CN105092674B - Method for producing a sensor element for detecting at least one property of a measurement gas in a measurement gas space - Google Patents
Method for producing a sensor element for detecting at least one property of a measurement gas in a measurement gas space Download PDFInfo
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/403—Cells and electrode assemblies
- G01N27/406—Cells and probes with solid electrolytes
- G01N27/407—Cells and probes with solid electrolytes for investigating or analysing gases
- G01N27/4073—Composition or fabrication of the solid electrolyte
Abstract
The invention relates to a method for producing a sensor element (10) for detecting at least one property of a gas in a measurement gas space, in particular for verifying the content of a gas component in the measurement gas or the temperature of the measurement gas, comprising the steps of: -preparing at least one solid-state electrolyte (12) having at least one functional element (14, 16, 18), -preparing a suspension having at least one ceramic filler and at least one starting material precursor, and-applying at least one first layer of the suspension at least in sections onto the solid-state electrolyte (12).
Description
Technical Field
A number of sensor elements and methods for detecting at least one property of a measurement gas in a measurement gas space are known from the prior art. In principle, any physical and/or chemical measurement gas property of the measurement gas can be used, wherein one or more properties can be detected. The invention is described below on the basis of the qualitative and/or quantitative detection of the gas component content of a measurement gas, in particular the detection of the oxygen content in the measurement gas. The oxygen content can be detected, for example, in the form of partial pressure and/or in the form of a percentage. Other properties of the measurement gas, such as temperature, may alternatively or additionally be detected.
Background
Such a sensor element may, for example, be formed by a so-called oxygen content sensor (lambda sensor), for example, known from Konrad Reif (Hrsg.) sensors in motor vehicles, 2010 first edition page 160-. The oxygen concentration in the exhaust gas and the air-fuel ratio in the combustion chamber can be determined over a wide range, for example, by means of a wide-band oxygen content sensor, in particular by means of a planar wide-band oxygen content sensor. The air number λ describes this air-fuel ratio.
Ceramic sensor elements are known from the prior art, in particular, which are based on the use of a solid body which is determined by electrolytic properties, i.e. on the ion conductor properties of this solid body. These solids can be, in particular, solid electrolytes of ceramics, for example zirconium dioxide (ZrO)2) Especially yttrium-stabilized zirconium dioxide (YSZ)And scandium-doped zirconium dioxide (ScSZ), which may contain small amounts of aluminum oxide (Al)2O3) And/or silicon dioxide (SiO)2) And (4) adding.
Increased functional requirements are placed on such sensor elements. The rapid operating behavior of the oxygen sensor after the engine has been started is of particular importance. This property is affected in essentially two ways. The first aspect relates to the rapid heating of the oxygen content sensor to its operating temperature, which is generally above 600 ℃, which can be achieved by corresponding application of heating elements or by reducing the range to be heated. Another aspect relates to robustness against thermal shock due to water hammer during operation. The thermal shock is based on the fact that the temperature in the exhaust pipe is below the dew point of water for a certain period of time after the engine has started, whereby water vapor generated during the combustion of the fuel condenses in the exhaust pipe. Thereby causing water droplets to form in the exhaust pipe. The heated oxygen content sensor ceramic may be damaged, or even destroyed, by the occurrence of water droplets due to thermal stress or fractures in the sensor ceramic.
Oxygen content sensors have therefore been developed which have a porous ceramic protective layer on their surface, which is also known as Thermo-Shock-Protection-schicht (tsp) or thermal Shock protective layer. This protective layer ensures that the water droplets present on the oxygen content sensor are distributed over a large area and reduces the local temperature gradients present in the solid electrolyte or the sensor ceramic. These oxygen content sensors also tolerate a certain condensate droplet size in the heated state without being damaged. The protective layer is generally applied to the sensor element in an additional process step. Different materials, such as aluminum oxide or spinel (MgAl), can be used for this purpose2O4) And coating techniques such as sputtering or dipping processes. It is known, for example, to apply thermal shock protective layers of porous alumina of uniform thickness by atmospheric pressure plasma sputtering (APS). The added particles are melted by this thermal technique coating process and accelerated on the solid electrolyte surface, thereby coating the entire solid electrolyte surface with a thermal shock protective layer. TSP is protected against by its limited permeabilityWater enters the solid electrolyte of the sensor element, which is at least partially made of zirconium dioxide, and cooling is limited by thermal conduction.
Despite the numerous advantages of the methods known from the prior art for producing sensor elements for oxygen content sensors, they still have potential for improvement. In order not to impair the function of the sensor element, but at the same time to be reliably protected from water droplets, for example from the exhaust gas stream of an internal combustion engine, the thickness, porosity, pore size, material and possibly the sequence and layer thickness of the thermal shock protection layer must be optimally selected. In this case, a conflict of goals is achieved in the optimization of the sensor element, which differ with regard to the two influencing variables. For example, a thick thermal shock protection layer reliably prevents water hammering, but as an additional substance adversely affects the heating properties of the sensor element. Furthermore, the open porosity of the plasma sputtered layer is changed by thermal aging, which affects the function of the oxygen content sensor.
Disclosure of Invention
A method for producing a sensor element for detecting at least one property of a measurement gas in a measurement space and a sensor element produced according to said method are therefore proposed, which at least largely avoid the disadvantages of the known methods and sensor elements and in which the robustness to thermal shocks can be improved without a significant increase in the thermal mass.
The method according to the invention comprises the following steps, preferably in the order indicated:
-preparing at least one solid-state electrolyte with at least one functional element,
preparing a suspension of a filler with at least one ceramic and at least one raw material, for example a precursor of the ceramic raw material, and
at least in sections, at least one first layer, if appropriate a plurality of layers, of the suspension is applied to the solid electrolyte.
The suspension may be coated on the solid-state electrolyte using impregnation and/or sputtering. The suspension may have a micropore forming agent made from at least one organic material. The method may further comprise solid state electricity after coating the suspensionAt least one heat treatment step of the electrolyte. The heat treatment step may be performed at a temperature of 100 ℃ to 200 ℃, for example 150 ℃. The method may further comprise at least one annealing step of the solid-state electrolyte after coating the suspension. The annealing step may be performed at a temperature of 500 ℃ to 1500 ℃, preferably at 1000 ℃ to 1200 ℃. The sensor element may further comprise a heating element for heating the solid-state electrolyte, wherein the heating element performs an annealing step. The matrix of the ceramic raw material is preferably made of SiO2In particular silicon dioxide (colloidal silica), alternatively of Al2O3Especially boehmite.
Ceramic raw material used as filler, especially Al2O3,ZrO2,MgO,TiO2,MgAl2O4,Al2TiO5,Mg(SiO4),SrTiO3And/or CeO2Particles with an average diameter of 1 μm to 50 μm and preferably about 5 μm to 20 μm can be present in the suspension, for example with an average diameter of 10 μm. Preferably, the filler consists of particles having a relatively narrow diameter distribution, e.g., a standard deviation of the particle size distribution of less than half the average diameter. In particular to a unimodal diameter distribution.
The suspension may have at least one pore former. At least in sections, a second layer of the suspension is applied to the first layer, wherein the second layer, after the annealing step, can have a different porosity, pore size and different starting material than the first layer. The suspension may be applied after the sensor element has been sintered. The solid electrolyte may have lateral surfaces and lateral edges, wherein the suspension is applied such that the first layer is thicker on the lateral edges than on the lateral surfaces. The method may be performed repeatedly for applying a plurality of layers one after the other and/or for generating a porosity gradient. For example, the suspension can be repeatedly applied and dried as a layer. The layers are then annealed collectively. Alternatively, the suspension can be applied and annealed repeatedly as a layer.
Within the scope of the present invention, a solid electrolyte is understood to mean an object or object having at least a segmented electrolyte characteristic, i.e. having an ion conductor characteristic. In particular, it may relate to ceramic solid electrolytes, either completely or in sections. This also includes the starting materials for the solid electrolyte and therefore consists of so-called green or grey blanks, which only become solid electrolytes after sintering.
Functional elements are understood within the scope of the invention as being elements which are selected from the following group of elements: electrodes, conductor strips, diffusion barriers, diffusion gaps, reference gas channels, heating elements, Nernst cells and pump cells. In this context, elements are understood in particular as meaning those which fulfill the essential chemical and/or physical and/or electrical and/or electrochemical function of the sensor element of the oxygen content probe.
By the term "coating suspension" is understood within the scope of the present invention a coating suspension in which the outer surface or surfaces of the solid electrolyte or a layer on which the suspension has been applied is at least partially covered by the sol, but not necessarily completely covered. It is thus possible to apply the suspension only to a defined section of the solid electrolyte or the sensor element, for example only on a defined lateral surface or edge, or only in a defined region of the solid electrolyte, which, for example, is located more inside the measurement gas space than other regions of the solid electrolyte, as viewed in the direction of the longitudinal extent of the sensor element.
Porosity is understood within the scope of the present invention as the ratio of the volume of the hollow space of the starting material or starting material mixture to the total volume, as a dimensionless measurement parameter. This measurement parameter can be given in particular as a percentage. Open porosity is understood here as the ratio of the hollow space volumes of the hollow spaces which are connected to one another and to the ambient air to the total hollow space volume. By a defined porosity is herein understood a porosity of at least 20%, preferably at least 30% and more preferably at least 40%, for example 45%. For technical reasons, a porosity of more than 80% is not included here, since this porosity can reduce the stability of the layer.
The term pore formers in the context of the present invention is understood to mean materials which are suitable for making the ceramic layer coated with the suspension porous and lighter. Such materials are, for example, sawdust and cork dust, starch, coal dust, polymer balls or polymeric fibres, especially short fibres. Carbon-based materials are understood in particular here, which burn during the so-called annealing process, while leaving hollow spaces.
The basic idea of the invention is to apply a particularly homogeneous, microporous, thin ceramic layer to a ceramic, optionally sintered sensor element by means of a sol-gel process. Working as a sol on SiO with very fine particles2Or alternatively Al2O3A preceding stage, a melt of a precursor (precursor). In order to apply thicker layers and to ensure the porosity and thermomechanical stability necessary for gas exchange (sensor function), ceramic fillers, for example ceramic oxides, in particular Al, are added to the sol2O3,ZrO2,MgO,TiO2,MgAl2O4,Al2TiO5,Mg(SiO4),SrTiO3And/or CeO2And if necessary, an organic micropore forming agent is added. The mean particle size of the fillers is, for example, from 1 μm to 50 μm and preferably about 10 μm.
After the coating process, for example dipping or sputtering, a heat treatment is carried out at about 100 ℃ to 200 ℃, which is used to dry the solution, for example to evaporate a solvent, for example water. The layer is annealed in a subsequent thermal process at a temperature of 500 ℃ to 1500 ℃, preferably 1000 ℃ to 1200 ℃. Where the matrix polymerizes into long chains and forms complexes around the ceramic filler.
After the thermal technology process, ceramic layers with a porosity of in particular 30% to 50% are being sought. The particles of filler in this ceramic layer are present as a thin matrix of polymeric matrix. Depending on the starting material, amorphous/crystalline SiO is possible here2Or finely divided crystalline Al2O3. The porosity can be adjusted by a suitable choice of the type of suspension, filler particles and additional pore formers, such as sawdust and cork dust, starch, coal dust, polymer balls or polymeric fibers, especially short fibers. By adjusting the viscosity and the process parameters, it is possible to dispense with the need to seal the gas inlet openings, for example by means of wax, glycol or water.
The thermal shock protection layer of the ceramic partially or completely protects the sensor element from water hammer (water shock). Furthermore, the layer thickness can be varied within a wide range: a thinner thermal shock protection layer has a smaller heat capacity and enables a faster detection function, i.e. an improved dynamic specification, with the same porosity. The method according to the invention furthermore makes it possible to apply a gradient layer with optimum thermal shock properties by selecting two or more different suspensions. For example, a first layer applied on the sensor element may have a higher porosity, i.e. a reduced thermal conductivity, followed by a second, thicker layer having a higher thermal capacity, which does not allow water to enter. The heating of the thermal shock protection layer can be achieved by self-heating of the sensor element due to the small layer thickness. Of course, a furnace process may alternatively or additionally be used for heating. When used as a base layer before the thermal technology coating process, the temperature load of the sensor element is reduced during the coating process. This results in an increased service life of the sensor element of the oxygen content probe.
The method according to the invention is an alternative method for applying a thermal shock protection layer on a sensor element. No mechanical damage is produced by using immersion or cold sputtering processes, as may occur in thermal technology coating processes. The uniform, homogeneous, microporous, thin ceramic layer provides complete or partial thermal shock protection while having a smaller thermal capacity, i.e., less quenching, than sputtering the cladding with an atmospheric pressure plasma. This also applies when the sol-gel layer provides only partial protection, and an additional modification of the protective tube for the oxygen content probe is required, which leads to complete protection during compounding.
The thermal shock protection layer applied according to the invention can be further improved with regard to thermal shock protection and sensor function by the following measures. One measure is to avoid macroscopically large cracks, for example by optimizing the heating process of the coating and in particular by reducing the heating rate. Another measure is to increase the porosity by changing the kind and content of the sol, the micropore former and the ceramic particles. Another measure is to achieve a higher layer thickness at the side edges by removing the non-dried suspension on the heating and sensing side and by targeted application on the side edges, which can be achieved by targeted adjustment of the rheological properties of the suspension or by multiple applications. Another measure is to achieve a higher layer thickness at the lateral edges by better wetting of the lateral edges by changing the sensor element edge grinding, for example chamfer circle grinding or multiple multi-surface grinding.
Drawings
Further details and features of the invention are given by the following description of preferred embodiments, which are illustrated in the accompanying drawings. The figures show:
figure 1 is a longitudinal section through a sensor element according to the invention,
fig. 2A-2B are various enlarged views of the sensor element at the location of the gas inlet holes.
Detailed Description
The sensor element 10 shown in fig. 1 can be used for verifying a physical and/or chemical property of a measurement gas, wherein one or more properties can be detected. The invention is described below, in particular, on the basis of qualitatively and/or quantitatively detecting the gas composition of a gas, in particular the oxygen content in a measurement gas. The oxygen content can be detected, for example, in the form of partial pressure and/or in the form of a percentage. In principle, however, other forms of gas components, such as nitrogen oxides, hydrocarbons and/or hydrogen, can also be detected. However, other properties of the measurement gas, such as temperature or pressure, may alternatively or additionally also be detected. The invention can be used in particular in the field of motor vehicle technology, whereby a gas space, in particular an exhaust pipe of an internal combustion engine, is measured and a gas, in particular an exhaust gas, is measured.
The sensor element 10 as an example of a planar oxygen content probe (lambda probe) has a solid electrolyte 12. The solid-state electrolyte 12 may be composed of a plurality of solid-state electrolyte layers, or include a plurality of solid-state electrode layers. The electrolyte 12 can be, in particular, a ceramic solid electrolyte 12, for example zirconium dioxide (ZrO)2) In particular yttrium-stabilized zirconium dioxide (YSZ) and scandium-doped zirconium dioxide (ScSZ), which may contain small amounts of aluminum oxide (Al)2O3) And/or silicon dioxide (SiO)2) And (4) adding. The solid electrolyte 12 has a structure ofOne less functional element. In the exemplary embodiment shown, the solid electrolyte 12 has, for example, a first electrode 14, a second electrode 16 and a heating element 18. The first electrode 14 is disposed on a surface 20 of the solid state electrolyte 12. The second electrode 16 is disposed inside the solid-state electrolyte 12.
Furthermore, the sensor element 10 has a gas inlet path 22. The gas inlet path 22 includes a gas inlet aperture 24. Both the first electrode 14 and the second electrode 16 surround the gas inlet opening 24, for example in the form of a ring. For example, the second electrode 16 is arranged in an electrode hollow space, not shown in detail, which is connected to the gas inlet opening 24 via a channel. For example, a diffusion barrier is provided in the channel, which reduces or even prevents the gas from flowing from the measurement gas space back into the electrode hollow space and only enables diffusion. The second electrode 16 is thus loaded with gas from the measurement gas space by diffusion barrier. The first electrode 14 and the second electrode 16 are interconnected by the solid-state electrolyte 12 and form a pump cell 26. The limiting of the pole current of the pump cell 26 can be adjusted by diffusion barrier.
The heating element 18 is arranged inside the solid-state electrolyte 12 on an extension of the direction of extension of the gas inlet openings 24. The heating element 18 serves to heat the pump cell 26, in particular to a temperature, for example 750 ℃ to 900 ℃, at which the pump cell 26 is able to conduct ions, in particular oxygen ions. Heating element 18 includes a heating zone 28 and a connecting wire 30. The heating element 18 is formed, for example, by a resistance heating element and is connected to a voltage source by means of a connecting line 30.
The solid-state electrolyte 12 may furthermore comprise reference gas channels, which are not shown in detail. The reference gas channel can be formed by a macroscopic reference air channel in which air is present with known properties, for example, the oxygen partial pressure. The reference gas channel can alternatively be formed by a non-macroscopic channel, but by a pumped reference, i.e. by an artificial reference. A third electrode is arranged, for example, in the electrode hollow space. The second electrode 16 is located, for example, opposite the third electrode. The fourth electrode can be arranged in the reference gas channel or, in the case of the pumping reference, on the insulating layer inside the solid-state electrolyte 12. The third electrode, the fourth electrode and the part of the solid-state electrolyte 12 between these two electrodes form an electrochemical cell, for example a Nernstzelle cell. With the pump cell 26, the pump flow can be set, for example, by means of the pump cell 26 in such a way that the condition λ =1 or another known component is present in the electrode hollow space. This component is still detected by the Nernst cell by measuring the Nernst voltage between the third electrode and the fourth electrode. From the measured nernst voltage, the composition inside the electrode hollow space can be inferred and the pump flow can be varied as necessary for setting the condition λ = 1. The composition of the exhaust gas can be inferred from the pump flow.
Preferably, an optional Nernst cell is arranged in the solid electrolyte 12 for measuring the respective residual oxygen content in the combustion exhaust gas, for the purpose of adjusting the combustion air/fuel ratio and thus for continuing the combustion, so that neither a fuel excess nor an air excess is produced. Since the temperature is still much below 300 ℃ in cold engines, the oxygen content probe and thus the control device do not operate or only operate very slowly during cold start. The solid-state electrolyte 12 of the sensor element 10 is therefore preferably provided with an electrical heating element 18, whereby the probe is brought quickly to the desired temperature after a cold start. In this way, operation with optimum emissions can be ensured already during the warm-up phase of the engine. Since the operation of oxygen content probes is well understood, for example from the prior art described above, a detailed description of the working principle is omitted.
The sensor element 10 further comprises a thermal shock protection layer 32. The thermal shock protection layer 32 may be at least partially made of a ceramic material. For example, the thermal shock protective layer 32 comprises porous alumina. For example, the thermal shock protective layer 32 has a porosity of 50%. The solid-state electrolyte 12 extends along a longitudinal length into the measurement gas space, from left to right with reference to the illustration of fig. 1. The sensor element 10 therefore comprises a connection-side end 34, which is located on the left with reference to the illustration in fig. 1, and a measurement-gas-space-side end 36, which is located on the right with reference to the illustration in fig. 1. As shown in fig. 1, the pump cell 26 is located near the end 36 on the measurement gas space side. The solid-state electrolyte 12 also includes side surfaces 38, one of which is the surface 20, and also end faces and side edges 40, which interconnect the side surfaces 38 or form transitions between the side surfaces 38. Lateral edges 40 may be rounded, square or chamfered. The thermal shock protective layer 32 is applied at least in sections on the solid-state electrolyte 12. For example, the thermal shock protection layer 32 is applied only in the vicinity of the end 36 on the measurement gas space side in a third of the longitudinal length dimension and covers all side surfaces there. Thus, referring to the view of fig. 1, the thermal shock protective layer 32 has a U-shaped cross-section. In particular, the thermal shock protection layer 32 covers the first electrode 14, wherein a porous ceramic electrode protection layer can be provided between the first electrode 14 and the thermal shock protection layer 32. In a variant, the gas inlet openings 24 are preferably not closed by the thermal shock protection layer 32, but rather open freely into the measurement gas space. At sufficient porosity it is possible or even desirable to close the gas inlet opening on the other side. The thermal shock protection layer 32 may alternatively cover all of the side surfaces 38 completely, or only the first electrode 14 and the gas entry holes 24. The exact position at which the thermal shock protective layer 32 is provided may be selected according to the respective application or mounting position of the sensor element 10.
The sensor element 10 is made according to the invention as follows. A solid electrolyte 12 having the above-described functional elements 14,16 and 18 is first prepared. For example, the solid electrolyte 12 is made of a plurality of solid electrolyte layers, which are printed in a known manner with the functional elements described above, i.e. with a first electrode 14, a second electrode 16 and a heating element 18. Known processes are, for example, so-called thin-film processes or multilayer processes. The solid electrolyte 12 is then co-sintered with the first electrode 14, the second electrode 16 and the heating element 18. The sintering can be carried out, for example, at a temperature of 1350 ℃ to 1550 ℃, in particular 1385 ℃, wherein the temperature is kept constant, for example, for 5.5 hours. Such a structure of the planar sensor element 10 is well known from the prior art described above and will therefore not be explained in detail.
Furthermore, a suspension having at least one ceramic filler and at least one raw material precursor is produced. The matrix is preferably made of SiO2Alternatively from Al2O3Especially boehmite. The matrix is preferably in the form of particles having a diameter of from 5nm to 50 nm. The content of the precursor in the suspension is, for example, 10 to 20 mass percentAnd (4) the ratio. The content of the ceramic filler in the suspension is, for example, 20-40% by weight.
Fig. 2A and 2B show different partial enlargements of the sensor element 10 in the region of the gas inlet opening 24. In particular, fig. 2A and 2B are top views of the sensor element 10 after application of the suspension. As is clearly visible in fig. 2A and 2B, the blocking of the gas inlet openings during the impregnation of the solid electrolyte 2 into the suspension by means of, for example, wax, glycol or water can be dispensed with by adjusting the viscosity and the process parameters. If the intrusion of the suspension is also prevented when the gas inlet openings 24 have a larger diameter and the thermal shock resistance of the gas inlet openings 24 is to be ensured, it is possible to apply a porous ceramic layer by screen printing or stencil printing before applying the suspension to the gas inlet openings 24 and then to sinter the solid-state electrolyte 12. The sol is then applied, wherein a dipping/sputtering process can be performed in such a way as to avoid closing the gas access holes 24 of the porous mask. For example, the first electrode 14, which forms the outer pump electrode of the pump cell 28, is covered by an electrode protection layer or by a sintered porous ceramic layer applied by screen or stencil printing. Wetting of the electrode protection layer and thus of the first electrode 14 by the suspension can be avoided by suitable process control and adjustment of the viscosity of the suspension. The closure of the diffusion barrier can be excluded after the completion of the sensor element 10 by means of a pump flow measurement.
The heat treatment step of the solid-state electrolyte 12 is engaged after the application of the suspension. The heat treatment step is performed at a temperature of 100 ℃ to 200 ℃ and preferably 140 ℃ to 160 ℃, e.g. 150 ℃.
Next, at least one annealing step of the solid-state electrolyte 12 is performed after the application of the suspension. The annealing step may be performed at a temperature of at least 500 ℃. The annealing step may be performed by external means or by heating element 18. For example, a voltage is applied to the heating element 18, thereby heating this element. The silica (silica gel) polymerization is achieved by an annealing step, for example by water splitting. Performing the annealing step with the heating element 18 is advantageous, because a better degassing of the oxidation products of the organic components is thereby ensured. The pore former burns by means of an annealing step, whereby in the ceramic layer formed from the sol, which is the thermal shock protective layer 32, a defined porosity, for example a porosity of 50%, is formed. This ensures that the gas phase process, for example diffusion, is only slightly modified compared to conventional sensor elements. The porosity can be adjusted by suitably selecting the kind of the suspension, the ceramic filler particles and the micropore forming agent. It is particularly emphasized that even higher porosities of, for example, 50%, 60% or 70% can be achieved thereby. The suspension is applied here in such a way that the thermal shock protection layer 32 produced thereby has the above-mentioned thickness after the annealing step, for example a thickness of 400 μm. If the annealing step is performed at a reduced heating rate, i.e. the temperature is increased more slowly, cracks in the thermal shock protective layer of the ceramic can be avoided or reduced.
Of course, the above steps may be repeated. For example, a second layer of the suspension is coated on the first layer, wherein the first layer has a higher porosity than the second layer after the annealing step. The thermal shock protection layer can thus be formed, for example, from a plurality of layers, which have a porosity gradient. For example, the coating is repeated, followed by heat treatment. If all desired layers are applied, they are annealed together. An annealing step may optionally be performed after each heat treatment of the layer.
Claims (12)
1. A method for processing a sensor element (10) for detecting at least one property of a gas in a measurement gas space, comprising the steps of:
-preparing at least one solid-state electrolyte (12) having at least one functional element (14, 16, 18),
-preparing a suspension having at least one ceramic filler and at least one raw material precursor, and
-at least sectionally coating the solid-state electrolyte (12) with at least one first layer of suspension,
by applying the suspension in sections is understood, among others, applying the suspension in such a way that the surface of the solid-state electrolyte, or the layer on which the suspension has been applied, is at least partially covered by the sol, but not necessarily completely covered,
wherein the method further comprises at least one heat treatment step of the solid-state electrolyte (12) after coating the suspension,
wherein the heat treatment step is performed at a temperature of 100 ℃ to 200 ℃,
wherein the method further comprises at least one annealing step of the solid-state electrolyte (12) after coating the suspension,
wherein the annealing step is performed at a temperature of 500 ℃ to 1500 ℃,
after the thermal technology process, ceramic layers with a porosity of 30% to 50% are sought,
wherein the first layer is coated at least in sections with a second layer suspension, wherein the first layer has a higher porosity after the annealing step than the second layer.
2. The method of claim 1, wherein said annealing step is performed at a temperature of 1000 ℃ to 1200 ℃.
3. The method according to claim 1, wherein the suspension is applied to the solid electrolyte (12) by means of dipping and/or spraying.
4. The method of claim 1, wherein said suspension comprises SiO2As a precursor and also has ceramic oxides as ceramic fillers.
5. The method of claim 4, wherein said ceramic oxide is Al2O3,ZrO2,MgO,TiO2,MgAl2O4,Al2TiO5,Mg(SiO4),SrTiO3And/or CeO2。
6. The method according to claim 1, wherein said solid state electrolyte (12) further comprises a heating element (18) for heating the solid state electrolyte (12), wherein said heating element (18) performs an annealing step.
7. The method of claim 1, wherein the precursor is in the form of particles having a diameter in the range of 5nm to 50 nm.
8. The method of claim 1, wherein the ceramic filler is present in suspension as particles having a diameter of 1 μm to 50 μm.
9. The method of claim 1, wherein said suspension has at least one micropore forming agent.
10. The method of claim 1, wherein the suspension is applied after sintering the solid electrolyte (12).
11. The method of claim 1, wherein the solid electrolyte (12) has side surfaces (38) and side edges (40), and wherein the suspension is applied such that the first layer is thicker on the side edges (40) than on the side surfaces (38).
12. The method according to claim 1, wherein the method is repeated for the successive application of a plurality of layers and/or for the generation of a gradient of porosity.
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| DE102014208832.1A DE102014208832A1 (en) | 2014-05-12 | 2014-05-12 | Method for producing a sensor element for detecting at least one property of a measuring gas in a measuring gas space |
| DE102014208832.1 | 2014-05-12 |
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| DE102016212349A1 (en) * | 2016-07-06 | 2017-08-24 | Continental Automotive Gmbh | Method for operating an oxygen sensor and oxygen sensor for determining an oxygen concentration in an intake tract |
| CN107159507B (en) * | 2017-05-27 | 2020-08-14 | 广州华凌制冷设备有限公司 | Sensor device protective layer coating tool and process, sensor device and air conditioner |
| CN113552201A (en) * | 2021-09-01 | 2021-10-26 | 浙江百岸科技有限公司 | Nitrogen-oxygen sensor chip with protective cap coating |
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|---|---|---|---|---|
| US4199425A (en) * | 1978-11-30 | 1980-04-22 | General Motors Corporation | Solid electrolyte exhaust gas sensor with increased NOx sensitivity |
| DE3017947A1 (en) * | 1980-05-10 | 1981-11-12 | Bosch Gmbh Robert | ELECTROCHEMICAL SENSOR FOR DETERMINING THE OXYGEN CONTENT IN GAS AND METHOD FOR PRODUCING SENSOR ELEMENTS FOR SUCH SENSOR |
| CN1441245A (en) * | 2002-02-28 | 2003-09-10 | 日本特殊陶业株式会社 | Prismatic ceramic heater, prismatic gas sensitive element and its producing method |
| CN1725005A (en) * | 2004-07-22 | 2006-01-25 | 日本特殊陶业株式会社 | Gas sensor and method for manufacturing the same |
| CN101561413A (en) * | 2008-04-14 | 2009-10-21 | 日本特殊陶业株式会社 | Laminated gas sensor element and gas sensor |
-
2014
- 2014-05-12 DE DE102014208832.1A patent/DE102014208832A1/en not_active Withdrawn
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2015
- 2015-05-11 CN CN201510235084.1A patent/CN105092674B/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4199425A (en) * | 1978-11-30 | 1980-04-22 | General Motors Corporation | Solid electrolyte exhaust gas sensor with increased NOx sensitivity |
| DE3017947A1 (en) * | 1980-05-10 | 1981-11-12 | Bosch Gmbh Robert | ELECTROCHEMICAL SENSOR FOR DETERMINING THE OXYGEN CONTENT IN GAS AND METHOD FOR PRODUCING SENSOR ELEMENTS FOR SUCH SENSOR |
| CN1441245A (en) * | 2002-02-28 | 2003-09-10 | 日本特殊陶业株式会社 | Prismatic ceramic heater, prismatic gas sensitive element and its producing method |
| CN1725005A (en) * | 2004-07-22 | 2006-01-25 | 日本特殊陶业株式会社 | Gas sensor and method for manufacturing the same |
| CN101561413A (en) * | 2008-04-14 | 2009-10-21 | 日本特殊陶业株式会社 | Laminated gas sensor element and gas sensor |
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| CN105092674A (en) | 2015-11-25 |
| DE102014208832A1 (en) | 2015-11-12 |
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