铝电解槽用新型TiB2-MoSi2复合阴极材料的低成本、净尺寸制备、组织与性能

Titanium diboride (TiB2) materials have good electrical conductivity and don't react with liquid aluminum (Al) and cryolite. Therefore, they can increase the outcome of aluminium, improve the current efficiency and reduce the pollution damage, when used as cathode materials for aluminum electrolytic cell. However, there are some problems with the TiB2 ceramics and their composites, such as high fabrication cost, large deformation during the sintering and difficulty in dencification and fabrication of large-sized products, which impair their application in aluminum electrolytic cell. This project comes up with for the first time a new method for the fabrication of low-cost, net dimentional (without deformation during the sintering), large-sized, high-density TiB2-MoSi2 composites. This method comprises the infiltration of a porous TiB2-Mo compact by molten silicon. Based on the optimization of the raw material proportion, adjustment of the pore structure of the preforms and control of the infiltration parameters, the dependence of the microstructures, phase interface, mechanical properties, electrical properties and erosion performance, etc. on the fabrication parameters will be studied systematically. This project will also illustrate the relevant methods and underlying mechanisms of improving the wettability of the preforms against molten silicon, controlling the infiltration capacity of molten silicon, reducing the volumetric proportions of the residue silicon and strengthening the residue silicon as well. This project will not only pave the way for the low-cost, net dimensional fabrication of high-density, high-performance TiB2-MoSi2 composites, but also contribute theoretically and technologically to the development and application of TiB2 composites as cathode materials for aluminum electrolytic cell.

因硼化钛(TiB2)材料具有优良的导电性和不与铝液及冰晶石反应的特点，用作铝电解槽阴极可以增大铝产量、提高电流效率、减少环境污染。然而，硼化钛陶瓷及其复合材料存在制备成本高、烧结过程中变形大、难以致密化和难以制备大尺寸制品的问题，制约了其在铝电解槽方面的应用。本项目提出一种适合制备大尺寸硼化钛复合材料的新方法，通过在TiB2-Mo坯体中熔渗硅，实现高致密度TiB2-MoSi2复合材料的低成本、净尺寸(无烧结变形)制备。项目从系统研究原料配比的优化、坯体孔隙结构的调控、熔渗参数的控制以及残留硅的强化等着手，分析材料的显微组织、相界面、力学性能、电学性能和侵蚀性能等的变化规律，阐述改善熔融硅对坯体润湿性、控制熔融硅熔渗量、降低残留硅体积分数和强化残留硅的方法和原理。研究工作将为致密度高、性能优良的TiB2-MoSi2复合材料的低成本、净尺寸制备以及在铝电解槽阴极上的应用提供理论基础和技术支撑。

硼化钛(TiB2)材料因具有优良的导电性和不与铝液及冰晶石反应的特点，可用作铝电解槽阴极材料。但TiB2阴极复合材料的现有制备工艺存在制备成本高、烧结过程中变形大、难以致密化和难以制备大尺寸、复杂形状制品的问题，限制了这一材料的推广应用。本项目针对这些问题，提出采用熔渗Si技术、低成本、净尺寸制备致密度高、性能优良的TiB2基新型铝电解槽阴极材料的技术。研究了坯体孔隙率的调控问题、熔融Si熔渗量的控制、残留Si强化机理以及材料的组织和性能，找出了降低残留Si含量、残留Si强化的原理和方法。项目的研究对于提高该材料的性能和净尺寸制备性能优良的TiB2阴极复合材料具有重要的理论意义和使用价值。取得的主要结果为：(1)随成形压力的增加，坯体孔隙率降低，复合材料中游离Si含量降低，当成形压力为200MPa时，材料的力学性能最佳，其开口气孔率、维氏硬度、抗弯强度和断裂韧性分别为0.90%、13GPa、354MPa和6.8MPa·m1/2。当TiB2的粗颗粒(28.9μm):中颗粒(6.9μm):细颗粒(3.7μm)为42:32:26时，可将材料中游离Si的含量降低至15vol%。(2)随着熔渗温度的提升，复合材料中SiC的含量呈增加趋势，MoSi2和游离Si的含量呈减少趋势，并且MoSi2颗粒尺寸明显增加；渗Si过程中，Mo向熔渗剂Si中扩散、流失，并与Si反应生成MoSi2，导致复合材料中MoSi2的含量降低。(3)当熔渗温度为1450℃，以酚醛树脂为强化元素C的C源，原料中同时引入8wt%C与15wt%Mo时，材料性能最佳，其开孔气孔率、抗弯强度、断裂韧性、维氏硬度和电阻率分别为0.40%、358MPa、6.0MPa·m1/2、20GPa和6.31×10-7Ω·m。(4)TiB2-MoSi2-SiC、TiB2-SiC和TiB2-MoSi2三种复合材料，在400~1350℃时均表现出良好的抗氧化性能；其电阻率均低于9.72×10-7Ω·m，远低于电解铝阴极材料国标值42×10-6Ω·m；实验室电解铝实验表明：以SiC为强化相时，所得TiB2基复合材料的抗侵蚀性最好，当原料C含量为25wt%时，复合材料残余Si的含量可降低至14vol.%；对应TiB2复合材料抗腐蚀性最好，其腐蚀速率为0.09mm/h。