Macro Grain Ammonium Paratungstate formation conditions(Ⅰ)

Grain size of ammonium paratungstate affects the grain size of tungsten powder. Macro grain ammonium paratungstate has large apparent density and flow ability which promote the property and quality of tungsten powder. Marketing demand for macron ammonium paratungstate enlarges year by year. Macro grain ammonium paratungstate formation conditions include the influence of temperature, adding seed crystal and （NH₄）₂WO_4, the influence of mixture.

1.Temperature. Rapid heating up and reduce the degree of super saturation before boiling up. It will not only improve producing efficiency, also reduce the production rate of metatungstate radical A （HW₆O₂₁^5-）and the conversion rate of metatungstate radical A to metatungstate radical B（H₂W₁₂O₄₂^10-）.

Medium temperature nucleary. Reduce the formation of crystal nucleus. During nucleary of ammonium paratungstate, raise temperature in a certain degree will make the crystal grain size smaller.

Formation under high temperature. Reduce the rate of second nucleary. After the first nucleary, the distribution of ammonium paratungstate grain size depends on the second nucleary. After the first nucleary, heating up rapidly, reduce mixing time, thus reduce the second nucleary and crystal broken degree.


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