Effect of manganese doping of corundum on the content and diffusion of water and other gases

Abstract

The content of volatile gas-liquid impurities, degassing and diffusion characteristics of Mn-doped corundum synthesized in a supercritical water fluid were determined using the method of kinetic thermodesorption mass spectrometry. Water is the main volatile impurity in the crystals of Mn-doped corundum. An increase in the concentration of manganese in corundum increases the water content in the low-temperature form and affects the high-temperature water release by the diffusion mechanism in different ways: for MnCl2-precursor, the content of the high-temperature form increases, and for KMnO4 – decreases. The introduction of manganese into corundum significantly lowers the water content in the structure compared to undoped corundum, which is a favorable factor in the production of transparent ceramics. Carbonaceous impurities (CO2, CO, hydrocarbons CxHy) are the second largest group of volatile gas-liquid impurities. With an increase in the manganese content in corundum (for both Mn precursors), the release of hydrogen decreases while the release of oxygen increases. The reduction of hydroxyls to hydrogen and the oxidation of manganese ions are most effective when the concentration of hydroxyls in the corundum structure is significantly higher than the concentration of manganese ions. The diffusion coefficients of water in corundum with various manganese concentrations and with different Mn precursors were determined. The obtained values of water diffusion coefficients and their temperature dependencies make it possible to calculate the degassing time of the material to a certain degree at any temperature.