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On the Effect of Cu(II) Impurity on the Growth Kinetics of Ammonium Oxalate Monohydrate Crystals from Aqueous Solutions
Author(s) -
Sangwal K.,
MielniczekBrzóska E.
Publication year - 2001
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/1521-4079(200110)36:8/10<837::aid-crat837>3.0.co;2-7
Subject(s) - impurity , supersaturation , nucleation , chemistry , kinetic energy , oxalate , aqueous solution , growth rate , crystal growth , kinetics , adsorption , ammonium oxalate , thermodynamics , crystallography , analytical chemistry (journal) , inorganic chemistry , chromatography , organic chemistry , physics , geometry , mathematics , quantum mechanics
The effect of concentration of Cu(II) ions and solution supersaturation on growth rates of different faces of ammonium oxalate monohydrate (AO) single crystals is studied at 30 °C and supersaturations up to 10%. It was observed that the growth rates of the (001) face of the crystals decrease while those of the (100) and (010) faces increase with an increase in the concentration of the impurity. Instead of analysing the dependence of face growth rates R on impurity concentration c i for different supersaturations σ in terms of Cabrera‐Vermilyea and Kubota‐Mullin models, the dependence of R on σ for different c i were analysed using spiral growth theory involving cooperating dislocation source and multiple nucleation model. It was found that both models describe the experimental data on growth kinetics satisfactorily. Analysis of the data revealed that an increase in the face growth rate with impurity concentration is associated with a decrease in the free energy of the growing face (thermodynamic effect) while a decrease in face growth rate with an increase in the concentration of the impurity is a kinetic effect involving a reduction in the value of the kinetic coefficient β for the motion of steps on the surface. It was also found that usually both effects take place simultaneously but one of them dominates during the growth of a face. The dependences of surface free energy and kinetic coefficient on impurity concentration follow Freundlich adsorption isotherm.