Quote:
Originally Posted by bojan
Some info on materials can be found here:
http://www.engineeringtoolbox.com/li...ents-d_95.html
http://www.engineeringtoolbox.com/th...ity-d_429.html
Material - thermal coefficient [(10-6 m/(m K))] thermal conductivity [W/(m K)]
Aluminum 22.2 205
Glass, Pyrex 4.0 1.05
So.. in principle aluminium is 5x better than glass in terms of expansion coefficient, but aluminium is 200x better in terms of conductivity - so less internal stresses, due to uniform thermal gradients inside material.
I imagine glass is much easier to figure and polish compared to aluminium... or not?
I think the homogenity of glass is definitelly better controlled.. and there is no issues with chemical stability of glass at melting temperatures.. while aluminium may even burn in normally oxigenated atmosphere.
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aluminium is 5x WORSE than glass. You want the mirror to not expand