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Ammonium chloride & Potassium nitrate


#1

Long ago, when I was a puppy - I vaguely remember using these two
chemicals. We used to put a pinch of ammonium chloride on top of the
molten alloy to “toughen” the resulting alloy, or a pinch of
potassium nitrate to “clean up” dubious scrap metal.

I cannot remember if this was explained to me, or why it seemed to
work. I do remember that it had to be done under a ventilating hood,
because it would produce nasty smelling smoke.

Does anyone out there know whether there is a scientific basis for
this? Or whether it is indeed, useful? It seemed to me that one or
the other treatment helped make rolling some alloys easier… less
tendency to crack…

Brian P. Marshall
Stockton Jewelry Arts School
708 W. Swain Rd.
Stockton, CA 95207
209-477-6535 Workshop/Classrooms


#2

We used to put a pinch of ammonium chloride on top of the
molten alloy to “toughen” the resulting alloy, or a pinch of
potassium nitrate to “clean up” dubious scrap metal.

Ammonium chloride was used a great deal in soft solder fluxes, and
plumbers used it when jointing lead pipes and tanks. Some modern lead
solder fluxes contain mostly zinc chloride, but also contain ammonium
chloride. The fumes that emanate from hot ammonium chloride fluxes
are composed of ammonium chloride, whilst not particularly poisonous,
one would do well not to inhale them too much. Potassium nitrate
supplies oxygen when heated, and would tend to oxidise copper, zinc
and other impurities and the ammon chloride would help dissolve them,
when they could be skimmed off the melt and so removed. I am unable
to say whether ammon chloride and pot nitrate would 'toughen an alloy,
but I doubt it.


#3
   Does anyone out there know whether there is a scientific basis
for this? Or whether it is indeed, useful? It seemed to me that one
or the other treatment helped make rolling some alloys easier...
less tendency to crack... 

Ammonium Chloride added to a melt of metal will help to remove some
of the baser metals. The reaction is simply that the chlorides of
these baser metals are insoluable in the melt, and slag off, so
available chlorine at the surface of the melt reacts with those baser
metals, causing their removal from the metal mass. And yes, it forms
lots of fumes, including chlorine gas… Do it only with excellent
ventilation…

Peter Rowe