GB730355A - Improvements in and relating to resistance elements - Google Patents

Abstract

730,355. Temperature - variable resistors. GENERAL ELECTRIC CO. July 8,< >1953 [July 12, 1952], No. 18943/53. Drawings to Specification. Class 37. Thermistor elements are made of resistance material comprising a compressed sintered mixture of metal sulphides including, by weight, from 2 to. 20 per cent molybdenum sulphide, 2 to 20 per cent zinc sulphide, 2 to 15 per cent of at least one sulphide selected from the group consisting of barium sulphide and calcium sulphide, the remainder consisting of an additional metal sulphide, e.g. :and particularly silver sulphide, exhibiting a definite break in its temperature-resistance curve (i.e. a steep decline in resistance value at a critical temperature). Preferably the calcium sulphide content is below 10 per cent and the zinc sulphide content from 5 to 15 per cent. Also for best results the molybdenum sulphide content should not be more than about twice the zinc sulphide content. Example compositions are made up of 12 parts silver sulphide, 0.5 part molybdenum disulphide, 0.5 part free sulphur and either (a) 1.2 parts zinc sulphide and 0.8 part barium sulphide or (b) 0.8 part zinc sulphide and 1.2 parts calcium sulphide. The method of preparing the materials and forming and stabilizing the thermistor elements is substantially the same as set forth in Specification 682,887. The specific use of zinc sulphide and either calcium sulphide or barium sulphide or both means the provision of thermistors having higher voltage and temperature ratings than those described in Specification 682,887. For D.C. zinc sulphide and calcium sulphide together ensure excellent operating characteristics whilst for A.C. mixtures comprising zinc sulphide and barium sulphide are preferred. The metal sulphide exhibiting a break in its temperatureresistance curve is referred to as the base sulphide and thermistor elements having different break point temperatures can be obtained by substituting other base metal sulphides such as the sulphides of sodium, potassium, copper, platinum, mercury, lead, antimony, aluminium, chromium, nickel and cadmium.