Technical Note: A High-Temperature, High-Pressure Window for In Situ Optical Observation and Raman Detection

A window was developed on a high-temperature, high-pressure refreshed autoclave to perform in situ tests. High-purity single crystal sapphire was used as window material to withstand the harsh environment and minimize the production of fluorescence. The cone-shaped internal structure enables a large light flux necessary for the in situ optical observation. Through this window, in situ optical observation and Raman tests were successfully performed in high-temperature, high-pressure water using a long-distance microscope and a custom-made Raman system. The formation of spinel oxide on 304 stainless steel in oxygenated water containing a high concentration of Ni cations was verified by in situ Raman tests.