Fine grain size ammonium paratungstate may be prepared by microwave-ultrasonic cooperative evaporation crystallization at higher temperature and without addition of surfactant.
A fine single crystal APT-4 with average particle size of 7.6μm, uniform particle size distribution and complete crystal form can be obtained under the following conditions:
Not stirred by machinery or under magnetism; No addition of surfactants; Under better APT preparation conditions - ultrasonic frequency of 25kHz, power of 1000W, microwave power of 700W, temperature of 80°C, ammonium tungstate (WO3) concentration of 212g/L, and the cooperative time of 15min.
Characteristics of Microwave-ultrasonic Cooperative Evaporation Crystallization to Prepare APT
1. The crystal structure of APT did not change according to the results of SEM, XRD and thermogravimetry - differential thermal analysis.
2. Particle size of fine APT:
(1) Increase with the increase of temperature;
(2) Decrease with the increasing concentration of ammonium tungstate;
(3) Decrease in the beginning and then increase as the increase of microwave-ultrasonic cooperative power;
(4) First increase and then decrease as the increase of microwave-ultrasonic cooperative time.
3. Overcome the shortcomings of the traditional APT process (crystallization process) such as slow crystallization rate and the influence of surfactant on the purity of APT.
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http://www.ammonium-paratungstate.com/english/index.html
