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Post by Deleted on Jul 21, 2014 8:56:38 GMT -8
You did not mention Sodium Silicate (waterglass) in your recipe above. I was under the impression that this was a necessary ingredient. Did your experiments prove otherwise? Or is waterglass necessary only when using different raw materials? I am careful and like to avoid if possible sources of hazard. Highly caustic liquids are sources of hazard. Nevertheless I got some water glass for my experiments and got to the conclusion that it is not absolutely required. If the particles are fine enough the sodium hydroxide will dissolve enough of the silica. Diatomaceous earth could serve as a source of very fine silica if needed.
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Post by owkaye on Jul 21, 2014 10:57:49 GMT -8
I see how Morticcio did it now. Basically he combined the batch box with lower heat riser in a single casting. Interesting ...
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Post by owkaye on Jul 21, 2014 11:20:10 GMT -8
Are you saying that one (and perhaps the only) purpose of waterglass is to provide silica to the chemical reaction? And that a waterglass alternative is to use sodium hydroxide to dissolve the required silica from another very fine grained material -- such as fine grog, diatomaceous earth, metakaolin, etc?
If this is correct I think I am finally beginning to understand some of the chemistry of geopolymerization. Thank you Karl.
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Post by owkaye on Jul 21, 2014 14:01:46 GMT -8
Karl, I found a cheap local source for NaOH (yay!) but when I researched "lime" I discovered two types: quicklime = CaO and hydrated lime = Ca(OH)2. Which do you recommend?
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Post by Deleted on Jul 22, 2014 0:43:52 GMT -8
Are you saying that one (and perhaps the only) purpose of waterglass is to provide silica to the chemical reaction? And that a waterglass alternative is to use sodium hydroxide to dissolve the required silica from another very fine grained material -- such as fine grog, diatomaceous earth, metakaolin, etc? Yes. the purpose of water glass is to provide dissolved silica. For safety I prefer to use powders over liquids. The Cold Climate Housing Research Center (CCHRC) uses powders too. cchrc.org/
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Post by photoman290 on Jul 22, 2014 0:57:45 GMT -8
Mixing certain geological materials and/or coal combustion byproducts in the presence of a strong base and water causes the material to quickly form strong chemical bonds without heat. This process has nothing to do with hydration. The resulting geopolymer material is usually stronger than concrete so it can be poured thinner. And it is exceptionally resistant to degradation at high temperatures. Is this correct? Yes, that is correct. Fly ash consists mostly of hollow balls with low thermal conductivity and a density below 1g/cm 3. There are light hollow ball fillers made from selected fly ash or by a special fusing of aluminosilicates which an even lower density. The hollow balls will form a strong but light matrix. Hollow balls need very little water for low viscosity. The hollow balls can also be used as an additive to lower the viscosity of other kinds of aluminosilicates. As I could not find a source of fly ash or metakaolin in Gemany I have only experimented with very fine grog and natural clays. About 80% very fine grog 10% lime and 10% sodium hydroxide worked great for me. Can be made very runny with more water, but then will take long to dry. I hope to get some fly ash and highly reactive metakaolin for experiments soon.
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Post by photoman290 on Jul 22, 2014 1:00:07 GMT -8
karl i have a source of metakaolin in the UK PM for for the details. i wont put them up here as don't want them being swamped with enquires.
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Post by Deleted on Jul 22, 2014 1:01:00 GMT -8
I found a cheap local source for NaOH (yay!) but when I researched "lime" I discovered two types: quicklime = CaO and hydrated lime = Ca(OH) 2. Which do you recommend? Quicklime reacts vigorously with water releasing a lot heat, which speeds up the chemical reactions significantly. With quicklime pot times of jus a few minutes are possible. For quicklime with water glass the processing time may become extremely short. Hydrated lime does not react violently, which gives more processing time. I am not very patient and thus have used quicklime in my experiments. The main purpose of lime is to speed up the chemical reactions and ensure curing at ambient temperatures. Lime has some other effects too.
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Post by erictoronto on Nov 15, 2014 20:30:17 GMT -8
Greetings all, this is my first post on the board. In the process of planning to build a very plain 4" cast core rocket heater. Focus right now is on the selection of materials for the core (the riser will be separate). As peterberg has suggested I will either source a high grade conventional castable or create my own castable mix with high grade materials. Goals for the core hot face are to take the abuse of loading in wood and thermal shock resistance. Maybe an expansion joint throughout the core but not sure what gasket material to use.
Am I right in saying that a minimal cast thickness will be more resistant to thermal shock? But at the same time a thinner core reduces the cold crushing strength?
Peterberg suggested a core thickness of 1.25".
Here are some points from a doc describing a product called Thermbond about thermal shock resistance: - stress occurs because of temp gradient between the surface and interior - need material with a low thermal expansion and high thermal conductivity such as mullite or silicon carbide - low modulus of elasticity = high elasticity - thermbond liquid phosphate bonded materials possess a flexible binder matrix with high elasticity
Do you agree that castables with high amounts of mullite or silicon are ideal? Anyone have experience with Thermbond?
Thanks in advance for your feedback, Eric in Toronto
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Post by peterberg on Nov 16, 2014 0:50:52 GMT -8
Hi Eric, welcome to the boards. It looks nice to do a 4" rocket heater but it is quite complicated to produce a first incarnation that'll work properly. I'd suggest you switch to a 6" system, much easier to get right the first time.
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Post by erictoronto on Nov 16, 2014 9:54:40 GMT -8
Thanks Peter, I'll take your advice and scale up to 6". Great to avoid hurdles from the get go.
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