I tried looking for this in a couple of places, but when it comes to asbestos, it seems that all anyone wants to talk about is how nasty the stuff is and that it’ll kill you. I want to know how it compares to modern stuff like kaowool, fiberglass, aerogels, and others in terms of things like R-value, melt point, etc.
What is being used today is more expensive to get the same R value, have more bulk, have a much lower melting point, takes more reenforcement.
Uh, aerogel, while more expensive than asbestos, is the best insulation known because of its low thermal transfer rate and has a melting point more than double of asbestos. I would suspect kaowool does as well, seeing as how its used to insulate furnaces operating at 1800+ degrees and asbestos begins to melt at 1400 degrees.
I would have a hard time believing asbestos uper limit is a low as 1400. That would make it hard to use in a steam engine room or working with Iron. But I will admit it has a long time since I have opened a text book
Wiki lists thermal decomposition for asbestos beginning at 1000C, which translates to just over 1800F. The furnances I worked with routinely ran at over 1800F (IIRC, we got them as high as 2400F with some regularity).
Generally, boilers had a blanket of steel around the asbestos, shielding it from the direct effect of the flame source, this would reduce (admittedly only very slightly) the amount of heat the asbestos was exposed to. The lack of oxygen in the environment would also slow down many potential chemical reactions that would be expected to occur in a high heat environment.
If by asbestos we mean chrysotile asbestos, it’s got a jellyroll construction, a flat sheet of multiple layers that then rolls up into a fiber. There is something about the chemistry of this that makes it very stable inside the lungs, so it doesn’t dissolve, and it remains an irritant and a pathway for cigarette smoke toxins to penetrate more deeply in one spot for many years. This makes it especially hazardous.
I think there are rock wools and ceramic fibers and other manmade refractory fibers for many of the things they use asbestos for.
Asbestos is also pretty good as a filter aid. You mix it with the stuff you want to filter, and it makes the filter cake remain more porous so the filter doesn’t plug so quickly. In applications like the filtration of fruit juices, where the slimy cake that results from all the broken cell walls tends to plug the filter, this is a big help. Then you can feet the asbestos to cattle, who get the fruit juice solids out of it. Apparently eating the stuff by the bucketfull doesn’t do them any harm. Of course, if you are trying to feed cattle, you’re probably not going to give them 30 years to develop cancer.
The problem with asbestos is the unit crystal size. The fibrous structure of the mineral (good for weaving into curtains and blankets) can break down into smaller and smaller peices, until you get to the smallest single crystal. This crystal is too small to be expelled by the lungs (coughed up), but too large to be absorbed. The result is that it stays in the lung, irritating the tissue, causing abnormal growth and the big “C”.
You can get the same effect with a certain particle size of silica or talc. It’s all abou tthe particle size. Asbestos itself is a miracle material…woven rock. Fabulous. Eat all you want, just don’t breathe it.
Ceramic Engineer RU '87.5
Uh, folks, I know asbestos is bad for you. I am not at all concerned about the health efffects of the stuff because I have no intention of playing with it. As I stated in my OP, I’m interested in things like how its R-value, melt ponts, etc. compares with modern materials used as insulation in high heat environments.
Shame this didn’t get more responses. Since I’ve been reading a bit of alternate history lately I’d be very interested to know if your standard time traveller magically transported back to the 1930s would be better off encouraging investment in fiberglass technology, or just telling everyone to wear good-quality boilersuits and respirators and make sure they wrap that shit up TIGHT. And discouraging smoking, obviously.
Its so bizarre. Quite literally everything I can find about asbestos is obsessed with how dangerous the stuff is, which is pretty well known. Russia and China still produce and use the crap, so the data on its R-value is out there, but I don’t speak either language, so I can’t go digging on sites that might have it which aren’t in English. Its like looking for information on the puffer fish and being told solely that its toxic, with no real mention of it being eaten in Japan!
I tried the search term “Thermal Conductivity of Asbestos” and got this page for the 1st hit. After a few unit conversions, I came up with an R-value for asbestos mill board of 12.4 per inch of thickness. Loose packed asbestos came in at 11.8 per inch.
Googling “Physical Properties of Asbestos” got me to this site (Warning-pdf) where I learned about all 6 types of asbestos. The melting point of asbestos ranges from 1100 °F to 1900 °F.
I think you must have dropped a decimal some place, as according to your first link, cotton has a lower thermal conductivity than asbestos, which would make it a better insulator (for things like houses, of course, and not high heat applications). Were that the case, I’d think that older houses (when they weren’t so concerned about things like fire prevention) would be more likely to have cotton insulation than asbestos.
Here’s the wiki page for insulation R-values, as you can see, the R-11 figure puts asbestos above everything save vacuum insulated panels. Now, I can believe that asbestos beats everything, save aerogels, but for it to be better than aerogels seems unlikely to me. Given our recent uptick in energy costs, and worries about global warming, if asbestos was truly double the R-value of most common forms of insulation, I’d think that there’d be a serious push to find ways to make the stuff safe and useable.
Using the Wiki factors would put asbestos at ~ R-1.4, and cotton would be better, but it is really flammable and asbestos is not flammable at all.
You can buy cotton insulation for housing today (often made from recycled denim), so it is an attractive insulation option. In the old days I can believe that it would also have been unpopular because of problems with it rotting when damp, and probable infestation with various celluloseophagic* critters.
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- I just made that up, but hopefully you know what I mean.
Almost any modern insulation is better than asbestos.
According to the link referenced above, asbestos is a worse insulator than Glass wool, Felt, Cork, Chalk, and Paper, and much worse than expanded Polystyrene.