# Platinum furnace



## skippy (Mar 20, 2013)

I'm wondering if it is possible to make a furnace capable of melting platinum? I melted a tiny bit of mixed pgm by taking the "nose" from an oxygen sensor (edt: and I filled it with mixed pgms) and heating it indirectly with the flame of my small oxygen/propane torch. After that, I started thinking that with the appropriate choice of refractory and burner tube if it wouldn't be possible to a make a tiny furnace capable of melting a few ounces of platinum or palladium at at time, the idea being that it would be better to have the metal, especially metal powders, indirectly heated to melting temperature rather than using the flame to transfer the heat, as some powder inevitably is being lost from being blown away. The temperatures needed are rather extreme, and the cycling of temperatures would be hard on the refractory, and the burner flame holder/tip would need to be alumina or zirconia likely but besides that is/has this ever done? I think it would be a cool thing to have, if it could be built for not too many dollars, and if it would have a practical life span. Other concerns might be whether the direct action of the flame would be too extreme on the crucible, it might be necessary to have an initial air/propane or air/hydrogen burner to give a more gentle heating. I wonder about this because I melted all the rest my PGMs in alumina crucbles with an oxy/acetlyene torch and sold them based on xrf, but I managed to crack every crucible I bought by the time I made all my buttons. I must have been doing something terribly wrong, besides the likely inadvisability if melting impure pgms Still it was quite an experience! Anyways, it's not something I can justify building for any practical reason right now, but if anyone has any thoughts I thought it might make a good discussion.

Also, if Lou is reading this, my thanks for talking with me on the phone about the PGMs a while back, I was itching to sell them and get some money for them, so I sold them melted on XRF analysis. It likely would have worked out better in most all respects to have gone the extra step to separate and refine them, but that's done with. Anyways, I've got a bunch of oxygen sensors to do, and I certainly intend to go the extra little step and get the Pt to a high purity with them, so I hope to be able to utilize your services in the future.

edit for clarification - I used the sensor nose as a crucible for pgms that I packed into it, it wasn't an attempt to recover the metals from the sensor itself.


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## jimdoc (Mar 20, 2013)

skippy said:


> I'm wondering if it is possible to make a furnace capable of melting platinum? I melted a tiny bit of mixed pgm by taking the "nose" from an oxygen sensor and heating it indirectly with the flame of my small oxygen/propane torch. After that, I started thinking that with the appropriate choice of refractory and burner tube if it wouldn't be possible to a make a tiny furnace capable of melting a few ounces of platinum or palladium at at time, the idea being that it would be better to have the metal, especially metal powders, indirectly heated to melting temperature rather than using the flame to transfer the heat, as some powder inevitably is being lost from being blown away. The temperatures needed are rather extreme, and the cycling of temperatures would be hard on the refractory, and the burner flame holder/tip would need to be alumina or zirconia likely but besides that is/has this ever done? I think it would be a cool thing to have, if it could be built for not too many dollars, and if it would have a practical life span. Other concerns might be whether the direct action of the flame would be too extreme on the crucible, it might be necessary to have an initial air/propane or air/hydrogen burner to give a more gentle heating. I wonder about this because I melted all the rest my PGMs in alumina crucbles with an oxy/acetlyene torch and sold them based on xrf, but I managed to crack every crucible I bought by the time I made all my buttons. I must have been doing something terribly wrong, besides the likely inadvisability if melting impure pgms Still it was quite an experience! Anyways, it's not something I can justify building for any practical reason right now, but if anyone has any thoughts I thought it might make a good discussion.
> 
> Also, if Lou is reading this, my thanks for talking with me on the phone about the PGMs a while back, I was itching to sell them and get some money for them, so I sold them melted on XRF analysis. It likely would have worked out better in most all respects to have gone the extra step to separate and refine them, but that's done with. Anyways, I've got a bunch of oxygen sensors to do, and I certainly intend to go the extra little step and get the Pt to a high purity with them, so I hope to be able to utilize your services in the future.



I think oxygen sensors only have platinum in them, no palladium.

Jim


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## skippy (Mar 20, 2013)

Yup - the metal I sold was mixed from cats. I won't be touching any cats for the foreseeable future, but I will be doing some sensors. 
If I were to have such a furnace and it worked for platinum, it would work for palladium, with the right fuel and such. Now that I think about it you would likely want one such furnace for pure platinum, one for platinum alloy, one for pure palladium... any way this is all just hypothetical right now, I'm just interested if it's possible, if it's a bad idea and why etc.


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## Lou (Mar 20, 2013)

The best crucible to melt platinum in is magnesia.

You'd be better off building a small arc furnace than trying to heat with oxy fuel...at least then it is blanketed with argon.
Pt forms alumnides, silicides, and others beside. Morgan Technical Ceramics makes superior dishes for melting it.

Nevertheless, a refractory that works well for lining and is insulating is bubble alumina.
Put an ITC-100 wash coat, as much of the heat will be radiative. It is possible to use it to 1900 C.

http://www.graystarllc.com/products/bubble-alumina


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## skippy (Mar 20, 2013)

Ok, thanks Lou, that's some good info. Another nice thing about an arc furnace would be that you wouldn't be losing exhaust heat. 
With a medium to heavy duty tig welder you could drive a a couple of tungsten electrodes, or better yet, maybe an array of electrodes that would ring around the crucible. A high frequency arc starter would be nice to avoid having to strike the arcs. I can see it now. Actually, dare I say it, it sounds almost simple!


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## Lou (Mar 20, 2013)

It is simple, in theory 

People make mini arc furnaces on sciencemadness and elsewhere quite frequently...


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## rusty (Mar 20, 2013)

Lou said:


> It is simple, in theory
> 
> People make mini arc furnaces on sciencemadness and elsewhere quite frequently...



Are they using AC or DC electrodes Lou.


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## skippy (Mar 21, 2013)

Heck yes Lou, and it just gets simpler the more I read about it too :shock: ! 
I searched and saw some carbon arc furnaces on the web and on sciencemadness on your suggestion. I would think tungsten electrodes would be better, because of the carbide formation issues, however I suppose tungsten vapour might get in the melt too... maybe it's not a problem with a lid on the crucible and a bit of argon flow to keep the gas changing? I dunno. 

I saw a lot of documents and articles talking about melting where one of the electrodes being a water cooled copper crucible :shock: It gives very high purity apparently. Of course even something like that is not impossible to build... 

I also saw a photo of some water cooled tungsten electrodes that an amateur was using in a arc furnace, but there were no details or pics on the furnace. I read many mentions of one Max Whitby's reduced pressure argon furnace, but no details or pics either.

I don't know if these water cooling measures are overkill, that's a lot more complicated than I would really consider. If a fairly simple arc furnace with tungsten or carbon electrodes and with no water cooled fancy electrodes and no vacuum tight casing could melt platinum and maintain commercial purity that would be sufficient for my potential needs. I don't know enough to say whether it's feasible or not, but I wasn't able to find any commercial or experimental precedent. It seems historically they jumped from flame melting to induction melting, and except for the fancy copper water cooled crucible type, arc melting was never used for platinum, which makes me wonder why. Hmmm. Lou, any thoughts on any of this?


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## skippy (Mar 21, 2013)

I also had another musing on this. Put the platinum in an appropriate crucible that is either a microwave susceptor or has a high temperature sceptor inside, cover and surround the crucible with the bubble alumina and apply microwave radiation. :idea: Platinum melting in your kitchen!


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## skippy (Mar 25, 2013)

I read an interesting article on the history of platinum melting published by the platinum metals review. hhttp://www.platinummetalsreview.com/article/53/4/209-215/ Lots of interesting history, and it's informative too. Apparently heating in a reducing flame is bad because it can reduce refractory metals in your crucible contaminating your platinum with calcium,magnesium, aluminum etc. I did not know that.


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## allenp (Mar 27, 2013)

We routinely melt 3 ounces lots of platinum in large magnesia cupels using an Oxy/Propane torch


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## skippy (Mar 27, 2013)

I believe there is some losses to torch melting, especially going from powder


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