Ceramic composite coating, optical glass forming mold and method for manufacturing the same

Abstract

This invention relates to the field of ceramic materials technology, and particularly to ceramic composite coatings, optical glass forming molds, and their preparation methods. In the ceramic composite coating, the density of the ceramic sealing layer is ≥92%, exhibiting superior performance compared to traditional yttrium-stabilized zirconia layers. This reduces the diffusion rate of oxygen into the graphite mold at high temperatures, significantly improving the oxidation resistance of the graphite mold at high temperatures. Furthermore, the coefficient of thermal expansion of the ceramic sealing layer is 4.5–6.5 × 10⁻⁶. ‑6 The coefficient of thermal expansion of the ceramic composite coating is close to that of the graphite mold, which ensures that the ceramic composite coating will not develop microcracks, cracks, or peeling due to thermal expansion mismatch during repeated thermal cycling. This ensures the interfacial bonding strength and structural stability between the ceramic composite coating and the graphite mold, and can significantly extend the service life of the graphite mold.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, and in particular to a ceramic composite coating, an optical glass forming mold, and a method for preparing the same. Background Technology

[0002] Graphite is commonly used as molds in glass manufacturing equipment used for glass bending and other glass forming operations. Graphite is effective for these applications because glass tends not to adhere to graphite, and because graphite is relatively easy to machine into the shape required by the mold. However, despite these advantages, the challenge of using graphite as a glass forming mold is that graphite is susceptible to oxidation at the temperatures of glass bending or other glass forming operations (e.g., at high temperatures of 400–900°C). Graphite oxidation can create pits or other defects on the mold surface, which can cause pitting or roughening of the optical glass surface, severely reducing the surface accuracy and optical performance of the optical glass, and significantly reducing the product yield. At the same time, high-temperature oxidation of graphite molds can rapidly wear down the mold body, shorten the mold life, increase the mold replacement frequency, and increase the total production cost of optical glass.

[0003] Currently, most composite coatings for graphite molds focus on reducing demolding resistance. For example, patent CN121535131A proposes a composite coating for graphite molds, comprising a yttrium-stabilized zirconia layer, a transition layer containing yttrium-stabilized zirconia and boron nitride, and a boron nitride layer sequentially arranged from the inner surface of the graphite mold outwards. However, in the aforementioned composite coating for graphite molds, the yttrium-stabilized zirconia layer is not dense enough to form a continuous and dense impermeability barrier. Therefore, oxygen can still easily diffuse through the composite coating into the graphite matrix, easily causing oxidation of the graphite mold. Furthermore, the coefficient of thermal expansion of the yttrium-stabilized zirconia layer differs significantly from that of the graphite matrix, resulting in poor thermal shock resistance. During repeated use of the mold, the coating is prone to cracking and peeling. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to solve the problems that existing composite coatings for graphite molds have poor thermal shock resistance, are prone to cracking and peeling, and are still insufficient in improving the oxidation resistance of graphite molds.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of this invention provides a ceramic composite coating, comprising a ceramic sealing layer and an insulating layer; the ceramic sealing layer has a density ≥92% and a coefficient of thermal expansion of 4.5~6.5×10⁻⁶. -6 / K.

[0006] In the ceramic composite coating, the raw materials for preparing the ceramic sealing layer include a borosilicate glass precursor, a first ceramic powder, and a second ceramic powder; the first ceramic powder is Al2O3 powder; and the second ceramic powder is ZrO2 powder or mullite.

[0007] In the ceramic composite coating, the mass ratio of the borosilicate glass precursor, the first ceramic powder, and the second ceramic powder is (6.5-7):(2-2.5):1.

[0008] In the ceramic composite coating, the borosilicate glass precursor is a borosilicate glass precursor sol, and the molar ratio of SiO2 to B2O3 in the borosilicate glass precursor sol is (3.5-4):(1-1.5).

[0009] In the ceramic composite coating, the isolation layer is a BN isolation layer; the contact angle of the BN isolation layer is ≥100° and the coefficient of friction is ≤0.2.

[0010] A second aspect of the present invention provides an optical glass forming mold, comprising a graphite mold and the ceramic composite coating described above; the ceramic composite coating is located on the surface of the graphite mold.

[0011] A third aspect of the present invention provides a method for preparing an optical glass forming mold, which is used to prepare the optical glass forming mold described above, comprising the following steps: S01. The pretreated graphite mold is immersed in the ceramic sealing layer slurry. After the immersion coating is completed, it is dried under a protective atmosphere and then sintered and densified to form a ceramic sealing layer on the surface of the graphite mold. S02. Immerse the graphite mold with the ceramic sealing layer into the isolation layer slurry. After the immersion coating is completed, dry it under a protective atmosphere and then cure it to form an isolation layer on the surface of the ceramic sealing layer. S03. The graphite mold with the ceramic composite coating is annealed under a protective atmosphere. After the annealing is completed, the optical glass forming mold is obtained.

[0012] In the method for preparing the optical glass forming mold, in step S02, the solid content of the isolation layer slurry is 25-27%.

[0013] In the method for preparing the optical glass forming mold, in step S03, the annealing temperature is 795-845℃, wherein during the annealing process, the temperature is increased to 795-845℃ at a heating rate of 3℃ / min, and then held at that temperature for 2 hours.

[0014] In the method for preparing the optical glass forming mold, in step S01, the thickness of the ceramic sealing layer is 5-80 μm, and the thickness of the isolation layer is 5-50 μm.

[0015] Beneficial effects: (1) The first aspect of the present invention provides a ceramic composite coating in which the density of the ceramic sealing layer is ≥92%, which is superior to the traditional yttrium-stabilized zirconia layer. It can reduce the diffusion rate of oxygen into the graphite mold at high temperature, thereby greatly improving the oxidation resistance of the graphite mold at high temperature and avoiding defects such as dents on the surface of the graphite mold; and the coefficient of thermal expansion of the ceramic sealing layer is 4.5~6.5×10 -6 The coefficient of thermal expansion of the ceramic composite coating is close to that of the graphite mold, which ensures that the ceramic composite coating will not develop microcracks, cracks, or peeling due to thermal expansion mismatch during repeated thermal cycling. This ensures the interfacial bonding strength and structural stability between the ceramic composite coating and the graphite mold, and can significantly extend the service life of the graphite mold.

[0016] (2) The second aspect of the present invention provides an optical glass forming mold. By setting a ceramic composite coating on the surface of a graphite mold, the optical glass forming mold can achieve an oxidation weight loss rate of ≤0.5% in an air atmosphere at 400-900°C, which is much lower than that of a graphite mold without a ceramic composite coating. Furthermore, the optical glass forming mold with the ceramic composite coating can be used continuously for optical glass forming for more than 15,000 times without oxidation defects such as dents appearing on its surface, thus ensuring that the formed optical glass can meet the high-precision forming requirements of optical components.

[0017] (3) The third aspect of the present invention provides a method for preparing an optical glass forming mold. By first preparing a ceramic sealing layer by dip coating and sintering to densify it, then preparing an isolation layer by dip coating and curing it, and finally annealing the whole, the ceramic sealing layer can fully fill the pores on the graphite surface and form a high-density oxygen barrier. At the same time, the isolation layer is uniformly attached to the surface of the ceramic sealing layer and forms a stable low surface energy anti-stick structure. Combined with drying, sintering, curing and annealing under a protective atmosphere throughout the process, it can not only avoid oxidation of the graphite mold and the ceramic composite coating at high temperature, but also release the internal thermal stress of the ceramic composite coating and improve the interlayer bonding strength, so that the ceramic composite coating and the graphite matrix are firmly bonded, without cracking or peeling, and finally prepare an optical glass forming mold with excellent oxidation resistance, anti-sticking and structural stability under high temperature conditions. Attached Figure Description

[0018] Figure 1 This is a flowchart of the preparation method of the optical glass forming mold provided by the present invention. Detailed Implementation

[0019] This invention provides a ceramic composite coating, an optical glass forming mold, and a method for preparing the same. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0020] The first aspect of this invention provides a ceramic composite coating, comprising a ceramic sealing layer and an isolation layer; the isolation layer is located outside the ceramic sealing layer; the ceramic sealing layer has a density ≥92% and a coefficient of thermal expansion of 4.5~6.5×10⁻⁶. -6 / K.

[0021] The aforementioned ceramic composite coating can be used on the surface of graphite molds. In this ceramic composite coating, the density of the ceramic sealing layer is ≥92%. Compared to traditional yttrium-stabilized zirconia layers, the ceramic sealing layer forms a continuous and dense anti-permeation barrier, which reduces the diffusion rate of oxygen into the graphite mold at high temperatures. This significantly improves the oxidation resistance of the graphite mold at high temperatures, preventing surface defects such as dents. Simultaneously, the high-density ceramic sealing layer provides a stable adhesion base for the outer isolation layer, significantly improving the interfacial bonding strength between the isolation layer and the sealing layer. Furthermore, the coefficient of thermal expansion of the ceramic sealing layer is 4.5–6.5 × 10⁻⁶. -6 The coefficient of thermal expansion of the ceramic composite coating is close to that of the graphite mold, which ensures that the ceramic composite coating will not develop microcracks, cracks, or peeling due to thermal expansion mismatch during repeated thermal cycling. This ensures the interfacial bonding strength and structural stability between the ceramic composite coating and the graphite mold, and can significantly extend the service life of the graphite mold.

[0022] To obtain the aforementioned ceramic sealing layer and improve its density and high-temperature resistance, in a preferred embodiment, the raw materials for preparing the ceramic sealing layer in the ceramic composite coating include a first ceramic powder and a second ceramic powder. The first ceramic powder can be Al2O3 powder, and the second ceramic powder can be ZrO2 powder. ZrO2 powder has high density, which can significantly improve the overall density of the ceramic sealing layer and enhance its oxygen barrier effect. Simultaneously, ZrO2 has excellent high-temperature stability, which can effectively improve the high-temperature resistance of the ceramic sealing layer.

[0023] However, ZrO2 is prone to crystal phase transformation during high-temperature thermal cycling, accompanied by significant volume expansion, which reduces the thermal stability and thermal shock resistance of the ceramic composite coating. To address this, the ceramic sealing layer also uses Al2O3 as a ceramic reinforcing phase. During the sintering and densification process of the ceramic sealing layer, Al2O3 can effectively inhibit the abnormal growth of ZrO2 grains, stabilize the ZrO2 crystal form, and weaken the volume effect caused by the ZrO2 phase transformation. This can improve the bonding strength between the ceramic sealing layer and the graphite mold surface (tensile strength of the ceramic sealing layer ≥15MPa), improve the overall thermal stability and thermal shock resistance of the ceramic composite coating, and ensure that the ceramic composite coating remains continuous, dense, crack-free, and non-peeling under high-temperature cycling.

[0024] To better match the thermal expansion coefficient of the ceramic sealing layer with that of the graphite mold and further improve the thermal shock resistance of the ceramic composite coating, in a preferred embodiment, the second ceramic powder can also be mullite. Mullite has a low thermal expansion coefficient, excellent high-temperature stability, and its thermal expansion characteristics are similar to those of the graphite mold. Therefore, it can reduce the thermal stress difference between the ceramic sealing layer and the graphite mold during heating and cooling, thereby effectively mitigating the risk of interface cracking and coating peeling caused by thermal cycling. At the same time, mullite has high strength and ablation resistance, and can synergistically improve the density and high-temperature structural strength of the ceramic sealing layer with Al2O3. While maintaining good oxygen barrier properties, it can also improve the thermal shock resistance and long-term service reliability of the ceramic composite coating.

[0025] Traditional composite coatings for graphite molds are mainly formed by high-temperature sintering of ceramic powder. However, it is difficult to form a continuous and dense glass-ceramic phase network inside the composite coating by relying solely on ceramic powder. Furthermore, the high sintering temperature increases the risk of oxidation of the graphite mold. Therefore, in order to ensure that the ceramic sealing layer described in this invention has a high density, in addition to using ceramic powder as the raw material for the ceramic sealing layer, this invention uses borosilicate glass precursor as the matrix material for the ceramic sealing layer. Borosilicate glass precursors can serve as the basic phase matrix for ceramic sealing layers. During the sintering process of ceramic sealing layers, a continuous and uniform glass-ceramic phase can be formed. This glass-ceramic phase has good fluidity and filling properties, which can fully fill the pores on the surface of graphite materials and stably bond with graphite materials. Furthermore, borosilicate glass precursors can lower the sintering temperature of ceramic sealing layers, promote rapid densification of ceramic sealing layers at lower temperatures, and reduce the generation of pores and microcracks. The resulting ceramic sealing layer structure is continuous and dense, without through-holes. It can effectively inhibit the diffusion of oxygen into the graphite mold and improve the interfacial bonding strength and thermal shock resistance of the coating. This avoids the failure problems such as cracking and peeling of ceramic composite coatings under high-temperature thermal cycling conditions, ensuring that the ceramic composite coating can play a long-term and stable role in oxygen barrier protection.

[0026] In ceramic sealing layers, the proportion of borosilicate glass precursor affects the density and high-temperature hardness of the sealing layer. When the proportion of borosilicate glass precursor in the ceramic sealing layer is too high, the glass phase softens and crystallizes during sintering, leading to a decrease in the high-temperature hardness and creep resistance of the ceramic sealing layer. This can cause cracking in the ceramic composite coating during long-term service. Conversely, when the proportion of borosilicate glass precursor in the ceramic sealing layer is too low, the amount of glass phase formed during sintering is insufficient to fully fill pores and interface gaps. This directly results in a decrease in the density of the ceramic sealing layer and a weaker interfacial bond between the ceramic sealing layer and the graphite matrix. Under high-temperature thermal cycling, this can easily lead to microcracks, cracking, or even peeling. Furthermore, increasing the sintering temperature to ensure densification further increases the oxidation risk of the graphite mold. In order to achieve high density of the ceramic sealing layer, improve the structural strength of the ceramic sealing layer and reduce the risk of graphite mold oxidation during the sintering process of the ceramic sealing layer, in a preferred embodiment, the mass ratio of the borosilicate glass precursor, the first ceramic powder and the second ceramic powder is (6.5-7):(2-2.5):1.

[0027] When the first ceramic powder is added at the above mass ratio, it can stabilize the ZrO2 crystal structure at the grain boundaries, inhibit abnormal grain growth, and weaken the phase transformation volume effect. This can improve the high-temperature structural strength and thermal shock resistance of the ceramic sealing layer, and prevent microcracks from appearing in the ceramic sealing layer under thermal cycling. When the second ceramic powder is added at the above mass ratio, it can further improve the density and high-temperature resistance of the ceramic sealing layer, and make the thermal expansion coefficient of the ceramic sealing layer highly matched with that of the graphite mold. This can reduce interfacial stress and prevent cracking and peeling of the ceramic composite coating.

[0028] Because borosilicate glass in frit form has large particles that are difficult to fully fill the micropores on the graphite surface and the gaps between the ceramic powder, and because the frit requires higher temperatures to soften and flow, it not only forces an increase in sintering temperature and significantly increases the risk of graphite oxidation, but also greatly increases the probability of cracking and peeling of the ceramic sealing layer. Therefore, in a preferred embodiment, the borosilicate glass precursor is preferably a borosilicate glass precursor sol. The borosilicate glass precursor sol exists in a liquid phase with controllable viscosity and excellent wettability, which can fully penetrate into the nano- and micro-sized pores on the graphite surface, thereby achieving uniform coating and filling throughout the entire area. Moreover, it can form a continuous and dense glass-ceramic phase structure at a lower temperature without significantly increasing the sintering temperature. This reduces the risk of oxidation of the graphite mold during sintering, and the controllable particle size of the sol can avoid stress concentration and poor interfacial bonding caused by coarse particles mixed in the coating, thus fundamentally eliminating the risk of coating cracking and peeling.

[0029] In the borosilicate glass precursor sol, the proportion of SiO2 directly affects the high-temperature viscosity, softening point, and sintering characteristics of the glass phase. If the SiO2 proportion in the sol is too high, the viscosity of the glass phase increases and the softening point rises at high temperatures. This requires increasing the sintering temperature of the ceramic sealing layer to achieve densification, which not only increases the oxidation risk of the graphite mold but also enhances the brittleness of the glass phase, making the ceramic composite coating prone to cracking. Conversely, if the SiO2 proportion in the sol is too low and the B2O3 proportion is too high, the glass phase is prone to excessive softening and creep at high temperatures. Furthermore, the number of cross-linking points in the sol system decreases, resulting in incomplete gelation. This leads to uneven shrinkage during the solidification of the ceramic sealing layer, making it highly susceptible to microcracks and internal pores, thereby reducing the density of the sealing layer and limiting its oxygen barrier capacity. Therefore, to avoid the above problems, the preferred molar ratio of SiO2 to B2O3 in the borosilicate glass precursor sol is (3.5–4):(1–1.5).

[0030] To reduce the risk of adhesion between molten glass and the graphite mold surface and improve demolding stability, in a preferred embodiment, the isolation layer is a BN isolation layer with a contact angle ≥100° and a friction coefficient ≤0.2. The BN isolation layer has extremely low surface energy and excellent self-lubricating properties, which can form a continuous and uniform inert isolation interface on the outside of the ceramic sealing layer. This prevents the molten optical glass from adhering to the graphite mold surface during the molding process at 400-900°C, significantly reducing demolding resistance and avoiding defects such as glass components sticking to the mold, missing corners, and surface scratches.

[0031] Meanwhile, the BN isolation layer can work synergistically with the inner ceramic sealing layer to prevent oxygen from diffusing into the graphite matrix, thereby improving the oxidation resistance life of the graphite mold. Furthermore, the low surface energy of the BN isolation layer enables the optical glass to achieve a smoother surface after molding, with a surface roughness Ra ≤ 0.1μm, which meets the high-precision molding requirements of optical components.

[0032] The second aspect of this invention provides an optical glass forming mold. By setting a ceramic composite coating on the surface of a graphite mold, the optical glass forming mold can achieve an oxidation weight loss rate of ≤0.5% in an air atmosphere at 400-900°C, which is much lower than that of a graphite mold without a ceramic composite coating. Furthermore, the optical glass forming mold with the ceramic composite coating can be used continuously for optical glass forming more than 15,000 times without oxidation defects such as dents appearing on its surface, ensuring that the formed optical glass can meet the high-precision forming requirements of optical components.

[0033] A third aspect of the present invention provides a method for preparing an optical glass forming mold, which is used to prepare the optical glass forming mold described above, comprising the following steps: S01. The pretreated graphite mold is immersed in the ceramic sealing layer slurry. After the immersion coating is completed, it is dried under a protective atmosphere and then sintered and densified to form a ceramic sealing layer on the surface of the graphite mold. S02. Immerse the graphite mold with the ceramic sealing layer into the isolation layer slurry. After the immersion coating is completed, dry it under a protective atmosphere and then cure it to form an isolation layer on the surface of the ceramic sealing layer. S03. The graphite mold with the ceramic composite coating is annealed under a protective atmosphere. After the annealing is completed, the optical glass forming mold is obtained.

[0034] In the preparation method of the optical glass forming mold provided by the present invention, by first dip-coating to prepare a ceramic sealing layer and sintering to densify it, then dip-coating to prepare an isolation layer and curing it, and finally annealing the whole, the ceramic sealing layer can fully fill the pores on the graphite surface and form a high-density oxygen barrier. At the same time, the isolation layer is uniformly attached to the surface of the ceramic sealing layer and forms a stable, low surface energy, non-stick structure. Combined with the drying, sintering, curing and annealing treatment under a protective atmosphere throughout the process, it can not only avoid the oxidation of the graphite mold and the ceramic composite coating at high temperature, but also release the internal thermal stress of the ceramic composite coating and improve the interlayer bonding strength, so that the ceramic composite coating and the graphite matrix are firmly bonded, without cracking or peeling, and finally prepare an optical glass forming mold with excellent oxidation resistance, non-sticking and structural stability under high temperature conditions.

[0035] As an example, in the preparation method of the optical glass forming mold provided by this invention, the protective atmosphere can be a nitrogen protective atmosphere or an argon protective atmosphere. Besides dip coating, ceramic sealing layer slurry and isolation layer slurry can also be sprayed. To improve the machinability of the optical glass forming mold, isostatic graphite with a purity ≥99.5% and a density of 1.8–2.0 g / cm³ can be selected as the mold substrate. Graphite materials with these parameters possess excellent machinability, high-temperature structural strength, and no adhesion to molten optical glass, thus meeting the basic requirements for the mold substrate.

[0036] To enhance the physical bonding and interfacial reliability between the ceramic sealing layer and the graphite surface, and to reduce the risk of ceramic composite coating detachment under thermal cycling conditions, after the graphite mold is formed, the cavity of the graphite mold can be roughened by sandblasting with 120-mesh Al2O3 sand. The sandblasting pressure is 0.6 MPa, and the sandblasting time is 60 seconds. This creates a uniform and moderately rough interface on the surface of the graphite mold cavity, effectively increasing the contact area between the ceramic sealing layer and the graphite mold, and improving the anchoring bond between them. After sandblasting, the treated graphite mold is ultrasonically cleaned with solvents such as acetone and anhydrous ethanol to remove contaminants from the mold surface and prevent them from affecting the adhesion of the ceramic sealing layer. After cleaning, the pre-treated graphite mold is placed in an oven to dry for 60 minutes at 120°C.

[0037] As an example, before preparing the ceramic sealing layer slurry, a borosilicate glass precursor can be prepared using the following method: H3BO3 is added to a mixture of anhydrous ethanol and deionized water and stirred at 25°C for 30 min; then TEOS (tetraethyl orthosilicate) is added dropwise, and stirring continues for 60 min after the addition is complete; finally, the mixture is stirred and aged at 25°C for 12 h to obtain the borosilicate glass precursor sol. After the sol is prepared, alumina and zirconium oxide are added to the borosilicate glass precursor sol to obtain the ceramic sealing layer slurry.

[0038] To ensure a continuous, uniform, and dense ceramic sealing layer forms on the surface of the graphite mold, effectively sealing the pores on the graphite surface and thus creating a highly efficient oxygen penetration barrier, the immersion time in the pretreated graphite mold into the ceramic sealing layer slurry is controlled to 3 minutes. After immersion, the graphite mold is removed from the slurry at a lifting speed of 5 mm / s, allowing the slurry to penetrate the surface pores and form a uniform coating on the graphite mold surface. Subsequently, the coating is dried at 80℃ for 30 minutes. After drying, the coating is sintered and densified under a nitrogen protective atmosphere (nitrogen flow rate 2 L / min). The heating rate is 5℃ / min, reaching 1200℃, and then held for 1 hour, causing the ceramic sealing layer to densify and form a stable bond with the graphite mold surface.

[0039] The thickness of the ceramic sealing layer affects its ability to suppress oxygen diffusion. Specifically, if the ceramic sealing layer is too thin, it cannot completely seal the graphite pores, resulting in insufficient oxygen protection. Conversely, if the thickness is too thick, internal stress is easily generated within the ceramic sealing layer, which can lead to cracking and peeling of the ceramic composite coating, thus hindering the improvement of the graphite mold's oxidation resistance. Therefore, to mitigate the impact of the ceramic sealing layer thickness on its ability to suppress oxygen diffusion, in a preferred embodiment, the thickness of the ceramic sealing layer is 5–80 μm. It is understood that to ensure the desired thickness of the ceramic sealing layer is achieved, the dipping, drying, and sintering densification processes can be repeated multiple times.

[0040] To ensure the isolation layer is continuously and uniformly distributed on the ceramic sealing layer and to enable it to stably perform its low surface energy anti-adhesion function, a graphite mold with the ceramic sealing layer is immersed in the isolation layer slurry for 2 minutes. After immersion, the graphite mold is removed from the slurry at a pulling speed of 5 mm / s, thus forming a continuous and uniform coating on the surface of the ceramic sealing layer. The coating is then dried at 80°C for 20 minutes. After drying, the coating is cured under a nitrogen protective atmosphere (nitrogen flow rate 2 L / min) to form the isolation layer. The curing temperature regime is as follows: heating rate 5°C / min, heating to 900°C and holding at that temperature for 1 hour.

[0041] The thickness of the isolation layer affects its ability to prevent glass adhesion. If the isolation layer is too thin, its anti-adhesion and synergistic oxygen barrier effects are insufficient; if it is too thick, it increases interfacial stress, causing damage and peeling of the ceramic composite coating during demolding. Therefore, to mitigate the impact of isolation layer thickness on its anti-adhesion ability, in a preferred embodiment, the isolation layer thickness is 5–50 μm. Similarly, to ensure the desired isolation layer thickness, the dipping, drying, and curing processes can be repeated multiple times.

[0042] For example, the BN used to form the BN isolation layer can be h-BN (hexagonal boron nitride) or c-BN (cubic boron nitride). The raw materials for preparing the isolation layer slurry may include, by mass percentage: 45-50% BN powder (D50 = 1-3 μm, purity ≥ 99%), 40-45% deionized water, 0.8-1.2% silane coupling agent KH550 / KH560, 0.6-1.0% polycarboxylate ammonium salt dispersant, 3-5% aqueous silica sol (silicon content 30%), 2-3% aqueous pure acrylic / silicone acrylic emulsion (aqueous binder), 0.1-0.2% hydroxyethyl cellulose (HEC), and 0.1-0.2% organosilicon defoamer.

[0043] When the BN solid content in the isolation layer slurry is too low, the isolation layer is prone to film discontinuity and defects, and the surface energy of the isolation layer increases, significantly reducing the anti-sticking and isolation effects. Conversely, when the BN solid content in the isolation layer slurry is too high, the residual stress inside the isolation layer increases, the bonding force with the ceramic sealing layer decreases, and this leads to demolding failure and cracking and peeling of the ceramic composite coating. Therefore, in the preparation method provided by this invention, the BN solid content in the isolation layer slurry is preferably 25-27%. This solid content ensures continuous and dense film formation of the isolation layer, low interfacial surface energy, and stable bonding force between the isolation layer and the ceramic sealing layer, balancing anti-sticking and demolding effects with high-temperature service reliability. Experiments show that the isolation layer provided by this invention does not exhibit oxidation or weight loss after nitrogen heat treatment at 900℃ for 1 hour.

[0044] During annealing, excessively rapid heating can lead to uneven heating within the ceramic composite coating, causing a rapid accumulation of thermal stress and potentially resulting in cracking, warping, or even peeling of the isolation layer and ceramic sealing layer. Conversely, excessively slow heating can prolong the production cycle, reduce preparation efficiency, and increase the risk of slight oxidation of the graphite matrix under prolonged high-temperature conditions. In a preferred embodiment, the annealing temperature is 795–845°C, with a nitrogen flow rate of 2 L / min. During annealing, the temperature is increased to 795–845°C at a rate of 3°C / min, and then held for 2 hours. This method effectively releases the internal stress generated during coating and sintering of the ceramic composite coating, optimizes the interlayer bonding, and makes the ceramic composite coating structure denser and more stable. Simultaneously, it balances production efficiency with mold oxidation resistance and safety, significantly improving the graphite mold's resistance to cracking and peeling under high-temperature thermal cycling and extending its long-term service life.

[0045] The following examples and comparative examples further illustrate the technical solution of the present invention.

[0046] Example 1 This embodiment provides a ceramic composite coating, including a ceramic sealing layer and an isolation layer; the isolation layer is located on the outside of the ceramic sealing layer.

[0047] The raw materials for preparing the ceramic sealing layer include borosilicate glass precursor, Al2O3 powder, and ZrO2 powder; the mass ratio of borosilicate glass precursor, Al2O3 powder, and ZrO2 powder is 7:2:1.

[0048] The borosilicate glass precursor is a borosilicate glass precursor sol, in which the molar ratio of SiO2 to B2O3 is 4:1. The insulating layer is an h-BN insulating layer.

[0049] This embodiment also provides an optical glass forming mold, including a graphite mold and a ceramic composite coating provided in this embodiment; the ceramic composite coating is located on the surface of the graphite mold.

[0050] This embodiment also provides a method for preparing an optical glass forming mold, including the following steps: S01. Immerse the pretreated graphite mold in the ceramic sealing layer slurry for 3 minutes. After immersion, remove the graphite mold from the ceramic sealing layer slurry at a lifting speed of 5 mm / s. Then, dry it in a nitrogen atmosphere (nitrogen flow rate 2 L / min) at 80℃ for 30 minutes. Afterward, perform sintering densification treatment (heating rate 5℃ / min, heating to 1200℃ and holding for 1 h) to form a ceramic sealing layer on the surface of the graphite mold. Repeat the immersion, drying, and sintering densification process multiple times to achieve a ceramic sealing layer thickness of 40 ± 0.5 μm. S02. Immerse the graphite mold with the ceramic sealing layer into the isolation layer slurry (h-BN solid content is 25%) for 2 minutes. After immersion, remove the graphite mold from the isolation layer slurry at a pulling speed of 5 mm / s and dry it in a nitrogen atmosphere (nitrogen flow rate 2 L / min) at 80℃ for 20 minutes. Then, perform curing treatment (the curing temperature regime is as follows: heating rate 5℃ / min, heating to 900℃ and holding for 1 hour) to form an isolation layer on the surface of the ceramic sealing layer. Repeat the immersion, drying, and curing process multiple times to make the thickness of the formed isolation layer 10 ± 0.5 μm. S03. The graphite mold with the ceramic composite coating is annealed under a protective atmosphere. After the annealing is completed, it is cooled to room temperature in the furnace to obtain the optical glass forming mold. The annealing temperature is 800℃, the nitrogen flow rate is 2L / min, and the temperature is increased to 800℃ at a rate of 3℃ / min during the annealing process, and then held at that temperature for 2 hours.

[0051] Example 2 This embodiment provides a ceramic composite coating, including a ceramic sealing layer and an isolation layer; the isolation layer is located on the outside of the ceramic sealing layer.

[0052] The ceramic sealing layer is prepared using raw materials including a borosilicate glass precursor, Al2O3 powder, and ZrO2 powder; the mass ratio of the borosilicate glass precursor, Al2O3 powder, and ZrO2 powder is 6.8:2.2:1. The borosilicate glass precursor is a borosilicate glass precursor sol, in which the molar ratio of SiO2 to B2O3 is 3.8:1.2. The isolation layer is an h-BN isolation layer.

[0053] This embodiment also provides an optical glass forming mold, including a graphite mold and a ceramic composite coating provided in this embodiment; the ceramic composite coating is located on the surface of the graphite mold.

[0054] This embodiment also provides a method for preparing an optical glass forming mold, which is the same as the method provided in Embodiment 1.

[0055] Example 3 This embodiment provides a ceramic composite coating, including a ceramic sealing layer and an isolation layer; the isolation layer is located on the outside of the ceramic sealing layer.

[0056] The ceramic sealing layer is prepared using raw materials including a borosilicate glass precursor, Al2O3 powder, and ZrO2 powder; the mass ratio of the borosilicate glass precursor, Al2O3 powder, and ZrO2 powder is 6.5:2.5:1. The borosilicate glass precursor is a borosilicate glass precursor sol, in which the molar ratio of SiO2 to B2O3 is 3.5:1.5. The isolation layer is an h-BN isolation layer.

[0057] This embodiment also provides an optical glass forming mold, including a graphite mold and a ceramic composite coating provided in this embodiment; the ceramic composite coating is located on the surface of the graphite mold.

[0058] This embodiment also provides a method for preparing an optical glass forming mold, which is the same as the method provided in Embodiment 1.

[0059] Comparative Example 1 This comparative example provides a ceramic composite coating, including a ceramic sealing layer and an isolation layer; the isolation layer is located on the outside of the ceramic sealing layer.

[0060] The ceramic sealing layer is prepared using raw materials including a borosilicate glass precursor, Al2O3 powder, and ZrO2 powder; the mass ratio of the borosilicate glass precursor, Al2O3 powder, and ZrO2 powder is 3:4:3. The borosilicate glass precursor is a borosilicate glass precursor sol, in which the molar ratio of SiO2 to B2O3 is 4:1. The isolation layer is an h-BN isolation layer.

[0061] This comparative example also provides an optical glass forming mold, including a graphite mold and a ceramic composite coating provided in this embodiment; the ceramic composite coating is located on the surface of the graphite mold.

[0062] This comparative example also provides a method for preparing an optical glass forming mold, which is the same as the method provided in Example 1.

[0063] Comparative Example 2 This comparative example provides a ceramic composite coating, including a ceramic sealing layer and an isolation layer; the isolation layer is located on the outside of the ceramic sealing layer.

[0064] The ceramic sealing layer is prepared using raw materials including a borosilicate glass precursor, Al2O3 powder, and ZrO2 powder; the mass ratio of the borosilicate glass precursor, Al2O3 powder, and ZrO2 powder is 8:1:1. The borosilicate glass precursor is a borosilicate glass precursor sol, in which the molar ratio of SiO2 to B2O3 is 4:1. The isolation layer is an h-BN isolation layer.

[0065] This comparative example also provides an optical glass forming mold, including a graphite mold and a ceramic composite coating provided in this embodiment; the ceramic composite coating is located on the surface of the graphite mold.

[0066] This comparative example also provides a method for preparing an optical glass forming mold, which is the same as the method provided in Example 1.

[0067] Comparative Example 3 This comparative example provides a ceramic composite coating, including a ceramic sealing layer and an isolation layer; the isolation layer is located on the outside of the ceramic sealing layer.

[0068] The ceramic sealing layer is prepared using borosilicate glass precursor and ZrO2 powder in a mass ratio of 7:3. The borosilicate glass precursor is a borosilicate glass precursor sol, in which the molar ratio of SiO2 to B2O3 is 4:1. The isolation layer is an h-BN isolation layer.

[0069] This comparative example also provides an optical glass forming mold, including a graphite mold and a ceramic composite coating provided in this embodiment; the ceramic composite coating is located on the surface of the graphite mold.

[0070] This comparative example also provides a method for preparing an optical glass forming mold, which is the same as the method provided in Example 1.

[0071] Comparative Example 4 This comparative example provides a ceramic composite coating, including a ceramic sealing layer and an isolation layer; the isolation layer is located on the outside of the ceramic sealing layer.

[0072] The raw materials for preparing the ceramic sealing layer include borosilicate glass precursor, Al2O3 powder, and ZrO2 powder; the mass ratio of borosilicate glass precursor, Al2O3 powder, and ZrO2 powder is 7:2:1.

[0073] The borosilicate glass precursor is a borosilicate glass precursor sol, in which the molar ratio of SiO2 to B2O3 is 4.5:0.5. The insulating layer is an h-BN insulating layer.

[0074] This comparative example also provides an optical glass forming mold, including a graphite mold and a ceramic composite coating provided in this embodiment; the ceramic composite coating is located on the surface of the graphite mold.

[0075] This comparative example also provides a method for preparing an optical glass forming mold, which is the same as the method provided in Example 1.

[0076] Comparative Example 5 This comparative example provides a ceramic composite coating, including a ceramic sealing layer and an isolation layer; the isolation layer is located on the outside of the ceramic sealing layer.

[0077] The raw materials for preparing the ceramic sealing layer include borosilicate glass precursor, Al2O3 powder, and ZrO2 powder; the mass ratio of borosilicate glass precursor, Al2O3 powder, and ZrO2 powder is 7:2:1.

[0078] The borosilicate glass precursor is a borosilicate glass precursor sol, in which the molar ratio of SiO2 to B2O3 is 3:2. The isolation layer is an h-BN isolation layer.

[0079] This comparative example also provides an optical glass forming mold, including a graphite mold and a ceramic composite coating provided in this embodiment; the ceramic composite coating is located on the surface of the graphite mold.

[0080] This comparative example also provides a method for preparing an optical glass forming mold, which is the same as the method provided in Example 1.

[0081] Comparative Example 6 This comparative example provides a ceramic composite coating, including a ceramic sealing layer and an isolation layer; the isolation layer is located on the outside of the ceramic sealing layer.

[0082] The raw materials for preparing the ceramic sealing layer include borosilicate glass precursor, Al2O3 powder, and ZrO2 powder; the mass ratio of borosilicate glass precursor, Al2O3 powder, and ZrO2 powder is 7:2:1.

[0083] The borosilicate glass precursor is a borosilicate glass precursor sol, in which the molar ratio of SiO2 to B2O3 is 4:1. The insulating layer is an h-BN insulating layer.

[0084] This comparative example also provides an optical glass forming mold, including a graphite mold and a ceramic composite coating provided in this embodiment; the ceramic composite coating is located on the surface of the graphite mold.

[0085] This comparative example also provides a method for preparing an optical glass forming mold. The only difference between this method and the method provided in Example 1 is that the solid content of h-BN in the isolation layer slurry used in step S02 is 15%.

[0086] The density and coefficient of thermal expansion of the ceramic sealing layer in the above embodiments and comparative examples were tested respectively, and the oxidation weight loss rate of the optical glass forming molds provided in the above embodiments and comparative examples was tested.

[0087] The density of the ceramic sealing layer was determined using the water displacement weighing method (densitometer method); the coefficient of thermal expansion of the ceramic sealing layer was tested using a pusher-type thermal expansion meter. The oxidation weight loss rate was calculated using the following formula: Oxidation weight loss rate = (m0...) m1) / m0×100%. Where m0 is the initial mass of the mold after preparation, and m1 is the mass of the mold after being kept at 400~900℃ in air atmosphere for 2 h.

[0088] The test results are shown in the table below.

[0089]

[0090] As shown in the table above, the ceramic sealing layer provided in Examples 1-3 has a density ≥92% and a coefficient of thermal expansion of 4.5~5.2×10⁻⁶. -6 / K not only outperforms traditional yttrium-stabilized zirconia layers, improving the oxidation resistance of graphite molds (oxidation weight loss ≤0.40%), but also has a thermal expansion coefficient that is close to that of molds using isostatic graphite as the substrate. This ensures the interfacial bonding strength and structural stability between the ceramic composite coating and the graphite mold, significantly extending the service life of the graphite mold.

[0091] Furthermore, comparing the test results of the ceramic sealing layer in Comparative Example 1 and the ceramic sealing layer in Example 1, it was found that the density of the ceramic sealing layer in Comparative Example 1 was lower. This was because the amount of borosilicate precursor in the raw materials for preparing the ceramic sealing layer was insufficient, resulting in an insufficient amount of glass phase formed during the sintering process. This glass phase could not fully fill the pores and interface gaps, leading to a decrease in the density of the ceramic sealing layer and an increase in its coefficient of thermal expansion. The test results of the oxidation weight loss rate in Comparative Example 1 also show that when the density of the ceramic sealing layer decreases, the graphite mold is prone to oxidation.

[0092] Furthermore, comparing the test results of the ceramic sealing layer of Comparative Example 2 and the ceramic sealing layer of Example 1, it was found that the density of the ceramic sealing layer of Comparative Example 2 was lower than that of the ceramic sealing layer of Example 1. This is because the amount of borosilicate precursor in the raw materials for preparing the ceramic sealing layer was too high. During the sintering process of the ceramic sealing layer, the glass phase softened and crystallized, which led to a decrease in the high-temperature hardness of the ceramic sealing layer. Microcracks were easily generated inside the coating, resulting in a decrease in the density of the ceramic sealing layer.

[0093] Furthermore, comparing the test results of the ceramic sealing layer of Comparative Example 3 and the ceramic sealing layer of Example 1, it was found that the density of the ceramic sealing layer of Comparative Example 3 was lower than that of the ceramic sealing layer of Example 1. At the same time, the coefficient of thermal expansion of the ceramic sealing layer increased. This is because the ceramic sealing layer of Comparative Example 3 lacks the crystal stabilizing and grain-inhibiting effect of Al2O3 on ZrO2, which increases the internal stress of the ceramic sealing layer and the coefficient of thermal expansion.

[0094] Furthermore, comparing the test results of the ceramic sealing layer in Comparative Example 4 and the ceramic sealing layer in Example 1, it was found that the density of the ceramic sealing layer in Comparative Example 4 was lower than that of the ceramic sealing layer in Example 1. This is because the SiO2 content in the borosilicate glass precursor sol used in Comparative Example 4 was too high, and the original sintering process could not meet the densification requirements of the ceramic sealing layer.

[0095] Furthermore, comparing the test results of the ceramic sealing layer of Comparative Example 5 and the ceramic sealing layer of Example 1, it was found that the density of the ceramic sealing layer of Comparative Example 5 was lower than that of the ceramic sealing layer of Example 1. This is because the proportion of B2O3 in the borosilicate glass precursor sol used in Comparative Example 5 was relatively high, the number of cross-linking points in the sol system was reduced, and the gelation was incomplete. This resulted in uneven shrinkage during the curing of the ceramic sealing layer, which easily generated microcracks and internal pores, thus leading to a decrease in the density of the sealing layer and limited oxygen barrier capacity.

[0096] Furthermore, comparing the test results of the ceramic sealing layer in Comparative Example 6 and the ceramic sealing layer in Example 1, it was found that when the BN solid content in the slurry used to form the isolation layer is low, it will affect the density of the ceramic sealing layer. This is because a low BN solid content will lead to discontinuous film formation of the isolation layer, the presence of pores and defects, and the inability to form a complete and dense covering layer on the surface of the ceramic sealing layer. This results in uneven heat distribution and weakened stress release effect during subsequent annealing, which in turn causes micro-shrinkage, micro-cracks and local porosity on the surface of the ceramic sealing layer, ultimately resulting in a decrease in the overall density of the ceramic sealing layer.

[0097] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. A ceramic composite coating, characterized in that, It includes a ceramic sealing layer and an insulating layer; the density of the ceramic sealing layer is ≥92%, and the coefficient of thermal expansion is 4.5~6.5×10. -6 / K.

2. The ceramic composite coating according to claim 1, characterized in that, The raw materials for preparing the ceramic sealing layer include a borosilicate glass precursor, a first ceramic powder, and a second ceramic powder; the first ceramic powder is Al2O3 powder; and the second ceramic powder is ZrO2 powder or mullite.

3. The ceramic composite coating according to claim 2, characterized in that, The mass ratio of the borosilicate glass precursor, the first ceramic powder, and the second ceramic powder is (6.5-7):(2-2.5):

1.

4. The ceramic composite coating according to claim 2, characterized in that, The borosilicate glass precursor is a borosilicate glass precursor sol, in which the molar ratio of SiO2 to B2O3 is (3.5-4):(1-1.5).

5. The ceramic composite coating according to claim 2, characterized in that, The isolation layer is a BN isolation layer; the contact angle of the BN isolation layer is ≥100° and the coefficient of friction is ≤0.

2.

6. An optical glass forming mold, characterized in that, The invention includes a ceramic composite coating disposed on the surface of a graphite mold; the ceramic composite coating is the ceramic composite coating described in any one of claims 1-5.

7. A method for preparing an optical glass forming mold, characterized in that, The process for preparing the optical glass forming mold according to claim 6 includes the following steps: S01. The pretreated graphite mold is coated with ceramic sealing layer slurry. After coating, it is dried under a protective atmosphere and then sintered and densified to form a ceramic sealing layer on the surface of the graphite mold. S02. Apply an isolation layer slurry to the graphite mold with the ceramic sealing layer. After the coating is completed, dry it under a protective atmosphere and then cure it to form an isolation layer on the surface of the ceramic sealing layer. S03. The graphite mold with the ceramic composite coating is annealed under a protective atmosphere. After the annealing is completed, the optical glass forming mold is obtained.

8. The method for preparing an optical glass forming mold according to claim 7, characterized in that, In step S02, the solid content of the isolation layer slurry is 25-27%.

9. The method for preparing an optical glass forming mold according to claim 7, characterized in that, In step S03, the annealing temperature is 795–845°C. During the annealing process, the temperature is increased to 795–845°C at a heating rate of 3°C / min, and then held at that temperature for 2 hours.

10. The method for preparing an optical glass forming mold according to claim 7, characterized in that, In step S01, the thickness of the ceramic sealing layer is 5–80 μm, and the thickness of the isolation layer is 5–50 μm.

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