Process and properties of rhenium powders prepared by hydrogen reduction

Rhenium powders are prepared by hydrogen reduction in tubular push-boat furnace, using ammonium perrhenate as the raw materials. The effects of ammonium perrhenate particle size, reduction temperature, hydrogen flow rate, and boat loading amount on the rhenium powder morphology, particle size, and oxygen content (mass fraction) were investigated. Furthermore, the vacuum deoxidation treatment was performed on the rhenium powders, and the effects of reduction temperature on the metallic impurity content (mass fraction) were analyzed. The results show that, after the primary hydrogen reduction at 350 ℃, the ammonium perrhenate is primarily converted into rhenium powders, with only trace amounts of intermediate oxides remaining; after the secondary reduction, the ammonium perrhenate is completely transformed into the rhenium powders. The ammonium perrhenate undergoes significant particle refinement during reduction; however, the particle size of rhenium powders primarily depends on that of the raw ammonium perrhenate. Rhenium powders prepared from medium and large-sized ammonium perrhenate mainly consist of the irregular flaky particles, along with a small amount of fine particles. Ultrafine ammonium perrhenate (approximately 5 μm) yields the rhenium powders composed of micro-nano particles after reduction. Reduction temperature is the primary factor affecting the oxygen content in rhenium powders. As the reduction temperature increases, the oxygen content in rhenium powders decreases. However, higher reduction temperature also enhances the tendency of rhenium powders to sinter and agglomerate. To obtain rhenium powders with lower oxygen content, the vacuum degassing is performed on the rhenium powders in vacuum furnace to reduce the oxygen partial pressure. The vacuum treatment of secondary reduced rhenium powders (oxygen mass fraction is 0.160%) is performed at 900 ℃ under 10^‒3 Pa for 2 h, reducing the oxygen mass fraction in rhenium powders to 0.063%. During the high-temperature reduction of ammonium perrhenate, the impurities from the furnace tube and boat may be introduced into the rhenium powders. The content of metallic impurities in the rhenium powders is independent of the reduction temperature and remains extremely low.