Monitoring of binder removal from injection molded ceramics using air-coupled ultrasound at high temperature

A pair of capacitance-type air-coupled ultrasonic transducers have been constructed that were capable of operating in air at temperatures of 500 to 600/spl deg/C. These devices were then used to monitor the pyrolytic removal of organic binder from injection molded silicon nitride ceramic components using air-coupled ultrasound inside a furnace at elevated temperatures. Through-thickness waveforms were obtained in the ceramic and compared with simultaneous measurements of the mass of the sample. Both the ultrasonic velocity and signal amplitudes could be used to monitor the change in mass of the injection molded ceramic, and other phenomena (such as softening and redistribution of the binder) were observed.