GB540844A - Resistance materials and methods of making the same - Google Patents

Abstract

540,844. Resistances. STANDARD TELEPHONES & CABLES, Ltd. June 21, 1940, No. 10706. Convention date, June 23, 1939. [Class 37] An electric resistance material having a negative temperature coefficient comprises the combined oxides of nickel, manganese, and cobalt, the resulting specific resistance varying between 1000 and 2x10<6> ohms/cm' depending on the relative proportions of the metals present. The halftemperatures (i.e. the temperature-range over which the resistance is doubled or halved) is below 70‹C throughout the above resistance-range and being in most cases within the limits of 140 ‹ and 20‹C, the range of measurement being taken as 0‹-25‹C. The Specification includes triangular curves showing lines of equal specific resistance and lines of equal half-temperature for all possible percentages of the oxides and the metals, so that, for a given specific resistance and halftemperature the percentage or percentages of each oxide or its metal element can be ascertained, and vice versa. Many numerical examples are given from these curves, Fig. 4-7 (not shown), and it is pointed out that high values of specific resistance are obtained for high nickel, manganese, or cobalt, and that half-temperatures of 30‹C or over are obtainable for low manganese (5-18 per cent) combined with relatively low nickel (4-30 per cent) and giving a wide resistance range. If the ratio of manganese to nickel varies between 1:1 and 12:1 a wide resistance-range is obtained with half-temperatures between 14‹ and 20‹ C. In manufacturing the resistances, the oxides in finely-divided state are intimately mixed and formed into bodies which are heated at temperatures of 800‹-1450‹C (the higher temperatures giving the lower resistance values) in an oxidizing, reducing, or inert atmosphere depending on the amount of oxide present and the resistance desired, the heat-treatment having no marked effect upon the half-temperature of the product. The bead of Fig. 1 is made by mixing the oxides into a paste with a binder such as a nitrate solution of one of the metals, for example, of cobalt, allowance for which is made in choosing the proportions of oxide. The head 10 is formed on platinum wires, dried and heat treated. In the disc of Fig. 2, the mixed oxides are pressed into a body 20 and heat treated, metal paste applied and leads 22 embedded therein. The unit is then heated to solidify the paste into electrodes 21 securing the leads. Alternatively the leads may be soldered to metal sprayed on to the solidified paste. The units may be enclosed in glass envelopes preferably evacuated to 10<-3> m.m. of mercury. A small bead of 0.03 in the diameter having a resistance 30,000 ohms at 25‹C and a half temperature of 18‹C. comprises 23 per cent NiO, 47 per cent Mn2O4, and 30 per cent Co2O3.