Ultrasonic velocity imaging of slip-cast silicon nitride ceramics

Slip casting is an established method of manufacturing components from engineering ceramics such as silicon nitride. These ceramics are to be tested using ultrasound in both their green state and sintered forms using velocity C-scanning techniques which complement conventional amplitude and defect C scans. This paper discusses two techniques for testing these materials: (1) the first technique uses a pad of sticky silicone based gel as a substitute for water in an immersion C-scanning system, thus allowing conventional probes and couplants to be used; (2) the second technique is entirely a non-contact one and uses a pulsed laser to generate the ultrasound and an air-coupled piezoelectric/epoxy composite transducer as a detector.