Aluminum composite reportedly stronger, lighter than carbon

In article . com,
Fred the Red Shirt wrote:

On Oct 4, 4:52 am, Darrel Toepfer wrote:
Ron Wanttaja wrote
:
...

Can "transparent aluminum" be far behind?


It's here now. Aluminum Oxide is transparent which is why telescope
mirrors which have a very thin layer to minimize defects, have to be
realuminized every few years ago.

Um, sort of, not quite.

Aluminum oxide forms quickly on pure aluminum surfaces, which is a good
thing, corrosion-wise; it's very hard, has little effect on
reflectivity, and thus makes for a good mirror coating.

The thing is, it's not so much something you do, specifically, as
something that happens when aluminum is exposed to oxygen. And if you
scratch the surface, the scratch gets an immediate re-coat. Not that
you'd want to scratch your mirror at all, if you could possibly avoid it.

Eventually, though, dust and other sources of wear damage it and the
aluminum under it, and you've got to redo the aluminum coating; it's
only a few millionths to a few thousandths thick, from glass to air, so
it's easy to damage.

Fortunately, it's an easy process, and last a *lot* longer than
silvering the mirror, even though the silvered mirror, for the first few
minutes anyway, is a couple percent better than aluminum.

Then corrosion sets in...

Could be worse, we could still be using electrum or speculum metal to
make mirrors.

Richard Riley wrote:

including trucks that collide with aircraft while they’re on the
ground."

That's really bad weather.

Most common type of structural repair on regional airliners by far is
damage from ground vehicles.

John

Could be worse, we could still be using electrum or speculum metal to
make mirrors.

Or using large vats of mercury.

In article ,
Chris Wells wrote:

Could be worse, we could still be using electrum or speculum metal to
make mirrors.

Or using large vats of mercury.

Actually, I think someone is doing just that.

A pool of mercury is spun up to form a curved surface, used as the
mirror for, I think, a solar telescope.

Lessee... Ah:

http://www.astro.ubc.ca/LMT/lm/index.html

The focal length is dependent on the rate of spin. Kewl.

The first ones were made in 1872, there are more modern ones in use now,
running up to 3m in diameter. Turns out to be several "someones", and
plans for more are being considered. Even proposals for putting some on
the moon.

Hold your breath in the observatory...

Or using large vats of mercury.

Actually, I think someone is doing just that.

I know, it was supposed to be a joke.

"JP" wrote

Here's more about it:
http://www.greencarcongress.com/2007...terial-fo.html

Did anyone see a thickness for the composite aluminum sandwich?
--
Jim in NC

On Oct 5, 5:26 pm, Steve Hix wrote:
In article . com,
Fred the Red Shirt wrote:

On Oct 4, 4:52 am, Darrel Toepfer wrote:
Ron Wanttaja wrote
:
...

Can "transparent aluminum" be far behind?

It's here now. Aluminum Oxide is transparent which is why telescope
mirrors which have a very thin layer to minimize defects, have to be
realuminized every few years ago.

Um, sort of, not quite.

Aluminum oxide forms quickly on pure aluminum surfaces, which is a good
thing, corrosion-wise; it's very hard, has little effect on
reflectivity, and thus makes for a good mirror coating.

The thing is, it's not so much something you do, specifically, as
something that happens when aluminum is exposed to oxygen. And if you
scratch the surface, the scratch gets an immediate re-coat. Not that
you'd want to scratch your mirror at all, if you could possibly avoid it.

Eventually, though, dust and other sources of wear damage it and the
aluminum under it, and you've got to redo the aluminum coating; it's
only a few millionths to a few thousandths thick, from glass to air, so
it's easy to damage.

Fortunately, it's an easy process, and last a *lot* longer than
silvering the mirror, even though the silvered mirror, for the first few
minutes anyway, is a couple percent better than aluminum.


Obviously you have not seen how a telescope mirror ages over the
years. The coating gradually becomes more and more transparent
over the years.

This happens even if you never clean, and therefor never damage
your mirror. It is certainly not due to wear! Clearly (no pun
intended)
the typical coating is thin enough that as the oxide layer slowly
thickens
the transparency rises.

Were wear alone responsible, the change would be episodic, not
gradual, and would not happen at all between cleanings.

Could be worse, we could still be using electrum or speculum metal to
make mirrors.

Yeah.

--

FF

In article .com,
Fred the Red Shirt wrote:

On Oct 5, 5:26 pm, Steve Hix wrote:
In article . com,
Fred the Red Shirt wrote:

On Oct 4, 4:52 am, Darrel Toepfer wrote:
Ron Wanttaja wrote
:
...

Can "transparent aluminum" be far behind?

It's here now. Aluminum Oxide is transparent which is why telescope
mirrors which have a very thin layer to minimize defects, have to be
realuminized every few years ago.

Um, sort of, not quite.

Aluminum oxide forms quickly on pure aluminum surfaces, which is a good
thing, corrosion-wise; it's very hard, has little effect on
reflectivity, and thus makes for a good mirror coating.

The thing is, it's not so much something you do, specifically, as
something that happens when aluminum is exposed to oxygen. And if you
scratch the surface, the scratch gets an immediate re-coat. Not that
you'd want to scratch your mirror at all, if you could possibly avoid it.

Eventually, though, dust and other sources of wear damage it and the
aluminum under it, and you've got to redo the aluminum coating; it's
only a few millionths to a few thousandths thick, from glass to air, so
it's easy to damage.

Fortunately, it's an easy process, and last a *lot* longer than
silvering the mirror, even though the silvered mirror, for the first few
minutes anyway, is a couple percent better than aluminum.

Obviously you have not seen how a telescope mirror ages over the
years.

Guess again.

It's easy to recoat the mirror, so it's not so much of a problem,
certainly less of one than dealing with silver corrosion.

The coating gradually becomes more and more transparent
over the years.

This happens even if you never clean, and therefor never damage
your mirror. It is certainly not due to wear! Clearly (no pun
intended)
the typical coating is thin enough that as the oxide layer slowly
thickens
the transparency rises.

Were wear alone responsible, the change would be episodic, not
gradual, and would not happen at all between cleanings.

Could be worse, we could still be using electrum or speculum metal to
make mirrors.

Yeah.

--

FF

On Oct 9, 11:53 pm, Steve Hix
wrote:
In article .com,
Fred the Red Shirt wrote:


...

Obviously you have not seen how a telescope mirror ages over the
years.

Guess again.

Well then you should have observed that the transparency increases
between cleanings.


It's easy to recoat the mirror, so it's not so much of a problem,
certainly less of one than dealing with silver corrosion.

While it is not a technologically daunting task, it is not cheap for
larger mirrors especially when you consider shipping. I have a 17.5"
mirror that will need realuminizing when I finally get around to
putting
it into a scope. It has been cleaned exactly once, but the coating
is nearly gone entirely after 30 years in storage.

Offhand, do you know anyone who recoats mirrors that size?

--

FF

"Fred the Red Shirt" wrote in message
oups.com...
While it is not a technologically daunting task, it is not cheap for
larger mirrors especially when you consider shipping. I have a 17.5"
mirror that will need realuminizing when I finally get around to
putting
it into a scope. It has been cleaned exactly once, but the coating
is nearly gone entirely after 30 years in storage.

Offhand, do you know anyone who recoats mirrors that size?

--

FF


Maybe these guys: http://www.newportglass.com/nigcap.htm

http://www.johndobson.org/links.html