Sciencemadness Discussion Board

Magnesium Oxide as a additive to furnace reractory - purity needed?

RogueRose - 4-2-2016 at 07:46

I've been looking for Magnesium Oxide to add to some fire bricks and refractory cement and have found "MagOx 54%" (feed grade) which seems reasonably priced. The thing is that I don't know what the other 46% is.

I've read that Mag hydroxide also has a very good heat resistant quality, both are rated around 5,100F so I guess either would do.

I can obtain MgCl2 and lime, which supposedly can be made into MagOxide when heated but am unsure of the heat required to do so and whether it would be prohibitive and achievable with what I have available (no carbide crucibles large enough).

Does anyone have any experience with feed grade MagOx and what it may also contain?

Detonationology - 4-2-2016 at 07:54

I know nothing in regarding the field of masonry, but why do you need magnesium oxide specifically? Is ordinary lime not suitable?

[Edited on 2-4-2016 by Detonationology]

UC235 - 4-2-2016 at 09:15

I strongly suspect that 54% is the weight% of magnesium in the product. Pure MgO would be 60% and I suspect the difference is calcium oxide or possibly just Mg(OH)2 since it is hygroscopic.

This form of MgO is not calcined and is designed to dissolve in an animal's stomach and function as a magnesium supplement. If you're looking to make Sorel Cement, I believe this is an appropriate material. As a refractory, you don't want this. You want dead burnt magnesia/magnesite which is non-hygroscopic and nonreactive but retains it's insulating properties.

[Edited on 4-2-2016 by UC235]

RogueRose - 4-2-2016 at 10:50

Quote: Originally posted by UC235  
I strongly suspect that 54% is the weight% of magnesium in the product. Pure MgO would be 60% and I suspect the difference is calcium oxide or possibly just Mg(OH)2 since it is hygroscopic.

This form of MgO is not calcined and is designed to dissolve in an animal's stomach and function as a magnesium supplement. If you're looking to make Sorel Cement, I believe this is an appropriate material. As a refractory, you don't want this. You want dead burnt magnesia/magnesite which is non-hygroscopic and nonreactive but retains it's insulating properties.

[Edited on 4-2-2016 by UC235]


Thanks for the information. When I looked into additives for refractory it simply said magnesium Oxide and didn't mention the different types. If the supplement type were to be used what would be the suspected results?

The mix I have used before with fairly good results is:

Bentonite clay powder - 2 parts
Portland Cement - 2 parts
Sand - 3 parts
Perlite - 3 parts

(I have gone to 10 parts of perlite on the mixture which lines the outer part of the container (say 1" thick) with 2" of the regular mix on the interior. This seems to save on weight as well as insulates better than the normal mixture.

The portland cement is hygroscopic, maybe not as much as the MgO, but it will all be mixed with water and allowed to cure for a couple weeks and then heated at a low temp (150-200) for a couple hours repeatedly, then slowly increasing temp by 200 degrees for 4 more heatings.

As a note, this was inteded to be used on the inner most 1" layer of the burn chamber where temps will be highest.

Thanks for the mention of the Sorel Cement. what a strange substance! Here is a link to a paper that discusses it:
Sorel Cement Study It looks like it can be made from MgO and MgCl2 and is fast drying and pretty tough - used for fast drying road repair.

Attachment: Sorel Cement Paper-3.pdf (1.5MB)
This file has been downloaded 439 times

chemrox - 4-2-2016 at 12:14

Quote: Originally posted by Detonationology  
I know nothing in regarding the field of masonry, but why do you need magnesium oxide specifically? Is ordinary lime not suitable?

[Edited on 2-4-2016 by Detonationology]

Why respond? This was all about refractory applications. It pisses me off when a post starts with "I know nothing about your question but I'm going to put my 2ȼ in anyway.."

RogueRose - 4-2-2016 at 12:52

Quote: Originally posted by chemrox  
Quote: Originally posted by Detonationology  
I know nothing in regarding the field of masonry, but why do you need magnesium oxide specifically? Is ordinary lime not suitable?

[Edited on 2-4-2016 by Detonationology]

Why respond? This was all about refractory applications. It pisses me off when a post starts with "I know nothing about your question but I'm going to put my 2ȼ in anyway.."


LOL, yeah that kind of thing always baffles me as well.

Detonationology - 4-2-2016 at 16:09

Quote: Originally posted by chemrox  
Quote: Originally posted by Detonationology  
I know nothing in regarding the field of masonry, but why do you need magnesium oxide specifically? Is ordinary lime not suitable?

[Edited on 2-4-2016 by Detonationology]

Why respond? This was all about refractory applications. It pisses me off when a post starts with "I know nothing about your question but I'm going to put my 2ȼ in anyway.."

Why did you feel the need to post an irrelevant response? It pisses me off when somebody posts an irrelevant response.

I was simply trying to elucidate the original need for MgO.

Why is CaO unacceptable for this application? It is very widely available and sold quite pure.

Knowing the similarities of elements of the same group, why was my question not applicable?

And I thought this forum was a place where people could freely spread their 2¢...

[Edited on 2-5-2016 by Detonationology]

Fulmen - 5-2-2016 at 02:11

UC235 is right, for refractory you will probably need fused magnesia.

I've worked at a local plant that makes it back when it was part of a magnesium plant, and the "MgO" they made then was a mix of MgO and Mg(OH)2. This was done in a large rotary kiln fed with precipitated hydroxide.
Don't remember the exact composition, but since Pure MgO is 60% and Mg(OH)2 is 41% Mg somewhere around 50% sounds reasonable. As UC235 said this was in order to ensure reactivity, "dead burned" would be too inert. They also sold this quality for other uses like fertilizer, feeds and paper mills.

After they closed the Mg-plant they kept making MgO for things like agriculture and paper production, and I believe they burned it harder at that point. But I doubt they ever made pure MgO.

Now they primarily make fused magnesia for refractories, this is done in arc furnaces capable of melting MgO (MP 2850°C). If fusing wasn't absolutely needed there's no way they'd do it as it's extremely energy and labor intensive.