DE102005017816A1 - Electro ceramic element such as a resistive layer having a PTC characteristic is formed by thermal spraying of PTC particles onto a carrier base - Google Patents

Abstract

The electrical device has an electrically conducting substrate [2] onto which is formed by thermal spraying a positive temperature coefficient, PTC, cold conductor ceramic layer [1]. The PTC layer contains Barium Titanium component. An electrically conducting layer [3] connects with the terminal [4].

Description

It becomes an electroceramic device with a resistance layer specified.

From the publication DE 297 02 813 U1 are resistance layers with PTC characteristic on a hotplate body known.

From the publication DE 197 39 758 A1 a method for the production of PTC resistors is known in which several layers of a PTC ceramic granules are pressed and sintered.

From the publication DE 35 41 705 A1 It is known to apply metal-ceramic catalyst compositions by flame spraying on substrates of metals or metal alloys.

A to be solved Task is to provide an electrical device with low indicate thermal losses.

According to one first embodiment becomes an electrical component with an electrically conductive carrier substrate indicated that with a resistive layer of a PTC ceramic (PTC = positive temperature coefficient) is coated. The PTC ceramic layer can therefore directly on the surface of the carrier substrate, preferably by means of a thermal spraying are generated.

The PTC ceramic is also referred to below as a PTC ceramic.

According to one second embodiment an electrical component is specified with a carrier substrate, on its surface produced by thermal spraying a PTC ceramic layer is. This PTC ceramic layer may, in a first preferred Variant barium titanate included. The PTC ceramic layer may contain vanadium oxide in a second preferred variant. The carrier substrate is preferably electrically conductive.

below be the components according to a first and a second embodiment and explained their advantageous embodiments and a manufacturing method specified.

The here specified electrical component with a carrier substrate and the functional unit comprising ceramic coating is in particular as a heating element of a heater or as overload protection suitable.

The function-relevant parameters of the functional unit, such as the room temperature resistance (R ₂₅ ) and the reference temperature (T _B ) are determined inter alia by the nature and the thickness of the ceramic layer. The reference temperature is understood to be a temperature beyond which the specific resistance of the ceramic layer increases abruptly. The reference temperature is also called Curie temperature. With the thermal spraying, it is possible to reproduce the structure of the ceramic layer with a high degree of accuracy and therefore to adjust the values of R ₂₅ and T _B as well as a predetermined, preferably low specific resistance of the ceramic layer very precisely, ie with only slight tolerance errors.

Under Thermal spraying is understood to mean a spraying process in which from a spray nozzle Coating powder at a temperature of at least 800 ° C emerges.

Under an electrically conductive Material is understood as a material that is at least semiconductive is. The material of the carrier substrate is preferably selected made of metals such. Al, Cu, Ni, Ti, Au, Ag, W, Mg, an Al, Cu, Ti, Mg, Cr-Ni alloy and / or semiconducting materials such. As silicon, silicon carbide or other carbides or silicides.

The carrier substrate is preferably provided in the form of a plate. The carrier substrate can z. B. made of a metal sheet, preferably an Al sheet be.

On that of the carrier substrate opposite side of the PTC ceramic layer An electrically conductive layer can be produced. The carrier substrate, the electrically conductive layer and the interposed PTC ceramic layer form a functional unit, preferably a heating element. The electrically conductive layer is preferably at least in their Contact area solderable been made and connected to a to be connected to a power source electrical Connection, z. In the form of a wire or a metal strip, preferably firmly connected by means of a solder mass.

The carrier substrate can itself as an electrical connection between the power source and the PTC ceramic layer can be used. In this case deleted Therefore, a aufzubringender additionally on the substrate electrical connection for contacting the heating element.

The PTC ceramic layer is a functional layer formed as a resistive layer having a positive temperature coefficient is. The PTC ceramic layer is to be distinguished from ceramic protective layers or catalyst layers.

The PTC ceramic layer is preferably in a direct thermal and electrical contact to the carrier substrate, which is preferably electrically conductive. In a good, preferably large-area thermal Coupling of the ceramic layer to a metallic carrier can the heat energy generated in the ceramic layer by a current flow from this ceramic layer over the metallic carrier directly discharged become. Thereby can thermal losses due to low thermal contact resistance across from one example by means of a primer layer with a Substrate connected or pressed to a substrate ceramic layer - what by a high thermal contact resistance is characterized - reduced become.

The ceramic layer preferably has barium titanate (BaTiO ₃ ) and / or vanadium oxide (V ₂ O ₃ ) as the base component, which is rendered conductive by doping with one or more elements. Advantageously, the dopants are yttrium and / or manganese, the total mass fraction being for example less than 5%, preferably less than 1%. For barium titanate, an excess of titanium over a stoichiometric composition of BaTiO _{3 is} advantageous for adjusting the electrical conductivity of the ceramic layer. The electrical conductivity can also be adjusted by a titanium deficiency.

The Ceramic material may further include one or more additives. These accessories can calcium, Strontium and / or lead. It is advantageous if the mentioned additions total less than 50 wt .-%, in an advantageous variant less than 10 wt .-% amount.

The conductive Ceramic layer is preferably applied in a thickness, the does not exceed 1 mm. In particular, it is possible by means of of thermal spraying of PTC ceramic layers in a thickness between 10 μm and 1 mm to produce. The thickness and the total mass of the PTC ceramic layer is opposite in this case usual PTC ceramic layers much smaller, so z. B. in heater applications due the low ceramic mass of the thermal efficiency significantly higher and the electric power input lower. Due to the low Layer thickness and the large area direct thermal contact between the substrate and the ceramic layer is a constant power dissipation possible. Due to the low Layer thickness also exists a big Saving potential of the ceramic material.

The Layer thickness of the ceramic layer is determined by process conditions during thermal spraying, in particular by a suitably selected injection duration adjustable. Thus, depending on the application, the optimum layer thickness will be realized.

The thermal spraying may preferably be carried out that immediately in the course of thermal spraying a uniform electrical conductive Ceramic coating with given properties on the substrate is generated, and therefore the shaping and sintering of the ceramic layer can be omitted.

The Thermal spraying is particularly well suited to large ceramic layers with a uniform thickness and to produce a homogeneous texture.

One carrier substrate can z. B. be structured in the form of a spiral or a meander. It is possible, instead of just a carrier substrate several independent, preferably in plan view to use honeycomb carrier substrates, by means of the conductive, preferably formed over a large area, thermally sprayed ceramic layer are to be connected together. The ceramic layer thus forms a bridge between the carrier substrates. The carrier substrates are preferably arranged at a small distance from each other. The Ceramic layer covers at least a portion of the respective Carrier substrate. The composite of the ceramic layer and the carrier substrates forms a functional unit, the z. B. is suitable as a Heizregisteraufbau. The thermal injected ceramic PTC thermistor connects the one another spaced support substrates preferably with each other directly, d. H. without an adhesive Intermediate layer between the ceramic layer and the substrates. Thus, a good thermal connection of the ceramic layer to the carrier substrates ensured.

at the production of the ceramic layer by means of thermal spraying can the carrier substrates be arranged on a base. The ceramic layer is then both on the carrier substrates as well as applied to the substrate.

It is possible in principle but not necessary, the underlay from the composite of the ceramic layer and the carrier substrates replace, wherein the ceramic layer is preferably self-supporting and sufficient is formed mechanically stable. Two spaced apart carrier substrates can as two different connections the functional unit used.

The ceramic layer can be patterned using a mask. You can, for example wise be structured into independent stripes that connect each other, the carrier substrates. By the use of a mask can during thermal spraying of the ceramic PTC thermistor on the preferably metallic carrier substrate, a pattern, for. B. a spiral or a meander to increase the effective path length of the current flow generated and thus the heating power per area can be increased.

verstanden, wobei T die Temperatur ist.A ceramic PTC thermistor layer can have the following properties: specific electrical resistance at room temperature between 1 Ω cm and 500 kΩ cm, the reference temperature between 0 and 350 ° C. In a preferred variant, the specific resistance value between 10 Ω cm and 150 kΩ cm and / or the reference temperature between 80 and 220 ° C. The temperature coefficient of the electrical resistance in the region of the Curie temperature of the material is typically between 0.05 and 0.35 / K, preferably between 0.1 and 0.2 / K. Under a temperature coefficient α of the electrical resistance R is a characteristic slope

understood, where T is the temperature.

It is possible, for example, the ceramic PTC thermistor layer with the above properties directly onto a carrier substrate made of metal (eg aluminum).

Further is a method for producing an electroceramic device specified. It is a to form a PTC ceramic layer provided suitable ceramic particles containing coating powder, to form a PTC ceramic layer on an electrical conductive carrier substrate is applied by thermal spraying.

The Applying the ceramic coating powder to the carrier substrate to produce a PTC ceramic layer is preferably carried out by means one of the methods of the process group of thermal spraying (different variants of plasma spraying, detonation spraying, High velocity flame spraying - HVOF). Such a made Ceramic layer preferably has a ferroelectric perovskite structure on.

The Coating powder may in one variant be agglomerated Ceramic particles in the form of granules containing ceramic powder to be available. The coating powder may alternatively be used as a Containing granules of ceramic particles sintered together Ceramic granules powder available stand.

Under A ceramic grain is a granule of agglomerated, not sintered Ceramic particles or a sintered ceramic Granalie to understand.

It is beneficial if the coating powder, whether not sintered Ceramic granules or sintered ceramic granules, a grain size between 5 and 250 μm having.

The Ceramic grain size is preferable to that for the respective application preferred method from the process group adapted to the thermal spraying. The grain size can be in a favorable Variant between 10 and 45 μm chosen be.

The open porosity of the coating powder or granule powder may be between 3 and 40 vol .-%, in a variant between 5 and 30 vol .-% amount. Under the open porosity is a relationship to understand the empty volume to the total volume of the powder. The empty volume comprises the spaces between the granules, but also open pores of ceramic granules.

The Production of the powder can be achieved by various process steps carried out be such as by agglomeration by spray drying. A subsequent one Sintering of the granules is also advantageous. The present as granules However, coating powder does not necessarily have to be pre-sintered. It is possible, Pre-sinter the ceramic powder from loose ceramic particles. At the Pre-sintering of the ceramic grains become electrically conductive ceramic grains whereas non-pre-sintered ceramic grains do not form during the course of the thermal process Splashing to a conductive Ceramic layer to be processed.

At the thermal spraying is the temperature of the coating powder when leaving a spray opening at least 800 ° C. In In a variant, the thermal spraying involves a presintered ceramic particle comprehensive coating powder at a temperature of at least 800 ° C off a spray opening apart. In a further variant, the thermal spraying a non-presintered coating powder at a temperature between 1100 ° C and 1400 ° C from a spray opening apart.

In the following, pre-sintering of a coating powder will be described. The sintering of ceramic grains is preferably carried out in capsules of a refractory material at a temperature which is between 800 and 1400 ° C. During this sintering process, one forms, inter alia, by process parameters such as sintering time, sintering temperature and Sintering atmosphere certain microstructure of the ceramic grains, which ensures predetermined electrical properties such as room temperature resistance, reference temperature, hot resistance, resistance increase or dielectric strength to be produced from the ceramic grains PTC ceramic layer.

Then be two embodiments the method for producing the electroceramic device treated with a PTC ceramic layer.

First embodiment:

The following raw materials are homogenized and deagglomerated: Ba-CO ₃ , SrCO ₃ , CaCO ₃ , SiO ₂ , TiO ₂ , MnCl ₂ , YCl ₃ . The stoichiometric composition is as follows: Ba 77.5 mol%, Ca 13 mol%, Sr 9 mol%, Si 2 mol%, Y 0.4 mol%, Mn 0.1 mol% and TiO ₂ 100.1 mol%. The proportions of the elements Ba, Sr, Ca, Y and Mn are normalized to 100 mol% in total. The proportions TiO ₂ and SiO ₂ are given relative to these 100%. These starting materials are mixed and dispersed in water with addition of organic binders. This mixture is called slip.

Of the Slip is pressed through a filter cloth in a filter press and dried in a drying oven. The filter residue is at a temperature from Z. B. 1100 ° C preferably calcined for two hours. The sales will be after cooling down broken, sieved and then with the addition of an organic Binder dispersed in water. The suspension is reduced to a particle size of Mean 2.5 μm in an annular gap mill ground.

The specified composition of the ceramic material and the specified Parameters such as the grain size, the Temperature and the sintering time should not be a limitation.

through Spray drying - preferably in a DC method - be in a variant granules with a mean granule diameter of Made 50 microns. The granules are preferably spherical.

The Sintering of the granules is z. B. at 1350 ° C for 1 hour and a cooling gradient of 3K / min in an air atmosphere carried out. To the cooling Gentle grinding and fractionation of the granules takes place through a sieve with a Siebmaschenweite of 63 microns and then by a sieve with a mesh size of 32 microns.

The Coating powder thus obtained having a particle size in the range between 32 and 63 μm with the help of a detonation spray system to a PTC ceramic layer processed. The spray distance, d. H. the distance between one Spray opening and the carrier substrate to be coated, is z. B. 150 mm at a detonation rate of 6.5 detonations per second. A detonation is a form of explosion in which the exploding The energy-releasing reaction front sets the speed of sound of explosive substance and a shock front forms. It can be an acetylene-oxygen mixture in the volume ratio of 0.8 can be used. As a carrier substrate For example, an aluminum sheet with dimensions of 100 × 10 × 1 mm may be used become. The PTC layer produced in this way is characterized firmly sintered together particles or crystallites, the firmly with the carrier substrate are connected.

The PTC ceramic layer may additionally z. B. by sputtering with an electrically conductive Layer to be coated. The electrically conductive layer can in all Variants either from a single layer z. B. Al, Ti or W or be composed of several sub-layers. Especially comes in the case of a multi-layer structure, the layer sequence chromium-nickel-silver into consideration.

Of the specific room temperature resistance and the reference temperature of thus produced functional unit is in a Vari ante 10 Ω cm or 80 ° C, wherein the layer thickness of the ceramic layer is 300 μm.

Second embodiment:

The following starting materials are homogenized and deagglomerated: BaCO ₃ , CaCO ₃ , SiO ₂ , TiO ₂ , Mn acetate, Dy acetate. The proportions of the elements Ba, Ca, Dy and Mn are normalized to 100 mol%. The proportions TiO ₂ and SiO ₂ are given relative to these 100%. The stoichiometric composition is as follows: Ba 84.35 mol%, Ca 15 mol%, Si 2 mol%, Dy 0.5 mol%, Mn 0.15 mol% and TiO ₂ 100 mol%. These starting materials are mixed and dispersed in water with the addition of an organic binder.

The Raw material suspension is then spray dried and as a debris at a temperature of 1150 ° C for two Calcined in hours. The cooled Turnover is broken, sieved and then with the addition of one organic binder dispersed in water and to a grain size of on average 3 μm in an annular gap mill ground.

By spray drying - preferably in a DC process - granules are produced in a variant with a mean granule diameter of 60 microns. The granules are in front preferably spherical.

Of the Organic binder can be expelled from the granules in an air atmosphere at 500 ° C.

The coating powder obtained is then processed with a vacuum plasma spray unit at a receiver pressure of 350 mbar with an Ar-H ₂ plasma and a plasma power of 45 kW to form a layer having a thickness of about 150 μm. As Trä germaterial can z. As an aluminum sheet with dimensions of 100 × 10 × 1 mm are used. The PTC layer produced in this way is characterized by solidly sintered particles or crystallites which are firmly connected to the carrier substrate.

The PTC ceramic layer may additionally z. B. by screen printing with an electrically conductive Paste, preferably aluminum paste, which is coated by a thermal treatment is baked at 850 ° C.

Of the specific room temperature resistance and the reference temperature of In the second example produced functional unit is z. B. 100 Ω cm or 140 ° C, where the layer thickness of the ceramic layer is 150 μm.

The individual specified in the first and second embodiments Procedural steps can be used in any combination with each other. for example can the PTC ceramic layer in the first example with a metal paste to be burned in instead the sputtered layer sequence are coated. Vice versa can in the second example on the PTC ceramic layer in the first example specified layer sequence as an electrically conductive layer be applied.

The PTC ceramic layer can be subjected to a thermal treatment after thermal spraying at a temperature T <800 ° C. The duration of such a treatment can, for. B. amount to several hours. In the course of the aftertreatment, the structure and therefore also the function-relevant properties such as R ₂₅ and T _{B of} the PTC ceramic layer change. The aftertreatment can therefore serve to set the predetermined values of R ₂₅ and T _B.

The electrical component will now be explained with reference to figures. It demonstrate:

1 in cross-section, a component with a PTC ceramic layer, which is applied directly to a carrier substrate;

2A and 2 B a section of a component with a plurality of interconnected by the PTC ceramic layer carrier substrates in a view from above and in cross section;

3A and 3B a detail of a component having a plurality of interconnected by the PTC ceramic layer honeycomb carrier substrates in a view from above ( 3A ) and in cross section ( 3B );

3C the device according to 3A and 3B in a perspective view from the right.

1 shows a preferably electrically conductive carrier substrate 2 and a PTC ceramic layer formed thereon 1 , The thin ceramic layer produced directly by the thermal spraying, ie without an intermediate layer on a metallic support, has a low thermal resistance, whereby the thermal contact resistance between the ceramic layer and the support is also low. This makes it possible to reduce the thermal resistance of the entire functional unit with respect to the thermal resistance in known components in a variant by more than 50%. The decoupled heating power increases as a result.

On the PTC ceramic layer 1 is an electrically conductive layer 3 z. B. generated by sputtering or baking a Me tallpaste. The electrically conductive layer 3 , the carrier substrate 2 and the interposed PTC ceramic layer 1 together form a functional unit, the z. B. can serve as a heating element.

The electrically conductive layer 3 is by means of a solder mass with a first electrical connection 4 the functional unit firmly connected.

An exposed end of the carrier substrate 2 serves as a second electrical connection 21 ,

In 2A and 2 B is a detail of a variant of the electroceramic device shown in which a plurality of spaced carrier substrates 201 . 202 by a PTC resistor layer applied by means of thermal spraying 1 connected to each other. In 2A . 2 B Of the multiple carrier substrates, only two are carrier substrates 201 . 202 shown. The PTC ceramic layer 1 and the carrier substrates 201 . 202 together form a functional unit, which on a preferably electrically insulating pad 5 is arranged. On the pad 5 may also be waived under certain circumstances.

In 3A . 3B and 3C is a detail of another variant of the electroceramic device shown in which a plurality of spaced apart honeycomb carrier substrates 203 . 204 and 205 by a PTC thermistor sprayed ceramic layers 1 connected to each other.

In 3A . 3B and 3C Of the multiple honeycomb carrier substrates, only three are carrier substrates 203 . 204 and 205 shown. How out 3A to 3C can be seen, has a honeycomb carrier substrate, a rectangular shaped sheet metal wall 2030 . 2040 respectively. 2050 (ie a hollow tube), which is a folded tes sheet 2032 . 2042 respectively. 2052 encloses, which is firmly connected at the edges of the folds with the sheet metal wall. This creates a flow-through honeycomb-shaped cross-section. The folded sheet is part of the carrier substrate.

The honeycomb carrier substrates 203 . 204 and 205 each have a plurality of planar contacts on their sides facing each other 2031 . 2041 respectively. 2051 on. Each carrier substrate thus provides (in the in 3A shown top view) is a comb-like structure. The flat contacts 2031 and 2041 respectively. 2041 and 2051 of two adjacent carrier substrates 203 and 204 respectively. 204 and 205 grip comb-like into one another and are preferably on both sides - on each side by a here strip-shaped PTC ceramic layer 1 and 11 - connected with each other. In the 3B shown second PTC ceramic layer 11 is in 3A below the first PTC ceramic layer shown 1 arranged and therefore not visible in this figure.

The two PTC ceramic layers 1 and the honeycomb carrier substrates 203 . 204 and 205 together form a functional unit, eg. B. a radiator. The PTC ceramic layers 1 Under certain circumstances, they can also only be applied on one side to the comb-shaped, intermeshing flat contacts 2031 and 2041 respectively. 2041 and 2051 the honeycomb carrier substrates 203 . 204 and 205 be upset.

The exposed ends of the carrier substrates 203 and 204 serve as electrical connections 22 and 23 ,

1

first PTC ceramic layer

11

second PTC ceramic layer

2

carrier substrate

201 202

carrier substrates

203 204, 205

honeycomb carrier substrates with flat

contacts on its the adjacent carrier substrate

facing page

2030 2040, 2050

rectangular shaped sheet metal wall (hollow tube)

2031 2041, 2051

flat contacts the honeycomb

carrier substrates

2032 2042, 2052

pleated Sheet of honeycomb

carrier substrates

21

when electrical connection area of the

carrier substrate 2

22 23

 when electrical connection area of the

carrier substrate 203 and 205

3

electrical conductive layer

4

electrical Connection for contacting the electrical

conductive layer 3

5

document

Claims (29)

Electrical component with an electrically conductive carrier substrate ( 2 ), on whose surface a PTC ceramic layer ( 1 ) is generated. Electrical component with a carrier substrate ( 2 ) and one on the surface of the carrier substrate ( 2 ) produced by thermal spraying PTC ceramic layer ( 1 ) containing barium titanate. Component according to claim 1 or 2, wherein the PTC ceramic layer ( 1 ) in direct thermal and electrical contact with the carrier substrate ( 2 ) stands. Component according to claim 1, wherein the PTC ceramic layer ( 1 ) is applied by thermal spraying. Component according to one of claims 1 to 4, wherein the PTC ceramic layer ( 1 ) firmly sintered together ceramic particles having a particle size between 5 and 250 microns. Component according to one of claims 1 to 5, wherein at least the surface of the carrier substrate ( 2 ) consists of Al or an Al alloy. Component according to one of claims 1 to 5, wherein at least the surface of the carrier substrate ( 2 ) consists of Cu, Cu alloy or SiC. Component according to one of claims 1 to 7, wherein the PTC ceramic layer ( 1 ) a ferroelectric perovskite structure based on Bari umtitanat has. The device of claim 8 wherein barium titanate is an excess on titanium. Component according to one of claims 1 to 9, wherein the PTC ceramic layer ( 1 ) has at least one additive whose proportion is between 10 and 50 wt .-%. Component according to claim 10, wherein the at least an additive selected is made of calcium, strontium and lead. Component according to one of claims 1 to 11, wherein the PTC ceramic layer ( 1 ) has at least one doping whose proportion is less than 5 wt.%. Component according to claim 12, wherein the at least a doping selected is from elements of the group of rare earths and their combination. Component according to claim 13, wherein the at least a doping selected is made of manganese, yttrium, dysprosium, samarium and their combination. Component according to one of claims 1 to 14, wherein the PTC ceramic layer ( 1 ) has a thickness smaller than 1 mm. Electrical component with a carrier substrate ( 2 ), on which a coating of a barium titanate containing PTC ceramic is produced, the thickness of which is smaller than 1 mm. Component according to one of claims 1 to 16, wherein the carrier substrate ( 2 ) an electrical connection to the PTC ceramic layer ( 1 ). Electrical component according to one of claims 1 to 17, wherein the PTC ceramic layer ( 1 ) has the following properties: - electrical resistance at room temperature between 1 Ω cm and 500 kΩ cm, - reference temperature between 0 ° C and 350 ° C, - temperature coefficient of electrical resistance in the range of the Curie temperature of the material of the PTC ceramic layer ( 1 ) between 5 and 35% / K. An electrical component according to claim 18, wherein the PTC ceramic layer ( 1 ) has at least one of the following properties: - electrical resistance at room temperature between 10 Ω cm and 150 kΩ cm, - reference temperature between 80 ° C and 220 ° C, - temperature coefficient of electrical resistance in the range of the Curie temperature of the material of the PTC ceramic layer ( 1 ) between 10 and 20% / K. Method for producing an electroceramic component, in which a coating powder for forming a PTC ceramic layer ( 1 ) on an electrically conductive carrier substrate ( 2 ) is applied by thermal spraying. Method for producing an electroceramic component, comprising the steps of: - a powder containing ceramic particles being pre-doped such that ceramic particles are made conductive, - the powder is used to form a PTC ceramic layer ( 1 ) on a carrier substrate ( 2 ) applied by thermal spraying. A method according to claim 20 or 21, wherein the PTC ceramic layer ( 1 ) is subjected to a thermal post-treatment at a temperature T <800 ° C. Method according to one of claims 20 to 22, wherein the thermal Spraying a plasma spray, detonation squirting or flame spraying is. Method according to one of claims 20 to 23, wherein a barium titanate-containing coating powder is provided, wherein the PTC ceramic layer ( 1 ) is produced with a perovskite structure. Method according to one of claims 20 to 24, wherein the PTC ceramic layer ( 1 ) is generated directly on an electrically conductive carrier substrate. Method according to one of claims 20 to 25, wherein using a mask, a patterned PTC ceramic layer ( 1 ) is produced. Method according to one of claims 20 to 26, wherein on the PTC ceramic layer ( 1 ) a layer ( 3 ) is produced from an electrically conductive material. A method according to any one of claims 20 to 27, wherein in the thermal Spraying the temperature of the coating powder when leaving a spray opening at least 800 ° C. A method according to any one of claims 20 to 27, wherein in the thermal Spraying a presintered ceramic particles coating powder coating at a temperature of at least 800 ° C separated from a spray orifice becomes.