Volatilization behaviour and volatilization kinetics of CaF2–Na2O–CaO–SiO2–Al2O3–MgO–B2O3 synthetic mould flux

Abstract

To reduce the volatilization of the volatile-containing slags and obtain accurate measurement results of slag performance, the volatility degree and deviation mechanism must be determined. Non-isothermal thermogravimetric analysis at different heating rates was used to establish the volatilization kinetic model, and it reveals the volatilization mechanism of CaF2–Na2O–CaO–SiO2–Al2O3–MgO–B2O3 synthetic sodium-containing fluoride mould flux. The results demonstrated that the evaporation of NaF and SiF4 was the decisive factor that led to the change in composition and deviation of properties of the tested slags. The most probable kinetic mechanism function for the evaporation of volatile component from sodium-containing fluoride mould flux could be expressed by $$g(\alpha ) = [ - \ln (1 - \alpha )]^{2/3}$$ , with an apparent activation energy of 164.866 kJ mol−1 and pre-exponential factor of 2.13 × 10−4 s−1, where α is the conversion rate at any time step in the volatilization process. The reaction mechanism was random nucleation followed by growth, which was the limiting factor for the volatilization of synthetic sodium-containing fluoride mould flux. The method of increasing heating rate and adding protection gas in the measurement system will help to obtain more accurate results of slag performance.