Precooling rate and reduction temperature effect on the characteristics of molybdenum powder by a novel freeze-drying method

Abstract

Nano molybdenum (Mo) powder is widely applied in diverse fields, including electronics, catalysis, energy storage, and advanced materials, due to its unique physical and chemical properties. In this work, nano-Mo powder was fabricated via the freeze-drying method. The influence of the freeze-drying precooling rate on the ammonium paramolybdate (AMP) morphology and reduction temperature on the Mo powder characteristics was investigated. The morphological characteristics of the precursor were retained during the conversion of AMP to MoO₃ and subsequent reduction to Mo, which lays a foundation for preparing Mo powder with controllable morphology. Increasing the reduction temperature from 700 °C to 900 °C increased the average particle size of Mo from 90.61 nm to 349.52 nm and increased particle adhesion; the optimal size (185.25 nm) occurred at 800 °C. While the precooling rate did not affect the roasted MoO₃ morphology, a slow rate yielded more uniform, finer Mo powder by stabilizing the ion distribution in the precursor solution, preventing solute segregation and asynchronous precipitation. A fast rate produced a smaller precursor powder but promoted particle growth during roasting. Hydrogen reduction followed a chemical vapor transport (CVT) mechanism. Adding polyvinyl pyrrolidone (PVP) enhanced AMP dispersibility in solution, which decomposed to create voids, improved overall powder dispersion, and significantly refined the Mo grains. The method produced nano-Mo powder with a favorable morphology and uniform, controllable quality.