5 ms·

The article lets me wonder: what is a molecule? I can see how one might arrive at Sc1.5Al0.5W3O12 - but that suggests that one Sc and one Al atom are shared be

by Beldin 5y ago

The article lets me wonder: what is a molecule? I can see how one might arrive at Sc1.5Al0.5W3O12 - but that suggests that one Sc and one Al atom are shared between two of this stuff's molecules. Anyone an idea why you wouldn't consider that one the molecule, i.e. Sc3AlW6O24?

dvh 5y ago
It's not a molecule, just like steel isn't FeC molecule.
- rand0mx1 5y ago
  An alloy is a mixture, no bond formation
  - kube-system 5y ago
    I’m confused. The article mentions the “bonds” of this substance, but doesn’t use any description more specific than “material” to describe it. Is this an alloy, or a molecule, or something different?
    - kortex 5y ago
      It's an alloy. See my other comment up-thread. The chemical formula here is an empirical formula - it describes the ratio in the bulk material. These are not discrete molecules but rather repeating crystal structures.
      - klyrs 5y ago
        Is it an alloy? The article doesn't say, but it mentions they tested it in powder form, and it sure does have a ton of oxygen. My guess is that it's a ceramic.
        kortex 5y ago
        Oh jeez. I'm actually not sure. The oxide definitely screams "ceramic" now that you mention it. I think I took the one thread mentioning "alloy" along with (the admittedly woo-ish) image of the aircraft skin and brain just stuck on "alloy," which implies "admixture of metals." I might also be thinking of Invar, an alloy with super low CTE. Scandium, aluminum, and tungsten oxides are all refractory ceramics, so I would reason that their mixed oxide is very similar. But tungsten (IV) oxide is conductive. Shrug, I was an organic chemist. The bonding structure is shown in the data pdf here[0]. It's a heavily networked orthorhombic lattice and (oof, it's been a hot minute since inorgo class) what looks like lots of coordinate bonds. It's definitely more alloy/ceramic than molecule, which is sort of the GP thread topic, but I can't tell if it's considered an alloy, ceramic, both, or neither. https://pubs.acs.org/doi/10.1021/acs.chemmater.1c01007 https://pubs.acs.org/doi/10.1021/acs.chemmater.1c01007
  - kortex 5y ago
    Incorrect-ish. Alloys have metallic bonds, colloquially a "sea of electrons." There are no[0] discrete, covalent bonds like you would find in nonmetallic molecules. But the atoms are absolutely bonded in the sharing electrons sense. This is what gives strength and toughness to metals. [0] - grossly oversimplifying here. Also I was mostly an organic chemist and didn't study metallurgy much.
deleted 5y ago
[deleted]
dbsmith83 5y ago
Since it isn't molecular you can scale it by any number. Oftentimes it seems that decimals will be used when the ratio is not fixed. I'm guessing that at different temperatures some of the atoms will move around, while bond distances will change and thus overall the volume stays consistent. > Not with this stuff, which the team observed across that huge temperature spectrum demonstrating "only minute changes to the bonds, position of oxygen atoms and rotations of the atom arrangements." The team says the exact mechanism behind this extreme thermal stability isn't totally clear, but that perhaps bond lengths, angles and oxygen atom positions are changing in concert with one another to preserve the overall volume.
projektfu 5y ago
https://en.wikipedia.org/wiki/Non-stoichiometric_compound https://en.wikipedia.org/wiki/Non-stoichiometric_compound
javajosh 5y ago
It makes me wonder: where does thermal expansion in solids come from, anyway? There seems to be a parallel with the ideal gas law, but because the nuclei are far more constrained, the bonds must be stretchy, and since the material has to have some way of storing heat in the steady state, the only place I can think of is vibration of the bond. But how does a vibrating bond lead to expansion? In theory a strong enough bond could store infinite energy, as the modes get higher.
- elcritch 5y ago
  Bond vibration is one. In crystalline materials those vibrations can produce phonons, or waves, of thermal energy. See: https://www.chemicool.com/definition/phonons.html https://www.chemicool.com/definition/phonons.html

by Beldin 5y ago

dvh 5y ago

It's not a molecule, just like steel isn't FeC molecule.

rand0mx1 5y ago
An alloy is a mixture, no bond formation
- kube-system 5y ago
  I’m confused. The article mentions the “bonds” of this substance, but doesn’t use any description more specific than “material” to describe it. Is this an alloy, or a molecule, or something different?
  - kortex 5y ago
    It's an alloy. See my other comment up-thread. The chemical formula here is an empirical formula - it describes the ratio in the bulk material. These are not discrete molecules but rather repeating crystal structures.
    - klyrs 5y ago
      Is it an alloy? The article doesn't say, but it mentions they tested it in powder form, and it sure does have a ton of oxygen. My guess is that it's a ceramic.
      - kortex 5y ago
        Oh jeez. I'm actually not sure. The oxide definitely screams "ceramic" now that you mention it. I think I took the one thread mentioning "alloy" along with (the admittedly woo-ish) image of the aircraft skin and brain just stuck on "alloy," which implies "admixture of metals." I might also be thinking of Invar, an alloy with super low CTE. Scandium, aluminum, and tungsten oxides are all refractory ceramics, so I would reason that their mixed oxide is very similar. But tungsten (IV) oxide is conductive. Shrug, I was an organic chemist. The bonding structure is shown in the data pdf here[0]. It's a heavily networked orthorhombic lattice and (oof, it's been a hot minute since inorgo class) what looks like lots of coordinate bonds. It's definitely more alloy/ceramic than molecule, which is sort of the GP thread topic, but I can't tell if it's considered an alloy, ceramic, both, or neither. https://pubs.acs.org/doi/10.1021/acs.chemmater.1c01007 https://pubs.acs.org/doi/10.1021/acs.chemmater.1c01007
- kortex 5y ago
  Incorrect-ish. Alloys have metallic bonds, colloquially a "sea of electrons." There are no[0] discrete, covalent bonds like you would find in nonmetallic molecules. But the atoms are absolutely bonded in the sharing electrons sense. This is what gives strength and toughness to metals. [0] - grossly oversimplifying here. Also I was mostly an organic chemist and didn't study metallurgy much.

deleted 5y ago

[deleted]

dbsmith83 5y ago

Since it isn't molecular you can scale it by any number. Oftentimes it seems that decimals will be used when the ratio is not fixed. I'm guessing that at different temperatures some of the atoms will move around, while bond distances will change and thus overall the volume stays consistent. > Not with this stuff, which the team observed across that huge temperature spectrum demonstrating "only minute changes to the bonds, position of oxygen atoms and rotations of the atom arrangements." The team says the exact mechanism behind this extreme thermal stability isn't totally clear, but that perhaps bond lengths, angles and oxygen atom positions are changing in concert with one another to preserve the overall volume.

projektfu 5y ago

https://en.wikipedia.org/wiki/Non-stoichiometric_compound https://en.wikipedia.org/wiki/Non-stoichiometric_compound

javajosh 5y ago

It makes me wonder: where does thermal expansion in solids come from, anyway? There seems to be a parallel with the ideal gas law, but because the nuclei are far more constrained, the bonds must be stretchy, and since the material has to have some way of storing heat in the steady state, the only place I can think of is vibration of the bond. But how does a vibrating bond lead to expansion? In theory a strong enough bond could store infinite energy, as the modes get higher.

elcritch 5y ago
Bond vibration is one. In crystalline materials those vibrations can produce phonons, or waves, of thermal energy. See: https://www.chemicool.com/definition/phonons.html https://www.chemicool.com/definition/phonons.html