# Which materials/compounds expand in response to cold temperatures?

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

• 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/… – anna v Nov 13 '12 at 20:49
• Isn't the typical example is water and ice? – user822 Dec 16 '12 at 8:55

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.

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

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).