In situ high-temperature corrosion with the environmental SEM

Electron microscopy has greatly aided in understanding the microstructure and morphological development of corrosion scales formed by high temperature oxidation and sulfidation of metals. However, this knowledge has been limited by the fact that the microstructure and morphological features could only be studied after corrosion had occurred. The recent development of the environmental scanning electron microscope (ESEM) permits actual in-situ observation of the evolution of high temperature corrosion scales at the scale-gas interface, allowing for a better understanding of the detailed mechanisms of scale growth. The objective of this study is to investigate the evolution of oxidation and sulfidation scales on various metals and alloys.R.A. Rapp and associates adapted a conventional SEM for oxidation studies by developing a stage that could be heated in excess of 1000 C. Because of the vacuum restrictions of the SEM, a gas pipe directed at the surface of the samples was utilized in order to increase the local oxygen partial pressure, and this resulted in low (0.2 Torr) but sufficient pressures for oxidation.