Preparation and characterization of nanopowder for emission materials by freeze-drying

Abstract

Nanopowder of rare earth tungsten for emission materials was prepared by freeze-drying process. The solution of ammonium metatungstate with rare earth nitrate was quench-frozen and dried in vacuum to produce the mixture of ammonium metatungstate and rare earth nitrate powder with high purity. Most of the powder existed in non-hygroscopic and non-crystalline state. During the experiment, the advantage of freeze-drying process was successfully achieved. High speed freezing also fixed the ion distribution that once formed in the solution. Due to less atomic moves during the subsequent sublimation process, the homogeneity of the original solution was retained. The freeze-dried compound, which consisted of ammonium metatungstate and rare earth nitrate, was reduced under various conditions to determine the effect of reaction conditions (temperature and time) on the particle size of the final rare earth tungsten powder. Experiments showed that the grain size of the powder mixture depended on the temperature and duration of the reduction process. The characterization of the powder mixture, microcompact and pellets were analyzed by means of XRD, FESEM and TEM throughout the whole experimental process.