Ultrafine Tungsten Carbide by Direct Reduction Carbonization Preparation

Ultra-fine cemented carbide made from ultra-fine tungsten carbide powder has the characteristics of high strength and high hardness, which effectively solves the contradiction between hardness and strength of traditional cemented carbide. It is widely used in making micro-drills for integrated circuit board, printing needles for dot matrix printers, precision tooling, cutting tools for difficult-to-process materials, woodworking tools, medical dental drills and so on.

Direct reduction carbonization technology is an advanced technology to produce ultra-fine tungsten carbide powder. It is generally used to heat tungsten-containing precursor powder and a certain proportion of carbon source in non-oxidizing atmosphere. The reduction reaction and carbonization reaction are carried out simultaneously to obtain tungsten carbide powder.

Researchers have developed a method to produce ultra-fine tungsten carbide powder with a total carbon content closer to stoichiometric carbon content and lower free carbon content. The process includes:

The mass percentage of carbon content in precursor powders is 14.5% and the remainder is Purple Tungsten WO_2.72. The mass percentage of chromium trioxide with precursor powders is 1%. The powders were milled in alcohol with a liquid-solid ratio of 400 ml/kg and a milling time of 24 hours. The powders after ball milling are dried in an oven at 80-95 ℃ for 3 hours. The dried powders are loaded into graphite boats and carbonized in a non-oxidizing atmosphere for the next time. The carbonization temperature is 1000-1100 ℃ and the carbonization time is 1 hour. The total carbon content was 5.96% when the carbonized products were mixed by ball milling for 3 hours. The carbon content is 6.15%. After 6 hours of ball milling and mixing, it is loaded into graphite boat and carbonized twice in H₂. The second carbonization temperature is 1200-1300 ℃, and the carbonization time is 1 hour. After milling and sieving the secondary carbide products for 6 hours, the total carbon content of ultrafine tungsten carbide powder is 6.15%, free carbon is 0.04%, BET particle size is 0.211 um, and the total carbon content is close to stoichiometric carbon content.

Compared with other tungsten sources, violet tungsten is a loose needle-like aggregate structure, which is more suitable for the preparation of fine particles in morphology. Therefore, in the process design, Purple Tungsten is milled by ball milling for a long time, with finer particle size, then directly reduced and carbonized under suitable conditions, and the carbon content of the product is better controlled by secondary carbonization. Therefore, the ultrafine tungsten carbide powder produced has narrow particle size distribution, better dispersion and uniformity, and its total carbon content is closer to stoichiometric carbon content, lower free carbon content and chemical purity reaches 99.8% above.

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