Benjaminza
Active member
Is there anybody that can give me a good recipe for making my own furnace crucible.
Best material for crucible
- Thread starter Benjaminza
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Picking up an older thread.... I downloaded and read the section on Magnesia crucibles: Here's a link to a full text document: Crucible Handbook; Schwartz & White
It looks like making crucibles is a thing. I looked at MgO crucibles: dry pressing is complicated and requires equipment and tools I don't have -- now I need to learn a bit about slip casting, cause that's the other way. --
I also need to know if I can start with MgO powder -- I don't have a ball mill. I also expect a slip crucible to be lighter, less durable, and more porous than a pressed crucible. Time to lurk around this site, then maybe the internet.
If someone has a 500-1000ml MgO crucible for sale, I might be interested
It looks like making crucibles is a thing. I looked at MgO crucibles: dry pressing is complicated and requires equipment and tools I don't have -- now I need to learn a bit about slip casting, cause that's the other way. --
I also need to know if I can start with MgO powder -- I don't have a ball mill. I also expect a slip crucible to be lighter, less durable, and more porous than a pressed crucible. Time to lurk around this site, then maybe the internet.
If someone has a 500-1000ml MgO crucible for sale, I might be interested
I have lurked this site and the interned, I came up empty. Legend has a lot of pressed MgO cupels; they won't work as the cup is small and the walls are thick. I need something with a deep cup, straight walls and preferably a lip for crucible tongs. I'm starting with powder, so I need something one the order of a 1kg crucible. I'd be happy to find any crucible that I can use with induction that will survive 2200C and an oxidizing environment.
I looked up molds that might be suitable for making my own pressed crucibles. I considered modifying a 50mm pellet press that's available on Amazon, but I don't think it would survive very long -- the mold is (probably heat treated) steel, there's a small amount of HCl in the mix and it's an abrasive powder. (I would make a new base with a counter-bore to hold a 30mm rod for the cup -- but it's $800 for the mold, new base, and 10kg of 99.95 MgO powder, and I only need 1-3 crucibles)
If anyone has a line on a stainless steel mold for pressing crucibles, that would help. Making just one is not really an option: the walls have to be smooth enough to allow the crucible to be ejected without damaging it. I'd have to have it made. It might be cost effective to make 10, but definitely not 1.
I looked up molds that might be suitable for making my own pressed crucibles. I considered modifying a 50mm pellet press that's available on Amazon, but I don't think it would survive very long -- the mold is (probably heat treated) steel, there's a small amount of HCl in the mix and it's an abrasive powder. (I would make a new base with a counter-bore to hold a 30mm rod for the cup -- but it's $800 for the mold, new base, and 10kg of 99.95 MgO powder, and I only need 1-3 crucibles)
If anyone has a line on a stainless steel mold for pressing crucibles, that would help. Making just one is not really an option: the walls have to be smooth enough to allow the crucible to be ejected without damaging it. I'd have to have it made. It might be cost effective to make 10, but definitely not 1.
Cupels do not go into Induction furnaces.
They are used in normal electric furnaces at around 800-1100 centigrade, and fired with the door open.
Many use plain Portland cement with success.
And they are one time use only
kaisernine
Active member
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- Nov 26, 2017
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what are you trying to melt / smelt? it's important. - also probably no material at 2200c that isn't a one time use in a oxidizing atmosphere unless you got some serious cash and even then they usually use that stuff under vacuum or inert gas.
I’m sold.
If you could point me to where I can order 2 x 1kg, MgO crucibles suitable for use in an induction furnace, I’d be ever so grateful.
I don’t want to make my own, I have enough to learn already.
Fudge. I was not intending a hijack…
I looked at making crucibles. I saw “slip casting” which requires a mold and is low density. I expect strength to be an issue and I don’t have a mold, so I’m not doing that.
The second method mentioned was compression. Compression requires a different mold, one that can withstand the pressure required to compact MgO with a H-press — I think I was going to need to step up to a 50 ton press to make a 50mm crucible.
In looking for MgO powder, I ran across the cupels. I don’t see any chemical or metallurgical reason a cupel couldn’t be used, although the cup shape will make
EM coupling harder.
I’m wanting to melt platinum and platinum-rhodium. I melted part of a wesgo crucible into platinum with a torch a few years ago. I’ve also blown powder out of a crucible with a torch.
I’d prefer to use an induction furnace & crucible. If I can’t find a crucible and a cupel won’t work, that’s going to suck.
I looked at making crucibles. I saw “slip casting” which requires a mold and is low density. I expect strength to be an issue and I don’t have a mold, so I’m not doing that.
The second method mentioned was compression. Compression requires a different mold, one that can withstand the pressure required to compact MgO with a H-press — I think I was going to need to step up to a 50 ton press to make a 50mm crucible.
In looking for MgO powder, I ran across the cupels. I don’t see any chemical or metallurgical reason a cupel couldn’t be used, although the cup shape will make
EM coupling harder.
I’m wanting to melt platinum and platinum-rhodium. I melted part of a wesgo crucible into platinum with a torch a few years ago. I’ve also blown powder out of a crucible with a torch.
I’d prefer to use an induction furnace & crucible. If I can’t find a crucible and a cupel won’t work, that’s going to suck.
For melting there are crucibles by the dosen out there.
I found hundreds of graphite, clay, silica, and alumina crucibles, many in 1-2kg sizes. But only 2-3 that were MgO — and available to me, and they seemed quite expensive for the sizes offered. I’m on the outside of both industries, I don’t use or make crucibles — I’m learning as I go.
I suspect that you know there are lots of suppliers out there , but I have Google, and this forum. I promise you, I searched for “MgO crucible for Induction furnace” “manganese oxide crucible induction” and a dozen other search variants on the forum first. Then I searched goigle, then I searched this forum for a few more days. There are several threads on crucible, most on where to buy & how to make your own — almost all of those relate to sub-1600c materials.
Is $160 for a 100ml crucible reasonable? Can I get an MgO crucible configured to be used in a small induction furnace? Can you provide a link to a supplier?
thanks
I suspect that you know there are lots of suppliers out there , but I have Google, and this forum. I promise you, I searched for “MgO crucible for Induction furnace” “manganese oxide crucible induction” and a dozen other search variants on the forum first. Then I searched goigle, then I searched this forum for a few more days. There are several threads on crucible, most on where to buy & how to make your own — almost all of those relate to sub-1600c materials.
Is $160 for a 100ml crucible reasonable? Can I get an MgO crucible configured to be used in a small induction furnace? Can you provide a link to a supplier?
thanks
So why do you specifically need MgO Crucibles?
For induction I'd think Graphite would be better, since the crucible itself would heat up and you will not be dependent of a "heel" to start the melting.
That's a big photo. Sorry about that.
I did not start out looking specifically for MgO, I looked for anything that could withstand 2200c for melting Rhodium/Platinum. Reading articles lead me to think that graphite carries a risk of carbide formation without oxygen and an oxidizing environment is corrosive to graphite. Maybe someone with experience could figure out how to use a graphite crucible without issue, but I don't think I can without a failed experiment or two. I'd like to avoid ruining a crucible and having a mess to boot.
MgO was the only material I could find that could be heated above 2100c in an oxidizing atmosphere -- which has worked so far with both Platinum and Rhodium. Most of the Rhodium is too finely divided (<50microns) to use a torch without wrapping in foil and sintering it first. Graphite would be great If I could find a crucible with an MgO liner -- I don't have a rhodium heel.
Yitria and Thoria may require vacuum for melting. -- I stopped reading about the chemistry, etc. when I couldn't find any except small laboratory crucibles.
I did not start out looking specifically for MgO, I looked for anything that could withstand 2200c for melting Rhodium/Platinum. Reading articles lead me to think that graphite carries a risk of carbide formation without oxygen and an oxidizing environment is corrosive to graphite. Maybe someone with experience could figure out how to use a graphite crucible without issue, but I don't think I can without a failed experiment or two. I'd like to avoid ruining a crucible and having a mess to boot.
MgO was the only material I could find that could be heated above 2100c in an oxidizing atmosphere -- which has worked so far with both Platinum and Rhodium. Most of the Rhodium is too finely divided (<50microns) to use a torch without wrapping in foil and sintering it first. Graphite would be great If I could find a crucible with an MgO liner -- I don't have a rhodium heel.
Yitria and Thoria may require vacuum for melting. -- I stopped reading about the chemistry, etc. when I couldn't find any except small laboratory crucibles.
What are the end use of the material?
If you are selling, I believe Graphite will do, if it is going to be kept ductile it is not.
Anyway, unless you have or can create a heel you will have to have a suceptor of kinds.
"...Graphite will do..."
I hear that's not so good at pgm melting temperature in atmosphere. I don't have access to a vacuum melter/furnace.
Will a graphite crucible survive a pgm melt at atmosphere? It doesn't have to survive more than one melt, but if it's swapping one time-consuming issue for another, I'd prefer to stick to what I have already or have someone else melt it.
I hear that's not so good at pgm melting temperature in atmosphere. I don't have access to a vacuum melter/furnace.
Will a graphite crucible survive a pgm melt at atmosphere? It doesn't have to survive more than one melt, but if it's swapping one time-consuming issue for another, I'd prefer to stick to what I have already or have someone else melt it.
You can increase the life span by covering it somewhat, there are even "paint" which can protect the inside of furnaces.
Nountaineer
Well-known member
I just had some failed smelts melted in an induction furnace containing platinum etc. He uses special graphite crucibles that are coated outside with cement for all melting including pgm.
