AFM observation of a retgersite crystal surface growing in a water-ethanol solution

In situ investigation of the growth and dissolution of retgersite crystals $\alpha$-NiSO$_4\cdot6$H$_2$O in water-ethanol solutions (10–50 wt% of ethanol) was made by atomic force microscopy (AFM). The habit of crystals grown in aqueous and water-ethanol solutions, as well as the Raman scattering spectra, were identical. It is shown that the typical peak of sulphate ions at 981 cm$^{-1}$ does not change after the addition of ethanol. Absorption spectra of aqueous and water-ethanol solutions also have similar characteristic features. AFM images of hillocks on the (001) face of retgersite crystals were obtained directly in the process of their growth. Using a series of distorted AFM images obtained in situ, a geometrical calculation scheme is given, which allows one to recover the real direction of the growth steps. The kinetic coefficient of growth steps in aqueous and water-ethanol solutions of retgersite is estimated.