The effect of quartz on natural fluorapatite decomposition during the preparation of calcium sulfoaluminate-based multiphase composites

In the research described in this paper, we prepared low-cost multiphase composites based on calcium sulfoaluminate (also known as ye’elimite) and fluorapatite. By utilizing the CaO originally present in fluorapatite, the sintering densification of these composites was enhanced. The influence of varying the SiO₂ content (0–5.4 wt.%) on the reactive sintering of fluorapatite, bauxite, and gypsum was investigated. Incorporating quartz led to the formation of various compositions, including calcium hexaluminate, fluorapatite, ye’elimite, and gehlenite. Quantitative phase analysis, conducted using the Rietveld method via Profex software at various sintering temperatures, demonstrated a relationship between quartz content and the preferential formation of gehlenite over ye’elimite within the 1300–1350 °C range. Additionally, the microstructure of the composites was significantly modified by quartz addition, leading to the development of hexagonal and circular grains after heat treatment at 1400 °C.