Will Helium Leak Through Hard Plastic?

If anyone is wondering why I didn’t specify what the container looked like or give any specifics, it’s because I don’t want anyone more experienced than me taking my idea and making money off of it.

"Hard plastic" is undefinable. The answer, with the information given is, yes. Leak rates? environments? Etc. The question requires a little research on you part is in order, first.

Polymers, as a group are not impermeable to passing He molecules.

https://www.qualitymag.com/.../93356-helium-leak-detection-for-plastic-containers-ad...

He is in short supply all over the world, so keep that in mind.

Lightweight Containment of Helium

Ok so I have no idea how to edit my post so I’ll simply answer the questions here. So as for the environment it would be used in water. The reason I put hard plastic is because I have not yet decided specifically on what type of plastic I will use or if it will be plastic at all. Plastic was simply what I thought would work best as it is light weight and durable. I did search the web before resorting to these forms but came up short handed. I hope this helps to better explain my questions.

The FAQ's tell you that you have 30 minutes to edit.

Still, "plastic" covers thousands of different materials, ALL of which are permeable to moisture and He, among other things.

Are you just replacing air with He at 14.7 PSI, or do you want to pressurize the container above that?

Tell us if you want to inflate party balloons too.

More use information is required for any intelligent answers.

Again, the answer to your original question is, yes.

Hindenbubble

"... it would be used in water." If "in water" is some outdoor use where rupture would lead to a bunch of small bubbles which would be rapidly diffused into the open air at the surface then you might be in a position to discount the usual reason for using He in many applications: explosion/fire safety. If you chose He because of its very low density then you get a two to one (diatomic H atomic mass: 1x2 vs monatomic He atomic mass: 4x1) lower density advantage by using hydrogen. Hydrogen also leaks out of most enclosures far more slowly than helium because of diatomic hydrogen's larger molecular size.

Since we are not privy to the actual application it is difficult to evaluate whether the "in water" usage sufficiently mitigates the explosion/fire safety issues of hydrogen. Thus, I propose using hydrogen instead of helium and leave the safety issues up to you. Realize that hydrogen without some oxidizer available is not going to explode nor burn and has the half density advantage previously described. At extreme pressures there is a possibility that hydrogen may act as the oxidizer for some materials(especially very reactive metals) and in these cases the other material will "burn" in the hydrogen environment so you should consult a chemist with detailed information about the pressures and materials you propose to use. Another phenomenon to consider is that hydrogen can adsorb on some materials(rust comes to mind.) If you are filling a rusty bucket with hydrogen, it may take a bit more than you anticipate to reach your desired pressure and you may need to count the weight of that "hidden" gas.

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thewildotter

A mylar balloon is a thin plastic container. I've had these balloons maintain their lift for a few months, but eventually, the tiny helium atoms do find their way out.

You do realize that putting more helium inside does not increase the buoyancy. The amount of buoyancy is the weight of the volume of air displaced minus the weight of the container and helium. The helium (or hydrogen) is there only to keep the balloon inflated and displacing air, and putting more in would decrease the buoyancy.

Correct, but. You left out one significant detail. Those mylar helium balloons aren't just mylar, they are aluminized mylar. That extremely thin layer of aluminum is what makes the balloon able to hold the helium for relatively long periods. Unless I'm mistaken, pure mylar (or any other common plastic) would not hold it for long.

You're right, there's got to be a conducting layer in there that makes for the interesting pyrotechnics when one is released underneath HT power lines!

It's impressive how well the aluminized mylar contains the helium. I suppose thicker plastic could also be aluminized, although, AFAIK, helium sold for party balloons is always sold in metal tanks.

I guess there's not much more to say without knowing a little more about what the OP intends to do.

Lighter weight flying taxi body components?

Levitating cheese ball tray for gamers?

Light weight helium cylinders?

"Lighter weight flying taxi body components?"

Any part strong enough to be a body component, hollow and sealed to hold helium, would be lighter still having a vacuum instead of helium.

"Levitating cheese ball tray for gamers?"

Assuming someone could get it balanced to begin with, take one cheeseball, or one slice, off the tray, and it will float up, up, and away.

"Light weight helium cylinders?"

Plastics don't generally take internal pressure well, unless they include some form of fiber wrapping.

Any part strong enough to be a body component, hollow and sealed to hold helium, would be lighter still having a vacuum instead of helium.

Yeah, that's the point I was trying to make in #5. I've seen helium called "lifting gas", leading some folks to believe that if you pump enough into an enclosure, you can make it levitate.

Yunoyeryte.

...and that aluminum is what makes them so reflective. Just a couple of weeks ago, the remains of one that had clearly exploded landed in the forest behind our place. The reflections caught my wife's eye, and I had to go investigate.

I can clearly imagine the pyrotechnics you mention. I haven't seen that, but I did once watch (and photograph) a pole transformer providing its final display. Quite a show!

I suspect your mylar balloon probably rose high enough that the pressure differential ripped the plastic.

I haven't witnessed a mylar balloon hitting power lines, but there are videos out there.

I did once see a transformer catch fire just as I was driving under it. And in Chicago, a transformer exploded, blowing a big smoke ring in the sky.

DK, has there been any experiments done using different metals and layers on mylar balloons, made onto contact with hv lines ( live or simulation ) . Light spectrum, intensity, frequency. ? Tony

Correct, but, I think the most significant detail is how the balloons are sealed. I believe they have an adhesive that seals off the filling port. I suspect most of the leakage takes place there.

They can also be sealed with heat by melting the port in the same way as the balloons edges..

Well the interesting question is, if the container is under water and nothing can migrate in, will the Helium still migrate out or will the higher pressure outside keep the Helium in even so the container is permeable for the Helium?

It depends greatly on whether the container is rigid or flexible. If the container is flexible, like the balloons we've been discussing, the pressure inside the balloon can be no lower than the outside pressure, so higher outside pressure means higher helium pressure, which will produce more rapid loss of helium.

I'm not quite sure about the case of a rigid container strong enough to withstand the outside pressure without crushing...

But then you can pump up the container to the pressure that the container sees at Water depth.

A hard plastic will have some resistance to the pressures involved. Being able to pump it up to a certain pressure most liklely will make it resistant to the pressure from the outside.

But if I get you right you expect the Helium to leak out anyway against the pressure?

In a rigid container this sounds implausible.

Lets hear what others have to say!

Leakage depends on the partial pressures of the gas in question, not on the total pressures of all substances present. Thus, in this example, some helium could leak outward.

That's a good point. I used to wonder why a rubber helium balloon only partially deflated but lost all its buoyancy. Then I read about partial pressures.

There are plenty of helium atoms inside leaking out, but almost zero outside trying to leak in. On the other hand, there are plenty of molecules of nitrogen and oxygen outside leaking in, but very little inside leaking out. Helium leaks out while air leaks in, until equilibrium is reached (air inside, air outside).

Helium does, however, leak faster both due to Graham's law, and I suspect, the small size of helium atoms compared with the diatomic gases in the air.

Expert Sought

Upon first reading of Graham's law, it appears that I may be mistaken regarding the relevance of quoted molecular vs monatomic sizes having any bearing upon effusion rate. Now diatomic gasses have energy stored not just in translation but also in oscillation and that may play some role. That may explain why many examples of Graham's law use exclusively polyatomic or exclusively monatomic gasses in comparison. At the moment I am leaning toward thinking that the molecular category(monatomic vs diatomic) of gas is not significant or not very significant and that the typical statement of the law is probably adequate. This means that diatomic hydrogen will leak out faster (inversely proportional to sqrt(2)) relative to helium (inversely proportional to sqrt(4)) instead of leaking more slowly as I previously believed. If you do expound on this, please include some comments on whether the hole sizes as they approach the Bohr radius make any difference. Is there, for example some (maximum existing) hole size cutoff below which effusion sharply diminishes for multi-atom molecules in a fashion not described in Graham's law?

Perhaps someone more versed in the kinetic theory of gasses can set the record straight.

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thewildotter

I was not familiar with Graham's law, nor was I familiar with the term "effusion", before reading the linked article. Upon study, I noticed that the article is using the term to describe passage of gasses through a tiny orifice. There should be no orifice involved in the leakage from a balloon, so I don't believe Graham's law applies.

"Diffusion is the flow of material from a region of high concentration to a region of low concentration. effusion is the flow of gas from high to low through an opening / hole or orifice." _{Math&Science 2024.}

Helium is the standard gas used for detection/location of leaks in high vacuum systems because of its combination of safety and rapid leak rate through materials OR tiny orifices.

dkwarner,

It was also my experience that helium was famous for a high leak rate through materials. I doubted myself because at some level even a crystal looks like atoms with interleaved orifice openings between each layer of the lattice. Consider x-ray diffraction studies of crystals. The question is, what is the smallest hole where Graham's law still applies. Does it become less than useful at sizes of holes expected in the materials of interest or not ?

I had no direct experience with leak rates for hydrogen. The kinetic theory of gasses makes sense in comparing hydrogen to other diatomic gasses, which is what I found in examples of Graham's law online in a casual survey. Hydrogen leaks faster than nitrogen, oxygen,... as one would expect from energy considerations through filter membranes(large holes relative to crystal lattice separations.) Per Graham's law one expects the effusion rate to be proportional to the inverse of the square root of the molecular weight as a consequence of 1/2mv² energy considerations. My question remains: At what hole size do other factors become dominant ?

I am aware that in waveguides electromagnetic energy has a sharp cutoff based on wavelength for the size of a tube it can traverse. Is there a similar phenomenon for gas penetration through various materials ? Does some phenomenon such as this clamp off the range of hole size applicability of Graham's law ? Is there such a thing, for example, as phase change for a single molecule from gas to liquid in a tight hole releasing such a blast of heat energy that forward progress through the previously open "hole" is effectively impeded by violent shaking and the collisions it is likely to produce ? Do polyatomic gas molecules get dissociated by the violence of the phase change ? Does the impact at the wall become inelastic ? Do the critically sized holes fill up with embedded gas daughter products. Does someone with a less vivid imagination have a credible model of what happens at the cusp ?

And for our OP, at what pressure and hole size does the hydrogen effusion rate clamp ?

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thewildotter < emphasis warranted by the post content

dk, I appreciate your opinion re Graham's law not applying. I both think you are right and hope that hydrogen is therefore, aside from safety, a good helium substitute. For either gas, it is important that the containing materials are not porous. For example, in time even liquid water would likely leak out of (or in to) a simple concrete shell container.

I did NOT go back and re-read the article, but I believe I remember something about the hole size related to the mean free path. A couple of articles indicated a mean free path of Oxygen or Nitrogen in STP air of ≈60 nm. Since an atom of Helium is smaller, it should have a somewhat longer mfp, but we're still talking mighty small holes!

thewildotter There is factual evidence from the antique vehicle storage field that water vapor will leak thru garage floors to cause rust on whatever is stored on the floor. Note: water vapor, not liquid water. Thus, all concrete floors should have a vapor barrier put down before the concrete is poured.

Lehman57,

Sure, I believe water vapor will leak through concrete. I was not attempting to claim that water vapor would not. I was simply using concrete as an example of a porous material. I have seen metal rapidly corrode on concrete floors. I have seen liquid water(which I will grant could have been condensation) on previously dry subterranean basement walls with no obvious cracks. I do not care, I was simply using water and concrete as an example of a well known porous material which could pass polyatomic molecules easily, and not particularly trying to distinguish between gaseous water and liquid water. I recommend if you want dry concrete, that you employ a vapor barrier and a dehumidifier. Ferrocement has a reputation for passing far less water of either phase, but that is a different discussion.

I am curious though, are you asserting that liquid water cannot pass through concrete unless it first undergoes a phase change to become a gas ?

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thewildotter

What about hydraulic cement?

Out of interest, how does water vapourise under a slab of concrete?

Getting the He in: When I worked at a National Lab doing experimental processing of Pu many years ago, we did the work inside He atmosphere glove boxes. When items were to come out of the glove boxes, they normally were put in sealed paint cans then into heavy vinyl tubes. The tubes had 3 heat seals across them, and were cut off, and out of the glove box, by cutting thru the middle seal. This isolated the item inside the vinyl tube--now a bag--under a He atmoshpere, and there were no valves. I was actually storing this stuff in large combination lock vaults. After a period of time (months?) the bag was tight against the can, because the He had leaked out thru the heavy vinyl.

Helium would most likely move through liberal hard plastic than it would through conservative hard plastic...

I think you are confusing helium with hot air!

I am a plastics engineer, permeability expert (worked with carbonated bevs and NASA helium-filled stratosphere balloons). Plastics differ widely in permeability. Metallizing with aluminum is good; a lot depends on how cheaply you need to make the product, and also service conditions. Silicon oxides in very-thin layer is good against oxygen but I don't know about helium. Sealing will be critical as even a few unmetallized strips or holes will allow leakage. Think a tiny pinhole in a gallon jug of water.

PS. There are no toxic plastics. The worldwide plastophobia is because they are corporate, variable, and based on chemistry not magic -- people need to believe the impossible (magic) to stay sane.

Helium will leak through most things. It is the pressure difference, the thickness and the nature of the material that determines the rate.

Oh, and the temperature, of course.

Some hard plastics, such as gas containers have a special non-permeable membrane in the plastic. These cans are non-metallic and will hold gas vapors for a long time. Do some math and see which molecules are bigger and if this would work for you. There are self-closing valves readily available on the market. That's all I can say without giving away too many of my own secrets.

Helium is good for soundproofing, that is it would be, if it didn't leak out so fast....

Let's do some experiments...

Probably would make a really good insulator from heat ....space blankets already work really well, add a layer of helium between two space blankets and insulate the entire house with that you could probably cool the whole house with a 1 ton AC unit...of course it would have to be recharged every year...at least until something comes along that can hold a helium charge indefinitely....