WO2021053695A1

WO2021053695A1 - High performance strengthened glass

Info

Publication number: WO2021053695A1
Application number: PCT/IN2020/050806
Authority: WO
Inventors: Dr. Jeetendra SEHGAL; Chunyu Chiu; Biswanath Sen
Original assignee: Avanstrate Inc.
Priority date: 2019-09-21
Filing date: 2020-09-20
Publication date: 2021-03-25
Also published as: CN115244018A

Abstract

Disclosed a cover glass and a glass composition that has higher Specific Strengthening Performance Factor (SSPF). The SSPF is defined as (Young's Modulus)/(Density * Coefficients of Linear Thermal Expansion (CTE) * Annealing Point). The SSPF is ion-exchangeable and is in a range from 6 Gm²/s² to 12 Gm²/s², making the glass relatively faster to strengthen by performing single and/or multiple ion exchanges. A depth of layer (DOL) greater than 20 microns and a compressive stress (CS) greater than 600 MPa (for cover glass thickness of 300 microns and more) and DOL greater than 5 microns and the CS greater than 300 MPa (for cover glass thickness of 300 microns and less) are reached in short time after performing single and/or multiple ion exchanges. The glass composition is well suited for single and/or multiple ion exchanges, resulting in better service durability and high sharp impact strength.

Description

HIGH PERFORMANCE STRENGTHENED GLASS BACKGROUND FIELD OF THE INVENTION Various embodiments of the disclosure generally relate to glass covers. More specifically, various embodiments of the disclosure relate to an ion-exchangeable glass and a glass composition of the ion-exchangeable glass that has higher Specific Strengthening Performance Factor (SSPF). DESCRIPTION OF THE RELATED ART Strengthened glasses produced by chemically strengthening glass substrates have been conventionally used, for example, as cover materials for protecting the display screens of various equipment such as mobile phones, digital cameras, and the like. The glass substrates for use as a protective member for such devices are required to have high mechanical strength, high Young’s modulus, and low density. For satisfying the requirement, the glass substrates are conventionally strengthened by ion exchange or the like. Glasses used for displays in electronic devices are typically chemically or thermally tempered to produce a surface compressive layer. This compressive layer serves to arrest flaws that can cause failure of the glass, including low tensile strength and slow cooling resulting in fragile toughening. Also, the speed of ion exchange in the conventional process is slow, thereby requiring more time for the ion exchange. In light of the foregoing, the present disclosure proposes single and/or multiple ion-exchangeable glass composition for a cover glass. More particularly, the present disclosure relates to ion-exchangeable glasses that are capable of achieving high speed of ion exchange, short period of time for ion exchange, high depth of layer (DOL), high tensile strength, and high surface compressive stress. OBJECTS OF THE INVENTION Some of the objects of the present disclosure are described herein. An object of the present disclosure is to provide a cover glass and a glass composition. Another object is to provide the cover glass and the glass composition for touch panel displays. Another object of the present disclosure is to provide the cover glass and the glass composition, that has high Specific Strengthening Performance Factor (SSPF). Another object of the present disclosure is to provide the cover glass with high strength by a chemical strengthening treatment through single and/or multiple ion exchanges. Another object of the present disclosure is to provide the cover glass having thickness from 20 microns to 2 mm. Another object of the present disclosure is to provide the cover glass that is light-weight. Other objects and advantages of the present disclosure will be more apparent from the following description, which are not intended to limit the scope of the present invention. SUMMARY OF THE INVENTION In an embodiment of the present disclosure, a cover glass and a glass composition have been disclosed. The present disclosure discloses an alkali aluminosilicate glass. The alkali aluminosilicate glass having a specific strengthening performance factor (SSPF) ranging from 6 Gm²/s² to 12 Gm²/s² is ion-exchangeable. The specific strengthening performance factor (SSPF) is obtained by following equation, SSPF = (Young’s modulus) / (Density * Coefficient of thermal expansion (CTE) * Annealing point). In an embodiment, the glass may be provided with high strength by a chemical strengthening treatment through single and/or multiple ion exchanges. When the SSPF is in a range from 6 Gm²/s² to 9 Gm²/s², the glass is relatively faster to strengthen by performing single and/or multiple ion exchanges. When a cover glass undergoes single and/or multiple ion exchanges, for example, two-step ion exchanges, the treatment results in a depth of layer (DOL) and a compressive stress (CS) in short time in the cover glass. For the ion exchanged cover glass with thickness greater than or equal to 300 microns, the DOL is greater than 20 microns and the CS is greater than 600 MPa. For the ion exchanged cover glass with thickness less than or equal to 300 microns, the DOL is greater than 5 microns and the CS is greater than 300 MPa. In an embodiment, the glass composition is well suited for the single and/or multiple ion exchanges, preferably two-step ion exchanges. In an embodiment, the glass composition may be suitable for the two-step ion exchange with compressive stress of greater than 300 MPa. In an embodiment, the glass composition is suitable for the two-step ion exchange with DOL more than 5 microns. As a result, better service durability, higher crack resistance, higher retained strength after damage, and high sharp impact strength are achieved for the glass, and the glass can survive a greater number of device drops before failure. In an embodiment, during the process of performing the two-step ion exchanges, firstly one ion pair is exchanged, followed by another ion exchange that reintroduces the original ion or introduces another ion in an outermost surface layer. In an embodiment, the ion exchange process may be based on a principle of exchange of ions present in the glass by ions of different sizes. When a larger ion is exchanged for a smaller ion in the glass, the larger ion literally stuffs the surface, putting it into compression with a balancing tensile stress in the interior. It is reported that the compressive stress generated is directly proportional to the glass volume where ion exchange has occurred. In an embodiment, the glass composition includes SiO₂ from about 50 mole % to about 80 mole %, Al₂O₃ from about 5 mole % to about 25 mole %, and B₂O₃ from about 0 mole % to about 15 mole %. In an embodiment, the glass composition further includes alkali metal oxides, wherein sum of total alkali metal oxides present in the glass composition, R₂O is from about 5 mole % to 30 mole %. In an embodiment, the alkali metal oxides are selected from group consisting of Li₂O, Na₂O, and K₂O. In an embodiment, the glass composition further includes alkaline oxides, wherein sum of total alkaline earth metal oxides present in the glass composition, RO is from about 0 mole % to about 15 mole %. In an embodiment, the alkaline earth metal oxides are selected from group consisting of MgO, CaO, SrO, and BaO. In an embodiment, the glass composition further includes P₂O₅ from about 0 mole % to about 10 mole %, ZnO from about 0 mole % to about 10 mole %, and ZrO₂ from about 0 mole % to about 10 mole %. In an embodiment, the glass composition further includes one or more refining agents such as SnO₂ from about 0 mole % to about 2.5 mole % and Fe₂O₃ from about 0 mole % to about 2.5 mole %. Further, it may also include other refining agents such as CeO₂, chloride, sulphate and the like. In an embodiment, the thickness of the cover glass is in a range from 20 microns to 2 mm. In an embodiment, the glass may be employed as substrates for touch-panel displays and back cover for these displays such as a liquid crystal display (LCD), a field emission display (FED), a plasma display (PD), an electroluminescence display (ELD), an organic light emitting diode (OLED) display, a micro LED, and the like. The glass may also be employed as substrates for cover glasses for solar batteries, substrates for magnetic disks, and window panes. These and other aspects, advantages, and salient features of the present disclosure will become apparent from the following detailed description. DETAILED DESCRIPTION In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures. It is also understood that, unless otherwise specified, terms such as “top,” “bottom,” “outward,” “inward,” and the like are words of convenience and are not to be construed as limiting terms. In addition, whenever a group is described as comprising at least one of a group of elements and combinations thereof, it is understood that the group may comprise, consist essentially of, or consist of any number of those elements recited, either individually or in combination with each other. Similarly, whenever a group is described as consisting of at least one of a group of elements or combinations thereof, it is understood that the group may consist of any number of those elements recited, either individually or in combination with each other. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range as well as any ranges therebetween. As used herein, the indefinite articles “a,” “an,” and the corresponding definite article “the” mean “at least one” or “one or more,” unless otherwise specified. It also is understood that the various features disclosed in the specification and the drawings can be used in any and all combinations. As used herein, the terms “glass article” and “glass articles” are used in their broadest sense to include any object made wholly or partly of glass. Unless otherwise specified, all compositions are expressed in terms of mole percent (mol %). Coefficients of thermal expansion (CTE) are expressed in terms of 10^-7/°C and represent a value measured over a temperature range from about 30°C to about 300°C, unless otherwise specified. Unless otherwise specified, all temperatures are expressed in terms of degrees Celsius (°C). As used herein the term “softening point” refers to the temperature at which the viscosity of a glass is approximately 1x10^7.6 poise (P). As used herein the term “annealing point” or “anneal point” refers to the temperature at which the viscosity of a glass is approximately 1x10^13.2 poise. As used herein the term “200 poise temperature (T^200P)” refers to the temperature at which the viscosity of a glass is approximately 200 poise, the term “10¹¹ poise temperature” refers to the temperature at which the viscosity of a glass is approximately 10¹¹ poise, the term “35 kP temperature (T^35kP)” refers to the temperature at which the viscosity of a glass is approximately 35 kilo Poise (kP), and the term “160 kP temperature (T^160kP)” refers to the temperature at which the viscosity of a glass is approximately 160 kP. It is noted that the terms “substantially” and “about” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. Cover glasses and glass compositions for producing the same of the present disclosure will be described in detail below. A cover glass, as described below, is used for protecting the display screen (for example, touch based displays) of electronic devices such as mobile phones, smart phones, tablets, wearables device, digital cameras, and the like. Cover glass used on the backside is required for better electromagnetic transmission besides providing strength to the device. However, the cover glasses are not limited to the aforementioned applications, and may also be employed, for example, as substrates for touch-panel displays, cover glasses for solar batteries, substrates for magnetic disks, and window panes. The present invention discloses a cover glass and a glass composition, which has higher Specific Strengthening Performance Factor (SSPF). The SSPF is defined as a ratio of a first value and a second value. The first value is defined by Young’s Modulus of the glass, and the second value is defined by a product of density, CTE, and annealing point of the glass. For example, the SSPF is represented by the following equation (1): (1)

In an embodiment, the glass may be provided with high strength by a chemical strengthening treatment through single and/or multiple ion exchanges. The chemical strengthening treatment is a method in which alkali ions having a large ionic radius are diffused into the surface of a glass substrate by single and/or multiple ion exchanges at a temperature not higher than the strain point of the glass. The strengthening treatment may be satisfactorily conducted even when the glass substrate has a small thickness, whereby desired mechanical strength can be obtained. Moreover, even when the glass substrate in which a compression stress layer has been formed is cut, this glass substrate does not break readily unlike glass substrates strengthened by physical strengthening methods, such as the air-cooling tempering method. In an embodiment, the glass may be provided with high speed of ion exchange, resulting in short period of time for the ion exchange. The performance of ion exchange and a depth of layer (DOL) for the glass increases, resulting in high surface compressive stress for the cover glass. Also, the cover glass is chemically toughened/tempered. In an embodiment, the glass composition for obtaining the cover glass includes various components such as SiO₂, Al₂O₃, and R₂O. Here, the cover glass is an alkali aluminosilicate glass. In an embodiment, the glass composition further includes other components such as at least one of B₂O₃, RO, P₂O₅, ZnO, ZrO₂, SnO₂, CeO₂, and Fe₂O₃. In an embodiment, SiO₂ is a component which forms a glass network. In case where the content of SiO₂ is too high, this glass is difficult to melt and form or this glass has too low coefficient of thermal expansion and is difficult to have the same coefficient of thermal expansion as peripheral materials. On the other hand, in case where the content of SiO₂ is too low, vitrification is difficult. In addition, such a glass has an increased coefficient of thermal expansion, which tends to be reduced in thermal shock resistance. Thus, an optimum mole % of SiO₂ is required for the glass composition. For example, the glass composition may include SiO₂ from about 50 mole % to about 80 mole %. In an embodiment, Al₂O₃ is a component which enhances suitability for single and/or multiple ion exchanges. Al₂O₃ further has an effect of enhancing the heat resistance and Young’s modulus of the glass. In case where the content of Al₂O₃ is too high, devitrified crystals are easy to separate out in the glass, making it difficult to form the glass by the overflow downdraw process or the like. Moreover, such a glass has an increased viscosity at high temperatures and is difficult to melt. When the content of Al₂O₃ is too low, there is a possibility that the glass cannot have sufficient suitability for single and/or multiple ion exchanges. From those standpoints, an optimum mole % of Al₂O₃ is required for the glass composition. For example, the glass composition may include Al₂O₃ from about 5 mole % to about 25 mole %. In an embodiment, B₂O₃ is a component which has an effect of lowering the liquidus temperature, high-temperature viscosity, and density of the glass and further has an effect of enhancing the suitability for single and/or multiple ion exchanges of the glass. The content thereof may be from about 0 mole % to about 15 mole %. On the other hand, in case where the content of B₂O₃ is too high, there is a possibility that ion exchange might leave stains on the surface or that the glass might have impaired water resistance or have a reduced liquidus viscosity and reduced Young’s modulus. In an embodiment, the glass composition further includes alkali metal oxides, wherein sum of alkali metal oxides, R₂O is in the range from about 5 mole % to 30 mole %. In an embodiment, the alkali metal oxides are selected from group consisting of Li₂O, Na₂O, and K₂O. In an embodiment, the glass composition further includes alkaline earth metal oxides, wherein sum of alkaline earth metal oxides, RO is in the range from about 0 mole % to about 15 mole %. In an embodiment, the alkaline earth metal oxides are selected from group consisting of MgO, CaO, SrO, and BaO. In an embodiment, the glass composition further includes P₂O₅ from about 0 mole % to about 10 mole %. P₂O₅ is an ingredient which enhances the suitability for the ion exchange of the glass and is highly effective especially in increasing the depth of the compression stress layer. Since, high P₂O₅ content may cause phase separation in the glass or impair water resistance, the content of P₂O₅ may be in a range of 0-10 mole %. In an exemplary embodiment, the glass may include ZnO from about 0 mole % to about 10 mole %. In an embodiment, the glass composition further includes one or more refining agents such as SnO₂ from about 0 mole % to about 2.5 mole % and Fe₂O₃ from about 0 mole % to about 2.5 mole %. Further, it may also include other refining agents such as CeO₂, chloride, sulphate and the like. In an embodiment, the thickness of glass obtained from the above glass composition is in the range from 20 microns to 2 mm. In an embodiment, the glass composition may or may not include ZrO₂. In one exemplary embodiment, the glass may be free of ZrO₂. In another exemplary embodiment, the glass may include ZrO₂ from about 0 mole % to about 10 mole %. In an embodiment, the SSPF of the glass may range from 6 Gm²/s² to 12 Gm²/s². When the SSPF is in a range from 6 Gm²/s² to 9 Gm²/s², the glass is relatively faster to strengthen by performing single and/or multiple ion exchanges. When a cover glass undergoes single and/or multiple ion exchanges, for example, two-step ion exchanges, the treatment results in a depth of layer (DOL) and a compressive stress (CS) in short time in the cover glass. For the ion exchanged cover glass with thickness greater than or equal to 300 microns, a depth of layer (DOL) is greater than 20 microns and a compressive stress (CS) is greater than 600 MPa. For the ion exchanged cover glass with thickness less than or equal to 300 microns, the DOL is greater than 5 microns and the CS is greater than 300 MPa. A compressive layer extends from the surface to the DOL or compression within the glass. The glass has a coefficient of thermal expansion which ranges from 49×10^-7/°C to 95.9×10^-7/°C. The glass has a Young’s Modulus which ranges from 60 to 95 GPa. In an embodiment, higher the Young’s modulus of the glass is, lesser the glass substrate bends. As a result, when the glass substrate is used in a touch panel display and the display is pushed with a pen or the like, then the liquid-crystal element disposed inside the device is less easy to be pressed and a display failure is less likely to occur. When the Young’s modulus is to be heightened, this may be attained by increasing the content of at least one of Al₂O₃, Li₂O, ZnO, MgO, and ZrO₂, or by reducing the content of B₂O₃. Table-1 illustrates non-limiting, exemplary glass compositions and its corresponding physical properties that include glass transition temperature (Tg), density, Young’s modulus (YM), coefficient of thermal expansion (CTE), anneal point, and SSPF.

Table-1: Exemplary compositions and physical properties of a glass Table-2 illustrates non-limiting, exemplary glass compositions and its corresponding physical properties that include glass transition temperature (Tg), density, Young’s modulus (YM), coefficient of thermal expansion (CTE), anneal point, and SSPF.

Table-2: Exemplary compositions and physical properties of a glass Table-3 illustrates non-limiting, exemplary glass compositions and its corresponding physical properties that include glass transition temperature (Tg), density, Young’s modulus (YM), coefficient of thermal expansion (CTE), anneal point, and SSPF.

Table-3: Exemplary compositions and physical properties of a glass Table-4 illustrates non-limiting, exemplary glass compositions and its corresponding physical properties that include glass transition temperature (Tg), density, Young’s modulus (YM), coefficient of thermal expansion (CTE), anneal point, and SSPF.

Table-4: Exemplary compositions and physical properties of a glass Table-5 illustrates non-limiting, exemplary glass compositions and its corresponding physical properties that include glass transition temperature (Tg), density, Young’s modulus (YM), coefficient of thermal expansion (CTE), anneal point, and SSPF.

Table-5: Exemplary compositions and physical properties of a glass Table-6 illustrates non-limiting, exemplary glass compositions and its corresponding physical properties that include density, Young’s modulus (YM), coefficient of thermal expansion (CTE), anneal point, and SSPF.

Table-6: Exemplary compositions and physical properties of a glass Table-7 illustrates non-limiting, exemplary glass compositions and its corresponding physical properties that include density, Young’s modulus (YM), coefficient of thermal expansion (CTE), anneal point, and SSPF.

Table-7: Exemplary compositions and physical properties of a glass Table-8 illustrates non-limiting, exemplary glass compositions and its corresponding physical properties that include density, Young’s modulus (YM), coefficient of thermal expansion (CTE), anneal point, and SSPF.

Table-8: Exemplary compositions and physical properties of a glass In an embodiment, the glass composition includes SiO₂ from about 50 mole % to about 80 mole %, Al₂O₃ from about 5 mole % to about 25 mole %, and B₂O₃ from about 0 mole % to about 15 mole %. In an embodiment, the glass composition further includes total alkali oxide R₂O from about 5 mole % to 30 mole %, wherein R is at least one of Li, Na, and K. In an embodiment, the glass composition further includes alkaline oxides RO from about 0 mole % to about 15 mole %, wherein R is at least one of Mg, Ca, Sr, and Ba. In an embodiment, the glass composition further includes P₂O₅ from about 0 mole % to about 10 mole %, ZnO from about 0 mole % to about 10 mole %, and ZrO₂ from about 0 mole % to about 10 mole %. In an embodiment, the glass composition further includes one or more refining agents such as SnO₂ from about 0 mole % to about 2.5 mole % and Fe₂O₃ from about 0 mole % to about 2.5 mole %. Further, it may also include other refining agents such as CeO₂, chloride, sulphate and the like. In one exemplary embodiment, the glass is preferably alkali aluminosilicate glass. In another exemplary embodiment, the glass is more preferably lithium aluminosilicate glass. In one exemplary embodiment, the glass composition includes from about 60 mole % to about 72.2 mole % SiO₂, from about 8.5 mole % to about 16.6 mole % Al₂O₃, from 0 mole % to about 4.3 mole % B₂O₃, from about 8.8 mole % to about 30 mole % R₂O, wherein R is at least one of Li, Na, and K, from 0 mole % to about 7.7 mole % of RO, wherein R is at least one of Mg, Ca, and Sr, and from about 0 mole % to about 3.2 mole % P₂O₅. The glass composition may further include ZnO from about 0 mole % to about 3.5 mole % and ZrO₂ from about 0 mole % to about 3 mole %. The glass composition may further include refining agent such as SnO₂ from about 0 mole % to about 0.2 mole %. The SSPF of the glass with the above composition is in a range from 6 Gm²/s² to 9 Gm²/s². The SSPF is Specific Strengthening Performance Factor and is defined as the ratio of (Young’s Modulus) / (Density * CTE * Annealing Point). In an exemplary embodiment, the glass composition for the cover glass further essentially consists of Li₂O from 5.3 mole % to 16.4 mole %. In an exemplary embodiment, the glass composition for the cover glass further essentially consists of Na₂O from 3.5 mole % to 11.9 mole %. In an exemplary embodiment, the glass composition for the cover glass further essentially consists of a ratio of Al₂O₃/R₂O ranging from 0.3 to 1.3. In an embodiment, the glass composition having the thermal coefficient of expansion ranges from about 49×10^-7/°C to about 95.9×10- ⁷/°C. In an embodiment, the glass composition having the Young’s modulus ranges from greater than or equal to 60 GPa to less than or equal to 95 GPa (i.e., 60 GPa £ Young’s modulus £ 95 GPa). In an embodiment, the glass composition having density ranges from 2.30 to 2.55 g/cc. Table-9 illustrates non-limiting, experimental exemplary glass compositions and its corresponding physical properties that include glass transition temperature (Tg), density, Young’s modulus (YM), coefficient of thermal expansion (CTE), anneal point, and devitrification temperature. Also, it describes whether the glass undergoes phase separation.

Table-9: Exemplary compositions and physical properties of a glass Table-9 focuses on chemically strengthened lithium and magnesium containing glass compositions. It describes the influence of magnesium on phase separation of glass. High amount of magnesium in the glass composition results in phase separation of glass during glass welding or cooling process. Glass with low amount of magnesium is used to obtain a glass free of phase separation. Such a glass is substantially free of As₂O₃ and Sb₂O₃. Below are the limitations applicable to obtain an ion exchangeable glass with no phase separation and low devitrification temperature. [{(MgO+K₂O)/SiO₂}*(Al₂O₃+Li₂O+Na₂O+P₂O₅)] £ 0.70 (2) (MgO+K₂O) £1.5 (3) (Al₂O₃+Li₂O+Na₂O+P₂O₅) £37 (4) Al₂O₃/ R₂O £1 (R₂O = Li₂O+ Na₂O+ K₂O) (5) In an embodiment, during the two-step ion exchange process, firstly one ion pair is exchanged, followed by another ion exchange that reintroduces the original ion or introduces another ion in an outermost surface layer. In an embodiment, the ion exchange process is based on a principle of exchange of ions present in the glass by ions of different sizes. When a larger ion is exchanged for a smaller ion in the glass, the larger ion literally stuffs the surface, putting it into compression with a balancing tensile stress in the interior. It is reported that the compressive stress generated, which is directly proportional to the glass volume where ion exchange has occurred. The ion exchangeable glass having a high CTE may be used as a cover glass. Once ion exchanged, the glass exhibits high resistance to cracking. In some embodiments, the glasses described herein are ion exchanged using known techniques in the art. In one exemplary embodiment, one set of samples of each composition may be ion exchanged in a single-step process by immersion in a molten salt bath (which is maintained at a temperature between 300^oC to 500^oC) containing more than 60 weight % KNO₃ and less than 20 weight % NaNO3 for a fixed number of hours such as greater than 0.5 hours. Two-step ion exchange process is performed by immersion in a molten salt bath (which is maintained at a temperature between 300^oC to 500^oC) containing more than 60 weight % KNO₃ and less than 20 weight % NaNO₃ for a fixed number of hours such as greater than 0.5 hours, followed by immersion in KNO₃ molten salt bath (which is maintained at a temperature between 300^oC to 500^oC) for a fixed number of hours such as greater than 0.5 hours. Immersion in the second ion exchange bath in accordance with the methods described hereinabove increases the compressive stress of all samples. Table-10 illustrates maximum depth of layer (DOL_ZERO) and compressive stress (CS) for each step of double (two-step) ion exchange process in different reaction conditions of specific glass compositions.

Table-10: Exemplary samples with DOL and CS for each step of double ion exchange process In an exemplary embodiment, alkali cations within a source of such cations (e.g., a molten salt, or “ion-exchange,” bath) are exchanged with smaller alkali cations within the glass to achieve a layer that is under the CS near the surface of the glass. The compressive layer extends from the surface to the DOL or compression within the glass. Each compressive layer has a maximum compressive stress (CS) at the surface of at least 300 MPa. The SSPF of the present invention helps in determining a glass composition that has high chemical strengthening rate during single and/or multiple ion exchange process. The SSPF allows to determine whether the chosen glass composition can have high chemical strengthening rate or not. Use of SSPF to determine chemical strengthening rate saves time and costs. In a special embodiment, the present disclosure further focuses on a backside cover glass for protecting backside of electronic devices such as mobile phones, smart phones, tablets, wearables device, digital cameras, and the like. Cover glass used on the backside is required for better electromagnetic transmission besides providing strength to the device. For design reasons, a coloration opaque appearance may be possible. One way to realize this is by including one or more transition elements in the glass melt. The one or more transition elements may be at least one of Nb₂O₅, ZrO₂, Fe₂O₃, V₂O₅, Y₂O₃, MnO₂, NiO, CuO, Cr₂O₃, Co₃O₄, CoO, Co₂O₃, and the like. The present disclosure provides the cover glass with high strength by a chemical strengthening treatment through single and/or multiple ion exchanges. The glass may be provided with high speed of ion exchange, resulting in short period of time for the ion exchange. The performance of ion exchange and DOL for the glass increases, resulting in high surface compressive stress for the glass cover. Also, the glass cover is provided with strong chemical toughening. The cover glass does not break readily unlike glass substrates strengthened by physical strengthening methods. Apart from strengthened cover glass, the present invention also describes glass-based articles such as glass ceramics. Method of controlled devitrification helps in converting the glass to a predominantly crystalline glass-ceramic material. Such glass ceramic composition comprises of TiO₂ from about 0 mole % to about 6 mole %. While typical embodiments have been set forth for the purpose of illustration, the foregoing description should not be deemed to be a limitation on the scope of the disclosure or appended claims. Accordingly, various modifications, adaptations, and alternatives may occur to one skilled in the art without departing from the spirit and scope of the present disclosure.

Claims

Claims: 1. An alkali aluminosilicate glass, the alkali aluminosilicate glass comprising: the alkali aluminosilicate glass having a specific strengthening performance factor (SSPF) ranging from 6 Gm²/s² to 12 Gm²/s² is ion-exchangeable, and wherein the specific strengthening performance factor (SSPF) is obtained by following equation, SSPF = (Young’s modulus) / (Density * Coefficient of thermal expansion (CTE) * Annealing point).

2. The alkali aluminosilicate glass as claimed in claim 1, wherein when the SSPF ranges from 6 Gm²/s² to 9 Gm²/s², the alkali aluminosilicate glass has high chemical strengthening rate during single or multiple ion exchanges.

3. The alkali aluminosilicate glass as claimed in claim 1, wherein the alkali aluminosilicate glass comprises: SiO₂ from 50 mole % to 80 mole %; Al₂O₃ from 5 mole % to 25 mole %; B₂O₃ from 0 mole % to 15 mole %; R₂O from about 5 mole % to 30 mole %, wherein R₂O represents the sum of alkali metal oxides present in the alkali aluminosilicate glass; RO from about 0 mole % to about 15 mole %, wherein RO represents the sum of alkaline earth metal oxides present in the alkali aluminosilicate glass; ZnO from 0 mole % to 10 mole %; ZrO₂ from 0 mole % to 10 mole %; and P₂O₅ from 0 mole % to 10 mole %.

4. The alkali aluminosilicate glass as claimed in claim 3, wherein ratio of Al₂O₃ to R₂O (Al₂O₃ (mole %)/ R₂O (mole %)) is in the range from 0.3 to 1.3.

5. The alkali aluminosilicate glass as claimed in claim 3, wherein the alkali metal oxides are selected from group consisting of Li₂O, Na₂O, and K₂O.

6. The alkali aluminosilicate glass as claimed in claim 3, wherein the alkaline earth metal oxides are selected from group consisting of MgO, CaO, SrO, and BaO.

7. The alkali aluminosilicate glass as claimed in claim 5, wherein the alkali aluminosilicate glass is a lithium aluminosilicate glass.

8. The alkali aluminosilicate glass as claimed in claim 3, wherein the alkali aluminosilicate is double ion exchanged.

9. The alkali aluminosilicate glass claimed in claim 3, wherein the alkali aluminosilicate glass is substantially free of Sb₂O₃, As₂O₃, or both.

10. The alkali aluminosilicate glass of claim 8, wherein the ion-exchanged alkali aluminosilicate glass of thickness less than or equal to 300 microns has a compressive layer extending from a surface of the alkali aluminosilicate glass to a depth of layer greater than 5 microns within the glass, and wherein the compressive layer has a maximum compressive stress at the surface of at least 300 MPa.

11. The alkali aluminosilicate glass of claim 8, wherein the ion-exchanged alkali aluminosilicate glass of thickness greater than or equal to 300 microns has a compressive layer extending from a surface of the alkali aluminosilicate glass to a depth of layer greater than 20 microns within the glass, and wherein the compressive layer has a maximum compressive stress at the surface of at least 600 MPa.

12. The alkali aluminosilicate glass as claimed in claim 1, wherein the alkali aluminosilicate glass has Young’s modulus in the range from 60 to 95 GPa.

13. The alkali aluminosilicate glass as claimed in claim 1, wherein the alkali aluminosilicate glass has a density in the range from 2.30 to 2.55 g/cc.

14. The alkali aluminosilicate glass as claimed in claim 1, wherein the alkali aluminosilicate glass has a coefficient of thermal expansion in the range from 49×10- ⁷/°C to 95.9×10^-7/°C.

15. The alkali aluminosilicate glass as claimed in claim 1, wherein the alkali aluminosilicate glass has an annealing point in the range from 450°C to 700°C.

16. The alkali aluminosilicate glass as claimed in claim 1, the alkali aluminosilicate glass has a glass transition temperature of greater than or equal to 440° C.

17. A chemically strengthened glass is obtained by chemically strengthening the alkali aluminosilicate glass according to claims 1 to 4.

18. An alkali aluminosilicate glass, the alkali aluminosilicate glass comprising: SiO₂ and Al₂O₃, wherein Al₂O₃ (mol%)/R₂O (mol%) is in the range from 0.3 to 1.3, wherein R₂O is sum of alkali metal oxides present in the alkali aluminosilicate glass, wherein the alkali aluminosilicate glass having a specific strengthening performance factor (SSPF) ranging from 6 Gm²/s² to 12 Gm²/s² is ion-exchangeable, and wherein the specific strengthening performance factor (SSPF) is obtained by following equation, SSPF = (Young’s modulus) / (Density * Coefficient of thermal expansion (CTE) * Annealing point).

19. The alkali aluminosilicate glass as claimed in claim 18, wherein the alkali metal oxides are selected from group consisting of Li₂O, Na₂O, and K₂O.

20. The alkali aluminosilicate glass as claimed in claim 19, wherein the alkali aluminosilicate glass is a lithium aluminosilicate glass.

21. The alkali aluminosilicate glass as claimed in claim 18, wherein when the SSPF ranges from 6 Gm²/s² to 9 Gm²/s², the alkali aluminosilicate glass has high chemical strengthening rate during single or multiple ion exchanges.

22. The alkali aluminosilicate glass as claimed in claim 19, wherein the alkali aluminosilicate glass comprises: SiO₂ from 50 mole % to 80 mole %; Al₂O₃ from 5 mole % to 25 mole %; B₂O₃ from 0 mole % to 15 mole %; R₂O from about 5 mole % to 30 mole %; RO from about 0 mole % to about 15 mole %, wherein RO represents the sum of alkaline earth metal oxides present in the alkali aluminosilicate glass; ZnO from 0 mole % to 10 mole %; ZrO₂ from 0 mole % to 10 mole %; and P₂O₅ from 0 mole % to 10 mole %.

23. The alkali aluminosilicate glass as claimed in claim 22, wherein the alkaline earth metal oxides are selected from group consisting of MgO, CaO, SrO, and BaO.

24. The alkali aluminosilicate glass as claimed in claim 23, wherein [{(MgO+K₂O)/SiO₂} *(Al₂O₃+Li₂O+Na₂O+P₂O₅)] £ 0.70 mole %.

25. The alkali aluminosilicate glass as claimed in claim 23, wherein (MgO+K₂O) £ 1.5 mole %.

26. The alkali aluminosilicate glass as claimed in claim 23, wherein (Al₂O₃+Li₂O+Na₂O+P₂O₅) £ 37 mole %.

27. The alkali aluminosilicate glass as claimed in claim 22, wherein the alkali aluminosilicate is double ion exchanged.

28. The alkali aluminosilicate glass as claimed in claim 22, wherein the glass is substantially free of Sb₂O₃, As₂O₃, or both.