EP1032022B1 - Metal halide lamp with ceramic discharge vessel - Google Patents

Abstract

A metal halide lamp with a ceramic discharge vessel, having conductive bushings comprising a cermet with a rare earth metal oxide-containing compound ceramic phase, is new. A metal halide lamp has a ceramic discharge vessel which has a filling comprising one or more rare earth metals and which is fitted with electrically conductive bushings passing vacuum-tightly through the vessel end seals. At least the discharge-facing front portion (45) of each bushing is in the form of a halide-resistant component of electrically conductive cermet comprising an electrically conductive phase and a ceramic phase which consists, at least at its surface accessible to the filling, of a compound of the ceramic base material with one or more rare earth metal oxides. Preferred Features: The cermet has a conductive phase of Mo, W, Re or their alloys or of MoSi2 and a ceramic phase of a garnet or perovskite of Al2O3 and one or more rare earth metal oxides.

Description

Technical field

The invention is based on a metal halide lamp with a ceramic discharge vessel according to the preamble of claim 1. It is in particular around metal halide lamps with an output of at least 100 W.

State of the art

A generic metal halide lamp with a ceramic discharge vessel and a halide-resistant bushing is already known from EP-A 587 238. The front part of the bushing facing the discharge can consist of an electrically conductive cermet (with a ceramic and a conductive phase). Aluminum oxide or also MgO, Sc ₂ O ₃ or Y ₂ O _{3 is} used as the ceramic phase. A halogen-resistant metal, for example tungsten, or molybdenum disilicide (MoSi ₂ ) is proposed as the conductive phase of the cermet. Filling components made from rare earth metal halides (SE) are usually used in these lamps. Here DyJ _{3 is} recommended. Alternatively, the use of the iodides of Sc, Y, Ho or Tm is recommended.

EP-A 887 839 recommends using a continuous cermet stick to be used for metal halide lamps with ceramic discharge tube.

A disadvantage of these designs is that after a short period of operation a large part of the ions of rare earth metals formed in the filling Reaction with the ceramic, usually aluminum oxide, is bound. Therefore, so far a clear overdose is necessary, however, because of the corrosive properties little is desired. Or you had to buy with economical dosage take that the maintenance and life of the lamp by effects like Color drift and increase in burning voltage was significantly limited.

Presentation of the invention

It is an object of the present invention to provide a metal halide lamp with a ceramic Discharge vessel according to the preamble of claim 1 with improved Provide lifetime.

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

The starting point of the present invention is the discovery that due to the high temperature in the area of the end face of the binding carrying out Rare earth metal ions from the filling preferably in the region of a front zone Implementation takes place, at least the surface of the part of the implementation that with is in contact with the discharge volume. Most of them are the frontal discharge end of the bushing since it is the highest temperature reached in operation. In contrast, the discharge vessel itself and the sealant (usually a stopper) significantly less affected.

Therefore, it may be sensible, the implementation in a front, especially halide-resistant Part and a less endangered rear part. The front part is a cermet component with a ceramic and an electrically conductive Phase.

A precise investigation shows that during the reaction of the rare earth metal ions with the ceramic phase of the cermet component, a connection is formed predominantly in the part of the cermet near the electrode, the chemical composition of which, in the case of aluminum oxide as ceramic, is approximately a garnet (SE ₃ Al ₅ O ₁₂ ) or Perovskite (SEAlO ₃ ) or a mixture of both. The same applies to other ceramics. If this chemically stable composition is reached after a short period of operation, it no longer changes over the course of the burning time or service life.

Now contains the ceramic phase of the cermet component, either the entire one Component or a zone on the surface facing the discharge from from the outset a considerable proportion (especially at least 40, especially more than 80 mol%) of a corresponding compound made of the ceramic base material and at least one rare earth oxide, the cermet component or its zone exposed to discharge, no longer bind rare earth metal from the filling. Therefore, the filling and thus the maintenance of the lamp over a long service life stable without using an overdose of the filling got to. The surface with a garnet or perovskite structure can be on the front and possibly also on the lateral surface of the cermet component.

In detail, according to the invention, it is a metal halide lamp ceramic discharge vessel, the discharge vessel having two ends which are closed with means for sealing. By these means there is one electrically conductive bushing passed vacuum-tight, on the one electrode is fastened with a shaft which projects into the interior of the discharge vessel. At least one front part of the feedthrough that faces the discharge is designed as a halide-resistant component made of electrically conductive cermet, that of an electrically conductive (especially metallic) and a ceramic Phase, which comprises a ceramic base material. The filling comprises at least a rare earth metal (i.e. Sc, Y, La and the 14 lanthanoids), mostly as a halide, or as a complex or elementary. At least on the face (Front) of the component consists of at least part of the ceramic phase Connection of the ceramic base material with one or more rare earth oxides.

The cermet component is preferably a pin or a tube. The cermet usually has a metal such as molybdenum or tungsten or rhenium or their alloys or a metal silicide such as MoSi ₂ as the electrically conductive phase.

The safest, but also the most complex, is when it covers the entire area Length of the component at least part of the ceramic phase from the connection of the ceramic base material with one or more rare earth oxides consists. The entire ceramic phase preferably consists of the connection of the ceramic base material and one or more rare earth oxides. The Cermet component can carry out the front part or the whole Form implementation.

The ceramic base material is usually polycrystalline aluminum oxide.

In a first embodiment, those used for the cermet component include Rare earth metal oxides are the oxides of one or more or all of them in the filling contained rare earth metals.

In a second embodiment, the rare earth oxides comprise the oxides of one or more rare earth metals not contained in the filling, in particular Y ₂ O ₃ .

In a third embodiment, a mixture of the two first embodiments used.

In a particularly preferred. Embodiment corresponds to the connection of the ceramic base material with one or more rare earth oxides Garnet or perovskite or a mixture of both. As a perovskite preferably oxides of La, Nd, Sm, Eu or Gd are used. As a garnet especially use oxides of Lu, Yb, Tm and Y. The remaining rare earth oxides are particularly suitable for both structures and their mixtures.

It is particularly simple and effective to use predominantly or exclusively an oxide of a rare earth metal with the smallest possible ion radius as the rare earth metal oxide. Because it seems as if the ions of these rare earth metals preferentially diffuse into the ceramic phase of the cermet component. In particular, it is sufficient to use a single rare earth oxide whose ionic radius is less than or equal to the ionic radius of the rare earth metal ion which has the smallest ionic radius in the filling. An effective ion radius up to a maximum of about 0.091 nm is recommended. Above all, the scandium ion (Sc ³⁺ ) is suitable, with a coordination number of 6. This embodiment has the advantage that it is independent of the particular choice of filling and therefore for multiple types can be used together.

This special cermet component is used in all metal halide lamps possible with ceramic discharge vessel, regardless of whether the seal by means of melting ceramics or by direct sintering.

In principle, the production of the special cermet can be carried out in a manner known per se by processing an appropriate powder mixture. The basic Suitability of such materials (especially yttrium aluminum garnet) for the lamp construction is already known, see US-A 5 698 948. There the material however used for discharge vessels. The requirement of Translucency does not matter in the implementation.

The means for sealing (usually a stopper) advantageously consists of ceramic or Cermet (for example, suitably doped aluminum oxide), the ceramic Base material of the cermet component is a ceramic main component of the agent corresponds to sealing, here aluminum oxide. This arrangement has the advantage that the thermal expansion coefficients of both parts are similar, so that a direct sintering of the cermet component in the stopper is particularly successful.

characters

Figur 1

eine Metallhalogenidlampe, im Schnitt

Figur 2

den Anteil verschiedener Seltenerdmetalle im Cermetstift

Figur 3

das Entladungsgefäß einer Metallhalogenidlampe, im Schnitt

Figur 4

ein weiteres Ausführungsbeispiel eines Cermetstifts

Figur 5

noch ein weiteres Ausführungsbeispiel eines Cermetstifts

Figur 6

ein weiteres Ausführungsbeispiel eines Entladungsgefäßes im Schnitt

The invention will be explained in more detail below with the aid of several exemplary embodiments. Show it:

Figure 1

a metal halide lamp, in section

Figure 2

the proportion of various rare earth metals in the cermet stick

Figure 3

the discharge vessel of a metal halide lamp, in section

Figure 4

another embodiment of a cermet stick

Figure 5

yet another embodiment of a cermet stick

Figure 6

a further embodiment of a discharge vessel in section

Description of the drawings

A metal halide lamp with an output of 250 W is shown schematically in FIG. It consists of a cylindrical outer bulb 1 made of quartz glass which defines a lamp axis and is squeezed (2) and base (3) on two sides. The axially arranged discharge vessel 4 made of Al ₂ O ₃ ceramic is bulged in the middle 5 and has two cylindrical ends 6a and 6b. It is held in the outer bulb 1 by means of two power leads 7, which are connected to the base parts 3 via foils 8. The power supply lines 7 are welded to bushings 9, 10 which are each fitted in an end plug 11 at the end of the discharge vessel.

The bushings 9, 10 are cermet pins with a diameter of approx. 1 mm, which consist of an electrically conductive cermet.

Both bushings 9, 10 extend over the entire length of the plug 11 and hold electrodes 14 on the discharge side, consisting of an electrode shaft 15 made of tungsten and one pushed on at the discharge end Spiral 16. The bushing 9, 10 is in each case with the electrode shaft 15 and butt welded to the external power supply 7.

The discharge vessel is filled with an inert ignition gas, e.g. Argon, and possibly mercury from additions to metal halides, thereof at least one rare earth metal.

End plugs 11 are used as means for sealing, which essentially consist of Al ₂ O ₃ , for example. It is also possible to use a non-conductive cermet with the main component Al ₂ O ₃ , with tungsten being present as a metallic component in a proportion of approximately 30% by weight (or molybdenum with a correspondingly higher proportion).

The bushing 9, 10 is sintered directly into the plug 11. More like that The plug 11 is also in each case in the cylindrical end 6 of the discharge vessel sintered directly (i.e. without glass solder or melting ceramic).

At the second end 6b there is also an axially parallel bore 12 in the plug 11 provided for evacuating and filling the discharge vessel in a known manner Way serves. This bore 12 is made after filling by means of a pin 13 or closed by means of melting ceramic. The pen usually consists of Ceramics or cermet.

For example, a cermet pen is suitable as bushing 9, 10, which in addition to ceramic phase with the base material aluminum oxide at least 44 vol .-% Contains metal (preferably between 45 and 75 vol .-%) and is electrically conductive. In particular 70 to 90% by weight of tungsten or 55 to 80% by weight of molybdenum is suitable (or an amount of rhenium equivalent in volume). The ceramic Phase consists entirely of garnet (see below).

A cermet with a lower percentage is suitable as the material for the end plug of metal as the feedthrough (preferably about half the proportion in the Implementation) contains. An essential property of the plug is that coefficient of thermal expansion between that of implementation and that of Discharge vessel is. The metal content of the stopper can also be zero.

The electrode is welded to the end face of the bushing before the bushing is sintered into the stopper. The weldable cermet pin is largely pre-sintered before it is finally sintered. Using the metal halides in the filling, a neutral white light color (HPS) is achieved (color temperature approx. 4300 K) with the participation of the following components (in% by weight):
9.0% TIJ; 32.5% NaJ; 19.5% each of the rare earth iodides Dy ₂ J ₃ , Ho ₂ J ₃ and Tm ₂ J ₃ .

The proportion of rare earth metal ions (in% by weight) was accordingly in the filling at the beginning:
Dy ³⁺ 5.8% and Ho ³⁺ 5.9% and Tm ³⁺ 6.0%.

A comparison was made between identical lamps with different compositions Cermet sticks performed, with a conventional one in the control group Cermet stick was used (only alumina as the ceramic phase). The cermet sticks according to the invention additionally used rare earth oxides.

By reaction with the filling, a stable structure corresponding to the chemical compound with 62.5 mol% (30.9% by weight) of aluminum oxide, 9.6 mol% (17) was formed during operation in the part of the conventional cermet stick near the electrodes , 4 wt%) dysprosium oxide, 11.5 mol% (21.1 wt%) holmium oxide and 16.4 mol% (30.6 wt%) thulium oxide, which is a garnet of chemical Formula 0.77 Dy ₂ O ₃ • 0.92 Ho ₂ O ₃ • 1.31 Tm ₂ O ₃ • 5 Al ₂ O ₃ . A total of 22% of the Dy contained therein, 27% of the Ho and 38% of the Tm was removed and stored in the cermet.

In the converted ceramic of the conventional cermet component, the rare earth ion with the smallest effective ion radius, namely Tm (about 0.088 nm ion radius, see Fig. 2), accumulated significantly more than the other two:
Dy ³⁺ 15.2% by weight; Ho ³⁺ 18.4 wt% and Tm ³⁺ 26.8 wt%.

So while in the filling the three rare earth metals in approximately the same concentration is contained in the cermet component - apparently because of the different Ion radii - the Ho diffuses in by 22% and the Tm by 77% more than the dy. It is extremely surprising that such small differences in the ionic radius can have such drastic consequences.

In a first exemplary embodiment of the invention, a cermet component was used, that from the outset as the ceramic phase, for example the natural one Equilibrium distribution used and thus anticipates this diffusion process:

31% by weight of aluminum oxide, 15% by weight of dysprosium oxide, 20% by weight of holmium oxide and 34 wt% thulium oxide.

In a second exemplary embodiment, a regular garnet was used as the ceramic phase for this cermet component, using only Tm ₂ O ₃ as the rare earth oxide with aluminum oxide as the base material.

The result was almost equivalent. The effective lifetimes of both Exemplary embodiments could be compared to the control group by more than one Factor of 1.5 can be increased. As expected, the first embodiment cut about 10% better than the second (since small amounts of the other rare earth metal ions diffused into the cermet), but this is relative slight improvement is not always justified by the significantly higher costs.

In a third exemplary embodiment, Sc ₂ O ₃ (or also Yb ₂ O ₃ ) is used as the rare earth metal oxide. Both ions have a smaller ion radius (0.075 or 0.087 nm) than the rare earth metal ions used in the filling. The life span achieved in this way corresponds approximately to that of the second exemplary embodiment.

In a second embodiment (Fig. 3) is at the ends of the approximately circular cylindrical Discharge vessel 25 each sintered a non-conductive plug 26 directly. The implementation is an electrically conductive cermet pin 9, 10 with a Metal content of 50% by volume. The rest is a ceramic phase. The plug 26 out Aluminum oxide consists of two concentric parts, an outer annular one Plug part 21 and an inner, about twice as long capillary tube 20. Nevertheless the capillary tube is about 50% compared to known capillary tube techniques , shorter. The large length of the capillary tube compared to the plug part 21 improved the sealing behavior. The cermet pin 9 is recessed in the capillary tube 20 and sintered there directly. The filling bore 22 is in the outer plug part 21 accommodated.

Since the cermet pin is used in a recessed manner, an Eu ₂ O ₃ perovskite structure is used as the ceramic phase only on its end face 19 over an axial length of approximately 1 mm, which gradually changes into the known structure with a pure aluminum oxide phase in a subsequent transition zone, which is used at the end of the pen.

Figure 4 shows a cermet pin 27, which is composed of two parts. The front front part 28 has a garnet structure as a ceramic phase with aluminum oxide as the base material and Er ₂ O ₃ as the rare earth oxide. It has an axial nose 29 with which it is fitted into a circular cylindrical bore of an extension part 30 arranged behind it. Both parts are connected by direct sintering.

Alternatively, both parts of the cermet pin 31, the cermets of which can be welded by the proportion of the metallic phase (Mo) being approximately 50% by volume, can be butt-welded to one another, as shown in FIG. 5. The front part 32 and the extension part 33 are approximately the same length. For the front part, YAG (yttrium aluminum garnet, 3 Y ₂ O ₃ • 5 Al ₂ O ₃ ) is used as a ceramic phase for a 500 µm wide zone on the front and the lateral surface. It has been found that effective protection against the diffusion of the rare earth metals from the filling into the cermet requires a zone of at least 200 µm in thickness. Good results are achieved with a thickness between 200 and 700 µm, provided that.

FIG. 6 shows a further exemplary embodiment in which the end of the cylindrical ceramic discharge vessel 40 (made of aluminum oxide) is closed by a ceramic end plate 41 and a tubular plug 42. A two-part bushing 43 is sealed by means of glass solder 44 in the stopper. The bushing 43 consists of a cermet pin 45 on the discharge side and a niobium pin 46 facing away from the discharge. The electrode 47 is fastened to the cermet pin. The surface of the cermet stick is covered by a 300 μm thick layer 48 of YAG. The conductive phase (60 vol.%) Of the cermet stick consists of MoSi ₂ , the ceramic phase (rest) consists of 50 mol.% Al ₂ O ₃ and 50 mol.% Of a mixture of YAG and Eu ₂ O ₃ - perovskite. The filling contains DyJ ₃ and CeJ ₃ as rare earth metal iodides.

Claims (13)

1. Metal halide lamp with a ceramic discharge vessel (4), the discharge vessel having two ends (6a, 6b) which are each closed off by sealing means, and in each case one electrically conductive lead-through (9, 10; 30) being guided through these means in a vacuum-tight manner, to which lead-through an electrode (14) is attached, which electrode projects into the interior of the discharge vessel, at least a front part (45) of the lead-through, which part faces toward the discharge, being designed as a halide-resistant component made from electrically conductive cermet which is composed of a first electrically conductive phase and a second ceramic phase, which comprises a ceramic base material, and the fill comprising at least one rare-earth metal including the metals yttrium and scandium, characterized in that at least at a surface (28; 32) of the cermet component which is accessible to the fill, at least some of the ceramic phase comprises the combination of the ceramic base material with one or more rare-earth metal oxides.
2. Metal halide lamp according to Claim 1, characterized in that the component made from cermet is in the form of a cermet pin (9, 10).
3. Metal halide lamp according to Claim 1, characterized in that the cermet contains, as the electrically conductive phase, molybdenum or tungsten or rhenium or their alloys or MoSi₂.
4. Metal halide lamp according to Claim 1, characterized in that in the entire component, part of the ceramic phase comprises the combination of the ceramic base material and one or more rare-earth metal oxides.
5. Metal halide lamp according to Claim 1, characterized in that the entire ceramic phase consists of the combination of the ceramic base material and one or more rare-earth metal oxides.
6. Metal halide lamp according to Claim 1,
   characterized in that the ceramic base material is aluminium oxide.
7. Metal halide lamp according to Claim 1, characterized in that the rare-earth metal oxides comprise the oxides of some or all of the rare-earth metals which are contained in the fill.
8. Metal halide lamp according to Claim 1, characterized in that the rare-earth metal oxides comprise the oxides of one or more rare-earth metals which are not contained in the fill, in particular Y₂O₃.
9. Metal halide lamp according to Claim 1, characterized in that the combination of the ceramic base material and the one or more rare-earth metal oxides corresponds to a garnet or perovskite or a mixture of the two.
10. Metal halide lamp according to Claim 1, characterized in that the rare-earth metal oxides used are predominantly or exclusively the oxides of rare-earth metals with the smallest possible ionic radius, in particular with an ionic radius which is less than or equal to the ionic radius of rare-earth metals contained in the fill.
11. Metal halide lamp according to Claim 1, characterized in that the fill contains the rare-earth metal as a halide.
12. Metal halide lamp according to Claim 1, characterized in that the sealing means (20) comprises ceramic or cermet, the ceramic base material of the cermet component (9) corresponding to a principal ceramic constituent of the sealing means.
13. Metal halide lamp according to Claim 1, characterized in that the surface is situated on the front side and, if appropriate, on the lateral surface of the cermet component.

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