Does Aluminum Coating on Telescope Mirrors Turn into Aluminum Oxide?

[anorlunda]

I saw on Nova thst large telescope mirrors have aluminum reflective coatings. Wouldn't that rapidly become an aluminum oxide costing?

Are the coatings coated to keep oxygen out?

 

[Drakkith]

Yes, when aluminum corrodes it forms a layer of aluminum oxide on the surface that protects the rest of the underlying aluminum from corroding. Aluminum oxide is transparent to visible light, so it makes an excellent coating for telescope mirrors.

 

[davenn]

anorlunda

pretty much all mirrors on reflector telescopes are aluminised even small scopes used for amateur use

I have 3 reflecting scopes with mirrors of 6", 8' and 9.25 " They all have an aluminium coating and then other coatings on top of that to protect the aluminium coating
and that is pretty much the standard

cheers
Dave

 

[Chronos]

Aluminum coatings are usually overcoated with silicon monoxide, or something similar. This is a good idea for a couple of reasons - increased reflectivity and improved coating life.

 

[pmacias]

I can confirm that aluminum oxide coatings are commonly used on telescope mirrors as a reflective surface. This is because aluminum oxide is a highly reflective material that can withstand the harsh conditions of space. However, there is a misconception that the coating will rapidly become aluminum oxide itself.

While it is true that aluminum will naturally oxidize when exposed to oxygen, the coating on telescope mirrors is designed to prevent this from happening. The aluminum is typically coated with a layer of protective material, such as silicon dioxide, that acts as a barrier to oxygen. This ensures that the aluminum remains reflective and does not become aluminum oxide.

In addition, the coatings are carefully applied in a controlled environment to minimize any exposure to oxygen. This helps to maintain the reflective properties of the aluminum and prolong the lifespan of the coating.

So to answer your question, the coatings on telescope mirrors are not coated to keep oxygen out, but rather to prevent the aluminum from oxidizing and maintain its reflective properties.