Excerpt from The Preparation, Properties, and Composition of Silundum: Dissertation Submitted in Partial Fulfilment of the of Ments for the Degree of Doctor of Philosophy, in the Faculty of Pure Science, of Columbia University
Silundum is a product of the electric furnace, and was discovered by Bolling, at Frankfort-on-the-Main, Germany. As early as 1900 he began the study of the use of the various silicon carbides as resistors, being led to this work by the fact that these carbides can be subjected to high temperatures without undergoing decomposition. His method was to mix the silicon carbide powder with various binders in order to hold the individual particles together. The mass is a non-conductor at low temperatures, but at about 700 - 800° C. it becomes conductive, thus being useless at a higher temperature.
By 1904 a process was worked out and patented by which it is possible to convert any piece of carbon, e. g., a crucible, brick, rod, etc., into silicon carbide. By this method resistors without any binding material are obtained, which will stand temperatures as high as 1650 - 1700° C. Previous to 1904, silicon carbide had been known in two conditions only - amorphous and crystalline - and it was supposed to be formed by the interaction of sublimed carbon and sublimed silicon. Bolling, however, discovered that silicon penetrates carbon when both are in a highly heated condition, but at too low a temperature for the carbon to have any appreciable vapor tension. He claimed that silicon at about 1600° C. exists in the form of vapor. Carbon at this temperature has an extremely small vapor pressure. According to Bolling"s definition, silundum is the product that is obtained when carbon is heated in an atmosphere of silicon vapor.
An electric furnace such as is used for the manufacture of carborundum was used for the preparation of silundum.
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