Strengthened glass with ultra-deep depth of compression

Abstract

μm within the glass article. The compressive stress profile includes a single linear segment or portion extending from the surface to the depth of compression DOC. Alternatively, the compressive stress profile may include an additional portion extending from the surface to a relatively shallow depth and the linear portion extending from the shallow depth to the depth of compression.

Description

[Technical Field]

[0001] This application claims priority to U.S. Provisional Application No. 62 / 073252, filed on October 31, 2014, in accordance with the Patent Act. The contents of that application are incorporated herein by reference in their entirety.

[0002] This invention relates to a chemically strengthened glass article. More specifically, this invention relates to chemically strengthened glass having a deep compression surface layer. [Previous Technology]

[0003] Tempered glass is widely used in electronic devices as cover plates or windows for portable or mobile electronic communication and entertainment devices (e.g., mobile phones, smartphones, tablets, video players, information terminal (IT) devices, laptops, and the like) and in other applications. As the use of tempered glass increases, it is becoming increasingly important to develop tempered glass materials with high resistance to damage (especially when subjected to tensile stress and / or when relatively deep cracks occur due to contact with hard / sharp surfaces). [Summary of the Invention]

[0004] The present invention provides a chemically strengthened glass article having at least one deep compression layer, the deep compression layer extending from the surface of the article into the interior of the article to a compression depth (DOC) of at least about 125 micrometers. In one embodiment, the compressive stress profile includes a single linear segment or portion extending from the surface to the compression depth (DOC). Alternatively, the compressive stress profile may include an additional portion extending from the surface to a relatively shallow depth and the linear portion extending from the shallow depth to the compression depth.

[0005] Therefore, one embodiment of the present invention provides a glass article having a thickness t and a compression region at the surface of the glass article, the compression region being subjected to a compressive stress CS s of at least about 120 MPa. The compression region extends from the surface to a compression depth DOC, wherein 0.1∙t ≤ DOC ≤ 0.25∙t, and the compression region has a compressive stress profile. The compressive stress profile has a first portion a extending from the surface to a depth da, and the compressive stress profile has a slope ma, wherein the depth da is equal to the compression depth, and -0.4 MPa / µm ≥ ma ≥ -3.0 MPa / µm. In some embodiments, the portion a is linear or substantially linear.

[0006] Another aspect of the present invention provides an alkali aluminosilicate glass comprising at least about 4 mol% of P₂O₅ and 0 mol% to about 4 mol% of B₂O₃, wherein 1.3 < [(P₂O₅ + R₂O) / M₂O₃] ≤ 2.3, wherein M₂O₃ = Al₂O₃ + B₂O₃, and R₂O is the sum of the monovalent cation oxides present in the alkali aluminosilicate glass. The alkali aluminosilicate glass is ion-exchanged and has a thickness t and a compression region. The compression region has a compressive stress CSs ranging from about 100 MPa to about 400 MPa at the surface of the alkali aluminosilicate glass, and the compression region extends from the surface to a compression depth DOC, where 0.1∙t ≤ DOC ≤ 0.25∙t. The compression region has a compressive stress profile. The compressive stress profile has a portion a extending from the surface to a depth da and a slope ma, where the depth da is equal to the compression depth DOC, and -0.4 MPa / µm ≥ ma ≥ -3.0 MPa / µm. In some embodiments, the portion a is linear or substantially linear.

[0007] Another aspect of the present invention provides a glass article having a thickness t and a compression region. The compression region has a compressive stress CSs at the surface of the glass article ranging from about 400 MPa to about 1200 MPa, and the compression region extends from the surface to a compression depth DOC, wherein 0.1∙t ≤ DOC ≤ 0.25∙t. The compression region has a compressive stress profile including: a first portion b extending from the surface to a depth db below the surface, and the first portion b having a slope mb, wherein -40 MPa / μm ≥ mb ≥ -200 MPa / μm; and a second substantially linear portion c extending from about dc to the compression depth DOC, and the second substantially linear portion c having a slope mc, wherein -0.4 MPa / μm ≥ mc ≥ -3.0 MPa / μm.

[0008] These and other forms, advantages and key features will become clear from the following embodiments, the accompanying drawings and the appended claims.

Implementation Method

[0019] In the following description, the same element symbols are used to represent all identical or similar parts in the several views shown in the figures. It should also be understood that, unless otherwise stated, terms such as "top," "bottom," "outward," "inward," and the like are convenience terms and should not be considered restrictive terms. Furthermore, whenever a group is described as including at least one element from a group of elements and a combination of such elements, it should be understood that the group may contain any number of such elements, or the group may consist primarily of any number of such elements, or the group may consist of any number of such elements, and such elements may exist independently or in combination with each other. Similarly, whenever a group is described as consisting of at least one element from a group of elements and a combination of such elements, it should be understood that the group may consist of any number of such elements in independent or combination with each other. Unless otherwise stated, when a numerical range is given, it includes the upper and lower limits of the range and any range between them. When used herein, unless otherwise stated, the indefinite articles “a”, “an”, and the corresponding definite article “the” mean “at least one” or “one or more”. It should also be understood that the various features disclosed in this specification and figures may be used in any combination or all combinations thereof.

[0020] The terms “glass article” and “glass article(s)” as used herein, in their broadest sense, may include any article made wholly or partially of glass. Unless otherwise stated, all glass composition is expressed in mole percent (mol%) and all ion exchange bath composition is expressed in weight percent (wt%).

[0021] It should be noted that the terms "substantially" and "about" are used herein to indicate the inherent uncertainty that may arise from any quantitative comparisons, numerical values, measurements, or other methods of representation. These terms are also used herein to indicate the degree to which the quantitative representation may vary with the reference object, but without altering the essential function of the subject matter. Therefore, "substantially MgO-free" glass means glass in which no MgO has been actively added or batch-blended, but which may contain very small amounts of MgO (e.g., ≥0.1 moles%) as impurities.

[0022] Referring to the entirety of these drawings and specifically to Figure 1, it should be understood that these drawings are for illustrative purposes of specific embodiments and are not intended to limit the scope of the disclosure or the appended claims. These drawings are not necessarily drawn to scale, and some features and views of these drawings may be enlarged or drawn in summary for clarity and simplicity.

[0023] The terms “depth of layer” and “DOL” used in this document refer to the compressibility layer depth measured by a surface stress meter (FSM) using a commercially available instrument (e.g., FSM-6000).

[0024] The terms "depth of compression" and "DOC" used in this document refer to the depth at which the stress inside the glass changes from compressive stress to tensile stress. At the DOC, the stress transitions from positive (compressive) stress to negative (tensile) stress, and therefore the stress at the DOC is zero.

[0025] Unless otherwise stated, as described herein, compressive stress (CS) and central tension (CT) are expressed in megabascals (MPa), layer depth (DOL) and depth of compression (DOC) are expressed in micrometers (μm), where 1 micrometer = 0.001 millimeters (mm), and thickness t is expressed in millimeters, where 1 millimeter = 1000 micrometers.

[0026] Unless otherwise stated herein, the term “crack” as used herein means that when a substrate is dropped or impacted by an object, the crack propagates to span the entire thickness and / or the entire surface of the substrate.

[0027] According to the scientific conventions generally used in the field of this art, compressive stress is represented as negative (<0) stress, and tensile stress is represented as positive (>0) stress. However, throughout this description, compressive stress CS is represented as a positive or absolute value, i.e., CS=|CS| as stated herein, and central tension or tensile stress is represented as a negative value, so as to better visualize the compressive stress profile described herein.

[0028] The term "slope (m)" as used herein refers to the slope of a segment or portion of the stress profile that is very close to a straight line. The predominant slope is defined as the average slope of the region of the approximately straight segment. In some regions, the absolute value of the second derivative of the stress profile is less than the ratio of the first derivative to approximately half the absolute value of the depth of the region, as shown in the following equation (4). For a steep shallow segment of the stress profile near the surface of the tempered glass object, for example, the substantially straight segment means that the absolute value of the second derivative of the stress profile at each point in this segment is less than the absolute value of the local slope of the stress profile divided by the depth at which the absolute value of the stress changes, multiplied by a factor of 2. Similarly, for a segment of the stress profile deeper inside the glass, the straight portion of the segment means that the absolute value of the local second derivative of the stress profile in this region is less than the absolute value of the local slope of the stress profile divided by half the absolute value of the DOC.

[0029] For a typical stress profile, imposing such a constraint on the second derivative ensures that the slope changes relatively slowly with depth, thereby reasonably and clearly defining the slope, which can be used to define the slope region that is considered important for a stress profile that is favorable to drop performance.

[0030] The relationship between stress distribution and depth x can be expressed by the following function: (1) and the relationship between the first derivative of the stress profile and depth can be expressed as: (2) and the second derivative is: (3).

[0031] If the shallow section extends to a depth ds, then in order to define the main slope, the straight part of the profile is the region shown in the following formula: (4).

[0032] If the deep section extends to a greater depth DOC, or to a greater depth dd, or to a depth DOL (in conventional terms), then the straight portion of the profile is the region shown in the following formula: (5).

[0033] The latter equation is also applicable to the 1-segment stress profile obtained by chemical strengthening through single ion exchange in a salt containing only a single alkali ion, wherein the alkali ion is different from the ion to be replaced in the glass.

[0034] Preferably, the straight section is selected from the region shown in the following formula: (6) where d represents the relative depth (shallow or deep) of the region.

[0035] The slope m of the linear segment of the compressive stress profile described in the text is defined as the absolute value of the slope, that is, m equals as stated in the text. More specifically, the slope m represents the absolute value of the slope of a stress profile in which compressive stress generally decreases with increasing depth.

[0036] This article describes a glass object that is chemically strengthened by ion exchange to obtain a specified compressive stress profile, thereby making the glass object less prone to damage when dropped from a specified height onto a hard, rough surface.

[0037] Compressive stress (CS) and the depth of the DOL layer have been stress profile parameters used for quality control of chemical strengthening for many years. Compressive stress (CS) provides an estimate of surface compression, which is an important parameter closely related to the magnitude of stress required to cause damage to a glass object, especially when the glass does not actually have deep mechanical cracks. Layer depth (DOL) is used as an approximate measure of the penetration depth of a larger (strengthening) cation (e.g., K+ in the process of exchanging Na+ with K+). A larger DOL indicates a greater depth of compression layer. A greater compression layer depth can protect the glass by suppressing deeper cracks and prevent crack failure when the glass is subjected to relatively low external stress.

[0038] Even when a glass object is bent to a slight to moderate degree, the bending moment will induce a stress distribution that is generally linear with the depth of the surface, with maximum tensile stress on the outer side of the bend, maximum compressive stress on the inner side of the bend, and zero stress at the so-called neutral surface (usually located inside). For tempered glass portions, this fixed-slope stress distribution induced by bending is added to the tempering stress profile, resulting in a net stress profile in the presence of external (bending) stress.

[0039] Under the presence of bending-induced stress, the compressibility depth (DOC) of the net stress profile differs from that of the stress profile without bending. Particularly during bending, the compressibility depth (DOC) decreases on the outer side of the bend. If the tempering stress profile has a relatively small stress slope near or below this DOC, then the DOC may decrease significantly during bending. In the net stress profile, the endpoints of medium-depth cracks may be exposed to tension; however, in the unbending state, the same crack endpoints are typically suppressed in the compressive region of the tempering stress profile. Therefore, during bending, medium-depth cracks may propagate and lead to fracture.

[0040] Bending stress is also important in drop tests. During mechanical vibration and wave propagation through a glass object, regions of localized stress that change over time occur. With increasing drop height, the glass object experiences higher time-varying stress upon contact with the floor surface and during subsequent vibrations. Therefore, some fracture failures may occur due to excessive post-contact tensile stress at the endpoints of relatively shallow cracks (which are generally harmless after tempering and without such time-varying stress).

[0041] The slope range described in this invention provides a good trade-off between the performance of glass objects in drop and bending tests. Stress measurement equipment (e.g., an FSM-6000 stress meter) can be used to collect or interpret relevant spectra of stress profiles for quality control during manufacturing, but such preferred slope ranges may be partially defined or limited in some cases by the performance and limitations of the stress measurement equipment. The layer depth (DOL) of the stress profile and the slope (by virtue of the slope of the relevant index profile of the stress profile) both affect the ability to interpret specific segments in the coupled spectrum, thereby affecting the ability to effectively control product quality.

[0042] Ion exchange is commonly used to chemically strengthen glass. In a particular instance, alkali metal cations from such a cation source (e.g., molten salt or an "ion exchange" bath) exchange with smaller alkali metal cations in the glass to create a layer under compressive stress (CS) near the glass surface. For example, potassium ions from a cation source typically exchange with sodium ions in the glass. This compressive layer extends from the surface into the interior of the glass to a depth.

[0043] Figure 1 shows a schematic cross-sectional view of a flat, ion-exchanged glass object. The glass object 100 has a thickness t, a first surface 110, and a second surface 112. In some embodiments, the thickness t of the glass object 100 is at least 0.15 mm and at most about (i.e., less than or equal to) 2.0 mm, or at most about 1.0 mm, or at most about 0.7 mm, or at most about 0.5 mm. Although the glass object 100 shown in the embodiment of Figure 1 is a flat planar sheet or plate, the glass object 100 may have other forms, such as three-dimensional shapes or other non-planar forms. The glass object 100 has a first compression region 120 that extends from the first surface 110 into the body of the glass object 100 to a compression depth (DOC) d1. In the embodiment shown in Figure 1, the glass object 100 also has a second compression region 122 extending from the second surface 112 to a second compression depth (DOC) d2. The glass object 100 also has a central region 130 extending from d1 to d2. The central region 130 is under tensile stress, and this tensile stress has a maximum value at the center of the central region 130, referred to as central tension or central stress (CT). The tensile stress of region 130 is balanced or canceled out by the compressive stress CS of regions 120 and 122. The depth d1 of the first compression region 120 and the depth d2 of the second compression region 122 protect the glass object 100 from crack propagation caused by sharp objects impacting the first surface 110 and the second surface 112 of the glass object 100, while the compressive stress CS minimizes the probability of crack growth and penetration through the depths d1 and d2 of the first compression region 120 and the second compression region 122.

[0044] The tempered glass object described herein has a maximum compressive stress CSs of at least about 150 million bascals (MPa). In some embodiments, the maximum compressive stress CSs is at least about 100 MPa, in other embodiments it is at least about 140 MPa, and in some embodiments it can be as high as about 400 MPa. In some embodiments, the maximum compressive stress CSs is located at the surface (located at surfaces 110 and 112 in Figure 1). However, in other embodiments, the maximum compressive stress CSs may be located in a compression region (120, 122) at a depth below the surface of the glass object. Each compression region (120, 122) extends from the surface of the glass object to a compression depth DOC (d1, d2) of at least about 95 micrometers to about 250 micrometers. In some embodiments, the DOC ranges from about 100 micrometers, and in other embodiments it is from about 140 micrometers to about 190 micrometers. The compression depth DOC (d1, d2) can also be expressed as the thickness t of the glass object 100. In some embodiments, 0.1∙t ≤ DOC ≤ 0.25∙t, and in other embodiments, 0.12∙t ≤ DOC ≤ 0.22∙t.

[0045] The compressive stress varies with the depth below the surface of the reinforced glass object, thus creating a compressive stress profile in the compression region. In some embodiments, the compressive stress profile exhibits a substantially linear relationship with the depth below the surface within the compression region, as schematically illustrated in Figure 2. In Figure 2, the compressive stress exhibits substantially linear behavior with the depth below the surface, resulting in a straight line a with a slope ma (in MPa / micrometer), which intersects the vertical y (CS) axis at CS s. The compressive stress (CS) profile an intersects the x-axis at the compression depth DOC. At this point, the total stress (tension + compression) is zero. Below DOC, the glass object is in a tensile state (CT), gradually approaching the center value CT. In a non-limiting example, there may be sub-regions where the tension increases from 0 to a maximum tension (absolute value) equal to CT, and regions where the tension is substantially constant and equal to CT.

[0046] In some embodiments, the substantially linear portion of the compressive stress profile a of the glass object described herein has a slope ma within a specified range. In Figure 2, for example, the slope ma of line a falls between the upper boundary δ2 and the lower boundary δ1; that is, δ2 ≤ ma ≤ δ1. In some embodiments, the slope ma is in the range of about -0.4 MPa / μm to about -3.0 MPa / μm. In some embodiments, -0.7 MPa / μm ≥ ma ≥ -2.7 MPa / μm, in other embodiments, -1.0 MPa / μm ≥ ma ≥ -2.0 MPa / μm, and in other embodiments, -1.5 MPa / μm ≥ ma ≥ -2.7 MPa / μm. When the slope ma has such values ​​and the depth of compression (DOC) is at least about 95 micrometers, the strengthened glass is particularly advantageous for resisting at least one breakage mode (e.g., extremely deep puncture) commonly encountered in certain device design field failure conditions.

[0047] In other embodiments, the compressive stress profile is composed of more than one substantially linear function, as illustrated in Figure 3. As seen in Figure 3, the compressive stress profile has a first segment or portion b and a second segment or portion c. The first portion b, from the reinforced surface of the glass object to the depth db, exhibits substantially linear behavior. The first portion b has a slope mb and a y-intercept of CS s. The second portion of the compressive stress profile extends from approximately the depth db to the compression depth DOC and has a slope mc. The compressive stress CS(db) at the depth db is expressed by the following formula: CS(db) ≈ CS s – db(mb) (7). In some embodiments, the depth db falls between approximately 3 micrometers and approximately 8 micrometers, i.e., 3 micrometers ≤ db ≤ 8 micrometers. In other embodiments, 3 micrometers ≤ db ≤ 10 micrometers. In still other embodiments, 3 micrometers ≤ db ≤ 15 micrometers.

[0048] Those skilled in the art will understand that the present invention is not limited to a compressive stress profile consisting of only two different parts. Instead, the compressive stress profile may include additional segments. In some embodiments, different linear portions or segments of the compressive stress profile may be connected by transition regions (not shown in the figures), in which the slope of the profile changes from a first slope to a second slope (e.g., from mb to mc).

[0049] As shown in Figure 3, the slope of portion b of the compressive stress profile is much steeper than that of portion c, i.e., |mb| >> |mc|. This conforms to the creation of a compressive stress profile with a "spike" at the surface of the glass object by performing multiple ion exchange processes in succession, thereby providing sufficient compressive stress at the surface to withstand cracks caused by impact or the propagation of some cracks.

[0050] In some embodiments, the compressive stress profiles b and c of the glass object described herein have slopes mb and mc, respectively, falling within a specified range. In Figure 3, for example, the slope mb of line segment / first portion b falls between the upper boundary δ3 and the lower boundary δ4, and the slope mc of line segment / first portion c falls between the upper boundary δ5 and the lower boundary δ6; that is, δ3 ≥ mb ≥ δ4, and δ5 ≥ mc ≥ δ6. In some embodiments, -40 MPa / μm ≥ mb ≥ -200 MPa / μm, and -0.7 MPa / μm ≥ mc ≥ -2.0 MPa / μm. In some embodiments, -40 MPa / μm ≥ mb ≥ -120 MPa / μm, and in some embodiments, -50 MPa / μm ≥ mb ≥ -120 MPa / μm. In some embodiments, the slope mc is in the range of about -0.4 MPa / μm to about -3.0 MPa / μm. In some embodiments, -0.7 MPa / μm ≥ mc ≥ -2.7 MPa / μm; in other embodiments, -1.0 MPa / μm ≥ mc ≥ -2.0 MPa / μm; and in still other embodiments, -1.5 MPa / μm ≥ mc ≥ -2.7 MPa / μm.

[0051] Compressive stress CS and the depth of the compressive layer (referred to as "layer depth" or DOL) are measured using methods known in the art. These methods include, but are not limited to, measuring surface stress (FSM) using commercially available equipment, such as the FSM-6000 manufactured by Luceo Ltd. in Tokyo, Japan, or similar equipment. Methods for measuring compressive stress and layer depth are described in ASTM 1422C-99 (titled "Standard Specification for Chemically Strengthened Flat Glass") and ASTM 1279.19779 (titled "Standard Test Method for Measuring Edge and Surface Stress in Annealed, Thermally Strengthened, and Fully Tempered Flat Glass by Nondestructive Photoelasticity"), the contents of which are incorporated herein by reference in their entirety. Surface stress measurement relies on the accurate measurement of the stress optical coefficient (SOC), which is related to the birefringence of the glass. The stress optical coefficient is thus measured using methods known in the art, such as the fiber method, the four-point bending method, and the bulk cylinder method. The fiber method and the four-point bending method are described in ASTM standard C770-98 (2008) entitled “Standard Test Method for Measuring the Stress Optical Coefficient of Glass,” the contents of which are incorporated herein by reference in their entirety.

[0052] In some embodiments, the relationship between CS and central tension CT can be approximately expressed as: CT=(CS•DOL) / (t–2DOL) (8), where t is the thickness of the glass object, expressed in micrometers (μm). In various paragraphs of this invention, central tension CT and compressive stress CS are expressed in megapascals (MPa), thickness t is expressed in either micrometers (μm) or millimeters (mm), and layer depth DOL is expressed in either micrometers (μm) or millimeters (mm) in the same manner as thickness t.

[0053] For reinforced glass objects where the compressive stress layer extends to a deeper depth within the glass, the FSM technique may encounter contrast problems that affect the observed DOL value. At deeper DOL values, there may be inappropriate contrast between the TE and TM spectra, making it more difficult to calculate the difference between the TE and TM spectra, and thus more difficult to measure the DOL. Furthermore, FSM software analysis cannot measure the compressive stress profile (i.e., it cannot measure the change in compressive stress with depth within the glass). Additionally, the FSM technique cannot measure the layer depth resulting from ion exchange of certain elements (e.g., ion exchange with sodium replacing lithium).

[0054] When DOL is a small fraction r of thickness t and the depth distribution of the coefficient profile reasonably approximates a simple linear truncated profile, the DOL measured using FSM technology tends to approximate the depth of compression (DOC) relatively well. When the DOL occupies a considerable portion of the thickness, for example, DOL ≥ 0.1∙t, the DOC is often significantly smaller than the DOL. For example, in the ideal case of a linear truncated profile, the relationship DOC = DOL (1-r) is maintained, where r = DOL / t.

[0055] Most TM and TE coefficient profiles have a curved portion near the bottom of the coefficient profile, which may be related to the relationship between DOC and DOL to some extent, but the DOC / DOL ratio usually decreases as r increases. For some profile shapes, it is even possible for DOC to be greater than or equal to DOL, especially when r < 0.02.

[0056] When the concentration distribution profile resulting from the introduction of a larger (enhancing) ion (e.g., K+) via ion exchange has two segments, with a substantially higher concentration in the segment closest to the surface and a substantially lower concentration in the segment covering a greater depth, the DOL measured by FSM technology is significantly smaller than the total chemical penetration depth of the larger ion. This result is the opposite of the case for a single-segment diffusion profile, in which the DOL provides a good estimate of the chemical penetration depth. In a two-segment profile, the DOC may be greater than or less than the DOL, depending on the thickness and the stress and depth parameters of the profile.

[0057] When low external stress is applied to tempered glass, the crack depth caused by breakage is more correlated with DOC than with DOL. The reason DOL is a highly significant parameter for chemical strengthening in simple single-segment stress profiles is its strong correlation with DOC. Furthermore, DOC is similar to DOL; over the years, DOL has typically been below 0.1∙t and, in most cases, below 0.05∙t. Therefore, for conventional chemically strengthened glasses, DOL is closely related to the depth of strength-limiting cracks.

[0058] As the importance of thinner cover glass (e.g., t < 0.5 mm) increases, and deeper and more complex stress profiles are introduced to improve drop performance while maintaining high strength under high stress tests (e.g., ring-to-ring (ROR) test, abrasion ring-to-ring (AROR) test, and four-point bending (4PB) test), the layer depth DOL deviates significantly from the compression depth DOC. Under low external stress conditions, fracture-induced cracks typically occur at a depth smaller than DOL but the same as DOC.

[0059] The following techniques have been developed for more accurate measurement of the depth of compression (DOC) and compressive stress profile of tempered glass objects.

[0060] U.S. Patent Application No. 13 / 463,322, filed May 3, 2012, entitled "Systems and Methods for Measuring the Stress Profile of Ion-Exchanged Glass" (hereinafter referred to as "Roussev I," and claiming priority to U.S. Provisional Application No. 61 / 489,800, filed May 25, 2011, with the same invention title), discloses two methods for obtaining detailed and accurate stress profiles (stress-depth relationship) of tempered or chemically strengthened glass. The methods involve collecting the spectra of bound optical modes of TM and TE polarization using prism coupling technology, and using the entire spectrum to obtain detailed and accurate TM refractive index profile nTM(z) and TE refractive index profile nTE(z). In some embodiments, the inverse Wentzel–Kramers–Brillouin (IWKB) method is used to obtain detailed coefficient profiles from the spectra of these modes. The contents of the above-described application methods are incorporated herein by reference in their entirety.

[0061] In another embodiment, the measured mode spectrum is matched with the numerically calculated spectrum of a number of predefined functional forms describing the shape of the coefficient profile, and the parameters of the best matching functional form are obtained to obtain a detailed coefficient profile. The detailed stress profile S(z) is calculated from the difference between the reconstructed TM coefficient profile and the TE coefficient profile using the known stress-optical coefficient (SOC) value: S(z)=[n TM(z)-n TE(z)] / SOC (9).

[0062] Because the SOC value is very small, the birefringence effect nTM(z)-nTE(z) at any depth z is a relatively small fraction (typically close to 1%) of either the exponent nTM(z) or the exponent nTE(z). To obtain a stress profile without significant distortion due to noise in the measured mode spectrum, these effective mode exponents must be measured with a precision of 0.00001 RIU (units of refractive index). The methods disclosed in Roussev I further include techniques applicable to the raw data that ensure such high precision in the measured mode exponents despite the presence of noise and / or poor contrast in the collected TE and TM mode spectra or mode spectral images. These techniques include noise-averaging, filtering, and curve fitting to find the corresponding limit values ​​in the mode at sub-pixel resolution.

[0063] Similarly, U.S. Patent Application No. 14 / 033,954, filed September 23, 2013, entitled "Systems and Methods for Measuring Birefringence in Glass and Glass-Ceramics" (hereinafter referred to as "Roussev II"), which claims priority to U.S. Provisional Application No. 61 / 706,891, filed September 28, 2012, with the same invention title, discloses several apparatuses and methods for optically measuring birefringence on the surfaces of glass and glass-ceramics (including opaque glass and glass-ceramics). Unlike Roussev I, which is used to identify modes of discontinuous spectra, the method disclosed in Roussev II relies on detailed angular intensity distribution analysis of TM and TE light reflected by the prism-sample interface in a prism-coupled measurement structure. The contents of the aforementioned application are incorporated herein by reference in their entirety.

[0064] In another disclosure method, after combining certain of the aforementioned signal adjustment techniques, the derivatives of the TM and TE signals can be determined. Using coefficients as previously determined using the device parameters, the position of the maximum derivative of the TM and TE signals with subpixel resolution is obtained, and the surface birefringence is proportional to the distance between the two maximum values.

[0065] Regarding the requirement for accurate intensity acquisition, such devices include several enhancement methods, such as using a light-scattering surface (static diffuser) near or on the prism's incident surface to improve the angular uniformity of illumination; using a movable diffuser to reduce light spots when the light source is continuous or partially continuous; and using a light-absorbing coating on a portion of the prism's incident and exit surfaces and on the prism's sides to reduce parasitic background (parasitic background easily distorts the intensity signal). Furthermore, the device may include an infrared source to measure opaque materials.

[0066] Furthermore, Roussev II reveals the wavelength range and attenuation coefficient of these research samples, and demonstrates that the wavelength range and attenuation coefficient of these research samples can be measured using the method described and the improved equipment. This range is defined as αsλ < 250πσs, where αs is the optical attenuation coefficient at the measurement wavelength λ, and σs is the expected stress value obtained from measurements performed with the precision typically required for practical applications. This broad range allows for meaningful measurements at wavelengths where significant optical attenuation occurs, rendering previous methods inapplicable. For example, Roussev II reveals the successful measurement of stress-induced birefringence in opaque white glass-ceramics at a wavelength of 1550 nm, where the attenuation is greater than approximately 30 dB / mm.

[0067] Although the foregoing mentions that the FSM technique has some issues at deeper DOL values, it remains a conventional and advantageous technique that can be used, given that there may be an error range of up to + / -20% at deeper DOL values. When used herein, the terms "layer depth" and "DOL" refer to the DOL value calculated using the FSM technique; however, the terms "compression depth" and "DOC" refer to the compression layer depth measured using the methods described in Roussev I and Roussev II.

[0068] As described above, the glass article can be chemically strengthened by ion exchange. In this process, larger ions with the same valence or oxidation state are typically used to replace or exchange ions on or near the glass surface. In embodiments where the glass article includes alkali aluminosilicate glass, the glass article is mainly composed of alkali aluminosilicate glass, or the glass article is composed of alkali aluminosilicate glass, the ions in the surface layer of the glass and the larger ions are monovalent alkali metal cations, such as Na+ (when Li+ is present in the glass), K+, Rb+, and Cs+. Alternatively, monovalent cations other than alkali metal cations (e.g., Ag+ or similar ions) can be used to replace the monovalent cations in the surface layer.

[0069] Ion exchange processes typically involve immersing glass objects in a molten salt bath containing larger ions, which exchange with smaller ions in the glass. Those skilled in the art will understand that the parameters of the ion exchange process (including, but not limited to, the composition and temperature of the bath, immersion time, number of immersions in one (or multiple) salt baths, use of multiple salt baths, additional steps such as annealing, cleaning, and similar parameters) are usually determined by the glass composition and the compressive stress and layer depth desired to be generated by the strengthening process. For example, ion exchange of alkali metal-containing glasses can be achieved by immersing the glass in at least one molten bath containing salts (e.g., but not limited to, nitrates, sulfates, and chlorides formed from larger alkali metal ions). The temperature of the molten salt bath is typically in the range of about 380ºC to about 450ºC, and the immersion time ranges from about 15 minutes to about 40 hours. However, temperatures and immersion times different from those described above can also be used.

[0070] Furthermore, non-limiting examples of ion exchange processes in which glass is immersed in multiple ion exchange baths and cleaned and / or annealed between such immersion steps are described in the following documents: U.S. Patent No. 8,561,429, granted October 22, 2013, entitled "Glass with Compressive Surface for Consumer Applications," which claims priority to U.S. Provisional Application No. 61 / 079,995, filed July 11, 2008. In these patents and provisional applications, glass is strengthened by immersing it in salt baths of different concentrations to perform multiple successive ion exchange treatments; and Christopher M. Lee et al., granted November 20, 2012, entitled "Dual Stage Ion Exchange for Chemical Strengthening of..." U.S. Patent No. 8,312,739, which claims priority to U.S. Provisional Application No. 61 / 084,398, filed July 29, 2008, concerning glass, strengthens the glass by subjecting it to ion exchange in a first bath diluted with effluent ions and subsequently immersing it in a second bath (the second bath having a lower effluent ion concentration than the first bath). The contents of U.S. Patent Nos. 8,561,429 and 8,312,739 are incorporated herein by reference in their entirety.

[0071] The compressive stress is established by chemically strengthening the glass object, for example, by strengthening the glass object using the ion exchange process described earlier. In the ion exchange process, a plurality of first metal ions in the outer region of the glass object exchange with a plurality of second metal ions, such that the outer region contains a plurality of second metal ions. Each of the first metal ions has a first ionic radius, and each of the second alkali metal ions has a second ionic radius. The second ionic radius is larger than the first ionic radius, and the presence of larger second alkali metal ions in the outer region will establish compressive stress in the outer region.

[0072] At least one of the first metal ion and the second metal ion is an alkali metal ion. The first ion may be a lithium ion, sodium ion, potassium ion, or rubidium ion. The second ion may be an ion of sodium, potassium, rubidium, or cesium, provided that the ionic radius of the second alkali metal ion is greater than the radius of the first alkali metal ion.

[0073] In some embodiments, the glass is strengthened in a single ion exchange step to produce the compressive stress profile shown in Figure 2. Typically, the glass is immersed in a molten salt bath containing a salt formed by a larger alkali metal cation. In some embodiments, the molten salt bath contains a salt formed by a larger alkali metal cation or is composed primarily of a salt formed by that larger alkali metal cation. However, the bath may contain small amounts (less than about 10% by weight in some embodiments, less than about 5% by weight in some embodiments, and less than about 2% by weight in other embodiments) of a salt formed by a smaller alkali metal cation. In other embodiments, the salt formed by the smaller alkali metal cation may constitute at least about 30% by weight of the ion exchange bath, or at least about 40% by weight of the ion exchange bath, or about 40% by weight to about 75% by weight of the ion exchange bath. This single ion exchange process can be carried out at a temperature of at least about 400°C, and in some embodiments at a temperature of at least about 440°C, for a time sufficient to achieve the desired depth of compression (DOC). In some embodiments, depending on the composition of the bath solution, the single-step ion exchange process can be carried out for at least 8 hours.

[0074] In another embodiment, the glass is strengthened in a two-step or dual-stage ion exchange method to produce the compressive stress profile shown in Figure 3. The first step of this process is to ion exchange the glass in the first molten salt bath described above. After the first ion exchange step is completed, the glass is immersed in a second ion exchange bath. The second ion exchange bath differs from the first bath in that it is separate from the first bath, and in some embodiments, the second ion exchange bath has a different composition from the first bath. In some embodiments, the second ion exchange bath contains only salts formed by larger alkali metal cations, although in some embodiments, small amounts of smaller alkali metal cations (e.g., ≤2 wt%; ≤3 wt%) may be present in the bath. Furthermore, the immersion time and temperature of the second ion exchange step may differ from those of the first ion exchange step. In some embodiments, the second ion exchange step is performed at a temperature of at least about 350°C, and in other embodiments, the second ion exchange step is performed at a temperature of at least about 380°C. The duration of the second ion exchange step is sufficient to achieve the desired shallow segment depth da. In some embodiments, the duration of the second ion exchange step may be 30 minutes or less. In other embodiments, the duration is 15 minutes or less, and in some embodiments, the duration ranges from about 10 minutes to about 60 minutes.

[0075] Because the second ion exchange step is used to introduce larger cations of a different concentration than those in the first ion exchange step into the alkali aluminosilicate glass object, or in some embodiments, the second ion exchange step is used to introduce cations completely different from those in the first ion exchange step into the alkali aluminosilicate glass object, the second ion exchange bath is different from the first ion exchange bath. In one or more embodiments, the second ion exchange bath may include at least about 95% by weight of a potassium-containing composition that introduces potassium ions into the alkali aluminosilicate glass object. In a specific embodiment, the second ion exchange bath may include about 98% by weight to about 99.5% by weight of a potassium-containing composition. Although the second ion exchange bath may include only at least one potassium salt, in a further embodiment, the second ion exchange bath may include 0% to 5% by weight or about 0.5% to 2.5% by weight of at least one sodium salt, such as NaNO3. In an exemplary embodiment, the potassium salt is KNO3. In a further embodiment, the temperature of the second ion exchange step may be 380°C or higher.

[0076] The purpose of the second ion exchange step is to create a “sudden increase” in compressive stress in the region immediately adjacent to the surface of the glass object, as shown in part b of the stress profile in Figure 3.

[0077] The glass articles described herein may include any glass chemically strengthened by ion exchange, or be primarily composed of any glass chemically strengthened by ion exchange. In some embodiments, the glass is an alkali aluminosilicate glass.

[0078] In one embodiment, the alkali aluminosilicate glass comprises or is mainly composed of the following components: at least one of aluminum oxide and boron oxide; and at least one of alkali metal oxide and alkaline earth metal oxide, wherein –15 moles ≤ (R₂O + R'O – Al₂O₃ – ZrO₂) – B₂O₃ ≤ 4 moles, wherein R is one of Li, Na, K, Rb and Cs, and R' is at least one of Mg, Ca, Sr and Ba. In some embodiments, the alkali aluminosilicate glass comprises or is mainly composed of the following components: about 62 mol% to about 70 mol% SiO2; 0 mol% to about 18 mol% Al2O3; 0 mol% to about 10 mol% B2O3; 0 mol% to about 15 mol% Li2O; 0 mol% to about 20 mol% Na2O; 0 mol% to about 18 mol% K2O; 0 mol% to about 17 mol% MgO; 0 mol% to about 18 mol% CaO; and 0 mol% to about 5 mol% ZrO2. In some embodiments, the glass comprises alumina and boron oxide and at least one alkali metal oxide, wherein -15 mol% ≤ (R₂O + R'O – Al₂O₃ – ZrO₂) – B₂O₃ ≤ 4 mol%, wherein R is at least one of Li, Na, K, Rb, and Cs, and R' is at least one of Mg, Ca, Sr, and Ba; wherein 10 ≤ Al₂O₃ + B₂O₃ + ZrO₂ ≤ 30, and 14 ≤ R₂O + R'O ≤ 25; wherein the silicate glass comprises or is mainly composed of the following components: 62–70 mol% SiO₂; 0–18 mol% Al₂O₃; 0–10 mol% B₂O₃; 0–15 mol% Li₂O; 6–14 mol% Na₂O; 0–18 mol% K₂O. 2O; 0–17 mol% MgO; 0–18 mol% CaO; and 0–5 mol% ZrO 2.The glass is described in U.S. Patent Application No. 12 / 277,573, filed November 25, 2008, entitled "Glasses Having Improved Toughness and Scratch Resistance," and in U.S. Patent Application No. 8,652,978, filed August 17, 2012, also entitled "Glasses Having Improved Toughness and Scratch Resistance," and both claims priority to U.S. Provisional Application No. 61 / 004,677, filed November 29, 2008. The contents of all the foregoing cases are incorporated herein by reference in their entirety.

[0079] In another embodiment, the alkali aluminosilicate glass comprises or is mainly composed of the following components: about 60 mol% to about 70 mol% SiO2; about 6 mol% to about 14 mol% Al2O3; 0 mol% to about 15 mol% B2O3; 0 mol% to about 15 mol% Li2O; 0 mol% to about 20 mol% Na2O; 0 mol% to about 10 mol% K2O; 0 mol% to about 8 mol% MgO; 0 mol% to about 10 mol% CaO; 0 mol% to about 5 mol% ZrO2; 0 mol% to about 1 mol% SnO2; 0 mol% to about 1 mol% CeO2; less than about 50 ppm As2O3; and less than about 50 ppm Sb2O3; wherein 12 mol% ≤ Li The alkali aluminosilicate glass comprises or is mainly composed of the following components: 60–70 mol% SiO₂; 6–14 mol% Al₂O₃; 0–3 mol% B₂O₃; 0–1 mol% Li₂O; 8–18 mol% Na₂O; 0–5 mol% K₂O; 0–2.5 mol% CaO; greater than 0 mol% to 3 mol% ZrO₂; 0–1 mol% SnO₂; and 0–1 mol% CeO₂, wherein 12 mol% < Li₂O + Na₂O + K₂O ≤ 20 mol%, and wherein the silicate glass comprises less than 50 ppm As₂O₃. In some embodiments, the alkali aluminosilicate glass comprises or is mainly composed of the following components: 60–72 mol% SiO₂; 6–14 mol% Al₂O₃; 0–3 mol% B₂O₃; 0–1 mol% Li₂O; 0–20 mol% Na₂O; 0–10 mol% K₂O; 0–2.5 mol% CaO; 0–5 mol% ZrO₂; 0–1 mol% SnO₂; and 0–1 mol% CeO₂, wherein 12 mol% ≤ Li₂O + Na₂O + K₂O ≤ 20 mol%, and wherein the silicate glass comprises less than 50 ppm As₂O₃ and less than 50 ppm Sb₂O₃.The glass is described in U.S. Patent No. 8,158,543, filed February 25, 2009, entitled "Fining Agents for Silicate Glasses"; U.S. Patent No. 8,431,502, filed June 13, 2012, entitled "Silicate Glasses Having Low Seed Concentration"; and U.S. Patent No. 8,623,776, filed June 19, 2013, entitled "Silicate Glasses Having Low Seed Concentration". All of these applications claim priority to U.S. Provisional Application No. 61 / 067,130, filed February 26, 2008. The contents of all the aforementioned cases are incorporated into this case in full by way of quotation.

[0080] In another embodiment, the alkali aluminosilicate glass comprises SiO2 and Na2O, wherein the glass has a temperature T 35 kp when the viscosity of the glass is 35 kpoise, and wherein the temperature T breakdown when zircon decomposes into ZrO2 and SiO2 is greater than T 35 kp. In some embodiments, the alkali aluminosilicate glass comprises or is mainly composed of the following components: about 61 mol% to about 75 mol% of SiO2; about 7 mol% to about 15 mol% of Al2O3; 0 mol% to about 12 mol% of B2O3; about 9 mol% to about 21 mol% of Na2O; 0 mol% to about 4 mol% of K2O; 0 mol% to about 7 mol% of MgO; and 0 mol% to about 3 mol% of CaO. The glass is described in U.S. Patent No. 8,802,581, filed August 10, 2010, by Matthew J. Dejneka et al., entitled "Zircon Compatible Glasses for Down Draw," which claims priority to U.S. Provisional Application No. 61 / 235,762, filed August 29, 2009. The contents of the aforementioned patents and applications are incorporated herein by reference in their entirety.

[0081] In another embodiment, the alkali aluminosilicate glass comprises at least 50 mol% SiO2 and at least one modifier selected from the group consisting of alkali metal oxides and alkaline earth metal oxides, wherein [(Al2O3 (moles%) + B2O3 (moles%)) / (∑alkali metal modifier (moles%))] > 1. In some embodiments, the alkali aluminosilicate glass comprises or is mainly composed of the following components: 50 mol% to about 72 mol% SiO2; about 9 mol% to about 17 mol% Al2O3; about 2 mol% to about 12 mol% B2O3; about 8 mol% to about 16 mol% Na2O; and 0 mol% to about 4 mol% K2O. In some embodiments, the glass comprises or is mainly composed of the following components: at least 58 mol% SiO2; at least 8 mol% Na2O; 5.5 mol% to 12 mol% B2O3; and Al2O3, wherein [(Al2O3 (moles%) + B2O3 (moles%)) / (∑alkali metal modifier (moles%))] > 1, Al2O3 (moles%) > B2O3 (moles%), and 0.9 < R2O / Al2O3 < 1.3. The glass described in U.S. Patent No. 8,586,492, filed August 18, 2010, entitled "Crack and Scratch Resistant Glass and Enclosures Made Therefrom," and U.S. Patent Application No. 14 / 082,847, filed November 18, 2013, also entitled "Crack and Scratch Resistant Glass and Enclosures Made Therefrom," claims priority to U.S. Provisional Application No. 61 / 235,767, filed August 21, 2009. The contents of all the above cases are incorporated herein by reference in their entirety.

[0082] In another embodiment, the alkali aluminosilicate glass comprises SiO2, Al2O3, P2O5 and at least one alkali metal oxide (R2O), wherein 0.75≤[(P2O5(moles%)+R2O(moles%)) / M2O3(moles%)]≤1.2, and M2O3=Al2O3+B2O3. In some embodiments, the alkali aluminosilicate glass comprises or is mainly composed of the following components: about 40 mol% to about 70 mol% of SiO2; 0 mol% to about 28 mol% of B2O3; 0 mol% to about 28 mol% of Al2O3; about 1 mol% to about 14 mol% of P2O5; and about 12 mol% to about 16 mol% of R2O. In some embodiments, it comprises about 40 mol% to about 64 mol% of SiO2; 0 mol% to about 8 mol% of B2O3; about 16 mol% to about 28 mol% of Al2O3; about 2 mol% to about 12 mol% of P2O5; and about 12 mol% to about 16 mol% of R2O. The glass described is found in U.S. Patent Application No. 13 / 305,271, filed November 28, 2011, entitled "Ion Exchangeable Glass with Deep Compressive Layer and High Damage Threshold," which claims priority to U.S. Provisional Application No. 61 / 417,941, filed November 30, 2010. The contents of the aforementioned applications are incorporated herein by reference in their entirety.

[0083] In yet another embodiment, the alkali aluminosilicate glass comprises at least about 50 mol% SiO2 and at least about 11 mol% Na2O and has a surface compressive stress of at least about 900 MPa. In some embodiments, the glass further comprises Al2O3 and at least one of the following: B2O3, K2O, MgO and ZnO, wherein -340 + 27.1·Al2O3 – 28.7·B2O3 + 15.6·Na2O – 61.4·K2O + 8.1·(MgO+ZnO) ≥ 0 mol. In a particular embodiment, the glass comprises or is primarily composed of the following components: about 7 mol% to about 26 mol% Al₂O₃; 0 mol% to about 9 mol% B₂O₃; about 11 mol% to about 25 mol% Na₂O; 0 mol% to about 2.5 mol% K₂O; 0 mol% to about 8.5 mol% MgO; and 0 mol% to about 1.5 mol% CaO. The glass is described in U.S. Patent Application No. 13 / 533,298, filed June 26, 2012, entitled "Ion Exchangeable Glass with High Compressive Stress," which claims priority to U.S. Provisional Application No. 61 / 503,734, filed July 1, 2011. The contents of the aforementioned applications are incorporated herein by reference in their entirety.

[0084] In other embodiments, the alkali aluminosilicate glass is ion-exchangeable and comprises: at least about 50 mol% SiO2; at least about 10 mol% R2O, wherein R2O comprises Na2O; Al2O3; and B2O3, wherein B2O3–(R2O–Al2O3)≥3 mol%. In some embodiments, the glass comprises: at least about 50 mol% SiO2; at least about 10 mol% R2O, wherein R2O comprises Na2O; Al2O3, wherein Al2O3 (mol%) < R2O (mol%); and 3 mol% to 4.5 mol% B2O3, wherein B2O3 (mol%)–(R2O (mol%)–Al2O3 (mol%))≥3 mol. In some embodiments, the glass comprises or is primarily composed of the following components: at least about 50 mol% SiO2; about 9 mol% to about 22 mol% Al2O3; about 3 mol% to about 10 mol% B2O3; about 9 mol% to about 20 mol% Na2O; 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, where appropriate, at least one of CaO, BaO, and SrO, wherein 0 mol% ≤ CaO + SrO + BaO ≤ 2 mol%. In some embodiments, after ion exchange, the glass has a Vickers crack initiation threshold of at least about 10 kgf. Such glasses are described in U.S. Patent Application No. 14 / 197,658, filed May 28, 2013, entitled "Zircon Compatible, Ion Exchangeable Glass with High Damage Resistance," which is a continuation of U.S. Patent Application No. 13 / 903,433, also filed May 28, 2013, entitled "Zircon Compatible, Ion Exchangeable Glass with High Damage Resistance." Both applications claim priority to U.S. Provisional Application No. 61 / 653,489, filed May 31, 2012. The contents of these applications are incorporated herein by reference in their entirety.

[0085] In some embodiments, the alkali aluminosilicate glass comprises: at least about 50 mol% of SiO2; at least about 10 mol% of R2O, wherein R2O comprises Na2O; Al2O3, wherein -0.5 mol% ≤ Al2O3 (mol%) – R2O (mol%) ≤ 2 mol%; and B2O3, wherein B2O3 (mol%) – (R2O (mol%) – Al2O3 (mol%)) ≥ 4.5 mol. In other embodiments, the glass has a zircon breakdown temperature (equal to the temperature at which the viscosity of the glass is above about 40 kpoise) and the glass comprises: at least about 50 mol% SiO2; at least about 10 mol% R2O, wherein R2O comprises Na2O; Al2O3; and B2O3, wherein B2O3 (mol%) – (R2O (mol%) – Al2O3 (mol%)) ≥ 4.5 mol. In some other embodiments, the glass is ion-exchanged, has a Vickers crack initiation critical value of at least about 30 kgf, and comprises: at least about 50 mol% of SiO2; at least about 10 mol% of R2O, wherein R2O comprises Na2O; Al2O3, wherein -0.5 mol% ≤ Al2O3 (mol%) – R2O (mol%) ≤ 2 mol%; and B2O3, wherein B2O3 (mol%) – (R2O (mol%) – Al2O3 (mol%)) ≥ 4.5 mol. Such glass is described in U.S. Patent Application No. 13 / 903,398, filed May 28, 2013, entitled "Ion Exchangeable Glass with High Damage Resistance," which claims priority to U.S. Provisional Application No. 61 / 653,485, filed May 31, 2012. The contents of these patent applications are incorporated herein by reference in their entirety.

[0086] In some embodiments, the alkali aluminosilicate glass comprises at least about 4 moles of P₂O₅, wherein (M₂O₃ (moles%) / RₓO (moles%)) < 1, wherein M₂O₃ = Al₂O₃ + B₂O₃, and wherein RₓO is the sum of monovalent and divalent cationic oxides present in the alkali aluminosilicate glass. In some embodiments, the monovalent and divalent cationic oxides are selected from the group consisting of: Li₂O, Na₂O, K₂O, Rb₂O, Cs₂O, MgO, CaO, SrO, BaO, and ZnO. In some embodiments, the glass comprises 0 moles of B₂O₃. In some embodiments, the glass is ion-exchanged to a layer depth of at least about 10 micrometers and contains at least about 4 moles of P₂O₅, wherein 0.6 < [M₂O₃(moles%) / RₓO(moles%)] < 1.4 or 1.3 < [(P₂O₅ + R₂O) / M₂O₃] ≤ 2.3, wherein M₂O₃ = Al₂O₃ + B₂O₃, RₓO is the sum of monovalent and divalent cationic oxides present in the alkali aluminosilicate glass, and R₂O is the sum of monovalent cationic oxides present in the alkali aluminosilicate glass. In one embodiment, the alkali aluminosilicate glass comprises at least about 4 mol% of P₂O₅ and 0 mol% to about 4 mol% of B₂O₃, wherein 1.3 < [(P₂O₅ + R₂O) / M₂O₃] ≤ 2.3, wherein M₂O₃ = Al₂O₃ + B₂O₃, and R₂O is the sum of monovalent cationic oxides present in the alkali aluminosilicate glass.In some embodiments, the glass is lithium-free and primarily consists of: about 40 mol% to about 70 mol% SiO2; about 11 mol% to about 25 mol% Al2O3; about 4 mol% to about 15 mol% P2O5; about 13 mol% to about 25 mol% Na2O; about 13 mol% to about 30 mol% RxO, wherein RxO is the sum of the alkali metal oxides, alkaline earth metal oxides and transition metal monooxides present in the glass; about 11 mol% to about 30 mol% M2O3, wherein M2O3 = Al2O3 + B2O3; 0 mol% to about 1 mol% K2O; 0 mol% to about 4 mol% B2O3; and 3 mol% or less TiO2, MnO, Nb2O5, MoO3, and Ta2O. 5. One or more of WO3, ZrO2, Y2O3, La2O3, HfO2, CdO, SnO2, Fe2O3, CeO2, As2O3, Sb2O3, Cl, and Br; the glass is free of lithium; and 1.3 < [(P2O5 + R2O) / M2O3] ≤ 2.3, where R2O is the sum of the monovalent cationic oxides present in the glass. The glass is described in U.S. Patent Application No. 13 / 678,013, filed November 15, 2012, entitled "Ion Exchangeable Glasses with High Crack Initiation Threshold," and in U.S. Patent Application No. 8,756,262, also filed November 15, 2012, entitled "Ion Exchangeable Glasses with High Crack Initiation Threshold." Both applications claim priority to U.S. Provisional Application No. 61 / 560,434, filed November 16, 2011. The contents of the aforementioned patents and patent applications are incorporated herein by reference in their entirety.

[0087] In other embodiments, the alkali aluminosilicate glass comprises: about 50 mol% to about 72 mol% of SiO2; about 12 mol% to about 22 mol% of Al2O3; up to about 15 mol% of B2O3; up to about 1 mol% of P2O5; about 11 mol% to about 21 mol% of Na2O; up to about 5 mol% of K2O; up to about 4 mol% of MgO; up to about 5 mol% of ZnO; and up to about 2 mol% of CaO. In some embodiments, the glass comprises: about 55 mol% to about 62 mol% SiO2; about 16 mol% to about 20 mol% Al2O3; about 4 mol% to about 10 mol% B2O3; about 14 mol% to about 18 mol% Na2O; about 0.2 mol% to about 4 mol% K2O; up to about 0.5 mol% MgO; up to about 0.5 mol% ZnO; and up to about 0.5 mol% CaO, wherein the glass is substantially free of P2O5. In some embodiments, Na2O+K2O-Al2O3 ≤ 2.0 mol%, and in some embodiments, Na2O+K2O-Al2O3 ≤ 0.5 mol%. In some embodiments, B₂O₃-(Na₂O+K₂O-Al₂O₃) > 4 mol%, and in some embodiments, B₂O₃-(Na₂O+K₂O-Al₂O₃) > 1 mol%. In some embodiments, 24 mol% ≤ RαlO₄ ≤ 45 mol%, where R is at least one of Na, K, and Ag. The glass is described in U.S. Provisional Application No. 61 / 909,049, filed November 26, 2013, by Matthew J. Dejneka et al., entitled "Fast Ion Exchangeable Glasses with High Indentation Threshold," the contents of which are incorporated herein by reference in their entirety.

[0088] In some embodiments, the glass described herein is substantially free of at least one of the following components: arsenic, antimony, barium, strontium, bismuth, and compounds of the foregoing elements. In other embodiments, such glass may include up to about 0.5 mol% Li₂O or up to about 5 mol% Li₂O, or in some embodiments, such glass may include up to about 10 mol% Li₂O. In other embodiments, such glass is free of Li₂O.

[0089] In some embodiments, the glass described herein, after ion exchange, is resistant to cracking caused by sharp or sudden impact. Therefore, such ion-exchanged glasses exhibit a Vickers crack initiation criticality of at least about 10 kgf to as high as about 50 kgf. In some embodiments, such glasses exhibit a Vickers crack initiation criticality of at least 20 kgf, and in some embodiments, such glasses exhibit a Vickers crack initiation criticality of at least about 30 kgf.

[0090] In some embodiments, the glass described herein may be drawn downward using processes known in the art (e.g., flow-through drawing, fusion drawing, re-drawing, and such processes) and has a liquid viscosity of at least 130 kpoise. In addition to the compositions listed above, various other ion-exchangeable alkali aluminosilicate glass compositions may also be used.

[0091] The tempered glass described herein is intended to be suitable for various two-dimensional and three-dimensional shapes and can be used in a variety of different applications, and is expected to have various thicknesses in this invention. In some embodiments, the thickness of the glass object ranges from about 0.1 mm to at most about 1.5 mm. In some embodiments, the thickness of the glass object ranges from about 0.1 mm to at most about 1.0 mm, and in some embodiments, the thickness of the glass object ranges from about 0.1 mm to at most about 0.5 mm.

[0092] The tempered glass object can also be defined by its central tension CT. In one or more embodiments, the CT of the tempered glass object described herein is ≤150 MPa, or ≤125 MPa, or ≤100 MPa. The central tension of the tempered glass is related to the brittle behavior of the tempered glass object.

[0093] In another embodiment, a method is provided for manufacturing a reinforced glass article having at least one compressive stress layer, wherein the at least one compressive stress layer extends from the surface of the reinforced glass article to a compressive depth (DOC) of at least about 125 micrometers. In some embodiments, the method includes a single ion exchange step in which the alkali aluminosilicate glass article is immersed in a first ion exchange bath at a temperature above 400°C for a sufficient duration such that, after the ion exchange step, the compressive stress layer has a compressive depth of at least about 100 MPa; in other embodiments, the compressive stress layer has a compressive depth of at least about 140 MPa to up to about 400 MPa.

[0094] The actual immersion time in the ion exchange bath can depend on many factors, such as the temperature and / or composition of the ion exchange bath, the diffusivity of cations in the glass, and the like. Therefore, it is worth considering whether various ion exchange time lengths are suitable. In examples where potassium cations exchange with sodium cations in the glass in the ion exchange bath, the bath solution typically contains potassium nitrate (KNO3). In some embodiments, the ion exchange step is carried out for at least about 5 hours. A longer ion exchange time is associated with a higher sodium ion content in the first ion exchange bath. In some embodiments, the first ion exchange bath may contain at least about 30% by weight of a sodium compound (e.g., sodium nitrate NaNO3 or a similar compound) to achieve the desired sodium ion content in the first ion exchange bath, or in some embodiments, the first ion exchange bath may contain at least about 40% by weight of a sodium compound (e.g., sodium nitrate NaNO3 or a similar compound) to achieve the desired sodium ion content in the first ion exchange bath. In some embodiments, the sodium compound comprises about 40% to about 60% by weight in the first ion exchange bath. In exemplary embodiments, the first ion exchange step is performed at a temperature of about 440°C or higher, and in some embodiments, the first ion exchange step is performed at a temperature up to about 500°C.

[0095] After the first ion exchange step, the strengthened glass article may have a maximum compressive stress (CS) of at least about 100 MPa, and in other embodiments, the strengthened glass article may have a maximum compressive stress (CS) of at least about 140 MPa, and in some embodiments, the strengthened glass article may have a maximum compressive stress (CS) of up to about 400 MPa. The first ion exchange step achieves a compression layer depth / compression depth DOC of about 100 micrometers to about 200 micrometers, and in some embodiments, a compression layer depth / compression depth DOC of about 140 micrometers to about 200 micrometers is achieved after the first ion exchange step.

[0096] In some embodiments, following the ion exchange step described above, a second ion exchange step may be performed, in which the alkali aluminosilicate glass object is immersed in a second ion exchange bath at a temperature of at least 350°C and up to about 450°C for a sufficient duration to create a sudden-change shallow layer segment with a depth of at least about 3 micrometers (db) (see Figure 3). In some embodiments, the composition and / or temperature of the second ion exchange bath differs from that of the first ion exchange bath. The second ion exchange step establishes a compressive stress of at least about 400 MPa to about 1200 MPa at the surface.

[0097] The second ion exchange step is a relatively rapid ion exchange step, as shown in Figure 3, which creates a compressive stress "peak" near the surface of the glass. In one or more embodiments, the second ion exchange step may be performed for up to about 30 minutes, or in other embodiments, the second ion exchange step may be performed for up to about 15 minutes, or in some embodiments, the second ion exchange step may be performed for about 10 minutes to about 60 minutes.

[0098] The ions fed into the alkali aluminosilicate glass article in the second ion exchange step are different from the ions provided in the first ion exchange step. Therefore, the composition of the second ion exchange bath differs from that of the first ion exchange bath. In some embodiments, the second ion exchange bath includes at least about 95% by weight of a potassium-containing component (e.g., KNO3) that provides potassium ions to the alkali aluminosilicate glass article. In a particular embodiment, the second ion exchange bath may include about 98% by weight to about 99.5% by weight of a potassium-containing component. Although the second ion exchange bath may include only one potassium salt (or multiple potassium salts), in further embodiments, the second ion exchange bath may include up to about 2% by weight or about 0.5% by weight to about 1.5% by weight of a sodium-containing component, such as NaNO3. In further embodiments, the temperature of the second ion exchange step may be 390°C or higher.

[0099] Fragile behavior has at least one of the following characteristics: a tempered glass object (e.g., a glass plate or sheet) breaks into multiple small pieces (e.g., ≤1 mm); the number of fragments formed per unit area of ​​the glass object; multiple cracks branching from an initial crack in the glass object; at least one fragment being forcefully ejected from its original position a specified distance (e.g., about 5 cm or about 2 inches); and any combination of the above-mentioned fracture behavior (size and density), crack behavior, and ejection behavior. The terms "fragile behavior" and "fragility" as used herein refer to such forceful or violent fracture patterns of a tempered glass object without any external constraints (e.g., coatings, adhesive layers, or the like). Although coatings, adhesive layers, and such materials may be used with tempered glass objects as described herein, these external constraints are not used when measuring the fragility or fragile behavior of the glass object.

[0100] Figures 4a and 4b illustrate examples of brittle and non-brittle behaviors exhibited by a tempered glass object when subjected to point impact using a scribing tool with a sharp tungsten carbide (WC) tip. The point impact test used to measure brittle behavior involves a device that applies a force to the surface of the glass object, a force sufficient to release the internally stored energy present in the tempered glass object. That is, the point impact force is sufficient to create at least one new crack on the surface of the tempered glass sheet and cause the crack to extend through the compressive stress CS region (i.e., layer depth) and into the region under central tension CT. The impact energy required to create a crack in the tempered glass sheet or to activate a crack in the tempered glass sheet depends on the compressive stress CS and layer depth DOL of the object, and thus on the conditions under which the glass sheet is strengthened (i.e., the conditions used when strengthening the glass using ion exchange). Otherwise, contact between each ion-exchange glass plate shown in Figures 13a and 13b and a sharp dart-shaped indenter (e.g., a scribing tool with a sharp tungsten carbide (WC) tip) would be sufficient to propagate a crack into an internal region of the glass plate under tensile stress. The force applied to the glass plate is just sufficient to reach the initiation point of this internal region, such that the energy driving crack propagation comes from the tensile stress within that internal region, rather than from the impact force of the dart on the outer surface. The extent of ejection can be measured, for example, by placing the glass sample in the center of a grid, striking the sample, and using the grid to measure the distance each fragment is ejected.

[0101] Referring to Figure 4a, glass plate a can be classified as fragile. Specifically, glass plate a shatters into numerous small, ejected fragments, exhibiting a high degree of crack branching from the initial crack. Approximately 50% of the fragments are smaller than 1 mm, and it is estimated that approximately 8 to 10 cracks branched from the initial crack. As seen in Figure 4a, the glass fragments are also ejected to a distance of approximately 5 cm from the original glass plate a. Glass objects exhibiting any of the above three criteria (i.e., multiple crack branching, ejection, and extreme fragmentation) can be classified as fragile. For example, if the glass only exhibits excessive crack branching but does not exhibit the aforementioned ejection or extreme fragmentation, the glass is still considered fragile.

[0102] Glass plates b, c (see Figure 4b) and d (see Figure 4a) are classified as unbreakable. In each of these samples, the glass plate breaks into a small number of large fragments. For example, glass plate b (see Figure 4a) breaks into two large pieces without crack branching; glass plate c (see Figure 4b) breaks into four pieces with two cracks branching from the initial crack; and glass plate d (see Figure 4a) breaks into four pieces with two cracks branching from the initial crack. Based on the absence of ejected fragments (i.e., no fragments were forcefully ejected more than 2 inches away from the original fragment location), the absence of visible fragments smaller than or equal to 1 mm, and the small number of observed crack branches, samples b, c, and d are classified as unbreakable or substantially unbreakable.

[0103] Based on the above, a fragility index (Table 1) can be established to quantify the degree of fragility or non-fragility exhibited by glass, glass-ceramics, and / or ceramic objects when impacted by another object. The index ranges from 1 to 5, where 1 represents non-fragility and 5 represents high fragility. This index can be used to describe different degrees of fragility or non-fragility. Fragility can be expressed using the index in the form of several parameters: 1) the percentage of fragments with a diameter (i.e., the maximum size) less than 1 mm ("Fragment Size" in Table 1); 2) the number of fragments formed per unit area (in this example, square centimeters cm²) of sample ("Fragment Density" in Table 1); 3) the number of cracks branching from the initial crack when impacted ("Crack Branching" in Table 1); and 4) the percentage of fragments ejected from the original position more than approximately 5 cm (or approximately 2 inches) when impacted ("Ejection Distance" in Table 1).

[0104] Table 1. Standards used to determine fragility and fragility index Fragility Fragility Index Fragment size (%≤ 1 mm) Fragment density (fragments / cm) 2 ) Crack branching Spray distance (% ≥5 cm) high 5 > 20 >7 > 9 >6 middle 4 10 < n ≤ 20 5 < n ≤ 7 7 < n ≤ 9 4 < n ≤ 6 Low 3 5 < n ≤ 10 3 < n ≤ 5 5 < n ≤ 7 2 < n ≤ 4 none 2 0 < n ≤ 5 1 < n ≤ 3 2 < n ≤ 5 0 < n ≤ 2 1 0 n≤ 1 n≤ 2 0

[0105] A fragility index can be assigned to a glass object if it meets at least one criterion associated with a specific index value. Alternatively, a fragility index range (e.g., a fragility index of 2 to 3) can be assigned to a glass object if it meets two specific fragility standards. The highest fragility index value can be assigned to the glass object based on the individual standards listed in Table 1. In many cases, it may be impossible to determine the values ​​of the individual standards, such as the fragment density listed in Table 1 or the percentage of fragments ejected more than 5 cm from their original location. Therefore, it is necessary to consider different standards, fragility behavior, and various alternative measurements of the fragility index individually, and assign a corresponding fragility level and fragility index to glass objects falling within a certain standard level. If the fragility index determined according to any one of the four standards listed in Table 1 is 3 or greater, the glass object is classified as fragile.

[0106] Applying the aforementioned fragility index to the samples shown in Figures 13a and 13b, glass plate a shattered into numerous small, ejected fragments, exhibiting a high degree of crack branching from the initial crack, resulting in many small glass pieces. Approximately 50% of the fragments were smaller than 1 mm, and it was estimated that approximately 8 to 10 cracks branched from the initial crack. Based on the criteria listed in Table 1, glass plate a has a fragility index between approximately 4 and 5 and is classified as having medium to high fragility.

[0107] A glass object with a fragility index of less than 3 (low fragility) can be considered as not easily broken or substantially not easily broken. Glass plates b, c, and d do not exhibit the following characteristics: fragments smaller than 1 mm in diameter, multiple cracks branching from the initial crack formed upon impact, or fragments ejected more than 5 cm from their original position. Glass plates b, c, and d are not easily broken and therefore have a fragility index of 1 (not easily broken).

[0108] As previously discussed, Figures 4a and 4b show that the difference in behavior observed between glass plate a (which exhibits fragile behavior) and glass plates b, c, and d (which exhibit non-fragile behavior) can be attributed to differences in the central tension CT among these test samples. The likelihood of such fragile behavior is one consideration when designing various glass products, such as displays for portable or mobile electronic devices (e.g., mobile phones, entertainment devices, and the like) and information (IT) terminal devices (e.g., laptops). Furthermore, the maximum values ​​of the compressive layer depth DOL and compressive stress CS that can be designed into or provided to glass objects are limited by this fragile behavior.

[0109] Therefore, in some embodiments, when subjected to a point impact sufficient to break the tempered glass object described herein, the tempered glass object exhibits a fragility index of less than 3. In other embodiments, the unbreakable tempered glass object may achieve a fragility index of less than 2 or less than 1.

[0110] When the tempered glass object described herein is repeatedly subjected to drop tests, the tempered glass object exhibits improved fracture resistance. The purpose of these drop tests is to assess the performance of such glass objects as display windows or covers for handheld electronic devices (such as mobile phones, smartphones, and the like) under normal use.

[0111] Figure 5a illustrates a typical ball drop test concept currently in use. The ball drop test assembly 250 includes a solid, hard substrate 212 (e.g., a granite slab or similar substrate) and a steel ball 230 with a predetermined mass and diameter. A glass sample 220 is fixed to the substrate 212, and sandpaper 214 with a desired grit size is placed on the upper surface of the glass sample 220 opposite to the substrate 212. The sandpaper 214 is placed on the glass sample 220 such that the rough surface 214a of the sandpaper 214 contacts the upper surface 222 of the glass sample 220. The steel ball 230 is dropped freely from a predetermined height h onto the sandpaper 214. The upper surface 222 or compression surface of the glass sample 220 contacts the rough surface 214a of the sandpaper 214, creating a crack in the surface of the upper surface / compression surface 222. This height h can be gradually increased until a maximum height is reached or the glass sample breaks.

[0112] The ball drop test 250 described above does not represent the actual behavior of glass when it falls onto and contacts a rough surface. On the contrary, it is well known that glass surfaces are stretched and bend outwards, rather than compressed and bend inwards as shown in Figure 5a.

[0113] The Inverse Ball on Sandpaper (IBoS) test is a dynamic component level test that simulates the main mechanism by which tempered glass objects used in mobile phones or handheld electronic devices break due to damage and bending, as outlined in Figure 5c. In this field, damage is introduced onto the top surface of the glass (a) in Figure 5c. Cracks are induced on the top surface of the glass, and the damage penetrates the compression layer (b) or the bending action or central tension on the top surface (c) causes the crack to propagate. The IBoS test is designed to simultaneously introduce damage onto the surface of the glass and cause the glass to bend under dynamic load.

[0114] Figure 5b schematically illustrates the IBoS testing apparatus. The apparatus 200 includes a test bench 210 and a ball 230. The ball 230 is a hard or solid ball, for example, a stainless steel ball or the like. In one embodiment, the ball 230 is a stainless steel ball weighing 4.2 grams and having a diameter of 10 millimeters. The ball 230 is dropped directly onto a glass sample 218 from a predetermined height h. The test bench 210 includes a solid base 212 comprising a hard, rigid material, such as granite or the like. A sheet 214 with an abrasive material disposed on its surface is placed on the upper surface of the solid base 212, such that the surface with the abrasive material faces upwards. In some embodiments, the sheet 214 is sandpaper with a 30-grit surface, and in other embodiments, the sheet 214 is sandpaper with a 180-grit surface. A glass sample 218 is secured to a sheet 214 using a sample holder 215, creating an air gap 216 between the glass sample 218 and the sheet 214. This air gap 216 allows the glass sample 218 to bend and impact the polished surface of the sheet 214 when struck by a ball 230. In one embodiment, all corners of the glass sample 218 are clamped to keep the bending action controlled only at the point of impact and ensure reproducibility. In some embodiments, the sample holder 214 and the test stage 210 are adjustable to accommodate sample thicknesses of up to approximately 2 mm. The air gap 216 ranges from approximately 50 micrometers to approximately 100 micrometers. Adhesive tape 220 can be used to cover the upper surface of the glass sample to collect fragments should the glass sample 218 break upon impact with the ball 230.

[0115] Various materials can be used as abrasive surfaces. In one particular embodiment, the abrasive surface is sandpaper, such as silica sandpaper or alumina sandpaper, engineering sandpaper, or any abrasive material with comparable hardness and / or sharpness known to those skilled in the art. In some embodiments, 30 grit sandpaper is used due to its known range of grit sharpness, more consistent surface morphology than concrete or asphalt, and the ability to produce a sample surface with the desired degree of surface damage.

[0116] In one embodiment, Figure 5d shows a method 300 for performing an IBoS test using the aforementioned apparatus 200. In step 310, a glass sample (see element 218 in Figure 5d) is placed in the previously described test bench 210 and secured within a sample holder 215, such that an air gap 216 is formed between the glass sample 218 and a sheet 214 with a polished surface. Method 300 assumes that the sheet 214 with the polished surface is already placed in the test bench 210. However, in some embodiments, the method may include placing the sheet 214 in the test bench 210 with the surface containing the polishing material facing upwards. In some embodiments (step 310a), the glass sample 218 is secured in the sample holder 215 after adhesive tape 220 is applied to the upper surface of the glass sample 218.

[0117] In step 320, a solid ball 230 of predetermined mass and size is dropped from a predetermined height h onto the upper surface of the glass sample 218, such that the ball 230 impacts approximately the center of the upper surface (or the tape 220 fixed to the upper surface) (i.e., within a radius of 1 mm, 3 mm, 5 mm, or 10 mm around the center of impact). After the impact in step 320, the degree of damage to the glass sample 218 is measured (step 330). As previously stated above, here, the term "fracture" means that when the substrate is dropped or impacted by an object, the crack expands to the entire thickness of the substrate and / or the entire surface.

[0118] In test method 300, after each drop, the glass plate 218 with a rough surface can be replaced to avoid the effects of "aging". Aging effects have been observed in repeated use on other types of drop test surfaces (e.g., concrete or asphalt).

[0119] Various predetermined drop heights h and height increments are typically used in test method 300. The test may, for example, begin with a minimum drop height (e.g., about 10 to 20 cm). Subsequently, the height may be increased by a predetermined height increment or different height increments with each subsequent drop. Once the glass sample 218 breaks or fractures, test 300 is terminated (step 331). Alternatively, if the drop height h reaches the maximum drop height (e.g., about 80 cm) but the glass does not break, the drop test method 300 may also be terminated, or step 320 may be repeated at the maximum height until the glass breaks.

[0120] In some embodiments, each glass sample 218 is subjected to the IBoS test method 300 only once at each predetermined height h. However, in other embodiments, each sample is tested multiple times at each height.

[0121] If glass sample 218 breaks (step 331 in Figure 5d), the IBoS test 300 ends (step 340). If it is observed that the ball falls from a predetermined drop height without breaking (step 332), the drop height is increased by a predetermined increment, for example, an increment of 5 cm, 10 cm, or 20 cm (step 334), and steps 320 and 330 are repeated until a sample breaks (step 331) or no sample breaks but the maximum test height is reached (step 336). When either step 331 or step 336 is reached, the test method 300 ends.

[0122] When the aforementioned tempered glass undergoes the aforementioned inverted ball drop test (IBoS) on sandpaper, where a ball is dropped from a height of 100 cm onto the glass surface, the damage resistance of the tempered glass can be expressed as a "survival rate". For example, in the IBoS drop test, if 3 out of 5 identical (or nearly identical) samples (i.e., having substantially the same composition and substantially the same CS and DOC or DOL after tempering) are dropped from a specified height without breaking, the tempered glass object can be described as having a 60% survival rate.

[0123] The survivability rate of tempered glass objects dropped from a predetermined height is measured using the IBoS test method and equipment described above. At least five identical (or nearly identical) tempered glass samples (i.e., having substantially the same composition and substantially the same CS and DOC or DOL) are tested, but a larger number of samples (e.g., 10, 20, 30, etc.) can be used to improve the reliability of the test results. Each sample is dropped once from a predetermined height (e.g., 80 cm), and the entire surface and / or thickness of the sample is visually inspected (i.e., examined with the naked eye) for any cracking (crack formation and propagation). If no cracking is observed after the sample is dropped, the sample is considered "survived." The survivability rate is defined as the percentage of samples that are not damaged in the drop test within the sample group. For example, if 7 out of 10 samples in a group are not damaged when dropped from a predetermined height, the survivability rate of the glass will be 70%.

[0124] When the tempered glass object described herein undergoes an abrasion ring-to-ring (AROR) test, the tempered glass object also exhibits improved surface strength. The strength of a material is defined as the stress at which it breaks. The abrasion ring-to-ring test is a method for measuring the surface strength of a flat glass sample, and the abrasion ring-to-ring test method described herein is based on ASTM C1499-09 (2013, titled "Standard Test Method for Monotonic Equibiaxial Flexural Strength of Advanced Ceramics at Ambient Temperature"). The contents of ASTM C1499-09 are incorporated herein by reference in their entirety. In one embodiment, prior to the ring-to-ring test, the glass sample was ground with silicon carbide (SiC) particles of size 90 using the method and apparatus described in Annex A2, "Grinding Procedure," of ASTM C158-02, "Standard Test Method for Measuring the Strength of Glass by Flexure (Measurement of Modulus of Rupture)" (2012). The contents of ASTM C158-02, and especially Annex 2, are incorporated herein by reference in their entirety.

[0125] Before conducting the ring-to-ring test, the surface of the glass sample was abraded using the equipment shown in Figure A2.1 of ASTM C158-02 as described in Annex 2 of ASTM C158-02 to standardize and / or control the surface defect condition of the sample. The sample surface was sandblasted with abrasive material at an air pressure of 304 kPa (44 psi) and a load of 15 psi. After the airflow stabilized, 5 cubic centimeters of abrasive material were added to the funnel, and the sample was sandblasted for 5 seconds after the abrasive material was added.

[0126] For the ring-to-ring test, as schematically shown in Figure 6, the glass sample has at least one wear surface 412. The glass sample is placed between two concentric rings of different sizes to measure the isotropic biaxial flexural strength (i.e., the maximum stress that the material can withstand when the material located between the two concentric rings is bent). In the wear ring-to-ring structure 400, a support ring 420 with a diameter of D 2 supports the wear glass sample 410. A force F is applied to the surface of the glass sample by means of a loading ring 430 with a diameter of D 1 using a loading unit (not shown in the figure).

[0127] The diameter ratio D1 / D2 of the loading ring and the support ring may range from about 0.2 to about 0.5. In some embodiments, D1 / D2 is about 0.5. The loading ring 430 and the support ring 420 should be concentrically aligned so that the accuracy is within 0.5% of the diameter D2 of the support ring. The accuracy of the load cell used for testing should be within ±1% of any load within the selected range. In some embodiments, the test is conducted at a temperature of 23±2°C and a relative humidity of 40±10%.

[0128] For the design of the retainer, the radius r of the protruding surface of the loading ring 430 is h / 2 ≤ r ≤ 3h / 2, where h is the thickness of the sample 410. The loading ring 430 and the support ring 420 are generally made of hardened steel with a hardness HRc > 40. ROR retainers are available commercially.

[0129] The deliberate destruction mechanism of the ROR test is used to observe the situation where the sample 410 is destroyed starting from the surface 430a inside the loading ring 430. Data analysis of damage occurring outside this area (i.e., the area between the loading ring 430 and the support ring 420) is omitted. However, because the glass sample 410 is both thin and has high strength, large deviations exceeding 1 / 2 of the sample thickness h are sometimes observed. Therefore, it is not uncommon to observe a fairly high proportion of cases where damage begins below the loading ring 430. Understanding the stress development (analyzed using strain gauges to collect stress development data) below and inside the ring, as well as the origin of damage in each sample, is necessary for accurate stress calculation. Therefore, the AROR test method focuses on measuring the peak load value at the point of destruction as the measured response.

[0130] The strength of glass depends on whether surface cracks occur. However, the probability of a crack of a specific size occurring cannot be precisely predicted, therefore the strength of glass is essentially a statistical result. Thus, the Weiss probability distribution is commonly used as a statistical representation of the obtained data.

[0131] Although several representative embodiments have been provided for illustrative purposes, the foregoing description should not be construed as limiting the scope of the present invention or the appended claims. Therefore, those skilled in the art can make various changes, adjustments, and substitutions without departing from the spirit and scope of the present invention or the appended claims. [Simplified Explanation of the Diagram]

[0009] Figure 1 is a schematic cross-sectional view of a chemically strengthened glass object;

[0010] Figure 2 is a schematic diagram of the compressive stress profile obtained by a single-step ion exchange process;

[0011] Figure 3 is a graphic representation of images showing that a tempered glass object exhibits fragile behavior when it breaks; and 2) does not exhibit non-fragile behavior when it breaks;

[0012] Figure 4a is a graphic representation of images showing that a tempered glass object exhibits fragile behavior when it breaks; and 2) does not exhibit non-fragile behavior when it breaks;

[0013] Figure 4b is a graphical representation of a reinforced glass sheet that exhibits non-fragile behavior upon breakage;

[0014] Figure 5a is a schematic cross-sectional view of an embodiment of the apparatus used to perform the Inverse Ball on Sandpaper Test (IBoS) method described in this invention;

[0015] Figure 5b is a schematic cross-sectional view used to illustrate the main mechanism by which tempered glass objects used in mobile electronic devices or handheld electronic devices often fail due to damage and bending.

[0016] Figure 5c is a schematic cross-sectional view used to illustrate the main mechanism by which tempered glass objects used in mobile electronic devices or handheld electronic devices often fail due to damage and bending.

[0017] Figure 5d is a flowchart of the method for conducting IBoS testing in the equipment described herein; and

[0018] Figure 6 is a schematic cross-sectional view of the ring-to-ring device. [Biomaterial Storage]

[0133] Domestic storage information (please note in order of storage institution, date, and number): None

[0134] Overseas Deposit Information (Please note in the order of deposit country, institution, date, and number) None

Claims

1. A glass article comprising an alkali aluminosilicate glass having a thickness t and a compression region having a compressive stress CSs at a surface of the glass article ranging from about 400 MPa to 1200 MPa, wherein the compression region extends from the surface to a compression depth DOC, wherein 0.1∙t ≤ DOC ≤ 0.25∙t, and the compression region having a compressive stress profile comprising: a. a first portion b, exhibiting substantially linear behavior and extending from the surface to a depth db below the surface, and having a slope mb; and b. a second portion c, extending from near the depth db to the compression depth DOC and having a slope mc, wherein |mb| >> |mc|, the slope mb being in the range of -40 MPa / μm to -200 MPa / μm, and the slope mc being in the range of -0.4 MPa / μm to -3.0 MPa / μm. The alkali aluminosilicate glass comprises: from about 40 mol% to about 70 mol% of SiO2; from more than 0 mol% to about 28 mol% of B2O3; from more than 0 mol% to about 28 mol% of Al2O3; up to about 1 mol% of P2O5 and from 0 mol% to 4 mol% of B2O3.

2. The glass article as claimed in claim 1, wherein the depth of compression (DOC) is in the range of 95 μm to 250 μm, preferably in the range of 100 μm to 190 μm.

3. The glass object as described in claim 1, wherein 0.12∙t ≤ DOC ≤ 0.22∙t.

4. The glass object as claimed in claim 1, wherein the thickness t is in the range of 0.1 mm to 2.0 mm.

5. The glass object as claimed in claim 4, wherein the thickness t is in the range of 0.1 mm to 1.5 mm.

6. The glass object as claimed in claim 5, wherein the thickness t is in the range of 0.1 mm to 1 mm.

7. The glass object as claimed in claim 1, wherein the slope mb is in the range of -40 MPa / μm to -120 MPa / μm.

8. The glass object as claimed in claim 7, wherein the slope mb is in the range of -50 MPa / μm to -120 MPa / μm.

9. A glass object as described in any one of claims 1 to 8, wherein the slope mc is in the range of -0.7 MPa / μm to -2.7 MPa / μm.

10. The glass object as claimed in claim 9, wherein the slope mc is in the range of -1.5 MPa / μm to -2.7 MPa / μm.

11. A glass object as described in any one of claims 1 to 8, wherein db is in the range of 3 µm to 15 µm.

12. The glass object as described in claim 11, wherein db is in the range of 3 µm to 10 µm.

13. The glass object as described in claim 12, wherein db is in the range of 3 µm to 8 µm.

14. A glass article as described in any one of claims 1 to 8, wherein the alkali aluminosilicate glass contains up to about 10 moles of Li₂O.

15. A glass article as described in any one of claims 1 to 8, wherein the glass is lithium-free.

16. A glass article as claimed in any one of claims 1 to 8, wherein 0.75 ≤ [(P₂O₅(moles%) + R₂O(moles%)) / M₂O₃(moles%)] ≤ 1.2, wherein M₂O₃ = Al₂O₃ + B₂O₃, and R₂O is the sum of monovalent cationic oxides present in the alkali aluminosilicate glass.

17. A glass article as claimed in any one of claims 1 to 8, wherein the glass comprises: 62 mol% to 70 mol% of SiO2; greater than 0 mol% to 18 mol% of Al2O3; greater than 0 mol% to 10 mol% of B2O3; 0 mol% to 15 mol% of Li2O; greater than 0 mol% to 20 mol% of Na2O; greater than 0 mol% to 18 mol% of K2O; greater than 0 mol% to 17 mol% of MgO; greater than 0 mol% to 18 mol% of CaO; and greater than 0 mol% to 5 mol% of ZrO2.

18. The glass article as claimed in claim 17, wherein the glass is substantially composed of: 62 mol% to 70 mol% SiO2; greater than 0 mol% to 18 mol% Al2O3; greater than 0 mol% to 10 mol% B2O3; 0 mol% to 15 mol% Li2O; greater than 0 mol% to 20 mol% Na2O; greater than 0 mol% to 18 mol% K2O; greater than 0 mol% to 17 mol% MgO; greater than 0 mol% to 18 mol% CaO; and greater than 0 mol% to 5 mol% ZrO2.

Images