ULTRASONIC IN-SITU MONITORING OF SINTERING IN ALUMINA

Ultrasonic waves were successfully employed to continuously monitor th e presence and level of residual porosity in pure alumina samples duri ng high temperature sintering. An alumina sample with initial porosity 29% was sintered at 1400-degrees-C for 4 hours. The magnitude of long itudinal velocity of 100kHz pulsed ultrasound was continuously monitor ed throughout the sintering cycle. Measurements were accomplished in s itu using a pulse-echo/through-transmission buffer rod waveguide techn ique employing magnetostrictive transducers and pressure friction acou stic coupling to the sample. A tungsten buffer rod protected a brazed Remendur magnetostrictive transducer rod from the temperature of the s intering furnace by keeping it near ambient temperature. With the pres ent method, porosity can be determined to within +/-1% of the absolute level. The technique is extendible to other ceramics as well as to me tals, and the opportunity exists for monitoring without requiring phys ical contact, such as by the use of pulsed laser sample excitation, an d laser interferometric signal extraction. The significance of such mo nitoring, with or without contact, is to provide input for a real-time adaptive or intelligent sintering process control system.