Interpretation of crystallization induction periods

The effect of dopants (over a concentration range from 1 to 10 mol %), namely KCl and oxalic acid (C2H2O4·2H2O, Oxa), on the growth process, crystalline perfection, and nonlinear optical (NLO) properties of ammonium dihydrogen phosphate (NH4H2PO4, ADP) single crystals grown by a slow evaporation solution growth technique has been investigated. The high-resolution X-ray diffraction (HRXRD) studies used to evaluate crystalline perfection reveal some interesting features on the ability of accommodating the dopants by the crystalline matrix. The remarkable and systematic increase in the broadness and asymmetry of the diffraction curves as the concentration increases clearly indicates that the dopants predominantly occupied the interstitial positions in the crystalline matrix. Due to the larger size of the Oxa molecule, the crystalline matrix could not accommodate these dopants, which led to the formation of a very low angle (tilt angle <1′) internal structural grain boundaries at high concentrations. The rela...

An Interesting Correlation between Crystalline Perfection and Second Harmonic Generation Efficiency on KCl-and Oxalic Acid-Doped ADP Crystals

This paper reviews the work made by the group of the present author on the effect of impurities on the kinetics of crystal growth in solutions. The impurity effect is here discussed in the light of the model proposed by Kubota and Mullin [J. Crystal Growth, 152 (1995) 86], in which impurities are assumed to be adsorbed on the step lines at kink sites following the Langmuir mechanisms for inhibition of step displacement with a modified pinning mechanism. Effects of impurity concentration and supersaturation on impurity action on crystal growth are discussed successfully for various crystallizing systems with different impurities. Temperature effect on the impurity action is also discussed. Non-steady as well as steady state crystal growth behavior in the presence of impurities is discussed. Growth rate hysteresis in the presence of impurities and the pH effect on the impurity action of trivalent metallic impurities are discussed as well.

Effect of Impurities on the Growth Kinetics of Crystals

The growth of crystals in solution

Publisher Summary This chapter reviews the fundamentals of impurity incorporation, solvent interaction, and solution thermodynamics. The advent of sophisticated molecular modeling tools coupled with the increasingly accurate means to determine crystal structure has led to a greater understanding of crystal surfaces, and consequently, of crystal surface impurity and crystal surface-solvent interactions. As crystallization is essentially a molecular recognition process that occurs on a grand scale, impurity and solvent influences can be rationalized in terms of intermolecular interactions. Because of the requirement of high-purity crystalline products, an understanding of the effects of solvents on purification is also necessary. The solvent can influence the separation efficiency through its effect on crystallization kinetics, solution thermodynamics, and crystal interface structure. The mass transport processes at the crystal-liquid interface play a central role in crystallization. The influence of solvent and impurities on the structure and growth rates of faces is discussed in the chapter, along with its effect on the incorporation of impurities. The solvent-solute-impurities interactions in solution interact with the interface during the crystallization process. With appropriate thermodynamic analysis, it is proved that these interactions ultimately affect crystallization as a purification process.

The influence of impurities and solvents on crystallization

The effect of sulfate ions on the growth of NaClO3 faces (100) and (111) has been investigated. The heat of adsorption on the active centers of growth for both types of faces has been derived from kinetic experimental data. Direct adsorption measurements have been performed which gave the heat of adsorption on the whole surface of each type of faces. A possible explanation of the experimental results is given.



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A Study of the Effect of Sulfate Ions on the Growth of Sodium Chlorate Crystals

The kinetics of crystallisation of ZnC2O4 · 2 H2O was investigated at 25°C and at different supersaturations. Zinc oxalate was prepared from pure zinc sulphate and oxalic acid solutions. The specific surface energy at the crystal-solution interface was calculated from the induction period and the Volmer relationship, while the critical nuclei dimension was found by means of the Thomson-Gibbs equation. With the decrease in supersaturation the size of the nuclei does not increase to infinity, but changes by 1–2 unit cells within a given supersaturation range.



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Influence of supersaturation on the kinetics of crystallisation of ZnC2O4 · 2H2O

The effective activation energies of crystal growth on the faces (100) of KCl, KBr, and KI crystals in water solutions have been determined. The values obtained have been compared with the respective crystal lattice energies according to Sletter and Mayer, as well as with the experimental ones. The activation energies of crystal growth are in strictest linear dependence on the heats of dehydration of the ions. This shows that the dehydration of the ions is most probably the rate-controlling stage of the process of crystal growth in solutions. This concept is supported by the results of an experimental study of the rates of growth on the faces (111) and (100) of NaClO3 crystals.



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A study of the rate‐controlling stage of the process of crystal growth in solutions

The influence of phenol on the habit of sodium chloride crystals was studied quantitatively. At small concentrations the presence of phenol has no influence whatsoever on the growth rate of the (100) face. At greater concentrations this growth rate increases. Spiral growth was observed on the (100) face by surface dissolution. Phenol slows down the growth rate of the (111) face, the energy barrier being about 600 cal/mole. Roughening of this face is observed when crystallization takes place from pure solutions and in the presence of small amounts of phenol. At a phenol concentration of 0.065 mole/l the growth rates of the (100) and (111) faces become equal.



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Influence of phenol on the habit of sodium chloride crystals

This paper is a review of our experimental research on the influence of the supersaturation, flow velocity and temperature on the linear crystallization rate of different faces of model crystal systems. The obtained experimental results are discussed in the light of the new theoretical treatments on crystal growth from low temperature solutions.



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E. Kirkova

Papers

A Study of the Effect of Sulfate Ions on the Growth of Sodium Chlorate Crystals

Influence of supersaturation on the kinetics of crystallisation of ZnC2O4 · 2H2O

A study of the rate‐controlling stage of the process of crystal growth in solutions

Influence of phenol on the habit of sodium chloride crystals

Influence of the flow velocity, supersaturation and temperature on the crystal growth from solutions