最新色国产精品精品视频,中文字幕日韩一区二区不卡,亚洲有码转帖,夜夜躁日日躁狠狠久久av,中国凸偷窥xxxx自由视频

A novel method to prepare ultrafine WC was proposed: the PbWO₄ prepared by hydrothermal synthesis was used as raw material, and WC was obtained through the carbothermic reduction-carburization process. PbWO₄ was used as the tungsten intermediate product to avoid the introduction of ammonia nitrogen reagent. The carbon reduction method can avoid the generation of water vapor and inhibit the growth of tungsten powder. Results show that more than 99.9wt% of W is extracted in the form of PbWO₄ from the Na₂WO₄ solution under the conditions of initial pH value of 7.0, reaction temperature of 160 °C, and reaction time of 4.5 h. Then, the homogeneous mixture of W and C is obtained by the carbothermic reduction of PbWO₄ at 950 °C for 3 h with the molar ratio of carbon:tungsten as 5. Pre-adding excessive carbon in the mixture can inhibit the agglomeration of tungsten powder. Subsequ-ently, the WC powder with particle size of about 60 nm is obtained by the carburization of the W and C mixture at 1200 °C for 6 h.