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Post by mintcake on Feb 25, 2014 6:28:00 GMT -8
I'm just wondering... putting thoughts together a bit... maybe someone can help who has more knowledge. 1. YTONG type low density "concrete" (which is actually (mostly?) calcium silicon hydrate, apparently), is insulating, wonderfully cheap, and supposed to be good to 1200C. According to a paper I skimmed, the main mineral which is supposed to be there breaks down at 1300C. I've found threads on e.g. goldrefiningforum.com talking about using it to 1200C. 2. Peterberg's maximum observed temperature was below 1200C. 3. YTONG dies fairly quickly in rocket stoves :-( 4. Suppliers of firebrick/chamotte chimney pieces proudly claim their products are resistant to chemical attacks. 5. We all know there are all sorts of acids, etc. in wood combustion gases. So I was wondering, is it the heat which is killing the YTONG blocks, the thermal cycling, or is it some kind of chemical attack? If it's the latter, then something like a layer of slip might make this a wonder-material. Has anyone tried doing it? If not I'll give it a go on my first practice build, but I don't want to prove that square wheels don't work if someone else has already. |
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Post by 2tranceform on Feb 25, 2014 10:22:30 GMT -8
I think the cause of the failure is the portland degrading in the heat. I read this, "Some disadvantages of AAC blocks and panels are that they do contain Portland cement, ....." This is from link. Definitely interesting stuff. I had never heard of it. I have now learned my quota of new information for the day. Time for cat videos on youtube link2  |
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Post by satamax on Feb 25, 2014 12:00:54 GMT -8
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Post by 2tranceform on Feb 25, 2014 12:43:53 GMT -8
Reading here, info, states that AAC does contain portland cement. AAC could be useful for insulating and providing structure in non hot face areas. |
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Post by satamax on Feb 25, 2014 19:22:11 GMT -8
Or tiled with thin firebricks  |
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Post by mintcake on Feb 26, 2014 1:21:33 GMT -8
I don't know where you are, but if you have access to ciment fondu, may be that would do the trick to protect ytong. In rual Romania... Just had half a cubic meter (aka one horse-drawn cartload) of local clay delivered for a local expert to rebuild our present tiled stove. That's being moved into a guest-room, making space in the living room for my build. The stove build will be followed by laying a beautiful new varnished wooden floor, so I get in trouble if the stove needs rebuilding after a year and I damage the floor. On the other hand, the floor is not going to be cheap, so there's not so much spare cash for the stove. The clay delivery cost about $6 US, I can get firebricks for $.74 and I've found a shop an hour's drive away where the internet price list says I can get various non-insulating castables for a price of about $40 / sack, or they also sell insulating boards for even more. I guess I need to try making some charcoal+clay mixtures to see how well they hold up. For lining the firebox of our tiled stove, the local guy mixed about .5kg of salt into the bucket of clay+sand mix he had. Does anyone know what that does? David |
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Post by Deleted on Feb 26, 2014 2:03:06 GMT -8
For lining the firebox of our tiled stove, the local guy mixed about .5kg of salt into the bucket of clay+sand mix he had. Does anyone know what that does? Thats an outdated low tech solution, but people like to do things as they have been done for centuries, even if better solutions have emerged. The salt and the othe ingredients will form sodium silicates at high temperatures. Very cheap, but remains of salt can build efflorescence at the surface and destroy it. Using sodium silicate is safer. |
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Post by mintcake on Feb 26, 2014 11:57:51 GMT -8
I've just been learning lots... Xella (YTONG's manufacturer) states in their environmental product declaration: "AAC consists mainly of tobermorite, a natural mineral." www.understanding-cement.com/autoclaved-aerated-concrete.html tells a lot about how it's made, and goes on to say that it's "1.1nm Anomalous tobermorite". Now we know... Does anyone have access to "Science Direct"? www.sciencedirect.com/science/article/pii/S0950061808002353 has an article about heat on AAC. From the abstract it looks like it's mainly talking about water-quenching the stuff, but it mentions 800C as a temperature where bad things start to happen. www.ncbi.nlm.nih.gov/pubmed/24159882 states "As the temperature increased to 724 degrees C, Si-O-H bonds were cleaved and dehydroxylation occurred. The XRD results showed that many diffraction peaks of tobermorite disappeared and the crystal structure was broken and collapsed. Then tobermorite tends to be disordered and amorphous. When the calcination temperature increased to 861 degrees C, the disordered structure recombined to wollastonite, and the crystal structure became ordered and stable. Finally, the structure completely transformed to 2M-wollastonite at 1 000 degrees C. It should include the process of high-temperature phase change of tobermorite: tobermorite --> dehydration tobermorite --> dehydroxylation tobermorite --> wollastonite." I have no idea what that does to the structural strength and other properties of the stuff. |
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Post by pyrophile on Mar 15, 2014 15:11:07 GMT -8
Even protected by thin bricks or coated with clay, I find Ytong rather fragile when heated at rather high temperatures.
Benoit
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Post by mintcake on Mar 21, 2014 22:22:53 GMT -8
Even protected by thin bricks or coated with clay, I find Ytong rather fragile when heated at rather high temperatures. Benoit I find thin ytong rather fragile at any temperature.. do you mean that it gets even more fragile? What sort of temperatures? |
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Post by pyrophile on Mar 30, 2014 8:59:52 GMT -8
Used in a firebox, protected by 5cm of firebrick, this material cracks. What I saw that the blocks fall in pieces only when you disassemble (distroy) the stove, not before. I sometimes use Ytong for quick trials/tests but it always suffers a lot!
But I use it as a isolated slab for my masonry stoves.10 cm thick. But only here!
I lived in Roumania for one year and an half, 20 years ago (my God, twenty!)in the region of Sibiu. One of the simplest way for your mortar is to find rather pure clay by asking to people like masons or potters. And add thin sreened sand, maybe 3 volumes of sand for one volume of clay. You should find people knowing old massstoves masons (sometimes old small farmers) around.
There are also massstoves firms and also craftsmen. Isn't there one on this forum?
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Post by mintcake on Apr 3, 2014 11:53:03 GMT -8
Thanks for the explanation pyrophile, I'll have to see what happens when I take my firebox (5cm thick sheets of ytong "design") and heat-riser (same sheets, trapezium shaped to make an octagon) apart.. That won't be for a few weeks, I expect. So far (5 burns) they seem to be holding up. Was your firebox from similar thin sheets, or was it from larger blocks? Lacking patience to build an arch, and not having an RSJ to hand, I slapped a few sheets of 5x20x60cm ytong on the top of my (red-brick) trial bell. This ytong roof is about 40cm above the heat-riser. After 2 firings I decided to be nosey and had a look inside. I really need to light this thing with less smoke, quite sooty inside already  . I took of a piece furthest from the heat riser, which was partly over the bell, and partly overhanging the edges. It looks like the heat there has caused shrinkage-cracking of the surface, (it's got crazy-paving style patterns in the soot) and also I've found that where the ytong was exposed to the heat it's about 4.95-4.96cm thick, compared to a consistent 4.98 cm where it wasn't. I obviously need to see what variation in thickness is normal, but I measured it in about 15 places and it seemed consistent on that sheet, at least. I'd imagine that that there'll be far more shrinkage in the firebox. So ~0.5% shrinkage not even in the firebox (Is that high? Someone correct me!). Maybe this shrinkage is what kills this stuff. |
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Post by pyrophile on Apr 4, 2014 13:48:38 GMT -8
Sometimes Ytong seems to handle heat BUT as you touch it, it falls into pieces. Above all in firebox! 5cm or 10, both suffer! But you will be the best placed to tell us. For me, heat kills Ytong!
Benoit
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Post by mintcake on Apr 20, 2014 12:29:22 GMT -8
Sometimes Ytong seems to handle heat BUT as you touch it, it falls into pieces. Above all in firebox! 5cm or 10, both suffer! But you will be the best placed to tell us. For me, heat kills Ytong! Benoit Hi... Quite a few test firings now, and some definite results: 1. My firebox is fine still. I wonder what we've done differently! I do notice that sand/clay clay doesn't stay stuck to it more than a firing or 2, which is a pain. Time to bite the bullet and start casting something soon.... On my vertically split bell test, after a single extended firing, I had my first heat induced failure. I had a 5cm thick sheet of ytong supended 20ish cm above and just to the side of the heat-riser. The lack of soot deposits in the central part showed that the bottom edge had been in the plume from the riser. There were patterns in the surface that showed there'd been shrinkage and number of surface cracks which went from the bottom (thin) edge towards the hot side of the partition, roughly 5cm apart. One was not just surface. It made a very zig-zag pattern (about 0.5 to 1cm per straight), so the piece didn't fall apart until I moved it, but was certainly all the way through. 2. My heat riser is made from sections, cut in trapezium form to make a 12.5cm (5in) octagon. So far, none of them have failed from heat, or shown any sign of cracking, but if a section falls over then it'll break on landing (even before firing) - ytong is brittle. 3. I've just tortured part of a roughly 10x10x1cm thick offcut - I broke off what was supposed to be half and ended up as a third, and ran a (propane) blow-torch on one side of it, until it was glowing nicely (red-orange). It didn't break, but it did BEND. Permanently. I'd sanded the sample flat before the test and instead of the heated bit sitting flat on its other half there's a very visible bend in the heated portion. I didn't have anything to measure it with, but its at least a millimetre, maybe 2. I can join the cold edge to the unheated portion, and it is clear that the heated edge does not match up any more. 4. I dropped water on a bit that had just been red hot and all it did was fizz at me. So I'd say it's pretty resistant to thermal shock. 5. I know that portland is used as part of some AAC recipies, but I'd say that there's only a trace (if any) left in my samples of 5cm ytong. I'm not seeing any crumbling or turning to powder. It's simply getting smaller. Pyrophile, according to the numbers I've seen, a facing of non-insulating fire bricks is only going to shave off a few tens of degrees, although it's going to protect it from thermal shocks (which it seems it copes with anyway), scratches, and mechanical shocks. It can't cope with those last two well, but I wouldn't want to put 5cm of fire brick anywhere near my hot face anyway - that much thermal mass would surely kill the burn efficiency. So, in conclusion, I'd say that what kills YTONG is significant heat-induced shrinkage.Based on the articles I found earlier, it looks like the manufactures are stretching things a bit by saying it's OK to 1200C, and that while it can cope with getting yellow hot (even white in places), it is NOT unchanged by these temperatures. According the the articles, the temperature that things happen at is around 720C. This is significantly better than portland-based products, and I don't think I'd hesitate to use it where I knew that it'd be staying below that temperature, but I'm not going to use it as hot-face in a masonry stove for my living room. Since the sheets I've been using are 60x20cm, and don't weigh much at all, I'm sure I'd be tempted to use it for a lid, if I had an oven or something that was going to get hit with the direct blast from the heat riser. |
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Post by pyrophile on Apr 21, 2014 7:43:08 GMT -8
Hi!
Well, I don't know what to say...
The last time I used Ytong was yesterday : 5 cm thick is not a lot, it is true, but it did not like heat! Failures appeared.
I don't what changes beetween our experiments but we have different results! As I wrote, I found that failures often appeared when I touched the plates.
I add that I did not use Ytong in heat riser but in different places in different kinds of stoves, including in batch box rocket nerally in protected areas.
Many of my firings can last for hours, maybe is it a reason for failures/shrinkage?
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