JPH0527941B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] This invention relates to improvements in electrodes used in high-pressure sodium lamps having unsaturated vapor pressure characteristics, and more particularly, to improvements in electron-emitting materials coated on these electrodes. It is something. [Prior Art] Generally, in a saturated vapor pressure type high-pressure sodium lamp, sodium and mercury are enclosed in the arc tube in excess of the amount that contributes to light emission in order to compensate for the loss of sodium during the lamp operation. has been done. These excess amounts of sodium and mercury form an amalgam in the coldest part of the arc tube. Therefore, there is a problem in that the vapor pressure within the arc tube is affected by changes in the temperature of the coldest part and the amalgam composition ratio. Furthermore, such high-pressure sodium lamps of the saturated vapor pressure type have the disadvantage that the lamp voltage increases during the lamp stroke and eventually goes out. On the other hand, by limiting the amount of encapsulated sodium and mercury,
In so-called unsaturated vapor pressure type high-pressure sodium lamps, in which all of the sodium and mercury enclosed in the lamp evaporate during operation, the vapor pressure inside the arc tube remains almost unchanged even if the temperature of the coldest part changes. It is already known that the lamp voltage is stable when the lamp is lit. However, in such an unsaturated vapor pressure type high-pressure sodium lamp, the amount of sodium sealed is very small, so even a small amount of sodium disappears has a significant effect on the lamp voltage. That is, there is a problem in that the lamp voltage gradually decreases as sodium disappears. It has been known for some time that the main cause of this loss of sodium is the gases, especially oxygen, released from the electrodes when starting and lighting the lamp. By the way, high-melting point metals such as tungsten have traditionally been used as electrode constituent materials for high-pressure sodium lamps, but it is difficult to provide sufficient electron emission even at high temperatures with tungsten alone, so electron emission is usually Electron emissivity is compensated for by using metal oxides with excellent properties. Such electron emissive metal oxides usually include
Alkaline earth metal oxides such as barium and calcium, thorium oxide, and the like are used. [Problem to be solved by the invention] By the way, in the electrode using a metal oxide as described above, the electrode temperature at the tip during lamp operation is approximately
It reaches 1700℃ and gradually decreases towards the end. During lighting operation, the electron emitting material (emitter), which is mainly composed of the metal oxide mentioned above, gradually evaporates and scatters from a portion near the tip and adheres to the inner surface of the arc tube. If the amount of electron emitting material attached to the inner surface of the arc tube increases, it becomes a major cause of a decrease in luminous flux. As a countermeasure to these problems, conventionally, the tungsten coil wound around the electrode core was formed into a double coil, and an electron emitting material was densely filled between the inner coil and the electrode core. A method is known in which the surface of the coil is structured so that the electron emitting material is not exposed as much as possible to suppress the evaporation of the electron emitting material. However, although the above-mentioned alkaline earth metal oxides have excellent electron emitting properties, their vapor pressure is relatively high at high temperatures, and it is difficult to completely suppress the evaporation of the oxides filled in the coil. . Also,
Oxides containing alkaline earth metals, or composite oxides with tungsten oxide, etc., partially decompose and evaporate at around 1300°, resulting in liberated alkaline earth metals,
Releases alkaline earth metal oxides, oxygen, etc. Among these decomposed vaporized components, oxygen in particular reacts with sodium to produce stable compounds with low vapor pressures. This generation of sodium oxide is one of the main causes of sodium loss in the arc tube.
Particularly in unsaturated vapor pressure type high-pressure sodium lamps, it is essential to suppress sodium loss due to the formation of sodium oxides as much as possible. In order to suppress the loss of sodium due to the formation of sodium oxides, it is necessary not only to use the unsaturated vapor pressure type high-pressure sodium lamp mentioned above, but also to use a sodium amalgam filled with sodium amalgam to the extent that not all but 80% or more of the filled amount evaporates during lighting. This is also a necessary requirement for high-pressure sodium lamps. In other words, if the lamp is filled with sodium amalgam to the extent that 80% or more of the amount evaporates during lighting, the composition ratio of the amalgam is the same as that of an unsaturated lamp.
It exhibits unsaturated vapor pressure characteristics rather than saturated vapor pressure characteristics, and it is equivalent to unsaturated vapor pressure lamps in that the loss of a small amount of sodium has a large effect on lamp characteristics, so the amount of fill Suppressing sodium loss is also an essential requirement for high-pressure sodium lamps with unsaturated vapor pressure characteristics, which contain an amount of sodium amalgam that evaporates not all but 80% or more. be. Note that thorium oxide has a high melting point and a relatively small work function, so it is used as an electron emitting material. However, since thorium oxide is an oxide of a radioactive isotope, it must be handled in accordance with the standards for handling radioactive materials, and there are many problems in terms of workability, so it is now gradually being used less and less as an electron emitting material. It's in the direction. The present invention was made to solve the above-mentioned problems with the electron emitting material applied to the electrode of the arc tube of a conventional high-pressure sodium lamp having unsaturated vapor pressure characteristics. To provide an electrode for a high-pressure sodium lamp having an unsaturated vapor pressure type characteristic and provided with an electron-emitting material that is difficult to use, thus reducing the lamp voltage drop during lamp movement, and not making it difficult to start a discharge. The purpose is to [Means and effects for solving the problems] As a result of various experiments and studies to solve the above-mentioned problems, the present invention has found that the electron emitting material of the electrode is 80 to 95% by weight. A mixture of yttrium oxide (Y ₂ O ₃ ) and 5 to 20% barium calcium tungstate (Ba ₂ CaWO ₆ ) is used. By using the mixture with the above composition as an electron emitting material, starting the discharge is not difficult, and
It is possible to reduce the lamp voltage drop due to the loss of sodium, and it is possible to extend the life of the lamp. [Example] An example will be described below. Prior to the description of the example, a conventional example will be described for comparison with the example. To prepare a conventional electrode for comparison, a suspension of barium calcium tungstate (Ba ₂ CaWO ₆ ) suspended in nitrocellulose lacquer and butyl acetate is first prepared.
As an electrode component, as shown in FIG. 1, a double coil 2 is arranged in contact with the outer periphery of an electrode core 1,
Furthermore, an extremely common electrode component for a 360 watt high pressure sodium lamp with a single coil 3 disposed on the outside thereof is used. Note that the tip of the electrode core rod 1 is
It protrudes 1.0mm from the tip of the coil. This electrode component is immersed in the suspension to apply the electron emitting material 4, and after drying, the electron emitting material 4 on the surface of the outer coil 3 is removed. Then about 1350
The electrode was constructed by firing and fixing it in a mildly reducing atmosphere furnace at ~1600°C. Next, examples of the present invention will be described. As the electron emitting material, in addition to the barium calcium tungstate (Ba ₂ CaWO ₆ ), yttrium oxide (Y ₂ O ₃ ) was mixed in various proportions, and these were used as an electrode component as shown in FIG. The materials were coated and fixed in the same manner as in the conventional example, and various electrodes with various mixing ratios of electron emitting materials were prepared. FIG. 2 shows an arc tube for a 360 watt high pressure sodium lamp incorporating electrodes made as described above. In the figure, reference numeral 5 denotes an arc tube body made of polycrystalline alumina, and conductive heat-resistant metal tubes 7a and 7b equipped with electrodes 6a and 6b are arranged at both ends of the arc tube body 5. , 7b and the arc tube 5 are hermetically sealed by a sealing frit. The arc tube with this structure contains 0.06 mg of sodium, an amount that can completely evaporate during lamp operation.
It is filled with 5.5 mg of mercury and 150 Torr of xenon as an auxiliary gas for starting, and is in a so-called unsaturated vapor pressure state. Next, these arc tubes were housed in an outer bulb (not shown), and a ballast for a 400W high-pressure mercury lamp was used to perform a blinking operation of 30 minutes on and 15 minutes off as an accelerated test, and the initial and 3000 blink operations were performed. The subsequent start-up time and lamp voltage drop were measured. Table 1 shows the composition of the electron emitting material, the mixing molar ratio, and the measurement results. The amount of electron emitting material applied to each electrode was approximately 2 mg.

〔Effect of the invention〕

As explained above in detail based on the examples,
The present invention relates to a high-pressure sodium lamp having an unsaturated vapor pressure type characteristic in which a small amount of sodium is sealed together with xenon gas and mercury inside the arc tube.
Since the electrodes were constructed by coating an electron-emitting material consisting of barium calcium tungstate, it was possible to reduce the lamp voltage drop due to the loss of sodium without making it difficult to start the discharge.
Lamp life can be improved. In addition, yttrium oxide and barium calcium tungstate, which are used as electron emitting substances, are harmless to the human body, so they are easy to handle.
Another advantage is that the lamp manufacturing process can be made easier and more reliable.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an electrode for a high-pressure sodium lamp, and FIG. 2 is a plan view of an arc tube of the high-pressure sodium lamp. In the figure, 1 is an electrode core, 2 is an inner double coil, 3 is an outer coil, 4 is an electron emitting material, 5 is an arc tube, 6a and 6b are electrodes, and 7a and 7b are conductive heat-resistant metal tubes.

Claims (1)

[Claims] 1. A mixture of 80-95% yttrium oxide (Y ₂ O ₃ ) and 5-20% barium calcium tungstate (Ba ₂ CaWO ₆ ) by weight is used as an electron emitting material. An electrode for high-pressure sodium lamps with unsaturated vapor pressure type characteristics. 2. The high-pressure sodium lamp having unsaturated vapor pressure characteristics is characterized in that sodium amalgam is sealed in the arc tube in an amount that completely evaporates during lighting operation. Electrode for sodium lamp. 3. The above-mentioned high-pressure sodium lamp with unsaturated vapor pressure characteristics is characterized in that the arc tube is filled with sodium amalgam in an amount that does not completely evaporate during lighting operation but evaporates more than 80% of the amount filled. An electrode for a high-pressure sodium lamp according to claim 1.