GB1148926A - Resistors - Google Patents

Abstract

1,148,926. Oxide-glass resistance film; oxides of Ir and Ru. INTERNATIONAL NICKEL Ltd. 11 Oct., 1967 [24 Oct., 1966], No. 47690/66. Headings C1A and C1M. [Also in Division H1] A composition adapted to be applied to a refractory non-conducting base and fired to form an electrical resistor comprises a mixture of powdered glass with from 2 to 90% by weight of ruthenium or iridium dioxide or both having a crystallite size not exceeding 500Š. The composition is advantageously a suspension of the mixture of metal oxide and glass in a liquid vehicle. Resistors made from such compositions have temperature coefficient of resistance (TCR) values more negative, and lower current noise values, than those made from metal oxides available commercially which have larger crystallites. To obtain the lowest TCR values the average size of the discrete particles of metal oxide should preferably be between 0À2 and 3 microns. The average size of the non-conducting glass particles is conveniently about 3À5 microns. In an example, the metal oxide particles are mixed with particles of a lead borosilicate glass of the composition 65% PbO, 25% SiO 2 , 10% B 2 O 3 in the proportion 25% dioxide to 75% glass. The mixture was suspended in a liquid medium consisting by weight of 2% ethyl cellulose, 10% dispersing agent, the balance being terpineol to form an ink, which was screen printed on to a base of the refractory material Forsterite (Mg 2 SiO 4 ), dried and then fired at 850‹ C. to form resistors having an average film thickness of 10 microns. Iridium dioxide of crystallite size less than 500Š is prepared by adding sodium bromate to iridium chloride solution, adjusting the pH to 7 with Na 2 CO 3 and boiling. The hydrated iridium dioxide precipitated may be dehydrated by heating in air at 700‹ C. and ground. Ruthenium dioxide of crystallite size less than 500Š is prepared by treating ruthenium chloride solution with NaOH until just alkaline and then acidifying with HCl to a pH 6-7. The suspension of hydrated dioxide may be washed with distilled H 2 O by decantation, then filtered and washed with hot distilled H 2 O. Alternatively, after washing by decantation, the suspension may be dialysed in an ion-selective membrane cell until the aqueous phase shows minimum conductivity. The dioxide may be dehydrated by heating to a temperature less than 500‹ C. The crystallites have an irregular basically hexagonal shape but often approached a spheroidal form. Reference has been directed by the Comptroller to Specification 1,091,917.