For my bachelor project, I am in need of an air tight (or very, very near air tight) container, which can withstand 750 C. My original thought was to have a steel container with a lid and gasket, but I was unable to find any gaskets that got anywhere near that. Does anyone know of a gasket material that will withstand that? Or have another idea as to how I can make an air tight container for this temperature? It will be sustained, likely 1-2 hours at a time, and will be about the size of a toaster. (just large enough for a crucible and some electrodes. Thank you in advance for any input!