Controlling Content of Sodium in Ammonium Paratungstate 1/3

In the tungsten metallurgy industry, ammonium paratungstate (APT) is an important intermediate, and the degree of purity of APT will affect the quality of tungsten products. The content of sodium can affect the particle size of tungsten powder. The APT with high sodium can be used to prepare coarse grain tungsten powder and APT with low sodium can be used to prepare thin tungsten powder. Tungsten powder is the main material for tungsten carbide, and the particle size of tungsten powder plays a key role in tungsten alloy properties. The properties of the alloy with fine grain tungsten powder are significantly higher than that of the tungsten powder with coarse grain. If tungsten powder particles are ultrafine particles, then properties of tungsten alloy will have a qualitative leap, to achieve the goal of high strength and hardness, thus expanding the application field.

In industry, in order to obtain fine particles of tungsten powder, reduce the content of sodium in APT is an effective way. Seven aspects such as rate of APT crystal, crystallization temperature and time and so on are analyzed to help reducing content of sodium in APT.
1.    APT crystallization rate
In the initial stage of APT crystallization, due to the over saturation of APT, both crystal-nucleation and crystal growth rate are very fast, small particles of APT are produced, at this time, sodium get inside crystal easily. Super-saturation of solution decreased rapidly with crystallization continue, the fine APT crystals with high content of sodium and surface dissolved easily, but the large crystals with less sodium continue growing, making sodium in APT decreased. And with the mother liquor concentrate, the concentration of Na+ increased, that making the contact area of apt and Na+ increased, sodium in APT rising again.

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