# Melting PtIr and PtRh alloys in graphite



## orvi (Dec 4, 2022)

Hi
I recently acquired some PtIr10 and PtRh10 contact points relays. I have no intention in refining the PtIr alloy from relays, as I cannot sell this quantity of Ir anyway. But I have a question.
I know that platinum can be melted in graphite, I have done it before, carburization isn´t that bad. On the other hand, I have no clue how would PtIr10 alloy behave during melting in graphite - as I have practically zero experience with chemistry and pyrometallurgy of iridium alloys. 

Does anybody know, if it is possible to melt this in ordinary graphite and not ending up making complex PGM carbide sticking to the crucible in a way it would need to be sawed out ?  
Secondly, I cannot measure carbon content in the alloy after melting. XRF does not show up carbon. So if it indeed carburize quite a bit, it can be pain to sell without costly ICP analysis.

Thank you for anything you could be willing to say 
orvi


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## Yggdrasil (Dec 4, 2022)

orvi said:


> Hi
> I recently acquired some PtIr10 and PtRh10 contact points relays. I have no intention in refining the PtIr alloy from relays, as I cannot sell this quantity of Ir anyway. But I have a question.
> I know that platinum can be melted in graphite, I have done it before, carburization isn´t that bad. On the other hand, I have no clue how would PtIr10 alloy behave during melting in graphite - as I have practically zero experience with chemistry and pyrometallurgy of iridium alloys.
> 
> ...


Do you need to use graphite at all?
Is the size and amount of the points too small to get a proper melt in the induction furnace?
If so, how about heating and fusing them under pressure to make a heel to start the melting?


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## orvi (Dec 4, 2022)

Yggdrasil said:


> Do you need to use graphite at all?
> Is the size and amount of the points too small to get a proper melt in the induction furnace?
> If so, how about heating and fusing them under pressure to make a heel to start the melting?


I cannot reliably heat up small quantities of materials which poorly catch the induction. So I need to use graphite crucible and stick in something like magnesia or quartz to prevent PGMs from creating carbides. But to heat up the magnesia inside to like 1900°C, outside need to be insanely hot, and graphite crucibles are burning pretty damn quickly - and not very much insulation materials withstand temperatures up to 2000°C  very uneffective way of melting it. 

Forge-welding the material is a very good idea. I think you maybe solved this issue - but I just need to find a way how to do it  For Pt alloys, melting it with oxy/propane maybe an option in magnesia, but unfortunately, I do not have enough oxygen from oxygen concentrator to get enough power to melt alloys like PtIr. I can make platinum alone with it, but this is barely working on few g batches. 5L O2/min is not enough. I think I would need to pair another concentrator to the thing to supply O2 properly.

Typically, palladium powder I melt in similar fashion - I transfer it to the quartz dish, "cake" the top with oxy/propane torch to make conductive crust, and then apply induction simultaneously with torch for a while, to the point metal start actually melting. Then, oxy/propane is detrimental to the job and cause too much spitting. So in the point, metal being self-sufficient on heating by induction, I turn the torch off and finish the melting with just induction. Nice thing is that copper isn´t catching the induction that much, so I do not unwantedly heat up the tip of the torch


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## Tjcary (Dec 4, 2022)

Certainly no expert in pyrometallurgy but im pretty sure they make high density ceramics that can handle the heat you need


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## Yggdrasil (Dec 4, 2022)

Tjcary said:


> Certainly no expert in pyrometallurgy but im pretty sure they make high density ceramics that can handle the heat you need


That is not his challenge, his challenge is to get a big enough conductive mass so the eddy currents from the induction furnace can start melting his metal. One trick to overcome this, is to use graphite to indirectly heat the crucible that heats the metal.


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## snoman701 (Dec 4, 2022)

Find someone with a tig welder and use a chunk of copper as a hearth to make a big enough heel for the induction melter to catch. Likely have to have an actively cooled piece of copper, but even with hand tools one could fashion a water cooled hearth that would melt some buttons.


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## orvi (Dec 5, 2022)

TIG has coame to my mind as I know it can be melted this way and few folks already using it to make heels. But finding somebody with TIG would be difficult. I need to somehow manage to solve this  

Altough, information about behavior during melting in straight graphite would be very nice to have, as directly melting in graphite would be the easiest thing to do.


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## Tjcary (Dec 5, 2022)

Are you against or have you considered using a collector metal? Longer processing time but with the right flux can melt at a lower temp


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## Yggdrasil (Dec 5, 2022)

Tjcary said:


> Are you against or have you considered using a collector metal? Longer processing time but with the right flux can melt at a lower temp


He is going to melt pure PtIr or PtRh
You don’t want to ruin that by mixing it with something less noble.


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## Lou (Dec 5, 2022)

Iridium doesn't form a carbide and the chief issue is the platinum getting ruined from C. It won't look ruined, but it'll be high enough that it'll have to be lean melted to get the C out and it'll crack when rolling. On a sensitive balance, this C pickup can probably be weighed.

Personally, I don't melt Pd unless it's a refining lot and I don't give a damn about what it picks up. As for PtIr, I am always melting and sampling them in air. Some of the Ir makes IrO2 which cooks off to a certain extent but it is what it is...

There are varying degrees of rightness in how things should be melted and that all depends on the final destination of the metal. If you're just sending it to the refiner, I'd torch melt up a few small pieces to let it grab and melt it in graphite. You can always bathe the graphite in argon to protect it against burning through.


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## orvi (Dec 5, 2022)

Lou said:


> Iridium doesn't form a carbide and the chief issue is the platinum getting ruined from C. It won't look ruined, but it'll be high enough that it'll have to be lean melted to get the C out and it'll crack when rolling. On a sensitive balance, this C pickup can probably be weighed.
> 
> Personally, I don't melt Pd unless it's a refining lot and I don't give a damn about what it picks up. As for PtIr, I am always melting and sampling them in air. Some of the Ir makes IrO2 which cooks off to a certain extent but it is what it is...
> 
> There are varying degrees of rightness in how things should be melted and that all depends on the final destination of the metal. If you're just sending it to the refiner, I'd torch melt up a few small pieces to let it grab and melt it in graphite. You can always bathe the graphite in argon to protect it against burning through.


That is very useful information, as always  Thanks for your insight Lou.

I do not mind too much about 1% or less carburization of the alloy, figures like 2-5% would be more concerning. My final goal is just homogenize the lot and make it into the form it is sellable. Eg to one slag of metal which could be zapped with XRF. They will refine it anyway at some point, so carbon wouldn´t be much of an issue when selling. I was more afraid of the scenario like melting high Rh alloys in graphite - that does not go well 
I would let them melt the stuff in place, but they use arc furnance and quite a bit of material can actually be vaporized on many instances, so I do not take any chances that they will say - sorry, melting loss was 7%... Which conveniently traps on the filter of the furnance, where they can get it for free


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## zachy (Dec 6, 2022)

I have a mineral that is 70% Ir, and 20% Rh, the rest is some Hirro and palladium. How can I melt this mineral? aqua regia does nothing. not even the molten salt of sodium bisulfate. It's a tough nut to crack...


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## Yggdrasil (Dec 7, 2022)

zachy said:


> I have a mineral that is 70% Ir, and 20% Rh, the rest is some Hirro and palladium. How can I melt this mineral? aqua regia does nothing. not even the molten salt of sodium bisulfate. It's a tough nut to crack...


You call it mineral, do you mean alloy?
If this is an alloy if high Ir/Rh like it looks like. You would need at least a HF Induction furnace to melt it.
Why do you want to melt it?


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## kurtak (Dec 7, 2022)

Hirro --- What is this - I have never heard of Hirro

Kurt


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## Yggdrasil (Dec 7, 2022)

kurtak said:


> Hirro --- What is this - I have never heard of Hirro
> 
> Kurt


Iron in Spanish


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## zachy (Dec 12, 2022)

Better I think I'm going to try a fusion with sodium peroxide as the document says


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## Lou (Dec 13, 2022)

It works, but be careful on the workup!!! You've been warned


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## zachy (Dec 14, 2022)

why do you have to be careful? it is dangerous?


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## Lou (Dec 15, 2022)

For pure iridium, peroxide fusions are ok. You can even do sinters and recycle the unreacted metallic iridium back. I have done these on a very large scale, 50-100 kg for Ru and Ir. Often times though, the filtration is absolutely positively...terrible!!! :-(

If for instance there is osmium or ruthenium, quite a bit of the toxic tetroxides can be made in a very quick manner if the fusion is quenched and improperly pH adjusted (the only way to make it filter in reasonable time frame for humans). This can potentially kill people in the immediate vicinity and persistently contaminate the work space such that the facility is uninhabitable without special treatment. A lot of the material people are getting and offering, particularly from your country, that is alluvial and a byproduct of gold gravity separation has osmium at similar concentrations to the iridium. 

Sad to say that just fusion on the osmiridium grains with sodium peroxide is not enough...it has to be ground to a fine powder and the material is extremely abrasive and hard and even tungsten carbide shatterboxes do not last long. If it is not ground, you will be conducting fusion after fusion after fusion after fusion. The joke that old old timers had about it in the research papers is just when you think you are done, you are only beginning. Often times 5-6 fusions are required to get quantitative solubility and more if using NaOH/NaNO3. The other aspect is during the grinding, the impact energy is high enough that locally high temps are made and osmium tetroxide is given off from the sample during the grinding process. This can be alleviated by grinding it in liquid nitrogen or doing so inside of the glove box. The glove box is the best friend for preparing samples of this material. Other people have done other things like melt it with white phosphorus or molten sulfur but I never liked that because the fumes from that process are also terrible.

Another issue is that the osmium (and ruthenium) does not always quantitatively distill, for one reason or another and is difficult to get out of the way and difficult to verify that it is out of the way. There is a lot of knowledge that goes with the first couple steps to make it so that it is safe to continue to refine the iridium. Sometimes it is absorbed onto the other PGM hydroxides with great tenacity. So when transferring the residues from distillation, if one is not careful, it is possible to be blinded by it (best case). It is also difficult to ICP...because of the high volatility, ICP numbers are often extremely high relative to what's left, if it is soluble. The flip side is the osmiridium is difficult to analyze so that the osmium estimation is usually low relative to what is there. In short, I would say this type of material is probably the worst material I have ever had to refine in my life.


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