Abstract:

In order to avoid the formation of η phase (Co₆W₆C or Co₃W₃C) that adversely affect the sintering process and its products in the preparation process ultra-fine WC-Co powder, we propose a technical route of pre-reduction of WO₃-Co₃O₄ to WO₂-Co and then deep reduction carbonization to WC-Co. The influence of Co content and cobalt source particle size on the pre-reduction process of WO₃-Co₃O₄ was investigated at 600℃ H₂-C₂H₄-Ar atmosphere in a fluidized-bed reactor, and the deep reduction and carbonization properties of the pre-reduced products were tested. The results show that the presence of Co can catalyze the splitting of C₂H₄ to separate H₂ and C, significantly accelerate the pre-reduction rate of WO₃, and the pre-reduction rate increases significantly with the increase of Co content. The carbon evolution rate and carbon evolution amount of ethylene also increase with the increase of Co content. Cobalt source particle size has a significant effect on the pre-reduction rate of WO₃ and carbon evolution rate of C₂H₄. In this experimental system, the carbon evolution rate of C₂H₄ in nano cobalt source system is about twice that of micron cobalt source system. Meanwhile, WO₃ in nano cobalt source system also has faster reduction rate. The pre-reduced product was calcined with methane partial pressure of 1.25% at 950℃ for 60 min, and fine WC-Co composite powder without η could be obtained.

Key words: WO₃-Co₃O₄ system, fluidized-bed, reduction, powder

摘要：

为避免超细WC-Co粉体制备过程中形成对烧结过程及其产物带来不利影响的η相（Co₆W₆C或Co₃W₃C），提出了WO₃-Co₃O₄预还原至WO₂-Co，再深度还原碳化至WC-Co的技术路线。主要考察了600℃，H₂-C₂H₄-Ar气氛条件下，Co含量及钴源粒径对WO₃-Co₃O₄预还原过程的影响规律，并对预还原产物进行了深度还原碳化性能测试。结果表明，Co的存在可催化C₂H₄裂解析出H₂和C，显著加快WO₃预还原速率，且随着Co含量增加其预还原速率显著增加；乙烯析碳速率和析碳量也随Co含量增加而增加。钴源粒径对WO₃还原速率和C₂H₄析碳速率有显著影响，本实验体系下，纳米钴源体系中C₂H₄析碳速率大约是微米钴源体系的2倍；同时，纳米钴源体系中WO₃也具有较快的还原速率。8%Co含量的预还原产物在950℃、甲烷分压1.25%条件下焙烧60 min，可获得无η相的WC-Co复合粉体。

关键词: WO₃-Co₃O₄体系, 流化床, 还原, 粉体