Preparation of ultrafine rhenium powders by CVD hydrogen reduction of volatile rhenium oxides

A novel CVD process for the preparation of ultrafine rhenium powders was investigated using ammonium perrhenate as starting materials. In the process, volatile rhenium oxides, such as ReO4 and Re2O7, were vaporized under a controlled oxidizing atmosphere via the pyrolysis of ammonium perrhenate, and carried into reduction zone by carrier gas, and there reduced into rhenium powders by hydrogen gas. Thermodynamic calculations indicated that Re2O7 could be prevented from further decomposition through controlling the oxygen partial pressure higher than 10−1.248 Pa in the pyrolysis of ammonium perrhenate. This result was further validated via DSC-TGA analysis of ammonium perrhenate. The typical rhenium powders prepared by the CVD method proposed show irregular polyhedron morphology with particle size in the range of 100-800 nm and a D50 of 308 nm. The specific surface area and oxygen content were measured to be 4.37 m2/g and 0.45%, respectively.