This promotes the formation of grain bridges which span across the crack, making it more difficult for the crack to propagate." Said Ziegler, "To enhance the toughness of a silicon nitride ceramic, it is often necessary to engineer a thin (nanoscale) film in the ceramic's grain boundaries, which cracks when the ceramic begins to fracture. For this to happen, however, the brittleness problem of the silicon nitride ceramics must be solved. Running at such high temperatures, the advanced gas turbines are expected to achieve a much higher thermal-to-electricity efficiency than today's steam-driven electrical power plants, while emitting far less greenhouse gases. These engines, which are projected for use in electrical power plants, among other applications, will burn fuel at temperatures of around 1200 degrees Celsius (2,192 degrees Fahrenheit), well beyond the tolerance of metals, even nickel-based super-alloys. Much attention is being focused on silicon nitride advanced ceramics, which are considered to be leading candidates as structural materials for future gas turbine engines. This information relates to ceramic toughness. Scanning transmission electron microscopy images of silicon nitride ceramic sintered with several different rare-earth elements show the atomic location of each rare-earth atom. Today's advanced ceramics are made from powders of complex chemical compounds and their production requires careful control at every stage of the process. The other co-authors were Christian Kisielowski and Nigel Browning of Berkeley Lab, Juan Idrobo of UC Davis and Michael Cinibulk of the Air Force Research Laboratory in Ohio.Ĭeramics are probably the oldest construction materials known, their use dating back thousands of years, when they were made from wet clay and baked at high temperatures until hard. Ritchie and Alexander Ziegler, a member of Ritchie's research group, were the principal authors of a paper by the collaboration which appears in the Dec. "Our findings are a prime factor in understanding the origin of the mechanical properties in advanced ceramics and should make it possible to do the precise tailoring in the future that will critically improve the performances of these materials over a wide range of applications," said Robert Ritchie, a materials scientist who has a joint appointment with Berkeley Lab's Materials Sciences Division and the University of California at Berkeley's Department of Materials Science and Engineering. These images revealed, for the first time, the exact location of each rare-earth atom in the final material and how their presence affected its toughness. Working with the unique facilities at Berkeley Lab's National Center for Electron Microscopy (NCEM), the collaboration has produced atomic-resolution images of silicon nitride ceramics that were sintered with oxides of rare earth elements to toughen them up and prevent cracks from spreading. Help, however, may be on the way.Ī collaboration of scientists led by researchers with the US Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has uncovered clues at the atomic level that could lead to a new generation of much tougher advanced ceramics to be used in applications like gas turbine engines.įrom left, Berkeley Lab scientists Nigel Browning, Alexander Ziegler (seated) and Robert Ritchie used this Scanning Transmission Electron Microscope to find new ways to toughen up advanced ceramics. Poor resistance to fracture damage has been the major drawback to the widespread use of advanced ceramics as structural materials. 29 - Advanced ceramics are wonderful materials: They withstand temperatures that would melt steel and resist most corrosive chemicals.
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