TWI594290B - Short arc discharge lamp - Google Patents

Description

Short arc discharge lamp

The present invention relates to short arc type discharge lamps, and more particularly to short arc type discharge lamps having a cathode material for good electron emission.

In general, a short arc type discharge lamp enclosed in a crucible used as a light source for a projector, and a short arc type discharge lamp in which mercury is enclosed as a light source for semiconductor exposure or LCD exposure, the cathode is used for the purpose of being a constant When lighting, the electrons are often released, so that the electron emission is easy to carry out, and the high melting point metal contains the electron emitting material.

Then, as the electron emissive material, in a short-arc discharge lamp that requires a point light source and a high-intensity, it is generally used as a temperature at which the operating temperature of the cathode tip can be increased.

However, since it is a radioactive substance, it has been gradually regulated in recent years and is required to replace the material.

As an alternative to the ruthenium, it is proposed to use a rare earth element and a compound thereof. The rare earth element is a work function (generally, the energy required for electrons to fly out from the surface of the material) is low and A substance with excellent electron emission is expected to be a substitute for strontium.

Japanese Laid-Open Patent Publication No. 2006-286236 (Patent Document 1) discloses a short arc type discharge lamp which contains tungsten as a cathode material and additionally contains lanthanum oxide (La ₂ O ₃ ) as an emitter material.

However, a rare earth oxide such as lanthanum oxide (La ₂ O ₃ ) has a vapor pressure higher than that of cerium oxide (ThO ₂ ), so that it is relatively easy to evaporate. Therefore, when a rare earth oxide is used instead of cerium oxide as an emitter material contained in the cathode, excessive evaporation of the rare earth oxide occurs, leading to an early exhaustion. There is a problem that the electron emission function of the cathode is lost due to the depletion of the emitter material, and flicker is generated and the life of the lamp is shortened.

In particular, a cathode that requires a high temperature operation, that is, a cathode having a current density of 90 A/mm ² or more is more conspicuous. Since the temperature at the front end of the cathode is close to the melting point when the current density is exceeded, the evaporation of tungsten as an electrode material becomes conspicuous.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2006-286236

The present invention is directed to the short-arc discharge lamp in which the cathode and the anode are disposed opposite to each other in the interior of the arc tube, and even if the rare earth oxide is added to the cathode as the emitter, the present invention can be prevented. The early exhaustion of the emitter and the electronic release function for a long time can be sought A long-term constructor of the flashing life of the lamp.

In order to solve the above problems, the present invention is characterized in that the cathode is formed by a main body portion and a front end portion joined to the front end side thereof, and the main body portion is made of tungsten to which a rare earth oxide is added as an emitter; The front end portion is made of pure tungsten, and the aspect ratio of the tungsten particles in the main body portion is larger than the aspect ratio of the tungsten particles in the front end portion.

Further, it is characterized in that the aspect ratio of the tungsten particles in the main body portion is 3 to 30; and the aspect ratio of the tungsten particles in the front end portion is less than 3.

Further, the rare earth oxide is characterized in that it contains any of cerium oxide, cerium oxide and cerium oxide.

According to the invention, the front end of the main body portion to which the rare earth oxide is added as the emitter material is joined to the front end portion formed of pure tungsten, and the aspect ratio of the tungsten particles in the main body portion is larger than that of the tungsten particles at the front end portion Since the aspect ratio is also large, since the tungsten particles in the main body portion are relatively long in the direction of the electrode axis, the area in which the emitter contacts the tungsten particles becomes large.

In the lamp lighting, in the tungsten solid-melting rare earth oxide, the rare earth metal of the related rare earth oxide has a small oxidation number and is easily melted. As a result, the rare earth oxides easily diffuse the grain boundaries. Specifically, in the case of cerium oxide, oxygen is lost and La ₂ O _{3 is} changed to LaO _x .

Then, in the body portion, because the grain boundary of tungsten is toward the electrode axis The direction is extended, and the diffusion path is linear along the axis, so it is easy to spread.

As described above, when the emitter that has diffused in the main body portion reaches the tip end portion, the temperature of the tip end portion is high, and the diffusion speed is increased. However, in the tip end portion, the aspect ratio of the tungsten particles is larger than that of the body portion. It is relatively small, and the diffusion does not proceed extremely, and it is almost suitable for the supply state of the emitter of the body portion, and moves toward the front end.

As a result, in the main body portion, the emitter rapidly diffuses, and in the tip end portion, the diffusion speed of the emitter is slowed, and the state in which the emitter is depleted early is suppressed. Therefore, the early loss can be suppressed, and the cathode having a long service life can be obtained. .

Further, the aspect ratio of the tungsten particles in the main portion is 3 to 30, and the aspect ratio of the tungsten particles at the tip end portion is less than 3, so that it is easy to diffuse La which is an emitter from a lower portion of the temperature, at a temperature. In the higher front end portion, the diffusion speed is restricted, and unnecessary evaporation can be suppressed. Further, since the emitter is present at the grain boundary of tungsten, the so-called anchoring effect suppresses grain growth and supplies a stable emitter.

Further, since the rare earth group oxide as the emitter includes any of cerium oxide, cerium oxide, and cerium oxide, the rare earth oxide is melted in the main portion during the operation of the lamp, and the diffusion toward the tip end is smoothly performed. A cathode having good electron emission characteristics can be obtained.

1‧‧‧Short arc discharge lamp

2‧‧‧Light tube

3‧‧‧ cathode

4‧‧‧Anode

5‧‧‧射极

31‧‧‧ Body Department

32‧‧‧ front end

Fig. 1 is an overall view of a short arc type discharge lamp having a cathode structure according to the present invention.

Fig. 2 is a view showing a cathode structure of an embodiment of the present invention.

Fig. 3 is an enlarged cross-sectional view showing a portion A of Fig. 2;

[Fig. 4] The emitter diffusion diagram of Fig. 2.

Fig. 5 is a view showing an example of a method of measuring an aspect ratio.

Fig. 6 is a graph showing the effects of the present invention.

Fig. 1 is a view showing the overall structure of a short arc type discharge lamp having a cathode structure of the present invention. The short arc type discharge lamp 1 is disposed inside the arc tube 2, and the cathode 3 and the anode 4 are disposed opposite to each other.

As shown in Fig. 2, the cathode 3 is formed by the body portion 31 and the end portion 32 before being joined to the front end thereof. The main body portion 31 is made of tungsten, and a rare earth oxide such as lanthanum oxide (La ₂ O ₃ ) is added as an emitter material.

The distal end portion 32 is joined to the distal end of the main body portion 31 by means of solid phase bonding or the like, that is, the surface facing the anode 4. Then, the front end portion 32 is made of pure tungsten which does not contain an emitter material, and is preferably made of pure tungsten of 4N or more.

However, as shown in FIG. 3, the aspect ratio of the tungsten particles of the main body portion 31 is larger than the aspect ratio of the tungsten particles of the distal end portion 32. This aspect ratio is an index indicating the relationship between the length and the width of the crystal grain, and when the length and the width are relatively large, the ratio indicating the length in the axial direction is large.

By having such a cathode structure, the following actions and effects can be obtained.

As shown in Fig. 4, the cathode is heated due to the lamp lighting, as included in Oxygen in the rare earth oxide of the emitter 5 of the main body portion 31 is solid-solubilized in tungsten, and the rare earth oxide is reduced to produce an oxide having a smaller oxidation number. As described above, since the melting point is lowered, melting occurs in the tungsten particles, and the grain boundary between the particles is mainly transmitted through the cathode body portion 31. The emitter follows the temperature gradient, and the diffusion speed increases toward the front end side of the cathode. In the distal end portion 32, the aspect ratio of the tungsten particles is smaller than that of the main body portion 31, and the moving path is not formed along the axial direction, so that it is difficult to move toward the front end of the cathode. .

In this manner, in accordance with the temperature gradient of the tip end of the cathode when the lamp is turned on, the structure (metal phase) of the tungsten particles is provided in the main body portion 31 so that the moving speed of the emitter 5 is slow, but it is easy to extend to the front end portion. In the distal end portion 32, although the moving speed of the emitter is fast, the tip end has a structure in which it is difficult to move immediately. Therefore, the emitter existing in the main body portion 31 can be used. The tip end portion of the cathode is rapidly diffused (moved), and the problem of interruption in supply can be eliminated. The emitter moving toward the distal end portion 32 can suppress the excessively rapid moving speed in the axial direction and can suppress early depletion.

Next, an example of a method of measuring the aspect ratio of tungsten (W) particles will be described with reference to FIG. 5.

Here, the measurement method by the tungsten cutting method will be described.

The cathode was cut in the axial direction, and the cross section was polished and etched, and when observed by a metal microscope at a magnification of 200 times, the shape of the cut crystal grains was observed in the cross section. According to the cutting method described in JISH0501, the longitudinal and horizontal straight lines are drawn on the photograph of the cross section, and the number of grain grains completely cut by each straight line is calculated, and the average value of the cut length is taken as the length of the crystal grain. And width.

The details will be described with reference to Fig. 5 (A) and (B). In Fig. 5(A), the number of crystal grains cut by the straight line A-A' is five, and the "average crystal grain length" is (the length of A1-A6)/5.

Similarly, when the straight line B-B' is examined, five crystal grains are cut, and "the average crystal grain width" is (the length of B1-B6)/5.

In Fig. 5(B), one crystal grain is cut by the straight line A-A', and "the average length of the crystal grain" is (the length of A1-A2) / 1. Similarly, when the straight line B-B' is examined, the number of crystal grains to be cut is seven, and the "average grain width" is (length of B1 - B8) / 7.

In the vertical and horizontal directions, 20 straight lines are drawn at equal intervals, and the "average crystal grain length or width" is obtained. Regarding the longitudinal direction, the average value of the "average crystal grain length" obtained by 20 degrees is defined as the "die length" of the region. Similarly, in the horizontal direction, the "average value of the average grain width" obtained by 20 degrees is defined as the "width of the crystal grain" in the region. Using the "length and width of the crystal grains", the aspect ratio of the tungsten (W) particles was determined.

Here, the ideal range of the aspect ratio of the tungsten particles as the cathode 3 is 3 to 30 in the main body portion 31 and less than 3 in the front end portion 32.

Further, the aspect ratio of the tungsten particles is obtained by heating the ingot of tungsten and swaging it in the radial direction, and the tungsten particles are shaped to extend in the direction of the axis, and by controlling the degree To get the best aspect ratio.

<Life test>

According to the following specifications, the structure of the cathode tip end portion 32 is made of pure tungsten, and the main body portion 31 is made of a plurality of kinds of cathodes including an emitter formed of a rare earth oxide.

The tip end portion 32 of the cathode is made of pure tungsten in which tungsten particles having an aspect ratio of less than 3 are mixed, and the total length (thickness) thereof is set to 2 mm.

The body portion 31 of the cathode has an aspect ratio of tungsten particles of 1, 2, 3, 5, 10, 20, 25, 30, respectively, and the tungsten contains La ₂ O ₃ (2.5 wt%) and ZrO ₂ (0.07 wt%). ) constitutes.

The main body portion 31 and the front end portion 32 of each aspect ratio are joined to produce various cathodes, and an ultrahigh pressure mercury lamp having a rated power consumption of 2 kW is produced.

The ultra-high pressure mercury lamp produced for the specifications of different cathodes was subjected to a life test to confirm the illuminance maintenance rate ‧ the occurrence of flicker and the cathode loss. In addition, regarding the illuminance maintenance rate, the lamp was continuously turned on, and the illuminance was measured, and the maintenance rate was set.

The results are revealed in Figure 6.

The "aspect ratio (1 to 30)" shown in Fig. 6 reveals the aspect ratio of the cathode body portion 31.

The aspect ratio of the front end portion 32 is less than three, and the lamp tube (length to width ratio 5 to 30) having an aspect ratio exceeding the length is not drastically dropped even if it exceeds 1500 hours, and can be used comfortably. The illuminance maintenance rate of the standard was 85%, and it was confirmed that the illuminance maintenance rate was maintained at 85% or more.

As described above, according to the present invention, the cathode is provided by the body portion And the front portion joined to the front portion thereof, the body portion is made of tungsten containing an emitter made of a rare earth oxide, the front end portion is made of pure tungsten, and the aspect ratio of the tungsten particles in the body portion is It is set to be larger than the aspect ratio of the front end portion, whereby a short arc type discharge lamp in which the emitter included in the main body portion is not depleted early and a cathode having a long service life can be obtained.

3‧‧‧ cathode

5‧‧‧射极

31‧‧‧ Body Department

32‧‧‧ front end

Claims (3)

A short arc type discharge lamp is a short arc type discharge lamp in which an anode and a cathode are arranged opposite to each other in an inner portion of an arc tube, and the cathode includes an emitter formed by a rare earth oxide, and the cathode is a body The portion is formed by a front end portion joined to the front end side of the main body portion, and the main body portion is made of tungsten containing an emitter made of a rare earth oxide, and the front end portion is made of pure tungsten. The aspect ratio of the tungsten particles in the main body portion is larger than the aspect ratio of the tungsten particles at the tip end portion; and the longitudinal direction of the tungsten particles is arranged along the axial direction of the cathode. The short arc type discharge lamp according to the first aspect of the invention, wherein the aspect ratio of the tungsten particles in the main body portion is 3 to 30; and the aspect ratio of the tungsten particles in the front end portion is less than 3. The short arc type discharge lamp according to the first or second aspect of the invention, wherein the rare earth oxide includes any of cerium oxide, cerium oxide and cerium oxide.