CN120202168A - Borosilicate glass with modified surface layer - Google Patents

Abstract

A glass substrate includes an alkali-containing body and an alkali-depleted surface layer. The alkali metal depleted surface layer is amorphous and comprises a substantially uniform composition. The alkali metal-containing body and the alkali metal-depleted surface layer include B ₂O₃ and SiO ₂. A method of forming a glass substrate having a modified surface layer includes providing a glass substrate having a concentration of an alkali metal, a glass transition temperature (Tg), and a surface layer. The glass substrate further includes B ₂O₃ and SiO ₂. The method further includes reducing the concentration of alkali metal in the surface layer such that the surface layer having a reduced concentration of alkali metal comprises a substantially uniform composition.

Description

Borosilicate glass with modified surface layer

Cross Reference to Related Applications

The present application claims priority from U.S. provisional application No. 63/428,767 filed on day 2022, 11, 30, in accordance with 35u.s.c. ≡119, the contents of which are incorporated herein by reference in their entirety.

Technical Field

The present disclosure relates to glass substrates having a modified surface layer, and more particularly, to glass substrates having an alkali-containing body and an alkali-depleted surface layer.

Background

Glasses formed or treated using known surface treatments (e.g., including melt-prepared glasses) typically comprise a surface layer that is at least partially crystalline or comprises crystalline portions, or may exhibit phase separation (i.e., non-uniform composition). In other known methods for modifying a surface layer (e.g. leaching or wet chemical treatment), the resulting surface layer comprises hydrogen, which may be present in the form of H ⁺、H₃O⁺、H₂ O or a combination thereof.

Thermal polarization has been used to alter the properties of glass. Thermal polarization generally involves applying a voltage to the glass. Known uses of thermal polarization include forming a depletion layer that inhibits alkali migration in photovoltaic glass, forming an interfacial barrier between display (or alkali-free) glass and silicon, and forming surface textures or performing selective area ion exchange with patterned electrodes.

Thermal polarization is also used to induce second order nonlinear properties, particularly for producing second order nonlinear optical properties of optical switches and devices. The polarization process is also very similar to so-called anodic bonding, which is used to bond alkali-containing or alkali-free glasses to other materials, in particular semiconductors.

The present disclosure provides glass substrates having various compositions of borosilicate and aluminoborosilicate families and surface layers having altered compositions and atomic structures. In an embodiment, the alkali metal concentration of the surface layer is reduced, and the bulk of the glass substrate comprises alkali metal. The surface layer comprises substantially all of the atomic structure of boron in a 3-coordinate state, while the bulk has a majority of the atomic structure of boron in a 4-coordinate state. The composition and atomic structure of the surface layer provide the glass substrate with various surface properties and performance attributes. For example, the surface layer may be used to improve corrosion resistance, diffusion barrier, hardness, elastic modulus, fatigue resistance, and damage resistance (e.g., abnormal deformation) of the glass substrate.

Disclosure of Invention

According to aspect (1), there is provided a glass substrate. The glass substrate includes an alkali-containing body and an alkali-depleted surface layer, wherein the alkali-depleted surface layer is amorphous and includes a substantially uniform composition, and wherein the alkali-containing body and the alkali-depleted surface layer include B ₂O₃ and SiO ₂.

According to aspect (2), there is provided the glass substrate of aspect (1), wherein the alkali-depleted surface layer comprises about 0.5 at% or less of alkali metal.

According to aspect (3), there is provided the glass substrate of aspect (1) or aspect (2), wherein the alkali metal depleted surface layer comprises an atomic structure comprising boron in a substantially 3-coordinated state.

According to aspect (4), there is provided the glass substrate of aspect (3), wherein more than about 60% of the total amount of boron in the alkali metal depleted surface layer is in the 3-coordinate state in terms of fraction.

According to aspect (5), there is provided the glass substrate of aspect (3), wherein greater than about 70% of the total amount of boron in the alkali metal depleted surface layer is in the 3-coordinate state in terms of fraction.

According to aspect (6), there is provided the glass substrate of aspect (3), wherein greater than about 75% of the total amount of boron in the alkali metal depleted surface layer is in the 3-coordinate state in terms of fraction.

According to aspect (7), there is provided the glass substrate according to any one of aspects (1) to (6), wherein the alkali metal-containing body includes an atomic structure including boron in a 3-coordinated state and boron in a 4-coordinated state.

According to aspect (8), there is provided the glass substrate of aspect (7), wherein more than about 51% of the total amount of boron in the alkali metal-containing host is in the 4-coordinate state in terms of fraction.

According to aspect (9), there is provided the glass substrate of any of aspects (1) to (8), wherein the alkali metal depleted surface layer is substantially free of non-bridging oxygen.

According to aspect (10), there is provided the glass substrate of aspect (9), wherein the alkali metal-containing body comprises non-bridging oxygen and bridging oxygen.

According to aspect (11), there is provided the glass substrate of aspect (10), wherein the alkali metal-containing body is substantially free of non-bridging oxygen.

According to aspect (12), there is provided the glass substrate of any one of aspects (1) to (11), wherein the alkali metal-containing host comprises an alkali metal oxide selected from Li ₂O、Na₂O、K₂O、Rb₂ O and Cs ₂ O.

According to aspect (13), there is provided the glass substrate of aspect (12), wherein the alkali metal-containing host comprises at least 1 mol% Na ₂O、K₂ O or Li ₂ O.

According to aspect (14), there is provided the glass substrate of aspect (12), wherein the alkali metal-containing body comprises at least 1 mol% Na ₂ O.

According to aspect (15), there is provided the glass substrate of any of aspects (1) to (14), wherein the alkali metal depleted surface layer comprises B ₂O₃ in a range of about 10 mol% to about 90 mol%.

According to aspect (16), there is provided the glass substrate of any one of aspects (1) to (15), wherein the alkali metal-depleted surface layer comprises a binary B ₂O₃-SiO₂ composition.

According to aspect (17), there is provided the glass substrate of any of aspects (1) to (16), wherein an atomic% of silicon is greater than an atomic% of boron.

According to aspect (18), a glass substrate is provided. The glass substrate includes a substrate thickness, an alkali-containing body having a bulk refractive index, and an alkali-depleted surface layer comprising a layer thickness in the range of about 10nm to about 3000nm, wherein the alkali-depleted surface layer comprises a layer refractive index less than the bulk refractive index, wherein the alkali-containing body and the alkali-depleted surface layer comprise B ₂O₃ and SiO ₂.

According to aspect (19), there is provided the glass substrate of aspect (18), wherein the atomic% of silicon is greater than the atomic% of boron.

According to aspect (20), a method of forming a glass substrate having a modified surface layer is provided. The method includes providing a glass substrate including a concentration of an alkali metal, a glass transition temperature (Tg) and a surface layer, the glass substrate including B ₂O₃ and SiO ₂, and reducing the concentration of the alkali metal in the surface layer, wherein the surface layer having a reduced concentration of the alkali metal includes a substantially uniform composition.

According to aspect (21), there is provided the method of aspect (20), wherein the atomic% of silicon is greater than the atomic% of boron.

According to aspect (22), there is provided the method of aspect (20) or aspect (21), wherein reducing the alkali metal concentration in the surface layer comprises contacting the surface of the glass substrate with an electrode, and thermally polarizing the glass substrate.

According to aspect (23), there is provided the method of aspect (22), wherein the electrode comprises an anode in contact with the anode surface of the glass substrate and a cathode in contact with the cathode surface of the glass substrate, and wherein the thermally polarizing comprises applying a voltage to the glass substrate such that the anode is positively biased with respect to the glass substrate to induce alkali depletion at the anode surface of the glass.

According to aspect (24), there is provided the method of aspect (22), wherein thermally polarizing comprises heating the glass substrate and the electrode to a temperature below Tg prior to applying a voltage to the glass substrate.

According to aspect (25), there is provided the method of aspect (22), wherein thermally polarizing comprises applying a voltage in the range of about 100 volts to about 10,000 volts to the glass substrate for a duration in the range of about 1 minute to about 6 hours.

According to aspect (26), there is provided the method of aspect (22), wherein the glass substrate is thermally polarized under vacuum in an inert gas atmosphere or a permeable gas atmosphere.

Drawings

FIG. 1 is a side view of a glass substrate according to an embodiment;

FIG. 2A is a ternary diagram of the precursor glass of example 1;

FIG. 2B shows the ternary diagram of FIG. 2A, wherein a composition comprising only network formers formed by thermally polarizing the precursor glass of example 1 is projected onto the B ₂O₃-SiO₂ binary edge of the ternary diagram;

FIGS. 3 through 7 show Secondary Ion Mass Spectrometry (SIMS) depth profiles of certain elements through an alkali-depleted surface layer of the selected glass of example 1 after thermal polarization;

FIG. 8 is a bar graph summarizing near-edge X-ray absorption fine structure (NEXAFS) spectral results for selected glasses of example 1 after thermal polarization;

FIG. 9 is a set of line graphs reporting molecular modeling changes in boron coordination state after thermal polarization of different alkali and alkaline earth borosilicate precursor glasses, and

FIG. 10 is a set of line graphs reporting molecular modeling changes in Young's modulus after thermally polarizing the different alkali and alkaline earth borosilicate precursor glasses of FIG. 9.

Detailed Description

For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It will be appreciated that this is not intended to limit the scope of the present disclosure. It is to be further understood that the present disclosure encompasses any alterations and modifications to the illustrated embodiments and encompasses further applications of the principles disclosed herein that would normally occur to one skilled in the art to which this disclosure pertains.

As used herein, the term "and/or" when used in a list of two or more items means that any one of the listed items may be employed alone, or any combination of two or more of the listed items may be employed. For example, if the composition is described as containing components A, B and/or C, the composition may contain A alone, B alone, C alone, a combination of A and B, a combination of A and C, a combination of B and C, or a combination of A, B and C.

In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.

As used herein, the term "about" means that the amounts, sizes, formulations, parameters, and other amounts and characteristics are not and need not be exact, but may be approximate and/or larger or smaller as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like and other factors known to those of skill in the art. When the term "about" is used to describe a value or an end point of a range, the disclosure should be understood to include the specific value or end point recited. Whether or not a numerical value or range endpoint in the specification recites "about," the numerical value or range endpoint is intended to include both embodiments, one modified by "about," and one not modified by "about. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

The terms "substantially," "substantially," and variations thereof as used herein are intended to indicate that the feature being described is equal to or substantially equal to the value or description, unless otherwise defined in association with a particular term or phrase. For example, a "substantially planar" surface is intended to mean a planar or substantially planar surface. Further, "substantially" is intended to mean that the two values are equal or substantially equal. In some embodiments, "substantially" may refer to values within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

Directional terms as used herein, such as up, down, right, left, front, rear, top, bottom, above, below, etc., refer only to the drawing figures and are not intended to imply absolute orientation.

As used herein, the terms "said," "a," or "an" mean "at least one," and should not be limited to "only one," unless explicitly indicated to the contrary. Thus, for example, reference to "a component" includes embodiments having two or more such components unless the context clearly indicates otherwise.

As used herein, the terms "atom%", or "atomic-%" refer to the proportion of the mole percent of each element in the glass composition, such as O, si, al, B, na, ca. Oxide glasses can also be conventionally described in terms of proportions of component oxides, each having a certain assumed oxygen stoichiometry, e.g., siO ₂、Al₂O₃、B₂O₃、Na₂ O, caO, etc. As used herein, the terms "mole% (mol%)", "mole% (mole%)" or "mole% (mole-%)" describe glass compositions in terms of the proportion of the mole percentages of the constituent oxides. The term "weight percent" or "weight-%" describes the glass composition in terms of the mass percent of the constituent oxides. Elements may be referred to interchangeably by their name or symbol (e.g., carbon or C, oxygen or O, etc.).

As shown in fig. 1, a first aspect of the present disclosure relates to a glass substrate 100 comprising an alkali-containing body 120 (interchangeably referred to as a "body") and an alkali-depleted surface layer 140. The alkali metal-containing host may comprise one or more alkali metal oxides selected from the group consisting of Li ₂O、Na₂O、K₂O、Rb₂ O and Cs ₂ O. In embodiments, the alkali metal depleted surface layer may be substantially alkali metal free or completely alkali metal free. For example, the alkali metal depleted surface layer may include about 0.5 atomic% or less alkali metal. The alkali metal depleted surface layer may be described as a borosilicate (i.e., atomic% of silicon > atomic% of boron) surface layer or a boroaluminosilicate surface layer (i.e., atomic% of silicon > atomic% of boron + atomic% of aluminum). The alkali metal depleted surface layer exhibits a composition and atomic structure that is different from the host while exhibiting uniformity of composition and/or atomic structure within and throughout the surface layer. The alkali-depleted surface layer is integral with the glass substrate and is not a coating or addition to the body.

In embodiments, the substrate thickness t of the glass substrate may be in the range of about 0.1mm to about 3.0mm, about 0.3mm to about 3mm, about 0.4mm to about 3mm, about 0.5mm to about 3mm, about 0.55mm to about 3mm, about 0.7mm to about 3mm, about 1mm to about 3mm, about 0.1mm to about 2mm, about 0.1mm to about 1.5mm, about 0.1mm to about 1mm, about 0.1mm to about 0.7mm, about 0.1mm to about 0.55mm, about 0.1mm to about 0.5mm, about 0.1mm to about 0.4mm, about 0.3mm to about 0.7mm, or about 0.3mm to about 0.55mm, and also include all subranges and sub-values between the endpoints of these ranges.

In embodiments, the layer thickness of the alkali metal depleted surface layer may be in the range of about 10nm to about 3000nm, about 10nm to about 2000nm, about 10nm to about 1000nm, about 10nm to about 900nm, about 10nm to about 800nm, about 10nm to about 700nm, about 10nm to about 600nm, about 10nm to about 500nm, about 50nm to about 1000nm, about 100nm to about 1000nm, about 200nm to about 1000nm, about 250nm to about 1000nm, about 300nm to about 1000nm, about 400nm to about 1000nm, about 500nm to about 1500nm, about 500nm to about 2000nm, about 500nm to about 2500nm, or about 500nm to about 3000nm.

In an embodiment, the alkali metal depleted surface layer has a substantially uniform composition. In an embodiment, the composition of the alkali metal depleted surface layer is substantially the same along the layer thickness of the surface layer. In an embodiment, the composition of the alkali metal depleted surface layer is substantially the same along its entire volume. As used herein, the phrase "homogeneous composition" refers to a composition that does not phase separate and/or does not include a portion of a composition that is different from other portions.

In embodiments, the alkali metal depleted surface layer may be substantially free of crystallites and/or substantially amorphous. For example, the alkali metal depleted surface layer may comprise less than about 1% crystallites by volume.

In an embodiment, the alkali metal depleted surface layer is substantially free of hydrogen. Such hydrogen may be present in the form of H ⁺、H₃O⁺、H₂ O or a combination thereof. In embodiments, the alkali metal depleted surface layer comprises about 0.1 atomic% or less hydrogen (e.g., about 0.08 atomic% or less hydrogen, about 0.06 atomic% or less hydrogen, about 0.05 atomic% or less hydrogen, about 0.04 atomic% or less hydrogen, about 0.02 atomic% or less hydrogen, or about 0.01 atomic% or less hydrogen). In contrast, glass substrates treated by leaching or other wet chemical treatments typically have a surface layer that contains hydrogen.

In alternative embodiments, the alkali metal depleted surface layer may inject hydrogen into its composition under certain thermal polarization conditions. For example, under conditions where thermal polarization occurs in air, the alkali metal depleted surface layer may contain an amount of hydrogen greater than the amount indicated in the previous paragraph.

In an embodiment, the alkali metal-containing body and the alkali metal-depleted surface layer comprise B ₂O₃ and SiO ₂. The alkali metal-containing body and the alkali metal-depleted surface layer each have an atomic structure including boron in one or more coordination states.

In an embodiment, the alkali metal depleted surface layer comprises boron in a 3-coordination state (interchangeably referred to as triangular B3 cells or simply B3) and boron in a 4-coordination state (interchangeably referred to as tetrahedral B4 cells or simply B4). In an embodiment, substantially all of the boron in the alkali metal depleted surface layer is in a 3-coordinate state. In an embodiment, a majority of the boron in the alkali metal depleted surface layer is in a 3-coordinate state. For example, about 55% to about 100% (e.g., about 60% to about 100%, about 65% to about 100%, about 70% to about 100%, about 75% to about 95%, about 80% to about 100%, and including all subranges and subranges between the endpoints of the ranges) of the total amount of boron in the alkali metal depleted surface layer is in a 3-coordinate state. In contrast, less than about 45% (e.g., less than about 40%, less than about 35%, less than about 30%, less than about 25%, less than about 20%, less than about 15%, less than about 10%, less than about 5%, or less than about 2.5%) of the total amount of boron in the alkali metal depleted surface layer is in the 4-coordinate state on a fraction basis.

In an embodiment, the alkali metal-containing body comprises boron in a 3-coordinate state and boron in a 4-coordinate state. In an embodiment, a majority (i.e., an amount greater than half of the total amount) of the boron in the alkali metal-containing host is in a 4-coordinate state. For example, the total amount of boron in the alkali metal-containing body is in a 4-coordinate state from about 51% to about 100% (e.g., from about 55% to about 100%, from about 60% to about 100%, from about 65% to about 100%, from about 70% to about 95%, from about 80% to about 100%, and including all subranges and subranges between the endpoints of the ranges) by fraction.

In some cases, the alkali metal depleted surface layer is substantially free of non-bridging oxygen, while in some embodiments, the alkali metal containing body comprises non-bridging oxygen and bridging oxygen. An alkali metal depleted surface layer may also be present or formed when the alkali metal containing body is substantially free of non-bridging oxygen.

In an embodiment, the alkali metal depleted surface layer includes B ₂O₃ in a range of about 1 mol% to about 90 mol%. In embodiments, the amount of B ₂O₃ may be in the range of about 1 mole% to about 80 mole%, about 1 mole% to about 70 mole%, about 1 mole% to about 60 mole%, about 1 mole% to about 50 mole%, about 5 mole% to about 90 mole%, about 10 mole% to about 90 mole%, about 20 mole% to about 90 mole%, about 30 mole% to about 90 mole%, about 1 mole% to about 55 mole%, 5 mole% to about 45 mole%, or about 3 mole% to about 35 mole%.

In an exemplary embodiment, the alkali metal depleted surface layer includes a binary B ₂O₃-SiO₂ composition, but may also include other non-alkali metal components.

The glass substrate prior to the thermal polarization treatment, as will be described herein, may comprise a variety of glass compositions. Such glass compositions used in glass substrates prior to heat polarization treatment and present in alkali-containing bodies after heat polarization treatment may be referred to herein as "precursor" glasses or glass compositions. Precursor compositions can range from simple alkali or alkaline earth silicates, borosilicates or boroaluminosilicates to more complex multicomponent glasses capable of forming altered surface layers by thermal polarization processes. In one embodiment, the alkali-containing body may exhibit signs of nano-scale phase separation, but when these glasses are thermally polarized, the layer comprises a single phase.

In an embodiment, the precursor glass composition is configured to form a homogeneous glass (i.e., no phase separation occurs, no devitrification (devitrified)).

In an embodiment, the precursor glass composition includes a certain alkali metal. For example, the precursor glass composition includes greater than or equal to 1 mole percent of an alkali oxide selected from the group consisting of Li ₂O、Na₂O、K₂O、Rb₂ O and Cs ₂ O. In an exemplary embodiment, the precursor glass composition includes greater than or equal to 1 mole percent Na ₂ O. For example, the precursor glass composition can include greater than or equal to 1 mole%, 1.5 mole%, 2 mole%, 3 mole%, 4 mole%, 5 mole%, 6 mole%, 7 mole%, 8 mole%, 9 mole%, or 10 mole% Na ₂ O.

In an embodiment, the precursor glass composition includes a certain boron. For example, the precursor glass composition includes greater than or equal to 1 mole% B ₂O₃. In embodiments, the precursor glass composition can include greater than or equal to 1 mole%, 1.5 mole%, 2 mole%, 3 mole%, 4 mole%, 5 mole%, 6 mole%, 7 mole%, 8 mole%, 9 mole%, 10 mole%, 15 mole%, or 20 mole% B ₂O₃.

In an embodiment, the precursor glass composition is a simple sodium borosilicate, including Na ₂O、B₂ O3 and SiO ₂. In one example, the precursor glass composition includes about 8.5 mol% to about 43 mol% Na ₂ O, about 9 mol% to about 87 mol% B ₂O₃, and about 9.5 mol% to about 88 mol% SiO ₂. In another example, the precursor glass composition includes about 9.5 mol% to about 39 mol% Na ₂ O, about 10 mol% to about 79.5 mol% B ₂O₃, and about 10.5 mol% to about 80 mol% SiO ₂.

In an embodiment, there is a relationship between the amounts of silicon and boron, silicon in atomic% > boron in atomic%. For example, the precursor glass composition includes about 8.7 mol% to about 21.5 mol% Na ₂ O, about 9 mol% to about 33 mol% B ₂O₃, and about 54 mol% to about 88 mol% SiO ₂. In another example, the precursor glass composition includes about 9.5 mol% to about 19.5 mol% Na ₂ O, about 10 mol% to about 30 mol% B ₂O₃, and about 60 mol% to about 80 mol% SiO ₂.

In embodiments, the precursor glass composition is an alkali-containing borosilicate, an alkali-containing boroaluminosilicate, or a combination thereof. In such embodiments, there is a relationship that the amount of silicon is greater than the amount of boron alone, the amount of aluminum alone, or the combined amount of boron and aluminum (e.g., atomic% of silicon > atomic% of aluminum + atomic% of boron). In an embodiment, the amount of alkali metal may be limited such that no more of the inverse glass of alkali metal than the network former is present. In such embodiments, there is a relationship between the amounts of alkali metal, aluminum, boron, and silicon, where the atomic% of alkali metal (atomic% of silicon + atomic% of aluminum + atomic% of boron).

In one exemplary embodiment, the precursor glass composition includes about 46 mol% to about 80 mol% SiO ₂, about 0 mol% to about 17 mol% Na ₂ O, about 8 mol% to about 25 mol% Al ₂O₃, about 2 mol% to about 15 mol% B ₂O₃, about 0 mol% to about 8 mol% MgO, about 0 mol% to about 5 mol% K ₂ O, about 0 mol% to about 11 mol% CaO, and about 0.05 mol% to about 0.5 mol% SnO ₂.

In another exemplary embodiment, the precursor glass composition includes about 57 mole% to about 67 mole% SiO ₂, about 1 mole% to about 14 mole% Na ₂ O, about 11 mole% to about 21 mole% Al ₂O₃, about 3 mole% to about 10 mole% B ₂O₃, about 0 mole% to about 5 mole% MgO, about 0 mole% to about 3 mole% K ₂ O, about 0 mole% to about 8 mole% CaO, and about 0.05 mole% to about 0.25 mole% SnO ₂.

In embodiments, the precursor glass composition may be substantially free of aluminum. For example, the precursor glass composition and/or the heat-polarized glass substrate may comprise less than about 1 mole percent or less than about 0.1 mole percent Al ₂O₃ or aluminum in any state.

In an embodiment, the alkali metal-containing body may comprise an amount of Na ₂ O that is about equal to the amount of B ₂O₃ present in the body.

Fining agents, such as SnO ₂ and other known fining agents, may be included in the precursor glass compositions described herein.

In an embodiment, the thermally polarized glass substrate exhibits a refractive index in the range of about 1.45 to about 1.55, wherein the refractive index of the alkali metal depleted surface layer is lower than the alkali metal containing host.

In embodiments, the glass substrate may exhibit an average strain-to-break rate (AVERAGE STRAIN-to-failure) at a surface on one or more opposing major surfaces of 0.5% or greater, 0.6% or greater, 0.7% or greater, 0.8% or greater, 0.9% or greater, 1% or greater, 1.1% or greater, 1.2% or greater, 1.3% or greater, 1.4% or greater, 1.5% or greater, or even 2% or greater, as measured using at least 5, at least 10, at least 15, or at least 20 samples using ball-on-ring testing (ball-on-RING TESTING). In embodiments, the glass substrate may exhibit an average strain-to-break rate of about 1.2%, about 1.4%, about 1.6%, about 1.8%, about 2.2%, about 2.4%, about 2.6%, about 2.8%, or about 3% or greater at a surface on one or more opposing major surfaces thereof.

After the heat polarization treatment, the glass substrates described herein may exhibit an elastic modulus (or young's modulus) in the range of about 30GPa to about 120 GPa. For example, the elastic modulus of the glass substrate may be in the range of about 30GPa to about 110GPa, about 30GPa to about 100GPa, about 30GPa to about 90GPa, about 30GPa to about 80GPa, about 30GPa to about 70GPa, about 40GPa to about 120GPa, about 50GPa to about 120GPa, about 60GPa to about 120GPa, or about 70GPa to about 120GPa, as well as all ranges and subranges therebetween.

In embodiments, the glass substrate may be strengthened or non-strengthened. For example, the strengthened glass substrate may be thermally polarized such that an alkali-depleted surface layer is formed atop the compressive stress layer in the strengthened glass substrate.

The glass substrate may be substantially flat or sheet-like, but other embodiments may utilize curved or other shapes or engraved substrates. The glass substrate may be substantially optically clear, transparent, and free of light scattering. In such embodiments, the glass substrate may exhibit an average total transmittance of about 85% or more, about 86% or more, about 87% or more, about 88% or more, about 89% or more, about 90% or more, about 91% or more, or about 92% or more over the range of light wavelengths.

Additionally or alternatively, the physical thickness of the glass substrate may vary along one or more dimensions thereof for aesthetic and/or functional reasons. For example, the edges of the glass substrate may be thicker than the more central regions of the glass substrate. The length, width, and physical thickness dimensions of the glass substrate may also vary depending on the application or use.

The glass substrate may be provided using various forming methods, which may include float glass processes and downdraw processes, such as fusion draw (fusion draw) and slot draw (slot draw).

The resulting glass substrates comprising the alkali-containing bodies and alkali-depleted surface layers described herein exhibit improved corrosion resistance, improved diffusion barrier properties, higher hardness and/or elastic modulus values, greater fatigue resistance, and/or improved damage resistance (via so-called anomalous deformation).

The glass network has near maximum connectivity, which is advantageous for achieving high hardness and/or high modulus. The lack of mobile alkali metals or other network modifiers means that the pathways for ion hopping conduction are very limited, translating into suppressed diffusion (also known as diffusion barrier) properties. Also, the lack of mobile alkali metal or other network modifiers will increase the number of molecules that are bound to the polymer by primarily ion exchange mechanisms (e.g.,) Corrosion resistance of the active chemical, most typical examples are acidic chemicals. Even in chemicals that do not act primarily through ion exchange mechanisms, the lack of non-bridging oxygen and high network connectivity is expected to result in reduced network dissolution, for example, in the neutrality of alkaline pH chemicals (considering the dissolution rate of silica at alkaline pH compared to other multicomponent glasses). The fatigue resistance and crack initiation of alkali-containing glasses are significantly worse than materials such as silica to those skilled in the art, and thus the alkali-depleted surface layer is expected to exhibit lower fatigue parameters and a high crack initiation threshold. Finally, the behavior of indentations in glass is structurally related to well-connected networks with a large free volume. Since the layers described in this disclosure are formed at temperatures well below Tg, these layers are expected to be far apart from the melt equilibrium structure that would otherwise be possible to obtain by melting, and thus may contain a large amount of free volume, thus anticipating abnormal deformation behavior and so-called as-grown damage resistance.

In an embodiment, the layer refractive index of the alkali metal depleted surface layer is less than the bulk refractive index of the alkali metal containing body. For example, the refractive index of the alkali metal depleted surface layer at a wavelength of about 550nm may be in the range of about 1.45 to about 1.55. This result is typically of sufficient refractive index contrast and thickness to produce a visible anti-reflection effect in the thermally polarized glass. Furthermore, in the case of borosilicate glass, the boron structural units in the alkali metal depleted surface layer change from tetrahedral B4 units to triangular B3 units. Triangle B3 cells may correspond to lower glass densities than corresponding B4 cells. This in turn may further increase the refractive index contrast between the polarizing material and the host material of the borosilicate, as compared to aluminosilicate glass.

In embodiments, a glass substrate having an alkali-containing body and an alkali-depleted surface layer may exhibit an increased modulus of elasticity as compared to an alkali-containing body (or a glass substrate prior to forming the alkali-depleted surface layer). For example, the elastic modulus of the glass substrate may be about 10% greater than the elastic modulus of the alkali-containing body (or the glass substrate prior to formation of the alkali-depleted surface layer). For example, when the alkali-containing body (or the glass substrate before forming the alkali-depleted surface layer) exhibits an elastic modulus of about 80GPa, the glass substrate exhibits an elastic modulus of about 90 GPa.

In embodiments, the hardness of the glass substrates described herein is also greater than the hardness of the alkali-containing body. For example, the hardness of the glass substrate may be about 10% or even 20% greater than the hardness of the alkali-containing body (or the glass substrate prior to forming the alkali-depleted surface layer). In one example, at an indentation depth of about 0nm to about 200nm, the hardness of the alkali-containing body (or the glass substrate prior to forming the alkali-depleted surface layer) may be about 6GPa, while the glass substrate exhibits a hardness of about 7 GPa. Unless otherwise indicated, the hardness values described herein refer to vickers hardness (VICKERS HARDNESS).

In an embodiment, the alkali-depleted surface layer also prevents ions from diffusing into the glass substrate or from the alkali-containing body to the alkali-depleted surface layer.

The glass substrates described herein may exhibit increased chemical durability in terms of resistance to dissolution in acid, water, or alkali. In some examples, the glass substrate exhibits a reduction in dissolution rate in acid, water, or base of about 1.5 times or more, or even about 10 times or more.

A second aspect of the present disclosure relates to a method of forming a glass substrate having a modified surface layer. The method includes providing a glass substrate including a concentration of alkali metal and a surface layer, and reducing the concentration of alkali metal in the surface layer. In an embodiment, the resulting surface layer having a reduced alkali metal concentration comprises a substantially uniform composition.

In an embodiment, reducing the alkali metal concentration in the surface layer comprises contacting the surface of the glass substrate with an electrode, and thermally polarizing the glass substrate.

Prior to the thermal polarization treatment, the surface of the glass substrate (and thus the surface layer) may be cleaned or treated to remove typical contaminants that may accumulate after molding, storage, and transportation. Alternatively, the glass substrate may be treated immediately after molding to eliminate the accumulation of contaminants.

The electrode for thermal polarization may comprise an anode in contact with the anode surface of the glass substrate and a cathode in contact with the cathode surface of the glass substrate. The anode surface is biased with a positive Direct Current (DC) voltage and the cathode surface is biased with a negative DC voltage.

In an embodiment, the electrode material is significantly more conductive than glass at the polarization temperature to provide field uniformity over the modified surface area. It is also desirable that the anode electrode material have a relative oxidation resistance to minimize the formation of interfacial oxides that may cause glass to adhere to the template. Exemplary anode electrode materials include noble metals (e.g., au, pt, pd, etc.) or oxidation resistant conductive films (e.g., tiN and TiAlN).

The cathode electrode material may also be electrically conductive to achieve field uniformity over the modified region as well. Exemplary materials for the cathode electrode material include materials that can accept alkali metal ions from glass, such as graphite. In embodiments, contact with the physical cathode electrode may not always be required due to surface discharge.

In embodiments, the electrodes are separate components that are in contact with the glass, and thus can be separated after processing without requiring a complicated removal step. The electrodes may generally comprise a host material, or take the form of a thin film, for example, a conductive film or coating deposited on glass to act as an electrode.

In embodiments, the electrodes may generally cover all or only a portion of the surface, and may be intermittent or patterned as desired. Patterning may be accomplished by any of a variety of methods, such as photolithography, machining, or other means.

The curvatures and/or flatness of the glass and electrode should be ideally matched to achieve a fairly intimate contact at the interface on the affected area. However, even if the initial contact is not intimate, the electrostatic charge at the interface will tend to pull the two surfaces into intimate contact when a voltage is applied, which is an inherent part of the process.

Thermal polarization may involve applying a voltage to the glass substrate such that the anode is positively biased with respect to the glass substrate, thereby inducing alkali depletion at the anode surface of the glass. The voltage may be a DC voltage or an AC voltage of a DC bias. The method may comprise heating the glass substrate and the electrode (i.e. the stack comprising anode/glass/cathode) to a temperature below Tg prior to applying the voltage to the glass substrate. In embodiments, the glass substrate and the electrode may be heated to a process temperature in the range of about 25 ℃ to about Tg or about 100 ℃ to about 300 ℃. In an embodiment, the equilibrium at the desired process temperature may be used for thermal polarization to ensure temperature uniformity.

In an embodiment, the thermal polarization process comprises applying a voltage in a range of about 100 volts to about 10,000 volts (e.g., about 100 volts to about 1000 volts) to the glass substrate for a duration in a range of about 1 minute to about 6 hours (e.g., about 5 minutes to about 60 minutes, or about 15 minutes to about 30 minutes). It should be appreciated that the time and voltage of the thermal polarization treatment may vary depending on the glass composition. In an embodiment, the glass substrate is thermally polarized in an inert gas environment (e.g., dry N ₂) or a permeable gas environment (e.g., he) under vacuum.

The voltage may be applied in one or more discrete steps to achieve the desired maximum value or stepped up (or increased) in a controlled/current limiting manner until the process voltage is reached. The various methods have the advantage of potentially avoiding thermal dielectric breakdown due to excessive current flow through the glass, especially low resistivity glass, allowing for higher final polarization voltages and possibly thicker surface layers. Alternatively, since breakdown strength varies with glass composition, surface conditions, and ambient temperature, the voltage application strategy of "instant-on" may also be silently known under certain conditions, and may be required for convenience.

After the thermal polarization treatment, the glass substrate may be cooled to a temperature in the range of about 25 ℃ to about 80 ℃ for subsequent processing. The voltage may be removed before or after cooling.

In embodiments, an apparatus suitable for performing the polarization process may comprise any system that can maintain the heat and voltage of the glass/electrode stack in a controlled manner while avoiding practical problems such as leakage current paths or arcing. In embodiments, the apparatus also provides control of the process atmosphere (e.g., under vacuum, in an inert gas environment such as dry N ₂ or in a permeable gas environment), which may minimize atmosphere effects and/or occluded gas at the interface. An exemplary apparatus suitable for performing thermal polarization processing is disclosed in U.S. provisional patent application Ser. No. 63/193,334, filed 3/21 at 2022, the disclosure of which is incorporated herein by reference in its entirety.

Examples

The various embodiments of the present disclosure may be better understood by reference to the following examples, which are provided by way of illustration. The present disclosure is not limited to the examples given herein.

Example 1

A series of sodium borosilicate glasses were melted and the composition was verified by inductively coupled plasma optical emission spectroscopy (ICP-OES). The results of the body composition are given in table 1 below. Table 1 contains the results of the measurement by ICP-OES (left) and the mapped target values used in the triplets of fig. 2A and 2B (right).

Table 1 body composition information for examples 1 to 10.

A ternary diagram summarizing the precursor glass composition and corresponding experimental strategy is shown in fig. 2A. The model glass in the Na ₂O-B₂O₃-SiO₂ system represents a "precursor" or bulk glass composition on which the depleted surface layer is synthesized by thermally polarizing the positively biased surface of the glass. After thermal polarization, the corresponding compositional effect is to create an alkali metal depleted surface layer, wherein the modifier species are driven out of the surface layer. The composition of the network-forming body alone produced in the alkali-depleted surface layer is projected onto the B ₂O₃-SiO₂ binary edge of the ternary diagram, as shown in fig. 2B. Unless stated herein, the bulk glass or alkali-containing bulk glass has the same composition, structure, and characteristics as the precursor glass prior to thermal polarization.

The use of simple ternary compositions as shown in table 1 allows for more definitive determination of structure while still maintaining relevance to commercial and other useful compositions. In addition, the composition was also selected to provide an example of a synthetic alkali metal depleted surface layer in which the final compositions overlapped each other but were formed from precursor glasses that differ from each other in initial composition and structure (i.e., indicating that alkali metal depleted surface layers having the same composition could be formed from a variety of precursor glasses). In this way, the effect of the precursor glass composition can also be investigated by varying the concentration and type of alkali charge balance species in the structure.

The glass sheets were made from the precursor glass compositions shown in table 1 and polished to flat test specimens with dimensions of about 25 to 50 square millimeters. The test specimen has a thickness of about 1.0 mm.

For thermal polarization, bulk high purity platinum (Pt) monoliths were obtained and polished to an optical finish. This element was placed in contact with the surface of each glass sheet to act as a positive bias electrode. On the cathode side of each glass sheet, a length of graphite foil (e.g., graphite foil supplied by Graftech International under the trademark). The electrode size is controlled so as not to cover the whole surface of the two sides of the glass, so that leakage current is reduced or eliminated.

After loosely stacking the electrodes and glass sheets, each such stack is introduced into a vacuum furnace and a dry nitrogen atmosphere is created and heated to a temperature between about 200 ℃ and 300 ℃. After equilibration at a temperature in this range for about 15 minutes, a voltage of about +300V was applied to the platinum electrode, with a current limit of a maximum of 1mA. An initial increase in current was observed followed by a slow decay with the formation of an alkali metal depleted surface layer. The voltage was applied for a period of about 15 minutes, then the heater was turned off, and the stack of electrodes and glass sheets was allowed to cool under voltage. When the temperature of the stack is below about 100 ℃, the voltage is removed, the chamber is vented, and the stack is manually separated.

The thermally polarized glass sheets were compared to the same glass sheets, either unpolarized or not, for various forms of analysis.

The presence, depth and composition of the alkali metal depleted surface layer and portions of the body were assessed using Secondary Ion Mass Spectrometry (SIMS). The results of these analyses of examples 4 to 8 of table 1 are summarized in fig. 3 to 7, respectively. In fig. 3-7, SIMS element depth profiles are presented as the concentration of elements noted in the corresponding legends on the forward biased surface as a function of depth (nm).

Figures 3 to 7 show the creation and presence of alkali metal depleted surface layers in various glass compositions with thicknesses in the range of about 100nm to about 500 nm.

X-ray photoelectron spectroscopy (XPS) analysis was performed to evaluate and quantify the composition of the alkali metal depleted surface layer, confirming the discovery of SIMS. The results are given in table 2 and reported as the average of three measurement points per sample.

Table 2 XPS data for the surface composition of the positively biased surface of the selected example.

Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was performed at the synchrotron facility to explore the structure of the sodium borosilicate polarized surface layer of selected examples and to see if the structure is uniquely distinct from the precursor glass. Data were acquired in partial electron yield (TEY) mode to ensure that the results represent the polarized layer structure (i.e., surface sensitive mode, top 2 to 5 nm) and were performed predominantly at B K edges. See "journal of amorphous solids (Boron coordination structure at the surfaces of sodium borosilicate and aluminoborosilicate glasses by B K-edge NEXAFS)",", J545, 10, 1, 2020 for a study of boron coordination structures (Boron coordination structure at the surfaces of sodium borosilicate and aluminoborosilicate glasses by B K-edge NEXAFS)"," at the surface of sodium borosilicate and aluminum borosilicate glass by B K edge NEXAFS," 120247 for detailed procedures. The primary measure of glass structure extracted from this analysis is the fraction of 4-fold coordinated boron relative to total boron. This parameter is called N ₄ =% B4/(% B3+% B4)

Fig. 8 summarizes the results of B K edge NEXAFS analysis comparing the polarized anode side surfaces after thermal polarization with the air fracture surface (representing the bulk glass structure) of examples 4-7. The results show that boron is predominantly converted to 3 coordination (N ₄.apprxeq.0) in the polarizing layer compared to the much higher N ₄ fraction (typically a mix of B3 and B4, i.e. N4> 0) in the parent glass. Without being bound by theory, this change is understood from the expectation of B ₂O₃-SiO₂ glass composition in the Na depletion layer, and therefore, no alkali metal is available for charge compensation of B in the 4-fold coordination state. This explanation assumes (and actually supports) that the depletion layer structure resynthesizes in situ at temperatures well below the Tg range of the parent glass, forming a unique layer structure, and meeting the bonding requirements of the remaining network former in the depletion layer, as discussed in Smith et al, journal of the american society of ceramics, 2019.102 (6): page 3037-3062.

A series of alkali and alkaline earth borosilicate glasses were subjected to molecular modeling to compare their structure before and after polarization. The compositions studied are shown in table 3 and comprise Na borosilicate, K borosilicate, mg borosilicate and Ca borosilicate. The mole fraction ratio of B ₂O₃/SiO₂ remains unchanged (i.e., about 0.51) in all simulated compositions. In table 3, m=na, K, mg or Ca, as shown in fig. 9 and 10

TABLE 3 precursor composition of molecular modeling

SiO 2 (mole%)	B 2O3 (mole%)	B 2O3/SiO2 (ratio)	M 2 O or MO (mole%)
				66.28	33.72	0.51	0
64.98	33.06	0.51	1.96
				61.94	31.51	0.51	6.54
58.65	29.84	0.51	11.50
				54.78	27.87	0.51	17.36
50.21	25.55	0.51	24.24

Fig. 9 shows the fractions of 3-coordinate boron (black) and 4-coordinate boron (red) in a series of alkali and alkaline earth borosilicate compositions shown in table 3. As shown in fig. 9, after thermal polarization, it can be observed that the coordination number of boron changes from the 4-coordination state to the 3-coordination state. FIG. 9 also shows that the conversion ratio of B4 to B3 increases with increasing network modifier content, because the fraction of B4 increases with increasing concentration.

Referring to fig. 10, molecular dynamics simulation shows that changes in coordination state also result in changes in young's modulus. Fig. 10 depicts young's modulus of molten ternary, molten binary, and binary sodium borosilicate obtained by thermal polarization, with different compositions. As shown, the young's modulus of the alkali depleted surface layer is typically lower than that of the host.

The results of the molecular simulation help to further determine/verify the broad applicability of thermal polarization, i.e., starting from a parent glass (e.g., the glasses disclosed herein) having a variety of different modifier species, an article with altered layers is produced.

While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the drawings and description are to be considered illustrative and not restrictive. It should be understood that only the preferred embodiment has been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.

Claims (26)

1. A glass substrate, comprising:

an alkali metal-containing body, and

The alkali metal is depleted of the surface layer,

Wherein the alkali metal depleted surface layer is amorphous and comprises a substantially uniform composition, and

Wherein the alkali metal-containing body and the alkali metal-depleted surface layer comprise B ₂O₃ and SiO ₂.

2. The glass substrate of claim 1, wherein the alkali-depleted surface layer comprises about 0.5 atomic percent or less alkali.

3. The glass substrate of claim 1 or claim 2, wherein the alkali-depleted surface layer comprises an atomic structure comprising boron in a substantially 3-coordinated state.

4. The glass substrate of claim 3, wherein greater than about 60% of the total amount of boron in the alkali metal depleted surface layer is in a 3-coordinate state on a fraction basis.

5. The glass substrate of claim 3, wherein greater than about 70% of the total amount of boron in the alkali metal depleted surface layer is in a 3-coordinate state on a fraction basis.

6. The glass substrate of claim 3, wherein greater than about 75% of the total amount of boron in the alkali metal depleted surface layer is in a 3-coordinate state on a fraction basis.

7. The glass substrate according to any one of claims 1 to 6, wherein the alkali metal-containing body comprises an atomic structure comprising boron in a 3-coordinated state and boron in a 4-coordinated state.

8. The glass substrate of claim 7, wherein greater than about 51% of the total amount of boron in the alkali-containing body is in a 4-coordinate state on a fraction basis.

9. The glass substrate of any of claims 1 to 8, wherein the alkali depleted surface layer is substantially free of non-bridging oxygen.

10. The glass substrate of claim 9, wherein the alkali-containing body comprises non-bridging oxygen and bridging oxygen.

11. The glass substrate of claim 10, wherein the alkali-containing body is substantially free of non-bridging oxygen.

12. The glass substrate of any of claims 1 to 11, wherein the alkali-containing body comprises an alkali oxide selected from Li ₂O、Na₂O、K₂O、Rb₂ O and Cs ₂ O.

13. The glass substrate of claim 12, wherein the alkali-containing body comprises at least 1 mole percent Na ₂O、K₂ O or Li ₂ O.

14. The glass substrate of claim 12, wherein the alkali-containing body comprises at least 1 mol% Na ₂ O.

15. The glass substrate of any of claims 1 to 14, wherein the alkali depleted surface layer comprises B ₂O₃ in a range of about 10 mol% to about 90 mol%.

16. The glass substrate of any of claims 1 to 15, wherein the alkali-depleted surface layer comprises a binary B ₂O₃-SiO₂ composition.

17. The glass substrate according to any one of claims 1 to 16, wherein the atomic% of silicon is greater than the atomic% of boron.

18. A glass substrate, comprising:

A substrate thickness;

An alkali metal-containing body having a bulk refractive index, and

An alkali metal depleted surface layer comprising a layer thickness in the range of about 10nm to about 3000nm,

Wherein the alkali metal depleted surface layer comprises a layer refractive index less than the bulk refractive index,

Wherein the alkali metal-containing body and the alkali metal-depleted surface layer comprise B ₂O₃ and SiO ₂.

19. The glass substrate of claim 18, wherein the atomic percent of silicon is greater than the atomic percent of boron.

20. A method of forming a glass substrate having a modified surface layer, comprising:

Providing a glass substrate comprising a concentration of an alkali metal, a glass transition temperature (Tg) and a surface layer, the glass substrate comprising B ₂O₃ and SiO ₂, and

Reducing the concentration of alkali metal in the surface layer,

Wherein the surface layer having a reduced alkali metal concentration comprises a substantially uniform composition.

21. The method of claim 20, wherein the atomic percent of silicon is greater than the atomic percent of boron.

22. The method of claim 20 or claim 21, wherein reducing the concentration of alkali metal in the surface layer comprises contacting a surface of the glass substrate with an electrode, and thermally polarizing the glass substrate.

23. The method of claim 22, wherein the electrode comprises an anode in contact with an anode surface of the glass substrate and a cathode in contact with a cathode surface of the glass substrate, and wherein thermally polarizing comprises applying a voltage to the glass substrate such that the anode is positively biased relative to the glass substrate to cause alkali depletion at the anode surface of the glass.

24. The method of claim 22, wherein thermally polarizing comprises heating the glass substrate and the electrode to a temperature below Tg prior to applying a voltage to the glass substrate.

25. The method of claim 22, wherein thermally polarizing comprises applying a voltage in a range of about 100 volts to about 10,000 volts to the glass substrate for a duration in a range of about 1 minute to about 6 hours.

26. The method of claim 22, wherein the glass substrate is thermally polarized under vacuum in an inert gas environment or a permeable gas environment.