Single-crystal calcium carbonate

INTRODUCTION This data sheet provides data for single crystal calcium carbonate. 

A single substance may crystallise in more than one of seven crystal systems, all of which differ in their lattice arrangement, and exhibit not only different basic shapes but also different physical properties. A substance capable of forming more than one different crystal is said to exhibit polymorphism, and the different forms are called polymorphs. Calcium carbonate, for example, has three polymorphs — calcite (hexagonal),... 

Dissociation of Calcium Carbonate A number of studies of this decomposition have concluded that Ea is similar to the dissociation enthalpy for equilibrium conditions, about 173 kJ mol 1. A study of the reaction in vacuum, below I 0-2 Pa (17), however, measured the activation energy as 205 kJ mol-1, or about 30 kJ mol-1 greater than the enthalpy of the dissociation process these values have been supported by subsequent studies (78). This study investigated the reaction between 934 and 1013 K through measurements, by a quartz microbalance, of the constant rate of mass loss during inward interface movement from a single flat reactant crystal face. 

The hardness of a material quantifies its resistance to permanent shape changes induced by applied mechanical forces such as fiiction or indentation by a sharp object. Scratch resistance is often measured on the Moh 1-10 scale and indentation hardness on the Vickers scale. Single crystal nonporous silicon has a Moh scale hardness of 6 (for comparison, diamond is 10, quartz is 7, calcium carbonate is 3, talc is 1). It has a Vickers hardness of 11.5 GPa. There have now been a few studies of the indentation hardness of porous silicon, with typical values for different types of porous silicon listed in Table 2. 

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