GB638436A - Resistance units and methods of making them - Google Patents

Abstract

638,436. Non-metal resistances; temperature variable resistances. WESTERN ELECTRIC CO., Inc. July 18, 1947, No. 19264. Convention date, May 17, 1939. [Class 37] Resistors possessing a negative temperature coefficient, for example thermistors, Figs. 1 and 2 (not shown), are made from a resistance material which comprises a compound of manganese oxide and an oxide of iron or nickel. Fig. 3 shows the relationship between specific resistance and atomic ratio of the metallic elements for a series of resistors made from different proportions of iron and manganese oxidescurve A-and different proportions of nickel and manganese oxides-curves B and C. If a mixture comprising finely divided oxides of iron and manganese, wherein the atomic ratio of the two metals Fe/Mn= 2.0 is heat treated at a temperature between 1000‹ C. and 1450‹ C., the compound manganese ferrite is formed and the specific resistance is a minimum. In curves B and C which are different due to different heat treatment, the minimum in specific resistance occurs between atomic ratios Mn/Ni=2.0 and 4.0 and corresponding to this minimum the product is a material in which a solid solution is formed between the compound nickel manganate and an excess oxide. It is stated that although in accordance with changes in heat treatment resistors of different specific resistances are produced, each will possess the same negative temperature coefficient. The Specification as open to inspection under Sect. 91 states that other combinations may be utilized, namely zinc and uranium or manganese and uranium or combinations selected from the oxides of aluminium magnesium, copper, zirconium, tin, chromium, cobalt, titanium and zinc. In the case of zinc and uranium or manganese and uranium it is stated that the minimum resistance for a specific heat treatment corresponds to an integral atomic ratio or nearly so, as in Fig. 3. This subject-matter does not appear in the Specification as accepted.