CN111505079A - Tubular sensing element with excellent performance and preparation method thereof - Google Patents

Abstract

The invention discloses a tubular sensing element with excellent performance and a preparation method thereof. One of the objectives of the present invention is to provide a tubular sensor element with excellent performance, wherein the inner catalytic electrode part of the sensor element is composed of a novel ceramic catalytic electrode, so that the sensor element provided by the present invention also has the characteristics of low cost and excellent catalytic performance. The invention also aims to provide a preparation method of the tubular sensing element with excellent performance, and the sensing element prepared by the method has the advantages of simple preparation process, low consumption of noble metal and good catalytic activity. Particularly, when a protective layer is required to be added, the protective layer and other parts of the sensing element can be prepared by adopting a co-firing process, so that the product process is simplified, and the bonding fastness of the protective layer and the solid electrolyte ceramic substrate is improved.

Description

A kind of tubular sensor element with excellent performance and preparation method thereof

technical field

The invention relates to the field of oxygen sensors, in particular to a tubular sensor element with excellent performance and a preparation method thereof.

Background technique

In the control system of the vehicle engine, it is a key technology for emission control to ensure that the engine works with the mixture of the best air-fuel ratio. The vehicle oxygen sensor is a key component used to control the air-fuel ratio of the engine mixture. The oxygen sensor is a A key component of the engine control unit (ECU) is the real-time feedback of the gas condition after the combustion of the oil-fuel mixture. The engine electronically controlled injection system precisely controls the air-fuel ratio (A/F, the mass ratio of air to gasoline) based on the signal provided by the oxygen sensor. .

The three-way catalytic converter is the most important external purification device installed in the automobile exhaust system. It can convert harmful gases such as CO, HC and NOx from automobile exhaust into harmless carbon dioxide, water and nitrogen through oxidation and reduction. . But in order to use the three-way catalytic converter effectively, the air-fuel ratio must be precisely controlled so that it is always close to the theoretical air-fuel ratio. Therefore, in the use of three-way catalytic conversion engine, the oxygen sensor is an indispensable element. When the air-fuel ratio of the mixture deviates from the theoretical air-fuel ratio, the purification ability of the three-way catalyst for CO, HC and NOX will drop sharply. The oxygen sensor installed in the exhaust pipe can detect the oxygen concentration in the exhaust gas and send it to the ECU. Feedback signal, the ECU controls the increase or decrease of the fuel injection amount of the injector, so that the air-fuel ratio of the mixture can be controlled near the theoretical value, so that the engine works in the state of the best air-fuel mixture ratio, that is, the best air-fuel ratio, which is the best air-fuel ratio for the engine. The exhaust gas purification of the three-way catalytic converter creates conditions.

Oxygen sensor is a measuring element that uses ceramic sensitive elements to measure the oxygen potential in the exhaust pipe of automobiles, and calculates the corresponding oxygen concentration according to the principle of chemical balance, so as to monitor and control the combustion air-fuel ratio to ensure product quality and exhaust emission standards. Oxygen sensors are generally divided into tubular oxygen sensors and chip oxygen sensors. Take the tubular zirconia oxygen sensor as an example to explain its working principle:

The tubular zirconia oxygen sensor is composed of a zirconia tube (referred to as a zirconium tube), a platinum electrode and a protective sleeve. The zirconium tube and the platinum electrode form a sensing element (refer to Figure 1). The solid electrolyte element made of zirconium is coated with a layer of platinum on the inner and outer sides of the zirconium tube to form inner and outer platinum electrodes. The inner side of the zirconium tube is open to the atmosphere, and the outer side is in contact with the exhaust gas. At the operating temperature, the oxidation-reduction reaction of oxygen gains and loses electrons in the three-phase interface area formed by the platinum electrode and zirconia. Under the catalysis of the electrode, it becomes oxygen molecule. Due to the high and low oxygen ion concentration on the inside and outside of the zirconium tube (generally, the oxygen concentration in the atmosphere is high on the inside, and the oxygen concentration in the exhaust gas is low on the outside), so there is a potential difference between the inside and outside electrodes. . Because the outer electrode is exposed to the exhaust gas, the oxygen ion concentration will change according to the actual working conditions, while the inner electrode is the reference air, and the oxygen ion concentration is unchanged. When the engine air-fuel ratio is lean, the oxygen concentration in the exhaust gas is relatively high, the oxygen concentration difference between the inner and outer electrodes is small, that is, the potential difference is small, and the output voltage signal of the oxygen sensor is close to 0V. Conversely, when the air-fuel ratio is rich, the oxygen concentration in the exhaust gas is relatively low, and the oxygen concentration difference between the inner and outer electrodes is large, that is, the potential difference is large, and the output voltage of the sensor is close to 1V. The typical response curve of the oxygen sensor is shown in Figure 2, where lambda is the air excess coefficient, that is, the ratio of the actual air-fuel ratio to the theoretical air-fuel ratio, an index used to determine the leanness of the mixture.

Please continue to refer to FIG. 1 , the electrodes in the sensing element of the oxygen sensor include a catalytic electrode part and a lead electrode part according to their functions during use. The catalytic electrode part is mainly used to catalyze the redox reaction and generate electrical signals, and the main function of the lead electrode part is to export the generated electrical signals. In the electrode preparation of the sensing element of the oxygen sensor, the key point of the technology is how to set a certain thickness of the electrode on the ceramic substrate (such as the platinum electrode mentioned above). The method of coating an electrode layer on a zirconium) substrate has not been adopted because the electrode layer is very easy to peel off. The commonly used technical solutions are co-firing technology of electrodes and solid electrolyte ceramics and electrode plating technology. The electroplating electrode technology refers to the patent application publication specification CN200310114168.7, etc. The advantages of the electroplating electrode are that the electrode layer prepared is very thin, the amount of use is small, it has more three-phase interfaces and good activity, and the amount of precious metal in the co-fired electrode is effectively solved. However, the bonding reliability between the electrode material and the substrate is relatively poor, and it is easy to peel off; and the electroplating process is relatively complicated, and it is easy to pollute the environment.

The co-firing technology of electrodes and solid electrolyte ceramics refers to the application number 200410064804.4, etc. The advantage of co-firing electrodes is that the bonding reliability between the electrode layer and the substrate is good, which improves the problem of easy peeling off of the directly coated electrode layer. A thick film is used, with a thickness of 6-10 microns, in which the platinum particles are micron or sub-nanometer noble metal particles, and the electrode material is co-fired at a high temperature of 1400-1550 ° C, the low-temperature catalytic activity of the electrode is relatively poor, and the three-phase The interface also has a certain loss, so under the condition of obtaining the same catalytic activity, more noble metal dosage is required, and the cost is high.

SUMMARY OF THE INVENTION

One of the objectives of the present invention is to provide a tubular sensing element with excellent performance, the internal catalytic electrode part of the sensing element is composed of a novel ceramic catalytic electrode, so the sensing element provided by the present invention also has the advantages of low cost, catalytic Features of excellent performance.

Another object of the present invention is to provide a method for preparing a tubular sensor element with excellent performance. The sensor element prepared by the method has a simple preparation process, a small amount of precious metal and good catalytic activity. Especially when a protective layer needs to be added, the protective layer can be prepared by a co-firing process with other components of the sensing element, which simplifies the product process and increases the bonding fastness between the protective layer and the solid electrolyte ceramic substrate.

The technical scheme of the present invention is: a tubular sensing element with excellent performance, comprising: a tubular ceramic substrate with an inner cavity extending inward from the bottom surface;

An outer electrode disposed on the outer surface of the ceramic base, which includes an outer catalytic electrode portion disposed around the end of the outer surface of the ceramic base, and a an external lead electrode part electrically connected to the external catalytic electrode part;

An inner electrode disposed on the wall of the inner cavity, comprising an inner catalytic electrode portion disposed around the end of the wall of the inner cavity, and disposed on the wall of the inner cavity and extending to the ceramic an inner lead electrode portion on the bottom surface of the main body that is electrically connected to the inner catalytic electrode portion;

Wherein, the internal catalytic electrode includes a catalytic electrode ceramic substrate formed on the inner cavity wall of the ceramic substrate and a noble metal disposed inside and on the surface of the catalytic electrode ceramic substrate, and the catalytic electrode ceramic substrate is the inner and outer surfaces of the catalytic electrode ceramic substrate. A porous ceramic with tiny three-dimensional pores, the precious metal is distributed in a three-dimensional network inside and on the surface of the porous ceramic; the external electrode is composed of a co-fired electrode.

Preferably, the noble metal is distributed on the surface of the tiny three-dimensional pores of the catalytic electrode ceramic substrate in the form of crystal grains, so that the noble metal forms a three-dimensional network structure inside and on the catalytic electrode ceramic substrate to facilitate the transmission of electrical signals.

Preferably, the sensing element further includes a protective layer, the protective layer covers the surface of the external electrode, and the protective layer is formed by co-sintering with the ceramic substrate and the external electrode.

Preferably, the inner lead electrode part of the inner electrode comprises a catalytic electrode ceramic base formed on the inner cavity wall of the ceramic base and a noble metal disposed inside and on the surface of the catalytic electrode ceramic base, the catalytic electrode ceramic The substrate is a porous ceramic with tiny three-dimensional pores inside and on the surface, and the precious metal is distributed in a three-dimensional network in the porous ceramic; or the inner lead electrode part of the internal electrode is composed of a co-fired electrode.

Preferably, the porosity of the catalytic electrode ceramic substrate is between 20% and 80%, and the thickness of the catalytic electrode ceramic substrate is 10-1000 microns.

The technical solution of the present invention also includes a tubular oxygen sensor, which includes the above tubular sensing element with excellent performance.

The technical solution of the present invention also includes the above-mentioned preparation method of the tubular sensing element with excellent performance, comprising the following steps:

providing a tubular solid electrolyte substrate green body, the solid electrolyte substrate green body having an inner cavity extending inward from the bottom surface; providing a co-fired electrode slurry; providing a slurry for forming a catalytic electrode ceramic matrix;

The co-fired electrode slurry was applied to the outer electrode region on the outer surface of the solid electrolyte substrate green body and the inner lead electrode portion region on the wall of the inner cavity, and the slurry for forming the catalytic electrode ceramic matrix was injected into the solid electrolyte substrate green body. The bottom of the inner cavity of the solid electrolyte substrate green body is then dried;

preparing a protective layer on the surface of the co-fired electrode slurry coated on the outer surface of the green substrate, followed by drying;

The solid electrolyte substrate green body, the co-fired electrode slurry coated on the outer surface of the solid electrolyte substrate green body, the co-fired electrode slurry on the wall of the inner cavity of the solid electrolyte substrate green body and the dried The slurries for forming the catalytic electrode ceramic substrate at the bottom of the inner cavity of the solid electrolyte substrate green body are co-sintered to obtain a solid electrolyte ceramic substrate, an outer electrode disposed on the outer surface of the fixed electrolyte ceramic substrate, and an inner cavity of the ceramic substrate The inner lead electrode part on the wall and the catalytic electrode ceramic substrate at the bottom of the inner cavity, wherein the catalytic electrode ceramic substrate is a porous ceramic with electrolyte properties and tiny three-dimensional pores inside and on the surface;

The precious metal salt solution is loaded into the catalytic electrode ceramic matrix, and then baked and decomposed to obtain the semi-finished product of the sensing element;

The semi-finished product of the sensing element is subjected to high temperature baking and aging treatment at 800-1300°C.

Preferably, the precious metal salt solution is chloroplatinic acid, platinum nitrate, platinum sulfite, rhodium chloride, ammonium chlororhodium, sodium hexachlororhodium, rhodium nitrate, palladium chloride, palladium nitrate, palladium sulfate solution One or more non-reactive mixtures.

Preferably, the slurry for forming the catalytic electrode ceramic matrix is prepared by the following method:

The powder of the solid oxide ceramics and the alcohol solution are ball-milled into a slurry, and then a pore-forming agent, a binder and a plasticizer are added to the slurry, and the ball-milling is continued to finally obtain a slurry for forming a catalytic electrode ceramic matrix.

Preferably, when the noble metal salt solution is loaded into the catalytic electrode ceramic substrate, and then decomposed by baking, the noble metal salt in the noble metal salt solution is decomposed into noble metal decomposition products, which are deposited on the tiny three-dimensional pores of the catalytic electrode ceramic substrate. , the semi-finished product of the sensor element is obtained;

After the semi-finished product of the sensing element is subjected to high-temperature baking and aging treatment at 800-1300° C., the precious metal salt in the precious metal salt solution is decomposed at high temperature to form precious metal grains, and the precious metal grains are distributed on the catalytic electrode ceramic matrix. The surface of the tiny three-dimensional pores, so that the precious metal forms a three-dimensional network structure inside and on the surface of the ceramic substrate of the catalytic electrode, which facilitates the transmission of electrical signals.

Preferably, the provided tubular solid electrolyte substrate green body is an unsintered solid electrolyte substrate green body,

During sintering, the solid electrolyte substrate green body and the catalytic electrode ceramic matrix-forming slurry applied to the surface of the solid electrolyte substrate green body are simultaneously sintered,

The sintering is carried out at a temperature of 1400°C to 1550°C.

Preferably, the solid electrolyte substrate green body is obtained by the following method:

Preparation of solid electrolyte substrate green body;

The prepared solid electrolyte substrate green embryo is subjected to high temperature baking and curing treatment at 800°C-1300°C.

Advantages of the present invention

1. The tubular sensing element with excellent performance provided by the present invention, its catalytic electrode part is a new type of ceramic catalytic electrode, and the structure of the new type of ceramic catalytic electrode is a three-dimensional network formed by precious metals in the porous solid electrolyte ceramic matrix. This structure greatly increases the number of three-phase interfaces between noble metals, porous solid electrolyte ceramics and oxygen, so that the new ceramic catalytic electrode also has excellent catalytic ability even when a small amount of noble metals can be used. The production cost is reduced to a certain extent, so the tubular sensor element with excellent performance provided by the present invention also has the characteristics of low cost and excellent catalytic performance.

2. Compared with the co-fired electrode, the internal catalytic electrode part of the tubular sensing element with excellent performance provided by the present invention has better catalytic activity without the noble metal being sintered at high temperature. Therefore, the tubular sensing element provided by the present invention has excellent performance The type sensing element has better catalytic activity.

3. The preparation method of the tubular sensing element with excellent performance provided by the present invention has a simple preparation process, especially when a protective layer needs to be added, the protective layer can be prepared by a co-firing process with other parts of the sensing element, which is simplified. At the same time of the product process, the bonding fastness of the protective layer and the solid electrolyte ceramic substrate is increased.

Description of drawings

FIG. 1 is a schematic diagram of the external and internal structures of a sensing element of a tubular oxygen sensor in the prior art.

Figure 2 is a typical response curve of an oxygen sensor.

3 is a schematic diagram of a process of forming a novel ceramic catalytic electrode provided by the first embodiment of the present invention.

FIG. 4 is a novel ceramic catalytic electrode provided by the first embodiment of the present invention.

FIG. 5 is a voltage rise curve diagram of the sample provided by the first embodiment of the present invention.

FIG. 6 is a reference diagram of a voltage jump curve when the N value is 21 according to the third embodiment of the present invention.

FIG. 7 is a process diagram of the preparation of the tubular sensing element with excellent performance provided by the fourth embodiment of the present invention.

Detailed ways

The technical solution of the present invention will be described in detail below with reference to the accompanying drawings 1-7 and the embodiments, wherein: 1. ceramic substrate; 2. external electrode; 21. external catalytic electrode part; 22. external lead electrode part; 3. internal electrode; 31 , Internal catalytic electrode part; 32, Internal lead electrode part; 4, New ceramic catalytic electrode; 41, Catalytic electrode ceramic substrate; 42, Precious metal.

It should be noted that the "sintering" mentioned in the full text of the present invention refers to converting powdery materials into dense bodies, which is a traditional process for making ceramics, and the sintering temperature is 1400°C-1550°C. The "co-firing" mentioned throughout the present invention refers to co-firing. The "co-fired electrode" mentioned in the whole text of the present invention refers to the electrode formed by co-firing the electrode and the solid electrolyte ceramic substrate in the prior art. For the specific preparation method of the co-fired electrode, please refer to the application document of the patent application number 200410064804.4 .

Novel ceramic catalytic electrode and preparation method thereof

In the first embodiment, the present invention discloses a novel ceramic catalytic electrode 4 and a preparation method thereof, and the novel ceramic catalytic electrode 4 can be used as an electrode of a sensing element of an oxygen sensor.

Please refer to FIG. 3 and FIG. 4 , the novel ceramic catalytic electrode 4 includes a catalytic electrode ceramic substrate 41 and a precious metal 42 disposed inside and on the surface of the catalytic electrode ceramic substrate. The catalytic electrode ceramic substrate 41 is honeycomb and porous ceramics with tiny three-dimensional pores on the surface, and the catalytic electrode ceramic matrix has solid electrolyte properties, that is, oxygen ion conductivity. The precious metal is distributed in a three-dimensional network in the porous ceramic. Specifically, the precious metal is distributed in the form of crystal grains on the surface of the tiny three-dimensional pores of the porous solid electrolyte ceramic. During the heat treatment of the precious metal crystal grains, Adjacent crystal grains are fused and connected to each other, so that the precious metal forms a three-dimensional network structure that is connected to each other on the surface of the tiny three-dimensional pores of the porous ceramic, which facilitates the transmission of electrical signals.

This kind of structure of precious metal with interconnected three-dimensional network distribution is formed on the surface of the tiny three-dimensional pores of porous ceramics with solid electrolyte properties (referred to as porous solid electrolyte ceramics in full), which greatly increases the amount of precious metals, porous solid electrolyte ceramics and oxygen. The number of three-phase interfaces between them, so that in the case of using a small amount of precious metal, the new ceramic catalytic electrode also has excellent catalytic ability, which greatly reduces the production cost. The specific experimental data can be found in the following.

It should be noted that the noble metal is preferably a platinum group noble metal. Further, the precious metal can be one or an alloy of platinum, palladium and rhodium.

In the novel ceramic catalytic electrode of the present invention, the catalytic electrode ceramic substrate is a porous solid electrolyte ceramic, and its porosity is between 20% and 80%. Due to its high porosity, precious metals are distributed in the porous solid in the form of crystal grains. The surface of the tiny three-dimensional pores of the electrolyte ceramic forms a three-dimensional network structure that is connected to each other, which is convenient for the transmission of electrical signals. Further, the porosity is preferably between 40%-60%.

It should be noted that the catalytic electrode ceramic substrate of the novel ceramic catalytic electrode of the present invention is a solid oxide ceramic that has electrical conductivity to oxygen ions within a certain temperature range (150°C-930°C). Preferably, the solid oxide ceramic is yttria doped zirconia, calcium oxide doped zirconia or yttria doped thorium oxide. The thickness of the catalytic electrode ceramic substrate is 10-1000 microns, wherein the preferred thickness is 100-300 microns.

The novel ceramic catalytic electrode of the present invention is formed on the surface of the ceramic substrate 1 having solid electrolyte properties. The ceramic substrate 1 is an oxide solid electrolyte known to those skilled in the art in the prior art, which can be used as a solid electrolyte part of an oxygen sensor, and has conductivity to oxygen ions, and is specifically a yttria-stabilized zirconia ceramic. The ceramic substrate 1 has a dense structure and cannot absorb liquid into the interior of the ceramic substrate.

A lead electrode can also be added on the surface of the above-mentioned ceramic substrate 1. The novel ceramic catalytic electrode is mainly used to catalyze the redox reaction and generate an electrical signal. The main function of the lead electrode is to derive the generated electrical signal.

It should be noted that the novel ceramic catalytic electrode of the present invention can be used as the entire electrode of the sensing element of the oxygen sensor, or only as a part of the electrode of the sensing element of the oxygen sensor. For example, the novel ceramic catalytic electrode is only used for oxygen The catalytic electrode portion of the electrode of the sensor element of the sensor and the lead electrode portion of the electrode of the sensor element of the oxygen sensor are prepared using other materials (eg, co-fired electrodes).

As shown in FIG. 2 and FIG. 3 , the first embodiment of the present invention also provides a method for preparing the above-mentioned novel ceramic catalytic electrode, which is as follows:

(1) Provide a solid electrolyte substrate green body; provide a slurry for forming a catalytic electrode ceramic matrix.

a. The solid electrolyte substrate green body and its preparation process are in the prior art. For example, the solid electrolyte substrate green body can be an unsintered zirconia solid electrolyte substrate green body, and the specific preparation process can refer to the following steps:

Step 1: Y2O3 with a purity of 99.9% is mixed with ZrO2 with a purity of not less than 99%, wherein the proportion of Y2O3 is 5 mol%. The mixture was thoroughly mixed and calcined at 1300°C for 2 hours.

Step 2: Ball milling the calcined mixture until D80 is less than 2.5 microns.

Step 3: By spray drying, spherical particles with an average particle size of 70 microns are obtained.

Step 4: The U-shaped green body is obtained by dry bag isostatic pressing, and the final shape is obtained by grinding on an automatic flow grinder.

Step 5: The prepared green body is baked and consolidated at 1000-1200°C.

b. The slurry for forming the catalytic electrode ceramic matrix includes solid oxide ceramic powder (such as yttrium oxide doped zirconia powder), alcohol solution, pore-forming agent (such as carbon powder), binder ( such as polyvinyl butyral) and plasticizers such as dibutyl phthalate. The proportion of the above-mentioned pore-forming agent will affect the porosity of the catalytic electrode ceramic matrix. Generally, the proportion of the pore-forming agent is proportional to the porosity of the catalytic electrode ceramic matrix, that is, the higher the proportion of the pore-forming agent, the higher the porosity. , the lower the ratio of pore-forming agent, the lower the porosity. The preparation method of the slurry for forming the catalytic electrode ceramic matrix is a conventional technique for preparing porous ceramics, and the preparation method can be as follows:

The powder of solid oxide ceramics is ball-milled with alcohol solution for 4 hours to make slurry, and then pore-forming agent, binder and plasticizer are added to the slurry, and the ball-milling is continued for 16 hours to obtain the catalytic electrode ceramic matrix. slurry.

(2) Coat the slurry for forming the catalytic electrode ceramic substrate on the surface of the solid electrolyte substrate green body, and then co-sinter to obtain the solid electrolyte ceramic substrate and the catalytic electrode with a thickness of 10-1000 microns formed on the surface of the solid electrolyte ceramic substrate Ceramic matrix, as shown in Figure 3. Wherein, the catalytic electrode ceramic substrate is a porous ceramic with electrolyte properties and tiny three-dimensional pores inside and on the surface.

Since the slurry for forming the catalytic electrode ceramic substrate is sintered together with the solid electrolyte substrate green body, the catalytic electrode ceramic substrate and the solid electrolyte ceramic substrate have good bonding properties and high bonding fastness.

(3) The precious metal salt solution is loaded into the catalytic electrode ceramic substrate, and then baked and decomposed to obtain a semi-finished catalytic electrode.

a, the precious metal salt solution is an aqueous solution of a class of compounds composed of precious metal ions and acid ions, such as chloroplatinic acid, platinum nitrate, platinum sulfite, rhodium chloride, ammonium chlororhodium, sodium hexachlororhodium, A non-reactive mixture of one or more of rhodium nitrate, palladium chloride, palladium nitrate, and palladium sulfate solution, preferably a saturated aqueous solution of chloroplatinic acid.

b. The above-mentioned loading of the noble metal salt solution into the catalytic electrode ceramic substrate means that after the catalytic electrode ceramic substrate contacts the noble metal salt solution, the noble metal salt in the noble metal salt solution is adsorbed into the catalytic electrode ceramic substrate by capillary action. Then, the catalytic electrode ceramic substrate adsorbed with the noble metal salt is subjected to baking and decomposition treatment, so that the noble metal salt is decomposed into noble metal decomposition products, which are deposited in the tiny three-dimensional pores of the catalytic electrode ceramic substrate.

(4) The semi-finished product of the catalytic electrode is subjected to high-temperature baking and aging treatment at 600-1000° C. to obtain the ceramic catalytic electrode of the present invention, as shown in FIG. 4 .

When the high temperature baking and aging treatment is performed at 600-1000 °C, the decomposed products of the precious metal are further decomposed to form precious metal grains. The precious metal grains are distributed on the surface of the tiny three-dimensional pores of the ceramic substrate of the catalytic electrode, and the adjacent precious metal grains are fused and connected to each other. Therefore, the precious metal crystal grains form a three-dimensional network structure that is connected to each other inside and on the surface of the ceramic substrate of the catalytic electrode, which facilitates the transmission of electrical signals.

Sensor element and method of making the same

In the second embodiment, the present invention discloses a sensing element and a preparation method thereof, the sensing element can be used as a sensing element of an oxygen sensor.

The sensing element includes a ceramic substrate 1 with solid electrolyte properties, and one or more electrodes arranged on the surface of the ceramic substrate 1, each electrode includes a catalytic electrode part and a lead electrode part, and the catalytic electrode part of each electrode connected to the lead electrode portion. Part or all of the catalytic electrode portion of the electrode is composed of the novel ceramic catalytic electrode provided by the first embodiment of the present invention. Since the specific structure and preparation method of the novel ceramic catalytic electrode have been described in detail above, they will not be repeated here, and please refer to the relevant description in the first embodiment.

It should be noted that the catalytic electrode part of a single electrode may be entirely composed of the novel ceramic catalytic electrode, or a part of the catalytic electrode part of a single electrode may be composed of the novel ceramic catalytic electrode, and the other part may be composed of other electrodes (such as co-fired electrodes). electrodes).

The electrode of the sensing element provided in this embodiment (including a catalytic electrode part and a lead electrode part, the catalytic electrode part is mainly used to catalyze the redox reaction and generate an electrical signal, and the main function of the lead electrode part is to derive the generated electrical signal) , can be all composed of new ceramic catalytic electrodes, or can be composed of new ceramic catalytic electrodes and electrodes commonly used in the prior art. For example, the catalytic electrode part is composed of new ceramic catalytic electrodes, and the lead electrode part is composed of co-fired electrodes.

It should be noted that the sensing element provided in this embodiment can be used in various existing concentration type tubular oxygen sensors or chip oxygen sensors. The specific structure of the sensing element used for the tubular oxygen sensor can be referred to Fig. 1, including a ceramic substrate and inner and outer electrodes. The ceramic substrate is tubular and has an inner cavity extending inward from the bottom surface. An outer electrode on the outer surface of the ceramic substrate and an inner electrode on the wall of the inner cavity; the outer electrode includes an outer catalytic electrode portion arranged around the end of the outer surface of the ceramic substrate, and an outer electrode portion arranged on the ceramic substrate an outer lead electrode part extending to the bottom surface of the ceramic body and electrically connected to the outer catalytic electrode part; the inner electrode includes an inner catalytic electrode arranged around the end of the wall part of the inner cavity and an inner lead electrode portion which is provided on the wall portion of the inner cavity, extends to the bottom surface of the ceramic body, and is electrically connected to the inner catalytic electrode portion.

In a specific embodiment of the sensing element for a tubular oxygen sensor, the outer catalytic electrode portion is composed of the novel ceramic catalytic electrode, and the outer lead electrode portion and the inner electrode of the outer electrode are composed of co-fired electrodes .

In another specific embodiment of the sensing element for a tubular oxygen sensor, the inner catalytic electrode portion is composed of the novel ceramic catalytic electrode, and the inner lead electrode portion and the outer electrode are composed of co-fired electrodes.

In yet another specific embodiment of the sensing element for a tubular oxygen sensor, the outer catalytic electrode portion and the inner catalytic electrode portion are composed of the novel ceramic catalytic electrode, the outer lead electrode portion and the inner lead electrode portion The electrode portion consists of co-fired electrodes.

In one embodiment of the sensing element used for the chip oxygen sensor, the ceramic substrate of the sensing element is in the shape of a sheet, and the electrodes of the sensing element include an external electrode disposed on the upper surface of the ceramic substrate and an outer electrode disposed on the ceramic substrate. the inner electrode on the lower surface of the ceramic substrate; the outer electrode includes an outer catalytic electrode part and an outer lead electrode part electrically connected with the outer catalytic electrode; the inner electrode includes an inner catalytic electrode part and an inner catalytic electrode part connected with the inner catalytic electrode The electrically connected inner lead electrode part, the inner catalytic electrode and the inner lead electrode are co-fired electrodes which are fired at a high temperature.

In a specific embodiment of the sensing element for a chip oxygen sensor, the outer catalytic electrode part is composed of the novel ceramic catalytic electrode, and the outer lead electrode part and the inner electrode of the outer electrode are composed of co-fired electrodes .

On the basis of the preparation method of the novel ceramic catalytic electrode provided by the first embodiment of the present invention, this embodiment also provides a preparation method of the above-mentioned sensing element, and the specific steps are as follows:

(1) providing a solid electrolyte substrate green body; providing a slurry for forming a catalytic electrode ceramic matrix; providing a slurry for forming a co-fired electrode slurry (referred to as co-fired electrode slurry in its entirety).

When the solid electrolyte substrate green body is tubular, for the preparation method of the solid electrolyte substrate green body, reference may be made to the preparation method of the solid electrolyte substrate green body provided in the first embodiment. When the solid electrolyte substrate green body is in the form of a sheet, the solid electrolyte substrate green body can be prepared by a tape casting process. The tape tape molding process is a molding method for ceramic products in the prior art, which is a current The relatively mature molding methods that can obtain high-quality, ultra-thin ceramics have been widely used in the production of advanced ceramics such as monolithic capacitor ceramics, thick-film and thin-film circuit substrates.

The co-fired electrode slurry is in the prior art, and specifically, it can be a high-temperature co-fired platinum slurry. For the preparation method, please refer to the application document of Patent Application No. 200410064804.4.

(2) Applying the slurry for forming the catalytic electrode ceramic matrix to the surface of the solid electrolyte substrate green body where the catalytic electrode portion needs to be prepared, and applying the co-firing slurry to the surface of the solid electrolyte substrate green body requires preparing lead wires The area of the electrode part is then sintered together with the solid electrolyte substrate green body, the slurry for forming the catalytic electrode ceramic matrix and the co-firing slurry on the surface of the green body to obtain the solid electrolyte ceramic substrate and the catalytic electrode disposed on the fixed electrolyte ceramic substrate A ceramic substrate and a lead electrode part, wherein the catalytic electrode ceramic substrate is a porous ceramic with electrolyte properties and microscopic three-dimensional pores inside and on the surface.

(3) Loading the precious metal salt solution into the catalytic electrode ceramic substrate, and then drying and decomposing treatment to obtain a semi-finished product of the sensing element.

(4) The semi-finished product of the sensing element is subjected to high-temperature baking and aging treatment at 600-1000° C. to obtain the sensing element provided in this embodiment.

The inventors of the present invention have found through a large number of experiments that, taking the oxygen sensor with the co-fired electrode as the catalytic electrode as a comparative example, the oxygen sensor with the sensing element provided in this embodiment can use less precious metals and have better performance. catalytic performance.

Using the co-fired electrode in the prior art as a catalytic electrode to make a sensing element, the oxygen sensor obtained after packaging is used as a comparative example, and the specific preparation process of the sensing element is as follows:

(1) Provide a solid electrolyte substrate green body; provide a co-fired electrode slurry.

(2) Co-firing slurry is applied to the area of the surface of the solid electrolyte substrate green body where the catalytic electrode portion and the lead electrode portion are required to be prepared, and then the product is sintered.

The specific parameters of the comparative example are: the solid electrolyte substrate green body is reinforced by baking at 1100 °C, and the sintering temperature is 1450 °C; the co-fired electrode is used as the catalytic electrode part and the lead electrode part at the same time, and the amount of platinum converted to the catalytic electrode part is total. is 0.006 grams.

The sensing element is prepared by using the preparation method of the sensing element provided in this embodiment, and the sensing element is packaged to obtain three oxygen sensors of sample 1, sample 2 and sample 3.

in:

Sample 1: The solid electrolyte substrate green body is reinforced by baking at 800 °C, and the sintering temperature is 1450 °C; the powder for preparing the slurry for forming the catalytic electrode ceramic matrix is yttria-stabilized zirconia, and the particle size distribution D10=0.1 micron, D50 = 5 microns, D90 = 7 microns; the precious metal salt solution uses a saturated aqueous solution of chloroplatinic acid, and the platinum loading of the new ceramic catalytic electrode obtained by conversion of chloroplatinic acid is 0.001 g; High temperature baking and aging treatment at 9000 ℃.

Sample 2: The solid electrolyte substrate green body is reinforced by baking at 1200°C; the platinum loading amount of the new ceramic catalytic electrode converted from chloroplatinic acid is 0.0013 g; other parameters and steps are the same as sample 1.

Sample 3: The solid electrolyte substrate green body is reinforced by baking at 1000°C; the powder for preparing the slurry to form the catalytic electrode ceramic substrate is still yttria-stabilized zirconia, with particle size distribution D10=0.34 micron, D50=0.53 micron, D90 = 1.02 microns; the noble metal salt solution still uses a saturated aqueous solution of chloroplatinic acid, and the platinum loading amount of the new ceramic catalytic electrode obtained by conversion of chloroplatinic acid is 0.001 g; other parameters and steps are the same as sample 1.

In order to compare the difference between the comparative example and the sample, a comparative test is carried out through a certain test. Test conditions: The product is packaged in a test fixture, and the oxygen sensor sensing signal is checked through the exhaust gas in the test equipment.

Heat the product first, and record the time when the voltage value reaches 900mV under the same conditions. Please refer to the following table data and the voltage rise graph in Figure 5.

Amount of platinum (g) Time to reach 900mV(s) Comparative ratio 0.006 32.2 Sample 1 0.001 24.8 Sample 2 0.0013 22.4 Sample 3 0.001 20.3

Table 1

It can be seen from the above Table 1 and Figure 5 that, compared with the co-fired electrode, the sensing element made of the novel ceramic catalytic electrode of the first embodiment of the present invention can greatly reduce the amount of precious metal. A faster voltage rise rate is achieved, that is, a better low-temperature catalytic performance is exhibited.

A novel tubular sensing element and its preparation method, and an oxygen sensor with the sensing element

In a third embodiment, the present invention discloses a novel tubular sensing element, a method for preparing the same, and an oxygen sensor having the sensing element. The overall structure of the new tubular sensing element is the same as the structure of the tubular sensing element in the prior art, please refer to FIG. 1, including a tubular ceramic substrate 1 with solid electrolyte properties, an outer electrode 2 and an inner electrode 3, The ceramic substrate 1 has an inner cavity extending inward from the bottom surface; the outer electrode 2 is arranged on the outer surface of the ceramic substrate 1, including an outer catalytic electrode part 21 arranged around the end of the outer surface of the ceramic substrate, and The outer lead electrode part 22 is arranged on the outer side of the ceramic base, extends to the bottom surface of the ceramic body, and is electrically connected to the outer catalytic electrode part; the inner electrode 3 is arranged on the wall of the inner cavity , including an inner catalytic electrode portion 31 arranged around the end of the wall portion of the inner cavity, and an inner catalytic electrode portion 31 disposed on the wall portion of the inner cavity, extending to the bottom surface of the ceramic body, and the inner catalytic electrode The inner lead electrode portion 32 that is electrically connected.

The difference between the novel tubular sensing element provided in this embodiment and the tubular sensing element in the prior art lies in the structure, material and preparation method of the external catalytic electrode portion. The external catalytic electrode portion of the tubular sensing element in the prior art generally uses a co-fired electrode, while the external catalytic electrode portion of the novel tubular sensing element provided in this embodiment is a novel ceramic provided by the first embodiment of the present invention. The catalytic electrode has the characteristics of less amount of noble metal but excellent catalytic performance and high bonding fastness between the electrode and the substrate.

Since the specific structure and preparation method of the novel ceramic catalytic electrode have been described in detail above, they will not be repeated here, and please refer to the relevant description in the first embodiment.

It should be noted that the outer lead electrode portion and the inner electrode of the outer electrode of the novel tubular sensor element provided in this embodiment may be composed of co-fired electrodes, or may be composed of the novel ceramic catalytic electrode provided in the first embodiment.

Further, in order to prevent the outer electrode of the sensing element of the oxygen sensor (that is, the electrode on the side in contact with the exhaust gas) from being corroded by the exhaust gas discharged from the engine, thereby reducing the catalytic performance of the precious metal (usually metal platinum), the new tubular type The sensing element further includes a protective layer covering the surface of the external electrode. The material of the protective layer is well known to those skilled in the art, and is composed of ceramics with solid electrolyte properties, specifically, alumina, magnesia-aluminum spinel, or zirconia-alumina composite materials. The protective layer can be prepared by ion spraying or secondary sintering.

On the basis of the preparation method of the sensing element provided by the second embodiment of the present invention, this embodiment provides a preparation method of the novel tubular sensing element, and the specific steps are as follows:

(1) providing a tubular solid electrolyte substrate green body, the solid electrolyte substrate green body having an inner cavity extending inward from the bottom surface; providing a slurry for forming a catalytic electrode ceramic matrix; providing a co-fired electrode slurry.

(2) Coating the slurry for forming the catalytic electrode ceramic matrix to the outer surface of the solid electrolyte substrate green body where the outer catalytic electrode portion needs to be prepared, and applying the co-firing slurry to the outer surface of the solid electrolyte substrate green body. The area where the lead electrode part needs to be prepared and the area on the wall of the inner cavity where the inner electrode needs to be prepared, and then co-sintered to obtain a solid electrolyte ceramic substrate, a catalytic electrode ceramic substrate disposed on the outer surface of the fixed electrolyte ceramic substrate, and an external lead The electrode part, and the inner electrode on the wall of the inner cavity of the ceramic substrate, wherein the catalytic electrode ceramic substrate is a porous ceramic with electrolyte properties and with tiny three-dimensional pores inside and on the surface.

(3) Loading the precious metal salt solution into the catalytic electrode ceramic substrate, and then performing drying treatment to obtain a semi-finished product of the sensing element.

(4) The semi-finished product of the sensing element is subjected to high-temperature baking and aging treatment at 600-1000° C. to obtain the sensing element provided in this embodiment.

This embodiment also provides an oxygen sensor obtained by encapsulating the sensing element provided in this embodiment. The inventor of the present invention compares the oxygen sensor fabricated from co-fired electrodes with the oxygen sensor provided in this embodiment in terms of the amount of platinum metal, the stability of the oxygen sensor, and the voltage jump frequency of the oxygen sensor through a large number of experiments. The advantages of the oxygen sensor provided by this embodiment are further demonstrated.

Test 1: Test of the amount of platinum metal and the stability of the oxygen sensor.

Comparative ratio:

The inner and outer electrodes of the sensing element are prepared according to the traditional co-fired electrode process, and the same packaging technology is used to make oxygen sensor samples 1 to 6. The internal and external catalytic electrodes of these six samples of oxygen sensors all use co-fired electrodes, and the internal and external catalytic electrodes are used. The amount of metal platinum used in the electrode portion was all 0.01 g. At around 350 degrees, test these 6 sample oxygen sensors. The test method is as follows:

The lambda value of the simulated exhaust was switched between 0.97 and 1.03. The sensor output at lambda=0.97 is called high voltage, and the sensor output at lambda=1.03 is called low voltage. The time when the voltage value jumps from 600mV to 300mV is called T2, and the time when the voltage value jumps from 300mV to 600mV is called T4. The test data of 6 products are shown in the following table:

Comparative ratio High voltage (mV) Low voltage (mV) T2(mS) T4(mS) Sample 1 867.4 52.87 259.2 126.9 Sample 2 837.64 61.65 352.2 84.2 Sample 3 853.36 60.73 246.5 97.3 Sample 4 875.11 52.34 160.7 128.1 Sample 5 857.26 66.53 268.4 89.1 Sample 6 844.44 52.49 355.5 102.1 average value 855.9 57.8 273.8 104.6 maximum value 875.1 66.5 355.5 128.1 minimum 837.6 52.3 160.7 84.2

Table 2

It can be seen from the above table that the dispersion difference between high voltage and T2 is relatively large. The high voltage dispersion is large, that is, the signal characteristic of the product has a large dispersion, which is likely to cause deviations in emission control. T2 dispersion is large, that is, the sensitivity of the product is unstable, which will also cause deviations in emission control.

Example:

The inner electrode of the sensing element is still prepared by the co-fired electrode process, and the outer electrode is prepared by the preparation method of the novel ceramic catalytic electrode provided in the first embodiment. Samples 1 to 6 are obtained according to the same packaging method as the comparative example. The amount of metallic platinum in the inner catalytic electrode part of the six oxygen sensors was all 0.01 g, the loading amount of metallic platinum in the outer catalytic electrode part was 0.002 g, and the thickness of the outer catalytic electrode part was 0.3 mm and the length was 5 mm.

According to the same test conditions and test methods as the comparative example, the following data are obtained:

Example High voltage (mV) Low voltage (mV) T2(mS) T4(mS) Sample 1 873.72 42.27 249.1 116.2 Sample 2 866.32 51.61 258.2 108.1 Sample 3 861.23 52.13 286.1 137.2 Sample 4 875.76 52.32 202.6 111.3 Sample 5 867.85 46.83 198.3 99.3 Sample 6 864.31 52.42 225.2 105.6 average value 868.2 49.6 236.6 113.0 maximum value 875.8 52.4 286.1 137.2 minimum 861.2 42.3 198.3 99.3

table 3

Comparing Table 2 and Table 3, it can be seen that the high voltage in Table 3 is a little higher on the whole, and the low voltage is a little lower on the whole, the consistency of T2 is good, and the value of T4 is slightly larger. In general, compared with the oxygen sensor made of co-fired electrodes, the amount of platinum metal in the external catalytic electrode part of the oxygen sensor provided in this embodiment is only 1/5 of the amount of metal platinum when the co-fired electrode is used as the external catalytic electrode part. However, the consistency of product performance is better, that is, the stability is better.

Test 2: Test of the amount of platinum metal and the voltage jump frequency of the oxygen sensor.

Comparative ratio:

According to the design scheme of using the same amount of metal platinum in the inner catalytic electrode part, and changing the amount of metal platinum in the outer catalytic electrode part (co-fired electrode), the sensing element was fabricated, and the oxygen sensor was packaged to make 9 samples, and the voltage was tested. Hopping frequency, the test method is as follows:

When the oxygen sensor outputs high voltage, at this time lambda=0.97, a signal to open the additional air valve is output, and the additional air valve on the device starts to open, at this time, the lambda value will switch from 0.97 to 1.03, and the output voltage of the oxygen sensor begins to drop. . When the output voltage of the oxygen sensor reaches 450mV, it will immediately give a signal to close the additional air valve. At this time, due to the hysteresis of the control, the voltage value will continue to drop for a period of time before it starts to rise. When the voltage rises to 450mV, it will start to rise again. Given the signal to open the extra air valve, due to the hysteresis of the control, the voltage value will continue to rise for a period of time before it starts to fall, so the voltage continues to oscillate around 450mV. The number of times the sensor jumps in a specified time is the value of N (for a clearer explanation of the voltage jump process, please refer to FIG. 6 , which is a voltage jump curve diagram when N=21). The test data of 9 samples are shown in the following table:

Comparative ratio Internal catalytic electrode dosage (g) Amount of external catalytic electrode (g) N value Sample 1 0.01 0.006 28 Sample 2 0.01 0.008 26 Sample 3 0.01 0.01 25 Sample 4 0.01 0.012 twenty three Sample 5 0.01 0.014 twenty one Sample 6 0.01 0.016 20 Sample 7 0.01 0.018 19 Sample 8 0.01 0.02 16 Sample 9 0.01 0.022 15

Table 4

Example:

The same design scheme as in the comparative example is adopted, that is, the same amount of platinum metal is used in the inner catalytic electrode part, and the amount of metal platinum in the outer catalytic electrode part (the new ceramic catalytic electrode provided in the first embodiment) is changed to make a sensing element. , and packaged into an oxygen sensor to make 9 samples. The thickness of the catalytic electrode ceramic substrate of the new ceramic catalytic electrode of the sample here is 0.3 mm, and the length is 5 mm or 10 mm. By weighing the amount of saturated chloroplatinic acid loaded, the amount of precious metal platinum is calculated for each sample.

Using the same test method as the comparative example, the test data of 9 samples are shown in the following table:

table 5

It can be seen from Table 4 and Table 5 that the smaller the N value, the more platinum metal is used. Comparing Table 4 and Table 5, it can be seen that the amount of platinum metal in the external catalytic electrode part of the embodiment is only one-tenth of the amount of the external catalytic electrode part of the comparative example, and the same or even lower voltage jump frequency can be achieved, that is, To achieve the same product performance, the amount of platinum metal in the novel ceramic catalytic electrode provided by the first embodiment of the present invention only needs to be one tenth of that of the co-fired electrode.

A tubular sensing element with excellent performance, a preparation method of the sensing element, and an oxygen sensor with the sensing element

In the fourth embodiment, the present invention discloses a tubular sensing element with excellent performance, a method for preparing the sensing element, and an oxygen sensor having the sensing element.

In the novel tubular sensing element disclosed in the third embodiment, since the outer catalytic electrode part adopts the novel ceramic catalytic electrode provided by the present invention, the protective layer of the sensing element cannot be co-fired with other parts of the sensing element. Process preparation can only be prepared by plasma spraying or secondary sintering. However, the production efficiency of plasma spraying is relatively low, the spraying equipment is relatively expensive and energy-intensive, and the production cost of a single product is relatively high. The preparation of the protective layer by the secondary sintering method, on the one hand, increases the complexity of the preparation process, and on the other hand, the binding force between the protective layer and the substrate is not as high as that of the existing products, and the protective layer is prone to fall off, resulting in the outer electrode being destroyed by exhaust gas. pollution problem.

Therefore, in the fourth embodiment, the tubular sensing element with excellent performance disclosed by the present invention adopts the novel ceramic catalytic electrode provided by the present invention for its inner catalytic electrode, and uses a co-fired electrode for its outer electrode. When the protective layer is added, the protective layer can be prepared by a co-firing process with other components of the sensing element, which simplifies the product process and increases the bonding fastness of the protective layer and the solid electrolyte ceramic substrate. Please refer to FIG. 1 for the overall structure of the tubular sensing element with excellent performance, including a tubular ceramic substrate 1 with solid electrolyte properties, an outer electrode 2 and an inner electrode 3, the ceramic substrate 1 has a bottom surface facing inward. The inner cavity formed by extension; the outer electrode 2 is arranged on the outer surface of the ceramic substrate 1, which includes an outer catalytic electrode portion 21 arranged around the end of the outer surface of the ceramic substrate, and an outer catalytic electrode portion 21 arranged on the outer side of the ceramic substrate. , an outer lead electrode portion 22 extending to the bottom surface of the ceramic body and electrically connected to the outer catalytic electrode portion; the inner electrode 3 is arranged on the wall of the inner cavity, The inner catalytic electrode portion 31 at the end of the wall portion of the cavity, and the inner lead electrode disposed on the wall portion of the inner cavity, extending to the bottom surface of the ceramic body, and electrically connected to the inner catalytic electrode portion Section 32. Wherein, the inner catalytic electrode part adopts the novel ceramic catalytic electrode provided by the present invention, and the outer electrode adopts a co-fired electrode.

Since the internal catalytic electrode part of the sensing element provided in this embodiment uses the novel ceramic catalytic electrode provided by the present invention, it has the characteristics of less noble metal consumption but excellent catalytic performance and high bonding fastness between the electrode and the substrate. Since the specific structure and preparation method of the novel ceramic catalytic electrode have been described in detail above, they will not be repeated here, and please refer to the relevant description in the first embodiment.

It should be noted that the inner lead electrode portion of the inner electrode of the tubular sensor element with excellent performance provided in this embodiment may be composed of a co-fired electrode or a novel ceramic catalytic electrode provided by the present invention.

Similarly, in order to prevent the outer electrode of the sensing element of the oxygen sensor (that is, the electrode on the side in contact with the exhaust gas) from being corroded by the exhaust gas discharged from the engine, thereby reducing the catalytic performance of precious metals (usually metal platinum), the new tubular type The sensing element further includes a protective layer covering the surface of the external electrode. The material of the protective layer is well known to those skilled in the art, and specifically may be alumina, magnesia-alumina spinel, or zirconia-alumina composite materials. The protective layer may be prepared by co-firing with other components of the sensing element.

On the basis of the preparation method of the sensing element provided by the second embodiment of the present invention, this embodiment also discloses a preparation method of the tubular sensing element with excellent performance, which includes:

providing a tubular solid electrolyte substrate green body, the solid electrolyte substrate green body having an inner cavity extending inward from the bottom surface; providing a co-fired electrode slurry; providing a slurry for forming a catalytic electrode ceramic matrix;

The co-fired electrode slurry is applied to the outer electrode region on the outer surface of the solid electrolyte substrate green body and the inner lead electrode portion region on the wall of the inner cavity, and the slurry for forming the catalytic electrode ceramic matrix is applied to the bottom of the inner cavity of the solid electrolyte substrate green body, and then drying;

preparing a protective layer on the surface of the co-fired electrode slurry coated on the outer surface of the green substrate, followed by drying;

The solid electrolyte substrate green body, the co-fired electrode slurry coated on the outer surface of the solid electrolyte substrate green body, the co-fired electrode slurry on the wall of the inner cavity of the solid electrolyte substrate green body and the dried The slurries for forming the catalytic electrode ceramic substrate at the bottom of the inner cavity of the solid electrolyte substrate green body are co-sintered to obtain a solid electrolyte ceramic substrate, an outer electrode disposed on the outer surface of the fixed electrolyte ceramic substrate, and an inner cavity of the ceramic substrate The inner lead electrode part on the wall and the catalytic electrode ceramic substrate at the bottom of the inner cavity, wherein the catalytic electrode ceramic substrate is a porous ceramic with electrolyte properties and tiny three-dimensional pores inside and on the surface;

The precious metal salt solution is loaded into the catalytic electrode ceramic substrate, and then dried to obtain the semi-finished product of the sensing element;

The semi-finished product of the sensing element is subjected to high temperature baking and aging treatment at 600-1000°C.

This embodiment also provides an oxygen sensor obtained by encapsulating the tubular sensing element with excellent performance provided by this embodiment. The oxygen sensor has the same amount of platinum metal and catalytic performance as the oxygen sensor provided in the third embodiment, while the preparation process is simpler and the preparation cost is lower.

The above are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the description and drawings of the present invention, or directly or indirectly applied in other related technical fields , are similarly included in the scope of patent protection of the present invention.

Claims (12)

1. A tubular sensing element having superior performance, comprising:

a tubular ceramic substrate having an inner cavity extending inwardly from a bottom surface;

the outer electrode is arranged on the outer surface of the ceramic substrate and comprises an outer catalytic electrode part which is arranged at the tail end of the outer surface of the ceramic substrate in a surrounding way, and an outer lead electrode part which is arranged on the outer side of the ceramic substrate, extends to the bottom surface of the ceramic body and is electrically connected with the outer catalytic electrode part;

the inner electrode is arranged on the wall of the inner cavity and comprises an inner catalytic electrode part which is arranged at the tail end of the wall of the inner cavity in a surrounding way, and an inner lead electrode part which is arranged on the wall of the inner cavity, extends to the bottom surface of the ceramic body and is electrically connected with the inner catalytic electrode part;

the internal catalytic electrode comprises a catalytic electrode ceramic matrix formed on the inner cavity wall of the ceramic substrate and precious metals arranged inside and on the surface of the catalytic electrode ceramic matrix, the catalytic electrode ceramic matrix is porous ceramic with micro three-dimensional pore channels inside and on the surface, and the precious metals are distributed in a three-dimensional net shape inside and on the surface of the porous ceramic; the outer electrode is composed of a co-fired electrode.

2. A tubular sensor element of superior performance according to claim 1, wherein: the noble metal is distributed on the surface of the micro three-dimensional pore channel of the catalytic electrode ceramic matrix in a crystal grain form, so that the noble metal forms a three-dimensional net structure in and on the surface of the catalytic electrode ceramic matrix, and the transmission of electric signals is facilitated.

3. A tubular sensor element of superior performance according to claim 1, wherein: the sensing element also comprises a protective layer, the protective layer covers the surface of the outer electrode, and the protective layer, the ceramic substrate and the outer electrode are sintered and molded together.

4. A tubular sensor element of superior performance according to claim 1, wherein: the internal lead electrode part of the internal electrode comprises a catalytic electrode ceramic matrix formed on the inner cavity wall of the ceramic substrate and precious metals arranged inside and on the surface of the catalytic electrode ceramic matrix, the catalytic electrode ceramic matrix is porous ceramic with micro three-dimensional pore channels inside and on the surface, and the precious metals are distributed in the porous ceramic in a three-dimensional net shape; or the inner lead electrode portion of the inner electrode is constituted by a co-fired electrode.

5. A tubular sensor element of superior performance according to claim 1, wherein: the porosity of the catalytic electrode ceramic matrix is 20-80%, and the thickness of the catalytic electrode ceramic matrix is 10-1000 microns.

6. A tubular oxygen sensor, characterized by: comprising a tube-type sensor element having excellent properties as set forth in any one of claims 1 to 5.

7. A method for preparing a tubular sensor element having excellent properties as defined in claim 3, comprising the steps of:

providing a tubular green solid electrolyte substrate having an inner cavity extending inwardly from a bottom surface; providing co-fired electrode slurry; providing a slurry forming a ceramic matrix of a catalytic electrode;

coating the co-fired electrode slurry on an outer electrode area of the outer surface of the solid electrolyte substrate green compact and an inner lead electrode area on the wall of the inner cavity, injecting the slurry for forming the catalytic electrode ceramic matrix to the bottom of the inner cavity of the solid electrolyte substrate green compact, and then carrying out drying treatment;

preparing a protective layer on the surface of the co-fired electrode slurry coated on the outer surface of the substrate green body, and then drying;

co-sintering the solid electrolyte substrate green compact, the co-fired electrode slurry coated on the outer surface of the solid electrolyte substrate green compact, the co-fired electrode slurry on the wall of the inner cavity of the solid electrolyte substrate green compact and the slurry forming the catalytic electrode ceramic matrix at the bottom of the inner cavity of the dried solid electrolyte substrate green compact to obtain a solid electrolyte ceramic substrate, an outer electrode arranged on the outer surface of the fixed electrolyte ceramic substrate, and an inner lead electrode part on the wall of the inner cavity of the ceramic substrate and the catalytic electrode ceramic matrix at the bottom of the inner cavity, wherein the catalytic electrode ceramic matrix is porous ceramic with electrolyte characteristics and micro three-dimensional pore passages in the inner part and the surface;

loading the noble metal salt solution into a catalytic electrode ceramic substrate, and then baking and decomposing to obtain a semi-finished sensing element;

and carrying out high-temperature baking and aging treatment on the semi-finished product of the sensing element at 800-1300 ℃.

8. The method for preparing a tubular sensor element having excellent properties as set forth in claim 7, wherein: the noble metal salt solution is one or a non-reaction mixture of more of chloroplatinic acid, platinum nitrate, platinum sulfite, rhodium chloride, ammonium chlororhodate, sodium hexachlororhodate, rhodium nitrate, palladium chloride, palladium nitrate and palladium sulfate solution.

9. The method for preparing a tubular sensor element having excellent properties as set forth in claim 7, wherein: the slurry for forming the ceramic matrix of the catalytic electrode is prepared by the following method:

ball-milling the powder of the solid oxide ceramic and an alcohol solution to prepare slurry, then adding a pore-forming agent, a binder and a plasticizer into the slurry, and continuing ball-milling to finally obtain the slurry for forming the ceramic matrix of the catalytic electrode.

10. The method for preparing a tubular sensor element having excellent properties as set forth in claim 7, wherein:

loading a noble metal salt solution into the catalytic electrode ceramic matrix, and then decomposing the noble metal salt in the noble metal salt solution into noble metal decomposers when baking and decomposing the noble metal salt solution, and depositing the noble metal decomposers in the micro three-dimensional pore channels of the catalytic electrode ceramic matrix to obtain a semi-finished product of the sensing element;

after the semi-finished sensing element is subjected to high-temperature baking and aging treatment at the temperature of 800-1300 ℃, the noble metal salt in the noble metal salt solution is decomposed at high temperature to form noble metal crystal grains, and the noble metal crystal grains are distributed on the surface of the micro three-dimensional pore channel of the catalytic electrode ceramic matrix, so that the noble metal forms a three-dimensional network structure in and on the surface of the catalytic electrode ceramic matrix, and the electrical signal is conveniently transmitted.

11. The method for preparing a tubular sensor element having excellent properties as set forth in claim 7, wherein:

the provided tubular solid electrolyte substrate green compact is an unsintered solid electrolyte substrate green compact,

simultaneously sintering the solid electrolyte substrate green compact and the catalytic electrode ceramic matrix-forming slurry applied to the surface of the solid electrolyte substrate green compact at the time of sintering,

the sintering is carried out at a temperature of 1400 ℃ to 1550 ℃.

12. The method for preparing a tubular sensor element having excellent properties as set forth in claim 7, wherein:

the solid electrolyte substrate green body is obtained by the following method:

preparing a solid electrolyte substrate green compact;

and (3) baking and curing the prepared solid electrolyte substrate green blank at the high temperature of 800-1300 ℃.

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