WO2007006281A2 - Light source, filament and method for producing a monocrystalline metal wire - Google Patents

Abstract

The invention relates to a light source, in particular, an incandescent lamp, which comprises a tube (2) and a filament (1) which can be heated and is arranged in the tube (2). The light source is embodied in such a manner that the operating life thereof and of the filament (1) is extended. As a result the filament (1 ) consists at least partially of monocrystalline filament material. The invention also relates to a filament (1) for the above-mentioned light source. The invention further relates to a method for producing a monocrystalline metal wire, in particular a filament (1) for a light source and a metal raw wire which is used as an initial material. According to said method, the raw wire is subjected, at least sectionally, to zone crystallisation which leads to the formation of an essentially monocrystalline metal structure.

Description

 LIGHT SOURCE, A FILAMENT, AND A METHOD OF MAKING A MONOCRYSTALLINE METAL WIRE

The present invention relates to a light source, in particular incandescent lamp, with a piston and a heatable filament arranged in the piston. Furthermore, the present invention relates to a filament for a light source and a method for producing a monocrystalline metal wire, in particular a filament for a light source, with a raw metal wire serving as a starting material.

Light sources of the type mentioned are known in practice and exist in various embodiments. Known light sources are formed, for example, as lamps or filaments with Glühfilamenten, filament filaments are known for example by directly electrically heated or inductively heated filaments. Filaments are made of metals or metal carbides or alloys with metals or metal carbides. Corresponding light sources are known as simple incandescent lamps, halogen lamps or tantalum carbide lamps.

All these previously known light sources or lamp types have in common that the filaments show recrystallization phenomena that lead to the destruction of the filament. The filaments are destroyed after a certain burning time. The annealing filament tears off and a mostly following arc then melts the ends of the break points. The filament breakage is often observed at overheated spots of the filament, these spots being referred to as "hotspots." The hotspots may be due to internal crystal phenomena of the filament or external conditions of an electromagnetic radiation field or field, e.g., an electron gas, surrounding the filament. For filament filaments such as tungsten filaments, tantalum filaments or metal carbide filaments, for example tantalum carbide filaments, the following model presentation may be used for filament breakage at hotspots.

Incandescent filaments with tungsten or metal carbide filaments require an internal transport process, the filament evaporating elements such as tungsten, tantalum, carbon or carbon compounds back on the filament returns to delay the onset of filament breakage. The recirculation is usually done primarily from the deposition of tungsten, tantalum, carbon or carbon compounds from a surrounding the filament gas atmosphere with a suitable gas composition and with a suitable partial pressure composition of the gas components in a certain temperature range.

The hotspots can be observed at or around crystal grain boundaries of the filaments. The crystal grain boundaries in the filaments are formed by planes or layers of large crystallographic lattice perturbations in which, for example, carbon is more mobile and can diffuse faster to the filament surface than in the lattice. This diffusion is promoted in electrically heated filaments by an elevated temperature, which can be caused by the increased heat loss at the current-traversed grain boundary layers due to their higher electrical resistance.

The greater possible loss of carbon in, for example, tantalum carbide lamps at the grain boundary areas of the filament surface leads there in the further consequence to an evaporation of tantalum carbide or even of metallic tantalum. The crystal grain boundary areas therefore show on the filament surfaces after a certain burning time under the microscope as grooves with, for example, V-shaped cross-sectional profile which have been eroded.

Since the model process now described is largely very similar for both metal filaments and metal carbide filaments, this model process should be described here only for metal carbide filaments such as tantalum carbide filaments. As a model requirement, approximately cylindrical filament sections are assumed and considered in the transport cycle of the filament surface evaporating and recycled to this carbon. The assumed approximately cylindrical surface is disturbed by grain boundary grooves.

The carbon that can be deposited on the filament from the surrounding gas atmosphere is atomic or molecular over the filament surface, for example in the form of CH or CO compounds, and electrically neutral or ionized before. The partial pressure or concentration is to be regarded as approximately homogeneous over the crystal compres- sion areas of the surface. The deposition of the carbon through an arbitrarily oriented imaginary surface on its projection surface on the undisturbed cylinder surface of the filament is therefore homogeneous. The carbon deposited on the actual filament surface can thus not uniformly cover the surface areas in which the observed grain boundary grooves are present in sections. Since the grain boundary groove portions, which are under screen projection areas of the same size as the non-groove portions, have a larger actual deposition surface than the regions of the non-groove portions, carbon coverage on the groove walls is thinner than in the regions outside the groove.

In the case of the presence of ionized tantalum or carbon or ionized tantalum compounds or carbon compounds, transport under the action of an electric field may occur toward the filament surface. This electric field may be due to a potential difference between the filament surface and the gas atmosphere around the filament because the partially ionized gas atmosphere has finite electrical conductivity and is in contact with other electrical components such as the lamp electrodes.

Another electric field builds up in filament filament electric filaments due to the electrical filament resistance between the opposing filament turns. For small filament lamps with typical filaments of 5 to 10 turns and operating voltages of 12 volts, the electrical voltage between adjacent turns is about 1 volt to 2 volts.

In addition, electric fields can arise from space charges resulting from the electron glow emission of the filament. For powder-metallurgically hot-pressed tantalum carbide report JH Ingold, E. Blue and WJ. Ozeroff an electron work function at the annealing emission of 3.97 eV between 1.300 K - 1.900 K with a Richardson constant of 37 A / cm ² K ² . For tantalum carbide wires BH Eckstein and R. Formann reported an electron work function of 3.17 eV between 1,600 K and 2,250 K with a Richardson constant of 0.22 A / cm ² K ² . K. Be cker and H. Ewest report a 2.8 times smaller electron glow emission with tantalum carbide compared to pure tantalum. From the data of Eckstein et al. According to Richardson, an electron glow emission of 357 A / cm ² at 4,000 K filament temperature can be estimated. For tungsten, the glow emission current at 3,000 K is 14.19 A / cm ² and at 3,655 K is 479.9 A / cm ² . Experimentally, an electron emission current of 5 mA per watt heating power was found for tungsten at 3,000 K, which can be extrapolated to 3,655 K to about 170 mA / W. At high temperatures, therefore, very high electron space charges occur around the filaments. For the above-mentioned 10-filament small filament winding coils with 0.5 mm coil radii and about 15 mm ² filament surface, when tantalum carbide is used as the filament material at a temperature of 4,000 K, possible saturation glow emission electron currents of up to 50 A can be estimated.

On the hot filament surface or between the hot helical turns, electrons from the annealing emission that are accelerated in the electric field between the helical turns can assist in ionizing atmospheric constituents there. The direct impact ionization in the ideal gas at 4,000 K is insufficient due to the maximum available kinetic energy impact of about 4.3 eV for a positive ionization of atoms such as W, Ta, C, H and O. The ionization energies of these elements are all above 7 eV.

Therefore, the occurrence of positively ionized gas components is unlikely. However, radicals resulting from the thermolysis of carbon compounds on the hot filament can pick up electrons from the electron gas surrounding the filament. The appearance of negatively charged ions is likely. Even uncharged gas atmosphere components can be entrained by a flow of glow electrons along the electric field lines. They then behave like ions and should therefore be called quasi-ions. On the hot filament surfaces, after a certain firing time, growth of needle-like crystals can be observed, the crystal needles being directed towards the next filament loop or along the field lines between the turns. Also, ionized carbon or ionized carbon compounds or their charged radicals or their quasi-ions are deposited less into the grooves than on non-groove surface areas as the electric field in grooves reduces or eventually disappears. The groove surface is therefore less supplied with recycled carbon than the non-groove surface.

The hot filament surface areas do not emit the light evenly. Non-groove portions of cylindrical portions radiate the light from the cylinder surface without re-radiation or reabsorption of this light in this non-groove portion. Grooved areas radiate the light under a certain reflection or self-absorption, because the opposite wall surfaces of the grooves partially radiate each other. The groove areas of the filament surface are therefore hotter than the non-groove areas.

Further heating of the groove areas or other areas with a faulty surface is effected by the current entry of the Glühemissionselektronen and the impact of charged gas constituents or quasi-ions on the filament surface. These are transported in the electric field between the turns of electrically heated filaments on the filament surface. There, the electrons enter the filament surface, the energy corresponding to their potential difference between their potential in the outer space of the filament and the potential in the filament, which just corresponds to the Glühemissionselektronenaustrittsarbeit in the form of heat. Although the energy balance is balanced, since the glow emission currents at the filament exit by the entrainment of the electron work function cooling, but these "external heating" not homogeneous but concentrated in certain filament surface areas, since they follow the electric field density and the electric field strength, the These areas include, among other things, the edges or the edges of the grain boundary grooves, which are heated even more strongly than non-groove areas by the incandescent emission electrons or the charged gas components impinging there.

The temperature-dependent evaporation rate and evaporation rate of carbon from the grooves is greater than that due to the higher temperature there of non-groove areas. Since the evaporation rate and evaporation rate of carbon or carbon compounds are greater in groove regions than in non-groove regions, and because the deposition rate of carbon or carbon compounds into the grooves is less than in non-groove regions, this can lead to undershoot of the groove regions with carbon.

The consequence, in the case of metal carbide filaments, may be a phase transition between metal carbide phases. In the case of tantalum carbide filaments, the most temperature stable gamma phase of the present tantalum carbide can convert to the less temperature stable beta or alpha phase, resulting in a further dramatic increase in carbon diffusion in the tantalum carbide lattice and consequent increase in carbon vapor deposition rate and vaporization rate in the groove region, and ultimately leads to the formation of bitan carbide. The carbon diffusion constant, for example, at 2,650 ⁰ C in Ta ₂ C is about 9 times higher than in TaC. Increasingly decarburized tantalum carbide, however, exhibits increasing electrical resistivity down to a molar composition of C / Ta = 0.75, which in the case of electrically heated filaments results in higher heat loss and hence further temperature increase in the increasingly decarburizing groove regions. Decarburization of the tantalum carbide in electrically heated filaments is thus self-accelerating.

The steadily increasing temperature rise in the groove areas can lead to additional evaporation of tantalum carbide or, after sufficient decarburization, even of metallic filament material, i. Tantalum, whereby the grooves enlarge and deepen. This again accelerates the above-described development or a further increase in temperature in the groove regions by, for example, the equally increasing radiation self-absorption.

The tantalum carbide shows a strong density change with increasing decarburization, whereby strong mechanical stresses can occur in the groove areas. This development is accompanied by a temperature-induced crystal grain growth in the filament as the burning time increases. Crystal grain growth does not stop until the crystal grains have reached the diameter of the filament wire. Then individual komgrenzen can stretch over the entire wire cross-section and form a continuous fracture plane or slip plane. The growing crystal Grain boundary layers already show a density change due to the strong lattice disturbances, which generates mechanical stresses.

Consequently, the largest lattice disturbance or the lowest mechanical strength of the filament together with the large mechanical stresses is present in the grooves and the boundary layers extending from here. At these self-induced break points breaks off after a certain burning time of the filament wire. To at least delay this behavior, it is known today that the filaments such as tungsten filaments are alloyed with metals such as rhenium or hafnium or doped with foreign metal oxides of thorium, aluminum, calcium, silicon or potassium. The alloy results in the formation of mixed crystals with lower crystal growth rates in the filament, whereas the extraneous metal oxide doping leads to lattice perturbations that retard or direct crystal grain growth, for example in the case of potassium clusters brought into the filament raw wire, which warp along the wire axis through the wire drawing process or longitudinal tracks form to produce a so-called stacked wire structure, which limits the high-temperature grain boundary sliding.

The present invention is therefore based on the object of specifying a light source, a filament for a light source and a method for producing a monocrystalline metal wire, after which an extension of the life of the light source and the filament and a higher mechanical stability of a usable as a filament metal wire with simplified production are reached.

The above object is achieved on the one hand by a light source with the features of claim 1. Thereafter, the light source is designed and refined such that the filament consists at least partially of monocrystalline filament material.

According to the invention it has been recognized that by a suitable choice of the crystal structure of the filament material, the above object is achieved in a surprisingly simple manner. For this purpose, the filament in the concrete is at least partially formed of monocrystalline filament material. The more extensive the filament is formed from monocrystalline filament material, the more advantageous it has Embodiment on the life of the light source. Since monocrystalline fi lament material has largely smooth surfaces, it has no or hardly any internal crystal grain boundaries and thus no electrical contact resistances at crystal grain boundaries or Kristallkorngrenzgleitebenen or fracture planes or inhomogeneous internal diffusion paths for Filamentmaterialbeimengungen such as doping or hydrogen or carbon or a superficial Kristallkorngrenzrillenbildung. Due to the monocrystalline nature, the material has a uniform evaporation rate and evaporation rate across the surface for filament material admixtures such as carbon or for filament material such as carbon compounds or filament metal. The material further has a homogeneous absorption rate over the surface for, for example, carbon and a uniform or continuous temperature distribution over the surface. Due to these characteristics, the occurrence of hotspots according to the above model is avoided, and thus the life of light sources with filament or filaments can be increased.

To realize a particularly high-quality monocrystalline structure of the fi lament material, the filament could at least partially consist of zone-crystallized filament material. With a zone crystallization, a largely monocrystalline structure can be achieved in a particularly reliable and simple manner. In particular, zone crystallization means the controlled or controlled progressive crystallization or recrystallization of the filament material. Such crystallization or recrystallization starts from an induced or already existing crystallization center with the consequence of the formation of a monocrystal or single crystal. Zone crystallization may be produced by the controlled deposition of, for example, epitaxial deposition of material from a gaseous phase or from a liquid phase such as a solution or dispersion or melt of seed crystals. Such a procedure generally produces reliable but slow crystal growth.

To realize a particularly rapid production of a zone-crystallized filament material, the zone crystallization could be limited by a spatially limited Heating the filament to be generated. In other words, there is a temperature-induced zone crystallization in a solid state.

The heating could be produced in a particularly simple and reliable manner by means of an electron or laser beam, through which the filament is guided or which is guided along the filament.

Alternatively, the heating could also be generated in a simple manner by means of inductive heating. The filament could be passed through an induction loop or the induction loop along the filament.

In another alternative, the heating could be generated by means of a noble gas plasma flame or a hydrogen plasma flame. This also makes it possible to achieve reliable regional crystallization in the form of zone crystallization.

To ensure a particularly advantageous surface area of the filament material, the filament material could be at least partially mechanically and / or electrically smoothed or polished.

The filament could comprise a metal or metal carbide or at least one alloy with a metal or metal carbide. In this case, the metal could be tantalum or tungsten in a particularly advantageous manner for realizing a particularly long life of the light source. In this regard, even more advantageous than tantalum carbide could be used as a metal carbide.

To ensure a particularly pure filament material, the raw material for the filament could be obtained from an electrolysis or from a vacuum melt. In this case, the solution used in the electrolysis could be an aqueous solution in a particularly advantageous manner. This ensures a particularly smooth and dense metal deposition.

The above object is further achieved according to claim 13 by a filament for a light source according to one of claims 1 to 12. Regarding the advantages of such a filament for a light source is referred to the preceding text to avoid repetition.

The above object is further achieved by a method for producing a monocrystalline metal wire, in particular a filament for a light source, having the features of claim 14, wherein a metallic raw wire serving as a starting material is used. Thereafter, the method is configured and further developed in such a way that the raw wire is subjected at least in regions to a zone crystallization producing a substantially monocrystalline metal structure.

According to the invention, it has been recognized that the use of zone crystallization solves the above problem in a surprisingly simple manner and enables a filament material with particularly high quality. Since zone crystallized film material is monocrystalline or at least substantially monocrystalline and has smooth surfaces, it has no or nearly no intrinsic crystal grain boundaries and thus no electrical crystal grain boundary resistances or crystal grain boundary planes or fracture planes or inhomogeneous internal diffusion paths for filament material admixtures such as dopants or hydrogen or carbon or surface crystal grain boundary groove formation , Due to its monocrystalline nature, the zone-crystallized filament material has a uniform evaporation rate and evaporation rate for filament material admixtures such as carbon or filament material such as carbon compounds or filament metal. It has a homogeneous absorption rate over the surface for, for example, carbon and a uniform or continuous temperature distribution over the surface. Because of these characteristics, the occurrence of hotspots according to the above model is avoided. As a result, the life of light sources, lamps or Leuchtkörpem is increased with such Glüh filament.

From EP 1 445 340 A2 a method for producing a monocrystalline metal wire is already known. In the known method recrystallization takes place during a plastic deformation of raw wires in the form of a twirling of two wires against each other or in the form of a twist of a wire about its wire axis during a heat treatment. The known method However, it has the disadvantage that it is only applicable to wires with wire thicknesses in the range between 0.01 to 5 microns and that the monocrystallized twisted wire must be rewound and stretched for use again or possibly must be brought into a different other form, what again can lead to crystal defects of the finished monocrystal.

The raw material for the wire must be such that it is applicable to the zone crystallization method. For this purpose, the raw material for the raw wire could be obtained in a particularly advantageous manner from an electrolysis or vacuum melt. This is particularly suitable for tantalum or tantalum carbide wires with respect to the raw tantalum. A preparation of, for example, powder metallurgical material or sintered material is less favorable because the sintered powdered material grains have embedded with different crystal orientation axes in the material and in the zone crystallization already pretend an undesirable direction of crystallization or act as multiple crystallization nuclei, of which grown in the considered zone simultaneously separate crystals, the again form undesirable grain boundaries. The advantage of raw material from electrolysis is the generally high chemical purity and the non-or little crystalline structure of the material. Material contamination disturbs namely the desired crystal growth and represent later lattice defects.

For example, the Elektrolysetantal is not deposited in the form of powders, but in the form of cathode solids such as rods, sheets or plates. In the electrolysis, therefore, an aqueous solution could be used in a particularly advantageous manner. Specifically, an electrolysis tantalum preparation could be made from an aqueous tantalum solution. Because of the low conductivity of the molten salt electrolytes, an electrolytic production process from a molten tantalum leads to the formation of coarse dentritic or flaky tantalum crystals. In the case of electrolysis tantalum deposition from an aqueous tantalum solution, on the other hand, high metal ion concentrations in the electrolyte-optionally with the aid of high electrolyte conductivity-and a high bath temperature together with a high nucleation rate lead to smooth and dense metal deposits. The nucleation rate can be determined by a high Ka be promoted thodentemperatur. The formation of unwanted polycrystals is thereby effectively avoided.

In a further advantageous manner, the raw material could be processed by means of wire-rolling machines and / or wire-rotary hammers and / or by means of wire drawing tools in a hot deformation to form the raw wire or filament semi-finished product. The lattice structure still present in the raw wire is so strongly destroyed and homogenized by such mechanical processing or by the associated strong plastic deformation that a subsequent recrystallization process can be carried out in a controlled manner.

Should the plastic deformation and homogenization of the lattice structure not be sufficient by the above mechanical machining operation, then the raw wire could be drawn over at least one roller to produce a bend in the raw wire. In this case, the raw wire could be repeatedly pulled over as small as possible roles or as thin as possible axes that the wire learns the smallest possible bending radii with the largest possible bending angles. In the most favorable manner, the raw wire could be pulled with a bending angle of 360 degrees and more on the role or on the rollers.

In a further advantageous manner, the raw wire could be pulled over several rollers whose axes are at predetermined angles to each other. In concrete terms, all successive roller axes or bending axes could each be further rotated by a certain angle relative to the following axis, so that the wire axis is bent into as many azimuth angles as possible in the range between 0 degrees and 360 degrees. The roller conveyor or the wire path in this multi-fold bending arrangement then shows an angular three-dimensional course.

With regard to the production of a filament, the raw wire could be wound around an axis to form a helix. This could be done by the last deflection of the raw wire in the Mehrfachbiegeanordnung to already produce the helical turn of a helical filament. Specifically, the wire could not be pulled over a final bending roll or bending axis but wound on the last bending axis. Such a bending axis could, for example, be a fixed cylindrical or pointed conical mandrel over which the wire is pushed or wound by means of a friction wheel or a friction roller, so that at the end of the dome on the mandrel tip an endless spiral or endless spiral takes place.

The zone crystallization according to the invention is a controlled or progressive advancing crystallization or recrystallization of the raw wire. To ensure particularly secure zone crystallization, zone crystallization could be generated by progressive crystallization emanating from an induced or already existing crystallization center in the raw wire. The consequence of this procedure is the formation of a single crystal or monocrystal.

A particularly rapid process for zone crystallization is carried out by a temperature-induced zone crystallization, wherein the raw wire for zone crystallization in a predetermined range heat could be supplied.

To prevent tearing of the wire in the zone crystallization process, the temperature generated in the raw wire could be selected below the melting temperature of the raw wire. The temperature could even be below the critical temperature of the yield strength of the filament wire.

In a further advantageous manner, an at least partially melting of the surface of the raw wire could be generated by the heat. As a result, surface irregularities originating from a previous mechanical wire processing could be leveled or smoothed. As a result, when using the metal wire as a filament in an incandescent lamp when lamp operation electric field spikes can be avoided, which could be generated by surface edges or surface tips on the filament surface. Such a partial reflow could be achieved if the wire temperature could be adjusted near the melting point of the wire material.

In view of a particularly reliable specification and definition of the heated region, the heat could be generated by means of an electron beam or laser beam focused on the raw wire. As a result, a particularly reliable specification of the range is possible, the heat to be supplied. In this case, a quasi-selective heating of the raw wire and a safe control of the to be expected menden range of the raw wire with the electron or laser beam possible because such electron or laser beams can be very precisely managed and controlled.

Concretely, the zone crystallization can be effected by heating an initial zone of the finished wire or the finished shaped filament by means of an electron beam or laser beam focused on a very small zone area of the wire or filament so that the recrystallization process in this Zone starts. When using an electron beam, this could be done in a vacuum.

With a view to uniformly heating the desired zone, the diameter of the electron beam or laser beam on the surface of the raw wire could substantially correspond to the wire gauge or the diameter of the raw wire. For safe and uniform zone crystallization of the raw wire at a predeterminable speed by the electron beam or laser beam or the electron beam or laser beam at a predeterminable speed along the raw wire could be performed. The guide or relative speed must be matched to the desired and generated zone temperature. This tuning or the residence time of the wire in the temperature zone where recrystallization can take place should ensure substantially complete recrystallization. In this case, the crystal induced in the heated initial zone continues to grow uniformly along the wire axis in accordance with the wire guiding speed or relative velocity, forming a single crystal along the wire.

As an alternative to heating by means of laser or electron beam, the heat could be generated by means of inductive heating. In this case, the raw wire for inductive heating at a predeterminable speed could be guided through an induction loop or an induction loop at a predeterminable speed along the rough-wire. In the case of inductive heating, the wire could be passed through a narrow induction loop in order to keep the recrystallization zone as narrow as possible. In a further alternative embodiment of the method, the heat could be generated by means of a noble gas plasma flame or a hydrogen plasma flame. Both in the case of heating by means of plasma flame or laser beam and in the case of inductive heating, it is advantageous that the heating process could be carried out in a gas atmosphere, for example in a noble gas atmosphere, inert gas atmosphere or hydrogen atmosphere.

To ensure a particularly controlled heating of a predeterminable region of the raw wire, a region of the wire which is not to be heated during the supply of heat could be cooled. As a result, an unintended recrystallization process outside the predefinable range can be largely suppressed due to the cooling. The cooling of the region not to be heated could be effected in a particularly simple manner by a gas or liquid stream or in a cooling bath. Alternatively or additionally, cooling could be by contact with a heat sink.

In particular, in the case of laser heating, inductive heating or heating by means of a noble gas plasma flame or hydrogen plasma flame, a targeted gas or liquid stream could be used to cool down the neighboring regions of the recrystallization zone so that the heat conduction via the wire does not lead to an early, uncontrolled recrystallization in the zone adjacent. rich, which are not warming at first.

In the case of zone heating by an electron beam, the zone secondary regions could advantageously be cooled down by solid-state contact cooling. A very simple apparatus arrangement could be realized if the zone crystallization is performed over a cooling bath surface such as a water bath surface or an oil bath surface. In this case, the wire could be pulled out of a water bath or oil bath from a wire spool and the laser beam, the induction loop or the heating flame could be positioned very close to the water surface or oil bath surface. As a result, very large temperature gradients could be achieved between the heated recrystallization zone and the not yet recrystallized wire area in the cooling bath. In a further advantageous manner, the surface of the zone-crystallized metal wire could be smoothed. Such a smoothing could be generated, for example, by mechanical polishing. Alternatively or additionally, the smoothing could be generated by a galvanic or electrical polishing. In concrete terms, a surface smoothing could take place by means of a galvanic surface polish or electropolishing of the wire following the recrystallization process. Mechanical polishing methods can also be used. In this way, hot spots generated by the surface incidence of glow emission electrons or the impact of charged gas constituents or quasi-ions can be suppressed.

Another advantage is that chemical surface corrosion can be reduced by later-used lamp atmosphere gas components such as halogen compounds. Such corrosion phenomena start on, for example, metal surfaces on surface lattice defects such as lattice step dislocations or lattice trenches such as scratches. In addition, hot spots are avoided, which are generated by a surface temperature increase from a Strahlungsreabsorption in, for example, grooves or voids.

In a further advantageous manner, after the zone crystallization, a further heating step for outgassing unwanted elements from the metal wire could take place. In the case of zone crystallization, which is not carried out in a vacuum, constituents of the gas atmosphere which are absorbed by the wire, such as, for example, noble gases, protective gas components or hydrogen, can optionally be outgassed in a further heat treatment. This fact is of particular importance for a filament material which exhibits high gas reactivity or gas absorptivity, such as tantalum.

The heating of the wire required for the zone crystallization can take place in different ways. For example, after a bending step, which is carried out for the destruction or homogenization of unwanted metal structures prior to the zone crystallization, a supply of heat by means of a heater. In a particularly advantageous embodiment, a supply of heat could be carried out by means of a heater after each bending step. hereby is a particularly reliable and well metered heating of the wire at predetermined locations allows. As a result, virtually the entire wire bending web of the wire could be controlled heated.

After the completion of the zone crystallization process and the optionally necessary degassing annealing and the optionally used polish, the now essentially monocrystalline wire can be brought into the filament shape necessary for the lamp design under consideration and installed in a lamp blank. During further processing of the lamp blank, for example during carburization of the tantalum wire to tantalum carbide in the production of tantalum carbide lamps, the monocrystalline structure of the filament remains largely intact.

If the final filament wire formation leads to lattice defects in the region of which recrystallization occurs again, for example during the burning of the lamp, then zone crystallization and optionally subsequent degas annealing can also be carried out only after filament formation. For this purpose, heating by means of a laser, for example an infrared laser, or by means of an electron beam is particularly suitable since these beams can both be tracked via a corresponding steering optics or electrostatic / electromagnetic deflection device of the fine shape of the filament.

The subsequently completed light source or the subsequently completed filament does not show the known from the prior art disadvantageous properties due to the monocrystalline Glühfilaments together with the originating from the zone crystallization high surface quality of the filament. The invention can therefore allow significantly longer lifetimes of the light source or the filament. The invention is advantageous wherever annealed filament lamps or filament filaments are destroyed by a recrystallization process of the filament.

There are now various possibilities for designing and developing the teaching of the present invention in an advantageous manner. For this purpose, on the one hand to the subordinate claims, on the other hand, the following explanation of a preferred embodiment of the invention with reference to the drawing. In the drawing shows the only one

Fig. In a schematic side view of an embodiment of a light source according to the invention.

The single FIGURE shows a schematic side view of an embodiment of a light source according to the invention. The light source has a heatable filament 1, wherein the filament 1 is arranged in a piston 2. The heating of the filament 1 via electrical contacts 3 and 4. With a view to extending the life of the light source and the filament 1, the filament 1 is at least partially made of monocrystalline filament material.

With regard to further advantageous embodiments and further developments of the teaching of the invention reference is made to avoid repetition on the one hand to the general part of the description and on the other hand to the accompanying claims.

Finally, it should be particularly emphasized that the previously purely arbitrary chosen embodiment is only for the purpose of discussing the teaching of the invention, but this limits to this embodiment.

Claims

claims 1. light source, in particular incandescent lamp, with a piston (2) and in the piston (2) arranged heatable filament (1), dad urch geken nzeichnet that the filament (1) at least partially consists of monocrystalline filament material. 2. Light source according to claim 1, characterized in that the filament (1) consists at least partially of zonenkristallisiertem filament material. 3. Light source according to claim 2, characterized in that the zone crystallization is generated by a spatially limited heating of the filament (1). 4. Light source according to claim 3, characterized in that the heating is generated by means of an electron beam or laser beam. 5. Light source according to claim 3, characterized in that the heating is generated by means of an inductive heating. 6. Light source according to claim 3, characterized in that the heating is generated by means of a noble gas plasma flame or a hydrogen plasma flame. 7. Light source according to one of claims 1 to 6, characterized in that the filament material is mechanically and / or electrically smoothed or polished. 8. Light source according to one of claims 1 to 7, characterized in that the filament (1) comprises a metal or metal carbide or at least one alloy with a metal or metal carbide. 9. Light source according to claim 8, characterized in that the metal is tantalum or tungsten. 10. Light source according to claim 8, characterized in that the metal carbide is tantalum carbide. 11. Light source according to one of claims 1 to 10, characterized in that the raw material for the filament (1) is obtained from an electrolysis or from a vacuum melt. 12. Light source according to claim 11, characterized in that the solution used in the electrolysis is an aqueous solution. 13. filament (1) for a light source according to one of claims 1 to 12. 14. A method for producing a monocrystalline metal wire, in particular a filament (1) for a light source according to one of claims 1 to 12, with a starting raw material serving as metallic raw wire, characterized in that the raw wire at least partially subjected to a substantially monocrystalline metal structure generating zone crystallization becomes. 15. The method according to claim 14, characterized in that a raw material for the raw wire is obtained from an electrolysis or vacuum melt. 16. The method according to claim 15, characterized in that an aqueous solution is used in the electrolysis. 17. The method according to any one of claims 14 to 16, characterized in that the raw material is processed by means of wire-rolling machines and / or wire hammers machines and / or by means of wire drawing tools in a hot deformation to the raw wire. 18. The method according to any one of claims 14 to 17, characterized in that the raw wire is pulled to produce a bend in the raw wire via at least one roller. 19. The method according to claim 18, characterized in that the raw wire is pulled with a bending angle of 360 degrees and more over the roller. 20. The method according to claim 18 or 19, characterized in that the raw wire is pulled over a plurality of rollers whose axes are at predetermined angles to each other. 21. The method according to any one of claims 14 to 20, characterized in that the raw wire is wound around an axis to form a coil. 22. The method according to any one of claims 14 to 21, characterized in that the zone crystallization is generated by an induced or already existing crystallization center in the raw wire outgoing progressive crystallization. 23. The method according to any one of claims 14 to 22, characterized in that the raw wire for zone crystallization in a predetermined range heat is supplied. 24. The method according to claim 23, characterized in that the temperature generated in the raw wire is selected below the melting temperature of the raw wire. 25. The method according to claim 23 or 24, characterized in that an at least partially melting of the surface of the raw wire is generated by the heat. 26. The method according to any one of claims 23 to 25, characterized in that the heat is generated by means of an focused on the raw wire electron beam or laser beam. 27. The method according to claim 26, characterized in that the diameter of the electron beam or laser beam on the surface of the raw wire substantially corresponds to the wire thickness or the diameter of the raw wire. 28. The method of claim 26 or 27, characterized in that the raw wire is guided at a predeterminable speed through the electron beam or laser beam or the electron beam or laser beam at a predeterminable speed along the raw wire. 29. The method according to any one of claims 23 to 28, characterized in that the heat is generated by means of an inductive heating. 30. The method according to claim 29, characterized in that the raw wire for inductive heating at a predeterminable speed is guided through an induction loop or an induction loop with a predeterminable speed along the raw wire. 31. The method according to any one of claims 23 to 30, characterized in that the heat is generated by means of a noble gas plasma flame or a hydrogen plasma flame. 32. The method according to any one of claims 23 to 31, characterized in that during the supply of heat not to be heated portion of the wire is cooled. 33. The method according to claim 32, characterized in that the cooling is carried out by a gas or liquid flow or in a cooling bath. 34. The method according to claim 32 or 33, characterized in that the cooling erfogt by contact with a heat sink. 35. The method according to any one of claims 14 to 34, characterized in that the surface of the zone-crystallized metal wire is subjected to a smoothing. 36. The method according to claim 35, characterized in that the smoothing is produced by a mechanical polishing. 37. The method according to claim 35 or 36, characterized in that the smoothing is produced by a galvanic or electrical polishing. 38. The method according to any one of claims 23 to 37, characterized in that after the zone crystallization, a further heating step for the outgassing of unwanted elements from the metal wire. 39. The method according to any one of claims 17 to 38, characterized in that after a bending step, a supply of heat by means of a heating device takes place. 40. The method according to claim 39, characterized in that after each bending step, a supply of heat by means of a heating device takes place.