Reaction behavior of MgF2 powder in hexafluoropropylene/air atmospheres at high temperatures

Abstract

The protection of fluorine-containing gases for magnesium melt is based on a dense composite film containing MgF2 on the melt surface. However, the stability of MgF2 is still a problem. In this paper, the reaction behavior of MgF2 powder in the atmosphere of air containing hexafluoropropylene (HFP) at 750–1000 °C was investigated. The results showed that the reaction was related to the concentration of HFP and temperature. In the atmosphere of air containing high concentration of HFP or at lower temperatures, MgF2 almost did not react. In the atmosphere of air containing low concentration of HFP or at higher temperatures, MgF2 underwent a reaction to convert to MgO. The kinetics of the reaction followed a linear or quasi-linear rate law in most cases, while it followed a mixed linear-parabolic rate law in air containing 0.05%, 0.01% and 0.005% HFP at 1000 °C and 0.01% HFP at 950 °C. The apparent activation energy was calculated to be 80.54 kJ mo1−1. These results help to better understand the protective mechanism of fluorine-containing gases on magnesium melt.