Effect of jet milled ultrafine powder on porous tungsten emitter components by micro injection molding

Abstract

Micro injection molding (μPIM) is currently the optimal solution for fabricating porous tungsten emitters with complex shapes. Considering the serious agglomeration of ultrafine powder, using this particle size for μPIM is detrimental to the molding of the components and the regulation of the pore structure. In this work, jet milling technology was applied as pretreatment to obtain uniformly dispersed ultrafine tungsten powder, and a needle-like porous tungsten emitter with uniform and adjustable pores was successfully prepared by μPIM. The effects of jet milling on the characteristics of ultrafine tungsten powder and μPIM process were investigated. After the jet milling treatment at 0.75 MPa and 12,000 rpm, the agglomerates in ultrafine powder were completely eliminated and the powder dispersion was optimized. The solid loading of feedstock was increased from 45% to 51%, and the corresponding rheological properties and debinding efficiency were also improved. Jet milled powder exhibited higher sintering activity and gained the same porosity (25%) at 1425 °C, lower than the 1500 °C of the as-received one. The porous tungsten obtained by jet milled powder had pores and skeletons with uniform size and distribution, which contributes to the adjustment of the pores. The pore size decreased from 338 nm to 263 nm, and the closed porosity decreased from 1.5% to 0.6%. This work is beneficial for further understanding the influence of jet milling on powder characteristics, μPIM process and pore characteristics, and highlights its potential application in the field of micro-pores complex parts.