A rare earth aluminosilicate glass-ceramic and a method for preparing the same

Abstract

This invention provides a rare-earth aluminosilicate microcrystalline glass and its preparation method, belonging to the field of glass product technology. By introducing rare-earth elements and zirconium dioxide, this invention reduces the lithium and aluminum content in the glass, not only lowering production costs and enabling large-scale low-cost applications, but also endowing the microcrystalline glass with excellent mechanical and light transmittance properties. The results of the embodiments show that the rare-earth aluminosilicate microcrystalline glass provided by this invention contains only uniformly distributed zirconium dioxide nanocrystals, with an average crystal size ≤30nm. The visible light transmittance of the rare-earth aluminosilicate microcrystalline glass is greater than 90%; simultaneously, the surface compressive stress of the rare-earth aluminosilicate microcrystalline glass is ≥800MPa, and the Vickers hardness is >700kgf / mm². 2 The fracture toughness can reach 1.33–1.41 MPa·m. 1 / 2 .

Description

Technical Field

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

[0002] Glass, a transparent material, effectively transmits light and possesses excellent corrosion resistance, making it an ideal choice for manufacturing products such as windows, mirrors, and displays. However, traditional glass typically suffers from drawbacks such as fragility and poor scratch resistance, limiting its applications. With the advancement of technology and the increasing prevalence of electronic products, especially in recent decades, mobile phones and tablets have become necessities in people's lives. These electronic devices are all equipped with touchscreen displays with cover glass. Demand drives technological progress, and people's performance requirements for touchscreen displays are constantly increasing.

[0003] In cover glass, the main types are alkali aluminosilicate glasses, namely sodium aluminosilicate glass and lithium aluminosilicate glass. Lithium aluminosilicate glass, in particular, has a lower glass transition temperature (Tg). Furthermore, lithium aluminosilicate glass can be chemically strengthened through ion exchange, significantly increasing its strength. Currently, efforts are mainly focused on adjusting and optimizing the glass composition and chemical strengthening formulations to improve the surface compressive stress and ion exchange layer depth of alkali aluminosilicate glass, but these methods still cannot meet the increasing application demands of touchscreen displays in electronic products.

[0004] Glass-ceramic, also known as glass ceramic, is a special type of glass composed of a microcrystalline phase and a residual glassy phase, exhibiting a dual-phase structure of microcrystalline and amorphous structures. The preparation of glass-ceramic can be viewed as the synthesis of crystals through controlled solid-state reactions in supercooled glass. These solid-state reactions can be triggered by high temperatures, i.e., heat treatment. Alternatively, nucleating agents such as TiO2, ZrO2, and noble metal nanoparticles can be added to induce glass crystallization at lower temperatures through heterogeneous nucleation. This allows the glass to precipitate uniform and fine crystals, thereby improving its hardness, fracture toughness, and drop resistance.

[0005] For touch displays, the glass-ceramic used must have high light transmittance. Currently, suitable glass-ceramic systems mainly include lithium aluminum silicate glass-ceramics and magnesium / zinc aluminum silicate glass-ceramics (spinel). Ion exchange is mainly carried out through lithium-sodium, lithium-potassium, and sodium-potassium exchanges, using larger ions to exchange smaller ions, creating compressive stress at the ion exchange site, inhibiting the propagation of microcracks on the glass surface, and improving properties such as hardness and fracture toughness. While transparent glass-ceramics have higher mechanical strength than ordinary glass, during the crystallization process, Li... + And Al 3+Generally, it participates in crystallization, which on the one hand reduces the number of ions that can undergo ion exchange, and on the other hand, when a large amount of Al is enriched in the crystal... 3+ Subsequently, the structure of the residual glass phase becomes more compact, which is not conducive to ion exchange. Publication number CN110217996A discloses that, in molar percentage, the average maximum stress layer depth after a two-step ion exchange with an alumina content of 22% is 93 μm, while the depths for contents of 17% and 18% are 106 and 98 μm, respectively. Therefore, non-alkali crystalline glass-ceramics are currently considered to be more effective at ion exchange.

[0006] Al2O3 plays a very positive role in improving the physical and chemical properties of glass. Meanwhile, the volume of the [AlO4] tetrahedron is larger than that of [SiO4], and the Na atoms bonded to [AlO4]-... + It exhibits better mobility. Therefore, Al2O3 needs to be introduced to promote ion exchange. However, simply increasing the Al2O3 content will increase the viscosity of high-alumina silicate glass, raise the melting temperature, and reduce its processing performance. For example, patent application CN113880438A discloses a method for preparing zirconia microcrystalline glass and terminals, with an alumina content of 17-22 mol%. Although the processing problems caused by the increased Al2O3 content can be improved by adding alkali metal oxides such as lithium oxide, it will weaken the mechanical properties of high-alumina silicate glass.

[0007] Lithium oxide has three main applications in current cover glass: 1. Participation in the crystallization of glass-ceramics. Lithium aluminum silicate glass-ceramics are typical network-formed glass that participates in the crystallization process, forming silicate crystals from the silicate glass matrix. To precipitate the desired lithium-containing crystalline phase, the amount of lithium used is generally greater than 12 mol%, or even higher. 2. Improving the processing problems caused by the increased Al2O3 content. 3. Participation in subsequent one- or two-step ion exchange processes. Due to the application requirements of lithium oxide, current cover glass products generally have excessively high lithium content. The price of lithium ore remains high due to the rapid development of lithium batteries and the global emphasis on new energy sources, which significantly increases the cost of lithium aluminum silicate glass-ceramics. The invention patent application with publication number CN113880438A improves the processing problems caused by excessively high Al2O3 content by adding 8–12 mol% lithium oxide and 6–10 mol% sodium oxide, while ensuring sufficient lithium and sodium elements for ion exchange in subsequent chemical strengthening processes. A higher content of Li2O will significantly increase the overall cost of the glass. At the same time, a higher content of Li2O and Na2O will have a greater tendency to crystallize, which will have great limitations in actual production and application. It will easily cause the microcrystalline glass to become foggy and de-transparent, making it difficult to meet the actual use requirements of existing touch screens.

[0008] Therefore, how to improve the light transmittance and mechanical properties of glass-ceramics while reducing the lithium and aluminum content has become a pressing technical problem to be solved in this field. Summary of the Invention

[0009] The purpose of this invention is to provide a rare earth aluminosilicate microcrystalline glass and its preparation method. The rare earth aluminosilicate microcrystalline glass provided by this invention has low lithium and aluminum content, low production cost, and advantages such as good light transmittance, high Vickers hardness, and high fracture toughness.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0011] This invention provides a rare-earth aluminosilicate microcrystalline glass, which, based on the molar percentage of oxides, comprises: SiO2: 56-62%; Al2O3: 10-18%; Na2O: 4-8%; Li2O: 4-10%; rare-earth oxides: 2-4%; ZrO2: 1-3%; MgO ≤ 4% and K2O ≤ 2%, wherein MgO and K2O are not simultaneously 0;

[0012] The crystal phase of the rare earth aluminosilicate microcrystalline glass is zirconium dioxide nanocrystals.

[0013] Preferably, the average crystal size of the zirconium dioxide nanocrystals is ≤30nm.

[0014] Preferably, the rare earth oxide includes at least one of La2O3, Y2O3 and CeO2.

[0015] Preferably, when the rare earth oxide contains La2O3, the molar percentage of La2O3 in the rare earth aluminosilicate microcrystalline glass is 1-3%; when the rare earth oxide contains Y2O3, the molar percentage of Y2O3 in the rare earth aluminosilicate microcrystalline glass is ≤2%; and when the rare earth oxide contains CeO2, the molar percentage of CeO2 in the rare earth aluminosilicate microcrystalline glass is ≤1%.

[0016] Preferably, the rare earth aluminosilicate microcrystalline glass satisfies the following condition based on the molar percentage of oxides: Al2O3+MgO-Li2O-Na2O-K2O≥0%.

[0017] This invention provides a method for preparing the rare-earth aluminosilicate microcrystalline glass described above, comprising the following steps:

[0018] (1) The raw materials are melted, shaped and annealed in sequence to obtain the base glass;

[0019] (2) Heat-treat the base glass obtained in step (1) to obtain microcrystalline glass containing ZrO2 crystals;

[0020] (3) The microcrystalline glass containing ZrO2 crystals obtained in step (2) is subjected to ion exchange in a salt bath to obtain rare earth aluminosilicate microcrystalline glass.

[0021] Preferably, the annealing holding temperature in step (1) is lower than the glass transition temperature Tg50±10℃.

[0022] Preferably, the heat treatment temperature in step (2) is 700-900℃ and the heat treatment time is 4-20h.

[0023] Preferably, the salt bath composition in step (3) includes 50-100 wt% NaNO3 and 0-50 wt% KNO3.

[0024] Preferably, the temperature of ion exchange in step (3) is 400-500℃ and the time of ion exchange is 5-20h.

[0025] This invention provides a rare-earth aluminosilicate microcrystalline glass, which, based on the molar percentage of oxides, comprises: SiO2: 56-62%; Al2O3: 10-18%; Na2O: 4-8%; Li2O: 4-10%; rare earth oxides: 2-4%; ZrO2: 1-3%; MgO ≤ 4% and K2O ≤ 2%, wherein MgO and K2O are not simultaneously 0; the crystal phase of the rare-earth aluminosilicate microcrystalline glass is zirconium dioxide nanocrystals. In the rare-earth aluminosilicate microcrystalline glass provided by this invention, SiO2 plays a crucial role in improving the structure and properties of the glass. The [SiO4] tetrahedron, as the basic building block of the glass network, provides excellent mechanical strength and chemical stability. Simultaneously, the high chemical inertness and low coefficient of thermal expansion of SiO2 give the glass excellent corrosion resistance and thermal stability under various environments. Therefore, the introduction of SiO2 can significantly improve the overall performance of the glass. Al2O3 also plays a very positive role in improving the physical and chemical properties of the glass. Aluminum forms [AlO4] tetrahedra in the microcrystalline glass. The volume of the [AlO4] tetrahedron is larger than that of [SiO4], and Na is bonded to [AlO4]-. + It exhibits better mobility, and the precipitation of ZrO2 is accompanied by the transfer of alkali metal ions. Before precipitation, ZrO2 exists in the glass as [ZrO6] octahedra, carrying two units of negative charge. At this point, Na is required. + Li + Ions neutralize to achieve charge balance, so when ZrO2 is precipitated, the Na surrounding [ZrO6]... + Li+ Alumina will transfer to the [AlO4]-tetrahedron, so the addition of alumina is more conducive to ion exchange, which can increase the depth of the exchange layer. Chemically strengthened glass-ceramics exhibit excellent mechanical properties. Na2O and Li2O are key exchange ions in the chemical strengthening of glass-ceramics. K2O, Na2O, and Li2O all belong to alkali metal oxides, which can increase the ion exchange rate and deepen the compressive stress layer. They can also act as a network disruptor, reducing the viscosity and melting temperature of the glass. The simultaneous presence of small amounts of K2O and Na2O can form a mixed alkali effect, optimizing a series of glass properties. Rare earth oxides can make the glass network structure denser, giving glass-ceramics better chemical stability and higher mechanical properties. The glass transition temperature, strength, and hardness are improved. By adding zirconium dioxide, zirconium dioxide nanocrystals are precipitated in the glass-ceramic. Thanks to the small size (less than 30 nm) and uniform crystallization of the zirconium dioxide nanocrystals, the glass-ceramic does not exhibit fogging or devitrification, ensuring excellent light transmittance. MgO exists in two coordination states (4-coordinate and 6-coordinate) in the glass, but mostly exists as [MgO6] octahedrons, making the glass structure more compact. MgO can also increase the surface compressive stress after ion exchange. At the same time, the content of lithium and aluminum elements in the glass-ceramic is lower, which can reduce its production cost while ensuring the performance of the glass-ceramic, thereby realizing low-cost large-scale application. The results of the embodiments show that the rare earth aluminosilicate microcrystalline glass provided by the present invention contains only uniformly distributed zirconium dioxide nanocrystals, and the average crystal size of the zirconium dioxide nanocrystals is ≤30nm. The visible light transmittance of the rare earth aluminosilicate microcrystalline glass is greater than 90%. At the same time, the surface compressive stress of the rare earth aluminosilicate microcrystalline glass is ≥800MPa, and the Vickers hardness is >700kgf / mm. 2 The fracture toughness can reach 1.33–1.41 MPa·m. 1 / 2 . Attached Figure Description

[0026] Figure 1 X-ray diffraction patterns of the base glass provided in Example 1 and rare earth aluminosilicate microcrystalline glasses obtained at different heat treatment temperatures;

[0027] Figure 2 X-ray diffraction patterns of the base glass provided in Example 4 and rare earth aluminosilicate microcrystalline glasses obtained at different heat treatment temperatures;

[0028] Figure 3 These are the TG-DSC images of the rare earth aluminosilicate microcrystalline glass obtained in Examples 1-4 of this invention;

[0029] Figure 4 The light transmittance curves of the rare earth aluminosilicate microcrystalline glass obtained in Examples 1-4 of this invention are shown. Detailed Implementation

[0030] This invention provides a rare-earth aluminosilicate microcrystalline glass, which, based on the molar percentage of oxides, comprises: SiO2: 56-62%; Al2O3: 10-18%; Na2O: 4-8%; Li2O: 4-10%; rare-earth oxides: 2-4%; ZrO2: 1-3%; MgO ≤ 4% and K2O ≤ 2%, wherein MgO and K2O are not simultaneously 0;

[0031] The crystal phase of the rare earth aluminosilicate microcrystalline glass is zirconium dioxide nanocrystals.

[0032] Based on the molar percentage of oxides, the rare-earth aluminosilicate microcrystalline glass provided by this invention comprises SiO2: 56-62%, preferably 57-61%, more preferably 58-60%, and even more preferably 59%. In this invention, SiO2 plays a very important role in improving the structure and properties of the glass. The [SiO4] tetrahedron, as the basic building block of the glass network, provides the glass with good mechanical strength and chemical stability. At the same time, the high chemical inertness and low coefficient of thermal expansion of SiO2 make the glass have excellent corrosion resistance and thermal stability in various environments. Therefore, the introduction of SiO2 can significantly improve the overall performance of the glass. However, simply increasing the SiO2 content will increase the melting temperature and process complexity of the glass, thereby reducing production efficiency. Therefore, in this invention, the molar percentage of SiO2 in the glass is controlled within the range of 56-62%.

[0033] Based on the molar percentage of oxides, the rare-earth aluminosilicate microcrystalline glass provided by this invention comprises Al2O3: 10-18%, preferably 12-17%, more preferably 14-17%, and even more preferably 15-16%. In this invention, Al2O3 plays a very positive role in improving the physical and chemical properties of the glass. Aluminum forms [AlO4] tetrahedra in the microcrystalline glass. The volume of the [AlO4] tetrahedra is larger than that of [SiO4], and Na is bonded to [AlO4]-. + It exhibits better mobility, and the precipitation of ZrO2 is accompanied by the transfer of alkali metal ions. Before precipitation, ZrO2 exists in the glass as [ZrO6] octahedra, carrying two units of negative charge. At this point, Na is required. + Li + Ions neutralize to achieve charge balance, so when ZrO2 is precipitated, the Na surrounding [ZrO6]... + Li +The ions will transfer to the [AlO4]-tetrahedron, so the addition of alumina is more conducive to ion exchange, which can increase the depth of the exchange layer. The chemically strengthened glass-ceramic exhibits excellent mechanical properties. However, if the Al2O3 content is too high, it will increase the viscosity of the glass, increase the melting temperature, and reduce the processing performance. Therefore, the molar percentage of Al2O3 in the glass is controlled within the range of 10-18%.

[0034] The rare-earth aluminosilicate microcrystalline glass provided by the present invention comprises Na₂O: 4-8%, preferably 5-7%, and more preferably 6%, based on the molar percentage of oxides. In the present invention, sodium can increase the depth of the exchange layer during ion exchange.

[0035] Based on the molar percentage of oxides, the rare-earth aluminosilicate microcrystalline glass provided by this invention comprises Li₂O: 4-10%, preferably 5-9%, more preferably 6-8%, and even more preferably 7%. In this invention, lithium can ensure the precipitation of lithium-containing crystalline phases in the microcrystalline glass while maintaining the effect of subsequent ion exchange strengthening; by using a lower amount of lithium added, the performance of the glass after ion exchange is guaranteed while the cost of the glass is greatly reduced, resulting in a large market application prospect; by controlling the amount of Li₂O doping, it is also possible to ensure that the crystalline phase of the microcrystalline glass contains only zirconium oxide crystals and does not contain Li-containing crystals.

[0036] In this invention, Na₂O and Li₂O are key exchange ions in the chemical strengthening of glass-ceramics. However, excessive Li₂O and Na₂O can lead to the precipitation of crystals in the glass. On the one hand, the precipitated crystals are difficult to control and easily form various crystal phases, such as β-quartz, β-quartz solid solution, and β-spodumene, which seriously affect the optical properties of the glass-ceramics. On the other hand, the precipitation of lithium-containing crystal phases reduces the number of exchangeable ions, affecting subsequent ion exchange strengthening. Therefore, this invention controls the molar percentage of Na₂O in the glass within the range of 4-8% and the molar percentage of Li₂O within the range of 4-10%. Furthermore, based on oxide molar percentages, the molar percentages of Na₂O and Li₂O satisfy the following relationship: 10% ≤ Li₂O + Na₂O ≤ 16%.

[0037] Based on the molar percentage of oxides, the rare-earth aluminosilicate microcrystalline glass provided by this invention comprises K2O ≤ 2%, preferably 0.5-2%, and more preferably 1-1.5%. In this invention, K2O, Na2O, and Li2O all belong to alkali metal oxides, which can increase the ion exchange rate and deepen the compressive stress layer, and can also act as a mesh-breaking agent, reducing the viscosity and melting temperature of the glass. The simultaneous presence of small amounts of K2O and Na2O can form a mixed alkali effect, which can optimize a series of glass properties; K + Radius compared to Na+ and Li + The maximum K₂O has a relatively low electric field strength, so its ability to bind with oxygen is weak; however, excessive K₂O will hinder Li₂O. + and Na + Ion exchange reduces surface stress, so the present invention controls the molar percentage of K2O in the glass to ≤2%.

[0038] Based on the molar percentage of oxides, the rare-earth aluminosilicate microcrystalline glass provided by the present invention comprises ≤4% MgO, preferably 0.5-4%, more preferably 1-3%, and even more preferably 1-2%. In the present invention, the MgO mainly acts as a network exogenous body. MgO exists in two coordination states in the glass (4-coordinate and 6-coordinate), but mostly exists as [MgO6] octahedrons, making the glass structure more compact. In ion exchange, MgO can increase the surface compressive stress of the rare-earth aluminosilicate microcrystalline glass obtained after ion exchange, but it will reduce the depth of the compressive stress layer. Therefore, the present invention controls the molar percentage of MgO to ≤4%.

[0039] In this invention, MgO and K2O are not both zero. By controlling the glass to contain at least one of MgO and K2O, this invention ensures that the light transmittance and mechanical properties of the glass-ceramic are improved while reducing the lithium and aluminum content.

[0040] The rare earth aluminosilicate glass-ceramics provided by this invention comprises 2-4% rare earth oxides, based on the molar percentage of oxides. In this invention, the rare earth oxides preferably include at least one of La₂O₃, Y₂O₃, and CeO₂, more preferably any one of La₂O₃, La₂O₃ and Y₂O₃, La₂O₃ and CeO₂, and La₂O₃, Y₂O₃, and CeO₂. In this invention, when the rare earth oxides contain La₂O₃, the molar percentage of La₂O₃ in the rare earth aluminosilicate glass-ceramics is preferably 1-3%, more preferably 2%; when the rare earth oxides contain Y₂O₃, the molar percentage of Y₂O₃ in the rare earth aluminosilicate glass-ceramics is preferably ≤2%, more preferably 1-2%; when the rare earth oxides contain CeO₂, the molar percentage of CeO₂ in the rare earth aluminosilicate glass-ceramics is preferably ≤1%, more preferably 0.5-1%. In this invention, the content of rare earth oxides, based on the molar percentage of oxides, satisfies the following relationship: La2O3 + CeO2 - Y2O3 ≥ 0. In this invention, rare earth oxides have a greater ionic field strength and higher dissociation energy than alkali metal and alkaline earth metal oxides, making them difficult to use as reinforcing structures for glass network structures. Therefore, rare earth elements are mostly distributed in the gaps of the glass network structure, serving as network modifiers. The addition of rare earth elements, due to their high charge and strong field, has a strong accumulation effect, making the glass network structure denser. This results in better chemical stability, higher glass transition temperature, strength, and hardness in the glass-ceramic. By controlling the type and amount of rare earth oxides, the hardness and other properties of the glass can be improved to a certain extent, resulting in performance superior to ordinary lithium aluminum silicon cover glass before and after crystallization. Excessive addition of rare earth oxides can lead to depolymerization of the glass network; therefore, this invention controls the molar percentage of rare earth oxides in the glass within the range of 2-4%.

[0041] Based on the molar percentage of oxides, the rare earth aluminosilicate microcrystalline glass provided by the present invention comprises ZrO2: 1-3%, preferably 2%. In this invention, ZrO2 possesses high hardness and fracture toughness, and its crystal size during crystallization is much smaller than the wavelength of visible light, resulting in extremely high transmittance. By adding zirconium dioxide, zirconium dioxide nanocrystals are precipitated in the glass-ceramic. Thanks to the small size (less than 30 nm) and uniform crystallization characteristics of the zirconium dioxide nanocrystals, the glass-ceramic does not exhibit fogging or devitrification, ensuring excellent light transmittance. Since ZrO2 has low solubility in silicate glass systems, excessively high content will cause glass devitrification. Furthermore, the introduction of ZrO2 increases the viscosity of the glass, reduces the coefficient of thermal expansion, and improves the alkali resistance. Considering that alkali metal ions and alkaline earth metal ions in this invention increase the solubility of ZrO2, and Al2O3 decreases the solubility of ZrO2, and combined with experimental findings that glass devitrification occurs when the molar content of ZrO2 reaches 4%, the molar percentage of ZrO2 in the glass is controlled within the range of 1-3%.

[0042] Based on the molar percentage of oxides, the rare-earth aluminosilicate microcrystalline glass provided by this invention preferably satisfies the following condition: Al2O3+MgO-Li2O-Na2O-K2O≥0%. In this invention, the crystallization of ZrO2 is related to the coordination of zirconium in the glass network. In systems with a high degree of polymerization (low non-bridging oxygen content), most of the ZrO2 crystals... 4+ It exists in 6-coordinated configurations, but also contains a certain amount of Zr. 4+ The ions exist in 8-coordinate configurations (CN = 8), sharing edges with the silicon-oxygen tetrahedra. Al₂O₃ and MgO form aluminum-oxygen tetrahedra and other structures in the glass network, which often carry a negative charge and require network modifier ions (Na₂O₃, Na₂O₃, and MgO). + Li + Charge compensation is performed, and this highly coordinated Zr (CN=8) is due to the network modifier ions (Na) in the system. + Li + Due to insufficient charge balance, Zr (CN=8) tends to form locally ordered Zr-rich structures. These Zr-rich regions become precursors for crystallization, promoting ZrO2 crystallization during heat treatment. Therefore, the above conditions must be met to ensure the precipitation of ZrO2 crystals.

[0043] In this invention, the rare-earth aluminosilicate microcrystalline glass has a crystalline phase of zirconium dioxide nanocrystals; the average crystal size of the zirconium dioxide nanocrystals is preferably ≤30nm; the zirconium dioxide nanocrystals are preferably uniformly distributed in the rare-earth aluminosilicate microcrystalline glass; the thickness of the rare-earth aluminosilicate microcrystalline glass is preferably ≤1mm, more preferably 1mm. By introducing zirconium dioxide into the microcrystalline glass, this invention can form uniformly distributed zirconium dioxide nanocrystals within the microcrystalline glass, thereby preventing fogging and devitrification, ensuring excellent light transmittance. When the thickness of the rare-earth aluminosilicate microcrystalline glass is ≤1mm, the visible light transmittance of the rare-earth aluminosilicate microcrystalline glass is greater than 90%.

[0044] In the rare-earth aluminosilicate microcrystalline glass provided by this invention, SiO2 plays a crucial role in improving the structure and properties of the glass. The [SiO4] tetrahedron, as the basic building block of the glass network, provides excellent mechanical strength and chemical stability. Simultaneously, the high chemical inertness and low coefficient of thermal expansion of SiO2 give the glass excellent corrosion resistance and thermal stability under various environments. Therefore, the introduction of SiO2 can significantly improve the overall performance of the glass. Al2O3 also plays a very positive role in improving the physical and chemical properties of the glass. Aluminum forms [AlO4] tetrahedra in the microcrystalline glass. The volume of the [AlO4] tetrahedron is larger than that of [SiO4], and Na is bonded to [AlO4]-. + It exhibits better mobility, and the precipitation of ZrO2 is accompanied by the transfer of alkali metal ions. Before precipitation, ZrO2 exists in the glass as [ZrO6] octahedra, carrying two units of negative charge. At this point, Na is required. + Li + Ions neutralize to achieve charge balance, so when ZrO2 is precipitated, the Na surrounding [ZrO6]... + Li + It will transfer to [AlO4]. -The addition of alumina around the tetrahedron is more conducive to ion exchange, increasing the depth of the exchange layer. Chemically strengthened glass-ceramics exhibit excellent mechanical properties. Na₂O and Li₂O are key exchange ions in the chemical strengthening of glass-ceramics. K₂O, Na₂O, and Li₂O, all alkali metal oxides, can increase the ion exchange rate and deepen the compressive stress layer. They can also break the network, reducing the viscosity and melting temperature of the glass. Small amounts of K₂O and Na₂O can create a mixed alkali effect, optimizing a range of glass properties. Rare earth oxides can make the glass network structure denser, giving glass-ceramics better chemical stability and higher mechanical properties. Glass transition temperature, strength, and hardness; ZrO2 has high hardness and fracture toughness. During crystallization, the grain size is much smaller than the wavelength of visible light, resulting in extremely high transmittance. By adding zirconium dioxide, zirconium dioxide nanocrystals are precipitated in the glass-ceramic. Thanks to the small size (less than 30 nm) and uniform crystallization of zirconium dioxide nanocrystals, the glass-ceramic does not exhibit fogging or devitrification, ensuring excellent light transmittance. MgO exists in two coordination states in glass (4-coordinate and 6-coordinate), but mostly exists as [MgO6] octahedrons, making the glass structure more compact. In ion exchange, MgO can also increase the surface compressive stress after ion exchange.

[0045] The rare-earth aluminosilicate microcrystalline glass provided by this invention has a zirconia nanocrystal crystal phase, which can prevent the microcrystalline glass from exhibiting phenomena such as fogging and devitrification, thus ensuring that the microcrystalline glass material has excellent light transmittance. The microcrystalline glass has a lower content of lithium and aluminum elements, which can reduce its production cost while ensuring the performance of the microcrystalline glass, thereby realizing low-cost large-scale application.

[0046] This invention also provides a method for preparing the rare-earth aluminosilicate microcrystalline glass described in the above technical solution, comprising the following steps:

[0047] (1) The raw materials are melted, shaped and annealed in sequence to obtain the base glass;

[0048] (2) Heat-treat the base glass obtained in step (1) to obtain microcrystalline glass containing ZrO2 crystals;

[0049] (3) The microcrystalline glass containing ZrO2 crystals obtained in step (2) is subjected to ion exchange in a salt bath to obtain rare earth aluminosilicate microcrystalline glass.

[0050] This invention involves melting, shaping, and annealing the raw materials sequentially to obtain basic glass.

[0051] The present invention does not impose any special limitations on the specific types, amounts, or methods of addition of the raw materials, as long as the amount of various oxides in the rare earth aluminosilicate microcrystalline glass meets the requirements.

[0052] This invention does not impose special requirements on the melting temperature and time; based on the technical knowledge of those skilled in the art, it is sufficient to keep the melt clear. In one embodiment of this invention, the melting temperature is 1550–1650°C.

[0053] The present invention does not impose any special limitations on the specific molding operation, and molding operations well known to those skilled in the art can be used.

[0054] In this invention, the annealing is preferably carried out in a muffle furnace. This invention does not specify a particular model of muffle furnace; any commercially available muffle furnace well-known to those skilled in the art can be used.

[0055] In this invention, the holding temperature for annealing is preferably lower than the glass transition temperature Tg50±10℃, more preferably lower than Tg50℃; the holding time for annealing is preferably 2-4 hours, more preferably 2.5-3.5 hours, and even more preferably 3 hours; the cooling method for annealing is preferably furnace cooling. This invention reduces the internal stress in the base glass through annealing; by controlling the parameters of the annealing process, the internal stress in the base glass can be further reduced.

[0056] After obtaining the base glass, the present invention performs heat treatment on the base glass to produce a microcrystalline glass containing ZrO2 crystals.

[0057] In this invention, the holding temperature of the heat treatment is preferably 700–900℃, more preferably 750–850℃, and even more preferably 800℃; the holding time of the heat treatment is preferably 4–20 h, more preferably 8–16 h, and even more preferably 10–12 h; the cooling method of the heat treatment is preferably furnace cooling. This invention, by heat treating the base glass, allows zirconium dioxide crystals to precipitate in the glass, thereby obtaining a microcrystalline glass containing ZrO2 crystals. By controlling the process parameters of the heat treatment, ZrO2 crystals can be fully precipitated, while not giving lithium crystals excessive nucleation and growth time, ensuring that the crystalline phase of the microcrystalline glass contains only zirconium oxide crystals and no Li-containing crystals.

[0058] After heat treatment, the product is preferably polished to obtain a microcrystalline glass containing ZrO2 crystals. The present invention does not have specific limitations on the polishing process, as long as the glass surface is smooth and free of impurities.

[0059] In this invention, the thickness of the microcrystalline glass containing ZrO2 crystals is preferably ≤1 mm, more preferably 0.5–1 mm, and even more preferably 0.8–1 mm. By controlling the thickness of the microcrystalline glass, this invention can further improve the light transmittance of the microcrystalline glass.

[0060] After obtaining the microcrystalline glass containing ZrO2 crystals, the present invention performs ion exchange on the microcrystalline glass containing ZrO2 crystals in a salt bath to obtain rare earth aluminosilicate microcrystalline glass.

[0061] In this invention, the salt bath composition preferably includes 50-100 wt% NaNO3 and 0-50 wt% KNO3, more preferably 60-90 wt% NaNO3 and 10-40 wt% KNO3, and even more preferably 70-80 wt% NaNO3 and 20-30 wt% KNO3. This invention enables ion exchange in a salt bath, allowing for sodium-to-lithium exchange, potassium-to-sodium exchange, and a small portion of potassium-to-lithium exchange; by controlling the composition of the salt bath, the efficiency of ion exchange can be improved.

[0062] In this invention, the ion exchange is preferably a low-temperature ion exchange; the ion exchange temperature is preferably 400–500°C, more preferably 420–480°C, and even more preferably 450°C; the ion exchange time is preferably 5–20 h, more preferably 10–15 h. This invention forms an ion exchange layer on the surface of glass-ceramics through ion exchange, enabling the glass-ceramics to form a surface compressive stress greater than 800 MPa, further enhancing the glass's performance. By controlling the composition of the salt bath and the parameters of the ion exchange, the stress layer depth of the surface compressive stress can reach 50–70 μm. The higher ion exchange layer depth and surface compressive stress result in chemically strengthened glass-ceramics with higher hardness and fracture toughness; the Vickers hardness of the glass after ion exchange is greater than 700 kgf / mm². 2 At the same time, using low-temperature ion exchange can avoid the effects of excessively high temperatures on zirconium dioxide crystals, such as causing the grains to become larger.

[0063] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0064] Examples 1-8

[0065] The compositions of the rare earth aluminosilicate microcrystalline glasses provided in Examples 1-8 are shown in Table 1, based on the molar percentage of oxides.

[0066] The method for preparing rare-earth aluminosilicate microcrystalline glass provided in Examples 1-8 consists of the following steps:

[0067] (1) The raw material is melted at 1600℃, then formed and annealed in sequence, and finally cooled in the furnace to obtain the base glass; the annealing is carried out in a muffle furnace; the holding temperature of the annealing is 50℃ lower than the glass transition temperature Tg, and the holding time of the annealing is 3h.

[0068] (2) The base glass obtained in step (1) is subjected to heat treatment, cooled in the furnace and then polished to obtain a microcrystalline glass containing ZrO2 crystals with a thickness of 0.8 mm; the heat treatment holding temperatures are 700℃, 750℃, 800℃, 850℃ and 900℃ respectively, and the heat treatment holding time is 10h, that is, corresponding to 700℃ / 10h, 750℃ / 10h, 800℃ / 10h, 850℃ / 10h and 900℃ / 10h in Table 2 respectively;

[0069] (3) The microcrystalline glass containing ZrO2 crystals obtained in step (2) is subjected to ion exchange in a salt bath to obtain rare earth aluminosilicate microcrystalline glass; the salt bath composition is: 60wt% NaNO3 and 40wt% KNO3; the ion exchange temperature is 450℃ and the ion exchange time is 5h.

[0070] The appearance characteristics of the base glass and the ZrO2 crystal-containing microcrystalline glass obtained during the preparation process of the rare earth aluminosilicate microcrystalline glass provided in Examples 1-8 are shown in Table 1:

[0071] Table 1 shows the composition of the rare-earth aluminosilicate microcrystalline glass provided in Examples 1-8, and the appearance characteristics of the base glass and the microcrystalline glass containing ZrO2 crystals during the preparation process.

[0072]

[0073]

[0074] As can be seen from the appearance characteristics of microcrystalline glass containing ZrO2 crystals in Table 1, the ZrO2 crystals precipitated inside the glass after heat treatment crystallization do not affect the colorless and transparent appearance of the microcrystalline glass.

[0075] The properties of the base glass obtained in step (1) of Examples 1-8, the microcrystalline glass containing ZrO2 crystals obtained in step (2), and the rare earth aluminosilicate microcrystalline glass obtained in step (3) were tested, and the results are shown in Table 2:

[0076] Table 2 shows the properties of the glass provided in Examples 1-8.

[0077]

[0078]

[0079] In Table 2, AP1 is the base glass. The temperature and time below AP1 represent the microcrystalline glass containing ZrO2 crystals obtained after 10 hours at different heat treatment temperatures. AP2 refers to the aluminosilicate glass obtained by direct ion exchange from the base glass. The temperature and time below AP2 represent the rare earth aluminosilicate microcrystalline glass obtained by ion exchange from the microcrystalline glass containing ZrO2 crystals obtained after 10 hours at different heat treatment temperatures from the base glass.

[0080] As can be seen from the results in Table 2, compared with the uncrystallized base glass, the rare-earth aluminosilicate microcrystalline glass obtained after crystallization in this invention exhibits improved Vickers hardness and fracture toughness. The Vickers hardness of the uncrystallized base glass ranges from 636 to 655 kgf / mm². 2 The rare-earth aluminosilicate microcrystalline glass containing ZrO2 crystals provided by this invention can achieve a Vickers hardness of 649–684 kgf / mm². 2 The fracture toughness of glass obtained by direct ion exchange of uncrystallized base glass is between 1.03 and 1.18 MPa·m. 1 / 2 The fracture toughness of the microcrystalline glass containing ZrO2 crystals obtained after crystallization can reach 1.30–1.38 MPa·m. 1 / 2 The fracture toughness of the rare-earth aluminosilicate microcrystalline glass obtained after ion exchange can reach 1.33–1.41 MPa·m. 1 / 2 Significant improvements were achieved.

[0081] As shown in Table 2, the precipitation of ZrO2 in rare-earth aluminosilicate glass-ceramics did not weaken the ion exchange capacity of the glass; instead, it increased the depth of the ion exchange layer. Regarding the surface compressive stress of chemically strengthened glass, with increasing ion exchange temperature (while maintaining the same ion exchange time), the surface compressive stress showed a trend of first increasing and then decreasing. Similarly, with prolonged ion exchange time (while maintaining a constant ion exchange temperature), the surface compressive stress also showed a trend of first increasing and then decreasing. This is a result of structural relaxation of the glass under high-temperature conditions (i.e., immersion in high-temperature molten salt). In the early stages of ion exchange, the increase in surface compressive stress is dominant, while in the later stages, structural relaxation under stress is dominant. As for the stress layer depth of chemically strengthened glass, the stress layer depth increases with increasing ion exchange temperature or prolonged time.

[0082] The rare earth aluminosilicate microcrystalline glass provided in Examples 1-8 of this invention can achieve a surface compressive stress CS≥800Mpa and a strengthening depth, i.e., ion exchange layer depth DOL>50μm, which is beneficial to improving drop resistance and better meets the application requirements of touch screens.

[0083] Figure 1 X-ray diffraction (XRD) patterns of the base glass provided in Example 1 and rare-earth aluminosilicate microcrystalline glasses obtained at different heat treatment temperatures. Figure 1 As can be seen, the heat treatment methods of 700℃ / 10h, 750℃ / 10h, and 800℃ / 10h used in Example 1 precipitated ZrO2 crystals. No crystallization occurred in the sample of Example 1 under the 700℃ / 10h heat treatment, while ZrO2 crystals precipitated under the 750℃ / 10h heat treatment, while the glass remained colorless and transparent. When the crystallization temperature was further increased to 800℃, the XRD diffraction peak intensity increased, indicating an increase in the degree of ZrO2 crystallization.

[0084] Figure 2 X-ray diffraction (XRD) patterns of the base glass provided in Example 4 and rare-earth aluminosilicate microcrystalline glasses obtained at different heat treatment temperatures. Figure 2 As can be seen, the heat treatment methods of 750℃ / 10h, 800℃ / 10h, and 850℃ / 10h used in Example 4 precipitated ZrO2 crystals. No crystallization occurred in the sample of Example 4 under the 750℃ / 10h heat treatment, while ZrO2 crystals precipitated under the 800℃ / 10h heat treatment, while the glass remained colorless and transparent. When the crystallization temperature was further increased to 850℃, the degree of ZrO2 crystallization increased, and the diffraction peak intensity became stronger.

[0085] Figure 3 These are the TG-DSC images of the rare-earth aluminosilicate microcrystalline glasses obtained in Examples 1-4 of this invention. From... Figure 3 It can be seen that the rare earth aluminosilicate microcrystalline glass obtained in Example 1 has a low aluminum and silicon content and a high lithium content, resulting in a low glass transition temperature Tg and a low crystallization peak temperature Tp.

[0086] Figure 4 These are the light transmittance curves of the rare-earth aluminosilicate microcrystalline glass obtained in Examples 1-4 of this invention. Figure 4 It can be seen that the transmittance of the microcrystalline glass of the present invention can reach more than 90% in the visible light band (380nm~780nm).

[0087] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1.A rare earth aluminosilicate glass-ceramic, having a composition in terms of mole percentage on an oxide basis as follows: SiO 2: 56-62%; Al 2O 3: 10-18%; Na 2O: 4-8%; Li 2O: 4-7%; rare earth oxide: 2-4%; ZrO 2: 1-3%; MgO≤4% and K 2O≤2%, wherein MgO and K 2O are not both 0; wherein the rare earth oxide comprises at least one of La 2O 3, Y 2O 3 and CeO 2; when La 2O 3 is contained in the rare earth oxide, the mole percentage of La 2O 3 in the rare earth aluminosilicate glass-ceramic is 1-3%; when Y 2O 3 is contained in the rare earth oxide, the mole percentage of Y 2O 3 in the rare earth aluminosilicate glass-ceramic is≤2%; when CeO 2 is contained in the rare earth oxide, the mole percentage of CeO 2 in the rare earth aluminosilicate glass-ceramic is≤1%; wherein the content of the rare earth oxide satisfies the following relationship: La 2O 3+CeO 2-Y 2O 3≥0; wherein the crystal phase of the rare earth aluminosilicate glass-ceramic is zirconia nanocrystal; wherein the average crystal size of the zirconia nanocrystal is≤30nm; wherein the rare earth aluminosilicate glass-ceramic satisfies the following condition: Al 2O 3+MgO-Li 2O-Na 2O-K 2O≥0% in terms of mole percentage on an oxide basis. 2.A method for preparing the rare earth aluminosilicate glass-ceramic of claim 1, comprising the following steps: (1) melting, forming and annealing raw materials to obtain a base glass; (2) heat treating the base glass obtained in step (1) to obtain a glass-ceramic containing ZrO 2 crystals; (3) ion exchanging the glass-ceramic containing ZrO 2 crystals obtained in step (2) in a salt bath to obtain the rare earth aluminosilicate glass-ceramic; wherein the annealing temperature in step (1) is lower than the glass transition temperature T g 50±10℃; wherein the heat treatment temperature in step (2) is 700-900℃ and the heat treatment holding time is 4-20h; wherein the salt bath in step (3) comprises 50-100wt% NaNO 3 and 0-50wt% KNO 3. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 3. The preparation method according to claim 2, characterized in that, The ion exchange temperature in the step (3) is 400-500 DEG C, and the ion exchange time is 5-20h.

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