钨矿中砷资源化利用和砷致钨粉细化及在WC-Co硬质合金中的应用

Arsenic (As) is removed and controlled as a detrimental impurity element in the process of tungsten metallurgy. However, tungsten powder was significantly refined by adding a certain amount of arsenic and it improved the mechanical properties of WC-Co cemented carbide which was found by our previous experimental. The arsenic can be regard as a useful alloying element to utilize and the formation of W-As compound will not harm to human body and environment in the preparation of cemented carbide. This project will provide theoretical and practical basis for the preparation of nanometer tungsten powder and ultrafine-grained WC-Co cemented carbide by direct utilize the arsenic in tungsten ores.The evolution of arsenic is understood by its effect on the morphology and structure of tungsten oxide. The refining mechanism of As in the hydrogen reduction process of tungsten oxide is understood by studying its effect on the nucleation and growth of tungsten powder. The carbonization mechanism of W-As composite nano-powder is understood by studying the existence form and distribution of As element in WC powder and building the model of As impacts on WC grain growth. The law of As effects on the microstructure and properties of cemented carbide is concluded by analysing its effect on the dissolution and precipitation of WC particles in the process of Co liquid phase sintering. The high-performance WC-Co cemented carbide is prepared by adjusting and optimizing the best addition amount of As.

传统观念砷作为有害杂质元素在钨冶金过程中去除并严格控制，但通过我们前期研究发现，均匀添加一定量的砷能显著细化钨粉、大幅改善WC-Co硬质合金的力学性能，同时会形成稳定的钨砷化合物不会对人体和环境造成危害。本项目拟深入开展研究工作为将砷作为有益合金元素应用于纳米W粉及超细晶WC-Co硬质合金制备提供理论和实验依据。研究As对氧化钨形貌及结构的影响，理解As的演变情况；研究As对W颗粒形核和长大的影响，理解As在氧化钨氢还原过程中致钨粉细化的机理；研究钨粉碳化过程中As的存在状态及分布情况，建立As对WC颗粒生长影响的模型，理解纳米W-As复合粉末的碳化机理；分析As在液相烧结过程中对WC颗粒在Co相中的溶解析出的影响，得出As对硬质合金组织与性能的影响规律，调整并优化As的最佳添加量，制备出高性能WC-Co硬质合金。

在钨冶金工业上，砷通常作为钨矿原料中的主要杂质元素而去除，而本研究则考虑利用其中的杂质元素砷来细化钨粉及制备超细晶WC-Co硬质合金。本项目采用“固-液”混合法，在仲钨酸铵原料中添加一定量的As元素，通过煅烧、氢还原、碳化、液相烧结等工艺，制备出粒度均匀的纳米W粉、超细WC粉和性能优异的超细晶WC-Co硬质合金。研究获得的主要结论如下：.1. APT-As前驱体复合粉末煅烧过程中，一部分As元素会以气态As2O3的形式从前驱体中逸出，另一部分与W、O元素结合形成W2O3(AsO4)2三元化合物，最终As将以As2O3和W2O3(AsO4)2的形式存在于氧化钨粉中。.2. 随着As含量的增加，W-As复合粉末的粒径逐渐减小。As含量0.1wt% 是W粉细化的临界值，当As含量达到1.0wt%时，可制备出平均粒径为80nm的W-As复合粉末。在WO3-As复合粉末氢还原过程中，生成的WAs2第二相为W形核提供形核核心，增加W的形核率，并形成“核（WAs2）—壳（W）”结构的W-As复合纳米粒子。.3. W粉被碳化后，As仍以WAs2的形式存在于WC粉中，制得的WC-1%As复合粉末分散性良好、粒径均匀，其平均粒径为0.22μm。在碳化过程中，WAs2分布于WC颗粒之间，阻碍了WC颗粒通过晶界迁移而长大，并减弱了细小WC颗粒之间的团聚作用。.4. 在WC-Co硬质合金液相烧结过程中，溶解于Co相内的WAs2将阻碍WC在Co相内的溶解及析出，进而抑制WC颗粒长大。YG6-1%As合金晶粒均匀，其平均晶粒尺寸为0.47μm。YG6-1%As合金的致密度、硬度及断裂韧性分别为97.3%、1239.8Hv、10.86Mpa·m1/2，与YG6合金相比，均有较大幅度地提高。