Cyclic Cluster Study on the Bulk Modulus and Hydration Pressure of Magnesia Expansion

Cyclic cluster studies with the quantum chemical method MSINDO were performed to elucidate the key properties of brucite concerning the magnesia expansion. A model is presented that allows the calculation of the compressibility of brucite under hydrostatic pressure. In this way, the bulk modulus of brucite can be determined via the binding energy. The elastic constants, Poisson's ratios, volume compressibility, and finally the bulk modulus were calculated and compared with the experimental values. Except for the component Ka of the compressibility, there is good agreement with the experimental values. Based on the bulk modulus, an expression for the volume change of brucite under pressure is derived. The hydration pressure of the periclase reaction with water to form brucite is related to the partial water vapor pressure. In this way, the maximum hydration pressure was determined.