High-Temperature Mass Spectrometric Study of the Vaporization of Oxycarbide MAX Phase Ceramics

Abstract

The vaporization of the carbide materials with the chemical compositions Ti₂SiC, Ti₃SiC₂, Ti₂AlC, Ti₃AlC₂, Zr₂AlC, and Zr₃AlC₂ containing MAX phases and of oxycarbide systems based on these materials with hafnia additives was examined by Knudsen effusion mass spectrometry at temperatures up to 2200 K. Atomic aluminum was identified as the major vapor species over the Ti₂AlC, Ti₃AlC₂, Zr₂AlC, and Zr₃AlC₂ samples at 1500 K. The silicon-containing samples were less volatile than the aluminum-containing carbide materials; they vaporized observably at temperatures above 1900 K to form Si, Si₂, SiC₂, and Si₂C vapor species. The addition of hafnia to the carbides under study led to the formation of oxygen-containing vapor species, particularly Al₂O and SiO, and to a decrease in total vapor pressure over the systems formed. The least volatile materials were samples of the Ti₂SiC–HfO₂ oxycarbide system, and among the aluminum-containing oxycarbide systems, samples of the Zr₂AlC–HfO₂ system containing up to 10 mol % hafnia and samples of the Ti₂AlC–HfO₂ system with a higher HfO₂ content.