Assembling-pairing-free catalytic combustion sensor and preparation method thereof

Abstract

The invention relates to the technical field of gas sensors, and particularly discloses an assembly-pairing-free catalytic combustion sensor and a preparation method thereof. Comprising a detection element, a compensation element and a supporting bracket, wherein the detection element and the compensation element are welded on the same bracket side by side; the detection element is composed of a gamma-Al2O3 carrier loaded with palladium nitrate and a platinum nitrate catalyst (the mass ratio of palladium to platinum is 2: 1-4: 1), and the compensation element is a composite ceramic body without a catalyst and is prepared by mixing seven oxides such as aluminum oxide (65-80%) and silicon dioxide (8-11%) according to a specific proportion. During preparation, the detection element is prepared into slurry through catalyst powder and an ethylene glycol solution, and the slurry is impregnated by a platinum wire coil and electrified to sinter and form; the compensation element is formed by blending slurry with composite oxide powder and an aluminum nitrate solution and adopting the same coil and sintering process. By innovating a compensation element material system and a preparation process, natural matching of initial resistance of the detection element and the compensation element is realized, and a traditional pairing process is thoroughly omitted.

Description

Technical Field

[0001] This invention relates to the field of gas sensor technology, and in particular to a catalytic combustion sensor that does not require assembly and pairing, and its preparation method. Background Technology

[0002] Catalytic combustion gas sensors, with their outstanding advantages such as fast response speed, excellent linearity in combustible gas detection, and long service life, have become indispensable core components in fields such as industrial safety monitoring and environmental gas detection. Their working principle is based on a Wheatstone bridge structure. The core principle involves a detection element loaded with precious metal catalysts such as platinum or palladium. During the catalytic combustion reaction of combustible gases, temperature changes occur, leading to changes in resistance and ultimately achieving quantitative detection of gas concentration. In this bridge system, the detection element must be paired with a reference compensation element, and their initial resistance values ​​must be highly matched to ensure initial bridge balance, laying the foundation for subsequent accurate detection. Therefore, the resistance matching between the detection element and the compensation element is the key factor determining the sensor's performance.

[0003] However, achieving high-precision resistance matching between the two has long been a fundamental challenge for traditional catalytic combustion sensor technology. Theoretically, the compensation element should be a "white element" without a catalyst. However, the detection element, due to the loading of a noble metal catalyst, exhibits significantly altered resistance characteristics, making it impossible for a "white element" made of purely inert materials to achieve resistance matching with the detection element. To resolve this contradiction, existing technologies generally employ chemical deactivation of the catalytic element to prepare the compensation element. This involves immersing the detection element in a specific deactivating agent solution and then sintering it with an electric current to achieve catalytic activity loss, thereby attempting to bring its resistance value closer to that of the detection element.

[0004] However, this chemical deactivation process has inherent flaws. It not only fails to fundamentally solve the resistance matching problem, but also gives rise to a series of chain problems: First, the process is highly volatile. Several key parameters, such as the concentration of deactivator, impregnation time, impregnation amount, sintering voltage and sintering time, will have a significant impact on the final resistance value of the compensation element. Even a small deviation in any parameter may lead to a large dispersion in the resistance value, making it difficult to achieve stable and consistent resistance characteristics. Secondly, poor component consistency directly leads to low production efficiency. Because the resistance values ​​of the manufactured detection and compensation components are scattered, they cannot be directly assembled and used. Special testing, screening and manual matching processes must be added before assembly. This process is cumbersome and time-consuming, which not only restricts the realization of automated production and capacity improvement, but also causes a large amount of unmatched components to be wasted, significantly increasing manufacturing costs. Third, the long-term reliability is insufficient. The compensation element and the detection element, which have undergone chemical deactivation treatment, have fundamental differences in internal material structure and composition characteristics. During the long-term operation of the sensor with power, the resistance drift trends of the two are difficult to synchronize due to factors such as ambient temperature fluctuations and current thermal effects. This leads to the destruction of the initial balance state of the bridge, causing zero-point drift of the sensor, which seriously affects the long-term measurement accuracy and reliability.

[0005] In summary, existing technologies for fabricating compensation elements based on chemical deactivation have consistently failed to overcome the core bottleneck of "difficulty in resistance matching." Furthermore, they suffer from multiple problems such as complex processes, poor element consistency, low production efficiency, and poor long-term stability. These technologies can no longer meet the industrial production requirements for high consistency, high-efficiency fabrication, and long-term reliable use of sensors. Therefore, there is an urgent need for a new technical solution that can achieve natural initial resistance matching between the detection element and the compensation element, thereby fundamentally solving the aforementioned technical pain points. Summary of the Invention

[0006] In view of this, embodiments of the present invention provide a catalytic combustion sensor that does not require assembly and pairing and its preparation method, in order to solve the technical problems in the traditional technology, where the compensation element needs to be prepared by "chemically deactivating" the catalytic element. However, the introduction of the catalyst changes the resistance characteristics of the detection element, which makes it impossible for the purely inert element to match. Furthermore, the chemical deactivation process itself is difficult to control precisely, ultimately resulting in poor element resistance consistency and low initial matching degree.

[0007] In a first aspect, embodiments of the present invention provide a catalytic combustion sensor that does not require assembly and pairing, comprising: A support frame, and detection and compensation elements welded to the support frame; The detection element is made of alumina-supported palladium nitrate and platinum nitrate catalyst; The compensation element is a catalyst-free composite ceramic body, which is made of a mixture including alumina, silicon dioxide, titanium dioxide, boron trioxide, sodium oxide, potassium oxide and zinc oxide.

[0008] Preferably, the mass ratio of palladium nitrate to platinum nitrate is 2:1 to 4:1.

[0009] Preferably, the composite ceramic body comprises: Alumina 65-80%, silicon dioxide 8-11%, titanium dioxide 4-8%, boron trioxide 3-5%, sodium oxide 2-4%, potassium oxide 2-4%, zinc oxide 1-3%.

[0010] Preferably, the alumina is γ-Al2O3.

[0011] Preferably, both the detection element and the compensation element are formed by sintering a platinum wire coil after immersing it in a corresponding slurry and then passing it through an electric current. The platinum wire has a diameter of 0.025~0.035mm, the platinum wire coil has 5~15 turns, the coil shaft diameter is 0.25~0.35mm, and the coil length is 0.50~0.90mm.

[0012] Preferably, the radius of the sintered sphere of the detection element is 0.35~0.45mm.

[0013] Preferably, the radius of the sintered sphere of the compensation element is 0.37~0.47mm.

[0014] Secondly, a method for preparing an assembly-free, pair-free catalytic combustion sensor is provided, for preparing the aforementioned assembly-free, pair-free catalytic combustion sensor; comprising: S1. Preparation steps of the detection element: Alumina was mixed and ground with palladium nitrate solution and platinum nitrate solution to obtain a homogeneous first type of mixture; The first type of mixture is dried and then ground again to obtain catalyst powder; Ethylene glycol solution is added to the catalyst powder to prepare a slurry for the detection element; The detection element is obtained by immersing a platinum wire coil into the detection element slurry and then solidifying the detection element slurry onto the surface of the platinum wire coil by sintering with electricity. S2. Preparation steps of the compensation element: Alumina, silicon dioxide, titanium dioxide, boron trioxide, sodium oxide, potassium oxide and zinc oxide are mixed and ground to obtain a homogeneous second type of mixture; The second type of mixture is dried and ground again to obtain a mixed powder; Aluminum nitrate solution is added to the mixed powder to form a slurry for compensating elements; The platinum wire coil is dipped into the compensation element slurry, and the compensation element slurry is solidified on the surface of the platinum wire coil by sintering with electricity, thereby obtaining the compensation element. S3. Sensor fusion fabrication steps: The detection element and the compensation element are respectively positioned at the preset installation positions of the bracket, and the detection element and the compensation element are electrically connected and mechanically fixed to the bracket through a welding process, thereby completing the manufacturing of the sensor.

[0015] Preferably, the mass concentration of the ethylene glycol solution used to prepare the slurry of the detection element is 10.0% to 40.0%; The mass concentration of the aluminum nitrate solution used to prepare the compensating element slurry is 1.0% to 10.0%.

[0016] Preferably, the step of sintering by electric current is as follows: Applying current to the platinum wire coil causes the coil's own resistance to heat up to a red-hot state, thereby achieving the sintering and molding of the attached paste.

[0017] The catalytic combustion sensor that does not require assembly and pairing and its preparation method provided by the present invention have the following beneficial effects: This invention achieves a natural and precise match between the initial resistance values ​​of the detection element and the compensation element by innovatively designing a composite oxide material system for the compensation element and optimizing the preparation process. This completely eliminates the cumbersome testing, screening, and manual matching processes in traditional processes, significantly improving production efficiency and product consistency. At the same time, it avoids resource waste caused by ineffective elements and significantly reduces manufacturing costs. The compensation element does not require the use of precious metal catalysts and abandons the chemical deactivation process, which reduces raw material costs and process energy consumption, and eliminates material structure differences caused by residual deactivating agents. This makes the resistance drift trends of the detection element and the compensation element highly coordinated, effectively suppressing sensor zero-point drift, significantly improving long-term measurement accuracy and reliability. This provides an efficient solution for the automated, large-scale production and high-precision, stable application of catalytic combustion sensors. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, and these are all within the protection scope of the present invention.

[0019] Figure 1 Comparative example: A comparison chart showing the pass rate of the zero-point output voltage of the sensor after the detection element and compensation element of each embodiment of the present invention are randomly welded to the same bracket to form a sensor. Figure 2 The zero-point change diagram of the sensor described in the embodiment of the present invention and Comparative Example 1 after being charged for 1 month. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In the description of the present invention, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements, but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, the element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Where there is no conflict, embodiments of the present invention and the various features thereof can be combined with each other, all of which are within the scope of protection of the present invention.

[0021] Example 1 This invention provides a method for preparing a non-assembly-pairing catalytic combustion sensor, comprising: Fabrication of detection elements: (1) Preparation of catalyst powder: Preparation of precursor solution: Accurately weigh 5.00 g of palladium nitrate (Pd(NO3)2), place it in a 100 ml volumetric flask, dissolve it with deionized water, dilute to the mark and shake well to obtain a palladium nitrate stock solution with a concentration of 50 mg / ml.

[0022] Weigh 1.26 g of platinum nitrate (Pt(NO3)2) accurately, place it in a 100 ml volumetric flask, dissolve it in deionized water, dilute to the mark and shake well to prepare a platinum nitrate stock solution with a concentration of 12.6 mg / ml.

[0023] Equal volume co-impregnation and post-treatment: Measure 2.00 ml of palladium nitrate stock solution and 2.00 ml of platinum nitrate stock solution, mix them, and then load them onto a 1.00 g spherical alumina support using the equal volume impregnation method.

[0024] The impregnated material was left to stand at room temperature for 4 hours, dried at 110°C for 12 hours, and calcined in air at 500°C for 4 hours to obtain a Pd-Pt / Al2O3 catalyst with a Pd:Pt metal mass ratio of approximately 3:1, which is the first type of mixture. The first type of mixture was then ground and pulverized to obtain catalyst powder.

[0025] (2) Preparation of slurry and coil load forming: Preparation of catalyst slurry: Weigh 0.5g of the Pd-Pt / Al2O3 catalyst powder prepared above, mix it with 2.0ml of 30% ethylene glycol aqueous solution, and stir until a uniform, viscous slurry without visible particles is formed.

[0026] Platinum wire coil treatment and dipping: Take a platinum wire coil with a diameter of 0.03 mm, 11 turns, a shaft diameter of 0.30 mm, and a length of 0.60~0.70 mm, immerse it in the above catalyst slurry, and slowly pull it out so that the slurry is evenly attached to the surface of the coil.

[0027] Molding by heating with electricity: Connect the two ends of the platinum wire coil dipped in catalyst slurry to an adjustable DC or AC power supply.

[0028] Adjust the voltage and current to gradually heat the platinum wire coil to a red-hot state within 60 seconds (estimated temperature 600~800℃), and maintain this state for 10 seconds.

[0029] During this process, the water and ethylene glycol in the slurry evaporate and burn rapidly, and the catalyst coating is sintered, forming a solid porous catalyst layer on the surface of the coil.

[0030] After the coil cools down, the final coil-type Pd-Pt / Al2O3 structured catalyst is obtained.

[0031] Fabrication of compensation elements: (1) Preparation of compensating material powder: Ingredients and Mixing: Accurately weigh the following raw materials according to the following mass percentages: 65% aluminum oxide (γ-Al2O3), 11% silicon dioxide (SiO2), 8% titanium dioxide (TiO2), 5% boron trioxide (B2O3), 4% sodium oxide (Na2O), 4% potassium oxide (K2O), and 3% zinc oxide (ZnO). Place the weighed powdered raw materials together in a mortar, add an appropriate amount of deionized water as a dispersion medium, and grind thoroughly for at least 2 hours until the mixture is homogeneous and free of particles.

[0032] Drying and grinding: Place the evenly ground slurry in a 120℃ oven and dry for 6 hours to completely remove moisture.

[0033] The dried lumpy material (i.e., the second type of mixture) is crushed in a mortar and passed through a 200-mesh sieve to obtain a uniformly composed compensating material mixed powder.

[0034] (2) Preparation of compensating element paste and coil load molding: Slurry preparation: Weigh 1.0 g of the prepared compensating material mixture powder and slowly add a 2.0% (w / w) aqueous solution of aluminum nitrate (Al(NO3)3·9H2O). Stir continuously to adjust the mixture into a slurry with suitable viscosity and good coating properties.

[0035] The amount of aluminum nitrate solution added should be just enough to form a uniform, coatable slurry. The mass-to-volume ratio of powder to solution is usually in the range of 1g:0.8~1.2ml.

[0036] Impregnation and sintering: A platinum wire coil of the same specifications as the one used to prepare the detection element was immersed in the aforementioned compensation material slurry and slowly withdrawn, allowing the slurry to adhere evenly to the coil surface. Subsequently, the coil was connected to a power source and sintered using the same heating method as the detection element.

[0037] During this process, the moisture in the slurry evaporates, aluminum nitrate decomposes into aluminum oxide, and the mixed oxide powder is sintered together to form a dense and robust compensation element layer on the coil surface. After the coil cools, the final compensation element is obtained.

[0038] Sensor fabrication: (1) Component soldering: The platinum wire leads of the detection element and the compensation element are directly soldered side by side to the corresponding pins of the same integrated sensor bracket.

[0039] The bracket is a standard, integrated structure that supports two components.

[0040] (2) Cover with a cap: Once the welded bracket is capped, a complete sensor is obtained.

[0041] Comparative Example 1 Preparation of detection element: exactly the same as in Example 1.

[0042] Compensation element preparation: The detection element of Example 1 was prepared after being deactivated by a deactivating agent.

[0043] Comparative Example 2 Preparation of detection element: exactly the same as in Example 1.

[0044] Compensation element preparation: slurry was prepared using only 1.00g of alumina (without catalyst loading), and the remaining steps were the same as in Example 1.

[0045] Example 2 Preparation of detection element: exactly the same as in Example 1.

[0046] Compensation element preparation: The proportion of the mixed powder is: 70% aluminum oxide, 10% silicon dioxide, 8% titanium dioxide, 4% boron trioxide, 3% sodium oxide, 3% potassium oxide, and 2% zinc oxide.

[0047] Example 3 Preparation of detection element: exactly the same as in Example 1.

[0048] Compensation element preparation: The proportion of the mixed powder is: 75% aluminum oxide, 9% silicon dioxide, 6% titanium dioxide, 4% boron trioxide, 2% sodium oxide, 2% potassium oxide, and 2% zinc oxide.

[0049] Example 4 Preparation of detection element: exactly the same as in Example 1.

[0050] Compensation element preparation: The proportion of the mixed powder is: 80% aluminum oxide, 8% silicon dioxide, 4% titanium dioxide, 3% boron trioxide, 2% sodium oxide, 2% potassium oxide, and 1% zinc oxide.

[0051] Performance Testing and Results Analysis Experiment 1: Test of the effect of non-assembly pairing To verify the superiority of the compensation element design described in this invention, a comparative experiment was conducted. The detection elements and compensation elements of each embodiment and comparative example were directly welded to the same bracket to form a sensor, and the zero-point output voltage of the sensor was tested (the pass standard is ±30mV).

[0052] Please see the results. Figure 1 Comparative Example 1 uses a traditional chemical deactivation method to treat the detection element to prepare the compensation element, and its zero-point pass rate after being directly welded into a sensor is only 30%. Comparative Example 2 uses a pure inert compensation element with a main body of alumina and contains no catalyst or specific composite oxide, and its zero-point pass rate is further reduced to 5%. In contrast, the zero-point pass rates of the sensors in the embodiments using the specific composite oxide material system provided by the present invention are all stable at over 90%.

[0053] The experimental results show a clear gradient, fully demonstrating that compared to existing technologies, this invention, through precise and targeted design of the compensation element composition, can extremely effectively achieve initial resistance matching between the detection element and the compensation element. This not only fundamentally solves the bottleneck problem of traditional processes relying on post-process screening and matching, achieving an industrial-scale effect of "assembly-free matching," but also highlights the significant technological advantages and industrialization value of this invention in improving product consistency, production efficiency, and yield.

[0054] Experiment 2: Long-term operational stability test To evaluate the long-term operational reliability of the sensors, a one-month continuous power-on aging test was conducted on the sensors described in each embodiment and Comparative Example 1.

[0055] Please see the results. Figure 2 Test results show that the zero-point drift values ​​of the sensors in each embodiment of the present invention are stable within an extremely narrow range of ±3mV; in contrast, the zero-point drift of the sensor in Comparative Example 1 (conventional chemical deactivation method) reached -6mV, and its stability is significantly inferior to that of the present invention.

[0056] This achievement has two key implications. First, it confirms the synergistic effect of material design. The results show that even in the absence of precious metal catalysts, the composite oxide compensation element designed with precise proportions can still achieve a high degree of synergy with the precious metal catalytic detection element in terms of its temperature coefficient of resistance and long-term aging characteristics, thereby ensuring the long-term stability of the bridge output.

[0057] Secondly, this invention breaks through the core bottleneck of traditional technology. It fundamentally solves the problem of differences in microstructure and composition between compensation and detection elements caused by chemical deactivation processes in traditional sensors, thus completely overcoming the resulting problems of asynchronous performance degradation and zero-point drift. This provides reliable technical support for sensors to achieve high precision and long-term maintenance-free operation.

[0058] Example 5 This invention provides a catalytic combustion sensor that does not require assembly or pairing. To address the shortcomings of existing technologies, the present invention aims to provide a catalytic combustion gas sensor in which the initial resistance values ​​of the detection element and the compensation element are naturally matched, thus achieving assembly-free pairing, thereby simplifying the production process, improving efficiency and product consistency.

[0059] The catalytic combustion sensor includes a support, and a detection element and a compensation element welded to the support; the detection element is made of alumina supported on palladium nitrate and platinum nitrate catalysts; the compensation element is a catalyst-free composite ceramic body, which is made of a mixture including alumina, silicon dioxide, titanium dioxide, boron trioxide, sodium oxide, potassium oxide and zinc oxide.

[0060] In this embodiment, a catalytic combustion sensor that requires no assembly or pairing includes a support and a detection element and a compensation element welded onto the support. After fabrication, the detection element and the compensation element can be directly welded onto the same support to form the sensor without resistance testing, screening, or manual pairing, thus achieving a manufacturing method that eliminates the need for assembly and pairing.

[0061] The detection element is made of an alumina support loaded with palladium nitrate and platinum nitrate catalysts. When powered on, it can catalytically combust combustible gases. The exothermic reaction causes the element temperature to rise, resulting in a change in resistance value, thus serving as the gas detection unit of the sensor.

[0062] This compensation element does not participate in the catalytic reaction of combustible gases in the sensor. Its main function is to serve as a reference arm in the bridge circuit to offset the influence of non-gaseous factors such as changes in ambient temperature and power fluctuations on the detection signal, thereby ensuring the stability and accuracy of the sensor output signal.

[0063] From the perspective of resistance mechanism, the total resistance of a catalytic combustion detection element is determined not only by the resistance of the platinum wire coil itself, but also by the equivalent resistance of the porous structure formed by the noble metal catalytic layer loaded on the alumina support, as well as the interfacial contact resistance between the platinum wire and the ceramic layer. Therefore, the resistance characteristics of the detection element are a composite resistance characteristic formed by the combined effect of multiple factors, rather than a single metal resistance.

[0064] In this embodiment, the compensation element is not simply designed using pure inert ceramic materials, but rather through a specific inorganic composite oxide system. Alumina, as the main framework phase, provides stable structural support and thermal stability for the compensation element. Boron trioxide, sodium oxide, and potassium oxide form a glassy phase during the electro-sintering process. This glassy phase can regulate the micro-contact state between ceramic particles and stabilize the conductive path. Titanium dioxide and zinc oxide, as weakly conductive or semi-conductive phases, introduce temperature-sensitive resistance contributions, resulting in a composite conductive network structure composed of the framework phase, glassy phase, and weakly conductive phase. Through this material system design, the number, distribution, and temperature response characteristics of the conductive paths formed by the compensation element after sintering match the conductive structure formed by the noble metal catalyst layer in the detection element in terms of equivalent resistance mechanism, thus ensuring that the resistance characteristics of the compensation element are consistent with those of the detection element.

[0065] Based on the aforementioned structural and material mechanism design, after the sensor is fabricated, the initial resistance values ​​of the detection element and the compensation element can be naturally matched. They can be directly assembled and used without subsequent resistance testing, screening, or manual pairing, fundamentally eliminating the "assembly and pairing" manufacturing step required in existing technologies. This significantly simplifies the sensor production process, reduces manual intervention and manufacturing costs, and improves production efficiency and batch consistency. Furthermore, because the compensation element does not contain catalysts and has not undergone chemical deactivation treatment, it avoids long-term instability caused by residual deactivating agents and differences in material structure. This ensures that the resistance change trends of the detection element and the compensation element remain consistent during long-term energized operation, effectively suppressing bridge zero-point drift and improving the long-term measurement stability and reliability of the sensor.

[0066] Compared with the traditional method of preparing compensation elements through chemical deactivation, this embodiment achieves a natural match between the resistance characteristics of the detection element and the compensation element through targeted design of the material system and conductivity mechanism without introducing catalysts and deactivation processes. It solves the problems of difficult resistance matching, large process fluctuations and poor consistency in the prior art from the theoretical and structural levels.

[0067] The key innovation of this invention lies in the precise design and coordinated control of the material composition of the compensation element, enabling its resistivity characteristics to be pre-matched with the catalyst-loaded detection element, thus achieving "pairing-free" operation. Specifically: using alumina, the same structural matrix as the detection element, ensures consistency in thermal expansion coefficient and long-term stability; introducing wide-bandgap, high-resistivity phases such as silica, titanium dioxide, and zinc oxide enhances the intrinsic resistance of the composite ceramic body; simultaneously, innovatively adding alkali metal oxides such as sodium oxide and potassium oxide as charge compensation and grain boundary modifiers allows for adjustment of carrier concentration and grain boundary barriers during sintering, thereby achieving fine-tuning of resistivity. Boron trioxide, as a co-solvent and glass phase forming agent, promotes sintering densification and microstructure uniformity, thus "locking in" the preset resistance value. By optimizing the proportions of the above components, the initial resistance value and temperature coefficient of resistance (TCR) of the compensation element can be preset within a narrow band range highly matched with the target detection element, fundamentally replacing the chemical deactivation and manual screening steps in traditional processes.

[0068] Furthermore, the metal mass ratio of palladium nitrate to platinum nitrate is 2:1 to 4:1.

[0069] The composite ceramic body comprises: 65-80% (mass percentage) alumina, 8-11% (mass percentage) silicon dioxide, 4-8% (mass percentage) titanium dioxide, 3-5% (mass percentage) boron trioxide, 2-4% (mass percentage) sodium oxide, 2-4% (mass percentage) potassium oxide, and 1-3% (mass percentage) zinc oxide; the alumina is γ-Al2O3; and the initial resistance values ​​of the detection element and the compensation element are naturally matched after preparation, and they can be directly assembled without screening and matching.

[0070] In this embodiment, the catalyst used in the detection element is composed of palladium nitrate and platinum nitrate supported on the surface of an alumina support, wherein the metal mass ratio of palladium nitrate to platinum nitrate is controlled within the range of 2:1 to 4:1. By limiting the above mass ratio, the resistance change characteristics of the detection element under energized operation are kept within a stable and controllable range while maintaining high catalytic activity, thereby providing a basis for resistance matching between the detection element and the compensation element.

[0071] Specifically, palladium, as the main catalytically active component, plays a dominant role in the catalytic combustion reaction of combustible gases; the introduction of platinum is used to adjust the thermal stability and electrical conductivity of the catalyst layer. When the mass ratio of palladium nitrate to platinum nitrate is lower than the aforementioned range, the overall electrical conductivity and thermal response characteristics of the catalyst layer deviate, easily leading to low resistance or unstable temperature response of the detection element. When the mass ratio is higher than the aforementioned range, the resistance contribution of the catalyst layer increases, and the dispersion between different batches increases, which is not conducive to achieving natural matching with the compensation element. Limiting the mass ratio of palladium nitrate to platinum nitrate to the range of 2:1 to 4:1 allows the detection element to obtain stable catalytic performance while keeping its equivalent resistance structure and resistance-temperature response characteristics within a suitable matching range.

[0072] Regarding the compensation element, the compensation element is a catalyst-free composite ceramic body, the composition of which, by mass percentage, includes: 65-80% alumina, 8-11% silicon dioxide, 4-8% titanium dioxide, 3-5% boron trioxide, 2-4% sodium oxide, 2-4% potassium oxide, and 1-3% zinc oxide, wherein the alumina is preferably γ-Al2O3.

[0073] In the above composition, γ-Al2O3 serves as the main framework phase, providing a stable porous structure and good thermal stability for the compensation element, enabling it to maintain long-term structural and dimensional stability during energized operation. Silica, boron trioxide, sodium oxide, and potassium oxide form a glassy phase during energized sintering, which is used to adjust the sintering density, stabilize the micro-contact state between particles, and suppress random fluctuations in the conductive path. Titanium dioxide and zinc oxide, as weakly conductive or semi-conductive phases, form temperature-sensitive resistance contribution pathways between the alumina framework, causing the compensation element to exhibit resistance change behavior similar to that of the detection element during heating.

[0074] By synergistically limiting the proportions of the above components, the compensation element forms a composite conductive network composed of a framework phase, a glass phase, and a weakly conductive phase after sintering. Its equivalent resistance source and resistance temperature response characteristics can match the conductive structure formed by the palladium-platinum catalyst layer in the detection element.

[0075] Based on the above-mentioned catalyst ratio design for the detection element and composite ceramic composition design for the compensation element, after the detection element and compensation element are prepared, their initial resistance values ​​can naturally fall into the same matching range. They can be directly welded onto the same bracket to form a sensor without subsequent resistance testing, screening, or manual pairing.

[0076] This not only fundamentally eliminates the cumbersome "assembly and pairing" process in existing technologies, significantly improving sensor production efficiency and product consistency and reducing manufacturing costs, but also ensures that the resistance change trends of the detection element and the compensation element remain consistent under long-term power-on conditions, effectively suppressing sensor zero-point drift and further enhancing the long-term stability and reliability of the sensor, since the compensation element does not contain a catalyst and has not undergone chemical deactivation treatment.

[0077] This invention abandons traditional compensation element solutions based on pure alumina or chemical deactivation. Instead, it selectively chooses seven oxides, including alumina, silica, and titanium dioxide, and sets specific mass ratios. Through the synergistic effect of these multiple oxides, the core electrical characteristics of the compensation element, such as room temperature resistivity and temperature coefficient of resistance, are precisely controlled. The resistivity characteristics of this composite system are designed to be highly compatible with the detection element based on a "γ-Al₂O₃-supported Pd-Pt catalyst." This not only offsets the influence of the noble metal catalyst in the detection element on the resistance but also, through the fluxing and structural adjustment effects of components such as silica and boron trioxide, ensures a natural fit between the resistivity substrate of the compensation element and the detection element, achieving resistance matching from the fundamental material properties.

[0078] Furthermore, both the detection element and the compensation element are formed by immersing a platinum wire coil in a corresponding slurry and then sintering it with electricity; wherein the diameter of the platinum wire is 0.025~0.035mm, the platinum wire coil has 5~15 turns, the shaft diameter of the platinum wire coil is 0.25~0.35mm, and the length of the platinum wire coil is 0.50~0.90mm.

[0079] Furthermore, the radius of the sintered sphere of the detection element is 0.35~0.45mm. The radius of the sintered sphere of the compensation element is 0.37~0.47mm.

[0080] In this embodiment, both the detection element and the compensation element use platinum wire coils as heating and conductive frameworks. The platinum wire coils are immersed in the corresponding detection element slurry or compensation element slurry, and then sintered by electric current to form an integrally shaped spherical structure.

[0081] The diameter of the platinum wire is controlled within the range of 0.025–0.035 mm, the number of turns of the platinum wire coil is 5–15, the coil shaft diameter is 0.25–0.35 mm, and the coil length is 0.50–0.90 mm. By synergistically limiting the above-mentioned platinum wire diameter and coil geometric parameters, the platinum wire coil can simultaneously meet the requirements of stable heating, uniform heat conduction, and repeatable resistance output under energized conditions.

[0082] Specifically, if the diameter of the platinum wire is smaller than the above range, it is prone to heat concentration or ablation due to excessive local current density when energized, leading to unstable coil resistance. If it is larger than the above range, the overall resistance value decreases and thermal inertia increases, which is not conducive to achieving resistance range matching between the sensing element and the compensation element. Limiting the diameter of the platinum wire to the range of 0.025 to 0.035 mm allows the coil body resistance to become a stable reference term in the resistance composition of the sensing element and the compensation element.

[0083] The number of coil turns, shaft diameter, and length collectively determine the spatial distribution density of the platinum wire inside the sphere and the effective heat conduction path. When the number of coil turns is controlled between 5 and 15, the shaft diameter is between 0.25 and 0.35 mm, and the length is between 0.50 and 0.90 mm, the platinum wire coil can form a uniform three-dimensional heat-conducting skeleton embedded inside the sphere after the paste is sintered. This allows the sphere to form a relatively uniform temperature field during the energization and heating process, thereby ensuring that the detection element and the compensation element have similar thermal response characteristics under working conditions.

[0084] Regarding sintering, the detection element forms a spherical structure after sintering with electricity, with its radius controlled between 0.35 and 0.45 mm; the compensation element also forms a spherical structure after sintering with electricity, with its radius controlled between 0.37 and 0.47 mm. By limiting the size range of the two types of spheres and making the radius of the compensation element slightly larger than that of the detection element, the equivalent thermal resistance and equivalent resistance of the compensation element can be finely adjusted while ensuring that the overall structure and heat capacity of both are similar.

[0085] From a mechanistic perspective, the radius of the sphere directly affects the length of the conductive path, pore structure, and thermal diffusion capacity formed after sintering of the slurry. In the detection element, due to the presence of the catalyst, the sphere generates additional heat when participating in the gas catalytic combustion reaction; the compensation element, with a slightly larger sphere size, achieves a similar thermal response delay and resistance change trend without participating in the catalytic reaction, thereby compensating for the thermo-electric behavior of the detection element at the overall structural level.

[0086] Based on the synergistic design of the platinum wire coil structural parameters, the impregnation and sintering process, and the sphere dimensions, the resistance values ​​of the detection and compensation elements after fabrication are jointly determined by the resistance of the platinum wire coil itself, the conductive network formed by the sintering slurry, and the geometry of the sphere. Furthermore, these determining factors exhibit a high degree of consistency between the two types of elements. Therefore, their initial resistance values ​​naturally fall within the expected matching range, allowing for direct assembly without additional resistance screening or manual pairing.

[0087] This not only ensures the consistency and long-term stability of the electrical performance of sensors across batches, but also further enhances the repeatability and engineering feasibility of the "no-assembly pairing" technology, providing a reliable structural and technological foundation for achieving large-scale automated production.

[0088] Specifically, from the perspective of resistance mechanism, the total resistance of a catalytic combustion detection element is determined by the resistance of the platinum wire itself, the interfacial contact resistance between the platinum wire and the ceramic layer, and the equivalent resistance of the porous structure formed by the noble metal catalytic layer. Traditional purely inert compensation elements, because the ceramic layer hardly participates in conductivity, have a fundamentally different resistance mechanism from those of detection elements, making it difficult to achieve initial resistance matching.

[0089] This invention introduces a composite ceramic system consisting of an alumina framework phase, a glassy phase, and a weakly conductive phase into the compensation element, enabling the compensation element to form a conductive path structure equivalent to the catalyst layer in the detection element after sintering. By combining the homogeneity of the detection element and the compensation element in terms of platinum wire specifications, sintering methods, and manufacturing processes, the overall resistance composition model of both is kept consistent, theoretically guaranteeing a high degree of matching between the initial resistance values ​​of the detection element and the compensation element. This matching is naturally achieved without the need for subsequent screening or assembly pairing.

[0090] Furthermore, since the initial resistance values ​​of the detection element and the compensation element are highly matched, the necessity of subsequent resistance matching and screening is fundamentally eliminated, saving the cumbersome assembly and pairing process in existing technologies, greatly improving production efficiency and product consistency, and reducing manufacturing costs. The compensation element does not use any precious metal catalysts, directly reducing raw material costs; the simplified process also reduces energy consumption and labor time. Because the compensation element is a true "white element" without the introduction of chemical deactivating agents, when the sensor is energized for a long time, the resistance drift trends of the two elements caused by factors such as ambient temperature fluctuations and current thermal effects are synchronized, effectively suppressing bridge imbalance caused by differences in element characteristics, thereby significantly improving the long-term measurement stability and reliability of the sensor.

[0091] Furthermore, after the composite ceramic body of the compensation element is sintered and formed by electric current, it forms a composite conductive network structure composed of an alumina framework phase, a glass phase, and a weakly conductive phase. The composite conductive network matches the conductive structure formed by the noble metal catalyst layer in the detection element in terms of the equivalent resistance source and conductive path distribution, thereby naturally matching the initial resistance value of the compensation element with that of the detection element.

[0092] In this embodiment, the compensation element is not simply made of a single insulating material, but rather a composite ceramic structure with equivalent conductive behavior is constructed by synergistic proportioning of various inorganic oxides and an electric sintering process.

[0093] Specifically, alumina serves as the main framework phase, providing a stable three-dimensional porous structure and high-temperature mechanical strength for the compensation element. Boron trioxide, sodium oxide, and potassium oxide form a low-melting-point glass phase during the electro-sintering process. This glass phase can coat and fix the oxide particles during the sintering stage, adjust the micro-contact state between particles, and stabilize the number of conductive paths. At the same time, the introduced titanium dioxide and zinc oxide serve as weakly conductive or semi-conductive phases, forming auxiliary conductive pathways between the alumina framework. This makes the compensation element as a whole exhibit an equivalent resistance source structure similar to the noble metal catalyst layer in the detection element.

[0094] Through the above structural design, the composite conductive network formed by the compensation element after sintering has a number of conductive paths, a distribution state, and temperature response characteristics that are very close to the structure of the catalyst layer in the detection element. Thus, it can achieve natural matching with the initial resistance of the detection element without the need for subsequent resistance adjustment or screening and matching.

[0095] Furthermore, the material composition of the compensation element is configured such that its temperature coefficient of resistance within the sensor's operating temperature range is consistent with that of the detection element, thereby maintaining the initial balance of the bridge under conditions of ambient temperature changes and power-on heating.

[0096] In this embodiment, the composite ceramic material of the compensation element is not only used to achieve initial resistance matching between the detection element and the compensation element, but also, through material system design, to ensure that the trend of its resistance change with temperature within the normal operating temperature range of the sensor is consistent with that of the detection element.

[0097] Specifically, because the noble metal catalyst is supported on the surface of the alumina support, the resistance change behavior of the detection element is not ideally metallic, but is affected by the porous structure, noble metal distribution, and thermal effects, exhibiting a composite resistance-temperature response characteristic. To address this characteristic, this invention introduces titanium dioxide and zinc oxide components with temperature-sensitive resistance characteristics into the compensation element, causing the compensation element to produce a resistance change trend similar to that of the detection element during heating.

[0098] Meanwhile, the glass phase in the compensation element plays a role in structural stability and nonlinear suppression of the aforementioned weakly conductive phase, avoiding abnormal fluctuations in the resistance-temperature characteristics caused by local phase transitions or abrupt changes in the conductive path. Therefore, the resistance-temperature coefficient of the compensation element can remain highly consistent with that of the sensing element within the actual operating temperature range, ensuring that the bridge remains in a stable equilibrium state under conditions such as ambient temperature changes and current heating.

[0099] Specifically, during long-term operation with power on, the direction and rate of resistance change of the detection element and the compensation element remain coordinated, thereby suppressing bridge imbalance and zero-point drift caused by differences in element aging.

[0100] In this embodiment, the detection element and the compensation element not only achieve resistance matching in the initial state, but also maintain the consistency of resistance change behavior under long-term power-on operation conditions.

[0101] Specifically, both the detection element and the compensation element use platinum wire coils of the same specifications as carriers, and the functional materials are directly solidified onto the coil surface through an electric sintering process. Due to the high degree of consistency between the two in terms of structural carrier, sintering method, and inorganic material system, the resistance change mechanism that dominates during long-term energization mainly comes from the stabilization process of the platinum wire microstructure and the process of the ceramic layer densification approaching saturation.

[0102] Unlike existing compensation elements prepared using chemical deactivation processes, the compensation element of this invention does not introduce any deactivating agents or chemical residues, thus avoiding non-cooperative aging behavior caused by differences in material composition. Therefore, under continuous aging conditions, the resistance change direction and rate of change of the sensing element and the compensation element can remain consistent, thereby effectively maintaining the long-term balance of the bridge, significantly reducing sensor zero-point drift, and improving long-term measurement stability and reliability.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An assembled-free paired catalytic combustion sensor, characterized by, The sensor comprises a bracket, a detection element and a compensation element welded on the bracket. The detection element is made of an alumina-supported palladium nitrate and platinum nitrate catalyst. The compensation element is a composite ceramic body without catalyst, which is made of a mixture including alumina, silica, titania, diboron trioxide, sodium oxide, potassium oxide and zinc oxide. The metal mass ratio of the palladium nitrate and platinum nitrate is 2:1-4:

1.

2. The assembled-free paired catalytic combustion sensor according to claim 1, wherein, The composition of the composite ceramic body includes:

3. The assembled-free paired catalytic combustion sensor of claim 1, wherein, Alumina 65-80%, silica 8-11%, titania 4-8%, diboron trioxide 3-5%, sodium oxide 2-4%, potassium oxide 2-4%, and zinc oxide 1-3%. The alumina is γ-Al2O3.

4. The assembled-free paired catalytic combustion sensor according to claim 3, characterized in that, The detection element and the compensation element are both formed by dipping a coil of platinum wire in the corresponding slurry and then sintering by electric heating.

5. The assembled-free paired catalytic combustion sensor of claim 1, wherein, The diameter of the platinum wire is 0.025-0.035 mm, the coil of the platinum wire has 5-15 turns, the axial diameter of the coil of the platinum wire is 0.25-0.35 mm, and the length of the coil of the platinum wire is 0.50-0.90 mm. The sintered ball of the detection element has a radius of 0.35-0.45 mm.

6. The assembled-free paired catalytic combustion sensor according to claim 5, characterized in that, The sintered ball of the compensation element has a radius of 0.37-0.47 mm.

7. The assembled-free paired catalytic combustion sensor of claim 5, wherein, The sensor comprises a bracket, a detection element and a compensation element welded on the bracket.

8. A method of making an assembled pair of catalytic combustion sensors for making an assembled pair of catalytic combustion sensors according to any one of claims 1 to 7; characterized in that, S1, a preparation step of the detection element: Mix alumina with a palladium nitrate solution and a platinum nitrate solution to obtain a first mixture; Dry and grind the first mixture again to obtain a catalyst powder; Add an ethylene glycol solution to the catalyst powder to prepare a detection element slurry; Dip a coil of platinum wire in the detection element slurry, and solidify the detection element slurry on the surface of the coil of platinum wire by electric heating sintering to obtain the detection element; S2, a preparation step of the compensation element: Mix alumina, silica, titania, diboron trioxide, sodium oxide, potassium oxide and zinc oxide to obtain a second mixture; Dry and grind the second mixture again to obtain a mixed powder; Add an aluminum nitrate solution to the mixed powder to prepare a compensation element slurry; Dip a coil of platinum wire in the compensation element slurry, and solidify the compensation element slurry on the surface of the coil of platinum wire by electric heating sintering to obtain the compensation element; S3, a fusion preparation step of the sensor: Position the detection element and the compensation element at the preset installation positions of the bracket, and realize electric connection and mechanical fixation of the detection element and the compensation element with the bracket by welding process to complete the manufacture of the sensor. The mass concentration of the ethylene glycol solution used to prepare the detection element slurry is 10.0%-40.0%; 9. The method of claim 8, wherein the catalytic combustion sensor is prepared by a process comprising: The mass concentration of the aluminum nitrate solution used to prepare the compensation element slurry is 1.0%-10.0%. The step of electric heating sintering is:

10. The method of claim 8, wherein the catalytic combustion sensor is a catalytic combustion sensor for an off-board fuel cell power plant. ​ A current is applied to the platinum wire coil, so that the platinum wire coil itself generates heat by its own resistance and is heated to a red-hot state, thereby achieving sintering and forming of the attached slurry.

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