氧化铝的真空碳热还原—氯化—歧化反应(英文)

通过XRD物相分析和热力学分析研究氧化铝的真空碳热还原—氯化—歧化反应。以氧化铝和石墨为原料,在真空下、1643-1843K的温度范围内进行实验。结果表明,AlCl3(g)与氧化铝碳热还原产生的Al2O(g)或Al(g)反应生成AlCl(g),该AlCl(g)在较低温度下歧化分解为金属铝和AlCl3(g);当压力为100Pa、温度为980K时,AlCl(g)的歧化反应率达到90%。生成的金属铝可以吸附催化CO歧化为C和CO2,并可以与CO二次反应形成Al4C3、Al2O3、C和CO2,导致铝产物中含有C、Al4C3和Al2O3。产物铝中所含的这些杂质随着AlCl(g)歧化反应温度的降低而减少。AlCl3(g)在接近室温的温度下冷凝下来。     

真空下碳热还原氧化铝的二次反应

通过热力学分析和实验研究了真空条件下碳热还原氧化铝的二次反应.热力学分析表明:低温、高压有利于碳热还原氧化铝的产物Al2O、Al与CO的二次反应.分别绘制了Al2O和Al在一定分压下,与CO的二次反应平衡曲线图,给出了各二次反应的CO平衡分压与温度的关系,根据CO的分压和温度、利用二次反应平衡曲线图分析二次反应的产物.氧化铝与石墨的真空碳热还原实验研究证实:Al2O与CO降低温度首先生成Al4O4C和C,Al与CO降低温度首先生成Al4O4C和Al4C3,符合根据二次反应平衡曲线图分析得到的结论,说明二次反应平衡曲线图的合理性.     

真空下碳热还原氧化铝的热力学

对真空条件下碳热还原氧化铝进行热力学研究.结果表明:在1 643～1 843 K的温度范围内,真空碳热还原氧化铝生成气体产物,该气体在温度降低时发生二次反应形成冷凝物,反应过程中体系压力保持在5～150 Pa.热力学分析表明:当体系压力为1～100 Pa时,在1 200～1 900 K的温度范围内,碳热还原氧化铝生成Al2O、Al和CO;生成Al2O的初始反应温度低于生成Al的初始反应温度,但反应温度高于一定值时,更易生成Al气体,该温度取决于体系的压力;当CO的分压分别为1、10和100 Pa时,Al2O稳定存在的温度分别高于1 462、1 560和1 674K,Al气体稳定存在的温度分别高于1 514、1635和1 777K.     

氧化铝在碳热还原-氯化法炼铝过程中的行为

采用XRD、气相色谱仪、EDS及质量损失等手段与方法,在不同反应温度、系统压力、添加剂及反应时间对氧化铝在碳热及氯化过程进行研究。结果表明:碳热与氯化过程生成的气体主要是CO,含量达98.4%(质量分数)以上;碳热过程在50～100Pa、高于1693K时,Al4O4C与Al4C3开始生成,且含量随着温度的升高与保温时间的延长而增加;在1Pa及1773K时,Al4O4C碳热转化为Al4C3;分别添加10%Fe2O3与10%SiO2(质量分数),在40～100Pa、1803K、保温120～150min时,可使物料质量损失率达到26.70%与30.13%,促进碳热过程向生成Al4O4C与Al4C3方向进行;温度高于1853K不利于该反应的进行;碳热-氯化过程是Al2O3与Al4O4C、Al4C3及AlCl3共同反应生成低价氯化铝AlCl,气态AlCl进入低温区歧解得到金属铝。     

TiB2合成反应机理的优势区相图分析

随着碳热还原反应的进行,B2O3被C还原生成B2O2,B2O2进一步被碳还原生成B4C.碳热还原TiO2和B2O3合成TiB2的反应机理如下在1200～1300℃温度下,TiO2被C还原成中间产物Ti3O5;在1250～1300℃温度范围,B2O3被C还原生成中间气相产物B2O2;当还原反应温度达到1300℃以上时,中间产物Ti3O5与B2O2一起被C还原生成TiB2.     

氟盐对炼镁还原渣中氧化铝浸出率的影响研究

以白云石和菱镁石为原料以铝粉为还原剂真空热还原炼镁过程中添加氟化钙可使镁还原率提高5%以上,还原温度降低50℃,还原后还原渣的主要物相为CaO.2Al2O3,加入的氟化钙在还原过程会参与反应生成氟铝酸钙。在实验室以氢氧化钠和碳酸钠的混合碱液对该含氟盐还原渣中氧化铝的浸出进行了研究,研究结果表明:经碱液浸出后还原渣中的CaO.2Al2O3全部被分解,还原渣中的氧化铝浸出率在70%以上,浸出渣的主要物相为CaCO3。含氟盐炼镁还原中氧化铝的浸出率比不含氟盐的氧化铝浸出率低10%以上,在还原过程中生成的氟铝酸钙和浸出过程中生成的水合铝酸钙是导致氧化铝损失增加的主要原因。     

电热法生产铝硅合金的理论研究

从理论角度系统研究了Al2O3-C系、SiO2-C系、Al2O3-SiO2-C系热力学。结果表明,在Al2O3-C系中,碳热还原氧化铝过程的中间产物Al4C3,它与A12O3、A1之间有很大的溶解度,导致铝的提取率较低,给利用电热法直接制备金属纯铝带来了困难。在Al2O3-SiO2-C系中,硅在很大程度上改善了铝还原的热力学条件,其中间产物Al4C3、SiC等碳化物分别与SiO2、Al2O3反应进而生成铝-硅合金,使电热法生产铝-硅合金得以实现。动力学研究结果表明,在电热法生产铝-硅合金中,Fe的存在使铝-硅合金生成反应的起始温度大大降低,且Fe与Al、Si在熔融状态下可以无限互溶,Fe还有助于破坏碳热还原过程中容易生成的碳化物。     

真空氯化亚铝歧化法从氧化铝中提取铝

研究了以氧化铝和石墨为原料真空氯化亚铝歧化法提取铝的条件,包括反应温度、预反应和冷凝器的结构。结果表明：在1643~1843 K的温度范围内,氧化铝与碳的反应程度随着反应温度的升高而提高,但铝的提取率首先随着反应温度的升高而提高,在1743 K时达到最高,继续升高反应温度,铝的提取率反而降低;氧化铝与碳进行预反应可以提高金属铝的提取率;金属铝与CO的接触面积越小、冷凝温度越低,C、Al4C3和Al2O3杂质的含量越低,这取决于冷凝器的结构。     

真空下氯化亚铝歧化法提取铝的设备研究

设计了真空刚玉管式炉和真空石墨炉。真空刚玉管式炉不适于进行氧化铝的碳热还原-氯化-歧化反应。真空石墨炉成功用于利用该反应提取铝的实验研究,其高温反应区的温度可以控制在25℃~1570±2℃的范围内,其三氯化铝升华区的温度可以控制在25℃~200±2℃的范围内,且真空石墨炉操作方便。     

1000°～1800°K温度范围内Al-C-O系的热力学分析

本文对1000～1800°K 温度范围内的 Al—C—O 系进行了热力学分析。以稳定性标准和化学计量极限为基础,在所研究的整个温度范围内,确定了用石墨还原氧化铝的平衡条件。实验资料和计算数据表明,氧化铝和石墨反应生成碳化铝,碳化铝再还原氧化铝。在可实现的还原体系中,高温和相当小的 P_(Al) 和 P_(CO)值有利于这些反应的进行。本研究中确定的稳定的碳氧化物平衡与其它作者所断定的那些稳定反应不相符合。因此,文中报导的是对体系的动力学而不是对稳定平衡有利的那些反应。按照直接还原过程的要求,探讨了低价卤化物反应的热化学性质。验证了借生成一氯化铝以分离还原的铝的可能性。指出了这一方法在还原时是有效的,但此法在氧化铝还原工艺中尚未采用。     

Silica behavior in the alumina carbothermic reduction-chlorination process

The behavior of silica was investigated experimentally in an alumina carbothermic reduction process and chlorination process in vacuum. The results showed that, first, SiC was produced by SiO₂ and C, and then Al₄SiC₄ was produced by Al₄C₃, Al₄O₄C, C, and SiC during the alumina carbothermic reduction process at about 1,763 K. C, Al₃C₄ and Al₄O₄C decreased and Al₄SiC₄ increased as content of SiO₂ increased. The following chlorination process was blocked, and the recovery rate of aluminum decreased quickly compared with that without silica. It was inferred that silica might be unfavorable for aluminum extracted from alumina by carbothermic reductionchlorination process in vacuum at about 1763 K.     

In Situ Production of Fe-TiC Nanocomposite by Mechanical Activation and Heat Treatment of the Fe2O3/TiO2/C Powder

In this study, Fe-TiC nanocomposite was synthesized by carbothermic reduction of activated Fe₂O₃, TiO₂, and graphite powder mixture. The effect of 0, 5, and 20?h of high energy ball milling of mixture on the reduction process was also investigated. Comparing the results of the thermogravimetry analysis of milled and un-milled mixtures clearly showed that the reduction temperature decreased due to the milling process. XRD pattern of 20?h milled powder mixture proved that Fe-TiC nanocomposite was formed after the heat treatment of activated powder at 1100°C for 1?h under vacuum. The microstructure studies of the milled mixture by scanning electron microscope revealed homogenous distribution of TiC particles in the Fe matrix.     

Direct carbothermic reduction of ilmenite concentrates by adding high dosage of Na2CO3 in microwave field

A clean and efficient route for the utilization of ilmenite concentrates was proposed by direct carbothermic reduction in microwave field. High dosage of Na₂CO₃, which can be recycled, was added to accelerate the reduction reaction of ilmenite concentrates. After microwave heating in the temperature range of 1073?1123 K for 20 min, the main products were Na₂TiO₃ and metallic Fe with the metallization ratios being as high as 92.67%?93.21%. The reduction products were processed by water leaching, ball-milling in CO₂ atmosphere and magnetic separation in turn. The final products after magnetic separation were Fe-rich materials and Ti-rich materials (90.04 wt.% TiO₂), which can be used to produce iron and TiCl₄ or TiO₂. The optimized heating temperature was 1123 K in terms of metallization ratios, magnetic separation and caking property of the reduction products. Besides, the reduction mechanism of ilmenite concentrates with the addition of Na₂CO₃ in microwave field was also proposed.     

Effects of MgO on the Reduction of Vanadium Titanomagnetite Concentrates with Char

The effects of MgO on the carbothermic reduction behavior of vanadium titanomagnetite concentrates (VTC) from Chengde, China, were investigated via temperature-programmed heating under nitrogen atmosphere in a sealed furnace. Gaseous product content was measured by using an infrared gas analyzer, and it was found that the addition of MgO to VTC with char decreased the reduction rate and reduction degree, and the utilization of CO in VTC reduction was also reduced. X-ray diffraction results showed that magnesium titanate (Mg₂TiO₄) was formed but FeTi₂O₅ was not observed in the VTC reduction process by adding 6 wt.% MgO, which can be explained by thermodynamic analysis. Scanning electron microscopy revealed that the enrichment of Mg in the unreacted core was the main reason that the further reduction of VTC was restricted. However, comparatively pure particles of Mg₂TiO₄ were generated, and the titanium and iron were separated well due to the combination of magnesium and titanium.     

Direct solid-state synthesis of tungsten carbide nanoparticles from mechanically activated tungsten oxide and graphite

Solid-state carbothermic reduction of tungsten oxide (WO₃) to nano-sized tungsten carbide (WC) particles was achieved by calcining mechanically activated mixtures of WO₃ and graphite at 1215 °C under vacuum condition. By experiments and thermodynamic calculations, the intermediate phases, WO_2.72, WO₂ and metallic tungsten (W), were observed at 741 °C, which decomposed to synthesize the final product (WC). Homogeneity increase and associated decrease in the diffusion path by mechanical milling and formation of these intermediates are mainly responsible for the successful production of WC. The process indicates that solid-state synthesis of WC nanoparticles directly from as-milled mixtures of tungsten oxide and graphite powder is possible.     

Role of chlorine in the oxidation resistance of Ti-45at.% Al-1.6at.%Mn intermetallic compound

In order to investigate the role of chlorine in the oxidation resistance of Ti-45at.%Al-1.6at.%Mn intermetallic compounds, specimens with and without chlorine were prepared by a reactive sintering and a remelting process, respectively, and then isothermally oxidized at temperatures of 800 to 1000°C. The oxidation resistance of reactive-sintered Ti-45at.%Al-1.6at.%Mn containing 0.02 wt.%Cl was superior to that of remelted specimens due to the formation of a protective Al₂O₃, layer. From the results of an EPMA line scan of a cross-section of the oxide layer, carbon and chlorine peaks were detected on the TiO₂ layer of the reactive-sintered specimens suggesting that TiO₂ can decompose to TiCl₄ through the reaction with Cl₂ and C (or CO). As a result of the chlorination of TiO₂, the growth of TiO₂ could be constrained and a protective A1₂O₃ scale was easily formed on the reactive-sintered alloy.     

Mechano-thermal reduction of molybdenite (MoS2) in the presence of Sulfur scavenger: New method for production of molybdenum carbide

In this research, carbothermic reduction of molybdenite in the presence of sodium carbonate as sulfur scavenger by mechanical activation and heat treatment was studied. Mechanical activation of the mixed powders of molybdenite, graphite and sodium carbonate with 1:4:2 mol ratios were carried out by ball milling process under argon atmosphere for 10,20,40,50 and 70 h. The X-ray diffraction (XRD) patterns of samples revealed that no reaction occurred in the mill even after 70 h of milling. In order to study the mechanism of carbothermic reduction of molybdenite in the presence of sodium carbonate, simultaneous thermal analysis (STA) under heating rate of 10, 15 and 20 °C/min was carried out on the activated samples. XRD patterns and thermodynamic analysis of reaction products indicated that carbothermic reduction of molybdenite in the presence of sodium carbonate was advanced through the formation of intermediate phases Na₂MoO₄, MoO₂ in which the final products were Mo₂C, Na₂S. For separation of these two products, leaching by HCl and hot water was used. The XRD patterns of leached products were shown that molybdenum carbide with high purity was produced. The kinetics of reduction reaction was investigated and it was found that mechanical activation lowered the reaction temperature and activation energy.     

Size-controlled synthesis of nano Mo powders via reduction of commercial MoO3 with carbon black and hydrogen

In the present work, a novel method was proposed to synthesize pure nano Mo powder via temperature programmed pre-reduction of commercial MoO₃ by carbon black, followed by deep deoxidation with hydrogen. It was found that the carbothermal reduction of MoO₃ included three stages: MoO₃ → MoO₂ → MoO₂ + Mo₂C → Mo. It can be concluded that the morphology and size of the obtained Mo particles are mainly determined at the carbothermic reduction stage. The dispersed nucleation and controlled growth are critical issues for controlling the particle sizes of Mo, which could be achieved at the carbothermic reduction stage by using the raw materials of the MoO₃ and carbon black. Whereas, when the MoO₃ was directly reduced by hydrogen or active carbon with a larger particle size, or commercial MoO₂ were reduced with the carbon black, the dispersed nucleation and controlled growth of products can't be achieved. Meanwhile, to reduce the residual carbon content in the final Mo product, in the carbothermic pre-reduction process, the small amount of MoO₂ was kept in the pre-reduced Mo powders, which was removed by hydrogen at the deep deoxidation stage. The content of residual carbon content in the final produced Mo nanopowders can be reduced to about 0.02%. This method has the advantages of simplicity, low cost, and high efficiency. Therefore, it has great potential for the industrial preparation of nano Mo powders in a large-scale.     

A low-cost,efficient, and industrially feasible pathway for large scale preparation of tungsten nanopowders

Tungsten (W) is the most commonly used high-temperature refractory metal in many critical fields such as aerospace, military and electronic industries etc. This paper proposes a low-cost, efficient, and industrially feasible pathway for large scale preparation of tungsten nanoparticles via the combination of carbothermic reduction and hydrogen reduction processes. The new strategy involves the preparation process of pre-reduction W powder by reducing commercial WO₃ with insufficient carbon black at 1050 °C or 1150 °C to avoid the residue of carbon, and the deep reduction process of pre-reduction W powder by hydrogen 725 °C. By this process, most of the oxygen in WO₃ was reduced by carbon, and W particles with a much smaller size could be obtained owing to the absence of the volatile tungsten oxide, such as WO₂(OH)₂, which leads to the serious increase of particle size during the hydrogen reduction process. Tungsten nanoparticles with average particle sizes of about 40 nm and 75 nm have been successfully synthesized at 1050 °C and 1150 °C, respectively, with the residual carbon content as low as about 0.01%. This process can be readily extended to a large-scale industrial production of W nanopowders. Additionally, this new strategy has great potential to prepare other pure metals (or nanopowders) from their metal oxides via combining of carbothermic reduction (main process) and further reduction of other reducing agents.     

Reduction roasting–magnetic separation of vanadium tailings in presence of sodium sulfate and its mechanisms

Reduction roasting with sodium sulfate followed by magnetic separation was investigated to utilize vanadium tailings with total iron grade of 54.90 wt% and TiO_2 content of 17.40 wt%. The results show that after reduction roasting–magnetic separation with sodium sulfate dosage of 2 wt% at roasting temperature of 1150 °C for roasting time of 120 min, metallic iron concentrate with total iron grade of 90.20 wt%, iron recovery rate of 97.56 % and TiO_2 content of 4.85 wt% is obtained and high-titanium slag with TiO_2 content of 57.31 wt% and TiO_2 recovery rate of 80.27 % is also obtained. The results show that sodium sulfate has a catalytic effect on the reduction of tailings in the novel process by thermodynamics, scanning electron microscopy(SEM) and X-ray diffraction(XRD) and reacts with silica and alumina in the tailings to form sodium silicate and sodium aluminosilicate. Migration of elements and chemical reactions destroy the crystal structures of minerals and promote the reduction of vanadium tailings, resulting in that iron grains grow to large size so that metallic iron concentrate with high total iron grade and low TiO_2 content is obtained.