Ultrafine Tungsten Carbide Powder Preparation by Direct Carbonization Reduction

Ultra-fine cemented carbide made of ultra-fine tungsten carbide powder has high strength and high hardness, which effectively solves the contradiction between hardness and strength of traditional cemented carbide. It is widely used in the manufacture of integrated circuit board micro drill bits and dot matrix printing. The table machine prints needles, precision tools, difficult-to-machine materials, woodworking tools, medical drills, etc.

Direct reduction carbonization is an advanced technology for the production of ultra-fine tungsten carbide powder. Generally, tungsten precursor powder and a certain proportion of carbon source are heated in a non-oxidizing atmosphere, and the reduction reaction and carbonization reaction are carried out simultaneously to obtain tungsten carbide powder. Because the carbon content in the production process is difficult to control, it is generally used to react with a certain proportion of carbon sources before adjusting the total carbon content of the reactants to a certain value. The second reaction was carried out. Compared with the traditional method of preparing ultrafine tungsten powder by hydrogen reduction and then carbonization, this method has the advantages of simple process and low production cost. Recently, ultrafine tungsten carbide powders with less free carbon and less stoichiometric carbon have been prepared by direct carbonization reduction method. The process includes the following steps:

The precursor powder mixture 2000g was prepared, in which the quality percentage of carbon black content was 14.5%, the remaining amount was Purple Tungsten WO_2.60, and the quality percentage of chromium trioxide with precursor powder was 1%. Alcohol is used as ball milling medium and the milling time is 24 hours. The powders after ball milling were dried for 3 hours in an oven at 80-95 ℃. The dried powders were carbonized once in a graphite boat. The carbonization temperature was 1000-1100 ℃ and the carbonization time was 1 hour. The total weight of material (c) is 1436 g, the total carbon content is 5.96%, the oxygen content is 0.45%, and the nitrogen content is 0.01%. So the B is 6.48, and the D is 5.97. According to the empirical formula set by the relationship between carbon, oxygen and nitrogen, A is 7.32g, the amount of carbon is allocated to 6.15% (the expected carbon content of the product). After 6 hours of ball milling and mixing, the graphite boat is loaded and carbonized twice in H₂. The second carbonization temperature is 1250-1300 C, and the carbonization time is 1 hour. After 6 hours ball milling and sieving of secondary carbide products, the total carbon content of ultrafine tungsten carbide powder was 6.14%, free carbon 0.04%, BET particle size 0.211 um. The fine distribution of ground Marlevin was a single-peak normal distribution with a diameter distance of 1.470, D10 of 0.391 um, D50 of 0.883 um, D90 of 1.689 um.

After high energy ball milling and mixing drying of precursor powders containing carbon black and purple tungsten, no additional gas is added to carry out one-time carbonization, and then the first-time carbonization product is mixed by ball milling, and the second-time carbonization product is milled and sifted to obtain uniform ultrafine tungsten carbide powder.

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