Improvements in or relating to processes for the production of extremely pure substances

摘要

In the production of extremely pure substances by deposition from a gas by thermo - chemical reaction, the deposited substance is absorbed in a depending liquid drop 4 of the same substance adhering to a solid rod 3 of the substance, liquid being simultaneously crystallized on to the rod. As crystallization proceeds the rod is withdrawn from the reaction chamber. The drop may initially be supported by a carrier of different material, e.g. carbon, graphite, quartz or tungsten, and the liquid may initially contain a seed crystal to determine the direction of crystallization. The liquid may be prevented from dripping by a blast of air or other gas or an electromagnetic field. The drop may alternatively be supported between two rods (Fig. 2, not shown). The two rods may be moved axially in opposite directions, or in the same direction, in the latter case producing a thickened rod. The reaction may be carried out directly on the surface of the hot liquid, a gaseous reactant being directed on to the drop from a pipe 2. The liquid may be heated by a high-frequency coil 5 after preheating by radiation or by atom, electron or ion bombardment, or (in the case of two rods) by passing a current through the rods and liquid drop. The reaction may be carried out some distance from the liquid and the deposited substance carried to the liquid by means of a temperature or pressure drop, a current of inert gas, e.g. a rare gas, or an electric discharge. Heat for the reaction may be provided by an electric discharge using alternating or direct current. The gas may be formed by vaporization of a solid, in which case direct current may be used, the solid being placed on the anode. Oscillations may be applied at the phase boundary between gas and liquid. When the drop of liquid is supported by an electromagnetic field, the oscillations may be produced by superimposing a low-frequency alternating electromagnetic field of small amplitude on the supporting field. Cooling means may be provided to solidify the liquid at the liquid-solid junction more rapidly. The rod or rods may be rotated, and special means, e.g. a rotating magnetic field, may be employed for the rotation of the liquid zone. Additives i.e. donors, acceptors, traps, recombination centres, &c., may be incorporated in the liquid zone. A current of steam, carbon monoxide or carbon dioxide at low pressure may be passed through the apparatus. The rod produced may be additionally purified by zone melting. Silicon may be deposited from silicon tetra-, hexa-, or octa-chloride, or silicochloroform. Hydrogen may also be present. Boron nitride may be obtained from B3N3H6 (triboron triamine), aluminium nitride from AlH3 NH3, and indium phosphide from InI3PH3. Other starting materials specified are: AlH3.PH3, AlH3.AsH3, GaH3.NH3, GaH3.PH3, InH3.NH3, AlCl3.NH3, AlCl3.PH3, AlCl3.AsH3.