JPH0426173B2 - - Google Patents

Description

[Detailed description of the invention]

[Purpose of the invention] (Industrial application field) This invention is used in electron tubes such as high-definition color picture tubes, high-quality image pickup tubes, projection tubes, or traveling wave tubes, and emits electron beams with high current density. The present invention relates to indirectly heated cathode structures, and particularly to improvements in cathode support sleeve materials. (Prior Art) The indirectly heated cathode assembly used in the above-mentioned electron tube generally has a structure in which a disk-shaped electron emitting section is supported by a support sleeve material. Since this cathode support sleeve is the component most exposed to high temperatures other than the heater, it must have sufficiently high mechanical strength at high temperatures. Generally, the thicker the support sleeve is, the higher its mechanical strength will be, but on the other hand, it will be heavier and cannot be structurally miniaturized. Furthermore, heat loss increases due to increased heat conduction, which is disadvantageous in that it becomes necessary to increase heating power. Especially in the case of an impregnated cathode structure, the operating temperature is 900℃ to 1100℃ (brightness temperature)
It is normal to operate at a relatively high temperature of
Moreover, in the aging process carried out prior to operation as an electron tube, the tube may be heated to about 1200°C. Furthermore, electron tubes using these indirectly heated cathode structures may be installed in artificial satellites, aircraft, ships, automobiles, etc.
More stringent vibration resistance is required. Under these circumstances, the support sleeve of the conventional impregnated cathode structure has
Tantalum (Ta) material has been mainly used. (Problems to be solved by the invention) However, the support sleeve made of Ta material is relatively difficult to process and weld, and its high specific gravity generates a large load during vibration, making it difficult to provide vibration resistance. be. The present invention aims to eliminate the above-mentioned drawbacks and provide an indirectly heated cathode structure that is made of a material that has excellent vibration resistance, strong material strength, especially thermal fatigue, is relatively easy to process, and can reduce heat capacity. purpose. [Structure of the Invention] (Means for Solving the Problems) The present invention is an indirectly heated cathode structure in which the main component of the sleeve supporting the electron emitting part is an alloy containing at least 85% by weight of niobium. . The remainder is at least one metal selected from the group consisting of titanium, zirconium, hafnium, vanadium, tantalum, molybdenum, and tungsten, and is an indirectly heated cathode structure containing these metals as alloy additive elements. (Function) According to the present invention, while Ta, which is the material of the conventional cathode support sleeve, has a specific gravity of 16.6, the niobium alloy material has a specific gravity of approximately 8.6, so the weight of the support sleeve can be reduced. It can be reduced to 50% or less. Furthermore, it can be stably processed into a thin-walled sleeve by drawing. Moreover, it has characteristics that can withstand thermal fatigue caused by heating and cooling, and vibration resistance characteristics are not impaired. (Example) An example will be described below with reference to the drawings. This embodiment is an example in which the present invention is applied to an impregnated cathode structure as shown in FIG. The disk-shaped electron emitting portion 11 is made of porous tungsten impregnated with an electron emitting substance and whose surface is coated with iridium (Ir). This disk-shaped electron emitting section 11 is formed by a cathode support sleeve 1 formed by a rhenium (Re) thin wire 12.
It is fitted into the top of 4. And a cylindrical shape with a bottom
It is welded and fixed within a cup 13 made of Re material. The outer surface of this cup 13 is secured by a cathode support sleeve. The cathode support sleeve 14 is
Its lower end is fixed to an outer support cylinder 16 made of Kovar (trade name) via three support straps 15 made of Nb or 1% Zr-Nb alloy. Note that inside the cathode support sleeve 14,
A heater (not shown) is inserted, and such a cathode assembly is assembled together with various grid electrodes and the like as an electron gun assembly, and is incorporated into an electron tube. Therefore, the cathode support sleeve 14 is manufactured by rolling and pressing a niobium (Nb) alloy material, which is an electrolytic melting material, into a cap with a wall thickness of approximately 25 μm and an outer diameter of 1.6 mm, and then laser processing to lengthen the cap.
Finished in a 6.4mm sleeve. The present inventors incorporated such an indirectly heated cathode structure into a triode tube capable of testing the emission characteristics, compared the emission characteristics and cut-off voltage characteristics before and after the vibration test, and determined the degree of deformation of the sleeve due to the vibration test. evaluated. Among these, data such as curve A1 in FIG. 2 was obtained as a result of cut-off voltage characteristics. In order to evaluate the sleeve material, a cathode structure using a support sleeve made of Ta having the same shape and dimensions as the conventional example was manufactured and evaluated in the same manner.
The result is a curve B1 shown in the figure. This vibration test is conducted in random mode, effective acceleration
10G, bandwidth 2000Hz, one vibration test time 2
The test was carried out repeatedly. For comparison, the wall thickness of the cathode support sleeve was 100μm and 200μm.
The vibration resistance of cathode assemblies using a Nb sleeve and a Ta sleeve were evaluated in the same manner as above. As a result, in the case of a sleeve having a wall thickness of 200 μm, there was almost no difference in the vibration resistance, that is, the amount of change in the cut-off voltage characteristics of the electron tube, depending on the sleeve material. On the other hand, the wall thickness is 100μ
In m, the Nb alloy sleeve was superior.
In other words, curve A2 shown in Figure 2 is for a 100 μm thick
For the Nb alloy sleeve, curve B2 is the result for a Ta sleeve of the same thickness. From these results, it is clear that the indirectly heated cathode assembly using the Nb alloy cathode support sleeve can reduce the cutoff voltage fluctuation value of the electron tube compared to the cathode assembly using the Ta sleeve. This result means that the deformation caused by the vibration test is extremely small in the Nb material, which has a relatively low specific gravity, and indicates that the cathode structure according to the present invention has excellent vibration resistance. In addition, Nb material has relatively good workability, and can be easily and stably press-formed or continuously drawn into thin sleeve-shaped materials, making it excellent for mass production. As a suitable example, Nb-based alloy material is replaced with pure Ta material and pure Ta material.
Table 1 shows the alloy composition of the sleeve, the cut-off voltage fluctuation value, and the drawing processability into the shape of the material sleeve in comparison with the Nb material. This experiment was conducted with the following contents. The indirectly heated cathode assembly was incorporated into a triode tube capable of testing emission characteristics, and the fluctuation of cut-off voltage after intermittent operation due to heater on/off was evaluated. By energizing the heater, the surface of the electron-emitting region was heated to a brightness temperature of 1100°C, which is higher than the normal operating temperature. The test was conducted for 500 hours with a schedule of 5 minutes of energization time and 10 minutes of energization stop time.

[Table] As is clear from the results of this example, an appropriate range is set for the amount of each additive metal. That is, when the additive metal is mainly single, when the additive metal is zirconium, it is 0.2 to 6.0% by weight, similarly, hafnium is 3 to 15% by weight, and vanadium is 1% by weight.
Molybdenum is 2 to 7% by weight, tungsten is 0.5 to 3% by weight, and tantalum is 2 to 5% by weight. On the other hand, in the case of composite addition, hafnium is 3 to 10% by weight and titanium is 0.2 to 3.0% by weight, hafnium is 3 to 10% by weight and zirconium is 0.2 to 1.0% by weight, vanadium is 1 to 4% by weight and zirconium is 0.2 to 1.0% by weight. %, 2-7% molybdenum and 0.2-1.0% zirconium, or 0.5-3.0% tungsten and 0.2-1.0% zirconium. The upper limit of each of these additive amounts is mainly the upper limit that allows sleeve processing in practical terms, and the upper limit corresponds to the lower limit that produces a remarkable effect on fatigue resistance. According to the data shown in Table 1, sleeves can be made with excellent, good, and fair workability, and a cut-off voltage of 2.0V or less shows a remarkable effect. The acceptable value is approximately the practical limit. In addition, we investigated the effect of sleeve wall thickness on the cut-off variation value by using a sleeve made of pure niobium and a sleeve made of niobium and 0.75% by weight zirconium alloy material, with wall thicknesses of 50 μm, 75 μm, and 100 μm, respectively. The above on/off test was conducted. As a result, for sleeves with wall thicknesses of 75 .mu.m and 100 .mu.m, there was almost no difference in thermal fatigue resistance, that is, variation in the cut-off voltage of the electron tube, depending on the material of the sleeve. On the other hand, the wall thickness is 50μ
The Nb-Zr alloy sleeve was superior in m. From these results, it is clear that an indirectly heated cathode structure using a niobium alloy exhibits excellent thermal fatigue resistance and can extremely reduce the cutoff fluctuation value during its life. The amount of alloy added is small, and while maintaining the good vibration resistance properties of pure niobium sleeves, it has better thermal fatigue resistance than pure niobium sleeves, and can withstand even harsher usage conditions. I can,
As a result, a high performance electron tube can be realized. Although the disk-shaped electron-emitting section is disposed inside the sleeve via the cup, it is also possible to provide the disk-shaped electron-emitting section directly on the sleeve. However, in that case, it is necessary to provide a member below the disk-shaped electron emitting section to prevent the electron emitting material from evaporating or penetrating toward the heater. Note that although the case of an impregnated cathode has been described above, the present invention can be widely applied to indirectly heated cathode structures such as oxide cathodes. [Effects of the Invention] As explained above, according to the present invention, the cathode sleeve is made of a reinforced niobium alloy, and therefore has a relatively small specific gravity and a relatively small heat capacity. Therefore, it has good vibration resistance as an indirectly heated cathode structure, and it is also possible to relatively reduce heating power. moreover,
It is possible to provide a cathode structure with excellent thermal fatigue resistance against repeated heating during cathode operation, which greatly contributes to the realization of highly reliable and high-performance electron tubes. It also has good processability, such as drawing into a long and thin sleeve shape, and is highly suitable for mass production.

[Brief explanation of drawings]

FIG. 1 is a partially cut away vertical sectional view of an embodiment of the indirectly heated cathode assembly of the present invention, and FIG. 2 is a characteristic diagram showing the cut-off voltage with respect to the number of repetitions of the vibration test. 11...electron emission section, 14...cathode support sleeve.

Claims (1)

[Scope of Claims] 1. An indirectly heated cathode assembly comprising a cathode support sleeve, an electron emitting section attached to a part of the support sleeve, and a heater disposed inside the support sleeve, comprising: The material of the support sleeve shall consist of a niobium alloy containing at least 85% by weight of niobium, with the remainder containing at least one metal selected from the group of titanium, zirconium, hafnium, vanadium, tantalum, molybdenum, and tungsten. An indirectly heated cathode structure characterized by: