EP3491886A1

EP3491886A1 - Infrared surface emitter and method for producing said infrared surface emitter

Info

Publication number: EP3491886A1
Application number: EP17740655.0A
Authority: EP
Inventors: Lotta Gaab; Thomas Piela; Christoph STERNKIKER; Jürgen Weber
Original assignee: Heraeus Noblelight GmbH
Current assignee: Heraeus Noblelight GmbH
Priority date: 2016-07-27
Filing date: 2017-07-05
Publication date: 2019-06-05
Also published as: US20190174580A1; WO2018019530A1; JP2019522335A; TW201804872A; KR20190032499A; DE102016113815A1; CN109479345A

Abstract

Known methods for producing an infrared surface emitter comprising a substrate consisting of an electrically insulating material, on the surface of which is mounted a conductor track consisting of an electrically conductive resistive material which generates heat when a current passes therethrough, comprise the following method steps: (a) preparing the substrate; (b) applying the conductor track to a surface of the substrate. On this basis, in order to provide a simple and cost-effective method for producing an infrared surface emitter which emits radiation homogeneously with a high radiant flux per unit area, according to the invention: in method step (a) a substrate is provided which is made from a composite material comprising an amorphous matrix component and an additional component in the form of a semiconductor material; and the conductor track is provided as a moulded body with a geometrically fixed shape, which in method step (b) is mounted on the surface of the substrate such that the conductor track and the substrate are permanently connected to each other.

Description

Infrared surface radiator and method for producing the infrared surface radiator Technical background

The present invention relates to a method for producing an infrared surface radiator with a substrate made of an electrically insulating material, on the surface of which a conductor track made of an electrically conductive and heat flow current-generating resistance material is applied, comprising the method steps:

(a) providing the substrate,

(b) applying the trace to a surface of the substrate.

Furthermore, the present invention relates to an infrared surface radiator with a substrate made of an electrically insulating material, on the surface of which a conductor track of an electrically conductive and, when current flows through, heat-generating resistance material is applied.

Infrared surface radiators in the context of the invention show a two-dimensional or three-dimensional radiation characteristic that is extended over a large area; They are used for example for polymerizing plastics or for curing paints or for drying paints on a heating material, but also for the thermal treatment of semiconductor wafers in the semiconductor or photovoltaic industry.

Infrared radiators according to the invention can be easily adapted to the geometry of a surface to be heated of a heating material due to their particular, especially areal radiation characteristic, so that a homogeneous irradiation two- or three-dimensionally designed Heizgut surfaces is made possible.

In contrast to infrared surface radiators, in which an electrical resistance element of a resistance material forms the actual heating element of the infrared surface radiator, in infrared surface radiators according to the invention, the resistance element serves to heat another component, here as The heat transfer from the electrical resistance element to the substrate may be based on conduction, convection and / or thermal radiation.

PRIOR ART Known infrared surface radiators frequently have a plurality of infrared radiators with a cylindrical radiator tube of quartz glass. In these surface radiators, the radiator tubes are arranged so that their longitudinal axes parallel to each other in a plane, whereby a flat lamp arrangement is obtained, the geometry of which is adaptable to that of a heating material to be irradiated. Within the radiator tube is usually a helical resistance wire, which has no or no significant contact with the radiator tube. The heat transfer from the resistance wire to the radiator tube is essentially due to thermal radiation.

In addition, infrared surface radiators are known in which a heating element is applied directly to a support (substrate). The substrate can have different spatial forms; For example, it can be plate-shaped, tile-shaped, planar, tubular or polyhedron-shaped. The heating element of this radiator is in direct contact with the carrier, so that a heat transfer from the conductor track to the carrier takes place primarily by heat conduction. From WO 1999/025154 A1, such an infrared surface radiator is known in which an electrical resistance element is in direct contact with a substrate made of quartz glass. The resistance element has meandering shape, for example, and is applied to the substrate surface by means of film, screen printing or thin-film technology and then baked. In this case, the printed conductor is in planar, direct contact with the quartz glass substrate, so that the heat transfer from the resistor element to the quartz glass substrate takes place predominantly by heat conduction and convection, which can have a positive effect on the power efficiency. A substrate made of quartz glass has a good corrosion, temperature and thermal shock resistance and it is available in high purity. Therefore, it is also suitable as a substrate material for an infrared radiator in high-temperature heating processes with high demands on purity and inertness. However, quartz glass basically has a comparatively low thermal conductivity and is even used as a heat insulator. Therefore, with thin substrate wall thicknesses there is a risk of inhomogeneous heat distribution, which in extreme cases on the opposite side of the substrate is shown as an image of the shape of the electrical resistance element. This can only be countered by a high occupancy density with tracks, which is expensive. On the other hand, thick substrate wall thicknesses suffer from power efficiency and reaction time (that is, fast temperature changes that require rapid heating and cooling of the substrate are not possible).

The printed conductors applied to the substrate usually have a small cross-sectional area, so that they are expensive to manufacture and have low resistance under mechanical stress. Therefore, it is possible that a defective trace is applied to the substrate during the manufacturing process. The application of faulty traces to a substrate is associated with high rejects and high manufacturing costs. This is especially true for printed conductors, which are produced using printing techniques - for example by screen printing or inkjet printing - in which any errors in the heating element are detectable only after completion of the printing process and thus after application to the substrate. In addition, the production of printed circuit traces is costly because the ink used for printing often contains high levels of precious metals, such as platinum, gold or silver.

Frequently, printed conductors are applied to a plastic film. In addition, a printed circuit board applied to a plastic in the production of infrared surface radiators has the disadvantage that it can only be used in a narrow temperature range, since plastic films generally have only a limited temperature resistance. Especially with printed conductors, the form the resistance element of a heating element, therefore, the use of printed circuit films has proved to be disadvantageous.

Technical task

The present invention is therefore based on the object of specifying a simple and cost-effective method for producing an infrared surface radiator, which exhibits a homogeneous radiation emission with high radiation power per unit area.

In addition, the object of the present invention is to provide an infrared surface radiator which has a high radiation power per unit area and, in particular, enables homogeneous heating with thin substrate wall thicknesses.

General description of the invention

With regard to the method for producing an infrared radiator, the abovementioned object is achieved on the basis of a method of the type mentioned at the outset by providing, in accordance with method step (a), a substrate which is manufactured from a composite material which is an amorphous matrix component as well as an additional component in the form of a semiconductor material, and that the conductor is provided as a shaped piece with geometrically solid form, which is applied in accordance with method step (b) on the surface of the substrate, that the conductor track and the substrate are permanently interconnected.

The present invention is based on the idea that an infrared surface radiator with high radiation power, such as a radiation power above 150,000 W / m ² , can be produced in a particularly simple and cost-effective manner if it is made on the one hand from a thermally excitable material and on the other hand as the conductor track is provided as a semi-finished product.

The fact that the conductor is provided as a prefabricated fitting with geometrically solid form, it is possible manufacturing defects in the production the track can occur early to detect. In particular, in comparison with a printed conductor produced using printing techniques, it is possible to check the conductor-track shaped pieces for their functional capability before the joining step with the substrate. As a separate component, for example, the printed conductor can simply be subjected to a voltage. As a result, it is possible to sort out a faulty trace, before the faulty trace is connected to the substrate, so that the formation of scrap can be reduced and thereby manufacturing costs can be reduced. Compared to printed conductors has a prefabricated, provided as a semifinished conductor further has the advantage that can be dispensed with the use of costly materials, such as expensive printing ink, on the one hand mostly a high proportion of precious metals, such as platinum, and on the other high demands their suitability as an ink.

The production of a conductor can be done by various manufacturing methods, for example by punching, laser beam cutting or casting. Preferably, the fitting is made from a sheet using a thermal separation process or by punching. The use of thermal cutting or punching processes enables the production of printed conductors in large quantities and thus helps to keep material and manufacturing costs low.

Due to the possible use of different production methods, materials can also be processed into a printed circuit, which can hardly or only with difficulty be processed by means of printing techniques. The fact that the conductor track is made of an electrically conductive and heat flow during heat flow generating resistance material, this acts as a heating element. A flat, homogeneously radiating infrared radiator with high radiation power, however, is only obtained when the conductor is brought into contact with the substrate. According to the invention the conductor track is applied as a shaped piece on the surface of the substrate and permanently connected to the substrate. In this case, the conductor track can be joined to the substrate both mechanically and thermally. be connected to or via a non-conductive layer. In the simplest case, the interconnect is attached to the substrate in loose composite.

The trace acts as a "local" heating element that can locally heat at least a portion of the substrate, and the trace is sized to heat a portion of the substrate made from the composite material As a result of the fact that the conductor track, in combination with the substrate, is in direct contact with the substrate surface, a particularly compact and therefore inexpensive infrared surface emitter is obtained.

The heat transfer from the electrical resistance element to Trägerhorde takes place primarily by heat conduction; but it can also be based on convection and or heat radiation.

The fact that the substrate comprises an amorphous matrix component and an additional component in the form of a semiconductor material, a substrate is obtained which can take a high-energy, excited state in which an emission of infrared radiation with high radiation power is particularly favored. The composition of the composite material is chosen so that the composite material forms the actual infrared radiation emitting element. The composite material contains the following components:

• The amorphous matrix component represents the largest part of the composite material in terms of weight and volume. It significantly determines the mechanical and chemical properties of the composite material; For example, its temperature resistance, strength and corrosion properties. The fact that the matrix component is amorphous - it is preferably made of glass - the geometric shape of the substrate compared to a substrate made of crystalline materials can be more easily adapted to the requirements of the specific application of the infrared surface radiator according to the invention. The matrix component can consist of undoped or doped quartz glass and, if appropriate, contain other oxidic, nitridic or carbidic components in addition to S1O2 in an amount of up to a maximum of 10% by weight. According to the invention, it is additionally provided that an additional component in the form of a semiconductor material is incorporated in the matrix component. It forms its own amorphous or crystalline phase dispersed in the amorphous matrix component.

A semiconductor has a valence band and a conduction band that can be separated by a forbidden zone of width up to ΔΕ »3 eV. The width of the forbidden zone is for example Ge 0.72 eV, Si 1, 12 eV, InSb 0.26 eV, GaSb 0.8 eV, AlSb 1.6 eV, CdS 2.5 eV. The conductivity of a semiconductor depends on how many electrons can pass the forbidden zone and enter the conduction band from the valence band. In principle, only a few electrons can jump over the forbidden zone at room temperature and enter the conduction band, so that a semiconductor usually has only a low conductivity at room temperature. However, the degree of conductivity of a semiconductor depends substantially on its temperature. As the temperature of the semiconductor material increases, so does the likelihood that sufficient energy will be available to lift an electron from the valence band into the conduction band. Therefore, in semiconductors, the conductivity increases with increasing temperature. Semiconductor materials therefore exhibit good electrical conductivity at sufficiently high temperatures.

The additional component is distributed evenly or deliberately unevenly as a separate phase. The additional component significantly determines the optical and thermal properties of the substrate; more precisely, it causes absorption in the infrared spectral range, that is the wavelength range between 780 nm and 1 mm. The additional component exhibits an absorption which is higher than that of the matrix component for at least part of the radiation in this spectral range. The phase regions of the additional component act as optical defects in the matrix and lead, for example, to the composite material - depending on the layer thickness - may appear visually black or grayish-black at room temperature. In addition, the impurities themselves have a heat-absorbing effect.

In the composite material, the additional component is preferably present in a type and amount which causes a spectral emissivity ε of at least 0.6 for wavelengths between 2 pm and 8 pm in the composite material at a temperature of 600 ° C. A particularly high emissivity can be achieved if the additional component is present as an additional component phase and has a non-spherical morphology with maximum dimensions of on average less than 20 μm, but preferably more than 3 μm.

The non-spherical morphology of the additional component phase also contributes to a high mechanical strength and a low cracking tendency of the composite material. The term "maximum dimension" refers to the longest extent of an isolated region with additional component phase, which is recognizable in the form of a cut The median value of all longest extensions in a micrograph forms the above-mentioned mean value.

According to Kirchhoff's law of radiation, the spectral absorbance x and spectral emissivity s of a real body in thermal equilibrium correspond to one another. cu = ελ (1) The additional component thus causes the substrate material to emit infrared radiation. The spectral emissivity ex can be calculated as follows with known directional hemispheric spectral reflectance Rgh and transmittance Tgh: £ λ = 1- gh - Tgh (2)

The term "spectral emissivity" is understood to mean the "spectral normal emissivity". This is determined using a measurement principle known as "Black-Body Boundary Conditions" (BBC), published in "DETERMINING THE TRANSMISSION AND EMITTANCE OF TRANSPARENT AND SEMITRANSPARENT MATERIALS AT ELEVATED TEMPERATURES"; J. Manara, M. Keller, D. Kraus, M. Arduini-Schuster; 5th European Thermal Sciences Conference, The Netherlands (2008).

The amorphous matrix component has a higher heat radiation absorption in the composite material, ie in conjunction with the additional component, than would be the case without the additional component. This results in improved heat conduction from the conductor into the substrate, a faster distribution of the heat and a higher radiation rate to the substrate. This makes it possible to provide a higher radiant power per unit area and to produce a homogeneous radiation and a uniform temperature field even with thin substrate wall thicknesses and / or with a comparatively low trace occupancy density. A substrate with a low wall thickness has a low thermal mass and allows rapid temperature changes. Cooling is not required for this. In a particularly preferred embodiment of the method according to the invention, the additional component is present in a type and amount which causes a spectral emissivity ε of at least 0.75 for wavelengths between 2 pm and 8 μm in the composite material at a temperature of 1000 ° C.

Accordingly, the composite material has a high absorption and emission capacity for thermal radiation between 2 μm and 8 μm, that is to say in the wavelength range of the infrared radiation. This reduces the reflection on the composite material Oberf laugh, so that, assuming a negligible transmission, a reflectance for wavelengths between 2 pm and 8 pm and at temperatures above 1000 ° C at a maximum of 0.25 and at temperatures of 600 ° C of maximum 0.4 results. Non-reproducible heating By reflected heat radiation tongues are thus avoided, which contributes to a uniform or desired non-uniform temperature distribution.

It has proven useful if the connection between conductor track and substrate is produced by a joining method, preferably by mechanical joining, by gluing or by welding.

Joining techniques provide a permanent connection of at least 2 components. The cohesion between the components can be created at least at individual joints. According to the invention, the conductor track is present as a shaped piece, that is to say it has a geometrically fixed shape. When joining conductor track and substrate, the substrate may be present in a geometrically solid form or as a shapeless material. Preferably, the substrate is also in geometrically solid form. This allows a particularly simple positioning of the conductor on the substrate.

The conductor track and the substrate can advantageously be connected to one another by mechanical joining, gluing, soldering, welding. With regard to the mechanical joining, in particular the pressing has proven itself. For this purpose, the substrate may be provided with a recess which corresponds to the shape of the conductor track, for example with a groove into which the conductor track is pressed. A connection of a glass substrate to a conductor track can alternatively take place with a glass solder. Glass solders are characterized by a particularly low softening temperature; they can be used for the production of thermally generated compounds of materials with glasses. The manufacturing process is similar to the soldering of metals, but glass solder joints are systematically attributed to the adhesive bonds. Adhesive bonds have the advantage that they are particularly easy to manufacture. In addition, the properties of the adhesive can be matched to the material properties of the materials to be joined. For example, the coefficient of thermal expansion of the adhesive (glass solder) is chosen so that it lies between the thermal expansion coefficient of the conductor track and the thermal expansion coefficient of the substrate. A weld joint is created by introducing energy into the trace and the substrate. In this case, both the conductor track and the substrate are at least partially melted and bonded together during cooling in the melting region. In a preferred modification of the method according to the invention, it is provided that the conductor track is connected to the surface of the substrate via a non-conductive layer.

A nonconductive layer acts electrically as an insulator; Although it can transport the heat generated by the track to the substrate, but can hardly generate heat itself. The non-conductive layer therefore contributes only to a limited extent to the heating of the substrate. The main energy input takes place through the conductor track, so that the geometric shape of the conductor track on the one hand determines the area of the substrate which is thermally excited, and on the other hand determines the extent of the heat input into the substrate. Therefore, deviations in the layer thickness of the nonconducting layer, and in particular uneven - possibly only partial - application of the non-conductive layer to the substrate have no significant effect on the heat input into the substrate and the substrate temperature distribution.

It has proved to be advantageous if a sheet of silicon carbide (SiC), molybdenum disilicide (M0S12), tantalum (Ta) or high temperature steel is used for the production of the molding.

The aforementioned materials silicon carbide (SiC), molybdenum disilicide (M0S12), tantalum (Ta) or high temperature steel are inexpensive compared to precious metals such as gold, platinum or silver. In addition, the aforementioned materials are difficult to process with printing process, but they can be easily converted into a shaped body, which can be used as a semi-finished product in the production of the infrared surface radiator. In addition, these materials have the advantage that they are resistant to oxidation in air, so that an additional, the conductor track covering layer (cover layer) for the protection of the conductor is not absolutely necessary. However, it has proven to be advantageous if a cover layer is provided, which is made of opaque quartz glass. Such a cover layer acts as a diffuse reflector and at the same time protects and stabilizes the conductor track. The production of such a covering layer of opaque quartz glass is described, for example, in WO 2006/021416 A1. It is produced from a dispersion containing amorphous SiO 2 particles in a liquid. This is applied to the conductor surface facing the substrate, dried to a greensheet and sintered at high temperature.

Advantageously, the shaped piece has a section with a spiral or meandering line pattern. This allows a uniform coverage of the substrate surface with a single trace. A single trace can be connected and controlled particularly easily to a power source.

In a preferred modification of the method according to the invention, prior to the application of the conductor track to the surface of the carrier according to method step (b), the shaped piece is provided at its ends with a conductor track whose cross-sectional area is greater than the cross-sectional area of the line pattern.

Preferably, the line pattern extends in a plane. In order to facilitate the electrical contacting of the conductor track, it has proved to be advantageous if the conductor track has a lower temperature in the region of its electrical contacting than in the heating area. In order to make this possible, the conductor track can be provided with a conductor track which has a larger cross-sectional area than the conductor track. Due to its larger cross-sectional area, the conduction path has a lower resistance; It is therefore much less heated than the tracks themselves.

The conductor track and the conductor track can form a unit which is formed in one piece or several pieces. An integral unit of conductor track and conductor track can be manufactured in a single method step, for example by punching out of a metal sheet or by laser beam cutting. In this case, for example, given a sheet thickness, the conductor path has a greater width than the conductor track. Alternatively, it is also possible to To connect web and line in an additional process step before they are applied as a unit on the surface of the substrate. For example, the conductor track and conductor track can be welded together. It has proven to be advantageous if contact elements are provided at the conductor track ends. Contact elements serve for the simplified electrical contacting of the conductor track; they preferably form a plug-in element of a plug connection. The connector is used for releasable connection of the contact element with an electrical power supply. As a result, a simple separation and connection of the interconnect to an electrical supply line, in particular with a current / voltage source, is made possible.

It has proven to be advantageous if the conductor track is made of the same material as the conductor track.

A connection between the conductor track and the conductor track can be produced particularly easily if both components are made of the same material, for example by soldering.

With regard to the infrared surface radiator, the above object is achieved, starting from an infrared surface radiator of the type mentioned in the present invention, that the substrate is made of a grain posit- material comprising an amorphous matrix component and an additional component in the form of a semiconductor material, and that the conductor as Form fitting geometrically solid form is applied to the surface of the substrate, that conductor track and carrier are permanently connected to each other.

The infrared surface radiator according to the invention has, on the one hand, a substrate of a thermally applicable material and, on the other hand, a geometrically fixed shape connected to the substrate.

The fact that the conductor is a shaped piece with a geometrically solid shape, this has a particularly high mechanical stability; It can also be manufactured with high accuracy. Compared to printed conductors has a prefabricated, provided as a semifinished conductor further has the advantage that can be dispensed with the use of costly materials, such as expensive printing ink, on the one hand mostly a high proportion of precious metals, such as platinum, and on the other high demands their suitability as an ink.

The production of the conductor can be done by various manufacturing methods, for example by punching, laser beam cutting or casting. In conjunction with the substrate, the printed conductor forms a flat, homogeneously radiating infrared radiator; it acts as a "local" heating element with which at least a portion of the substrate can be locally heated The conductor is dimensioned to heat a portion of the substrate made of a particular material, namely a composite material, which is a By virtue of the substrate comprising an amorphous matrix component and an additional component in the form of a semiconductor material, a substrate is obtained which contains a high-energy, In the case of the composition of the composite material, reference is made to the above explanations of the method according to the invention.

In a preferred embodiment of the infrared surface radiator according to the invention it is provided that a plurality of conductor tracks are applied to the substrate with a geometrically solid shape, which are each individually electrically actuated bar.

The provision of a plurality of conductor tracks allows individual control and adaptation of the irradiance achievable with the infrared surface radiator. On the one hand, the radiation power of the substrate can be adjusted by a suitable choice of the distances between adjacent conductor track sections. In this case, portions of the substrate are heated to different degrees so that they emit infrared radiation with different irradiances. Alternatively, the tracks can be individually controlled electrically, so that they are operated with different operating voltages or operating currents. In fact, it has been shown that, in particular, the edge regions of the substrate are frequently heated to a low level than the center region of the substrate. One possible reason for this is that there is a larger temperature gradient in the edge area compared to its surroundings, so that the edge area cools faster than, for example, the center area of the infrared surface radiator. A variation of the operating voltages or operating currents applied to the respective strip conductors enables a simple and rapid adaptation of the substrate temperature distribution.

It has proven useful if the amorphous matrix component is quartz glass, and the semiconductor material is present in elemental form, wherein the weight fraction of the semiconductor material is in the range between 0.1% to 5%.

In this context, it has proved to be advantageous if the amorphous matrix component and the additional component have electrically insulating properties at temperatures below 600 ° C.

Quartz glass is an electrical insulator and, in addition to high strength, has good corrosion, temperature and thermal shock resistance; It is also available in high purity. Therefore, it is also suitable as a matrix material for high-temperature heating processes with temperatures up to 1,100 ° C. Cooling is not required.

The finely divided areas of a semiconductor phase act as optical impurities in the matrix on the one hand and cause the substrate material - depending on the layer thickness - to appear visually black or grayish-blackish at room temperature. On the other hand, the impurities also affect the overall heat absorption of the composite material. This is mainly due to the properties of the finely distributed phases of the elementary semiconductor, according to which on the one hand the energy between valence band and conduction band (band gap energy) decreases with temperature and on the other hand with sufficiently high activation energy electrons are lifted from the valence band in the conduction band, what with a significant increase in the absorptive onscoefficient. The thermally activated occupation of the conduction band results in the semiconductor material being able to be somewhat transparent at room temperature for certain wavelengths (such as from 1000 nm) and becoming opaque at high temperatures. With increasing temperature of the composite material, therefore, absorption and emissivity may increase dramatically. This effect depends, among other things, on the structure (amorphous / crystalline) and doping of the semiconductor.

Preferably, the additional component is elemental silicon. Pure silicon shows, for example, from about 600 ° C, a significant increase in emissions, which reaches a saturation from about 1,000 ° C.

The semiconductor material and in particular the preferably used, elemental silicon therefore cause blackening of the glassy matrix component at room temperature, but also at elevated temperature above, for example, 600 ° C. This achieves a good emission characteristic in the sense of a broadband, high emission at high temperatures. The semiconductor material, preferably the elemental silicon, forms a self-dispersed Si phase dispersed in the matrix. This may contain a plurality of semimetals or metals (but metals up to a maximum of 50% by weight, better still not more than 20% by weight, based in each case on the weight fraction of the additional component), the composite material exhibiting no open porosity but instead at most a closed porosity of less than 0.5% and a specific gravity of at least 2.19 g / cm ³ . He is therefore suitable for carrier hordes, where it depends on purity or gas-tightness of the material from which the carrier Horde is made. The heat absorption of the composite material depends on the proportion of the additional component. The proportion by weight of the additional component should therefore preferably be at least 0.1%. On the other hand, a high volume fraction of the additional component can impair the chemical and mechanical properties of the matrix. In view of this, the proportion by weight of the additional components is preferably in the range between 0.1% and 5%. It has proven particularly useful if the amorphous matrix component is quartz glass and preferably has a chemical purity of at least 99.99% S1O2 and a cristobalite content of at most 1%. A low cristobalite content of the matrix of 1% or less ensures a low devitrification tendency and thus a low risk of cracking when used as an infrared surface radiator so that high demands are also made on particle freedom, purity and inertness, as is generally the case in semiconductor manufacturing processes ,

EXEMPLARY EMBODIMENT The invention will be explained in more detail below on the basis of exemplary embodiments and drawings. This shows in a schematic representation

Figure 1 shows a first embodiment of an infrared surface radiator according to the invention, on the substrate surface, a prefabricated conductor molding is applied, Figure 2 shows an embodiment of a method for producing an infrared surface radiator, wherein a prefabricated conductor is provided as a molded piece and connected to the surface of the substrate .

FIG. 3 shows a side view of a second embodiment of an infrared surface radiator according to the invention, in which a glass layer is applied to the surface covered with a conductor track,

4 shows a side view of a third embodiment of an infrared surface radiator according to the invention, in which the conductor track is connected to the substrate surface via a glass solder, and FIG. 5 shows a side view of a fourth embodiment of an infrared surface radiator according to the invention, in which the conductor track and the substrate are connected to one another mechanically by press-fitting are. FIG. 1 shows a first embodiment of an infrared surface radiator according to the invention, to which the reference number 100 is assigned overall. The infrared surface radiator 100 has a plate-shaped substrate 101, a conductor 102 and two conductor tracks 103a, 103b for electrically contacting the conductor track 5102.

The plate-shaped substrate 101 comprises an amorphous matrix component in the form of quartz glass. In the matrix component, a phase of elemental silicon in the form of non-spherical regions is homogeneously distributed. The plate-shaped substrate 101 has a length l of 100 mm, a width b of 100 mm and a thickness of 2 mm.

The conductor 102 is made of one piece; It forms a flat, planar, three-dimensional shaped piece that can be easily placed on the plate-shaped substrate 101. The conductor 102 is made of high-temperature steel (2.4816) and produced by punching from a steel plate plate. At the ends of the conductor 102, a respective line path 103a, 103b is arranged, which was punched out of the steel plate together with the conductor track 102. In an alternative embodiment of the infrared radiator according to the invention (not shown in FIG. 1), the conductor paths 03a, 103b are welded to ends of the conductor track 102. The production method for an infrared surface radiator with welded-on conductor tracks will be described in more detail below with reference to FIG.

Insofar as the same reference numerals as in FIG. 1 are used in the embodiments shown in other figures, identical or equivalent components and components are referred to, as explained in greater detail above with reference to the description of the first embodiment of the infrared surface radiator according to the invention.

With reference to FIG. 2, a method according to the invention for producing the infrared surface radiator 100 will be explained in more detail using an example.

Production of the Substrate 101 (Semi-Finished Product 1) The preparation is based on the Schlickergießverfahrens, as described in WO 2015/067 688 A1. Amorphous silica grain is pre-cleaned in a hot chlorination process, care being taken that the content of cristobalite is below 1% by weight. Quarzglaskörnung with particle sizes in the range between 250 μιη and 650 μιη wet-ground with deionized water, so that forms a homogeneous Grundschiicker having a solids content of 78%.

Subsequently, the grinding balls are removed from the base schicker and it is a supplement in the form of silicon powder mixed in an amount until a solids content of 83 wt .-% is reached. The silicon powder contains mainly non-spherical powder particles with a narrow particle size distribution whose D97 value is about 10 μm and whose fine fraction has been removed in advance with particle sizes of less than 2 μm.

The slurry filled with the silicon powder is homogenized for a further 12 hours. The weight fraction of the silicon powder in the total solids content is 5%. The SiO 2 particles in the finished homogenized slip show a particle size distribution which is characterized by a D 50 value of about 8 μm and by a D 9 o value of about 40 μm.

The slurry is poured into a die casting mold of a commercial die casting machine and dewatered through a porous plastic membrane to form a porous green body. The green body has the shape of a rectangular plate. To remove bound water, the green body is dried at about 90 ° C for 5 days in a ventilated oven. After cooling, the resulting porous blank is mechanically machined almost to the final dimension of the quartz glass plate to be produced with the plate thickness of 4 mm. For sintering the blank this is heated in a sintering oven under air within 1 hour to a heating temperature of 1390 ° C and held at this temperature for 5 hours.

The quartz glass plate thus obtained forms the substrate 101. It consists of a gas-tight composite material with a density of 2.1958 g / cm ³ , in which in a matrix of opaque quartz glass separate, non-spherical regions are distributed homogeneously from elemental Si phase whose size and morphology largely correspond to those of the Si powder used. The maximum dimensions are on average (median value) in the range of about 1 pm to 10 pm. The matrix is visually translucent to transparent. On microscopic examination it shows no open pores and possibly closed pores with maximum dimensions of on average less than 10 μm; the density calculated on the basis of the density is 0.37%. The composite material is stable in air up to a temperature of about 1 .150 ° C.

Production of the conductor 102 (semifinished product 2) To produce the conductor 102, a shaped piece is punched out of a tantalum sheet having a thickness of 0.2 mm, a width of 500 mm and a length of 2000 mm, which is to form the conductor. The punching is done with a punch in the form of a punch, with a flat base serves as a counterpart. The punched-out conductor track 102 has a meander-shaped line course and comprises two meandering structures arranged next to one another in a plane. Figure 2-1 shows the punched conductor 102. The conductor tracks 102 extends over a length of 60 mm and a width of

60 mm.

Welding the conductor 102 with the conductor paths 103a, 103b The conductor 102 forms the so-called "hot" zone of the radiator in the finished infrared surface radiator 100. For the electrical contacting of the conductor 102, a "cold" zone is required. As shown in Figure 2-II, become to this

Purpose conductor paths 103a, 103b welded to the ends of the conductor 102. The conductor paths 103a, 03b are identical; they have a length of 40 mm, a width of 5 mm at a thickness of 0.4 mm.

Applying the conductor track 102 provided with the conductor tracks 103a, 103b to the substrate 101

FIG. 2-III shows the printed conductor 102 provided with the conductor tracks 103a, 103b as it is applied to the substrate 101. First, the conductor 102 placed on top of the substrate 101. A glass solder is applied and then heated to softening temperature, so that liquid glass solder closes the conductor 102 and the substrate surface. After sintering the glass solder, the conductor 2 and the substrate 101 are allowed to cool to form the glass solder joining compound.

Applying a reflector layer (optional)

Subsequently, a slurry layer is applied to the upper side of the substrate 101 and the printed conductor 102 applied thereon. This slip is obtained by modifying the SiO 2 base slip, as already described above (without an addition of silicon powder), by mixing amorphous SiO 2 grain in the form of spherical particles having a grain size of 5 μm into the homogeneous, stable base slip until a solids content of 84 wt .-% is reached. This mixture is homogenized for 12 hours in a drum mill at a speed of 25 rpm. The slip thus obtained has a solids content of 84% and a density of about 2.0 g / cm ³ . The SiO 2 particles in the slurry obtained after grinding the quartz glass grains show a particle size distribution which is characterized by a D 50 value of about 8 μm and by a D 90 value of about 40 μm.

The slip is sprayed on top of the pre-alcoholic cleaned substrate 101 for a few seconds. On the substrate 101 thereby forms a uniform slurry layer with a thickness of about 2 mm. The dried slurry layer is crack-free and has an average thickness of slightly less than 2 mm.

The dried slurry layer is then sintered under air in a sintering furnace.

FIG. 3 shows a side view of a second embodiment of an infrared surface radiator according to the invention, to which the reference number 300 is assigned overall. The infrared surface radiator 300 has a plate-shaped substrate 301, a conductor 302 and a cover layer 303. The plate-shaped substrate 301 has a rectangular shape with a plate thickness of 2.5 mm. It consists of a composite material with a matrix of quartz glass. The matrix is visually translucent to transparent. It shows under microscopic observation no open pores and possibly closed pores with maximum dimensions of on average less than 10 μηι. In the matrix, a phase of elemental silicon in the form of non-spherical regions is homogeneously distributed. Their weight content is 5%. The maximum dimensions of the silicon phase ranges are on average (median value) in the range of about 1 μητι to 10 μηι. The composite material is gas-tight, has a density of 2.19 g / cm ³ and is stable in air up to a temperature of about 150 ° C.

On the one hand, the embedded silicon phase contributes to the opacity of the composite material as a whole, and it has effects on the optical and thermal properties of the composite material. This shows at high temperatures a high absorption of heat radiation and a high emissivity. At room temperature, the emissivity of the composite material is measured using an integrating sphere. This allows the measurement of the directed hemispheric spectral reflectance Rgh and the directed hemispherical spectral transmittance Tgh, from which the normal spectral emissivity is calculated. The measurement of the emissivity at elevated temperature takes place in the wavelength range of 2 to 18 pm by means of an FTIR

Spectrometer (Bruker IFS 66v Fourier Transform Infrared (FTIR)), to which a BBC sample chamber is coupled via additional optics, using the BBC measurement principle mentioned above. The sample chamber has temperature-controllable blackbody environments in front of and behind the sample holder in the half-chambers and a beam exit opening with detector. The sample is heated to a predetermined temperature in a separate oven and taken for measurement in the beam path of the sample chamber with the blackbody environments set at a predetermined temperature. The intensity detected by the detector is composed of an emission, a reflection and a transmission component, namely intensity emitted by the sample itself, intensity incident on and reflected from the front half-space, and intensity from the back hemisphere to the sample falls and is transmitted by this. To determine the individual quantities of emission, reflection and transmittance, three measurements must be carried out.

The emissivity measured in the wavelength range from 2 μιη to about 4 μιη depends on the temperature. The higher the temperature, the higher the emission. At 600 ° C, the normal emissivity in the wavelength range from 2 μιη to 4 μηη is above 0.6. At 1000 ° C, the normal emissivity in the entire wavelength range between 2 pm and 8 μm is above 0.75. The conductor 302 is made of a tantalum sheet by cutting it with a laser beam into a molding. The fitting has a geometrically fixed shape; it is integrally formed and has the shape of an Archimedean spiral, in which adjacent portions of the conductor 302 have a distance a of 2 mm. The conductor 302 has a cross-sectional area of at least 0.02 mm ² at a width of 1 mm and a thickness of 20 μηη. At both ends of the spiral tantalum contacts (not shown) are welded to the track. The contacts have a cross-sectional area of at least 0.5 mm ² . The fact that the contacts have a larger cross-sectional area than the conductor track, they show a lower electrical resistance than the conductor 302; they are therefore heated less strongly than the conductor 302 at current flow. The contacts therefore cause a lowering of the temperature, so that an electrical contacting conductor 302 is simplified via the contacts.

The conductor track 302 is fixedly connected to the substrate 301 by applying a cover layer 303 made of glass to the surface 304 of the substrate 301 provided with the conductor track. The cover layer 303 is made of a glass whose thermal expansion coefficient is in a range between the thermal expansion coefficient of the substrate and the thermal expansion coefficient of the wiring. The thermal expansion coefficient of the substrate 301 is 0.54 10 ^-6 K ^-1 , and the thermal expansion coefficient of the conductor 302 is 6.4 10 ^-6 K ^-1 and the thermal expansion coefficient of the cover layer 303 is approx 0.54 10 ^"6 K ^-1. The cover layer 303 has an average layer thickness of 1 to 8 mm. The cover layer 303 covers the entire heating area of the substrate 301. It covers the conductor 302 and thus fully shields the conductor 302 from chemical or mechanical influences from the environment.

FIG. 4 shows a side view of a third embodiment of an infrared surface radiator according to the invention, to which the reference numeral 400 as a whole is assigned. The infrared surface radiation 400 comprises a substrate 301, as described in the description of FIG. 3, as well as a conductor track 402 and a cover layer 403. The track 402 is connected to the substrate surface 404 via a glass solder 407.

The conductor track 402 shows a meander-shaped course which covers a heating surface of the substrate 301 so tightly that a uniform spacing of 1.5 mm remains between adjacent conductor track sections. In the cross section shown, the conductor 402 has a cross-sectional area of 0.05 mm ² with a width of 1 mm and a thickness of 50 ym.

Glass solders are low-softening glasses; they belong to the group of adhesives. The glass soldering process is similar to soldering metals. Due to the low softening temperature of the glass solder this is liquid at the processing temperature. The substrate, however, is solid at the processing temperature.

As a glass solder, a glass paste of glass powder and an organic binder is used, for example, the glass solder no. G018-385 Schott AG, Mainz, Germany. This glass solder has a thermal expansion coefficient α (20-300) of 8.4 ppm / K, a density of 3.14 g / cm ³ , a glass transition temperature of 992 ° C and a melting temperature of 1000 ° C.

In the production of the infrared surface radiator 400, the conductor track is first produced as a shaped piece by punching out of a sheet of high-temperature steel. Subsequently, it is heated to the surface of the substrate 301 and applied a glass solder layer. On the glass solder layer, the track 402 is on and this together with the glass solder layer heated until the glass solder layer softens so that upon cooling of the glass solder layer, a joint between glass solder layer and substrate 301 on the one hand and glass solder layer and tracks 402 on the other. Finally, to protect against mechanical and chemical stress, the conductor track 402 and the glass solder layer are provided with a cover layer 403 made of a transition glass whose thermal expansion coefficient is in the range between the thermal expansion coefficient glass solder and the thermal expansion coefficient of the conductor track 402. FIG. 5 shows a side view of a fourth embodiment of an infrared surface radiator 500 according to the invention, in which conductor track 402 and substrate 501 are mechanically connected to one another by being pressed in.

The substrate 501 is made of the same material as the substrate 301 of FIG. 3. It differs from the substrate 301 known from FIG. 3 in that the surface of the substrate 501 is provided with a groove 502 corresponding to the geometric shape of the conductor 402. The groove width at the base is 1, 2 mm; the groove depth is 0.04 mm. The side surfaces of the groove 502 are slightly inclined; This facilitates the mechanical connection between conductor 402 and substrate 501. On the surface of the substrate 502 and the conductor 402, a cover layer 503 made of quartz glass is applied. In an alternative embodiment (not shown) no cover layer is provided. The cover layer 503 has the function of protecting the track 402 from chemical and mechanical influences. In particular, conductor tracks made of highly heat-resistant steel or molybdenum disilicide have a high temperature resistance, so that it is possible to dispense with a cover layer.

Claims

claims

Method for producing an infrared surface radiator with a substrate made of an electrically insulating material, on the surface of which a conductor track made of an electrically conductive and, in the case of current flow, heat-generating resistance material is applied, comprising the method steps:

(a) providing the substrate,

(b) applying the trace to a surface of the substrate

characterized in that according to method step (a) a substrate is provided, which is made of a composite material comprising an amorphous matrix component and an additional component in the form of a semiconductor material, and that the conductor is provided as a molding, which according to method step (b ) is applied to the surface of the substrate such that conductor track and substrate are permanently connected to each other.

A method according to claim 1, characterized in that the compound of conductor track and substrate is produced by a joining method, preferably by mechanical joining, by gluing or by welding.

A method according to claim 1 or 2, characterized in that the conductor track is connected via a non-conductive layer with the surface of the substrate.

Method according to one of the preceding claims, characterized in that the shaped piece is produced from a sheet using a thermal separation process or by punching.

Method according to one of the preceding claims, characterized in that for the production of the molding a workpiece made of silicon umcarbide (SiC), molybdenum disilicide (M0S12), tantalum (Ta) or high temperature solid steel is used.

Method according to one of the preceding claims, characterized in that prior to the application of the conductor track on the surface of the substrate according to method step (b), the shaped piece is provided at its ends with a conduit whose cross-sectional area is greater than the cross-sectional area of the line pattern.

A method according to claim 6, characterized in that the conductor track is made of the same material as the conductor track.

Infrared surface radiator with a substrate made of an electrically insulating material, on the surface of a conductor of an electrically conductive and heat flow during current flow resistance material is applied, characterized in that the substrate is made of a composite material having an amorphous matrix component and an additional component in the form a semiconductor material, and that the conductor track is formed as a shaped piece and is applied to the surface of the substrate such that the conductor track and the carrier are permanently connected to one another.

9. infrared surface radiator according to claim 8, characterized in that on the substrate a plurality of conductor track fittings are applied, which are each individually controlled electrically.