|||||||||||||||| US005258.687A United States Patent (19) 11 Patent Number: 5,258,687 Duggan et al. (45. Date of Patent: Nov. 2, 1993

54 MERCURY WAPOR DISCHARGE DEVICE (56) References Cited 75 Inventors: George L. Duggan, Bedford; David A. U.S. PATENT DOCUMENTS Goodman, Amesbury; Nanu Brates, 3,170,081 2/1965 Rokosz ...... 313/631 Malden, all of Mass. 4,044,276 8/1977 Keeffe et al...... 33/346R 0. 4,210,840 7/1980 Bhalla ...... 313/328 (73) Assignee: GTE Products Corporation, Danvers, 4,783,611 11/1988 Vogels et al...... 33/628 X Mass. 5, 11,108 5/1992 Goodman et al...... 313/628 X * Notice: The portion of the term of this patent Primary Examiner-Sandra L. O'Shea subsequent to May 5, 2009 has been Assistant Examineral-Ashok Patel disclaimed. Attorney, Agent, or Firm-Robert E. Walter; William H. McNeil (21) Appl. No.: 714,795 22 Feded: Jun,un. -3,13, 1991 In57 a mercury vapor arcABS discharge CT tube having a pair of 51) Int. Cli...... H01J 1/16 electrodes, an emissive material disposed on the elec 52 U.S. C...... 313/346 R; 313/346 DC; trodes consists essentially of a single phase compound of 313/344; 313/628; 313/630,313/631; 313/639 BaxSri-Y2O4 where x is from about 0.25 to about 0.95. 58) Field of Search ...... 313/346R, 346 DC, 571, 313/628, 631, 638, 310,344, 350, 335, 630, 639 3 Claims, 1 Drawing Sheet

U.S. Patent Nov. 2, 1993 5,258,687

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5,258,687 1. 2 MERCURY WAPOR DSCHARGE DEVICE BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of a high pressure mer CROSS REFERENCE TO RELATED cury vapor arc discharge tube in accordance with this APPLICATIONS invention. FIG. 2 is an expanded sectional view of an electrode U.S application entitled Vapor Discharge Device, configuration containing the emission material. filed Dec. 14, 1990, as Ser. No. 07/627,529, now U.S. Pat. No. 5,111,108, relates to an emissive material of DESCRIPTION OF THE PREFERRED barium/strontium/yttrium oxide on an electrode. O EMBODIMENT As shown in FIG. 1, the high pressure mercury vapor FIELD OF THE INVENTION arc tube 1 is made of high silica glass, for example, The present invention relates to an emissive material quartz, includes press seals 2 at each end. An electrode for use in a mercury vapor discharge lamp. 3 at each end of the arc tube 1 is connected to a molyb 15 denum ribbon or foil 4 which is connected, in turn, to DESCRIPTION OF THE PRIOR ART external lead-in-wire 5. The arc tube 1 includes a start ing electrode 6. The ribbon 4 is utilized to obtain a glass High intensity discharge mercury vapor lamps have a to metal seal. In the preparation of the arc tube 1, typi quartz arc tube containing mercury as the light emitting cally, the ribbon 4 and electrode 6 components are member. The mercury vapor lamp arc tube uses only 20 welded together and the resulting structure is inserted mercury as the fill component except for a starting gas, into the end of the silica tube 1 which is heated to about typically argon. The resulting lamp discharge yields the 2050 C. and pinched onto the ribbon 4. After pinch well known mercury high pressure line spectrum with sealing, the arc tube is exhausted of air and filled with infrared, visible and ultraviolet radiation. Such lamps argon, and, depending on wattage, an accurate dose of typically have tungsten electrodes with an emissive 25 mercury. material disposed on each electrode. U.S. Pat. No. The lamp lumen maintenance, starting, and life are all 4,044,276 to Keeffe et al. describes an emission mix for dependent to some extent on the quality of the main high pressure mercury lamps comprising barium oxide, electrodes 3. As illustrated in FIG. 2, the electrode calcium oxide and hafnium oxide. A mixture of barium comprises a tungsten rod 7 having an inner tungsten coil 30 8 encircling a portion of rod 7 and secured thereto. carbonate, calcium carbonate, and hafnium dioxide is Outer tungsten coil 9 is threaded on coil 8. In the pre coated on the electrode. The resulting emissive oxide ferred embodiment, the coil is formed of a screw mixture is formed after firing in hydrogen at 1500 C. to wrapped base section of tungsten wire with an over decompose the carbonates. The resulting emissive oxide screw section which is backwound over the base sec deteriorates when exposed to ambient atmosphere by 35 tion. The rod 7 is disposed on the axis of the windings. trapping water vapor. As a result, unless the fired elec The emitting or emissive material 10 is disposed in the trodes are immediately processed into sealed arc tubes, voids or recesses between coils 8 and 9. Coil 8 may have their effectiveness will diminish rapidly with time. It is some open turns, as shown in FIG. 2, to accommodate believed that both barium and calcium oxides, which more emitting material 10. are known to react vigorously and exothermally with The emissive material disposed on each electrode water vapor, contributes to the instability of the emis consist essentially of a single phase reaction product and sive mixture by forming hydroxides. Additionally, ex compound having a formula Bay.Sri-Y2O4 wherein x posure of barium oxide in air to carbon dioxide may is from about 0.05 to about 0.95. More preferably x is result in the reformation of barium carbonate so as to from about 0.5 to about 0.75. Although these latter 45 compositions having a higher barium concentration are add to the instability of the mixture. Due to the instabil more reactive with moisture, they are preferred since ity of the emissive mixture, difficulties in achieving the higher barium concentration results in a more emis manufacturing uniformity and consistent lamp perfor sive electrode. The higher barium content, the greater mance may be encountered. the mass loss rate. Desirably, mass loss rate of the emit 50 ter is sufficient to maintain a supply of electroactive SUMMARY OF THE INVENTION alkaline earth metal species to the cathode emitting It is an object of the present invention, to provide an surface over the life of the lamp, but sufficiently low so emissive material that has enhanced stability in air. as to be present on the electrode for the life of the lamp. It is a further object of the invention to achieve en If the amount of the emitter is undesirably low, the lamp hanced consistency in the operation of mercury lamps 55 suffers from poor lumen maintenance due to tungsten manufactured from electrodes coated with the emissive evaporation caused by overheating of the electrodes as electrode emission declines. material of the present invention. Preferably, the molar ratio of (Ba--Sr)Y is less than In accordance with the present invention, there is about 0.5, and more preferably about 0.5 to about 0.3. provided a high pressure mercury vapor arc discharge At ratios above 0.5, alkaline earth oxide rich phases tube comprising a pair of electrodes sealed through such as BaO, SrO, or BasY4O9 may be formed. Such opposite ends thereof, a fill within said tube consisting phases are very reactive with moisture in the air and are essentially of mercury and a starting gas, and means to desirably avoided. At ratios less than about 0.5, an ex connect current to each electrode of said pair of elec cess of Y2O3 is present in the reaction mixture to assure trodes, and an emissive material disposed on said pair of 65 complete reaction of the barium and strontium com electrodes consisting essentially of a single phase com pounds to avoid the formation of the simple oxides of pound of BaSr1-Y2O4 whereinx is from about 0.05 to barium and strontium. The final reacted emissive mate about 0.95. rial desirably contains excess yttria. Typically, yttria is 5,258,687 3 4. present in amounts less than about 10 molar percent. mix is then placed in an alumina crucible. The crucible Preferably, the quantities of barium carbonate, stron is placed into a furnace and heated for 6 hours to about tium carbonate and yttrium oxide are reacted to pro 1500 C. After 23 hours of heating at 1500 C., the fur duce an emitter composition, having about 2 to about 6 nace is cooled over a 6-hour period of time and the molar percent Y2O3 in the reacted mixture of the emit 5 crucible removed. The resulting material was identified ter material. by x-ray diffraction analysis to be almost entirely the It is contemplated that the emissive material may single phase compound having the above formulation, incorporate minor amounts, preferably less than about BaSr1-Y2O4, wherein is 0.50 with a about 4% of twenty five percent, and more preferably less than yttrium oxide being present. The material was mixed about five per cent by weight of additional ingredients O with zirconia grinding media as previously set forth in which do not deleterious affect the performance of the methanol and roller milled at 60 rpm for about 6 hours. emissive material. Such additional ingredients, in addi The resulting slurry was separated from the milling tion to yttria, may also include other rare earth oxides, media with the milling media being rinsed in methanol. hafnium oxide, zirconium oxide, and other oxides such The average particle size of the reacted emissive mate as aluminum oxide, calcium oxide, and mixtures thereof. Starting powders are chemically reacted to form the rial was about 3.5 microns. The resulting slurry con finally reacted emissive material. It is contemplated that tained 575 grams of the emissive material having the starting powders may be incorporated into the elec above formula with 850 ml of methanol. About 2500 trode and reacted in situ to give the finally reacted coils were impregnated with the slurry. H10OW mer emissive material. cury lamps were subsequently manufactured from the It is contemplated that the precursor powders may be 20 coated electrodes prepared in the above manner. The reacted prior to incorporation on or into the electrode. lamps were life tested. The 100 hour and 500 hour pho Such powders may be incorporated in situ on the elec tometry results show that the lamps containing the trode and subsequently reacted. Typical starting pow electrodes as prepared above had superior lumen output ders comprise the carbonates, nitrates, hydroxides, oxa than two control groups. In addition, the critical mini lates and oxides of barium, strontium and yttrium or 25 mum starting volts to assure starting reliability at -20' other materials. In preparing the coated electrodes, the F. was measured in the test lamps after 100 hours. The precursor powders may be slurried in a suitable carrier minimum starting volts of less than 161 volts was favor such as Inethanol or water, and milled with an appropri able. The nominal lamp operation in volt for the lamps ate milling media. The resultant powder mix is dried. containing the above electrodes remained constant for Such drying will typically be at about 50' C. when a 30 100 hour and 500 hour tests. methanol slurry is used and about 80 C. for a water In another life test to evaluate the BSY2 electrode slurry. The dried mix is then preferably fired to react emissive coating in H10OW and H175W lamps, lamps the precursor materials and form a reacted mixture of were aged to 3000 and 2000 hours respectively. The barium-strontium-yttrate. The resulting compound is H10OW test results show the BSY2 containing lamps to comminuted to an appropriate particle size and mixed 35 be superior in lumen output to the controls. The lumen with a suitable carrier. The resulting slurry containing output, nominal lamp operating voltage and minimum the emissive mix is coated on the respective electrodes. starting voltage at -20' F. all meet required lamp spec ifications. The BSY2 containing H175W lamps have a Example 1 5% lower lumen maintenance than the controls. The One mole of barium carbonate, one mole of strontium 40 nominal lamp operating voltage is well within the 130 V carbonate, and 2.08 moles of yttrium oxide powders specification. were admixed, slurried in methanol, and vibration ball We claim: milled with zirconia for two hours. The resultant pow 1. A high pressure mercury vapor arc discharge tube der mix was dried at about 50 C. and then fired in air at comprising a pair of electrodes sealed through opposite 1500 C. for twenty-two hours to produce a reacted 45 ends thereof, a fill within said tube consisting essentially mixture of barium, strontium, and yttrium oxides. In of mercury and a starting gas, and means to connect particular, Ba0.5Sr0.5Y2O4 was produced. This com current to each electrode of said pair of electrodes, each pound was then vibration ball milled in methanol with of said electrodes includes a rod portion and an encir zirconia media. The material resulting from this process cling coil comprising an inner coil section and an outer was shown by X-ray diffraction analysis and scanning 50 coil section, said outer coil section being backwound electron microscopy (SEM) analysis to be almost en over said inner coil section whereby recesses are cre tirely the single phase compound having the above ated between said inner coil section and said outer coil formula with about 4% Y2O3. section, and an emissive material disposed in said reces ses, said emissive material consisting essentially of a Example 2 55 single phase compound being characterized by the ab About 83.97 grams of barium carbonate, 62.80 grams sence of additional separate phases comprising barium of strontium carbonate, and 200 grams of yttrium oxide carbonate, strontium carbonate and yttrium oxide were placed in a 1000 ml polyethylene bottle that is wherein said single phase comprises reacted BaSr1-- about one-half filled with zirconia grinding media. De Y2O4 wherein x is from about 0.05 to about 0.95. ionized water is added so as to cover the ingredients. 2. A high pressure mercury vapor arc discharge tube Next, the bottle is placed on a roller mill and milled at according to claim 1 wherein said emissive material 60 rpm for about 4 hours. After milling, the resulting disposed on each electrode consist essentially of a single slurry is poured into beaker and the milling media is phase reacted compound having a formula BaSr.-- rinsed twice with water and added to the slurry. Next, Y2O4 wherein x is form about 0.25 to about 0.75. the resulting mixture is placed in a drying oven at 85 C. 65 3. A high pressure mercury vapor arc discharge tube and evaporated to dryness. Final drying is performed at according to claim 2 wherein the molar ratio of 150 C. for about 4 hours. The resulting precursor mix (Ba--Sr)/Y is from about 0.5 to about 0.3. is scraped out and ground in a mortar and pestle. The a