Some areas of the evil meant lair are not for the eyes of the average minion. There is only one way in and out of this area, there is no door blocking the way, but a lava waterfall pouring from the ceiling, completely covering the section of the corridor. The lava is actively recycled and a mechanism "opens" the waterfall from the center when the villain approaches.

Is this setup possible? Are there materials that can consistently contain molten rock without melting?

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    Yes, it's even easy but you can be more worried about your energy bill – jean Oct 19 at 16:03
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    Have you tried asking Syndrome how he did it on Nomanisan Island? – Engineer Toast Oct 19 at 16:37
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    It will also serve to keep your "special" minions humble since, even once the lava flow stops they will have to wait a while before the area is cool enough to get near and cross. – ShadoCat Oct 19 at 18:29
  • @EngineerToast wow! that is pretty cool – SilverCookies Oct 21 at 14:44
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    One thing to keep in mind is the effect of the heat radiation. Have you ever forged something? Held a piece of yellow-hot metal in front of you? Well, you feel the heat, even at quite a distance, and even when the object is small. Now think of the effect of a lava fall that's at least 2m high and 2m wide. You won't be able to stand anywhere near it. It'll roast you alive. To make this workable, you would need the lava to disappear completely from view when it's switched off, and you need some serious cooling of the corridor before and after to avoid it getting red-hot as well. – cmaster Oct 21 at 20:24
up vote 25 down vote accepted

Consider using molten metal instead!

Most of the problems facing your lava waterfall can be avoided by using a more easily workable material. Relative to lava, almost all molten metals emit more heat and light than lava at a given temperature as you can see from the chart below. (stainless steel, tungsten, copper, aluminium, etc. almost all metals will follow this pattern)

Molten metal colors by temperature

In addition to aesthetics, metals can be heated using induction which is much more efficient and compact than whatever mechanism would heat your lava. This process also makes no direct contact with the metal in question, so it will not wear out as easily.

Induction heating of a metal rod

By using electromagnetic induction from a high-energy coil, the molten metal's temperature can be very accurately controlled and will also cool more quickly than stone (meaning the transport system needed to recycle it will be much easier to create and maintain).

Let's suppose you were to use a molten metal like tin or pure iron (avoid steel due to the sparks of super heated carbon that jump out). It can be made to flow much more easily (and better resemble a waterfall) than lava. It is highly receptive to inductive heating. It releases none of the toxic fumes that true lava would, and unlike lava, it can even be moved around using a ceramic pump. Furthermore, molten metal can be more easily contained, guided, split, or pushed out of the way to reveal your door due to its lower viscosity at higher temperatures.

Suppose the following for your villainous lair!

your passageway to the uber-secret room is disguised as the idealized lava wall you desire, radiating heat and light to whatever specifications you wish. The flow of metal falls cleanly from a slot in the ceiling into a tungsten grate in the floor that drains it away into a reservoir by a trough. the metal cools during this process, becoming easier to transport, but not solidifying. It is pumped through a series of tubes that have inductive coils around them as shown which sustain the metal at this temperature:

enter image description here

From there, the molten metal is taken back up into the ceiling where a series of final high-energy coils return it to the yellow glowing radiance you desire. It is then flowed back over the lip of the ceiling, completing the loop.

In order to reveal the secret massage, one need only turn off the pump, or one could divert the flow to stop only the middle of the lava wall. One need only cross the glowing tungsten grating (perfectly safe if done quickly enough) and behind the wall is a hallway or catwalk or door to your lair.

Edit: also consider this design used by foundries to improve laminar (smooth) flow and prevent strain on the pump

Molten metal pump and flow schematic

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    Note that using any oxidation-sensitive metal will slowly degrade the quality of the liquid metal with time. I recommend using silver (see my own answer for details). – Gimelist Oct 20 at 4:22
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    "metals emit more heat and light than lava [...] as you can see from the chart" - um, that chart doesn't mention lava or metal, so I don't see how it helps. – npostavs Oct 21 at 22:58

Go ahead and make lava.

https://www.gamma-meccanica.it/mineral-wool-production-lines/rock-wool/melting-furnace/?lang=en

stone wool factory

Rock is melted and whipped into insulation. Depicted - a factory doing just that. More here on this related question - Can stone be "recycled" by melting and cooling it?

For purposes of making a glowing molten wall, you could use other industrial processes - a metal refinery has all sorts of glowing hot molten stuff pouring here and there (hopefully mostly there). Or a glass recycling plant. Bonus - your Evil Lair could have a plausible raison d'être as a factory of some sort.

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    +1 for the last idea. A molten metal radiation curtain, that is the limit of mad science. Molten metal is used in a certain type of metal jet microfocus x-ray systems that need to replenish the target continuously because the tight electron beam would erode it otherwise. – KalleMP Oct 19 at 17:02
  • Lava ≠ molten metal. The two are fundamentally different, and depending on the type of rock and lava, the melting points can differ by hundreds of degrees. The only common things between them, is that they are liquid and glow. – Gimelist Oct 20 at 4:11
  • @Gimelist: Not all liquid metals will glow, for instance mercury as an extreme case. Conversely, some metals can glow white-hot and still remain solid, like the tungsten of an incandescent light filament. – jamesqf Oct 20 at 5:40
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    @jamesqf indeed, but in the context of this question, the thing has to be liquid to make a waterfall, and be very hot. Liquid mercury would kill people by drowning or toxicity, not heat. Tungsten is irrelevant because you can't make a waterfall out of it. Interestingly, aluminium and zinc are two examples of metals that melt before glowing (at least in daylight), but they oxidise so rapidly so they're useless in a circular system. – Gimelist Oct 20 at 6:07
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    @Gimelist While people have drowned in surprisingly shallow water (all you need to drown is to have your mouth/nose submerged), it's rather tricky to get submerged in mercury. That stuff is just so insanely heavy that it would feel more like a sleeping mat than a pond of liquid to the human touch: Only about 7% of a body need to be below the mercury surface for the body to float! Conversely, if you were fully submerged in mercury, you would experience an upward force in the range of about 750 to 1250 kg, depending on your weight. – cmaster Oct 21 at 20:08

Ceramics would work nicely. They would hold up well in the heat and wouldn't deform under load like softer metals could. However they would be subject to wear. Modular units should be used so they can be replaced as they fail.

A simple ceramic Archimedes screw could be used to pump the lava. The screw should be long enough to put the drive mechanism a safe distance from the heat. To avoid the replacement of the screw in the event of a failure there should a sufficient gap between the screw and the pipe for lava to escape back down the pump if the screw stops or seizes.

Locks should be implemented to segregate top, pump, and bottom sections for maintenance.

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    This potentially sounds like a really practical solution, but your answer is a bit short, could you flesh it out at all? For example, can ceramics actually take the heat of molten lava without being damaged? Can ceramics be shaped into an archimedes screw? Any examples or backing information you can add will improve the quality of your answer. – Ruadhan Oct 19 at 13:15
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    @Ruadhan Thanks. Ceramics can be cast in any shape. The screw wouldn't have thin sharp edges, like a machine screw. It would have to have thick rounded edges like a worm screw. There would be a lot of abrasive wear against the ceramic. If the lava temperature and flow was carefully controlled an equilibrium could be maintained that created a thin crust of solidified lava at the ceramic surface that protected it from wear. – Skek Tek Oct 19 at 16:08

Withstanding the heat is the easy part.

Continuously flowing lava is by far harder than the heat, even the air is too cold and will cause lava to solidify. lava falls are temporary occurrences. the better you want it to flow the hotter it has to be. Lava is also extremely abrasive and will scour material very quickly, like faster than most industrial abrasive processes quickly. flowing lava can carve away inches of concrete in a single event.

As for containing it, yeah that's the easy part. We even have steel alloys that will handle it just fine, tungsten steels can handle even hte hottest lavas. even the hottest lavas are only 2000 degrees celsius, to get it to flow easily you only need to get it to around 1200 degrees. You will need to replace your container often however as no matter what it is it will wear away/out fairly quickly.

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    No lavas on earth reach 2000 °C. Some in earth's history may have been 1600 °C. It is extremely rare to see a modern lava hotter than 1300 °C. – Gimelist Oct 20 at 4:24
  • I was using the temprature for magma since we don't know where the lava is coming from, while not technically "lava" it gives a good high maximum. – John Oct 21 at 13:41

Evil super-vilian security theater!

Instead of making a true lava waterfall, make a liquid that has the same appearance, but is significantly cooler. I find a vinegar/baking soda with some red dye added to usually be sufficient, but with the resources to construct an evil lair in the first place, you're going to be able to produce a higher quality psuedo-lava. Once you have that, any sort of typical indoor waterfall setup will work.

Also install industrial heaters in the walls radiating heat into the corridor, so that the heat from even approaching the lava waterfall is unpleasant or even painful, and everyone will be convinced that it's a genuine lava waterfall.

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    Yeah, syrup and hot melt glue come to mind. That would be awesome in a man cave, sign an accident waiver before coming to visit. – KalleMP Oct 19 at 17:05
  • I like this answer, since it's easy enough to circumvent a molten flow, anyway. The super villain really does need a lock on the door behind the lava flow. (The flow itself would be expensive to maintain, and cheap to get around, with a flat piece of metal.) – jpaugh Oct 21 at 18:25

Sapphire.

She's one of my favorite gems too

I'm serious! Here's an interesting thing: Randall Munroe was once asked what could be used instead of glass for a hypothetical lava lamp that containing actual lava. His response includes some interesting tidbits:

You have a few choices for transparent materials that could hold the lava without rupturing and splattering half the classroom with red-hot droplets. Fused quartz glass would be a great choice. It's the same stuff they use in high-intensity lamp bulbs, the surface of which can easily get up to mid-range lava temperatures. Another possibility is sapphire, which stays solid up to 2,000°C, and is commonly used as a window into high-temperature chambers.

🎶 Go ahead and try to hit me if you're able...

If the sapphire wall/floor/ceiling is thick enough, it will not be too transparent.

But if you are not into gems and want to save some money, you could, you know, just build your room out of the stuff that lava usually flows over.

  • This answer deserves an upvote for the Steven Universe reference alone. – Matteo Tassinari Oct 20 at 9:07
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    @MatteoTassinari When I saw the question I immediately thought of Sapphire because Garnet can withstand lava due to her and Ruby (both are the same gem in real life, just with different impurities). But I think I actually got downvotes for that. I got a couple ones and an edit trying to take the image off. Go figure (pun intended). – Renan Oct 20 at 12:07
  • @Renan garnet is not ruby – Gimelist Oct 21 at 3:06
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    @Gimelist I meant sapphire and ruby are two variants of the same gem. Garnets are somerhing else entirely, and so is the cartoon Garnet, but the show lore goes like that. – Renan Oct 21 at 12:42
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    @Renan It is a pretty huge image, especially for someone who doesn't get the reference. (It looks like trolling until you notice the rest of the answer.) You could insert the image as HTML instead of markdown, so you can adjust its height. Something like <img height="300" alt="She's one of my favorite gems too" src="https://i.stack.imgur.com/QELHN.png">. – jpaugh Oct 21 at 18:21

Are there materials that can consistently contain molten rock without melting?

Lava is a bad choice.

The problem is that most ceramic furnace materials will slowly react with your lava. You also need a very high temperature for your lava (higher than 1200 °C) for it to actually flow (or add sodium, but it will evaporate eventually requiring you to refill it occasionally).

Lavas are reactive with most of the stuff they get into contact with. Pretty much the only materials with a high-enough melting point that will not react with the lava (thus changing the composition of the lava and the container) are platinum and iridium, and they are expensive. Really expensive. If you want to build a system of pumps and tubes to move the lava around, you will need so much platinum or iridium that I'm not certain there is enough of it out there being mined, or you might actually temporarily increase the prices so much to cause a global financial crisis.

Use molten silver, held in ceramic.

Silver has several properties that you want:

  1. It's cheap. Well, cheaper than platinum.
  2. Liquid silver is not viscous. Lava is - so it flows much better, doesn't get stuck in the system, and looks much better for the visual effect. Here's a example from YouTube.
  3. It is not reactive. Silver is a noble metal, so it can runs for months in your plumbing without anything happening to the silver or the plumbing.
  4. It has low melting point. Melts at around 960 °C. This requires less energy to melt it (also lower heat capacity than rocks) = cheaper, easier.
  5. The low melting point leads to it being easy to use with ceramic tools (btw - ceramic = synthetic rock). Cheap materials such as alumina (aka sapphire), silica, zirconia, etc will be excellent and easy to use in the plumbing system and pumps. Heck, you can even use temperature-resistant glass for the added effect of actually seeing the liquid silver flowing through the system.

You could just use something that only looks like lava, like water or oil, and is still hot enough to burn anyone that touches it. And it's much easier & cheaper to heat & pump, and any metal or glass could contain & direct it easily, building a moving waterfall should be no problem.

Nearly boiling water is plenty dangerous (and would add a cool "steamy" effect), or hot oil could be downright lethal (185C/365F).

Yosemite National Park's Horsetail waterfall sometimes looks like Glowing Lava and that's just natural sunlight:

enter image description here

With oil it could look similar to a big "lava lamp" if you wanted a clear glass area somewhere too:

enter image description here

So I would suggest using real lava is virtually impossible, and this lethally scalding hot oil is a better solution.

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