Puring the crystallization of APT crystals, temperature has double effects on APT crystals. On the one hand, rising temperature will increase the growth rate of the crystalline grains, and help to make coarse grain APT. On the other hand, higher temperature will lead to rapid volatilization of NH3 and cause the over- saturation of the solution ,and a large amount of nuclei were formed. In this case coarse grain crystals can not be obtained. Therefore , it is necessary to find out which effect on APT crystals plays a dominant role in the crystallization process of APT.
Solution with different initial concentrations of (NH4)2WO4 were used for studying the influence of temperature on the apparent density and FSSS size. The results show the apparent density and FSSS size increase obviously with the raising of temperature, and APT crystals with an density more than 1.8g/m-3 and a FSSS size more than 32 um are obtained at temperature higher than 90℃. This is because at higher temperature, the activity of the active center on the surface of crystalline grains increases, and the rate of nucleating is slower than that of crystal growing. It was clearly observed through a microscope that the APT crystals made at higher temperature are coarser than that obtained at lower temperature.
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