Ultrasonic characterization of green and sintered ceramics. II: Frequency domain

Nondestructive techniques, such as ultrasonics, have the capability of analyzing elastic as well as microstructural properties. The conventional ultrasonic measurements conducted are those of velocity and attenuation. Ultrasonic velocity is considered as more of a macroscopic property and is mainly used for determination of elastic properties, although in many cases it may be used to determine microstructural changes. Ultrasonic velocity measurements have been used to characterize colloidally processed ceramics. This paper focuses on ultrasonic attenuation measurements of partially sintered, colloidally processed alumina using 5--30-MHz frequencies. Such measurements are very sensitive to the microstructure and can depend on a variety of parameters, e.g., the volume fraction and the nature of porosity, grains and second phases. A continuous evaluation of attenuation measurements at various stages of densification might provide significant information about the state of microstructural evolution.