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.
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.
WE love Visitors, that's why we live in a secluded cabin deep in the woods.
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?
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."
Last Edit: May 14, 2015 14:19:55 GMT -8 by pyrophile
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.
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?
Last Edit: May 16, 2015 11:55:01 GMT -8 by pyrophile
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
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.
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.
dan1941300: If possible in metric cm, how many Celsius at the chimney? Is there anything you would do different if building again? Sorry for my bad english, my language is german, austrian. thx a lot
May 11, 2018 9:38:02 GMT -8
smarty: Dan my batchbox reached 1150C so refractory cement rated to at least 1200C
May 21, 2018 22:53:56 GMT -8
mercedes: Not sure where this question will end up...I just registered. HOW THICK SHOULD PERLITE/VERMICULATE/CLAY INSULATION BE BEHIND THE THERMAL BATTERY/COB BENCH IF IT BACKS UP TO A STRAW BALE WALL? Thanks! Can you please also post me: email@example.com thnx!!
May 28, 2018 20:05:23 GMT -8
kkp: Mercedes: Benches don't get real hot. In fact, they are rather cool compared to other areas. You shouldn't need a mix like you described
Jun 7, 2018 18:10:52 GMT -8
maartenmartens: beste Peter, ik heb je eergisteren een mail gestuurd via het contact formulier op je website , heb je die goed ontvangen ? mvg Maarten Martens, architect - geobioloog (mail betreffende de bouw van onze eigen RMH)
Jun 20, 2018 13:21:57 GMT -8
martinm: any one here with info \ experience with heat (from a mass heater) distribution with ducts throughout two storey house ?
Sept 8, 2018 22:58:52 GMT -8
padica: Good morning, this is a wonderful subject, please someone can help me with the theme of double and triple combustion, how it is achieved, theory and design, thank you
Sept 15, 2018 7:13:40 GMT -8
wiscojames: I'm afraid you won't get a response to such a vague question - I suggest reading through some of the threads related to your questions before asking for an explanation. People will be very generous with their knowledge if your question is more specific.
Sept 18, 2018 4:48:00 GMT -8
daniel: in my experience as I am working now on something of that nature, I have thought of making a heat exchanger and distributing the heat through vents using a slower fan. Now after a few years I realize that mass heaters give out primarily radiant heat, for
Nov 30, 2018 12:48:38 GMT -8
coastalrocketeer: Anyone posting in this shout box... if you have something you want people to see and respond to, create a thread in the appropriate forum section... this is not the place...
Dec 16, 2018 18:10:49 GMT -8
vesuvius: High Temperature Glass options,
Jan 4, 2019 16:28:17 GMT -8
vesuvius: Do any of you have experience with using the glass from home oven doors on a rocket stove? I'd like to have a viewing port on my stove but don't want to fork out for new ceramic glass. Any thought as to whether it would take the heat of a rocket stove?
Jan 4, 2019 16:30:40 GMT -8
yaya: you dont need the blowair for that temp..
Jan 13, 2019 16:43:57 GMT -8
flybywire: Glass window from an old washing machine is designed to take high temps. Cheap solution to your need.
Jan 27, 2019 0:10:58 GMT -8
coastalrocketeer: Anyone posting in this shout box... if you have something you want people to see and respond to, create a thread in the appropriate forum section... this is not the place to have a discussion... it is for short announcements
Feb 7, 2019 0:11:23 GMT -8
coastalrocketeer: you won’t likely get replies to questions here, and it is not a spot that makes holding an ongoing discussion possible...
Feb 7, 2019 0:12:22 GMT -8