Diesel, iron or aluminum, from your parent post, are difficult to explode… (personally, no clue about magnesium); and the point of the latter two is that you can “store” energy by upstreaming its consumption when power is available, you don’t necessarily need to produce an actual reversible energy store.
> and the point of the latter two is that you can “store” energy by upstreaming its consumption when power is available
Are you sure the parent isn't referring to something like a rust (iron-air) battery? Aluminum, Iron, and Magnesium are all viable battery chemistries.
Side note - I'm pretty certain you don't actually need to make contents of a ship explode to easily sink it with explosives.
I'm actually somewhat concerned that between drones and smart mines - we've never had a better chance of completely ruining our ability to do ocean based shipping during combat.
You may have seen that Colombian drug cartels are already using Starlink-piloted "sea drones" to do ocean-based shipping through blockades. The US Coast Guard estimates that 90% of crewed narcosubs get through: https://www.youtube.com/watch?v=5aPLXdtbLZ0
But still not explosive at scale. It’s a surface area issue, a small strip of magnesium explodes when dropped in water but a 100t cargo of magnesium sinking in a harbor would be a huge fire.
> a small strip of magnesium explodes when dropped in water
No it doesn't.
Magnesium metal burns because the boiling point of magnesium is just 1091 C, so extremely reactive vapor is readily produced. But it would be very hard to heat it that high in water unless it was ignited first. It will then continue to burn under water.
Yes, safety is a significant disadvantage of the use of magnesium as portable stored energy, but if your ship's payload is already on fire, in most cases the shipment will not be very successful anyway, and loss of the ship is a serious possibility.
If a hypothetical ship full of magnesium sinks without catching the magnesium on fire first, the magnesium will probably not catch fire from exposure to water. Perhaps if it's sufficiently finely divided, which seems like a bad idea.
I agree, the point is you’re not risking something like:
https://en.wikipedia.org/wiki/Halifax_Explosion “At least 1,782 people, largely in Halifax and Dartmouth, were killed by the blast, debris, fires, or collapsed buildings, and an estimated 9,000 others were injured.”
“Nearly all structures within an 800-metre (half-mile) radius, including the community of Richmond, were obliterated.[3] A pressure wave snapped trees, bent iron rails, demolished buildings, grounded vessels (including Imo, which was washed ashore by the ensuing tsunami), and scattered fragments of Mont-Blanc for kilometres. Across the harbour, in Dartmouth, there was also widespread damage.[4] A tsunami created by the blast wiped out a community of Mi'kmaq who had lived in the Tufts Cove area for generations.”
Not with magnesium ingots or dry magnesium, no; but, because the water–magnesium reaction is exothermic, spontaneous, and gas-producing, I'm pretty sure there's a range of ratios where wet magnesium does constitute an explosive if it's finely divided, at least a low explosive like gunpowder, so such an accident could happen.
It seems unlikely to happen by accident because at stoichiometry you need more water than magnesium, and I don't think spontaneous explosion is a real risk with magnesium. The International Magnesium Association's safe handling guide https://cdn.ymaws.com/www.intlmag.org/resource/resmgr/safety... does mention that magnesium swarf can spontaneously combust in the presence of water, but I think swarf is too coarse to explode. It recommends keeping wet magnesium swarf under water to prevent it from heating up enough to spontaneously ignite.
But presumably you'd be shipping the magnesium in the form of plates, ingots, or rolls rather than powder, swarf, or loose foil.
Even magnesium powder wouldn’t detonate when you’re talking tons of the stuff on a boat for the same reason small hydrogen balloons can go bang, but the Hindenburg just created a huge conflagration. You get limited mixing due to the volumes of material involved. Even burning across several seconds is just vastly less dangerous than an actual detonation.
Same issue with grain silos exploding because of the mixture of fuel with oxygen, but flour just burns etc.
Yes, that's why I said, "dry magnesium, no". A pile of dry magnesium powder only burns at the surface as air diffuses into it. If you have it mixed with the oxidizer so that the flame can propagate through the whole mixture, it will, and the propagation speed is determined by factors like the reaction speed, gas production, and thermal conductivity. The reaction speed in turn is governed by the particle size, since the reaction only takes place at particle surfaces; it goes to completion faster when particle size gets smaller.
Small hydrogen balloons do not in fact go bang; they just create small conflagrations. What goes bang are small balloons filled with a near-stoichiometric mixture of hydrogen and oxygen, such as you get from the simplest forms of water electrolysis.
The stoichiometric mixture of magnesium with water is 1.36 grams of water per gram of magnesium (which is 1.74g/cc, so this 58-wt%-water mixture is 70% water by volume), the enthalpy of formation of H₂O is -285.83kJ/mol, and the enthalpy of formation of MgO is -601.6kJ/mol. So this reaction:
Mg + H₂O → MgO + H₂
yields 315.8kJ/mol, which is to say, 315.8kJ per 24.3 grams of magnesium, or per 58 grams of mixture, about 5.4MJ/kg, about an 18% higher energy density than TNT. And the hot hydrogen gas produced will carry the heat produced by the reaction into nearby areas, igniting them and resulting in a flame propagation velocity that's higher than thermal conduction alone.
For a large enough particle size, you won't get an explosion, and you may even lose most of your water as steam; but for a small enough particle size and an oxidizer concentration close enough to stoichiometric, you will. Some nanothermites consisting of magnesium nanoparticles with an oxidizer such as iron oxide even reliably detonate.
So, it's a potential safety hazard, but it seems like one that should be easy enough to guard against.
It’s not a supersonic detonation but even normal balloons pop with a small bang, pure hydrogen balloons are louder. Though a you mention hydrogen + oxygen is significantly more extreme.
Yes, it's easy to imagine cases where people go around sinking ships; narcosubs, Red Sea oil shipping, and Russian warships in the Black Sea are of course dealing with that threat currently, but as hostilities escalate it's likely to increase. But energy in the form of shipped fuel intrinsically provides some minimal level of such local resilience—for it to work, you need at least a stockpile of fuel big enough to last until the next ship is expected to unload, which is orders of magnitude longer than the milliseconds before a cable cut affects you—and can provide arbitrarily large amounts of it.
The metal fuels in particular have the merit that you can use them in precisely such mass-produced batteries rather than to produce thermal power. As I alluded to in my grandparent comment, aluminum-air batteries were mass-produced in the 01960s.
Sure but moving from a few centralized sources of fossil fuels to a globally distributed and decentralized network of sources of synthetic biofuels means transport distances are a tiny percentage of what they are with fossil fuels.
This consequently scales down the scale of any spill or security issue.
Like the difference between nicking a capillary and nicking an aorta.
I think the idea of "peacetime" is probably outdated. Not in the sense that I think people should fight, but in the sense that their fighting will no longer be limited to certain geographic areas, and people will fight, so all of us will be at constant risk of both infrastructural damage and violent death.
I don't think peacetime is outdated, but we do live in a time of increasing tensions and classical and asymetric conflicts, mixed with an increasing amount of people who believe they have nothing left to loose. So yes, I also prefer the concept of local ressilience as opposed to having many critical infrastructure points where everything else will collapse if those are damaged. Solar, Wind and batteries can go a long way here, to keep at least critical systems running.
I don't think any of tensions, classical conflicts, asymmetric conflicts, the amount of people with nothing left to "loose", or all of these together, are at particularly unusual levels compared to the previous 6000 years, though they're higher than they were 20 years ago. But, for most of that time, warfare was geographically localized; you could avoid directly experiencing warfare by not being a soldier and living inside a country that wasn't being actively invaded, or on the national border between two countries that weren't at war with each other or being actively invaded. Sometimes that was easier said than done, but most people managed it most of the time.
Even without autonomous weapons, we're rapidly moving toward the future of borderless war without end so vividly envisioned in Slaughterbots https://www.youtube.com/watch?v=9CO6M2HsoIA. Ukraine is already an order of magnitude past the headline number it opens with, "Customer pilots directed almost 3,000 precision strikes last year."
Local ressilence is needed in any case and mass produced batteries can provide that safety.