NAS microcrystalline glass powder and preparation method thereof
By combining the sol-gel method with a one-step sintering and recrystallization process, the problems of component inhomogeneity and high energy consumption of NAS microcrystalline glass powder were solved, and powder with high density and high crystallinity was prepared, which is suitable for electronic packaging and other fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-09
- Publication Date
- 2026-04-14
AI Technical Summary
Existing methods for preparing NAS microcrystalline glass powder suffer from problems such as component inhomogeneity, volatilization loss, and high energy consumption, making it difficult to obtain highly dense and highly crystalline powders, thus limiting their application in high-end electronic packaging.
By employing a sol-gel method combined with a one-step sintering and recrystallization process, and through precursor formulation design and heat treatment optimization, inorganic matter removal and viscous flow densification are achieved in the mid-temperature region. Subsequently, crystalline phase precipitation occurs under the guidance of uniform nucleation points, forming a microstructure with high density and fine, uniform grains.
We have achieved high density and high crystallinity NAS microcrystalline glass powder, which has high mechanical strength, low coefficient of thermal expansion and low dielectric loss, meets the requirements of low temperature co-firing, reduces energy consumption and raw material costs, and is suitable for electronic packaging, ceramic bonding, composite matrix and other fields.
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Figure CN121850377A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of glass-ceramic technology, and in particular to a NAS glass-ceramic powder and its preparation method. Background Technology
[0002] Sodium aluminum silicon (Na2O-Al2O3-SiO2, abbreviated as NAS) glass-ceramics, as an important branch of the glass-ceramic family, have shown significant application potential in fields such as electronic packaging substrates, low-temperature co-fired ceramics (LTCC) materials, high-temperature coatings, heat-resistant vessels, and nuclear waste solidification carriers due to their wide availability of raw materials, low cost, tunable coefficient of thermal expansion, good chemical stability, moderate mechanical strength, and excellent electrical insulation properties. Especially in the field of electronic packaging, with the development of 5G communication, the Internet of Things, and power electronic devices towards higher frequencies, higher integration, and higher reliability, more stringent requirements are placed on the performance of packaging materials: they need to possess low-temperature co-firing characteristics (typically <900 ℃) that match metal electrodes (such as Ag, Cu), excellent high-frequency dielectric properties (low dielectric constant and loss), and high dimensional stability and thermomechanical reliability. NAS glass-ceramics, because their main crystalline phases (such as nepheline, albite, β-aluminosilicate, etc.) can form and remain stable at relatively low temperatures, have become one of the ideal candidate materials to achieve the above requirements.
[0003] Currently, the preparation of NAS microcrystalline glass powder mainly relies on the following methods, but these methods all have inherent technical bottlenecks, which restrict the controllable synthesis and industrial application of high-performance NAS microcrystalline glass powder: 1. Traditional high-temperature melting-quenching-pulverization-crystallization method. This method is the most classic preparation process. Sodium carbonate, alumina, quartz sand and other raw materials are melted and homogenized at a high temperature of 1400~1550 ℃. Then the melt is water quenched or pressed into sheets and rapidly cooled to obtain amorphous glass. Then it is mechanically crushed and ball milled to obtain glass powder. Finally, the glass powder is subjected to precise nucleation and crystallization heat treatment to induce the precipitation of the target crystalline phase. Its core shortcomings are mainly: (1) the problem of component uniformity and volatilization loss. During the high-temperature melting process, sodium ions (Na +(1) High activity and easy volatility (especially in the form of Na2O), which leads to a serious deviation of the final product composition from the design formula, affecting the reproducibility and consistency of key properties such as crystal phase type and thermal expansion coefficient. At the same time, it is difficult for A2O3 and SiO2 to be completely miscible and homogenized at high temperature, which easily produces micro-phase separation or aluminum-rich / silicon-rich regions. (2) High energy consumption and long process chain. The process involves two high energy consumption steps: "high temperature melting" and "subsequent crystallization heat treatment", and requires multiple processes such as melt forming, crushing, and ball milling. The process is complex and the production cost is high. (3) Defects in powder morphology and performance. The powder obtained by mechanical crushing has a wide particle size distribution, irregular morphology (many sharp edges), and poor flowability and bulk density. More importantly, the subsequent crystallization treatment of amorphous glass powder is a solid-state phase transformation. Crystals usually grow non-uniformly from the surface or internal defects of the powder, which can easily lead to uneven grain size distribution, difficulty in accurately controlling crystallinity, and excessive glass phase residue inside the powder. This affects the density, mechanical uniformity, and dielectric stability of the sintered body prepared from the powder.
[0004] 2. Sol-gel method. The sol-gel method can theoretically overcome the defects of the above methods in terms of component inhomogeneity because it can achieve uniform mixing of molecular-level components in the liquid phase. It has become an important method for preparing high-performance glass and ceramic powders. The general process of preparing NAS materials by the existing sol-gel method is as follows: using tetraethyl orthosilicate (TEOS), aluminum nitrate, sodium nitrate or sodium acetate as precursors, hydrolysis-condensation is carried out to form a gel, and then drying, pre-calcination (removing organic or inorganic matter and forming amorphous dry gel powder), high temperature crystallization heat treatment and other steps are taken to obtain microcrystalline glass powder. Although it has advantages, there are still the following technical defects: (1) The kinetic contradiction between "densification" and "crystallization" is amplified. The traditional sol-gel route adopts a two-step method of "first preparing amorphous powder and then crystallizing independently". The amorphous NAS dry gel powder formed in the pre-calcination stage has extremely high specific surface area and activity. When subjected to crystallization heat treatment, the sintering and densification process of powder particles and the precipitation and growth process of crystal phases highly overlap in temperature and time and compete fiercely. Once the crystal phase (such as nepheline) in the NAS system begins to form, its rigid framework will instantly "freeze" the viscous flow of the particles, severely hindering further densification. This leads to the common phenomenon of "premature crystallization": that is, the powder crystallizes in large quantities before it reaches sufficient densification, and the final product is a porous, low-strength "crystalline porous body" rather than a dense "microcrystalline glass". Although it can be partially alleviated by adding mineralizers or adjusting the heating rate, the fundamental contradiction remains unresolved. (2) Special control problem of sodium component. In the sol-gel process, the hydrolysis rate of sodium source and nucleating agent differs greatly from that of other precursors, which easily leads to uneven distribution of sodium ions and titanium ions in the gel network. In the drying and pre-calcination stages, the migration and volatilization of sodium ions and titanium ions with the solvent are more significant, making it difficult to accurately control the sodium content of the final product, which directly affects the formation temperature and type of the target crystal phase. (3) Process complexity and cracking problem. During the conversion from wet gel to dry gel, the huge capillary force makes the gel body very easy to crack and pulverize, making it difficult to obtain a complete large block of dry gel. Multi-step heat treatment also increases the complexity of process control and energy consumption.
[0005] In summary, the current major challenges in the preparation of NAS glass-ceramic powders are as follows: the sol-gel method, which enables molecular-level mixing, cannot produce ideal powders with high density and crystallinity due to limitations imposed by traditional heat treatment methods; while the melt method, which can produce dense particles, cannot solve the problems of component uniformity, volatilization loss, and powder morphology control. This contradiction severely restricts the application of NAS glass-ceramic in high-end fields (especially in electronic packaging fields requiring low-temperature co-firing and high reliability).
[0006] Therefore, existing technologies still need to be improved and developed. Summary of the Invention
[0007] Based on the shortcomings of the prior art, the purpose of this invention is to provide a NAS microcrystalline glass powder and its preparation method, aiming to solve the problems of the existing sol-gel method in obtaining high-density, high-crystallinity NAS microcrystalline glass and the problems of component inhomogeneity and volatilization loss in the existing high-temperature melting method.
[0008] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing NAS microcrystalline glass powder, comprising the following steps: A sol is provided, which is prepared by means of the following components in parts by weight: 12-15 parts aluminum silicate, 7-9 parts NaOH, 60-70 parts water, 1.0-5.8 parts nano-vaporized SiO2 and 1-1.3 parts TiO2; The sol was dried to obtain a dry gel; The dry gel was heated to 750-850 °C at a heating rate of 3-5 °C / min and held at that temperature for 0.5-1 h. After cooling to room temperature, NAS microcrystalline glass block was obtained. The NAS microcrystalline glass block is crushed and ball-milled to obtain the NAS microcrystalline glass powder.
[0009] Optionally, the method for preparing the sol includes the following steps: NaOH, aluminum silicate, and nano-vaporized SiO2 are mixed and stirred at a preset temperature for a first preset time. TiO2 is then added, and stirring continues at the preset temperature for a second preset time.
[0010] Optionally, the preset temperature is 75~90 ℃, the first preset time is 2~7 h, and the second preset time is 0.5~1 h.
[0011] Optionally, the drying temperature is 100~150℃.
[0012] Optionally, the specific surface area of the nano-vaporized SiO2 is 400~800 m². 2 / g.
[0013] Optionally, the TiO2 has a rutile crystal form.
[0014] Optionally, the dry gel is heated to 800-850 °C at a heating rate of 3-5 °C / min and held at that temperature for 0.5-1 h.
[0015] In a second aspect, the present invention provides a NAS microcrystalline glass powder, wherein the powder is prepared by the preparation method described above.
[0016] Optionally, the crystal phases of the NAS microcrystalline glass powder include sodium nepheline and Na2Al2SiO6.
[0017] Beneficial Effects: This invention employs a sol-gel method combined with a one-step sintering-recrystallization process to prepare low-melting-point NAS microcrystalline glass powder, resolving the temporal contradiction between densification and crystallization. Specifically, through precursor formulation design and optimized heat treatment regime, it ensures that inorganic matter in the precursor is gently removed in the mid-temperature range (approximately 300-400 °C) during the programmed temperature rise heat treatment process, while simultaneously forming a highly active amorphous NAS transition phase rich in mesopores but with moderate skeletal strength. Within this temperature range, particles undergo significant viscous flow driven by surface energy, rapidly filling pores and achieving rapid densification of the main structure. Subsequently, when the temperature rises to a specific crystallization range, densification is essentially complete. Then, during cooling, guided by uniformly distributed nucleation sites (provided by the gel network's own structure), the target crystalline phase precipitates uniformly from the already densified glass matrix (i.e., "recrystallization"). This "densification first, crystallization later" sequence successfully avoids the premature formation of crystals hindering densification. Furthermore, the recrystallization mode ensures that the crystallization process takes place in a dense, chemically homogeneous matrix, thereby obtaining an ideal microstructure with high crystallinity and small, uniform grain size (nanometer to submicron). This results in the NAS microcrystalline glass prepared by this invention having high mechanical strength, low coefficient of thermal expansion, low dielectric constant, and low dielectric loss, which can be applied to fields such as electronic packaging, ceramic bonding, melting aids, composite material matrices, and low-temperature co-fired ceramics.
[0018] Furthermore, the molecular-level mixing of the sol-gel in this invention, combined with the low melting temperature of the one-step sintering method, ensures uniform composition and prevents sodium ion volatilization, guaranteeing a high degree of consistency between the chemical composition of the final product and the designed formulation, with minimal batch-to-batch performance fluctuations. Further benefiting from the high reactivity resulting from the molecular-level uniform mixing of the sol-gel method and the high-viscosity flow characteristics of the precursor in the one-step method, the method provided by this invention can lower the melting temperature for preparing NAS microcrystalline glass powder by 100-200 °C compared to the traditional sol-gel method, and by approximately 600-700 °C compared to the melting method, while achieving a glassy density close to the theoretical density, meeting the requirements for low-temperature co-firing.
[0019] The preparation method provided by this invention has simple steps, significantly shortens the production cycle, uses a low melting temperature, reduces overall energy consumption, conforms to the development direction of green manufacturing, and significantly reduces raw material costs compared with the traditional sol-gel method. It also effectively solves the problems of existing sol-gel methods in obtaining high-density, high-crystallinity NAS microcrystalline glass, as well as the problems of component inhomogeneity and volatilization loss in existing high-temperature melting methods. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the preparation process of NAS microcrystalline glass powder in an embodiment of the present invention.
[0021] Figure 2 The images show the XRD patterns of the NAS microcrystalline glass powders prepared in Examples 1 and 2.
[0022] Figure 3 The image shows the XRD pattern of the NAS glass powder prepared in Comparative Example 1.
[0023] Figure 4 The images shown are TEM images and energy dispersive spectroscopy (EDS) images of the NAS microcrystalline glass powder prepared in Example 1. (a) is a TEM image and an EDS image of the boxed region therein, and (b) is an enlarged view of the boxed region in (a). Detailed Implementation
[0024] This invention provides a NAS microcrystalline glass powder and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining this invention and are not intended to limit this invention.
[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0026] This invention provides a method for preparing NAS microcrystalline glass powder, wherein, as shown in the embodiments of the present invention... Figure 1 As shown, it includes the following steps: S1. A sol is provided, which is prepared by the following components in parts by weight: 12-15 parts aluminum silicate, 7-9 parts NaOH, 60-70 parts water, 1.0-5.8 parts nano-vaporized SiO2 and 1-1.3 parts TiO2; S2. After drying the sol, a dry gel is obtained; S3. The dry gel is heated to 750-850 °C at a heating rate of 3-5 °C / min and held at that temperature for 0.5-1 h. After cooling to room temperature, NAS microcrystalline glass block is obtained. S4. The NAS microcrystalline glass block is crushed and ball-milled to obtain the NAS microcrystalline glass powder.
[0027] In this invention, gelation is achieved during the sol drying process to form a wet gel, which continues to form a dry gel as drying progresses. Then, a one-step sintering and recrystallization process is employed, allowing the dry gel to undergo three stages—"inorganic decomposition and expulsion," "amorphous network condensation and densification melting sintering," and "crystal nucleation and growth"—in a sequential and natural transition at a lower temperature. Before large-scale crystal nucleation, a "melting window" with optimal viscous flowability is created for the amorphous NAS precursor. Driven by surface energy, the particles undergo significant viscous flow, rapidly filling pores and achieving rapid densification of the main structure. During the subsequent cooling process, guided by uniformly distributed nucleation sites (provided by a nucleating agent), the target crystalline phase precipitates uniformly from the already densified glass matrix under the action of the nucleating agent (i.e., "recrystallization"). This invention employs a sol-gel combined low-temperature sintering and recrystallization process. This method utilizes low melting temperatures, low energy consumption, simple steps, and high efficiency. The resulting NAS microcrystalline glass exhibits uniform composition, high density and crystallinity, high mechanical strength, and low coefficient of thermal expansion, dielectric constant, and dielectric loss. It can be applied in fields such as electronic packaging, ceramic bonding, melting aids, composite material matrices, and low-temperature co-fired ceramics. This invention effectively solves the problems of existing sol-gel methods in obtaining highly dense and highly crystallinous NAS microcrystalline glass, as well as the problems of component inhomogeneity and volatilization loss inherent in existing high-temperature melting methods.
[0028] In this embodiment, aluminum silicate and NaOH provide the core components of NAS glass-ceramic powder. Furthermore, the sol prepared by the reaction of aluminum silicate and NaOH requires a lower temperature and can significantly shorten the reaction time. Nano-vaporized SiO2, on the one hand, readily reacts with alkaline solutions due to its high specific surface area and amorphous state; on the other hand, its content can be adjusted to control the melting temperature of the glass-ceramic.
[0029] Specifically, this invention employs a sol-gel method combined with a one-step sintering-recrystallization process to prepare low-melting-point NAS microcrystalline glass powder, resolving the temporal contradiction between densification and crystallization. Through precursor formulation design and optimized heat treatment regime, inorganic matter in the precursor is gently removed in the mid-temperature range (approximately 300-400 °C) during the programmed temperature rise heat treatment process, while simultaneously forming a highly active amorphous NAS transition phase rich in mesopores but with moderate skeletal strength. Within this temperature range, particles undergo significant viscous flow driven by surface energy, rapidly filling pores and achieving rapid densification of the main structure. Subsequently, when the temperature rises to a specific crystallization range, densification is essentially complete. Then, during cooling, guided by uniformly distributed nucleation sites (provided by the gel network's own structure), the target crystalline phase precipitates uniformly from the already densified glass matrix (i.e., "recrystallization"). This "densification first, crystallization later" sequence successfully avoids the premature formation of crystals hindering densification. Furthermore, the recrystallization mode ensures that the crystallization process takes place in a dense, chemically homogeneous matrix, thereby obtaining an ideal microstructure with high crystallinity and small, uniform grain size (nanometer to submicron). This results in the NAS microcrystalline glass prepared by this invention having high mechanical strength, low coefficient of thermal expansion, low dielectric constant, and low dielectric loss, which can be applied to fields such as electronic packaging, ceramic bonding, melting aids, composite material matrices, and low-temperature co-fired ceramics.
[0030] Furthermore, in this embodiment of the invention, the molecular-level mixing nature of the sol-gel, combined with the low melting temperature in the one-step sintering method, ensures uniform composition and prevents sodium ions from volatilizing, guaranteeing that the chemical composition of the final product is highly consistent with the designed formulation, with minimal batch-to-batch performance fluctuations. Further benefiting from the high reactivity resulting from the molecular-level uniform mixing of the sol-gel method and the high-viscosity flow characteristics of the precursor in the one-step method, the melting temperature used in preparing NAS microcrystalline glass powder using the method provided in this embodiment of the invention can be reduced by 100-200 °C compared to the traditional sol-gel method, and by approximately 600-700 °C compared to the melting method, while achieving a glass body with near-theoretical density, meeting the requirements for low-temperature co-firing.
[0031] In step S1, in some embodiments, the method for preparing the sol includes the following steps: NaOH, aluminum silicate, and nano-vaporized SiO2 are mixed and stirred at a preset temperature for a first preset time. TiO2 is then added, and stirring continues at the preset temperature for a second preset time.
[0032] In some embodiments, the preset temperature is 75~90℃ (e.g., 75℃, 80℃, 85℃ or 90℃, etc.), the first preset time is 2~7 h (e.g., 2 h, 3 h, 4 h, 5 h, 6 h or 7 h, etc.), and the second preset time is 0.5~1 h (e.g., 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h or 1 h, etc.).
[0033] In some embodiments, the specific surface area of the nano-vaporized SiO2 is 400~800 m². 2 / g (for example, it can be 400 m) 2 / g、450 m 2 / g、500 m 2 / g、550 m 2 / g、600 m 2 / g、650 m 2 / g、700 m 2 / g、750 m 2 / g or 800 m 2 / g etc.). Such a specific surface area is more conducive to the reaction of nano-gas phase SiO2 with alkaline solution.
[0034] In some embodiments, the TiO2 is in the rutile crystal form. Rutile TiO2 is more stable at high temperatures, serving as nucleation sites for glass-ceramics and crystallizing to ultimately obtain a nanoscale microcrystalline phase.
[0035] In step S2, in some embodiments, the drying temperature is 100~150℃ (e.g., 100℃, 110℃, 120℃, 130℃, 140℃ or 150℃, etc.).
[0036] In step S3, in some embodiments, the dry gel is heated to 800-850°C at a heating rate of 3-5°C / min and held at that temperature for 0.5-1 h.
[0037] This invention also provides a NAS microcrystalline glass powder, which is prepared using the preparation method described above.
[0038] The NAS microcrystalline glass powder provided in this embodiment has high mechanical strength, low coefficient of thermal expansion, low dielectric constant and dielectric loss, and can be applied to fields such as electronic packaging, ceramic bonding, melting aid, composite matrix, and low temperature co-fired ceramics.
[0039] The present invention will be further described below through specific embodiments.
[0040] Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.
[0041] In the following embodiments, the specific surface area of the nano-vaporized SiO2 used is 600 m². 2 / g, all TiO2 used is rutile TiO2.
[0042] Example 1 This embodiment provides a method for preparing NAS microcrystalline glass powder, which includes the following steps by weight: Dissolve 7.2 parts of NaOH in 60 parts of deionized water to obtain a NaOH solution.
[0043] 12.78 parts of aluminum silicate powder (chemical formula 3Al2O3·2SiO2) and 1.6 parts of nano-vaporized SiO2 powder were slowly added to the above NaOH solution and dispersed evenly to obtain a stable suspension solution. Then, the solution was heated in a water bath at 80 °C and magnetically stirred for 6.5 h to obtain a light yellow sol.
[0044] Add 1.0 part of TiO2 powder to the above light yellow sol, and continue to stir magnetically for 0.5 h under water bath heating at 80 ℃ to obtain a uniform sol.
[0045] The obtained homogeneous sol was dried completely at 120 °C, then heated to 800 °C at a heating rate of 5 °C / min and held at that temperature for 1 h (until completely melted), and then naturally cooled to room temperature (recrystallization occurred during cooling) to obtain NAS microcrystalline glass bulk material. The above-mentioned microcrystalline glass blocks were crushed and ball-milled to obtain NAS microcrystalline glass powder with a particle size D. 50 It is 14 μm.
[0046] Example 2 This embodiment provides a method for preparing NAS microcrystalline glass powder, which includes the following steps by weight: Dissolve 7.2 parts of NaOH in 60 parts of deionized water to obtain a NaOH solution.
[0047] 12.78 parts of aluminum silicate powder and 5.0 parts of nano-vaporized SiO2 powder were slowly added to the above NaOH solution and dispersed evenly to obtain a stable suspension solution. Then, the solution was heated in a water bath at 85 °C and magnetically stirred for 7 h to obtain a light yellow sol.
[0048] Add 1.25 parts of TiO2 powder to the above light yellow sol, and continue to stir magnetically for 0.5 h under water bath heating at 85 ℃ to obtain a uniform sol.
[0049] The obtained homogeneous sol was dried completely at 105 °C, then heated to 850 °C at a heating rate of 5 °C / min and held at that temperature for 1 h (until completely melted), and then naturally cooled to room temperature (recrystallization occurred during cooling) to obtain NAS microcrystalline glass bulk.
[0050] The above-mentioned microcrystalline glass block was crushed and ball-milled to obtain NAS microcrystalline glass powder.
[0051] Example 3 This embodiment provides a method for preparing NAS microcrystalline glass powder, which includes the following steps by weight: Dissolve 7.2 parts of NaOH in 60 parts of deionized water to obtain a NaOH solution.
[0052] 12.78 parts of aluminum silicate powder and 3.0 parts of nano-vaporized SiO2 powder were slowly added to NaOH solution and dispersed evenly to obtain a stable suspension solution. Then, the solution was heated in a water bath at 90 °C and magnetically stirred for 2 h to obtain a light yellow sol.
[0053] Add 1.2 parts of TiO2 powder to the above light yellow sol, and continue to stir magnetically for 0.5 h under water bath heating at 90 ℃ to obtain a uniform sol.
[0054] The obtained homogeneous sol was dried completely at 110 °C, then heated to 850 °C at a heating rate of 5 °C / min and held at that temperature for 1 h (until completely melted), and then naturally cooled to room temperature (recrystallization occurred during cooling) to obtain NAS microcrystalline glass bulk material. The above-mentioned microcrystalline glass block was crushed and ball-milled to obtain NAS microcrystalline glass powder.
[0055] Example 4 This embodiment provides a method for preparing NAS microcrystalline glass powder, which includes the following steps by weight: Dissolve 7.2 parts of NaOH in 60 parts of deionized water to obtain a NaOH solution.
[0056] 12.78 parts of aluminum silicate powder and 1.0 parts of nano-vaporized SiO2 powder were slowly added to the above NaOH solution and dispersed evenly to obtain a stable suspension slurry. Then, the slurry was heated in a water bath at 75 °C and magnetically stirred for 6 h to obtain a light yellow sol.
[0057] Add 1.0 part of TiO2 powder to the above light yellow sol, and continue to stir magnetically for 0.5 h under water bath heating at 75 ℃ to obtain a uniform sol.
[0058] The obtained homogeneous sol was dried completely at 150 °C, then heated to 800 °C at a heating rate of 5 °C / min and held at that temperature for 1 h (until completely melted), and then naturally cooled to room temperature (recrystallization occurred during cooling) to obtain NAS microcrystalline glass bulk material. The above-mentioned microcrystalline glass block was crushed and ball-milled to obtain NAS microcrystalline glass powder.
[0059] Comparative Example 1 This comparative example provides a method for preparing NAS glass powder, which, by mass, includes the following steps: Dissolve 7.2 parts of NaOH in 60 parts of deionized water to obtain a NaOH solution.
[0060] 12.78 parts of aluminum silicate powder and 1.6 parts of nano-vaporized SiO2 powder were slowly added to the above NaOH solution and dispersed evenly to obtain a stable suspension solution. Then, the solution was heated in a water bath at 80 °C and magnetically stirred for 6.5 h to obtain a light yellow sol.
[0061] The obtained pale yellow sol was dried completely at 120 °C, then heated to 850 °C at a heating rate of 5 °C / min and held at that temperature for 1 h (until completely melted), and then naturally cooled to room temperature to obtain NAS glass block.
[0062] The above-mentioned NAS glass block was crushed and ball-milled to obtain NAS glass powder.
[0063] In addition, the obtained pale yellow sol was dried completely at 120 °C, then heated to 1000 °C at a heating rate of 5 °C / min and held at that temperature for 1 h (until it was completely melted), and then naturally cooled to room temperature to obtain NAS glass block; The above-mentioned NAS glass block was crushed and ball-milled to obtain NAS glass powder.
[0064] test: (1) X-ray diffraction (XRD) tests were performed on the NAS microcrystalline glass powders prepared in Examples 1 and 2. The results are as follows: Figure 2 As shown. XRD tests were performed on the NAS glass powder prepared in Comparative Example 1, and the results are as follows. Figure 3 As shown.
[0065] Depend on Figure 2It can be seen that the NAS microcrystalline glass powder prepared in Example 1 mainly consists of the nepheline phase and a small amount of Na2Al2SiO6 phase, and the matrix is an amorphous glassy state, indicating the formation of a microcrystalline glass structure. The XRD pattern of the NAS microcrystalline glass powder prepared in Example 2 (sintered at 850 °C) is similar to that of the NAS microcrystalline glass powder prepared in Example 1 (sintered at 800 °C), with no other phases generated. However, the diffraction peaks become sharper and the full width at half maximum (FWHM) decreases, indicating that the NAS microcrystalline glass powder prepared by sintering at 850 °C has better crystallinity than that prepared by sintering at 800 °C.
[0066] In addition, Figure 2 The absence of rutile phase diffraction peaks indicates both its low content and that TiO2 has acted as a nucleating agent for the glass. The sol-gel mixture, with the addition of the nucleating agent, can form glass-ceramics at low temperatures. Compared to the melting method, this significantly lowers the formation temperature of glass-ceramics and greatly reduces the compositional inhomogeneity caused by high-temperature Na ion volatilization. Furthermore, compared to the traditional sol-gel method, only a single sintering process is required to achieve recrystallization.
[0067] Depend on Figure 3 It can be seen that the XRD pattern of the NAS glass powder prepared in Comparative Example 1 (without the addition of TiO2 powder during preparation) mainly shows broadened diffraction peaks, and the matrix is an amorphous glass, without the formation of microcrystalline glass. This indicates that TiO2, as a nucleating agent, has a good nucleation effect, and microcrystalline glass cannot be formed without the addition of TiO2.
[0068] (2) The NAS microcrystalline glass powder prepared in Example 1 was subjected to transmission electron microscopy and energy dispersive spectroscopy tests, and the results are as follows: Figure 4 As shown, a large number of nanocrystals are dispersed in the amorphous glass matrix, with an average particle size of approximately 3 nm. The main components of the nanocrystals are Na, Al, O, and Si, the same as the nepheline phase, and a small amount of Ti is also present. This indicates that during the phase separation stage of the glass-ceramic formation process, the nepheline phase and a small amount of Na₂Al₂SiO₆ nucleate and grow on the surface of the TiO₂ nucleating agent. Combined with the above XRD analysis results, it can be seen that the glass-ceramic has a high content of nanocrystalline phase (i.e., high crystallinity).
[0069] (3) The NAS microcrystalline glass blocks prepared in Examples 1-4 were tested for bending strength, coefficient of thermal expansion, average dielectric constant (tested by waveguide method) in X band (8.2~12.4 GHz) and dielectric loss. The results are shown in Table 1.
[0070] Table 1. Test results of NAS microcrystalline glass blocks in Examples 1-4
[0071] As can be seen, the NAS microcrystalline glass powder prepared in the embodiments of the present invention has high flexural strength, low coefficient of thermal expansion, low dielectric constant and low dielectric loss.
[0072] In summary, this invention provides a NAS microcrystalline glass powder and its preparation method. This invention employs a sol-gel method combined with a one-step sintering-recrystallization process to prepare low-melting-point NAS microcrystalline glass powder, resolving the temporal contradiction between densification and crystallization. Specifically, through precursor formulation design and optimized heat treatment regime, it ensures that inorganic matter in the precursor is gently removed in the mid-temperature range (approximately 300-400 °C) during the programmed temperature rise heat treatment process, while simultaneously forming a highly active amorphous NAS transition phase rich in mesopores but with moderate skeletal strength. Within this temperature range, particles undergo significant viscous flow driven by surface energy, rapidly filling pores and achieving rapid densification of the main structure. Subsequently, when the temperature rises to a specific crystallization range, densification is essentially complete. Then, during cooling, guided by uniformly distributed nucleation sites (provided by the gel network's own structure), the target crystalline phase precipitates uniformly from the already densified glass matrix (i.e., "recrystallization"). This "densification first, crystallization later" sequence successfully avoids the premature formation of crystals hindering densification. Furthermore, the recrystallization mode ensures that the crystallization process takes place in a dense, chemically homogeneous matrix, thereby obtaining an ideal microstructure with high crystallinity and small, uniform grain size (nanometer to submicron). This results in the NAS microcrystalline glass prepared by this invention having high mechanical strength, low coefficient of thermal expansion, low dielectric constant, and low dielectric loss, which can be applied to fields such as electronic packaging, ceramic bonding, melting aids, composite material matrices, and low-temperature co-fired ceramics.
[0073] Furthermore, the molecular-level mixing of the sol-gel in this invention, combined with the low melting temperature of the one-step sintering method, ensures uniform composition and prevents sodium ion volatilization, guaranteeing a high degree of consistency between the chemical composition of the final product and the designed formulation, with minimal batch-to-batch performance fluctuations. Further benefiting from the high reactivity resulting from the molecular-level uniform mixing of the sol-gel method and the high-viscosity flow characteristics of the precursor in the one-step method, the method provided by this invention can lower the melting temperature for preparing NAS microcrystalline glass powder by 100-200 °C compared to the traditional sol-gel method, and by approximately 600-700 °C compared to the melting method, while achieving a glassy density close to the theoretical density, meeting the requirements for low-temperature co-firing.
[0074] The preparation method provided by this invention has simple steps, significantly shortens the production cycle, uses a low melting temperature, reduces overall energy consumption, conforms to the development direction of green manufacturing, and significantly reduces raw material costs compared with the traditional sol-gel method. It also effectively solves the problems of existing sol-gel methods in obtaining high-density, high-crystallinity NAS microcrystalline glass, as well as the problems of component inhomogeneity and volatilization loss in existing high-temperature melting methods.
[0075] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.
Claims
1. A method for preparing NAS microcrystalline glass powder, characterized in that, Includes the following steps: A sol is provided, which is prepared by means of the following components in parts by weight: 12-15 parts aluminum silicate, 7-9 parts NaOH, 60-70 parts water, 1.0-5.8 parts nano-vaporized SiO2 and 1-1.3 parts TiO2; The sol was dried to obtain a dry gel; The dry gel was heated to 750-850 °C at a heating rate of 3-5 °C / min and held at that temperature for 0.5-1 h. After cooling to room temperature, NAS microcrystalline glass block was obtained. The NAS microcrystalline glass block is crushed and ball-milled to obtain the NAS microcrystalline glass powder.
2. The preparation method according to claim 1, characterized in that, The method for preparing the sol includes the following steps: NaOH, aluminum silicate, and nano-vaporized SiO2 are mixed and stirred at a preset temperature for a first preset time. TiO2 is then added, and stirring continues at the preset temperature for a second preset time.
3. The preparation method according to claim 2, characterized in that, The preset temperature is 75~90 ℃, the first preset time is 2~7 h, and the second preset time is 0.5~1 h.
4. The preparation method according to claim 1, characterized in that, The drying temperature is 100~150℃.
5. The preparation method according to claim 1, characterized in that, The specific surface area of the nano-vaporized SiO2 is 400~800 m². 2 / g.
6. The preparation method according to claim 1, characterized in that, The TiO2 has a rutile crystal form.
7. The preparation method according to claim 1, characterized in that, The dry gel was heated to 800-850 °C at a heating rate of 3-5 °C / min and held at that temperature for 0.5-1 h.
8. A NAS microcrystalline glass powder, characterized in that, It is prepared by the preparation method according to any one of claims 1-7.
9. The NAS microcrystalline glass powder according to claim 8, characterized in that, The crystalline phases of the NAS microcrystalline glass powder include sodium nepheline and Na2Al2SiO6.