GB360013A - Improvements in non-metallic electrical resistance bodies - Google Patents

Abstract

360,013. Resistance materials. BOSCH AKT.-GES., R., 4, Militõrstrasse, Stuttgart, Germany.-(Assignees of Biefeld, K. ; 17, Augsburgerstrasse, Munich, Germany.) July 28, 1930, No. 22638. Convention date, Aug. 3, 1929. [Class 37.] A resistance consists of a mixture of insoluble metal salts, the base of which is a metal forming compounds stable at high temperatures, while the acid radical is a heat-stable oxidation stage of a metal or metalloid. The acid radical of the salt may consist of an oxygen compound of iron, cobalt, nickel, manganese, tungsten, molybdenum, uranium, or chromium. The specific resistance may be regulated by the admixture of a nonconducting substance, for example oxides, silicates, borates, or other salts of light metals such as calcium, barium, strontium, magnesium, or aluminium. The conducting compound may be a heavy metal salt of light or heavy metals, for example copper chromate, iron tungstate, magnesium chromate, or aluminium ferrate, prepared by precipitation or fusion. Ferrosoferric oxide or ferrate of iron having the formula Fe(FeO2)2 may be employed and may be mixed with mangano-manganic oxide to obtain an increased negative temperature coefficient, or with chromic oxide to obtain a higher current-carrying capacity. The materials are finely ground and sieved, mixed in the desired ratio, and moulded under great pressure with or without binding agents such as waterglass, boric acid, &c. After drying, the resistance is annealed at about 1000‹ C., with or without sintering. The ends are metallized electrolytically or by spraying, for making connections thereto. Alternatively the pulverized resistance mass may be filled into an insulating container provided with current leads. Graphite or carbon powder may be added to prevent adherence of the particles. Instead of an insulating casing, a metal tube closed at the bottom and having a concentric rod or tube forming the other electrode may be employed, the current passing radially between the electrodes. The resistance unit may be insulated by a thin layer of enamel, giving a high efficiency for heating water or acid.