DIY Refractories On Alloy Avenue

[ronyon]

www.alloyavenue.com/vb/archive/index.php/t-5.html?s=d56fdee1e8e3c74e0cf0c765dd367491

Good thread, lots of info to steal.

[2tranceform]

Wow, a lot of info! Thanks.

[oboblomov]

Jan 21, 2014 8:44:45 GMT -8 2tranceform said:

Wow, a lot of info! Thanks.

Double Wow! So much concentrated information. Going to have to read this over several times to make it stick (in my head.)

So now I begin to see what karl has been telling us all along. Thanks very much ronyon.  Very useful information.

obob

[Vortex]

Absolute mine of information, thanks.

[raandyd]

Jan 20, 2014 22:00:45 GMT -8 ronyon said:

www.alloyavenue.com/vb/archive/index.php/t-5.html?s=d56fdee1e8e3c74e0cf0c765dd367491

Good thread, lots of info to steal.

would bathroom 4" x 4" glazed tile work for the fire box  or 12"x12" floor stone, or granite countertop   will any of these work for fire box?

[raandyd]

would bathroom 4" x 4" glazed tile work for the fire box or 12"x12" floor stone, or granite countertop will any of these work for fire box?

[ronyon]

Thanks guys, glad to bring something new to the forum!
As for the usr of tile or stone, the usual objections to such materials is their reactions to rapid temperature changes (thermal shock).
The counter top may also be sealed with some chemical that will burn and emit toxins etc.

[ronyon]

HWooldridge



02-04-2012, 07:02 PM



I've been reviewing this thread again over the past few days and was curious about using a much higher alumina percentage in a DIY mix. This would be intended as a hotface applied to 2600 Fiberfrax Duraboard or Plicast KL3000 castable to protect against flux and slag (heat source is propane). While perusing the MSDS sheets for several commercial products, they appear to depend primarily on alumina with SIO2. For example, Plistix 900F is advertised as a hotface and is listed at over 90% alumina. Subsequently, I was thinking along the lines of:







75% Alumina



10% Mullite (100 mesh)



10% White Silica Sand (300 mesh)



5% Kaolin







Any thoughts? I haven't tried this yet but we live only about 12 miles from a well stocked ceramics supplier so it's pretty easy to get both chemicals and raw materials at decent prices.





Anon



02-05-2012, 02:33 AM



There isn't too much wrong with making mullite + alumina. Alumina is expensive in pure form, so that's one reason you might not use more than you need, and it's also slightly less thermal shock resistant than mullite (though not approaching as bad as crystalline silica). If you want to use abrasion grit alumina instead of crushed mullite for your coarse grogs, go right ahead, but that doesn't contribute much to the chemistry when it's coarse.







I wouldn't add silica. Use kyanite or mullite grog in varying grits--that has the bonus that it will contribute substantial amounts of alumina, making it necessary to add less of the pure stuff. Also, 5% bentonite would be fine, but you'd need more like 20% or 25% kaolin to stick the mix together. And you don't really need more 300 mesh stuff anyway if you're going to add a bunch of fine alumina, you need coarser grogs, like some 30-50 mesh, and perhaps more of the 100 mesh than 1

This looks very good. The hotface that they speak of sees like it would translate well to a rocket core and riser, if you were planning on insulating separately. I like the idea of separate insulation, as that is one  less property that must be incorporated into the core material.

[Deleted]

Jan 21, 2014 20:46:17 GMT -8 ronyon said:

75% Alumina
10% Mullite (100 mesh)
10% White Silica Sand (300 mesh)
5% Kaolin

The sand makes no sense in a high alumina mix for a melting pot not even for a stove.
The mullite makes not much sense for a stove too.

Alumina is one of the hardest materials and therefore has a high thermal conductivity,
higher than some steel grades.(30 W/(m · K)) Melting point 2,072 °C, 3,762 °F

The thermal expansion coefficient of mullite is changing at about 1100 ° C,
which has a destructive effect on the refractory structure.
Mullite may also be produced when burning aluminous clay (kaolin) at about 1200 °C.
The formation of mullite raises the refractoriness of silica significantly,
and was therefore a closely guarded secret of German alchemists for many hundred years.

At temperatures above 1100 °C kyanite decomposes into mullite and vitreous silica,
with expansion up to 20%, thus it would be better to use mullite instead of kyanite.

[ronyon]

How about just kaolin and alumina since it seems that the kaolin degenerates into mullite?

[Deleted]

Jan 22, 2014 9:12:21 GMT -8 ronyon said:

How about just kaolin and alumina since it seems that the kaolin degenerates into mullite?

Mullite is an improvement not a degeneration.

Yes, you could just use kaolin and alumina.

Alumina is relatively expensive.
Alumina increases abrasion resistance and thermal conductivity.
However even with 75% alumina content the thermal conductivity
of the fired mix will only slightly exceed 1 W/m.°K.
For significantly higher thermal conductivity one would have to go into the upper 90% range.
One could build insulation from carbon nano tubes.

[ronyon]

Yea, the by degeneration I meant "change into".
I am not clear on the significance of thermal conductivity, is it good or bad?

[Deleted]

Jan 22, 2014 11:43:40 GMT -8 ronyon said:

I am not clear on the significance of thermal conductivity, is it good or bad?

Depends on what you want.
In general, conductive materials are less susceptible to thermal shock,
as thermal gradients will be smaller.

en.wikipedia.org/wiki/Thermal_shock