Influences of Sr2+ Doping on Microstructure,Giant Dielectric Behavior,and Non-Ohmic Properties of CaCu3Ti4O12/CaTiO3 Ceramic Composites

The microstructure, dielectric response, and nonlinear current-voltage properties of Sr²⁺-doped CaCu₃Ti₄O₁₂/CaTiO₃ (CCTO/CTO) ceramic composites, which were prepared by a solid-state reaction method using a single step from the starting nominal composition of CCTO/CTO/xSrO, were investigated. The CCTO and CTO phases were detected in the X-ray diffraction patterns. The lattice parameter increased with increasing Sr²⁺ doping concentration. The phase compositions of CCTO and CTO were confirmed by energy-dispersive X-ray spectroscopy with elemental mapping in the sintered ceramics. It can be confirmed that most of the Sr²⁺ ions substituted into the CTO phase, while some minor portion substituted into the CCTO phase. Furthermore, small segregation of Cu-rich was observed along the grain boundaries. The dielectric permittivity of the CCTO/CTO composite slightly decreased by doping with Sr²⁺, while the loss tangent was greatly reduced. Furthermore, the dielectric properties in a high-temperature range of the Sr²⁺-doped CCTO/CTO ceramic composites can be improved. Interestingly, the nonlinear electrical properties of the Sr²⁺-doped CCTO/CTO ceramic composites were significantly enhanced. The improved dielectric and nonlinear electrical properties of the Sr²⁺-doped CCTO/CTO ceramic composites were explained by the enhancement of the electrical properties of the internal interfaces.     

氧化共沉淀法制备纳米级掺锑α—Fe2O3气敏陶瓷粉料

氧化共沉淀法制备纳米级掺锑α┐Ｆｅ２Ｏ３气敏陶瓷粉料王忠春＊＊刘尔生陈耐生＊黄金陵（福州大学化学系福州３５０００２）关键词α－Ｆｅ２Ｏ３陶瓷，锑掺杂气敏材料，纳米材料１９９６－１０－０５收稿，１９９７－０４－２２修回福建省科委资助项目＊＊现在上海硅酸...     

CePO_4/Ce-ZrO_2可加工陶瓷性能与断裂机制研究

以Ce ZrO2为基体,通过复合不同加入量的第二相CePO4颗粒,研究了陶瓷材料力学性能的变化,并借助加载能谱仪(EDS)的扫描电子显微镜(SEM)对材料弯曲断口及压痕裂纹扩展方式进行分析。当CePO4加入量为25%时,虽然材料力学性能有一定下降,但已经能用WC刀具进行加工。材料的弯曲断口显示,CePO4在两相体系中的断裂呈层片状形式;加入CePO4后,由于两相之间弱结合界面的存在,压痕裂纹扩展形式发生明显变化,由连续扩展机制过渡为不连续扩展。由这两种机制形成的材料断裂过程是阶段性的,在实际中可以用作材料最终破坏前的预报。     

Sol-Gel Preparation of Ceramic Coatings for Electrical, Laser, Space Engineering and Power

The brief review, based on long-term experience of authors on preparation of temperature-resistant electric insulating and optical light-reflecting ceramic coatings on metal surface is offered. The main components of TEOS-, H₃PO₄- and alkali silicates-derived sols and suspensions for deposition of ceramic coatings are listed. Some features of preparation of the coatings from the sols containing fillers are analysed. Two approaches to improve bending and electrical strength of flexible insulation are developed. The techniques of synthesis of modified fillers for preparing gas-proof and anticorrosive coatings are offered. The wide functional possibility and extensive list of application areas of the coatings and some materials prepared from sols with fillers, including on far prospect are given.     

Direct Synthesis of Ceramic Membranes by Sol-Gel Process

Ceramic ultrafiltration and nanofiltration membranes (TiO₂) are prepared by sol-gel route using a special arrangement which allows the reaction of the reactants directly in the pores of a tubular Al₂O₃ support or on its surface, respectively. By this direct synthesis the number of technological steps can be reduced which is the main advantage of the method. The produced layers are well joined with the Al₂O₃ support and the reaction can be adjusted by various technological parameters. The dried and sintered coatings are characterized by X-Ray diffraction, FESEM and AFM. In addition, pore size distribution and filtration properties are investigated and discussed.     

溶胶-凝胶法制备Bi-Pb-Sr-Ca-Cu-O微粉

以金属醋酸盐为原料,用溶胶-凝胶技术制备了Bi-Pb-Sr-Ca-Cu-O微粉,并用TG、DTA、IR、XRD和TEM等手段对Bi_1.85Pb_0.35Sr_1.9Ca₂Cu_3.1O_y粉末的热分解和晶化行为以及粉末粒度进行了分析测试,并用此微粉制备出以2223相为主要物相、零电阻为105K的高温陶瓷超导体。     

Determination of cake thickness and porosity during cross-flow ultrafiltration on a plane ceramic membrane surface using an electrochemical method

The thickness and the porosity of a deposit during ultrafiltration experiments are determined using an electrochemical method. Twenty microelectrodes are mounted flush to a ceramic plane membrane and maps of deposit thickness are determined for three inlet/outlet distributors configurations. Combining an electrochemical method and a step transient method, the determination of the thickness and the porosity of a particles deposit is performed. These local thickness and porosity values are analyzed thanks to wall shear stress local measurements obtained in a previous work [Sep. Sci. Technol. 37 (10) (2002) 2251]. The results emphasize the heterogeneity of the deposit thickness, especially in zones of low wall shear stress. Furthermore, the porosity values of the deposit are ranged between 0.3 and 0.8 as a function of the location at the membrane surface.     

Study on microstructure and mechanical properties relationship of short fibers/rubber foam composites

Research on short fibers/rubber foam composites is rarely found in the literature. In this paper, microcellular rubber foams unfilled (MF), strengthened by pretreated short fibers (MFPS) and untreated short fibers (MFUS) are prepared, respectively. The microstructure and mechanical properties of the three composites have been studied via scanning electron microscope (SEM) and mechanical testing, respectively. The SEM results show that both pretreated and untreated short fibers disperse uniformly in the composites and in bidimensional orientation. Moreover, the pretreated short fibers have much better adhesion with the rubber matrix than untreated ones. The experimental results also indicate that the introduction of short fibers is mainly responsible for the great enhancement of most mechanical properties of the microcellular rubber foams, and the good interfacial adhesion of the short fibers with the matrix contributes to the more extensive improvement in the mechanical properties. It is also found that the reinforcement effect of short fibers to compressive modulus strongly depends on the density of microcellular rubber foams, the orientation of short fiber and the deformation ratio. The compressive modulus of microcellular rubber foams at the normalized density less than 0.70 and beyond 0.70 is predicted by the modified Simple Blending Model and the Halpin-Kerner Model, respectively. The theoretically predicted values are in good accordance with the experimental results.     

二氧化硅修饰纳米氧化锆陶瓷材料的制备及性能

以二甲基二乙氧基硅烷为硅源,在水溶液中成功制备了SiO2修饰纳米ZrO2颗粒;利用透射电子显微镜、热重分析仪、X射线衍射仪、红外光谱仪分析了样品的形貌和结构;将SiO2/ZrO2与α-Al2O3制成陶瓷材料,考察了其机械性能.结果表明,所制备的SiO2/ZrO2晶粒均一,直径约为10nm,硅原子在SiO2/ZrO2中以Si―O―Zr键合形式存在,SiO2不影响ZrO2的晶型.引入SiO2使得ZrO2晶粒细化、尺寸均匀性提高;SiO2/ZrO2/Al2O3陶瓷气孔率小,具有致密的显微结构和优异的机械性能.     

纳米孔莫来石陶瓷材料的制备

以正硅酸乙酯(TEOS)提供硅源、纳米氧化铝(d90=50 nm)提供铝源,通过溶胶-凝胶法与超临界干燥技术,制备了分散纳米氧化铝的SiO2气凝胶块体,所得复合气凝胶块体经1200℃、1300℃热处理后,得到了纳米孔莫来石陶瓷材料。XRD测试表明:凝胶体在1 200℃热处理后发生了莫来石化,1300℃莫来石化基本完成。压汞仪与场发射扫描电镜结果显示:凝胶块体经1 200、1 300℃热处理后,形成了具有纳米多孔结构的莫来石陶瓷材料,其骨架结构包含有200~400 nm的大孔,以及大量位于其孔壁上的6~30 nm的介孔。由于莫来石化的进行,热处理后的陶瓷材料的纳米孔结构具有更高的热稳定性。