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Reversing the trend of nature

Exploring the atomic mechanisms that govern anti-thermal behavior

Martin Harmer and his team are exploring a phenomenon about which very little is currently known: atoms that behave in a manner contrary to nature.

The W.M. Keck Foundation has awarded the team a $1 million grant to discover and study the mechanisms that govern newly-discovered anti-thermal characteristics in materials—properties that seem to contradict accepted conventions of physics. The project could revolutionize scientists’ basic understanding of thermal processes and inform the development of new materials that withstand higher temperatures.

Harmer, the Alcoa Foundation Professor of materials science and engineering, collaborates on the project with Elizabeth Holm and Gregory S. Rohrer, both professors of materials science and engineering at Carnegie Mellon University, along with new Lehigh postdoctoral researchers Amanda Krause and Christopher Marvel ’12, ’16 Ph.D., and a team of students.

For Lehigh, the Keck project represents a significant milestone—a partnership with an organization renowned for supporting “impossible” science and engineering projects with the potential to create tremendous impact.

Pursuing atomic scofflaws

The atoms in solids typically move exponentially faster with increasing temperature, obeying a classical law of physics. This fundamentally limits the properties and performance of materials. A major challenge in condensed matter science is to overcome this tendency in order to produce materials that are more resilient.

The Keck team believes that the cause of the anti-thermal phenomenon lies in the behavior of what are known as grain boundaries, or the interfaces between microscopic crystals that form materials. The team has identified examples of several anti-thermal processes where the atomic motion actually becomes slower, or does not change at all, as temperature increases. Some materials have been found to melt upon cooling, or solidify upon heating—behaviors that have been detected in isolated cases within metals, ceramics, semiconductors, polymers and biomaterials.

The researchers’ goal is to discover and study the mechanisms that govern this intriguing behavior, and use this knowledge to design new materials with enhanced thermal performance.

Consider, for example, how a breakthrough in anti-thermal material design could impact airline travel.

An important factor in jet engine design is a protective aluminum oxide coating on the engine’s turbine blades. The coating is roughly 10 micrometers thick—about one tenth of a sheet of paper. As hot air causes the oxide layer to grow and flake off, the blades are left exposed to an oxidative and corrosive environment and eventually fail catastrophically. Anti-thermal behaviors could be leveraged to limit growth of the oxide layer, saving billions of dollars in fuel and maintenance cost.

As another example, the team believes their work could unleash the power of nanocrystals—materials that shatter current records for strength and other mechanical properties. However, at room temperature nanocrystals are known to degrade 66 orders of magnitude faster than conventional materials. Greater understanding of the mechanisms of anti-thermal degradation could unleash the full capability of nanocrystalline materials for use across a broad range of industries and applications.

A long, pioneering trail

Prior to the Keck project, Harmer and collaborators pioneered a concept known as grain boundary complexions, which treats grain boundaries as distinct states of matter in thermodynamic equilibrium. Harmer described the concept of grain boundary complexions in an article in Science magazine in 2011.

With support from the Keck Foundation, Harmer and his colleagues will drive the design of new materials and develop further techniques for the study of grain boundaries. The group will also apply a novel method for measuring grain boundary motion inside multigrain materials, and connect those findings to highthroughput computer simulations using Lehigh’s world-class atomic resolution electron microscopy facilities to directly image atoms that demonstrate antithermal behavior.

Says Harmer: “This project will allow us to explore uncharted territory that could potentially uncover the secrets of nature’s counterintuitive thermal behavior and pioneer new approaches to materials science.”