0
$\begingroup$

The question is obviously outlandish, but I'm curious about the napkin-math involved in estimating this. I don't know much material science and seems like an interesting exercise.

If I could carve a cannon out of a giant diamond, how much pressure could it resist before breaking?

To quote Wikipedia:

Used in so-called diamond anvil experiments to create high-pressure environments, diamonds are able to withstand crushing pressures in excess of 600 gigapascals (6 million atmospheres).[17]

I'm assuming the larger the diamond the more pressure it could take. So it seems like a reasonable starting point is to work out how much radial pressure a semi-hollow diamond sphere of radius $R$ and thickness $T$ before it explodes/cracks. But of course, like a balloon, adding a small hole will change the pressure distribution and cause it to shatter --so maybe there is a better model for this type of thing?

Improve this question
$\endgroup$
6
  • $\begingroup$ Pressure is not the whole of what comes out of a nuclear weapon. Taking pressure is not the whole of what a gun barrel must withstand even in a more mundane gun. $\endgroup$
    – Dan
    Commented Jan 6, 2022 at 22:35
  • $\begingroup$ @Dan, what else must a mundane gun need to take? Does heat matter on that time scale? $\endgroup$
    – Steven Sagona
    Commented Jan 6, 2022 at 22:36
  • 1
    $\begingroup$ Bigger is not better when it comes to brittle failure... $\endgroup$
    – Jon Custer
    Commented Jan 6, 2022 at 22:50
  • $\begingroup$ Diamonds are hard, but hard is not the same as being tough and absorbing a lot of energy. A diamond baseball bat would be very easy to break compared to a wood baseball bat. $\endgroup$
    – DKNguyen
    Commented Jan 6, 2022 at 23:04
  • $\begingroup$ @DKNguyen, am I incorrect in thinking that a solid diamond would be the best material to not crack when receiving a large force? $\endgroup$
    – Steven Sagona
    Commented Jan 6, 2022 at 23:06

2 Answers 2

Reset to default
7
$\begingroup$

Gunpowder generates a huge volume of gas when it burns, and the gas is what propels the projectile out of the tube.

A nuclear weapon is different. If you detonated a nuclear weapon out in the vacuum of space, the explosion would be very small as compared to when you detonate it in the atmosphere. That's because all a nuclear weapon does is, it gets really hot really fast.

You've heard of "red hot." You've heard of "white hot." A nuclear weapon gets "X-Ray hot." If you want to destroy a city using a nuclear weapon, what you do is explode the weapon in the air, maybe a mile up. (Optimum height probably depends on the size of the weapon.) The X-rays from the weapon are absorbed by the surrounding air, heating the air to white heat, and causing an enormous pulse in pressure. The white-hot expanding blast of air is the "nuclear fireball" that causes all of the structural damage to targets on the ground below.

You don't get that if you trigger the weapon in an enclosed space (e.g., in underground nuclear tests.)

Improve this answer
$\endgroup$
7
  • $\begingroup$ Not that being in outer space is going to help you survive the explosion - there is still lots of energy coming out which will impact you (literally and figuratively). $\endgroup$
    – Jon Custer
    Commented Jan 6, 2022 at 22:49
  • $\begingroup$ @JonCuster, I almost was going to add that if you tried to put a nuke in a gun barrel behind a projectile, then both the projectile and the gun barrel would be turned to plasma within microseconds. No point in asking whether the barrel would "crack!!" So, yeah. Same thing would happen to an astronaut who was sitting too close to a nuclear "explosion" in outer space. Further out, the astronaut would merely be roasted, inside and out. Further still, and the astronaut might survive the heat effects, but die a few days later from the massive X-Ray dose. $\endgroup$
    – Solomon Slow
    Commented Jan 6, 2022 at 22:58
  • $\begingroup$ Don't forget the neutrons! $\endgroup$
    – Jon Custer
    Commented Jan 6, 2022 at 22:58
  • $\begingroup$ @SolomonSlow, thanks for the very helpful answer. I didn't realize that the explosions force is mostly a spherical "pressure-pulse" of air being pushed out due to high temperatures at the center. But, if the cannon had air in it, wouldn't it effectively be the same thing? I think the comments answer this part: the increased temperature would cause the diamonds to basically melt before the air could propel out the bullet. $\endgroup$
    – Steven Sagona
    Commented Jan 6, 2022 at 23:10
  • $\begingroup$ @SolomonSlow, but if there's air in it, will the radiation from the nuke actually reach the diamond before getting absorbed by the air? $\endgroup$
    – Steven Sagona
    Commented Jan 6, 2022 at 23:12
3
$\begingroup$

Contributor Solomon Slow has written an answer that I upvoted. I just want to say something about the physics of using a diamond anvil.

In the case of a diamond anvil the load on the diamond jaws is compressive load. When diamond anvil is manufactured such that the diamond can perform to its maximum capability then of any material diamond can bear the highest compressive load.

However, I expect that diamond will be quite brittle and fragile under tension.


The material that is used when the load is tensile load is high tensile strength fiber wrapping.

For example: inside the propellent tanks of rockets used for launching payload to orbit there are small tanks filled with Helium under extremely high pressure. As the propellent is depleted Helium is released to maintain a high pressure inside the propellant tank.

These vessels are referred to as COPV Composite Overwrapped Pressure Vessel.

Improve this answer
$\endgroup$
5
  • $\begingroup$ Except, what I left out of my answer is that the gun barrel and the projectile both would be instantly turned to plasma. Plasma has no tensile strength at all. $\endgroup$
    – Solomon Slow
    Commented Jan 6, 2022 at 23:05
  • $\begingroup$ @SolomonSlow Indeed. A giant cannon charged with a nuclear weapon is the ultimate example of a device that destroys itself rather than whatever it is aimed at. $\endgroup$
    – Cleonis
    Commented Jan 6, 2022 at 23:10
  • $\begingroup$ Thanks for the answer. A very interesting observation! Now, I am struggling to get an intuition for why a diamond would be fragile under tension. Any intuition why it would be the case? I thought diamonds are strong because it's basically a giant molecule -- and because its symmetric carbon molecular bonds are keeping it together in all directions. I guess this isnt the full story? $\endgroup$
    – Steven Sagona
    Commented Jan 6, 2022 at 23:29
  • $\begingroup$ @StevenSagona A diamond is just a crystal. So is a computer chip (silicon). Or salt. Or most metals. $\endgroup$
    – DKNguyen
    Commented Jan 7, 2022 at 1:33
  • $\begingroup$ @DKNguyen To clarify that most metals are not single crystals, but rather a bunch of crystals stuck together, and much of their ability to flex is a result of those crystals moving past each other while still staying stuck together. This is also why cast iron is much stiffer than forged iron, cast iron contains much larger crystals because of how it is formed and how it cools. Tempering metal reduces this stiffness by allowing smaller crystals to form (smaller crystals in metal can move past each other more easily than large crystals) $\endgroup$
    – Kevin
    Commented Jan 7, 2022 at 18:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.