9
$\begingroup$

Which materials or compounds expand in response to cold temperatures? This material or compound should expand at a slow (yet constant rate), from 0 to about 20 months when in the temperature range from −25 °C to −10 °C.

Also, the compound should not react with plastic, or be toxic to humans or the environment.

Please explain why the compound does this as well.

$\endgroup$
3
  • 2
    $\begingroup$ This seems to me to be a chemistry question. I found one compound pubs.acs.org/doi/abs/10.1021/ja106711v , Cubic ScF3 from the references in the wiki article en.wikipedia.org/wiki/… $\endgroup$
    – anna v
    Commented Nov 13, 2012 at 20:49
  • 3
    $\begingroup$ Isn't the typical example is water and ice? $\endgroup$
    – user822
    Commented Dec 16, 2012 at 8:55
  • $\begingroup$ Given the condition "expand at a slow (yet constant rate), from 0 to about 20 months..." I doubt that any chemical would meet that requirement! There are substances in a metastable state, such as supercooled water, that could sit for a year and then suddenly expand, but for a gradual, slow growth, I doubt any such thing exists. $\endgroup$ Commented May 14 at 21:22

3 Answers 3

8
$\begingroup$

In old time printing using type, the alloy used for the type was designed to have a zero coefficient of thermal expansion over a wide range so that they type did not change shape when cast at a high temperature and then cooled off.

It is very likely that slight modifications of that formula would yield an alloy with either a positive or negative thermal coefficient.

$\endgroup$
1
  • $\begingroup$ "expand at a slow (yet constant rate), from 0 to about 20 months..." Nope, type metal is not going to take a year or more to expand! $\endgroup$ Commented May 14 at 21:18
7
$\begingroup$

Perhaps one of the most studied materials to exhibit negative thermal expansion is cubic zirconium tungstate $(\ce{ZrW2O8}).$

$\endgroup$
1
  • $\begingroup$ "expand at a slow (yet constant rate), from 0 to about 20 months..." Why would you think there's a time delay on that expansion? $\endgroup$ Commented May 14 at 21:19
6
$\begingroup$

It's already been mentioned that certain liquid-solid phase transitions are accompanied by negative thermal expansion (NTE). This also includes elements ($\ce{Si, Ga, Ge, Sb, Bi, Pu}$), alloys (Wood's metal) and numerous materials (zeolites, quartz, tugstates etc.) that obey virial expansion due to the way atoms are packed in a crystal lattice:

$$\frac{p}{RT} = \frac{1}{V_m} + \frac{B_{2V}(T)}{V_m^2} + \frac{B_{3V}(T)}{V_m^3} + \ldots$$

where $p$ - pressure, $R$ - gas constant, $T$ - temperature, $B_{iV}(T)$ - $i$-virial coefficient, $V_m$ - molar volume.


There is also another physicochemical phenomenon called Gough–Joule effect. If mechanical stress is applied to the elastomer or rubber string which is subsequently heated, the polymer contracts as a result of the intensive growth of the role of the entropy factor (the maximum entropy in polymers occurs in the coil-like ordering of the molecules). This effect is also utilized in the rubber-band heat engine (Feynman wheel).

$\endgroup$
2
  • $\begingroup$ "expand at a slow (yet constant rate), from 0 to about 20 months..." Why would you think there's a time delay on that expansion? $\endgroup$ Commented May 14 at 21:19
  • $\begingroup$ @DrMoishePippik A time delay? The question specifically mentions a constant low rate, which I interpret as lack of delays. Anyhow, I don't have a solid example as to how exactly this could be achieved, but I guess one would want to look into composite materials with sandwiched alternating layers (à la matryoshka doll) of materials with both thermal insulation and NTE properties. $\endgroup$
    – andselisk
    Commented May 14 at 22:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.