Strengthened glass articles with deep outer compression from ion exchange on cylindrically thermally induced bending stress profile

Abstract

A strengthened glass article having a cylindrical sidewall with an outer surface, an inner surface, and a radial thickness extending between the outer surface and the inner surface in a radial direction is provided. The strengthened glass article has an asymmetric axial stress profile including: an outer compressive stress region extending radially inward from the outer surface to an outer depth of compression (outer DOC); an inner compressive stress region extending radially outward from the inner surface to an inner DOC; and a central tension region disposed radially between the outer DOC and the inner DOC. The asymmetric axial stress profile has an outer elbow in compression, and the outer elbow is a region on the asymmetric axial stress profile proximate the outer surface and at which a slope of the axial stress profile changes magnitude.

Description

SP24-255STRENGTHENED GLASS ARTICLES WITH DEEP OUTER COMPRESSION FROM ION EXCHANGE ON CYLINDRICALLY THERMALLY INDUCED BENDING STRESS PROFILECROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Serial No. 63 / 699,446 filed on September 26, 2024, the content of which is relied upon and incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present specification generally relates to strengthened glass articles, in particular strengthened glass articles having high mechanical strength and methods of strengthening the glass articles.BACKGROUND

[0002] Historically, glass has been used to produce a variety of articles. For example, because of its hermeticity, optical clarity, and excellent chemical durability relative to other materials, glass has been a preferred material for pharmaceutical applications, including, without limitation, vials, syringes, ampoules, cartridges, and other glass articles. The glass used in pharmaceutical packaging must have adequate mechanical and chemical durability so as to not affect the stability of the pharmaceutical formulations contained therein. Glasses having suitable chemical durability include those glass compositions within the ASTM standard ‘Type IA’ and ‘Type IB’ glass compositions which have a proven history of chemical durability.

[0003] A concern for food and drug manufacturers is providing glass containers having sufficient strength to minimize damage and breakage caused by external sources of damage, such as handling and / or transport of the glass containers. While glass containers are superior to many alternative materials, they are not unbreakable and occasionally experience damage from handling and / or transport. The damage can be in the form of obvious damage (e.g., cracks or chips) or in the form of surface damage (e.g., flaws extending from the surface into the glass) that can reduce the strength of the glass containers.SP24-255SUMMARY

[0004] The present disclosure is directed to strengthened glass articles having at least one wall, where the wall has a compressive stress region and a central tension region. The wall of the strengthened glass articles has an asymmetric axial stress profile that provides high compressive stress (CS) at the surfaces of the glass and deep depth of compression from the outer surface. The greater depth of compression and compressive stress at the outer surface provide increased strength to the outer surface of the strengthened glass article compared to conventional strengthened glass articles.

[0005] According to a first aspect disclosed herein, a strengthened glass article is provided comprising a cylindrical sidewall having an outer surface, an inner surface, and a radial thickness extending between the outer surface and the inner surface in a radial direction, wherein the strengthened glass article has an asymmetric axial stress profile comprising: an outer compressive stress region extending radially inward from the outer surface to an outer depth of compression (outer DOC); an inner compressive stress region extending radially outward from the inner surface to an inner DOC; and a central tension region disposed radially between the outer DOC and the inner DOC, wherein: the asymmetric axial stress profile has an outer elbow in compression; and the outer elbow is a region on the asymmetric axial stress profile proximate the outer surface and at which a slope of the axial stress profile changes magnitude.

[0006] According to a second aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein the axial stress is measured by optical retardation.

[0007] According to a third aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein: a graph of axial stress as a function of depth in the glass from the outer surface has an outer surface stress tangent line and a center stress tangent line; the outer surface stress tangent line is a line tangent to the graph of axial stress at the outer surface; the center stress tangent line is a line tangent to the graph of axial stress in the central tension region; and an intersection point between the outer surface stress tangent line and the center stress tangent line is in compression.

[0008] According to a fourth aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein the asymmetric axial stress profile has an inner elbow in tension, wherein the inner elbow is a region on the asymmetric axial stress profileSP24-255 proximate the inner surface and at which a slope of the asymmetric axial stress profile changes magnitude and direction.

[0009] According to a fifth aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein: the outer compressive stress region comprises a first compressive stress region extending from the outer surface to an outer depth of diffusion and a second compressive stress region extending from the outer depth of diffusion to the outer DOC; in the first compressive stress region, the glass has a concentration gradient of one or more alkali metals; in the second compressive stress region, a concentration of each alkali metal species in the glass is constant and equal to a bulk concentration of each of the alkali metal species; the outer depth of diffusion is a depth in the glass measured from the outer surface and at which a concentration gradient of the one or more alkali metals becomes zero; and at the outer depth of diffusion, an axial stress profile of the glass is in compression.

[0010] According to a sixth aspect disclosed herein, the strengthened glass article according to aspect 5 is provided, wherein:where DOCouter is the outer DOC, and DODouter is the outer depth of diffusion.

[0011] According to a seventh aspect disclosed herein, the strengthened glass article according to aspect 6 is provided, wherein:D0Couter- > 1.1D0Douterwhere DOCouter is the outer DOC, and DODouter is the outer depth of diffusion.

[0012] According to an eighth aspect disclosed herein, the strengthened glass article according to aspect 6 is provided, wherein:500where DOCouter is the outer DOC, and DODouter is the outer depth of diffusion.

[0013] According to a ninth aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein a magnitude of a slope of a tangential stress component in the glass is greater than a magnitude of a slope of a tangential stress componentSP24-255 in a comparative glass article having the same geometry and strengthened only by ion exchange.

[0014] According to a tenth aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein: an inner depth of diffusion is a depth in the glass measured from the inner surface and at which a concentration gradient of one or more alkali metals becomes zero; and the inner depth of diffusion is greater than the inner DOC.

[0015] According to an eleventh aspect disclosed herein, the strengthened glass article according to aspect 10 is provided, wherein the inner depth of diffusion is in the central tension region.

[0016] According to a twelth aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein the outer DOC is greater than the inner DOC.

[0017] According to a thirteenth aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein a maximum axial central tension is closer to the inner surface than the outer surface.

[0018] According to a fourteenth aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein a compressive stress (CS) at the outer surface is greater than a CS at the inner surface.

[0019] According to a fifteenth aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein:where DOCouter is the outer DOC, DOCinner is the inner DOC, and t is the radial thickness of the strengthened glass article.

[0020] According to a sixteenth aspect disclosed herein, the strengthened glass article according to aspect 15 is provided, wherein:

[0021] According to a seventeenth aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein a geometrically induced ratio of the outer DOC to the inner DOC is from 1.01 to 2000.SP24-255

[0022] According to an eighteenth aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, a distance between a maximum central tension and the inner surface of the strengthened glass article is less than or equal to 50% the radial thickness of the cylindrical side wall.

[0023] According to a nineteenth aspect disclosed herein, the strengthened glass article according to aspect 18 is provided, a distance between a maximum central tension and the inner surface of the strengthened glass article is less than or equal to 25% the radial thickness of the cylindrical side wall.

[0024] According to a twentieth aspect disclosed herein, the strengthened glass article according to aspect 1 is provided, wherein the glass article is a pharmaceutical container.

[0025] According to a twenty-first aspect disclosed herein, a method of making a strengthened glass article is provided, the method comprising: forming a glass article comprising a cylindrical sidewall having an outer surface, an inner surface, and a radial thickness extending between the outer surface and the inner surface in a radial direction; introducing an initial compressive stress in the outer surface of the glass article to produce an initial axial stress profile in the glass article, wherein the initial axial stress profile has a maximum compressive stress at the outer surface and a maximum tension at the inner surface of the glass article; ion-exchanging the glass article having the initial axial stress profile to produce a strengthened glass article, wherein the strengthened glass article has an asymmetric axial stress profile comprising: an outer compressive stress region extending radially inward from the outer surface to an outer depth of compression (outer DOC); an inner compressive stress region extending radially outward from the inner surface to an inner depth of compression (inner DOC); and a central tension region disposed radially between the outer DOC and the inner DOC, wherein: a graph of axial stress as a function of depth in the glass from the outer surface has an outer surface stress tangent line and a center stress tangent line; the outer surface stress tangent line is a line tangent to the graph of axial stress at the outer surface; the center stress tangent line is a line tangent to the graph of axial stress in the central tension region; and an intersection point between the outer surface stress tangent line and the center stress tangent line is in compression.

[0026] According to a twenty-second aspect disclosed herein, the method of making a strengthened glass article according to aspect 21 is provided, wherein introducing the initialSP24-255 compressive stress in the outer surface comprises introducing a thermally induced stress profde in the cylindrical sidewall.

[0027] According to a twenty-third aspect disclosed herein, the method of making a strengthened glass article according to aspect 22 is provided, wherein introducing the thermally induced stress profde in the cylindrical sidewall comprises annealing the glass article and cooling the cylindrical sidewall at an increased cooling rate, wherein the increased cooling rate produces the thermally-induced stress profde in the cylindrical sidewall.

[0028] According to a twenty-fourth aspect disclosed herein, the method of making a strengthened glass article according to aspect 21 is provided, wherein introducing the initial compressive stress in the outer surface comprises subjecting the outer surface of the cylindrical sidewall to a preliminary ion-exchange process without ion-exchanging the inner surface of the cylindrical side wall.

[0029] According to a twenty-fifth aspect disclosed herein, the method of making a strengthened glass article according to aspect 21 is provided, wherein:<? / , > 0.275 • CT^QX T 2.247 • CT[QX wherein ob is the initial compressive stress in the outer surface, Cljox is the a central tension at a middle of the cylindrical sidewall for a comparative glass article subjected only to ion exchange under the same conditions and without introducing the bending stress; and the middle of the cylindrical sidewall is equal to a point halfway between the inner surface and the outer surface of the cylindrical sidewall.

[0030] These and other aspects, advantages, and salient features will become apparent from the following detailed description, the accompanying drawings, and the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 schematically depicts a perspective view of a portion of a strengthened glass article, according to embodiments shown and described herein;

[0032] FIG. 2 graphically depicts an axial stress profile (axial stress (y-axis) as a function of radial position in the glass (x-axis)) for strengthened glass articles, according to embodiments shown and described herein;SP24-255

[0033] FIG. 3 graphically depicts an axial stress profile (axial stress (y-axis) as a function of radial position in the glass (x-axis)) for glass articles strengthened by ion-exchange only, according to embodiments shown and described herein;

[0034] FIG. 4 graphically depicts an axial stress profile (axial stress (y-axis) as a function of radial position in the glass (x-axis)) for glass articles having a thermally-induced axial stress profile, according to embodiments shown and described herein;

[0035] FIG. 5 graphically depicts axial stress (y-axis) as a function of depth from the outer surface (x-axis) for strengthened glass articles with different magnitudes of initial axial stress profile introduced to the glass article prior to ion-exchange, according to embodiments shown and described herein;

[0036] FIG. 6 graphically depicts axial stress (y-axis) as a function of depth from the outer surface (x-axis) for strengthened glass articles with different magnitudes of initial axial stress profile of 0 MPa, 20 MPa, and 50 MPa to the glass article prior to ion-exchange, according to embodiments shown and described herein;

[0037] FIG. 7 graphically depicts central tension (CT), compressive stress at the surface (CS), and depth of compression (DOC) for various glass articles strengthened by ion-exchange only, according to embodiments shown and described herein;

[0038] FIG. 8 graphically depicts a modeled stress intensity factor (y-axis) as a function of flaw depth (x-axis) for strengthened glass articles with three different ion-exchanged CT levels with no initial stress profiled introduced into the glass, according to embodiments shown and described herein;

[0039] FIG. 9 graphically depicts a modeled stress intensity factor (y-axis) as a function of flaw depth (x-axis) for strengthened glass articles with three different ion-exchanged CT levels and with a "bend" stress of 8 MPa for each, according to embodiments shown and described herein;

[0040] FIG. 10 graphically depicts a modeled stress intensity factor (y-axis) as a function of flaw depth (x-axis) for strengthened glass articles having constant CT level of 5.4 MPa but with three different levels of bend stress, according to embodiments shown and described herein;

[0041] FIG. 11 graphically depicts flaw depths at Ki = Ko (y-axis) as a function of bend stress (x-axis) (i.e., magnitude of initial stress profde introduced into the glass) for strengthenedSP24-255 glass articles with various ion-exchanged CT values, according to embodiments shown and described herein;

[0042] FIG. 12 graphically depicts a required bend stress (y-axis) for a given CT (x-axis) to achieve a deepest critical flaw depth (i.e., flaw depth when Ki=Ko) in strengthened glass articles, according to embodiments shown and described herein;

[0043] FIG. 13 graphically depicts flaw depth (y-axis) as a function of contact force (x- axis) from the sharp damage analytical modeling of strengthened glass articles, according to embodiments shown and described herein;

[0044] FIG. 14 graphically depicts retained strength (y-axis) as a function of flaw depth (x- axis) for sharp damage analytical modeling of strengthened glass articles, according to embodiments shown and described herein;

[0045] FIG. 15 graphically depicts depth of compression (y-axis) as a function of bend stress (i.e., compressive bending stress) added to the outer surface of the glass article (x-axis) prior to ion-exchange, according to embodiments shown and described herein;

[0046] FIG. 16 graphically depicts axial stress (y-axis) as a function of depth from the inner surface (x-axis) for strengthened glass articles with different magnitudes of initial axial stress profde introduced to the glass article prior to ion-exchange, according to embodiments shown and described herein;

[0047] FIG. 17 graphically depicts critical contact force required to produce a flaw extending into a CT region (y-axis) as a function of a bend stress introduced to an outer surface by an initial axial stress profile (x-axis) for strengthened glass articles, according to embodiments shown and described herein;

[0048] FIG. 18 graphically depicts critical flaw depth (y-axis) as a function of bend stress introduced to an outer surface by an initial axial stress profile (x-axis) for the strengthened glass articles, according to embodiments shown and described herein; and

[0049] FIG. 19 graphically depicts retained strength profiles of the outer surface (y-axis) as a function of flaw depth into the outer surface (x-axis) for strengthened glass articles, according to embodiments shown and described herein.SP24-255DETAILED DESCRIPTION

[0050] Reference will now be made in detail to embodiments of strengthened glass articles and methods of making the strengthening glass articles, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. Referring to FIG. 1 , one embodiment of a strengthened glass article 100 disclosed herein is schematically depicted. The strengthened glass articles 100 comprise a cylindrical sidewall 102 having an outer surface 104, an inner surface 106, and a radial thickness t extending between the outer surface 104 and the inner surface 106 in a radial direction. Referring to FIG. 2, the strengthened glass articles 100 have an asymmetric axial stress profile 108 comprising an outer compressive stress region 110 extending radially inward from the outer surface 104 to an outer depth of compression (outer DOC 114), an inner compressive stress region 130 extending radially outward from the inner surface 106 to an inner DOC 134, and a central tension region 140 disposed radially between the outer DOC 114 and the inner DOC 134. The asymmetric axial stress profile 108 has an outer elbow 112 in compression, where the outer elbow 112 is a region on the asymmetric axial stress profile 108 proximate the outer surface 104 and at which a slope of the axial stress profile 108 changes magnitude. The outer elbow 112 being in compression means that the stress in the glass at the outer elbow 112 is compressive stress and the outer elbow 112 is in the compressive stress region 110 between the outer surface 104 and the outer DOC 114. The asymmetric axial stress profile 108 of the strengthened glass articles 100 provides a deeper outer DOC 114 and greater compressive stress (CS) at the outer surface 104 compared to ion-exchange alone, which increases the surface strength of the strengthened glass article and increases the depth to which flaws must penetrate into the glass to reach the central tension region, thereby reducing damage to the strengthened glass articles 100 caused by self-propagation of flaws through and across the glass.

[0051] 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 withSP24-255 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.

[0052] As used herein, "glass article" refers to an article comprising a glass, such as a glass container for example.

[0053] As used herein, "depth of compression" (abbreviated DOC) refers to a depth within the glass, from the inner surface and / or outer surface, at which the stress in the glass transitions from compressive stress in a compressive stress region to tensile stress in a central tension region.

[0054] As used herein, "depth of layer" (abbreviated DOL) or "depth of diffusion" (abbreviated DOD) refer to a depth within the glass, from the inner surface and / or outer surface, at which a magnitude of a concentration gradient of at least one alkali metal species in the glass falls to zero and the concentrations of all the alkali metal species in the glass are reduced to the bulk concentrations of those alkali metal species in the glass.

[0055] As used herein, the term "bend stress" refers to a compressive stress at the outer surface of a glass article after introduction of the initial axial stress profile and prior to ionexchange.

[0056] As used herein, the term "ion-exchange CT" is the central tension (CT) in the central tension region produced or expected from ion-exchange only, without the introduction of the initial axial stress profile.

[0057] Referring to the drawings in general and to FIG. 1 in particular, it will be understood that the illustrations are for the purpose of describing particular embodiments and are not intended to limit the disclosure or appended claims thereto. The drawings are not necessarily to scale, and certain features and certain views of the drawings may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness.

[0058] Glass is a preferred material for many applications, such as but not limited to pharmaceutical packaging, cover glass for electronics, or glass for augmented reality (AR)SP24-255 devices, for several reasons, including optical clarity, hermeticity, and chemical inertness. Glass articles, such as but not limited to pharmaceutical packages, electronics cover glass, AR glass, or other glass articles, may experience damage to one or more surfaces, such as damage caused by handling, assembling, filling, use, or other actions. Damage to the surfaces of the glass articles can cause reductions in strength and breakage of the glass article. To improve the surface strength of the glass articles, the glass articles may be strengthened by the introduction of a compressive stress. The compressive stresses produced in the glass must be overcome to produce flaws that extend into the central tension region of the glass or all the way through the thickness of the glass. Such compressive stress may be introduced by methods that include, but are not limited to thermal tempering, chemical tempering by ion exchange, lamination of glasses or glasses and plastics (e.g., glass / glass or glass / plastic / glass lamination) having different moduli and / or coefficients of thermal expansion (CTE), and / or coatings of materials having moduli and / or CTE that differ from those of the glass.

[0059] Many conventional glass articles are chemically strengthened through ionexchange, which involves exchanging smaller ions in the glass for larger ions. The larger ions require more space in the glass matrix, leading to the development of compressive stress within the glass in regions into which the larger ions diffuse during ion-exchange. Ion-exchange alone imparts relatively shallow compressive stress regions (i.e., depths of compression measured in the 10's of micrometers) at the surfaces of the glass article, such as at the inner surface and outer surface of a cylindrical-shaped glass article (e.g., pharmaceutical containers, etc.). Through conservation of energy, the compressive stresses proximate the inner and outer surfaces of the glass are balanced by tensile forces in the center of the glass. As a result of the shallow compressive stress regions resulting from ion-exchange, most of the glass thickness after ion-exchange is under tension in a central tension region of the glass. For flaws that penetrate through the compressive stress regions and into the central tension region, the central tension (CT) in the central tension region can drive fast or slow propagation of flaws, causing them to develop into through cracks or breaks in the glass. Thus, flaws with depth dimensions greater than or equal to the depth of compression (DOC), which is the thickness of the compressive stress region in a conventional ion-exchanged glass article, have the potential for propagation into cracks and breaks facilitated by the central tension. The large thickness (e.g., 0.9+ mm) of the constant low central tension region combined with slow flaw growth velocities when the stress intensity factor is near the minimum threshold for growth (threshold stress intensity factor Ko) can cause very long delays in the failure of the glass articles.SP24-255

[0060] In the case of pharmaceutical containers, flaws that propagate all the way through the thickness of the glass can compromise the integrity of the pharmaceutical container, leading to contamination or spoliation of the contents of the pharmaceutical containers. Thus, for pharmaceutical containers, it is desired to have the surface strength improvement provided by ion-exchanging the surfaces of the glass article to create compressive stress regions, but with low central tension to reduce risk of delayed crack formation and breakage caused by delayed propagation of flaws through and across the glass. Strengthening without delayed breakage may also be advantageous in other applications, such as electronics cover glass, AR glass, or other application, where delayed breakage may expose electronic components to moisture or other degrading elements from the atmosphere.

[0061] Ideally, the risk of delayed breakage would be reduced by increasing the DOC without sacrificing the magnitude of the compressive stress (CS) near the surface of the glass article. The high CS at the surface provides surface strength to resist surface damage, and the greater DOC increases the depth required for flaws to reach the central tension region. However, the kinetics of ion diffusion and stress relaxation limit the ability to achieve these types of stress profiles using typical processes, such as single-step ion-exchange. Shortening or cooling the ion-exchange cycle to keep the CT below a CT threshold for delayed flaw propagation reduces the DOC, which allows for shallower flaws to enter the CT region. Further, shortening or cooling the ion-exchange cycle to keep the CT below the CT threshold for propagation of flaws may not be feasible at scale due to salt melting point and machine speed limitations.

[0062] Producing a stress profile having a greater CT but with a deeper DOC may be beneficial for some products, such as pharmaceutical containers. The deeper DOC would require flaws to penetrate deeper to reach the CT region, and the greater CT would ensure that cracks or deep flaws penetrating into the CT region to propagate through and across the glass to quickly and completely break the glass, rendering the glass article completely unusable and easily identifiable, as discussed in U.S. Patent No. 9,850,162, granted December 26, 2017, and entitled "Glass Packaging Ensuring Container Integrity", the entire contents of which are incorporated herein by reference. These glass articles with high CT and deep DOC would have a reduced risk of relatively shallow flaws reaching the CT region and propagating into cracks and breaks. However, operations such as filling, inspection, and assembly at customer locations can sometimes introduce deeper flaws that extend all the way to the CT region. The propagationSP24-255 of these deeper flaws, as a result of the high CT, may increase overall breakage and cracks in a packaging population after filling, inspection, and assembly. Breakage and / or through cracks may decrease parenteral product safety by introducing particulates or breaching sterility of the pharmaceutical containers. Mitigating these failure modes slows down production, increasing costs for high value drug products.

[0063] In some conventional glass articles, glass coatings may be applied to one or more surfaces of the glass articles to increase the surface strength. However, glass coatings that mitigate the creation of glass flaws in ion-exchanged glass may be expensive, introduce additional material risks, and / or increase process complexity. Damage that occurs prior to application of a glass coating may also slowly propagate over time due to the central tension, and this propagation is not mitigated by the coating. Equipment can be redesigned to reduce or prevent glass-to-glass contact and other sources of surface damage. However, equipment redesign to prevent glass-to-glass contact and other surface damage can be prohibitively expensive.

[0064] Accordingly, an ongoing need exists for strengthened glass articles that have high strength and reduce the risk of breakage caused by self-propagation of flaws. The present disclosure is directed to strengthened glass articles having an axial stress profile that is asymmetric, which provides for high compressive stress at the outer surface of the strengthened glass article from ion-exchange and a deeper DOC at the outer surface compared to ionexchange by itself. The strengthened glass articles disclosed herein having the asymmetric axial stress profile provide reduced risk of flaws extending into the CT region of the glass and, thus, exhibit less CT driven flaw propagation. The strengthened glass articles have the high strength of ion-exchanged glass but with a reduced risk of breakage and cracking in field applications that result in flaws in the glass, such as the filling and assembly of pharmaceutical packaging and electronic devices.

[0065] The strengthened glass articles having the asymmetric axial stress profile described herein are produced by introducing an initial axial stress profile in the glass and then ionexchanging the glass to produce the asymmetric axial stress profile having high CS and a deep DOC at the surface that is expected to have the greatest exposure to surface damage (e.g., the outer surface of a pharmaceutical container) . In embodiments, the strengthened glass articles may have a cylindrical sidewall made from cylindrical tubing. Formed glass tubing has an inherent stress profile with the outer surface in compression and the inner surface in tension.SP24-255Intentional external cooling of cylindrical parts superimposes a bending stress in the cylindrical sidewall that results in a deep compression region with similar magnitude as the central tension (CT) in low CT ion exchange conditions. Further ion-exchange of the glass article produces the strengthened glass article having the asymmetric axial stress profile. Although described in the present disclosure in the context of strengthened glass articles having a cylindrical sidewall, it is understood that the asymmetric stress profile can be produced in other geometries to provide similar results.

[0066] For the case of pharmaceutical containers, the strengthened glass articles, such as vials, syringes, cartridges, vacuum cartridges, etc., having the asymmetric axial stress profiled described herein would require surface flaws to be much deeper, compared to ion-exchanged glass articles, in order to reach a region in the glass with sufficient central tension to propagate into cracks and breaks in the glass. The strengthened glass articles disclosed herein are expected to provide superior surface strength, resistance to surface damage, and reduced propensity for delayed crack formation and breakage, compared to conventional ion-exchanged glass articles, among other features.

[0067] Referring now to FIG. 1, a portion of a strengthened glass article 100, according to embodiments disclosed herein, is schematically depicted. The strengthened glass article 100 has a cylindrical sidewall 102 centered about a center axis A of the strengthened glass article 100. Embodiments of the strengthened glass articles 100 will be described herein in the context of a cylindrical form factor having a cylindrical sidewall 102. However, it is understood that the methods disclosed herein and the strengthened glass articles having the stress profiles described herein can have other form factors, such as flat sheets, contoured shapes, cover glass shapes, or other shapes other than having a shape with a cylindrical sidewall.

[0068] Referring again to FIG. 1, the cylindrical sidewall 102 may have an outer surface 104, an inner surface 106, and a thickness t extending radially between the outer surface 104 and the inner surface 106. The outer surface 104 and the inner surface 106 may be cylindrical having a generally circular cross-sectional shape. The outer surface 104 may have an outer radius Ro, and the inner surface 106 may have an inner radius Ri, where the outer radius Roand inner radius Ri are measured as the radial distance of each surface from the center axis A of the strengthened glass article 100.

[0069] The cylindrical sidewall 102 of the strengthened glass article 100 may have an axial stress profile that is asymmetric with respect to the radial direction through the thickness of theSP24-255 cylindrical sidewall. The term "axial stress" refers to an axial component of a stress vector at a given point in the glass, which is the component of the stress vector in the axial direction (i.e., the + / -Z direction of the cylindrical coordinate axis in FIG. 1). The direction of the axial stress vector depends on whether the axial stress is a compressive stress or a tensile strain (i.e., in compression or in tension). In cylindrical coordinates, the other components of the stress vector at a given point in the glass are the "radial stress" and the "tangential stress." The radial stress is the component of the stress vector in the radial direction (i.e., in the + / -r direction of the cylindrical coordinate axis in FIG. 1). The tangential stress is the component of the stress vector in the angular direction (i.e., in the + / -O (theta) direction of the cylindrical coordinate axis in FIG. 1). The tangential stress may be referred to as the "hoop stress."

[0070] The axial stress as a function of radial position between the outer surface 104 and the inner surface 106 of the cylindrical sidewall 102 of the strengthened glass article 100 may be measured through optical retardation, as described herein. Referring now to FIG. 2, an axial stress profde (y-axis) as a function of radial distance (x-axis) between the outer surface 104 and the inner surface 106 for one embodiment of the strengthened glass article 100 disclosed herein is graphically depicted. In FIG. 2, horizontal line B represents the transition between compression and tension (i.e., zero stress at the transition between compressive stress and tensile strain). The vertical line labeled Rcrepresents the radial center of the cylindrical wall, which is halfway between the inner surface 106 and the outer surface 104 on a radial line (i.e., Rc = Ri + [(Ro-R) / 2]). As shown in FIG. 2, the strengthened glass articles 100 disclosed herein have an axial stress profile that is asymmetric, meaning that the stress profile from Rc to Ri is not a mirror image of the stress profile from Rcto Ro. The asymmetric axial stress profile of the strengthened glass articles 100 has an outer compressive stress region 110 having an outer elbow 112 and an outer DOC 114, where the outer elbow 112 is below line B and is, therefore, in compression (i.e., the axial stress at the outer elbow 112 is a compressive stress), and the outer DOC 114 extends deep into the glass article from the outer surface 104.

[0071] The axial stress profile 108 of the strengthened glass containers 100 disclosed herein may be produced by introducing an initial axial stress profile in the cylindrical sidewall 102 of a glass article and then ion-exchanging the glass article. The initial axial stress profile and the ion-exchange axial stress profile from ion-exchange are additive in the glass, which results in the axial stress profile 108 of the strengthened glass containers 100 disclosed herein being asymmetric, as shown in FIG. 2.SP24-255

[0072] The axial stress profile in FIG. 2 is different from the axial stress profile obtained from ion-exchange by itself. Referring to FIG. 3, an ion-exchange axial stress profile 300 for a conventional glass article strengthened by ion-exchange only is graphically depicted. As shown in FIG. 3, the ion-exchange axial stress profile 300 is generally symmetric about the center of the cylindrical sidewall 102, which is line Rc in FIG. 3. The ion-exchange axial stress profile 300 includes an outer compressive stress region 310, an inner compressive stress region 330, and a central tension region 340 disposed between the outer compressive stress region 310 and the inner compressive stress region 330. The outer DOC 314 may be generally the same as the inner DOC 334. The tensile stress may continue to increase form the outer DOC 314 and the inner DOC 334 to a central tension plateau 342. In the central tension plateau 342, the central tension in the glass is generally constant with radial position. The ion-exchange axial stress profile 300 has an outer elbow 312 and an inner elbow 332, which are the points where the stress transitions to the central tension plateau 342 (i.e., gradient in the stress becomes about zero). In the ion-exchange axial stress profile 300, the outer elbow 312 and the inner elbow 332 are both in the central tension region 340, meaning that the axial stresses at the outer elbow 312 and the inner elbow 332 are both in tension. As shown in FIG. 3, the outer DOC 314 in the ion-exchange axial stress profile 300 is shallow, due to the limitation of ion-exchange, as previously discussed.

[0073] The ion-exchange axial stress profile 300 of FIG. 3 can be modified to produce the axial stress profile 108 of FIG. 2 by introducing an initial axial stress profile in the cylindrical sidewall 102 prior to conducting the ion-exchange. For instance, in embodiments, a bending stress profile may be introduced into the cylindrical sidewall 102 of the glass article by thermal means. Basically, heating the cylindrical sidewall 102 and then cooling the cylindrical sidewall 102 will naturally produce a bending stress within the cylindrical sidewall 102 due to the geometry of the cylindrical sidewall 102. Formed glass tubing has an inherent stress profde with the outer surface 104 in compression and the inner surface 106 in tension. Intentional external cooling of cylindrical glass articles superimposes a bending stress that results in a deep compression region at the outer surface 104.

[0074] Referring now to FIG. 4, a thermally-induced axial stress profde 400 produced from heating and cooling the cylindrical sidewall with no ion-exchange is graphically depicted. As shown in FIG. 4, the shape of the initial axial stress profde in the cylindrical sidewall 102, before ion-exchange, appears like a bending stress with a compression region 410, a tensionSP24-255 region 440, and a DOC 412 near the middle of the wall thickness (i.e., near the line designated with Rc). The thermally-induced axial stress profde 400 has the axial stress in compression at the outer surface 104 and in tension at the inner surface 106, and the axial stress changes at a constant rate of change between the outer surface 104 and the inner surface 106. The magnitude of the compressive stress is greatest at the outer surface 104, and the tension has the greatest magnitude at the inner surface 106. This axial stress profde is due to the cooling rate of the tubing, from the outside in, also called a thermal cooling stress. The magnitude of the tension at the inner surface 104 may be the similar to or larger than the low target central tension from ion-exchange by itself. The superposition of the low CT ion-exchange axial stress-profde (e.g., the axial stress profile 300 in FIG. 3) over a bending stress profile (e.g., the thermally-induced stress profile 400 in FIG. 4) that is higher in compression than the low CT ion-exchange axial stress profile will effectively deepen the compressive stress layer, resulting in the deeper outer compressive stress region 110 in FIG. 2. In the resulting axial stress profile in FIG. 2, the depth at which the CT is large enough to be a concern (e.g. 5 MPa) does not develop until much deeper in the glass. Since the bending stress increases tension near the inner wall, the maximum CT in the axial stress profile (FIG. 2) produced from superimposing the low CT ion-exchange axial stress profile 200 (FIG. 3) and the bending stress profile 300 (FIG. 4) would become the sum of the two, for example reaching to more than 10 MPa.

[0075] Because of the deeper compression from the thermal bending stress, a choice could be made to go with a higher CT from ion exchange further increasing the CT near the inside to make the failure transition less delayed and more intentionally significant. While it is desirable for relatively shallow flaws to remain arrested and not develop into a crack, it is desirable in some cases for relatively deep flaws or cracks to further propagate into easily detectable breaks, so that intact containers with sterility breaches cannot be delivered to a customer.

[0076] Although described herein in terms of a thermally-induced axial stress profile 400 in FIG. 4, it is understood that other methods may be suitable for producing the initial stress profile in the glass. The initial stress profile may have a high compressive stress at the outer surface 104 or surface that is expected to experience the greater amount of contact surface damage. The initial stress profile may have a high tensile stress at the inner surface 106, or a surface that is expected to have the least amount of contact surface damage.

[0077] When the ion-exchange axial stress profile 200 of FIG. 3 is overlaid on the thermally-induced axial stress profile 300 of FIG. 4 (or other initial stress profile), the axialSP24-255 stress profiles add together to produce the axial stress profile 108 of FIG. 2. Basically, at each radial positon between the outer surface 104 and the inner surface 106, the stress from each profile is added together, resulting in the axial stress profile 108 in FIG. 2. As will be discussed further herein, the axial stress profile 108 of the strengthened glass articles 100 can be produced by introducing the initial axial stress profile in the glass article, such as by creating a thermally- induced axial stress profile, and then ion-exchanging the glass article to overlay the ionexchange axial stress profile 200 onto the initial axial stress profile (e.g., the thermally-induced axial stress profile 300 of FIG. 4) to produce the asymmetric axial stress profile 108 of FIG. 2. Other methods of introducing the initial axial stress profile are contemplated.

[0078] Referring again to FIG. 2, the axial stress profile 108 of the strengthened glass article 100 disclosed herein comprises the outer compressive stress region 110, the inner compressive stress region 130, and the central tension region 140. In the outer compressive stress region 110 and the inner compressive stress region 130, the stress in the glass is compressive stress. In the central tension region 140, the stress in the glass is tensile strain. The axial stress profile 108 has the outer DOC 114 at the transition between the outer compressive stress region 110 and the central tension region 140. The inner DOC 134 is the point where the inner compressive stress region 130 transitions to the central tension region 140.

[0079] The axial stress profile 108 may be characterized by an outer elbow 112. The outer elbow 112 is disposed in the outer compressive stress region 110. The outer elbow 112 may be a transition point between a first outer compressive stress region 120 and a second outer compressive stress region 122. In the first outer compressive stress region 120, the compressive stress represents the sum of the compressive stress contributed by the initial axial stress and the compressive stress contributed by the ion-exchange. In the second compressive stress region 122, the compressive stress represents the compressive stress resulting from the initial stress profile reduced by the tension introduced by the ion-exchange. In other words, in the second compressive stress region 122, the initial axial stress profile (e.g., the thermally-induced axial stress profile 400 or FIG. 4) contributes compressive stress, but the subsequent ion-exchanges reduces this compressive stress in the second compressive stress region 122. At the outer elbow 112, the stress gradient changes magnitude from the high stress gradient in the first compressive stress region 120 to the lower stress gradient in the second compressive stress region 120. In embodiments, the magnitude of the stress gradient in the second compressive stress region 122 is less than the magnitude of the stress gradient in the first compressive stress region 120.SP24-255

[0080] Referring again to FIG. 2, the axial stress profile 108 may be characterized by an inner elbow 132. At the inner elbow 132, a gradient in the axial stress changes magnitude and direction. In between the inner surface 106 and the inner elbow 132, the ion-exchange axial stress profile (e.g., FIG. 3) contributes compressive stress and the initial axial stress profile introduced to the glass prior to ion exchange (e.g., thermally-induced axial stress profile 400 from FIG. 4) contributes tension, resulting in a high magnitude of the stress gradient and a direction towards increasing CT. At the inner elbow 132, the compressive stress contribution from the ion-exchange axial stress profile (e.g., axial stress profile 300 in FIG. 3) switches to central tension, and this central tension is added to the central tension contributed by the initial axial stress profile (e.g., thermally-induced axial stress profile 400 from FIG. 4). In embodiments, the inner elbow 132 may correspond generally to the point in the cylindrical sidewall 102 having the maximum CT. Since the CT in the central tension region of the initial axial stress profile decreases to the DOC, the stress gradient from the inner elbow 132 to the outer DOC 114 has a direction towards decreasing CT.

[0081] Referring again to FIG. 2, the outer elbow 112 is in the outer compressive stress region 110 and is, therefore, in compression. The outer elbow 112 can be thought of as the transition point between the compression being primary provided by the ion-exchange in the first compressive stress region 120 to the compression being primary provided by the initial axial stress profile in the second compressive stress region 122. The ion-exchange provides the high CS at the outer surface 104, which increases the surface strength. However, the contribution of the initial axial stress profile to compression increases the outer DOC 114 well beyond the contribution from the ion-exchange and well beyond the farthest penetration of the ion-exchange ions into the glass from the outer surface 104. As previously discussed, this increased outer DOC 114 greatly increases the depth at which flaws must penetrate into the outer surface 104 in order to reach the CT region 140.

[0082] Referring now to FIG. 5, axial stress (y-axis) as a function of depth from the outer surface of the cylindrical sidewall (x-axis) is shown for a conventional glass article strengthened by ion-exchange only and for strengthened glass articles produced through introduction of an initial axial stress profile followed by ion-exchange. In FIG. 5, positive values of stress correspond to compression and negative values correspond to tension. The axial stress was measured using optical retardation according to the methods described herein. The ion-exchange conditions were constant. The initial axial stress profile was gradually increasedSP24-255 from a bend stress of 1 MPa to a bend stress of 10 MPa, where the bend stress refers to the compressive stress at the outer surface 104 after introducing the initial axial stress profile and before the ion-exchange. The reference numbers for FIG. 5 are provided in Table 1.Table 1

[0083] The approximate outer DOC resulting from the strengthening for each of the strengthened glass articles was estimated from FIG. 5 and the estimated values are shown in Table 1. As shown in FIG. 5 and Table 1, when the initial axial stress profile is increased to a certain bend stress (i.e., compressive stress at the outer surface 104 after introduction of the initial axial stress profile and prior to ion-exchange), such as a bend stress equal to 6 MPa in Table 1, the outer DOC increases dramatically. Without being bound by any particular theory, it is believe that when the bend stress of the initial axial stress profile introduced to the glass reaches a certain threshold bend stress value, then the contributions of the initial axial stress profile to the compression stress proximate the outer surface 104 become greater than the central tension produced by the ion-exchange, thereby increasing the outer DOC and deepening the outer compressive stress region 110. As shown in FIG. 5, when the bend stress of the initial axial stress profile is greater than or equal to about 6 MPa (ref. no. 514), the outer elbow 112 is above the zero line, indicating that the outer elbow 112 is in compression. At less than 6 MPa bend stress (ref. nos. 502-512), the axial stress profile after ion-exchange transitions fromSP24-255 compression to tension at a point shallower than the outer elbow 112, resulting in the outer elbow 112 being in tension. When the outer elbow 112 is in tension, the outer DOC 114, which is the depth at which the axial stress profile transitions from compression to tension in FIG. 5, is shallower. The bend stress that results in the outer elbow 112 being in compression may depend on the glass composition, geometry, or both of the strengthened glass article 100.

[0084] Referring now to FIG. 6, the axial stress profiles starting from the outer surface 104 for various strengthened glass articles are graphically depicted. Reference number 600 is the axial stress profile for a strengthened glass article strengthened by ion-exchange only. Reference number 610 is the axial stress profile for a strengthened glass article strengthened by introducing the initial stress profile having a bend stress of 20 MPa followed by ionexchange. Reference number 210 is the axial stress profile for a strengthened glass article strengthened by introducing the initial stress profile having bend stress of 50 MPa followed by ion-exchange. In FIG. 6, zero depth (x-axis) corresponds to the outer surface 104 of the strengthened glass article, and zero stress (y-axis) is the transition between tension (indicated as negative stress) and compression (indicated as positive stress).

[0085] In the axial stress profile 600 for the strengthened glass article strengthened by ionexchange only, an outer surface stress tangent line 602 can be drawn as a straight line that is tangent to the axial stress profile 600 at the outer surface 104. Additionally, a center stress tangent line 604 can be drawn as a straight line that is tangent to the axial stress profile 600 in the middle of the cylindrical sidewall (e.g., a depth of about 200 pm in FIG. 6). The outer surface stress tangent line 602 and the center stress tangent line 604 intersect at intersection point 606. As shown in FIG. 6, in the axial stress profile 600 for the strengthened glass article strengthened by ion-exchange only, the center stress tangent line 604 is generally horizontal (indicating a stress gradient of about zero, as expected from strengthening by ion-exchange only), and the intersection point 606 is in the tension region (i.e., the stress at the depth of the intersection point 606 is less than zero in FIG. 6).

[0086] For the axial stress profile 620 for the strengthened glass article strengthened by introducing the initial stress profile followed by ion-exchange, an outer surface stress tangent line 622 can be drawn as a straight line that is tangent to the axial stress profile 620 at the outer surface 104. Additionally, a center stress tangent line 624 can be drawn as a straight line that is tangent to the axial stress profile 620 in the middle of the cylindrical sidewall (e.g., a depth of about 200 pm in FIG. 6). For the axial stress profile 620 for the strengthened glass articleSP24-255 strengthened by introducing the initial stress profde followed by ion-exchange, the outer surface stress tangent line 622 and the center stress tangent line 624 intersect at the intersection point 626. In contrast to axial stress profde 600, for which the intersection point 606 is in tension, the intersection point 626 for the axial stress profde 620 is in compression (i.e., the stress at the depth of the intersection point 626 is positive, which is in the compression region). As shown in FIG. 6, when the intersection point 626 is in the compression region, the outer DOC 114 is at a much greater depth in the glass compared to having the intersection point 606 in the tension region. As shown in FIG. 6, the axial stress profde 620 for the strengthened glass article strengthened by introducing the initial axial stress profde followed by ion-exchange has an outer DOC (about 130 pm) that is about double the outer DOC (about 65 pm) for the axial stress profde 600 for the glass article strengthened by ion-exchange only.

[0087] Thus, the strengthened glass articles 100 disclosed herein can be characterized by having an intersection point between an outer surface stress tangent line and a center stress tangent line of the axial stress profde, where the intersection point is in compression. When the intersection point of the outer surface stress tangent line and the center stress tangent line is in compression, the outer DOC is extended much deeper into the glass from the outer surface 104 compared to strengthening by ion-exchange only. When the intersection point is in compression, the outer DOC is significantly greater than the outer DOC when the intersection point is in tension. In embodiments, the strengthened glass article 100 has the cylindrical sidewall 102 having the outer surface 104, the inner surface 106, the radial thickness, and an asymmetric axial stress profde, where the axial stress profde comprises the outer compressive stress region 110 extending radially inward from the outer surface 104 to the outer DOC 114, the inner compressive stress region 130 extending radially outward from the inner surface 106 to the inner DOC 134, and the central tension region 140 disposed radially between the outer DOC 114 and the inner DOC 134. The graph of the axial stress as a function of depth in the glass from the outer surface 104 (i.e., axial stress profde) has an outer surface stress tangent line and a center stress tangent line, wherein the intersection point between the outer surface stress tangent line and the center stress tangent line is in compression.

[0088] Referring again to FIG. 2, the outer compressive stress region 110 has the first compressive stress region 120 and the second compressive stress region 122. The first compressive stress region 120 may extend from the outer surface outer surface 104 to an outer depth of diffusion DODouter 116. The DODouter 116 is a depth in the glass from the outer surfaceSP24-255104 at which depth a concentration gradient of the one or more alkali metals becomes zero. In other words, during the ion-exchange process in the second strengthening step of the methods disclosed herein, alkali metal ions are diffused into the outer surface 104 of the cylindrical sidewall 102, and the DODouter 116 is the depth to which the ion-exchange alkali metal ions penetrate into the glass from the outer surface 104. The second compressive stress region 122 may extend from the outer depth of diffusion DODouter 116 to the outer DOC 114. In the first compressive stress region 120, the glass may have a concentration gradient of one or more alkali metals, which results from the ion-exchange in the second step of the strengthening process. In the second compressive stress region 122, the concentration of each alkali metal species in the glass is constant and about equal to the bulk concentration of each of the alkali metal species in the glass prior to strengthening. The outer depth of diffusion DODouter 116 may generally correspond to the outer elbow 112 where the slope of the axial stress profile changes from the steeper slope in the first compressive stress region 120 to the smaller slope in the second compressive stress region 122. In embodiments, at the outer depth of diffusion (DODouter 116), the axial stress profile 108 of the glass is in compression. In contrast, for glass articles strengthened by ion-exchange only, the DODouter 116 is in the tension region. When the DODouter 116 is in compression, the outer DOC 114 is deeper into the glass compared to the DODouter 116 and also deeper into the glass from the outer surface 104 compared to a glass article strengthened by ion-exchange only.

[0089] In embodiments, the outer DOC 114 may be greater than the outer depth of diffusion by a factor of greater than 1, or greater than or equal to 2, or greater than or equal to 5, or greater than or equal to 10, or greater than or equal to 20, or greater than or equal to 30, or greater than or equal to 40, or greater than or equal to 50, or greater than or equal to 60, or greater than or equal to 70, or greater than or equal to 80, or greater than or equal to 90, or greater than or equal to 100, or greater than or equal to 200, or greater than or equal to 300, or greater than or equal to 400, or greater than or equal to 500. In embodiments, the ratio of the outer DOC 114 (DOCouter) divided by the outer depth of diffusion (DODouter) is greater than 1, and less than or equal to 500, such as from 1 to 500. In embodiments, the outer DOC 114 of the strengthened glass article 100 may be greater than the outer DOC 114 of a comparative glass article strengthened by ion-exchange only by a factor of greater than 1, where the comparative glass article has the same shape, same glass composition, and same ion-exchange conditions compared to the strengthened glass article 100, just without introducing the initial axial stress profile prior to ion exchange.SP24-255

[0090] Referring again to FIG. 2, the axial stress profile 108 of the strengthened glass articles 100 disclosed herein may be characterized by an inner depth of diffusion DODinner 136, which is a depth in the glass measured from the inner surface 106 and at which a concentration gradient of the alkali metals in the glass becomes zero. In other words, the depth to which the larger ions penetrate into the glass from the inner surface 106 as a result of the ion-exchange step is referred to as the inner depth of diffusion DODinner 136. The inner depth of diffusion DODinner 136 may generally correspond to the inner elbow 132, which is where the slope of the axial stress profile changes in magnitude and direction proximate the inner surface 106 of the cylindrical sidewall 102. At the inner depth of diffusion DODinner 136 the contribution to the axial stress profile from the ion-exchange transitions from compression to tension, resulting in the change in magnitude and direction of the slope of the axial stress profile 108 at the inner elbow 112. In embodiments, the DODinner 136 may be greater than the inner DOC 134. The DODinner 136 may be in tension, such as being in the central tension region 140 of the cylindrical side wall 102.

[0091] Referring again to FIG. 2, in embodiments, the axial stress profile of the cylindrical sidewall 102 of the strengthened glass articles 100 disclosed herein have the outer DOC 114 that is greater than the inner DOC 134. The relationship between the outer DOC 114 and the inner DOC 124 for the strengthened glass articles 100 can be described by Equation 1 (EQU. 1). In EQU. 1, DOCouter is the outer DOC 114, DOCinner is the inner DOC 134, and t is the radial thickness of the cylindrical sidewall 102 between the outer surface 104 and inner surface 106, and X is 0, or 0.01, or 0.05.

[0092] In embodiments, a geometrically induced ratio of the outer DOC 114 to the inner DOC 134 may be greater than or equal to about 1.01, greater than or equal to about 1.1, greater than or equal to about 1.5, or even greater than or equal to about 2. In embodiments, the geometrically induced ratio of the outer DOC 114 to the inner DOC 134 may be less than or equal to about 2000, such as less than or equal to about 1000, less than or equal to about 500, less than or equal to about 100, or even less than or equal to about 10. In embodiments, the geometrically induced ratio of the outer DOC 114 to the inner DOC 134 may be from about 1.01 to about 2000, such as from about 1 .05 to about 1000, from about 1. 1 to about 500, from about 1.5 to about 100, from about 2 to about 10, or any ranges or subranges therebetween.SP24-255

[0093] The axial stress profiles of the strengthened glass articles 100 disclosed herein may be further characterized by the relationship between the compressive stress at the outer surface 104 compared to the compressive stress at the inner surface 106. Referring again to FIG. 2, in embodiments, the axial stress profile of the strengthened glass articles 100 disclosed herein may exhibit an outer compressive stress (CSouter) that is greater than an inner compressive stress (CSinner), where CSouter is the axial compressive stress measured at the outer surface 104 of the cylindrical sidewall 102 and CSinner is the axial compressive stress measured at the inner surface 106 of the cylindrical sidewall 102. In embodiments, a difference between the CSouter and the CSinner may be, in embodiments, about twice the bend stress, or great than or equal to twice the bend stress, or greater than or equal to about 10 MPa.

[0094] The axial stress profiles for the strengthened glass articles 100 disclosed herein may also be characterized by the location of the maximum axial central tension within the cylindrical sidewall 102. Referring again to FIG. 2, the maximum axial central tension in the cylindrical sidewall 102 may occur at or around the inner elbow 132 and may correspond to the maximum absolute value of the central tension in the central tension region. The maximum axial central tension may be at a depth within the cylindrical sidewall 102 that is closer to the inner surface 106 than it is to the outer surface 104. In embodiments, a ratio of a depth of the maximum axial central tension from the inner surface 106 of the cylindrical sidewall 102 to the thickness of the cylindrical sidewall 102 may be less than 0.5, such as less than or equal to about 0.45, less than or equal to about 0.4, less than or equal to about 0.35, less than or equal to about 0.3, or even less than or equal to about 0.25. In embodiments, a distance between a maximum central tension and the inner surface 106 of the strengthened glass article 100 is less than 50 % the radial thickness t of the cylindrical side wall 102, such as less than or equal to about 45%, less than or equal to about 40%, less than or equal to about 35%, less than or equal to about 30%, or even less than or equal to about 25%.

[0095] The strengthened glass articles 100 disclosed herein may also be characterized by the tangential stress component in the cylindrical sidewall 102. The strengthened glass articles 100 disclosed herein can be distinguished from glass articles strengthened by only ionexchange by looking at the tangential stress component of the stress vector in the glass (i.e., the hoop stress). The magnitude of the slope of the tangential stress component as a function of depth in the glass of the strengthened glass article 100 is greater than a magnitude of a slopeSP24-255 of a tangential stress component in a comparative glass article having the same geometry, the same glass composition, and strengthened only by ion-exchange.

[0096] The strengthened glass articles 100 disclosed herein may be cylindrical glass articles, such as packages, containers, vessels, or other glass articles comprising a glass and adapted to contain pharmaceutical products or vaccines, and foodstuff containers (e.g., bottles, baby food jars, etc.) in a hermetic and / or sterile state. The glass articles strengthened by the method disclosed herein may be used for glass containers, such as pharmaceutical containers, having the mechanical strength to resist external damage. As used herein, terms such as "container" and "vessel" refer to any article that is adapted to hold a solid or fluid for storage. The container may, in some embodiments, be sealable. The glass articles may be used for containers or vessels, such as vials for holding sterile substances such as a vaccine, biologic, pharmaceutical, foodstuff, solution, or the like. Non-limiting examples of such containers include glass vials, bottles, food jars, cartridges, syringes, ampules, or the like.

[0097] Although described herein in the context of cylindrical glass articles, such as pharma containers, the strengthened glass articles can have other shapes having at least one wall, while still having the asymmetric axial stress profde in the wall. Other shape factors include but are not limited to cover glass for electronic devices, VR glass, strengthened glass for aerospace or automotive applications, or other form factor. The strengthened glass articles 100 may be adapted to any other application in which one surface of the glass is expected to encounter surface damage more than the other surfaced of the glass.

[0098] The strengthened glass articles 100 disclosed herein may be produced by methods that include forming a glass article, introducing an initial axial stress profde in the sidewall, and then ion-exchanging the glass article to produce the strengthened glass article 100 having the asymmetric axial stress profde. Referring again to FIG. 2, in embodiments, the asymmetric axial stress profde in the strengthened glass article 100 may have the outer compressive stress region 110 extending radially inward from the outer surface 104 to the outer DOC 114; the inner compressive stress region 130 extending radially outward from the inner surface 106 to the inner DOC 134; and the central tension region 140 disposed radially between the outer DOC 114 and the inner DOC 134. Referring again to FIG. 6, a graph of the axial stress as a function of depth in the glass from the outer surface 104 has the outer surface stress tangent line and the center stress tangent line; the outer surface stress tangent line is a line tangent to the graph of axial stress at the outer surface; the center stress tangent line is a line tangent toSP24-255 the graph of axial stress in the central tension region; and an intersection point between the outer surface stress tangent line and the center stress tangent line is in compression. The asymmetric axial stress profde in the strengthened glass article 100 may have any of the features or characteristics previously discussed herein for the axial stress profile.

[0099] Forming the glass article may comprise forming a glass article having a sidewall having an outer surface, an inner surface, and a thickness extending between the outer surface and the inner surface. In embodiments, the glass article may be a cylindrical glass article having the cylindrical sidewall 102, which has the outer surface 104, the inner surface 106, and radial thickness extending between the outer surface 104 and the inner surface 106 in a radial direction. The glass article may be formed from glass tubing using any suitable tube converting process or other suitable glass forming process, and is not particularly limited by the method used to make the starting glass article.

[0100] Introducing the initial axial stress profile in the sidewall, such as in the cylindrical sidewall 102, may include introducing an initial compressive stress at the outer surface of the glass article, wherein introducing the initial compressive stress produces the initial axial stress profile. The initial axial stress profile may have a maximum compressive stress at the outer surface 104 and a maximum tension at the inner surface 106 of the glass article. In embodiments, introducing the initial compressive stress in the outer surface 104 may comprise introducing a thermally induced stress profile in the cylindrical sidewall 102. In embodiments, introducing the thermally induced stress profile in the cylindrical sidewall 102 may comprise annealing the glass article and cooling the cylindrical sidewall at an increased cooling rate, wherein the increased cooling rate produces the thermally induced stress profile in the cylindrical sidewall 102. The cooling rate may depend on the composition of the glass used to produce the glass article. For a cylindrical sidewall 102, due to the different radii of the outer surface 104 and inner surface 106, the outer surface 104 and inner surface 106 expand and contract at different rates during heating and cooling, respectively. Thus, when the cooling rate is increased, the difference in the rates of thermal contraction between the outer surface 104 and the inner surface 106 produces a bending stress in the cylindrical sidewall 102. If the cooling rate is slow, thermal relaxation will relax away any bending stress. Thus, the cooling rate must be sufficiently high to generate the bending stress in the cylindrical sidewall.

[0101] In embodiments, introducing the initial compressive stress in the outer surface 104 may comprise subjecting the outer surface 104 of the cylindrical sidewall 102 to a preliminarySP24-255 ion-exchange process without ion-exchanging the inner surface 106 of the cylindrical sidewall 102, such as by masking or otherwise prevent contact of the ion-exchange bath with the inner surface 106 of the cylindrical sidewall 102. Other methods of introducing the initial axial stress profile in the sidewall of the glass article are contemplated, as long as the method results in a compressive stress region proximate the surface most likely to encounter the most surface damage (e.g., outer surface 104) and a central tension region proximate the surface expected to receive the least surface damage (e.g., inner surface 106).

[0102] The amount of axial stress introduced into the cylindrical sidewall 102 in the step of introducing the initial stress profile in the cylindrical sidewall 102 may depend on the glass composition, the geometry of the glass article, the ion-exchange conditions of the second ionexchange step, or combinations thereof. In embodiments, the amount of initial stress in the cylindrical sidewall can be estimated from Equation 2 (EQU. 2) ab> (0.275 ■ CT'ox) + (2.247 ■ CT1OX) EQU. 2

[0103] In EQU. 2, Ob is the initial compressive stress in the outer surface 104; CTiox is the a central tension at a middle of the cylindrical sidewall 102 for a comparative glass article subjected only to ion exchange under the same conditions and without introducing the initial axial stress; and the middle of the cylindrical sidewall is equal to a point halfway between the inner surface 106 and the outer surface 104 of the cylindrical sidewall 102.

[0104] Following introduction of the initial stress profde in the cylindrical sidewall 102, the methods may include ion-exchanging the glass article having the initial axial stress profde to produce the strengthened glass article having the asymmetric axial stress profde. During the ion-exchange process, the glass article may be submersed in an ion-exchange bath that may include an alkali metal salt, such as alkali metal nitrates, alkali metal sulfates, or other alkali metal salts. The alkali metal salts of the ion-exchange bath may have larger alkali metals, such as potassium, rubidium, cesium, or combinations thereof. In embodiments, the alkali metal salt of the ion-exchange bath may be a potassium salt. During the ion-exchange, the larger alkali metal ions from the ion-exchange bath may diffuse into the surface regions of the glass to replace smaller metal ions, such as lithium and / or sodium ions. In embodiments, the alkali metal salt of the initial ion-exchange bath may be potassium nitrate.

[0105] The ion-exchange bath may be maintained at an initial ion-exchange temperature of greater than or equal to 300 °C and less than or equal to 550 °C, such as from 350 °C to 450SP24-255°C, from 375 °C to 425 °C, or any ranges or subranges therebetween. At temperatures greater than about 550 °C, thermal relaxation in the glass may be more significant, which may reduce the compressive stress in the surface region resulting from introduction of the potassium ions to the surface region. The upper temperature range of the initial ion-exchange process may be further limited by the chemistry of the initial ion-exchange bath and side reactions with the components. For example, potassium nitrate may thermally decompose or react with other constituents of the initial ion-exchange bath at temperatures greater than about 550 °C.

[0106] The glass article may be submersed in the ion-exchange bath for an ion-exchange time sufficient to produce the desired compressive stress (CS) at the outer surface 104 of the strengthened glass article 100. In embodiments, the initial ion-exchange time may be from 0. 1 hr to 1 hr, from 0. 1 hr to 0.9 hr, from 0.1 hr to 8 hr, from 0.3 hr to 1 hr, from 0.3 hr to 0.9 hr, or even from 0.3 hr to 0.8 hr. At ion-exchange times greater than about 1 hour, thermal relaxation of the glass caused by exposure of the glass to the ion-exchange temperature for the extended period of time may reduce the compressive stress in the surface regions created by introduction of the larger alkali metal ions. Maintaining the ion-exchange time at less than or equal to 1 hour may minimize thermal relaxation in the glass, thereby preserving the compressive stress resulting from introduction of the larger alkali metal ions. The ion-exchange time at high temperature may also be limited by the chemistry of the ion-exchange bath and side reactions with components of the ion-exchange bath.

[0107] In some embodiments, the method may include subjecting the strengthened glass article to a final rinse and / or final wash following the ion-exchange process to remove excess alkali metal salts and other reagents from the surfaces of the strengthened glass article. The final rinse may include dip rinsing the strengthened glass article in water, such as deionized water.

[0108] The strengthened glass articles disclosed herein are not particularly limited by the glass composition, as long as the glass composition is able to be ion-exchanged to produce the desired axial stress profiles. Examples include but are not limited to borosilicate glasses, aluminosilicate glasses, alkali aluminosilicate glasses, or any other type of glass able to be ion- exchanged. In embodiments, the strengthened glass articles 100 may include borosilicate glasses (ASTM E438-92 (Standard Specification for Glasses in Laboratory Apparatus) Type 1, class A glasses - 3.3 ppm / K, Type 1, class B glasses - 5.1 ppm / K) that are typically used as containers for pharmaceuticals, serum, vaccines, and the like. In embodiments, theSP24-255 strengthened glass articles 100 may comprise an aluminosilicate glass. In embodiments, the aluminosilicate glass may include at least one alkali metal oxide. In embodiments, the strengthened glass article 100 may include a glass composition that is within the ASTM standard type lb glass compositions.

[0109] In embodiments, the strengthened glass articles 100 may comprise a chemically durable glass such as that described in U.S. Patent No. 9, 145,329, filed October 25, 2012 and granted September 29, 2015, by Melinda Drake et al., entitled "Alkaline Earth Aluminosilicate Glass Compositions with Improved Chemical and Mechanical Durability," the entire contents of which are incorporated herein by reference. In embodiments, the glasses described therein include from about 67 mol% to about 75 mol% SiO2; from about 6 mol% to about 10 mol% AI2O3; from about 5 mol% to about 12 mol% alkali oxide; and from about 9 mol% to about 15 mol% of alkaline earth oxide. The alkali oxide comprises at least Na2O and K2O. In other embodiments, the glasses described therein comprise from about 67 mol% to about 75 mol% SiCU; from about 6 mol% to about 10 mol% AI2O3; from about 5 mol% to about 12 mol% alkali oxide; and from about 9 mol% to about 15 mol% of alkaline earth oxide. The alkaline earth oxide comprises at least one of SrO and BaO.

[0110] In embodiments, the strengthened glass articles 100 may comprise a chemically durable glass such as that described in described in U.S. Patent No. 8,980,777, filed October 25, 2012 and granted March 17, 2015, by Paul S. Danielson et al., entitled "Glass Compositions with Improved Chemical and Mechanical Durability," the entire contents of which are incorporated herein by reference in their entirety. In embodiments, such glasses may include from about 67 mol% to about 78 mol% SiO2; from about 3 mol% to about 13 mol% alkaline earth oxide; X mol% AI2O3; and Y mol% alkali oxide. The alkali oxide may include Na2O in an amount greater than 8 mol% and a ratio of Y:X which is greater than 1. In other embodiments, such glasses may include from about 67 mol% to about 78 mol% SiCf: from about 3 mol% to about 13 mol% alkaline earth oxide, wherein the alkaline earth oxide may include CaO in an amount greater than or equal to 0.1 mol% and less than or equal to 1.0 mol%; X mol% AI2O3, wherein X is greater than or equal to 2 mol% and less than or equal to about 10 mol%; Y mol% alkali oxide, wherein a ratio of Y:X is greater than 1.

[0111] In embodiments, the strengthened glass articles 100 may comprise an alkali aluminosilicate glass as described in U.S. Patent 7,666,511 by Adam J. Ellison et al., entitled "Down-Drawable, Chemically Strengthened Glass for Cover Plate," fded July 27, 2007, theSP24-255 contents of which are incorporated herein by reference in their entirety. In embodiments, the these alkali aluminosilicate glasses may include: from about 64 mol% to about 68 mol% SiC ; from about 12 mol% to about 16 mol% Na20; from about 8 mol% to about 12 mol% AI2O3; from 0 mol% to about 3 mol% B2O3; from about 2 mol% to about 5 mol% K2O; from about 4 mol% to about 6 mol% MgO; and from 0 mol% to about 5 mol% CaO; wherein: 66 mol% < SiO2 + B2O3 + CaO < 69 mol%; Na20 + K2O + B2O3 + MgO + CaO + SrO > 10 mol%; 5 mol% < MgO + CaO + SrO < 8 mol%; (Na2O + B2O3) - AI2O3 > 2 mol%; 2 mol% < Na2O - AI2O3 < 6 mol%; and 4 mol% < (Na2O + K2O) - AI2O3 < 10 mol%.

[0112] In embodiments, the strengthened glass articles 100 may comprise an alkali aluminosilicate glass described in U.S. Patent No. 8,158,543, fded November 25, 2008, by Matthew J. Dejneka et al., entitled "Glasses Having Improved Toughness and Scratch Resistance," the entire contents of which are incorporated herein by reference. In embodiments, these alkali aluminosilicate glasses may include: at least one of alumina, and at least one of an alkali metal oxide and an alkali earth metal oxide, wherein -15 mol% < (R2O + R'O - AI2O3 - ZrCU) - B2O3 < 4 mol%, where R is one of Li, Na, K, Rb, and Cs, and R' is one of Mg, Ca, Sr, and Ba. In some embodiments, the alkali aluminosilicate glass may include: from about 62 mol% to about 70 mol.% SiCU; from 0 mol% to about 18 mol% AI2O3; from 0 mol% to about 10 mol% B2O3; from 0 mol% to about 15 mol% Li2O; from 0 mol% to about 20 mol% Na2O; from 0 mol% to about 18 mol% K2O; from 0 mol% to aboutl7 mol% MgO; from 0 mol% to about 18 mol% CaO; and from 0 mol% to about5 mol% ZrO2.

[0113] In embodiments, the strengthened glass articles 100 may comprise an alkali aluminosilicate glass described in U.S. Patent No. 8, 158,543, by Sinue Gomez et al., entitled "Fining Agents for Silicate Glasses," filed February 25, 2009 and granted April 17, 2012, the entire contents of which are incorporated herein by reference. In embodiments, these alkali aluminosilicate glasses may include: from about 60 mol% to about 70 mol% SiCL; from about 6 mol% to about 14 mol% AI2O3; from 0 mol% to about 15 mol% B2O3; from 0 mol% to about 15 mol% Li2O; from 0 mol% to about 20 mol% Na2O; from 0 mol% to about 10 mol% K2O; from 0 mol% to about 8 mol% MgO; from 0 mol% to about 10 mol% CaO; from 0 mol% to about 5 mol% ZrO2; from 0 mol% to about 1 mol% SnO2; from 0 mol% to about 1 mol% CeO2; less than about 50 ppm AS2O3; and less than about 50 ppm Sb2O3; wherein 12 mol% < Li2O + Na2O + K2O < 20 mol% and 0 mol% < MgO + CaO < 10 mol%.SP24-255

[0114] In embodiments, the strengthened glass articles 100 may comprise an alkali aluminosilicate glass described in U.S. Patent No. 8,802,581 by Matthew J. Dejneka et al., entitled "Zircon Compatible Glasses for Down Draw," fded August 10, 2010 and granted August 12, 2014, the entire contents of which are incorporated herein by reference. In embodiments, these alkali aluminosilicate glasses may include SiCh and Na2O, wherein the glass has a temperature Tsskp at which the glass has a viscosity of 35 kilo poise (kpoise), wherein the temperature Tbreakdown at which zircon breaks down to form ZrC and SiCh is greater than Tsskp. In embodiments, the alkali aluminosilicate glass may include: from about 61 mol % to about 75 mol% SiCh; from about 7 mol % to about 15 mol% AI2O3; from 0 mol% to about 12 mol% B2O3; from about 9 mol %to about 21 mol% Na2O; from 0 mol % to about 4 mol% K2O; from 0 mol%to about 7 mol% MgO; and 0 mol% to about 3 mol% CaO.

[0115] In embodiments, the strengthened glass articles 100 may comprise an alkali aluminosilicate glass described in U.S. Patent No. 8,586,492 by Kristen U. Barefoot et al., entitled "Crack And Scratch Resistant Glass and Enclosures Made Therefrom," filed August 18, 2010 and granted November 19, 2013, the entire contents of which are incorporated herein by reference. In embodiments, these alkali aluminosilicate glasses may include at least 50 mol% SiC>2 and at least one modifier selected from the group consisting of alkali metal oxides and alkaline earth metal oxides, wherein [(AI2O3 (mol%) + B2O3(mol%)) / (^alkali metal modifiers(mol%))] > 1. In embodiments, the alkali aluminosilicate glass may include: from 50 mol% to about 72 mol% SiCh; from about 9 mol% to about 17 mol% AI2O3; from about 2 mol% to about 12 mol% B2O3; from about 8 mol% to about 16 mol% Na2O; and from 0 mol% to about 4 mol% K2O.

[0116] In embodiments, the strengthened glass articles 100 may comprise an alkali aluminosilicate glass described in U.S. Patent No. 9,346,703 by Dana C. Bookbinder et al., entitled "Ion Exchangeable Glass with Deep Compressive Layer and High Damage Threshold," filed November 28, 2011 and granted May 24, 2016, the entire contents of which are incorporated herein by reference. In embodiments, the alkali aluminosilicate glass may include SiCh, AI2O3, P2O5, and at least one alkali metal oxide (R2O), wherein 0.75 < [(P2Os(mol%) + R2O(mol%)) / M2O3(mol%)] < 1.2, where M2O3 = AI2O3 + B2O3. In embodiments, the alkali aluminosilicate glass may include: from about 40 mol% to about 70 mol% SiCh; from 0 mol% to about 28 mol% B2O3; from 0 mol% to about 28 mol% AI2O3; from about 1 mol% to about 14 mol% P2O5; and from about 12 mol%to about 16 mol% R2O; and, in certain embodiments,SP24-255 from about 40 to about 64 mol% SiCh; from 0 mol% to about 8 mol% B2O3; from about 16 mol% to about 28 mol% AI2O3; from about 2 mol% to about 12% P2O5; and from about 12 mol% to about 16 mol% R2O.

[0117] In embodiments, the strengthened glass articles 100 may comprise an alkali aluminosilicate glass described in U.S. Patent No. 9,156,724, fded November 15, 2012, by Timothy M. Gross, entitled "Ion Exchangeable Glass with High Crack Initiation Threshold," fded November 16, 2011 and granted October 13, 2015, the entire contents of which are incorporated herein by reference. In embodiments, the alkali aluminosilicate glasses may include at least about 4 mol% P2O5, wherein (M2O3(mol%) / RxO(mol%)) < 1, wherein M2O3 = AI2O3 + B2O3, and wherein RXO is the sum of monovalent and divalent cation oxides present in the alkali aluminosilicate glass. In embodiments, the monovalent and divalent cation oxides are selected from the group consisting of Li2O, Na2O, K2O, Rb2O, CS2O, MgO, CaO, SrO, BaO, and ZnO. In embodiments, the glass may include 0 mol% B2O3.

[0118] In embodiments, the strengthened glass articles 100 may comprise an alkali aluminosilicate glass described in U.S. Patent No. 9,290,413, by Matthew J. Dejneka et al., entitled "Ion Exchangeable Glass with High Compressive Stress," fded June 26, 2012 and granted March 22, 2016, the entire contents of which are incorporated herein by reference. In embodiments, the alkali aluminosilicate glass may include at least about 50 mol% SiCh and at least about 11 mol% Na2O. In embodiments, the glass further comprises AI2O3 and at least one of B2O3, K2O, MgO and ZnO, wherein -340 + 27.I AI2O3 - 28.7 B2O3 + 15.6 Na2O - 6I.4 K2O + 8. 1 (MgO + ZnO) > 0 mol%. In embodiments, the glass may include: from about 7 mol%to about 26 mol% AI2O3; from 0 mol% to about 9 mol% B2O3; from about 11 mol% to about 25 mol% Na2O; from 0 mol% to about 2.5 mol% K2O; from 0 mol% to about 8.5 mol% MgO; and from 0 mol% to about 1.5 mol% CaO.

[0119] In embodiments, the strengthened glass articles 100 may comprise an alkali aluminosilicate glass described in U.S. Patent No. 8,951,927, fded May 31, 2012 and granted February 10, 2015, by Matthew J. Dejneka et al., and entitled "Zircon Compatible, Ion Exchangeable Glass with High Damage Resistance," the entire contents of which are incorporated herein by reference. In embodiments, the alkali aluminosilicate glasses may include at least about 50 mol% SiO2; at least about 10 mol% R2O, wherein R2O comprises Na2O; AI2O3, wherein AhO3(mol%) < R2O(mol%); and B2O3, and wherein B2O3(mol%) - (R2O(mol%) - AhO3(mol%)) > 3 mol%. In embodiments, the glass comprises: at least aboutSP24-25550 mol% SiCh, from about 9 mol% to about 22 mol% AI2O3; from about 3 mol% to about 10 mol% B2O3; from about 9 mol% to about 20 mol% Na2O; from 0 mol% to about 5 mol% K2O; at least about 0. 1 mol% MgO, ZnO, or combinations thereof, wherein 0 < MgO < 6 and 0 < ZnO < 6 mol%; and, optionally, at least one of CaO, BaO, and SrO, wherein 0 mol% < CaO + SrO + BaO < 2 mol%.

[0120] In embodiments, the strengthened glass articles 100 may comprise an alkali aluminosilicate glass described in U.S. Patent No. 9,517,967, granted on December 13, 2016, by Matthew J. Dejneka et al., and entitled "Ion Exchangeable Glass with High Damage Resistance," the entire contents of which are incorporated herein by reference. In embodiments, the alkali aluminosilicate glasses described hereinabove may include: at least about 50 mol% SiO2; at least about 10 mol% R2O, wherein R2O comprises Na2O; AI2O3, wherein -0.5 mol%< AhO3(mol%) - R2O(mol%) < 2 mol%; and B2O3, wherein B2O3(mol%) - (R2O(mol%) - AhO3(mol%)) > 4.5 mol%. In embodiments, the glasses comprise: at least about 50 mol% SiCh, from about 12 mol% to about 22 mol% AI2O3; from about 4.5 mol% to about 10 mol% B2O3; from about 10 mol% to about 20 mol% Na2O; from 0 mol% to about 5 mol% K2O; at least about 0. 1 mol% MgO, ZnO, or combinations thereof, wherein 0 mol% < MgO < 6 and 0< ZnO < 6 mol%; and, optionally, at least one of CaO, BaO, and SrO, wherein 0 mol% < CaO + SrO + BaO < 2 mol%.

[0121] In embodiments, the alkali aluminosilicate glasses described hereinabove may be substantially free of (i.e., contain 0 mol% of) of at least one of lithium, boron, barium, strontium, bismuth, antimony, and arsenic. In embodiments, the alkali aluminosilicate glasses described hereinabove may be down-drawable by processes known in the art, such as slotdrawing, fusion drawing, re-drawing, and the like, and may have a liquidus viscosity of at least 130 kilopoise. In embodiments, the alkali aluminosilicate glasses described hereinabove may be suitable for tube drawing and re-forming from tubes and the like and may have a liquidus viscosity of at least 10 kilopoise and, in embodiments, at least about 40 kilopoise.

[0122] In embodiments, the glass of the strengthened glass articles 100 may be ionexchangeable borosilicate glass as described in U.S. Patent No. 11,168,019, by Robert Anthony Schaut, et al., granted November 9, 2021 and entitled "Ion Exchangeable Borosilicate Glass Compositions and Glass Articles Formed from the Same," the entire contents of which are incorporated herein by reference. These ion-exchangeable borosilicate glasses may have a composition that may be more easily ion-exchanged compared to existing, commercially-SP24-255 available borosilicate glasses, which are not easily strengthened through ion-exchange. In embodiments, the ion-exchangeable borosilicate glasses may include greater than or equal to 72 mol.% and less than or equal to 82 mol.% SiC ; greater than or equal to 1 mol.% and less than or equal to 6 mol.% AI2O3; greater than or equal to 3 mol.% and less than or equal to 16 mol.% B2O3; greater than or equal to 5 mol.% and less than or equal to 12 mol.% Na20; greater than or equal to 0.30 mol.% and less than or equal to 1.5 mol.% K2O; greater than or equal to 0.10 mol.% and less than or equal to 6.00 mol.% MgO; and greater than or equal to 0.50 mol.% and less than or equal to 4.0 mol.% CaO. The ion-exchangeable borosilicate glass may be capable of being strengthened by ion-exchange and may have a thickness t. The concentration(s) of the constituent components of the ion-exchangeable borosilicate glass may be such that: 13 < 0.0308543 * (188.5 + ((23.84*A12O3)+(-16.97*B2O3) + (69.10*Na2O) + (-213.3*K2O)) + ((Na2O-7.274)2*(-7.3628) + (A1203-2.863)*(K20-0.520)*(321.5) + (B2O3-9.668)*(K2O-0.520)*(-39.74))) / t.TEST METHODS

[0123] Compressive Stress and DOC

[0124] Compressive stress and DOC may be measured using those means known in the art. Such means include, but are not limited to, measurement of surface stress (FSM) using commercially available instruments such as the FSM-6000, manufactured by Luceo Co., Ltd. (Tokyo, Japan), or the like, and methods of measuring compressive stress and depth of compression are described in ASTM 1422C-99, entitled “Standard Specification for Chemically Strengthened Flat Glass,” and ASTM 1279.19779 “Standard Test Method for NonDestructive Photoelastic Measurement of Edge and Surface Stresses in Annealed, Heat- Strengthened, and Fully-Tempered Flat Glass,” the contents of which are incorporated herein by reference in their entirety. Surface stress measurements rely upon the accurate measurement of the stress optical coefficient (SOC), which is related to the birefringence of the glass. SOC in turn is measured by those methods that are known in the art, such as fiber and four point bend methods, both of which are described in ASTM standard C770-98 (2008), entitled “Standard Test Method for Measurement of Glass Stress-Optical Coefficient,” the contents of which are incorporated herein by reference in their entirety, and a bulk cylinder method.

[0125] Axial Stress ProfileSP24-255

[0126] To measure the axial stress and determine the axial stress profile, the strengthened glass article is sectioned in the transverse direction to produce an annular disk (i.e., the strengthened glass article is cut along a plane perpendicular to the center axis A at two points to create the annular disk) to produce an axial view of the cylindrical sidewall. The disk is polished and then optical retardation measurements are taken according to standard test method ASTM F218-13.

[0127] Potassium Concentration Profile

[0128] The composition of the glass, in particular the concentration profile of potassium ions in the glass as a function of depth within the glass, can be determined using electron probe micro-analysis (EPMA) using an electron probe microanalyzer.EXAMPLES

[0129] The various embodiments of the strengthened glass articles and methods disclosed herein will be further clarified by the following examples. The examples are illustrative in nature, and should not be understood to limit the subject matter of the present disclosure.

[0130] Comparative Example 1 : Syringes Strengthened by Ion Exchange Only

[0131] In Comparative Example 1, glass syringes were ion-exchanged in a single ionexchange step and then evaluated for CS, DOC, and CT. The syringes of Comparative Example 1 were ion exchanged in a single step in a potassium nitrate bath at 375 °C for an ion-exchange time of 35 minutes to achieve low CT and high CS at the outer surface. The CS, DOC, and CT of the glass syringes of Comparative Example 1 were evaluated using UV-FSM, as described herein, and the results are shown in FIG. 7. For the data in FIG. 7, 33 syringes were measured, each measurement was the average of 5 measurements at the same location. The CT was found to be only around 4-5 MPa and the CS at the inner surface and outer surface was over 700 MPa for the syringes. Thus, a superimposed thermal bending -like stress on the order of 4 MPa would substantially reduce tension in the outer half of the syringe as the CT is only around 4-5 MPa. Compression would remain high on the inner surface as the CS is over 700 MPa.

[0132] Example 2: Fracture Mechanics Models

[0133] In Example 2, fracture mechanics models are performed to determine what levels of bend stress are best for different levels of CT for strengthened glass articles strengthened according to methods disclosed herein. As used in the examples, the term "bend stress" refers to the magnitude of the compressive stress at the outer surface of the glass article resulting fromSP24-255 introduction of the initial axial stress profile in the glass article prior to ion-exchange. Thus, when a bend stress of 10 MPa is indicated, an initial axial stress profile is first introduced to the glass article such that the compressive stress at the outer surface is 10 MPa. The inner surface would then have a tensile stress of -10 MPa to balance the compressive stress of +10 MPa at the outer surface. The bend stress refers to the value of the compressive stress at the outer surface after introducing the initial axial stress profile and before subjecting the glass article to the ion-exchange strengthening step.

[0134] In the fracture mechanics modeling in Example 2, an erfc function was assumed with a glass thickness of t=0.9 mm and a range of different CTs. The stress intensities Ki were calculated using a weight function approach on the combined ion exchange + bend stress profiles, as described by Hieronim et al., "Calculation of Stress Intensity Factors for Cracks Sugjected to Arbitrary Non-Linear Stress Fields," European Structural Integrity Society, 25, 1999, 261-274, ISBN 9780080433363, available at httos: / / doi.org / 10, 1016 / S1566- 1369(99)80020-x. The stress intensity can be calculated by integrating the stresses o(x) along the crack length with the appropriate weight function m(x,a), as shown in Equation 3 (EQU. 3). Id.

[0135] The form of the weight function in EQU. 3 is provided in Equation 4 (EQU. 4). In EQU. 4, Mi, M2, and M3 are functions that are fit and tabulated in Hieronim et al.

[0136] The threshold stress intensity factor used is Ko=O.35 MPa.m1 / 2. Below the threshold stress intensity factor, flaws will not grow, and above the threshold stress intensity factor, flaws grow sub-critically (with Ki< Kic the toughness, where KIC is the stress intensity factor above which flaws in the glass grow critically).

[0137] Referring now to FIG. 8, the modeled stress intensity factor (y-axis) as a function of flaw depth (x-axis) is provided for three different ion-exchanged CT levels with no "bend" stress (i.e., no initial stress profile introduced into the glass). In FIG. 8, reference number 802SP24-255 identifies the threshold stress intensity factor Ko, and reference number 804 identifies Kic, which is the stress intensity factor above which the flaws grow critically. The data series identified with reference number 806 has a CT of 2.2 MPa, the data series identified with reference number 808 has a CT of 3.7 MPa, and the data series identified with reference number 810 has a CT of 6.3 MPa. As shown in FIG. 8, when flaws have Ki > Ko, in this case Ko = 0.35 MPa.m1 / 2, the flaw will grow slowly or sub-critically . However, if Ki > Kic, which in this case KIC = 0.7 MPa.m1 2, the flaws would grow rapidly or critically.

[0138] Referring now to FIG. 9, the modeled stress intensity factor (y-axis) as a function of flaw depth (x-axis) is provided for three different ion-exchanged CT levels with abend stress (i.e., compressive stress at the outer surface in the initial stress profile) of 8 MPa for each. In FIG. 9, reference number 902 identifies the threshold stress intensity factor Ko, and reference number 904 identifies Kic. The data series identified with reference number 906 has an ionexchange CT of 2.2 MPa, the data series identified with reference number 908 has an ionexchange CT of 3.7 MPa, and the data series identified with reference number 910 has an ionexchange CT of 6.3 MPa. As shown in FIG. 9, for a given bend stress (e.g., compressive stress of 8 MPa at the outer surface in the initial stress profile), it is better to have a lower CT from ion-exchange, since the flaws have to penetrate deeper (i.e., greater flaw depth) in order to automatically propagate through and across the glass.

[0139] Referring now to FIG. 10, the modeled stress intensity factor (y-axis) as a function of flaw depth (x-axis) is provided for constant ion-exchanged CT level of 5.4 MPa but with three different levels of the bend stress (i.e., compressive stress at the outer surface in the initial stress profile). In FIG. 10, reference number 1002 identifies the threshold stress intensity factor Ko, and reference number 1004 identifies Kic. The data series identified with reference number 1006 has a bend stress of 8 MPa, the data series identified with reference number 1008 has a bend stress of 4 MPa, and the data series identified with reference number 1010 has no bend stress (i.e., bend stress = 0). As shown in FIG. 10, for a given ion-exchange CT (i.e., ionexchange CT = 5.4 MPa in FIG. 10), it is better to have a greater bending stress, such that the compressive side is the outside with the flaws, as this will increase the depth of flaws able to propagate, as well as narrow the range of flaw depths that grow sub-critically.

[0140] For a range of various low ion-exchange CT values, the flaw depth at which the stress intensity factor reaches the threshold, Ko, was calculated as a function of the applied bend stress profile. Referring now to FIG. 11, the flaw depths at Ki = Ko (y-axis) as a functionSP24-255 of bend stress (x-axis) (i.e., magnitude of initial stress profde introduced into the glass) for the glass articles with various low ion-exchange CT values is provided. Correspondence between ion-exchange CT and reference numbers in FIG. 11 are provided in Table 2. As shown in FIG. 11, there exists a particular level of bend stress that maximizes the flaw depth. For lower ionexchange CT, the required bend stress is lower than for higher ion-exchange CT levels. However, overall, the general trend is that lower CT from ion-exchange permits deeper flaws. Thus, there is a particular bend stress for a given ion-exchange CT level that results in the deepest allowable flaw that would be arrested and not grow. This is important since a part or product that can withstand deep damage events tend to be stronger than those that cannot.Table 2

[0141] Referring now to FIG. 12, the required bend stress (y-axis) for a given ion-exchange CT (x-axis) to achieve the deepest critical flaw depth (when Ki=Ko) is provided. FIG. 12 provides the maxima of the bend stress for each data series in FIG. 11. As shown in FIG. 12, the required bend stress to achieve the deepest critical flaw depth increases with increasing ionexchange CT. Analytical curve fitting of the FIG. 12 data produces the relationship in EQU. 2.

[0142] Example 3: Sharp Damage and Retained Strength Analytical Modeling

[0143] In Example 3, sharp damage analytical modeling and retained strength analytical modeling on strengthened glass articles having abend stress (i.e., initial stress profile) and ionexchange stress profile are conducted. Sharp damage analytical modelling allows the evaluation of the contact force required to cause flaws of different depths. The sharp damageSP24-255 analytical modeling is performed for strengthened glass articles having an ion-exchange CT of 6.3 MPa and an imposed bending stress ranging from 0 MPa to 10 MPa. As discussed herein, the ion-exchange CT refers to the CT provide by ion-exchange only.

[0144] Referring now to FIG. 13, the flaw depth (y-axis) as a function of contact force (x- axis) from the sharp damage analytical modeling is graphically depicted. Reference number 1302 indicates the data series for bend stress equal to zero, reference number 1304 indicates the data series for the bend stress equal to 5 MPa, and reference number 1306 indicates the data series for bend stress equal to 10 MPa. Reference numbers for the other data series are omitted for purposes of clarity. No catastrophic propagation was observed, as expected for the low tensile energy of the ion-exchange CT of 6.3 MPa. The results shown in FIG. 13 demonstrate that when comparing maximum flaw depths from FIGS. 11 and 12, a 66% growth in contact force can be achieved by introducing 5 MPa bend stress for ion-exchange CT of 6.3 MPa. For 0 MPa bend stress, a 59 Newton (N) force causes a 320 pm flaw, while for a 5 MPa bend stress, a 98 N force causes a 440 pm flaw. Thus, the additional bending stress profde improves the glass’s ability to withstand sharp contact forces before causing delayed failures.

[0145] Referring now to FIG. 14, retained strength (y-axis) as a function of flaw depth (x- axis) for the sharp damage analytical modeling is graphically depicted. In FIG. 14, reference number 1402 indicates the modeling data for bend stress equal to 0, and reference number 1406 indicates the modeling data for bend stress equal to 10 MPa. Reference numbers for bend stress 1-9 are omitted for purposes of clarity. No catastrophic propagation was observed, as expected for the low tensile energy of the ion-exchange CT of 6.3 MPa. As shown in FIG. 14, the strength of the article is improved with the addition of the bend stress, as evidenced by the higher curve with the bend stress (1406) as compared to without the bend stress (1402).

[0146] Example 4 : Bend Stress Range

[0147] In Example 4, ranges for the initial bend stress for producing the strengthened glass articles are evaluated. When considering what bending stress to introduce to the glass article prior to ion-exchange in order to produce the desired axial stress profile in the strengthened glass article, the data in FIG. 12 can provide the ideal bending for each ion exchange CT. However, it is important to define a reasonable lower limit as well. The transition at the lower end of the range for bend stress may be defined by the ion-exchange CT. The DOC in the outer surface of the strengthened glass article may begin to significantly increase when the bending stress (i.e., initial stress profile introduced to the glass article prior to ion-exchange) is greaterSP24-255 than the ion-exchange CT, which is the CT in the central tension region provided by the ionexchange alone.

[0148] Referring now to FIG. 15, the outer DOC as a function of the compressive bend stress added to the outer surface of the strengthened glass article is provided for strengthened glass articles having ion-exchange CT of 5 MPa. As shown in FIG. 15, the outer DOC starts to significantly grow when the compressive bend stress introduced to the outer surface exceeds this value of the CT from ion-exchange, such as when the bend stress is greater than about 5 MPa. Thus, the transition point at which the bend stress begins to have a significant effect on the outer DOC can be defined by the CT expected from ion-exchange by itself. As a result, for an ion-exchange CT of 5 MPa (i.e., CT expected from ion-exchange only), the range of bend stress can be from about 6 MPa (FIG. 15) to about 18 MPa (FIG. 12). The larger the bend stress introduced into the glass article in the initial axial stress profile, the better the effect on the outer DOC.

[0149] Referring again to FIG. 5, the combined axial stress profile (y-axis) as a function of the depth into the glass from the outer surface 104 (x-axis) is provided for strengthened glass articles with ion-exchange CT of 5 MPa and various values of bend stress introduced in the initial axial stress profile. Correspondence between the reference numbers in FIG. 5 and the bend stress introduced in the initial axial stress profile are provided in Table 1. As shown in FIG. 5 and Table 1, when the initial axial stress profile is increased to a certain bend stress, such as a bend stress equal to 6 MPa in Table 1, the outer DOC increases dramatically. Without being bound by any particular theory, it is believe that when the bend stress of the initial axial stress profile introduced to the glass reaches a certain threshold bend stress value, then the contributions of the initial axial stress profile to the compression stress proximate the outer surface 104 become greater than the central tension produced by the ion-exchange, thereby increasing the outer DOC and deepening the outer compressive stress region 110. As shown in FIG. 5, when the bend stress of the initial axial stress profile is greater than or equal to about 6 MPa (ref. no. 514), the outer elbow 112 is above the zero line, indicating that the outer elbow 112 is in compression. At less than 6 MPa bend stress (ref. nos. 502-512), the axial stress profile after ion-exchange transitions from compression to tension at a point shallower than the outer elbow 112, resulting in the outer elbow 112 being in tension. When the outer elbow 112 is in tension, the outer DOC 114, which is the depth at which the axial stress profile transitions from compression to tension in FIG. 5, is shallower.SP24-255

[0150] Referring now to FIG. 16, the combined axial stress profile (y-axis) as a function of the depth into the glass from the inner surface 106 (x-axis) is provided for strengthened glass articles with ion-exchange CT of 5 MPa and various values of bend stress introduced in the initial axial stress profile. Table 1 provides correspondence between the reference numbers in FIG. 16 and the bend stress. As shown in FIG. 16, as the bend stress increases from 0 MPa (ref. no. 502) to 10 MPa (ref. no. 522), the magnitude of the central tension increases from 5 to 15 (i.e., absolute value of the central tension). Thus, increasing the bend stress in the initial stress profile increases the central tension proximate the inner surface 106. However, since most of the surface damage is expected to be at the outer surface 104 and not the inner surface 106, the high central tension near the inner surface 106 is not a large concern. The compressive stress (CS) at the inner surface 106 is still much greater, providing some surface strength and damage protection for the inner surface 106.

[0151] Example 5: Deep Ion-Exchange

[0152] In Example 5, the previous modeling is applied to strengthened glass articles with a deep stress profile from ion-exchange. In Example 5, the ion-exchange step investigate has an axial stress profile having a diffusion depth of the ion-exchange ions of about 50 pm, which results in an ion-exchange CT of 40 MPa and a CS at the outer surface 104 of about 570 MPa. Referring again to FIG. 6, the axial stress profiles starting from the outer surface 104 for various strengthened glass articles are graphically depicted. Reference number 600 is the axial stress profile for a strengthened glass article strengthened by ion-exchange only. Reference number 610 is the axial stress profile for a strengthened glass article strengthened by introducing the initial stress profile having a bend stress of 20 MPa followed by ion -exchange. Reference number 210 is the axial stress profile for a strengthened glass article strengthened by introducing the initial stress profile having bend stress of 50 MPa followed by ion-exchange. In FIG. 6, zero depth (x-axis) corresponds to the outer surface 104 of the strengthened glass article, and zero stress (y-axis) is the transition between tension (indicated as negative stress) and compression (indicated as positive stress).

[0153] The sharp damage analytical modeling and retained strength analytical modeling from Example 3 are applied to the strengthened glass articles with the deeper ion-exchange diffusion depths. The bend stress of the initial axial stress profile was increased from 0 to about 80 MPa. Referring now to FIG. 17, the critical contact force required to produce a flaw extending into the CT region (y-axis) as a function of the bend stress introduced to the outerSP24-255 surface by the initial axial stress profile (x-axis) is provided. Referring to FIG. 18, the critical flaw depth (y-axis) as a function of the bend stress introduced to the outer surface by the initial axial stress profile (x-axis) is provided. As shown in FIGS. 17 and 18, increasing the bend stress of the initial axial stress profile provides a significant benefit in terms of the force needed to produce a flaw that exhibits self-propagation through the glass and in terms of the flaw depth required for the flaw to exhibit self-propagation. As shown in FIGS. 17, a 20 MPa bend stress results in a 71% increase in the critical contact force compared to 0 bend stress, and a 50 MPa bend stress results in a 234% increase in the critical contact force compared to 0 bend stress. As shown in FIG. 18, a 20 MPa bend stress provides a 75% increase in the critical flaw depth compared to 0 bend stress, and a 50 MPa bend stress provides a 127% increase in the critical flaw depth compared to 0 bend stress.

[0154] The magnitude of the bend stress of the initial axial stress profile also has a significant benefit with respect to the retained strength. Referring now to FIG. 19, retained strength profiles of the outer surface (y-axis) as a function of flaw depth into the outer surface (x-axis) for strengthened glass articles having an ion-exchanged CT of 6.3 MPa and bend stress ranging from 0 MPa to 50 MPa is provided. As shown in FIG. 19, increasing the bend stress of the initial axial stress profile increases the retained strength at each flaw depth.

[0155] While various embodiments of the strengthened glass articles and methods for producing the strengthened glass articles have been described herein, it should be understood that it is contemplated that each of these embodiments and techniques may be used separately or in conjunction with one or more embodiments and techniques.

[0156] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

SP24-255What is claimed is:CLAIMS1. A strengthened glass article comprising a cylindrical sidewall having an outer surface, an inner surface, and a radial thickness extending between the outer surface and the inner surface in a radial direction, wherein the strengthened glass article has an asymmetric axial stress profile comprising: an outer compressive stress region extending radially inward from the outer surface to an outer depth of compression (outer DOC); an inner compressive stress region extending radially outward from the inner surface to an inner DOC; and a central tension region disposed radially between the outer DOC and the inner DOC, wherein: the asymmetric axial stress profile has an outer elbow in compression; and the outer elbow is a region on the asymmetric axial stress profile proximate the outer surface and at which a slope of the axial stress profile changes magnitude.

2. The strengthened glass article of claim 1, wherein the axial stress is measured by optical retardation.

3. The strengthened glass article of claim 1, wherein: a graph of axial stress as a function of depth in the glass from the outer surface has an outer surface stress tangent line and a center stress tangent line; the outer surface stress tangent line is a line tangent to the graph of axial stress at the outer surface; the center stress tangent line is a line tangent to the graph of axial stress in the central tension region; and an intersection point between the outer surface stress tangent line and the center stress tangent line is in compression.

4. The strengthened glass article of claim 1, wherein the asymmetric axial stress profde has an inner elbow in tension, wherein the inner elbow is a region on the asymmetric axial stress profile proximate the inner surface and at which a slope of the asymmetric axial stress profile changes magnitude and direction.SP24-2555. The strengthened glass article of claim 1, wherein: the outer compressive stress region comprises a first compressive stress region extending from the outer surface to an outer depth of diffusion and a second compressive stress region extending from the outer depth of diffusion to the outer DOC; in the first compressive stress region, the glass has a concentration gradient of one or more alkali metals; in the second compressive stress region, a concentration of each alkali metal species in the glass is constant and equal to a bulk concentration of each of the alkali metal species; the outer depth of diffusion is a depth in the glass measured from the outer surface and at which a concentration gradient of the one or more alkali metals becomes zero; and at the outer depth of diffusion, an axial stress profile of the glass is in compression.

6. The strengthened glass article of claim 5, wherein:where DOCouter is the outer DOC, and DODouter is the outer depth of diffusion.

7. The strengthened glass article of claim 6, wherein:where DOCouter is the outer DOC, and DODouter is the outer depth of diffusion.

8. The strengthened glass article of claim 6, wherein:where DOCouter is the outer DOC, and DODouter is the outer depth of diffusion.

9. The strengthened glass article of claim 1, wherein a magnitude of a slope of a tangential stress component in the glass is greater than a magnitude of a slope of a tangentialSP24-255 stress component in a comparative glass article having the same geometry and strengthened only by ion exchange.

10. The strengthened glass article of claim 1, wherein: an inner depth of diffusion is a depth in the glass measured from the inner surface and at which a concentration gradient of one or more alkali metals becomes zero; and the inner depth of diffusion is greater than the inner DOC.

11. The strengthened glass article of claim 10, wherein the inner depth of diffusion is in the central tension region.

12. The strengthened glass article of claim 1, wherein the outer DOC is greater than the inner DOC.

13. The strengthened glass article of claim 1, wherein a maximum axial central tension is closer to the inner surface than the outer surface.

14. The strengthened glass article of claim 1, wherein a compressive stress (CS) at the outer surface is greater than a CS at the inner surface.

15. The strengthened glass article of claim 1, wherein:where DOCouter is the outer DOC, DOCinner is the inner DOC, and t is the radial thickness of the strengthened glass article.

16. The strengthened glass article of claim 15, wherein:SP24-25517. The strengthened glass article of claim 1, wherein a geometrically induced ratio of the outer DOC to the inner DOC is from 1.01 to 2000.

18. The strengthened glass article of claim 1, a distance between a maximum central tension and the inner surface of the strengthened glass article is less than or equal to 50% the radial thickness of the cylindrical side wall.

19. The strengthened glass article of claim 18, a distance between a maximum central tension and the inner surface of the strengthened glass article is less than or equal to 25% the radial thickness of the cylindrical side wall.

20. The strengthened glass article of claim 1, wherein the glass article is a pharmaceutical container.

21. A method of making a strengthened glass article, the method comprising: forming a glass article comprising a cylindrical sidewall having an outer surface, an inner surface, and a radial thickness extending between the outer surface and the inner surface in a radial direction; introducing an initial compressive stress in the outer surface of the glass article to produce an initial axial stress profde in the glass article, wherein the initial axial stress profile has a maximum compressive stress at the outer surface and a maximum tension at the inner surface of the glass article; ion-exchanging the glass article having the initial axial stress profile to produce a strengthened glass article, wherein the strengthened glass article has an asymmetric axial stress profile comprising: an outer compressive stress region extending radially inward from the outer surface to an outer depth of compression (outer DOC); an inner compressive stress region extending radially outward from the inner surface to an inner depth of compression (inner DOC); and a central tension region disposed radially between the outer DOC and the inner DOC, wherein: a graph of axial stress as a function of depth in the glass from the outer surface has an outer surface stress tangent line and a center stress tangent line;SP24-255 the outer surface stress tangent line is a line tangent to the graph of axial stress at the outer surface; the center stress tangent line is a line tangent to the graph of axial stress in the central tension region; and an intersection point between the outer surface stress tangent line and the center stress tangent line is in compression.

22. The method of claim 21, wherein introducing the initial compressive stress in the outer surface comprises introducing a thermally induced stress profde in the cylindrical sidewall.

23. The method of claim 22, wherein introducing the thermally induced stress profde in the cylindrical sidewall comprises annealing the glass article and cooling the cylindrical sidewall at an increased cooling rate, wherein the increased cooling rate produces the thermally-induced stress profde in the cylindrical sidewall.

24. The method of claim 21, wherein introducing the initial compressive stress in the outer surface comprises subjecting the outer surface of the cylindrical sidewall to a preliminary ion-exchange process without ion-exchanging the inner surface of the cylindrical sidewall.

25. The method of claim 21, wherein:(Tj, > 0.275 • CT + 2.247 • CTJQX wherein ob is the initial compressive stress in the outer surface, CTiox is the a central tension at a middle of the cylindrical sidewall for a comparative glass article subjected only to ion exchange under the same conditions and without introducing the bending stress; and the middle of the cylindrical sidewall is equal to a point halfway between the inner surface and the outer surface of the cylindrical side wall.

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