Abstract: A system is described for forming accurately spherical and centered fluid-filled shells, especially of high melting temperature material. Material which is to form the shells is placed in a solid form in a container, and the material is rapidly heated to a molten temperature to avoid recrystallization and the possible generation of unwanted microbubbles in the melt. Immediately after the molten shells are formed, they drop through a drop tower whose upper end is heated along a distance of at least one foot to provide time for dissipation of surface waves on the shells while they cool to a highly viscous, or just above melting temperature so that the bubble within the shell will not rise and become off centered. The rest of the tower is cryogenically cooled to cool the shell to a solid state.

Abstract: The improved, heterogeneous catalysts are in the form of gas-impervious, hollow, thin-walled spheres (10) suitably formed of a shell (12) of metal such as aluminum having a cavity (14) containing a gas at a pressure greater than atmospheric pressure. The wall material may be, itself, catalytic or the catalyst can be coated onto the sphere as a layer (16), suitably platinum or iron, which may be further coated with a layer (18) of activator or promoter. The density of the spheres (30) can be uniformly controlled to a preselected value within .+-.10 percent of the density of the fluid reactant such that the spheres either remain suspended or slowly fall or rise through the liquid reactant.

Abstract: Amorphous metals are produced by forming a molten droplet (115) of metal from source (126) and deploying the droplet into a focused acoustical levitating field or by dropping the unit through spheroidizing zone (116) slow quenching zone (118) and fast quenching zone (120) in which the droplet is rapidly cooled by in the standing acoustic wave field produced between half-cylindrical acoustic driver (168) and focal reflector (166) or curved driver (38) and reflector (50). The cooling rate can be further augmented by first cryogenic liquid collar (160) and second cryogenic liquid jacket (170) surrounding the drop tower (112). The sphere (117) is quenched to an amorphous solid which can survive impact in the unit collector (124) or is retrieved by vacuum chuck (20).

Abstract: Systems are described for the acoustic levitation of objects, which enable the use of a sealed rigid chamber to avoid contamination of the levitated object. The apparatus includes a housing forming a substantially closed chamber, and means for vibrating the entire housing at a frequency that produces an acoustic standing wave pattern within the chamber.

Abstract: A small object (12, FIG. 2) is coated by holding it in the pressure well (20) of an acoustic standing wave pattern, and then applying a mist of liquid coating material (42) at low velocity into the pressure well. The pressure gradient within the well forces the mist particles to be pushed against the object. A lower frequency acoustic wave (for oscillator 28, FIG. 4) also can be applied to the coated object, to vibrate it so as to evenly distribute the coated material. The same lower frequency vibrations can be applied to an object in the shape of a hollow sphere, to center the inner and outer surfaces of the sphere while it remains suspended.

Abstract: An acoustic levitation system is described, which can utilize a single acoustic source (12) and a small reflector (14) to stably levitate a small object (16) while the object is processed as by coating or heating it. The system includes a concave acoustic source (12) which has locations on opposite sides of its axis that vibrate towards and away from a focal point (36, FIG. 2) to generate a converging acoustic field. A small reflector (14) is located near the focal point, and preferably slightly beyond it, to create an intense acoustic field that stably supports a small object near the reflector. The reflector can be located about one-half wavelength (L, FIG. 3) from the focal point and can be concavely curved to a radius of curvature (L) of about one-half the wavelength, to stably support an object one-quarter wavelength (N) from the reflector.