On the low temperature synthesis of alloys by precipitation reactions

Abstract

The low temperature synthesis of Mo-W alloys by a precipitation reaction has been studied in detail. Electron microscopy, thermogravimetric analysis, and powder X-ray diffraction measurements show that the precipitation of ammonium paramolybdate and ammonium paratungstate from a water-alcohol mixture leads to the formation of a homogeneous heteropolymetallate (NH 4) 6(Mo 7− n W n O24)·4H 2O. Reduction of this intermediate, under hydrogen at 700 °C, yields Mo-W alloys. X-ray photoelectron spectroscopy reveals that the alloy surface is oxidized and enriched in tungsten. The wider implications of this work for other alloy preparations are discussed.