A high-alumina pyrophyllite glass fiber and its preparation method

Abstract

This invention relates to the field of glass fiber, and provides a high-alumina pyrophyllite glass fiber and its preparation method. The glass fiber is composed of high-alumina pyrophyllite, quartz sand, titanium dioxide, limestone, dolomite, soda ash, and borax. The fiber contains plate-like pyrophyllite microcrystals with crystal planes arranged parallel to the fiber axis, with an average diameter of 20.0–45.0 nm and a thickness of 2.0–5.0 nm. The preparation method includes ball milling of the high-alumina pyrophyllite, ultrasonic exfoliation and surface modification treatment, batch mixing, melting and homogenization at 1490–1510℃, melting and drawing at 1360–1380℃ to control the axial orientation of the microcrystals, and segmented heat treatment to stabilize the structure. The resulting glass fiber has a tensile strength of 2800–3200 MPa and an axial thermal conductivity of 1.2–1.6 W / (m·K), significantly improved in strength and thermal conductivity compared to ordinary pyrophyllite glass fiber. It is suitable for the preparation of high-performance composite materials in aerospace, electronic packaging, and high-end construction fields.

Description

Technical Field

[0001] This invention relates to the field of glass fiber, and specifically to a high-alumina pyrophyllite glass fiber and its preparation method. Background Technology

[0002] With the rapid development of aerospace, electronic packaging, new energy vehicles, and high-end buildings, the demand for high-performance glass fiber materials is becoming increasingly urgent. In aerospace composite material manufacturing, glass fiber, as a reinforcing phase, needs to withstand extreme mechanical loads and temperature changes, requiring excellent tensile strength to ensure the reliability and safety of structural components. In the field of electronic packaging, as chip power density continues to increase, heat dissipation has become a key bottleneck restricting the performance of electronic devices, urgently requiring glass fiber materials with high thermal conductivity to construct efficient thermal management systems. Simultaneously, the demand for lightweight, high-strength, and thermally conductive materials for new energy vehicle power battery systems is also rapidly increasing to achieve lightweight design and thermal safety management of battery packs. Furthermore, the development of green and intelligent buildings places higher demands on the comprehensive performance of glass fiber materials, requiring both structural strength and good thermal conductivity to improve building energy efficiency. Therefore, developing new glass fiber materials with both high strength and high thermal conductivity is of significant strategic importance for promoting technological progress in related industries, enhancing product competitiveness, and meeting increasingly stringent application requirements.

[0003] However, the development of pyrophyllite glass fiber currently faces technical bottlenecks due to insufficient strength and thermal conductivity, severely restricting its promotion in high-end applications. In the traditional preparation process of pyrophyllite glass fiber, the layered structure of the pyrophyllite mineral is not effectively utilized and controlled, resulting in an unsatisfactory internal microstructure. This prevents the full utilization of the mechanical properties of pyrophyllite, making it difficult for the tensile strength of the final product to meet the application requirements of high-performance composite materials. Simultaneously, in terms of thermal conductivity, existing technologies mainly rely on the intrinsic thermal conductivity of the glass matrix, lacking effective thermal path design and microstructure optimization strategies. This leads to low heat transfer efficiency, failing to meet the urgent needs of modern electronic devices and thermal management systems for efficient heat dissipation. Furthermore, limitations in the preparation process are also a significant cause of insufficient performance, including insufficient raw material pretreatment, unoptimized melt drawing process parameters, and the absence of post-processing. These factors combined result in poor dispersion and low orientation of pyrophyllite microcrystals within the fiber, thus affecting the overall performance of the material. For example, Chinese patent CN118270989A discloses a pyrophyllite micro powder composition for glass fiber, glass fiber and its application, but it has shortcomings in terms of insufficient strength and thermal conductivity. Summary of the Invention

[0004] (1) Technical problems to be solved

[0005] The purpose of this invention is to provide a high-alumina pyrophyllite glass fiber and its preparation method, thereby solving the problems of insufficient strength and thermal conductivity of current pyrophyllite glass fibers.

[0006] (2) Technical solution

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A high-alumina pyrophyllite glass fiber comprises the following raw materials in parts by weight: 45.0-55.0 parts high-alumina pyrophyllite, 25.0-35.0 parts quartz sand, 0.5-1.5 parts titanium dioxide, 8.0-12.0 parts limestone, 4.0-8.0 parts dolomite, 3.0-6.0 parts soda ash, and 2.0-4.0 parts borax;

[0009] The glass fiber contains plate-like pyrophyllite microcrystals, the crystal planes of which are arranged parallel to the glass fiber axis, and the orientation degree of the microcrystals is 0.7 to 0.85 according to the Herman orientation factor.

[0010] Furthermore, the average diameter of the flaky pyrophyllite microcrystals ranges from 20.0 to 45.0 nm, the average thickness ranges from 2.0 to 5.0 nm, and the volume fraction of the microcrystals is 4.5% to 9.5%.

[0011] Furthermore, the Al2O3 content in the high-alumina pyrophyllite is 21-26.5%.

[0012] Furthermore, the glass fiber has a tensile strength of 2800–3200 MPa, an axial thermal conductivity of 1.2–1.6 W / (m·K), and a fiber diameter of 8–25 μm.

[0013] This invention employs a synergistic reinforcement design of high-alumina pyrophyllite and titanium dioxide, primarily to enhance the strength and thermal conductivity of glass fibers. Through a carefully designed multi-component formulation system, high-alumina pyrophyllite, as the main functional phase, improves the matrix strength. Simultaneously, the high alumina content in high-alumina pyrophyllite significantly improves the bonding strength of the glass network, enhancing the overall mechanical properties of the material. Titanium dioxide, as a preferred nucleating agent, significantly lowers the nucleation energy barrier of pyrophyllite crystals when its content is controlled within the range of 0.5–1.5 parts. When the content exceeds 1.5 wt%, it easily generates a TiO2 self-crystalline phase, affecting performance. This allows the crystals to be dispersed in the glass matrix at the nanoscale, forming a unique micro-reinforcement structure. Quartz sand, as a network forger, synergistically constructs a stable silicon-oxygen network framework with high-alumina pyrophyllite. The addition of limestone and dolomite modulates the glass's melting properties and the density of the network structure. Soda ash and borax further optimize the melting process performance and the continuity of the glass network. Most importantly, by precisely controlling the fabrication process, the crystal planes of the pyrophyllite microcrystals are aligned parallel to the glass fiber axis. This highly ordered microstructure design optimizes the load transfer path and establishes heat conduction channels. The parallel-distributed nanosheet microcrystals significantly reduce axial thermal resistance by minimizing interfacial scattering. Simultaneously, their high aspect ratio structure effectively disperses the load through stress transfer mechanisms when subjected to axial loads. The synergistic effect of the interfaces between high-alumina pyrophyllite, titanium dioxide, and the glass matrix further enhances the overall performance of the composite system, resulting in a significant improvement in mechanical strength and thermal conductivity while maintaining the good processing properties of glass fibers.

[0014] This invention also discloses a method for preparing high-alumina pyrophyllite glass fiber, comprising the following steps:

[0015] S1. High-alumina pyrophyllite was ball-milled, ultrasonically exfoliated, and surface-modified to obtain surface-modified flaky pyrophyllite microcrystalline powder.

[0016] S2. Mix the surface-modified flaky pyrophyllite microcrystalline powder and the remaining raw materials in proportion to obtain a mixture;

[0017] S3. Melt the mixture at 1490-1510℃ and keep it at that temperature for 25-35 minutes to obtain a glass melt;

[0018] S4. The microcrystals are fiberized at 1360-1380℃ using a melt drawing process, and the drawing tension and stretching rate are controlled to make the microcrystals oriented along the glass fiber axis.

[0019] S5. A segmented heat treatment process is used to obtain high-alumina pyrophyllite glass fiber with a microcrystalline orientation structure.

[0020] Furthermore, the ball milling process in step S1 is as follows: the high-alumina pyrophyllite raw material is placed in a planetary ball mill, zirconia balls are used as the ball milling medium, the ball-to-material ratio is controlled at 20:1 to 30:1, and the ball milling is carried out for 3 to 5 hours at a speed of 320 to 380 rpm.

[0021] Furthermore, the ultrasonic ablation process in step S1 includes the following sub-steps:

[0022] a) Disperse the ball-milled powder in deionized water at a mass ratio of 1:8 to 1:12 to form a suspension;

[0023] b) Add polyvinylpyrrolidone dispersant to the suspension, wherein the amount of dispersant added is 0.1 to 0.5 wt% of the powder mass;

[0024] c) The suspension is subjected to ultrasonic treatment for 50 to 70 minutes at an ultrasonic power of 350 to 450 W and a frequency of 20 to 30 kHz, while maintaining the system temperature at 38 to 42 °C during the treatment.

[0025] d) Centrifuge the ultrasonically treated suspension at 4500–5500 rpm for 8–12 minutes;

[0026] e) Wash the separated solids with deionized water 3 to 5 times.

[0027] Further, the surface modification process in step S1 is as follows: the cleaned microcrystalline powder is redispersed in anhydrous ethanol to prepare a suspension with a mass fraction of 6-10%, 4-6 vol% deionized water is added and the pH is adjusted to 4.0-5.0 with acetic acid, and 0.8-1.2% of γ-aminopropyltriethoxysilane by weight of the microcrystalline powder is slowly added under stirring. The mixture is continuously stirred at 65-75°C for 1.5-2.5 hours until the grafting rate reaches 85-95%. Then, the unreacted coupling agent is removed by centrifugation, and the mixture is washed 2-4 times with anhydrous ethanol. Finally, the surface-modified microcrystalline powder is vacuum dried at 110-120°C for 2-4 hours.

[0028] Furthermore, the wire drawing process parameters in step S4 are: drawing speed 6-14 m / min, wire tension 12-28 cN / tex, and drawing ratio 350-650 times.

[0029] Furthermore, step S5 employs a programmable segmented heat treatment process, comprising: a first stage in which the drawn glass fiber is heated from ambient temperature to 300-400°C at a heating rate of 5-15°C / min, and held at this temperature for 30-60 minutes to eliminate internal stress; a second stage in which the glass fiber is further heated from 300-400°C to 580-620°C at a heating rate of 5-15°C / min, and held at this temperature for 100-140 minutes to promote microcrystalline orientation stabilization; and a third stage in which the glass fiber is cooled to ambient temperature at a cooling rate of 5-10°C / min.

[0030] This invention employs an integrated preparation process of ball milling, ultrasonic exfoliation, surface modification, melt drawing, and segmented heat treatment, primarily used to enhance the strength and thermal conductivity of glass fibers. Through the mechanical force of a planetary ball mill and zirconia ball media, the layered structure of high-alumina pyrophyllite is initially disrupted and refined, laying the foundation for subsequent ultrasonic exfoliation. With the assistance of polyvinylpyrrolidone dispersant, the ultrasonic exfoliation process utilizes the cavitation effect of ultrasound to further exfoliate the layered structure of pyrophyllite, producing plate-like microcrystals with a high aspect ratio. This staged treatment method achieves precise control over the size and morphology of the microcrystals. In the surface modification process, the introduction of γ-aminopropyltriethoxysilane coupling agent plays a crucial interfacial bridging role. Its amino terminus forms chemical bonds with the hydroxyl groups on the pyrophyllite surface, while the siloxane terminus exhibits good compatibility with the glass matrix, significantly improving the interfacial bonding strength between the microcrystals and the matrix and eliminating the adverse effects of interfacial defects on material properties. During the high-temperature melting process at 1490–1510℃, the pretreated lamellar microcrystals undergo partial dissolution, and their residual micro- and nanoparticles serve as high-quality crystal nuclei, uniformly dispersed in the glass melt. The fiber drawing process, through precise control of tensile tension and drawing rate, creates conditions for subsequent directional crystallization. The segmented heat treatment process is particularly ingenious. The first stage of low-temperature treatment effectively eliminates the internal stress generated during the fiber drawing process, avoiding the negative impact of stress concentration on fiber strength. The second stage of high-temperature treatment at 580–620℃ achieves in-situ recrystallization of lamellar pyrophyllite microcrystals, forming an axially oriented microcrystalline structure under the induction of the fiber drawing stress field. The synergistic effect of multiple process steps, such as ball milling, ultrasonic exfoliation, surface modification, dissolution-recrystallization orientation, and heat treatment stabilization, achieves comprehensive optimization of microcrystalline dispersion, interfacial bonding, and structural order, resulting in a significant improvement in both mechanical and thermal conductivity of the final glass fiber.

[0031] (3) Beneficial technical effects

[0032] 1. This invention achieves a significant improvement in the strength and thermal conductivity of glass fiber through the synergistic reinforcement design of high-alumina pyrophyllite and titanium dioxide. Titanium dioxide acts as a nucleating agent to promote the orderly precipitation of microcrystals, quartz sand constructs a stable framework, and flux optimizes process performance. The synergistic effect of each component forms an axially oriented lamellar microcrystalline structure. Through stress transfer mechanism and interface scattering control, mechanical properties and thermal conductivity are improved simultaneously. Compared with traditional pyrophyllite glass fiber, it has obvious technical advantages in high-end fields such as aerospace composite materials and electronic packaging.

[0033] 2. This invention employs an integrated process of ball milling, ultrasonic exfoliation, surface modification, melt drawing, and segmented heat treatment. Through the synergistic effect of mechanical crushing and ultrasonic cavitation, precise exfoliation of the pyrophyllite layered structure is achieved. The interface bridging of γ-aminopropyltriethoxysilane coupling agent improves the bonding between microcrystals and matrix. The high-temperature melting-drawing stress field-heat treatment crystallization synergistically induces the axial orientation of microcrystals. The synergistic optimization of each process step achieves the unity of microcrystal dispersion, interface bonding, and structural order. Compared with traditional processes, this significantly improves the mechanical strength and thermal conductivity of glass fibers. Attached Figure Description

[0034] Figure 1 This is a morphology diagram of the high-alumina pyrophyllite raw material used in Example 1 of the present invention.

[0035] Figure 2 This is a microstructure morphology diagram of high-alumina pyrophyllite glass fiber in Example 1 of the present invention.

[0036] Figure 3 This is a microstructure diagram of the high-alumina pyrophyllite glass fiber of Comparative Example 4 of the present invention.

[0037] Figure 4 This is a microstructure diagram of the high-alumina pyrophyllite glass fiber of Comparative Example 6 of the present invention.

[0038] Figure 5 This is a comparison diagram of the mechanical properties of embodiments and comparative examples of the present invention.

[0039] Figure 6 This is a comparison diagram of the thermal and hardness properties of the materials in the embodiments and comparative examples of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0041] Example 1

[0042] A high-alumina pyrophyllite glass fiber comprises the following raw materials in parts by weight: 45.0 parts high-alumina pyrophyllite, 25.0 parts quartz sand, 0.5 parts titanium dioxide, 8.0 parts limestone, 4.0 parts dolomite, 3.0 parts soda ash, and 2.0 parts borax.

[0043] The glass fiber contains lamellar pyrophyllite microcrystals, the crystal planes of which are arranged parallel to the glass fiber axis; the orientation degree of the microcrystals is 0.7 according to the Herman orientation factor.

[0044] In this embodiment, the average diameter of the flaky pyrophyllite microcrystals is in the range of 20.0 nm, the average thickness is 2.0 nm, and the volume fraction of the microcrystals is 3.5%.

[0045] The Al2O3 content in the high-alumina pyrophyllite of this embodiment is 21%.

[0046] The glass fiber in this embodiment has a tensile strength of 2800 MPa, an axial thermal conductivity of 1.2 W / (m·K), and a fiber diameter of 8 μm.

[0047] This embodiment describes a method for preparing high-alumina pyrophyllite glass fiber, comprising the following steps:

[0048] S1. High-alumina pyrophyllite was ball-milled, ultrasonically exfoliated, and surface-modified to obtain surface-modified flaky pyrophyllite microcrystalline powder.

[0049] S2. Mix the surface-modified flaky pyrophyllite microcrystalline powder and the remaining raw materials in proportion to obtain a mixture;

[0050] S3. Melt the mixture at 1490℃ and keep it at that temperature for 25 minutes to homogenize it, thus obtaining a glass melt;

[0051] S4. The microcrystals are fiberized using a melt drawing process at 1360℃, and the drawing tension and stretching rate are controlled to ensure that the microcrystals are oriented along the glass fiber axis.

[0052] S5. A segmented heat treatment process is used to obtain high-alumina pyrophyllite glass fiber with a microcrystalline orientation structure.

[0053] In step S1 of this embodiment, the ball milling process is as follows: the high-alumina pyrophyllite raw material is placed in a planetary ball mill, zirconia balls are used as the ball milling medium, the ball-to-material ratio is controlled at 23:1, and the ball milling is carried out for 3.6 hours at a speed of 338 rpm.

[0054] The ultrasonic ablation process in step S1 of this embodiment includes the following sub-steps:

[0055] a) Disperse the ball-milled powder in deionized water at a mass ratio of 1:9.2 to form a suspension;

[0056] b) Add polyvinylpyrrolidone dispersant to the suspension, wherein the amount of dispersant added is 0.2 wt% of the powder mass;

[0057] c) The suspension was ultrasonically treated for 56 minutes at an ultrasonic power of 380W and a frequency of 23kHz, while the system temperature was maintained at 39°C during the treatment.

[0058] d) The ultrasonically treated suspension was centrifuged at 4800 rpm for 9 minutes;

[0059] e) Wash the separated solids three times with deionized water.

[0060] In step S1 of this embodiment, the surface modification process is as follows: the cleaned microcrystalline powder is redispersed in anhydrous ethanol to prepare a suspension with a mass fraction of 7.2%, 4.6 vol% deionized water is added and the pH is adjusted to 4.3 with acetic acid, and 0.9% by weight of γ-aminopropyltriethoxysilane is slowly added while stirring. The mixture is continuously stirred at 68°C for 1.8 hours until the grafting rate reaches 88%. Then, the unreacted coupling agent is removed by centrifugation, and the mixture is washed twice with anhydrous ethanol. Finally, the surface-modified microcrystalline powder is vacuum dried at 113°C for 2.6 hours.

[0061] In step S4 of this embodiment, the wire drawing process parameters are: drawing speed 8m / min, line tension 17cN / tex, and drawing ratio 440 times.

[0062] Step S5 of this embodiment adopts a programmable segmented heat treatment process, including: a first stage, heating the drawn glass fiber from ambient temperature to 330°C at a heating rate of 8°C / min, and maintaining the temperature within this range for 39 minutes to eliminate internal stress; a second stage, continuing to heat the glass fiber from 330°C to 592°C at a heating rate of 8°C / min, and maintaining the temperature within this range for 112 minutes to promote microcrystalline orientation stabilization; after the heat treatment is completed, cooling to ambient temperature at a cooling rate of 7°C / min.

[0063] Example 2

[0064] A high-alumina pyrophyllite glass fiber comprises the following raw materials in parts by weight: 48.0 parts high-alumina pyrophyllite, 28.0 parts quartz sand, 0.8 parts titanium dioxide, 9.2 parts limestone, 5.2 parts dolomite, 3.9 parts soda ash, and 2.6 parts borax.

[0065] The glass fiber contains lamellar pyrophyllite microcrystals, the crystal planes of which are arranged parallel to the glass fiber axis; the orientation degree of the microcrystals is 0.7 according to the Herman orientation factor.

[0066] In this embodiment, the average diameter of the flaky pyrophyllite microcrystals is in the range of 28.0 nm, the average thickness is 2.9 nm, and the volume fraction of the microcrystals is 5.0%.

[0067] The Al2O3 content in the high-alumina pyrophyllite of this embodiment is 23%.

[0068] The glass fiber in this embodiment has a tensile strength of 2920 MPa, an axial thermal conductivity of 1.3 W / (m·K), and a fiber diameter of 13 μm.

[0069] This embodiment describes a method for preparing high-alumina pyrophyllite glass fiber, comprising the following steps:

[0070] S1. High-alumina pyrophyllite was ball-milled, ultrasonically exfoliated, and surface-modified to obtain surface-modified flaky pyrophyllite microcrystalline powder.

[0071] S2. Mix the surface-modified flaky pyrophyllite microcrystalline powder and the remaining raw materials in proportion to obtain a mixture;

[0072] S3. Melt the mixture at 1496℃ and keep it at that temperature for 28 minutes to homogenize it, thus obtaining a glass melt;

[0073] S4. The microcrystals are fiberized using a melt drawing process at 1366℃, and the drawing tension and stretching rate are controlled to ensure that the microcrystals are oriented along the glass fiber axis.

[0074] S5. A segmented heat treatment process is used to obtain high-alumina pyrophyllite glass fiber with a microcrystalline orientation structure.

[0075] In step S1 of this embodiment, the ball milling process is as follows: the high-alumina pyrophyllite raw material is placed in a planetary ball mill, zirconia balls are used as the ball milling medium, the ball-to-material ratio is controlled at 20:1, and the ball milling is carried out for 3 hours at a speed of 320 rpm.

[0076] The ultrasonic ablation process in step S1 of this embodiment includes the following sub-steps:

[0077] a) Disperse the ball-milled powder in deionized water at a mass ratio of 1:8 to form a suspension;

[0078] b) Add polyvinylpyrrolidone dispersant to the suspension, wherein the amount of dispersant added is 0.1 wt% of the powder mass;

[0079] c) The suspension was ultrasonically treated for 50 minutes at an ultrasonic power of 350W and a frequency of 20kHz, while maintaining the system temperature at 38°C during the treatment.

[0080] d) The ultrasonically treated suspension was centrifuged at 4500 rpm for 8 minutes;

[0081] e) Wash the separated solids three times with deionized water.

[0082] In step S1 of this embodiment, the surface modification process is as follows: the cleaned microcrystalline powder is redispersed in anhydrous ethanol to prepare a suspension with a mass fraction of 6%, 4 vol% deionized water is added and the pH is adjusted to 4.0 with acetic acid, and 0.8% of the weight of γ-aminopropyltriethoxysilane is slowly added under stirring. The reaction is continuously stirred at 65°C for 1.5 hours until the grafting rate reaches 85%. Then, the unreacted coupling agent is removed by centrifugation, and the powder is washed twice with anhydrous ethanol. Finally, the surface-modified microcrystalline powder is vacuum dried at 110°C for 2 hours.

[0083] In step S4 of this embodiment, the wire drawing process parameters are: drawing speed 6m / min, line tension 12cN / tex, and drawing ratio 350 times.

[0084] Step S5 of this embodiment adopts a programmable segmented heat treatment process, including: a first stage, heating the drawn glass fiber from ambient temperature to 300°C at a heating rate of 5°C / min, and maintaining the temperature within this range for 30 minutes to eliminate internal stress; a second stage, continuing to heat the glass fiber from 300°C to 580°C at a heating rate of 5°C / min, and maintaining the temperature within this range for 100 minutes to promote microcrystalline orientation stabilization; after the heat treatment is completed, cooling to ambient temperature at a cooling rate of 5°C / min.

[0085] Example 3

[0086] A high-alumina pyrophyllite glass fiber comprises the following raw materials in parts by weight: 51.0 parts high-alumina pyrophyllite, 31.0 parts quartz sand, 1.1 parts titanium dioxide, 10.4 parts limestone, 6.4 parts dolomite, 4.8 parts soda ash, and 3.2 parts borax.

[0087] The glass fiber contains lamellar pyrophyllite microcrystals, the crystal planes of which are arranged parallel to the glass fiber axis; the orientation degree of the microcrystals is 0.8 according to the Herman orientation factor.

[0088] In this embodiment, the average diameter of the flaky pyrophyllite microcrystals is in the range of 35.0 nm, the average thickness is 3.8 nm, and the volume fraction of the microcrystals is 6.5%.

[0089] The Al2O3 content in the high-alumina pyrophyllite of this embodiment is 24%.

[0090] The glass fiber in this embodiment has a tensile strength of 3040 MPa, an axial thermal conductivity of 1.4 W / (m·K), and a fiber diameter of 18 μm.

[0091] This embodiment describes a method for preparing high-alumina pyrophyllite glass fiber, comprising the following steps:

[0092] S1. High-alumina pyrophyllite was ball-milled, ultrasonically exfoliated, and surface-modified to obtain surface-modified flaky pyrophyllite microcrystalline powder.

[0093] S2. Mix the surface-modified flaky pyrophyllite microcrystalline powder and the remaining raw materials in proportion to obtain a mixture;

[0094] S3. Melt the mixture at 1502℃ and keep it at that temperature for 31 minutes to homogenize it, thus obtaining a glass melt;

[0095] S4. The microcrystals are fiberized using a melt drawing process at 1372℃, and the drawing tension and stretching rate are controlled to ensure that the microcrystals are oriented along the glass fiber axis.

[0096] S5. A segmented heat treatment process is used to obtain high-alumina pyrophyllite glass fiber with a microcrystalline orientation structure.

[0097] In step S1 of this embodiment, the ball milling process is as follows: the high-alumina pyrophyllite raw material is placed in a planetary ball mill, zirconia balls are used as the ball milling medium, the ball-to-material ratio is controlled at 30:1, and the ball milling is carried out for 5 hours at a speed of 380 rpm.

[0098] The ultrasonic ablation process in step S1 of this embodiment includes the following sub-steps:

[0099] a) Disperse the ball-milled powder in deionized water at a mass ratio of 1:12 to form a suspension;

[0100] b) Add polyvinylpyrrolidone dispersant to the suspension, wherein the amount of dispersant added is 0.5 wt% of the powder mass;

[0101] c) The suspension was ultrasonically treated for 70 minutes at an ultrasonic power of 450W and a frequency of 30kHz, while maintaining the system temperature at 42°C during the treatment.

[0102] d) The ultrasonically treated suspension was centrifuged at 5500 rpm for 12 minutes;

[0103] e) Wash the separated solids five times with deionized water.

[0104] In step S1 of this embodiment, the surface modification process is as follows: the cleaned microcrystalline powder is redispersed in anhydrous ethanol to prepare a suspension with a mass fraction of 10%, 6 vol% deionized water is added and the pH is adjusted to 5.0 with acetic acid, 1.2% by weight of γ-aminopropyltriethoxysilane is slowly added under stirring, and the reaction is continuously stirred at 75°C for 2.5 hours until the grafting rate reaches 95%. Then, the unreacted coupling agent is removed by centrifugation, and the powder is washed 4 times with anhydrous ethanol. Finally, the surface-modified microcrystalline powder is vacuum dried at 120°C for 4 hours.

[0105] In step S4 of this embodiment, the wire drawing process parameters are: drawing speed 14m / min, line tension 28cN / tex, and drawing ratio 650 times.

[0106] Step S5 of this embodiment adopts a programmable segmented heat treatment process, including: a first stage, heating the drawn glass fiber from ambient temperature to 400°C at a heating rate of 15°C / min, and maintaining it at this temperature for 60 minutes to eliminate internal stress; a second stage, continuing to heat the glass fiber from 400°C to 620°C at a heating rate of 15°C / min, and maintaining it at this temperature for 140 minutes to promote microcrystalline orientation stabilization; after the heat treatment is completed, cooling it to ambient temperature at a cooling rate of 10°C / min.

[0107] Example 4

[0108] A high-alumina pyrophyllite glass fiber comprises the following raw materials in parts by weight: 55.0 parts high-alumina pyrophyllite, 35.0 parts quartz sand, 1.5 parts titanium dioxide, 12.0 parts limestone, 8.0 parts dolomite, 6.0 parts soda ash, and 4.0 parts borax.

[0109] The glass fiber contains lamellar pyrophyllite microcrystals, the crystal planes of which are arranged parallel to the glass fiber axis; the orientation degree of the microcrystals is 0.85 according to the Herman orientation factor.

[0110] In this embodiment, the average diameter of the flaky pyrophyllite microcrystals is in the range of 45.0 nm, the average thickness is 5.0 nm, and the volume fraction of the microcrystals is 8.5%.

[0111] The Al2O3 content in the high-alumina pyrophyllite of this embodiment is 26.5%.

[0112] The glass fiber in this embodiment has a tensile strength of 3200 MPa, an axial thermal conductivity of 1.6 W / (m·K), and a fiber diameter of 25 μm.

[0113] This embodiment describes a method for preparing high-alumina pyrophyllite glass fiber, comprising the following steps:

[0114] S1. High-alumina pyrophyllite was ball-milled, ultrasonically exfoliated, and surface-modified to obtain surface-modified flaky pyrophyllite microcrystalline powder.

[0115] S2. Mix the surface-modified flaky pyrophyllite microcrystalline powder and the remaining raw materials in proportion to obtain a mixture;

[0116] S3. Melt the mixture at 1510℃ and keep it at that temperature for 35 minutes to homogenize it, thus obtaining a glass melt;

[0117] S4. The microcrystals are fiberized using a melt drawing process at 1380℃, and the drawing tension and stretching rate are controlled to ensure that the microcrystals are oriented along the glass fiber axis.

[0118] S5. A segmented heat treatment process is used to obtain high-alumina pyrophyllite glass fiber with a microcrystalline orientation structure.

[0119] In step S1 of this embodiment, the ball milling process is as follows: the high-alumina pyrophyllite raw material is placed in a planetary ball mill, zirconia balls are used as the ball milling medium, the ball-to-material ratio is controlled at 26:1, and the ball milling is carried out at a speed of 356 rpm for 4.2 hours.

[0120] The ultrasonic ablation process in step S1 of this embodiment includes the following sub-steps:

[0121] a) Disperse the ball-milled powder in deionized water at a mass ratio of 1:10.4 to form a suspension;

[0122] b) Add polyvinylpyrrolidone dispersant to the suspension, wherein the amount of dispersant added is 0.3 wt% of the powder mass;

[0123] c) The suspension was ultrasonically treated for 62 minutes at an ultrasonic power of 410W and a frequency of 26kHz, while maintaining the system temperature at 40°C during the treatment.

[0124] d) Centrifuge the ultrasonically treated suspension at 5100 rpm for 10 minutes;

[0125] e) Wash the separated solid with deionized water four times.

[0126] In step S1 of this embodiment, the surface modification process is as follows: the cleaned microcrystalline powder is redispersed in anhydrous ethanol to prepare a suspension with a mass fraction of 8.4%, 5.2 vol% deionized water is added and the pH is adjusted to 4.6 with acetic acid, and 1.0% of the weight of γ-aminopropyltriethoxysilane is slowly added under stirring. The reaction is continuously stirred at 71°C for 2.1 hours until the grafting rate reaches 91%. Then, the unreacted coupling agent is removed by centrifugation, and the powder is washed three times with anhydrous ethanol. Finally, the surface-modified microcrystalline powder is vacuum dried at 116°C for 3.2 hours.

[0127] In step S4 of this embodiment, the wire drawing process parameters are: drawing speed 11m / min, line tension 22cN / tex, and drawing ratio 530 times.

[0128] Step S5 of this embodiment adopts a programmable segmented heat treatment process, including: a first stage, heating the drawn glass fiber from ambient temperature to 360°C at a heating rate of 11°C / min, and holding it at this temperature range for 48 minutes to eliminate internal stress; a second stage, continuing to heat the glass fiber from 360°C to 604°C at a heating rate of 11°C / min, and holding it at this temperature range for 124 minutes to promote microcrystalline orientation stabilization; after the heat treatment is completed, cooling it to ambient temperature at a cooling rate of 8°C / min.

[0129] Comparative Example 1

[0130] It is basically the same as Example 1, except that titanium dioxide is not added. The lack of a nucleating agent leads to uneven crystal precipitation and difficulty in controlling the size.

[0131] Comparative Example 2

[0132] The method is basically the same as in Example 1, except that the amount of titanium dioxide used is 2.5 parts, which exceeds the optimized range and leads to the formation of the TiO2 self-crystalline phase, affecting the orderly precipitation of pyrophyllite microcrystals and the homogeneity of the glass matrix.

[0133] Comparative Example 3

[0134] It is basically the same as Example 1, except that the Al2O3 content in the high-alumina pyrophyllite is 18%.

[0135] Comparative Example 4

[0136] The process is basically the same as in Example 1, except that only ball milling is performed in step S1, and the ultrasonic peeling process is omitted. Surface modification is performed directly after ball milling.

[0137] Comparative Example 5

[0138] The process is basically the same as in Example 1, except that in step S1, alumina balls are used as the grinding medium in the ball milling process, and the ball-to-material ratio is 15:1.

[0139] Comparative Example 6

[0140] It is basically the same as Example 1, except that the ultrasonic power of the ultrasonic peeling process in step S1 is 250W.

[0141] Comparative Example 7

[0142] The process is basically the same as in Example 1, except that in step S1, the surface modification process does not add γ-aminopropyltriethoxysilane coupling agent, and only uses anhydrous ethanol for cleaning and drying.

[0143] Comparative Example 8

[0144] The process is basically the same as in Example 1, except that in step S1, 3-aminopropyltrimethoxysilane is used instead of γ-aminopropyltriethoxysilane for the surface modification process.

[0145] Comparative Example 9

[0146] It is basically the same as Example 1, except that the melting temperature in step S3 is 1420°C.

[0147] Comparative Example 10

[0148] It is basically the same as Example 1, except that the wire drawing temperature in step S4 is 1320°C.

[0149] Comparative Example 11

[0150] It is basically the same as Example 1, except that the stretching speed in step S4 is 4 m / min.

[0151] Comparative Example 12

[0152] The process is basically the same as in Example 1, except that the segmented heat treatment process in step S5 is omitted, and the drawn glass fiber is directly cooled to ambient temperature at a rate of 10°C / min.

[0153] Comparative Example 13

[0154] It is basically the same as Example 1, except that the second stage heat treatment temperature in step S5 is 520°C.

[0155] Performance testing:

[0156] Tensile strength test experiment: High-alumina pyrophyllite glass fiber monofilaments were used as the test object to evaluate the axial tensile strength and elastic modulus of the material. The test principle is based on the stress-strain response characteristics of the material under uniaxial tensile load. The experimental method uses a monofilament tensile testing machine. Single fibers with a diameter of 8-25 μm and an effective length of 25 mm are fixed between clamps and stretched at a constant rate of 1 mm / min until fracture. The load-displacement curve is recorded. The test is conducted according to ASTM D3379 standard. Key parameters include ambient temperature 23±2℃, relative humidity 50±10%, and preload 0.05 N. Data processing: Tensile strength σ=Fmax / A and elastic modulus E=Δσ / Δε are calculated from the load-displacement curves. Each test group consists of no fewer than 30 fibers, and the average value is taken and the standard deviation is calculated.

[0157] Thermal conductivity testing experiment: High-alumina pyrophyllite glass fiber bundles were used as the test object to determine the material's thermal conductivity along the fiber axis. The testing principle is based on the steady-state heat conduction theory, calculating the thermal conductivity by measuring the temperature gradient under stable heat flow conditions. The experimental method employed the heat flux meter method. The fiber bundle was placed in a heat flux meter testing device, with the hot end temperature set at 40℃ and the cold end temperature at 20℃. After thermal equilibrium was reached, the heat flux density and temperature difference were measured. Key parameters included an ambient temperature of 25±1℃, relative humidity ≤60%, and a testing time of no less than 60 minutes to ensure thermal equilibrium. Data processing used the formula λ=q·L / (A·ΔT) to calculate the thermal conductivity, where q is the heat flux density, L is the sample length, A is the cross-sectional area, and ΔT is the temperature difference. Five parallel samples were tested in each group.

[0158] Nanoindentation Hardness Testing Experiment: Using the cross-section of a high-alumina pyrophyllite glass fiber monofilament as the test object, a single fiber is embedded in epoxy resin and polished to a mirror-like surface. The purpose of the test is to evaluate the microhardness and elastic modulus of the material, and to deeply analyze the differences in mechanical properties between the glass matrix and the lamellar microcrystal interface. The test principle is based on nanoindentation technology. A diamond indenter is pressed into the material surface under a small load, and the complete load-displacement curve is recorded to calculate the hardness and modulus parameters. The experimental method uses a nanoindenter (Hysitron TI 950). Ten test points are arranged in a grid pattern on the fiber cross-section surface. A peak load of 2000 μN is applied to each point, and the load is held for 10 seconds to ensure creep stability. The loading and unloading rates are both 200 μN / s. The test is performed according to ISO 14577-1:2015, "Instrumented testing of hardness and other parameters of materials". Key parameters included ambient temperature of 25±2℃, relative humidity of 50±5%, indenter geometry of a Berkovich triangular pyramid, and a test point spacing of at least 20μm to avoid stress influence. Data processing employed the Oliver-Pharr theoretical model to extract Vickers hardness (HV) and reduced elastic modulus (Er) from the load-displacement curve. Young's modulus (E) was calculated using Poisson's ratio correction. The final report included the average value and standard deviation of the 10 test points.

[0159] Chemical corrosion resistance test: High-alumina pyrophyllite glass fiber bundles were used as the test object, and the chemical stability of the fiber bundles in a dry state was evaluated. The purpose of the test was to assess the corrosion resistance of the material in acidic and alkaline environments, simulating the stability of the interface between lamellar microcrystals and the glass matrix under wet chemical processing conditions. The test principle is based on chemical immersion testing, which quantitatively evaluates the chemical stability of the material by measuring the mass change and mechanical property retention rate before and after immersion. The fiber bundles were immersed in aqueous solutions with pH=2 (adjusted by hydrochloric acid) and pH=12 (adjusted by sodium hydroxide) for 168 hours at room temperature. After immersion, they were thoroughly rinsed with deionized water and dried to constant weight. The mass loss rate and the retention rate of single filament tensile strength were measured. Key parameters included a solution volume to sample mass ratio ≥50:1, immersion temperature 23±2℃, immersion time 168 hours, and pH control accuracy ±0.1. Data processing was used to calculate the mass loss rate = (mass before immersion - mass after immersion) / mass before immersion × 100% and the strength retention rate = (strength after immersion / initial strength) × 100%. Five parallel samples were tested for each condition, and the mean and standard deviation were calculated.

[0160] The properties of the fibers from Examples 1-4 and Comparative Examples 1-13 are summarized in Table 1. The absence of titanium dioxide nucleating agent led to uncontrolled precipitation of pyrophyllite crystallites, resulting in uneven crystallite size distribution and reduced crystallite quantity. This reduced load transfer efficiency, significantly decreased tensile strength and elastic modulus. Simultaneously, increased crystallite spacing affected phonon transport paths, significantly decreased axial thermal conductivity, and reduced interfacial bonding quality between crystallites and the matrix, leading to decreased nanohardness. Chemical stability deteriorated due to increased interfacial defects. Excessive titanium dioxide addition triggered the formation of TiO2 self-crystalline phase, which competed with pyrophyllite crystallites for precipitation, disrupting the ordered arrangement of crystallites and creating stress concentration points in the matrix, thus reducing the material's mechanical properties. The presence of the TiO2 phase also altered the uniformity of the glass network structure, affecting the continuity of the heat conduction path. Insufficient Al2O3 content in high-alumina pyrophyllite limited the formation of tetracoordinated aluminum units, weakening the cross-linking strength of the glass network, leading to decreased material rigidity, tensile strength, and elastic modulus. Furthermore, insufficient aluminum content affected the structural stability of the pyrophyllite crystallites, making them more susceptible to chemical corrosion in acidic and alkaline environments.

[0161] The omission of the ultrasonic exfoliation step in the ball milling process prevents the complete removal of the pyrophyllite layered structure, retaining a large number of blocky and granular fragments instead of ideal lamellar crystals. The reduced aspect ratio of the crystals leads to decreased load transfer efficiency, and the difference in orientation weakens anisotropy. The axial thermal conductivity decreases due to discontinuous heat conduction paths. Changing the milling media from zirconia balls to alumina balls reduces milling efficiency and may introduce aluminum contamination, altering the material composition. The lower ball-to-material ratio further weakens the mechanical force, resulting in insufficient destruction of the pyrophyllite layered structure and decreased precision in crystallite size control. Insufficient ultrasonic exfoliation power weakens the cavitation effect, reducing the degree of layered structure removal, decreasing the number of lamellar crystals with undesirable aspect ratios, and directly impacting axial mechanical and thermal conductivity due to reduced crystallite orientation.

[0162] The complete absence of the coupling agent eliminates the chemical bonding bridging effect between the microcrystals and the glass matrix, significantly reducing the interfacial bonding strength. This leads to a substantial decrease in load transfer efficiency, resulting in a marked reduction in tensile strength and elastic modulus. Interfacial defects become weak points for crack initiation and propagation. Simultaneously, voids and defects at the interface increase the penetration path of chemical media, severely deteriorating the material's chemical corrosion resistance. Changes in the type of coupling agent affect the strength and stability of the interfacial chemical bonds; different molecular structures result in varying reactivity with the hydroxyl groups on the pyrophyllite surface, leading to relatively poor interfacial bonding. Excessively low melting temperatures result in incomplete dissolution of high-alumina pyrophyllite, poor homogeneity of the glass matrix, and residual undissolved particles becoming stress concentration sources, while also affecting the uniform precipitation and dispersion of microcrystals.

[0163] Low drawing temperatures increase the viscosity of the glass melt, limiting the directional alignment of microcrystals during the drawing process. Reduced microcrystal orientation directly impacts axial properties, while higher viscosity may lead to increased internal stress during drawing. Insufficient drawing speed reduces the driving force for microcrystal orientation, making it difficult for microcrystals to achieve sufficient axial alignment under the drawing stress field. Insufficient orientation weakens anisotropy, resulting in underutilization of axial mechanical and thermal conductivity properties. The lack of segmented heat treatment prevents effective elimination of internal stress generated during drawing, and microcrystals cannot achieve stable orientation crystallization through heat treatment. Both microcrystal orientation and structural stability are negatively affected, preventing the material from reaching its optimal performance. Insufficient heat treatment temperature limits the recrystallization and orientation stabilization of microcrystals. Incomplete microcrystal structure and poor orientation stability make them prone to orientation relaxation in subsequent applications, affecting long-term performance stability.

[0164] from Figure 1-6 The analysis results show that the high-alumina pyrophyllite raw material used in Example 1 of this invention exhibits a distinct layered microcrystalline structure. The high-alumina pyrophyllite glass fiber obtained after processing this raw material using the process of this invention (…) Figure 2) exhibits a uniform and dense microstructure, with regularly arranged layered precipitates forming inside the fibers, while Comparative Example 4 ( Figure 3 ) and Comparative Example 6 ( Figure 4 The glass fibers exhibit an irregular microstructure, with obvious amorphous regions and structural defects, which directly leads to performance differences, as shown in the mechanical property comparison diagram (). Figure 5 As can be seen, the tensile strength and elastic modulus of the embodiments of the present invention are significantly higher than those of the comparative example. (See the comparison diagram of material thermal and hardness properties). Figure 6 This further confirms the superiority of the process of the present invention. The axial thermal conductivity and nanohardness of the example group both exceed those of the comparative group. This is attributed to the unique layered microcrystalline structure design and disk-shaped precipitate control technology of the present invention, which effectively improves the comprehensive performance of the material.

[0165] Table 1 summarizes the performance of fibers from Examples 1-4 and Comparative Examples 1-13.

[0166]

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high alumina pyrophylhte glass fiber characterized in that, The raw materials include the following weight parts: high-aluminum pyrophyllite 45.0-55.0 parts, quartz sand 25.0-35.0 parts, titanium dioxide 0.5-1.5 parts, limestone 8.0-12.0 parts, dolomite 4.0-8.0 parts, soda ash 3.0-6.0 parts, borax 2.0-4.0 parts; The glass fiber is internally distributed with flaky pyrophyllite microcrystals, and the crystal layer surface direction is arranged in parallel to the axial direction of the glass fiber; The microcrystal orientation degree is 0.7-0.85 by Herman orientation factor; The average diameter of the flaky pyrophyllite microcrystal is 20.0-45.0 nm, the average thickness is 2.0-5.0 nm, and the microcrystal volume ratio is 4.5-9.5%; The Al2O3 content in the high-aluminum pyrophyllite is 21-26.5%; The preparation method of the high-aluminum pyrophyllite glass fiber includes the following steps: S1. Ball milling, ultrasonic peeling and surface modification are performed on the high-aluminum pyrophyllite to obtain surface-modified flaky pyrophyllite microcrystal powder; S2. The surface-modified flaky pyrophyllite microcrystal powder and the remaining raw materials are mixed in proportion to obtain a mixture; S3. The mixture is melted and homogenized at 1490-1510℃ for 25-35 minutes to prepare a glass melt; S4. Fiberization is performed at 1360-1380℃ by using a melt drawing process, and the drawing tension and drawing rate are controlled to orient the microcrystals along the axial direction of the glass fiber; S5. A segmented heat treatment process is used to obtain high-aluminum pyrophyllite glass fiber with microcrystal orientation structure; The drawing process parameters in step S4 are: drawing speed 6-14 m / min, linear tension 12-28 cN / tex, and drawing ratio 350-650 times; The segmented heat treatment process in step S5 includes: in the first stage, the drawn glass fiber is heated from ambient temperature to 300-400℃ at a heating rate of 5-15℃ / min, and kept constant at this temperature interval for 30-60 minutes to eliminate internal stress; in the second stage, the glass fiber is continuously heated from 300-400℃ to 580-620℃ at a heating rate of 5-15℃ / min, and kept constant at this temperature interval for 100-140 minutes to promote microcrystal orientation stabilization; after heat treatment, the glass fiber is cooled to ambient temperature at a cooling rate of 5-10℃ / min.

2. A high aluminous pyrophylhte glass fiber as claimed in claim 1, wherein, The tensile strength of the glass fiber is 2800-3200 MPa, the axial thermal conductivity coefficient is 1.2-1.6 W / (m·K), and the fiber diameter is 8-25 μm.

3. A high aluminous pyrophylhte glass fiber as claimed in claim 1, wherein, The ball milling process in step S1 is: the high-aluminum pyrophyllite raw material is placed in a planetary ball mill, zirconia balls are used as the ball milling medium, the ball-to-material ratio is controlled at 20:1-30:1, and the ball milling is performed at a rotation speed of 320-380 rpm for 3-5 hours.

4. A high aluminous pyrophylhte glass fiber as in claim 1 wherein, The ultrasonic peeling process in step S1 includes the following sub-steps: a) The milled powder is dispersed in deionized water to form a suspension at a mass ratio of 1:8-1:12; b) Polyvinylpyrrolidone dispersant is added to the suspension, and the addition amount of the dispersant is 0.1-0.5 wt% of the mass of the powder; c) ultrasonic treatment of the suspension at an ultrasonic power of 350-450 W and a frequency of 20-30 kHz for 50-70 minutes, while maintaining the temperature of the system at 38-42℃; d) centrifugal separation of the suspension after ultrasonic treatment at a rotation speed of 4500-5500 rpm for 8-12 minutes; e) washing of the obtained solid with deionized water for 3-5 times.

5. A high aluminous pyrophylhte glass fiber as claimed in claim 1, wherein, The surface modification process in step S1 is as follows: the washed microcrystalline powder is dispersed again in anhydrous ethanol to form a suspension with a mass fraction of 6-10%, 4-6 vol% deionized water is added and the pH is adjusted to 4.0-5.0 with acetic acid, 0.8-1.2% of the weight of the microcrystalline powder of γ-aminopropyltriethoxysilane is slowly added under stirring, and the reaction is continuously stirred at 65-75℃ for 1.5-2.5 hours until the grafting rate reaches 85-95%, then the unreacted coupling agent is removed by centrifugal separation, and the surface-modified microcrystalline powder is washed with anhydrous ethanol for 2-4 times, and finally the surface-modified microcrystalline powder is vacuum dried at 110-120℃ for 2-4 hours.

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