High reflectivity ceramic, method of manufacture and application to a desk lamp

Abstract

The application discloses a kind of high reflectivity ceramics, preparation method and application on desk lamp, belong to ceramic material technical field.The ceramic is by HfO2 Nanoparticle and Bi2O3-B2O3-SiO2 matrix powder as main raw material by weight parts, add nucleating agent and binder, by compounding, pressing, gradient sintering is obtained.The principle is: using the difference of Bi2O3-B2O3-SiO2 matrix and HfO2 thermal expansion coefficient, compression stress is applied to HfO2 grain in cooling process, induce t-HfO2 to m-HfO2 martensitic phase change and form high-density nanometer twin crystal in grain interior;The refractive index difference at twin crystal boundary produces interface reflection, and the Fresnel reflection of HfO2 / matrix interface is coordinated, so that the visible light diffuse reflectivity reaches 92-98%, while sintering densification gives ceramic high bending strength (≥120 MPa).The application process is controllable, product performance is excellent, and has wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, specifically to a composite ceramic with high visible light reflectivity, its preparation method, and its application in a table lamp. Background Technology

[0002] As a widely used lighting device in daily life, the luminous efficacy and uniformity of a desk lamp directly affect the user experience. The reflector cup or inner wall of the lampshade typically requires a high-reflectivity material to improve light utilization efficiency, reduce light loss, and enhance lighting uniformity. Commonly used reflective materials include polished metal surfaces (such as aluminum and silver), white paint, or white ceramics. However, metal surfaces are prone to oxidation, leading to a significant decrease in reflectivity over long-term use. While white paint is relatively inexpensive, it suffers from poor heat resistance, is prone to aging and peeling, and uneven coating thickness can negatively impact reflectivity. Ceramic materials possess inherent advantages such as high hardness, heat resistance, corrosion resistance, and aging resistance. However, the reflectivity of traditional white ceramics (such as alumina ceramics) typically depends on the scattering of light by pores within the material; higher porosity results in higher reflectivity. However, high porosity severely weakens mechanical strength, leading to brittleness and easy breakage.

[0003] Furthermore, traditional high-porosity ceramics have large surface roughness, making it difficult to achieve complex shapes (such as the curved or arc-shaped surfaces required for desk lamp reflectors) through machining. Surface polishing also closes pores and reduces reflectivity. Therefore, existing reflective materials for desk lamps present a trade-off between high reflectivity, high mechanical strength, and good formability. To address this issue, there is an urgent need in the field to develop a novel ceramic material that achieves high visible light reflectivity without relying on high porosity, while also possessing excellent mechanical properties and machinability, to meet the practical needs of the desk lamp industry for high-performance reflective components. Summary of the Invention

[0004] This invention addresses the problems of low reflectivity, easy aging, or poor mechanical properties in existing reflective materials for desk lamps by providing a high-reflectivity ceramic, its preparation method, and its application in desk lamps. This ceramic utilizes a nanotwinned structure formed by HfO2 nanocrystals within a Bi2O3-B2O3-SiO2 matrix, combining the refractive index difference between HfO2 and the matrix to achieve efficient diffuse reflection of visible light while maintaining good mechanical properties and thermal stability.

[0005] A high-reflectivity ceramic material, prepared by weight, is composed of the following components: HfO2 nanoparticles: 15-40 parts; Bi2O3-B2O3-SiO2 matrix powder: 50-80 parts; Nucleating agent: The dosage is 5%-15% of the weight of HfO2, and the particle size is 10-20nm; Binder: 3%-8% of the total weight of HfO2 and Bi2O3-B2O3-SiO2 matrix powder.

[0006] The HfO2 nanoparticles have a purity of ≥99.99% and an average particle size of ≤100 nm.

[0007] The composition of the Bi2O3-B2O3-SiO2 matrix powder, in molar fraction, is: Bi2O3 45-60 mol%, B2O3 15-35 mol%, SiO2 15-35 mol%.

[0008] The nucleating agent is selected from one or two of TiO2 and ZrO2.

[0009] The adhesive is selected from one or two of PVA, PEG or carboxymethyl cellulose.

[0010] The present invention also provides a method for preparing the high reflectivity ceramic, comprising the following steps: Step 1: Prepare Bi2O3-B2O3-SiO2 matrix powder using the sol-gel method according to the stated molar ratio; Step 2: Add HfO2 nanoparticles to deionized water and disperse them by ultrasonication. Add nucleating agent and dispersant, stir, centrifuge, wash, and dry to perform surface pretreatment. Step 3: Mix the Bi2O3-B2O3-SiO2 matrix powder obtained in Step 1 with the HfO2 nanoparticles pretreated in Step 2 according to the target weight ratio, add binder and deionized water, ball mill the mixture, and then spray dry or vacuum dry to obtain composite powder. Step 4: Press the composite powder under a pressure of 20-50 MPa to obtain a green body; Step 5: Perform gradient sintering of the green body under a protective atmosphere: First sintering: from room temperature to 500-650℃, heating rate 1-3℃ / min, hold for 1-2 hours; Second sintering: 650-800℃, heating rate 5-10℃ / min, holding time 1-2 hours; Third sintering: 800-1000℃, heating rate 2-5℃ / min, holding time 2-4 hours; Annealing: Cool in the furnace or at a rate of 2-5℃ / min to room temperature to obtain high reflectivity ceramics.

[0011] Further, the specific conditions for the sol-gel method described in step one are as follows: using bismuth nitrate, boric acid, and tetraethyl orthosilicate as raw materials, dissolving them in ethylene glycol methyl ether and deionized water, adjusting the pH to 2-3, stirring at 60-80℃ for 2-4 hours to form a sol, then drying at 100-120℃ to form a dry gel, and finally heat-treating at 500-700℃ for 2-4 hours, grinding through a 200-mesh sieve to obtain Bi2O3-B2O3-SiO2 matrix powder.

[0012] Furthermore, the dispersant mentioned in step two is ammonium polyacrylate, and the amount used is 0.5%-1.0% of the weight of HfO2.

[0013] Furthermore, in step three, the weight ratio of Bi2O3-B2O3-SiO2 matrix powder to HfO2 is (50-80):(15-40), preferably 3:2 to 5:1.

[0014] Furthermore, the protective atmosphere described in step five is nitrogen or argon, with a flow rate of 2-5 L / min.

[0015] Furthermore, the molding described in step four involves loading the composite powder into a metal mold and pressing it into a plate-shaped or arc-shaped green body under a pressure of 20-50 MPa, holding the pressure for 1-3 minutes.

[0016] This invention also provides the application of the high-reflectivity ceramic in desk lamps, specifically as a reflector cup, reflective lampshade, or lamp base lining component, used to efficiently reflect light emitted from the light source, improving luminous efficiency and illumination uniformity. The ceramic component can be directly pressed into shape using a mold or sintered and then processed into an arc or curved shape suitable for the desk lamp.

[0017] The high reflectivity ceramic of the present invention is based on the following synergistic enhancement mechanism: The coefficient of thermal expansion of the Bi2O3-B2O3-SiO2 matrix (CTE≈10-12×10) -6 / K) and HfO2 (CTE≈6-7×10 -6 There are significant differences between t-HfO2 and m-HfO2 nanocrystals ( / K). During the cooling process after high-temperature sintering, the matrix applies compressive constraint stress to the dispersed HfO2 nanocrystals, inducing a martensitic phase transformation from t-HfO2 to m-HfO2, and forming high-density nanotwins within the grains. The spatial constraint at the nanoscale significantly reduces the phase transformation temperature, allowing the twins to exist stably at lower temperatures. m-HfO2 is a birefringent crystal, with different refractive indices on both sides of the twin boundaries, causing incident light to be reflected at the twin boundaries. Multiple twin boundaries form multiple reflection paths, significantly enhancing backscattering.

[0018] Meanwhile, a refractive index difference exists between the HfO2 grains (refractive index n≈2.1) and the Bi2O3-B2O3-SiO2 matrix (n≈1.6-1.7), resulting in Fresnel reflection at the grain / Bi2O3-B2O3-SiO2 interface. The synergistic effect of nanotwin interface reflection and interface Fresnel reflection produces highly efficient diffuse reflection of visible light.

[0019] Compared with the prior art, the present invention has the following beneficial effects: By utilizing the synergistic effect of interfacial reflection from HfO2 nanotwins and Fresnel reflection from the HfO2 / Bi2O3-B2O3-SiO2 matrix interface, the ceramic achieves a diffuse reflectance of 92%-98% in the visible light band (400-780 nm), significantly superior to ordinary white ceramics. Due to its high sintering density (porosity <5%), it does not rely on pore scattering, resulting in a flexural strength of 120-180 MPa and a Vickers hardness of 5-7 GPa, making it resistant to breakage. This inorganic all-ceramic system withstands temperatures above 800℃ and exhibits no aging or discoloration issues with long-term use. Using powder pressing and gradient sintering processes, it can fabricate curved and rounded surfaces for lamps, and the surfaces can be polished or used directly. The ceramic material prepared by this invention does not contain harmful heavy metals such as lead and cadmium, complying with RoHS standards. Detailed Implementation

[0020] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0021] Main raw material information HfO2 nanoparticles: 99.99% purity, average particle size 80 nm, purchased from Aladdin. Bi(NO3)3·5H2O: Analytical grade H3BO3: Analytical purity Tetraethyl orthosilicate (TEOS): Analytical grade TiO2 sol (solid content 20%, particle size 10-20 nm): self-made ZrO2 sol (solid content 20%, particle size 10-20 nm): self-made PVA (degree of polymerization 1750±50): Industrial grade Ammonium polyacrylate (PAA-NH4): Analytical grade Alumina powder (α-Al₂O₃): purity 99.9%, average particle size 1 μm Silica powder (SiO2): purity 99.9%, average particle size 1 μm Performance testing Reflectivity: The total reflectivity in the 400-800nm ​​band was measured using a UV-Vis spectrophotometer (with integrating sphere) in accordance with GB / T 2680-2021.

[0022] Bending strength: according to GB / T 6569-2006, three-point bending method.

[0023] Vickers hardness: according to GB / T 16534-2009, load 1 kgf, hold for 15 s.

[0024] Coefficient of thermal expansion: according to GB / T 16535-2008, heating rate 5℃ / min.

[0025] Phase analysis: X-ray diffraction (XRD), Cu Kα.

[0026] Example 1

[0027] Step 1: Preparation of Bi2O3-B2O3-SiO2 matrix powder Weigh out 48.5 g of Bi(NO3)3·5H2O, 4.64 g of H3BO3, and 5.2 g of TEOS, using a molar ratio of Bi2O3:B2O3:SiO2 = 50:25:25. Dissolve Bi(NO3)3·5H2O in 50 mL of ethylene glycol methyl ether, H3BO3 in 30 mL of deionized water, and TEOS in 20 mL of anhydrous ethanol. After mixing, adjust the pH to 2.5 by adding dilute nitric acid dropwise, and stir at 70°C for 3 hours. Dry the sol at 110°C to form a gel, then heat-treat at 600°C for 3 hours, and grind through a 200-mesh sieve to obtain Bi2O3-B2O3-SiO2 matrix powder.

[0028] Step 2: HfO2 pretreatment Take 20 parts by weight of HfO2 nanoparticles (the actual amount used in the examples corresponds to the parts by weight), add 200 mL of deionized water, and ultrasonically disperse for 30 minutes. Add ZrO2 sol (2.0 parts by weight based on ZrO2, i.e., 10% of the weight of HfO2) and 0.15 parts by weight of ammonium polyacrylate, and stir for 1 hour. Centrifuge, wash three times with deionized water, and dry at 90°C for 12 hours.

[0029] Step 3: Preparation of composite powder Take 56 parts by weight of Bi2O3-B2O3-SiO2 matrix powder from step one, 20 parts by weight of HfO2 from step two pretreatment (matrix powder:HfO2≈2.8:1), add 4 parts by weight of PVA (approximately 5% of the total weight of HfO2 and matrix powder), add 40 mL of deionized water, and ball mill for 6 hours (300 rpm). Spray dry the slurry to obtain the composite powder.

[0030] Step 4: Molding The composite powder was loaded into a circular stainless steel mold with a diameter of 50 mm and pressed into shape under a pressure of 30 MPa for 2 minutes to obtain a circular green sheet (about 3 mm thick).

[0031] Step 5: Gradient sintering The green blank was placed in a tube furnace and nitrogen gas was introduced (flow rate 3 L / min). The sintering procedure was as follows: First sintering: room temperature to 600℃, heating rate 2℃ / min, holding for 1.5 hours; Second sintering: 600 to 750℃, heating rate 8℃ / min, holding for 1.5 hours; Third sintering: 750 to 950℃, heating rate 3℃ / min, holding for 3 hours; Annealing, followed by furnace cooling to room temperature. This yielded a high-reflectivity ceramic disc with a diameter of approximately 48 mm and a thickness of approximately 2.5 mm.

[0032] Performance testing: Total visible light reflectance (average 400-800 nm) is 96.2%, flexural strength is 156 MPa, Vickers hardness is 6.2 GPa, and coefficient of thermal expansion (room temperature - 500℃) is 9.8 × 10⁻⁶. -6 / K, the main crystalline phase is m-HfO2 (XRD shows characteristic peak broadening, indicating the presence of nanotwins).

[0033] Application in desk lamps: The circular piece is cut into an arc shape to match the reflector of the desk lamp and then fitted onto the inner wall of the reflector in the LED desk lamp. Compared to ordinary white ceramic reflectors, the illuminance at the light center is increased by 28%, and the uniformity of the light spot is significantly improved.

[0034] Example 2

[0035] The difference from Example 1 is as follows: the composition of the Bi2O3-B2O3-SiO2 matrix powder was adjusted to 55 mol% Bi2O3, 20 mol% B2O3, and 25 mol% SiO2; the weight of HfO2 was increased to 35 parts (46 parts of matrix powder), and TiO2 sol was used as the nucleating agent (12% of the weight of HfO2). The maximum sintering temperature was increased to 980℃. Performance: reflectivity 97.1%, flexural strength 142 MPa, Vickers hardness 5.9 GPa.

[0036] Example 3

[0037] The difference from Example 1 is that the weight of HfO2 is reduced to 20 parts (64 parts of matrix powder), and the nucleating agent is ZrO2 + TiO2 (each accounting for half, with a total amount of 8% of the weight of HfO2). The maximum sintering temperature is 920℃. Properties: reflectivity 93.5%, flexural strength 168 MPa, Vickers hardness 6.4 GPa.

[0038] Comparative Example 1 The difference from Example 1 is that no nucleating agent is added in step two. Everything else is the same. Performance: Reflectivity 82.3%, flexural strength 98 MPa, XRD shows insufficient HfO2 crystallization with no obvious twinning peaks.

[0039] Comparative Example 2 The difference from Example 1 is that in step five, the temperature was directly increased to 950℃ at a rate of 5℃ / min and held for 3 hours. Performance: Reflectivity 88.6%, microcracks appeared in the sample, and the flexural strength was only 72 MPa.

[0040] Comparative Example 3 The difference from Example 1 is that in steps one and three, the Bi2O3-B2O3-SiO2 matrix powder is replaced with an equal weight of α-Al2O3 powder. That is, the composite powder consists of: 56 parts by weight of Al2O3 powder, 20 parts by weight of pretreated HfO2, and 4 parts by weight of PVA. The remaining preparation steps are exactly the same as in Example 1. Performance: Reflectivity 78.5%, flexural strength 112 MPa, Vickers hardness 7.8 GPa. XRD shows the main crystalline phase is α-Al2O3 and a small amount of m-HfO2, with no twinning broadening characteristics.

[0041] Comparative Example 4 The difference from Example 1 is that in steps one and three, the Bi2O3-B2O3-SiO2 matrix powder is replaced with an equal weight of SiO2 powder. That is, the composite powder consists of: 56 parts by weight of SiO2 powder, 20 parts by weight of pretreated HfO2, and 4 parts by weight of PVA. The remaining preparation steps are exactly the same as in Example 1. Performance: Reflectivity 72.3%, flexural strength 45 MPa (sample is porous and brittle), hardness could not be measured. XRD showed that it mainly consisted of quartz and a small amount of m-HfO2.

[0042] Table 1. Performance Summary of Each Embodiment and Comparative Example

[0043] As shown in Table 1, Examples 1-3 using the Bi2O3-B2O3-SiO2 matrix of this invention all achieved a reflectivity of over 93.5% (maximum 97.1%) and a flexural strength ≥142 MPa. The mechanism lies in the difference in thermal expansion coefficients between the Bi2O3-B2O3-SiO2 matrix and HfO2 (approximately 4-6 × 10⁻⁶). -6 During the cooling process, compressive stress is applied to HfO2, inducing a t→m phase transformation and forming high-density nanotwins. The refractive index difference on both sides of the twin boundary generates interfacial reflection, which, in conjunction with the Fresnel reflection at the HfO2 / matrix interface, achieves efficient diffuse reflection. At the same time, gradient sintering densifies the matrix (porosity <5%), ensuring high mechanical strength.

[0044] Comparative Example 1, without the addition of a nucleating agent, showed a reflectivity reduced to 82.3% and a flexural strength of 98 MPa, demonstrating that the nucleating agent is key to inducing twin formation. Comparative Example 2, using rapid sintering (without gradient), showed microcracks in the sample, with a reflectivity of 88.6% and a strength of only 72 MPa, indicating that gradient sintering (slow debinding and staged heating) is essential for eliminating thermal stress and preventing cracking.

[0045] Comparative Example 3 uses Al2O3 to replace the Bi2O3-B2O3-SiO2 matrix, and the difference in thermal expansion coefficient between Al2O3 and HfO2 is too small (only 1-2×10). -6 The matrix (HfO2) cannot form twins, resulting in a reflectivity of only 78.5%. Comparative Example 4, using SiO2 instead, although exhibiting a large difference in thermal expansion, cannot be densified at 950℃. The resulting matrix is ​​porous and unable to transmit constraint stress, leading to a reflectivity of only 72.3% and a strength of only 45 MPa. These two comparisons demonstrate that the matrix not only needs sufficient thermal expansion mismatch with HfO2 but also requires good sintering densification capabilities.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A high-reflectivity ceramic, characterized in that, It is prepared from the following components in parts by weight: HfO2 nanoparticles: 15-40 parts; Bi2O3-B2O3-SiO2 matrix powder: 50-80 parts; Nucleating agent: The amount used is 5%-15% of the weight of HfO2, and the nucleating agent is selected from one or two of TiO2 and ZrO2, with a particle size of 10-20nm; Binder: 3%-8% of the total weight of HfO2 and Bi2O3-B2O3-SiO2 matrix powder; The composition of the Bi2O3-B2O3-SiO2 matrix powder, in molar fraction, is: Bi2O3 45-60 mol%, B2O3 15-35 mol%, SiO2 15-35 mol%.

2. A high-reflectivity ceramic according to claim 1, characterized in that, The HfO2 nanoparticles have a purity of ≥99.99% and an average particle size of ≤100 nm.

3. The high reflectivity ceramic according to claim 1, characterized in that, The adhesive is selected from PVA, PEG or carboxymethyl cellulose.

4. A method for preparing high-reflectivity ceramic as described in claim 1, characterized in that, Includes the following steps: Step 1: Prepare Bi2O3-B2O3-SiO2 matrix powder using the sol-gel method according to the stated molar ratio; Step 2: Add HfO2 nanoparticles to deionized water and disperse them by ultrasonication. Add nucleating agent and dispersant, stir, centrifuge, wash, and dry to perform surface pretreatment. Step 3: Mix the Bi2O3-B2O3-SiO2 matrix powder obtained in Step 1 with the HfO2 nanoparticles pretreated in Step 2 according to the target weight ratio, add binder and deionized water, ball mill the mixture, and then spray dry or vacuum dry to obtain composite powder. Step 4: Press the composite powder under a pressure of 20-50 MPa to obtain a green body; Step 5: Perform gradient sintering of the green body under a protective atmosphere: First sintering: from room temperature to 500-650℃, heating rate 1-3℃ / min, hold for 1-2 hours; Second sintering: 650-800℃, heating rate 5-10℃ / min, holding time 1-2 hours; Third sintering: 800-1000℃, heating rate 2-5℃ / min, holding time 2-4 hours; Annealing: Cool in the furnace or at a rate of 2-5℃ / min to room temperature to obtain high reflectivity ceramics.

5. The preparation method according to claim 4, characterized in that, The specific conditions for the sol-gel method described in step one are as follows: using bismuth nitrate, boric acid, and tetraethyl orthosilicate as raw materials, dissolving them in ethylene glycol methyl ether and deionized water, adjusting the pH to 2-3, stirring at 60-80℃ for 2-4 hours to form a sol, drying to form a dry gel, and then heat-treating at 500-700℃ for 2-4 hours.

6. The preparation method according to claim 4, characterized in that, The dispersant mentioned in step two is ammonium polyacrylate, and the amount used is 0.5%-1.0% of the weight of HfO2.

7. The preparation method according to claim 4, characterized in that, The weight ratio of Bi2O3-B2O3-SiO2 matrix powder to HfO2 in step three is (50-80):(15-40).

8. The preparation method according to claim 4, characterized in that, The protective atmosphere described in step five is nitrogen or argon, with a flow rate of 2-5 L / min.

9. The preparation method according to claim 4, characterized in that, The molding process described in step four involves loading the composite powder into a metal mold and pressing it into a plate-shaped or arc-shaped green body under a pressure of 20-50 MPa for 1-3 minutes.

10. The application of a high-reflectivity ceramic as described in claims 1-3 or a high-reflectivity ceramic prepared by the method of any one of claims 4-9 in a table lamp, characterized in that, The ceramic is used as a reflector cup, reflector shade, or lamp base lining component for a table lamp.

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