Preparation Of Spherical Porous Tungsten Powder

Porous tungsten powder was prepared by spray drying-hydrogen reduction with WO3 as starting material. The de-ion water, surfactant PEG and pore-forming agent were milled together with WO3 to produce uniform slurry which changed into precursor spheres after spray drying. And porous tungsten powder was obtained by the reduction of precursor spheres in the hydrogen atmosphere. The effect of milling time, pH value, surfactant content and mass fration of WO3 on the apparent viscosity of slurry were studied. The optimum technologies for slurry were determined. The influence of surfactant, variety and content of pore-forming agent, mass fraction of WO3, a second phase raw material (APT) added to the slurry, technologies of spray drying and reduction on phase constitute,morphology and porosity of tungsten powder were investigated .Parameters that control the formation of particle shape and morphology in spray drying was discussed; And application of porous tungsten powder was explored. During the present experiment, the phase constitute of powder was explored by XRD; the morphology and porosity of tungsten powder were studied by a combination of SEM, BET and apparent density; the microstructure was studied by optical microscope.The result showed that:1) a lower apparent viscosity of slurry was obtained with ball milling time of 24 hours, pH value of 3.2, (NH4)2CO3 content of 10%, PEG content of 0.5% and WO3 mass fraction of 40%.2)The optimum content for surfactant PEG is 0.5%. If pore-forming agent is (NH4)2CO3, relatively better porosity and morphology of tungsten powder was obtained when its content is 10%; If pore-forming agent is PVA, relatively better porosity and morphology of tungsten powder was obtained when its content is 6%; If pore-forming agent is (NH4)2CO3 with PVA, porosity of tungsten was increased. If a second phase raw powder was added to the slurry simultaneously, poros- ity was increased furthermore. The optimum mass fraction of WO3 for formation of porous tungsten powder was 40%. Fine particles were received when rotate speed of atomizing disc was 27000 r/min and rotate speed of feed pump was 32r/min. The optimum reduction technology was deoxidized at 820℃for 90min with a calefactive velocity of 3℃/min.In spray drying, particle formation process was most probably affec-ted by the relationship between diffusion of solute and surface recession (Pe) and the saturation of the solute. When Pe=1 was coupled with a large solute solubility, the resulting dry particles were expected to have little or no void space; When Pe>1was coupled with a large evaporation velocity of solvent, the resulting dry particles were expected to be hollow or porous even if solute solubility is large; When solute solubility was very small, rapid surface accumulation of solute led to formation of shell or porous particles even if Pe<1. Particle shape was characterized by Bond numberβ. The particle was nearly spherical at values ofβâ†'0 and became flat when the values of fβincrease. Compared to W60Gu alloy prepared by ordinary tungsten powder, the microstructure of alloy prepared by porous tungsten powder was fine and uniform.