Anisotropic Dissolution Of Calcite And Epitaxial Crystal Growth Of Aragonite-Type Carbonates

In this paper, we use calcite as the main research object, in-depth study the phenomenon of calcite crystal (104) and (001) faces orientation dissolved in the electrolyte solution. And achieved the epitaxial crystal growth of aragonite-type carbonate crystals on calcite crystals, explored the (104) plane, as substrate via the interface-coupled dissolution-precipitation reaction.Calcite, with exposed (104) face, after 15 h dissolution reaction in 20 mmol·L-1 Cu(NO3)2 solution by 50℃, the original planar structure outer surface formed into a covering a wide range of hexagonal pyramidal array structure, which has a parallel diraction with the calcite crystal [001] orientation. After characterization and detailed analysis by XRD, SEM, EDXs and TEM, the array structure is due to the anisotropic dissolution of calcite crystals. The morphology of array structure could be controled in some extent by simply changing the experiment conditions:via changing the reaction time, the array structure, caused by anisotropic dissolution, is rapid growth in short time (t<1h), and the rate of crystal growth is become lower with the increase of reaction time in middle-long time period (1<t<72 h), and finally, the size of epitaxial crystal is invariable with the reaction of anisotropic dissolution achieve the balance point. Beside this if we use various electrolyte solutions (e.g. other copper salts, calcium salts and acids) to dissolved calcite, the micro-cones array can be formed with similar morphology.Applying the the experimental method of interface-coupled dissolution-precipitation reaction in geology study, the epitaixal growth between aragonite-type carbonates crystal (including strontianite, SrCO3; witherite, BaCO3; cerussite, PbCO3)and calcite (104) plane has been achieved. The process of this spacial reaction including:the dissolution of calcite substrate with the CO32-released into solution; Sr2+, Ba2+, Pb2+ions using the CO32- that released by calcite substrate the achieve precipitation reaction, this two part composite the interface-coupled dissolution-precipitation reaction. After extensive analysis and integration of experimental data, the mutual coupling of dissolution and precipitation reactions in time and space is proven, and led to the formation of core-shall structure, in which the core have the morphology of approximation six-party ladder platform formed by the residual of dissolving calcite; aragonite-type carbonate crystals crystals formed by precipitation as a shell. Research and report of composite structure of epitaxial growth has never been done before, so that this study with a high scientific value. In addition, using focused ion beam sputtering the crystal samples that after reaction via micro-nanofabrication, so that the crystal interface of epitaxial growth to be detailed characterization by high-resolution transmission electron microscopy (HRTEM), which got the visual evidence and complete information of the crystal epitaxial growth in first time.In addition, the orientation dissolution of biomass calcite - sea urchin spicules cross-section (corresponding to the calcite (001) crystal face) had been also briefly studied in this paper. Calcite found in the orientation of biomass can also be dissolved to form a crystal [001] to point to micro-cone array structure.The morphology of micro-cone structure achieved via the dissolution of geological mineral calcite and sea urchin spicules is not the same, structures formed by biomass calcite have more slender and uneven side-surface.