Ammonium Paratungstate Preparation -- Freezing Crystallization Method
Ammonium paratungstate (APT) is an important part of tungsten smelting, whether it is using chemical precipitation method, ion exchange method or extraction method, they all have to through the process of ammonium trioxide to produce qualified APT.
APT is an important tungsten intermediate products , the higher the puritythe greater the value, so APT preparation process is also the further purification of tungsten.
Freezing crystallization method is one of the most commonly used methods for the preparation of ammonium paratungstate, which is the use of liquid ammonia to freeze the APT, so called frozen crystals.
The freeze crystallization method was carried out in a liquid nitrogen cooled vacuum drier, and the ammonium tungstate solution was poured into an enamel plate pre-filled with liquid nitrogen (the volume ratio of ammonium tungstate solution to liquid nitrogen was 1: 2), stirring it and then crystallized water and APT at the same time, Along with enamel disc quickly moved to the vacuum dryer, removed the water and free ammonia distillation under vacuum conditions, leaving a dry white amorphous and loose with 11 crystal water of ammonium paratungstate.
Produced APT by freezing crystallization method, chemical purity and raw material liquid did not change, but the average particle size can be obtained in 0.6 to 1.3 microns of superfine powder of ammonium paratungstate, and composition of paricle size was balanced, and the distribution of various impurities or additives was uniform. So often use this method to making W - the composition such as Re, W - Cu composite powder evenly.
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