EP1958238B1 - Metal halide lamp - Google Patents

Abstract

The invention relates to a metal halide lamp comprising a ceramic discharge vessel (10), characterized in that an MoV leadthrough is connected to a PCA element (Al2O3) by means of a specific adhesive layer containing Al and Mo.

Description

Technical area

The invention relates to a metal halide lamp according to the preamble of claim 1. These are lamps with a ceramic discharge vessel, which find particular application in general lighting.

State of the art

From the US-B 6 590 342 Already a metal halide lamp is known. The bushing is sealed by means of glass solder in a stopper. To better match the thermal expansion coefficient, a layer of molybdenum aluminide, Mo3Al, is applied to the bushing. Other intermetallic components are also proposed for the layer.

The bushing is a pin whose inner part is made of molybdenum. The layer also has the additional purpose of being particularly resistant to halogens of the filling.

The publication EP 0 052 844 A1 discloses a high pressure sodium discharge lamp with a feed made of a MoV alloy sealed by a frit in a PCA part.

Presentation of the invention

It is an object of the present invention to make the sealing of the implementation as permanent as possible and to achieve improved adhesion between implementation and environment.

This object is solved by the characterizing features of claim 1. Particularly advantageous embodiments can be found in the dependent claims.

The closure technology for high-pressure discharge lamps with a ceramic discharge vessel has not yet been satisfactorily solved. For the closure, feedthroughs of a MoV alloy as a tube or pin are now inserted directly into the end of a discharge vessel made of Al ₂ O ₃ . There is no longer a need for a stopper made of a cermet consisting of moieties Mo and Al ₂ O ₃ .

Preferably, a tube is used as the feedthrough, since it has more elastic properties than a pin. It is essential that the implementation has a MoV part, wherein the implementation may also have other parts, such as a niobium part as the outer part or a core of another material. The MoV part is treated by means of an alitation process. Subsequently, this system is inserted directly into the open end of a PCA green body. The PCA part is either a plug or the direct end of a discharge vessel of transparent Al ₂ O ₃ or similar. if necessary, it can also be a cermet part of the components Mo and Al ₂ O ₃ .

In contrast, in the prior art using glass solder, the interfacial connection between a molybdenum duct, particularly a pipe, and a plug or end of the discharge vessel is unsatisfactory because the inert molybdenum does not react with glass solder. Thus, there is only one physical bond between a molybdenum feedthrough and a glass solder with bad adhesion. In the constant temperature change between the operating condition and the lamp is switched off, therefore, there is the formation of cracks, which ultimately leads to leakage and thus the lamp failure.

According to the invention, glass solder or ceramic is now dispensed with at this point. A better adhesion of the implementation of the PCA part, in particular the end of the ceramic discharge vessel, is -ggf. waiving a cermet plug by a special adhesive layer, which is based on the activation of the surface of the implementation achieved. By means of an alitization process, also called alumetation process, aluminum is transferred to the surface of the molybdenum-vanadium alloy, in particular via the gas phase. At first, a high Al-containing layer is formed, hereinafter referred to simply as (MoV) 3Al8 layer. This happens in a diffusion process that is temperature- and time-dependent. For this purpose, in particular MoV tubes are placed in an Al-containing powder bed mixture and annealed at temperatures between 800 and 1200 ° C in a protective gas atmosphere. In the surface of the lead-through, a gradient structure of an Al-rich AlxMoyVz phase is formed on the outside, similar to an A18Mo3 phase, which is followed by Almeric phases AlwMoyVz phase, similar to Mo3Al, which further into the MoV. Structure of the tube passes. The index w is significantly smaller than x. The aluminum from this near-surface outer phase is capable of in the direct sintering of the green body, in which a shrinkage of the green body is achieved in the order of about 10 to 30%, which the execution provisionally seals--, as a result of the heat treatment in the direct sintering, a reaction with the oxygen of the PCA part, so the plug or preferably the end of the discharge vessel, each consisting predominantly of Al ₂ O ₃ (PCA), enter and thus a To create firm connection between the plug and the end of the discharge vessel and the implementation. In this case, the adhesive layer converts partially or completely into a cermet of Mo, V and Al ₂ O ₃ .

In principle, this type of sealing can also be used for a system consisting of MoV part of the leadthrough and a cermet plug made of Mo and Al ₂ O ₃ , with the proportions Mo: V having to be chosen differently than in the case of adaptation of the thermal expansion coefficient pure Al ₂ O ₃ plug. however, in the following, the term PCA part will be used for all these variants.

In this way, the seal between the MoV-containing bushing or the MoV part of the bushing and the PCA part, in particular plug or end of the discharge vessel, significantly improved. Preferably, the adhesive partner is the direct end of the discharge vessel, because then a completely glass solder-free simple and secure connection is possible, which allows a reliable seal by combining a direct sintering with additional adhesive layer.

Particularly preferably, during the direct sintering process, a protective gas of inert gas such as in particular argon and / or nitrogen N2 is used, which in a specific embodiment contains a small proportion of 20 to 200 ppm oxygen O2. This improves the implementation in the adhesive layer. Depending on the process, therefore, the adhesive layer consists either only partially or more or less completely of a cermet of Mo, V and Al ₂ O ₃ , whereby proportions of the initially present MoxAlyVz layers can be obtained with gradient structure.

Since cracking takes place in the case of using unalloyed pure Mo pipes as a bushing due to the different coefficients of thermal expansion after the sintering process despite good adhesion, a MoV alloy in the sealing area of the bushing is used instead of Mo. The alloy is adjusted so that its thermal expansion coefficient is about 8 x 10 ^-6 K ^-1 . Thus it is ideally adapted to the so-called PCA, ie polyceramic Al ₂ O ₃ . However, the alloy can also be adjusted so that an adaptation to a cermet plug is possible by increasing the Mo content.

MoV is similar to pure Mo alitieren. The Al portion of the alloy reacts well enough to accomplish an adhesive layer. This Alitierungsprozess is time and temperature dependent, so that initially forms in the adhesive layer, a gradient structure with Al-richer and Al-poorer phases.

The proportion of vanadium in the molybdenum-vanadium alloy (MoV), the adaptation to pure PCA should be below 50 wt .-%. Preferably, a proportion of vanadium in the range of 20 to 40 wt .-%, since then the relative expansion differences can be kept sufficiently small. In the case of adaptation to a cermet of Mo and Al ₂ O ₃ , the proportion of vanadium should be much smaller in Range of, for example, about 8 to 25 wt .-%, since the coefficient of thermal expansion of vanadium in the order of 9.6 x 10 * ^-6 K ^-1 . In contrast, that of molybdenum is much smaller, it is about 5.7 x 10 * ^-6 K ^-1 .

The good adhesion is achieved by the temporary formation of an intermetallic microstructure which forms as a gradient structure from the Mo content of the base material of the feedthrough to the ceramic. The formation of cracks, which previously had their origin at the interface implementation / ceramic, thereby significantly reduced.

The tube dimensions of the MoV-containing bushing may be conventional, such as in EP-A 528 428 explained. In particular, the passage is preferably a tube with a diameter of 0.5 to 3 mm. The wall thickness is for example 100 to 300 microns.

At the high temperature of the direct sintering process of typically 1700 to 1900 ° C., the (MoV) 3A18 "layer located on the outside of the leadthrough from MoV reacts with the oxygen at the surface of the ceramic, so that in this layer Al is converted to Al ₂ O ₃ , whereby the original (MoV) 3A18 becomes an Al poorer phase. This resulting Cermet Mo-A1203 forms in its reaction a toothed layer, which ensures particularly good adhesion. The reaction in the cermet plug occurs mainly on the surface of larger grains of Al ₂ O ₃ , where the Al is very reactive.

The treatment for producing the reactive oxygen is promoted in particular by using a protective gas during the direct sintering, consisting of an inert gas-oxygen mixture, wherein only small amounts of oxygen may be added to the inert gas, preferably argon and / or nitrogen. These are in the order of a partial pressure of 20 to 200 ppm, in particular at most 100 ppm. If more oxygen is added, molybdenum on the surface oxidizes to MoO2 or MoO3. These substances are volatile and are not suitable for improving adhesion.

characters

Figur 1

eine Metallhalogenidlampe, im Schnitt, schema- tisch;

Figur 2

eine Darstellung des Verbindungsmechanismus, schematisch;

Figur 3

ein Detail aus Figur 1, schematisch.

In the following the invention will be explained in more detail with reference to several embodiments. Show it:

FIG. 1

a metal halide lamp, in section, schematically;

FIG. 2

an illustration of the connection mechanism, schematically;

FIG. 3

a detail from FIG. 1 , schematic.

Description of the preferred embodiment

In FIG. 1 schematically is a metal halide lamp shown with an outer bulb 1 made of tempered glass or. Quartz glass, which has a longitudinal axis and is closed on one side by a plate smelting 2. At the plate smelting 2, two power supply lines are led outwards (not visible). They end in a base 5. In the outer bulb, a two-sided sealed ceramic discharge vessel 10 made of Al ₂ O ₃ (PCA) with a filling of metal halides is inserted axially. The discharge vessel 10 may be cylindrical or inwardly spherical or elliptical with capillary ends 21.

Electrodes 3, which are fastened to feedthroughs made of MoV, protrude into the discharge vessel. The passage is preferably a tube, but may also be a pin. In particular, the implementation may also be divided into two and consist only of the front end of the implementation of MoV.

There is an ignitable gas from the group of noble gases in the discharge vessel. Further there is in the discharge vessel, a mixture of metal halides as known per se, for example, iodides of Na Tl and Dy and possibly mercury. Ca can also be used as a halide.

In FIG. 2 schematically the connection between MoV tube and an Al ₂ O ₃ stopper is shown in detail. In this case, the passage 6 made of a molybdenum-vanadium alloy with 30 wt .-% vanadium is shown as a base material 11, on the surface of a thin first layer 12 of AlxMoyVz formed with a high proportion of Al. This layer is formed by an Alitierungsprozess. Under suitably chosen reaction conditions, the aluminum diffuses into deeper layers of the leadthrough to form one or more AlxMoyVz thin layers 13 containing less Al and formed between the thin first layer and the MoV backbone. This layer sequence is achieved by the diffusion of the aluminum into the surface of the MoV tube. The Alitierung takes place at 700 to 1200 ° C over a duration, which is in the order of a few hours. Depending on the procedure lead to up to six analytically detectable different layers that can merge more or less continuously. A typical example is four layers, which have a mean empirical formula for AlxMoyVz with the normalization x + y + z = 1 of A10, 71V0, 12Mo0.17 for the first layer, A10, 66V0, 07Mo0, 27 for the second layer, A10 , 40V0, 34Mo0, 26 for the third layer and A10, 22V0, 31Mo0, 47 for the fourth layer.

The aluminized MoV tube is now inserted into the green plug and directly sintered. The aluminum from the layer of AlxMoyVz on the surface of the bushing reacts with the direct sintering with the oxygen content of the stopper 14 made of Al ₂ O ₃ , so that a thin adhesive layer 20 is formed on the surface of the plug above the base body 15. This is due to partial or complete conversion of the AlxMoyVz intermetallic phases of the MoV tube, creating a chemical, permanent bond. The layers 12, 13 of the intermetallic phases together form the new adhesive layer 20, which consists partly, predominantly or completely of a cermet of Mo and Al ₂ O ₃ .

Real forms not a smooth interface, but a gradual gradient, these layers merge smoothly into each other. In particular, the boundary surface of the same concentration is suddenly unstable, so that a close toothing arises, similar to FIG. 3 shown schematically.

FIG. 3 shows another embodiment in which a MoV tube is inserted directly into the end 21 of a ceramic discharge vessel. It is in it by direct sintering held, similar to FIG. 2 described. In this case, the implementation is shown as a MoV tube 11, to which the end 21 is connected via the novel adhesive layer 20 to the outside. The gearing is not shown to scale.

The implementation does not have to consist entirely of molybdenum-vanadium alloy. It is sufficient if it consists partially, in the sealed part of MoV. For example, a back part of the bushing may be niobium, as known per se, or the MoV part may have a core of other material, as also known per se.

The PCA part, in which the bushing is sintered directly, can be, for example, a plug, or the end of the discharge vessel, or else another intermediate part. PCA stands for polykeramic Al ₂ O ₃ , as known per se.

Claims (6)

1. Metal halide lamp, which comprises a light-permeable ceramic discharge vessel 10 consisting of Al₂O₃ (PCA), leadthroughs 6 protruding into the discharge vessel 10 through openings at its ends 21, each leadthrough 6 being manufactured at least partially from molybdenum/vanadium alloy, referred to below as the MoV part 11, and bearing an electrode 3, the leadthrough being sealed off in the opening, characterized in that the MoV part 11 of the leadthrough is sealed off in a PCA part 14 via an adhesive layer 20, which contains Al and Mo at the same time.
2. Metal halide lamp according to Claim 1, characterized in that the adhesive layer partially comprises an intermetallic layer AlxMOyVz, which has a gradient.
3. Metal halide lamp according to Claim 1, characterized in that the leadthrough is a tube.
4. Metal halide lamp according to Claim 1, characterized in that the leadthrough is joined to the PCA part, which is either a stopper or directly the end of the discharge vessel, preferably using direct sintering.
5. Metal halide lamp according to Claim 1, characterized in that the adhesive layer partially or completely comprises a cermet, which contains Mo, V and Al₂O₃.
6. Method for producing a metal halide lamp according to Claim 1, a joint between a PCA part and the MoV part of the leadthrough being achieved by the following steps: (a) by means of an alitization process Al is diffused into the surface of the MoV part; (b) the alitized MoV part is inserted into the green PCA part (c) direct sintering with heat treatment, possibly with supply of a protective gas, which in particular has a low proportion of oxygen of at most 200 ppm, with an adhesive layer being formed in the region of the alitization.

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