JP4424941B2 - Perforated sintered electrode - Google Patents

Description

  The present invention relates to a porous sintered electrode used as an electrode of a discharge lamp, for example, a porous sintered electrode used as an electrode of a flash lamp used as a pulse light source.

As an electrode of a high-pressure discharge lamp, an electrode in which an electron-emitting substance is added to a refractory metal is known. Patent Document 1 is an example of such an electrode, in which a refractory metal powder is sintered to form a porous electrode, and the hole is filled with an electron-emitting material. In addition, it is described that by generating a discharge in a relatively large area, it is possible to suppress local concentration of the discharge and suppress consumption of the electrode.
JP 2000-505939 A (pages 5-8, FIG. 1)

  By the way, in the point light source type discharge lamp, it is necessary to concentrate and fix the discharge position. However, when the discharge is concentrated at a specific position, in the conventional electrode, the electrode is consumed as described above, and as a result, the discharge position fluctuates. In addition, in the conventional electrode, in order to improve the responsiveness at the time of lighting, for example, the electron emission ability has been improved by increasing the content of the easy electron emitting material. Since radioactive material ions are released, it takes time to extinguish the ions, and the response at the time of extinction is reduced. For this reason, when such a conventional electrode with improved electron emission capability is used, for example, when performing pulsed light emission with a flash lamp, there is a problem that erroneous light emission such as continuous lighting occurs. It was happening.

  Accordingly, the present invention provides a perforated sintered electrode for a discharge lamp that can concentrate the discharge position while suppressing the consumption of the electrode, and has improved the response at the time of turning on / off. Let it be an issue.

To solve the above problem, perforated sintered electrode of the discharge lamp according to the present invention, after forming the tungsten containing material likely to emit electrons less than 20 wt% of a metal injection molding, the discharge tip by Rukoto Sintered It is characterized by being manufactured integrally including the part and having a density after sintering of 12 g / cc or more.

  That is, the concentration of the easy-electron emitting material is set to be relatively low, while the filling density of tungsten is increased. Here, by forming by metal injection molding, it is possible to easily and surely make the filling density of tungsten in the discharge part a desired state.

  The porous sintered electrode preferably has a pointed tip shape. Furthermore, the electron-emitting material is preferably barium aluminate or a mixture of scandium oxide and an alkaline earth metal carbonate.

  As described above, by increasing the density of tungsten after sintering, the strength and heat resistance of the discharge portion are improved and the consumption thereof is suppressed. Therefore, lighting stability is maintained and life characteristics are improved. Further, by appropriately controlling the electron emission capability, it is possible to make the ion annihilation time appropriate and achieve both lighting / extinguishing responsiveness.

  By making the tip shape pointed, discharge can be reliably concentrated on the tip. Moreover, since the strength and heat resistance of the discharge part are high, the tip part of the electrode is consumed in a curved shape, so that the amount of movement of the discharge position is reduced.

  In addition, when such an easy-electron emitting material is used, it is possible to achieve both lighting / extinguishing responsiveness.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same reference numerals are given to the same components in the drawings as much as possible, and duplicate descriptions are omitted.

1 and 2 are schematic views of a flash lamp which is a discharge lamp using a discharge lamp electrode according to the present invention, in which FIG. 1 is a transverse sectional view and FIG. 2 is a longitudinal sectional view. In this flash lamp 10, a cathode 2 and an anode 3 are arranged in a cylindrical glass container 1 so as to face each other with a stem introduction pin 6. Electrodes 4 and 5 called trigger probes for starting discharge are arranged in front of the opposing surfaces of the cathode 2 and the anode 3, respectively. Each electrode 2 to 5 is connected to an external circuit by external terminals 7 _{1 to} 7 ₄ drawn out of the glass container 1. Xenon gas is sealed in the glass container 1.

  FIG. 3 is an enlarged view of the cathode 2. The side facing the anode 3 has a conical shape, and the opposite side has a cylindrical shape (pointed shape) having a cylindrical shape. The cathode 2 has, for example, a total length of 3 to 5 mm and a diameter of 2 mm, and the length of the tip cone portion is 1 mm.

  The cathode 2 is manufactured by the following metal injection molding (Metal Injection Molding = MIM) method. FIG. 4 is a flowchart for explaining the manufacturing process of the cathode 2. First, a mold having a predetermined space is prepared (step S1). This space has a shape in which the cathode 2 to be manufactured is enlarged at a predetermined ratio. On the other hand, a tungsten powder with an average particle diameter of 2 to 8 μm, an electron-emitting material consisting of a barium aluminate or a mixture of scandium oxide and an alkaline earth metal carbonate, and a resin such as polypropylene added to paraffin wax The binder made of the thermoplastic polymer material thus obtained is kneaded to form a granule having a diameter of about several millimeters as a raw material (step S2 = raw material generation step). Here, the ratio of the tungsten powder to the easy electron emitting material is less than 20% by weight of the easy electron emitting material, and a predetermined amount of binder that enables fluidization is added thereto.

  Next, the raw material thus prepared is heated to about 100 ° C. to 200 ° C. to be in a fluid state, and injection molded into the mold space prepared in step S1 (step S3 = injection molding process). When the injection-molded raw material is solidified in the mold, the solidified molded product is taken out from the mold (step S4). Then, the molded product is heated in an inert gas with a predetermined temperature profile and then cooled to perform degreasing to evaporate and remove the binder component (step S5 = degreasing step). The degreased molded product is further heated to 1400-1500 ° C. in vacuum to perform sintering for bonding tungsten powder (step S6 = sintering step). Thereby, the cathode 2 which is a porous sintered electrode is obtained.

  In the cathode 2 manufactured in this way, the filling density of tungsten can be uniformly increased up to the discharge tip of the cathode 2. This packing density is adjusted to 12 g / cc or more. Since the density of pure tungsten is 19.32 g / cc, the cathode 2 is mixed with an electron emitting material having a lighter density than this, and is a perforated electrode having many fine holes. The upper limit of the density is smaller than this pure tungsten density and is about 19 g / cc.

A voltage is applied from an external power source connected to the external terminals 7 ₁ , 7 ₂ between the anodes 3 (not including easy electron emitting materials) manufactured in the same manner as the cathode 2 thus prepared, and the external terminals 7 ₃ , 7 _4. By applying trigger energy to the trigger probe (applying a pulse voltage), a dielectric breakdown occurs between the electrodes to generate a discharge, and the enclosed xenon gas emits light.

  According to the present invention, since the tungsten is uniformly and densely filled up to the discharge tip of the cathode 2 and is firmly bonded by sintering, the strength of the discharge tip is the conventional type. It becomes stronger than the electrode. Therefore, consumption of the electrodes can be suppressed, and discharge can be performed at a stable position for a long time. For this reason, it can suppress that a discharge position moves and light emission position moves by repeating light emission. Furthermore, by suppressing the concentration of the electron-emitting material contained in the cathode 2, the discharge position can be concentrated at the tip, and the amount of residual ions (electrons) after voltage application can be suppressed, preventing continuous lighting. Suppresses mis-emission. Therefore, the on / off response is improved.

  In the above description, the case of a xenon flash lamp has been described as an example. However, the electrode for a discharge tube according to the present invention is also suitable as an electrode for a discharge tube that requires other lighting / light-off responsiveness.

  As an electron-emitting substance, a single element or a mixture of oxides of group IIIa of periodic table of elements such as scandium, yttrium, lanthanum, cerium, thorium, and alkaline earth metals such as calcium, barium, strontium, etc. Can do.

  In order to confirm the effect of improving the stability of the light output of the xenon-flash lamp by using the electrode of the present invention, the inventor of the present application uses each of the electrodes according to the present invention and the conventional type electrode. Experiments were conducted to compare the stability of light output. Hereinafter, the comparison result will be described.

  As the cathode 2, several types of four types of electrodes A to D having different tungsten filling densities were prepared. The filling density of each of the cases A to D was adjusted to 16.5, 12.4, 11.8, and 11.3. Of these, case A and case B are electrodes according to the present invention, using tungsten powder having an average particle diameter of about 3 μm, and adding about 5% by weight of an electron-emitting material to 95% by weight of tungsten. This was manufactured using the MIM method described above. This easy-electron emitting material is a mixture of 10 alkaline earth metal carbonates by weight with respect to scandium oxide 1. The alkaline earth metal carbonate is about 60% barium carbonate, about 35% by weight. Strontium carbonate, about 5% by weight calcium carbonate. On the other hand, the case C and the case D are manufactured by using the same material (tungsten and an electron-emitting substance) and sintering after press molding.

  A 10-watt xenon-flash lamp having these electrodes was prepared, and a continuous pulse was emitted to examine the difference in the electrode consumption state. The structure of the xenon-flash lamp body used in the experiment was a cylindrical shape having a diameter of 20 mm and a height of 19.5 mm, and the distance between the electrodes was set to 1.5 mm. The lighting conditions were an input energy of 0.1 J, a main discharge voltage of 1000 V, a lighting frequency of 100 Hz, and after 300 hours of lighting operation, the state of wear caused by sputtering due to discharge was examined.

  A method for determining the consumption state will be described with reference to FIG. As shown in FIG. 5A, the cathode 2 at the time of creation has a sharp tip. When the tip portion is consumed due to discharge, the tip surface is a curved surface as shown in FIG. 5B, and when the tip surface is consumed flat as shown in FIG. It may be exhausted as a state. Therefore, when it is consumed in a flat shape, the degree of wear is represented by the maximum diameter of the tip surface. The degree of wear was expressed by the maximum diameter.

  FIG. 6 is a graph in which the average value of the degree of wear of each of the electrodes in cases A to D examined in this manner is plotted against the tungsten density of the cathode 2. As is apparent from the figure, the degree of wear increases as the tungsten density decreases, and in cases C and D where the tungsten density is less than 12 g / cc, the wear degree exceeds 0.7 mm and the wear is severe. Moreover, since the discharge position is not concentrated because it is consumed in a planar shape, and the discharge distance becomes long, the light emission position also varies greatly. On the other hand, Cases A and B with a tungsten density of 12 g / cc or more have a low degree of wear and wear on the curved surface, so that it is easy to maintain the concentration of discharge positions, and the actual discharge distance is also This is shorter than the case of flat wear with the same wear level, and the influence of wear such as fluctuation of the light emission position is reduced. For this reason, in the electrodes according to the present invention (cases A and B), the concentration of the discharge position is easier to maintain than in the conventional electrodes (cases C and D), and the electrode wears more than the difference in the numerical value of the degree of wear. It was confirmed that the discharge distance can be prevented from extending and contribute to the discharge stability.

  In each case, after 300 hours of operation time, the lamp is turned on for 5 minutes at a lighting cycle of 100 Hz, and the difference between the maximum light output and the minimum light output is divided by the average light output by multiplying by 100 to improve the light stability. Asked. The light stability was 5.06% and 7.49% in Case C and Case D, respectively, and unstable results were obtained, but in Case A and Case B, 3. . 32%, 3.67%, and less than 5%, confirming that light stability is ensured.

It is a cross-sectional view of a flash lamp which is a discharge lamp using a discharge lamp electrode according to the present invention. It is a longitudinal cross-sectional view of the flash lamp which is a discharge lamp using the electrode for discharge lamps concerning this invention. It is an enlarged view of the cathode 2 of FIG. 1, FIG. 4 is a flowchart for explaining a manufacturing process of the cathode 2. It is a figure explaining the determination method of the consumption state of an electrode. 6 is a graph in which the average value of the degree of wear of each of the electrodes in cases A to D is plotted against the tungsten density of the cathode 2.

Explanation of symbols

1 ... glass container, 2 ... cathode, 3 ... anode, 4,5 ... trigger probe (electrode), 6 ... stem introduction _{pin 7} 1-7 4 _... external terminal, 10 ... Flash lamp.

Claims (3)

A porous sintered electrode for a discharge lamp,
After the tungsten containing material likely to emit electrons less than 20% by weight molded by metal injection molding, is manufactured integrally, including the discharge tip by Rukoto by sintering, that the density after sintering was 12 g / cc or more A porous sintered electrode characterized.   2. The perforated sintered electrode according to claim 1, wherein the tip shape is a pointed shape.   3. The perforated sintered electrode according to claim 1, wherein the electron-emitting material is barium aluminate or a mixture of scandium oxide and an alkaline earth metal carbonate.

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