Abstract Zinc oxide containing either Ni or Co dopants in various proportions has been investigated. Only zincite phase was found by XRD analysis. Incorporation of Ni or Co into the ZnO structure resulted in a marked shift in the XRD peaks. Remarkable microstructural uniformity was obtained by the addition of 1 mol-% of either Ni or Co oxides. Densification was achieved through atomic diffusion along grain boundaries. All samples showed non-linear I–V dependence. Ni concentration had a non-monotonic effect on breakdown voltage and the non-linear coefficient decreased with increasing Ni content. In contrast, breakdown voltage and non-linear coefficient increased with increasing CoO content.
{"title":"Nickel or cobalt doped zinc oxide varistors","authors":"H. I. Saleh, E. El-Meliegy","doi":"10.1179/096797804X4600","DOIUrl":"https://doi.org/10.1179/096797804X4600","url":null,"abstract":"Abstract Zinc oxide containing either Ni or Co dopants in various proportions has been investigated. Only zincite phase was found by XRD analysis. Incorporation of Ni or Co into the ZnO structure resulted in a marked shift in the XRD peaks. Remarkable microstructural uniformity was obtained by the addition of 1 mol-% of either Ni or Co oxides. Densification was achieved through atomic diffusion along grain boundaries. All samples showed non-linear I–V dependence. Ni concentration had a non-monotonic effect on breakdown voltage and the non-linear coefficient decreased with increasing Ni content. In contrast, breakdown voltage and non-linear coefficient increased with increasing CoO content.","PeriodicalId":350675,"journal":{"name":"British Ceramic Transactions","volume":"133 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124275617","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}
Abstract The electrical properties of Ba1–xSrxSn0·15Ti0·85O3 (BSST) (x=0, 0·03, 0·06, 0·09) ceramics synthesised by the precursor solution method were investigated by impedance spectroscopy in the temperature range from room temperature to 500°C. SEM micrographs show the grain distribution. Nyquist plots reveal the presence of a bulk effect for x=0 and of bulk and grain boundary effects for x=0·03, 0·06 and 0·09. Variation in bulk ac conductivity as a function of frequency demonstrates that the compounds exhibit Arrhenius type electrical conductivity. The ac activation energy increases with increasing Sr concentration.
{"title":"Impedance spectroscopy of Ba1–xSrxSn0·15Ti0·85O3 ceramics","authors":"S. Sen, R. Choudhary, P. Pramanik","doi":"10.1179/096797804X4196","DOIUrl":"https://doi.org/10.1179/096797804X4196","url":null,"abstract":"Abstract The electrical properties of Ba1–xSrxSn0·15Ti0·85O3 (BSST) (x=0, 0·03, 0·06, 0·09) ceramics synthesised by the precursor solution method were investigated by impedance spectroscopy in the temperature range from room temperature to 500°C. SEM micrographs show the grain distribution. Nyquist plots reveal the presence of a bulk effect for x=0 and of bulk and grain boundary effects for x=0·03, 0·06 and 0·09. Variation in bulk ac conductivity as a function of frequency demonstrates that the compounds exhibit Arrhenius type electrical conductivity. The ac activation energy increases with increasing Sr concentration.","PeriodicalId":350675,"journal":{"name":"British Ceramic Transactions","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114506161","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}
Abstract There has been a surge of interest in polymer–clay nanocomposites over the past decade. This review surveys these new materials with emphasis on the debate surrounding interaction mechanisms and the behaviour of intercalated polymer in clay galleries. Swelling properties, high cation exchange capacities, high aspect ratio and large surface area give smectite clays the new role of high performance filler for thermoplastic or thermosetting polymers for the creation of intercalated or exfoliated nanocomposites. These nanocomposites can be prepared by three routes: in situ polymerisation, solution methods, or melt processing. Modification of either clay or polymer can change the type of polymer–clay composite. X-ray diffraction and transmission electron microscopy are often employed as the main characterisation techniques to establish the state of the clay. A very low volume fraction of clay significantly improves the mechanical and barrier properties of the pristine polymer, which makes these nanocomposites very promising materials.
{"title":"Polymer–clay nanocomposites: an overview with emphasis on interaction mechanisms","authors":"Biqiong Chen","doi":"10.1179/096797804X4592","DOIUrl":"https://doi.org/10.1179/096797804X4592","url":null,"abstract":"Abstract There has been a surge of interest in polymer–clay nanocomposites over the past decade. This review surveys these new materials with emphasis on the debate surrounding interaction mechanisms and the behaviour of intercalated polymer in clay galleries. Swelling properties, high cation exchange capacities, high aspect ratio and large surface area give smectite clays the new role of high performance filler for thermoplastic or thermosetting polymers for the creation of intercalated or exfoliated nanocomposites. These nanocomposites can be prepared by three routes: in situ polymerisation, solution methods, or melt processing. Modification of either clay or polymer can change the type of polymer–clay composite. X-ray diffraction and transmission electron microscopy are often employed as the main characterisation techniques to establish the state of the clay. A very low volume fraction of clay significantly improves the mechanical and barrier properties of the pristine polymer, which makes these nanocomposites very promising materials.","PeriodicalId":350675,"journal":{"name":"British Ceramic Transactions","volume":"82 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129424395","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}
J. Ma, X.-P. Lin, Zhenhua Xie, H. Miao, B. Zhang, Yi-Bing Cheng
Abstract Aqueous gelcasting with a low toxicity monomer system has attracted increasing attention. The present study attempts to enhance the flexural strength of green bodies gelcast from a low toxicity hydroxyethyl methacrylate (HEMA) system by introducing an appropriate amount of the water soluble polymer polyvinylpyrrolidone (PVP). The rheological properties and gelling characteristics of PVP–HEMA/Al2O3 suspensions were examined. In addition, the flexural strength and microstructure of the gelcast green and sintered bodies are discussed.
{"title":"Gelcasting of alumina ceramic in mixed PVP–HEMA systems","authors":"J. Ma, X.-P. Lin, Zhenhua Xie, H. Miao, B. Zhang, Yi-Bing Cheng","doi":"10.1179/096797804X4583","DOIUrl":"https://doi.org/10.1179/096797804X4583","url":null,"abstract":"Abstract Aqueous gelcasting with a low toxicity monomer system has attracted increasing attention. The present study attempts to enhance the flexural strength of green bodies gelcast from a low toxicity hydroxyethyl methacrylate (HEMA) system by introducing an appropriate amount of the water soluble polymer polyvinylpyrrolidone (PVP). The rheological properties and gelling characteristics of PVP–HEMA/Al2O3 suspensions were examined. In addition, the flexural strength and microstructure of the gelcast green and sintered bodies are discussed.","PeriodicalId":350675,"journal":{"name":"British Ceramic Transactions","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122107229","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}
Abstract The aim of this work was to study the effect of Nd3+ doping on the structural, dielectric and electrical properties of Pb(SnTi)O3 ceramics, to give materials with the general formula (Pb1–xNdx)(Sn0·45Ti0·55)1–x/4O3(x=0, 0·05, 0·07, 0·1). These materials were synthesised using a conventional high temperature solid state reaction technique. X-ray diffraction studies at room tempera- ture revealed orthorhombic symmetry, and uniform grain size distribution throughout the surface of the samples for x=0·05–0·1 was observed by SEM. Study of the dielectric behaviour of compounds as a function of temperature shows that with increasing concentration of Nd3+ the dielectric constant maximum decreases; transition temperature Tc shifts to lower temperatures for x=0–0·07 but increases again at x=0·1. It is observed that at each concentration of Nd3+ the dielectric constant ϵ′ reaches a maximum at the same Curie temperature for all three test frequencies (1, 10, 100 kHz), which reveals the non-relaxor ferroelectric behaviour of these materials.
{"title":"Effect of Nd doping on structural, dielectric and electrical properties of Pb(SnTi)O3 ferroelectric ceramics","authors":"B. Das, R. Choudhary, P. Mahapatra","doi":"10.1179/096797804X4565","DOIUrl":"https://doi.org/10.1179/096797804X4565","url":null,"abstract":"Abstract The aim of this work was to study the effect of Nd3+ doping on the structural, dielectric and electrical properties of Pb(SnTi)O3 ceramics, to give materials with the general formula (Pb1–xNdx)(Sn0·45Ti0·55)1–x/4O3(x=0, 0·05, 0·07, 0·1). These materials were synthesised using a conventional high temperature solid state reaction technique. X-ray diffraction studies at room tempera- ture revealed orthorhombic symmetry, and uniform grain size distribution throughout the surface of the samples for x=0·05–0·1 was observed by SEM. Study of the dielectric behaviour of compounds as a function of temperature shows that with increasing concentration of Nd3+ the dielectric constant maximum decreases; transition temperature Tc shifts to lower temperatures for x=0–0·07 but increases again at x=0·1. It is observed that at each concentration of Nd3+ the dielectric constant ϵ′ reaches a maximum at the same Curie temperature for all three test frequencies (1, 10, 100 kHz), which reveals the non-relaxor ferroelectric behaviour of these materials.","PeriodicalId":350675,"journal":{"name":"British Ceramic Transactions","volume":"50 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121905117","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 : 2004-10-01DOI: 10.1179/096797804225018697
K. Tan, A. Olofinjana
Abstract Samples of naturally occurring mudstone clay fired at temperatures higher than 1150°C exhibited unusual swelling, with localised densification and glassy shell and apparent bulk density of about 700 kg m-3. The swelling was a result of the development of a foam type macroporous structure during sintering. Thermal analysis indicated that the development of the foam structure started at around 1150°C, and that it was not accompanied by any detectable mass change. A combination of thermal analysis and X-ray diffraction data suggest that macroporosity developed as a result of volumetric expansion accompanying thermally induced vitrification of the starting crystalline phases. It is believed that the transition to amorphous phase leads to release of structurally locked water molecules, which at high temperature behave as supercritical steam and act as a porogenic agent.
在高于1150°C的温度下烧制的天然泥岩粘土样品表现出异常的膨胀，具有局部致密化和玻璃壳，表观容重约为700 kg m-3。膨胀是在烧结过程中形成泡沫型大孔结构的结果。热分析表明，泡沫结构的发展始于1150°C左右，并且没有伴随着任何可检测的质量变化。热分析和x射线衍射数据的结合表明，大孔隙的形成是伴随着初始晶相的热诱导玻璃化的体积膨胀的结果。人们认为，向非晶相的转变导致结构锁定的水分子的释放，这些水分子在高温下表现为超临界蒸汽并起致孔剂的作用。
{"title":"Evolution of macroporosity in fired mudstone clay","authors":"K. Tan, A. Olofinjana","doi":"10.1179/096797804225018697","DOIUrl":"https://doi.org/10.1179/096797804225018697","url":null,"abstract":"Abstract Samples of naturally occurring mudstone clay fired at temperatures higher than 1150°C exhibited unusual swelling, with localised densification and glassy shell and apparent bulk density of about 700 kg m-3. The swelling was a result of the development of a foam type macroporous structure during sintering. Thermal analysis indicated that the development of the foam structure started at around 1150°C, and that it was not accompanied by any detectable mass change. A combination of thermal analysis and X-ray diffraction data suggest that macroporosity developed as a result of volumetric expansion accompanying thermally induced vitrification of the starting crystalline phases. It is believed that the transition to amorphous phase leads to release of structurally locked water molecules, which at high temperature behave as supercritical steam and act as a porogenic agent.","PeriodicalId":350675,"journal":{"name":"British Ceramic Transactions","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131897359","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}
Abstract A mixture of Al2O3 and GdAlO3 was melted and rapid quenched to produce an amorphous film. Dense eutectic composites were consolidated from ground amorphous powder using both conventional and spark plasma sintering (SPS). Conventional sintering at temperatures above 1600°C for 24 h was required for complete sintering. However, using SPS complete sintering could be obtained at temperatures between 1300 and 1500°C with no soaking. The SPS technique could consolidate ultrafine eutectic structure from rapid quenched amorphous material, whilst conventional sintering was not successful owing to grain growth. A combination of rapid quenching and SPS resulted in an ultrafine eutectic Al2O3–GdAlO3 structure.
{"title":"Eutectic Al2O3–GdAlO3 composite consolidated by combined rapid quenching and spark plasma sintering technique","authors":"Young-Hwan Han, M. Nagata, N. Uekawa, K. Kakegawa","doi":"10.1179/096797804X4231","DOIUrl":"https://doi.org/10.1179/096797804X4231","url":null,"abstract":"Abstract A mixture of Al2O3 and GdAlO3 was melted and rapid quenched to produce an amorphous film. Dense eutectic composites were consolidated from ground amorphous powder using both conventional and spark plasma sintering (SPS). Conventional sintering at temperatures above 1600°C for 24 h was required for complete sintering. However, using SPS complete sintering could be obtained at temperatures between 1300 and 1500°C with no soaking. The SPS technique could consolidate ultrafine eutectic structure from rapid quenched amorphous material, whilst conventional sintering was not successful owing to grain growth. A combination of rapid quenching and SPS resulted in an ultrafine eutectic Al2O3–GdAlO3 structure.","PeriodicalId":350675,"journal":{"name":"British Ceramic Transactions","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123748140","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}
Abstract Low fusion fluorophlogopite–leucite containing porcelain was prepared for use in dental restorations without metal substrates. Simultaneous crystallisation of fluorophlogopite and leucite phases with uniform evenly dispersed grains was achieved. Platy mica crystals and tetragonal leucite colonies crystallised in the porcelain to add strength through reinforcement of the glassy matrix. Further, chemical composition and the crystallisation process were regulated to avoid the formation of a parasitic forsterite phase. Crystallisation of fluorophlogopite begins at 620°C and of leucite at 750°C. Optimum crystallisation of the leucite–mica phase mixture in the porcelain was realised on heating between 850–930°C for 5–15 min.
{"title":"Low fusion fluorophlogopite–leucite containing porcelain","authors":"E. El-Meliegy","doi":"10.1179/096797804X4222","DOIUrl":"https://doi.org/10.1179/096797804X4222","url":null,"abstract":"Abstract Low fusion fluorophlogopite–leucite containing porcelain was prepared for use in dental restorations without metal substrates. Simultaneous crystallisation of fluorophlogopite and leucite phases with uniform evenly dispersed grains was achieved. Platy mica crystals and tetragonal leucite colonies crystallised in the porcelain to add strength through reinforcement of the glassy matrix. Further, chemical composition and the crystallisation process were regulated to avoid the formation of a parasitic forsterite phase. Crystallisation of fluorophlogopite begins at 620°C and of leucite at 750°C. Optimum crystallisation of the leucite–mica phase mixture in the porcelain was realised on heating between 850–930°C for 5–15 min.","PeriodicalId":350675,"journal":{"name":"British Ceramic Transactions","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128306542","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}
Abstract Mixed conducting anode materials for solid oxide fuel cells are desirable in order to extend the electron transfer reaction zone for fuel gas conversion and to minimise the nickel content for achieving a redox stable anode. Partial substitution by titania in yttria stabilised zirconia (YSZ) is known to increase the electronic conductivity in reducing atmospheres. Nine different compositions were selected from the quasi ternary phase diagram according to principles used in statistical design of experiments covering the whole stoichiometric regime relevant for ionic applications. The dc electrical conductivity values increase strongly with high Ti contents under reducing (Ar–4%H2) conditions, whereas they decrease continuously with increasing Ti content under oxidising conditions (air). The results clearly show that the chosen screening process for materials selection can considerably reduce the number of samples. For solid oxide fuel cell anodes, the compositions in the YO1.5–ZrO2–TiO2 system should be restricted to low Ti contents.
{"title":"Statistical design of experiments for evaluation of Y–Zr–Ti oxides as anode materials in solid oxide fuel cells","authors":"F. Tietz, I. Arul Raj, D. Stöver","doi":"10.1179/096797804X4213","DOIUrl":"https://doi.org/10.1179/096797804X4213","url":null,"abstract":"Abstract Mixed conducting anode materials for solid oxide fuel cells are desirable in order to extend the electron transfer reaction zone for fuel gas conversion and to minimise the nickel content for achieving a redox stable anode. Partial substitution by titania in yttria stabilised zirconia (YSZ) is known to increase the electronic conductivity in reducing atmospheres. Nine different compositions were selected from the quasi ternary phase diagram according to principles used in statistical design of experiments covering the whole stoichiometric regime relevant for ionic applications. The dc electrical conductivity values increase strongly with high Ti contents under reducing (Ar–4%H2) conditions, whereas they decrease continuously with increasing Ti content under oxidising conditions (air). The results clearly show that the chosen screening process for materials selection can considerably reduce the number of samples. For solid oxide fuel cell anodes, the compositions in the YO1.5–ZrO2–TiO2 system should be restricted to low Ti contents.","PeriodicalId":350675,"journal":{"name":"British Ceramic Transactions","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2004-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133117361","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：