A PTC ceramic gas heating element and a method for manufacturing the same

Abstract

This invention relates to a PTC ceramic gas heating element and its preparation method. The PTC ceramic gas heating element comprises: a PTC ceramic sheet with a microporous structure or a PTC ceramic sheet with a gradient microporous structure as a substrate, and a single-sided metal electrode or a double-sided metal electrode coated on the surface of the substrate; preferably, the composition of the substrate is selected from barium titanate-based PTC ceramic or vanadium oxide-based PTC ceramic.

Description

Technical Field

[0001] This invention belongs to the field of electronic ceramic materials and components, specifically relating to a PTC ceramic gas heating element and its preparation method. Background Technology

[0002] PTC ceramic material is a semiconducting ferroelectric ceramic that exhibits a step increase in resistance above the Curie temperature due to a phase transition. Because of its resistance-temperature, voltage-current, and current-time properties, PTC ceramic material can be used in electronic components such as constant temperature heating, overcurrent protection, and temperature sensors, and is widely used in home appliances, the automotive industry, aerospace, and other fields.

[0003] Heating flowing gas is one of the important applications of PTC ceramic heating technology. For example, Chinese Patent 1 (Application No. 201821397677.3) discloses a bladeless fan that uses a large-pore honeycomb porous PTC ceramic as the heating element, ensuring smooth airflow within the porous PTC ceramic. Another example is Chinese Patent 2 (Application No. 201720110676.5), which discloses an air-floating baking platform where high-pressure gas is heated by a heating device composed of PTC or electric heating tubes and then flows out through a porous baking plane, supporting and baking electronic components on the platform. These patents all involve the application of PTC gas heating with large-pore porous structures, while no applications of microporous PTC materials and structures have been reported. Summary of the Invention

[0004] Based on the above background, the purpose of this invention is to provide a PTC ceramic gas heating element that combines intelligent heating, gas permeability throttling, and pressure control functions, as well as its preparation method. The PTC ceramic gas heating element prepared by this method has a gradient microporous structure and a permeability of 10... -16 ~10 -11 m 2 This range is suitable for gas heating and throttling pressure control in various high-precision equipment, thereby further improving the rigidity, accuracy and static and dynamic characteristics of the overall components.

[0005] On one hand, the present invention provides a PTC ceramic gas heating element, comprising: a PTC ceramic sheet with a microporous structure or a PTC ceramic sheet with a gradient microporous structure as a substrate, and a single-sided metal electrode or a double-sided metal electrode coated on the surface of the substrate (the PTC ceramic sheet with a microporous structure or the PTC ceramic sheet with a gradient microporous structure); preferably, the composition of the substrate (the PTC ceramic sheet with a microporous structure or the PTC ceramic sheet with a gradient microporous structure) is selected from barium titanate-based PTC ceramics or vanadium oxide-based PTC ceramics.

[0006] In this invention, the principle for improving the stiffness, load-bearing capacity, and accuracy of the component lies in increasing the viscosity of the gas medium by heating a PTC ceramic sheet with a gradient microporous structure. The increase in gas viscosity can enhance the throttling effect, thereby improving the stiffness of the component. On the other hand, it increases the gas film damping of the component system, thereby strengthening the stability of the component and further improving the load-bearing capacity, stiffness, and accuracy.

[0007] Preferably, the micropore distribution type of the PTC ceramic sheet with gradient micropore structure is a sandwich-like structure or a progressive structure; the sandwich-like structure includes an intermediate layer and at least one side layer distributed on both sides of the intermediate layer, and the open porosity of the intermediate layer is less than the open porosity of the side layer.

[0008] Preferably, when the PTC ceramic sheet with gradient microporous structure is an A / B / C / D / E / F / G progressive structure, the open porosity is arranged in a manner that decreases from 35% to 45% to 5% to 15% along the air inlet direction or increases from 5% to 15% to 35% to 45% along the air inlet direction; the micropore diameter is 200nm to 200μm.

[0009] Preferably, when the PTC ceramic sheet with gradient microporous structure is a sandwich-like structure, the structure of the PTC ceramic sheet with gradient microporous structure includes: A / B / A, A / B / C / B / A, or A / B / C / D / C / B / A, etc.

[0010] Preferably, when the PTC ceramic sheet with gradient microporous structure is a sandwich-like structure, the open porosity of the middle layer is 5% to 20%; the open porosity of the outermost side layer is 35% to 45%; and the micropore diameter is 200 nm to 200 μm.

[0011] Preferably, when the PTC ceramic sheet with gradient microporous structure is a sandwich-like structure, the thickness of the middle layer of the PTC ceramic sheet with gradient microporous structure is 0.3 to 3 mm, and the thickness of each side layer is 0.3 to 1 mm.

[0012] Preferably, when the PTC ceramic sheet with gradient microporous structure is a progressive structure, the thickness of each layer of the PTC ceramic sheet with gradient microporous structure is 0.3–3 mm. The total thickness of the PTC ceramic sheet with microporous structure is 1–6 mm.

[0013] Preferably, the material of the single-sided metal electrode or the double-sided metal electrode includes gold, silver, copper, nickel, tungsten, molybdenum, platinum and their alloys; the single-sided metal electrode is a single-sided interdigitated electrode.

[0014] Preferably, the permeability of the PTC ceramic sheet with the gradient microporous structure is 10. -16 ~10 -11 m2 .

[0015] Preferably, the Curie temperature of the PTC ceramic sheet with the gradient microporous structure is 50–300°C.

[0016] On the other hand, the present invention provides a method for preparing a PTC ceramic gas heating element, comprising the following steps:

[0017] (1) Add pore-forming agents with different contents and different particle sizes to PTC ceramic raw material powder, and obtain green ceramic blanks containing different pore-forming agents by dry pressing or casting molding methods.

[0018] (2) The obtained green ceramic blanks containing different pore-forming agents are stacked and molded again according to the structural design of PTC ceramic sheets with gradient micropore structure to obtain PTC ceramic blanks with gradient pore structure.

[0019] (3) The obtained green ceramic blanks containing different pore-forming agents or PTC ceramic blanks with gradient pore structures are sintered to obtain PTC ceramic sheets with microporous structures or PTC ceramic sheets with gradient microporous structures.

[0020] (4) Polish the PTC ceramic sheet with gradient pore structure on both sides with mirror polishing, and then fabricate metal electrodes on one or both sides of the ceramic sheet to obtain a PTC ceramic gas heating element.

[0021] Preferably, in step (1), the pore-forming agent is selected from at least one of graphite powder, starch, and PMMA; the particle size of the pore-forming agent is 200 nm to 200 μm; and the amount of the pore-forming agent added is 5 wt% to 30 wt% of the total mass of the pore-forming agent and the PTC ceramic raw material powder.

[0022] Preferably, in step (3), the sintering temperature is 1300℃~1360℃ and the time is 0.5~3 hours.

[0023] Beneficial effects:

[0024] This invention optimizes the dosage and particle size of the pore-forming agent to obtain a PTC ceramic gas heating element with suitable permeability and throttling characteristics; through a series of Curie temperature PTC material formulation designs, heating temperature requirements under different working conditions can be met; through multi-layer ceramic processes to achieve gradient pore design, the rigidity and stability of the component are improved while ensuring throttling characteristics; and the surface of the PTC gas heating element is mirror-polished to ensure the accuracy of the gas film layer thickness.

[0025] The PTC ceramic gas heating element is particularly suitable for gas heating and throttling pressure control in high-precision equipment. Its principle is to increase the viscosity of the gas medium by heating it and to achieve throttling pressure control by designing a flow channel with a specific pore gradient. At the same time, it improves the overall rigidity, accuracy, static and dynamic characteristics and throttling characteristics of the component. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the PTC ceramic gas heating element used in this invention. Mark 1 represents the wires connected to the heating element, including 1a and 1b. Mark 2 represents the metal counter electrodes, including two opposing pieces 2a and 2b. The electrode materials can be, but are not limited to, gold, silver, copper, nickel, tungsten, molybdenum, platinum, and their alloys. Preparation methods can include, but are not limited to, screen printing, vapor deposition, ion plating, sputtering, etc. The electrodes can be applied to one or both sides of the heating element. The interdigitated electrode pattern is not limited to a circular ring; it can be any type of opposing pattern. Mark 3 represents the microporous PTC ceramic heating element. For ease of explanation, the gas-facing side is shown as 3a, and the gas-repellent side as 3b. Both 3a and 3b are mirror-polished surfaces. Mark 4 represents the air-bearing support. Mark 5 represents the gas film layer, typically 10-30 μm thick. The gas medium passes through the PTC ceramic heating element via surface 3a and enters the space between surface 3b and support 4 to form a gas film layer 5. The gas temperature in the gas film layer 5 is determined by the design temperature of the PTC heating element. It provides support and lubrication for the support and affects the static and dynamic characteristics of the air-bearing support. The PTC ceramic heating element 3 is installed in the support base (not shown), with the electrode surface 3a facing away from the support.

[0027] Figure 2 The image in Figure 1 shows the SEM morphology of samples doped with different pore-forming agents in Example 1 (scale bar is 80 μm). Figure 2 Image a shows the morphology of a 750-800 mesh graphite powder sample doped with 10 wt%. Figure 2 Image b shows the morphology of an 80-120 mesh graphite powder sample doped with 10 wt%. Figure 2 Image c represents the morphology of an 80-120 mesh graphite powder sample doped with 15 wt%. Figure 2 In the image, d represents the morphology of an 80-120 mesh graphite powder sample doped with 20 wt%.

[0028] Figure 3This is a longitudinal cross-sectional schematic diagram of the gradient microporous PTC ceramic sandwich structure heating element of Example 3. The diagram shows a three-layer structure, where layer A contains a pore-forming agent with slightly larger particles or a slightly higher dosage, and layer B contains a pore-forming agent with slightly smaller particles or a slightly lower dosage, forming an A / B / A sandwich gradient pore structure. This ensures air permeability while improving the element's rigidity and stability. More layers can be selected according to actual needs, such as A / B / C / B / A, A / B / C / D / C / B / A, etc. The micropores of different sizes in each layer of the stack can be controlled by the content and particle size of the pore-forming agent.

[0029] Figure 4 This is a longitudinal cross-sectional schematic diagram of the gradient microporous PTC ceramic progressively decreasing structure heating element of Example 4. The diagram shows a schematic diagram of a 5-layer progressively decreasing structure heating element, where layer C contains pore-forming agents with slightly larger particle sizes or slightly higher dosages, and layers D to G contain pore-forming agents with progressively smaller particle sizes or progressively lower dosages, forming a C / D / E / F / G progressively decreasing structure. In practical applications, a progressively increasing structure can be designed according to requirements.

[0030] Figure 5 The above are typical RT curves of PTC ceramic heating elements prepared in Examples 1 / 2 / 3 / 4. Detailed Implementation

[0031] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0032] In this disclosure, the PTC ceramic gas heating element includes: a PTC ceramic sheet with a gradient microporous structure, and single / double-sided metal electrodes coated on the ceramic surface. Compared with traditional PTC heating elements, the PTC ceramic gas heating element prepared by the method of this invention combines intelligent heating and gas throttling functions, improving the rigidity, accuracy, static and dynamic characteristics, and other performance of the heating element, making it suitable for gas heating and throttling pressure control in high-precision equipment. The PTC ceramic sheet with the gradient microporous structure includes sandwich-like structures such as A / B / A, A / B / C / B / A, and A / B / C / D / C / B / A, as well as progressive structures such as A / B / C / D / E / F / G.

[0033] In this disclosure, the PTC ceramic is breathable, with a gas permeability of up to 10. -16 -10 -11 m 2 The temperature can be adjusted within a certain range, and it also has heating, ventilation, throttling and pressure control functions; the Curie temperature of the PTC ceramic can be adjusted within the range of 50-300℃, and its working voltage can be adjusted according to the room temperature resistance of the PTC ceramic.

[0034] In one embodiment of the present invention, the method for preparing a PTC ceramic gas heating element includes steps such as PTC ceramic raw material powder formulation control, molding and sintering, and electrode coating. The following exemplarily describes the method for preparing a PTC ceramic gas heating element.

[0035] Preparation of PTC ceramic raw material powder. BaCO3, TiO2, CaCO3, Nb2O5, SrCO3, Pb3O4, V2O5, and other raw materials are weighed according to a given stoichiometric ratio, ball-milled in a mixing drum, dried in an oven, and then synthesized in a high-temperature electric furnace. SrCO3 and Pb3O4 are Curie temperature shifting agents; one or more can be selectively added as needed to obtain a mixed powder. Preferably, the material:ball:anhydrous ethanol ratio during mixing drum ball milling is 1:3:1.5–4.5, the ball milling speed is 550–650 r / min, the ball milling time is 22–24 hours, and the drying temperature after ball milling is 80℃–90℃. The preferred synthesis process conditions are 1140℃–1160℃ for 2 hours. The synthesized mixed powder, along with trace dopants Al2O3, SiO2, and MnCO3, is weighed according to a given stoichiometric ratio, placed in a ball mill, dried in an oven, and pre-fired in a high-temperature electric furnace to obtain PTC ceramic raw material powder. Preferably, the mixing drum ball milling ratio is 1:3:0.8-1.5 (material:balls:anhydrous ethanol), the milling speed is 550-650 r / min, the milling time is 22-24 hours, and the drying temperature after milling is 80℃-90℃. The preferred pre-firing process conditions are 900℃-1100℃ for 2 hours.

[0036] Different amounts and particle sizes of pore-forming agents are added to PTC ceramic raw material powder, and green ceramic blanks containing different pore-forming agents are obtained by dry pressing or casting. The PTC ceramic raw material powder used includes, but is not limited to, barium titanate-based PTC ceramics and vanadium oxide-based PTC ceramics. The pore-forming agents include, but are not limited to, ceramic pore-forming agents such as graphite powder, starch, and PMMA, wherein the pore-forming agent content is 5wt% to 30wt%. As an example, PTC ceramic powder and purchased pore-forming agents are mixed in a specific ratio, ball-milled in a planetary ball mill, and then dried in an oven. Preferably, the pore-forming agent is 80-800 mesh graphite powder; the ratio of material:ball:anhydrous ethanol is 1:3:0.8-1.5; the planetary ball milling time is 60-120 mins, and the ball milling speed is 180-240 r / min. The drying temperature is preferably 80℃-90℃.

[0037] PTC ceramic green bodies containing different pore-forming agents are stacked and formed again according to a gradient pore structure design to obtain a PTC ceramic green body with a gradient pore structure. The micropore size can be controlled by the content and particle size of the pore-forming agent; the gradient micropore structure can be achieved by stacking multiple layers of green ceramic green bodies with different pore-forming agents. The multi-layer structure includes, but is not limited to, sandwich-like structures such as A / B / A, A / B / C / B / A, and A / B / C / D / C / B / A, as well as progressive structures such as A / B / C, A / B / C / D, A / B / C / D / E, and A / B / C / D / E / F. As an example, a certain amount of PVA is added to the PTC ceramic raw material for granulation and pressed into green bodies; or multi-layer green bodies are made through multi-layer ceramic processes such as casting and stacking, wherein the stacking process can be extended to more layers according to actual needs. Preferably, the amount of PVA added is in the range of 5wt%-9wt%. Preferably, the green blank is formed by dry pressing and / or cold isostatic pressing, with a pre-pressing pressure of 1-1.5 T / cm. 2 Holding time: 1-3 minutes; Cold isostatic pressing: 2-3 T / cm 2 The holding time is 5-8 minutes. Preferably, the green blank is formed by multi-layer stacking, with a stacking pressure of 3-5 MPa, a stacking temperature of 60-80℃, and a stacking time of 30-50 seconds.

[0038] PTC ceramic sintering technology is used to sinter green ceramic blanks or PTC ceramic blanks containing different pore-forming agents to obtain PTC ceramic sheets with a gradient pore structure. As an example, the PTC ceramic blank is placed in a high-temperature electric furnace for debinding, and then sintered into a ceramic component. Preferably, the debinding process involves holding at 600-800℃ for 2 hours, and the sintering process involves holding at 1300-1360℃ for 1 hour, followed by natural cooling in the furnace.

[0039] The PTC ceramic sheet is mirror-polished on both sides, and then metal electrodes are fabricated on one or both sides of the ceramic sheet. The PTC ceramic element is mechanically mirror-polished on both sides, and its surface is ultrasonically cleaned and dried before its permeability is tested. The surface of the PTC ceramic element is coated with electrodes, and the permeability of the element after electrode coating is tested. The metal electrodes can be single-sided or double-sided electrodes. The electrode material can be, but is not limited to, gold, silver, copper, nickel, tungsten, molybdenum, platinum, and their alloys. The electrode pattern can be designed according to the shape of the PTC ceramic heating element and the back-end components; its preparation method includes, but is not limited to, ceramic electrode processes such as screen printing, vapor deposition, ion plating, and sputtering; the metal electrode has a connection area for connecting to a power cord. The opposite ends of the interdigitated electrodes are connected to wires, which are then connected to the positive and negative terminals of the power supply. The connection method between the interdigitated electrodes and the wires can be, but is not limited to, welding or bonding. The power is turned on, and the surface temperature of the heating element is tested using temperature measuring paper or an infrared thermal imager.

[0040] The ceramic PTC gas heating element was installed in the overall assembly and its performance was tested.

[0041] Currently, there are few reports on the application of PTC ceramics with gradient microporous structures in gas heating and throttling pressure control in high-precision equipment. In this invention, the PTC ceramic material is beneficial for improving the overall performance of air flotation devices. Furthermore, heating the gas flowing through the air flotation device can increase its viscosity, thereby enhancing the throttling effect and improving its stiffness and stability. Simultaneously, the gradient pore structure of the material can also achieve the regulation of the throttling effect.

[0042] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are all within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below. The following example illustrates the application of a barium titanate-based PTC ceramic gas heater to an air-bearing support.

[0043] Example 1:

[0044] (1) First, the raw materials BaCO3, TiO2, SrCO3, CaCO3, and Nb2O5 are mixed according to the stoichiometric ratio of the formula with a PTC ceramic Curie temperature of 100℃. 0.855 Sr 0.08 Ca 0.06 Y 0.005 Ti 1.01 O3 was weighed. The weighed raw materials were placed in a ball mill barrel, and anhydrous ethanol was poured in, with the ratio of material:ball:anhydrous ethanol being 1:3:2. After mixing for 24 hours by ball milling (601 r / min), the mixture was placed in an 80℃ oven to dry, and after being sieved through a 20-mesh sieve, it was placed in a high-temperature electric furnace and kept at 1150℃ for 2 hours to obtain the synthesized powder.

[0045] (2) The above-mentioned synthetic powder, as well as trace dopants such as Al2O3, SiO2 and MnCO3, are weighed and mixed according to the designed mass percentage (synthetic powder: Al2O3: SiO2: MnCO3 = 99.86: 0.02: 0.10: 0.02). The ratio of material: ball: anhydrous ethanol is 1:3:1. After mixing for 24 hours by ball milling (601 r / min), the mixture is placed in an oven at 80℃ and dried. After sieving through a 20-mesh sieve, it is placed in a furnace and kept at 1000℃ for 2 hours to obtain PTC ceramic powder.

[0046] (3) A certain percentage of graphite powder was added to the obtained PTC ceramic powder, including 10wt%, 15wt%, 17.5wt%, and 20wt%. The graphite powder was then divided into two specifications: 80-120 mesh and 750-800 mesh. The mixture was then ball-milled in a planetary ball mill (material:ball:anhydrous ethanol ratio of 1:3:1, rotation speed 203r / min) for 60mins, and then dried in an oven at 80℃ to obtain a mixed powder.

[0047] (4) Add a certain amount of PVA to the obtained mixed powder for granulation, sieve through a 40-mesh sieve, and dry compress on a tablet press (select a pressure of 1T / cm). 2 Pre-formed into circular sheets with a diameter of 35 mm and a thickness of 5 mm (holding time 1 min), and then cold isostatically pressed on an isostatic press (pressure 2 T / cm). 2 The PTC ceramic preform (thickness 5 mm) was obtained by holding the pressure for 5 min.

[0048] (5) Place the PTC ceramic blank into a high-temperature furnace and heat it to 700℃ at 2℃ / min. Hold it for 2 hours and then remove the glue.

[0049] (6) Continue to sinter at 1300℃ at 6℃ / min for 1 hour, and then cool naturally in the furnace to obtain PTC ceramic sheet 3 with a thickness of 4.2mm;

[0050] (7) The upper and lower surfaces 3a and 3b of the above PTC ceramic sheet 3 are mirror polished, cleaned in an ultrasonic device, and dried in an oven at 80°C (the thickness of the mirror polished PTC ceramic sheet is 4.0 mm).

[0051] (8) After drying, a layer of ohmic silver paste was screen-printed on side 3a of the PTC ceramic sheet. After drying at 80℃, the sheet was placed in an oven and heated to 500℃ at a rate of 2℃ / min, held for 20 minutes to form a metal electrode. Its resistance-temperature characteristics and permeability were then tested. The resulting ceramic sheet had a room temperature resistance of 10⁻¹¹⁰Ω and a permeability of 10⁻¹⁰Ω. -16 -10 -11 m 2 The temperature resistance curve shows that the Curie temperature of the material is approximately 98°C.

[0052] (9) Using the same stencil, print three layers of surface electrodes on the 3a side of the PTC ceramic sheet 3 with the ohmic electrodes printed above, and cover it with the ohmic electrodes. After drying in an 80°C oven, place it in a high-temperature electric furnace and heat it to 500°C at a rate of 2°C / min, holding it at that temperature for 20 minutes to fire the metal electrodes 2a and 2b. Solder the wires 1a and 1b to the area where the interdigitated electrodes are designed, and connect a 24V power supply for a heating test. Within 1 minute after the power is turned on, the surface temperature of the ceramic sheet reaches approximately 100°C;

[0053] (10) Table 1 below shows some of the sample performance parameters described in this embodiment. Figure 2 The image shows the surface morphology of some samples in this embodiment. Three heating elements were installed on the air flotation support, the power was turned on, and 1MPa compressed air was introduced to support the air flotation system normally.

[0054] Table 1 shows the test data for some samples in Example 1:

[0055]

[0056] Example 2:

[0057] (1) First, the raw materials such as BaCO3, TiO2, SrCO3, CaCO3, and Nb2O5 are mixed according to the chemical stoichiometry of the formula with a PTC ceramic Curie temperature of 75℃. 0.795 Sr 0.17 Ca 0.03 Y 0.005 Ti 1.01 O3 was weighed, and the weighed raw materials were placed into a ball mill barrel. Anhydrous ethanol was poured in, with the ratio of material:ball:anhydrous ethanol being 1:3:2. After mixing for 24 hours by ball milling (601 r / min), the mixture was placed in an 80℃ oven to dry. After being sieved through a 20-mesh sieve, the mixture was placed in a high-temperature electric furnace and kept at 1150℃ for 2 hours to synthesize.

[0058] (2) Weigh and mix the above-synthesized powder, as well as trace dopants such as Al2O3, SiO2 and MnCO3 according to the designed mass percentage (synthesized powder: Al2O3: SiO2: MnCO3 = 99.46: 0.04: 0.45: 0.05). The ratio of powder: ball: anhydrous ethanol is 1:3:1. After mixing for 24 hours by ball milling (601 r / min), place it in an 80℃ oven to dry. After sieving through a 20-mesh sieve, place it in a furnace and keep it at 1000℃ for 2 hours to synthesize.

[0059] (3) Add 10 wt% graphite powder to the PTC ceramic powder obtained above and mix. The graphite powder is available in two sizes: 80-120 mesh and 750-800 mesh. Place it in a planetary ball mill (material:ball:anhydrous ethanol ratio of 1:3:1, rotation speed 203 r / min) and ball mill for 60 mins, then place it in an oven to dry at 80℃.

[0060] (4) The obtained PTC ceramic powder is granulated with a certain amount of PVA, sieved through a 40-mesh sieve, and then dry-pressed on a tablet press (pressure 1T / cm). 2 Pre-formed into 35mm diameter discs (holding time 1 minute), then cold isostatically pressed on an isostatic press (pressure 2T / cm). 2 The PTC ceramic preform (thickness 5 mm) was obtained by holding the pressure for 5 min.

[0061] (5) Place the PTC ceramic green body into the furnace and heat it to 700℃ at 2℃ / min. Hold it for 120 minutes and then remove the glue.

[0062] (6) Continue to heat the temperature to 1330℃ at 6℃ / min and hold for 1 hour for sintering. Then, let it cool naturally in the furnace to obtain PTC ceramic sheet 3 with a thickness of 4.2mm.

[0063] (7) The upper and lower surfaces 3a and 3b of the above PTC ceramic sheet 3 are mirror polished, cleaned in an ultrasonic device and dried in an oven at 80°C (the thickness of the mirror polished PTC ceramic sheet is 4.0 mm).

[0064] (8) After drying, a layer of ohmic silver paste was screen-printed on side 3a of the PTC ceramic sheet. After drying at 80℃, the sheet was placed in an oven and heated to 500℃ at a rate of 2℃ / min, held for 20 minutes to form a metal electrode. Its resistance-temperature characteristics and permeability were then tested. The resulting ceramic sheet had a room temperature resistance of approximately 10⁻⁸ Ω and a permeability of approximately 10⁻⁸ Ω. -16 -10 -11 m 2 The order of magnitude, the temperature resistance curve shows that the material's Curie temperature is approximately 75°C;

[0065] (9) Using the same stencil, print three layers of surface electrodes on the 3a side of the PTC ceramic sheet 3 with the ohmic electrodes printed above, and cover it with the ohmic electrodes. After drying at 80°C, place it in an oven and heat it to 500°C at 2°C / min for 20 minutes to fire metal electrodes 2a and 2b. Solder wires 1a and 1b to the area designed with the interdigitated electrodes, and connect a 24V DC power supply for heating test. Within 1 minute after the power is turned on, the surface temperature of the ceramic sheet reaches about 80°C;

[0066] (10) Table 2 below shows the performance parameters of some samples described in this embodiment. Three heating elements were installed on the air flotation support, the power was turned on, and 1MPa compressed air was introduced to support 4 for normal air flotation.

[0067] Compared to Example 1, Example 2 uses a different PTC material formulation with varying Curie temperatures. While maintaining the same order of magnitude in material permeability and electrical properties, it achieves normal air flotation while lowering the air film temperature. Similarly, adding an appropriate amount of Pb oxide can increase the Curie temperature of the PTC material, thereby raising the air film temperature.

[0068] Table 2 shows the test data for some samples in Example 2.

[0069]

[0070] Example 3:

[0071] (1) As described in Example 1, PTC ceramic powder with a Curie temperature around 100°C was prepared. Two types were selected: 20wt% / 80-120 mesh graphite powder (powder A) and 10wt% / 750-800 mesh graphite powder (powder B). They were formed into green ceramic tapes by tape casting and cut into green ceramic sheets of a specified size (30mm×30mm) (each green ceramic sheet is 600μm thick). They were placed on a stacking table in the order of A / B / A and formed into multilayer ceramic blanks by a stacking process (stacking pressure: 3MPa, stacking temperature: 60°C, stacking time: 30s).

[0072] (2) Place the ABA multilayer PTC ceramic blank into a high-temperature electric furnace and heat it to 700℃ at 2℃ / min. Hold it for 120 minutes to remove the glue.

[0073] (3) Continue to heat the temperature to 1300℃ at 6℃ / min and hold for 1 hour for sintering. Then, let it cool naturally in the furnace to obtain PTC ceramic element 3 with a thickness of 1.46mm. Figure 3 The figure shown is a longitudinal cross-sectional view of the PTC heating element obtained after the implementation of this embodiment;

[0074] (4) The upper and lower surfaces 3a and 3b of the above PTC ceramic sheet 3 are mirror polished, cleaned in an ultrasonic device and dried in an oven at 80°C (the total thickness of the PTC ceramic sheet after mirror polishing is 1.4 mm).

[0075] (5) After drying, a layer of ohmic silver paste was screen-printed on side 3a of the PTC ceramic sheet. After drying at 80℃, the sheet was placed in an oven and heated to 500℃ at a rate of 2℃ / min, and held for 20 minutes to form a metal electrode. Its resistance-temperature characteristics and permeability were then tested. The resulting multilayer ceramic sheet had a room temperature resistance of 10⁻³⁰Ω and a permeability of 10⁻³⁰Ω. -16 -10 -11 m 2 The temperature resistance curve shows that the Curie temperature of the material is approximately 96°C.

[0076] (6) Using the same stencil, print three layers of surface electrodes on the 3a side of the PTC ceramic sheet 3 with the ohmic electrodes printed above, and cover it with the ohmic electrodes. After drying at 80°C, place it in an oven and heat it to 500°C at a rate of 2°C / min, holding it at that temperature for 20 minutes to produce metal electrodes 2a and 2b. Solder the wires 1a and 1b onto the PTC ceramic sheet with the printed electrodes obtained above, and connect it to a 24V DC power supply for a heating test. Within one minute of power-on, the surface temperature of the ceramic sheet reaches approximately 100°C.

[0077] Table 3 shows the test data for some samples in Example 3.

[0078]

[0079] Example 4:

[0080] (1) As described in Example 1, PTC ceramic powder with a Curie temperature around 100°C was prepared. Five types were selected: 17.5wt% / 80-120 mesh graphite powder (powder C), 20wt% / 750-800 mesh graphite powder (powder D), 17.5wt% / 750-800 mesh graphite powder (powder E), 15wt% / 80-120 mesh graphite powder (powder F) and 10wt% / 80-120 mesh graphite powder (powder G). They were formed into green ceramic tapes by tape casting and cut into green ceramic sheets of a specified size (30mm×30mm) (each green ceramic sheet was 450μm thick). C / D / E / F / G were placed on a stacking table in sequence and formed into multilayer ceramic blanks by a stacking process (stacking pressure: 3MPa, stacking temperature: 60°C, stacking time: 30s).

[0081] (2) Place the CDEFG multilayer PTC ceramic blank into a high-temperature electric furnace and heat it to 700℃ at 2℃ / min. Hold it for 120 minutes to remove the glue.

[0082] (3) Continue to heat the temperature to 1300℃ at 6℃ / min and hold for 1 hour for sintering. Then, let it cool naturally in the furnace to obtain PTC ceramic element 3 with a thickness of 1.82mm. Figure 4 The figure shown is a longitudinal cross-sectional view of the PTC heating element obtained after the implementation of this embodiment;

[0083] (4) The upper and lower surfaces 3a and 3b of the above PTC ceramic sheet 3 are mirror polished, cleaned in an ultrasonic device and dried in an oven at 80°C (the total thickness of the PTC ceramic sheet after mirror polishing is 1.78 mm).

[0084] (5) After drying, a layer of ohmic silver paste was screen-printed on side 3a of the PTC ceramic sheet. After drying at 80℃, the sheet was placed in an oven and heated to 500℃ at a rate of 2℃ / min, and held for 20 minutes to form a metal electrode. Its resistance-temperature characteristics and permeability were then tested. The resulting multilayer ceramic sheet had a room temperature resistance of 10⁻²⁰Ω and a permeability of 10⁻²⁰Ω. -16 -10 -11 m 2 The temperature resistance curve shows that the Curie temperature of the material is approximately 95°C.

[0085] (6) Using the same stencil, print three layers of surface electrodes on the 3a side of the PTC ceramic sheet 3 with the ohmic electrodes printed above, and cover it with the ohmic electrodes. After drying at 80°C, place it in an oven and heat it to 500°C at a rate of 2°C / min, holding it at that temperature for 20 minutes to produce metal electrodes 2a and 2b. Solder the wires 1a and 1b onto the PTC ceramic sheet with the printed electrodes obtained above, and connect it to a 24V DC power supply for a heating test. Within one minute of power-on, the surface temperature of the ceramic sheet reaches approximately 100°C.

[0086] Table 4 shows the test data for some samples in Example 4.

[0087]

[0088] The above embodiments are intended only to enable those skilled in the art to understand the design concept of the present invention and implement it accordingly, and should not be construed as limiting the present invention. Any modifications and variations made in accordance with the spirit of the present invention should be within the scope of protection of the claims.

Claims

1. A method of making a PTC ceramic gas heating element, characterized in that, A PTC ceramic sheet with a gradient microporous structure serves as the substrate, and a single-sided or double-sided metal electrode is coated on the surface of the substrate. The substrate is composed of barium titanate-based PTC ceramics or vanadium oxide-based PTC ceramics. The PTC ceramic sheet with the gradient microporous structure has an open porosity of 5%–45%, a micropore size of 200 nm–200 μm, and a permeability of 10. -16 ~10 -11 m 2 The micropore distribution type of the PTC ceramic sheet with gradient micropore structure is a sandwich-like structure or a progressive structure. The preparation of the PTC ceramic sheet with the gradient microporous structure includes: (1) The raw materials of barium titanate-based PTC ceramics or vanadium oxide-based PTC ceramics with a Curie temperature range of 50-300℃ are ball-milled, mixed and dried, and then synthesized at 1140℃~1160℃ to obtain mixed powder. (2) PTC ceramic powder is obtained by ball milling and drying the mixed powder and trace dopants of Al2O3, SiO2 and MnCO3, followed by pre-firing at 900℃-1100℃. (3) PTC ceramic powder is mixed with a pore-forming agent by ball milling, drying and molding to obtain a PTC green ceramic blank; green ceramic blanks containing different contents and / or different particle sizes of pore-forming agents are stacked and molded to obtain a PTC green ceramic blank with a gradient microporous structure. (4) The PTC green ceramic blank is debonded at 600-800℃ and sintered at 1300℃-1360℃ to obtain PTC ceramic sheets with gradient microporous structure.

2. The method of claim 1, wherein the PTC ceramic gas heating element is prepared by the steps of: The pore-forming agent is selected from at least one of graphite powder, starch, and PMMA; the particle size of the pore-forming agent is 200 nm to 200 μm; the amount of the pore-forming agent added is 5 wt% to 30 wt% of the total mass of the pore-forming agent and the PTC ceramic raw material powder.

3. A PTC ceramic gas heating element produced according to the production method of claim 1 or 2, characterized in that When the micropore distribution type of the PTC ceramic sheet with gradient micropore structure is a sandwich-like structure, the sandwich-like structure includes an intermediate layer and at least one side layer distributed on both sides of the intermediate layer, and the open porosity of the intermediate layer is less than the open porosity of the side layer.

4. The PTC ceramic gas heating element according to claim 3, characterized in that When the PTC ceramic sheet with a gradient microporous structure is a progressive structure, the open porosity is arranged in a manner that decreases from 35% to 45% to 5% to 15% along the air inlet direction or increases from 5% to 15% to 35% to 45% along the air inlet direction.

5. The PTC ceramic gas heating element according to claim 3, characterized in that When a PTC ceramic sheet with a gradient microporous structure has a sandwich-like structure, the structure of the PTC ceramic sheet with a gradient microporous structure includes: A / B / A, A / B / C / B / A, or A / B / C / D / C / B / A.

6. The PTC ceramic gas heating element according to claim 3, characterized in that, When the PTC ceramic sheet with gradient microporous structure is a sandwich-like structure, the open porosity of the middle layer is 5% to 20%; and the open porosity of the outermost side layer is 35% to 45%.

7. The PTC ceramic gas heating element according to any one of claims 3-6, characterized in that, When the PTC ceramic sheet with gradient microporous structure is a sandwich-like structure, the thickness of the middle layer of the PTC ceramic sheet with gradient microporous structure is 0.3 to 3 mm, and the thickness of each side layer is 0.3 to 1 mm. Alternatively, when the PTC ceramic sheet with gradient microporous structure is a progressive structure, the thickness of each layer of the PTC ceramic sheet with gradient microporous structure is 0.3 to 3 mm. The total thickness of the PTC ceramic sheet with a gradient microporous structure is 1 to 6 mm.

8. The PTC ceramic gas heating element according to any one of claims 3-6, characterized in that, The materials of the single-sided or double-sided metal electrode include gold, silver, copper, nickel, tungsten, molybdenum, platinum and their alloys; the single-sided metal electrode is a single-sided interdigitated electrode.

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