Study of Devitrification of Lithium Glass

An etching technique has been found which allows the devitrification phenomena in glass to be followed. Using this technique a study was made on 30 mole % Li₂O-SiO₂ glass at temperatures of 520°, 560°, and 600°C. By studying the average crystal size versus time at a given temperature, the growth rate was determined. It was found to be 7.5 × 10⁻⁴, 8 × 10⁻³, and 3 × 10⁻² cm. per hour for the three temperatures. The nucleation of crystals appeared to be linear with time at each temperature. An activation energy of 49 kcal. per mole was found for the growth process. Crystals were identified as Li₂Si₂O₅.     

An ESR and Time-Resolved CIDEP Study of the Light-Induced Yellowing Processes of Tmp Paper

Integral ESR and time-resolved CIDEP techniques applied to the study of the light-induced yellowing of bleached and unbleached TMP samples provide some further insights into the nature and the mechanisms of the processes. The identity of the phenoxy and ketyl free radical intermediates involved in mese processes is established and the primary triplet photochemical mechanisms of their formation are characterized. The radical scavenging mechanisms responsible for the inhibition of light-induced yellowing in the TMP system by ascorbic acid and triphenylmethyl thiol are formulated.     

陶瓷产品“失透”的研究与实践

通过对陶瓷失透产品特征的分析,阐述了陶瓷产品产生失透的机理,提出了在实际工作中解决失透这一陶瓷产品缺陷的措施。     

Devitrification behaviour of plasma-sprayed glass coatings

Glass and glass-ceramic coatings on ceramic tiles have been manufactured by plasma-spraying high-performance CAS (in wt%—SiO₂, 60%; Al₂O₃, 15%; CaO, 23%; others, traces) and CZS (in wt%—SiO₂, 50%; CaO, 31%; ZrO₂, 16.5%; Al₂O₃, 2%; others, traces) glass frits. The CZS system has a surface crystallization at about 1050 °C. Such behaviour would not easily allow to obtain a fully crystalline bulk glass-ceramic, but the defectiveness of the plasma-sprayed coating supplies many nucleation sites. Thus, it becomes completely crystalline and well sintered after a 850 °C for 30 min + 1050 °C for 15 min treatment. The CAS frit, designed not to produce significant crystallization, is well sintered after a 850 °C for 30 min + 950 °C for 30 min thermal treatment, but remains too brittle due to its glassy nature. A 1050 °C treatment allows a few pseudowollastonite crystals to form in a glassy matrix; their formation also hinders sintering. Thus, mechanical properties are inferior to heat-treated plasma-sprayed CZS.     

Devitrification of Glasses in the Akermanite-Gehlenite System

The devitrification behavior of specimens with compositions 2CaO · (1- x )MgO · x Al₂O₃· (2- x )SiO₂, 0≤ x ≤1, was studied. The crystallizing phases were identified by X-ray diffraction, and the transformation temperatures were determined by differential thermal and/or thermodilatometric analysis. The microhomogeneity of the glasses was investigated by electron microscopy and small-angle X-ray scattering. Glasses with x ≤0.6 devitrify through an intermediate phase, merwinite. Conclusions are drawn about the mechanism of devitrification, taking into account phase separation and the possible distribution of the different anions in the glasses studied. The activation energy for the first stage of devitrification was calculated on the basis of a Johnson-Mehl growth-rate equation for x = 0.4.     

硅酸铝陶瓷玻璃纤维的脱硫

标准等级的硅酸铝陶瓷纤维在1050℃以上温度显示出脱硫特征,以结晶莫来石相为主。在实验室条件下、在900-1350℃之间加热处理后进行浸渍,标准陶瓷纤维的室温X射线衍射研究表明,在1250℃存在一个未知的“X”相,在1250℃以上主要形成莫来石相。未知的“X”相在20为30-31°和34—35°之间显示出其特性峰(Cu-Kα辐射),在1350℃随着浸渍时间的延长这些峰变得尖锐。莫来石形成的活化能为(18.8±0.3)kcal·mol-1。     

Effect of Oxide Devitrification on Oxidation Kinetics of SiC

The effect of oxide crystallinity on the oxidation rate of silicon carbide was investigated. CVD SiC coupons were oxidized in a clean TGA reactor system at 1300°C initially in flowing oxygen, immediately annealed in argon, and then reoxidized, all in situ and without cooling (so as to preserve oxide integrity). The parabolic rate constants determined for the preoxidation regime (of mainly amorphous oxide film) and reoxidation regime (of devitrified oxide) were compared. The oxidation rate decreased by a factor of }30 following full oxide crystallization induced by the anneal.     

Effect of Trace Impurities on Devitrification of Vitreous Silica

Devitrification rates were measured for a series of vitreous silica glasses doped with trace levels of alkali metal oxide (1.6 to 57.8 molar ppm) and aluminum oxide (22 to 73.3 molar ppm). The devitrification rate varies inversely with the molar ratio of aluminum oxide to alkali metal oxide, a direct consequence of the effect of these trace impurities on viscosity .     

Thermodilatometric Characterization for Devitrification of a Micaceous Dental Glass-Ceramic

The devitrification of an uncerammed micaceous glass-ceramic used for dental applications was studied by thermodilatometry and compared with the kinetics of mica crystallization studied by differential thermal analysis. The thermodilatometry plots and their derivative plots revealed thermally impeded processes, namely, structural relaxation, glass softening and nucleation, and crystallization, and they were characterized by glass-transition temperature, glass-softening temperatures, and crystallization temperature. The heating-rate dependence for these characteristic temperatures was used to determine the activation energy for structural relaxation of 338 kJ·mol^-1, the activation energy for viscous flow of 276 kJ·mol^-1, and the apparent activation energy for crystallization of 286 kJ·mol^-1 by one model and 342 kJ·mol^-1 by another model. The similar magnitudes for these activation energies suggested the mechanisms for different thermal processes involved analogous molecular motions. Furthermore, the activation energy for crystallization of the micaceous phase of the glass-ceramic could be estimated from thermodilatometry plots, because it was comparable in magnitude to that obtained from the widely used nonisothermal differential thermal analysis method. Finally, the dilatometry and scanning electron microscopy studies strengthened the earlier opinion that the devitrification of the base glass is a single-step process, that is, without occurrence of an intermediate phase before the formation of the final crystalline phase.     

Effect of Devitrification on Creep Deformation in Glass-Containing Ceramics

Many commercial structural ceramics contain glass. This glass is often unstable and devitrifies during creep at elevated temperatures. Two models for this process have been developed, in order to understand how devitrification affects measured creep parameters. They indicate that when creep data are measured after a constant amount of creep strain, the effect of devitrification can be large. Moreover, if devitrification is stress-state dependent, a different creep rate on the tensile and compressive sides of a bend bar is predicted. This can contribute to the redistribution of stress across a bend bar and complicate the analysis of creep data obtained in bending.     

Effect of Nitriding on Electrolysis and Devitrification of High-Silica Glasses

Devitrification occurs near the cathode when reconstructed high-silica glasses and fused quartz undergo electrolysis at 900°C. The crystalline phase is cristobalite and results from a concentration of alkali ions. Subsequent and more superficial crystallization around the alkali-rich spot is caused by interaction of the glass with alkali vapors coming from the central spot. The degree of devitrification increases with the alkali content of the glass. Devitrification at constant alkali level can be reduced in reconstructed glasses by nitriding the porous glass with ammonia at a high temperature before consolidation. Devitrification decreases and viscosity and electrical resistivity increase as the nitriding temperature increases 500° to 1000°C. Nitrided glasses are more resistant to electrolytically induced devitrification than is fused quartz.     

Optimization Study of Residuum Hydrotreating Processes

This paper presents an optimization study of catalytic hydrotreating reactors processing heavy residuum feedstock. The focus is on conversion, throughput and catalyst life. The core of the proposed optimization model is a cost function representing the essential economical parameters of hydrotreating processes and accounts for additional costs imposed by deeper desulfurization in addition to the monetary benefit of lower sulfur products. Operational variables are estimated using a mathematical model, which accounts for catalyst deactivation. Simulation results are presented to illustrate the effect of various operating variables on the process performance. An industrial scale atmospheric residue desulfurization process has been selected as a typical hydrotreating unit to demonstrate the capabilities of the optimization model. Optimization results were found quite reliable and consistent with actual industrial practices.     

Alumina as a Devitrification Inhibitor during Sintering of Borosilicate Glass Powders

Cristobalite is formed when borosilicate glass (Corning Code 7740) is sintered at temperatures ranging from 700^o to 1000^o C. The precipitation kinetics, determined by XRD analysis, exhibit a characteristic incubation period which decreases with increasing sintering temperature, from 60-120 min at 700^oC to 3-5 min at 1000^o C. Activation analysis of precipitation shows an activation energy of 75 kJ/mol, which is close to that for the diffusion of Na+ in borosilicate glass, suggesting mass-transport controlled kinetecs. ^1.,5With added alumina content greater than a critical value, however, the cristobalite formation in the borosilicate glass is completely prevented at the sintering temperatures investigated. The critical alumina content is found to decrease with decreasing alumina particle size but with increasing sintering temperature. The above result, similar to observations previously made in a binary glass mixture containing a low-softening borosilicate glass (BSG) and a high-softening high silica glass (HSG) ³ is attributed to a strong coupling between Al³⁺ from alumina and Na⁺ from borosilicate glass. The coupling reaction causes segregation of Na⁺ in boraosilicate glass to alumina, thus forming a Na⁺-and Al³⁺-rich reaction layer around alumina particles far too rapid for cristobalite formation.     

Effect of Aluminum and Neodymium Admixtures on Devitrification of Silica Glasses

This investigation concerned the devitrification kinetics (in the temperature range 1100° to 1500°C) of silica glasses doped with aluminum oxide (0.1 and 1.0 mol%), neodymium oxide (0.08 and 0.25 mol%), and with aluminum and neodymium oxides simultaneously, at their mutual molar ratio close to 4. The glasses were obtained by electric melting of quartz under vacuum and by the sol/gel method. On the basis of the obtained results, conclusions have been drawn concerning the mode in which the admixtures become incorporated into the silica glasses as well as the structural differences between the melted and sol/gel glasses.     

低废采矿技术的研究

阐述了矿山在生产中尽量少出废石的低废采矿技术。综合利用顺采出的废石,确实无用的废渣返回充填到井下,修复利用废弃巷道和采空区,储存矿山自身产生的废渣和工业废渣,缓解废石场与耕地争地的矛盾。建立无生态危害的低废采矿系统,使我国矿业能持续发展。     

废对苯二甲酸综合回收利用的优化工艺研究

研究了以废对苯二甲酸(PTA含量85%～95%)与甲醇为原料,对甲苯磺酸为催化剂,催化酯化得到对苯二甲酸二甲酯(DMT)。通过正交实验法优化得到最佳反应条件为:50 mmol的废PTA,催化剂量为0.5 g,反应温度为130℃,甲醇用量为130 mL。在此反应条件下DMT平均酯化率达到(83.1±2.3)%,产物经纯化后DMT纯度达99.5%以上。     

生物脱氮新工艺研究进展

分析了传统生物脱氮工艺存在的问题,系统介绍了短程硝化-反硝化,厌氧氨氧化、同时硝化反硝化、好氧除氨工艺、全自养脱氮工艺等生物脱氮新工艺的机理、特点和研究现状,同时指出了新技术存在的问题和今后研究的发展趋势.