In situ AFM study of the interaction between calcite {101¯ 4} surfaces and super saturated Mn2+–CO3 2- aqueous solutions

Abstract

Growth of rhodochrosite(MnCO3) on calcite(101¯ 4) substrates from supersaturated aqueous solutions was observed in situ using anatomic force microscope (AFM). The supersaturation with respectto rhodochrosite (expressed as βrhod=a[Mn2+]a[CO3 2-]/Ksp, rhod.; where a[Mn2+] and a[CO3 2-] are the activities of Mn2+ and CO3 2- in the aqueous solution)ranged from 48.89 to 338.04. After an induction period, nuclei of the new phase are forme don the calcite substrate. These nuclei readily reach a significan the ight (2.270.2 nm), which remained approximately constant during their lateral spread. The characteristics of the growth pattern of islands of the newly for med phase i ndicate that the reexists an epitaxial relation ship bet ween the new phase and the calcite substrate. The islands showa highly anisotropic growth, preferentiallys preading along [421¯ ] on the calcite substrate at a rate up to 15 times faster than along [010]. As a result, the islands develop needle and sword blade-like morphologies, elongated along [421¯ ] and showing different truncated ends. This unusual elongation is interpreted as the result from a kinetic effect, which is controlled by both the structural characteristic of the calcite (101¯ 4) surface and the structure and elastic properties of the over growing phase. The lateral growth of islands leads to their coalescence and the formation of aquite homogeneous nanometric layer. The characteristics of the epitaxial growth are in a reement with a Volmer–Weber growth mechanism controlling the formation of the epitaxy. The results obtained in the se experiment sare compared with those obtained in several similar systems.