Doloma

Abstract: In this study, pure (with no additives) and mill scale (98.66 wt.% Fe2O3 content) added (up to 1.5 wt.%) natural dolomite of Selcuklu-Konya-Turkey fired at 1600–1700 °C for 2–6 h using the one-stage process. The resulting bulk densities and apparent porosities of the sintered doloma are investigated. According to the results of experiments with 15 sintered samples, sintering temperature, soaking time and increase of mill scale amount were found to increase the bulk density and thus decrease the observed apparent porosity. In hydration resistance tests, it seemed that the same characteristics also increased the resistance. Furthermore, EDX analysis of the dolomas that were sintered at three different temperatures each with 0.5 wt.% mill scale additions and also at 1700 °C/2 h with 0–1 wt.% mill scale additions were performed. Quantities of Fe2+,3+ inside the periclase (MgO) were examined. Bulk density of pure doloma (CaO·MgO) was calculated using density values of both pure CaO and MgO given in the literature. The difference between the extrapolated value of the measured densities and bulk density of doloma, which is calculated from literature data without porosity is very close.

Abstract: Simultaneous grain growth of the lime (CaO) and periclase (MgO) phases was studied in a synthetic, hydroxide-derived doloma over the temperature range 1400° to 1700°C. The grain growth kinetic exponents were 5 and 6 and the activation energies 333±45 and 437±47 kJ/mol for the CaO and MgO phases, respectively. The large kinetic exponents are attributed to the topological restraints of the two phases on the growth of one another. The parameters suggest that the grain growth of the CaO may be governed by Ca2+ diffusion within the CaO phase for it is the continuous phase in the microstructure. In most instances for grain growth of the MgO phase, the Mg2+ must diffuse through the lime phase, and this process is believed to be limited by movement of associated defects involving Mg2+ within the CaO structure.