Oops, I got alumina stuck to and in my platinum

[aurelius]

I was playing around with my induction heater tonight and got the platinum to melt into a blob, but I ended up breaking the crucible to get the metal out. Is there any way to clean it up and get the alumina out? Also, I was under the impression that melting Pt in alumina didn't require Flux.

Where did I go wrong?

 

[Yggdrasil]

Since Pt melts at 1770 C and maximum operating temperature for Alumina crucibles is around 1750 C.
I guess it was just overheated.
Regarding clean up, maybe hot concentrated NaOH.
But that is a flesh eater so be careful.
I hope someone else has something
less dangerous to suggest.
Remelt in Zirconia crucible maybe?

 

[aurelius]

Since Pt melts at 1770 C and maximum operating temperature for Alumina crucibles is around 1750 C.
I guess it was just overheated.
Regarding clean up, maybe hot concentrated NaOH.
But that is a flesh eater so be careful.
I hope someone else has something
less dangerous to suggest.
Remelt in Zirconia crucible maybe?

Ah, yeah, that could be it. I'd read from multiple posts here that small amounts of Pt could be melted in alumina. Maybe should I try it in my MgO crucibles? Those are what I have on hand right now.

If I could avoid having to deal with NaOH, that'd be great

 

[Lou]

MgO or CaO is better.

You can simply take an oxyfuel torch and "flame polish" the button surface with an oxidizing flame. The alumina will melt into hard transparent globules (sapphire, right?). Then it will be very shiny and cleaned up and the surface rid of any PtAl compounds.

Melting small quantities of platinum like that is always a pain as it is much more easily contaminated by the melting crucible.

 

[aurelius]

MgO or CaO is better.

You can simply take an oxyfuel torch and "flame polish" the button surface with an oxidizing flame. The alumina will melt into hard transparent globules (sapphire, right?). Then it will be very shiny and cleaned up and the surface rid of any PtAl compounds.

Melting small quantities of platinum like that is always a pain as it is much more easily contaminated by the melting crucible.

Ah, thanks for the tips. So, umm.. not having an oxyfuel torch, would I be able to re-heat this piece in MgO and have something similar happen? I'd imagine, if I can get it up to temp and hold it for a while, the alumina can maybe melt via conductive heat?

I like your idea from my other post about just making my own MgO crucibles. I'll try and look more into that. In the meantime, I had some custom made that are this size so they fit 1:1 into the same coil. If I end up burning through them faster than I'd hope, then I'll almost certainly make my own.

 

[Lou]

It’s better to do it with a flame. It “pushes” the impurities off.

Many times if I have an occlusion or something stuck that I know will damage a rolling mill, I will heat the block up in the furnace and then torch a selected area until the crap is consolidated into one globule. Sometimes you can “stick” the melted ceramic impurity to a quartz rod.

 

[Yggdrasil]

Interesting Lou.

Sadly I have not found much regarding pure CaO crucibles.
I guess it is not suited for slip casting.
At least not with water

I found something with MgO and slip casting.
But they had to use pure alcohol in stead of water.

Do anyone here have some documents regarding CaO crucibles?

 

[aurelius]

It’s better to do it with a flame. It “pushes” the impurities off.

Many times if I have an occlusion or something stuck that I know will damage a rolling mill, I will heat the block up in the furnace and then torch a selected area until the crap is consolidated into one globule. Sometimes you can “stick” the melted ceramic impurity to a quartz rod.

Ah. That makes so much sense. Time to start digging a new rabbit hole

 

[aurelius]

It’s better to do it with a flame. It “pushes” the impurities off.

Many times if I have an occlusion or something stuck that I know will damage a rolling mill, I will heat the block up in the furnace and then torch a selected area until the crap is consolidated into one globule. Sometimes you can “stick” the melted ceramic impurity to a quartz rod.

Ah. That makes so much sense. Time to start digging a new rabbit hole

Hmm, would it be possible to use MAPP to do this? I don't have any torches currently, and hadn't really planned on getting into that. That'd be a bit cheaper entry point for me

 

[etack]

most car shops will have an oxy torch. you might find you have a friend with one post to your FB friends.

some welding shops will have rentals too.

Eric

 

[Lou]

They're only a few hundred dollars new. I suggest you purchase one and a good set of shade 7 glasses!

 

[Geo]

Wouldn't boiling sulfuric acid dissolve the alumina without effecting the metal?

 

[aurelius]

They're only a few hundred dollars new. I suggest you purchase one and a good set of shade 7 glasses!

Hey Lou, I've got some feelers locally to get stuff like that. I tried to re-melt it in an MgO, and it seems to have removed most of the impurities, but I also seem to still have the issue of the platinum sticking to the crucible as it cools.

Is that just a "didn't turn the crucible over and knock the piece out quick enough" issue?

Or is that an issue where there's still some alumina and that stuck? I noticed that near the top of the blob where it touches the sidewall, is one such place where it stuck.

I got some fresh 9995 on the way to play with from scratch, so I'll try and update soon!

 

[Lou]

Wouldn't boiling sulfuric acid dissolve the alumina without effecting the metal?

Not if it’s been heated substantially. Alpha modification is insoluble as hell.


Boil the MgO in HCl.

 

[aurelius]

Wouldn't boiling sulfuric acid dissolve the alumina without effecting the metal?

Not if it’s been heated substantially. Alpha modification is insoluble as hell.


Boil the MgO in HCl.

Assuming the boil MgO in HCl was for me - I meant that the button is stuck in the crucible. I was under the impression it wouldn't stick to MgO when it cooled. I'm pretty much a noob, so I may have missed some context in that detail. I just want to be able to pop the button/ingot out of the crucible when it is cool enough