A Nuclear Probe to Explore Earth’s Interior • Hacker News Board

Re: A Nuclear Probe to Explore Earth’s Interior

#41

Post by ridgeguy » Wed, Jul 30, 2014, 4:03 AM UTC

The post states that tungsten "...has a low corrosion rate at elevated temperatures." This is not accurate.

Tungsten oxidizes in air beginning around 600°C and as the temperature increases, the tungsten oxide layer scales off, exposing underlying metal to further oxidation. (see, for example, http://labfus.ciemat.es/AR/2011/C_004/AM_4x.pdf)

Tungsten is great for high temperature use in vacuum, neutral (the inert gases) or reducing environments (hydrogen, for example). You can use it nearly up to its melting point in those conditions if you aren't too dependent on structural integrity.

In oxidizing environments (air, oxygen, water, halogens, silicates, etc.) it fails quite rapidly. Molten rock is replete with chemical species that react with tungsten at elevated temperatures.

At 2000°C, the tungsten blanket covering the Co60 heat source would be corroded away, I'll guess, within a week of launch on its journey to the center of the earth.

Although it would be incredibly costly, they might have better luck with iridium or rhenium.

Nevertheless, a fun mission to think about.

Re: A Nuclear Probe to Explore Earth’s Interior

#42

Post by BorisMelnik » Wed, Jul 30, 2014, 4:19 AM UTC

if they get to the center they will find the gnomes, which won't end well.

Re: A Nuclear Probe to Explore Earth’s Interior

#43

Post by gulpahum » Wed, Jul 30, 2014, 4:37 AM UTC

This sounds like a controlled version of the China syndrome. http://en.wikipedia.org/wiki/Nuclear_meltdown#China_Syndrome

Re: A Nuclear Probe to Explore Earth’s Interior

#44

Post by Natsu » Wed, Jul 30, 2014, 4:43 AM UTC

ridgeguy wrote: post #41

The post states that tungsten "...has a low corrosion rate at elevated temperatures." This is not accurate. Tungsten oxidizes in air beginning around 600°C and as the temperature increases, the tungsten oxide layer scales off, exposing underlying metal to further oxidation. (see, for example, http://labfus.ciemat.es/AR/2011/C_004/AM_4x.pdf ) Tungsten is great for high temperature use in vacuum, neutral (the inert gas…

> A self-sinking probe is basically a dumb probe measuring less than 100 cm in diameter - a lump of nuclear waste encapsulated in a tungsten sphere and sunk into the ground.

Even more so if you wonder if it couldn't be a way to dispose of waste. Also, if corrosion was an issue, perhaps they could coat it with something?

Re: A Nuclear Probe to Explore Earth’s Interior

#45

Post by privong » Wed, Jul 30, 2014, 4:45 AM UTC

TallGuyShort wrote: post #40

toomuchtodo wrote: post #18

Earlier quoted context omitted.

Increase in density as you get closer to the core.

On top of which gravity is going to lessen as you get to the center of mass, so even a little resistance will eventually become extremely significant...

Only 100 km down, the gravitational acceleration would not be reduced by very much. Assuming the Earth is spherical and has uniform density, the probe would only be below ~3% of the mass and would be less than 2% closer in distance. So the acceleration felt by the probe would only vary by a few percent.

Re: A Nuclear Probe to Explore Earth’s Interior

#46

Post by RachelF » Wed, Jul 30, 2014, 4:53 AM UTC

bediger4000 wrote: post #35

A Caltech professor, David Stevenson, proposed a temperature-resistant probe immersed in a blob of molten iron: Stevenson, David J. Mission to Earth's Core - A Modest Proposal. Nature, 423, 239-240, 2003a. No radioactivity necessary, and the PDF is here: http://mathcs.albion.edu/~mbollman/Honors/ToTheCore!.pdf

What prevents it from cooling down?

Re: A Nuclear Probe to Explore Earth’s Interior

#47

Post by msds » Wed, Jul 30, 2014, 4:59 AM UTC

ISL wrote: post #15

Crito wrote: post #12

Earlier quoted context omitted.

I imagine the safe way of deploying the thing would be to assemble it on-site, over the bore hole, robotically. Don't have any humans anywhere near the entire operation as long as all of that cobalt is in the same place (deliver it to the site with several delivery missions, each only having a relatively safe amount of cobalt). (Apparently the cobalt would be inserted into the tungsten sphere as a not-yet-liquid sphe…

Tungsten is usually sintered with a binder. I'm unaware of any welding techniques that work with it. For a similar fabrication job, check out the LARES satellite (which is awesome, elegant, and the densest free-falling object in the Solar System): http://www.esa.int/Our_Activities/Launchers/Launch_vehicles/...

Laser, electron-beam and atomic-hydrogen (no, not crackpot-conspiracy-theory "HHO" atomic hydrogen) welding can work with tungsten, in theory...

Re: A Nuclear Probe to Explore Earth’s Interior

#48

Post by entangledqubit » Wed, Jul 30, 2014, 5:47 AM UTC

A patent for a similar device from back in the 60s: http://www.google.com/patents/US3115194

Happened to see it while archiving the inventor's papers. :)

Re: A Nuclear Probe to Explore Earth’s Interior

#49

Post by spingsprong » Wed, Jul 30, 2014, 5:58 AM UTC

Would this produce a new volcano?

Or would the magma just freeze as it travels through the relatively cool hole?

Re: A Nuclear Probe to Explore Earth’s Interior

#50

Post by youaredoomed » Wed, Jul 30, 2014, 6:03 AM UTC

Why not place the sphere into a pre-made hole so it will make it to the center of the planet faster?