Nanotubes used to reinforce ceramics

Materials scientists have created a ceramic material reinforced with carbon nanotubes that is tougher than conventional ceramics, conducts electricity and acts as a heat exchanger.

A ceramic material reinforced with carbon nanotubes has been made by materials scientists at the University of California, Davis.

The new material is said to be far tougher than conventional ceramics, conducts electricity and can both conduct heat and act as a thermal barrier, depending on the orientation of the nanotubes.

Ceramic materials are very hard and resistant to heat and chemical attack, making them useful for applications such as coating turbine blades, said Amiya Mukherjee, professor of chemical engineering and materials science at UC Davis, who leads the research group. But they are also very brittle.

The researchers mixed powdered alumina (aluminium oxide) with five to ten percent carbon nanotubes and a further five percent finely milled niobium.

Mukherjee and research colleagues Guodong Zhan, Joshua Kuntz and Javier Garay treated the mixture with an electrical pulse in a process called spark-plasma sintering. This process consolidates ceramic powders more quickly and at lower temperatures than conventional processes.

The resulting new material has up to five times the fracture toughness – resistance to cracking under stress – of conventional alumina.

‘It’s a lot more forgiving under service application when you have a dynamic load,’ said Mukherjee.

The material is said to show electrical conductivity ten trillion times greater than pure alumina, and seven times that of previous ceramics made with nanotubes.

The material also has interesting thermal properties, conducting heat in one direction, along the alignment of the nanotubes, but reflecting heat at right angles to the nanotubes, making it an attractive material for thermal barrier coatings, Mukherjee added.