The effect of heat treatment on colemanite processing: a ceramics application

Boron oxide (B2O3), water content, particle size, and specific surface area are important parameters in colemanite (2CaO3B2O35H2O) in the production of glasses especially of E-glass, boron carbide (B4C) and borides (CaB6, LaB6, SiB6, LiB6, MgB2, TiB2, and TaB2 etc.) which are used in ceramics applications. Calcination, a thermal treatment method, is known to affect these parameters significantly. In this study, differential thermal analysis (DTA)-TG, X-ray diffraction (XRD), SEM, BET and chemical analysis were performed on Turkish colemanites before and after calcination. The results are compared in order to elucidate the influence of calcination on processing. An application in the ceramic industry for the production of CaB6 is demonstrated. Results indicate that the raw colemanite could be processed through calcination in the temperature range of 400 and 600 °C without milling. Calcination is shown to have a significant impact on colemanite similar to that of the milling process. As a result, colemanite was upgraded to ∼58 wt.% B2O3 for <250 μm yielding a specific surface area of 2.8 m2/g. This is higher than that of milled colemanite. Because of the crystal water of colemanite, CaB6 is not produced from uncalcined colemanite, but easily produced from colemanite calcined at 600 °C.