【作者】 姚建明；

【导师】 张廷安；

【作者基本信息】 东北大学 ， 有色金属冶金， 2009， 硕士

【摘要】 高钛铁是指含钛量为65%～75%的钛铁合金,是一种用途较为广泛的特种铁合金。目前制备优质高钛铁的主要方法为重熔法,但该方法采用废钛材为原料,生产成本较高,限制了其广泛应用。传统的铝热还原法制备的高钛铁存在氧含量高,杂质多等缺点。我国受废钛材原料的限制,主要采用铝热还原法制备钛铁。针对铝热法制备钛铁的技术难点,为了提高铝热法制备钛铁的质量,本论文提出了基于铝热还原-真空精炼法制备低氧优质高钛铁的新工艺,即将铝热还原得到的粗高钛铁进行真空精炼以达到脱氧去夹杂的目的。通过对铝热反应绝热温度以及单位热效应的计算,结果表明反应过程中单靠铝热反应放出的热量来维持体系的能量平衡是不够的,这也是造成铝热法高钛铁质量差的主要原因,因此需要通过外界对体系提供热量来维持反应的正常进行。铝及镁还原TiO₂体系的热力学计算结果表明:Al-TiO₂反应体系TiO₂生成Ti₂O₃最容易反应,TiO₂生成TiO的反应次之,TiO生成Ti在热力学上最为困难,添加CaO能明显降低吉布斯自由能,使其反应更容易发生。Mg-TiO₂反应体系与Al-TiO₂反应体系类似,但是一些反应达到平衡时的温度更低。采用DTA技术研究了以Al、Mg为还原剂的还原反应动力学过程,利用Freeman-Carroll法对动力学过程进行了分析探讨,计算了反应的表观活化能和反应级数。Al还原TiO₂的反应表观活化能为164.497kJ·mol^-1,反应级数为0.4144。Al还原TiO₂体系中添加CaO后会导致反应滞后,反应1252℃左右进行,反应表观活化能为93.676kJ·mol^-1,反应级数为0.00789。Mg还原TiO₂反应表观活化能为383.235kJ·mol^-1,反应级数为0.591。Al-Mg还原TiO₂在573℃出现的放热峰为Mg还原TiO₂,表观活化能为404.01kJ·mol^-1,反应级数为0.5838,而在1244℃左右的放热峰为Al还原反应,表观活化能为208.083kJ·mol^-1,反应级数为0.1655。研究了精炼钛铁基本渣系的物化性能,CaO-Al₂O₃-TiO₂中低含量的TiO₂能降低熔渣的黏度,增强其流动性,当TiO₂超过一定量导致渣系初晶温度的提高以及熔渣过热度的降低,熔渣的黏度增大。添加适量的MgO能够有效改善CaO-Al₂03-TiO₂三元渣的流动性。通过计算得出熔渣高温段的黏流活化能,其变化趋势与渣系黏度测量值变化趋势相吻合。根据炉渣结构的共存理论与CaO-Al₂O₃-TiO₂三元渣系在不同温度和TiO₂成分下黏度的文献值,建立了三元渣系的作用浓度和黏度计算模型,结果表明随着TiO₂含量的增加,TiO₂作用浓度增加,低含量的TiO₂能够降低熔渣的黏度,但是随着TiO₂含量的继续增加,液态渣的黏度增加,恶化熔渣流动性,计算值与文献值、实测值吻合。并利用该模型计算了不同CaO/Al₂O₃比值下渣系的低熔点相和高熔点相的浓度,与文献吻合,佐证了共存理论模型对该渣系的适用性,具有很好的理论价值和实际意义。通过对精炼高钛铁产品微观结构与化学成分的分析,并与原料高钛铁相比较,发现精炼能够有效地去除粗钛铁中的氧化铝等夹杂,起到辅助降低氧含量的目的。直接重熔的合金中相明显较少,基本以FeTi相,钛氧固溶体,铁钛氧固溶体和铁的氧化物形式存在。铝热还原制备的合金中相较复杂,且夹杂相较多。二次精炼所得的合金致密,Al残留含量由3.51%下降到2.17%,Si残留含量由2.16%下降到0.81%,尤其是氧含量由12.20%下降到3.20%,基本符合优质高钛铁的技术指标。更多还原

【Abstract】 High titanium ferroalloy is a kind of special ferroalloys containing 65%～75% titanium, which has broad applications. At pressent, the major method of producing top-quality high titanium ferroalloy is remelting, however, this method is used waste titanium as raw materials and the production cost is relatively high, which restricts its extensive application. The high titanium ferroalloy prepared by traditional aluminothermy reduction process has many defects, such as high oxygen and impurity contents. Due to the limitation of waste titanium in China, the method of Alumino-thermic reduction was mostly used in industry. In order to improve the quality of titanium ferroalloy produced by Alumino-thermic reduction, focusing on the existing technical difficulties in the preparation of titanium ferroalloy, this paper presents a new process basing on Alumino-thermic reduction-vacuum melting, that is to refine the crude production of high titanium ferroalloy produced by Alumino-thermic reduction so as to remove the oxygen and impurity.According to the calculations of adiabatic temperatures and unit thermal effect by thermite reaction, the heat that released only by thermite reaction is not enough to maintain the system’s energy equilibrium during reaction procedure. This is also the leading cause for low quality of high titanium ferroalloy prepared by aluminothermy; therefore it needs the outside to provide heat to maintain the system’s normal reaction.The thermodynamic calculation results of Al-TiO₂ and Mg-TiO₂ reaction systems indicate that the TiO₂→Ti₂O₃ reaction occurs most easily, TiO₂→TiO reaction the second, and TiO→Ti reaction occurs most difficultly, and adding CaO could evidently reduce Gibbs Free Energy and make the reaction more easily. Mg-TiO₂ reaction system is similar to Al-TiO₂ reaction, but some reactions reach the equilibrium at lower temperatures.The reaction process kinetics used Al,Mg as reducing agent were studied by DTA technology, the kinetic mechanisms were analyzed by Freeman-Carroll method to calculate the reaction’s apparent activation energies and the reaction orders. The apparent activation energy of Al reducing TiO₂ is 164.497 kJ·mol^-1 and reaction order is 0.4144. The addition of CaO in the Al+TiO₂ reaction system delays the reaction, with the reaction occurring at the temperature around 1252℃, the apparent activation energy is 93.676 kJ·mol^-1 and reaction order is 0.00789. The activation energy is 93.676 kJ·mol^-1 and reaction order is 0.00789. The apparent activation energy of Mg reducing TiO₂ is 383.235 kJ·mol^-1 and reaction order is 0.591. The exothermic peak is the reaction between Mg+TiO₂ when the temperature is 573℃in the Al+Mg+TiO₂ reaction systems, the apparent activation energy is 404.01 kJ·mol^-1 and reaction order is 0.5838. While the other exothermic peak at 1244℃is reaction between Al+ TiO₂, the apparent activation energy is 208.083 kJ·mol^-1 and reaction order is 0.16552.The physicochemical properties of main refining titanium ferroalloy slags are studied;low content TiO₂ can reduce viscosity of CaO-Al₂O₃-TiO₂ slag systems and increase their fluidity. While TiO₂ reaches a certain value, the liquidus temperature of the system and the reduction in the degree of superheat of the slag melt goes up, which result the viscocity of slags increased.Adding appropriate amount of MgO to the CaO-Al₂O₃-TiO₂ slags can improve the fluidity of the slags effectively. By calculation, the variation trend of slags’ viscous flow activation energies of the slag systems are in accordance with the trend of measured viscosities of slag samples.According to the coexistence theory of slag structure and the referenced viscosities of CaO-Al₂O₃-TiO₂ at different temperatures and TiO₂ compositions,the calculation of mass action concentrations and viscosity for CaO-Al₂O₃-TiO₂ slag system has been established.The computation results showed that along with the increase of TiO₂ content, the action concentrations of TiO₂ were increasing, and low content TiO₂ can reduce the viscosity of the slags, But when the TiO₂ continued to increase, the viscosity of slag would increase, the fluidity of slag become worse, and the calculated results agree well with the values of reference and actual experiments record before.Also,the concentration of high melting point phase and low melting point phase at the different rate of CaO/Al₂O₃ are calculated by this theory computation model,which are identical with the references.This confirmed the applicability of the coexistence theory for the slag system, which has important theoretic value and practical meaning for the viscisity estimation.Microstructure and chemical compositions of high titanium ferroalloy throughrefining are analysed and high titanium ferroalloy prepared by aluminothermy are compared with, the paper found that refining could remove inclusions such as Al₂O₃ from the raw high tatinium ferroalloy efficiently,so as to aid to reduce the oxygen indirectly. It was found that phases in titanium ferroalloy prepared by remelting are comparatively less and the main phases were FeTi, titanyl solid solution, FeTiO solid solution and iron oxides. While phases in titanium ferroalloy prepared by aluminothermy method are comparatively complex and phases of inclusion are relatively much more. The productions prepared from refining have compact structure. The residual Al content of 3.51% decreased to 2.17%, and residual Si content from 2.16% down to 0.81%, especially oxygen content from 12.20% to 3.2%, which are in accord with the technical index of good-quality high titanium ferroalloy.更多还原