Piecewise Evaporation Crystallization Method Parameter Setting

The application of tungsten elements is very extensive. In order to improve the wear resistance of parts, the most fundamental method is to reduce the particle size of tungsten elements in the material to improve the wear resistance of super hard dies and bits.

Ammonium para tungstate is the most important product in the process of tungsten smelting. Now the most commonly used method of producing ammonium para tungstate is evaporation crystallization. It has very important technical knowledge to control the growth of crystals by parameter in the process of evaporation and crystallization.

The crystallization process of solution can be divided into four stages: initial concentration, nucleation precipitation, crystal growth and crystal aging. The proportion of solution, volume of solution and the proportion of solid and liquid in the four stages are different. Different stirring speeds are used in different periods of crystallization. The number of nuclei and the growth speed of crystal can be controlled in different periods of time, and the number of crystal nuclei can be influenced eventually.

The fractional crystallization of ammonium tungstate was obtained by adding the ammonium tungstate solution into the crystallizer by evaporative crystallization. The crystal of small particle size was obtained by drying the crystallized crystallized crystal. The concrete steps of the sectional evaporation crystallization were as follows:

(1) The ammonium tungstate solution is heated to 60°C.

(2) The temperature is controlled at 59-61°C, and the stirring speed is 45r/min, maintaining for 0.8 hours.

(3) The temperature is controlled at 61-63°C, and the stirring speed is 40r/min, maintaining for 0.6 hours.

(4) The temperature is controlled at 64-66°C, and the stirring speed is 35r/min, maintaining for 1.3 hours.

(5) The temperature is controlled at 67-69°C, and the stirring speed is 30r/min, maintaining for 1 hours.

(6) The temperature is controlled at 71-73°C, and the stirring speed is 25r/min, maintaining for 0.7 hours.

(7) The temperature is controlled at 63-65°C, and the stirring speed is 20r/min, maintaining for 0.5 hours.

(8) The temperature is controlled at 61-63°C, and the stirring speed is 15r/min, maintaining for 0.9 hours.

By controlling the temperature and agitation of evaporation crystallization by piecewise control and combining with the exact time ratio, the velocity of initial concentration in the evaporation crystallization process is accelerated to a certain extent, at the same time, it also lays the foundation for the subsequent refining of crystal nuclei, while increasing the quantity of crystal nucleus precipitation. It also achieved the effect of refining the crystal nucleus, realizing the rapid saturation of crystal growth during the evaporation crystallization process, and keeping it stable while shortening the crystal growth time, realizing the stable forming of the crystal aging during the evaporation crystallization process, and ensuring the consistency of the formed crystal.

The above method is simple and practical, and the effect is obvious. The crystal growth is achieved by controlling the stirring time, speed and temperature, thus the final crystal performance is controlled, and the production of the small size ammonium para tungstate crystal is achieved.

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