Effect of Mn(II) ions on the growth of ammonium oxalate monohydrate crystals from aqueous solutions:

I. Growth habit and surface morphology

 K. Sangwal, E. Mielniczek-Brzóska (2), and J. Borc (1)

(1) Department of Applied Physics, Institute of Physics, Technical University of Lublin, ul. Nadbystrzycka 38, 20-618 Lublin, Poland

(2) Institute of Chemistry and Environmental Protection, Pedagogical University of Czestochowa, ul. Armii Krajowej 13/15, 42-200 Czestochowa, Poland

Abstract

     The effect of concentration of Mn(II) ions on the growth habit and the surface micromorphology of different as-grown faces of ammonium oxalate monohydrate (AO) single crystals grown from aqueous solutions was studied at a constant temperature of 30°C and predefined supersaturations up to 20%. It was observed that the growth habit and the surface morphology of the crystals strongly depend on the supersaturation used for growth and the impurity concentration in the solution. The experimental results were analysed in terms of connected nets determined from different projections of the structure of AO crystals. Analysis of the observations revealed that: (1) the directions of connected nets corresponding to basic growth units composed of single (NH4)2C2O4 ·H2O molecules are in excellent agreement with the low-index crystallographic directions of the orientations of growth layers, (2) all faces appearing in the growth morphology of AO crystals are F faces, and (3) the {001} face growing from pure aqueous solutions is essentially a kinetically rough face but the presence of Mn(II) impurity leads to their appearance in the morphology due to increase in the strength of bonds of the connected nets composing the surface graph.