JPH02226647A - Electrode for discharge lamp - Google Patents

Abstract

PURPOSE:To obtain a discharge lamp cathode with stable arch by mixing a W and an alkaline earth metal oxide powders in a specific weight ratio, sintering the powder mixture, forming the tip part into a corn-like shape and a reverse conical shape caved part in the tip, and forming a fine hole in the caved part. CONSTITUTION:In an electrode main body comprised of a connection part, a base part, and a cylindrical part, a sintered body 2 is inserted in the cylinder part to form a cathode. The corn-like tip 2a of the sintered body 2 has the summit angle theta and a fine hole 10 is formed in the bottom of the caved part 9. The sintered body 2 is prepared by mixing a high melting point metal powder such as W and an alkaline earth metal oxide powder in a ratio e.g. 100:(10-20) weight ratio and sintering the mixture. Ba diffused from the inside of the fine hole is spread in the periphery of the tip 11. As a result, in the case of low electric current, an arch is maintained within the periphery 11 of the tip but in the case electric current becomes high, an arch is maintained just like covering the periphery 11 of the tip. Owing to this, even when the current is increased, drastic increase of current density is prevented. A cathode with stable arch, low blacking of a bulb, and little sintering loss of the tip is thus obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Technology] The present invention relates to electrodes used in rare gas discharge lamps such as xenon short arc discharge lamps and other discharge lamps.

[Conventional technology]

For cathodes of short arc discharge lamps such as xenon short arc discharge lamps and round ultra-high pressure mercury lamps, thoriated tungsten (hereinafter referred to as ThW) is used for boat fishing. This is because the vapor pressure of thorium, which acts as a thermionic emission material (hereinafter referred to as an emitter), is relatively low, so it has the advantage that there is little blackening of the bulb during use of the discharge lamp. However, since the cathode operating temperature for efficient thermionic emission is around 2000°C, tungsten recrystallization and crystal growth are rapid, and thorium diffusion from the inside of Th- to the electrode tip is slow. In short-arc discharge lamps, electrical characteristics such as current and voltage are quickly affected by changes in the distance between electric bridges. easy.

In order to solve the above problem, recently,
As disclosed in 61, etc.,
94, the use of alkaline earth metal oxides as emitters in discharge lamps with relatively low power consumption was considered, and it was put into practical use in xenon short-arc discharge lamps with power consumption of less than 500. It has come to the point where it is offered. The advantage of this cathode is that, as described in the above-mentioned published application, if an alkaline earth metal oxide is used, for example, in a composite oxide with aluminum oxide, the cathode can operate at a temperature of 1300°C. This means that it exhibits high thermionic emissivity. In this way, since the cathode temperature can be set much lower than in the case of ThW, the recrystallization of tungsten is slow and the amount of burning at the tip of the cathode is reduced, resulting in good arc stability.

However, as mentioned above, the power consumption of lamps using this cathode in practical use is currently less than 500W.
As the power consumption increases and the current value increases,
Blackening of the bulb is likely to occur.

This is also due to the fact that the vapor pressure of alkaline earth metals is higher than that of thorium.

[Object of the present invention]

The present invention was made in view of the above circumstances, and its purpose is to suppress the progression of the blackening phenomenon even in discharge lamps with slightly higher power consumption or higher current values. An object of the present invention is to provide a cathode suitable for a discharge lamp, particularly a short-arc discharge lamp equipped with a cathode using an alkaline earth metal oxide.

[Means to achieve the purpose]

In order to achieve the above object, in the present invention, the electrode is configured as follows.

That is, the main part is constructed by inserting a sintered body into the cylindrical part of an electrode body consisting of a connecting part, a base part, and a cylindrical part, and the sintered body is mixed with powder of a high-melting point metal such as tungsten. Mixed powder with alkaline earth metal oxide powder, the former in a weight ratio of 1
00, the latter is mixed and fired at a ratio of 10 to 20, and the shape of the tip is a cone-shaped tip with a spherical recess formed and a pore formed at the bottom of the recess. do.

[Effect]

The tip of the sintered body containing an alkaline earth metal oxide is not simply sharpened into a needle shape, but has a ground-spherical recess, and a pore is provided at the bottom of the recess. The alkaline earth metal that diffuses from the pores first spreads mainly into the mortar, making it easier to control the starting point of the discharge arc to a specific location and supporting the arc in a predetermined area. Therefore, the current density at the cathode tip decreases.

Furthermore, by regulating the lower and upper limits of the amount of alkaline earth metal oxide to the high melting point metal constituting the sintered body, such as 10 to 20 in weight ratio for the former 100, it is possible to The supply of alkaline earth metals is carried out appropriately so that the overall supply of alkaline earth metals is not too much or too little, maintaining the fulcrum and lighting properties of the arc, and speeding up the progress of blackening of the bulb. to suppress

Even if the current value increases, arc support is possible even at the top circumference of the mortar, so even if the current value increases,
A significant increase in current density at the cathode tip can be suppressed.

〔Example〕

FIG. 1 is an explanatory diagram of an example of a xenon short arc discharge lamp using the electrode of the present invention.

1 is an electrode body, and 2 is a sintered body, which is used as a cathode. 3 is an anode, and 4 is an anode lead rod that supports the anode. Reference numeral 5 denotes a molybdenum metal tube for airtight sealing, which is embedded in a tube section 7 connected to a spherical valve 6. 8 is an external lead, power consumption is 500W, voltage 2
5V, current 2OA.

The filled gas is xenon gas.

FIG. 2 is an enlarged view of the cathode of the discharge lamp of FIG. The electrode body 1 is made of highly malleable molybdenum metal.
a is the connection part with the molybdenum metal tube, 1b is the base part, 1
c is a cylindrical portion. A sintered body 2 having a cone-shaped tip 2a is pushed into this cylindrical portion and fixed by caulking using the malleability of the electrode body. 1d shows a recess created by caulking.

FIG. 3 is an enlarged view of the cone-shaped tip 2a of the sintered body 2. At the tip, a cone-shaped recess 9 is formed with an expansion angle θ of approximately 90''.The expansion angle θ2 of the cone is approximately 8
It is 0°. 10 is a pore provided at the bottom of the recess 9, and to give an example of dimensions, the diameter of the top circumference 11 is about In, the diameter of the pore is about Q, 3 mm, and the depth is about 2 ridges. . Expansion angle θ
1 and 02 may be changed somewhat depending on the power consumption and current value of the discharge lamp.

The composition of the sintered body is ff1f! of tungsten. Barium aluminate 15 is mixed with T85 and then fired and molded.

Now, as explained in the [Function] section above, the pores 10
The barium that diffuses from inside the mortar is
spreads within the area of Therefore, if the current value is small,
The arc is supported within the top circumference 11, but when the current value increases, the arc is supported so as to cover the top circumference 11 as well. This prevents a significant increase in current density even if the current value increases. Naturally, barium diffuses into the top periphery 11 from the surface 12 of the cone, but since the temperature is higher in the pores and the inner surface of the mortar, the main source of barium is the latter. Therefore, the arc support portion can be reliably defined within the mortar or in an area including the top circumference of the mortar.

By the way, as shown in the figure, the sintered body 2 is exposed inside the bulb and faces the anode, so too much barium content is undesirable because it accelerates the blackening of the bulb, so the upper limit is , 20 as stated in the claims. The lower limit is set to 10 in order to ensure that barium can be easily supplied from the pores and that the supply amount is sufficient.

The cathode configured as described above can be used for short arc discharge lamps with power consumption up to about 1100, for example.
When examining the change in light intensity depending on the lighting time of the discharge lamp of the above example, assuming that the initial value was 100, the brightness after 3000 hours was 85. In other words, it can be seen that the light intensity attenuation due to the blackening of the bulb is extremely small. In addition, the arc stability (a value indicating how much the brightness changes at a certain point of the arc), which is a measure of the "wobble" of the arc, is 5.
Even after 000 hours had elapsed, it was possible to suppress the deviation to ±0.5χ.

In addition to the aluminate in the example, examples of barium complex oxides include tungstate (e.g. [1aO-W
O2) is also very good.

[Effects of the Invention] As can be understood from the description of the above embodiments, the present invention has the following advantages:
When used as a cathode in a short-arc discharge lamp, (a) good arc stability, (b) less blackening of the bulb compared to barium-based lamps, and (c) low operating temperature of the cathode to avoid burnout of the tip. This provides advantages such as suppressing changes in the distance between the electrodes. Furthermore, this electrode can be used as is as an electrode for long-arc mercury lamps used in AC power sources, and of course the power consumption is 5.
It can also be used as a cathode for discharge lamps with less than 0 OW.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of an example of a xenon short arc discharge lamp in which the electrode of the present invention is used, Fig. 2 is an explanatory diagram of the electrode body and sintered body, and Fig. 3 is an explanatory diagram of the tip of the sintered body. FIG. In the figure, l is the electric field body, 2 is the sintered body, 3 is the anode, and 5
1 is a molybdenum metal cylinder, 6 is a valve, 7 is a technical tube part, 9 is a recessed part, 10 is a pore, and 11 is a top circumference.

Claims (1)

[Claims] An electrode for a discharge lamp comprising a sintered body inserted into the cylindrical part of an electrode body consisting of a connecting part, a base part, and a cylindrical part, the sintered body being made of a material such as tungsten. A mixed powder of high melting point metal powder and alkaline earth metal oxide powder is mixed and fired at a weight ratio of 10 to 20 when the former is 100, and the shape of the tip is as follows: An electrode for a discharge lamp, characterized in that a cone-shaped recess is formed at the tip of the cone, and a pore is formed at the bottom of the recess.