GB625501A - Electrical resistive elements and methods of making them - Google Patents

Abstract

625,501. Non-metal resistances; couplings. WESTERN ELECTRIC CO., Inc. Aug. 1, 1947, No. 20988. Convention date, Sept. 19, 1942. [Classes 37 and 38 (i)] In producing heat-treated mixtures of manganese and copper oxides as resistance elements the rate of cooling determines the specific resistivity of the finished product. The invention is particularly applicable in the manufacture of thermistor elements, Figs. 1, 2 and 3, which require a low resistivity and high resistance temperature coefficient. The rate of cooling is chosen according to the atomic ratio of copper to manganese and is slow for elements high in copper and rapid for elements in which manganese is predominant. The sintering temperature is preferably within the range 600‹ to 1450‹ C. and is high for manganese rich mixtures and low for copper rich mixtures; 1000‹ C. is chosen for mixtures in which there are approximately equal atomic proportions of each metal. The Specification includes mathematical and graphical analysis, Figs. 4 to 7 (not shown), to show that resistors according to the invention possess a high temperature dependent factor for a required value of resistivity at 0‹ C. and a satisfactory "figure of merit " b for example with b= - 3.0. The derivation of this term is given in the analysis. In Fig. 3, the rod-shaped element 30 may have caps 31 as electrodes, friction held or secured by conductive cement. In Figs. 1 and 2, a paste containing silver or silver compound, a fusible glass and an organic substance is spread over the surface of the elements 10, 20 and the organic substance removed by drying. The elements are then baked at, for example, 475‹ C., to fuse the glass and bind the silver to form adherent electrodes 11, 22.