Researchers at Purdue University have demonstrated a featherweight metamaterial that combines high strength with electrical conductivity and thermal insulation, suggesting potential applications from buildings to aerospace.

The composite combines nanolayers of a ceramic called aluminium oxide with graphene, which is an extremely thin sheet of carbon. Although both the ceramic and graphene are brittle, the new metamaterial has a honeycomb microstructure that provides super-elasticity and structural robustness.

Graphene would ordinarily degrade when exposed to high temperature, but the ceramic imparts high heat tolerance and flame-resistance, properties that might be useful as a heat shield for aircraft. Researchers said the lightweight, high-strength and shock-absorbing properties could make the composite a good substrate material for flexible electronic devices and “large strain sensors.”

And because it has high electrical conductivity and yet is an excellent thermal insulator, the composite might be used as a flame-retardant, thermally insulating coating, as well as sensors and devices that convert heat into electricity, said Gary Cheng, an associate professor in the School of Industrial Engineering at Purdue University.

20170815_EETI_Purdue-graphe-composite (cr) Figure 1: A new composite material combines ultra-lightweight with flame-resistance, super-elasticity and other attributes. Here, the material is viewed with a scanning electron microscope, while its flame resistance is put to the test. (Source: Purdue University)

The composite material is made of interconnected cells of graphene sandwiched between ceramic layers. The graphene scaffold, referred to as an aerogel, is chemically bonded with ceramic layers using a process called atomic layer deposition.

“We carefully control the geometry of this graphene aerogel,” he said. “And then we deposit very thin layers of the ceramic. The mechanical property of this aerogel is multifunctional, which is very important. This work has the potential of making graphene a more functional material.”

The process might be scaled up for industrial manufacturing, Cheng said.

The group will next work on how to enhance the material’s properties, possibly by changing its crystalline structure, scaling up the process for manufacturing and controlling the microstructure to tune material properties.