The goal of this research is to study the corrosion processes in refractory metals and refractory metal-bearing alloys. The primary focus will be on the characterization of the microstructural evolution of corrosion scales using thermogravimetry, SEM, TEM, and XTEM techniques. Specifically, the sulfidation of Niobium, Niobium- bearing Chromium alloys, and Iron-Chromium-Niobium and Chromium- Molybdenum systems will be investigated. In addition, in-situ oxidation and hot-corrosion of pure Chromium, Nickel-Chromium alloys, and NickelAluminide will also be studied in the Environmental Scanning Electron Microscope (ESEM). This will be the first application of ESEM to high temperature oxidation and sulfidation of metals. The research is expected to help with the development of new corrosion resistant alloys by contributing to the fundamental understanding of corrosion mechanisms.