Study of Zircon-Dolomite Reactions Monitored by Neutron Thermodiffractometry

The reaction mechanism that takes place in ZrSiO₄-Mg Ca(CO₃)₂ mixtures was studied in air up to 1300°C by collecting neutron diffraction patterns during the heating ramp. Neutron diffraction intensities were used to monitor and establish the mechanism of reaction that occurs in successive stages. (a) MgCa(CO₃)₂ decomposition yielding MgO and CaCO₃; (b) CaCO₃ decomposition; (c) reactions between CaO, MgO, and ZrSiO₄ involving the formation of phases such as: tetragonal-ZrO₂, α-Ca₂SiO₄, and Ca₃MgSi₂O₈, some of them acting as transitory phases; and (d) formation of CaZrO₃. The results obtained by this technique agree with data obtained by differential thermal analysis and thermogravimetry. The final product has a porous structure, due to the release of CO₂, with a very narrow pore size distribution (≈1 μm). This open-porosity can be controlled by tailoring the reaction sintering process.