CN111505082A

CN111505082A - Novel tubular sensing element and preparation method thereof

Info

Publication number: CN111505082A
Application number: CN201910098212.0A
Authority: CN
Inventors: 杨玉海; 郭杰烽; 陈珍强
Original assignee: Suzhou Industrial Park Trans Automobile Electronics Co ltd
Current assignee: Suzhou Industrial Park Trans Automobile Electronics Co ltd
Priority date: 2019-01-31
Filing date: 2019-01-31
Publication date: 2020-08-07

Abstract

The invention discloses a novel tubular sensing element and a preparation method thereof. One of the objectives of the present invention is to provide a novel tubular sensor element with low cost and high performance, wherein the external catalytic electrode part of the sensor element is composed of a novel ceramic catalytic electrode, and therefore, 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 novel tubular sensing element, and the sensing element prepared by the method has the advantages of simple process operation, good binding property of an electrode material and a ceramic matrix, low consumption of noble metal and good catalytic activity. Is particularly suitable for the technical field of oxygen sensors.

Description

Novel tubular sensing element and preparation method thereof

Technical Field

The invention relates to the field of oxygen sensors, in particular to a novel tubular sensing element and a preparation method thereof.

Background

In a control system of a vehicle engine, ensuring that the engine works with a mixture with an optimal air-fuel ratio is a key technology of emission control, a vehicle oxygen sensor is a key component for controlling the air-fuel ratio of the mixture of the engine, the oxygen sensor is a key element for feeding back the gas condition after oil-gas mixture combustion to an Engine Control Unit (ECU) in real time, and an engine electronic control injection system accurately controls the air-fuel ratio (A/F, mass ratio of air to gasoline) according to signals provided by the oxygen sensor.

The three-way catalyst is the most important external purifying device installed in the automobile exhaust system, and can convert harmful gases such as CO, HC and NOx discharged by automobile exhaust into harmless carbon dioxide, water and nitrogen through oxidation and reduction. However, in order to effectively use the three-way catalyst, it is necessary to accurately control the air-fuel ratio so that it is always close to the stoichiometric air-fuel ratio. Therefore, the oxygen sensor is an indispensable element in using a three-way catalytic conversion engine. When the air-fuel ratio of the mixture deviates from the theoretical air-fuel ratio, the purification capacity of the three-way catalyst for CO, HC and NOx is rapidly reduced, an oxygen sensor arranged in an exhaust pipe can detect the concentration of oxygen in the exhaust gas, a feedback signal is sent to an ECU, and the ECU controls the increase and decrease of the fuel injection quantity of an oil injector, so that the air-fuel ratio of the mixture can be controlled to be close to the theoretical value, the engine can work in the state of the optimal air-fuel mixture ratio, namely the optimal air-fuel ratio, and conditions are created for the exhaust gas purification of the three-way catalyst of the engine.

The oxygen sensor is a measuring element which utilizes a ceramic sensitive element to measure the oxygen potential in an automobile exhaust pipeline, calculates the corresponding oxygen concentration by a chemical equilibrium principle, and achieves the purposes of monitoring and controlling the combustion air-fuel ratio so as to ensure the product quality and the exhaust emission to reach the standard. The oxygen sensor is generally divided into a tubular oxygen sensor and a plate oxygen sensor, and the tubular zirconium dioxide oxygen sensor is taken as an example to explain the working principle:

the tubular zirconia oxygen sensor comprises a zirconia tube (zirconium tube for short), a platinum electrode, a protective sleeve and the like, wherein the zirconia tube and the platinum electrode form a sensing element (refer to fig. 1), the zirconia tube is a solid electrolyte element made of zirconia containing a small amount of yttrium, and a layer of platinum is coated on the inner side and the outer side of the zirconia tube to form an inner platinum electrode and an outer platinum electrode. The inner side of the zirconium tube is communicated with the atmosphere, and the outer side of the zirconium tube is contacted with the exhaust gas. At the use temperature, oxygen generates oxidation-reduction reaction of gain-loss electrons in a three-phase interface area formed by the oxygen, the platinum electrode and the zirconium oxide, the oxygen in the zirconium tube is changed into oxygen ions under the catalysis of the platinum electrode, the oxygen ions outside the zirconium tube are changed into oxygen molecules under the catalysis of the platinum electrode, and because the oxygen ion concentration on the inner side and the outer side of the zirconium tube is high and low (generally, the oxygen concentration in the atmosphere on the inner side is high, and the oxygen concentration in the waste gas on the outer side is low), a potential difference exists between the inner side electrode and the outer side electrode. The outer electrode is exposed in the exhaust gas, the oxygen ion concentration changes according to different actual working conditions, while the inner electrode is reference air, and the oxygen ion concentration is unchanged. When the air-fuel ratio of the engine is lean, the oxygen concentration in the exhaust gas is relatively high, the oxygen concentration difference between the inner electrode and the outer electrode is small, namely the potential difference is small, and the output voltage signal of the oxygen sensor is close to 0V. On the contrary, when the air-fuel ratio is rich, the oxygen concentration in the exhaust gas is relatively low, 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. An oxygen sensor typical response curve is shown in FIG. 2, where lambda is the air excess factor, i.e., the ratio of actual to theoretical air-fuel ratio, used as an index to determine the degree of leanness of the mixture.

With continued reference to fig. 1, the electrodes of the sensing element of the oxygen sensor include a catalytic electrode portion and a lead electrode portion, as viewed during use. The catalytic electrode part is mainly used for catalyzing oxidation-reduction reaction and generating an electric signal, and the lead electrode part is mainly used for leading out the generated electric signal. The key point of the technology in the preparation of electrodes for sensing elements of oxygen sensors is how to arrange electrodes with a certain thickness on a ceramic substrate (such as the platinum electrodes mentioned above), and there have been early methods of coating an electrode layer directly on a ceramic substrate (the ceramic may be the zirconia mentioned above), but the electrode layer is not adopted because of its high peeling tendency. The commonly adopted technical scheme at present is a co-firing technology of an electrode and solid electrolyte ceramic and an electrode electroplating technology. The electroplating electrode technology refers to patent application publication specifications CN200310114168.7 and the like, and the electroplating electrode has the advantages that the prepared electrode layer is very thin, the using amount is small, more three-phase interfaces and good activity are provided, the problem of large using amount of the co-fired electrode noble metal is effectively solved, but the bonding reliability between the electrode material and the substrate is poor, and the electrode material is easy to peel off; and the electroplating process is relatively complex and is easy to pollute the environment.

The co-firing technology of the electrode and the solid electrolyte ceramic refers to application No. 200410064804.4, etc., the co-firing electrode has the advantages of good bonding reliability between the electrode layer and the substrate, and improved peeling problem of the directly coated electrode layer, and has the disadvantages that the electrode adopts a thick film with the thickness of 6-10 microns, wherein the platinum particles are micron-sized or sub-nanometer-sized noble metal particles, and the electrode material is co-fired at 1550 ℃ through high temperature of 1400 ℃ plus materials, the low-temperature catalytic activity of the electrode is poor, and meanwhile, a three-phase interface has certain loss, so under the condition of obtaining the same catalytic activity, more noble metal is needed, and the cost is high.

Disclosure of Invention

One of the objectives of the present invention is to provide a novel tubular sensor element with low cost and high performance, wherein the external catalytic electrode part of the sensor element is composed of a novel ceramic catalytic electrode, and therefore, 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 novel tubular sensing element, and the sensing element prepared by the method has the advantages of simple process operation, good binding property of an electrode material and a ceramic matrix, low consumption of noble metal and good catalytic activity. Is particularly suitable for the technical field of oxygen sensors.

The technical scheme of the invention is as follows: a novel tubular sensing element comprises a tubular ceramic substrate with an inner cavity extending inwards from the 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 external catalytic electrode comprises a catalytic electrode ceramic matrix formed on the surface of the ceramic matrix and precious metals arranged inside and on the surface of the catalytic electrode ceramic matrix, the catalytic electrode ceramic matrix is porous ceramic with small 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.

Preferably, 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 network structure inside and on the surface of the catalytic electrode ceramic matrix, and is convenient for transmitting an electrical signal.

Preferably, the external lead electrode part of the external electrode comprises a catalytic electrode ceramic base body formed on the surface of the ceramic base and noble metals arranged inside and on the surface of the catalytic electrode ceramic base body, and/or the internal electrode comprises a catalytic electrode ceramic base body formed on the inner cavity wall of the ceramic base and noble metals arranged inside and on the surface of the catalytic electrode ceramic base body; or the external lead electrode part and the internal electrode of the external electrode are formed by co-fired electrodes;

the catalytic electrode ceramic matrix is porous ceramic with micro three-dimensional pore channels inside and on the surface, and the noble metal is distributed in a three-dimensional net shape inside and on the surface of the porous ceramic.

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

Preferably, the sensing element further comprises a protective layer, and the protective layer covers the surface of the external electrode.

The technical scheme of the invention also comprises a tubular oxygen sensor which comprises the novel tubular sensing element.

The technical scheme of the invention also comprises a preparation method of the novel tubular sensing element, which comprises the following steps: providing a tubular solid electrolyte substrate green body having an inner cavity formed extending inwardly from a bottom surface; providing a slurry forming a ceramic matrix of a catalytic electrode; providing co-fired electrode slurry;

coating slurry for forming a catalytic electrode ceramic matrix on an area, needing an external catalytic electrode part, of the outer surface of a solid electrolyte substrate green body, coating co-fired slurry on the area, needing a lead electrode part, of the outer surface of the solid electrolyte substrate green body and an area, needing an internal electrode, of the wall of an inner cavity, and then sintering together to obtain a solid electrolyte ceramic substrate, a catalytic electrode ceramic matrix and an external lead electrode part which are arranged on the outer surface of the fixed electrolyte ceramic substrate, and an internal electrode on the wall of the inner cavity of the ceramic substrate, wherein the catalytic electrode ceramic matrix is porous ceramic with electrolyte characteristics and micro three-dimensional pore channels inside and on 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 the temperature of 600-1000 ℃.

Preferably, 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 solutions.

Preferably, 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.

Preferably, when the noble metal salt solution is loaded into the catalytic electrode ceramic matrix and then baked and decomposed, the noble metal salt in the noble metal salt solution is decomposed into noble metal decomposers which are deposited 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 600-.

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

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 ℃.

Preferably, the green solid electrolyte substrate 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 ℃.

THE ADVANTAGES OF THE PRESENT INVENTION

1. According to the novel tubular sensing element provided by the invention, the external catalytic electrode part is a novel ceramic catalytic electrode, the structure of the novel ceramic catalytic electrode is that precious metals form communicated three-dimensional net distribution in the porous solid electrolyte ceramic matrix, and the structure greatly increases the number of three-phase interfaces among the precious metals, the porous solid electrolyte ceramic and oxygen, so that the novel ceramic catalytic electrode also has excellent catalytic capability under the condition that a small amount of precious metals can be used, and the production cost is greatly reduced, therefore, the novel tubular sensing element provided by the invention also has the characteristics of low cost and excellent catalytic performance.

2. Compared with a co-fired electrode, the external catalytic electrode part of the novel tubular sensing element provided by the invention has better catalytic activity because noble metal is not sintered at high temperature, so that the novel tubular sensing element provided by the invention has better catalytic activity.

3. According to the preparation method of the novel tubular sensing element, the catalytic electrode ceramic substrate of the novel ceramic catalytic electrode is prepared on the solid electrolyte which is not sintered and then is sintered together, so that the combination height of the catalytic electrode ceramic substrate and the solid electrolyte substrate is high, and the novel tubular sensing element provided by the invention has no problem that the catalytic electrode layer falls off.

4. Compared with the experimental data of the sensing element manufactured by taking the co-fired electrode as the external catalytic electrode part, the metal platinum dosage of the external catalytic electrode of the novel tubular sensing element provided by the invention is only 1/5 of the metal platinum dosage when the co-fired electrode is taken as the external catalytic electrode part, but the consistency of the catalytic performance of the product is better, namely the stability of the catalytic performance is better.

5. Compared with the experimental data of the sensing element manufactured by taking the co-fired electrode as the external catalytic electrode part, the consumption of the external catalytic electrode metal platinum of the novel tubular sensing element provided by the invention is only 1/10 of the consumption of the metal platinum when the co-fired electrode is taken as the external catalytic electrode part, and the product can reach the same or even lower voltage jump frequency as a comparative product, namely the same or better product performance is achieved.

Drawings

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

FIG. 2 is a typical response curve for an oxygen sensor.

Fig. 3 is a schematic diagram of a process for forming a novel ceramic catalytic electrode according to a first embodiment of the present invention.

Fig. 4 is a view of a novel ceramic catalytic electrode according to a first embodiment of the present invention.

Fig. 5 is a graph of the voltage rise of a sample provided by the first embodiment of the present invention.

Fig. 6 is a reference diagram of a voltage transition curve when N is 21 according to a third embodiment of the present invention.

Fig. 7 is a diagram of a process for preparing a tubular sensor element having excellent performance according to a fourth embodiment of the present invention.

Detailed Description

The technical solution of the present invention is described in detail below with reference to the accompanying drawings 1 to 7 and embodiments, in which: 1. a ceramic substrate; 2. an outer electrode; 21. an outer catalytic electrode portion; 22. an external lead electrode portion; 3. an inner electrode; 31. an inner catalytic electrode section; 32. an inner lead electrode portion; 4. novel ceramic catalytic electrodes; 41. a catalytic electrode ceramic matrix; 42. a noble metal.

It should be noted that the term "sintering" as used throughout the present invention refers to the conversion of a powdery material into a dense body, which is a conventional process for making ceramics, with a sintering temperature of 1400 ℃ to 1550 ℃. Reference throughout this specification to "co-firing" is to co-sintering. The term "co-fired electrode" as used throughout the present invention refers to an electrode formed by co-firing an electrode and a solid electrolyte ceramic substrate in the prior art, and the specific manner of co-firing an electrode can refer to the application document with patent application number 200410064804.4.

Novel ceramic catalytic electrode and preparation method thereof

In a first embodiment, the present invention discloses a novel ceramic catalytic electrode 4 and a method for making the same, the novel ceramic catalytic electrode 4 being useful as an electrode for a sensing element of an oxygen sensor.

Referring to fig. 3 and 4, the novel ceramic catalytic electrode 4 includes a catalytic electrode ceramic base 41 and a noble metal 42 disposed inside and on a surface of the catalytic electrode ceramic base, the catalytic electrode ceramic base 41 is honeycomb-shaped, and is a porous ceramic having micro three-dimensional pore channels inside and on a surface thereof, and the catalytic electrode ceramic base has a solid electrolyte characteristic, that is, has oxygen ion conductivity. The noble metal is distributed in the porous ceramic in a three-dimensional net shape, specifically, the noble metal is distributed on the surface of a tiny three-dimensional pore channel of the porous solid electrolyte ceramic in a crystal grain shape, and adjacent crystal grains are fused and connected with each other in the heat treatment process of the noble metal crystal grains, so that the noble metal forms a three-dimensional net structure which is mutually communicated on the surface of the tiny three-dimensional pore channel of the porous ceramic, and the transmission of an electric signal is facilitated.

The structure of mutually communicated noble metals in three-dimensional net distribution is formed on the surface of the tiny three-dimensional pore channel of the porous ceramic with the solid electrolyte characteristic (the porous solid electrolyte ceramic is abbreviated as the porous solid electrolyte ceramic in the whole text), so that the number of three-phase interfaces among the noble metals, the porous solid electrolyte ceramic and oxygen is greatly increased, and the novel ceramic catalytic electrode also has excellent catalytic capability under the condition of using a small amount of noble metals, and the production cost is greatly reduced. Specific experimental data can be found below.

The noble metal is preferably a platinum group noble metal. Further, the noble metal may be one or more of platinum, palladium and rhodium.

According to the novel ceramic catalytic electrode, the ceramic matrix of the catalytic electrode is porous solid electrolyte ceramic, the porosity of the ceramic matrix is 20-80%, and due to the high porosity, precious metals are distributed on the surface of a tiny three-dimensional pore channel of the porous solid electrolyte ceramic in a crystal grain form to form a mutually communicated three-dimensional net structure, so that electric signals can be conveniently transmitted. Further, the porosity is preferably between 40% and 60%.

The catalytic electrode ceramic substrate of the novel ceramic catalytic electrode of the present invention is a solid oxide ceramic having a conductivity to oxygen ions in a certain temperature range (150 to 930 degrees). Preferably, the solid oxide ceramic is yttria-doped zirconia, calcia-doped zirconia or yttria-doped thoria. The thickness of the catalytic electrode ceramic matrix 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 a ceramic substrate 1 having solid electrolyte characteristics. The ceramic substrate 1 is an oxide solid electrolyte known to those skilled in the art, is a solid electrolyte part that can be used as an oxygen sensor, has conductivity to oxygen ions, and is specifically yttria-stabilized zirconia ceramic. The ceramic substrate 1 has a dense structure and cannot absorb liquid into the interior of the ceramic substrate.

Lead electrodes can be additionally arranged on the surface of the ceramic substrate 1, the novel ceramic catalytic electrode is mainly used for catalyzing oxidation-reduction reaction and generating electric signals, and the lead electrodes are mainly used for leading out the generated electric signals.

The novel ceramic catalytic electrode of the present invention may be used as the whole electrode of the sensor element of the oxygen sensor, or may be used as only a part of the electrode of the sensor element of the oxygen sensor, for example, the novel ceramic catalytic electrode is used only as the catalytic electrode portion of the electrode of the sensor element of the oxygen sensor, and the lead electrode portion of the electrode of the sensor element of the oxygen sensor is prepared using another material (for example, co-fired electrode).

As shown in fig. 2 and fig. 3, the first embodiment of the present invention further provides a method for preparing the above novel ceramic catalytic electrode, which comprises the following steps:

(1) providing a green solid electrolyte substrate; a slurry for forming a ceramic matrix for a catalytic electrode is provided.

a. The green solid electrolyte substrate and the preparation process thereof are the prior art, for example, the green solid electrolyte substrate may be an unsintered green zirconia solid electrolyte substrate, and the preparation process thereof may specifically refer to the following steps:

step 1: Y2O3 having a purity of 99.9% was mixed with ZrO2 having a purity of not less than 99%, wherein Y2O3 was contained in a proportion of 5 mol%. The mixture was thoroughly mixed and calcined at 1300 ℃ for 2 hours.

Step 2: the calcined mix was ball milled until D80 was less than 2.5 microns.

And step 3: by spray drying, spherical particles with an average particle size of 70 μm were obtained.

And 4, step 4: and (4) obtaining a U-shaped green body through dry bag type isostatic pressing, and grinding on an automatic flow grinder to obtain a final shape.

And 5: the prepared green body is baked and reinforced at the temperature of 1000-1200 ℃.

b. The slurry for forming the catalytic electrode ceramic matrix comprises powder of solid oxide ceramic (such as yttrium oxide doped zirconium oxide powder), alcohol solution, pore-forming agent (such as carbon powder), binder (such as polyvinyl butyral) and plasticizer (such as dibutyl phthalate). The porosity of the catalytic electrode ceramic matrix is affected by the proportion of the pore-forming agent, and generally, the proportion of the pore-forming agent is in direct proportion to the porosity of the catalytic electrode ceramic matrix, namely, the porosity is high when the proportion of the pore-forming agent is high, and the porosity is low when the proportion of the pore-forming agent is low. The preparation method of the slurry for forming the ceramic matrix of the catalytic electrode is a conventional technology for preparing porous ceramics, and the preparation method can be as follows:

ball-milling the powder of the solid oxide ceramic and an alcohol solution for 4 hours to prepare slurry, then continuously adding a pore-forming agent, a binder and a plasticizer into the slurry, and continuously ball-milling for 16 hours to obtain the slurry for forming the catalytic electrode ceramic matrix.

(2) The slurry forming the catalytic electrode ceramic matrix was applied to the surface of the solid electrolyte substrate green body, and then co-sintered to obtain a catalytic electrode ceramic matrix having a thickness of 10 to 1000 μm formed on the surfaces of the solid electrolyte ceramic substrate and the solid electrolyte ceramic substrate, as shown in fig. 3. The catalytic electrode ceramic matrix is porous ceramic with electrolyte characteristics and micro three-dimensional pore channels in the interior and on the surface.

The slurry for forming the catalytic electrode ceramic matrix is sintered together with the solid electrolyte substrate green body, so that the catalytic electrode ceramic matrix and the solid electrolyte ceramic substrate have good bonding property and high bonding fastness.

(3) And (3) loading the noble metal salt solution into the catalytic electrode ceramic substrate, and then carrying out baking decomposition treatment to obtain a catalytic electrode semi-finished product.

a. The noble metal salt solution is an aqueous solution of a compound composed of noble metal ions and acid radical ions, and can be a non-reaction mixture of one or more of chloroplatinic acid, platinum nitrate, platinum sulfite, rhodium chloride, ammonium chlororhodate, sodium hexachlororhodate, rhodium nitrate, palladium chloride, palladium nitrate and palladium sulfate solution, and preferably a saturated aqueous solution of chloroplatinic acid.

b. The loading of the noble metal salt solution into the catalytic electrode ceramic substrate means that the noble metal salt in the noble metal salt solution is absorbed into the catalytic electrode ceramic substrate through capillary action after the catalytic electrode ceramic substrate contacts the noble metal salt solution. Then the catalytic electrode ceramic matrix attached with the noble metal salt is baked and decomposed, so that the noble metal salt is decomposed into noble metal decomposers which are deposited in the tiny three-dimensional pore channels of the catalytic electrode ceramic matrix.

(4) The semi-finished product of the catalytic electrode is subjected to high-temperature baking and aging treatment at the temperature of 600-1000 ℃, and the ceramic catalytic electrode of the invention is obtained, as shown in figure 4.

When the high-temperature baking and aging treatment is carried out at the temperature of 600-.

Sensing element and preparation method thereof

In a second embodiment, the present invention discloses a sensing element capable of being used as a sensing element of an oxygen sensor, and a method for manufacturing the same.

The sensing element comprises a ceramic substrate 1 with solid electrolyte characteristics and one or more electrodes arranged on the surface of the ceramic substrate 1, wherein each electrode comprises a catalytic electrode part and a lead electrode part, and the catalytic electrode part of each electrode is connected with the lead electrode part. The catalytic electrode portion of some or all of the electrodes is comprised of the novel ceramic catalytic electrode provided in the first embodiment of the present invention. Since the specific structure and the preparation method of the novel ceramic catalytic electrode have been described in detail above, detailed descriptions thereof are omitted, and reference is made to the related description in the first embodiment.

It should be noted that the catalytic electrode portion of the single electrode may be composed entirely of the novel ceramic catalytic electrode, or a portion of the catalytic electrode portion of the single electrode may be composed of the novel ceramic catalytic electrode and another portion of the catalytic electrode portion may be composed of other electrodes (e.g., co-fired electrodes).

The electrodes (including catalytic electrode portion and lead electrode portion, catalytic electrode portion mainly used catalytic oxidation reduction reaction to produce the electric signal, the main effect of lead electrode portion is to derive the electric signal that produces) of the sensing element that this embodiment provided can all be by novel ceramic catalytic electrode composition, also can be by novel ceramic catalytic electrode and the electrode composition commonly used in the prior art, for example catalytic electrode portion comprises novel ceramic catalytic electrode composition, and lead electrode portion comprises co-firing electrode.

It should be noted that the sensing element provided in this embodiment may be used in various existing concentration type tubular oxygen sensors or sheet type oxygen sensors. The specific structure of the sensing element for the tubular oxygen sensor can refer to fig. 1, and comprises a ceramic substrate and inner and outer electrodes, wherein the ceramic substrate is tubular and is provided with an inner cavity extending inwards from the bottom surface, and the electrodes comprise the outer electrode arranged on the outer surface of the ceramic substrate and the inner electrode arranged on the wall of the inner cavity; the outer electrode comprises an outer catalytic electrode part arranged at the tail end of the outer surface of the ceramic substrate in a surrounding manner, and an outer lead electrode part which is arranged at 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 comprises an inner catalytic electrode part which is arranged at the tail end of the wall part of the inner cavity in a surrounding mode, and an inner lead electrode part which is arranged on the wall part of the inner cavity, extends to the bottom face of the ceramic body and is electrically connected with the inner catalytic electrode part.

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

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

In one embodiment of the sensing element for the chip type oxygen sensor, the ceramic substrate of the sensing element is in a chip shape, and the electrodes of the sensing element comprise outer electrodes arranged on the upper surface of the ceramic substrate and inner electrodes arranged on the lower surface of the ceramic substrate; the outer electrode comprises an outer catalytic electrode part and an outer lead electrode part electrically connected with the outer catalytic electrode; the internal electrode comprises an internal catalysis electrode part and an internal lead electrode part electrically connected with the internal catalysis electrode, and the internal catalysis electrode and the internal lead electrode are co-fired electrodes which are fired at a high temperature.

In a specific embodiment of the sensor element for a chip oxygen sensor, the external catalytic electrode portion is composed of the novel ceramic catalytic electrode, and the external lead electrode portion and the internal electrode of the external 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, the embodiment further provides a preparation method of the sensing element, which includes the following specific steps:

(1) providing a green solid electrolyte substrate; providing a slurry forming a ceramic matrix of a catalytic electrode; providing a paste for forming the co-fired electrode paste (referred to as the co-fired electrode paste in short in the whole text).

When the green solid electrolyte substrate is in a tubular shape, the method for producing the green solid electrolyte substrate may be referred to the method for producing the green solid electrolyte substrate provided in the first embodiment. When the solid electrolyte substrate green body is in a sheet shape, the solid electrolyte substrate green body can be prepared by a tape casting process, the tape casting process is a ceramic product forming method in the prior art, is a mature forming method capable of obtaining high-quality and ultra-thin ceramic chips at present, and is widely applied to the production of advanced ceramics such as monolithic capacitor ceramic chips, thick film circuit substrates and thin film circuit substrates.

The co-fired electrode slurry is the prior art, specifically can be a high-temperature co-fired platinum slurry, and the manufacturing method thereof can refer to the application document with the patent application number of 200410064804.4.

(2) The method comprises the steps of coating slurry for forming a catalytic electrode ceramic matrix on a region, needing a catalytic electrode part, on the surface of a solid electrolyte substrate green body, coating co-fired slurry on the region, needing a lead electrode part, on the surface of the solid electrolyte substrate green body, and then sintering the solid electrolyte substrate green body, the slurry for forming the catalytic electrode ceramic matrix on the surface of the green body and the co-fired slurry together to obtain the solid electrolyte ceramic substrate, the catalytic electrode ceramic matrix and the lead electrode part, wherein the catalytic electrode ceramic matrix is porous ceramic with electrolyte characteristics and micro three-dimensional pore channels in the interior and on the surface of the porous ceramic.

(3) And (3) loading the noble metal salt solution into the catalytic electrode ceramic substrate, and then carrying out drying decomposition treatment to obtain a semi-finished product of the sensing element.

(4) And (3) carrying out high-temperature baking aging treatment on the semi-finished product of the sensing element at the temperature of 600-1000 ℃ to obtain the sensing element provided by the embodiment.

Through a large number of experiments, the inventor of the invention finds that an oxygen sensor with a co-fired electrode as a catalytic electrode is a comparative example, and the oxygen sensor with the sensing element provided by the embodiment can have more excellent catalytic performance under the condition of using less noble metal.

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

(1) providing a green solid electrolyte substrate; a co-fired electrode paste is provided.

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

The specific parameters of the comparative examples are: baking and reinforcing the solid electrolyte substrate green compact at 1100 ℃, wherein the sintering temperature is 1450 ℃; the co-fired electrode was used as both a catalytic electrode portion and a lead electrode portion, and the amount of platinum converted to the catalytic electrode portion was 0.006 g in total.

The method for manufacturing the sensor element provided in this example was used to prepare a sensor element, and the sensor element was encapsulated, thereby obtaining three oxygen sensors, sample 1, sample 2, and sample 3. Wherein:

sample 1: baking and reinforcing the solid electrolyte substrate green blank at 800 ℃, wherein the sintering temperature is 1450 ℃; the powder for preparing the slurry for forming the ceramic matrix of the catalytic electrode is yttria-stabilized zirconia, the particle size distribution of which is D10-0.1 micrometer, D50-5 micrometer and D90-7 micrometer; the precious metal salt solution uses a saturated aqueous solution of chloroplatinic acid, and the loading amount of platinum of the novel ceramic catalytic electrode obtained by converting the chloroplatinic acid is 0.001 g; the catalytic electrode ceramic matrix deposited with the noble metal salt is subjected to high-temperature baking aging treatment at 9000 ℃.

Sample 2: baking and reinforcing the solid electrolyte substrate green body at 1200 ℃; the loading amount of platinum of the novel ceramic catalytic electrode obtained by converting chloroplatinic acid is 0.0013 g; other parameters and procedures were the same as in sample 1.

Sample 3: baking and reinforcing the solid electrolyte substrate green body at 1000 ℃; the powder of the slurry for forming the ceramic matrix of the catalytic electrode was still yttria-stabilized zirconia, with a particle size distribution of D10 ═ 0.34 micrometers, D50 ═ 0.53 micrometers, and D90 ═ 1.02 micrometers; the precious metal salt solution still uses a saturated aqueous solution of chloroplatinic acid, and the loading amount of platinum of the novel ceramic catalytic electrode obtained by converting the chloroplatinic acid is 0.001 g; other parameters and procedures were the same as in sample 1.

In order to compare the differences between the comparative examples and the samples, comparative tests were carried out by passing certain tests. The test conditions are as follows: and packaging the product in a test tool, and detecting the induction signal of the oxygen sensor through waste gas in the test equipment.

The product was heated and the time to reach 900mV was recorded under the same conditions, see the following table data and the voltage rise plot of fig. 5.

	Platinum dosage (g)	Time to 900 mV(s)
			Comparative example	0.006	32.2
Sample 1	0.001	24.8
			Sample 2	0.0013	22.4
Sample 3	0.001	20.3

TABLE 1

As can be seen from table 1 and fig. 5, compared with the co-fired electrode, the sensing element manufactured by using the novel ceramic catalytic electrode according to the first embodiment of the present invention achieves a faster voltage rising speed under the condition of greatly reducing the amount of noble metal, i.e., shows more excellent low-temperature catalytic performance.

Novel tubular sensing element, preparation method thereof and oxygen sensor with sensing element

In a third embodiment, the present invention discloses a novel tubular sensing element, a method of making the same, and an oxygen sensor having the sensing element. The overall structure of the novel tubular sensing element is the same as that of a tubular sensing element in the prior art, please refer to fig. 1, which comprises a tubular ceramic substrate 1 with solid electrolyte characteristics, an external electrode 2 and an internal electrode 3, wherein the ceramic substrate 1 is provided with an inner cavity formed by extending inwards from the bottom surface; the outer electrode 2 is arranged on the outer surface of the ceramic substrate 1 and comprises an outer catalytic electrode part 21 arranged at the tail end of the outer surface of the ceramic substrate in a surrounding mode and an outer lead electrode part 22 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 3 is arranged on the wall of the inner cavity, and comprises an inner catalytic electrode part 31 arranged around the tail end of the wall of the inner cavity, and an inner lead electrode part 32 arranged on the wall of the inner cavity, extending to the bottom surface of the ceramic body and electrically connected with the inner catalytic electrode part.

The novel tubular sensing element provided by the embodiment is different from the tubular sensing element in the prior art in the structure, material and preparation method of the external catalytic electrode part. The external catalytic electrode portion of the tubular sensing element in the prior art generally uses a co-fired electrode, and the external catalytic electrode portion of the novel tubular sensing element provided in this embodiment is the novel ceramic catalytic electrode provided in the first embodiment of the present invention, and has the characteristics of low precious metal consumption, excellent catalytic performance, and high electrode-substrate bonding fastness.

Since the specific structure and the preparation method of the novel ceramic catalytic electrode have been described in detail above, detailed descriptions thereof are omitted, and reference is made to the related description in the first embodiment.

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

Further, in order to prevent the outer electrode (i.e., the electrode on the side contacting with the exhaust gas) of the sensing element of the oxygen sensor from being corroded by the exhaust gas discharged from the engine, thereby degrading the catalytic performance of the noble metal (generally, platinum metal is used), the novel tubular sensing element further comprises a protective layer, and the protective layer covers the surface of the outer electrode. The material of the protective layer is well known to those skilled in the art and is composed of a ceramic having the characteristics of a solid electrolyte, and specifically may be alumina, magnesia-alumina spinel, zirconia-alumina composite, or the like. The protective layer can be prepared by means of 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, which includes the following specific steps:

(1) providing a tubular green solid electrolyte substrate having an inner cavity extending inwardly from a bottom surface; providing a slurry forming a ceramic matrix of a catalytic electrode; a co-fired electrode paste is provided.

(2) The method comprises the steps of coating slurry for forming a catalytic electrode ceramic matrix on an area, needing an external catalytic electrode part, of the outer surface of a solid electrolyte substrate green body, coating co-fired slurry on the area, needing a lead electrode part, of the outer surface of the solid electrolyte substrate green body and an area, needing an internal electrode, of the wall of an inner cavity, and then sintering together to obtain the solid electrolyte ceramic substrate, the catalytic electrode ceramic matrix and the external lead electrode part which are arranged on the outer surface of the fixed electrolyte ceramic substrate, and the internal electrode on the wall of the inner cavity of the ceramic substrate, wherein the catalytic electrode ceramic matrix is porous ceramic with electrolyte characteristics and micro three-dimensional pore channels inside and on the surface.

(3) And (3) loading the noble metal salt solution into the catalytic electrode ceramic substrate, and then carrying out drying treatment to obtain a semi-finished product of the sensing element.

The present embodiment also provides an oxygen sensor obtained by encapsulating the sensor element provided in the present embodiment. The inventor of the present invention compares the oxygen sensor manufactured by co-firing the electrodes with the oxygen sensor provided in this embodiment in terms of the amount of platinum used, the stability of the oxygen sensor, and the voltage jump frequency of the oxygen sensor through a large number of experiments, and further demonstrates the advantages of the oxygen sensor provided in this embodiment.

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

Comparative example:

the inner electrode and the outer electrode of the sensing element are prepared according to the traditional co-firing electrode process, oxygen sensor samples 1 to 6 are prepared by adopting the same packaging technology, the co-firing electrodes are used for the inner catalytic electrode part and the outer catalytic electrode part of the 6 sample oxygen sensors, and the consumption of the metal platinum of the inner catalytic electrode part and the outer catalytic electrode part is 0.01 g. The 6 sample oxygen sensors were tested at around 350 degrees by the following method:

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

comparative example	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 No. 4	875.11	52.34	160.7	128.1
					Sample No. 5	857.26	66.53	268.4	89.1
Sample No. 6	844.44	52.49	355.5	102.1
					Mean value of	855.9	57.8	273.8	104.6
Maximum value	875.1	66.5	355.5	128.1
					Minimum value	837.6	52.3	160.7	84.2

TABLE 2

It can be seen from the above table that the dispersion of the high voltage and T2 is relatively large. The high voltage dispersion is large, that is, the signal characteristic dispersion of the product is large, which easily causes the deviation of emission control. Large T2 variation, i.e., unstable product sensitivity, can also cause emissions control to drift.

Example (b):

the inner electrode of the sensing element is still prepared by adopting a co-firing electrode process, the outer electrode is prepared by adopting 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 mode with the comparative example, the dosage of the metal platinum of the inner catalytic electrode part of the 6 oxygen sensors is 0.01g, the loading amount of the metal platinum of the outer catalytic electrode part is 0.002g, the thickness of the outer catalytic electrode part is 0.3mm, and the length of the outer catalytic electrode part is 5 mm.

The test was carried out under the same test conditions and test methods as the comparative examples, and the following data were obtained:

examples	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 No. 4	875.76	52.32	202.6	111.3
					Sample No. 5	867.85	46.83	198.3	99.3
Sample No. 6	864.31	52.42	225.2	105.6
					Mean value of	868.2	49.6	236.6	113.0
Maximum value	875.8	52.4	286.1	137.2
					Minimum value	861.2	42.3	198.3	99.3

TABLE 3

Comparing table 2 and table 3, it can be seen that the high voltage of table 3 is higher overall, the low voltage is lower overall, the T2 consistency is better, and the T4 value is slightly larger. In summary, compared with the oxygen sensor manufactured by the co-fired electrode, the amount of the platinum metal used in the external catalytic electrode part of the oxygen sensor provided by this embodiment is only 1/5, which is the amount of the platinum metal used in the co-fired electrode as the external catalytic electrode part, but the consistency of the product performance is better, that is, the stability is better.

And (3) testing 2: and testing the dosage of the metal platinum and the voltage jump frequency of the oxygen sensor.

Comparative example:

the method comprises the following steps of manufacturing a sensing element according to a design scheme that the same amount of metal platinum is used for an internal catalytic electrode part and the amount of metal platinum of an external catalytic electrode part (co-fired electrode) is changed singly, packaging the sensing element into an oxygen sensor to manufacture 9 samples, and testing the voltage jump frequency of the oxygen sensor, wherein the testing method comprises the following steps:

when the oxygen sensor outputs high voltage, lambda is 0.97 at the moment, a signal for opening the extra air valve is output, the extra air valve on the equipment starts to open, the lambda value is switched from 0.97 to 1.03 at the moment, and the voltage output by the oxygen sensor starts to drop. When the voltage output by the oxygen sensor reaches 450mV, a signal for closing the extra air valve is immediately given, at the moment, the voltage value can continuously fall for a period of time to start rising due to the control hysteresis, when the voltage rises to 450mV, a signal for opening the extra air valve is given again, the voltage value can continuously rise for a period of time to start falling due to the control hysteresis, and therefore the voltage continuously oscillates up and down at 450 mV. The number of times the sensor makes a transition within a predetermined time is recorded as N (for a clearer explanation of the voltage transition process, refer to fig. 6, which is a graph of the voltage transition when N is 21). The test data for the 9 samples are shown in the following table:

comparative example	Inner catalysis electrode dosage (g)	External catalytic electrode dosage (g)	Value of N
				Sample
1	0.01	0.006	28
				Sample 2	0.01	0.008	26
Sample 3	0.01	0.01	25
				Sample No. 4	0.01	0.012	23
Sample No. 5	0.01	0.014	21
				Sample No. 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 (b):

the same design as the comparative example was used, i.e., the amount of platinum metal used in the outer catalytic electrode portion (the novel ceramic catalytic electrode provided in the first example) was changed only in accordance with the amount of platinum metal used in the inner catalytic electrode portion, and the sensing element was fabricated and packaged into an oxygen sensor to produce 9 samples. The thickness of the ceramic substrate of the catalytic electrode of the novel ceramic catalytic electrode of the sample is 0.3mm, the length is 5mm or 10mm, and the dosage of the precious metal platinum obtained by each sample is calculated by weighing the loaded saturated chloroplatinic acid.

The test data for the 9 samples using the same test method as the comparative example are shown in the following table:

TABLE 5

As can be seen from tables 4 and 5, the smaller the N value, the more platinum metal is used. As can be seen from comparison of tables 4 and 5, the amount of platinum used in the external catalytic electrode of the example is only one tenth of the amount used in the external catalytic electrode of the comparative example, and the same or even lower voltage jump frequency can be achieved, that is, the same product performance can be achieved.

Tubular sensing element with excellent performance, preparation method of sensing element and oxygen sensor with sensing element

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

In the novel tubular sensor element disclosed in the third embodiment, since the external catalytic electrode part of the novel tubular sensor element adopts the novel ceramic catalytic electrode provided by the invention, the protective layer of the sensor element cannot be prepared by a co-firing process with other parts of the sensor element, and can only be prepared by plasma spraying or secondary sintering. However, the production efficiency of plasma spraying is low, the spraying equipment is expensive and consumes much energy, and the production cost of a single product is high. The protective layer is prepared by a secondary sintering method, on one hand, the complexity of the preparation process is increased, and in addition, the binding force of the protective layer and the substrate is not as high as that of the existing product, so that the problem that the outer electrode is polluted by waste gas due to the fact that the protective layer is easy to fall off exists.

Therefore, in the fourth embodiment, the tube sensor with excellent performance disclosed by the invention has the advantages that the internal catalytic electrode part adopts the novel ceramic catalytic electrode provided by the invention, and the external electrode adopts the co-fired electrode, so that when a protective layer needs to be added, the protective layer can be prepared with other parts of the sensor by adopting the co-firing process, the product process is simplified, and the bonding strength of the protective layer and the solid electrolyte ceramic substrate is improved. Referring to fig. 1, the general structure of the tubular sensing element with excellent performance includes a tubular ceramic substrate 1 with solid electrolyte characteristics, an external electrode 2 and an internal electrode 3, wherein the ceramic substrate 1 has an inner cavity formed by extending inwards from the bottom surface; the outer electrode 2 is arranged on the outer surface of the ceramic substrate 1 and comprises an outer catalytic electrode part 21 arranged at the tail end of the outer surface of the ceramic substrate in a surrounding mode and an outer lead electrode part 22 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 3 is arranged on the wall of the inner cavity, and comprises an inner catalytic electrode part 31 surrounding the tail end of the wall of the inner cavity, and an inner lead electrode part 32 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 part adopts the novel ceramic catalytic electrode provided by the invention, and the external electrode adopts a co-fired electrode.

The novel ceramic catalytic electrode provided by the invention is used in the internal catalytic electrode part of the sensing element provided by the embodiment, and has the characteristics of small noble metal consumption, excellent catalytic performance and high bonding strength between the electrode and the substrate. Since the specific structure and the preparation method of the novel ceramic catalytic electrode have been described in detail above, detailed descriptions thereof are omitted, and reference is made to the related description in the first embodiment.

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

Also, in order to prevent the outer electrode (i.e., the electrode on the side contacting with the exhaust gas) of the sensing element of the oxygen sensor from being corroded by the exhaust gas discharged from the engine and thus degrading the catalytic performance of the noble metal (generally, platinum metal is used), the novel tubular sensing element further includes a protective layer covering the surface of the outer electrode. The material of the protective layer is well known to those skilled in the art, and specifically may be alumina, magnesia alumina spinel, zirconia alumina composite material, or the like. 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 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, coating the slurry for forming the catalytic electrode ceramic matrix on 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 a noble metal salt solution into a catalytic electrode ceramic substrate, and then drying to obtain a semi-finished product of the sensing element;

The present embodiment also provides an oxygen sensor obtained by encapsulating the tube-type sensing element provided by the present embodiment with excellent performance. The oxygen sensor has the same metal platinum dosage and catalytic performance as the oxygen sensor provided by the third embodiment, and meanwhile, the preparation process is simpler and the preparation cost is lower.

The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A novel tubular sensing element, comprising:

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

2. The novel tubular sensing element of 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. The novel tubular sensing element of claim 1, wherein: the external lead electrode part of the external electrode comprises a catalytic electrode ceramic base body formed on the surface of the ceramic base and precious metals arranged inside and on the surface of the catalytic electrode ceramic base body, and/or the internal electrode comprises a catalytic electrode ceramic base body formed on the wall of the inner cavity of the ceramic base and precious metals arranged inside and on the surface of the catalytic electrode ceramic base body; or the external lead electrode part and the internal electrode of the external electrode are formed by co-fired electrodes;

4. The novel tubular sensing element of 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.

5. The novel tubular sensing element of claim 1, wherein: the sensing element also comprises a protective layer which covers the surface of the external electrode.

6. A tubular oxygen sensor, characterized by: comprising a novel tubular sensor element according to any one of claims 1 to 5.

7. A method of making a novel tubular sensing element according to any one of claims 1 to 5, comprising:

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

8. The method of making a novel tubular sensing element according to 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 of making a novel tubular sensing element according to claim 7, wherein: the slurry for forming the ceramic matrix of the catalytic electrode is prepared by the following method:

10. The method of making a novel tubular sensing element according to 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;

11. The method of making a novel tubular sensing element according to claim 7, wherein:

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

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

12. The method of making a novel tubular sensing element according to claim 7, wherein:

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

preparing a solid electrolyte substrate green compact;