A high-temperature-resistant thick-film type humidity-sensitive element for a steam oven and a preparation process thereof

Abstract

The application discloses a preparation process of a high-temperature-resistant thick-film type humidity-sensitive element for a steam oven, and steps are as follows: (1) preparation of humidity-sensitive resistor powder; (2) preparation of humidity-sensitive thick-film paste; (3) preparation of thick-film humidity-sensitive resistor; and (4) preparation of humidity-sensitive element. The application has the following beneficial effects: 1. The high-temperature-resistant thick-film type humidity-sensitive element prepared by the application has stable working performance under high temperature and high humidity; 2. The high-temperature-resistant thick-film type humidity-sensitive element prepared by the application has good high-temperature-resistant performance; and 3. The high-temperature-resistant thick-film type humidity-sensitive element prepared by the application does not generate organic volatile substances and harmful impurities during use, and has high food contact safety.

Description

Technical Field

[0001] This invention discloses a high-temperature resistant thick-film humidity-sensitive element for steam ovens and its preparation process. Background Technology

[0002] Steam ovens, as a new type of kitchen appliance that combines steam cooking and hot air baking, have been widely used in home kitchens, central kitchens, chain restaurants and food industrial processing fields due to their combined cooking characteristics of "low temperature to lock in freshness and high temperature to crisp bake". They can retain the nutritional components of food to the maximum extent (such as vitamin C retention rate is more than 30% higher than traditional baking) and restore the original flavor of food.

[0003] The core of the cooking effect of a steam cooking oven depends on the precise closed-loop control of the internal humidity (usually within ±3%RH accuracy). As the core detection element of this control system, the performance of the humidity sensor directly determines the intelligence level, energy efficiency ratio and cooking effect stability of the steam cooking oven.

[0004] Furthermore, there is still no mature solution for humidity-sensitive elements used in steam cooking ovens, given their unique coupled working environment characterized by high temperatures (operating temperature 50–200℃, self-cleaning temperature 400–450℃), high humidity (70–90%RH), significant steam condensation, and abundant oil fumes and impurities. Existing humidity-sensitive elements have the following shortcomings: ① Insufficient high-temperature resistance – Self-cleaning failure: During steam cooking, volatile oils, sauce vapors, and protein decomposition products from the food form an organic dirt layer inside the oven cavity and on the sensor surface. To achieve the self-cleaning function, steam cooking ovens need to periodically start a high-temperature pyrolysis program (400–450℃, for 30–60 minutes). Currently available polymeric moisture-sensitive materials (such as polyimide, cellulose acetate butyrate, etc.) generally have glass transition temperatures below 200℃. At high temperatures of 400–450℃, they are prone to thermal decomposition, carbonization, or matrix softening, leading to irreversible degradation of the moisture-sensitive characteristics of the moisture-sensitive element, failing to meet the long-term stability requirements under the "cooking-cleaning" cycle.

[0005] ② Deterioration of humidity sensing characteristics in high humidity areas - lack of accuracy and repeatability: In the actual working temperature range (50~200℃) and high humidity range (70%RH~90%RH) of steam cooking ovens, existing ceramic humidity-sensitive materials (such as spinel-based ceramic materials and perovskite-based ceramic materials) generally suffer from sensitivity decay and condensation corrosion under high temperature and high humidity, and cannot be used stably for a long time.

[0006] ③ Food safety compliance risks: As a component that shares the internal environment with food, the materials of humidity sensors must comply with element leaching limits and meet the migration limits for heavy metals (Pb, Cd, As, etc.) stipulated in GB 4806.9-2016 "Metallic Materials and Articles for Food Contact" and / or EU (EC) No 1935 / 2004. Under operating conditions above 400°C, the materials must not release toxic or harmful gases (such as halogens, sulfides, nitrogen oxides, etc.). Existing humidity sensors primarily focus on electrical performance, lacking a systematic assessment and design for food contact safety. Summary of the Invention

[0007] Purpose of the invention: In view of the above-mentioned defects of the prior art, the present invention aims to provide a high-temperature resistant thick film type humidity-sensitive element for steam ovens and its preparation process. It can withstand self-cleaning high temperature of 400℃, has good repeatability of humidity changes in high humidity of 70%RH~90%RH, has high sensitivity of thick film structure, and is safe for food contact, thus meeting the requirements of working in special environments in steam ovens.

[0008] Technical solution: A process for preparing a high-temperature resistant thick-film humidity-sensitive element for a steam oven, comprising the following steps: (1) Preparation of humidity-sensitive resistor powder; (2) Preparation of wet-sensitive thick film slurry; (3) Preparation of thick film humidity-sensitive resistors; (4) Preparation of humidity-sensitive element.

[0009] A high-temperature resistant thick-film humidity-sensitive element for steam ovens is prepared by any one of the above-described preparation processes.

[0010] Beneficial Effects: The high-temperature resistant thick-film humidity-sensitive element for steam ovens and its preparation process disclosed in this invention have the following beneficial effects: 1. The high-temperature resistant thick-film humidity-sensitive element for steam ovens prepared by this invention has stable working performance under high temperature and high humidity conditions; 2. The high-temperature resistant thick-film type humidity-sensitive element prepared by this invention has good high-temperature resistance for use in steam ovens; 3. The high-temperature resistant thick film type humidity-sensitive element prepared by this invention for use in steam ovens will not produce volatile organic compounds or harmful impurities during use, and has high food contact safety. Attached Figure Description

[0011] Figure 1 This is a flowchart of the preparation process of a high-temperature resistant thick-film humidity-sensitive element for a steam oven, as disclosed in this invention.

[0012] Figure 2 This is a schematic diagram showing the electrical test results of the humidity-sensitive element prepared in Example 1.

[0013] Figure 3 This is a schematic diagram of the high-temperature resistance test results of the humidity-sensitive element prepared in Example 1. Detailed Implementation

[0014] The specific embodiments of the present invention are described in detail below.

[0015] The "range" disclosed in this invention is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 10–50 is listed for a specific parameter, it is also expected that ranges of 10–40 and 20–50 are also included. Furthermore, if the minimum range values ​​are 1 and 2, and the maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0–5" means that all real numbers between "0–5" have been listed herein; "0–5" is merely a shortened representation of these numerical combinations.

[0016] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0017] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0018] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0019] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0020] Unless otherwise specified, the reaction will proceed under normal temperature and pressure conditions.

[0021] Unless otherwise specified, all parts or percentages are by weight or by weight percentage.

[0022] In this invention, all the substances used are known substances that can be purchased or synthesized by known methods.

[0023] In this invention, all the devices or equipment used are conventional devices or equipment known in the art and are readily available.

[0024] This invention provides a thick-film humidity sensor and its preparation process for high-temperature and high-humidity applications in steam ovens. The method mainly involves adjusting the ceramic powder formulation to obtain a humidity-sensitive powder with excellent linearity and high sensitivity. This powder is then mixed with an organic carrier to prepare a thick-film slurry, which is subsequently printed onto the interdigitated electrodes of an alumina substrate. After sintering, the humidity sensor is obtained. Specifically, the high-temperature resistant thick-film humidity sensor for steam ovens, from bottom to top, consists of an alumina ceramic substrate, interdigitated electrodes, a humidity-sensitive thick film, and a YSZ thin film.

[0025] The bottom layer is an alumina ceramic substrate; The bottom interdigitated electrode is coated on the surface of an alumina ceramic substrate. The bottom interdigitated electrode is a Pt bottom interdigitated electrode or an Au bottom interdigitated electrode with a thickness of 8-12 μm. A moisture-sensitive material thick film is coated on the surface of the bottom interdigital electrode with a thickness of 10-50 μm. Its main component is barium titanate. As an inorganic ceramic material, barium titanate has good biocompatibility and is an inorganic compound that is not easily absorbed by the human body. Its preparation process has no harmful additive residues and can meet the safety requirements of indirect contact between the inner cavity of the steam cooking oven and food steam. YSZ film, a porous yttrium oxide-stabilized zirconia film, provides protection. With a thickness of 5–200 nm, it prevents oil and dirt adhesion while being breathable, further enhancing food contact safety.

[0026] A process for preparing a high-temperature resistant thick-film humidity-sensitive element for a steam oven includes the following steps: (1) Preparation of humidity-sensitive resistor powder; (2) Preparation of wet-sensitive thick film slurry; (3) Preparation of thick film humidity-sensitive resistors; (4) Preparation of humidity-sensitive element.

[0027] Furthermore, the steps of step (1) are as follows: (11) Add neodymium oxide powder, niobium oxide powder and MO powder to barium titanate powder to obtain a mixed powder; (12) According to the ratio of material: ball: water = 1: (1~2): (1~1.5), put the mixed powder obtained in step (11), zirconia balls and deionized water into a ball mill and ball mill for at least 12 hours to obtain a mixture; (13) After ball milling, the mixture obtained in step (12) is taken out and dried. Then the dried mixture is placed in a muffle furnace and pre-fired at 900℃~1100℃ for 1~2h to obtain pre-fired powder. (14) Add appropriate amounts of B2O3, Li2CO3 and SiO2 to the pre-calcined powder to obtain a second mixture. Then, according to the ratio of material:ball:water = 1:(1.5~2.5):(0.8~1.5), add the second mixture, zirconia balls and deionized water to a ball mill and grind for at least 12 hours to obtain a secondary mixture. (15) Powder sieving: After the secondary mixture is poured out and dried, the dried material is passed through a 50-mesh sieve to obtain the wet-sensitive resistor powder.

[0028] Furthermore, the particle size of the barium titanate powder in step (11) is 10 to 100 nm.

[0029] Furthermore, in step (11), the MO powder is either magnesium oxide powder or manganese oxide powder.

[0030] Furthermore, in step (11), the amount of barium titanate powder used is 100 moles; The amount of neodymium oxide powder added is 0.5–1.5 moles; The amount of niobium oxide powder added is 0.05 to 0.5 moles; The amount of MO powder added is 0.05 to 0.5 moles.

[0031] The main function of Nd oxide (neodymium oxide) is to improve the structural stability of humidity sensors, enhance the temperature and humidity stability of humidity sensors, and improve the response sensitivity in the low humidity range (relative humidity < 40%).

[0032] The role of niobium oxide powder: to inhibit the formation of oxygen vacancies during sintering and improve the thermal stability of the humidity-sensitive element resistor; The role of MO powder: MO powder works synergistically with Nd oxide to regulate the migration rate of conductive ions in the humidity-sensitive medium, meet the insulation resistance requirements of humidity-sensitive elements at different operating temperatures, and improve the linearity of humidity response.

[0033] Furthermore, the total mass of the pre-calcined powder obtained in step (13) is used as the basis; In step (14), the amount of B2O3 added is 1.0~2.5wt%; the amount of Li2CO3 added is 0.5~2.0wt%; and the amount of SiO2 added is 0.5~2.0wt%. The addition of the glass phase components (B2O3, Li2CO3 and SiO2) is to lower the sintering temperature of the second mixture so that it matches the sintering temperature of the bottom electrode, and to adjust the sintering shrinkage rate of the thick film to prevent the generation of microcracks.

[0034] Furthermore, step (2) is as follows: (21) Preparation of organic carrier: Add 40-60 parts of terpineol, 20-30 parts of diethylene glycol butyl ether, 5-10 parts of tributyl citrate, 10-20 parts of ethyl cellulose, and 2-3 parts of hydrogenated castor oil to the reactor. Then heat and stir the reactor in a water bath at 60-80°C for 20-40 minutes to obtain the organic carrier. (22) Preparation of slurry: Add an appropriate amount of wet-sensitive resistor powder and dispersant obtained in step (1) to the organic carrier obtained in step (21) to obtain a mixture. Then place the mixture in a homogenizer and mix at a speed of at least 1200 r / min for at least 5 min. After completion, take it out and then grind and slurry it on a three-roll mill 3 to 6 times. After completion, wet-sensitive thick film slurry is obtained.

[0035] Furthermore, in step (22), based on the total mass of the organic carrier obtained in step (21), the amount of wet-sensitive resistor powder obtained in step (1) added is 50wt%-60wt%, and the amount of dispersant added is 1wt%-3wt%.

[0036] Furthermore, in step (22), the dispersant is one of polyphosphate salt and polyacrylamide.

[0037] Furthermore, the viscosity of the wet-sensitive thick film slurry obtained in step (22) is controlled at 120 to 200 Pa·s.

[0038] Furthermore, the specific steps of step (3) are as follows: (31) The bottom interdigitated electrode was prepared on an alumina ceramic substrate by thick film printing. (32) Preparation of the thick film of the humidity-sensitive resistor: Using a 200-325 mesh screen, the thick film slurry obtained in step (2) is coated onto the surface of the bottom interdigital electrode obtained in step (31) to form a thick film of the humidity-sensitive resistor by single or multiple printing processes: (33) Sintering: The bottom interdigital electrode coated with the thick film of the humidity-sensitive resistor in step (32) is sintered at high temperature. After sintering, the thick film humidity-sensitive resistor is obtained.

[0039] Furthermore, the thickness of the bottom interdigital electrode prepared in step (31) is 8-12 μm.

[0040] Furthermore, the bottom interdigital electrode prepared in step (31) is a Pt bottom interdigital electrode or an Au bottom interdigital electrode.

[0041] Furthermore, the thickness of the humidity-sensitive resistor thick film in step (32) is controlled to be between 10 and 50 μm.

[0042] Furthermore, the sintering process for step (33) is as follows: A staged sintering method is adopted. In the first stage, the temperature is raised from room temperature to 500℃ at a rate of 1-3℃ / min, and then held at 500℃ for 10-30min. The second stage involves raising the temperature from 500℃ to 800-850℃ at a rate of 3-10℃ / min, and then holding the temperature at 800-850℃ for 10-30 minutes. The third stage: Cool the furnace to below 200℃.

[0043] Furthermore, the specific steps of step (4) are as follows: YSZ thin films are prepared on the thick film humidity-sensitive resistor obtained in step (3) by ALD method or magnetron sputtering method, and the humidity-sensitive element is obtained after completion.

[0044] Furthermore, the YSZ thin film refers to a porous yttrium oxide-stabilized zirconia thin film with a yttrium oxide doping content of 3–6 mol%; The thickness of YSZ thin films ranges from 5 to 200 nm.

[0045] A high-temperature resistant thick-film humidity-sensitive element for steam ovens is prepared by any one of the above-described preparation processes.

[0046] In one embodiment: A process for preparing a high-temperature resistant thick-film humidity-sensitive element for a steam oven includes the following steps: (1) Preparation of humidity-sensitive resistor powder; (2) Preparation of wet-sensitive thick film slurry; (3) Preparation of thick film humidity-sensitive resistors; (4) Preparation of humidity-sensitive element.

[0047] Furthermore, the steps of step (1) are as follows: (11) Add neodymium oxide powder, niobium oxide powder and MO powder to barium titanate powder to obtain a mixed powder; (12) According to the ratio of material: ball: water = 1:1:1, put the mixed powder obtained in step (11), zirconia balls and deionized water into a ball mill and ball mill for 12 hours to obtain the mixture; (13) After ball milling, the mixture obtained in step (12) is taken out and dried. Then the dried mixture is placed in a muffle furnace and pre-fired at 900°C for 2 hours to obtain pre-fired powder. (14) Add appropriate amounts of B2O3, Li2CO3 and SiO2 to the pre-calcined powder to obtain a second mixture. Then, according to the ratio of material:ball:water = 1:1.5:0.8, add the second mixture, zirconia balls and deionized water to a ball mill and grind for 12 hours to obtain a secondary mixture. (15) Powder sieving: After the secondary mixture is poured out and dried, the dried material is passed through a 50-mesh sieve to obtain the wet-sensitive resistor powder.

[0048] Furthermore, the barium titanate powder in step (11) has a particle size of 10 nm.

[0049] Furthermore, in step (11), the MO powder is magnesium oxide powder.

[0050] Furthermore, in step (11), the amount of barium titanate powder used is 100 moles; The amount of neodymium oxide powder added is 0.5 moles; The amount of niobium oxide powder added is 0.05 molar parts; The amount of MO powder added is 0.05 moles.

[0051] Furthermore, the total mass of the pre-calcined powder obtained in step (13) is used as the basis; In step (14), the amount of B2O3 added is 1.0 wt%; the amount of Li2CO3 added is 0.5 wt%; and the amount of SiO2 added is 0.5 wt%.

[0052] Furthermore, step (2) is as follows: (21) Preparation of organic carrier: 40 parts of terpineol, 20 parts of diethylene glycol butyl ether, 5 parts of tributyl citrate, 10 parts of ethyl cellulose, and 2 parts of hydrogenated castor oil were added to the reactor. The reactor was then heated and stirred in a water bath at 60°C for 40 minutes. After completion, the organic carrier was obtained. (22) Preparation of slurry: Add an appropriate amount of wet-sensitive resistor powder and dispersant obtained in step (1) to the organic carrier obtained in step (21) to obtain a mixture. Then place the mixture in a homogenizer and mix at a speed of 1200 r / min for 5 min. After completion, take it out and grind it three times on a three-roll mill. After completion, wet-sensitive thick film slurry is obtained.

[0053] Furthermore, in step (22), based on the total mass of the organic carrier obtained in step (21), the amount of wet-sensitive resistor powder obtained in step (1) added is 50 wt%, and the amount of dispersant added is 1 wt%.

[0054] Furthermore, in step (22), the dispersant is a polyphosphate salt.

[0055] Furthermore, the viscosity of the wet-sensitive thick film slurry obtained in step (22) is controlled at 120 Pa·s.

[0056] Furthermore, the specific steps of step (3) are as follows: (31) The bottom interdigitated electrode was prepared on an alumina ceramic substrate by thick film printing. (32) Preparation of the thick film of the humidity-sensitive resistor: Using a 200-mesh screen, the thick film slurry obtained in step (2) is coated onto the surface of the bottom interdigital electrode obtained in step (31) to form a thick film of the humidity-sensitive resistor by a single printing process: (33) Sintering: The bottom interdigital electrode coated with the thick film of the humidity-sensitive resistor in step (32) is sintered at high temperature. After sintering, the thick film humidity-sensitive resistor is obtained.

[0057] Furthermore, the thickness of the bottom interdigital electrode prepared in step (31) is 8 μm.

[0058] Furthermore, the bottom interdigital electrode prepared in step (31) is a Pt bottom interdigital electrode.

[0059] Furthermore, the thickness of the humidity-sensitive resistor thick film in step (32) is controlled at 10 μm.

[0060] Furthermore, the sintering process for step (33) is as follows: A staged sintering method was adopted. In the first stage, the temperature was raised from room temperature to 500℃ at a rate of 1℃ / min, and then held at 500℃ for 10min. The second stage involves heating from 500℃ to 800℃ at a rate of 3℃ / min, and then holding at 800℃ for 10 minutes. The third stage: Cool the furnace to below 200℃.

[0061] Furthermore, the specific steps of step (4) are as follows: YSZ thin film was prepared on the thick film humidity-sensitive resistor obtained in step (3) using the ALD method, and the humidity-sensitive element was obtained after completion.

[0062] Furthermore, the YSZ thin film refers to a porous yttrium oxide-stabilized zirconia thin film with a yttrium oxide doping concentration of 3 mol%; The thickness of the YSZ thin film is 5 nm.

[0063] A high-temperature resistant thick-film humidity-sensitive element for steam ovens is prepared by any one of the above-described preparation processes.

[0064] In another embodiment: A process for preparing a high-temperature resistant thick-film humidity-sensitive element for a steam oven includes the following steps: (1) Preparation of humidity-sensitive resistor powder; (2) Preparation of wet-sensitive thick film slurry; (3) Preparation of thick film humidity-sensitive resistors; (4) Preparation of humidity-sensitive element.

[0065] Furthermore, the steps of step (1) are as follows: (11) Add neodymium oxide powder, niobium oxide powder and MO powder to barium titanate powder to obtain a mixed powder; (12) According to the ratio of material: ball: water = 1:2:1.5, put the mixed powder obtained in step (11), zirconia balls and deionized water into a ball mill and ball mill for 24 hours to obtain a mixture; (13) After ball milling, the mixture obtained in step (12) is taken out and dried. Then the dried mixture is placed in a muffle furnace and pre-fired at 1100°C for 1 hour to obtain pre-fired powder. (14) Add appropriate amounts of B2O3, Li2CO3 and SiO2 to the pre-calcined powder to obtain a second mixture. Then, according to the ratio of material:ball:water = 1:2.5:1.5, add the second mixture, zirconia balls and deionized water to a ball mill and grind for 24 hours to obtain a secondary mixture. (15) Powder sieving: After the secondary mixture is poured out and dried, the dried material is passed through a 50-mesh sieve to obtain the wet-sensitive resistor powder.

[0066] Furthermore, the barium titanate powder in step (11) has a particle size of 100 nm.

[0067] Furthermore, in step (11), the MO powder is manganese oxide powder.

[0068] Furthermore, in step (11), the amount of barium titanate powder used is 100 moles; The amount of neodymium oxide powder added is 1.5 moles; The amount of niobium oxide powder added is 0.5 moles; The amount of MO powder added is 0.5 moles.

[0069] Furthermore, the total mass of the pre-calcined powder obtained in step (13) is used as the basis; In step (14), the amount of B2O3 added is 2.5wt%; the amount of Li2CO3 added is 2.0wt%; and the amount of SiO2 added is 2.0wt%.

[0070] Furthermore, step (2) is as follows: (21) Preparation of organic carrier: 60 parts of terpineol, 30 parts of diethylene glycol butyl ether, 10 parts of tributyl citrate, 20 parts of ethyl cellulose, and 3 parts of hydrogenated castor oil were added to the reactor. The reactor was then heated and stirred in an 80°C water bath for 20 minutes. After completion, the organic carrier was obtained. (22) Preparation of slurry: Add an appropriate amount of wet-sensitive resistor powder and dispersant obtained in step (1) to the organic carrier obtained in step (21) to obtain a mixture. Then place the mixture in a homogenizer and mix at a speed of 1800 r / min for 20 min. After completion, take it out and then grind and slurry it 6 times on a three-roll mill. After completion, wet-sensitive thick film slurry is obtained.

[0071] Furthermore, in step (22), based on the total mass of the organic carrier obtained in step (21), the amount of wet-sensitive resistor powder obtained in step (1) added is 60 wt%, and the amount of dispersant added is 3 wt%.

[0072] Furthermore, in step (22), the dispersant is polyacrylamide.

[0073] Furthermore, the viscosity of the wet-sensitive thick film slurry obtained in step (22) is controlled at 200 Pa·s.

[0074] Furthermore, the specific steps of step (3) are as follows: (31) The bottom interdigitated electrode was prepared on an alumina ceramic substrate by thick film printing. (32) Preparation of the thick film of the humidity-sensitive resistor: Using a 325-mesh screen, the thick film slurry obtained in step (2) is coated onto the surface of the bottom interdigital electrode obtained in step (31) to form a thick film of the humidity-sensitive resistor by multiple printing processes: (33) Sintering: The bottom interdigital electrode coated with the thick film of the humidity-sensitive resistor in step (32) is sintered at high temperature. After sintering, the thick film humidity-sensitive resistor is obtained.

[0075] Furthermore, the thickness of the bottom interdigital electrode prepared in step (31) is 12 μm.

[0076] Furthermore, the bottom interdigital electrode prepared in step (31) is an Au bottom interdigital electrode.

[0077] Furthermore, the thickness of the humidity-sensitive resistor thick film in step (32) is controlled at 50 μm.

[0078] Furthermore, the sintering process for step (33) is as follows: A staged sintering method was adopted. In the first stage, the temperature was raised from room temperature to 500℃ at a rate of 3℃ / min, and then held at 500℃ for 30min. The second stage involves heating from 500℃ to 850℃ at a rate of 10℃ / min, and holding at 850℃ for 30min. The third stage: Cool the furnace to below 200℃.

[0079] Furthermore, the specific steps of step (4) are as follows: YSZ thin film was prepared on the thick film humidity-sensitive resistor obtained in step (3) by magnetron sputtering, and the humidity-sensitive element was obtained after completion.

[0080] Furthermore, the YSZ thin film refers to a porous yttrium oxide-stabilized zirconia thin film with a yttrium oxide doping content of 6 mol%; The thickness of the YSZ thin film is 200 nm.

[0081] A high-temperature resistant thick-film humidity-sensitive element for steam ovens is prepared by any one of the above-described preparation processes.

[0082] In yet another embodiment: A process for preparing a high-temperature resistant thick-film humidity-sensitive element for a steam oven includes the following steps: (1) Preparation of humidity-sensitive resistor powder; (2) Preparation of wet-sensitive thick film slurry; (3) Preparation of thick film humidity-sensitive resistors; (4) Preparation of humidity-sensitive element.

[0083] Furthermore, the steps of step (1) are as follows: (11) Add neodymium oxide powder, niobium oxide powder and MO powder to barium titanate powder to obtain a mixed powder; (12) According to the ratio of material: ball: water = 1:1.5:1.2, put the mixed powder obtained in step (11), zirconia balls and deionized water into a ball mill and ball mill for 18 hours to obtain a mixture; (13) After ball milling, the mixture obtained in step (12) is taken out and dried. Then the dried mixture is placed in a muffle furnace and pre-fired at 1000°C for 1.5 hours to obtain pre-fired powder. (14) Add appropriate amounts of B2O3, Li2CO3 and SiO2 to the pre-calcined powder to obtain a second mixture. Then, according to the ratio of material:ball:water = 1:2:1, add the second mixture, zirconia balls and deionized water to a ball mill and grind for 16 hours to obtain a secondary mixture. (15) Powder sieving: After the secondary mixture is poured out and dried, the dried material is passed through a 50-mesh sieve to obtain the wet-sensitive resistor powder.

[0084] Furthermore, the barium titanate powder in step (11) has a particle size of 40 nm.

[0085] Furthermore, in step (11), the MO powder is magnesium oxide powder.

[0086] Furthermore, in step (11), the amount of barium titanate powder used is 100 moles; The amount of neodymium oxide powder added is 1 mole; The amount of niobium oxide powder added is 0.1 molar. The amount of MO powder added is 0.2 moles.

[0087] Furthermore, the total mass of the pre-calcined powder obtained in step (13) is used as the basis; In step (14), the amount of B2O3 added is 1.8wt%; the amount of Li2CO3 added is 1.2wt%; and the amount of SiO2 added is 1.2wt%.

[0088] Furthermore, step (2) is as follows: (21) Preparation of organic carrier: 50 parts of terpineol, 25 parts of diethylene glycol butyl ether, 7.5 parts of tributyl citrate, 15 parts of ethyl cellulose, and 2.5 parts of hydrogenated castor oil were added to the reactor. The reactor was then heated and stirred in a water bath at 70°C for 30 minutes. After completion, the organic carrier was obtained. (22) Preparation of slurry: Add an appropriate amount of wet-sensitive resistor powder and dispersant obtained in step (1) to the organic carrier obtained in step (21) to obtain a mixture. Then place the mixture in a homogenizer and mix at a speed of 1500 r / min for 10 min. After completion, take it out and grind it 4 times on a three-roll mill. After completion, wet-sensitive thick film slurry is obtained.

[0089] Furthermore, in step (22), based on the total mass of the organic carrier obtained in step (21), the amount of wet-sensitive resistor powder obtained in step (1) added is 55wt%, and the amount of dispersant added is 2wt%.

[0090] Furthermore, in step (22), the dispersant is polyacrylamide.

[0091] Furthermore, the viscosity of the wet-sensitive thick film slurry obtained in step (22) is controlled at 150 Pa·s.

[0092] Furthermore, the specific steps of step (3) are as follows: (31) The bottom interdigitated electrode was prepared on an alumina ceramic substrate by thick film printing. (32) Preparation of the thick film of the humidity-sensitive resistor: Using a 250-mesh screen, the thick film slurry obtained in step (2) is coated onto the surface of the bottom interdigital electrode obtained in step (31) to form a thick film of the humidity-sensitive resistor by multiple printing processes: (33) Sintering: The bottom interdigital electrode coated with the thick film of the humidity-sensitive resistor in step (32) is sintered at high temperature. After sintering, the thick film humidity-sensitive resistor is obtained.

[0093] Furthermore, the thickness of the bottom interdigital electrode prepared in step (31) is 9 μm.

[0094] Furthermore, the bottom interdigital electrode prepared in step (31) is an Au bottom interdigital electrode.

[0095] Furthermore, the thickness of the humidity-sensitive resistor thick film in step (32) is controlled at 30 μm.

[0096] Furthermore, the sintering process for step (33) is as follows: A staged sintering method was adopted. In the first stage, the temperature was raised from room temperature to 500℃ at a rate of 2℃ / min, and then held at 500℃ for 20min. The second stage involves heating from 500℃ to 830℃ at a rate of 5℃ / min, and holding at 830℃ for 20min. The third stage: Cool the furnace to below 200℃.

[0097] Furthermore, the specific steps of step (4) are as follows: YSZ thin film was prepared on the thick film humidity-sensitive resistor obtained in step (3) by magnetron sputtering, and the humidity-sensitive element was obtained after completion.

[0098] Furthermore, the YSZ thin film refers to a porous yttrium oxide-stabilized zirconia thin film with a yttrium oxide doping concentration of 5 mol%. The thickness of the YSZ thin film is 100 nm.

[0099] A high-temperature resistant thick-film humidity-sensitive element for steam ovens is prepared by any one of the above-described preparation processes.

[0100] Example 1 like Figure 1 As shown, a process for preparing a high-temperature resistant thick-film humidity-sensitive element for a steam oven includes the following steps: (1) Preparation of humidity-sensitive resistor powder; (2) Preparation of wet-sensitive thick film slurry; (3) Preparation of thick film humidity-sensitive resistors; (4) Preparation of humidity-sensitive element.

[0101] Furthermore, the steps of step (1) are as follows: (11) Add neodymium oxide powder, niobium oxide powder and MO powder to barium titanate powder to obtain a mixed powder; (12) According to the ratio of material: ball: water = 1:1.5:1.25, put the mixed powder obtained in step (11), zirconia balls and deionized water into a ball mill and ball mill for 24 hours to obtain a mixture; (13) After ball milling, the mixture obtained in step (12) is taken out and dried. Then the dried mixture is placed in a muffle furnace and pre-fired at 1000°C for 2 hours to obtain pre-fired powder. (14) Add appropriate amounts of B2O3, Li2CO3 and SiO2 to the pre-calcined powder to obtain a second mixture. Then, according to the ratio of material:ball:water = 1:2:1, add the second mixture, zirconia balls and deionized water to a ball mill and grind for 18 hours to obtain a secondary mixture. (15) Powder sieving: After the secondary mixture is poured out and dried, the dried material is passed through a 50-mesh sieve to obtain the wet-sensitive resistor powder.

[0102] Furthermore, the barium titanate powder in step (11) has a particle size of 20 nm.

[0103] Furthermore, in step (11), the MO powder is magnesium oxide powder.

[0104] Furthermore, in step (11), the amount of barium titanate powder used is 100 moles; The amount of neodymium oxide powder added is 0.5 moles; The amount of niobium oxide powder added is 0.5 moles; The amount of MO powder added is 0.5 moles.

[0105] Furthermore, the total mass of the pre-calcined powder obtained in step (13) is used as the basis; In step (14), the amount of B2O3 added is 1.5wt%; the amount of Li2CO3 added is 2wt%; and the amount of SiO2 added is 0.5wt%.

[0106] Furthermore, step (2) is as follows: (21) Preparation of organic carrier: 50 parts of terpineol, 20 parts of diethylene glycol butyl ether, 8 parts of tributyl citrate, 20 parts of ethyl cellulose, and 2 parts of hydrogenated castor oil were added to the reactor. The reactor was then heated and stirred in an 80°C water bath for 30 minutes. After completion, the organic carrier was obtained. (22) Preparation of slurry: Add an appropriate amount of wet-sensitive resistor powder and dispersant obtained in step (1) to the organic carrier obtained in step (21) to obtain a mixture. Then place the mixture in a homogenizer and mix at a speed of 1200r / min for 20min. After completion, take it out and grind it 4 times on a three-roll mill. After completion, wet-sensitive thick film slurry is obtained.

[0107] Furthermore, in step (22), based on the total mass of the organic carrier obtained in step (21), the amount of wet-sensitive resistor powder obtained in step (1) added is 55wt%, and the amount of dispersant added is 2wt%.

[0108] Furthermore, in step (22), the dispersant is polyacrylamide.

[0109] Furthermore, the viscosity of the wet-sensitive thick film slurry obtained in step (22) is controlled at 180 Pa·s.

[0110] Furthermore, the specific steps of step (3) are as follows: (31) The bottom interdigitated electrode was prepared on an alumina ceramic substrate by thick film printing. (32) Preparation of the thick film of the humidity-sensitive resistor: Using a 250-mesh screen, the thick film slurry obtained in step (2) is coated onto the surface of the bottom interdigital electrode obtained in step (31) to form a thick film of the humidity-sensitive resistor by multiple printing processes: (33) Sintering: The bottom interdigital electrode coated with the thick film of the humidity-sensitive resistor in step (32) is sintered at high temperature. After sintering, the thick film humidity-sensitive resistor is obtained.

[0111] Furthermore, the thickness of the bottom interdigital electrode prepared in step (31) is 10 μm. The number of electrodes is 18, the electrode linewidth is 0.15 mm, the electrode spacing is 0.35 mm, and the electrode length is 5 mm.

[0112] Furthermore, the bottom interdigital electrode prepared in step (31) is a Pt bottom interdigital electrode.

[0113] Furthermore, the thickness of the humidity-sensitive resistor thick film in step (32) is controlled at 25 μm.

[0114] Furthermore, the sintering process for step (33) is as follows: A staged sintering method was adopted. In the first stage, the temperature was raised from room temperature to 500℃ at a rate of 2℃ / min, and then held at 500℃ for 20min. The second stage involves heating from 500℃ to 800℃ at a rate of 5℃ / min, and then holding at 800℃ for 20 minutes. The third stage: Cool the furnace to below 200℃.

[0115] Furthermore, the specific steps of step (4) are as follows: YSZ thin film was prepared on the thick film humidity-sensitive resistor obtained in step (3) using the ALD method, and the humidity-sensitive element was obtained after completion.

[0116] Furthermore, the YSZ thin film refers to a porous yttrium oxide-stabilized zirconia thin film with a yttrium oxide doping concentration of 5 mol%. The thickness of the YSZ thin film is 50 nm.

[0117] A high-temperature resistant thick-film humidity-sensitive element for steam ovens is prepared by any one of the above-described preparation processes.

[0118] The high-temperature resistant thick-film humidity sensor prepared in Example 1 for use in a steam oven was tested, and the test results are as follows: 1. The humidity-sensitive element prepared in Example 1 was tested under operating conditions of 90°C and 85% RH. The results are as follows: Figure 2 As shown: The humidity-sensitive element prepared in Example 1 exhibits stable resistance and performance under high temperature and high humidity conditions.

[0119] 2. After the humidity-sensitive element prepared in Example 1 was kept at 450℃ for 3 hours, and then operated at 90℃ / 85%RH for 2 hours, the test results were as follows: Figure 3 As shown, the humidity-sensitive resistor prepared in Example 1 can withstand a high temperature of 450°C and its resistance value does not drift significantly within 2 hours, and it can still work stably.

[0120] 3. High food contact safety: The barium titanate film is prepared using high-purity inorganic raw materials, free of volatile organic compounds and harmful impurities. It also strictly complies with the requirements of the "National Food Safety Standard for General Safety Requirements for Food Contact Materials and Articles" (GB4806.1—2016), and has passed the total migration test for food contact materials, with a total migration ≤10mg / dm³. 2 It meets the limited standards, is suitable for scenarios where the inner cavity of a steam oven is in indirect contact with food steam, poses no food safety risks, and ensures the safety of the food cooking process.

[0121] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A process for preparing a high-temperature resistant thick-film humidity-sensitive element for a steam oven, characterized in that, The steps are as follows: (1) Preparation of humidity-sensitive resistor powder; (2) Preparation of wet-sensitive thick film slurry; (3) Preparation of thick film humidity-sensitive resistors; (4) Preparation of humidity-sensitive element.

2. The preparation process of a high-temperature resistant thick-film humidity-sensitive element for a steam oven as described in claim 1, characterized in that, The steps of step (1) are as follows: (11) Add neodymium oxide powder, niobium oxide powder and MO powder to barium titanate powder to obtain a mixed powder; (12) According to the ratio of material: ball: water = 1: (1~2): (1~1.5), put the mixed powder obtained in step (11), zirconia balls and deionized water into a ball mill and ball mill for at least 12 hours to obtain a mixture; (13) After ball milling, the mixture obtained in step (12) is taken out and dried. Then the dried mixture is placed in a muffle furnace and pre-fired at 900℃~1100℃ for 1~2h to obtain pre-fired powder. (14) Add appropriate amounts of B2O3, Li2CO3 and SiO2 to the pre-calcined powder to obtain a second mixture. Then, according to the ratio of material:ball:water = 1:(1.5~2.5):(0.8~1.5), add the second mixture, zirconia balls and deionized water to a ball mill and grind for at least 12 hours to obtain a secondary mixture. (15) Powder sieving: After the secondary mixture is poured out and dried, the dried material is passed through a 50-mesh sieve to obtain the wet-sensitive resistor powder.

3. The preparation process of a high-temperature resistant thick-film humidity-sensitive element for a steam oven as described in claim 2, characterized in that, The barium titanate powder in step (11) has a particle size of 10–100 nm, and / or In step (11), the MO powder is either magnesium oxide powder or manganese oxide powder.

4. The preparation process of a high-temperature resistant thick-film humidity-sensitive element for a steam oven as described in claim 2, characterized in that, In step (11), the amount of barium titanate powder used is 100 moles; The amount of neodymium oxide powder added is 0.5–1.5 molar parts; The amount of niobium oxide powder added is 0.05 to 0.5 moles; The amount of MO powder added is 0.05 to 0.5 moles, and / or The total mass of the pre-calcined powder obtained in step (13) is used as the basis; In step (14), the amount of B2O3 added is 1.0 to 2.5 wt%; the amount of Li2CO3 added is 0.5 to 2.0 wt%; and the amount of SiO2 added is 0.5 to 2.0 wt%.

5. The preparation process of a high-temperature resistant thick-film humidity-sensitive element for a steam oven as described in claim 1, characterized in that, The steps of step (2) are as follows: (21) Preparation of organic carrier: Add 40-60 parts of terpineol, 20-30 parts of diethylene glycol butyl ether, 5-10 parts of tributyl citrate, 10-20 parts of ethyl cellulose, and 2-3 parts of hydrogenated castor oil to the reactor. Then heat and stir the reactor in a water bath at 60-80°C for 20-40 minutes to obtain the organic carrier. (22) Preparation of slurry: Add an appropriate amount of wet-sensitive resistor powder and dispersant obtained in step (1) to the organic carrier obtained in step (21) to obtain a mixture. Then place the mixture in a homogenizer and mix at a speed of at least 1200 r / min for at least 5 min. After completion, take it out and then grind and slurry it on a three-roll mill 3 to 6 times. After completion, wet-sensitive thick film slurry is obtained.

6. The preparation process of a high-temperature resistant thick-film humidity-sensitive element for a steam oven as described in claim 5, characterized in that, In step (22), based on the total mass of the organic carrier obtained in step (21), the amount of the moisture-sensitive resistor powder obtained in step (1) added is 50wt%-60wt%, the amount of the dispersant added is 1wt%-3wt%, and / or In step (22), the dispersant is one of a polyphosphate salt and a polyacrylamide, and / or The viscosity of the wet-sensitive thick film slurry obtained in step (22) is controlled at 120-200 Pa·s.

7. The preparation process of a high-temperature resistant thick-film humidity-sensitive element for a steam oven as described in claim 1, characterized in that, The specific steps of step (3) are as follows: (31) The bottom interdigitated electrode was prepared on an alumina ceramic substrate by thick film printing. (32) Preparation of the thick film of the humidity-sensitive resistor: Using a 200-325 mesh screen, the thick film slurry obtained in step (2) is coated onto the surface of the bottom interdigital electrode obtained in step (31) to form a thick film of the humidity-sensitive resistor by single or multiple printing processes: (33) Sintering: The bottom interdigital electrode coated with the thick film of the humidity-sensitive resistor in step (32) is sintered at high temperature. After sintering, the thick film humidity-sensitive resistor is obtained.

8. The preparation process of a high-temperature resistant thick-film humidity-sensitive element for a steam oven as described in claim 7, characterized in that, The thickness of the bottom interdigital electrode prepared in step (31) is 8-12 μm, and / or The interdigitated bottom electrode prepared in step (31) is a Pt interdigitated bottom electrode or an Au interdigitated bottom electrode, and / or The thickness of the humidity-sensitive resistor thick film in step (32) is controlled to be 10–50 μm, and / or The sintering process for step (33) is as follows: A staged sintering method is adopted. In the first stage, the temperature is raised from room temperature to 500℃ at a rate of 1-3℃ / min, and then held at 500℃ for 10-30min. The second stage involves raising the temperature from 500℃ to 800-850℃ at a rate of 3-10℃ / min, and then holding the temperature at 800-850℃ for 10-30 minutes. The third stage: Cool the furnace to below 200℃.

9. The preparation process of a high-temperature resistant thick-film humidity-sensitive element for a steam oven as described in claim 1, characterized in that, The specific steps of step (4) are as follows: YSZ thin film is prepared on the thick film humidity-sensitive resistor obtained in step (3) by ALD method or magnetron sputtering method, and the humidity-sensitive element is obtained after completion; Preferably, the YSZ thin film refers to a porous yttrium oxide-stabilized zirconia thin film, with a yttrium oxide doping content of 3-6 mol%; Preferably, the thickness of the YSZ film is 5–200 nm.

10. A high-temperature resistant thick-film humidity-sensitive element for a steam oven, characterized in that, Prepared by the preparation process described in any one of claims 1-9.

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