WorldWideScience

Sample records for alumina

  1. Bauxite and alumina

    Science.gov (United States)

    Bray, E.L.

    2009-01-01

    The article provides information on bauxite and alumina mining. U.S. states like Alabama, Arkansas and Georgia produced small amounts of bauxite and bauxitic clays for nonmetallurgical uses. Total metallurgical-grade bauxite imports in 2008 is cited. The leading suppliers of bauxite to the U.S. are Jamaica, Guinea and Brazil. The estimated domestic production of alumina in 2008 is mentioned. It also discusses consumption and prices of both bauxite and alumina.

  2. Porous Alumina Films with Width-Controllable Alumina Stripes

    Directory of Open Access Journals (Sweden)

    Huang Shi-Ming

    2010-01-01

    Full Text Available Abstract Porous alumina films had been fabricated by anodizing from aluminum films after an electropolishing procedure. Alumina stripes without pores can be distinguished on the surface of the porous alumina films. The width of the alumina stripes increases proportionally with the anodizing voltage. And the pores tend to be initiated close to the alumina stripes. These phenomena can be ascribed to the electric field distribution in the alumina barrier layer caused by the geometric structure of the aluminum surface.

  3. Porous Alumina Films with Width-Controllable Alumina Stripes

    OpenAIRE

    Huang Shi-Ming; Pu Lin; Shi Yi; Huang Kai; Wu Zhi-Ming; Ji Li; Kang Jun-Yong

    2010-01-01

    Abstract Porous alumina films had been fabricated by anodizing from aluminum films after an electropolishing procedure. Alumina stripes without pores can be distinguished on the surface of the porous alumina films. The width of the alumina stripes increases proportionally with the anodizing voltage. And the pores tend to be initiated close to the alumina stripes. These phenomena can be ascribed to the electric field distribution in the alumina barrier layer caused by the geometric structure o...

  4. Microporous alumina ceramic membranes

    Science.gov (United States)

    Anderson, Marc A.; Sheng, Guangyao

    1993-01-01

    Several methods are disclosed for the preparation microporous alumina ceramic membranes. For the first time, porous alumina membranes are made which have mean pore sizes less than 100 Angstroms and substantially no pores larger than that size. The methods are based on improved sol-gel techniques.

  5. Reuse of activated alumina

    Energy Technology Data Exchange (ETDEWEB)

    Hobensack, J.E. [Martin Marietta Energy Systems, Inc., Piketon, OH (United States)

    1991-12-31

    Activated alumina is used as a trapping media to remove trace quantities of UF{sub 6} from process vent streams. The current uranium recovery method employs concentrated nitric acid which destroys the alumina pellets and forms a sludge which is a storage and disposal problem. A recently developed technique using a distilled water rinse followed by three dilute acid rinses removes on average 97% of the uranium, and leaves the pellets intact with crush strength and surface area values comparable with new material. Trapping tests confirm the effectiveness of the recycled alumina as UF{sub 6} trapping media.

  6. Alumina Technology Roadmap

    Energy Technology Data Exchange (ETDEWEB)

    none,

    2002-02-01

    The Alumina Technology Roadmap outlines a comprehensive long-term research and development plan that defines the industry's collective future and establishes a clear pathway forward. It emphasizes twelve high-priority R&D areas deemed most significant in addressing the strategic goals.

  7. Solid Lubricant For Alumina

    Science.gov (United States)

    Dellacorte, Christopher; Pepper, Stephen V.; Honecy, Frank S.

    1993-01-01

    Outer layer of silver lubricates, while intermediate layer of titanium ensures adhesion. Lubricating outer films of silver deposited on thin intermediate films of titanium on alumina substrates found to reduce sliding friction and wear. Films provide effective lubrication for ceramic seals, bearings, and other hot sliding components in advanced high-temperature engines.

  8. Nanoindentation of shock deformed alumina

    International Nuclear Information System (INIS)

    In the current study, the experimental results on the nanoindentation response of both as prepared and shock recovered alumina of 10 μm grain size and identical processing history are presented and analyzed. The shock recovery experiments were deliberately conducted with gas gun arrangements at shock pressures much above the Hugoniot Elastic Limit (HEL) of alumina. The nanoindentation experiments were conducted at 10-1000 mN load with a Berkovich indenter. The nanohardness and Young's modulus value of shock recovered alumina were always lower than those of the as prepared alumina samples. Subsequently, the detailed characterizations of the shock recovered alumina samples by X-ray diffraction, scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were utilized to understand the reasons behind the drop in nanohardness and Young's modulus of shock recovered alumina samples.

  9. High Temperature Stability of Potassium Beta Alumina

    Science.gov (United States)

    Williams, R. M.; Kisor, A.; Ryan, M. A.

    1996-01-01

    None. From Objectives section: Evaluate the stability of potassium beta alumina under potassium AMTEC operating conditions. Evaluate the stability regime in which potassium beta alumina can be fabricated.

  10. Adsorptive desulfurization by activated alumina.

    Science.gov (United States)

    Srivastav, Ankur; Srivastava, Vimal Chandra

    2009-10-30

    This study reports usage of commercial grade activated alumina (aluminum oxide) as adsorbent for the removal of sulfur from model oil (dibenthiophene (DBT) dissolved in n-hexane). Bulk density of alumina was found to be 1177.77 kg/m(3). The BET surface area of alumina was found to decrease from 143.6 to 66.4 m(2)/g after the loading of DBT at optimum conditions. The carbon-oxygen functional groups present on the surface of alumina were found to be effective in the adsorption of DBT onto alumina. Optimum adsorbent dose was found to be 20 g/l. The adsorption of DBT on alumina was found to be gradual process, and quasi-equilibrium reached in 24 h. Langmuir isotherm best represented the equilibrium adsorption data. The heat of adsorption and change in entropy for DBT adsorption onto alumina was found to be 19.5 kJ/mol and 139.2 kJ/mol K, respectively. PMID:19523762

  11. Alumina-Reinforced Zirconia Composites

    Science.gov (United States)

    Choi, Sung R.; Bansal, Narottam P.

    2003-01-01

    Alumina-reinforced zirconia composites, used as electrolyte materials for solid oxide fuel cells, were fabricated by hot pressing 10 mol percent yttria-stabilized zirconia (10-YSZ) reinforced with two different forms of alumina particulates and platelets each containing 0 to 30 mol percent alumina. Major mechanical and physical properties of both particulate and platelet composites including flexure strength, fracture toughness, slow crack growth, elastic modulus, density, Vickers microhardness, thermal conductivity, and microstructures were determined as a function of alumina content either at 25 C or at both 25 and 1000 C. Flexure strength and fracture toughness at 1000 C were maximized with 30 particulate and 30 mol percent platelet composites, respectively, while resistance to slow crack growth at 1000 C in air was greater for 30 mol percent platelet composite than for 30 mol percent particulate composites.

  12. Alumina supported iridium catalysts - preparation

    International Nuclear Information System (INIS)

    This report describes the method employed in the preparation of alumina supported iridium catalysts, with metal contents between 30 and 40%, that will be used for hydrazine monopropellant decomposition. (author)

  13. Gelcasting polycrystalline alumina

    Energy Technology Data Exchange (ETDEWEB)

    Janney, M.A. [Oak Ridge National Lab., TN (United States)

    1997-04-01

    This work is being done as part of a CRADA with Osram-Sylvania, Inc. (OSI) OSI is a major U.S. manufacturer of high-intensity lighting. Among its products is the Lumalux{reg_sign} line of high-pressure sodium vapor arc lamps, which are used for industrial, highway, and street lighting. The key to the performance of these lamps is the polycrystalline alumina (PCA) tube that is used to contain the plasma that is formed in the electric arc. That plasma consists of ionized sodium, mercury, and xenon vapors. The key attributes of the PCA tubes are their transparency (95% total transmittance in the visible region), their refractoriness (inner wall temperature can reach 1400{degrees}C), and their chemical resistance (sodium and mercury vapor are extremely corrosive). The current efficiency of the lamps is very high, on the order of several hundred lumens / watt. (Compare - incandescent lamps -13 lumens/watt fluorescent lamps -30 lumens/watt.) Osram-Sylvania would like to explore using gelcasting to form PCA tubes for Lumalux{reg_sign} lamps, and eventually for metal halide lamps (known as quartz-halogen lamps). Osram-Sylvania, Inc. currently manufactures PCA tubes by isostatic pressing. This process works well for the shapes that they presently use. However, there are several types of tubes that are either difficult or impossible to make by isostatic pressing. It is the desire to make these new shapes and sizes of tubes that has prompted Osram-Sylvania`s interest in gelcasting. The purpose of the CRADA is to determine the feasibility of making PCA items having sufficient optical quality that they are useful in lighting applications using gelcasting.

  14. Dynamic Tensile Response of Structured Alumina-Al Composites

    Science.gov (United States)

    Atisivan, Raj; Bandyopadhyay, Amit; Gupta, Yogendra

    2001-06-01

    Plate impact experiments were carried out to examine the high strain-rate tensile response of alumina-aluminum composites with tailored microstructures. A novel processing technique was used to fabricate interpenetrating phase alumina-aluminum composites with controlled and reproducible microstructures. Fused deposition modeling (FDM), a commercially available rapid prototyping technique, was used to produce the controlled porosity mullite ceramic preforms. Alumina-Al composites were then processed via reactive metal infiltration of porous mullite ceramics. With this approach, both the micro as well as the macro structures can be designed via computer aided design (CAD) to tailor the properties of the composites. Two sets of dynamic tensile experiments were performed. In the first, the metal content was varied between 23 and 39 wt. percent. In the second, the microstructure was varied while holding the metal content nearly constant. Samples with higher metal content, as expected, displayed better spall resistance. For a given metal content, samples with finer metal diameter showed better spall resistance. Relationship of the microstructural parameters on the dynamic tensile response of the structured composites will be discussed. Work supported by DOE.

  15. Transport properties of alumina nanofluids

    International Nuclear Information System (INIS)

    Recent studies have showed that nanofluids have significantly greater thermal conductivity compared to their base fluids. Large surface area to volume ratio and certain effects of Brownian motion of nanoparticles are believed to be the main factors for the significant increase in the thermal conductivity of nanofluids. In this paper all three transport properties, namely thermal conductivity, electrical conductivity and viscosity, were studied for alumina nanofluid (aluminum oxide nanoparticles in water). Experiments were performed both as a function of volumetric concentration (3-8%) and temperature (2-50 deg. C). Alumina nanoparticles with a mean diameter of 36 nm were dispersed in water. The effect of particle size was not studied. The transient hot wire method as described by Nagaska and Nagashima for electrically conducting fluids was used to test the thermal conductivity. In this work, an insulated platinum wire of 0.003 inch diameter was used. Initial calibration was performed using de-ionized water and the resulting data was within 2.5% of standard thermal conductivity values for water. The thermal conductivity of alumina nanofluid increased with both increase in temperature and concentration. A maximum thermal conductivity of 0.7351 W m-1 K-1 was recorded for an 8.47% volume concentration of alumina nanoparticles at 46.6 deg. C. The effective thermal conductivity at this concentration and temperature was observed to be 1.1501, which translates to an increase in thermal conductivity by 22% when compared to water at room temperature. Alumina being a good conductor of electricity, alumina nanofluid displays an increasing trend in electrical conductivity as volumetric concentration increases. A microprocessor-based conductivity/TDS meter was used to perform the electrical conductivity experiments. After carefully calibrating the conductivity meter's glass probe with platinum tip, using a standard potassium chloride solution, readings were taken at various

  16. Ion guiding in alumina capillaries

    DEFF Research Database (Denmark)

    Juhász, Z.; Sulik, B.; Biri, S.;

    2009-01-01

    Transmission of a few keV impact energy Ne ions through capillaries in anodic alumina membranes has been studied with different ion counting methods using an energy dispersive electrostatic spectrometer, a multichannel plate (MCP) array and sensitive current-measurement. In the present work, we...

  17. MECHANICAL BEHAVIOUR OF ALUMINA-ZIRCONIA COMPOSITE BY SLURRY METHOD

    OpenAIRE

    JYOTI PRAKASH; DEVENDRA KUMAR; KALYANI MOHANTA

    2011-01-01

    Alumina has got some excellent properties like chemical inertness, thermal and mechanical strength against hazardous environment. Alumina is a good ceramic material which is being used for structuralapplications. To enhance the toughness and strength of the body some Zirconia is also used with it. The use of Zirconia in alumina is known as toughening of alumina. One difficulty arises, when alumina and alumina toughened composite are sintered , because the low sinterability of Alumina-Zirconia...

  18. Processing and Performance of Alumina Fiber Reinforced Alumina Composites

    Institute of Scientific and Technical Information of China (English)

    P.Y.Lee; T.Uchijima; T.Yano

    2003-01-01

    Processing of alumina fiber-reinforced alumina matrix composites by hot-pressing was described. The mechanical properties of the composites fabricated by different sintering conditions including temperature and pressure have been investigated. The results indicated that the higher sintering temperature and pressure corresponded to the higher bulk density and higher maximum strength of the composite, whereas the pseudo-ductility of the composite was lower. The preliminary results of the composite with monazite-coated fibers showed that maximum strength could be improved up to 35% compared with the noncoated fiber composite in the same sintering condition. Moreover, the fracture behavior of the composite changed from completely brittle fracture to non-brittle fracture under the suitable sintering conditions. SEM observation of the fracture surface indicated that the coating worked as a protective barrier and avoided sintering of the fibers together even at high temperature and pressure during densification process.

  19. Sintering behaviour of spinel–alumina composites

    Indian Academy of Sciences (India)

    Soumen Pal; A K Bandyopadhyay; P G Pal; S Mukherjee; B N Samaddar

    2009-04-01

    Study of alumina–magnesia binary phase diagram reveals that around 40–50 wt% alumina dissolves in spinel (MgAl2O4) at 1600°C. Solid solubility of alumina in spinel decreases rapidly with decreasing temperature, which causes exsolution of alumina from spinel phase. Previous work of one of the authors revealed that the exsolution of alumina makes some interlocking structures in between alumina and spinel phases. In the present investigation, refractory grade calcined alumina and spinel powder were used to make different batch compositions. Green pellets, formed at a pressure of 1550 kg cm-2 were fired at different temperatures of 1500°, 1550° and 1600°C for 2 h soaking time. Bulk density, percent apparent porosity, firing shrinkage etc were measured at each temperature. Sintering results were analysed to understand the mechanism of spinel–alumina interactions. SEM study of present samples does not reveal the distinct precipitation of needle shaped -alumina from spinel, but has some effect on densification process of spinel–alumina composites. Microstructural differences between present and previous work suggest an ample scope of further work in spinel–alumina composites.

  20. Synthesis of zirconia toughened alumina

    International Nuclear Information System (INIS)

    This paper deals with the synthesis of zirconia toughened alumina (ZTA) and evaluation of its mechanical properties. ZTA ceramics were prepared by partial chemical route. High purity alumina (particle size 0.48 μm) was coated with yttria stabilised zirconia through solution techniques. Small amounts of dopants such as MgO, MnO and TiO2 were added to ZTA as densification aids. These powders were calcined at 650 deg C for 1 hour, followed by wet ball milling, compaction, sintering at 1600 deg C for 2.5 hour. Sintered density values upto 90% of theoretical density of ZTA were achieved. Hardness values upto 1800 VPN and modulus of rupture values upto 180 MPa were obtained. (author)

  1. Bauxite Mining and Alumina Refining

    OpenAIRE

    Donoghue, A. Michael; Frisch, Neale; Olney, David

    2014-01-01

    Objective: To describe bauxite mining and alumina refining processes and to outline the relevant physical, chemical, biological, ergonomic, and psychosocial health risks. Methods: Review article. Results: The most important risks relate to noise, ergonomics, trauma, and caustic soda splashes of the skin/eyes. Other risks of note relate to fatigue, heat, and solar ultraviolet and for some operations tropical diseases, venomous/dangerous animals, and remote locations. Exposures to bauxite dust,...

  2. Synthesis of high porosity, monolithic alumina aerogels

    Energy Technology Data Exchange (ETDEWEB)

    Poco, J F; Satcher, J H; Hrubesh, L W

    2000-09-20

    Many non-silica aerogels are notably weak and fragile in monolithic form. Particularly, few monolithic aerogels with densities less than 50kg/m3 have any significant strength. It is especially difficult to prepare uncracked monoliths of pure alumina aerogels that are robust and moisture stable. In this paper, we discuss the synthesis of strong, stable, monolithic, high porosity (>98% porous) alumina aerogels, using a two-step sol-gel process. The alumina aerogels have a polycrystalline morphology that results in enhanced physical properties. Most of the measured physical properties of the alumina aerogels are superior to those for silica aerogels for equivalent densities.

  3. Influence of Alumina Addition on the Optical Property of Zirconia/Alumina Composite Dental Ceramics

    Institute of Scientific and Technical Information of China (English)

    JIANG Li; LIAO Yunmao; LI Wei; WAN Qianbing; ZHAO Yongqi

    2011-01-01

    The influence of various alumina additions on the optical property of zirconia/alumina composite ceramics was investigated.The relative sintered densities,transmittances,color and the microstructure of the composite ceramics were studied.The experimental results showed that the relative sintered densities and transmittances decreased with alumina addition.The lightness increased obviously but the chroma change was small.Pure zirconia nanopowders sintered densely could obtain the relatively high transmittance,while the transmittance and the lightness of slight addition changed significantly.The zirconia/alumina composite ceramics with alumina addition less than 7.5wt% could achieve the relatively stable and reliable optical properties.

  4. Fracture toughness of advanced alumina ceramics and alumina matrix composites used for cutting tool edges

    OpenAIRE

    M. Szutkowska

    2012-01-01

    Purpose: Specific characteristics in fracture toughness measurements of advanced alumina ceramics and alumina matrix composites with particular reference to α-Al2O3, Al2O3-ZrO2, Al2O3-ZrO2-TiC and Al2O3-Ti(C,N) has been presented.Design/methodology/approach: The present study reports fracture toughness obtained by means of the conventional method and direct measurements of the Vickers crack length (DCM method) of selected tool ceramics based on alumina: pure alumina, alumina-zirconia composit...

  5. Characterization and application of electrospun alumina nanofibers

    Science.gov (United States)

    2014-01-01

    Alumina nanofibers were prepared by a technique that combined the sol–gel and electrospinning methods. The solution to be electrospun was prepared by mixing aluminum isopropoxide (AIP) in ethanol, which was then refluxed in the presence of an acid catalyst and polyvinylpyrolidone (PVP) in ethanol. The characterization results showed that alumina nanofibers with diameters in the range of 102 to 378 nm were successfully prepared. On the basis of the results of the XRD and FT-IR, the alumina nanofibers calcined at 1,100°C were identified as comprising the α-alumina phase, and a series of phase transitions such as boehmite → γ-alumina → α-alumina were observed from 500°C to 1,200°C. The pore size of the obtained γ-alumina nanofibers is approximately 8 nm, and it means that they are mesoporous materials. The kinetic study demonstrated that MO adsorption on alumina nanofibers can be seen that the pseudo-second-order kinetic model fits better than the pseudo-first-order kinetic model. PMID:24467944

  6. MECHANISMS OF INITIAL SINTERING OF A FINE ALUMINA POWDER

    OpenAIRE

    S. Raman; Doremus, R.; R. German

    1986-01-01

    The mechanism of initial sintering of alumina was explored by electron microscopy and X-ray diffraction. The transformation of gamma to alpha alumina influenced sintering behavior. This transformation appears to involve plastic deformation in the alumina. Sintering of fine alpha alumina powder directly occurs with an activation energy close to that of grain boundary diffusion of oxygen.

  7. Dissolution Kinetics of Alumina Calcine

    Energy Technology Data Exchange (ETDEWEB)

    Batcheller, Thomas Aquinas

    2001-09-01

    Dissolution kinetics of alumina type non-radioactive calcine was investigated as part of ongoing research that addresses permanent disposal of Idaho High Level Waste (HLW). Calcine waste was produced from the processing of nuclear fuel at the Idaho Nuclear Technology and Engineering Center (INTEC). Acidic radioactive raffinates were solidified at ~500°C in a fluidized bed reactor to form the dry granular calcine material. Several Waste Management alternatives for the calcine are presented in the Idaho High Level Waste Draft EIS. The Separations Alternative addresses the processing of the calcine so that the HLW is ready for removal to a national geological repository by the year 2035. Calcine dissolution is the key front-end unit operation for the separations alternative.

  8. Alumina forming iron base superalloy

    Science.gov (United States)

    Yamamoto, Yukinori; Muralidharan, Govindarajan; Brady, Michael P.

    2014-08-26

    An austenitic stainless steel alloy, consists essentially of, in weight percent 2.5 to 4 Al; 25 to 35 Ni; 12 to 19 Cr; at least 1, up to 4 total of at least one element selected from the group consisting of Nb and Ta; 0.5 to 3 Ti; less than 0.5 V; 0.1 to 1 of at least on element selected from the group consisting of Zr and Hf; 0.03 to 0.2 C; 0.005 to 0.1 B; and base Fe. The weight percent Fe is greater than the weight percent Ni. The alloy forms an external continuous scale including alumina, and contains coherent precipitates of .gamma.'-Ni.sub.3Al, and a stable essentially single phase FCC austenitic matrix microstructure. The austenitic matrix is essentially delta-ferrite-free and essentially BCC-phase-free.

  9. Alumina Thin Film Growth: Experiments and Modeling

    OpenAIRE

    Wallin, Erik

    2007-01-01

    The work presented in this thesis deals with experimental and theoretical studies related to the growth of crystalline alumina thin films. Alumina, Al2O3, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. Many of the possibilities of alumina, and the problems associated with thin film synthesis of the material, are due to the existence of a range of different crystalline phases. Controlling the formation of the desired phase and the transformati...

  10. Characterization and application of electrospun alumina nanofibers

    OpenAIRE

    Kim, Jeon-Hee; Yoo, Seung-Joon; Kwak, Dong-Heui; Jung, Heung-Joe; KIM, Tae-Young; Park, Kyung-Hee; Lee, Jae-Wook

    2014-01-01

    Alumina nanofibers were prepared by a technique that combined the sol–gel and electrospinning methods. The solution to be electrospun was prepared by mixing aluminum isopropoxide (AIP) in ethanol, which was then refluxed in the presence of an acid catalyst and polyvinylpyrolidone (PVP) in ethanol. The characterization results showed that alumina nanofibers with diameters in the range of 102 to 378 nm were successfully prepared. On the basis of the results of the XRD and FT-IR, the alumina nan...

  11. Recent Development of High Alumina Refractories in China

    Institute of Scientific and Technical Information of China (English)

    WANGJin-xiang; LIUJie-hua

    1994-01-01

    The paper reviews the achievements which have been attained recently in China in high alumina refractories raw materials and their products,including 1) homogenization ,urification and electric fusion of high alumina raw materials and synthesizing of spinel from natural raw materials;2) processing principle and characteristics and microstructural features of creep-resistance high alu-mina brick ,alumina-magnesia-carbon brick and thermal shock resistanced high alumina brikc and their application in practice.

  12. Burned Microporous Alumina-Graphite Brick

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    @@ 1 Scope This standard specifies the definition,classifica-tion,technical requirements,test methods,inspection rules,marking,packing,transportation and quality certificate of burned microporous alumina-graphite brick.

  13. Acoustic Emission and Damage Characteristics of Alumina

    Institute of Scientific and Technical Information of China (English)

    REN Hui-lan; NING Jian-guo; HE Jian-hua

    2009-01-01

    gy, AE counts, AE amplitude changing with loading time are analyzed for the notched alumina specimen. It is indicated that AE characteristic parameters reflect the damage process and fracture of material.

  14. Loss tangent measurements on unirradiated alumina

    Energy Technology Data Exchange (ETDEWEB)

    Zinkle, S.J.; Goulding, R.H. [Oak Ridge National Lab., TN (United States)

    1996-04-01

    Unirradiated room temperature loss tangent for sapphire and several commercial grades of polycrystalline alumina are complied for frequencies between 10{sup 5} and 4x10{sup 11} Hz. Sapphire exhibits significantly lower values for the loss tangent at frequencies up to 10{sup 11} Hz. The loss tangents of 3 different grades of Wesgo alumina (AL300, AL995, AL998) and 2 different grades of Coors alumina (AD94, AD995) have typical values near {approx}10{sup -4} at a frequency of 10{sup 8} Hz. On the other hand, the loss tangent of Vitox alumina exhibits a large loss peak tan d{approx} 5x10{sup -3} at this frequency.

  15. Reactivity of non-stoichiometric black alumina

    International Nuclear Information System (INIS)

    Oxides such as alumina, when divided or poorly crystallized, show enhanced physico-chemical properties with respect to those of non-divided crystals of the same solids. A stoichiometric difference may even be produced in the alumina, which brings about a new modification of its properties. However its characteristics of hydrogen chemisorption or of catalytic activity in ethylene hydrogenation do not appear to depend on the stoichiometric difference. (author)

  16. Point defects in alumina studied by thermoluminescence

    OpenAIRE

    Papin, Eric; Grosseau, Philippe; Guilhot, Bernard; Benabdesselam, Mourad; Iacconi, Philibert

    1997-01-01

    Alpha alumina powders have been produced by thermal treatment under controlled atmosphere of highly pure gamma alumina. The influence of the atmosphere and the addition of dopants (Mg2+, Cr3+, Th4+) were studied by thermoluminescence (TL). TL is a technique which gives information about point defects. It allowed to reveal the presence of oxygen and aluminium vacancies. The sintering of undoped powders prepared under different atmosphere was investigated by dilatometry. Powders prepared under ...

  17. Dissolution of alumina in stainless steelmaking slags

    Energy Technology Data Exchange (ETDEWEB)

    Divakar, M.; Lahiri, A.K. [Indian Inst. of Science, Bangalore (India). Dept. of Metallurgy; Goernerup, M. [Uddeholm Technology AB (Sweden)

    2001-02-01

    Dissolution of alumina in stainless steelmaking slags was studied by conducting laboratory scale experiments on typical slags in the temperature range 1823-1923 K. The mechanism of dissolution was studied under the actual steelmaking conditions where several phenomena such as simultaneous reduction of chromium, iron and vanadium oxides by carbon, in-situ gas generated due to the reduction, foam/emulsion formation occur. The kinetics of alumina dissolution are studied under the influence of the above mentioned phenomena. (orig.)

  18. Monitoring Transport Across Modified Nanoporous Alumina Membranes

    OpenAIRE

    Steinle, Erich D.; Andrew L. Molder; Hardin, Jonathan L.; Ravikanth Kona; Penumetcha, Sai S.

    2007-01-01

    This paper describes the use of several characterization methods to examine alumina nanotubule membranes that have been modified with specific silanes. The function of these silanes is to alter the transport properties through the membrane by changing the local environment inside the alumina nanotube. The presence of alkyl groups, either long (C18) or short and branched (isopropyl) hydrocarbon chains, on these silanes significantly decreases the rate of transport of permeant molecules through...

  19. Silicide characterization at alumina-niobium interfaces

    OpenAIRE

    McKeown, JT; Radmilovic, Velimir R; Gronsky, R.; Glaeser, AM

    2011-01-01

    Alumina–niobium interfaces formed by liquidfilm-assisted joining with copper/niobium/copper interlayers exhibited microstructures that depend on the nature of the alumina components. Characterization of these interfaces in the transmission electron microscope provided insight on the relationship between interfacial microstructure and fracture performance. Interfaces between sapphire and niobium and those between high-purity (99.9%) polycrystalline alumina and niobium were free of secondary ph...

  20. Alumina Recovery from Kaolin with Mineral Impurities

    Institute of Scientific and Technical Information of China (English)

    SI Peng; QIAO Xiuchen; YU Jianguo

    2012-01-01

    The alumina recovery from low grade kaolin (K-JS) treated through thermal and mechanical methods was investigated.High grade kaolin (K-SX) was used as comparison.The optimum calcination temperatures for K-JS and K-SX were both 600 ℃,which resulted in 89.34wt% of alumina extraction from K-JS and 83.37wt% from K-SX.With the increase in calcination temperature,the chemical reactivity of calcined K-JS and K-SX to acid decreased.Mechanical treatment was much more effective in increasing the alumina extraction from activated kaolin.Around 99wt% of alumina was extracted from K-JS ground for 10 hours and 95wt% of alumina was extracted from K-SX ground for 20 hours.The IR results showed that the substitute of Al for Si occurred in calcined K-SX,however,the impurities in K-JS decreased this substitute.More alumina could be extracted from low grade kaolin than that from high grade kaolin under identical thermal or mechanical conditions.

  1. Alumina Inlay Failure in Cemented Polyethylene-backed Total Hip Arthroplasty

    OpenAIRE

    Iwakiri, Kentaro; Iwaki, Hiroyoshi; Minoda, Yukihide; Ohashi, Hirotsugu; Takaoka, Kunio

    2008-01-01

    Alumina-on-alumina bearings for THA have markedly improved in mechanical properties through advances in technology; however, alumina fracture is still a concern. We retrospectively reviewed 77 patients (82 hips) with cemented alumina-on-alumina THAs to identify factors relating to alumina failure. The mean age of the patients at surgery was 63 years. The prostheses had a cemented polyethylene-backed acetabular component with an alumina inlay and a 28-mm alumina head. Revision surgery was perf...

  2. Monitoring Transport Across Modified Nanoporous Alumina Membranes

    Directory of Open Access Journals (Sweden)

    Erich D. Steinle

    2007-11-01

    Full Text Available This paper describes the use of several characterization methods to examinealumina nanotubule membranes that have been modified with specific silanes. The functionof these silanes is to alter the transport properties through the membrane by changing thelocal environment inside the alumina nanotube. The presence of alkyl groups, either long(C18 or short and branched (isopropyl hydrocarbon chains, on these silanes significantlydecreases the rate of transport of permeant molecules through membranes containingalumina nanotubes as monitored via absorbance spectroscopy. The presence of an ionicsurfactant can alter the polarity of these modified nanotubes, which correlates to anincreased transport of ions. Fluorescent spectroscopy is also utilized to enhance thesensitivity of detecting these permeant molecules. Confirmation of the alkylsilaneattachment to the alumina membrane is achieved with traditional infrared spectroscopy,which can also examine the lifetime of the modified membrane. The physical parameters ofthese silane-modified porous alumina membranes are studied via scanning electronmicroscopy. The alumina nanotubes are not physically closed off or capped by the silanesthat are attached to the alumina surfaces.

  3. High contrast laser marking of alumina

    International Nuclear Information System (INIS)

    Highlights: • Laser marking of alumina using near infrared (NIR) lasers was experimentally analyzed. • Color change produced by NIR lasers is due to thermally induced oxygen vacancies. • Laser marking results obtained using NIR lasers and green laser are compared. • High contrast marks on alumina were achieved. - Abstract: Alumina serves as raw material for a broad range of advanced ceramic products. These elements should usually be identified by some characters or symbols printed directly on them. In this sense, laser marking is an efficient, reliable and widely implemented process in industry. However, laser marking of alumina still leads to poor results since the process is not able to produce a dark mark, yielding bad contrast. In this paper, we present an experimental study on the process of marking alumina by three different lasers working in two wavelengths: 1064 nm (Near-infrared) and 532 nm (visible, green radiation). A colorimetric analysis has been carried out in order to compare the resulting marks and its contrast. The most suitable laser operating conditions were also defined and are reported here. Moreover, the physical process of marking by NIR lasers is discussed in detail. Field Emission Scanning Electron Microscopy, High Resolution Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy were also employed to analyze the results. Finally, we propose an explanation for the differences of the coloration induced under different atmospheres and laser parameters. We concluded that the atmosphere is the key parameter, being the inert one the best choice to produce the darkest marks

  4. Superplastic properties of alumina-zirconia composites

    International Nuclear Information System (INIS)

    Superplastic deformation of two alumina-zirconia composites batches: the first with tetragonal ZrO2 stabilised with 3 mol.% Y2O3 and the second with ZrO2 stabilised with 2 mol.% Y2O3 (containing alumina volume fraction 10 - 86%) was studied. Grain sizes of two constituents were about 0.18-0.37 μm in the batch 1 and 0.36-0.14 μm in the batch 2. The composites were studied as a function of stress (20-130 MPa) and temperature (1451-1623 K) in compressive and bending tests. The strain rate was analysed in function of alumina volume fraction. It appeared that, the bigger than predicted by the rule of mixture strain rate decrease in function of alumina volume fraction is caused by improved creep resistance due to zirconium and yttrium ions doping of alumina grains. In zirconia grains modified interface-controlled Coble creep and simultaneously the intragranular dislocations motions contribute to the accommodation of grain boundary sliding (which is now thought to be main mechanism of superplastic behaviour). (author)

  5. Dielectric Performance of a High Purity HTCC Alumina at High Temperatures - a Comparison Study with Other Polycrystalline Alumina

    Science.gov (United States)

    Chen, Liangyu

    2014-01-01

    A very high purity (99.99+%) high temperature co-fired ceramic (HTCC) alumina has recently become commercially available. The raw material of this HTCC alumina is very different from conventional HTCC alumina, and more importantly there is no glass additive in this alumina material for co-firing processing. Previously, selected HTCC and LTCC (low temperature co-fired ceramic) alumina materials were evaluated at high temperatures as dielectric and compared to a regularly sintered 96% polycrystalline alumina (96% Al2O3), where 96% alumina was used as the benchmark. A prototype packaging system based on regular 96% alumina with Au thickfilm metallization successfully facilitated long term testing of high temperature silicon carbide (SiC) electronic devices for over 10,000 hours at 500 C. In order to evaluate this new high purity HTCC alumina for possible high temperature packaging applications, the dielectric properties of this HTCC alumina substrate were measured and compared with those of 96% alumina and a previously tested LTCC alumina from room temperature to 550 C at frequencies of 120 Hz, 1 KHz, 10 KHz, 100 KHz, and 1 MHz. A parallel-plate capacitive device with dielectric of the HTCC alumina and precious metal electrodes were used for measurements of the dielectric constant and dielectric loss of the co-fired alumina material in the temperature and frequency ranges. The capacitance and AC parallel conductance of the capacitive device were directly measured by an AC impedance meter, and the dielectric constant and parallel AC conductivity of the dielectric were calculated from the capacitance and conductance measurement results. The temperature and frequency dependent dielectric constant, AC conductivity, and dissipation factor of the HTCC alumina substrate are presented and compared to those of 96% alumina and a selected LTCC alumina. Other technical advantages of this new co-fired material for possible high packaging applications are also discussed.

  6. Challenges and Strategies in the Synthesis of Mesoporous Alumina Powders and Hierarchical Alumina Monoliths

    Directory of Open Access Journals (Sweden)

    Anne Galarneau

    2012-02-01

    Full Text Available A new rapid, very simple and one-step sol-gel strategy for the large-scale preparation of highly porous γ-Al2O3 is presented. The resulting mesoporous alumina materials feature high surface areas (400 m2 g−1, large pore volumes (0.8 mL g−1 and the ��-Al2O3 phase is obtained at low temperature (500 °C. The main advantages and drawbacks of different preparations of mesoporous alumina materials exhibiting high specific surface areas and large pore volumes such as surfactant-nanostructured alumina, sol-gel methods and hierarchically macro-/mesoporous alumina monoliths have been analyzed and compared. The most reproducible synthesis of mesoporous alumina are given. Evaporation-Induced Self-Assembly (EISA is the sole method to lead to nanostructured mesoporous alumina by direct templating, but it is a difficult method to scale-up. Alumina featuring macro- and mesoporosity in monolithic shape is a very promising material for in flow applications; an optimized synthesis is described.

  7. Mechanical properties of free standing porous anodic alumina films

    OpenAIRE

    Ignashev, E.; Shulgov, V.

    2012-01-01

    Free-standing films of anodic alumina obtained from the one-sided anodization of aluminum were studied. The flexural strength of free-standing porous anodic alumina films to the lateral bending, circular bending, and microhardness were studied.

  8. Dynamical Mechanical Properties for AD90 Alumina

    Institute of Scientific and Technical Information of China (English)

    REN Hui-lan; NING Jian-guo; LI Ping

    2007-01-01

    The dynamic response of polycrystalline alumina was investigated in the pressure range of 0 -13 GPa by planar impact experiments.Velocity interferometer system for any reflector(VISAR) was used to obtain free surface velocity profile and determine the Hugoniot elastic limit,and manganin gauges were employed to obtain the stress-time histories and determine Hugoniot curve.Both the free surface particle velocity profiles and Hugoniot curves indicate the dispersion of the "plastic" wave for alumina.With the measured stress histories,the complete histories of strain,particle velocity,specific volume and specific internal energy are gained by using path line principle of Lagrange analysis.The dynamic mechanical behaviors for alumina under impact loading are analyzed,such as nonlinear characteristic,strain rate dependence,dispersion and declination of shock wave in the material.

  9. Synthesis and characterization of alumina precursor and alumina to be used as nano composite; Sintese e caracterizacao de precursores de alumina e alumina para uso em nanocompositos

    Energy Technology Data Exchange (ETDEWEB)

    Antunes, M.L.P., E-mail: malu@sorocaba.unesp.b [Universidade Estadual Paulista Julio de Mesquita Filho (UNESP), Sorocaba, SP (Brazil); Santos, H. Souza [Universidade de Sao Paulo (IF/USP), SP (Brazil). Inst. de Fisica; Santos, P. Souza [Universidade de Sao Paulo (EP/USP), SP (Brazil). Escola Politecnica

    2009-07-01

    With the evolution of nanomaterials technology, mainly in the 90s, it was possible to observe produced composites with alumina matrix and nanomaterial as reinforcing materials. It results in a significant improvement of mechanical proprieties of these composites. Thenceforth the study of synthesis and characterization of nanostructured materials has attracted great scientific interest. In this perspective, the aim of this work is to present an experimental procedure to obtain nordstrandite (aluminum hydroxide) with nanometric dimensions. Nordstrandite synthesis, obtained by the reaction of slightly amalgamated aluminum foil with aqueous ethylene glycol, which allows the control of the size of crystal produced. This control could be confirmed by X-Ray Diffraction and Electron Microscopy. Thermal transformation study is also presented. This study allowed the identification of transition aluminas that have potential to produce nanometric aluminas. (author)

  10. Blocking of grain reorientation in self-doped alumina materials

    International Nuclear Information System (INIS)

    Alumina nanoparticles 10-20 nm in diameter were nucleated on alumina particles, 150 nm average diameter, by a colloidal route followed by calcination. It is shown that after sintering, the final grain size is up to 20% smaller due to the addition of the alumina nanoparticles. Electron backscattered diffraction analysis shows that whereas a correlation in the relative crystalline orientations between neighbouring grains exists in the pure materials, the addition of alumina nanoparticles results in a random crystalline orientation.

  11. A Novel Processing Route for Ni-doped Alumina Composites

    Institute of Scientific and Technical Information of China (English)

    JING Mao-xiang; SHEN Xiang-qian; ZHOU Jian-xin; LI Dong-hong; LI Wang-xing

    2006-01-01

    Alumina-based composites containing 0-15wt% Ni metallic phase were produced by hot press-sintering Ni-coated alumina powders. The Ni-coated alumina powders were prepared by the aqueous heterogeneous precipitation of alumina micro-powders and nickel sulfate salt followed by reduction process. The microstructural features and dispersion of Ni phase in Ni-coated alumina powders and the subsequent alumina-Ni cermets were investigated using scanning electron microscope (SEM), X-ray diffractometer (XRD), and transmission electron microscope (TEM). The relative density of the hot press-sintered composites was measured with the Archimedes' method while the fracture strength and the fracture toughness were defined with the three-point bending method and the micro-indentation fracture method. In the formation of alumina-Ni cermets from sintered Ni-coated alumina powders, Ni phase to some extent limits the densification rate and stifles the coarsening and growing process of alumina grains. The Ni phase is found to be located at the interfaces and the triple-joint junctions of alumina grains which results into alteration of the fracture mode of alumina and its increased fracture strength and fracture toughness if compared with monolithic alumina.

  12. Tribological properties of nanoscale alumina-zirconia composites

    NARCIS (Netherlands)

    Kerkwijk, B.; Winnubst, A.J.A.; Verweij, H.; Mulder, E.J.; Metselaar, H.S.C.; Schipper, D.J.

    1999-01-01

    The tribological properties of zirconia (Y-TZP), alumina and their composites, alumina dispersed in zirconia (ADZ) and zirconia-toughened alumina (ZTA), were investigated. These ceramics are made by colloidal processing methods such that well-defined, homogeneous microstructures with submicron grain

  13. 21 CFR 73.1010 - Alumina (dried aluminum hydroxide).

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 1 2010-04-01 2010-04-01 false Alumina (dried aluminum hydroxide). 73.1010... GENERAL LISTING OF COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1010 Alumina (dried aluminum hydroxide). (a) Identity. (1) The color additive alumina (dried aluminum hydroxide) is a white,...

  14. 40 CFR 721.10120 - Siloxane modified alumina nanoparticles (generic).

    Science.gov (United States)

    2010-07-01

    ... 40 Protection of Environment 30 2010-07-01 2010-07-01 false Siloxane modified alumina... Specific Chemical Substances § 721.10120 Siloxane modified alumina nanoparticles (generic). (a) Chemical... as siloxane modified alumina nanoparticles (PMN P-05-687) is subject to reporting under this...

  15. Study of the molybdenum retention in alumina; Estudio de la retencion de molibdeno en alumina

    Energy Technology Data Exchange (ETDEWEB)

    Wilkinson, Maria V.; Mondino, Angel V.; Manzini, Alberto [Comision Nacional de Energia Atomica, Buenos Aires (Argentina). Centro Atomico Ezeiza. Radioquimica y Quimica de las Radiaciones

    2002-07-01

    The Argentine National Atomic Energy Commission routinely produces {sup 99} Mo by fission of highly enriched uranium contained in targets irradiated in RA-3 reactor. The current process begins with the dissolution of the irradiated target in a basic media, considering the possibility of changing the targets, it could be convenient to dissolve them in acid media. The use of alumina as a first separation step in acid dissolution processes is already known although it is necessary to determine both the type of alumina to be used and the separation conditions. The study of molybdenum retention in alumina was performed at laboratory scale, using Mo-99 as radiotracer. Different kinds of alumina were tried, varying charge solution acidity. Influence of uranium concentration in the loading solution on molybdenum retention was also studied. (author)

  16. Study on alumina-alumina brazing for application in vacuum chambers of proton synchrotron

    International Nuclear Information System (INIS)

    The paper describes an experimental study to standardize vacuum brazing process to obtain satisfactory high purity alumina brazed joints for application in rapid cycle proton synchrotron machine. Two different brazing routes, adopted for making alumina-alumina brazed joints, included (i) multi-step Mo-Mn metallization and brazing with BVAg-8 alloy and (ii) advanced single-step active brazing with CuSil-ABA alloy. Brazed alumina specimens, prepared by both the routes, yielded ultra high vacuum compatible, helium leak tight and bakeable joints. Active-brazed specimens exhibited satisfactory strength values in tensile and four-point bend tests. Metallized-brazed specimens, although exhibited relatively lower tensile strength than the targeted value, displayed satisfactory flexural strength in four-point bend test. The results of the study demonstrated that active brazing is the simple and cost effective alternative to conventional metallization route for producing satisfactory brazed joints for application in rapid cycle proton synchrotron machine. (author)

  17. Selective metallization of alumina by laser

    NARCIS (Netherlands)

    Shrivastva, P.B.; Boose, C.A.; Kolster, B.H.; Harteveld, C.; Meinders, B.

    1991-01-01

    Nickel has been selectively deposited on an alumina substrate without any pretreatment from a flow of a nickel acetate solution using the focused beam of an excimer laser. Nickel spots as well as nickel lines were drawn and subsequently plated with an electroless Ni-B coating. Excellent adhesion of

  18. Adsorption of Nitrogen on Organized Mesoporous Alumina

    Czech Academy of Sciences Publication Activity Database

    Čejka, Jiří; Veselá, Lenka; Rathouský, Jiří; Zukal, Arnošt

    Amsterdam : Elsevier, 2002 - (Sayari, A.; Jaroniec, M.), s. 429-436 - ( Studies in Surface Science and Catalysis.. 141). [International Symposium on Nanoporous Materials /3./. Ottawa (CA), 12.06.2002-15.06.2002] R&D Projects: GA MŠk ME 404 Institutional research plan: CEZ:AV0Z4040901 Keywords : alumina * nitrogen * adsorption Subject RIV: CF - Physical ; Theoretical Chemistry

  19. Method of making nanocrystalline alpha alumina

    Science.gov (United States)

    Siegel, Richard W.; Hahn, Horst; Eastman, Jeffrey A.

    1992-01-01

    Method of making selected phases of nanocrystalline ceramic materials. Various methods of controlling the production of nanocrystalline alpha alumina and titanium oxygen phases are described. Control of the gas atmosphere and use of particular oxidation treatments give rise to the ability to control the particular phases provided in the aluminum/oxygen and titanium/oxygen system.

  20. Mechanical properties of zirconia-toughened alumina

    International Nuclear Information System (INIS)

    Bend samples of four compositions of zirconia-toughened alumina were heat treated at 10000C for 100 and 500 H and tested for strength and fracture toughness at room temperature. These results are compared with as-received properties, as well as stress rupture and stepped-temperature stress rupture data

  1. Dielectric Performance of High Purity HTCC Alumina at High Temperatures - A Comparison Study with Other Polycrystalline Alumina

    Science.gov (United States)

    Chen, Liang-Yu

    2012-01-01

    A very high purity (99.99+) high temperature co-fired ceramic (HTCC) alumina has recently become commercially available. The raw material of this HTCC alumina is very different from conventional HTCC alumina, and more importantly there is no glass additive in this co-fired material. Previously, selected HTCC and LTCC (low temperature co-fired ceramic) alumina materials were evaluated at high temperatures as dielectric and compared to a regularly sintered 96 polycrystalline alumina (96 Al2O3), where 96 alumina was used as the benchmark. A prototype packaging system based on regular 96 alumina with Au thick-film metallization successfully facilitated long term testing of high temperature silicon carbide (SiC) electronic devices for over 10,000 hours at 500C. In order to evaluate this new HTCC alumina for possible high temperature packaging applications, the dielectric properties of this HTCC alumina substrate were measured and compared with those of 96 alumina and a LTCC alumina from room temperature to 550C at frequencies of 120 Hz, 1 KHz, 10 KHz, 100 KHz, and 1 MHz. A parallel-plate capacitive device with dielectric of the HTCC alumina and precious metal electrodes were used for measurements of the dielectric constant and dielectric loss of the co-fired alumina material in the temperature and frequency ranges. The capacitance and AC parallel conductance of the capacitive device were directly measured by an AC impedance meter, and the dielectric constant and parallel AC conductivity of the dielectric were calculated from the capacitance and conductance measurement results. The temperature and frequency dependent dielectric constant, AC conductivity, and dissipation factor of the HTCC alumina substrate are presented and compared to those of 96 alumina. Other technical advantages of this new co-fired material for possible high packaging applications are also discussed.

  2. MECHANICAL BEHAVIOUR OF ALUMINA-ZIRCONIA COMPOSITE BY SLURRY METHOD

    Directory of Open Access Journals (Sweden)

    JYOTI PRAKASH

    2011-02-01

    Full Text Available Alumina has got some excellent properties like chemical inertness, thermal and mechanical strength against hazardous environment. Alumina is a good ceramic material which is being used for structuralapplications. To enhance the toughness and strength of the body some Zirconia is also used with it. The use of Zirconia in alumina is known as toughening of alumina. One difficulty arises, when alumina and alumina toughened composite are sintered , because the low sinterability of Alumina-Zirconia forced the compact to give very low density body. To overcome this problem alumina and alumina composites are made from slurry method which gives nearly theoretical density. The combined effect of alumina and Zirconia on the phase transformation and microstructure development of heat-treated Alumina-Zirconia composites has been studied. Slurry is prepared by adding water, dispersant, binder and anti-foaming agent. In the present study, Sintering schedule is optimized and kept constant for all samples. After sintering, mechanical behaviour of the composite has been studied.

  3. Effect of thermal residual stresses on the strength for both alumina/Ni/alumina and alumina/Ni/nickel alloy bimaterials

    OpenAIRE

    Hattali, Lamine; Stéphane, Valette; Ropital, Francois; Mesrati, Nadir; Tréheux, Daniel

    2009-01-01

    This paper describes some technical limitations encountered in joining ceramics-ceramics or ceramics-metals, and how, to some extent, they have been practically overcome. The effect of the residual stresses on the strength of joints fabricated between alumina-alumina or alumina and the nickel base alloy HAYNES 214TM using a solid-state bonding technique with Ni interlayer was studied. Finite element analyses (FEA) for the elastic-plastic and elastic-plastic-creep behavior have also been used ...

  4. Degradation of alumina and zirconia toughened alumina (ZTA) hip prostheses tested under microseparation conditions in a shock device

    CERN Document Server

    Uribe, Juliana; Gremillard, Laurent; Reynard, Bruno

    2013-01-01

    This paper considers the degradation of alumina and zirconia toughened alumina vs. alumina for hip implants. The materials are as assumed to be load bearing surfaces subjected to shocks in wet conditions. The load is a peak of force; 9 kN was applied over 15 ms at 2 Hz for 800,000 cycles. The volumetric wear and roughness are lower for ZTA than for alumina. The long ZTA ageing did not seem to have a direct influence on the roughness. The ageing increased the wear volumes of ZTA and it was found to have a higher wear resistance compared to alumina.

  5. Characterization of Glasses in One Type of Alumina Rich Fly Ash by Chemical Digestion Methods: Implications for Alumina Extraction

    OpenAIRE

    Lijun Zhao; Hanshuang Xiao; Baodong Wang; Qi Sun

    2016-01-01

    In recent years, one type of alumina rich fly ash (ARFA) with about 50 wt% of alumina has been extensively investigated for alumina extraction in China. Due to the silica in ARFA, alumina extraction would have to generate a huge amount of solid waste. There is a growing interest in the glasses in ARFA, because they are composed mainly of silica and could be removed prior to alumina extraction. In this work, the glasses in ARFA have been investigated by chemical methods, that is, acid and base...

  6. Graphene coated with alumina and its utilization as a thermal conductivity enhancer for alumina sphere/thermoplastic polyurethane composite

    International Nuclear Information System (INIS)

    Graphene was oxidized with H2O2 to introduce additional anchoring sites for effective alumina coating on graphene by the sol–gel method. The X-ray photoelectron spectroscopy studies showed that the oxygen-containing groups such as hydroxyl group useful for coating were introduced by the oxidation. The transmission electron microscopy images and thermogravimetric analysis data demonstrated that the additional anchoring sites enhanced the efficiency of the alumina coating. A small amount of alumina-coated graphene synergistically improved the thermal conductivity of the alumina sphere/thermoplastic polyurethane (TPU) composite without any increase in the electrical conductivity, because the electrical conductivity of graphene effectively decreased by the alumina coating. Moreover, the synergistic effect of a small amount of graphene was enhanced by the alumina coating, and the stiffening of the alumina sphere/TPU composite due to the added graphene was alleviated by the alumina coating. - Highlights: • Oxidation of graphene with H2O2 introduced anchoring sites for alumina coating. • The anchoring sites improved the efficiency of alumina coating on graphene. • The alumina-coated graphene synergistically enhanced the thermal conductivity

  7. Rheological Properties of Aqueous Nanometric Alumina Suspensions

    Energy Technology Data Exchange (ETDEWEB)

    Chuanping Li

    2004-12-19

    Colloidal processing is an effective and reliable approach in the fabrication of the advanced ceramic products. Successful colloidal processing of fine ceramic powders requires accurate control of the rheological properties. The accurate control relies on the understanding the influences of various colloidal parameters on the rheological properties. Almost all research done on the rheology paid less attention to the interactions of particle and solvent. However, the interactions of the particles are usually built up through the media in which the particles are suspended. Therefore, interactions of the particle with the media, the adsorbed layers on the particle surface, and chemical and physical properties of media themselves must influence the rheology of the suspension, especially for the dense suspensions containing nanosized particles. Relatively little research work has been reported in this area. This thesis addresses the rheological properties of nanometric alumina aqueous suspensions, and paying more attention to the interactions between particle and solvent, which in turn influence the particle-particle interactions. Dense nanometric alumina aqueous suspensions with low viscosity were achieved by environmentally-benign fructose additives. The rheology of nanometric alumina aqueous suspensions and its variation with the particle volume fraction and concentration of fructose were explored by rheometry. The adsorptions of solute (fructose) and solvent (water) on the nanometric alumina particle surfaces were measured and analyzed by TG/DSC, TOC, and NMR techniques. The mobility of water molecules in the suspensions and its variation with particle volume fractions and fructose additive were determined by the {sup 17}O NMR relaxation method. The interactions between the nanometric alumina particles in water and fructose solutions were investigated by AFM. The results indicated that a large number of water layers were physically bound on the particles

  8. High-pressure phases of alumina

    Science.gov (United States)

    Lyle, Matthew; Pickard, Chris; Needs, Richard

    2014-03-01

    Alumina (Al2O3) has been widely used as a pressure standard in static diamond anvil cell experiments and is a major chemical component of the Earth. So a detailed knowledge of its high-pressure stability is of great importance in both materials science and deep Earth science. A phase transition is known to occur at roughly 80-100 GPa between corundum and the Rh2O3 (II) structure. A second phase transition to the CaIrO3 structure occurs at even higher pressures. Here we present a computational structure search to reveal three additional structures which are competitive at these pressures but hitherto unknown to be stable in high-pressure alumina.

  9. Li + ion diffusion in nanoscale alumina coatings

    Science.gov (United States)

    Johannes, Michelle; Bernstein, Noam

    Nanoscale coatings of alumina are used to stabilize surfaces for a variety of technologies. Diffusion of ions through these coatings is of primary importance: in some cases, diffusion is unwanted (e.g. corrosion) and in others (e.g. electrode materials), it is necessary. In this work DFT and AIMD calculations are used to investigate Li+ ion diffusion through a nano-layer of alumina, examining the phase (alpha, gamma, and amorphous), ion concentration, and electron count dependence. We look at the role of the surface itself in promoting diffusion. One of our main findings is that as the number of ions or charge increases, the diffusivity rises. We show how our data can explain electrochemical data from coated LiCoO2 cathodes and may point toward better and more efficient coatings for stabilizing electrodes.

  10. Slip casting alumina with Na-CMC

    Energy Technology Data Exchange (ETDEWEB)

    Ruys, A.J.; Sorrell, C.C. [Univ. of New South Wales, Sydney, New South Wales (Australia)

    1996-11-01

    Many forming methods are in common use for engineering ceramics. Of these, slip casting is an ideal forming method because of its low cost, simplicity and flexibility, potential for uniform particle packing and suitability to the production of articles of intricate shape. Slip casting nonclay materials, such as alumina, requires the use of both a deflocculant and a binder. There are many commercially available deflocculants and binders that can be tested in alumina casting slips. However, determination of a suitable deflocculant/binder combination and quantification of the optimal additions of the deflocculant/binder pair can be time consuming. Certain deflocculants are capable of acting as binders. One such additive is sodium carboxymethylcellulose (Na-cmc), a cellulose ether. Na-cmc is a powerful binder. It is a member of the carbohydrate binder group--the binder group with the strongest binding power. It is capable of acting as a deflocculant in glazes and nonclay casting slips.

  11. Microstructural evolution of alumina-zirconia nanocomposites

    International Nuclear Information System (INIS)

    Ceramic materials have limited use due to their brittleness. The inclusion of nanosized particles in a ceramic matrix, which are called nanocomposites, and ceramic processing control by controlling the grain size and densification can aid in obtaining ceramic products of greater strength and toughness. Studies showed that the zirconia nano inclusions in the matrix of alumina favors an increase in mechanical properties by inhibiting the grain growth of the matrix and not by the mechanism of the transformation toughening phase of zirconia. In this work, the microstructural evolution of alumina nanocomposites containing 15% by volume of nanometric zirconia was studied. From the results it was possible to understand the sintering process of these nanocomposites. (author)

  12. Activation of consolidation processes of alumina ceramics

    Science.gov (United States)

    Matrenin, S. V.; Zenin, B. S.; Tayukin, R. V.

    2016-02-01

    The methods for activating sintering ceramics based on Al2O3 by mechanical activation in the planetary mill, by adding in the mixture of nanopowders (NP) Al, Al2O3, and submicron powder TiO2, and by applying the technology of spark plasma sintering (SPS) are developed. It has been shown that adding the nanopowder up to 20 wt. % Al2O3 in a coarse powder α-Al2O3 activates the sintering process resulting in increased density and hardness of the sintered alumina ceramics. Substantial effect of increasing density of alumina ceramics due to adding the submicron powder TiO2 in the compound of initial powder mixtures has been established.

  13. Mesoscale Modelling of the Response of Aluminas

    International Nuclear Information System (INIS)

    The response of polycrystalline alumina to shock is not well addressed. There are several operating mechanisms that only hypothesized which results in models which are empirical. A similar state of affairs in reactive flow modelling led to the development of mesoscale representations of the flow to illuminate operating mechanisms. In this spirit, a similar effort is undergone for a polycrystalline alumina. Simulations are conducted to observe operating mechanisms at the micron scale. A method is then developed to extend the simulations to meet response at the continuum level where measurements are made. The approach is validated by comparison with continuum experiments. The method and results are presented, and some of the operating mechanisms are illuminated by the observed response

  14. Phototransferred thermoluminescence and exoemission in alpha alumina

    Energy Technology Data Exchange (ETDEWEB)

    Iacconi, P.; Lapraz, D.; Alessandri-Fraccaro, M.F.; Addi, D. (Univ. de Nice-Sophia Antipolis (France). Lab. d' Emission Electronique et de Luminescence)

    1990-01-01

    {alpha}-Al{sub 2}O{sub 3}, irradiated by ionising radiation and submitted to UV illumination, presents a phototransfer phenomenon that is characterised by thermoluminescence (TL) and by thermostimulated exoelectronic emission (TSEE). The TL and the TSEE glow curves of {alpha}-alumina from -196 to 700{sup 0}C are compared, to parallel one phototransfer observation with another and to draw various conclusions concerning the stability of the traps involved in dosimetric applications. (author).

  15. Selective metallization of alumina by laser

    OpenAIRE

    Shrivastva, P.B.; Boose, C.A.; Kolster, B.H.; Harteveld, C; Meinders, B.

    1991-01-01

    Nickel has been selectively deposited on an alumina substrate without any pretreatment from a flow of a nickel acetate solution using the focused beam of an excimer laser. Nickel spots as well as nickel lines were drawn and subsequently plated with an electroless Ni-B coating. Excellent adhesion of the metallized layers was achieved, since with laser irradiation, both etching and deposition took place simultaneously.

  16. Tribological behaviour of anodised alumina nanohoneycombs

    OpenAIRE

    Wang, Shuo; 王硕

    2012-01-01

    Anodic alumina nanohoneycombs (AAO) have been widely used because of its convenient fabrication and controllable pores’ geometry. A lot of investigations have been conducted to study its physical and chemical properties. However, the mechanical properties, especially tribological properties, of such a popular nanomaterial still remain almost unknown. In this project, a series of scratch experiments were conducted on AAO films fabricated by a two-step anodisation method. The testing system...

  17. Separation of tungsten and rhenium on alumina

    Directory of Open Access Journals (Sweden)

    MILOVAN SM. STOILJKOVIC

    2004-09-01

    Full Text Available The conditions for the efficient separation of tungsten(VI and rhenium (VII on alumina were established. The distribution coefficients Kd for tungstate and perrhenate anions, as well as the separation factors a (a = KdWO42-/Kd ReO4- were determined using hydrochloric or nitric acid as the aqueous media. A solution of sodium chloride in the pH range 2–6 was also examined. Under all the tested experimental conditions, alumina is a much better adsorbent for tungsten than for rhenium. The obtained results indicated that the best separation of these two elements is achieved when 0.01– 0.1 mol dm-3 HCl or 1.0 mol dm-3 HNO3 are used as the aqueous media. If NaCl is used as the aqueous phase, the best separation is achieved with 0.20 mol dm-3 NaCl, pH 4–6. Under these experimental conditions, the breakthrough and saturation capacities of alumina for tungsten at pH 4 are 17 and 26 mg W/g Al2O3, respectively. With increasing pH, these values decrease. Thus, at pH 6 they are only 4 and 13 mg W/g Al2O3, respectively.

  18. Synthesis and characterization of single-crystalline alumina nanowires

    Institute of Scientific and Technical Information of China (English)

    ZHAO Qing; XU Xiang-yu; ZHANG Hong-zhou; CHEN Yao-feng; XU Jun; YU Da-peng

    2005-01-01

    Alumina nanowires were synthesized on large-area silicon substrate via simple thermal evaporation method of heating a mixture of aluminum and alumina powders without using any catalyst or template. The phase structure and the surface morphology of the as-grown sample were analyzed by X-ray diffractometry(XRD) and scanning electron microscopy (SEM), respectively. The chemical composition and the microstructure of the as-grown alumina nanowires were characterized using transmission electron microscope(TEM). The nanowires are usually straight and the single crystalline has average diameter of 40 nm and length of 3 - 5 μm. The growth direction is along the [002] direction. Well aligned alumina nanowire arrays were observed on the surface of many large particles. The catalyst-free growth of the alumina nanowires was explained under the framework of a vapor-solid(VS)growth mechanism. This as-synthesized alumina nanowires could find potential applications in the fabrication of nanodevices.

  19. Free-standing alumina nanobottles and nanotubes pre-integrated into nanoporous alumina membranes

    International Nuclear Information System (INIS)

    A novel interfacial structure consisting of long (up to 5 μm), thin (about 300 nm), highly-ordered, free-standing, highly-reproducible aluminum oxide nanobottles and long tubular nanocapsules attached to a rigid, thin (less than 1 μm) nanoporous anodic alumina membrane is fabricated by simple, fast, catalyst-free, environmentally friendly voltage-pulse anodization. A growth mechanism is proposed based on the formation of straight channels in alumina membrane by anodization, followed by neck formation due to a sophisticated voltage control during the process. This process can be used for the fabrication of alumina nanocontainers with highly controllable geometrical size and volume, vitally important for various applications such as material and energy storage, targeted drug and diagnostic agent delivery, controlled drug and active agent release, gene and biomolecule reservoirs, micro-biologically protected platforms, nano-bioreactors, tissue engineering and hydrogen storage. (paper)

  20. Atmospheric Moisture Content Effects on Ionic Liquid Wettability of Alumina

    OpenAIRE

    Brittle, S.; Samuel, A; W. B. Zimmerman

    2014-01-01

    The contact angles or wettability of 7 Ionic Liquids, on an alumina substrate, have been measured under two different storage conditions. The first using a small amount of moisture content, the second with no moisture content. The contact angle of Ionic Liquid droplets on an alumina substrate were measured using an Attension Theta instrument with automated software. The results show that a small amount of moisture improves the wettability of the Ionic Liquid – alumina system and therefore sub...

  1. Corrosion of Refractory Alumina-Graphite and Alumina-Graphite-Zirconia in Slag Containing Titania

    Institute of Scientific and Technical Information of China (English)

    XU Yuan; LIU Qing-cai; BAI Chen-guang; CHEN Deng-fu; Joseph W Newkirk

    2004-01-01

    The corrosion of refractory alumina-graphite and alumina-graphite-zirconia in the slag containing titania was studied by immersion tests (quasi-static and dynamic tests). Combining direct observation with microscopic investigations, a mechanism for corrosion was proposed based on the oxidation of graphite and the dissolution of refractory components. During the corrosion process, there are some special phenomena and laws that can be explained by the relation between the corrosion rate and the TiO2 mass percent, the rotational refractory velocity and the morphology of the deteriorated layer.

  2. Challenges and Strategies in the Synthesis of Mesoporous Alumina Powders and Hierarchical Alumina Monoliths

    OpenAIRE

    Anne Galarneau; Alexander Sachse; Sarah Hartmann

    2012-01-01

    A new rapid, very simple and one-step sol-gel strategy for the large-scale preparation of highly porous γ-Al2O3 is presented. The resulting mesoporous alumina materials feature high surface areas (400 m2 g−1), large pore volumes (0.8 mL g−1) and the ��-Al2O3 phase is obtained at low temperature (500 °C). The main advantages and drawbacks of different preparations of mesoporous alumina materials exhibiting high specific surface areas and large pore volumes such as surfactant-nanostructured alu...

  3. Rheology of Alumina-Based Graphite-Containing Castables

    Institute of Scientific and Technical Information of China (English)

    YE Fangbao; M. Rigaud; LIU Xinhong; ZHONG Xiangchong

    2005-01-01

    In this work, the rheological behavior of ultra-low cement alumina-based castables with addition of flake graphite and extruded graphite pellets has been investigated by using IBB rheometer. Emphasis has been laid on the influence of the type and amount of carbon addition on rheological properties of the alumina-based castables and the results are compared with corresponding alumina castable samples without any carbon addition. It is found that alumina-based castables with extruded graphite pellets have good rheological behavior and flowability with lower water demand ( < 6. 3% )and no segregation during the shearing of castable.

  4. Modelling the initial stage of porous alumina growth during anodization

    Science.gov (United States)

    Aryslanova, E. M.; Alfimov, A. V.; Chivilikhin, S. A.

    2013-05-01

    Artificially on the surface of aluminum there may be build a thick layer of Al2O3, which has a porous structure. In this paper we present a model of growth of porous alumina in the initial stage of anodizing, identifying dependencies anodizing parameters on the rate of growth of the film and the distance between the pores and as a result of the created model equations were found for changes in the disturbance of alumina for the initial stage of anodizing aluminum oxide porous border aluminum-alumina and alumina-electrolyte, with the influence of surface diffusion of aluminum oxide.

  5. Tribological and stability investigations of alkylphosphonic acids on alumina surface

    International Nuclear Information System (INIS)

    Alumina substrates are commonly used for various micro-/nanoelectromechanical systems (MEMS/NEMS). For efficient and lifetime longevity of these devices, lubricant films of self-assembled monolayers (SAMs) with nanometer thickness are increasingly being employed. In the present paper, we report preparation, tribological and stability investigations of alkylphosphonic acids on the alumina surface. The alkylphosphonic acids were prepared on the alumina surface using the liquid phase deposition method. The effectiveness of modification of the alumina surface by alkylphosphonic acids was investigated using water contact angle measurements, secondary ion mass spectrometry, X-ray photoelectron and infrared spectroscopy. Frictional behavior in milinewton load range was studied by microtribometry. It is shown that surface modification of the alumina surface by alkylphosphonic acids reduces the coefficient of friction values compared to the unmodified alumina. In comparison to the non-modified alumina surface, all tested alkylphosphonic acids cause a decrease in the friction coefficients in friction tests for counterparts made from different materials, such as steel, zirconia and silicon nitride. It is also found that the alumina surface modified by alkylphosphonic acids with longer chain has a higher degree of hydrophobicity and lower coefficient of friction. The best frictional properties are obtained for the system consisting of the alumina surface modified by n-octadecylphosphonic acid and silicon nitride counterpart. Stability tests in different environmental conditions: laboratory, acidic and alkaline solutions were also monitored.

  6. Degradation of alumina and zirconia toughened alumina (ZTA) hip prostheses tested under microseparation conditions in a shock device

    OpenAIRE

    Uribe, Juliana; Geringer, Jean; Gremillard, Laurent; Reynard, Bruno

    2011-01-01

    This paper considers the degradation of alumina and zirconia toughened alumina vs. alumina for hip implants. The materials are as assumed to be load bearing surfaces subjected to shocks in wet conditions. The load is a peak of force; 9 kN was applied over 15 ms at 2 Hz for 800,000 cycles. The volumetric wear and roughness are lower for ZTA than for alumina. The long ZTA ageing did not seem to have a direct influence on the roughness. The ageing increased the wear volumes of ZTA and it was fou...

  7. Pengaruh Pemasukan Alumina Terhadap Operasi Tungku Reduksi di PT. Inalum Kuala Tanjung

    OpenAIRE

    Sudjana, Putra Eka

    2015-01-01

    Produksi aluminium cair di PT INALUM memerlukan bahan baku utama berupa alumina (Al2O3). Pemasukan alumina (Al2O3) mempunyai dua metode yaitu Regular Feeding dan Demand Feeding. Metode demand feeding yang digunakan yaitu pemasukan alumina (Al2O3) berdasarkan kebutuhan . Konsentrasi alumina (Al2O3) pada operasi tungku reduksi berkisar antara 2% - 4%. Konsentrasi alumina (Al2O3) < 1% akan menyebabkan terjadinya efek anoda atau anode effect (AE) dan konsentrasi alumina (Al2O3) ...

  8. Sulfuric Acid and Ammonium Sulfate Leaching of Alumina from Lampang Clay

    OpenAIRE

    Numluk, Paweena; Chaisena, Aphiruk

    2012-01-01

    The rapid development of the global alumina industry has led to a considerable increase in the production alumina and processing of alumina from non-bauxitic sources. Lampang clays comprise various minerals that contain about 22.70 wt% of extractable alumina. Local clay was ground, activated by calcination and treated with sulfuric acid to extract alumina. In the activation step, the effects of temperature and time on the extraction of alumina and iron were investigated. The leaching experime...

  9. IMPROVED CORROSION RESISTANCE FOR ALUMINA REFRACTORY

    Energy Technology Data Exchange (ETDEWEB)

    John P. Hurley; Patty L. Kleven

    1999-04-30

    In order to increase the efficiency of advanced coal-fired power systems, higher working fluid temperatures must be reached. Some system surfaces will have to be protected by covering them with corrosion-resistant refractories. Corrosion is the degradation of the material surfaces or grain boundaries by chemical reactions with melts, liquids, or gases causing loss of material and, consequently, a decrease in the strength of the structure. In order to develop methods of reducing corrosion, the microstructure that is attacked must be identified along with the mechanism and rates of attack. Earlier tests with several commercially available high-temperature castable refractories showed that the fused-alumina aggregate grains within the materials had the highest corrosion resistance of any of the castable materials. However, the cement holding the grains was easily attacked. Therefore, to improve the corrosion resistance and thermomechanical properties of alumina-based refractories, we attempted to change the cement to a more corrosion- and erosion-resistant bonding material through the addition of rare-earth oxides (REO). Phase diagrams were used to identify stable high-melting-temperature materials within the lanthanide-alumina series that could modify the bonding phase of the alumina-based refractory. Two mechanisms of reducing corrosion were investigated. One was the formation of corrosion-resistant layers within the refractory. The other was increased sintering to increase strength and seal continuous pores that would reduce slag penetration. Garnets (Re{sub 3}Al{sub 5}O{sub 12}) and perovskites (ReAl{sub 2}O{sub 3}), where Re is the REO, are two of the stable high-melting-temperature materials identified that were believed could be formed in the refractory matrix to help reduce corrosion rates. For the base refractory, Plicast 99 made by Plibrico was chosen. It is a 99% alumina castable composed of fused alumina aggregate and a cement made primarily from Alphabond

  10. NMR Revealed Activated Alumina-Water Interaction

    Institute of Scientific and Technical Information of China (English)

    ZHOU Rui; ZHOU Yan; HU Kai; JI Zhen-ping; CHENG Gong-zhen

    2005-01-01

    Three different spin-lattice relaxation times (T1) of water were obtained in activated alumina-water slurry system, which indicate that there exist three states of water: bound water, pore water and bulk water. The chemical shift (δH) decreases as the amount of water added to the system increases due to the differences in contribution of these three states of water in the samples. The δH value for adsorbed water decreases nearly linearly and T1 increases with elevating temperature, which result from the decrease in the content of bound water by the increase in thermal motion.

  11. Improved Synthesis Of Potassium Beta' '-Alumina

    Science.gov (United States)

    Williams, Roger M.; Jeffries-Nakamura, Barbara; Ryan, Margaret A.; O'Connor, Dennis E.; Kisor, Adam; Underwood, Mark

    1996-01-01

    Improved formulations of precursor materials synthesize nearly-phase-pure potassium beta' '-alumina solid electrolyte (K-BASE) powder. Materials are microhomogeneous powders (or, alternatively, gels) containing K(+,) Mg(2+), and Al(3+). K-BASE powder produced used in potassium-working-fluid alkali-metal thermal-to-electric conversion (K-AMTEC), in which heat-input and heat-rejection temperatures lower than sodium-working-fluid AMTEC (Na-AMTEC). Additional potential use lies in purification of pottassium by removal of sodium and calcium.

  12. Conduction mechanism of single-crystal alumina

    Science.gov (United States)

    Will, Fritz G.; Delorenzi, Horst G.; Janora, Kevin H.

    1992-01-01

    The fully guarded three-terminal technique was used to perform conductivity measurements on single-crystal alumina at temperatures of 400-1300 C. The conductivity was also determined as a function of time at various temperatures and applied fields. Further, the fractions of the current carried by Al and O ions (ionic transference numbers) were determined from long-term transference experiments in the temperature range 1100-1300 C. A mathematical model of the conduction mechanism is proposed, and model predictions are compared with experimental results.

  13. Nanotube Arrays in Porous Anodic Alumina Membranes

    Institute of Scientific and Technical Information of China (English)

    Liang LI; Naoto KOSHIZAKI; Guanghai LI

    2008-01-01

    This review summarizes the various techniques developed for fabricating nanotube arrays in porous anodic alumina membranes (AAMs). After a brief introduction to the fabrication process of AAMs, taking carbons, metals, semiconductors, organics, biomoleculars, and heterojunctions as typical examples, attention will be focused on the recently established methods to fabricate nanotubes in AAM, including electrochemical deposition, surface sol-gel, modified chemical vapor deposition, atomic layer deposition, and layer-by-layer growth. Every method is demonstrated by one or two reported results. Finally, this review is concluded with some perspectives on the research directions and focuses on the AAM-based nanotubes fields.

  14. 3.5. Drying of cryolite-alumina concentrate

    International Nuclear Information System (INIS)

    This article is devoted to drying of cryolite-alumina concentrate. The drying process of cryolite-alumina concentrate at isothermal and polythermal conditions was studied. The kinetics and mechanism of the process were studied as well. The kinetics of concentrate drying under isothermal conditions was studied in air bath and results are presented.

  15. Textural stability of titania–alumina composite membranes

    NARCIS (Netherlands)

    Kumar, Krishnankutty-Nair P.; Keizer, Klaas; Burggraaf, Anthonie J.

    1993-01-01

    Textural evolution (porosity reduction, pore and crystallite growth) in titania–alumina composite membranes has been studied using thermal analysis, X-ray diffraction, field emission scanning electron microscopy and N2 physisorption techniques. The presence of alumina in the membranes improved the t

  16. Dynamic compressive and tensile strengths of spark plasma sintered alumina

    Science.gov (United States)

    Girlitsky, I.; Zaretsky, E.; Kalabukhov, S.; Dariel, M. P.; Frage, N.

    2014-06-01

    Fully dense submicron grain size alumina samples were manufactured from alumina nano-powder using Spark Plasma Sintering and tested in two kinds of VISAR-instrumented planar impact tests. In the first kind, samples were loaded by 1-mm tungsten impactors, accelerated to a velocity of about 1 km/s. These tests were aimed at studying the Hugoniot elastic limit (HEL) of Spark Plasma Sintering (SPS)-processed alumina and the decay, with propagation distance, of the elastic precursor wave. In the tests of the second kind, alumina samples of 3-mm thickness were loaded by 1-mm copper impactors accelerated to 100-1000 m/s. These tests were aimed at studying the dynamic tensile (spall) strength of the alumina specimens. The tensile fracture of the un-alloyed alumina shows a monotonic decline of the spall strength with the amplitude of the loading stress pulse. Analysis of the decay of the elastic precursor wave allowed determining the rate of the irreversible (inelastic) strains in the SPS-processed alumina at the initial stages of the shock-induced inelastic deformation and to clarify the mechanisms responsible for the deformation. The 1-% addition of Cr2O3 decreases the HEL of the SPS-processed alumina by 5-% and its spall strength by 50% but barely affects its static properties.

  17. Radiation dose determination by using powder Seydisehir alumina

    International Nuclear Information System (INIS)

    Thermoluminescence dosimeters (TLDs) is a passive dose measurement method used for the supervision, quality control and calibration during radiation dose measurements. Nowadays TLDs, including alumina, are largely used and investigated due to high sensitivity, physical and chemical stability, and re-usefulness. In this work, powder form of Seydisehir alumina is used as a thermoluminescence material and α and β radiation doses were measured.

  18. Dynamic compressive and tensile strengths of spark plasma sintered alumina

    International Nuclear Information System (INIS)

    Fully dense submicron grain size alumina samples were manufactured from alumina nano-powder using Spark Plasma Sintering and tested in two kinds of VISAR-instrumented planar impact tests. In the first kind, samples were loaded by 1-mm tungsten impactors, accelerated to a velocity of about 1 km/s. These tests were aimed at studying the Hugoniot elastic limit (HEL) of Spark Plasma Sintering (SPS)-processed alumina and the decay, with propagation distance, of the elastic precursor wave. In the tests of the second kind, alumina samples of 3-mm thickness were loaded by 1-mm copper impactors accelerated to 100–1000 m/s. These tests were aimed at studying the dynamic tensile (spall) strength of the alumina specimens. The tensile fracture of the un-alloyed alumina shows a monotonic decline of the spall strength with the amplitude of the loading stress pulse. Analysis of the decay of the elastic precursor wave allowed determining the rate of the irreversible (inelastic) strains in the SPS-processed alumina at the initial stages of the shock-induced inelastic deformation and to clarify the mechanisms responsible for the deformation. The 1-% addition of Cr2O3 decreases the HEL of the SPS-processed alumina by 5-% and its spall strength by 50% but barely affects its static properties.

  19. Depositing Adherent Ag Films On Ti Films On Alumina

    Science.gov (United States)

    Honecy, Frank S.

    1995-01-01

    Report discusses cleaning of ceramic (principally, alumina) substrates in preparation for sputter deposition of titanium intermediate films on substrates followed by sputter deposition of outer silver films. Principal intended application, substrates sliding parts in advanced high-temperature heat engines, and outer silver films serve as solid lubricants: lubricating properties described in "Solid Lubricant for Alumina" (LEW-15495).

  20. Comparison of deep desulfurization methods in alumina production process

    Institute of Scientific and Technical Information of China (English)

    刘战伟; 李旺兴; 马文会; 尹中林; 武国宝

    2015-01-01

    Several methods of deep desulfurization in alumina production process were studied, and the costs of these methods were compared. It is found that most of the S2− in sodium aluminate solution can be removed by adding sodium nitrate or hydrogen peroxide in digestion process, and in this way the effect of S2− on alumina product quality is eliminated. However, the removal efficiency of2-23SOin sodium aluminate solution is very low by this method. Both S2− and2-23SO in sodium aluminate solution can be removed completely by wet oxidation method in digestion process. The cost of desulfurization by wet oxidation is lower than by adding sodium nitrate or hydrogen peroxide. The results of this research reveal that wet oxidation is an economical and feasible method for the removal of sulfur in alumina production process to improve alumina quality, and provide valuable guidelines for alumina production by high-sulfur bauxite.

  1. Morphology and transmittance of porous alumina on glass substrate

    Energy Technology Data Exchange (ETDEWEB)

    Guo Peitao, E-mail: guopeitao@hotmail.com [Wuhan University of Technology. Wuhan (China); Xia Zhilin [Wuhan University of Technology. Wuhan (China); Key Laboratory of Low Dimensional Materials and Application Technology, Xiangtan University, Ministry of Education, Xiangtan (China); Xue Yiyu [Wuhan University of Technology. Wuhan (China); Huang Caihua [China Three Gorges University, Yichang (China); Zhao Lixin [Wuhan University of Technology. Wuhan (China)

    2011-02-01

    The porous optical film has higher threshold of laser-induced damage than densified films, for the study of mechanism of laser-induced damage of porous optical film with ordered pore structure. Porous anodic alumina (PAA) film with high transmittance on glass substrate has been prepared. Aluminum film was deposited on glass substrate by means of resistance and electron beam heat (EBH) evaporation. Porous alumina was prepared in oxalic acid solution under different anodizing conditions. At normal incidence, the optical transmittance spectrum over 300-1000 nm spectra region was obtained by spectrophotometer. SEM was introduced to analysis the morphology of the porous alumina film. The pore aperture increased with the increase of anodizing voltage, which resulted in a rapid decrease of the pore concentration and the optical thickness of porous alumina film. Damage morphology of porous alumina film is found to be typically defects initiated, and the defect is the pore presented on the film.

  2. Preliminary joining experiment of alumina pipes by using ceramics sleeve

    International Nuclear Information System (INIS)

    Preliminary experiments on alumina ceramics pipes joining by using shrinkable alumina sleeve and high melting point oxide solder have been carried out. Sleeves were prepared by way of sintering at relatively low temperature to shrink 1% during following joining process. As solder, alumina-calcia system was selected and paste containing alumina and calcium carbonate powder mixture was prepared. Joining was carried out by inserting the paste between sleeve and pipes, and by heating at 1500degC in air. By the shrink of sleeve and the formation of interface by solder, it was possible to realize the joined pipe without the vacuum leakage. The airtightness of the joined alumina pipes is almost equal to it of the metal pipe welding. (author)

  3. Dispersion Caused by Carbon Dioxide During Secondary Alumina Dissolution: A Lab-Scale Research

    Science.gov (United States)

    Yang, Youjian; Gao, Bingliang; Wang, Zhaowen; Shi, Zhongning; Hu, Xianwei; Yu, Jiangyu

    2014-06-01

    Secondary alumina is the byproduct of dry scrubbing in aluminum smelting. Secondary alumina has superior dissolution characteristics to primary alumina. Secondary alumina dissolves in pieces in molten cryolite, which results in larger contact area and better diffusion kinetics. In this work, the dissolution phenomenon of primary alumina, secondary alumina, and primary alumina doped with sodium carbonate or calcium carbonate (mass ratio = 10:1, 20:1) was observed and compared to estimate carbon-induced dispersion in industrial secondary alumina. Temperature fluctuations during sample dissolution were measured to evaluate the benefits of preheating on alumina dissolution. It was found that carbon mixed in secondary alumina significantly influences the dispersion of alumina particles at the moment of feeding, and thermodynamic analysis also shows that the combustion heat from carbon facilitates dispersion.

  4. Modified-starch Consolidation of Alumina Ceramics

    Institute of Scientific and Technical Information of China (English)

    JU Chenhui; WANG Yanmin; YE Jiandong; HUANG Yun

    2008-01-01

    The alumina ceramics with the homogeneous microstructure and the higher density were fabricated via the modified-starch consolidation process by 1.0 wt%of a modified starch as a consolidator/binder.The swelling behavior of the modified oxidized tapioca starch was analyzed by optical microscope,and two other corn starches(common corn starch and high amylose COrn starch)were also analyzed for comparison.The modified starch used as a binder for the consolidation swelled at about 55℃.began to gelatinize at 65℃ and then was completely gelatinized at 75℃.But the corn starches could not be completely gelatinized even at 80℃for 1 h.The high-strength green bodies(10.6 MPa)with the complex shapes were produced.The green bodies were sintered without any binder burnout procedure at 1700℃and a relative density of 95.3% was obtained for the sintered bodies,which is similar to that of the sintered sample formed by conventional slip casting.In addition,the effect of temperature on the apparent viscosity of the starch/alumina slurry in the process was investigated,and the corresponding mechanism for the starch consolidation was discussed.

  5. Properties of Transition Metal Doped Alumina

    Science.gov (United States)

    Nykwest, Erik; Limmer, Krista; Brennan, Ray; Blair, Victoria; Ramprasad, Rampi

    Crystallographic texture can have profound effects on the properties of a material. One method of texturing is through the application of an external magnetic field during processing. While this method works with highly magnetic systems, doping is required to couple non-magnetic systems with the external field. Experiments have shown that low concentrations of rare earth (RE) dopants in alumina powders have enabled this kind of texturing. The magnetic properties of RE elements are directly related to their f orbital, which can have as many as 7 unpaired electrons. Since d-block elements can have as many as 5 unpaired electrons the effects of substitutional doping of 3d transition metals (TM) for Al in alpha (stable) and theta (metastable) alumina on the local structure and magnetic properties, in addition to the energetic cost, have been calculated by performing first-principles calculations based on density functional theory. This study has led to the development of general guidelines for the magnetic moment distribution at and around the dopant atom, and the dependence of this distribution on the dopant atom type and its coordination environment. It is anticipated that these findings can aid in the selection of suitable dopants help to guide parallel experimental efforts. This project was supported in part by an internship at the Army Research Laboratory, administered by the Oak Ridge Institute for Science and Education, along with a grant of computer time from the DoD High Performance Computing Modernization Program.

  6. Combination for electrolytic reduction of alumina

    Science.gov (United States)

    Brown, Craig W.; Brooks, Richard J.; Frizzle, Patrick B.; Juric, Drago D.

    2002-04-30

    An electrolytic bath for use during the electrolytic reduction of alumina to aluminum. The bath comprises molten electrolyte having the following ingredients: AlF.sub.3 and at least one salt selected from the group consisting of NaF, KF, and LiF; and about 0.004 wt. % to about 0.2 wt. %, based on total weight of the molten electrolyte, of at least one transition metal or at least one compound of the metal or both. The compound is, a fluoride; oxide, or carbonate. The metal is nickel, iron, copper, cobalt, or molybdenum. The bath is employed in a combination including a vessel for containing the bath and at least one non-consumable anode and at least one dimensionally stable cathode in the bath. Employing the instant bath during electrolytic reduction of alumina to aluminum improves the wetting of aluminum on a cathode by reducing or eliminating the formation of non-metallic deposits on the cathode.

  7. Lightweight alumina refractory aggregate. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Swansiger, T.G.; Pearson, A.

    1996-07-16

    Objective was to develop a lightweight, high alumina refractory aggregate for use in various high performance insulating (low thermal conductivity) refractory applications (e.g., in the aluminium, glass, cement, and iron and steel industries). A new aggregate process was developed through bench and pilot-scale experiments involving extrusion of a blend of calcined and activated alumina powders and organic extrusion aids and binders. The aggregate, with a bulk density approaching 2.5 g/cc, exhibited reduced thermal conductivity and adequate fired strength compared to dense tabular aggregate. Refractory manufacturers were moderately enthusiastic over the results. Alcoa prepared an economic analysis for producing lightweight aggregate, based on a retrofit of this process into existing Alcoa production facilities. However, a new, competing lightweight aggregate material was developed by another company; this material (Plasmal{trademark})had a significantly more favorable cost base than the Alcoa/DOE material, due to cheap raw materials and fewer processing steps. In late 1995, Alcoa became a distributor of Plasmal. Alcoa estimated that {ge}75% of the market originally envisioned for the Alcoa/DOE aggregate would be taken by Plasmal. Hence, it was decided to terminate the contract without the full- scale demonstration.

  8. Ultrasonic analysis of sintered alumina pellets

    International Nuclear Information System (INIS)

    Uranium dioxide pellets are used as fuel in Pressurized Water Reactors. These pellets require some degree of porosity to accommodate fission products generated during the burning of fuel. It is usual to utilize the Archimedes method to determine the sintered pellet porosity. For the determination of closed pores, samples of pellets need to be analyzed using micrography to calculate the distribution of the pores. The ultrasonic group of the Nuclear Engineering Institute (IEN) is developing a nondestructive characterization through ultrasonic technique in the frequency domain, this technique will permit to minimize the time for determination of porosity and increase the accuracy of measurement using only one technique, taking into account pores open and closed, and to be capable to analyze 100% of the pellets. Several studies have been conducted in order to validate this method. In this work, the frequency spectrum from alumina pellets were obtained by a 5MHz frequency transducer and by means of scanning electron microscope (SEM), it was possible to investigate the interior of the material and to associate its structure to the behavior of the ultrasonic wave. Each sintering temperature showed a characteristic ultrasonic signal that could be associated with the Alumina porosity. This result showed that this method is very sensitive to the pore distribution in the material because, even within the same temperature group, variations occurred according to distribution of pore sizes. (author)

  9. Terbium luminescence in alumina xerogel fabricated in porous anodic alumina matrix under various excitation conditions

    International Nuclear Information System (INIS)

    Terbium-doped alumina xerogel layers are synthesized by the sol-gel method in pores of a porous anodic alumina film 1 μm thick with a pore diameter of 150–180 nm; the film is grown on a silicon substrate. The fabricated structures exhibit terbium photoluminescence with bands typical of trivalent terbium terms. Terbium X-ray luminescence with the most intense band at 542 nm is observed for the first time for such a structure. Morphological analysis of the structure by scanning electron microscopy shows the presence of xerogel clusters in pore channels, while the main pore volume remains unfilled and pore mouths remain open. The data obtained confirm the promising applications of fabricated structures for developing matrix converters of X-rays and other ionizing radiations into visible light. The possibilities of increasing luminescence intensity in the matrix converter are discussed.

  10. Microstructural evolution of alumina-zirconia nanocomposites; Evolucao microestrutural de nanocompositos alumina-zirconia

    Energy Technology Data Exchange (ETDEWEB)

    Ojaimi, C.L.; Chinelatto, A.S.A.; Chinelatto, A.L. [Universidade Estadual de Ponta Grossa (UEPG), PR (Brazil); Pallone, E.M.J.A., E-mail: christianelago@yahoo.com.br [Universidade de Sao Paulo (USP), Pirassununga, Sao Paulo, SP (Brazil). Faculdade de Zootecnia e Engenharia de Alimentos

    2012-07-01

    Ceramic materials have limited use due to their brittleness. The inclusion of nanosized particles in a ceramic matrix, which are called nanocomposites, and ceramic processing control by controlling the grain size and densification can aid in obtaining ceramic products of greater strength and toughness. Studies showed that the zirconia nano inclusions in the matrix of alumina favors an increase in mechanical properties by inhibiting the grain growth of the matrix and not by the mechanism of the transformation toughening phase of zirconia. In this work, the microstructural evolution of alumina nanocomposites containing 15% by volume of nanometric zirconia was studied. From the results it was possible to understand the sintering process of these nanocomposites. (author)

  11. Dissolution kinetics for alumina in cryolite melts. Distribution of alumina in the electrolyte of industrial aluminium cells

    Energy Technology Data Exchange (ETDEWEB)

    Kobbeltvedt, Ove

    1997-12-31

    This thesis contributes to the understanding of which factors determine the rate of dissolution of alumina added to the bath in alumina reduction cells. Knowing this may help reduce the occurrences of operation interruptions and thus make it possible to produce aluminium using less energy. When alumina powder was added to a stirred cryolite melt, the alumina dissolved in two distinct main stages. In the first stage, the dissolution rate was very high, which reflects dissolution of single alumina grains that are being dispersed in the bath upon addition. In the second stage, lumps of alumina infiltrated with bath dissolved at a rate considerably slower than that of the first stage. The formation of these alumina agglomerates is the most important contributor to slow dissolution. The parameters varied in the experiments were convection, batch size, and temperature of the bath and of the added alumina. Increased gas stirring of the bath speeded up dissolution in both stages but the size of the batch was of little significance. Increasing the bath temperature had no effect in the first stage but speeded up dissolution considerably in the second stage. Compared to adding alumina at room temperature, preheating it to a high temperature (600 {sup o}C) increased the dissolution rate in the first stage while preheating to lower temperatures (100-300 {sup o}C) decreased the dissolution rate. In the second stage, preheating slowed the dissolution. The two latter phenomena of reduced dissolution rates are ascribed to the removal of moisture from the alumina upon preheating. The bath flow and the distribution of alumina in the bath were measured in four different types of cells. It was found that if a certain asymmetry of the magnetic field traverse to the cell was present, due to the presence of risers, then loops of high velocity bath flow occurred near the short ends of the cell. Thus, alumina added near the short ends is effectively transferred away from the feeding

  12. Scattering and absorption coefficients of silica-doped alumina aerogels.

    Science.gov (United States)

    Fu, Tairan; Tang, Jiaqi; Chen, Kai; Zhang, Fan

    2016-02-01

    Alumina-based aerogels are especially useful in many applications due to their excellent stability at high temperatures. This study experimentally analyzed the radiative properties of silica-doped alumina aerogels through spectral directional-hemispherical measurements for wavelengths of 0.38-25 μm. The silica-doped alumina aerogel samples were prepared with a 1.4∶1 molar ratio of silica to alumina. A two-flux model was used to describe the radiation propagation in a 1D scattering absorbing sample to derive expressions for the normal-hemispherical transmittances and reflectances based on the transport approximation. The normal-hemispherical transmittances and reflectances were measured at various spectral wavelengths and sample thicknesses using the integrating sphere method. The spectral absorption and transport scattering coefficients of silica-doped alumina aerogels were then determined from the measured normal-hemispherical data. The absorption and transport scattering coefficients of silica-doped alumina aerogels are (0.1  cm-1, 36  cm-1) and (0.1  cm-1, 112  cm-1) for wavelengths of 0.38-8.0 μm. The spectral transport scattering coefficient varies in the opposite direction from the spectral absorption coefficient for various wavelengths. The radiative properties for silica and alumina aerogels were quite different for the absorption coefficient for wavelengths of 2.5-8.0 μm and for the transport scattering coefficient for wavelengths of 0.38-2.5 and 3.5-6.0 μm. The measured radiative properties were used to predict the spectral normal-hemispherical reflectance and transmittance of the silica-doped alumina aerogels for various sample thicknesses and wavelengths. The predicted values do not change for the sample thicknesses greater than a critical value. The analysis provides valuable reference data for alumina aerogels for high-temperature applications. PMID:26836071

  13. Ballistic Performance of Alumina and Zirconia-toughened Alumina Against 7.62 Armour Piercing Projectile

    Directory of Open Access Journals (Sweden)

    S G. Savio

    2014-09-01

    Full Text Available A study was carried out to compare the ballistic performance of high purity alumina and zirconia-toughened alumina (ZTA using depth of penetration (DoP test configuration against 7.62 mm armour piercing (AP ammunition. The effect of tile thickness on the differential efficiency factor (DEF was studied for tile thickness in the range of 3 mm to 6 mm for alumina tiles and 3 mm to 5 mm for ZTA tiles. The DEF is found to increase as tile thickness increases. An analysis on the failed shots showed that the residual shot weight does not follow a single linear relationship with ceramic tile thickness unlike the residual DoP for all thicknesses of tiles. Post-ballistic analysis on ceramic powder for particle size distribution was carried out and the results are presented.Defence Science Journal, Vol. 64, No. 5, September 2014, pp.477-483, DOI:http://dx.doi.org/10.14429/dsj.64.6745

  14. Mechanical behavior of alumina and alumina-feldspar based ceramics in an acetic acid (4%) environment

    International Nuclear Information System (INIS)

    This study investigates the mechanical properties of alumina-feldspar based ceramics when exposed to an aggressive environment (acetic acid 4%). Alumina ceramics containing different concentrations of feldspar (0%, 1%, 5%, 10%, or 40%) were sintered at either 1300, 1600, or 1700 oC. Flaws (of width 0%, 30%, or 50%) were introduced into the specimens using a saw. Half of these ceramic bodies were exposed to acetic acid. Their flexural strength, KIC, and porosity were measured and the fractured samples were evaluated using scanning electronic- and optical microscopy. It was found that in the ceramic bodies sintered at 1600 oC, feldspar content up to 10% improved flexural strength and KIC, and reduced porosities. Generally, it was found that acetic acid had a weakening effect on the flexural strength of samples sintered at 1700 oC but a beneficial effect on KIC of ceramics sintered at 1600 oC. It was concluded that alumina-based ceramics with feldspar content up to 10% and sintered at higher temperatures would perform better in an aggressive environment similar to oral cavity.

  15. Aluminum matrix composites reinforced with alumina nanoparticles

    CERN Document Server

    Casati, Riccardo

    2016-01-01

    This book describes the latest efforts to develop aluminum nanocomposites with enhanced damping and mechanical properties and good workability. The nanocomposites exhibited high strength, improved damping behavior and good ductility, making them suitable for use as wires. Since the production of metal matrix nanocomposites by conventional melting processes is considered extremely problematic (because of the poor wettability of the nanoparticles), different powder metallurgy routes were investigated, including high-energy ball milling and unconventional compaction methods. Special attention was paid to the structural characterization at the micro- and nanoscale, as uniform nanoparticle dispersion in metal matrix is of prime importance. The aluminum nanocomposites displayed an ultrafine microstructure reinforced with alumina nanoparticles produced in situ or added ex situ. The physical, mechanical and functional characteristics of the materials produced were evaluated using different mechanical tests and micros...

  16. Crystallography of Alumina-YAG-Eutectic

    Science.gov (United States)

    Farmer, Serene C.; Sayir, Ali; Dickerson, Robert M.; Matson, Lawrence E.

    2000-01-01

    Multiple descriptions of the alumina-YAG eutectic crystallography appear in the ceramic literature. The orientation between two phases in a eutectic system has direct impact on residual stress, morphology, microstructural stability, and high temperature mechanical properties. A study to demonstrate that the different crystallographic relationships can be correlated with different growth constraints was undertaken. Fibers produced by Laser-Heated Float Zone (LHFZ) and Edge-defined Film-fed Growth (EFG) were examined. A map of the orientation relationship between Al2O3 and Y3Al5O12 and their relationship to the fiber growth axis as a function of pull rate are presented. Regions in which a single orientation predominates are identified.

  17. Fracture simulation for zirconia toughened alumina microstructure

    CERN Document Server

    Kim, Kyungmok; Forest, Bernard

    2013-01-01

    Purpose - The purpose of this paper is to describe finite element modelling for fracture and fatigue behaviour of zirconia toughened alumina microstructures. Design/methodology/approach - A two-dimensional finite element model is developed with an actual $Al{_2}O{_3}$ - 10 vol% $ZrO{_2}$ microstructure. A bilinear, time-independent cohesive zone law is implemented for describing fracture behaviour of grain boundaries. Simulation conditions are similar to those found at contact between a head and a cup of hip prosthesis. Residual stresses arisen from the mismatch of thermal coefficient between grains are determined. Then, effects of a micro-void and contact stress magnitude are investigated with models containing residual stresses. For the purpose of simulating fatigue behaviour, cyclic loadings are applied to the models. Findings - Results show that crack density is gradually increased with increasing magnitude of contact stress or number of fatigue cycles. It is also identified that a micro-void brings about...

  18. Cast alumina forming austenitic stainless steels

    Science.gov (United States)

    Muralidharan, Govindarajan; Yamamoto, Yukinori; Brady, Michael P

    2013-04-30

    An austenitic stainless steel alloy consisting essentially of, in terms of weight percent ranges 0.15-0.5C; 8-37Ni; 10-25Cr; 2.5-5Al; greater than 0.6, up to 2.5 total of at least one element selected from the group consisting of Nb and Ta; up to 3Mo; up to 3Co; up to 1W; up to 3Cu; up to 15Mn; up to 2Si; up to 0.15B; up to 0.05P; up to 1 total of at least one element selected from the group consisting of Y, La, Ce, Hf, and Zr; alumina, and a stable essentially single phase FCC austenitic matrix microstructure, the austenitic matrix being essentially delta-ferrite free and essentially BCC-phase-free. A method of making austenitic stainless steel alloys is also disclosed.

  19. Optimized alumina coagulants for water treatment

    Science.gov (United States)

    Nyman, May D.; Stewart, Thomas A.

    2012-02-21

    Substitution of a single Ga-atom or single Ge-atom (GaAl.sub.12 and GeAl.sub.12 respectively) into the center of an aluminum Keggin polycation (Al.sub.13) produces an optimal water-treatment product for neutralization and coagulation of anionic contaminants in water. GaAl.sub.12 consistently shows .about.1 order of magnitude increase in pathogen reduction, compared to Al.sub.13. At a concentration of 2 ppm, GaAl.sub.12 performs equivalently to 40 ppm alum, removing .about.90% of the dissolved organic material. The substituted GaAl.sub.12 product also offers extended shelf-life and consistent performance. We also synthesized a related polyaluminum chloride compound made of pre-hydrolyzed dissolved alumina clusters of [GaO.sub.4Al.sub.12(OH).sub.24(H.sub.2O).sub.12].sup.7+.

  20. Processing of silicon nitride and alumina nanosize powders

    Energy Technology Data Exchange (ETDEWEB)

    Gonzalez, E.J.; Piermarini, G.; Hockey, B.; Malghan, S.G. [National Inst. of Standard and Technology, Gaithersburg, MD (United States)

    1995-08-01

    The effects of pressure on the compaction and subsequent processing of nanosize {gamma} alumina powders were studied. A 3 mm diameter piston/cylinder die was used to compact the nanosize powders to pressures of 1 and 2.5 GPa. The green bodies were sintered at temperatures up to 1600{degrees}C. Results show that green body density can be increased by higher compaction pressures. It appears that as a result of the {gamma}-to-{alpha} transformation in alumina, higher green density does not necessarily produce a higher density sintered alumina body. The microstructures of the sintered bodies are described in terms of porosity and phase content.

  1. Reaction of Sillimnite with Alumina at Elevated Temperatures

    Institute of Scientific and Technical Information of China (English)

    SHENYang-yun; SHENYi

    1996-01-01

    The reaction of sillimanite with alumina at temperatures 1650℃ an 1750℃ has been investigated.The results have shown that,in the laboratory test conditions,the higher the alumina content,the lower will be the amounts of glass-phse of the fired body and the higher will be the formation of mullite .In the present tests,however,the reaction in concern has not been completed,the reaction in concern has not been completed.Some uncombined residual alumina still exist in the form of corundum.

  2. Blister formation in alumina thin films bombarded with xenon ions

    International Nuclear Information System (INIS)

    Blisters have been observed in evaporated alumina thin films after xenon irradiation. The aim of this study is to further understand the mechanisms responsible for such a process. Surface blistering dependence on the thickness of the alumina films as well as irradiation fluence, temperature and post-irradiation thermal annealing have been investigated. From our experimental results, it has been proved that the substrate-alumina interface is not responsible for blistering. The application of a gas pressure model and a lateral compressive stress model shows that the latter seems to be more adequate in explaining blister formation. (author)

  3. Wenshan’s 800,000-ton Alumina Project Completed

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    <正>On September 26,2012,the completion ceremony of the 800,000-ton alumina project was held at the alumina factory in Matang Industrial Park, Wenshan city,Yunnan.Wenshan’s 800,000-ton alumina project and its supporting mining construction projects have been listed as one of 20 major industrial construction projects of Yunnan. The project covers an area of approximately 5,500 mu,with an estimated total investment of RMB 4,987 million. It is invested and built

  4. 3.6. Chlorination of alumina containing waste products

    International Nuclear Information System (INIS)

    Chlorination of alumina containing waste products is considered in this article. Based on conducted studies following optimal conditions of chlorination of alumina containing waste products with reducer - coal were found: temperature - 750-850 deg C, chlorination duration -1-1,5 hours, quantity of reducer - 30% and size of particles - 0,1 mm. Based on conducted studies following optimal conditions of chlorination of alumina containing waste products with reducer - natural gas were found: temperature - 650-750 deg C, chlorination duration - 2 hours, chlorine to methane ratio is 4:1 and size of particles - 0,2-0,3 mm.

  5. Porous alumina based ordered nanocomposite coating for wear resistance

    Science.gov (United States)

    Yadav, Arti; Muthukumar, M.; Bobji, M. S.

    2016-08-01

    Uniformly dispersed nanocomposite coating of aligned metallic nanowires in a matrix of amorphous alumina is fabricated by pulsed electrodeposition of copper into the pores of porous anodic alumina. Uniform deposition is obtained by controlling the geometry of the dendritic structure at the bottom of pores through stepwise voltage reduction followed by mild etching. The tribological behaviour of this nanocomposite coating is evaluated using a ball on flat reciprocating tribometer under the dry contact conditions. The nanocomposite coating has higher wear resistance compared to corresponding porous alumina coating. Wear resistant nanocomposite coating has wide applications especially in protecting the internal surfaces of aluminium internal combustion engines.

  6. Alumina Paste Sublimation Suppression Barrier for Thermoelectric Device

    Science.gov (United States)

    Paik, Jong-Ah (Inventor); Caillat, Thierry (Inventor)

    2014-01-01

    Alumina as a sublimation suppression barrier for a Zintl thermoelectric material in a thermoelectric power generation device operating at high temperature, e.g. at or above 1000K, is disclosed. The Zintl thermoelectric material may comprise Yb.sub.14MnSb.sub.11. The alumina may be applied as an adhesive paste dried and cured on a substantially oxide free surface of the Zintl thermoelectric material and polished to a final thickness. The sublimation suppression barrier may be finalized by baking out the alumina layer on the Zintl thermoelectric material until it becomes substantially clogged with ytterbia.

  7. Characterization of Glasses in One Type of Alumina Rich Fly Ash by Chemical Digestion Methods: Implications for Alumina Extraction

    Directory of Open Access Journals (Sweden)

    Lijun Zhao

    2016-01-01

    Full Text Available In recent years, one type of alumina rich fly ash (ARFA with about 50 wt% of alumina has been extensively investigated for alumina extraction in China. Due to the silica in ARFA, alumina extraction would have to generate a huge amount of solid waste. There is a growing interest in the glasses in ARFA, because they are composed mainly of silica and could be removed prior to alumina extraction. In this work, the glasses in ARFA have been investigated by chemical methods, that is, acid and base digestions. The chemical compositions have been measured by XRF for ARFA from the digestion processes. The K2O standard, XRD, and FTIR spectroscopies were successfully used to define the digestions processes, and size analysis and SEM-EDX provided rich information on particle transformations. As a result, acid and base digestion methods were found to produce very similar results for the glasses in ARFA. The K2O standard was attributed to the formation of glasses by illites, and TiO2 and Fe2O3 were proposed to originate from ilmenite in alumina rich coals (ARC. Some implications of the results were also discussed for the alumina extraction from ARFA.

  8. Direct spray pyrolysis of aluminum chloride solution for alumina preparation

    Institute of Scientific and Technical Information of China (English)

    吕国志; 张廷安; 王龙; 马思达; 豆志河; 刘燕

    2014-01-01

    The effects of pyrolysis mode and pyrolysis parameters on Cl content in alumina were investigated, and the alumina products were characterized by XRD, SEM and ASAP. The experimental results indicate that the spray pyrolysis efficiency is higher than that of static pyrolysis process, and the reaction and evaporation process lead to a multi-plot state of the alumina products by spray pyrolysis. Aluminum phase starts to transform intoγ-Al2O3 at spray pyrolysis temperature of 600 °C, which is about 200 °C lower than that of static pyrolysis process. The primary particle size of γ-Al2O3 product is 27.62 nm, and Cl content in alumina products is 0.38%at 800 °C for 20 min.

  9. Structure and surface properties of praseodymium modified alumina

    International Nuclear Information System (INIS)

    Mixed PrO2-Al2O3 oxides with different PrO2 content (1-20 wt.%) were prepared by wetness impregnation of γ-alumina with aqueous solution of praseodymium nitrate. The samples were characterized by different techniques, using surface adsorption-desorption of N2 (SBET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), temperature-programmed reduction (TPR) and temperature-programmed desorption of CO2 (TPD-CO2). TGA and XRD showed the presence of small praseodymium oxide species on the alumina surface. XPS and DRS detected electron deficient interaction between deposited praseodymium oxide and alumina. It was observed a lower reduction temperature for supported Pr oxide species compared to that of the bulk Pr6O11. TPD-CO2 studies suggested that the deposition of Pr oxide on alumina leaded to increase of the basicity of mixed oxides.

  10. Fused Cast Alumina Refractory Products for Glass Tank Furnace

    Institute of Scientific and Technical Information of China (English)

    SHEN Keyin

    2006-01-01

    @@ 1 Subject and Scope The standard specifies the requirement, testing method, inspection rule and requirements for the labeling, packing, shipping and storing of the fused cast alumina refractory products for glass tanks.

  11. Aluminum microstructures on anodic alumina for aluminum wiring boards.

    Science.gov (United States)

    Jha, Himendra; Kikuchi, Tatsuya; Sakairi, Masatoshi; Takahashi, Hideaki

    2010-03-01

    The paper demonstrates simple methods for the fabrication of aluminum microstructures on the anodic oxide film of aluminum. The aluminum sheets were first engraved (patterned) either by laser beam or by embossing to form deep grooves on the surface. One side of the sheet was then anodized, blocking the other side by using polymer mask to form the anodic alumina. Because of the lower thickness at the bottom part of the grooves, the part was completely anodized before the complete oxidation of the other parts. Such selectively complete anodizing resulted in the patterns of metallic aluminum on anodic alumina. Using the technique, we fabricated microstructures such as line patterns and a simple wiring circuit-board-like structure on the anodic alumina. The aluminum microstructures fabricated by the techniques were embedded in anodic alumina/aluminum sheet, and this technique is promising for applications in electronic packaging and devices. PMID:20356280

  12. High Alumina Refractory Bricks for Electric Arc Furnace Roofs

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    @@ 1 Scope This standard specifies the sort, technical requirement, test method, inspection rules, marking, packing, transportation, storage and quality certification of high alumina refractory bricks for electric arc furnace roofs.

  13. Superhydrophobic alumina surface based on stearic acid modification

    International Nuclear Information System (INIS)

    A novel superhydrophobic alumina surface is fabricated by grafting stearic acid layer onto the porous and roughened aluminum film. The chemical and phase structure, morphology, and the chemical state of the atoms at the superhydrophobic surface were investigated by techniques as FTIR, XRD, FE-SEM, and XPS, respectively. Results show that a super water-repellent surface with a contact angle of 154.2o is generated. The superhydrophobic alumina surface takes on an uneven flowerlike structure with many nanometer-scale hollows distribute in the nipple-shaped protrusions, and which is composed of boehmite crystal and γ-Al2O3. Furthermore, the roughened and porous alumina surface is coated with a layer of hydrophobic alkyl chains which come from stearic acid molecules. Therefore, both the roughened structure and the hydrophobic layer endue the alumina surface with the superhydrophobic behavior.

  14. Removing Fluoride Ions with Continously Fed Activated Alumina.

    Science.gov (United States)

    Wu, Yeun C.; Itemaking, Isara Cholapranee

    1979-01-01

    Discussed is the mathematical basis for determining fluoride removal during water treatment with activated alumina. The study indicates that decreasing particle size decreases the pore diffusion effect and increases fluoride removal. (AS)

  15. Recent advances in silica-alumina refractory: A review

    Directory of Open Access Journals (Sweden)

    Chaouki Sadik

    2014-06-01

    Full Text Available In this article, the elaboration and the characterization of silica-alumina refractory have been reviewed. Refractory oxides encompass a broad range of unary, binary, and ternary ceramic compounds that can be used in structural, insulating, and other applications. This paper provides a historical perspective on the elaboration and the use of silica-alumina refractory, reviews applications for refractory oxides, describes typical processing routes, overviews fundamental structure–property relations, and summarizes the properties of these materials.

  16. Adsorption of textile dye onto modified immobilized activated alumina

    OpenAIRE

    Wasti, A.; Ali, Awan M.

    2015-01-01

    The study describes the synthesis of modified immobilized activated alumina (MIAA) and its application for the removal of textile dye from aqueous media. Immobilization was carried out by using the sol–gel method while modifications were made during the synthesis by adding powder activated alumina. Batch adsorption experiments were carried out at 20 ± 1 °C to see the effect of different parameters like contact time, stirring rate, initial concentration of the dye and dose of MIAA. The removal...

  17. Preparation of spherical hollow alumina particles by thermal plasma

    International Nuclear Information System (INIS)

    Spherical hollow particles were prepared from solid alumina powders using DC arc thermal plasma, and then spray coating was performed with the as-prepared particles. Operating variables for the hollow particle preparation process were additional plasma gas, input power, and carrier gas flow rate. The spherical hollow alumina particles were produced in the case of using additive gas of H2 or N2, while alumina surface was hardly molten in the pure argon thermal plasma. In addition, the hollow particles were well produced in high power and low carrier gas conditions due to high melting point of alumina. Hollow structure was confirmed by focused ion beam-scanning electron microscopy analysis. Morphology and size distribution of the prepared particles that were examined by field emission-scanning electron microscopy and phase composition of the particles was characterized by X-ray diffraction. In the spray coating process, the as-prepared hollow particles showed higher deposition rate. - Highlights: ► Spherical hollow alumina powder was prepared by non-transferred DC arc plasma. ► Diatomic gasses were added in Ar plasma for high power. ► Prepared hollow alumina powder was efficient for the plasma spray coating

  18. High toughness alumina ceramics with elongated grains developed from seeds

    Institute of Scientific and Technical Information of China (English)

    XIE; Zhipeng; (谢志鹏); GAO; Lichun; (高立春); LI; Wenchao; (李文超); XU; Lihua; (徐利华); WANG; Xidong; (王习东)

    2003-01-01

    In the present paper, the influence of α-Al2O3 seeds and sintering methods on elongated grain growth and fracture toughness is investigated. The preparation of alumina ceramics started with commercial aluminum hydroxide. Abrasives were introduced to the starting materials by wet-grinding of high-purity alumina milling balls. Abrasives, playing the role of seeds, lowered the transformation temperature of aluminum hydroxide to alumina. Microstructures with elongated grains were developed by hot-pressing for the above calcined powders containing α-Al2O3 seeds, and alumina grain shapes changed with the amount of seeds introduced. However, only equiaxed grains were observed for the samples pressureless sintered. Fracture toughness of the alumina ceramics was dramatically improved by elongated grains. For the sample hot-pressed at 1600℃ for 2 h under 40 MPa pressure, fracture toughness reached 7.1 MPa·m1/2, which is much higher than that of normal alumina ceramics without elongated grains. In addition, high flexural strength of 630 MPa for the hot-pressed samples was also obtained.

  19. Characterization and performance of alumina inserts reinforced with zirconia

    International Nuclear Information System (INIS)

    Alumina-based ceramics reinforced with zirconia were produced as inserts to be used as cutting tools. The objective of this work was to characterize and to evaluate the inserts as well as their performance in service. Additions of zirconia varying from 0.05 up to 0.20 wt% were done in alumina in order to select that composition presenting the best mechanical behavior. To do this, four-point bending mechanical strength, hardness and fracture toughness measurements were carried out. The best performance was found for alumina processing 0.010 wt.% of zirconia addition. The addition of zirconia was made with the objective of giving higher toughness to the insert throughout the microcracking reinforcing mechanism. The alumina reinforced inserts were compared with inserts of alumina without zirconia. It was accomplished by performing machining tests onto a SAE 1045 steel. The obtained results indicated that the zirconia reinforcement was able to improve the performance of the alumina cutting tools considerably. (author)

  20. Adsorption of itaconic acid from aqueous solutions onto alumina

    Directory of Open Access Journals (Sweden)

    JELENA J. GULICOVSKI

    2008-08-01

    Full Text Available Itaconic acid, IA (C5H6O4, was investigated as a potential flocculant for the aqueous processing of alumina powders. The adsorption of IA, as a function of its concentration and pH value of the solution, onto the alumina surface was studied by the solution depletion method. The stability of the suspensions in the presence of itaconic acid was evaluated in light of the surface charge of the alumina powder used, the degree of dissociation of IA, as well as the sedimentation behavior and rheology of the suspensions. It was found that the adsorption process is extremely pH dependent; the maximum adsorption of IA onto alumina surface occurring at a pH close to the value of the first IA dissociation constant, pKa1. Also, IA does not influence the value of the point of zero charge of alumina. It was shown that IA represents an efficient flocculant for concentrated acidic alumina suspensions.

  1. Antibacterial activity of zinc oxide-coated nanoporous alumina

    International Nuclear Information System (INIS)

    Highlights: ► Atomic layer deposition was used to deposit ZnO on nanoporous alumina membranes. ► Scanning electron microscopy showed continuous coatings of zinc oxide nanocrystals. ► Activity against B. subtilis, E. coli, S. aureus, and S. epidermidis was shown. - Abstract: Nanoporous alumina membranes, also known as anodized aluminum oxide membranes, are being investigated for use in treatment of burn injuries and other skin wounds. In this study, atomic layer deposition was used for coating the surfaces of nanoporous alumina membranes with zinc oxide. Agar diffusion assays were used to show activity of zinc oxide-coated nanoporous alumina membranes against several bacteria found on the skin surface, including Bacillus subtilis, Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermidis. On the other hand, zinc oxide-coated nanoporous alumina membranes did not show activity against Pseudomonas aeruginosa, Enterococcus faecalis, and Candida albicans. These results suggest that zinc oxide-coated nanoporous alumina membranes have activity against some Gram-positive and Gram-negative bacteria that are associated with skin colonization and skin infection.

  2. Dynamic yield and tensile strengths of spark plasma sintered alumina

    International Nuclear Information System (INIS)

    Fully dense alumina samples with 0.6 μm grain size were produced from alumina powder using Spark Plasma Sintering and tested in two types of VISAR-instrumented planar impact tests. In the tests of the first type the samples of 0.28 to 6-mm thickness were loaded by 1-mm tungsten impactors accelerated up to a velocity of about 1 km/s. These tests were aimed to study the Hugoniot elastic limit (HEL) of the SPS-processed alumina and the decay of the elastic precursor wave with propagation distance. In the second type of test the samples of ∼3-mm thickness were loaded by 1-mm copper impactors accelerated up to velocities 100-1000 m/s. These tests were aimed to study the dynamic tensile (spall) strength of the alumina. The data on tensile fracture of the alumina demonstrate a monotonic decline of the spall strength with the amplitude of the loading stress pulse. The data on the decay of the elastic precursor wave allows for determining the rates of the irreversible (inelastic) strains in the SPS-processed alumina at the initial stages of shock-induced inelastic deformation and, thus, to derive some conclusions concerning the mechanisms responsible of the deformation.

  3. Antibacterial activity of zinc oxide-coated nanoporous alumina

    Energy Technology Data Exchange (ETDEWEB)

    Skoog, S.A. [Joint Department of Biomedical Engineering, University of North Carolina and North Carolina State University, Box 7115, Raleigh, NC 27695-7115 (United States); Bayati, M.R. [Department of Materials Science and Engineering, North Carolina State University, Box 7907, Raleigh, NC 27695-7907 (United States); Petrochenko, P.E. [Joint Department of Biomedical Engineering, University of North Carolina and North Carolina State University, Box 7115, Raleigh, NC 27695-7115 (United States); Division of Biology, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD 20993 (United States); Stafslien, S.; Daniels, J.; Cilz, N. [Center for Nanoscale Science and Engineering, North Dakota State University, 1805 Research Park Drive, Fargo, ND 58102 (United States); Comstock, D.J.; Elam, J.W. [Energy Systems Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Narayan, R.J., E-mail: roger_narayan@msn.com [Joint Department of Biomedical Engineering, University of North Carolina and North Carolina State University, Box 7115, Raleigh, NC 27695-7115 (United States); Department of Materials Science and Engineering, North Carolina State University, Box 7907, Raleigh, NC 27695-7907 (United States)

    2012-07-25

    Highlights: Black-Right-Pointing-Pointer Atomic layer deposition was used to deposit ZnO on nanoporous alumina membranes. Black-Right-Pointing-Pointer Scanning electron microscopy showed continuous coatings of zinc oxide nanocrystals. Black-Right-Pointing-Pointer Activity against B. subtilis, E. coli, S. aureus, and S. epidermidis was shown. - Abstract: Nanoporous alumina membranes, also known as anodized aluminum oxide membranes, are being investigated for use in treatment of burn injuries and other skin wounds. In this study, atomic layer deposition was used for coating the surfaces of nanoporous alumina membranes with zinc oxide. Agar diffusion assays were used to show activity of zinc oxide-coated nanoporous alumina membranes against several bacteria found on the skin surface, including Bacillus subtilis, Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermidis. On the other hand, zinc oxide-coated nanoporous alumina membranes did not show activity against Pseudomonas aeruginosa, Enterococcus faecalis, and Candida albicans. These results suggest that zinc oxide-coated nanoporous alumina membranes have activity against some Gram-positive and Gram-negative bacteria that are associated with skin colonization and skin infection.

  4. Annealing Would Improve beta" - Alumina Solid Electrolyte

    Science.gov (United States)

    Williams, Roger; Homer, Margie; Ryan, Margaret; Cortez, Roger; Shields, Virgil; Kisor, Adam

    2003-01-01

    A pre-operational annealing process is under investigation as a potential means of preventing a sudden reduction of ionic conductivity in a Beta"-alumina solid electrolyte (BASE) during use. On the basis of tests, the sudden reduction of ionic conductivity, followed by a slow recovery, has been found to occur during testing of the solid electrolyte and electrode components of an alkali metal thermal-to-electric converter (AMTEC) cell. At this time, high-temperature tests of limited duration have indicated the superiority of the treated BASE, but reproducible tests over thousands of hours are necessary to confirm that microcracking has been eliminated. The ionic conductivity of the treated BASE is also measured to be higher than untreated BASE at 1,073 K in low-pressure sodium vapor. Microcracking resulting in loss of conductivity was not observed with treated BASE in one high-temperature experiment, but this result must be duplicated over very long testing times to be sure of the effect. Shorter annealing times (10 to 20 hours) were found to result in significantly less loss of mass; it may be necessary for the packed powder mixture to evolve some Na2O before the Na2O can leave the ceramic.

  5. Microstructure Analysis of Thermally Etched Alumina Ceramics

    Directory of Open Access Journals (Sweden)

    Fudurić Jelača, M.

    2008-12-01

    Full Text Available Ceramography is the art and science of preparation, examination, and evaluation of ceramic microstructures. Microstructure is the structure level approximately 0.1 to 100 μ m between the wavelength of visible light and the resolution limit of the naked eye. The microstructure includes most grains, secondary phases, grain boundaries, pores, microcracks, hardness microindentations. Investigation and evaluation of ceramic microstructure is very important because a number of mechanical, optical, thermal, electrical and other properties of ceramics are significantly affected by the microstructure. The techniques for ceramographic preparation are divided into five parts: sawing, mounting, grinding, polishing and etching.In this paper a method for preparation of a cold isostatically pressed high purity alumina ceramics (α-Al2O3 is described. Microstructure analysis of prepared ceramics was performed by means of optical microscopy (OM, scanning electron microscopy (SEM and atomic force microscopy (AFM. Porosity is determined on the polished sample; grain size is measured after thermal etching. The mean grain diameter is determined by means of lineal-intercept method, circular-intercept method and image analysis.

  6. Coprecipitated nickel-alumina methanation catalysts

    International Nuclear Information System (INIS)

    In the last few years there has been a renewed interest in the methanation reaction CO+3H2=CH4+H2O. The investigations described in this thesis were performed in relation to the application of this reaction, within the framework of the so-called 'NFE' project, also called 'ADAM' and 'EVA' project. This project, which has been under investigation in West Germany for some years, aims at the investigation of the feasibility of transporting heat from a nuclear high temperature reactor by means of a chemical cycle. A promising possibility to realize such a cycle exists in applying the combination of the endothermic steam reforming of methane and the exothermic methanation reaction. This thesis describes the investigations into a certain type of methanation catalyst, viz. a coprecipitated nickel-alumina catalyst, with the aim to give more insight into the interrelationship between the preparation conditions on the one hand and catalyst properties such as activity and stability on the other hand. (Auth.)

  7. Thermal Conductivity of Alumina and Silica Nanofluids

    Science.gov (United States)

    Castellanos, Julian G. Bernal

    This thesis studies the effects of the base fluid, particle type/size, and volumetric concentration on the thermal conductivity of Alumina and Silica nanofluids. The effects of base fluid were observed by preparing samples using ethylene glycol (EG), water, and mixtures of EG/water as the base fluid and Al2O3 (10 nm) nanoparticles. The particles type/size and volumetric concentration effects were tested by preparing samples of nanofluids using Al2O3 (10nm), Al2O3 (150nm), SiO2 (15 nm), and SiO2 (80 nm) nanoparticles and ionized water as base fluid at different volumetric concentrations. All samples were mixed using a sonicator for 30 minutes and a water circulator to maintain the sample at room temperature. The thermal conductivity was measured using a Thermtest Transient Plane Source TPS 500S. The effects of gravity, Brownian motion and thermophoresis were also studied. EG produced the highest thermal conductivity enhancement out of all base fluids tested. Smaller particle size produced a higher enhancement of thermal conductivity, while the volumetric concentration did not have a significant effect in the thermal conductivity enhancement. Finally, gravity, Brownian diffusion and thermophoresis effects played a role in the total enhancement of the thermal conductivity. The nanoparticles were observed to settle rapidly after sonication suggesting gravity effects may play a significant role.

  8. EFFECT OF SPINEL ADDITION ON THE SINTERING BEHAVIOR AND MICROSTRUCTURE OF ALUMINA-SPINEL CERAMICS

    OpenAIRE

    Emre Yalamac

    2014-01-01

    Sintering behaviors of alumina-spinel powder mixtures were investigated up to 1600oC using a vertical dilatometer. Final density and microstructure of pure alumina, magnesium aluminate spinel (MgAl2O4) ceramics and ceramic composites with different alumina-spinel ratio were examined. As a result, the densification and final density of alumina-spinel composites were affected by addition of 10 wt. % and 20 wt. % spinel into alumina. Non-stoichiometric alumina-rich spinel phase was d...

  9. Ion polarization behavior in alumina under pulsed gate bias stress

    International Nuclear Information System (INIS)

    Alkali metal ion incorporation in alumina significantly increases alumina capacitance by ion polarization. With high capacitance, ion-incorporated aluminas become promising high dielectric constant (high-k) gate dielectric materials in field-effect transistors (FETs) to enable reduced operating voltage, using oxide or organic semiconductors. Alumina capacitance can be manipulated by incorporation of alkali metal ions, including potassium (K+), sodium (Na+), and lithium (Li+), having different bond strengths with oxygen. To investigate the electrical stability of zinc tin oxide-based transistors using ion incorporated alumina as gate dielectrics, pulsed biases at different duty cycles (20%, 10%, and 2% representing 5 ms, 10 ms, and 50 ms periods, respectively) were applied to the gate electrode, sweeping the gate voltage over series of these cycles. We observed a particular bias stress-induced decrease of saturation field-effect mobility accompanied by threshold voltage shifts (ΔVth) in potassium and sodium-incorporated alumina (abbreviated as PA and SA)-based FETs at high duty cycle that persisted over multiple gate voltage sweeps, suggesting a possible creation of new defects in the semiconductor. This conclusion is also supported by the greater change in the mobility-capacitance (μC) product than in capacitance itself. Moreover, a more pronounced ΔVth over shorter times was observed in lithium-incorporated alumina (abbreviated as LA)-based transistors, suggesting trapping of electrons in existing interfacial states. ΔVth from multiple gate voltage sweeps over time were fit to stretched exponential forms. All three dielectrics show good stability using 50-ms intervals (20-Hz frequencies), corresponding to 2% duty cycles

  10. The mechanical reliability of alumina scales and coatings

    Energy Technology Data Exchange (ETDEWEB)

    Alexander, K.B.; Pruebner, K.; Tortorelli, P.F. [Oak Ridge National Lab., TN (United States)

    1996-08-01

    The mechanical integrity of oxide scales ultimately determines their ability to protect materials from corrosion and other environmental effects arising from deleterious reactions with gases and condensable products. The microstructure and mechanical behavior of alumina products thermally grown or deposited on Fe-28 at.% Al intermetallic alloys are being characterized in order to develop the knowledge and means to control the mechanical reliability of alumina scales by microstructural manipulation through design and processing. Mechanical characterization involved gravimetric data from cyclic oxidation experiments, in-situ observation of oxidized specimens undergoing flexural loading in a scanning electron microscope, and measurements of hardness, elastic modulus and cracking resistance by nanoindentation. Values of cracking thresholds for Al{sub 2}O{sub 3} scales were consistent with other measurements for surface and bulk alumina. The oxidation behavior of Fe{sub 3}Al alloys coated with a thin (0.5 - 1 {mu}m) alumina film deposited by plasma synthesis has been studied. During exposure in the oxidizing environment, new oxide was formed between the coating and the substrate. The presence of the deposited amorphous oxide inhibited the subsequent thermal oxidation of the metal. Because the thermally grown alumina forms under the deposit, the adherence of the coating is controlled by the strength of the metal/oxide interface that develops during oxidation.

  11. Plasma Processes : Plasma sprayed alumina coatings for radiation detector development

    Indian Academy of Sciences (India)

    Mary Alex; V Balagi; K R Prasad; K P Sreekumar; P V Ananthapadmanabhan

    2000-11-01

    Conventional design of radiation detectors uses sintered ceramic insulating modules. The major drawback of these ceramic components is their inherent brittleness. Ion chambers, in which these ceramic spacers are replaced by metallic components with plasma spray coated alumina, have been developed in our Research Centre. These components act as thin spacers that have good mechanical strength as well as high electrical insulation and replace alumina insulators with the same dimensions. As a result, the design of the beam loss monitor ion chamber for CAT could be simplified by coating the outer surface of the HT electrode with alumina. One of the chambers developed for isotope calibrator for brachytherapy gamma sources has its outer aluminium electrode (60 mm dia × 220 mm long) coated with 250 thick alumina (97%) + titania (3%). In view of potential applications in neutron-sensitive ion chambers used in reactor control instrumentation, studies were carried out on alumina 100 to 500 thick coatings on copper, aluminium and SS components. The electrical insulation varied from 108 ohms to 1012 ohms for coating thicknesses above 200 . The porosity in the coating resulted in some fall in electrical insulation due to moisture absorption. An improvement could be achieved by providing the ceramic surface with moisture-repellent silicone oil coating. Irradiation at Apsara reactor core location showed that the coating on aluminium was found to be unaffected after exposure to 1017 nvt fluence.

  12. Aluminas with dispersoids. Tribologic properties and in vivo aging.

    Science.gov (United States)

    Mandrino, A; Moyen, B; Ben Abdallah, A; Treheux, D; Orange, D

    1990-07-01

    Three base alumina ceramics with dispersoids: monoclinic zirconia alumina (A5Z), tetragonal zirconia alumina (A20Z) and aluminalon (Aa20) have been investigated because of their improved mechanical properties with reference to pure alumina (AI203). Bending strength and fracture toughness are twice higher than alumina for the most toughened. These two parameters were measured by four-points bending tests after 1 week, 1, 2, 3, 6, 12 months of non loaded in vivo aging in wistar rats. They showed a little decrease for AI203 and Aa20 and a total stability for A5Z and A20Z even after one year. For tribologic study of the ceramic/polyethylene combination, cylinder against plane and pin on flat tests were conducted on an alternative movement with hip parameters of speed and load in presence of ringer solution. For the most representative test (pin on disk), the friction coefficients were nearly the same for all materials but UHMWPE wear volume was twice lower against A20Z than against AI203. A20Z/UHMWPE combination would be very interesting as new friction couple for total hip arthroplasty. Further studies are currently conducted. PMID:2397268

  13. Enriched fluoride sorption using alumina/chitosan composite

    International Nuclear Information System (INIS)

    Alumina possesses an appreciable defluoridation capacity (DC) of 1566 mg F-/kg. In order to improve its DC, it is aimed to prepare alumina polymeric composites using the chitosan. Alumina/chitosan (AlCs) composite was prepared by incorporating alumina particles in the chitosan polymeric matrix, which can be made into any desired form viz., beads, candles and membranes. AlCs composite displayed a maximum DC of 3809 mg F-/kg than the alumina and chitosan (52 mg F-/kg). The fluoride removal studies were carried out in batch mode to optimize the equilibrium parameters viz., contact time, pH, co-anions and temperature. The equilibrium data was fitted with Freundlich and Langmuir isotherms to find the best fit for the sorption process. The calculated values of thermodynamic parameters indicate the nature of sorption. The surface characterisation of the sorbent was performed by FTIR, AFM and SEM with EDAX analysis. A possible mechanism of fluoride sorption by AlCs composite has been proposed. Suitability of AlCs composite at field conditions was tested with a field sample taken from a nearby fluoride-endemic village. This work provides a potential platform for the development of defluoridation technology.

  14. Synthesis and structural evaluation of freeze-cast porous alumina

    International Nuclear Information System (INIS)

    In this work we fabricated alumina samples by the freeze-casting technique using tert-butanol as the solvent. The prepared materials were examined by scanning electron microscopy and X-ray microtomography. Next, they were coated with sol–gel silica films by dip-coating. Permeability tests were carried out in order to assess the permeation behavior of the materials processed in this study. We observed that the sintering time and alumina loading showed a remarkable effect on both the structural properties and flexural strength of the freeze-cast samples. Nitrogen adsorption tests revealed that the silica prepared in this study exhibited a microporous structure. It was observed that the presence of silica coatings on the alumina surface decreased the CO2 permeance by about one order of magnitude. Because of the similar kinetic diameters of nitrogen and carbon dioxide, the CO2/N2 system showed a separation efficiency that was lower than that observed for the He/CO2 and He/N2 systems. We noticed that increasing the feed pressure improved the separation capacity of the obtained materials. - Highlights: • Porous alumina samples obtained by the freeze-casting technique • Microporous silica coating prepared by a simple sol–gel dip-coating methodology • Samples examined by SEM, μ-CT, and nitrogen sorption tests • Mechanical tests were carried out in the freeze-cast samples. • The presence of silica coatings on the alumina surface decreased the CO2 permeance

  15. The nature of hydrogen in γ-alumina

    International Nuclear Information System (INIS)

    Gibbs free energy models are derived from the calculated electronic and phonon structure of two possible models of γ-alumina, a defective spinel phase and a hydrogenated spinel phase. The intrinsic vacancies and hydrogen in the two structural models give rise to a considerable configurational (residual) entropy and significantly contribute to thermodynamic stability and physical-chemical properties of γ-alumina, which was neglected in previous studies but considered in this work. The electronic densities of states, calculated using a hybrid functional for the two structural models of γ-alumina, are presented. The dynamic stability of the two phases is confirmed by full-spectrum phonon calculations. The two phases share many similarities in their electronic structure, but can be distinguished by their vibrational spectra and specific heat. The defective spinel is found to be the ground state of γ-alumina, while the hydrogenated spinel to be a metastable phase. However, dehydration of the metastable phase into the ground state is expected to be slow due to the low diffusion rate of H, which leaves hydrogen as a locked-in impurity in γ-alumina.

  16. Modifying alumina red mud to support a revegetation cover

    Science.gov (United States)

    Xenidis, A.; Harokopou, A. D.; Mylona, E.; Brofas, G.

    2005-02-01

    Alumina red mud, a fine-textured, iron-rich, alkaline residue, is the major waste product of bauxite digestion with caustic soda to remove alumina. The high alkalinity and salinity as well as the poor nutrient status are considered to be the major constraints of red mud revegetation. This research was conducted to evaluate the ameliorating effect of gypsum, sewage sludge, ferrous sulfate, ammonium sulfate, ammonium nitrate, and calcium phosphate on alumina red mud. The effectiveness of the mixtures was evaluated by applying extraction tests and performing experiments using six plant species. Gypsum amendment significantly reduced the pH, electrical conductivity, and sodium and aluminum content of red mud. Sewage sludge application had an extended effect in improving both the soil structure and the nutrient status of the gypsum-amended red mud. Together with the gypsum and sewage sludge, calcium phosphate application into red mud enhanced plant growth and gave the most promising results.

  17. New adsorbent, silver-alumina for radioactive iodine filter

    International Nuclear Information System (INIS)

    Silver-alumina adsorbent has been developed for the iodine filter installed in the off-gas treatment system of a radioactive waste tank vent. In order to improve the removal efficiency under a highly humid atmosphere and to reduce susceptibility to contaminants in the air, the optimum average pore size of alumina was determined to be about 600 A when the impregnated silver compound was silver nitrate. The holding capability of impregnated silver was also improved by developing a double pore structure alumina. The effects of chemical forms and contaminants on the removal efficiency were explained by an ionic reaction mechanism at high relative humidity, which involves water vapor adsorption in micropores by capillary condensation followed by formation of a silver iodide compound

  18. Studies on synthesis of alumina nanopowder from synthetic Bayer liquor

    International Nuclear Information System (INIS)

    Procedure for synthesis of alumina nanopowder from Bayer liquor (synthetic sodium aluminate solution) is investigated. Cooling, ageing and then addition of 3 ml/l Tiron (1,2-dihydroxy-3,5-benzene disulfonic acid disodium salt) to the supersaturated liquor affect purity and fineness of the nanopowder product. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX) analyses indicate that purity of the alumina nanopowder increases with the aging time. Experimental observations show that highly pure alumina nanopowders could be produced by direct calcination of cold gelatinous sodium aluminate solution followed by careful washing at a Tiron concentration of 3 ml/l NaOH

  19. Calculation of the effective emissivity of blackbodies made of alumina

    International Nuclear Information System (INIS)

    Blackbodies are sources of temperature radiation that are used for calibration of radiation thermometers. Their effective emissivity should be close to the value of 1 to approximate an ideal Planckian radiator. Their effective emissivity depends on the geometry of their cavity and the used material. It can be estimated by measurements, but often it is calculated by numerical methods. For typical graphite blackbodies, it was shown in the past that high effective emissivities better than 0.999 can be reached. In this paper, calculations of the effective emissivity of a alumina blackbody are presented. Alumina is a new material for blackbodies, with different radiation properties. Using two calculation methods (integrative cavity method and Monte Carlo method), the effective cavity emissivity for blank and coated alumina is estimated. It is shown that effective spectral emissivities up to 0.999 87 can be reached. (paper)

  20. Origin of High-Alumina Basalt, Andesite, and Dacite Magmas.

    Science.gov (United States)

    Hamilton, W

    1964-10-30

    The typical volcanic rocks of most island arcs and eugeosynclines, and of some continental environments, are basalt, andesite, and dacite, of high alumina content. The high-alumina basalt differs from tholeiitic basalt primarily in having a greater content of the components of calcic plagioclase. Laboratory data indicate that in the upper mantle, below the level at which the basaltic component of mantle rock is transformed by pressure to eclogite or pyroxenite, the entire basaltic portion probably is melted within a narrow temperature range, but that above the level of that transformation plagioclase is melted selectively before pyroxene over a wide temperature range. The broad spectrum of high-alumina magmas may represent widely varying degrees of partial melting above the transformation level, whereas narrow-spectrum tholeiite magma may represent more complete melting beneath it. PMID:17794034

  1. Thermal and Electrical Characterization of Alumina Substrate for Microelectronic Applications

    International Nuclear Information System (INIS)

    This paper reports the effect of sintering temperature on thermal and electrical properties of alumina material as substrate for microelectronic devices. Alumina materials in the form of green sheet with 1 mm thickness were sintered at 1100 deg. C, 1300 deg. C and 1500 deg. C for about 20 hours using heating and cooling rates of 2 deg. C/min. The densities were measured using densitometer and the microstructures of the samples were analyzed using SEM micrographs. Meanwhile thermal and electrical properties of the samples were measured using flash method and impedance analyzer respectively. It was found that thermal conductivity and thermal diffusivity of the substrate increases as sintering temperature increases. It was found also that the dielectric constant of alumina substrate increases as the sintering temperature increases.

  2. Pressureless sintering behavior of injection molded alumina ceramics

    Directory of Open Access Journals (Sweden)

    Liu W.

    2014-01-01

    Full Text Available The pressureless sintering behaviors of two widely used submicron alumina (MgOdoped and undoped with different solid loadings produced by injection molding have been studied systematically. Regardless of the sinterability of different powders depending on their inherent properties, solid loading plays a critical role on the sintering behavior of injection molded alumina, which greatly determines the densification and grain size, and leads to its full densification at low temperatures. As compared to the MgO-doped alumina powder, the undoped specimens exhibit a higher sinterability for its smaller particle size and larger surface area. While full densification could be achieved for MgO-doped powders with only a lower solid loading, due to the fact that MgO addition can reduce the detrimental effect of the large pore space on the pore-boundary separation.

  3. Alumina Template-Dependant Growth of Cobalt Nanowire Arrays

    Directory of Open Access Journals (Sweden)

    L. Malferrari

    2009-01-01

    Full Text Available Different electrochemical regimes and porous alumina were applied for template synthesis of cobalt nanowire (nw arrays, revealing several peculiar cases. In contrast to quite uniform filling of sulfuric acid alumina templates by alternating current deposition, nonuniform growth of the Co nw tufts and mushrooms was obtained for the case of oxalic acid templates. We showed herein for the first time that such configurations arise from the spontaneous growth of cobalt nw groups evolving from the cobalt balls at the Al/alumina interface. Nevertheless, the uniform growth of densely packed cobalt nw arrays, up to tens of micrometers in length, was obtained via long-term direct current galvanostatic deposition at low current density using oxalic acid templates one-side coated by conducting layer. The unique point of this regime is the formation of hexagonal lattice Co nws with a preferred (100 growth direction.

  4. Fabrication of alumina films with laminated structures by ac anodization

    International Nuclear Information System (INIS)

    Anodization techniques by alternating current (ac) are introduced in this review. By using ac anodization, laminated alumina films are fabricated. Different types of alumina films consisting of 50–200 nm layers were obtained by varying both the ac power supply and the electrolyte. The total film thickness increased with an increase in the total charge transferred. The thickness of the individual layers increased with the ac voltage; however, the anodization time had little effect on the film thickness. The laminated alumina films resembled the nacre structure of shells, and the different morphologies exhibited by bivalves and spiral shells could be replicated by controlling the rate of increase of the applied potentials. (paper)

  5. Intrinsic and extrinsic luminescence of nanosize transition alumina powders

    International Nuclear Information System (INIS)

    Luminescence spectroscopy in the VUV-visible range under electron-beam excitation and synchrotron radiation was applied to investigate electronic properties of alumina nanopowders, which were prepared using the combustion synthesis method. By varying reaction and post treatment conditions we were able to prepare phase pure samples and powders with mixtures of α- and γ-phases mainly. In addition to the well-known 7.6 eV luminescence of STE of α-alumina, all samples possessed complex emission bands in UV range (3–5 eV) which originate from intrinsic excitonic emissions and extrinsic electronic excitations. -- Highlights: ► Luminescent spectroscopy of nanosized alumina powders was studied at 8 K. ► The crystalline structure of samples was analysed. ► Luminescent spectra, lifetimes and absorption onsets were discussed

  6. Plastic deformation and sintering of alumina under high pressure

    International Nuclear Information System (INIS)

    Plastic deformation of alumina (Al2O3) under high pressure was investigated by observing the shape changes of spherical particles, and the near fully dense transparent bulks were prepared at around 5.5 GPa and 900 °C. Through analyzing the deformation features, densities, and residual micro-strain of the Al2O3 compacts prepared under high pressures and temperatures (2.0–5.5 GPa and 600–1200 °C), the effects of plastic deformation on the sintering behavior of alumina have been demonstrated. Under compression, the microscopic deviatoric stress caused by grain-to-grain contact could initiate the plastic deformation of individual particles, eliminate pores of the polycrystalline samples, and enhance the local atomic diffusion at the grain boundaries, thus produced transparent alumina bulks

  7. Alumina composites for oxide/oxide fibrous monoliths

    International Nuclear Information System (INIS)

    Most work on ceramic fibrous monoliths (FMs) has focused on the Si3N4/BN system. In an effort to develop oxidation-resistant FMs, several oxide systems have recently been examined. Zirconia-toughened alumina and alumina/mullite appear to be good candidates for the cell phase of FMs. These composites offer higher strength and toughness than pure alumina and good high-temperature stability. By combining these oxides, possibly with a weaker high-temperature oxide as the cell-boundary phase, it should be possible to product a strong, resilient FM that exhibits graceful failure. Several material combinations have been examined. Results on FM fabrication and microstructural development are presented

  8. Effects of yttrium on the sintering and microstructure of alumina-silicon carbide "nanocomposites"

    OpenAIRE

    Cock, AM; Shapiro, IP; Todd, RI; Roberts, SG

    2005-01-01

    Alumina and alumina-based "nanocomposites" with 2 and 5 vol% silicon carbide and varying amounts of yttria (0-1.5 wt%) have been prepared by pressureless sintering in the temperature range 1450°-1650°C. The effects of composition and sintering temperature on density and microstructure are reported. Yttria inhibited sintering in alumina, but enhanced the sinterability of the nanocomposites. It also induced abnormal grain growth in both alumina and nanocomposites, but strongly bimodal grain siz...

  9. Hydrogen removal from e-beam deposited alumina thin films by oxygen ion beam

    International Nuclear Information System (INIS)

    Hydrogen interstitials and oxygen vacancies defects create energy levels in the band gap of alumina. This limits the application of alumina as a high-k dielectric. A low thermal budget method for removal of hydrogen from alumina is discussed. It is shown that bombardment of alumina films with low energy oxygen ion beam during electron beam evaporation deposition decreases the hydrogen concentration in the film significantly

  10. Direct current plasma spraying of mechanofused alumina-steel particles

    OpenAIRE

    Bouneder, Mohamed; Ageorges, Hélène; El Ganaoui, M.; Pateyron, Bernard; Fauchais, Pierre

    2009-01-01

    Paper project pages 26 Stainless steel particles (60 µm in mean diameter) cladded with an alumina shell (2 µm thick and manufactured by mechanofusion) were sprayed with an Ar-H2 (53-7 slm) d.c. plasma jet (I = 500 A, P = 28 kW, \\rho_th = 56 %). Two main types of particles were collected in flight, as close as 50 mm downstream of the nozzle exit: particles with a steel core with pieces of alumina unevenly distributed at their surface and those consisting of a spherical stainless steel parti...

  11. Behaviour modelling of two aluminas in divergent spherical pyrotechnical experiments

    International Nuclear Information System (INIS)

    Two pure aluminas of different characteristics have been subjected to the propagation of a longitudinal divergent spherical shock wave through pyrotechnical experiments. An approach combining a phenomenological analysis and numerical 1D-calculations is proposed to study the behaviour of these aluminas submitted to that type of wave loading. The modelling, proposed in a previous paper, is refined and gives satisfying experimentation-calculation correlations. An analysis of the influence exerted by the various encountered phenomena (plastic activity, pore closure, microcracking) is performed. The significant consequence of the activation of damage with an extension criterion is also underlined. (orig.)

  12. Inelastic neutron scattering studies of methyl chloride synthesis over alumina

    OpenAIRE

    Lennon, David; Parker, Stewart F.

    2014-01-01

    Not only is alumina the most widely used catalyst support material in the world, it is also an important catalyst in its own right. One major chemical process that uses alumina in this respect is the industrial production of methyl chloride. This is a large scale process (650 000 metric tons in 2010 in the United States), and a key feedstock in the production of silicones that are widely used as household sealants. In this Account, we show how, in partnership with conventional spectroscopic a...

  13. Comparative study on sintered alumina for ballistic shielding application

    International Nuclear Information System (INIS)

    This work presents a development of the armor made from special ceramic materials and kevlar. An experimental investigation was conducted to study the ballistic penetration resistance on three samples taken from sintered alumina: a commercial one and two formulations A and B made in IAE/CTA. The main differences between the two formulations was the grain size and bend resistance. The knowledge of the mechanisms during the penetration and perforation process allowed to apply a ductile composite laminate made form kevlar under the alumina to delay its rupture. The last ballistic test showed how a Weibull's modulii and other mechanical properties are able to improve ballistic penetration resistance. (author)

  14. Synthesis of alumina based on industrial waste material

    OpenAIRE

    López-Andrés, Sol; Fillali, Laila; Jiménez, José Antonio; Tayibi, Hanan; Padilla, Isabel; López-Delgado, Aurora

    2011-01-01

    A hazardous waste generated in slag milling process by the aluminium industry was used as a raw material for the synthesis of alumina, α-Al2O3. This waste is considered as hazardous material in the European legislation due to the release of toxic gases (hydrogen, ammonia, methane and hydrogen sulphide) in the presence of water. The process developed in this work allows to obtaining 1 ton of alumina from 4 tons of hazardous waste and generates an inert solid residue consisting principally of s...

  15. CRACK PROPAGATION BEHAVIOR AND LIFETIME PREDICTION IN ALUMINA AND ZIRCONIA

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    The lifetime prediction of ceramics is discussed on the basis of the relationship between stress intensity factor KI and crack velocity v. The effects of water environment, the cyclic loading and microstructure of material on KI-v characteristics are studied by carrying out the crack growth tests by the double torsion (DT) method under the static and cyclic loading in both environments of air and water for alumina and zirconia. KI-v characteristics determined by the double torsion method are used to predict time-to-failure under the cyclic loading of alumina and zirconia ceramics. The predictions agree qualitatively with the experimental results.

  16. Adsorption of textile dye onto modified immobilized activated alumina

    OpenAIRE

    Ayesha Wasti; M. Ali Awan

    2016-01-01

    The study describes the synthesis of modified immobilized activated alumina (MIAA) and its application for the removal of textile dye from aqueous media. Immobilization was carried out by using the sol–gel method while modifications were made during the synthesis by adding powder activated alumina. Batch adsorption experiments were carried out at 20 ± 1 °C to see the effect of different parameters like contact time, stirring rate, initial concentration of the dye and dose of MIAA. The removal...

  17. Pengaruh Temperatur Bath Terhadap Alumina Solubility Pada Tungku Reduksi Di PT Inalum Kuala Tanjung

    OpenAIRE

    Rahman, Syahri

    2010-01-01

    Alumina solubility is maximum aluminium oxide concentration of the cryolite electrolyte depend on its composition. The factors that affect to the quantity of alumina solubility are cryolite temperature (NA3AlF6), %AlF3, and %CaF2 in cryolite. From observation data, know that if cryolite temperature high, so alumina solubility provided high too.

  18. Catalytic cleavage of lignin b-O-4 link mimics using copper on alumina and magnesia-alumina

    OpenAIRE

    Strassberger, Z.; Alberts, A.H.; Louwerse, M.J.; Tanase, S.; Rothenberg, G.

    2013-01-01

    Copper on γ-alumina and on mixed magnesia-alumina, Cu/MgO-Al2O3, catalyse the hydrodeoxygenation (HDO) of β-O-4 lignin-type dimers, giving valuable aromatics. The typical selectivity to phenol is as high as 20%. By changing the support's acidity we can modify the dispersion of copper. Interestingly, more HDO occurs with larger copper agglomerates than with finely dispersed particles. The presence of copper also increases the selectivity of the HDO cleavage. Three different pathways are hypoth...

  19. Substrate-induced coagulation (SIC) of nano-disperse alumina in non-aqueous media: The dispersibility and stability of alumina in N-methyl-2-pyrrolidinone

    OpenAIRE

    Basch, Angelika; Strnad, Simona

    2011-01-01

    This work investigated colloidal properties such as the zeta-potential, the electrophoretic mobilities and the wetting behaviour of alumina dispersed in non-aqueous media. Non-aqueous dispersions of alumina were prepared in the solvent N-methyl-2-pyrrolidinone (NMP). The wetting behaviour of alumina in NMP was characterized by the powder contact angle method and the Wilhemy plate method. The behaviour of the dispersion should provide information for the development of a substrate-induced coag...

  20. Relevance of alumina grit analysis in zircaloy fabrication process

    International Nuclear Information System (INIS)

    Zirconium based alloys are the natural choice for both fuel element and in-core structural components in the water cooled thermal reactors, namely BWRs, PWRs and PHWRs. Nuclear Fuel Complex (NFC), Hyderabad is engaged in the production of zirconium based alloys that are used as hardware in the nuclear industry. After hot working of zircaloy, due to its reactivity, an oxide layer is formed on its surfaces. Hence to remove this oxide layer grit blasting operation using alumina grit sand is followed during which the particles of the sand gets fragmented and the oxide layer on the material thus gets dislodged. Thus alumina grit plays a prominent role in the zircaloy fabrication process. In order to have an ideal and effective removal of the oxide layer from the zircaloy surface, knowledge about the composition of the grit with respect to Al2O3, SiO2, TiO2, Fe2O3, CaO and MgO is essential. Therefore the chemical compositional analysis of alumina grit for confirming to specification becomes an essential step in the Quality Assurance (QA) programme for acceptance of the material. The present paper describes the analytical methodology followed in our laboratory for the chemical analysis of alumina grit samples used in the grit blasting operations

  1. N-doped mesoporous alumina for adsorption of carbon dioxide

    Institute of Scientific and Technical Information of China (English)

    Jayshri A.Thote; Ravikrishna V.Chatti; Kartik S.Iyer; Vivek Kumar; Arti N.Valechha; Nitin K.Labhsetwar; Rajesh B.Biniwale; M.K.N.Yenkie; Sadhana S.Rayalu

    2012-01-01

    N-doped mesoporous alumina has been synthesized using chitosan as the biopolymer template.The adsorbent has been thoroughly investigated for the adsorption of CO2 from a simulated flue gas stream (15% CO2 balanced with N2) and compared with commercially available mesoporous alumina procured from SASOL,Germany.CO2 adsorption was studied under different conditions of pretreatment and adsorption temperature,inlet CO2 concentration and in the presence of oxygen and moisture.The adsorption capacity was determined to be 29.4 mg CO2/g of adsorbent at 55℃.This value was observed to be 4 times higher in comparison to that of commercial mesoporous alumina at a temperature of 55℃.Basicity of alumina surface coupled with the presence of nitrogen in template in synthesized sample is responsible for this enhanced CO2 adsorption.Adsorption capacity for CO2 was retained in the presence of oxygen; however moisture had a deteriorating effect on the adsorption capacity reducing it to nearly half the value.

  2. Alumina and Zirconia Based Layered Composites:Part 1 Preparation

    Czech Academy of Sciences Publication Activity Database

    Hadraba, Hynek; Maca, K.; Chlup, Zdeněk

    2009-01-01

    Roč. 412, - (2009), s. 221-226. ISSN 1013-9826 R&D Projects: GA ČR(CZ) GA106/06/0724 Institutional research plan: CEZ:AV0Z20410507 Keywords : electrophoretic deposition * alumina * zirconia Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass

  3. High rate reactive magnetron sputtering of alumina coatings

    Czech Academy of Sciences Publication Activity Database

    Bulíř, Jiří; Novotný, Michal; Pokorný, Petr; Lančok, Ján; Musil, Jindřich

    Warrendale, PA: MRS , 2009. s. 27-28. ISBN N. [E- MRS 2009 Spring Meeting. 08.06.2009-12.06.2009, Strasbourg] Institutional research plan: CEZ:AV0Z10100522 Keywords : reactive pulsed magnetron sputtering * alumina * optical emission spectroscopy * mass spectroscopy Subject RIV: BH - Optics, Masers, Lasers

  4. Dynamical stability of the alpha and theta phases of alumina

    DEFF Research Database (Denmark)

    Lodziana, Zbigniew; Parlinski, K.

    2003-01-01

    Using density functional calculations the phonon dispersion relations, phonon density of states, and free energy of theta and alpha phases of alumina are investigated. The temperature dependence of the free energy indicates that entropy contributes to the destabilization of the alpha phase at the...

  5. Multifunctional substrates of thin porous alumina for cell biosensors

    KAUST Repository

    Toccafondi, Chiara

    2014-02-27

    We have fabricated anodic porous alumina from thin films (100/500 nm) of aluminium deposited on technological substrates of silicon/glass, and investigated the feasibility of this material as a surface for the development of analytical biosensors aiming to assess the status of living cells. To this goal, porous alumina surfaces with fixed pitch and variable pore size were analyzed for various functionalities. Gold coated (about 25 nm) alumina revealed surface enhanced Raman scattering increasing with the decrease in wall thickness, with factor up to values of approximately 104 with respect to the flat gold surface. Bare porous alumina was employed for micro-patterning and observation via fluorescence images of dye molecules, which demonstrated the surface capability for a drug-loading device. NIH-3T3 fibroblast cells were cultured in vitro and examined after 2 days since seeding, and no significant (P > 0.05) differences in their proliferation were observed on porous and non-porous materials. The effect on cell cultures of pore size in the range of 50–130 nm—with pore pitch of about 250 nm—showed no significant differences in cell viability and similar levels in all cases as on a control substrate. Future work will address combination of all above capabilities into a single device.

  6. Controlled growth of single nanowires within a supported alumina template

    Energy Technology Data Exchange (ETDEWEB)

    Vlad, A [Unite de Dispositifs Integres et Circuits Electroniques, Universite Catholique de Louvain (UCL), Place de Levant, 3, B-1348 Louvain-la-Neuve (Belgium); Matefi-Tempfli, M [Unite de Physico-Chimie et de Physique des Materiaux, UCL, Place Croix du Sud, 1, B-1348 Louvain-la-Neuve (Belgium); Faniel, S [Unite de Dispositifs Integres et Circuits Electroniques, Universite Catholique de Louvain (UCL), Place de Levant, 3, B-1348 Louvain-la-Neuve (Belgium); Bayot, V [Unite de Dispositifs Integres et Circuits Electroniques, Universite Catholique de Louvain (UCL), Place de Levant, 3, B-1348 Louvain-la-Neuve (Belgium); Melinte, S [Unite de Dispositifs Integres et Circuits Electroniques, Universite Catholique de Louvain (UCL), Place de Levant, 3, B-1348 Louvain-la-Neuve (Belgium); Piraux, L [Unite de Physico-Chimie et de Physique des Materiaux, UCL, Place Croix du Sud, 1, B-1348 Louvain-la-Neuve (Belgium); Matefi-Tempfli, S [Unite de Physico-Chimie et de Physique des Materiaux, UCL, Place Croix du Sud, 1, B-1348 Louvain-la-Neuve (Belgium)

    2006-10-14

    A simple technique for fabricating single nanowires with well-defined position is presented. The process implies the use of a silicon nitride mask for selective electrochemical growth of the nanowires in a porous alumina template. We show that this method allows the realization of complex nanowire patterns as well as arrays of single nanowires with a precise position and spacing.

  7. Controlled growth of single nanowires within a supported alumina template

    Science.gov (United States)

    Vlad, A.; Mátéfi-Tempfli, M.; Faniel, S.; Bayot, V.; Melinte, S.; Piraux, L.; Mátéfi-Tempfli, S.

    2006-10-01

    A simple technique for fabricating single nanowires with well-defined position is presented. The process implies the use of a silicon nitride mask for selective electrochemical growth of the nanowires in a porous alumina template. We show that this method allows the realization of complex nanowire patterns as well as arrays of single nanowires with a precise position and spacing.

  8. Alumina-encapsulated vaccine formulation with improved thermostability and immunogenicity.

    Science.gov (United States)

    Zhou, Hangyu; Wang, Guangchuan; Li, Xiao-Feng; Li, Yaling; Zhu, Shun-Ya; Qin, Cheng-Feng; Tang, Ruikang

    2016-05-11

    Developing vaccine formulations with excellent thermostability and immunogenicity remains a great challenge. By in situ encapsulating a live-attenuated strain of human enterovirus 71 (EV71) in alumina, we obtained a robust vaccine formulation named EV71@NanoAlum, which features significantly enhanced thermostability and immunogenicity. This attempt follows a material-based tactic for vaccine improvement. PMID:27098047

  9. Grafting of alumina on SBA-15: Effect of surface roughness

    Czech Academy of Sciences Publication Activity Database

    Zukal, Arnošt; Šiklová, Helena; Čejka, Jiří

    2008-01-01

    Roč. 24, č. 17 (2008), s. 9837-9842. ISSN 0743-7463 R&D Projects: GA AV ČR KAN100400701 Institutional research plan: CEZ:AV0Z40400503 Keywords : alumina-grafted materials * SBA-15 * Nitrogen adsorption Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.097, year: 2008

  10. Interaction of alumina with liquid Pb83Li17 alloy

    International Nuclear Information System (INIS)

    Highlights: • The role of oxygen in the interaction of alumina with Pb83Li17 alloy was studied. • Li of Pb83Li17 alloy undergoes oxidation even in flowing high pure argon atmosphere. • It was seen that alumina reacts with Pb83Li17 alloy at 550 °C to form LiAlO2 compound. • The reaction is rapid in the presence of oxygen and happens more slowly in the presence of flowing argon. - Abstract: Eutectic lead lithium (Pb83Li17) alloy is being considered a coolant, neutron multiplier and tritium breeder for International Thermonuclear Experimental Reactor (ITER) and Fusion Power Reactors (FPR). In order to reduce the magneto-hydrodynamic drag (MHD) and to prevent corrosion of structural materials due to the flow of lead lithium (Pb83Li17) alloy, alumina (Al2O3) is proposed as a candidate ceramic coating material. Interaction of liquid Pb83Li17 alloy with Al2O3 at the operating temperature of these reactors is therefore an important issue. The present paper deals with the characterization of Pb83Li17 alloy and its interaction with Al2O3 at the reactor operating temperature. The interaction was studied using EPMA, XRD and thermal analysis technique. The result indicates that alumina can interact with Pb83Li17 alloy at 550 °C even in high purity argon atmosphere. The role of oxygen in the interaction process has also been discussed

  11. Nanocomposite formed by titanium ion implantation into alumina

    International Nuclear Information System (INIS)

    Composites of titanium nanoparticles in alumina were formed by ion implantation of titanium into alumina, and the surface electrical conductivity measured in situ as the implantation proceeded, thus generating curves of sheet conductivity as a function of dose. The implanted titanium self-conglomerates into nanoparticles, and the spatial dimensions of the buried nanocomposite layer can thus be estimated from the implantation depth profile. Rutherford backscattering spectrometry was performed to measure the implantation depth profile, and was in good agreement with the calculated profile. Transmission electron microscopy of the titanium-implanted alumina was used for direct visualization of the nanoparticles formed. The measured conductivity of the buried layer is explained by percolation theory. We determine that the saturation dose, φ0, the maximum implantation dose for which the nanocomposite material still remains a composite, is φ0 = 2.2 × 1016 cm−2, and the corresponding saturation conductivity is σ0 = 480 S/m. The percolation dose φc, below which the nanocomposite still has basically the conductivity of the alumina matrix, was found to be φc = 0.84 × 1016 cm−2. The experimental results are discussed and compared with a percolation theory model

  12. Radiative properties of radially nonisothermal alumina particles with multiphase

    International Nuclear Information System (INIS)

    Accurate prediction of radiative properties of alumina (Al2O3) particle with phase transition is essential to both spray deposition of coatings and solid aluminized rocket plume diagnostics. In this paper, a theoretical model based on the electromagnetic theory is applied to determine thermal radiation of a radially inhomogeneous alumina particle having a radial temperature distribution, where a concise and efficient algorithm is developed for the calculation. The internal absorption efficiencies for single phase and multiphase particle are calculated and discussed. The absorption efficiency at the surface of multiphase alumina spherical particle is calculated by the effective-medium sphere mode, and the result is compared with that of multilayered sphere model, which shows that effective-medium sphere mode gives similar results when each layer's thickness is much less than the wavelength of the incident light. The effect of temperature difference between the center and the surface on the spectral radiant flux of multiphase alumina particle is also analyzed in this paper.

  13. State of the art: alumina ceramics for energy applications

    International Nuclear Information System (INIS)

    Prominent ceramic raw materials and products manufacturers were surveyed to determine the state of the art for alumina ceramic fabrication. This survey emphasized current capabilities and limitations for fabrication of large, high-density, high-purity, complex shapes. Some directions are suggested for future needs and development

  14. Urbach's rule criteria in alumina irradiated with ions

    International Nuclear Information System (INIS)

    Irradiation of dielectrics with ions is available for aims of the optical, mechanical and other properties modification. The defect localized states effect on alumina optical absorption properties depends on ability of incorporated elements to substitute the lattice cations. The complex energetic spectrum of the defect localized states demands the generalized approaches which characterize the radiation induced disorder in materials as a whole. The Urbach's rule criteria for the absorption spectra of alumina irradiated with the silicon, chromium and titanium ions (Φ=1017 cm-2, Ei=100 keV) were investigated. The induced defect, their clusters and hard solid solution effect on the Urbach's equation parameters was determined. Analysis the reasons of the absorption change was given. Absorption spectra of irradiated alumina were subjected the Urbach's rule as all it criteria were fulfilled. This is stipulated by the static disorder in crystalline lattice induced by substitution defects, intrinsic defects and cluster formation on its base. A common focal point in absorption spectrums situated at 4.4 eV was fixed. This Urbach's focus is determine by the processes of defects clusterization, the energetic characteristics of clusters and depend on ability of the implanted ions to form the hard solid solutions in alumina. A correlation between the interband and exponential absorption parameters indicates to synthesis in Al2O3 a new strongly defect material having band gap width near the 4.5 eV and absorption edge stipulated by the defect cluster levels. (authors)

  15. Preparation of highly-ordered carbon nanotube arrays in the anodized alumina template

    International Nuclear Information System (INIS)

    A highly-ordered, hexagonally arranged alumina nanopore template was prepared by self-organized two-step anodization process of aluminium in oxalic acid solution. Highly parallel pores were obtained within domains of a few micrometers. Highly-ordered, parallel carbon nanotube arrays were successfully grown in the alumina template nanopores by chemical vapor deposition catalyzed by alumina itself. The nanotube arrays are suitable for channeling of particle beams. The structures of aluminium, alumina template and carbon nanotubes were characterized by scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD). The growth mechanism and formation condition of both alumina template and carbon nanotube were discussed. (authors)

  16. Zirconia-alumina coupling: aging of zirconia should be kept out of concern

    Energy Technology Data Exchange (ETDEWEB)

    Villermaux, F. [Norton Desmarquest Fine Ceramics, Evreux (France)

    2001-07-01

    Zirconia-alumina coupling already demonstrated its advantages as ceramic-ceramic bearing compared to alumina-alumina system: equivalent wear performance but higher mechanical reliability and increase of design possibilities (more neck lengths - head Oe22.22 mm). The last step for the in-vitro validation of this system was to investigate the wear behavior with aged zirconia head. Some hip simulator tests have been performed with artificially aged zirconia heads and showed no significant influence on the zirconia-polyethylene or zirconia-alumina wear performance. Then, zirconia-alumina can really be considered as reliable ceramic-ceramic system and aging should be kept out of concern. (orig.)

  17. Effects of maternal exposure to nano-alumina during pregnancy on neurodevelopment in offspring mice

    Institute of Scientific and Technical Information of China (English)

    丁勇

    2013-01-01

    Objective To observe the effects of maternal exposure to nano-alumina during pregnancy on the neurodevelopment in offspring mice.Methods Female ICR mice were exposed to nano-alumina 10 d before mating,and the nano-alumina exposure lasted till offspring mice were born.All the female mice were randomly divided into 5groups:solvent control group (saline) ,nano-carbon group (11.76 mg/ml) ,microalumina group (50 mg/ml) ,50 nm alumina group (50 mg/ml) ,and 13 nm alumina group (50 mg/ml) .All the mice were treated by

  18. Development of an imaging system for the detection of alumina on turbine blades

    International Nuclear Information System (INIS)

    An imaging system capable of detecting alumina on turbine blades by acquiring LED-induced fluorescence images has been developed. Acquiring fluorescence images at adjacent spectral bands allows the system to distinguish alumina from fluorescent surface contaminants. Repair and overhaul processes require that alumina is entirely removed from the blades by grit blasting and chemical stripping. The capability of the system to detect alumina has been investigated with two series of turbine blades provided by Rolls-Royce plc. The results illustrate that the system provides a superior inspection method to visual assessment when ascertaining whether alumina is present on turbine blades during repair and overhaul processes. (paper)

  19. Synthesis and structural evaluation of freeze-cast porous alumina

    Energy Technology Data Exchange (ETDEWEB)

    Souza, Douglas F., E-mail: souzadf@outlook.com [Department of Metallurgical and Materials Engineering, Federal University of Minas Gerais — UFMG, Avenida Presidente Antônio Carlos, 6627, Campus UFMG, Belo Horizonte, MG CEP: 31270-901, Escola de Engenharia, bloco 2, sala 2230 (Brazil); Nunes, Eduardo H.M., E-mail: eduardohmn@gmail.com [Department of Metallurgical and Materials Engineering, Federal University of Minas Gerais — UFMG, Avenida Presidente Antônio Carlos, 6627, Campus UFMG, Belo Horizonte, MG CEP: 31270-901, Escola de Engenharia, bloco 2, sala 2230 (Brazil); Pimenta, Daiana S.; Vasconcelos, Daniela C.L. [Department of Metallurgical and Materials Engineering, Federal University of Minas Gerais — UFMG, Avenida Presidente Antônio Carlos, 6627, Campus UFMG, Belo Horizonte, MG CEP: 31270-901, Escola de Engenharia, bloco 2, sala 2230 (Brazil); Nascimento, Jailton F.; Grava, Wilson [Petrobras/CENPES, Avenida Horácio Macedo 950, Cidade Universitária, Ilha do Fundão, Rio de Janeiro, RJ CEP:21941-915 (Brazil); Houmard, Manuel [Department of Materials Engineering and Civil Construction, Federal University of Minas Gerais — UFMG, Avenida Presidente Antônio Carlos, 6627, Campus UFMG, Belo Horizonte, MG CEP: 31270-901, Escola de Engenharia, bloco 1, sala 3304 (Brazil); Vasconcelos, Wander L., E-mail: wlv@demet.ufmg.br [Department of Metallurgical and Materials Engineering, Federal University of Minas Gerais — UFMG, Avenida Presidente Antônio Carlos, 6627, Campus UFMG, Belo Horizonte, MG CEP: 31270-901, Escola de Engenharia, bloco 2, sala 2230 (Brazil)

    2014-10-15

    In this work we fabricated alumina samples by the freeze-casting technique using tert-butanol as the solvent. The prepared materials were examined by scanning electron microscopy and X-ray microtomography. Next, they were coated with sol–gel silica films by dip-coating. Permeability tests were carried out in order to assess the permeation behavior of the materials processed in this study. We observed that the sintering time and alumina loading showed a remarkable effect on both the structural properties and flexural strength of the freeze-cast samples. Nitrogen adsorption tests revealed that the silica prepared in this study exhibited a microporous structure. It was observed that the presence of silica coatings on the alumina surface decreased the CO{sub 2} permeance by about one order of magnitude. Because of the similar kinetic diameters of nitrogen and carbon dioxide, the CO{sub 2}/N{sub 2} system showed a separation efficiency that was lower than that observed for the He/CO{sub 2} and He/N{sub 2} systems. We noticed that increasing the feed pressure improved the separation capacity of the obtained materials. - Highlights: • Porous alumina samples obtained by the freeze-casting technique • Microporous silica coating prepared by a simple sol–gel dip-coating methodology • Samples examined by SEM, μ-CT, and nitrogen sorption tests • Mechanical tests were carried out in the freeze-cast samples. • The presence of silica coatings on the alumina surface decreased the CO{sub 2} permeance.

  20. Advanced morphological analysis of patterns of thin anodic porous alumina

    International Nuclear Information System (INIS)

    Different conditions of fabrication of thin anodic porous alumina on glass substrates have been explored, obtaining two sets of samples with varying pore density and porosity, respectively. The patterns of pores have been imaged by high resolution scanning electron microscopy and analyzed by innovative methods. The regularity ratio has been extracted from radial profiles of the fast Fourier transforms of the images. Additionally, the Minkowski measures have been calculated. It was first observed that the regularity ratio averaged across all directions is properly corrected by the coefficient previously determined in the literature. Furthermore, the angularly averaged regularity ratio for the thin porous alumina made during short single-step anodizations is lower than that of hexagonal patterns of pores as for thick porous alumina from aluminum electropolishing and two-step anodization. Therefore, the regularity ratio represents a reliable measure of pattern order. At the same time, the lower angular spread of the regularity ratio shows that disordered porous alumina is more isotropic. Within each set, when changing either pore density or porosity, both regularity and isotropy remain rather constant, showing consistent fabrication quality of the experimental patterns. Minor deviations are tentatively discussed with the aid of the Minkowski measures, and the slight decrease in both regularity and isotropy for the final data-points of the porosity set is ascribed to excess pore opening and consequent pore merging. - Highlights: • Thin porous alumina is partly self-ordered and pattern analysis is required. • Regularity ratio is often misused: we fix the averaging and consider its spread. • We also apply the mathematical tool of Minkowski measures, new in this field. • Regularity ratio shows pattern isotropy and Minkowski helps in assessment. • General agreement with perfect artificial patterns confirms the good manufacturing

  1. Advanced morphological analysis of patterns of thin anodic porous alumina

    Energy Technology Data Exchange (ETDEWEB)

    Toccafondi, C. [Istituto Italiano di Tecnologia, Department of Nanophysics, Via Morego 30, Genova I 16163 (Italy); Istituto Italiano di Tecnologia, Department of Nanostructures, Via Morego 30, Genova I 16163 (Italy); Stępniowski, W.J. [Department of Advanced Materials and Technologies, Faculty of Advanced Technologies and Chemistry, Military University of Technology, 2 Kaliskiego Str., 00-908 Warszawa (Poland); Leoncini, M. [Istituto Italiano di Tecnologia, Department of Nanostructures, Via Morego 30, Genova I 16163 (Italy); Salerno, M., E-mail: marco.salerno@iit.it [Istituto Italiano di Tecnologia, Department of Nanophysics, Via Morego 30, Genova I 16163 (Italy)

    2014-08-15

    Different conditions of fabrication of thin anodic porous alumina on glass substrates have been explored, obtaining two sets of samples with varying pore density and porosity, respectively. The patterns of pores have been imaged by high resolution scanning electron microscopy and analyzed by innovative methods. The regularity ratio has been extracted from radial profiles of the fast Fourier transforms of the images. Additionally, the Minkowski measures have been calculated. It was first observed that the regularity ratio averaged across all directions is properly corrected by the coefficient previously determined in the literature. Furthermore, the angularly averaged regularity ratio for the thin porous alumina made during short single-step anodizations is lower than that of hexagonal patterns of pores as for thick porous alumina from aluminum electropolishing and two-step anodization. Therefore, the regularity ratio represents a reliable measure of pattern order. At the same time, the lower angular spread of the regularity ratio shows that disordered porous alumina is more isotropic. Within each set, when changing either pore density or porosity, both regularity and isotropy remain rather constant, showing consistent fabrication quality of the experimental patterns. Minor deviations are tentatively discussed with the aid of the Minkowski measures, and the slight decrease in both regularity and isotropy for the final data-points of the porosity set is ascribed to excess pore opening and consequent pore merging. - Highlights: • Thin porous alumina is partly self-ordered and pattern analysis is required. • Regularity ratio is often misused: we fix the averaging and consider its spread. • We also apply the mathematical tool of Minkowski measures, new in this field. • Regularity ratio shows pattern isotropy and Minkowski helps in assessment. • General agreement with perfect artificial patterns confirms the good manufacturing.

  2. Luminescence characterisation of alumina substrates using cathodoluminescence microscopy and spectroscopy

    International Nuclear Information System (INIS)

    Polycrystalline alumina (Al2O3) substrates, found in many electronic devices and proposed as dosemeters in emergency situations, were invstigated using a scanning electron microscope (SEM) equipped with cathodoluminescence (CL) and elemental analysis probes. The characteristics of the CL spectra, surface morphology, and impurity content of the Al2O3 substrates were examined and compared with those of single crystal dosimetry-grade Al2O3:C. Whereas the CL spectrum, measured from 250 to 800 nm, for the Al2O3:C, contained resolved bands located at ∼340 nm and at ∼410 nm, the spectrum measured with the Al2O3 substrate was significantly broader, extending from ∼250 to ∼450 nm, and also included a narrow band at 695 nm. While it is likely that the accepted model of recombination at F+ (∼340 nm) and F (∼410 nm) in Al2O3:C also applies to the substrate, it is suggested that the presence of impurities within the alumina give rise to additional recombination centres. The 695 nm emission has been assigned to a Cr3+ ion impurity in previous work on alumina and a band indicated at ∼300 nm may be associated with Mg2+ or Ca2+, the presence of which was confirmed by elemental mapping. Comparison of the spatial distribution of CL with the surface morphology and elemental composition of the samples indicates that the components of the emission spectrum can be qualitatively correlated with impurity content and morphological features of the samples. - Highlights: • Morphological (SEM) and elemental characterisation (EDS/WDs) of alumina substrates. • Cathodoluminescence (CL) emission spectroscopy of alumina substrates. • Close relationship of the CL emission with the SEM and EDs/WDS characteristics

  3. Processing and Mechanical Properties of Various Zirconia/Alumina Composites for Fuel Cell Applications

    Science.gov (United States)

    Choi, Sung R.; Bansal, Narottam P.

    2002-01-01

    Various electrolyte materials for solid oxide fuel cells were fabricated by hot pressing 10 mol% yttria-stabilized zirconia (10-YSZ) reinforced with two different forms of alumina, particulates and platelets, each containing 0 to 30 mol% alumina. Flexure strength and fracture toughness of both particulate and platelet composites at ambient temperature increased with increasing alumina content, reaching a maximum at 30 mot% alumina. For a given alumina content, strength of particulate composites was greater than that of platelet composites, whereas, the difference in fracture toughness between the two composite systems was negligible. No virtual difference in elastic modulus and density was observed for a given alumina content between particulate and platelet composites. Thermal cycling up to 10 cycles between 200 to 1000 C did not show any effect on strength degradation of the 30 mol% platelet composites, indicative of negligible influence of CTE mismatches between YSZ matrix and alumina grains.

  4. High alumina metamorphic rocks of the Kings Mountain district, North Carolina and South Carolina

    Science.gov (United States)

    Potter, Donald Brandreth

    1954-01-01

    The following evidence suggests that high alumina quartzite in this district is of metasedimentary origin: high alumina quartzite occurs as well defined thin beds that can be traced up to three and one half miles along strike; many outcrops of high alumina quartzite exhibit compositional layering (i.e., kyanigte quartzite is interlayered with staurolite quartzite, and with non-kyanitic magnetiferous quartzite); high alumina quartzite beds occur in a conformable sequence of high alumina metasedimentary and metavolcanic schists. It is suggested that the high alumina quartzite beds are metamorphosed beds of sandy or silty clay; these beds probably represent one stage in the deposition of fine grained clayey clastic sediments. No evidence was found to support the view of Smith and Newcombe (1951) that the kyanite at Henry Knob developed by hudrothermal introduction of alumina. The present study indicates that kyanite in the kyanite quartzite here, as throughout the district, is of metasedimentary origin.

  5. Study on the bound water of several high specific surface-area oxides (beryllia, alumina, silica-alumina)

    International Nuclear Information System (INIS)

    This study is concerned with the bound water of several oxides (beryllia, alumina, silica-alumina) at different steps of their dehydration (heating temperatures between 150 and 1100 deg. C). The following techniques have been used simultaneously: Thermal analysis (a new method has been developed), nitrogen adsorption (study of the texture), Diborane hydrolysis (qualitative and quantitative analysis of surface water), Infra-red spectrography (in the absorption range of water), Nuclear magnetic resonance (in the resonance range of protons). Thanks to these different techniques, five kinds of bound water have been observed. Attention is called on the great influence of the thermal treatment conditions on the evolution of the products resulting from the decomposition of alumina α-trihydrate Al(OH)3 and beryllium α-hydroxide, in the course of the dehydration. Moreover, the author emphasizes the peculiar properties of the two kinds of oxides (alumina and beryllia) prepared through a new method of treatment under low pressure and constant speed of decomposition. Such particular features concern mainly texture, bound water, and consequently, also catalytic activity. (author)

  6. EFFECTIVE ELASTIC PROPERTIES OF ALUMINA-ZIRCONIA COMPOSITE CERAMICS - PART 4. TENSILE MODULUS OF POROUS ALUMINA AND ZIRCONIA

    Directory of Open Access Journals (Sweden)

    W. Pabst

    2004-12-01

    Full Text Available In this fourth paper of a series on the effective elastic properties of alumina-zirconia composite ceramics the influence of porosity on the effective tensile modulus of alumina and zirconia ceramics is discussed. The examples investigated are alumina and zirconia ceramics prepared from submicron powders by starch consolidation casting using two different types of starch, potato starch (median size D50 =47.2 µm and corn starch (median size D50 =13.7 µm. The dependence of effective tensile moduli E, on the porosity f, measured for porosities in the ranges of approx. 19-55 vol.% and 10-42 vol.% for alumina and zirconia, respectively, using a resonant frequency technique, was evaluated by fitting with various model relations, including newly developed ones. A detailed comparison of the fitting results suggests the superiority of the new relation E/E0 = (1 - f·(1 - f/fC, developed by the authors (with the tensile modulus of the dense ceramic material E0 and the critical porosity fC, over most other existing fit models. Only for special purposes and well-behaved data sets the recently proposed exponential relation E/E0 = exp [-Bf/(1 - f] and the well-known Phani-Niyogi relation E/E0 = (1 - f/fCN might be preferable.

  7. A study on heat transfer characteristics of spherical and fibrous alumina nanofluids

    International Nuclear Information System (INIS)

    Highlights: ► Spherical and fibrous alumina nanoparticles were prepared by pulsed wire evaporation and hydrolysis methods. ► Fibrous alumina nanofluid exhibited higher thermal conductivity enhancement than spherical one due to entangled structure of nanofibers with high aspect-ratio. ► Decreasing rate of viscosity with temperature for fibrous alumina nanofluid was much larger than that for spherical one. - Abstract: Ethylene glycol based nanofluids containing spherical/fibrous alumina nanoparticles were synthesized by pulsed wire evaporation and hydrolysis methods. The crystallographic and morphological properties of the prepared nanoparticles were analyzed by X-ray diffraction, nitrogen gas adsorption and transmission electron microscopy. The average diameter of spherical alumina nanoparticles was about 80 nm and the alumina nanofibers exhibited a high aspect ratio (length/width). The viscosity and thermal conductivity of the spherical/fibrous alumina nanofluids were experimentally measured in the temperature range from 25 to 80 °C. For the fibrous alumina nanofluid, the increase of temperature raised thermal conductivity but lowered viscosity. On the other hand, for the spherical alumina nanofluid, both thermal conductivity and viscosity were decreased with increasing temperature. In particular, the fibrous alumina nanofluid exhibited a higher enhancement of thermal conductivity than the spherical one due to the well-connected structure between entangled nanofibers with high aspect ratio.

  8. Effects of single and two stages anodizing on nonporous anodic alumina template at different potentials

    International Nuclear Information System (INIS)

    The porous anodic alumina has extensive applications as mold or template for filling the highly ordered patterned ID nanomaterials (semiconductors, magnetic nanowires etc.) and as a mask for nano dots of different materials. Pores in anodic alumina synthesized under appropriate conditions are self organized. Pore density, pore diameter, interpore distance may be changed through variation of different parameter such as anodic potential, choice of electrolyte, temperature and kind of pre-treatment. The porous anodic alumina has been synthesized by single and double stage anodizing at different potentials. The potentials used were 40V, 50V, 60V and 70V. By comparison of ordered pore formation under both the conditions, it has been found that pores formed in doubly anodized alumina are more ordered/organized than in singly anodized anodic alumina at same potential used for both type of synthesis. SEM images revealed that the pore density in the singly anodized alumina was greater than in doubly anodized alumina prepared under the same potential. Using the SEM image, the pore diameter in the case of doubly anodized alumina was found to be in the range of 50- 70 nm, whereas, for singly anodized alumina pore diameter was found to be in the range of 50-100 nm. Scanning electron Microscope images and electrochemical parameters showed that two stage anodizing is better than single stage anodizing to achieve highly ordered nanoporous alumina template. (author)

  9. Study of preparation and surface morphology of self-ordered nanoporous alumina; Estudo da preparacao e da morfologia de superficie de alumina nanoporosa auto-organizada

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigues, Elisa Marchezini; Martins, Maximiliano Delany, E-mail: elisamarch@gmail.com, E-mail: MG.mdm@cdtn.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG. (Brazil); Silva, Ronald Arreguy, E-mail: arregsilva@yahoo.com.br [Centro Universitario de Belo Horizonte (UniBH), Belo Horizonte, MG (Brazil)

    2013-07-01

    Nanoporous alumina is a typical material that exhibits self-ordered nanochannels spontaneously organized in hexagonal shape. Produced by anodizing of metallic aluminum, it has been used as a template for production of materials at the nanoscale. This work aimed to study the preparation of nanoporous alumina by anodic anodizing of metallic aluminum substrates. The nanoporous alumina was prepared following the methodology proposed by Masuda and Fukuda (1995), a two-step method consisting of anodizing the aluminum sample in the potentiostatic mode, removing the layer of aluminum oxide (alumina) formed and then repeat the anodization process under the same conditions as the first anodization. This method produces nanoporous alumina with narrow pore diameter distribution and well-ordered structure. (author)

  10. Nano α-alumina powders from aluminium dross waste

    International Nuclear Information System (INIS)

    The paper describes a solvo thermal chemical process to recycle aluminium dross waste into nano α-alumina powder. The process includes washing to remove the unwanted sodium follow by dissolving of this waste with dilute acid. The solvo thermal process then proceed with addition of propanol to crystallize the aluminium hydroxide. XRD analysis of this crystal shows that it belongs to Gibbs site (Al(OH)3). The crystals were then calcined at 1300 degree C where white powder was produced. Characteristic studies were then performed on this powder using XRD, SEM, EDX and particle size analysis showing that it has single α-alumina crystal phase with almost spherical shape. As the initial particle size is coarse and had a mean particle size of 3.80 μm, high speed wet milling was used and enable to reduce it to 0.49 μm. (Author)

  11. Synthesis of Porous Nano Alumina Powder by Combustion Method

    International Nuclear Information System (INIS)

    Development of Porous Alumina powder by combustion technique using glysine fuel and aluminum nitrate as and oxidizer is able to produce porous Alpha alumina powders. Thermodynamic modeling of the combustion reaction show that as the fuel to oxidant ratio increases, the amount of gases produced and adiabatic flame temperature also increase. X-ray diffraction showed the amorphous structure for as-synthesized powder and present of well-crystallized a- Al2O3 after calcination at 1100 degree Celsius. Morphology microstructure of pore size ranging between 134-495 nm were observed by SEM. The crystallite size (Scherrer) is observed at ∼568.2 A and FWHM 0.143 degree. (author)

  12. Catalyst materials based on plasma-processed alumina nanopowder

    Directory of Open Access Journals (Sweden)

    Dubencovs Konstantins

    2012-01-01

    Full Text Available A platinum catalyst for glycerol oxidation by molecular oxygen has been developed applying the extractive-pyrolytic method and using, as a support, a fine alumina powder with an average particle size of 30-60 nm processed by plasma technology. The extractive-pyrolytic method (EPM allows affixing small amounts of catalytic metals (1-5% with the particle size ranging from several nanometers to several tens of nanometers onto the surface of the support. The prepared material - 4.8 wt. % platinum on nano-sized alumina - can be used as a catalyst for glycerol oxidation by oxygen with conversion up to 84%, in order to produce some organic acids (glyceric and lactic acid with a selectivity of about 60%.

  13. Epitaxial growth of tungsten nanoparticles on alumina and spinel surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez-Suarez, T; Lopez-Esteban, S; Pecharroman, C; Esteban-Cubillo, A; Moya, J S [Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Cientificas (CSIC), C/ Sor Juana Ines de la Cruz 3, 28049, Cantoblanco, Madrid (Spain); Diaz, L A; Torrecillas, R [Nanomaterials and Nanotechnology Research Center (CINN), Consejo Superior de Investigaciones CientIficas (CSIC), C/ Francisco Pintado Fe 26, 33011, Oviedo, Asturias (Spain); Gremillard, L [Universite de Lyon, INSA-Lyon, MATEIS, UMR CNRS 5510, 20 avenue Albert Einstein, Villeurbanne F-69621 (France)], E-mail: jsmoya@icmm.csic.es

    2008-05-28

    Isolated tungsten nanoparticles ({alpha}-W and {beta}-W phase) were synthesized and epitaxially grown on alumina and spinel particle surfaces with an average tungsten size of {<=}20 nm for a low tungsten content (of {<=}1.5 vol%). Using tungsten (VI) ethoxide alcoholic solutions, tungsten trioxide hydrated precursors were attached to a ceramic grains surface as a nanoparticle coating. High-resolution transmission electron microscopy (HRTEM) micrographs showed epitaxial interfaces between alumina, spinel and metallic tungsten. This epitaxial growth is assumed to be due to the effect of water vapour on the sublimation of ortho-tungstic acid during the reduction process in a hydrogen atmosphere. The planes involved in the epitaxy were found to be (22-bar 0){sub Al2O3} parallel (121){sub W} and (311){sub MgAl2O4} parallel (110){sub W}.

  14. Effect of alumina on silicon carbide bodies with clay bonding

    International Nuclear Information System (INIS)

    Components made of silicon carbide are very important ceramic products due to their good resistance against thermal shocks. Home made of such products having silicate bonding usually have various defects in their structures. In this research effects of alumina addition on the components made of silicon carbide with clay bonding have been investigated, in order to see its effects on mechanical and structural properties such as blistering. Addition of up to 15 weights %. Al2O3 improved thermal shock resistance and increased bending strength from 25 MPa to 32 MPa due to Al2O3 transformation to mullite. However, when the amounts of alumina exceed 15 weights % mechanical strength as well as resistance to thermal shock reduced due to reman ing of Al2O3 in the components after sintering

  15. Preparation of zirconia-alumina powder by co-precipitation

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A zirconia-alumina powder with a near spherical shape and an average size of 0.1 ~ 0.2μm was prepared byco-precipitation. XRD analysis shows that α-Al2O3 phase may be directly transformed from amorphous in calcining the hydroxide composite. The ZrO2-Al2O3 composite ceramics manufactured from this powder has the maximum fracture toughness of 9 M Pa·m- 1/2 at 15 % ZrO2 and 740 MPa fracture strength at 5 % ZrO2. Zirconia grains about 1 μm in diameter aredispersed uniformly in the alumina ceramic matrix

  16. Positron energy-loss measurements in thin alumina films

    International Nuclear Information System (INIS)

    Transmitted-positron energy loss measurements were performed on approximately 100A alumina films with incident positron energies ranging from 0.5 to 3.0 keV. The positrons were electrostatically focussed on the film and the transmitted positrons were energy analyzed using a four-grid retarding field analyzer coupled with a two-stage channel electron multiplier plate connected with a phosphor screen. A strong transmitted elastic peak as well as indications of discrete energy losses were detected in these measurements. The observed discrete loss effects occurred at an average energy of approx. 25 eV and possibly approx. 50 eV. These findings are consistent with reported electron loss peaks due to plasmon excitation in alumina films

  17. Melt processing of Bi--2212 superconductors using alumina

    Science.gov (United States)

    Holesinger, Terry G.

    1999-01-01

    Superconducting articles and a method of forming them, where the superconducting phase of an article is Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.y (Bi-2212). Alumina is combined with Bi-2212 powder or Bi-2212 precursor powder and, in order to form an intimate mixture, the mixture is melted and rapidly cooled to form a glassy solid. The glassy solid is comminuted and the resulting powder is combined with a carrier. An alternative to melting is to form the mixture of nanophase alumina and material having a particle size of less than about 10 microns. The powder, with the carrier, is melt processed to form a superconducting article.

  18. Process for High-Rate Fabrication of Alumina Nanotemplates

    Science.gov (United States)

    Myung, Nosang; Fleurial, Jean-Pierre; Yun, Minhee; West, William; Choi, Daniel

    2007-01-01

    An anodizing process, at an early stage of development at the time of reporting the information for this article, has shown promise as a means of fabricating alumina nanotemplates integrated with silicon wafers. Alumina nanotemplates are basically layers of alumina, typically several microns thick, in which are formed approximately regular hexagonal arrays of holes having typical diameters of the order of 10 to 100 nm. Interest in alumina nanotemplates has grown in recent years because they have been found to be useful as templates in the fabrication of nanoscale magnetic, electronic, optoelectronic, and other devices. The present anodizing process is attractive for the fabrication of alumina nanotemplates integrated with silicon wafers in two respects: (1) the process involves self-ordering of the holes; that is, the holes as formed by the process are spontaneously arranged in approximately regular hexagonal arrays; and (2) the rates of growth (that is, elongation) of the holes are high enough to make the process compatible with other processes used in the mass production of integrated circuits. In preparation for fabrication of alumina nanotemplates in this process, one first uses electron-beam evaporation to deposit thin films of titanium, followed by thin films of aluminum, on silicon wafers. Then the alumina nanotemplates are formed by anodizing the aluminum layers, as described below. In experiments in which the process was partially developed, the titanium films were 200 A thick and the aluminum films were 5 m thick. The aluminum films were oxidized to alumina, and the arrays of holes were formed by anodizing the aluminum in aqueous solutions of sulfuric and/or oxalic acid at room temperature (see figure). The diameters, spacings, and rates of growth of the holes were found to depend, variously, on the composition of the anodizing solution, the applied current, or the applied potential, as follows: In galvanostatically controlled anodizing, regardless of the

  19. Electrochemically grown metallic nanocomb structures on nanoporous alumina templates

    International Nuclear Information System (INIS)

    Electrochemical growth of metallic nanocomb structures on anodized alumina templates is described. Nanocombs originate from the orderly growth and merger of very thin (d=15±5 nm) metallic nanowires which do not completely fill much larger pores (d∼100 nm) in the alumina template (t≤3 μm). Instead, the nanowires prefer growing along the inner corners of the hexagonal pores, coalescing into a highly ordered structure as they emerge, resulting a metallic form reminiscent of the topology of the original template. We disclose here the typical processing conditions and the microstructure of this previously unknown material as observed with a scanning electron microscope (SEM) and energy dispersive x-ray (EDX) spectroscopy. It is shown that Au nanocombs have an anomalous EDX spectra and can emit electrons at a field of ∼1 kV/cm.

  20. Interfacial characterization of alumina-to-alumina joints fabricated using silver–copper–titanium interlayers

    International Nuclear Information System (INIS)

    Two Ag–Cu–Ti interlayers with different compositions (Ag–35.3Cu–1.75Ti and Ag–26.7Cu–4.5Ti) were used to join sintered polycrystalline Al2O3 having different amounts of porosity to investigate the effect of titanium and porosity contents on evolution of interfacial chemistry and microstructures. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS) were used to characterize the interfacial microstructure. Two reaction layers, Ti2O and Cu3Ti3O, were found at the interface of Ag–Cu–Ti interlayers and Al2O3 using a series of simulated and experimental selected area diffraction patterns (SADP) of TEM and EDS. The total thickness of Ti2O and Cu3Ti3O reaction layers at the interfaces increases with increasing amounts of Ti in the Ag–Cu–Ti interlayers but is independent of the porosity content in the Al2O3. Two possible formation mechanisms of Ti2O and Cu3Ti3O reaction layers at the interface of Ag–Cu–Ti interlayers and Al2O3 have been proposed based on the interfacial characterization performed in the present study. - Highlights: • Effect of alumina porosity and % Ti in interlayer on interface structure delineated • SEM, EDS, XRD, TEM with SADP used to delineate phases, compositions, crystallography • Ti2O and Cu3Ti3O reaction layers identified and their formation mechanisms proposed

  1. Proton adsorption onto alumina: extension of multisite complexation (MUSIC) theory

    Energy Technology Data Exchange (ETDEWEB)

    Nagashima, K.; Blum, F.D.

    1999-09-01

    The adsorption isotherm of protons onto a commercial {gamma}-alumina sample was determined in aqueous nitric acid with sodium nitrate as a background electrolyte. Three discrete regions could be discerned in the log-log plots of the proton isotherm determined at the solution pH 5 to 2. The multisite complexation (MUSIC) model was modified to analyze the simultaneous adsorption of protons onto various kinds of surface species.

  2. Impact loading of an aluminum/alumina composite

    OpenAIRE

    Johnson, J.; Hixson, R.; Gray, G

    1994-01-01

    The combined demands of increased strength and reduced weight in modern dynamic structural applications require improved understanding of composite materials subject to impact conditions. In order to isolate and identify individual contributions to composite material behavior under these conditions, an experimental and theoretical program was undertaken to examine dynamic behavior of an aluminum/alumina composite consisting of a 6061-T6 aluminum matrix containing elastic, spherical Al2O3 incl...

  3. INVESTIGATION OF THERMAL SHOCK BEHAVIOUR IN ALUMINA BASED REFRACTORY BRICKS

    OpenAIRE

    N. Sinan KÖKSAL; B. Sadık ÜNLÜ; Cevdet MERİÇ

    2003-01-01

    cUnderstanding of mechanical and thermal properties of refractory bricks used in industry is an important aspect to determine appropriate operating conditions. In this study, commercial refractory materials used in the sector of iron steel 45 % and 80 % alumina (Al2O3) of content refractory bricks were investigated. To determinate thermal shock behavior and mechanical properties of samples, thermal shock tests were applied by quenching in the water at the temperature differences of 500, 70...

  4. Results of recent KROTOS FCI tests. Alumina vs. corium melts

    Energy Technology Data Exchange (ETDEWEB)

    Huhtiniemi, I.; Magallon, D.; Hohmann, H. [Commission of the European Communities, Ispra (Italy). Joint Research Center

    1998-01-01

    Recent results from KROTOS fuel-coolant interaction experiments are discussed. Five tests with alumina were performed under highly subcooled conditions, all of these tests resulted in spontaneous steam explosions. Additionally, four tests were performed at low subcooling to confirm, on one hand, the suppression of spontaneous steam explosions under such conditions and, on the other hand, that such a system is still triggerable using an external initiator. The other test parameters in these alumina tests included the melt superheat and the initial pressure. All the tests in the investigated superheat range (150 K - 750 K) produced a steam explosion and no evidence of the explosion suppression by the elevated initial pressure (in the limited range of 0.1 - 0.375 MPa) was observed in the alumina tests. The corium test series include a test with 3 kg of melt under both subcooled and near saturated conditions at ambient pressure. Two additional tests were performed with subcooled water; one test was performed at an elevated pressure of 0.2 MPa with 2.4 kg of melt and another test with 5.1 kg of melt at ambient pressure. None of these tests with corium produced a propagating energetic steam explosion. However, propagating low energy (about twice the energy of the trigger pulse) events were observed. All corium tests produced significantly higher water level swells during the mixing phase than the corresponding alumina tests. Present experimental evidence suggests that the water depletion in the mixing zone suppresses energetic steam explosions with corium melts at ambient pressure and in the present pour geometry. Processes that could produce such a difference in void generation are discussed. (author)

  5. Deposition of Layered Double Hydroxides on Alumina Support

    Czech Academy of Sciences Publication Activity Database

    Kovanda, F.; Jirátová, Květa; Koloušek, D.

    Szeged : University of Szeged, 2010 - (Zaharia, L.), s. 748 ISSN 0324-6523. [Mid-European Clay Conference (MECC 2010) /5./. Budapest (HU), 25.08.2010-29.08.2010] R&D Projects: GA ČR GAP106/10/1762; GA ČR GA106/09/1664 Institutional research plan: CEZ:AV0Z40720504 Keywords : alumina support * hydroxydes * ldh Subject RIV: CI - Industrial Chemistry, Chemical Engineering

  6. Porous Alumina and Zirconia Ceramics With Tailored Thermal Conductivity

    Czech Academy of Sciences Publication Activity Database

    Gregorová, E.; Pabst, W.; Sofer, Z.; Jankovský, O.; Matějíček, Jiří

    2012-01-01

    Roč. 395, č. 1 (2012), 012022-012022. ISSN 1742-6588. [European Thermal Sciences Conference (Eurotherm)/6./. Poitiers, 04.09.2012-07.09.2012] Institutional support: RVO:61389021 Keywords : Ceramics * alumina * zirconia * porosity * thermal conductivity * pore-forming agent * oxide ceramics * starch * porosity Subject RIV: JK - Corrosion ; Surface Treatment of Materials http://iopscience.iop.org/1742-6596/395/1/012022/pdf/1742-6596_395_1_012022.pdf

  7. Ordered Nanomaterials Thin Films via Supported Anodized Alumina Templates

    OpenAIRE

    Mohammed eES-SOUNI; Salah ehabouti

    2014-01-01

    Supported anodized alumina template films with highly ordered porosity are best suited for fabricating large area ordered nanostructures with tunable dimensions and aspect ratios. In this paper we first discuss important issues for the generation of such templates, including required properties of the Al/Ti/Au/Ti thin film heterostructure on a substrate for high quality templates. We then show examples of anisotropic nanostructure films consisting of noble metals using these templates, discus...

  8. Ordered Nanomaterial Thin Films via Supported Anodized Alumina Templates

    OpenAIRE

    Es-Souni, Mohammed; Habouti, Salah

    2014-01-01

    Supported anodized alumina template films with highly ordered porosity are best suited for fabricating large-area ordered nanostructures with tunable dimensions and aspect ratios. In this paper, we first discuss important issues for the generation of such templates, including required properties of the Al/Ti/Au/Ti thin-film heterostructure on a substrate for high-quality templates. We then show examples of anisotropic nanostructure films consisting of noble metals using these templates, discu...

  9. Fischer-Tropsch synthesis on alumina supported cobalt catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Bechara, R.; Balloy, D.; Vanhove, D.

    1997-11-01

    Physico-chemical properties of Co/Al{sub 2}O{sub 3}-gamma were investigated by XRD, XPS, thermogravimetry and catalytic measurements. Interactions between the metal and its support were found for catalysts prepared from alumina with the greater specific area. For the Fischer-Tropsch synthesis, the products distribution appeared not to be sensitive to the cobalt particle size, but seems to depend on the degree of cobalt reduction.

  10. Directional solidification of the alumina-zirconia ceramic eutectic system

    International Nuclear Information System (INIS)

    It is possible to produce alumina-zirconia ceramic samples through existing solidification techniques. The resulting microstructures typically consist of rods of zirconia in an alumina matrix, although a lamellar structure has been noted in some cases. In nearly all cases, colony growth was present which may possibly result from grain size, repeated nucleation events, and lamellar oscillations. In the same vein, it appears that the amount of impurities within the system might be the underlying cause for the colony growth. Colony growth was diminished through impurity control as the higher purity samples exhibited colony free behavior. In addition to colony formations, faceted alumina dendrites or nonfaceted zirconia dendrites may result in the ceramic if the sample is solidified out of the coupled zone. In all cases, for larger-sized Bridgman samples, a lower limit in the eutectic spacing was noted. The solidification model which includes the kinetic effect has been developed, although the effect appears to be negligible under present experimental conditions. A spacing limit might also occur due to the result of heat flow problems. Heat flow out of the ceramic is difficult to control, often causing radial and not axial growth. This behavior is exaggerated in the presence of impurities. Thus, higher purity powders should always be used. Higher purity samples, in addition to yielding a more microstructurally uniform ceramic, also showed increased directionality. In the future, the kinetic model needs to be examined in more detail, and further research needs to be accomplished in the area of molten ceramics. Once better system constants are in place, the kinetic model will give a better indication of the behavior in the alumina-zirconia system

  11. Moisture-Induced Alumina Scale Spallation: The Hydrogen Factor

    Science.gov (United States)

    Smialek, James L.

    2010-01-01

    For some time the oxidation community has been concerned with interfacial spallation of protective alumina scales, not just upon immediate cool down, but as a time-delayed phenomenon. Moisture-induced delayed spallation (MIDS) and desktop spallation (DTS) of thermal barrier coatings (TBCs) refer to this process. It is most apparent for relatively adherent alumina scales that have survived initial cool down in a dry environment, have built up considerable thickness and strain energy, and have been somewhat damaged, such as by cyclic oxidation cracking. Indeed, a "sensitive zone" can be described that maximizes the observed effect as a function of all the relevant factors. Moisture has been postulated to serve as a source of interfacial hydrogen embrittlement. Hydrogen is derived from reaction with aluminum in the alloy at an exposed interface. The purpose of this monograph is to trace the close analogy of this phenomenon to other hydrogen-induced effects, such as embrittlement of aluminides and blistering of alloys and anodic alumina films. A formalized, top-down, logic-tree structure is presented as a guide to this discussion. A theoretical basis for interfacial weakening by hydrogen is first cited, as are demonstrations of hydrogen detection as a reaction product or interfacial species. Further support is provided by critical experiments that recreate the moisture effect, but by isolating hydrogen from other potential causative factors. These experiments include tests in H 2-containing atmospheres or cathodic hydrogen charging. Accordingly, they strongly indicate that interfacial hydrogen, derived from moisture, is the key chemical species accounting for delayed alumina scale spallation.

  12. Electroless Fabrication of Cobalt Alloys Nanowires within Alumina Template

    OpenAIRE

    Nazila Dadvand; Kipouros, Georges J.

    2007-01-01

    A new method of nanowire fabrication based on electroless deposition process is described. The method is novel compared to the current electroless procedure used in making nanowires as it involves growing nanowires from the bottom up. The length of the nanowires was controlled at will simply by adjusting the deposition time. The nanowires were fabricated within the nanopores of an alumina template. It was accomplished by coating one side of the template by a thin layer of palladium in order t...

  13. Dependence of the Stabilization of -Alumina on the Spray Process

    Czech Academy of Sciences Publication Activity Database

    Stahr, C.Ch.; Saaro, S.; Berger, L.-M.; Herrmann, M.; Dubský, Jiří; Neufuss, Karel

    2007-01-01

    Roč. 16, 5-6 (2007), s. 822-830. ISSN 1059-9630 R&D Projects: GA ČR(CZ) GA106/05/0483 Institutional research plan: CEZ:AV0Z20430508 Keywords : -Al2O3 stabilization * alumina * chromia * solid solution * X-ray diffraction Subject RIV: JK - Corrosion ; Surface Treatment of Materials Impact factor: 1.204, year: 2007

  14. Ion irradiation effect of alumina and its luminescence

    Energy Technology Data Exchange (ETDEWEB)

    Aoki, Yasushi; Yamamoto, Shunya; Naramoto, Hiroshi [Japan Atomic Energy Research Inst., Takasaki, Gunma (Japan). Takasaki Radiation Chemistry Research Establishment; My, N.T.

    1997-03-01

    The luminescence spectra of single crystalline alpha-alumina and ruby which has 0.02% of Cr{sub 2}O{sub 3} as a impurity, induced by 200 keV He{sup +} and Ar{sup +} irradiation were measured at room temperature as a function of irradiation dose. The analysis of the measured spectra showed the existence of three main luminescence features in the wavelength region of 250 to 350 nm, namely anionic color centers, F-center at 411 nm and F{sup +}-center at 330 nm and a band observed around 315 nm. As alpha-alumina was irradiated with He{sup +}, F-center and F{sup +}-center luminescence grew and decayed, but the behaviors of those were different from each other. It seems that a concentration quenching occurred on the F-center luminescence in the dose range above 1x10{sup 14} He/cm{sup 2}. Furthermore, F-center luminescence was strongly suppressed in ruby, compared with that in alumina. On the other hand, the luminescence band around 315 nm appeared only in the early stage of irradiation and did not show its growth part. The dose dependent behavior was similar to that of Cr{sup 3+} emission at 695 nm (R-line) in ruby in both cases of He{sup +} and Ar{sup +} irradiation. Based on the experimental results mentioned above, the processes of defect formation and excitation in alumina in the early stage of ion irradiation will be discussed. (author)

  15. Surface tension of liquid alumina from contactless techniques

    International Nuclear Information System (INIS)

    Full Text: We report new data on surface tension of liquid alumina from 2300 to 3200 K. Aerodynamic levitation of CO2 laser heated liquid drops allowed contactless measurement of vibration frequencies directly related to surface tension. Consistent data were obtained on drops of various weights ranging from 20 to 160 mg. It was also shown that oxydo-reducing character of the atmosphere does not modify sensible the results. (author)

  16. Nanocarbon-Coated Porous Anodic Alumina for Bionic Devices

    OpenAIRE

    Morteza Aramesh; Wei Tong; Kate Fox; Ann Turnley; Dong Han Seo; Steven Prawer; Kostya (Ken) Ostrikov

    2015-01-01

    A highly-stable and biocompatible nanoporous electrode is demonstrated herein. The electrode is based on a porous anodic alumina which is conformally coated with an ultra-thin layer of diamond-like carbon. The nanocarbon coating plays an essential role for the chemical stability and biocompatibility of the electrodes; thus, the coated electrodes are ideally suited for biomedical applications. The corrosion resistance of the proposed electrodes was tested under extreme chemical conditions, su...

  17. Short cycle brazing of an alumina dispersion strengthened copper alloy

    International Nuclear Information System (INIS)

    An alumina dispersion strengthened copper alloy (with 0.07 wt, % alumina) has been proposed for several specialized applications in fusion reactors, such as the stabilizer in superconducting magnets and the structural material for divertors and limiters. In this research, brazed joints of the alumina dispersion strengthened copper alloy were developed using resistance heating brazing. The BCuP-3 brazing alloy was chosen based upon its low activation characteristics. Brazing was conducted using a GLEEBLE 1500 system with which time, temperature, and stress were precisely controlled. Butt-brazed joints with different brazing times were evaluated based on tensile and bending fatigue properties. Results from these tests reveal that the optimum braze time is approximately 1 minute at 8000C with a holding stress of 0.5 MPa. Metallography examinations were conducted on both the as brazed structure and the fracture surfaces. In the former, a transition layer (about 10 μm tick) was formed between the braze metal and the base alloy. Microhardness measurements across the braze did not show any hardening or softening effect due to the brazing process. Metallography of the fractured tensile and fatigue samples showed that cracks always penetrated through the interface between the transition layer and the braze metal. Semiquantitative energy dispersive x-ray spectroscopy (EDS) analysis was also performed across the joint. Profiles of P and Ag showed that P diffused very quickly into base metal along grain boundaries. A strong Al peak (associated with the detection of Al2O3) was found that corresponded with the transition layer. The presence of the alumina particles in the transition zone restricts the grain growth process in this region, resulting in relatively fine grain size

  18. Formation of Corundum Phase in Plasma Sprayed Alumina Coatings

    Czech Academy of Sciences Publication Activity Database

    Dubský, Jiří; Chráska, Pavel; Kolman, Blahoslav Jan; Stahr, C.Ch.; Berger, L.-M.

    Brisbane: Materials Australia, 2007, s. 62-62. [The 16th International Federation for Heat Treatment and Surface Engineering (IFHTSE) Congress/16th./. Brisbane (AU), 30.10.2007-1.11.2007] R&D Projects: GA ČR(CZ) GA106/05/0483 Institutional research plan: CEZ:AV0Z20430508 Keywords : Phase transformatin * Plasma spraying * Alumina * Chromia Subject RIV: JK - Corrosion ; Surface Treatment of Materials

  19. Directional solidification of the alumina-zirconia ceramic eutectic system

    Energy Technology Data Exchange (ETDEWEB)

    Boldt, C.

    1994-07-27

    It is possible to produce alumina-zirconia ceramic samples through existing solidification techniques. The resulting microstructures typically consist of rods of zirconia in an alumina matrix, although a lamellar structure has been noted in some cases. In nearly all cases, colony growth was present which may possibly result from grain size, repeated nucleation events, and lamellar oscillations. In the same vein, it appears that the amount of impurities within the system might be the underlying cause for the colony growth. Colony growth was diminished through impurity control as the higher purity samples exhibited colony free behavior. In addition to colony formations, faceted alumina dendrites or nonfaceted zirconia dendrites may result in the ceramic if the sample is solidified out of the coupled zone. In all cases, for larger-sized Bridgman samples, a lower limit in the eutectic spacing was noted. The solidification model which includes the kinetic effect has been developed, although the effect appears to be negligible under present experimental conditions. A spacing limit might also occur due to the result of heat flow problems. Heat flow out of the ceramic is difficult to control, often causing radial and not axial growth. This behavior is exaggerated in the presence of impurities. Thus, higher purity powders should always be used. Higher purity samples, in addition to yielding a more microstructurally uniform ceramic, also showed increased directionality. In the future, the kinetic model needs to be examined in more detail, and further research needs to be accomplished in the area of molten ceramics. Once better system constants are in place, the kinetic model will give a better indication of the behavior in the alumina-zirconia system.

  20. Controlled fabrication of patterned lateral porous alumina membranes

    International Nuclear Information System (INIS)

    Confined lateral alumina templates are fabricated with different pore sizes by changing the acid electrolyte and the anodization voltage. The control of the number of pore rows down to one dimension is also achieved, by controlling the thickness of the starting aluminum film as well as the anodization voltage. We observe that the mechanism of pore formation in the lateral regime is very similar to that in the classical vertical situation

  1. Controlled growth of single nanowires within a supported alumina template

    DEFF Research Database (Denmark)

    Vlad, A.; Mátéfi-Tempfli, M.; Faniel, S.;

    2006-01-01

    A simple technique for fabricating single nanowires with well-defined position is presented. The process implies the use of a silicon nitride mask for selective electrochemical growth of the nanowires in a porous alumina template. We show that this method allows the realization of complex nanowire...... patterns as well as arrays of single nanowires with a precise position and spacing. © IOP Publishing Ltd....

  2. Proton Adsorption onto Alumina: Extension of Multisite Complexation (MUSIC) Theory.

    Science.gov (United States)

    Nagashima; Blum

    1999-09-01

    The adsorption isotherm of protons onto a commercial gamma-alumina sample was determined in aqueous nitric acid with sodium nitrate as a background electrolyte. Three discrete regions could be discerned in the log-log plots of the proton isotherm determined at the solution pH 5 to 2. The multisite complexation (MUSIC) model was modified to analyze the simultaneous adsorption of protons onto various kinds of surface species. Copyright 1999 Academic Press. PMID:10441408

  3. Intensifying digestion of diaspore and separation of alumina and silica

    Institute of Scientific and Technical Information of China (English)

    李小斌; 彭志宏; 刘桂华; 周秋生

    2003-01-01

    It was found that there lies a linear relationship among the thermodynamic data of complicate inorganic compounds with similar components. A method for estimating the thermodynamic data of complicate compound and a thermodynamic database involving alumina production were developed. It was found that the alumina digestion rate of activated diasporic bauxite by means of heat field increased much due to the structure aberration, i.e, from perfect structure to unstable corundum. The results from thermodynamic calculation and experiments showed that it was feasible for desilication at atmospheric pressure, and the effects on equilibrium concentration of SiO2 included temperature, mole ratio of Na2O/Al2O3 (αk), caustic and Na+ concentration. The technology of desilication of green liquor at atmosphere and separation of alumina and silica in aluminate solution with high concentration were established. The reaction activity of compounds containing silica and the converting law among compounds were studied, and the prototype technology of desilication products by hydrotreatment was also developed.

  4. Dielectric properties of alumina/zirconia composites at millimeter wavelengths

    International Nuclear Information System (INIS)

    Alumina-zirconia composites with ZrO2 contents up to 20% and negligible porosity were investigated at millimeter (mm) wavelengths to determine the changes appearing in the dielectric properties of pure alumina ceramics when unstabilized or partially stabilized ZrO2 is added to improve the mechanical strength. It is demonstrated that it essential to distinguish between the contributions of the monoclinic and the tetragonal phase of zirconia (m-ZrO2, t-ZrO2). Permittivity is raised with increasing content of either phases; the effective permittivity can be assessed by the rule of mixtures (Maxwell-Garnett formulation of the generalized Clasussius-Mossotti relation) using permittivity values of 10 for Al2O3, 14-21 for m-ZrO2 and 40-45 for t-ZrO2. The permittivity data show only a small variation in the investigated range of 9-145 GHz. For the dielectric loss, there is evidence of a predominant contribution of m-ZrO2; in addition, the marked increase in loss with frequency becomes sharper. The t-ZrO2, which is responsible for strengthening, does not show any significant influence on losses. It is therefore concluded, that ZrO2 strengthening of alumina is feasible without affecting mm-wave losses at room temperature as long as the presence of m-ZrO2 is avoided

  5. Nanostructural Engineering of Nanoporous Anodic Alumina for Biosensing Applications

    Directory of Open Access Journals (Sweden)

    Josep Ferré-Borrull

    2014-07-01

    Full Text Available Modifying the diameter of the pores in nanoporous anodic alumina opens new possibilities in the application of this material. In this work, we review the different nanoengineering methods by classifying them into two kinds: in situ and ex situ. Ex situ methods imply the interruption of the anodization process and the addition of intermediate steps, while in situ methods aim at realizing the in-depth pore modulation by continuous changes in the anodization conditions. Ex situ methods permit a greater versatility in the pore geometry, while in situ methods are simpler and adequate for repeated cycles. As an example of ex situ methods, we analyze the effect of changing drastically one of the anodization parameters (anodization voltage, electrolyte composition or concentration. We also introduce in situ methods to obtain distributed Bragg reflectors or rugate filters in nanoporous anodic alumina with cyclic anodization voltage or current. This nanopore engineering permits us to propose new applications in the field of biosensing: using the unique reflectance or photoluminescence properties of the material to obtain photonic barcodes, applying a gold-coated double-layer nanoporous alumina to design a self-referencing protein sensor or giving a proof-of-concept of the refractive index sensing capabilities of nanoporous rugate filters.

  6. Environmental Sustainability of the Alumina Industry in Western Europe

    Directory of Open Access Journals (Sweden)

    Valentina Dentoni

    2014-12-01

    Full Text Available The implementation of European policies on environmental protection is enforcing some substantial modifications in the processing methods and technologies traditionally adopted in the alumina industry and, in particular, in the management of the alumina residue produced. The article analyses the evolution of the alumina production and the residue disposal practices in Western Europe. Some critical aspects regarding the legal implementation of the EU Directive on the landfill of waste are highlighted and discussed. With reference to the requirements established for the landfill of non-hazardous waste, a key point is represented by the possibility of reducing the deposit protection measures if the collection and treatment of leachate is not necessary. The flexibility introduced by the Directive is not incorporated into the Italian law; this fact may represent a major issue in the prospect of disposal conversion from wet to dry methods for companies operating in Italy, as it may endanger the economic sustainability of the plants’ upgrade, as well as the opportunity to attract outside investments.

  7. Investigations of vapour explosions with alumina-droplets in sodium

    International Nuclear Information System (INIS)

    Within the analysis of severe hypothetical fast breeder accidents the consequence of a fuel-coolant interaction has to be considered, i.e. the thermal interaction between hot molten fuel and sodium. Experiments have been performed to study the thermal fragmentation of a molten alumina droplet in sodium. Alumina temperatures up to 3100 K and sodium temperatures up to 1143 K were used. For the first time film boiling of alumina drops in sodium was achieved. With some droplets undergoing film boiling, the fragmentation was triggered by an externally applied pressure wave. In these experiments, the trigger was followed promptly by a strong reaction pressure wave if and only if a contact temperature threshold of TI=2060 K±160 K was exceeded. In agreement with similar experiments in which other materials were studied, this threshold corresponds to an interfacial temperature close to the homogeneous nucleation temperature of the vapourising liquid. Based on the present and previous experimental results a model concept of thermal fragmentation is developed. (orig./HP)

  8. Investigation of vapor explosions with alumina droplets in sodium

    International Nuclear Information System (INIS)

    Within the analysis of severe hypothetical fast breeder accidents the consequence of a fuel-coolant interaction has to be considered i.e. the thermal interaction between hot molten fuel and sodium. Experiments have been performed to study the thermal fragmentation of a molten alumina droplet in sodium. Alumina temperatures up to 3100 K and sodium temperatures up to 1143 K were used. For the first time film boiling of alumina drops in sodium was achieved. With some droplets undergoing film boiling, the fragmentation was triggered by an externally applied pressure wave. The trigger was followed promptly by a strong reaction pressure wave if and only if a contact temperature threshold of TI=2060±160 K was exceeded. In agreement with similar experiments in which other materials were studied this threshold corresponds to an interfacial temperature close to the homogeneous nucleation temperature of the vaporising liquid. Based on the present and previous experimental results a model concept of thermal fragmentation is developed. (orig.)

  9. Thermodynamics of selenium sorption on alumina and montmorillonite

    Directory of Open Access Journals (Sweden)

    Jean-Pierre Morel

    2015-12-01

    Full Text Available The effect of pH and temperature on the thermodynamics of selenium sorption on alumina and montmorillonite was investigated. The equilibrium constants were obtained from batch experiments carried out at 25 and 40°C, under acidic and near to neutral conditions. Microcalorimetry was used to measure directly the enthalpy change upon sorption. These data were analysed by taking into account the different reactions that occur during the sorption process (the acid–base equilibria in the bulk solution on the one hand and the complexation equilibria between surface sites of the solid and solution species on the other hand. This was done using a simple surface model which assumes that the thermodynamic properties of the aluminol surface sites of both alumina and montmorillonite are identical. Two of the considered reactions were found to predominate, one under acidic conditions and one at near neutral pH. The microcalorimetric data allowed to check that the temperature effect on selenium sorption on alumina and montmorillonite can be correctly predicted simply using the above assumption concerning the sorption sites and by applying van’t Hoff relation both to the homogeneous and heterogeneous reactions.

  10. Nanocarbon-Coated Porous Anodic Alumina for Bionic Devices

    Directory of Open Access Journals (Sweden)

    Morteza Aramesh

    2015-08-01

    Full Text Available A highly-stable and biocompatible nanoporous electrode is demonstrated herein. The electrode is based on a porous anodic alumina which is conformally coated with an ultra-thin layer of diamond-like carbon. The nanocarbon coating plays an essential role for the chemical stability and biocompatibility of the electrodes; thus, the coated electrodes are ideally suited for biomedical applications. The corrosion resistance of the proposed electrodes was tested under extreme chemical conditions, such as in boiling acidic/alkali environments. The nanostructured morphology and the surface chemistry of the electrodes were maintained after wet/dry chemical corrosion tests. The non-cytotoxicity of the electrodes was tested by standard toxicity tests using mouse fibroblasts and cortical neurons. Furthermore, the cell–electrode interaction of cortical neurons with nanocarbon coated nanoporous anodic alumina was studied in vitro. Cortical neurons were found to attach and spread to the nanocarbon coated electrodes without using additional biomolecules, whilst no cell attachment was observed on the surface of the bare anodic alumina. Neurite growth appeared to be sensitive to nanotopographical features of the electrodes. The proposed electrodes show a great promise for practical applications such as retinal prostheses and bionic implants in general.

  11. Dispersions of pyrogenic alumina in pentylcyanobiphenyl studied by deuteron NMR

    Science.gov (United States)

    Yim, C. T.

    2009-09-01

    Dispersions of hydrophilic (Aeroxide Alu C) and hydrophobic (Aeroxide Alu C 805) pyrogenic alumina (Al2O3) in liquid crystal 4' -n-pentyl-4-cyanobiphenyl (5CB) were investigated with deuteron nuclear magnetic resonance. The disorder effects of Al2O3 particles on the orientational order of liquid-crystal media and on the field-induced director configuration were studied as a function of alumina density in samples prepared by zero-field cooling and in-field cooling procedures. The order parameters and their variation with alumina density suggest a stronger disordering effect from the nonpolar surface of Alu C 805 particles. For dispersions of hydrophobic Alu C 805 experiments involving in-field cooling from the isotropic phase indicate that the director of “disordered” domains can be aligned, though not perfectly, by the field-aided annealing process. But the same in-field cooling procedure has shown rather limited alignment effects for hydrophilic Alu C/5CB samples. The more robust network of hydrophilic gel possibly coupled with weak liquid-crystal-network interactions could be responsible for the observed behavior. Spectra recorded during in-field cooling and within the isotropic-nematic coexistence region reveal the augmentation of the disorder strength during the transition and illustrate the effect of field-aided annealing. The stability of the aligned states as revealed by deuteron NMR is described. The results are discussed in comparison with previous studies of aerosil dispersions in alkylcyanobiphenyl.

  12. Near-field radiative heat transfer in mesoporous alumina

    International Nuclear Information System (INIS)

    The thermal conductivity of mesoporous material has aroused the great interest of scholars due to its wide applications such as insulation, catalyst, etc. Mesoporous alumina substrate consists of uniformly distributed, unconnected cylindrical pores. Near-field radiative heat transfer cannot be ignored, when the diameters of the pores are less than the characteristic wavelength of thermal radiation. In this paper, near-field radiation across a cylindrical pore is simulated by employing the fluctuation dissipation theorem and Green function. Such factors as the diameter of the pore, and the temperature of the material are further analyzed. The research results show that the radiative heat transfer on a mesoscale is 2∼4 orders higher than on a macroscale. The heat flux and equivalent thermal conductivity of radiation across a cylindrical pore decrease exponentially with pore diameter increasing, while increase with temperature increasing. The calculated equivalent thermal conductivity of radiation is further developed to modify the thermal conductivity of the mesoporous alumina. The combined thermal conductivity of the mesoporous alumina is obtained by using porosity weighted dilute medium and compared with the measurement. The combined thermal conductivity of mesoporous silica decreases gradually with pore diameter increasing, while increases smoothly with temperature increasing, which is in good agreement with the experimental data. The larger the porosity, the more significant the near-field effect is, which cannot be ignored. (paper)

  13. Alumina Based 500 C Electronic Packaging Systems and Future Development

    Science.gov (United States)

    Chen, Liang-Yu

    2012-01-01

    NASA space and aeronautical missions for probing the inner solar planets as well as for in situ monitoring and control of next-generation aeronautical engines require high-temperature environment operable sensors and electronics. A 96% aluminum oxide and Au thick-film metallization based packaging system including chip-level packages, printed circuit board, and edge-connector is in development for high temperature SiC electronics. An electronic packaging system based on this material system was successfully tested and demonstrated with SiC electronics at 500 C for over 10,000 hours in laboratory conditions previously. In addition to the tests in laboratory environments, this packaging system has more recently been tested with a SiC junction field effect transistor (JFET) on low earth orbit through the NASA Materials on the International Space Station Experiment 7 (MISSE7). A SiC JFET with a packaging system composed of a 96% alumina chip-level package and an alumina printed circuit board mounted on a data acquisition circuit board was launched as a part of the MISSE7 suite to International Space Station via a Shuttle mission and tested on the orbit for eighteen months. A summary of results of tests in both laboratory and space environments will be presented. The future development of alumina based high temperature packaging using co-fired material systems for improved performance at high temperature and more feasible mass production will also be discussed.

  14. Superhydrophobicity of Bionic Alumina Surfaces Fabricated by Hard Anodizing

    Institute of Scientific and Technical Information of China (English)

    Jing Li; Feng Du; Xianli Liu; Zhonghao Jiang; Luquan Ren

    2011-01-01

    Bionic alumina samples were fabricated on convex dome type aluminum alloy substrate using hard anodizing technique.The convex domes on the bionic sample were fabricated by compression molding under a compressive stress of 92.5 MPa.The water contact angles of the as-anodized bionic samples were measured using a contact angle meter (JC2000A) with the 3 μL water drop at room temperature.The measurement of the wetting property showed that the water contact angle of the unmodified as-anodized bionic alumina samples increases from 90° to 137° with the anodizing time.The increase in water contract angle with anodizing time arises from the gradual formation of hierarchical structure or composite structure.The structure is composed of the micro-scaled alumina columns and pores.The height of columns and the depth of pores depend on the anodizing time.The water contact angle increases significantly from 96° to 152° when the samples were modified with self-assembled monolayer of octadecanethiol (ODT),showing a change in the wettability from hydrophobicity to super-hydrophobicity.This improvement in the wetting property is attributed to the decrease in the surface energy caused by the chemical modification.

  15. Formation process of a strong water-repellent alumina surface by the sol-gel method

    International Nuclear Information System (INIS)

    A novel strong water-repellent alumina thin film is fabricated by chemically adsorbing stearic acid (STA) layer onto the porous and roughened aluminum film coated with polyethyleneimine (PEI). The formation process and the structure of the strong water-repellent alumina film are investigated by means of contact angle measurement and atomic force microscope (AFM). Results show that the water contact angles for the alumina films increase with the increase of the immersion time in the boiling water, and meanwhile, the roughness of the alumina films increases with the dissolution of the boehmite in the boiling water. Finally, the strong water-repellent film with a high water contact angle of 139.1 deg. is obtained when the alumina films have distinct roughened morphology with some papillary peaks and porous structure. Moreover, both the roughened structure and the hydrophobic materials of the STA endow the alumina films with the strong water-repellence.

  16. Comparative study on sintered alumina for ballistic shielding application; Estudo comparativo entre aluminas sinterizadas visando aplicacao em blindagem balistica

    Energy Technology Data Exchange (ETDEWEB)

    Melo, Francisco Cristovao Lourenco de; Goncalves, Diniz Pereira [Centro Tecnico Aeroespacial (CTA), Sao Jose dos Campos, SP (Brazil). Inst. de Aeronautica e Espaco

    1997-12-31

    This work presents a development of the armor made from special ceramic materials and kevlar. An experimental investigation was conducted to study the ballistic penetration resistance on three samples taken from sintered alumina: a commercial one and two formulations A and B made in IAE/CTA. The main differences between the two formulations was the grain size and bend resistance. The knowledge of the mechanisms during the penetration and perforation process allowed to apply a ductile composite laminate made form kevlar under the alumina to delay its rupture. The last ballistic test showed how a Weibull`s modulii and other mechanical properties are able to improve ballistic penetration resistance. (author) 3 refs.

  17. Analysis of bridging stress effect of polycrystalline aluminas using double cantilever beam method III. Bridging stress distribution of polycrystalline aluminas

    Energy Technology Data Exchange (ETDEWEB)

    Sohn, K.S.; Lee, S.H.; Baik, S.G. [Pohang University of Science and Technology, Pohang (Korea, Republic of)

    1996-04-01

    The purpose of the present study is to investigate the microstructural effect on the R-curve behavior in three aluminas with different grain size distributions by analyzing the bridging stress distribution. The crack opening displacement (COD) according to the distance behind the stationary crack tip was measured using an in situ SEM fracture method. the measured COD values in the fine-grained alumina agreed well with Wiederhorn`s solution, while they deviated from Wiederhorn`s solution in the two coarse-grained aluminas because of the increase of the crack closure due to the grain interface bridging in the crack wake. A numerical fitting procedure was conducted by the introduction of the power-law relation and the current theoretical model, together with the measured COD`s, in order to obtain the bridging stress distribution. The results indicated that the bridging stress function and the R-curve computed by the current model were consistent with those computed by the power-law relation, providing a reliable evidence for the bridging stress analysis of the current model. the strain-softening exponent in the power-law relation, n, was calculated to be the range from 2 to 3, and was closely related to the grain size distribution. Thus, it was concluded from the current theoretical model that the grain size distribution affected greatly the bridging stress distribution, thereby resulting in the quantitative analysis of microfracture of polycrystalline aluminas through correlating the local-fracture-controlling microstructure. (author) 25 refs., 14 figs.

  18. Chemical Modification of Porous Alumina for Nanowire Templating and NEXAFS Spectroscopy of Aqueous ATP

    OpenAIRE

    Kelly, Daniel Nicholas

    2010-01-01

    Part One: Chemical Modification of Porous Alumina for Nanowire Templating: A modified sol-gel technique and subsequent polymer coating technique was used to modify the size of nanowires grown via electrodeposition in porous alumina templates. The porous alumina film is initially soaked in a water-containing solution prior to exposure to a different solution of 3-aminopropyltriethoxysilane in toluene. The amount of water in the aqueous solution correlates with the thickness of silane coating ...

  19. The effect of alumina nanofillers size and shape on mechanical behavior of PMMA matrix composite

    OpenAIRE

    Ben Hasan Somaya Ahmed; Dimitrijević Marija M.; Kojović Aleksandar; Stojanović Dušica B.; Obradović-Đuričić Kosovka; Jančić-Heinemann Radmila M.; Aleksić Radoslav

    2014-01-01

    Composites with the addition of alumina nanofillers show improvement in mechanical properties. The PMMA polymer was used as a matrix and two different types of nanofillers, having extremely different shapes were added in the matrix to form the composite. Reinforcements were based on alumina nanoparticles having either spherical shape or whiskers having the length to diameter ratio of 100. The influence of alumina fillers size, shape and fillers loading on m...

  20. Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions

    OpenAIRE

    Schebaum, Oliver; Drewello, Volker; Auge, Alexander; Reiss, Günter; Münzenberg, Markus; Schuhmann, Henning; Seibt, Michael; Thomas, Andy

    2010-01-01

    Using magnetron sputtering, we have prepared Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions with tunnel barriers consisting of alumina, magnesia, and magnesia-alumina bilayer systems. The highest tunnel magnetoresistance ratios we found were 73% for alumina and 323% for magnesia-based tunnel junctions. Additionally, tunnel junctions with a unified layer stack were prepared for the three different barriers. In these systems, the tunnel magnetoresistance ratios at optimum annealing te...

  1. Effect of Calcination on the Sintering of Gel-Derived, Zirconia-Toughened Alumina

    OpenAIRE

    Exter, den, P.; Winnubst, Louis; Leuwerink, Theo H.P.; Burggraaf, Anthonie J.

    1994-01-01

    The densification behavior of ZrO2 (+ 3 mol% Y2O3)/85 wt% Al2O3 powder compacts, prepared by the hydrolysis of metal chlorides, can be characterized by a transition- and an α-alumina densification stage. The sintering behavior is strongly determined by the densification of the transition alumina aggregates. Intra-aggregate porosity, resulting from calcination at 800°C, partly persists during sintering and alumina phase transformation and negatively influences further macroscopic densification...

  2. A Study on the Effect of Nano Alumina Particles on Fracture Behavior of PMMA

    OpenAIRE

    Arezou Sezavar; Seyed Mojtaba Zebarjad; Seyed Abdolkarim Sajjadi

    2015-01-01

    In the current research, the role of nano-sized alumina on deformation and fracture mechanism of Poly Methyl Methacrylate (PMMA) was investigated. For this purpose, PMMA matrix nanocomposite reinforced with different wt% of alumina (i.e., 5, 10 and 15) were fabricated using the compression molding technique. Tensile properties of produced nanocomposites were studied using Zwick Z250 apparatus at cross head speed of about 5 mm/min. In order to specify the role of alumina nanoparticles on defor...

  3. Effect of Heat Treatment of the Alumina Powder on the Microstructure and Properties of Coatings

    OpenAIRE

    Prozorova Mayya; Kovaleva Marina; Arseenko Marii; Yapryntsev Maxim; Novikov Vseslav; Sirota Vyacheslav; Tyurin Yurii; Kolisnichenko Oleg; Vasilik Nikolay

    2015-01-01

    The alumina powder was treated at a high temperature (1000°C). Dense (porosity of less than 2%), solid (1280 ± 30 HV0.3) and wear-resistant coatings based on heat-treated alumina powder were obtained by a multi-chamber detonation sprayer on the steel substrate. The microstructure, microhardness and the wear resistance of the alumina coatings were investigated.

  4. Effects of particle size and coating on decomposition of alumina-extracted residue from high-alumina fly ash.

    Science.gov (United States)

    Wang, Zehua; Ma, Shuhua; Tang, Zhenhua; Wang, Xiaohui; Zheng, Shili

    2016-05-01

    The effective removal of alkali in the alumina-extracted reside (AER) obtained by extracting alumina from high-alumina fly ash is the premise for realizing the utilization of the silicon component in the fly ash. Sodium was removed from the AER by a decomposition reaction. The effects of the particle size and reactant coating on the decomposition reaction of AER were studied, and the results showed that by decreasing the particle size, the decomposition reaction rate of AER could be enhanced obviously and the Na2O content of the products could be decreased effectively. In addition, the process and mechanism of the decomposition reaction of AER and the reaction kinetics were investigated. The results revealed that the decomposition reaction of AER started from the outer surface of the AER particles. The reaction kinetics corresponded with shrinking unreacted core models. Furthermore, the decomposition reaction rate of AER could be enhanced obviously by decreasing the particle size because the effect of product layer diffusion was weakened when the particle size of AER was decreased. PMID:26844406

  5. Fracture behavior of monazite-coated alumina fiber-reinforced alumina-matrix composites at elevated temperature

    International Nuclear Information System (INIS)

    High-temperature strength, fracture behavior and microstructure were observed for monazite-coated alumina fiber-reinforced alumina matrix composites hot-pressed at 1200-1300degC. The composites with 27-41 vol% alumina fiber showed no significant change in strength at 25-1100degC. However, the strength of the composites decreased markedly at a test temperature higher than 1100degC. The composites hot-pressed at a temperature lower than 1250degC fractured in a pseudoductile manner in the test temperature range from 25degC to 1100degC. Young's modulus of the elastic region decreased with increasing test temperature. These composites showed larger deformation at a test temperature above 1100degC. On the other hand, the composites hot-pressed at more than 1250degC fractured in a brittle manner at 25degC-1200degC of test temperature. The fracture energy of the composite increased with increasing test temperature and decreased with sintering temperature. (author)

  6. Viscosity of aqueous and cyanate ester suspensions containing alumina nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Lawler, Katherine [Iowa State Univ., Ames, IA (United States)

    2009-01-01

    The viscosities of both aqueous and cyanate ester monomer (BECy) based suspensions of alumina nanoparticle were studied. The applications for these suspensions are different: aqueous suspensions of alumina nanoparticles are used in the production of technical ceramics made by slip casting or tape casting, and the BECy based suspensions are being developed for use in an injection-type composite repair resin. In the case of aqueous suspensions, it is advantageous to achieve a high solids content with low viscosity in order to produce a high quality product. The addition of a dispersant is useful so that higher solids content suspensions can be used with lower viscosities. For BECy suspensions, the addition of nanoparticles to the BECy resin is expected to enhance the mechanical properties of the cured composite. The addition of saccharides to aqueous suspensions leads to viscosity reduction. Through DSC measurements it was found that the saccharide molecules formed a solution with water and this resulted in lowering the melting temperature of the free water according to classic freezing point depression. Saccharides also lowered the melting temperature of the bound water, but this followed a different rule. The shear thinning and melting behaviors of the suspensions were used to develop a model based on fractal-type agglomeration. It is believed that the structure of the particle flocs in these suspensions changes with the addition of saccharides which leads to the resultant viscosity decrease. The viscosity of the BECy suspensions increased with solids content, and the viscosity increase was greater than predicted by the classical Einstein equation for dilute suspensions. Instead, the Mooney equation fits the viscosity behavior well from 0-20 vol% solids. The viscosity reduction achieved at high particle loadings by the addition of benzoic acid was also investigated by NMR. It appears that the benzoic acid interacts with the surface of the alumina particle which may

  7. On the possibility of producing alumina ceramic with a slight electrical conductivity

    CERN Document Server

    Caspers, Fritz

    1989-01-01

    Antistatic alumina ceramic is desirable for certain particle accelerator applications. In general, highly insulating surface close to a charged particle beam must be avoided in order to prevent the formation of ion pockets and other unwanted electrical effects. For the AA vacuum chamber (UHV), an antistatic ferrite has been produced and successfully installed. The fabrication of antistatic alumina might be possible in a similar way. By using certain metal oxides in the cement, which holds the alumina particles together, a slight conductivity could be obtained after the firing and sintering process, without deteriorating the mechanical and outgassing properties of the alumina compound.

  8. The Effect of Novel Synthetic Methods and Parameters Control on Morphology of Nano-alumina Particles.

    Science.gov (United States)

    Xie, Yadian; Kocaefe, Duygu; Kocaefe, Yasar; Cheng, Johnathan; Liu, Wei

    2016-12-01

    Alumina is an inorganic material, which is widely used in ceramics, catalysts, catalyst supports, ion exchange and other fields. The micromorphology of alumina determines its application in high tech and value-added industry and its development prospects. This paper gives an overview of the liquid phase synthetic method of alumina preparation, combined with the mechanism of its action. The present work focuses on the effects of various factors such as concentration, temperature, pH, additives, reaction system and methods of calcination on the morphology of alumina during its preparation. PMID:27206644

  9. The equation of state of two alumina-filled epoxy resins

    International Nuclear Information System (INIS)

    The shock Hugoniots of two different alumina-epoxy particulate composites have been measured in terms of shock velocity, particle velocity and shock stress. Both shock velocities and shock stresses increase with increasing amounts of alumina loading. The shock velocity-particle velocity relationships have been shown to be linear, and that with increasing alumina, behaviour shifts from a viscous to a response more commonly seen in metals and ceramics. Comparisons of the calculated hydrodynamic pressure and shock stress suggest that these materials have a constant shear strength with increasing shock stress. Finally, comparison of the material with the highest amount of alumina, with the work of others, shows close agreement

  10. Determination of calcium and magnesium in nuclear grade alumina by ion chromatography technique

    International Nuclear Information System (INIS)

    A simple method for solubilization of alumina and separation of magnesium and calcium from alumina matrix was developed by initial coprecipitation of those elements with iron(III) hydroxide. Calcium and magnesium were later separated from iron chloride anionic complex in a Dowex 1-X 10 anionic exchange resin. The ion chromatography tecnnique was employed for the analysis of calcium and magnesium. One hundred percent recovery for calcium and magnesium was obtained in their separation from alumina. A precision of 6% and 10% for magnesium and calcium, respectively, was obtained in alumina samples analysis which contain less than 0,02% of magnesium and less than 0,08% of calcium. (Author)

  11. Synthesis and characterization of platinum supported on alumina doped with cerium catalyst

    International Nuclear Information System (INIS)

    The synthesis and characterization of gamma-alumina doped with cerium as platinum support for the automobile exhaust catalyst are described. Platinum/alumina/ceria catalyst were prepared by impregnation of hexachloroplatinic acid and sintered at 500 degree Celsius to obtain metal dispersions of 1.0 wt%. Catalyst distribution inside the powder and the effects of the addition of cerium to alumina were analyzed by the scanning electron microscopy (SEM) and x-ray fluorescence spectroscopy (XRF). The results showed that the alumina - supported catalysts contained well dispersion of the noble metal

  12. The Effect of Novel Synthetic Methods and Parameters Control on Morphology of Nano-alumina Particles

    Science.gov (United States)

    Xie, Yadian; Kocaefe, Duygu; Kocaefe, Yasar; Cheng, Johnathan; Liu, Wei

    2016-05-01

    Alumina is an inorganic material, which is widely used in ceramics, catalysts, catalyst supports, ion exchange and other fields. The micromorphology of alumina determines its application in high tech and value-added industry and its development prospects. This paper gives an overview of the liquid phase synthetic method of alumina preparation, combined with the mechanism of its action. The present work focuses on the effects of various factors such as concentration, temperature, pH, additives, reaction system and methods of calcination on the morphology of alumina during its preparation.

  13. The effect of alumina nanofillers size and shape on mechanical behavior of PMMA matrix composite

    Directory of Open Access Journals (Sweden)

    Ben Hasan Somaya Ahmed

    2014-01-01

    Full Text Available Composites with the addition of alumina nanofillers show improvement in mechanical properties. The PMMA polymer was used as a matrix and two different types of nanofillers, having extremely different shapes were added in the matrix to form the composite. Reinforcements were based on alumina nanoparticles having either spherical shape or whiskers having the length to diameter ratio of 100. The influence of alumina fillers size, shape and fillers loading on mechanical properties of prepared composite were studied using the nanoindentation measurements and dynamic mechanical analysis. It was observed that both alumina whiskers and alumina spherical nanoparticles added in the PMMA matrix improved the mechanical properties of the composite but the improvement was significantly higher with alumina whisker reinforcement. The concentration of the reinforcing alumina spherical nanoparticles and alumina whiskers in PMMA matrix varied up to 5 wt. %. The best performance was obtained by the addition of 3 wt. % of alumina whiskers in the PMMA matrix with regard to mechanical properties of the obtained composite.

  14. HF Formation Upon Addition of Different Industrial Aluminas to Cryolitic Baths

    OpenAIRE

    Sommerseth, Camilla

    2011-01-01

    The aluminium smelter at Hydro Sunndal has experienced problems with an unexpected increased loss of AlF3 from the electrolyte when using a certain quality of alumina. One hypothesis considered was that the fluoride loss was a direct result of unusually high HF formation when the quality was added to the cryolitic melt. This work has set out to study the HF formation potential of three different industrial alumina qualities. Alumina A was an alumina quality that worked well in the smelter. Al...

  15. Complex processing of fluorine- and alumina comprising wastes of aluminium production

    International Nuclear Information System (INIS)

    Present article is devoted to complex processing of fluorine- and alumina comprising wastes of aluminium production. The composition and optimal parameters of soda-alkaline treatment of solution, obtained at sulfuric acid decomposition of fluorine- and alumina comprising wastes of aluminium production was defined. The conducted studies shown that from sulphate comprising solution at soda-alkaline treatment it is possible to obtain the alumina, fluoric salts and building materials. The flowsheet of complex processing of fluorine- and alumina comprising wastes was elaborated and proposed.

  16. Effect of sintering atmosphere on the pore-structure stability of cerium-doped nanostructured alumina

    OpenAIRE

    Kumar, Krishnankutty-Nair P.; Tranto, Janne; Balagopal N., Nair; Kumar, Jalajakumari; Hoj, Jacob W.; Engell, John E.

    1994-01-01

    Pore-structure stability of pure and Ce-doped alumina in air and argon atmospheres was studied using DTA, TGA, N2 ads./des. and XRD with a view to understand the importance of the ionic size of the dopant cation on the pore-structure stability of alumina. The ionic size effect was studied by heat treating the Ce-alumina system in both oxidizing and reducing atmospheres to have Ce4+ (87 pm) and Ce3+ (106 pm) respectively. No compound formation between Ce and alumina was observed. In the case o...

  17. Silver as Anode in Cryolite—Alumina-Based Melts

    OpenAIRE

    Kucharik, M.; Chamelot, Pierre; Cassayre, Laurent; Taxil, Pierre

    2007-01-01

    The anodic behaviour of silver was investigated in cryolite—alumina-based melt. Silver has a lower melting point (ca. 960◦C) than the other metals considered as possible inert materials for aluminium electrolysis. The working temperature used in aluminium industry is approximately 960◦C, depending on the melt composition. Therefore, the stability of silver during the anodic process was tested at 870◦C in an acidic electrolyte consisting of 65.5 mass % Na3AlF6 + 22.9 mass % AlF3 + 5.7 mass ...

  18. Preparation of alumina-zirconia composites containing microfibers

    Czech Academy of Sciences Publication Activity Database

    Hadraba, Hynek; Chlup, Zdeněk; Drdlík, D.

    Bratislava: Slovenská akademie věd, 2015 - (Lenčéš, Z.; Valúchová, J.). s. 73-73 ISBN 978-80-971648-3-6. [Engineering Ceramics 2015. 10.05.2015-14.05.2015, Smolenice castle] R&D Projects: GA MŠk(CZ) ED1.1.00/02.0068; GA ČR(CZ) GA15-06390S Institutional support: RVO:68081723 Keywords : alumina * zirconia * fibres * laminates * electrophoretic deposition Subject RIV: JH - Ceramics, Fire-Resistant Materials and Glass

  19. Pressing behaviour of spray dried alumina-zirconia granules

    International Nuclear Information System (INIS)

    In this study, spray drying of alumina-zirconia slurries on a pilot scale, and their pressing behaviour were investigated. Slurries were prepared at 50 wt-% solid loading. An acrylic polymer emulsion, polyethylene glycol, and stearic acid were used as a binder, plasticizer, and lubricant, respectively. Granules produced had a mean size of 85 μm with spherical morphology and smooth surfaces with considerably good flow behaviour. When polyethylene glycol was not used, granules were rather hard such that it was very difficult to break down the granule structure even at a pressure of 195 MPa. (orig.)

  20. Dealuminated Mesoporous Silica-Alumina as Carrier for Pt Catalysts

    Czech Academy of Sciences Publication Activity Database

    Gulková, Daniela; Vít, Zdeněk; Kaluža, Luděk; Zdražil, Miroslav

    Messina: Samperi Editore - Messina, 2009 - (Perathoner, S.; Quartieri, S.; Casella, A.), P10-1-P10-2 ISBN 978-88-86038-58-4. [Czech-Italian- Spanish Trilateral Meeting on Catalysis and Micro/Meso-Porous Materials /3./. Acireale,Sicily (IT), 21.06.2009-25.06.2009] R&D Projects: GA ČR GA104/09/0751 Institutional research plan: CEZ:AV0Z40720504 Keywords : mesoporous silica-aluminas * catalysts * dealumination Subject RIV: CC - Organic Chemistry

  1. Electrochemically replicated smooth aluminum foils for anodic alumina nanochannel arrays.

    Science.gov (United States)

    Biring, Sajal; Tsai, Kun-Tong; Sur, Ujjal Kumar; Wang, Yuh-Lin

    2008-01-01

    A fast electrochemical replication technique has been developed to fabricate large-scale ultra-smooth aluminum foils by exploiting readily available large-scale smooth silicon wafers as the masters. Since the adhesion of aluminum on silicon depends on the time of surface pretreatment in water, it is possible to either detach the replicated aluminum from the silicon master without damaging the replicated aluminum and master or integrate the aluminum film to the silicon substrate. Replicated ultra-smooth aluminum foils are used for the growth of both self-organized and lithographically guided long-range ordered arrays of anodic alumina nanochannels without any polishing pretreatment. PMID:21730530

  2. Functionally graded alumina-based thin film systems

    Science.gov (United States)

    Moore, John J.; Zhong, Dalong

    2006-08-29

    The present invention provides coating systems that minimize thermal and residual stresses to create a fatigue- and soldering-resistant coating for aluminum die casting dies. The coating systems include at least three layers. The outer layer is an alumina- or boro-carbide-based outer layer that has superior non-wettability characteristics with molten aluminum coupled with oxidation and wear resistance. A functionally-graded intermediate layer or "interlayer" enhances the erosive wear, toughness, and corrosion resistance of the die. A thin adhesion layer of reactive metal is used between the die substrate and the interlayer to increase adhesion of the coating system to the die surface.

  3. Macroporous silica–alumina composites with mesoporous walls

    Indian Academy of Sciences (India)

    Gautam Gundiah

    2001-04-01

    Macroporous silica–alumina composites with mesopores have been prepared by employing polymethylmethacrylate beads as templates in the presence of the cationic surfactant, N-cetyl-N,N,N-trimethylammonium bromide. The Si/Al ratio in the composites has been varied between 4.5 and 48 and the occurrence of mesopores has been verified by X-ray diffraction. The surface areas of the samples vary between 676 and 1038 m2g–1, with the highest value in the sample with Si/Al = 48.

  4. Oxygen tracer diffusion in single-crystal alumina

    Science.gov (United States)

    Cawley, James D.; Halloran, John W.; Cooper, Alfred R.

    1991-01-01

    Oxygen tracer diffusion coefficients are determined in single-crystal alumina samples with differing dopant levels using the gas-exchange technique. The diffusion direction is parallel to the c-axis and the ambient PO2 is 1 atm (100,000 Pa) for all experiments except a single run with a low PO2, approximately 10 to the -15th atm (10 to the -10th Pa) produced by a CO/CO2 mixture. The diffusion is insensitive to both impurities and ambient PO2. The insensitivities are discussed in terms of point-defect clustering. Prior tracer studies are compared and discussed.

  5. Synthesis of alumina-α using chemical and activation energy por microwave; Sintese de alumina-α utilizando ativacao quimica e energia por microondas

    Energy Technology Data Exchange (ETDEWEB)

    Cartaxo, J.M.; Galdino, M.N.; Neves, G.A., E-mail: juliana@dema.ufcg.edu.br [Universidade Federal de Campina Grande (DEMA/UFCG), PB (Brazil). Unidade Academica de Engenharia de Materiais; Campos, L.F.A.; Menezes, R.R. [Universidade Federal da Paraiba (UFPB), PB (Brazil). Dept. de Engenharia de Materiais; Kiminami, R.H.G.A. [Universidade Federal de Sao Carlos (UFSC), SP (Brazil)

    2012-07-01

    With the great technological advances of alumina, this study aimed to synthesize the α-alumina and chemical activation using microwave energy from aluminum nitrate precursor. The synthesized powders were characterized by X-ray diffraction, thermal analysis (DTA and TGA) and surface area by BET. The chemical activation process was conducted by varying the concentration of the acid solution and exposure time of the material solution. The results proved the effectiveness of chemical activation by accelerating the synthesis process. The results of thermal analysis can observe the thermal decomposition temperature and the possible nucleation of new phases of alumina. The results of X-ray diffraction showed that the powders have the structure of α-alumina with specific areas ranging from 3 to 15m{sup 2}/g pore diameters between 190 to 485nm. (author)

  6. Pilot tests of application of cryolite-alumina concentrate in aluminium production

    International Nuclear Information System (INIS)

    The results of pilot tests of obtaining method and application of cryolite-alumina concentrate obtained from sludge in aluminium production are considered. Chemical and mineralogical composition of initial raw material and cryolite-alumina concentrate are studied. The tests are shown that concentrate can be used as anode cover of electrolytic cells.

  7. The Formation and Dissolution of Crust Upon Alumina Addition into Cryolite Electrolyte

    Science.gov (United States)

    Yang, Youjian; Gao, Bingliang; Wang, Zhaowen; Shi, Zhongning; Hu, Xianwei

    2015-09-01

    The properties of the alumina agglomerate/crust formed upon smelting grade alumina feeding and the corresponding dissolution rates in cryolite electrolyte were studied using a suspended weighing device. A series of experiments was designed to investigate the dissolution rate of the crust at various temperatures and the effects of initial alumina concentration in the electrolyte on the formation process and properties of the crust. Initial results showed that under experimental non-stirring conditions, a large proportion as high as 54-64% of the fed alumina participated in the formation of the crust upon feeding at 1233-1238 K (960-965°C). The dissolution rate of the crust decreased greatly with the increase of initial alumina concentration and the decrease of operating temperature. The mass of the crust increased significantly at high initial alumina concentrations and decreased temperature, while the alumina content of the crust showed a slight decreasing trend. Other parameters of the crust such as volume density and gas-filling fraction were also measured. The influence of physical stirring on alumina dissolution rate was also discussed.

  8. A Review of Alumina Feeding and Dissolution Factors in Aluminum Reduction Cells

    Science.gov (United States)

    Lavoie, Pascal; Taylor, Mark P.; Metson, James B.

    2016-08-01

    Modern aluminum reduction cells use point feeding technology to replenish alumina as it is consumed by the electrolytic process. The dissolution of alumina has become increasingly difficult to control as the cell sizes and electrolysis intensity have increased. The mass of alumina added per unit time is now much higher than a decade ago, and must take place within a smaller electrolyte mixing volume. In order to replenish the alumina concentration evenly, the alumina needs to be delivered, dispersed, dissolved, and distributed throughout the reduction cell. The dissolution itself follows a 4-step process that can be limited by a multitude of factors. The status of the research on each of these factors is reviewed in the present paper. Although research in laboratory cells has been conducted many times, and the impact of many factors on dissolution has been measured, published observations of alumina feeding on industrial cells are very sparse, especially regarding the dissolution dynamics in the space-time domain and the impact of the feeder hole condition. The present paper therefore presents a qualitative model of the factors governing alumina dissolution in industrial cells and offers the hypothesis that maintenance of the feeder hole condition is central to ensuring alumina dissolution and prevention of sludging.

  9. High field matching effects in superconducting Nb porous arrays catalyzed from anodic alumina templates

    DEFF Research Database (Denmark)

    Vinckx, W.; Vanacken, J.; Moshchalkov, V.V.;

    2007-01-01

    parallel pores. Its pore diameter and interpore distance are set by careful tuning of the anodization parameters. A superconducting Nb thin film is deposited directly onto the alumina film. The porous alumina acts as a template and it allows Nb to form a periodic pinning array during its growth. Pinning...

  10. [Research on bending strength and fracture toughness of alumina-glass composite].

    Science.gov (United States)

    Luo, X; Zhao, Y; Tian, J; Chao, Y; Zhang, S; Zhang, Y

    1998-12-01

    To develop a new ceramic material that can be machined and infiltrated with glass, a porous alumina blank sintered at 1350 degrees C was made of high purity, super fine alpha-alumina and then infiltrated with glass in this study. The density, bending strength and fracture toughness of the partially sintered alumina and alumina-glass composite were determined. The results indicated that the porous alumina density was 2.12 g/cm3, the three point bending strength 102 MPa, the fracture toughness 1.61 MPam1/2; that the alumina-glass composite density was 3.85 g/cm3, the three point bending strength 385 MPa, and the fracture toughness 4.05 MPam1/2. By SEM and EDXA analysis, lanthanum boroslicate glass was completely infiltrated into the 3 mm thick porous alumina blank for 6 h at 1150 degrees C. These suggest that the new developed alumina blank is suited for clinical use. PMID:10743233

  11. Investigation of small molecular weight poly(acrylic acid) adsorption on γ-alumina

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Lei; Luo, Shi-Zhong [College of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065 (China); Wang, Bin, E-mail: bin_wang@scu.edu.cn [College of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065 (China); Guo, ZhanHu [Chemical and Biomolecular Engineering Department, University of Tennessee, Knoxville, TN 37996 (United States)

    2015-08-01

    Highlights: • Small molecular weight poly(acrylic acid) incorporated on γ-alumina. • PAA adsorbed primarily on outer surface of alumina at low pH. • PAA infiltrated inside alumina pore at high pH. • Polymer chain reptation motion during the infiltration. - Abstract: The interactions between poly(acrylic acid) (PAA) and alumina have been widely investigated. In this study, the pattern of small molecular weight PAA (M{sub W} 3000) interaction with γ-alumina has been dissected. The alumina/PAA hybrids were prepared at pH 4.0, 5.5, and 7.0, respectively. Nitrogen absorption–desorption analysis, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and elemental analysis were conducted to illustrate the characteristics of the hybrids. At pH 4.0, the coiled PAA conformation yielded polymer adsorption primarily on alumina outer surface. At higher pH values, the more stretched PAA molecules were able to infiltrate inside the alumina pores. The phenomenon is explained by the polymer chain reptation motion model. Coiled polymer chains are not oriented enough to penetrate the oxide pore channels. In contrary, stretched polymer chains are more likely to move along the pore channels.

  12. Investigation of small molecular weight poly(acrylic acid) adsorption on γ-alumina

    International Nuclear Information System (INIS)

    Highlights: • Small molecular weight poly(acrylic acid) incorporated on γ-alumina. • PAA adsorbed primarily on outer surface of alumina at low pH. • PAA infiltrated inside alumina pore at high pH. • Polymer chain reptation motion during the infiltration. - Abstract: The interactions between poly(acrylic acid) (PAA) and alumina have been widely investigated. In this study, the pattern of small molecular weight PAA (MW 3000) interaction with γ-alumina has been dissected. The alumina/PAA hybrids were prepared at pH 4.0, 5.5, and 7.0, respectively. Nitrogen absorption–desorption analysis, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and elemental analysis were conducted to illustrate the characteristics of the hybrids. At pH 4.0, the coiled PAA conformation yielded polymer adsorption primarily on alumina outer surface. At higher pH values, the more stretched PAA molecules were able to infiltrate inside the alumina pores. The phenomenon is explained by the polymer chain reptation motion model. Coiled polymer chains are not oriented enough to penetrate the oxide pore channels. In contrary, stretched polymer chains are more likely to move along the pore channels

  13. A Review of Alumina Feeding and Dissolution Factors in Aluminum Reduction Cells

    Science.gov (United States)

    Lavoie, Pascal; Taylor, Mark P.; Metson, James B.

    2016-05-01

    Modern aluminum reduction cells use point feeding technology to replenish alumina as it is consumed by the electrolytic process. The dissolution of alumina has become increasingly difficult to control as the cell sizes and electrolysis intensity have increased. The mass of alumina added per unit time is now much higher than a decade ago, and must take place within a smaller electrolyte mixing volume. In order to replenish the alumina concentration evenly, the alumina needs to be delivered, dispersed, dissolved, and distributed throughout the reduction cell. The dissolution itself follows a 4-step process that can be limited by a multitude of factors. The status of the research on each of these factors is reviewed in the present paper. Although research in laboratory cells has been conducted many times, and the impact of many factors on dissolution has been measured, published observations of alumina feeding on industrial cells are very sparse, especially regarding the dissolution dynamics in the space-time domain and the impact of the feeder hole condition. The present paper therefore presents a qualitative model of the factors governing alumina dissolution in industrial cells and offers the hypothesis that maintenance of the feeder hole condition is central to ensuring alumina dissolution and prevention of sludging.

  14. Design Manual: Removal of Fluoride from Drinking Water Supplies by Activated Alumina

    Science.gov (United States)

    This document is an updated version of the Design Manual: Removal of Fluoride from Drinking Water Supplies by Activated Alumina (Rubel, 1984). The manual is an in-depth presentation of the steps required to design and operate a fluoride removal plant using activated alumina (AA)...

  15. Modification of alumina matrices through chemical etching and electroless deposition of nano-Au array for amperometric sensing

    Directory of Open Access Journals (Sweden)

    Valinčius Gintaras

    2007-01-01

    Full Text Available AbstractSimple nanoporous alumina matrix modification procedure, in which the electrically highly insulating alumina barrier layer at the bottom of the pores is replaced with the conductive layer of the gold beds, was described. This modification makes possible the direct electron exchange between the underlying aluminum support and the redox species encapsulated in the alumina pores, thus, providing the generic platform for the nanoporous alumina sensors (biosensors with the direct amperometric signal readout fabrication.

  16. Effects of Variable Aspect-Ratio Inclusions on the Electrical Impedance of an Alumina Zirconia Composite at Intermediate Temperatures

    Science.gov (United States)

    Goldsby, Jon C.

    2010-01-01

    A series of alumina-yttria-stabilized zirconia composites containing either a high aspect ratio (5 and 30 mol%) hexagonal platelet alumina or an alumina low aspect ratio (5 and 30 mol%) spherical particulate was used to determine the effect of the aspect ratio on the temperature-dependent impedance of the composite material. The highest impedance across the temperature range of 373 to 1073 K is attributed to the grain boundary of the hexagonal platelet second phase in this alumina zirconia composite.

  17. Comparative Study of Indentation Size Effects in As-Sintered Alumina and Alumina Shock Deformed at 6.5 and 12 GPa

    OpenAIRE

    CHAKRABORTY, RIYA; Mukhopadhyay, Anoop K.; Keshaw D. Joshi; Rav, Amit; Mandal, Ashok K.; Bysakh, Sandip; Sampad K. Biswas; Satish C. Gupta

    2012-01-01

    Nanohardness of alumina ceramics determines its performance in all contact-related applications because the issue of structural integrity gets determined at the nanoscale of contact. In spite of the wealth of the literature, however, it is not yet known in significant details how the high-strain rate flyer-plate impact at different pressure affects the nanohardness of dense, coarse grain alumina ceramics. Thus, the load controlled nanoindentation experiments were performed with a Berkovich in...

  18. Effect of Physiochemical Properties and Bath Chemistry on Alumina Dissolution Rate in Cryolite Electrolyte

    Science.gov (United States)

    Yang, Youjian; Gao, Bingliang; Wang, Zhaowen; Shi, Zhongning; Hu, Xianwei

    2015-05-01

    The relationships of dissolution rate to alumina specifications and bath chemistry including electrolyte composition, operating temperature and superheat were investigated. The key physiochemical properties of industrial alumina samples were tested including moisture content, loss on ignition, surface area and phase composition. The dissolution of these samples in several bath compositions was observed through a quartz crucible equipped with a visual recording system. The dissolution rate increased with increasing loss on ignition and surface area. The operating temperatures and existing alumina concentration in the electrolyte had a greater impact on the alumina dissolution rate than the minor change of the bath compositions and superheat. Same trends were also obtained for the lab-calcined alumina samples.

  19. Processing, nano indentation and scratch testing of alumina-coated YTZP

    Energy Technology Data Exchange (ETDEWEB)

    Valle, J.; Anglada, M.; Ferrari, B.; Baudin, C.

    2015-10-01

    In this work, alumina-coated YTZP materials are proposed as means to combine the mechanical reliability of YTZP with the stiffness and hardness of alumina. Additionally, compressive stresses are developed in the alumina coating when cooling from the sintering temperature due to the thermal expansion mismatch between alumina and YTZP. The proposed processing method involves dipping of pre-sintered YTZP specimens in stable alumina suspensions and co-sintering of the dipped specimens. The influence of the processing parameters on the macro and microstructure of the materials has been established. Berkovich indentation has been performed to determine the Young's modulus of the substrates and coatings. The structural integrity of the coatings has been analysed using scratch tests. The Young's modulus. The optimised specimens present high resistance to scratch up to loads of 150 N. (Author)

  20. Micromechanics of deformation in porous liquid phase sintered alumina under hertzian contact

    Energy Technology Data Exchange (ETDEWEB)

    DIGIOVANNI,ANTHONY A.; CHAN,HELEN M.; HARMER,MARTIN P.; NIED,HERMAN F.

    2000-05-15

    A series of fine-grained porous alumina samples, with and without a liquid phase, were fabricated in compositions matched closely to commercially available alumina used as a microelectronic substrates. Hertzian indentation on monolithic specimens of the glass-containing samples produced a greater quasi-ductile stress-strain response compared to that observed in the pure alumina. Maximum residual indentation depths, determined from surface profilometry, correlated with the stress-strain results. Moreover, microstructural observations from bonded interface specimens revealed significantly more damage in the form of microcracking and under extreme loading, pore collapse, in the glass-containing specimens. The absence of the typical twin faulting mechanism observed for larger-grained alumina suggests that the damage mechanism for quasi-ductility in these fine-grained porous alumina derived from the pores acting as a stress concentrator and the grain boundary glass phase providing a weak path for short crack propagation.

  1. Mechanical performance of alumina reinforced with NbC, TiC and WC

    Directory of Open Access Journals (Sweden)

    Wilson Acchar

    2012-12-01

    Full Text Available The incorporation of refractory hard particles in Al2O3-based composites may inhibit grain growth of the matrix, which could significantly contribute to mechanical performance of the composite. The present study aimed to investigate the potential use of NbC as alumina reinforcing material, as an alternative to other carbides such as TiC and WC. Alumina was mixed with a fixed carbide concentration of 30 wt.(% in a ball mill and uniaxially hot-pressed at 1650 ºC under a load of 30 MPa in an inert atmosphere. X-ray diffraction revealed no oxidation products were present after the sintering process. Microstructure analyses indicate a homogeneous carbide distribution in the alumina matrix. Results obtained in this study show that alumina reinforced with NbC is a composite material with properties comparable to those of alumina reinforced with WC and TiC, thereby making it good reinforcing material.

  2. Study of preparation and surface morphology of self-ordered nanoporous alumina

    International Nuclear Information System (INIS)

    Nanoporous alumina is a typical material that exhibits self-ordered nanochannels spontaneously organized in hexagonal shape. Produced by anodizing of metallic aluminum, it has been used as a template for production of materials at the nanoscale. This work aimed to study the preparation of nanoporous alumina by anodic anodizing of metallic aluminum substrates. The nanoporous alumina was prepared following the methodology proposed by Masuda and Fukuda (1995), a two-step method consisting of anodizing the aluminum sample in the potentiostatic mode, removing the layer of aluminum oxide (alumina) formed and then repeat the anodization process under the same conditions as the first anodization. This method produces nanoporous alumina with narrow pore diameter distribution and well-ordered structure. (author)

  3. Processing, nano indentation and scratch testing of alumina-coated YTZP

    International Nuclear Information System (INIS)

    In this work, alumina-coated YTZP materials are proposed as means to combine the mechanical reliability of YTZP with the stiffness and hardness of alumina. Additionally, compressive stresses are developed in the alumina coating when cooling from the sintering temperature due to the thermal expansion mismatch between alumina and YTZP. The proposed processing method involves dipping of pre-sintered YTZP specimens in stable alumina suspensions and co-sintering of the dipped specimens. The influence of the processing parameters on the macro and microstructure of the materials has been established. Berkovich indentation has been performed to determine the Young's modulus of the substrates and coatings. The structural integrity of the coatings has been analysed using scratch tests. The Young's modulus. The optimised specimens present high resistance to scratch up to loads of 150 N. (Author)

  4. Bond strength of a resin cement to high-alumina and zirconia-reinforced ceramics : The effect of surface conditioning

    NARCIS (Netherlands)

    Felipe Valandro, Luiz; Ozcan, Mutlu; Bottino, Marco Cicero; Bottino, Marco Antonio; Scotti, Roberto; Della Bona, Alvaro

    2006-01-01

    Purpose: The aim of this study was to evaluate the effect of two surface conditioning methods on the microtensile bond strength of a resin cement to three high-strength core ceramics: high alumina-based (In-Ceram Alumina, Procera AllCeram) and zirconia-reinforced alumina-based (in-Ceram Zirconia) ce

  5. The interface structure and band alignment at alumina/Cu(Al) alloy interfaces-Influence of the crystallinity of alumina films

    International Nuclear Information System (INIS)

    Both epitaxial and amorphous ultra-thin alumina films were grown on a Cu-9 at.%Al(1 1 1) substrate by selective oxidation of Al in the alloy in ultra high vacuum. The crystallinity of the alumina films was controlled by oxidation temperature. The photoelectron spectra of Al 2p, O 1s and valence band were measured in-situ during oxidation. The influence of the crystallinity on the interface structure between the alumina films and the substrate was discussed by analyzing the Al 2p spectra composed of multiple peaks. The energy difference between the Fermi level of the substrate and the valence band maximum of the alumina films (band offset) was derived from the valence band spectra. The energy band alignment at the interface between each of the two alumina films and the substrate was revealed by combining the binding energy values of the core levels with the band offset values. The influence of the alumina crystallinity on the band alignment was discussed.

  6. Adsorption of textile dye onto modified immobilized activated alumina

    Directory of Open Access Journals (Sweden)

    Ayesha Wasti

    2016-06-01

    Full Text Available The study describes the synthesis of modified immobilized activated alumina (MIAA and its application for the removal of textile dye from aqueous media. Immobilization was carried out by using the sol–gel method while modifications were made during the synthesis by adding powder activated alumina. Batch adsorption experiments were carried out at 20 ± 1 °C to see the effect of different parameters like contact time, stirring rate, initial concentration of the dye and dose of MIAA. The removal efficiency of Cibacron reactive yellow dye with an initial concentration of 400 mg/L was greater than 90% for 90 min contact time. Langmuir and Freundlich adsorption isotherms were applied which fitted the data with an R2 value of 0.99. The maximum adsorption capacity of MIAA was 25 mg/g at the initial dye concentration of 400 mg/L. MIAA can be regenerated thermally and chemically with the dye removal efficiency remained above 85% during the first 4 regeneration cycles. Thermal regeneration was achieved in a muffle furnace at 450 °C while chemical regeneration was done by immersing MIAA in 0.1 M NaOH solution for 2 h. MIAA also proved effective for the adsorption of dyes from actual textile wastewater giving a removal efficiency of 75%.

  7. YBCO nanowires grown by the alumina template method

    International Nuclear Information System (INIS)

    YBa2Cu3Ox (YBCO) nanowires are grown by the anodized alumina template method, starting from pre-sintered YBCO powder. As templates, we have employed commercially available alumina templates with pore diameters of 30 nm and 100 nm, and an overall thickness of 50 μm. An oxygen annealing step is required to obtain superconducting nanowires. Superconductivity with a transition temperature of 88 K is confirmed by means of magnetic susceptibility measurements. The resulting nanowires are analyzed in detail employing electron microscopy and atomic force microscopy. The separation of the nanowires of the templates is not yet established, but individual nanowires of up to 10 μm length could be separated from the template. In several cases, the template pores are not completely filled by the superconducting material, which implies that the observed length is similar to what could be expected from regular grain growth. Resistance measurements using cut pieces of the filled templates were carried out as a function of temperature. These pieces were covered with Au films on top and bottom in order to provide the electric contacts. The measurements confirmed the magnetically determined critical temperatures.

  8. Synthesis of magnesium aluminate spinel by periclase and alumina chlorination

    International Nuclear Information System (INIS)

    Highlights: • Use of chlorination for the synthesis of magnesium aluminate spinel. • The reagents used were alumina, periclase and chlorine. • Isothermal and non-isothermal assays were performed in air and Cl2–N2 flows. • The chlorination produced magnesium aluminate spinel at 700 °C. • Selectivity of the chlorination reaction to obtain spinel is very high. - Abstract: A pyrometallurgical route for the synthesis of magnesium aluminate spinel by thermal treatment of a mechanical mixture containing 29 wt% MgO (periclase) and 71 wt% Al2O3 (alumina) in chlorine atmosphere was developed and the results were compared with those obtained by calcining the same mixture of oxides in air atmosphere. Isothermal and non-isothermal assays were performed in an experimental piece of equipment adapted to work in corrosive atmospheres. Both reagents and products were analyzed by differential thermal analysis (DTA), X-ray diffraction (XRD) and X-ray fluorescence (XRF). Thermal treatment in Cl2 atmosphere of the MgO–Al2O3 mixture produces magnesium aluminate spinel at 700 °C, while in air, magnesium spinel is generated at 930 °C. The synthesis reaction of magnesium aluminate spinel was complete at 800 °C

  9. Alumina ceramics prepared with new pore-forming agents

    Directory of Open Access Journals (Sweden)

    Zuzana Živcová

    2008-06-01

    Full Text Available Porous ceramics have a wide range of applications at all length scales, ranging from fi ltration membranes and catalyst supports to biomaterials (scaffolds for bone ingrowths and thermally or acoustically insulating bulk materials or coating layers. Organic pore-forming agents (PFAs of biological origin can be used to control porosity, pore size and pore shape. This work concerns the characterization and testing of several less common pore-forming agents (lycopodium, coffee, fl our and semolina, poppy seed, which are of potential interest from the viewpoint of size, shape or availability. The performance of these new PFAs is compared to that of starch, which has become a rather popular PFA for ceramics during the last decade. The PFAs investigated in this work are in the size range from 5 μm (rice starch to approximately 1 mm (poppy seed, all with more or less isometric shape. The burnout behavior of PFAs is studied by thermal analysis, i.e. thermogravimetry and differential thermal analysis. For the preparation of porous alumina ceramics from alumina suspensions containing PFAs traditional slip casting (into plaster molds and starch consolidation casting (using metal molds are used in this work. The resulting microstructures are investigated using optical microscopy, combined with image analysis, as well as other methods (Archimedes method of double-weighing in water, mercury intrusion porosimetry.

  10. Fabrication of zirconia toughened alumina ceramics by different sintering methods

    International Nuclear Information System (INIS)

    A zirconia/alumina composition of 15 wt% ZrO2/85 wt% Al2O3 was fabricated from a powder mixture by uni-axial and cold isostatic pressing (CIPing). The uni-axially pressed powder compacts were hot pressed at 1600 deg C in a graphite die in a dynamic nitrogen atmosphere. The CIPed pellets were sintered in air at 1600 deg C. Some of these pellets were hot isostatically pressed (HIPed) in a graphite furnace in an argon atmosphere at 100 MPa at 1500 deg C and 1600 deg C. The green CIPed pellets were sintered and HIPed (sinter/HIPed) in the same cycle by sintering at 1600 deg C followed by HIPing at the same temperature. The sinter + HIPed (1500 deg C) pellet had the highest relative density (>99%) with an open porosity of almost zero. It also had the lowest closed porosity. All the pellets had a relative density of > 98%, but the sintered pellets had the highest total porosity. The microstructure of the pellets examined by scanning electron microscopy confirmed these observations and also showed the zirconia phase was evenly distributed. The X-ray diffraction analysis showed the pellets to contain tetragonal and monoclinic zirconia except for the sinter/HIPed pellet which contained monoclinic zirconia. The different sintering methods have given a greater understanding for microsturctural control and processing of zirconia toughened alumina. 9 refs., 2 tabs., 5 figs

  11. Synthesis of magnesium aluminate spinel by periclase and alumina chlorination

    Energy Technology Data Exchange (ETDEWEB)

    Orosco, Pablo, E-mail: porosco@unsl.edu.ar [Instituto de Investigaciones en Tecnología Química (INTEQUI), Chacabuco y Pedernera, San Luis (Argentina); Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis Chacabuco y Pedernera, San Luis (Argentina); Barbosa, Lucía [Instituto de Investigaciones en Tecnología Química (INTEQUI), Chacabuco y Pedernera, San Luis (Argentina); Instituto de Ciencias Básicas (ICB), Universidad Nacional de Cuyo Parque General San Martín, Mendoza (Argentina); Ruiz, María del Carmen [Instituto de Investigaciones en Tecnología Química (INTEQUI), Chacabuco y Pedernera, San Luis (Argentina); Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis Chacabuco y Pedernera, San Luis (Argentina)

    2014-11-15

    Highlights: • Use of chlorination for the synthesis of magnesium aluminate spinel. • The reagents used were alumina, periclase and chlorine. • Isothermal and non-isothermal assays were performed in air and Cl{sub 2}–N{sub 2} flows. • The chlorination produced magnesium aluminate spinel at 700 °C. • Selectivity of the chlorination reaction to obtain spinel is very high. - Abstract: A pyrometallurgical route for the synthesis of magnesium aluminate spinel by thermal treatment of a mechanical mixture containing 29 wt% MgO (periclase) and 71 wt% Al{sub 2}O{sub 3} (alumina) in chlorine atmosphere was developed and the results were compared with those obtained by calcining the same mixture of oxides in air atmosphere. Isothermal and non-isothermal assays were performed in an experimental piece of equipment adapted to work in corrosive atmospheres. Both reagents and products were analyzed by differential thermal analysis (DTA), X-ray diffraction (XRD) and X-ray fluorescence (XRF). Thermal treatment in Cl{sub 2} atmosphere of the MgO–Al{sub 2}O{sub 3} mixture produces magnesium aluminate spinel at 700 °C, while in air, magnesium spinel is generated at 930 °C. The synthesis reaction of magnesium aluminate spinel was complete at 800 °C.

  12. Scratch induced failure of plasma sprayed alumina based coatings

    International Nuclear Information System (INIS)

    Highlights: ► Scratch induced failure of alumina based coatings including nanostructured is reported. ► Ceramic is deposited on bond coat instead of steel, emulating a realistic situation. ► Lateral force data is supplemented with microscopy to observe coating failure. ► The failure mechanism during scratching has been identified. ► Critical load of failure has been calculated for each bond-top coat combination. -- Abstract: A set of plasma sprayed coatings were obtained from three alumina based top coat and two bond coat powders. Scratch test was undertaken on these coatings, under constant and linearly varying load. Test results include the lateral force data and scanning electron microscope (SEM) images. Failure occurred by large area spallation of the top coat and in most cases tensile cracks appeared on the exposed bond coat. The lateral force showed an increasing trend with an increase in normal load up to a certain point and beyond this, it assumed a steady average value. The locations of coating spallation and occurrence of maximum lateral force did not coincide. A bond coat did not show a significant role in determining the scratch adhesion strength.

  13. Solid solubility and diffusivity in an alumina/zirconia system

    International Nuclear Information System (INIS)

    Polycrystalline zirconia-coated single crystal sapphire fiber displays reconstruction of the sapphire surface in regions of contact with zirconia grains. This is a concern where ZrO2-coated sapphire fiber is desired for reinforcement of ceramic matrices. Previous work has demonstrated pitting is partially attributed to impurity-induced transient liquid phase formation with local dissolution of alumina; however, the extent of reconstruction witnessed via microscopy suggests that other mechanisms are active. The present study has addressed the issue of solid solubility and interdiffusivity to more thoroughly understand the solid state mechanisms contributing to pitting. Single crystal sapphire and zirconia were ion implanted with zirconium and yttrium, and aluminum, respectively, and then subjected to diffusion anneals at 1,200--1,600 C to study redistribution of implanted cations. Secondary Ion Mass Spectroscopy (SIMS) was used to profile the redistribution of implanted ions for measurement of diffusion coefficients and solubility limits after heat treatments. The results will offer a significant set of data on interface stability in the alumina/zirconia system

  14. Structural, optical and mechanical properties of amorphous and crystalline alumina thin films

    International Nuclear Information System (INIS)

    Thin films of amorphous alumina of thickness 350 nm were deposited on fused silica substrates by electron beam evaporation. Amorphous films were annealed at several temperatures in the range: 400–1130 °C and changes in film crystallinity, short-range structure, optical and mechanical properties were studied. X-ray diffraction studies found that crystallization starts at 800 °C and produces γ and δ-alumina, the latter phase grows with heat treatment and the sample was mostly δ and θ-alumina after annealing at 1130 °C. The as-deposited amorphous alumina films have low hardness of 5 to 8 GPa, which increases to 11 to 12 GPa in crystalline sample. 27Al Magic Angle Spinning Nuclear Magnetic Resonance was used to study the short-range order of amorphous and crystalline alumina films and it was found that amorphous alumina film contains AlO5 and AlO4 structural units in the ratio of 1:2. The concentration of AlO5 was significantly suppressed in crystalline film, which contains 48% of Al3+ ions in AlO6, 7% in AlO5 and 45% in AlO4 units. - Highlights: • Structure–property correlations in alumina films grown by electron-beam evaporation • Amorphous films crystallize into γ and δ-alumina on annealing in air at 800 °C. • δ and θ-alumina films are stable up to 1130 °C and do not transform to α-phase. • Amorphous alumina films contain [5]Al and [4]Al structural units in the ratio of 1:2. • [5]Al decreases whereas [6]Al concentration increases on crystallization

  15. Morphology-controlled electrochemical sensing amaranth at nanomolar levels using alumina

    International Nuclear Information System (INIS)

    Highlights: ► A facile way to tune morphology and sensing properties of alumina was developed. ► Oxidation activities of amaranth on alumina surface were morphology-dependent. ► Alumina microfibers were more active and greatly increased the signal of amaranth. ► Sensitive, rapid, selective and accurate method was developed for amaranth detection. -- Abstract: Different-shaped aluminas were readily prepared via hydrothermal reaction. It was found that the morphology and the electrochemical sensing properties of alumina were heavily dependent on the reaction time. When extending the reaction time from 6 h to 24 h, the obtained alumina samples changed from amorphous bumps to regular microfibers in diameter of 200 nm, as confirmed by scanning electron microscopy. Transmission electron microscopy observation revealed that longer reaction time was beneficial for the formation of porous and uniform fiber-like structures. Electrochemical tests proved that alumina microfibers were more active for the oxidation of amaranth and exhibited much higher enhancement effect, compared with alumina bumps. On the surface of alumina microfibers, the oxidation peak currents of amaranth increased remarkably. The influences of pH value, amount of alumina microfibers, and accumulation time on the signal enhancement of amaranth were discussed. As a result, a novel electrochemical method was developed for the detection of amaranth. The linear range was from 1 to 150 nM, and the detection limit was 0.75 nM after 1-min accumulation. The analytical application in drink samples was investigated, and the results consisted with the values that obtained by high-performance liquid chromatography

  16. Inelastic neutron scattering studies of methyl chloride synthesis over alumina.

    Science.gov (United States)

    Lennon, David; Parker, Stewart F

    2014-04-15

    Not only is alumina the most widely used catalyst support material in the world, it is also an important catalyst in its own right. One major chemical process that uses alumina in this respect is the industrial production of methyl chloride. This is a large scale process (650,000 metric tons in 2010 in the United States), and a key feedstock in the production of silicones that are widely used as household sealants. In this Account, we show how, in partnership with conventional spectroscopic and reaction testing methods, inelastic neutron scattering (INS) spectroscopy can provide additional insight into the active sites present on the catalyst, as well as the intermediates present on the catalyst surface. INS spectroscopy is a form of vibrational spectroscopy, where the spectral features are dominated by modes involving hydrogen. Because of this, most materials including alumina are largely transparent to neutrons. Advantageously, in this technique, the entire "mid-infrared", 0-4000 cm(-1), range is accessible; there is no cut-off at ~1400 cm(-1) as in infrared spectroscopy. It is also straightforward to distinguish fundamental modes from overtones and combinations. A key parameter in the catalyst's activity is the surface acidity. In infrared spectroscopy of adsorbed pyridine, the shifts in the ring stretching modes are dependent on the strength of the acid site. However, there is a very limited spectral range available. We discuss how we can observe the low energy ring deformation modes of adsorbed pyridine by INS spectroscopy. These modes can undergo shifts that are as large as those seen with infrared inspectroscopy, potentially enabling finer discrimination between acid sites. Surface hydroxyls play a key role in alumina catalysis, but in infrared spectroscopy, the presence of electrical anharmonicity complicates the interpretation of the O-H stretch region. In addition, the deformations lie below the infrared cut-off. Both of these limitations are irrelevant

  17. On the comparison of the ballistic performance of 10% zirconia toughened alumina and 95% alumina ceramic target

    International Nuclear Information System (INIS)

    Ballistic performance of different type of ceramic materials subjected to high velocity impact was investigated in many theoretical, experimental and numerical studies. In this study, a comparison of ballistic performance of 95% alumina ceramic and 10% zirconia toughened alumina (ZTA) ceramic tiles was analyzed theoretically and experimentally. Spherical cavity model based on the concepts of mechanics of compressible porous media of Galanov was used to analyze the relation of target resistance and static mechanical properties. Experimental studies were carried out on the ballistic performance of above two types of ceramic tiles based on the depth of penetration (DOP) method, when subjected to normal impact of tungsten long rod projectiles. Typical damaged targets were presented. The residual depth of penetration on after-effect target was measured in all experiments, and the ballistic efficiency factor of above two types ceramic plates were determined. Both theoretical and experimental results show that the improvement on ballistic resistance was clearly observed by increasing fracture toughness in ZTA ceramics.

  18. Iron migration from the anode surface in alumina electrolysis

    Energy Technology Data Exchange (ETDEWEB)

    Zhuravleva, Elena N.; Drozdova, Tatiana N.; Ponomareva, Svetlana V. [Siberian Federal University, Krasnoyarsk, 660041 (Russian Federation); Kirik, Sergei D., E-mail: kiriksd@yandex.ru [Siberian Federal University, Krasnoyarsk, 660041 (Russian Federation); Institute of Chemistry and Chemical Technology SB RAS, Krasnoyarsk, 660036 (Russian Federation)

    2013-01-15

    Highlights: Black-Right-Pointing-Pointer Corrosion destruction of two-component iron-based alloys in high-temperature aluminum electrolysis in the cryolite alumina melt has been studied. Black-Right-Pointing-Pointer It was found that at the first stage oxidative polarization of iron atoms on the anode surface into Fe{sup 2+} takes place. Black-Right-Pointing-Pointer Fe{sup 2+} interacts with cryolite melt producing FeF{sub 2}. Black-Right-Pointing-Pointer FeF{sub 2} gives oxides FeAl{sub 2}O{sub 4}, Fe{sub 3}O{sub 4}, Fe{sub 2}O{sub 3}. Black-Right-Pointing-Pointer The participation of oxygen in the corrosion has not been observed. - Abstract: Corrosion destruction of two-component iron-based alloys used as an anode in high-temperature alumina electrolysis in the melt of NaF/KF/AlF{sub 3} electrolyte has been considered. Ni, Si, Cu, Cr, Mn, Al, Ti in the amount of up to 10% have been tested as the dopants to an anode alloys. The composition of the corrosion products has been studied using X-ray diffraction, scanning electron microscopy and electron microprobe analysis. It has been established that the anode corrosion is induced by a surface electrochemical polarization and iron atom oxidation. Iron ions come into an exchange interaction with the fluoride components of the melted electrolyte, producing FeF{sub 2}. The last interacts with oxyfluoride species transforming into the oxide forms: FeAl{sub 2}O{sub 4}, Fe{sub 3}O{sub 4}, Fe{sub 2}O{sub 3}. Due to the low solubility, the iron oxides are accumulated in the near-electrode sheath. The only small part of iron from anode migrates to cathode that makes an production of high purity aluminum of a real task. The alloy dopants are also subjected to corrosion in accordance with electromotive series resulting corrosion tunnels on the anode surface. The oxides are final compounds which collect in the same area. The corrosion products form an anode shell which is electronic conductor at electrolysis temperature. The

  19. Iron migration from the anode surface in alumina electrolysis

    International Nuclear Information System (INIS)

    Highlights: ► Corrosion destruction of two-component iron-based alloys in high-temperature aluminum electrolysis in the cryolite alumina melt has been studied. ► It was found that at the first stage oxidative polarization of iron atoms on the anode surface into Fe2+ takes place. ► Fe2+ interacts with cryolite melt producing FeF2. ► FeF2 gives oxides FeAl2O4, Fe3O4, Fe2O3. ► The participation of oxygen in the corrosion has not been observed. - Abstract: Corrosion destruction of two-component iron-based alloys used as an anode in high-temperature alumina electrolysis in the melt of NaF/KF/AlF3 electrolyte has been considered. Ni, Si, Cu, Cr, Mn, Al, Ti in the amount of up to 10% have been tested as the dopants to an anode alloys. The composition of the corrosion products has been studied using X-ray diffraction, scanning electron microscopy and electron microprobe analysis. It has been established that the anode corrosion is induced by a surface electrochemical polarization and iron atom oxidation. Iron ions come into an exchange interaction with the fluoride components of the melted electrolyte, producing FeF2. The last interacts with oxyfluoride species transforming into the oxide forms: FeAl2O4, Fe3O4, Fe2O3. Due to the low solubility, the iron oxides are accumulated in the near-electrode sheath. The only small part of iron from anode migrates to cathode that makes an production of high purity aluminum of a real task. The alloy dopants are also subjected to corrosion in accordance with electromotive series resulting corrosion tunnels on the anode surface. The oxides are final compounds which collect in the same area. The corrosion products form an anode shell which is electronic conductor at electrolysis temperature. The electrolysis of alumina occurs beyond the corrosion shell. The rate limiting step in the corrosion is the electrolyte penetration through corrosion shell to the anode surface. The participation of the released oxygen in the corrosion has

  20. Laser Welding of Alumina Ceramic Substrates with Two Fixed Beams

    Science.gov (United States)

    Sedore, Blake William Clark

    Laser welding was investigated as a potential joining technology for alumina ceramic substrates. The objective of this study was to develop a method to preheat the ceramic using a single defocused laser beam prior to welding. Engineering ceramics are employed in a variety of systems and environments due to their unique properties. Joining technologies must be developed to facilitate the manufacture of complex or large ceramic components. Laser welding is advantageous as it forms joints rapidly, and does not introduce intermediate materials to form the bond, which can have deleterious effects. The Laser Machining System (LMS) at Queen's University was adapted for this study. A defocused far-infrared (FIR) laser beam was positioned to overlay a focused near-infrared (NIR) laser beam; the defocused FIR beam preheated the ceramic substrate and the focused NIR beam formed the weld. A finite element model was developed in COMSOL MultiPhysics to simulate the preheating processes and to develop a preheating protocol. The protocol was implemented using the FIR beam and adjusted to achieve preheating temperatures of 1450, 1525, and 1600°C. Welds were performed on 1 mm thick alumina plates using the preheating protocols and NIR beam powers of 25, 50, and 75 W. Weld speed was held constant throughout the study at 0.5 mm/s. The preheating protocols were successful at achieving near-constant preheating temperatures, with standard deviations below 32 degrees. Partially penetrating welds were formed with the NIR beam at 25 W, and fully penetrating welds at 50 and 75 W. Large pores were present in the 25 W and 50 W welds. Minimal porosity was observed in the welds formed at 75 W. All of the welded plates experienced a transverse fracture that extended perpendicular to weld, and a longitudinal fracture extending parallel to the weld. This study shows that a fixed defocused laser beam can successfully preheat alumina substrates to the high temperatures required for welding; however

  1. Pulsed laser deposition of alumina coating for corrosion protection against liquid uranium

    International Nuclear Information System (INIS)

    Alumina coatings find wide applications as tribological coatings and as corrosion protective coatings for structural materials against chemical attack. We have investigated alumina coatings deposited on Stainless Steel (SS) substrates via pulsed laser deposition (PLD) technique. Characterization tests performed on these coatings including their compatibility with liquid uranium suggests alumina to be a potential candidate as a coating material for handling and containment of liquid uranium. We present here results of our detailed parametric study including dependence of average mass removal rate on laser fluence and ablation geometry and average deposition efficiency during PLD. These measurements provide vital inputs facilitating proper choice of process parameters for PLD runs. Deposited coatings have been characterized in terms of their microstructure, surface profile, adhesion to substrate, crystalline phase and corrosion resistance against liquid uranium. Our PLD based alumina coatings have shown a high degree of compaction and excellent corrosion resistance to molten uranium even upto a temperature of 1165 °C. - Highlights: • Alumina films deposited on stainless steel via pulsed laser deposition (PLD) technique. • PLD alumina films investigated as potential corrosion protective coatings. • Deposited coatings have been characterized in terms of their microstructure and crystalline phase. • Corrosion resistance of coatings against liquid uranium was tested. • Results suggest PLD alumina films have a promising potential for containment of molten uranium

  2. Preparation and electrochemical performance of sulfur-alumina cathode material for lithium-sulfur batteries

    Energy Technology Data Exchange (ETDEWEB)

    Dong, Kang [Faculty of Material Science and Chemistry, China University of Geosciences, 388 Lumo Road, 430074 Wuhan (China); Wang, Shengping, E-mail: spwang@cug.edu.cn [Faculty of Material Science and Chemistry, China University of Geosciences, 388 Lumo Road, 430074 Wuhan (China); Zhang, Hanyu; Wu, Jinping [Faculty of Material Science and Chemistry, China University of Geosciences, 388 Lumo Road, 430074 Wuhan (China)

    2013-06-01

    Highlights: ► Micron-sized alumina was synthesized as adsorbent for lithium-sulfur batteries. ► Sulfur-alumina material was synthesized via crystallizing nucleation. ► The Al{sub 2}O{sub 3} can provide surface area for the deposition of Li{sub 2}S and Li{sub 2}S{sub 2}. ► The discharge capacity of the battery is improved during the first several cycles. - Abstract: Nano-sized sulfur particles exhibiting good adhesion with conducting acetylene black and alumina composite materials were synthesized by means of an evaporated solvent and a concentrated crystallization method for use as the cathodes of lithium-sulfur batteries. The composites were characterized and examined by X-ray diffraction, environmental scanning electron microscopy and electrochemical methods, such as cyclic voltammetry, electrical impedance spectroscopy and charge–discharge tests. Micron-sized flaky alumina was employed as an adsorbent for the cathode material. The initial discharge capacity of the cathode with the added alumina was 1171 mAh g{sup −1}, and the remaining capacity was 585 mAh g{sup −1} after 50 cycles at 0.25 mA cm{sup −2}. Compared with bare sulfur electrodes, the electrodes containing alumina showed an obviously superior cycle performance, confirming that alumina can contribute to reducing the dissolution of polysulfides into electrolytes during the sulfur charge–discharge process.

  3. Effect of different sources of alumina on the microstructure and mechanical properties of the triaxial porcelain

    Directory of Open Access Journals (Sweden)

    G. Gralik

    2014-12-01

    Full Text Available Porcelains composed of kaolin-quartz-feldspar are called triaxial porcelains. The use of alumina as a substitute for quartz in porcelains has been developed for some time. The results show a significant improvement in their mechanical properties, but alumina has a high cost. The possibility of using alternative materials as a source of alumina with lower cost was investigated. In this work, alternative raw materials were used as a source of alumina: refractory bauxite, primary aluminum hydroxide, reprecipitated aluminum hydroxide. Compositions with commercial alumina and quartz were also formulated to better understand the effects of adding these alternative materials. The raw materials were milled, dried, and characterized by analysis of the particle size distribution, X-ray diffraction, and X-ray fluorescence. The compositions were formulated by replacing the different sources of alumina in the formulation of porcelain. The compositions studied were shaped by pressing and sintered at different temperatures (1150-1400 ºC. The results showed that the use of bauxite and aluminum hydroxide as an alternative source of Al2O3 is viable. The impurities contained in refractory bauxite contributed to the lower values of flexural strength found in compositions having refractory bauxite as a source of alumina. The compositions with reprecipitated aluminum hydroxide showed a high mechanical resistance at low sintering temperatures, while compositions with aluminum hydroxide obtained by the Bayer process achieved good results of mechanical strength in a wide temperature range.

  4. Evaluation of hemocompatibility and in vitro immersion on microwave-assisted hydroxyapatite–alumina nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Radha, G. [National Centre for Nanoscience and Nanotechnology, University of Madras, Guindy campus, Chennai - 600025 (India); Balakumar, S., E-mail: balasuga@yahoo.com [National Centre for Nanoscience and Nanotechnology, University of Madras, Guindy campus, Chennai - 600025 (India); Venkatesan, Balaji; Vellaichamy, Elangovan [Department of Biochemistry, University of Madras, Guindy campus, Chennai - 600025 (India)

    2015-05-01

    This study reports the microwave-assisted synthesis and characterization of nHAp (nano-hydroxyapatite)–alumina composites. The crystalline phase and interaction of alumina with nHAp was analyzed using X-ray diffraction (XRD) and Raman microscopy analysis, respectively. High resolution transmission electron microscopy (HRTEM) micrographs exhibit morphological changes of nHAp composites with increasing alumina concentrations. Microhardness studies reveal the enhanced mechanical strength of nHAp10 and nHAp20 nanocomposites than pure nHAp. In vitro bioactivity of the nanocomposites was studied by immersing samples in simulated body fluid (Hank's solution) for 21 days. The surface of biomineralized samples were analyzed using field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). Hemolytic assay revealed acceptable compatibility for varying concentrations of all the samples. Cell proliferation assay was systematically investigated for 1 day and 3 days on Saos-2 osteoblast-like cell lines and it was found that nHAp nanocomposites improved the proliferation. - Highlights: • The microwave-assisted hydroxyapatite (nHAp)–alumina nanocomposites were prepared. • Structural and interaction between nHAp and alumina have been explored. • Increased alumina concentration enhanced mechanical strength of the nHAp. • Trace elements from SBF, incorporated on nHAp–alumina nanocomposite surface, were characterized by FESEM and EDX techniques. • Hemocompatibility of the samples were evaluated and the results are in accordance with ASTM standards.

  5. Evaluation of hemocompatibility and in vitro immersion on microwave-assisted hydroxyapatite–alumina nanocomposites

    International Nuclear Information System (INIS)

    This study reports the microwave-assisted synthesis and characterization of nHAp (nano-hydroxyapatite)–alumina composites. The crystalline phase and interaction of alumina with nHAp was analyzed using X-ray diffraction (XRD) and Raman microscopy analysis, respectively. High resolution transmission electron microscopy (HRTEM) micrographs exhibit morphological changes of nHAp composites with increasing alumina concentrations. Microhardness studies reveal the enhanced mechanical strength of nHAp10 and nHAp20 nanocomposites than pure nHAp. In vitro bioactivity of the nanocomposites was studied by immersing samples in simulated body fluid (Hank's solution) for 21 days. The surface of biomineralized samples were analyzed using field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). Hemolytic assay revealed acceptable compatibility for varying concentrations of all the samples. Cell proliferation assay was systematically investigated for 1 day and 3 days on Saos-2 osteoblast-like cell lines and it was found that nHAp nanocomposites improved the proliferation. - Highlights: • The microwave-assisted hydroxyapatite (nHAp)–alumina nanocomposites were prepared. • Structural and interaction between nHAp and alumina have been explored. • Increased alumina concentration enhanced mechanical strength of the nHAp. • Trace elements from SBF, incorporated on nHAp–alumina nanocomposite surface, were characterized by FESEM and EDX techniques. • Hemocompatibility of the samples were evaluated and the results are in accordance with ASTM standards

  6. Preparation and electrochemical performance of sulfur-alumina cathode material for lithium-sulfur batteries

    International Nuclear Information System (INIS)

    Highlights: ► Micron-sized alumina was synthesized as adsorbent for lithium-sulfur batteries. ► Sulfur-alumina material was synthesized via crystallizing nucleation. ► The Al2O3 can provide surface area for the deposition of Li2S and Li2S2. ► The discharge capacity of the battery is improved during the first several cycles. - Abstract: Nano-sized sulfur particles exhibiting good adhesion with conducting acetylene black and alumina composite materials were synthesized by means of an evaporated solvent and a concentrated crystallization method for use as the cathodes of lithium-sulfur batteries. The composites were characterized and examined by X-ray diffraction, environmental scanning electron microscopy and electrochemical methods, such as cyclic voltammetry, electrical impedance spectroscopy and charge–discharge tests. Micron-sized flaky alumina was employed as an adsorbent for the cathode material. The initial discharge capacity of the cathode with the added alumina was 1171 mAh g−1, and the remaining capacity was 585 mAh g−1 after 50 cycles at 0.25 mA cm−2. Compared with bare sulfur electrodes, the electrodes containing alumina showed an obviously superior cycle performance, confirming that alumina can contribute to reducing the dissolution of polysulfides into electrolytes during the sulfur charge–discharge process

  7. Atomistic simulation and virtual diffraction characterization of stable and metastable alumina surfaces

    International Nuclear Information System (INIS)

    The structures of select alumina surfaces are studied using molecular statics and molecular dynamics simulations and are characterized using virtual diffraction methods. First, bulk alumina simulations are performed to validate the transferability of the ReaxFF potential to model different alumina phases. Bulk alumina simulations accurately predict α-Al2O3 as the lowest energy crystalline phase; however, they unexpectedly predict an even lower-energy amorphous phase. At 0 K, virtual X-ray diffraction patterns of the bulk crystalline phases and select alumina surfaces are validated by experimental studies. Molecular statics simulations of select alumina surfaces are consistent with prior first-principles studies. However, molecular dynamics simulations show that many surfaces experience significant reconstructions at temperatures below what is expected from experiments. It is believed that premature surface reconstructions are biased by the predicted lower-energy amorphous phase and occur due to the extra degrees of freedom allowed by the free surfaces as well as the available thermal energy during dynamics. Discrete peaks appearing in virtual selected-area electron diffraction patterns indicate that the reconstructions are not fully amorphous due to lattice constraints imposed by the internal bulk structure. Bulk and surface energies are tabulated for each simulation to be used in future predictive mesoscale models of polymorphic alumina

  8. Strengthening mechanisms and fracture surface characteristics of silicate glass matrix composites with inclusion of alumina particles of different particle sizes

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Minghui, E-mail: mhchen@imr.ac.cn [State Key Laboratory for Corrosion and Protection, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Zhu, Shenglong; Wang, Fuhui [State Key Laboratory for Corrosion and Protection, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)

    2013-03-15

    Strengthening mechanisms of silicate glass by the inclusion of alumina particles of different volume fractions and different particle sizes are reported. The formulas of three responsible strengthening mechanisms, based on inclusion/crack interactions and interfacial elemental diffusion, were deduced; these include crack deflection, crack bridging and interdiffusion. The strength of the glass/alumina composites increased with inclusion fraction, but followed strengthening mechanisms that varied with alumina particle size. Crack deflection and bridging mechanisms dominated in strengthening for the glass/alumina (at mean particle size of 6 μm) composites while interdiffusion mechanism played a major role in the glass/alumina (at mean particle size of 1 μm) composites. The theoretical deduction of strengthening mechanisms depending on the particle size of alumina inclusions was demonstrated by the experimental strength data and fracture surface characteristics of the glass/alumina composites.

  9. Strengthening mechanisms and fracture surface characteristics of silicate glass matrix composites with inclusion of alumina particles of different particle sizes

    International Nuclear Information System (INIS)

    Strengthening mechanisms of silicate glass by the inclusion of alumina particles of different volume fractions and different particle sizes are reported. The formulas of three responsible strengthening mechanisms, based on inclusion/crack interactions and interfacial elemental diffusion, were deduced; these include crack deflection, crack bridging and interdiffusion. The strength of the glass/alumina composites increased with inclusion fraction, but followed strengthening mechanisms that varied with alumina particle size. Crack deflection and bridging mechanisms dominated in strengthening for the glass/alumina (at mean particle size of 6 μm) composites while interdiffusion mechanism played a major role in the glass/alumina (at mean particle size of 1 μm) composites. The theoretical deduction of strengthening mechanisms depending on the particle size of alumina inclusions was demonstrated by the experimental strength data and fracture surface characteristics of the glass/alumina composites

  10. Contribution of aluminas and aluminosilicates to the formation of PCDD/Fs on fly ashes.

    Science.gov (United States)

    Potter, Phillip M; Dellinger, Barry; Lomnicki, Slawomir M

    2016-02-01

    Chlorinated aromatics undergo surface-mediated reactions with metal oxides to form Environmentally Persistent Free Radicals (EPFRs) which can further react to produce polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Previous work using laboratory-made fly ash surrogates composed of transition metal oxides deposited on silica powder has confirmed their ability to mimic fly ash in the production of PCDD/Fs. However, little is known about the propensity of aluminas and aluminosilicates, other components of fly ash, to form PCDD/Fs. A fly ash sample containing both alumina and mullite, an aluminosilicate, was tested for PCDD/F formation ability and compared to PCDD/F yields from the thermal degradation of 2-monochlorophenol (2-MCP) precursor over γ-alumina, α-alumina, and mullite. A packed-bed flow reactor was used to investigate the thermal degradation of 2-MCP over the various catalysts at 200-600 °C. Fly ash gave similar PCDD/F yields to surrogates made with similar transition metal content. γ-alumina, which is thermodynamically unfavorable, was very catalytically active and gave low PCDD/F yields despite a high destruction of 2-MCP. Mullite and α-alumina, the thermodynamically favorable form of alumina, yielded higher concentrations of dioxins and products with a higher degree of chlorine substitution than γ-alumina. The data suggest that certain aluminas and aluminosilicates, commonly found in fly ash, are active catalytic surfaces in the formation of PCDD/Fs in the post-flame cool zones of combustion systems and should be considered as additional catalytic surfaces active in the process. PMID:26615490

  11. Phase transformations in spray-dried alumina-zirconia composite powders

    International Nuclear Information System (INIS)

    Hydrated alumina-zirconia composite powders containing 7.5, 10.0, 12.5 wt % zirconia in the final oxidized state were prepared by spray-drying the inorganic salt derived gels. These gels were prepared by hydrolysing the metals salts with ammonia. The average particle size and surface area of this powder is found to be 6 microns and 6.92 m2/g respectively. Infrared spectra reveals the presence of adhesive water. In order to evaluate the phase transformation temperature, the powder samples were calcined at different temperatures ranging from 650 to 1500 degC for 30 minutes. X-ray diffraction patterns of the spay-dried as well as the calcined powders up to 850 degC revealed the powders are amorphous. Crystallized phases started forming after 900 degC and the first crystallized phase is tetragonal zirconia. Broad peaks of Θ-alumina were also found. This tetragonal phase is retained even after the treatment at 1500 degC. Some amount of Θ-alumina is transformed into α-alumina after 1000 degC, and this transformation is over by the formation of well crystallized α-alumina after 1300 degC. A comparison made with pure alumina shows that the presence of zirconia retards the formation of α-alumina, since pure alumina powder contains only α-alumina, after 950 degC treatment. The increasing amount of zirconia has no profound influence on this effect in the compositions studied. Differential thermal analysis (DTA) and thermal gravimetric analysis (TGA) were also used as a complement to the x-ray diffraction in determining the transformation temperature. (author). 12 refs., 7 figs

  12. Fabrication of nanoscale alumina on NiAl(1 0 0) with a scanning tunneling microscope

    International Nuclear Information System (INIS)

    Highlights: ► Nanoscale alumina was fabricated on NiAl(1 0 0) surface with a STM tip. ► Varied powers (bias × current) give two distinct modes of oxidation. ► In the high-power mode alumina forms on the surface near the tip. ► In the low-power mode alumina grows along direction [0 0 1] or [0 1 0] of NiAl(1 0 0). ► The grown alumina strips have minimal width about 3 nm. - Abstract: Nanoscale alumina was fabricated on NiAl (1 0 0) surface using a scanning tunneling microscope in an ultrathin vacuum condition. With the tunneling current greater than 0.4 nA and the power (bias voltage × tunneling current) greater than 0.24 nW, Al and pre-adsorbed O atoms were activated to form alumina (with thickness 0.25–1.0 nm) on the surface directly vicinal to the tip; the width and thickness of the grown alumina strips are controllable by the current and bias. With an evidently smaller power and a smaller bias (≦1.0 V), crystalline alumina were grown along direction [0 0 1] or [0 1 0] of NiAl(1 0 0) in the tip-scanned area of either O-chemisorbed or oxidized surfaces, independent of the direction of tip movement. The alumina strips grown through the latter mode have minimal width near 3 nm.

  13. Contribution to the study of porous or very finely divided alumina

    International Nuclear Information System (INIS)

    An amorphous porous alumina having a large surface area can be made non-stoichiometric by a treatment at 500 - 700 deg C in a vacuum. The oxygen deficit after a treatment at 500 deg C, and the aluminium deficit after a treatment at 700 deg C, give rise to semiconductor properties successively of type n and of the type p. A crystallized δ-alumina in the form of non-porous spherical grains compressed at a pressure of 1 to 5 metric tons/cm2 is also non-stoichiometric with a deficit of oxygen or of aluminium. None of these phenomena could be observed with a sample which had not been compressed. The favorable influence of oxygen on the recrystallization process of amorphous alumina, and on the δ-α, transformation of crystallized alumina has been demonstrated. Furthermore, the strains produced by the compression of the δ-alumina make possible its transformation in air into a at a temperature lower than the temperature necessary to observe this phenomenon with non-compressed δ-alumina. Amorphous alumina undergoes an intergranular sintering at 500 deg C and an intergranular sintering at 1 000 deg C. Only the latter occurs in the case of spherical alumina grains. For these, the strains brought about by the compression cause a lowering of 100 deg C in the threshold sintering temperature, with respect to the temperature required to produce the phenomena in a non-compressed sample. The amount of sintering in a crystallized alumina pellet depends, as well, on the rate of rise of temperature. This study tends to show that new properties, or at least unusual solid-state properties, can be observed on disorganised solids or on solids which are crystallized but which have a large surface area and a certain amount of strain. (author)

  14. Topotactic preparation of textured alumina ceramics from dehydroxylation of gibbsite films

    International Nuclear Information System (INIS)

    In this paper, textured alumina ceramics were prepared from dehydroxylation of gibbsite films and the pseudomorphic and topotactic nature of the dehydroxylation of textured gibbsite films has been investigated. First, the precursor film with a (001)-textured structure was obtained via vacuum filtration deposition of diluted aqueous suspensions of gibbsite nanoplatelets. Subsequently, (001)-textured α-alumina ceramics were successfully achieved by sintering of the deposited gibbsite films without addition of α-alumina seeds. The Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) results show that, during the phase transition from gibbsite to α-alumina, both layered morphology and crystal's axis orientation have been retained to a considerable extent. For the first time, a direct XRD evidence of gibbsite topotactic dehydroxylation to the α-alumina phase is presented. It is believed that the method described here exploits gibbsite's pseudomorphic and topotactic dehydroxylation, not on individual particles scale but on a bulk form. The resulting structure can be considered as inorganic scaffolds which can have applications for fabrication of dense, textured alumina-based ceramics and other layered/textured nanocomposites. - Highlights: • Gibbsite nanoplatelets were assembled on their basal plane to form (001)-textured films. • Textured alumina ceramics were prepared by sintering textured gibbsite films without addition of α-alumina seeds. • Both pseudomorphic and topotactic aspects were exploited in bulk form instead of individual nanoparticulate size. • Direct XRD evidence of the topotactic dehydroxylation from gibbsite to α-alumina is presented in this work

  15. Reactive Spreading of a Lead-Free Solder on Alumina

    Energy Technology Data Exchange (ETDEWEB)

    Gremillard, L.; Saiz, E.; Radmilovic, V.R.; Tomsia, A.P.

    2005-12-01

    The wetting of Sn3Ag-based alloys on Al{sub 2}O{sub 3} has been studied using the sessile-drop configuration. Small additions of Ti decrease the contact angle of Sn3Ag alloys on alumina from 115 to 23 degrees. Adsorption of Ti-species at the solid-liquid interface prior to reaction is the driving force for the observed decrease in contact angle, and the spreading kinetics is controlled by the kinetics of Ti dissolution into the molten alloy. The addition of Ti increases the transport rates at the solid-liquid interface, resulting in the formation of triple-line ridges that pin the liquid front and promote a wide variability in the final contact angles.

  16. Indentation fatigue in silicon nitride, alumina and silicon carbide ceramics

    Indian Academy of Sciences (India)

    A K Mukhopadhyay

    2001-04-01

    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 microhardness tester at various loads in the range 1–20 N. Subsequently, the gradual evolution of the damage was characterized using an optical microscope in conjunction with the image analysing technique. The materials were classified in the order of the decreasing resistance against repeated indentation fatigue at the highest applied load of 20 N. It was further shown that there was a strong influence of grain size on the development of resistance against repeated indentation fatigue on the same spot. Finally, the poor performance of the sintered silicon carbide was found out to be linked to its previous thermal history.

  17. Tailorable advanced blanket insulation using aluminoborosilicate and alumina batting

    Science.gov (United States)

    Calamito, Dominic P.

    1989-01-01

    Two types of Tailorable Advanced Blanket Insulation (TABI) flat panels for Advanced Space Transportation Systems were produced. Both types consisted of integrally woven, 3-D fluted core having parallel faces and connecting ribs of Nicalon yarns. The triangular cross section flutes of one type was filled with mandrels of processed Ultrafiber (aluminoborosilicate) stitchbonded Nextel 440 fibrous felt, and the second type wall filled with Saffil alumina fibrous felt insulation. Weaving problems were minimal. Insertion of the fragile insulation mandrels into the fabric flutes was improved by using a special insertion tool. An attempt was made to weave fluted core fabrics from Nextel 440 yarns but was unsuccessful because of the yarn's fragility. A small sample was eventually produced by an unorthodox weaving process and then filled with Saffil insulation. The procedures for setting up and weaving the fabrics and preparing and inserting insulation mandrels are discussed. Characterizations of the panels produced are also presented.

  18. Multi-Objective Optimization for Alumina Laser Sintering Process

    Science.gov (United States)

    Fayed, E. M.; Elmesalamy, A. S.; Sobih, M.; Elshaer, Y.

    2016-09-01

    Selective laser sintering processes has become one of the most popular additive manufacturing processes due to its flexibility in creation of complex components. This process has many interacting parameters, which have a significant influence on the process output. In this work, high purity alumina is sintered through a pulsed Nd:YAG laser sintering process. The aim of this work is to understand the effect of relevant sintering process parameters (laser power and laser scanning speed) on the quality of the sintered layer (layer surface roughness, layer thickness and vector/line width, and density). Design of experiments and statistical modeling techniques are employed to optimize the process control factors and to establish a relationship between these factors and output responses. Model results have been verified through experimental work and show reasonable prediction of process responses within the limits of sintering parameters.

  19. Controllable fabrication of porous alumina templates for nanostructures synthesis

    International Nuclear Information System (INIS)

    Porous alumina templates (AAO) has attracted significant interest due to the fact that they are readily fabricated through a simple procedure and are extremely popular templates in nanoscience studies. In this paper, the effects of different pore-widening treatments on the pore quality of the AAO templates were investigated. Results show that, through a highly controllable chemical pore-widening process at low temperature, different pore dimensions and diameters of the AAO templates can be easily achieved in a nanometer-scale way without changing the interpore distance. Combining with anodization voltage control, AAO templates with desired size distribution can be obtained, which will be extremely useful in template technology and masks for lithographic application. Also, silver nanorods/wires of different dimensions have been fabricated from above AAO templates after pore diameter adjustments. Such nanostructure materials hold high potential for electronics, optics, mechanics and sensing technology.

  20. Optimization of yttria additions in zirconia toughened alumina

    International Nuclear Information System (INIS)

    The stress-induced transformation of included zirconia from tetragonal phase to monoclinic phase offers an important contribution to toughening of ceramic composites. Stabilization of the tetragonal phase is affected by the zirconia content and its grain size, and by stabilizing agents such as yttria. The zirconia phases in zirconia toughened alumina (ZTA) with several levels of zirconia (5 to 40 vol%) and yttria additions (O to 3.0 mol% of zirconia) were analyzed by quantitative X-ray diffraction. The combined effect of zirconia and yttria on hardness, toughness, and retention of the tetragonal phase was investigated. The amount of yttria required to stabilize the optimum mixture of tetragonal and monoclinic zirconia was determined for 5 vol% zirconia. Copyright (1998) Australasian Ceramic

  1. Ordered Nanomaterials Thin Films via Supported Anodized Alumina Templates

    Directory of Open Access Journals (Sweden)

    Mohammed eES-SOUNI

    2014-10-01

    Full Text Available Supported anodized alumina template films with highly ordered porosity are best suited for fabricating large area ordered nanostructures with tunable dimensions and aspect ratios. In this paper we first discuss important issues for the generation of such templates, including required properties of the Al/Ti/Au/Ti thin film heterostructure on a substrate for high quality templates. We then show examples of anisotropic nanostructure films consisting of noble metals using these templates, discuss briefly their optical properties and their applications to molecular detection using surface enhanced Raman spectroscopy. Finally we briefly address the possibility to make nanocomposite films, exemplary shown on a plasmonic-thermochromic nanocomposite of VO2-capped Au-nanorods.

  2. Mechanical Properties and Fracture Behaviour of Multilayer Alumina Composites

    Institute of Scientific and Technical Information of China (English)

    ZHENG Xinguo; ZHAO Fei; ZHANG Jinyong

    2015-01-01

    Adopting a ceramic/polymer multilayer structure design to simulate the structure of nacre is usually believed to be an effective way to increase the toughness of ceramic composites at the expense of the material's bending strength. However, in this study, we found that both the bending strength and the toughness could be improved simultaneously when using a certain Al2O3/Kevlar multilayer composite design compared to pure alumina samples with the same dimensions. The fracture behaviour of the Al2O3/Kevlar multilayer composite was studied to ifnd a reason for this improvement. The results showed that the complex and asymmetrical stresses occurring in the Kevlar-reinforced layers were the main reason for the differences in fracture behaviour. We expect our results to open up new ways for the design of future high performance ceramic composites.

  3. Beam profile monitor using alumina screen and CCD camera

    International Nuclear Information System (INIS)

    A pair of beam profile monitors using alumina ceramic screens (Al2O3) and CCD cameras has been developed for diagnosis of a linac beam at the 1.3 GeV electron synchrotron of the Institute for Nuclear Study, the University of Tokyo (INS-ES). Since both the light decay-time of the screen and a shutter speed of the camera are relatively short, about 10 msec or less and 1 msec, respectively, this system is able to measure the beam profile for each pulse of the linac beam operated at a repetition rate of 21.5 Hz. Detailed analysis of the beam profile is made using the stored data on the personal computer. On the other hand, a light spot on the screen is displayed directly on a monitor display. (author)

  4. Alumina Volatility in Water Vapor at Elevated Temperatures

    Science.gov (United States)

    Opila, Elizabeth J.; Myers, Dwight L.

    2003-01-01

    The volatility of alumina in high temperature water vapor was determined by a weight loss technique. Sapphire coupons were exposed at temperatures between 1250 and 1500 C, water partial pressures between 0.15 and 0.68 atm in oxygen, total pressure of 1 atm, and flowing gas velocities of 4.4 cm/s. The pressure dependence of sapphire volatility was consistent with AI(OH)3(g) formation. The enthalpy of reaction to form Al(OH)3(g) from sapphire and water vapor was determined to be 210 +/- 20 kJ/mol, comparing favorably to other studies. Microstructural examination of tested sapphire coupons revealed surface etching features consistent with a volatilization process.

  5. Nanoporous Anodic Alumina: A Versatile Platform for Optical Biosensors

    Directory of Open Access Journals (Sweden)

    Abel Santos

    2014-05-01

    Full Text Available Nanoporous anodic alumina (NAA has become one of the most promising nanomaterials in optical biosensing as a result of its unique physical and chemical properties. Many studies have demonstrated the outstanding capabilities of NAA for developing optical biosensors in combination with different optical techniques. These results reveal that NAA is a promising alternative to other widely explored nanoporous platforms, such as porous silicon. This review is aimed at reporting on the recent advances and current stage of development of NAA-based optical biosensing devices. The different optical detection techniques, principles and concepts are described in detail along with relevant examples of optical biosensing devices using NAA sensing platforms. Furthermore, we summarise the performance of these devices and provide a future perspective on this promising research field.

  6. Electroless Fabrication of Cobalt Alloys Nanowires within Alumina Template

    Directory of Open Access Journals (Sweden)

    Nazila Dadvand

    2007-01-01

    Full Text Available A new method of nanowire fabrication based on electroless deposition process is described. The method is novel compared to the current electroless procedure used in making nanowires as it involves growing nanowires from the bottom up. The length of the nanowires was controlled at will simply by adjusting the deposition time. The nanowires were fabricated within the nanopores of an alumina template. It was accomplished by coating one side of the template by a thin layer of palladium in order to activate the electroless deposition within the nanopores from bottom up. However, prior to electroless deposition process, the template was pretreated with a suitable wetting agent in order to facilitate the penetration of the plating solution through the pores. As well, the electroless deposition process combined with oblique metal evaporation process within a prestructured silicon wafer was used in order to fabricate long nanowires along one side of the grooves within the wafer.

  7. Formation of complex anodic films on porous alumina matrices

    Indian Academy of Sciences (India)

    Alexander Zahariev; Assen Girginov

    2003-04-01

    The kinetics of growth of complex anodic alumina films was investigated. These films were formed by filling porous oxide films (matrices) having deep pores. The porous films (matrices) were obtained voltastatically in (COOH)2 aqueous solution under various voltages. The filling was done by re-anodization in an electrolyte solution not dissolving the film. Data about the kinetics of re-anodization depending on the porosity of the matrices were obtained. On the other hand, the slopes of the kinetic curves during reanodization were calculated by two equations expressing the dependence of these slopes on the ionic current density. A discrepancy was ascertained between the values of the calculated slopes and those experimentally found. For this discrepancy a possible explanation is proposed, related to the temperature increase in the film, because of that the real current density significantly increases during re-anodization.

  8. The high-pressure phase of alumina and implications for Earth's D″ layer

    OpenAIRE

    Artem R. Oganov; Ono, Shigeaki

    2005-01-01

    Using ab initio simulations and high-pressure experiments in a diamond anvil cell, we show that alumina (Al2O3) adopts the CaIrO3-type structure above 130 GPa. This finding substantially changes the picture of high-pressure behavior of alumina; in particular, we find that perovskite structure is never stable for Al2O3 at zero Kelvin. The CaIrO3-type phase suggests a reinterpretation of previous shock-wave experiments and has important implications for the use of alumina as a window material i...

  9. Detection of foreign phases in doped a-alumina powders by thermoluminescence

    OpenAIRE

    Sallé, Christian; Ferey, Frédérique; Grosseau, Philippe; Guilhot, Bernard; Iacconi, Philibert; Benabdesselam, Mourad; Fantozzi, Gilbert

    2003-01-01

    The thermoluminescence (TL) after excitation by UV or X-rays radiation of doped a-alumina powders is investigated. In the case of zirconia, the alumina-zirconia composites present five of the characteristic peaks of zirconia at -170, -145, -90, 0 and 95°C. After a thermal treatment of mixed oxides, a new peak is observed at -35°C in TL. This peak reveals the presence of stabilized tetragonal zirconia in the material. In the case of calcium, the TL curves of a-alumina doped by calcium present ...

  10. Introduction of bridging and pendant organic groups into mesoporous alumina materials.

    Science.gov (United States)

    Grant, Stacy M; Woods, Stephan M; Gericke, Arne; Jaroniec, Mietek

    2011-11-01

    Incorporation of organic functionalities into soft-templated mesoporous alumina was performed via organosilane-assisted evaporation induced self-assembly using aluminum alkoxide precursors and block copolymer templates. This strategy permits one to obtain mesoporous alumina-based materials with tailorable adsorption, surface and structural properties. Isocyanurate, ethane, mercaptopropyl, and ureidopropyl-functionalized mesoporous alumina materials were synthesized with relatively high surface area and large pore volume with uniform and wormhole-like mesopores. The presence of organosilyl groups within these hybrid materials was confirmed by IR or Raman spectroscopy and their concentration was determined by elemental analysis. PMID:21988174

  11. Ceramic characteristics of alumina obtained by using ammonium aluminum sulphate as precursor

    International Nuclear Information System (INIS)

    A method has been developed for the production of alumina for Advanced Ceramics through the synthesis of ammonium aluminum sulphate. A concentrated commercial ammonium hydroxide were used. The yield of the synthesis process was determined by the titration curves. The characterization of the synthesis products was carried out by X-ray diffraction, differential thermal analysis and particle size distribution. After the calcination of ammonium aluminum sulphate and the obtainment of alumina, test bodies were made, sintered at 1650 deg C, and then their ceramical properties were determined and compared against those of reference commercial alumina. (author)

  12. Pembuatan Keramik Paduan Cordierit-Alumina Sebagai Bahan Refraktori dan Karakterisasinya

    OpenAIRE

    Kaston Sijabat

    2008-01-01

    Telah dilakukan pembuatan Keramik paduan Cordierit 2MgO.2Al2O3.5SiO2- Alumina (Al2O3) dengan menggunakan bahan baku lokal melalui reaksi padatan. Bahan baku yang digunakan untuk mendapatkan serbuk Cordierit adalah pasir silika sebagai sumber SiO3, magnesit (MgCO3) sebagai sumber MgO dan alumina teknis sebagai sumber AL2O3. Dari hasil pembuatan keramik paduan Cordierit - Alumina maka dilakukan karakterisasi meliputi Porositas, Densitas, Pengujian Koefisien Ekspansi Termal, Kuat Patah dan Anali...

  13. Cryogenic infrared filter made of alumina for use at millimeter wavelength

    OpenAIRE

    Inoue, Yuki; Matsumura, Tomotake; Hazumi, Masashi; Lee, Adrian T.; Okamura, Takahiro; Suzuki, Aritoki; Tomaru, Takayuki; YAMAGUCHI, Hiroshi

    2013-01-01

    We propose a high thermal conductivity infrared (IR) filter using alumina for use in millimeter wave detection systems. We constructed a prototype two-layer anti-reflection (AR) coated alumina filter with a diameter of 100mm and a thickness of 2mm, and characterized its thermal and optical properties. The transmittance of this filter at 95GHz and 150GHz is 97% and 95% while the estimated 3dB cutoff frequency is at 450GHz. The high thermal conductivity of alumina minimizes thermal gradients. W...

  14. Modeling of lunar basalt petrogenesis - Sr isotope evidence from Apollo 14 high-alumina basalts

    International Nuclear Information System (INIS)

    This paper reexamines the Sr isotope data available for the Apollo 14 high-alumina basalts in light of the assimilation and fractional crystallization (AFC) process model proposed by Neal et al. (1987, 1988, 1989). Positive linear correlations of Sr-87/Sr-86 with Rb-87/Rb-86 and the Sr abundance (both leading to KREEP) are used as evidence of such an AFC process in the petrogenesis of Apollo 14 high-alumina basalts. The existing Sr isotope data for Apollo 14 high-alumina basalts suggest that there were three AFC cycles. 33 refs

  15. A method for the control of alumina concentration in aluminum reduction cells

    OpenAIRE

    Jens G. Balchen

    1992-01-01

    The paper presents a new method for the control of the concentration of the alumina in electrolysis cells for the production of aluminium. The method is based upon the well known fact that apparent resistivity of the cell is a function of the alumina concentration so that the resistivity has the lowest value around the concentration of three per cent and increases in both directions. The method uses the cross correlation between a perturbation of the feed flow of alumina into the cell and the...

  16. The low-temperature loss tangent of adsorbed water in alumina

    Science.gov (United States)

    Khasawneh, Mazin; Sarabi, Bahman; Khalil, M. S.; Stoutimore, M. J. A.; Gladchenko, Sergiy; Wellstood, F. C.; Lobb, C. J.; Osborn, Kevin

    2012-02-01

    Superconducting quantum information circuits use various amorphous dielectrics for capacitors, and alumina is the ubiquitous barrier material for Josephson junctions within these devices. The exposure of the devices to air allows water molecules to penetrate the dielectric films along grain boundaries, and become adsorbed onto internal surfaces. In this study we plan to use ALD-grown alumina and titanium oxide to study the penetration of water through films. Using blocking layers to selectively prevent water penetration, we then plan to measure the difference in the low-temperature loss tangent between an alumina film which is exposed to air and one which is not.

  17. Photonic stop bands in quasi-random nanoporous anodic alumina structures

    CERN Document Server

    Maksymov, Ivan; Pallares, Josep; Marsal, Lluis F

    2011-01-01

    The existence of photonic stop bands in the self-assembled arrangement of pores in porous anodic alumina structures is investigated by means of rigorous 2D finite- difference time-domain calculations. Self-assembled porous anodic alumina shows a random distribution of domains, each of them with a very definite triangular pattern, constituting a quasi-random structure. The observed stop bands are similar to those of photonic quasicrystals or random structures. As the pores of nanoporous anodic alumina can be infiltrated with noble metals, nonlinear or active media, it makes this material very attractive and cost-effective for applications including inhibition of spontaneous emission, random lasing, LEDs and biosensors.

  18. Synthesis of highly thermally stable lanthanum-doped ordered mesoporous alumina

    International Nuclear Information System (INIS)

    Highly thermally stable lanthanum-doped ordered mesoporous alumina has been prepared in a sol-gel system with salicylic acid and citric acid as interfacial protectors. When the molar ratio of alumina to lanthanum is 25.5, most La3+ ions in the resulting alumina structure showed tetracoordination. Moreover, the as-obtained sample exhibits a surface area of 305 m2 g-1 when calcined at 400 oC and can maintain an ordered mesostructure with a high surface area of 205 m2 g-1 even when treated at 1000 oC, demonstrating its high thermal stability.

  19. Optical Basicity and Nepheline Crystallization in High Alumina Glasses

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, Carmen P.; McCloy, John S.; Schweiger, M. J.; Crum, Jarrod V.; Winschell, Abigail E.

    2011-02-25

    The purpose of this study was to find compositions that increase waste loading of high-alumina wastes beyond what is currently acceptable while avoiding crystallization of nepheline (NaAlSiO4) on slow cooling. Nepheline crystallization has been shown to have a large impact on the chemical durability of high-level waste glasses. It was hypothesized that there would be some composition regions where high-alumina would not result in nepheline crystal production, compositions not currently allowed by the nepheline discriminator. Optical basicity (OB) and the nepheline discriminator (ND) are two ways of describing a given complex glass composition. This report presents the theoretical and experimental basis for these models. They are being studied together in a quadrant system as metrics to explore nepheline crystallization and chemical durability as a function of waste glass composition. These metrics were calculated for glasses with existing data and also for theoretical glasses to explore nepheline formation in Quadrant IV (passes OB metric but fails ND metric), where glasses are presumed to have good chemical durability. Several of these compositions were chosen, and glasses were made to fill poorly represented regions in Quadrant IV. To evaluate nepheline formation and chemical durability of these glasses, quantitative X-ray diffraction (XRD) analysis and the Product Consistency Test were conducted. A large amount of quantitative XRD data is collected here, both from new glasses and from glasses of previous studies that had not previously performed quantitative XRD on the phase assemblage. Appendix A critically discusses a large dataset to be considered for future quantitative studies on nepheline formation in glass. Appendix B provides a theoretical justification for choice of the oxide coefficients used to compute the OB criterion for nepheline formation.

  20. Iron migration from the anode surface in alumina electrolysis

    Science.gov (United States)

    Zhuravleva, Elena N.; Drozdova, Tatiana N.; Ponomareva, Svetlana V.; Kirik, Sergei D.

    2013-01-01

    Corrosion destruction of two-component iron-based alloys used as an anode in high-temperature alumina electrolysis in the melt of NaF/KF/AlF3 electrolyte has been considered. Ni, Si, Cu, Cr, Mn, Al, Ti in the amount of up to 10% have been tested as the dopants to an anode alloys. The composition of the corrosion products has been studied using X-ray diffraction, scanning electron microscopy and electron microprobe analysis. It has been established that the anode corrosion is induced by a surface electrochemical polarization and iron atom oxidation. Iron ions come into an exchange interaction with the fluoride components of the melted electrolyte, producing FeF2. The last interacts with oxyfluoride species transforming into the oxide forms: FeAl2O4, Fe3O4, Fe2O3. Due to the low solubility, the iron oxides are accumulated in the near-electrode sheath. The only small part of iron from anode migrates to cathode that makes an production of high purity aluminum of a real task. The alloy dopants are also subjected to corrosion in accordance with electromotive series resulting corrosion tunnels on the anode surface. The oxides are final compounds which collect in the same area. The corrosion products form an anode shell which is electronic conductor at electrolysis temperature. The electrolysis of alumina occurs beyond the corrosion shell. The rate limiting step in the corrosion is the electrolyte penetration through corrosion shell to the anode surface. The participation of the released oxygen in the corrosion has not been observed.

  1. Damping Behavior of Alumina Epoxy Nano-Composites

    Science.gov (United States)

    Katiyar, Priyanka; Kumar, Anand

    2016-05-01

    Polymer nano composites, consisting of a polymer matrix with nanoparticle filler, have been predicted to be one of the most beneficial applications of nanotechnology. Addition of nano particulates to a polymer matrix enhances its performance by capitalizing on the nature and properties of the nano-scale fillers. The damping behavior of composites with nano structured phases is significantly different from that of micro structured materials. Viscoelastic homopolymer exhibit a high material damping response over a relatively narrow range of temperature and frequencies. In many practical situations, a polymeric structure is required to possess better strength and stiffness properties together with a reasonable damping behavior. Viscoelastic polymers show higher loss factor beyond the glassy region which comes with a significant drop in the specific modulus. Addition of nano alumina particles to epoxy leads to improved strength and stiffness properties with an increase in glass transition temperature while retaining its damping capability. Experimental investigations are carried out on composite beam specimen fabricated with different compositions of alumina nano particles in epoxy to evaluate loss factor, tan δ. Impact damping method is used for time response analysis. A single point Laser is used to record the transverse displacement of a point on the composite beam specimen. The experimental results are compared with theoretical estimation of loss factor using Voigt estimation. The effect of inter phase is included in theoretical estimation of loss factor. The result reveals that the study of interface properties is very important in deriving the overall loss factor of the composite since interface occupies a significant volume fraction in the composite.

  2. Rational engineering of nanoporous anodic alumina optical bandpass filters

    Science.gov (United States)

    Santos, Abel; Pereira, Taj; Law, Cheryl Suwen; Losic, Dusan

    2016-08-01

    Herein, we present a rationally designed advanced nanofabrication approach aiming at producing a new type of optical bandpass filters based on nanoporous anodic alumina photonic crystals. The photonic stop band of nanoporous anodic alumina (NAA) is engineered in depth by means of a pseudo-stepwise pulse anodisation (PSPA) approach consisting of pseudo-stepwise asymmetric current density pulses. This nanofabrication method makes it possible to tune the transmission bands of NAA at specific wavelengths and bandwidths, which can be broadly modified across the UV-visible-NIR spectrum through the anodisation period (i.e. time between consecutive pulses). First, we establish the effect of the anodisation period as a means of tuning the position and width of the transmission bands of NAA across the UV-visible-NIR spectrum. To this end, a set of nanoporous anodic alumina bandpass filters (NAA-BPFs) are produced with different anodisation periods, ranging from 500 to 1200 s, and their optical properties (i.e. characteristic transmission bands and interferometric colours) are systematically assessed. Then, we demonstrate that the rational combination of stacked NAA-BPFs consisting of layers of NAA produced with different PSPA periods can be readily used to create a set of unique and highly selective optical bandpass filters with characteristic transmission bands, the position, width and number of which can be precisely engineered by this rational anodisation approach. Finally, as a proof-of-concept, we demonstrate that the superposition of stacked NAA-BPFs produced with slight modifications of the anodisation period enables the fabrication of NAA-BPFs with unprecedented broad transmission bands across the UV-visible-NIR spectrum. The results obtained from our study constitute the first comprehensive rationale towards advanced NAA-BPFs with fully controllable photonic properties. These photonic crystal structures could become a promising alternative to traditional optical

  3. Influence of additives on the stability of the phases of alumina

    International Nuclear Information System (INIS)

    Problems with the stability of gamma alumina in catalytic reactions have been solved with the inclusion of additives during the synthesis of alumina. These additives stabilize the temperature of phase transition allowing the use of metastable alumina at high temperatures, but the mechanisms of action of additives are not well defined. It is known that each family of additive or additives behaves in different ways for this stabilization. This work aimed to study the performance of MgO and ZrO2, respectively at different concentrations in alumina synthesized via Pechini. The samples were analyzed by DSC, X-ray diffraction, measurement of specific surface area by BET analysis, and infrared analysis. The results showed an increase in transition temperature for both additives, and a different changes for specific surface area, showing that MgO and ZrO2 work on improving the stability but with distinct mechanisms. (author)

  4. The drying of cryolite-, alumina containing concentrate getting from aluminium production wastes

    International Nuclear Information System (INIS)

    The purpose of present work is studying of drying of cryolite-, alumina containing concentrate getting after pulp filtration at isothermal and polythermal conditions with investigations of kinetics and chemistry process

  5. Kinetics of titanium and zirconium oxides dissolution in cryolite-alumina melt

    International Nuclear Information System (INIS)

    Data on kinetics of dissolution of titanium and zirconium oxides in cryolite-alumina melt were obtained. Temperature dependences of dissolution rate of titanium and zirconium oxides in pure cryolite were studied as well. The apparent activation energy of dissolution process (Esub(p)), determined according to the slope of straigh lines in lg(V/ωsup(1/2))-1/T coordinates, equals consequently 115kJ/mol for TiO2 and 144.6 kJ/mol for ZrO2. The activation energy of alumina dissolution equals 88kJ/mol. Such difference means that the process of titanium and zirconium oxide dissolution in cryolite is rather impeded, as compared to alumina. This fact can be related with the formation of fluoride and oxyfluoride complexes, which transport from dissolution zone proceeds with considerable energetic difficulties, as compared to alumina dissolution

  6. A method for the control of alumina concentration in aluminum reduction cells

    Directory of Open Access Journals (Sweden)

    Jens G. Balchen

    1992-01-01

    Full Text Available The paper presents a new method for the control of the concentration of the alumina in electrolysis cells for the production of aluminium. The method is based upon the well known fact that apparent resistivity of the cell is a function of the alumina concentration so that the resistivity has the lowest value around the concentration of three per cent and increases in both directions. The method uses the cross correlation between a perturbation of the feed flow of alumina into the cell and the resulting response in measured voltage across the cell. The cross-correlation is proportional to the slope of the resistivity against concentration curve, making it possible to control the alumina flow, to achieve a desired slope. The method has much in common with other methods presently in use which require a much more complicated computation scheme.

  7. Optical properties of amorphous alumina dust in the envelopes around O-rich AGB stars

    CERN Document Server

    Suh, Kyung-Won

    2016-01-01

    We investigate optical properties of amorphous alumina (Al_2O_3) dust grains in the envelopes around O-rich asymptotic giant branch (AGB) stars considering the laboratory measured optical data. We derive the optical constants of amorphous alumina in a wide wavelength range that satisfy the Kramers-Kronig relation and reproduce the laboratory measured data. Using the amorphous alumina and silicate dust, we compare the radiative transfer model results with the observed spectral energy distributions. Comparing the theoretical models with the observations on various IR two-color diagrams for a large sample O-rich AGB stars, we find that the amorphous alumina dust (about 10-40 %) mixed with amorphous silicate can reproduce much more observed points for the O-rich AGB stars with thin dust envelopes.

  8. In situ observation of the role of alumina particles on the crystallization behavior of slags

    Energy Technology Data Exchange (ETDEWEB)

    Orrling, C.

    2000-09-01

    The confocal laser scanning microscope (CLSM) allows crystallization behavior in liquid slags to he observed in situ at high temperatures. Slags in the lime-silica-alumina-magnesia system are easily tinder cooled and it is possible to construct time temperature transformation (TTT) diagrams for this system. The presence of solid alumina particles its these liquid slags was studied to determine if these particles act as heterogeneous nucleation sites that cause she precipitation of solid material within slags. The introduction of alumina particles reduced the incubation time for the onset of crystallization and increased the temperature at which crystallization was observed in the slags to close to the liquidus temperature for the slag. Crystal growth rates are in a good agreement with Ivantsov's solution of the problem of diffusion controlled dendritic growth. Alumina appears to be a potent nucleating agent in the slag systems that were studied. (author)

  9. Relationship Between Liquor Yield, Plant Capacity Increases, and Energy Savings in Alumina Refining

    Science.gov (United States)

    Ter Weer, Peter-Hans

    2014-09-01

    The mechanisms of alumina trihydrate precipitation and controlling parameters, and the methods and technologies affecting liquor yield/productivity in alumina refining, have been described in several publications [e.g., Refs. Alamdari et al. ( Light Metals 1998, pp. 133-137, 1998), Moretto and Power ( Proc. 1990 Alumina Quality Workshop, Perth, Australia, pp. 154-165, 1990)]. However, the relationship between increasing liquor yield, on the one hand, and plant production capacity increases and related energy savings, on the other, has been under-emphasized. This article addresses this issue and provides estimates of plant production capacity increases and steam and power energy savings as a function of precipitation yield increases resulting from the implementation of plant adaptations. Conclusions are that increasing precipitation yield in an alumina refinery results overall in a significant improvement of project economics and interestingly improves a refinery's direct and indirect environmental performance, thus, addressing two of the three "pillars" of sustainable development (economic, environmental, and social).

  10. Effect of low-dimensional alumina structures on viability of L 929 cells

    Energy Technology Data Exchange (ETDEWEB)

    Fomenko, Alla N., E-mail: alserova@ispms.tsc.ru; Korovin, Matvey S., E-mail: msk@ispms.tsc.ru; Bakina, Olga V., E-mail: ovbakina@ispms.tsc.ru; Kazantsev, Sergey O., E-mail: kzso@ispms.tsc.ru; Glazkova, Elena A., E-mail: eagl@ispms.tsc.ru; Svarovskaya, Natalia V., E-mail: nvsv@ispms.tsc.ru; Lozhkomoev, Aleksandr S., E-mail: asl@ispms.tsc.ru [National Research Tomsk Polytechnic University, Tomsk, 634050 (Russian Federation)

    2015-10-27

    In the study, we estimated the cytotoxicity of alumina nanoparticles differing in shape (nanofibers, nanoplates, nanosheets, agglomerates of nanosheets) and close in physicochemical properties (particle size, specific surface area, phase composition, and zeta potential). The alumina structures were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) data, low-temperature nitrogen adsorption, and dynamic light scattering (DLS). The cytotoxicity was estimated on fibroblast cells of the L929 line. It was found that a more adverse effect on the cells was exerted by alumina nanofibers and nanosheets. The action of nanosheets on the cells was inhibitory and was of about the same level, irrespective of the observation period. The effect of alumina nanosheet agglomerates and nanoplates on the cell proliferation was weak even at an exposure time of 72 h.

  11. SURFACE TENSION OF MOLTEN IF STEEL CONTAINING Ti AND ITS INTERFACIAL PROPERTIES WITH SOLID ALUMINA

    Institute of Scientific and Technical Information of China (English)

    L.C. Zhong; M. Zeze; K. Mukai

    2004-01-01

    Surface tension of molten IF steel containing Ti and contact angle between the liquid steel and solid alumina were measured with sessile droplet method under Ar gas atmosphere at 1500, 1575 and 1600℃. The results show that titanium decreases the surface tension of the molten IF steel and the contact angle. The interfacial tension between the molten IF steel containing Ti and solid alumina decreases with increase in titanium content. The work of adhesion between molten IF steel containing Ti and solid alumina decreases slightly at 1550℃, but increases at 1600℃ with increasing titanium content. It can be deduced that fine bubbles and fine alumina inclusions are easily entrapped in solidifying interface for IF steel containing Ti.

  12. TSEE from aluminas and spinels subjected to Ar+-ion irradiation

    International Nuclear Information System (INIS)

    TSEE from Ar+-ion and/or X-ray irradiated alumina and spinel was investigated. A TSEE peak at 150 deg C from X-ray irradiated alumina was suppressed when the alumina was further irradiated by Ar+-ions. A TSEE peak at 300 deg C was observed for Ar+-ion irradiated alumina and was suppressed by the combined effect of Ar+-ion and X-ray irradiations. Only weak TSEE peaks were observed between 250 and 350 deg C in Ar+-ion irradiated spinels. Generally, sprayed spinel specimens showed weaker TSEE peaks than the specimens of a single-crystal spinel. This is attributable to the fact that a plasma-sprayed spinel becomes amorphous more easily than its single crystals. X-ray irradiated spinel single-crystal showed well-defined TSEE when they were not irradiated with Ar+-ions. (author)

  13. Fabrication of hydrophobic alumina aerogel monoliths by surface modification and ambient pressure drying

    International Nuclear Information System (INIS)

    Hydrophobic crack-free alumina aerogel monoliths were fabricated by -Si(CH3)3 (trimethylsilyl substituent) modification of alcogels followed by an ambient pressure drying procedure. One-step solvent exchange and surface modification were simultaneously progressed by immersing alumina alcogels in trimethylmethoxysilane (TMMOS)/hexane solution. It is found that the hydrophobic property of alumina aerogels is affected by the contents of TMMOS from the measurements of contact angle and Fourier transform infrared spectrometry. Thermogravimetry/differential scanning calorimetry analyses reveal that the modified aerogels maintain their hydrophobic behavior up to a temperature of 260 deg. C. The structure and morphology of the obtained hydrophobic alumina aerogels were characterized by the measurements of N2 physical adsorption and scanning electron microscopy, which showed that they were highly porous materials with narrow slit-like pore geometry and a high degree of pore size uniformity.

  14. Preparation and study of thermally stable washcoat aluminas for automotive catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Ismagilov, Z.R.; Shkrabina, R.A.; Koryabkina, N.A.; Arendarskii, D.A.; Shikina, N.V. [Boreskov Institute of Catalysis, Novosibirsk (Russian Federation)

    1998-12-31

    Porous and thermally stable washcoating layer on mechanically strong support is an important component in both oxidative and three-way catalysts used for car exhaust gas cleaning. The washcoat provides a high and stable surface area for dispersion of the active component of the catalysts consisting of platinum and /or palladium. Usually for the preparation of this layer aluminas modified by La, Ce, Zr, Si etc. are used. As it was shown elsewhere the properties of modified aluminas depend on the method of introduction of the additives. In this work we present the results on the preparation and study of model alumina systems modified by La, Ce and Zr as well as of monolith supports washcoated by optimal compositions of alumina and additives. 6 refs.

  15. Fused Cast Alumina Refractory Products for Glass Melting Furnace JC/T 494-92(96)

    Institute of Scientific and Technical Information of China (English)

    Zhang Xiaohui; Chai Junlan

    2008-01-01

    @@ 1 Scope This standard specifies the technical require-ments, test methods, inspection rules, marking, pack-ing, transportation, and storage of fused cast alumina refractory products for glass melting furnace.

  16. Modification of surface properties of silica-alumina by irradiation with gamma-rays

    International Nuclear Information System (INIS)

    Coprecipitated silica-alumina gel was prepared to contain 11.8 mol.% alumina. The gel was calcined at 523, 673, 823, 973 and 1173 K. The calcination products were irradiated by γ-rays (15-75 Mrad). Nitrogen adsorption at 77 K, water vapour adsorption at 303 K, pyridine chemisorption at 423 K were measured for non-irradiated and γ irradiated silica-alumina samples. The dehydration of isopropanol was measured at 553 K and at a carrier gas flow rate = 25 ml/min. ''gamma-Irradiation (30-75 Mrad) caused appreciable changes in textural properties of silica-alumina. The extents of these changes depend on the irradiation dose and on the pre-calcination temperature. Irradiation with γ-rays decreased the surface acid density and consequently the activity of the irradiated sample towards acid catalyzed reactions decreased. (author)

  17. Microwave-assisted brazing of alumina ceramics for electron tube applications

    Indian Academy of Sciences (India)

    2016-04-01

    Alumina was joined with alumina using microwave-assisted and conventional brazing methods at 960$^{\\circ}$C for 15 min using TiCuSil (68.8Ag–26.7Cu–4.5Ti in wt.%) as the brazing alloy. The brazed joints were characterizedby X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, Vickers microhardness evaluation, brazing strength measurement and helium leak test. X-ray diffraction analysis confirmed the formationof Ti-based compounds at the substrate-filler alloy interfaces of the microwave and conventionally brazed joints. The elemental compositions at the joint cross-section were determined by energy dispersive X-ray analysis. Vickers microhardness measurement indicated reliable joint performance for the microwave-assisted brazed joints during actual application in an electron tube. Brazing strength measurement and helium leak test provided the evidence forgood alumina-alumina joint formation.

  18. Low-temperature carbon monoxide oxidation catalysed by regenerable atomically dispersed palladium on alumina

    Science.gov (United States)

    Peterson, Eric J.; Delariva, Andrew T.; Lin, Sen; Johnson, Ryan S.; Guo, Hua; Miller, Jeffrey T.; Hun Kwak, Ja; Peden, Charles H. F.; Kiefer, Boris; Allard, Lawrence F.; Ribeiro, Fabio H.; Datye, Abhaya K.

    2014-09-01

    Catalysis by single isolated atoms of precious metals has attracted much recent interest, as it promises the ultimate in atom efficiency. Most previous reports are on reducible oxide supports. Here we show that isolated palladium atoms can be catalytically active on industrially relevant γ-alumina supports. The addition of lanthanum oxide to the alumina, long known for its ability to improve alumina stability, is found to also help in the stabilization of isolated palladium atoms. Aberration-corrected scanning transmission electron microscopy and operando X-ray absorption spectroscopy confirm the presence of intermingled palladium and lanthanum on the γ-alumina surface. Carbon monoxide oxidation reactivity measurements show onset of catalytic activity at 40 °C. The catalyst activity can be regenerated by oxidation at 700 °C in air. The high-temperature stability and regenerability of these ionic palladium species make this catalyst system of potential interest for low-temperature exhaust treatment catalysts.

  19. Synthesis of ultrafine alumina powders using egg white as complexing medium

    International Nuclear Information System (INIS)

    Synthesis of alumina powders through chemical methods has been attracting much attention of researchers in the past few years, due to the ability to produce powders in nanometric scale with high degree of purity. In this work, there were synthesized alumina powders through a chemical route, using egg white as a complexing medium and aluminium nitrate as the source of Al3+ cations. Egg white contains ovalbumin, a protein which acts effectively on the isolation of aluminium cations during the mixing process, enabling the formation of ultrafine alumina powders in a relatively economic and environmentally friendly way. The powders obtained by calcinations of the precursor resin were characterized by X-ray diffraction, specific surface area measurements, infrared spectroscopy and scanning electron microscopy. It was observed that the egg white, present at the reaction medium, allowed obtaining transition alumina powders, with high degree of purity. (author)

  20. Characterization of calcium phosphate coating and zinc incorporation on the porous alumina scaffolds

    Directory of Open Access Journals (Sweden)

    Hermes de Souza Costa

    2007-03-01

    Full Text Available Bone ingrowth requires materials with the existence of open and interconnected pores with diameters larger than 150 µm for proper circulation of nutrients. Such materials must possess enough mechanical strength to avoid failure whilst offering a bioactive surface for bone regeneration. We have developed porous ceramic alumina scaffold with compressive strength that achieves 3.3 MPa by replication method by using the network structure of cellular polymer foam. However, the biocompatibility of ceramics based on Al2O3 requires further improvement so that it could have strong bonding to natural bone tissue. To address this problem of the interface between alumina and bone, we have developed a novel calcium phosphate with Zn2+ (CaP-Zn coating onto porous alumina ceramic scaffold by impregnating with calcium phosphate/poly(vinyl alcohol slurry. The tri-dimensional alumina scaffold coated with CaP-Zn was extensively characterized by SEM, EDS and FTIR.

  1. Atomic layer deposition of TiO2 thin films on nanoporous alumina templates: Medical applications

    Science.gov (United States)

    Narayan, Roger J.; Monteiro-Riviere, Nancy A.; Brigmon, Robin L.; Pellin, Michael J.; Elam, Jeffrey W.

    2009-06-01

    Nanostructured materials may play a significant role in controlled release of pharmacologic agents for treatment of cancer. Many nanoporous polymer materials are inadequate for use in drug delivery. Nanoporous alumina provides several advantages over other materials for use in controlled drug delivery and other medical applications. Atomic layer deposition was used to coat all the surfaces of a nanoporous alumina membrane in order to reduce the pore size in a controlled manner. Neither the 20 nm nor the 100 nm TiO2-coated nanoporous alumina membranes exhibited statistically lower viability compared to the uncoated nanoporous alumina membrane control materials. Nanostructured materials prepared using atomic layer deposition may be useful for delivering a pharmacologic agent at a precise rate to a specific location in the body. These materials may serve as the basis for “smart” drug delivery devices, orthopedic implants, or self-sterilizing medical devices.

  2. Research on toughening mechanisms of alumina matrix ceramic composite materials improved by rare earth additive

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xihua; LIU Changxia; LI Musen; ZHANG Jianhua

    2008-01-01

    Mixed rare earth elements were incorporated into alumina ceramic materials. Hot-pressing was used to fabricate alumina matrix composites in nitrogen atmosphere protection. Microstructures and mechanical properties of the composites were tested. It was indicated that the bending strength and fracture toughness of alumina matrix ceramic composites sintered at 1550℃ and 28 Mpa for 30 min were improved evidently. Besides mixed rare earth elements acting as a toughening phase, AlTiC master alloys were also added in as sintering assistants, which could prompt the formation of transient liquid phase, and thus nitrides of rare earth elements were produced. All of the above were beneficial for improving the mechanical properties of alumina matrix ceramic composites.

  3. Life Studies of Metal Films on Beta-Alumina at High Temperature

    Science.gov (United States)

    Williams, R.; Kisor, A.; Fiebig, B.; Cortez, R.; Ryan, M.; Shields, V.; Homer, M.

    2000-01-01

    Applications of metallic films on sodium beta-alumina solid electrolyte (BASE) ceramic in technology for the alkali metal thermal to electric converter (AMTEC) include both electrode and metallization functions.

  4. Use of neutron diffraction in alumina-matrix ceramics research: A 10 year perspective

    International Nuclear Information System (INIS)

    Full text: The Materials Research Group at Curtin University has made extensive use of the Lucas Heights neutron powder diffraction facilities over the last decade. The paper will summarise the following neutron diffraction experiments all of which involved high-temperature, real-time measurements with the MRPD diffractometer: 1) Microstructure development in zirconia-dispersed aluminas (van Riessen, 1997) in which phase composition changes and residual strain development were examined as the material cooled to room temperature following sintering. 2) Calcination of gibbsite to α-alumina (Gan, 1996). A highlight of this study was the observation of co-existing tetragonal and cubic polymorphs of γ-alumina. 3) Study of the liquid-phase-sintering of an alumina-matrix ceramic composition (Latella, 1995; Latella et al, 1998). Here the influence of the post-sintering cooling rate on phase composition was examined with particular reference to wear-resistant behaviour

  5. Adsorption and desorption of uranium on nano goethite and nano alumina

    International Nuclear Information System (INIS)

    The nano goethite and nano alumina were synthesized to investigate the effect of nanoscale size on adsorption-desorption of U(VI) from aqueous solution. It was determined that the site densities of nanoparticles are higher than α-alumina and goethite, whereas slight effect of carbonate on adsorption of U(VI) onto nanoparticles was observed. The maximum adsorption capacities of nano alumina and nano goethite were ∼151 and 79 mg/g, respectively. The batch desorption indicated stronger binding affinity of U(VI) for nanoparticles as compared to non-nanoparticles, which were consistent with the results of surface complexation modeling assuming weak and strong sites for nanoparticles while weak sites for α-alumina and goethite. (author)

  6. Effect of low-dimensional alumina structures on viability of L 929 cells

    International Nuclear Information System (INIS)

    In the study, we estimated the cytotoxicity of alumina nanoparticles differing in shape (nanofibers, nanoplates, nanosheets, agglomerates of nanosheets) and close in physicochemical properties (particle size, specific surface area, phase composition, and zeta potential). The alumina structures were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) data, low-temperature nitrogen adsorption, and dynamic light scattering (DLS). The cytotoxicity was estimated on fibroblast cells of the L929 line. It was found that a more adverse effect on the cells was exerted by alumina nanofibers and nanosheets. The action of nanosheets on the cells was inhibitory and was of about the same level, irrespective of the observation period. The effect of alumina nanosheet agglomerates and nanoplates on the cell proliferation was weak even at an exposure time of 72 h

  7. Alumina Volatility in Water Vapor at Elevated Temperatures: Application to Combustion Environments

    Science.gov (United States)

    Opila, Elizabeth J.; Myers, Dwight L.

    2003-01-01

    The volatility of alumina in high temperature water vapor was determined by measuring weight loss of sapphire coupons at temperatures between 1250 and 1500 C, water vapor partial pressures between 0.15 and 0.68 atm in oxygen, at one atmosphere total pressure, and a gas velocity of 4.4 centimeters per second. The variation of the volatility with water vapor partial pressure was consistent with Al(OH)3(g) formation. The enthalpy of reaction to form Al(OH)3(g) from alumina and water vapor was found to be 210 plus or minus 20 kJ/mol. Surface rearrangement of ground sapphire surfaces increased with water vapor partial pressure, temperature and volatility rate. Recession rates of alumina due to volatility were determined as a function of water vapor partial pressure and temperature to evaluate limits for use of alumina in long term applications in combustion environments.

  8. Effect of sintering temperature on densification and mechanical properties of pressureless sintered CNT-alumina nanocomposites

    International Nuclear Information System (INIS)

    Carbon nanotubes (CNTs) exhibit excellent mechanical, electrical and thermal properties thus have been considered for applications in the production of nanocomposite materials. This work presents results of sintered CNTs-reinforced alumina nanocomposites that can be used for many structural and engineering applications. Gas purging sonication (GPS) was used to achieve homogeneous dispersion of CNTs in alumina powder. Nanocomposites were synthesized by conventional pressureless sintering technique using varying amounts of CNTs in alumina matrix. Densification, hardness and fracture toughness of the resulted nanocomposites were examined. It is found that considerable improvement in fracture toughness at 1 wt% CNT-alumina nanocomposite has occurred. Role of CNTs in improving the fracture toughness of nanocomposites is explained which is attributed to well known bridging and pullout mechanism of CNTs in the matrix

  9. Alumina Templates on Silicon Wafers with Hexagonally or Tetragonally Ordered Nanopore Arrays via Soft Lithography

    International Nuclear Information System (INIS)

    Due to the potential importance and usefulness, usage of highly ordered nanoporous anodized aluminum oxide can be broadened in industry, when highly ordered anodized aluminum oxide can be placed on a substrate with controlled thickness. Here we report a facile route to highly ordered nanoporous alumina with the thickness of hundreds-of-nanometer on a silicon wafer substrate. Hexagonally or tetragonally ordered nanoporous alumina could be prepared by way of thermal imprinting, dry etching, and anodization. Adoption of reusable polymer soft molds enabled the control of the thickness of the highly ordered porous alumina. It also increased reproducibility of imprinting process and reduced the expense for mold production and pattern generation. As nanoporous alumina templates are mechanically and thermally stable, we expect that the simple and cost effective fabrication through our method would be highly applicable in electronics industry

  10. Mechanical Properties of a Graded Alumina-Zirconia Composite Prepared by Centrifugal Slip Casting

    International Nuclear Information System (INIS)

    Compositionally graded composite of alumina-20 vol%zirconia was fabricated by using centrifugal casting incorporated with relatively thin slip. An EPMA analysis exhibited a nearly linear variation of the alumina/zirconia ratio along the centrifugal direction; zirconia tended to accumulate in the bottom section, while alumina in the top section. Such a graded structure exhibited a considerably higher flexural strength when the alumina rich surface was subjected to a tensile stress than compositionally uniform composite of the same average composition. Fracture toughness measurement across the specimen thickness by indentation method revealed that the crack lengths along the vertical and horizontal directions were different. The anisotropy of the fracture toughness was accounted for by the variation of the residual stress across the specimen thicknesss

  11. Mechanical Properties of a Graded Alumina-Zirconia Composite Prepared by Centrifugal Slip Casting

    Science.gov (United States)

    Hara, Yasuyuki; Onda, Tetsuhiko; Hayakawa, Motozo

    2008-02-01

    Compositionally graded composite of alumina-20 vol%zirconia was fabricated by using centrifugal casting incorporated with relatively thin slip. An EPMA analysis exhibited a nearly linear variation of the alumina/zirconia ratio along the centrifugal direction; zirconia tended to accumulate in the bottom section, while alumina in the top section. Such a graded structure exhibited a considerably higher flexural strength when the alumina rich surface was subjected to a tensile stress than compositionally uniform composite of the same average composition. Fracture toughness measurement across the specimen thickness by indentation method revealed that the crack lengths along the vertical and horizontal directions were different. The anisotropy of the fracture toughness was accounted for by the variation of the residual stress across the specimen thicknesss

  12. Particle Size Distribution, Powder Agglomerates and Their Effects on Sinterability of Ultrafine Alumina Powders

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    An intensive study of the particle size distribution of four commercial ultrafine alumina powders to obtain information about the powder agglomeration and relate them to the compactibility and the sinterability has been made.

  13. Oxidation resistance of YSZ-alumina composites compared to normal YSZ TBC coatings at 1100 deg. C

    International Nuclear Information System (INIS)

    Highlights: → This work aims to study the oxidation behavior of plasma sprayed YSZ-alumina composites coatings. → The composites TBC coatings of YSZ-alumina showed better oxidation resistance than normal YSZ. → The durability of composite coating with alumina is a novel method and has not been reported before. - Abstract: In the present work oxidation behavior of plasma sprayed YSZ-alumina composite TBC coatings on Ni-base (IN-738LC) super alloy substrate was studied and compared to normal YSZ. Cyclic oxidation process in 4 h intervals was performed in an air electrical furnace at 1100 deg. C and the specimens were cooled in the furnace during each cycle. Preliminary checking was done with naked eye and further investigation was achieved using scanning electron microscopy. If there were any cracks or spallation in the coating's edge, the tests were stopped, the time was recorded and coating microstructure was studied. YSZ-alumina composites were made by applying alumina layer at the top of YSZ or mixed with YSZ as a TBC layer on the bond coat. Composite coatings of YSZ-alumina having alumina as a top coat and the mixed YSZ-alumina layer, showed better resistance than normal YSZ in oxidation test. It was observed that alumina overlay on YSZ has promoted the oxidation resistance of the coatings for longer times by preventing infiltration of oxygen through YSZ layer.

  14. Thermodynamic and spectroscopic investigations of aluminas and thermodynamic studies of other solid systems

    Energy Technology Data Exchange (ETDEWEB)

    Healy, M.H.

    1987-01-01

    This dissertation describes thermodynamic studies of the adsorption of a variety of liquid and gaseous bases on to a variety of solid acids, such as transition aluminas, a sulfonic acid resin (Dowex), graphite and anthracite coal. Fourier transform infrared spectroscopy studies were also conducted to identify the type, strength, and quantity of acid sites present on two transition aluminas, delta-theta and kappa. Heats of immersion of delta-theta and kappa aluminas into a variety of adsorbates of differing base strengths and geometries were obtained to quantify heterogeneous Lewis acid-base behavior. An in situ infrared spectroscopy investigation was conducted using four basic adsorbates to identify the acidic sites present on delta-theta and kappa aluminas. For two adsorbates, pyridine and 2,6-lutidine, adsorption studies were conducted between 298 and 983 K and at adsorbate pressures spanning from 1.33 Pascal (Pa) to 1.33 kPa. The adsorption of acetonitrile and n-butylamine was conducted at 298K using adsorbate pressures ranging from 0.66 Pa to 8.65 kPa. With all of the adsorbates a Lewis acid coordination site, designated as an outer or weaker site, and hydrogen-bonded complexes are identified. Broensted acid coordination is detected only when a strongly basic adsorbate, n-butylamine, is employed as the probe molecule. The strength of the sites, as quantified with pyridine is similar on both aluminas; however, with acetonitrile, a stronger coordination complex is formed on kappa alumina than on delta-theta alumina. The environment surrounding the acid site affects the adsorption of 2,6-lutidine; although it is a stronger base towards protonic acids than pyridine and might be expected to interact more strongly with alumina, only a weakly bound species is formed.

  15. Preparation and characterization of electrolytic alumina deposit on austenitic stainless steel

    OpenAIRE

    El Hajjaji, Souad; El Alaoui, Sidi Mohammed; Simon, Patrice; Guenbour, Abdellah; Ben Bachir, Ali; Puech-Costes, Edith; Maurette, Marie-Thérèse; Aries, Lucien

    2005-01-01

    Conversion coating modified by alumina has been studied as a way for improving the resistance to thermal oxidation of an austenitic stainless steel. Conversion coating, characterized by a particular morphology and strong interfacial adhesion with the substrate, facilitate the electrochemical deposition of ceramic layers and enhance their adhesion to the substrate. The influence of the current density and treatment time on alumina deposit was studied using statistical experimental designs like...

  16. Chemo-mechanical softening during in situ nanoindentation of anodic porous alumina with anodization processing

    OpenAIRE

    Cheng, C; Ngan, AHW

    2013-01-01

    Simultaneous application of mechanical stresses on a material as it undergoes an electrochemical reaction can result in interesting coupling effects between the chemical and mechanical responses of the material. In this work, anodic porous alumina supported on Al is found to exhibit significant softening during in situ nanoindentation with anodization processing. Compared with ex situ nanoindentation without anodization processing, the in situ hardness measured on the alumina is found to be m...

  17. Defect-free nanostructured alumina coating doped with noble metal nanoparticles

    International Nuclear Information System (INIS)

    Nanostructured alumina coatings loaded with platinum or gold nanoparticles were prepared by two different methods. In the first method the alumina coatings were prepared in the presence of metal ions, which were reduced using UV irradiation once the film was deposited. In the second method, polyvinylpyrrolidone-stabilized nanoparticles were first synthesized and then incorporated in the coating. The texturation of the coating occurred in a last step by hot water treatment.

  18. Features of the interaction of alumina and silica with carbon-containing reducing agents

    Energy Technology Data Exchange (ETDEWEB)

    Kondratenko, A.P.

    1976-01-01

    In the mining of Ekibastuz coals, a rock containing 35 to 49% of coal substance and 60 to 65% of mineral fractions, mainly silica and alumina, is sent to the waste dump. When this rock is heated in an inert atmosphere above 1500 C the alumina and silica are reduced by the carbon present, as a result of which, in prinicple, it is possible to obtain a number of valuable products. These reactions are discussed.

  19. Improved mechanical and thermomechanical properties of alumina substrate via iron doping

    International Nuclear Information System (INIS)

    We present a method to improve the overall properties of sintered alumina substrate via iron doping that has a higher fracture toughness, lower thermal conductivity, lower thermal expansion coefficient and comparable dielectric constant than pure alumina. Such properties are beneficial for harsh environment electronic packages. X-ray and electron probe microanalyses concluded that toughening is likely caused by multiple phase strengthening and ruled out crack bridging or grain boundary strengthening

  20. Preparation of Porous Alumina Film on Aluminum Substrate by Anodization in Oxalic Acid

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Self-ordering of the cell arrangement of the anodic porous alumina was prepared in oxalic acid solution at a constant potential of 40V and at a temperature of 20°C. The honeycomb structure made by one step anodization method and two step anodization method is different.Pores in the alumina film prepared by two step anodization method were more ordered than those by one step anodization method.

  1. Effects of Several Factors on Viscosity of Alumina-spinel Slurries

    Institute of Scientific and Technical Information of China (English)

    SHA Jianmin; LIU Kaiqi; LIU Zuocai

    2004-01-01

    The effects of several commercial dispersants, including AN- 2000, ammonium polyacrylate , sodium tripolyphosphate, sodium hexametaphosphate, and of solids loading and of electro-fused magnesia on rheological propertiesof aqueous alumina-spinel slurries were studied.The results reveal that AN- 2000 is the most effective one among the selected dispersants for alumina-spinel slurries.With 0.5% weight of AN-2000, the 57vol% solids loadobtained at shear rate of 50s-1 .

  2. Charge-induced reversible bending in nanoporous alumina-aluminum composite

    Science.gov (United States)

    Cheng, Chuan; Ngan, A. H. W.

    2013-05-01

    Upon electrical charging, reversible bending was found in nanoporous anodic alumina-aluminum foil composites, as directly observed by an optical microscope and detected by in situ nanoindentation. The bending is thought to be the result of charge-induced surface stresses in the nanoporous alumina. The results suggest the possibility of a type of composite foil materials for applications as micro-scale actuators to transform electrical energy into mechanical energy.

  3. Effect of Nano-Crystalline Boehmite Addition on Sintering and Properties of Alumina Ceramics

    OpenAIRE

    GUNAY, Esin; Ozturk, Yusuf; SARIGUZEL, Meryem

    2012-01-01

    In this study, alumina ceramics containing up to 10 wt% of boehmite were sintered at 1550, 1600 and 1650ºC for 1 hour. Water absorption, weight loss, porosity and density values were measured after sintering. Boehmite content caused flocculation during mixing in water suspension. Formation of boehmite agglomerates was clearly seen in SEM examination and also it was observed that there were different shrinkages in alumina matrix and in boehmite agglomerates and this caused gaps around agg...

  4. High Temperature Pt/Alumina Co-Fired System for 500 C Electronic Packaging Applications

    Science.gov (United States)

    Chen, Liang-Yu; Neudeck, Philip G.; Spry, David J.; Beheim, Glenn M.; Hunter, Gary W.

    2015-01-01

    Gold thick-film metallization and 96 alumina substrate based prototype packaging system developed for 500C SiC electronics and sensors is briefly reviewed, the needs of improvement are discussed. A high temperature co-fired alumina material system based packaging system composed of 32-pin chip-level package and printed circuit board is discussed for packaging 500C SiC electronics and sensors.

  5. Diffuse X-ray scattering and far infrared absorption of barium and lead β" aluminas

    DEFF Research Database (Denmark)

    Hayes, W.; Kjær, Kristian; Pratt, F. L.; Schonfeld, B.

    1985-01-01

    The authors have carried out high-momentum-resolution studies in diffuse X-ray scattering of barium and lead B" aluminas in the temperature range 20-700 degrees C. They have also measured the vibrational spectra of these compounds between 2K and 300K in the energy range 10-100 cm-1. The results are...... discussed in terms of preferential occupation of a cation sublattice in the conduction slab of B" alumina and of cation clustering....

  6. Estimation of thermal shock resistance of fine porous alumina by infrared radiation heating method

    OpenAIRE

    Iwamoto, Yuji; Honda, Sawao; Ogihara, Yuki; Kishi, Tsunego; イワモト, ユウジ; ホンダ, サワオ; 岩本, 雄二; 本多, 沢雄

    2009-01-01

    The thermal shock resistance of α-alumina porous capillary, the support material for hydrogen-permselective microporous ceramic membrane was studied. To study the effect of porosity on the thermal shock resistance systematically, porous alumina with different porosities was fabricated, and the thermal shock resistance of the fabricated samples as well as the porous capillary was estimated by the infrared radiation heating method. The mechanical and thermal properties concerned to the thermal ...

  7. Synthesis of alumina/YAG 20 vol% composite by co-precipitation

    OpenAIRE

    Radosław Lach; Krzysztof Haberko; Mirosław Bućko

    2011-01-01

    Co-precipitation of alumina/YAG precursor from aluminum and yttrium nitrate solution with ammonium carbonate results in dawsonite. Its crystallographic parameters differ from the compound precipitated with no yttrium additive. It suggests that yttrium ions become incorporated into the dawsonite structure. The DSC/TG and X-ray diffraction measurements show decomposition of dawsonite at elevated temperatures resulting in γ-Al2O3 and then δ- and θ-alumina modifications. Full transformation to α-...

  8. FABRICATION OF POROUS ALUMINA CERAMICS WITH CORN STARCH IN AN EASY AND LOW-COST WAY

    OpenAIRE

    Zhengwei Nie; Yuyi Lin

    2015-01-01

    Porous alumina ceramics with different porosity were fabricated by combining the starch consolidation process with the gel-casting process using corn starch as a pore-forming agent and a binder. The bulk density, porosity, and microstructure of the obtained alumina ceramics were studied. It was found that the total porosity range of sintered samples with contents varying from 0 to 50 vol. % is 14.8 - 55.3 % and the total porosity increased with the increase of starch content. Moreove...

  9. Production of sintered alumina from powder; optimization of the sinterized parameters for the maximum mechanical resistence

    International Nuclear Information System (INIS)

    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 (Al2O3), 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.)

  10. Effects of composition on the mechanical response of alumina-filled epoxy.

    Energy Technology Data Exchange (ETDEWEB)

    Montgomery, Stephen Tedford

    2009-10-01

    The effect of composition on the elastic responses of alumina particle-filled epoxy composites is examined using isotropic elastic response models relating the average stresses and strains in a discretely reinforced composite material consisting of perfectly bonded and uniformly distributed particles in a solid isotropic elastic matrix. Responses for small elastic deformations and large hydrostatic and plane-strain compressions are considered. The response model for small elastic deformations depends on known elastic properties of the matrix and particles, the volume fraction of the particles, and two additional material properties that reflect the composition and microstructure of the composite material. These two material properties, called strain concentration coefficients, are characterized for eleven alumina-filled epoxy composites. It is found that while the strain concentration coefficients depend strongly on the volume fraction of alumina particles, no significant dependence on particle morphology and size is observed for the compositions examined. Additionally, an analysis of the strain concentration coefficients reveals a remarkably simple dependency on the alumina volume fraction. Responses for large hydrostatic and plane-strain compressions are obtained by generalizing the equations developed for small deformation, and letting the alumina volume fraction in the composite increase with compression. The large compression plane-strain response model is shown to predict equilibrium Hugoniot states in alumina-filled epoxy compositions remarkably well.

  11. Thermal stability and microstructure of catalytic alumina composite support with lanthanum species

    Science.gov (United States)

    Ozawa, Masakuni; Nishio, Yoshitoyo

    2016-09-01

    Lanthanum (La) modified γ-alumina composite was examined for application toward thermostable catalytic support at elevated temperature. La added alumina was prepared through an aqueous process using lanthanum (III) nitrate and then characterized by surface area measurement, X-ray powder diffraction (XRD), differential thermal analysis (DTA), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoemission spectroscopy (XPS) and surface desorption of CO2. It was found that the properties depended on the La content and heat treatment temperatures. The characterization of the surface, structural and chemical properties of La-Al2O3 showed the existence of a strong interaction between the La species and alumina via formation of new phase and modified surface in Al2O3 samples. LaAlO3 nanoparticle formed among alumina particles by the solid phase reaction of Al2O3 and La2O3. The increase of the surface basicity of La modified alumina was demonstrated using CO2 temperature programmed desorption experiments. The controlled surface interaction between La oxide and alumina provide the unique surface and structural properties of the resulting mixed oxides as catalysts and catalytic supports.

  12. Preparation and characterization of superhydrophobic surfaces based on hexamethyldisilazane-modified nanoporous alumina

    Directory of Open Access Journals (Sweden)

    Sanli Deniz

    2011-01-01

    Full Text Available Abstract Superhydrophobic nanoporous anodic aluminum oxide (alumina surfaces were prepared using treatment with vapor-phase hexamethyldisilazane (HMDS. Nanoporous alumina substrates were first made using a two-step anodization process. Subsequently, a repeated modification procedure was employed for efficient incorporation of the terminal methyl groups of HMDS to the alumina surface. Morphology of the surfaces was characterized by scanning electron microscopy, showing hexagonally ordered circular nanopores with approximately 250 nm in diameter and 300 nm of interpore distances. Fourier transform infrared spectroscopy-attenuated total reflectance analysis showed the presence of chemically bound methyl groups on the HMDS-modified nanoporous alumina surfaces. Wetting properties of these surfaces were characterized by measurements of the water contact angle which was found to reach 153.2 ± 2°. The contact angle values on HMDS-modified nanoporous alumina surfaces were found to be significantly larger than the average water contact angle of 82.9 ± 3° on smooth thin film alumina surfaces that underwent the same HMDS modification steps. The difference between the two cases was explained by the Cassie-Baxter theory of rough surface wetting.

  13. Phase transformation studies on YSZ doped with alumina. Part 1: Metastable phases

    International Nuclear Information System (INIS)

    The goal of this study is to clarify the effect of the addition of Al2O3 on the grain boundaries of yttria stabilized zirconia using high resolution transmission electron microscopy. Basically excessive concentration of alumina, which is not solved in YSZ, segregates within YSZ matrix. Alumina segregates as grains between YSZ grains and as particles within YSZ grain boundaries. t' metastable phase was detected within the grains of the sintered YSZ powders. By adding alumina into the primary YSZ powders and sintering it all together, metastable tetragonal phases appear in the grain boundaries between YSZ and segregated alumina grains. Similar phenomenon was detected in the boundaries of the two neighboring grains of YSZ doped with Alumina. Appearance of these phases might be due to the accumulated strain energies which are generated because of the alumina segregation into grain boundaries and matrix of YSZ. Hence, by controlling the dopant concentration, it could be possible to form YSZ structured by t' metastable phase. Fabrication of this material is in the great attention of the high temperature applications due to the high resistive properties of the t' metastable phase against high temperature degradation of the YSZ.

  14. Zirconia toughened SiC whisker reinforced alumina composites small business innovation research

    Science.gov (United States)

    Loutfy, R. O.; Stuffle, K. L.; Withers, J. C.; Lee, C. T.

    1987-01-01

    The objective of this phase 1 project was to develop a ceramic composite with superior fracture toughness and high strength, based on combining two toughness inducing materials: zirconia for transformation toughening and SiC whiskers for reinforcement, in a controlled microstructure alumina matrix. The controlled matrix microstructure is obtained by controlling the nucleation frequency of the alumina gel with seeds (submicron alpha-alumina). The results demonstrate the technical feasibility of producing superior binary composites (Al2O3-ZrO2) and tertiary composites (Al2O3-ZrO2-SiC). Thirty-two composites were prepared, consolidated, and fracture toughness tested. Statistical analysis of the results showed that: (1) the SiC type is the key statistically significant factor for increased toughness; (2) sol-gel processing with a-alumina seed had a statistically significant effect on increasing toughness of the binary and tertiary composites compared to the corresponding mixed powder processing; and (3) ZrO2 content within the range investigated had a minor effect. Binary composites with an average critical fracture toughness of 6.6MPam sup 1/2, were obtained. Tertiary composites with critical fracture toughness in the range of 9.3 to 10.1 MPam sup 1/2 were obtained. Results indicate that these composites are superior to zirconia toughened alumina and SiC whisker reinforced alumina ceramic composites produced by conventional techniques with similar composition from published data.

  15. Effect of the synthetic method on the catalytic activity of alumina: Epoxidation of cyclohexene

    International Nuclear Information System (INIS)

    Graphical abstract: Temperature influence on percent conversion and selectivity in the epoxidation of cyclohexene using commercial alumina as a catalyst. - Highlights: • Aluminum oxide was synthesized using Pechini method. • The alumina obtained showed a mix of boehmite and γ-alumina phases. • We research an economically feasible method to obtain alumina for use as a catalyst. • Alumina obtained by Pechini showed high percent conversion and/or selectivity. • The best results were 78% conversion and 78% selectivity to epoxidation reactions. - Abstract: Al2O3 was prepared from different inorganic precursors via the Pechini method and compared with Al2O3 prepared by the sol–gel method. Structural characterization of these materials was carried out by FTIR, X-ray diffraction (XRD), N2 adsorption at −196 °C and transmission electron microscopy (TEM). The solids were tested in the epoxidation of cyclohexene and a difference in their catalytic activities was observed. The characterization results indicate that the samples prepared by Pechini have a mixture of γ-alumina and boehmite, a condition favoring catalytic activity, whereas the sol–gel sample is less crystalline due to higher boehmite content. These results indicate that both the nature of the precursor and the method of synthesis strongly affect the catalytic activity of Al2O3

  16. Biocompatibility assessment of spark plasma-sintered alumina-titanium cermets.

    Science.gov (United States)

    Guzman, Rodrigo; Fernandez-García, Elisa; Gutierrez-Gonzalez, Carlos F; Fernandez, Adolfo; Lopez-Lacomba, Jose Luis; Lopez-Esteban, Sonia

    2016-01-01

    Alumina-titanium materials (cermets) of enhanced mechanical properties have been lately developed. In this work, physical properties such as electrical conductivity and the crystalline phases in the bulk material are evaluated. As these new cermets manufactured by spark plasma sintering may have potential application for hard tissue replacements, their biocompatibility needs to be evaluated. Thus, this research aims to study the cytocompatibility of a novel alumina-titanium (25 vol. % Ti) cermet compared to its pure counterpart, the spark plasma sintered alumina. The influence of the particular surface properties (chemical composition, roughness and wettability) on the pre-osteoblastic cell response is also analyzed. The material electrical resistance revealed that this cermet may be machined to any shape by electroerosion. The investigated specimens had a slightly undulated topography, with a roughness pattern that had similar morphology in all orientations (isotropic roughness) and a sub-micrometric average roughness. Differences in skewness that implied valley-like structures in the cermet and predominance of peaks in alumina were found. The cermet presented a higher surface hydrophilicity than alumina. Any cytotoxicity risk associated with the new materials or with the innovative manufacturing methodology was rejected. Proliferation and early-differentiation stages of osteoblasts were statistically improved on the composite. Thus, our results suggest that this new multifunctional cermet could improve current alumina-based biomedical devices for applications such as hip joint replacements. PMID:25956565

  17. Coating hydroxyapatite/alpha alumina composites by mechanical alloying

    International Nuclear Information System (INIS)

    The biomaterials field has become a vital area, as these materials can enhance the quality and longevity of human life and science and technology associated with this field has now led to multi-million dollar business. Hydroxyapatite [Ca10(PO4)6(OH)2-HA] and alumina ceramics materials have been clinically applied in many areas of dentistry and orthopaedics. Their widespread use is based on a combination of good strength, modest fracture toughness, high wear resistance, good biocompatibility and excellent corrosion resistance. Alumina has also been used in jaw bone reconstruction. Other clinical applications include knee prostheses, bone segment replacements, bone screws, middle ear bone substitutes, and corneal replacements. Optimization of the surface structure of materials is of great concern at the present time since most failures occur on the surface (fatigue, fretting corrosion, corrosion, wear, etc.). As a result, improving the surface properties would greatly enhance the overall behaviour of materials. It is widely recognized that titanium displays poor wear resistance and that its fatigue performance depends to a large extent on its surface properties. The newly developed process, mechanical alloying MA, is therefore of considerable technological importance since it provides the possibility of dramatically improving the surface properties of titanium. Presented work describes the effect of MA treatment, as a non-conventional solid-state process, on the microstructure of IA/α-Al2O3 composites. Also, the necessary conditions for coating HA/α- Al2O3 composites on Ti-substrate were examined. To make HA and Al2O3 composites, α-Al2O3 powder was used because of its better sinterability than γ-AI2O3. HA/α-Al2O3 was successfully deposited on Ti-substrate by mechanical alloying (MA). From the X-Ray Diffraction (XRD) the as-synthesized and heat treated samples between 300C and 600C have not any phase transition or decomposition. From the scanning electron

  18. Preparation and characterization of alumina hollow fiber membranes

    Institute of Scientific and Technical Information of China (English)

    Tao WANG; Yuzhong ZHANG; Guangfen LI; Hong LI

    2009-01-01

    With the rapid development of membrane technology in water treatment, there is a growing demand for membrane products with high performance. The inorganic hollow fiber membranes are of great interest due to their high resistance to abrasion, chemical/thermal degradation, and higher surface area/volume ratio therefore they can be utilized in the fields of water treatment. In this study, the alumina (Al2O3) hollow fiber membranes were prepared by a combined phase-inversion and sintering method. The organic binder solution (dope) containing suspended Al2O3 powders was spun to a hollow fiber precursor, which was then sintered at elevated tempera-tures in order to obtain the Al2O3 hollow fiber membrane. The dope solution consisted ofpolyethersulfone (PES), N-methyl-2-pyrrolidone (NMP) and polyvinylpyrrolidone (PVP), which were used as polymer binder, solvent and additive, respectively. The prepared Al2O3 hollow fiber membranes were characterized by a scanning electron microscope (SEM) and thermal gravimetric analysis (TG). The effects of the sintering temperature and Al2O3/PES ratios on the morphological structure, pure water flux, pore size and porosity of the membranes were also investigated extensively. The results showed that the pure water flux, maximum pore size and porosity of the prepared membranes decreased with the increase in Al2O3/PES ratios and sintering temperature. When the Al2O3/PES ratio reached 9, the pure water flux and maximum pore size were at 2547L/m2·h and 1.4μm, respectively. Under 1600℃ of sintering temperature, the pure water flux and maximum pore size reached 2398 L/(m2·h) and 2.3 μm, respectively. The results showed that the alumina hollow fiber membranes we prepared were suitable for the microfiltration process. The morphology investigation also revealed that the prepared Al2O3 hollow fiber membrane retained its'asymmetric structure even after the sintering process.

  19. The dominant effect of alumina on nearfield plume radiation

    Science.gov (United States)

    Laredo, David; Netzer, David W.

    1993-11-01

    Solid propellant rocket motors can achieve high specific impulse with metal fuel additives such as aluminum. Combustion of aluminum produces condensed alumina particles. Besides causing performance losses in the nozzle, the condensed Al2O3 particles are the major source of primary smoke in the exhaust plume. The particulate matter can also have major effects upon the plume i.r. signature. High number densities of particles can block gas-phase radiation from the plume. They can also be the source of radiation, especially the larger particles which exit the nozzle not in thermal equilibrium with the gas. In the past, the expected effects of particle size on the plume i.r. signature have been determined almost exclusively from predictions made with flow and radiation codes. The aim of the present work was to investigate the role of the Al/Al2O3 particles from a highly loaded solid propellant (up to 16% in weight) on the plume radiation of a small rocket motor (5 cm in diameter). The spatial variation of particle size distribution was simultaneously measured with the overall radiation of a portion of the plume in the i.r. band (3.5-5.0 microns). In micro-motors, operating with highly aluminized solid propellant, the condensed particles in the near exhaust plume were the major source of radiation in the 3.5-5 micron wavelength band. Motors with longer residence time and operating at medium chamber pressures produced more particles in the micron sized range. The role of after burning was predominately confined to reheating of the alumina particles to a higher temperature, at which the condensed Al2O3 radiated more than gaseous species. Even with 30% Al2O3 in the plume, the plume of small motors can be considered as approximately conical in shape, with volume distributed radiating sources. Motor conditions producing larger particles in the plume core were thus found to increase plume radiation from that region. The overall apparent emissivity of the plume was between 0

  20. Rapid fabrication of self-ordered porous alumina with 10-/sub-10-nm-scale nanostructures by selenic acid anodizing.

    Science.gov (United States)

    Nishinaga, Osamu; Kikuchi, Tatsuya; Natsui, Shungo; Suzuki, Ryosuke O

    2013-01-01

    Anodic porous alumina has been widely investigated and used as a nanostructure template in various nanoapplications. The porous structure consists of numerous hexagonal cells perpendicular to the aluminum substrate and each cell has several tens or hundreds of nanoscale pores at its center. Because the nanomorphology of anodic porous alumina is limited by the electrolyte during anodizing, the discovery of additional electrolytes would expand the applicability of porous alumina. In this study, we report a new self-ordered nanoporous alumina formed by selenic acid (H2SeO4) anodizing. By optimizing the anodizing conditions, anodic alumina possessing 10-nm-scale pores was rapidly assembled (within 1 h) during selenic acid anodizing without any special electrochemical equipment. Novel sub-10-nm-scale spacing can also be achieved by selenic acid anodizing and metal sputter deposition. Our new nanoporous alumina can be used as a nanotemplate for various nanostructures in 10-/sub-10-nm-scale manufacturing. PMID:24067318

  1. Influence of Polymer Restraint on Ballistic Performanceof Alumina Ceramic Tiles

    Directory of Open Access Journals (Sweden)

    P.R.S. Reddy

    2008-03-01

    Full Text Available An experimental study has been carried out to evaluate the influence of confinement ofalumina ceramic tiles through polymer restraint, on its ballistic performance. Tiles of 99.5 per centpurity alumina were subjected to ballistic impact against 7.62 mm armour piercing projectiles atvelocities of about 820 m/s. The tiles of size 75 mm x 75 mm x 7 mm were confined on both facesby effectively bonding varying numbers of layers of polymer fabrics. These were then bondedto a 10 mm thick fibre glass laminate as a backing using epoxy resin. High performance polyethyleneand aramid polymer fabrics were used in the current set of experiments for restraining the tiles.Comparative effects of confinement on energy absorption of tiles with varied number of layersof fabrics were evaluated. It was observed that by providing effective confinement to the tile,energy absorption could be doubled with increase in areal density by about 13 per cent.Photographs of the damage and the effects of restraint on improvement in energy absorptionof ceramic tiles are presented and discussed.

  2. INVESTIGATION OF THERMAL SHOCK BEHAVIOUR IN ALUMINA BASED REFRACTORY BRICKS

    Directory of Open Access Journals (Sweden)

    N. Sinan KÖKSAL

    2003-02-01

    Full Text Available cUnderstanding of mechanical and thermal properties of refractory bricks used in industry is an important aspect to determine appropriate operating conditions. In this study, commercial refractory materials used in the sector of iron steel 45 % and 80 % alumina (Al2O3 of content refractory bricks were investigated. To determinate thermal shock behavior and mechanical properties of samples, thermal shock tests were applied by quenching in the water at the temperature differences of 500, 700, 900 and 1000 0 C. Three point bending test was examined for changes occured in the microstructure of materials. The critical temperature difference, modulus of rupture (MOR, changes of elastic modulus (E, thermal shock parameters such as resistance to crack initiation (R and resistance to crack propagation (R''' were calculated. Not with thermal treatment samples was examined same properties in the room temperature and to compare results of tests. The critical temperature difference of materials was found to be about 600 0 C. Crack start from samples of edges, space of spilling grains and microcracks occured around grains and they cause a damage by connecting to each other.

  3. Surface modification of nanoporous alumina membranes by plasma polymerization

    International Nuclear Information System (INIS)

    The deposition of plasma polymer coatings onto porous alumina (PA) membranes was investigated with the aim of adjusting the surface chemistry and the pore size of the membranes. PA membranes from commercial sources with a range of pore diameters (20, 100 and 200 nm) were used and modified by plasma polymerization using n-heptylamine (HA) monomer, which resulted in a chemically reactive polymer surface with amino groups. Heptylamine plasma polymer (HAPP) layers with a thickness less than the pore diameter do not span the pores but reduce their diameter. Accordingly, by adjusting the deposition time and thus the thickness of the plasma polymer coating, it is feasible to produce any desired pore diameter. The structural and chemical properties of modified membranes were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM) and x-ray electron spectroscopy (XPS). The resultant PA membranes with specific surface chemistry and controlled pore size are applicable for molecular separation, cell culture, bioreactors, biosensing, drug delivery, and engineering complex composite membranes

  4. Anodisation with dynamic current control for tailored alumina coatings

    Science.gov (United States)

    Sieber, M.; Althöfer, I.; Höhlich, D.; Scharf, I.; Böttger, D.; Böttger, S.; Böttger, E.; Lampke, T.

    2016-03-01

    The anodic oxidation process is commonly used to refine the surface of aluminium and its alloys. Compared to the substrate, the alumina layers produced by anodising exhibit an increased hardness and chemical resistance. Thus, the corrosion and wear resistance are generally improved. The coatings are also electrically isolating and may serve decorative purposes. Applying a time-variant, dynamic electrical process control by pulse-current or current-steps is a promising approach to improve the coating properties, which is partially deployed in an industrial scale. In the present work, the influence of dynamic electrical process control on the coating properties is examined by means of a design of experiments (DOE). The effects of various electrolyte compositions and temperatures as well as processing time are considered with regard to coating thickness, hardness, wear resistance and the electrical energy consumption during the formation of the coatings. Information about the statistical significance of the effects of the parameters on the considered properties is obtained by an analysis of variance (ANOVA).

  5. Solvent mediated assembly of nanoparticles confined in mesoporous alumina.

    Energy Technology Data Exchange (ETDEWEB)

    Alvine, K. J.; Pontoni, D.; Shpyrko, O. G.; Pershan, P. S.; Cookson, D. J.; Shin, K.; Russell, T. P.; Brunnbauer, M.; Stellacci, F.; Gang, O.; BNL; Massachusetts Inst. of Tech.; Univ. of Massachusetts; Harvard Univ.; Univ. Massachusetts

    2006-01-01

    The controlled self-assembly of thiol stabilized gold nanocrystals in a mediating solvent and confined within mesoporous alumina was probed in situ with small angle x-ray scattering. The evolution of the self-assembly process was controlled reversibly via regulated changes in the amount of solvent condensed from an undersaturated vapor. Analysis indicated that the nanoparticles self-assembled into cylindrical monolayers within the porous template. Nanoparticle nearest-neighbor separation within the monolayer increased and the ordering decreased with the controlled addition of solvent. The process was reversible with the removal of solvent. Isotropic clusters of nanoparticles were also observed to form temporarily during desorption of the liquid solvent and disappeared upon complete removal of liquid. Measurements of the absorption and desorption of the solvent showed strong hysteresis upon thermal cycling. In addition, the capillary filling transition for the solvent in the nanoparticle-doped pores was shifted to larger chemical potential, relative to the liquid/vapor coexistence, by a factor of 4 as compared to the expected value for the same system without nanoparticles.

  6. Pyrolysis of plastic waste using alumina-pumice as catalyst

    International Nuclear Information System (INIS)

    Efforts to convert plastic waste to liquid fuel have been carried out, but the yield was not so promising yet. Various catalysts have been studied to drive the product more to the liquid fuel. In this study, alumina-pumice produced from cheap local materials, was used as catalyst. Solid polyethylene plastic waste was melted in a feed compartment surrounding the tube reactor, and the vapor flowed downward through the catalyst bed which was supported by small glass marbles. Air and water coolers were used to cool and condense the product. Liquid and uncondensable gas were collected in receivers and bottle filled with brine, respectively. The physical properties of a specific liquid product were tested according to the ASTM methods. Liquid and gas products increased with time and temperature, and the rate of liquid and gas formations followed first order reaction. Using 100 g of plastic waste and 40 g of catalyst, the favorable time and temperature of pyrolysis were 105 minutes and 653-673 K, respectively. Under this condition, 86 - 87 % of liquid, 45 - 53 mL/g of gas, and 1% of solid residue were obtained. The quantity of liquid product was higher than the previous work (which was just 70-75 %) and its physical properties were between those of kerosene and diesel oil. The gross heating value of the liquid was 49 796.03 J/g, and the gas burnt with yellow flame and some soot. (Author)

  7. Ni Catalysts Supported on Modified Alumina for Diesel Steam Reforming

    Directory of Open Access Journals (Sweden)

    Antonios Tribalis

    2016-01-01

    Full Text Available Nickel catalysts are the most popular for steam reforming, however, they have a number of drawbacks, such as high propensity toward coke formation and intolerance to sulfur. In an effort to improve their behavior, a series of Ni-catalysts supported on pure and La-, Ba-, (La+Ba- and Ce-doped γ-alumina has been prepared. The doped supports and the catalysts have been extensively characterized. The catalysts performance was evaluated for steam reforming of n-hexadecane pure or doped with dibenzothiophene as surrogate for sulphur-free or commercial diesel, respectively. The undoped catalyst lost its activity after 1.5 h on stream. Doping of the support with La improved the initial catalyst activity. However, this catalyst was completely deactivated after 2 h on stream. Doping with Ba or La+Ba improved the stability of the catalysts. This improvement is attributed to the increase of the dispersion of the nickel phase, the decrease of the support acidity and the increase of Ni-phase reducibility. The best catalyst of the series doped with La+Ba proved to be sulphur tolerant and stable for more than 160 h on stream. Doping of the support with Ce also improved the catalytic performance of the corresponding catalyst, but more work is needed to explain this behavior.

  8. Two-level tunneling systems in amorphous alumina

    Science.gov (United States)

    Lebedeva, Irina V.; Paz, Alejandro P.; Tokatly, Ilya V.; Rubio, Angel

    2014-03-01

    The decades of research on thermal properties of amorphous solids at temperatures below 1 K suggest that their anomalous behaviour can be related to quantum mechanical tunneling of atoms between two nearly equivalent states that can be described as a two-level system (TLS). This theory is also supported by recent studies on microwave spectroscopy of superconducting qubits. However, the microscopic nature of the TLS remains unknown. To identify structural motifs for TLSs in amorphous alumina we have performed extensive classical molecular dynamics simulations. Several bistable motifs with only one or two atoms jumping by considerable distance ~ 0.5 Å were found at T=25 K. Accounting for the surrounding environment relaxation was shown to be important up to distances ~ 7 Å. The energy asymmetry and barrier for the detected motifs lied in the ranges 0.5 - 2 meV and 4 - 15 meV, respectively, while their density was about 1 motif per 10 000 atoms. Tuning of motif asymmetry by strain was demonstrated with the coupling coefficient below 1 eV. The tunnel splitting for the symmetrized motifs was estimated on the order of 0.1 meV. The discovered motifs are in good agreement with the available experimental data. The financial support from the Marie Curie Fellowship PIIF-GA-2012-326435 (RespSpatDisp) is gratefully acknowledged.

  9. Aggregation and settling in aqueous polydisperse alumina nanoparticle suspensions

    CERN Document Server

    Witharana, Sanjeeva; Xu, Dan; Lai, Xiaojun; Ding, Yulong

    2012-01-01

    Nanoparticle suspensions (also called nanofluids) are often polydisperse and tend to settle with time. Settling kinetics in these systems are known to be complex and hence challenging to understand. In this work, polydisperse spherical alumina (Al2O3) nanoparticles in the size range of ~10-100nm were dispersed in water and examined for aggregation and settling behaviour near its isoelectric point (IEP). A series of settling experiments were conducted and the results were analysed by photography and by Small Angle X-ray Scattering (SAXS). The settling curve obtained from standard bed height measurement experiments indicated two different types of behaviour, both of which were also seen in the SAXS data. But the SAXS data were remarkably able to pick out the rapid settling regime as a result of the high temporal resolution (10s) used. By monitoring the SAXS intensity, it was further possible to record the particle aggregation process for the first time. Optical microscopy images were produced on drying and drie...

  10. Lightweight alumina refractory aggregate: Phase 3, Full-scale demonstration

    Energy Technology Data Exchange (ETDEWEB)

    Swansiger, T.G.; Pearson, A.

    1996-07-16

    Technical problems (higher than target fired density, and poor intermediate strength after burnout but before sintering) were addressed and solved; solution involved use of large loading of CP-5 alumina (controlled pore, rehydratable), increased loading of one of the binders, and a steam aging step. Resistance of the lightweight aggregate in a brick formulation to steel slag penetration was assessed in a preliminary test and found to be almost as good as that of T-64. Pelletized process economic feasibility study was updated, based on production levels of 10,000 and 20,000 mt/year, the most up- to-date raw material costs, and the assumption of a retrofit into the Arkansas plant tabular production facility. For the 10,000 mt/y production level, the required selling price of 35% more than the T- 64 selling price exceeds the {le}25% objective. The market survey will determine whether to proceed with the full scale demonstration that will produce at least 54.4 mt (120,000 lb) of the aggregate for incorporation into products, followed by end-user testing and evaluation.

  11. Preparation and FMR analysis of Co nanowires in alumina templates

    Energy Technology Data Exchange (ETDEWEB)

    Kartopu, G. [School of Engineering, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Department of Physics, Bozok University, 66500 Yozgat (Turkey)], E-mail: giray.kartopu@nottingham.ac.uk; Yalcin, O. [Department of Physics, Bozok University, 66500 Yozgat (Turkey); Kazan, S.; Aktas, B. [Department of Physics, Gebze Institute of Technology, 41400 Gebze, Kocaeli (Turkey)

    2009-05-15

    Magnetic and structural properties of a high aspect ratio Co nanowire (NW) array electrodeposited in free-standing porous alumina template with a pore diameter of {approx}200 nm are studied. Considered collectively, X-ray diffraction analysis, magnetometer and ferromagnetic resonance (FMR) measurements indicate that both the c-axis of crystal structure and the easy axis of magnetization are aligned preferentially perpendicular to the NW axis. The FMR spectra are characterized with very broad (a few kG) breadths and exhibit asymmetric shape in low field region due to under-saturation effects. Surprisingly, FMR spectra also revealed the presence of a spin-wave mode (SWM) as the applied field direction approached parallel to the film plane, i.e. perpendicular to the NWs. A brief discussion on this observation is provided. Further, characteristic magnetic parameters of the studied NW array were obtained by fitting the field angle-dependent FMR spectra and resonance field by using an analytical model that considers various factors affecting the total anisotropy.

  12. Combustion chemical vapor deposition (CCVD) of LaPO4 monazite and beta-alumina on alumina fibers for ceramic matrix composites

    International Nuclear Information System (INIS)

    This research used the low cost, open atmosphere combustion chemical vapor deposition (CCVDSM) method to efficiently deposit protective coatings onto alumina fibers (3M NextelTM610) for use in ceramic matrix composites (CMCs). La-monazite (LaPO4) and beta-alumina were the primary candidate debonding coating materials investigated. The coated fibers provide thermochemical stability, as well as desired debonding/sliding interface characteristics to the CMC. Dense and uniform La-phosphate coatings were obtained at deposition temperatures as low as 900-1000 C with minimal degradation of fibers. However, all of the β-alumina phases required high deposition temperatures and, thus, could not be applied onto the NextelTM610 alumina fibers. The fibers appeared to have complete and relatively uniform coatings around individual filaments when 420 and 1260 filament tows were coated via the CCVD process. Fibers up to 3 feet long were fed through the deposition flame in the laboratory of MicroCoating Technologies (MCT). TEM analyses performed at Wright-Patterson AFB on the CCVD coated fibers showed a 10-30 nm thick La-rich layer at the fiber/coating interface, and a layer of columnar monazite 0.1-1 μm thick covered with sooty carbon of <50 nm thick on the outside. A single strength test on CCVD coated fibers performed by 3M showed that the strength value fell in the higher end of data from other CVD coated samples. (orig.)

  13. Technology of obtaining of cryolite and aluminium fluoride from alumina- and fluoride containing wastes of aluminium production

    International Nuclear Information System (INIS)

    This article is devoted to technology of obtaining of cryolite and aluminium fluoride from alumina- and fluoride containing wastes of aluminium production. Thus, the investigations on elaboration of technology of obtaining of cryolite and aluminium fluoride from alumina- and fluoride containing wastes of aluminium production by means of sulfuric acid decomposition method are carried out. The optimal parameters of technological processes are found. The physicochemical analysis of fluoride containing wastes is conducted. The flowsheet of obtaining of cryolite, aluminium fluoride and alumina from alumina- and fluoride containing wastes is presented.

  14. Preparation and characterization of multilayer mesoporous γ-alumina membrane obtained via sol-gel using new precursors

    OpenAIRE

    Tafrishi R.; Taheri-Nassaj E.; Sadighzadeh A.; Eskandari M. Jafari

    2015-01-01

    In this paper, a mesoporous γ-alumina membrane coated on a macroporous α-alumina support via sol-gel method has been reported. A crack-free γ-alumina membrane was obtained by adding PVA to the alumina solution and optimum parameters of roughness, temperature and porosity were achieved. The support was dip-coated in different solutions using two new different solvents with different particle size distributions. Using these two solvents led to the uniform distribution of pore size in the final ...

  15. Enhanced fluoride adsorption by nano crystalline γ-alumina: adsorption kinetics, isotherm modeling and thermodynamic studies

    Science.gov (United States)

    Chinnakoti, Prathibha; Chunduri, Avinash L. A.; Vankayala, Ranganayakulu K.; Patnaik, Sandeep; Kamisetti, Venkataramaniah

    2016-06-01

    Nano materials in particular nano oxides with enhanced surface area and an excellent catalytic surface serve as potential adsorbents for defluoridation of water. In the present study nano γ-alumina was synthesized through a simple and low cost, surfactant assisted solution combustion method. As synthesized material was characterized by XRD and FESEM for its phase, size and morphological characteristics. Surface properties have been investigated by BET method. Nano γ-alumina was further used for a detailed adsorption study to remove fluoride from water. Batches of experiments were performed at various experimental conditions such as solution pH, adsorbent dose, initial fluoride concentration and contact time to test the defluoridation ability of γ-alumina. Fluoride Adsorption by nano sized γ-alumina was rapid and reached equilibrium within two hours. The adsorption worked well at pH 4.0, where ˜96 % of fluoride was found to be adsorbed on adsorbent. It was possible to reduce fluoride levels to as low as 0.3 mg/L (within the safe limit of WHO: ≤1.5 mg/L) from an initial fluoride levels of 10 mg/L. This could be achieved using a very small quantity, 1 g/L of γ-alumina at pH 4 within 1 h of contact time. Defluoridation capacity of nano γ-alumina was further investigated by fitting the equilibrium data to various isotherm as well as kinetic models. The present study revealed that γ-alumina could be an efficient adsorbent for treating fluoride contaminated water.

  16. Agentes ligantes para concretos refratários: sílica coloidal e alumina hidratável Colloidal silica and hydratable alumina as refractory binder agents

    Directory of Open Access Journals (Sweden)

    M. R. Ismael

    2007-06-01

    Full Text Available Sílica coloidal e alumina hidratável destacam-se como importantes alternativas à substituição do cimento de aluminato de cálcio como agentes ligantes para concretos refratários aluminosos. Baseando-se nas vantagens e desvantagens destes agentes ligantes isentos de CaO, é razoável supor que a combinação de ambos poderia maximizar os benefícios e reduzir os aspectos negativos observados quando estes são individualmente aplicados. A elevada permeabilidade devido à presença de sílica coloidal poderia reduzir os riscos de explosão durante a secagem das composições ligadas por alumina hidratável. Em paralelo, a porosidade total do sistema contendo sílica coloidal poderia ser diminuída devido à presença de alumina hidratável. Neste trabalho, o desempenho de concretos refratários aluminosos contendo sílica coloidal e alumina hidratável como sistema ligante foram avaliados quanto ao comportamento de mistura, permeabilidade, porosidade aparente, resistência mecânica e perfil de secagem.Colloidal silica and hydratable alumina can be pointed out as important substitutes to the calcium aluminate cements as calcium-free binders for refractory castables. Based on the advantages and drawbacks of these binders, it is reasonable to consider that their combination could maximize the advantages and reduce the negative aspects observed when they are individually used. The high permeability level generated by the colloidal silica would reduce the risks of explosive spalling of hydratable alumina containing castables during first heat-up. Additionally, the total porosity of the colloidal silica containing systems could be decreased due to the hydration of the HA. In the present work, colloidal silica and hydratable alumina were combined in a new calcium-free binding system. Their rheological behavior, permeability level, apparent porosity, mechanical strength and drying rate profile were compared with the performance of each binder

  17. Sulfur and Moisture Effects on Alumina Scale and TBC Spallation

    Science.gov (United States)

    Smialek, James L.

    2007-01-01

    It has been well established that a few ppmw sulfur impurity may segregate to the interface of thermally grown alumina scales and the underlying substrate, resulting in bond degradation and premature spallation. This has been shown for NiAl and NiCrAl-based alloys, bare single crystal superalloys, or coated superalloys. The role of reactive elements (especially Y) has been to getter the sulfur in the bulk and preclude interfacial segregation. Pt additions are also very beneficial, however a similar thermodynamic explanation does not apply. The purpose of the present discussion is to highlight some observations of these effects on Rene'142, Rene'N5, PWA1480, and PWA1484. For PWA1480, we have mapped cyclic oxidation and spallation in terms of potential sulfur interfacial layers and found that a cumulative amount of about one monolayer is sufficient to degrade long term adhesion. Depending on substrate thickness, optimum performance occurs if sulfur is reduced below about 0.2-0.5 ppmw. This is accomplished in the laboratory by hydrogen annealing or commercially by melt-fluxing. Excellent 1150 C cyclic oxidation is thus demonstrated for desulfurized Rene'142, Rene'N5, and PWA1484. Alternatively, a series of N5 alloys provided by GE-AE have shown that as little as 15 ppmw of Y dopant was effective in providing remarkable scale adhesion. In support of a Y-S gettering mechanism, hydrogen annealing was unable to desulfurize these alloys from their initial level of 5 ppmw S. This impurity and critical doping level corresponds closely to YS or Y2S3 stoichiometry. In many cases, Y-doped alloys or alloys with marginal sulfur levels exhibit an oxidative sensitivity to the ambient humidity called Moisture-Induced Delayed Spallation (MIDS). After substantial scale growth, coupled with damage from repeated cycling, cold samples may spall after a period of time, breathing on them, or immersing them in water. While stress corrosion arguments may apply, we propose that the underlying

  18. Characteristics of the Na/beta-alumina/Na cell as a sodium vapor pressure sensor

    International Nuclear Information System (INIS)

    The EMF and voltage-current characteristics for a galvanic cell with the configuration Na vapor (P1)/sodium beta-alumina/Na vapor (P2) were studied. It was verified that the EMF followed the Nernst relation over a wide pressure range. For example, when P1 = 2 x 10-2 mm Hg and beta-alumina temperature = 3400C, the measured EMF agreed with the calculated value in P2 range from 10-5 to 10-2 mm Hg. At lower pressure range, the measured EMF showed a negative deviation. Coexisting argon gas did not influence the cell EMF characteristic. In an atmosphere containing oxygen, the measured EMF was very high at first. Then it decreased and finally approached a value which agreed with the Nernst equation after several hours. At low beta-alumina temperatures, current saturation was observed in the voltage versus current relation with the anode on the P2 side. Although the sodium pressure could be determined from saturating current measurement, the measurable pressure range was narrower than that for EMF measurement. At high beta-alumina temperature, current saturation was not clear. Values of 6 x 10-6 (Ω cm)-1 for the electron conductivity and 6 x 10-10 (Ω cm)-1 for the hole conductivity at 3400C were obtained for beta-alumina from the voltage-current characteristics at low sodium pressure. (Auth.)

  19. High-temperature corrosion testing of alumina and zirconia in uranium hexafluoride environment

    International Nuclear Information System (INIS)

    Uranium fluoride gases are proposed as primary candidate fuels for ultrahigh-temperature gas core or vapor core reactor systems for a variety of space power applications. In these systems, the peak temperature of the fissioning gas can be as high as 5000 K and the inner wall temperature of the reactor cavity is within the range of 1000 to 2000 K. Two kinds of alumina, sapphire and polycrystal alpha alumina, and CaO partially stabilized zirconia are exposed to uranium hexafluoride gas in temperatures ranging from 973 to 1473 K and from 873 to 1073 K, respectively. Exposure tests are conducted in a UF6 flowing loop with an alumina reaction tube housed in a 1500 K electric-heated furnace. The reaction rates are measured using a discontinuous gravimetric method. The morphology of the exposed surfaces was observed by optical microscopy and scanning electron microscopy, and the reaction products were identified by x-ray diffraction and energy dispersive x-ray spectroscopy. Results indicate that alumina provides a relatively higher service temperature in UF6 environment. However, due to the highly reactive and chemically aggressive nature of UF6 at high temperatures, the maximum service temperature of alumina for a UF6-based gas core reactor is limited to 1273 K. Zirconia at temperatures above 973 K is not compatible with UF6

  20. Highly-sensitive Detection of Salvianolic Acid B using Alumina Microfibers-modified Electrode

    International Nuclear Information System (INIS)

    Alumina microfibers with porous structures were prepared through hydrothermal reaction, and then used to modify the surface of carbon paste electrode (CPE). After modification with alumina microfibers, the electrochemical activity of CPE was found to be greatly improved. On the surface of alumina microfibers-modified CPE, the oxidation peak current of salvianolic acid B, a main bioactive compound in Danshen with anti-oxidative and anti-inflammatory effects, was remarkably increased compared with that on the bare CPE surface. The influences of pH value, amount of alumina microfibers and accumulation time were studied. Based on the strong signal amplification effects of alumina microfibers, a novel electrochemical method was developed for the detection of salvianolic acid B. The linear range was from 5 μg L-1 to 0.3 mg L-1, and the detection limit was 2 μg L-1 (2.78 nM) after 1-min accumulation. The new method was successfully used to detect salvianolic acid B in ShuangDan oral liquid samples, and the recovery was over the range from 97.4% to 102.9%

  1. Emission study of alumina plasma produced by a KrF laser

    Energy Technology Data Exchange (ETDEWEB)

    Yahiaoui, K., E-mail: kyahiaoui@cdta.dz [Centre de Développement des Technologies Avancées, cité 20 aout 1956, BP 17, Baba Hassen, Alger (Algeria); Abdelli-Messaci, S.; Messaoud-Aberkane, S.; Kerdja, T. [Centre de Développement des Technologies Avancées, cité 20 aout 1956, BP 17, Baba Hassen, Alger (Algeria); Kellou, H. [Université des Sciences et de la Technologie Houari Boumediene, BP 32, El-Allia, 16111 Bab-Ezzouar, Alger (Algeria)

    2014-03-01

    We report on the plasma emission formed from an α-alumina target when irradiated by laser into vacuum and through oxygen gas. Two diagnostic tools have been used: ICCD camera fast imaging and optical emission spectroscopy. The alumina plasma was induced by a KrF laser beam at a wavelength of 248 nm and pulse duration of 25 ns. The laser fluence was set to 8 J/cm{sup 2} and the oxygen pressure was varied from 0.01 to 5 mbar. By using the ICCD camera, two dimensional images of the plasma expansion were taken at different times. Depending on oxygen pressure and time delay, the expansion behavior of the plasma showed free expansion, plume splitting, shock wave formation, hydrodynamic instability and deceleration of the plume. Using optical emission spectroscopy, the plasma emission revealed the presence of neutral Al I, Al II, Al III into vacuum and under oxygen ambiance. The molecular emission of aluminum oxide (AlO) was detected only in oxygen ambiance. It should be noted that no oxygen lines were observed. Finally, the evolution of the electronic temperature along the normal axis from the target surface, into vacuum, was estimated using the Boltzmann plot method. - Highlights: • Ablated mass measurements of α-alumina target irradiated by a laser in nanosecond regime. • Optical emission spectroscopy of alumina plasma. • Fast imaging diagnostic of alumina plume using ICCD camera.

  2. Agglomeration, sedimentation, and cellular toxicity of alumina nanoparticles in cell culture medium

    International Nuclear Information System (INIS)

    The cytotoxicity of alumina nanoparticles (NPs) was investigated for a wide range of concentration (25–200 μg/mL) and incubation time (0–72 h) using floating cells (THP-1) and adherent cells (J774A.1, A549, and 293). Alumina NPs were gradually agglomerated over time although a significant portion of sedimentation occurred at the early stage within 6 h. A decrease of the viability was found in floating (THP-1) and adherent (J774A.1 and A549) cells in a dose-dependent manner. However, the time-dependent decrease in cell viability was observed only in adherent cells (J774A.1 and A549), which is predominantly related with the sedimentation of alumina NPs in cell culture medium. The uptake of alumina NPs in macrophages and an increased cell-to-cell adhesion in adherent cells were observed. There was no significant change in the viability of 293 cells. This in vitro test suggests that the agglomeration and sedimentation of alumina NPs affected cellular viability depending on cell types such as monocytes (THP-1), macrophages (J774A.1), lung carcinoma cells (A549), and embryonic kidney cells (293).

  3. ATOMIC LAYER DEPOSITION OF TITANIUM OXIDE THIN FILMS ONNANOPOROUS ALUMINA TEMPLATES FOR MEDICAL APPLICATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Brigmon, R.

    2009-05-05

    Nanostructured materials may play a significant role in controlled release of pharmacologic agents for treatment of cancer. Many nanoporous polymer materials are inadequate for use in drug delivery. Nanoporous alumina provides several advantages over other materials for use in controlled drug delivery and other medical applications. Atomic layer deposition was used to coat all the surfaces of the nanoporous alumina membrane in order to reduce the pore size in a controlled manner. Both the 20 nm and 100 nm titanium oxide-coated nanoporous alumina membranes did not exhibit statistically lower viability compared to the uncoated nanoporous alumina membrane control materials. In addition, 20 nm pore size titanium oxide-coated nanoporous alumina membranes exposed to ultraviolet light demonstrated activity against Escherichia coli and Staphylococcus aureus bacteria. Nanostructured materials prepared using atomic layer deposition may be useful for delivering a pharmacologic agent at a precise rate to a specific location in the body. These materials may serve as the basis for 'smart' drug delivery devices, orthopedic implants, or self-sterilizing medical devices.

  4. Study of Mechanical Properties and Fracture Mode of Alumina-Silicon Carbide Nanocomposites

    Science.gov (United States)

    Rahimnezhad Yazdi, A.; Baharvandi, H. R.; Abdizadeh, H.; Ehsani, N.

    In this study Al2O3-SiC nanocomposites have been fabricated by mixing of alumina and silicon carbide nano powders, followed by hot pressing at 1700°C. The mechanical properties and fracture mode of Al2O3-SiC nanocomposites containing different volume fractions (5, 10 and 15%) of nano scale SiC particles were investigated and compared with those of alumina. Al2O3-SiC powders were prepared by planetary milling in isopropanol. Fracture mode of specimens was investigated by means of scanning electron microscopy. Nanocomposites were tougher than alumina when they were hot pressed at the same temperature, and the values of nanocomposite's flexural strength and hardness were higher than those of alumina. Flexural strength, hardness and fracture toughness of the nanocomposites increase by increasing the volume percent of SiC up to 10% and then decrease slightly. The Scanning electron microscopy observations showed that fracture mode changes from intergranular for alumina to transgranular for nanocomposites. Finally X-ray diffraction analysis couldn't detect any chemical reactions between Al2O3 and SiC particles.

  5. Preparation and characterization of ultrafine alumina via sol-gel polymeric route

    International Nuclear Information System (INIS)

    Ultrafine alumina powder was prepared through resin formation between urea and formaldehyde. Aluminium stearate soap was introduced during resin preparation. Ethylene glycol was used to terminate the thermosetting reaction. Calcination of the product was carried out at 700, 1000, 1100, 1300 and 1400 deg. C to obtain aluminium oxide. IR and Raman spectroscopic analysis indicated the occupation of Al3+ at different sites in the polymer network (C=O, -NH2, C-O, -NH, and -CH2OH). X-ray diffraction of powder calcined at 1000 deg. C revealed the presence of a mixture of α- and θ-alumina together, while a mixture of α- and β-alumina phases were obtained on calcination at 1400 deg. C. Transmission electron microscope (TEM) examination of the powder fired at 700 deg. C showed uniform grains in the form of clusters with average size between 22.02 and 30.5 nm. Clusters are multi-particles as evident from the electron diffraction pattern. Crystallite size of alumina powder calcined at 1000 deg. C was found to be ∼25.67 nm, while that of powder calcined at1400 deg. C was ∼30.52 nm. The calculated specific surface area of alumina powder calcined at 1000 deg. C was 59.17 m2 g-1, while that calcined at 1400 deg. C was 49.77 m2 g-1

  6. Nanoscale-alumina induces oxidative stress and accelerates amyloid beta (Aβ) production in ICR female mice

    Science.gov (United States)

    Shah, Shahid Ali; Yoon, Gwang Ho; Ahmad, Ashfaq; Ullah, Faheem; Amin, Faiz Ul; Kim, Myeong Ok

    2015-09-01

    The adverse effects of nanoscale-alumina (Al2O3-NPs) have been previously demonstrated in both in vitro and in vivo studies, whereas little is known about their mechanism of neurotoxicity. It is the goal of this research to determine the toxic effects of nano-alumina on human neuroblastoma SH-SY5Y and mouse hippocampal HT22 cells in vitro and on ICR female mice in vivo. Nano-alumina displayed toxic effects on SH-SY5Y cell lines in three different concentrations also increased aluminium abundance and induced oxidative stress in HT22 cells. Nano-alumina peripherally administered to ICR female mice for three weeks increased brain aluminium and ROS production, disturbing brain energy homeostasis, and led to the impairment of hippocampus-dependent memory. Most importantly, these nano-particles induced Alzheimer disease (AD) neuropathology by enhancing the amyloidogenic pathway of Amyloid Beta (Aβ) production, aggregation and implied the progression of neurodegeneration in the cortex and hippocampus of these mice. In conclusion, these data demonstrate that nano-alumina is toxic to both cells and female mice and that prolonged exposure may heighten the chances of developing a neurodegenerative disease, such as AD.

  7. The model thin film alumina catalyst support suitable for catalysis-oriented surface science studies

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • New model catalyst on “AlOx-thin film/FeCrAl” support is presented. • Metal substrate minimizes sample charging, allows fast and uniform heating. • Surface is rough to model the catalyst support's morphology. • Planar alumina is stable in air/gases/solutions and similar to γ-Al2O3. • New model support is suitable for in situ XPS, STM, TPD, TPR, etc. - Abstract: The preparation of thin continuous alumina film at the surface of metal substrate in UHV (ultra high vacuum) conditions is described. The peculiarities of the obtained films studied by XPS (X-ray photoelectron spectroscopy) and STM (scanning tunneling microscopy) are discussed. The long-term durability of the oxide film was tested and proved both under ambient conditions and in acidic aqueous solutions. The stability of the planar alumina samples toward oxidation by oxygen was checked in the wide ranges of gas pressure and sample temperature. The suggested procedure ensures the controlled and reproducible preparation of thin alumina films – model support appropriate for wet chemistry catalyst preparation, suitable for STM and for other Surface Science techniques studies of alumina supported metal catalysts

  8. Preparation and characterization of alpha alumina nanoparticles by in-flight oxidation of flame synthesis

    International Nuclear Information System (INIS)

    Highlights: • Flame synthesis is a compact approach for the synthesis of metal oxide nanoparticles. • Single phase alumina nanoparticles have been synthesized from commercial aluminium powders. • Spherical particle is confirmed by TEM analysis. • Photoluminescence study is discussed elaborately. -- Abstract: Alpha alumina nanoparticles were synthesized from micron-sized commercial aluminium powders by in-flight oxidation of flame synthesis. The synthesized alumina nanoparticles were characterized using X-ray diffraction (XRD) and α phase alumina was confirmed. The average grain sizes were estimated to be 98 nm using Scherer’s formula. The formation of alumina nanoparticles was identified by scanning electron microscopy (SEM). Transmission electron microscopy (TEM) study shows the different sized spherical nanoparticles ranging from 70 nm to 150 nm. The energy dispersive X-ray analysis (EDAX) confirms the presence of aluminium and oxygen in the α-Al2O3 nanoparticles. The Photoluminescence spectrum of α-Al2O3 nanoparticles reveals the presence of a large amount of oxygen vacancies

  9. Emission study of alumina plasma produced by a KrF laser

    International Nuclear Information System (INIS)

    We report on the plasma emission formed from an α-alumina target when irradiated by laser into vacuum and through oxygen gas. Two diagnostic tools have been used: ICCD camera fast imaging and optical emission spectroscopy. The alumina plasma was induced by a KrF laser beam at a wavelength of 248 nm and pulse duration of 25 ns. The laser fluence was set to 8 J/cm2 and the oxygen pressure was varied from 0.01 to 5 mbar. By using the ICCD camera, two dimensional images of the plasma expansion were taken at different times. Depending on oxygen pressure and time delay, the expansion behavior of the plasma showed free expansion, plume splitting, shock wave formation, hydrodynamic instability and deceleration of the plume. Using optical emission spectroscopy, the plasma emission revealed the presence of neutral Al I, Al II, Al III into vacuum and under oxygen ambiance. The molecular emission of aluminum oxide (AlO) was detected only in oxygen ambiance. It should be noted that no oxygen lines were observed. Finally, the evolution of the electronic temperature along the normal axis from the target surface, into vacuum, was estimated using the Boltzmann plot method. - Highlights: • Ablated mass measurements of α-alumina target irradiated by a laser in nanosecond regime. • Optical emission spectroscopy of alumina plasma. • Fast imaging diagnostic of alumina plume using ICCD camera

  10. Study on vacuum brazing of high purity alumina for application in proton synchrotron

    International Nuclear Information System (INIS)

    Highlights: • Study compares Mo–Mn metallization and active brazing routes for joining alumina. • Targeted application: UHV chamber of proton synchrotron. • Both kinds of joints were UHV compatible with helium leak rate <1.1 × 10−10 mbar l/s. • Active brazed joints met tensile and flexural strength design requirement (>50 MPa). • Active brazing is a simpler and economical route for joining high purity alumina. - Abstract: The paper describes an experimental study to evaluate two different vacuum brazing processes to obtain high purity alumina (99.7%) joints suitable for application in rapid cycle proton synchrotron. Two different brazing routes, adopted for making alumina–alumina brazed joints, included (i) multi-step Mo–Mn metallization, followed by brazing with BVAg-8 alloy and (ii) advanced single-step active brazing with CuSil-ABA® alloy. Both the brazing routes yielded helium leak tight and ultra-high vacuum (pressure < 10−9 mbar) compatible joints. Active-brazed specimens exhibited tensile and mean flexural strengths of 62 and 110 MPa, respectively. Metallized-brazed specimens, although associated with relatively lower tensile strength (35 MPa) than the targeted value (>50 MPa), displayed higher mean flexural strength of 149 MPa. The results of the study demonstrated that active brazing is a simple and cost effective alternative to conventional multi-step metallization route for producing quality joints of high purity alumina for application in rapid cycle proton synchrotron machine

  11. The model thin film alumina catalyst support suitable for catalysis-oriented surface science studies

    Energy Technology Data Exchange (ETDEWEB)

    Nartova, Anna V., E-mail: avnartova@gmail.com [Boreskov Institute of Catalysis SB RAS, Lavrentieva Ave., 5, Novosibirsk, 630090 (Russian Federation); Novosibirsk State University, Pirogova St., 2, Novosibirsk, 630090 (Russian Federation); Bukhtiyarov, Andrey V., E-mail: avb@catalysis.ru [Boreskov Institute of Catalysis SB RAS, Lavrentieva Ave., 5, Novosibirsk, 630090 (Russian Federation); Kvon, Ren I., E-mail: kvon@catalysis.ru [Boreskov Institute of Catalysis SB RAS, Lavrentieva Ave., 5, Novosibirsk, 630090 (Russian Federation); Bukhtiyarov, Valerii I., E-mail: vib@catalysis.ru [Boreskov Institute of Catalysis SB RAS, Lavrentieva Ave., 5, Novosibirsk, 630090 (Russian Federation); Novosibirsk State University, Pirogova St., 2, Novosibirsk, 630090 (Russian Federation)

    2015-09-15

    Graphical abstract: - Highlights: • New model catalyst on “AlOx-thin film/FeCrAl” support is presented. • Metal substrate minimizes sample charging, allows fast and uniform heating. • Surface is rough to model the catalyst support's morphology. • Planar alumina is stable in air/gases/solutions and similar to γ-Al{sub 2}O{sub 3}. • New model support is suitable for in situ XPS, STM, TPD, TPR, etc. - Abstract: The preparation of thin continuous alumina film at the surface of metal substrate in UHV (ultra high vacuum) conditions is described. The peculiarities of the obtained films studied by XPS (X-ray photoelectron spectroscopy) and STM (scanning tunneling microscopy) are discussed. The long-term durability of the oxide film was tested and proved both under ambient conditions and in acidic aqueous solutions. The stability of the planar alumina samples toward oxidation by oxygen was checked in the wide ranges of gas pressure and sample temperature. The suggested procedure ensures the controlled and reproducible preparation of thin alumina films – model support appropriate for wet chemistry catalyst preparation, suitable for STM and for other Surface Science techniques studies of alumina supported metal catalysts.

  12. Coating of Fe, Ni on α-alumina microspheres by heterogeneous precipitation

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The precursors with NiCO3 · 2Ni(OH)2 · 2H2O, Fe2O3 · nH2O coated alumina microspheres were prepared by the aqueous heterogeneous precipitation using metal salts, ammonium bicarbonate and α-Al2O3 micropowders as the starting materials. Magnetic metal Ni, α-Fe coated alumina, core-shell structural microspheres were successfully obtained by thermal reduction of the precursors at 700 ℃ for 2 h, respectively. Powders of the precursors and the resultant metal (Ni, α-Fe) coated alumina micropowders were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The results show that optimized precipitation parameters are concentration of alumina micropowders of 15 g/L, rate of adding reactants of 5 mL/min and pH value of 7.5.And under the optimized conditions, the spherical precursors without aggregations or agglomerations are obtained,then transferred into Ni, α-Fe coated alumina microspheres by thermal reduction. It is possible to adjust metal coating thicknesses and fabricate a multilayer structured metal/ceramics, core-shell mierospherical powder materials.

  13. Fracture Strength of Zirconia and Alumina Ceramic Crowns Supported by Implants.

    Science.gov (United States)

    Traini, Tonino; Sorrentino, Roberto; Gherlone, Enrico; Perfetti, Federico; Bollero, Patrizio; Zarone, Ferdinando

    2015-07-01

    Due to the brittleness and limited tensile strength of the veneering glass-ceramic materials, the methods that combine strong core material (as zirconia or alumina) are still under debate. The present study aims to evaluate the fracture strength and the mechanism of failure through fractographic analysis of single all-ceramic crowns supported by implants. Forty premolar cores were fabricated with CAD/CAM technology using alumina (n = 20) and zirconia (n = 20). The specimens were veneered with glass-ceramic, cemented on titanium abutments, and subjected to loading test until fracture. SEM fractographic analysis was also performed. The fracture load was 1165 (±509) N for alumina and 1638 (±662) N for zirconia with a statistically significant difference between the two groups (P = 0.026). Fractographic analysis of alumina-glass-ceramic crowns, showed the presence of catastrophic cracks through the entire thickness of the alumina core; for the zirconia-glass-ceramic crowns, the cracks involved mainly the thickness of the ceramic veneering layer. The sandblast procedure of the zirconia core influenced crack path deflection. Few samples (n = 3) showed limited microcracks of the zirconia core. Zirconia showed a significantly higher fracture strength value in implant-supported restorations, indicating the role played by the high resistant cores for premolar crowns. PMID:24779915

  14. Effect of templates on the synthesis of organized meso porous alumina

    International Nuclear Information System (INIS)

    Organized meso porous materials represent a class of molecular sieves because of its high potential for commercial applications in adsorption and catalysis. In this study, organized meso porous alumina was synthesized by the sol-gel method using various organic templates, i.e. cationic, neutral and anionic surfactants. Surface porosity of the synthesized alumina obtained exhibit materials in the meso pore ranges. The morphology of the samples consists of wormhole-like meso structure in the nano-region (20 - 70 nm). Sample with cetyl trimethylammonium bromide as cationic templates has the narrowest pore distribution centred at 8 nm as compared to samples synthesized with Triton X-114 (neutral) and stearic acid (anionic). All samples showed only Lewis acidity. Acidity and meso porous character present in these meso porous alumina samples showed that this material has potential as catalyst support and also used in Lewis acid catalyzed reactions. Study showed that the cationic surfactant is a better template to obtain uniform meso porous alumina that might be due to the weak interaction between the template and the surface of the alumina. (author)

  15. Alumina-Forming MAX Phases in Turbine Material Systems

    Science.gov (United States)

    Smialek, James L.; Harder, Bryan J.; Garg, Arnita; Nesbitt, James A.

    2015-01-01

    Coatings for high temperature turbine components are based on low conductivity YSZ thermal barriers and protective NiAl, NiCoCrAlY bond coats. Good oxidation hot corrosion resistance, intermediate CTE, and strain tolerance of Ti2AlC and Cr2AlC MAX phases are thus of special interest. Their alumina scale growth follows a cubic law in accord with FeCrAlY alloys, with oxygen grain boundary diffusivity: Dgb 1.8 x 10-10 exp(-375 kJmole) m3s. Protective cubic kinetics are also found in high pressure burner rig (6 atm., 25 ms) and TGA tests of MAXthal 211Ti2AlC. The initial portion (0.1 hr) is dominated by fast TiO2 growth (with little evidence of scale volatility in high pressure water vapor, as found for SiO2 scales). Bulk Ti2AlC and Cr2AlC substrates show promise as potential bond coats for YSZ TBCs in 1000-1200 C furnace life (500 h) tests. Cr2AlC is proving to be very resistant to 700-900 C Na2SO4 hot corrosion and is of interest for disk alloys. Preliminary diffusion bonded Cr2AlC-superalloy hybrid couples have survived 1000 hr interrupted furnace tests at 800C with no indication of cracking or debonding. Diffusion zones of -NiAl+Cr7C3 were produced in these above 1000 C, but did not grow to any great extent after 1000 hr at 800 C. Processing as coatings presents challenges, however the basic properties of MAX phases provide novel opportunities for high temperature turbine components.

  16. Diffusivity in Alumina Scales Grown on Al-MAX Phases

    Science.gov (United States)

    Smialek, James L.

    2014-01-01

    Ti3AlC2, Ti2AlC, and Cr2AlC are oxidation resistant MAX phase compounds distinguished by the formation of protective Al2O3 scales with well controlled kinetics. A modified Wagner treatment was used to obtain interfacial grain boundary diffusivity, deltaD(sub gb,O,int.), from scale growth rates and corresponding grain size. It is based on the p(O2)(exp -1/6) dependency of the double charged oxygen vacancy and oxygen diffusivity, coupled with the effective diffusion constant for short circuit grain boundary paths. Data from the literature for MAX phases was analyzed accordingly, and deltaD(sub gb,O,int.) was found to nearly coincide with the Arrhenius line developed for Zr-doped FeCrAl, where: deltaD(sub gb,O,int.) = 1.8x10(exp -10) exp(-375 kJ/RT) cubic meters/s. Furthermore, this oxidation relation suggests the more general format applicable to bulk samples under ambient conditions: deltaD(sub gb,O) = 7.567x10(exp -8) exp(-544 kJ/RT) p(O2)(exp -1/6) cubic meters/[s x Pa(exp -1/6)]. Data from many other FeCrAl(X) studies were similarly assessed to show general agreement with the relation for deltaD(sub gb,O,int.). This analysis reinforces the view that protective alumina scales grow by similar mechanisms for these Al-MAX phases and oxidation resistant FeCrAl alloys.

  17. Studies of alumina coatings formation by detonation-gun spraying

    International Nuclear Information System (INIS)

    In this paper the mechanism of detonation sprayed alumina coatings formation has been described. The detonation gun DNP5M was used spray AI/sub 2/O/sub 3/ powders having rticle diameters were between 10 and 14 micro meter. The D-Gun has L A 79 a 0.8 m-length barrel with convergent variable cross-section by volume of 0.0006 m3. The rate of fire 2.1 cycle. Per second during samples spraying was used. There is strong dependence of characteristics of obtained coatings from powder cloud location in the barrel composition of gas mixture, and barrel filling factor by gas mixture. The monotone decreasing of hardness am cross-section area of solitary coatings layers was detected. The retention of fair quantity of alpha AI/sub 2/O/sub 3/ into gas detonation sprayed coatings is connected with reduced cooling rate of solitary coatings layers, as well as with possibility of coating formation from partially melted particles at high velocity collision with substrate surface. Usually for obtaining high content of corundum AI/sub 2/O/sub 3/ into gas detonation sprayed coatings, the thickness of solitary coatings layers is increasing up to 8-18 micro meter. However, the content of alpha- AI/sub 2/O/sub 3/ into coatings depends also on other factors; increase of frequency of powder particles -substrate surface collisions during formation of solitary coatings layers; additional generation of heat due to conversion of kinetic energy to thermal; essential increase of contact temperature as result of crystallization temperature increase during impact with velocity close to 500 m/sec; and corresponding decrease of time for processing of transfer gamma-AI/sub 2/O/sub 3/ alpha-AI/sub 2/O/sub 3/ with temperature increase. (author)

  18. Studies of the hydrogen held by solids. 23. Low temperature adsorption of H2 and D2 and their separation factors on alumina, fluorided alumina, and molybdena-alumina surfaces

    International Nuclear Information System (INIS)

    Adsorption isotherms of H2 and of D2 at 78 K have been determined for alumina and modified alumina surfaces. In all cases plots of P/sub H2/ vs. P/sub D2/ for constant amounts adsorbed were linear. This behavior has been predicted by statistical thermodynamics and is shown to follow from equations used to describe chemisorption data. Values of separation factors (S) were derived from the slopes of these curves. This was justified by the earlier statistical thermodynamic formulation and by derivations from Henry's law and Langmuir adsorption isotherms. The adsorption data, however, obeyed accurately the Freundlich law and it is shown that this does not lead to the usual definition of S, i.e., a ratio of adsorption equilibrium constants. The surfaces could also be characterized in terms of fractional coverage (theta) or the amount adsorbed (n/sub H2/) at constant pressure. When the parent aluminas were dehydroxylated at increasingly higher temperature, both theta and S increased, but when surfaces were fluorided, S increased while theta decreased. Impregnation with Ga3+ greatly increased S with little change in theta, but when a molybdenum monolayer was grown onto the surface the changes in these properties were relatively small. Reduction of the molybdenum-alumina surface with H2, however, effected increases in both theta and S, whereas the latter was substantially decreased when the reducing agent was CO. Comparison is made of the present values of S with those obtained by the chromatographic method. 6 figures, 2 tables

  19. Spectrophotometric determination of silicon in alumina grit used for sand blasting of zircaloy tubes

    International Nuclear Information System (INIS)

    This paper describes a spectrophotometric method for the determination of silicon in alumina grit used for sand blasting of surface of zircaloy tubes including the inner surface. The spectrophotometric method involves fusion of the alumina grit with a mixture of sodium carbonate and borax, dissolution of the fused melt, addition of necessary reagents and measurement of absorbance of the solution at 815 nm. The molar extinction coefficients obtained for silico-molybdenum blue complex in the absence and presence of matrix respectively are 1.7309 x 104 and 1.6278 x 104 L mol-1 cm-1.The RSD achieved in this method is 1.1% (n=10) at 1% silica in alumina grit. (author)

  20. Optimisation of alumina - silicon carbide dispersions and the fabrication of nanocomposite ceramic materials

    International Nuclear Information System (INIS)

    Ceramic nanocomposite materials have been reported to have good mechanical properties. However, close control of the fabrication process must be maintained in order to achieve good dispersion of the secondary phase within the matrix which is essential if these good properties are to be obtained. To date, only powder processing in organic media has been reported. The processing conditions of alumina-silicon carbide nanocomposites have been investigated. Processing was carried out in aqueous and organic media. Optimisation of dispersion involved measurement of the zeta potential of alumina and silicon carbide aqueous slurries, selection of organic mixing media as well as the type and quantity of dispersing agent. Dense materials were obtained by hot pressing of the optimised powders. Microstructural analysis and mechanical property assessment have been carried out. A strength improvement of 30% was achieved by the addition of 5 vol% SiC to alumina. (orig.)

  1. Desorption of Furfural from Bimetallic Pt-Fe Oxides/Alumina Catalysts

    Directory of Open Access Journals (Sweden)

    Gloria Lourdes Dimas-Rivera

    2014-01-01

    Full Text Available In this work, the desorption of furfural, which is a competitive intermediate during the production of biofuel and valuable aromatic compounds, was studied using pure alumina, as well as alumina impregnated with iron and platinum oxides both individually and in combination, using thermogravimetric analysis (TGA. The bimetallic sample exhibited the lowest desorption percentage for furfural. High-resolution transmission electron microscopy (HRTEM imaging revealed the intimate connection between the iron and platinum oxide species on the alumina support. The mechanism of furfural desorption from the Pt-Fe/Al2O3 0.5%-0.5% sample was determined using physisorbed furfural instead of chemisorbed furfural; this mechanism involved the oxidation of the C=O group on furfural by the catalyst. The oxide nanoparticles on γ-Al2O3 support helped to stabilize the furfural molecule on the surface.

  2. Kinetics of zirconium oxide reduction with aluminium in the cryolite-alumina melt

    International Nuclear Information System (INIS)

    Studies on aluminothermal reduction of ZrO2 solutions in cryolite-alumina melt depending on the initial concnetration of ZrO2 in the electrolyte, alumina content, mole ratio NaF:AlF3 (cryolite ratio) and on the temperature are carried out. The coefficient of zirconium ion diffusion in the cryolite-alumina melt at 1273 K, which constitutes 4.186x10-9 m2/s, is calculated. Activation energy of the reduction process is 51.04 kJ/mol. It is shown that the rate of zirconium oxide reduction is determined by the process of zirconium ion delivery to the surface of the metallic phase

  3. Influence of the alumina microstructure and composition in thermoluminescence for using in dosimetry

    CERN Document Server

    Silva, M R

    2001-01-01

    Among its various applications alumina may be used in thermoluminescent dosimeters (TLD) to radiations. The TLD are commonly used to determine the absorbed doses of radiation received in many application fields as nuclear installations, radiodiagnostic and radiotherapy in medicine. In this work it was developed a study of the influence of the microstructure, grain size and composition on the thermoluminescent properties in alumina (pure and carbon doped). The alumina and carbon powders used as starting materials were characterized by x-ray diffraction (XRD), chemical analysis, particle size distribution and surface area were determined by and BET analysis, respectively. The Al sub 2 O sub 3 samples were sintered at 1650 deg C in air for one, three, five, seven and ten hours. The carbon doped samples were sintered using the same temperature for one hour, in a graphite resistance furnace in argon. Sintered materials were further characterised for phase composition and microstructure by XRD and scanning electron...

  4. Alumina Matrix Composites with Non-Oxide Nanoparticle Addition and Enhanced Functionalities

    Directory of Open Access Journals (Sweden)

    Dušan Galusek

    2015-01-01

    Full Text Available The addition of SiC or TiC nanoparticles to polycrystalline alumina matrix has long been known as an efficient way of improving the mechanical properties of alumina-based ceramics, especially strength, creep, and wear resistance. Recently, new types of nano-additives, such as carbon nanotubes (CNT, carbon nanofibers (CNF, and graphene sheets have been studied in order not only to improve the mechanical properties, but also to prepare materials with added functionalities, such as thermal and electrical conductivity. This paper provides a concise review of several types of alumina-based nanocomposites, evaluating the efficiency of various preparation methods and additives in terms of their influence on the properties of composites.

  5. Prediction of fracture characteristic of particle-reinforced alumina-based composites

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Residual microstresses in particle reinforced alumina/SiC and alumina/mullite composites were calcu- lated. The results indicated that there existed a linear relation between matrix microstresses and the particle contents in the composites. The influence of stress state on crack propagating and grain boundary strengthening was analyzed. Ratios of grain boundary toughness to grain toughness of these composites were calculated in view of microstress analysis, and percentage of transgranular fracture (PTF) that increases with the microstress in the alumina matrix was then deduced. The relationship between microstructure, component, matrix microstresses, and PTF was established. Therefore, the fracture characteristic was predicted on basis of the particle content and distribution in addition to the microstructure of the composites.

  6. FUNCTIONALLY GRADED ALUMINA/MULLITE COATINGS FOR PROTECTION OF SILICON CARBIDE CERAMIC COMPONENTS FROM CORROSION; FINAL

    International Nuclear Information System (INIS)

    The main objective of this research project was the formulation of processes that can be used to prepare compositionally graded alumina/mullite coatings for protection from corrosion of silicon carbide components (monolithic or composite) used or proposed to be used in coal utilization systems (e.g., combustion chamber liners, heat exchanger tubes, particulate removal filters, and turbine components) and other energy-related applications. Since alumina has excellent resistance to corrosion but coefficient than silicon carbide, the key idea of this project has been to develop graded coatings with composition varying smoothly along their thickness between an inner (base) layer of mullite in contact with the silicon carbide component and an outer layer of pure alumina, which would function as the actual protective coating of the component. (Mullite presents very good adhesion towards silicon carbide and has thermal expansion coefficient very close to that of the latter.)

  7. Effects of Nickel Distribution on the Strengthening and Toughening of Alumina Ceramics

    Institute of Scientific and Technical Information of China (English)

    Mohamed. M. El-Sayed Seleman

    2008-01-01

    Three types of composite materials were designed and fabricated by hot pressing powder blends of alumina with 20 vol. pct nickel particles. The composites differ in the shape, size and distribution of the nickel particles.Composite microstructures are described and measurements of density, hardness, flexure strength, and fracture toughness are reported. The results showed that the fracture strength of the composite with dispersed nickel particles is higher than the other two composites (network microstructure and mixed microstructure) and the alumina matrix. For all the composites studied, tougher materials than the monolithic alumina were produced.The fracture toughness of the composite with a network microstructure is much higher than that of the other composites. The toughening mechanisms were described based on the observation of the fracture surfaces and the crack-particle interactions. Moreover, the parameters for microstructural tailoring of these materials have been deduced. The toughening of the produced composites was explained in light of the interracial bond strength.

  8. A hybrid approach to the surface biofunctionalization of nanostructured porous alumina

    Energy Technology Data Exchange (ETDEWEB)

    Silvan, Miguel Manso; Ruiz, Josefa Predestinacion Garcia [Departamento de Fisica Aplicada y Departamento de Biologia Molecular, Facultad de Ciencias, Universidad Autonoma de Madrid, Unidad Asociada GMNF (ICMM-CSIC), 28049 Madrid (Spain); Centro de Investigaciones Biomedicas en Red, Bioingenieria Biomateriales y Nanomedicina (CIBERbbn) (Spain); Gonzalez, Ruy Sanz [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, 28049 Madrid (Spain); Velez, Manuel Hernandez [Departamento de Fisica Aplicada y Departamento de Biologia Molecular, Facultad de Ciencias, Universidad Autonoma de Madrid, Unidad Asociada GMNF (ICMM-CSIC), 28049 Madrid (Spain)

    2010-02-15

    The application of nanostructured porous alumina templates as a solid support in biomedical assays requires a surface biofunctionalization process that has been addressed in this work by an hybrid aminopropyl-triethoxysilane/tetraisopropyl-orthotitanate (APTS/ TIPT) self assembled film. The nanostructured porous alumina templates are activated in a peroxide solution before immersion in the biofunctionalizing APTS/TIPT solution. The biofunctionalization process was followed up by UV-vis spectroscopy, which confirmed the modification of the dielectric structure of the alumina surface. The influence of the biofunctionalization step in an immunological assay was carried out by fluorescence microscopy. Results confirm the gain in activity after the immobilization of an FITC labelled mouse Igg. Specific biological recognition in a bovine serum albumin (BSA)-antiBSA assay is proved afterwards by shifts observed in the reflectance interferograms thus providing a fast biosensing transducer platform. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Micrometer size grains of hot isostatically pressed alumina and its characterization

    Indian Academy of Sciences (India)

    A K Mallik; S Gangadharan; S Dutta; D Basu

    2010-08-01

    Alumina samples were prepared from two different particle size powders. Finer particle compacts when heated along with coarser particle compacts at same processing temperatures produce bigger grain microstructures due to higher grain growth. An unconventional method of etching by molten V2O5 was adopted to look at the microstructure for accuracy in reported data. On an average starting with finer particles give microstructure with a grain size of 5.5 m and starting with coarser particles, give microstructure with 2.2 m average grain size. The flexural strength is around 400 MPa for alumina samples prepared from finer powder in comparison with about 550 MPa for alumina samples prepared from coarser powder. The Vickers hardness in 5.5 m grain microstructure is around 20 GPa in comparison to about 18 GPa in microstructure with smaller grains of 2.2 m size.

  10. Ceramic joining through reactive wetting of alumina with calcium aluminate refractory cements

    Indian Academy of Sciences (India)

    K Geetha; A M Umarji; T R N Kutty

    2000-08-01

    Compositions in CaO–Al2O3 system have been prepared by gel–to–crystallite conversion method. Reactive powders of 1 : 2, 1 : 1, 2 : 1 and 3 : 1 of CaO and Al2O3 compositions were obtained by calcining the product at 800–1200°C. Fine grained powders were used as refractory cement for joining alumina ceramics. An optimum temperature of 1450°C for 4 h produced joints of satisfactory strength. The microstructure and X-ray phase analysis of the fractured joint surface clearly indicate reactive wetting of the alumina ceramics. This wetting enhances the joining of alumina substrates and can be attributed to the formation of Ca12Al14O33 liquid phase. The results are explained by using CaO–Al2O3 phase diagram.

  11. Effect of anodizing voltage on the sorption of water molecules on porous alumina

    Energy Technology Data Exchange (ETDEWEB)

    Vrublevsky, I., E-mail: vrublevsky@bsuir.edu.by [Belarusian State University of Informatics and Radioelectronics, Department of Micro and Nanoelectronics, 220013 Minsk (Belarus); Chernyakova, K. [Belarusian State University of Informatics and Radioelectronics, Department of Micro and Nanoelectronics, 220013 Minsk (Belarus); Bund, A.; Ispas, A.; Schmidt, U. [Fachgebiet Elektrochemie und Galvanotechnik, Technische Universitaet Ilmenau, 98693 Ilmenau (Germany)

    2012-05-01

    The amount of water adsorbed on different centers on the surface of oxalic acid alumina films is a function of the anodizing voltage. It is decreased with increasing the anodizing voltage from 20 up to 50 V, came up to maximum value at 20-30 V and slightly increased at voltages above 50 V. Water adsorption by oxide films formed at voltages below 50 V can be due to the negative surface charge that is present on the alumina surface. The negative surface charge disappears in the films formed at voltages higher than 50 V, and thus, the water is adsorbed on aluminum ions in a tetrahedral and octahedral environment. The correlation between anodizing conditions of aluminum in oxalic acid and the structure and composition of anodic alumina was established by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), thermogravimetric and differential thermal analyses (TG/DTA).

  12. Growth behavior of anodic porous alumina formed in malic acid solution

    Science.gov (United States)

    Kikuchi, Tatsuya; Yamamoto, Tsuyoshi; Suzuki, Ryosuke O.

    2013-11-01

    The growth behavior of anodic porous alumina formed on aluminum by anodizing in malic acid solutions was investigated. High-purity aluminum plates were electropolished in CH3COOH/HClO4 solutions and then anodized in 0.5 M malic acid solutions at 293 K and constant cell voltages of 200-350 V. The anodic porous alumina grew on the aluminum substrate at voltages of 200-250 V, and a black, burned oxide film was formed at higher voltages. The nanopores of the anodic oxide were only formed at grain boundaries of the aluminum substrate during the initial stage of anodizing, and then the growth region extended to the entire aluminum surface as the anodizing time increased. The anodic porous alumina with several defects was formed by anodizing in malic acid solution at 250 V, and oxide cells were approximately 300-800 nm in diameter.

  13. Effect of anodizing voltage on the sorption of water molecules on porous alumina

    International Nuclear Information System (INIS)

    The amount of water adsorbed on different centers on the surface of oxalic acid alumina films is a function of the anodizing voltage. It is decreased with increasing the anodizing voltage from 20 up to 50 V, came up to maximum value at 20-30 V and slightly increased at voltages above 50 V. Water adsorption by oxide films formed at voltages below 50 V can be due to the negative surface charge that is present on the alumina surface. The negative surface charge disappears in the films formed at voltages higher than 50 V, and thus, the water is adsorbed on aluminum ions in a tetrahedral and octahedral environment. The correlation between anodizing conditions of aluminum in oxalic acid and the structure and composition of anodic alumina was established by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), thermogravimetric and differential thermal analyses (TG/DTA).

  14. Using lithium glass infiltration to enhance the properties of alumina bodies

    Directory of Open Access Journals (Sweden)

    Wilson Acchar

    2008-12-01

    Full Text Available The use of an infiltration process to improve the properties of sintered materials has been widely investigated. This work describes the research carried out in the manufacturing of lithium glass-infiltrated alumina. The infiltration material consisted of a mixture of elements such as Li2O, ZrO2, SiO2 Al2O3, CaO and La2O3. Alumina specimens were sintered in air at 1400 °C for 2 hours. A number of samples were then submitted to the infiltration process at 1400 °C for 15 minutes. Sintered and infiltrated specimens were characterized by X ray diffraction, apparent density, open porosity, flexural strengths and scanning electron microscopy. The results showed that the infiltration process considerably improves the properties of alumina bodies.

  15. Dynamic modulus and damping of boron, silicon carbide, and alumina fibers

    Science.gov (United States)

    Dicarlo, J. A.; Williams, W.

    1980-01-01

    The dynamic modulus and damping capacity for boron, silicon carbide, and silicon carbide-coated boron fibers were measured from -190 to 800 C. The single fiber vibration test also allowed measurement of transverse thermal conductivity for the silicon carbide fibers. Temperature-dependent damping capacity data for alumina fibers were calculated from axial damping results for alumina-aluminum composites. The dynamic fiber data indicate essentially elastic behavior for both the silicon carbide and alumina fibers. In contrast, the boron-based fibers are strongly anelastic, displaying frequency-dependent moduli and very high microstructural damping. The single fiber damping results were compared with composite damping data in order to investigate the practical and basic effects of employing the four fiber types as reinforcement for aluminum and titanium matrices.

  16. The influence of the deposition parameters on the porosity of thin alumina films on steel

    Directory of Open Access Journals (Sweden)

    DUSAN KICEVIC

    2004-03-01

    Full Text Available The influence of the deposition parameters on the porosity of thin alumina films electrophoretically deposited on steel from aqueous suspensions was investigated. The effects of the applied voltage, deposition time, suspension temperature and the solid content of the aqueous suspension on the porosity of the obtained alumina films have been determined using optical microscopy coupled with image analysis. It was shown that the lowest film porosity was obtained from a suspension containing 20 wt.% alumina powder at the lowest applied voltage (30 V, for a longer deposition time (10 min using a suspension temperature of 30 ºC. This behavior can be explained by the smaller amount of hydrogen evolved on the cathode during the electrophoretic deposition process.

  17. Manufacturing of high-strength aluminum/alumina composite by accumulative roll bonding

    International Nuclear Information System (INIS)

    The ARB process used as a technique in this study provides an effective alternative method for manufacturing high-strength aluminum/alumina composites. The microstructural evolution and mechanical properties of the aluminum/15 vol.% alumina composite are reported. The composite shows an excellent alumina particle distribution in the matrix. It is found that by increasing the number of ARB cycles, not only does elongation increase in the composites produced but also the tensile strength of the Al/15 vol.% Al2O3 composite improves by 4 times compared to that of the annealed aluminum used as the original raw material. Fracture surfaces after tensile tests are observed by scanning electron microscopy (SEM) to investigate the failure mode. Observations reveal that the failure mode in both ARB-processed composites and monolithic aluminum is of the shear ductile rupture type.

  18. Enhanced gas separation factors of microporous polymer constrained in the channels of anodic alumina membranes

    Science.gov (United States)

    Chernova, Ekaterina; Petukhov, Dmitrii; Boytsova, Olga; Alentiev, Alexander; Budd, Peter; Yampolskii, Yuri; Eliseev, Andrei

    2016-08-01

    New composite membranes based on porous anodic alumina films and polymer of intrinsic microporosity (PIM-1) have been prepared using a spin-coating technique. According to scanning electron microscopy, partial penetration of polymer into the pores of alumina supports takes place giving rise to selective polymeric layers with fiber-like microstructure. Geometric confinement of rigid PIM-1 in the channels of anodic alumina causes reduction of small-scale mobility in polymeric chains. As a result, transport of permanent gases, such as CH4, becomes significantly hindered across composite membranes. Contrary, the transport of condensable gases (CO2, С4H10), did not significantly suffer from the confinement due to high solubility in the polymer matrix. This strategy enables enhancement of selectivity towards CO2 and C4H10 without significant loss of the membrane performance and seems to be prospective for drain and sweetening of natural gas.

  19. Effect of chemical composition and alumina content on structure and properties of ceramic insulators

    Indian Academy of Sciences (India)

    Arman Sedghi; Nastaran Riahi-Noori; Naser Hamidnezhad; Mohammad Reza Salmani

    2014-04-01

    In the present work, six electrical porcelain compositions with different amount of alumina and silica have been prepared and fired in an industrial furnace at 1300°C. Density, porosity, bending strength and electrical strength were measured in the samples. In order to find a relationship between properties and sample microstructures, samples were analyzed by scanning electron microscope (SEM) and x-ray diffraction (XRD) techniques. The results showed that, with chemical composition of 53.5 wt.% SiO2 and 37.5 wt.% alumina, highest electrical strength of 21.97 kV/mm was achieved in fabricated electrical porcelains. Increasing amount of alumina up to 30 wt.% decreases quartz and cristobalite phases, but increases corundum phase 3 to 5 times. SEM observation revealed that dense particles and uniform distribution of long and thin needle shaped mullite are predominant in sample microstructures with highest electrical strength.

  20. High Porosity Alumina as Matrix Material for Composites of Al-Mg Alloys

    International Nuclear Information System (INIS)

    The sophisticated industry and technologies require higher and higher assumptions against mechanical strength and surface hardness of ceramic reinforced metal alloys and metal matrix composites. Applying the well-known alumina powders by dry pressing technology and some special pore-forming additives and sintering technology the authors have successfully developed a new, high porosity alumina matrix material for composites of advenced Al-Mg alloys. The developed new matrix material have higher than 30% porosity, with homogenous porous structure and pore sizes from few nano up to 2–3 mm depending on the alloys containments. Thanks to the used materials and the sintering conditions the authors could decrease the wetting angles less than 90° between the high porosity alumina matrix and the Al-Mg alloys. Applied analytical methods in this research were laser granulometry, scanning electron microscopy, and X-ray diffraction. Digital image analysis was applied to microscopy results, to enhance the results of transformation

  1. FUNCTIONALLY GRADED ALUMINA/MULLITE COATINGS FOR PROTECTION OF SILICON CARBIDE CERAMIC COMPONENTS FROM CORROSION

    Energy Technology Data Exchange (ETDEWEB)

    Prof. Stratis V. Sotirchos

    2001-02-01

    The main objective of this research project was the formulation of processes that can be used to prepare compositionally graded alumina/mullite coatings for protection from corrosion of silicon carbide components (monolithic or composite) used or proposed to be used in coal utilization systems (e.g., combustion chamber liners, heat exchanger tubes, particulate removal filters, and turbine components) and other energy-related applications. Since alumina has excellent resistance to corrosion but coefficient than silicon carbide, the key idea of this project has been to develop graded coatings with composition varying smoothly along their thickness between an inner (base) layer of mullite in contact with the silicon carbide component and an outer layer of pure alumina, which would function as the actual protective coating of the component. (Mullite presents very good adhesion towards silicon carbide and has thermal expansion coefficient very close to that of the latter.)

  2. Minimum and Full Fluidization Velocity for Alumina Used in the Aluminum Smelter

    Directory of Open Access Journals (Sweden)

    Paulo Douglas S. de Vasconcelos

    2011-11-01

    Full Text Available Fluidization is an engineering unit operation that occurs when a fluid (liquid or gas ascends through a bed of particles, and these particles get a velocity of minimum fluidization enough to stay in suspension, but without carrying them in the ascending flow. As from this moment the powder behaves as liquid at boiling point, hence the term “fluidization”. This operation is widely used in the aluminum smelter processes, for gas dry scrubbing (mass transfer and in a modern plant for continuous alumina pot feeding (particles’ momentum transfer. The understanding of the alumina fluoride rheology is of vital importance in the design of fluidized beds for gas treatment and fluidized pipelines for pot feeding. This paper shows the results of the experimental and theoretical values of the minimum and full fluidization velocities for the alumina fluoride used to project the state of the art round non‐metallic air‐fluidized conveyor of multiples outlets.

  3. 5.3. Obtaining of cryolite-alumina concentrate from carbon-, and fluorine containing wastes by burning method

    International Nuclear Information System (INIS)

    The method of obtaining of cryolite-alumina concentrate from carbon-, and fluorine containing wastes by means of burning method was elaborated. The flowsheet of obtaining of cryolite-alumina concentrate from carbon-, and fluorine containing wastes by means of burning method was considered and presented in this article.

  4. 5.4. Obtaining of cryolite-alumina concentrate and alkaline coagulant from non-washed sludge

    International Nuclear Information System (INIS)

    On the base of researches of physicochemical composition and properties of sludge the new method of obtaining of cryolite-alumina concentrate and alkaline coagulant from non-washed sludge of gas purification was elaborated. The flowsheet of obtaining of cryolite-alumina concentrate from non-washed sludge of aluminium production was considered and presented in this article.

  5. Discovery of homogeneously dispersed pentacoordinated Al(V) species on the surface of amorphous silica-alumina

    CERN Document Server

    Wang, Zichun; Yi, Xianfeng; Zhou, Cuifeng; Rawal, Aditya; Hook, James; Liu, Zongwen; Deng, Feng; Zheng, Anmin; Baiker, Alfons; Huang, Jun

    2016-01-01

    The dispersion and coordination of aluminium species on the surface of silica-alumina based materials are essential for controlling their catalytic activity and selectivity. Al(IV) and Al(VI) are two common coordinations of Al species in the silica network and alumina phase, respectively. Al(V) is rare in nature and was found hitherto only in the alumina phase or interfaces containing alumina, a behavior which negatively affects the dispersion, population, and accessibility of Al(V) species on the silica-alumina surface. This constraint has limited the development of silica-alumina based catalysts, particularly because Al(V) had been confirmed to act as a highly active center for acid reactions and single-atom catalysts. Here, we report the direct observation of high population of homogenously dispersed Al(V) species in amorphous silica-alumina in the absence of any bulk alumina phase, by high resolution TEM/EDX and high magnetic-field MAS NMR. Solid-state 27Al multi-quantum MAS NMR experiments prove unambigu...

  6. Low-temperature-annealed alumina/polyimide gate insulators for solution-processed ZnO thin-film transistors

    International Nuclear Information System (INIS)

    Highlights: • The surface property of the polyimide gate insulator was successfully modified by the introduction of a low-temperature-annealed amorphous alumina interlayer. • The alumina/polyimide gate insulator showed excellent electrical insulating properties. • The solution-processed ZnO TFT with the alumina/polyimide gate insulator exhibited reasonable TFT performance. - Abstract: We report here a low-temperature-annealed alumina/polyimide gate insulator with excellent electrical insulating properties for solution-processed ZnO TFTs. In this study, 150 nm-thick polyimide and 20 nm-thick alumina thin films were deposited by a simple spin-coating followed by a 200 °C-annealing process. With the deposition of the alumina interlayer, the surface of the polyimide film was successfully modified. We prepared ZnO TFTs annealed at 230 °C to investigate the potential of the prepared gate insulator. The field-effect mobility and the on/off current ratio of solution-processed ZnO TFTs with an alumina/polyimide gate insulator were 0.11 cm2/V s and 1.8 × 105, respectively, whereas a ZnO TFT with a polyimide gate insulator was inactive. The alumina interlayer introduced here might provide a compatible interface for the ZnO semiconductor

  7. A combined HRND and HREM study of degradation collapse in NH4+/H3O+ β"-alumina

    DEFF Research Database (Denmark)

    Thomas, John O.; Eriksson, Anders; Kjems, Jørgen; Petford, Amanda

    High resolution neutron diffraction (HRND) from single crystals, and high resolution electron microscopy (HREM) are combined to study the deammoniation of NH4+/H3O+ β"-alumina on heating above 200°C. HRND shows the emergence of extra reflections which cannot be indexed in terms of the original β"-alumina...

  8. Evolution mechanism of alumina coating layer on rutile TiO2 powders and the pigmentary properties

    International Nuclear Information System (INIS)

    The evolution of alumina coating layers on rutile TiO2 particle surfaces was investigated starting from aluminum sulfate by a chemical liquid deposition method. The morphology of the alumina coating layers was determined by transmission electron microscopy. The chemical structure and the evolution mechanism of the alumina coating layers on TiO2 surfaces were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and powder X-ray diffraction techniques. The dispersibility of the alumina-coated TiO2 powders was determined by dynamic laser scattering (DLS) mode. The alumina coating layers existed in boehmite phase, AlOOH, and anchored at the surfaces of TiO2 via Ti-O-Al bond. The formation of alumina coating layers on TiO2 surfaces depended on the pH value of the deposition solution and the alumina loading. After coated by alumina layer, the dispersibility, whiteness, brightness, and light scattering index of the resultant samples were promoted.

  9. Diffusion of Cr, Fe, and Ti ions from Ni-base alloy Inconel-718 into a transition alumina coating

    International Nuclear Information System (INIS)

    Heat treating metals at high temperatures trigger diffusion processes which may lead to the formation of oxide layers. In this work the diffusion of Cr, Fe and Ti into an alumina coating applied to Inconel-718 is being investigated. Mass gain measurements, UV–vis spectroscopy and transmission electron microscopy were applied in order to study the evolution of the diffusion process. It was found that mainly Cr as well as minor amounts of Fe and Ti are being incorporated into the alumina coating upon prolonged heat treatment at 700 °C. It could be shown that alumina coatings being void of Cr have the same oxidation related mass gain as uncoated samples. However, incorporation of Cr into the alumina coating decreased their mass gain below that of uncoated substrates forming a Cr oxide scale only. - Highlights: ► We investigated the diffusion of Cr into alumina coatings applied on IN-718. ► The ingress of Cr led to the formation of mixed alumina/chromium coatings. ► The mass gain of mixed alumina/chromium coatings was compared to uncoated IN-718. ► The mixed alumina/chromium coatings improved the oxidation resistance of IN-718.

  10. DC bias effect on alternating current electrical conductivity of poly(ethylene terephthalate)/alumina nanocomposites

    Science.gov (United States)

    Nikam, Pravin N.; Deshpande, Vineeta D.

    2016-05-01

    Polymer nanocomposites based on metal oxide (ceramic) nanoparticles are a new class of materials with unique properties and designed for various applications such as electronic device packaging, insulation, fabrication and automotive industries. Poly(ethylene terephthalate) (PET)/alumina (Al2O3) nanocomposites with filler content between 1 wt% and 5 wt% were prepared by melt compounding method using co-rotating twin screw extruder and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and precision LCR meter techniques. The results revealed that proper uniform dispersion at lower content up to 2 wt% of nano-alumina observed by using TEM. Aggregation of nanoparticles was observed at higher content of alumina examined by using SEM and TEM. The frequency dependences of the alternating current (AC) conductivity (σAC) of PET/alumina nanocomposites on the filler content and DC bias were investigated in the frequency range of 20Hz - 1MHz. The results showed that the AC and direct current (DC) conductivity increases with increasing DC bias and nano-alumina content upto 3 wt%. It follows the Jonscher's universal power law of solids. It revealed that σAC of PET/alumina nanocomposites can be well characterized by the DC conductivity (σDC), critical frequency (ωc), critical exponent of the power law (s). Roll of DC bias potential led to an increase of DC conductivity (σDC) due to the creation of additional conducting paths with the polymer nanocomposites and percolation behavior achieved through co-continuous morphology.

  11. Spark plasma sintering of alumina nanopowders produced by electrical explosion of wires.

    Science.gov (United States)

    An, Vladimir; Khasanov, Alexey; de Izarra, Charles

    2015-01-01

    Alumina nanopowders produced by electrical explosion of wires were sintered using the spark plasma sintering technique. The results of XRD analysis show that the main phase in the compacted nanopowders is α-Al2O3. According to the SEM observations, the sintered alumina nanopowder consists of micron-sized faceted grains and nano-sized necked grains. The increase in sintering temperature resulted in a higher density of the sintered powders: from 78.44 to 98.21 % of theoretical density. PMID:26543716

  12. Deformation of an alumina-zirconia-silicon carbide-whisker reinforced composite

    Energy Technology Data Exchange (ETDEWEB)

    Calderon-Moreno, J.M.; DeArellano-Lopez, A.R.; Dominguez-Rodriguez, A. [Seville Univ. (Spain). Dept. de Fisica de La Materia Condensada; Routbort, J.L. [Argonne National Lab., IL (United States); Leasky, T. [Materials and Electrochemical Research Corp., Tucson, AZ (United States)

    1993-04-01

    Alumina-zirconia composites (MERC) with the addition of 0 and 28 vol % of silicon carbide whiskers have been deformed under compression at constant rate at 1450C, in air. Mechanical results are compared with the behavior of a commercial alumina (ARCO) with analogous proportions of silicon carbide-whiskers (0 and 30 vol %), under the same testing conditions. Flow stresses are typically higher for ARCO materials than for MERC materials. The addition of SiC whiskers increases flow stresses in ARCO composites, and decreases them for MERC samples. Microstructural observations confirm that the change in flow stress is the result of the presence of a glass phase in the MERC samples.

  13. Effect of change in cation composition of cryolite-alumina melts on anodic overwork

    International Nuclear Information System (INIS)

    Stationary polarization of platinum and glass carbon anodes in minor KF and LiF doped cryolite-alumina melt at different concentrations of alumina is searched in laboratory cell. Individual additive of LiF results in the raise of anode overvoltage by 50-80 mV at glass carbon and ∼25 mV at platinum anodes. Substitution of part of Na+ ions for Li+ in the amount to ∼3.7 mol.% of LiF (∼1.8 mas.%) results in the low polarization

  14. An electrochemical impedance study on cermet anodes in alumina-saturated molten cryolite

    International Nuclear Information System (INIS)

    This paper reports on electrochemical impedance spectra of NiO-NiFe2O4-Cu cermet anodes in alumina-saturated molten cryolite at anodic potentials above the decomposition potential of alumina which exhibited a loop with a characteristic frequency of about 1 Hz. A similar feature was observed using platinum anodes under the same experimental conditions. Analysis of these data suggests the loop was due to gas bubbling. Features associated with charge-transfer processes were not sufficiently resolved to determine the corrosion properties of the cermet anode

  15. Physical and chemical studying of cryolite-, alumina containing wastes of aluminium industry

    International Nuclear Information System (INIS)

    The purpose of present work is investigation of compositions and properties of cryolite-, alumina containing wastes of aluminium industry and determination of chemistry changes taking place during reprocessing process. After studying of above mentioned process authors became to conclusion that physical and chemical studying of cryolite-, alumina containing wastes of aluminium industry and products of their reprocessing by roentgen-phase and derivative-graphic methods showed that in the mud composition and dump screening of solid wastes Al2O3, Na3AlF6, C, Na2CO3, NaHCO3, NaF, SlO2 present

  16. The reaction kinetics of NiCl2 in silica alumina gel matrix

    Science.gov (United States)

    Mallick, Sathi; Das, G. C.; Mukherjee, S.; Mitra, M. K.

    2006-08-01

    Insitu isothermal reduction of NiCl2 by dextrose in silica alumina gel matrix has been carried out between 800 and 950 °C under nitrogen atmosphere. The predominant mechanism of reaction is found to be nucleation and growth. X-ray diffraction (XRD) analyses of reacted samples confirm the presence of metallic Ni, nickel aluminate and finely dispersed alumina in the reacted samples. The average particle size of nickel has been determined by transmission electron micrograph (14 nm) as well as XRD (17±2 nm).

  17. Effective Stress Reduction in Diamond Films on Alumina by Carbon Ion Implantation

    Institute of Scientific and Technical Information of China (English)

    方志军; 夏义本; 王林军; 张伟丽; 马哲国; 张明龙

    2002-01-01

    We show the effective stress reduction in diamond films by implanting carbon ions into alumina substrates prior to the diamond deposition. Residual stresses in the films are evaluated by Raman spectroscopy and a more reliable method for stress determination is presented for the quantitative measurement of stress evolution. It is found that compressive stresses in the diamond films can be partly offset by the compressive stresses in the alumina substrates, which are caused by the ion pre-implantation. At the same time, the difference between the offset by the pre-stressed substrates and the total stress reduction indicates that some other mechanisms are also active.

  18. Alumina reinforced tetragonal zirconia (TZP) composites. Final technical report, July 1, 1993--December 31, 1996

    International Nuclear Information System (INIS)

    This final technical report summarizes the significant research results obtained during the period July 1, 1993 through December 31, 1996 in the DOE-supported research project entitled, open-quotes Alumina Reinforced Tetragonal Zirconia (TZP) Compositesclose quotes. The objective of the research was to develop high-strength and high-toughness ceramic composites by combining mechanisms of platelet, whisker or fiber reinforcement with transformation toughening. The approach used included reinforcement of Celia- or yttria-partially-stabilized zirconia (Ce-TZP or Y-TZP) with particulates, platelets, or continuous filaments of alumina

  19. Silver nanoparticles supported on alumina-​a highly efficient and selective nanocatalyst for imine reduction

    DEFF Research Database (Denmark)

    Poreddy, Raju; Garcia-Suarez, Eduardo J.; Riisager, Anders;

    2014-01-01

    Silver nanoparticles supported on alumina were prepared and tested in the catalytic reduction of various imines to primary and secondary amines and were shown to be exceptionally active and chemoselective. Furthermore, the catalytic activity of the prepared nanocatalyst was also tested in the...... organic synthesis. Due to the mild reaction conditions and high conversion as well as high selectivity, we consider that the utilization of silver nanoparticles supported on alumina represents an attractive and environmentally friendly alternative to the current synthesis of N-alkyl amines....

  20. Facile Synthesis of Mesoporous γ-Alumina using Starch as Template

    Institute of Scientific and Technical Information of China (English)

    Xu Benjing; Long Jun; Tian Huiping; Zhu Yuxia

    2009-01-01

    Mesoporous alumina was prepared by using starch as the structure-directing template in an aqueous system. The resultant samples were characterized by using different methods such as the X-ray diffractomctry, the transmission electron microscopy, the nitrogen adsorption-desorption analysis and the solid MAS NMR. The results showed that the prepared mesoporous v-alumina had high surface area and uniform pore size distribution, and its specific surface area and the pore size could bc tuned by changing the pH value of the starting solution.