Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J61/00—Gas-discharge or vapour-discharge lamps
  • H01J61/02—Details
  • H01J61/04—Electrodes; Screens; Shields
  • H01J61/06—Main electrodes
  • H01J61/073—Main electrodes for high-pressure discharge lamps
  • H01J61/0735—Main electrodes for high-pressure discharge lamps characterised by the material of the electrode
  • H01J61/0737—Main electrodes for high-pressure discharge lamps characterised by the material of the electrode characterised by the electron emissive material

Definitions

• the present invention is directed to a duplex composite member suitable for use in lamps, as either an electrode and/or a filament element.
• This duplex composite member has two component parts; (1) a core composed of one type of tungsten-based material, and (2) a shell composed of a different tungsten-based material.
• the duplex composite member of the present invention may have desirable surface properties such as resistance to chemical attack and/or mechanical shock and vibration, making it especially well suited for applications in incandescent lamps, metal halide discharge lamps, and/or halogen incandescent lamps.
• Electrode and/or filament failure due to mechanical shock and/or chemical attack is a recognized problem in the lighting industry.
• U.S. Patent No. 4,413,205 describes in detail how the tungsten conductors to the coiled filament of a halogen incandescent lamp are locally pitted and chemically attacked by bromine in such a manner that they break and the lamp fails.
• the 4,413,205 patent suggests one method for reducing this chemical attack problem, namely, modifying the conductor material to a tungsten - ­rhenium (Re) alloy containing at least 0.1% Re.
• the present invention is directed to an alternate solution to the problems of chemical attack and/or mechanical shock of electrodes and/or filaments, which does not suffer the disadvantages discussed above.
• the present invention provides a tungsten-based duplex composite member, e.g., wire or rod, which combines the emissive, nonsag, or other desirable qualities of an inner tungsten-based core material with a different combination of properties, for example, resistance to corrosive attack, by the presence of a different tungsten-based material as an outer sheath or shell surrounding the core material.
• a tungsten-based duplex composite member e.g., wire or rod, which combines the emissive, nonsag, or other desirable qualities of an inner tungsten-based core material with a different combination of properties, for example, resistance to corrosive attack, by the presence of a different tungsten-based material as an outer sheath or shell surrounding the core material.
• an electrode is formed from a duplex composite member, composed of a thoriated tungsten core (W - Th02) and a thin tungsten-rhenium (Re) shell.
• W - Th02 thoriated tungsten core
• Re thin tungsten-rhenium
• any rhenium emission is limited to an insignificant amount (i.e., that vaporized from the thin shell, especially at the tip of the electrode).
• duplex composite members are provided by thoriated tungsten discharge electrodes in which it is desirable to have two different concentrations of thoria (ThO2) in the element, a first concentration in the core of the duplex composite member and a second concentration in the shell or surface of the member.
• the thoria concentration in the shell portion of the duplex composite may be either lower or high than the thoria concentration in the core portion.
• duplex composite member of the present invention One desirable objective which can be facilitated by the use of the duplex composite member of the present invention is the ability to draw thoriated core tungsten to much finer sizes (i.e., smaller diameters) than heretofore feasible.
• the limit of wire sizes for thoriated tungsten was no lower than about 0.020 inch in diameter.
• drawn wire of 0.017 inches in diameter has readily been prepared. Unlike the 0.020 inch diameter wire previously prepared, this 0.017 inch diameter wire is especially well suited for use in low wattage metal halide lamps, i.e. 40 to 100 watts.
• the present invention provides a tungsten-based duplex composite member, e.g., wire or rod, which combines the emissive, nonsag, or other desirable qualities of an inner tungsten-based core material, with a different combination of properties, for example, resistance to attack, by the presence of a different tungsten-based material as an outer sheath or shell surrounding the core material.
• a tungsten-based duplex composite member e.g., wire or rod, which combines the emissive, nonsag, or other desirable qualities of an inner tungsten-based core material, with a different combination of properties, for example, resistance to attack, by the presence of a different tungsten-based material as an outer sheath or shell surrounding the core material.
• tungsten-based material is defined as tungsten-containing compositions suitable for use as filament and/or electrode members in lamps, especially incandescent lamps, metal halide discharge lamps, and halogen incandescent lamps. Typically tungsten makes up at least about 95 percent (by weight), or more, of such compositions.
• Core materials may include thoriated tungstens, for example, tungsten compositions containing thoria in the range of from about 0.5 to about 5.0 percent (by weight).
• tungsten-based materials which may constitute the core include nondoped, i.e., commercially pure (CP) tungsten, potassium (K) doped nonsag tungsten (normally used in incandescent filaments), and tungsten alloys. Such materials are known to the skilled artisan in the lighting field.
• core materials include tungsten modified with emissive materials such as CeO2, La2O3, Sc2O3, HfO2, ZrO2, and the like, in concentrations ranging up to about 5 percent (by weight). Combinations of these emitters with and without thoria may also be employed as a tungsten-based core material herein.
• tungsten-based core material is provided by Japanese Patent No. 58-129741 which describes the use of a tungsten electrode containing 20 ppm aluminum (Al). This Al level substantially exceeds currently specified levels of this element in wire).
• any of the above described core materials may be employed, with the proviso that the core material and the shell material of any given duplex composite member are not the same.
• attack and corrosion-resistant tungsten-rhenium alloys may also be used as shell materials.
• Such (Re)alloys, containing up to about 5% Re (by weight) will also promote mechanical shock and vibration resistance, making the duplex composite member especially well suited for use as incandescent filaments for applications involving such shock and vibration, while minimizing the amount of expensive Re which must be used and enhancing the luminous efficacy by the use of a K-doped, nonsag core.
• Such a combination with a tungsten-rhenium (W-Re) shell around a potassium (K)-doped, nonsag core enables the composite to be used as the filament of a halogen incandescent amp, in which separate internal conductors are not required.
• duplex composites are prepared by isostatically cold pressing the preblended and preplaced powders together into a billet with the core preplaced concentrically within the shell.
• the billet is then densified by sintering at a high temperature and reduced to wire of the desired diameters by the usual tungsten processing methods of rolling, swaging, and drawing.
• Duplex composite electrodes with a 2% thoria core inside a 1% thoria shell were prepared for testing in both 100 watt and 400 watt metal halide lamps (Sylvania Metalarc lamps).
• the 2% thoria core When viewed as a polished cross-section, the 2% thoria core is clearly revealed in contrast to the 1% thoria shell, which has a much coarser grain structure, being attributed to the larger grain size following the previous recrystallization-anneal.
• the mold used in this example consisted of three main sections, a cylindrically shaped outer PVC mold support tube (2.25 in. I.D. ⁇ 20 in.); a cylindrically shaped outer mold member (2 in. I.D. ⁇ 24 in.) and a cylindrically shaped stainless steel inner mold/fill tube (1 in. ⁇ 36 in.).
• a portion of the upper section of the stainless steel inner mold/fill tube was flared out to a diameter of 2 in. to act as a funnel for the introduction of powders.
• a segment of hard rubber At the bottom of the outer PVC mold support tube was placed a segment of hard rubber, which acted as a shock absorber.
• This duplex composite started by adding 3,000 grams of W-2% ThO2 powder to the central fill tube of the mold described above. At the same time, 1,000 grams of W-1% ThO2 powder was placed in the space between the mold and the central fill tube.
• the entire assembly was gently tapped during the filling operation until the prescribed amounts of both powders were added to the mold. At the end of the filling operation the levels of powder in the core and the outer shell were approximately the same.
• One critical aspect of filling is that the powders are only loosely packed into the mold since tight packing prevents the removal of the central filling tube.
• the mold After filling and the extraction of the fill tube, the mold was sealed, then cold isostatically pressed at a pressure of approximately 45,000 lbs per square inch.
• the pressed powder compact was then solid state sintered for about 12 hours at about 2,100°C in a hydrogen atmosphere producing a composite ingot weighing about 13 kg with a density of 17.6 g/cc, i.e., about 93% of the theoretical density.
• the resulting ingot was about 1.5 inches in diameter by about 19 inches long.
• the W-1% ThO2 shell comprised about 70% of the ingot volume with the W-2% ThO2 making up the remainder, producing an ingot with an average ThO2 content of 1.34% by analysis.
• Reduction of the ingot began first by rolling on a two-high rolling mill from 1.5 to 1.0 inch in diameter in multiple-passes at a temperature above 1300°C. After recrystallization, the ingot was rolled twice at a temperature above 1400°C on a multiple stand rolling mill manufactured by Frederick Kocks Co., to a diameter of about 0.3 inch with an intermediate recrystallization.
• the ingot was further reduced to about 0.1 inch diameter by multiple-pass swaging with three more recrystallization anneals. Because the diffusivity of ThO2 in tungsten is very low for all of the processing temperatures employed herein, the interface between the W-1% ThO2 outer shell and the W-2% ThO2 core remains distinct, maintaining the duplex composite structure. Below 0.1 inch diameter the ingot was drawn into wire using conventional wiredrawing practices for W-ThO2 wire.
• the duplex composite wire made thereby was drawn to 0.039 inch diameter.
• Cathode rods for 400 watt metal halide lamps were prepared therefrom by centerless grinding to 0.0365 inch diameter and sectioning the ground rods into 1/2 inch lengths. These members were used to prepare seventeen 400 watt Metalarc-type lamps (having an arc tube fill comprising Na, Sc, I, and Hg) each of which lighted and operated normally in accordance with their design ratings.
• a duplex composite member is also prepared, using essentially the same procedures set forth in Example I, but with a non-thoriated core of tungsten encased in a shell of 2% thoria. 100 Watt Metalarc type amps made therefrom are found to start much faster than the standard Metalarc amps having a 1% thoria electrode.
• the lamps will also demonstrate improved lumen maintenance, especially when compared to prior art lamps with the same rapid starting characteristics, but wherein 2% thoriated tungsten makes up the entire electrode.

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• Powder Metallurgy (AREA)
• Discharge Lamp (AREA)

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Citations (9)

• 1987
  • 1987-11-24 CA CA000552607A patent/CA1305512C/en not_active Expired - Lifetime
  • 1987-12-21 JP JP32162587A patent/JPS63168963A/ja active Pending
  • 1987-12-22 DE DE19873751379 patent/DE3751379T2/de not_active Expired - Fee Related
  • 1987-12-22 EP EP87119051A patent/EP0272687B1/de not_active Expired - Lifetime

Patent Citations (9)

Non-Patent Citations (5)

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