectric dispenser and was sintered at 200°C in N 2 gas condition. The printed electrodes were made with various widths and thicknesses. Surface morphology of electrode was analyzed using scanning electron microscope (SEM) and atomic force microscope (AFM). Reliable dimensions for printed electronics were found from this study. Single-crystalline silicon solar cells were tested under four-point bending to find the feasibility of directly integrating them onto a carbon fiber/epoxy composite laminate. These solar cells were not able to withstand 0.2% strain. On the other hand, thin-film amorphous silicon solar cells were subjected to flexural fatigue loadings. The current density-voltage curves were analyzed at different cycles, and there was no noticeable degradation on its performance up to 100 cycles. A multifunctional composite laminate which can harvest and store solar energy was fabricated using printed electrodes. The integrated printed circuit board (PCB) was co-cured with a carbon/epoxy composite laminate by the vacuum bag molding process in an autoclave; an amorphous silicon solar cell and a thin-film solid state lithium-ion (Li-ion) battery were adhesively joined and electrically connected to a thin flexible PCB; and then the passive components such as resistors and diodes were electrically connected to the printed circuit board by silver pasting. Since a thin-film solid state Li-ion battery was not able to withstand tensile strain above 0.4%, thin Li-ion polymer batteries were tested under various mechanical loadings and environmental conditions to find the feasibility of using the polymer batteries for our multifunctional purpose. It was found that the Li-ion polymer batteries were stable under pressure and tensile loading without any noticeable degradation on its charge and discharge

  18. Vacuum-sintered body of a novel apatite for artificial bone

    Science.gov (United States)

    Tamura, Kenichi; Fujita, Tatsushi; Morisaki, Yuriko

    2013-12-01

    We produced regenerative artificial bone material and bone parts using vacuum-sintered bodies of a novel apatite called "Titanium medical apatite (TMA®)" for biomedical applications. TMA was formed by chemically connecting a Ti oxide molecule with the reactive [Ca10(PO4)6] group of Hydroxyapatite (HAp). The TMA powders were kneaded with distilled water, and solid cylinders of compacted TMA were made by compression molding at 10 MPa using a stainless-steel vessel. The TMA compacts were dried and then sintered in vacuum (about 10-3 Pa) or in air using a resistance heating furnace in the temperature range 1073-1773 K. TMA compacts were sintered at temperatures greater than 1073 K, thus resulting in recrystallization. The TMA compact bodies sintered in the range 1273-1773 K were converted into mixtures composed of three crystalline materials: α-TCP (tricalcium phosphate), β-TCP, and Perovskite-CaTiO3. The Perovskite crystals were stable and hard. In vacuum-sintering, the Perovskite crystals were transformed into fibers (approximately 1 µm in diameter × 8 µm in length), and the fiber distribution was uniform in various directions. We refer to the TMA vacuum-sintered bodies as a "reinforced composite material with Perovskite crystal fibers." However, in atmospheric sintering, the Perovskite crystals were of various sizes and were irregularly distributed as a result of the effect of oxygen. After sintering temperature at 1573 K, the following results were obtained: the obtained TMA vacuum-sintered bodies (1) were white, (2) had a density of approximately 2300 kg/m3 (corresponding to that of a compact bone or a tooth), and had a thermal conductivity of approximately 31.3 W/(m·K) (corresponding to those of metal or ceramic implants). Further, it was possible to cut the TMA bodies into various forms with a cutting machine. An implant made of TMA and inserted into a rabbit jaw bone was covered by new bone tissues after just one month because of the high

  19. Analysis of Laser Sintering Technology

    Directory of Open Access Journals (Sweden)

    Vladislav Markovič

    2014-02-01

    Full Text Available The new, high-tech development and customization is one ofthe most important factors in promoting the country‘s economicgrowth indicators. The economic downturn in the industryrequires technology and equipment using a minimumof raw materials and providing maximum performance. Thisstatement perfectly describes the innovative, forward-looking,cost-effective laser powder sintering (SLS technology. Here,thanks to the latest engineering achievements, product surfacesare modified and improved, they gain new characteristics. SLSis viable in automobile, engineering, construction, aerospace,aircraft, printing, medical and other areas.In order to create a product which meets the standards andtechnical documentation it is necessary to use and ensure highquality of raw materials, high-end equipment, qualified personnel,the working environment with proper climatic conditions, ergonomics,etc. But all of these, the quality of the product becomesthe decisive indicators meaningless if know how to properly selectthe laser processing operation. Scanning speed, beam power,pulse frequency, protective gases, powder layer thickness – allof them are the physical and mechanical characteristics of thechange in a small range changes the quality of the product of thefuture, the field of application and performance characteristics.

  20. Silicon Nanocrystal Synthesis in Microplasma Reactor

    Science.gov (United States)

    Nozaki, Tomohiro; Sasaki, Kenji; Ogino, Tomohisa; Asahi, Daisuke; Okazaki, Ken

    Nanocrystalline silicon particles with grains smaller than 5 nm are widely recognized as a key material in optoelectronic devices, lithium battery electrodes, and bio-medical labels. Another important characteristic is that silicon is an environmentally safe material that is used in numerous silicon technologies. To date, several synthesis methods such as sputtering, laser ablation, and plasma-enhanced chemical vapor deposition (PECVD) based on low-pressure silane chemistry (SiH4) have been developed for precise control of size and density distributions of silicon nanocrystals. In this study, we explore the possibility of microplasma technologies for efficient production of mono-dispersed nanocrystalline silicon particles on a micrometer-scale, continuous-flow plasma reactor operated at atmospheric pressure. Mixtures of argon, hydrogen, and silicon tetrachloride were activated using a very-high-frequency (144 MHz) power source in a capillary glass tube with volume of less than 1 μl. Fundamental plasma parameters of the microplasma were characterized using optical emission spectroscopy, which respectively indicated electron density of 1015 cm-3, argon excitation temperature of 5000 K, and rotational temperature of 1500 K. Such high-density non-thermal reactive plasma can decompose silicon tetrachloride into atomic silicon to produce supersaturated silicon vapor, followed by gas-phase nucleation via three-body collision: particle synthesis in high-density plasma media is beneficial for promoting nucleation processes. In addition, further growth of silicon nuclei can be terminated in a short-residence-time reactor. Micro-Raman scattering spectra showed that as-deposited particles are mostly amorphous silicon with a small fraction of silicon nanocrystals. Transmission electron micrography confirmed individual 3-15 nm silicon nanocrystals. Although particles were not mono-dispersed, they were well separated and not coagulated.

  1. Synthesis of Silicon Nanocrystals in Microplasma Reactor

    Science.gov (United States)

    Nozaki, Tomohiro; Sasaki, Kenji; Ogino, Tomohisa; Asahi, Daisuke; Okazaki, Ken

    Nanocrystalline silicon particles with a grain size of at least less than 10 nm are widely recognized as one of the key materials in optoelectronic devices, electrodes of lithium battery, bio-medical labels. There is also important character that silicon is safe material to the environment and easily gets involved in existing silicon technologies. To date, several synthesis methods such as sputtering, laser ablation, and plasma enhanced chemical vapor deposition (PECVD) based on low-pressure silane chemistry (SiH4) have been developed for precise control of size and density distributions of silicon nanocrystals. We explore the possibility of microplasma technologies for the efficient production of mono-dispersed nanocrystalline silicon particles in a micrometer-scale, continuous-flow plasma reactor operated at atmospheric pressure. Mixtures of argon, hydrogen, and silicon tetrachloride were activated using very high frequency (VHF = 144 MHz) power source in a capillary glass tube with a volume of less than 1 μ-liter. Fundamental plasma parameters of VHF capacitively coupled microplasma were characterized by optical emission spectroscopy, showing electron density of approximately 1015 cm-3 and rotational temperature of 1500 K, respectively. Such high-density non-thermal reactive plasma has a capability of decomposing silicon tetrachloride into atomic silicon to produce supersaturated atomic silicon vapor, followed by gas phase nucleation via three-body collision. The particle synthesis in high-density plasma media is beneficial for promoting nucleation process. In addition, further growth of silicon nuclei was able to be favorably terminated in a short-residence time reactor. Micro Raman scattering spectrum showed that as-deposited particles were mostly amorphous silicon with small fraction of silicon nanocrystals. Transmission electron micrograph confirmed individual silicon nanocrystals of 3-15 nm size. Although those particles were not mono-dispersed, they were

  2. Silicon nanowires: structure and properties

    International Nuclear Information System (INIS)

    Nezhdanov, A.V.; Mashin, A.I.; Razuvaev, A.G.; Ershov, A.V.; Ignatov, S.K.

    2006-01-01

    An attempt to grow silicon nanowires has been made by electron beam evaporation on highly oriented pyrolytic substrate. Needle-like objects are located along the normal to a substrate (density 2 x 10 11 cm -2 ). For modeling quasi-one-dimensional objects calculations of nuclear structure and energy spectra have been accomplished. A fullerene-like structure Si 24 is proposed as a basic atomic configuration of silicon nanowires [ru

  3. The influence of green microstructure and sintering parameters on precipitation process during copper-nickel-zinc ferrites sintering

    Directory of Open Access Journals (Sweden)

    Barba, Antonio

    2014-04-01

    Full Text Available Microstructural changes that occur during heat treatment of copper-nickel-zinc ferrites have been studied. The process of precipitation of the two types of crystals that occur during the sintering process has been analyzed. It is found that this process depends on dry relative density of the press specimens and on the following sintering parameters: sintering temperature, sintering time and cooling rate of the thermal cycle. Crystal precipitates characterization have been done by scanning electron microscopy (SEM, energy-dispersive X-ray (EDX analysis, X-ray diffraction (XRD, and X-ray photoelectron spectroscopy (XPS. These techniques have allowed to determine the nature of these crystals, which in this case correspond to zinc and copper oxides. It has been used two chemical reactions to explain the bulk precipitation and subsequent re-dissolution of these crystal precipitates during sintering.En este trabajo se han estudiado los cambios microestructurales que se producen durante el tratamiento térmico de las ferritas de cobre-níquel-cinc y se ha analizado el proceso de precipitación de los dos tipos de cristales que aparecen durante el proceso de sinterización. Se ha encontrado que este proceso depende de la densidad relativa en seco de las muestras compactadas y de las siguientes variables de la etapa de sinterización: temperatura y tiempo de sinterización y velocidad de enfriamiento. La caracterización de los cristales precipitados se ha realizado por microscopía electrónica de barrido (MEB, microanálisis por dispersión de energía de rayos X (EDX, difracción de rayos X (DRX, y espectroscopía de fotoelectrones de rayos X (XPS. Estas técnicas han permitido determinar la naturaleza de estos cristales, que en este caso corresponden a los óxidos de cinc y de cobre. Se han propuesto dos reacciones químicas que permiten explicar el proceso de precipitación y la posterior re-disolución de estos cristales precipitados durante la

  4. Grain growth in uranium nitride prepared by spark plasma sintering

    Science.gov (United States)

    Johnson, Kyle D.; Lopes, Denise Adorno

    2018-05-01

    Uranium mononitride (UN) has long been considered a potential high density, high performance fuel candidate for light water reactor (LWR) and fast reactor (FR) applications. However, deployability of this fuel has been limited by the notable resistance to sintering and subsequent difficulty in producing a desirable microstructure, the high costs associated with 15N enrichment, as well as the known proclivity to oxidation and interaction with steam. In this study, the stimulation of grain growth in UN pellets sintered using SPS has been investigated. The results reveal that by using SPS and controlling temperature, time, and holding pressure, grain growth can be stimulated and controlled to produce a material featuring both a desired porosity and grain size, at least within the range of interest for nuclear fuel candidates. Grain sizes up to 31 μm were obtained using temperatures of 1650 °C and hold times of 15 min. Evaluation by EBSD reveal grain rotation and coalescence as the dominant mechanism in grain growth, which is suppressed by the application of higher external pressure. Moreover, complete closure of the porosity of the material was observed at relative densities of 96% TD, resulting in a material with sufficient porosity to accommodate LWR burnup. These results indicate that a method exists for the economic fabrication of an 15N-bearing uranium mononitride fuel with favorable microstructural characteristics compatible with use in a light water-cooled nuclear reactor.

  5. Multiple recycling of NdFeB-type sintered magnets

    Energy Technology Data Exchange (ETDEWEB)

    Zakotnik, M. [Department of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom)], E-mail: miha.zakotnik@gmail.com; Harris, I.R.; Williams, A.J. [Department of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom)

    2009-02-05

    Some fully dense, sintered NdFeB-type magnets (employed in VCM disc drives) have been subjected to a recycling process using the hydrogen decrepitation (HD) process. After a brief milling treatment, the powder was aligned, pressed and re-sintered and this procedure was repeated four times with a progressive fall in the density and in the magnetic properties. The chemical analysis indicated that this was due to the progressive oxidation of the Nd-rich material and to some Nd loss by evaporation. The procedure was then repeated but with the addition (blending) of a fine powder of neodymium hydride after the first cycle. It was found that the addition of 1 at.% of neodymium at each stage was sufficient to maintain the density and the magnetic properties of the recycled magnets up to and including the 4th cycle. Inductively coupled plasma (ICP) and metallographic analysis indicated that the neodymium hydride additions compensated for the neodymium loss due to evaporation and to oxidation so that the proportion of Nd-rich material remained approximately constant. The additional amount of Nd{sub 2}O{sub 3} in the blended recycled magnets appeared to inhibit grain growth on the 3rd and 4th cycles when compared to that of the unblended magnets. The next challenge is to see if the process can be scaled-up to an industrial scale.

  6. Compaction and sintering of nickel powder used encapsulation of irradiation targets

    International Nuclear Information System (INIS)

    Miyano, Rosana S.L.; Guimaraes, Raquel R.F.L.; Rossi, Jesualdo L.; Wendhausen, Paulo A.P.; Evangelista, Leandro L.

    2015-01-01

    The objective of this study was to develop an alternative way to produce targets for irradiation containing uranium, for the pair of 99 Mo production 99m Tc radionuclide. These targets were obtained by powder metallurgy, the compact serving as means for encapsulation a uranium cylinder to be irradiated. The targets were compacted in an axial hydraulic press applying different pressures up to 800 MPa. The sintering temperature was 600 °C in hydrogen atmosphere and it was used two sintering cycles, one for 4 h and the for 4 h plus 8 h time. The nickel powder was of high purity, that in order to provide the sealing of the fissile content within the compacted. The bulk density of compacted was evaluated by the method geometric. The porosity was measured by mercury porosimetry technique. The microstructure was investigated by optical microscopy. The results obtained with sintering powders involving confirm the feasibility of achieving a casing for uranium targets. (author)

  7. Optimization of thorium oxalate precipitation conditions relative to thorium oxide sinterability

    International Nuclear Information System (INIS)

    White, G.D.; Bray, L.A.; Hart, P.E.

    1980-01-01

    The effect of thorium oxalate precipitation conditions on derived oxide sinterability was investigated with the objective of producing ThO 2 powder that could be sintered to high density without premilling. Precipitation conditions examined were temperature, digestion time and agitation method which were employed in a two-level factorial experimental design to delineate their effects. The two levels for each of the factors, respectively, were 10 0 C and 70 0 C, 15 min and 360 min, and mechanical stirrer and a homogenizer that imparted both mechanical and ultrasonic agitation. The ThO 2 derived from each of the precipitation trials was characterized with respect to morphology, surface area, and crystallite size as well as sinterability. Only precipitation temperature had a significant effect upon all the properties of the derived oxide powders

  8. Syntheses and sintering of materials in view of nuclear waste storage

    International Nuclear Information System (INIS)

    Picot, V.; Glorieux, B.; Montel, J.M.; Deschanels, X.; Jorion, F.

    2005-01-01

    In the context of nuclear waste conditioning, the solid solution monazite-brabantite is extensively studied. Previous works have already shown its potential ability to confine minor actinides with excellent performance in term of chemical durability and structural stability. This present work concerns the synthesis and the sintering of such matrices. The challenge is to propose a synthesis and a sintering processes able to ensure the containment of actinides up to 10%wt. (Am, Cm, Np) in dense matrices (about 95% of the theoretical density). Those processes have to be performed on the equipment similar to that used in a facility dedicated to the high-level radioactive materials studies (glove box and hot cell). The optimized protocols, implying mixer-mill, synthesis by solid reaction at high temperature, uniaxial press compaction and sintering, are presented and discussed. (authors)

  9. Age hardening of a sintered Al-Cu-Mg-Si-(Sn) alloy

    International Nuclear Information System (INIS)

    Kent, D.; Schaffer, G.B.; Drennan, J.

    2005-01-01

    The age hardening response of a sintered Al-3.8 wt% Cu-1.0 wt% Mg-0.70 wt% Si alloy with and without 0.1 wt% Sn was investigated. The sequence of precipitation was characterised using transmission electron microscopy. The ageing response of the sintered Al-Cu-Mg-Si-(Sn) alloy is similar to that of cognate wrought 2xxx series alloys. Peak hardness was associated with a fine, uniform dispersion of lath shaped precipitates, believed to be either the β'or Q' phase, oriented along α directions and θ' plates lying on {0 0 1} α planes. Natural ageing also resulted in comparable behaviour to that observed in wrought alloys. Porosity in the powder metallurgy alloys did not significantly affect the kinetics of precipitation during artificial ageing. Trace levels of tin, used to aid sintering, slightly reduced the hardening response of the alloy. However, this was compensated for by significant improvements in density and hardness

  10. Effect of grain size on the hardness and reactivity of plasma-sintered beryllium

    International Nuclear Information System (INIS)

    Kim, Jae-Hwan; Nakamichi, Masaru

    2014-01-01

    Beryllium and its intermetallic compounds have attracted great attention as promising neutron multipliers in fusion reactors. In this study, mechanical and chemical properties of fabricated plasma-sintered beryllium (PS-Be) with different grain-sizes are investigated. Density and hardness analysis results of the fabricated PS-Be samples infer that a smaller grain size in the sintered Be indicates higher porosity and hardness. Sintered Be with a large grain size exhibits better resistance toward oxidation at 1273 K in dry air and at 1073 K in Ar/1% H 2 O, since oxidation at the grain boundaries of the determines the rate. In contrast, at 1273 K in Ar/1% H 2 O, a catastrophic oxidation is indicated by the increase of weight of the samples and the generation of H 2 from the bulk Be

  11. Evaluation of thermal properties of sintered beryllium oxide produced from Indian beryl ore

    International Nuclear Information System (INIS)

    Nair, Sathi R.; Ghanwat, S.J.; Patro, P.K.; Syambabu, M.; Mawal, N.E.; Mahata, T.; Sinha, P.K.

    2014-01-01

    Beryllium oxide (BeO) ceramics possess many interesting properties such as good thermal conductivity, high electrical resistivity, high chemical and thermal stability, low dielectric constant, low dielectric loss and low neutron absorption coefficient. These properties lead to its wide use in vacuum electronics technology, nuclear technology, microelectronics and photoelectron technology. The above properties depend on the purity of the material as well as density and microstructure of the sintered body. For high temperature application thermal conductivity and thermal expansion are two important parameters. In the present study, high purity fine BeO powder has been prepared by beryllate route starting with crude beryllium hydroxide. The powder has been sintered at 1550℃ and sintered samples have been evaluated for its thermal properties

  12. Enhanced Densification of PM Steels by Liquid Phase Sintering with Boron-Containing Master Alloy

    Science.gov (United States)

    Vattur Sundaram, Maheswaran; Surreddi, Kumar Babu; Hryha, Eduard; Veiga, Angela; Berg, Sigurd; Castro, Fransisco; Nyborg, Lars

    2018-01-01

    Reaching high density in PM steels is important for high-performance applications. In this study, liquid phase sintering of PM steels by adding gas-atomized Ni-Mn-B master alloy was investigated for enhancing the density levels of Fe- and Mo- prealloyed steel powder compacts. The results indicated that liquid formation occurs in two stages, beginning with the master alloy melting (LP-1) below and eutectic phase formation (LP-2) above 1373 K (1100 °C). Mo and C addition revealed a significant influence on the LP-2 temperatures and hence on the final densification behavior and mechanical properties. Microstructural embrittlement occurs with the formation of continuous boride networks along the grain boundaries, and its severity increases with carbon addition, especially for 2.5 wt pct of master alloy content. Sintering behavior, along with liquid generation, microstructural characteristics, and mechanical testing revealed that the reduced master alloy content from 2.5 to 1.5 wt pct (reaching overall boron content from 0.2 to 0.12 wt pct) was necessary for obtaining good ductility with better mechanical properties. Sintering with Ni-Mn-B master alloy enables the sintering activation by liquid phase formation in two stages to attain high density in PM steels suitable for high-performance applications.

  13. Spark plasma sintering of tungsten-yttrium oxide composites from chemically synthesized nanopowders and microstructural characterization

    International Nuclear Information System (INIS)

    Yar, M.A.; Wahlberg, Sverker; Bergqvist, Hans; Salem, H.G.; Johnsson, Mats; Muhammed, Mamoun

    2011-01-01

    Nano-crystalline W-1%Y 2 O 3 (wt.%) powder was produced by a modified solution chemical reaction of ammonium paratungstate (APT) and yttrium nitrate. The precursor powder was found to consist of particles of bimodal morphology i.e. large APT-like particles up to 20 μm and rectangular yttrium containing ultrafine plates. After thermal processing tungsten crystals were evolved from W-O-Y plate like particles. spark plasma sintering (SPS) was used to consolidate the powder at 1100 and 1200 deg. C for different holding times in order to optimize the sintering conditions to yield high density but with reduced grain growth. Dispersion of yttrium oxide enhanced the sinterability of W powder with respect to lanthanum oxide. W-1%Y 2 O 3 composites with sub-micron grain size showed improved density and mechanical properties as compared to W-La 2 O 3 composites. Sample sintered in two steps showed improved density, due to longer holding time at lower temperature (900 deg. C) and less grain growth due to shorter holding time at higher temperature i.e. 1 min at 1100 deg. C.

  14. Investigation of the sintering of barytocalcite with BaCO{sub 3} as a secondary phase for immobilizing carbon-14

    Energy Technology Data Exchange (ETDEWEB)

    Massoni, Nicolas, E-mail: nicolas.massoni@cea.fr [CEA, DEN, DTCD, SECM, Marcoule, BP17171, F-30207 Bagnols-sur-Cèze (France); Le Gallet, Sophie [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 6303 CNRS-Université Bourgogne Franche-Comté, 9 Av. Alain Savary, BP 47870, 21078 Dijon Cedex (France)

    2016-08-01

    The effect of a secondary phase (BaCO{sub 3}) on the sintering of synthetic barytocalcite has been investigated. It was found that this phase impacts the sintering positively by lowering the sintering activation energy from 230 to 160 kJ mol{sup −1}, by increasing the shrinkage rate and by reaching higher densities. However, BaCO{sub 3,} originally dispersed in the powder, was segregated by diffusion during sintering with a large part of it being located at the grain boundaries. The dense pellet is made of both phases barytocalcite and BaCO{sub 3}, what should be avoided to give the best leaching resistance. Thus the BaCO{sub 3} presence should be limited as much as possible by controlling the reactants stoichiometry during the synthesis. - Highlights: • Lowers the sintering activation energy from 230 to 160 kJ mol{sup −1}. • Changes the sintering process from volume diffusion to grain boundary diffusion. • Increases the shrinkage rate and allows to reach higher densities of the pellet.

  15. Influence of Sintering Temperature on Hardness and Wear Properties of TiN Nano Reinforced SAF 2205

    Science.gov (United States)

    Oke, S. R.; Ige, O. O.; E Falodun, O.; Obadele, B. A.; Mphalele, M. R.; Olubambi, P. A.

    2017-12-01

    Conventional duplex stainless steel degrade in wear and mechanical properties at high temperature. Attempts have been made by researchers to solve this problems leading to the dispersion of second phase particles into duplex matrix. Powder metallurgy methods have been used to fabricate dispersion strengthened steels with a challenge of obtaining fully dense composite and grain growth. This could be resolved by appropriate selection of sintering parameters especially temperature. In this research, spark plasma sintering was utilized to fabricate nanostructured duplex stainless steel grade SAF 2205 with 5 wt.% nano TiN addition at different temperatures ranging from 1000 °C to 1200 °C. The effect of sintering temperature on the microstructure, density, hardness and wear of the samples was investigated. The results showed that the densities and grain sizes of the sintered nanocomposites increased with increasing the sintering temperature. The microstructures reveal ferrite and austenite grains with fine precipitates within the ferrite grains. The study of the hardness and wear behaviors, of the samples indicated that the optimum properties were obtained for the sintering temperature of 1150 °C.

  16. Processing and properties of mechanically alloyed sintered steels with hard inclusions

    International Nuclear Information System (INIS)

    Gutsfeld, C.

    1991-10-01

    The aim of this work was the development of mechanically alloyed sintered steels with inert hard inclusions and their characterisation concerning the mechanical properties and the sliding wear behaviour. For this material concept the hard materials NbC, TiC, TiN and Al 2 O 3 were chosen with volume contents upto 20%. Mechanical alloying of the raw powders is a necessary prerequisit for an extreme fine and homogeneous microstructure and good mechanical and wear properties. Through a connecting powder annealing a conventional powder metallurgical processing with cold pressing and sintering is possible. For the consolidation pressureless liquid phase sintering initiated through phosphorus contents of 0,6% is suitable. Because of the strong hampering of grain growth through the included hard particles sintering densities upto 99% TD are possible with extreme fine microstructures. The mechanical properties can be varied in wide ranges. So tensile strengths of 1150 MPa, elongations at fracture of 17%, hardness of over 800 HV and fatigue strengths of 370 MPa have been reached. Throughout HIP or sinter forging the mechanical properties can be improved furthermore. (orig.) [de

  17. Laser-Induced Reductive Sintering of Nickel Oxide Nanoparticles under Ambient Conditions

    KAUST Repository

    Paeng, Dongwoo; Lee, Daeho; Yeo, Junyeob; Yoo, Jae-Hyuck; Allen, Frances I.; Kim, Eunpa; So, Hongyun; Park, Hee K.; Minor, Andrew M.; Grigoropoulos, Costas P.

    2015-01-01

    © 2015 American Chemical Society. This work is concerned with the kinetics of laser-induced reductive sintering of nonstoichiometric crystalline nickel oxide (NiO) nanoparticles (NPs) under ambient conditions. The mechanism of photophysical reductive sintering upon irradiation using a 514.5 nm continuous-wave (CW) laser on NiO NP thin films has been studied through modulating the laser power density and illumination time. Protons produced due to high-temperature decomposition of the solvent present in the NiO NP ink, oxygen vacancies in the NiO NPs, and electronic excitation in the NiO NPs by laser irradiation all affect the early stage of the reductive sintering process. Once NiO NPs are reduced by laser irradiation to Ni, they begin to coalesce, forming a conducting material. In situ optical and electrical measurements during the reductive sintering process take advantage of the distinct differences between the oxide and the metallic phases to monitor the transient evolution of the process. We observe four regimes: oxidation, reduction, sintering, and reoxidation. A characteristic time scale is assigned to each regime.

  18. Reactive sintering and microstructure development of tungsten carbide-AISI 304 stainless steel cemented carbides

    Energy Technology Data Exchange (ETDEWEB)

    Fernandes, C.M. [Department of Materials and Ceramics Engineering, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal); CEMUC-Mechanical Engineering Department, University of Coimbra, Rua Luís Reis Santos, Pinhal de Marrocos, 3030-788 Coimbra (Portugal); Oliveira, F.J. [Department of Materials and Ceramics Engineering, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal); Senos, A.M.R., E-mail: anamor@ua.pt [Department of Materials and Ceramics Engineering, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal)

    2017-06-01

    Sintering of WC-stainless steel (SS) composites within a typical binder range from 6 up to 15 wt% SS was investigated through constant heating rate dilatometry, in vacuum conditions, complemented by differential thermal analysis and by the study of the high temperature wetting behavior of SS on WC. The densification starts ∼900 °C with a typical densification curve for all compositions, where three distinct regions are discernible: the first one with a slow densification rate, followed by a second region where a sharp increase in the densification rate up to a maximum value dependent on the binder amount is observed and, finally, a third one with a slowdown of the densification rate until the end of the thermal cycle. The attained final density at 1450 °C is dependent on the binder amount, increasing proportionally to its initial content. The final microstructure presents a normal grain size distribution and appreciable amounts of eta-phase, besides the major WC phase and residual iron rich phase. The reactive densification behavior and the role of the liquid phase are interpreted accordingly with structural and kinetic data. - Highlights: • Sintering of WC-AISI304 composites starts ∼900 °C and involves three stages. • Densification is largely dominated by a reactive liquid phase sintering process. • Eta-phase constitutes a transient liquid phase during sintering. • Sintering cycles are dependent on the initial binder content.

  19. Routine instrumental procedures to characterise the mineralogy of modern and ancient silica sinters

    Energy Technology Data Exchange (ETDEWEB)

    Herdianita, N. Rina [Auckland Univ., Dept. of Geology, Auckland (New Zealand); Institute of Technology, Dept. of Geology, Bandung (Indonesia); Rodgers, Kerry A. [Auckland Univ., Dept. of Geology, Auckland (New Zealand); Australian Museum, Sydney, NSW (Australia); Browne, Patrick R.L. [Auckland Univ., Dept. of Geology, Auckland (New Zealand); Auckland Univ., Geothermal Inst., Auckland (New Zealand)

    2000-02-01

    Tightly constrained determinative methods can be used to characterise the silica minerals (opal-A, opal-CT, opal-C, quartz, moganite) and physical properties of silica sinters. Optimal X-ray powder diffraction operating parameters indicate silica lattice order/disorder using untreated, dry, <106 {mu}m powders scanned at 0.6deg 2{theta}/min with a step size of 0.01deg from 10-40deg 2{theta} and an internal Si standard. Simultaneous differential thermal and thermogravimetric analysis of 15.0 {+-}0.1 mg sinter samples of <106 {mu}m grain size, at a heating rate of 20degC/min in dry air, identify thermal events associated with dehydration, organic combustion, and changes of state. Where abundant organic matter is present, nitrogen is the preferred atmosphere for thermal analysis. Thermogravimetric-determined water contents of sinters differ from Penfield determinations reflecting the differing nature of the two techniques. Laser Raman microprobe techniques can be used to explore the mineralogy of particular sinter morphologies and habits down to 10 {mu}m diameter. The nature of the silica species present can assist in characterising individual sinter deposits and, combined with textural, density and/or porosity determinations, can lead to a better understanding of the hydrology and palaeohydrology of a geothermal prospect. (Author)

  20. Laser-Induced Reductive Sintering of Nickel Oxide Nanoparticles under Ambient Conditions

    KAUST Repository

    Paeng, Dongwoo

    2015-03-19

    © 2015 American Chemical Society. This work is concerned with the kinetics of laser-induced reductive sintering of nonstoichiometric crystalline nickel oxide (NiO) nanoparticles (NPs) under ambient conditions. The mechanism of photophysical reductive sintering upon irradiation using a 514.5 nm continuous-wave (CW) laser on NiO NP thin films has been studied through modulating the laser power density and illumination time. Protons produced due to high-temperature decomposition of the solvent present in the NiO NP ink, oxygen vacancies in the NiO NPs, and electronic excitation in the NiO NPs by laser irradiation all affect the early stage of the reductive sintering process. Once NiO NPs are reduced by laser irradiation to Ni, they begin to coalesce, forming a conducting material. In situ optical and electrical measurements during the reductive sintering process take advantage of the distinct differences between the oxide and the metallic phases to monitor the transient evolution of the process. We observe four regimes: oxidation, reduction, sintering, and reoxidation. A characteristic time scale is assigned to each regime.