STUDY OF PREPARATION AND PROPERTY OF YBa_2Cu_3O_(7-δ)-Ag_x COMPOSITE SUPERCONDUCTORS PREPARED BY SOL-GEL PROCESS

YBa_2Cu_3O_(7-δ)-Ag_x composite superconductorswere prepared by hybrid sintering process using YBa_2Cu_3O_(7-δ)-Ag_x ultrafine powder and AgO_2 finepower,which were pre-pared by sol-gel process and precipitation process respective-ly.The effect of the Ag content on superconducting cricticaltransition temperature of YBa_2Cu_3O_(7-δ)-Ag_x was not evident aslong as YBa_2Cu_3O_(7-δ)-Ag_x can form continuous network.ButAg can increase superconduction crictical current and densityof the composite superconductors.The normal state(i.e.non-superconducting state at room temperature)resistivity shows apercolation threshold at 20%～30% Ag,whereas the super-conduction network shows a percolationthreshold at 70%～80% Ag.     

THE CHARACTERISTICS OF THE PRESSURELESS SINTERED Si_3N_4-MgO-Ce0_2 CERAMICS

An investigation of the pressureless sintering of Si3N4 with MgO-CeO2 revealed that MgO-CeO2 is a most effective sintering aid for silicon nitride. The amount of MgO-CeO2 and sintering conditions have a strong influence on the densification behaviour and mechanical properties of the sintered materials. The effect of the additive and sintering conditions are discussed. The silicon nitride pressureless sintered with MgO-CeO2 retained a relative density of 98. 5% and a bending strength of 950 MPa. The Si Mg-Ce-O-N system is of great value for application and theoretical study.     

化学气相沉积技术的研究及在无机材料制备中的应用进展（待续）

本文论述了化学气相沉积（ＣＶＤ）技术的基本原理、特点及影响其过程的因素；对近期发展起来的、具有广泛应用前景的几种典型的ＣＶＤ方法；热灯丝ＣＶＤ，高频及微波等离子体ＣＶＤ，激光ＣＶＤ，金属有机化合物ＣＶＤ的特点进行了阐述。     

NiAl金属间化合物改性研究

采用自反应高温合成技术及粉末冶金工艺制备了ＮｉＡｌ金属间化合物及其合金。通过三点弯曲和常温压缩实验法研究了ＮｉＡｌ金属间化合物及其改性后材料的常温性能。结果表明：合金元素硼明显提高了ＮｉＡｌ材料的常温强度但塑性改善不大；合金元素铁使ＮｉＡｌ材料的常温变形能力有一定的改善。采用自洽物离散文分Ｘα方法对合金化前后材料的键性进行计算，并由此来说明化学键的变化对材料性能的影响。     

RESEARCH ON PREPARATION OF ULTRAFINE ALN POWDERS

The high purity of ultrafine power(UFP)of a-luminium nitride(AlN) are prepared by the reaction of nitrogenplasma with metal aluminium in D.C.plasma reactr.Both thenitriding principle and the AlN nucleation mechanism are stud-ied.The rusults,indicate that the chemical reaction in the forma-tion process of AlN UFP is very complicated and the nitridingreaction is corelated to the concentration of reactants and thetemperature.The particle size cav be adjusted by controlling thepartial pressure of the reactants,the temperature and the react-ing rate.     

A NEW APPROXIMATE SOLUTION TO THE MULTIPLE SCATTERING THEORY FOR THE ELASTIC PROPERTIES OF HETEROGENEOUS MATERIALS

The multiple scattering theory has been apowerful tool in determining the effective prop-erties of heterogeneous materials.In this pa-per,a simple relationship between the scatteringtheory and the micromechanics theory based onthe Eshelby principle has been suggested.Ac-cording to the relationship,a new and simpleapproximate solution to the exact multiple scat-tering theory has been given in terms ofEshelby’s S-tensor.The solution easily showsthose known results for isotropic compositeswith spherical inclusions and for tracnsverselyisotropic composites,and first gives non-self-consistent(average t-matrix)and symmetric self-consistent(effective medium or coherentpotential) approximate results for isotropiccomposites with spheroidal inclusions.     

HIGH-Tc SUPERCONDUCTIVITY AND PERCOLATION

On microscopic and microstructural lev-els,the relations between high Tc superconduc-tivity and percolation have been discussed.On themicroscopic level,the critical oxygen concentra-tion in YBa_2Cu_30_7 with Tc around 90 K hasbeen obtained in terms of percolation.On themicrostruclural level,the percolation considera-tions have provided,usefully theoretical basisfor materials design of metal/high-Tc super-conducting phase(nonmetal)composites.     

粉煤灰火山灰活性与结构的关系及提高其活性的途径

本文作者选用了十家电厂的粉煤灰,采用重选、磁选等方法进行了颗粒的分选,测定了原状粉煤灰及各分选玻璃质颗粒的化学组成;应用扫描电镜观察粉煤灰的颗粒形貌,应用 X-射线对粉煤灰中的玻璃质颗粒进行了相分析。在上述试验的基础上,将粉煤灰颗粒分为三大类:第一类为球形颗粒,按其表面光滑程度和富集氧化物的不同,又可分为两种,一是表面比较光滑的富集氧化钙的富钙玻璃珠,另一种是表面比较粗糙的富集氧化铁的富铁玻璃珠;第二类为多孔颗粒,按其化学组分的不同,也可分为两种,一是富集了粉煤灰中较多的氧化硅和氧化铝的多孔玻璃颗粒,另一种是含碳的多孔碳粒;第三类为形状不规则的颗粒,也可再分为矿物碎屑与玻璃碎屑。关于粉煤灰的火山灰活性,过去的研究工作者,注意了其与化学组成,玻璃体含量的关系,也注意了与比表面积、需水量的关系。但是,很少人研究火山灰活性与玻璃体结构的关系。本文作者开展了这方面的研究,进一步揭示粉煤灰具有火山灰活性的本质,并且采用作者提出的评定粉煤灰的火山灰活性方法,测定了粉煤灰中各玻璃质颗粒的活性。认为:富钙玻璃珠具有最大的活性,而多孔玻璃颗粒具有较小的活性。关于进一步提高粉煤灰活性的问题,特别为人们所注意。我们在研究了粉煤灰玻璃体结构及表面特征的基础上,提出了新的物理--化学表面处理方法,对粉煤灰进行改性,获得了大幅度提高粉煤灰活性的效果。     

关于矿渣玻璃的结构及其特性的研究

深入研究粒状高炉矿渣的水硬活性与其结构的关系对揭示矿渣具有潜在胶凝性能的本质具有重要意义。本文评述了常用的表征矿渣水硬活性的化学分析法和强度试验法的优缺点;分析了CaO—MgO—Al_2O_3—S_1O_2四元体系中各种阳离子对矿渣玻璃体结构的影响;应用现代玻璃结构的理论,提出了衡量矿渣玻璃体水硬活性的指标(Egt,Ent)及其计算方法。试验表明,Egt和Ent的计算值和矿渣在一定条件下的溶出度及矿渣水泥的抗压度有一定的相关。     

交联改性PAMPS质子交换膜的制备与性能

制备了聚2-丙烯酰胺-2-甲基丙磺酸（PAMPS）质子交换膜并对其进行交联改性,研究了膜的含水率、溶胀率、拉伸强度、高温保水率、质子电导率等性能.结果表明,PAMPS均质膜的质子导电率很高（0.32 S/cm）,但溶胀率过高、机械强度差.交联改性后,膜保持高的导电率（3% MBA,0.076 S/cm）和高温保水性能,且膜的溶胀率大幅度降低,机械强度显著提高（3% MBA,23.6 MPa）.