No. The thing that make the shuttle tiles so great as shuttle tiles is that their rate of heat transfer is very, very small. You can heat one up to a very high temperature but then can hold it in your hand because it is such a good thermal insulator (I remember someone demonstrating this on TV in the early days of the shuttle).
If you got a bunch of them really hot they would hold the heat for a very long time. They would also release it so slowly that they would make very poor tent heaters. Your tent will undoubtedly be releasing heat faster to the environment around it than the tiles will be releasing it into your tent.
You can, however, use rocks and bricks as heaters. You have to be careful because some types of rocks fracture (even “explode”) when heated, but for a long time people have heated rocks in fires and used them to boil liquids (you put the hot rocks in a pot or bag of water/broth), heat up bed clothes, and re-radiate heat, such as the rocks/bricks of a fireplace radiating heat for awhile after the fire goes out.
It doesn’t need to be high tech ceramic; we do sweat lodges with hot stones from the fire. But watch that it doesn’t touch any part of your tent and be very certain it won’t tip over. Better yet, use a teepee or yurt with no ground cloth or with a hearth cutout. Failing that, a coffee can filled with smaller hot stones and placed on a couple of two by fours works. Again, don’t let it fall over or you’ll melt a hole in your tent.
In college, I actually messed around with the black shuttle tiles (technically called High-temperature reusable surface insulation). During an open house exhibit, I’d light up an acetylene torch and heat the black surface up to about 1100° C while holding the back of the tile with my hand* After the demo ended, the black surface would cool to the touch in about a minute.
I repeated this heat treatment about 40 to 50 times that day, and the back, along with the sides of the tile never got warm.
Hairline cracks started developing on the black surface, but never did open up to expose the white surface. Someone later did crack a small part of the tile and hit with the torch. It promptly melted the black material into a heavily glazed crater. You would expect that, however, because the white silica is such a poor conductor of heat.
The tiles were remarkable in that the white portion not only looked like Styrofoam, but even felt and weighed like Styrofoam. The only clue that told you it wasn’t was the white portion of tile was slightly friable with a gritty feel. And a good wallop with a pencil could crack the black surface which is user_hostile rated at being about the same strength as an eggshell.
It’s remarkable how these delicate hunks of highly refined sand survived the rigors of the whole launch campaign over and over again.
One thing I didn’t realize till now: since the white silica was 90% void, that meant the tile had to “out-gas” all of the trapped air during launch. If the air were to remain entrained it would ruptured the tile trying to escape.
*In retrospect, the only safety gear I had on hand was fire extinguisher. No gloves, no safety glasses, nothing; that was the young and stupid thing to do in those days).
These statements of slow release of heat don’t make sense to me.
Sounds to me like these things essentially shed heat, and release what little they absorb very quickly.
I’d say the energy went into the surroundings, about the same as if you held the burning torch with it touching nothing.
Am I missing something here? Are you guys saying the heat gets “trapped” in the interior of the tile? If so, if a tile was heated significantly, then held in one’s hand a minute later, would breaking open the tile yield a very hot substance?
I’m exhausted, so my answer is likely to suffer a lot of poor grammar.
The tiles do absorb heat, just not very much. Think about what it would mean if they did.
And there are two parts to the surroundings: 1) The Shuttle Tile and 2) everything else. Most of the heat radiated as infrared into everything else. The residual heat migrated through the tile.
90% of tile is empty space. Think of it as holding a piece of very exotic fiberglass insulation.
Back in the 80’s, there was film demonstrating how the silica (white portion) of a Shuttle was heated up till the brick glowed yellow. Then they’d pull it out with a pair of tongs. A few seconds later, someone would pick up the tile on the edges* with their bare fingers–the middle still glowing yellow in the middle.
There are two effects working against each other here. The poor heat capacity means that it will cool rapidly because it can’t hold much heat. Think about a chocolate chip cookie out of the oven. You can eat the now cooked “dough” without too much pain because it has low heat-capacity, but once you bite into a “chip” and hear your tongue sizzling, you’ve now just experienced “high” heat capacity. Conversely, it will take for the chip to cool down to the same temperature as the dough, because the thermal conductivity of the cookie “dough” isn’t all that great. Same with a Shuttle Tile, but without the chocolate chips. Once the Shuttle lands, I’ve been told, the inner surfaces of Space Shuttle actually rise a few degrees on the ground after landing, because the re-entry thermal pulse is finally migrated all the way through.
*You didn’t grab the middle of the tile, it was still freaking hot.
I saw a demo showing how the shuttle tiles were cut to shape. One of the things done on the video was to heat the tile in a furnace at an extremely high temperature for a long time (16h IIRC) – long enough to equilibriate.
When removed from the furnace the tile had a soft orange glow. Within 60 seconds the corners and edges looked white and the tile could be picked up with bare fingers. The temperature inside was still freakishly hot. Just due to the poor thermal conductivity that heat had a difficult time escaping. Like any hot object with a high thermal conductivity, a very steep thermal gradient was achieved – there existed a huge temperature difference between two points only millimetres apart. The net result is that you had a lot of heat energy trapped inside the tile. That heat energy took its time to conduct to the edge. The edge wasn’t radiating heat quickly because the surface temperature was so low. This is the opposite of what you want in a radiating heater.
In addition, the total thermal capacity of the tile is pretty small. This is for two reasons.
The material has a low heat capacity. That is, a small number of Joules of energy per kg of material per degree of temperature.
The material is not dense. This means that the mass is low. Energy contained is proportional to mass and so there isn’t a whole lot there.
If you want a material that can absorb heat energy and radiate it off in a tent, then you could do a lot worse than a hot billy of water.
Water has a heat capacity much greater than metals and roughly 10 times greater than rocks.
The rate of heat transfer can be controlled through stirring and transfer to different shaped vessels to control the surface area.
You are limited to a ceiling of 100°C for water and so your temperature differential is not going to be the same as a 400° rock. This limits the radiant energy output. However there is an advantage to this from a safety and handling point of view. I am not sure I want anything that hot in my tent.
You don’t need to cart the water around with you from one location to another. It can be sourced from your campsite. I haven’t had the same experience with shuttle tiles.
So, in short, you probably want to go low-tech not high tech on this one. A hot water bottle would be better for your purpose than a shuttle tile.
Come to think of it, if you’re camping, you can probably just get a few solar showers and wrap them in your sleeping bags, packs, or clothes. They’re lightweight and cheap. Fill them up with water, let them sit in the sun, and at night you can carry them into your tent and they’ll slowly release their heat over the next few hours if you insulate them well with your gear.
In the Army we would take a 32 gal trash can with an immersion heater and fill with sand. Then top off with water. Light the heater and boil off the water. The hot sand would stay hot for hours. With no need for a fire guard. You could try a #10 can of fine sand and boil off water. It should stay hot for an hour or so.