Pub Date : 1988-11-01DOI: 10.1111/J.1551-2916.1988.TB00289.X
M. Borom, R. Bolon, M. Brun
The oxidation of silicide carbide dispersed phases in oxide matrices has been shown to proceed by oxygen diffusion. Silica formed by the reaction of oxygen with silicon can react with the matrix oxide to form a silicate, which may control the rate of diffusion of oxygen to the reaction interface. Two dispersed phase systems with compositionally similar reaction products, but with distinctly different activation energies for diffusion, have been studied to elucidate the oxidation mechanism. The oxidation of SiC particulates with the liberation of CO gas was found to occur totally at the reaction-product/bulk-material interface. The oxidation of MoSi{sub 2} particulates was found to occur in three stages represented by three zones in the reaction product. Mechanical separation of phases was observed to occur with the silicide dispersion because of the extrusion of the viscous silicate to the surface via gaseous evolution.
{"title":"Oxidation mechanism of MoSi sub 2 particles dispersed in mullite","authors":"M. Borom, R. Bolon, M. Brun","doi":"10.1111/J.1551-2916.1988.TB00289.X","DOIUrl":"https://doi.org/10.1111/J.1551-2916.1988.TB00289.X","url":null,"abstract":"The oxidation of silicide carbide dispersed phases in oxide matrices has been shown to proceed by oxygen diffusion. Silica formed by the reaction of oxygen with silicon can react with the matrix oxide to form a silicate, which may control the rate of diffusion of oxygen to the reaction interface. Two dispersed phase systems with compositionally similar reaction products, but with distinctly different activation energies for diffusion, have been studied to elucidate the oxidation mechanism. The oxidation of SiC particulates with the liberation of CO gas was found to occur totally at the reaction-product/bulk-material interface. The oxidation of MoSi{sub 2} particulates was found to occur in three stages represented by three zones in the reaction product. Mechanical separation of phases was observed to occur with the silicide dispersion because of the extrusion of the viscous silicate to the surface via gaseous evolution.","PeriodicalId":7260,"journal":{"name":"Advanced Ceramic Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82793566","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1988-11-01DOI: 10.1111/J.1551-2916.1988.TB00285.X
R. Hoeppener, H. Bowen
Submicrometer, equiaxed, spherical silica particles with a low surface area and high density were synthesized by the controlled hydrolysis of SiCl{sub 4} with water. Two approaches were used: low-temperature synthesis in acetonitrile ({minus}20{degree}C, 10 {times} surplus of water) and synthesis in a water-in-hexane emulsion (10{degree}C, stoichiometric amounts of water). The yield of spherical powder synthesized in acetonitrile was 29% and in the water-in-hexane emulsion, 84%.
{"title":"Dense silica spheres produced by reacting SiCl sub 4 with water","authors":"R. Hoeppener, H. Bowen","doi":"10.1111/J.1551-2916.1988.TB00285.X","DOIUrl":"https://doi.org/10.1111/J.1551-2916.1988.TB00285.X","url":null,"abstract":"Submicrometer, equiaxed, spherical silica particles with a low surface area and high density were synthesized by the controlled hydrolysis of SiCl{sub 4} with water. Two approaches were used: low-temperature synthesis in acetonitrile ({minus}20{degree}C, 10 {times} surplus of water) and synthesis in a water-in-hexane emulsion (10{degree}C, stoichiometric amounts of water). The yield of spherical powder synthesized in acetonitrile was 29% and in the water-in-hexane emulsion, 84%.","PeriodicalId":7260,"journal":{"name":"Advanced Ceramic Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79314084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1988-11-01DOI: 10.1111/J.1551-2916.1988.TB00287.X
J. K. Walker
TiB{sub 2} powder can be produced by the reaction of TiO{sub 2} with B{sub 4}C. The reaction proceeds first by a borothermic reduction, producing TiB{sub 2}, TiBO{sub 3}, B{sub 2}O{sub 3}, and carbon. A high-temperature carbothermic process completes the reaction. Excess B{sub 2}O{sub 3} can bee removed by either evaporation or reduction to a volatile oxide, depending on firing conditions. Because of the mechanisms involved in B{sub 2}O{sub 3} removal, the final TiB{sub 2} purity is insensitive to the stoichiometry of the initial precursor blend.
{"title":"Synthesis of TiB sub 2 by the borothermic/carbothermic reduction of TiO sub 2 with B sub 4 C","authors":"J. K. Walker","doi":"10.1111/J.1551-2916.1988.TB00287.X","DOIUrl":"https://doi.org/10.1111/J.1551-2916.1988.TB00287.X","url":null,"abstract":"TiB{sub 2} powder can be produced by the reaction of TiO{sub 2} with B{sub 4}C. The reaction proceeds first by a borothermic reduction, producing TiB{sub 2}, TiBO{sub 3}, B{sub 2}O{sub 3}, and carbon. A high-temperature carbothermic process completes the reaction. Excess B{sub 2}O{sub 3} can bee removed by either evaporation or reduction to a volatile oxide, depending on firing conditions. Because of the mechanisms involved in B{sub 2}O{sub 3} removal, the final TiB{sub 2} purity is insensitive to the stoichiometry of the initial precursor blend.","PeriodicalId":7260,"journal":{"name":"Advanced Ceramic Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73738798","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1988-11-01DOI: 10.1111/J.1551-2916.1988.TB00278.X
K. Nickel, M. Hoffmann, P. Greil, G. Petzow
Thermodynamic equilibria were calculated to determine optimum fabrication conditions for SiC-whisker-reinforced Si{sub 3}N{sub 4} composite ceramics. Results of calculations indicate that pressureless sintering in a nitrogen atmosphere of 0.1 MPa may be performed at temperatures up to 2,123 K (1,850{degree}C) without whisker or matrix degradation. In addition, gas pressure sintering at temperatures up to 2,373 K (2,100{degree}C) requires a nitrogen pressure of 1 to 10 MPa. Hot isostatic pressing (total pressure {ge} 100 MPa) at 2,273 K (2,000{degree}C) can yield undegraded composite materials only when the nitrogen partial pressure in a gas mixture with an inert gas is kept between 1 to 10 MPa.
{"title":"Thermodynamic calculations for the formation of SiC-whisker-reinforced Si sub 3 N sub 4 ceramics","authors":"K. Nickel, M. Hoffmann, P. Greil, G. Petzow","doi":"10.1111/J.1551-2916.1988.TB00278.X","DOIUrl":"https://doi.org/10.1111/J.1551-2916.1988.TB00278.X","url":null,"abstract":"Thermodynamic equilibria were calculated to determine optimum fabrication conditions for SiC-whisker-reinforced Si{sub 3}N{sub 4} composite ceramics. Results of calculations indicate that pressureless sintering in a nitrogen atmosphere of 0.1 MPa may be performed at temperatures up to 2,123 K (1,850{degree}C) without whisker or matrix degradation. In addition, gas pressure sintering at temperatures up to 2,373 K (2,100{degree}C) requires a nitrogen pressure of 1 to 10 MPa. Hot isostatic pressing (total pressure {ge} 100 MPa) at 2,273 K (2,000{degree}C) can yield undegraded composite materials only when the nitrogen partial pressure in a gas mixture with an inert gas is kept between 1 to 10 MPa.","PeriodicalId":7260,"journal":{"name":"Advanced Ceramic Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80957941","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1988-11-01DOI: 10.1111/J.1551-2916.1988.TB00286.X
M. Rajaram, T. Tsai, E. Friebele
The surface deformation induced in various low-thermal-expansion glasses and glass-ceramics by 2-MeV electron irradiation was measured and found to be significantly greater in the glass-ceramics. Sublinear growth of the deformation occurred at doses > 10{sup 7} rd; the deformation decreased with increasing sample thickness for a given dose. Temperatures > 500{degree}C were required to fully anneal the deformation in all samples.
{"title":"Radiation-induced surface deformation in low-thermal-expansion glasses and glass-ceramics","authors":"M. Rajaram, T. Tsai, E. Friebele","doi":"10.1111/J.1551-2916.1988.TB00286.X","DOIUrl":"https://doi.org/10.1111/J.1551-2916.1988.TB00286.X","url":null,"abstract":"The surface deformation induced in various low-thermal-expansion glasses and glass-ceramics by 2-MeV electron irradiation was measured and found to be significantly greater in the glass-ceramics. Sublinear growth of the deformation occurred at doses > 10{sup 7} rd; the deformation decreased with increasing sample thickness for a given dose. Temperatures > 500{degree}C were required to fully anneal the deformation in all samples.","PeriodicalId":7260,"journal":{"name":"Advanced Ceramic Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80626119","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1988-11-01DOI: 10.1111/J.1551-2916.1988.TB00284.X
C. Lim, T. Iseki
Quantitative characterization of the microstructure of reaction-sintered SiC bodies prepared under various conditions was performed experimentally to observe the formation and transportation of both intergranular fine-grained and nodular fine-grained {beta}-SiC. The results showed that, by lowering the sintering temperature (min. {approx} 1,420{degree}C), the quantity of {beta}-SiC increased progressively from the outside of the specimen toward its center. However, the {beta}-SiC was almost completely transported onto the larger grain through liquid Si at 1,600{degree}C under vacuum. It was concluded that the formation of the fine-grained {beta}-SiC was due to the higher degree of supersaturation in the lower temperature outer region of the specimen.
{"title":"Formation and transportation of intergranular and nodular fine-grained. beta. -SiC in reaction-sintered SiC","authors":"C. Lim, T. Iseki","doi":"10.1111/J.1551-2916.1988.TB00284.X","DOIUrl":"https://doi.org/10.1111/J.1551-2916.1988.TB00284.X","url":null,"abstract":"Quantitative characterization of the microstructure of reaction-sintered SiC bodies prepared under various conditions was performed experimentally to observe the formation and transportation of both intergranular fine-grained and nodular fine-grained {beta}-SiC. The results showed that, by lowering the sintering temperature (min. {approx} 1,420{degree}C), the quantity of {beta}-SiC increased progressively from the outside of the specimen toward its center. However, the {beta}-SiC was almost completely transported onto the larger grain through liquid Si at 1,600{degree}C under vacuum. It was concluded that the formation of the fine-grained {beta}-SiC was due to the higher degree of supersaturation in the lower temperature outer region of the specimen.","PeriodicalId":7260,"journal":{"name":"Advanced Ceramic Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75670415","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1988-11-01DOI: 10.1111/J.1551-2916.1988.TB00283.X
Luchen Hwan, W. Willis, S. Suib, F. Galasso
{"title":"Synthesis and Characterization of SiC-Reinforced Silicon Composites Produced by Chemical Vapor Deposition","authors":"Luchen Hwan, W. Willis, S. Suib, F. Galasso","doi":"10.1111/J.1551-2916.1988.TB00283.X","DOIUrl":"https://doi.org/10.1111/J.1551-2916.1988.TB00283.X","url":null,"abstract":"","PeriodicalId":7260,"journal":{"name":"Advanced Ceramic Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75725446","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1988-11-01DOI: 10.1111/J.1551-2916.1988.TB00279.X
M. I. Osendi, B. Bender, D. Lewis
Two zirconia-toughened aluminas, one with a small addition of titanium dioxide, have been studied to determine their mechanical behavior between room temperature and 1,300{degree}C. Room-temperature fracture toughness and bend strength were also determined in samples aged at 1,00{degree}C for 720 h. Results show that the titania addition enhances the inelastic behavior of the composite at 1,300{degree}C. Segregation of Ti on alumina grain boundaries was also measured.
{"title":"Influence of TiO sub 2 on the mechanical properties at high temperature of zirconia-toughened alumina","authors":"M. I. Osendi, B. Bender, D. Lewis","doi":"10.1111/J.1551-2916.1988.TB00279.X","DOIUrl":"https://doi.org/10.1111/J.1551-2916.1988.TB00279.X","url":null,"abstract":"Two zirconia-toughened aluminas, one with a small addition of titanium dioxide, have been studied to determine their mechanical behavior between room temperature and 1,300{degree}C. Room-temperature fracture toughness and bend strength were also determined in samples aged at 1,00{degree}C for 720 h. Results show that the titania addition enhances the inelastic behavior of the composite at 1,300{degree}C. Segregation of Ti on alumina grain boundaries was also measured.","PeriodicalId":7260,"journal":{"name":"Advanced Ceramic Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75219176","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1988-11-01DOI: 10.1111/J.1551-2916.1988.TB00290.X
Sheng-Wei Lin, K. Kao
The resistivity of BaTiO{sub 3}-based, positive-temperature-coefficient (PTC) ceramic materials is not significantly affected by applied magnetic fields at temperatures below the Curie temperature, {Tc}, but it increases with increasing magnetic field when temperatures exceed {Tc}. The rate of this increase diminishes gradually as the magnetic field is further increased. The magnetic field effects are stronger for magnetic fields parallel to than transverse to the electric current flow. A brief discussion of the experimental results is given.
{"title":"Galvanomagnetic effects in BaTiO sub 3 -based, PTC ceramic materials","authors":"Sheng-Wei Lin, K. Kao","doi":"10.1111/J.1551-2916.1988.TB00290.X","DOIUrl":"https://doi.org/10.1111/J.1551-2916.1988.TB00290.X","url":null,"abstract":"The resistivity of BaTiO{sub 3}-based, positive-temperature-coefficient (PTC) ceramic materials is not significantly affected by applied magnetic fields at temperatures below the Curie temperature, {Tc}, but it increases with increasing magnetic field when temperatures exceed {Tc}. The rate of this increase diminishes gradually as the magnetic field is further increased. The magnetic field effects are stronger for magnetic fields parallel to than transverse to the electric current flow. A brief discussion of the experimental results is given.","PeriodicalId":7260,"journal":{"name":"Advanced Ceramic Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73500656","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1988-11-01DOI: 10.1111/J.1551-2916.1988.TB00280.X
L. Wong, S. Laurich-McIntyre, R. Bradt
Annealing an aluminosilicate ceramic modified the strength distribution by creating a threshold strength level, which was readily observed on a Weibull plot. The threshold strength appeared to develop through surface-defect healing or modification and was maximized for annealing at 1,200{degree}C. It deteriorated for higher temperature annealing heat treatments, coincident with the extensive growth of large mullite crystals within the microstructure.
{"title":"Development of a threshold strength in an aluminosilicate ceramic by annealing","authors":"L. Wong, S. Laurich-McIntyre, R. Bradt","doi":"10.1111/J.1551-2916.1988.TB00280.X","DOIUrl":"https://doi.org/10.1111/J.1551-2916.1988.TB00280.X","url":null,"abstract":"Annealing an aluminosilicate ceramic modified the strength distribution by creating a threshold strength level, which was readily observed on a Weibull plot. The threshold strength appeared to develop through surface-defect healing or modification and was maximized for annealing at 1,200{degree}C. It deteriorated for higher temperature annealing heat treatments, coincident with the extensive growth of large mullite crystals within the microstructure.","PeriodicalId":7260,"journal":{"name":"Advanced Ceramic Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"1988-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77791663","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：