Wikipedia:Reference desk/Archives/Science/2014 July 16

= July 16 =

Thermal conductivity of Invar 36 alloy (Fe+Ni)
Where can I find data on the thermal conductivity of Invar over a range of temperatures, say from 300 K to the melting point? By Googling I could only find a value for 290 K and thereabouts. 144.138.223.252 (talk) 03:07, 16 July 2014 (UTC)

Black iridescent duck
I have a picture, but its resolution is so bad that there's no point of attaching it. Can anyone identify what a black, iridescent duck might be? It was seen in Hamilton, Ontario, is somewhat larger than the many mallards swimming around it, and is completely iridescent black (similar to a European starling), except for the head, which is closer to an extremely dark iridescent green. Its head resembles a mallards except for the black beak. While the swimming mallard resembles an "L" on its side, this duck's profile resembles a checkmark. The beak is black, as are the wings and feet. The closest thing I could find is the Cayuga duck, but the image on the article shows it being all green, while the sighted duck is mostly black except for the head.  Bramble claw  x  03:30, 16 July 2014 (UTC)


 * Iridescence means it "appears to change color as the angle of view or the angle of illumination changes". Given that, it could well be the Cayuga duck, just viewed at a different angle or light than in the pic. And, of course, as with any species, there will be some variation on color from individual to individul. StuRat (talk) 03:38, 16 July 2014 (UTC)

Battery
Why has no one managed to design a massive battery to store electricity. I can be done on a small scale, why not a big one. I know that water can be stored to produce electricity but that is not the point.85.211.132.74 (talk) 06:16, 16 July 2014 (UTC)


 * You mean something with masses of poisonous and corrosive chemicals that degrade and leak into the environment? There's been enough cases of even small batteries catching fire and generating noxious smoke. What's the point of that when you can do it cleanly and efficiently otherwise? Lifting water up to a lake is very efficient. Flywheels too are very good though big ones need very strong containment for safety reasons. Even storing hydrogen produced by electrolysis or making fuels from that must be preferable to using tons of batteries. Dmcq (talk) 07:39, 16 July 2014 (UTC)


 * It has been done. http://www.popsci.com/science/article/2012-01/china-builds-worlds-largest-battery-36-megawatt-hour-behemoth 196.214.78.114 (talk) 08:03, 16 July 2014 (UTC)


 * I'm not even surprised: that's where our batteries go when we dispose of them... - ¡Ouch! (hurt me / more pain) 08:39, 16 July 2014 (UTC)


 * Of course that's not a massive battery but a massive array of batteries. There is no need to make really large battery - you just need to connect a lot of small ones together in parallel and you can make an array with as much storage as you like. I'm not so sure it is true to say that Pumped-storage hydroelectricity is efficient though. Our article says "Although the losses of the pumping process makes the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand, when electricity prices are highest". I'm sure the capital cost of building such storage is pretty high and you need a massive area to store the water too. Richerman    (talk) 15:20, 16 July 2014 (UTC)


 * It does not make sense. Batteries are either very inefficient (0.6) or only fairly efficient (0,8) but then very expensive. Additionaly a very big battery is stationary ofcourse so its anyway cheaper and more efficient to enshure electrical power supply by combining a network with some backup like a generator powered by a diesel engine. --Kharon (talk) 16:13, 16 July 2014 (UTC)
 * The article on you pointed at about pumped storage says 'PSH reported energy efficiency varies in practice between 70% and 80%, with some claiming up to 87%'. That's pretty good and the reason it is done so often. And unlike a good battery they don't degrade to only storing half the charge after two years. Flywheel energy storage and Power to gas describe the other options I mentioned and an overview is at Energy storage. Dmcq (talk) 16:44, 16 July 2014 (UTC)


 * About the only application I can see for a massive battery would be if it was connected to some technology to capture lightning strikes. However, I suspect that a massive supercapacitor would be better for this, and could then be used to either power a city or the charge could be converted to long-term energy storage, like by raising water to a higher elevation. StuRat (talk) 16:46, 16 July 2014 (UTC)
 * I just had a look at using batteries and my guess would be that for a large fixed site the best option would probably be to use a big array of car batteries. These are long lasting and hold their change well and are pretty efficient even if they don't have anywhere near the best power density. Dmcq (talk) 16:58, 16 July 2014 (UTC)


 * The electromotive force (voltage) of an electrochemical cell is determined by the choice of electrode materials and the electrolyte; not by the size of the cell. So a very large electrochemical cell would have a very modest emf - perhaps no more than 2 or 3 volts. It would perhaps be practical to assemble a very large battery consisting of a very great number of cells in both series and parallel so the resulting battery has a suitably large emf and is also capable of supplying a suitably large current. User:Dmcq and others have also implied the same thing by talking about a large array of car batteries. Dolphin  ( t ) 07:24, 17 July 2014 (UTC)


 * 20 or so years ago the term "car battery" would be understood unambiguously to mean the lead-acid type that powers the starter, ignition and lights. Now however, a variety of battery types are used for electric car propulsion so that a "car battery" might be any one of several types: lead-acid, nickel-iron, nickel-metal hydride, molten salt (Zebra), lithium-ion or lithium-ion polymer. Wikipedia has articles about each type. 84.209.89.214 (talk) 19:02, 18 July 2014 (UTC)

Metastability
Is it accurate to say that all chemical explosives are metastable? 24.5.122.13 (talk) 08:09, 16 July 2014 (UTC)


 * Not according to the usual meaning of 'metastable' as applied to chemical compounds. Although, technically speaking, exothermic reactions indicate that the reactants are metastable compared to the products. Note 'technically speaking'. 'Metastable' usually means that the compound has a ground-state configuration accessible by overcoming an activation energy, without decomposing explosively, or otherwise. Plasmic Physics (talk) 09:58, 16 July 2014 (UTC)


 * Wikipedia could use some editing on this point. We have no metastable compound and articles like magnesium oxide use it in this 'technical' sense.  It strikes me that this concept can be used to describe anything from, say, a piece of paper in air that could be set on fire to a single molecule that could and eventually will break down (diamond to nitrogen triiodide).  But there is a much more limited situation in which an individual molecule, without rearrangement, can go from a high energy state to a lower energy state (all-trans-retinal vs. 11-cis-retinal).  What I would like to see more about though are the molecules that don't even undergo isomerization, but somehow manage to hold onto energy for some seconds within their structure.  These are important and typically find use in large essentially semiconductor arrays (chlorophyll and accessory pigments) but also there's the classic photoluminescence of a fluorescent frisbee, etc.  I wouldn't mind a guided tour through this batch of concepts. Wnt (talk) 16:31, 16 July 2014 (UTC)
 * Lacking an article on metastability in chemistry it's hard to tell, but isn't that concept just the chemical version of general bistability (with the possibility of more than two ground states)? "ground-state configuration accessible by overcoming an activation energy" looks like it would fit right in with the general dynamical systems language and diagrams in the bistability article. That article even mentions activation energy for info on the chemistry-specific case. I see a key distinction similar to what you point out though: a piece of paper in air is an excitable system, but probably wouldn't be considered metastable, in the sense of Plasmic's "without decomposing" We don't usually consider wood to be a type of ash, and vice versa... SemanticMantis (talk) 17:12, 16 July 2014 (UTC)
 * Metastable means one of two things in chemistry:
 * A system which is in a local potential energy minimum which is NOT an absolute potential energy minimum. The Wikipedia article title Metastability actually has a nice graphic that explains this type of metastability.  That is, the system will remain in a state of metastability indefinitely if unperturbed, but where a small perterbation will generally set it moving to a new state spontaneously
 * A system which is thermodynamically unstable, but whose kinetics is so slow that it appears on human time scales to be stable. That is, the system is spontaneously changing, but doing so so slowly that for all practical purposes, it cannot be observed to be changing.
 * See, for example, the two definitions under "World English Dictionary" here.
 * In simplest terms, metastable means "stable-ish" or "stable enough" or "sorta stable, but not really stable-stable" or something like that. -- Jayron  32  23:11, 16 July 2014 (UTC)
 * This makes sense, thanks. After some reflection, I'm confident that it's not wrong to describe chemical explosives as metastable. Confusingly, they might not fit into certain strict senses of chemical metastability (because the end products have undergone several major chemical changes compared to the original substance), but they are clearly metastable from a dynamical systems perspective, because the system is relatively inert and stable to small perturbations, until a perturbation of high enough energy initiates the explosive reactions. SemanticMantis (talk) 17:15, 17 July 2014 (UTC)

SemanticMantis, Wikipedia does not lack articles on metastability in chemistry. Metastability in electronics is an inevitable result of any attempt to map a continuous domain to a discrete one. It is demonstrated when a flip-flop receives too short setup and hold times to arrive at a bistable state. It is a probable but not essential consequence of the flip-flop's metastability that random thermal noise will eventually drive it into one of its stable states Q=0 or Q=1, unrelated to earlier inputs (data on which is lost).

The etymology of the prefix meta- shows it to have long been a catch-all for different things: 

Metastability as a concept in chemistry offers a description of the collective behaviour of atoms but it may be misleading to consider stages in a chain of reactions as states of metastability for two reasons:

1) Reaction products are never permanently isolated. That we can speak of an ignition temperature needed to initiate burning or an explosion demonstrates that there is an irreversible route to increase the combined Entropy of the system and its environment; it just isn't happening right now. On a cosmological scale, every physical state of every thing is arguably a metastable state on the decay path to the end of everything when there will be no thermodynamic free energy to sustain processes such as computation and life. Metastability in substances thus seems exposed by way of a Reductio ad absurdum to be an oxymoron.

2) States of matter are statistical views of states of particles so we must ask whether there is a metastable particle. Whether a Nuclear isomer can qualify depends on our concept of time because the mysterious Isotopes of tantalum, which is present in natural tantalum a rare metal that you probably have at most one use for that you didn't know about samples at about 1 part in 8,300, has a half-life of at least 1015 years, likely longer than the age of the universe. That seems "stable" for practical purposes, but in the view of quantum mechanical uncertainty the Matter wave nature of fundamental particles forbids stable exact measurement of them.

The term metastability is a semantic construction with necessarily time-limited scope. A Dice is in a metastable state all the time until it is rolled, but from a deterministic perspective the stable end result was never in doubt. Albert was sure that God "is not playing at dice". However there would be no Divine Comedy nor Summa Theologica if Dante and Thomas respectively had not envisioned God as player in a metastable standoff between good and evil. While a Western philosopher (Buridan) conceives man as an ass unable to save himself from a metastable dilemma, there is more common sense to hear from an Islamic source: 84.209.89.214 (talk) 22:56, 17 July 2014 (UTC)
 * Yes, fine, but you're arguing why the word metastable should not be used because either a) the etymology of meta or b) the futility of determining between a metastable state and a truly stable state when the only stable state is the heat death of the universe.  That's fun to do, and probably makes you feel superior to everyone whom you think has it wrong, and it must the make you feel really good because the whole entire world has it wrong according to you.  Still, that's a useless tangent to take us on, because lots of people DO use the word to mean very specific things, and it's more useful to help the OP understand what people mean when they use the word, than to try to show the OP how smart you are because you can use your unassailable logic to prove the entire scientific world, and their use of that word, wrong... -- Jayron  32  01:03, 18 July 2014 (UTC)