DE1589230A1 - Electrical discharge vessel - Google Patents

Description

The invention relates to discharge vessels, in particular on low-pressure mercury vapor discharge tubes, such as fluorescent lamps.

It is known to be used as electrodes in low pressure mercury vapor discharge vessels, such as fluorescent lamps, oxide cathodes to use; these are made by Double helix or so-called triple helix made of tungsten with a fine filament wound around the tungsten double! a carbonate bond of barium, strontium and calcium carbonate coated, the coated structures in a discharge vessel and these carbonates are then subjected to thermal decomposition while the gas is discharged from the tube is sucked off, whereby barium, strontium and calcium oxide is formed. The oxide layers formed in this way have a high

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specific resistance and low thermal conductivity. As a result, cathode spots with high temperature in places and cathode spots which form the centers of glow electron emission form in a discharge vessel in which these cathodes are used. When such a discharge vessel is switched on, this temperature of the cathode spots does not change due to their thermal inertia, but the cathode spots continue to have a high temperature, both during the ignition or the extinction of the arc of the cathodes in all alternating current periods. Therefore, with the known cathodes, at the time of ignition and extinction of the arc, the glow electron current Ig naturally becomes stronger than the discharge current IjJ ₁ . this in turn has a strong radio interference noise effect.

In order to prevent the formation of such annoying noise in To avoid fluorescent lamps, numerous attempts have been made to reduce the thermal conductivity of the oxide layers in such Electrodes used to improve lamps. For example, it is known (Japanese Patent 1581/1964) that the lower the temperature of the cathode spots by increasing the thickness

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the oxide layer was reduced to 30 µ or less, so that the thermal conductivity of the cathodes is quite improved and thereby the cathode spots were enlarged. However, this method does not give good results because of it the absolute volume of the electron-emitting oxides and this in turn reduces the life of the discharge tube. Furthermore, it is known (Japanese Patent-8391 / 1965) to close the spaces between the slopes to prevent excessive temperature rise in the coils due to the mutual radiation that •, by

The cathode spots appear in the interior of the filament and its temperature is reduced. However, lamps with such an arrangement produce a when lit. Radio interference noise of the order of magnitude of 35 dB and is sufficient does not meet the requirements for non-radio interference fluorescent lamps. "..- '..

The invention is based on the object of the discharge vessels to improve and in particular to manufacture low-pressure mercury vapor discharge vessels such as fluorescent lamps, those in the broadcast frequency band of width 535 to 1605 kHz cause very little radio interference.

According to the invention, a practically usable one becomes Fluorescent tube ,, which is essentially noise-free, viz

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a radio interference noise? of 15 dB or less and at which the tube does not go black with use. achieved a cathode emitter, which mainly consists of barium, strontium and calcium oxide, the iron-cobalt boride contain; the high melting point and a considerably higher one Have thermal conductivity than ordinary ion crystals and which have been stabilized by replacing part of this iron with one or more substances from the group of titanium, zircon, Hafnium, vanadium, mob, tantalum, chromium, molybdenum, tungsten, Aluminum and silicon replaced and furthermore a reducing metal powder from the group of zirconium, hafnium, iobium and tantalum contains.

These powdered reducing metals, namely zirconium, hafnium, mob and tantalum, prevent on satisfactory Way that 'the metal borides during the thermal decomposition of the carbonates that occur during the suction of the gas takes place from the discharge vessels, oxidize.

Experiments have shown that the discharge vessel according to the invention has the oxide cathodes made of a substance consisting of barium, strontium and calcium oxide and containing 1 wt. F <> metal borides, according to the composition formula (0.45 Fe. 0.4 Co. 0.05 Ti. 0.05 A]) 2 $] -j, as well as 3 wt. $ Zircon - each based on the total

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weight - .these oxides - has a considerably higher noise reduction effect compared to conventional discharge vessels in which the cathodes are made of such oxides. If a fluorescent lamp according to the invention is subjected to a test by connecting it to a generally known parallel capacitor of 0.006 ρ F, an extremely low noise intensity of only 15 dB or less is obtained in the entire radio ^{frequency band between 535 and <3 1605 kHz.}

On the attached drawing are those for a radio receiver occurring noise values by a fluorescent lamp according to the invention and a; conventional fluorescent lamp shown.

In this drawing, curve 1 gives the Outghintensitat a fluorescent lamp using a conventional oxide again,:

The reasons for the considerable reduction in cathode vibrations according to curve 2, which applies to the oxide cathodes with an inclusion of metal borides, are not yet completely cleared; however, as it was discovered during this experiment, that the cathode spots were larger than those at a conventional oxide cathode and since the temperature of the

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Cathode spot in the former was "lower" than in the the latter, it is believed that one of the reasons is that the metal borides have much higher thermal conductivity than the barium, strontium and calcium oxides.

Due to the better noise reduction effect through the metal boride is supposed to have a certain relationship between the metal borides and the electron-emitting ones Oxides.

The metal borides used according to the invention are polyelement metal borides corresponding to the composition formula (1-xy) Fe. xCo. 0.5yMe | ^ B ₂ , where Me means one or more metals from the group consisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum and silicon. A mixture of the metal borides described above and the barium,. Strontium and calcium carbonates applied. · The coated electrodes are ^{heated to approx. 1200 °} C. while the gas is sucked out of the fluorescent lamp} the carbonates mentioned are consequently decomposed by the heat and the so-called oxide electrodes are created.

Therefore, the added metal borides must have a melting point of at least 1300 ⁰ C and must not oxidize,

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when they are heated to a temperature of the order of magnitude of 1200 ^° C. in a carbon dioxide atmosphere.

Iron boride can form two different compounds, namely Fe2B and FeB. Cobalt boride can also form two different compounds, namely C02B and CoB. Their melting points are 1389 ⁰ C, 1550 C ^0, 1265 ⁰ C, and 135 ° ⁰ C. The melting points of Fe2B and C02B are slightly lower than those of FeB and CoB. However, a metal boride that has a higher proportion of boron than FeB and CoB significantly reduces the life of the cathode emitter. For example, a fluorescent lamp whose cathodes consist of an emitter containing 5% by weight of FeB has a service life of approx. 2000 hours. A fluorescent lamp whose cathodes consist of an emitter containing 5 wt. FeoB, however, has a service life of approx. 5000 hours / A lamp whose cathodes consist of an emitter containing 1 wt. Fe2B has a service life of 8000 hours or more . For this reason, iron-cobalt borides with a composition formula of (Fe. Co ^ B. If the volume fraction of boron is less than according to the chemical formula, this leads to the development of free iron or cobalt; however, this oxidizes - as already mentioned above - the metal boride easily

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Above composition formula preferably a somewhat larger one Volume fraction of boron, namely ζ = 1 to 1.15, than the chemical Composition corresponds. However, if ζ) 1.15, the service life of the lamp will be impaired and for this reason one should avoid that the boron content is higher than this limit value.

If the metal boride consists of a simple substance such as Fe2B, this oxidizes to a certain extent during the decomposition of the electrodes; this results in an end-zone blackening after a lighting time of approx. 1000 hours. This blackening is due to the mercury oxide particles that form due to the combination of the remaining pollutant gases, especially oxygen with mercury, which are in the Place the inside of the tube about 3 cm in front of the electrodes.

Although this end zone blackening has no effect on the life of the fluorescent lamp, it has a very negative impact on the commercial value of the lamp. Since CooB has better oxidation resistance at high temperatures than FeB, such blackening can largely be stopped if CO 2B is added to the cathode emitter. However, since the C02B has a low melting point of 1265 ⁰ C, the use of C00B as a simple substance creates a yellowish-brown color

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Darkening of the terminal areas of the tube behind the Electrodes after a possible lighting time of 1000 hours. If, on the other hand, a substance of the composition is used

_a B- | -r | (where 0.15 ^ χ - 0.6), in which 15 to 60 io of the iron of the compound &? B is replaced by cobalt, then both the formation of the end zone blackening and the formation of the blackening in the terminal areas are the Lamp largely avoided compared to the use of a simple substance such as Fe £ B or C02B. In the above composition, if χ 2 is 0.15, there is a danger that the lamp is subjected to end zone blackening as well as a drill using P ^ B as a simple substance. If χ y 0.6, then the lamp} becomes slightly black at its terminal areas, just as when using the simple material C02B,

The metal borides used according to the invention are poly element borides, which are mainly composed of the iron-cobalt borides of the composition formula I (1-xy) Fe. xCo. yMe UB ₂ *, with part of the iron being replaced by one or more substances from the group consisting of titanium, zirconium, hafnium, vanadium, mob, tantalum, chromium, molybdenum, tungsten, aluminum and silicon. In the composition formula, the range y is between 0.01 and 05 «

The titanium, zirconium, vanadium, niobium, tantalum, chromium, Molybdenum, tungsten, aluminum and silicon borides have a lot

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• high melting points. The melting point of Mo? B is 2000 ⁰ C, that of Ti ₂ B is 2790 ⁰ C, that of Zr ₂ B 3040 ⁰ C and that of W ₂ B is 277O ⁰ C. So you have melting points around 2000 ⁰ C or above. Since these substances have a high resistance to oxidation and remain chemically stable at high temperatures compared to the simple iron-cobalt borides, the discharge lamp with an emitter which has the above composition with the addition of the above borides has the great advantage that the from Their blackening developed during the glow is very slight and that their radio interference noise reduction effect is hardly reduced either. The metals with high melting points such as titanium, zircon, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum and silicon can are exchanged in an amount range of y = 0.01 to 0.3 and preferably 0.03 to 0.1 If I, which indicates the amount to be replaced by these metals with the high melting points, is below 0.01, the The stability increasing effect of the emitter at high temperatures is decreased, while on the other hand, if this amount is over 0.3, it is rather difficult to obtain a solid solution of boron to achieve iden.

For the oxide cathodes that contain these metal borides, a noise interference reduction effect is noticeable,

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when the cathodes contain 0.05% by weight or more of such metal borides. To avoid QuaIitätsabweichung the goods during ■ production and equally good? Jaren to erlalter], the borides are advantageously in a proportion of the order of magnitude of 0.1 to 2 f "added. Although the noise interference reduction effect can just as well be achieved if more than 2% by weight of metal borides are added, an addition of more than 10% by weight of metal boride means a reduction in the proportion of barium, strontium and calcium oxides. This generally results in a shorter service life of the lamp and such an excess of metal boride additive is disadvantageous. ■

As described above, the addition of an additive is consisting of one or more reducing metal powders with high melting points of the group zirconium, hafnium, Niobium and tantalum, in a proportion of the order of magnitude of 1 to 8% by weight, to the oxides of the cathodes according to the invention necessary to prevent the lamp from blackening during lighting and also to extend the life of the lamp to achieve. By using these additives in an amount of less than 1 wt / o the desired effect is impaired, while an addition of more than 8 wt. $ reduces the Electron emissivity of the kithodes and therefore both extremes are undesirable. ,

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example 1

Barium carbonate 35 g

Strontium carbonate 35 g

Calcium carbonate, 29 g (0.45Fe. 0.4Co. 0.05Ti. 0.05AX) ₂ B ₁ J 1 g

Zircon 3g

Example 2

Barium carbonate 35 g

Strontium carbonate 35 g

Calcium carbonate 29 g (0.5Fe. 0.4Co. 0.03Zr, 0.02Hf ^ B-jj ¹ S

Zircon 3 g

Example 3

Barium carbonate 35 g Strontium carbonate .35 g ■ calcium carbonate 29 g (0.7Fe. 0.2Co. 0.05Mo) ₂ B ₁ J 2 g Zircon 2 g hafnium 1 g Example 4

Barium carbonate 35 g

Strontium carbonate 35 g

Calcium carbonate 29 g

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(0.7Fe. Q.2Co. 0 . 009 8 4 97 .05W) 2 ^B 1.1 1 G Zircon 2 G Hafnium. 1 G Example 5 Barium carbonate 35 G Strontium carbonate 35 G Calcium carbonate 29 G (0.7Fe. 0.2Co. 0. , 03V . 0.02Nb) pi ■] 1 G Zircon 2 G Niobium. '■■■' 1 G Example 6 Barium carbonate 35 G Strontium carbonate / 35 G Calcium carbonate 29 G (0.7Fe. 0.2Co. 0. 03Ta .. '0.02Si) ₉ B ₁ λ 1 G Zircon 2 G niobium Λ G Example J
■ ■ Barium carbonate 35 G Strontium bicarbonate 35 G Calcium carbonate 29 G (0.5Co. 0.4Fe. OJ 05Cr) 2 ^B 1.1 1 G ■ zircon CVJ G Tantalum 3 G 036 S.

Example 8

Barium carbonate 35 g

Strontium carbonate 35 g

CalGium carbonate 29 g (0.5Go. 0.4Fe. 0.03Cr. 0.02Mo) ₂ B ₁ J 1g

Zircon 2g

Tantalum. 3g

The mixtures according to the above examples, which are described in Nitrocellulose-butyl acetate solutions were slurried on Applied to the double and triple filaments - made of tungsten. The coated coils were subjected to thermal decomposition, while the gas was sucked out of the discharge vessels. Meder pressure mercury vapor discharge vessels were provided oxide cathodes consisting of these pendulums, ternary carbonates of the above-described composition ratios were found as the above-mentioned barium, strontium and calcium carbonates used.

Those prepared in the manner described above. Fluorescent lamps were tested by connecting them to commonly used parallel capacitors of 0.006 u. All As can be seen from curve 2, lamps showed that the interference noise was in a frequency band with a width of 535 to 1605 kHz was at most 15 dB and that the lifespan of the jenir

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corresponded to the usual charge vessels. Consequently can the lamps produced according to the invention are almost completely free from noise Fluorescent lamps are called ..

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Claims (1)

-.16- 15P9230 "Claim: Discharge vessel with cathodes that have a cathode emitter are coated, which consists mainly of barium, strontium and calcium oxides, characterized in that that the emitter - based on the weight of the oxides - contains 0.05 to 10% by weight of a substance [(1-xy) Fe. xCo.0.5yMe] ₂ B _z , where 0.15 ^ χ ^ 0.6, 0.01 * y * 0.3, 1 ^ ζ i 1.15 and which consists mainly of iron-cobalt-borides, in which part of the iron is replaced by one or more metals Me of the group titanium, zirconium, hafnium, laJ:. ^> Γι whether tantalum, chromium, molybdenum, tungsten, aluminum and silicon is replaced, ■ i - - and that the mixture of these oxides and the substance 1 to 8 Weight ^ - based on the weight of the oxides - one or more contains reducing metals with high melting points of the group zirconium, hafnium, molybdai and tantalum. 009849/0369 BATH