A ceramic material reinforced with carbon nanotubes has been made by materials scientists at UC Davis. The new material is 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 (aluminum oxide) with 5 to 10 percent carbon nanotubes and a further 5 percent finely milled niobium. Carbon nanotubes are sheets of carbon atoms rolled up into tiny hollow cylinders. With diameters measured in nanometers -- billionths of an inch -- they have unusual structural and conducting properties.
The researchers (postdoctoral scholar Guodong Zhan, graduate students Joshua Kuntz and Javier Garay, and Mukherjee) 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 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 shows electrical conductivity ten trillion times greater than pure alumina, and seven times that of previous ceramics made with nanotubes. It 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 said.
The work is published in the August issue of Applied Physics Letters.
Certainly newer and better materials can be expected to lower the costs of building or operating a variety of types of equipment, structures, and means of transportation. But seems more exciting to this commentator is the question of what structures and new ground, air, or space vehicles each new materials advance might make possible. Can carbon nanotubes make ceramics and other materials strong enough to make hypersonic scramjet space launch vehicles feasible some day? They are tougher and better at conducting and reflecting heat. Perhaps they will help.
|Share |||Randall Parker, 2003 September 21 06:04 PM Materials Advances|