Types of Anion-Cation Packing of Mineral Surfaces and Their Manifestation in Various Processes

摘要

Possible types of anion-cation packing of mineral surface were evaluated.Their role was estimated for the decoration of minerals with gold under vacuum(process simulating crystallization on a surface),mineral growth and intergrowth,adsorption,surface diffusion,and other surface processes.It was shown that there are two distinct types(I and II)of mineral surfaces differing in the character of crystallization of gold nanoparticles during decoration.Type I includes surfaces showing predominant formation of gold nanoparticles(5-15 nm)on growth(dissolution,evaporation)steps,dislocations,and point defects.These surfaces are represented by packed layers of O~(-2)anions,alternating anions and cations,and identical atoms.Type II includes surfaces with the statistical distribution(10~(9-12)cm~(-2))of gold nanoparticles(5-30 nm).Such patterns are characteristic of surfaces with packing of OH~-groups,OH~-in combination with O~(-2),and with the statistical distribution of anions and cations.Type I surfaces show low adsorption capacity and a large extent of diffusion on them(approx 10~(3-4)nm).In contrast,type II surfaces have high adsorption capacity and low(approx 50 nm)surface diffusion.Minerals dominated by type I surfaces grow by the layer and spiral mechanisms,and those dominated by type II surfaces grow by the normal mechanism.