NMR IMAGING OF ADVANCED COMPOSITES Charles G. Fry McDonnell Douglas Research Laboratories Mail Code 111-1041, P.O. Box 516 St. Louis, Missouri 63166 Martin J. Lizak* and Mark S. Conradi Department of Physics Washington University St. Louis, Missouri 63130 *Massachusetts General Hospital NMR Center, 149 13th Street Charlestown, MA 02129 INTRODUCfION Ceramic materials offer low weight, high temperature stability, good wear resistance and good hardness, and are thus becoming increasingly important materials in high temperature applications such as heat engines, heat shields and aerospace leading edge structural compo- nents. Ceramic materials tend to be brittle in nature, however, and their mechanical proper- ties are sensitive to many types of flaws which can be produced in manufacturing. These flaws are currently difficult to detect with nondestructive techniques, and have thus re- mained poorly characterized. 1 ,2 For this reason, new NDE methods are needed to help enable the large-scale implementation of ceramics, and overcome the poor reliability and reproducibility common to current ceramic manufacturing processes. We are exploring new nuc1ear magnetic resonance (NMR) imaging techniques ulti- mately directed at characterizing critical flaws in ceramics, but also with more general application to the characterization of the porous structure of these materials. 3 In this paper, we present techniques based on observing agas imbibed into the ceramic. Open porosity, a necessary criteria for these techniques, is often of fundamental importance to ceramic manufacturing. During the early stages of most manufacturing processes, the ceramic must necessarily have open porosity to allow evolution of gases. The densification of this porous network is a critical process for determining the final properties of the ceramic. Other processes, such as chemical vapor deposition techniques, rely by nature on open porosity. Finally, many c1asses of ceramics, inc1uding ceramic foams, sensors and filters, rely on the porosity as a fundamental design property. Unlike other NDE schemes, NMR techniques are not inherently affected by the sampIe thickness or geometry, and can potentially be applied throughout the various stages of manufacture. Thus, NMR imaging of imbibed fluids promises to provide detailed nondestructive characterization of these materials. Review 0/ Progress in Quantitative Nondestructive Evaluation, Vol. 11 Edited by D.O. Thompson and D.E. Chimenti, Plenum Press, New York, 1992 655