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Comment by tomatotomato37 | Hacker News Reader

I'm curious what the thermal management system on this looks like. On one hand, vacuum being in essence a perfect insulator works in favor of keeping the silicon hot for the very long time it takes to pull a boule while requiring very little energy. On the other hand, you have to make sure the control electronics don't also heat up to 1000C. I'm also curious how you keep the molten silion separate from the crystal without gravity keeping it in the crucible. I bet a lot of interesting engineering going on here.

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Vacuum is only a nearly perfect insulator until a few hundred °C. After that, radiation dominates over every other form of heat exchange, and it stops making any difference.

A couple of meters long steel rod with a dissipator on the end can easily keep electronics at Earth surface temperatures even if you heat the other end to 1000°C.

The air on earth is taking the heat from the dissipators more than blackbody radiation.

Something like a vacuum flask, I imagine. Vacuum is a very good insulator already and you minimise radiative heat transfer (infrared glow) by making a surface shiny and metallic usually (low emissivity)

If you have to bring your own vacuum flask, don't you lose half the benefit of doing it in space?

Isn't the primary benefit the lack of gravity?

You can reduce metals through vacuum pyrolysis at much lower temperatures without a reducing agent if you have a vacuum. This could make industrial scale processing of steel relatively easy on the moon.

Reducing ferric oxide to magnetite, perhaps, but I think if you tried that with ferrous oxide you'd get iron vapor coming off along with the oxygen.

An issue with any high temperature process is things start evaporating. This is part of why carbothermal reduction of aluminum oxide doesn't work: at the required temperature aluminum oxide is volatile.

(There are thermochemical water splitting technologies that exploit partially reducing transition or rare earth oxides at high temperature, then reacting them with steam at a bit lower temperature to make hydrogen. I believe cerium oxides are the current best approach there, although still not competitive.)

I imagine you just need the flask part, the vacuum is rather easy in space.

Good electrical conductors are also good thermal conductors. It's a fun system challenge to minimize what needs to be hot, but some things will have to get hot. It could be reduced to a photodiode, transistor, and a relay.

But how do you get the power to the heater in a compact way?

Diamond is my favorite exception to this, one of the best thermal conductor and insulators.

Boron nitride too. I guess the thermal vibrations transmit well through a stiff microstructure.

One notable exception to this is superconductors. One might naively think that because superconductors have zero electrical resistance, they also have zero thermal resistance. But this is wrong (sorry, Larry Niven)! The superconducting charge carriers (Cooper Pairs) have zero entropy, so they can't carry heat. Thermal conductivity of a superconducting material drops when it becomes superconductive.

I believe high Tc superconductors have been used (or at least proposed to be used) as current leads for carrying current into low Tc superconductors from somewhat higher temperature normal conductors.

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