A microcrystalline glass, a preparation method thereof and application thereof

Abstract

The application discloses a low-cost lithium-free microcrystalline glass and a preparation method and application thereof, and belongs to the technical field of electronic cover plate materials. The microcrystalline glass takes pre-melted micro-powder of sodium feldspar 69-75% and in-situ synthesized micro-powder of calcium feldspar as main raw materials, is supplemented with a ZrO2 / TiO2 composite crystal nucleus agent 2.1-4.5%, and a small amount of MgO, CaO and K2O performance adjusting groups. The microcrystalline glass is obtained by two-stage melting at 1430-1480 DEG C in a weak reduction-neutral atmosphere, overflow down-draw forming, gradient annealing, two-stage crystallization at 650 DEG C nucleation and 735-770 DEG C crystallization, and K + / Na + ion exchange strengthening, and has high transmittance, high surface compressive stress, high hardness and excellent drop resistance. The application discards lithium resources and high-purity alumina, reduces raw material cost and energy consumption, and is suitable for electronic device cover plates such as smart phones.

Description

Technical Field

[0001] This invention relates to the field of glass technology, and in particular to a microcrystalline glass, its preparation method, and its application. Background Technology

[0002] Glass-ceramics, also known as glass-ceramics, are multiphase composite materials formed by controlling the precipitation of a large number of uniformly distributed micron or nano-sized crystals in glass under specific heat treatment conditions. They combine the amorphous structure of traditional glass with the polycrystalline properties of ceramics, exhibiting advantages in mechanical properties, thermal stability, chemical corrosion resistance, and optical transmittance. Therefore, they are widely used in architectural decoration, electronic displays, aerospace, medical devices, and high-end consumer electronics.

[0003] Traditional glass-ceramics are typically manufactured using high-purity chemical raw materials such as alumina, sodium carbonate, silicon dioxide, and soda ash as basic components. However, these raw materials are not only expensive, but also require melting at temperatures of 1500-1600℃ or even higher due to the high melting points of alumina and silicon dioxide. This results in enormous energy consumption throughout the melting process, hindering the large-scale industrial production and cost control of glass-ceramics.

[0004] With the rapid development of the electronics and information industry, the demand for high-performance cover glass for terminal devices such as smartphones, tablets, and laptops continues to grow. Currently, the mainstream cover glass system is lithium aluminum silicate microcrystalline glass, whose excellent drop resistance, surface hardness, and optical transparency make it the preferred material for high-end electronic products. However, in recent years, driven by industries such as new energy vehicle power batteries, the price of lithium resources has risen sharply, directly increasing the raw material cost of lithium-containing microcrystalline glass, further compressing profit margins and affecting supply chain security. Dependence on lithium resources also makes the supply chain vulnerable to market price fluctuations, making it difficult to meet the demand for low-cost, sustainable industrialization.

[0005] In existing technologies, to improve the mechanical properties and thermal stability of glass-ceramics, high alumina content is often used to precipitate reinforcing crystalline phases such as nepheline or spodumene. Chinese invention patent application CN115893851A discloses a glass-ceramic for electronic cover plates, which prepares a homogeneous glass melt by high-temperature melting at 1550-1630℃. However, this technical solution has significant drawbacks. The high melting temperature of 1550-1630℃ not only increases energy consumption and carbon emissions but also imposes stringent requirements on the refractory materials of the melting furnace, hindering the large-scale production and green manufacturing transformation of glass-ceramics.

[0006] Against this backdrop, it is particularly urgent to develop a new type of microcrystalline glass system that can meet the requirements of electronic cover glass for high transmittance, high strength, good thermal stability and processing performance, while effectively reducing raw material costs and energy consumption. Summary of the Invention

[0007] (a) Technical problems to be solved In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a low-cost lithium-free microcrystalline glass based on natural feldspar minerals and its preparation method, which solves the technical problems of high raw material cost, excessively high melting temperature, high energy consumption, and difficulty in large-scale application of traditional lithium aluminum silicon microcrystalline glass due to its reliance on high-purity chemical raw materials and lithium resources.

[0008] (II) Technical Solution To achieve the above objectives, the main technical solutions adopted by the present invention include: 1. A microcrystalline glass, characterized in that it comprises the following components, each component being a percentage by weight of the total mass of the raw materials: the first component is the main raw material micro powder, the second component is a composite nucleating agent, and the third component is a performance regulating component; wherein the main raw material micro powder accounts for 91% to 97% by weight, and the main raw material micro powder is composed of pre-melted albite micro powder and synthetic calcium feldspar micro powder, wherein the albite micro powder accounts for 69% to 75% of the total mass of the raw materials, and the remainder is calcium feldspar micro powder; The composite nucleating agent is composed of ZrO2 and TiO2, wherein ZrO2 accounts for 2% to 4% of the total mass of the raw materials and TiO2 accounts for 0.1% to 0.5%. The performance-adjusting component has a weight percentage of 0% to 9% and is selected from one or more of MgO 0% to 5%, CaO 0% to 3% and K2O 0% to 1%.

[0009] In some embodiments, the mass percentage of the albite micro powder is: 10%–28% Al2O3, 5%–14.8% Na2O, with the remainder being SiO2 and unavoidable trace impurities; the impurities include, but are not limited to, at least one of Fe2O3, K2O, CaO, MgO and TiO2, and the total content of the impurities does not exceed 3%; the particle size of the albite micro powder is ≤20μm.

[0010] In some embodiments, the method for preparing anorthite micro powder is characterized by comprising the following steps: Step S1: Prepare the ingredients according to the stoichiometric ratio of calcium feldspar CaO·Al2O3·2SiO2, with a molar ratio of CaO:Al2O3:SiO2=1:1:2. The alumina source is industrial aluminum hydroxide, the calcium source is industrial calcium carbonate, and the silicon source is kaolin. Step S2: Mix the industrial aluminum hydroxide, calcium carbonate and kaolin and ball mill them to obtain a mixture; Step S3: After the mixture is formed, it is dried by keeping it at 60-65℃ for 5-7 hours and then at 100-110℃ for 24-28 hours. Step S4: Calcine the mixture at 1200°C to 1250°C for 2 to 4 hours to obtain the sintered product; Step S5: The sintered product is crushed, ball-milled or air-jet pulverized, and sieved to obtain anorthite powder with a particle size of 1-50 μm.

[0011] Secondly, this application provides a method for preparing the microcrystalline glass as described above, characterized by comprising the following steps: Step 1: Pre-calcining unmelted albite micro powder with a particle size ≤20μm at 1100℃~1200℃ in air atmosphere for 2~4 hours to obtain pre-melted albite micro powder; Step 2: Mix ZrO2 and TiO2 according to the target ratio using high-energy ball milling or air jet milling for 2-4 hours to obtain a uniformly dispersed composite nucleating agent powder; wherein ZrO2 accounts for 2% to 4% of the total mass of the raw materials, and TiO2 accounts for 0.1% to 0.5%; Step 3: According to the proportions described in claim 1, place the pre-molten sodium feldspar powder, synthetic calcium feldspar powder, pre-dispersed composite nucleating agent and performance regulating components in a mixer and mix for 30-60 minutes under an inert atmosphere to obtain a highly uniform batch. Step 4: Add the batch material to the platinum crucible and perform preliminary melting under a weak reducing atmosphere. Then switch to a neutral atmosphere to complete high-temperature melting and clarification to obtain a homogeneous glass melt without bubbles or streaks.

[0012] Step 5: The molten glass is formed into a plate-shaped precursor using the overflow and downward drawing method, and then subjected to gradient annealing. The gradient annealing includes holding the glass near the glass transition temperature to eliminate rapid cooling stress, followed by slow cooling and holding again to further relax internal stress, and finally obtaining a precursor glass with low residual stress.

[0013] Step 6: Perform a two-stage gradient crystallization treatment on the precursor glass.

[0014] In some embodiments, step 6 is further included to perform a two-stage gradient crystallization process on the precursor glass, specifically including a first-stage nucleation and a second-stage crystallization. The first stage of nucleation involves holding the temperature at 650±5℃ for 1.5-2.5 hours; the second stage of crystallization involves raising the temperature to 735-770℃ at a rate of 2.4-3℃ / min, holding the temperature for 3-5 hours, and then naturally cooling to obtain the microcrystalline glass.

[0015] In some embodiments, the method further includes step 7, ion strengthening; the ion strengthening conditions are to immerse the microcrystalline glass in a KNO3-NaNO3 mixed molten salt at 410-450°C for ion exchange for 4-6 hours, wherein the molar ratio of KNO3 to NaNO3 in the mixed molten salt is 7-7.5:2.5-3.

[0016] In some embodiments, in step 4, the weak reducing atmosphere is a mixture of N2 and CO with a volume ratio of N2:CO = 95-97:3-5; the neutral atmosphere is high-purity N2.

[0017] In some embodiments, in step 4, under a weak reducing atmosphere, the temperature is increased to 1300-1350°C at a rate of 5-8°C / min and held for 2-3 hours to allow the main material to be fully pre-melted and to remove structural water and carbonate decomposition gases; then, the temperature is switched to a neutral atmosphere and the temperature is increased to 1430-1480°C and held for melting for 3-5 hours to promote the formation and homogenization of the glass network; then, the temperature is lowered to 1420-1450°C and clarified for 1.5-2.5 hours to obtain a homogeneous glass melt without bubbles or streaks.

[0018] In some embodiments, in step 5, gradient annealing involves holding at 580±20°C for 1 hour to eliminate rapid cooling stress, then slowly cooling at a rate of 2-4°C / min to 500-550°C, and holding at this temperature range for 3-4 hours before furnace cooling.

[0019] Thirdly, this application provides an electronic device cover, characterized in that it is made of the aforementioned microcrystalline glass.

[0020] (III) Beneficial Effects This invention eliminates the expensive chemical raw materials such as lithium carbonate and high-purity alumina required in traditional lithium-aluminum-silicon systems. Instead, it primarily uses natural sodium feldspar powder, supplemented by anorthite powder synthesized in situ from industrial aluminum hydroxide, calcium carbonate, and kaolin as the main component. Although industrial aluminum hydroxide is used as the aluminum source in the anorthite synthesis process, its cost is far lower than that of high-purity alumina, and most of the alumina actually comes from natural sodium feldspar minerals. This reduces raw material procurement costs and avoids supply chain risks caused by fluctuations in lithium resource prices, meeting the urgent needs of the electronic materials industry for low-cost and sustainable development.

[0021] Thanks to the eutectic properties of sodium feldspar and calcium feldspar, and the fluxing effect of the internal alkali / alkaline earth metal oxides, this invention controls the glass melting temperature at 1430-1480℃, which is about 100-150℃ lower than that of traditional lithium-containing microcrystalline glass. This reduces energy consumption and carbon emissions, lessens the erosion of the furnace refractory materials, extends equipment life, and provides support for green and low-carbon manufacturing.

[0022] By using a composite nucleating agent composed of ZrO2 and TiO2, combined with a two-stage gradient crystallization treatment, a uniform and fine microcrystalline phase is induced, resulting in a glass-ceramic material that possesses high hardness, good bending strength, and excellent thermal stability. Simultaneously, a gradient annealing process effectively eliminates internal stress, yielding a plate-like precursor with low warpage and high flatness, meeting the dimensional accuracy requirements of electronic cover plates.

[0023] The raw materials used are all common industrial minerals or chemicals. The preparation process, including pre-firing, mixing, melting, molding, annealing, crystallization, and ion exchange, is carried out using existing electronic glass production lines without the need for special equipment modifications. It has good scale-up potential and economic benefits.

[0024] In summary, this invention, without relying on lithium resources and significantly reducing the use of high-purity alumina, has successfully developed a low-cost, low-energy-consumption, and high-performance lithium-free microcrystalline glass through mineral raw material compounding and process innovation. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 These are scanning electron microscope images of the microcrystalline glass prepared in Examples 1-3 of the present invention, wherein R01, R02, and R03 correspond to Examples 1, 2, and 3, respectively.

[0027] Figure 2 The diffraction pattern of the glass-ceramic before crystallization; Figure 3 The diffraction pattern of the microcrystalline glass after crystallization is shown. Figure 4 DTA analysis charts for microcrystalline glass with different ratios. Detailed Implementation

[0028] The embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application. This application can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0029] These embodiments are provided to make the application thorough and complete, and to fully express the scope of the application to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​illustrated in these embodiments should be interpreted as merely exemplary and not as limiting.

[0030] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0031] In this application, percentages unless otherwise specified refer to mass percentages.

[0032] The combination of albite and calcium feldspar is not a simple mixing process. Instead, it leverages the inherent eutectic properties of the minerals and the fluxing effect of alkali / alkaline earth metal oxides to effectively lower the overall melting temperature to 1430-1480℃, superior to the 1550-1630℃ required by traditional lithium-containing systems. Albite provides stable network-forming ability and a moderate coefficient of thermal expansion, while calcium feldspar enhances structural density and chemical stability. At high temperatures, they form a calcium-albite solid solution crystal phase (as shown in the XRD pattern), which not only improves mechanical strength but also ensures high visible light transmittance.

[0033] Pre-dispersion of composite nucleating agents via high-energy ball milling is a key process step for achieving uniform crystallization. If ZrO2 and TiO2 are directly dry-mixed in their original powder form, they are difficult to distribute uniformly in the glass matrix, resulting in excessively high or low local nucleus concentrations. This leads to coarse grains, uneven distribution, and even microcracks, affecting strength and optical properties. However, after pre-dispersion via high-energy ball milling, the nucleating agent particles are refined and highly dispersed, providing numerous uniform nucleation sites for subsequent two-stage crystallization. This results in small, densely distributed crystallites, ultimately yielding materials with high hardness, high fracture toughness, and good impact resistance.

[0034] The matching of the two-stage gradient crystallization regime with the gradient annealing process further unlocks the material's potential. The first stage of low-temperature nucleation ensures that crystal nuclei are fully formed without growing, while the second stage of heated crystallization promotes orderly crystal growth and avoids stress concentration caused by non-uniform crystallization.

[0035] Gradient annealing effectively relaxes the rapid cooling stress generated during the overflow pull-down molding process, providing a precursor with low residual stress for subsequent crystallization, which ensures the flatness and dimensional stability of the electronic cover plate.

[0036] The switching between weak reducing and neutral atmospheres in melting, along with auxiliary processes such as ion strengthening, collectively constitute a complete technological chain for high-performance glass-ceramics. A weak reducing atmosphere helps remove structural water and carbonate decomposition gases from the raw materials, preventing bubble formation; a neutral atmosphere ensures the clarity and homogenization of the molten glass. K / Na ion exchange forms a compressive stress layer on the surface, improving bending strength and impact resistance. Example 1 This embodiment prepares a low-cost lithium-free microcrystalline glass, specifically including the following steps: Step 1: Commercially available sodium feldspar micro powder with an average particle size of 15μm (tested to contain 19.3% Al2O3, 10.61% Na2O, total impurities ≤2%, and the remainder being SiO2) is pre-calcined in air at 1100℃ for 2 hours to obtain pre-molten sodium feldspar micro powder.

[0037] Step 2: Weigh industrial calcium carbonate, aluminum hydroxide, and kaolin according to the stoichiometric ratio of calcium feldspar (molar ratio CaO:Al2O3:SiO2=1:1:2). Add the raw materials to a planetary ball mill and ball mill at 300 rpm for 4 hours to obtain a uniform slurry. After preliminary drying at 60℃ for 5 hours, transfer the slurry to a 100℃ oven for 24 hours to dry completely. Press the dried mixture into 50mm cylindrical blanks and calcine them at 1200℃ in air atmosphere for 2 hours at a heating rate of 5℃ / min. After coarse crushing with a jaw crusher, use an air jet mill with a feed pressure of 0.7MPa and a classifying wheel speed of 8000 rpm for ultrafine grinding. Finally, pass the material through a 325-mesh standard sieve with a pore size of 45μm, collect the undersize material, and determine the average particle size D using a laser particle size analyzer. 50 =22μm, to obtain synthetic calcium feldspar micro powder.

[0038] 2.0 wt% ZrO2 and 0.1% TiO2 by total mass percentage were loaded into a zirconia ball mill jar, and zirconia grinding balls (ball-to-material mass ratio of 15:1) were added. After sealing, the jar was evacuated to 9.7 Pa, and then filled with high-purity argon gas to atmospheric pressure. This evacuation and filling process was repeated 3 times to replace the air. Subsequently, the jar was ball-milled in a planetary ball mill at 400 rpm for 3 hours to obtain a uniformly dispersed composite nucleating agent powder.

[0039] Step 3: 69.5% pre-melted sodium feldspar powder, 27% synthetic calcium feldspar powder, the above-mentioned composite nucleating agent powder, 0.8% MgO, 0.5% CaO, and 0.1% K2O are ball-milled and mixed for 40 minutes under argon protection.

[0040] Step 4: Add the batch material to a platinum crucible, introduce a N2:CO = 97:3 mixed gas, heat to 1300℃ at 6℃ / min and hold for 2 hours; switch to high-purity N2, continue heating to 1430℃ to melt for 3 hours, and clarify at 1420℃ for 1.5 hours to obtain a homogeneous glass melt.

[0041] Step 5: The clarified molten glass is slowly cooled to 1180°C at a rate of 1°C / min and held at this temperature for 45 minutes for homogenization. Then, the molten glass is stably introduced into the overflow tank through a platinum flow pipe. The molten glass is injected into the platinum overflow tank and formed into a 1.0mm thick plate at 1180°C using the overflow pull-down method at a pull-down rate of 4m / h. Immediately after forming, it is placed in an annealing furnace and held at 580°C for 1 hour, then slowly cooled to 500°C at a rate of 3°C / min and held at this temperature for 3 hours before being cooled in the furnace to obtain low-stress precursor glass.

[0042] Step 6: Perform two-stage crystallization on the precursor glass, nucleating at 650℃ for 1.5 hours, and then crystallizing at 770℃ for 3 hours by increasing the temperature at 2.4℃ / min.

[0043] Step 7: Immerse the crystallized glass in a KNO3-NaNO3 molten salt with a molar ratio of 7:3 at 410℃ for ion exchange for 4 hours.

[0044] Example 2 This embodiment prepares a low-cost lithium-free microcrystalline glass, specifically including the following steps: Step 1: Commercially available sodium feldspar micro powders from different manufacturers with an average particle size of 14μm (tested to contain 20.1% Al2O3, 10.7% Na2O, total impurities ≤2%, and the remainder being SiO2) were pre-calcined in air at 1150℃ for 3 hours to obtain pre-molten sodium feldspar micro powders.

[0045] Step 2: Weigh industrial calcium carbonate, aluminum hydroxide, and kaolin according to the stoichiometric ratio of calcium feldspar (molar ratio CaO:Al2O3:SiO2 = 1:1:2). Add the raw materials to a planetary ball mill and ball mill at 300 rpm for 4 hours to obtain a uniform slurry. After preliminary drying at 63℃ for 5 hours, transfer the slurry to a 110℃ oven for 24 hours to dry completely. Press the dried mixture into 50 mm cylindrical blanks and calcine them at 1220℃ in air atmosphere for 2.5 hours at a heating rate of 5℃ / min. After coarse crushing with a jaw crusher, use an air jet mill with a feed pressure of 0.7 MPa and a classifying wheel speed of 8000 rpm for ultrafine grinding. Finally, sieve through a 325-mesh standard sieve, collect the undersize material, and determine the average particle size D using a laser particle size analyzer. 50 =20μm, to obtain synthetic calcium feldspar micro powder.

[0046] 3.0 wt% ZrO2 and 0.3% TiO2 were loaded into a zirconia ball mill jar, and zirconia grinding balls (ball-to-material mass ratio of 15:1) were added. After sealing, the jar was evacuated to 9.7 Pa, and then filled with high-purity argon gas to atmospheric pressure. This evacuation and filling process was repeated 3 times to replace the air. Subsequently, the jar was ball-milled in a planetary ball mill at 400 rpm for 3 hours to obtain a uniformly dispersed composite nucleating agent powder.

[0047] Step 3: 69.1% pre-melted sodium feldspar powder, 21.9% synthetic calcium feldspar powder, the above-mentioned composite nucleating agent powder, 3.0% MgO, 2.0% CaO, and 0.7% K2O; ball mill and mix for 50 minutes under argon protection.

[0048] Step 4: Add the batch material to a platinum crucible, introduce a N2:CO=96:4 mixed gas, heat to 1325℃ at 7℃ / min and hold for 2.5 hours; switch to high-purity N2, continue heating to 1455℃ to melt for 4 hours, and clarify at 1435℃ for 2 hours to obtain a homogeneous glass melt.

[0049] Step 5: The clarified molten glass is slowly cooled to 1190°C at a rate of 1.5°C / min and held at this temperature for 50 minutes for homogenization. Then, the molten glass is stably introduced into the overflow tank through a platinum flow pipe. The molten glass is injected into the platinum overflow tank and formed into a 1.0 mm thick plate at 1180°C using the overflow pull-down method at a pull-down rate of 3 m / h. Immediately after forming, it is placed in an annealing furnace and held at 590°C for 1 hour. Then, it is slowly cooled to 525°C at a rate of 3°C / min and held at this temperature for 3.5 hours before being cooled in the furnace to obtain low-stress precursor glass.

[0050] Step 6: Perform two-stage crystallization on the precursor glass, nucleating at 655℃ for 2 hours, and then crystallizing at 765℃ for 4 hours by increasing the temperature at 2.7℃ / min.

[0051] Step 7: Immerse the crystallized glass in a KNO3-NaNO3 molten salt with a molar ratio of 7.25:2.75 at 430℃ for ion exchange for 5 hours.

[0052] Example 3 This embodiment prepares a high thermal stability lithium-free microcrystalline glass, specifically including the following steps: Step 1: Commercially available sodium feldspar powder with an average particle size of 12 μm (tested to contain 20.3% Al2O3, 10.5% Na2O, total impurities ≤2%, and the remainder being SiO2) is pre-calcined in air at 1200℃ for 4 hours to obtain pre-molten sodium feldspar powder.

[0053] Step 2: Weigh industrial calcium carbonate, aluminum hydroxide, and kaolin according to the stoichiometric ratio of calcium feldspar (molar ratio CaO:Al2O3:SiO2=1:1:2). Add the raw materials to a planetary ball mill and ball mill at 300 rpm for 4 hours to obtain a uniform slurry. After preliminary drying at 60℃ for 5 hours, transfer the slurry to a 100℃ oven for 24 hours to dry completely. Press the dried mixture into 50mm cylindrical blanks and calcine them at 1200℃ in air atmosphere for 2 hours at a heating rate of 5℃ / min. After coarse crushing with a jaw crusher, use an air jet mill with a feed pressure of 0.7MPa and a classifying wheel speed of 8000 rpm for ultrafine grinding. Finally, pass the material through a 325-mesh standard sieve with a pore size of 45μm, collect the undersize material, and determine the average particle size D using a laser particle size analyzer. 50 =22μm, to obtain synthetic calcium feldspar micro powder.

[0054] 3.5% ZrO2 and 0.5% TiO2 by mass were loaded into a zirconia ball mill jar, and zirconia grinding balls (ball-to-material mass ratio of 15:1) were added. After sealing, the jar was evacuated to 9.7 Pa, and then filled with high-purity argon gas to atmospheric pressure. This evacuation and filling process was repeated 3 times to replace the air. Subsequently, the jar was ball-milled in a planetary ball mill at 400 rpm for 3 hours to obtain a uniformly dispersed composite nucleating agent powder.

[0055] Step 3: Weigh out 74.3% of pre-molten sodium feldspar powder, 20.2% of synthetic calcium feldspar powder, the above-mentioned composite nucleating agent powder, 0.5% of MgO, 0.7% of CaO, and 0.3% of K2O according to the total mass percentage; and ball mill them together for 60 minutes under argon protection.

[0056] Step 4: Add the batch material to a platinum crucible, introduce a N2:CO=95:5 mixed gas, heat to 1350℃ at 8℃ / min and hold for 3 hours; switch to high-purity N2, continue heating to 1480℃ to melt for 5 hours, and clarify at 1450℃ for 2.5 hours to obtain a homogeneous glass melt.

[0057] Step 5: The clarified molten glass is slowly cooled to 1180°C at a rate of 2°C / min and held at this temperature for 60 minutes for homogenization. Then, the molten glass is stably introduced into the overflow tank through a platinum flow pipe. The molten glass is injected into the platinum overflow tank and formed into a 1.0 mm thick plate at 1180°C using the overflow pull-down method at a pull-down rate of 4 m / h. Immediately after forming, it is placed in an annealing furnace and held at 600°C for 1 hour, then slowly cooled to 550°C at a rate of 4°C / min and held at this temperature for 4 hours before being cooled in the furnace to obtain low-stress precursor glass.

[0058] Step 6: Perform two-stage crystallization on the precursor glass, nucleating at 650℃ for 2.5 hours, and then crystallizing at 740℃ for 5 hours by increasing the temperature at 3℃ / min.

[0059] Step 7: Immerse the crystallized glass in a KNO3 and NaNO3 molten salt with a molar ratio of 7.5:2.5 at 450°C for ion exchange for 5 hours.

[0060] Comparative Example 1 This comparative example is the same as Example 3 in all other respects, except that in step 1, the sodium feldspar powder was not pre-calcined at 1200°C, and the original commercially available sodium feldspar powder was used directly in the mixing.

[0061] Comparative Example 2 This comparative example is the same as Example 3 in all other respects, except that the main raw material powder is completely replaced with synthetic calcium feldspar powder, accounting for 94.5% by weight, and no sodium feldspar powder is added.

[0062] Comparative Example 3 This comparative example is the same as Example 3 in all other respects, except that the main raw material powder is completely replaced with pre-melted sodium feldspar powder, accounting for 94.5% by weight, and no calcium feldspar powder is added.

[0063] Comparative Example 4 This comparative example is the same as Example 3 in all other respects, except that ZrO2 and TiO2 were not pre-dispersed by high-energy ball milling, but were directly added to the mixer in their original powder form for dry mixing.

[0064] Comparative Example 5 This comparative example is the same as Example 3 in all other respects, except that in step 4 the high-temperature melting temperature is increased to 1550°C and held for 5 hours, and the clarification temperature is set to 1530°C and clarified for 2.5 hours.

[0065] Comparative Example 6 This comparative example is the same as Example 3 in all other respects, except that the first stage heat preservation temperature is reduced from 600°C to 520°C and kept at this temperature for 1 hour; then it is slowly cooled to 480°C at 4°C / min and kept at this temperature for 3.5 hours before being cooled with the furnace.

[0066] Comparative Example 7 This comparative example is the same as Example 3 in all other respects, except that only the first stage of nucleation is performed at 650°C for 2.5 hours, followed by natural cooling, without the second stage of crystallization.

[0067] Comparative Example 8 This comparative example is the same as Example 3 in all other respects, except that the first stage of nucleation is omitted, and crystallization is carried out directly by heating to 740°C at 2.4°C / min and holding for 5 hours.

[0068] Comparative Example 9 This comparative example is the same as Example 3 in all other respects, except that the performance adjustment components are adjusted to 7% MgO, 0% CaO, 0% K2O, 70.3% sodium feldspar powder, 18.7% calcium feldspar powder, and the composite nucleating agent remains unchanged at 3.5% ZrO2 and 0.5% TiO2.

[0069] Comparative Example 10 This comparative example is the same as Example 3 in all other respects, except that the proportion of sodium feldspar powder in the main raw materials is reduced to 60%, while that of calcium feldspar powder is increased to 34.5%.

[0070] Comparative Example 11 This comparative example is the same as Example 3 in all other respects, except that the proportion of sodium feldspar powder in the main raw materials is increased to 80%, while that of calcium feldspar powder is reduced to 14.5%.

[0071] Comparative Example 12 This comparative example is the same as Example 3 in all other respects, except that the composite nucleating agent is adjusted to 6% ZrO2 and 1.0% TiO2, sodium feldspar micro powder accounts for 72%, and calcium feldspar micro powder accounts for 19.5%, while the performance-adjusting components remain unchanged.

[0072] Comparative Example 13 This comparative example is the same as Example 3 in all other respects, except that in step 4, the melting is carried out entirely in an air atmosphere, without switching between a weak reducing atmosphere of N2 / CO and a neutral atmosphere of high-purity N2.

[0073] Comparative Example 14 This comparative example is the same as Example 3 in all other respects, except that the clarification temperature is changed from 1450°C to 1380°C, which is lower than the temperature required for complete homogenization of the molten glass.

[0074] Comparative Example 15 This comparative example is the same as Example 3 in all other respects, except that pre-melted albite powder is not used. Instead, analytical grade Al2O3, Na2CO3, and SiO2 are weighed at an oxide mass ratio of Al2O3:Na2O:SiO2 = 20.3:10.5:69.2, where Na2O is provided by Na2CO3. This mixed powder is not pre-melted or calcined and is directly added to the mixer in step 3 along with other components. The total addition amount is 74.3%, and the remaining components and process conditions remain unchanged.

[0075] Comparative Example 16 This comparative example is the same as Example 3 in all other respects, except that synthetic anorthite powder is not used. Instead, analytically pure Al2O3, CaCO3, and SiO2 are mixed and prepared in an oxide mass ratio of CaO:Al2O3:SiO2 = 20.1:36.7:43.2 (corresponding to the theoretical composition of anorthite CaO·Al2O3·2SiO2). The total addition amount is 20.2%, and the other components remain unchanged.

[0076] like Figure 1 As shown, the SEM images of the microcrystalline glass obtained in Examples 1 to 3 all exhibit a uniform and dense microcrystalline structure with a reasonable grain size distribution and no obvious defects, indicating that the components and heat treatment regime described in this invention can stably obtain high-performance microcrystalline glass.

[0077] Figure 2 The X-ray diffraction pattern of the precursor glass prepared in Example 1 of this invention, i.e., the uncrystallized glass, is shown. A broad amorphous peak appears at 2θ=22°, indicating that it has a uniform amorphous structure with no obvious crystal precipitation, which is consistent with the typical characteristics of annealed glass formed by overflow pull-down method.

[0078] Figure 3The image shows the XRD pattern of the same sample after a two-stage gradient crystallization process. Multiple sharp diffraction peaks appear, corresponding to the anorthite and sodium feldspar crystal phases. Based on this, it is determined to be an anorthite solid solution, confirming that the crystallization process successfully induced crystallization.

[0079] Figure 4 The graphs show the DTA analysis of microcrystalline glass with different ratios. The horizontal axis represents temperature, and the vertical axis represents temperature difference ΔT. The graphs show multiple exothermic peaks with peak temperatures of 763℃ in Example 1, 756℃ in Example 2, 735℃ in Example 3, and 714℃ in Comparative Example 14. The crystallization temperature needs to be slightly higher than the DTA exothermic peak temperature to ensure sufficient crystal growth and complete crystallization, and to avoid incomplete crystallization or performance degradation due to insufficient temperature.

[0080] In this invention, the embodiments and comparative examples use a UV-Vis spectrophotometer, referring to GB / T40415 standard, to test the transmittance (i.e., visible light transmittance) in the wavelength range of 250~800nm. Using an SLP2000, according to standards GB / T18144 and ASTM1422C-99, the surface compressive stress and stress layer depth are tested. Microhardness testing uses a microhardness tester with a diamond square pyramid indenter with a 136° angle between its faces. A load is applied to the sample surface to form an indentation. The hardness value (HV) is calculated using the Vickers hardness formula based on the applied test force and the measured diagonal length of the indentation. Fracture toughness testing is performed using a computer-controlled electronic universal testing machine, according to national standard GB / T 23806—2009.

[0081] Drop resistance testing was conducted using a CNC drop tester. The sample was fixed in a fixture simulating the entire machine structure and dropped freely from a specified height onto a rigid impact surface. Its drop resistance was assessed by observing whether it cracked or broke. Four-point bending strength testing was performed using a computer-controlled electronic universal testing machine, in accordance with ASTM C158. Impact resistance testing was conducted using a falling ball impact tester. A 200 g steel ball was used to impact nine different locations on the sample surface. The maximum impact energy (J) that the sample could withstand without breaking was used as the evaluation index.

[0082]

[0083] In Comparative Example 1, the lack of pre-calcination of albite resulted in residual structural water, carbonates, or organic impurities in the raw materials. These impurities released gas during the high-temperature melting stage, forming microbubbles or streaks and disrupting the homogeneity of the glass melt. The unmelted albite had insufficient reactivity and was difficult to fully miscible with calcium feldspar, hindering the uniform precipitation of the calcium-sodium feldspar solid solution crystal phase. This led to coarse and unevenly distributed grains, which in turn weakened the mechanical properties and optical transmittance.

[0084] In Comparative Examples 2 and 3, the use of albite or anorthite as the main raw material alone disrupted the eutectic system formed by the two. Although albite has good fluxing properties, its coefficient of thermal expansion is too high and its chemical stability is insufficient when used alone; while pure anorthite has a high melting point and poor fluidity, making it difficult to achieve complete melting and clarification below 1480℃. This results in an incomplete glass network, with residual unmelted particles becoming stress concentration sources, significantly reducing strength and impact resistance.

[0085] In Comparative Example 4, the lack of pre-dispersion of the composite nucleating agent caused ZrO2 and TiO2 to agglomerate in the glass matrix, failing to provide uniform and high-density nucleation sites. This resulted in excessively dense nuclei in some areas and a lack of nuclei in others, leading to heterogeneous crystallization. Some areas experienced excessive crystal growth, forming microcracks, while other areas remained amorphous, resulting in an overall non-uniform structure that compromised fracture toughness and the continuity of the surface compressive stress layer.

[0086] Excessive temperatures exacerbate the erosion of platinum crucibles, causing trace platinum particles or impurities to dissolve into the molten glass, forming scattering centers and reducing optical transmittance. High temperatures also enhance the volatilization of alkali metal oxides, causing the glass composition to deviate from the designed ratio, affecting the concentration of network modifiers, and consequently interfering with subsequent crystallization, leading to an imbalance in the types or proportions of precipitated phases. While high temperatures are beneficial for clarification, prolonged high-temperature holding can cause excessive deagglomeration of the glass network, reducing its structural relaxation ability after cooling and making it more prone to accumulating internal stress during annealing and crystallization. High melting temperatures do not improve the dispersion of nucleating agents but increase energy consumption and lead to a wider distribution of crystallite size and a decrease in crystal phase uniformity, resulting in a systematic weakening of fracture toughness, surface compressive stress, and impact resistance. Therefore, this invention precisely controls the melting temperature at 1430-1480℃, which is the optimal choice while ensuring sufficient melting and clarification, and balancing compositional stability, equipment compatibility, and crystallization controllability.

[0087] In Comparative Example 6, because the annealing initiation temperature was much lower than Tg, the glass was in a high-viscosity rigid state with extremely weak atomic migration ability, making it impossible to effectively relax the structural and thermal stresses generated during the molding process. Although the two-stage gradient annealing process was still used in form, the lack of an effective stress release window near Tg resulted in a still high level of residual stress in the precursor glass, affecting the subsequent crystallization uniformity and the mechanical and optical properties of the final product.

[0088] Comparative Examples 7 and 8 only underwent nucleation. Comparative Example 7 only had crystal nuclei without crystal growth, and the material was still mainly amorphous, so it could not obtain the microcrystalline strengthening effect. Comparative Example 8 lacked uniform nucleation in the early stage, and direct heating caused the spontaneous nucleation rate to run out of control. The crystals were large and disordered, and it was also impossible to form a dense and high-strength microcrystalline network.

[0089] The lack of atmosphere control in Comparative Example 13 and the insufficient clarification temperature in Comparative Example 14 resulted in the inability of raw material decomposition gases to be effectively discharged, introducing bubbles and hydroxyl impurities. Comparative Example 14 resulted in high glass melt viscosity and insufficient homogenization. Both of these factors increased defects in the glass matrix, creating hidden dangers for subsequent crystallization, ultimately leading to decreased transmittance and deteriorated strength.

[0090] The proportions of Comparative Examples 9-12 were unbalanced, and Comparative Examples 15 and 16 reverted to the high-purity chemical raw material route. Although they may have partially retained performance, they essentially deviated from the core principles of this invention: low cost, low energy consumption, and high performance integration. This was due to factors such as excessive MgO inhibiting crystallization, an imbalanced sodium / calcium ratio disrupting network connectivity, or being forced to increase melting temperature by not utilizing the fluxing advantages of natural minerals. Furthermore, the data showed that Comparative Examples 15 and 16 did not perform as well as this application, because they ignored the influence of raw material morphology and reaction pathways on glass structure formation. The pre-melted albite micropowder and in-situ synthesized calcium feldspar micropowder used in this invention are not merely component sources, but participate in melting as active microparticles with specific crystal structures or partial network connectivity, improving reaction uniformity and melt homogenization efficiency. In contrast, Comparative Examples 15 and 16 directly mixed unreacted oxide powders, which required complex and kineticly slow steps such as carbonate decomposition, solid-phase diffusion, and network reconstruction during high-temperature melting, easily leading to micro-region segregation of components, residual bubbles, and uneven glass melt. This structural defect directly affects subsequent crystallization behavior, making it difficult to form the uniform and fine calcium-sodium feldspar solid solution crystal phase observed in the examples. Instead, it easily precipitates separated albite or calcium feldspar single phases, causing problems such as increased grain boundaries, refractive index mismatch, and microcrack initiation, thereby reducing optical transmittance, fracture toughness, and flexural strength. In addition, the heterogeneous glass matrix also weakens the nucleation efficiency of the composite nucleating agent, resulting in uneven grain distribution and local amorphous residues, further deteriorating mechanical and impact resistance properties. Even without considering cost factors, simply relying on high-purity chemical raw materials without pretreatment of raw materials and utilization of minerals cannot reproduce the high-performance microcrystalline glass structure achieved by this invention.

[0091] While specific embodiments of this application have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of this application. Those skilled in the art should understand that modifications can be made to the above embodiments or equivalent substitutions can be made to some technical features without departing from the scope and spirit of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any manner.

Claims

1. A microcrystalline glass, characterized in that, The product comprises the following components, each component being a percentage by weight of the total mass of the raw materials: the first component is the main raw material powder, the second component is the composite nucleating agent, and the third component is the performance regulating component; wherein, the main raw material powder accounts for 91% to 97% by weight, and the main raw material powder is composed of pre-melted sodium feldspar powder and synthetic calcium feldspar powder, wherein the sodium feldspar powder accounts for 69 to 75% of the total mass of the raw materials, and the remainder is calcium feldspar powder; The composite nucleating agent is composed of ZrO2 and TiO2, wherein ZrO2 accounts for 2% to 4% of the total mass of the raw materials and TiO2 accounts for 0.1% to 0.5%. The performance-adjusting component has a weight percentage of 0% to 9% and is selected from one or more of MgO 0% to 5%, CaO 0% to 3% and K2O 0% to 1%.

2. The microcrystalline glass according to claim 1, characterized in that, A method for preparing calcium feldspar powder, characterized by comprising the following steps: Step S1: Prepare the ingredients according to the stoichiometric ratio of calcium feldspar CaO·Al2O3·2SiO2, with a molar ratio of CaO:Al2O3:SiO2=1:1:

2. The alumina source is industrial aluminum hydroxide, the calcium source is industrial calcium carbonate, and the silicon source is kaolin. Step S2: Mix the industrial aluminum hydroxide, calcium carbonate and kaolin and ball mill them to obtain a mixture; Step S3: After the mixture is formed, it is dried by keeping it at 60-65℃ for 5-7 hours and then at 100-110℃ for 24-28 hours. Step S4: Calcine the mixture at 1200°C to 1250°C for 2 to 4 hours to obtain the sintered product; Step S5: The sintered product is crushed, ball-milled or air-jet pulverized, and sieved to obtain anorthite powder with a particle size of 1-50 μm.

3. The microcrystalline glass according to claim 1, characterized in that, The mass percentage of the albite micro powder is: Al2O3 10%~28%, Na2O 5%~14.8%, with the remainder being SiO2 and unavoidable trace impurities; the impurities include, but are not limited to, at least one of Fe2O3, K2O, CaO, MgO and TiO2, and the total content of the impurities does not exceed 3%; the particle size of the albite micro powder is ≤20μm.

4. A method for preparing the microcrystalline glass according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Pre-calcine unmelted albite micro powder with a particle size ≤20μm at 1100℃~1200℃ in air atmosphere for 2~4 hours to obtain pre-melted albite micro powder; Step 2: Mix ZrO2 and TiO2 according to the target ratio using high-energy ball milling or air jet milling for 2-4 hours to obtain a uniformly dispersed composite nucleating agent powder; wherein ZrO2 accounts for 2% to 4% of the total mass of the raw materials, and TiO2 accounts for 0.1% to 0.5%; Step 3: According to the proportions described in claim 1, place the pre-molten sodium feldspar powder, synthetic calcium feldspar powder, pre-dispersed composite nucleating agent and performance regulating components in a mixer and mix for 30-60 minutes under an inert atmosphere to obtain a highly uniform batch. Step 4: Add the batch material to the platinum crucible and perform preliminary melting under a weak reducing atmosphere. Then switch to a neutral atmosphere to complete high-temperature melting and clarification to obtain a homogeneous glass melt without bubbles or streaks. Step 5: The molten glass is formed into a plate-shaped precursor by the overflow and downward drawing method, and then subjected to gradient annealing. The gradient annealing includes holding the glass near the glass transition temperature to eliminate rapid cooling stress, followed by slow cooling and holding the glass again to further relax the internal stress, and finally obtaining a precursor glass with low residual stress. Step 6: Perform a two-stage gradient crystallization treatment on the precursor glass.

5. The method for producing microcrystalline glass according to claim 4, characterized in that, The process also includes step 6, which involves a two-stage gradient crystallization treatment of the precursor glass, specifically comprising a first-stage nucleation and a second-stage crystallization. The first stage of nucleation involves holding the temperature at 650±5℃ for 1.5-2.5 hours; the second stage of crystallization involves raising the temperature to 735-770℃ at a rate of 2.4-3℃ / min, holding the temperature for 3-5 hours, and then naturally cooling to obtain the microcrystalline glass.

6. The method for producing microcrystalline glass according to claim 4, characterized in that, It also includes step 7, ion strengthening; the ion strengthening conditions are to immerse the microcrystalline glass in a KNO3-NaNO3 mixed molten salt at 410-450℃ for ion exchange for 4-6 hours, wherein the molar ratio of KNO3 to NaNO3 in the mixed molten salt is 7-7.5:2.5-3.

7. The method for producing microcrystalline glass according to claim 4, characterized in that, In step 4, the weak reducing atmosphere is a mixture of N2 and CO with a volume ratio of N2:CO = 95-97:3-5; the neutral atmosphere is high-purity N2.

8. The method for producing microcrystalline glass according to claim 4, characterized in that, In step 4, under a weak reducing atmosphere, the temperature is increased to 1300-1350℃ at a rate of 5-8℃ / min and held for 2-3 hours to allow the main material to be fully pre-melted and to remove structural water and carbonate decomposition gases. The atmosphere is then switched to neutral, and the temperature is further increased to 1430-1480℃ and held for melting for 3-5 hours to promote the formation and homogenization of the glass network. The temperature is then reduced to 1420-1450℃ and clarified for 1.5-2.5 hours to obtain a homogeneous glass melt without bubbles or streaks.

9. The method for producing microcrystalline glass according to claim 4, characterized in that, In step 5, gradient annealing involves holding at 580±20℃ for 1 hour to eliminate rapid cooling stress, then slowly cooling at a rate of 2-4℃ / min to 500-550℃, and holding at this temperature range for 3-4 hours before furnace cooling.

10. A cover plate for an electronic device, characterized in that, Made of the microcrystalline glass as described in any one of claims 1-3.

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