Graduate student next to measurement system

Materials designed to bend as they ‘breathe’ in extreme conditions

Image credit: Massachusetts Institute of Technology

A team of engineers based at Massachusetts Institute of Technology (MIT) have developed mechanical components which expand and contract as they allow oxygen in and out.

Thanks to the extreme temperatures found inside a nuclear reactor, carrying out maintenance work puts severe strain on equipment. Knowing that machine components degrading under heat was causing trouble, MIT researchers have developed a new way to make mechanical actuators which can be used in these extreme environments.

The technology works on the basis of metal oxide materials, similar to those found in rechargeable batteries. During charging and discharging cycles, ions move in and out of the material. These motions cause the material to expand and contract.

Repeated changes in volume can be a serious issue for industrial machinery, causing cracks to form, degrading performance and inducing short-circuits. Components such as fuel cells have their lifetimes reduced by these motions.

For high-temperature mechanical components, the researchers argue, these expansions and contractions are not a troublesome side effect, but a potentially helpful phenomenon. By coupling these metal oxides with more rigid materials, it is possible to create actuators which are forced to bend when the oxide expands and contracts.

According to Professor Krystyn Van Vliet, professor of materials science and engineering at MIT, a probe-based measurement system for high-temperature conditions that she and her colleagues developed made the finding possible. The system was used to measure how oxygen cycled in and out of the metal oxide.

To make the measurements, the researchers deposited a layer of metal oxide - praseodymium-doped cerium oxide – on a substrate, and observed the flow of oxygen using their own detection system.

“These materials are special because they ‘breathe’ oxygen in and out, and change volume, and that causes the substrate to bend,” said Professor Van Vliet.

While they demonstrated the process using one particular metal oxide, the researchers say the findings could apply to a variety of other material. They report their findings in Nature Materials.

Typically, materials used to create motion by applying electricity, such as piezoelectric devices (used in surgical equipment, weapons, instruments, power supply and many other areas) do not work well at high temperatures. The new system developed by MIT researchers could be used to open up a new area of sensors and actuators which function above 500°C.

These devices could be used by maintenance robots in nuclear reactors and to open and close valves in other intensely hot environments, the researchers suggest.

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