JPS61126736A - Manufacture of emitter tube for electric discharge lamp - Google Patents

Abstract

PURPOSE:To prevent any cracks from developing in the area of glass cement used to join a translucent ceramic tube and a terminal cap together by immersing a terminal cap made of ceramic in a tungstate solution and then sintering the terminal cap to convert its surface into cermet. CONSTITUTION:An electrode core bar hole 5 and a lead wire hole 6 are formed in a terminal cap prepared by subjecting a high-purity alumina powder with a mean grain diameter of at most 1mu preferably at most 0.1mu to pressure molding. Next, after being immersed in a tungstate solution of a proper concentration and then is dried, the terminal cap is preliminarily sintered in an atmosphere of hydrogen at about 1,300 deg.C for about 2hr. Next, after an electrode core bar 3 and a lead wire 4 are buried in the holes 5 and 6 respectively, the thus obtained body is sintered in either an atmosphere of hydrogen or a vacuum at about 1,850 deg.C for about 3hr. As the result, the peripheral surface of the terminal cap is converted into cermet and therefore becomes highly conductive. after that, glass cement is used to airtightly fix the terminal cap to the end of a translucent ceramic tube 1.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides a method for closing both sides of a translucent ceramic tube with end caps of ceramic wire, and sealing mercury, rare gases, metal halides, etc. inside the tube. The present invention relates to an improvement in a method for manufacturing an arc tube for a discharge lamp, which is formed by enclosing a substance.

(Prior Art) FIG. 3 shows a row of end structures of arc tubes for discharge lamps in which the ends of a translucent ceramic tube are closed with ceramic end caps. In the figure, 1 is a translucent ceramic tube;
Reference numeral 2 denotes a ceramic end cap that is airtightly fixed to the end of the translucent ceramic tube 1 with glass cement. In the center of this end cap 2, a current-carrying conductor 3 made of a heat-resistant metal such as niobium is fixed airtight with glass cement. Inside the translucent ceramic tube 1, metal halides such as sodium iodide and thallium iodide are sealed together with mercury and a rare gas. An arc tube for a discharge lamp having such a structure can be operated at a much higher temperature than an arc tube made of quartz glass, so it has the great advantage of providing a discharge lamp with high efficiency and high color rendering properties. However, on the other hand, the niobium conductor is corroded by the halogen sealed inside the arc tube, making it impossible to light up within a short period of time. No. 9, No. 4 excluding such defects.
As shown in the figure, a structure has also been proposed in which the end of a translucent ceramic tube 1 is closed with an end camp 2' made of conductive cermet that is resistant to halogen attack at high temperatures. However, such a structure has the drawback that the difference in thermal expansion between the translucent ceramic tube 1 and the end cap 2' is large, and therefore cracks occur in the glass cement that connects the two, which tends to cause leakage accidents. (Objective of the Invention) An object of the present invention is to provide a method for manufacturing an arc tube that can easily and reliably produce an arc tube for single-release lamps that eliminates the various drawbacks described above.

(Structure of the Invention) FIG. 1 shows the end structure of an arc tube for an order electric lamp manufactured according to the present invention. In the figure, reference numeral 1 denotes a translucent ceramic tube, and reference numeral 2 denotes a ceramic aqueduct that is airtightly fixed to the end of the translucent ceramic tube 1 with glass cement. The end cap 2 is made of the same material as the translucent ceramic tube 1; for example, if the translucent ceramic tube 1 is alumina ceramic, the end cap 2 is also made of the same alumina ceramic. The surface of the end cap 2 is made of cermet by the following method. Reference numerals 3 and 4 are an upper electrode shaft and a lead wire, which are implanted and fixed in the end camp 2, respectively. Next, a method for manufacturing the above arc tube will be described.

End cap 2t as shown in FIG.
First, a ceramic material is pressure molded.

When edge camp 2 is made of alumina ceramic f:
High purity alumina powder having an average particle diameter of 1 μm or less, preferably 0.1 μm or less is granulated and press-formed into a predetermined end cap shape. An electrode mandrel embedding hole 5 and a lead wire embedding hole 6f are provided in the molded body during or after press molding. Next. Then, if necessary, the lake cap molded body is fired for about 3 hours in a hydrogen gas atmosphere at a temperature of about 1300°C. Then, insert the electrode mandrel 3 and the lead wire 4 into the electrode mandrel embedding hole 5 and the lead wire embedding hole 6, respectively.
After planting, the end cap molded body is fired for about 3 hours at a temperature of about 1850° C. in a hydrogen gas atmosphere or in a vacuum. As a result, the outer periphery of the end cap is made into a cermet, and the resistivity is 8×1O−6T2+I×10−5T+
If it is around 0.8 (10-'Ω・0R) (T is the ambient temperature), it becomes a good conductor with no practical problems. Appropriate ohmic contact can be obtained between the cermet formed on the outer periphery of the end cap 2 and the electrode mandrel 3 and lead wire 4.

It is. Finally, the end camp thus obtained is airtightly fixed to the end of the translucent ceramic tube 1 with glass cement, as shown in FIG.

A metal halide is sealed inside the translucent ceramic tube 1 together with mercury and a rare gas when or after the end cap is fixed (after the end cap is fixed, it is sealed through an exhaust pipe).

The tungstate solution is prepared as follows.

That is, mix and stir sodium nitrite and caustic soda, heat the mixture at 270 to 310°C, and pour the mixed solution.
After adding an appropriate amount of tungsten metal powder to the solution,
A precipitate is obtained by cooling. This precipitate is then dissolved in water to form an aqueous solution.

In addition, it has been found that the best way to implant electrical terminals and lead wires into the steel cap is to immerse the end cap molded body in the above-mentioned tungstate solution, pre-sinter it, and then do so after the final firing. . However, the end cap molded body may be first calcined, then immersed in a tungstate solution, and then the electrode mandrel etc. may be implanted therein.

(Effects of the Invention) As explained above, the present invention turns the surface of the end cap into a cermet simply by immersing the end cap molded body made of ceramic in a tungstate solution and firing it.
Compared to the case where tungsten powder is mixed in advance with ceramic powder and formed into 1R, it is possible to obtain an end cap that is easier to manufacture, has stable quality, and is lower in cost. An arc tube using such an end camp has the great advantage of having extremely high resistance to attack by halogen vapor at high temperatures.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the end of an arc tube for a discharge lamp manufactured according to the present invention, Fig. 2 is an enlarged sectional view of an end cap used for the same end, and Figs. 3 and 4 are of a conventional discharge lamp. FIG. 1 and 2, 1... Translucent ceramic tube, 2... End camp, 3... Electrode mandrel, 4...
Lead wire, 5... Electrode mandrel embedding hole, 6... Lead wire embedding hole.

Claims (1)

[Claims] When manufacturing an arc tube for a discharge lamp in which both ends of a translucent ceramic tube are closed with ceramic end caps, an electrode mandrel embedding hole and a lead wire embedding hole are provided in the molded body of the end cap material. Then, the entire molded body is immersed in a tungstate solution, and then, if necessary, the molded body is pre-baked, and then the electrode mandrel and lead wire are embedded in the electrode mandrel embedding hole and the lead wire embedding hole, respectively. Furthermore, the method for producing an arc tube for a discharge lamp is characterized in that the molded body is fired to form an end cap, and the end cap is attached and fixed to the end of a translucent ceramic tube.