FR2815172A1 - LAMP WITHOUT MERCURY WITH COLD HOLLOW CATHODS WITH FLUORESCENCE LUMINESCENCE FOR DECORATIVE COLORED LIGHTING OR LUMINOUS SIGNS - Google Patents

Abstract

The invention relates to a mercury-free lamp with activated cold hollow cathodes (4) comprising a tubular hollow body (2) made of glass, the interior of which is covered with a fluorescent powder, which comprises cathode electrodes at both ends. cold hollow (4) activated and which is filled with a rare gas mixture, characterized in that the rare gas mixture comprises 90% to 99% neon and up to 1% of a rare gas or a mixture of rare gases of blocking or complement, the remainder being constituted by xenon, and the activated cold hollow cathodes (4) have an active layer (6) comprising barium fluoride (BaF2) or a compound containing an element of Group III B of the Periodic Table of the Elements.Application: decorative colored lighting and illuminated signs.

Description

The invention relates to cold hollow cathode lamps with

  luminescence / fluorescence, in particular for decorative colored lighting and

illuminated signs.

  These lamps are produced in a hollow tubular glass body whose interior is covered with a fluorescent powder. The tube thus powdered is sealed at its two ends by electrodes and filled with a pure rare gas or

  of a mixture of rare gases. Mercury is also added.

  These electrodes operate as emissive cathodes for half of two alternations from an alternative source and passively as an anode.

during the other half-cycle.

  They are called "cold hollow cathodes" or "cold cold emitting cathodes" because the emission of electrons by the cathode is mainly obtained by a secondary emission under ionic impacts

  while thermionic emission plays a marginal role.

  These cold cathodes generally have a cylinder

metallic activated.

  Thus, following an electrical discharge in the gaseous medium of the tube, between the two electrodes, the mercury in the state of metallic vapor emits invisible UV radiation which is transformed into visible radiation by the

fluorescent powder.

  Mercury is however a toxic product, dangerous for humans and the environment. In addition, it generates phenomena of light pollution condemned by amateur astronomers as well as the protectors of volatile species and rare insects. In addition, it causes

  also shadow areas in the tube during cold periods.

  The invention aims in particular to overcome these drawbacks.

  To this end, it offers a mercury-free lamp with activated cold hollow cathodes, comprising a tubular hollow glass body the interior of which is covered with a fluorescent powder, which has at its two ends electrodes with activated cold hollow cathodes and which is filled with a mixture of rare gases, characterized in that the mixture of rare gases comprises from 90% to 99% of neon and up to 1% of a rare gas or a mixture of blocking rare gases or in addition, the rest being xenon, and the activated cold hollow cathodes have an active layer comprising barium fluoride (BaF2) or a compound containing an element

  of group III B of the Periodic Table of the Elements.

  Thanks to these arrangements, a tubular lamp or tube is produced

  discharge allowing fluorescence to be obtained without UV radiation

  specific for mercury. Indeed, this is obtained thanks to radiation

  far ultraviolet and ultraviolet generated by the neon-xenon mixture.

  The lifetime of such a tube is longer than that of a mercury tube because no amalgam stains the fluorescent powder, due to the absence of mercury. This absence of mercury also allows operation up to an ambient temperature of around -30 C and allows operation with a very regular voltage and lower than that of a tube.

  classic mercury. In practice, the voltage gain is greater than 10%.

  In addition, the colors obtained are very saturated and

provide excellent contrast.

  The element of group III B of the Periodic Table of the Elements is preferably chosen from scandium, yttrium and lanthanum, ie a lanthanide, scandium and yttrium being attached to the family

lanthanides.

  The corresponding preferred compounds are chosen from the group comprising lanthanum oxide (La203), lanthanum hexaboride (LaB6), scandium oxide (Sc203), a mixture of lanthanum oxide and titanium oxide (La203. 2TiO3), a mixture of mixed barium oxide and

  titanium and yttrium oxide (BaTiO3. Y203) and their associations.

  The products that have given the best results are barium fluoride (BaF2) and the BaTiO3 mixture. Y203 in proportions ranging from% to 30% for one and from 30% to 70% for the other. Indeed, they allow

  to obtain a minimum cathodic drop and, consequently, a gain in voltage.

  Also preferably, the pressure of the mixture of rare gases

  is between 1 and 10 mbar (1bar = 105 Pa).

  The rare or blocking or complementary gas (s) are, as for

  them, chosen from the group comprising argon, krypton, and helium.

  According to a preferred embodiment, each cathode comprises a metal cylinder whose internal face is covered with the active layer, while a tubular ceramic sheath covers the external face of this cylinder. The ceramic may be silica, alumina (oxide

  aluminum), or a mixture of these oxides with each other or with other oxides.

  The invention also relates, in a second aspect, to the use of a lamp as defined above for decorative colored lighting or

in a luminous sign.

  Secondary characteristics and advantages of the invention

  may emerge from the description which follows by way of example, in

  reference to the single appended figure which represents, in longitudinal section,

  one end of a discharge tube, provided with a hollow cathode electrode.

  According to the embodiment chosen and shown, the mercury-free luminescence / fluorescence lamp 1 comprises a tubular hollow body 2 made of glass, whether straight or not. This glass is chosen from the glasses conventionally used for fluorescent tubes, namely hard glasses based on borosilicate, soft lead or lead-free glasses or soft soda-lime glasses. In practice, the internal diameter of this tubular hollow body 2 is between 4 and 36 mm, for a wall thickness included

between 1 and 1.3 mm.

  The inside of this tube is covered with a conventional fluorescent powder or a mixture of this kind of fluorescent powders, on a

  thickness, in practice, between 6 and 12 μm.

  A central current input conductor 3 or two lateral conductors pass through the glass at each of the ends of the body 2. It is produced from a nickel-based alloy and welded at one of its ends to a metallic cold hollow cathode electrode 4. The tubular hollow body 2 naturally has a second electrode of this kind at its opposite end. This electrode 4 comprises a metal support 5 in the form of a cylinder closed at the end welded to the central conductor 3 and coaxial with the axis of the tubular body 2. In longitudinal section, this cylindrical support 5 has the shape of a U. preferably this metal support 5 is made of ultra pure iron (99.99% purity) of the "Telar Low Carbon" type and is protected by nickel plating without a brightening agent over a thickness of 4 to 8 μm or by oxidation

  controlled to ensure a deposit of blue / black magnetite oxide.

  The internal face of this metallic support 5 is coated with an active layer 6, obtained by coating this face with a powder based on the compounds and / or mixtures defined above. Preferably, BaF2 or a BaTiO3 mixture is used. Y203 in proportions ranging from 70 to 30% for one

and 30 to 70% for the other.

  Typically, 4 to 12 mg of such a powder is applied to the

  internal face of the metal support 5.

  A ceramic sheath 7 also surrounds the exterior of this metal support 5 in order to increase the longevity of these hollow cathode electrodes 4 and their resistance to demetallization under the effect of repeated shocks from the ions and electrons present at the l inside the tubular hollow body 2. This ceramic may be silica, alumina or a mixture of these oxides

between them or with other oxides.

  A shield 8 made of non-porous soapstone and a mica washer 9 supporting the cylinder 5 complete the electrode 4. This shield 8 is intended to avoid

  tearing of the metal from the front edge of the cylindrical metal support 5.

  Finally, the tubular hollow body 2 is filled with the mixture of rare gases of purity 40 to 55 N, comprising at least 90% of neon and up to 1% of a gas or a mixture of blocking or complement gases. chosen from the group consisting of argon, krypton and helium, the rest being

with xenon.

  Depending on the diameter of the tubular hollow body 2, the pressures of

  filling varies, in practice, from I to 10 mbar.

  As regards the manufacture of such a lamp 1, it will be noted that the interior of the tubular body 2 can be powdered dry or wet with ethyl acetate or with demineralized water with additives, before be subjected to annealing in the oven in order to obtain a perfectly homogeneous deposit of fluorescent powder (s). The cold hollow cathode electrodes 4 are then put in place and the tube is sealed at both ends. The enclosure thus formed is then bombarded by electric discharge inside the enclosure under partial vacuum (approximately 10-3 mbar). Then the enclosure is degassed to descend to a pressure below 10-3 mbar, typically up to 10-6 mbar, before filling this enclosure with the mixture of neon, xenon and blocking or additional gas, under a

  very low filling pressure between 1 and 10 mbar.

  Typically, it has been found that with a filling pressure of 3 mbar for a mixture of rare gases at 1% xenon, an optimum luminance is obtained with a very low operating intensity, of the order of 25 mA, by means of a fluorescent powder having its maximum emission at 525 nm. The cathodic drop and the tube voltage are then at their minimum, the voltage gain obtained compared to a mercury tube

being 10%.

  Of course, the invention is not limited to the example described above.

  above, but embraces all the variants of execution within the reach of

the skilled person.

Claims (8)

  1. Mercury-free lamp with activated cold hollow cathodes (4) comprising a tubular hollow body (2) made of glass, the interior of which is covered with a fluorescent powder, which has at its two ends electrodes with cold hollow cathodes (4) activated and which is filled with a mixture of rare gases, characterized in that the mixture of rare gases contains from 90% to 99% of neon and up to 1% of a rare gas or a mixture of rare gases blocking or complement, the remainder consisting of xenon, and the activated cold hollow cathodes (4) have an active layer (6) comprising barium fluoride (BaF2) or a compound containing an element of group III B   of the Periodic Classification of the Elements.   2. mercury-free lamp according to claim 1, characterized in that the element of group III B of the Periodic Table of the Elements   is taken from scandium, yttrium and lanthanum.   3. Mercury-free lamp according to claim 1 or 2, characterized in that the compound is chosen from the group comprising lanthanum oxide (La203), lanthanum hexaboride (LaB6), scandium oxide (Sc203) , a mixture of lanthanum oxide and titanium oxide (La203. 2TiO3), a mixture of mixed barium oxide and titanium and yttrium oxide (BaTiO3. Y203) and their associations.   4. mercury-free lamp according to claim 1, characterized in that the active layer (6) comprises barium fluoride (BaF2) or a   mixture of mixed barium and titanium oxide and yttrium oxide (BaTiO3.   Y203) in proportions ranging from 70% to 30% for one and from 30% to 70% for the other.   5. Mercury-free lamp according to any one of claims   previous, characterized in that the pressure of the mixture of rare gases is between 1 and 10 mbar.   6. Mercury-free lamp according to any one of claims   above, characterized in that the rare blocking or complement gas (s) are chosen from the group comprising argon, krypton, and   helium. 7. Mercury-free lamp according to any one of the preceding claims, characterized in that each cathode comprises a cylinder   metal (5) whose internal face is covered with the active layer (6), while a tubular sheath (7) in ceramic covers the external face of this cylinder.   8. Use of a lamp as defined in any one of claims 1 to 7, for decorative colored lighting or in a neon sign.