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
  • H01J61/067—Main electrodes for low-pressure discharge lamps
  • H01J61/0675—Main electrodes for low-pressure discharge lamps characterised by the material of the electrode
  • H01J61/0677—Main electrodes for low-pressure discharge lamps characterised by the material of the electrode characterised by the electron emissive material
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2922—Nonlinear [e.g., crimped, coiled, etc.]
  • Y10T428/2925—Helical or coiled
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2933—Coated or with bond, impregnation or core
  • Y10T428/294—Coated or with bond, impregnation or core including metal or compound thereof [excluding glass, ceramic and asbestos]
  • Y10T428/2958—Metal or metal compound in coating

Definitions

• This invention relates to cathodes for electric discharge devices and more particularly to cathodes provided with an improved electron emissive material, to
• the invention is especially adapted for use in photographic flashtubes operating with cold cathodes.
• Photographic flashtubes give a high intensity flash of very short duration and may be fired intermittently by means of a portable power pack as pictures are taken. They comprise a small diameter glass tube, filled with a rare gas such as xenon, the tube being provided at each end respectively with a cathode and an anode between which the electric arc discharge in the gas takes places. When used with portable photographic equipment, it is desirable to provide a flashtube operating at low voltages which increases the reliability of the unit particularly when batteries in the power pack become weak.
• the instant invention has among its ob-' jects to provide an emissive material for cathodes of electric discharge devices such as flashtubes which makes possible operation of the tube at low voltage and which also provides for efiective electron emission under cold cathode operating conditions.
• Another object is to provide a highly effective emissive material for discharge cathodes which utilizes barium aluminate having an excess of aluminum oxide together with some elementary barium bound into a com posite crystal matrix.
• barium oxide itself (BaO) is an eifective emissive material for cathodes of electric discharge devices but this material has the disadvantage that it is subject to sputtering from the cathode to the walls of the discharge tube.
• such emissive material is deposited on the Walls of the glass tube adjacent the cathodes with the resultant blackening of the tube thereby reducing the light output, and therefore the efiiciency of the flashtube.
• Barium oxide does have the advantage of a relatively high melting point which is in the neighborhood of l'900 C. so that this emissive material can withstand the high temperatures which occur at the spots on the cathodes where electron emission takes place and between which the electric discharge or flash takes place.
• the compound BaO-Al O has the very desirable high melting point, it is very low in electron emissivity and is unsuited for use as an activating material for cathodes of electric discharge devices such as flashtubes because of the high starting voltage required to flash the tube. If barium oxide (BaO) is added to increase the emissivity it will be found, as previously indicated, that the melting point of the compound drops rapidly. If the amount of barium oxide in the barium aluminate is further reduced to less than one mole ,a further reduction in emissivity takes place but the melting point remains ,at a satisfactory level about 1800" G.
• the emissivity of the barium aluminate may be greatly increased without an appreciable reduction in the melting point by converting part of the barium oxide in the barium aluminate to elementary barium. It is believed supporting electron emissive material; this increases the life of the flashtube and reduces end blackening adjaa highly eflfective emissive material.
• the barium is dispersed throughout the barium aluminate crystal, the result being that the crystal provides
• the emissivity of the aluminate system, including elementary barium, is in excess of the emissivity of barium oxide alone.
• the increasedemissivity is due to the increased amount of elementary barium which may be bound in the crystal matrix of BaO-Al O as distinguished from the amount of barium which can be held by barium oxide (BaO) crystals.
• the emissive material thus described for activating cathodes may be prepared by mixing commercially available compounds of barium oxide-aluminum oxide (BaO-Al O with powdered aluminum and then activating the material by heating to convert part of the barium oxide to elementary barium. In manufacture of cathodes for electric discharge devices a mixture may be deposited on the .metal cathode and activated by heating in position.
• barium oxide-aluminum oxide BaO-Al O
• a mixture may be deposited on the .metal cathode and activated by heating in position.
• the activated emisisve material of the invention is characterized by the formula (xBaO.Al O ).yBa wherein there is an excess of aluminum oxide in the barium oxidealuminum oxide crystal to provide a compound having a high melting point. -x therefore must be equal to or less than 1.
• the lower limit of x is determined by the minimum quantity of barium oxide in the emissive material which will give satisfactory emission characteristics. x may range from 1 mole to as low as 0.1 mole; however, optimum results are obtained when x is in the range of 1 mole to 0.34 mole.
• the limits y of elementary barium are believed to be determined by the required number of emitting centers bonded in the barium aluminate crystal to give good emissivity.
• the upper limit of the elementary barium does not appear to be critical as some excess of elementary barium merely acts as a getter. An excess of elementary barium may be desirable for this reason; a large excess of barium,
• the electricdischa rge device or fiashtube is provided with conventional cold cathode constructions such as nickel grids, iron cups or tungsten coils.
• the emissive material is applied to the cathodes before activation. This may be accomplished by dipping'the cathode into a dry powder mixture, by dipping it into a slurry of the mixture with butyl acetate, by insertingparticles or pellets or the pressed material into or onto the cathode, orin'any other conventional method. Because of the good adhesion of the dry powder to tungsten coils, the dry method is probably easiest and works well fonportable flashtubes having tungsten c'oil "cathodes.
• the wet method is preferred but care should be taken to dry the cathodes thoroughly before the-heating operation hereinafter described or the emissive material may discolor and fiake off.
• An important advantage to the emission material according to the present invention is that a coating thickness hardly visible to the naked eye is sufficient.
• the cathode After coating, the cathode is heated for activation of the emissive material.
• the cathode may be heated to a temperature between 600 C. and 1200" C.;'however, about 600 C. appears to be a sufliciently high temperature. Activation at this comparatively low temperature makes it possible to construct the cathodes of low meltingpoint metals such as iron or nickel. -An' important advantage of this cathode is that no gases are evolved .during a'ctivation. Any'conventional method of heating may be,
• Cathodes provided with an electron emissive-material h ave'been constructed as follows:
• xample 1.-A coiled tungsten wire cathode having an emissive material with approximately the composition 1.43 (0.34BaO.Al O ')l.27Ba has been constructed by first grinding 94.2.grams of commercially available barium aluminate having the formula l.76BaO.Al O into a powder and mixing it with 5.8grams of aluminum powder (average particle size 0003 mm.). This mixture was thenpressed into pellets with'a pressure of 10 kilopounds per square inch and the pellets'recrushed in a mortar. Thclg'rinding, weighing and pressing was done inan airconditioned, low-humidity room, andthe material stored in a desiccator.
• the barium aluminate-aluminum mixture wasthenapplied to the cathode tungsten coils by dipping thecoils into the dry powder.
• the emissive material was thenactivated by heating the coated-coil to about 660 C. by means of the fires which seal the cathode to "the glass tube of the fiashtube.
• This mixture was prepared as above and the dry mixture applied to the cathode. It was then activated by heating to atemperature of about 660 .C.
• An emissive material of barium aluminate may be synthesizedand partially reduced-by aluminum .during the activation of thecathode .itselfin .a single step.
• Compounds consisting ofmixtures of barium. carbonate (BaCOg), .aluminum oxide (A1 0 and aluminum (Al) powder have been successfully reacted to produce upon being heated activated cathodes of the same compositions as the ones'described above.
• Photographic flashtubes provided with cathodes having an emissive material have been constructed, tested, and compared with flashtubes heretofore manufactured but in which the cathodes comprised a nickel screen on which a barium-aluminum alloy had been vaporized.
• One standard type of photographic flashtube now commercially available and provided with such cathodes has a rated starting voltage of 305 volts with a standard deviation in the starting voltage of 20.3 volts.
• An allotment of 100 photographic flashtubes in which the cathodes were provided with emissive material comprising the barium-aluminate-barium compound according to the invention showed an average starting voltage of 286 volts with a standard deviation of 18.2 volts.
• Another type of standard photographic flashtube currently available has a starting voltage of 182 volts with a standard deviation in starting voltage of 14.8 volts.
• Another allotment of 30 flashtubes was constructed in which the nickel screen cathode was replaced with tungsten coil cathodes having a barium aluminate emissive material of the composition according to the invention.
• the average starting voltage of this allotment of flashtubes was 168 volts with a standard deviation of volts.
• the starting voltage of the flashtube is reduced thereby increasing its reliability and effectiveness. Operation of the improved flashtubes up to 7000 flashes showed very little blackening of the flashtube whereas 6 the described standard lamps used as a basis of comparison showed that their light output was reduced b about 50% at 5000 flashes.
• Still another type of flashtube was designed for repetitive. application and made with an emission material in accordance with this invention.
• the average life of these tubes before they began missing was 765,000 flashes; whereas, similar lamps with standard'cathodes do not exceed 250,000 flashes and are accompanied by early blackening.
• the barium aluminate cathodes showed very little blackening until near the end of their life.
• test results show that photographic flashtubes having cathodes provided with an activated emissive material composed of Al O and Ba bound in a BaAl O crystal matrix in the appropriate proportion range show very good maintenance in operation with little bulb blackening making the flashtubes particularly adaptable for use with portable photographic equipment.
• a cathode comprising a conducting core and an emissive material applied thereto corresponding to the formula (xBaO-Al O )-yBa wherein x is between 0.1 and 1 and y is between 0.5x and 2.6x.
• a cathode comprising a conducting core and an emissive material applied thereto having essentially the formula 0.33BaO-Al O -yBa wherein y is between 0.5 and 0.89.
• An activated emissive material for a discharge cathode corresponding to the formula (xBaO-Al O -yBa wherein x is between 0.1 and 1 and y is between 0.5x and 2.6x.
• An activated emissive material for a discharge cathode represented by the formula 0.33BaO-Al 0 -yBa wherein y is between 0.5 and 0.89.

Landscapes

• Solid Thermionic Cathode (AREA)

Priority Applications (4)

Applications Claiming Priority (1)

Publications (1)

Family

ID=24629268

Family Applications (1)

Country Status (3)

Cited By (2)

Citations (6)

• 0
  • NL NL227293D patent/NL227293A/xx unknown
  • NL NL112306D patent/NL112306C/xx active
• 1957
  • 1957-04-29 US US655534A patent/US2871196A/en not_active Expired - Lifetime
• 1958
  • 1958-04-02 GB GB10567/58A patent/GB824902A/en not_active Expired

Patent Citations (6)

Also Published As

Similar Documents