高铝瓷中二次莫来石对电瓷强度的影响

研究了铝氧原料种类及长石用量对铝质高强度电瓷中二次莫来石结晶形态的影响。结果表明:以工业氧化铝为原料时易形成颗粒状二次莫来石,以铝矾土为原料时有利于形成针状莫来石,用部分工业氧化铝替代铝矾土则可改善二次莫来石的网状结构,显著提高电瓷的机械强度。适当增加长石含量,可促进二次莫来石晶体生长并提高电瓷的致密度和机械强度。     

Sulfated zirconia grafted on a mesoporous silica aerogel: Influence of the preparation parameters on textural, structural and catalytic properties

Silica supported sulfated zirconia catalysts were synthesized via a new method by grafting sulfated zirconia on the surface of a silica aerogel previously prepared. The main parameters studied in this work were the S/Zr, Zr/Si molar ratios and the support nature. The synthesized solids were characterized using XRD, N₂ physisorption at 77 K, TG-DTA/SM, sulfur chemical analysis and adsorption–desorption of pyridine followed by infrared spectroscopy. These solids were tested in the n-hexane isomerization reaction. Two types of mesopores were observed on the silica aerogel. This mesoporosity was affected depending on the preparation parameters.

The increase of the Zr/Si molar ratio induces the decrease of the size of zirconia particles deposed on the support. In this case, appreciable amounts of sulfur are retained with the presence of a relatively strong Brönsted and Lewis acid sites on the catalyst surface. A high density of Brönsted sites seems to be interesting in the n-hexane isomerization reaction.     

氧化锆负载双金属复合催化剂的制备与性能表征

以硝酸铝为助剂,硝酸铜为铜物种前驱体,正丁醇锆为载体前驱体,采用蒸汽水解法一步合成出了具有纯四方相结构的负载型介孔Al-Cu/ZrO2复合双金属催化剂。通过对复合催化剂进行XRD、N2吸附、H2-TPR等表征,分析了不同铝助剂含量和铜含量对复合催化剂结构性能的影响规律。结果表明,当铝助剂质量分数为3%、铜质量分数为20%时,复合催化剂具有良好的晶相结构,比表面积可达100 m^2/g,铜物种还原温度为175℃~238℃且与氧化锆载体表面之间相互作用强、分散性高。     

用乳液法制备ZrO2纳米球形颗粒

利用二甲苯为油相,span-80为表面活性剂,Zr(NO3)4或NH3的水溶液为水相,采用单乳液和双乳液的方法制备了含3%(摩尔分数)Y2O3的ZrO2前驱体粉,经过600℃锻烧2h后获得了四方相ZrO2纳米粉.用TG-DTA、XRD、TEM、BET和激光粒度分析等分析手段对粉末及其前驱体进行了分析和表征,试验结果表明:二甲苯/span-80/水相体系具有较大的含水量,能改善目前用乳液法制粉产量低的缺点,利用该体系制粉的最佳体积配比为V(二甲苯):V(span-80):V(水相)＝95:5:25.按照该配比设计的单乳液法和双乳液法均能获得形状为球形、团聚较少的四方相纳米粉末,但采用双乳液法比单乳液法所获得的粉末粒度分布更均匀、粒径更小,粒径约15nm.     

浅谈多晶莫来石纤维在轧钢加热炉上的应用

为了节约能源、改善操作环境,湘钢高线、棒材厂在加热炉上试用了多晶莫来石纤维.本文对材料的选用、施工、使用效果进行了分析,运用传热学原理计算出了多晶莫来石纤维在轧钢加热炉上的节能效果.     

Solid-State Ionics: Roots, Status, and Future Prospects

This review represents the authors' view of the evolution of solid-state ionics over approximately the past 100 years. A brief history, introducing milestones of the development of this discipline, is followed by a short summary of the theory of ionic conduction in the bulk and the more recently developed theory of ionic conduction at interfaces. The central part of the article gives examples of ionic-conducting materials systems with structures ranging from one- to three-dimensional disorder. Important experimental techniques for analyzing ionic conduction, including alternating-current impedance spectroscopy, direct-current coulometry, and direct-current current-voltage measurements with blocking electrodes, are also summarized. The main technological applications, that is, batteries, solid-oxide fuel cells, electrochemical sensors, electrochromic windows, and oxygen-separation membranes, are reviewed. Finally, new concepts in solid-state ionics are presented, including the investigation of new materials (such as nanostructured phases), the study of boundaries (for example, using microelectrodes), the development of computational techniques, and the connections with other classes of materials (notably magnetic and semiconducting materials).     

A second ceramic age—A new materials frontier

A second ceramic age started in the mid-twentieth century as a new, exciting materials frontier. Electroceramics with phenomenally wide range of electrical resistivity (spread over 30 orders of magnitude) span insulators, semiconductors, metal-like conductors, ionic conductors, and, recently, superconductors. They also include ferroelectrics, piezoelectrics, pyroelectrics and electro-optics beside ferrites. Advances in electroceramics have been fascinating and rapid, leading to unprecedented rates of industrial growth. Age-old limitations of poor mechanical strength and brittleness of ceramics are being overcome by outstanding toughness and strength achieved in zirconiabased ceramics exploiting the martensitic transformation at the tetragonal-monoclinic phase change. The dimensional changes at this transition which prevented the use of zirconia earlier has now been turned into a mechanism for toughening ceramics to significant levels. Ceramics with near-zero overall thermal expansion coefficient offer new opportunities to science and industry. Distinguished Materials Scientist of the Year Award Lecture presented at the MRSI meeting, New Delhi, on February 9, 1991. Professor E C Subbarao, born on 8 August 1928 in Narsapur, Andhra Pradesh received his B.Sc. Tech degree in Glass Technology from Banaras Hindu University, Varanasi in 1949, his B.S. and M.S. degrees in Ceramic Engineering from the University of Washington, Seattle, WA, USA in 1952 and 1953 and his Ph.D. degree in Ceramic Technology from the Pennsylvania State University, University Park, PA, USA in 1957. He was employed by the Parry and Co. Ltd., Ranipet, TN from 1949 to 1951 and as a Research and Fellow Engineer by Westinghouse Research Laboratories, Pittsburgh, Pa, USA from 1956 to 1963. Joining the Metallurgical Engineering Department of the Indian Institute of Technology, Kanpur in 1963 as an Associate Professor, he continued as a Professor from 1964 to 1981. He is the Founder-Director of the Tata Research Development and Design Centre, Pune since 1981. At IIT, Kanpur, he organised the Metallurgical Engineering Department as its first Head from 1963 to 1967 and the Inter-disciplinary Program in Materials Science as its first Convenor from 1971 to 1975. He was also the first Dean of Faculties at IIT, Kanpur from 1966 to 1972. Professor Subbarao published or edited nine books and published over 140 papers. He was elected a Fellow of the Indian National Science Academy, the Indian Academy of Sciences, the Indian Institute of Ceramics, and the (International) Academy of Ceramics. He has been awarded the National Metallurgists Award, the Homi Bhabha Award in Applied Science, and the Varshnei Memorial Award.     

Support Effect in Supported Ni Catalysts on Their Performance for Methane Partial Oxidation

Supported nickel catalysts were prepared by impregnation of La₂O₃, MgO and ZrO₂ substrates and tested in the partial oxidation of methane to synthesis gas at atmospheric pressure. Nickel interacted strongly with La₂O₃ forming a deficient LaNiO_3- perovskite structure upon calcination. Upon reduction at 973 K, the Ni/La₂O₃ catalysts that resulted were highly active and selective for syngas production. By contrast, a separate and readily reducible NiO phase was formed on the ZrO₂ support. Because the interaction of metallic nickel particles on ZrO₂ is weak, the catalysts underwent deactivation by sintering of metal particles during on-stream operation as confirmed by photoelectron spectroscopy. The relatively high activity of the Ni/MgO systems was associated with the formation of a highly stable cubic Ni-Mg-O solid solution, in which nickel remains highly dispersed during the methane partial oxidation reaction.     

Experimental Investigation on the Reliability of Thermal Wave Interferometry in the Thermophysical Characterization of Plasma Sprayed Coatings

The main focus of this work is to compare thermal diffusivity and effusivity data resulting from thermal wave interferometry (TWI) experiments on tungsten coatings of different thicknesses with those obtained using reference techniques, namely, the laser flash method and scanning electron microscopy (SEM). The deviations between TWI and the latter techniques are discussed in terms of lack of data in the low frequency range. The investigation shows that the lack of data at low frequencies does not affect diffusivity measurements, while it has a strong effect on effusivity measurements for thermally thick coatings. The conclusions of this experimental study are in good agreement with theoretical predictions resulting from a sensitivity analysis reported in a previous study.     

Oxidation Behavior of SiC-Whisker-Reinforced Alumina-Zirconia Composites

During high-temperature oxidation in air, SiC-whisker-reinforced Al₂O₃—ZrO₂ composites degrade by the formation of a whisker-depleted mullite-zirconia scale. The reaction kinetics have been studied as a function of time and temperature for composites with whiskers preoxidized for different times. The evolution of the microstructure has been investigated by optical, scanning and transmission electron microscopy. Possible reaction mechanisms have been discussed. A model compatible with our observations on Al₂O₃—ZrO₂—SiC and the results reported in the literature for Al₂O₃—SiC whisker composites is proposed: The oxidation occurs at an internal reaction front. Oxygen diffuses along dislocations and grain boundaries through the mullite scale to react at this front with silicon carbide, thereby forming amorphous silica and graphite. Silica penetrates grain boundaries and further reacts with alumina and zirconia to form mullite and zircon, while the second reaction product, graphite, is oxidized into carbon monoxide when the reaction front moves deeper into the sample.