GB691280A - Sparking plug electrode - Google Patents

Abstract

In a sparking plug electrode consisting of a compacted sintered mixture of silver or silver alloy and a refractory oxide, the constituents being initially in a finely divided condition and wherein the refractory oxide is distributed throughout the body of the silver along the grain boundaries of the crystals thereof, the refractory oxide constitutes approximately 0.01-10 per cent by weight of the mixture. The refractory oxide may consist of any one or more of the alkaline earth metals of Group II of the Periodic Table referred to in the "International Critical Tables" (Vol. 1) such as beryllium, strontium or barium or of metals of Groups III for instance aluminium, scandium, yttrium and rare earth metals (Atomic Nos. 57-71) such as lanthanum, cerium or neodymium, IV e.g. zirconium or thorium and V e.g. vanadium or columbium or the sesquioxide of chromium in Group VI. The electrode may be produced by making a paste of silver powder and distilled water and adding thorium nitrate, the mixture being stirred whilst drying over a water bath; the dry powder is passed through a 100 mesh sieve and then pressed into a bar before being sintered for approximately one hour at 800-900 DEG C so that the material is converted into one having a compacted finely grained crystalline structure whilst the thorium nitrate decomposes to thorium oxide. The bar is then either swaged, rolled or drawn and after annealing finally cold worked to the required shape. The refractory oxides, the most suitable of which are the oxides of thorium, beryllium and aluminium, may be provided in the form of a dry powder, a paste or as a salt solution adapted to be decomposed to the oxide by heating. The silver may comprise an alloy having a major proportion of silver and a minor proportion, generally not exceeding 20 per cent, of elements taken either from the group of precious metals, for instance gold or platinum group metals such as platinum, palladium, or ruthenium or from the group of base metals, for instance copper.