GB1382353A - Method of heat treating a material - Google Patents

Abstract

1382353 Crystallizing from a melt; zone melting PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 28 July 1972 [31 July 1971] 35393/72 Heading B1S [Also in Division F4] Crystals including monocrystals are made by passing a temperature gradient through a melt in a vessel e.g. a crucible, located in a chamber the walls of which are heat-transmitting and surrounded by a container spaced from the chamber, the said temperature gradient being formed by establishing an interface between vapourized heat transfer medium and a gas inert to the medium. The surrounding container which is insulated contains a heattransmitting wall through which heat is passed to vapourize a heat-transfer medium contained in the space between the chamber and the crucible. The movement of the interface is controlled by increasing or decreasing the amount of heat supplied to the transfer medium. The transfer medium may be potassium, sodium, lithium, cadmium, caesium, an alloy or an organic compound e.g. a hydrocarbon. The inert gas may be argon, nitrogen, neon, helium or air under normal atmospheric pressure provided it is not reactive with the medium. The inert gas is always at constant pressure. If desired, in the space between the chamber and container, a porous mass having a capillary structure may be present connecting the heat transmission walls of the chamber and container. The porous mass may be compressed steel wool, wire gauze, or a network of glass fibres. As shown, a tubular treatment chamber 1 is bounded by a heat transmission wall 2, of container 3. The latter contains a heat transmission wall 4 through which thermal energy from heating coil 5 is supplied to the container. The power supplied to coil 5 is controlled by device 6. The container 3, insulated from the surroundings by layer 7, comprises a gas buffer space 8 in communication with gas storage container 9 containing a control valve 11. The container 3, contains the medium e.g. sodium, and in operation the location of the interface 10, is determined by the power of the heating coil 5. The material to be crystal-. lized is contained in vessel 12, suspended from a frame 13. In modifications, the container may have its longitudinal axis horizontal and space 8, as the flow back of the medium is not under gravity, filled with a porous mass preferably compressed steel wool. Also two chambers may be present in the container (Figure 6 not shown). The apparatus may also be used for zone-melting purification.