DEVELOPMENT OF NMR IMAGING PROBES FOR ADVANCED CERAMICS N. Gopalsami, G.A. Forster. S.L. Dieckman. and W.A. Ellingson Materials and Components Technology Division INTRODUCTION R. E. Botto Chemistry Division Argonne National Laboratory Argonne, Illinois 60439 Nuclear magnetic resonance imaging (NMRI) holds the potential for the non-destructive evaluation of ceramics and for the improvement of ceramic processing in general. It can provide valuable diagnostic information about the spatial variations of binders. plasticizers. sintering aids. deflocculants. and other organics in injection-molded and slip-cast green ceramics. Poor distribution of these organics, after subsequent processing steps such as sintering, hot isostatic pressing, and machining, can lead to final parts that are defective and/or with poor mechanical properties. Despite the advances in NMRI in the medical area. few efforts [1-4] have been made to apply NMRI to materials studies because of the need for special imaging probes and techniques. A major difference between the two applications is in the line widths of NMR spectra. For example, the line width of proton spectra from the organics in green ceramic materials [2] is about 2500 Hz, compared to a few Hz in biological systems. Because linear gradient fields are used in NMR imaging to frequency-label spatial positions, the gradient strength required to resolve two positions in space must be high enough to ensure that the difference in the resonance fre- quencies between these two positions is greater than the line widths of the resonances. The imaging of ceramics with a spatial resolution of 100 for example, would require a gradient strength of 50 Glcm. Another difference is in the imaging technique. While spin-warp imaging is used in medical systems, the method of choice for materials with short spin-spin relaxation time, Tz. (large line widths correspond to short Tz) is back-projection. This method allows the NMR response (FID) to be detected immediately after the RF excitation. thus preserving the maximum signal intensity. Back-projection, however, poses more stringent specifications on the probe design, requiring (1) highly uniform gradient and RF fields. (2) well-balanced gradient fields between the orthogonal axes, and (3) strict alignment of the static. gradient. and RF fields with respect to the center of the sample space. Also. the RF bandwidth must be great enough to span the entire range of frequencies produced by the gradient fields. This paper presents the design and test results of a special imaging probe built at Argonne to meet these requirements for ceramics characterization. PROBE DESIGN The imaging probe (Fig. 1) is designed to be used in an 89-mm vertical bore, 2.35-T superconducting magnet in conjunction with a Bruker CXP-100 Review of Progress in Quantitative Nondestructive Evaluation, Vol. 9 Edited by D.O. Thompson and D.E. Chimenti Plenum Press, New York, 1990 861