Ceramic composite body

Abstract

A ceramic composite body for an electrochemical sensor element, comprising a horizontal layer structure comprising laminated ceramic films (11, 12, 13) and a vertical layer structure extending at right angles thereto, which lies in at least one through-hole (14, 15) made in a ceramic film (12) consisting of a solid electrolyte, characterized in that the ceramic film (12) has a central through-hole (14) and two outer through-holes (15a, 15b) arranged on opposite sides of the central through-hole (14), that the central through-hole (14) has, on opposite wall surfaces of the hole wall, a layer structure comprising an electrically conductive layer (18) covering the wall surface and a porous protective layer (20) covering the latter, and that the two outer through-holes (15a,15b) each has, on the wall surface of the hole wall closer to the central through-hole (14), a layered structure comprising an electrically conductive layer (18) covering the wall surface, a porous diffusion barrier (19) covering the wall surface, and a porous protective layer (20) covering the diffusion barrier (19), and each of the protective layers (20) defines a cavity (28) in the three through-holes (14, 15).

Description

State of the art

[0001] The invention relates to a ceramic composite body with a horizontal layer structure comprising laminated ceramic films and a method for its production.

[0002] In a known method for manufacturing a PTC temperature sensor (DE 37 33 192 C1), holes are punched out of an electrically insulating ceramic foil, e.g., an aluminum oxide (Al2O3) foil, and through-holes are created in the holes. For this purpose, a paste of platinum-aluminum oxide cermite (Pt / Al2O3) is sucked through the holes. Alternatively, the punched holes are covered with an Al2O3 insulation layer and, on top, with an electrically conductive Pt / Al2O3 cermite. Slayer. A PTC resistance track is printed on the foil provided with the vias, and a contact surface is printed on the reverse side of the foil facing away from it. An interlaminar binder layer is printed on a second ceramic foil made of Al2O3, and the two foils are laminated together using pressure and temperature and subjected to a sintering process. The PTC temperature sensor produced in this way is a composite body with a horizontal layer structure formed by the ceramic foils, the contact surfaces, and the resistance track, and a vertical layer structure formed by the vias in the holes.

[0003] Further ceramic composite bodies are known from EP 2 058 650 A1, JP 2003 - 83930 A, US 2008 / 0 302 661 A1 and US 2009 / 0 308 651 A1. Disclosure of the invention

[0004] The inventive method with the features of claim 7 has the advantage that, by individually and successively introducing layers with different functional properties, such as electrical insulation, electrical conductivity, or protection against external influences, into the at least one through-hole by suctioning the corresponding material through the through-hole and subsequently drying the material deposited in the hole before initiating the next coating step, vertical, electrochemical measuring cell structures can also be created, regardless of the hole shape. This makes it possible to produce advantageous sensor element layouts that enable miniaturization, for example, of broadband lambda sensors and nitrogen oxide sensors.

[0005] The measures listed in the further claims enable advantageous further developments and improvements of the method specified in claim 7.

[0006] According to an advantageous embodiment of the invention, the suspension of the respective material is drawn through successively from different sides of the ceramic foil. This achieves a uniform layer thickness for each material layer.

[0007] According to an advantageous embodiment of the invention, before creating the vertical layer structure, the at least one through-hole is chamfered at the opposite edges of the hole. The chamfers on the two hole edges optimize the flow of the suspension during suction, which also contributes to achieving a uniform layer thickness of the individual material layers across the hole wall.

[0008] The composite body produced in particular according to the method according to the invention with the features of claim 1 has the advantage of realizing a sensor element with two electrochemical measuring cells, with which two separately supplied measuring gas streams can be measured comparatively against the same reference gas. When used as a sensor element for an exhaust gas or lambda probe, the measuring gas streams can be two different exhaust gas streams, one of which is taken from a first combustion cylinder and the other from a second combustion cylinder of the internal combustion engine, thus enabling individual cylinder control. In another application, the two measuring gas streams can be derived from the same exhaust gas and measured via, for example, different diffusion barriers and different electrodes. One application is, for example,a sensor element for a nitrogen oxide sensor with a passive measuring electrode that only measures oxygen and an active measuring electrode that measures oxygen and nitrogen oxide.

[0009] The composite body produced in particular by the method according to the invention with the features of claim 3 has the advantage of realizing a sensor element with a vertically aligned electrochemical measuring cell that is highly suitable for miniaturization in terms of manufacturing technology. Depending on the loading of the gas inlet openings in the vertical layer structure, the measuring cell can be operated as a Nernst cell for a λ=1 probe or as a pump cell for a lean probe based on the limiting current principle. Short description of the drawings

[0010] The invention is described in more detail below with reference to exemplary embodiments illustrated in the drawings. They show: Fig. 1 a partial perspective view of a composite body, Fig. 2 a section along the line II - II in Fig. 1, Fig. 3 a section along the line III - III in Fig. 2, Fig. 4 a partial top view of a ceramic foil with several, not yet separated sensor elements for each composite body according to Fig. 1 to 3, Fig. 5 shows a partial section of a composite body according to a further embodiment, Fig. 6 a section along the line VI- VI in Fig. 5.

[0011] The two in Fig. 1 to 3 and in Fig. 5 and Fig. The ceramic composite bodies outlined in Figure 6 have a horizontal layer structure with laminated ceramic foils 11, 12, 13 and a vertical layer structure perpendicular to the horizontal layer structure with several adjacent material layers with different functional properties. The vertical layer structure is created by machining at least one through-hole 14, 15 ( Fig. 2 and Fig. 3) or 16 ( Fig. 5 and Fig. 6) is incorporated and the hole wall is coated with several adjacent material layers with different functional properties. This coating is carried out in successive coating steps in that with each coating step a suspension of the respective material is sucked through the at least one through-hole 14, 15 or 16 and the ceramic film 12 is subjected to a drying process before a further coating step is carried out. The suction of the suspension of the respective material is preferably carried out successively from different sides of the ceramic film 12, wherein the flow of the suspension through the through-hole 14, 15 or 16 is optimized by chamfering the through-holes 14, 15 or 16 at the hole edges facing away from one another. The through-holes 14, 15 or16 are manufactured by punching, drilling, milling, or laser cutting and can have any desired shape. In the exemplary embodiments shown here, the at least one through-hole 14, 15, or 16 is rectangular or slot-like, but it can also be circular, oval, or structured, e.g., as a grid.

[0012] To produce the composite body according to the Fig. 1 to 3 are placed in a green film 17 ( Fig. 4) two different types of through-holes 14, 15 are incorporated from a solid electrolyte, also called a solid ion conductor, e.g. yttrium-stabilized zirconium oxide, from which the ceramic foil 12 is later obtained, whereby one through-hole 15 alternates with another through-hole 14. A suspension of electrically conductive material, e.g. platinum cermite, is first sucked through all through-holes 14, 15, whereby material is deposited on opposite wall surfaces of the hole walls and an electrically conductive layer 18 is formed with a layer thickness of 5 to 50 µm. In the subsequent drying process, to which the green foil 17 is subjected, the introduced conductive layers 18 dry. After the conductive layers 18 have dried, a suspension of a porous material, e.g.Aluminum oxide provided with a pore-forming agent is sucked through, so that a diffusion barrier 19 of the desired layer thickness is deposited on the opposing conductive layers 18 in the through-holes 15. After drying the diffusion barriers 19 by subjecting the green film 17 to a drying process again, a suspension of a porous protective material, e.g., aluminum oxide, is sucked through all through-holes 14, 15, so that a porous protective layer 20 is deposited on the one hand on the electrically conductive layers 18 in the through-holes 14 and on the other hand on the diffusion barriers 19 in the through-holes 15. A cavity 28 remains between the protective layers 20 in all through-holes 14, 15.

[0013] The green film 17 thus provided with the vertical layer structure is cut along the dash-dotted lines 21 leading centrally through the through holes 15 into Fig. 4, so that several identical sections 171 of the green film 17 are formed. Each section 171 of the green film 17 forms a ceramic film 12, as in the horizontal layer structure of the ceramic composite body according to Fig. 1 to 3. This ceramic foil 12 is placed on a carrier foil 13, e.g., made of aluminum oxide, and covered by a cover foil 13, e.g., made of aluminum oxide. A through-opening 22 is formed in the cover foil 13 such that it opens into the through-hole 14 in the cavity 28 located between the two porous protective layers 20. The ceramic foils 11, 12, 13 are laminated together using pressure and temperature and then subjected to a sintering process.

[0014] The composite body produced in this way according to Fig. 1 to 3 has a horizontal layer structure formed by the ceramic foils 11, 12, 13, and a vertical layer structure formed by the conductive layers 18, diffusion barriers 19, and protective layers 20 formed in the central ceramic foil 12. In the slot-like, central through-hole 14 in the foil 12 consisting of a solid electrolyte, the opposing hole walls are provided with an electrically conductive layer 18 and a porous protective layer 20 covering the conductive layer.The slit-like half-holes 15a and 15b located to the left and right of the central through-hole 14 in the ceramic foil 12, which consists of a solid electrolyte, are formed by separating the foil sections 171 from a respective through-hole 15 in the green foil 17 and thus each carry an electrically conductive layer 18, a diffusion barrier 19, and a protective layer 20 covering the diffusion barrier 19 on their wall surface closer to the central through-hole 14. Such a composite body for an electrochemical sensor element thus has two Nernst cells with vertically aligned electrodes. With such a sensor element, two separately supplied measuring gas streams can be measured comparatively against the same reference gas. The values ​​shown in . Fig. 1 and Fig. 2 measuring gas flows symbolized by arrows A and B are fed to the outer half-holes 15a and 15b, while the one in Fig. 1 and Fig. 2, the reference gas stream symbolized by arrow C enters the through-hole 22 in the ceramic foil 12. The gas-sensitive electrodes of the two Nernst cells, formed by the electrically conductive layers 18, are thus exposed to the measurement gas once directly by the reference gas and once via the diffusion barriers 19. In the application of an exhaust gas probe, the reference gas is air, and the two measurement gas streams A and B are exhaust gases from different combustion cylinders of the internal combustion engine. If one Nernst cell is designed with a passive measuring electrode that measures oxygen and the other Nernst cell with an active measuring electrode that measures oxygen and nitrogen oxide, both measurement gas streams A and B can be the same exhaust gas.

[0015] In the Fig. 5 and Fig.6, all three ceramic foils 11, 12 and 13 are made of an insulating material, e.g., aluminum oxide (Al2O3). The middle ceramic foil 12 contains a vertical layer structure consisting of two electrically conductive layers 18 and an intermediate solid electrolyte layer 23. As already mentioned at the beginning, this vertical layer structure is created by machining a hole 16 into the middle ceramic foil 12 before laminating the three ceramic foils 11, 12, 13 together. By successively sucking through two suspensions containing electrically conductive material on the one hand and solid electrolyte material on the other, the opposite hole walls are first covered with the electrically conductive layers 18. Then, a solid electrolyte layer 23 covering both electrically conductive layers 18 is introduced between the electrically conductive layers 18.The suction process is designed such that the conductive layer 18 is deposited on each hole wall with a visible thickness of 5 to 50 µm, and the solid electrolyte layer 23 has a layer thickness of 5 to 100 µm. Between the two suction processes and after the last suction process, the ceramic foil 12 is subjected to a drying process. The ceramic foil 13 acting as the carrier layer and the ceramic foil 11 acting as the cover layer are each provided with a gas inlet opening 24 and 25, respectively. The gas inlet opening 24 opens at one electrically conductive layer 18, and the gas inlet opening 25 opens at the other electrically conductive layer 18. Electrical leads 26 and 27 to the electrically conductive layers 18 are integrated into the gas inlet openings 24 and 25.

[0016] Such a composite body forms an electrochemical sensor element for a gas sensor with a Nernst cell with a vertical electrode structure. If one gas inlet opening 24 is supplied with a reference gas and the other gas inlet opening 25 with a measurement gas, such as the exhaust gas of an internal combustion engine, the sensor element measures the oxygen content in the exhaust gas as a λ=1 probe. If exhaust gas is supplied to both gas inlet openings 24, 25, the sensor element can be operated as a lean-burn probe according to the limiting current principle. This requires that one of the two gas inlet openings 24, 25 is either filled with a diffusion barrier material or is dimensioned such that it itself acts as a diffusion barrier.

Claims

[1] Ceramic composite body for an electrochemical sensor element, with a horizontal layer structure comprising laminated ceramic films (11, 12, 13) and with a vertical layer structure running at right angles thereto, which lies in at least one through-hole (14, 15) made in a ceramic film (12) consisting of a solid electrolyte, characterized bythat the ceramic film (12) has a central through-hole (14) and two outer through-holes (15a, 15b) arranged on opposite sides of the central through-hole (14), that the central through-hole (14) has on opposite wall surfaces of the hole wall in each case a layer structure consisting of an electrically conductive layer (18) covering the wall surface and a porous protective layer (20) covering the latter, and that the two outer through-holes (15a, 15b) each have on the wall surface of the hole wall closer to the central through-hole (14) a layer structure consisting of an electrically conductive layer (18) covering the wall surface, a porous diffusion barrier (19) covering the latter, and a porous protective layer (20) covering the diffusion barrier (19), and each of the protective layers (20) in the three through-holes (14, 15) has a Cavity (28) is limited. [2] Ceramic composite body according to claim 1, characterized bythat the cavity (28) of the central through-hole (14) is supplied with a reference gas (C) and the cavities (28) of the two outer through-holes (15a, 15b) are each supplied with a measuring gas stream (A, B). [3] Ceramic composite body for an electrochemical sensor element with a horizontal layer structure comprising laminated, electrically insulating ceramic films (11, 12, 13) and with at least one vertical layer structure running at right angles thereto, which lies in at least one through-hole (16) made in one of the ceramic films (12), characterized bythat the vertical layer structure has two electrically conductive layers (18) covering the opposite wall surfaces of the perforated wall and a solid electrolyte layer (23) covering both electrically conductive layers (18), and that gas inlet openings (24, 25) are present in the horizontal layer structure, one of which opens into one of the two electrically conductive layers (18). [4] Ceramic composite body according to claim 3, characterized by that one of the gas inlet openings (24, 25) is supplied with a measuring gas and the other of the gas inlet openings (24, 25) is supplied with a reference gas. [5] Ceramic composite body according to claim 3, characterized by that the two gas inlet openings (24, 25) are supplied with the same measuring gas and one of the gas inlet openings (24, 25) is filled with a porous material forming a diffusion barrier or is dimensioned such that it forms a diffusion barrier for the measuring gas. [6] Ceramic composite body according to one of claims 1 to 5, characterized by that the through holes (14, 15; 16) are designed as slots extending over the width of the ceramic film (12). [7] A method for producing a ceramic composite body according to any one of the preceding claims, characterized by that the production of the vertical layer structure is carried out in individual, successive coating steps by sucking a suspension of the respective material through the through-hole (14, 15; 16) with each coating step and subjecting the ceramic film (12) to a drying process. [8] Method according to claim 7, characterized by that the suction of the suspension of the respective material is carried out successively from different sides of the ceramic foil (12). [9] Method according to claim 7 or 8, characterized bythat before producing the vertical layer structure, the at least one through hole (14, 15; 16) is chamfered at the hole edges facing away from one another. [10] Method according to one of claims 7 to 9, characterized by that the through hole (14, 15; 16) is punched, drilled, milled or lasered in a desired shape, e.g. circular, oval, rectangular, slit-like or structured, e.g. as a grid. [11] Method according to one of claims 7 to 10, characterized by that the coating is carried out with an electrically insulating material in a layer thickness of 5 to 100µm. [12] Method according to one of claims 7 to 11, characterized by that the coating is carried out with an electrically conductive material in a layer thickness of 5 to 50µm. [13] Method according to one of claims 7 to 12, characterized bythat the coating is carried out with a solid electrolyte in a layer thickness of 5 to 100µm.

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