DIY refractory mixtures

[Deleted]

Ciment Fondu (Calcium Aluminate Cement, CAC) is the binder (10% to 50%)
of many refractory mixtures, common aggregates are grog (mullite, kyanite),
perlite, clay and calcined alumina.
Ciment fondu is obtained by fusing alumina and bauxide at high temperatures.
Iron ore serves a a flux to lower fusing temperature to about 1400°C.
Ciment Fondu is resistant to heat, abrasion and corrosion, and is rapid setting.

Raw composition of Ciment Fondu
Al2O3 40%-80%, CaO 20%-40%, Fe2O3 0%-15% , SiO2 0.5%-5%%
Standard composition of Ciment Fondu is roughly
Al2O3 40%, CaO 40%, Fe2O3 15% , SiO2 5%
High alumina Ciment Fondu
Al2O3 80%, CaO 19.5%, Fe2O3 0% , SiO2 0.5%

In refractory mixtures Ciment Fondu can be replaced by lime and fine calcined
alumina silicates and maybe additional calcined alumina, which will result in longer setting times,
as the calcium aluminate needs to form first.
Smaller amounts of Ciment Fondu could be even replaced by ordinary portland cement.

Sample compositions can be found in the technical data here
www.tflhouston.com/refractories/technical-data.php

The cement cauld also be replaced by geopolymer binder.

DIY Refractories
Pro: Huge savings possible.
Con: Nobody else to blame.

[photoman290]

looking forward to getting back to making some refractories. January in cornwall is not the time to be working outside though.

[redhawk]

I'm looking forward to being at the point where I can make some molds and start making some refractories to test my design for a cooking stove and oven. Thanks for this great link. I found lots of good info there.

[Deleted]

Anorthite CaAl2Si2O8 / CaO Al2O3 2(SiO2) Melting point 1550°C / 2822°F
Al Aluminum 2 19.3967 %
Ca Calcium 1 14.4059 %
O Oxygen 8 46.0071 %
Si Silicon 2 20.1903 %


CaO 1 Mol Molar mass (g/mol): 56.0778 ~ 20.16 %
Al2O3 1 Mol Molar mass (g/mol): 101.96136 ~ 36,65 %
SiO2 2 Mol Molar mass (g/mol): 60.08439 ~ 43.19 %
Total mass: 278.2080 g

CaOH 1 Mol Molar mass (g/mol): 57.0858 ~ 20.44 %
Al2O3 1 Mol Molar mass (g/mol): 101.96136 ~ 36,52 %
SiO2 2 Mol Molar mass (g/mol): 60.08439 ~ 43.04 %
Total mass: 279.2080 g

Mulcoa 200 grog with about 20% lime would come pretty close to the formula above
and give good cold strength.
Anorthite will form if fired above 900°C.

High alumina clay with 20% lime  will gain sufficient strength to be castable,
but requires firing for good strength.
May need some fiber to prevent cracking while drying.


Anorthite is the high temperature end member of plagioclase,
albite NaAlSi3O8 is with 1135°C - 1170°C the low end member.

Anorthite forms in calcium rich fly ash geopolymers and raises temperature resistance.
Albite forms at higher SI/Al ratios in sodium geopolymers and is responsible for high compressive strength.

[pyrophile]

Donkey gave his recipes for refractory mix using aggregates bond together by a clay-ash slip. I read that Clay + ash is also used in different countries to make resistant slab for outside.

What is exactly (well, not too exactly neither!) the chemical action of ashes?
Thank you

Benoit

[Deleted]

Wood ashes consist of silicon dioxide and metal oxides,
mainly CaO.
The chemical action of ashes with water is similar to roman cement.
At high temperatures ashes promote ceramic hardening of clays.
www.fpl.fs.fed.us/documnts/pdf1993/misra93a.pdf
en.wikipedia.org/wiki/Fly_ash
en.wikipedia.org/wiki/Bottom_ash

[pyrophile]

My competence is very limited in chemistry...but as ashes are used in ceramics as a fluxing agent to diminish melting temperature of clay, like iron oxydes, I thought that it could be a problem at high temperatures.
Their pouzzzolanic action isn't rather at low temperature?

Benoit

[pyrophile]

I found a few things in the book "The self reliant potter : refractories and kilns" :
For making refractory slabs an d saggars, il is said "if the firing temperature is below 1250°C, an addition of 5-12% talc will improve resistance to thermal shock. Talc will reduce the melting point and therefore can be used only at lower temperatures."

Maybe is it the same for ashes , good at rather low tempretaure and to avoid at higher temps?

It is also said, about insulating brick making : "Some ashes have high contents of minerals which lower the melting point. These are usefull in glases but not in firebricks.
Ashes high in potash and soda should have these soluble minerals removed by washing so that they are less caustic to work with. The removal of soda and potash will also raise the melting point."

It is said that, in the contrairy, rice-husks ahes (and rice straw, a bit less) can be used because they contain 90% of amorphous silica. As amrpheous silica is less refractory, those bricks "are unsuitable for high temperatures. Ash bricks may be used in low temperature kilns."

[josephcrawley]

I use would ash in pottery glazes. They do not melt until the ball park of 2300f.

[Deleted]

Alumina, silica and aluminosilicate have melting points around or above 1600°C / 2912 °F
Sintering does not require liquefaction, but the glass transition temperature must be reached.
It would be extremely expensive to make any pottery, bricks or even cement without any kind of flux.
For commercially viable products fluxes are indispensable.
Eg. porcelain may contain around 50% flux.
Even most high refractory cements are produced with help of flux to make them affordable.

[pyrophile]

In fact, I rather think that, in the walls of the firebox, only 2 to 4 cm will be fired and only a few millimetres could (in certain conditions) soften, but being always cooled by the thickness of the firebox' walls. The inside of the firebox is not very hot, the heat riser much more. The walls of the firebox must not reach 600°C where they should glow red cherry. Isn't it at those low temps that ashes have an hardener (pouzzolanic?) effect on clays?

[Deleted]

Pozzolanic reaction is defined as a chemical reaction with lime.
Water is required.
Reactions with hydroxides of other alkaline earth  metals or alkali metals are similar,
based on alkali attack, dissolution and chemical rearrangement.

Ceramic hardening means generaly sintering.
Once the glass transition temperature is reached the molecules in the materials
diffuse across the boundaries of the particles,
fusing the particles together and creating one solid piece.
A chemical rearrangement may happen too, which may alter the glass transition temperature.
Usualy ceramic sintering happens around 1200°C / 2192 °F,
but additional fluxes eg. ashes may lower the sintering temperature to around 750°C / 1382 °F.

The recipe for making a glass frit at around 750°C / 1382 °F is two parts of ash and one part sand.
At the second stage the glass frit is molten to glass at around 1200°C / 2192 °F.
Now you can make your own "forest glass" if you like.

A low sintering temperature may also be achived by adding glass powder
with a low glass transition temperature  as a sintering aid.
That is much simpler, but not free as ash.
Glass transition of Soda-lime glass 520–600°C, ZBLAN fluoride glass 235°C.
en.wikipedia.org/wiki/Glass_transition_temperature

In another thread an old refractory patent "FIRE-CLAY SUBSTITUTE" containing some glass was mentioned.
Now you know the purpose of the glass in the mixture.
www.google.com/patents/US1056031

[kpolano]

I'm wondering about casting a mix of lime and perlite. I'm really just going on a random idea and hope to avoid cement. Anyone done anything with lime and perlite? or even lime, clay, and perlite?
Cheers.

[Deleted]

Perlite ia a natural pozzolan.
To make a binder with lime the perlite must be a pulverized.
Eg. by filling a jar with perlite and some hard balls or stones
and shaking it until the perlite is pulverized.
Mix the pulverized perlite and lime with water, then fill the binder with perlite.

Use of Perlite as a Pozzolanic Addition in Lime Mortars
dergipark.ulakbim.gov.tr/gujs/article/download/1060000317/1060000155

DIY Ball Mill - Cheap Under $10
www.youtube.com/watch?v=wR3ZlV-cTxI

[pyrophile]

Thanks, Karl!