Ammonium paratungstate is heated in a rotary furnace with wet dust collection, the vaporized crystal water is discharged first, and then a large amount of combined ammonia is lost, and finally tungsten trioxide (industrial) is formed.
Blue tungsten oxide has the characteristics of good activity, larger than surface, easy doping and maintaining the original crystal shape. Therefore, both at home and abroad have attached great importance to the production of blue tungsten oxide. According to the characteristics of ammonia pyrolysis and discharge during ammonium paratungstate, yellow tungsten trioxide is reduced to blue tungsten oxide due to the hydrogen generated by ammonia decomposition. The reaction formula is as follows:
Domestic manufacturers tend to connect the rotary head degasing box of the original production of tungsten trioxide with the water seal device that can control the positive and negative pressure in the furnace, and the tail discharge box is connected with the spiral and vibrating screen with a certain upward slope. In this way, when producing tungsten trioxide, the tail discharge box is opened to make part of the air enter the furnace, and qualified tungsten trioxide can be produced according to needs. When producing blue tungsten oxide, the positive pressure in the furnace is controlled, which is generally 88 — 294pa. Oxygen index can be controlled between 2.96 and 2.72, and according to the requirements of production technology, reasonable selection of furnace temperature system and related parameters. In the production of tungsten trioxide, the negative pressure in the furnace should be controlled within 88-294 Pa, so as to ensure ample air in the furnace, and oxidize the low-price blue tungsten oxide generated locally by reduction into yellow tungsten trioxide.
Furnace structure and parameters. In industry, wet dust collection in rotary furnace and positive and negative pressure adjustment in the furnace are used to produce blue tungsten oxide and tungsten trioxide. The phase composition and color of the products largely depend on the size of the furnace tube, tilt Angle and the speed of the furnace tube. The correct selection of furnace structure parameters and furnace temperature system can achieve the purpose of controlling the oxygen index, color and particle size of blue tungsten oxide.
Control of temperature, pressure, feeding amount and material residence time. Once the furnace structure is selected, the furnace temperature system, the pressure in the furnace, the feeding amount and the material residence time will become the main adjustable parameters. When the temperature was increased and the positive pressure in the furnace was controlled, the decomposition rate of ammonium paratungstate increased, the hydrogen reduction atmosphere was strengthened, and the components of blue tungsten WO2.90 obtained from the decomposition products increased (see photo 1). When the temperature was increased again, the crysta.
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