An assembled-free paired catalytic combustion sensor and a preparation method thereof

Abstract

The application relates to the technical field of gas sensors, and particularly discloses a catalytic combustion sensor free of assembly pairing and a preparation method thereof; the catalytic combustion sensor comprises a detection element, a compensation element and a supporting bracket, the detection element and the compensation element are welded side by side on the same bracket; the detection element is composed of a gamma-Al2O3 carrier loaded with a palladium nitrate and 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 catalyst, which is made of seven oxides such as alumina (65-80%) and silicon dioxide (8-11%) mixed in a specific ratio. During preparation, the detection element is formed by slurry prepared by mixing catalyst powder and ethylene glycol solution, platinum gold wire coil immersion and electric sintering; the compensation element is formed by slurry prepared by mixing composite oxide powder and aluminum nitrate solution, and the same coil and sintering process are adopted. The application realizes the natural matching of the initial resistances of the detection element and the compensation element by innovating the material system and the preparation process of the compensation element, and the traditional pairing process is completely saved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas sensor, in particular to a catalytic combustion sensor without assembly pairing and a preparation method thereof. BACKGROUND

[0002] The catalytic combustion type gas sensor has become an indispensable core device in the fields of industrial safety monitoring and environmental gas detection, due to its fast response speed, excellent combustible gas detection linearity and long service life. Its working principle is based on the Wheatstone bridge structure, and the core is to generate temperature change in the combustible gas catalytic combustion reaction through the detection element loaded with platinum, palladium and other noble metal catalysts, thereby causing the resistance value to change, and finally realizing the quantitative detection of gas concentration. In this bridge system, the detection element must be used in pairs with the reference compensation element, and the initial resistance values of the two must be highly matched to ensure the initial balance of the bridge and lay the foundation for subsequent accurate detection. Therefore, the resistance matching of the detection element and the compensation element is the key to determining the performance of the sensor.

[0003] However, achieving high-precision resistance matching between the two has been a fundamental problem faced by traditional catalytic combustion sensor technology for a long time. In theory, the compensation element should be a "white element" without catalyst, but the detection element changes its resistance characteristics significantly due to the loading of noble metal catalysts, which makes it impossible for the "white element" made of pure inert material to form resistance matching with the detection element. To solve this contradiction, the existing technology generally uses chemical deactivation treatment of the catalytic element to prepare the compensation element, that is, by immersing the detection element in a specific deactivator solution and then sintering to achieve loss of catalytic activity, thereby trying to make its resistance value closer to that of the detection element.

[0004] However, this chemical deactivation process has inherent defects, which not only fails to fundamentally solve the resistance matching problem, but also derives a series of chain problems:

[0005] First, the process fluctuation is extremely large. The concentration of deactivator, immersion time, immersion amount, sintering voltage and sintering time and other key parameters will significantly affect the final resistance value of the compensation element. A small deviation in any parameter can cause a large dispersion in the resistance value, making it difficult to achieve stable and consistent resistance characteristics.

[0006] Second, poor element consistency directly leads to low production efficiency. Since the resistance values of the prepared detection element and compensation element are scattered, they cannot be directly assembled and used, and a special testing, screening and manual pairing process must be added before assembly. This process is tedious and time-consuming, not only restricting the realization of automated production and the improvement of production capacity, but also causing a large amount of waste of elements that cannot be paired, significantly increasing the manufacturing cost.

[0007] Thirdly, the long-term reliability is insufficient. The compensation element and the detection element treated by chemical inactivation have essential differences in internal material structure and component characteristics. In the long-term working process of the sensor, the resistance drift trends of the two elements affected by environmental temperature fluctuations, current thermal effects and other factors are difficult to be synchronized, which leads to the destruction of the initial balance state of the electric bridge, causes the zero point drift of the sensor, and seriously affects the long-term measurement accuracy and use reliability.

[0008] In summary, the existing technology path for preparing the compensation element based on the chemical inactivation method has always failed to break through the core bottleneck of "resistance matching difficulty", and is accompanied by multiple problems such as complex process, poor element consistency, low production efficiency, and poor long-term stability, which cannot meet the needs of industrial production for high consistency, high efficiency preparation and long-term reliable use of the sensor. Therefore, a new technical solution that can realize the natural matching of the initial resistance of the detection element and the compensation element is urgently needed to solve the above technical problems from the root. SUMMARY

[0009] Therefore, the embodiments of the present application provide a catalytic combustion sensor free of assembly pairing and a preparation method thereof, to solve the technical problems in the prior art that the compensation element needs to be prepared by "chemical inactivation" of the catalytic element, but the introduction of the catalyst changes the resistance characteristics of the detection element, leading to the fact that the pure inert element cannot be matched, and the chemical inactivation process itself is difficult to control accurately, resulting in poor element resistance consistency and low initial matching degree.

[0010] In a first aspect, the embodiments of the present application provide a catalytic combustion sensor free of assembly pairing, comprising:

[0011] a support, and a detection element and a compensation element welded on the support;

[0012] The detection element is made of an alumina supported palladium nitrate and platinum nitrate catalyst;

[0013] The compensation element is a composite ceramic body without a catalyst, and the composite ceramic body is made of a mixture including alumina, silicon dioxide, titanium dioxide, diboron trioxide, sodium oxide, potassium oxide and zinc oxide.

[0014] Preferably, the metal mass ratio of the palladium nitrate and the platinum nitrate is 2:1 to 4:1.

[0015] Preferably, the composition of the composite ceramic body includes:

[0016] alumina 65-80%, silicon dioxide 8-11%, titanium dioxide 4-8%, diboron trioxide 3-5%, sodium oxide 2-4%, potassium oxide 2-4%, and zinc oxide 1-3%.

[0017] Preferably, the alumina is γ-Al2O3.

[0018] Preferably, the detection element and the compensation element are both formed by dipping a coil of platinum wire into a corresponding slurry and then sintering by electric current;

[0019] Preferably, the diameter of the platinum wire is 0.025-0.035 mm, the coil of the platinum wire is 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.

[0020] Preferably, the radius of the sintered ball of the detection element is 0.35-0.45 mm.

[0021] Preferably, the radius of the sintered ball of the compensation element is 0.37-0.47 mm.

[0022] In a second aspect, a preparation method of a catalytic combustion sensor without assembly and pairing is provided, which is used to prepare the catalytic combustion sensor without assembly and pairing described above; the preparation method comprises the following steps:

[0023] S1, a preparation step of a detection element:

[0024] Alumina is mixed and ground with a palladium nitrate solution and a platinum nitrate solution to obtain a first type of mixture;

[0025] The first type of mixture is dried and ground again to obtain a catalyst powder;

[0026] An ethylene glycol solution is added to the catalyst powder to form a detection element slurry;

[0027] A coil of platinum wire is dipped into the detection element slurry for dipping, and the detection element slurry is solidified on the surface of the coil of platinum wire by sintering by electric current, thereby obtaining a detection element;

[0028] S2, a preparation step of a compensation element:

[0029] Alumina, silicon dioxide, titanium dioxide, diboron trioxide, sodium oxide, potassium oxide, and zinc oxide are mixed and ground to obtain a second type of mixture;

[0030] The second type of mixture is dried and ground again to obtain a mixed powder;

[0031] An aluminum nitrate solution is added to the mixed powder to form a compensation element slurry;

[0032] A coil of platinum wire is dipped into the compensation element slurry for dipping, and the compensation element slurry is solidified on the surface of the coil of platinum wire by sintering by electric current, thereby obtaining a compensation element;

[0033] S3, the fusion preparation step of the sensor:

[0034] The detection element and the compensation element are respectively positioned and arranged at the preset mounting position of the support, and the detection element and the compensation element are electrically connected and mechanically fixed with the support through a welding process, so that the manufacturing of the sensor is completed.

[0035] Preferably, the mass concentration of the ethylene glycol solution used to prepare the detection element slurry is 10.0% to 40.0%;

[0036] The mass concentration of the aluminum nitrate solution used to prepare the compensation element slurry is 1.0% to 10.0%.

[0037] Preferably, the step of electrically sintering is:

[0038] An electric current is applied to the platinum wire coil, so that the resistance of the platinum wire coil itself generates heat and heats to a red-hot state, thereby realizing sintering and forming of the attached slurry.

[0039] The catalytic combustion sensor and the preparation method thereof provided by the application have the following beneficial effects:

[0040] The application realizes natural and accurate matching of initial resistance values of the detection element and the compensation element from the root, completely eliminates the cumbersome testing, screening and manual pairing process in the traditional process, greatly improves the production efficiency and product consistency, avoids resource waste caused by invalid elements, and significantly reduces the manufacturing cost; the compensation element does not need to use a noble metal catalyst and discards the chemical deactivation process, which reduces the raw material cost and process energy consumption, eliminates the material structure difference caused by the residual deactivator, makes the resistance drift trend of the detection element and the compensation element highly cooperative, effectively suppresses the zero point drift of the sensor, significantly improves the long-term measurement accuracy and use reliability, and provides an efficient solution for automatic and large-scale production and high-precision and stable application of the catalytic combustion sensor. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed in the embodiments of the application will be briefly introduced below. For those skilled in the art, other drawings can also be obtained on the premise of not creating labor, and these are within the protection scope of the application.

[0042] Figure 1 : Comparison chart of qualified rate of sensor zero point output voltage after the detection element and the compensation element of the comparative example and each embodiment of the application are randomly welded to the same support to form a sensor;

[0043] Figure 2 Zero-point change graph of the sensor described in Example and Comparative Example 1 after being charged for one month. DETAILED DESCRIPTION

[0044] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. It should be noted that in this document, relational terms such as first and second and the like are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In the description of the present application, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application and simplify the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. Moreover, the terms "comprise", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or further includes elements inherent in such a process, method, article or device. Without more limitations, the elements defined by the statement "comprise" do not exclude the presence of other identical elements in the process, method, article or device that includes the elements. If there is no conflict, the embodiments of the present application and the various features in the embodiments can be combined with each other, and all within the scope of protection of the present application.

[0045] Example 1

[0046] The embodiments of the present application provide a preparation method of an assembled and paired catalytic combustion sensor, comprising:

[0047] Preparation of the detection element:

[0048] (1) Preparation of the catalyst powder:

[0049] Preparation of the precursor solution:

[0050] Accurately weigh 5.00 g of palladium nitrate (Pd (NO3) 2), place it in a 100 ml volumetric flask, dissolve it with deionized water and dilute to the mark, and shake well to obtain a palladium nitrate stock solution with a concentration of 50 mg / ml.

[0051] Another 1.26 g of platinum nitrate (Pt (NO3)2) was accurately weighed into a 100 ml volumetric flask, dissolved with deionized water and diluted to the mark and shaken well to prepare a platinum nitrate stock solution with a concentration of 12.6 mg / ml.

[0052] Equal volume co-impregnation and post-treatment:

[0053] 2.00 ml of the palladium nitrate stock solution and 2.00 ml of the platinum nitrate stock solution were measured and mixed, and then used for equal volume impregnation on 1.00 g of spherical alumina carrier.

[0054] The impregnated material was allowed 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 prepare a Pd-Pt / Al2O3 catalyst with a Pd:Pt mass ratio of about 3:1, i.e. a first type of mixture, and the first type of mixture was ground to obtain a catalyst powder.

[0055] (2) Preparation of slurry and loading of coil:

[0056] Preparation of catalyst slurry:

[0057] 0.5 g of the Pd-Pt / Al2O3 catalyst powder prepared above was weighed and mixed with 2.0 ml of a 30% mass concentration ethylene glycol aqueous solution, and stirred until a uniform, non-granular, viscous slurry was formed.

[0058] Treatment and dipping of platinum-gold wire coil:

[0059] A platinum-gold wire coil with a wire diameter of 0.03 mm, a number of turns of 11, a shaft diameter of 0.30 mm, and a length of 0.60-0.70 mm was immersed in the above catalyst slurry, slowly taken out, and the slurry was evenly attached to the surface of the coil.

[0060] Electric heating forming:

[0061] The platinum-gold wire coil dipped with the catalyst slurry was connected to an adjustable direct current or alternating current power supply at both ends.

[0062] The voltage and current were adjusted so that the platinum-gold wire coil gradually heated to a red-hot state (estimated temperature 600-800°C) within 60 s and maintained this state for 10 s.

[0063] During this process, the water and ethylene glycol in the slurry evaporated and burned rapidly, and the catalyst coating was sintered to form a firm porous catalytic layer on the surface of the coil.

[0064] After the coil cooled down, the final coil type Pd-Pt / Al2O3 structured catalyst was obtained.

[0065] Preparation of compensating element:

[0066] (1) Preparation of compensation material powder:

[0067] Batching and mixing:

[0068] The raw materials are weighed according to the following mass percentages: alumina (γ-Al2O3) 65%, silicon dioxide (SiO2) 11%, titanium dioxide (TiO2) 8%, diboron trioxide (B2O3) 5%, sodium oxide (Na2O) 4%, potassium oxide (K2O) 4%, and zinc oxide (ZnO) 3%. The weighed powder raw materials are placed in a mortar together, and an appropriate amount of deionized water is added as a dispersion medium. The mixture is ground thoroughly for more than 2 hours until it is uniform and has no particle feel.

[0069] Drying and crushing:

[0070] The ground slurry is placed in an oven at 120°C and dried for 6 hours to completely remove the water.

[0071] The dried blocky material (i.e., the second mixture) is crushed with a mortar and passed through a 200-mesh screen to obtain a uniform composition of the compensation material mixed powder.

[0072] (2) Preparation of compensation element slurry and coil loading:

[0073] Slurry preparation:

[0074] 1.0 g of the above-prepared compensation material mixed powder is weighed and slowly added to an aluminum nitrate (Al(NO3)3·9H2O) aqueous solution with a mass fraction of 2.0%. The mixture is stirred continuously to prepare a slurry with appropriate viscosity and good coating properties.

[0075] The amount of aluminum nitrate solution added is just enough to form a uniform and coatable slurry. Typically, the mass-to-volume ratio of the powder to the solution is in the range of 1 g: 0.8-1.2 ml.

[0076] Immersion and electrical sintering:

[0077] A platinum wire coil of the same specification as the detection element is used to immerse in the above compensation material slurry, slowly pulled out, and the slurry is evenly attached to the surface of the coil. Then, the coil is connected to the power supply and sintered and formed using the same heating method as the detection element.

[0078] In this process, the water in the slurry evaporates, the aluminum nitrate decomposes into alumina, and the mixed oxide powder is sintered into one body, forming a dense and firm compensation element layer on the surface of the coil. After the coil cools down, the final compensation element is obtained.

[0079] Sensor preparation:

[0080] (1) Element welding:

[0081] The platinum wire leads of the detection element and the compensation element are directly and side by side welded on the corresponding pins of the same integral sensor holder.

[0082] The holder is a standard, two-element supporting integral structure.

[0083] (2) Covering the cap:

[0084] Covering the cap on the holder after welding, and obtaining the complete sensor.

[0085] Comparative Example 1

[0086] Preparation of the detection element: exactly the same as Example 1.

[0087] Preparation of the compensation element: prepared after the deactivation of the detection element of Example 1 by a deactivator.

[0088] Comparative Example 2

[0089] Preparation of the detection element: exactly the same as Example 1.

[0090] Preparation of the compensation element: only 1.00 g of alumina (without catalyst loading) is used to prepare the slurry, and the remaining steps are the same as Example 1.

[0091] Example 2

[0092] Preparation of the detection element: exactly the same as Example 1.

[0093] Preparation of the compensation element: the ratio of the mixed powder is: alumina 70%, silicon dioxide 10%, titanium dioxide 8%, diboron trioxide 4%, sodium oxide 3%, potassium oxide 3%, zinc oxide 2%.

[0094] Example 3

[0095] Preparation of the detection element: exactly the same as Example 1.

[0096] Preparation of the compensation element: the ratio of the mixed powder is: alumina 75%, silicon dioxide 9%, titanium dioxide 6%, diboron trioxide 4%, sodium oxide 2%, potassium oxide 2%, zinc oxide 2%.

[0097] Example 4

[0098] Preparation of the detection element: exactly the same as Example 1.

[0099] Preparation of the compensation element: the ratio of the mixed powder is: alumina 80%, silicon dioxide 8%, titanium dioxide 4%, diboron trioxide 3%, sodium oxide 2%, potassium oxide 2%, zinc oxide 1%.

[0100] Performance test and result analysis

[0101] Test 1, free assembly matching effect test

[0102] To verify the superiority of the composition design of the compensation element, comparative experiments were conducted. The detection elements and compensation elements of each example 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 qualified standard is ± 30 mV).

[0103] The results are shown in Table 1. Figure 1 Comparative example 1 used the traditional chemical inactivation method to process the detection element to prepare the compensation element, and the zero point qualified rate of the sensor directly welded was only 30%; comparative example 2 used a pure inert compensation element with an aluminum oxide main body and no catalyst and specific composite oxides, and the zero point qualified rate was further reduced to 5%. In contrast, the sensor zero point qualified rate of each example using the specific composite oxide material system provided by the present application is stable at more than 90%.

[0104] The above experimental results form a clear gradient, fully proving that compared with the prior art, the present application can very effectively realize the initial resistance value matching between the detection element and the compensation element by precisely targeted design on the composition of the compensation element. This not only fundamentally solves the bottleneck problem that the traditional process must rely on post-screening matching, achieves the industrialization effect of "free assembly matching", and further highlights the significant process superiority and industrialization value of the present application in improving product consistency, production efficiency and qualified rate.

[0105] Test 2, long-term running stability test

[0106] To evaluate the long-term running reliability of the sensor, the sensor of each example and comparative example 1 was subjected to a one-month continuous power aging test.

[0107] The results are shown in Table 2. Figure 2 The test results show that the zero point drift of the sensor of each example of the present application is stable in an extremely narrow range of ± 3 mV; in contrast, the zero point drift of the sensor of comparative example 1 (traditional chemical inactivation method) reaches -6 mV, and its stability is significantly inferior to that of the present application.

[0108] This achievement has double key significance. First of all, it proves the synergistic effect of material design. The results show that even without a noble metal catalyst, the composite oxide compensation element of the present application with precise proportioning design can still achieve high synergy with the noble metal catalytic detection element in terms of resistance temperature coefficient and long-term aging characteristics, thereby ensuring the persistent stability of the bridge output.

[0109] Second, it breaks through the core bottleneck of traditional technology, and solves the difference in microstructure and composition between the compensation element and the detection element caused by the chemical inactivation process of the traditional sensor, thereby completely overcoming the performance asynchronous decay and zero drift problems. This provides reliable technical support for the high-precision, long-term maintenance-free operation of the sensor.

[0110] Embodiment 5

[0111] The embodiment of the present application provides a catalytic combustion sensor without assembly pairing. In view of the shortcomings of the prior art, the purpose of the present application is to provide a catalytic combustion gas sensor. The initial resistance values of the detection element and the compensation element in the sensor are naturally matched, and assembly pairing can be realized without assembly pairing, thereby simplifying the production process, improving efficiency and product consistency.

[0112] The catalytic combustion sensor comprises a support, and a detection element and a compensation element welded on the support; the detection element is made of an alumina carrier loaded with palladium nitrate and platinum nitrate catalyst; the compensation element is a composite ceramic body without catalyst, and the composite ceramic body is made of a mixture comprising alumina, silicon dioxide, titanium dioxide, diboron trioxide, sodium oxide, potassium oxide and zinc oxide.

[0113] In the embodiment, a catalytic combustion sensor without assembly pairing comprises a support and a detection element and a compensation element welded on the support. The detection element and the compensation element do not need to be subjected to resistance testing, screening or manual pairing after being prepared, and can be directly welded on the same support to form a sensor, thereby realizing a manufacturing method without assembly pairing.

[0114] The detection element is made of an alumina carrier loaded with palladium nitrate and platinum nitrate catalyst, which can catalyze the combustion reaction of combustible gas in the energized working state, and the temperature of the element is raised due to the heat released by the reaction, so that the resistance value changes, serving as a gas detection unit of the sensor.

[0115] The compensation element does not participate in the catalytic reaction of combustible gas in the sensor, and its main role is to serve as a reference arm in the electric bridge, which is used to offset the influence of non-gas factors such as environmental temperature change and power fluctuation on the detection signal, so as to ensure the stability and accuracy of the sensor output signal.

[0116] From the resistance composition mechanism, the total resistance of the catalytic combustion type detection element is not only determined by the platinum gold coil body resistance, but also includes the equivalent resistance of the porous structure formed by the noble metal catalyst layer loaded on the surface of the alumina carrier, and the interface contact resistance between the platinum gold wire and the ceramic layer. Therefore, the resistance characteristics of the detection element are the composite resistance characteristics formed by the joint action of multiple factors, rather than a single metal resistance.

[0117] In the present embodiment, the compensation element is not simply made of pure inert ceramic material, but is designed through a specific inorganic composite oxide system. Alumina serves as the main framework phase, providing stable structural support and thermal stability for the compensation element; boron trioxide, sodium oxide and potassium oxide form a glass phase during the sintering process, which can adjust the micro-contact state between ceramic particles and stabilize the conductive path; titanium dioxide and zinc oxide serve as weakly conductive or semi-conductive phases, introducing temperature-sensitive resistance contribution, so that the compensation element as a whole forms a composite conductive network structure composed of framework phase, glass phase and weakly conductive phase. Through the above material system design, the number, distribution pattern and response characteristics of the conductive paths formed after the sintering of the compensation element are matched with the conductive structure formed by the noble metal catalytic layer in the detection element in terms of equivalent resistance formation mechanism, so that the resistance characteristics of the compensation element can be consistent with those of the detection element.

[0118] Based on the above structural and material mechanism design, after the preparation of the sensor, the initial resistance values of the detection element and the compensation element can be naturally matched, without the need for subsequent resistance testing, screening or manual pairing for direct assembly and use, which fundamentally eliminates the manufacturing link of "assembly pairing" in the prior art. In this way, on the one hand, the production process of the sensor is significantly simplified, the manual intervention and manufacturing cost are reduced, and the production efficiency and batch consistency are improved; on the other hand, since the compensation element does not contain a catalyst and has not been subjected to chemical inactivation treatment, it avoids the long-term instability factors caused by the residual of the inactivator and the difference in material structure, so that the resistance change trends of the detection element and the compensation element remain consistent during long-term energization, effectively inhibiting the bridge zero drift, and improving the long-term measurement stability and use reliability of the sensor.

[0119] Compared with the traditional technical solution of preparing a compensation element by chemical inactivation method, the present embodiment realizes the natural matching of the resistance characteristics of the detection element and the compensation element without introducing a catalyst and inactivation process through the targeted design of the material system and the conductive mechanism, which solves the problems of resistance matching difficulty, large process fluctuation and poor consistency in the prior art from the theoretical and structural aspects.

[0120] The key innovation of the present application is that, through the accurate design and synergistic regulation of the material composition of the compensation element, its resistance characteristics are pre-matched with the detection element loaded with a catalyst, thereby realizing "pairing-free". Specifically: the same alumina as the detection element is used as the structural matrix, ensuring the consistency of the thermal expansion coefficient and long-term stability; by introducing silicon dioxide, titanium dioxide, zinc oxide and other wide-bandgap high-resistance phases, the intrinsic resistance of the composite ceramic body is improved; at the same time, alkali metal oxides such as sodium oxide and potassium oxide are innovatively added as charge compensation and grain boundary modifiers, which can adjust the carrier concentration and grain boundary barrier during sintering, thereby realizing fine "tuning" of the resistivity. Boron trioxide as a cosolvent and glass phase former promotes sintering densification and microstructure uniformity, thereby "locking" the pre-set resistance value. By optimizing the proportion of each component, the initial resistance value and temperature coefficient (TCR) of the compensation element can be pre-set in a narrow band highly matched with the target detection element, thereby fundamentally replacing the chemical inactivation and manual screening steps in the traditional process.

[0121] Further, the metal mass ratio of the palladium nitrate and platinum nitrate is 2:1-4:1.

[0122] The composition of the composite ceramic body includes: 65-80% (mass percent) of alumina, 8-11% (mass percent) of silicon dioxide, 4-8% (mass percent) of titanium dioxide, 3-5% (mass percent) of boron trioxide, 2-4% (mass percent) of sodium oxide, 2-4% (mass percent) of potassium oxide, and 1-3% (mass percent) of 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 pairing.

[0123] In the present embodiment, the catalyst used by the detection element is composed of palladium nitrate and platinum nitrate loaded on the surface of an alumina carrier, and the metal mass ratio of the palladium nitrate and platinum nitrate is controlled in the range of 2:1-4:1. By limiting the above mass ratio, the resistance change characteristics of the detection element under the power-on working state are in a stable and controllable range while maintaining high catalytic activity, thereby providing basic conditions for the resistance matching between the detection element and the compensation element.

[0124] Specifically, palladium as the main catalytically active component plays a leading role in the catalytic combustion reaction of combustible gas; the introduction of platinum is used to adjust the thermal stability and electrical conductivity of the catalytic layer. When the mass ratio of palladium nitrate and platinum nitrate is lower than the above range, the overall electrical conductivity and thermal response characteristics of the catalytic layer deviate, which easily leads to low resistance or unstable temperature response of the detection element; when the mass ratio is higher than the above range, the resistance contribution of the catalytic layer increases, and the discreteness between different batches increases, which is not conducive to the natural matching with the compensation element. Limiting the mass ratio of palladium nitrate and platinum nitrate to the range of 2:1 to 4:1 can make the detection element obtain stable catalytic performance while keeping the equivalent resistance composition and resistance temperature response characteristics within the matching interval.

[0125] In terms of the compensation element, the compensation element is a composite ceramic body without catalyst, which includes, in terms of mass percentage, 65-80% of alumina, 8-11% of silicon dioxide, 4-8% of titanium dioxide, 3-5% of diboron trioxide, 2-4% of sodium oxide, 2-4% of potassium oxide, and 1-3% of zinc oxide, wherein the alumina is preferably γ-Al2O3.

[0126] In the above composition, γ-Al2O3 as the main skeleton phase provides the compensation element with a stable porous structure and good thermal stability, so that the compensation element maintains long-term stability in structure and size during the power-on working process; silicon dioxide, diboron trioxide, sodium oxide, and potassium oxide form a glass phase during the power-on sintering process, which is used to adjust the sintering density, stabilize the micro-contact state between particles, and inhibit the random fluctuation of the conductive path; titanium dioxide and zinc oxide as weakly conductive or semiconductive phases form temperature-sensitive resistance contribution paths between the alumina skeletons, so that the compensation element presents similar resistance change behavior to the detection element during the heating process.

[0127] Through the synergistic limitation of the proportion of each component, the compensation element forms a composite conductive network composed of skeleton phase, glass phase, and weakly conductive phase after sintering and shaping, and its equivalent resistance source and resistance temperature response characteristics can be matched with the conductive structure formed by the palladium-platinum catalytic layer in the detection element.

[0128] Based on the above catalyst proportion design of the detection element and the composite ceramic composition design of the compensation element, after the preparation of the detection element and the compensation element is completed, the initial resistance values of the two can naturally fall within the same matching interval, without the need for subsequent resistance testing, screening, or manual pairing, and can be directly welded on the same bracket to form a sensor.

[0129] Therefore, not only the cumbersome "assembly pairing" process in the prior art is fundamentally saved, the production efficiency and product consistency of the sensor are significantly improved, and the manufacturing cost is reduced, but also the resistance change trend of the detection element and the compensation element under the long-term energized working condition is consistent due to the fact that the compensation element does not contain a catalyst and is not subjected to a chemical inactivation treatment, the sensor zero drift is effectively inhibited, and the long-term stability and use reliability of the sensor are further improved.

[0130] In the present application, the traditional pure alumina or chemically inactivated compensation element scheme is abandoned, seven oxides such as alumina, silica, titanium dioxide, etc. are selected in a targeted manner and set to a specific mass ratio, and through the synergistic effect of multi-oxide, the core electrical properties such as room temperature resistivity and resistance temperature coefficient of the compensation element are precisely controlled. The resistance characteristics of the composite system are designed to be highly compatible with the "γ-Al2O3 supported Pd-Pt catalyst" detection element, which not only offsets the influence of noble metal catalyst in the detection element on the resistance, but also through the fluxing and structure adjusting effect of components such as silicon dioxide and boron trioxide, the resistance base of the compensation element and the detection element form a natural adaptation, realizing resistance matching from the material essence.

[0131] Further, the detection element and the compensation element are both formed by dipping a platinum wire coil into the corresponding slurry and then sintering by energization; wherein the diameter of the platinum wire is 0.025-0.035mm, the number of turns of the platinum wire coil is 5-15, the axial diameter of the platinum wire coil is 0.25-0.35mm, and the length of the platinum wire coil is 0.50-0.90mm.

[0132] Further, the radius of the sintered ball of the detection element is 0.35-0.45mm. The radius of the sintered ball of the compensation element is 0.37-0.47mm.

[0133] In the present embodiment, the detection element and the compensation element both use a platinum wire coil as a heating and conducting framework, and by dipping the platinum wire coil into the corresponding detection element slurry or compensation element slurry and then sintering by energization, an integrally formed spherical structure is formed.

[0134] The diameter of the platinum wire is controlled within the range of 0.025-0.035mm, the number of turns of the platinum wire coil is 5-15, the axial diameter of the platinum wire coil is 0.25-0.35mm, and the length of the platinum wire coil is 0.50-0.90mm. Through the synergistic limitation of the above platinum wire diameter and coil geometric parameters, the platinum wire coil can meet the requirements of stable heating, uniform heat conduction and repeatable resistance output under energized conditions.

[0135] Specifically, if the diameter of the platinum wire is less than the above range, the risk of heat concentration or ablation due to excessive local current density during energization is easy to occur, resulting in unstable coil resistance; if the diameter of the platinum wire is greater than the above range, the overall resistance value is reduced and the thermal inertia is increased, which is not conducive to the matching of the resistance interval between the detection element and the compensation element. Limiting the diameter of the platinum wire to the range of 0.025-0.035 mm can make the coil body resistance become a stable reference item in the resistance composition of the detection element and the compensation element.

[0136] The number of turns, the diameter and the length of the coil together determine the spatial distribution density and the effective heat conduction path of the platinum wire inside the sphere. When the number of turns is controlled to be 5-15 turns, the diameter is 0.25-0.35 mm, and the length is 0.50-0.90 mm, the platinum wire coil can form a three-dimensional heat conduction skeleton uniformly embedded in the interior of the sphere after sintering of the slurry, so that a relatively consistent temperature field is formed in the sphere during energization and heating, thereby ensuring that the detection element and the compensation element have similar thermal response characteristics in the working state.

[0137] In terms of sintering and forming, the detection element forms a spherical structure after being energized and sintered, with a spherical radius controlled to be 0.35-0.45 mm; the compensation element forms a spherical structure after being energized and sintered, with a spherical radius controlled to be 0.37-0.47 mm. By limiting the size interval of the two types of spheres and making the spherical 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 thermal capacity of the two are similar.

[0138] From a mechanism point of view, the spherical radius directly affects the length of the conductive path, the pore structure and the heat diffusion capacity after sintering of the slurry. In the detection element, due to the presence of the catalyst, the sphere will generate additional heat when participating in the catalytic combustion reaction of the gas; the compensation element obtains similar thermal response delay and resistance change trend by slightly larger spherical size without participating in the catalytic reaction, thereby realizing the thermal-electric behavior compensation with the detection element at the overall structure level.

[0139] Based on the synergistic design of the above platinum wire coil structure parameters, the impregnation and energization sintering process, and the sphere size, the resistance value of the detection element and the compensation element after preparation is determined by the platinum wire coil body resistance, the conductive network formed by the sintered slurry, and the sphere geometry, and the determining factors have high consistency between the two types of elements. Therefore, the initial resistance values of the two can naturally fall into the expected matching interval, without the need for additional resistance screening or manual pairing, and the assembly can be completed directly.

[0140] Therefore, not only the consistency and long-term stability of the electrical performance between batches of sensors are ensured, but also the repeatability and engineering feasibility of the "assembly-free pairing" technical solution are further strengthened, thereby providing a reliable structure and process basis for realizing large-scale automatic production.

[0141] Specifically, from the perspective of resistance formation mechanism, the total resistance of the catalytic combustion type detection element is jointly determined by the platinum wire body resistance, the platinum wire and ceramic layer interface contact resistance, and the equivalent resistance of the porous structure formed by the noble metal catalyst layer. The traditional pure inert compensation element is almost not involved in the conduction, and its resistance formation mechanism is essentially different from that of the detection element, so it is difficult to achieve initial resistance matching.

[0142] The present application introduces a composite ceramic system composed of alumina skeleton phase, glass phase and weak conductive phase into the compensation element, so that the compensation element forms a conductive path structure equivalent to the catalytic layer in the detection element after sintering. Combined with the homology of the detection element and the compensation element in platinum wire specifications, sintering methods and manufacturing processes, the total resistance formation model of the two is consistent, which theoretically ensures the high matching of the initial resistance values of the detection element and the compensation element. This matching can be naturally achieved without subsequent screening or assembly pairing.

[0143] Further, since the initial resistance values of the detection element and the compensation element are highly matched, the necessity of subsequent resistance matching screening is fundamentally eliminated, the cumbersome assembly pairing process in the prior art is omitted, the production efficiency and product consistency are greatly improved, and the manufacturing cost is reduced. The compensation element does not use noble metal catalyst at all, which directly reduces the raw material cost; the simplified process flow also reduces energy consumption and working hours. Since the compensation element is a true "white element" and does not introduce a chemical deactivator, the resistance drift trends of the two caused by factors such as environmental temperature fluctuations and current heat effects are synchronized during long-term powered operation of the sensor, effectively inhibiting the bridge imbalance caused by the difference in element characteristics, thereby significantly improving the long-term measurement stability and reliability of the sensor.

[0144] Further, the composite ceramic body of the compensation element forms a composite conductive network structure composed of alumina skeleton phase, glass phase and weak conductive phase after powered sintering, and the composite conductive network matches the conductive structure formed by the noble metal catalyst layer in the detection element in terms of equivalent resistance source and conductive path distribution, so that the initial resistance values of the compensation element and the detection element are naturally matched.

[0145] In the present embodiment, the compensation element is not simply composed of a single insulating material, but a composite ceramic structure with equivalent conductive behavior is constructed through the synergistic proportioning of multiple inorganic oxides and the powered sintering process.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] In the embodiment, the detection element and the compensation element not only achieve resistance matching in the initial state, but also can keep consistency of resistance change behavior under long-term energized operation condition.

[0154] Specifically, the detection element and the compensation element both use platinum wire coils of the same specification as the carrier, and the functional material is directly solidified on the surface of the coil through the energized sintering process. Due to the high consistency of the two in the structural carrier, the sintering method and the inorganic material system, the resistance change mechanism mainly derived from the stabilization process of the platinum wire microstructure and the densification process of the ceramic layer tending to saturation in the long-term energized process.

[0155] Unlike the compensation element prepared by the existing chemical inactivation process, the compensation element of the present application does not introduce any inactivator or chemical residue, avoiding the non-synergistic aging behavior caused by the difference in material composition. Therefore, under the condition of continuous energized aging, the resistance change direction and rate of the detection element and the compensation element can remain consistent, thereby effectively maintaining the long-term balance of the bridge, significantly reducing the sensor zero drift, and improving the long-term measurement stability and use reliability.

[0156] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A catalytic combustion sensor that does not require assembly and pairing, characterized in that, include: 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; 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%; 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. 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. 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.

2. The catalytic combustion sensor without assembly and pairing according to claim 1, characterized in that, The mass ratio of palladium nitrate to platinum nitrate is 2:1 to 4:

1.

3. The catalytic combustion sensor without assembly and pairing according to claim 1, characterized in that, The alumina is γ-Al2O3.

4. A method for preparing a catalytic combustion sensor that does not require assembly and pairing, used to prepare a catalytic combustion sensor that does not require assembly and pairing as described in any one of claims 1-3; characterized in that, include: 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.

5. The method for preparing the assembly-free catalytic combustion sensor according to claim 4, characterized in that, The mass concentration of the ethylene glycol solution used to prepare the slurry for 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%.

6. The method for preparing the assembly-free catalytic combustion sensor according to claim 4, characterized in that, 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.

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