Ultrafine Tungsten Powder Preparation by Direct Reduction

Ammonium paratungstate is an important raw material for preparing tungsten products. At present, the main process of industrial production of tungsten powder is calcining ammonium paratungstate into blue tungsten, then reducing in hydrogen to prepare tungsten powder. The particle size of tungsten powder prepared by this method is mostly between 2 and 4 microns, which has become the main raw material for preparing tungsten alloys in the fields of military industry and medical devices.

However, due to the high microhardness of tungsten, the formability of the powder is poor, so it needs to add binder to form, which is very disadvantageous to large-scale production. In recent years, ultrafine tungsten powder has been the focus of research. The main reason is that ultrafine tungsten powder is the raw material of high quality X-ray tube tungsten target and tungsten foil with thickness up to micron. The purity and particle size of tungsten powder prepared by the existing technical methods are well controlled. But ammonium paratungstate needs to be dried and the reduction is carried out in two stages. Therefore, there are shortcomings of high energy consumption, low efficiency and complex process. So how to simplify the production process?

Recently, some scholars have published a method of preparing ultrafine tungsten powder by direct reduction. The process is simple and direct, requiring only one stage and two steps of reduction. The specific operations are as follows:

Step 1: Weigh 0.9kg wet ammonium paratungstate and 0.1kg blue tungsten powder. Ammonium paratungstate and blue tungsten powder were mixed in a mixer for 1.5 h.

Step 2: Put the wet mixed powder into the molybdenum boat with the loading capacity of 500g/boat, and push the boat into the tubular furnace after loading. According to counter-flow hydrogen, the flow rate of hydrogen in the furnace tube is controlled at 0.2-0.7L/min, the temperature is 600 ℃, the time is 50 min. After cooling, the reduced powder material is taken out.

Using ammonium paratungstate as raw material, the drying process of ammonium paratungstate was reduced, the process time was shortened, and the wet mixing of ammonium paratungstate and blue tungsten improved the output of tungsten powder, and the particle size of tungsten powder was uniform and reliable. One-step direct reduction of wet powders without degrading is conducive to large-scale production.

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