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Sample records for beryllia alumina silica-alumina

  1. 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.

  2. Catalytic performances of kaoline and silica alumina in the thermal degradation of polypropylene

    Institute of Scientific and Technical Information of China (English)

    Achyut K Panda; R K Singh

    2011-01-01

    Polypropylene was cracked thermally and catalytically in the presence of kaoline and silica alumina in a semi batch reactor in the temperature range 400 ℃ ~ 550 ℃ in order to obtain suitable liquid fuels. The dependencies between process temperatures, types of catalyst, feed compositions and product yields of the obtained fuel fractions were found. It was observed that up to 450 ℃ thermal cracking temperature, the major product of pyrolysis was liquid oil and the major product at other higher temperatures (475 ℃ ~550 ℃2 ) are viscous liquid or wax and the highest yield of pyrolysis product is 82.85% by weight at 500 ℃. Use of kaoline and silica alumina decreased the reaction time and increased the yield of liquid fraction. Again the major pyrolysis product in catalytic pyrolysis at all temperatures was low viscous liquid oil. Silica alumina was found better as compared to kaoline in liquid yield and in reducing the reaction temperature. The maximum oil yield using silica alumina and kaoline catalyst are 91% and 89.5% respectively. On the basis of the obtained results hypothetical continuous process of waste polypropylene plastics processing for engine fuel production can be presented.

  3. REY-zeolite and silica-alumina mixed support for hydrotreating heavy gas oil

    Energy Technology Data Exchange (ETDEWEB)

    Sambi, I.S.; Mann, R.S. (Univ. of Ottawa, Ottawa, ON (Canada))

    1989-04-01

    Rare earth exchanged Y-type zeolite (REY-zeolite) was dispersed in a silica-alumina gel to prepare catalyst supports with better hydrogenolysis activity. Such support material showed improved hydrotreating properties compared to commercial catalysts, expecially for heavy gas oils. Statistical experimental designs used to optimize the composition of such mixed supports suggested a composition of 10 wt.% silica, 25 wt.% zeolite and 65 wt.% alumina as optimum for hydrotreating a heavy gas oil (343{sup 0}C to 525{sup 0}C fraction) obtained from hydrocracking of Athabasca bitumen. The kinetic parameters were then evolved for teh optimum catalyst. 6 refs., 7 figs., 10 tabs.

  4. 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...

  5. Size-selective recognition of catecholamines by molecular imprinting on silica-alumina gel.

    Science.gov (United States)

    Ling, Tzong-Rong; Syu, Yau Zen; Tasi, Yau-Ching; Chou, Tse-Chuan; Liu, Chung-Chiun

    2005-12-15

    The preparation of a catecholamine receptor was carried out using a molecular imprinting method with silica-alumina gel to form complementary structures for template recognition. The molecularly imprinted polymer (MIP) was synthesized by the condensation of silicate from tetraethyl orthosilictate (TEOS) under hydrothermal conditions at 60 degrees C. Aluminum chloride was added as a functional monomer to increase the material's rebinding ability. The selectivity of the MIP receptor prepared with different ratios of template to Si and Al, was examined with seven analytes including: dopamine, epinephrine, norepinephrine, ascorbic acid, homovanillic acid, uric acid, and l-tyrosine. The results showed a size selective effect for the receptors with respect to the recognition of the catecholamines. Some factors affecting the recognition ability were investigated including: the solution pH of analytes, surface capping on the MIP, and the imprinting pH of the silica-alumina solution. Also, the catecholamine MIP films on quartz crystal microbalance (QCM) electrodes were fabricated as sensors for in situ monitoring of the analytes in a 2-propanol solution.

  6. Operando study of iridium acetylacetonate decomposition on amorphous silica-alumina for bifunctional catalyst preparation.

    Science.gov (United States)

    Nassreddine, Salim; Bergeret, Gérard; Jouguet, Bernadette; Geantet, Christophe; Piccolo, Laurent

    2010-07-28

    The decomposition of iridium acetylacetonate Ir(acac)(3) impregnated on amorphous silica-alumina (ASA) has been investigated by combined thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS) and by in situ X-ray diffraction (XRD). The resulting Ir/ASA hydrotreating catalysts have also been characterized by transmission electron microscopy (TEM). The effects of heating treatments under oxidative, reductive or inert gas flows are compared with each other and with similar experiments on ASA-supported acetylacetone (acacH). It is shown that Ir(acac)(3) undergoes exothermic combustion during calcination in air, leading to agglomerated IrO(2) particles. Conversely, direct reduction involves hydrogenolysis of the acac followed by hydrogenation of the ligand residues to alkanes and water. These two processes are catalyzed by Ir clusters, the gradual growth of which is followed in situ by XRD. The resulting nanoparticles are highly and homogeneously dispersed.

  7. Effect of support on catalytic cracking of bio-oil over Ni/silica-alumina

    Science.gov (United States)

    Sunarno, Herman, Syamsu; Rochmadi, Mulyono, Panut; Budiman, Arief

    2017-03-01

    Depletion of petroleum and environmental problem have led to look for an alternative fuel sources In many ways, biomass is a potential renewable source. Among the many forms of biomass, oil palm empty fruit bunch (EFB) is a very attractive feedstock due to its abudance, low price and non-competitiveness with the food chain. EFB can be converted bio-oil by pyrolysis process. but this product can not be used directly as a transportation fuel, so it needs upgrading bio-oil through a catalytic cracking process. The catalyst plays an important role in the catalytic cracking process. The objective of this research is to study the effect of Ni concentrations (1,3,5 and 7 wt.%) on the characteristics of the catalyst Ni / Silica-Alumina and the performance test for the catalytic cracking of bio-oil. Preparation of the catalyst Ni / Silica-Alumina was done by impregnation at 80°C for 3 hours, then done to calcination and reduction at 500°C for 2 hours. The performance test was conducted on catalytic cracking temperature of 500°C. Results show that increasing concentration of Ni from 1 to 7 %, the pore diameter of the catalyst decreased from 35.71 to 32.70 A and surface area decreased from 209.78 to 188.53 m2/gram. With the increase of Ni concentration, the yield of oil reduced from 22.5 to 11.25 %, while the heating value of oil increased from 34.4 to 36.41MJ/kg.

  8. A novel silica alumina-based backfill material composed of coal refuse and fly ash.

    Science.gov (United States)

    Yao, Yuan; Sun, Henghu

    2012-04-30

    In this paper, a systematic study was conducted to investigate a novel silica alumina-based backfill material composed of coal refuse and fly ash. The coal refuse and fly ash had different properties under various thermal activation temperatures (20 °C, 150 °C, 350 °C, 550 °C, 750 °C and 950 °C). It is known that a thermal activation temperature ranging from 20 °C to 950 °C significantly increases the flowability and pozzolanic properties of the coal refuse; however, the flowability of fly ash decreases when the activation temperature is higher than 550 °C because of a severe agglomeration phenomenon on its surface. An optimal design for this backfill material was determined to include an activated portion composed of 5% coal refuse at 750 °C and 15% fly ash at 20 °C. This combination yields the best performance with excellent flowability, a high compressive strength and a low bleeding rate. The microanalysis results corresponded well with the performance tests at different activation conditions. In the coal refuse, kaolinite peaks began to decrease because of their transformation into metakaolin at 550 °C. Chlorite peaks disappeared at 750 °C. Muscovite peaks decreased at 750 °C and disappeared at 950 °C. During this process, muscovite 2M(1) gradually dehydroxylated to muscovite HT. Furthermore, this paper examined the environmental acceptance and economic feasibility of this technology and found that this silica alumina-based backfill material composed of coal refuse and fly ash not only meets EPA requirements but also has several advantages in industry feasibility when compared with hydraulic backfill, rock backfill and paste backfill.

  9. Highly selective PdCu/amorphous silica-alumina (ASA) catalysts for groundwater denitration.

    Science.gov (United States)

    Xie, Yongbing; Cao, Hongbin; Li, Yuping; Zhang, Yi; Crittenden, John C

    2011-05-01

    Catalytic nitrate reduction is a promising technology in groundwater purification. In this study, PdCu bimetallic catalysts supported on an industrial amorphous silica-alumina (ASA) were synthesized and used to simulate catalytic removal of nitrate in groundwater. The catalysts exhibited very high activity and the highest catalytic selectivity toward N₂O and N₂ was 90.2%. The optimal Pd/Cu weight ratio was four. Relatively low reduction temperature was found benefit the catalytic stability and 300 °C was the appropriate reduction temperature during catalyst preparation. With an average particle size 5.4 nm, the metal particles were very uniformly distributed on the catalyst surface prepared with the codeposition method. This kept the catalyst more stable than the PdCu/Al₂O₂ catalyst with larger metal particles. According to XRD, TEM, and XPS results, the metals maintained zero-valence but aggregated by about 2 nm during the denitration reaction, which caused gradual deactivation of the catalysts. Little leaching of Cu and Pd from the catalyst might also have a slightly negative impact to the stability of the catalysts. A simple treatment was found to redistribute the particles on the deactivated catalysts, and high catalytic activity was recovered after this process.

  10. Dehydration of Glycerin to Acrolein Over Heteropolyacid Nano-Catalysts Supported on Silica-Alumina.

    Science.gov (United States)

    Kang, Tae Hun; Choi, Jung Ho; Choi, Jun Seon; Song, In Kyu

    2015-10-01

    A series of H3PW12O40 nano-catalysts supported on silica-alumina (XH3PW12O40/SA (X = 10, 15, 20, 25, and 30)) with different H3PW12O40 content (X, wt%) were prepared, and they were applied to the dehydration of glycerin to acrolein. The effect of H3PW12O40 content on the physicochemical properties and catalytic activities of XH3PW12O40/SA nano-catalysts was investigated. Surface area and pore volume of XH3PW12O40/SA catalysts decreased with increasing H3PW12O40 content. Formation of H3PW12O40 aggregates was observed in the catalysts with high H3PW12O40 loading. Brønsted acidity of the catalysts showed a volcano-shaped trend with respect to H3PW12O40 content. It was revealed that yield for acrolein increased with increasing Brønsted acidity of XH3PW12O40/SA catalysts. Brønsted acidity of XH3PW12O40/SA catalysts served as a crucial factor determining the catalytic performance in the dehydration of glycerin. Among the catalysts tested, 25H3PW12O40/SA catalyst with the largest Brønsted acidity showed the best catalytic performance.

  11. Effect of Plasma Spheroidization Process on the Microstructure and Crystallographic Phases of Silica, Alumina and Nickel Particles

    Institute of Scientific and Technical Information of China (English)

    HU Peng; YAN Shikai; YUAN Fangli; BAI Liuyang; LI Jinlin; CHEN Yunfa

    2007-01-01

    During the plasma spheroidization process powders undergo different changes in their microstructures and crystal phases. In this paper, simple calculation of heat transfer between the plasma and a suspended particle was performed based on three hypotheses for the purpose of guiding experiments. Experimental investigation of the crystal phases and microstructural changes during the plasma processing was made using silica, alumina and nickel powders as starting materials. It has been revealed from the experimental results that these materials undergo different changes in crystal phases and microstructures, and these changes are essentially determined by the structures, properties and aggregate states of the starting materials.

  12. Large Mesopore Generation in an Amorphous Silica-Alumina by Controlling the Pore Size with the Gel Skeletal Reinforcement and Its Application to Catalytic Cracking

    Directory of Open Access Journals (Sweden)

    Hiroyuki Nasu

    2012-09-01

    Full Text Available Tetraethoxy orthosilicate (TEOS was used not only as a precursor of silica, but also as an agent which reinforces the skeleton of silica-gel to prepare an aerogel and resultant silica and silica-alumina with large pore size and pore volume. In this gel skeletal reinforcement, the strength of silica aerogel skeleton was enhanced by aging with TEOS/2-propanol mixed solution to prevent the shrink of the pores. When silica aerogel was reinforced by TEOS solution, the pore diameter and pore volume of calcined silica could be controlled by the amount of TEOS solution and reached 30 nm and 3.1 cm3/g. The results from N2 adsorption measurement indicated that most of pores for this silica consisted of mesopores. Silica-alumina was prepared by the impregnation of an aluminum tri-sec-butoxide/2-butanol solution with obtained silica. Mixed catalysts were prepared by the combination of β-zeolite (26 wt% and prepared silica-aluminas with large mesopore (58 wt% and subsequently the effects of their pore sizes on the catalytic activity and the product selectivity were investigated in catalytic cracking of n-dodecane at 500 °C. The mixed catalysts exhibited not only comparable activity to that for single zeolite, but also unique selectivity where larger amounts of branched products were formed.

  13. Sorption of acetaminophen, 17alpha-ethynyl estradiol, nalidixic acid, and norfloxacin to silica, alumina. and a hydrophobic medium.

    Science.gov (United States)

    Lorphensri, Oranuj; Intravijit, Jittipong; Sabatini, David A; Kibbey, Tohren C G; Osathaphan, Khemarath; Saiwan, Chintana

    2006-04-01

    Two pure minerals and a hydrophobic medium were selected to study sorption of pharmaceuticals. The sorption of four pharmaceuticals, acetaminophen (analgesic), 17alpha-ethynyl estradiol (synthetic hormone), nalidixic acid (antibiotic), and norfloxacin (antibiotic), was evaluated with silica, alumina, and Porapak P (a hydrophobic medium). Alumina and silica were selected to represent positively charged and negatively charged aquifer mineral surfaces at neutral pH, respectively, while Porapak P was selected to represent the hydrophobic organic content of an aquifer medium. At neutral pH, acetaminophen, the least hydrophobic pharmaceutical, showed no significant sorption to any of the media, while 17alpha-ethynyl estradiol, the most hydrophobic pharmaceutical, showed significant sorption to Porapak P. Nalidixic acid, which has a carboxyl functional group that is anionic at neutral pH, showed significant adsorption to the positively charged alumina. Norfloxacin, with both a carboxyl (anionic) and a piperazynyl (cationic) group, can exist in four forms (neutral, cationic, anionic, and zwitterionic) depending on the aqueous pH. Norfloxacin also showed significant adsorption than nalidixic acid. Both nalidixic acid and norfloxacin adsorbed to silica and Porapak P to a much lower extent. The pH dependence of nalidixic acid and norfloxacin adsorption to silica and alumina was also studied by varying the pH between 4 and 11. The maximum adsorption of nalidixic acid to alumina occurred near its pKa (pH approximately 6), where the combination of cationic alumina and anionic nalidixic produced maximum adsorption. The maximum adsorption of norfloxacin to alumina was observed at pH approximately 7, which was the region where the zwitterionic form dominated. This research demonstrates that the adsorption of ionizable pharmaceuticals is strongly dependent on the system pH, the pharmaceutical properties (pKa and hydrophobicity), and the nature of the surface charge (point of zero

  14. Acid-base bifunctional catalysis of silica-alumina-supported organic amines for carbon-carbon bond-forming reactions.

    Science.gov (United States)

    Motokura, Ken; Tomita, Mitsuru; Tada, Mizuki; Iwasawa, Yasuhiro

    2008-01-01

    Acid-base bifunctional heterogeneous catalysts were prepared by the reaction of an acidic silica-alumina (SA) surface with silane-coupling reagents possessing amino functional groups. The obtained SA-supported amines (SA-NR2) were characterized by solid-state 13C and 29Si NMR spectroscopy, FT-IR spectroscopy, and elemental analysis. The solid-state NMR spectra revealed that the amines were immobilized by acid-base interactions at the SA surface. The interactions between the surface acidic sites and the immobilized basic amines were weaker than the interactions between the SA and free amines. The catalytic performances of the SA-NR2 catalysts for various carbon-carbon bond-forming reactions, such as cyano-ethoxycarbonylation, the Michael reaction, and the nitro-aldol reaction, were investigated and compared with those of homogeneous and other heterogeneous catalysts. The SA-NR2 catalysts showed much higher catalytic activities for the carbon-carbon bond-forming reactions than heterogeneous amine catalysts using other supports, such as SiO2 and Al2O3. On the other hand, homogeneous amines hardly promoted these reactions under similar reaction conditions, and the catalytic behavior of SA-NR2 was also different from that of MgO, which was employed as a typical heterogeneous base. An acid-base dual-activation mechanism for the carbon-carbon bond-forming reactions is proposed.

  15. Highly luminescent and ultrastable CsPbBr{sub 3} perovskite quantum dots incorporated into a silica/alumina monolith

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhichun; Kong, Long; Huang, Shouqiang; Li, Liang [School of Environmental Science and Engineering, Shanghai Jiao Tong University (China)

    2017-07-03

    We successfully prepared QDs incorporated into a silica/alumina monolith (QDs-SAM) by a simple sol-gel reaction of an Al-Si single precursor with CsPbBr{sub 3} QDs blended in toluene solution, without adding water and catalyst. The resultant transparent monolith exhibits high photoluminescence quantum yields (PLQY) up to 90 %, and good photostability under strong illumination of blue light for 300 h. We show that the preliminary ligand exchange of didodecyl dimethyl ammonium bromide (DDAB) was very important to protect CsPbBr{sub 3} QDs from surface damages during the sol-gel reaction, which not only allowed us to maintain the original optical properties of CsPbBr{sub 3} QDs but also prevented the aggregation of QDs and made the monolith transparent. The CsPbBr{sub 3} QDs-SAM in powder form was easily mixed into the resins and applied as color-converting layer with curing on blue light-emitting diodes (LED). The material showed a high luminous efficacy of 80 lm W{sup -1} and a narrow emission with a full width at half maximum (FWHM) of 25 nm. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Platinum nanocrystals supported by silica, alumina and ceria: metal support interaction due to high-temperature reduction in hydrogen

    Science.gov (United States)

    Penner, S.; Wang, D.; Su, D. S.; Rupprechter, G.; Podloucky, R.; Schlögl, R.; Hayek, K.

    2003-06-01

    Regular Pt nanoparticles, obtained by epitaxial deposition on NaCl surfaces, were supported by thin films of silica, alumina and ceria and subjected to hydrogen reduction at temperatures up to 1073 K. The changes in morphology and composition were followed by (HR)TEM, electron diffraction and EELS, and the results were supported by theoretical calculations. The structural changes of the Pt particles upon reduction at 773 K and above are surprisingly similar despite the differing chemical properties of the three supports. Some platelet- and cube-like geometries exhibit double lattice periodicities in high resolution images and electron diffraction patterns. With increasing reduction larger aggregates of more complex appearance and structure are formed. Surface reconstruction under hydrogen and alloy formation are considered as responsible for this effect. Most likely, the first step is identical on all three systems and consists in the topotactic formation of Pt rich Pt 3Me (Me=Si, Al, Ce) under the influence of hydrogen, followed by transformation into diverging structures of lower Pt content and different crystallography. Density functional calculations were performed for deriving energies of formation of PtMe and Pt 3Me compounds.

  17. Effect of Yb3+ concentration on Er3+ luminescence properties of sol-gelderived silica-alumina xerogels

    Institute of Scientific and Technical Information of China (English)

    K.Tran Ngoc; S.Pelli; G.C.Righini; H.Pham Thanh; C.Nguyen Duc; C.Armellini; A.Chiasera; M.Ferrari; Y.Jestin; M.Montagna; E.Moser

    2006-01-01

    @@ Er3+/Yb3+ co-doped silica-alumina monolithic xerogels were prepared with the same concentration on 2 000 Er/Si ppm and 6 000 Al/Si ppm.The Yb/Si content was varied from 0 to 4 000 ppm.Densification of the samples was achieved by thermal treatment in air at 950 ℃ for 120 hours with a heating rate 0.1 ℃/min.Photoluminescence spectroscopy was used to obtain information about the effective excitation efficiency of Er3+ ions by co-doping with Yb3+ ions.The infrared-to-visible up-conversion luminescence has been investigated upon continuous wave excitation at 980 nm.The samples exhibit red,green and blue up-conversion emission.It is found that the intensity of up-conversion luminescence increases with increasing Yb3+ doping concentration.An opposite behavior is observed for the 4I13/2 luminescence of the Er3+ ions.

  18. EPR study of the astaxanthin n-octanoic acid monoester and diester radicals on silica-alumina.

    Science.gov (United States)

    Focsan, A Ligia; Bowman, Michael K; Shamshina, Julia; Krzyaniak, Matthew D; Magyar, Adam; Polyakov, Nikolay E; Kispert, Lowell D

    2012-11-08

    The radical intermediates of the n-octanoic monoester and n-octanoic diester of astaxanthin were detected by pulsed EPR measurements carried out on the UV-produced radicals on silica-alumina artificial matrix and characterized by density functional theory (DFT) calculations. Previous Mims ENDOR for astaxanthin detected the radical cation and neutral radicals formed by proton loss from the C3 (or C3') position and from the methyl groups. Deprotonation of the astaxanthin neutral radical formed at the C3 (or C3') position resulted in a radical anion. DFT calculations for astaxanthin showed that the lowest energy neutral radical forms by proton loss at the C3 (or C3') position of the terminal ring followed by proton loss at the methyl groups of the polyene chain. Contrary to astaxanthin where proton loss can occur at either end of the symmetrical radical, for the diester of astaxanthin, this loss is prevented at the cyclohexene ends and is favored for its methyl groups. The monoester of astaxanthin, however, allows formation of the neutral radical at C3' and prevents its formation at the opposite end where the ester group is attached. At the terminal ring without the ester group attached, migration of proton from hydroxyl group to carbonyl group facilitates resonance stabilization, similarly to already published results for astaxanthin. However, cw EPR shows no evidence of a monoester radical anion formed. This study suggests the different radicals of astaxanthin and its esters that would form in a preferred environment, either hydrophobic or hydrophilic, depending on their structure.

  19. Synthesis and characterization of bifunctional transition-metal/silica-alumina catalysts for the chloromethane conversion to hydrocarbons

    Energy Technology Data Exchange (ETDEWEB)

    Sousa, J.F. [Universidade Federal de Rio de Grande do Norte (UFRN), Natal, RN (Brazil). Programa de Pos-Graduacao em Engenharia Quimica; Rojas, L.O.A.; Nascimento, J.C. [Universidade Federal de Rio de Grande do Norte (UFRN), Natal, RN (Brazil). Programa de Pos-Graduacao em Engenharia Quimica; Centro de Tecnologias do Gas (CTGAS), Natal, RN (Brazil)], E-mail: leopoldo@ctgas.com.br; Ruiz, J.A.C. [Centro de Tecnologias do Gas (CTGAS), Natal, RN (Brazil); Benachour, M. [Universidade Federal de Pernambuco (UFPE), Recife, PE (Brazil). Programa de Pos-Graduacao em Engenharia Quimica

    2008-10-15

    In this work bifunctional (metal-acid) catalysts of Fe, Ni, Fe{sub 2}O{sub 3} and NiO over amorphous silica alumina support were characterized (acidity) and evaluated for the conversion of chloromethane in a fixed bed reactor. Temperature program tests TPD (Temperature Programmed Desorption) and TPR (Temperature Programmed Reduction) were performed to characterize the chemisorption sites for the impregnated and unimpregnated support. New adsorption sites were created on the metal supported catalysts. The conversion yield of chloromethane was evaluated for the five materials. The highest conversion conversion (85%) was observed for the unmodified support (SiAl) after 6 of reaction at 860 K and a WHSV (Weight Hourly Space Velocity) of 4,5 h{sup -1}. The best selectivity toward desirable hydrocarbons (C{sup 3}, C{sup 4}) was found for the Fe-SiAl catalyst. C{sup 3} was also found in the products stream when Ni/SiAl and NiO/SiAl catalysts were tested. Ni catalysts were the most favorable to methane production. The catalytic tests showed coke formation in all materials. For the SiAl support the desorption energy of chloromethane, determined by TPD runs, was 101,9 KJ/mol. The metals presented lower desorption energies (75,2 KJ/mol for Ni and 133,4 KJ/mol for Fe) than the oxides (190,1 KJ/mol for Fe{sub 2}O{sub 3} and 322,4 KJ/mol for NiO). (author)

  20. Extrudate versus Powder Silica Alumina as Support for Re2O7 Catalyst in the Metathesis of Seed Oil-Derivatives – A Comparison

    Directory of Open Access Journals (Sweden)

    Bassie B. Marvey

    2009-01-01

    Full Text Available Self- and cross-metathesis of fatty acid methyl esters (FAMEs was investigated using a silica alumina supported Re2O7 catalyst. Although a 3 wt% Re2O7/SiO2-Al2O3/SnBu4 is already active for the metathesis of unsaturated FAMEs, the results have shown that particle size of silica alumina support has a profound influence on its activity and selectivity. Consequently, high substrate conversions coupled with improved product yields (for mono- and diesters and reaction rates were obtained upon using powder, as opposed to extrudate silica alumina as the support material. Diesters are platform compounds for the synthesis of polymers and fragrances. In this paper a comparative outline of the influence of particle size of silica alumina (extrudate versus powder on catalytic performance of a 3 wt% Re2O7/SiO2-Al2O3/SnBu4 for self- and cross-metathesis of FAMEs is made. Low surface area and diffusion constraints associated with extrudates were identified as some of the factors leading to low catalytic activity and selectivity.

  1. Study on Filtration Performance of Silica/Alumina Slurry in the Process of Recycling Mother Liquor of NaY Zeolite

    Institute of Scientific and Technical Information of China (English)

    Guo Yaoqing; Ma Yuelong; Deng Jinghui

    2004-01-01

    In order to recover the SiO2 contained in the mother liquor in the course of NaY zeolite synthesis to minimize pollution, the influence of various preparation conditions on the filtering velocity of gel slurry was studied using the SiO2/Al2O3 gel recovered from the NaY mother liquor in the laboratory. The results of study had shown that at a SiO2/A12O3 ratio in the feed equating to 9:1 the SiO2 recovery rate and Al2O3utilization rate were high with a faster flow velocity of the filtrate. The pH value of the system had great impact on the flow velocity of filtrate. Between the two methods for regulating the pH value, the one for formation of silica/alumina gel slurry by addition of sulfuric acid prior to adding aluminium sulfate in the solution could secure a faster filtration velocity. The filtration velocity was decreased in tandem with increasing SiO2 concentration in mother liquor, meanwhile an increase in dry filter cake yield.

  2. Research and Development of a New Silica-Alumina Based Cementitious Material Largely Using Coal Refuse for Mine Backfill, Mine Sealing and Waste Disposal Stabilization

    Energy Technology Data Exchange (ETDEWEB)

    Henghu Sun; Yuan Yao

    2012-06-29

    Coal refuse and coal combustion byproducts as industrial solid waste stockpiles have become great threats to the environment. To activate coal refuse is one practical solution to recycle this huge amount of solid waste as substitute for Ordinary Portland Cement (OPC). The central goal of this project is to investigate and develop a new silica-alumina based cementitious material largely using coal refuse as a constituent that will be ideal for durable construction, mine backfill, mine sealing and waste disposal stabilization applications. This new material is an environment-friendly alternative to Ordinary Portland Cement. The main constituents of the new material are coal refuse and other coal wastes including coal sludge and coal combustion products (CCPs). Compared with conventional cement production, successful development of this new technology could potentially save energy and reduce greenhouse gas emissions, recycle vast amount of coal wastes, and significantly reduce production cost. A systematic research has been conducted to seek for an optimal solution for enhancing pozzolanic reactivity of the relatively inert solid waste-coal refuse in order to improve the utilization efficiency and economic benefit as a construction and building material.

  3. Bifunctional heterogeneous catalysis of silica-alumina-supported tertiary amines with controlled acid-base interactions for efficient 1,4-addition reactions.

    Science.gov (United States)

    Motokura, Ken; Tanaka, Satoka; Tada, Mizuki; Iwasawa, Yasuhiro

    2009-10-19

    We report the first tunable bifunctional surface of silica-alumina-supported tertiary amines (SA-NEt(2)) active for catalytic 1,4-addition reactions of nitroalkanes and thiols to electron-deficient alkenes. The 1,4-addition reaction of nitroalkanes to electron-deficient alkenes is one of the most useful carbon-carbon bond-forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA-supported amine (SA-NEt(2)) catalyst enabled selective formation of a double-alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA-NEt(2) catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Furthermore, the SA-NEt(2) catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron-deficient alkenes. The solid-state magic-angle spinning (MAS) NMR spectroscopic analyses, including variable-contact-time (13)C cross-polarization (CP)/MAS NMR spectroscopy, revealed that acid-base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid-base interactions.

  4. Ceria nanoparticles vis-à-vis cerium nitrate as corrosion inhibitors for silica-alumina hybrid sol-gel coating

    Science.gov (United States)

    Lakshmi, R. V.; Aruna, S. T.; Sampath, S.

    2017-01-01

    The present work provides a comparative study on the corrosion protection efficiency of defect free sol-gel hybrid coating containing ceria nanoparticles and cerium nitrate ions as corrosion inhibitors. Less explored organically modified alumina-silica hybrid sol-gel coatings are synthesized from 3-glycidoxypropyltrimethoxysilane and aluminium-tri-sec-butoxide. The microemulsion derived nanoparticles and the hybrid coatings are characterized and compared with coatings containing cerium nitrate. Corrosion inhibiting capability is assessed using electrochemical impedance spectroscopy. Scanning Kelvin probe measurements are also conducted on the coatings for identifying the apparent corrosion prone regions. Detailed X-ray photoelectron spectroscopy (XPS) analysis is carried out to comprehend the bonding and corrosion protection rendered by the hybrid coatings.

  5. A comparison between Cu-ZSM-5, Cu-S-1 and Cu-mesoporous-silica-alumina as catalysts for NO decomposition

    Energy Technology Data Exchange (ETDEWEB)

    Moretti, Giuliano [Centro CNR `SACSO`, Dipartimento di Chimica, Universita `La Sapienza`, Piazzale A. Moro 5, 00185 Rome (Italy); Dossi, Carlo; Fusi, Achille; Recchia, Sandro; Psaro, Rinaldo [Centro CNR `CSSSCMTBSO`, Dipartimento di Chimica Inorganica, Metallorganica e Analitica, Universita di Milano, Via Venezian 21, 20133 Milan (Italy)

    1998-01-04

    We prepared H-ZSM-5 (Si/Al=80), amorphous mesoporous silica-alumina (MSA, Si/Al=90), and Silicalite-1 (S-1) according to the methods described by Bellussi and co-workers, and compared their ion-exchange capacity for copper ions. The Cu-ZSM-5, Cu-MSA and Cu-S-1 samples thus obtained have been investigated as catalysts for the NO decomposition reaction at 773K.We found that using copper acetate solutions with concentrations in the range 0.008M{<=}[Cu{sup 2+}]{<=}0.1M, both at room temperature and at 323K, it is very easy to prepare over-exchanged Cu-ZSM-5, Cu-S-1 and Cu-MSA catalysts. XRD and Vis-UV DRS techniques show that after thermal treatments of the fresh samples in air at 823K for 4h no segregation of CuO phase occurs, suggesting the presence of low nuclearity [Cu{sub n}O{sub x}(OH){sub y}]{sup q+} species (q=2(n-x)-y{>=}0). These results were confirmed by TPR studies. At 773K only over-exchanged Cu-ZSM-5 catalysts showed NO decomposition activity (NO 1% in He, W/F=0.1gs/cm{sup 3}) with a turnover frequency essentially determined by the Si/Al ratio, in agreement with previous literature data. Instead, the activity of Cu-S-1 and Cu-MSA catalysts was not measurable under our experimental conditions.The present results confirm that the framework topology and the presence of framework AlO{sup -}{sub 4} species are fundamental to develop active copper species for NO decomposition. It is demonstrated that the active sites in Cu-ZSM-5 consist of copper species strongly anchored to framework AlO{sup -}{sub 4} species. The most active sites, as they occur only on ZSM-5 support with the lower Si/Al atomic ratios, might consist of dimeric Cu species (Cu{sup +}...Cu{sup 2+}...O{sup -}) strongly anchored to next-nearest-neighbour framework AlO{sub 4}{sup -} species

  6. Low temperature hydrogenolysis of waxes to diesel range gasoline and light alkanes: Comparison of catalytic properties of group 4, 5 and 6 metal hydrides supported on silica-alumina

    KAUST Repository

    Norsic, Sébastien

    2012-01-01

    A series of metal hydrides (M = Zr, Hf, Ta, W) supported on silica-alumina were studied for the first time in hydrogenolysis of light alkanes in a continuous flow reactor. It was found that there is a difference in the reaction mechanism between d 0 metal hydrides of group 4 and d 0 ↔ d 2 metal hydrides of group 5 and group 6. Furthermore, the potential application of these catalysts has been demonstrated by the transformation of Fischer-Tropsch wax in a reactive distillation set-up into typical gasoline and diesel molecules in high selectivity (up to 86 wt%). Current results show that the group 4 metal hydrides have a promising yield toward liquid fuels.

  7. 氮掺杂硅铝固载TiO2多孔材料的制备及其光催化性能分析%Preparation of Nitrogen-doped TiO2 Porous Materials with Silica-alumina Carrier and Its Photocatalytic Property

    Institute of Scientific and Technical Information of China (English)

    刘昌涛; 张超武; 徐彬; 肖玲; 王芬

    2012-01-01

    以硅、铝和钛的无机盐为初始反应物,采用水热法制得了具有光催化活性的氮掺杂硅铝固载TiO2多孔材料(N/TiO2-SiAl).采用XRD、FESEM、FTIR、UV-Vis等现代分析技术分析表征了所得样品的物相结构及形貌;以甲基橙为探针在模拟太阳光下考察样品的光催化性能.结果表明:N/TiO2-SiAl为蜂窝状多孔材料,具有较大的比表面积;锐钛矿相TiO2以Si-O-Ti键的形式结合在无定形硅铝骨架中,并且硅铝骨架能够抑制锐钛矿相TiO2向金红石相转变;氮掺杂能够使TiO2的光响应范围向可见光区移动,在模拟太阳光照射120 min后N/TiO2-SiAl对甲基橙的降解率达到90%以上,具有较高的光催化性能,重复使用4次后降解率依然在80%以上,具有较强的光催化循环使用性能.%Inorganic compounds containing SiO2. A12O3 and TiO2 were used as initial reactants to form silicate framework and to carry TiO2. With urea as nitrogen source, the nitrogen-doped TiOv porous materials with silica-alumina carrier (N/TiO2-SiAl) were fabricated first by hydrothermal method to form product precursor and then by follow-up sintering procedure. The phase configuration and morphology of the samples were characterized via XRD, FESEM, FTIR and UV-Vis diffuse reflectance. The photocatalytic activity to visible-light of the products was investigated using methyl-orange as the photodegrading compound. The results show that this material is featured of greater specific area and well-crystalline anatase octahedrite TiO2 uniformly distributed in the amorphous silica-alumina framework which can restrain the change from anatase to rutile. N-doping could make the light absorption of the TiO2 obviously extended into visible-light region, and increase the visible-light responsive photocatalytic activity. The results of photocatalytic degradation of methyl orange show that the sample exhibits high photocatalytic activity under solar irradiation and methyl orange

  8. Texture study of divided solids by gas adsorption: application to beryllia, alumina and to gels and oxides; Contribution a l'etude, par adsorption gazeuse, de la texture des solides divises. Application a l'alumine, a la glucine et a differents gels et oxydes

    Energy Technology Data Exchange (ETDEWEB)

    Rouquerol, F. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1965-12-01

    A certain number of porous materials have been studied in an adsorption apparatus developed by us and leading to a measurement of the surface area with a reproducibility as good as 1/1 000. We have shown that this is only obtained at the cost of a number necessary precautions in the measurement of the gaseous volume adsorbed in a monomolecular layer (especially in the case of microporous solids). It also appears convenient to substitute argon to nitrogen, the latter being sensitive to chemical or electrical interactions with the adsorbent. Calculation methods of the pore size distribution are analyzed and discussed. The experimental data shows that the thickness of the multi-molecular layer must be estimated from the number of layers given by Shull using a layer thickness of 3.6 angstrom. A new method of analysis of the desorption curve is also given. We have also shown that a certain number of lamellar, non porous, systems, such as Be(OH){sub 2} present a hysteresis branch on the adsorption isotherm of type I or II. Using the numerical data obtained by our method together with the information provided by the electronic microscope, we have been able to conclude that this hysteresis can be ascribed to the lack of rigidity of the solid. On the contrary, samples of microporous texture (r < 20 A) of the type of beryllia, provide the case, which we have been able to characterize, of porous materials which do not exhibit a hysteresis phenomenon. The above conclusions have allowed us to describe the evolution of the texture during their progressive dehydration (thermal treatment from 150 to 1100 C) of two series of samples, namely beryllia and alumina. (author) [French] A l'aide d'un appareil d'adsorption que nous avons mis au point, et qui permet d'atteindre Une reproductibilite de 1/1000 dans la mesure des surfaces specifiques, nous avons etudie de nombreux solides divises. Nous montrons qu'il est indispensable, de prendre des precautions (en

  9. Preparation and Study of Dielectric Property of Polyimide Films Hybrided with Nano Silica-alumina Oxide%纳米硅/铝氧化物杂化聚酰亚胺薄膜的制备与电性能研究

    Institute of Scientific and Technical Information of China (English)

    梁凤芝; 陈磊; 陈昊; 范勇

    2011-01-01

    A nano-alumina sol was synthesized by hydrothermal process and a silica sol was prepared by sol-gel method, then they were doped into polyamic acid matrix. A series of inorganic nano-hybrid polyimide films were prepared by adjusting the molar ratio of nano-silicon/ aluminum oxides whose total content is 24%. The structure and properties of the films were characterized by SEM and measured by corona discharge measuring equipment and breakdown strength measuring system respectively. The results show that inorganic nano particles are well dispersed in the polyimide matrix when a little amount of silica sol is doped; the corona-resistant time of hybrid films is much longer than that of pure film and when the molar ratio of nano-silicon/ aluminum oxides is 1:13, the corona-resistant time reaches up to 62.15h; When increasing the doping amount of silica sol, the breakdown strength of the doped films first decreases and then increases, but is lower than that of the undoped film.%采用水热法制备纳米氧化铝溶胶,溶胶-凝胶法制备氧化硅溶胶,并将两者掺杂到聚酰亚胺(PI)基体中.实验中固定无机物掺杂总量为24%,通过调整纳米硅/铝氧化物的摩尔比,制备出一系列的无机纳米杂化聚酰亚胺薄膜.利用扫描电子显微镜(SEM)、耐电晕测试装置、耐击穿测试装置对薄膜进行了表征与测试.结果表明:硅溶胶掺杂量较小时,纳米粒子能较好地分散在聚酰亚胺基体中;杂化薄膜的耐电晕时间比纯膜有较大幅度提高,硅/铝摩尔比为1:13时,耐电晕时间达到62.15 h;随着硅溶胶掺杂量的增加,杂化薄膜的击穿强度先减小后增大,但均比纯膜的低.

  10. Investigation of the beryllia ceramics molding process by the hot casting method

    Science.gov (United States)

    Zhapbasbaev, U. K.; Ramazanova, G. I.; Sattinova, Z. K.

    2013-03-01

    Results of mathematical simulation of the ceramics molding process by the hot casting method are presented. The mathematical model describes the motion of beryllia liquid thermoplastic slurry in a form-building cavity subject to solidification. Velocity and temperature profiles providing homogeneous properties of the beryllia ceramics in the process of molding by the hot casting method are obtained.

  11. Preparation of Silica-Alumina Hollow Spheres with a Single Surface Hole by Co-axial Microchannel☆

    Institute of Scientific and Technical Information of China (English)

    Jinyuan Wang; Yujun Wang; Guangsheng Luo

    2014-01-01

    Si/Al composite hollow spheres with a surface hole were prepared with the co-axial microchannel in a one-step method. It is easy to use the technique for size control and continuous operation. At Si/Al ratio between 4 and 5, a hole forms on the surface, due to the fast gelation process and high viscosity of the sol. Scanning electron micros-copy, nitrogen adsorption–desorption isotherms, and mercury intrusion method are used to characterize the samples. The hole size is 40–150μm and the particle size is 450–600μm. The size can be adjusted by the flow rate of the oil phase.

  12. Silica-alumina molar ratio and some factors effect on the synthesis of zeolites from fly ash

    Institute of Scientific and Technical Information of China (English)

    SUN Yue-zhi; FU Ke-ming; ZHU Hong; ZHU Tian-lin

    2009-01-01

    In order to improve the activity and eliminate some impurities, pretreatment was used before hydrothermal synthesis. The fly ash was mixed with an aqueous NaOH solution, the alkali melted fly ash was also adopted, which is hydrothermally treated at about 104 ℃, and the liquid/solid ratio was controlled at 6:1. In order to control Si/AI molar ratio, SiO2 or Al2O3 powers were added to the fly ash. The results of XRD and SEM show that the alkali melted can activate fly ash and eliminate its quartz and mullite, along with the improvement of Si/AI molar ratio and alkalinity. In addition, zeolite Na-A changes into sodalite gradually, and nepheline is the synthesized intermediate product. Those results were discussed on the basis of a formation mechanism of zeolite from fly ash.

  13. SORPTION OF ACETAMINOPHEN, 17-&ALPHA;-ETHYNYLESTRADIOL, NALIDIXIC ACID, AND NORFLOXACIN TO SILICA, ALUMINA, AND A HYDROPHOBIC MEDIUM. (R829005)

    Science.gov (United States)

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  14. 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)

  15. Effect of Support on Metathesis of n-Decane: Drastic Improvement in Alkane Metathesis with WMe5 Linked to Silica-Alumina

    KAUST Repository

    Samantaray, Manoja

    2015-03-11

    [WMe6] (1) supported on the surface of SiO2-Al2O3(500) (2) has been extensively characterized by solid-state NMR spectroscopy, elemental analysis, and gas quantification, which clearly reveal the formation of a mixture of monopodal and bipodal species with the migration of methyl from W to Al. The supported species SiO2-Al2O3(500) (2) transformed at 120°C into two types of carbynic centers, one of which is cationic and the other neutral. These species are very efficient for the metathesis of n-decane. Comparison with already-synthesized neutral bipodal tungsten indicates that the high increase in activity is due to the cationic character of the grafted tungsten.

  16. A New Phase Change Material Based on Potassium Nitrate with Silica and Alumina Nanoparticles for Thermal Energy Storage

    Science.gov (United States)

    Chieruzzi, Manila; Miliozzi, Adio; Crescenzi, Tommaso; Torre, Luigi; Kenny, José M.

    2015-06-01

    In this study different nanofluids with phase change behavior were developed by mixing a molten salt base fluid (KNO3 selected as phase change material) with nanoparticles using the direct synthesis method. The thermal properties of the nanofluids obtained were investigated. Following the improvement in the specific heat achieved, these nanofluids can be used in concentrating solar plants with a reduction of storage material. The nanoparticles used (1.0 wt.%) were silica (SiO2), alumina (Al2O3), and a mix of silica-alumina (SiO2-Al2O3) with an average diameter of 7, 13, and 2-200 nm respectively. Each nanofluid was prepared in water solution, sonicated, and evaporated. Measurements of the thermophysical properties were performed by DSC analysis, and the dispersion of the nanoparticles was analyzed by SEM microscopy. The results obtained show that the addition of 1.0 wt.% of nanoparticles to the base salt increases the specific heat of about 5-10 % in solid phase and of 6 % in liquid phase. In particular, this research shows that the addition of silica nanoparticles has significant potential for enhancing the thermal storage characteristics of KNO3. The phase-change temperature of potassium nitrate was lowered up to 3 °C, and the latent heat was increased to 12 % with the addition of silica nanoparticles. These results deviated from the predictions of theoretical simple mixing model used. The stored heat as a function of temperature was evaluated for the base salt, and the nanofluids and the maximum values obtained were 229, 234, 242, and 266 J/g respectively. The maximum total gain (16 %) due to the introduction of the nanoparticles (calculated as the ratio between the total stored heat of the nanofluids and the base salt in the range of temperatures 260-390 °C) was also recorded with the introduction of silica. SEM and EDX analysis showed the presence of aggregates in all nanofluids: with silica nanoparticles they were homogenously present while with alumina and

  17. 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.

  18. Porous Alumina Films with Width-Controllable Alumina Stripes.

    Science.gov (United States)

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

    2010-08-21

    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.

  19. 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.

  20. Bauxite and alumina

    Science.gov (United States)

    Bray, E.L.

    2010-01-01

    The article reports on the global market performance of bauxite and alumina in 2009 and presents an outlook for their 2010 performance. There were only several U.S. states that could produce bauxite and bauxitic clays including Georgia, Arkansas, and Alabama. The prices for imported refractory-grade calcined bauxite ranged between 426 U.S. dollars and 554 dollars per ton.

  1. Prediction of alumina penetration

    Energy Technology Data Exchange (ETDEWEB)

    Mandell, D A

    1993-02-01

    The MESA hydrocode was used to predict two-dimensional tests of L/D 10 and L/D 15 tungsten rods impacting AD 90 alumina with a steel backing. The residual penetration into the steel is the measured quantity in these experiments conducted at the Southwest Research Institute (SWR). The interface velocity as a function of time between an alumina target and a lithium fluoride window, impacted by an alumina disk at velocities between 544 m/s and 2329 m/s, was also predicted. These one-dimensional flyer plate experiments were conducted at Sandia National Laboratories using Coors AD 995 alumina. The material strength and fracture models are important in the prediction of ceramic experiments. The models used in these predictions are discussed. The penetrations in the two-dimensional tests were predicted to 11.4 percent or better. In five of the six experiments, the predicted penetration depth was deeper than the measured value. This trend is expected since the calculation is based on ideal conditions. The results show that good agreement between the 1-D flyer plate data and the MESA predictions exists at the lower impact velocities, but the maximum velocity is overpredicted as the flyer plate velocity increases. At a flyer plate velocity of 2329 m/s the code overpredicted the data by 12.3 percent.

  2. 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.

  3. Calcium aluminate in alumina

    Science.gov (United States)

    Altay, Arzu

    The properties of ceramic materials are determined not only by the composition and structure of the phases present, but also by the distribution of impurities, intergranular films and second phases. The phase distribution and microstructure both depend on the fabrication techniques, the raw materials used, the phase-equilibrium relations, grain growth and sintering processes. In this dissertation research, various approaches have been employed to understand fundamental phenomena such as grain growth, impurity segregation, second-phase formation and crystallization. The materials system chosen was alumina intentionally doped with calcium. Atomic-scale structural analyses of grain boundaries in alumina were carried on the processed samples. It was found that above certain calcium concentrations, CA6 precipitated as a second phase at all sintering temperatures. The results also showed that abnormal grain growth can occur after precipitation and it is not only related to the calcium level, but it is also temperature dependent. In order to understand the formation mechanism of CA6 precipitates in calcium doped alumina samples, several studies have been carried out using either bulk materials or thin films The crystallization of CA2 and CA6 powders has been studied. Chemical processing techniques were used to synthesize the powders. It was observed that CA2 powders crystallized directly, however CA6 powders crystallized through gamma-Al 2O3 solid solution. The results of energy-loss near-edge spectrometry confirmed that gamma-Al2O3 can dissolve calcium. Calcium aluminate/alumina reaction couples have also been investigated. All reaction couples were heat treated following deposition. It was found that gamma-Al2O3 was formed at the interface as a result of the interfacial reaction between the film and the substrate. gamma-Al 2O3 at the interface was stable at much higher temperatures compared to the bulk gamma-Al2O3 formed prior to the CA6 crystallization. In order to

  4. Bauxite Mining and Alumina Refining

    Science.gov (United States)

    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, alumina dust, and caustic mist in contemporary best-practice bauxite mining and alumina refining operations have not been demonstrated to be associated with clinically significant decrements in lung function. Exposures to bauxite dust and alumina dust at such operations are also not associated with the incidence of cancer. Conclusions: A range of occupational health risks in bauxite mining and alumina refining require the maintenance of effective control measures. PMID:24806720

  5. Gelcasting Polycrystalline Alumina

    Energy Technology Data Exchange (ETDEWEB)

    Janney, M.A.; Zuk, K.J.; Wei, G.C.

    2000-01-01

    OSRAM SYLVANIA INC. is a major U.S. manufacturer of high-intensity lighting. Among its products is the Lumalux TM 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 ({approximately}97% total transmittance in the visible), their refractoriness (inner wall temperature can reach l2OOC), and their chemical resistance (sodium and mercury vapor are extremely corrosive). The current efficiency of the lamps is very high, up to 100 initial lumens per watt. (Compare incandescent lamps 10-20 lumens per watt, fluorescent lamps 25-90 lumens per watt.)

  6. Silica-alumina-niobia (SiO{sub 2}/Al{sub 2}O{sub 3}/Nb{sub 2}O{sub 5}) matrix obtained by the sol-gel processing method: new material for online extraction of zinc ions

    Energy Technology Data Exchange (ETDEWEB)

    Tarley, Cesar Ricardo T.; Avila, Thiago C. de; Segatelli, Mariana G.; Lima, Giovana de F., E-mail: ctarleyquim@yahoo.com.b [Universidade Federal de Alfenas, MG (Brazil). Dept. de Ciencias Exatas; Scheeren, Carla W.; Dias, Silvio Luis P. [Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS (Brazil). Inst. de Quimica; Peregrino, Gabrielly dos S.; Ribeiro, Emerson S. [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil). Inst. de Quimica

    2010-07-01

    In the present work, a new material, SiO{sub 2}/Al{sub 2}O{sub 3}/Nb{sub 2}O{sub 5} (designated as SiAlNb), was evaluated as an adsorbent in a flow injection spectrophotometric method for online preconcentration and determination of trace amounts of Zn{sup 2+} ions. The preconcentration method is based on Zn{sup 2+} adsorption onto the surface of SiAlNb in alkaline medium (pH 9.0). The elution step is carried out using HNO{sub 3} solution, followed by reaction of the Zn{sup 2+} ions with 1-(2-pyridylazo)-2-naphtol (pan) in ammoniacal buffer solution (pH 9.3) containing Tween-80. The [Zn(pan){sub 2}] complex formed is determined at 560 nm. The method presented a linear range between 7.6 and 180.0 mug L{sup -1} (r 0.9992) and limits of detection and quantification of 2.3 and 7.6 mug L{sup -1}, respectively. According to the Langmuir linear model, the maximum adsorption capacity was found to be 7.0 mg of Zn{sup 2+} g-1 of SiAlNb. The proposed method was successfully applied to the Zn{sup 2+} determination in water samples (lake, mineral, tap) and certified reference material (TORT-2 Lobster Hepatopancreas). (author)

  7. Alumina-magnesia Refractory Castables

    Institute of Scientific and Technical Information of China (English)

    Wang Jing

    2010-01-01

    @@ 1 Scope This standard specifies the classification,technical requirements,test methods,quality appraisal procedures,packing,marking,transportation,storage,and quality certificate of alumina-magnesia refractory castables.

  8. 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.

  9. Transport properties of alumina nanofluids

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Kau-Fui Vincent; Kurma, Tarun [Department of Mechanical and Aerospace Engineering, University of Miami, Coral Gables, FL 33124 (United States)], E-mail: kwong@miami.edu

    2008-08-27

    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{sup -1} K{sup -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

  10. Transport properties of alumina nanofluids.

    Science.gov (United States)

    Wong, Kau-Fui Vincent; Kurma, Tarun

    2008-08-27

    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 °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 °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

  11. 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...

  12. Alumina Coating on Carbon Fibers by Sol-Gel Method

    OpenAIRE

    2006-01-01

    Alumina precursor film was coated on carbon fibers by a sol-gel method using aluminum alkoxide solution. The optimum coating condition for the concentration of alumina alkoxide and silane coupling agent was determined to uniformly coat alumina precursor on carbon fibers. Alumina precursor converted to alumina ceramics by heating at 750℃. SEM and EPMA showed that alumina ceramics was uniformly coated on carbon fibers. The thickness of alumina layer increased with increasing coating times. The ...

  13. 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.

  14. 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.

  15. Wettability of Aluminum on Alumina

    Science.gov (United States)

    Bao, Sarina; Tang, Kai; Kvithyld, Anne; Tangstad, Merete; Engh, Thorvald Abel

    2011-12-01

    The wettability of molten aluminum on solid alumina substrate has been investigated by the sessile drop technique in a 10-8 bar vacuum or under argon atmosphere in the temperature range from 1273 K to 1673 K (1000 °C to 1400 °C). It is shown that the reduction of oxide skin on molten aluminum is slow under normal pressures even with ultralow oxygen potential, but it is enhanced in high vacuum. To describe the wetting behavior of the Al-Al2O3 system at lower temperatures, a semiempirical calculation was employed. The calculated contact angle at 973 K (700 °C) is approximately 97 deg, which indicates that aluminum does not wet alumina at aluminum casting temperatures. Thus, a priming height is required for aluminum to infiltrate a filter. Wetting in the Al-Al2O3 system increases with temperature.

  16. Acetic acid mediated interactions between alumina surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Sato, Kimiyasu, E-mail: sato.kimiyasu@aist.go.jp [National Institute of Advanced Industrial Science and Technology (AIST), Anagahora 2266-98, Shimoshidami, Moriyama-ku, Nagoya 463-8560 (Japan); Y Latin-Small-Letter-Dotless-I lmaz, Hueseyin [National Institute of Advanced Industrial Science and Technology (AIST), Anagahora 2266-98, Shimoshidami, Moriyama-ku, Nagoya 463-8560 (Japan); Gebze Institute of Technology, Materials Science and Engineering Department, 41400, Gebze-Kocaeli (Turkey); Ijuin, Atsuko; Hotta, Yuji; Watari, Koji [National Institute of Advanced Industrial Science and Technology (AIST), Anagahora 2266-98, Shimoshidami, Moriyama-ku, Nagoya 463-8560 (Japan)

    2012-02-01

    Low-molecular-weight organic acids have been known to modify colloidal stability of alumina-based suspensions. We investigated interaction forces between alumina surfaces mediated by acetic acid which is one of the simplest organic acids. Forces between alumina surfaces were measured using the colloid-probe method of atomic force microscope (AFM). Repulsive forces attributed to steric repulsion due to adsorbed molecules and electrostatic repulsion dominated the interaction. Results of rheological characterization of the alumina slurry containing acetic acid supported the finding.

  17. Structural Effects of Lanthanide Dopants on Alumina

    Science.gov (United States)

    Patel, Ketan; Blair, Victoria; Douglas, Justin; Dai, Qilin; Liu, Yaohua; Ren, Shenqiang; Brennan, Raymond

    2017-01-01

    Lanthanide (Ln3+) doping in alumina has shown great promise for stabilizing and promoting desirable phase formation to achieve optimized physical and chemical properties. However, doping alumina with Ln elements is generally accompanied by formation of new phases (i.e. LnAlO3, Ln2O3), and therefore inclusion of Ln-doping mechanisms for phase stabilization of the alumina lattice is indispensable. In this study, Ln-doping (400 ppm) of the alumina lattice crucially delays the onset of phase transformation and enables phase population control, which is achieved without the formation of new phases. The delay in phase transition (θ → α), and alteration of powder morphology, particle dimensions, and composition ratios between α- and θ-alumina phases are studied using a combination of solid state nuclear magnetic resonance, electron microscopy, digital scanning calorimetry, and high resolution X-ray diffraction with refinement fitting. Loading alumina with a sparse concentration of Ln-dopants suggests that the dopants reside in the vacant octahedral locations within the alumina lattice, where complete conversion into the thermodynamically stable α-domain is shown in dysprosium (Dy)- and lutetium (Lu)-doped alumina. This study opens up the potential to control the structure and phase composition of Ln-doped alumina for emerging applications.

  18. Structural Effects of Lanthanide Dopants on Alumina

    Energy Technology Data Exchange (ETDEWEB)

    Patel, Ketan; Blair, Victoria; Douglas, Justin; Dai, Qilin; Liu, Yaohua; Ren, Shenqiang; Brennan, Raymond

    2017-01-06

    Lanthanide (Ln3+) doping in alumina has shown great promise for stabilizing and promoting desirable phase formation to achieve optimized physical and chemical properties. However, doping alumina with Ln elements is generally accompanied by formation of new phases (i.e. LnAlO3, Ln2O3), and therefore inclusion of Ln-doping mechanisms for phase stabilization of the alumina lattice is indispensable. In this study, Ln-doping (400 ppm) of the alumina lattice crucially delays the onset of phase transformation and enables phase population control, which is achieved without the formation of new phases. The delay in phase transition (θ → α), and alteration of powder morphology, particle dimensions, and composition ratios between α- and θ-alumina phases are studied using a combination of solid state nuclear magnetic resonance, electron microscopy, digital scanning calorimetry, and high resolution X-ray diffraction with refinement fitting. Loading alumina with a sparse concentration of Ln-dopants suggests that the dopants reside in the vacant octahedral locations within the alumina lattice, where complete conversion into the thermodynamically stable α-domain is shown in dysprosium (Dy)- and lutetium (Lu)-doped alumina. This study opens up the potential to control the structure and phase composition of Ln-doped alumina for emerging applications.

  19. 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.

  20. Alumina forming iron base superalloy

    Energy Technology Data Exchange (ETDEWEB)

    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.

  1. 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.

  2. 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.

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

    Directory of Open Access Journals (Sweden)

    M. Szutkowska

    2012-10-01

    Full Text Available 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 composite with unstabilized and stabilized zirconia, alumina–zirconia composite with addition of TiC and alumina–nitride-carbide titanium composite with 2wt% of zirconia. Specimens were prepared from submicro-scale trade powders. Vicker’s hardness (HV1, fracture toughness (KIC at room temperature, the indentation fracture toughness, Young’s modulus and apparent density were also evaluated. The microstructure was observed by means of scanning electron microscopy (SEM.Findings: The lowest value of KIC is revealed by pure alumina ceramics. The addition of (10 wt% unstabilized zirconia to alumina or a small amount (5 wt% of TiC to alumina–zirconia composite improve fracture toughness of these ceramics in comparison to alumina ceramics. Alumina ceramics and alumina-zirconia ceramics reveal the pronounced character of R-curve because of an increasing dependence on crack growth resistance with crack extension as opposed to the titanium carbide-nitride reinforced composite based on alumina. R-curve has not been observed for this composite.Practical implications: The results show the method of fracture toughness improvement of alumina tool ceramics.Originality/value: Taking into account the values of fracture toughness a rational use of existing ceramic tools should be expected.

  4. 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.

  5. 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.

  6. Alumina Carbon Refractory Products for Continuous Casting

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    @@ 1 Scope This standard specifies the classification.techni-cal requirements,test methods,inspection rules,packing,marking,transportation,storage and quality certificate of alumina carbon refractory products for continuous casting.

  7. Direct foaming porous alumina ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Salvini, V.R.; Sandurkov, B.A.; Klein-Gunnewiek, R.F.; Pandolfelli, V.C. [Federal Univ. of Sao Carlos, Materials Engineering Dept., FIRE Associate Lab., Sao Carlos, SP (Brazil)

    2007-07-01

    This paper presents the work carried out in order to improve the properties of these porous alumina ceramics, concerning their application as thermal insulating. Changes in solid content of ceramic suspension, variations of pore forming agents and other additives were carried out and their effects on the green and the sintered mechanical strength are also shown. According to the literature, several starch types seem to be attractive pore forming agents as well as binders for porous ceramics. Most of them consist of a mixture of two polysaccharide types, amylose (linear) and amylopectin (highly branched). Corn, potato and rice starches were used in the present study because of their difference in size and shape. In order to increase the mechanical strength of the sintered porous ceramics a part of the Al{sub 2}O{sub 3} in the composition was replaced by Al(OH){sub 3}. Due to the changes of the composition and additives, porosities up to 81% and a mechanical strength of 15 MPa were obtained. (orig.)

  8. Bioactive glass-ceramics coatings on alumina

    Energy Technology Data Exchange (ETDEWEB)

    Vitale Brovarone, C.; Verne, E.; Lupo, F. [Politecnico di Torino (Italy). Materials Science and Chemical Eng. Dept.; Moisescu, C. [Jena Univ. (Germany). Otto-Schott-Inst. fuer Glaschemie; Zanardi, L.; Bosetti, M.; Cannas, M. [Eastern Piemont Univ., Novara (Italy). Medical Science Dept.

    2001-07-01

    In this work, aiming to combine the mechanical performances of alumina with the surface properties of a bioactive material, we coated full density alumina substrates by a bioactive glass-ceramic GC. This latter was specially tailored, in term of costituents and specific quantity to have a thermal expansion coefficient close to that of alumina (8.5-9{sup *}10{sup -6}/ C) which is lower than most of the bioactive glasses and glass-ceramics already in use. In this way, we sought to avoid, as much as possible, the crack formation and propagation due to residual stresses generated by the thermal expansion coefficients mismatch. Furthermore, the high reactivity of alumina toward the glass-ceramic was carefully controlled to avoid deep compositional modification of the GC that will negatively affect its bioactivity. At this purpose, an intermediate layer of an appropriate glass G was coated prior to coat the bioactive glass-ceramic. On the materials obtained, preliminary biological tests have been done to evaluate glass-ceramic biocompatibility respect to alumina. (orig.)

  9. 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.

  10. High contrast laser marking of alumina

    Energy Technology Data Exchange (ETDEWEB)

    Penide, J. [Applied Physics Department, University of Vigo, EEI, Lagoas-Marcosende, 9, Vigo 36310 (Spain); Quintero, F., E-mail: fquintero@uvigo.es [Applied Physics Department, University of Vigo, EEI, Lagoas-Marcosende, 9, Vigo 36310 (Spain); Riveiro, A. [Applied Physics Department, University of Vigo, EEI, Lagoas-Marcosende, 9, Vigo 36310 (Spain); Fernández, A. [Department of Engineering Design, University of Vigo, Escuela de Ingeniería Industrial, Campus Universitario, Vigo E-36310 (Spain); Val, J. del [Applied Physics Department, University of Vigo, EEI, Lagoas-Marcosende, 9, Vigo 36310 (Spain); Comesaña, R. [Materials Engineering, Applied Mechanics and Construction Department, University of Vigo, EEI, Lagoas-Marcosende, Vigo E-36310 (Spain); Lusquiños, F.; Pou, J. [Applied Physics Department, University of Vigo, EEI, Lagoas-Marcosende, 9, Vigo 36310 (Spain)

    2015-05-01

    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.

  11. 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.

  12. 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.

  13. 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)

  14. Iron films deposited on porous alumina substrates

    Science.gov (United States)

    Yamada, Yasuhiro; Tanabe, Kenichi; Nishida, Naoki; Kobayashi, Yoshio

    2016-12-01

    Iron films were deposited on porous alumina substrates using an arc plasma gun. The pore sizes (120 - 250 nm) of the substrates were controlled by changing the temperature during the anodic oxidation of aluminum plates. Iron atoms penetrated into pores with diameters of less than 160 nm, and were stabilized by forming γ-Fe, whereas α-Fe was produced as a flat plane covering the pores. For porous alumina substrates with pore sizes larger than 200 nm, the deposited iron films contained many defects and the resulting α-Fe had smaller hyperfine magnetic fields. In addition, only a very small amount of γ-Fe was obtained. It was demonstrated that the composition and structure of an iron film can be affected by the surface morphology of the porous alumina substrate on which the film is grown.

  15. 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.

  16. 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.

  17. 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

  18. Nanomechanical humidity detection through porous alumina cantilevers

    Directory of Open Access Journals (Sweden)

    Olga Boytsova

    2015-06-01

    Full Text Available We present here the behavior of the resonance frequency of porous anodic alumina cantilever arrays during water vapor adsorption and emphasize their possible use in the micromechanical sensing of humidity levels at least in the range of 10–22%. The sensitivity of porous anodic aluminium oxide cantilevers (Δf/Δm and the humidity sensitivity equal about 56 Hz/pg and about 100 Hz/%, respectively. The approach presented here for the design of anodic alumina cantilever arrays by the combination of anodic oxidation and photolithography enables easy control over porosity, surface area, geometric and mechanical characteristics of the cantilever arrays for micromechanical sensing.

  19. Microwave fast sintering of submicrometer alumina

    Directory of Open Access Journals (Sweden)

    Romualdo Rodrigues Menezes

    2010-09-01

    Full Text Available Commercially available alumina powder with high-purity submicrometer particle size and narrow particle size distribution was fully densified by a microwave hybrid fast firing technique. The alumina compacts were surrounded by susceptor material, which helped the heating of the samples, and sintered in a microwave oven at a frequency of 2.45 GHz and a power level of 1.8 kW. The sintered samples reached densities of 99% in sintering cycles of 30 to 40 minutes, a much shorter time than conventional sintering processes. The sintered samples showed uniform microstructures with powder particle size/average grain size rations higher than 1:2.

  20. 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)

  1. Third-generation alumina-on-alumina ceramic bearings in cementless total hip arthroplasty.

    Science.gov (United States)

    Lusty, P J; Tai, C C; Sew-Hoy, R P; Walter, W L; Walter, W K; Zicat, B A

    2007-12-01

    Wear debris has been implicated in the pathogenesis of osteolysis. Alumina-on-alumina ceramic bearings have a low wear rate, which may reduce the prevalence of osteolysis. The purpose of this study was to determine the rates of wear and osteolysis associated with modern cementless hip arthroplasty with alumina-on-alumina bearings at five years. We analyzed a series of 301 third-generation alumina-on-alumina cementless primary total hip replacements in 283 patients. The average age of the patients at the time of the arthroplasty was fifty-eight years. All procedures were performed with use of the same surgical technique and the same implant at a single center. At a minimum of five years postoperatively, ten patients had died and twenty-two patients were lost to follow-up. We assessed patients clinically and radiographically, and all retrieved bearings were analyzed for wear. At the time of the latest follow-up, the mean Harris hip score was 95 points. All surviving implants had radiographic evidence of stable bone ingrowth. There were nine revisions of one or both components. Four stems were revised following periprosthetic fracture, one stem was revised because of aseptic loosening at two months, and one stem was revised to facilitate a femoral shortening osteotomy. Two cups were revised because of psoas tendinitis, and both components of one arthroplasty were revised because of impingement and osteolysis. The rate of survival of both components, with revision because of aseptic loosening or osteolysis as the end point, was 99% at seven years. The retrieved femoral heads showed an early median wear rate of 0.2 mm(3) per year. Cementless primary total hip prostheses with a third-generation alumina-on-alumina bearing showed very low wear and were associated with minimal osteolysis at the time of follow-up, at a minimum of five years.

  2. LOW TEMPERATURE SINTERING OF ALUMINA BIOCERAMIC UNDER NORMAL PRESSURE

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Superfine alumina powder with high purity (mean particle size is less than 0. 35μm) were used as main starting material for sintering alumina ceramic. A multiple additive MgO-ZrO2 (Y2O3) was homogeneously added into the batch by the chemical coprecipitation method. Sintering of alumina bioceramic at low tempera ture (<1600C) was achieved resulting in a dense and high strength alumina ceramic with the bending strength up to 382 MPa and an improved fracture toughness. Mechanism that the multiple additives promote the sintering of alumina ceramic is discussed on the base of XRD and SEM analysis.

  3. Thermal Conductivity of Alumina-Toughened Zirconia Composites

    Science.gov (United States)

    Bansal, Narottam P.; Zhu, Dong-Ming

    2003-01-01

    10-mol% yttria-stabilized zirconia (10YSZ)-alumina composites containing 0 to 30 mol% alumina were fabricated by hot pressing at 1500 C in vacuum. Thermal conductivity of the composites, determined at various temperatures using a steady-state laser heat flux technique, increased with increase in alumina content. Composites containing 0, 5, and 10-mol% alumina did not show any change in thermal conductivity with temperature. However, those containing 20 and 30-mol% alumina showed a decrease in thermal conductivity with increase in temperature. The measured values of thermal conductivity were in good agreement with those calculated from simple rule of mixtures.

  4. Stabilization of Self-Assembled Alumina Mesophases

    NARCIS (Netherlands)

    Perez, Lidia Lopez; Perdriau, Sebastien; ten Brink, Gert; Kooi, Bart J.; Heeres, Hero Jan; Melian-Cabrera, Ignacio

    2013-01-01

    An efficient route to stabilize alumina mesophases derived from evaporation-induced self-assembly is reported after investigating various aspects in-depth: influence of the solvent (EtOH, s-BuOH, and t-BuOH) on the textural and structural properties of the mesophases based on aluminum

  5. 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

  6. Stabilization of Self-Assembled Alumina Mesophases

    NARCIS (Netherlands)

    Perez, Lidia Lopez; Perdriau, Sebastien; ten Brink, Gert; Kooi, Bart J.; Heeres, Hero Jan; Melian-Cabrera, Ignacio

    2013-01-01

    An efficient route to stabilize alumina mesophases derived from evaporation-induced self-assembly is reported after investigating various aspects in-depth: influence of the solvent (EtOH, s-BuOH, and t-BuOH) on the textural and structural properties of the mesophases based on aluminum tri-sec-butoxi

  7. alumina phase transformation from thermal decomposition of ...

    African Journals Online (AJOL)

    HOD

    INTRODUCTION. Alumina is one of the major components used as catalyst support ... used for processing petroleum, gas, petrochemicals and for other ... The extent and total conversion to the corundum ... purification, vegetable glues, porcelain cements, natural deodorant ..... Catalyst in Steam Reforming of Dimethyl ether:.

  8. 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.

  9. 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.

  10. Surface modification of alumina nanoparticles with silane coupling agents

    Energy Technology Data Exchange (ETDEWEB)

    Prado, Luis A.S.A.; Sriyai, Montira; Ghislandi, Marcos; Schulte, Karl [Technische Universitaet Hamburg-Harburg, Hamburg (Germany). Inst. fuer Kunststoffe und Verbundwerkstoffe (M-11); Barros-Timmons, Ana [University of Aveiro (Portugal). Dept. of Chemistry. Centro de Investigacao em Materiais Ceramicos e Compositos (CICECO)

    2010-07-01

    In the present paper we describe the surface modification of alumina nanoparticles using epoxy-containing alkoxysilanes (silane coupling agents, SCA). The materials were characterized using infrared spectroscopy and solid-state nuclear magnetic resonance. Whereas, neat alumina nanoparticles could be expectedly modified with the afore mentioned SCA, as evidenced by {sup 13}C CPMAS NMR, the presence of arylsulphonates at the surface of alumina caused the ringopening polymerization of the epoxide. This polymerization reaction facilitated the surface modification of alumina by the SCA. X-ray powder diffraction and {sup 27}Al MAS NMR clearly demonstrated that in spite of the SCA polymerization, there were neither structural changes nor phase transitions in the alumina after the surface modification. The surface modification decreased the thermal stability of alumina, in comparison to pristine alumina nanoparticles. (author)

  11. Synthesis of alumina-α using aluminium acetate; Sintese de alumina-α utilizando acetato de aluminio

    Energy Technology Data Exchange (ETDEWEB)

    Cartaxo, J.M.; Galdino, M.N.; Neves, G.A., E-mail: lulianamelo25@gmail.com [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Unidade Academica de Engenharia de Materiais; Menezes, R.R.; Ferreira, H.S. [Universidade Federal da Paraiba (UFPB), Joao Pessoa, PB (Brazil). Departamento de Engenharia de Materiais

    2011-07-01

    In the face of great technological importance of alumina, this paper aims to synthesize the α-alumina using chemical activation from aluminum acetate. The synthesized powders were characterized by X-ray diffraction and thermal analysis. The results obtained proved the thermal decomposition of the precursor, as well as possible metastable phases of alumina before the phase transformation in α. There was also difficult to obtain α-alumina from aluminum acetate, on the other hand there was, comparatively, that the chemical activation accelerated the synthesis of α-alumina. (author)

  12. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ki Tae; Dao, Trung Dung [Department of Chemistry, Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 680-749 (Korea, Republic of); Jeong, Han Mo, E-mail: hmjeong@mail.ulsan.ac.kr [Department of Chemistry, Energy Harvest-Storage Research Center, University of Ulsan, Ulsan 680-749 (Korea, Republic of); Anjanapura, Raghu V. [Center for Emerging Technologies, Jain Global Campus, Jain University, Jakkasandra, Ramanagara 562-112 (India); Aminabhavi, Tejraj M. [Soniya College of Pharmacy, S. R. Nagar, Dharwad 580-002 (India)

    2015-03-01

    Graphene was oxidized with H{sub 2}O{sub 2} 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 H{sub 2}O{sub 2} 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.

  14. Rheological Properties of Aqueous Nanometric Alumina Suspensions

    Energy Technology Data Exchange (ETDEWEB)

    Li, Chuanping [Iowa State Univ., Ames, IA (United States)

    2004-01-01

    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 17O 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

  15. 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

  16. Control of the γ-alumina to α-alumina phase transformation for an optimized alumina densification

    Energy Technology Data Exchange (ETDEWEB)

    Lamouri, S.; Hamidouche, M.; Bouaouadja, N.; Belhouchet, H.; Garnier, V.; Fantozzi, G.; Trelkat, J.F.

    2017-07-01

    In this work, we studied the aptitude to sintering green bodies using γ-Al2O3 transition alumina as raw powder. We focused on the influence of the heating rate on densification and microstructural evolution. Phase transformations from transition alumina γ→δ→θ→α-Al2O3 were studied by in situ X-rays diffraction from the ambient to 1200°C. XRD patterns revealed coexistence of various phase transformations during the heating cycle. DTA and dilatometry results showed that low heating rate leads to a significant reduction of the temperature of the α-Al2O3 alumina formation. Around 1190, 1217 and 1240°C were found when using 5, 10 and 20°C/min of heating rate, respectively. The activation energy for θ-Al2O3→α-Al2O3 transformation calculated by Kissinger and JMA equations using dilatometry method were 464.29 and 488.79kJ/mol, respectively and by DTA method were 450.72 and 475.49kJ/mol, respectively. In addition, the sintering of the green bodies with low heating rate promotes the rearrangement of the grains during θ-Al2O3→α-Al2O3 transformation, enhancing the relative density to 95% and preventing the development of a vermicular structure. (Author)

  17. Control of the γ-alumina to α-alumina phase transformation for an optimized alumina densification

    Directory of Open Access Journals (Sweden)

    Samir Lamouri

    2017-03-01

    Full Text Available In this work, we studied the aptitude to sintering green bodies using γ-Al2O3 transition alumina as raw powder. We focused on the influence of the heating rate on densification and microstructural evolution. Phase transformations from transition alumina γ → δ → θ → α-Al2O3 were studied by in situ X-rays diffraction from the ambient to 1200 °C. XRD patterns revealed coexistence of various phase transformations during the heating cycle. DTA and dilatometry results showed that low heating rate leads to a significant reduction of the temperature of the α-Al2O3 alumina formation. Around 1190, 1217 and 1240 °C were found when using 5, 10 and 20 °C/min of heating rate, respectively. The activation energy for θ-Al2O3 → α-Al2O3 transformation calculated by Kissinger and JMA equations using dilatometry method were 464.29 and 488.79 kJ/mol, respectively and by DTA method were 450.72 and 475.49 kJ/mol, respectively. In addition, the sintering of the green bodies with low heating rate promotes the rearrangement of the grains during θ-Al2O3 → α-Al2O3 transformation, enhancing the relative density to 95% and preventing the development of a vermicular structure.

  18. Influence of alumina characteristics on glaze properties

    Directory of Open Access Journals (Sweden)

    Arrufat, S.

    2010-10-01

    Full Text Available Aluminium oxide is a synthetic raw material manufactured from bauxite by the Bayer process, whose Al2O3 content typically exceeds 99%. Four main types of alumina can be defined, depending on the processing used: hydrargillite Al(OH3, boehmite AlOOH, transition aluminas (calcined at low temperatures, 1000 °C, with an intermediary crystallographic structure between hydrates and alpha alumina, and α-Al2O3 (calcined at high temperatures, >1100 °C. In glaze manufacturing, α-Al2O3 is the main type of alumina used. This raw material acts as a matting agent: the matt effect depends on alumina particle size and content in the glaze. This study examines the effect of the degree of alumina calcination on glaze technical and aesthetic properties. For this purpose, aluminas with different degrees of calcination were added to a glaze formulated with a transparent frit and kaolin, in order to simplify the system to be studied. The results show that, depending on the degree of calcination, alumina particles can react with the glaze components (SiO2, CaO, and ZnO to form new crystalline phases (anorthite and gahnite. Both crystallisations extract CaO and ZnO from the glassy phase, increasing glassy phase viscosity. The variation in crystalline phases and glassy phase viscosity yields glazes with different technical and aesthetic properties.

    El óxido de aluminio es una materia prima sintética fabricada a partir de la bauxita por medio del proceso Bayer, cuyo contenido de Al2O3 supera, por regla general, el 99%. Se pueden definir cuatro tipos de alúmina, en función del tipo de proceso usado: hidrargilita Al(OH3, boehmita AlOOH, alúminas de transición (calcinadas a bajas temperaturas, 1000 °C, con una estructura cristalográfica intermedia entre los hidratos y la alfa alúmina, y la α-Al2O3 (calcinada a

  19. Impact of AD995 alumina rods

    Energy Technology Data Exchange (ETDEWEB)

    Chhabildas, L.C.; Furnish, M.D.; Reinhart, W.D. [Sandia National Labs., Albuquerque, NM (United States); Grady, D.E. [Applied Research Associates, Inc., Albuquerque, NM (United States)

    1997-10-01

    Gas guns and velocity interferometric techniques have been used to determine the loading behavior of an AD995 alumina rod 19 mm in diameter by 75 mm and 150 mm long, respectively. Graded-density materials were used to impact both bare and sleeved alumina rods while the velocity interferometer was used to monitor the axial-velocity of the free end of the rods. Results of these experiments demonstrate that (1) a time-dependent stress pulse generated during impact allows an efficient transition from the initial uniaxial strain loading to a uniaxial stress state as the stress pulse propagates through the rod, and (2) the intermediate loading rates obtained in this configuration lie between split Hopkinson bar and shock-loading techniques.

  20. Nanoparticles in alumina: Microscopy and Theory

    Science.gov (United States)

    Idrobo, Juan C.; Halabica, Andrej; Rashkeev, Sergey; Glazoff, Michael V.; Boatner, Lynn A.; Haglund, Richard F.; Pennycook, Stephen. J.; Pantelides, Sokrates T.

    2007-03-01

    Transition-metal nanoparticles formed by ion implantation in alumina can be used to modify the optical properties of naturally oxidized and anodized aluminum. Here, we report atomic-resolution Z-contrast images using a scanning transmission electron microscope (STEM) of CoFe and other metal nanoparticles in alumina. We also report electron energy loss spectra (EELS) and relate them to visual appearance and optical properties. Finally, we report first-principles density- functional calculations of nucleation mechanisms for these nanoparticles. This research was sponsored by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. Department of Energy, under contract DE-AC05- 00OR22725 with Oak Ridge National Laboratory, managed and operated by UT-Battelle, by NSF grant No. DMR-0513048, and by Alcoa Inc.

  1. Silica containing highly porous alumina ceramic

    Science.gov (United States)

    Svinka, R.; Svinka, V.; Zake, I.

    2011-04-01

    Porous alumina ceramic were produced by slip casting of aqueous alumina slurry with added small amount of metallic aluminium powder. Pores form in result of chemical reaction of aluminum with water by hydrogen gas evolution reaction and solidification of suspension. Porosity of such materials sintered at a temperature of 1600 - 1750°C varies from 60 to 90%. Pore size distribution and mechanical strength of these materials depend largely on the grain size of used raw materials. The major part of pores in the materials produced without additive of silica are larger than 10 ±m, but with 5 - 10 wt.% additive of silica in the raw mix pore size decreases considerably. The sintering shrinkage decreases to 2.5%. Coefficient of thermal expansion equally decreases from 8.9-10-6 K-1 to 7.1 10-6 K-1 and classification temperature increases to 1600°C, while deformation at high temperature decreases considerably.

  2. Improvement in nanoscale contact resistance of alumina

    Energy Technology Data Exchange (ETDEWEB)

    Bhattacharya, Manjima; Chakraborty, Riya; Mandal, Ashok Kumar [CSIR - Central Glass and Ceramic Research Institute, Kolkata (India); Dey, Arjun [CSIR - Central Glass and Ceramic Research Institute, Kolkata (India); ISRO Satellite Centre, Thermal Systems Group, Bangalore (India); Mukhopadhyay, Anoop Kumar [CSIR - Central Glass and Ceramic Research Institute, Kolkata (India); Central Glass and Ceramic Research Institute, Kolkata 32 (India)

    2012-06-15

    In all contact-related applications such as the wear-resistant inserts, biomedical implants, high strain rate impact-resistant plates, etc., nanohardness, i.e. the intrinsic contact resistance at the nano scale, plays a major role. In spite of the wealth of literature, the studies on nanohardness of dense, coarse-grain alumina ceramics which represent many commercial varieties; have reasonably good hardness at the macro scale and characteristically exhibit R-curve behaviour, are far from significant. Here, to the best of our knowledge, we report for the first time the experimental observations of the increase in intrinsic contact resistance at the nano scale with the loading rate applied to a high-density ({proportional_to}95 % of theoretical) coarse-grain ({proportional_to}20 {mu}m) alumina ceramics. These observations were explained in terms of the initiation of nanoscale plasticity and maximum shear stress generated just underneath the nanoindenter. (orig.)

  3. Tribology of alumina-graphite composites

    Science.gov (United States)

    Yu, Chih-Yuan

    Alumina-graphite composites, which combine high wear resistance and self-lubricity, are a potential and promising candidate for advanced tribological applications. The processing, mechanical properties and tribology of alumina-graphite composites are discussed. Full density is difficult to achieve by a pressureless sintering route. Porosity of the composites increases with graphite content which causes the strength, modulus of elasticity, and hardness of the composites to decrease. The increased porosity does cause the fracture toughness to slightly increases. Tribology of alumina-graphite composites was studied with a pin-on-disk tribometer with emphasis on the following aspects: the graphite content in both pin and disk, the graphite flake size and the orientation of the graphite flakes. Scan electronic microscopy (SEM) and X-ray diffraction are utilized to examine and characterize the wear debris and the worn surface. Results confirmed that it is necessary to optimize the structure and the supply of lubricant to improve the tribological behavior and that the arrangements of sliding couples also affect the tribology of self-lubricated ceramic composites. Continuous measurements of the friction coefficients were collected at high frequency in an attempt to correlate the tribology of alumina-graphite composites to vibrations introduced by friction. While these measurements indicate that the time frequency behavior of tribology is an important area of study, conclusions regarding the frequency response of different sliding couples could not be definitively stated. Finally, a new concept connecting instantaneous wear coefficient and instantaneous contact stress is proposed for prediction of wear behavior of brittle materials.

  4. Ultraviolet photoluminescence of porous anodic alumina films

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Photoluminescence (PL) properties of porous anodic alumina (PAA) films prepared by using electrochemical anodization technique in a mixed solution of oxalic and sulfuric acid have been investigated. The PAA films have an intensive ultraviolet PL emission around 350 nm, of which a possible PL mechanism has been proposed. It was found that the incorporated oxalic ions, which could transform into PL centers and exist in the PAA films, are responsible for this ultraviolet PL emission.

  5. 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.

  6. Porous Aluminas: The bio template method for the synthesis of stable high surface area aluminas; Aluminas porosas: El metodo de bio-replica para la sintesis de aluminas estables de alta superficie especifica

    Energy Technology Data Exchange (ETDEWEB)

    Benitez Guerrero, M.; Perez Maqueda, L.; Pena Castro, P.; Pascual Cosp, J.

    2013-07-01

    Development of porous alumina has been the objective of numerous studies in recent decades, due to the intrinsic properties of aluminium oxide, such as high melting point, low thermal conductivity, chemical inertness and corrosion resistance which, in addition to a high surface area and permeability, make aluminas being used for many different industrial and technical applications. The crystallographic and textural stability of alumina acquires significant importance in those processes involving high temperatures; however, most of the synthesis methods yield metastable oxides of little interest in high-temperature processes due to the transformation to alpha phase, with the consequent reduction in surface area. The present article reviews diverse procedures for obtaining porous alumina with high specific surface area, including methods and strategies for preparing high surface alpha-alumina. Within this framework, the paper analyzes the results obtained through bio replica of lignocellulose materials. This technology allows preparing aluminas with the complex structural hierarchy of the lignocellulose templates. (Author)

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

    Science.gov (United States)

    Fang, Jinghua; Levchenko, Igor; (Ken Ostrikov, Kostya

    2014-08-01

    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.

  8. Influence of TAC on Dispersion of Aqueous Nano Alumina Suspension

    Institute of Scientific and Technical Information of China (English)

    ZHAO Wei; YANG De-an; SONG Jian-jing; YANG Zi; LIANG Chong; XU Ming-xia; XU Ting-xian

    2004-01-01

    The stability of aqueous nano alumina powder suspensions with and without dispersant tri-ammonium citrate (TAC) was investigated by measuring zeta potential at different pH values. The isoelectric point (IEP) of alumina powder shifts towards more acidic pH range by adding TAC dispersant. The results illustrate that adsorption of TAC on alumina powder surface existed in the aqueous suspension, which leads to a high stability of the suspension.

  9. Novel self assembly behavior for γ-alumina nanoparticles

    Institute of Scientific and Technical Information of China (English)

    Osama Saber

    2012-01-01

    In this study,self assembly behavior was induced for γ-alumina nanoparticles by adsorption of dimethyl disulfide.Following this trend,we have developed a chemical process to obtain γ-alumina in the nano scale.Scanning electron microscopy images of the prepared γ-alumina showed big and strong agglomeration of the nanoparticles indicating that these nanoparticles have strong surface forces.Transmission electron microscopy images confirmed that the γ-alumina nanoparticles 3-7 nm in size were converted to uniform spherical shape in the size range of 1-2 mm after shaking with dimethyl disulfide in the presence of n-hexane at room temperature.This phenomenon did not appear in the case of alumina in the micro scale.The surface properties of the prepared γ-alumina in the nano scale were characterized and compared with the γ-alumina in the micro scale by using low temperature nitrogen adsorption-desorption system,indicating that the specific surface area of the prepared γ-alumina nanoparticles is larger than that of the γ-alumina in the micro scale.Furthermore,micro-and meso-pores were observed for the γ-alumina nanoparticles while only mesoporous structure was detected for the γ-alumina in the micro scale.These experimental results suggested that the self assembly behavior of the γ-alumina nanoparticles may be due to the selective adsorption of dimethyl disulfide in the micropores of these nanoparticles to act as bridge linking the nanoparticles.

  10. 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.

  11. 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.

  12. Aqueous combustion synthesis and characterization of zirconia-alumina nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Kishan, J.; Mangam, Venu; Reddy, B.S.B.; Das, Siddhartha [Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur, West Bengal 721302 (India); Das, Karabi, E-mail: karabi@metal.iitkgp.ernet.i [Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur, West Bengal 721302 (India)

    2010-02-04

    The zirconia-alumina nanocomposite powders with 3-48 mol% of alumina are prepared by aqueous combustion synthesis technique using stoichiometric amounts of aluminium nitrate, zirconyl nitrate and glycine. The nanopowders are compacted uniaxially and sintered at 1000 {sup o}C temperature in a muffle furnace. Thermodynamic modeling of the combustion reaction shows that, as the alumina content increases, the amount of gases produced increases with a decrease in the adiabatic flame temperature. The green and sintered densities of cold press composite powders decrease with an increase in the mol% of alumina.

  13. 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.

  14. Methanol synthesis in a countercurrent gas-solid-solid trickle flow reactor. An experimental study

    NARCIS (Netherlands)

    Kuczynski, M.; Oyevaar, M.H.; Pieters, R.T.; Westerterp, K.R.

    1987-01-01

    The synthesis of methanol from CO and H2 was executed in a gas-solid-solid trickle flow reactor. The reactor consisted of three tubular reactor sections with cooling sections in between. The catalyst was Cu on alumina, the adsorbent was a silica-alumina powder and the experimental range 498–523 K,

  15. 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.

  16. Anisotropic shrinkage characteristics of tape cast alumina

    Science.gov (United States)

    Patwardhan, Jaideep Suresh

    Dimensional control during sintering is a major issue in ceramics processing to avoid high post-sintering costs associated with machining of the fired ceramic part to desired tolerances and dimensions. Ceramic forming processes such as tape casting, injection molding, and extrusion involve shear of anisotropic particles resulting in preferential alignment of the particles in the green body. This preferential alignment causes directionality in mechanical, electrical, optical, and magnetic properties and most importantly warpage or distortion during sintering. A large effort has been devoted to synthesizing ceramic green bodies with minimal density gradients and uniform packing and modeling the sintering behavior evolution but little effort has been devoted to characterizing orientation of particles and the effect of preferential alignment on sintering shrinkage anisotropy. A systematic study was initiated to study the effect of processing variables such as shear rate, solids loading, temperature, and binder content on aqueous tape cast alumina. Three different alumina systems: A16-SG, Baikowski RC-UFX DBM and RC-LS DBM were investigated. Aqueous tapes of high solids loading alumina (56 vol. %) were tape cast at various speeds and thicknesses and assuming plane Couette flow a shear rate regime of 21--270 s-1 was investigated. Higher shear rates and high solids loading resulted in higher in-plane anisotropy whereas the anisotropy in the thickness direction was higher for low solids loading systems. The anisotropy was found to be fairly constant above a certain critical shear rate (˜100 s-1) irrespective of the temperature and the solids loading and this correlated with the viscosity-shear rate relationship of the cast slips. The higher shrinkage anisotropy in the thickness direction for the low solids loading systems (35 and 45 vol. %) was attributed to the higher amount of organics in the slip required to sustain the suitable viscosity for tape casting and

  17. 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.

  18. Intercalation of water into lithium. beta. -alumina

    Energy Technology Data Exchange (ETDEWEB)

    Dudney, N J; Bates, J B; Wang, J C; Brown, G M; Larson, B C; Engstrom, H

    1981-01-01

    Infrared absorption, neutron diffraction and weight loss techniques have been used to investigate the hydration of single crystals of Li ..beta..-alumina. The hydration is a reversible intercalation reaction. Up to approximately two water molecules per formula unit can penetrate the conduction plane. Other protonated species are formed from the dissociation of the molecular water. The rate of hydration is controlled by the diffusion of water in the conduction plane. A likely diffusion mechanism requires dissociation of the water and an interstitialcy motion of the oxygen.

  19. Vapor-phase Beckmann rearrangement of cyclohexanone oxime over solid acid catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Murakami, Y.; Saeki, Y.; Ito, K.

    1978-01-01

    Of various catalysts tested for the conversion of cyclohexanone oxime to epsilon-caprolactam, best results were obtained with the catalyst having the strongest acid sites, silica-alumina, which gave 60% selectivity at 100% conversion at 330/sup 0/C, 0.505 g catalyst hr/mole, and 0.0563 atm cyclohexanone oxime partial pressure. A decline in activity without loss of selectivity was observed for all catalysts as carbonaceous deposits formed with time on stream (e.g., the caprolactam yield on silica-alumina declined to 90% after 120 min and to 35% after 270 min). Pulse reactor tests with silica-alumina with and without preadsorbed caprolactam showed that cyclohexanone oxime adsorbed even more strongly than the strongly adsorbed caprolactam. The mechanism is discussed. Graphs and 21 references.

  20. 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 Section 73.1010 Food and Drugs FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN SERVICES GENERAL LISTING OF COLOR ADDITIVES EXEMPT FROM CERTIFICATION Drugs § 73.1010 Alumina (dried...

  1. 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

  2. Chemical modification/grafting of mesoporous alumina with polydimethylsiloxane (PDMS)

    NARCIS (Netherlands)

    Pinheiro de Melo, A.F.; Nijmeijer, A.; Sripathi, V.G.P.; Winnubst, A.J.A.

    2015-01-01

    A method for polydimethylsiloxane grafting of alumina powders is described which involves chemical modification of the surface of mesoporous (5 nm) γ-alumina flakes with a linker (3-aminopropyltriethoxysilane: APTES), either by a solution phase (SPD) or a vapour phase (VPD) reaction, followed by PDM

  3. Chemical modification/grafting of mesoporous alumina with polydimethylsiloxane (PDMS)

    NARCIS (Netherlands)

    Pinheiro de Melo, A.F.; Nijmeijer, Arian; Sripathi, V.G.P.; Winnubst, Aloysius J.A.

    2015-01-01

    A method for polydimethylsiloxane grafting of alumina powders is described which involves chemical modification of the surface of mesoporous (5 nm) γ-alumina flakes with a linker (3-aminopropyltriethoxysilane: APTES), either by a solution phase (SPD) or a vapour phase (VPD) reaction, followed by

  4. Development of Reproducing Alumina-Magnesia-Carbon Bricks

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The reproducing alumina-magnesia-carbon bricks were prepared with the dumped bricks as starting materials. The bulk density, apparent porosity, crushing strength, modolus of rupture and slag resistance of the specimen were analyzed. The results show that the used refractories can be reused and recycled by the right method. The reproducing alumina-magnesia-carbon bricks with better abilities were prepared.

  5. 40 CFR 721.10120 - Siloxane modified alumina nanoparticles (generic).

    Science.gov (United States)

    2010-07-01

    ... nanoparticles (generic). 721.10120 Section 721.10120 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... 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...

  6. 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.

  7. Thermal Conductivity of Alumina-reinforced Zirconia Composites

    Science.gov (United States)

    Bansal, Narottam P.

    2005-01-01

    10-mol% yttria-stabilized zirconia (10SZ) - alumina composites containing 0-30 mol% alumina were fabricated by hot pressing at 1500 C in vacuum. Thermal conductivity was determined at various temperatures using a steady-state laser heat flux technique. Thermal conductivity of the composites increased with increase in alumina content. Composites containing 0, 5, and 10-mol% alumina did not show any change in thermal conductivity with temperature. However, those containing 20 and 30-mol% alumina showed a decrease in thermal conductivity with increase in temperature. The measured values of thermal conductivity were in good agreement with those calculated from the Maxwell-Eucken model where one phase is uniformly dispersed within a second major continuous phase.

  8. Thermal shock behavior of rare earth modified alumina ceramic composites

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Junlong; Liu, Changxia [Ludong Univ., Yantai (China). School of Transportation

    2017-05-15

    Alumina matrix ceramic composites toughened by AlTiC master alloys, diopside and rare earths were fabricated by hot-pressing and their thermal shock behavior was investigated and compared with that of monolithic alumina. Results showed that the critical thermal shock temperature (ΔT) of monolithic alumina was 400 C. However, it decreased to 300 C for alumina incorporating only AlTiC master alloys, and increased with further addition of diopside and rare earths. Improvement of thermal shock resistance was obtained for alumina ceramic composites containing 9.5 wt.% AlTiC master alloys and 0.5 wt.% rare earth additions, which was mainly attributed to the formation of elongated grains in the composites.

  9. 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.

  10. 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.

  11. Thermal Shock Behaviour of Alumina-Iron Composites

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Thermal shock behaviour was investigated for two morphologically different composites comprising an alumina matrix and 20 vol. pct Fe particles for a wide range of quenching temperature differences (△T=100~800°C) and compared to a monolithic alumina. The retained strength and critical quenching temperature difference, △Tc, of the two composites were a significant improvement over the values for the respective monolithic alumina. Crack lengths and densities were shown to be greater for the alumina than for the two composites at all quenching temperature differences. The thermal shock resistance parameters for monolithic alumina and the two composites were calculated according to their mechanical and physical properties. The calculated results agree well with the experimental one and indicate possible explanations for the differences in thermal shock behaviour.

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

    NARCIS (Netherlands)

    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,

  13. 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.

  14. 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.

  15. Parsing abnormal grain growth in specialty aluminas

    Science.gov (United States)

    Lawrence, Abigail Kremer

    Grain growth in alumina is strongly affected by the impurities present in the material. Certain impurity elements are known to have characteristic effects on abnormal grain growth in alumina. Specialty alumina powders contain multiple impurity species including MgO, CaO, SiO2, and Na 2O. In this work, sintered samples made from alumina powders containing various amounts of the impurities in question were characterized by their grain size and aspect ratio distributions. Multiple quantitative methods were used to characterize and classify samples with varying microstructures. The grain size distributions were used to partition the grain size population into subpopulations depending on the observed deviation from normal behavior. Using both grain size and aspect ratio a new visual representation for a microstructure was introduced called a morphology frequency map that gives a fingerprint for the material. The number of subpopulations within a sample and the shape of the distribution on the morphology map provided the basis for a classification scheme for different types of microstructures. Also using the two parameters a series of five metrics were calculated that describe the character of the abnormal grains in the sample, these were called abnormal character values. The abnormal character values describe the fraction of grains that are considered abnormal, the average magnitude of abnormality (including both grain size and aspect ratio), the average size, and variance in size. The final metric is the correlation between grain size and aspect ratio for the entire population of grains. The abnormal character values give a sense of how different from "normal" the sample is, given the assumption that a normal sample has a lognormal distribution of grain size and a Gaussian distribution of aspect ratios. In the second part of the work the quantified measures of abnormality were correlated with processing parameters such as composition and heat treatment conditions. A

  16. Fabrication of Alumina Nanowires from Porous Alumina Membranes by Etching in Phosphoric Acid Solution

    Science.gov (United States)

    Wang, Xuehua; Li, Chengyong; Ma, Lianjiao; Cao, Hong; Zhang, Baohua

    Alumina nanowires (ANWs) with high aspect ratios were synthesized by the chemical etching of porous alumina membranes (PAMs) in phosphoric acid solution. The morphology and structure of ANWs were analyzed by SEM and XRD, respectively. The results showed that the typical features of ANWs are around 35 nm in diameter and around 20 μm in length, the crystalline structure of the ANWs was amorphous, which was in accordance with that of the PAMs. Furthermore, the morphology of the PAMs was characterized by AFM and SEM in detail. On the basis of AFM and SEM observations, a possible formation mechanism of ANWs was discussed, and the inhomogeneous of the dissolution between the triple points and the side walls was considered to be the essential factor deciding the formation of ANWs.

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

    Energy Technology Data Exchange (ETDEWEB)

    Gaponenko, N. V., E-mail: nik@nano.bsuir.edu.by [Belarusian State University of Informatics and Radioelectronics (Belarus); Kortov, V. S. [Yeltsin Ural Federal University (Russian Federation); Orekhovskaya, T. I.; Nikolaenko, I. A. [Belarusian State University of Informatics and Radioelectronics (Belarus); Pustovarov, V. A.; Zvonarev, S. V.; Slesarev, A. I. [Yeltsin Ural Federal University (Russian Federation); Prislopski, S. Ya. [National Academy of Sciences of Belarus, Stepanov Institute of Physics (Belarus)

    2011-07-15

    Terbium-doped alumina xerogel layers are synthesized by the sol-gel method in pores of a porous anodic alumina film 1 {mu}m 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.

  18. 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)

  19. Deformation Behaviour of Coarse Grain Alumina under Shock Loading

    Science.gov (United States)

    Gupta, Satish

    2013-06-01

    To develop better understanding of the shock wave induced deformation behavior of coarse grain alumina ceramics, and for measurement of its Hugoniot Elastic Limit (HEL), in-situ and recovery gas gun experiments have been carried out on coarse grain alumina (grain size ~ 10 μm), prepared in the form of discs (>99.9% TMD) by pressure-less sintering of alpha alumina powder at 1583 K. The HEL value of 1.9 GPa has been determined from the kink in the pressure history recorded using piezoresistance gauge and also from the free surface velocity history of the sample shocked to 9 GPa. The nano-indentation measurements on the alumina samples shocked to 6.5 GPa showed hardness value 15% lower than 21.3 GPa for unshocked alumina, and strong Indentation Size Effect (ISE); the hardness value was still lower and the ISE was stronger for the sample shocked to 12 GPa. The XRD measurements showed reduced particle size and increased microstrains in the shocked alumina fragments. SEM, FESEM and TEM measurements on shock treated samples showed presence of grain localized micro- and nano-scale deformations, micro-cleavages, grain-boundary microcracks, extensive shear induced deformations, and localized micro-fractures, etc. These observations led to the development of a qualitative model for the damage initiation and its subsequent growth mechanisms in shocked alumina. The work performed in collaboration with K.D. Joshi of BARC and A.K. Mukhopadhyay of CGCRI.

  20. Tuning the Chemoselective Hydrogenation of Nitrostyrenes Catalyzed by Ionic Liquid-Supported Platinum Nanoparticles

    DEFF Research Database (Denmark)

    Beier, Matthias Josef; Andanson, Jean-Michel; Baiker, Alfons

    2012-01-01

    Pt nanoparticles (NPs) in the range of 1.7–3.4 nm were synthesized in an ionic liquid (IL). Subsequent immobilization on various solid supports (silica, alumina, titania, carbon nanotubes (CNTs)) in some cases proved to be beneficial. These catalysts exhibited excellent performance in the chemose......Pt nanoparticles (NPs) in the range of 1.7–3.4 nm were synthesized in an ionic liquid (IL). Subsequent immobilization on various solid supports (silica, alumina, titania, carbon nanotubes (CNTs)) in some cases proved to be beneficial. These catalysts exhibited excellent performance...

  1. Study on Thermal Insulation Zeolite by Coal Fly Ash

    OpenAIRE

    Huiping Song; Nan Zheng; Fangbin Xue; Fangqin Cheng

    2014-01-01

    This paper takes the coal fly ash as the material and makes zeolite with low thermal conductivity under a two-step synthesis for the purpose of thermal insulation. It studies main factors affecting zeolite such as the different concentration of NaOH, the solid-liquid ratio, the silica-alumina ratio, and the crystallization temperature. The optimal conditions were obtained that the NaOH concentration was 3 mol/L, the solid-liquid ratio was 10 : 1, the silica-alumina ratio was 2, and the crysta...

  2. 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

  3. 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

  4. Design and fabrication of alumina micro reciprocating engine

    Institute of Scientific and Technical Information of China (English)

    JIN Peng; GAO Yu-long; LIU Nan; JIANG Kylie

    2008-01-01

    Microengines are regarded as the potential replacements for batteries. Aimed at the unsatisfactory thermal property of silicon used in the combustion chambers, ceramics are chosen as the construction material in this paper. The fabrication process where alumina has been chosen as the microengine material is discussed. Vigorous FEA has been carried out, and it is found that the material satisfies the stress and deformation require-ments of the design. Then the alumina fabrication process is described. Soft reusable polydimethylsiloxane (PDMS) moulds are produced from SU-8 resist masters, and alumina microengine parts are produced using the PDMS moulds. Images of the ceramic components show that the fabrication satisfies the design requirements.

  5. 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.

  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. Special requirements for alumina ceramic of ESG electrode bowl

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jun-an; XUE Kai; ZHANG Jia-tai; ZHANG Qiang

    2004-01-01

    At present ESG (Electrostatic Suspended Gyro) is the most precise inertia element in the world. The electrode bowl, which has direct effect on the precision of ESG, is a key part to ESG. Through the analysis of the function and characteristic of the electrode bowl in hollow rotor ESG and the present situation of new material development in the world, the alumina ceramic is regarded as the best material for the electrode bowl of hollow rotor ESG. By analyzing the present situation of alumina ceramic in the world, main technique requirements have been put forward for the alumina ceramic of ESG electrode bowl which is also fit for solid rotor ESG.

  8. 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

  9. Porous Alumina Based Capacitive MEMS RH Sensor

    CERN Document Server

    Juhasz, L; Timar-Horvath, Veronika; Desmulliez, Marc; Dhariwal, Resh

    2008-01-01

    The aim of a joint research and development project at the BME and HWU is to produce a cheap, reliable, low-power and CMOS-MEMS process compatible capacitive type relative humidity (RH) sensor that can be incorporated into a state-of-the-art, wireless sensor network. In this paper we discuss the preparation of our new capacitive structure based on post-CMOS MEMS processes and the methods which were used to characterize the thin film porous alumina sensing layer. The average sensitivity is approx. 15 pF/RH% which is more than a magnitude higher than the values found in the literature. The sensor is equipped with integrated resistive heating, which can be used for maintenance to reduce drift, or for keeping the sensing layer at elevated temperature, as an alternative method for temperature-dependence cancellation.

  10. 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...

  11. Electrochemical modification process of anodic alumina membrane

    Institute of Scientific and Technical Information of China (English)

    YU Mei; LIU Jian-hua; LI Song-mei

    2006-01-01

    The modification procedure of anodic alumina membrane(AAM) was studied. The AAM structure after modification was characterized by nickel nanowires prepared in AAM. Scanning electron microscopy was used to characterize the topography and structure properties of the AAM and nickel nanowires. The transformation of the current during the voltage reduction was studied. The mechanism of current and structure change during modification was discussed. The results show that a root structure produces after the AAM modification. The length of the root structure depends on the velocity of the voltage reduction. Slow voltage reduction leads to a large length of the root structure,otherwise,a short length of the root structure. At the end of the modification,the barrier layer is thin enough to be passed by electrons. Hence,the direct electrodeposition of one-dimensional nanowires can be carried out on the AAM with barrier layer and aluminum matrix successfully without any other treatments.

  12. 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.

  13. 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...

  14. 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.

  15. High Alumina Refractory Mortars GB/T 2994-2008

    Institute of Scientific and Technical Information of China (English)

    Wang Jing; Chai Junlan

    2009-01-01

    @@ 1 Scope This standard specifies the classification, techni-cal requirements, test methods, quality appraisal pro-cedure, packing, marking, transportation, storage and quality certificate of high alumina refractory mortars.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Superhydrophobic alumina surface based on stearic acid modification

    Energy Technology Data Exchange (ETDEWEB)

    Feng Libang, E-mail: lepond@hotmail.com [School of Mechatronic Engineering, Lanzhou Jiaotong University, Lanzhou 730070 (China); Zhang Hongxia; Mao Pengzhi; Wang Yanping; Ge Yang [School of Mechatronic Engineering, Lanzhou Jiaotong University, Lanzhou 730070 (China)

    2011-02-15

    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 154.2{sup o} 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 {gamma}-Al{sub 2}O{sub 3}. 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.

  1. Synthesis of beta alumina from aluminum hydroxide and oxyhydroxide precursors

    CSIR Research Space (South Africa)

    Van Zyl, A

    1993-02-01

    Full Text Available Two aluminium oxyhydroxides, boehmite and pseudoboehmite, and two aluminium hydroxides, bayerite and gibbsite, have been investigated as precursors for the synthesis of the solid electrolyte, beta alumina. Reaction pathways and products have been...

  2. Electronic Structure of High-Pressure Alumina Polymorphs

    Institute of Scientific and Technical Information of China (English)

    LIU Xiao-Lei; DUAN Wen-Hui; GU Bing-Lin

    2000-01-01

    Electronic properties are investigated for three alumina polymorphs (corundum, Rb2 O3 (Ⅱ) and Pbnm perovskite),which are predicted as the stable structures under different pressure range, by means of the first-principles molecular dynamics method within local density functional framework. The similarity in electronic properties of the polymorphs of alumina is observed. The effect of possible phase transitions on ruby (Cr+3-doped Al2 O3)fluorescences is discussed.

  3. CSL grain boundary distribution in alumina and zirconia ceramics

    OpenAIRE

    Vonlanthen, Pierre; Grobéty, Bernard

    2008-01-01

    The distributions of general and coincidence site lattice (CSL) grain boundaries (GBs) in texture-free alumina and zirconia ceramics sintered at two different temperatures were investigated based on electron backscatter diffraction (EBSD) measurements. Results were compared with the distributions obtained from random 2D spatial models and with calculated random distributions reported in the literature. All alumina samples independent on sintering temperature show the same characteristic devia...

  4. Preparation of spherical hollow alumina particles by thermal plasma

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Wonkyung [Department of Chemical Engineering, INHA University, 253 Yonghyun-dong, Nam-gu, Incheon 402‐751 (Korea, Republic of); Regional Innovation Center for Environmental Technology of Thermal Plasma (RIC-ETTP), INHA University, 253 Yonghyun-dong, Nam-gu, Incheon 402‐751 (Korea, Republic of); Choi, Sooseok [Center for Advance Research in Fusion Reactor Engineering, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151‐742 (Korea, Republic of); Oh, Seung-Min [Daejoo Electronic Materials Co., 1236‐10 Jeongwang-dong, Siheung-si, Kyunggi-do 429‐848 (Korea, Republic of); Park, Dong-Wha, E-mail: dwpark@inha.ac.kr [Department of Chemical Engineering, INHA University, 253 Yonghyun-dong, Nam-gu, Incheon 402‐751 (Korea, Republic of); Regional Innovation Center for Environmental Technology of Thermal Plasma (RIC-ETTP), INHA University, 253 Yonghyun-dong, Nam-gu, Incheon 402‐751 (Korea, Republic of)

    2013-02-01

    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 H{sub 2} or N{sub 2}, 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.

  5. 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.

  6. 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.

  7. Procoagulant behavior and platelet microparticle generation on nanoporous alumina.

    Science.gov (United States)

    Ferraz, Natalia; Hong, Jaan; Karlsson Ott, Marjam

    2010-05-01

    In the present work, we have investigated platelet microparticle (PMP) generation in whole blood after contact with nanoporous alumina. Alumina membranes with pore sizes of 20 and 200 nm in diameter were incubated with whole blood and the number of PMP in the fluid phase was determined by flow cytometry. The role of the complement system in PMP generation was investigated using an analog of the potent complement inhibitor compstatin. Moreover, the procoagulant activity of the two pore size membranes were compared by measuring thrombin formation. Results indicated that PMP were not present in the fluid phase after whole blood contact with either of the alumina membranes. However, scanning electron microscope micrographs clearly showed the presence of PMP clusters on the 200 nm pore size alumina, while PMP were practically absent on the 20 nm membrane. We probed no influence of complement activation in PMP generation and adhesion and we hypothesize that other specific material-related protein-platelet interactions are taking place. A clear difference in procoagulant activity between the membranes could also be seen, 20 nm alumina showed 100% higher procoagulant activity than 200 nm membrane. By combining surface evaluation and flow cytometry analyses of the fluid phase, we are able to conclude that 200 nm pore size alumina promotes PMP generation and adhesion while the 20 nm membrane does not appreciably cause any release or adhesion of PMP, thus indicating a direct connection between PMP generation and nanoporosity.

  8. Alumina Concentration Detection Based on the Kernel Extreme Learning Machine.

    Science.gov (United States)

    Zhang, Sen; Zhang, Tao; Yin, Yixin; Xiao, Wendong

    2017-09-01

    The concentration of alumina in the electrolyte is of great significance during the production of aluminum. The amount of the alumina concentration may lead to unbalanced material distribution and low production efficiency and affect the stability of the aluminum reduction cell and current efficiency. The existing methods cannot meet the needs for online measurement because industrial aluminum electrolysis has the characteristics of high temperature, strong magnetic field, coupled parameters, and high nonlinearity. Currently, there are no sensors or equipment that can detect the alumina concentration on line. Most companies acquire the alumina concentration from the electrolyte samples which are analyzed through an X-ray fluorescence spectrometer. To solve the problem, the paper proposes a soft sensing model based on a kernel extreme learning machine algorithm that takes the kernel function into the extreme learning machine. K-fold cross validation is used to estimate the generalization error. The proposed soft sensing algorithm can detect alumina concentration by the electrical signals such as voltages and currents of the anode rods. The predicted results show that the proposed approach can give more accurate estimations of alumina concentration with faster learning speed compared with the other methods such as the basic ELM, BP, and SVM.

  9. Porous alumina and zirconia ceramics with tailored thermal conductivity

    Science.gov (United States)

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

    2012-11-01

    The thermal conductivity of porous ceramics can be tailored by slip casting and uniaxial dry pressing, using either fugitive pore formers (saccharides) or partial sintering. Porous alumina and zirconia ceramics have been prepared using appropriate powder types (ungranulated for casting, granulated for pressing) and identical firing regimes (but different maximum temperatures in the case of partial sintering). Thermal diffusivities have been measured by the laser- and xenon-flash method and transformed into relative thermal conductivities, which enable a temperature-independent comparison between different materials. While the porosity can be controlled in a similar way for both materials when using pore formers, partial sintering exhibits characteristic differences between alumina and zirconia (for alumina porosities below 45 %, full density above 1600 °C, for zirconia porosities below 60 %, full density above 1300 °C). The different compaction behavior of alumina and zirconia (porosity after pressing 0.465 and 0.597, respectively) is reflected in the fact that for alumina the relative conductivity data of partially sintered materials are below the exponential prediction, while for zirconia they coincide with the latter. Notwithstanding these characteristic differences, for both alumina and zirconia it is possible to tailor the thermal conductivity from 100 % down to approx. 15 % of the solid phase value.

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

    Science.gov (United States)

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

    2014-05-01

    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.

  11. Influence of additives on the stability of the phases of alumina; Influencia de aditivos na estabilidade das fases da alumina

    Energy Technology Data Exchange (ETDEWEB)

    Rosario, D.C.C.; Gouvea, D., E-mail: deisedorosario@usp.br [Universidade de Sao Paulo (USP), SP (Brazil). Departamento de Engenharia Metalurgica e de Materiais. Laboratorio de Processos Ceramicos

    2011-07-01

    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 ZrO{sub 2}, 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 ZrO{sub 2} work on improving the stability but with distinct mechanisms. (author)

  12. Effect of alumina composition and surface integrity in alumina/epoxy composites on the ultrasonic attenuation properties.

    Science.gov (United States)

    Cho, Eikhyun; Park, Gwanwoo; Lee, Jae-Wan; Cho, Sung-Min; Kim, Taekyung; Kim, Joongeok; Choi, Wonjoon; Ohm, Won-Suk; Kang, Shinill

    2016-03-01

    We report a method of fabricating backing blocks for ultrasonic imaging transducers, using alumina/epoxy composites. Backing blocks contain scatterers such as alumina particles interspersed in the epoxy matrix for the effective scattering and attenuation of ultrasound. Here, the surface integrity can be an issue, where the composite material may be damaged during machining because of differences in strength, hardness and brittleness of the hard alumina particles and the soft epoxy matrix. Poor surface integrity results in the formation of air cavities between the backing block and the piezoelectric element upon assembly, hence the increased reflection off the backing block and the eventual degradation in image quality. Furthermore, with an issue of poor surface integrity due to machining, it is difficult to increase alumina as scatterers more than a specific mass fraction ratio. In this study, we increased the portion of alumina within epoxy matrix by obtaining an enhanced surface integrity using a net shape fabrication method, and verified that this method could allow us to achieve higher ultrasonic attenuation. Backing blocks were net-shaped with various mass fractions of alumina to characterize the formability and the mechanical properties, including hardness, surface roughness and the internal micro-structure, which were compared with those of machined backing blocks. The ultrasonic attenuation property of the backing blocks was also measured.

  13. Cast alumina forming austenitic stainless steels

    Energy Technology Data Exchange (ETDEWEB)

    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; <0.3Ti+V; <0.03N; and, balance Fe, where the weight percent Fe is greater than the weight percent Ni, and wherein the alloy forms an external continuous scale comprising 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.

  14. Nanoparticle assisted coagulation of aqueous alumina suspensions

    Directory of Open Access Journals (Sweden)

    Abdullah Fatih Çetinel

    2012-02-01

    Full Text Available Colloidal processing of ceramics offers a high potential to achieve homogeneous microstructures with improved material properties. In this study, a novel forming method is investigated, which was already applied successfully for the fabrication of ceramic matrix composites (CMC, but is also considered to be a suitable direct casting technique for the fabrication of advanced ceramics with tailored microstructure and properties. The so-called nanoparticle assisted coagulation method (NPAC represents a modification of the hydrolysis-assisted solidification (HAS technique. It promises green components with high green strength, uniform density as well as homogeneous and tailored microstructure. Electrostatically stabilized colloidal suspensions with high solid loadings were produced by dispersing various fractions of submicron alumina powder and aluminium hydroxide nano-powder in water without use of any organic binder. Rheology and coagulation kinetics of suspensions and green part properties were studied regarding to modifications of pH value, setting temperature, amount of setting agent, amount of nano-powder, solids loading and process parameters like ultrasound treatment. It could be revealed that the homogeneous core-shell arrangement of submicron and nanoparticles in the colloidal state can be transmitted to the green state, which improves the microstructure and green density of the green parts. For this, the NPAC method is seen as a promising technique for the fabrication of advanced ceramics with tailored microstructure and properties.

  15. Mechanical properties of alumina porcelain during heating

    Science.gov (United States)

    Šín, Peter; Podoba, Rudolf; ŠtubÅa, Igor; Trník, Anton

    2014-11-01

    The mechanical strength and Young's modulus of green alumina porcelain (50 wt. % of kaolin, 25 wt. % of Al2O3, and 25 wt. % of feldspar) were measured during heating up to 900 °C and 1100 °C, respectively. To this end, we used the three point-bending method and modulated force thermomechanical analysis (mf-TMA). The loss liberation - of the physically bound water (20 - 250 °C) strengthens the sample and Young's modulus increases its values significantly. The dehydroxylation that takes place in the range of 400 - 650 °C causes a slight decrease in Young's modulus. On the other hand, the mechanical strength slightly increases in this temperature range, although it has a sudden drop at 420 °C. Beyond the dehydroxylation range, above 650 °C, both Young's modulus and mechanical strength increase. Above 950 °C, a sharp increase of Young's modulus is caused by the solid-state sintering and the new structure created by the high-temperature reactions in metakaolinite.

  16. Alumina-on-alumina total hip replacement for femoral neck fracture in healthy patients

    Directory of Open Access Journals (Sweden)

    Moretti Lorenzo

    2011-02-01

    Full Text Available Abstract Background Total hip replacement is considered the best option for treatment of displaced intracapsular fractures of the femoral neck (FFN. The size of the femoral head is an important factor that influences the outcome of a total hip arthroplasty (THA: implants with a 28 mm femoral head are more prone to dislocate than implants with a 32 mm head. Obviously, a large head coupled to a polyethylene inlay can lead to more wear, osteolysis and failure of the implant. Ceramic induces less friction and minimal wear even with larger heads. Methods A total of 35 THAs were performed for displaced intracapsular FFN, using a 32 mm alumina-alumina coupling. Results At a mean follow-up of 80 months, 33 have been clinically and radiologically reviewed. None of the implants needed revision for any reason, none of the cups were considered to have failed, no dislocations nor breakage of the ceramic components were recorded. One anatomic cementless stem was radiologically loose. Conclusions On the basis of our experience, we suggest that ceramic-on-ceramic coupling offers minimal friction and wear even with large heads.

  17. 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.

  18. 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.

  19. Peltier heats in cryolite melts with alumina

    Energy Technology Data Exchange (ETDEWEB)

    Flem, B.E.; Ratkje, S.K.; Sterten, A. [Univ. of Trondheim (Norway)

    1996-10-01

    The Seebeck coefficient was measured for cells with electrolytes of molten mixtures of sodium fluoride and aluminum fluoride saturated with alumina. The electrodes were either a pair of oxygen electrodes or a pair of aluminum electrodes. For the molar ratio NaF/AlF{sub 3} equal to 1.8, 1.2 and 1.0, the authors obtained the Seebeck coefficients {minus}1.80 mV K{sup {minus}1} at 971 C, {minus}1.63 mV K{sup {minus}1} at 813.6 C and {minus}0.583 mV K{sup {minus}1} at 758 C, respectively, for the oxygen electrodes. For the aluminum electrodes, the authors obtained the Seebeck coefficient {minus}1.23 mV K{sup {minus}1} at 962 C, for the molar ratio NaF/AlF{sub 3} equal to 1.8. The results suggest that there is a substantial reversible heat consumption at the anode during aluminum electrolysis and a large reversible heat production at the cathode. The highest temperature in the Hall-Heroult cell is then closer to the cathode than the anode. The transported entropies of Al{sup 3+} and O{sup 2{minus}} were calculated to be 77 J mol{sup {minus}1} K{sup {minus}1} and 10 J mol{sup {minus}1} K{sup {minus}1}, respectively, when the molar ratio NaF/AlF{sub 3} was equal to 1.0.

  20. Challenges in Additive Manufacturing of Alumina

    Science.gov (United States)

    Gonzalez, Hugo

    Additive manufacturing is seen by many as the holy grail of manufacturing, the ability to produce parts nearly autonomously. Adding material rather than removing it would eliminate the need for expensive resources and machining. The recent expiration of key 3D printing patents has led to many advances in the field and has dramatically lowered the prices of 3D printers, making them accessible to the average individual. The one area where additive manufacturing is still in its infancy is in ceramics. Ceramic materials have advantages over polymers and metals such as corrosion resistance, insulating behavior, high stiffness and high temperature stability that make them attractive in industries such as aerospace, medical, and electronics. Processing and machining ceramics however is difficult and expensive as it requires high temperature furnaces and diamond tooling. There are currently two companies that produce printers capable of printing technical ceramics, Lithoz in Germany and 3D Ceram in France. The issue is that both of these printers retail for over $100,000. The work in this thesis intends to show the challenges associated with setting up a ceramic 3D printer at a fraction of that cost for 3D printing of alumina. The first such challenge was creating a photopolymer resin that could be loaded with a large volume percent of aluminum oxide powder while maintain its curability and low viscosity. Several combinations of monomers and dispersants were evaluated before coming to the conclusion that the use of a hexanediol diacrylate monomer and quarternary ammonia acetate were the most effective in suspending volume sold loadings of over 40% while maintaining a low viscosity. The next challenge was adapting an inexpensive polymer printer to use the powder loaded resin. Various printer parameters were modified and different window coatings were implemented to create a print. The issue of the layers curing on the build area window however, proved to be difficult to

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

    Directory of Open Access Journals (Sweden)

    Hiroyo Segawa

    2014-01-01

    Full Text Available 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.

  2. 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.

  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. 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.

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

    Science.gov (United States)

    Ahmad, S.; Ibrahim, A.; Alias, R.; Shapee, S. M.; Ambak, Z.; Zakaria, S. Z.; Yahya, M. R.; Mat, A. F. A.

    2010-03-01

    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° C, 1300° C and 1500° C for about 20 hours using heating and cooling rates of 2° 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.

  6. Energy transfer in porous anodic alumina/rhodamine 110 nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Elhouichet, H., E-mail: habib.elhouichet@fst.rnu.tn [Laboratoire de Physico-Chimie des Materiaux Mineraux et leurs Applications, Centre National de Recherches en Sciences des Materiaux, B.P. 95, Hammam-Lif 2050 (Tunisia); Departement de Physique, Faculte des Sciences de Tunis, University of Tunis Elmanar 2092 Tunis (Tunisia); Harima, N.; Koyama, H. [Hyogo University of Teacher Education, Kato, Hyogo 673-1494 (Japan); Gaponenko, N.V. [Belarusian State University of Informatics and Radioelectronics, P. Browki St. 6, 220013 Minsk (Belarus)

    2012-09-15

    We have used porous anodic alumina (PAA) films as templates for embedding rhodamine 110 (Rh110) molecules and examined their photoluminescence (PL) properties in detail. The analysis of the polarization memory (PM) of PL strongly suggests that there is a significant energy transfer from PAA to Rh110 molecules. The effect of annealing the PAA layer on the PL properties of the nanocomposite has been studied. The results show that the energy transfer becomes more efficient in annealed PAA. - Highlights: Black-Right-Pointing-Pointer Porous anodic alumina-rhodamine 110 nanocomposites are elaborated. Black-Right-Pointing-Pointer Efficient energy transfer from the host to Rh110 molecules is evidenced from measurements of photoluminescence and degree of polarization memory spectra. Black-Right-Pointing-Pointer Thermal annealing of porous anodic alumina can improve the process of excitation transfer.

  7. Porous Alumina as a Promising Biomaterial for Public Health.

    Science.gov (United States)

    Bragazzi, Nicola Luigi; Gasparini, Roberto; Amicizia, Daniela; Panatto, Donatella; Larosa, Claudio

    2015-01-01

    Porous aluminum is a nanostructured material characterized by unique properties, such as chemical stability, regular uniformity, dense hexagonal porous lattice with high aspect ratio nanopores, excellent mechanical strength, and biocompatibility. This overview examines how the structure and properties of porous alumina can be exploited in the field of public health. Porous alumina can be employed for fabricating membranes and filters for bioremediation, water ultrafiltration, and microfiltration/nanofiltration, being a promising technique for having clean and fresh water, which is essential for human health. Porous alumina-based nanobiosensor coated with specific antibodies or peptides seem to be a useful tool to detect and remove pathogens both in food and in water, as well as for environmental monitoring. Further, these applications, being low-energy demanding and cost-effective, are particularly valuable in resource-limited settings and contexts, and can be employed as point of use devices in developing countries, where there is an urgent need of hygiene and safety assurance.

  8. 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.

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

    OpenAIRE

    Gralik,G.; Chinelattot,A. L.; A. S. A. Chinelatto

    2014-01-01

    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 hydrox...

  10. Factors contributing to the breakdown of sodium beta-alumina

    Energy Technology Data Exchange (ETDEWEB)

    Buechele, A.C.

    1982-05-01

    Clarification of the breakdown process occurring during charge transfer in sodium beta alumina solid electrolytes was derived from: (1) studying the effects of molten sodium contact at 350/sup 0/C on single crystal sodium beta alumina and polycrystalline sodium beta alumina; (2) determination of critical current density by monitoring acoustic emissions accompanying crack growth in sodium/sodium beta alumina/sodium cells subjected to linear current ramping at 1 mA cm/sup -2/ sec/sup -1/; (3) failure analysis conducted on cycled electrolytes, some from commercial sodium/sulfur cells, which had been subjected to up to 703 Ahr cm/sup -2/ of charge transfer. Gray coloration developing in beta aluminas in contact with molten sodium was found to be a consequence of formation, through reduction by sodium, of oxygen vacancies charge compensated by electrons. Electronic conductivity of the electrolyte increases as a result. No second phase formation was detected. Colored electrolytes from sodium/sulfur cells show evidence of a newly recognized degradation mechanism in which fracture occurs when sodium is reduced and deposited internally under pressure as metal in regions where an electronic conductivity gradient exists. Heating colored beta aluminas in air produces reoxidation and bleaching. Kinetics and other properties of the coloration and bleaching processes were determined. Critical current density was found to bear an inverse relation to average electrolyte grain size. Evidence was found in the cycled electrolytes for a slow crack growth mechanism and a progressive mode of degradation advancing from the sulfur electrode interface. Implications of the findings for the construction and operation of sodium/sulfur battery systems are discussed.

  11. Effect of Filler Composition on the Brazing of Alumina to Copper Using Ultrasonic Wave

    Institute of Scientific and Technical Information of China (English)

    Khalid M. HAFEZ; Masaaki NAKA

    2003-01-01

    An ultrasonic wave was applied during brazing of alumina to Cu. First alumina was metallized by applying ultrasonicwave in braze bath. Then the metallized alumina was brazed with Cu using the same filler alloy. The filler used wereZn-Al alloys and Zn-Sn A

  12. Cylindrical Three-Dimensional Porous Anodic Alumina Networks

    Directory of Open Access Journals (Sweden)

    Pedro M. Resende

    2016-11-01

    Full Text Available The synthesis of a conformal three-dimensional nanostructure based on porous anodic alumina with transversal nanopores on wires is herein presented. The resulting three-dimensional network exhibits the same nanostructure as that obtained on planar geometries, but with a macroscopic cylindrical geometry. The morphological analysis of the nanostructure revealed the effects of the initial defects on the aluminum surface and the mechanical strains on the integrity of the three-dimensional network. The results evidence the feasibility of obtaining 3D porous anodic alumina on non-planar aluminum substrates.

  13. Atomistic force field for alumina fit to density functional theory.

    Science.gov (United States)

    Sarsam, Joanne; Finnis, Michael W; Tangney, Paul

    2013-11-28

    We present a force field for bulk alumina (Al2O3), which has been parametrized by fitting the energies, forces, and stresses of a large database of reference configurations to those calculated with density functional theory (DFT). We use a functional form that is simpler and computationally more efficient than some existing models of alumina parametrized by a similar technique. Nevertheless, we demonstrate an accuracy of our potential that is comparable to those existing models and to DFT. We present calculations of crystal structures and energies, elastic constants, phonon spectra, thermal expansion, and point defect formation energies.

  14. Controllable synthesis and characterization of alumina/MWNT nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Nemeth, Zoltan; Hernadi, Klara [Department of Applied and Environmental Chemistry, University of Szeged, Rerrich Bela ter 1, 6720 Szeged (Hungary); Marko, Kata; Erdohelyi, Andras [Department of Physical Chemistry and Material Science, University of Szeged, Aradi ter 2, 6720 Szeged (Hungary); Forro, Laszlo [Laboratory of Physics of Complex Matter, IPMC, EPFL, 1026 Ecublens (Switzerland)

    2011-11-15

    The aim of this work is to develop a controllable synthesis pathway which produces a stable alumina layer on the surface of carbon nanotubes by impregnation method. Precursor compounds such as aluminium isopropoxide and aluminium-acetyl-acetonate were used to cover the surface of multiwalled carbon nanotubes (MWNTs) under different solvent conditions. As-prepared alumina coverages were characterized by TEM, SEM, SEM-EDX, TG and X-ray diffraction techniques. Results revealed that homogeneous coverage can be achieved in a controllable way. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Mechanical properties of tricalcium phosphate-alumina composites

    Science.gov (United States)

    Sakka, S.; Ben Ayed, F.; Bouaziz, J.

    2012-02-01

    Tricalcium phosphate and alumina powder were mixed in order to elaborate biphasic ceramics composites. This study deals to produce bioceramics composites sintered at various temperatures for differents times. The characterization of samples, before and after the sintering process was investigated, using X-Ray diffraction, scanning electronic microscopy, 31P and 27Al nuclear magnetic resonance and differential thermal analysis. Mechanical properties of biphasic composites were studied using Brazilian test. The tricalcium phosphate - 75 wt% alumina composites mechanical resistance increased with sintered temperature. The mechanical resistance reach it's optimum value (8.6 MPa) at 1550°C for two hours.

  16. 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.

  17. A one-pot synthesis of 1,6,9,13-tetraoxadispiro(4.2.4.2)tetradecane by hydrodeoxygenation of xylose using a palladium catalyst

    Science.gov (United States)

    In an effort to expand the number of biobased chemicals available from sugars, xylose has been converted to 1,6,9,13-tetraoxadispiro(4.2.4.2)tetradecane in a one-pot reaction using palladium supported on silica-alumina as the catalyst. The title compound is produced in 35-40% yield under 7 MPa H2 pr...

  18. Ion effects in the adsorption of carboxylate on oxide surfaces, studied with quartz crystal microbalance

    NARCIS (Netherlands)

    Wang, Lei; Siretanu, Igor; Duits, Michel H.G.; Cohen Stuart, Martien A.; Mugele, Frieder

    2016-01-01

    We chose water-soluble sodium hexanoate as a model organic molecule to study the role of salt ions (Ca2+, Na+, Cl−) in the adsorption of carboxylates to mineral surfaces (silica, alumina, gibbsite) of variable surface charge and chemistry. Quartz crystal microbalance (QCM-D) measurements reveal a qu

  19. Influence of Si/Al ratio on hexane isomers adsorption equilibria

    NARCIS (Netherlands)

    Ferreira, A.F.P.; Mittelmeijer-Hazeleger, M.C.; Bliek, A.; Moulijn, J.A.

    2008-01-01

    In this work we aim to have a better knowledge of the influence of silica/alumina ratio (SAR) on the adsorption equilibrium of hexane isomers on MFI zeolites. With a manometric set-up coupled with a micro-calorimeter we did address adsorption properties and heats of adsorption of n-hexane, 2-methylp

  20. Selective conversion of butane into liquid hydrocarbon fuels on alkane metathesis catalysts

    KAUST Repository

    Szeto, Kaï Chung

    2012-01-01

    We report a selective direct conversion of n-butane into higher molecular weight alkanes (C 5+) by alkane metathesis reaction catalysed by silica-alumina supported tungsten or tantalum hydrides at moderate temperature and pressure. The product is unprecedented, asymmetrically distributed towards heavier alkanes. This journal is © 2012 The Royal Society of Chemistry.

  1. Research Opportunities for Materials with Ultrafine Microstructures

    Science.gov (United States)

    1989-12-31

    Ulrich, 1984). Alkoxides are the organometallic precursors for silica, alumina, titania, and zirconia , among others. A catalyst is used to start...selectively added to the clusters by these methods. The extension of this technology to include excitation of gaseous species in corona -discharge free

  2. First acidic macro-mesocellular aluminosilicate monolithic foams "SiAl(HIPE)" and their catalytic properties.

    Science.gov (United States)

    Debecker, Damien P; Boissière, Cédric; Laurent, Guillaume; Huet, Stéphanie; Eliaers, Philippe; Sanchez, Clément; Backov, Rénal

    2015-09-25

    A new type of acidic macrocellular and mesoporous silica-alumina foam is obtained via a one pot alkaline sol-gel route coupled with a concentrated emulsion-based templating technique. The mixed oxide monolith exhibits high surface acidity, translating into excellent performance in the acid-catalyzed dehydration of bioethanol to ethene.

  3. Thermal Conductivity of Composites of Beryllia and Lithium Titanate

    Science.gov (United States)

    Rath, B. N.; Ghanwat, S. J.; Kaity, Santu; Danani, Chandan; Kulkarni, R. V.; Alur, V. D.; Sathiyamoorthy, D.; Anantharaman, S.

    2013-11-01

    The International Thermonuclear Experimental Reactor (ITER) is designed to demonstrate the scientific and technological feasibility of fusion power for energy purposes. Wide varieties of solid breeders and multiplier materials have been proposed for fusion blankets. Beryllium and lithium titanate (Li2TiO3) have been accepted as neutron multiplier and breeder materials, respectively. However, swelling of beryllium due to helium and tritium permeation through metallic beryllium and low thermal conductivity of lithium titanate have caused serious limitations when ITER is in the demo version. It has been well established that BeO due its highest thermal conductivity among the known ceramics, low neutron absorption cross section, and high neutron reflection cross section is a good neutron multiplier. In the present investigation, a novel ceramic single compound of BeO-Li2TiO3 was synthesized, keeping the BeO content to Li2TiO3 in the volume ratio of 80:20, 75:25, 65:35, and 55:45 with the aim of maintaining the tritium breeding ratio as more than one, and characterized for phases present by x-ray diffraction and scanning electron microscopy.

  4. High modulus invert analog glass compositions containing beryllia

    Science.gov (United States)

    Bacon, J. F. (Inventor)

    1974-01-01

    Glass compositions having a Young's modulus of at least 15 million psi and a specific modulus of at least 110 million inches consisting essentially of, in mols, 10-45% SiO2, 2-15% Li2O, 3-34% BeO, 12-36% of at least one bivalent oxide selected from the group consisting of CaO, ZnO, MgO and CuO, 10-39% of at least one trivalent oxide selected from the group consisting of Al2O3, B2O3, La2O3, Y2O3 and the mixed rare earth oxides, the total number of said bivalent and trivalent oxides being at least three, and up to 10% of a tetravalent oxide selected from the group consisting of ZrO2, TiO2 and CeO2.

  5. 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...

  6. Effect of La2O3 on Microstructure and Transmittance of Transparent Alumina Ceramics

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Optically transparent alumina ceramics were fabricated by conventional process and sintered without pressure in H2 atmosphere. The results indicate that relative densities of alumina specimens increase to theoretical densities (T.D.) with increasing content of La2O3. With increasing holding time during sintering, much less pores and larger grains were found in the sintered alumina samples. Higher transmittance was achieved in alumina codoped with MgO and La2O3 as compared with that doped with MgO only. The total-transmittance of alumina sample is up to 86% at a wavelength range of 300~800 nm.

  7. A General Procedure for Surface Modification of Nano-alumina and Its Application to Dendrimers

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    A general procedure for surface modification of nano-alumina using N, N'-dicyclohexyl-carbodiimide (DCC) mediated amidation is reported. Aliphatic and aromatic carboxylic acids reacted smoothly with nano-alumina pretreated with 3-aminopropyltriethoxysilane in the presence of DCC, giving modified aluminas having organic surfaces. The grafted aluminas have been characterized qualitatively by FT-IR or 13C CPMAS NMR spectroscopy, and quantitatively by thermogravimetric analysis and elemental analysis. The procedure was applied to polyether dendrons bearing carboxyl groups at the focal points, giving successful grafting of dendrimers onto nano-alumina.

  8. Joining between alumina and metal by use of plasma sprayed Ni-Al coating on alumina. Alumina ni plasma yoshashita Ni-Al kinzoku himaku wo kaishite no alumina kinzoku tono setsugo

    Energy Technology Data Exchange (ETDEWEB)

    Murakami, N.; Kishitake, K.; Hasebe, M.; Kobayashi, T.; Murashige, K. (Kyushu Institute of Technology, Kitakyushu (Japan). Faculty of Engineering)

    1993-06-30

    A ceramic material is joined and compounded with a metal by spraying another metal on the ceramic material, and then joined with the intended metal because of small adhesion strength in both materials. Adhesion strength of the spraying metal is important even in this case. The present experiment performed plasma spraying of Ni-Al mixed powder on alumina to investigate effects of the heating on the adhesion strength. Solder joining of Ni-Al sprayed alumina with soft steel rod and copper rod was also tested. As a result, the adhesion strength of as-sprayed Ni-Al film on the alumina was about 5 MPa and maximum of 10 MPa. Heating the materials to 1173 K for 10 hours or longer provided an average strength of 20 MPa and a maximum strength of 35 MPa. Improving the adhesion strength requires spinel to be produced through reactions on the interface. It was found that alumina can be joined with metal easily by going through this film. 12 refs., 6 figs.

  9. Development of Cast Alumina-Forming Austenitic Stainless Steels

    Science.gov (United States)

    Muralidharan, G.; Yamamoto, Y.; Brady, M. P.; Walker, L. R.; Meyer, H. M., III; Leonard, D. N.

    2016-11-01

    Cast Fe-Ni-Cr chromia-forming austenitic stainless steels with Ni levels up to 45 wt.% are used at high temperatures in a wide range of industrial applications that demand microstructural stability, corrosion resistance, and creep strength. Although alumina scales offer better corrosion protection at these temperatures, designing cast austenitic alloys that form a stable alumina scale and achieve creep strength comparable to existing cast chromia-forming alloys is challenging. This work outlines the development of cast Fe-Ni-Cr-Al austenitic stainless steels containing about 25 wt.% Ni with good creep strength and the ability to form a protective alumina scale for use at temperatures up to 800-850°C in H2O-, S-, and C-containing environments. Creep properties of the best alloy were comparable to that of HK-type cast chromia-forming alloys along with improved oxidation resistance typical of alumina-forming alloys. Challenges in the design of cast alloys and a potential path to increasing the temperature capability are discussed.

  10. Laser-induced prenucleation of alumina for electroless plating

    NARCIS (Netherlands)

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

    1991-01-01

    This paper deals with the deposition of palladium from decomposition of a thin palladium acetate layer on rough and porous alumina ceramic surfaces by irradiating it with a UV excimer laser. The palladium acetate layer was formed from a combination of propyl glycol methyl ether acetate solvent and p

  11. Development of Cast Alumina-Forming Austenitic Stainless Steels

    Science.gov (United States)

    Muralidharan, G.; Yamamoto, Y.; Brady, M. P.; Walker, L. R.; Meyer, H. M., III; Leonard, D. N.

    2016-09-01

    Cast Fe-Ni-Cr chromia-forming austenitic stainless steels with Ni levels up to 45 wt.% are used at high temperatures in a wide range of industrial applications that demand microstructural stability, corrosion resistance, and creep strength. Although alumina scales offer better corrosion protection at these temperatures, designing cast austenitic alloys that form a stable alumina scale and achieve creep strength comparable to existing cast chromia-forming alloys is challenging. This work outlines the development of cast Fe-Ni-Cr-Al austenitic stainless steels containing about 25 wt.% Ni with good creep strength and the ability to form a protective alumina scale for use at temperatures up to 800-850°C in H2O-, S-, and C-containing environments. Creep properties of the best alloy were comparable to that of HK-type cast chromia-forming alloys along with improved oxidation resistance typical of alumina-forming alloys. Challenges in the design of cast alloys and a potential path to increasing the temperature capability are discussed.

  12. Experiments on individual alumina-supported adatoms and clusters

    Science.gov (United States)

    Nilius, N.; Cörper, A.; Bozdech, G.; Ernst, N.; Freund, H.-J.

    2001-08-01

    To contribute to an understanding of growth conditions and electronic properties of metal clusters on technologically relevant oxides we have examined the mobility of individual, alumina-supported Pt-adatoms and the optical properties of single supported Ag-clusters. Using field-ion microscopy (FIM) we have prepared and imaged an individual Pt-adatom at approximately 40 K, both on the apex plane of a [1 1 0]-oriented NiAl tip and on a thin alumina film, grown on the same NiAl specimen by oxidation. On the alumina film, the onset temperature for Pt surface diffusion approaches 100 K being distinctively lower than the value 165 K measured on NiAl(1 1 0). Employing the tip of a scanning tunneling microscope (STM) as a local electron source, photon emission from individual, alumina-supported Ag-clusters was spectroscopically analyzed. The occurrence of a distinct emission line is explained by the decay of a collective electron oscillation (Mie-plasmon resonance). For decreasing Ag-cluster diameter, the emission lines (i) shift to higher energies and (ii) their widths increase. To explain these observations, we discuss (i) the reduced screening of the plasmon oscillation due to the Ag 4d electrons and (ii) an enhanced electron surface scattering rate in small clusters.

  13. 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...

  14. Gas and surface diffusion in modified γ-alumina systems

    NARCIS (Netherlands)

    Uhlhorn, R.J.R.; Keizer, K.; Burggraaf, A.J.

    1989-01-01

    The transport of pure gases through a microporous membrane is described. The alumina-based membrane (pores 2.5-4 nm) is suitable for Knudsen diffusion separation. To improve the separation factor, interaction with and mobility on the pore wall of one of the gases of a mixture is necessary. To introd

  15. Capillary condensation in porous alumina observed by positronium lifetime spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Ivanov, Eugeniu [National Institute for Nuclear Physics and Engineering-Horia Hulubei, Atomistilor Street 407, CP MG 06, Magurele, Bucharest (Romania); Center for Advanced Studies in Physics of the Roumanian Academy, Casa Academiei Romane, Calea 13 Septembrie No. 13, Bucharest (Romania); Vata, Ion [National Institute for Nuclear Physics and Engineering-Horia Hulubei, Atomistilor Street 407, CP MG 06, Magurele, Bucharest (Romania)], E-mail: vata@ifin.nipne.ro; Toderian, Stefan; Dudu, Dorin; Rusen, Ion; Stefan, Nitisor [National Institute for Nuclear Physics and Engineering-Horia Hulubei, Atomistilor Street 407, CP MG 06, Magurele, Bucharest (Romania)

    2008-10-31

    The PALS method based on time distribution measurements has been used to study capillary condensation of different gases adsorbed in microporous alumina powder. The isotherms exhibit features which are associated with a shifted gas-liquid transition. The sorption and desorption processes are irreversible presenting a hysteresis effect. Suggestions on some new aspects of the capillary condensation dynamics are made.

  16. Structure and surface properties of praseodymium modified alumina

    Energy Technology Data Exchange (ETDEWEB)

    Tankov, I. [Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria); Pawelec, B. [Instituto de Catalisis y Petroleoquimica, CSIC, Cantoblanco, 28049 Madrid (Spain); Arishtirova, K. [Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria); Damyanova, S., E-mail: soniad@ic.bas.bg [Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia (Bulgaria)

    2011-10-15

    Mixed PrO{sub 2}-Al{sub 2}O{sub 3} oxides with different PrO{sub 2} content (1-20 wt.%) were prepared by wetness impregnation of {gamma}-alumina with aqueous solution of praseodymium nitrate. The samples were characterized by different techniques, using surface adsorption-desorption of N{sub 2} (S{sub BET}), 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 CO{sub 2} (TPD-CO{sub 2}). 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 Pr{sub 6}O{sub 11}. TPD-CO{sub 2} studies suggested that the deposition of Pr oxide on alumina leaded to increase of the basicity of mixed oxides.

  17. Ionic Segregation on Grain Boundaries in Thermally Grown Alumina Scales

    Energy Technology Data Exchange (ETDEWEB)

    Pint, Bruce A [ORNL; Unocic, Kinga A [ORNL

    2012-01-01

    This study first examined segregation behaviour in the alumina scale formed after 100 h at 1100 C on bare and MCrAlYHfSi-coated single-crystal superalloys with {approx}10 ppma La and Y. For the bare superalloy, Hf and Ti were detected on the grain boundaries of the inner columnar alumina layer. Increasing the oxidation temperature to 1200 C for 2 h did not change the segregation behavior. With the bond coating, both Y and Hf were segregated to the grain boundaries as expected. However, there was evidence of Ti-rich oxide particles near the gas interface suggesting that Ti diffused from the superalloy through the coating. To further understand these segregation observations with multiple dopants, other alumina-forming systems were examined. Alumina scale grain boundary co-segregation of Ti with Y is common for FeCrAl alloys. Co-segregation of Hf and Ti was observed in the scale formed on co-doped NiAl. No La segregation was detected in the scale formed on NiCrAl with only a 19 ppma La addition, however, the scale was adherent.

  18. Osseointegration of alumina bioceramic granules: A comparative experimental study

    Science.gov (United States)

    Rerikh, V. V.; Avetisyan, A. R.; Zaydman, A. M.; Anikin, K. A.; Bataev, V. A.; Nikulina, A. A.; Sadovoy, M. A.; Aronov, A. M.; Semantsova, E. S.

    2016-08-01

    To perform a comparative analysis of osseointegration of bioceramic alumina-based granules, hydroxyapatite-based granules, and deproteinized bone granules. The experiment was conducted on 52 adult male Kyoto-Wistar rats weighing 350 to 520 g. The animals were divided into five matched groups that differed only in the type of an implanted material. The granules were implanted in the lumbar vertebral bodies and in the distal right femur of each laboratory animal. Two months after surgery, the animals were euthanized, followed by tissue sampling for morphological studies. An examination of specimens from the groups with implanted alumina granules revealed the newly formed trabecular bone with remodeling signs. The bone tissue filled the intragranular space, tightly adhering to the granule surface. There was no connective tissue capsule on the border between bone tissue and alumina granules. Cylindrical bioceramic alumina-based granules with an open internal channel have a higher strength surpassing than that of analogs and the osseointegration ability close to that of hydroxyapatite and deproteinized bone granules.

  19. Sol-gel based alumina powders with catalytic applications

    Science.gov (United States)

    Crişan, Maria; Zaharescu, Maria; Kumari, Valluri Durga; Subrahmanyam, Machiraju; Crişan, Dorel; Drăgan, Nicolae; Răileanu, Mălina; Jitianu, Mihaela; Rusu, Adriana; Sadanandam, Gullapelli; Krishna Reddy, Jakkidi

    2011-10-01

    The sol-gel process provides a new approach to the preparation of oxide materials and offers many advantages for making catalysts. Since homogeneous mixing can be achieved at the molecular scale, the chemical reactivity of the oxide surface can be greatly enhanced; thus powders with high surface area and optimized pore size distribution can be obtained at low temperatures. In the present work NiO/Al 2O 3 sol-gel catalysts were obtained by simultaneous gelation of aluminium isopropoxide and nickel nitrate. A comparative study with pure sol-gel alumina was also realized. By physical-structural studies the changes induced by the introduction of the Ni precursor, before and after aluminium alkoxide hydrolysis were highlighted. The introduction of Ni at the beginning of the reaction favors γ-Al 2O 3 crystallization. When Ni is added at the end of reaction, it delays the alumina crystallization and induces the disorder of the lattice. The obtained Ni doped sol-gel derived alumina has been used as catalyst in the finished form for glycerol reforming to generate H 2 for fuel cell applications. Some evaluation results of Ni-doped alumina combined with TiO 2 in photocatalytic glycerol reforming reaction have been included.

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

    Energy Technology Data Exchange (ETDEWEB)

    Hauth, W.E.; Stoddard, S.D.

    1978-01-01

    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.

  1. Thin alumina and silica films by chemical vapor deposition (CVD)

    NARCIS (Netherlands)

    Hofman, R.; Morssinkhof, R.W.J.; Fransen, T.; Westheim, J.G.F.; Gellings, P.J.

    1993-01-01

    Alumina and silica coatings have been deposited by MOCVD (Metal Organic Chemical Vapor Deposition) on alloys to protect them against high temperature corrosion. Aluminium Tri-lsopropoxide (ATI) and DiAcetoxyDitertiaryButoxySilane (DAOBS) have been used as metal organic precursors to prepare these ce

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  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. Porous alumina, zirconia and alumina/zirconia for bone repair: fabrication, mechanical and in vitro biological response.

    Science.gov (United States)

    Hadjicharalambous, Chrystalleni; Buyakov, Ales; Buyakova, Svetlana; Kulkov, Sergey; Chatzinikolaidou, Maria

    2015-04-23

    Zirconia (ZrO2) and alumina (Al2O3) based ceramics are widely used for load-bearing applications in bone repair due to their excellent mechanical properties and biocompatibility. They are often regarded as bioinert since no direct bone-material interface is created unless a porous structure intercedes, leading to better bone bonding. In this regard, investigating interactions between cells and porous ceramics is of great interest. In the present study, we report on the successful fabrication of sintered alumina A-61, zirconia Z-50 and zirconia/alumina composite ZA-60 ceramics with medium porosities of 61, 50 and 60%, respectively, indicating a bimodal pore size distribution and good interconnectivity. They exhibit elastic moduli of 3-10 GPa and compressive strength values of 60-240 MPa, similar to those of human cortical bone.We performed in vitro cell-material investigations comparing the adhesion, proliferation and differentiation of mouse pre-osteoblasts MC3T3-E1 on the three porous materials. While all three ceramics demonstrate a strong cell attachment, better cell spreading is observed on zirconia-containing substrates. Significantly higher cell growth was quantified on the latter ceramics, revealing an increased alkaline phosphatase activity, higher collagen production and increased calcium biomineralization compared to A-61. Hence, these porous zirconia-containing ceramics elicit superior biological responses over porous alumina of similar porosity, promoting enhanced biological interaction, with potential use as non-degradable bone grafts or as implant coatings.

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

    Science.gov (United States)

    Basch, Angelika; Strnad, Simona

    2011-01-20

    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 coagulation (SIC) coating process of nano-sized alumina in non-aqeous media. SIC is a dip-coating process that coats pretreated but chemically different surfaces with nano-sized particles. It was found that the anionic surfactant dioctyl sulfosuccinate (AOT) had no stabilizing effect on alumina dispersed in NMP.

  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. Protective coating for alumina-silicon carbide whisker composites

    Science.gov (United States)

    Tiegs, Terry N.

    1989-01-01

    Ceramic composites formed of an alumina matrix reinforced with silicon carbide whiskers homogenously dispersed therein are provided with a protective coating for preventing fracture strength degradation of the composite by oxidation during exposure to high temperatures in oxygen-containing atmospheres. The coating prevents oxidation of the silicon carbide whiskers within the matrix by sealing off the exterior of the matrix so as to prevent oxygen transport into the interior of the matrix. The coating is formed of mullite or mullite plus silicon oxide and alumina and is formed in place by heating the composite in air to a temperature greater than 1200.degree. C. This coating is less than about 100 microns thick and adequately protects the underlying composite from fracture strength degradation due to oxidation.

  11. Alumina lightweight ceramics modified with plasma synthesized nanopowders

    Science.gov (United States)

    Zake, I.; Svinka, R.; Svinka, V.; Palcevskis, E.

    2011-12-01

    The aim of this study is to clarify possibilities of using plasma synthesized Al2O3 and SiC nanopowders as additives in alumina lightweight ceramics prepared by slip casting. Each plasma synthesized nanopowder (PSNP) was incorporated in the material by a different method, because of their diverse influence on the properties of slip. Al2O3 PSNP was introduced in the matrix in form of aqueous suspension. SiC nanopowder was added directly to raw materials. Bending strength, bulk density, apparent porosity and thermal shock resistance were determined to evaluate the influence of these additives. The effect of Al2O3 PSNP addition on the properties of material depends on the initial sintering temperature. SiC particles during sintering oxidize into SiO2 and then in the reaction with alumina form mullite. Addition of SiC considerably improves bending strength and thermal shock resistance.

  12. 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}.

  13. Measurements of prompt radiation induced conductivity of alumina and sapphire

    Energy Technology Data Exchange (ETDEWEB)

    Hartman, E. Frederick [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Zarick, Thomas Andrew [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Sheridan, Timothy J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Preston, Eric F. [ITT Coporation, Colorado Springs, CO (United States)

    2011-04-01

    We performed measurements of the prompt radiation induced conductivity in thin samples of Alumina and Sapphire at the Little Mountain Medusa LINAC facility in Ogden, UT. Five mil thick samples were irradiated with pulses of 20 MeV electrons, yielding dose rates of 1E7 to 1E9 rad/s. We applied variable potentials up to 1 kV across the samples and measured the prompt conduction current. Analysis rendered prompt conductivity coefficients between 1E10 and 1E9 mho/m/(rad/s), depending on the dose rate and the pulse width for Alumina and 1E7 to 6E7 mho/m/(rad/s) for Sapphire.

  14. 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

  15. 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.

  16. Optical characterization of gold coated over nanostructured alumina films

    Science.gov (United States)

    Aslan, Mustafa M.

    2014-02-01

    The gold coated over nanostructured alumina (GCON-A) films were investigated for layers' thicknesses and optical properties between 400 and 800 nm wavelength. First GCON-A films were fabricated in three steps: atomic layer deposition of alumina, hot water treatment, and gold deposition. Then, polarization maintained angular reflectance measurements were taken with a spectroscopic ellipsometry. Layer thicknesses, effective refractive indices, and absorption coefficients of films were determined through regression analysis on the ellipsometry data. To investigate the optical properties of the GCON-A films further, reflection measurements were taken by the visible spectroscopy. All these results verify that it is feasible to tune optical properties of the GCON-A films.

  17. 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%.

  18. Synthesis of catalysts supported in {gamma}-alumina; Sintese de catalisadores suportados na {gamma}-alumina

    Energy Technology Data Exchange (ETDEWEB)

    Pereira, Luiza Gabriel; Silva, A.J.N.; Santos, I.M.G.; Souza, A.G. [Paraiba Univ, Joao Pessoa, PB (Brazil). Dept. de Quimica. Lab. de Termoquimica e Materiais]. E-mail: luizagaby@yahoo.com.br; Fernandes Junior, V.J.; Araujo, A.S. [Rio Grande do Norte Univ., Natal, RN (Brazil). Dept. de Quimica. Lab. de Combustiveis

    2003-07-01

    Fuels contain a great amount of undesirable pollutants as asphaltenes, metals, sulfides and nitrogen compounds. The content of sulfur in petroleum is around 1%,. When burned, fuels liberate SO{sub x}, the greatest air pollutant . The maximum sulfur quantity in diesel is {approx}350 wppm, but in agreement to European specifications, this content will fall to 50 wppm up to 2005. To remove this sulfur a deep hydrodesulfurization is necessary, requiring high performance catalysts. This way, in this work, the following catalysts were synthesized, using Pechini method: MoO{sub 3} containing Ni and/or Co supported on {gamma}-alumina, with the formulas Co{sub x}Mo{sub 1-x}O{sub 3}/Al{sub 2}O{sub 3}, Ni{sub x}Mo{sub 1-x}O{sub 3}/Al{sub 2}O{sub 3} and Ni{sub x/2}Co{sub x/2}Mo{sub 1-x}O{sub 3}/Al{sub 2}O{sub 3} where x 0,01, 0,02 and 0,03 in mol percentage. This method was proposed, due to its high stoichiometry control, purity, reproducibility and homogeneity. All catalysts were submitted to thermal treatment at 500 deg C to 700 deg C and characterized by thermogravimetry, infrared spectroscopy, X-ray diffraction. Results indicate the stabilization of the requested composition at around 622 deg C. The X-ray diffraction results indicate that secondary phase increases with dopant amount. (author)

  19. MICROWAVE JOINING OF ALUMINA CERAMIC AND HYDROXYLAPATITE BIOCERAMIC

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    Microwave joining is a rapid developmental new techniqu e in recent years.This paper introduces a new microwave joining equipment which was made by our lab,succeeds in alumina ceramic-hydroxylapatite bioceramic j o in in the equipment, and analyzes the join situation of join boundary by using s canni ng electron microscope(SEM),this paper analyzes the mechanism of microwave joini ng also.

  20. Single Crystal Structure Determination of Alumina to 1 Mbar

    Science.gov (United States)

    Dong, H.; Zhang, L.; Prakapenka, V.; Mao, H.

    2014-12-01

    Aluminum oxide (Al2O3) is an important ceramic material and a major oxide in the earth. Additionally, alumina is a widely used pressure standard in static high-pressure experiments (Cr3+-bearing corundum, ruby). The changes of its crystal structure with pressure (P) and temperature (T) are important for its applications and understanding its physical properties in the deep Earth. There have been numerous reports on the high P-T polymorphs of alumina. Previous theoretical calculations and experiments suggest that the crystal structure of Al2O3 evolves greatly at high P-T. In this study, we used the newly developed multigrain crystallography method combined with single-crystal x-ray diffraction analysis technique for the structure determination of alumina at high P-T to provide single-crystal structure refinement for high-pressure phases of Al2O3. Alumina powder was mixed with ~10% Pt and Ne was used as both pressure transmitting media and thermal insulating layers during laser-heating. Coarse-grained aggregates of Al2O3 were synthesized in a laser-heated diamond anvil cell. The structure change of Al2O3 was monitored by in situ x-ray diffraction at ~1 Mbar and 2700 K. The results allow us to distinguish the structural differences between the Rh2O3 (II) structure (space group Pbcn) and perovskite structure (space group Pbnm) for the first high-pressure phase of Al2O3. More detailed results will be discussed in the later work.

  1. 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)

  2. Friction and Wear of Sintered Alumina at High Temperature

    OpenAIRE

    Senda, Tetsuya; TAKAHASHl, Chiori; UEMATSU, Susumu; Amada, Shigeyasu

    1991-01-01

    The frictional behavior of alumina ceramics was investigated at various temperatures up to 1200℃. The coefficient of friction decreased with increasing temperature and this temperature dependency became more pronounced as higher contact pressures were applied. Wear loss at room temperature could be interpreted as being caused by one of either two different behavior modes. These have a rate difference of a factor of ten. At temperatures higher than 800℃, the wear loss was far less than that at...

  3. Thin alumina and silica films by chemical vapor deposition (CVD)

    OpenAIRE

    Hofman, R.; Morssinkhof, R.W.J.; Fransen, T.; Westheim, J.G.F.; Gellings, P.J.

    1993-01-01

    Alumina and silica coatings have been deposited by MOCVD (Metal Organic Chemical Vapor Deposition) on alloys to protect them against high temperature corrosion. Aluminium Tri-lsopropoxide (ATI) and DiAcetoxyDitertiaryButoxySilane (DAOBS) have been used as metal organic precursors to prepare these ceramic coatings. The influence of several process steps on the deposition rate and surface morphology is discussed. The deposition of SiO2 at atmospheric pressure is kinetically limited below 833 K ...

  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. 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.

  6. Mullite/SiAlON/alumina composites by infiltration processing

    Energy Technology Data Exchange (ETDEWEB)

    Albano, M.P.; Scian, A.N. [Centro de Tecnologia de Recursos Minerales y Ceramica, Buenos Aires (Argentina)

    1997-01-01

    The formation of mullite/SiAlON/alumina composites was studied by infiltrating a SiAlON/alumina-base composite with two different solutions, followed by thermal treatment. The base composite was prepared from a mixture of tabular Al{sub 2}O{sub 3} grains, fume SiO{sub 2}, and aluminum powders. The mixture was pressed into test bars and nitrided in a nitrogen-gas (N{sub 2}) atmosphere at 1,480 C. The infiltrants were prehydrolyzed ethyl polysilicate solution and ethyl polysilicate-aluminum nitrate solution. The composites were infiltrated under vacuum, cured at 100 C, and precalcined in air at 700 C. This infiltration process was repeated several times to produce bars that had been subjected to multiple infiltrations, then the bars were calcined in a N{sub 2} atmosphere at 1,480 C to obtain mullite/SiAlON/alumina composites. The infiltration process increased the percentage of nitrogenous crystalline and mullite phases in the matrix; therefore, a decrease of the composite microporosity was observed. The infiltration increased the mechanical strength of the composites. Of the two composites, the one produced using prehydrolyzed ethyl polysilicate as the infiltrant had a higher mechanical strength, before and after being subjected to a severe thermal shock.

  7. 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.

  8. Zirconia-alumina-nanodiamond composites with gemological properties

    Science.gov (United States)

    Díaz, Luis A.; Montes-Morán, Miguel A.; Peretyagin, Pavel Y.; Vladimirov, Yuriy G.; Okunkova, Anna; Moya, José S.; Torrecillas, Ramón

    2014-02-01

    Nanodiamonds have excellent mechanical and optical properties with a wide range of potential applications as a filler material for nanocomposites. Here, we present a new family of zirconia-alumina-nanodiamond composites using two main processing routes: (1) a colloidal method, and (2) power mixing homogenization. Composites with detonation nanodiamonds quantities ranging within 0.3-5 vol.% followed by a pulsed electrical current sintering at a temperature range from 1,200 to 1,500 °C have been analyzed, and a significant enhancement in mechanical properties, i.e., indentation hardness (16.17 GPa), fracture toughness (15.5 MPa m1/2), and bending strength (1,600 MPa), could be observed. To support these excellent properties, TEM, color, reflectivity, and Raman spectroscopy measurements were also carried out. The microstructure of the composites is very homogeneous with average grain sizes between 200 and 500 nm depending on the processing temperature. Two morphologies are present: (a) intergranular dispersion of alumina grains and nanodiamonds distributed along the grain boundaries of the ZrO2 matrix, and (b) intragranular nano-dispersion of ZrO2 particles with sizes 20-80 nm located inside the alumina grains. In the present article, we show, for the first time in the scientific literature, a continuous palette of gray color gradation of new ceramic materials of metalized colors (white index L* 98-40) for gemological applications.

  9. 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.

  10. High strength alumina produced by direct coagulation casting

    Energy Technology Data Exchange (ETDEWEB)

    Baader, F.H.; Will, J.; Tieche, D. [Swiss Federal Institute of Technology, Zuerich (Switzerland)

    1995-09-01

    Direct Coagulation Casting is a new colloidal forming technique. Double layer stabilized, concentrated alumina suspensions are solidified by shifting the suspensions pH from 4 towards the isoelectric point at 9 using the in situ enzyme-catalyzed decomposition of urea. This reaction minimizes the repulsive forces between the suspended particles. The remaining, attractive Van der Waals forces form a stiff particle network. Suspensions with low viscosities (0.3 Pa*s, 59 vol%) were prepared at pH 4. Deagglomeration of the suspensions by ball milling reduced the agglomerate size below 5 pm. The coagulation kinetics could be influenced either by the urease concentration or by the suspension temperature. Process variables were established, providing long idle times, which allowed additional filtration and degassing steps. Coagulation was followed by drying and sintering, whereby densities of more than 3.97 g/cm{sup 3}, a 4-point bending strength of 685 MPa (HIPed) and a high reliablility (m = 40) for high purity alumina were achieved. DCC has the potential to improve the reliability of alumina components of complex shape, as well as to avoid expensive molding.

  11. 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.

  12. 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.

  13. 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.

  14. Removing Bacillus subtilis from fermentation broth using alumina nanoparticles.

    Science.gov (United States)

    Mu, Dashuai; Mu, Xin; Xu, Zhenxing; Du, Zongjun; Chen, Guanjun

    2015-12-01

    In this study, an efficient separation technology using Al2O3 nanoparticles (NPs) was developed for removing Bacillus subtilis from fermentation broth. The dosage of alumina nanoparticles used for separating B. subtilis increased during the culture process and remained stable in the stationary phase of the culture process. The pH of the culture-broth was also investigated for its effects on flocculation efficiency, and showed an acidic pH could enhance the flocculation efficiency. The attachment mechanisms of Al2O3 NPs to the B. subtilis surface were investigated, and the zeta potential analysis showed that Al2O3 NPs could attach to B. subtilis via electrostatic attachment. Finally, the metabolite content and the antibacterial effect of the fermentation supernatants were detected and did not significantly differ between alumina nanoparticle separation and centrifugation separation. Together, these results indicate a great potential for a highly efficient and economical method for removing B. subtilis from fermentation broth using alumina nanoparticles. Copyright © 2015 Elsevier Ltd. All rights reserved.

  15. Physical Properties of Copper Based MMC Strengthened with Alumina

    Directory of Open Access Journals (Sweden)

    Kaczmar J. W.

    2014-06-01

    Full Text Available The aim of this work is the development of Cu-Al2O3 composites of copper Cu-ETP matrix composite materials reinforced by 20 and 30 vol.% Al2O3 particles and study of some chosen physical properties. Squeeze casting technique of porous compacts with liquid copper was applied at the pressure of 110 MPa. Introduction of alumina particles into copper matrix affected on the significant increase of hardness and in the case of Cu-30 vol. % of alumina particles to 128 HBW. Electrical resistivity was strongly affected by the ceramic alumina particles and addition of 20 vol. % of particles caused diminishing of electrical conductivity to 20 S/m (34.5% IACS. Thermal conductivity tests were performed applying two methods and it was ascertained that this parameter strongly depends on the ceramic particles content, diminishing it to 100 Wm-1K-1 for the composite material containing 30 vol.% of ceramic particles comparing to 400 Wm-1K-1 for the unreinforced copper. Microstructural analysis was carried out using SEM microscopy and indicates that Al2O3 particles are homogeneously distributed in the copper matrix. EDS analysis shows remains of silicon on the surface of ceramic particles after binding agent used during preparation of ceramic preforms.

  16. 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.

  17. Wear and flexural strength comparisons of alumina/feldspar resin infiltrated dental composites.

    Science.gov (United States)

    Le Roux, A R; Lachman, N; Walker, M; Botha, T

    2008-11-01

    Incorporating a feldspar chemical bond between alumina filler particles is expected to increase the wear-resistant and flexural strength properties. An investigation was carried out to evaluate the influence of the feldspar chemical bonding between alumina filler particles on wear and flexural strength of experimental alumina/feldspar dental composites. It was hypothesized that wear resistance and flexural strength would be significantly increased with increased feldspar mass. Alumina was chemically sintered and bonded with 30% and 60% feldspar mass, silanized and infiltrated with UDMA resin to prepare the dental restorative composite material. Higher wear-resistant characteristics resulted with increased feldspar mass of up to 60% (p 0.05). Feldspar chemical bonding between the alumina particles may improve on the wear-resistance and flexural strength of alumina/feldspar composites.

  18. Behavior of alumina barrier layer in the supporting electrolytes for deposition of nanowired materials

    Energy Technology Data Exchange (ETDEWEB)

    Jagminas, Arunas, E-mail: jagmin@ktl.mii.l [Institute of Chemistry, A. Gostauto 9, 01108 Vilnius (Lithuania); Cesuniene, Asta [Institute of Chemistry, A. Gostauto 9, 01108 Vilnius (Lithuania); Vrublevsky, Igor [Department of Microelectronics, Belarusian State University of Informatics and Radioelectronics, 6 Brovka str, Minsk 220013 (Belarus); Jasulaitiene, Vitalija; Ragalevicius, Rimas [Institute of Chemistry, A. Gostauto 9, 01108 Vilnius (Lithuania)

    2010-03-30

    In this study, we report the results obtained investigating the behavior of sulfuric and chromic acid alumina templates in typical supporting electrolytes frequently used for alternating current (ac) deposition of various nm-scaled materials. Qualitative analysis of voltammetric profiles taken for as-grown, ac-treated and annealed alumina films in a conventional tetraborate re-anodizing solution revealed dramatical changes in the properties of alumina barrier layer during ac treatment in these supporting electrolytes even at low current density. These changes were related here with the transport of protons through the barrier layer during ac treatment, discharge at the metal/oxide interface and hydrogenation of alumina material by hydrogen atoms in an upward way. This conclusion comes from the behavior of Pt/Hg|alumina|Me{sup z+} electrode and the valence band X-ray photoelectron spectra taken from the inner part of alumina barrier layer material before and after the ac treatment.

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

    Energy Technology Data Exchange (ETDEWEB)

    Feng Libang, E-mail: lepond@hotmail.com [School of Mechatronic Engineering, Lanzhou Jiaotong University, 88 West Anning Road, Lanzhou 730070 (China); Li Hui; Song Yongfeng; Wang Yulong [School of Mechatronic Engineering, Lanzhou Jiaotong University, 88 West Anning Road, Lanzhou 730070 (China)

    2010-03-01

    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.

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

    Science.gov (United States)

    Feng, Libang; Li, Hui; Song, Yongfeng; Wang, Yulong

    2010-03-01

    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° 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.

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

    Directory of Open Access Journals (Sweden)

    Arezou Sezavar

    2015-04-01

    Full Text Available 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 deformation and fracture mechanism of PMMA, microscopic evaluation was performed using scanning electron microscope (SEM. The achieved results prove that tensile properties of PMMA depend on alumina wt%. For example, addition of 15 wt% alumina to PMMA causes an increase of about 25% modulus of elasticity. Micrographs taken from the fracture surface of PMMA and its nanocomposites show deformation and fracture mechanism of PMMA changes as alumina is added to it.

  2. 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.

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

    Directory of Open Access Journals (Sweden)

    Prozorova Mayya

    2015-01-01

    Full Text Available 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. The Effect of Alumina Dispersant Powder on the Workability of Chromia Based Refractory for IGCC Application

    Science.gov (United States)

    Ming, Zhao Jing; Xun, Yang Zheng; Hong, Hwang Kyu; Hwan, Park Sang

    2011-10-01

    The quality of refractory applied on IGCC is a key factor that affects the cost of production. The workability and microstructure of chromia based castable are varied by introducing different type of alumina dispersant powder, such as active alumina powder. In this study, three types of active alumina powder are added to improve the workability. It's proved that the specific surface area and particle size distribution of fine powders in matrix part greatly affect the flow values and microstructures.

  5. Electromotive force measurements on cells involving beta-alumina solid electrolyte

    Science.gov (United States)

    Choudhury, N. S.

    1973-01-01

    Open-circuit emf measurements have been made to demonstrate that a two-phase, polycrystalline mixture of beta-alumina and alpha-alumina could be used as a solid electrolyte in galvanic cells with reversible electrodes fixing oxygen or aluminum chemical potentials. These measurements indicate that such a two-phase solid electrolyte may be used to monitor oxygen chemical potentials as low as that corresponding to Al and Al2O3 coexistence (potentials of about 10 to the minus 47th power atm at 1000 K). The activity of Na2O in beta-alumina in coexistence with alpha-alumina was also determined by emf measurements.

  6. 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

    Vortex pinning in a superconducting Nb thin film deposited on an anodically grown alumina template is investigated. Anodic oxidation of aluminium layers permits under specific conditions the formation of highly ordered porous alumina, a membrane-like structure consisting of triangular arrays...... of 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...

  7. 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.

  8. 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.

  9. Surface insulating properties of titanium implanted alumina ceramics by plasma immersion ion implantation

    Science.gov (United States)

    Zhu, Mingdong; Song, Falun; Li, Fei; Jin, Xiao; Wang, Xiaofeng; Wang, Langping

    2017-09-01

    The insulating property of the alumina ceramic in vacuum under high voltage is mainly limited by its surface properties. Plasma immersion ion implantation (PIII) is an effective method to modify the surface chemical and physical properties of the alumina ceramic. In order to improve the surface flashover voltage of the alumina ceramic in vacuum, titanium ions with an energy of about 20 keV were implanted into the surface of the alumina ceramic using the PIII method. The surface properties of the as-implanted samples, such as the chemical states of the titanium, morphology and surface resistivity, were characterized by X-ray photoelectron spectroscopy, scanning electron microscope and electrometer, respectively. The surface flashover voltages of the as-implanted alumina samples were measured by a vacuum surface flashover experimental system. The XPS spectra revealed that a compound of Ti, TiO2 and Al2O3 was formed in the inner surface of the alumina sample. The electrometer results showed that the surface resistivity of the implanted alumina decreased with increased implantation time. In addition, after the titanium ion implantation, the maximum hold-off voltage of alumina was increased to 38.4 kV, which was 21.5% higher than that of the unimplanted alumina ceramic.

  10. PENGARUH PERBEDAAN SIFAT PENYANGGA ALUMINA TERHADAP SIFAT KATALIS HYDROTREATING BERBASIS NIKEL-MOLIBDENUM

    Directory of Open Access Journals (Sweden)

    Maria Ulfah

    2012-11-01

    Full Text Available EFFECT OF ALUMINA SUPPORT PROPERTIES ON THE NICKEL-MOLIBDENUM BASE HYDROTREATING CATALYST. Effect of surface characteristics of three species of synthesized γ-alumina (alumina-1, alumina-2 and alumina-3 on characteristics NiMo catalysts has been studied. Those aluminas are derived from boehmite Catapal B by varying rasio mol nitric acid to boehmite. A sol-gel method is used to synthesize γ-Al2O3 support. The Nitrogen adsorption, X-ray diffraction (XRD, Temperature Programmed Reduction (TPR of H2, Temperature Programmed Desorption (TPD of NH3, and mechanical strength are used to characterize the supports and catalysts. The results showed that the surface area alumina affects the formation of crystalline MoO3 in the NiMo catalyst, while γ-Al2O3-3 support which has the highest surface area (about 195 m2/g compared to the other two types of alumina (>195 m2/g does not have a crystalline MoO3. The formation of crystalline MoO3 is not influenced by the acidity alumina. Based on the results of XRD, it is  indicated that the supported alumina-3 NiMo catalyst (having the highest acid strength shows that there is no presence of crystalline MoO3. Pore size distribution of support did not change significantly after the deposition of Ni and Mo oxides. Mechanical strength of support also affects the strength NiMo catalyst. Support alumina-3 which has the highest mechanical strength gives the mechanical strength of the highest NiMo catalyst. Pengaruh sifat penyangga γ-alumina hasil pengembangan (alumina-1, alumina-2 dan alumina-3 pada karakter katalis hydrotreating nikel-molibdenum (NiMo telah dipelajari. Ketiga jenis γ-alumina diturunkan dari boehmite “Catapal B” dengan menvariasikan nisbah mol asam nitrat terhadap boehmite. Pembuatan γ-alumina menggunakan metoda sol-gel. Adsorpsi Nitrogen, X-ray difraksi (XRD, Temperature Programmed Reduction (TPR H2, Temperature Programmed Desorption (TPD NH3, dan kekuatan mekanik digunakan untuk

  11. 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

  12. 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

  13. Intermetallic strengthened alumina-forming austenitic steels for energy applications

    Science.gov (United States)

    Hu, Bin

    In order to achieve energy conversion efficiencies of >50 % for steam turbines/boilers in power generation systems, materials required are strong, corrosion-resistant at high temperatures (>700°C), and economically viable. Austenitic steels strengthened with Laves phase and Ni3Al precipitates, and alloyed with aluminum to improve oxidation resistance, are potential candidate materials for these applications. The creep resistance of these alloys is significantly improved through intermetallic strengthening (Laves-Fe 2Nb + L12-Ni3Al precipitates) without harmful effects on oxidation resistance. This research starts with microstructural and microchemical analyses of these intermetallic strengthened alumina-forming austenitic steels in a scanning electron microscope. The microchemistry of precipitates, as determined by energy-dispersive x-ray spectroscopy and transmission electron microscope, is also studied. Different thermo-mechanical treatments were carried out to these stainless steels in an attempt to further improve their mechanical properties. The microstructural and microchemical analyses were again performed after the thermo-mechanical processing. Synchrotron X-ray diffraction was used to measure the lattice parameters of these steels after different thermo-mechanical treatments. Tensile tests at both room and elevated temperatures were performed to study mechanical behaviors of this novel alloy system; the deformation mechanisms were studied by strain rate jump tests at elevated temperatures. Failure analysis and post-mortem TEM analysis were performed to study the creep failure mechanisms of these alumina-forming austenitic steels after creep tests. Experiments were carried out to study the effects of boron and carbon additions in the aged alumina-forming austenitic steels.

  14. Kinetic studies of the sucrose adsorption onto an alumina interface

    Science.gov (United States)

    Singh, Kaman; Mohan, Sudhanshu

    2004-01-01

    An account is given of an experimental kinetic study of adsorption of analar reagent sucrose (ARS) onto an alumina interface spectrometrically ( λmax=570 nm) at pH 8.0 and at room temperature. The adsorption isotherm is a typical Langmuirian isotherm (S-type) and adsorption parameters have been deduced according to the Langmuir's model. The adsorption coefficient evaluated from the Langmuir's equation was found to be 2.52×10 2 l mol -1. Adsorption mechanism has been interpreted on the basis of metal-saccharide interaction as found in organometallic compounds and interaction due to negatively charged ends on the disaccharide molecules and positively charge groups on the surface on alumina which depends on the pH value. The effects of variation in experimental conditions of the adsorption system have also been investigated. The adsorption exhibited a typical response to the pH effect and on going towards the PZC the net charge decreases and any reaction making dependence on charge and maximum adsorption (amount) was found near the isoelectric point of alumina (pH 9.0). The presence of ions like Cl -, SO 42- and PO 43- affect the adsorbed amount quantitatively and it seems that these anions compete with sucrose for the positively charged surface sites. The addition of similar concentration of cations was found to reduce the adsorbed amount. The temperature was found to have an inverse effect on adsorption. The additions of catonic and anionic detergents influence both the adsorbed amount and the adsorption rate. The thermodynamics of the titled adsorption model indicates the spontaneous and exothermic nature. The negative value of entropy is an indication of probability of favorable and complex nature of the adsorption.

  15. Silicon carbide whisker-zirconia reinforced mullite and alumina ceramics

    Science.gov (United States)

    Becher, Paul F.; Tiegs, Terry N.

    1987-01-01

    The flexural strength and/or fracture toughness of SiC whisker-reinforced composites utilizing mullite or alumina as the matrix material for the composite are increased by the addition of zirconia in a monoclinic or tetragonal phase to the matrix. The zirconia addition also provides for a lower hot-pressing temperature and increases the flexural strength and/or fracture toughness of the SiC whisker-reinforced composites over SiC whisker-reinforced composites of the similar matrix materials reinforced with similar concentrations of SiC whiskers.

  16. 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.

  17. Toughening and strengthening mechanism of zirconia-alumina multiphase ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Yu, M.Q.; Fan, S.G. [Research Inst. of Synthetic Crystals, Beijing, BJ (China); Shen, Q.; Zhang, L.M. [Wuhan Univ. of Technology (China)

    2003-07-01

    In the present study, the effect of compositions on the mechanical properties of zirconia-alumina multiphase ceramics was studied. The results showed that with the variety of ZrO{sub 2} content, the change of bending strength and fracture toughness of the multiphase ceramics exhibited a saddle shape which could be divided into three zones: ZTA, ADZ, and Transition zone. The mechanism of toughening and strengthening in each zone was mainly analyzed, and it was found that stress-induced transformation toughening of ZrO{sub 2} and dispersion strengthening of Al{sub 2}O{sub 3} were the two main factors. (orig.)

  18. Optical properties of porous anodic alumina embedded Cu nanocomposite films

    Science.gov (United States)

    Liu, Huiyuan; Sun, Huiyuan; Liu, Lihu; Hou, Xue; Jia, Xiaoxuan

    2015-06-01

    Porous anodic alumina embedded Cu with iridescent colors were fabricated in copper sulfate electrolyte. The films display highly saturated colors after being synthesized by an ac electrodeposition method. Tunable color in the films is obtained by adjusting anodization time, and can be adjusted across the entire visible range. Theoretical results of the changes in the structural color according to the Bragg-Snell formula are consistent with the experimental results. The films could be used in many areas including decoration, display and multifunctional anti-counterfeiting applications.

  19. Development of technology and applications based on porous alumina nanostructures

    OpenAIRE

    Vojkuvka, Lukas

    2009-01-01

    La disertación ha sido organizada de la siguiente manera. En el primer capítulo se presenta el estado del arte, donde se exponen algunos conceptos básicos de las propiedades electroquimicaselectroquímicas del alumino, las fases del crecimiento de los poros y el proceso de auto-ordenación de los mismos. El segundo capítulo de la tesis esta relacionado con la preparación y caracterización morfológica de las muestras de alumina porosa. >En el capítulo 4 se desglosan los resultados obtenidos de l...

  20. Recovery of alumina and some heavy metals from sulfate liquor

    Directory of Open Access Journals (Sweden)

    M.N. El Hazek

    2016-05-01

    Full Text Available The gibbsite bearing shale occurrence in the Paleozoic sedimentary sequence of SW Sinai, Egypt, was found to be associated with several metal values. From sulfate liquor prepared by proper leaching, the recovery of these metal values has been studied. Alumina was first separated in the form of potash alum followed by Cu-selective extraction by hydroxyoxime LIX-973N solvent. Then U recovery using an anionic exchange resin Amberlite IRA-400 was achieved. For the associated heavy metal Zn, it was subsequently extracted using di-2-ethylhexyl phosphoric acid. The relevant factors affecting the extraction process were adequately studied.

  1. Alcohol dehydration: Mechanism of ether formation using an alumina catalyst

    Energy Technology Data Exchange (ETDEWEB)

    Shi, B.; Davis, B.H. [Univ. of Kentucky, Lexington, KY (United States)

    1995-12-01

    Ether formation during the dehydration of secondary alcohols, namely, 2-butanol, 3-pentanol, and 1-cyclopentylethanol, was investigated. Using the proper reaction conditions, the yield of di-2-butyl ether during the dehydration of 2-butanol on alumina can be as high as 40%. That ether is formed by adding an alcohol to the alkene is ruled out by the results from deuterium tracer studies. Results from experiments using S(+)- 2-butanol suggest that the formation of di-2-butyl ether occurs by a S{sub N}2-type mechanism. 33 refs., 5 figs., 3 tabs.

  2. 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.

  3. Development of a PDMS-grafted alumina membrane and its evaluation as solvent resistant nanofiltration membrane

    NARCIS (Netherlands)

    Pinheiro de Melo, A.F.; Hoogendoorn, D.; Nijmeijer, A.; Winnubst, A.J.A.

    2014-01-01

    A new solvent resistant nanofiltration (SRNF) membrane is developed by grafting a PDMS polymer into the pores of a 5 nm γ-alumina ceramic membrane. These PDMS-grafted γ-alumina membranes were attained through a two-step synthesis. The linking agent, 3-aminopropyltriethoxysilane (APTES), was first ap

  4. STUDY OF CATALYTIC CYCLISATION OF (+-CITRONELLAL WITH Zn/γ-ALUMINA AS CATALYST

    Directory of Open Access Journals (Sweden)

    Elvina Dhiaul Iftitah

    2010-06-01

    Full Text Available The reaction of catalytic cyclisation of (+-citronellal has been done using g-alumina and Zn/γ-alumina as catalysts. Zn/γ-alumina catalyst was prepared by impregnation of ZnBr2 into solid of γ-alumina in methanol as a solvent. The calcination process is performed on Muchalal reactor at 400 oC. The reactions were carried out under nitrogen gas atmosphere by mixing 5 mL sample and 1.0 g catalyst at 90-95 oC for 3 hours. The product of reaction was analyzed using GC, FT-IR and GC-MS. The reaction of cyclization of (+-citronellal with γ-alumina catalyst did not give targeted product as well as reaction with Zn/g-alumina catalyst. Whereas, the reactions with Zn/γ-alumina catalyst gave four compounds of isopulegol stereoisomer. Conversion of (--Isopulegol, (+-Neoisopulegol, (+-Isoisopulegol and (+-Neoisoisopulegol  were 64,29%, 18,80%, 9,20% and 3,32% respectively. For that reason, the transformation of (+-sitronelal using Zn/γ-alumina was considered to be the best catalyst. A reaction mechanism is proposed where the (+-citronellal molecule binds to a catalyst Lewis acid site via the aldehyde oxygen and the π-electrons of the double bond. Subsequent protonation of the aldehyde via a neighbouring Bronsted acid site initiates the cyclisation to isopulegol.   Keywords: catalytic cyclisation, impregnation, (+-isopulegol

  5. 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.

  6. Morphology and thermal properties of compatibilized PA12/PP blends with boehmite alumina nanofiller inclusions

    CSIR Research Space (South Africa)

    Ogunniran, ES

    2011-12-01

    Full Text Available -1 Morphology and Thermal Properties of Compatibilized PA12/PP Blends with Boehmite Alumina Nanofiller Inclusions 1. Elijah Soba Ogunniran1, 2. Rotimi Sadiku1, 3. Suprakas Sinha Ray2,*, 4. Nyambeni Luruli3 Keywords: ? boehmite alumina; ? morphology...

  7. Polyethyleneglycol grafting of γ-alumina membranes for solvent resistant nanofiltration

    NARCIS (Netherlands)

    Tanardi, C.R.; Catana, Romina; Barboiu, Mihai; Ayral, André; Vankelecom, I.F.J.; Nijmeijer, A.; Winnubst, A.J.A.

    2016-01-01

    A method is presented for grafting mesoporous g-alumina (pore size 5 nm), supported on an a-alumina ceramic membrane, with polyethylene glycols (PEG). The grafting performance of g-Al2O3 powders with various PEG grafting agents, having different molecular weights, alkoxy groups, and ureido functiona

  8. Ge Honglin: Expand and Consolidate Chemical Alumina to Create World Top-class Brand

    Institute of Scientific and Technical Information of China (English)

    2015-01-01

    On June 9,Chinalco convened discussion meeting on integrated utilization of chemical alumina and red mud.Ge Honglin,Chairman and Secretary of the Party Leadership Group of Chinalco,emphasized:"It is imperative to unswervingly expand and consolidate chemical alumina,create world top-class brand,continually propel red mud integrated utilization,and improve integrated utilization rate of resources."

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

    NARCIS (Netherlands)

    Exter, den Peter; 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 agg

  10. Effect of Microstructure of Composite Powders on Microstructure and Properties of Microwave Sintered Alumina Matrix Ceramics

    Institute of Scientific and Technical Information of China (English)

    Hanmin Bian; Yong Yang; You Wang; Wei Tian; Haifu Jiang; Zhijuan Hu; Weimin Yu

    2013-01-01

    Two kinds of different structured alumina-titania composite powders were used to prepare alumina matrix ceramics by microwave sintering.One was powder mixture of alumina and titania at a micron-submicron level,in which fused-and-crushed alumina particles (micrometers) was clad with submicron-sized titania.The other was powder mixture of alumina and titania at nanometer-nanometer level,in which nano-sized alumina and nano-sized titania particles were homogeneously mixed by ball-milling and spray dried to prepare spherical alumina-titania composite powders.The effect of the microstructure of composite powders on microstructure and properties of microwave sintered alumina matrix ceramics were investigated.Nano-sized composite (NC) powder showed enhanced sintering behavior compared with micro-sized composite (MC) powders.The asprepared NC ceramic had much denser,finer and more homogenous microstructure than MC ceramic.The mechanical properties of NC ceramic were significantly higher than that of MC ceramic,e.g.the flexural strength,Vickers hardness and fracture toughness of NC ceramic were 85.3%,130.3% and 25.7% higher than that of MC ceramic,respectively.The improved mechanical properties of NC ceramic compared with that of MC ceramic were attributed to the enhanced densification and the finer and more homogeneous microstruc.ture through the use of the nanostructured composite powders.

  11. Nanostructural characterization of large-scale porous alumina fabricated via anodizing in arsenic acid solution

    Science.gov (United States)

    Akiya, Shunta; Kikuchi, Tatsuya; Natsui, Shungo; Suzuki, Ryosuke O.

    2017-05-01

    Anodizing of aluminum in an arsenic acid solution is reported for the fabrication of anodic porous alumina. The highest potential difference (voltage) without oxide burning increased as the temperature and the concentration of the arsenic acid solution decreased, and a high anodizing potential difference of 340 V was achieved. An ordered porous alumina with several tens of cells was formed in 0.1-0.5 M arsenic acid solutions at 310-340 V for 20 h. However, the regularity of the porous alumina was not improved via anodizing for 72 h. No pore sealing behavior of the porous alumina was observed upon immersion in boiling distilled water, and it may be due to the formation of an insoluble complex on the oxide surface. The porous alumina consisted of two different layers: a hexagonal alumina layer that contained arsenic from the electrolyte and a pure alumina honeycomb skeleton. The porous alumina exhibited a white photoluminescence emission at approximately 515 nm under UV irradiation at 254 nm.

  12. Crystallography-Induced Correlations in Pore Ordering of Anodic Alumina Films

    NARCIS (Netherlands)

    Roslyakov, Ilya V.; Koshkodaev, Dmitry S.; Eliseev, Andrei A.; Hermida-Merino, Daniel; Petukhov, Andrei V.; Napolskii, Kirill S.

    2016-01-01

    A crystallographic approach to tailoring the morphology and ordering degree of the porous structure of alumina films obtained by anodization of single-crystalline aluminum is discussed. The examination of porous structure of anodic alumina films formed on low-index and vicinal planes of Al single cr

  13. Synthesis and characterization of alumina application in support of zeolite membrane; Sintese e caracterizacao de alumina para aplicacao com o suporte de membrana zeolitica

    Energy Technology Data Exchange (ETDEWEB)

    Barbosa, A.S.; Rodrigues, M.G.F., E-mail: antoniellybarbosa@yahoo.com.br [Universidade Federal de Campina Grande (UFCG), PB (Brazil). Unidade Academica de Engenharia Quimica

    2012-07-01

    Much interest has been aroused in process applications using zeolite membrane. The physicochemical properties of the support have a strong effect on the quality of zeolite membrane. This work is to synthesize and characterize alumina for use as a support for zeolite membrane. In this work was synthesized α-alumina: 40% alumina, 0.2% for PABA, 0.5% oleic acid and 59.3% ethyl alcohol. The mixture was ground in ball mill and placed in an oven for 24 hours at 60 °C, allowed to stand for 24h. The pressing was performed with 4 tons. The pressed material was subjected to sintering at 1400 °C/hour. The samples were characterized by EDX, XRD and SEM. The results for the media by XRD showed that they are crystalline and pure. By EDX was observed that the supports consist essentially of alumina. (author)

  14. 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)

  15. Microstructure-mechanical behaviour relationship in alumina-calcium exaluminate composites; Relaciones microestructura-comportamiento mecanico en materiales de alumina-hexaluminato calcico

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Herencia, A. J.; Moreno, R.; Baudin, C.

    2001-07-01

    The grain growth behaviour of dense alumina materials has been modified by the addition of calcium hexaluminate particles. Maximum dispersion has been obtained by colloidal processing routes. The influence of sintering temperature (1500-1600 degree centigree) on the size and shape of the alumina grains has been established. The mechanical behaviour of three composite materials with the same composition ({approx}10 vol% CA{sub 6}) and large microstructural differences has been studied in comparison with that of monophasic alumina of the same grain size. The influence of grain size and shape on toughness has been established. R-curve behaviour has been detected during fracture of the material with the alumina grains presenting the largest shape factor. (Author) 18 refs.

  16. Thermal-shock Resistance of a Ceramic Comprising 60 Percent Boron Carbide and 40 Percent Titanium Diboride

    Science.gov (United States)

    Yeomans, C M; Hoffman, C A

    1953-01-01

    Thermal-shock resistance of a ceramic comprising 60 percent boron carbide and 40 percent titanium diboride was investigated. The material has thermal shock resistance comparable to that of NBS body 4811C and that of zirconia, but is inferior to beryllia, alumina, and titanium-carbide ceramals. It is not considered suitable for turbine blades.

  17. Interactions of L-alanine with alumina as studied by vibrational spectroscopy.

    Science.gov (United States)

    Garcia, Ana R; de Barros, Ricardo Brito; Fidalgo, Alexandra; Ilharco, Laura M

    2007-09-25

    The interactions of L-alanine with gamma- and alpha-alumina have been investigated by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). L-alanine/alumina samples were dried from aqueous suspensions, at 36.5 degrees C, with two amino acid concentrations (0.4 and 0.8 mmol g-1) and at different pH values (1, 6, and 13). The vibrational spectra proved that the nature of L-alanine interactions with both aluminas is the same (hydrogen bonding), although the groups involved depend on the L-alanine form and on alumina surface groups, both controlled by the pH. For samples prepared at pH 1, cationic L-alanine [CH3CH(NH3+)COOH] displaces physisorbed water from alumina, and strong hydrogen bonds are established between the carbonyl groups of alanine, as electron donors, and the surface Al-OH2+ groups of alumina. This occurs at the expense of alanine dimer dissociation and breaking of intramolecular bonds. When samples are prepared at pH 6, the interacting groups are Al-OH2+ and the carboxylate groups of zwitterionic L-alanine [CH3CH(NH3+)COO-]. The affinity of L-alanine toward alumina decreases, as the strong NH3+...-OOC intermolecular hydrogen bonds prevail over the interactions with alumina. Thus, for a load of 0.8 mmol g-1, phase segregation is observed. On alpha-alumina, crystal deposition is even observed for a load of 0.4 mmol g-1. At pH 13, the carboxylate groups of anionic L-alanine [CH3CH(NH2)COO-] are not affected by alumina. Instead, hydrogen bond interactions occur between NH2 and the Al-OH surface groups of the substrate. Complementary N2 adsorption-desorption isotherms showed that adsorption of L-alanine occurs onto the alumina pore network for samples prepared at pH 1 and 13, whereas at pH 6 the amino acid/alumina interactions are not strong enough to promote adsorption. The mesoporous structure and the high specific surface area of gamma-alumina make it a more efficient substrate for adsorption of L-alanine. For each alumina, however, it is

  18. Cellulose extraction from Zoysia japonica pretreated by alumina-doped MgO in AMIMCl.

    Science.gov (United States)

    Liu, Le; Ju, Meiting; Li, Weizun; Jiang, Yang

    2014-11-26

    In this study, alumina-doped MgO was produced as a solid alkali for lignocellulose pretreatment. Pretreatment with alumina-doped MgO disrupted the lignocellulose structure and significantly reduced the lignin content of the Z. japonica. After pretreatment, Z. japonica showed significant solubility in 1-allyl-3-methylimidazolium chloride (AMIMCl). The similar high solubility of pretreated Z. japonica samples by original alumina-doped MgO and used alumina-doped MgO also proved that alumina-doped MgO had strong stability, which can be recycled and used repeatedly. The regenerated cellulose was similar to microcrystalline cellulose according to FTIR and NMR analyses. Compared to microcrystalline cellulose, only the crystallinity of the regenerated cellulose decreased.

  19. Investigation of Mechanical Behavior of Alfa and Gamma Nano- Alumina/ Epoxy Composite Made By Vartm

    Directory of Open Access Journals (Sweden)

    P. Ghabezi

    2016-06-01

    Full Text Available In this paper, the mechanical properties (flexural and tensional modulus and strength are investigated by manufacturing Epoxy/Glass Nano-composite samples with different Nano-particle wt% (Nano-Alumina to find optimum conditions. The alpha and Gamma grade of Nano alumina were added to the epoxy system with the weight percentage of 1, 2, 3, 4, 5 and 6. The experimental results show that the maximum flexural stiffness in Alfa and Gamma Nano-alumina composite is related to 6 wt% and 4 wt% samples, respectively. And the highest tensional stiffness in Alfa and Gamma Nano-alumina composite is related to 4 wt% and 5 wt% samples, respectively. Also the highest toughness for Alfa and Gamma Nano-composites is observed for 4 wt% and 3 wt% samples and in the same way Nano-alumina in grade Alfa with 1 wt% and Gamma with 3 wt% have highest failure strain.

  20. 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)

  1. Robust Mechanical Properties of Electrically Insulative Alumina Films by Supersonic Aerosol Deposition

    Science.gov (United States)

    Lee, Jong-Gun; Cha, You-Hong; Kim, Do-Yeon; Lee, Jong-Hyuk; Lee, Tae-Kyu; Kim, Woo-Young; Park, Jieun; Lee, Dongyun; James, Scott C.; Al-Deyab, Salem S.; Yoon, Sam S.

    2015-08-01

    Electrically insulating alumina films were fabricated on steel substrates using supersonic aerosol deposition and their hardness and scratchability were measured. Alumina particles (0.4-μm diameter) were supersonically sprayed inside a low-pressure chamber using between 1 and 20 nozzle passes. These alumina particles were annealed between 300 and 800 K to determine the temperature's effect on film crystal size (37-41 nm). Smoother surface morphology and increased electrical resistance of the thin films were observed as their thicknesses grew by increasing the number of passes. Resistances of up to 10,000 MΩ demonstrate robust electrical insulation. Significant hardness was measured (1232 hv or 13.33 GPa), but the alumina films could be peeled off with normal loads of 36 and 47 N for films deposited on stainless steel and SKD11 substrates, respectively. High insulation and hardness confirm that these alumina films would make excellent electrical insulators.

  2. 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.

  3. 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.

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

    NARCIS (Netherlands)

    Valandro, L.F.; Ozcan, M.; Bottino, M.C.; Bottino, M.A.; Scotti, R.; Della Bona, A.

    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

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

    NARCIS (Netherlands)

    Valandro, L.F.; Ozcan, M.; Bottino, M.C.; Bottino, M.A.; Scotti, R.; Della Bona, A.

    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)

  7. Interfaces fracas em compósitos de matriz cerâmica de alumina/alumina

    OpenAIRE

    Hablitzel,M.P.; Garcia,D.E.; Hotza,D.

    2011-01-01

    O uso de cerâmicas estruturais é limitado por sua fratura frágil. Compósitos de matriz cerâmica (CMCs) são materiais que possuem reforços estruturais que atuam aumentando a energia necessária para que o material se frature. O presente artigo apresenta uma alternativa para a produção de CMCs em que matriz e fibras são constituídas de alumina. Os mecanismos responsáveis pelo aumento da tenacidade ocorrem devido a uma interfase porosa entre matriz e fibras.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Yuanyuan [School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China); Gan, Tian [College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang 464000 (China); Wan, Chidan [School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China); Wu, Kangbing, E-mail: kbwu@hust.edu.cn [School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2013-02-18

    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.

  9. Extraction and characterization of alumina nanopowders from aluminum dross by acid dissolution process

    Science.gov (United States)

    Sarker, Md. Saifur Rahman; Alam, Md. Zahangir; Qadir, Md. Rakibul; Gafur, M. A.; Moniruzzaman, Mohammad

    2015-04-01

    A significant amount of aluminum dross is available as a waste in foundry industries in Bangladesh. In this study, alumina was extracted from aluminum dross collected from two foundry industries situated in Dhamrai and Manikgang, near the capital city, Dhaka. Aluminum dross samples were found to approximately contain 75wt% Al2O3 and 12wt% SiO2. An acid dissolution process was used to recover the alumina value from the dross. The effects of various parameters, e.g., temperature, acid concentration, and leaching time, on the extraction of alumina were studied to optimize the dissolution process. First, Al(OH)3 was produced in the form of a gel. Calcination of the Al(OH)3 gel at 1000°C, 1200°C, and 1400°C for 2 h produced γ-Al2O3, (α+γ)-Al2O3, and α-alumina powder, respectively. Thermal characterization of the Al(OH)3 gel was performed by thermogravimetric/differential thermal analysis (TG/DTA) and differential scanning calorimetry (DSC). The phases and crystallite size of the alumina were determined by X-ray diffraction analysis. The dimensions of the alumina were found to be on the nano level. The chemical compositions of the aluminum dross and alumina were determined by X-ray fluorescence (XRF) spectroscopy. The microstructure and morphology of the alumina were studied with scanning electron microscopy. The purity of the alumina extracted in this study was found to be 99.0%. Thus, it is expected that the obtained alumina powders can be potentially utilized as biomaterials.

  10. 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.

  11. Thermochemical Analysis of Molybdenum Thin Films on Porous Alumina.

    Science.gov (United States)

    Lee, Kyoungjin; de Lannoy, Charles-François; Liguori, Simona; Wilcox, Jennifer

    2017-01-12

    Molybdenum (Mo) thin films (thickness thin-film composites were stable below 300 °C but had no reactivity toward gases. Mo thin films showed nitrogen incorporation on the surface as well as in the subsurface at 450 °C, as confirmed by X-ray photoelectron spectroscopy. The reactivity toward nitrogen was diminished in the presence of CO2, although no carbon species were detected either on the surface or in the subsurface. The Mo thin films have a very stable native oxide layer, which may further oxidize to higher oxidation states above 500 °C due to the reaction with the porous anodized alumina substrate. The oxidation of Mo thin films was accelerated in the presence of oxidizing gases. At 600 °C in N2, the Mo thin film on anodized alumina was completely oxidized and may also have been volatilized. The results imply that choosing thermally stable and inactive porous supports and operating in nonoxidizing conditions below 500 °C will likely maintain the stability of the Mo composite. This study provides key information about the chemical and structural stability of a Mo thin film on a porous substrate for future membrane applications and offers further insights into the integrity of thin-film composites when exposed to harsh conditions.

  12. Synthesis of Alumina Thin Films Using Reactive Magnetron Sputtering Method

    Science.gov (United States)

    Angarita, G.; Palacio, C.; Trujillo, M.; Arroyave, M.

    2017-06-01

    Alumina (Al2O3) thin films were deposited on Si (100) by Magnetron Sputtering in reactive conditions between an aluminium target and oxygen 99.99% pure. The plasma was formed employing Argon with an R.F power of 100 W, the dwelling time was 3 hours. 4 samples were produced with temperatures between 350 and 400 ºC in the substrate by using an oxygen flow of 2 and 8 sccm, the remaining parameters of the process were fixed. The coatings and substrates were characterized using Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) in order to compare their properties before and after deposition. The films thicknesses were between 47 and 70 nm. The results show that at high oxygen flow the alumina structure prevails in the coatings while at lower oxygen flow only aluminum is deposited in the coatings. It was shown that the temperature increases grain size and roughness while decreasing the thicknesses of the coatings.

  13. Oxidation of Alumina-Forming MAX Phases in Turbine Environments

    Science.gov (United States)

    Smialek, James; Garg, Anita; Harder, Bryan; Nesbitt, James; Gabb, Timothy; Gray, SImon

    2017-01-01

    Protective coatings for high temperature turbine components are based on YSZ thermal barriers and oxidation resistant, alumina-forming NiAl or NiCoCrAlY bond coats. Ti2AlC and Cr2AlC MAX phases are thus of special interest because of good oxidation resistance and CTE that can match Al2O3 and YSZ. Their alumina scales grow according to cubic kinetics due to grain growth in the scale, with initial heating dominated by fast TiO2 growth. Protective cubic kinetics are also found in high pressure burner rig tests of MAXthal 211 Ti2AlC, but with reduced rates due to volatile TiO(OH)2 formation in water vapor. YSZ-coatings on bulk Ti2AlC exhibit remarkable durability up to 1300C in furnace tests and at least a 25x life advantage compared to superalloys. At another extreme, Cr2AlC is resistant to low temperature Na2SO4 hot corrosion and exhibits thermal cycling stability bonded to a superalloy disk material. Accordingly, sputtered Cr2AlC coatings on disk specimens prevented hot corrosion detriments on LCF. Breakaway oxidation (Ti2AlC), scale spallation (Cr2AlC), interdiffusion, and processing as coatings still present serious challenges. However the basic properties of MAX phases provide some unusual opportunities for use in high temperature turbines.

  14. 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.

  15. Wet chemical synthesis of nickel supported on alumina catalysts; Sintese de catalisadores de niquel suportado em alumina por via umida

    Energy Technology Data Exchange (ETDEWEB)

    Freire, Ranny Rodrigues; Costa, Talita Kenya Oliveira; Morais, Ana Carla da Fonseca Ferreira; Costa, Ana Cristina Figueiredo de Melo; Freitas, Normanda Lino de, E-mail: normanda@ufcg.edu.br [Universidade Federal de Campina Grande (UFCG), PB (Brazil)

    2016-07-01

    Heterogenic catalysts are those found to be in a different phase on the reaction when compared to the reactants and products. Preferred when compared to homogeneous catalysts due to the easiness on which the separation is processed. The objective of this study is to obtain and characterize Alumina based catalysts impregnated with Nickel (Al{sub 2}O{sub 3}), by wet impregnation. The alumina was synthesized by combustion reaction. Before and after the impregnation the catalysts were characterized by X-ray diffraction (XRD), granulometric analysis, the textural analysis will be held by nitrogen adsorption (BET), energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). The results show a presence of a stable crystalline phase of Al2O3 in all the studied samples and after the impregnation the second phase formed was of NiO and NiAl{sub 2}O{sub 4}. The Al{sub 2}O{sub 3} e Ni/Al{sub 2}O{sub 3} catalysts resulted in clusters with a medium diameter of 18.9 and 14.2 μm, respectively. The catalysts show a medium-pore characteristic (medium pore diameter between 2 and 50 nm), the superficial area to Al{sub 2}O{sub 3} and Ni/Al{sub 2}O{sub 3} catalysts were 8.69 m{sup 2}/g and 5.56 m{sup 2}/g, respectively. (author)

  16. X-ray residual stress measurement of alumina detonation coating. Bakuhatsu yosha alumina himaku no X sen zanryu oryoku sokutei

    Energy Technology Data Exchange (ETDEWEB)

    Tanaka, K.; Mine, N. (Kyoto University, Kyoto (Japan). Faculty of Engineering); Suzuki, K. (Niigata University, Niigata (Japan). Faculty of Engineering); Kawase, R. (Ariake Institute of Technology, Fukuoka (Japan))

    1991-01-15

    Alumina ceramics were coated on mild steel by a detonation gun with different amounts of detonation gas, and residual stresses in coated films were measured by X-ray diffraction from the (844) plane of {gamma}-alumina by Cu-K {alpha} radiation. Cracks and pores were observed on the film surface and cross section. The pore increased and the film bulk density decreased with a decrease in amount of detonation gas, and the mechanical Young {prime} s modulus decreased with an increase in pore. Since strains measured mechanically were those in the film bulk with pores while strains measured by X-ray were average values in only crystalline phases, the X-ray Young {prime} s modulus was larger than the mechanical one. The residual stress in films was a large tensile stress and distributed uniformly in films. The residual tensile stress decreased with an increase in amount of detonation gas, however, it was rather insensitive to the film thickness and surface grinding after coating. 10 refs., 8 figs., 2 tabs.

  17. Infrared radiative properties of alumina up to the melting point: A first-principles study

    Science.gov (United States)

    Yang, J. Y.; Xu, M.; Liu, L. H.

    2016-11-01

    The high thermal emission of alumina dominates the radiative heat transfer of rocket exhaust plume. Yet numerous experimental measurements on radiative properties of alumina at high temperatures vary considerably from each other and cannot provide physical insight into the underlying mechanism. In this work, the ab initio molecular dynamics (AIMD) method and ab initio parameterized Drude model are combined to predict the radiative properties of alumina for temperatures up to 2327 K (the melting point) in the spectral range 1-12 μm. Contributed by different microscopic processes, the optical absorption of alumina in the spectral range 1-4 and 4-12 μm is described by two distinct methods. In the spectral range 4-12 μm, the multi-phonon process mainly contributes to optical absorption and can be simulated by the AIMD method based on the linear response theory. While in the spectral range 1-4 μm, the optical absorption is mainly caused by intrinsic carriers and can be effectively described by the ab initio parameterized Drude model. The first-principles calculations can successfully predict the infrared radiative properties of alumina at high temperatures and well reproduce the literature experiments. Moreover, the theoretical simulations verify that alumina can retain its semiconducting character even in the liquid phase and there emerges sharp increase in the near-infrared optical absorption of alumina upon melting.

  18. Properties of micro-nano particle size admixtures of alumina at different sintering condition

    Science.gov (United States)

    Sifat, Rahin; Akter, Manira; Rashid, A. K. M. Bazlur

    2016-07-01

    Among various ceramic materials, alumina is mostly used material for its hardness and strength. There is a difference between the properties of alumina due to their different particle size. Also different holding time in the sintering temperature has effect on the sintering of alumina of different particle size. In this study, micro alumina and nano alumina were mixed in different ratios and sintered at different sintering condition to compare their mechanical properties that varied due to their different particle size distribution. In this work, conventional solid state sintering route was followed to prepare final samples. Six different particle size ratio of alumina (micro:nano= 100:0, 95:5, 90:10, 10:90, 5:95, 0:100) with a doping of 0.1% MgO were used. The sintering temperature was 1500° C but sintering condition was different. After comparing the mechanical properties, it has been observed that relatively improved properties can be obtained by increasing nano particle percentages in the micro alumina than the reverse mixture.

  19. [Characterization of alumina adobe and sintered body of GI-infiltrated ceramic].

    Science.gov (United States)

    Wang, H; Chao, Y; Liao, Y; Liang, X; Zhu, Z; Gao, W

    2001-06-01

    This study was conducted to elucidate the mechanism of formation of porous structure by investigating the porosity of the alumina adobe and sintered body of GI-II Infiltrate Ceramic, and its role in strengthening and toughening this kind of ceramic composite. The alumina powder size-mass distribution was obtained by BI-XDC powder size analysis device; the open pore parameters of alumina adobe and sintered body were analyzed using the mercury pressure method. Their fracture surfaces were observed under scanning electronic microscope. Fine powder had two main size groups of 0.09-0.1 micron and 0.2-0.5 micron, respectively, and coarse powder, with size between 1.5 to 4.5 microns, occupied the majority of powder mass. Alumina adobe's pores became larger after sintering. The median pore radii of adobe and sintered body were 0.2531 micron and 0.3081 micron, respectively; the average pore radii changed from 0.0956 micron to 0.1102 micron. Under scanning electronic microscope, fine alumina powders were fused partially together and their surfaces were blunted, but coarse powders did not show such phenomena. The alumina size distribution contributes to the formation of porous structure of alumina sintered body. This porous structure is not only the shape skeleton but also the mechanical skeleton of GI-II Infiltrated Ceramic. It plays an important role in raising the mechanical properties of this kind of ceramic composite.

  20. 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.

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

    Science.gov (United States)

    Zhang, Yuanyuan; Gan, Tian; Wan, Chidan; Wu, Kangbing

    2013-02-18

    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.

  2. 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.

  3. Preparation of Micro-Porous Alumina Sheet Support for Ceramic Membrane by Extrusion

    Science.gov (United States)

    Hemra, Khanthima; Atong, Duangduen; Aungkavattana, Pavadee

    Among several types of ceramic membrane developed for a half of century, alumina is the most extensive advantage. In this study, many types of alumina with different particle size distributions were used as a starting material for fabrication of support sheet ceramic membrane using extrusion process. The investigation focused on the alumina dough components composed of some organic binders and water. The organic binder of about 12 wt. % was required in order for dough to be easily extruded, while the amount of water added to the dough depended on the particle size of alumina powder. The particle size and size distribution of starting powder showed strong effects on pore size of sintered alumina support. The pore size decreased when smaller particle size of starting powder was used. In addition, the pore volume of the sintered alumina decreased with increasing the sintering temperature due to improvement in densification, while pore size remained the same. The mechanical strength of alumina supports was also influenced by the particle size of starting powder; the finer particle size resulted in the higher mechanical strength. However, in order to obtain a good flux for the membrane, a high mechanical strength of the support along with its effective porosity is critical concerns. In this work, the support sintered at 1450°C provided a proper porosity of approximately 40% with an acceptable mechanical strength of 30-45MPa.

  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. Photoluminescence properties of heat-treated porous alumina films formed in oxalic acid

    Energy Technology Data Exchange (ETDEWEB)

    Vrublevsky, I., E-mail: vrublevsky@bsuir.edu.b [Belarusian State University of Informatics and Radioelectronics Minsk, Department of Micro and Nanoelectronics, 220013 Minsk (Belarus); Chernyakova, K. [Belarusian State University of Informatics and Radioelectronics Minsk, Department of Micro and Nanoelectronics, 220013 Minsk (Belarus); Ispas, A.; Bund, A.; Gaponik, N.; Dubavik, A. [Technische Universitaet Dresden, Physikalische Chemie und Elektrochemie, 01062 Dresden (Germany)

    2011-05-15

    Photoluminescence and optical properties of as-anodized and heat-treated at 500 {sup o}C porous alumina films formed in a 0.3 M oxalic acid at 40 V have been studied. The FTIR indicates that the oxalate ions are embedded in the anodic alumina as chelating bidentate structures and further heating up to 500 {sup o}C does not cause any change in ion coordination. The results of time-resolved spectroscopy show the presence of two luminescence centers both in the as-anodized and heat-treated anodic alumina films with lifetimes of about 0.25 and 4.0 ns. The F{sup +}-centers in anodic alumina are responsible for the luminescence peak at about 420 nm, with a lifetime of about 4.0 ns. The luminescence peak at about 480 nm, with lifetime of about 0.25 ns, can be attributed to the luminescence of carboxylate ions existing in bulk of anodic alumina. - Research highlights: {yields} Photoluminescence and optical properties of porous alumina films have been studied. {yields} In anodic alumina the oxalate ions are embedded as chelating bidentate structures. {yields} The results show the presence of two luminescence centers. {yields} The F{sup +}-centers are responsible for the peak at 420 nm with a lifetime of 4.0 ns. {yields} The peak at 480 nm with a lifetime of 0.25 ns can be attributed to carboxylate ions.

  6. Metastable zirconia-yttria-alumina ceramics: Structure, processing and properties

    Science.gov (United States)

    Zhou, Xinzhang

    2002-09-01

    Metastable phases of zirconia-yttria-alumina produced by atmospheric plasma spray and subsequent quenching were studied. Two kinds of quenching methods were used: water quenching and splat quenching. Quenching rates were estimated to be 104°C/s for water quenching and between 105--107°C/s for splat quenching. Five compositions of sprayed dried powders (pure alumina, TZ3Y20A, TZ3Y57A, TZ3Y80A and pure zirconia) were plasma sprayed and quenched. The phases and microstructures of the plasma sprayed powders and thin films were investigated by XRD and FESEM. It was found that at different compositions and quenching rates, different high temperature phases formed. These phases are metastable at room temperature and can be in the form of an extended solid solution phase, an intermediate phase, or an amorphous structure. The grain sizes of the metastable phases are below 50 nm, as determined by XRD peak broadening. At the eutectic composition, zirconia-rich fibers (50 nm in diameter) uniformly distributed in an alumina-rich matrix were observed. 2-D and 3-D metastable phase diagrams were constructed to explain the metastable phase formation. Plasma spraying can be used to fabricate ceramic nanocomposites either by pressure-assisted sintering or spray forming of the metastable powders. Mechanical properties of TZ3Y20A specimens produced by plasma spray forming on steel substrates were studied. The dependence of the 4-point bend strength on plasma spray parameters was studied by a 26-2 statistical experimental design. It was found that the bend strength was sensitive to both standoff distance and scanning speed. The results of study show much promise in applications of the metastable ceramics. Firstly, homogeneous nucleation and growth of stable phases during sintering and high creep rate at elevated temperatures will result in uniformly dense nanoceramic composites. Secondly, extended solid solutions of rare earth elements in glass will greatly enhance the optical

  7. Contact fatigue response of porcelain-veneered alumina model systems.

    Science.gov (United States)

    Stappert, Christian F J; Baldassarri, Marta; Zhang, Yu; Stappert, Dina; Thompson, Van P

    2012-02-01

    Fatigue damage modes and reliability of hand-veneered (HV) and over-pressed (OP) aluminum-oxide layer structures were compared. Influence of luting cement thickness on mechanical performance was investigated. Sixty-four aluminum-oxide plates (10 × 10 × 0.5 mm) were veneered with hand built-up or pressed porcelain (0.7 mm) and adhesively luted (50- or 150-μm cement thickness) to water-aged composite resin blocks (12 × 12 × 4 mm). Single-load-to-failure and fatigue tests were performed with a spherical tungsten carbide indenter (d = 6.25 mm) applied in the center of the veneer layer. Specimens were inspected with polarized-reflected-light and scanning electron microscopy. Use-level probability Weibull curves were plotted with two-sided 90% confidence bounds, and reliability at 75,000 cycles and 250 N load was calculated. For all specimens but two OP with 50-μm cement thickness, failure was characterized by flexural radial cracks initiating at the bottom surface of the alumina core and propagating into the veneering porcelain before cone cracks could extend to the porcelain/alumina interface. HV specimens showed higher reliability compared to OP. Those with 50-μm cement thickness were more reliable relative to their 150-μm counterparts (HV_50 μm: 95% (0.99/0.67); HV_150 μm: 55% (0.92/0.01); OP_50 μm: 69% (0.84/0.48); OP_150 μm: 15% (0.53/0.004)). Similar failure modes were observed in HV and OP specimens. Radial cracks developing in the core and spreading into the veneer are suggested to cause bulk fracture, which is the characteristic failure mode for alumina core crowns. However, the highest resistance to fatigue loading was found for the HV specimens with thin cement thickness, while the lowest occurred for the OP with thick cement layer.

  8. Removal of hazardous anions from aqueous solutions by La(III)- and Y(III)-impregnated alumina

    Energy Technology Data Exchange (ETDEWEB)

    Wasay, Syed Abdul; Tokunaga, Shuzo [National Inst. of Materials and Chemical Research, Ibaraka (Japan); Park, S.W. [Keimyung Univ., Daegu City (Korea, Democratic People`s Republic of)

    1996-06-01

    New adsorbents, La(III)- and Y(III)-impregnated alumina, were prepared for the removal of hazardous anions from aqueous solutions. A commercially available alumina was impregnated with La(III) or Y(III) ions by the adsorption process. The change in the surface charge due to the impregnation was measured by acid/base titration. The adsorption rate and the capacity of the alumina for La(III) and Y(III) ions were determined. The adsorption characteristics of the La(III)- and Y(III)-impregnated alumina and the original alumina for fluoride, phosphate, arsenate and selenite ions were analyzed under various conditions. The pH effect, dose effect, and kinetics were studied. The removal selectivity by the impregnated alumina was in the order fluoride > phosphate > arsenate > selenite. The impregnated alumina has been successfully applied for the removal of hazardous anions from synthetic and high-tech industrial wastewaters.

  9. Pd-Pt Catalysts on Fluorinated Alumina Support Studied by X-Ray Absorption Fine Structure

    Science.gov (United States)

    Yan, Wensheng; Li, Zhongrui; Wei, Zheng; Wei, Shiqiang

    2007-02-01

    A series of bi-metallic Pd-Pt catalysts supported on both pristine and fluorinated alumina supports were investigated with x-ray absorption spectroscopy. It was found that Pd and Pt form small alloy particles on the pristine alumina support; the composition and the cluster size of the PdPt bimetallic alloys, and the electronic properties of the metals were significantly altered on the fluorinated support. The remarkable increase in sulfur tolerance of the PdPt metallic clusters supported on the fluorine pretreated alumina can be attributed to an electronic depletion of the metals, large particle size and direct participation of the acid sites in the reaction.

  10. EFFECT OF NANOPOWDER ADDITION ON THE FLEXURAL STRENGTH OF ALUMINA CERAMIC - A WEIBULL MODEL ANALYSIS

    Directory of Open Access Journals (Sweden)

    Daidong Guo

    2016-05-01

    Full Text Available Alumina ceramics were prepared either with micrometer-sized alumina powder (MAP or with the addition of nanometer-sized alumina powder (NAP. The density, crystalline phase, flexural strength and the fracture surface of the two ceramics were measured and compared. Emphasis has been put on the influence of nanopowder addition on the flexural strength of Al₂O₃ ceramic. The analysis based on the Weibull distribution model suggests the distribution of the flexural strength of the NAP ceramic is more concentrated than that of the MAP ceramic. Therefore, the NAP ceramics will be more stable and reliable in real applications.

  11. Rare earth-doped alumina thin films deposited by liquid source CVD processes

    Energy Technology Data Exchange (ETDEWEB)

    Deschanvres, J.L.; Meffre, W.; Joubert, J.C.; Senateur, J.P. [Ecole Nat. Superieure de Phys. de Grenoble, St. Martin d`Heres (France). Lab. des Materiaux et du Genie Phys.; Robaut, F. [Consortium des Moyens Technologiques Communs, Institut National Polytechnique de Grenoble, BP 75, 38402 St Martin d`Heres (France); Broquin, J.E.; Rimet, R. [Laboratoire d`Electromagnetisme, Microondes et Optoelectronique, CNRS-Ecole Nationale Superieure d`Electronique et Radioelectricite de Grenoble, BP 257, 38016 Grenoble, Cedex (France)

    1998-07-24

    Two types of liquid-source CVD processes are proposed for the growth of rare earth-doped alumina thin films suitable as amplifying media for integrated optic applications. Amorphous, transparent, pure and erbium- or neodymium-doped alumina films were deposited between 573 and 833 K by atmospheric pressure aerosol CVD. The rare earth doping concentration increases by decreasing the deposition temperature. The refractive index of the alumina films increases as a function of the deposition temperature from 1.53 at 573 K to 1.61 at 813 K. Neodymium-doped films were also obtained at low pressure by liquid source injection CVD. (orig.) 7 refs.

  12. Transport properties of anodic porous alumina for ReRAM

    Energy Technology Data Exchange (ETDEWEB)

    Kato, S; Nigo, S; Lee, J W; Mihalik, M; Kitazawa, H; Kido, G [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047 (Japan)], E-mail: KATO.Seiichi@nims.go.jp

    2008-03-15

    A voltage-induced bistable switching effect has been studied for M/AlO{sub x}/Al devices made of the anodic porous alumina with a top electrode of aluminium (or silver) to develop a next generation memory (AlO{sub x}-ReRAM). The resistance state of memory is switched between OFF-state (high resistance) and ON-state (low resistance), where the resistance ratio is higher than 10{sup 4}. In the thermally stimulated current (TSC) measurement, a narrow band was observed around 290 K, indicating the conduction mechanism comes from a kind of impurity band in the energy gap. An anomaly was also observed around 290 K in the temperature dependence of resistance at the ON-state.

  13. 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.

  14. Stress determination in thermally grown alumina scales using ruby luminescence

    Energy Technology Data Exchange (ETDEWEB)

    Renusch, D.; Veal, B.W.; Koshelev, I.; Natesan, K.; Grimsditch [Argonne National Lab., IL (United States); Hou, P.Y. [Lawrence Berkeley Lab., CA (United States)

    1996-06-01

    By exploiting the strain dependence of the ruby luminescence line, we have measured the strain in alumina scales thermally grown on Fe-Cr- Al alloys. Results are compared and found to be reasonably consistent with strains determined using x rays. Oxidation studies were carried out on alloys Fe - 5Cr - 28Al and Fe - 18Cr - 10Al (at.%). Significantly different levels of strain buildup were observed in scales on these alloys. Results on similar alloys containing a ``reactive element`` (Zr or Hf) in dilute quantity are also presented. Scales on alloys containing a reactive element (RE) can support significantly higher strains than scales on RE-free alloys. With the luminescence technique, strain relief associated with spallation thresholds is readily observed.

  15. 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.

  16. Sodium-Beta Alumina Batteries: Status and Challenges

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Xiaochuan; Lemmon, John P.; Sprenkle, Vincent L.; Yang, Zhenguo

    2010-09-05

    Sodium-beta alumina batteries, have been extensively developed for a few decades and encouraging progress has been achieved so far. The anode is typically molten sodium while the cathode can be molten sulfur (Na-S battery) or solid transition metal halides plus a liquid phase secondary electrolyte (e.g., ZEBRA battery). The electrolyte typically used is a β"-Al2O3 solid membrane. The issues prohibiting broad commercialization of this type of technology are dependent on the materials used, but can be broadly described as relatively high cost, safety (particularly for the Na-S couple), and low power. This paper offers a review on materials and designs for the batteries and discusses the challenges ahead for further technology improvement.

  17. 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.

  18. Removal of mercury from an alumina refinery aqueous stream.

    Science.gov (United States)

    Mullett, Mark; Tardio, James; Bhargava, Suresh; Dobbs, Charles

    2007-06-01

    Digestion condensate is formed as a by-product of the alumina refinery digestion process. The solution exhibits a high pH and is chemically reducing, containing many volatile species such as water, volatile organics, ammonia, and mercury. Because digestion condensate is chemically unique, an innovative approach was required to investigate mercury removal. The mercury capacity and adsorption kinetics were investigated using a number of materials including gold, silver and sulphur impregnated silica and a silver impregnated carbon. The results were compared to commercial sorbents, including extruded and powdered virgin activated carbons and a sulphur impregnated mineral. Nano-gold supported on silica (88% removal under batch conditions and 95% removal under flow conditions) and powdered activated carbon (91% under batch conditions and 98% removal under flow conditions) were the most effective materials investigated. The silver and sulphur impregnated materials were unstable in digestion condensate under the test conditions used.

  19. 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.

  20. 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.

  1. Synthesis of Cordierite from Rectorite-Talc-Alumina without Additives

    Institute of Scientific and Technical Information of China (English)

    XU Xiao-hong; WU Jian-feng; HU Shu-guang

    2004-01-01

    Rectorite,Talc and alumina were used to obtain high-quality cordierite with stoichiometric composition (51.3 wt% SiO2,34.9 wt% Al2O3,13.8 wt% Al2O3).The water absorption,apparent porosity,bulk density,thermal expansion coefficient,crystalline phases and microstructure were tested by means of X-ray diffractometer(XRD),scanning electronic microscopy(SEM),Archimedes immersion technique,etc.This work systematically studied the synthesizing process of the cordierite.The result shows that the cordierite can be synthesized at a lower temperature and within a wider temperature range by using the rectorite as clay raw materials.

  2. Studies on Alumina Incorporated Polyesteramide Derived from Meliaazedarach Seed Oil

    Directory of Open Access Journals (Sweden)

    A. Hasnat

    2016-10-01

    Full Text Available Polyesteramide resin (MAPEAM was prepared from N,N-bis(2-hydroxy ethyl Meliaazedarach oil fatty amide (HEMAFA a precursor of natural renewable resource using polycondensation reaction with maleic acid. With the view to improve the physico-mechenical properties aluminium was incorporated in backbone of the polymer to obtain the alumina incorporated polyesteramide resin of Meliaazedarach seed oil (Al-MAPEAM. The physico-chemical analyses and spectroscopic techniques were used for the characterization of Al-MAPEAM polymeric resin. The film properties of the Al-MAPEAM were also investigated in different corrosive environments as per standard reported methods. Studies shows that syntheses ofaluminium incorporated polyesteramide using Meliaazedarach seed oil as a starting material provides a more practicable utilization to it.

  3. 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.

  4. 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.

  5. Fatigue strength testing of LTCC and alumina ceramics bonds

    Science.gov (United States)

    Dąbrowski, A.; Matkowski, P.; Golonka, L.

    2012-12-01

    In this paper the results of fatigue strength tests of ceramic joints are presented. These tests have been performed on the samples subjected to thermal and vibration fatigue as well as on the reference samples without any additional loads. The main goal of the investigation was to determine the strength of hybrid ceramics joints using tensile testing machine. The experiment enabled evaluation of fatigue effects in the mentioned joints. Geometry of test samples has been designed according to FEM simulations, performed in ANSYS FEM environment. Thermal stress as well as the stress induced by vibrations have been analyzed in the designed model. In the experiments two types of ceramics have been used — LTCC green tape DP951 (DuPont) and alumina ceramic tape. The samples have been prepared by joining two sintered ceramic beams made of different types of material. The bonds have been realized utilizing low temperature glass or a layer of LTCC green tape.

  6. Impact loading of an aluminum/alumina composite

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, J.N.; Hixson, R.S.; Gray, G.T. III

    1994-02-01

    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 Al{sub 2}O{sub 3} inclusions (10 percent by volume, average diameter {approximately}25 microns). Parallel impact experiments are conducted on these composites and on pure 6061-T6 aluminum samples. This combination provides a direct and immediate qualitative picture of the effect of Al{sub 2}O{sub 3} inclusions the dynamic response of the composite in compression, release, and spallation. Additional experimental information is provided by post-shock reload tests of shock-recovered samples at quasi-static and intermediate strain rates.

  7. Corrosion performance of alumina scales in coal gasification environments

    Energy Technology Data Exchange (ETDEWEB)

    Natesan, K. [Argonne National Laboratory, Argonne, IL (United States)

    1997-12-31

    Corrosion of metallic structural materials in complex gas environments of coal gasification is a potential problem. The corrosion process is dictated by concentrations of two key constituents: sulfur as H{sub 2}s and C1 as HCl. This paper examines the corrosion performance of alumina scales that are thermally grown on Fe-base alloys during exposure to O/S mixed-gas environments. The results are compared with the performance of chromia-forming alloys in similar environments. The valuable information on corrosion performance of alloys whose surfaces were enriched with Al by the pack-diffusion process, by the electrospark deposition process, or by weld overlay techniques, is also discussed.

  8. Corrosion performance of alumina scales in coal gasification environments

    Energy Technology Data Exchange (ETDEWEB)

    Natesan, K.

    1997-02-01

    Corrosion of metallic structural materials in complex gas environments of coal gasification is a potential problem. The corrosion process is dictated by concentrations of two key constituents: sulfur as H{sub 2}S and Cl as HCl. This paper examines the corrosion performance of alumina scales that are thermally grown on Fe-base alloys during exposure to O/S mixed-gas environments. The results are compared with the performance of chromia-forming alloys in similar environments. The paper also discusses the available information on corrosion performance of alloys whose surfaces were enriched with Al by the pack-diffusion process, by the electrospark deposition process, or by weld overlay techniques.

  9. AFM, SEM and TEM Studies on Porous Anodic Alumina

    Science.gov (United States)

    Zhu, Yuan Yuan; Ding, Gu Qiao; Ding, Jian Ning; Yuan, Ning Yi

    2010-04-01

    Porous anodic alumina (PAA) has been intensively studied in past decade due to its applications for fabricating nanostructured materials. Since PAA’s pore diameter, thickness and shape vary too much, a systematical study on the methods of morphology characterization is meaningful and essential for its proper development and utilization. In this paper, we present detailed AFM, SEM and TEM studies on PAA and its evolvements with abundant microstructures, and discuss the advantages and disadvantages of each method. The sample preparation, testing skills and morphology analysis are discussed, especially on the differentiation during characterizing complex cross-sections and ultrasmall nanopores. The versatility of PAAs is also demonstrated by the diversity of PAAs’ microstructure.

  10. AFM, SEM and TEM Studies on Porous Anodic Alumina

    Directory of Open Access Journals (Sweden)

    Zhu YuanYuan

    2010-01-01

    Full Text Available Abstract Porous anodic alumina (PAA has been intensively studied in past decade due to its applications for fabricating nanostructured materials. Since PAA’s pore diameter, thickness and shape vary too much, a systematical study on the methods of morphology characterization is meaningful and essential for its proper development and utilization. In this paper, we present detailed AFM, SEM and TEM studies on PAA and its evolvements with abundant microstructures, and discuss the advantages and disadvantages of each method. The sample preparation, testing skills and morphology analysis are discussed, especially on the differentiation during characterizing complex cross-sections and ultrasmall nanopores. The versatility of PAAs is also demonstrated by the diversity of PAAs’ microstructure.

  11. Damping Behavior of Alumina Epoxy Nano-Composites

    Science.gov (United States)

    Katiyar, Priyanka; Kumar, Anand

    2016-10-01

    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.

  12. 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.

  13. 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.

  14. 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

  15. Dependence of copper species on the nature of the support for dispersed CuO catalysts.

    Science.gov (United States)

    Gervasini, Antonella; Manzoli, Maela; Martra, Gianmario; Ponti, Alessandro; Ravasio, Nicoletta; Sordelli, Laura; Zaccheria, Federica

    2006-04-20

    Copper catalysts prepared by chemisorption-hydrolysis technique over silica (Cu/Si) and silica-alumina (Cu/SiAl) supports were studied to understand the role of the support on the nature and surface properties of the copper species stabilized on their surfaces. The morphological and surface properties of the copper phases have been characterized by complementary techniques, such as HRTEM, EXAFS-XANES, EPR, XPS, and FTIR. For the FTIR investigation, molecular probes (CO and NO) were also adsorbed on the surfaces to test the reactivity of the copper species. Moreover, the catalytic performances of the two catalysts have been compared in the HC-SCR reaction (NO reduction by C(2)H(4)) performed in highly oxidant conditions. The superior activity and selectivity of the supported silica-alumina catalyst with respect to that supported on silica could be related with the different nature of the copper species stabilized on the two supports, as emerged from the results obtained from the spectroscopic investigations. Small and well-dispersed CuO particles were present on silica, whereas isolated copper ions predominated on silica-alumina, likely in regions rich in alumina that made some exchangeable sites available, as indicated by FTIR spectra of adsorbed CO. The less positive global charge of copper species on Cu/SiAl than in Cu/Si has been confirmed by EPR, XPS, and EXAFS-XANES analyses.

  16. Characterization of AMC commercial bricks with different alumina qualities; Caracterizacion de ladrillos comerciales AMC con diferentes calidades de alumina

    Energy Technology Data Exchange (ETDEWEB)

    Muñoz, V.; Camerucci, Maria A.; Martinez, A.G. Tomba [Instituto de Investigaciones en Ciencia y Tecnologia de Materiales (INTEMA), CONICET - Fac. de Ingenieria (UNMdP), Mar del Plata (Argentina)

    2011-07-01

    The study of commercial bricks Al{sub 2}O{sub 3}-MgO-C (AMC) has some advantages over the analysis of materials prepared in the laboratory, but requires a complete characterization. This paper presents the results of the characterization of commercial bricks AMC with different types of alumina aggregates used in ladles floor. The same is done by several complementary techniques: XRD, DTA / TGA, EPR, volume density and apparent porosity, dilatometric analysis, microstructural analysis by low magnification and scanning electron microscopy (SEM) coupled with analysis Energy dispersive X-ray (EDX) and determination of mechanical properties at room temperature (Young's modulus, stress and strain at fracture). The main characteristics and differences in the composition and microstructure, essential data for further analysis of the mechanical behavior and resistance to slag attack of these refractories, are determined. (author)

  17. Investigations of mechanical and wear properties of alumina/titania/fire-clay reinforced epoxy composites

    Science.gov (United States)

    Patel, Vinay Kumar; Chauhan, Shivani; Sharma, Aarushi

    2016-05-01

    In this work, the effect of various particulates (alumina, titania, fire clay) reinforcements on mechanical and wear properties of epoxy composites have been studied with a prime motive of replacing the costly alumina and titania by much economical fire clay for high mechanical strength and/or wear resistant materials. Fire clay based epoxy composites delivered better mechanical (both tensile and impact) properties than the alumina filled or neat epoxy composites and slightly lower than titania reinforced composites, which qualified the fire clay a very suitable cost effective alternatives of both alumina and titania for high mechanical strength based applications. However, the poor wear behavior of fire clay reinforced composites revealed its poor candidacy for wear and tear applications.

  18. 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.

  19. 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.

  20. Magnesia Bricks and Magnesia Alumina Bricks GB/T 2275-2007

    Institute of Scientific and Technical Information of China (English)

    Wang Jing; Peng Xigao

    2010-01-01

    @@ 1 Scope This standard specifies the classification,techni-cal requirements,test methods,quality appraisal pro-cedures,marking,packing,transportation,storage and quality certificate of magnesia bricks and magnesia alumina bricks.

  1. 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.

  2. Vertically aligned nanowires on flexible silicone using a supported alumina template prepared by pulsed anodization

    DEFF Research Database (Denmark)

    Mátéfi-Tempfli, Stefan; Mátéfi-Tempfli, M.

    2009-01-01

    Carpets of vertically aligned nanowires on flexible substrates are successfully realized by a template method. Applying special pulsed anodization conditions, defect-free nanoporous alumina structures supported on polydimethylsiloxane (PDMS), a flexible silicone elastomer, are created. By using...

  3. 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.

  4. Characterisation of dynamic behaviour of alumina ceramics: evaluation of stress uniformity

    Directory of Open Access Journals (Sweden)

    Zhiyong Wang

    2015-10-01

    Full Text Available Accurate characterisation of dynamic behaviour of ceramics requires the reliable split-Hopkinson pressure bar (SHPB technique and the condition of uniaxial homogeneous specimen deformation. In this study, an experimentally validated 3D finite element model of the full scale SHPB experiment was developed to quantitatively evaluate the wave propagation in the bars and the stress distribution/evolution in the alumina specimen. Wave signals in both the SHPB experiments and the finite element model were analysed to characterise the dynamic behaviour of alumina. It was found that the equilibrium of both stresses within the specimen and forces at the specimen ends can be established in the intermediate stage of deformation. The validity of stress uniformity in the alumina specimen supports the assumption of uniaxial homogeneous specimen deformation in the SHPB and validates the characterisation of dynamic behaviour of alumina ceramics.

  5. 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.

  6. Effect of 20kHz ultrasound on alumina hydrate precipitation from seeded sodium aluminate solution

    Institute of Scientific and Technical Information of China (English)

    赵继华; 陈启元

    2002-01-01

    The effect of 20kHz ultrasound on alumina hydrate precipitation from seeded sodium aluminate solution was studied. Compared with alumina hydrate precipitation without treatment of ultrasound, the precipitation time is reduced from 30h to 15h when the precipitation ratio is 45% under 20kHz ultrasound. Furthermore, agglomeration is increased and the growth rate of alumina hydrate is increased under 20kHz ultrasound by comparing the crystal size distribution and the SEM photographs. As a result, the average size of alumina hydrate is increased by 3.7μm. The structure of product is not changed according to the results of X-ray powder deflection.

  7. Optical Properties of Amorphous Alumina Dust in the Envelopes around O-Rich AGB Stars

    Science.gov (United States)

    Suh, Kyung-Won

    2016-08-01

    We investigate optical properties of amorphous alumina (Al_2O_3) dust grains in the envelopes around O-rich asymptotic giant branch (AGB) stars using laboratory measured optical data. We derive the optical constants of amorphous alumina over a wide wavelength range that satisfy the Kramers-Kronig relation and reproduce the laboratory 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 observations on various IR two-color diagrams for a large sample of O-rich AGB stars, we find that the amorphous alumina dust (about 10-40%) mixed with amorphous silicate better models the observed points for the O-rich AGB stars with thin dust envelopes.

  8. Theoretical and phenomenological analogies between flash sintering and dielectric breakdown in α-alumina

    Science.gov (United States)

    Biesuz, Mattia; Luchi, Piero; Quaranta, Alberto; Sglavo, Vincenzo M.

    2016-10-01

    α-alumina pre-sintered samples were subjected to flash sintering at 1200 °C under differing electric field strengths. The analysis of the relation between the incubation time and pre-sintering temperature clearly shows that the presence of pores and surfaces within the sample plays a central role in field-assisted sintering behavior of the material. The observed behavior is accounted for by the strong non-linear electrical conductivity shown by porous alumina at high field strength. The observed non-ohmic conductivity can also be related to the "pre-breakdown" behavior previously described by Frenkel. Literature results suggest that the field involved in flash sintering of alumina is comparable with the dielectric strength at high temperature. We can also state that dielectric breakdown and flash sintering in alumina are associated with similar physical phenomena.

  9. Stability of trapped charges in sapphires and alumina ceramics: Evaluation by secondary electron emission

    Science.gov (United States)

    Zarbout, K.; Si Ahmed, A.; Moya, G.; Bernardini, J.; Goeuriot, D.; Kallel, A.

    2008-03-01

    The stability of trapped charges in sapphires and alumina ceramics is characterized via an experimental parameter expressing the variation of the secondary electron emission yield between two electron injections performed in a scanning electron microscope. Two types of sapphires and polycrystalline alumina, which differ mainly by their impurity content, are investigated in the temperature range 300-663K. The stable trapping behavior in sapphires is attributed to trapping in different defects, whose nature depends on the purity level. In alumina ceramics, the ability to trap charges in a stable way is stronger in samples of high impurity content. In the low impurity samples, stable trapping is promoted when the grain diameter decreases, whereas the reverse is observed in high impurity materials. These behaviors can stem from a gettering effect occurring during sintering. The strong dependence of the variation of the secondary electron emission yield on the grain diameter and impurities enables a scaling of the stable trapping ability of alumina materials.

  10. Mechanical behaviors of alumina ceramics doped with rare-earth oxides

    Institute of Scientific and Technical Information of China (English)

    YAO Yijun; LI Chuncheng; WANG Ling; JIANG Xiaolong; QIU Tai

    2010-01-01

    The effects of three types of additives Y2O3, La2O3, and Sm2O3 on the sintering and mechanical behaviors of alumina ceramics were investigated. The bending strengths of alumina ceramics with Sm2O3 and Y2O3 additions were 455 and 439 MPa, respectively, higher than that with La2O3 addition. The fracture toughness of the ceramics with Sm2O3 and Y2O3 were also higher than that with La2O3 addition. The fracture mode of rare earth oxides doped alumina ceramics exhibited obvious transgranular fractures as well as intergranular fracture. The results of research show that the improvement of bending strength and fracture toughness of alumina ceramics with rare earth oxides was achieved by refining the grain size and strengthening the grain boundary.

  11. Enhancement of critical heat flux in pool boiling using atomic layer deposition of alumina

    Science.gov (United States)

    Feng, Bo; Weaver, Keith; Peterson, G. P.

    2012-01-01

    Alumina nano coatings on platinum (Pt) micro wires were fabricated using atomic layer deposition. During the pool boiling heat transfer, the critical heat flux (CHF) of Pt/Alumina in de-ionized water was found to have a two-fold enhancement compared to that of the same Pt bare wire. The CHF was shown to increase with coating thickness of alumina up to a thickness of 20 nm. Coating thicknesses in excess of 20 nm had no additional influence on the CHF. The enhancement of the CHF is the result of the superwetting property of the amorphous alumina coatings, which significantly increases the liquid film thickness, enhancing the rewetting of the "hot spot."

  12. 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.

  13. 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.

  14. A Comparative Study of Solvothermal and Sol-Gel-Derived Nanocrystalline Alumina Catalysts for Ethanol Dehydration

    National Research Council Canada - National Science Library

    Wannaborworn, Mingkwan; Praserthdam, Piyasan; Jongsomjit, Bunjerd

    2015-01-01

    .... Also, a commercial alumina was used for comparison purposes. The results showed that the catalytic activity depends on the properties of catalyst derived from different preparation methods and reaction temperature...

  15. 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.

  16. Influence of Unstable Non-equilibrium Liquid Iron Oxide on Clustering of Alumina Particles in Steel

    National Research Council Canada - National Science Library

    Mizoguchi, Toshiaki; Ueshima, Yoshiyuki; Sugiyama, Masaaki; Mizukami, Kazumi

    2013-01-01

    .... It was found that a small amount of liquid FeO could accelerate the clustering of alumina inclusions in aluminum-killed steel because of the strong liquid-capillary negative pressure of liquid FeO...

  17. Effect of alumina particle additions of the aging kinetics of 6061 aluminum matrix composites

    OpenAIRE

    Allen, Susan Marie.

    1990-01-01

    Approved for public release, distribution is unlimited Differential scanning calorimetry (DSC) was conducted using a monolithic 6061 aluminum material and two 6061 aluminum matrix composite materials. The composite materials were reinforced with 10 volume percent and 15 volume percent alumina particles. Electrical resistivity and hardness measurements during isothermal aging treatments were also conducted. The effects of prior aging and alumina particle additions on the growth kinetics and...

  18. 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.

  19. Chinese Standards on Refractories Shaped Insulating Refractory Product-High Alumina Bricks

    Institute of Scientific and Technical Information of China (English)

    Yu Lingyan

    2009-01-01

    @@ 1 Scope This standard specifies the classification,shape and dimension,technical requirements,test methods,quality appraisal procedure,packing,marking,transportation,storage,and quality certificate of high alumina insulating bricks. High alumina insulating bricks are used as working layer which contacts with fire directly,insulating layer,or inner lining of the kilns which does not react with the high temperature molten materials and corrosion gases.

  20. 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.

  1. Microstructures of nanosized alumina powders synthesized by sol-gel method

    Institute of Scientific and Technical Information of China (English)

    王晶; 张波

    2002-01-01

    The microstructures of nanosized alumina powders prepared by sol-gel routine were systematically studied with transmission electron microscopy and X-ray diffractometer. It was found that the morphologies of alumina gel powders change in the orders of caterpillar- thorn- granular-dumbbell shaped structures during calcining at temperatures from 20℃ to 800℃, 1200℃ and 1300℃. The caterpillar shaped structure composed of strings with a diameter of 5nm.

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

    OpenAIRE

    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...

  3. Mechanical properties and microstructural evolution of alumina-zirconia nanocomposites by microwave sintering

    OpenAIRE

    Benavente Martínez, Rut; Salvador Moya, Mª Dolores; Penaranda-Foix, Felipe L.; Pallone, Eliria; Borrell Tomás, María Amparo

    2014-01-01

    Microwave sintering has emerged in recent years as a novel method for sintering a variety of materials that have shown significant advantages against conventional sintering procedures. This work involved an investigation of microwave hybrid fast firing of alumina–zirconia nanocomposites using commercial alumina powder and monoclinic nanometric zirconia. The suspensions were prepared separately in order to obtain 5, 10 and 15 vol% of ZrO2 in the alumina matrix. The samples were sinter...

  4. Effect of cooling rate on the microstructure and porosity of alumina produced by freeze casting

    OpenAIRE

    Nieto Isabel María; Rodríguez-Parra Jesús M.; Moreno Rodrigo

    2012-01-01

    Freeze casting is a well-known shaping technique to produce materials with directional porosity. One of the major problems is the difficulty to control the cooling rate thus leading to gradients in pore size and homogeneity. This work deals with the manufacture of alumina ceramics with directional porosity by freeze casting of aqueous suspensions. An experimental set-up was prepared in order to apply different cooling rates. Freeze casting tests were done with an aqueous alumina suspens...

  5. Residual strain scanning of alumina-based ceramic composites by neutron diffraction

    Science.gov (United States)

    Ruiz-Hervias, J.; Bruno, G.; Bueno, S.; Gurauskis, J.; Baudín, C.; Fan, K. Y.

    2014-11-01

    Residual strain profiles were measured by neutron diffraction in alumina-aluminum titanate ceramic composites sintered at two different temperatures, namely 1450 and 1550°C. The results show that irrespective of the direction and the sintering temperature, the obtained profiles are almost flat, with very similar results for both temperatures. In addition, the results demonstrate that the alumina is in compression whereas the aluminium titanate is subjected to tensile residual stresses.

  6. Low temperature synthesis of nano alpha-alumina powder by two-step hydrolysis

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Ting; Guo, Xiaode, E-mail: guoxiaodenj@sina.com; Zhang, Xiang; Wang, Zhixiang; Shi, Jinqiu

    2016-01-15

    Highlights: • The nano α-Al{sub 2}O{sub 3} with good dispersion was prepared by two-step hydrolysis. • α-Al{sub 2}O{sub 3} powders were added as seed particles in the hydrolysis. • This article indicated that the glucose could impel the γ-Al{sub 2}O{sub 3} transformed to α-Al{sub 2}O{sub 3} directly. • This article indicated that the addictive of α-Al{sub 2}O{sub 3} seed could improve the phase transformation rate of γ-Al{sub 2}O{sub 3} to α-Al{sub 2}O{sub 3}. • In this article, the pure α-Al{sub 2}O{sub 3} could be obtained by calcining at 1000 °C for 1.5 h. - Abstract: The ultral fine alpha-alumina powder has been successfully synthesized via two-step hydrolysis of aluminum isopropoxide. Glucose and polyvinyl pyrrolidone were used as surfactants during the appropriate processing step. The alpha-alumina powder was used as seed particles. Several synthesis parameters, such as the amount of seeds, surfactants, and calcination temperature, were studied by X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), Thermogravimetry-differential scanning calorimetry (TG-DSC), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results showed that glucose greatly lower the phase transformation temperature of alpha-alumina by impelling the gamma-alumina transformed to alpha-alumina directly, and the seed could improve the phase transformation rate of alpha-alumina, the polyvinylpyrrolidone have an effect on preventing excessive grain growth and agglomeration of alpha-alumina powder. Comparatively well dispersed alpha-alumina powder with particle size less than 50 nm can be synthesized through this method after calcinations at 1000 °C for 2 h.

  7. Desorption of Furfural from Bimetallic Pt-Fe Oxides/Alumina Catalysts

    OpenAIRE

    Gloria Lourdes Dimas-Rivera; Javier Rivera de la Rosa; Carlos J. Lucio-Ortiz; José Antonio De los Reyes Heredia; Virgilio González González; Tomás Hernández

    2014-01-01

    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 betwe...

  8. 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 .

  9. Alumina ceramic as a biomaterial for use in afterloading radiation catheters for hyperthermia.

    Science.gov (United States)

    Ferraro, F T; Salcman, M; Broadwell, R D; Sewchand, W; Neuberth, G

    1989-08-01

    A major technical challenge to the use of interstitial hyperthermia in malignant brain tumors is the production of a well-defined, uniform hyperthermal field. In theory, A 915-MHz microwave antenna should allow fewer antennas to be used and cause less mechanical brain damage; however, standard radiation afterloading catheters require antennas to be 12 cm long; this is clearly impractical for intracranial use. Since alumina ceramic (Al2O3) catheters permit short microwave antennas (3-5 cm in length) to function properly in neural tissue, it is important to test the biocompatibility of alumina for use in combined interstitial microwave hyperthermia and brachytherapy. A 5-mm length of alumina catheter was implanted into the brains of 15 white rats. The animals were killed at 3, 7, 14, 28, and 56 days. Histological examination revealed only minor mechanical damage and no encapsulation until 1 month; even then, the glial wall was only a few cell layers thick. Five animals received implants and were killed at similar intervals for x-ray microanalysis with the scanning electron microscope. No migration of aluminum into the brain was detected when compared with two control animals that did not receive implants and an alumina blank. Although we measured 50% attenuation of the radiation from iridium-192 sources in alumina catheters as compared with conventional ones, alumina catheters can still be used for interstitial radiation by increasing either the activity of the seeds or the duration of treatment.

  10. Experimental Investigations on Tribological Behaviour of Alumina Added Acrylonitrile Butadiene Styrene (ABS Composites

    Directory of Open Access Journals (Sweden)

    T. Panneerselvam

    2016-09-01

    Full Text Available Composite materials are multifunctional in nature, which can be custom-made based on the nature of the applications. The challenge of composite materials lie on complementing the properties of one another i.e. materials which go in the making of composites strengthen each other by inhibiting their weaknesses. Polymers are one of the widely used materials which serve a wide spectrum of engineering needs. In the present work, the tribological behaviour of a composite containing Acrylonitrile Butadiene Styrene (ABS and traces of Alumina is experimentally investigated. Alumina is added to ABS in various percentages such as 1%, and 3% by weight in order to improve the wear resistance of the polymer. Central Composite Design was used to design the experiments and a standard Pin-On-Disk apparatus was used to conduct the experiments. It is observed from the test results that the addition of alumina significantly enhances the wear behavior of the polymer. However, adding more percentage of alumina has led to adverse effect on wear resistance of polymer materials. Abrasive wear mechanism is found to be predominant in the case of alumina added composite materials. It is also found that 1% alumina added composite exhibits excellent wear properties compared to other materials.

  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. Can zinc aluminate-titania composite be an alternative for alumina as microelectronic substrate?

    Science.gov (United States)

    Roshni, Satheesh Babu; Sebastian, Mailadil Thomas; Surendran, Kuzhichalil Peethambharan

    2017-01-01

    Alumina, thanks to its superior thermal and dielectric properties, has been the leading substrate over several decades, for power and microelectronics circuits. However, alumina lacks thermal stability since its temperature coefficient of resonant frequency (τf) is far from zero (‑60 ppmK‑1). The present paper explores the potentiality of a ceramic composite 0.83ZnAl2O4-0.17TiO2 (in moles, abbreviated as ZAT) substrates for electronic applications over other commercially-used alumina-based substrates and synthesized using a non-aqueous tape casting method. The present substrate has τf of + 3.9 ppmK‑1 and is a valuable addition to the group of thermo-stable substrates. The ZAT substrate shows a high thermal conductivity of 31.3 Wm‑1K‑1 (thermal conductivity of alumina is about 24.5 Wm‑1K‑1), along with promising mechanical, electrical and microwave dielectric properties comparable to that of alumina-based commercial substrates. Furthermore, the newly-developed substrate material shows exceptionally good thermal stability of dielectric constant, which cannot be met with any of the alumina-based HTCC substrates.

  13. 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.

  14. Flexibility of experimental alumina/feldspar and SR ADORO dental composites.

    Science.gov (United States)

    Le Roux, A R; Lachman, N

    2010-03-01

    Flexure of a dental composite can be detrimental to the success of a restoration. Flexibility considerations are thus important when comparing dental materials to optimize the success of resin restorations. Flexibility of 5.6 x 18.0 x 2.0 mm3 experimental alumina/feldspar and SR ADORO dental composites specimens were compared. It was hypothesized that alumina/feldspar composites would be less flexible under a load than SR ADORO composites and that the flexibility would decrease significantly as the feldspar content was increased. Alumina was chemically sintered or bonded with 40%, 50% and 60% feldspar mass, silanized and infiltrated with urethane dimethacrylate (UDMA) to prepare the alumina/feldspar dental restorative composite specimens. Three point bending tests were performed in the Instron 44 machine for flexural comparison to SR ADORO. The alumina/feldspar specimens showed lower flexibility (mm displacement) than SR ADORO (p dental composites may provide added marginal seal benefit. However confirmation via in vivo function of alumina/feldspar dental composites is recommended.

  15. 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.

  16. Porous alumina-hydroxyapatite composites through protein foaming-consolidation method.

    Science.gov (United States)

    Sopyan, I; Fadli, A; Mel, M

    2012-04-01

    This report presents physical characterization and cell culture test of porous alumina-hydroxyapatite (HA) composites fabricated through protein foaming-consolidation technique. Alumina and HA powders were mixed with yolk and starch at an adjusted ratio to make slurry. The resulting slip was poured into cylindrical shaped molds and followed by foaming and consolidation via 180 °C drying for 1 h. The obtained green bodies were burned at 600 °C for 1 h, followed by sintering at temperatures of 1200-1550 °C for 2 h. Porous alumina-HA bodies with 26-77 vol.% shrinkage, 46%-52% porosity and 0.1-6.4 MPa compressive strength were obtained. The compressive strength of bodies increased with the increasing sintering temperatures. The addition of commercial HA in the body was found to increase the compressive strength, whereas the case is reverse for sol-gel derived HA. Biocompatibility study of porous alumina-HA was performed in a stirred tank bioreactor using culture of Vero cells. A good compatibility of the cells to the porous microcarriers was observed as the cells attached and grew at the surface of microcarriers at 8-120 cultured hours. The cell growth on porous alumina microcarrier was 0.015 h(-1) and increased to 0.019 h(-1) for 0.3 w/w HA-to-alumina mass ratio and decreased again to 0.017 h(-1) for 1.0 w/w ratio.

  17. Can zinc aluminate-titania composite be an alternative for alumina as microelectronic substrate?

    Science.gov (United States)

    Roshni, Satheesh Babu; Sebastian, Mailadil Thomas; Surendran, Kuzhichalil Peethambharan

    2017-01-01

    Alumina, thanks to its superior thermal and dielectric properties, has been the leading substrate over several decades, for power and microelectronics circuits. However, alumina lacks thermal stability since its temperature coefficient of resonant frequency (τf) is far from zero (−60 ppmK−1). The present paper explores the potentiality of a ceramic composite 0.83ZnAl2O4-0.17TiO2 (in moles, abbreviated as ZAT) substrates for electronic applications over other commercially-used alumina-based substrates and synthesized using a non-aqueous tape casting method. The present substrate has τf of + 3.9 ppmK−1 and is a valuable addition to the group of thermo-stable substrates. The ZAT substrate shows a high thermal conductivity of 31.3 Wm−1K−1 (thermal conductivity of alumina is about 24.5 Wm−1K−1), along with promising mechanical, electrical and microwave dielectric properties comparable to that of alumina-based commercial substrates. Furthermore, the newly-developed substrate material shows exceptionally good thermal stability of dielectric constant, which cannot be met with any of the alumina-based HTCC substrates. PMID:28084459

  18. NOTE: Fabrication of a gecko-like hierarchical fibril array using a bonded porous alumina template

    Science.gov (United States)

    Suryadi Kustandi, Tanu; Samper, Victor Donald; Ng, Wan Sing; Chong, Ai Shing; Gao, Han

    2007-10-01

    We report a new method to fabricate a hierarchical microfibril array by using bonded porous alumina templates. The fabrication approach extends a powerful and well-established technique of creating porous alumina to create a polymer multilevel structure, mimicking the hierarchical structure of gecko adhesive foot hairs. The nanoporous alumina (pore diameter ≈60 nm; interpore distance ≈100 nm) was generated by the anodization of an aluminum film in an oxalic acid solution. The microporous alumina was produced by exploiting the parallel wafer-scale processing of conventional lithography and anisotropic chemical etching of the thick film of anodic alumina pores. The micro- and nanoporous alumina membranes were subsequently brought into intimate contact and their bonding was accomplished by means of capillary forces and then van der Waals bonding. Hierarchical polymeric microfibrils (fibril diameter ≈10 µm fibril length ≈70 µm) with nanofibril arrays at their tips were obtained after depositing a desired material into the pores and selective etching of the template membranes. The nanofibril has a lateral dimension of approximately 60 nm with length-to-diameter aspect ratios as high as 100:1.

  19. Decomposição catalítica de óleo de soja em presença de diferentes zeólitas

    Directory of Open Access Journals (Sweden)

    Santos Frances R.

    1998-01-01

    Full Text Available The catalytic decomposition of soybean oil was studied in a fix bed reactor at 673 and 773 K and using amorphous silica-alumina and the zeolites USY, H-Mordenite and H-ZSM-5 as catalysts. Both the selectivity and the catalytic activity were determined by studying the product composition resulting from the chemical reactions. Physicochemical characteristics of the catalysts were obtained by X-ray fluorescence, Fourier Transform infrared spectroscopy, 29Si and 27Al Nuclear Magnetic Ressonance and textural analysis. The zeolites USY and H-ZSM-5, showing higher Brönsted acidity, yielded products with higher concentration in aromatic hydrocarbons, whereas with both H-Mordenite and amorphous silica-alumina the main products were paraffins.

  20. 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.

  1. Nano or micro grained alumina powder? A choose before sintering

    Directory of Open Access Journals (Sweden)

    Román, R.

    2008-12-01

    Full Text Available Two different wet routes have been used to synthesize alumina powders in order to compare the characteristics of the final product and its behaviour during sintering. The Homogeneous Precipitation (HP gives rise to nanoparticulated powders of about 2 nm. However, such particles quickly aggregate and grow with calcination temperature. The Polymerized Organic-Inorganic Synthesis (POI produces homogeneous particle size powders (about 1 micron after resin charring. The characterization of the powder surface is the basis of an efficient process control. Particle characterization parameters (morphology, crystallinity and degree of aggregation are characterized by different techniques, such as DTA/TG, IR, XRD, SEM and TEM, and compared between these synthesis methods. The results show the evolution from the amorphous to the corundum alumina phase for both processes and their ability for sintering, as well discuses the beneficial of nanoparticles obtained by HP during sintering.

    Se han utilizado dos diferentes síntesis por vía húmeda para la preparación de polvos de alúmina con el fin de comparar las características de los productos finales y su comportamiento durante la sinterización. La Precipitación Homogénea (HP da lugar a polvos nanoparticulados de unos 2nm. Se observa sin embargo, como estas partículas se agregan rápidamente y crecen con la temperatura de calcinación. La Síntesis por Polimerización Orgánica-Inorgánica (POI produce polvos de tamaño de partícula homogéneo (en torno a 1 micra después de la descomposión de la resina. La caracterización de la superficie de los polvos es la base de un control eficiente del proceso. Los parámetros de caracterización de las partículas obtenidas (morfología, cristalinidad y grado de agregación se obtienen por diferentes técnicas como DTA/TG, IR, XRD, SEM y TEM, y se comparan entre estos métodos de síntesis. Los resultados muestran la evolución desde el amorfo a la fase

  2. 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

    2013-09-25

    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.

  3. Investigation of mechanical properties based on grain growth and microstructure evolution of alumina ceramics during two step sintering process

    Science.gov (United States)

    Khan, U. A.; Hussain, A.; Shah, M.; Shuaib, M.; Qayyum, F.

    2016-08-01

    Alumina ceramics having small grain size and high density yield good mechanical properties, which are required in most mechanical applications. Two Step Sintering (TSS) is used to develop dense alumina ceramics. In this research work the effect of sintering temperatures on microstructure and density of the alumina specimens developed by using TSS has been investigated. It has been observed that TSS is more efficient in controlling grain growth and increasing the density as compared to One Step Sintering (OSS) of alumina. Scanning electron micrographs of sintered alumina specimens have been compared. It has been observed that TSS proves to be a better technique for increasing density and controlling grain growth of alumina ceramics than OSS. More relative density, hardness, fracture toughness and small grain size was achieved by using TSS over OSS technique.

  4. A novel method for preparing ultra-fine alumina-borate oxide fibres via an electrospinning technique

    Science.gov (United States)

    Dai, Hongqin; Gong, Jian; Kim, Hakyong; Lee, Doukrae

    2002-10-01

    Alumina-borate/PVA composite fibres were prepared using sol-gel processing and an electrospinning technique. After calcination of the thin fibres, ultra-fine fibres of alumina-borate oxide with a diameter of about 550 nm could be prepared. The fibres were characterized by SEM, XRD and FT-IR. The results showed that the crystalline phase and morphology of alumina-borate fibres were largely influenced by the calcination temperature.

  5. Studies on Carbon-Fly Ash Composites with Chopped PANOX Fibers

    OpenAIRE

    Patel,Rakesh V; Manocha, S.

    2013-01-01

    Chemical analysis and morphological studies of fly ash reveals the complex chemical constituents present as spherical particles with diameter of less than 25 μm. The constituents of fly ash are silica, alumina, iron oxide, titanium dioxide, calcium and magnesium oxide, and other trace elements. The use of thermosetting as well thermoplastic polymer matrix has been made by several workers to develop polymer matrix fly ash particulate composites by using the hard and abrasive properties of fly ...

  6. New hydrocracking catalysts increase throughput, run length

    Energy Technology Data Exchange (ETDEWEB)

    Huizinga, T. [Shell Internationale Petroleum Mij., The Hague (Netherlands); Theunissen, J.M.H. [Rayong Refinery Co. Ltd., Rayong (Thailand); Minderhoud, H.; Veen, R. van [Koninklijke/Shell-Lab., Amsterdam (Netherlands)

    1995-06-26

    An improved, second-stage hydrocracking catalyst has been developed by combining stabilized Y zeolites with amorphous silica alumina cracking components. A commercial application of this catalyst, along with a new, first-stage zeolitic hydrocracking catalyst, resulted in increased unit throughput and cycle length. The paper discusses the hydrocracking process, first-stage catalysts, second-stage catalysts, hydrogenation process, commercial results, and product properties.

  7. Synthesis and Modification of Clinoptilolite

    OpenAIRE

    Pavlina Ambrozova; Jindrich Kynicky; Tomas Urubek; Vinh Dinh Nguyen

    2017-01-01

    Clinoptilolite is a natural mineral with exceptional physical characteristics resulting from its special crystal structure, mainstreamed into a large zeolite group called heulandites. An overall view of the research related to the synthesis, modification and application of synthetic clinoptilolite is presented. A single phase of clinoptilolite can be hydrothermally synthesized for 1–10 days in an autoclave from various silica, alumina, and alkali sources with initial Si/Al ratio from 3.0 to 5...

  8. Evaluation of low cost/high temperature insulation, July 1974 - June 1975

    Science.gov (United States)

    Strauss, E. L.

    1975-01-01

    Six fiber products and six insulation blankets comprising silica, alumina, zirconia, mullite, and mixed ceramic systems were subjected to furnace exposures up to 500 hours at temperatures of 1000 to 1600 C and evaluated for chemical and dimensional stability and for changes in thermal conductivity. Alumina, zirconia, and mullite fibers were fabricated into reusable surface insulation (RSI) tile by water-felting and reimpregnation with ethyl silicate. Specimens were exposed to 25 thermal cycles at 1200 C and 1400 C and a pressure of 10 and 32 torr, respectively. Production costs for 930 sq m (10,000 sq ft) of blanket insulation and of alumina RSI tile were developed.

  9. Segregation phenomena at growing alumina/alloy interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Peggy Y.

    2005-03-30

    The chemistry and structure at the scale/alloy interface are important factors governing scale adhesion. The chemical changes can occur from segregation of impurities in the alloy, such as sulphur and carbon, or alloying elements such as chromium, aluminium and reactive elements. This paper reviews studies of the changes of interfacial composition with oxidation time for Al{sub 2}O{sub 3} formed on several model alumina-forming alloys, and tries to relate that to the interfacial strength. Results show that sulphur segregation to oxide/metal interfaces can indeed occur, but the type and amount of segregants at the interface depend on the alloy composition and the interface structure. Co-segregation of impurities with alloying elements can also occur, resulting in multi-layer segregants at the interface. Sulphur-containing interfaces are indeed weaker, but the major role of sulphur is to enhance interfacial void formation. Reactive elements in the alloy not only gather sulfur but also exert an additional positive effect on scale adhesion.

  10. Sulfide capacity of high alumina blast furnace slags

    Science.gov (United States)

    Shankar, Amitabh; Görnerup, Märten; Seetharaman, S.; Lahiri, A. K.

    2006-12-01

    Sulfide capacities of high alumina blast furnace slags were experimentally determined using the gas-slag equilibration technique. Two different slag systems were considered for the current study, namely, CaO-SiO2-MgO-Al2O3 quaternary and CaO-SiO2-MgO-Al2O3-TiO2 quinary system. The liquid slag was equilibrated with the Ar-CO-CO2-SO2 gas mixture. Experiments were conducted in the temperature range of 1773 to 1873 K. The effects of temperature, basicity, and the MgO and TiO2 contents of slags on sulfide capacity were studied. As expected, sulfide capacity was found to increase with the increase in temperature and basicity. At the higher experimental temperature, titania decreases the sulfide capacity of slag. However, at the lower temperature, there was no significant effect of titania on the sulfide capacity of slag. Sulfide capacity increases with the increase in MgO content of slag if the MgO content is more than 5 pct.

  11. Surface modification of nanoporous alumina membranes by plasma polymerization.

    Science.gov (United States)

    Losic, Dusan; Cole, Martin A; Dollmann, Björn; Vasilev, Krasimir; Griesser, Hans J

    2008-06-18

    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.

  12. 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.

  13. 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.

  14. Tailoring thermal conductivity via three-dimensional porous alumina

    Science.gov (United States)

    Abad, Begoña; Maiz, Jon; Ruiz-Clavijo, Alejandra; Caballero-Calero, Olga; Martin-Gonzalez, Marisol

    2016-12-01

    Three-dimensional anodic alumina templates (3D-AAO) are an astonishing framework with open highly ordered three-dimensional skeleton structures. Since these templates are architecturally different from conventional solids or porous templates, they teem with opportunities for engineering thermal properties. By establishing the mechanisms of heat transfer in these frameworks, we aim to create materials with tailored thermal properties. The effective thermal conductivity of an empty 3D-AAO membrane was measured. As the effective medium theory was not valid to extract the skeletal thermal conductivity of 3D-AAO, a simple 3D thermal conduction model was developed, based on a mixed series and parallel thermal resistor circuit, giving a skeletal thermal conductivity value of approximately 1.25 W·m-1·K-1, which matches the value of the ordinary AAO membranes prepared from the same acid solution. The effect of different filler materials as well as the variation of the number of transversal nanochannels and the length of the 3D-AAO membrane in the effective thermal conductivity of the composite was studied. Finally, the thermal conductivity of two 3D-AAO membranes filled with cobalt and bismuth telluride was also measured, which was in good agreement with the thermal model predictions. Therefore, this work proved this structure as a powerful approach to tailor thermal properties.

  15. 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...

  16. Tailoring thermal conductivity via three-dimensional porous alumina.

    Science.gov (United States)

    Abad, Begoña; Maiz, Jon; Ruiz-Clavijo, Alejandra; Caballero-Calero, Olga; Martin-Gonzalez, Marisol

    2016-12-09

    Three-dimensional anodic alumina templates (3D-AAO) are an astonishing framework with open highly ordered three-dimensional skeleton structures. Since these templates are architecturally different from conventional solids or porous templates, they teem with opportunities for engineering thermal properties. By establishing the mechanisms of heat transfer in these frameworks, we aim to create materials with tailored thermal properties. The effective thermal conductivity of an empty 3D-AAO membrane was measured. As the effective medium theory was not valid to extract the skeletal thermal conductivity of 3D-AAO, a simple 3D thermal conduction model was developed, based on a mixed series and parallel thermal resistor circuit, giving a skeletal thermal conductivity value of approximately 1.25 W·m(-1)·K(-1), which matches the value of the ordinary AAO membranes prepared from the same acid solution. The effect of different filler materials as well as the variation of the number of transversal nanochannels and the length of the 3D-AAO membrane in the effective thermal conductivity of the composite was studied. Finally, the thermal conductivity of two 3D-AAO membranes filled with cobalt and bismuth telluride was also measured, which was in good agreement with the thermal model predictions. Therefore, this work proved this structure as a powerful approach to tailor thermal properties.

  17. 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.

  18. Sulfur Impurities and the Microstructure of Alumina Scales

    Science.gov (United States)

    Smialek, James L.

    1997-01-01

    The relationship between the microstructure of alumina scales, adhesion, and sulfur content was examined through a series of nickel alloys oxidized in 1100 to 1200 deg. C cyclic or isothermal exposures in air. In cyclic tests of undoped NiCrAl, adhesion was produced when the sulfur content was reduced, without any change in scale microstructure. Although interfacial voids were not observed in cyclic tests of NiCrAl, they were promoted by long-term isothermal exposures, by sulfur doping, and in most exposures of NiAl. Two single crystal superalloys, PWA 1480 and Rene' N5, were also tested, either in the as-received condition or after the sulfur content had been reduced to less than 1 ppmw by hydrogen annealing. The unannealed alloys always exhibited spalling to bare metal, but interfacial voids were not observed consistently. Desulfurized PWA 1480 and Rene' N5 exhibited remarkable adhesion and no voidage for either isothermal or cyclic exposures. The most consistent microstructural feature was that, for the cases where voids did form, the scale undersides exhibited corresponding areas with ridged oxide grain boundaries. Voids were not required for spallation nor were other microstructural features essential for adhesion. These observations are consistent with the model whereby scale spallation is controlled primarily by interfacial sulfur segregation and the consequent degradation of oxide-metal bonding.

  19. Sinter-hipping of zirconia and alumina/zirconia composites

    Energy Technology Data Exchange (ETDEWEB)

    Solomah, A.G. (Kernforschungsanlage Juelich GmbH (Germany, F.R.). Inst. fuer Chemische Technologie)

    1989-01-01

    Pressureless sintered yttria-tetragonal zirconia polycrystals (Y-TZP) and yttria-partially stabilized zirconia (X-PSZ) containing different compositions of alumina (Y-PSZ/Al{sub 2}O{sub 3}) were hot-isostatically pressed, as a post-sintering processing technique, producing near theoretically dense materials (> 99.5% TD). Hipping has no measurable effect on hardness (H) and fracture toughness (K{sub IC}= of Y-TZP and Y-PSZ/Al{sub 2}O{sub 3} composites, as they were determined using Vicker's indentation technique. No changes in the crystalline phases due to hiping were observed. Low-temperature annealing has caused severe degradation to Y-TZP while for Y-PSZ/Al{sub 2}O{sub 3} composites no surface cracking was observed, but a loss in K{sub IC} was noticed, depending on Al{sub 2}O{sub 3} content. High-temperature annealing has insignificant effect on H and K{sub IC} of Y-TZP, while a loss in K{sub IC} was observed for Y-PSZ/Al{sub 2}O{sub 3} composites due to the increase in the mole fraction of cubic phase of zirconia with consistent decrease in the fraction of tetragonal phase as it has been confirmed by X-ray diffraction. (orig.).

  20. Zirconia toughened alumina (ZTA) powders: ultrastructural and histological analysis.

    Science.gov (United States)

    Spinelli, M S; Maccauro, G; Graci, C; Cittadini, A; Magnani, G; Sangiorgi, S; Del Bravo, V; Manicone, P F; Raffaelli, L; Muratori, F; Sgambato, A

    2011-01-01

    Ceramic materials, as Alumina and Zirconia, has made an improvement in the choice of new biomaterials for the load bearing application in dental and orthopaedic implants. These materials has shown mechanical resistance to high stress related to weight bearing and low debris in time. For this reason they are indicated on young patients implant, with high demanding activities and long life expectance. In literature however the risk of chronic inflammation due to chronic wear debris release and the possibility of carcinogenesis, is still to be definitively investigated. Another point to investigate is the acute reaction of the tissue in case of acute release of powders of these materials. The aim of this study was to investigate the possible local and systemic acute effects of ceramic precursors in form of powders of different size when released into articular joint. Powders of ZTA were implanted in the knee joint of twenty-four New Zealand white adult rabbits, that were sacrificed at 1,3,6, and 12 months. Radiographic, histological and immunoistochemestry analysis were conducted on periprosthetic tissue and peripheral organs, to verifying local host response and systemic toxic effects.

  1. 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.

  2. Bacteria repelling on highly-ordered alumina-nanopore structures

    Science.gov (United States)

    Kim, Sunghan; Zhou, Yan; Cirillo, Jeffrey D.; Polycarpou, Andreas A.; Liang, Hong

    2015-04-01

    Bacteria introduce diseases and infections to humans by their adherence to biomaterials, such as implants and surgical tools. Cell desorption is an effective step to reduce such damage. Here, we report mechanisms of bacteria desorption. An alumina nanopore structure (ANS) with pore size of 35 nm, 55 nm, 70 nm, and 80 nm was used as substrate to grow Escherichia coli (E. coli) cells. A bacteria repelling experimental method was developed to quantitatively evaluate the area percentage of adherent bacterial cells that represent the nature of cell adhesion as well as desorption. Results showed that there were two crucial parameters: contact angle and contact area that affect the adhesion/desorption. The cells were found to be more easily repelled when the contact angle increased. The area percentage of adherent bacterial cells decreased with the decrease in the contact area of a cell on ANS. This means that cell accessibility on ANS depends on the contact area. This research reveals the effectiveness of the nanopored structures in repelling cells.

  3. 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.

  4. Infrared Spectroscopy Studies on sol-gel prepared alumina Powders

    Directory of Open Access Journals (Sweden)

    Majid JAFAR TAFRESHI

    2015-03-01

    Full Text Available Gamma-alumina fine particles were synthesized by sol-gel process. Aluminum tri-sec-butoxide (ATB, anhydrous ethyl alcohol (EtOH, water (H2O and hydrochloric acid (HCl were used as starting materials. Different samples were synthesized with EtOH/ATB=60/1, HCl/ATB=0.08/1 and H2O/ATB=1/1 ratios and calcined at different temperatures. Molar ratios of H2O/ATB (from 1 to 25 and HCl/ATB (from 0.08 to 0.4 were changed for some other samples, during synthesizing process. The products were characterized by both XRD and FTIR measurements. Studies were carried out on the effect of calcination temperature and change of H2O/ATB and HCl/ATB ratios on structure and processes involved in phase transformations.DOI: http://dx.doi.org/10.5755/j01.ms.21.1.4872

  5. Corrosion leaking of preheater weldment in alumina factories

    Institute of Scientific and Technical Information of China (English)

    ZHANG Li; CHEN Wen-mi; GONG Zhu-qing; LIU Hong-zhao

    2005-01-01

    Stress corrosion cracking (SCC) and anticorrosion measures of TU42C weld-joint were studied by constant load experiments and pickling experiments. The results show that in 40%(mass fraction) NaOH solution at 110 ℃, caustic SCC occurs in TU42C weld-joints at the applied potential of -1 020 mV(vs SCE) for 3 d while at the potential of -950 mV(vs SCE) for 10 d. All the cracks are intergranular. In the 10% sulfuric acid, the cracks have the most negative self-corrosion potential -432.5 mV(vs SCE) and are active to be further corroded by the acid. Because of the same corrosion behaviour as the lab weldment, preheater's cracking in alumina factories is attributed to the combining actions of previous caustic SCC in Bayer solutions and continuous acid corrosion by pickling with the addition of RD. The following measures are effective to prevent the corrosion failure of preheater, such as postweld heat treatment at 620 ℃ to relax the residual weld stress, addition of CC3 and L826 as the corrosion inhibitors to improve the pickling and cleaning by the high pressure water instead of by pickling.

  6. Colloidal processing of alumina with MgO additions

    Energy Technology Data Exchange (ETDEWEB)

    Lyckfeldt, O. [Swedish Ceramic Inst., Goeteborg (Sweden); Ferreira, J.M.F. [Dept. of Ceramics and Glass Engineering, Univ. of Aveiro (Portugal)

    1997-12-31

    Both rheological studies and casting studies were made to evaluate the effects of adding MgO (0.10 wt%) to alumina slips with a solids loading of 45 vol%, stabilised either with a polyacrylic acid (Dispex A40, Allied Colloids Ltd, UK) or with a low M{sub w} sulphonic acid (Tiron, Aldrich Chemie, Germany). Tiron and Dispex are expected to give electrostatic and electrosteric stabilisation, respectively. The addition of MgO gave significant effects displayed by increased viscosity and elasticity of the slips and a considerable decrease in density of slip-cast and filter-pressed bodies. When the casting pressure increased, there was also a general tendency that the density of filter-pressed bodies decreased with well-stabilised slips (without MgO), but increased when the slip was weakly flocculated (with MgO). This was explained by the casting rate dependency under stabilised slip conditions, and the compressibility of the filter-pressed cakes formed using flocculated slips. Furthermore, it was shown that Tiron gave a higher degree of deflocculation both with addition of MgO and without MgO, indicating that the electrostatic stabilising mechanism dominates the particle interactions whereas steric effects are less important at the solids loading used. (orig.) 5 refs.

  7. 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).

  8. HEAT TRANSFER ENHANCEMENT USING ALUMINA NANOFLUID IN CIRCULAR MICRO CHANNEL

    Directory of Open Access Journals (Sweden)

    K. S. ARJUN

    2017-01-01

    Full Text Available In this study, thermal and flow behavior models for circular microchannel using water and its nanofluids with alumina as a coolant fluid in single phase flow have been developed. A finite volume-based CFD technique is used and models are solved by using Fluent Solver. The 2D axis symmetric geometry with structured mesh and 100 x 18 nodes are used for single phase flow with Al2O3 nanoparticles of 23 nm average diameter. Viscous laminar and standard k-ε models are used to predict the steady temperature in laminar and turbulent zone. The heat transfer enhancement upto 83% in laminar and turbulent zones are obtained with the Re ranging from 5 to 11980 and particle volume concentration from 0 to 5%. Even though the pressure drop increases with increase in Re, it is comparatively less compared to the corresponding decrease in temperature. The increase in temperature depends on Re and Pe; but the temperature distribution is found to be independent of radial position even for very low Pe. Comparison with analytical results both in laminar and turbulent zone is provided to justify the assumptions introduced in the models and very close agreement is observed statistically. Nusselt number can well predict the analytical data.

  9. Oxygen grain-boundary transport in polycrystalline alumina using wedge-geometry bilayer samples: Effect of Y-doping

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, H. [Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015 (United States)] [Center for Advanced Materials and Nanotechnology, Lehigh University, Bethlehem, PA 18015 (United States); Caram, H.S.; Schiesser, W.E. [Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015 (United States); Rickman, J.M.; Chan, H.M. [Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015 (United States)] [Center for Advanced Materials and Nanotechnology, Lehigh University, Bethlehem, PA 18015 (United States); Harmer, M.P., E-mail: mph2@lehigh.edu [Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015 (United States)] [Center for Advanced Materials and Nanotechnology, Lehigh University, Bethlehem, PA 18015 (United States)

    2010-04-15

    Novel wedge-geometry, dual-layer alumina samples, both undoped and 500 ppm Y{sup 3+}-doped, were studied in the temperature regime 1250-1400 deg. C to determine the effect of Y{sup 3+} on oxygen grain-boundary transport in alumina. The samples consisted of a wedge-shaped, single-phase alumina top layer, diffusion bonded to an alumina/Ni substrate containing a fine, uniform dispersion of Ni marker particles (0.5 vol.%). The extent of the alumina spinel oxidation layer was measured as a function of the wedge thickness for a series of heat-treatment conditions. Models of the transport behavior were used to derive values for the rate constants (k) in both the alumina top layer and the alumina/Ni substrate. It was found that the presence of yttrium slows oxygen grain-boundary diffusion in alumina by a factor of {approx}5 (at 1300 deg. C), and increases the corresponding activation enthalpy for oxidation from 407 {+-} 20 to 486 {+-} 34 kJ mol{sup -1}. Microstructural observations suggested that yttrium also slows Ni outward diffusion. A comparison of the different k values revealed that, at 1300 deg. C, the presence of Ni alone enhances transport by a factor of {approx}2 relative to undoped alumina.

  10. Effect of ultrasonic transmission rate on microstructure and properties of the ultrasonic-assisted brazing of Cu to alumina.

    Science.gov (United States)

    Ji, Hongjun; Chen, Hao; Li, Mingyu

    2017-01-01

    Fluxless brazing of bare alumina with Cu was conducted with an ultrasonic-assisted brazing technique by a Zn-14wt.%Al filler. The shear strength of Cu/alumina joints (84MPa) exhibited 27% larger than the alumina/Cu joints (66MPa) due to different intermetallic phases and their morphologies formed in the seam under the same parameters, which are probably attributed to the transmission rate of ultrasonic energy varying with density of the ultrasonic horn-contacted materials. Overgrowth of stalactite-like CuZn5 contributes to better thermal dissipation of the ultrasonic-assisted brazed Cu/alumina joints.

  11. Development of unique catalysts for hydrodenitrogenation of coal-derived liquids. Annual report, September 15, 1979-September 15, 1980

    Energy Technology Data Exchange (ETDEWEB)

    Katzer, J.R.; Stiles, A.B.; Kwart, H.

    1980-12-15

    Hydrodenitrogenation of quinoline and decahydroquinoline has been studied employing several catalysts: Bronsted and Lewis acid catalysts without metal, and silica-alumina, ..gamma..-alumina and magnesia impregnated with molybdenum, tungsten, nickel or cobalt. Our results show that nitrogen removal rate was highest for molybdenum on alumina and tungsten on silica-alumina or alumina catalysts. Nitrogen abstraction using ..gamma..-alumina support is considerably faster than with magnesia support. Several catalysts have been prepared and tested, with the emphasis on understanding the role of acidity in the carbon-nitrogen bond scission reaction. Hydrodenitrogenation of quinoline has been studied by using Ni,Mo/chlorided or fluorided alumina catalysts, with various halide concentrations. Preliminary results from this study indicate that halogenation of ..gamma..-alumina catalysts slightly enhanced the hydrogenolysis activity but showed little effect on the hydrogenation activity. Initial results from phenothiazine hydroprocessing show that carbon-sulfur bonds in the reactant are broken much faster than the carbon-nitrogen bonds. Data relevant to this reaction are being evaluated, utilizing kinetic analysis to give quantitative rates of C-N and C-S bond scission and the extents and rates of hydrogenation. Note: this report contains 5th, 6th, 7th and 8th quarterly reports.

  12. Model heterogeneous acid catalysts and metal-support interactions: A combined surface science and catalysis study

    Energy Technology Data Exchange (ETDEWEB)

    Boszormenyi, I.

    1991-05-01

    This (<100 [Angstrom]) silica-alumina layers were tested as potential model heterogeneous acid catalysts for combined surface science and catalysis studies. Three preparation methods were used: oxidation of r3 [times] r3 R30 Al/Si(111) structure in UHV; deposition on Si(lll) from aqueous solution; and argon ion beam sputter deposition in UHV. The homogeneous thin layers are amorphous, and the chemical environment of surface atoms is similar to that of Si, Al and oxygen atoms on high surface area acid catalysts. Since the ion beam-deposited thin layer of silica-alumina has the same composition as the target zeolite this deposition method is a promising tool to prepare model catalysts using practical catalyst targets. The silica-alumina layers are active in cumene cracking, a typical acid catalyzed reaction. In order to clearly distinguish background reactions and the acid catalyzed reaction at least 20 cm[sup 2] catalyst surface area is needed. Two series of model platinum-alumina catalysts were prepared in a combined UHV -- high pressure reactor cell apparatus by depositing alumina on polycrystalline Pt foil and by vapor depositing Pt on a thin alumina layer on Au. Both model surfaces have been prepared with and without chlorine. AES, CO desorption as well as methyl cyclopentane (MCP) hydrogenolysis studies indicate that the Pt surface area is always higher if a chlorination step is involved. Selectivity patterns in MCP ring opening on Pt-on-alumina'' and on alumina-on-Pt'' are different; only the former is a linear combination of selective and statistical ring opening. Product distribution, however, changes with coverage and reaction time. The properties of the two model catalyst systems and role of chlorine in MCP hydrogenolysis are also discussed.

  13. Model heterogeneous acid catalysts and metal-support interactions: A combined surface science and catalysis study

    Energy Technology Data Exchange (ETDEWEB)

    Boszormenyi, I.

    1991-05-01

    This (<100 {Angstrom}) silica-alumina layers were tested as potential model heterogeneous acid catalysts for combined surface science and catalysis studies. Three preparation methods were used: oxidation of r3 {times} r3 R30 Al/Si(111) structure in UHV; deposition on Si(lll) from aqueous solution; and argon ion beam sputter deposition in UHV. The homogeneous thin layers are amorphous, and the chemical environment of surface atoms is similar to that of Si, Al and oxygen atoms on high surface area acid catalysts. Since the ion beam-deposited thin layer of silica-alumina has the same composition as the target zeolite this deposition method is a promising tool to prepare model catalysts using practical catalyst targets. The silica-alumina layers are active in cumene cracking, a typical acid catalyzed reaction. In order to clearly distinguish background reactions and the acid catalyzed reaction at least 20 cm{sup 2} catalyst surface area is needed. Two series of model platinum-alumina catalysts were prepared in a combined UHV -- high pressure reactor cell apparatus by depositing alumina on polycrystalline Pt foil and by vapor depositing Pt on a thin alumina layer on Au. Both model surfaces have been prepared with and without chlorine. AES, CO desorption as well as methyl cyclopentane (MCP) hydrogenolysis studies indicate that the Pt surface area is always higher if a chlorination step is involved. Selectivity patterns in MCP ring opening on ``Pt-on-alumina`` and on ``alumina-on-Pt`` are different; only the former is a linear combination of selective and statistical ring opening. Product distribution, however, changes with coverage and reaction time. The properties of the two model catalyst systems and role of chlorine in MCP hydrogenolysis are also discussed.

  14. Electron paramagnetic resonance studies of beta-alumina, a prototype glass

    Energy Technology Data Exchange (ETDEWEB)

    Kurtz, Steven Ross

    1980-01-01

    Electron paramagnetic resonance techniques are used to study single crystal Na, K, and Li beta-alumina. Color centers are introduced into this material by irradiating the samples with electrons at liquid nitrogen temperature. Using electron paramagnetic resonance and electron nuclear double resonance, the color centers generated in this manner are identified, and their location within the material is determined. For one of these centers, an F/sup +/ center, the electron spin relaxation rate is measured over the range 2 to 20/sup 0/K using the pulse saturation and recovery technique. These measurements reveal an exceptionally fast relaxation rate with anomalous temperature and microwave frequency dependence. Beta-alumina is a structurally unique system. It is partially disordered and consists of ordered blocks of aluminum oxide separated by planar disordered regions. Extensive measurements have shown that beta-alumina displays properties identical to those observed for glasses at low temperature as a result of this limited structural disorder. These glass-like properties have been explained by proposing that atomic tunneling occurs in beta-alumina at low temperature producing a system of localized two level states. A model is developed which quantitatively describes the electron spin relaxation data. The proposed relaxation mechanism couples the color center spin to the phonon induced relaxation of a nearby localized two level tunneling state. A detailed comparison shows that this model is in good agreement with earlier heat capacity, thermal conductivity, and dielectric susceptibility measurements in beta-alumina.

  15. 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.

  16. 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; Ul Amin, Faiz; Kim, Myeong Ok

    2015-10-01

    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.

  17. Identification of the odour and chemical composition of alumina refinery air emissions.

    Science.gov (United States)

    Coffey, P S; Ioppolo-Armanios, M

    2004-01-01

    Alcoa World Alumina Australia has undertaken comprehensive air emissions monitoring aimed at characterising and quantifying the complete range of emissions to the atmosphere from Bayer refining of alumina at its Western Australian refineries. To the best of our knowledge, this project represents the most complete air emissions inventory of a Bayer refinery conducted in the worldwide alumina industry. It adds considerably to knowledge of air emission factors available for use in emissions estimation required under national pollutant release and transfer registers (NPRTs), such as the Toxic Releases Inventory, USA, and the National Pollutant Inventory, Australia. It also allows the preliminary identification of the key chemical components responsible for characteristic alumina refinery odours and the contribution of these components to the quality, or hedonic tone, of the odours. The strength and acceptability of refinery odours to employees and neighbours appears to be dependent upon where and in what proportion the odorous gases have been emitted from the refineries. This paper presents the results of the programme and develops a basis for classifying the odour properties of the key emission sources in the alumina-refining process.

  18. Potline dry scrubbing technology : development of an innovative alumina injection system

    Energy Technology Data Exchange (ETDEWEB)

    Vendette, H. [Solios Environnement Inc., Montreal, PQ (Canada); Moras, A. [Alcoa Canada, Deschambault, PQ (Canada); Dando, N.R. [Alcoa Technical Center, Alcoa Center, PA (United States)

    2006-07-01

    This paper presented the first test results of an innovative approach to alumina dry scrubbers used to capture fluoride emissions coming from aluminium electrolysis potlines. The concept behind the development of the new alumina injection system was also presented. The system was created for primary aluminium producers to recover fluoride compounds that are then recycled in the electrolysis cells of the Hall-Heroult potline. This paper described the relationship that exists between the emissions of gaseous fluoride and the fluoride saturation level of the alumina. An efficient air pollution control device was developed in response to concerns regarding fluoride emissions. The challenges facing the integration of this relation into the development of a new generation of alumina dry scrubber was discussed along with the proposed innovative scheme that challenged conventional industry practices. To validate this innovative approach, Solios in partnership with Alcoa Primary Metals, modified one of the Aluminerie de Deschambault's system by providing new temporary equipment to its operating units and submitting the equipment to several test campaigns. During the first trials of the alumina cascade feeding system, reductions in fluoride emissions were about 50 per cent. Although stack emissions account for only 10 to 20 per cent of the total plant fluoride emissions, and are therefore not the primary source of fluoride emissions, such drastic reductions from potline dry scrubbers should help smelter operators to maintain the lowest possible fluoride emissions year round, even during the hottest summer days. 5 refs., 5 figs.

  19. 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.

  20. Highly-sensitive Detection of Salvianolic Acid B using Alumina Microfibers-modified Electrode

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Dong; Zheng, Xiaoyong; Xie, Xiafeng; Yang, Xiaofeng; Zhang, Huajie [Wenzhou Medical Univ., Wenzhou (China)

    2013-11-15

    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{sup -1} to 0.3 mg L{sup -1}, and the detection limit was 2 μg L{sup -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. Surface modification of nanoporous alumina surfaces with poly(ethylene glycol).

    Science.gov (United States)

    Popat, Ketul C; Mor, Gopal; Grimes, Craig A; Desai, Tejal A

    2004-09-14

    Nanoporous alumina surfaces have a variety of applications in biosensors, biofiltration, and targeted drug delivery. However, the fabrication route to create these nanopores in alumina results in surface defects in the crystal lattice. This results in inherent charge on the porous surface causing biofouling, that is, nonspecific adsorption of biomolecules. Poly(ethylene glycol) (PEG) is known to form biocompatible nonfouling films on silicon surfaces. However, its application to alumina surfaces is very limited and has not been well investigated. In this study, we have covalently attached PEG to nanoporous alumina surfaces to improve their nonfouling properties. A PEG-silane coupling technique was used to modify the surface. Different concentrations of PEG for different immobilization times were used to form PEG films of various grafting densities. X-ray photoelectron spectroscopy (XPS) was used to verify the presence of PEG moieties on the alumina surface. High-resolution C1s spectra show that with an increase in concentration and immobilization time, the grafting density of PEG also increases. Further, a standard overlayer model was used to calculate the thickness of PEG films formed using the XPS intensities of the Al2p peaks. The films formed by this technique are less than 2.5 nm thick, suggesting that such films will not clog the pores which are in the range of 70-80 nm.

  2. Effects of Starch on Properties of Alumina-based Ceramic Cores

    Directory of Open Access Journals (Sweden)

    LI Fengguang

    2016-12-01

    Full Text Available In order to improve the poor leachability of alumina-based ceramic cores, different amount of starch was added to the specimens as pore former. Alumina-based ceramic cores were prepared by hot injection technology using corundum powder as base material, paraffin wax and beeswax as plasticizer, silica powder and magnesium oxide powder as mineralizing agent, wherein the parameters of the hot injection process were as follows:temperature of the slurry was 90℃, hot injection pressure was 0.5 MPa and holding time was 25 s. The effects of starch content on the properties of alumina-based ceramic cores were studied and discussed. The results indicate that during sintering period, the loss of starch in the specimens makes porosity of the alumina-based ceramic cores increase. When starch content increases, the room-temperature flexural strength of the ceramic cores reduces and the apparent porosity increases; the volatile solvent increases and the bulk density decreases. After being sintered at 1560℃ for 2.5 h, room-temperature flexural strength of the alumina-based ceramic cores with starch content of 8%(mass fraction is 24.8 MPa, apparent porosity is 47.98% when the volatile solvent is 1.92 g/h and bulk density is 1.88 g/cm3, the complex properties are optimal.

  3. 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.

  4. Designing robust alumina nanowires-on-nanopores structures: superhydrophobic surfaces with slippery or sticky water adhesion.

    Science.gov (United States)

    Peng, Shan; Tian, Dong; Miao, Xinrui; Yang, Xiaojun; Deng, Wenli

    2013-11-01

    Hierarchical alumina surfaces with different morphologies were fabricated by a simple one-step anodization method. These alumina films were fabricated by a new raw material: silica gel plate (aluminum foil with a low purity of 97.17%). The modulation of anodizing time enabled the formation of nanowires-on-nanopores hybrid nanostructures having controllable nanowires topographies through a self-assembly process. The resultant structures were demonstrated to be able to achieve superhydrophobicity without any hydrophobic coating layer. More interestingly, it is found that the as-prepared superhydrophobic alumina surfaces exhibited high contrast water adhesion. Hierarchical alumina film with nanowire bunches-on-nanopores (WBOP) morphology presents extremely slippery property which can obtain a sliding angle (SA) as low as 1°, nanowire pyramids-on-nanopores (WPOP) structure shows strongly sticky water adhesion with the adhesive ability to support 15 μL inverted water droplet at most. The obtained superhydrophobic alumina surfaces show remarkable mechanical durability even treated by crimping or pressing without impact on the water-repellent performance. Moreover, the created surfaces also show excellent resistivity to ice water, boiling water, high temperature, organic solvent and oil contamination, which could expand their usefulness and efficacy in harsh conditions.

  5. 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.

  6. 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

  7. MECHANICAL BEHAVIOUR OF THERMOPLASTIC STARCH/MONTMORILLONITE/ALUMINA TRIHYDRATE NANOCOMPOSITES

    Directory of Open Access Journals (Sweden)

    FIRNAAZ AHAMED

    2016-09-01

    Full Text Available Thermoplastic starch (TPS is a biodegradable biopolymer that has exhibited great prospects to replace conventional synthetic polymers in commercial applications. However, one of the most critical limitations of TPS is the lack of crucial mechanical properties. This study proposes the novel combination of cassava starch, montmorillonite nanoclay (MMT and alumina trihydrate (ATH in the form of a nanocomposite which is expected to demonstrate improved mechanical properties. The nanocomposites were processed through melt-extrusion in twin-screw extruder where loadings of MMT and ATH were varied between 1 to 6 wt% and 26 to 37 wt%, respectively. The mechanical properties were evaluated through tensile testing according to ASTM D882. The fractured surfaces of the specimens were evaluated using scanning electron microscopy (SEM to further validate the mechanical properties of the nanocomposites. The melt viscosity and processability of the nanocomposites were also evaluated through melt flow index (MFI testing according to ASTM D1238. Presence of MMT and ATH in TPS demonstrated increase in Young’s modulus, maximum tensile stress and decrease in elongation at break up to 57.6 MPa, 5.1 MPa and 39.2%, respectively. In the presence of ATH, increase in loading of MMT continued to improve Young’s modulus and maximum tensile stress while declining elongation at break. Without ATH, MMT was only capable of improving mechanical strength up to a loading of 3 wt% where adverse effects were observed when the loading was further increased to 6 wt%. Increase in loadings of both MMT and ATH, simultaneously were found to depreciate the MFI and thus, the processability of the nanocomposites.

  8. The Effect of Post-grinding Heat Treatment of Alumina and Ag-Cu-Ti Braze Preform Thickness on the Microstructure and Mechanical Properties of Alumina-to-Alumina-Brazed Joints

    Science.gov (United States)

    Kassam, Tahsin Ali; Nadendla, Hari Babu; Ludford, Nicholas; Buisman, Iris

    2016-08-01

    Alumina-to-alumina-brazed joints were formed using 96.0 and 99.7 wt.% Al2O3 and TICUSIL® (68.8Ag-26.7Cu-4.5Ti wt.%) preforms of different thicknesses. Brazing was conducted in a vacuum of 1 × 10-5 mbar at 850 °C for 10 minutes. Joint strengths were evaluated using four-point bend testing and were compared to flexural strengths of standard test bars. Post-grinding heat treatment, performed at 1550 °C for 1 hour, did not affect the average surface roughness or grain size of either grades of alumina but affected their average flexural strengths with a small increase for 96.0 wt.% Al2O3 and a small decrease for 99.7 wt.% Al2O3. As the TICUSIL® preform thickness was increased from 50 to 100 µm, the average strengths of both 96.0 and 99.7 wt.% Al2O3 brazed joints improved. Joints made using 100-µm-thick TICUSIL® preforms predominantly consisted of Cu-Ti phases which formed due to excess Ti in the interlayers and non-uniform Ag-rich outflow. Brazed joints of 96.0 wt.% Al2O3 made using 100-µm-thick TICUSIL® preforms achieved an average joint strength of 238 MPa with consistent failure in the ceramic.

  9. The Effects of Solid Phase Additives on Sintering Properties of Alumina Bioceramic

    Institute of Scientific and Technical Information of China (English)

    WANG Xin-yu; LI Shi-pu; HE Jian-hua; JIANG Xin; LI Jian-hua

    2003-01-01

    In order to reduce the sintering temperature and improve the preparing conditions of alumina bioceramics,the Mg-Zr-Y composite solid phase additives were added into high purity Al2O3 micro-powder by chemical coprecipitation method.The powder was shaped under 200MPa cold isostatic pressure,and then the biscuits were sintered at 1600℃ under normal pressure.The sintered alumina materials were tested and the sintering mechanism was discussed.The results show that physical properties of the material were improved comparatively.The Mg-Zr-Y composite solid additives could promote the sintering of alumina bioceramics and the mechanism is solid phase sintering.

  10. Electric field dependent dielectric response of alumina/silicone oil colloids

    Science.gov (United States)

    Magallon, Louis; Tsui, Stephen

    2014-03-01

    We investigate the dielectric response of a mixture of alumina nanopowder and silicone oil. Frequency and electric field dependent measurements of another insulating colloid, i.e., urea-coated Ba0.8Rb0.4TiO(C2O4)2 nanoparticles immersed in silicone oil, revealed universal dielectric response (UDR) characteristics and, with the application of high voltage, a negative capacitance. Alumina in silicone oil represents a simpler system in which to perform similar dielectric investigation. This colloid is sandwiched in a parallel plate capacitor cell, and the complex impedance is measured via lock-in amplifier at various frequencies and applied dc biases. Furthermore, we will compare and discuss the dielectric behaviors of different sized suspended alumina particles.

  11. Effect of magnesium addition on the wetting of alumina by aluminium

    Science.gov (United States)

    Sangghaleh, Ali; Halali, Mohammad

    2009-07-01

    In this report the wetting behaviour between polycrystalline alumina substrates and molten aluminium doped with magnesium as a wetting agent has been studied using the sessile drop technique. The time required for equilibrium attainment is investigated. To explore the formation of possible phases at the interface, electron microscopic studies along with EDX analysis have been employed. It is found that magnesium reduces the time and temperature required for equilibrium in the Al/Al 2O 3 system. The Al-7 wt% Mg and Al-10 wt% Mg alloys can wet alumina at temperatures as low as 900 °C. It is also found that molten aluminium doped with magnesium can wet polycrystalline alumina at temperatures below 1000 °C. A thin reaction layer was observed at the Al-Mg/Al 2O 3 interface in the present study.

  12. 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.)

  13. 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.

  14. 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.

  15. Recovery of alumina and ferric oxide from Bayer red mud rich in iron by reduction sintering

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-bin; XIAO Wei; LIU Wei; LIU Gui-hua; PENG Zhi-hong; ZHOU Qiu-sheng; QI Tian-gui

    2009-01-01

    A great amount of red mud generated from alumina production by Bayer process not only threatens the environment but also causes waste of secondary resources. High-iron-content red mud from Bayer process was employed to recover alumina and ferric oxide by the process of reduction-sintering, leaching and then magnetic beneficiation. Results of thermodynamic analyses show that ferric oxide should be reduced to Fe if reduction of ferric oxide and formation of sodium aluminate and calcium silicate happen simultaneously. Experimental results indicate that alumina recovery of Bayer red mud can reach 89.71%, and Fe recovery rate and the grade of magnetite concentrate are 60.67% and 61.78%, respectively, under the optimized sintering conditions.

  16. Atomic-scale non-contact AFM studies of alumina supported nanoparticles

    DEFF Research Database (Denmark)

    Jensen, Thomas Nørregaard; Meinander, Kristoffer; Simonsen, Søren Bredmose

    ATOMIC-SCALE NON-CONTACT ATOMIC FORCE STUDIES OF ALUMINA SUPPORTED NANOPARTICLES Thomas N. Jensen, Kristoffer Meinander, Flemming Besenbacher and Jeppe V. Lauritsen Interdisciplinary Nanoscience Center, Aarhus University, DK-8000 Aarhus C, Denmark Heterogeneous catalysis plays a crucial role...... at the nanometre scale [1]. When operated in the so-called non-contact mode (nc-AFM), this technique yields genuine atomic resolution and offers a unique tool for atomic-scale studies of clean surfaces, as well as, nanoparticles and thin films on these surfaces irrespective of the substrate being electrically...... conducting or non-conducting [2]. We use nc-AFM to study the growth, shape and size of nanoparticles on spinel and alumina surfaces. In addition to this, we have grown a transition alumina thin film on a spinel surface in order to characterize such a film as well as studying the catalytic properties...

  17. Photoluminescent behavior of heat-treated porous alumina films formed in malonic acid

    Energy Technology Data Exchange (ETDEWEB)

    Vrublevsky, I., E-mail: vrublevsky@bsuir.edu.by [Department of Micro and Nanoelectronics, Belarusian State University of Informatics and Radioelectronics, 6 Brovka str, Minsk 220013 (Belarus); Jagminas, A. [Institute of Chemistry, A.Gostauto 9, LT-01108 Vilnius (Lithuania); Hemeltjen, S.; Goedel, W.A. [Institut fuer Chemie, Technische Universitaet Chemnitz, D-09107 (Germany)

    2010-01-15

    In the present work IR spectroscopy, electron probe microanalysis (EPMA) and photoluminescence (PL) spectral measurements were applied to study the effect of treatment temperature (T) on compositional and luminescent properties of malonic acid alumina films. Our studies have shown that the heat treatment of anodic alumina films at investigated temperatures from 100 up to 700 deg. C changes their photoluminescence spectra considerably. An increase in T results in the PL intensity growth. When reaching its maximum at 600 deg. C the luminescence intensity then decreases drastically with further T growth. The films heat-treated at 500 and 600 deg. C demonstrate asymmetrical PL band with Gaussian peaks at 437 and 502 nm. We proved that the malonic acid species incorporated into the alumina bulk during the film formation are responsible for photoluminescence band with its peak at 437 nm.

  18. Synthesis of mesoporous alumina using polyvinyl alcohol template as porosity control additive

    Directory of Open Access Journals (Sweden)

    Zoltán Ecsedi

    2007-12-01

    Full Text Available The effects of polyvinyl alcohol (PVA template and calcinations temperatures on the characteristics of the alumina films were investigated. The samples were prepared by sol-gel method using aluminium triisopropylate precursor. The variation of microstructure, pore size and pore volume, were determined by nitrogen adsorption/desorption analysis and the macropore size distribution was determined using mercury porosimetry. TEM and SEM were used to observe the texture of these samples and the particle morphology. Experimental observation after drying and annealing shows that it is possible to produce crack free nanoporous alumina films using polyvinyl alcohol template. The obtained alumina samples have macroporous microstructure (with the average pore diameter dav = 34.9 μm, for sample prepared with 42.5 wt% of PVA addition and annealed at 1000°C with high portion of mesopores (with the average pore diameter Dav = 14.0 nm for the same sample.

  19. 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.

  20. Sintering behavior of alumina-niobium carbide ceramics from polymer-filler mixtures

    Energy Technology Data Exchange (ETDEWEB)

    Acchar, W.; Wolff, D.M.B. [Programa de Doutorado em Engenharia e Ciencia dos Materiais-UFRN, Univ. Federal do Rio Grande do Norte, Natal, RN (Brazil); S. Dantas, A.C. da [Programa de Pos-graduacao em Engenharia Mecanica-UFRN, Univ. Federal do Rio Grande do Norte - Natal, RN (Brazil)

    2003-07-01

    Studies have been developed in the literature to obtain alternative ceramic cutting tools with better properties as tungsten carbide and silicon nitride. Results have showed that the addition of titanium carbide, tungsten carbide or niobium carbide has improved the wear resistance and hardness of alumina. This work presents a study about preparation and characterization of an alumina reinforced with niobium carbide. The composite material is produced using polymer-filler mixtures. Samples with 60 wt.% polysiloxane and a mixture of 40 wt.% of niobium and alumina powder were mixed, uniaxially pressed at 200 C and sintered in flowing argon at 1200 C, 1400 C and 1600 C. The composite materials were characterized by X-ray diffraction (XRD), density measurements, fracture strength and microstructural analysis. The 60 wt% polymer+40 wt% Nb showed the presence of new crystalline phases such as NbC, Nb{sub 5}Si{sub 3} and Nb{sub 3}Si. (orig.)

  1. 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.

  2. 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.

  3. 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, C4H10), 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.

  4. 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.

  5. 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.

  6. Monazite coatings on short alumina fibers using layer-by-layer assembly technique

    Energy Technology Data Exchange (ETDEWEB)

    Li Bo; Shen Liya; Liu Xiaozhen; Zhang Shuihe; Wu Chunfang; Liu Wenjing

    2004-01-15

    Rhabdophane cerous phosphate particles were deposited on short alumina fibers, using an aqueous precursor and layer-by-layer assembly technique. A polyelectrolyte, Na{sup +} salt of poly(acrylic acid), was employed for the surface modification of alumina fibers in the coating process. Subsequent heat treatment caused the transition of the coatings from rhabdophane to monazite. Dense, uniform monazite coatings on the alumina fibers were obtained by multiple coating steps. The precursor phase evolution was studied with differential thermal analysis/thermogravimetric analysis and X-ray diffractometry. The morphology and structure of the coatings were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffractometry. The variables controlling the coating process are discussed.

  7. Alumina supported carbon composite material with exceptionally high defluoridation property from eggshell waste.

    Science.gov (United States)

    Lunge, Sneha; Thakre, Dilip; Kamble, Sanjay; Labhsetwar, Nitin; Rayalu, Sadhana

    2012-10-30

    A new alumina supported carbon composite material called "Eggshell Composite" (EC) was synthesized from eggshell waste as calcium source for selective fluoride adsorption from water. The effect of various synthesis parameters like eggshell (ES): Eggshell membrane (ESM) ratio, aluminium loading, mixing time and calcinations temperature to optimize the synthesis conditions for selective fluoride removal has been studied. It was observed that the synthesis parameters have significant influence on development of EC and in turn on fluoride removal capacity. EC synthesized was characterized for elemental composition, morphology, functionality and textural properties. Results showed that EC obtained from eggshell modified with alumina precursor is more selective and efficient for fluoride removal. Langmuir and Freundlich isotherm were used to obtain ultimate fluoride removal capacity. The calcium and alumina species in EC shows synergistic effect in fluoride adsorption process. Fluoride sorption studies were carried out in synthetic, groundwater and wastewater. EC proved to be a potential, indigenous and economic adsorbent for fluoride removal.

  8. 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).

  9. 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.

  10. Modelling the growth of porous alumina matrix for creating hyperbolic media

    Science.gov (United States)

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

    2016-08-01

    Porous aluminum oxide is a regular self-assembled structure. During anodization it is possible to control nano-parameters of the structure using macroscopic parameters of anodization. Porous alumina films can be used as a template for the creation of hyperbolic media. In this work we consider the anodization process, our model takes into account the influence of layers of aluminum and electrolyte on the rate of growth of aluminum oxide, as well as the effect of surface diffusion. As a result of our model we obtain the minimum distance between centers of alumina pores in the beginning of anodizing process. We also present the results obtained by numerical modelling of hyperbolic media based on porous alumina film.

  11. Superior thermal conductivity of transparent polymer nanocomposites with a crystallized alumina membrane

    Directory of Open Access Journals (Sweden)

    Md. Poostforush

    2014-04-01

    Full Text Available The properties of novel thermoconductive and optically transparent nanocomposites have been reported. The composites were prepared by the impregnation of thermoset resin into crystallized anodic aluminum oxide (AAO. Crystallized AAO synthesized by annealing amorphous AAO membrane at 1200°C. Although through-plane thermal conductivity of nanocomposites improved up to 1.13 W•m–1•K–1 (39 vol% alumina but their transparency was preserved (Tλ550 nm ~ 72%. Integrated annealed alumina phase, low refractive index mismatch between resin and alumina and formation of nano-optical fibers through the membrane resulted in such marvel combination. This report shows a great potential of these types of nanocomposites in ‘heat management’ of lightening devices.

  12. Synthesis of β"-Alumina from Powder Mixtures Using Thermal P lasma Processing

    Science.gov (United States)

    Fukumasa, Osamu; Sakiyama, Satoshi; Esaki, Hirotoshi

    1998-10-01

    Thermal plasma processing, using the plasma jet with high speed and high heat capacity under reduced pressure (generator and the feed ring, and also confirmed that this reactor generates stable plasma jets with high heat capacity for various operation conditions. With the use of this plasma jet reactor, synthesis of thermoelectric materials (β"-alumina) for the Alkali Metal Thermo-Electric Converter (AMTEC) has been studied. Under not only atmospheric pressure but also low pressure, thin-films of β"-alumina are successfully synthesized from the powder mixtures, i.e. α-Al_2O_3, Na_2CO3 and MgO. Powder species ratio, jet temperature, jet power and substrate position affect strongly synthesis of β"-alumina.

  13. 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...

  14. 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.

  15. 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.)

  16. A Numerical Formula for General Prediction of Interface Bonding between Alumina and Aluminum-Containing Alloys

    Directory of Open Access Journals (Sweden)

    Michiko Yoshitake

    2014-01-01

    Full Text Available Interface termination between alumina and aluminum-containing alloys is discussed from a viewpoint of thermodynamics by extending the authors’ previous discussion on the interface termination between alumina and pure metal. A numerical formula to predict interface bonding at alumina-aluminum-containing alloys is proposed. The effectiveness of the formula is examined by extracting information on interface termination from experimental results and first-principle calculations in references. It is revealed that the prediction by the formula agrees quite well with the results reported in the references. According to the formula, a terminating species can be switched from oxygen to aluminum, which had been actually demonstrated experimentally. The formula uses only basic quantities of pure elements and the formation enthalpy of oxides. Therefore it can be applied for most of aluminum-containing alloys in the periodic table and is useful for material screening in developing interfaces with particular functions.

  17. Pore surface fractal analysis of PEG and La(III-doped mesoporous alumina obtained by the sol–gel method

    Directory of Open Access Journals (Sweden)

    TATJANA B. NOVAKOVIĆ

    2010-06-01

    Full Text Available Active porous alumina was prepared via a sol–gel method and subjected to thermal treatment in the temperature range 500–1200 °C. The addition of lanthanum effectively inhibited the surface area loss of the aluminas. Fractal analysis from nitrogen adsorption isotherm was used to study the pore surface roughness of alumina samples with different chemical compositions (PEG, PEG and lanthanum and calcinations conditions in terms of the surface fractal dimension, d. The Mahnke and Mögel (MM model was used to determine the value of d of La(III-doped alumina. Following the MM model, the d value of the activated aluminas increased as the calcination temperature increased from 500 to 700 °C but decreased after calcination at 1000, 1100 and 1200 °C. The addition of polyethylene glycol (PEG 5600 to the boehmite sol reduced the surface fractal of the activated alumina due to the heterogeneous distribution of the pores. With increasing La(III concentration from 0.015 to 0.045 mol La(III/ /mol Al(III, the d value of La-modified alumina samples decreased, indicating a smoother surface. The obtained PEG+La-doped boehmite sol can be used as a precursor dispersion for the deposition of mesoporous alumina coatings on stainless steel foil, by the spray pyrolysis method.

  18. New insights into the active surface species of silver alumina catalysts in the selective catalytic reduction of NO

    NARCIS (Netherlands)

    Korhonen, S.T.; Beale, A.M.; Newton, M.A.; Weckhuysen, B.M.

    2011-01-01

    The performance of silver alumina catalysts and silver aluminate was studied in the selective catalytic reduction (SCR) of NO by propene. The use of boehmite during the impregnation step ensured a strong interaction between the silver species and the alumina surface in the final calcined catalyst.

  19. Making coke a more efficient catalyst in the oxidative dehydrogenation of ethylbenzene using wide-pore transitional aluminas

    NARCIS (Netherlands)

    Zarubina, V.; Nederlof, C.; Linden, B. van der; Kapteijn, F.; Heeres, H.J.; Makkee, M.; Melián-Cabrera, I.

    2014-01-01

    The thermal activation of a silica-stabilized gamma-alumina impacts positively on the oxidative dehydrogenation of ethylbenzene (EB) to styrene (ST). A systematic thermal study reveals that the transition from gamma-alumina into transitional phases at 1050 degrees C leads to an optimal enhancement o

  20. Wear behavior of SiC, Cr{sub 3}C{sub 2} and WC doped alumina

    Energy Technology Data Exchange (ETDEWEB)

    Mindivan, H.; Cimenoglu, H.; Kayali, E.S. [Istanbul Technical Univ., Dept. of Metallurgy and Materials Engineering, Istanbul (Turkey); Bakan, H.I. [Tubitak, MAM, Gebze-Kocaeli (Turkey)

    2004-07-01

    In this study, the wear behavior of the pure and carbide (SiC, Cr{sub 3}C{sub 2}, and WC) doped alumina was investigated. Carbide doping increased the hardness and improved the wear resistance, significantly. WC doped alumina exhibited the highest hardness and wear resistance. (orig.)

  1. Durability of feldspathic veneering ceramic on glass-infiltrated alumina ceramics after long-term thermocycling.

    Science.gov (United States)

    Mesquita, A M M; Ozcan, M; Souza, R O A; Kojima, A N; Nishioka, R S; Kimpara, E T; Bottino, M A

    2010-01-01

    This study compared the bond strength durability of a feldspathic veneering ceramic to glass-infiltrated reinforced ceramics in dry and aged conditions. Disc shaped (thickness: 4 mm, diameter: 4 mm) of glass-infiltrated alumina (In-Ceram Alumina) and glass-infiltrated alumina reinforced by zirconia (In-Ceram Zirconia) core ceramic specimens (N=48, N=12 per groups) were constructed according to the manufacturers' recommendations. Veneering ceramic (VITA VM7) was fired onto the core ceramics using a mold. The core-veneering ceramic assemblies were randomly divided into two conditions and tested either immediately after specimen preparation (Dry) or following 30000 thermocycling (5-55 ºC±1; dwell time: 30 seconds). Shear bond strength test was performed in a universal testing machine (cross-head speed: 1 mm/min). Failure modes were analyzed using optical microscope (x20). The bond strength data (MPa) were analyzed using ANOVA (α=0.05). Thermocycling did not decrease the bond strength results for both In-Ceram Alumina (30.6±8.2 MPa; P=0.2053) and In-Ceram zirconia (32.6±9 MPa; P=0.3987) core ceramic-feldspathic veneering ceramic combinations when compared to non-aged conditions (28.1±6.4 MPa, 29.7±7.3 MPa, respectively). There were also no significant differences between adhesion of the veneering ceramic to either In-Ceram Alumina or In-Ceram Zirconia ceramics (P=0.3289). Failure types were predominantly a mixture of adhesive failure between the veneering and the core ceramic together with cohesive fracture of the veneering ceramic. Long-term thermocycling aging conditions did not impair the adhesion of the veneering ceramic to the glass-infiltrated alumina core ceramics tested.

  2. Defluoridation of water using activated alumina in presence of natural organic matter via response surface methodology.

    Science.gov (United States)

    Samarghandi, Mohammad Reza; Khiadani, Mehdi; Foroughi, Maryam; Zolghadr Nasab, Hasan

    2016-01-01

    Adsorption by activated alumina is considered to be one of the most practiced methods for defluoridation of freshwater. This study was conducted, therefore, to investigate the effect of natural organic matters (NOMs) on the removal of fluoride by activated alumina using response surface methodology. To the authors' knowledge, this has not been previously investigated. Physico-chemical characterization of the alumina was determined by scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), and X-ray diffractometer (XRD). Response surface methodology (RSM) was applied to evaluate the effect of single and combined parameters on the independent variables such as the initial concentration of fluoride, NOMs, and pH on the process. The results revealed that while presence of NOM and increase of pH enhance fluoride adsorption on the activated alumina, initial concentration of fluoride has an adverse effect on the efficiency. The experimental data were analyzed and found to be accurately and reliably fitted to a second-order polynomial model. Under optimum removal condition (fluoride concentration 20 mg/L, NOM concentration 20 mg/L, and pH 7) with a desirability value of 0.93 and fluoride removal efficiency of 80.6%, no significant difference was noticed with the previously reported sequence of the co-exiting ion affinity to activated alumina for fluoride removal. Moreover, aluminum residual was found to be below the recommended value by the guideline for drinking water. Also, the increase of fluoride adsorption on the activated alumina, as NOM concentrations increase, could be due to the complexation between fluoride and adsorbed NOM. Graphical abstract ᅟ.

  3. 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.

  4. Evolution of an alumina-magnesia/self-forming spinel castable. Part II: physico-chemical and mechanical properties

    Directory of Open Access Journals (Sweden)

    Gutiérrez-Campos D.

    1999-01-01

    Full Text Available This study was carried out in conjunction with the investigation, reported in Part I, on the microstructural characteristics of an alumina-spinel castable with several percentages of MgO content. Bulk density and cold crushing strength of samples were evaluated dried and at three fired states (1000, 1200, 1400 °C. Results indicate little influence of MgO additions on physico-chemical properties of the alumina-magnesia/self-forming spinel castable. Characteristics compared with those reported for conventional alumina-spinel castables did not show large difference in values. Therefore, the alumina-magnesia/self-forming spinel castable could be a possible material for substitution of the conventional alumina-spinel castable.

  5. Carbon covered alumina prepared by the pyrolysis of sucrose: A promising support material for the supported Pt-Sn-bimetallic dehydrogenation catalysis

    NARCIS (Netherlands)

    Luo, S.; He, S.; Li, X.R.; Seshan, K.

    2014-01-01

    Sucrose was pyrolyzed on gamma alumina surface to prepare carbon covered alumina (CCA) material. Alumina and CCA supported Pt–Sn catalysts were prepared by the complex impregnation method under vacuum. Dehydrogenation of n-octadecane was performed to study the effect of carbon addition, Pt loading a

  6. Carbon covered alumina prepared by the pyrolysis of sucrose: A promising support material for the supported Pt-Sn-bimetallic dehydrogenation catalysis

    NARCIS (Netherlands)

    Luo, S.; He, Songbo; Li, X.R.; Seshan, Kulathuiyer

    2014-01-01

    Sucrose was pyrolyzed on gamma alumina surface to prepare carbon covered alumina (CCA) material. Alumina and CCA supported Pt–Sn catalysts were prepared by the complex impregnation method under vacuum. Dehydrogenation of n-octadecane was performed to study the effect of carbon addition, Pt loading

  7. Carbon covered alumina prepared by the pyrolysis of sucrose: A promising support material for the supported Pt-Sn-bimetallic dehydrogenation catalysis

    NARCIS (Netherlands)

    Luo, S.; He, Songbo; Li, X.R.; Seshan, Kulathuiyer

    2014-01-01

    Sucrose was pyrolyzed on gamma alumina surface to prepare carbon covered alumina (CCA) material. Alumina and CCA supported Pt–Sn catalysts were prepared by the complex impregnation method under vacuum. Dehydrogenation of n-octadecane was performed to study the effect of carbon addition, Pt loading a

  8. In-situ preparation of polymer-coated alumina nanopowders by chemical vapor synthesis

    Energy Technology Data Exchange (ETDEWEB)

    Schallehn, M.; Winterer, M.; Weirich, T.E.; Hahn, H. [Inst. of Materials Science, Darmstadt Univ. of Technology, Darmstadt (Germany); Keiderling, U. [Hahn-Meitner-Inst., Berlin (Germany)

    2003-01-01

    Nanocrystalline alumina particles coated with polyethylene have been prepared by a two-step chemical vapor synthesis (CVS) process using a hot-wall reactor to synthesize the nanocrystalline alumina core, and a RF plasma reactor for the subsequent polymer coating. The particle radius is about 4 nm, with the radius of the ceramic core being about 2.5 nm and the coating thickness about 1.5 nm. The powders have been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), small-angle neutron scattering (SANS), and high-resolution transmission electron microscopy (HRTEM). (orig.)

  9. 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

    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.......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...

  10. Effective stress reduction in diamond films on alumina by carbon ion implantation

    CERN Document Server

    Fang Zhi Jun; Wang Li; Zhang Wei; Ma Zhe Guo; Zhang Ming

    2002-01-01

    The authors 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

  11. Peptide bond formation of alanine on silica and alumina surfaces as a catalyst

    Science.gov (United States)

    Sánchez Arenillas, M.; Mateo-Martí, E.

    2012-09-01

    Polymerization of amino acids has been important for the origin of life because the peptides may have been the first self-replicating systems. The amino acid concentrations in the oceans may have been too diluted in the early phases of the Earth. The formation of the biopolymers could have been due to the catalytic action of various minerals (such as silica or alumina). Our work is based on the comparison between alumina and silica minerals with and without prior activation of their silanol groups for the formation of peptide bonds using alanina like amino acid which it is the simplest quiral amino acid.

  12. Mechanical properties correlation to processing parameters for advanced alumina based refractories

    Directory of Open Access Journals (Sweden)

    Dimitrijević Marija M.

    2012-01-01

    Full Text Available Alumina based refractories are usually used in metallurgical furnaces and their thermal shock resistance is of great importance. In order to improve thermal shock resistance and mechanical properties of alumina based refractories short ceramic fibers were added to the material. SEM technique was used to compare the microstructure of specimens and the observed images gave the porosity and morphological characteristics of pores in the specimens. Standard compression test was used to determine the modulus of elasticity and compression strength. Results obtained from thermal shock testing and mechanical properties measurements were used to establish regression models that correlated specimen properties to process parameters.

  13. Intense Photoluminescence and Movement of OpticalAbsorption Edge in Alumina Aerogels

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Alumina aerogels with high porosity of nanometer size were prepared from Al, n-butanol andethyl acetoacetate by the sol-gel route and the N2 supercritical extraction drying technique.Optical experiment results showed that for alumina aerogels after annealing at 500℃ for 4 h pneintense blue emission band appeared in the wavelength range of 400 to 800 nm, and the opticalabsorption edge moved from 8.0 eV of coarse grain Al2O3 to 3~5 eV and with increasing theannealing temperature, this luminescence band presented blue shifts. The reasons of these newoptical properties are discussed in detail.

  14. 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.

  15. Significance of structure–property relationship in alumina based porcelain insulators to achieve quality

    Indian Academy of Sciences (India)

    Parvati Ramaswamy; S Vynatheya; S Seetharamu

    2005-12-01

    The catastrophic failures of porcelain insulators in power lines can be minimized by understanding the structure–property relationship that governs the performance. A study addressing the materials aspects has been conducted on alumina based porcelain insulators used in 25 kV railway traction lines. This article asserts the controls exercised by chemical composition, crystalline structural phases and microstructure on the functional reliability and durability of the insulators. Influences of the total alumina, -Al2O3 (corundum) and -quartz contents, microstructural features including morphologies of mullite needles, quartz and corundum grains in the alumino silicate glassy matrix, large inhomogeneities in matrix constituents and composition have been highlighted.

  16. Adsorption of pesticides onto quartz, calcite, kaolinite, and α-alumina

    DEFF Research Database (Denmark)

    Clausen, Liselotte; Fabricius, Ida Lykke; Madsen, L.

    2001-01-01

    adsorption characteristics of selected pesticides. Investigated mineral phases included quartz, calcite, kaolinite, and alpha -alumina. Selected pesticides comprised atrazine (6-chloro-N-2-ethyl-N-4-isopropyl-1,3,5-triazine-2,4-diamine isoproturon [3-(4-isopropyl-phenyl)-1,1-dimethylurea)], mecoprop [(RS)-2...... due to formation of Ca-pesticide-surface complexes. Adsorption of the uncharged pesticides (atrazine and isoproturon) was detected only on kaolinite. The lack of adsorption on alpha -alumina indicates that the uncharged pesticides have a greater affinity for the silanol surface sites (= SiOH) than...

  17. Numerical investigation on friction welding of alumina / AA 6063 T6 joints

    Science.gov (United States)

    Hynes, N. Rajesh Jesudoss; Velu, P. Shenbaga; Tharmaraj, R.; Kumar, R.

    2016-05-01

    Friction welding is the most suitable candidate for joining the dissimilar materials such as AA 6063 T6 alloy/Alumina for critical situations in high temperature and high corrosion resistance applications. In the present work, the numerical simulation was carried out to understand the mechanism of joining of AA 6063 T6 alloy/ Alumina rod by friction welding process. The developed thermo mechanical model is a highly nonlinear due to the interaction between the temperature fields and time dependent of the material properties. The developed numerical tool could be used to predict the temperature distribution, stress, strain and deformation of the dissimilar joints.

  18. Support acidity influence in NiMoS (Nickel and Molybdenum) catalyst for Marlim diesel; Influencia da acidez do suport de catalisadores NiMoS (Niquel e Molibidenio) no hidrotratamento de diesel Marlim

    Energy Technology Data Exchange (ETDEWEB)

    Ferraz, Sheila Guimaraes de Almeida; Zotin, Jose Luiz; Jesus, Anderson Gomes de; Santos, Bruno Martins; Medeiros, Marcus Vinicius Costa [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES)

    2008-07-01

    The specification of diesel points to the reduction of the sulfur content, of the final boiling point, of the density range and increase of the cetane number. These two last properties are directly related with the ability of the hydrotreating catalytic system in promoting the hydrogenation of aromatic structures and ring opening of the naphthenic compounds, which are both associated to low cetane number. In such way, more acidic catalysts, able to promote the cracking of naphthenic structures, should be evaluated for the diesel HDT. Three bifunctional NiMo catalysts with the same metal content, different acidity and similar active phase dispersion were prepared using alumina, silica-alumina and alumina-Y zeolite as supports. These catalysts were evaluated in a micro-reactor unit for diesel HDT aiming to correlate their activity with the support acidity. The alumina and alumina-zeolite supported catalysts presented better performance than the one supported on silica-alumina. NiMo/alumina-zeolite showed higher cetane and density improvement, associated with a slight decrease in the initial boiling point. (author)

  19. Mechanical resistance of the alumina reinforced by Si C nanometric particles; Resistencia mecanica da alumina reforcada por particulas nanometricas de Si C

    Energy Technology Data Exchange (ETDEWEB)

    Borsa, Carlos E. [Sao Carlos Univ., SP (Brazil). Dept. de Engenharia de Materiais; Tood, Richard I. [University of Manchester Inst. of Science and Technology (UMIST), Manchester (United Kingdom); Brook, Richard J. [Oxford Univ. (United Kingdom). Dept. of Materials

    1997-12-31

    The strength behavior of nano sized Si C particles reinforced alumina was investigated. Hot techniques, namely, mechanical mixture of powders and chemical precipitation of the alumina matrix or of the Si C phase, was used to prepare fully dense materials. The results obtained, characterised by SEM and TEM, showed that the microstructure obtained presented great differences in the microstructure, different Al{sub 2} O{sub 3} matrix. Despite these differences in the microstructure, no distinctive variation in the flexure strength was observed. This indicated that the critical flaw presented in all materials was the same and was probably related with surfaces defects, originated from the machining, rather than from the microstructure. The improvement in the flexure strength over the unreinforced Al{sub 2} O{sub 3} was small (around 10%). (author) 7 refs., 2 tabs., 1 fig.

  20. Understanding improved osteoblast behavior on select nanoporous anodic alumina

    Directory of Open Access Journals (Sweden)

    Ni S

    2014-07-01

    Full Text Available Siyu Ni,1 Changyan Li,1 Shirong Ni,2 Ting Chen,1 Thomas J Webster3,4 1College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai, People’s Republic of China; 2Department of Pathophysiology, Wenzhou Medical University, Wenzhou, People’s Republic of China; 3Department of Chemical Engineering, College of Engineering, Northeastern University, Boston, MA, USA; 4Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, Saudi Arabia Abstract: The aim of this study was to prepare different sized porous anodic alumina (PAA and examine preosteoblast (MC3T3-E1 attachment and proliferation on such nanoporous surfaces. In this study, PAA with tunable pore sizes (25 nm, 50 nm, and 75 nm were fabricated by a two-step anodizing procedure in oxalic acid. The surface morphology and elemental composition of PAA were characterized by field emission scanning electron microscopy and X-ray photoelectron spectroscopy analysis. The nanopore arrays on all of the PAA samples were highly regular. X-ray photoelectron spectroscopy analysis suggested that the chemistry of PAA and flat aluminum surfaces were similar. However, contact angles were significantly greater on all of the PAA compared to flat aluminum substrates, which consequently altered protein adsorption profiles. The attachment and proliferation of preosteoblasts were determined for up to 7 days in culture using field emission scanning electron microscopy and a Cell Counting Kit-8. Results showed that nanoporous surfaces did not enhance initial preosteoblast attachment, whereas preosteoblast proliferation dramatically increased when the PAA pore size was either 50 nm or 75 nm compared to all other samples (P<0.05. Thus, this study showed that one can alter surface energy of aluminum by modifying surface nano-roughness alone (and not changing chemistry through an anodization process to improve osteoblast density, and, thus, should be