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How much more effective (if at all) would metallic hydrogen explosives be against armored targets?

In this setting metallic hydrogen can be cheaply manufactured and contained in a metastable state within small pressurized canisters (potentially as small as a hand grenade). This is also true of canisters of liquid or solid oxygen. Assume price here is comparable to that of conventional explosives.

It should be assumed that all combatants in this settings are well armored cyborgs. So infantry should be treated as more comparable to CBRN protected light armored vehicles than to modern day infantry. Meaning that thermobaric weapons are dramatically less effective.

Not sure if this is a particularly efficient design, but I'm imagining: A canister of metallic hydrogen in the center. With a thin ring of conventional explosives separating it from a ring shaped canister of solid or liquid oxygen that it rests within. I would guess you want a stoichiometric ratio of oxygen and hydrogen atoms. Also not sure if one should be trying to make the explosive shaped, or if it's too powerful for that to matter. I don't know if I'd be better served just replacing the oxygen in this design with more metallic hydrogen either.. Since a lot of the energy is coming from the metallic hydrogen turning into H2 anyway.

If my proposed explosive design is flawed, then use the best design you can think of to compare to conventional explosives.

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I don't believe that metallic hydrogen would be a good 'explosive' to use against armoured targets despite its likely effectiveness against unarmoured targets.

The trouble with metallic hydrogen is that when it is released from containment, unless it is metastable (which is unlikely but possible), it will instantly expand in all directions, and will begin mixing with the surrounding air. As it does so, it will cool, making ignition with the oxygen in the air unlikely unless extra energy is added. Even if an ignition source is added to the device in order to cause a hydrogen-oxygen thermobaric effect, it will still produce a roughly spherical shockwave.

A spherical shockwave is not a good way to penetrate armour. It is, in effect, little different to the spherical cannon-balls used in black-powder artillery. While it may cause spalling as may occur with a HESH round if enough energy is transferred in a sufficiently small area, it is relatively easy to make spalling a non-issue with spall liners.

In order to cause damage to armoured targets, the current standard is to use kinetic energy penetrators, which may be some sort of projectile fired from a gun, an explosively-formed penetrator, or a shaped charge. I can't see metallic hydrogen being particularly well-suited toward its use in any of these devices due to its inherent instability and need for containment. While it may be possible to make metallic hydrogen do these jobs, it wouldn't be easy or cheap, and in warfare, the whole idea is to increase the difficulty and the costs for the enemy, not yourself.

If you're after an advanced explosive that isn't currently possible to manufacture, consider the possibilities of octaazacubane or cubic gauche Nitrogen They are solids that are thought to be stable at room temperature and pressure, detonate at very high velocities, carry a large amount of energy per unit mass, and produce nothing but nitrogen gas as a by-product.

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    $\begingroup$ For the life of me, I can't fathom how that nitrogen cube is supposed to be stable at room temperature... anything else with that many nitrogens is typically not long for this world! $\endgroup$
    – Cadence
    Commented Feb 3 at 12:47
  • $\begingroup$ @Cadence We haven't been able to assemble any yet... and that probably accounts for its ridiculous detonation speed and energy content. $\endgroup$
    – Monty Wild
    Commented Feb 3 at 12:52
  • $\begingroup$ For those who want a sense of scale: TNT releases 4.1kJ/g. Cubic gauche nitrogen is predicted to release 10-33 kJ/g, according to Wikipedia. $\endgroup$
    – Cort Ammon
    Commented Jun 10 at 15:29
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Yes, but the chemistry is irrelevant. You (are hypothesized to) need about 60 million pounds per square inch to contain metallic hydrogen. Suppose you have 10 cubic inches of hand grenade (or 10 cubic inches of anything else) under 60 million PSI. That's 50 million foot-pounds of mechanical potential energy, the energy released by about 40 pounds of conventional explosives, stored in internal pressure alone. Releasing some chemical potential energy by burning a little splash of rocket fuel is a rounding error.

Whatever godlike technology you're using to contain 60 million pounds of force per square inch of hand grenade is probably even scarier.

The flip-side of this is that if you don't want infantrimen wielding automatic weapons whose individual bullets hit like heavy artillery shells, who go to war in indestructible, impenetrable armor that's been used by a hundred men before them, and who go home in watertight sealed coffins after their liquified bodies are vacuumed out of their unblemished indestructible armor, grenade-sized containers of metallic hydrogen are not something that you want in your story.

The other flip side is that unless your story is about chemical engineers working for an arms manufacturer or a military procurement office, none of your characters are going to know or care anything about the chemistry of their hand grenades, anyway.

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    $\begingroup$ Metallic hydrogen is thought to be metastable - it requires inconceivable pressures to create, but once created, it's stable under ordinary conditions. (In theory. So far as I'm aware, nobody has ever actually accomplished this.) That's the property that makes it interesting to sci-fi authors. $\endgroup$
    – Cadence
    Commented Feb 5 at 12:56
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Well, regarding your design, I suspect that the ring of conventional explosive might be not needed (other than maybe as a fuse to detonate the metallic hydrogen?). The oxygen might be unnecessary as well, since theoretically once the metallic hydrogen unleashes it's initial recombination explosion it should also spread itself all over the place. It would likely also mix the H2 with the atmosphere much like how the initial charge of a thermobaric bomb mixes it's charge with the oxygen it will need later. Therefore, the most efficient metallic hydrogen warhead design might really just be a block of metallic hydrogen with a fuse to detonate it when needed (not to mention that metallic hydrogen recombination gives 216MJ/KG while H2 combustion "only" release 140-142KJ/KG, so taking care to maximise this part won't help that much either.

Now, moving on to comparison with conventional explosives, let's assume conventional=TNT. According to wikipedia the density of TNT is 1.654 g/cm3, therefore for each cm^3 you get 1.65 g of TNT equivalence. Now, for metallic hydrogen, you get 0.7g/cm^3, so you'd get 151,200J/cm^3, divide that by 4184 and you will see that it's RE factor is 36.138, or for each cm^3 of metallic hydrogen you get a equivalence of ~36grams of TNT.

However, the fun does not end here. After that recombination explosion you still have 0.7g of H2 ready to burn. Assuming that half of them manages to find a oxygen to react with, this adds 49,652.75J, or 11.867 grams of TNT equivalent. In total the blast is 48 times more potent than a block of TNT of the same size.

According to fandom a M795 shell's weight only has ~25% occupied by explosives, but for a Metallic Hydrogen shell (note that you only get to use it this way if you're launching it with a coilgun, with a conventional gun or a railgun I suspect that the heat would detonate the metallic hydrogen INSIDE your barrel with all the gentleness of 48 times it's own size in TNT) you would likely only need the "Warhead" because it is it's own structural support. therefore it's effectiveness might actually be much higher than what the tnt equivalence initially suggests

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