🚀 go-pugleaf

ericc@nntp-server.caltech.edu (Eric Y. Chang) wrote in message news:<app86o$kjm$2@naig.caltech.edu>...
> N. Thornton (bigcat@meeow.co.uk) wrote:
> ...
> : maybe I'm mistaken, but it at least sounds quite straightforward. Put
> : the copper bit in a glass tube, held up on glass, put scraps of iron
> : in the tube, pass flammable gas thru the tube, and heat the iron
> : pieces. The iron evaporates and lands on the copper bit, while the gas
> : prevents it oxidising.
> 
> Does this really work?  What is the vapor pressure of iron at
> comfortable temperatures for glass?  

I would imagine its miniscule, but it was enough to mirror coat
whatever it was.


> What is the driving force
> causing the iron vapor to preferentially condense on the copper?

I just assumed there wasn't one, that is just went everyhere. Could be
wrong of course. I'm not claiming any great understanding of it here,
just that it worked.


> Have you tried this or seen it done?

Yup, only once. I was following someone else's instructions, it wasn't
my idea.
I'm having some uncertainty here about what metal I was plating
though... I can't be sure if it was iron. Could have been something
with lower mp/bp.


> The flux of iron vapor
> will be an axial diffusion across the stream of gas.  It will be
> driven by the differing vapor pressures of iron at the supposedly
> cooler copper tip vs the iron pieces.  This diffusion flux will
> be substantially smaller than the flow rate.  So the deposition
> will be attenuated by the ratio of the characteristic times for
> convection to diffusion.  The latter will be on the order of
> seconds, while the former will be on the order of days.  Most
> of the iron (small amount anyway) should leave the tube.

I expect it did. I dont see that as a problem though. Its not as if
iron's expensive or toxic.

I think you're mistook about a diffusion time of days though. Once
something is in gas form it diffuses very fast. Even liquids don't
take days. I would expect the times for gas to flow through and vapour
to diffuse across would be, at worst, of the same order.


> Have you tried this?  It seems like a very interesting process.

Yes, quite some time ago, and it did work. It puzzled me that the
stuff didn't all just condense in the gas, but enough plated to make
the little mirror.

I remember oxide powder was put in the tube rather than plain metal.
One could put the target close to the vapour source, rather than have
the gas all flowing between the 2, to get better deposition.

A slobbering iron would want a far thicker coating than a mirror of
course.

I still think an arc would be better though. Perhaps carbon with metal
filings in?

Regards, NT