US3070550A - Cathodes for electron tubes - Google Patents

Description

United States Patent 3,070,550 CATHQDES FOR ELECTRON TUBES Saburo Aoi and Noboru Murata, Tokyo, Japan, assignors to Oki Electric Industry Company, Ltd., Tokyo, Japan,

a corporation of Japan No Drawing. Filed Feb. 17, 1960, Ser. No. 9,182 Claims priority, application Japan Feb. 25, 1959 1 Claim. (Cl. 252-621) This invention relates to cathodes for electron tubes which have a high efficiency of electron emission at compartively low temperature.

It is an object of the invention to provide cathodes for electron tubes which can emit suificient electrons without raising the heating temperature excessively.

It is another object of the invention to provide an improved cathode for electron tubes which will not become deformed and will not spatter electrodes surrounding the cathode.

It is a further object of the invention to provide a low melting point oxide mixture for cathodes to reduce the temperature for activation in vacuum in the manufacturing process of cathodes.

In conventional cathodes for electron tubes which consist of porous metals containing oxide mixtures of two or more ingredients such a barium oxide, aluminum oxide, calcium oxide, magnesium oxide and strontium oxide, the melting points of the oxide mixtures are generally above 1300 C. and as high as 1700 C. Therefore, an excessively high temperature is required for impregnation, which makes the manufacturing of cathodes difiicult. Furthermore, since the efficiency of electron emission at 1000 C. is inferior, the heating temperature for such cathodes must be raised to at least 1100 C. in order to obtain sufiicient electron emission. Consequently, the life of heating filaments for cathodes is shortened, the cathodes deform more readily, and surrounding electrodes surrounding the cathodes, are spattered by material emitted by the cathode.

According to this invention, oxide mixtures of barium oxide, beryllium oxide and calcium oxide as shown in the following table are melted in a hydrogen furnace, coagulated, crushed and then impregnated into tungsten or other heat resisting porous metals in vacuum or at- "ice mospheres of hydrogen, argon, etc. at such melting temperatures as shown in the table:

As seen on the above table, the melting temperatures are lower than those of conventional oxide mixtures and temperatures for activation in vacuum may be limited so as not to exceed 1030 C., which greatly facilitates the manufacturing of cathodes. The cathodes made in accordance with the present invention will emit sufficient electrons as shown in the table. Moreover, in these cathodes the life of heating filaments is materially extended, the cathode-supporting metals will not deform, and the electrodes surrounding the cathode will not be spattered. Therefore, the cathodes according to this invention are superior to known cathodes when used for electron tubes as they afford long-life and high reliability to the tubes. These advantages are important in electron tubes generally and are particularly important in high power tubes such as microwave magnetrons and the like. For instance, the cathode impregnated with the mixture of 2 mols of barium oxide, 1 mol of beryllium oxide and 1 mol of calcium oxide emit an electron emission of 9.6 amperes per sq. cm. and afiords stable operation during continuous operation of 1,500 hours or more.

What is claimed is:

Cathodes for electron tubes comprising heat-resisting porous metals impregnated with oxide mixtures of barium oxide, beryllium oxide and calcium oxide in mixture proportions of 2 to 3 mols, 1 to 2 mols and V2 to 1 mol respectively.

References Cited in the file of this patent UNITED STATES PATENTS 2,902,621 Winter Sept. 1, 1959