Thermodynamic and Kinetic Stability of Refractory Materials at Ultra-High Temperatures.

摘要

Using the newly developed measurement technique of Laser Vaporization Mass Spectrometry (LVMS), new vapor pressure data for hafnium oxide and alpha silicon carbide at ultra high temperature have been obtained. The technique uses pulsed lasers to heat a surface on the timescale of 15 ns, providing an effectively containerless environment. Time-resolved mass spectra establish that the vaporization process is occuring under at least local equilibrium conditions. The vapor pressure data are compared with extrapolations from the literature. The agreement for HfO2 is excellent, while the comparison for SiC indicates a significant discrepancy. Both instrumental and physio-chemical influences affecting the measurements are discussed, and the possibility of a different vaporization mechanism for SiC under vacuum vaporization conditions is suggested. Preliminary optical spectroscopic approaches, to supplement the current indirect methods, to the direct measurement of surface temperatures under short pulse laser heating conditions are presented.