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?
Best Answer
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.)