Arsenic Assisted Tungsten Carbide Powder Refinement

arsenicTungsten carbide powder is the main raw material for the preparation of cemented carbide. At present, the preparation of ultra-fine tungsten carbide powder mainly includes conventional tungsten oxide hydrogen reduction-carbonization method, tungsten oxide direct reduction carbonization method, plasma chemical synthesis method, mechanical alloying method. The quality of tungsten powder directly affects the performance of cemented carbide products. In order to obtain high-performance ultra-fine WC-Co cemented carbide, the grain size of tungsten carbide must be controlled. Therefore, the preparation of ultrafine tungsten carbide powder with good dispersibility and uniform particle size distribution is the key technology for the preparation of ultrafine grained WC-Co cemented carbide.

In order to overcome the deficiencies of the prior art, some scholars have proposed a method for preparing ultrafine tungsten carbide powder by using arsenic (As) ammonium metatungstate (AMT). The main steps are as follows:

(1) Preparation of ammonium metatungstate-arsenic precursor composite powder.

First, a certain amount of elemental arsenic is dissolved in a concentration of 65%~68% nitric acid solution. After the arsenic is completely dissolved, ammonium metatungstate is added to the arsenic nitrate solution, and the arsenic content of the raw material is 0.01~5wt. %; electric stirring to make the raw materials are evenly mixed, and then dried in an oven, the oven temperature is 70-90 °C, the time is 8 ~ 10h, after grinding, the ammonium metatungstate-arsenic precursor composite powder is obtained.

(2) Preparation of tungsten trioxide powder.

The prepared ammonium metatungstate-arsenic precursor composite powder is placed in a box-type electric resistance furnace and calcined in an air atmosphere at a calcination temperature of 580 to 620 °C and a holding time of 2 to 4 h to prepare a yellow tungsten trioxide powder.

(3) Carbon blending of a tungsten trioxide powder composite powder.

The mixture was prepared by mass ratio of carbon black to tungsten trioxide powder of 0.20:1 to 0.22:1, and dry-milled for 2 hours using a planetary ball mill.

(4) Preparation of ultrafine tungsten carbide powder by direct reduction carbonization of tungsten trioxide.

The powder mixture of the ball-milled tungsten trioxide powder and carbon black is placed in a tubular atmosphere furnace, and reduction carbonization is directly performed in an Ar atmosphere at a heating rate of 5 °C / min, a carbonization temperature of 1380 to 1420 °C, and a carbonization time of 1~3h, ultra-fine tungsten carbide powder was prepared.

It was found that arsenic has significant refinement effect on W and WC grains during the preparation of WC-Co cemented carbide. The high-temperature direct reduction carbonization method of tungsten trioxide is used, and the effect of arsenic on the growth inhibition of tungsten carbide particles is utilized to prepare ultrafine tungsten carbide powder having a uniform particle size. The method can not only improve the content of combined carbon in the tungsten carbide powder, but also effectively control the sharp growth of WC grains during the high temperature carbonization process. This method is also applicable to the preparation of ultrafine tungsten carbide powder from various arsenic-containing tungsten raw materials.

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