3 ms·
I am twenty years removed from it, but I used to be well-informed on this kind of thing; I have a PhD in mineral physics. Let's see how well I can explain this
by adw 7y ago
I am twenty years removed from it, but I used to be well-informed on this kind of thing; I have a PhD in mineral physics.
Let's see how well I can explain this (haven't read the article, yet, sorry! Waiting for a plane...)
So you're no doubt familiar with the physics of a vibrating string; it resonates at wavelengths (length of string, 2 * length of string, 3 * length of string... n as n->inf). So you can express any vibrational state of the string as sum(intensity * wavelength); so you can represent the state of the string as a vector of intensities on a basis of allowable vibrations of the string.
Let's call these _vibrational modes_. Let's assume occupancy of these modes is quantized. It's (sort of...) the same as energy levels of atomic orbitals in electronic structure, if you remember that from chemistry classes; the way it's not the same is important (bosons vs fermions) but not at this level of handwaving :-)
So this is how solids store energy, and we call this energy "heat".
A reasonable approximation for a crystalline structure is balls – point masses – connected by springs, where the springs are covalent bonds, plus electrostatic effects between point charges. Intuitively, you can follow that the same kind of _vibrational spectrum_ will arise from this arrangement (in the same kind of way; the solutions of the differential equation of this system of forces under periodic boundary conditions). So materials have resonant frequencies in the same way guitar strings do.
Therefore, this vibrational spectrum defines the thermal behavior of a material; heat capacity, thermal conductance, etc etc etc etc. Each of these vibrational modes is also tied to a collective motion of the particles in the material, which (if sufficiently violent) will tear the structure apart – there's the solid-to-liquid phase transition – or, more subtly, if lost will lower the symmetry of the crystal structure, which gives rise to solid-to-solid phase transitions (an example would be alpha to beta quartz, which will crack your crockery if you leave it in the oven on a cleaning cycle; https://en.wikipedia.org/wiki/Quartz_inversion https://en.wikipedia.org/wiki/Quartz_inversion).
There's a lot of depth here, as you can imagine!
- diegoperini 7y ago> A reasonable approximation for a crystalline structure is balls – point masses – connected by springs, where the springs are covalent bonds, plus electrostatic effects between point charges. Thanks! This is a great analogy.
- infinite8s 7y agoThis is the model used by most chemical simulation codes (that don't account for quantum chemistry). See for example the LAMMPS simulation software (https://lammps.sandia.gov/ https://lammps.sandia.gov/)
- adw 7y agoIf anything I wrote has been original, it would have been a big red flag :-)
- agumonkey 7y agoWell written I must say. Makes me very curious about crystals and material physics (especially since I got interested in low level electronics and semi conductors). Any suggestion to read ?
- adw 7y agoNot really light reading, but any good solid-state physics textbook would cover most of this. I learned from https://www.amazon.co.uk/Introduction-Mineral-Sciences-Andrew-Putnis/dp/0521429471 https://www.amazon.co.uk/Introduction-Mineral-Sciences-Andre..., which is quite a bit more explicitly mineral-sciences focussed.
- agumonkey 7y agoAight, I'll see if I can digest it.
- correct_horse 7y agoI think you meant to say length of string, length of string / 2, length of string / 3, ... https://en.wikipedia.org/wiki/Harmonic https://en.wikipedia.org/wiki/Harmonic
- 7373737373 7y agoThis reminds me of this Sixty Symbols video which explains why light is slower in media such as glass than in a vacuum: https://www.youtube.com/watch?v=CiHN0ZWE5bk https://www.youtube.com/watch?v=CiHN0ZWE5bk The incoming light wave causes an avalanche of secondary waves through electromagnetically perturbing the individual atoms, and the superposition of all these results in a wave that seems to travel slower than the speed of light.
- jcims 7y agoThis is so cool, thank you. I dabble informally and quite primitively with signal processing, so the idea of vibrational spectrums in a crystalline structure really resonates (hurrr). Now i have a whole new set of mental imagery to process when i pick up the pan with a handle that had the handle a little too close to the flame. Thanks!!
- stjohnswarts 7y agoI hate to mess with your physics education but silicone covers for all your metal pan handles is a godsend, even for atheists.
- peter_d_sherman 7y agoGreat information! Also, (and I may be totally wrong about this!), the concept of Annealing from metallurgy -- seems related to that of Quartz Inversion: https://en.wikipedia.org/wiki/Annealing_(metallurgy) https://en.wikipedia.org/wiki/Annealing_(metallurgy)
- kragen 7y agoWell, both annealing and dunting ("quartz inversion") have to do with the crystalline structure of materials, but that's where the similarity ends. There are many important crystalline phase transitions in metallurgy that are more similar to dunting; the most important of many examples is probably the ferrite-to-austenite transition in steels at 700–1400°. But annealing is not such a crystalline phase transition.