High-Temperature Creep and Dislocation Etch Pits in Polycrystalline Beryllium Oxide

Compressive creep of high-density polycrystalline beryllium oxide was investigated in the range 1850° to 2050°C. Creep rate was dependent on the applied stress to the 2.5 power, and the apparent activation energy for creep was 145 kcal/mole. Etch pit studies showed that the dislocation density in tested specimens was two orders of magnitude greater than that in assintered material. The diffusion process controlling creep was ascribed to volume diffusion of the anion. The deformation behavior was governed by dislocation motion.     

Self-Diffusion of Beryllium in Polycrystalline Beryllium Oxide

The self-diffusion of beryllium in polycrystalline beryllium oxide was measured from 1330° to 2135°C with the ⁷Be tracer. Results are compared with the findings of other investigators, and it is concluded that the differences reported are due to variations in impurity and porosity contents. Diffusion has been shown to be via a vacancy mechanism, with such impurities as aluminum and silicon being the principal contributors of vacancies. A roll-over in the plot of log D versus 1/ T , where D is the diffusion coefficient and T is absolute temperature, was found in this study as in some others. Above about 1500°C the activation energy is no higher than 62 kcal, whereas it is 92 kcal at lower temperatures. It is suggested that this roll-over is due to aluminum impurity. There appears to be a temperature-independent anisotropy of diffusion, with the rate in the 〈 c 〉 direction being 30% higher than that in the 〈 a 〉 direction. It is concluded that for this and other investigations the diffusion coefficient of beryllium in beryllium oxide above the rollover temperature is governed by impurities and in this region it is given by the formula

where F_p is the fraction of porosity and N_v is the molar fraction of vacancies introduced by impurities. There is sufficient scatter in individual 〈 a 〉 and 〈 c 〉 diffusion values so that there is no value in discriminating between directions in this formula.     

Sintering Behavior of Beryllium Oxide

The sintering behavior of beryllia in a reducing atmosphere was studied between 1500° and 2100°C. Above 1700°C. the firing temperature had only a small effect on the density after heating for 24 hours. Examination of the time dependence of sintering showed that at 1700°C. during the first 3 to 5 hours there was a large increase in the density of the body accompanied by a simultaneous rapid rate of grain growth. Firing for longer times resulted in more moderate increases in both density and grain growth. The grain-growth characteristics of beryllia were unchanged by most oxide additions although compacts of higher density resulted. Oxide additives which formed a liquid phase at the sintering temperature enhanced both the sinterability and grain growth of beryllia.     

Compressive Creep of Polycrystalline Beryllium Oxide

Compressive creep of polycrystalline beryllium oxide was studied in the temperature range 2500° to 2800°F. The apparent activation energy for creep was 96.0 kcal per mole and the creep rate was linearly dependent on the applied stress. Results were consistent with the Nabarro-Herring creep mechanism. Experimental evidence showed that extrapolation of data to 3200°F was possible.     

Initial Sintering Kinetics of Beryllium Oxide

The initial sintering kinetics of beryllium oxide are examined, including the effects of calcining temperature, purity, and water-vapor content of the sintering atmosphere. Sintering occurs by a diffusion mechanism in dry-air atmospheres. Small additions of MgO to BeO increase the sintering rate markedly. The diffusion constant calculated from sintering data for pure BeO is three orders of magnitude lower than the measured diffusion of Be in BeO. Water vapor in the sintering atmosphere slows the shrinkage rate of pure BeO.     

High-Temperature Plastic Deformation of Polycrystalline Beryllium Oxide

High-density specimens were plastically deformed under four-point transverse bending. Tests were conducted in vacuum in the region 1400° to 1700°C under stresses of 1000 to 4500 psi. The activation energy for creep was 99.0 kcal/mole. Creep rate was directly proportional to the applied stress and inversely proportional to the square of the grain diameter. The deformation behavior is ascribed to a Nabarro-Herring type mechanism. Results show that creep was the same in tension and compression.     

利用酸性CuCl2蚀刻废液制备微米级Cu2O粉体

以含CuCl2酸性蚀刻废液为原料,葡萄糖为还原剂,采用液相还原法制备分散性好的微米级Cu2O粉. 实验确定最佳制备条件为：反应温度80℃,终点pH值8~9,反应时间1 h,还原剂和铜离子摩尔比为0.8. 所制Cu2O产品纯度为99.34%,Cu回收率可达99.7%. 进一步采用XRD, SEM, LZS, TG等手段对产物进行表征,结果表明产品为高纯Cu2O,粒径为1.8~2.2 mm,空心多面体结构,且常温下抗氧化性好,有可能用于催化剂、涂料、染料等的制备.     

Crystallite Growth of Beryllium Oxide Powders and Its Inhibition by Adsorbed Phosphate

Low-temperature sintering of beryllium oxide powders from 300° to 1000°C was studied by measuring crystallite growth and changes in specific surface. Sintering is enhanced by the presence of water vapor. Adsorbed phosphate almost completely inhibits sintering up to 850°C, even in water vapor at 10 torr.     

碱性蚀刻盐的研制

介绍了一种在现代印制板生产中使用的碱性蚀刻盐及其工作原理。