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Platinum air pockets troubles


#1

I’m working with Pt 95 at the moment and seem to be getting a heap
of air pockets forming each time I try welding or melting the
metal.The join can look perfect on the surface but on filing or
further melting there’s plenty of pin head and smaller sized
cavities.What am I doing to cause this?

Is this some sort of contamination? I’m using an LPG and oxygen
Little Torch, on a Pt crucible back, no borax or carbon or fluxes in
contact, pickled in nitric before each annealing. If its
contamination as opposed to technique, is it easy to get the metal
back to being clean again? …or does it go back to the refiner.
Thanks for any help. Colin.


#2
 I'm working with Pt 95 at the moment and seem to be getting a
heap of  air pockets forming each time I try welding or melting the
metal 

If the alloy you are using is a cobalt platinum, then this is just
the nature of the beast. It tends to more porosity in torch welding.
Be sure your torch flame is close to neutral, not strongly
oxidizing. You don’t want a reducing flame either, but close to
neutral. That may help. And take care not to overheat too much.
One solution to joins, is instead of welding, use the plumb platinum
solders. They’re a perfect color match, work well with cobalt
platinums, and solve the problem of porosity in seams. If you’ve
got a laser welder, use argon shielding.

Peter


#3

Hey Colin…

The only thing that I could think of is heat. You are either not
getting the piece hot enough or you are heating it too much. You
wouldn’t have a problem with it not being clean since you have
cleaned it with nitric acid which rids the piece of all
contaminates.

However without seeing the piece, this is only a theory, but it is
the best one I can give.

Richard