# Bought a drum of Magnesium Oxide yesterday



## Anonymous (Dec 5, 2010)

I went to a nasa auction and one of the things I bought was a few big drums,3 of them have activated charcoal and phosphoric acid,and 1 drum has 40 pounds of Maglite 100% Magnesium Oxide.I want to make my own crucibles but I do not know what percentage of Hcl I am suppose to be using.Does anyone have any experience with it?


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## Irons (Dec 6, 2010)

Adding HCl will dissolve the Magnesium Oxide and give you Magnesium Chloride. That's not what you want.


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## HAuCl4 (Dec 6, 2010)

One can make fine cupels with magnesite MgCO3, and a little cement. Dunno what to make with MgO, but I'll be reading this thread!.


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## Anonymous (Dec 6, 2010)

Irons said:


> Adding HCl will dissolve the Magnesium Oxide and give you Magnesium Chloride.


No it won't.
http://pubs.acs.org/doi/abs/10.1021/ie50268a016


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## Palladium (Dec 6, 2010)

mic said:


> Irons said:
> 
> 
> > Adding HCl will dissolve the Magnesium Oxide and give you Magnesium Chloride.
> ...



http://www.chemguide.co.uk/inorganic/period3/oxidesh2o.html


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## Irons (Dec 6, 2010)

mic said:


> Irons said:
> 
> 
> > Adding HCl will dissolve the Magnesium Oxide and give you Magnesium Chloride.
> ...



Compressed Sorel Cement
http://en.wikipedia.org/wiki/Sorel_cement
The Magnesium Chloride is produced in situ with the addition of dilute HCl.


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## skippy (Dec 6, 2010)

You can also slip cast the magnesium oxide. http://www.freepatentsonline.com/3116155.pdf
Slip casting doesn't need a fancy press and die either


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## Anonymous (Dec 6, 2010)

skippy said:


> You can also slip cast the magnesium oxide. http://www.freepatentsonline.com/3116155.pdf
> Slip casting doesn't need a fancy press and die either


Thanks skippy,I knew I could mix it with Hcl without any problems,I just needed some help explaining what to do from there.This should work fine considering I have access to molds already.I will just find a nice large mouth vase mold and use it,or make one with plaster and fire it.
Thanks again.


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## skippy (Dec 6, 2010)

No prob, let us know how it works out!


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## Anonymous (Dec 6, 2010)

Definitely.The wife is going to pick me up some fireclay and silica right now,I want to make several different crucibles and see which one works best.


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## turtlesteve (Dec 10, 2010)

I second the slip casting suggestion, this is by far the best bet for making crucibles/dishes. Your main concern will be getting a good dispersion of the powder and mixing well - you should be able to mix 30+ volume percent of powder (at least ~1.5 g of powder for every 1 g of water) and the slurry should still be easy to pour. If you don't achieve this initially you will need to adjust the pH (this is the purpose of the HCl indicated in the patent posted above) or possibly add some dispersant. Always add the powder to the water, and any pH adjustment or dispersant addition should be done before powder is added. The more different powders you add to the same slurry, the more difficult this will be.

Steve


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## Anonymous (Dec 10, 2010)

Thanks.
I got 4 molds last night to slip cast with,and was going to try pour some this weekend.
I had planned on using just the MgO and very dilute Hcl.I wasn't going to add fireclay or anything else to the mix.I also bought some stuff to make a couple of pressed crucibles.This way I can fire quite a few at a time and see which result is the best.
Do you see any problem with using only the MgO?Or should I add something too that?


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## turtlesteve (Dec 10, 2010)

It will probably work just fine with the HCl, depending on the quality of your powder. Ideally you would ball-mill it for a short time to help break up the powder and mix it well. Add the HCl to the water first, maybe pH = 4-5. Check the pH as you add powder as it will probably start to rise, you should continually add more HCl as needed to keep the pH near this level. If the pH goes basic the slurry with clump and will stay clumped, even if you lower the pH again - you'll have to start over. Your goal should be to mix >1.5g powder per g of water, and still have a fluid. 1g : 1g would be acceptable but not ideal. If you lower the pH to ~3 and still don't get good results (paste instead of liquid) I would stop because adding more acid probably won't help. At this point you would need to try a dispersant, such as ammonium poly(methacrylate).

Pour the slip into plaster molds, wait ~10-15 minutes, and pour the remainder back into the original container. Let the crucibles dry for a couple days before firing.

Keep in mind you will need quite a high temperature to get the MgO sintered. Think 1300-1600C. Temperatures at the low end of this range will give you porous crucibles, but this is not likely to be a problem for melting metals, and is obviously needed for cupellation.

Edit - as another note, pure MgO crucibles might not resist thermal shock well - i.e. don't know how they'll stand up to torch melting.

Steve


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## Anonymous (Dec 10, 2010)

Very insightful steve.Thank you for breaking it down for me.I have preached at others to utilize the "seach" feature,however this is one time when it is pretty much useless.


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