HELP on Coefficient of LINEAR THERMAL EXPANSION (ppm/░C) at NTP
Almost all substances contract on cooling (and ergo, expand on heating), with most contraction occurring at higher temperatures, with relatively little occurring below liquid nitrogen temperatures of 77K. Thus thermal contraction is highly non-linear with contraction approaching zero at absolute zero. The values shown are for normal temperatures, 20░C in parts per million per degree Centigrade. As can be seen, Phosphorus has the largest thermal expansion coefficient at 125ppm/░C, with the alkali metals coming close seconds. The expansion coefficient generally increases across each group, thus the value for Lithium is 56ppm/░C, whilst that for Caesium is 97ppm/░C. The transition elements and Lanthanides have relatively low expansion coefficients together with some of the light the semiconductors, but Carbon in the form of diamond has the lowest at 1.2ppm/░C. Being liquid at room temperature, the value for Mercury is the bulk expansion coefficient.
Zirconium tungstate is unusual in having a negative temperature coefficient of expansion over a very wide temperature range. It contracts by 0.75% on heating from 1 Kelvin, near absolute zero, to 777░ Celsius. See Zirconium.
At certain specific temperatures some elements either expand or contract abruptly whilst undergoing a phase transition from one crystal form to another of differing density. For instance, iron decreases in volume by 1.1% on changing from a body centred cubic lattice to a hexagonal close packed lattice as the temperature increases through 907 Celsius. Iron also experiences a volume increase of 0.6% in changing from the hexagonal close packed to another body centred cubic lattice on crossing 1397░ Celsius. But all these changes in volume are abrupt and associated with a phase change from one crystal lattice to another. See Crystalline Form.
