【作者】 刘紫兰；

【导师】 李强；

【作者基本信息】 福州大学 ， 材料学， 2005， 硕士

【摘要】 本文采用XRD、SEM等分析手段比较研究了WO3-G系和WO3-G-Co3O4系两种组分的混合粉末经高能球磨后分步进行还原和碳化反应制备超细WC与WC-Co粉末材料的过程。球磨过程能量转化计算表明,随着球磨机转速Ω的增大,磨球的平均线速度呈线性增大。随着球粉比RBP增大,碰撞频率f显著增大,平均自由程S显著减小,略有减小。WO3-G系和WO3-G-Co3O4系原始粉末在球磨过程中,随着时间的延长,粉末不断细化,在不同阶段开始诱发WO3向WO2的还原反应。随球磨机转速Ω的增大,球磨粉末的晶粒尺寸显著减小。球粉比对WO3和石墨的固态还原反应有显著影响,随球粉比增大,固态反应的诱发时间缩短。Co3O4的添加有利于提高球磨效率。选择供后续还原和碳化用球磨粉末的优化球磨工艺参数为:对WO3-G系,球粉比40:1,球磨机转速500r/min,球磨时间12h;对WO3-G-Co3O4系,球粉比30:1,球磨机转速500r/min,球磨时间12h。该两组工艺球磨后粉末的晶粒尺寸在70-100nm范围。经优化球磨工艺球磨的WO3-G系和WO3-G-Co3O4系粉末在流动H2和Ar混合气氛中还原时,随着还原温度的升高和还原时间的延长,WO3-G系球磨粉末中WO3的主要转变顺序为:WO3→WO2.9→WO2→W;WO3-G-Co3O4系中WO3的主要转变顺序为:WO3→WO2.9→WO2.72→WO2→W。确定WO3-G系和WO3-G-Co3O4系球磨粉末的优化还原工艺为还原温度700℃,还原时间2h,还原粉末的晶粒尺寸在100-200nm范围。经优化还原工艺还原后的WO3-G系和WO3-G-Co3O4系粉末在流动的Ar气中碳化时,随着碳化温度的升高和碳化时间的延长,WO3-G系中,首先形成W2C相,继续碳化逐渐转化为WC。WO3-G-Co3O4系碳化反应主要过程为:W(Co3W)→Co6W6C→Co3W3C→W2C→WC。Co对还原和碳化反应都具有催化作用。确定优化碳化工艺为:WO3-G系还原粉末碳化温度1000℃,碳化时间2h,碳化得到的WC晶粒尺寸在400-500nm范围。WO3-G-Co3O4系还原粉末碳化温度900℃,碳化时间2h,碳化得到的WC-Co复合粉末中WC晶粒尺寸在200-300nm范围。更多还原

【Abstract】 Synthesis of ultrafine WC and WC-Co powders respectively using WO3-G and WO3-G-Co3O4 powder mixtures as starting materials by high energy ball milling followed by reduction and carburization has been comparatively investigated by XRD and SEM techniques. The energy transfer calculation during milling revealed that the mean velocity of milling ball increased linearly with the increase of milling speed Ω. The increase of the ball-to-powder weight ratio RBP resulted in significant increase of average impact frequency f, decrease of average free path S, and slight decline of milling ball velocity . During the milling of WO3-G and WO3-G-Co3O4 starting powders, the size of milled powders gradually decreased with the increase of the milling time, and the reduction reaction of WO3 to WO2 occured at different stages. With the higher milling speed Ω, the grain size would be finer. The ball-to-powder weight ratio RBP had a significant effect on solid-state reduction reaction between WO3 and graphite. The higher RBP, the shorter is the incubation period of the reduction reaction. Addition of Co3O4 is helpful to the improvement of the milling efficiency. The optimum milling process parameters were ball-to-powder weight ratio RBP of 40:1, milling speed Ω of 500r/min, miling time of 12h in WO3-G system, and RBP of 30:1, Ω of 500r/min, miling time of 9h in WO3-G-Co3O4 system. The grain size of final milled powders was in the range of 70-100nm.The WO3-G and WO3-G-Co3O4 powders milled by optimum milling process were respectively subjected to reduction reaction in a flowing gas mixture of H2 and Ar. With the increase of reduction temperature and time, the main reaction sequence appears as WO3→WO2.9→WO2→W in WO3-G system, and the main reaction sequence appears as WO3→WO2.9→WO2.72→WO2→W in WO3-G-Co3O4 system. The optimun reduction process parameters were reduction temperature of 700℃, redction time of 2h. The grain size of final reduced powders was in the range of 100-200nm.The powder reduced by optimum reduction process was carburized in a flowing Ar. In WO3-G system, with the carburation temperature and time increased, W2C formed at first, <WP=4>furthermore, it gradually converted to WC. With the increase of carburation temperature and time, the main carburization reaction sequence appears as W(Co3W)→Co6W6C→Co3W3C→W2C→WC in WO3-G-Co3O4 system. Co had catalysis on the reduction and carburization reaction. The optimun carburization process parameters were carburization temperature of 1000℃, carburization time of 2h. The grain size of final WC was in the range of 400-500nm. The optimum carburization process parameters were carburization temperature of 900℃, carburization time of 2h. The size of WC grain in the final WC-Co composite powders was in the range of 200-300nm.更多还原