Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J7/00—Details not provided for in the preceding groups and common to two or more basic types of discharge tubes or lamps
  • H01J7/14—Means for obtaining or maintaining the desired pressure within the vessel
  • H01J7/18—Means for absorbing or adsorbing gas, e.g. by gettering
  • H01J7/183—Composition or manufacture of getters
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
  • H01J9/38—Exhausting, degassing, filling, or cleaning vessels
  • H01J9/395—Filling vessels

Definitions

• the tablet comprises a mixture of a powdered mercury compound and a stoichiometric excess of a reducing agent.
• the reducing agent is a non-vaporative getter metal such as a zirconium-aluminum alloy.
• the reducing agent has fractions of different particle sizes.
• the present invention relates to a process for filling discharge tubes, or discharge'ampoules with mercury and for removing residual obnoxious gases from said tubes or ampoules.
• the minimum amounts of mercury to be introduced within the ampoule may vary from a few milligrams to 'a few decigrams.
• mercury compounds used to this purpose are, for example, mercury sulphide, oxide, and tungstate.
• the powder of the mercury compound to be decomposed is usually mixed with a powder reducing chemical, such as iron, nickel, zirconium, magnesium and the like, intended to facilitate the reduction of the mercury compound and to absorb the noxious gases "as they are evolved.
• reducing agents such as iron and nickel does not ensure a sufiiciently quick absorption of the gases which are evolved upon decomposition of mercury compounds, so that the advantages of these materials are limited ones.
• More active reducing materials such as zirconium, lead to explosive reaction and it has been suggested, in order that a delayed reaction may be achieved, that a second reducing agent be added, of a less active type.
• Conventional mixtures of powdered reducing agents are zirconium-iron, zirconium-nickel and others. It has been practically ascertained; however, that the gases which are evolve-d during the reaction in which mercury is set tree are not completely removed.
• the gettering activity of the residues formed, for example, by HgO, Fe, and Zr
• the gettering activity of the residues has proven to be wholly negligible aft-er evaporation of mercury, mainly due to the presence of the less active reducing agent (e.g. iron) which is alloyed to the very active reducing agent (e.g. zirconium).
• the process according to the present invention for filling discharge containers with mercury is also of the kind which employs tablets formed by a powdered mercury compound and a powdered reducing agents. Said tablets are placed upon a suitable receptacle in the con tainer .and after suitably degassing the ampoule the container can be heated so as to prime the reaction leading to mercury evaporation.
• An object of the present invention is to improve said conventional methods by permitting a complete removal from within the ampoule of the gases evolved during the reaction leading to mercury release, and by giving merc-ury yields close to the theoretical values.
• Another fundamental object of the present invention is to provide tablets which not only are capable of setting mercury free as they are heated to the proper reaction temperature but also of being active thereafter as non-evaporable getters so as to absorb the noxious gases during the' life-time of the lamp or the like. That is, the mercury containing tablets should also contain a reducing agent such as to promptly absorb, during the reaction with the mercury compound, all the reaction products and all the foreign gases which are present in the powdered mercury compound without expending all their physico-chemica-l properties thus being capable of exhibiting, thereafter, satisfactory getter features towards the noxious gases during the whole lifetime of the discharge tube.
• the coarse fraction acts as a thermal retarder, in that each granule exposes a tiny surface to the exothermic reaction which sets mercury free, thus providing a relatively large mass to be heated by the heat of reaction, the consequence being that the vehemence of the reaction is mitigated.
• the size of the large granules is such to permit the diffusion of the surface reaction products towards the inside, thus contributing towards the evaporation of mercury without however reaching the end point of their activity.
• the surface of the large granules is thus in a position to absorb, by displaying a getter action, the noxious gases during the lifetime of the discharge container.
• a grain size mixture of reducing materials such as provided by the present invention, enables to operate with a single active material which, by reacting in part only, subsequently displays a getter function in the discharge container.
• the weight ratio of the reducing active material powder to the powdered mercury compound should be, according to the invention, such that the former be strongly in excess with respect to the minimum amount which is necessary for a complete reaction with the mercury compound.
• the properties and physico-chemical specifications of the reducing agent should be such, according to the in vention, that the reducing agent is only slightly active at the degassing temperature (about 360 C.) so as not to react with air or with the mercury-evolving compound either.
• the reducing agent should be very active at the temperature of mercury evolution reac tion (about 800 C.) so as to immediately react with all the evolved gases and absorb in any case all of those small amounts which may have locally escaped.
• the reducing agent should allow a rapid diffusion of the products which are formed on the surface of every granule towards the inside thereof so as to maintain said surface reasonably clean until the whole granule mass has been exhausted.
• the reducing agent should undergo, upon its reaction with the mercury compound, modifications such as to cause the formation of strongly active unstable structures for the absorption of the noxious gases.
• the powdered mercury compound as contained in the tablets used in the process according to the invention should be of fine grain size so as to obtain a complete reaction with the reducing agent together with an immediate blocking of the gases evolved upon the thermal decomposition of the mercury compound.
• the lower limit of the grain size is posed by reason of cost, amount of included gases and problems attendant to health and safety of personnel during manufacture.
• Aluminium-Zirconium alloy (84% Zr and 16% Al, by
• wt. 30% by weight of granules having a size from to 210 microns
• Weight ratio alloy to HgO variable from 2:1 to 6:1 as a function of the purity of the gases evolved as mercury is evaporated and of the desired delaying action of the exothermic reaction.
• a powdered material which is only slightly active at the degassing temperature and has a grain size such as to comprise, along with a fine grain size fraction, fraction of relatively coarse grain size.
• a process for filling a discharge container with mercury and removing noxious gases comprising the steps of:
• a process for filling a discharge container with mercury and removing noxious gases comprising the steps of:
• a process for filling a discharge container with mercury and removing noxious gases comprising the steps of:
• a mercury-releasing tablet capable of sorbing noxious gases, said tablet comprising a mixture of:
• a mercury-releasing tablet capable of sorbing noxious gases comprising a mixture of:

Landscapes

• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Gas Separation By Absorption (AREA)
• Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)
• Discharge Lamp (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=11098590

Family Applications (1)

Country Status (4)

Cited By (8)

Citations (2)

• 1965
  • 1965-12-24 CH CH1782765A patent/CH455038A/it unknown
• 1966
  • 1966-01-05 DE DE19661514658 patent/DE1514658B1/de active Pending
  • 1966-01-05 US US518789A patent/US3385644A/en not_active Expired - Lifetime
  • 1966-01-07 GB GB870/66A patent/GB1105222A/en not_active Expired

Patent Citations (2)

Also Published As

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