GB736165A - Improvements in or relating to methods of purifying materials - Google Patents

Abstract

A material having at least one impurity displaying differential solubility in solid and liquid phases of the material is refined by preparing a quantity of the impure material in the liquid phase, freezing a zone of the material and causing the frozen zone to traverse the liquid for a distance appreciably greater than the zone thickness whilst ensuring that at no time is the whole of the material returned to the liquid phase. According to Provisional Specification phosphorus is purified by melting it in a long glass trough within a chamber containing an inert atmosphere, e.g. nitrogen. A frozen zone is formed in the phosphorus by passing a cooling fluid, e.g. brine, through a tubing coil surrounding the trough and mounted within the chamber. The thickness of the frozen zone is preferably one tenth of the trough length and the trough is passed longitudinally through the coil to cause the frozen zone to traverse the phosphorus. When the frozen zone approaches the far end of the trough the impure liquid at that end may be drained off and the frozen zone remelted, or the frozen zone may be passed to the extreme end to freeze in the impurities and the solid material then separated from the remaining pure liquid phosphorus. The pure phosphorus may be frozen to provide a solid ingot or subjected to further refining treatments.ALSO:A material having at least one impurity displaying differential solubility in solid and liquid phases of the material is purified by preparing a quantity of impure material in the liquid phase, freezing a zone of the material and causing the frozen zone to traverse the liquid for a distance appreciably greater than the zone thickness whilst ensuring that at no time is the whole of the material returned to a solid phase. Gallium is purified by melting it in a long glass trough within a chamber containing an inert atmosphere, e.g. nitrogen. A number of separate frozen zones are formed in the gallium by passing a cooling fluid, e.g. brine, through a number of tubing coils surrounding the trough and spaced apart within the chamber. The size of the coils and their spacing is such that the length of each frozen zone and of each liquid region between them is one-tenth of the trough length. The trough is then passed longitudinally through successive coils to cause the frozen zones to traverse the gallium, and the process is finally halted before the last frozen zone has traversed the whole length of the trough. The purified gallium may be obtained by freezing the remaining zone rapidly and then cutting off one or both ends of the bar containing the impurity, or by draining away one or more of the regions of the liquid gallium remaining, the pure gallium either being obtained from that drained away or from that left in the trough according to the type of impurity present. Whilst traversing the trough the gallium may be kept molten by heating coils on either side of each cooling coil and the liquid may be agitated mechanically or by ultrasonic waves. In the case of high melting-point materials the frozen zone may be produced by allowing the material to lose heat by radiation.