[en] In order to characterize inhomogeneities in monolithic ceramics, signal characterization of backscattered 25 MHz focussed, pulsed ultrasound has been applied in a step by step approach. The first step was to examine voids in glass. These were optically characterized as spheres with diameters of 30 to 120 μm. Correlations were made with the ultrasonic signals returned. A mathematical model for ultrasound scattering from spheres in an elastic medium based on Ying and Truell's work was used to predict the frequency response characteristics for voids. The next step involved the manufacture of spherical particles of zirconia in the size range of 20 to 200 μm diameter which were also imbedded in glass. The model was modified to calculate the backscattering of ultrasound from inhomogeneities of known elastic constants. The most recent step was the introduction of spherical inclusions into crystallizable glass. Optical characterization was made, then the glass was crystallized to introduce a host matrix structure similar to that of a ceramic. Using appropriate values for elastic constants, experimental and theoretical results are found to be well correlated. This presentation review the work down on inhomogeneities in glasses and its application to defect characterization in ceramics

[en] The authors use ultrasonic techniques to detect and characterize microspherical defects in model ceramics. Long term creep effects and growth of defects due to stress can lead ultimately to failure of a component. Using ultrasonic techniques for detection facilitates the scanning of the component under computer control; and the use of focussed transducers can yield high sound intensity at the site of a defect and give pin-point spatial resolution. The present study utilized commercial transducers operating at 25 MHz and defects larger than 30 μm. Through the application of monotone plane wave theory to the sound field at the focus of a pulsed transducer, information about the character of the scattered ultrasound has been obtained. In order to overcome the obstacle of nondestructive evaluation of ceramics regarding the lack of optically characterisable defects, spherical and near spherical oxide particles were imbedded in glass. The use of glass as a model host matrix facilitates complete optical characterization of the defect and scattering theory can be compared with experiment to reach a better understanding of the processes involved

[en] H₃O⁺-β/β^-alumina and H₃O⁺ rare-earth silicates (HNRS where R = rare earth ion) hydronium-ion conductors were prepared by ion exchanging alkali-ion precursors. Conductivity measurements show the HNRS to be superior hydronium-ion conductors but physically less stable. The hydronium-ion conductors investigates suffer reversible degradation between 120 and 400 degC. (author). 19 refs.; 5 figs.; 2 tabs