7 ms·
Some alloys don't change size when heated – recent work on why
- lr4444lr 3y agoCool. What would applications be here? Could we for example make basic alloys of vehicles, railroad tracks, and refrigeration systems more resilient when they undergo temperature variations, and therefore last longer?
- bediger4000 3y agoTraditionally, holding optics or some other delicate sensors that we want to stay aligned, or at least point in the same direction consistently.
- ScoobleDoodle 3y agoBlackbird SR-72? SR-71 leaks before take off in anticipation of the thermal expansion plugging everything up. https://nodum.org/was-sr-71-blackbird-leaking-fuel/ https://nodum.org/was-sr-71-blackbird-leaking-fuel/
- brilee 3y agoThe heat generated by drag at such high speeds means that titanium was, at the time, the only suitable material due to is high melting temperature.
- barelyauser 3y agoNot high melting point but its ability to remain strong at high temperature.
- hinkley 3y agoAn annealed aircraft is not a particularly safe aircraft, yes.
- sadhorse 3y agoOnly precision applications can afford the high cost of specialized materials. All the things you mentioned are unrelated, as they are cost driven and steel will always win.
- nuancebydefault 3y agoFrom the understanding of the mechanisms that cause this invariance, many other applications could be derived, that even don't need the invariance property. For example materials of which cooling systems (e.g. Peltier-like) can be made. Also their measurement methods seem pretty advanced and could be used within other research like in the area of nano technology.
- mitthrowaway2 3y agoYes, the main value would probably be in better understanding the temperature / pressure / volume / magnetism relationship within invar-like materials. Perhaps the result will be new piezomagnetic applications, or magnetocooling applications, and so on.
- Cthulhu_ 3y agoWell, they knew the effect existed, so applications are already in use; this just explains the how, which I'm sure makes the effect more predictable - and allows for researchers to find more alloys with this effect in a focused manner, instead of via trial and error. As for applications, it probably won't be garden variety appliances, thermal expansion isn't much of an issue there and designs for all of the things you mentioned have been tweaked a hundred years ago to deal with thermal expansion (although railroad tracks are still an issue sometimes). And of course there's other parameters, like wear resistance; nickel is a pretty soft metal I believe. But, things like precision industry or space will find a use for this. Sattelites have to deal with hundreds of degrees of temperature variation.
- _yb2s 3y agoI disagree, even modern cars have a lot of unsolved problems with thermal expansion and cracking causing failures of cylinder heads, gaskets, exhaust manifolds, turbochargers, etc. It may be solved in principle, but certainly not in practice.
- barelyauser 3y agoThere are problems that are game stoppers and there are problems that are unavoidable. Cars work. Yes, if you drive 1 million miles you will have cracks in the engine due to thermal expansion, but who cares? Make a new engine and get over it. Now consider a space elevator. Material problems are a game stopper.
- MichaelZuo 3y agoThese problems are already solved for very high end aftermarket exhaust systems, which use Inconel.
- dublinben 3y ago"Modern" cars run on electricity and don't have any of those parts or their corresponding problems.
- buryat 3y agowho needs to read the article? > That anomalous behavior makes these alloys useful in applications where extreme precision is required, such as in the manufacture of parts for clocks, telescopes, and other fine instruments.
- Ellentonnq 3y ago[dead]
- golem14 3y agohttps://en.wikipedia.org/wiki/Invar https://en.wikipedia.org/wiki/Invar gives a few hints.
- burnished 3y agoNo need - you ever cross a bridge and note a mesh of metal teeth? Thats for thermal expansion. Its already designed around and isnt generally noticeable - for steel it is 0.0000065 / °F [0]. [0] https://www.metalsales.us.com/thermal-expansion https://www.metalsales.us.com/thermal-expansion
- loeg 3y agoWould be nice to not have the holes though.
- burnished 3y agoWhy is that? I've already put all my knowledge on the topic on display so I can't tell if this is a joke about aesthetics or if there is actually something neat having to do with the gaps
- hinkley 3y agoI know from tales of professional cycling that those metal bridges are vastly disproportionately responsible for broken bones. They're also squirrely when wet, and if you've ever ridden across one on a bike or a motorcycle, they are fucking terrifying because you can see the river below you, and the railings for some reason tend to be very low. And while I understand that many bridges don't really prevent runoff into the water flowing beneath them, metal mesh bridges really can't.
- maxbond 3y agoI'm not sure you're talking about the same thing though, I think they meant these thermal expansion joints, not necessarily a bridge made from metal mesh: https://i.pinimg.com/originals/4d/82/91/4d8291e022bd14c87985df11fad1be1e.jpg https://i.pinimg.com/originals/4d/82/91/4d8291e022bd14c87985... I know that picture is a mesh, I thought it had the best detail, but they're on paved bridges too: https://siamagazin.com/wp-content/uploads/2018/03/23h32h-min-1.jpg https://siamagazin.com/wp-content/uploads/2018/03/23h32h-min...
- metal_am 3y agoForms and tooling for composites are a big one in the aerospace world. Keeps dimensional stability better through autoclave cycles.
- hinkley 3y agoI was going to say something similar but then I started having doubts. For precision instruments you probably want devices that have exactly the same modulus of expansion as what you are cutting. So that 0.15m is always 0.15m no matter the temperature of the factory. For molds you would want the outer mold to shrink slower than the molded material, but would you perhaps not want an inner mold to shrink faster? So that the material pulls away from both as it cures/cools (I'm asking, I don't know)?
- bluGill 3y agoProbably not. You typically cannot change one variable in isolation with an alloy, so while you can gain in one area other things change as well. Strength - both compression and tension, hardness, resistance to bending, springiness, melting temperature, are just a few of the properties (note that the properties have engineering names and common names - I mixed with no concern so there is duplication)
- Terr_ 3y ago> That anomalous behavior makes these alloys useful in applications where extreme precision is required, such as in the manufacture of parts for clocks, telescopes, and other fine instruments.
- JKCalhoun 3y agoTangent: reminded me for some reason of the lengths (ha ha) clock makers went to to account for the expansion and contractions of the clock pendulum. To keep consistent time the length of the pendulum too needed to remain constant. Enter the brilliant John Harrison: https://en.wikipedia.org/wiki/Gridiron_pendulum https://en.wikipedia.org/wiki/Gridiron_pendulum
- twism 3y agoautomatic weapons
- w10-1 3y agoA summary to motivate reading the paper: Invar, a nickle-iron alloy, was commercially highly relevant for accuracy of mechanical watch balance springs in the 19th century. Investigations of that presumably lead to the 1920 Nobel in physics. The article claims to produce the first equation to model this effect accurately, together with an experimental technique to validate the main components. This would support in-silico material exploration, esp. predictions for high temperatures that induce expansion. But because this demonstrates phase shifts in how electrons interact, the significance could be broader that just the use of constant-size invar (iron/nickel alloy). Paper excerpts: ---- Here we use a thermodynamic Maxwell relation to explicitly separate the contributions to thermal expansion from phonons and spins. [...] These two contributions were measured by nuclear resonant X-ray scattering on Invar under pressure. We find that a competition with phonons is necessary to complete the explanation of the near-zero thermal expansion of Invar. An advantage to [our] equation is that the two main components of thermal expansion—phonon and magnetic—can be experimentally obtained by nuclear resonant X-ray scattering Excellent agreement between experiment and theory is found. There is a remarkable spin–lattice coupling, and a precise cancellation of the phonon and spin contributions that causes the anomalously low thermal expansion in Invar near ambient conditions of T and P. Furthermore, the transition to a more typical thermal expansion at higher pressures is shown to arise from the magnetic transition to the paramagnetic state that quenches the negative contribution from the spin system. Finally, the electronic contribution is found to have only a small effect on thermal expansion.
- wolverine876 3y agoIs 'invar' a class of materials, a specific material, or both? From the OP: > There is, however, a class of metal alloys called Invars (think invariable), that stubbornly refuse to change in size and density over a large range of temperatures.
- serf 3y agoits a small set of nickel iron alloys that are available (to machinists at least) in a few configurations dictated by their iron/nickel content. with the addition of cobalt it becomes Kovar, a metal that is common for telescope use or joints where metal bonds to glass. they're all fairly proprietary and expensive. I've used Invar a lot in the production of heated press platens.
- MichaelZuo 3y agoIt's a very interesting effect, magnetism 'perfectly cancelling' out thermal expansion. Are there any other cases where magnetism is responsible for something this subtle?
- mturmon 3y agoHow about the Zeeman effect, in which strong magnetic fields in locations where light is emitted, will cause the spectral lines associated with emitting material to split? The strength of the magnetic field is encoded in how broadly the line is split, allowing us to make spatially-resolved maps of the magnetic field of the Sun ("magnetograms"). Like getting the chemical composition of the emitting surface of the Sun, it's the kind of thing you'd think sounds impossible until some clever physicist figures out how to exploit it. See the little animation at the top of the page: https://en.wikipedia.org/wiki/Zeeman_effect https://en.wikipedia.org/wiki/Zeeman_effect
- RugnirViking 3y agoI dont remember what its called but I always liked the magnetic braking thing where if you drop a ferrous cylinder through a copper tube it falls slowly with constant speed, because the magnetism induces current which induces a braking force
- eulgro 3y agoEddy currents
- cromwellian 3y agoHot take: If the Earth's core is Iron-Nickel, is it an Invar, and therefore, there's an effect too reduce earthquakes from expansion from heat movement being lower, or is the pressure alone enough to counteract that?
- 0xfae 3y agoThe core of the earth changes temperature very slowly. So any effect is probably pretty minimal. I would guess that comparatively huge thermal characteristics from the churning and moving of the crust and mantle due to plate tectonics probably overshadows this.
- pfdietz 3y agoThe core of the Earth is also far beyond the temperature/pressure at which this invar effect occurs.
- metal_am 3y agoThe article somewhat downplays the historical understanding of this. (It's understandable! This is a dense topic!) The impact of spin states has been known for a looong time. My first introduction to the topic was Zener's 1955 paper The Impact of Magnetism on Metallurgy.
- iancmceachern 3y agoYou can do this with composites too. You can even create materials with slightly negative CTEs