Composite ceramic foam and method for producing the same, heating core, liquid heating device

Abstract

The application relates to the technical field of heat-conducting ceramic materials, and particularly relates to a composite ceramic foam, a preparation method thereof, a heating core and a liquid heating device. The preparation method comprises the following steps: providing core-shell fillers and alumina hollow microspheres, wherein the core-shell fillers comprise an inner core and a shell layer coated on the outer surface of the inner core, and the alumina hollow microspheres comprise alumina hollow microsphere powder and an alumina hollow microsphere preform; the core-shell fillers and the alumina hollow microsphere powder are mixed with a dispersing agent and a sintering aid to prepare composite ceramic foam slurry; the alumina hollow microsphere preform is mixed with the composite ceramic foam slurry and subjected to drying treatment to obtain a composite ceramic foam blank; and finally, sintering is carried out to obtain the composite ceramic foam. The composite ceramic foam material product prepared by the application has the effects of high porosity, high mechanical strength, high thermal conductivity and uniform heat conduction performance, can be well used in a heating core of a heating device, and has a good application prospect.

Description

Technical Field

[0001] This application belongs to the field of thermally conductive ceramic materials technology, and particularly relates to a composite ceramic foam and its preparation method, heating core, and liquid heating device. Background Technology

[0002] Foam ceramics are high-temperature porous ceramic materials with a three-dimensional network structure, characterized by high-temperature resistance, such as alumina ceramic foam. With the expansion of applications for porous ceramic foams, how to better utilize their performance has attracted significant attention from the global materials science community. Some existing electronic heating devices utilize porous ceramic foams or high thermal conductivity ceramic composite materials in their heating cores, offering advantages such as high efficiency, environmental friendliness, and energy saving.

[0003] However, currently, single ceramic foams generally struggle to balance mechanical properties, porosity, and liquid conductivity, making it difficult to accommodate uniform transport of the aerosol matrix within the heating core. Furthermore, porous composite ceramic materials using blends of different thermally conductive fillers exhibit weak interfacial bonding and high interfacial thermal resistance, making it difficult to form a continuous three-dimensional thermally conductive network. This results in localized hotspot concentration and uneven heating during heating core operation.

[0004] Therefore, the ceramic foam materials currently used in heating elements still need improvement. Summary of the Invention

[0005] The purpose of this application is to provide a composite ceramic foam, its preparation method, a heating core, and a liquid heating device, aiming to solve the technical problem of how to form a composite ceramic foam with superior overall performance for effective use as a heating material in a heating device. To achieve the above-mentioned objective, the technical solution adopted in this application is as follows: In a first aspect, this application provides a method for preparing composite ceramic foam, comprising: The invention provides core-shell fillers and hollow alumina microspheres; wherein the core-shell filler comprises a core and a shell covering the outer surface of the core, the core comprises at least one of silicon carbide, boron nitride, aluminum nitride, and boron nitride, and the shell comprises at least one of ferric oxide and magnetite; the hollow alumina microspheres are morphologically defined as hollow alumina microsphere powder and hollow alumina microsphere preforms. The core-shell filler and the alumina hollow microsphere powder are formulated with dispersant and sintering aid to prepare a composite ceramic foam slurry. The alumina hollow microsphere preform is mixed with the composite ceramic foam slurry and then dried to obtain a composite ceramic foam preform. The composite ceramic foam blank is sintered to obtain a composite ceramic foam.

[0006] The preparation method provided in this application first prepares a composite ceramic foam slurry by mixing core-shell fillers and alumina hollow microsphere powder with dispersants and sintering aids. Then, the alumina hollow microsphere preform is mixed with the composite ceramic foam slurry, further dried, and sintered to obtain a composite ceramic foam. During this process, the core-shell fillers provide stable core-shell heterogeneous thermally conductive fillers, effectively reducing the interfacial thermal resistance with the matrix. Simultaneously, the shell layer on the surface of the core-shell fillers assists in the directional growth of grains during sintering, improving the continuity of the thermally conductive network. It can also form an open-cell hierarchical porous structure and a continuously interconnected three-dimensional thermally conductive reinforcing skeleton with the alumina hollow microspheres. Through the integrated drying and sintering process of the composite ceramic foam slurry, the final composite ceramic foam material product achieves high porosity, high mechanical strength, high thermal conductivity, and uniform thermal conductivity. The composite ceramic foam material prepared in this application can be well used in the heating core of heating devices, possessing advantages such as controllable pore structure, uniform thermal field distribution, good process repeatability, and suitability for industrial mass production.

[0007] In some possible implementations, the mass ratio of the core-shell filler to the alumina hollow microsphere powder is 1:3 to 5:1; And / or, the mass ratio of the alumina hollow microsphere preform to the alumina hollow microsphere powder is 6:4 to 7:3; And / or, the mass ratio of the core to the shell in the core-shell packing is 100:(5~20). And / or, the average particle size of the core-shell packing is 2.02 μm to 5.10 μm, and the average thickness of the shell layer is 10 nm to 100 nm; And / or, the alumina hollow microspheres have an average outer diameter of 600 nm to 2.56 μm and an average wall thickness of 50 nm to 300 nm.

[0008] By selecting the mass ratio and size of the core-shell filler and alumina hollow microspheres, the core-shell filler and alumina hollow microspheres can be used to construct a better three-level open-pore hierarchical porous structure consisting of millimeter-scale three-dimensional through-pores, micrometer-scale hollow spherical cavities, and nanometer-scale mesopores, as well as a continuous and interconnected three-dimensional thermally conductive reinforcement framework.

[0009] In some possible implementations, the sintering process includes: first heating to 400℃~600℃ and holding for 1~2 hours, then heating to 1100℃~1300℃ and holding for 2~3 hours, and then heating to 1450℃~1750℃ and holding for 1~5 hours. And / or, the mixing process includes repeatedly vacuum impregnating the alumina hollow microsphere preform in the composite ceramic foam slurry 2 to 4 times, each time for 10 to 20 minutes; And / or, the drying process includes: drying at 80℃~110℃ for 10h~15h.

[0010] The above sintering process sequentially involves a debinding stage, a solid-state reaction stage, and a densification sintering stage, ultimately achieving excellent densification of the ceramic skeleton and the construction of a three-dimensional thermally conductive network. The impregnation process of the alumina hollow microsphere preform with the composite ceramic foam slurry ensures the slurry is fully and uniformly immersed in the preform. The aforementioned drying treatment allows for better evaporation of the solvent from the composite ceramic foam slurry, resulting in a uniform composite ceramic foam preform.

[0011] In some possible implementations, the solid content in the composite ceramic foam slurry is 40% to 60%; And / or, at least one of defoamer and toughening agent may be added to the composite ceramic foam slurry; And / or, the dispersant accounts for 1% to 2% of the total weight of the core-shell filler and the alumina hollow microsphere powder; And / or, the dispersant includes at least one of polyethylene glycol, ammonium polyacrylate, sodium hexametaphosphate, and sodium tripolyphosphate; And / or, the sintering aid accounts for 1% to 4% of the total weight of the core-shell filler and the alumina hollow microsphere powder; And / or, at least one of the following sintering aids: MgO-Al2O3-SiO2 composite system, Y2O3-Al2O3-SiO2 multiphase system, CaO-Al2O3-SiO2 multiphase system, and B2O3-Al2O3-SiO2 multiphase system.

[0012] By adjusting the composition of the composite ceramic foam slurry and selecting additives, a composite ceramic foam slurry with uniform dispersion can be obtained, so that a composite ceramic foam with uniform thermal conductivity can be formed in subsequent sintering.

[0013] In some possible implementations, the preparation steps of the core-shell packing include: Silane coupling agents are grafted onto the surface of the core material to obtain modified core powder; The modified core powder was mixed with an iron source to form a suspension, the pH of the system was adjusted to 10-11, the reaction was continuously stirred, and then vacuum dried to obtain the core-shell filler.

[0014] The solvothermal in-situ growth preparation of the core-shell filler described above can grow a continuous and uniform nanoscale shell layer in situ on the surface of the core powder, thereby constructing a stable chemically bonded core-shell heterogeneous thermally conductive filler.

[0015] In some possible implementations, the volume average particle size Dv50 of the core material is 2 μm to 5 μm; And / or, the silane coupling agent accounts for 1% to 3% of the mass of the core material; And / or, the silane coupling agent includes at least one of KH550, KH792, and KH602; And / or, the duration of the continuous stirring reaction is 1 h to 3 h; And / or, the vacuum drying conditions include vacuum drying at 50℃~60℃ for 20h~24h.

[0016] By adjusting the core material size, silane coupling agent, and process parameters during the solvothermal in-situ growth of core-shell fillers, a continuous and uniform shell layer can be formed on the core surface, which is less prone to agglomeration.

[0017] In some possible implementations, the preparation steps of the alumina hollow microsphere preform include: Aluminum source, binder and surfactant are dispersed in water to obtain aluminum source foam slurry; The sponge template is immersed in the aluminum source foam slurry for impregnation, then the excess slurry is squeezed out and dried to obtain a sponge preform loaded with aluminum source. The sponge preform is subjected to step-heat oxidation and hollowing to obtain the alumina hollow microsphere preform.

[0018] The aforementioned preparation process of the alumina hollow microsphere preform can be based on in-situ oxidation and cavitation using the Kirkendall effect. This process not only endows the alumina hollow microspheres with a complete hollow microsphere structure, making them less prone to cracking and collapse, but also allows them to serve as supporting units and thermally conductive bridging units for the porous framework. The volume expansion during the subsequent sintering and oxidation process offsets the sintering shrinkage, achieving near-net-shape composite ceramic foam.

[0019] In some possible implementations, the stepped heating includes: heating to 700℃~1000℃ at a heating rate of 0.5~1℃ / min and holding at that temperature for 3h~8h; And / or, the impregnation treatment includes vacuum impregnation for 5 to 10 minutes.

[0020] The step-heating process in the preparation of alumina hollow microsphere preforms can effectively control the Al2O3 crystal transformation, achieve gradual phase transformation, and obtain alumina hollow microsphere preforms with better hollow microsphere structure; moreover, the impregnation process can fully immerse the sponge template in the aluminum source foam slurry.

[0021] In some possible implementations, the sponge template includes at least one of polyurethane sponge, melamine sponge, and cellulose sponge; And / or, the aluminum source includes at least one of aluminum powder, aluminum isopropoxide, and aluminum nitrate; And / or, the adhesive comprises at least one of polyvinyl alcohol, sodium carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylamide, polyvinylpyrrolidone, and methylcellulose; And / or, the surfactant includes at least one of sodium dodecyl sulfate and sodium alkylbenzene sulfonate; And / or, based on the total weight of the aluminum source foam slurry, the aluminum source accounts for 20% to 30%, the surfactant accounts for 0.5% to 1.0%, and the binder accounts for 1% to 3%.

[0022] By adjusting the components and content of each component in the aluminum source foam slurry, a uniform and stable aluminum source foam slurry can be obtained. The aforementioned sponge template can be well immersed in the aluminum source foam slurry, and subsequent degreasing yields a porous preform of alumina hollow microspheres with a porous framework.

[0023] Secondly, this application provides a composite ceramic foam, which is prepared by the preparation method of the first aspect of this application.

[0024] The composite ceramic foam provided in this application is prepared by a unique preparation method. The core-shell filler therein can form an open-cell hierarchical porous structure and a continuous three-dimensional thermally conductive reinforcing skeleton with alumina hollow microspheres. The high porosity, high mechanical strength, high thermal conductivity and uniform thermal conduction performance of such composite ceramic foam material can be well used in the heating core of heating devices.

[0025] Thirdly, this application provides a heating core, including a heating component, wherein the heating component includes the composite ceramic foam provided in the second aspect of this application.

[0026] The metal heating element in the heating core of this application includes the composite ceramic foam of this application. Based on the high porosity, high mechanical strength, high thermal conductivity and uniform heat conduction performance of the composite ceramic foam material, the heating core of this application has excellent heating performance and liquid conduction ability when in use, and the heat field is uniformly distributed and has a long service life.

[0027] Fourthly, this application provides a liquid heating device, including the heating element provided in the third aspect of this application.

[0028] The liquid heating device of this application includes the heating element provided in the third aspect of this application. Based on the advantages of the heating element of this application, the liquid heating device of this application has excellent heating performance, liquid conductivity and service life.

[0029] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the preparation method of the composite ceramic foam provided in this application. Detailed Implementation

[0032] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0033] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0034] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0035] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0036] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0037] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0038] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0039] The term "aerosol" broadly refers to all colloids that can be suspended in the air. The particle size of aerosols is generally about 10 nm to 10 μm, but can be, for example, 10 nm to 1000 nm. This application mainly refers to suspended microparticles / mixtures of suspended particles generated when a heating device is in operation, formed by heating an aerosol generation matrix, and the vapor inhaled by the user is this type of aerosol.

[0040] The term "aerosol generating matrix" refers to a raw material that can generate aerosols upon heating. It is a basic component used in heating devices, whether in liquid, solid, or paste form. Aerosol generating matrix components can consist of various flavoring agents and flavoring substances. Heating and vaporizing the aerosol generating matrix can form aerosols for users to inhale.

[0041] The term "heating device" refers to a device that can heat the object to be heated, i.e., the aerosol-generating matrix, to form an aerosol, such as a liquid heating device or an electronic heating device. Heating devices typically use built-in heating elements (e.g., heating cores) to precisely heat a specially formulated aerosol-generating matrix to a specific temperature, causing some substances in the matrix to evaporate and generate an aerosol for user use. In liquid heating devices, "liquid" includes not only cases where the object to be heated is liquid, but also cases where solid substances (including pastes) liquefy under certain conditions.

[0042] Additionally, SiC@Fe3O4 represents a core-shell structured heterogeneous filler with silicon carbide (SiC) as the core and iron(III) oxide (Fe3O4) as the shell, with @ indicating a core-shell coating structure. PU: Polyurethane, used as a molding template for porous ceramic foam in this application embodiment. PVA: Polyvinyl alcohol, which can be used as a slurry binder in this application embodiment. SDS: Sodium dodecyl sulfate, which can be used as a surfactant in this application embodiment. MAS: Magnesium oxide-alumina-silica (MgO-Al2O3-SiO2) multiphase sintering aid, used to lower the ceramic sintering temperature and promote grain densification.

[0043] Kirkendall effect: When two metals with different diffusion rates diffuse, vacancies are formed at corresponding positions on the diffusion interface due to the difference in atomic diffusion rates, and these vacancies converge to form pores. In the embodiments of this application, hollow Al2O3 microspheres can be prepared based on this effect.

[0044] Thermal conductivity: A physical quantity characterizing the thermal conductivity of a material, measured in W / (m²). K), the higher the value, the better the thermal conductivity.

[0045] Hierarchical porous structure with open pores: refers to a material that simultaneously contains interconnected open pore structures of different sizes. In some embodiments of this application, the constructed hierarchical porous structure with open pores can be a three-level pore structure composed of millimeter-scale three-dimensional through pores, micrometer-scale hollow spherical cavities, and nanometer-scale mesopores.

[0046] The existing porous ceramic foam or high thermal conductivity ceramic composite material used in electronic heating devices generally have the following problems: (1) It is difficult to balance thermal conductivity, porosity and mechanical strength: Although the existing high porosity alumina ceramic foam has good liquid conductivity, its mechanical strength is extremely low (compressive strength is only 0.79~1.35 MPa), which makes it difficult to meet the structural stability of the heating core and is prone to cracking and powdering; while high thermal conductivity SiC ceramics are mostly dense structures with insufficient porosity and poor liquid conductivity, making it difficult to adapt to the uniform transport of aerosol matrix. In other words, a single ceramic system is difficult to achieve the synergistic improvement of the above three core properties. (2) Uneven thermal field distribution and high interfacial thermal resistance: Existing porous ceramics mostly use physical blending of different thermally conductive fillers. The fillers are only mechanically bonded, resulting in weak interfacial bonding and high interfacial thermal resistance. It is difficult to form a continuous three-dimensional thermally conductive network, which leads to local hot spot concentration and uneven heating when the heating core is working. It is also very easy to cause problems such as aerosol matrix cracking, dry burning, and core scorching. At the same time, the single pore size structure is difficult to take into account both the liquid conduction rate and liquid retention performance, further aggravating the thermal field imbalance.

[0047] Based on this, this application provides a composite ceramic foam that combines the aforementioned properties and exhibits superior overall performance. Such a composite ceramic foam material can be well used as a heating material in heating devices. The technical solution is described in detail below.

[0048] In a first aspect, embodiments of this application provide a method for preparing composite ceramic foam. For example... Figure 1 As shown, the preparation method of this application embodiment includes: S01: Provides core-shell fillers and alumina hollow microspheres; wherein, the core-shell filler includes a core and a shell covering the outer surface of the core, the core includes at least one of silicon carbide, boron nitride, aluminum nitride, and boron nitride, and the shell includes at least one of ferric oxide and magnetite; the morphology of the alumina hollow microspheres includes alumina hollow microsphere powder and alumina hollow microsphere preforms; S02: Core-shell filler and alumina hollow microsphere powder are formulated with dispersant and sintering aid to prepare composite ceramic foam slurry; S03: The alumina hollow microsphere preform is mixed with the composite ceramic foam slurry and then dried to obtain the composite ceramic foam blank. S04: The composite ceramic foam blank is sintered to obtain composite ceramic foam.

[0049] In this embodiment, core-shell fillers and alumina hollow microsphere powder are first formulated with dispersants and sintering aids to prepare a composite ceramic foam slurry. Then, the alumina hollow microsphere preform is further mixed with the composite ceramic foam slurry, dried, and sintered to obtain a composite ceramic foam. During this process, the core-shell fillers provide stable core-shell heterogeneous thermally conductive fillers, effectively reducing the interfacial thermal resistance with the matrix. Simultaneously, the shell layer on the surface of the core-shell fillers assists in the directional growth of grains during sintering, improving the continuity of the thermally conductive network. It can also form an open-cell, hierarchical porous structure and a continuously interconnected three-dimensional thermally conductive reinforcing skeleton with the alumina hollow microspheres. Through the integrated drying and sintering process of the composite ceramic foam slurry, the final composite ceramic foam material product achieves high porosity, high mechanical strength, high thermal conductivity, and uniform thermal conductivity. The composite ceramic foam material prepared in this application can be well used in the heating core of heating devices, possessing advantages such as controllable pore structure, uniform heat field distribution, good process repeatability, and suitability for industrial mass production.

[0050] Step S01 is the preparation step of composite ceramic foam raw material components.

[0051] The core material of the core-shell packing can be at least one of silicon carbide (SiC), aluminum nitride (AlN), boron nitride (BN), and boron carbide (B4C). The shell material can be at least one of iron(III) oxide (Fe3O4) and iron oxide (Fe2O3). For example, the core-shell packing can be a SiC@Fe3O4 core-shell heterogeneous thermally conductive packing. Such a core-shell packing has better thermal conductivity.

[0052] In the embodiments of this application, the core-shell filler can be prepared in various ways, such as solvothermal method, atomic layer deposition (ALD), chemical vapor deposition (CVD), etc. The above methods can construct a nanoshell on the surface of the core material, thereby achieving atomic-level precise control of the shell thickness.

[0053] In some possible implementations, the preparation steps of the core-shell filler include: grafting a silane coupling agent onto the surface of the core material to obtain a modified core powder; preparing a suspension of the modified core powder with an iron source, adjusting the pH of the system to 10-11, and continuously stirring the reaction to allow in-situ growth of the shell layer on the surface of the core material; and then vacuum drying to obtain the core-shell filler. In this application, the core-shell filler is prepared by solvothermal in-situ growth, which allows for the in-situ growth of a continuous and uniform nanoscale shell layer on the surface of the core powder, thereby constructing a stable chemically bonded shell heterogeneous thermally conductive filler. For example, SiC can be used as the core powder, and it can be a divalent iron source or a trivalent iron source, ultimately obtaining a SiC@Fe3O4 core-shell heterogeneous thermally conductive filler.

[0054] In some possible implementations, the iron source for forming the ferric oxide shell can be a ferric iron source; for example, the iron source can be ferric chloride or a metallic iron salt precursor such as ferric sulfate. The iron source for forming the magnetite shell can be a ferrous iron source or a ferric iron source. For example, the iron salt precursor can be a combination of ferrous chloride and ferric chloride, or a metallic iron salt such as ferrous sulfate and ferric sulfate. Furthermore, by adjusting the core size, silane coupling agent, and process parameters during the solvothermal in-situ growth of the core-shell filler, ferric oxide or magnetite can form a continuous and uniform shell that is less prone to agglomeration.

[0055] For example, the average thickness of the grown shell can be 10 nm to 100 nm, such as 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc. The average particle size of the finally prepared core-shell filler is 2.02 μm to 5.10 μm, such as 2.03 μm, 2.05 μm, 2.06 μm, 2.08 μm, 2.10 μm, etc.

[0056] In some possible implementations, the volume-average particle size (Dv50) of the core material is 2 μm to 5 μm; that is, the particle size corresponding to a cumulative volume distribution of 50%. As a core-shell structure, it can dominate the thermal phase.

[0057] In some possible implementations, the silane coupling agent accounts for 1% to 3% of the core material mass. Adding this proportion of silane coupling agent can effectively modify the core surface, which is more conducive to shell growth. Optionally, the silane coupling agent includes at least one of KH550 (γ-aminopropyltriethoxysilane), KH792 (N-(β-aminoethyl)-γ-aminopropyltrimeth(eth)oxysilane), and KH602 (N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane). The above-mentioned silane coupling agent introduces an amino group (-NH2) by condensing an alkoxy group with the existing hydroxyl group on the core surface, thereby promoting uniform nucleation and growth of the shell.

[0058] In some possible implementations, the step of grafting a silane coupling agent onto the core surface includes: taking silicon carbide as an example, adding micron-sized SiC powder to a mixed solvent of anhydrous ethanol and water to prepare a suspension with a mass percentage of 8-12 wt%, then adding a silane coupling agent accounting for 1-3 wt% of the silicon carbide powder, ultrasonically dispersing for 30-60 min, and finally filtering, washing, and drying to obtain modified silicon carbide powder.

[0059] In some possible implementations, modified core powder is prepared into a suspension with an iron source, the pH of the system is adjusted to 10-11, and the reaction is continuously stirred for 1-3 hours, followed by vacuum drying to obtain the core-shell filler. Taking SiC@Fe3O4 core-shell heterogeneous thermally conductive filler as an example, silane coupling agent-modified silicon carbide powder is prepared into a suspension with divalent iron and trivalent iron sources, the pH of the system is adjusted to 10-11, and the reaction is continuously stirred for 1-3 hours. Specifically, ammonia water can be added dropwise under nitrogen protection to adjust the pH of the system to 10-11, and then the reaction is continuously stirred for 1-3 hours, which allows for the uniform growth of the shell layer on the silicon carbide surface.

[0060] In some possible implementations, vacuum drying conditions include vacuum drying at 50-60°C for 20-24 hours. For example, after adjusting the pH of the system to 10-11 and continuously stirring the reaction, the mixture is separated and then vacuum dried under the above conditions to obtain a core-shell heterogeneous thermally conductive packing.

[0061] In some embodiments, taking SiC@Fe3O4 core-shell heterogeneous thermally conductive filler as an example, the in-situ growth of the shell layer includes: dispersing modified silicon carbide powder in water to prepare a uniform suspension of 6-10 wt%; purging with high-purity nitrogen to remove oxygen; adding two iron salt precursors at a Fe²⁺ to Fe³⁺ molar ratio of 1:2; mechanically stirring until completely dissolved; heating to 50-60°C; adding ammonia dropwise under nitrogen protection to adjust the pH of the system to 10-11; continuously stirring the reaction for 1-3 hours to grow the shell layer in situ. Subsequently, after the reaction is completed, magnetic separation is performed; the filtrate is washed alternately with deionized water and anhydrous ethanol until neutral; and then the SiC@Fe3O4 core-shell heterogeneous thermally conductive filler is vacuum dried.

[0062] In the above process, the shell thickness can be controlled by adjusting the amount of iron salt precursor added, and the shell coating amount can be controlled to be 5%~20% of the core powder mass, resulting in a continuous and uniform shell layer and preventing filler agglomeration. Specifically, in some embodiments, the mass ratio of the core to the shell in the prepared core-shell filler can be 100:(5~20). In some embodiments, the average particle size of the prepared core-shell filler is 2.02μm~5.10μm, and the average shell thickness is 10nm~100nm. When the shell coating amount is 5%~20% of the core powder mass, the final shell thickness is approximately 10nm~100nm.

[0063] In this embodiment, the alumina hollow microspheres can be prepared in various ways, such as the sol-gel method or the in-situ oxidation method based on the Kirkendall effect. The aluminum powder precursor can be replaced with aluminum sources such as aluminum isopropoxide or aluminum nitrate to prepare Al2O3 hollow microspheres.

[0064] The morphology of alumina hollow microspheres includes alumina hollow microsphere powder and alumina hollow microsphere preforms. Alumina hollow microsphere preforms of a certain size can be prepared according to the needs of actual composite ceramic foam products. For alumina hollow microsphere powder, preforms can be prepared first using the same method, and then ground into powder.

[0065] In some possible implementations, the preparation steps of the alumina hollow microsphere preform include: dispersing an aluminum source, binder, and surfactant in water to obtain an aluminum source foam slurry; immersing a sponge template in the aluminum source foam slurry for impregnation, then squeezing out excess slurry and drying to obtain a sponge preform loaded with the aluminum source; and subjecting the sponge preform to step-heat oxidation and cavitation to obtain the alumina hollow microsphere preform. The above-mentioned preparation process of the alumina hollow microsphere preform can be based on in-situ oxidation and cavitation using the Kirkendall effect. This process not only allows the alumina hollow microspheres to have a complete hollow microsphere structure, making them less prone to cracking and collapse, but also allows them to serve as supporting units and thermally conductive bridging units for a porous framework. The volume expansion during the subsequent sintering and oxidation process offsets the sintering shrinkage, achieving near-net-shape composite ceramic foam.

[0066] In some possible implementations, the aluminum source includes at least one of aluminum powder, aluminum isopropoxide, and aluminum nitrate. For example, embodiments of this application use spherical aluminum powder (volume average particle size Dv). 50 =500nm~2μm) as a precursor for Al2O3 hollow microspheres.

[0067] In some possible implementations, the binder in the formulated aluminum source foam slurry includes at least one selected from polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyacrylamide (HEC), polyvinylpyrrolidone (PVP), and methyl cellulose (MC); the surfactant includes at least one selected from sodium alkyl sulfate and sodium alkylbenzene sulfonate; for example, sodium dodecyl sulfate or sodium dodecylbenzene sulfate. Both the aforementioned binder and surfactant can ensure that the formulated aluminum source foam slurry is uniformly dispersed and stable.

[0068] In some possible implementations, the prepared aluminum source foam slurry, based on its total weight, comprises 20%–30% aluminum source, 0.5%–1.0% surfactant, and 1%–3% binder. By further adjusting the content of each component in the aluminum source foam slurry, a more uniform and stable aluminum source foam slurry can be obtained. For example, in some embodiments, aluminum source powder is added to an aqueous binder solution and ultrasonically dispersed for 20–40 min to prepare a uniform suspension slurry with an aluminum content of 20–30 wt%; then, 0.5–1.0 wt% surfactant is added, and the mixture is stirred at high speed (1000–1500 rpm) for 5–10 min to obtain a uniform and stable aluminum source foam slurry.

[0069] In some possible implementations, the sponge template is pre-cleaned before use. For example, the sponge template can be ultrasonically cleaned with ethanol, dried, and then completely immersed in the preceding aluminum source foam slurry.

[0070] In some possible implementations, the immersion treatment of the sponge template in aluminum source foam slurry includes vacuum impregnation for 5 to 10 minutes. This allows the sponge template to be fully immersed in the aluminum source foam slurry. After vacuum impregnation, excess slurry is squeezed out, and the material is dried by forced air to obtain a sponge preform loaded with aluminum source.

[0071] In some possible implementations, the sponge template includes at least one of polyurethane sponge, melamine sponge, and cellulose sponge. The aforementioned sponge template can be well impregnated with aluminum-source foam slurry, and subsequent degreasing yields a porous preform of alumina hollow microspheres with a porous framework.

[0072] The aforementioned organic porous sponge template can be used to prepare customized resin sponge templates through 3D printing technology, thereby achieving directional design of the pore structure.

[0073] In some possible implementations, the step-heating oxidation and cavitation process of the aluminum-loaded sponge preform includes heating to 700-1000℃ at a rate of 0.5-1℃ / min and holding at that temperature for 3-8 hours. This process allows for in-situ oxidation and cavitation of the aluminum source, forming Al2O3 hollow microspheres based on the Kirkendall effect, while simultaneously degreasing the sponge template. This process effectively controls the Al2O3 crystal transformation, achieving a gradual phase transition and yielding alumina hollow microspheres with a better hollow microsphere structure. For example, in some implementations where the aluminum source is aluminum powder, this application embodiment controls the Al2O3 crystal transformation through step-heating, achieving a gradual phase transition from Al to γ-Al2O3 to θ-Al2O3 to α-Al2O3.

[0074] Step S02 is the preparation step of composite ceramic foam slurry.

[0075] For example, according to the required proportions, core-shell fillers and alumina hollow microsphere powder can be formulated with dispersants and sintering aids to prepare composite ceramic foam slurry. For alumina hollow microsphere powder, a preform can be prepared first using the same method, and then the preform can be ground into powder according to the required proportions.

[0076] Alumina hollow microsphere preform: As a macroscopic framework, it provides millimeter-level through-holes, accounting for approximately 100% of the final product volume. Alumina hollow microsphere powder: When mixed with core-shell filler to form a composite ceramic foam slurry, it fills the pores of the preform, achieving a filling rate of 80%~90%. Mass ratio: Based on a total weight of 100% alumina hollow microspheres, the alumina hollow microsphere preform comprises 60%~70%, and the alumina hollow microsphere powder filling portion comprises 30%~40%. That is, in the final composite ceramic foam product, the mass ratio of alumina hollow microsphere preform to alumina hollow microsphere powder is (6:4)~(7:3).

[0077] In some possible implementations, the mass ratio of core-shell filler to alumina hollow microsphere powder is 1:3 to 5:1. This ratio, when mixed to prepare composite ceramic foam slurry, can be filled into alumina hollow microsphere preforms, resulting in better mechanical strength. Further, the mass ratio of the core to the shell in the core-shell filler is 100:(5~20); the average particle size of the core-shell filler is 2.02 μm to 5.10 μm, and the average thickness of the shell is 10 nm to 100 nm; the average outer diameter of the alumina hollow microspheres is 600 nm to 2.56 μm, and the average wall thickness is 50 nm to 300 nm. By selecting the mass ratio and size of the core-shell filler to the alumina hollow microspheres, a better three-level open-pore hierarchical porous structure—millimeters-scale three-dimensional through-pores, micrometer-scale hollow spherical cavities, and nanometer-scale mesopores—and a continuously interconnected three-dimensional thermally conductive reinforcing framework can be constructed.

[0078] For example, in some embodiments, three-dimensional through-holes with a pore size of approximately 100 μm to 1000 μm can be obtained by replicating with a sponge template; micron-sized hollow spherical cavities with an inner diameter of approximately 400 nm to 2.5 μm can be provided by using alumina hollow microspheres; and nano-sized mesopores with a pore size of approximately 2 nm to 50 nm can be formed by the gaps between ceramic grains.

[0079] In some possible implementations, the solid content of the composite ceramic foam slurry is 40% to 60%; the dispersant accounts for 1% to 2% of the total weight of the core-shell filler and alumina hollow microsphere powder; and the sintering aid accounts for 1% to 4% of the total weight of the core-shell filler and alumina hollow microsphere powder. A uniform composite ceramic foam slurry can be obtained through the above proportions.

[0080] For example, the preparation steps of composite ceramic foam slurry include: weighing core-shell filler powder and Al2O3 hollow microsphere powder according to the set mass ratio, adding water, 1~2wt% of dispersant and 1~4wt% of sintering aid of total powder mass, ball milling for 2~4 hours, ball-to-material ratio of 5:1, to obtain a uniform composite ceramic foam slurry with a solid content of 40~60wt%.

[0081] In some possible implementations, the dispersant includes at least one of polyethylene glycol (PEG), ammonium polyacrylate (PAA-NH4), sodium hexametaphosphate (SHMP), and sodium tripolyphosphate (STPP); the above dispersants have good dispersibility. In some embodiments, the sintering aid may be at least one of the following: MgO-Al2O3-SiO2 composite system (MAS), Y2O3-Al2O3-SiO2 multiphase system (YAS), CaO-Al2O3-SiO2 multiphase system (CAS), and B2O3-Al2O3-SiO2 multiphase system (BAS).

[0082] Taking MAS sintering aid as an example, at around 1200~1300℃, the MAS system first forms a eutectic liquid phase. The liquid phase wets the core-shell filler and the surface of the Al2O3 hollow microspheres, promoting material diffusion. The liquid phase reacts with Al2O3 to generate magnesium aluminum spinel (MgAl2O4) and mullite (3Al2O3). Intermediate phases such as 2SiO2 fill the interparticle gaps and promote the densification of the ceramic skeleton. Finally, the MAS sintering aid remains in the final ceramic and exists at the grain boundaries in the form of magnesium aluminum spinel, mullite and a small amount of glass phase, which plays a role in strengthening the grain boundaries and improving mechanical strength.

[0083] The aforementioned multiphase sintering aids not only contain no heavy metal elements, but can also further reduce the sintering temperature and optimize the interfacial bonding performance.

[0084] In some possible implementations, at least one of defoamers and toughening agents can be added to the composite ceramic foam slurry. For example, polydimethylsiloxane defoamer can be added in trace amounts (e.g., 0.5-1 wt% of the total powder mass) to regulate the stability of the composite ceramic foam slurry. Nanoscale ZrO2 particles (<5% of the total powder mass) can also be added as a toughening phase to further improve the material's thermal shock resistance and mechanical strength.

[0085] In some possible implementations, alumina hollow microspheres are added in the form of alumina hollow microsphere preforms and alumina hollow microsphere powder, with a mass ratio of alumina hollow microsphere preforms to alumina hollow microsphere powder of (6:4) to (7:3). The alumina hollow microsphere powder is formulated into a composite ceramic foam slurry (wherein the mass ratio of core-shell filler to alumina hollow microsphere powder is 1:3 to 5:1), and the alumina hollow microsphere preforms are mixed with the composite ceramic foam slurry.

[0086] In some possible implementations, the alumina hollow microsphere preform is repeatedly vacuum-impregnated in the composite ceramic foam slurry 2-4 times, each time for 10-20 minutes. This yields a more uniform and dense composite ceramic foam. For example, the Al2O3 hollow microsphere porous preform is completely immersed in the composite ceramic foam slurry, vacuum-impregnated for 10-20 minutes, and repeated 2-4 times, with drying after each impregnation, ultimately obtaining a uniformly dispersed composite ceramic foam preform.

[0087] In summary, the embodiments of this application can obtain a composite ceramic foam slurry with uniform dispersion by adjusting the composition of the composite ceramic foam slurry and selecting additives, so that a composite ceramic foam with uniform thermal conductivity can be formed by subsequent sintering.

[0088] Step S03 is the step of forming a composite ceramic foam green body.

[0089] In some possible implementations, the drying process includes drying at 80℃~110℃ for 10h~15h. This drying process allows for better evaporation of the solvent in the composite ceramic foam slurry impregnated in the alumina hollow microsphere preform, resulting in a uniform composite ceramic foam preform. For example, after preparing the composite ceramic foam slurry and vacuum impregnating the Al2O3 hollow microsphere porous preform, it is dried at 80℃~110℃ for 10h~15h to obtain the composite ceramic foam preform.

[0090] Step S04 is the composite ceramic foam sintering and molding step.

[0091] The sintering process can be carried out in a high-purity argon atmosphere or a nitrogen atmosphere, which can effectively reduce the risk of oxidation of the core and shell filler at high temperatures, thereby improving the performance stability of the sintered product material.

[0092] In some possible implementations, the sintering process includes: first heating to 400℃~600℃ and holding for 1~2 hours, then heating to 1100℃~1300℃ and holding for 2~3 hours, and then heating to 1450℃~1750℃ and holding for 1~5 hours. This sintering process sequentially passes through a degreasing stage (400℃~600℃, holding for 1~2 hours to remove residual organic matter), a solid-state reaction stage (promoting the interfacial reaction between the core-shell filler and Al2O3 to form a chemically bonded transition layer and reduce interfacial thermal resistance), and a densification sintering stage (densifying the ceramic skeleton and constructing a three-dimensional thermally conductive network), ultimately yielding the composite ceramic foam required in this application.

[0093] The sintering process described above not only promotes grain growth but also facilitates the exchange of grain growth and interfacial bonding. Furthermore, it ensures a complete and thorough solid-phase reaction, which is beneficial for the better and more stable formation of interfacial bonds and pore structures.

[0094] In some embodiments, the heating rate during the degreasing stage can be 2~5℃ / min, the heating rate during the solid-state reaction stage can be 2~5℃ / min, and the heating rate during the densification sintering stage can be 2~5℃ / min. This makes the entire reaction process more stable.

[0095] In some possible implementations, after sintering, the material is cooled to room temperature (25~30℃) to obtain a porous composite ceramic foam product.

[0096] The aforementioned sintering process is less prone to cracking and pore structure collapse, exhibits minimal performance fluctuations, and allows for near-net-shape molding, thus effectively meeting the high-precision and high-consistency mass production requirements of heating cores. Ultimately, the embodiments of this application, through a combination of raw material adjustments and sintering parameters, can directionally control the porosity, pore size distribution, thermal conductivity, and mechanical strength of the material. The resulting composite ceramic foam, used in the heating core, exhibits uniform heating, good thermal conductivity, and structural stability.

[0097] Secondly, this application provides an embodiment of a composite ceramic foam. The composite ceramic foam of this embodiment is prepared by the preparation method described above in the embodiment of this application.

[0098] In this embodiment, a composite ceramic foam is obtained by combining core-shell fillers and alumina hollow microspheres through a unique slurry preparation and sintering process. The core-shell fillers and alumina hollow microspheres can construct an open-cell hierarchical porous structure and a continuously interconnected three-dimensional thermally conductive reinforcing skeleton. The high porosity, high mechanical strength, high thermal conductivity, and uniform thermal conduction properties of this composite ceramic foam material make it well-suited for use in the heating core of heating devices.

[0099] For example, in some embodiments of this application, taking SiC@Fe3O4 core-shell heterogeneous thermally conductive filler as an example, a continuous and uniform Fe3O4 nanoshell layer is grown in situ on the surface of SiC powder using a solvothermal method to construct a chemically bonded SiC@Fe3O4 core-shell heterogeneous thermally conductive filler. This can reduce the interfacial thermal resistance between the filler and the matrix, while the Fe3O4 shell layer can assist in the directional growth of grains during sintering, optimizing the continuity of the thermally conductive network; and based on Kirkendall… The effect involves preparing Al2O3 hollow microsphere preforms through in-situ oxidation and cavitation of spherical aluminum powder. These preforms serve as supporting units and thermally conductive bridging units for the porous framework. The volume expansion during the oxidation process offsets the sintering shrinkage, achieving near-net-shape molding. Finally, the aforementioned core-shell filler is combined with Al2O3 hollow microsphere powder. Through a foam slurry impregnation process followed by in-situ reaction sintering of the Al2O3 hollow microsphere preforms, a three-level (millimeter-level three-dimensional through-pores - micrometer-level hollow spherical cavities - nanometer-level mesopores) open-pore hierarchical porous structure and a continuously interconnected three-dimensional thermally conductive network are constructed. This achieves synergistic optimization of the porosity, mechanical strength, thermal conductivity, and thermal uniformity of the composite ceramic foam material, thus well meeting the application requirements of heating cores in electronic heating devices.

[0100] Thirdly, embodiments of this application provide a heating element. Specifically, the heating element of this application includes a heating component, which includes the composite ceramic foam described above in this application.

[0101] The heating core in this embodiment of the application has the advantages of high porosity, high mechanical strength, high thermal conductivity and uniform heat conduction performance based on the composite ceramic foam material. Therefore, when the heating core of this embodiment of the application is used, it has good heating performance and liquid conduction ability, and the heat field distribution is uniform and the service life is long.

[0102] Fourthly, this application provides a liquid heating device. Specifically, the liquid heating device of this application embodiment includes the heating element provided in the third aspect of this application embodiment.

[0103] Based on the advantages of the heating element in this embodiment, the liquid heating device of this application has excellent heating performance, liquid conductivity and service life.

[0104] The present application will be further described in detail below with reference to specific embodiments.

[0105] The raw materials used in the examples are as follows: Core-shell structure thermally conductive filler material: micron-sized SiC powder: D v50 =2~5μm, purity ≥99.5%, core-shell structure with the inner core and dominant thermal phase; ferrous chloride hexahydrate (FeCl2) 4H2O), ferric chloride hexahydrate (FeCl3) 6H2O): Analytical grade, Fe3O4 shell precursor; Silane coupling agent KH550: Analytical grade, SiC powder surface modifier; Anhydrous ethanol, deionized water: Analytical grade, dispersion medium; Ammonia (25%~28%): Analytical grade, pH adjuster and precipitant.

[0106] Al2O3 hollow microsphere raw material: spherical aluminum powder: D v50 =500nm~2μm, purity ≥99.9%, Al2O3 hollow microsphere precursor; Polyvinyl alcohol (PVA): degree of polymerization 1750±50, degree of alcoholysis 99%, binder; Sodium dodecyl sulfate (SDS): analytical grade, surfactant and foam stabilizer; Deionized water: dispersion medium.

[0107] Molding and sintering aids: Polyurethane (PU) sponge template: 60~100PPI, open-cell structure, porous skeleton molding template; MAS multiphase sintering aids: MgO-Al2O3-SiO2, D v50 ≤1μm, added at 1~4wt% of total powder mass; Polyethylene glycol 2000 (PEG2000): analytical grade, dispersant, added at 1~2wt% of total powder mass; Polydimethylsiloxane: analytical grade, defoamer, added in trace amounts to regulate slurry stability.

[0108] Example 1 A composite ceramic foam, the detailed preparation steps are as follows: Step 1: Preparation of SiC@Fe3O4 core-shell heterogeneous thermally conductive filler.

[0109] 1.1) Surface pretreatment of SiC powder: Pretreatment of micron-sized SiC powder (D 50=2~5μm) was added to a mixed solvent of anhydrous ethanol and deionized water (volume ratio 3:1) to prepare a 10wt% suspension. 2wt% KH550 of SiC powder was added, and the mixture was ultrasonically dispersed for 30min, mechanically stirred in a water bath at 60℃ for 2h, filtered, washed 3 times with anhydrous ethanol, and vacuum dried at 80℃ for 12h to obtain the modified SiC powder.

[0110] 1.2) Solventothermic in-situ growth of Fe3O4 shell: Modified SiC powder was dispersed in deionized water in a three-necked flask to prepare an 8wt% homogeneous suspension. High-purity nitrogen was introduced for 30 min to remove oxygen. The Fe2+ layer was then grown in situ. + With Fe³ + Ferrous chloride and ferric chloride were added in a molar ratio of 1:2 and mechanically stirred for 30 min until completely dissolved. The temperature was raised to 60℃, and ammonia was slowly added dropwise under nitrogen protection to adjust the pH of the system to 10-11. The reaction was continued with stirring for 1 h. After the reaction, magnetic separation was performed, and the filtrate was washed alternately with deionized water and anhydrous ethanol until neutral. The filtrate was then vacuum dried at 60℃ for 24 h to obtain SiC@Fe3O4 core-shell heterogeneous thermally conductive filler. The Fe3O4 coating amount was controlled to be 10% of the SiC powder mass, and the silicon carbide core D v50= 3μm, with an iron oxide shell of about 30nm.

[0111] Step 2: Preparation of porous Al2O3 hollow microspheres based on the Kirkendall effect.

[0112] 2.1) Preparation of aluminum powder foam slurry: Add spherical aluminum powder to 2wt% PVA aqueous solution, ultrasonically disperse for 20 min to prepare a uniform suspension slurry; add 0.8wt% SDS of the total slurry mass, and mechanically stir at 1500 rpm for 10 min to obtain a uniform and stable aluminum powder foam slurry (total weight 100%: aluminum powder 25wt%, PVA 2.0wt%, SDS 0.8wt%, deionized water 72.2wt%).

[0113] 2.2) Template impregnation and preforming: After ultrasonic cleaning with ethanol for 20 minutes and drying, the PU sponge template is completely immersed in foam slurry, vacuum impregnated for 10 minutes, excess slurry is squeezed out, and it is dried at 65°C for 24 hours to obtain a PU sponge preform loaded with aluminum powder.

[0114] 2.3) Low-temperature pre-oxidation and cavitation: The sponge preform is placed in a muffle furnace and heated to 700~1000℃ at 0.5℃ / min in an air atmosphere and held for 3~8h to achieve in-situ oxidation and cavitation of aluminum powder. Based on the Kirkendall effect, Al2O3 hollow microspheres are formed. At the same time, the PU template is degreased to obtain a porous preform of Al2O3 hollow microspheres.

[0115] The Al2O3 hollow microsphere powder in the prepared composite ceramic foam slurry can be obtained by grinding its preform. The dimensions of the alumina hollow microspheres are: average outer diameter 1.5μm, average inner diameter 1.2μm, and average wall thickness 300nm.

[0116] Step 3: Preparation of composite ceramic foam slurry and shaping of green body.

[0117] 3.1) Composite Slurry Preparation: Weigh SiC@Fe3O4 core-shell filler and Al2O3 hollow microsphere powder according to the set mass ratio, add deionized water, PEG2000, and MAS sintering aid, and ball mill at high speed for 2 hours. The ball-to-material ratio is 5:1 to obtain a uniform composite ceramic foam slurry with a solid content of 50wt% (total weight 100%: SiC@Fe3O4 39.75wt%, Al2O3 hollow microspheres 7.95wt%, PEG2000 0.8wt%, MAS 1.5wt%, deionized water 50.0wt%). In the composite ceramic foam slurry, the feed ratio of SiC@Fe3O4:Al2O3 is 5:1.

[0118] 3.2) Secondary impregnation and preparation of green body: The porous preform of hollow Al2O3 microspheres was completely immersed in the composite ceramic foam slurry and impregnated twice under vacuum (10 min each time). After each impregnation, it was dried at 80℃ for 2 h and finally dried at 110℃ for 12 h to obtain the SiC@Fe3O4-Al2O3 composite ceramic foam green body.

[0119] Step 4: High-temperature reaction sintering and finished product preparation.

[0120] The green blank was placed in an atmosphere sintering furnace and sintered under a high-purity argon atmosphere according to the following step temperature increase regime: 4.1) Degreasing stage: Increase the temperature to 600℃ at a rate of 2℃ / min and hold for 1 hour; 4.2) Solid-state reaction stage: Increase the temperature to 1200℃ at a rate of 5℃ / min and hold for 2 hours; 4.3) Densification sintering stage: Heat to 1450℃ at 3℃ / min and hold for 1 hour; Finally, the furnace was allowed to cool naturally to room temperature to obtain the SiC@Fe3O4-Al2O3 porous composite ceramic foam product.

[0121] Example 2-10 The differences between this example and Example 1 are shown in Table 1.

[0122] Comparative Examples 1-2 The differences between Example 5 and Example 6 are shown in Table 2.

[0123] Performance testing methods (1) Mechanical properties: The three-point bending method was tested according to GB / T 6569-2006, with a sample size of 4 mm × 3 mm × 36 mm, a span of 30 mm, and a loading rate of 0.5 mm / min; the compressive strength was tested according to GB / T 1964-1996, with a sample size of 20 mm × 20 mm × 20 mm, a loading rate of 0.5 mm / min, and the average value of 5 samples in each group was taken.

[0124] (2) Porosity and pore size distribution: The total porosity was tested by the Archimedes drainage method according to GB / T 25995-2010; the pore size distribution was tested by the mercury porosimetry method, and the average value of 3 samples in each group was taken.

[0125] (3) Thermal conductivity: The thermal conductivity was tested by laser flash method according to GB / T 22588-2008 at a test temperature of 25℃. The average value of 3 samples in each group was taken.

[0126] (4) Thermal uniformity test: Using an infrared thermal imager, the sample is made into a standard heating core (cylindrical, diameter = 6mm, length = 10mm), and works continuously for 30s at a rated working power of 8W (3.7V voltage, resistance ≈ 1.7Ω). The difference between the highest and lowest surface temperatures is recorded. The smaller the difference, the better the thermal uniformity. The average value of 5 samples is taken for each group.

[0127] The test results for Examples 1-10 are shown in Table 1, and the test results for Comparative Examples 1-2 are shown in Table 2.

[0128] Table 1

[0129] Table 2

[0130] Based on the data results in Tables 1 and 2 above, we can conclude that: In the embodiments of this application, the flexural strength (302~356 MPa), compressive strength (12.5~17.2 MPa), and thermal conductivity (41.8~51.3 W / (m²)) of all embodiments are specified. The K values ​​were significantly higher than all comparative examples, and the maximum temperature difference in the thermal field (4.2~8.2℃) was much lower than that of the comparative examples, with the porosity stably controlled within the range of 45.3%~58.2%. Among them, Example 5 showed the best overall performance, achieving the optimal balance between "liquid conduction-liquid locking-thermal conduction-strength," and its overall performance far exceeded that of other examples and all comparative examples, making it better suited to the usage requirements of the heating element in electronic heating devices.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing composite ceramic foam, characterized in that, include: The invention provides core-shell fillers and hollow alumina microspheres; wherein the core-shell filler comprises a core and a shell covering the outer surface of the core, the core comprises at least one of silicon carbide, boron nitride, aluminum nitride, and boron nitride, and the shell comprises at least one of ferric oxide and magnetite; the hollow alumina microspheres are morphologically defined as hollow alumina microsphere powder and hollow alumina microsphere preforms. The core-shell filler and the alumina hollow microsphere powder are formulated with dispersant and sintering aid to prepare a composite ceramic foam slurry. The alumina hollow microsphere preform is mixed with the composite ceramic foam slurry and then dried to obtain a composite ceramic foam preform. The composite ceramic foam blank is sintered to obtain a composite ceramic foam.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the core-shell filler to the alumina hollow microsphere powder is 1:3~5:1; And / or, the mass ratio of the alumina hollow microsphere preform to the alumina hollow microsphere powder is 6:4 to 7:3; And / or, the mass ratio of the core to the shell in the core-shell packing is 100:(5~20). And / or, the average particle size of the core-shell packing is 2.02 μm to 5.10 μm, and the average thickness of the shell layer is 10 nm to 100 nm; And / or, the alumina hollow microspheres have an average outer diameter of 600 nm to 2.56 μm and an average wall thickness of 50 nm to 300 nm.

3. The preparation method according to claim 1, characterized in that, The sintering process includes: first heating to 400℃~600℃ and holding for 1~2 hours, then heating to 1100℃~1300℃ and holding for 2~3 hours, and then heating to 1450℃~1750℃ and holding for 1~5 hours. And / or, the mixing process includes repeatedly vacuum impregnating the alumina hollow microsphere preform in the composite ceramic foam slurry 2 to 4 times, each time for 10 to 20 minutes; And / or, the drying process includes: drying at 80℃~110℃ for 10h~15h.

4. The preparation method according to claim 1, characterized in that, The solid content in the composite ceramic foam slurry is 40%~60%; And / or, at least one of defoamer and toughening agent may be added to the composite ceramic foam slurry; And / or, the dispersant accounts for 1% to 2% of the total weight of the core-shell filler and the alumina hollow microsphere powder; And / or, the dispersant includes at least one of polyethylene glycol, ammonium polyacrylate, sodium hexametaphosphate, and sodium tripolyphosphate; And / or, the sintering aid accounts for 1% to 4% of the total weight of the core-shell filler and the alumina hollow microsphere powder; And / or, the sintering aid includes at least one of the following: MgO-Al2O3-SiO2 multiphase system, Y2O3-Al2O3-SiO2 multiphase system, CaO-Al2O3-SiO2 multiphase system, and B2O3-Al2O3-SiO2 multiphase system.

5. The preparation method according to any one of claims 1-4, characterized in that, The preparation steps of the core-shell packing include: Silane coupling agents are grafted onto the surface of the core material to obtain modified core powder; The modified core powder was mixed with an iron source to form a suspension, the pH of the system was adjusted to 10-11, the reaction was continuously stirred, and then vacuum dried to obtain the core-shell filler.

6. The preparation method according to claim 5, characterized in that, The volume average particle size Dv50 of the core material is 2μm~5μm; And / or, the silane coupling agent accounts for 1% to 3% of the mass of the core material; And / or, the silane coupling agent includes at least one of KH550, KH792, and KH602; And / or, the duration of the continuous stirring reaction is 1 h to 3 h; And / or, the vacuum drying conditions include vacuum drying at 50℃~60℃ for 20h~24h.

7. The preparation method according to any one of claims 1-4, characterized in that, The preparation steps of the alumina hollow microsphere preform include: Aluminum source, binder and surfactant are dispersed in water to obtain aluminum source foam slurry; The sponge template is immersed in the aluminum source foam slurry for impregnation, then the excess slurry is squeezed out and dried to obtain a sponge preform loaded with aluminum source. The sponge preform is subjected to step-heat oxidation and hollowing to obtain the alumina hollow microsphere preform.

8. The preparation method according to claim 7, characterized in that, The stepped heating includes: heating to 700℃~1000℃ at a heating rate of 0.5~1℃ / min, and holding at that temperature for 3h~8h; And / or, the impregnation treatment includes vacuum impregnation for 5 to 10 minutes.

9. The preparation method according to claim 7, characterized in that, The sponge template includes at least one of polyurethane sponge, melamine sponge, and cellulose sponge; And / or, the aluminum source includes at least one of aluminum powder, aluminum isopropoxide, and aluminum nitrate; And / or, the adhesive comprises at least one of polyvinyl alcohol, sodium carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylamide, polyvinylpyrrolidone, and methylcellulose; And / or, the surfactant includes at least one of sodium alkyl sulfate and sodium alkylbenzene sulfonate; And / or, based on the total weight of the aluminum source foam slurry, the aluminum source accounts for 20% to 30%, the surfactant accounts for 0.5% to 1.0%, and the binder accounts for 1% to 3%.

10. A composite ceramic foam, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

11. A heating element, characterized in that, It includes a heating element, which includes the composite ceramic foam of claim 10.

12. A liquid heating device, characterized in that, Includes the heating element as described in claim 11.

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