Preparation of tantalum nanopowders through hydrogen reduction of TaCl 5 vapor

Abstract

Tantalum powders, ranging from 14 to 56 nm in primary particle size, were produced through hydrogen reduction of TaCl 5 vapor in a furnace aerosol reactor. The mass of the precursor, solid TaCl 5, was instantaneously measured during vaporization with a load cell to determine and control the precursor concentration at the reactor inlet. Tantalum pentachloride to tantalum conversion was 35% and 98% at 1000 and 1400 °C, respectively. The primary particle size increased with increasing the evaporator temperature and the hydrogen flow rate. The tantalum powder produced was amorphous at 1000 °C and crystalline at 1400 °C. The XRD peaks of the as-produced powders shifted towards lower angles due to the partial dissolution of hydrogen in the tantalum. Upon removal of the hydrogen through heat treatment in a vacuum, the shift disappeared. The oxygen content of the powder was 6.0 to 6.9 wt.%, with an oxide layer about 3 nm thick formed on individual particles. Through thermogravimetric analysis in air, the powders were found to be resistant to further oxidation at up to 200 °C, but to have been completely oxidized at 400 °C.