Patrick,
I stand corrected - I had not appreciated that it is the chromium in stainless
steel that is oxidised during anodising, in place of the iron content. I
guess for brass it is that aluminium that is oxidised at the surface, to do
the same thing that it would in pure aluminium. By calling brass not a pure
metal, I simply meant that it was not composed of just one metal, but was an
alloy of several. Can the surface oxide layers of metals other than aluminium
be stained the same way aluminium can?
I am still not sure about referring to anodising as a form of electroplating,
since anodising involves the oxidisation of the surface layer of the metal,
while electroplating involves the deposition of a layer of a second metal on
top of the base metal - although the processes to achieve this are, I agree,
very similar.
In any case, this is probably a good time to call a halt to this branch of the
discussion - I fear we are heading rapidly off-topic, and we know how much
that upsets some people!!
Richard
pbowen@intellinetics.com on 29Nov2000 07:05 PM
To: Richard B Gosling/1M/Caterpillar@Caterpillar
mikeginter@frii.net@INTERNET
pbowen@intellinetics.com@INTERNET
spitfires@autox.team.net@INTERNET
cc:
Subject: RE: Chrome or black trim ?? comment?
Retain Until: 29/12/2000 Retention Category: G90 - Information and
Reports
Perkins Confidential: Green
Richard close, anodizing is simply a form of electroplating. Any
metal
that conducts electricity can be anodized, the problem is the resulting
quality and usefulness. For the coating to be high quality it must have a
stable and durable surface to attach to.
Brass is a pure metal, just a combo of two and sometimes more, typically
simple shiny brass is composed of 75% copper and 25% zinc, aluminum and tin
are added to create stability and resistance to oxidation in very small
quantities.
Stainless steel is any number of metallic substances with a very low carbon
content, while containing a minimum of 10.5% chromium and often nickel and
molybdenum. The chromium reacts on the surface creating chromium oxide
which creates corrosion resistance and the stability and durability
required.
So they are definitely able to be anodized.
Patrick Bowen
-----Original Message-----
From: Richard B Gosling [mailto:Gosling_Richard_B@perkins.com]
Sent: Wednesday, November 29, 2000 12:51 PM
To: mikeginter; pbowen; spitfires
Subject: Re: Chrome or black trim ?? comment?
Patrick and Mike,
I disagree that all metals can be anodised. Anodising (UK spelling with s
not
z!) aluminium (UK again with extra 'i'!) takes advantage of the fact that
aluminium oxide is very stable, and bonds very well to the aluminium
underneath - the process uses electrolysis to encourage a layer of
aluminium
at the surface to oxidise. This protects the metal underneath (pure
aluminium
is very reactive), and also aluminium oxide can be stained, hence the
colour
can be applied. Hooray for my old A-level chemistry exam from 10 years ago
-
I haven't quite forgotten it all yet!
We all know, however, that iron oxide is NOT stable, or bonds well to the
surface - it goes yukky and brown and flakes off, because it is RUST!!
Therefore steel, which is mostly iron, CANNOT be anodised. Stainless steel
is
iron mixed with a little of another metal (don't know what), which
dissuades
it from rusting.
There may well be processes that give a similar effect to anodising on the
surface of steel, and I couldn't honestly say what is possible with brass
(particularly since that is not a pure metal) so I'll keep quiet on that
subject! It is possible that the word has become mis-used over time, to
describe processes that give a similar finish to anodising, but are in fact
completely different.
Richard and Daffy (who would look great, and rust-free, with a body made
entirely of anodised shiny aluminium!)
|