Materials that shrink when heated

Feb 09, 2012
Invar, also known as FeNi36, is an iron-nickel alloy notable for its lack of expansion or contraction with temperature changes.

One common reason that people with fillings experience toothache is that their fillings expand at a different rate to the original tooth when, for example, drinking a hot drink. Contrary to intuition, however, not all materials expand when heated - some actually contract. Recent research on these so-called negative thermal expansion (NTE) materials has led to the discovery of alloys exhibiting unexpectedly large thermal contraction.

Controlling the thermal expansion of composites is important for producing nanometer-scale , as well as the next-generation fuel cells and . An ability to combine NTE materials with 'normal' materials which expand upon heating ensures a reduction in thermal expansion in a composite material - something that people with tooth fillings would appreciate. An example of such a composite is Invar, an iron-nickel alloy with a uniquely low coefficient of thermal expansion. As a result it is used where high dimensional stability is required, such as precision instruments, clocks or seismic creep gauges.

Koshi Takenaka at the Department of Science, Nagoya University in Japan works on NTE materials for practical applications. In the latest issue of Science and Technology of Advanced Materials he summarizes the physical mechanisms governing NTE with emphasis on recent developments.

Takenaka notes that, "NTE materials will expand our capability of thermal-expansion control, opening a new paradigm of materials science and technology thermal-expansion-adjustable composites". One challenge facing the scientist is that the addition of NTE materials to composites leads to undesirable instabilities at interfaces. New methods for producing stable interfaces between the host composite and NTE compensators are of critical importance. Nevertheless, the so-called 'one-component' materials - such as manganese antiperovskites, zirconium vanadates, and tungstates - exhibiting negligible thermal expansion offer a promising route towards achieving this goal.

Explore further: Scientist hopes to improve rare earth purification process

More information: 'Negative thermal expansion materials: Technological key for control of thermal expansion' by Koshi Takenaka, Science and Technology of Advanced Materials Vol. 13 (2012) 013001. iopscience.iop.org/1468-6996/13/1/013001

add to favorites email to friend print save as pdf

Related Stories

Magnetic actuation enables nanoscale thermal analysis

Jan 12, 2012

Polymer nano-films and nano-composites are used in a wide variety of applications from food packaging to sports equipment to automotive and aerospace applications. Thermal analysis is routinely used to analyze ...

Researchers measure nanometer scale temperature

Dec 19, 2011

Illinois researchers have developed a new kind of electro-thermal nanoprobe that can independently control voltage and temperature at a nanometer-scale point contact. It can also measure the temperature-dependent ...

Recommended for you

Chemists eye improved thin films with metal substitution

Jul 21, 2014

The yield so far is small, but chemists at the University of Oregon have developed a low-energy, solution-based mineral substitution process to make a precursor to transparent thin films that could find use ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

that_guy
not rated yet Feb 09, 2012
I always thought it was because the filling conducts heat or cold better. I didn't even think about the difference in expansion and contraction. Interesting.