Radiation cooling ceramic tile and preparation method thereof

Abstract

This invention relates to the field of building ceramics technology, and discloses a radiation-cooled ceramic brick and its preparation method. The radiation-cooled ceramic brick includes a base glaze layer and a reflective heat-insulating surface glaze layer. The raw materials of the base glaze layer include kaolin, calcined kaolin, porous alumina powder, quartz, calcined talc, nepheline, potassium feldspar, sodium feldspar, trivalent europium ion-doped magnesium aluminum spinel powder, and zirconium silicate. The purpose of the base glaze layer formulation design is to design a base glaze with an expansion coefficient close to that of ordinary base glazes in existing qualified ceramic bricks, while simultaneously introducing porous alumina and trivalent europium ions (Eu³). + By doping with magnesium aluminum spinel powder, the coefficient of thermal expansion of the base glaze layer is kept consistent with that of the conventionally produced body and the reflective heat-insulating glaze layer. This ensures that the structure of the porous alumina is not damaged, and solves the problem that the reflectivity and emissivity of the glaze are difficult to improve effectively when the coefficients of thermal expansion of the base glaze layer are inconsistent with those of the body and the glaze layer.

Description

Technical Field

[0001] This invention relates to the field of building ceramics technology, and in particular to a radiation-cooled ceramic brick and its preparation method. Background Technology

[0002] With increasing environmental awareness, radiative cooling technology, which can effectively reduce building surface temperature, has attracted widespread market attention. As a primary material for building exterior cladding, ceramic tiles with radiative cooling function can reflect solar radiation and emit mid- and far-infrared energy into outer space, thus achieving passive cooling. This demonstrates enormous application potential and commercial value in green building, energy conservation and emission reduction, and improving the urban environment.

[0003] However, with the increasing demands on material performance in the market, existing radiation-cooled ceramic tiles are facing new challenges while improving performance. For example, Chinese patent CN119591321A discloses a radiation-cooled glaze that uses magnesium aluminum spinel doped with metal oxides to balance the difference in thermal expansion coefficients between nanoporous alumina and the lightweight body. While this technology addresses the uneven stress distribution within the body to some extent, a significant difference in thermal expansion coefficients between the body and the glaze remains a problem in practical applications, given that the thermal expansion coefficient of the porous lightweight body is 7.3 × 10⁻⁶. -6 ~7.6×10 -6 K -1 The coefficient of thermal expansion is 6×10, which is significantly higher than that of conventional glazes. -6 ~7×10 -6 K -1 During the firing and cooling process, the shrinkage of the green body is much greater than that of the glaze layer, resulting in the glaze layer being subjected to extremely high compressive stress. This mismatch will directly lead to severe convex deformation of the brick, which not only damages the flatness of the product, but also easily causes the porous structure to collapse and be damaged, affecting the radiative cooling performance. At the same time, defects such as pinholes and glaze bubbles will also appear on the glaze surface, affecting the decorative effect and functional life of the ceramic brick. Summary of the Invention

[0004] To address the aforementioned shortcomings, the present invention aims to propose a radiation-cooled ceramic brick and its preparation method, thereby solving the problem in the prior art where the thermal expansion coefficients of the porous glaze layer and the body do not match, affecting the glaze surface performance.

[0005] To achieve this objective, the present invention adopts the following technical solution: A type of radiant cooling ceramic tile includes a base glaze layer and a reflective heat-insulating surface glaze layer. The base glaze layer comprises, by weight, the following raw materials: 5-12 parts of kaolin 1-5 parts of calcined kaolin 10-20 parts of porous alumina powder 10-20 parts of quartz Burn 1-5 parts of talc. Nepheline 12-25 parts Potassium feldspar 3-8 parts, 30-40 parts of albite, 5-10 parts of trivalent europium ion-doped magnesium aluminum spinel powder Zirconium silicate 5-10 parts.

[0006] Preferably, the porous alumina powder has a particle size of 200-325 mesh and a porosity of 23-30%, and the trivalent europium ion-doped magnesium aluminum spinel powder has a particle size of 325-500 mesh.

[0007] Preferably, the base glaze layer is fired from a base glaze comprising the following chemical composition, according to a specific mass ratio: SiO2 50~60%, Al2O3 25~30%, Fe2O3 0.1~0.4%, TiO2 0.1~0.25%, CaO 0.2~1%, MgO 1.5~3.5%, K2O 1~3.5%, Na2O 2~5%, ZrO2 2~5%, Weight loss upon ignition at 1000℃ is 1-3%.

[0008] Preferably, the raw materials of the reflective heat-insulating glaze layer, by weight, include: 5-10 parts of kaolin 5-10 parts titanium dioxide 25-35 parts of zirconium white frit, Potassium feldspar 20-35 parts, 15-25 parts wollastonite 5-12 parts of barium carbonate; The raw materials for the zircon white frit include 12-20 parts of kaolin, 8-15 parts of zircon powder, 30-42 parts of quartz, 3-8 parts of zinc oxide, 3-8 parts of tricalcium phosphate, and 20-42 parts of fluxing components.

[0009] Preferably, the reflective heat-insulating glaze layer is formed by firing a glaze comprising the following chemical composition, according to a specific mass ratio: SiO2 45~52%, Al2O39~15%, Fe2O3 0.1~0.4%, TiO2 7~12%, CaO 8~15%, MgO 1~3%, BaO 2~6%, ZnO 1.5~5%, K2O 2~5%, Na2O 0.5~3%, ZrO2 2~4.5%, P2O5 0.2~1.5%, Weight loss upon ignition at 1000℃ is 2-5%.

[0010] Preferably, the fluxing component comprises the following raw materials in parts by weight: 5-12 parts of dolomite, 10-20 parts of calcite Potassium carbonate 5-10 parts.

[0011] Preferably, the chemical composition of the zirconium white ingot includes: SiO2 52~57%, Al2O35~12%, Fe2O3 0.1~0.5%, TiO2 0.01~0.5%, CaO 3~12%, MgO 1.0~4.5%, K2O 2~7%, ZnO 3~9%, ZrO2 6~12%, P2O5 1~4%.

[0012] A method for preparing radiation-cooled ceramic bricks, comprising the following steps: A. Preparation of the base glaze: A1. Weigh 100 parts of the raw materials according to the proportion of the base glaze layer; A2. Add the weighed raw materials to the ball mill, and add 40 parts water and 0.12~5 parts grinding aid according to the mass ratio, and then ball mill. A3. Grind the balls until the specific gravity of the output balls is 1.8~1.87 g / cm³. 3 The fineness is 0.5~0.8g, which is measured by the amount of residue on a 325-mesh sieve after 200g of slurry is passed through, and the base glaze is prepared accordingly. B. Apply a base glaze to the ceramic tile blank, controlling the amount of glaze to be 58~62g / (350mm×350mm); C. Apply reflective heat-insulating glaze, controlling the amount of glaze application to be 50~55g / (350mm×350mm); D. Firing to obtain radiation-cooled ceramic bricks.

[0013] Preferably, the preparation of the surface glaze is also included: S1. Weigh 100 parts of raw materials according to the proportion of raw materials for the reflective heat insulation glaze layer; S2. Add the weighed raw materials to the ball mill, and add 40 parts water and 0.12~5 parts grinding aid according to the mass ratio, and then ball mill. S3, ball milling until the ball specific gravity is 1.85~1.9g / cm³ 3 The fineness is 0.4~0.6g, which is measured by the amount of residue on a 325-mesh sieve after 200g of slurry is passed through it to obtain the surface glaze.

[0014] Preferably, the method also includes the preparation of zirconium white frit: the raw materials of zirconium white frit are mixed evenly according to the proportion, heated to a firing temperature of 1500~1600℃ for firing, and held at the firing temperature for 0.1~1h, then discharged and cooled to obtain zirconium white frit.

[0015] The technical solution provided by this invention may include the following beneficial effects: 1. The purpose of the base glaze formulation design is to design a base glaze with an expansion coefficient close to that of ordinary base glazes used in existing qualified ceramic tiles, while introducing porous alumina and trivalent europium ions (Eu³). + By incorporating magnesium aluminum spinel powder, the coefficient of thermal expansion of the glaze layer remains unchanged after firing, ensuring that the porous alumina structure is not damaged and effectively improving the glaze's reflectivity. The porous alumina forms a porous glaze layer in the base layer, allowing the glaze to retain its interconnected pores after sintering. This structure not only reflects visible and near-infrared light but also reduces heat absorption, effectively dissipating heat into space for cooling.

[0016] Eu³ + It has a relatively large ionic radius, approximately 0.947 Å, and is six-coordinated, significantly larger than Mg²⁺. + The ionic radius is 0.72 Å and Al³ + The ionic radius is 0.535 Å. Doping it into a spinel lattice causes significant lattice distortion, disrupting local symmetry and thus enhancing phonon-phonon coupling emission, one of the main emission mechanisms in the mid- and far-infrared bands, especially >5 μm. Furthermore, doping with Eu³⁺… + It can introduce oxygen vacancy defects to form intermediate energy levels, promote multiphoton absorption and non-emission energy transfer, and indirectly improve the emission efficiency in the 8~14μm infrared band.

[0017] In spinel structures, a large amount of transition metal europium oxide crystallizes due to the close packing of oxygen ions. The unit cell contains a large number of tetrahedral and octahedral interstices, which are easily occupied by other cations to dope and modify the spinel structure, thereby improving the infrared emission performance of spinel materials.

[0018] 2. Porous alumina has a refractive index of 1.05–1.14 and an internal porous structure, possessing high band gap characteristics and a superior refractive index for the solar radiation band. Because the band gap of alumina far exceeds that of the highest-energy ultraviolet light in sunlight, ceramic tiles made from it can effectively control the absorption of sunlight, absorbing only a very small amount of solar energy. Simultaneously, its low refractive index further promotes efficient scattering of sunlight within its hierarchical porous structure. The energy of chemical bond vibrations in alumina is precisely located around 12 micrometers, giving the cooling ceramic a high-mid-infrared emissivity of 92%.

[0019] 3. The zircon white frit used in this scheme contains zircon powder with zirconium silicate as the main component. After firing, it can form two compounds containing zirconium silicate with a refractive index of 1.9 and zirconium oxide with a refractive index of 2.2. Under the action of a large amount of fluxing components, the supersaturated zirconium oxide will precipitate microcrystals. With zinc oxide as a crystallizing agent, the zircon white frit is rich in a large amount of microcrystalline zirconium oxide. Utilizing its excellent chemical temperature resistance and refractive index that is significantly higher than that of the glass phase, it forms a strong reflection and scattering effect in the glaze. By introducing this high-whiteness and high-turbidity zircon white frit into the glaze system, the whiteness and turbidity of the fired glaze can be improved more effectively.

[0020] When zirconium white frit is applied to surface glazes, specifically in the titanium sphene glaze system of this scheme, a white glaze with high solar reflectance can be prepared. During the glaze firing process, the microcrystalline zirconium oxide in the zirconium white frit serves as a heterogeneous nucleus, inducing an interfacial reaction between it and titanium dioxide. This generates uniformly distributed titanium sphene microcrystals with controlled particle size in situ, constructing a zirconium-titanium composite reflective layer. Thus, while ensuring the hardness and stain resistance of the glaze, extremely high solar reflectance and extremely high stain resistance are achieved.

[0021] 4. In the raw materials of the reflective heat-insulating glaze, under the condition that zirconium white frit provides phosphate as a phase separation and crystallization agent, wollastonite reacts with titanium dioxide at high temperature to precipitate titanium sphene microcrystals in situ. The grains are small and uniform, the glaze is delicate and dense, and the opacification effect is good. This solves the problem that it is difficult to have both high solar reflectance and high anti-fouling performance in conventional titanium sphene glazes when titanium sphene powder is used directly.

[0022] 5. The formed reflective heat-insulating glaze layer contains titanium dioxide crystals, zirconium oxide crystals, titanium sphene crystals, and a glass matrix with refractive indices of 2.71, 2.2, 1.9, and 1.5, respectively, creating a refractive index gradient. Materials with different refractive indices can construct multiple diffuse reflection paths, optimizing the overall optical uniformity of the reflective heat-insulating glaze layer and reducing solar transmission and absorption. In particular, titanium sphene crystals, due to their high refractive index, when precipitated at micron and submicron levels, have grain sizes close to the visible light band, resulting in a strong opaque state on the glaze surface. This leads to highly efficient Mie scattering and reflection, further increasing the solar reflectance and achieving a high solar reflectance of 0.92. The proposed reflective heat-insulating glaze layer simultaneously considers solar reflectance, whiteness, opacity, and anti-fouling performance. Detailed Implementation

[0023] To facilitate understanding of the present invention, a more complete description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0024] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] A type of radiant cooling ceramic tile includes a base glaze layer and a reflective heat-insulating surface glaze layer. The base glaze layer comprises, by weight, the following raw materials: 5-12 parts of kaolin 1-5 parts of calcined kaolin 10-20 parts of porous alumina powder 10-20 parts of quartz Burn 1-5 parts of talc. Nepheline 12-25 parts Potassium feldspar 3-8 parts, 30-40 parts of albite, 5-10 parts of trivalent europium ion-doped magnesium aluminum spinel powder Zirconium silicate 5-10 parts.

[0027] Radiation cooling is defined as follows: solar reflectance ≥ 0.92 in the 0.3–2.5 μm wavelength range and emissivity ≥ 0.92 in the 8–13 μm wavelength range. These two different test indicators characterize a material's ability to reflect, absorb, and emit heat.

[0028] The purpose of the base glaze formulation design is to create a base glaze with an expansion coefficient close to that of ordinary base glazes used in existing qualified ceramic tiles, while introducing porous alumina and trivalent europium ions (Eu³). + By incorporating magnesium aluminum spinel powder, the glaze, after firing, ensures that the coefficient of thermal expansion of the base glaze layer is 6×10⁻⁶, the same as that of the conventionally produced body and the reflective heat-insulating glaze layer. -6 ~7×10 -6 K -1 Maintaining consistency ensures the porous alumina structure remains intact, effectively improving the glaze's reflectivity and emissivity. The porous alumina forms a porous glaze layer in the base layer, allowing the glaze to retain its interconnected pores after sintering. This structure not only reflects visible and near-infrared light but also emits mid-infrared light, reducing heat absorption and effectively dissipating heat into space for cooling. In a specific embodiment, the coefficient of thermal expansion of the base glaze layer is 6.53 × 10⁻⁶. -6 K -1 It matches the coefficient of thermal expansion of the body and the glaze on the surface.

[0029] Eu³ + It has a relatively large ionic radius, approximately 0.947 Å, and is six-coordinated, significantly larger than Mg²⁺. + The ionic radius is 0.72 Å and Al³ + The ionic radius is 0.535 Å. Doping it into a spinel lattice causes significant lattice distortion, disrupting local symmetry and thus enhancing phonon-phonon coupling emission, one of the main emission mechanisms in the mid- and far-infrared bands, especially >5 μm. Furthermore, doping with Eu³⁺… + It can introduce oxygen vacancy defects to form intermediate energy levels, promote multiphoton absorption and non-emission energy transfer, and indirectly improve the emission efficiency in the 8~14μm infrared band.

[0030] A preferred method for preparing trivalent europium ion-doped magnesium aluminum spinel powder is as follows: 0.5 parts by weight of europium trioxide, 24.5 parts by weight of magnesium oxide powder, and 75 parts by weight of aluminum oxide powder are weighed, mixed evenly, and then calcined in an electric arc furnace at a high temperature of 2200℃. After cooling, the mixture is crushed into powder to obtain trivalent europium ion-doped magnesium aluminum spinel powder. A large amount of transition metal europium oxide crystallizes in the spinel structure due to the close packing of oxygen ions. The unit cell contains numerous tetrahedral and octahedral interstices, which are easily occupied by other cations to dope and modify the spinel structure, thereby improving the infrared emission performance of the spinel material.

[0031] Furthermore, porous alumina has a refractive index of 1.05–1.14, an internal porous structure, and possesses high band gap characteristics and a superior refractive index for the solar radiation band. Because the band gap of alumina far exceeds that of the highest-energy ultraviolet light in sunlight, the ceramic tiles made from it can effectively control the absorption of sunlight, absorbing only a very small amount of solar energy. Simultaneously, its low refractive index further promotes efficient scattering of sunlight within its hierarchical porous structure. The energy of chemical bond vibrations in alumina is precisely located around 12 micrometers, giving the cooling ceramics a high-mid-infrared emissivity of 92%.

[0032] In a specific embodiment, kaolin is a plastic raw material that provides binding and flowability. If too much is used, the slurry will have poor flowability; if too little is used, the binding will be poor.

[0033] Calcined kaolin is a ridge-like raw material. If too much is used, the firing temperature of the glaze will be high and the coefficient of expansion will be small; if too little is used, the glaze will have more glass phase and the firing temperature will be low.

[0034] The porous alumina powder is made of porous lightweight alumina, which has a high firing temperature and high porosity. If too much is used, the coefficient of expansion of the glaze will decrease and the firing temperature will be high; if too little is used, the firing temperature will be low and the pores will be easily filled by the glass phase, which will not achieve the purpose of forming a porous structure layer and reduce the emissivity.

[0035] Quartz is a glassy silicon-oxygen tetrahedral material and a ridge aggregate. If too much is used, the coefficient of expansion will be small, affecting the flatness; if too little is used, there will be less glassy phase in the glaze, and the firing temperature will be high.

[0036] Talc is used as a fluxing component. If too much is used, the glaze will have a low firing temperature and a high glass phase; if too little is used, the glaze will have a high firing temperature and a low glass phase.

[0037] Nepheline mainly provides potassium and sodium, which adjust the expansion coefficient of the glaze. Too much nepheline results in a low expansion coefficient, while too little results in a high expansion coefficient.

[0038] Potassium feldspar is a fluxing component. If too much is used, there will be more glass phase and a larger coefficient of expansion; if too little is used, there will be less glass phase and less expansion absorption.

[0039] Sodium feldspar is a fluxing component. If too much is used, there will be more glass phase and a larger coefficient of expansion; if too little is used, there will be less glass phase and less expansion absorption.

[0040] Trivalent europium ion-doped magnesium aluminum spinel powder is an effective component for improving the reflectivity of glazes. If the amount used is too small, the effect of improving the reflectivity will not be obvious. If the amount used is too large, it will affect the coefficient of expansion of the glaze surface and make the coefficient of expansion smaller.

[0041] Zirconium silicate is a whitening agent in glazes. If too much is used, the cost of the glaze will be high and the coefficient of expansion will be small; if too little is used, the whiteness of the glaze will be poor.

[0042] The reflective heat-insulating glaze layer can be any existing reflective heat-insulating ceramic glaze. This solution optimizes the base glaze formula and combines it with existing reflective heat-insulating ceramic glaze as the top glaze layer, enabling the ceramic tile to maintain high emissivity while achieving perfect expansion matching with the body. This solves the problem of mismatch between the thermal expansion coefficients of the porous glaze layer and the body in existing technologies, effectively improving the high reflectivity of the base glaze layer, while reducing glaze bubbles, resulting in radiative cooling ceramic tiles with good flatness and excellent glaze quality.

[0043] Preferably, the porous alumina powder has a particle size of 200-325 mesh and a porosity of 23-30%, and the trivalent europium ion-doped magnesium aluminum spinel powder has a particle size of 325-500 mesh.

[0044] Porous alumina powder is a lightweight material. If the particle size is too small, it is easily filled with glassy particles, and its physical structure is easily damaged. Porous alumina powder with a porosity of 23-30% corresponds to the lowest refractive index of 1.05-1.14, and has the strongest ability to reflect light waves transmitted from the surface glaze layer again.

[0045] If the particle size of trivalent europium ion-doped spinel powder is too small, it is prone to agglomeration, which affects the performance of the glaze.

[0046] Preferably, the base glaze layer is fired from a base glaze comprising the following chemical composition, according to a specific mass ratio: SiO2 50~60%, Al2O3 25~30%, Fe2O3 0.1~0.4%, TiO2 0.1~0.25%, CaO 0.2~1%, MgO 1.5~3.5%, K2O 1~3.5%, Na2O 2~5%, ZrO2 2~5%, Weight loss upon ignition at 1000℃ is 1-3%.

[0047] Preferably, the raw materials of the reflective heat-insulating glaze layer, by weight, include: 5-10 parts of kaolin 5-10 parts titanium dioxide 25-35 parts of zirconium white frit, Potassium feldspar 20-35 parts, 15-25 parts wollastonite 5-12 parts of barium carbonate; The raw materials for the zircon white frit include 12-20 parts of kaolin, 8-15 parts of zircon powder, 30-42 parts of quartz, 3-8 parts of zinc oxide, 3-8 parts of tricalcium phosphate, and 20-42 parts of fluxing components.

[0048] The zircon white frit used in this scheme contains zircon powder with zirconium silicate as the main component. After firing, it can form two compounds containing zirconium silicate with a refractive index of 1.9 and zirconium oxide with a refractive index of 2.2. Under the action of a large amount of fluxing components, the supersaturated zirconium oxide will precipitate microcrystals. With zinc oxide as a crystallizing agent, the zircon white frit is rich in a large amount of microcrystalline zirconium oxide. Utilizing its excellent chemical temperature resistance and refractive index that is significantly higher than that of the glass phase, it forms a strong reflection and scattering effect in the glaze. By introducing this high-whiteness and high-turbidity zircon white frit into the glaze system, the whiteness and turbidity of the fired glaze can be improved more effectively.

[0049] Tricalcium phosphate, a phosphorus-containing component, is driven by thermodynamic instability. In its high-temperature molten state, the phosphate-containing melt enters a thermodynamically unstable region due to reduced miscibility between components. During cooling, it spontaneously separates into two or more glassy phases with different compositions. Phosphates form a phosphate network with silica, altering the melt's structural viscosity and promoting the nucleation and growth of phase-separated droplets. In the preparation of zirconium white frit, it acts as a nucleating agent, guiding the orderly precipitation of zirconium oxide crystals. Furthermore, in the subsequent firing process of glazes, phosphates act as a phase-separating agent, significantly enhancing the phase-separation tendency of the glaze in lime glaze systems. The phase separation forms droplets or crystallized micro-regions, which, due to their different refractive indices from the matrix glass, produce light scattering, forming opacity and thus improving the glaze's opacity, scattering, and diffuse reflection effects.

[0050] Tricalcium phosphate (TCP) has a wide range of applications in the industry, demonstrating good maturity and higher stability. Its main components are P₂O₅ and CaO. Calcium oxide is used in formulations to increase its content and is also a source of titanium sphene calcium. In glazes, TCP primarily functions as an opacifier and phase separation promoter, improving the glaze's hiding power and whiteness. Simultaneously, TCP reduces the melt viscosity of the glaze, improving its fluidity and enhancing its anti-fouling properties. Using TCP avoids the use of fluorine and chlorine impurities in apatite, which lower the glaze's melting temperature and prevents the corrosive effects of these impurities on equipment. Compared to dicalcium phosphate (DHP) and calcium dihydrogen phosphate (CDHP), TCP exhibits better high-temperature stability, making it more suitable for high-temperature glaze systems requiring high-temperature stability and opacification.

[0051] The high viscosity of zircon white frit during preparation necessitates a large amount of fluxing agents to reduce its high-temperature viscosity. Excessive zircon powder makes it difficult to feed the frit, while insufficient powder results in low zirconium oxide content and limited whitening effect. Too little zinc oxide limits crystallization and significantly impacts glaze whiteness; too much further enhances fluxing, similarly reducing whiteness. Excessive phosphate addition leads to high gloss, a high glassy phase, and low whiteness in the subsequent glaze; too little results in limited crystallization and phase separation, failing to achieve the desired effect. Kaolin's main components are active silica and alumina; excessive kaolin results in high frit viscosity, making feeding difficult; insufficient kaolin leads to an excessive glassy phase, affecting glaze whiteness. Quartz is the main component of glassy silicon-oxygen tetrahedra; too little quartz results in a low glassy phase, high glaze viscosity, and feeding difficulty; too much quartz may lead to an excessive glassy phase during subsequent glaze firing, affecting glaze whiteness.

[0052] When the aforementioned zirconium white frit is applied to the surface glaze, specifically in the titanium sphene system glaze of this scheme, a white glaze with high solar reflectance can be prepared. During the glaze firing process, the microcrystalline zirconium oxide in the zirconium white frit serves as a heterogeneous nucleus, inducing an interfacial reaction between it and titanium dioxide. This generates uniformly distributed titanium sphene microcrystals with controlled particle size in situ, constructing a zirconium-titanium composite reflective layer. Thus, while ensuring the hardness and stain resistance of the glaze, extremely high solar reflectance and extremely high stain resistance are achieved.

[0053] Further explanation: In the raw materials of the reflective heat-insulating glaze, under the condition that zirconium white frit provides phosphate as a phase separation and crystallization agent, wollastonite and titanium dioxide react at high temperature to precipitate titanium sphene microcrystals in situ. The grains are small and uniform, the glaze is delicate and dense, and the opacification effect is good. This solves the problem that conventional titanium sphene glazes cannot achieve both high solar reflectance and high anti-fouling performance when titanium sphene powder is used directly.

[0054] In specific embodiments, kaolin in the reflective heat-insulating glaze serves as a plastic material, providing suspension and viscosity. Excessive use results in poor glaze fluidity; insufficient use leads to poor adhesion between the glaze and the base glaze layer. Titanium dioxide is the main component for synthesizing titanium sphene. Excessive use results in a large amount of golden-red titanium dioxide on the glaze, causing the glaze color to yellow; insufficient use results in fewer titanium sphene crystals, affecting the reflectivity. Zirconium white frit mainly introduces zirconium oxide microcrystals. Excessive use increases glaze cost and reduces titanium sphene microcrystals, also lowering the reflectivity; insufficient use reduces the whitening effect of the glaze, further lowering the reflectivity. Potassium feldspar is a fluxing component. Excessive use results in a higher glass phase, increasing glaze transparency and lowering the reflectivity; insufficient use results in a rough glaze with poor anti-fouling properties. Furthermore, boric acid and sodium feldspar are avoided as fluxing components, as their high transparency after firing can negatively impact the whiteness of the glaze. Wollastonite, mainly composed of Ca3Si3O9, is the primary component in the synthesis of titanite. Excessive use leads to a higher concentration of the glassy phase, reducing reflectivity; insufficient use results in fewer titanite crystals, also lowering reflectivity. Barium carbonate is the main component forming barium feldspar crystals. Excessive use inhibits titanite crystal growth, decreasing reflectivity; insufficient use leads to the formation of a glassy phase, resulting in higher glaze gloss.

[0055] Using the aforementioned raw materials, the resulting reflective heat-insulating glaze layer contains titanium dioxide crystals, zirconium oxide crystals, titanium sphene crystals, and a glass matrix with refractive indices of 2.71, 2.2, 1.9, and 1.5, respectively. This creates a refractive index gradient, allowing the materials with different refractive indices to construct multiple diffuse reflection paths. This optimizes the overall optical uniformity of the reflective heat-insulating glaze layer and reduces solar transmission and absorption. In particular, due to its high refractive index, when titanium sphene crystals precipitate at micron and submicron levels, the grain size approaches the visible light band, resulting in a strongly opaque state on the glaze surface. This leads to highly efficient Mie scattering and reflection, further increasing the solar reflectance and achieving a high solar reflectance of 0.92.

[0056] Titanite crystals are monoclinic with a complex oxygen octahedral network; their crystal structure consists of Ca... 2+ Ti 4+ It is composed of SiO4 tetrahedra, in which Ti 4+ Located in a distorted octahedral coordination environment surrounded by oxygen ions, this structure results in a high abundance of phonons in the lattice vibration modes, especially forming dense phonon absorption and re-emission channels in the mid- and far-infrared bands.

[0057] The eutectic point of CaO-SiO2 binary eutectic is about 1436℃, that of CaO-TiO2 binary eutectic is about 1460℃, and that of CaO-TiO2-SiO2 ternary eutectic is about 1350℃. With the help of fluxing components such as potassium, sodium, calcium, magnesium, and zinc in the glaze, the eutectic melting point of titanium sphene will be further reduced to a firing temperature of about 1200℃ suitable for ceramic tiles. When the titanium dioxide in the raw material has a high Ca and Si content, a large amount of titanium sphene crystals will precipitate after firing, melting, and cooling.

[0058] After the precipitation of titanite crystals, a small amount of excess TiO2 glaze precipitates as rutile TiO2 crystals. TiO2, as one of the most potent white pigments and scatterers, has a refractive index as high as 2.71. Rutile TiO2 is tetragonal with a close-packed structure, making its structure more stable. 4+ With high charge density and strong polarization, it can significantly enhance the thermal excitation of the lattice dipole moment, strengthen the coupling between photons and lattice vibrational phonons, promote the emission efficiency of infrared photons, improve infrared emissivity, and achieve higher scattering in the infrared band. Specifically, the glaze is white, but the rutile crystals will give it a slightly yellowish tint. If there is an excess of TiO2, the yellow tint will become more pronounced. Therefore, the amount of TiO2 used must be limited to ensure that the glaze is milky white with a slight yellowish tint without turning into a yellow glaze.

[0059] In addition, high barium content can react with kaolin to form barium feldspar crystals, while low barium content will exist in the glaze in a glassy state, which increases the transparency and gloss of the glaze. High barium content exists in the glaze in the form of barium feldspar crystals. Since the crystals exist in the glaze in granular or columnar form, and the reflectivity of the crystals is different from that of the glassy state, the gloss of the glaze is effectively reduced.

[0060] The aforementioned reflective heat-insulating glaze layer simultaneously considers solar reflectance, whiteness, opacity, and stain resistance.

[0061] Preferably, the reflective heat-insulating glaze layer is formed by firing a glaze comprising the following chemical composition, according to a specific mass ratio: SiO2 45~52%, Al2O39~15%, Fe2O3 0.1~0.4%, TiO2 7~12%, CaO 8~15%, MgO 1~3%, BaO 2~6%, ZnO 1.5~5%, K2O 2~5%, Na2O 0.5~3%, ZrO2 2~4.5%, P2O5 0.2~1.5%, Weight loss upon ignition at 1000℃ is 2-5%.

[0062] Preferably, the fluxing component comprises the following raw materials in parts by weight: 5-12 parts of dolomite, 10-20 parts of calcite Potassium carbonate 5-10 parts.

[0063] Dolomite's main components are calcium oxide and magnesium oxide, calcite's main component is calcium oxide, and potassium carbonate mainly provides potassium oxide. All are used as fluxing components; too little addition results in high viscosity of the zirconium white frit, making feeding difficult, while too much leads to a higher glass phase and poor whitening effect. The combined application of dolomite and calcite simultaneously increases the CaO content in the glaze. Using these raw materials allows for a direct visual observation of the approximate calcium, magnesium, and potassium content in the flux system. As a simple substitution, other materials that can decompose to release calcium oxide, magnesium oxide, or potassium oxide at firing temperatures can also be used, such as potassium nitrate replacing potassium carbonate.

[0064] Preferably, the chemical composition of the zirconium white ingot includes: SiO2 52~57%, Al2O35~12%, Fe2O3 0.1~0.5%, TiO2 0.01~0.5%, CaO 3~12%, MgO 1.0~4.5%, K2O 2~7%, ZnO 3~9%, ZrO2 6~12%, P2O5 1~4%.

[0065] A method for preparing radiation-cooled ceramic bricks, comprising the following steps: A. Preparation of the base glaze: A1. Weigh the raw materials according to the proportion of the base glaze layer; A2. Add the weighed raw materials to the ball mill, add water and grinding aid according to the mass ratio, and then ball mill. A3. Grind the balls until the specific gravity of the output balls is 1.8~1.87 g / cm³. 3 The fineness is 0.5~0.8g, which is measured by the amount of residue on a 325-mesh sieve after 200g of slurry is passed through, and the base glaze is prepared accordingly. B. Apply a base glaze to the ceramic tile blank, controlling the amount of glaze to be 58~62g / (350mm×350mm); C. Apply reflective heat-insulating glaze, controlling the amount of glaze application to be 50~55g / (350mm×350mm); D. Firing to obtain radiation-cooled ceramic bricks.

[0066] The specific gravity is controlled to ensure that the base glaze slurry meets the basic requirements for glazing during the glazing process, resulting in minimal thickness variation when applied to the body. Within this range, a higher specific gravity leads to better glazing results. The ball milling fineness is controlled to ensure that the uniformity of the glaze slurry particle size matches a firing temperature of approximately 1200℃. Excessive fineness results in an excessively high firing temperature; conversely, insufficient fineness results in an excessively low firing temperature.

[0067] The amount of glaze applied determines the thickness of the base glaze layer and the reflective heat-insulating glaze layer. The base glaze needs to be of a certain thickness to cover the black color of the body. At the same time, different thicknesses correspond to different amounts of porous alumina and rare earth-doped spinel, which affects the reflectance measurement results. However, when the glaze slurry has a high specific gravity, glaze drift is likely to occur during glaze application, resulting in significant thickness deviations in the glaze layer.

[0068] Specifically, the firing temperature of the glaze is 1180~1230℃, the thickness of the base glaze layer is 0.19~0.21mm, and the thickness of the reflective heat insulation glaze layer is 0.16~0.17mm.

[0069] Preferably, the preparation of the surface glaze is also included: S1. Weigh the raw materials according to the proportion of the raw materials for the reflective heat insulation glaze layer; S2. Add the weighed raw materials to the ball mill, add water and grinding aid according to the mass ratio, and then ball mill. S3, ball milling until the ball specific gravity is 1.85~1.9g / cm³ 3 The fineness is 0.4~0.6g, which is measured by the amount of residue on a 325-mesh sieve after 200g of slurry is passed through it to obtain the surface glaze.

[0070] Preferably, the method also includes the preparation of zirconium white frit: the raw materials of zirconium white frit are mixed evenly according to the proportion, heated to a firing temperature of 1500~1600℃ for firing, and held at the firing temperature for 0.1~1h, then discharged and cooled to obtain zirconium white frit.

[0071] The purpose of controlling the firing temperature of zirconium white frit to above 1500℃ is to ensure that the zirconium white frit has a suitable high-temperature viscosity for feeding, while an appropriate curing time ensures that the zirconium white frit can effectively precipitate titanium sphene crystals during the subsequent glaze firing process. The firing temperature and curing time are mutually adjustable. Generally, the higher the firing temperature, the shorter the curing time can be, while the longer the curing time, the longer the zirconium oxide crystallization time and the greater the number of crystals. However, it is necessary to avoid the problem of excessively long firing times leading to an increase in the glass phase content in the glaze. One purpose of zirconium white frit is to provide zirconium oxide crystals; secondly, because the calcium phosphate formed during frit firing is introduced into the raw material, it promotes titanium sphene crystallization; and thirdly, the frit contains a large amount of calcium oxide components, which promote titanium sphene crystallization during secondary applications.

[0072] In a specific embodiment, the temperature curve for sintering zircon white frit is set as follows: 0~300℃ for 2h, 300~1530℃ for 2.5h, and 1530℃ for 0.5h.

[0073] The preparation methods of the base glaze in Examples 1-3 are as follows: A. Preparation of the base glaze: A1. Weigh 100 parts of the raw materials according to the proportions of the base glaze layer shown in Table 1. A2. Add the weighed raw materials to the ball mill, and according to the mass ratio, add 40 parts water, 0.12 parts sodium carboxymethyl cellulose, 0.42 parts sodium tripolyphosphate, and 0.05 parts preservative, and then ball mill. A3. Grind the balls until the specific gravity of the output balls is 1.8~1.87 g / cm³. 3 The fineness is 0.5~0.8g, which is used to prepare the base glaze; The preparation method of Comparative Example 1 is the same as that of Example 1, except that the amount of porous alumina powder is changed to 5 parts and the amount of albite is changed to 45 parts.

[0074] The preparation method of Comparative Example 2 is the same as that of Example 1, except that the amount of trivalent europium ion-doped magnesium aluminum spinel powder is changed to 4 parts, and the amount of porous alumina powder is changed to 18 parts accordingly.

[0075] The preparation methods of the zirconium white frits in Examples 4-6 are as follows: After weighing and mixing the raw materials according to the proportions shown in Table 3, the temperature curves were set as follows: 0~300℃ for 2h, 300~1530℃ for 2.5h, and 1530℃ for 0.5h. After heating and firing, the materials were discharged and cooled to obtain zirconium white frit.

[0076] The methods for preparing the reflective heat-insulating glaze in Examples 7-11 are as follows: S1. Weigh 100 portions of raw materials according to the proportions shown in Tables 5 to 7. S2. Add the weighed raw materials to the ball mill, and according to the mass ratio, add 40 parts water, 0.12 parts sodium carboxymethyl cellulose, 0.42 parts sodium tripolyphosphate and 0.05 parts preservative, and then ball mill. S3, ball milling until the ball specific gravity is 1.85~1.9g / cm³ 3 A glaze slurry with a fineness of 0.4~0.6g was prepared. S4. Use glaze slurry for glazing, and control the amount of glaze to be 50~55g / (350mm×350mm); The preparation method of Comparative Example 3 is the same as that of Example 7, except that Comparative Example 3 uses the same amount of titanium sphene powder instead of titanium dioxide.

[0077] The preparation method of Comparative Example 4 is the same as that of Example 7, except that quartz is used instead of wollastonite in Comparative Example 4.

[0078] Finally, the anti-fouling level was tested according to GB / T3810.14-2016, and the solar reflectance (wavelength 300nm~2500nm) was tested according to GB / T 31389-2015. The test data are shown in Table 9 below.

[0079] The base glaze and reflective heat-insulating surface glaze of the ceramic tiles in Examples 12-16 are combined as shown in Table 10 below, and the preparation methods are as follows: B. Apply a base glaze to the ceramic tile blank, controlling the amount of glaze to be 58~62g / (350mm×350mm); C. Apply reflective heat-insulating glaze, controlling the amount of glaze application to be 50~55g / (350mm×350mm); D. Firing to obtain radiation-cooled ceramic bricks.

[0080] Finally, the anti-fouling level was tested according to GB / T3810.14-2016, the solar reflectance (wavelength 300nm~2500nm) was tested according to GB / T 31389-2015, and the emissivity was tested according to ASTM C1371-15. The specific data are shown in Tables 1 to 10 below.

[0081] Table 1. Raw materials / parts by weight of base glaze

[0082] Table 2 Chemical composition of base glaze raw materials / %

[0083] Table 3. Raw materials / parts by weight of zirconium white ingot

[0084] Table 4 Chemical composition of zirconium white ingot / %

[0085] Table 5 Raw materials / parts by weight for reflective heat-insulating glaze layer

[0086] Table 6 Raw materials / parts by weight for reflective heat-insulating glaze layer

[0087] Table 7 Raw materials / parts by weight for reflective heat-insulating glaze layer

[0088] Table 8 Chemical composition of reflective heat-insulating glaze layer / %

[0089] Table 9 Summary of Test Performance of Reflective Heat Insulation Glaze Layer

[0090] In Comparative Example 3, because titanium sphene powder was directly added to the glaze, the content of titanium sphene crystals was significantly less than that of titanium dioxide crystals on the glaze surface. Therefore, it was necessary to increase the amount of titanium sphene powder. At the same time, in the application of a large amount of titanium sphene powder, it was necessary to control the particle size of the titanium sphene powder to ensure that it was not dissolved by the glass phase in the glaze. Generally, the particle size was required to be larger than that of ordinary glaze. The addition of a large amount of titanium sphene powder led to unstable glaze performance and made it difficult to control the anti-fouling performance.

[0091] In Comparative Example 4, due to a significant decrease in the calcium oxide content in the formula, the glaze's crystalline composition is no longer dominated by titanium sphene, but rather becomes a titanium-based yellow glaze. The reason for this is that, with the TiO2 content remaining essentially unchanged, TiO2 is in an absolute excess state in the glaze, dissolving into the vitreous layer, resulting in a very distinct yellow glaze surface and a sharp decrease in solar reflectance.

[0092] Table 10 Summary of Glaze Combinations and Test Performance of Ceramic Tiles

[0093] Examples 12-14 all use the base glaze layer of this scheme combined with the conventional top glaze layer of Comparative Example 3. It can be seen that the ceramic tiles prepared by using the base glaze layer of this scheme have high emissivity. However, since Comparative Example 3 uses titanium sphene powder instead of titanium dioxide in the top glaze layer, the firing temperature of the top glaze is relatively lower. During the sintering process, the top glaze layer melts and seals prematurely, while the base glaze layer is still in the degassing stage. The gas generated by the base glaze is forced to pass through the sealed top glaze layer, which greatly increases the probability of pinholes and pores on the glaze surface. The anti-fouling level drops to level 4, and the reflectivity is also insufficient due to the limitations of conventional glaze performance.

[0094] Examples 15-17 employ a combination of the specific base glaze layer and the reflective heat-insulating surface glaze layer of this scheme. Their solar reflectance all reach above 0.923, their emissivity is above 0.921, and their anti-fouling rating reaches level 5. This demonstrates the high synergy between the base glaze and the surface glaze in terms of chemical composition, coefficient of expansion, and firing pace, achieving not only excellent radiative cooling performance but also superior surface quality.

[0095] Comparative Example 5 represents a conventional glaze combination in existing technology. While it offers good reflectivity, its anti-fouling performance and emissivity are difficult to improve effectively. In particular, its anti-fouling rating is only level 3. The reason for this is that the base glaze contains a large amount of sodium oxide, which generates a strong fluxing effect, leading to overfiring of the base glaze layer during the firing process. Overfiring causes a surge in porosity within the base glaze, which not only damages its structural stability but also directly affects the smoothness of the surface glaze layer, resulting in a significant decrease in anti-fouling performance.

[0096] Comparative Example 6 shows that the pores of the porous alumina in the base glaze layer are filled, which affects the reflectivity and emissivity of the glaze.

[0097] Comparative Example 7 showed insufficient emissivity due to insufficient use of trivalent europium ion-doped magnesium aluminum spinel powder in the base glaze layer.

[0098] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0099] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A type of radiative cooling ceramic brick, characterized in that, The base glaze layer and the reflective heat-insulating surface glaze layer are included. By weight, the raw materials for the base glaze layer include: 5-12 parts of kaolin 1-5 parts of calcined kaolin 10-20 parts of porous alumina powder 10-20 parts of quartz Burn 1-5 parts of talc. Nepheline 12-25 parts Potassium feldspar 3-8 parts, 30-40 parts of albite, 5-10 parts of trivalent europium ion-doped magnesium aluminum spinel powder Zirconium silicate 5-10 parts.

2. The radiative cooling ceramic brick according to claim 1, characterized in that: The porous alumina powder has a particle size of 200-325 mesh and a porosity of 23-30%, while the trivalent europium ion-doped magnesium aluminum spinel powder has a particle size of 325-500 mesh.

3. The radiative cooling ceramic brick according to claim 1, characterized in that, According to the mass ratio, the base glaze layer is fired from a base glaze comprising the following chemical composition: SiO2 50~60%, Al2O3 25~30%, Fe2O3 0.1~0.4%, TiO2 0.1~0.25%, CaO 0.2~1%, MgO 1.5~3.5%, K2O 1~3.5%, Na2O 2~5%, ZrO2 2~5%, Weight loss upon ignition at 1000℃ is 1-3%.

4. The radiative cooling ceramic brick according to claim 1, characterized in that, The raw materials of the reflective heat-insulating glaze layer, by weight, include: 5-10 parts of kaolin 5-10 parts titanium dioxide 25-35 parts of zirconium white frit, Potassium feldspar 20-35 parts, 15-25 parts wollastonite 5-12 parts of barium carbonate; The raw materials for the zircon white frit include 12-20 parts of kaolin, 8-15 parts of zircon powder, 30-42 parts of quartz, 3-8 parts of zinc oxide, 3-8 parts of tricalcium phosphate, and 20-42 parts of fluxing components.

5. The radiative cooling ceramic brick according to claim 1, characterized in that, According to the mass ratio, the reflective heat-insulating glaze layer is fired from a glaze comprising the following chemical composition: SiO2 45~52%, Al2O3 9~15%, Fe2O3 0.1~0.4%, TiO2 7~12%, CaO 8~15%, MgO 1~3%, BaO 2~6%, ZnO 1.5~5%, K2O 2~5%, Na2O 0.5~3%, ZrO2 2~4.5%, P2O5 0.2~1.5%, Weight loss upon ignition at 1000℃ is 2-5%.

6. The radiative cooling ceramic brick according to claim 4, characterized in that, The fluxing component comprises the following raw materials in parts by weight: 5-12 parts of dolomite, 10-20 parts of calcite Potassium carbonate 5-10 parts.

7. A radiation-cooled ceramic brick according to claim 4, characterized in that, The chemical composition of the zirconium white ingot includes: SiO2 52~57%, Al2O3 5~12%, Fe2O3 0.1~0.5%, TiO2 0.01~0.5%, CaO 3~12%, MgO 1.0~4.5%, K2O 2~7%, ZnO 3~9%, ZrO2 6~12%, P2O5 1~4%.

8. A method for preparing a radiation-cooled ceramic brick, characterized in that, The method for preparing the radiation-cooled ceramic brick according to any one of claims 1-7 comprises the following steps: A. Preparation of the base glaze: A1. Weigh the raw materials according to the proportion of the base glaze layer; A2. Add the weighed raw materials to the ball mill, add water and grinding aid according to the mass ratio, and then ball mill. A3. Grind the balls until the specific gravity of the output balls is 1.8~1.87 g / cm³. 3 The fineness is 0.5~0.8g, which is measured by the amount of residue on a 325-mesh sieve after 200g of slurry is passed through, and the base glaze is prepared accordingly. B. Apply a base glaze to the ceramic tile blank, controlling the amount of glaze to be 58~62g / (350mm×350mm); C. Apply reflective heat-insulating glaze, controlling the amount of glaze application to be 50~55g / (350mm×350mm); D. Firing to obtain radiation-cooled ceramic bricks.

9. The method for preparing radiation-cooled ceramic bricks according to claim 8, characterized in that, It also includes the preparation of the surface glaze: S1. Weigh the raw materials according to the proportion of the raw materials for the reflective heat insulation glaze layer; S2. Add the weighed raw materials to the ball mill, add water and grinding aid according to the mass ratio, and then ball mill. S3, ball milling until the ball specific gravity is 1.85~1.9g / cm³ 3 The fineness is 0.4~0.6g, which is measured by the amount of residue on a 325-mesh sieve after 200g of slurry is passed through it to obtain the surface glaze.

10. The method for preparing radiation-cooled ceramic bricks according to claim 9, characterized in that, It also includes the preparation of zirconium white frit: after the raw materials of zirconium white frit are mixed evenly in proportion, the temperature is raised to a firing temperature of 1500~1600℃ for firing, and the firing temperature is held for 0.1~1h. The material is then discharged and cooled to obtain zirconium white frit.

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