Patent Application
20150132579
The disclosure relates to ion exchangeable glasses. More particularly, the disclosure relates to ion exchangeable glasses that comprise either transition metals or rare earth metals.
In applications such as cover plates or windows for portable or mobile electronic communication and entertainment devices, glasses are typically strengthened by either chemical or thermal means.
The present disclosure provides glasses that are ion exchangeable. The glasses comprise at least one of a transition metal oxide or a rare earth oxide and have compositions that simultaneously promote a surface layer having a high compressive stress and deep depth of layer or, alternatively, ion exchanged to a given compressive stress or depth of layer in a reduced ion exchange time.
Accordingly, one aspect of the disclosure is to provide an alkali aluminosilicate glass. The alkali aluminosilicate glass is ion exchangeable and comprises at least 50 mol % SiO2, Al2O3, at least one metal oxide selected from the group consisting of transition metal oxides and rare earth metal oxides, and at least one alkali metal oxide R2O, wherein the at least one alkali metal oxide includes Na2O, and wherein Al2O3(mol %)−Na2O(mol %)≦2 mol %.
A second aspect of the disclosure is to provide an alkali aluminosilicate glass. The alkali aluminosilicate glass comprises at least 50 mol % SiO2, Al2O3, at least one metal oxide selected from the group consisting of transition metal oxides and rare earth metal oxides, and at least one alkali metal oxide R2O, wherein the at least one alkali metal oxide includes Na2O, wherein Al2O3(mol %)−Na2O(mol %)≦2 mol %. The alkali aluminosilicate glass is ion exchanged and has a surface and a layer under compressive stress extending from the surface to a depth of layer, wherein the compressive stress is at least about 1 GPa and the depth of layer is at least about 20 μm.
A third aspect of the disclosure is to provide a method of making an ion exchanged alkali aluminosilicate glass. The method comprises providing an alkali aluminosilicate glass, the alkali aluminosilicate glass comprising at least 50 mol % SiO2, Al2O3, at least one metal oxide selected from the group consisting of transition metal oxides and rare earth metal oxides, and at least one alkali metal oxide R2O, wherein the alkali metal oxide includes Na2O, and wherein Al2O3(mol %)−Na2O(mol %)≦2 mol %; and ion exchanging the alkali aluminosilicate glass for a predetermined time to form a layer under a compressive stress of at least about 1 GPa, the layer extending from s surface of the alkali aluminosilicate glass to a depth of layer.
These and other aspects, advantages, and salient features will become apparent from the following detailed description, the accompanying drawings, and the appended claims.
a-f are plots of transmission ultraviolet-visible-near infrared (UV-Vis-NIR) spectra of glasses described herein, measured before and after ion exchange;
a-e are plots of temperature dependence of the sodium-potassium interdiffusion coefficient for glasses selected from Tables 1a-d;
a-e are plots of depth of layer as a function of compressive stress for annealed samples ion exchanged at 410° C. in technical grade KNO3 for 4, 8, and 16 hours;
a and 5b are plots showing the effect of substituting different oxides for Al2O3 on the compressive stress at a fixed depth of layer of 50 μm and the ion exchange time required to achieve a depth of layer of 50 μm; and
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” and “glasses” includes both glasses and glass ceramics. The terms “glass article” and “glass articles” are used in their broadest sense to include any object made wholly or partly of glass and/or glass ceramic. As used herein, the terms “alkali metal oxide” and “alkali oxide” refer to the oxides of the alkali metals and are considered to be equivalent terms. Similarly, the terms “alkaline earth metal oxide” and “alkaline earth oxide” refer to the oxides of the alkaline earth metals and are considered to be equivalent terms.
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.
Described herein are ion exchangeable glasses that may be used to produce chemically strengthened glass sheets by ion exchange. The compositions of these glasses are chosen to promote simultaneously high compressive stress and deep depth of layer or reduced ion exchange time by including at least one transition metal oxide or rare earth oxide in the glass composition. Not all of the glass compositions described herein are fusion formable, and may be produced by other methods known in the art, such as the float glass process or the slot draw process.
Accordingly, alkali aluminosilicate glasses comprising at least one of a transition metal oxide and a rare earth oxide, at least 50 mole % (mol %) SiO2, alumina (Al2O3) and at least one alkali metal oxide R2O, wherein the alkali metal oxide includes Na2O, and wherein Al2O3(mol %)−Na2O(mol %)≦2 mol %. When ion exchanged, the alkali aluminosilicate glasses described herein may have a layer (also referred to herein as a compressive layer) under a compressive stress CS of at least about 1 gigaPascal (GPa) that extends from at least one surface of the alkali aluminosilicate glass into the central portion of the glass to a depth of layer (depth of layer, or DOL). In some embodiments, the depth of layer DOL is at least 20 microns (μm) and, in other embodiments, at least 30 μm.
The at least one transition metal oxide or rare earth oxide may, in some embodiments, include at least one of niobium oxide (Nb2O5), vanadium oxide (V2O5), zirconium (ZrO2), iron oxide (Fe2O3), yttrium oxide (Y2O3), and manganese oxide (MnO2). In some embodiments, the alkali aluminosilicate glass comprises: from about 62 mol % to about 72 mol % SiO2; from about 5 mol % to about 12 mol % Al2O3; from 12 mol % to about 16 mol % Na2O; and from more than 1 mol % to about 10 mol % of at one least metal oxide selected from the group consisting of transition metal oxides and rare earth metal oxides including, but not limited to, those described hereinabove.
Non-limiting examples of the glass compositions described herein and selected properties are listed in Tables 1a-d. In the examples listed, six different transition metal oxides were each added to a crucible-melt base glass (“base” in Tables 1a, 2, and 3). These oxides were added either to the top of the base glass melt or partially substituted for an oxide. Compositions were analyzed by x-ray fluorescence and/or inductively coupled plasma (ICP). Anneal and strain points were determined by beam bending viscometry, and softening points were determined by parallel plate viscometry. The coefficients of thermal expansion (CTE) values in Tables 1a-d represent the average value between room temperature and 300° C. Liquidus temperatures reported in Tables 1a-d are for 24 hours, elastic moduli were determined by resonant ultrasound spectroscopy, and refractive indices are reported for 589.3 μm. Stress optic coefficient (SOC) was determined by the diametral compression method.
Glass color was observed on 1 mm thick glass samples and is reported in Table 2. Transmission ultraviolet-visible-near infrared (UV-Vis-NIR) spectra measured before and after ion exchange are shown in
Properties of the glasses listed in Table 1a-d after ion exchange for fixed exchange times are provided in Table 2. Compressive stress (CS), expressed in gigapascals (GPa), and depth of layer (DOL), expressed in microns (μm), were obtained as a result of treatment of annealed samples in molten salt baths comprising technical grade KNO3. The ion exchange treatments were carried out in the molten salt baths at 410° C. for 4, 8, and 16 hours, and for 8 hours at 370° C. and 450° C. The temperature dependence of the sodium-potassium interdiffusion coefficient for glasses selected from Tables 1a-d are plotted in
Times required to ion exchange glasses selected from the compositions listed in Tables 1a-d to a fixed depth of layer of 50 μm are listed in Table 3. The compressive stress at a fixed depth of layer of 50 μm and ion exchange time required to a depth of layer of 50 μm were calculated from ion exchange data obtained at 410° C. for annealed samples immersed for various times in the technical grade KNO3 salt bath. Values in parentheses in Table 3 indicate that the ion exchange properties of the glasses are inferior to those of the base glass composition, whereas values which are not parenthesized indicate that the ion exchange properties are superior to those of the base glass composition. Depth of layer is plotted as a function of compressive stress in
In the glass compositions described herein, SiO2 serves as the primary glass-forming oxide, and comprises from about 62 mol % to about 72 mol % of the glass. The concentration of SiO2 is high enough to provide the glass with high chemical durability that is suitable for applications such as, for example, touch screens or the like. However, the melting temperature (200 poise temperature, T200) of pure SiO2 or glasses containing higher levels of SiO2 is too high, since defects such as fining bubbles tend to appear in the glass. In addition, SiO2, in comparison to most oxides, decreases the compressive stress created by ion exchange. Accordingly, in some of the glasses described herein, transition metal oxides and/or rare earth oxides are substituted for SiO2.
Alumina (Al2O3), which comprises from about 5 mol % to about 12 mol % of the glasses described herein, may also serve as a glass former. Like SiO2, alumina generally increases the viscosity of the melt. An increase in Al2O3 relative to the alkalis or alkaline earths generally results in improved durability of the glass. The structural role of the aluminum ions depends on the glass composition. When the concentration of alkali metal oxides R20 is greater than that of alumina, all aluminum is found in tetrahedral, four-fold coordination with the alkali metal ions acting as charge-balancers. This is the case for all of the glasses described herein. Divalent cation oxides (RO) can also charge balance tetrahedral aluminum to various extents. Elements such as calcium, strontium, and barium behave equivalently to two alkali ions, whereas the high field strength of magnesium ions cause them to not fully charge balance aluminum in tetrahedral coordination, resulting instead in formation of five- and six-fold coordinated aluminum. Al2O3 enables a strong network backbone (i.e., high strain point) while allowing relatively fast diffusivity of alkali ions, and thus plays an important role in ion-exchangeable glasses. High Al2O3 concentrations, however, generally lower the liquidus viscosity of the glass. One alternative is to partially substitute other oxides for Al2O3 while maintaining or improving ion exchange performance of the glass.
The glasses described herein comprise from about 12 mol % to about 16 mol % Na2O and, optionally, at least one other alkali oxide such as, for example, K2O. Alkali oxides (Li2O, Na2O, K2O, Rb2O, and Cs2O) serve as aids in achieving low melting temperature and low liquidus temperatures of glasses. The addition of alkali oxides, however, increases the coefficient of thermal expansion (CTE) and lowers the chemical durability of the glass. In order to achieve ion exchange, a small alkali oxide (such as, for example, Li2O and Na2O) must be present in the glass to exchange with larger alkali ions (e.g., K+) from a molten salt bath. Three types of ion exchange may typically be carried out: Na+-for-Li+ exchange, which results in a deep depth of layer but low compressive stress; K+-for-Li+ exchange, which results in a small depth of layer but a relatively large compressive stress; and K+-for-Na+ exchange, which results in an intermediate depth of layer and compressive stress. A sufficiently high concentration of the small alkali oxide is necessary to produce a large compressive stress in the glass, since compressive stress is proportional to the number of alkali ions that are exchanged out of the glass. Accordingly, the glasses described herein comprise from 12 mol % to about 16 mol % Na2O. The presence of a small amount of K2O generally improves diffusivity and lowers the liquidus temperature of the glass, but increases the CTE (Table 1d). Partial substitutions of Rb2O and/or Cs2O for Na2O decrease CS and DOL (Tables 3 and 4). While K+-for-Na+ exchange is described for the transition metal containing glasses described herein, ion exchange between alkali cation pairs (e.g., Na+-for-Li+ or Rb+-for K+) are within the scope of this disclosure.
Divalent cation oxides (such as alkaline earth oxides and ZnO) also improve the melting behavior of the glass. With respect to ion exchange performance, however, the presence of divalent cations tends to decrease alkali mobility. The effect of divalent ions on ion exchange performance is especially pronounced with larger divalent cations such as, for example, SrO, BaO, and the like. Furthermore, smaller divalent cation oxides generally enhance compressive stress more than larger divalent cations. MgO and ZnO, for example, offer several advantages with respect to improved stress relaxation while minimizing adverse effects on alkali diffusivity. Higher concentrations of MgO and ZnO, however, promote formation of forsterite (Mg2SiO4) and gahnite (ZnAl2O4), or willemite (Zn2SiO4), thus causing the liquidus temperature of the glass to rise very steeply with increasing MgO and/or ZnO content. MgO is the only divalent cation oxide in the glasses described herein. In some embodiments, transition metal oxides are substituted for at least a portion of the MgO in the glass while maintaining or improving the ion exchange performance of the glass.
Glasses typically also contain oxides that are added to eliminate and reduce defects, such as gaseous inclusions or “seeds,” within the glass. In some embodiments, the glasses described herein comprise SnO2 in the usual role as a fining agent. Alternatively, other oxides such as, but not limited to, As2O3 and/or Sb2O3 may serve as fining agents. The fining capacity is generally increased by increasing the concentration of SnO2 (or As2O3 and/or Sb2O3) but, as these oxides are comparatively expensive raw materials, it is desirable to add no more than is required to drive the concentration of gaseous inclusions to an appropriately low level.
In addition to the oxides described above, the glasses described herein further comprise at least one transition metal oxide and/or rare earth oxide. In some embodiments, these transition metal oxides and rare earth oxides include, but are not necessarily limited to, Nb2O5, ZrO2, Fe2O3, V2O5, Y2O3, and MnO2. The structural roles of these oxides and their impact on the ion exchange properties (CS and DOL) are described below.
The introduction of Nb2O5 in silicate glasses has been used in materials with, for example, non-linear optical coefficient and laser glasses of high-stimulated emission parameters. Nb2O5 acts as a network former even in low concentrations, as it forms Si—O—Nb network bonds. This substitution increases the anneal point, refractive index, and elastic moduli of the glass, but lowers the liquidus viscosity (Table 1a). With increasing degrees of substitution of Nb2O5 for MgO, the compressive stress created by ion exchange at 410° C. to a fixed DOL of 50 μm increases but the ion exchange time required to reach 50 μm DOL also increases (
Zirconia (ZrO2) helps to improve the chemical durability of the glass. In the presence of charge-compensating cations, six-fold coordinated zirconium is inserted in the silicate network by forming Si—O—Zr bonds. Hence, the [ZrO6]2− groups are charge-compensated by two positive charges; i.e., either two alkali ions or one alkaline earth ion. Because SiO2 generally decreases the compressive stress due to ion exchange, ZrO2 is partially substituted for SiO2 in some of the glasses described herein. Zirconia substitution increases the anneal point, refractive index, and elastic moduli of the glass, but lowers the liquidus viscosity (Table 1a). With respect to ion exchange performance, the substitution of ZrO2 for SiO2 dramatically increases the CS at a fixed DOL of 50 μm, whereas the time required to ion exchange the glass to a DOL of 50 μm increases (Table 3). Adding 1.5 mol % ZrO2 on top of the base glass composition and scaling all other oxides proportionally also increases CS and decreases DOL (
Iron is present in glasses as Fe2+, Fe3+, or metallic free iron)(Fe0). Unless reducing melting conditions are employed, however, only Fe2+ and Fe3+ will be present in significant concentrations. The structural roles of Fe2+ and Fe3+ differ markedly. Depending on the ratio [Fe3+]/[ΣFe], where [Fe3+] is the Fe3+ concentration and [ΣFe] is the total concentration of Fe2+ and Fe3+, Fe3+ can act as a network former (coordination number IV or V) and/or a network modifier (coordination number V or VI), whereas Fe2+ iron is generally considered to be a network modifier. As both ferric and ferrous iron can be present in liquids, changes in the oxidation state of iron can significantly affect the degree of iron polymerization. Therefore, any melt property that depends on the number of non-bridging oxygens (NBO) per tetrahedron (NBO/T) will also be affected by the ratio [Fe3+]/[ΣFe]. The structural role of Fe2+ is thus similar to that of Mg2+ or Ca2+. The structural role of Fe3+ is similar to that of Al3+, as tetrahedral Fe3+ also requires the presence of charge-compensating cations. In certain embodiments of the glasses described herein, iron oxide is substituted for both MgO and Al2O3 (Table 1b). Due to the intense dark coloring of these iron-containing glasses, it was not possible to determine their SOC. Consequently, the SOC value of the base glass was used as an approximate value when calculating compressive stresses resulting from ion exchange. Substitution of iron for aluminum significantly increases CS and decreases DOL (
Vanadium is another oxide that exists in different redox states in glasses and thus possesses different structural roles depending on the redox state. Usually, vanadium occurs in the states of V3+, V4+, and V5+ in glasses. The role of V5+ may be similar to that of P5+; i.e., V5+ can remove modifiers such as, for example, Na+, from the silicate network to form various alkali vanadate species. Hence, V2O5 can be present in various phosphate-like structural units such as pyrovanadate and metavanadate units. P2O5 is known to dramatically increase DOL and decrease CS. In some embodiments of the glasses described herein, V2O5 has been introduced into the base glass in various ways (Table 1b). Substituting V for Al increases DOL, but dramatically lowers CS (
Silicate glasses containing yttria (Y2O3) generally have high glass transition temperatures, low electrical conductivity, and high chemical durability. The trivalent cation Y3+ is chemically similar to Al3+. In the glasses described herein, Y2O3 is partially substituted for Al2O3 at levels of 2, 5, and 10 mol % (Table 1c). When 2 mol % Y2O3 was substituted for Al2O3, a small increase in compressive stress was observed and the diffusivity decreased. Compressive stress and depth of layer could not be determined for samples in which 5 and 10 mol % Y2O3 were substituted for Al2O3. Hence, the role Y2O3 is very different from that of Al2O3 with respect to ion exchange properties.
Manganese ions mostly exist in glasses in the Mn2+ and Mn3+ oxidation states. Mn2+ occupies primarily network-forming positions within MnO4 structural units, whereas Mn3+ occupies mostly network-modifying positions. The influence of manganese on ion exchange performance should thus strongly depend on the redox chemistry. When MnO2 is substituted for Al2O3, both CS and DOL decrease dramatically (
The glasses described herein, particularly when ion exchanged, may be used as cover plates or windows for portable or mobile electronic communication and entertainment devices, such as cellular phones, music players, and information terminal (IT) devices, such as laptop computers and the like.
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 or appended claims.
This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 61/653,495 filed on May 31, 2012 the content of which is relied upon and incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US13/42805 | 5/28/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61653495 | May 2012 | US |
