Studies on the Kinetics of Carbon Tetrachloride Chlorination of Refractory Metal Oxides

Studies on the kinetics of chlorination of the oxides of titanium, zirconium, niobium and tantalum by carbon tetrachloride gas in dilution with nitrogen, at low and moderate temperatures, have been carried out. In each case, the effect of time, temperature, partial pressure of carbon tetrachloride and the particle size, on the chlorination of the oxide, has been studied. The influence of some physico-chemical properties of the oxides and their halides on the kinetics process, has been discussed. The chlorination results below and above the dissociation temperature of carbon tetrachloride (～ 773 K) have been examined to find out the difference in the kinetics by CCl₄ and those by elemental carbon and chlorine. From these kinetics results, the mechanism of the chlorination of each of the oxides, has been established and compared. The optimum experimental conditions for preparing the metal chlorides, keeping in view of the maximum utilisation of the carbon tetrachloride, have been established. The merits of carbon tetrachloride as a chlorinating agent, have been highlighted. From these kinetics results, the scope for chlorinating the refractory metal oxides, as well as their mixed oxides, at lower temperatures and lower partial pressures of carbon tetrachloride, with the scope for recycling the reagent, has been briefly discussed. Some preliminary results on the preferential chlorination of these oxides by carbon tetrachloride present in a typical tin slag, have been presented, to further substantiate the merits of carbon tetrachloride as a low temperature chlorinating agent.     

Reduction Kinetics of Metal Oxides by Hydrogen

In this paper, a new kinetic model has been developed for reduction of metal oxides with hydrogen under both isothermal and non‐isothermal conditions. This model describes the kinetics of single reductive reaction and double reductive reactions by considering the diffusion and chemical reaction controlling mechanisms. In particular, the model is in the analytic form of expressing the reduction extent as an explicit function of time, temperature, radius of the particle, and hydrogen partial pressure, which is convenient for using and theoretical analysis. The reduction kinetics of nickel oxide, natural ilmenite, and Fe₂MoO₄ agree well with the theoretical results by the present model.     

Micropyretic Synthesis of Refractory Metal Intermetallic Compounds

The processing of refractory metal intermetallic compounds by micropyretic synthesis has been discussed in this article. The advantages of this process have been elaborated with the synthesis of intermetallic compounds in view. Microstructures of the synthesized alloys have been examined in detail and compared with the conventionally produced microstructure. The effect of different process parameters on the process and on the synthesized microstructure has been described. Special emphasis is given on the synthesis of aluminides of Nb and Ti and NiTi. The mechanism of micropyretic synthesis of the aforementioned intermetallic compounds from elemental powders has been studied by arresting the synthesis process midway. This has resulted in preservation of the unsynthesized material on one side, the fully synthesized material on the other and intermediate stages of synthesis frozen in between. A detailed microstructural characterization has been carried out around the arrested synthesis front in order to establish the sequence of synthesis.     

Micropyretic Synthesis of Refractory Metal Intermetallic Compounds

Abstract

The processing of refractory metal intermetallic compounds by micropyretic synthesis has been discussed in this article. The advantages of this process have been elaborated with the synthesis of intermetallic compounds in view. Microstructures of the synthesized alloys have been examined in detail and compared with the conventionally produced microstructure. The effect of different process parameters on the process and on the synthesized microstructure has been described. Special emphasis is given on the synthesis of aluminides of Nb and Ti and NiTi. The mechanism of micropyretic synthesis of the aforementioned intermetallic compounds from elemental powders has been studied by arresting the synthesis process midway. This has resulted in preservation of the unsynthesized material on one side, the fully synthesized material on the other and intermediate stages of synthesis frozen in between. A detailed microstructural characterization has been carried out around the arrested synthesis front in order to establish the sequence of synthesis.     

微生物分解难处理金矿的动力学研究

在均匀混合的间歇式反应器中用氧化亚铁硫杆菌分解难处理金矿,研究了不同粒度矿粒分解的动力学。结果表明,细菌在矿粒表面的吸附符合兰格穆尔等温吸附式,等温吸附常数KA不受粒度大小的影响,而单位质量矿粒的最大吸收量XAm随着粒度的增大而减小。建立了用于描述细菌生长和矿石分解的动力学方程式,其与试验数据能很好的吻合,矿石的初始粒度对吸附在矿粒表面的细菌的生长以及矿石的分解都有很大的影响。     

我国有色金属工业耐火材料的现状与展望

详细介绍我国有色金属冶炼的各种设备所使用的耐火材料及存在的问题，并从耐火材料的材质、新技术的应用以及耐火材料的生产管理等方面提出建议。     

金属掺杂改性钙钛矿型氧化物的研究进展

钙钛矿型氧化物由于其结构的稳定性和特殊的物化性能,日益成为材料科学领域的研究热点.但是其催化活性偏低,尤其是带隙能较高,不能高效吸收太阳光谱中丰富的可见光,限制了该技术的推广.利用金属元素掺杂改性钙钛矿型氧化物是有效改善其光催化性能的方法之一.目前利用金属元素掺杂改性钙钛矿型氧化物光催化剂的制备方法主要有溶胶-凝胶法、...     

飞机机轮炭/炭刹车盘金属件铆接工艺分析

飞机机轮炭/炭刹车盘上金属保护件与炭/炭盘配合好坏直接影响炭/炭盘的安全使用.文章介绍了飞机机轮炭/炭刹车盘的使用性能,炭/炭刹车盘金属保护件的作用、金属保护件材料性能和加工要求,主要对炭/炭刹车盘与金属保护件铆接工艺作了详细地介绍和分析,对铆接后的炭/炭刹车盘组件的质量和使用效果进行了跟踪评估,并对B757-200、A320等飞机炭/炭盘对金属保护件的要求和技术参数作了分析.     

Evaluation of Biodegradation Potential of Carbon Tetrachloride and Chlorophenols under Acidogenic Condition

Biodegradability of chlorinated aliphatic (carbon tetrachloride) and aromatic (chlorophenol) compounds under acidogenic condition was investigated at pH of 5.0 to 5.5. Batch tests were used to evaluate biodegradability, adsorption capacity, and inhibitory effects of the chlorinated compounds on the fermentative microbial consortium. The biodegradability of carbon tetrachloride differed from that of the chlorophenols tested. Carbon tetrachloride was degraded to dichloromethane, and its adsorption onto the biomass was minimal. Inhibition of the acidogenic process was not observed for carbon tetrachloride at 10?mg/L. Chlorophenols (penta, tri, di, and mono) were not degraded at all, even after addition of vitamin supplements, increased incubation time, and increased primary to secondary substrate ratio. Chlorophenol removed from the aqueous phase by adsorption can be recovered from the acidogenic sludge. Pentachlorophenol was inhibitory to the acidogenic culture, whereas 2-chlorophenol was not. Microbial community analysis revealed the bacteria therein were primarily rumen and enteric bacteria. The results showed that it is possible to dechlorinate at least an aliphatic chlorinated compound under acidogenic conditions.     

碳、硅铁及碳化硅对白钨矿还原动力学的影响

在实验室用15 kW碳管炉进行碳粉、硅铁粉(75％Si)、碳化硅粉对白钨矿粉(67．25％WO3)还原动力学影响的研究。结果表明,碳还原白钨矿的反应级数为二级,反应表观活化能为234．6 kJ／mol;碳在较低温度下,反应性能差,当温度达到1 400℃时,反应剧烈;随温度升高,硅铁的还原性能比较平稳,反应产生SiO₂,使渣量增加;碳化硅高温反应性能好(≥1 400℃);碳和硅铁适合较低合金化率(3％W),碳化硅适宜用于较高的合金化率(≥5％W)。     

Inactivation Kinetics of the Cyanobacterial Toxin Microcystin-LR by Free Chlorine

Worldwide, the increasing occurrence of toxins produced by cyanobacteria in water bodies used as source waters for drinking water has become an important public health issue. Microcystin-LR is one of the most commonly found cyanotoxins. A detailed evaluation of the free chlorine induced inactivation kinetics of extracellular microcystin-LR is presented in this study. Rate constants needed for chlorine inactivation of the toxin were derived from the data. The effects of varied pH, chlorine dose, toxin concentration, and temperature on the rate of inactivation were evaluated. Batch chlorination experiments were run using carbonate-buffered Milli-Q water at three different initial toxin concentrations (1, 2, and 8?μg/L), three different chlorine doses (1, 3, and 9?mg/L), and three different pH values (6.0, 7.5, and 9.0) at 11, 20 and 29°C. The study showed that extracellular microcystin-LR was inactivated by free chlorine and the inactivation rate was affected by pH. The highest inactivation rates were observed at pH 6.0 and the lowest at pH 9.0.     

金属基复合材料热磨损过程中氧化物的研究现状及展望

综述了金属基复合材料热磨损过程中碎片颗粒的形成和运动模型，氧化物产生的条件及形成机理，分析了氧化物釉层形成的具体阶段及影响因素，并在介绍有关氧化物釉层研究现状的基础上，展望了未来金属基复合材料热磨损过程中有关氧化物研究的趋势。     

难选高硅氧化锌矿碱浸出动力学

研究了氢氧化钠处理难选高硅氧化锌矿的浸出动力学,考察了搅拌强度、浸出反应温度、氢氧化钠初始浓度对锌的浸出速率的影响。利用等浸出率法来确定其表观活化能和反应级数,得到表观活化能E=45.7 kJ/mol,属于化学反应控制;其反应级数K=1.4。实验结果表明,提高反应温度可显著提高锌的浸出率,而增大搅拌强度却对锌的浸出率基本无影响。     

难熔金属碳化物调配的精准计算

通过产量因子和浓缩因子等新概念的引入，从物料的调配着手，导出了碳氧调配、炉料配碳等一系列公式，并确立了这些公式与目标碳氧含量的函数关系。通过混合氧化物概念的引入，解决了多元碳化物调配中各组元相互牵制的问题，将多元碳化物和一元碳化物的计算统一起来。计算过程精准可靠。     

Carbothermal Solid State Reduction of Stable Metal Oxides

The paper considers carbothermal solid state reduction of manganese, titanium and aluminium oxides in argon, helium and hydrogen. The difference in reduction in helium and argon was reflected by different diffusion coefficients of gaseous reactants and products, which are much higher in helium than in argon. When carbothermal reduction took place in hydrogen, it was involved in the reduction process by reducing oxides to suboxides and forming methane. Manganese and titanium oxides were reduced to carbide Mn₇C₃ and oxycarbide Ti(O_xC_1‐x) correspondingly, while products of alumina reduction included carbide Al₄C₃ and vapours of Al and Al₂O, which were re‐oxidised to Al₄O₄C outside the reactor and deposited in the lower temperature zone. Gas atmosphere had a profound effect on the extent and rate of reduction. This effect was different in reduction of different oxides. Reduction of manganese oxides was the fastest in hydrogen, and faster in helium than in argon. Reduction of titania in argon and helium proceeded with about the same rate and was much faster in hydrogen than in the inert atmospheres. The rate and extent of alumina reduction in hydrogen and helium were higher than in argon, although no significant difference was observed in alumina reduction in hydrogen and helium. This reflects differences in reduction mechanisms, which are discussed in the paper.     

氧化物型杂质或添加剂对铁氧化物还原动力学的影响

系统地评估了铁氧化物还原动力学中氧化物型杂质或添加剂的影响,进行了必要的量化分析.其影响的特点与杂质含量,杂质存在形式和加入方法,样品的初始化学组成和物理性状,还原剂的种类,反应温度,还原分数等多种因素有关.     

Cu/Fe双金属去除四氯化碳的研究

[目的]探讨Cu/Fe双金属去除四氯化碳的性能.[方法]以四氯化碳(CT)为靶污染物,采用分批试验研究了Cu/Fe双金属去除CT的可行性,并研究了铜化率、投加量及pH对CT去除效果的影响;采用柱试验考察了Cu/Fc双金属去除CT的长效性.[结果]Cu/Fe双金属对CT有良好的去除性能,CT终去除率可达97.90%;在试验条件下,铜化率越高、投加量越大,Cu/Fe双金属对CT去除效果越好;偏酸性环境有利于Cu/Fe双金属对CT的去除;对于CT的去除,Cu/Fe双金属比零价铁更具有长效性,其寿命是零价铁的2倍以上.[结论]为双金属脱氯研究提供了理论依据.     

Effects of Transition Metal Oxides on Thermal Conductivity of Mould Fluxes

The thermal conductivity of the mould fluxes containing transition metal oxides was measured by hotline method at different temperatures. The relationship between the thermal conductivity of mold fluxes and the contents of transition metal oxides was discussed. The synthetic slags were composed of 30.0% — 35.4% CaO, 34.7% — 38.6% SiO₂, 6% Al₂O₃, 9% Na₂O, 14.4% CaF₂, 0–4% Cr₂O₃ and 0–8% MnO in mass percent. The results indicated that Cr₂O₃ and MnO had a negative effect on thermal conductivity of mold fluxes. The thermal conductivity of mold fluxes was about 0.25 — 0.55 W/(m K) when the temperature reached 1300 °C, and it increased sharply to about 1.32–1.99 W/(m K) when the temperature reduced from 1300 to 1000 °C. The thermal conductivity of mold fluxes containing Cr₂O₃ and MnO was 10%—25% lower than those of original fluxes. The decrease in thermal conductivity was attributed to the change of molecular structure of mold fluxes. In addition, the poor integrity and regulation of polycrystal structure, complexity of crystal structure, and effects of impurities in the boundary and lattice distortion leaded to the reduction in the thermal conductivity. Na₂CrO₄, Mn₂SiO₄ and other minor phases were also found in the samples containing Cr₂O₃ and MnO, respectively.     

稀土氧化物对焊缝金属抗高温氧化腐蚀性能的影响

本文通过在焊条药皮中分别添加微量稀土氧化物Ｌａ２Ｏ３及ＣｅＯ２,研究其对焊条熔敷金属在空气中和含硫气氛中抗高温氧化及腐蚀性能的影响。结果表明：微量稀土氧化物在焊条药皮中的加入,对其熔敷金属抗高温氧化性能有所提高,对在含硫气氛中的抗高温腐蚀性能有显著提高,添加Ｌａ２Ｏ３的焊条熔敷金属比添加ＣｅＯ２的焊条具有更好的抗高温硫腐蚀性能。     

机械合金化制备金属难熔化合物

在介绍机械合金化特点的同时，重点研究和讨论了机械合金化制备金属难熔化合物的过程及机理，并认为机械合金化是制备难熔化合物及其材料的一种行之有效的方法。