Method for the manufacture and self-diagnosis of a particle sensor

Abstract

Method for producing a resistive particle sensor (1) for detecting particles in a gas stream, wherein the particle sensor (1) comprises an electrode system (2) of at least two electrodes (3, 4) and at least one semiconducting material (5), wherein the semiconducting material (5) contacts the electrodes (3, 4), wherein the semiconducting material (5) is at least one oxide selected from the group consisting of rare-earth-rare-earth mixed oxides, rare-earth-zirconium mixed oxides, alkaline-earth-zirconium mixed oxides, transition-metal-zirconium mixed oxides, rare-earth-aluminum mixed oxides, alkaline-earth-aluminum mixed oxides, transition-metal-aluminum mixed oxides, rare-earth-titanium mixed oxides, barium-titanium mixed oxides, transition-metal-titanium mixed oxides, rare-earth-indium mixed oxides, Alkaline earth indium mixed oxides, transition metal indium mixed oxides, rare earth zinc mixed oxides, alkaline earth zinc mixed oxides, transition metal zinc oxide mixed oxides, samarium oxide, yttrium oxideTerbium oxide and / or mixtures thereof, comprising, wherein a voltage is applied to the electrodes (3, 4) and the semiconducting material (5) under an atmosphere free of oxidizing and / or reducing agents, the voltage being selected such that at least one metal of the semiconducting material (5) is at least partially reduced or oxidized in the regions of the semiconducting material (5) which contact the electrodes (3, 4), characterized in that both electrodes (3, 4) are connected simultaneously at the same potential relative to the semiconducting material (5).

Description

The present invention relates to a particle sensor, a method for its manufacture and a method for its operation. State of the art In the near future, particulate emissions, particularly from vehicles during operation, will be legally required to be monitored after the diesel particulate filter (DPF) has passed through the system, and the functionality of this monitoring system (On-Board Diagnostics, OBD) must be ensured. Furthermore, a diesel particulate filter load prediction system for regeneration control is necessary to guarantee high system reliability with fewer, more efficient, fuel-saving regeneration cycles and to enable the use of cost-effective filter materials, such as cordierite. Resistive particle sensors offer one possibility for this. Resistive particle sensors have an electrode system with at least two metallic electrodes freely exposed to the exhaust gas. In so-called interdigital electrode systems, at least two comb-like electrodes interlock. Under the influence of a voltage applied to the electrodes and the resulting electric field, the particles to be detected, especially soot particles, are deposited on or between the electrodes. Once a certain amount of particles has accumulated, this leads to a short circuit of the electrodes and thus to a change in resistance and / or impedance between the electrodes, which allows conclusions to be drawn about the particle deposition. Since the particulate sensor is installed downstream of the diesel particulate filter in an on-board diagnostics application, there are no particles in the exhaust gas at the sensor's location when the filter is functioning correctly, which would otherwise generate a signal. However, the absence of a signal could also indicate that the particulate sensor is defective and therefore fails to detect a faulty filter. Lambda sensors are used to determine the oxygen content in the exhaust gas of combustion engines. The widely used binary lambda sensors, based on the Nemst principle, monitor compliance with a constant lambda value λ=1, at which these sensors exhibit their greatest sensitivity. However, these sensors have low sensitivity in the lean range (λ>1), which is why they are not suitable for measuring larger lambda ranges, for example, from λ=0.8 down to near-air, which is required in lean-burn engines such as direct injection and diesel engines. Resistive lambda sensors offer an alternative. These sensors utilize a mixed-conducting oxide ceramic whose electrical resistance, at sufficiently high temperatures (e.g., 600 °C to 1100 °C), depends on the oxygen content of the surrounding atmosphere and can be used as a measure of the oxygen concentration. However, resistive lambda sensors are not widely used due to the high temperature dependence of their resistance and the insufficient chemical stability of many semiconducting materials under exhaust gas conditions. From DE 10 2006 048 354 A1, a method and a sensor element for determining the components of a gas mixture, in particular exhaust gas from internal combustion engines, are already known, in which the concentration of particles and the concentration of at least one gaseous component of the gas mixture are determined simultaneously or with a time delay using the same sensor element. The concentration of particles is determined by measuring the electrical resistance between the electrodes of the sensor element, and the concentration of the gaseous component is determined by measuring the electrical potential or pumping current applied to the electrodes of the sensor element. Disclosure of the invention The present invention relates to a resistive particle sensor comprising an electrode system of at least two electrodes and at least one semiconducting material contacting the electrodes, and characterized in that the semiconducting material is at least one oxide selected from the group consisting of rare-earth-rare-earth mixed oxides, rare-earth-zirconium mixed oxides, alkaline-earth-zirconium mixed oxides, transition-metal-zirconium mixed oxides, rare-earth-aluminum mixed oxides, alkaline-earth-aluminum mixed oxides, transition-metal-aluminum mixed oxides, rare-earth-titanium mixed oxides, barium-titanium mixed oxides, transition-metal-titanium mixed oxides, rare-earth-indium mixed oxides, alkaline-earth-indium mixed oxides, transition-metal-indium mixed oxides, and rare-earth-zinc mixed oxides. alkaline earth zinc mixed oxides, transition metal zinc oxide mixed oxides, samarium oxide, yttrium oxide, terbium oxide and / or mixtures thereof, comprises or consists of. For the purposes of this invention, the term "particle" can be understood to mean gaseous, solid, and / or liquid particles. In particular, for the purposes of this invention, the term "particle" can be understood to mean conductive particles, such as soot particles, and / or conductive droplets and / or oxygen. Within the scope of the present invention, the term "mixed oxide" can be understood to mean a mixture of at least two oxides of different elements. In particular, within the scope of the present invention, the term "mixed oxide" can be understood to mean a mixture of at least two oxides of different elements in which the stoichiometric proportions of the individual oxides are essentially of the same order of magnitude. For example, in a mixed oxide, the ratio between the element with the largest stoichiometric amount and each of the other elements can be in the range of 1:1 to 1:0.01. For the purposes of the present invention, the term "contacting" can be understood to mean, in particular, that the semiconducting material contacts the electrodes in such a way that the electrodes can be electrically connected via the semiconducting material. The materials used according to the invention have the advantage that they ensure reversible oxygen incorporation or removal and / or good bonding of the electrodes, in particular platinum-based electrodes, to the semiconducting material, and / or can exhibit high exhaust gas stability and / or high aging resistance. The particle sensor according to the invention has the advantage that it can be used as a resistive particle sensor, a resistive liquid sensor, and / or an oxygen sensor, for example, as a resistive lambda probe. In particular, the particle sensor according to the invention can be used for the detection of conductive particles, conductive liquids, and / or for determining the oxygen concentration in a gas stream, especially in the exhaust gas of an internal combustion engine, for example, of a motor vehicle or a combustion plant. Advantageously, the particle sensor according to the invention is also based on a simple measuring principle and a simple and cost-effective design. In one embodiment of the particle sensor according to the invention, the particle sensor is a resistive particle sensor, in particular a soot particle sensor. Advantageously, in addition to particle detection, the functionality, and in particular the integrity, of the particle sensor can also be checked in the absence of adhering particles, as part of a "self-diagnosis." Therefore, the semiconducting material can also be referred to as a self-diagnostic material, for example, as a self-diagnostic layer. The self-diagnostic function of the particle sensor can be based on the measurement of the conductivity, in particular on the basis of oxide ion and / or electron conductivity, or the electrical resistance of the semiconducting material. The conductivity or resistance of the semiconducting material can be determined with one electrode connected cathodically and the other electrode connected anodically.Advantageously, the electrode system can be checked for functionality as a unit and / or the sensitivity of the diagnostic procedure can be optimized. For use in a particle sensor, the semiconducting material preferably exhibits low conductivity during the particle measurement phase and high conductivity during the diagnostic phase. Semiconducting materials whose conductivity or resistance depends on temperature and oxygen partial pressure and which, at their self-diagnostic temperature, exhibit conductivity suitable for diagnosis while maintaining sufficiently high insulating properties during particle measurement have proven particularly advantageous for use in a particle sensor.For use in a particle sensor, the semiconducting material preferably exhibits a specific electrical conductivity of ≥ 10⁻⁵ S / m, for example ≥ 10⁻³ S / m, particularly ≥ 0.1 S / m, from a temperature of ≥ 400 °C, for example ≥ 500 °C, especially ≥ 550 °C, and / or from a λ of ≥ 0.8, especially ≥ 1.1. By utilizing the temperature dependence and the oxygen cross-sensitivity, a high degree of accuracy in the self-diagnostic measurement can advantageously be achieved when the oxygen content of the exhaust gas is known. In another embodiment of the particle sensor according to the invention, the particle sensor is an oxygen sensor, in particular a resistive lambda probe. For use in a lambda probe, the semiconducting material preferably has a substantially constant electrical resistance value at least over a temperature range, for example, from ≥ 700 °C to 5900 °C. In this way, temperature fluctuations, for example, due to changes in the flow, can advantageously be tolerated without distorting the measurement of the oxygen concentration. Furthermore, for use in a lambda probe, the semiconducting material preferably has a distinct characteristic curve over the entire lambda range, i.e., from λ = 0.8 to air, with simultaneously low temperature dependence. For use in a lambda probe, the semiconducting material also preferably has an oxygen sensitivity (m).In this way, lambda jumps can lead to a change in resistance within an order of magnitude, which is why the measuring range can be designed to be correspondingly small. In a preferred embodiment of the particle sensor according to the invention, the semiconducting material comprises at least one oxide selected from the group consisting of rare-earth-rare-earth mixed oxides, rare-earth-zirconium mixed oxides, alkaline earth-zirconium mixed oxides, transition metal-zirconium mixed oxides, rare-earth-titanium mixed oxides, barium-titanium mixed oxides, transition metal-titanium mixed oxides, samarium oxide, yttrium oxide, terbium oxide, and / or mixtures thereof. For example, the semiconducting material can consist of at least one oxide selected from this group. In a particularly preferred embodiment of the particle sensor according to the invention, the semiconducting material comprises at least one oxide selected from the group consisting of terbium-rare earth mixed oxides, rare earth-zirconium mixed oxides, calcium-zirconium mixed oxides, lanthanum-zirconium mixed oxides, barium-titanium mixed oxides, samarium oxide, yttrium oxide, terbium oxide and / or mixtures thereof. For example, the semiconducting material can consist of at least one oxide selected from this group. In a further, particularly preferred embodiment of the particle sensor according to the invention, the semiconducting material further comprises gadolinium oxide. In a further, particularly preferred embodiment of the particle sensor according to the invention, the semiconducting material comprises at least one oxide selected from the group consisting of terbium-yttrium mixed oxides, terbium-samarium mixed oxides, terbium-gadolinium mixed oxides, terbium-yttrium-samarium mixed oxides, terbium-yttrium-gadolinium mixed oxides, terbium-samarium-gadolinium mixed oxides, and / or mixtures thereof. For example, the semiconducting material can consist of at least one oxide selected from this group. Such semiconducting materials can be p-type, meaning that the electrical resistance can decrease unambiguously with increasing oxygen content over the entire lambda range (λ>0.8).Furthermore, such semiconducting materials can be characterized by exhibiting a differentiable resistance (unique characteristic curve) and / or an oxygen sensitivity m of ≥ 0.1 to ≤ 0.3 over a large lambda range, particularly from λ = 0.8 to air, which can be unambiguously assigned to a specific oxygen partial pressure. Such semiconducting materials can also exhibit lambda sensitivity starting at a temperature of approximately 400 °C. The operating temperature can therefore be selected between 400 °C and 1000 °C. These temperatures can be achieved, for example, by a heating device, particularly an integrated one. Advantageously, such semiconducting materials can exhibit a resistance plateau (see Fig. 2) in the temperature range from 2700 °C to ≤ 900 °C.When used as an oxygen sensor / lambda probe, a temperature of 800 °C is therefore advantageous, as a temperature fluctuation of ± 100 K at this temperature does not significantly affect the determination of the oxygen content (low cross-sensitivity to temperature). Furthermore, such materials can exhibit good adhesion to electrodes, particularly with little or no interdiffusion or secondary phase formation, and / or high chemical stability, especially in the lambda range λ>0.8. In addition, such semiconducting materials can exhibit resistance characteristics that are advantageous for the functional diagnosis of the sensor: for example, high resistance at small lambda values ​​or low temperatures, such as in the case of a heater failure, and / or critically low lambda values ​​in the event of a sensor defect, such as a broken contact.It is assumed that the temperature dependence of the electrical resistance of these materials is based on a hopping conduction mechanism. The specific resistance of the semiconducting material and the plateau can advantageously be adjusted via the proportion of terbium, yttrium, samarium and / or gadolinium (see Fig. 2 ). For example, the following may apply: - the proportion of terbium from > 0% to ≤ 90%, in particular from ≥ 1% to ≤ 50%, and / or - the proportion of yttrium from ≥ 0% to ≤ 99%, in particular from ≥ 25% to ≤ 99%, and / or - the proportion of samarium from ≥ 0% to ≤ 50%, in particular from ≥ 25% to ≤ 50%, and / or - the proportion of gadolinium from ≥ 0% to ≤ 50%, in particular from ≥ 40% to ≤ 50%, based on the total stoichiometric amount, wherein the percentage proportions of the individual elements are selected such that they add up to 100%. In a further, particularly preferred embodiment of the particle sensor according to the invention, the semiconducting material comprises samarium oxide, yttrium oxide, terbium oxide, barium titanate, La₂Zr₂O₇, and / or CaZrO₃. In particular, the semiconducting material can consist of samarium oxide, yttrium oxide, terbium oxide, barium titanate, La₂Zr₂O₇, and / or CaZrO₃. Preferably, the semiconducting material has a pyrochlore-like crystal structure. Such semiconducting materials have proven particularly advantageous for use in a resistive particle sensor. Within the scope of the present invention, the semiconducting material can, for example, be designed as a ceramic sintered body, thick film, thin film, ceramic foil or conductor track. In a further preferred embodiment of the particle sensor according to the invention, the particle sensor has a layer made of the semiconducting material. The electrode system can be arranged on the layer of semiconducting material. For example, the layer of semiconducting material can partially or completely contact the electrode system. In a further preferred embodiment of the particle sensor according to the invention, the particle sensor also comprises an insulating layer. For example, the insulating layer can comprise or consist of aluminum oxide and / or glass. The layer of semiconducting material can, in particular, be arranged on top of the insulating layer. In principle, the layer of semiconducting material can cover the insulating layer either completely or partially. In one embodiment, the layer of semiconducting material covers only a portion of the insulating layer. In this way, the sensor design can advantageously be simplified for separate circuitry of the electrodes. In a further preferred embodiment of the particle sensor according to the invention, at least one metal, for example zirconium, of the semiconducting material has, at least partially, a lower or higher oxidation state in the areas of the semiconducting material that contact the electrodes than the same metal in the other areas of the semiconducting material. Such an embodiment according to the invention can be achieved by the manufacturing process described below and advantageously results in improved bonding of the electrode material, in particular platinum, to the semiconducting material as well as improved conductivity. In a further embodiment of the particle sensor according to the invention, the electrode system comprises at least three, in particular at least four, electrodes. For example, the resistance measurement can be carried out using two-wire, three-wire, or four-wire measurement. In a further, preferred embodiment of the particle sensor according to the invention, the electrode system is an interdigital electrode system consisting of at least two interlocking interdigital electrodes in a comb-like manner. In a further preferred embodiment of the particle sensor according to the invention, the electrodes comprise a precious metal, for example platinum and / or gold. In a further, particularly preferred embodiment of the particle sensor according to the invention, the electrodes are formed from a zermet of at least one noble metal, in particular platinum, and the semiconducting material. For example, the proportion of the semiconducting material, based on the total weight of the zermet, can range from 0.1% by weight to ≤ 20% by weight, and in particular from ≥ 5% by weight to ≤ 15% by weight. In this way, an improved bond between the electrode and the semiconducting material can be ensured. In particular, this advantageously allows good bonding of the electrodes to the semiconducting material to occur already during the manufacture of the particle sensor, especially during sintering. In a further, particularly preferred embodiment of the present invention, the electrodes (3, 4) have a porosity of ≥ 15%, for example, from ≥ 5% to 20%. This has the advantage that oxygen can be supplied to the semiconducting material more easily and no oxygen depletion occurs. In a further, particularly preferred embodiment of the present invention, the surface of the particle sensor, in particular the semiconducting material, has a partial or complete impregnation with at least one metal that catalyzes flammable gases, in particular the reduction of oxygen to oxygen ions. Within the scope of the present invention, "impregnation" can be understood as a type of coating based on spaced-apart, for example, island-shaped, catalytic metal regions. In this way, the sensor according to the invention can also be used for the detection of flammable gases without directly short-circuiting the electrodes via the catalytically active metal. For example, platinum and / or palladium, in particular platinum, are suitable as catalytic metals.Impregnation has the advantage that, especially during driving, bound oxygen can be more easily converted during self-diagnosis, thus avoiding a reduction of the semiconducting material during the operation of the particle sensor. In a further preferred embodiment of the particle sensor according to the invention, the particle sensor has leads and contacts for connecting the electrodes. The leads and / or contacts can comprise or consist of a precious metal, for example platinum and / or gold. In a further preferred embodiment of the particle sensor according to the invention, the particle sensor comprises a support layer. The support layer can, for example, serve as a substrate for the semiconducting material and / or for the heating device and / or temperature measuring device described later. The support layer can, for example, comprise or consist of aluminum oxide, zirconium oxide, and / or magnesium oxide. If the support layer is made of a conductive material, it is preferably separated from the semiconducting material and the electrodes by at least one insulating layer. In a further, particularly preferred embodiment of the particle sensor according to the invention, the particle sensor comprises a temperature measuring device. In a further, particularly preferred embodiment of the particle sensor according to the invention, the particle sensor comprises a heating device. The heating device can be based on a wire loop, a thick-film or thin-film structure. The heating device can, for example, be made of an oxidation-resistant material, in particular platinum. Preferably, the heating device is separated from the semiconducting material and the electrodes by at least one insulating layer. A further aspect of the present invention relates to a method for producing a particle sensor according to the invention, in which a voltage is applied to the electrodes and the semiconducting material under an atmosphere free of oxidizing and / or reducing agents, in particular free of oxygen, wherein the voltage is selected such that at least one metal, for example zirconium, of the semiconducting material is at least partially reduced or oxidized in the regions of the semiconducting material that contact the electrodes. The method according to the invention has the advantage that the metal(s), in particular zirconium, of the semiconducting material is partially reduced to lower valence states or oxidized to higher valence states at the interface between the electrodes and the semiconducting material, resulting in improved bonding of the electrode material to the semiconducting material and improved conductivity. The manufacturing process according to the invention can, for example, be carried out under a nitrogen atmosphere. Advantageously, the process according to the invention is carried out at a temperature at which the semiconducting material is conductive. For the reduction of a metal, the electrodes can be connected as cathodes. Within the scope of the present invention, it is possible both to connect both electrodes simultaneously with the same potential relative to the semiconducting material and also to connect the electrodes sequentially with a potential relative to the semiconducting material. The manufacturing process according to the invention can advantageously be carried out as part of the final inspection of a particle sensor produced by a conventional method, which is referred to as the basic inspection or the 100% inspection. The formation of the interdigital electrode system and the semiconducting material can be carried out within the framework of the manufacturing process according to the invention using conventional methods known for the production of particle sensors, for example by a screen printing process. In a preferred embodiment of the manufacturing process according to the invention, the process further comprises the process step of partially or completely impregnating the surface of the particle sensor, in particular the semiconducting material, with at least one metal that catalyzes flammable gases, in particular the reduction of oxygen to oxygen ions. Platinum and / or palladium, especially platinum, are suitable for this purpose. The impregnation can be carried out, for example, by spraying the particle sensor with a solution of the metal, in particular a low concentration, or by immersing it in such a solution. Another object of the present invention is a particle sensor manufactured according to the manufacturing process according to the invention. A further object of the present invention is a method for the self-diagnosis of a particle sensor according to the invention, in particular a resistive particle sensor, in which, in a self-diagnosis phase: a voltage is applied to the electrodes; and the resulting conductivity or the resulting electrical resistance is measured and compensated with respect to the temperature measured by a temperature measuring device and the oxygen partial pressure measured by an oxygen measuring device; and the resulting result is output as a measure of the function of the particle sensor. The temperature can be measured, for example, by the particle sensor's temperature measuring device. The oxygen partial pressure can be determined, for example, by an oxygen sensor, such as a (broadband) lambda probe, which is connected upstream of the particle sensor. After compensating for the electrical conductivity or electrical resistance with respect to its dependence on temperature and oxygen partial pressure, it is advantageous to make a statement about the particle sensor's condition. In particular, any damage can be detected and the integrity of the particle sensor can be verified. Drawings Further advantages and advantageous embodiments of the invention are illustrated by the drawings and explained in the following description. It should be noted that the drawings are for descriptive purposes only and are not intended to limit the invention in any way. Fig. 1a shows a schematic top view of an embodiment of a particle sensor according to the invention; Fig. 1b shows a schematic cross-section through the embodiment of a particle sensor according to the invention shown in Fig. 1a; Fig. 2 shows a graph illustrating the temperature dependence of the resistivity of several terbium mixed oxides; Fig. 3 shows a graph illustrating the temperature dependence of the absolute resistivity values ​​of several terbium mixed oxides; Fig.Figure 4 shows a graph illustrating the electrical resistance of a terbium-yttrium mixed oxide as a function of lambda at different sample temperatures; and Figure 5 shows a graph illustrating the long-term stability of a terbium-yttrium mixed oxide under periodic lambda stress. Figures 1a and 1b show that, in this embodiment, the particle sensor 1 according to the invention comprises an interdigital electrode system 2 with two interdigital electrodes 3, 4 and a semiconducting material 5 which contacts the interdigital electrodes 3, 4. Figures 1a and 1b show in particular that, in this embodiment, the particle sensor 1 according to the invention has a layer of the semiconducting material 5, wherein the interdigital electrode system 2 is arranged on the layer of semiconducting material 5 and the layer of semiconducting material 5 completely contacts the interdigital electrode system 2. Figures 1a and 1b further show that, in this embodiment, the particle sensor 1 according to the invention has an insulating layer 6 on which the layer of semiconducting material 5 is arranged. In the context of Figures 1a and 1b, the particle sensor 1 according to the invention has an insulating layer 6 on which the layer of semiconducting material 5 is arranged.In the embodiment shown in Figure 1b, the layer of semiconducting material 5 covers only the area of ​​the insulating layer 6 located beneath the electrode system 2. This advantageously simplifies the particle sensor design for separate connection of the electrodes 3 and 4. Figures 1a and 1b further show that, in this embodiment, the particle sensor 1 according to the invention has leads 7 and 8 and contacts 9 and 10 for connecting the electrodes 3 and 4. Fig. 2 illustrates the temperature dependence of the resistivity of several terbium mixed oxides. The measurement geometry for recording the data illustrated in Fig. 2 corresponded essentially to that shown in Figs. 1a and 1b. Reference numeral 11 denotes the measurement data of a terbium-yttrium-samarium mixed oxide comprising 50% terbium, 25% yttrium, and 25% samarium. Reference numeral 12 denotes the measurement data of a terbium-yttrium-samarium mixed oxide comprising 30% terbium, 25% yttrium, and 45% samarium. Reference numeral 13 denotes the measurement data of a terbium-gadolinium mixed oxide comprising 30% terbium and 70% gadolinium. Reference numeral 14 denotes the measurement data of a terbium-yttrium mixed oxide comprising 30% terbium and 70% yttrium. Reference numeral 15 denotes the measurement data of a terbium-yttrium mixed oxide comprising 10% terbium and 90% yttrium.Reference numeral 16 denotes the measurement data of a terbium-yttrium mixed oxide comprising 3% terbium and 97% yttrium. Fig. 2 shows that, with a suitable material composition, the initially exponential temperature dependence of the resistivity plateaus at high temperatures. Figure 3 illustrates the temperature dependence of the absolute resistance values ​​of several terbium mixed oxides. The absolute resistance values ​​were measured on a thick film of the mixed oxides. The reference numerals denote the mixed oxides described in connection with Figure 2. Except for the measurements at 700 °C, all measurements were taken in air with an oxygen content of 20%. Only at 700 °C were measurements taken at both 20% and 1% oxygen contents. The scatter bars in Figure 3 indicate the oxygen partial pressure dependence of the resistance when changing from an oxygen content of 20% to 1%. Figure 2 shows that the oxygen dependence is maintained at the temperature plateau. Figure 4 illustrates the electrical resistance of a terbium-yttrium mixed oxide, comprising 5% terbium and 95% yttrium, as a function of lambda at different sample temperatures. The measurement was performed on a thick-film sample. The sample was heated in air. The repeated lambda jumps (0.8, 0.9, 1.1; 1.3) were realized around the base oxygen partial pressure of 3% O₂. Figure 4 shows that lambda jumps result in a resistance change within an order of magnitude. The measuring range can therefore advantageously be designed to be correspondingly small. Figure 5 illustrates the long-term stability of a terbium-yttrium mixed oxide, comprising 10% terbium and 90% yttrium, under periodic lambda stress. Figure 5 shows the resistance of a thick-film sensor based on this terbium-yttrium mixed oxide as a function of periodic lambda jumps (1.3; 1.1; 0.8) at 700 °C. Figure 5 shows that no aging effects could be observed in the depicted time period of approximately 24 hours, indicating high chemical stability of the material under exhaust gas conditions.

Claims

Method for producing a resistive particle sensor (1) for detecting particles in a gas stream, wherein the particle sensor (1) comprises an electrode system (2) of at least two electrodes (3, 4) and at least one semiconducting material (5), wherein the semiconducting material (5) contacts the electrodes (3, 4), wherein the semiconducting material (5) is at least one oxide selected from the group consisting of rare-earth-rare-earth mixed oxides, rare-earth-zirconium mixed oxides, alkaline-earth-zirconium mixed oxides, transition-metal-zirconium mixed oxides, rare-earth-aluminum mixed oxides, alkaline-earth-aluminum mixed oxides, transition-metal-aluminum mixed oxides, rare-earth-titanium mixed oxides, barium-titanium mixed oxides, transition-metal-titanium mixed oxides, rare-earth-indium mixed oxides, Alkaline earth indium mixed oxides, transition metal indium mixed oxides, rare earth zinc mixed oxides, alkaline earth zinc mixed oxides, transition metal zinc oxide mixed oxides, samarium oxide, yttrium oxideterbium oxide and / or mixtures thereof, comprising, wherein a voltage is applied to the electrodes (3, 4) and the semiconducting material (5) under an atmosphere free of oxidizing and / or reducing agents, the voltage being selected such that at least one metal of the semiconducting material (5) is at least partially reduced or oxidized in the regions of the semiconducting material (5) which contact the electrodes (3, 4), characterized in that both electrodes (3, 4) are connected simultaneously at the same potential relative to the semiconducting material (5). The method according to claim 1, characterized in that the method further comprises the process step: partial or complete impregnation of the surface of the particle sensor (1) with at least one metal which catalyzes flammable gases. Method for self-diagnosis of a resistive particle sensor (1) for detecting particles in a gas stream, wherein the self-diagnosis detects any damage to the particle sensor (1) and verifies the integrity of the particle sensor, wherein the particle sensor comprises an electrode system (2) of at least two electrodes (3, 4) and at least one semiconducting material (5), wherein the semiconducting material (5) contacts the electrodes (3, 4), wherein the semiconducting material (5) is at least one oxide selected from the group consisting of rare-earth-rare-earth mixed oxides, rare-earth-zirconium mixed oxides, alkaline-earth-zirconium mixed oxides, transition-metal-zirconium mixed oxides, rare-earth-aluminum mixed oxides, alkaline-earth-aluminum mixed oxides, transition-metal-aluminum mixed oxides, rare-earth-titanium mixed oxides, barium-titanium mixed oxides, Transition metal-titanium mixed oxides, rare earth-indium mixed oxides, alkaline earth-indium mixed oxides, transition metal-indium mixed oxides,rare earth zinc mixed oxides, alkaline earth zinc mixed oxides, transition metal zinc oxide mixed oxides, samarium oxide, yttrium oxide, terbium oxide and / or mixtures thereof, wherein in a self-diagnostic phase a voltage is applied to the electrodes (3, 4); and the resulting conductivity or electrical resistance is measured and compensated with respect to the temperature measured by a temperature measuring device and the oxygen partial pressure measured by an oxygen measuring device; and the resulting result is output as a measure of the function of the particle sensor (1).

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