5 ms·

i always wondered why membranes. can we not drill 0.2nm holes in silicon for instance?

by pestatije 4y ago

criddell 4y ago
If you had a thin sheet of silicon filled with 0.2nm holes, wouldn't that be a membrane?
- AnthonBerg 4y ago
  Not if it’s thick and/or rigid, right?
  - brookst 4y ago
    What would be the advantage? Presumably it would have to be very thin, so rigidity seems like it would just mean fragility. Are you seeing it differently?
    - AnthonBerg 3y ago
      Just speculating!
- VygmraMGVl 4y ago
  Yes, that would be a membrane. There a number of membranes with larger pores that are fabricated like above, but out of polycarbonate (track etch membranes). Some people have also experimented with single and double layers of graphene with a few very small pores. Because they are so thin, you don't need as much porosity for high transport rates. You still have fouling issues, though.
- derefr 4y ago
  What you're picturing has a name: https://en.wikipedia.org/wiki/Fritted_glass https://en.wikipedia.org/wiki/Fritted_glass. It's used in a https://en.wikipedia.org/wiki/B%C3%BCchner_funnel https://en.wikipedia.org/wiki/B%C3%BCchner_funnel instead of filter paper, to efficiently separate liquids from solids. Also, if you take some fritted glass and wrap it around a solid core, such that the holes don't go anywhere — i.e. they're just pits that water molecules (but not anything larger) can enter, and then get stuck there by surface tension — then you've get https://en.wikipedia.org/wiki/Molecular_sieve https://en.wikipedia.org/wiki/Molecular_sieve s.
- SideburnsOfDoom 4y ago
  > If you had a thin sheet of silicon filled with 0.2nm holes That's literally individual silicon atoms removed "The nearest neighbour distance is 0.235 nm" https://www.princeton.edu/~maelabs/mae324/glos324/silicon.htm https://www.princeton.edu/~maelabs/mae324/glos324/silicon.ht...
mechagodzilla 4y ago
Silicon lattice spacing is ~0.5 nm - you're talking about a single atom
SideburnsOfDoom 4y ago
> can we not drill 0.2nm holes in silicon for instance? I think that this is interesting question, and should not be waved away with "just drill some 0.2nm holes, use a real small drill bit" 0.2nm is tiny, given that it's on a scale that impacts how H2O molecules behave. It's also smaller than our ability to make the circuits in computer chips, which are currently > 1 mn (1). Use a laser? Light with a comparable wavelength is x-rays. As used in the chip manufacturing (2) This is about size of the spacing between individual atoms (3) So it seems like a material with 0.2nm holes "drilled" into it would be a major engineering feat at least. 1) https://research.ibm.com/blog/1nm-chips-vtfet-ruthenium https://research.ibm.com/blog/1nm-chips-vtfet-ruthenium 2) https://en.wikipedia.org/wiki/X-ray_lithography https://en.wikipedia.org/wiki/X-ray_lithography 3) https://en.wikipedia.org/wiki/Atomic_spacing https://en.wikipedia.org/wiki/Atomic_spacing
Someone 4y ago
I’m not sure we can do that. Even if we could, drilling millions of holes is a lot of work. Also, for membranes, it’s not only the size and shape of the ‘holes’ that count. Many have specific chemical properties that do not solely filter on particle size.
TylerE 4y ago
That would cost 10000000x as much to manufacture. Think making a net versus hollowing a solid cube of steel into a net.
ftxbro 4y ago
no shade but this is peak "can't we just" hacker news energy
- chmod600 4y ago
  What's wrong with "can't we just" questions? Lots of curious laypersons here, and it's often a useful way to learn. Usually it's pretty easy for an expert to answer such questions.
  - ftxbro 4y ago
    nothing wrong with it that's why i put no shade
  - SideburnsOfDoom 3y ago
    It's only wrong if you push the follow-through onto others. That's lazy. If you're really curious, spend 5 minutes on it. In this case, if you ask "can we just do this" you should follow through with "how big is that actually, what's of comparable size?" We can all google this, or learn how to. It's a useful way to learn. You won't learn how to find things out, by always just asking "can't we just" questions and walking away. In this case, soon you'd find out that 0.2nm is on the same scale as the spacing between individual atoms in a silicon crystal. Literal "drill" bits for removing 1 atom at a time are obviously out of the question. It is 10x smaller than the 2nm, the scale of the best x-ray lithography computer chip manufacturing processes.
- comex 4y ago
  I’d say that peak “can’t we just” comes with an assumption that we could just, which is quite different from this comment which comes off to me as hoping to learn why we can’t just.
  - derefr 4y ago
    I often want to honestly ask "why we can't just do X", but I feel like I end up coming off as asking "can't we just do X" no matter how hard I try to phrase it otherwise. I feel like this is a place where English grammar just doesn't give you any good options.
whimsicalism 4y ago
i don't think you quite grasp how small that is
- TylerE 4y ago
  Yeah, the smallest drill bits regularly commercially available are on the order of 1mm. That’s 6 orders of magnitude.
  - SideburnsOfDoom 4y ago
    Individual silicon atoms in a crystal are around 0.2nm apart. https://www.princeton.edu/~maelabs/mae324/glos324/silicon.htm https://www.princeton.edu/~maelabs/mae324/glos324/silicon.ht... So no, you don't get drill bits that are 1-2 atoms wide. Also it would take a long time to "drill" a useful number of holes if you do it one by one. Use X-ray lithography maybe? The wavelength can be short enough and it might be more feasible to do in bulk.
klyrs 4y ago
You can "drill" 5nm holes in aluminum oxide[1]. Which is pretty sweet, but calling that process "drilling" is a gross misnomer. The finest drills[2] out there are measured in hundreds of nm, and still take several seconds to get through relatively thin material. To drill the billions of holes you'd need for a reverse osmosis membrane, you'd die before it was finished. [1] https://en.m.wikipedia.org/wiki/Anodic_aluminium_oxide https://en.m.wikipedia.org/wiki/Anodic_aluminium_oxide [2] https://www.tpc.toray/en/technology/hole/hol_005.html https://www.tpc.toray/en/technology/hole/hol_005.html

i always wondered why membranes. can we not drill 0.2nm holes in silicon for instance?

criddell 4y ago

If you had a thin sheet of silicon filled with 0.2nm holes, wouldn't that be a membrane?

AnthonBerg 4y ago
Not if it’s thick and/or rigid, right?
- brookst 4y ago
  What would be the advantage? Presumably it would have to be very thin, so rigidity seems like it would just mean fragility. Are you seeing it differently?
  - AnthonBerg 3y ago
    Just speculating!
VygmraMGVl 4y ago
Yes, that would be a membrane. There a number of membranes with larger pores that are fabricated like above, but out of polycarbonate (track etch membranes). Some people have also experimented with single and double layers of graphene with a few very small pores. Because they are so thin, you don't need as much porosity for high transport rates. You still have fouling issues, though.
derefr 4y ago
What you're picturing has a name: https://en.wikipedia.org/wiki/Fritted_glass https://en.wikipedia.org/wiki/Fritted_glass. It's used in a https://en.wikipedia.org/wiki/B%C3%BCchner_funnel https://en.wikipedia.org/wiki/B%C3%BCchner_funnel instead of filter paper, to efficiently separate liquids from solids. Also, if you take some fritted glass and wrap it around a solid core, such that the holes don't go anywhere — i.e. they're just pits that water molecules (but not anything larger) can enter, and then get stuck there by surface tension — then you've get https://en.wikipedia.org/wiki/Molecular_sieve https://en.wikipedia.org/wiki/Molecular_sieve s.
SideburnsOfDoom 4y ago
> If you had a thin sheet of silicon filled with 0.2nm holes That's literally individual silicon atoms removed "The nearest neighbour distance is 0.235 nm" https://www.princeton.edu/~maelabs/mae324/glos324/silicon.htm https://www.princeton.edu/~maelabs/mae324/glos324/silicon.ht...

mechagodzilla 4y ago

Silicon lattice spacing is ~0.5 nm - you're talking about a single atom

SideburnsOfDoom 4y ago

> can we not drill 0.2nm holes in silicon for instance? I think that this is interesting question, and should not be waved away with "just drill some 0.2nm holes, use a real small drill bit" 0.2nm is tiny, given that it's on a scale that impacts how H2O molecules behave. It's also smaller than our ability to make the circuits in computer chips, which are currently > 1 mn (1). Use a laser? Light with a comparable wavelength is x-rays. As used in the chip manufacturing (2) This is about size of the spacing between individual atoms (3) So it seems like a material with 0.2nm holes "drilled" into it would be a major engineering feat at least. 1) https://research.ibm.com/blog/1nm-chips-vtfet-ruthenium https://research.ibm.com/blog/1nm-chips-vtfet-ruthenium 2) https://en.wikipedia.org/wiki/X-ray_lithography https://en.wikipedia.org/wiki/X-ray_lithography 3) https://en.wikipedia.org/wiki/Atomic_spacing https://en.wikipedia.org/wiki/Atomic_spacing

Someone 4y ago

I’m not sure we can do that. Even if we could, drilling millions of holes is a lot of work. Also, for membranes, it’s not only the size and shape of the ‘holes’ that count. Many have specific chemical properties that do not solely filter on particle size.

TylerE 4y ago

That would cost 10000000x as much to manufacture. Think making a net versus hollowing a solid cube of steel into a net.

ftxbro 4y ago

no shade but this is peak "can't we just" hacker news energy

chmod600 4y ago
What's wrong with "can't we just" questions? Lots of curious laypersons here, and it's often a useful way to learn. Usually it's pretty easy for an expert to answer such questions.
- ftxbro 4y ago
  nothing wrong with it that's why i put no shade
- SideburnsOfDoom 3y ago
  It's only wrong if you push the follow-through onto others. That's lazy. If you're really curious, spend 5 minutes on it. In this case, if you ask "can we just do this" you should follow through with "how big is that actually, what's of comparable size?" We can all google this, or learn how to. It's a useful way to learn. You won't learn how to find things out, by always just asking "can't we just" questions and walking away. In this case, soon you'd find out that 0.2nm is on the same scale as the spacing between individual atoms in a silicon crystal. Literal "drill" bits for removing 1 atom at a time are obviously out of the question. It is 10x smaller than the 2nm, the scale of the best x-ray lithography computer chip manufacturing processes.
comex 4y ago
I’d say that peak “can’t we just” comes with an assumption that we could just, which is quite different from this comment which comes off to me as hoping to learn why we can’t just.
- derefr 4y ago
  I often want to honestly ask "why we can't just do X", but I feel like I end up coming off as asking "can't we just do X" no matter how hard I try to phrase it otherwise. I feel like this is a place where English grammar just doesn't give you any good options.

whimsicalism 4y ago

i don't think you quite grasp how small that is

TylerE 4y ago
Yeah, the smallest drill bits regularly commercially available are on the order of 1mm. That’s 6 orders of magnitude.
- SideburnsOfDoom 4y ago
  Individual silicon atoms in a crystal are around 0.2nm apart. https://www.princeton.edu/~maelabs/mae324/glos324/silicon.htm https://www.princeton.edu/~maelabs/mae324/glos324/silicon.ht... So no, you don't get drill bits that are 1-2 atoms wide. Also it would take a long time to "drill" a useful number of holes if you do it one by one. Use X-ray lithography maybe? The wavelength can be short enough and it might be more feasible to do in bulk.

klyrs 4y ago

You can "drill" 5nm holes in aluminum oxide[1]. Which is pretty sweet, but calling that process "drilling" is a gross misnomer. The finest drills[2] out there are measured in hundreds of nm, and still take several seconds to get through relatively thin material. To drill the billions of holes you'd need for a reverse osmosis membrane, you'd die before it was finished. [1] https://en.m.wikipedia.org/wiki/Anodic_aluminium_oxide https://en.m.wikipedia.org/wiki/Anodic_aluminium_oxide [2] https://www.tpc.toray/en/technology/hole/hol_005.html https://www.tpc.toray/en/technology/hole/hol_005.html