US3519864A - High pressure electric discharge device with barium peroxide getter and getter mounting structure - Google Patents

Description

'w. c. GUNGLE E AL HIGH PRESSURE ELECTRIC DISCHARGE DEVICE WITH BARIUM PEROXIDE GETTER AND GETTER MOUNTING STRUCTURE Filed Dec. 29, 1966 United States Patent US. Cl. 313-25 5 Claims ABSTRACT OF THE DISCLOSURE Barium peroxide is disposed within a high pressure electric discharge device to getter hydrogen which is entrapped therein. To hold the barium peroxide, the material is placed between a pair of foraminous plates which are opaque to ultraviolet light. The getter is disposed in the device at a location where it will be subjected to ambient temperatures between about 150 and 427 C.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to high pressure electric discharge devices and particularly to those which utilize fills of mercury or mercury and halogens. Such devices generally include a quartz arc tube which contains the fill and is supported upon a wire frame which is disposed within an outer bulbous envelope.

Description of the prior art High pressure electric discharge devices containing mercury and also those containing mercury and halogens are known to the art. The art has recognized that hydrogen, which can be a contaminant in these devices, is detrimental to the operation. When trapped within the bulbous envelope, the hydrogen diffuses through the quartz wall of the arc tube and adversely affects starting voltages. The hydrogen migrates into the arc tube and forms in the case of iodine fills, hydrogen iodide, which is a volatile iodine containing species and exists as a gas at temperatures even as low as F. At low ambient temperatures, the elfect of hydrogen contamination is especially noticeable because the presence of the corresponding iodide produces high starting voltages. Moreover, the presence of hydrogen iodide in the arc tube results in a high value of voltage required to reignite the lamp each half cycle of alternating current during the warm-up phase of the lamp operation. This voltage, referred to hereafter as reignition voltage, is an important parameter in determining whether a lamp can operate reliably on a given ballast circuit. The lower it is, the more reliable will be operation, or conversely the more economical will be the ballast design to reach a desired level of reliability.

We have discovered that one of the major sources of hydrogen in such devices is the bulbous envelope. Ultraviolet light emitted from the arc tube releases hydrogen from hydroxyl radicals which are entrapped in the glass jacket.

Getters, that is materials which entrap extraneous gases, have previously been utilized in such devices. Gettering, as usually practiced in the art, involves flashing or vola tilizing barium metal to react with gases, thereby removing them from the system. However, such procedures not only remove the hydrogen, but also getter nitrogen which is intentionally added. Since a gas should be present within the envelope, replacement of the nitrogen with argon would be required since this gas is not gettered. But because the use of argon reduces the potential where 3,519,864 Patented July 7, 1970 arcing between elements of the lamp can occur, it is not as satisfactory as nitrogen. Thus, the use of conventional barium getters has serious disadvantages. The same is true of the so-called flashless getters, such as zirconium, tantalum, cerium or alloys containing these metals, such as are known to the art. All of these react rapidly with nitrogen as well as hydrogen and would require replacement of the nitrogen fill gas of the outer jacket by argon.

SUMMARY OF THE INVENTION We have discovered that barium peroxide can be used as a getter for hydrogen and can be disposed adjacent to the arc tube for such purposes if certain precautions are taken. The gettering reaction, BaO +H Ba(OH) proceeds at reasonably rapid rates at temperatures above about C. Above this temperature, the hydrogen will then be removed from the outer jacket about as fast as it is generated and diffused. Barium peroxide, on the other hand, does not react to a significant degree with nitrogen at these temperatures.

However, if the ambient temperatures are too high, barium peroxide will decompose to yield barium oxide and oxygen, while barium hydroxide will decompose to yield barium oxide and water. But we have discovered that if the barium peroxide is disposed in the device at a location which is consistent with the temperature limitations set forth, these problems of competing reactions will not occur. We have found that if the barium peroxide is located in a zone in the device where the temperature is between about 150 and 427 C., that the barium peroxide will effectively getter the hydrogen and not produce the deleterious by-products, and may be used for this purpose in the presence of the conventional outer jacket filling pressure of nitrogen, without significant reaction between barium peroxide and nitrogen.

While these temperature ranges are important, we have also discovered that the barium peroxide should not be irradiated with ultraviolet light from the arc tube, since such irradiation decomposes the barium peroxide very rapidly to barium oxide and oxygen. The oxygen which is generated, severely reacts with the wire frame and can also rupture molyzdenum foil sections which are disposed in the press seals of the arc tube.

Barium peroxide is normally obtained as a very fine powder and the successful use of this material depends upon designing a container for it. We have discovered that this container should be opaque to ultraviolet light although permeable to the gas in the jacket, while still preventing the powder particles from falling into the outer jacket of the device. The container may be, for example, a pair of foraminous plates, sealed at the periphery and containing the barium peroxide. The foramina may be apertures punctured in the plates or porous plates may be utilized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of a high pressure electric discharge device utilizing the gettering device of our invention.

FIG. 2 is an exploded view of a gettering device shown in FIG. 1 and adapted to be mounted within the high pressure electric discharge device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 of the drawings, the device includes a generally tubular outer bulbous envelope 1 having a bulbous central portion and a conventional base 14 attached to the bottom thereof. Extending inwardly from the base and inside of the envelope 1 is a mount 15 having a pair of stiff lead-in wires 12 and 16 in electrical conducting relation with the base 14. Disposed upon one of the stiff lead-in wires 12 is a lower U-shaped support 8 welded thereto. The U-shaped support 8 comprises a pair of vertical wires 23 and 24 rising from a horizontal base wire 25. The upper ends of the lower U-shaped support 8 are welded together with a lower strap 7 which in turn supports an arc tube 2. Preferably, the lower strap includes two sections abutting against either side of the arc tube 2 thereby holding it firmly in place and touching only the press seal of the arc tube and not the body. Generally, both sides of the lower strap 7 can be of identical construction. A pair of bumpers 26 are welded to the lower U-shaped support 8 and abut against the tubular portion of walls of the outer-bulbous envelope 1, thereby stabilizing the structure within the lamp. Preferably, these bumpers are made of a resilient material so that if the lamp is jarred, they will absorb much of the shock.

Since the lower U-shaped support 8 is electrically connected to the stiff lead-in wire 12, the support 8 forms part of the circuit in the device. Current passes from the base 14 into the lower U-shaped support 8 and thence to lead-in wire 21 which in turn is connected to a cathode 4 in the arc tube. It is sometimes desirable to place an insulating shield about the lead-in wire 21 to prevent arcing within the lamp and between the various elements. Current passes from the lead-in wire 21 to the cathode 4 through an intermediary molybdenum foil section 6.

The other side of the circuit is formed through the stiff lead-in wire 16 which is preferably bent out of place so that parts on one side of the line are insulated from those on the other side. A resistor 13 is attached to the stiff lead-in wire associated therewith and thence to a connector 27 which in turn leads through a molybdenum foil section 6 to a starting probe 5. A bimetal 22 is disposed between lead-in 21 and the lead-in wire 29 which is attached to the starting probe 5. The bimetal 22 is biased open when the device is turned off, but upon starting it biases closed against the lead-in wires to the probe 5, thereby establishing the same current potential at the probe and the cathode 4. Such closing prevents electrolysis between the probe and cathode.

At the other end of the arc tube 2, an upper support is mounted within the tubular portion of bulbous envelope 1. The support frame 10 includes a horizontal section 18 having vertical supports 17 and 19 depending downwardly therefrom and attached at the free ends to an upper strap 11 which surrounds the press seal of arc tube 2 and rigidly holds it in place. Preferably, the construction and disposition of upper strap 11 is similar to lower strap 7. A pair of upper bumpers 9 are mounted upon the vertical sections 17 and 19 of the upper support 10 and resiliently abut against the sides of the tubular portion of the bulbous envelope 1. Such disposition prevents breakage of the lamp if the arc tube is shaken or dropped.

A lead-in wire 28 extends to the outside of the arc tube 2 and is attached at its inner end to a molybdenum foil section 6 and thence to a cathode 3. An electrical connection is made between stiff lead-in wire 16 and leadin wire 28 through a thin conducting lead 20 which may be of any suitable conducting material. Preferably, the conducting lead 20 is as distantly removed from the arc tube 2 as possible, generally by bending it around the perimeter of the outer bulbous envelope 1.

Disposed in an area where the ambient temperature is between about 150 and 427 C. is a gettering device 34 which removes hydrogen from the space encompassed within the bulbous envelope 1. The gettering device 34 may be attached to the upper support 10 and preferably is located where it will not be in the direct path of ultraviolet light generated by the arc tube 2.

Referring to FIG. 2, the form of gettering device shown therein includes a pressed wafer 40 of barium peroxide pellets. Each pellet is formed by placing 0.2 gm. quantities of barium peroxide in a press and increasing the pressure to about 6000 p.s.i. The green compact is then fired in oxygen at atmospheric pressure at a temperature of 4 about 300 C. for 15 minutes to sinter it together. A predetermined number of pellets can then be placed in the gettering device.

The gettering device 34 shown includes a pair of outer foraminous plates 36 which are joined together at the edges by welding or crimping. Disposed inside the outer foraminous plates are a pair of inner foraminous plates 41. The foramina 38 are randomly disposed on the plates 36 and 41 and are slightly smaller than the outside diameter of the barium peroxide particles. Preferably they are sulficiently few in number that loose particles movable within the device canont find a hole and fall out in appreciable numbers. When the plates 36 and 41 are abutted together, the foramina 38 are not in alignment and ultraviolet light cannot penetrate appreciably. Aperture disc 42 mounted inside of plates 41 supports the barium peroxide thereagainst. As an alternative, porous or foraminous nickel or steel plates also have applicability. A plate may be joined to the edge of a barium oxide containing vessel or two foraminous plates may be joined together with the barium peroxide sandwiched therebetween. The hydrogen in the envelope 1 can then freely move through the foramina 38 and react with the barium peroxide.

In a 1000 watt lamp, we have determined that no more than 3 gms. of barium peroxide need be used while in 400 and 175 watt lamps, quantities of 1 gm. and 0.4 gm., respectively, are the maximum necessary.

When using the gettering device, we have found that hydrogen in the outer jacket is substantially eliminated. Reignition voltages of 1000 watt lamps are reduced to 50 v. on lamps which have been aged for 1000 hours. The reignition voltage of the control lamp was v. After 1000 hours of aging, in watt lamps, reignition voltages are reduced from 130 v. (control lamp) to 30 v. (test lamp). Low temperature (-20 C.) starting voltage is reduced in 175 watt lamps from 225 v. (control lamp) to v. after 1000 hours. Moreover, the performance after 1000 hours is substantially better than the zero hour or initial performance, thereby indicating that the getter has even removed hydrogen which was originally present inside of the arc tube 2; this hydrogen has appreciably diffused outward through the quartz wall of the arc tube into the outer jacket where the getter could react with it.

It is apparent that modifications and changes can be made within the spirit and scope of the instant invention, but it is our intention only to be limited by the scope of the following claims.

As our invention, we claim:

1. A high pressure electric discharge device comprising: a bulbous glass envelope; a quartz glass are tube disposed within said bulbous envelope; means to form an electric discharge within said are tube; said electric discharge emitting both visible and ultraviolet light; hydrogen getter means disposed within said bulbous envelope, said means being substantially opaque to ultraviolet light and including at least one foraminous plate retaining a charge of barium peroxide which will react with hydrogen continually released from the glass during operation of the arc tube due to the action of said ultraviolet light, as well as with hydrogen present from all other sources.

2. The device according to claim 1 wherein the getter means is disposed in a location in said device wherein it is subjected to temperatures between about 150 to 427 C.

3. The device according to claim 1 wherein the foraminous getter means is opaque to the transmission of ultraviolet light.

4. The device according to claim 3 wherein the getter means comprises a pair of foraminous plates sealed to each other at the edges and holding a predetermined quantity of barium peroxide.

5. The device according to claim 4 wherein said getter means includes an outer pair of formaminous plates having raised central portions; an inner pair of foraminous plates having raised central portions, said latter central portions being smaller in size than the central portions of the outer pair of foraminous plates, the central portions of each of the inner foraminous plates adapted to fit inside of the central portions of each of the outer foraminous plates, said inner foraminous plates being arranged in a back-to-back relationship with each other, so as to form a cavity for said barium peroxide,

' the foramina on said inner and said outer plates being randomly disposed relative to each other so as to render the getter means substantially opaque to the transmission of ultraviolet light but to provide a passage for the flow of gas.

References Cited UNITED STATES PATENTS 335,158 2/1886 Thomson.

Glans 2060.4

Lederer 313-174 Gaidies et a1. 313-25 De Graafl' 313-174 Slack et a1. 313-174 X Kenty et al. 313-25 Schmidt 313-184 JAMES W. LAWRENCE, Primary Examiner 10 P. C. DEMEO, Assistant Examiner US. Cl. X.R.

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