From toilets to catalytic converters, ceramics are found everywhere. But two problems have limited their usefulness — they crack, and are difficult to work into intricate shapes. Tobias Schaedler and colleagues at HRL Laboratories in Malibu, California, have used 3-D printing to solve both problems. The team, which has published its work in Science, is developing a 3-D printed ceramic for use in hypersonic aircraft.
Humans have used ceramics for at least 26,000 years. They’re hard, chemically inert and heat-resistant. That makes them perfect for diverse uses – cooking vessels, industrial ball bearings, coatings for artificial hip joints, even sculpture. But, because of the microscopic holes formed by air pockets during manufacture, they are brittle, and because of their heat-resistance, they are difficult to melt and mould into complex shapes.
To overcome these problems, Schaedler’s team formulated a liquid “ink” rich in silicon, carbon and oxygen, the same elements found in clay used to make traditional ceramics. But instead of being clumped in coarse grains, these molecules float freely in solution. The ink also contained a UV light-sensitive glue, as commonly used in 3-D printing.
To print an object, carefully aimed beams of UV light were used to stick the molecules tightly together, leaving no pores. The printed object was then fired at high temperatures to form the finished product, as with traditional ceramics.
Schaedler’s material is tough. A 3-D-printed ceramic mesh survived temperatures of 1,700 °C and carried 10 times more weight before cracking than conventional ceramics — “impressive” says Yi-Bing Cheng, materials engineer at Monash University in Melbourne.
The idea has caught the eye of the US Defense Advanced Research Projects Agency in Arlington, Virginia, which is funding Schaedler’s team to print ceramic hull parts for hypersonic jets. Currently, conventional ceramics reinforced with fibres are used to protect the aircraft from the extreme heat generated during hypersonic flight, but printed ceramics could decrease the weight of the jets’ hulls by 50%, says Schaedler.
“We’ve never been able to make materials like this before,” says Charles Sorrell, ceramics engineer at the University of New South Wales. “It’s a clever technique that’s industrially feasible.”