Sciencemadness Discussion Board - Alumina crucible

Alumina crucible

Alienwhoexploreyourplanet - 11-8-2011 at 08:24

Hi everyone , i'm new here , i have a question , if someone can help me thanks a lot , i know its very hard to melt aluminium oxide , something around 2072 °C , so i'm very curious to know how they can make an alumina crucible ( with 99 % aluminium oxide for example ) , do they use a mold or something ?

thanks

hissingnoise - 11-8-2011 at 08:45

Quote:

Hi everyone , i'm new here . . .

Hmmm, you've come all this way to put a technological question to a species which has just recently ventured out from the 'safety' of its caves?
Er, thermite . . .

Alienwhoexploreyourplanet - 11-8-2011 at 08:59

The question is about crucible hissingnoise

[Edited on 11-8-2011 by Alienwhoexploreyourplanet]

Bot0nist - 11-8-2011 at 09:29

He mentioned termite, which would burn at sufficient temps to get the job done. I doubt that's what they use to manufacture them though. I am not well versed on the subject but you may want to look into glassy carbon. A member recently did a thread on its use as an exotic anode and mentioned that there main use is in high temp crucible making.

p.s. He was just being friendly I imagine. Commenting on your moniker.
Do you come in peace...?

[Edited on 11-8-2011 by Bot0nist]

Alienwhoexploreyourplanet - 11-8-2011 at 09:50

Thanks for the answer Bot0nist , the reason i'm here is that i want to do an alkaline fusion , so i'm looking for a suitable crucible , i want to understand more about them first ( thats the reason of my topic ) , alumina is one of them and why not glassy carbon so i'll think about too ..

PS : Yes i'm peacefull , me and the other little green heads

[Edited on 11-8-2011 by Alienwhoexploreyourplanet]

Magpie - 11-8-2011 at 10:39

Quote: Originally posted by Alienwhoexploreyourplanet

i want to do an alkaline fusion , so i'm looking for a suitable crucible

I have done alkaline fusions in a nickel crucible. They can be done in steel also if you want to use a piece of capped pipe.

I'm just guessing but I think that an alumina crucible would be made by sintering alumina that has first been pressed into the desired shape.

[Edited on 11-8-2011 by Magpie]

Alienwhoexploreyourplanet - 11-8-2011 at 10:47

Thanks Magpie , this link http://encyclopedia2.thefreedictionary.com/Alkali-Resistant+... is the confirmation of what you said about nickel with other metallic materials and nonmetallic inorganic materials who are all suitable for alkaline fusion , and about alumina crucible thats an idea i'll look if there is an interressant patent about alumina crucibles around the net .

hissingnoise - 11-8-2011 at 12:25

We mean you no harm, but some(?) of us can't resist taking the piss . . .

blogfast25 - 11-8-2011 at 12:38

Alumina is attacked by alkali, inclluding molten alkali, forming aluminates. Contamination of your fusion product and damage to the crucible are likely.

Steel or nickel are a better choice. Not to mention cheaper.

Alienwhoexploreyourplanet - 11-8-2011 at 12:39

No everyone is nice here , and i prefer when they're nice and helpful in the same time ..

Alienwhoexploreyourplanet - 11-8-2011 at 12:43

Quote: Originally posted by blogfast25

Alumina is attacked by alkali, inclluding molten alkali, forming aluminates. Contamination of your fusion product and damage to the crucible are likely.

Steel or nickel are a better choice. Not to mention cheaper.

Excuse me blogfast25 but Aluminum oxide is the most stable (with zirconium oxide) to the action of molten sodium hydroxide at 540°C see my link http://encyclopedia2.thefreedictionary.com/Alkali-Resistant+...

[Edited on 11-8-2011 by Alienwhoexploreyourplanet]

Neil - 11-8-2011 at 15:19

I've made ~90% alumina crucibles via slip casting with the ~10% being silica from the high alumina low silica clay I used as a binder.

To do so you make a mould of your crucible shape, cast it into a block of plaster and then separate the two.

Once the plaster cast is dry a 'slip' can be poured in, then poured out leaving you with a crucible.

Any silica, iron, chloride, magnesium or calcium in the crucible will ruin it when you go to fire it, if you have sintering the alumina in mind.

I've also made crucibles of alumina/silica with thermite by fusing a tube of material with a thermite reaction and then coating the fused shape with slip and letting the whole thing dry before firing. Bloody useless really.

Anyway once you have the crucible cast, it needs to be fired hot enough and long enough to sinter it. Expect shrinkage and horrible horrible failure the first couple times.

I'd personally stick with metals or buy the crucibles.

pottery forums have all the relevant charts.

Alienwhoexploreyourplanet - 11-8-2011 at 16:16

Thanks Neil that's very instructive , as you know silica is not a good thing if you want to do an alkaline fusion so the best is an alumina crucible with pure alumina

Morgan - 11-8-2011 at 17:16

I bought some fused quartz crucibles from these guys but they also sell some alumina products. It might do for your needs.
http://www.advaluetech.com/alumina-crucibles.html
http://www.advaluetech.com/alumina-crucibles.html

Some tidbits.
http://www.azom.com/article.aspx?ArticleID=1389

Forgive me.
http://us.mt.com/us/en/home/products/Laboratory_Analytics_Br...

Alienwhoexploreyourplanet - 11-8-2011 at 18:48

Thanks a lot Morgan , thats exactly the kind of crucible i'm looking for , and the price is very interressant

watson.fawkes - 11-8-2011 at 19:33

I was doing some reading a couple of years ago on the production of this subject. Unfortunately, I don't believe I have copies of the papers I read any longer, but I recall the gist of them.

MgO is used as a sintering agent for alumina, but are rather low percentages, not more that 0.5% as I recall. There some might interesting work out there studying grain growth in this system. It's thought that MgO forms a low-melting eutectic with alumina and that pure alumina re-crystallizes out of this at grain boundaries, increasing grain size and promoting densification.

The temperatures involved, though, are quite high. I don't recall exactly, but I remember that it's way above cone 10, making direct electrical heat with nichrome or Kanthal wires infeasible. I seem to recall that MoSi2 elements would reach that temperature, but I wasn't interested in springing for that expense in fixed costs.

IrC - 11-8-2011 at 20:30

Since you are new to this solar system I will help you with this. Aliens must always listen to magpie and blogfast25 on things of this nature. I can give you a handful of alumina crucibles destroyed doing what you wish to do. I experimented with various hydroxides making aluminate glow powders and can say from experience invest in the nickel crucible you will not be sorry. This only because I could not afford a platinum one, nickel crucibles are expensive enough. Chemicals such as NaOH and alumina crucibles do not get along well at elevated temperatures. I do not agree on the cheaper comment I have many alumina crucibles, they were not as expensive as nickel.

Magpie - 11-8-2011 at 21:19

Here's a source for nickel crucibles:

http://www.crscientific.com/nickelcrucibles.html

Alienwhoexploreyourplanet - 12-8-2011 at 02:07

Thanks a lot watson.fawkes for the explanation , i think there is lot of advantage to use an alumina crucible , and yes IrC and Magpie , it's true that nickel crucible will resist more than any other crucible but the price is here to melt everyone lol .. in my link http://encyclopedia2.thefreedictionary.com/Alkali-Resistant+... they talk about copper too , that look very cool because i have more copper than any other material in my lab , what do u think about this material ?

[Edited on 12-8-2011 by Alienwhoexploreyourplanet]

Neil - 12-8-2011 at 04:30

With my post I assumed you were talking about making a zirconia based crucible not a pure alumina one. I think you are missing the key, your reference said:

"Many oxides, including Cr2O3, ZrO2, HfO2, ThO2, CeO2, Al2O3, and CdO, are stable in aqueous alkaline media at room temperature and upon heating; they react with molten alkalies. Aluminum oxide and zirconium oxide are the most stable to the action of molten sodium hydroxide at 540°C"

at the top of the article it says "The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased."

Out on my limb I would suggest there is a translation error. a google search comes back with references to zirconia crucibles for molten caustics. Perhaps the original article referred to zirconia bonded with alumina crucibles? I assume the original article was in russian....

Ether-way an alumina crucible is going to turn into mush. I've seen a pinch of wood ash eat a fist full of alumina based furnace refractory, a crucible is not going to do any better. Listen to irC...

watson.fawkes - 12-8-2011 at 05:00

Quote: Originally posted by Alienwhoexploreyourplanet

i think there is lot of advantage to use an alumina crucible , and yes IrC and Magpie , it's true that nickel crucible will resist more than any other crucible but the price is here to melt everyone

First, molten alkali and alumina are not compatible. You could get a (compatible) crucible of molten alkali, drop the alumina crucible in it, and dissolve it.

Suppose even that this wasn't the case. The furnace you need to make alumina crucibles yourself isn't trivial. Even just the refractories need to fire alumina aren't cheap, much less the heating system and adequate controls. If you're trying to save money, DIY alumina crucibles are just not the way to go.

If you want to save money, buy some nickel sheet metal. Then pound on it enough to make a crucible. The tools needed are way cheaper. The techniques are basically the same as for custom auto body work. Remember to anneal while working.

blogfast25 - 12-8-2011 at 05:11

Quote: Originally posted by Alienwhoexploreyourplanet

Yawn. 540 C? Use a soup can. I mean, I thought you were going to FUSE something, you know?

Beware of free dictionaries that create 'content' to cram it with adverts. Bauxite (mineral alumina) is dissolved in 50 % NaOH at much lower temperatures than 540 C on an industrial scale. Admitted: the Bauxite is powdered very finely. Al is an amphoteric element, so if you want to contaminate your fusion with a good dollop of aluminate, go right ahead son. You know best!

No, honestly!

[Edited on 12-8-2011 by blogfast25]

Alienwhoexploreyourplanet - 12-8-2011 at 05:18

Quote: Originally posted by blogfast25

[rquote=218680&tid=17248&
Beware of free dictionaries that create 'content' to cram it with adverts. Bauxite (mineral alumina) is dissolved in 50 % NaOH ate much lower temperatures than 540 C. Admitted: the Bauxite is powdered very finely. Al is an amphoteric element, so if you want to contaminate your fusion with a good dollop of aluminate, go right ahead son.

No, honestly!

[Edited on 12-8-2011 by blogfast25]

The reference is the Great Soviet Encyclopedia, 3rd Edition (1970-1979) i understand now why the soviet union melted so fast

[Edited on 12-8-2011 by Alienwhoexploreyourplanet]

Fleaker - 12-8-2011 at 08:04

NaOH does indeed attack even sintered alumina readily.

Silver or gold are great for oxidizing base fusion. Nickel and zirconium are acceptable if it's just base.

Alienwhoexploreyourplanet - 12-8-2011 at 12:59

Thanks Fleaker , so i think the conclusion is that nickel is the key , if you want a clean alkaline fusion without any contamination .

peach - 16-8-2011 at 12:42

Acetylene with pure oxygen burns at 3160°C. And there are things that burn hotter. It is not hard to melt even the pure refractories.

I would not recommend trying to make your own crucibles for these immense applications. The risk of harm from them splitting on unloading is high.

In addition, if the temperature is not high enough, and the melt complete, you will end up with a Gooch crucible. That is a porous crucible.

Another problem is purity. Alumina and other refractory crucibles are usually used when the temperature is not only high, but a pure environment is needed to ensure the contents won't corrode the crucible and the crucible won't contaminate the contents.

[Edited on 16-8-2011 by peach]