Non-Chemical Melting refined gold

[bswartzwelder]

Once you have refined your gold, most likely it is a very fine powder. I have seen in numerous places to heat your graphite mold prior to pouring molten gold into it. Steam explosions can be very nasty. Why is it that no one ever puts the powdered gold into the mold and then places the mold into the kiln for melting? That way you would bring the temperature up slowly and let it cool off slowly as well. I am assuming something in this method is bad for the mold?

 

[samuel-a]

It depends on type of mold and environment.

Iron mold can not be usedfor your suggested method in any environment since it will fuse with the gold/silver.
When the metal is poured into a relatively (to the melt) cold mold it will not fuse as it start freezing upon contact, also, the mold is sooted or oiled before hand to help prevent fusion of the metals.

Graphite molds can't be used in open air as they degrade (C --> CO2).
They could however be used that way under inert gas or vacume in a sealed chamber, where the heat is radiated (heating coils) or inspired from within (Induction). it had been discussed here before.

ps - there's no steam explosion while pouring metals to cold mold, it's actually a very violant thermal shock... I can't say that i fully understand the why and how, but is is very similar to molen slag/glass being poured in to water = explosion, or Thermite burns above ice = big explosion.

 

[Harold_V]

ps - there's no steam explosion while pouring metals to cold mold, it's actually a very violant thermal shock...

I'm not sure I agree, Sam. Indications are there is steam generated, especially if the mold is preheated with a torch, and not heated hot enough. In that case, it can be quite obvious that moisture is the problem, resulting from combustion of the torch gasses.

The one thing I know for sure is that pouring molten metals to a cold mold isn't the smartest thing a guy can do, what ever the reason. Same for inserting cold metal in a crucible with molten metal. In that case, the cool metal condenses moisture from the exhaust stream of the furnace. It almost assures an explosion.

Harold

 

[samuel-a]

I stand corrected... it think...

I wrote that sentence under assumption that the mold is dry of moisture and maybe the OP meant metals steam.

Oh well... guess it's time to get some rest.. :shock:

 

[bswartzwelder]

Thanks, Sam and everyone else who posted. From Dr. A. K. Williams book, he stated that in a kiln, because of the heat, there is not enough oxygen for flour in a flux to burn. If I take a kiln, put in my graphite mold with gold powder in it, and then slowly add a heavier than air gas (Argon from my welding setup), then it would be ok. There wouldn't be anything for the graphite to react with. The kiln heats up relatively slowly as compared to the thermal shock of adding molten metal to mold and any moisture in the graphite gets boiled off. The Argon prevents any nasty reaction from damaging the mold.

 

[samuel-a]

Thanks, Sam and everyone else who posted. From Dr. A. K. Williams book, he stated that in a kiln, because of the heat, there is not enough oxygen for flour in a flux to burn. If I take a kiln, put in my graphite mold with gold powder in it, and then slowly add a heavier than air gas (Argon from my welding setup), then it would be ok. There wouldn't be anything for the graphite to react with. The kiln heats up relatively slowly as compared to the thermal shock of adding molten metal to mold and any moisture in the graphite gets boiled off. The Argon prevents any nasty reaction from damaging the mold.

Sounds doable.

 

[qst42know]

Unless that kiln seals exceptionally well it will cost quite a bit in argon to skip the cost of a dish and heating a mold. Thermal currents alone will dilute your argon if the kiln isn't sealed.

What's a fill up cost you?

 

[bswartzwelder]

I've only ever had one small bottle filled and although the price didn't seem that outrageous even then. Having said that, I don't think it would be too cost prohibitive. Once you put a blanket of gas in the kiln, you turn on the power and the gas that's in there heats up, expands, and becomes less dense. I see your point. Especially if there are any leaks in the bottom. I have heard to heat the mold to 600 degrees F., but was wondering how do others heat their molds and what do they use to ensure the temperature is hot enough? Or is it just heat the darn thing, pretty much any temperature over the boiling point of water will siffice.

I live in Maryland and was outside panning some concentrates today. The temp was in the low 50's, but seemed a lot colder than that. Guess I'll just set up a workbench area in the basement where I can use the fine gold recovery sluice, the blue bowl concentrator, a kiln, and have a 6 inch pipe going through the wall with an inline fan to keep out the nasty gasses which I will be producing.

 

[Harold_V]

Unless that kiln seals exceptionally well it will cost quite a bit in argon to skip the cost of a dish and heating a mold. Thermal currents alone will dilute your argon if the kiln isn't sealed.

I agree. Unless a furnace is constructed such that it is intended to have an inert atmosphere, convection will swap atmosphere quickly. They simply aren't sealed well. You'd have to introduce gas at a regular and steady rate, and even then you may be troubled by some oxygen. The only way I can see you wouldn't would be if you maintained a positive pressure in the furnace during melting.

Harold

 

[eeTHr]

...a kiln, and have a 6 inch pipe going through the wall with an inline fan to keep out the nasty gasses which I will be producing.

Basements, or any room in a residence, is generally not a good place to work at refining. I'm not familiar with running a kiln, but it doesn't sound like a good place for that, either.

The six inch inline fan could easily fall short of clearing out the air down there. You should ask about it in a separate thread, to get better information from some of our experts in that sort of stuff. Both you and your family could suffer serious injury or death, from inadequately exhausting fumes, either from a kiln or from refining.

A fume hood for the refining, and I think an overhead hood for the kiln is considered minimum for safety, and even then, not in a residence.

Please check it all out on the forum here, before risking it.