Double layer oxide cathode with reducing agent

July 25, 1967 h. j. lemmens etal 3,333,141

DOUBLE LAYER OXIDE CATHODE WITH REDUCING AGENT

Original Filed March 2, 1962

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INVENTORJ

HENDRICKW J-LENMEN-S

PIETER ZALM :n'

United States Patent Office Patented July 25, 1967 cathode. The manufacture of cathodes according to the invention is not more difficult than that of the conventional oxide cathodes, since only layers of a few microns in thickness are formed during each spraying operation, so that a layer of a few tens of microns is obtained only after many spraying operations.

The support of the layers is a cathode body preferably consisting of galvanic nickel or cobalt without admixtures. Apart from its slightly higher price, cobalt has the advantage that it has only half the evaporation rate of nickel.

The invention will now be described more fully with reference to the accompanying drawing, which shows* a cathode body with activated layers according to the invention.

Referring to the drawing, reference numeral 1 designates a nickel tube, on which a nickel hood 2 having a wall thickness of 0.1 mm. is welded. This hood consists of galvanic nickel without admixtures. Onto the hood 2 is sprayed a layer 3 of barium-strontium carbonate of 60μ in thickness, containing 3% by weight of titanium hydride. Onto this layer 3 is sprayed a layer* 4 of calciumstrontium carbonate of 20μ in thickness without any admixture. After the cathode has been provided with a filament body and mounted in the tube, the carbonates are decomposed by heating into oxides, also the titanium hydride being then dissociated into metallic titanium.

With test diodes the cathodes described above yielded, with a current density of 1.5 A./cm.², lifetimes from 1200 to 1500 hours and with a current density of 1 A./cm.²lifetimes from 2000 to 2500 hours. It should be noted, in addition, that with a test diode the results will, in general, be less favorable than with normal tubes, since in a test diode the anode usually has a higher temperature. The lifetimes indicated above apply to a cathode tempera³⁵ ture of 760° C. The top layer may also consist of bariumstrontium-calcium carbonate.