Abstract
Molten copper was atomized by using a conical water jet in air and nitrogen to examine effects of atmosphere on properties of powders. With increasing water pressure of more than 100 kg/cm2, geometrical standard deviation σg for particle size distribution increases in nitrogen, but does not change in air. Oxygen contents of powders atomized in nitrogen and air are 0.04 and 0.12 wt%, respectively. Particles are composed of lots of fine spheres which may come to a critical size in the breakup of droplets. The relationship between critical size d and surface tension γ is given by dair/dN2=γair/γN2=0.89. Atomizing at the temperature range of 1200-1270°C under a water pressure of 135 kg/cm2 with a flow-rate of 320 1/min in nitrogen atmosphere, the apparent density attains a minimum, as low as 2.0 g/cm3 for 145/200 mesh powder, and σg a maximum. Compactibility of this kind of powder is improved by annealing at 500-600°C for 1 hr. in hydrogen. Compacts pressed at 1 t/cm2 show a density ratio of 65% and a rattler's value of 1.5%.
