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Author: Subject: Substances with near room temp phase change
marko
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[*] posted on 27-3-2012 at 01:55
Substances with near room temp phase change


Hi, I was thinking of making a sort of.. fuzzy thermometer, with a few vials of substances that change phase near room temp. Not sure what would be useful here.
The only two I can think of would be glacial acetic acid, and tert-butanol. Any other ideas? I suppose solutions would be fine too.

Idea is essentially - have vials labelled 18, 19, 20, 21, 22 (degrees C), if 20 through 22 are frozen, then ambient temp is ~19 degrees. Something like this.

The other idea was an outdoor version, so same deal but larger steps, maybe 5 degrees.

Kind of silly, but, curious anyway. Bonus for things that are fairly benign, in case the 'thermometer' is damaged.
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[*] posted on 27-3-2012 at 03:24


http://en.wikipedia.org/wiki/NaK
http://en.wikipedia.org/wiki/Galinstan
adjust the ratio of the alloy and any melting point (within normal range) could be obtained
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Wizzard
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[*] posted on 27-3-2012 at 05:45


I would use a very slender graduated cylender filled with butane, with a soda bottle on top. As the heat causes a pressure increase (as the butane boils), there will be less collected in the graduated cylender at the bottom.

At -0.5*c, the butane will want to be a liquid. At 30*C, I'm quite certain it's still far less than the 200PSI useful limit for a plastic soda bottle.
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marko
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[*] posted on 27-3-2012 at 13:12


Problem with galinstan is that it wets to glass, so I don't think it will be easy to see in a vial.

NaK is a little uh.. exceeding my capability at the current time.
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bahamuth
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[*] posted on 27-3-2012 at 14:04


DMSO is a nice one, 18-19 degrees Celsius.

Cyclohexanol is also a good one at around 26 degrees C.

A "Stormglass" (google it) works by temperature also, producing different structures of crystals by the different temperatures.

Try out small scale the different compositions and make a large one that suits your ambient temp.




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Twospoons
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[*] posted on 27-3-2012 at 16:33


bahamuth : thanks for the "stormglass" tip. What a neat idea. I love it how these weird little things crop up from time to time.



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peach
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[*] posted on 28-3-2012 at 02:21


Glacial is a good idea. It definitely works in the UK if it's left in a garage. It's like opening an advent calendar wondering what state it'll be in. Different masses (in any of these examples) will provide differing amounts of lag, with larger values giving a general trend over the days, rather than the immediate temperature.

Caesium. Not particularly safe or easy to get, but MP is 28C.

I've been making a fair bit of diethyl ether recently (BP 34), likely contaminated with dimethyl ether (BP -27?C) and methyl ethyl ether (BP -8?C). With the lower boiling ethers in there, it keeps popping the stoppers off the flasks I put it in, so I opted for a balloon in the meantime, which humorously erects or goes flaccid based on the room temperature.

Maybe a balanced composition of ethers, with a smiley face drawn on the balloon, could indicated STP.

Honey, butter and chocolate*** are infamous for going from solid to liquid and back over a relatively narrow range for a natural product. I expect an interesting sweep of temperatures could be achieved merely by mixing those together (diary cream?). Some cooking oils will solidify if left in the fridge; which I have seen a student do, thinking it belonged there (they had servants at home, literally). A benefit of using something like honey or chocolate is that their epic sugar content and dryness means they effectively never go off; archaeologists have found still edible honey buried in a tomb in Egypt, put there thousands of years ago. Honey also has the nice property of going from transparent to opaque depending on the state. It'd be good if you had something like an hourglass that turned it's self over each day.

There are probably combinations of wax (mixed with oils) that will also work at room temperature. Google around 'freezing point depression', 'boiling point elevation' and 'eutectic'. Unfortunately, many of the examples will be solely water / salt, but that would still be useful for winter.

One place to start could be with Phase Change grease used on computer CPUs.



Quote:
An early form of device for showing changes in heat, typically a tube in which a liquid rises and falls. The first known thermoscopes were by Galileo Galilei in about 1592; the first clear diagram of a thermoscope was published in 1617 by Giuseppe Biancani. The addition of a scale makes it a thermometer, but this quantification (and the concept of temperature) did not arise till later.

-Thermoscope

I realise you were after state changes, but on a related note: Galileo's thermometer



***The melting point of chocolate and it's solidification is one of the hardest parts of making it. It needs a great deal of time in conching mills (like paint) to grind it as smooth as possible. If it cools incorrectly, it comes out like grit. This US documentary from the ?late 70s?/ ?early 80s? provides an excellent overview of the entire process: 'The Great American Chocolate Factory'.

[Edited on 28-3-2012 by peach]
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[*] posted on 28-3-2012 at 13:01


I read of some (fairly) famous scientist who kept a bottle of diphenylmethane on his desk.
If it melted he and the class took the day off to go swimming.
Given the melting point of this compound they may have ended up as better swimmers than chemists or it may be that my memory fails me and it was diphenyl ether.
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turd
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[*] posted on 29-3-2012 at 02:25


One problem with the plan: First order phase transitions are often marked by distinct hysteresis. Second order phase transitions often don't finish as they should (the trailing can go over 100 K and more!).
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[*] posted on 29-3-2012 at 02:49


A problem with some compounds is that they can be very hard to solidify, due to undercooling. I have a bottle of glacial acetic acid and even after days of strong cold (e.g. only 10 C) it still is a liquid. And then, at a certain day it suddenly has solidified. The same is true for tert-butyl alcohol (which melts at around 25 C). It remains liquid at 18 C for many many days.



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turd
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[*] posted on 29-3-2012 at 09:46


Was that a case of "great minds think alike" or rather "fools seldom differ". ;):D
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barley81
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[*] posted on 29-3-2012 at 11:50


Menthol can be purchased easily on eBay. It has a melting point of 30-40˚C. It does supercool easily, though.
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[*] posted on 31-3-2012 at 19:00


Diphenyl Ether
http://depositfiles.com/files/k6o7up5xp

Thank board member solo for this
http://www.sciencemadness.org/talk/member.php?action=viewpro...

.
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