Experimental Research Of ADP Solution Stability And Crystal Growth

The large-size ammonium dihydrogen phosphate (ADP) crystal has been applied in production and practice for a long time, which is a member of KDP crystal family. The investigation of ADP crystal attracts more attention for its multiplier effect of laser, electro-optic effect, piezoelectric effect and many other special features. The researches focus on how to maximize crystal's growth rate, shorten the growth cycle, reduce costs, and improve the quality of the crystal.Recently, with the deep understanding of ADP crystal's property and the exploitation of new purposes, ADP crystal becomes more and more important in the human beings'life. As a result, the research is continued. However, there is no experimental investigation and related calculations about its induction period by changing pH value although predecessors have done some researches about nucleation of ADP crystal. In addition, so far, the papers that growth kinetics and growth mechanisms of the (100) surface of ADP crystal with different pH values are studied by measuring the growth rate have also not been found. For these reasons, ADP crystal growth experiments were carried out in the present paper. The main works can be summarized as follows:①The solubility of ADP in H2O with different pH values in the temperature range from 30℃to 60℃were determined by weighed method,and the solubility curves are given. At last, the experiment results were explained.②For different pH values,the nucleation of ADP supersaturation solution was investigated at different temperature. The induction period was measured for different growth conditions of ADP solution by the method of photography, and the influence of some factors such as pH value, temperature and supersaturation ratios on the induction period was discussed. According to the classical homogeneous nucleation theory, nucleation parameters such as solid-liquid interfacial tension, radius of critical nucleus and others were calculated using the experimentally determined values of the induction period. The microscopic reason of improving the stability of the ADP solution by changing pH value was also been estimated through the analysis of the nucleation parameters. At last, by comparing the calculated value of the surface entropy factor with theory, the surface growth model of ADP crystal in these experiments was identified.③The growth rates of the (100) face of ADP crystal with different pH values were investigated at different supersaturations at 40℃. And the edge free energy of the (100) face of ADP crystal with different pH values were calculated when the growth was controlled by 2D nucleation mechanism. Finally, the topography of the (100) surface of ADP crystal with different pH values at different supersaturations were observed by ex situ AFM. It was found that there were 2D nucleations appearing in the crystal surface with pH=2.5 and pH=5.0 at lower supersaturations compared with the normal pH.