Abstract
The coprecipitation has generally been studied to eliminate impurities from the precipitates and also investigated by PFHS (precipitation from homogeneous solution) method. In the present investigation the coprecipitation of zinc with copper 8-hydroxyquinolate having dimorphism has been studied from a stand point of crystal transformation.
To a mixed solution of copper and zinc was added 8-acetoxyquinoline solution at pH 9 and the solution was stirred at 25°C. After various time intervals the precipitates formed were analyzed chemically and examined by the electron microscopy and the X-ray diffraction methods.
The logarithmic distribution law held through the precipitation process and the distribution coefficient obtained was 0.025. The precipitates initially formed were composed of needle crystals of copper 8-hydroxy-quinolate belonged to the tetragonal system and were associated with a small amount of zinc. When zinc 8-hydroxyquinolate whose crystal system was monoclinic began to be formed, the needle crystals started to dissolve and transformed to plate crystals belonged to the monoclinic system. The transformed copper 8-hydroxyquinolate deposited at the same time with zinc 8-hydroxyquinolate and they formed a solid solution.
When zinc 8-hydroxyquinolate was precipitated by the PFHS method in the presence of needle crystals of copper 8-hydroxyquinolate, the concentration of copper in the solution increased temporarily and then a solid solution of copper and zinc 8-hydroxyquinolates belonged to the monoclinic system was produced.
The transformation of the needle crystals of copper 8-hydroxyquinolate (unstable form) to the plate crystals (stable form) was promoted by the deposition of zinc 8-hydroxyquinolate.
