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Post by Marcel on Jan 25, 2013 12:39:25 GMT -8
Has anyone ever tried to make a burn tunnel and riser from porcelain tiles? It seems they are very fire-resistant, you can cut it with a dry diamond blade ( in my case ) and glue it together with refractory cement ( the paste ).
Read on the Internet about a test where they put 500C on one side, and measured only 100C on the other side. The test did not mention higher temperatures, but it seems it could stand MUCH higher temperatures.
I would be tempted to make one, but a double version, tunnel in tunnel, with a mix of perlite and refractory cement in between.
What do you think? …….Any experience?
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Post by brocken on Jun 12, 2013 18:32:20 GMT -8
wondering if anyone has tried this, maybe as a lining inside of a steel pipe/tube?
Dave
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Post by Donkey on Jun 13, 2013 8:05:14 GMT -8
I have not tried it, though I expect that heat shock would break the tiles. Materials like porcelain, even though they can take higher temperatures, tend to be sensitive to very quick temperature changes.
One way to find out for sure: try it in a test model someplace safe and non-permanent first.
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Post by brocken on Jun 13, 2013 13:29:36 GMT -8
Thanks for the info. I also have some 24"X24"X1" fire brick slabs/sheets that came from the inside of a fireplace that I have been thinking of cutting up with a diamond saw for a lining. Guess I'll head to the tile store and see what they think will take the heat the best and give a few a try.
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Post by patamos on Jan 9, 2014 8:04:58 GMT -8
Catching up on older threads here as i explore about core options... Carving up an old kiln shelf would be bomber. I did this last summer for the suspended deck of a rocket beehive black oven. On the down side, cutting it eats up diamond tip blades like all get out.
p
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Post by Marcel on Jun 11, 2015 7:03:29 GMT -8
Finally, after 2.5 years starting this post, I have made my burner of porcelain tiles, see the video. As far as I could see and evaluate, it is not the high temperature that lets the tiles break, as I have heated up a tile in an oven to 550 Celsius. The problem is more too much difference in temperature in the same piece. I had no problems whatsoever in the riser, but the problems occurred in the vertical walls next to the pellet bucket. I measured in the same piece 520 Celsius and 6 inches further only 180 Celsius. No explosion or whatever, it was the same sound as when you break a tile with a tile cutter. Lol….still it was not a nice sound……..
BTW, this is a rather small burner, dimensions burning chamber only 50 x 55 mm.
Cheers
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Post by jallenkaiser on Oct 11, 2020 13:38:08 GMT -8
I know this is an old thread, but I've been wondering A LOT about this topic...
I'm thinking of using much smaller 1-inch hexagonal porcelain tiles in much the same manner: pressing them into castable refractory inside a feed tube and burn tunnel as a hard internal liner, to give a more abrasion-resistant surface to the areas which have wood feedstock sliding against/through them during the burn. (The underlying primary structure of the rocket would be firebrick for the feed tube and burn tunnel, and ceramic board for the riser.)
My theory is that A) the smaller 1" pieces won't have as much temperature variation within each tile as the wider 4"+ square tiles, and B) that the wider-angled (120°) corners of the hexagonal shapes won't crack as easily as the 90°-angled corners of square shapes.
One concern I have, though, is that the porcelain tiles — being more dense than ceramic board or firebrick — might hold heat and cause back-draft once the wood fuel is finished burning... so the solution may be to line the ENTIRE feed-tube, burn-tunnel AND riser with the same porcelain tiling.
I'm also thinking that white porcelain tiles may absorb less IR heat than darker colors (like black) would... so perhaps there would be a thermal advantage to using white porcelain tile in the feed tube and burn tunnel, while using black porcelain tile in the riser liner... the theory being that the darker porcelain of the riser would continue to encourage the draft to flow in the correct direction, even as combustion slows and eventually ends.
I'm curious if anyone else has experimented with porcelain tiles in the feed and burn tunnel this way, so as to save myself the $ and time of experimentation if I can learn from someone else's experience.
The idea was prompted by Erica Wisener's comment that she often will press tile into the floor of the cleanout chamber to let an overzealous cleaner know when they've hit the floor of the chamber, rather than digging through the ash and into the actual structure, continuing to scoop out the soft cob.
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Post by gadget on Oct 25, 2020 22:31:03 GMT -8
I know this is an old thread, but I've been wondering A LOT about this topic... I'm thinking of using much smaller 1-inch hexagonal porcelain tiles in much the same manner: pressing them into castable refractory inside a feed tube and burn tunnel as a hard internal liner, to give a more abrasion-resistant surface to the areas which have wood feedstock sliding against/through them during the burn. (The underlying primary structure of the rocket would be firebrick for the feed tube and burn tunnel, and ceramic board for the riser.) My theory is that A) the smaller 1" pieces won't have as much temperature variation within each tile as the wider 4"+ square tiles, and B) that the wider-angled (120°) corners of the hexagonal shapes won't crack as easily as the 90°-angled corners of square shapes. One concern I have, though, is that the porcelain tiles — being more dense than ceramic board or firebrick — might hold heat and cause back-draft once the wood fuel is finished burning... so the solution may be to line the ENTIRE feed-tube, burn-tunnel AND riser with the same porcelain tiling. I'm also thinking that white porcelain tiles may absorb less IR heat than darker colors (like black) would... so perhaps there would be a thermal advantage to using white porcelain tile in the feed tube and burn tunnel, while using black porcelain tile in the riser liner... the theory being that the darker porcelain of the riser would continue to encourage the draft to flow in the correct direction, even as combustion slows and eventually ends. I'm curious if anyone else has experimented with porcelain tiles in the feed and burn tunnel this way, so as to save myself the $ and time of experimentation if I can learn from someone else's experience. The idea was prompted by Erica Wisener's comment that she often will press tile into the floor of the cleanout chamber to let an overzealous cleaner know when they've hit the floor of the chamber, rather than digging through the ash and into the actual structure, continuing to scoop out the soft cob. Sounds like a cool experiment. One of the biggest challenges for ceramics is the cycling hot to cold and back. The growing and shrinking causes breaks at the point where the crystalline structures bind to each other resulting in breakdown and crumbling. Different problem to the cracking issues. Low expansion ceramics just have higher cycle lives but typically higher prices. Floor tile is probably not low expansion ceramics like you would find in kiln ware which I believe is usually mullite. Then the glaze on the tile will probably have some fluxes in there for color and flow. A dull or low sheen tile may be best. If its easy to repair it could work for a season or two. I will say, I was surprised to learn how hot the first upper tunnel brick gets in RMH's. I have seen mine glowing bright orange many times. Not un common to fuse ash to the upper bricks in the burn tunnel. I tried to use a ceramic pizza tray in a heater once. It cracked the first time i used it. I left it in there and it broken into about 50 small pieces after a while. It was a high grade ceramic not to much different then a kiln shelf. I guess there is to much temperature gradient in wood heaters. Of course I saved it for grog. |
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Forsythe
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Post by Forsythe on Aug 6, 2021 4:31:59 GMT -8
I tried to use a ceramic pizza tray in a heater once. It cracked the first time i used it. I left it in there and it broken into about 50 small pieces after a while. It was a high grade ceramic not to much different then a kiln shelf. I guess there is to much temperature gradient in wood heaters.. Oh, man…I wish I had seen your comment sooner. I literally just bought 8 of these (12x 15x 0.6 inch) cordierite ceramic pizza stones that were “used, like new” from Amazon prime warehouse (approximately half-price at $14 each, so not a HUGE loss, I guess) but I was thinking the cordierite ceramic would hold up specifically because of its resistance to thermal shock. (And I think it was Patamos who mentioned something about cordierite being great for the vortex-type top-shelf)…and…seeing as kiln shelves are often made of cordierite, I thought I was having a stroke of genius. 😅 I guess I’ll take the wet tile saw to one of them and try lining a ceramic fiberboard rocket with it…if it cracks and crumbles, I might be able to use the rest of them downstream in the thermal mass…just not in (or immediately above) the firebox, itself. Gadget, do you happen to remember if your pizza stone was regular ceramic? Or did it it happen to be cordierite like I purchased? the glaze on the tile will probably have some fluxes in there for color and flow. Yeah, my concern with the white porcelain in particular would be that glaze. IIRC, white-glazed porcelain tiles almost always use lead in glaze mix— which normally isn’t an issue for floor and wall tiles because you don’t eat off of them and they never get hot enough to degrade the glaze… but…at the hottest rocket stove temps… you could very possibly end up vaporizing the lead in the glaze and putting it into the exhaust gasses… and the superfine ash that you’ll then risk kicking up when you clean out the system. I could be wrong in my hypothesis there, but…I sure wouldn’t want to risk it with lead, myself. (White porcelain like on the outer skin and after the firebox/riser would be okay, though — that’s what has been used in many, many kachelofen for a few hundred years without degradation to the glaze.) |
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Post by pianomark on Aug 6, 2021 12:49:09 GMT -8
I used a kiln shelf for the ceiling of my batchbox stove, haven't had any problems after two winters. Maybe the pizza stones are too thin? I too once considered using them as a lining inside an insulated firebrick core, but then ended up building my firebox with regular firebrick, with the used kiln shelf as the ceiling (1" thick). Good luck with your build, please report back with your experience.
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Forsythe
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Post by Forsythe on Sept 21, 2021 13:01:41 GMT -8
I used a kiln shelf for the ceiling of my batchbox stove, haven't had any problems after two winters. Maybe the pizza stones are too thin? I suppose I should start my own thread with the info I just learned, but in summary: I just had the privilege of touring a local kaolin facility and speaking with a gentleman who has been using (and air-float refining for commercial sale) a high-alumina kaolin clay since the 1970s. He’s a potter by trade, but produces **all** of his own equipment — including both the machinery of the plant AND his refractory materials like firebrick, kiln shelves, etc… (the man is a polymath and I couldn’t take notes fast enough…but what I learned was outstanding.) His kiln shelves are the same thicknesses as most pizza stones (between 0.60 inches, and 0.75 inches thick, respectively) They are produced from this local calcined kaolin (heated to approx 800°C / 1450°F.) That calcining temperature breaks the tetrahedral structure of kaolin’s aluminosilicate, freeing the Si and Al to react in new crystaline phases (making it “metakaolin”) He then adds either calcined kyanite or pre-purchased mullite — **synthethized mullite being the calcined form of kyanite itself**— and rolls the metakaolin/mullite mix into slabs and fires those to vitrifying temps. Kyanite (and it’s precursor mullite) contain magnesium — and react with the metakaolin to produce increasingly long mullite / kyanite needles throughout the slab…turning it to cordierite. He noted that some people complain about the thin shelves warping/sagging and eventually cracking — but that this is due to the incomplete conversion and evolution of mullite/kyanite crystals — and that every time the newly produced cordierite is re-fired, the crystal structure grows stronger and more interlocked. …and if the slabs were made too thickly, then the crystal propagation would actually take too long in the slab’s center…which makes it a weak spot prone to sagging and then cracking. As for any incomplete mullite/kyanite in early firings: he simply keeps an eye on the new kiln shelves and flips them over if they show signs of bending — a few subsequent firings will typically straighten the slab back out AND produce more crystal propagation, making the slab stronger until there is no more sagging. (He pulled a homebrew cordierite slab out of one of his kilns to show me how flat and straight it was — “flip it over and take a look at the date stamp when I made that” he said. …1978. That flawless cordierite shelf was 0.75 inches thick and has been fired in a natural gas kiln at least every two days — for almost 45 years straight! Another reason for making cordierite relatively thin: it’s a crystal matrix, and, (even though it has an extremely low overall coefficient of thermal expansion) — will do any minute expansion *in only one direction*. …thus a thicker slab of cordierite will have a higher risk of their crystal matrices un-aligned…and they’ll pull against each other on thermal expansion, potentially leading to crack propagation. So the TLDR: thinner cordierite is actually stronger than thicker cordierite, and it typically only gets stronger the more times it’s fired. Oh, and a bonus tidbit: he highly recommended a book called “Ceramic Science for the Potter” which is filled with recipes for many kinds of clay-based refractories — including this recipe and a similar one [making use of talc instead of mullite or calcined kyanite. Talc is both a vitrifying flux AND a source of magnesium used to grow the mullite / kyanite crystals in the clay body upon firing.] I’ve just purchased that book (currently out of print but I found a used copy on Abe Books for $30) and 1200lbs of raw kaolin from him (which he practically GAVE me free… less than a penny per pound.) along with a lot more tips, advice and encouragement in my grundofen project. I’ll be sure to start a new thread shortly with what I try, learn, and make. |
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Post by Deleted on Sept 27, 2021 7:18:28 GMT -8
Kyanite (and it’s precursor mullite) contain magnesium — and react with the metakaolin to produce increasingly long mullite / kyanite needles throughout the slab…turning it to cordierite. Wrong. webmineral.com/data/Kyanite.shtml
Cordierite ceramics were prepared by using talc, alumina and kaolin clay as starting materials.
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Forsythe
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Post by Forsythe on Sept 28, 2021 8:35:17 GMT -8
Like I said— I couldn’t take notes fast enough… and I’m still waiting on the book I ordered to be delivered. But I have been reading quite a bit of research on this online since I made this post. Turns out I was partially wrong and partially right, and — hate to tell you this, Karl— but you are partially wrong, too. What I was wrong about was what contained the magnesium. But his recipe DID use kyanite for the mullite, with a secondary source of magnesium — and it was NOT talc. Cordierite ceramics were prepared by using talc, alumina and kaolin clay as starting materials. The research clearly shows that starting with a high mullite content increases the formation of cordierite both in quantity and in breadth of firing range [before the Al203 starts converting to the much-less-reactive corundum], that kyanite is a great source of existing mullite, and that talc is not the only source of magnesium used to make cordierite. Furthermore, Kyanite, mullite, and kaolin are all sources of alumina — in the form of aluminosilicate, to be exact. Talc is only an okay-ish source for the magnesium component, but talc is magnesium PLUS much more silica — which lowers the overall sintering temperature and thus it’s working temperature range. (The extra silica acts as flux, reducing the refractoriness.) …and in order to get the Al2O3 content back into the optimal range again [if you’re starting with kaolin, which is only 37-42ish% Al2O3 to begin with,] then, yeah, you have to add more alumina…from somewhere… …but if you source your magnesium component from something *other than talc*, then you avoid poisoning the composition’s Al/Si ratio with all that extra silica. Regarding Cordierite’s composition: “The ideal chemistry to produce the crystals is 13.8% MgO, 34.8% Al2O3 and 51.4% SiO2 (2MgO, 2Al2O3, 5SiO2). Talc, kaolin and raw alumina powder can be blended to produce this chemistry (**other materials are also used e.g. aluminum hydroxide, steatite and other MgO minerals**).” www.scientific.net/MSF.509.199“Thermal Analysis and Evolution of Phases during the Synthesis of Cordierite with Kyanite and Talc” www.osti.gov/servlets/purl/6757432“…Kyanite converts to acicular mullite more readily, and at lower temperatures, even though it has a lower alumina/silica ratio…” www.researchgate.net/publication/238367895_Fabrication_of_cordierite_powder_from_magnesium-aluminum_hydroxide_and_sodium_silicate_Its_characteristics_and_sinteringceramics.onlinelibrary.wiley.com/doi/abs/10.1111/j.1151-2916.1998.tb02442.x“Synthesis and Sintering of Cordierite from Ultrafine Particles of Magnesium Hydroxide and Kaolinite” www.scientific.net/AMR.412.73Low-Temperature Combustion Synthesis of Cordierite Powder and its Characteristic link.springer.com/article/10.1007%2FBF02767899Change in the phase composition of corundum-mullite-cordierite refractories under heat treatment www.hindawi.com/journals/amse/2021/6678297/Effect of Particle Size and Sintering Temperature on the Formation of Mullite from Kyanite and Aluminum Mixtures www.minsocam.org/ammin/AM47/AM47_1273.pdf“Phase Transformations in silica-alumina-magnesia mixtures as examined by continuous X-ray diffraction” …so, *yes*, he did use kyanite, and *no* he did not use talc, (because that would have lowered the alumina content with too much silica, necessitating even more alumina additions to keep from fluxing the whole blend below its useful refractoriness.) …and I’ve also learned in much of this reading that there is indeed a difference between pizza stone cordierite and kiln shelf cordierite— all dependent upon the other impurities and fluxes involved in bringing about the glassy phase between mullite, spinel, protoenstatite, and cristobalite that react in crystallizing cordierite — either in transition or upon cooling. It’s totally conceivable that a pizza-stone cordierite could fail in the firebox of a rocketstove if it was made with a low-temp sintering composition, highly fluxed with silica (talc) and/or other oxides. THOSE cordierites can form a glassy phase as low as 1000°C… whereas kiln shelf formulations starting from mullite (as in this kyanite mix) can form closer to 1300-1400°C) |
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Post by gadget on Sept 29, 2021 13:44:13 GMT -8
I suspect allot of the pizza trays are not true cordierite or a lower grade and this could be some of the problem. I have some real Cordierite diffuser panels from a large gas heater I took apart and they are pretty durable and definitely have that yellow off white color.
Still makes a good grog if it fails
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