What is the best crucible for induction melting PGM's?

[Risen]

Hello,

I'm building my own induction heater, and I need to know what type of crucible can be used to melt the PGM's powders.

I already melt silver powder using a graphite crucible.
Here is a 160g button that I melted and let it cool down in the crucible.



I'm asking this because the building of the induction heater is much simplier when you use a electricaly conductive crucible.

Types of crucible that I have heard of:
Graphite crucible (have the reduction atmosphere, the carbon from the crucible can contaminate the palladium, or other PGM's??)
Tungsten crucible
Iridium crucible

The other option is the use of a non-conductive crucible with a metal sheet of the metal powder to be melted, what type of non-conductive crucible can be used?
Alumina?? The high oxygen content is not a issue at 1700~2000°C?
silica melts at this temperatures...


Thanks!!

 

[Lou]

Don't use metal or graphite for PGMs.

Typically platinum is melted in air in a high power density induction furnace. Properly calcined "clinker" sponge will melt as is. If you're melting PGM blacks, you'll probably want to have a starter heel to couple with the field and slowly add the powder and ramp up the power. In practice, easier to use a briquetter. Too much power too fast and it'll blow it right out of the crucible! As you're probably doing small batches, you might want to press it into a pellet.

A zirconia crucible loaded with Pt or Rh sponge is placed set into a alumina crucible and loosely filled with zircon sand. You can probably use this product http://www.zircarceramics.com/pages/particulates/ib100.htm

Zirconia crucibles are pretty fragile and have a higher temperature rating but alumina has better thermal shock resistance.

If you're casting less than a few kg of Pt, you'll need to keep it in the furnace under heat while you pour. If one is making billet, high intensity spot light, water-cooled copper mold, and be sure to be wearing aluminized protective gear or you're in for radiative burns!

 

[Risen]

Thanks Lou!

That was very helpfull!

Do you have a zirconia crucible/alumina crucible supplier to indicate?

The two main PGMs to be melted is platinum and palladium, alumina can be used instead of zirconia? (I think alumina is cheaper and easier to find..)

Let me see if I understand completely, the PGMs sponge is placed in a zirconia crucible, and on top of the PGM, the crucible is filled with zircon sand, then that crucible is "inserted" (what "bagged" means?) in a alumina crucible?

Following your indications, the crucible lasts how many melting cycles?

The function of the zircon sand is to prevent reaction of the metals with atmospheric gases? Or have some other function, like borax?
If the metal is melted in vaccum, the zircon sand is needed?

I searched in the forum but didn't find a complete answer, where I can find a list of the metals with it's melting incompatibilities?

Lou, for another application I'm planning (make sapphire windows from alumina), do you sell iridium sheet /iridium crucibles?

Thank you very much!

 

[Lou]

Morgan Technical Ceramics


If the quantity is small, you can get away with alumina. Pd must of course be melted under argon, CO2, or vacuum.
How long the crucible lasts is contingent on many things, notably the presence (or lack) of fluxing agents.

No, the yttria-stabilized zirconia crucible is loaded with sponge, covered temporarily and put inside of or nested in the alumina crucible and that is loosely filled with zircon sand around the zirconia crucible. I was not clear about what I said and will edit it accordingly, my apologies. The sand is just used to insulate the alumina from the intense heat and act as a cushion for expansion and contraction. You need not do any of that.

Don't worry about metal compatibilities because you were already advised not to melt PGMs in metal (excluding a water-cooled copper hearth).

I do not roll Ir (not exactly easy for anyone, look at its bulk modulus). Most Ir crucibles are electroformed from molten cyanide baths via a proprietary, nasty technology by JM. If not done that way, they are electron beam welded together. I don't do any of that, only very occasionally melt the pure metal and what little experience working it I have makes me shudder.
I do see used crucibles from time to time, how big do you need (liter, 10 liter, bigger?).

I would like some sapphire windows preferably in a specific arrangement for a project I am working on where I need to continuously take a reading on a high pressure abrasive slurry.

 

[Dan Dement]

Risen,

I have had a similar challenge with sponge. I have compressed Pd up to 50 tons pressure and in an smaller Induction/vacuum caster (Seit Supercast 13 TI Caster) using a Tanabe Crucibles from Romanoff. You really have to pull a good vacuum and back wash with Argon or the Palladium will come out brittle. One of the problems that I had is right before the pellets melted, the pellets explode causing a volcano effect of powder. Also, I have pushed the melting of stubborn melting powder and fried the coils in my Induction melter. Expensive mistake that you do not repeat. Quick learning curve with expenses north of $10,000.

Hopefully you will find the correct combination of power and frequency to aid in your success with this project. From what I have experienced, the equipment necessary is going to beyond my budget and limited in use. Between the sponge to metal loss and the cost of the additional cost of limited use, I found buying bullion a better use of my capital and time.

Lou is the man to best guide you. Best of Luck,

Dan

 

[Risen]

Lou,

I understood now the setting of the zirconia-alumina crucible, that is very clever!

Should borax be used as flux when melting PGM's?

The Ir crucible I'm planning the acquire is a small one, +-170 mL, similar size of those graphite crucible for electric furnaces, if it works then we can expand to something bigger! One with 5 cm diameter x 5 cm height crucible would be the best choice!

There are smaller Ir crucibles? How much it cost? Can you PMSG mw with the price?

Soon the sapphire windows are perfect, I would gladly give a couple to you, but it will take some time (probably +-3 months) as we are developing the equipment and we still need the crucible, until we have everything right the maximum size of the window will probably be +-4,5cm in diameter.

Thanks!


Dan,

Regarding the operation frequency of the induction heater, I'm running always near the resonant frequency (my "hardware" allows ~57 kHz, but it can be changed by rearranging the induction coil or the tank capacitor), the power control is achieved by DC voltage variation. Induction heaters tend to be a little expensive, but you can make one yourself, there's this site that explain everything very detailed, the development of a DIY unit! A 3 kW unit should easily melt ~2 Kg of gold or ~1 Kg of silver in a graphite crucible.

http://mindchallenger.com/inductionheater/

Thanks!

 

[Lou]

No borax! Destroy your crucibles and it will boil away at these temperatures.


Supposedly there is a company that makes flux for PGMs... Dan would remember their name. I never put much stock in it.


I don't have a price on the crucibles. If one came in that was usable and I didn't want to keep it for one reason or another, I could keep you in mind. Usually they are either very big (kgs) or very small (tens of grams). Not much middle ground. Very rare to see.

 

[joubjonn]

Can I ask what your plans for the induction furnace are? Very curious. I would also like to build my own, I did see some plans online for one but it looked very labor intensive.

 

[Risen]

I do not have any plans for my induction heater >.<, I build it myself, but never put it on paper.

But I can direct you for someone that has a top project: http://4hv.org/e107_plugins/forum/forum_viewtopic.php?140297.post and https://github.com/joshcam/ReactorForge

Building an safe very powerful Induction heater is a VERY VERY labor intensive project for someone that don't know electronics/electrics, but the theory is very simple.

As a chemist, who didn't know anything from eletronics when I started, it took me 3 years (I only worked on the project 1x weekly) to reach this point.

I posted a video making silver beads in water : https://www.youtube.com/watch?v=FnW--P1MMI8 and one with my setup https://www.youtube.com/watch?v=HNWQAEeYkAs

Lou:
I emailed JM, and they sent me a catalog, they have a 175 mL crucible that suits my needs, but I think the guy sent me a platinum and not an iridium catalog, maybe they are similar in size..
Do you know how they make the price of the crucible? Precious metal content + labor, how much for labor? 500, 1000?
Thanks

 

[Lou]

Try a heckuva lot more than that, sir.

I always thought JM fab'd products were overpriced relative to other suppliers, but their quality is very high. Usually there's an order minimum.

A 175 mL crucible will be several tens of thousands of dollars but they don't exactly go bad. If you need to clean them, HF!

 

[samuel-a]

Have you spoke with Heraeus?

 

[Lou]

You also should consider shielding that coil with some metal so you avoid any RF burns and/or disturbances.


Good work!

How many kW is the furnace?

 

[Risen]

First I want to post about the Al2O3 and ZrO2 crucibles, the prices I found on the internet:

Stanford Advanced Materials

Product: Zirconia Crucibles
Dimensions: OD 50mm × H 80mm x WT 4mm
Purity: 99%
Quantity: 20 pc
Unit Price: $190.00/pc(Total of $3,800.00)

Product: Zirconia Crucibles
Dimensions: OD OD 40mm × H 50mm x WT 2.9mm
Purity: 99%
Quantity: 20 pc
Unit Price: $115.00/pc(Total of $2,300.00)

Product: Alumina Crucible
Dimensions: OD 50mm × H 80mm x WT 4mm
Purity: 99%
Quantity: 20 pc
Unit Price: $30.00/pc(Total of $600.00)

Product: Alumina Crucible
Dimensions: OD 40mm × H 50mm x WT 2.9mm
Purity: 99%
Quantity: 20 pc
Unit Price: $30.00/pc(Total of $600.00)

I bought two alumina crucibles from JOMON Ceramics, but I did not melt anything in it yet.

Then the kind off-topic conversation about Ir Crucibles for melting alumina:

Lou:
Try a heckuva lot more than that, sir.

I always thought JM fab'd products were overpriced relative to other suppliers, but their quality is very high. Usually there's an order minimum.

A 175 mL crucible will be several tens of thousands of dollars but they don't exactly go bad. If you need to clean them, HF!

I contacted several Ir crucible suppliers and JM is the cheapest, because they produce a very thin crucible, like platinum ones. The manufacturing charge range from U$$1500(JM) to U$$3800(Furuya)

JM
Ir Crucible based on JM drawing STD/71035 – 65mm top I/D x 39mm bottom I/D x 71mm high x 0.5mm thick
Quantity 2 off
Estimated weight 147.2 gms/each
Manufacturing Charge £900.00/each
Metal Charge To come from exchange account
at time of quotation = U$$3070 for Ir + £900.00 labor / per unit


Stanford Advanced Materials
Product1: Iridium Crucible
Diameter = 50 mm
Height = 50 mm
Wall Thickness = 2.0 mm
Bottom Thickness = 2.0 mm
Purity: 99.99%
Quantity: 1 pc
Unit Price: $16,184.00/pc

Furuya Metal Co.
ID:50 * IH:100 * Wall: 1.5 * Bottom: 1.5 mm
Fabrication Fee U$$3800/pc
Iridium metal 22,7 toz (at U$$649.47) = U$$ 14750
Ir metal loss 0,681 toz = U$$442
Total for 1 pc = U$$ 18991

Then I quoted Tungsten crucibles:

Plansee Tungsten Crucible:
Material W Crucible Dia 50/1,5/100 mm
Minimun Quantity: 2 PCE

Ø 50 +/- 8 mm x 100 +/- 0,8 mm
wallthickness 1,5 +/-0,4 mm
bottomthickness 2 +/-0,3 mm
surface: Ra <5

EUR 2425.21 for 2 pc = 1212.60 per unit



Lou:
I think JM crucible will last much shorter then Furuya or Stanford because of it's thickness, do happen to know what's the life span of this type of crucible?

With my induction heater I reached 2,9 kW. The next step on the IH building is to automatize everything!

I made some tests and the magnetic field is very tightly closed in the copper coil, so even keeping metalic objects close to the coil doesn't seem to interact with the magnetic field.

But since I'm going to build a vaccum chamber, I'm planning on doing a stainless steel box, that will serve as the vaccum chamber and a Faraday's cage!


Samuel-a:
I did not spoke with Heraeus, since I do not plan in buying the crucible yet, and perhaps Lou can find a used one =)

Thanks!

 

[Lou]

I think the JM crucible is grown electrochemically through some dark art of molten cyanide electroforming.

The others are probably rolled and then electron beam welded to a EDM cut plate on the bottom hence the range in price--one is much easier to fabricate.


You should probably just get the JM crucible and use it as a liner for W (or else graphite w/MgO in between) as it's all going to be under vac or argon anyway. At that temperature, some of the Ir will migrate into the W and make a WIr diffusion layer. I've seen similar things happen with Re-lined W crucibles (which were several feet across).

Besides, this is only for crystal pulling of Al2O3 and the like.


If you plan on melting Pt/Pd/Rh or their alloys, obviously get the YSZ (yttria-stabilized zirconia) crucible to melt in and you want to either have the right frequency for melting powder, or else make a small starter button in air (you can melt Pd in air with H2/O2, just degas it thoroughly under hi-vac as you melt it). Keep your melt times short.

Lou

 

[DinarAndDirham]

...Typically platinum is melted in air in a high power density induction furnace. Properly calcined "clinker" sponge will melt as is. If you're melting PGM blacks, you'll probably want to have a starter heel to couple with the field and slowly add the powder and ramp up the power. In practice, easier to use a briquetter. Too much power too fast and it'll blow it right out of the crucible! As you're probably doing small batches, you might want to press it into a pellet...

Lou, what force would we need to press Pd sponge into pellets? would 10 ton/inch² suffice?

I've tried searching for some lab to medium scale metal powder/sponge briquetter's but to no avail.

As you stated, it won't be efficient for large quantities. To which extend will it be still efficient?

If I understood correctly, using Pd pellets we can melt it as is, without any worries of too much power too fast. If we try to directly melt Pd sponge without a high frequency induction furnace, we use a starter heel, slowly add Pd sponge and increase power slowly over time as we are adding powder?

Thanks!

Kind regards,

Ben

 

[Lou]

You can only do that if your Pd is to be re-refined.

If you want monolithic Pd ingot, send me a private message. I can supply you 50 or 100 oz vac induction cast 99,95+ Pd.

If you want pellets, I can make your sponge into pellets

 

[zachy]

What is the best frequency to melt platinum?

 

[g_axelsson]

What is the best frequency to melt platinum?

That depends on charge size and if it is powder or solid chunks.

For powders the frequency in an induction melter needs to be very high until it starts to melt. To get around that problem it is common to include a solid piece of metal (if my memory serves me it's called a heal) that would melt at lower frequency.

Göran

 

[DaniH]

I need a self ignating crucibles for induction.
Graphite is one option, silicon carbide also self ignate in induction'?

 

[Yggdrasil]

I need a self ignating crucibles for induction.
Graphite is one option, silicon carbide also self ignate in induction'?

What do you mean?
A crucible that heats in the magnetic field?
If so I think the only option is Graphite and that is not recommended with PGMs.
Depending on its intended use after that is.

So what form has the PGM?