NONDESTRUCTIVE EVALUATION OF GREEN-STATE CERAMICS USING MICROMACHINEDAIR-COUPLED CAPACITANCE TRANSDUCERS

Air-coupled ultrasound has been used to study the manufacture of ceram ic components by both slip casting and injection moulding. A capacitan ce transducer, designed to operate at high temperatures, was used as b oth a source and receiver with a 500 kHz bandwidth to pass ultrasound through 3 mm thick green-state injection-moulded and slip-cast samples of silicon nitride. The transducers were C-scanned over the entire ar ea of the sample in order to locate density changes which could lead t o problems in the firing stage. Additionally: through-transmitted wave forms at 150 degrees C were obtained, indicating that the technique ma y be useful for performing measurements at high temperatures. (C) 1998 Elsevier Science B.V.