Abstract
Ultrasonic in-situ observation of alumina particles in molten aluminum at temperature up to 800°C is presented. A focused ultrasonic sensor is employed for the high temperature measurement with a high spatial resolution. The sensor mainly consists of a conventional piezoelectric transducer, a taper-shaped clad buffer rod as a waveguide and a cooling system. Martensitic stainless steel is used as a material for the buffer rod and an acoustic lens is fabricated at the probe end of the rod. In order to examine the focusing ability of the acoustic lens, the acoustic field near the focusing zone is numerically evaluated by a finite difference method. Using the developed focused ultrasonic sensor, backscattered echoes from alumina particles of 160µm suspended in the molten aluminum at 800°C have been observed clearly in pulse echo mode at 10MHz. The effect of the size and the aggregation condition of the particle on the backscattered echoes has also been examined.
