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Post by Karl L on Jun 23, 2020 5:37:22 GMT -8
I've been building a DSR2 batch rocket core using Superwool HT board for the heat riser and top box lining.
Superwool is biosoluable, which is why I am using it.
This board was rated at 1300C by the seller. However the datasheet says
Classification Temperature: 1275C
Continous use temperature: 1177C
When I pulled the core out of the bell after the first burn, I noticed that *some* edges of the Superwool board were 'fluffy' and disintegrating. I noticed this on *one* of the two very small pieces to either side of the top box exit port (the piece on the other side was OK!). I didn't notice this kind of damage in the heat riser, even though I've heard this is the hottest part of the system.
Anyone got any experience of using Superwool HT board in a batch rocket or DSR2?
Any one seen this kind of damage?
Thanks!
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Post by Vortex on Jun 23, 2020 8:35:45 GMT -8
The edges of the piece of Fibrefrax duraboard brand CFB I bought a few years ago were so fragile and easily abraded that I ended up wrapping the board in clingfilm until the stove was ready for the first firing. It's done 2 full winters in the stove since and been fine otherwise.
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Post by Karl L on Jun 23, 2020 11:09:31 GMT -8
That's useful information, though I don't know if the boards are made from the same material?
With the board I have, it was only after firing that the disintegration happened.
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Post by Vortex on Jun 24, 2020 1:50:31 GMT -8
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Post by foxtatic on Oct 15, 2020 4:47:43 GMT -8
Wondering if it's anything like the stuff I just tested. Posted a 40 second video of my results here youtu.be/lwmUGAVHQtk and started a new thread about it. Have you continued to use your questionable material with ok results? |
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Post by Vortex on Oct 15, 2020 5:00:18 GMT -8
Yes, just replied in your other thread
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Forsythe
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Post by Forsythe on Oct 2, 2021 8:13:01 GMT -8
I've been building a DSR2 batch rocket core using Superwool HT board for the heat riser and top box lining. Superwool is biosoluable, which is why I am using it. Worth noting that all biosoluble ceramics become increasingly bio-insoluble when heated into the 1100°C range and above. Peter had noted recently that a ceramics supplier had informed him that their ceramic fiber product would convert to cristobalite upon heating to batch box temps… but all ceramics undergo crystal phase changes in this way when heated to the temps we’re using. For those of us using these ceramic products, we should all be aware that the products we’re putting into our stoves are physio-mechanically not the same as the material resulting from being fired at temperature — in exactly the same way that a “green” kaolin clay pot is not the same material once it has been bisque-fired in a low-fire kiln [analogous to new-in-box ceramic wool] — and that same pot is yet another new, different material once it has been glaze-fired in a high-fire kiln to convert it to porcelain. Al203 (alumina) may be biosoluble… but after heating to 1200-1300°C in the presence of fluxing agents like potassium, (from feldspar,) that Al2O3 is now a crystalline matrix including cristobalite, mullite, etc. That’s the nature of firing aluminosilicate-based ceramics at these temperatures. (More on potassium in a sec.) This board was rated at 1300C by the seller. However the datasheet says Classification Temperature: 1275C Continous use temperature: 1177C When I pulled the core out of the bell after the first burn, I noticed that *some* edges of the Superwool board were 'fluffy' and disintegrating. I noticed this on *one* of the two very small pieces to either side of the top box exit port (the piece on the other side was OK!). I didn't notice this kind of damage in the heat riser, even though I've heard this is the hottest part of the system. Anyone got any experience of using Superwool HT board in a batch rocket or DSR2? Any one seen this kind of damage? Thanks! So…that thing I mentioned about potassium (from feldspar) being used to convert Al2O3 Alumina to crystobalite (*and porcelain*)? … one of the principle components of wood ash is potassium. [That’s even where potassium gets its name. “Potassium” or “potash” derived from “pot-ashium” is a caustic alkali that — when mixed with leftover fats in the cooking pot from a woodfire— creates a type of buffered soap that has been used by humans for hundreds if not thousands of years.] That potassium — along with various small amounts of other metal oxides like sodium, etc. — fluxes the surface of ceramics in traditional woodfire pottery kilns — covering the surface of stoneware and porcelain with a glossy, flaky, crystaline phase that woodfire potters call “snot.” It’s desirable on solid stoneware bodies because the surface isn’t porous… but when you have a HIGHLY porous structure like ceramic fiber… the potash/potassium soda-ash/sodium penetrates deeply into the body of the fiber structure, fluxes it, and compromises its structural integrity, creating new and different crystal phases. The shape of the DSR2’s switchback in the direction of combustion gas flow is going to impregnate that top/rear section with a lot more potash —a lot more quickly— than the vertical riser of a traditional batch box rocket (which doesn’t have those sudden 180° bends at such high temperature.) So…if you use ceramic fiber board as the “hot face” in a firebox or short-profile switchback rocketstove (like the DSR-2, vortex stove, or walker riserless core) — then it would probably be best to seal that board with colloidal silica prior to the first firing. That should slow the penetration of wood ash (potassium / sodium / elemental metals in wood combustion byproducts) from infiltrating and compromising the ceramic fiber as quickly. |
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Post by Deleted on Oct 2, 2021 9:30:07 GMT -8
So…that thing I mentioned about potassium (from feldspar) being used to convert Al2O3 Alumina to crystobalite Nonsense. Cristobalite is a high-temperature polymorph of quartz and, in contrast to this, occurs only very rarely in nature. Cristobalite forms at temperatures above 1470 ° C. For this reason, cristobalite is synthetically produced from pure quartz in a rotary kiln at approx. 1,500 ° C for industrial purposes. en.wikipedia.org/wiki/Cristobalite |
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Forsythe
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Post by Forsythe on Oct 2, 2021 11:33:43 GMT -8
So…that thing I mentioned about potassium (from feldspar) being used to convert Al2O3 Alumina to crystobalite Nonsense. Cristobalite is a high-temperature polymorph of quartz and, in contrast to this, occurs only very rarely in nature. Cristobalite forms at temperatures above 1470 ° C. For this reason, cristobalite is synthetically produced from pure quartz in a rotary kiln at approx. 1,500 ° C for industrial purposes. en.wikipedia.org/wiki/Cristobalite Y’know, Karl, this is the second time in as many posts that you’ve been flippantly dismissive of the content I’ve posted and insulting toward my intelligence. It’s also the second time that your contemptuous “correction” of what I’ve said is demonstrably incorrect. Arrogance isn’t a good look on anyone, but you really can’t afford to be both arrogant and wrong — so perhaps it’s time to temper your cocksure condescension with some basic civility and mutual respect towards others in this forum. I only came here to learn and discuss ideas about rocketstove tech amongst fellow experimenters. Can we please keep that focus/attitude? Look at the very same Wikipedia article you linked: imgur.com/QteSB7wOr the research papers I posted in response to your mis-correction the last time: imgur.com/DS8RLICOr just simply Google it. imgur.com/6e3smIS |
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Post by Deleted on Oct 2, 2021 12:26:27 GMT -8
Just take every word exactly as I wrote it and in the same context. |
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Post by peterberg on Oct 2, 2021 12:29:58 GMT -8
My source mentioned that same 800ºC as the starting point for forming christobalite.
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Forsythe
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Post by Forsythe on Oct 2, 2021 14:03:28 GMT -8
Just take every word exactly as I wrote it and in the same context. I’m sorry, but I don’t understand how any context it may have had would be relevant or useful to the discussion, which is regarding aluminosilicate ceramic fiber insulation. Perhaps it lost meaningful context because the snippet you lifted from my post was taken out of it’s own context, which is in regards to aluminosilicate fired hot enough to produce cristobalite… if you read what I wrote in it’s own original context, that’s abundantly clear: Al203 (alumina) may be biosoluble… but after heating to 1200-1300°C in the presence of fluxing agents like potassium, (from feldspar,) that Al2O3 is now a crystalline matrix including cristobalite, mullite, etc. That’s the nature of firing aluminosilicate-based ceramics at these temperatures. (More on potassium in a sec.) So…that thing I mentioned about potassium (from feldspar) being used to convert Al2O3 Alumina to crystobalite (*and porcelain*)? Cristobalite conversion happens to [kaolin] porcelain and [kaowool] alumina ceramic fiber starting at around 800°C (as Peter’s source also stated) and is often completed at around 1100°C or slightly above [*depending on the fluxes present*]….that entire range is within rocketstove temps. The important discussion is that kaolin/kaowool is no longer biosoluble nor medically inert once heated to rocketstove temps, —*especially in the flame path*— because it converts to cristobalite. IMHO, it’s dangerous misinformation to other forum users’ health & safety to call all of that extremely important information “nonsense,” as you say… Why do that? Is it the semantic triviality over the difference between ceramics commonly referred to as “alumina” (which even when “pure” still contain ~ 1% silica) —and “aluminosilicate” — at the expense of people’s well-being who might ignore these material safety warnings because someone purporting to be an expert dismissed them as “nonsense”? …Isn’t that highly irresponsible? It’s the combo of aluminum oxides, silicon oxides, and other metallic elements (potassium, sodium, iron, titanium, etc.) that flux the whole blend into cristobalite here. (Which is only a respiratory health hazard when those crystals are in small enough particulate form to inhale...eg: fiber blanket.) The aluminum oxide is not only intimately intertwined in that aluminosilicate crystal matrix — it’s critical to its formation at the temperatures and chemical compositions which are relevant to the topic of the entire forum. We’re dealing with real-world materials, not a stoichiometric formula or theoretical abstraction. Rocketstoves don’t draw or burn cleanly when they don’t have some form of riser or flue to establish draft, and “alumina” ceramic blanket is made of aluminosilicate, which can easily convert to fine particulate crystobalite once fired in a rocketstove. Those are the practical realities and human health hazards we shouldn’t obfuscate or deny, but rather: educate around and mitigate …in my opinion. |
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Post by Deleted on Oct 2, 2021 15:18:00 GMT -8
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Forsythe
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Post by Forsythe on Oct 2, 2021 17:21:12 GMT -8
Being cryptic isn’t helping anybody, Karl. If you have a point, be very specific in stating it. Otherwise, yes, you’re just spouting nonsense and attempting to smokescreen your unsafe misinformation. The article you linked directly contradicts what you posted earlier, regarding: A) the low formation temperature of crystobalite, and B) the necessity of flux materials for just such low-temp crystobalite formation (Which is exactly the case-in-point we were talking about.) It literally supports all the info I posted above, and comports with the entire premise re: ceramic fiber products’ conversion to crystobalite —regularly— and at rocketstove temps, and in the flux provided by rocketstove flame paths. *Not* exclusively at 1450-1500° degrees, and certainly not “rarely.” (So…thanks for finally acknowledging the truth, albeit indirectly, I guess?) C) It’s also behind a pay-wall, except for the first page. Neat. D) It’s a study about quartz sandstone. We’re talking about kaolin and kaolin aluminosilicates converting to crystobalite, here. …So what *exactly* is your point? What biosoluble aluminosilicate ceramic fiber board is made from pure Pennsylvania sandstone? None. Plain, free-silica is ALREADY a respiratory silicosis hazard. In the context of this thread and its discussion, this paper is an obviously irrelevant red herring. E) It was also published in 1934… There have been a lot more studies with more accurate and detailed information — *on the relevant material: aluminosilicate, specifically that of kaolin* — which have been published in the last 87 years… and which don’t reside behind a paywall… and are relevant to the discussion of ceramic fiber board in the flame path of a rocketstove. |
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Post by Deleted on Oct 3, 2021 4:09:45 GMT -8
Cristobalite forms spontaneously (within bodies) at temperatures above 1100C from very fine quartz found in some clays, from finely ground silica powder and from molecular silica liberated during the formation of mullite from kaolin.
"Mullite forms above 1100°C. It is extremely unlikely that it will ever happen in a rocket stove."
If feldspar is present in the body then any available molecular silica is taken up in the formation of silicates, and thus cristobalite does not form.
Waterglass and other reagents will have the same effect as feldspar.
Red is from a link provided by me.
Other parts of the link explain pretty well.
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