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The Case of the Missing Alumina Martha L. Mecartney, University of California, Irvine, DMR 0606063

1. 2. Elongated Lath-Shaped Grains of Magnetoplumbite LaMgAl 9 O 11. 3. LaPO 4. ZrO 2. LaMgAl 9 O 11. MgAl 2 O 4. The Case of the Missing Alumina Martha L. Mecartney, University of California, Irvine, DMR 0606063.

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The Case of the Missing Alumina Martha L. Mecartney, University of California, Irvine, DMR 0606063

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  1. 1 2 Elongated Lath-Shaped Grains of Magnetoplumbite LaMgAl9O11 3 LaPO4 ZrO2 LaMgAl9O11 MgAl2O4 The Case of the Missing AluminaMartha L. Mecartney, University of California, Irvine, DMR 0606063 Superplastic ceramics that are shape-formed easily at high temperatures can be made using multiple phases of ceramics. In this example, alumina (Al2O3),spinel (MgAl2O4),monazite(LaPO4) and zirconia (ZrO2) were used to make a multi-phase ceramic with a fine grain size. This material demonstrated easy deformation during mechanical testing at high temperatures, but a closer evaluation of the microstructure using scanning electron microscopy (SEM) showed that the alumina (Al2O3) phase was missing for samples processed at very high temperatures. Upon further examination, long lath-shaped grains were discovered (Fig. 1). Energy dispersive spectroscopy (EDS) in the SEM confirmed that the composition of these unusually shaped grains is an unexpected magnetoplumbite (LaMgAl9O11) phase that most likely formed from a liquid generated during sintering that dissolved some of the monazite (LaPO4) and spinel (MgAl2O4) which then reacted with the alumina (Al2O3) to form LaMgAl9O11. This lath-shaped magnetoplumbite grew rapidly, encapsulating the non-reactive ZrO2 grains in its path (Fig. 2). The different phases in this ceramics composite can be easily identified using backscattered electron contrast in the SEM. Lowest density phases are the darkest since electrons are not backscattered as efficiently as for the higher density phases which appear lighter (Fig. 3).

  2. Broader ImpactsMartha L. Mecartney, University of California, Irvine, DMR 0606063 A superplastic four phase ceramic fabricated with alumina (Al2O3), spinel (MgAl2O4), monazite (LaPO4) and zirconia (ZrO2) , proved to be machin-able as shown below. A tungsten carbide tip was used to drill a 1 mm hole with 50N pressure, approximately the typical pressure exerted by a person using a hand held drill. Machinable ceramics have potential for use in applications where materials with high corrosion resistance and low thermal conductivity are needed. This NSF grant trains students in research techniques and the scientific process, and also provides opportunities for the students to present their own research at national professional conferences. The above picture shows students from Professor Mecartney’s research group from UC Irvine attending the 2009 American Ceramic Society Annual Meeting in Pittsburgh to present their research. From left to right, poster presenter DanJu Men (graduate student supported on NSF 0606063 ), Juan Lucio (undergrad researcher), Mai Ng (graduate student partially supported on NSF 0606063), and Chris Hoo (graduate student supported on NSF 0606063). All students either presented an oral talk or a poster on their research at this meeting. (Picture taken by graduate student Matt Weeks, permission granted for use.)

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