Re: [ATM] glued aluminium mirror cell update

["Dream - Telescopes & Accessories, Inc." <shane@dreamscopes.com>]

George,

It *might* give the resin a little more strength but I think the biggest 
issue is something else, for Andreas anyway.  You also can get into issues 
with the oxidation of metals while in another compound.  For example, steel 
reinforced concrete is slowly starting to be replaced by composite 
reinforcement in concrete.  This is because the expansion/contraction of 
concrete allows the steel rebar to start oxidizing.  The rust increases the 
size of the steel and therefore causes even larger cracks.  And so on and 
so forth until the steel reinforced concrete fails.  This is why composites 
are replacing steel in this application.  Composites do not corrode.  Plus 
they are lighter and stronger than steel (I'm referring to carbon 
fiber).  So installations can be done with back hoes instead of large 
cranes, in certain size applications.

Although it might seem like the epoxy completely encases the aluminum 
powder, on a molecular level, this probably isn't the case.  So I would not 
be surprised if epoxy and aluminum powder, over time, did the same thing 
that the above steel reinforced concrete is doing.

In composites a much stronger matrix for secondary bonding is pulp or 
fiber, not powder, bubbles, spheres or the like.  The longer the fiber, the 
stronger it makes the epoxy/resin.  Resin is much, much weaker than carbon 
fiber so we try to "tie" bonds together in a slightly different way to 
minimize that weakness.  Adding carbon fibers, if in large enough quantity, 
will also reduce the CTE of the resin/mixture.

For metals, welding would be stronger but I think Andreas was just trying 
to put something together in a simple fashion that didn't involve a great 
deal of equipment or investment.  Then again, welding has to be prepped and 
done right just the same.  So no method is fool proof because us "fools" 
are involved in it!

One more thing to mention about epoxy.  It is more sensitive than other 
resin systems, like polyester or vinyl-ester resin, to proper mix 
ratio.  This could have been a forth issue causing Andreas problems.  It's 
the variables that kill you.  Reduce them and you should greatly reduce the 
chance of failures.

Thank you.

Sincerely,
Shane Santi - Owner
Dream - Telescopes & Accessories, Inc.
http://www.dreamscopes.com
610 - 365 - 2833


This is more of a question than suggestion:  Is there any advantage to 
adding powdered aluminum to the epoxy mixture prior to mixing?

George 

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