Could I use molten lava as a permanent design feature--like a moat?

[Yllaria]

Would that much liquid nitrogen cause a permanent fog around the base? Hmmm. I’m trying to decide if that’s a plus or a minus.

[Sunspace]

@Quercus

Really, the only issues with molten iron are

1. the energy needed to keep it molten
2. I’d have gotten away with a two-item list if it weren’t for that meddling Opal!
3. cooling the fortress near the moat

Sunspace’s ideas about reverse air-curtains makes sense; that will help with thermal management, especially as we use the hot air to do something useful.

The moat lining is easy: commercially available firebrick should do it (though it will need to be rebuilt regularly) without needing a fancy R&D effort or complex heist of NASA material (though I’m all for including a complex heist as part of the plan, of course).

Well, I was intending the insulation to cut down the energy required to keep the moat contents molten. Would gold require less energy to keep fluid than iron?

What about using some substance at around 300C instead of 1000C? I’m thinking some kind of molten wax or plastic. That’s hot enough to be dangerous while greatly-reducing the energy requirements. ISTR that blackbody energy dissipation is proportional to the fourth power of the temperature, but I could be wrong. (That’s what I have minions for.)

On the other hand, if we have enough energy, due to our earth-mantle tap or whatever, we can go with the original temperatures.

A liquid-nitrogen moat would be more vulnerable to crossing; all the attacker need do is pour enough water into it and build an ice bridge. I think I’ll reserve the LN moat for cosmetic duty just outside my apartments. With a trap-door bridge, of course.

[Stathol]

<derail>
By any chance, does the OP play Dwarf Fortress?

If you don’t, you really should…

Protecting a fortress with a lava-based doomsday device figures heavily into the epic tale of Boatmurdered
</derail>

[Fish]

@Sunspace

A liquid-nitrogen moat would be more vulnerable to crossing; all the attacker need do is pour enough water into it and build an ice bridge.

And a rebreather or a scuba tank, of course. That much liquid nitrogen is bound to create an oxygen-poor layer of air nearby, don’t you think?

[Sunspace]

@Fish

And a rebreather or a scuba tank, of course. That much liquid nitrogen is bound to create an oxygen-poor layer of air nearby, don’t you think?

True. That could be handled by a moat exhaust as I described earlier, though. Though it might be good to keep the oxygen-poor air and use it to fill corridors and passageways that aren’t being used, as an additional barrier against intruders.

[Chronos]

I know sodium in its pure state is incredibly reactive, but what if the moat had a ‘buffer’ of noble gas, one that was denser than air that would form a layer to keep the sodium from reacting to the ambient oxygen?

Wouldn’t work. All gases dissapate into each other; they won’t stay layered indefinitely. Some of the heavier gases do stay layered for long enough to do neat demos like pouring them over a candle flame, or floating a very lightweight boat in them, but we’re still only talking minutes at most.

[Coil]

@Sunspace

Well, I was intending the insulation to cut down the energy required to keep the moat contents molten. Would gold require less energy to keep fluid than iron?

When deciding between iron or gold I think the Evil Overlord would have to think about how long he is going to be using his molten moat. Gold may be more expensive but if it saves on energy it could be cheaper in the long run. On the other hand if you expect meddling heroes pretty soon you could go for the cheaper iron alternative.

[Wiltshire]

Use radioactive lava, it’s self-heating.

[Kobal2]

@Sunspace

A liquid-nitrogen moat would be more vulnerable to crossing; all the attacker need do is pour enough water into it and build an ice bridge. I think I’ll reserve the LN moat for cosmetic duty just outside my apartments. With a trap-door bridge, of course.

Wouldn’t a moat of molten metal be liable to the same thing ? Dump enough water in it, and it’ll cool down and solidify at some point, or am I missing something (like a rudimentary knowledge of physics) ?

[Quercus]

@Kobal2

Wouldn’t a moat of molten metal be liable to the same thing ? Dump enough water in it, and it’ll cool down and solidify at some point, or am I missing something (like a rudimentary knowledge of physics) ?

The difference is, with a liquid-nitrogen moat, you’re not dumping water on it to change the temperature, you’re dumping water on it to form a solid bridge over the moat. You could just as easily use planks of wood or whatever to form the bridge, but the water is easier to transport.

[malenkylizards]

@Der_Trihs

How about molten gold ? Sure, it’s expensive; but that’s what extortion schemes with death rays are for. Besides being stylish, having your gold supply molten would make it harder for a minion to pocket and carry off; and your victims would polish up prettily once they cool.

Alright, so say we’re working with the reasonable aforementioned estimate of 1300 cubic feet, for a ten foot wide, one foot deep moat around a 60x60 foot fortress, which really doesn’t seem that befitting a fortress size for an evil mad scientist AND all his henchmen…though admittedly, perhaps it’s only 60x60 feet on the surface.

That works out to, I think, 24,889,280 ounces. These days, if I’m not mistaken, gold is over $1000 per ounce, sooo…$24,889,280,000. Not bad, barely over a quarter of the AIG bailout and barely over a third of Warren Buffett’s pre-wall-street-collapse net worth.

Still…$24 billion could buy a loooooot of frickin’ sharks with frickin’ lasers on their head.

[malenkylizards]

Anyway, I have to say that previous idea of molten plastic has a nice ring to it, only you’ve got to call it molten polymer, because, well, you’ve just got to call it a polymer. But it’s got to be polymer that can be ELECTRIFIED. Possible, guys? How about polymer that, when electrified, solidifies very quickly? That has the nasty possibility of, oh, say, it’s hot liquid plastic, but you’ve got this suit that protects you from the heat, but what you don’t know is that when you submerge to get to the door hidden under the plastic lake, sensors detect your presence and electrify the plastic, sealing you in until your oxygen runs out, or the laser-sharks bred to survive in hot plastic can be deployed. An elegant solution for the THRIFTY mad scientist.