aluminothermics

Century Dictionary and Cyclopedia

1. n. A collective name for the processes in which high temperatures are produced by the chemical combination of oxygen and aluminium. It has been known for some time that high temperature could be obtained by the formation of alumina, but the operation was not practically applied previous to the invention of the process patented by Dr. Hans Goldschmidt. This consists in mixing finely powdered aluminium with some pulverized metallic oxid (e. g., Fe₃O₄), and then raising the temperature to the point where reaction takes place through which the aluminium deprives the other metal of its oxygen, forming A1₂O₃. This reaction generates a great quantity of heat and a very high temperature. The process is used for the production of pure metals which it has not before been possible to isolate completely and in a pure form, such as chromium, manganese, etc. Another very important application of the aluminothermic process is to welding. In this thermit (which see) is placed in a specially prepared crucible of refractory material and the reaction is started by means of an igniter. The fluid mass of iron produced is poured into a mold placed around the joint to be welded. This process is especially useful for welding conductor-rails, defective castings, and parts of broken machinery which must be repaired at the places where they are in use. When the aluminothermic process is used for the separation of metals, an important by-product is formed, namely, the melted aluminium oxid or alumina. It is an artificial corundum and has been called corubin. Its uniform hardness makes it far superior to natural corundum or emery for grinding and polishing purposes. A great obstacle in the way of the use of aluminothermic processes has been the lack of some means of starting the reaction, which requires a high temperature. Dr. Goldschmidt accomplishes this by using an igniter consisting usually of a readily reducible oxid, such as barium peroxid, mixed with finely powdered aluminium. The reaction of this mixture may be started by means of a match. A pinch of this mixture placed upon the thermit or other aluminothermic mixture will serve to start the reaction. Once started, the main reaction will propagate itself, since the temperature produced is probably above 3000° C., and higher than can be obtained in any other artificial way except by the electric arc.