Nano Tungsten Powder Preparation with Arsenic and Phosphorus Ammonium Paratungstate

Nanocrystalline WC-Co cemented carbide has been widely used in cutting tools, impact tools and wear resistant parts, because of its high hardness and high strength. Nano tungsten powder with uniform particle size and good dispersibility is the key technology for the preparation of high performance nanocrystalline WC-Co cemented carbide.

During the study, the scholars found that the arsenic element has a remarkable refining effect on the tungsten powder during the hydrogen reduction process of tungsten oxide. The uniform tungsten powder can be prepared by conventional tungsten oxide reduction process. However, the arsenic and phosphorus in tungsten ore are usually associated with the alkali decomposition of tungsten ores in industry. The content of arsenic and phosphorus in sodium tungstate solution is high.

Some scholars have proposed a method of preparing nano tungsten powder with ammonium para tungstate and ammonium tungstate with arsenic and phosphorus, solved the problem of the joint removal of arsenic and phosphorus in tungsten metallurgical process. By saving the purification and removal of arsenic and phosphorus, the arsenic and phosphorus are retained in ammonium paratungstate or ammonium wamattrate, it can be made by calcining and hydrogen reduction. The process of preparing nano tungsten powder with uniform particle size is as follows:

(1) Ammonium paratungstate (APT) is 99.4wt%, arsenic is 0.3wt% and phosphorus is 0.3wt%. 0.30g As was dissolved in nitric acid with 100ml mass fraction of 65%~68%. It was heated by 10h and the heating temperature was 30°C. After As is completely dissolved, 99.40g APT and 1.44g ammonium phosphate ((NH₄)₃PO₄) are added to the nitric acid solution of As, and the electric stirring is used to mix the raw materials thoroughly.

(2) After the raw materials were mixed evenly, they were dried in an oven at 80°C for 10h and the precursor powder of ammonium partrunate containing arsenic and phosphorus was prepared.

(3) The composite powder of ammonium para tungstate containing arsenic and phosphorus was put into a box resistance furnace and roasted in air atmosphere directly. The calcined temperature was 600°C, and the yellow tungsten trioxide powder was prepared for 2h.

(4) The yellow tungsten trioxide powder was put into a tube atmosphere furnace and was reduced by hydrogen. The heating rate was 5°C/min, the reduction temperature was 800°C, the heat preservation time was 3H. The nanometer tungsten powder was prepared.

The tungsten powder made according to the above method is nanoscale, with good dispersion and uniform particle size distribution. The average particle size of nano tungsten powder is 43nm by SEM and XRD diffraction patterns.

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