Containerless processing at high temperatures using acoustic levitation

Abstract

Containerless processing of a specimen while it is heated to high temperatures can be accomplished using acoustic levitation. This involves the creation of sufficiently strong and suitably shaped acoustic fields and it is more easily achieved in the microgravity of space. This technique permits the heating, melting, reacting, cooling, and solidification of a substance without contamination or heterogenous nucleation caused by contact with the container. It further enables the processing of materials for which there is no acceptable crucible material. These acoustic containment techniques have been demonstrated in space at temperatures to 1800K in early sounding rocket and space shuttle experiments. Newly developed approaches can improve the processing capabilities at higher temperatures and provide more contamination-free environments. Advanced techniques are described which facilitate the development of inert or reducing atmospheres in excess of 2000K. Recent testing, in the laboratory and aboard the NASA KC-135 aircraft, of a high temperature acoustic positioner has demonstrated the effectiveness of a specimen motion damping system and the control of specimen spin. These new techniques can produce the extremely quiescent states which help enable the study of deep undercooling processes. The high degree of specimen stability also permits more accurate measurement of high temperature material properties.