Non-Chemical Molten silver/pgm spattering

[jsargent]

I'm wondering if anyone has had this happen... Last night I poured a one ounce slug of melted silver I had used to collect a few grams of PGM from an ore digest. I poured it into a round cast iron fence pipe cap that I have used many times for the same purpose. The mold was dry but not pre-heated. When the hot metal hit the mold about a third of it exploded in a spray of fine beads. :shock: Now I have poured hundreds of times and never had this happen. I am certain the mold was dry, but it was a little rusty. Could the PGM content of the hot metal have reacted with the rust film to liberate gas or was it just residual moisture trapped in the rust that caused this to happen? Or something else?

 

[qst42know]

Rust is a porous compound and could have had moisture in it. Or your cold mold may have condensed some of the humidity from the super heated air surrounding your molten metal. Your mold has to be at least above the dew point. The source of the moisture is not that important, avoiding it is. Foundries adding new metal to a melt also have to introduce it slowly to avoid the same problem. I have experienced steam explosions casting fishing sinkers while adding metal and from spilling molten lead on damp concrete. Though I was not injured I learned my lesson. :wink:

 

[goldsilverpro]

If the mold wasn't heated, how did you know it was dry? It obviously wasn't.

 

[jsargent]

Rust is a porous compound and could have had moisture in it. Or your cold mold may have condensed some of the humidity from the super heated air surrounding your molten metal. Your mold has to be at least above the dew point. The source of the moisture is not that important, avoiding it is. Foundries adding new metal to a melt also have to introduce it slowly to avoid the same problem. I have experienced steam explosions casting fishing sinkers while adding metal and from spilling molten lead on damp concrete. Though I was not injured I learned my lesson. :wink:

Yep the porous rust could and probably did hold some moisture.

 

[jsargent]

If the mold wasn't heated, how did you know it was dry? It obviously wasn't.

You're right... it was probably invisible moisture trapped in the thin layer of rust in the mold. I should have heated it first. But, I also know platinum does funny things at high temperature so I was wondering if there could have been a high temperature chemical reaction between the rust and the platinum fraction of the molten metal? I know that if one tries to cupel a lead prill with a high percentage of platinum it will often splatter metal beads as the last of the lead is absorbed into the bone ash cupel. I thought something similar might have happened when I did this pour.

 

[Lou]

Platinum is renowned for its tendency not to do funny things at high temperature, hence its use in laboratory apparatus.

Of course it does readily alloy with metals, react with sulfur, salt, and a few other things if heated together.



Sounds like a steam explosion to me.