EP1156505A1 - Process of producing an electrical lamp - Google Patents

Abstract

Production of an electric lamp having a SiO2 glass bulb and a current feed made from a foil of molybdenum or a doped molybdenum alloy comprises post-treating the foil before squeezing into the glass bulb so that on 5-60 % of the foil surface produce non-connecting island regions of material agglomerates. Preferred Features: The material agglomerates consist of yttrium oxide or yttrium mixed oxide, or titanium or titanium mixed oxide.

Description

The invention relates to a method for producing an electric lamp with a lamp bulb made of SiO ₂ or a glass containing a high amount of SiO ₂ and a power supply which comprises a film made of molybdenum or a doped molybdenum alloy squeezed into the lamp bulb.

In the case of electric lamps with a lamp bulb made of glass, the current required to operate the lamp must be fed into the interior of the lamp bulb via special power supplies. Especially in the case of lamps with a lamp bulb made of silica or a high SiO ₂ -containing glass, such as, for example, halogen incandescent lamps, metal halide lamps, high-pressure mercury lamps or high-pressure xenon lamps, such a power supply consists of an outer current conductor entering the glass from one Molybdenum foil squeezed or melted in a vacuum-tight manner in the glass as well as from an inner current conductor (eg holding wire, filament, electrode).

In order to achieve a vacuum-tight squeezing or melting of the molybdenum foil in the glass, in particular in the case of silica glass or high SiO ₂ -containing glasses and molybdenum in spite of the very different thermal expansion coefficients, the foil is very thin (typically 15 to 50 µm), with a high Widths to thickness ratio (typically> 50) and has tapered side edges.
The much thicker outer and inner conductor must be welded to this thin molybdenum foil, the inner conductor often consisting of tungsten. In the case of current conductors made of tungsten in particular, this is associated with very high welding temperatures, which can lead to embrittlement and subsequently to rupture of the molybdenum foil. Film tears can also occur during the squeezing or melting process, on the one hand caused by the relative movement between the glass and the film, on the other hand by the build-up of tensile stresses during the cooling process, at temperatures which are below the relaxation temperature of the glass.

It has to improve the mechanical strength of the molybdenum foil proven, instead of pure molybdenum doped molybdenum alloys use.

DE-C-29 47 230 describes a molybdenum foil in which 0.25 to 1% yttrium oxide particles are dispersed, with the advantage that this film has better welding behavior and due to the heat input during less brittle of welding. An important reason for the top one 1% limit is the realization that foils with higher dispersoid contents only are formable to a limited extent and result in a too high film strength, which the Voltage reduction in the lamp base area during the cooling process negatively influenced during the crushing process and cracks in the quartz glass can lead.

EP-B-0 275 580 describes a molybdenum alloy especially for fusible links with 0.01 to 2% by weight of Y ₂ O ₃ and 0.01 to 0.8% by weight of molybdenum boride, which in comparison to fusible links consists of a K -Si-doped molybdenum alloy has improved recrystallization and manufacturing properties.

In addition to the mechanical properties of the molybdenum foil, it is also very important to improve the service life. This is determined on the one hand by the oxidation resistance of the molybdenum foil, and on the other hand by the adhesive strength between the molybdenum foil and the silica or high SiO ₂ -containing glass.

EP-B-0 691 673 describes a band-shaped power supply Molybdenum-yttrium oxide base, which additionally contains 0.03 to 1% by weight of cerium oxide a ratio of cerium oxide to yttrium oxide of 0.1 to 1. A film with this Compared to a film doped with yttrium oxide a significantly improved oxidation behavior.

Together, all molybdenum materials doped with yttrium oxide show improved film adhesion, which can be attributed, among other things, to a surface reaction between Y ₂ O ₃ and SiO ₂ to form an yttrium silicate.

Improved resistance to oxidation can also be achieved by metallic coating of the molybdenum foil with Ta, Nb, V, Cr, Zr, Ti, Y, La, Sc and Hf in accordance with DE-C-30 06 846, but with the connection of the above Metals to SiO _{2 is} a very bad one, so that with the exception of Cr layers, these coatings have not been used in practice.

A special formation of oxidation-resistant layers made of chrome, Nickel, nickel-chromium alloys or molybdenum silicide is in the DE-B-21 52 349.

EP-B-0 309 749 describes a fusion between molybdenum and a glass-like material, the part of the molybdenum which is exposed to the oxidizing environment being coated with alkali metal silicate. However, this does not favorably affect the connection between the molybdenum and the glass. Molybdenum nitride layers in accordance with EP-A-0 573 114, phosphide layers in accordance with EP-B-0 551 939, or SiO ₂ layers in accordance with DE-A-20 58 213 have also become known for the external oxidation protection.

Attempts have also been made to improve the oxidation resistance by ion implantation in accordance with US Pat. No. 5,021,711. However, this process is very complex and does not lead to an improvement in the Mo / SiO ₂ adhesion.

DE-A-196 03 300 describes a molybdenum film which contains 0.01 to 1% by weight of silicates and / or aluminates and / or aluminates rich in alkali and alkaline earth metals from one or more elements from groups IIIb and / or IVb of the periodic table. This doping prevents the occurrence of cracks in the pinch seal due to the high mechanical stresses in the molybdenum-quartz glass composite. However, an improvement in the film adhesion compared to films which are doped with Y ₂ O ₃ or Y mixed oxide is not achieved.

Attempts were also made to improve the SiO ₂ / Mo adhesion by roughening the film, for example by sandblasting, in accordance with EP-A-0 871 202. However, this process is very complex and leads to the installation of internal stresses in the molybdenum foil.

Overall, it can be stated that molybdenum foils which are doped with Y ₂ O ₃ or Y mixed oxide are most widespread for squeezed current leads in the lamp industry. In the case of lamps which are subject to very high thermal loads, such as, for example, very compact metal halide lamps, the Mo / SiO ₂ adhesion is often not sufficient with these power supplies.

The object of the present invention is therefore a method for Production of an electric lamp with a glass lamp bulb and a squeezed power supply from a film made of molybdenum or to create a doped molybdenum alloy, in which the above described disadvantages are largely avoided.

According to the invention this is achieved in that a conventional sintered metallurgical and forming process before the Squeezing in the glass flask is treated in such a way that 5 to 60 percent by area of the film surface essentially not contiguous island-like areas of material agglomerates with of the Raw film of different surface structure and / or Material composition made of molybdenum or its alloys Titanium, from silicon or from an oxide, a mixed oxide and / or one oxidic compound with a vapor pressure of less than 10 mbar each arise at 2,000 ° C.

In this way it is achieved that there is a large surface area during the squeezing or melting process, as a result of which the adhesive strength between the film and the glass and thus also the service life of the lamp is significantly improved. The film adhesion is still surprisingly improved even if the material agglomerates present on the film before the melting process are partially or completely dissolved in the silica glass or high SiO ₂ -containing glass during the crushing or melting process.

Oxides such as Al ₂ O ₃ , ZrO ₂ , Y ₂ O ₃ , TiO ₂ , silicates, aluminates, but also Mo, Ti, Si or their alloys are suitable as materials for the material agglomerates.

It has proven particularly useful if a film is used whose Surface area of at least 5 percent by area to a maximum of 20 percent by area consists of non-contiguous agglomerates of substances.

The average size of the individual fabric agglomerates is advantageously less than 5 µm.

In a particularly advantageous embodiment of the invention, it has proven when a film is used, the material agglomerates of Yttrium oxide or yttrium mixed oxide exist.

In a further particularly advantageous embodiment of the invention, it has has proven itself when a film is used, the material agglomerates of Titanium oxide or titanium mixed oxide exist.

For the formation of non-contiguous agglomerates, this has Application of a slip or deposition from the gas phase has proven itself, followed by an annealing treatment at a temperature between 500 ° C and 1,400 ° C. This makes it easy to apply Fabric agglomerates with sufficient adhesive strength for further processing reached.

In the following, the invention will be explained using manufacturing examples and Comparative measurements explained in more detail.

example 1

500 g of 99.5% pure yttrium oxide powder with an average particle size of the primary particles of 230 nm were dispersed in 50 g of nitrocellulose and 750 ml of alcohol-based solvent. The slip thus produced was applied to a pickled molybdenum film measuring 2.5 mm × 0.025 mm using immersion technology. This was then annealed in a single pass at a temperature of 1200 ° C in dry hydrogen. The area fraction Y ₂ O ₃ was 12%, with an average Y ₂ O ₃ agglomerate size of 1.5 μm.

Example 2

A slip consisting of 350 g of 99.7% titanium silicate powder with an average particle size of the primary particles of 630 nm, 50 g of nitrocellulose and 750 ml of alcohol-based solvent was prepared as described in Example 1 and applied to a pickled Mo-Y mixed oxide Foil measuring 2.5 mm × 0.025 mm (Y ₂ O ₃ content: 0.48% by weight, Ce ₂ O ₃ content: 0.07% by weight) was applied.

This was then run in at a temperature of 1200 ° C annealed dry hydrogen. The film surface was through SEM / image analysis characterized, the area percentage of titanium silicate particles 17% was, with a mean titanium silicate agglomerate size of 1.1 microns.

Example 3

A slip consisting of 400 g of 99.2% pure yttrium silicate powder with an average grain size of the primary particles of 840 nm, 50 g of nitrocellulose and 750 ml of alcohol-based solvent was prepared as described in Example 1 and applied to a pickled Mo-Y mixed oxide Foil measuring 2.5 mm × 0.025 mm (Y ₂ O ₃ content: 0.48% by weight, Ce ₂ O ₃ content: 0.07% by weight) was applied. This was then annealed in a single pass at a temperature of 1,200 ° C in dry hydrogen. The area fraction of the yttrium silicate particles was 29%, with an average yttrium silicate agglomerate size of 3.2 µm.

Example 4

A slip consisting of 250 g of 99.9% pure silicon powder with an average particle size of the primary particles of 210 nm, 50 g of nitrocellulose and 750 ml of alcohol-based solvent was prepared as described in Example 1 and applied to a pickled Mo-Y mixed oxide Foil measuring 2.5 mm × 0.025 mm (Y ₂ O ₃ content: 0.48% by weight, Ce ₂ O ₃ content: 0.07% by weight) was applied. This was then annealed in a single pass at a temperature of 950 ° C in dry hydrogen. The area fraction of the Si / MoSi ₂ particles was 13%, with an average Si / MoSi ₂ agglomerate size of 2.3 µm.

Example 5

A slip consisting of 1,000 g of 99.98% pure molybdenum powder with an average particle size of the primary particles of 1.5 μm, 50 g of nitrocellulose and 750 ml of alcohol-based solvent was prepared as described in Example 1 and on a Mo-Y film (Y ₂ O ₃ content: 0.48% by weight, Ce ₂ O ₃ content: 0.07% by weight) of dimensions 2.5 mm x 0.025 mm, the side edges of which were shaped like knife-edge edges by mechanical deformation (edge angle 25 °) , applied. This was then annealed in dry hydrogen at a temperature of 1,400 ° C.

The area fraction of the Mo particles was approximately 50% with a medium one Mo agglomerate size of 2.9 µm.

The films according to the invention from Examples 1 to 5 were used for In the usual way, 20 MR 16 halogen lamps each. For Standard Mo-Y mixed oxide foils such as they also for the production of the coated films according to the examples 2 to 4 were used in the uncoated state for the production of 20 MR 16 halogen lamps used. 10 lamps were placed under each usual operating conditions at a base temperature of 400 ° C, the remaining 10 lamps under difficult operating conditions with a Base temperature of 450 ° C, operated until its failure.

The service lives achieved are shown in Table 1.

The table clearly shows that the lamps according to the invention with the coated molybdenum foils have an up to 35% longer service life than the lamps according to the prior art with the uncoated molybdenum foils. foil Service life at 400 ° C base temperature [h] Service life * at 450 ° C base temperature [h] Mo-0.48% by weight Y ₂ O ₃ 0.07% by weight Ce ₂ O ₃ 760 380 according to example 1 980 510 according to example 2 990 500 according to example 3 1,010 490 according to example 4 820 450 according to example 5 790 440

Claims (7)

Method for producing an electric lamp with a lamp bulb made of SiO ₂ or a glass containing a high amount of SiO ₂ and a power supply which comprises a film made of molybdenum or a doped molybdenum alloy squeezed into the lamp bulb
characterized in that a raw film produced by customary sintered metallurgical and forming processes is aftertreated before being squeezed in the glass bulb in such a way that island-like areas of material agglomerates with surface structure and / or material composition different from the raw film on essentially 5 to 60 area percent of the film surface , from molybdenum or its alloys, from titanium, from silicon or from an oxide, a mixed oxide and / or an oxidic compound with a vapor pressure of less than 10 mbar at 2,000 ° C. A method of manufacturing an electric lamp according to claim 1,
characterized in that a film is used for squeezing, the surface of which consists of at least 5 area percent to a maximum of 20 area percent of non-contiguous agglomerates of material. A method for producing an electric lamp according to claim 1 or 2, characterized in that a film is used for squeezing, in which the average size of the individual material agglomerates is less than 5 µm. Method for producing an electric lamp according to one of claims 1 to 3, characterized in that the material agglomerates consist of yttrium oxide or yttrium mixed oxide. Method for producing an electric lamp according to one of claims 1 to 3, characterized in that the material agglomerates consist of titanium oxide or titanium mixed oxide. A method for producing an electric lamp according to one of claims 1 to 5, characterized in that a film is used for squeezing, in which the non-contiguous agglomerates of material by applying a slip or deposition from the gas phase and subsequent annealing at a temperature between 500 ° C and 1,400 ° C. Molybdenum foil according to one of claims 1 to 6 in post-treated Version for use in electric lamps.