Asked by: S Bhat, Howrah, India
Polymers like rubber shrink on heating as their molecular chains curl up, and water shrinks when warmed from its freezing point to around 4°C. After that, though, it behaves normally, and expands on warming.
In contrast, so-called negative thermal expansion (NTE) materials never behave themselves. Discovered in 1959, they include zirconium tungstate, whose bizarre crystal structure means that it keeps shrinking as it’s warmed from any temperature above absolute zero (-273°C) to over 770°C.
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Robert is a science writer and visiting professor of science at Aston University.