EP1178519B1 - Quartz vessel with at least one current feedthrough, method of manufacturing a gastight connection between the two, and its application in a gas discharge lamp - Google Patents

Description

The invention relates to an SiO ₂ glass bulb with at least one feedthrough made of a gas-tight composite material, the composite material being formed from a noble metal with a melting point> 1700 ° C. and SiO ₂ , and the composite material being at least partially covered with an SiO ₂ layer is. The invention further relates to a high-power discharge lamp and a method for producing a gas-tight connection between an SiO ₂ glass bulb and a current leadthrough.

Current feedthroughs made of metal or a composite material for SiO ₂ glass bulbs are known. The term "composite" is understood to mean a combination of different material groups. Here the combination between a glass material and a metallic material is particularly affected. When forming a gas-tight connection between the material SiO ₂ and an electrically conductive, metallic or metal-containing current leadthrough, there is basically the problem that the metal parts of the current leadthrough are on the one hand only poorly wetted by viscous SiO ₂ . On the other hand, the low coefficient of thermal expansion of SiO ₂ compared to that of a metal makes the formation of a gas-tight connection considerably difficult. Since the metallic or metal-containing current leadthrough shrinks more than the SiO _{2 of} the glass bulb when cooling after melting, there is a tendency to form a gap at the interface between the glass bulb and the current leadthrough. Although this risk can be reduced by minimizing the thickness of the feedthrough, the positioning and handling of very thin feedthroughs, for example in the form of a film, is difficult. In order to nevertheless be able to produce a gas-tight connection, relatively complex solutions have hitherto been proposed.

For example, EP 0 938 126 A1 describes a leadthrough made of a composite material for a lamp, in particular a discharge lamp, the composite material being formed from SiO ₂ and metal and the metal content changing over the length of the leadthrough. The metal content can change from 0 to 100%. The side with the low molybdenum content is connected gas-tight to the lamp bulb in the direction of the discharge space of the lamp. In this case, only the end face of the current leadthrough, which consists mainly or entirely of SiO _2, is in direct contact with the gas in the discharge space. A metal electrode holder is sintered into the current feedthrough on the side of the low metal content, this holder immersing so far into the current feedthrough that direct contact is made with a composite area in which the SiO ₂ content is ≤ 80%. This creates an electrical contact between the bracket and the metal-rich side of the current feedthrough. A metal powder of molybdenum with an average particle size d ₅₀ of 1 μm and a glass powder with an average particle size d ₅₀ of 5.6 μm are disclosed for the composite material.
EP 0 930 639 A1 likewise discloses a current feedthrough with a metal content which changes over its length together with an SiO ₂ lamp bulb, tungsten, platinum, nickel, tantalum and zircon being mentioned as suitable metals for the composite material in addition to molybdenum. To protect the metal-rich end of the current lead-through from oxidation, a protective layer made of glass, metal oxide, noble metal or chrome is provided, which partially covers the part of the current lead-through protruding from the lamp bulb. The gas-tight fusion between the current leadthrough and the lamp bulb is arranged in a region of the current leadthrough in which the metal is present in the composite material with less than 2%.
However, the production of a current leadthrough with a metal concentration that changes over the length of the current leadthrough is expensive in terms of apparatus. Different powders have to be produced and arranged in layers. In addition, when an electrode is melted into the leadthrough, attention must be paid to the electrical conductivity of the individual layers and thus to the immersion depth of the electrode in the leadthrough in order to produce a continuous electrical contact. The fusion with the SiO ₂ lamp bulb must take place in a certain length section of the current lead-through with a very low metal concentration in order to be able to achieve a gas-tight connection. In the case of high thermal loads in the area of the current lead-through, corrosion can also occur with the non-oxidation-resistant metals such as molybdenum.

EP 0 074 507 A2 describes a material for electrical contacts, in particular Low power contacts, and a process for its manufacture. The material becomes one Precious metal with 1 to 50 vol .-% glass, preferably a precious metal powder with a Particle size of ≤ 250 µm and a glass powder with an average particle size of ≤ 50 µm is used. Gold, silver, palladium and their alloys are used as precious metals.

The problem arises of providing a gas-tight, corrosion-resistant feedthrough for an SiO ₂ glass bulb, preferably a discharge lamp, which has a high electrical conductivity and which is easy to manufacture and to handle.

The problem is solved in that the noble metal and the SiO _{2 are} homogeneously distributed in the composite material, that a noble metal portion is present in the composite material in a range from ≥ 10% by volume to ≤ 50% by volume and that the SiO ₂ layer the composite material is covered at least in the area of the connection with the SiO ₂ glass bulb.
The SiO _{2 used} for the formation of the composite material should have a purity of ≥ 97% by weight. Contamination in SiO ₂ , which can be attributed, for example, to alkalis or alkaline earths, can therefore be tolerated up to approximately 3% by weight.
Due to the SiO ₂ layer, this current feedthrough can be fused gas-tight with the SiO ₂ glass bulb over its entire length or even only in any partial area. Only a single composite powder is required to make it. Since the electrical feedthrough has a consistently high electrical conductivity over its entire length, it is not necessary to pay attention to its immersion depth in the composite material when an electrode is melted into the electrical feedthrough. The proportion of noble metal in the current leadthrough can be used to set the thermal expansion coefficient, which is preferably chosen for the current leadthrough in the range from <5.10 ^-6 1 / K. It was recognized as a particularly advantageous property of the current feedthrough that the composite material with SiO ₂ and the noble metal component is easily deformable in the range from 10 10% by volume to 50 50% by volume at temperatures of approximately approximately 1200 ° C. At temperatures greater than approximately 1600 ° C, current feedthroughs designed as rods, for example, bend under their own weight without cracks up to an angle of 90 ° without impairing the electrical conductivity of the material. Aligning or straightening such a feedthrough is thus possible.

Although these mechanical properties correspond to those of pure quartz glass, it is astonishing that they also apply to the composite material with its high electrical conductivity and current transmission capacity. A measured current transmission capacity of 20 amperes for a rod made of composite material with a diameter of 2 mm indicates a coherent network of the noble metal component, which would normally be stiff and hardly deformable. This combination of properties of the composite material, which is formed from the deformation properties of the pure quartz glass and the conductivity of the noble metal, enables precise and very simple mounting of electrodes or contact pins on the current leadthrough. For example, a tungsten electrode can be attached to the end of the current leadthrough, which points in the direction of the interior of the glass bulb, by heating the electrode together with the powder mixture. Sintering into already formed composite material is also possible. In addition, an electrode can also be inserted into viscous composite material heated to around 1200 ° C. In all three cases, a sufficiently conductive electrical connection is generated in a simple manner. The connection of a contact pin to the current bushing on the end facing away from the glass bulb is possible in the same way. Aligning or correcting the position and position of the electrode or the contact pin and correcting the straightness of the current feedthrough itself can also be carried out at temperatures of approximately 1200 ° C. The composite material is preferably formed by heating a powder mixture of noble metal powder and SiO ₂ glass powder. The noble metal can also be formed by a noble metal alloy. The noble metals platinum, rhodium, ruthenium, rhenium and iridium have proven to be particularly suitable for the composite material. An electrical conductivity of the current feedthrough should preferably be selected in the range of> 0.01 m / Ωmm ² . The thickness of the SiO ₂ layer should be in the range from 5 to 25 μm, but in particular in the range from 7 to 15 μm. A noble metal powder which has a specific surface according to BET (Brunauer-Emmett-Teller) in the range from 0.01 to 10 m ² / g is particularly suitable. It is also advantageous to use a precious metal powder with an average particle size (d ₅₀ ) in the range from 3 to 30 μm. The SiO ₂ glass powder preferably has a BET specific surface area in the range from 10 to 100 m ² / g. An average particle size (d ₅₀ ) for the SiO ₂ glass powder in the range from 0.1 to 10 μm has proven successful. It is particularly cost-effective if there is only a noble metal content in the composite material in a range from 10% by volume to 25% by volume.

The use of the SiO ₂ glass bulb with current feedthrough for high-performance discharge lamps is ideal because of the high corrosion resistance, conductivity and gas tightness of the feedthrough.

The problem is solved for a method in that the powder mixture is heated to a maximum of 1200-1600 ° C., that after the heating, the SiO ₂ layer is applied to the gas-tight composite material in the region of the connection with the SiO ₂ glass bulb Current feedthrough is introduced into an opening of the SiO ₂ glass bulb and is gas-tightly connected to the SiO ₂ glass bulb in the region of the SiO ₂ layer at a temperature> 1600 ° C.
The SiO ₂ layer is preferably applied to the composite material in the form of a paste or a suspension by spraying or printing or dipping, the SiO ₂ layer subsequently being baked onto the composite material.
The SiO ₂ layer can also be applied to the composite material by vapor deposition, sputtering, chemical deposition or thermal spraying.

For a process using the noble metals ruthenium and / or rhenium and / or iridium for the composite, the problem is also solved in that the powder mixture is heated to a maximum of 1200-1600 ° C., that the gas-tight composite material at least partially after heating Temperature ≥ 1600 ° C is annealed in an oxygen-containing atmosphere, whereby the noble metal is oxidized and evaporated on the surface of the composite material and at least in the area of connection with the SiO ₂ glass bulb of the lamp, the SiO ₂ layer is generated that the current feedthrough into a Opening of the SiO ₂ glass bulb is introduced and gas-tight connection in the region of the SiO ₂ layer at a temperature> 1600 ° C with the SiO ₂ glass bulb.
This process uses the knowledge that the metals ruthenium, rhenium and iridium, which form volatile oxides, oxidize and evaporate on the surface when the composite material is heated to a temperature ≥ 1600 ° C in an atmosphere containing oxygen. During the annealing, a closed thin SiO ₂ layer forms around the composite material, which prevents the metal from evaporating further and can be fused perfectly and gas-tight with the SiO _{2 of} the glass capsule. The fusion is mechanically so stable that an atomic bond is presumably formed between the SiO _{2 of} the glass capsule, the SiO ₂ layer produced by annealing and the SiO ₂ in the composite material.

Air is preferably used as the atmosphere containing oxygen, but pure oxygen or other gas mixtures which have an oxygen content can also be used.
It is particularly advantageous if the temperature is gradually increased to a maximum of 1200-1600 ° C. when the powder mixture is heated.
A method in which the powder mixture is shaped before heating is inexpensive. It has proven to be useful to press or extrude the powder mixture before it is heated. If an unshaped powder mixture is heated, which is of course also possible, the resulting composite material must be shaped. Due to the higher strength of the composite material, this usually has to be achieved by means of low-cost cutting processes.

Bsp. 1 ein Verfahren zur Herstellung einer Stromdurchführung mit Ruthenium,

Bsp. 2 ein weiteres Verfahren zur Herstellung einer Stromdurchführung mit Ruthenium,

Bsp. 3 eine Leitfähigkeitsmessung an einer Stromdurchführung mit Ruthenium,

Bsp. 4 eine Strombelastbarkeitsprüfung an einer Stromdurchführung mit Ruthenium,

Bsp. 5 eine mögliche Art der Montage einer Elektrode und eines Kontaktstiftes und

Bsp. 6 eine weitere mögliche Art der Montage einer Elektrode und eines Kontaktstiftes.

Fig. 1 eine Entladungslampe mit SiO₂-Entladungsgefäß

The following examples 1 to 6 and FIG. 1 are intended to explain the subject matter of the invention by way of example. So shows

Example 1 a method for producing a current leadthrough with ruthenium,

Example 2 a further method for producing a leadthrough with ruthenium,

Example 3 a conductivity measurement on a leadthrough with ruthenium,

Example 4 a current carrying capacity test on a current lead-through with ruthenium,

Ex. 5 a possible way of mounting an electrode and a contact pin and

Example 6 another possible way of mounting an electrode and a contact pin.

Fig. 1 shows a discharge lamp with SiO ₂ discharge vessel

Example 1:

A noble metal powder made of ruthenium with a BET specific surface area of 0.96 m ² / g and an average particle size d ₅₀ of 9.4 μm is used for the powder mixture.
The SiO ₂ is used with a BET specific surface area of 53 m ² / g and an average particle size d ₅₀ of 4.4 μm. 75 vol .-% SiO ₂ powder and 25 vol .-% precious metal powder are mixed homogeneously with the addition of distilled water and processed into a paste. This paste is extruded into a strand with a diameter of 2.5 mm and dried in air. The dried strand is heated to 1500 ° C. in an inert atmosphere, preferably in argon, at a heating rate of at most 15 ° C./min, a gradual heating by keeping the temperature constant at 500 ° C., 800 ° C. and 1100 ° C. 30 minutes each. The final temperature of 1500 ° C is held for 2 hours. The cooled composite strand with a diameter of 1.9 mm is coated evenly thinly with a paste consisting only of SiO ₂ with a BET specific surface area of 53 m ² / g and an average particle size d ₅₀ of 4.4 μm with the addition of distilled water is formed. The paste is dried in air and baked on the composite strand at 1550 ° C. for 30 minutes. The composite strand coated with a <0.1 mm thick SiO ₂ layer or the current feedthrough is cut to a length of 25 mm and - if necessary after mounting an electrode and a contact pin - inserted into the tubular opening of an SiO ₂ glass capsule, the tubular one Opening has an inner diameter of 2mm and an outer diameter of 5.9mm. The area of the tubular opening is locally heated to approximately 1700 ° C., for example with a hydrogen flame. As a result, the tubular opening collapses onto the feedthrough and forms a gas-tight, mechanically stable bond. A micrograph of the connection point from the glass capsule to the current lead-through showed no transition lines, which are formed, for example, by inhomogeneities such as pores, cracks or structural differences, between the composite material and the SiO ₂ layer or between the SiO ₂ layer and the glass capsule, but it was merely a uniform SiO ₂ phase.

Example 2:

According to Example 1, a composite strand is produced, a final temperature of 1300 ° C. being maintained during the gradual heating. The composite strand is annealed at 1620 ° C in air for 30 minutes. At the beginning of the annealing process, ruthenium oxide evaporates briefly. After cooling, the composite material is coated on all sides with a thin SiO ₂ layer and the feedthrough can be melted into a tubular opening in the glass capsule according to Example 1.

Example 3:

A noble metal powder made of ruthenium with a BET specific surface area of 0.29 m ² / g and an average particle size d ₅₀ of 5.0 μm is used for the powder mixture. The SiO ₂ is used with a BET specific surface area of 53 m ² / g and an average particle size d ₅₀ of 4.4 μm. 88 vol .-% SiO ₂ powder and 12 vol .-% precious metal powder are mixed homogeneously with the addition of distilled water and processed into a paste. This paste is extruded into a strand with a diameter of 2.5 mm and dried in air. The dried strand is heated to 1300 ° C in an inert atmosphere, preferably in argon, at a heating rate of at most 15 ° C./min, a gradual heating by keeping the temperature constant at 500 ° C., 800 ° C. and 1100 ° C. 30 minutes each. The final temperature of 1300 ° C is held for 2 hours. The composite strand is annealed at 1620 ° C in air for 30 minutes. At the beginning of the annealing process, ruthenium oxide evaporates briefly. After cooling, the composite material is coated on all sides with a thin SiO ₂ layer.
The current feedthrough produced in this way is freed of the SiO ₂ layer on the end faces and subjected to an electrical conductivity test. The conductivity value was 0.047m / Ωmm ² .

Example 4:

The current feedthrough from Example 2 with a diameter of 1.9 mm was subjected to a current carrying capacity test. For this purpose, the rod-shaped feedthrough was clamped between two copper terminals and supplied with electricity in air. The current could be increased to a value of 20 amperes, whereby the current feedthrough heated up to approximately 1700 ° C. Only an increase in the current to 22 amperes caused the feedthrough to melt. This results in a possible current density of a remarkable 7.05 A / mm ² for the tested current implementation.

Example 5:

A noble metal powder made of ruthenium with a BET specific surface area of 0.96 m ² / g and an average particle size d ₅₀ of 9.4 μm is used for the powder mixture.
The SiO ₂ is used with a BET specific surface area of 53 m ² / g and an average particle size d ₅₀ of 4.4 μm. 75 vol .-% SiO ₂ powder and 25 vol .-% precious metal powder are mixed homogeneously with the addition of distilled water and processed into a paste. This paste is extruded into a strand with a diameter of 2.5 mm and dried in air. The dried strand is heated to 1300 ° C. in an inert atmosphere, preferably in argon, at a heating rate of at most 15 ° C./min, a gradual heating by keeping the temperature constant at 500 ° C., 800 ° C. and 1100 ° C. 30 minutes each. The final temperature of 1300 ° C is held for 2 hours. After cooling, the current leadthrough is cut to a length of 15 mm and a blind hole with a depth of 3 mm and a diameter of 1 mm is drilled in the end faces of the composite strand. A tungsten wire electrode is inserted into one of the blind holes and a contact pin made of molybdenum into the other. The surface of the composite strand is then coated evenly thinly with a paste which is formed only from SiO ₂ with a BET specific surface area of 53 m ² / g and an average particle size d ₅₀ of 4.4 μm with the addition of distilled water. The paste is dried in air and baked at 1550 ° C for 30 minutes on the composite strand, which has the electrode and the contact pin.
A conductive, mechanically stable connection is created between the composite material and the electrode, as well as the composite material and the contact pin.

Example 6:

A noble metal powder made of ruthenium with a BET specific surface area of 0.96 m ² / g and an average particle size d ₅₀ of 9.4 μm is used for the powder mixture.
The SiO ₂ is used with a BET specific surface area of 53 m ² / g and an average particle size d ₅₀ of 4.4 μm. 75 vol .-% SiO ₂ powder and 25 vol .-% precious metal powder are mixed homogeneously with the addition of distilled water and processed into a paste. This paste is extruded into a strand with a diameter of 2.5 mm and dried in air. The dried strand is heated to 1300 ° C in an inert atmosphere, preferably in argon, at a heating rate of at most 15 ° C./min, a gradual heating by keeping the temperature constant at 500 ° C., 800 ° C. and 1100 ° C. 30 minutes each. The final temperature of 1300 ° C is held for 2 hours. The composite strand is cooled, cut to a length of 15 mm and then annealed at 1620 ° C. in air for 30 minutes. At the beginning of the annealing process, ruthenium oxide evaporates briefly. After cooling, the composite material is coated on all sides with a thin SiO ₂ layer. The current feedthrough is heated to 1500 ° C on one end and a tungsten wire electrode is pressed into the viscous composite material by about 2 mm. in the same way, the contact pin is attached to the other end of the feedthrough.
A conductive, mechanically stable connection is created between the composite material and the electrode, as well as the composite material and the contact pin.

FIG. 1 shows a discharge lamp in the sense of the inventive solution, which has a current feedthrough 1 and an SiO ₂ glass bulb in the form of a discharge vessel 2. The discharge vessel 2 has a tubular section 3 in the region of the current leadthrough 1 with an opening into which the current leadthrough 1 is melted. The current feedthrough 1 is formed from a composite material 1a, which is surrounded by a thin SiO ₂ layer 1b. The end of the current feedthrough 1, which projects into the discharge space of the discharge vessel 2, has a tungsten electrode 4. The end of the current lead-through 1, which protrudes from the discharge vessel 2, has a contact pin 5 made of molybdenum.

Claims (22)

1. SiO₂ glass bulb having at least one current lead-through comprising a gas-tight composite material, the composite material being formed from a noble metal having a melting point > 1700°C and from SiO₂ and being at least partly covered with an SiO₂ layer, characterized in that the noble metal and the SiO₂ are homogeneously distributed in the composite material, that a proportion of noble metal in a range from ≥ 10% by volume to ≤ 50% by volume is present in the composite material and that the SiO₂ layer covers the composite material at least in the region of the joint with the SiO₂ glass bulb.
2. SiO₂ glass bulb according to Claim 1, characterized in that the composite material is formed by heating a powder mixture comprising noble metal powder and SiO₂ glass powder.
3. SiO₂ glass bulb according to Claim 1 or 2, characterized in that the noble metal is formed from a noble metal alloy.
4. SiO₂ glass bulb according to any of Claims 1 to 3, characterized in that the noble metal is formed from platinum and/or rhodium.
5. SiO₂ glass bulb according to any of Claims 1 to 3, characterized in that the noble metal is formed from ruthenium and/or rhenium and/or iridium.
6. SiO₂ glass bulb according to any of Claims 1 to 5, characterized in that the current lead-through has an electrical conductivity of > 0.01 m/Ωmm².
7. SiO₂ glass bulb according to any of Claims 1 to 6, characterized in that the SiO₂ layer has a thickness in the range of 5 - 25 µm.
8. SiO₂ glass bulb according to Claim 7, characterized in that the thickness of the SiO₂ layer is 7 - 15 µm.
9. SiO₂ glass bulb according to any of Claims 2 to 8, characterized in that the noble metal powder has a BET specific surface area in the range from 0.01 to 10 m²/g.
10. SiO₂ glass bulb according to any of Claims 2 to 9, characterized in that the noble metal powder has a median particle size (d₅₀) in the range from 3 to 30 µm.
11. SiO₂ glass bulb according to any of Claims 2 to 10, characterized in that the SiO₂ glass powder has a BET specific surface area of from 10 to 100 m²/g.
12. SiO₂ glass bulb according to any of Claims 2 to 11, characterized in that the SiO₂ glass powder has a median particle size (d₅₀) in the range from 0.1 to 10 µm.
13. SiO₂ glass bulb according to any of Claims 1 to 12, characterized in that the proportion of noble metal in the composite material is in a range from ≥ 10% by volume to 25% by volume.
14. High-power discharge lamp comprising an SiO₂ glass bulb according to any of Claims 1 to 13.
15. Process for the production of a gas-tight joint between an SiO₂ glass bulb and a current lead-through according to any of Claims 1 to 13, characterized in that the powder mixture is heated to not more than 1200 - 1600°C, that the SiO₂ layer is applied to the gas-tight composite material in the region of the joint with the SiO₂ glass bulb after the heating, that the current lead-through is introduced into an opening of the SiO₂ glass bulb and is joined gas-tight to the SiO₂ glass bulb in the region of the SiO₂ layer at a temperature > 1600°C.
16. Process according to Claim 15, characterized in that the application of the SiO₂ layer to the composite material is effected in the form of a paste or of a suspension by spraying or printing or immersion and that the SiO₂ layer is fired on the composite material.
17. Process according to Claim 15, characterized in that the application of the SiO₂ layer to the composite material is effected by vapour deposition, sputtering, chemical deposition or thermal spraying.
18. Process for the production of a gas-tight joint between an SiO₂ glass bulb and a current lead-through according to Claim 5, characterized in that the powder mixture is heated to not more than 1200 - 1600°C, that, after the heating, the gas-tight composite material is at least partly ignited at a temperature of ≥ 1600°C in an oxygen-containing atmosphere, with the result that the noble metal is oxidized and vaporized on the surface of the composite material and the SiO₂ layer is produced at least in the region of the joint with the SiO₂ glass bulb of the lamp, that the current lead-through is introduced into an opening of the SiO₂ glass bulb and is joined gas-tight with the SiO₂ glass bulb in the region of the SiO₂ layer at a temperature > 1600°C.
19. Process according to Claim 18, characterized in that air is used as the oxygen-containing atmosphere.
20. Process according to any of Claims 15 to 19, characterized in that the temperature during the heating is increased stepwise to not more than 1200 - 1600°C.
21. Process according to any of Claims 15 to 20, characterized in that the powder mixture is moulded prior to heating.
22. Process according to Claim 21, characterized in that the powder mixture is compression moulded or extruded prior to heating.

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