High elastic modulus ultra-low expansion glass-ceramics and method of making same

Abstract

The application belongs to the technical field of glass-ceramics material, and particularly relates to high-elastic-modulus ultra-low-expansion glass-ceramics and a preparation method thereof. The basic component range of the high-elastic-modulus ultra-low-expansion glass-ceramics comprises Li2O: 1-5%, Al2O3: 20-30%, SiO2: 50-70%, and MgO: 3-6% in terms of mass percentage. The above-mentioned formula is used for batching, mixing, melting, forming, annealing, and crystallization heat treatment. In the forming process, the leakage pipe is heated by using a three-stage precise temperature control mode. In the crystallization heat treatment, a two-step crystallization process is adopted. Firstly, the temperature is kept at 500-600 DEG C for 10-20 hours, which is a nucleation stage to generate predetermined crystal nuclei. Then, the temperature is increased to 700-800 DEG C, and the temperature is kept for 10-20 hours to make new crystal phases precipitate on the nucleating agent. The glass-ceramics prepared by the application has high elastic modulus and low thermal expansion coefficient. In addition, three-stage precise temperature control can be realized in the leakage forming, and controlled crystallization can be realized in the crystallization heat treatment.

Description

Technical Field

[0001] This invention belongs to the field of microcrystalline glass materials technology. Specifically, this invention relates to a high elastic modulus microcrystalline glass and its preparation method. In particular, it relates to a microcrystalline glass with high elastic modulus and ultra-low coefficient of thermal expansion for optical fiber reinforcement. Background Technology

[0002] The ultra-low expansion microcrystalline glass of the L2O-Al2O3-SiO2 system has a thermal expansion coefficient that is only a few thousandths that of metals and a few hundredths that of ceramics or glass. It truly achieves zero expansion when heated and zero contraction when cooled, maintaining dimensional stability even in extremely harsh environments, making it the material with the best dimensional stability currently available. Ultra-low expansion microcrystalline glass with a high elastic modulus can be used to reinforce optical fibers. Specifically, before coating the optical fiber with an organic coating, an outer cladding layer with better flexibility than quartz glass is developed on the surface of the bare fiber to prevent the generation and propagation of fractures, thereby increasing the tensile strength of the quartz fiber. In addition, it can be used in sensing, spectral analysis, process control and laser transmission, laser medicine, measurement technology, criminal investigation, information transmission, and lighting. Its applications are being promoted in various fields such as electronics, medicine, bioengineering, materials processing, sensing technology, and national defense.

[0003] The elastic modulus reflects a material's ability to resist elastic deformation caused by external forces. A higher elastic modulus value indicates a greater stress required for the glass-ceramic to undergo elastic deformation, thus providing greater protection and reinforcement for silica optical fibers. Currently, the glass phase content in existing ultra-low expansion glass-ceramics is approximately 20% or higher, but the elastic modulus of the glass phase is relatively low, resulting in an elastic modulus of only about 90 GPa for ultra-low expansion glass-ceramics. To enable the glass-ceramic to reinforce silica optical fibers, its elastic modulus typically needs to reach above 120 GPa. Currently, the only way to significantly increase the elastic modulus is by reducing the volume fraction of the glass phase in the glass-ceramic material. However, the coefficient of thermal expansion of glass-ceramics is related to the volume fractions of both the crystalline and glass phases. Excessively reducing the volume fraction of the glass phase can cause an increase in the absolute value of the coefficient of thermal expansion, even by orders of magnitude. To ensure that reducing the glass phase content does not affect the coefficient of thermal expansion of the glass-ceramic, the glass phase content can be controlled by optimizing the glass-ceramic material formulation and achieving precise and controllable crystallization, allowing the glass-ceramic to simultaneously possess ultra-low expansion and high elastic modulus properties.

[0004] Currently, the preparation process of glass-ceramics includes steps such as batching, mixing, melting, forming, annealing, and crystallization. Chinese invention patent CN 114477771 B discloses a transparent glass-ceramic with high elastic modulus and high hardness, and its preparation method. Its formula includes SiO2, Al2O3, Y2O3, ZnO, NaO, Li2O, and B2O3, solving the problem of the inability to simultaneously achieve chemical strengthening, elastic modulus, and optical properties in glass-ceramics. However, the main crystalline phase of the resulting glass-ceramic is Y2Zr2O7, with a thermal expansion coefficient between 40 and 60 × 10⁻⁶. -7 / ℃.

[0005] CN200910083102.3 describes an ultra-low expansion microcrystalline glass for laser gyroscopes and its preparation method. The formula includes SiO2, Al2O3, Li2O, NaO, K2O, MgO, ZnO, P2O5, TiO2, ZrO, and Sb2O3 / As2O3, with a crystalline phase content of 70%–85% and a thermal expansion coefficient of 1–5 × 10⁻⁵. -8 / ℃. Its crystalline phase content, coefficient of thermal expansion, and elastic modulus limit its further applications. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a high elastic modulus and ultra-low expansion microcrystalline glass and its preparation method. The microcrystalline glass prepared by this method has a high elastic modulus and a low coefficient of thermal expansion, and can achieve precise three-stage temperature control during the extrusion molding process and controlled crystallization during the crystallization heat treatment.

[0007] The complete technical solution of this invention includes:

[0008] A method for preparing high elastic modulus ultra-low expansion microcrystalline glass includes the following steps:

[0009] (1) Component design: The basic component range of the high elastic modulus ultra-low expansion microcrystalline glass, by mass percentage, includes: Li2O: 1-5%, Al2O3: 20-30%, SiO2: 50-70%, and MgO: 3-6%;

[0010] (2) Microcrystalline glass extrusion molding and crystallization

[0011] The ingredients are prepared, mixed, melted, shaped, annealed, and crystallized according to the formula described in step (1).

[0012] During the molding process, the material leakage tube is heated using a three-stage precise temperature control method;

[0013] In the crystallization heat treatment, a two-step crystallization process is adopted. First, the temperature is kept at 500-600℃ for 10-20 hours, which is the nucleation stage, to generate the predetermined crystal nuclei. Then, the temperature is raised to 700-800℃ and kept at 10-20 hours to allow the new crystal phase to precipitate on the nucleating agent.

[0014] Furthermore, the composition of the high elastic modulus ultra-low expansion microcrystalline glass also includes: NaO and K2O: 0.5-2%, ZnO: 0-2%, P2O5: 4-7%, TiO2: 1-3%, ZrO: 1-3%, and B2O3: 1-4%.

[0015] Furthermore, the raw materials of the microcrystalline glass are composed of a certain proportion of crushed microcrystalline glass waste and new material, with a mass percentage of microcrystalline glass waste: new material of (1:7) to (2:8).

[0016] Furthermore, in the basic glass raw materials, Li2O is introduced in the form of carbonate, while NaO and K2O are introduced in the form of nitrate.

[0017] Furthermore, the main crystalline phase of the prepared microcrystalline glass is β-quartz solid solution, and it contains a small amount of spinel phase, with a glass phase content of 10-20%.

[0018] Furthermore, the coefficient of thermal expansion of the microcrystalline glass is between 5.7 and 6.5 × 10⁻⁶. -8 / ℃, with an elastic modulus above 120GPa.

[0019] The advantages of this invention over the prior art include:

[0020] 1. The batching material consists of a certain proportion of crushed microcrystalline glass waste and new material. Utilizing microcrystalline waste can not only achieve optimal resource allocation and sustainable development, enabling waste to be reused, saving resources, and being green and environmentally friendly, but also improve the quality of molten glass and avoid the generation of bubbles. In the raw material formula, Li2O is introduced in the form of carbonate, and NaO and K2O are introduced in the form of nitrate, which is conducive to the uniform mixing of raw materials during batching and can effectively remove bubbles from the molten glass during the melting stage.

[0021] 2. A new three-stage precise control technology for the dripping tube enables low-defect forming of ultra-low expansion microcrystalline glass. The biggest difference between dripping and casting is that the molten glass is constantly stirred as it drips from the platinum crucible, effectively preventing the formation of central streaks and significantly improving glass quality and yield. However, ultra-low expansion microcrystalline glass has high viscosity during high-temperature melting, and its viscosity varies greatly with temperature. During forming, even small temperature fluctuations can cause significant changes in the viscosity of the molten glass, potentially leading to defects such as streaks or forming bubbles. The segmented precise temperature control technology for the dripping tube effectively avoids the formation of central streaks and secondary bubbles caused by excessively high temperatures in the upper part of the dripping tube in a one- or two-stage temperature control structure, thus achieving low-defect forming of ultra-low expansion microcrystalline glass.

[0022] 3. Under a given formula, the controlled crystallization process plays a decisive role in the coefficient of thermal expansion and the type and quantity of crystals. A two-step crystallization process is employed: first, the crystals are held at 500–600℃ for 10–20 hours to generate predetermined crystal nuclei; then, the temperature is raised to 700–800℃ and held for another 10–20 hours, allowing new crystalline phases to precipitate on the nucleating agent, and the crystals grow to the desired size and quantity. The one-step method involves holding the crystal at a temperature with a relatively fast nucleation rate and a slower crystal growth rate for a period of time. For the crystallization of this microcrystalline glass, the two-step method, which involves nucleation followed by growth, can produce microcrystalline glass products with finer grains, higher content, and more uniform structure compared to the one-step method. The grain type, grain size, and content are precisely controlled by crystallization temperature and holding time, so that the main crystalline phase is β-quartz solid solution, while containing an appropriate amount of spinel phase. The crystalline phase content is controlled above 80%, and the grain size is controlled within 50nm. At the same time, the crystal and glass are fully interwoven and tightly connected, so that the microcrystalline glass material achieves both high elastic modulus and ultra-low expansion coefficient.

[0023] 4. The main crystalline phase of the glass-ceramic obtained in this invention is β-quartz solid solution, which is completely different in crystalline phase from the glass-ceramic disclosed in CN 114477771 B, belonging to a different glass-ceramic system, and the coefficient of thermal expansion is controlled between 5.7 and 6.5 × 10⁻⁶. -8 The temperature is two orders of magnitude lower than that of patent CN 114477771 B, and it can further achieve controlled crystallization to prepare microcrystalline glass with high elastic modulus and low coefficient of thermal expansion, which is not covered by that patent. Therefore, this invention can obtain microcrystalline glass with high elastic modulus and low coefficient of thermal expansion with β-quartz solid solution as the main crystalline phase, which can more effectively improve the dimensional stability of microcrystalline glass in extremely harsh environments and its ability to resist elastic deformation caused by external forces.

[0024] 5. The crystalline phase content obtained in this invention should be controlled at over 80%, and the coefficient of thermal expansion should be controlled at 5.7–6.5 × 10⁻⁶. -8In addition to the required temperature, it must also possess a high elastic modulus, which is not addressed in CN200910083102.3. Furthermore, the present invention employs a three-stage precise temperature control technology for the extrusion molding of microcrystalline glass, effectively avoiding defects such as central streaks or bubbles in the product, significantly improving the quality and yield of the glass, and achieving low-defect molding of ultra-low expansion microcrystalline glass. By adopting a controlled crystallization method, the difficulties and core processes in the preparation of microcrystalline glass with high elastic modulus and ultra-low expansion coefficient are overcome, controlling the types and contents of internal crystalline phases and glass phases within the required range, thus preparing microcrystalline glass that can be used for applications such as optical fiber reinforcement. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the three-stage precise temperature control method used in the material leakage tube of the present invention.

[0026] Figure 2 This is a diagram showing the grain size of the microcrystalline glass of the present invention.

[0027] Figure 3 The results show the thermal expansion coefficient of the microcrystalline glass of this invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] A high elastic modulus and ultra-low expansion microcrystalline glass and its preparation method, comprising the following steps:

[0030] (1) Component Design

[0031] This high-elasticity, ultra-low-expansion microcrystalline glass comprises a base glass with the following composition by mass percentage: Li₂O: 1–5%, Al₂O₃: 20–30%, SiO₂: 50–70%, and MgO: 3–6%. In addition to these oxides, a certain amount of other oxides are added to adjust properties and lower the crystallization temperature. The composition of these oxides is as follows: NaO and K₂O: 0.5–2%, ZnO: 0–2%, P₂O₅: 4–7%, TiO₂: 1–3%, ZrO: 1–3%, and B₂O₃: 1–4%. The batching consists of a certain proportion of crushed microcrystalline glass waste and virgin material, with a mass percentage ratio of 1:7 to 2:8. Utilizing the microcrystalline waste achieves waste recycling, resource conservation, and environmental protection, while also improving the quality of the molten glass. In the basic glass raw materials, Li2O is introduced in the form of carbonate, while NaO and K2O are introduced in the form of nitrate. This is beneficial for the raw materials to be mixed evenly during batching and can effectively remove air bubbles from the molten glass during the melting stage.

[0032] In the microcrystalline glass prepared by this invention, the amount of each component added has a crucial influence on the final microstructure and properties of the microcrystalline glass. Among the main oxides, a certain proportion of MgO can generate an appropriate amount of spinel phase after crystallization, which improves the elastic modulus of the microcrystalline glass. In addition, MgO can reduce the crystallization tendency and rate, thereby lowering the glass melting and forming temperatures. Furthermore, divalent Mg ions, being network exooxides, have a high electric field strength, which slows down the hardening rate of the glass and improves its forming performance. Among the added components, K₂O and Na₂O act as fluxes, mainly providing free oxygen, increasing the number of free oxygen atoms in the glass network structure, increasing the O / Si ratio in the glass structure, causing bond breakage, and thus lowering the melting temperature. However, because such fluxes increase the coefficient of thermal expansion of the glass, reducing its thermal stability, chemical stability, and mechanical strength, excessive amounts cannot be introduced. ZnO, as a flux, can reduce the high-temperature viscosity of the glass, thereby lowering the melting temperature. Moreover, a certain proportion of ZnO can also reduce the coefficient of thermal expansion of the microcrystalline glass. TiO2, ZrO2, and P2O5 serve as a composite nucleating agent, enabling the formation of micro-nuclei within the glass during the two-step crystallization nucleation stage, thus promoting glass crystallization. The appropriate introduction of B2O3, as a network former, acts as a network supplement, increasing the strength of the microcrystalline glass. Through the above component design and combined with the preparation method of this invention, the main crystalline phase of the prepared microcrystalline glass can be β-quartz solid solution, such as... Figure 2 As shown, the grain size is less than 50 nm. It contains a small amount of spinel phase, with a glass phase content of 10–20%, and a coefficient of thermal expansion of 5.7–6.5 × 10⁻⁶. -8 / ℃, such as Figure 3 As shown, the elastic modulus is above 120 GPa.

[0033] (2) Microcrystalline glass extrusion molding and controlled crystallization

[0034] The steps for preparing ultra-low expansion microcrystalline glass according to the above formula include: ingredient preparation, mixing, melting, forming, annealing, and crystallization heat treatment. Among these, for example... Figure 1 As shown, the discharge tube is heated using a three-stage precise temperature control method. Under a given formula, the controlled crystallization process plays a decisive role in the coefficient of thermal expansion and the type and quantity of crystals. A two-step crystallization process is adopted. First, the temperature is raised to 500-600℃ and held for 10-20 hours. This step is the nucleation stage, which is a prerequisite for generating the predetermined crystal nuclei. Then, the temperature is raised to 700-800℃ and held for 10-20 hours. The new crystalline phase precipitates on the nucleating agent, allowing the crystals to grow to the required crystal size and quantity, thus enabling the microcrystalline glass material to have both high elastic modulus and ultra-low coefficient of thermal expansion.

[0035] Specifically, it includes:

[0036] 1) Ingredients:

[0037] Following the formula in step (1), select the corresponding microcrystalline glass waste and virgin materials for batching, based on the base glass components and other oxide components. Strictly control the proportions of various components during the batching process to ensure that the final glass possesses the desired properties.

[0038] 2) Mixing:

[0039] After the ingredients are prepared, the various raw materials are mixed evenly according to the formula ratio. The purpose is to ensure that the various components are fully mixed and to avoid the formation of uneven structure or components. In this invention, a ball mill or a mixer can be used for mixing.

[0040] 3) Melting:

[0041] After the raw materials are mixed evenly according to the mass percentage, they are poured into a platinum crucible and heated to melt until they are completely melted to form a glass melt, ensuring that all raw materials are completely melted and mixed evenly.

[0042] 4) Molding:

[0043] The molten glass is formed by using a perforated molding method, where the molten glass flows into the molding die through segmented, precisely temperature-controlled perforated pipes.

[0044] In this step, temperature control at each stage has a crucial impact on the glass forming quality. On one hand, near the outlet of the sputtering tube, the melt temperature needs to be stabilized at the ideal pouring temperature to ensure stable forming and solidification to obtain the desired crystalline and glassy phases and achieve the designed properties. On the other hand, the temperature above the sputtering tube needs to be controlled. This ensures a certain temperature to maintain suitable fluidity for stable pouring, while also preventing excessively high temperatures at the top of the sputtering tube from generating secondary bubbles. To address these requirements, this invention employs a three-stage precise temperature control method for heating the sputtering tube, such as... Figure 1 As shown, a three-stage temperature control device is used, consisting of a first temperature control mechanism, a second temperature control mechanism, and a third temperature control mechanism from top to bottom. These mechanisms control the temperature of the leakage tube in stages. In this embodiment, each temperature control mechanism can use resistance heating. The heating power is designed to ensure that the melt reaches a reasonable temperature within the leakage tube and forms an ideal temperature gradient. Based on heat transfer process calculations and actual measurements, the following method is specifically selected:

[0045]

[0046] P3=k2L b P1 (2)

[0047]

[0048] In the formula, P1 is the heating power of the first temperature control mechanism, and the unit is kW. P0 is the reference heating power, which is taken as 3kW here. T0 is the reference temperature, which is 1550℃ here. T is the temperature of the melt entering the leakage pipe, and the unit is ℃. k1 is the upper section temperature control power coefficient, and the value range is 0.8 to 1.2. a is the upper section temperature control power index, and the value range is 0.4 to 0.6. k1 and a are determined by the specific heat capacity of the melt and the radiative heat dissipation conditions of the upper section of the leakage pipe. Their ranges are obtained by regression fitting based on the measured data.

[0049] P3 represents the heating power of the third temperature control mechanism, k2 is the heat dissipation coefficient of the discharge tube (ranging from 1.1 to 1.3), L is the length of the discharge tube (1.1m), and b is the heat dissipation index (0.5). The power of the second temperature control mechanism is the average of the power of the upper and lower temperature control mechanisms. Through this temperature control method, the melt can be kept relatively stable at 1550℃ in the upper section and at approximately 1500℃ at the lower outlet.

[0050] 5) Annealing:

[0051] After the glass products are formed, they are annealed at 480℃~520℃ to eliminate internal stress and enhance the stability, optical properties and mechanical properties of the glass.

[0052] 6) Crystallization heat treatment:

[0053] Crystallization heat treatment involves holding the glass at a specific temperature and time to induce the formation of microcrystalline structures from certain components. The time and temperature of the crystallization heat treatment are critical parameters, requiring precise control based on the desired microcrystalline structure and properties. This invention employs a two-step crystallization process: first, holding the glass at 500–600°C for 10–20 hours constitutes the nucleation stage, a prerequisite for generating predetermined crystal nuclei; then, the temperature is raised to 700–800°C and held for another 10–20 hours, allowing new crystalline phases to precipitate on the nucleating agent, resulting in crystal growth to the desired grain size and quantity. This process gives the microcrystalline glass material both high elastic modulus and an ultra-low coefficient of thermal expansion.

[0054] Example 1

[0055] The mass percentage of crushed microcrystalline glass waste and virgin material is 1:5, with the following composition: Li₂O: 2.5%, Al₂O₃: 25%, SiO₂: 57.5%, MgO: 4%, NaO and K₂O: 1% each, ZnO: 1.5%, P₂O₅: 3.5%, TiO₂: 1.5%, ZrO: 1.5%, and B₂O₃: 1%. Li₂O, NaO, and K₂O are converted into carbonates and nitrates in corresponding proportions. The raw materials are weighed according to the designed glass composition. After thorough mixing and stirring, the mixture is placed in a platinum crucible and melted at 1520℃ for 6 hours. After extrusion molding through a three-stage precisely temperature-controlled extrusion tube, it undergoes an annealing process followed by controlled crystallization. The nucleation stage temperature is 550℃ for 15 hours, and the crystallization stage temperature is 750℃ for 15 hours. After crystallization, the mixture is cooled in the furnace to obtain ultra-low expansion microcrystalline glass. The main crystalline phase is β-quartz solid solution with a grain size of less than 50 nm, and it contains a certain amount of spinel phase, with a crystalline phase content of 85%. The elastic modulus is 120 GPa, the average grain size is 48 nm, and the coefficient of thermal expansion is 6.0 × 10⁻⁶. -8 / ℃.

[0056] By using the method of the present invention, a high elastic modulus microcrystalline glass and its preparation can be achieved, the microcrystalline glass having a high elastic modulus and an ultra-low coefficient of thermal expansion.

[0057] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing high elastic modulus ultra-low expansion microcrystalline glass, characterized in that, Includes the following steps: (1) Component design: The basic component range of the high elastic modulus ultra-low expansion microcrystalline glass, by mass percentage, includes: Li2O: 1~5%, Al2O3: 20~30%, SiO2: 50~70%, MgO: 3~6%, NaO and K2O: 0.5~2%, ZnO: 0~2%, P2O5: 4~7%, TiO2: 1~3%, ZrO: 1~3%, B2O3: 1~4%, and the sum of the mass percentages of each component is 100%; (2) Microcrystalline glass extrusion molding and crystallization According to the formula in step (1), the ingredients are prepared, mixed, melted, shaped, annealed, and crystallized under heat treatment. During the molding process, the material leakage tube is heated using a three-stage precise temperature control method. A three-stage temperature control device is used, consisting of a first temperature control mechanism, a second temperature control mechanism, and a third temperature control mechanism, from top to bottom, to control the temperature of the material leakage tube in stages. The heating power of each temperature control mechanism is selected as follows: （1） （2） （3） In the formula, The heating power of the first temperature control mechanism is in kW. The base heating power is 3kW. The reference temperature is 1550℃. The temperature of the melt entering the feed tube, in °C. This is the power coefficient for the upper temperature control stage, with a value ranging from 0.8 to 1.

2. This is the power index for the upper-stage temperature control, with a value range of 0.4 to 0.

6. The heating power of the third temperature control mechanism, The heat dissipation coefficient of the leakage tube ranges from 1.1 to 1.

3. The length of the discharge tube. The heat dissipation index is 0.

5. Through the above temperature control methods, the melt is stabilized at 1550℃ in the upper section and at 1500℃ at the lower outlet. In the crystallization heat treatment, a two-step crystallization process is adopted. First, the temperature is kept at 500~600℃ for 10~20h, which is the nucleation stage, to generate the predetermined crystal nuclei. Then, the temperature is raised to 700~800℃ and kept at 10~20h to allow the new crystal phase to precipitate on the nucleating agent.

2. The method for preparing a high elastic modulus ultra-low expansion microcrystalline glass according to claim 1, characterized in that, The raw materials of microcrystalline glass are composed of a certain proportion of crushed microcrystalline glass waste and new material, with a mass percentage of microcrystalline glass waste: new material of (1:7)~(2:8).

3. The method for preparing a high elastic modulus ultra-low expansion microcrystalline glass according to claim 1, characterized in that, In the basic glass raw materials, Li2O is introduced in the form of carbonate, while NaO and K2O are introduced in the form of nitrate.

4. A high-elastic-modulus, ultra-low-expansion microcrystalline glass prepared by the method of claim 3, characterized in that, The main crystalline phase of the microcrystalline glass is β-quartz solid solution, and it contains a small amount of spinel phase, with a glass phase content of 10-20%.

5. The microcrystalline glass according to claim 4, characterized in that, The coefficient of thermal expansion of the microcrystalline glass is between 5.7 and 6.5 × 10⁻⁶. -8 / ℃, with an elastic modulus above 120GPa.

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