JPH0219574B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a discharge lamp, and more particularly to a method for manufacturing an electrode installed at the end of a discharge tube of a metal vapor discharge lamp. Conventionally, for example, a metal vapor discharge lamp containing a metal halide has had a structure as shown in FIG. In FIG. 1, reference numeral 1 denotes an arc tube made of transparent quartz glass, in which mercury, a rare gas, and a metal halide are sealed.
Electrodes 2a and 2b are sealed and arranged opposite to each other at both ends of the arc tube 1, and these electrodes are connected to molybdenum foils 3a and 3 sealed to both ends of the arc tube 1.
They are respectively connected to external lead-in lines 4a and 4b via lines b. Heat insulating films 5, 5 are applied to both ends of the arc tube 1, and holding plates 6, 6 are attached. The holding plates 6, 6 are fixed by welding to the tips of U-shaped support frames 9, 10, respectively, thereby holding the arc tube 1 within the outer tube 14. At this time, the external lead-in wire 4a extending outward from one end of the arc tube 1 is connected to the support frame 9 by the ribbon lead 7, and the support frame 9 is welded to the stem lead 11. The other stem lead 12 is connected to an external lead-in wire 4b extending outward from the other end of the arc tube 1 by an arc-shaped conducting wire 8. These two stem leads 11 and 12 are respectively connected to predetermined parts of a base 13 provided at the end of the outer tube 14. Electrode 2 inside the arc tube in such a discharge lamp
a, 2b are shown enlarged in Fig. 2,
Electrode core wire 1 made of heat-resistant metal such as tungsten
5, and a coil 1 wound around this electrode core wire.
Further, an electron emitting material 18 made of scandium oxide and tungsten powder is coated around this coil. By the way, the scandium oxide used in this electron emitting material is effective because it brings good results to the lamp characteristics, but in order to remove the impurities contained in the scandium oxide, conventional
Vacuum treatment was performed at a temperature of . however,
This treatment of scandium oxide in vacuum had the following drawbacks. That is, according to the conventional treatment method, scandium oxide is placed in a heat-resistant metal container, housed in a quartz furnace core tube, set in a vacuum heating device, and then the inside of the furnace core tube is roughly evacuated. However, since scandium oxide is a fine powder,
If the roughing pot is not gradually opened, scandium oxide will scatter from the metal container and contaminate the exhaust system. Therefore, not only the amount of scandium oxide to be treated is small, but also it takes a long time to reach the degree of vacuum of 1×10 ⁻⁵ to 1×10 ⁻⁶ Torr necessary for heat treatment. In addition, after reaching the vacuum level, if the temperature is gradually increased while maintaining the pressure, especially H ₂ O, CO, etc. will be released, so the temperature will rise to 400℃
The degree of vacuum deteriorates significantly at around 500°C, and if heat treatment is performed at this time, the metal container will oxidize and the impurity gas will be adsorbed by scandium oxide, making the treatment ineffective. Therefore, in the conventional method, 1 × 10 ^-5 Torr is always
It was necessary to carry out the treatment while maintaining the following conditions, and as with the rough evacuation described above, a long time was required. Moreover, as the temperature rises, the hydrocarbons contained in scandium oxide become lower grade hydrocarbons.
It decomposes into CO and CO ₂ and is released, but it also has the disadvantage that carbon remains due to lack of oxygen in a vacuum. As described above, conventional vacuum processing methods not only cannot process large quantities of scandium oxide, but also require a long time to process and have the disadvantage that impure gases cannot be completely removed. Therefore, an object of the present invention has been made to solve such conventional problems, and provides a method for manufacturing an electrode for a discharge lamp, which is made by coating scandium oxide with an electron emitting material from which impurities have been effectively removed. Our goal is to provide the following. Hereinafter, the method for producing an electron emitting material of the present invention will be described in more detail by showing preferred embodiments thereof and conventional examples for comparison with the embodiments. First, as a conventional example, 0.1t, 16 x 16 square, length 26
Approximately 3 gr of scandium oxide was placed in a 2 mm molybdenum processing container and set in a vacuum processing apparatus. As for the processing conditions, as mentioned above, the pressure of the processing equipment is 1×
When the temperature drops below 10 ^-5 Torr, the electric furnace begins to raise the temperature.
However, as impure gas is discharged as the temperature rises, the pressure inside the device fluctuates, but the pressure is always 1×
Increase the temperature while maintaining 10 ^-5 Torr. Target temperature 1100℃
After reaching this point, the process was completed by maintaining the temperature for 10 minutes. The processing time required so far was about 8 hours. Tungsten powder, nitrocellulose lacquer, and butyl acetate were added to the scandium oxide treated in this way to prepare an electron emitting material suspension, which was applied to an electrode and then heated in vacuum at 1980° C. for 1 minute. Electron emitting material 1 produced in this way
Electrodes 2a and 2b having an inner diameter of 18 mm and containing an appropriate amount of mercury, argon gas, and compounds such as scandium and sodium are used.
A 400W metal vapor discharge lamp equipped with an arc tube 1 with a length of 44 mm between a and 2b was manufactured. When a lighting test was conducted on this metal vapor discharge lamp, the luminous flux maintenance rate after 6000 hours of lighting was 75%. Next, examples of the present invention will be described. As an example of the scandium oxide treatment, as shown in Fig. 3, scandium oxide 20 is placed in a quartz furnace core tube 19, which is a first heat-resistant metal oxide container with an inner diameter of 60 mm and a length of 1.300 mm, and the interior thereof is open to the atmosphere. A second heat-resistant metal oxide container, ie, a quartz boat 21, was placed therein, and heat treatment was performed at 1100° C. for 10 minutes in a siliconite electric furnace 22. The treatment time required for this treatment was about 3.5 hours, and the amount of scandium oxide used in this example was 40 gr, which allows a large amount to be treated in a short time. In addition, it is released when the temperature rises.
H ₂ O, OH, CO, CO ₂ and other impure gases are released to the outside of the furnace core tube, but the method for this is as shown in Figure 4, by flowing air from one end of the furnace core tube. It is good to discharge. Using the electron emitting material thus produced, an electron emitting material suspension was prepared in the same manner as in the conventional example, and a 400W metal vapor discharge lamp was manufactured and a lighting test was conducted. As a result, the luminous flux maintenance rate after 6000 hours of lighting was 80%. Table 1 shows this conventional example and the embodiment of the present invention in a table.

[Table] As shown above, when comparing the conventional vacuum treatment and the atmospheric treatment method of the present invention, the scandium oxide treatment time of the present invention is significantly shorter, and the amount of treatment is 40 gr, compared to the conventional method. Moreover, when a discharge lamp was formed using this, the luminous flux maintenance rate was 5% higher after 6000 hours of lighting. In particular, the reason for this high luminous flux maintenance factor is thought to be that residual carbon, which could not be removed by conventional vacuum processing, was removed, making it an excellent electron emitting material. In addition, in the above embodiment of the present invention, impurity gas was discharged by flowing air from one end of the furnace core tube, but if oxygen gas was flowed instead of air, even better quality scandium oxide with impurity gas removed could be obtained. Can be done. Further, the heat treatment temperature needs to be 800° C. or higher, and it has been found that impurities cannot be removed sufficiently below this temperature. It should be noted that the effects of the present invention can be explained in more detail as follows. Ordinary commercially available scandium oxide powder contains trace amounts of OH ^- , CO ₃ ^2- , and Cl ^- as impurities. For example, taking the case of CO ₃ ^2- , heating Sc ₂ (CO ₃ ) ₂ in vacuum――――→ Sc ₂ O ₃ +1/2C+3/2CO ₂ ↑ (1) Sc ₂ (CO ₃ ) ₂ ＋1/2O ₂ sealed container in atmosphere――――――――→ Sc ₂ O ₃ +2CO ₂ ↑ (2) Sc ₂ (CO ₃ ) ₂ +1/2O ₂ in oxidizing gas flow――――――――→ Sc ₂ O ₃ +2CO ₂ ↑ (3) In the case of a sealed container in the atmosphere (reaction (2)), the partial pressure of CO ₂ in the zero atmosphere inside the container increases with heat treatment, so some leftward reactions also occur, and impurities The components are carried into the discharge lamp. On the other hand, in reaction (3) of the present invention, the released CO ₂ is quickly flowed out of the container by the oxygen flow, so the reaction proceeds only in the right direction, yielding highly pure scandium oxide. . As explained above, the present invention accommodates scandium oxide powder in a second heat-resistant metal oxide that is open to a space surrounded by a first heat-resistant metal oxide container, and The oxidizing gas is introduced from one end of the oxide container, and the oxidizing gas is allowed to flow out from the other end, and the scandium oxide powder is heated by a heating device installed outside the first heat-resistant metal oxide. After heating at a temperature of 800°C or higher, a suspension containing an electron emitting material containing scandium oxide powder and tungsten powder is applied to an electrode component, and the electron emitting material is removed by high-temperature heat treatment. Since the electrode for a discharge lamp is completed by fixing the scandium oxide powder to the electrode component, according to this manufacturing method, the scandium oxide powder is isolated from an external heating device and is housed in an oxidizing gas flow to perform heat treatment. Therefore, impurity gases such as OH and CO are removed, and a high-purity oxide powder that is unaffected by impurity gases and has very little residual carbon is obtained, which is used as an electron emitting material. As a result, it is possible to obtain a luminous flux maintenance rate superior to that of conventional discharge lamps.

[Brief explanation of drawings]

Fig. 1 is a front view showing a metal vapor discharge lamp, Fig. 2 is a sectional view showing an enlarged electrode of the metal vapor discharge lamp,
3 and 4 are cross-sectional views schematically showing a processing apparatus for heat-treating scandium oxide to produce an electron-emitting material according to the present invention. 1... Arc tube, 2a, 2b... Electrode, 15...
Electrode core wire, 18... Electron emitting material, 22... Siliconite electric furnace. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1 Scandium oxide powder is contained in a second heat-resistant metal oxide which is open to a space surrounded by the first heat-resistant metal oxide container, and scandium oxide powder is oxidized from one end of the first heat-resistant metal oxide container. While the oxidizing gas is flowing in and the oxidizing gas is flowing out from the other end, the scandium oxide powder is heated by a heating device installed outside the first heat-resistant metal oxide.
After heating to a temperature of 800°C or higher, a suspension containing an electron emitting substance containing scadium oxide powder and tungsten powder is applied to an electrode component, and the electron emitting substance is heated by high temperature heat treatment. A method of manufacturing an electrode for a discharge lamp, characterized in that the electrode for a discharge lamp is completed by fixing the electrode to the electrode constituent member.