Kinetics of etching and dissolution of gel-grown CdC2O4·3H2O crystals

The kinetics of etching and dissolution of cadmium oxalate trihydrate single crystals in selective etchants such as 1 M HCl, 1 M HNO₃, 10% chromic acid, 4M NH₄Cl, 4M CdCl₂ and 4 M NH₄Cl-1 M HCl solutions are studied. Contrary to a previous report on semiconductor etching, in the present investigation the activation energy of etching in solvents having a reaction-rate controlled mechanism of dissolution was lower than in those having a diffusion-rate controlled dissolution mechanism. Three 3-component etch systems, i.e., HCl-NH₄Cl-H₂O, HCl-CdCl₂-H₂O, and NH₄Cl-CdCl₂-H₂O, are employed and constant etch rate contours are plotted which enable the part played by each component in association with the other components in the system to be understood.