| 摘要 |
1,170,880. Electrode materials and processing. SIEMENS A.G. 20 June, 1968 [21 June, 1967], No. 29335/68. Heading H1D. A thorium film thermionic cathode comprises a carrier of high melting-point metal containing thorium oxide with a surface coating consisting of an inner layer of tungsten carbide and an outer layer of a high melting-point metal through which thorium can migrate and which has a higher escape energy than tungsten, e.g. osmium or rhenium, the outer layer providing the emissive surface. The carrier metal may be tungsten or a tungsten-rhenium alloy containing 5-25% by weight rhenium. The thickness of the osmium or rhenium outer layer is preferably about 5 Á to ensure an adequate supply of thorium by diffusion through the layer, i.e. a dispersing action, and also to ensure sufficient separation of the carbide layer and the emissive surface. The outer layer may be deposited on the tungsten carbide layer electrolytically or, preferably, by a non-electrical chemicallyreducing deposition from an appropriate solution. |
