This question is way beyond my area of expertise. I checked the ASM Handbooks on corrosion (Volume 13, 13A, 13B, 13C) and all of them have some information on molten salt corrosion. As you have alluded to, removing the probe from the molten salts and exposing it to air makes this an even more challenging problem. I suggest you start with the ASM Handbooks and then check the literature references to see if you can get your question answered. For example, the article in ASM Handbook Volume 13  "High Temperature Corrosion in Molten Salts" has a section entitled "Literature on Molten Salt Corrosion" and lists several references that might be useful. Good luck!