I want to use Zinc Selenide optics at 400 C. Various references say it melts at 1500 to 1800 C but one of them also says its maximum use temperature is 300 C. Why? What would go wrong at 400 C? Suppose I want it transparent for IR radiation of 8 to 9 um wavelength.
OK, found out more at http://www.cvdmaterials.com/pdf/Temp%20Dependency%20Data.pdf.
“It should be noted that both zinc selenide and
zinc sulfide oxidize at an appreciable rate at
temperatures >300°C which limit their use at high
temperatures in an oxidizing environment (air).”
That being said, what’s “appreciable”? Do lens surfaces erode at a micrometer per year and change the optical abberations? Or does a solid component evolve into dust in a day?
I supect that the oxidized surface is significantly less transparent to IR than the zinc selenide is. I can’t find an article detailing the specifics, however.
Ok, here is some possibly relevant information (you have to pay to view the entire article, I believe).