On the crystallinity and the stoichiometry of the calcite surface

• Published in: Journal of colloid and interface science 1976-01, Vol.57 (1), p.148-161
• Main Authors: Goujon, G, Mutaftschiev, B
• Format: Article
• Language: English
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(76)90184-3

The specific heat of immersion of calcite in water and the pH of saturated aqueous solutions depend on the powders used. For ground crystals, the heat of immersion and pH values are very high because of a partial surface decomposition of about 30% during thermal treatment and also, in regard to the first parameter, because of the breaking of surface bonds during grinding. Heating these powders in vacuum or treating them in a CO 2 atmosphere restores a certain crystallinity to the surface; the two treatments combined, followed by an outgassing at room temperature, allow the surface calcium carbonate to be restituted. On the other hand, calcite crystals, limited only by singular faces, have low heat of immersion and pH values which are not affected by the preceding treatments. The mass spectrometry studies of the gases released by the two types of calcite powders from room temperature to 500°C show that their surfaces do not dissociate throughout the whole temperature range. However, if the ground powders are treated with carbon dioxide, they release a quantity of this gas equivalent to some 30% of a calcium carbonate monolayer and at a temperature much lower than that of bulk decomposition.