JPS6340230A - Manufacture of heater of indirectly heated cathode - Google Patents

Abstract

PURPOSE:To obtain a heater preventing deterioration and thermal deformation of its core wire, by heating a coated body in a reducing atmosphere and forming thereon an insulation layer consisting of an alumina powder sintered stuff containing a specified wt % of tungsten powder. CONSTITUTION:In the case of tungsten ratio of 3%, 38,8g of an alpha type alumina powder with average particle diameter of 3mum, and 1.2g of the tungsten powder with average particle diameter of 0.8mum are used to form an insulation layer. And in the case of the tungsten ration of 20%, 32g of the alpha type alumina with average particle diameter of 3mum, and 8g of the tungsten powder with average particle diameter of 0.8mum are used, and a suspension is formed under exactly the same condition as the case of the tungsten ratio of 3%. Then, after the surface of a filament which is made of 3% of rhenium contained tungsten core wire and wound in a coil form is coated with the each suspension by means of spray, it is heat treated in a hydrogen furnace for about 5 minutes at about 1680 deg.C, then a molybdenum core metal of the filament is fused and eliminated in the mixed acid, thus a heater is formed. This heater is prevented from deterioration and deformation of its core wire.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to the formation of an insulator on a heater used in an indirectly heated cathode, and in particular to prevent deterioration of the core wire and minimize thermal deformation of the heater. Moreover, a low-cost heater is provided.

(Prior art) In an indirectly heated cathode that functions as an electron radiation source for an electron tube, the outer surface of a cathode sleeve into which a heater is inserted is coated with an electron radiation material, and heating mainly by radiation generated by energization of this heater causes Thermionic electrons are emitted from this electron emitting material, and this heater is made by coating a core wire mainly made of tungsten with alumina as an insulator. In such an indirectly heated cathode, a colored heater is used in order to efficiently transfer the heat generated by the heater to the electron emitting material through the cathode sleeve in order to improve the heating efficiency.

This colored heater has a structure in which a colored layer mainly made of tungsten oxide such as SU03 is provided on an alumina layer covering a tungsten core wire, as shown in JP-A-51-139251. The techniques disclosed in Japanese Patent Publication No. 52962 include a method in which a tungsten core wire is coated with an alumina layer and then impregnated with a tungsten ammonium solution, and a structure in which three or more alumina layers and tungsten layers are alternately laminated according to Japanese Patent Publication No. 40-9219. It has been known.

These are method A, in which two or more alumina insulating layers and colored layers are alternately laminated, and the alumina layer is impregnated with salts or oxides such as tungsten ammonia, which serve as a source of coloring substances, and then converted into metallic tungsten by reduction treatment. It can be roughly divided into Type B, and all of them improve the heating efficiency of the indirectly heated cathode.

(Problems to be Solved by the Invention) The above-mentioned method A employs a structure in which an alumina layer and a tungsten layer, which have different properties, are laminated. When used intermittently for 5 to 10 years at a temperature of 1000°C or higher, such as in a color TV, a complicated deformation that cannot be controlled due to strain occurs at the boundary between the two layers, which shortens the life of the heater. be.

Moreover, since each layer is formed separately, it is undeniable that the cost becomes relatively high due to the increased number of man-hours.

On the other hand, in Method B, a high temperature reduction sintering process (1600 to 170
0℃) is essential, but the decomposition gas from these tungsten compounds 02. N2, NH, etc. react with the tungsten or molybdenum core mandrel at high temperatures, causing embrittlement, which in turn shortens the life of the heater core wire.

Regarding the cracked gas, see NASA Tech Note
(D-1581) 1963 etc.,
It is also known that tungsten and molybdenum recrystallize and become brittle due to high-temperature treatment, and that the recrystallization temperature decreases due to the influence of impurities.

An object of the present invention is to provide a novel method for manufacturing an indirectly heated cathode heater that overcomes the above-mentioned difficulties, and in particular prevents deterioration and thermal deformation of the core wire.

[Structure of the invention]

(Means for solving the problem) In order to achieve this object, in the present invention, tungsten powder having an average particle size equal to or smaller than that of alumina powder is used, and 3 to 20% by weight of the tungsten powder is added along with the alumina powder to an appropriate amount. A method was adopted in which a suspension was created using a binder, the suspension was deposited in a single layer on the heater core wire, and then the suspension was sinked in a reducing atmosphere.

(Function) The average particle size of the alumina powder that adheres to the heater core wire is generally 1 μl to 5 μl as a rule of thumb, and the specific surface area of tungsten powder that is equal to or smaller than the average particle size of the alumina powder is This increase in surface energy is not only advantageous in terms of thermal efficiency, but also reduces the thermal load necessary for sintering the insulating film covering the heater core wire.

If the sintering temperature exceeds 1800° C., the tungsten core wire of the heater becomes brittle at high temperatures and the life of the furnace is shortened. Temperature 1 at which such problems are unlikely to occur
In order to obtain sufficient sintering at 700°C, in the present invention, the average particle size of the tungsten powder is selected to be smaller than that of the alumina powder, and in particular, it is preferably 1/2 or less of the average particle size of the alumina powder. Of course, even in the heater core wire coating layer obtained by coating the heater core wire with this mixed powder using the usual spraying method, electrodeposition method, or precipitation method and then sintering it in a reducing atmosphere, the tungsten particles are not dissolved in the alumina particles. Evenly distributed.

However, by changing the tungsten particle/alumina particle ratio,
If the number of tungsten particles is increased, the appearance becomes darker and the heat efficiency to the cathode is improved, but the insulation between the reheater and the cathode, where the tungsten particles tend to connect with each other, is reduced.

On the other hand, if the amount of tungsten particles is too small, the appearance becomes whitish and the insulation improves, but the thermal efficiency to the cathode deteriorates, leading to an increase in the heater temperature, and the insulation deteriorates.

After examining this relationship in detail, we found that it is best to mix the tungsten powder with the alumina powder at a mixing ratio of 5 to 10% by weight; if it is less than 3% by weight, the thermal efficiency deteriorates, causing the heater temperature to rise and the insulation to deteriorate. However, if a mixed powder exceeding 20% by weight is used, the tungsten particles adhering to the heater core wire will connect with each other, resulting in the above-mentioned point.

This relationship is shown in FIG. 1, where the horizontal axis represents the blending ratio (%) of tungsten powder and alumina powder, and the vertical axis represents the dielectric breakdown voltage of the heater.

After completing the heater by applying this mixed powder to the heater core wire by spraying, precipitation, or electrodeposition, the heater is assembled into a color cathode ray tube together with a fast-acting cathode, and the surface temperature of the heater is increased to 10
Adjust to 90'K in the same way as a conventional heater. Figure 1 shows that the color cathode ray tube was energized with 150% of its rated current, a DC voltage was applied across the cathode heater, and the voltage at which dielectric breakdown occurred in the heater was investigated.

As is clear from this table, the tungsten content is 7.5
% shows the best value, and 3% and 20% show values equivalent to non-colored heaters. Based on these results, in the present invention, the content of tungsten powder is limited to 3% to 20%. However, 5 to 10% is definitely within the range that does not cause any problems.

(Example) The invention will be explained in detail with reference to FIGS. 2a, b and 3. FIG.

An example in which the heater is formed by a spraying method will be explained, but the necessary suspension composition will be shown first. α-type alumina powder 3 with average particle size 3
7 g, 3 g of tungsten powder with an average particle size of 0.8 μm (tungsten ratio 7.5%), 59 g of butyl acetate and 1 g of nitrocellulose were added to a 50On++2 container,
Stir at 40 rpm for 5 hours to form a suspension.

When the tungsten ratio is 3%, 38.8 g of α-type alumina powder with an average particle size of 3 μm and 1.2 g of tungsten powder with an average particle size of 0.8 μs are used, and when the tungsten ratio is 20%, the average particle size is 3 μm. Using 32 g of α-type alumina powder and 8 g of tungsten powder with an average particle size of 0.8/ffi, a suspension was further formed under exactly the same conditions as when the tungsten ratio was 5%.

Next, each suspension was applied to the surface of a filament made by winding a 3% rhenium-containing tungsten core wire into a coil shape by spraying to a thickness of 100 μs, and then treated in a hydrogen furnace at 1680°C for 5 minutes, and then mixed with molybdenum in a mixed acid as usual. The core metal is melted and removed to form a heater.

The tungsten-containing alumina layer deposited on this rhenium-containing tungsten core wire looks dark gray because of the uniformly dispersed tungsten powder, but its cross-sectional model is shown in Figures 2a and b. In the tungsten alumina layer 2, small-sized tungsten particles 3 are uniformly dispersed in the alumina particles 4, and the heater shape is 1.
At 680°C, almost no deformation was observed compared to before the heat treatment process, and there was a clear difference from the conventional two-layer heater.

〔Effect of the invention〕

An interlocking cathode using this heater is installed in a color cathode ray tube, and the tube is energized with a heater current of 150% of the rated value, and with a potential difference of 210V applied between the cathode heater, 90 seconds ON/90 seconds OFF. The test was carried out for 5,000 hours with 5 heaters each (15 heaters each), and the number of heaters that suffered dielectric breakdown between the heater/cathode is shown in Figure 6.

In this figure, the horizontal axis shows the tungsten/alumina ratio, and the vertical axis shows the number of heaters that caused dielectric breakdown in this test.
At tungsten ratios of 3% and 20%, dielectric breakdown occurs only slightly, and at 5-15%, no problem occurs.

From this point as well, the effectiveness of the present application is clear.

Furthermore, when we inspected the heater that had suffered dielectric breakdown, it was found that the degree of deformation was clearly smaller than that of a conventional two-layer heater.

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'14. yr<t, .

A speed V-type cathode using a heater containing 75% tungsten is incorporated into a color cathode ray tube, and this
The heater current was turned ON for 10 seconds and OFF for 10 seconds, and the time taken for disconnection was compared with that of a heater made using an ammonium tungstate solution.

As a result, the heater of the present invention was 0/10.30 in 200 hours.
The conventional product showed 1710 at 0 hours, while the conventional product showed 200.
Time: 3/10.300 hours: 4/11, which clearly shows the superiority of the heater of the present invention. In addition, when both heaters were subjected to a 90° repeated bending disconnection test after hydrogen treatment at 1700°C for 10 minutes, the results were 3 times (1 to 16) for the conventional product and 10 times (8 to 14) for the inventive heater. It was an advantage.

These results can be understood from the fact that the heater of the present invention had clearly less tungsten crystal growth than the conventional heater.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between tungsten content and dielectric breakdown voltage of the heater, FIG. It is a figure which shows a content rate and the number of dielectric breakdowns of a heater.

Claims (2)

[Claims] (1) The heater core wire is coated with an insulating layer-forming material mainly composed of alumina powder containing tungsten powder, and this coating is heated in a reducing atmosphere to form alumina powder containing 3 to 20% by weight of tungsten powder. A method for manufacturing an indirectly heated cathode heater, comprising forming an insulating layer made of a powder sintered body. (2) Claim 1, characterized in that the average particle size of the tungsten powder is smaller than the average particle size of the alumina powder.
A method for manufacturing an indirectly heated cathode heater as described in .