Got to thinking about this last week… can we build a machine that will operate at red-hot (or yellow-hot) temperatures? I gather that conventional combustion wouldn’t work, because everything would be hot, and the fire wouldn’t be contained, but would pure mechanical parts like gears and struts work? What about electronics? How viscous is lava?
Aside from thermal considerations, if it’s going to be actually immersed in lava, it has to not react chemically with molten silica. My guess would be that iridium would be a good material to start with.
I try not to respond to GQ with inanities. But I have to say, I mis-read the thread title and thought the OP was asking, “Can we build a machine that will function in Iowa?” And I was all, “What’s wrong with Iowa?”
Carry on.
It’s a legit engineering question, IMO.
The melting point of platinum is 1768.3 °C which is well above the temperature of lava. It comes down to what it would do I guess and how long would it last. There have to be other materials that can take the heat too.
Is my comment that confusing? It seems pretty clear to me that I am the one posting the inanity! Not the OP.
A “subterrane,” up lavascope.
Are there any lava flows that go from the surface to depths lower than Challenger Deep?
It seems that you’d need a good insulator, whatever you want the thing to do. I know Aerogel is a good insulator.
IIRC, there are ceramics that can withstand >2000K. Tungsten melts at 3695K. So I think you can make mechanisms out of these.
Tungsten is conductive, so you can use electricity. I think you can even make motors and solenoids.
As for electronics, maybe vacuum tubes can be made to operate at these temperatures? I don’t think any semiconductor works at such temperatures, not even diamond.
Of course, if you don’t need it to operate in lava indefinitely, all you need is good insulation and a large mass to act as a heat (cold) reservoir. A phase-change material would be best (e.g. a block of ice).
I dunno - you ever been to Iowa? 
We’re talking 2000 degree F which is about twice the temperature of Venus. The Soviets sent some probes to Venus and they didnt last long in the heat. Venera-9 was able for function for an hour before the heat broke it.
I really dont think you can make a usable machine that will function in lava. Perhaps some kind of mechanically powered novelty, but not much more.
The difference between Venera and this theoretical machine is that this machine doesn’t have to meet the weight and power requirements to fit on a spacecraft.
Of course, these sorts of questions are always too open-ended to answer. I envision some sort of submersible drilling rig. Power/coolant conduits to the surface would work, and the internals could be cooled by an external coolant source. What requirements would this machine have to have?
You’re going to have to keep the surface of the machine (and those conduits) above the temperature at which lava congeals.
What about insulators?
Hmm. Electric motors, relays and electromechanical parts, gears and bearings… is there anything like a lubricant that would work at these temperatures, or would it be roller-bearings only?
No, no, I want it to operate indefinitely at a nice yellow-hot (or whatever lava is) temperature. It shouldn’t need insulation.
I suppose that the ‘operate immersed in lava’ might be a second-stage requirement.
I thought we did this. I seem to recall a thread from 6-7 years ago about a real life probe someone was trying to build or had built to dig into the Earth’s mantle. Could have been a dream, let me do some searching…
Would a active cooling (refrigeration) system be OK, where heat from the core was ‘pumped’ to the outside and transferred to the lava so the heart of the machine and for that matter the energy storage that is used can be at a lower temperature? That would also solve the problem of the device being encased in rock.
For refrigeration to work the system needs to be able to radiate it’s stored up heat into the outside environment. Heat transfers from the higher temperature coolant or heatsink into the lower temperature air or water, thus cooling the system. In this case though, the outside environment is lava which is so much hotter than anything the machine will be producing that the heat transfer would go the wrong way. Instead of radiating heat your coolant or heatsink will absorb it and make your problem even worse.
Her comment isn’t to be read:
Respond to GQ-with-inanities.
It is to be read (moving the words around a little):
respond with inanities to GQ.