Research On Preparation Of Ultrafine Tungsten Powder And Tungsten Carbide Powder

Refractory metal tungalloy, which has a series of excellent physicalproperties, has been widely used in several industries includingsemiconductor manufacturing industry. Ultrafine tungsten powder andtungsten carbide powder are the main raw materials of high-qualitytungsten-base electrical contact alloys, electronic packaging materials,sputtering target materials of refractory gate and barrier layer in integratedcircuit, electronic emission materials, etc. The quality of ultrafine tungstenpowder and tungsten carbide powder has direct influence on the performanceof these tungsten-base electronic materials, thus the manufacturing ofhigh-quality ultrafine tungsten powder and tungsten carbide powder is crucialto semiconductor manufacturing industry.The preparation of ultrafine tungsten powder by hydrogen reductionmethod, the preparation of ultrafine tungsten carbide powder by carbonizationof tungsten powder, and air stream pulverizing and grading of ultrafinepowders are introduced.The influence factors of particle size and uniformity of tungsten powder areinvestigated based on hydrogen reduction theories, and the raw material forproducing ultrafine tungsten powder is determined according to analysis ofmicrostructures of different tungsten oxides and contrast experiment. Theresults show that ultrafine tungsten powder can be prepared under theconditions of forward hydrogen flow, low reduction temperature, highhydrogen flow-rate, low hydrogen moisture and thin batch layer. The specialpore structure of tungsten violet oxide gives it good air permeability andenables prompt ventilation of vapors under reduction atmosphere, thusproduces fine and epigranular tungsten powder, and yet charging amount and hydrogen flow-rate have little effect on particle size of tungsten powder.Meanwhile, under dry hydrogen atmosphere, tungsten violet oxide can bereduced directly to W without generating WO2, thus enables the production ofepigranular ultrafine tungsten powder. The process conditions should beoptimized to avoid the generation of WO2agglomerations. Finally the optimalprocess condition for producing ultrafine tungsten powder is established byexperimental verification, and ultrafine tungsten powder is produced. Themethods for preventing oxidation and spontaneous combustion are introduced,and also how to improve production capacity.The preparation of ultrafine tungsten carbide powder is actually thecarbonization of ultrafine tungsten powder. In this paper, the influence factorsof particle size of tungsten carbide powder is investigated, the results showthat the most important factor is the particle size and particle size distributionof tungsten powder. As the carbonization process is realized by the reactionwith carbonaceous gases on the surface of tungsten particles and by solid statediffusion of carbon black, the effect of carbonization temperature,carboni-zation time and carbon content of mixtures on particle size oftungsten carbide powder are relatively less. The optimal process condition forproducing ultrafine tungsten carbide powder is established by experimentalverification, and ultrafine tungsten carbide powder is produced.The ultrafine powders prepared are highly agglomerated and with broadparticle size distribution. Experiments show that the technology of air streamclassifying has significant effect on increase of the fineness and uniformity ofultrafine powders. Superfine pulverizing grader has high productionefficiency and low energy consumption, and yet is easy to operate and control.Air stream pulverizing and grading produces ultrafine powder with lessagglomeration and narrow particle size distribution. Superfine pulverizinggrader significantly improves production efficiency of ultrafine powders.