Liquid nitrogen.

It’s the same kind of nitrogen you’re breathing from the air around you, just in liquid form. But according to Hollywood, it can slow down Terminators, or shatter human heads.

And according to my middle school science teacher, it can also bring joy to  children around the world. Maybe you have memories of  someone coming to your classroom and showing off some cool  tricks with liquid nitrogen. Like smashing a frozen racquetball, or mixing it with cream and  sugar to make ice cream.

But whether we’re talking about  fictional murders or real life desserts, liquid nitrogen gets the job  done because it’s super cold. Roughly -196 degrees Celsius. At sea level, that’s the  temperature at which molecular nitrogen changes from a gas  to a liquid, or vice versa.

And over the years, scientists  have found a bunch of uses for liquid nitrogen that are way more impressive than any special effect or  classroom demonstration. [♫INTRO] Okay, using liquid nitrogen to freeze dirt might not sound impressive at first. But frozen dirt can be super useful, especially if you’re digging a big tunnel. Because tunnels have a tendency to collapse unless they’ve been fortified.

And freezing the ground can  keep a giant underground hole stable while workers  build permanent structures, like tunnels for cars or trains  and vertical mine shafts. Or maybe you don’t need to dig a big hole. Maybe you want to cut off or  redirect contaminants or groundwater.

Freezing specific parts of the  ground can help you do that, too. No one’s pumping liquid nitrogen directly into the earth or anything, though. Instead, they insert pipes into the ground and run liquid nitrogen through  them, freezing the nearby ground.

Of course, you don’t have to use  liquid nitrogen to freeze dirt. It can also be done with brine,  which is just super salty water that can stay liquid at way colder  temperatures than regular water. And brine generally is the cheaper option.

But liquid nitrogen has its advantages. If you have a leak, you don’t have to worry about a harmful compound leaching into the ground. Because remember, it’s literally the same stuff that’s above ground in the air.

And not only are the freezing  systems quicker to install, but because liquid nitrogen is way, way colder, it does the freezing part much faster, too. Brine takes 20 to 30 days to  completely freeze the ground. Liquid nitrogen can do it in 5 to 7.

In other words, it's great  for emergencies or projects that need to be completed in a hurry. For example, it was used to help  stop contaminated water leaks after the meltdown of the  Fukushima nuclear plant in 2011. That sure sounds coo– What?

So apparently, I’m not allowed  to end any of these segments by calling the application “cool”  because the pun is too unoriginal. I used my one allotment in  the title of this video. Freezing dirt is great, but what  about getting the dirt on a criminal?

Liquid nitrogen can help detectives do that, too! You probably know how relentlessly  a piece of duct tape resists your efforts to remove it,  especially when it’s stuck to itself. Which is every time you try to tear  a piece off of the stupid roll.

Well, sometimes crime scene  investigators think there might be a fingerprint hiding  between layers of duct tape. And retrieving it can seem pretty impossible… …unless you have some liquid nitrogen! For this, investigators can use a liquid nitrogen gun to separate the pieces of tape.

And according to research from 2011, liquid nitrogen can help  retrieve clearer fingerprints than either a chemical  specifically meant to neutralize the tape’s adhesive, or just angrily  ripping the tape pieces apart. The researchers also noted that the results vary depending on how you apply the liquid nitrogen. For example, if you dunk the tape  into a tank of liquid nitrogen, it does a good job at neutralizing the adhesive.

But the tape can also become brittle. Using a cotton swab soaked in  liquid nitrogen can work too, but you have to keep re-dunking  your swab into the liquid nitrogen because there's only so  much it can hold at a time, and the nitrogen will keep boiling off. So CSIs may need to refine the technique, but a little liquid nitrogen  could potentially mean the difference between catching a bad guy or not.

But it probably won’t ever save you from throwing that frustrating roll of duct tape  through your living room window. Moondust might sound like something  fun and fluffy for astronauts to lay down in and make the  lunar equivalent of snow angels. But it’s not.

It’s more like microscopic shards  of glass that will shred your spacesuit fabric, gunk up your  electronics and airtight seals, and… once you get back  inside… get into your lungs. So after getting covered in moondust, your first instinct might  be to try brushing it off. But on top of all the damage moondust  can do, it’s also super clingy.

So not only will that brushing motion press those shards into whatever you’re trying to clean, they won’t really go anywhere  when you think you’re done. In fact, during the Apollo missions  that’s exactly what happened. Some of the very expensive space suits were essentially ruined by moon dust.

So when we eventually send  humans back to the Moon, we need to have a better way  for them to deal with it. And in 2023, researchers used liquid nitrogen to remove about 98 percent of that clingy moondust from sample fabric swatches…including some worn by Barbie dolls inside a small vacuum chamber! And the liquid nitrogen washing method caused way less damage to the suits  compared to the methods used by Apollo astronauts,  like vacuuming and brushing.

The science behind this unique  space-suit laundry service is the Leidenfrost effect,  which describes what happens when you place a cold liquid next  to a significantly hotter surface. Some of the liquid vaporizes,  creating an insulating layer of gas between the surface  and the rest of the liquid. And when super chilly liquid  nitrogen meets the moon dust resting on the much-warmer-by-comparison fabric, the dust forms little beads and floats away.

Now, the researchers weren’t  entirely sure how this works, but the liquid nitrogen sort of wraps  itself around the moon dust particles. And as the gas expands during boiloff, it may cause the dust to become airborne. If this tech ever gets adopted,  astronauts would hypothetically come back from a moonwalk,  enter an airlock as per usual, and take a liquid nitrogen shower  before doffing their helmets and suits and going about their moon business.

And thanks to all that liquid nitrogen  converting to gas, this shower would also help pressurize the  airlock while the suits get clean. Yay multitasking! There is one big caveat  with this research, though.

It hasn’t been tested in an  actual lunar environment, or with actual space suits, or actual moon dust. And the team behind this research  acknowledged that the Moon’s lower gravity and extreme  temperature changes would probably affect how well  this cleaning process works. But maybe they can do some follow-up research by flying a Ken doll up there to test it out… and then his job can be Moon Beach!

Most of you probably didn’t  get to handle the containers of liquid nitrogen when you got that classroom demo. Because yeah, you probably  don’t want a 12 year old to accidentally spill a liquid  that cold on their pants. But there is another pretty big hazard that comes with mishandling liquid nitrogen.

As it boils and returns to a gaseous state, it will displace most if not  all of the oxygen in the area. And you might remember, you need  oxygen to, like, breathe and stuff. And that’s why if you bring  liquid nitrogen up and elevator, you have to put it in the elevator  by itself, because if it leaks it’s not going to silently suffocate anyone.

But maybe we can use this  suffocation power for good! In theory, you could dump a  buttload of liquid nitrogen onto a forest fire to starve it of the  oxygen it needs to keep burning. In practice, this is challenging.

Because forest fires, you might recall, are hot. And liquid nitrogen vaporizes at -196 degrees. Now, vaporized nitrogen could still hypothetically slow down a fire since it’s cold.

And it’s denser than normal air so it would sink toward the ground rather  than automatically float up into the greater atmosphere. But fires also have hot updrafts  that could mess that up. So it’s better to keep any  nitrogen fire suppressant in a liquid state for as long as possible.

But how can you get it anywhere near the core of a massive forest fire? Well back in 2016, some scientists proposed filling an aircraft with insulated,  finned capsules of liquid nitrogen and then dropping them on the core of a forest fire from a safe distance. The fins would help the capsules spin in a controlled manner while they fell.

And as they spun, they’d spray out some of their liquid nitrogen kind of like a lawn sprinkler. The rest of the liquid nitrogen would be released when they smashed into the ground. To test their design, the team  filled a prototype with water and dropped it from the top of  a 17-meter tall parking garage.

The prototype spun as anticipated  and dispersed some of the water, but not very much given the low drop height. In a forest fire, it’d need to  come from like 200 meters, minimum. And unfortunately, not much has been done to develop this tech for real-world use.

But forest fires aren’t the only fires that you can suppress with liquid nitrogen. Scientists have also proposed  it as a quick and effective way to snuff out fires in  enclosed spaces, from coal mines, to utility tunnels, to computer data centers. And speaking of hypothetical  uses for liquid nitrogen… Back in the 1980s and 90s, some  people thought nitrogen cars were the future.

Mostly because  electric cars, like, sucked back then. Like, do you remember the ComutaCar? No?

Well that’s because it wasn’t very memorable. The ComutaCar was an early electric vehicle with a maximum speed of about 56 kilometers per hour and a maximum range of about 64 kilometers. It did look a lot like a miniature  version of the Tesla truck, though, so I guess we’ve come full circle… Anyway, liquid nitrogen powered  vehicles seemed pretty futuristic compared to the electric cars  that were available at the time.

And even today, there are researchers who think a liquid nitrogen car would be a huge  improvement over an electric car. Because while electric cars  don’t produce emissions, their batteries have environmental costs. They’re made from toxic  materials that have to be mined, and the energy used to charge them doesn’t always come from renewable sources.

So a liquid nitrogen car might  make better environmental sense than an electric car, especially  considering how they work. The engine would be very  similar to a steam engine. But instead of boiling water to make steam, the engine's power would come  from vaporized liquid nitrogen.

The nitrogen vapor would turn the motor, and the only exhaust produced would be nitrogen. And nitrogen isn’t considered a pollutant because the stuff already makes up  78 percent of the atmosphere. Which obviously makes them  better for the environment than any gas-guzzler.

But how  might they compare to modern EVs? Well, some researchers at  Washington University claim that liquid nitrogen cars could match the performance and range of modern electric vehicles. And they’d be affordable and easy to maintain.

They also noted that the demand for liquid nitrogen fuel could  actually help reduce pollution. Because to make liquid  nitrogen, you start by sucking and compressing a bunch of air. And that air has to get "scrubbed"  to remove carbon dioxide.

Of course, there are the usual safety concerns. You don’t want to accidentally  spill the fuel on you or try to fill up in a closed garage. And the fact that liquid nitrogen  creates a lot of pressure as it vaporizes means there’s  some risk of explosion.

Although you wouldn’t have to worry about a battery bursting in flames, which you may have noticed has  been a problem with some vehicles. But with all those hypothetical pros, why aren’t we all driving liquid nitrogen cars? Well, it’s complicated.

Until recently, you needed an  expensive heat exchanger to quickly vaporize the liquid nitrogen, so  the concept wasn’t very practical. And now that electric cars are pretty standard, it would be hard to woo the auto industry in a completely different direction. You know, again… So we might not be taking a bunch of air and turning it into a fuel for  the next “Car of the Future”.

But you know what we can do instead? Turn it into a different kind of energy source. Because sometimes, green energy gatherers like solar panels and wind  turbines generate electricity that isn’t going to be used right away.

This energy is often stored in  batteries, but as we’ve established, batteries come with their  own environmental downsides. So as an alternative, scientists have proposed using that excess energy to liquefy air. Some of the energy is used  to remove gasses like CO2 and water that won’t liquify  as the temperature drops.

Instead they’ll freeze solid,  so they’re basically impurities. But after that little bit of cleanup,  you use the rest of the energy to cool your air down until  it condenses into a liquid. And then you hold that liquid in a vacuum chamber so it can’t heat back up.

To get energy back out of the  system, all you have to do is let the liquid air warm  up and turn back into a gas. The gas will be shunted towards a turbine. And using a fluid to drive a turbine and make electricity isn’t novel at all.

That’s what most power plants out there are doing, whether they involve burning fossil  fuels, splitting uranium atoms, or running a bunch of water from one  side of a giant dam to the other. This technology has been  tested in the United Kingdom, and plans are underway for larger  plants that will be capable of storing significant amounts of energy. For example, there’s a facility near Manchester that’s currently under construction, and should one day store enough  energy to power 480,000 homes.

So you see, liquid nitrogen has more uses than filling an hour of science class. It may be able to help make the  world a little greener by putting out wildfires, replacing Teslas,  and storing excess green energy. Though making ice cream is pretty cool, too.

We may have come to the end of the episode, but we haven’t come to the end of  blathering on about cool science. Or, the science behind cold stuff. Because our spinoff podcast, SciShow Tangents, has another 38 minutes dedicated to cold!

You can check it out by clicking  the link in the description. Maybe grab a blanket and a cup of tea, though. I’m already getting chilly just thinking about it.

Thanks for watching! [♫OUTRO]