Preparation method of composite functional ceramsite for electromagnetic wave absorption and concrete

Abstract

The application relates to the technical field of building materials, in particular to a preparation method of composite functional ceramsite for electromagnetic wave absorption and concrete. The preparation method of the composite functional ceramsite for electromagnetic wave absorption comprises the following steps: pre-mixing a ceramsite base raw material and micron-grade rutile type titanium dioxide powder according to a preset ratio, then mechanically mixing to obtain uniform mixed powder, then adding water into the mixed powder and preparing green balls; subsequently, the green balls are placed in a sintering device and dried in an environment with a temperature of 105-150 DEG C, then sintering is carried out, and finally natural cooling is carried out to obtain the composite functional ceramsite; the mass of the rutile type titanium dioxide powder accounts for 0.5-20% of the total mass of the raw materials; and the ceramsite base raw material is at least one of clay, shale, fly ash and waste ceramic powder. The problem that the wave-absorbing material is not easy to be uniformly and stably mixed in the concrete in the concrete preparation process in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a method for preparing composite functional ceramsite for electromagnetic wave absorption and concrete. Background Technology

[0002] With the explosive growth of wireless communication technology and electronic devices, electromagnetic interference and radiation pollution in space are becoming increasingly serious problems. As the main carrier and environment for electromagnetic wave propagation, building structures are effectively protected by absorbing electromagnetic waves. Since concrete itself does not possess wave-absorbing capabilities, conductive or magnetic wave-absorbing agents are typically added, combined with a porous structure, to impart wave-absorbing capabilities.

[0003] Currently, the main technical approaches to introducing microwave absorption functionality into concrete include: 1. Post-composite process: applying a microwave-absorbing coating to the hardened concrete surface. 2. Physical mixing method: directly dry-mixing nano- or micro-sized microwave-absorbing agents (such as carbon nanotubes, graphene, and carbonyl iron powder) with concrete raw materials. 3. Functional aggregate preparation method: impregnating or spraying a microwave-absorbing material slurry onto the surface of ordinary expanded clay or expanded perlite.

[0004] The aforementioned technical solutions all have certain drawbacks during implementation. For example, the post-composite process suffers from weak adhesion, easy aging and detachment, and poor durability, and it cannot absorb electromagnetic waves intruding into the building's interior. Physical mixing methods result in uneven dispersion; due to the extremely high specific surface energy and hydrophilic / hydrophobic differences of the microwave absorber, it easily agglomerates during concrete mixing, failing to achieve uniform dispersion at the cement paste and aggregate interface. This leads to low microwave absorption efficiency, significant material waste, and severely impacts the workability and strength of the concrete. In functional aggregate preparation methods, the functional layer and aggregate in the produced functional aggregate are merely physically attached, easily peeling off and pulverizing during the high-intensity mixing process of concrete production, failing to guarantee functional durability. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing composite functional ceramsite for electromagnetic wave absorption and concrete, in order to solve the problem that the wave-absorbing material is not easy to be uniformly and stably mixed in the concrete during the concrete preparation process in the prior art.

[0006] A method for preparing composite functional ceramsite for electromagnetic wave absorption involves pre-mixing ceramsite base materials and micron-sized rutile titanium dioxide powder in a predetermined ratio, followed by mechanical mixing for at least 2 hours to obtain a uniform mixed powder. Water is then added to the mixed powder, and a granulator is used to form raw material balls. These raw material balls are then placed in a sintering apparatus and dried at 105–150°C until the moisture content is below 2%. The temperature in the sintering apparatus is then raised to 1150–1250°C and held for 30–90 minutes for sintering. Finally, natural cooling is performed to obtain the composite functional ceramsite. The rutile titanium dioxide powder accounts for 0.5%–20% of the total mass of the raw materials, and the ceramsite base material is at least one of clay, shale, fly ash, and waste ceramic powder.

[0007] Furthermore, when the temperature inside the sintering equipment is raised to 1150℃~1250℃, the temperature is increased to 1150℃~1250℃ at a rate of 5~10℃ / min.

[0008] Furthermore, during the sintering process, an oxidizing atmosphere is maintained inside the sintering equipment.

[0009] Furthermore, the mechanical mixing is ball milling or high-speed shear mixing.

[0010] Furthermore, the rutile titanium dioxide powder accounts for 2% to 10% of the total mass of the raw materials.

[0011] Furthermore, the particle size of the rutile titanium dioxide powder is 3-7 μm.

[0012] Furthermore, the diameter of the raw material balls is 5-20 mm.

[0013] The beneficial effects of the method for preparing composite functional ceramsite for electromagnetic wave absorption in this invention are as follows: In this invention, the ceramsite base material and titanium dioxide powder are mixed and then formed into raw material balls to facilitate uniform mixing of the materials, ensuring that titanium dioxide is evenly distributed within the ceramsite. Mechanical mixing for at least two hours ensures uniform mixing, and the prolonged mixing time allows the materials to collide with the mixing equipment, preventing agglomeration and also serving to grind and crush the particles. Adding water facilitates the molding into raw material balls. Since the raw material balls contain a certain amount of moisture, drying is performed before sintering. This avoids cracking caused by sudden high temperatures and also allows for the slow evaporation of moisture, resulting in a microporous structure within the raw material balls. The formation of rutile phase facilitates the formation of a porous internal structure in the final ceramic particles, and also allows for the removal of moisture, preventing it from participating in subsequent chemical reactions. Sintering is then carried out at high temperatures in the sintering equipment, allowing the rutile titanium dioxide powder to undergo solid-state reactions and interdiffusion with the base materials, thus being incorporated into the crystal lattice or grain boundaries of the aluminosilicate ceramic matrix, forming a structurally integrated functional body. The rutile phase is a thermodynamically stable phase of TiO2, and does not undergo crystal transformation, volume shrinkage, or lattice distortion at the ceramic particle sintering temperature of 1150–1250℃, ensuring a stable sintering process and controllable pore structure and mechanical properties. The rutile phase also exhibits a higher intrinsic dielectric constant and more stable dielectric loss, ranging from 2–18... The absorption performance within the GHz target frequency band is highly predictable; and the rutile phase has moderate chemical activity, which can undergo a moderate solid-state reaction with the aluminosilicate matrix during sintering to generate a titanate functional crystal phase, taking into account both dielectric performance improvement and mechanical strength of the ceramic particles. Finally, the titanium dioxide in the ceramic particles is uniformly dispersed and fixed by the ceramic particles. Through the above preparation method, spherical or ellipsoidal particles with a dense glaze layer on the surface and a porous internal structure can be obtained. The matrix of the ceramic particles is aluminosilicate ceramic, which is uniformly composited with titanium and iron elements from the raw materials. This solves the problem that the microwave absorbing material is not easy to be uniformly and stably mixed in the concrete during the concrete preparation process in the prior art.

[0014] Furthermore, ceramsite has a strong hygroscopic effect. When heated at a slower rate before sintering, it is easier to slowly expel the remaining moisture inside the ceramsite. In addition, it can also prevent the ceramsite from cracking and deforming, and allow thermal stress to be released evenly.

[0015] Furthermore, by maintaining an oxidizing atmosphere, carbon and its low-valence oxides are fully oxidized, while the crystalline phase of the metal is stabilized, ensuring its ability to absorb electromagnetic waves.

[0016] Furthermore, ball milling or high-speed shear mixing can enhance the grinding effect on the material.

[0017] A type of concrete for electromagnetic wave absorption comprises cement, water, fine aggregate, admixtures, and coarse aggregate, wherein the coarse aggregate is composite functional ceramsite prepared by the above-described preparation method; the volume of the composite functional ceramsite accounts for 30% to 100% of the total volume of the coarse aggregate.

[0018] Furthermore, the concrete also includes conductive fibers and / or conductive particles, wherein the conductive fibers are steel fibers or carbon fibers, and the conductive particles are graphite or carbon black.

[0019] The beneficial effects of the concrete used for electromagnetic wave absorption in this invention are as follows: In this invention, composite functional ceramsite is used as coarse aggregate. This coarse aggregate is prepared by the above-mentioned method. It consists of spherical or ellipsoidal particles with a dense glazed layer on the surface and a porous internal structure. The matrix of the ceramsite is aluminosilicate ceramic, which is uniformly composited with titanium and iron elements derived from the raw materials. Because the titanium dioxide in the aggregate is uniformly distributed and the ceramsite has a porous internal structure, the problem of the wave-absorbing material not being uniformly and stably mixed in the concrete during the concrete preparation process in the prior art is solved. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below through specific embodiments. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0021] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0022] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0023] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two components. They can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0024] To better understand the technical solution of the present invention, the present invention will be described in detail below.

[0025] In Example 1 of the preparation method of composite functional ceramic particles (hereinafter referred to as composite functional ceramic particles) for electromagnetic wave absorption in this invention: The method for preparing composite functional ceramic particles in this embodiment involves mixing rutile titanium dioxide powder with raw material powder to form raw material balls, and then sintering the raw material balls to form the aforementioned composite functional ceramic particles, thereby enabling the titanium dioxide powder to be more uniformly and stably dispersed in building materials.

[0026] Typically, titanium dioxide includes rutile titanium dioxide and anatase titanium dioxide. In this embodiment, rutile titanium dioxide is explicitly selected as the sole microwave absorbing phase. The reasons are as follows: Differences in crystal stability: Rutile phase is a thermodynamically stable phase of TiO2. It does not undergo crystal transformation, volume shrinkage, or lattice distortion at the sintering temperature of ceramsite of 1150–1250℃, which can ensure the stability of the sintering process of ceramsite and the controllability of pore structure and mechanical properties; while anatase phase is a metastable phase. It will undergo irreversible phase transformation and volume shrinkage at high temperatures, which can easily lead to stress concentration, cracking, or strength fluctuations inside the ceramsite.

[0027] Dielectric property differences: Rutile phase has a higher intrinsic dielectric constant and more stable dielectric loss, and its absorption performance is highly predictable in the 2–18 GHz target frequency band; Anatase phase transition process introduces uncertain defects and interfaces, resulting in fluctuations in electromagnetic parameters, making it difficult to achieve stable broadband absorption effect.

[0028] Differences in reaction controllability: Rutile phase has moderate chemical activity and can undergo a moderate solid-state reaction with the aluminosilicate matrix during sintering to generate titanate functional crystal phase, balancing dielectric performance improvement and mechanical strength of ceramic particles; Anatase has excessive activity and is prone to excessive reaction with alkaline earth metal ions in the matrix, consuming the glass phase and destroying the ceramic particle sintering system, leading to sintering failure.

[0029] In summary, the selection of rutile TiO2 is a necessary choice to achieve the unity of "stable microwave absorption performance, controllable sintering process, and reliable structural performance" in this invention.

[0030] Specifically, the following steps are used in the preparation of ceramsite: Step 1. Homogenization and mixing of raw materials: The ceramsite base raw material powder and micron-sized rutile titanium dioxide (TiO2) powder are premixed in a predetermined ratio to obtain a mixed powder; wherein the mass of the rutile titanium dioxide powder accounts for 0.5% to 20% of the total mass of the raw materials, preferably 2% to 10%; the base raw material is one or more of clay, shale, fly ash, and waste ceramic powder; Step 2. High-intensity activation mixing: The mixed powder obtained in Step 1 is subjected to high-intensity mechanical mixing for a time of not less than 2 hours to obtain a highly uniform mixed powder; the high-intensity mechanical mixing is ball milling or high-speed shear mixing; during the mixing process, agglomeration is prevented on the one hand, and grinding is also performed again to crush any large particles that may exist; Step 3. Granulation: Add an appropriate amount of water to the mixed powder and granulate it using a granulator to form raw material balls of a preset size; in this embodiment, the size of the raw material balls is 5-20mm. Of course, for later use, the size can be made more uniform. Step 4. Drying: Dry the raw material balls at 105-150°C until the moisture content is below 2%; specifically, heating can be continued until the weight no longer changes. Step 5. Integrated sintering: Place the dried raw material pellets in a sintering equipment, heat them to 1150℃~1250℃ at a rate of 5~10℃ / min under an oxidizing atmosphere, and hold them at this temperature for 30~90 minutes. Then cool them naturally to obtain the composite functional ceramsite.

[0031] Through sintering, rutile titanium dioxide powder undergoes a solid-phase reaction and interdiffusion with the base raw materials at high temperatures, thereby being incorporated into the crystal lattice or grain boundaries of the aluminosilicate ceramic matrix to form a structurally integrated functional body. The composite functional ceramic particles formed in this way have a dense glazed layer on the surface and a porous internal structure. The matrix of the ceramic particles is aluminosilicate ceramic, with titanium and iron elements derived from the raw materials uniformly incorporated within. Macroscopically, the ceramic particles exhibit a uniformly colored cross-section without any visible agglomeration points of functional phase powder. The porous structure allows electromagnetic waves to be guided into the ceramic particles for absorption and dissipation. Furthermore, the uniform distribution of titanium dioxide within the ceramic particles, as a wave-absorbing material, enhances its wave-absorbing function.

[0032] Compared with the prior art, the present invention has the following outstanding advantages: A fundamental technological innovation that completely solves the problems of dispersion and bonding: This invention pioneers a "raw material homogenization-integrated sintering" approach. In the powder stage, high-intensity mixing achieves microscopically uniform dispersion of the functional phases, and the chemical reaction of high-temperature sintering permanently "anchors" them within the ceramic network. This fundamentally avoids the coating detachment problem of post-loading processes and the agglomeration problem of physical mixing methods.

[0033] Durable and stable function, with a lifespan synchronized with the structure: The functional phase forms a chemical bond with the matrix through a solid-phase reaction, becoming part of the intrinsic properties of the ceramsite. This functional ceramsite is wear-resistant and alkali-resistant, and its electromagnetic function does not decay during concrete mixing or long-term use, achieving functional durability with the same lifespan as the building structure.

[0034] Structure determines performance, realizing broadband absorption potential: The ceramsite prepared by this method integrates multiple absorption mechanisms, including dielectric loss (from rutile TiO2 and its reaction products), interfacial polarization loss (from numerous "ceramic-pore" micro-interfaces), and macroscopic structural scattering (the non-homogeneous medium formed by millimeter-scale aggregates in concrete). The synergistic effect of these multiple mechanisms theoretically gives the concrete prepared with this method outstanding potential for achieving efficient electromagnetic wave absorption across a wide frequency range (2–18 GHz).

[0035] It has excellent engineering compatibility and a clear prospect for industrialization: the final product is ceramsite aggregate with standard particle size. Concrete mixing plants can achieve large-scale production of wave-absorbing concrete without changing any existing equipment and processes, and the threshold for promotion is extremely low.

[0036] With strong performance designability, the pore structure, strength and composite dielectric properties of ceramic particles can be effectively controlled by adjusting the amount of rutile TiO2, introducing an iron source (Fe2O3) and optimizing the sintering process, so as to meet the customized requirements of absorption frequency band and intensity for different application scenarios.

[0037] Specifically, preparation experiments were conducted using specific proportions: Weigh the raw materials: fly ash (85wt%), clay (10wt%), and rutile TiO2 powder (average particle size 5μm, 5wt%).

[0038] Preparation: Weigh the raw materials according to the above proportions and pour them into a planetary ball mill. Use zirconia balls as the grinding medium, with a ball-to-material ratio of 3:1, and a rotation speed of 300 rpm for 3 hours to obtain a homogeneous mixed powder. Add an appropriate amount of water to the mixed powder and form raw material balls with a diameter of 10–15 mm on a disc granulator. Place the raw material balls in an oven and dry them at 120℃ for 6 hours until constant weight. Place the dried raw material balls in a box-type resistance furnace and heat them to 1180℃ at a rate of 8℃ / min under air atmosphere, hold for 60 minutes, and then turn off the power and cool them to room temperature with the furnace.

[0039] Upon observation, the obtained ceramsite was dark gray with a smooth, glazed surface and a porous internal structure. When the ceramsite was broken, the fresh cross-section showed a uniform color, and under a magnifying glass, there were no white TiO2 powder agglomeration spots, indicating that TiO2 had been fully integrated with the matrix.

[0040] Conduct a test on the control group: Take commercially available ordinary ceramsite (with a basic composition similar to that in the example), immerse it in a silica sol binder containing 5% nano-TiO2, remove and dry it, and heat-treat it at 550°C for 1 hour to cure the coating.

[0041] Two equal amounts of ceramsite were added to cement mortar and stirred for 5 minutes. In the control group, the stirred water was cloudy with sediment at the bottom, and a large amount of the coating peeled off; in the example group, the stirred water was clear with no sediment, and the functional phase did not peel off. This clearly demonstrates the significant advantage of this invention in terms of functional stability.

[0042] In Example 2 of the preparation method of composite functional ceramic particles for electromagnetic wave absorption (hereinafter referred to as composite functional ceramic particles) in this invention: The preparation method in this embodiment is basically the same as that in Example 1 for the preparation of composite functional ceramsite, the only difference being the raw materials. In this embodiment, iron is added to the raw materials. Specifically, 83 wt% fly ash, 10 wt% clay, 5 wt% rutile TiO2, and 2 wt% industrial iron oxide red (Fe2O3) are used as raw materials and mixed. The same preparation steps as in Example 1 are followed to obtain composite functional ceramsite. Observation shows that the ceramsite is reddish-brown, with a glazed surface, porous interior, uniform cross-sectional color, and no functional phase agglomeration.

[0043] In Examples 1 and 2, relying on titanium / iron elements to provide intrinsic dielectric loss, porous structure to optimize impedance matching, and macroscopic aggregate to form multiple scattering, the prepared concrete can achieve effective absorption of reflection loss RL < -10 dB (absorption rate > 90%) in a wide frequency range of 2–18 GHz with a reasonable thickness. The bandwidth and stability are significantly better than the traditional scheme of physically mixed absorbing agent or surface coated aggregate.

[0044] In an embodiment of the concrete used for electromagnetic wave absorption in this invention: In this embodiment, the composite functional ceramsite prepared in Example 1 or Example 2 is used as coarse aggregate. Specifically, the raw materials used in the preparation include cement, water, fine aggregate, admixtures, and the aforementioned composite functional ceramsite as coarse aggregate. In the mixing ratio, the volume of the composite functional ceramsite accounts for 30% to 100% of the total volume of the coarse aggregate. In addition, conductive fibers or conductive particles can be added to the concrete. The conductive fibers are steel fibers or carbon fibers, and the conductive particles are graphite or carbon black. They synergistically construct a composite wave-absorbing system with the composite functional ceramsite.

[0045] To better understand its performance, the aforementioned composite functional expanded clay aggregate was used to replace the natural crushed stone (coarse aggregate) in the C30 ordinary concrete mix design by volume. The mixture was then stirred, molded, and cured for 28 days using conventional methods to prepare concrete specimens. The specimens showed good workability, indicating that the functional expanded clay aggregate was fully compatible with the concrete process.

[0046] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing composite functional ceramic particles for electromagnetic wave absorption, characterized in that: The ceramsite base material and micron-sized rutile titanium dioxide powder are premixed according to a preset ratio, and then mechanically mixed for no less than 2 hours to obtain a uniform mixed powder. Water is then added to the mixed powder and a granulator is used to form raw material balls. The raw material balls are then placed in a sintering device and dried at 105-150°C until the moisture content is less than 2%. The temperature in the sintering device is then raised to 1150-1250°C and held for 30-90 minutes for sintering. Finally, natural cooling is performed to obtain the composite functional ceramsite. The rutile titanium dioxide powder accounts for 0.5% to 20% of the total mass of the raw materials, and the ceramsite base material is at least one of clay, shale, fly ash, and waste ceramic powder.

2. The method for preparing composite functional ceramic particles for electromagnetic wave absorption according to claim 1, characterized in that: When the temperature inside the sintering equipment is raised to 1150℃~1250℃, the temperature is increased to 1150℃~1250℃ at a rate of 5~10℃ / min.

3. The method for preparing composite functional ceramic particles for electromagnetic wave absorption according to claim 2, characterized in that: During the sintering process, the sintering equipment is kept in an oxidizing atmosphere.

4. The method for preparing composite functional ceramic particles for electromagnetic wave absorption according to any one of claims 1-3, characterized in that: The mechanical mixing is ball milling or high-speed shear mixing.

5. The method for preparing composite functional ceramic particles for electromagnetic wave absorption according to any one of claims 1-3, characterized in that: The rutile titanium dioxide powder accounts for 2% to 10% of the total mass of the raw materials.

6. The method for preparing composite functional ceramic particles for electromagnetic wave absorption according to any one of claims 1-3, characterized in that: The rutile titanium dioxide powder has a particle size of 3-7 μm.

7. The method for preparing composite functional ceramic particles for electromagnetic wave absorption according to any one of claims 1-3, characterized in that: The diameter of the raw material balls is 5-20 mm.

8. A type of concrete for electromagnetic wave absorption, characterized in that: It comprises cement, water, fine aggregate, admixtures and coarse aggregate, wherein the coarse aggregate is a composite functional ceramsite prepared by the preparation method according to any one of claims 1-7; the volume of the composite functional ceramsite accounts for 30% to 100% of the total volume of the coarse aggregate.

9. The concrete for electromagnetic wave absorption according to claim 8, characterized in that: The concrete also contains conductive fibers and / or conductive particles, wherein the conductive fibers are steel fibers or carbon fibers, and the conductive particles are graphite or carbon black.