JPH0118535B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing an oxide cathode used as a filament for an electron tube cathode or the like.

Structure of conventional examples and their problems Filaments for electron tube cathodes, especially linear filaments, are made of extremely thin core wires with a diameter of 10 to 30 μm made of tungsten alloy containing rhodium oxide, etc., and are made of electron radioactive substances such as barium carbonate, calcium, strontium, etc. A coating coated with fine powder of alkaline earth metal carbonate to a thickness of about 10 to 15 μm is used. A so-called electrodeposition method is generally used to coat this core wire with the carbonate powder. That is, a long core wire is continuously electrodeposited, wound up as it is on a winding frame, and taken out from the winding frame as needed when being incorporated into a cathode ray tube or the like. Furthermore, after incorporating the core wire into the tube, the inside of the tube such as a cathode ray tube is placed under high vacuum and fired at a temperature of approximately 400°C to decompose and remove the organic solvent and binder contained in the electrodeposited layer. . After that, when calcined at a temperature of about 950℃, the alkaline earth metal carbonate becomes an oxide [(Ba・Sr・Ca)O]
degenerates into After that, at a temperature of about 1100°C, it is activated, that is, the oxygen of the oxide is removed, and free Ba,
Create Sr and Ca to increase donor electron density. In this way, a cathode ray tube is formed.

However, with such conventional manufacturing methods, it has not been possible to obtain a high electron emission density and a stable emission current over a long period of time. The reason for this seems to be that there is a problem with the conventional electrodeposition method. The problems with the conventional electrodeposition method are described below. In conventional methods, a binder made of nitrocellulose, which is easily soluble in organic solvents and easily decomposed at temperatures below 400°C, is added to the electrodeposition solution in order to improve the mechanical strength of the electrodeposition layer. Further, in order to perform electrodeposition efficiently, a quaternary ammonium salt represented by [(CH ₃ ) ₃ -N-R]X is added to the electrodeposition solution as an electrolyte. Here, R is an alkyl group having 12 to 18 carbon atoms, and X is a halogen. The binder and electrolyte were decomposed and removed by passing an electric current through the electrodeposited core wire or by heating the core wire from the outside.

However, as a result of studies conducted by the present inventors, it has been found that conventional electrolytes and binders have the following problems. First, it was found that in conventional electrolytes, halogens in the electrodeposition solution combine with Ba, Sr, and Ca during the activation stage, preventing the donor electron density from increasing. Furthermore, by using a binder made of nitrocellulose, it is expected that the mechanical strength of the coated carbonate will be improved, but the thickness of the electrodeposition layer is not uniform in the longitudinal direction of the core wire, and the coated carbonate is A high electron emission density could not be obtained due to the fact that the particle sizes were not uniform.

Purpose of the Invention In view of such conventional problems, the present invention uses an electrolyte containing a reducing element that does not contain halogen to reduce and activate the alkaline earth metal oxide that is the main component in activation. The present invention provides a method for producing an oxide cathode that enables high electron emission density by using an atomic alkaline earth metal.

Structure of the Invention The method for producing an oxide cathode of the present invention uses an electron-emitting substance containing an alkaline earth metal oxide as a main component.
An ammonium salt containing one of the reducing elements W, Al, Mg, and Co is mixed with an electrolyte and a binder to form a mixture, and this mixture is electrodeposited on the surface of a high-melting metal.

Description of Examples 10 to 40% of an alkaline earth metal carbonate, which becomes an electron radioactive substance, is added to an organic solvent containing 25 to 30% by weight of a ketone such as methyl ethyl ketone and 25 to 30% by weight of an alcohol such as isopropyl alcohol. weight percent and binder from 3 to 10
Add the weight percent to create an electrodeposition solution. As the binder, it is desirable to use organic glass such as polymethyl methacrylate in consideration of compatibility with alkaline earth metal carbonates. In _the above electrodeposition solution, _an ammonium salt _represented by _the general formula [( _{MH 4 )}
A small amount _of an alkylamide represented by the general formula [CH ₃ (CH ₂ ) _Y CH=CH(CH ₂ ) _Z CONH ₂ ] is added as an electrolyte. Ammonium tungstate ( _{NH 4 ) 2 WO 4 is an ammonium salt} represented by _the general formula [ ₍ NH _{4 )} For example, lauric acid amide CH ₃ (CH ₂ ) ₁₀ CONH ₂ , general formula [CH ₃
(CH ₂ ) _Y CH=CH (CH ₂ ) _Z CONH ₂ ], for example, oleic acid amide
CH ₃ (CH ₂ ) ₇ CH=CH (CH ₂ ) ₇ CONH ₂ can be used.

A linear oxide cathode is manufactured by performing electrodeposition on a core wire using an electrodeposition liquid having such a composition. That is, electrodeposition was performed on a long core wire made of a tungsten alloy using the above electrodeposition liquid.

The linear oxide cathode thus obtained is shown in the figure below. In the figure, 1 is a core wire, and 2 is a coated carbonate. As shown in the figure, the coated carbonate is about 1 to
When looking at the cross section of the filament, which was composed of 3 μm spherical particles 3 and cut at arbitrary intervals, it was found that the film thickness was uniform. After electrodeposition, the linear oxide cathode was wound onto a reel. In this way, we succeeded in producing a linear oxide cathode in an unactivated state.

Next, the excellent electron emission performance of this filament will be explained. First, the procedure for pulling out this filament and assembling it into an actual electron tube will be described. The filament is taken out from the spool, inserted into an electron tube such as a cathode ray tube, and placed under vacuum.
Fire at a temperature below 400℃. Through this firing,
The electrolyte alkylamide is completely removed by evaporation, and ammonium tungstate is converted to tungstic acid and remains in the electrodeposited layer. Polymethyl methacrylate, which is a binder, becomes a monomer gas, is completely decomposed and removed, and is discharged outside the tube. Afterwards,
When calcined at a temperature of 950°C or higher, the alkaline earth metal salt is modified into an oxide [(Ba, Ca, Sr)O]. Furthermore, at a temperature of about 1100°C, activation is performed, that is, removing oxygen from the oxide to create free Ba, Sr, and Ca to increase the donor electron density. At this time, the ammonium tungstate used as the electrolyte has already been converted into tungstic acid by firing at a temperature of 400° C. or lower. At 1100°C, the oxygen in tungstic acid has a higher vapor pressure than tungsten, so the oxygen evaporates, leaving behind tungsten.Tungsten has reducing properties, so it has the function of activating alkaline earth metal oxides. Also, Ba
BaWO ₃ , BaWO ₄ and BaWO ₆ are formed as intermediate layers between the atoms, and these intermediate layer compounds have low resistance and little evaporation, and are particularly effective in increasing mechanical strength.

Thus, in the electron tube manufactured from the filament of the present invention, a high electron emission density of 10 to 20 mA/cm could be obtained for a long time at a relatively low operating temperature of about 850 DEG C. after activation.

In addition, conventional linear oxidation using an organic solvent, an alkaline earth metal carbonate, and a quaternary ammonium salt represented by [(CH ₃ ) ₃ -N-R _] After activation, the object cathode is approximately
At an operating temperature of 850 DEG C., only an order of magnitude lower electron emission density of about 1 to 2 mA/cm could be obtained.

In addition, in the present invention, an example was shown in which ammonium tungstate was used as an electrolyte, but Al,
A similar effect was observed with ammonium salts containing reducing elements such as Mg and Co. Further, when organic glass is used as a binder as in the above embodiment, it is possible to form an alkaline earth metal carbonate that is compatible with the electron radioactive substance and has a uniform film thickness and particle size in the longitudinal direction of the core wire. Therefore, in the above example, lauric acid amide and oleic acid amide, which are compatible with organic glass as a binder, are used as an organic electrolyte, but the alkyl amide group represented by the above general formula is suitable as an electrolyte. They have similar properties and are completely decomposed and removed by firing at 400°C or less after electrodeposition, and other organic electrolytes may be used as long as they are compatible with the binder.

Furthermore, the present invention can be applied to oxides of any shape, not just linear, and can be applied to devices that require higher electron emission sources.

In particular, thin planar cathode ray tubes have a diameter of 20
A large number of linear filaments of about 45 μm are used. Such a filament is required to have an electron emission density of about 10 to 20 mA/cm at a low operating temperature for a long time, and the present invention can satisfy this condition.

Effects of the Invention According to the present invention, a stable and high-density emission current can be extracted from a filament for an electron tube cathode, and a high-performance linear filament can be obtained.

[Brief explanation of drawings]

The figure is an external view of an oxide cathode according to an embodiment of the present invention. 1...Core wire, 2...Coated carbonate.

Claims (1)

[Claims] 1. A mixture is formed by mixing an electron radioactive substance mainly composed of an alkaline earth metal oxide with an ammonium salt electrolyte and a binder containing one of the reducing elements W, Al, Mg, and Co. , a method for producing an oxide cathode, which comprises electrodepositing this mixture on the surface of a high-melting point metal.