Mineralogical studies of phase transitions and disorder in calcium phosphates: Brushite and biologic apatite
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Calcium phosphate minerals are ubiquitous on Earth's surface. They form in igneous, metamorphic and sedimentary rocks, and can be found in soils. They also take part in biological mineralization, as major components of mineralized tissues, i.e. bones and teeth. Apatite group minerals are the most abundant calcium phosphates. Understanding calcium phosphate minerals, specifically the apatite group minerals, is of importance for many scientific disciplines such as: geology and Earth sciences, chemistry, life sciences and material sciences. We identified important problems in the realm of calcium phosphate and biomineral research, and developed new methods to assist in solving these problems. Several problems we address are the occurrence of disorder, interlayering and the formation of intermediate phases. This part of my research is a new approach to the problem of disorder in calcium phosphate minerals. The models allow us to identify the ratio of minerals present and the stacking sequence in calcium phosphate interlayered system. Another problem we address is the formation of an amorphous calcium phosphate phase during heating and recrystallization of brushite and crystallization of monetite. We identified a way of quantifying the formation of the amorphous phase. This method can be applied to any other calcium phosphate system where the amorphous phase forms. Our new approach to understanding and modeling the calcium phosphate crystallization process, subsequent phase transitions, and interlayering of two or more phases contributes in the realization of the paths that take place during the formation of an amorphous phase and ways to distinguish different interlayering sequences between minerals in the apatite group.