| 摘要 |
<p>919,419. Cathode materials and processing. PHILIPS ELECTRICAL INDUSTRIES Ltd. Jan. 20, 1960 [Jan. 23, 1959], No. 2082/60. Class 39 (1). In a method of making an impregnated cathode, at least part of the surface of a porous refractory body 10 is carbonized or provided with a layer of carbon and the body is impregnated through the resulting carbide or carbon layer 15 with pre-molten barium aluminate. The body 10 is afterwards incorporated into a cathode structure 17, at least part of its surface being free of carbon and carbide to constitute a high-emission area 12. Non-porous parts of the cathode structure, e.g. molybdenum cylinder 17, may also be carbonized to reduce emission therefrom. Carbonization of porous body 10, which may be of tungsten, or a tungsten-molybdenum alloy, or a tantalum-molybdenum alloy, may be effected by embedding it in carbon or graphite powder and heating to a temperature of 1200‹ to 1700‹ C. for 5 to 15 minutes to form a carbide layer 10 to 40 microns thick, the area 12 being protected against carbonization by a templet or having its carbide coating removed afterwards by mechanical treatment or by heating alternately in a reducing and in an oxidizing atmosphere. Alternatively, a layer of carbide may be sprayed or painted on to the surface of body 10 and caused to adhere thereto by sintering, or the porous body may be heated in naphthalene vapour. As a further alternative a layer of carbon or graphite powder or a compound such as sugar, which decomposes to carbon on heating, may be used, the layer of carbon being brushed off after impregnation, a protective layer of tungsten, which may have been provided on the high emission areas, also being removed. A composite porous body can also be formed by welding together carbonized and non-carbonized parts. A specific example is given.</p> |
