I am working with molten KI (potassium iodide) as a flux in a synthesis process. At the moment, sealed quartz vessels are used - I put solid KI in to it, seal it, and it melts at 700degC in an oven, then I take it out, it solidifies and brakes my quartz vessel. So far, I was not able to find a suitable substitute material, that can handle molten KI and Sulfur at the same time. Questions are: What are the metals/materials used in solar thermal plants? I searched and found only brief mentioning of hastelloy. Why does KI brakes the vessel? - when salt solidifies, it should contract and not expand? Does it binds itself to quartz surface and pulls it? What are the dangers of working with molten KI, when it is not under protective atmosphere, and is just in a lab room inside opened crucible? Will it oxidize? If there is a literature you can suggest me to read about working with molten salts, and safety? Thank You!