EP1805785B1 - Incandescent lamp having an illuminant that contains a high-temperature resistant metal compound - Google Patents

Abstract

The invention relates to an incandescent lamp (1) which is provided with an illuminant (7) which is inserted in a bulb (2) together with a filling in a vacuum-tight manner, the illuminant (7) comprising a metal carbide that has a melting point above that of tungsten. The bulb also comprises a source and a sink for a material of which the illuminant is depleted during use.

Description

Technical area

The invention relates to an incandescent lamp with a luminous body containing a high-temperature-resistant metal compound, according to the preamble of claim 1. It is in particular bulbs with a carbide-containing filament, in particular the invention relates to halogen incandescent lamps having a luminous body of TaC, or whose luminous body TaC contains as a component or coating.

State of the art

From many writings, an incandescent lamp with a luminous element containing a high temperature resistant metal compound is known. A still unresolved problem is the severely limited lifetime. An in WO-A 01/15206 option shown is to connect the lamp with a separate frame for mounting.

A common method of solving the problem of preventing vaporization of filament material is by using circular processes. In this case, the filling gas, a further chemical substance is added, which reacts in colder areas with the evaporated material to a relatively volatile compound, which does not deposit on the bulb wall. This compound is transported in the build-up concentration gradient - namely high concentration near the bulb wall, low concentration near the filament - in the direction of the filament. At the high temperatures near the filament, it decomposes to decompose into the material of the filament and the added chemical substance; the material of the filament is attached to this again.

Examples: (a) Tungsten-halogen cycle process

The tungsten evaporating from the filament combines at lower temperatures near the bulb wall to tungsten halides, which are volatile at temperatures above about 200 ° C and do not deposit on the bulb wall. This prevents a tungsten failure on the bulb wall. The tungsten halide compounds are transported back by diffusion and possibly also convection to the hot filament, where they decompose. The freed tungsten is again attached to the filament. However, the tungsten i.allg. not transported back to the same site from which it has evaporated, but deposited at a location of different temperature, i. the cycle is not regenerative. An exception is the fluorine cycle.

(b) Carbon-hydrogen cycle in TaC lamps

The gaseous carbon formed upon decomposition of the TaC is transported towards the bulb wall, where it reacts with hydrogen to form hydrocarbons such as methane. These hydrocarbons are transported back to the hot filament, where they decompose again. The carbon is released again and can attach to the filament. However, at low temperatures, the hydrocarbons decompose below 1000 K, so that the return of carbon is not targeted to the hottest spots of the filament.

If, as in the last-described example, the evaporation from the luminous element is relatively strong and the compound carrying the cyclic process is stable only at very low temperatures, such as the hydrocarbons in the last example, the luminous body will be rapidly destroyed, because it will rapidly attack the evaporating material like carbon impoverished in the last example. Overall, the carbon is relatively fast from the hottest points of the filament to the colder places of the filament or the outlets transported to the luminous body, which can also cause problems, for example by Windungsschluss. Only a very small proportion of the transported back carbon reaches the hottest point of the helix (very low degree of regeneration). In addition, the back reaction of the carbon with the hydrogen to hydrocarbons proceeds in any case only with a relatively large excess of hydrogen sufficiently fast, so that a blackening of the piston is avoided.

1. (a) erstens das Material vom Leuchtkörper relativ schnell abdampft bzw. abtransportiert wird,
   und
2. (b) zweitens das abgedampfte Material nur bei sehr niedrigen Temperaturen eine chemische Verbindung eingeht,
   für viele Anwendungsfälle nicht ausreichend, weil wegen der nur sehr geringen Rückführung von Material zur den Stellen, von denen es abtransportiert wurde, der Leuchtkörper schnell zerstört wird.

In summary, in such cases as in the case of the TaC lamp, the use of a cyclic process in which:

1. (a) firstly the material evaporates or is removed relatively quickly from the luminous element,
   and
2. (b) second, that the evaporated material forms a chemical compound only at very low temperatures,
   not sufficient for many applications, because because of the very low return of material to the bodies from which it was removed, the luminous body is destroyed quickly.

As a way to solve the problem is in WO-A 03/075315 described the regeneration of the filament out of a depot out. From the depot continuously evaporates a chemical substance, which supplies the luminous body that substance to which it is depleted again. For example, it describes how a TaC luminous body is regenerated from a polymer impregnated with an organic compound (eg acetone). The gas phase is permanently supplied with a chemical compound, which also contains carbon; In this case, carbon is provided continuously, which can replace the evaporated by the filament carbon again. The disadvantage here is that changes the composition of the gas phase and the luminous body continuously by the permanently supplied chemical compound; a lamp operation in stable conditions is hardly possible. The concentration of carbon in the gas phase is constantly increased, which eventually leads to the deposition of carbon in inappropriate places such as the ends of the luminous element or finally the bulb wall. An enrichment of carbon in the luminous body is not desirable because it changes the properties of the filament continuously. An enrichment of hydrogen in the gas phase leads by increasing the heat conduction to an increasing cooling of the filament.

In summary, a stable operation of a lamp with a continuously evaporating from a depot chemical compound is not possible because the composition of the gas phase and possibly also the filament itself change continuously.

Another option is in the WO patent 03/075315 describes the mutual regeneration of two alternately operated luminous body. This evaporates from a at high temperatures (over 3000 K) operated "active" luminous body permanently from carbon and is transported to a second at relatively low temperatures (at or below 2000 K) operated "inactive" filament, where it separates or attaches , Is the "active" filament depleted of carbon, it is switched; the previously "inactive" filament is operated at high temperature and the previously "active" filament is kept at low temperature. The now "inactive" filament is regenerated by the "active" carbon-evaporating filament. This is disadvantageous in that one needs two luminous bodies, between which must be constantly switched.

Presentation of the invention

It is an object of the present invention to provide an incandescent lamp with a luminous body, which contains a high-temperature-resistant metal compound, and in particular a carbide-containing luminous body, or even a metal, according to the preamble of claim 1, which allows a long life and the problem overcomes the depletion of the filament on a evaporating component.

These objects are achieved by the characterizing features of claim 1. Particularly advantageous embodiments can be found in the dependent claims.

The term high temperature resistant metal compound means compounds whose melting point is near the melting point of tungsten, sometimes even higher. The material of the luminous body is preferably TaC or Ta ₂ C. However, carbides of Hf, Nb or Zr and, moreover, alloys of these carbides are suitable. Further, nitrides or borides of such metals. Common to these compounds is the property that a luminous body made of this material depletes in operation on at least one element. However, the principle described below is equally applicable to filaments of metals. The term metal compound used below is therefore not to be understood as limiting, but by way of example. The statements made therein are analogously applicable to metals.

If a lamp is operated at high temperatures, it comes - depending on the nature of the material of the filament - to evaporate material or components of the material. The evaporated material or its constituents are replaced by e.g. Convection, diffusion or thermal diffusion removed and deposit elsewhere in the lamp, e.g. on the bulb wall or frames. The evaporation of the material or its components leads to a rapid destruction of the filament. Due to the material which separates on the bulb wall, the transmission of the light is greatly reduced.

Examples:

1. (a) The tungsten evaporating from a tungsten filament is transported to the bulb wall in a conventional incandescent lamp and deposits there.
2. (b) A tantalum carbide flare operated at high temperatures decomposes to form the brittle Ta ₂ C subcarbide melting at lower temperatures relative to TaC and gaseous carbon which is transported to and settles to the flask wall.

The task is to minimize by appropriate measures evaporation from the lamp or to undo.

In order to avoid a depletion of the filament on the evaporating component, such a concentration of the evaporating component is adjusted from the outside, that in the ideal case, evaporation and sublimation keep the balance and the filament is thus neither depleted nor enriched in the component in question. The adjustment of the required concentration over the luminous element is to be realized by a continuous transport of a substance containing the component in question from a source into a sink. The continuous deposition of the material supplied from the source avoids a change in the composition of the gas phase and enables operation of the luminous element under constant conditions.

In one possible design of a lamp with TaC filament, the source of a solid, or liquid, hydrocarbon, which is introduced into the lamp so that builds up on the source material, a certain vapor pressure of gaseous hydrocarbon. This hydrocarbon is transported by diffusion or convection into the interior of the lamp, where it decomposes at higher temperatures near the filament. The luminous body is thus in a carbon-enriched atmosphere; a decomposition of the filament is thereby prevented. Ideally, the filament does not emit carbon to the environment, nor is carbon enriched in it. In other words, a balance between carbon deposition and carbon evaporation sets in the luminous body. At lower temperatures near the bulb wall, the carbon reacts again Back to hydrogen hydrocarbons. At a suitable temperature attached wire, for example, from one of the materials iron, nickel, cobalt, platinum or molybdenum sufficiently large surface, the hydrocarbon decomposes with deposition of solid carbon (soot). This process corresponds approximately to the cracking of hydrocarbons in suitable catalysts known from the technical chemistry, in which case - in contrast to the reaction regime in plants of the chemical industry - the deposition of carbon on the catalyst is desired. Overall, therefore, carbon continuously exits from one source and is re-deposited in a sink. The filament of the lamp is thus neither enriched in carbon, nor depleted of carbon; In addition, the carbon concentration in the gas phase is kept constant.

The hydrogen can preferably be used analogously. As a hydrogen sink, the permeable quartz piston wall acts at high temperatures. At lower temperatures, the resulting hydrogen can be trapped by iodine (reaction to hydrogen iodide, the resulting hydrogen iodide is not critical to its effect on the maintenance of the lamp, because it does not interfere with the chemistry of the metal carbide nor the physical properties of the filler gas (especially the thermal conductivity Another way of attaching the released hydrogen (ie, a sink of hydrogen) is to use metals such as zirconium or hafnium or niobium or tantalum, which "getter" hydrogen at appropriate temperatures.

It should be pointed out again that the existence of a sink is important to the functionality of the lamp. In the absence of sinks for carbon and hydrogen, either the gas phase or the luminous body would accumulate on the respective element; the consequence of this would be a change in the operating data of the lamp.

In particular, the transport processes described in the last paragraphs can still be superimposed by one or more cycle processes.

If, for example, in a lamp with a luminous body made of TaC carbon is transported continuously - in part in the form of hydrocarbons - from a source to a sink, this transport process by adding a halogen-containing compound, a tantalum-halogen cycle can be superimposed, which the of Filament evaporated tantalum prevents the deposition on the piston wall and at least partially transported back to the filament, as in the unpublished application DE-Az 103 56 651.1 described. These are expressly referred to. Furthermore, it is conceivable for a TaC lamp to superimpose a carbon cycle process on the described permanent transport of carbon from a source into a sink, for example a CH, C-halogen, CS or CN cycle process as in the application DE-Az 103 56 651.1 described.

The sinking metals may be e.g. in the form of wires or plates welded to the frame or the power supply, or wound as a coating coil directly around the power supply, or e.g. in the form of wires to be squeezed directly. It is essential in particular when using catalytically active metals as sinks that the surface of these metals is sufficiently large, since the surface is continuously covered with carbon ("poisoning" of the catalyst) in order to obtain the effectiveness of the catalyst. Also, the coating of Wendelabgängen or power supplies with serving as a sink metals is another embodiment.

In another embodiment, elemental carbon is used as the source of carbon. This may be present, for example, in the form of carbon compacts, graphite fibers or carbon black deposited on a substrate, diamond in the form of DLC or graphite. The carbon is maintained at a "medium" temperature, which must be just enough so that the resulting vapor pressure of the carbon at the location of the hot filament results in a carbon partial pressure which is approximately equal to the carbon equilibrium vapor pressure above the tantalum carbide. Thus keep the luminous body of tantalum carbide carbon deposition and carbon evaporation equilibrium; a Dekarburierung the filament is avoided. If the carbon reaches colder areas near the bulb wall, it reacts with hydrogen or halogens to (possibly halogenated) hydrocarbons; This prevents the deposition of carbon on the piston wall. The decomposition of the hydrocarbon then takes place on a catalyst, in which case the carbon deposits on the surface of the catalyst and the hydrogen is liberated again. In this case, you do not need a sink for the hydrogen or possibly the halogen, which indeed prevent only the deposition of the carbon on the piston wall and transport the bonded in the form of hydrocarbon carbon to the catalyst. The hydrogen or optionally the halogen thus serves only as a means of transport to transport the carbon and is not consumed. Overall, in this case, carbon is transported from the carbon source (carbon compact, graphite fibers, diamond such as DLC, graphite layers, carbon black, etc.) to the carbon sink (eg, nickel, iron, molybdenum wire) where it deposits again.

In one embodiment of the carbon source, the carbon is deposited on a few turns of the filament metal carbide filament. Preferably, the carbon deposition takes place on the outer turns of the coil at lower temperatures than in the middle of the filament. Since the vapor pressure over pure carbon is greater than the carbon vapor pressure over tantalum carbide, the source of pure carbon is attached at lower temperatures than the hot coil center. As a result, as far as possible the carbon equilibrium vapor pressure over the middle of the hot coil should be set and achieved that no carbon-transporting gradient of the carbon partial pressure is produced via the luminous body.

The last described approach is also useful for circumventing problems related to the relatively low impact strength of the tantalum carbide during transport of the lamps to the customer. One option for circumventing this problem is to complete the carburization only after the lamps have been transported to the customer during the firing process and initially to leave at least one tantalum core in the TaC luminous element. In order to complete the carburization at the customer then, you have to perform the burning of the lamp not yet completely durchkarburierten luminous body large amounts of carbon. If you store these large amounts of carbon in the form of gaseous hydrocarbons in the gas atmosphere or in the form of continuously evaporating solid hydrocarbons, the carburization reaction very large amounts of hydrogen are released, which then have a negative effect on the efficiency of the lamp because of the increase in thermal conductivity. Also, because the reaction with the hydrocarbon is not complete, the large amounts of carbon released that must be held in the gas phase also present a problem. This problem can be overcome in the manner described by leaving the incompletely fully carburized luminescent body is located in a continuous stream of carbon from a source of carbon. The non-carburizing carbon reacts with hydrogen to form hydrocarbons, thereby preventing the deposition of carbon on the piston wall. The hydrocarbon eventually decomposes back to a catalyst, depositing the unneeded carbon and liberating the hydrogen. It comes with a relatively small amount of hydrogen, because it is not consumed, but only serves to transport the carbon to the carbon sink. In particular, the amount of hydrogen remains constant and does not increase permanently during carburization. If the permeability of the hydrogen can no longer be neglected at high piston temperature, in particular in the case of a quartz glass flask, then the hydrogen can be replaced by the hydrogen Use of iodine near the piston wall to be intercepted and stabilized as hydrogen iodide.

Another way to realize a carbon source is to use a tantalum carbide coated carbon fiber. At high operating temperatures, the carbon diffuses through the tantalum carbide layer; a depletion of the Tantalkarbidschicht of carbon is thus avoided. However, the carbon released thereby into the gas space leads to a rapid blackening of the piston wall, if no countermeasures are taken. By trapping the carbon with hydrogen, blackening of the bulb can be prevented if the bulb temperatures are not too high. However, very large amounts of hydrogen are needed to "catch" the carbon as completely as possible before its deposition on the bulb wall. This can be avoided by decomposing the hydrocarbon at a catalyst maintained at a suitable temperature, eg a wire of nickel, iron, etc. Here, the carbon is deposited on the nickel wire, while the hydrogen is released again and is available for reaction with more carbon available. Thus, the hydrogen serves only as a "vehicle" to intercept carbon transported by the luminous body by the formation of hydrocarbon and to transport it to the carbon sink (eg wire made of nickel, molybdenum, etc.). Overall, no hydrogen is consumed in this transport mechanism, ie it comes with a relatively small amount of hydrogen. If one would alternatively implement a cyclic process, one would have to use very large amounts of hydrogen in order to trap the transported in large concentration by the filament carbon by formation of hydrocarbons or build such a high concentration of hydrocarbons near the bulb wall that the return of carbon to the Luminous body exactly compensates for the removal. Using such large amounts of hydrogen would greatly reduce the efficiency of the lamp. As a further possibility of the embodiment of a source, it makes sense to coat the filament with the material to which it is depleted and which is to be supplied from a source again, and then again a layer of the actual filament material from the outside on this layer applied. If a luminous element eg consists of a metal carbide such as tantalum carbide or hafnium carbide, a layer of carbon is deposited on the surface of the filament of metal carbide. On this layer of carbon, a layer of a metal carbide is then applied again. When carbon from the outer metal carbide layer evaporates during lamp operation, carbon immediately diffuses from the inside of the enclosed carbon layer and prevents depletion of the outer metal carbide layer of carbon. In this regard, the operation is quite similar to that of a metal carbide coated carbon fiber. In this approach, however, is of advantage that in the manufacture of the luminous body can be used largely established in halogen lamp process technology. The application of the carbon coating is carried out, for example, according to a CVD method in the stud lamp, for example by decomposition of methane (1 bar pressure) at a temperature of about 2,500 K on the filament. The application of the metal carbide outer layer is carried out in the CVD method, for example, by simultaneous thermal decomposition of metal halides such as tantalum halide and methane; Of course, it is also possible to use other metal compounds or hydrocarbons as precursor. By setting suitable stoichiometric ratios of the starting compounds, the metal carbide can then be deposited directly on the surface of the luminous element, eg according to TaCl ₅ + CH ₄ + x H ₂ -> TaC + 5 HCl + (x - ½) H ₂ . The hydrogen serves here to avoid the deposition of soot. It is also possible to deposit only the metal on the carbon surface of the filament and then to react (ie carburize) in an atmosphere containing, for example, methane, carburizing from the outer carbon-containing atmosphere and from the inside from the carbon layer starts. A disadvantage of this method, however, is that the volume change occurring in the transformation of the metal into metal carbide causes relatively large layer stresses. Therefore, a simultaneous deposition of the metal and the carbon in the stoichiometric ratio is advantageous.

In the latter embodiment, the materials of the inner material (e.g., wire) of metal carbide and the outer layer of metal carbide need not necessarily be identical. For example, For example, the inner wire may be tantalum carbide, while the outer layer applied to the carbon layer may be hafnium carbide or HfC-4TaC alloy. HfC or the alloy HfC-4TaC has lower vapor pressures than pure tantalum carbide. However, since hafnium is significantly more expensive than tantalum, the amount of hafnium used can be significantly reduced in this way.

As a further source of carbon, sintered materials with carbon come into consideration, such as in US 3,405,328 described. It describes how metal carbides such as tantalum carbide with dissolved carbon can be produced by sintering processes at high temperatures and high pressures in autoclaves. These materials, which are to serve as the filament material, then contain significantly more carbon than is to be expected according to the stoichiometry of the TaC. The patent also describes the use of mixtures of various carbides in order to increase the impact strength of the filament.

Further options for carbon sinks are metals such as tungsten, tantalum, zirconium, etc., which form carbides at suitable temperatures. The operating temperature of these metals depends in particular on the flow of carbon coming from the luminous element; Common temperatures are in the range between 1800 ° C and 2500 ° C. Hydrogen is preferably used in the use of these metals in order to prevent the carbon from being deposited on the bulb wall and to form carbon. Sink to transport. If one were to forego the hydrogen, then the carbon transported by the luminous body would - if it does not accidentally strike the carbide-forming metal on its way from the luminous body - deposit on the bulb wall. With additional use of hydrogen, the carbon first reacts with the hydrogen to form a hydrocarbon, such as methane, which then decomposes back to the carbide-forming metal to transfer the carbon to the carbide-forming metal and release the hydrogen.

Other possible catalysts for the decomposition of hydrocarbons are aluminum, molybdenum or magnesium silicates.

Another possibility for use as carbon source is the use of tantalum carbide or other carbides. If, for example, a rod of tantalum carbide not flowed through by the current is brought to a temperature corresponding to the luminous element, then the suitable equilibrium vapor pressure of carbon is established above the tantalum carbide, in which vaporization or deposition of carbon no longer takes place on the luminous element. This can be achieved, for example, by introducing a rod / wire made of tantalum carbide inside on the axis of a spiral of tantalum carbide (analogous to a coil with internal feedback, as it is used for IRC lamps, in the case of the metal carbide but the wire on the coil axis is not traversed by the current), wherein the turns of the current-carrying TaC wire coil must not touch the non-current rod made of TaC to avoid a short circuit. The rod must be at virtually the same temperature as the adjacent turns. It must under no circumstances be significantly colder than the adjacent windings, ie the heat dissipation along the rod must be limited - for example, by choosing a sufficiently small diameter. Above the rod, an equilibrium vapor pressure of carbon is established. The carbon becomes in the radially outward concentration gradient at the current carrying TaC Wendeln transported over to the piston wall. The individual turns of the TaC helix are therefore in a constant stream of carbon, with the carbon partial pressure corresponding to the equilibrium pressure across the helices. The carbon transported to the outside reacts again with hydrogen near the bulb wall to form hydrocarbons, which then decompose on a suitable catalyst as described above, with deposition of carbon and liberation of hydrogen. Overall, therefore, carbon is transported from the rod of TaC on the axis of the helix past the turns of the TaC helix to the carbon sink, the carbon partial pressure approximately corresponding to the carbon equilibrium pressure at the individual windings and thus stabilizing the turns made of TaC become. In other words, the carbon which evaporates from the individual turns of the TaC helix and is transported outwards is replaced from the inside by the carbon which evaporates from the TaC rod. The advantage of using a rod of TaC over the use of a rod of pure carbon, for example, is that at the same temperature the carbon vapor pressure over pure carbon is orders of magnitude higher than that over tantalum carbide, thus unnecessarily high carbon transport would be required produce and sometimes even deposit carbon on the TaC helix. The advantage of using a TaC rod on the helix axis whose temperature profile corresponds as closely as possible to that of the helix is that the carbon equilibrium pressures, which prevent decomposition of the luminous body, are then automatically adjusted at the individual turns of the TaC helix.

As a source of carbon in addition to the carbon itself and carbon-hydrogen compounds and compounds of carbon with other elements into consideration.

Advantageously, for example, carbon and fluorine-containing polymers can be used, as they arise, for example, in the polymerization of tetrafluoroethylene C ₂ F ₄ (eg polytetrafluoroethylene PTFE, brand name "Teflon" at the company DUPONT). In the decomposition of these compounds are formed in the gas phase compounds such as CF ₄ , C ₂ F ₄ , etc. which decompose only at very high temperatures near the filament and thereby release carbon and fluorine. The advantage here is that the carbon is released especially or practically exclusively at high temperature sites. The carbon is thus transported specifically to locations of high luminous body temperature. Because of the targeted reflux to higher temperature sites can be used here with relatively low flows of carbon or relatively low partial pressures of gaseous CF compounds. The liberated fluorine reacts on the wall to form gaseous SiF ₄ , which then scarcely intervenes in the reaction process and also does not have a negative effect on the efficiency of the lamp, such as hydrogen, because of increased heat conduction. The released carbon can again - unless it is used up in the wall reaction with CO formation - first bound by a transport partner such as chlorine in colder areas and then decomposed on a hot metal wire, the carbon is deposited again and the chlorine is released (carbon sink). Since in the wall reaction two F atoms release an O atom and in polytetrafluoroethylene in about two F atoms a C atom comes, the carbon is largely reacted with the liberated in the wall reaction oxygen to CO.

The present invention is particularly suitable for low-voltage lamps with a voltage of at most 50 V, because the necessary filament can be made relatively solid and for the wires preferably a diameter between 50 microns and 300 microns, especially at most 150 microns for general lighting purposes with maximum power of 100 W, exhibit. Thick wires up to 300 μm are used in particular for photo-optical applications up to a power of 1000 W. Particularly preferably, the invention is used for one-sided squeezed lamps, since the luminous body can be kept relatively short, which also reduces the susceptibility to breakage. But the application to double-sided squeezed lamps and lamps for mains voltage operation is possible.

The term rod as used herein means a means formed as a solid rod or, in particular, a thin wire.

The described concept can be applied in a variety of ways to special chemical transport systems. In a specific embodiment, it is used for a design of a carbon-sulfur cycle. As described in DE Az 10358262.2 CS decomposes only at temperatures well above 3000 K, the degree of dissociation of CS increases strongly with increasing temperature. Thus, the CS cycle process is suitable for transporting the carbon back to the hottest point along the helix, thus slowing down or preventing the formation of "hot spots". When using this CS system, it should now be taken into consideration that the compound CS transporting the carbon in the high-temperature region is disproportionated at temperatures below about 2200 K according to 2 CS -> CS ₂ + C, whereby carbon is deposited on the frame or on the helical outlets. If, on the other hand, CS ₂ is transported back to higher temperature sites by diffusion or through the flow, it decomposes into CS and sulfur at T> 2200 K, the sulfur acting in a decarburizing manner on the metal carbide luminous body. Therefore, it is advantageous to coat the filament or its outlets in the range above 2200 K with a carbon layer. The sulfur atoms liberated in this temperature range then react with the carbon to CS; a decarburization of the metal carbide filament is avoided. Over the life of this carbon coating is used up slowly. On the other hand, carbon is released and deposited at lower temperatures below about 2200 K in the disproportionation of the CS. In summary, the CS system thus transports the carbon from places of higher temperature with T> 2200K to places of lower temperature with T <2200 K. Without the reservoir of carbon for T> 2200 K (source) or the deposition of carbon at T <2200 K (sink), it is difficult to achieve stationary operating conditions.

The methodology described here can also be applied to incandescent bodies of materials other than metal carbides, borides or nitrides. As an example, an application to pure metals such as tungsten is described below. To generate a life-prolonging regenerative cycle in which "hot spots" are cured on the luminous body, in the literature, the fluorine cycle described, cf. eg (a) J. Schröder, Kino-Technik no. 2, 1965 , (b) Dittmer, Klopfer, Rees, Schroder, JCS Chem. Comm, 1973 , The regenerative effect of the fluorine cycle process is based on the fact that tungsten fluorides decompose only at temperatures above about 2500 K, with the tungsten is preferably deposited again at the hottest points. An essential difficulty in the use of fluorine is that fluorine reacts on the bulb wall to Silliciumtetrafluorid SiF ₄ , where in addition still oxygen is released. The fluorine bound in the SiF ₄ is no longer available for further reaction in the halogen cycle. Therefore, several possibilities for passivating the bulb wall are mentioned in the literature, cf. eg Schröder, PHILIPS Techn. Rundschau 1963/64, p. 359 on the use of Al ₂ O ₃ . Another possibility arises when using the concept discussed here. For this purpose, high molecular weight compounds of carbon and fluorine such as polytetrafluoroethylene are used as fluorine source. These compounds decompose slowly at higher temperatures, forming low molecular weight carbon and fluorine containing species in the gas phase. Liberated fluorine reacts on tungsten surfaces in the temperature range between approx. 1600K and 2400K to form tungsten fluorides. Frame parts or spiral outlets of tungsten present at appropriate temperatures are therefore preferably thickened in order to be able to provide the cycle with sufficient tungsten. The tungsten fluorides thus formed are transported to higher temperature sites where they preferentially decompose at higher temperature sites. Thus, tungsten is deliberately transported back to the hottest places of the filament. Upon impact of fluorine or fluorine-containing compounds on the glass wall of the bulb, fluorine reacts to form SiF ₄ and is therefore not available for further participation in chemical transport reactions. The wall reaction also releases oxygen. Since in the polytetrafluoroethylene on two fluorine atoms, a carbon atom and in the wall reaction each release two fluorine atoms an oxygen atom, stoichiometrically, the released in the wall reaction oxygen can be completely gegettert by the carbon to CO. Since liberated carbon is usually otherwise bound, for example in the form of carbides, the gettering of the oxygen by the carbon is usually not complete. If necessary, therefore, other getters such as phosphorus must be used. The tungsten fluorides formed at the tungsten reservoir do not become convective or diffuse completely transported in the direction of the luminous element or not fully implemented there; a part is transported in the direction of the piston wall. There, the tungsten fluorides decompose at least in part, releasing fluorine, which reacts with the wall in the manner described, and tungsten. In order to avoid blackening of the lamp bulb, the simultaneous use of bromine is recommended. As a result, tungsten (oxy) bromides can be formed and the bulb wall is kept clean. The tungsten oxybromides decompose at temperatures far below those of the filament. That is, the tungsten bound in them is mainly deposited on the frame or the Wendelabgängen., This superimposed W-Br (-O) cycle process is thus not regenerative, it serves only to keep the lamp bulb clear.

The basic principle described here - the continuous transport of a substance from a source into a sink - can be applied in two other embodiments, which are not part of the invention, but also examples, which are only to facilitate the understanding of the invention, on the means of transport is used to keep the piston clear as well as the return of material to the filament. Here, the situation may arise that either the transport means is continuously removed by reaction or absorption with parts of the frame or the piston wall of the gas phase (sink), or that it is continuously introduced by desorption or chemical reaction in the gas phase (source). In order to achieve stationary conditions in the gas phase, it is therefore recommended in such a case; in addition, when a sink occurs, a source and, in the event of a source, an additional sink in the lamp.

As a first example merely facilitating the understanding of the invention, the continuous transport of hydrogen from a source to a sink is treated. The source of hydrogen may be hydrogen stored in the luminous element (metal carbide), hydrogen taken up in the supply lines or getter (possibly bound as metal hydride, eg tantalum hydride). When carburizing hydrogen can be enriched in the vertical lamp via the hydrogen partial pressure and the temperature distribution in the lamp and the supply lines. In lamp operation other temperature distributions prevail than when carburizing. Typically, the lamp temperature in lamp operation is about 3300 K - 3600 K higher than when carburizing (2800 K - 3100 K); In addition, when carburizing higher hydrogen partial pressures can be used. Therefore, when carburizing at a suitable temperature located parts of the frame, for example, tantalum or niobium can absorb hydrogen. Later in lamp operation, these rack parts are at a higher temperature in an atmosphere that is less Contains hydrogen, and therefore give off hydrogen (source). Parts of the frame located at a significantly lower temperature absorb this hydrogen (sink). For example, with lamps with TaC luminaires with integral filament outlets (similar to in FIG. 1 ) the helical outlets are not carburized during carburizing; Thus, tantalum is available in a wide range of temperatures, so that in any case places occur that can act as a source or sink. Furthermore, quartz glass can serve as a source of hydrogen, which is possible via the setting of a suitable content of OH groups in the glass (via the vacuum annealing of the quartz glass). The filling gas introduced later must take this material rearrangement into account. If necessary, other compounds or metals which are used as hydrogen storage such as zirconium, can be used as sources of hydrogen. These components are attached to the frame or the Wendelabgängen that at the temperature setting itself hydrogen is released relatively slowly over relatively long periods.

The second example merely facilitating the understanding of the invention relates to the use of sulfur in a lamp with metal carbide filament and an integral design of helix and Wendelabgängen, ie helical and Wendelabgänge are integrally made of a tantalum wire and then the filament carburized. When carburizing the helical outlets are not completely mitcarburiert, ie here you will find tantalum or Tantalsubcarbid Ta2C. In this range of lower temperatures, sulfur in the lamp is converted to the very stable compound tantalum sulfide and the sulfur is thus removed from the gas phase (sink). The gas withdrawn from the gas phase must be constantly replenished (source) in order to maintain a CS cycle process. This can be done, for example, by permanent evaporation of CH3CSCH3 from a reservoir impregnated therewith (eg made of rubber). For lamps with extremely low bulb temperatures below about 100 ° C elemental sulfur can serve as a source, which already at low temperatures has a considerable vapor pressure and melts slightly above 100 ° C. The use of higher melting high molecular weight mercaptans as a sulfur source is also possible.

Brief description of the drawings

Figur 1

eine Glühlampe mit Carbid-Leuchtkörper gemäß einem Ausführungs- beispiel;

Figur 2

eine Glühlampe mit Carbid-Leuchtkörper gemäß einem zweiten Aus- führungsbeispiel;

Figur 3 bis 5

eine Glühlampe mit Carbid-Leuchtkörper gemäß weiteren Ausfüh- rungsbeispielen.

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

FIG. 1

an incandescent lamp with carbide filament according to an embodiment;

FIG. 2

an incandescent lamp with carbide filament according to a second embodiment;

FIGS. 3 to 5

an incandescent lamp with carbide filament according to further embodiments.

Preferred embodiment of the invention

FIG. 1 shows an incandescent incandescent lamp 1 with a piston made of quartz glass 2, a pinch 3, and inner power supply lines 10, the films 4 in the pinch with a filament 7 connect. The filament 7 is a simple coiled, axially arranged wire of TaC, the ends 14 are uncoiled and projecting transversely to the lamp axis. The outer leads 5 are attached to the outside of the foils 4.

The design described here can also be applied, for example, to lamps with luminous bodies of other metal carbides, e.g. Hafnium carbide, zirconium carbide, niobium carbide, transferred. The use of alloys of different carbides is possible. In addition, the use of borides or nitrides, in particular of rhenium nitride or osmium boride, is possible.

In general, the lamp preferably uses a filament of tantalum carbide, which preferably consists of a single-coiled wire. Zirconium carbide, hafnium carbide, or an alloy of various carbides, such as, for example, are also suitable as the filament material, which is preferably a coiled wire US-A 3 405 328 described.

The piston is typically made of quartz glass or hard glass with a piston diameter between 5 mm and 35 mm, preferably between 8 mm and 15 mm.

The filling is mainly inert gas, in particular noble gas such as Ar, Kr or Xe, possibly with the addition of small amounts (up to 15 mol%) of nitrogen. This is typically a hydrocarbon, hydrogen and a halogen additive.

An addition of halogen is useful regardless of possible carbon-halogen cycle processes or transport processes to prevent vaporized metals from the filament of metal carbide deposition on the piston wall and possible to transport back to the filament. This is a metal-halogen cyclic process such as in the application DE-Az 103 56 651.1 described. In particular, the following circumstance is important: The more the evaporation of carbon from the luminous body can be pushed back, the lower the evaporation of the metallic component, see eg JA Coffmann, GM Kibler, TR Riethof, AA Watts: WADD-TR-60-646 Part I (1960s ).

Concrete embodiments that illustrate the essence of the invention are set forth below.

(A) Embodiments of lamp with a luminous body of TaC and with a solid hydrocarbon as a source

Of the aliphatic hydrocarbons are usually due to the otherwise low melting point only high molecular weight compounds in question (eg, the melting point of C ₅₆ H ₁₁₄ only just below 100 ° C, which is too little for most applications, unless the use of liquid compounds is possible). More suitable are aromatic hydrocarbons such as anthracene (melting point 216 ° C), naphthacene (melting point 355 ° C), corons (melting point 440 ° C), which also have the advantage that significantly less hydrogen is introduced into the lamp per carbon atom , For example, the vapor pressure of anthracene is just below the melting point by 50 mbar, at 145 ° C just above 1 mbar. By locating the source in a range of suitable temperatures, one can set a suitable vapor pressure. The vapor pressure of the hydrocarbon has to be adjusted approximately in such a way that the molar concentration of carbon atoms that occurs after its complete decomposition on the TaC luminous body is of the order of the equilibrium concentration of C atoms above the luminous body; the exact value depends on details (eg distance of the C source to the filament and to the sink, rate of decomposition of the hydrocarbons at the sink, etc.). When using anthracene as the source of carbon, the appropriate temperature for the source is in the range between 120 ° C and 150 ° C, when the distance between the filament located at eg 3400 K and the source is about 3 cm and the deposition of the carbon after decomposition of the hydrocarbons takes place at a about 400 ° C - 800 ° C hot nickel wire. The cold filling pressure in such a lamp is in the range around 1 bar; the inert gas (eg argon, krypton) preferably contains 2 mbar - 20 mbar hydrogen H ₂ , 0.5 mbar CH ₂ Br ₂ and 2 mbar - 20 mbar iodine. By the bromine, the deposition of tantalum is to be prevented on the piston (see DE-Az 103 56 651.1), and by the iodine to be released during the evaporation and decomposition of the anthracene released hydrogen in the form of HJ. HJ here represents a sink for the released hydrogen.

FIG. 1 shows schematically an example of a possible design of the source and sink for a single-pinch lamp. The source 6 uses as source material a solid hydrocarbon 8 deposited on the end of a wire rod 9, often called a middle holder, of tungsten. The rod 9 is supported by being connected to an additional sheet 11 in the center of the pinch seal 3. This can for ease of insertion have an outer wire approach 12, which typically consists of molybdenum.

The sink 13 is realized by coating coils 15 on one or both power supply lines 10. These coils consist for example of nickel wire. This can be located in the inner volume, near the pinch, or even protrude into the pinch, as shown on the right helix 15.

In this embodiment, both source and sink must be operated at relatively low temperatures, typically below about 500 ° C, as found near the piston wall. With regard to introduction, the use of the power supply leads 10 near the pinch 3 is the simplest. Alternatively, the source could be attached to one power supply 10 and the drain to the other power supply 10.

The end of the middle holder 9 is coated here with the serving as source material hydrocarbon. Although this embodiment is easy to manufacture, one has to accept that the transport from the source into the sink takes place mainly at the luminous body 7. However, since a certain time is required for the decomposition of the hydrocarbon on the catalyst, which is formed here by the sink of nickel wire, in the steady state in the entire gas phase, even outside the direct path from the source to the sink, an increased concentration at hydrocarbon or carbon.

An advantage for the operation is therefore the use of an arrangement as in FIG. 2 where the source 16 consists of a holder 18 made of tungsten crushed in the pump tip 17, at whose end facing the filament 7 the source material 19 is seated, namely a hydrocarbon which has been deposited as a solid.

The sink is realized here by the lower part 21 of the power supply leads 22 close to the pinch. This part 21 consists of molybdenum, which serves as a catalyst in the decomposition of the hydrocarbons. The upper part 20 of the power supply is integrally formed by the carbide of the filament. The lower parts 21 protrude into the pinch.

In this geometric arrangement, the luminous body 7 is located in the material flow, which forms from the source 16 to the sink 21. In FIG. 2 the lower part of the inner power supply 22 is made of molybdenum, referred to as Catalyst in the decomposition of hydrocarbons and thus acts as a sink.

(B) Embodiment of a lamp with a luminous body of TaC and with a carbon source

The consisting of TaC filament 23, see FIG. 3 , is operated at a temperature between 3300 K and 3600 K. To generate a suitable carbon partial pressure at the location of the TaC luminous body, the carbon source 24 is maintained in the temperature range between 2700 K and 3000 K. Hydrogen is added to the inert gas (krypton, argon) in such a way that the partial pressure of the hydrogen in the range is preferably between 2 mbar H ₂ and 20 mbar H ₂ to avoid the deposition of the carbon on the piston wall and the transport of the carbon to the sink , In this case, no hydrogen is released from the source, so that no sink for hydrogen is needed. The carbon source is at such a high temperature that there is no direct reaction with the hydrogen. As a sink for decomposition of the hydrocarbon is, for example, again at 400 ° C - 800 ° C operated wires or plates made of nickel or iron or molybdenum, or at temperatures around 500 ° C operated aluminosilicate.

FIG. 3 shows a possible geometry for such a lamp. As carbon source 24, C deposits in the "upper" region of the power supply lines 25 act near the transition region to the coil 23, where comparatively high temperatures already exist. Depending on the embodiment of the helix with regard to the helical temperature profiles, carbon deposition on the outer turns of the luminescent body may also be expedient. The power supply is here an integral departure from the helix 23. Instead of the C deposits C-fibers can be wound around the outlet. The sink 26 is here a coating coil made of iron, which is coated with platinum. It is near the pinch, so it is appropriate at much lower temperatures.

(c) Example of a geometry with a source located on the helical axis

An example of a source disposed on the axis of the luminous element is in FIG FIG. 4 shown. Here is an existing TaC rod 27 in the lamp axis, which is also the axis of the lamp. The rod 27 has approximately the same temperature profile in the region of the helix 28 as the helix itself. The helix is wound to such an extent that the rod 27 fits into its axis without contact. The sink is again formed by coating helices 26, as in FIG FIG. 3 , They are made of molybdenum. The rod 27 is similar to a middle holder 9 as in FIG. 1 supported. He may in particular extend into a pump seats 29, see dashed embodiment. As a result, he is better locked.

(d) Example of use with a double-sided lamp

FIG. 5 shows a possible arrangement for a two-sided pinch lamp 30. Here you can advantageously source 31 and sink 32 on the different sides of the filament 33 arrange so that the filament 33 is due to the geometric arrangement in the transport stream from the source 31 to the sink 32. The bruises are designated 39.

The source 31 is a carbon deposit (soot) or a carbon fiber wound around the power supply 34. The sink 32 is the part of a power supply, which is made of molybdenum and is arranged away from the luminous body 33. This part is connected via a weld point 35 to the outlet 36 of the luminous body made of TaC.

Advantageously, the entire temperature spectrum is available here on both sides of the luminous element 33 in the axial direction, so that, for example, the C source is arranged at relatively high temperatures in the vicinity of the luminous element and the drain at lower temperatures farther away from the luminous element on the other side can. In the in FIG. 5 As shown, the molybdenum outlet acts as a sink.

As the filament material, a metal or a metal compound is suitable, whose melting point is in the vicinity of the melting point of tungsten, preferably at least 3000 ° C and more preferably above that of tungsten. Besides tungsten, rhenium, osmium and tantalum are particularly suitable.

Claims (24)

1. Incandescent lamp having an illuminant which contains a high-temperature resistant metal compound (7) and having electrodes (10) which hold the illuminant (7), the illuminant being introduced vacuum-tightly together with a filling in a bulb (2), the material of the illuminant comprising a metal or a metal compound, in particular a metal carbide, whose melting point lies close to the melting point of tungsten, preferably at least at 3000°C and particularly preferably above that of tungsten, the illuminant containing a material which becomes depleted of at least one chemical element owing to chemical decomposition and/or evaporation during operation, and a source for this element being fitted in the bulb, the source delivering the element of which the illuminant is depleted, characterized in that a sink for this chemical element is also fitted in the bulb, the element which the illuminant emits progressively during the lifetime being deposited on the sink with the aid of a transport medium comprising hydrogen and/or a halogen, so that overall there is a continuous flux of the described element from the source to the sink, the concentration of the relevant element being essentially steady at any position in the lamp, apart from startup processes, the illuminant in steady-state operation being in equilibrium with the partial atmosphere of the element constantly transported past it, imposed from the outside by the interaction of the source and sink, so that the illuminant is prevented from being depleted of the element in question.
2. Incandescent lamp according to Claim 1, characterized in that the illuminant is enclosed by a bulb of glass, in particular quartz glass or hard glass, or ceramic, in particular Al₂O₃.
3. Incandescent lamp according to Claim 1, characterized in that at least one base gas in the form of an inert gas, in particular noble gas and/or nitrogen, is used as the filling.
4. Incandescent lamp according to Claim 1, characterized in that the metal compound is a metal carbide, for example tantalum carbide, zirconium carbide or hafnium carbide or alloys of different metal carbides.
5. Incandescent lamp according to Claim 4, characterized in that the source consists of a solid or liquid hydrocarbon or halogenated hydrocarbon which is operated in the temperature range of between 100°C and 400°C, and which releases carbon during decomposition.
6. Incandescent lamp according to Claim 4, characterized in that the source consists of hydrogen, in particular carbon black or graphite fibers or of fabric or carbon moldings, the carbon being transported to the sink by material additionally introduced as a constituent of the filling, from the group hydrogen and/or halogen, this material reacting in cooler regions with the carbon to form hydrocarbons or halogenated hydrocarbons, this hydrocarbon decomposing again at the sink while depositing carbon and releasing the transport medium.
7. Incandescent lamp according to Claim 4, characterized in that the source consists of a graphite body, in particular graphite fibers, coated with the corresponding metal carbide, the carbon being transported to the sink by material additionally introduced as a constituent of the filling, from the group hydrogen and/or halogen, this material reacting in cooler regions with the carbon to form hydrocarbons or halogenated hydrocarbons, this hydrocarbon decomposing again at the sink while depositing carbon and releasing the transport medium.
8. Incandescent lamp according to Claim 4, characterized in that the source consists of a sintered material containing carbon, the carbon being transported to the sink by material additionally introduced as a constituent of the filling, from the group hydrogen and/or halogen, this material reacting in cooler regions with the carbon to form hydrocarbons or halogenated hydrocarbons, this hydrocarbon decomposing again at the sink while depositing carbon and releasing the transport medium.
9. Incandescent lamp according to Claim 4, characterized in that a rod fastened in the vicinity of the illuminant, in particular an axially arranged rod, made of the same metal carbide as the illuminant is used as the source for the carbon, the longitudinal temperature profile of which corresponds to that of the illuminant consisting of the same metal carbide, and hydrogen and optionally halogen are used as a medium for transporting the carbon to the sink.
10. Incandescent lamp according to Claim 4, characterized in that a rod fastened in the vicinity of the axis of the illuminant, made of a second metal carbide is used as the source for the carbon, the vapor pressure of which at a given temperature is greater than that of the metal carbide of the illuminant wire, in order to compensate for the losses by thermal conduction along the wire fastened in the axis of the filament, and hydrogen and optionally halogen are used as a medium for transporting the carbon to the sink.
11. Incandescent lamp according to one of Claims 5 to 10, characterized in that the sink for the carbon consists of a catalytically active metal, in particular nickel or iron or molybdenum or cobalt or platinum, on which the optionally halogenated hydrocarbons decompose while depositing carbon and releasing hydrogen and optionally halogen.
12. Incandescent lamp according to one of Claims 5 to 10, characterized in that the sink for the carbon consists of a carbide-forming metal, in particular of nickel or iron or molybdenum or cobalt or platinum, on which the optionally halogenated hydrocarbons decompose while forming metal carbides and releasing hydrogen and optionally halogen.
13. Incandescent lamp according to one of Claims 5 to 10, characterized in that the sink for the carbon consists of aluminium, magnesium or molybdenum silicates.
14. Incandescent lamp according to one of Claims 11 to 13, characterized in that the filling contains iodine, the released hydrogen being bound by reaction with iodine to form hydrogen iodide so that the iodine has the function of a gaseous sink for the hydrogen.
15. Incandescent lamp according to one of Claims 11 to 13, characterized in that the released hydrogen escapes through the hot quartz bulb wall, so that the sink for the hydrogen is provided by the permeation of the hot bulb wall.
16. Incandescent lamp according to one of Claims 11 to 13, characterized in that a hydrogen-affine metal is introduced into the bulb, the released hydrogen being bound or "gettered" by the hydrogen-affine metal, in particular zirconium or hafnium or niobium or tantalum.
17. Incandescent lamp according to Claim 4, characterized in that a fluorinated, in particular perfluorinated hydrocarbon, in particular PTFE, which delivers perfluorinated carbon compounds as decomposition products at high temperatures, it is used as the source.
18. Incandescent lamp according to Claim 17, characterized in that the carbon is transported by means of halogen, preferably chlorine to the sink which consists of a catalytically active metal or a carbide-forming metal, in particular nickel, iron, molybdenum, cobalt, platinum, tungsten or tantalum.
19. Incandescent lamp according to one of the preceding claims, characterized in that the filling gas additionally contains a halogen compound and optionally hydrogen, sulfur or a cyanide compound, in order to prevent the metal and optionally the carbon from depositing on the bulb wall and to transport it back as much as possible to the illuminant.
20. Incandescent lamp according to Claim 4, characterized in that the illuminant is coated with the material of which it is depleted and which is intended to be fed back to a source, and forms a first layer, and then a second layer of the illuminant material per se is applied from the outside onto this first layer.
21. Incandescent lamp according to Claim 4, characterized in that the source consists of a body made of the same or another metal carbide, coated first with carbon in a first layer and then with metal carbide in a second layer, the carbon being transported to the sink by material additionally introduced as a constituent of the filling, from the group hydrogen and/or halogen, this material reacting in cooler regions with the carbon to form hydrocarbons or halogenated hydrocarbons, this hydrocarbon decomposing again at the sink while depositing carbon and releasing the transport medium.
22. Incandescent lamp according to Claim 21, characterized in that the outer second layer is an alloy of different metal carbides, in particular an alloy of tantalum carbide and hafnium carbide.
23. Incandescent lamp according to Claims 1 to 3, wherein the illuminant consists of a metal.
24. Incandescent lamp according to Claim 23, characterized in that the illuminant consists of tungsten and in that a high molecular weight carbon and fluorine compound slowly decomposes over the lifetime of the lamp, fluorine being released which reacts to form tungsten fluorides at a tungsten reservoir applied in the temperature range between 1600 K and 2400 K and therefore having the function of a source which transports tungsten back preferentially to the hottest position on the illuminant, and the fluorine from the tungsten fluorides not converted at the illuminant reacting on the bulb wall to form gaseous SiF₄, or the tungsten being accumulated by a superimposed boron cycle process at cooler positions of the framework and thus having the function of a sink for tungsten and fluorine.

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