Study Of Anisotropic Properties Of KDP And ADP Crystal Growth

Crystallization from solution is a routine unit operation used in the chemical industries. In order to obtain ideal products, it is necessary to control these factors which can influence crystal properties. The prediction and control of crystal morphology have abstracted much attention. Knowing the relationship between the growth habit and growth condition is significant for solving the kinetics problems caused by crystal growth. Starting from the microscopic characteristics of crystals, this thesis exploringly studies the growth morphology of KDP-family crystals and their mechanical property by the chemical bond method.KDP-family crystals possess excellent nonlinear optical (NLO) properties, which are strongly related to their various structural configurations and chemical bonding between constitutes units. According to the oriented distribution of chemical bond, the relationship between the crystal growth and growth habit was studied. By applying the model to the controllable growth of ammonium dihydrogen phosphate (ADP) crystallites under different pH, the predictions accurately reproduce the experimental observations in which the reform of hydrogen bonds between H2PO4-groups retards the growth along a-and b-directions and leads to the morphology transition from the podgy to slender. It provides an extensible way for the predictive design of crystal growth experiments.One of the major growth inhibitors in the KDP system is the metal ions like Fe3+which are unavoidable present during growth process. These impurities can cause changes in crystal habits that involve the introduction of a new series of high index faces inclined at an angle a to the{200} faces. In this thesis, a structural model is presented to interpret the habit modification of single crystals in terms of the step geometries relationship between crystal faces. The adsorption of impurities on the step would not give a smooth tapered effect until the growth rate Rhoi of profile facets reduces to some critical growth rate Rcri. Their morphology importance can be estimated on the basis of the chemical bond-geometric approach. The current work provides a new insight on how changes affecting elementary steps on one face are translated into the emergence of a new crystallographic face, which can facilitate the understanding of their physical and chemical properties at the atomic scale.With deeper studying of KADP mixed crystal property, an approach is proposed to characterize the anisotropy in KADP crystallographic frame using the oriented distribution of chemical bond as a key parameter. The structural instability was determined by comparing the deviation of the normal and calculated valence states. Since the effect of the geometric size of constituent cations (K+or NH4-), the instability along c axis quickly accumulates with increasing the content of NH4+and reaches the biggest when the molar ratio of ADP/(ADP+KDP) approaches to60%. Meanwhile the mechanical hardness of KADP crystals degrades seriously in this region, which is qualitatively estimated by the chemical bond method. The current work mainly reflects the inner relationship between the crystal structure, chemical bond and crystal property, and the interaction law of the external condition.