An analysis of flow and mass transfer of solution growth of NH4H2PO4 crystals by the modified seed mounting geometries

Abstract

A modified seed mounting geometry is proposed, aiming to improve the distribution homogeneity of the supersaturation on the crystal face during the growth of ammonium dihydrogen phosphate (NH4H2PO4, ADP) crystals. To evaluate the modification, three dimension transient numerical simulation of flow and solute transfer involved in the growth of ADP crystals have been performed. The effects of flow on the surface supersaturation distribution is analyzed in detail. Compared with the ordinary seed mounting geometry, the modified geometry is able to suppress the formation of flow stagnation regions near the prismatic surface and improve the magnitude and the distribution homogeneity of the supersaturation. Particularly even at a lower rotation rate (ω = 30 rpm), the distribution of the surface supersaturation still possesses a better uniformity under the modified geometry. Meanwhile, with the increase of rotation rate, there is an improvement in the magnitude and the distribution of the supersaturation on the crystal surfaces. The effects of natural convection adjacent to prismatic faces can be ignored when rotation rate is equal to or greater than 50 rpm. Moreover, as the crystal size increases, the magnitude of the supersaturation on the prismatic surface declines a little, and its uniformity deteriorates gradually. Consequently, as the crystal growing, it should increase the rotation rate appropriately. Finally, etching studies reveal that the ADP crystals with higher quality can be obtained by modifying the seed mounting geometry simply.