The degradation mechanism of Mo_xW_1-xSi₂ ultrahigh-temperature heating elements fabricated by selfpropagating high-temperature synthesiswas investigated. The Mo_xW_1-xSi₂ specimens (with and without post-annealing) were subjected to ADTs (accelerated degradation tests) at temperatures up to 1,700℃ at heating rates of 3, 4, 5, 7, and 14℃/min. The surface loads of all the specimen heaters were increased with the increase in the target temperature. For the Mo_xW_1-xSi₂ specimens without annealing, many pores and secondary-phase particles were observed in the microstructure; the surface load increased to 23.9 W/㎠ at 1,700℃, while the bending strength drastically reduced to 242 MPa. In contrast, the Mo_xW_1-xSi₂ specimens after post-annealing retained single- Mo_xW_1-xSi₂ phases and showed superior durability after the ADT. Consequently, it is thought that the formation of microcracks and coarse secondary phases during the ADT are the main causes for the degraded performance of the Mo_xW_1-xSi₂ heating elements without post-annealing.

Al2O3 films on silicon carbide were fabricated by Aerosol deposition with annealing temperatureat 800℃ and 1,000℃. The effect of thermal treatment on physical properties of Al2O3 thin films has beeninvestigated by XRD (X-ray diffraction), AFM (atomic force microscope), SEM (scanning electronmicroscope), and AES (auger electron spectroscopy). Also electrical properties have been investigated byKeithley 4,200 semiconductor parameter analyzer to explain the interface trapped charge density (Dit),flatband voltage (VFB) and leakage current (Io). Al2O3 films become crystallized with increasingtemperature by calculating full width at half maximum (FWHM) of diffraction peaks, also surfacemorphology is observed by topography measurement in non-contact mode AFM. Dit was 2.26×10-12eV-1.cm-2 at 800℃ annealed sample, which is the lowest value in all samples. Also the sample annealedat 800℃ has the lowest leakage current of 4.89×10-13 A.