Hello, everyone. I want to process a metal mirror. This type of mirror is used at 60kPa, 370 degrees Celsius with up to 200ppm concentration of SO3 gas.
I currently have three options for making this mirror. One method is to use aluminum alloy as a substrate and gold as a coating. Another method is to use copper as a base material and gold as a coating. The third method is to use copper as the base material, chrome as the intermediate coating, and gold as the outer coating. I wonder which one is better for long-term use? Besides, what better way than these three? thank you
If this task is considered only from the point of view of chemistry, aluminum base is better than copper base, because copper oxidizes quickly in atmosphere containing SO3 at 350°C.
But aluminum alloys are not the best choice either, because they soften significantly at 350°C.
Austenitic stainless steels and nickel-based alloys with a high (from 20%) chromium content offer much better mechanical and chemical properties under the above conditions.
If, in addition to chemical stability, you also have requirements for the highest possible hardness of the base material, then you either come to non-metallic materials (glass, ceramics and glass-ceramics) or to alloys such as Ni50Cr50, which offer extreme chemical resistance as well as very high hardness.
Also, gold is not the best choice for a mirror coating, rhodium is much better for this.
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