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Chlorine and oxidation of low carat gold alloys


#1

I am searching for regarding the action of chlorine on
the corrosion and oxidation of lower carat gold alloys, are youable
to refer me to relavant publications, or possibly some one to
communicate more completley on this subject.

Thank You
Anthony


#2

Chlorine as a gas is a reduction agent, they use a chlorine
atmosphere for the continuous soldering of chain in mass production.
As for corrosion, the chloride salts formed from reaction with gold
alloys are not very soluble campared to metals higher up in the
periodic table and the amount of metal forming chlorides will be
minimal. That is why to make photographic salts you need to dissolve
your metal in nitric/aqua regia and then react with
hydrochloric/hydrobromic acid to get the silver/gold/platinum halide.
With a low carat alloy you are going to get a slight enrichment of
gold where other metals have reacted preferentially. Many old low
carat alloys have all sorts of things in them so oxidation will
generally be because a slightly etched surface has more free surface
energy (bigger surface area and more atoms not surrounded by other
stable atoms/molecules) and therefore more prone to oxidation. Heat
will probably have a greater degree of influence on the overall
oxidation of your alloy.

Nick Royall


#3
they use a chlorine atmosphere for the continuous soldering of
chain in mass production. 

Dont you mean ammonia? I have never heard of anyone using chlorine
as a reducing gas for furnace brazing.

James Binnion
James Binnion Metal Arts


#4
Chlorine as a gas is a reduction agent 

Chlorine is actually an oxidizing agent. You must be thinking of
something else.

Al Balmer
Pine City, NY


#5
 Dont you mean ammonia? I have never heard of anyone using chlorine
 as a reducing gas for furnace brazing.

Either way it sounds nasty CIA


#6

No, it was a continuous process done in a tube furnace with a
chlorine atmosphere. Biggest chain making plant in Britain.

Nick Royall


#7

Chlorates are strongly oxidising. Heat most plastics in a chlorine
atmosphere and you change many of the carbon bonds from a single
chain to a double chain bond. End result is a shrunken but
incredibly strong material.

Nick Royall


#8
Chlorates are strongly oxidising. 

This is why I am having a very hard time believing that chlorine was
used as the cover gas in a furnace soldering system. I have searched
and cannot find any references to using chlorine as a cover gas. In
fact the only references I can find about chlorine in soldering
furnace atmosphere refers to it as a contaminant that causes
problems in soldering.

James Binnion
James Binnion Metal Arts


#9

I have to agree with James here. In the course of my work for
different companies I have visited a large number of the UK silver
manufacturing companies and I have not seen one where a 'chlorine’
atmosphere is used for furnace brazing (soldering). Indeed, given
that most brazing alloys (solders) used with silver alloys contain
some zinc this system would not give you a sound joint.

The use of high hydrogen atmospheres, sourced from cracked ammonia,
where the hydrogen content acts as the ‘flux’ for the joining process
are common for furnace brazing (soldering) and I wonder if this is
where a misunderstanding has occurred?

Charles Allenden


#10

No, this was for 9ct gold chain, not silver. The company is and was
the largest silver chain manufacturer in the UK and is now part of
the Cooksons metals group. The thread started by asking about
chlorine and oxidation so I gave an example of Cl used for preventing
oxidation and as happens with many threads on this forum (and most
others) a certain amount of creep occurs to the original point thus
leading to talking at crossed purposes. With regard to reduction, you
can also use the example of salt glazed stoneware pottery and in the
alteration of the characteristics of some plastics. A friend of mine
did her PhD in characterisation of polyethylene compounds and a trick
to make a plastic that could be used as body armour was to heat it in
a chlorine atmosphere. I have done this with crisp (potato chip)
packets and you end up with a shrunken packet that is inpenetrable.
the chlorine breaks down some of the bonds and you get double chain
carbon molecules instead of single chain and HCl and other rather
nasty byproducts.

Having said that it was 34 years ago since I was interviewed for a
job there so it may be that the explanations of various processes
given to me at the time were incorrect or things may have changed
since then.

Nick Royall