Salt bath system for strengthening glass articles and method for regenerating molten salt

Abstract

Embodiments of the present disclosure relate to a salt bath system for strengthening glass articles, comprising: a salt bath tank defining a first interior volume enclosed by at least one sidewall; a salt bath composition in the first interior volume comprising an alkali metal salt; a retention device defining a second interior volume enclosed by at least one sidewall and comprising a regeneration medium in the second interior volume; and a circulation device positioned adjacent to an inlet of the retention device, wherein the circulation device is operable to circulate the salt bath composition through the retention device. Methods for regenerating molten salt are also disclosed.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 078,488, filed September 15, 2020, pursuant to 35 USC §119, the contents of which are incorporated herein by reference in their entirety. background Technical Field

[0004] This disclosure relates to systems and methods for chemically strengthening glass articles, and more particularly, to salt bath systems for strengthening glass articles and methods for regenerating molten salt. Background Technology

[0006] Tempered or hardened glass can be used in a variety of applications. For example, due to its physical durability and shatter resistance, hardened glass products can be used in consumer electronics devices, such as smartphones and tablets, as well as pharmaceutical packaging. To improve the efficiency of the hardening process, conventional hardening processes, such as conventional ion exchange processes, often involve immersing multiple glass products in a single salt bath in batches. However, as hardened glass products are continuously produced in batches within the same salt bath, the ion exchange process naturally leads to a decrease in the effectiveness of the salt bath. While various methods can be employed to reduce and / or prevent this decrease in salt bath effectiveness, these methods can also introduce various complications into the ion exchange process.

[0007] Therefore, there is a need for alternative salt bath systems for strengthening glass products and alternative methods for regenerating molten salt. Summary of the Invention

[0008] According to a first aspect of this disclosure, a salt bath system for strengthening glass articles may include: a salt bath tank defining a first internal volume enclosed by at least one sidewall; a salt bath composition comprising an alkali metal salt located in the first internal volume; a retention device located in the first internal volume, wherein the retention device defines a second internal volume enclosed by at least one sidewall and includes a regeneration medium located in the second internal volume; and a circulation device positioned adjacent to the inlet of the retention device, wherein the circulation device is operable to circulate the salt bath composition through the retention device.

[0009] According to a second aspect of this disclosure, a salt bath system for strengthening glass articles may include: a salt bath tank defining a first internal volume enclosed by at least one sidewall; a salt bath composition comprising an alkali metal salt located in the first internal volume; a retention device located outside the first internal volume and fluidly connected to the first internal volume, wherein the retention device defines a second internal volume enclosed by at least one sidewall and includes a regeneration medium located in the second internal volume; and a circulation device located in the first internal volume and adjacent to the inlet of the retention device, wherein the circulation device is operable to circulate molten salt bath through the retention device.

[0010] The third aspect of this disclosure may include the second aspect, wherein the temperature of the second internal volume is 3°C or more lower than the temperature of the first internal volume.

[0011] The fourth aspect of this disclosure may include any one of the first to third aspects, wherein the regeneration medium comprises silica aggregates, alkali metal phosphates, porous metal oxides, or combinations thereof.

[0012] The fifth aspect of this disclosure may include any one of the first to fourth aspects, wherein the average particle size of the regeneration medium is from 5 μm to 5,000 μm.

[0013] The sixth aspect of this disclosure may include any one of the first to fifth aspects, wherein 90% or more of the regenerated media have an average particle size greater than 5 μm.

[0014] The seventh aspect of this disclosure may include any one of the first to sixth aspects, wherein the regeneration medium includes particles, rings, saddles, spheres, engineered monoliths, honeycombs, fibers, felts, active layers coated on or impregnated in an inert carrier, or combinations thereof.

[0015] The eighth aspect of this disclosure may include any one of the first to seventh aspects, wherein the salt bath composition located in the first internal volume is substantially free of recycled materials.

[0016] The ninth aspect of this disclosure may include any one of the first to eighth aspects, wherein the circulation device includes an impeller, a pump, an air injection system, or a combination thereof.

[0017] The tenth aspect of this disclosure may include any one of the first to ninth aspects, wherein the circulation device is operable to circulate the salt bath composition through the retention device at a rate of 0.001 vol / hr to 10 vol / hr.

[0018] The 11th aspect of this disclosure may include any one of the 1 to 10 aspects, wherein the inlet of the retention device is enclosed by a sieve containing an opening, the effective diameter of which is less than or equal to 15% of the average particle size of the regeneration medium; the outlet of the retention device is enclosed by a sieve containing an opening, the effective diameter of which is less than or equal to 15% of the average particle size of the regeneration medium; or both the inlet and outlet of the retention device are enclosed by sieves containing openings, the effective diameter of which is less than or equal to 15% of the average particle size of the regeneration medium.

[0019] The 12th aspect of this disclosure may include any one of the 1 to 11 aspects, wherein the second internal volume includes a first regeneration region and a second regeneration region located downstream of the first regeneration region.

[0020] The 13th aspect of this disclosure may include the 12th aspect, wherein the first regeneration region includes a first regeneration medium; and the second regeneration region includes a second regeneration medium, the second regeneration medium being different from the first regeneration medium.

[0021] The 14th aspect of this disclosure may include the 13th aspect, wherein the retention device includes a sieve located between a first regeneration zone and a second regeneration zone, wherein the sieve includes an opening with a diameter smaller than the average particle size of at least one of the first regeneration medium and the second regeneration medium.

[0022] According to a 15th aspect of this disclosure, a method for regenerating molten salt may include: circulating molten salt through a retention device located in a first internal volume of a salt bath, the molten salt including one or more impurities formed during an ion exchange process, and the retention device including a regeneration medium located in a second internal volume defined by the retention device; and contacting the molten salt with the regeneration medium in the retention device, wherein the contact reduces the concentration of one or more impurities in the molten salt.

[0023] According to a 16th aspect of this disclosure, a method for regenerating molten salt may include: circulating molten salt through a retention device located outside a first internal volume defined by a salt bath, the molten salt including one or more impurities formed during an ion exchange process, and the retention device including a regeneration medium located in a second internal volume defined by the retention device; and contacting the molten salt with the regeneration medium in the retention device, wherein the contact reduces the concentration of one or more impurities in the molten salt.

[0024] The 17th aspect of this disclosure may include the 16th aspect, wherein the temperature of the second internal volume is 3°C or more lower than the temperature of the first internal volume.

[0025] The 18th aspect of this disclosure may include any one of aspects 15 to 17, wherein the one or more impurities include: lithium nitrate, alkali metal nitrite, alkali metal oxide, alkaline earth metal nitrite, alkaline earth metal oxide, or a combination thereof.

[0026] The 19th aspect of this disclosure may include any one of aspects 15 to 18, wherein the regeneration medium comprises silicic acid, alkali metal phosphate, alkali metal carbonate, porous metal oxide, or a combination thereof.

[0027] The 20th aspect of this disclosure may include any one of aspects 15 to 19, wherein the average particle size of the regeneration medium is from 5 μm to 5,000 μm.

[0028] The 21st aspect of this disclosure includes any one of aspects 15 to 20, wherein 90% or more of the regenerated media have an average particle size greater than 5 μm.

[0029] The 22nd aspect of this disclosure may include any one of aspects 15 to 21, wherein the regeneration medium includes particles, rings, saddles, spheres, engineered monoliths, honeycombs, fibers, felts, active layers coated on or impregnated in an inert carrier, or combinations thereof.

[0030] The 23rd aspect of this disclosure may include any one of aspects 15 to 22, wherein the salt bath composition located in the first internal volume is substantially free of recycled materials.

[0031] The 24th aspect of this disclosure may include any one of aspects 15 to 23, wherein the molten salt is circulated through the retention device at a rate of 0.001 vol / hr to 10 vol / hr.

[0032] The 25th aspect of this disclosure may include any one of aspects 15 to 24, further comprising: heating a salt bath composition comprising an alkali metal salt to an ion exchange temperature to form a molten salt; and immersing a glass article in the molten salt to allow ion exchange to occur between the molten salt and the glass article, wherein the ion exchange between the molten salt and the glass article forms the one or more impurities in the molten salt.

[0033] It should be understood that the foregoing general description and the following detailed description both depict various embodiments and are intended to provide an overall assessment or framework for understanding the nature and characteristics of the claimed subject matter. The included drawings provide a further understanding of the various embodiments and are incorporated in and form a part of this specification. The drawings illustrate the various embodiments described herein and, together with the description, serve to explain the principles and operation of the claimed subject matter. Attached Figure Description

[0034] The following detailed description of the embodiments of this disclosure can be better understood when read in conjunction with the accompanying drawings, in which:

[0035] Figure 1A A portion of the ion exchange process is schematically depicted based on one or more embodiments shown and described herein;

[0036] Figure 1B A portion of the ion exchange process is schematically depicted based on one or more embodiments shown and described herein;

[0037] Figure 2A A portion of the ion exchange process is schematically depicted based on one or more embodiments shown and described herein;

[0038] Figure 2B A portion of the ion exchange process is schematically depicted based on one or more embodiments shown and described herein;

[0039] Figure 3A A portion of the ion exchange process is schematically depicted based on one or more embodiments shown and described herein;

[0040] Figure 3B A portion of the ion exchange process is schematically depicted based on one or more embodiments shown and described herein;

[0041] Figure 4A A general flow diagram of a salt bath system for strengthening glass articles is schematically depicted according to one or more embodiments shown and described herein.

[0042] Figure 4B A general flow diagram of a salt bath system for strengthening glass articles is schematically depicted according to one or more embodiments shown and described herein.

[0043] Figure 4C Based on one or more embodiments shown and described herein, a schematic depiction is provided. Figure 4B and 4C The retention device shown is for a salt bath system used to strengthen glass products;

[0044] Figure 5A According to one or more embodiments shown and described herein, the figure illustrates how the volume (mL; y-axis) of the surface hydrolysis-resistant titrant varies with time (day; x-axis) for salt bath systems that use various amounts of regenerated media to strengthen glass articles;

[0045] Figure 5BAccording to one or more embodiments shown and described herein, the illustration shows how the volume (mL; y-axis) of the surface hydrolysis resistant titrant varies with the number of glass articles being strengthened (vials per kilogram of alkali metal salt; x-axis) for salt bath systems that use various amounts of regenerative media to strengthen glass articles.

[0046] Figure 6A According to one or more embodiments shown and described herein, the variations of surface compressive stress (MPa; left y-axis) and compression depth (μm; right y-axis) over time (day; x-axis) are illustrated for a salt bath system used for strengthening glass articles; and

[0047] Figure 6B According to one or more embodiments shown and described herein, the surface compressive stress (MPa; left y-axis) and compression depth (μm; right y-axis) vary with the number of glass articles being strengthened (vials per kilogram of alkali metal salt; x-axis) for a salt bath system used to strengthen glass articles.

[0048] When description Figures 4A-4C The simplified schematic diagram does not include various valves, temperature sensors, electronic controllers, etc., that may be used and are well known to those skilled in the art. However, those skilled in the art will understand that these components are within the scope of this disclosure.

[0049] in addition, Figures 4A-4C In simplified diagrams, arrows indicate the transfer or flow of material. However, arrows can also refer to transfer lines, such as pipes, that transfer material between two or more system components. Arrows connected to one or more system components indicate inlets or outlets within a given system component, while arrows connected to only one system component indicate system outlets leaving or entering the system. The direction of the arrow generally corresponds to the primary direction of material movement or the direction of material movement contained within the physical transfer line indicated by the arrow.

[0050] Figures 4A-4C Arrows in a simplified diagram can also indicate process steps that transport material from one system component to another. For example, an arrow pointing from a first system component to a second system component can indicate that material is “transferred” from the first system component to the second system component. This can include material “leaving” or “removing” from the first system component and material “introducing” into the second system component.

[0051] The various embodiments of this disclosure will now be described in detail, some of which are illustrated in the accompanying drawings. Detailed Implementation

[0052] The embodiments described herein relate to a salt bath system for strengthening glass articles and a method for regenerating molten salt. According to this disclosure, a salt bath system for strengthening glass articles generally includes a salt bath tank defining a first internal volume enclosed by at least one sidewall; a salt bath composition located within the first internal volume; a retention device located within the first internal volume; and a circulation device positioned adjacent to the inlet of the retention device. The salt bath composition may contain an alkali metal salt. The retention device may define a second internal volume enclosed by at least one sidewall and may include a regeneration medium located within the second internal volume. The circulation device is operable to circulate the salt bath composition through the retention device. According to this disclosure, a method for regenerating molten salt generally includes: circulating molten salt through the retention device located within the first internal volume of the salt bath tank; and contacting the molten salt with the regeneration medium in the retention device. The molten salt may include one or more impurities formed during an ion exchange process. The retention device may include a regeneration medium located within a second internal retention volume defined by the retention device. The contact may reduce the concentration of the one or more impurities in the molten salt bath. Various embodiments of the systems and methods of this disclosure will be described herein with specific reference to the accompanying drawings.

[0053] The directional terms used in this article, such as up, down, left, right, front, back, top, and bottom, are only for reference to the accompanying drawings and are not intended to imply absolute orientation.

[0054] As used herein, the indefinite articles “a” and “an” when referring to elements of this disclosure mean that at least one of these elements is present. While these indefinite articles are conventionally used to indicate that the noun they modify is singular, in this disclosure, the indefinite articles “a” and “an” also include plural forms, unless otherwise stated. Similarly, as used herein, the definite article “the” also indicates that the noun modified in this disclosure can be singular or plural, unless otherwise stated.

[0055] As used herein, the term "or" is inclusive and specific, and the term "A or B" means "A, B, or A and B". Alternatively, the term "or" may be used in an exclusive sense only when expressly specified in this disclosure, for example, the terms "either of A or B" or "one of A or B".

[0056] Unless otherwise specified, the terms “salt bath composition,” “salt bath,” “molten salt,” etc., as used herein are equivalent terms and refer to a solution or medium used to achieve an ion exchange process with glass (or glass-ceramic) articles, in which cations on the surface of the glass article are replaced or exchanged with cations present in the salt bath. It should be understood that the salt bath may include at least one alkali metal salt, such as potassium nitrate (KNO3) and / or sodium nitrate (NaNO3), which can be liquefied by heat or otherwise heated to a substantially liquid phase.

[0057] As used herein, the term "chemical durability" refers to the ability of a glass composition to resist degradation after exposure to specified chemical conditions. Specifically, the chemical durability of glass articles described herein is based on USP... <660> The “Surface Glass Test” (2017) in “Containers–Glass” is evaluated in water.

[0058] It should be understood that a material stream can be named according to its components, and the components used to name the material stream can be the main components of the material stream (e.g., 50 wt.% to 100 wt.%, 70 wt.% to 100 wt.%, 90 wt.% to 100 wt.%, 95 wt.% to 100 wt.%, 99 wt.% to 100 wt.%, 99.5 wt.% to 100 wt.%, or 99.9 wt.% to 100 wt.%). For example, a salt bath composition stream from a salt bath tank to a retention device can contain 50 wt.% to 100 wt.% of the salt bath composition, and therefore, the material stream can also be named "salt bath composition". It should also be understood that when a material flow containing a component is disclosed as being transferred from one system component to another, that component is also disclosed as being transferred from that system component to the other system component. For example, a disclosed salt bath composition flow from a first system component to a second system component should be understood as equivalently disclosing a salt bath composition being transferred from the first system component to the second system component.

[0059] Unless otherwise expressly stated, no method described herein should be construed as requiring its steps to be performed in a specific order, or requiring any device to have a particular orientation. Therefore, if a method claim does not actually describe the order in which its steps are to be followed, or if any device does not actually describe the order or orientation of its components, or if the claims or description do not otherwise specifically state that the steps are limited to a specific order, or do not describe a specific order or orientation of the device components, then in no way should the order or orientation be inferred. This applies to any possible non-expressive basis of interpretation, including: logical questions concerning the arrangement of steps, operational flow, the order of components, or the orientation of components; questions of obvious meaning derived from grammatical organization or punctuation; and questions of the number or type of embodiments described in the description.

[0060] First refer to Figure 1A and 1B The diagram schematically depicts a conventional ion exchange process. The ion exchange process involves immersing a glass article 105 in a salt bath 100. The glass article 105 may contain relatively small cations 130, such as alkali metal cations, for example, Li. + and / or Na + Cations. Salt bath 100 may include molten salt 101 containing relatively large cations 120 (i.e., relative to cation 130 of the glass article). That is, the atomic radius of cation 120 may be larger than that of cation 130. Cation 120 may, for example, contain alkali metal cations, such as potassium (K). + Cations 120. When heated to the elevated temperature that produces molten salt 101, larger cations 120 may have dissociated from the salts (e.g., alkali metal nitrates) present in the salt bath 100. When the glass article 105 is immersed in the salt bath 100, cations 130 in the glass article 105 may diffuse from the glass article 105 into the molten salt 101. Now refer to Figure 1B Following this diffusion, cations 120 from molten salt 101 can replace cations 130 in glass article 105. This replacement of smaller cations in glass article 105 by larger cations from molten salt 101 generates surface compressive stress (CS) at the surface of glass article 105, which extends to the depth of compression (DOC), thereby increasing the mechanical strength of glass article 105 and improving its resistance to breakage.

[0061] Generally, multiple glass products can be batch-immersed in a single salt bath to improve the efficiency of the ion exchange process. However, as batch production of strengthened glass products continues in the same salt bath, the ion exchange process naturally leads to a decrease in the effectiveness of the salt bath. One reason for this decrease in effectiveness may be the formation of undesirable substances in the molten salt. Specifically, during the ion exchange process, alkali metal nitrates present in the salt bath can decompose into alkali metal nitrites and / or alkali metal oxides in the molten salt. For example, the following equation indicates the decomposition of alkali metal nitrates into alkali metal nitrites:

[0062] MNO3 ⇌ MNO2 + 1 / 2O2 [M: Group 1 metals of IUPAC]

[0063] Both alkali metal nitrates and alkali metal nitrites can be further decomposed into alkali metal oxides, as indicated by the following equation:

[0064] MNO2 ←→ M2O + NO x [M:IUPAC Group 1 Metals]

[0065] For example, in the presence of potassium nitrate (KNO3) in a salt bath, KNO3 decomposes into two main decomposition products at temperatures above approximately 400°C: potassium nitrite (KNO2) and potassium oxide (K2O). Other alkali metal nitrates, such as sodium nitrate and lithium nitrate, can decompose into their corresponding alkali metal nitrites and alkali metal oxides at temperatures even below those of KNO3 (i.e., less than or equal to 400°C).

[0066] The presence of alkali metal oxides (e.g., K₂O) in molten salts can degrade the properties of glass articles treated therein. Specifically, alkali metal oxides in molten salts can inappropriately etch the surface of the glass articles during ion exchange. This etching can damage the surface of the glass articles, potentially adversely affecting a variety of properties. For example, visible etching and surface damage can form on glass articles subjected to ion exchange in molten salts containing a K₂O concentration greater than or equal to 0.5 wt%. Even when glass articles undergo ion exchange in salt baths containing a K₂O concentration significantly less than 0.5 wt% (i.e., 0.05 wt% or even 0.005 wt%), the presence of K₂O can lead to a significant decrease in the mechanical strength of the glass articles.

[0067] Neutralizing the salt bath can reduce or prevent damage to the surface of glassware during ion exchange. That is, by reducing or eliminating the alkali metal oxides present in the salt bath, damage to the surface of glassware during ion exchange can be reduced or prevented. This can be achieved, at least in part, by including a regeneration medium, such as silicic acid, in the salt bath. As used herein, the term "silicic acid" can refer to silicic acids, such as orthosilicic acid (Si(OH)4), and the corresponding silicates, which are the conjugate bases of silicic acid. Silicic acids generally react with alkali metal oxides to form non-reactive products, as indicated by the following equation:

[0068] M₂O + SiO₂ → M₂SiO₃ [M: IUPAC Group 1 metal]

[0069] Silicic acid can also react with common contaminants in molten salts, such as calcium cations (Ca). 2+ ) and magnesium cations (Mg 2 + It can adhere to the surface of glass products and hinder the ion exchange process.

[0070] Another reason for this decline in salt bath effectiveness may be due to the "poisoning" of the molten salt by undesirable cations initially present in the glass. For example, while lithium-containing glass can offer several benefits, such as faster and more efficient ion exchange processes, a lithium cation concentration as low as 1% by weight in the molten salt bath (i.e., lithium cations exchanged from the glass and entering the salt bath during ion exchange) can reduce achievable surface compressive stress and depth of compression in the glass. Even when the lithium cation concentration in the molten salt is less than 1% by weight, lithium cations can still hinder the ion exchange process, and as the lithium cation concentration in the molten salt naturally increases during the ion exchange process, it can result in significantly different compressive stresses and depths of compression between batches of strengthened glass.

[0071] A salt bath that has been poisoned by an unwanted cation (e.g., lithium cation) can be regenerated by adding a regeneration medium (e.g., phosphate). For example, now refer to Figure 2A and 2B It depicts a salt bath 200 containing poisoned molten salt 202. The poisoned salt bath 202 contains lithium cations 230 and relatively large cations 220 (i.e., relative to the lithium cations 230 in glass articles), such as sodium and / or potassium cations. The poisoned molten salt 202 can be regenerated by adding phosphate 240. When introduced into the poisoned molten salt 202, phosphate 240 can dissociate to form cations and phosphate ions (PO4). -3The phosphate anions present in the poisoned molten bath 202 can react with lithium cations 230 and selectively precipitate them. This selective precipitation reaction produces insoluble lithium phosphates 250, such as lithium phosphate (Li3PO4), dilithium sodium phosphate (Li2NaPO4), and / or lithium disodium phosphate (LiNa2PO4), and generates regenerated molten salt 211 suitable for further ion exchange processes. In other words, the presence of phosphates provides favorable conditions for the removal of lithium cations from the salt bath by precipitation.

[0072] Specifically, the poisoned molten salt can be regenerated by "adding" phosphate to the salt bath (i.e., introducing phosphate between batches), such as... Figure 2A and 2B As shown, or phosphates may be present during the ion exchange process, such as Figure 3A and 3B As shown. For example, a glass article 305 containing lithium cation 330 can be immersed in a mixture containing phosphate 340 and a relatively large cation 320 (i.e., relative to the lithium cation 330 of the glass article), such as sodium and / or potassium cations. As the lithium cation 330 diffuses from the glass article 305, phosphate anions that have dissociated from the phosphate 340 can react with the dissolved lithium cation 230 and selectively precipitate the dissolved lithium cation 230 to produce insoluble lithium phosphate 350 and regenerated molten salt 311.

[0073] As shown above, various methods can be employed to reduce and / or prevent the decline in salt bath efficiency. However, while the introduction of regeneration media (such as silica and / or phosphate) can reduce and / or prevent the decline in salt bath efficiency caused by the ion exchange process, these regeneration media may also introduce new complications into the ion exchange process.

[0074] For example, when excessively large silica particles are introduced into a salt bath, the silica may fail to effectively neutralize the molten salt. Specifically, when the average size of the silica particles is too large, they may settle more rapidly to the bottom of the molten salt, potentially reducing the likelihood of interaction and reaction between the silica and alkali metal oxides. Large silica particles can also accumulate as sludge at the bottom of the salt bath over time, until the system needs to be shut down and the salt bath replaced. Conversely, when the average particle size of the silica particles is too small, they may adhere to the surface of glass products undergoing ion exchange in the molten salt bath. This adhesion can lead to defects, rendering the glass unsuitable for commercial use, or at least requiring additional processing, increasing production costs and reducing efficiency.

[0075] Similarly, adding phosphates to a salt bath can lead to the formation of insoluble sludge that must be removed from the salt bath and / or phosphate crystals that can adhere to glass particles. For example, while lithium cations preferably bind to phosphates relative to other alkali metal cations present in the salt bath, such as sodium and potassium cations, as the lithium cation concentration decreases, phosphates can begin to react with these other alkali metal cations to form alkali metal phosphates, which can associate to form phosphate crystals. Phosphate crystals can adhere to the surface of glass articles undergoing ion exchange in molten salt. The presence of phosphate crystals on the surface of glass articles can hinder the ion exchange process, reduce the compressive stress and depth of compression achieved, and, upon removal, can result in depressions and / or protrusions on the surface of the glass articles. Even with maximally reduced phosphate crystal formation, insoluble lithium phosphates will accumulate in the salt bath over time, necessitating periodic cessation of the process to remove sludge and restore the salt bath to its original composition.

[0076] This disclosure relates to a salt bath system for strengthening glass articles and a method for regenerating molten salt, which utilizes a regeneration medium (e.g., silica and / or phosphate) to effectively regenerate the molten salt while reducing or preventing undesirable effects associated with these regeneration media present in the molten salt.

[0077] Now for reference Figure 4A and 4B The diagram schematically depicts a salt bath system 400. The salt bath system 400 may include a salt bath tank 402. The salt bath tank 402 may define a first internal volume 404 enclosed by at least one sidewall 406, and a salt bath composition 408 may be placed in the first internal volume 404. The salt bath system 400 may also include a retention device 410 located within the first internal volume 404. The retention device 410 may define a second internal volume 412 enclosed by at least one sidewall 414. One or more regeneration media may be located in the second internal volume 412. The salt bath system may also include a circulation device 416 located adjacent to the inlet 418 of the retention device 410.

[0078] In embodiments, the salt bath composition 408 may comprise an alkali metal salt. For example, the salt bath composition 408 may comprise an alkali metal nitrate, such as potassium nitrate (KNO3), sodium nitrate (NaNO3), lithium nitrate (LiNO3), or a combination thereof. In embodiments, based on the total weight of the salt bath composition 408, the salt bath composition 408 may comprise more than 90 wt.% of the one or more alkali metal salts. For example, based on the total weight of the salt bath composition 408, the salt bath composition 408 may comprise 90 wt.% to 99.9 wt.%, 90 wt.% to 99 wt.%, 90 wt.% to 97 wt.%, 90 wt.% to 95 wt.%, 90 wt.% to 93 wt.%, 93 wt.% to 99.9 wt.%, 93 wt.% to 99.5 wt.%, 93 wt.% to 99 wt.%, 93 wt.% to 97 wt.%, etc. One or more alkali metal salts, ranging from 93 wt.% to 95 wt.%, 95 wt.% to 99.9 wt.%, 95 wt.% to 99.5 wt.%, 95 wt.% to 99 wt.%, 95 wt.% to 97 wt.%, 97 wt.% to 99.9 wt.%, 97 wt.% to 99.5 wt.%, 97 wt.% to 99 wt.%, 99 wt.% to 99.9 wt.%, 99 wt.% to 99.5 wt.%, or 99.5 wt.% to 99.9 wt.%.

[0079] In embodiments, the concentration of the alkali metal salt in the salt bath composition 408 can be balanced based on the composition of the glass article to ensure that the provided ion exchange process increases both the surface compressive stress at the glass article surface after the ion exchange process and the compression depth after the ion exchange process. For example, based on the total concentration of the salt bath composition 408, the salt bath composition 408 may contain a potassium nitrate concentration greater than the sodium nitrate concentration, or based on the total concentration of the salt bath composition 408, the salt bath composition 408 may contain a sodium nitrate concentration greater than the potassium nitrate concentration. A higher sodium nitrate concentration than potassium nitrate in the salt bath composition, combined with a longer residence time in the molten salt bath, can result in a deeper compression depth in the glass article.

[0080] In an embodiment, the salt bath composition 408 may optionally contain less than or equal to 1 wt.% lithium nitrate based on the total weight of the salt bath composition 408. For example, based on the total weight of the salt bath composition 100, the salt bath composition 408 may contain the following amounts of lithium nitrate: 0.01 wt.% to 1 wt.%, 0.01 wt.% to 0.8 wt.%, 0.01 wt.% to 0.6 wt.%, 0.01 wt.% to 0.3 wt.%, 0.01 wt.% to 0.2 wt.%, 0.01 wt.% to 0.1 wt.%, 0.1 wt.% to 1 wt.%, 0.1 wt.% to 0.8 wt.%, 0.1 wt.% to 0.6 wt.%. 0.1 wt.% to 0.3 wt.%, 0.1 wt.% to 0.2 wt.%, 0.2 wt.% to 1 wt.%, 0.2 wt.% to 0.8 wt.%, 0.2 wt.% to 0.6 wt.%, 0.2 wt.% to 0.3 wt.%, 0.3 wt.% to 1 wt.%, 0.3 wt.% to 0.8 wt.%, 0.3 wt.% to 0.6 wt.%, 0.6 wt.% to 1 wt.%, 0.6 wt.% to 0.8 wt.%, or 0.8 wt.% to 1 wt.%. When the concentration of lithium nitrate is too high (i.e., greater than 1 wt.%)—this is by including lithium nitrate in the salt bath composition and / or by diffusion from the glass article via lithium cations—the molten salt can be considered poisoned, which adversely affects the ion exchange process. Poisoned molten salts can reduce the compressive stress and depth of compression of glass products compared to those subjected to ion exchange processes in unpoisoned molten salts. Conversely, molten salt baths may be unsuitable for strengthening some products (e.g., glass-ceramic products) when the lithium nitrate concentration is too low (i.e., less than 0.01 wt.%). Specifically, excess lithium cations can act as nucleating agents, promoting the formation of one or more crystalline phases. These excess lithium cations can diffuse from the glass-ceramic product during the ion exchange process and can lead to a reduction in the amount of crystallization achieved and an increase in sodium-rich regions within the glass-ceramic product. Sodium-rich regions in glass-ceramic products can lead to corrosion and / or cracking.

[0081] The salt bath composition 408 can be used to achieve an ion exchange process, in which the metal cations of the glass article exchange with the alkali metal cations in the alkali metal salt of the salt bath composition 408. Once the salt bath composition 408 is placed in the first internal volume 404, the salt bath composition 408 can be heated to a temperature sufficient to produce molten salt (also known as the ion exchange temperature), thereby facilitating the ion exchange process. In an embodiment, the salt bath composition 408 can be heated to a temperature of 350°C to 500°C. For example, the salt bath composition can be heated to the following temperatures: 350°C to 475°C, 350°C to 450°C, 350°C to 425°C, 350°C to 400°C, 350°C to 375°C, 375°C to 500°C, 375°C to 475°C, 375°C to 450°C, 375°C to 425°C, 375°C to 400°C, 400°C to 500°C, 400°C to 475°C, 400°C to 450°C, 400°C to 425°C, 425°C to 500°C, 425°C to 475°C, 425°C to 450°C, 450°C to 500°C, 450°C to 475°C, or 475°C to 500°C. However, if the ion exchange temperature is too high, it may be difficult to adequately control the ion exchange process, and the degradation rate of alkali metal salts, for example, in salt bath composition 408, may increase.

[0082] Still referencing Figure 4A The salt bath system 400 may include a retention device 410 located within a first internal volume 404. The retention device 410 may define a second internal volume 412 enclosed by at least one sidewall 414. One or more regeneration media may be located within this second internal volume 412. The retention device 410 may allow contact between the salt bath composition 408 and the regeneration media, thereby reducing and / or preventing any reduction in the efficacy of the salt bath composition 408. Furthermore, since all and / or most of the regeneration media used in the salt bath system 400 are located within the retention device 410, any undesirable byproducts of the one or more regeneration media remain within the retention device 410.

[0083] As a result, complications associated with the use of the regeneration medium can be reduced and / or completely prevented, such as silica adhering to the glass surface and / or insoluble lithium phosphate sludge accumulating in the salt bath 402. The retention device 410 can then significantly extend the lifespan of the salt bath composition 408 and increase the overall yield of the strengthening process, which can significantly reduce operating costs. Moreover, since the regeneration medium remains separate from the salt bath composition 408, it can be removed, renewed, and / or replaced when consumed without replacing the salt bath composition 408. This further increases the efficiency of the salt bath system 400 compared to conventional salt bath systems that directly introduce the regeneration medium into the salt bath composition.

[0084] In some embodiments, the retention device 410 may comprise any container adapted to contact the molten salt (i.e., the salt bath composition 408 heated to a temperature of 350°C to 500°C) on its inner and outer surfaces. For example, in some embodiments, the retention device 410 may comprise portions of one or more SAE 304 stainless steel tubes of size 8 and gauge 10. In other embodiments (not shown), the retention device 410 may comprise one or more containers, such as baskets and / or bags made of stainless steel mesh, which allow the salt bath composition 408 to flow through the retention device 410 but prevent displacement of the regeneration medium.

[0085] As mentioned above, one or more regeneration media may be located in the second internal volume 412 of the retention device 410. As used herein, the term "regeneration media" refers to any material that enables the effective precipitation, filtration, binding, reduction of concentration, or removal from the molten salt bath of one or more materials (also referred to as impurities and / or contaminants) that are formed during the ion exchange process and / or are considered to adversely affect the glass article's ion exchange or are undesirable in the salt bath composition. For example, the regeneration media may include silicic acid, which, as described above, can react with and remove the decomposition products of alkali metal salts from the salt bath composition 408. Similarly, the regeneration media may include phosphates, which, as described above, can precipitate excess lithium cations from the salt bath composition 408. The regeneration media may also include alkali metal carbonates, such as potassium carbonate (K₂CO₃), which may be suitable for sodium washing (i.e., reducing sodium nitrate to an appropriate concentration); and filter media suitable for removing debris and contaminants from the salt bath composition 408.

[0086] The regeneration medium can be any form suitable for filling the retention device 410 while allowing the salt bath composition 408 to flow sufficiently through the retention device 410. For example, the regeneration medium includes granules, rings, saddles, spheres, engineered monoliths, honeycombs, fibers, felts, active layers coated on or impregnated in an inert carrier, or combinations thereof. As described in detail herein, one or more regeneration media can be contained in the retention device 410 via sidewalls 414 and one or more barriers disposed at the inlet and outlet of the retention device 410. The barriers can be one or more sieves that allow the salt bath composition 408 to flow through the retention device 410 so that the salt bath composition 408 contacts the regeneration medium, but prevent the regeneration medium from shifting from the retention device 410 and entering the first internal volume 404 of the salt bath tank 402.

[0087] In embodiments where the regeneration medium is granular, the average particle size of the granular regeneration medium can be from 5 μm to 5,000 μm. For example, in embodiments where the regeneration medium is granular, the average particle size of the granular regeneration medium can be 5 μm to 2,000 μm, 5 μm to 1,000 μm, 5 μm to 500 μm, 5 μm to 100 μm, 5 μm to 50 μm, 50 μm to 5,000 μm, 50 μm to 2,000 μm, 50 μm to 1,000 μm, 50 μm to 500 μm, or 50 μm to 100 μm. The particle sizes are 100 μm to 5,000 μm, 100 μm to 2,000 μm, 100 μm to 1,000 μm, 100 μm to 500 μm, 500 μm to 5,000 μm, 500 μm to 2,000 μm, 500 μm to 1,000 μm, 1,000 μm to 5,000 μm, 1,000 μm to 2,000 μm, or 2,000 μm to 5,000 μm. In embodiments, greater than or equal to 90% of the regeneration medium may have a particle size greater than 5 μm. For example, greater than or equal to 92%, 94%, 96%, 98%, 99%, or 99.5% of the regeneration medium may have a particle size greater than 5 μm. When the average particle size of the particulate regeneration medium is too small (i.e., less than 5 μm), the regeneration medium may be overcrowded, and the pressure drop across the retention device 410 may be too large for the efficient operation of the salt bath system 400. Conversely, when the average particle size of the particulate regeneration medium is larger (i.e., greater than 5 μm), some substances, such as insoluble lithium phosphate, can advantageously deposit on the surface of the larger particles. This reduces the amount of relatively small substances that can leave the retention device 410 and contaminate the salt bath composition 408.

[0088] In embodiments, the regeneration medium may comprise silica aggregates. As used herein, the term "silicone aggregate" may refer to a cluster or unit formed by aggregating silica nanoparticles into individual clumps. As described above, the silica aggregates can react with the decomposition products of the one or more alkali metal salts in the salt bath composition 408 to form non-reactive (e.g., non-etching or non-corroding surfaces of glass articles) silicates and water. Thus, the silica aggregates can reduce the concentration of decomposition products of the alkali metal salts in the salt bath composition 408 and neutralize the salt bath composition 408.

[0089] In embodiments, as measured by laser diffraction particle size analysis, the silica aggregates can have an average particle size of 5 μm to 400 μm. For example, as measured by laser diffraction particle size analysis, the silica aggregates can have the following average particle sizes: 5 μm to 350 μm, 5 μm to 300 μm, 5 μm to 250 μm, 5 μm to 200 μm, 5 μm to 50 μm, 50 μm to 400 μm, 50 μm to 350 μm, 50 μm to 300 μm, 50 μm to 250 μm, 50 μm to 400 μm, 50 μm to 350 μm, 50 μm to 250 μm, 50 μm to 30 ... The particle sizes range from 200 μm to 200 μm, 200 μm to 400 μm, 200 μm to 350 μm, 200 μm to 300 μm, 200 μm to 250 μm, 250 μm to 400 μm, 250 μm to 350 μm, 250 μm to 300 μm, 300 μm to 400 μm, 300 μm to 350 μm, or 350 μm to 400 μm. When the silica aggregates have a small average particle size (e.g., less than 5 μm), any silica aggregates that displace from the retention device 410 due to any circumstances may readily adhere to the surface of the glass article and cause defects, making the glass article unsuitable for commercial use.

[0090] In implementation methods, the specific surface area of ​​the silica aggregates can be greater than or equal to 200 m², as measured by the Brunauer–Emmett–Teller (BET) method. 2 / g. For example, the specific surface area of ​​silica aggregates can be 200m². 2 / g to 600m 2 / g、200m 2 / g to 550m 2 / g、200m 2 / g to 500m 2 / g、200m 2 / g to 450m 2 / g、200m 2 / g to 400m 2 / g、200m 2 / g to 350m 2 / g、200m 2 / g to 300m 2 / g、200m 2 / g to 250m 2 / g、250m 2 / g to 600m 2 / g、250m 2 / g to 550m 2 / g、250m 2 / g to 500m 2 / g、250m 2 / g to 450m2 / g、250m 2 / g to 400m 2 / g、250m 2 / g to 350m 2 / g、250m 2 / g to 300m 2 / g、300m 2 / g to 600m 2 / g、300m 2 / g to 550m 2 / g、300m 2 / g to 500m 2 / g、300m 2 / g to 450m 2 / g、300m 2 / g to 400m 2 / g、300m 2 / g to 350m 2 / g, 350m 2 / g to 600m 2 / g, 350m 2 / g to 550m 2 / g, 350m 2 / g to 500m 2 / g, 350m 2 / g to 450m 2 / g, 350m 2 / g to 400m 2 / g、400m 2 / g to 600m 2 / g、400m 2 / g to 550m 2 / g、400m 2 / g to 500m 2 / g、400m 2 / g to 450m 2 / g、450m 2 / g to 600m 2 / g、450m 2 / g to 550m 2 / g、450m 2 / g to 500m 2 / g、500m 2 / g to 600m 2 / g、500m 2 / g to 550m 2 / g or 550m 2 / g to 600m 2 / g. The specific surface area of ​​silica aggregates can be directly related to the reaction rate constant (k) between the silica aggregates and the decomposition products of alkali metal salts, as described herein. That is, the larger the specific surface area of ​​the silica aggregates, the greater their potential to react with the decomposition products present in the molten salt bath. This allows for better control of the properties of the salt bath composition 408 and increased chemical durability of glass products while using fewer silica aggregates.

[0091] In this embodiment, the regeneration medium may include a sufficient amount of silica aggregates to effectively neutralize the salt bath composition 408. The surface hydrolysis resistance (SHR) of glass articles that have undergone ion exchange in a molten salt bath is the most reliable indicator for determining the degree to which the salt bath composition 408 has been neutralized. The surface hydrolysis resistance of the glass articles can be determined via USP... <660> The surface glass test, detailed in the text, is used to measure the surface hydrolysis resistance of glass articles. When measuring the surface hydrolysis resistance of glass articles using this test, the glass vials or containers constituting the glass articles are filled with carbon dioxide-free water or purified water. The filled vials or containers are then subjected to autoclave circulation at approximately 121°C for approximately 1 hour. The resulting leachate in the vials or containers is then titrated to neutral with a weak hydrochloric acid (e.g., 0.01M HCl) in the presence of methyl red. The titrant volume per 100 mL of leachate is used to determine the surface hydrolysis resistance of the glass articles. Generally, a larger titrant volume corresponds to poorer chemical durability (i.e., the leachate contains more glass components released from the glass, thus requiring more titrant to compensate for the pH change due to the presence of glass components). Poorer chemical durability, in turn, generally corresponds to greater damage to the glass article surface and a higher concentration of alkali metal oxides in the salt bath used for ion exchange.

[0092] In strengthened glass articles, especially those intended for use as pharmaceutical packaging, low titrant volumes and / or high chemical durability are desirable. Generally, a titrant volume of less than 1.5 mL is desirable for Type I glass. However, as mentioned above, decomposition products (e.g., basic hydroxides or basic oxides) are present in the molten salt bath used for ion exchange, which can corrode and / or etch the surface of the glass article. This etching can lead to an increase in titrant volume, corresponding to reduced chemical durability. Typically, the titrant volume of strengthened glass articles will increase depending on the time spent undergoing ion exchange. That is, the longer the glass article is in contact with the molten salt bath, the larger the titrant volume. For example, glass articles undergoing approximately 3 hours of ion exchange may result in a titrant volume of approximately 0.9 mL, while glass articles undergoing approximately 10 hours of ion exchange may result in a titrant volume of approximately 1.1 mL. As a result, the chemical durability of tempered glass products undergoing ion exchange in neutralized molten salts can be improved compared to tempered glass products that undergo ion exchange in conventional molten salts (i.e., molten salts that have not been neutralized by silica aggregates, which therefore include basic hydroxides and / or basic oxides).

[0093] In embodiments, particularly in embodiments where a salt bath system is used to strengthen glass articles intended for use as pharmaceutical packaging, the regeneration medium may include 0.1 wt.% to 10 wt.% of silica aggregates, based on the total weight of the salt bath composition. For example, based on the total weight of the salt bath composition, the regeneration medium may contain silica aggregates in the following amounts: 0.1 wt.% to 7 wt.%, 0.1 wt.% to 5 wt.%, 0.1 wt.% to 3 wt.%, 0.1 wt.% to 1 wt.%, 0.1 wt.% to 0.5 wt.%, 0.5 wt.% to 10 wt.%, 0.5 wt.% to 7 wt.%, 0.5 wt.% to 5 wt.%, 0 0.5 wt.% to 3 wt.%, 0.5 wt.% to 1 wt.%, 1 wt.% to 10 wt.%, 1 wt.% to 7 wt.%, 1 wt.% to 5 wt.%, 1 wt.% to 3 wt.%, 3 wt.% to 10 wt.%, 3 wt.% to 7 wt.%, 3 wt.% to 5 wt.%, 5 wt.% to 10 wt.%, 5 wt.% to 7 wt.%, or 7 wt.% to 10 wt.%. When the regeneration medium comprises less silica aggregates (i.e., less than 0.1 wt.%), the entire amount of silica can react to non-reactive silicates and water before the molten salt can be effectively neutralized.

[0094] In embodiments, the regeneration medium may include one or more phosphates capable of precipitating excess lithium cations from the salt bath composition 408. In embodiments, the phosphate may include alkali metal phosphates, such as trisodium phosphate (Na3PO4), tripotassium phosphate (K3PO4), disodium hydrogen phosphate (Na2HPO4), dipotassium hydrogen phosphate (K2HPO4), and sodium tripolyphosphate (Na5P3O4). 10 Potassium tripolyphosphate (K5P3O) 10 The phosphate may be sodium dihydrogen pyrophosphate (Na₂H₂P₂O₇), tetrasodium pyrophosphate (Na₄P₂O₇), potassium pyrophosphate (K₄P₂O₇), sodium trimetaphosphate (Na₃P₃O₉), potassium trimetaphosphate (K₃P₃O₉), or combinations thereof. In embodiments, the phosphate may comprise anhydrous phosphate, such as anhydrous trisodium phosphate, which may contain 10 percent (10%) or less water and may have a chemical purity of at least 97% or greater. As described above, the phosphate may dissociate into cations (e.g., sodium and / or potassium cations) and phosphate anions, the phosphate anions selectively precipitating lithium cations to produce insoluble lithium phosphate and maintaining a suitable lithium nitrate concentration in the salt bath composition 408.

[0095] In embodiments, as measured by laser diffraction particle size analysis, the phosphate can have an average particle size of 5 μm to 400 μm. For example, as measured by laser diffraction particle size analysis, the phosphate can have the following average particle sizes: 5 μm to 350 μm, 5 μm to 300 μm, 5 μm to 250 μm, 5 μm to 200 μm, 5 μm to 50 μm, 50 μm to 400 μm, 50 μm to 350 μm, 50 μm to 300 μm, 50 μm to 250 μm, 50 μm to 250 μm, 50 μm to 350 μm, 50 μm to 300 μm, 50 μm to 250 μm, 50 μm to 3 ... The particle sizes are 200 μm to 200 μm, 200 μm to 400 μm, 200 μm to 350 μm, 200 μm to 300 μm, 200 μm to 250 μm, 250 μm to 400 μm, 250 μm to 350 μm, 250 μm to 300 μm, 300 μm to 400 μm, 300 μm to 350 μm, or 350 μm to 400 μm. When phosphates have a small average particle size (e.g., less than 5 μm), any phosphate that has migrated from the holding device due to any circumstances may easily adhere to the surface of the glass article and cause defects, making the glass article unsuitable for commercial use. Additionally, a larger average particle size (e.g., greater than or equal to 5 μm) can reduce the solubility of phosphates in the salt bath composition 408 at the ion exchange temperature, thereby reducing the amount of excess phosphate anions in the molten salt bath, which, as mentioned above, can form phosphate crystals on the surface of the glass article.

[0096] In an embodiment, the regeneration medium may contain an amount of phosphate based on the total weight of the salt bath composition, sufficient to effectively maintain the concentration of lithium nitrate in the salt bath composition at less than or equal to 1 wt.%. Based on the total weight of the salt bath composition, the regeneration medium may contain an amount of phosphate ranging from 0.1 wt.% to 10 wt.%. For example, based on the total weight of the salt bath composition, the regeneration medium may contain the following amounts of phosphate: 0.1 wt.% to 7 wt.%, 0.1 wt.% to 5 wt.%, 0.1 wt.% to 3 wt.%, 0.1 wt.% to 1 wt.%, 0.1 wt.% to 0.5 wt.%, 0.5 wt.% to 10 wt.%, 0.5 wt.% to 7 wt.%, 0.5 wt.% to 5 wt.%, 0.5 wt.% to 3 wt.%, 0.5 wt.% to 1 wt.%, 1 wt.% to 10 wt.%, 1 wt.% to 7 wt.%, 1 wt.% to 5 wt.%, 1 wt.% to 3 wt.%, 3 wt.% to 10 wt.%, 3 wt.% to 7 wt.%, 3 wt.% to 5 wt.%, 5 wt.% to 10 wt.%, or 7 wt.% to 10 wt.%. When the amount of phosphate contained in the regeneration medium is less than 0.1 wt.%, all or most of the phosphate anions dissociated from the phosphate may precipitate before the ion exchange process is complete, leading to an increase in the lithium cation concentration in the molten salt. Therefore, the amount of lithium nitrate in the salt bath composition 408 increases to more than 1 wt.%. In contrast, when the amount of phosphate contained in the regeneration medium is greater than 10 wt.%, the concentration of lithium nitrate in the salt bath composition 408 can be reduced to less than 0.01 wt.%, resulting in excessive diffusion of lithium cations from the glass product and an increase in sodium-rich areas within the glass product.

[0097] In embodiments, the regeneration medium may include one or more materials (also referred to as filter media) capable of filtering one or more contaminants from the salt bath composition 408. As used herein, the term "contaminant" refers to debris introduced into the salt bath composition 408 during normal operation of the salt bath system. That is, a contaminant is any material or compound in the salt bath composition that is generally considered undesirable and / or may adversely affect the ion exchange process. Contaminants may include dust / debris, broken glass shards, particles resulting from corrosion or wear of components of the salt bath system (e.g., the salt bath tank), nitrogen oxides, excess water, or combinations thereof. In embodiments, the filter media may include porous membranes and / or matrices, such as porous metal oxides, stainless steel powder briquettes or meshes, porous alumina filters, porous silica filters, or combinations thereof. The filter media may bind and / or retain contaminants while allowing the salt bath composition 408 to flow relatively freely, thereby effectively filtering all or part of the contaminants from the salt bath composition 408.

[0098] In an embodiment, as measured by a mercury porosimeter (MIP), the filter medium may have an average pore size of less than or equal to 20 μm. For example, as measured by MIP, the filter media may have the following pore sizes: 0.2μm to 20μm, 0.2μm to 16μm, 0.2μm to 12μm, 0.2μm to 8μm, 0.2μm to 4μm, 0.2μm to 2μm, 2μm to 20μm, 2μm to 20μm, 2μm to 16μm, 2μm to 12μm, 2μm to 8μm, 2μm to 4μm, 4μm to 20μm, 4μm to 16μm, 4μm to 12μm, 4μm to 8μm, 8μm to 20μm, 8μm to 16μm, 8μm to 12μm, 12μm to 20μm, 12μm to 16μm, or 16μm to 20μm. When the filter medium has a small average pore size (e.g., less than 0.2 μm), the pressure drop across the filter medium may be too large. In contrast, when the filter medium can have a large average pore size (e.g., greater than 20 μm), a large amount of contaminants may pass through the filter medium without being filtered out from the salt bath composition 408.

[0099] Now for reference Figure 4C The figure depicts an enlarged view of the retention device 410. (As shown) Figure 4C As shown, the retention device may include one or more "regeneration zones" located within the second internal volume 412, each regeneration zone containing one or more regeneration media. As used herein, the term "regeneration zone" refers to a portion of the internal volume that is at least partially separated from the rest of the internal volume by separators and / or barriers. For example, Figure 4C The retention device 410 shown includes a first regeneration zone 420, a second regeneration zone 422, and a third regeneration zone 424. Figure 4CThe retention device 410 shown includes sieves 426a-426d located between regeneration zones and enclosing the inlet 418 and outlet 428 of the retention device 410. Sieves 426a-426d allow the salt bath composition 408 to flow through the sieves while preventing the regeneration medium from moving through them. In one embodiment, sieves 426a-426d may include openings with an effective diameter less than or equal to 15% of the average particle size of the regeneration medium. In another embodiment, sieves 426a-426d may include openings with an effective diameter less than or equal to 10%, 5%, or 2.5% of the average particle size of the regeneration medium. In some embodiments, sieves 426a-426d may include a mesh with an average opening size smaller than the average particle size of the regeneration medium located in the second internal volume 412. Therefore, the one or more sieves may have a sieve number greater than or equal to 70. In some embodiments, the sieves may have sieve sizes of 70, 80, 100, 120, 140, 170, 200, 230, 270, 325, 400, 450, 500, or even 635, based on the American National Industrial Fabric Standard (ASTM-E11). In other embodiments, sieves 426a-426d may include porous filtration devices, such as sintered porous metal, ceramic, or glass, with an average opening size smaller than the average particle size of the regeneration medium located in the second internal volume 412.

[0100] In some embodiments, each regeneration zone may include a majority of one type of regeneration medium. For example, in one embodiment, a first regeneration zone 420 may contain more than 50 wt.% of phosphate, based on the total weight of the regeneration medium in the first regeneration zone 420; while a second regeneration zone 422 may contain more than 50 wt.% of silicate aggregates, based on the total weight of the regeneration medium in the second regeneration zone 422. In some embodiments, each regeneration zone may include only one type of regeneration medium. For example, a first regeneration zone 420 may contain more than 99 wt.% of phosphate, based on the total weight of the regeneration medium in the first regeneration zone 420. In other embodiments, each regeneration zone may be a blend and / or gradient of two or more regeneration media.

[0101] Refer again Figures 4A-4CBecause the regeneration medium is prevented from leaving the regeneration zone, the retention device 410 allows the salt bath composition 408 to be regenerated (e.g., to precipitate excess lithium cations from the salt bath composition 408 and / or to neutralize the salt bath composition 408), while also preventing unwanted regeneration byproducts from entering the first internal volume 404. Therefore, in embodiments, the portion of the salt bath composition 408 located in the first internal volume 404 and outside the second internal volume 410 may be substantially free of regeneration medium. As used herein, “substantially free” of a compound may mean that the mixture contains less than 0.1 wt.% of that compound. For example, a salt bath composition that may be substantially free of regeneration medium may contain amounts of regeneration medium of less than 0.1 wt.%, less than 0.08 wt.%, less than 0.06 wt.%, less than 0.04 wt.%, less than 0.02 wt.%, or less than 0.01 wt.%, based on the total weight of the salt bath composition 408.

[0102] Refer again Figure 4A The retaining device 410 may be located within the first internal volume 404. However, it should be understood that other embodiments are also considered and are feasible. For example, see reference... Figure 4B Alternatively or additionally, the salt bath system 400 may include a retention device 410 located outside the first internal volume 404. Positioning the retention device 410 outside the first internal volume 404 allows for the regeneration of the salt bath composition 408 at a temperature lower than the ion exchange temperature of the salt bath composition 408. Without being bound by any particular theory, it is believed that regenerating the salt bath composition 408 at a temperature lower than the ion exchange temperature of the salt bath composition 408 can improve the efficiency of the one or more regeneration media. For example, as described herein, phosphate anions that have dissociated from phosphate can selectively precipitate excess lithium cations to produce lithium phosphate. However, as the temperature of the salt bath composition 408 increases, the solubility and dissociation of lithium phosphate also increase, while the ability of phosphate anions to precipitate lithium cations decreases. Therefore, in embodiments where the retention device 410 is located outside the first internal volume 404, the efficiency of the one or more regeneration media can be maximized. However, it should be understood that the salt bath composition 408 should remain liquid (i.e., molten salt) throughout the regeneration process; otherwise, the salt bath system 400 may become inoperable because the salt bath composition 408 cannot flow through the retention device 410. In fact, even if the salt bath composition 408 remains a liquid with a significant viscosity, the increased efficiency of the one or more regeneration media may be offset by the reduced flow rate of the salt bath composition 408 through the retention device 410.

[0103] Still referencing Figures 4A-4C The salt bath system may include a circulation device 416 adjacent to the inlet 418 of the retention device 410. Although Figures 4A-4CThe inlet 418 of the retention device 410 shown is adjacent to the bottom of the salt bath tank 402, but it should be understood that in other embodiments, the inlet 418 of the retention device 410 may be adjacent to the top of the salt bath tank 402. The circulation device 416 is operable to circulate the salt bath composition 408 through the retention device 410. In operation, the circulation device is operable to introduce the salt bath composition 408 into the inlet 418, through a first regeneration zone 420, through a second regeneration zone 422 downstream of the first regeneration zone 420, through a third regeneration zone 422 downstream of the second regeneration zone 422, and out of the retention device 410 through the outlet 428. As used herein, the term "downstream" refers to the location of a component of the system relative to the direction in which material flows through the system. For example, if material flowing through the system encounters a first component before encountering a second component, the second component of the system may be considered "downstream" of the first component of the system. The circulation of the salt bath composition 408 through the retention device 410 is not subject to the control of the salt bath composition 408. It is believed that the circulation of the salt bath composition in the first internal volume 404 can improve the uniformity and availability of the desired material throughout the first internal volume 404, and thus improve the uniformity of the reinforced glass articles produced by the salt bath system 400.

[0104] The circulation device 416 may include any means suitable for circulating the salt bath composition 408 through the retention device 410. For example, the circulation device 416 may include a pump (e.g., an electromagnetic pump), an impeller, an aeration system (e.g., an oxygen bubbler), or a combination thereof. The circulation device 416 may be selected based on various factors, such as the composition of the salt bath composition 408, the location of the retention device 410 (e.g., within and / or outside the first internal volume 404 of the salt bath tank 402), and / or the location of the inlet 418 of the retention device 410 (e.g., an impeller may be more suitable when the inlet 418 of the retention device 410 is adjacent to the surface of the salt bath tank 402). In embodiments, the salt bath composition 408 may be circulated without the need for a mechanical agitator (e.g., a pump or impeller). For example, a localized area of ​​the salt bath composition 408 adjacent to the inlet 418 may be selectively heated, thermally inducing the circulation of the salt bath composition 408 by the buoyancy difference of the selectively heated portion of the salt bath. In embodiments, the retention device 410 may be directly connected to the circulation device 416. For example, in an embodiment where the one or more baskets and / or bags are made of stainless steel mesh, the retention device 410 may be directly connected to an impeller that causes the retention device 410 to rotate through a first internal volume 404 of the salt bath 402 and causes the salt bath composition 408 to circulate through the retention device 410.

[0105] In an embodiment, the salt bath composition 408 can be circulated through the retention device 410 at a rate sufficient to effectively regenerate the molten salt. Therefore, the salt bath composition 408 can be circulated through the retention device 410 at a rate of 0.001 vol / hr to 10 vol / hr. More simply, 0.1% to 2000% of the total volume of the salt bath composition 408 can be circulated through the retention device 410 per hour. In an embodiment, the salt bath composition 408 can be circulated through the retention device 410 at the following rates: 0.001 vol / hr to 1 vol / hr, 0.001 vol / hr to 0.1 vol / hr, 0.001 vol / hr to 0.01 vol / hr, 0.01 vol / hr to 10 vol / hr, 0.01 vol / hr to 1 vol / hr, 0.01 vol / hr to 0.1 vol / hr, 0.1 vol / hr to 10 vol / hr, 0.1 vol / hr to 1 vol / hr, or even 1 vol / hr to 10 vol / hr. When the flow rate of the salt bath composition 408 through the retention device 410 is too fast (i.e., greater than 10 vol / hr), the glass articles undergoing ion exchange in the molten salt may be disturbed, which can lead to glass breakage. Conversely, when the flow rate of the salt bath composition 408 through the retention device 410 is too slow (i.e., less than 0.001 vol / hr), the molten salt may not be regenerated fast enough to prevent a decline in the effectiveness of the salt bath.

[0106] In this implementation, the circulation device 416 may be positioned adjacent to the bottom of the salt bath 402. Without being bound by any particular theory, it is assumed that contaminants and / or regeneration media displaced from the retention device will generally have a greater density than the molten salt and will therefore settle to the bottom of the salt bath 402 over time. Therefore, when the circulation device 416 is positioned adjacent to the bottom of the salt bath 402, the portion of molten salt that is more likely to contain contaminants and loosened regeneration media will preferentially circulate through the retention device 410. This reduces the number of times the salt bath is exchanged through the retention device before the molten salt is regenerated.

[0107] As described above, the salt bath composition 408 of the salt bath system can be heated to the ion exchange temperature to form a molten salt, and one or more glass articles can be immersed in the molten salt bath to achieve ion exchange between the molten salt bath and the glass articles. Although, for example Figure 1A and 1BThe glass article 105 is shown to be completely submerged in the salt bath 100; however, it should be understood that in embodiments, only a portion of the glass article 105 may be in contact with the salt bath 100. The glass article 105 may be brought into contact with molten salt by immersion in the salt bath 100, or by spraying, dipping, or other similar means of bringing the glass article 105 into contact with the salt bath 100. The glass article 105 may be in contact with the salt bath 100 multiple times, including but not limited to immersing the glass article 105 in the salt bath 100.

[0108] Glass articles can be treated with molten salt for a sufficient time to establish surface compressive stress on the surface of the glass article, and this surface compressive stress extends to the depth of compression. In embodiments, the glass articles can be treated with a molten salt bath for approximately 20 minutes to approximately 20 hours. For example, the glass articles can be treated with a molten salt bath for the following durations: approximately 20 minutes to approximately 15 hours, approximately 20 minutes to approximately 10 hours, approximately 20 minutes to approximately 5 hours, approximately 20 minutes to approximately 1 hour, approximately 1 hour to approximately 20 hours, approximately 1 hour to approximately 15 hours, approximately 1 hour to approximately 10 hours, approximately 1 hour to approximately 5 hours, approximately 5 hours to approximately 20 hours, approximately 5 hours to approximately 15 hours, approximately 5 hours to approximately 10 hours, approximately 10 hours to approximately 20 hours, approximately 10 hours to approximately 15 hours, or approximately 15 hours to approximately 20 hours.

[0109] As the ion exchange process progresses, the salt bath composition 408 can be continuously regenerated, as described above. For example, as the ion exchange process progresses, the salt bath composition 408 can be circulated via a circulation device 416 through a retention device 410 located within and / or outside the first internal volume 404 of the salt bath tank 402. The circulation of the salt bath composition 408 through the retention device 410 may include one or more regeneration media within a defined internal volume, thereby removing one or more impurities formed during the ion exchange process from the salt bath composition 408. More simply, the circulation of the salt bath composition 408 through the retention device 410 contacts the salt bath composition 408 with the one or more regeneration media, which can reduce the concentration of one or more impurities formed during the ion exchange process and continuously regenerate the salt bath composition 408.

[0110] In this embodiment, after the ion exchange process, the glass article is removed from contact with the molten salt bath. The resulting glass article, having undergone ion exchange, may have compressive stress on its surface that extends to the depth of compression. This compressive stress and depth of compression increase the glass article's resistance to breakage after mechanical damage; therefore, the glass article can be a strengthened glass article after the ion exchange process.

[0111] Example

[0112] The following embodiments illustrate one or more features of this disclosure. It should be understood that these embodiments are not intended to limit the scope of this disclosure or the appended claims.

[0113] Example 1

[0114] In Example 1, the concept of this disclosure was evaluated on a 10 kg scale. A retention / circulation combination device was prepared comprising two wire baskets constructed of SAE 304 stainless steel, each basket containing 5 g of silica aggregate, the baskets being attached to a stainless steel impeller, which in turn was attached to an electric motor. The wire baskets were then lowered into 10 kg of molten salt composed of industrial-grade potassium nitrate (i.e., greater than 98.5 wt.% potassium nitrate) at a rate sufficient to induce convection through the wire baskets. Then, over a period of 29 days, 20 batches of glass vials, each comprising 45 Type I glass vials (as described in U.S. Patent No. 8,551,898), were subjected to an ion exchange process at 470°C for 5.5 hours in a molten salt bath. The wire baskets were removed from the molten salt before each ion exchange process and replaced after each ion exchange process. After the ion exchange process was completed, the vials were... <660> The Surface Glass Test, detailed in the text, measures the surface temperature and humidity (SHR) of each glass vial. The process is repeated in 10 batches over approximately 13 days, excluding silicate in the baskets. The results are plotted as a function of time and the number of glass vials per kilogram of molten salt, as illustrated in the graph. Figure 5A and 5B .

[0115] like Figure 5A and 5B As shown, when the mesh basket contained no silica, the expected titrant volume of the Type I glass (approximately 1.3 mL) was exceeded 7 days prior. That is, when the mesh basket contained no silica, each kilogram of molten salt could effectively strengthen fewer than 25 glass vials. Conversely, when a total of 10 grams of silica was contained, the expected titrant volume of the Type I glass was exceeded only after approximately 20 days. That is, when the mesh basket contained 10 grams of silica, each kilogram of molten salt could effectively strengthen nearly 70 glass vials. This indicates that a regeneration medium containing silica can effectively neutralize molten salt, even when the regeneration medium is confined to a single area of ​​the molten salt. In fact, the presence of silica nearly tripled the lifetime of the molten salt, which significantly increased the efficiency of the ion exchange process.

[0116] Example 2

[0117] In Example 2, the compressive stress and compression depth of the glass vials from Example 1, which underwent an ion exchange process in the presence of a total of 10 grams of silica, were measured. Specifically, the compressive stress and compression depth of each batch of glass vials were measured, and graphs were plotted as a function of time and as a function of the number of glass vials per kilogram of molten salt. The compressive stress was measured using a surface stress meter (FSM), a commercially available instrument, such as the FSM-6000 from Orihara Industrial Co., Ltd., Japan. The compression depth was measured at a wavelength of 596 nm using the same commercially available instrument. Figure 6A and 6B The results of Example 2 are illustrated.

[0118] like Figure 6A and 6B As shown, the compressive stress and depth of compression of the glass vials remained relatively constant over the 30 days of salt bath use, during which more than 85 vials underwent ion exchange. Although the depth of compression decreased slightly, the compressive stress reached after 25 days was almost identical to that reached on day 1. This further confirms that the regeneration medium containing silica can effectively neutralize molten salt, even when the regeneration medium is confined to a single area of ​​molten salt.

[0119] It should be noted that any two quantitative values ​​assigned to a property can constitute a range of that property, and all combinations of ranges formed by the quantitative values ​​of all statements of a given property are considered in this disclosure.

[0120] It should be noted that the appended claims use the term "wherein" as a conjunction. For the purpose of defining the art, it should be noted that this term is introduced into the claims as an open-ended conjunction to introduce a description of a series of features of the structure, and should be understood in a similar manner to the more commonly used open-ended introductory term "comprising".

[0121] The subject matter of this disclosure has been described in detail and specific aspects have been referenced. It should be noted that the various details of these aspects should not be construed as implying that such details are essential components of these aspects. Rather, the appended claims should be considered as the sole expression of the scope of this disclosure and the corresponding scope of the various embodiments described herein. Furthermore, it will be apparent that modifications and variations may be made without departing from the scope of the appended claims.

Claims

1. A salt bath system for strengthening glass articles, the salt bath system comprising: A salt bath tank that defines a first internal volume, the first internal volume being enclosed by at least one sidewall; A salt bath composition located in a first internal volume, the salt bath composition comprising an alkali metal salt; A retention device located in a first internal volume, wherein the retention device defines a second internal volume enclosed by at least one sidewall and includes a regeneration medium located in the second internal volume; and A circulation device located near the inlet of the retention device, wherein the circulation device is operable to circulate the salt bath composition through the retention device. The regeneration medium includes silica aggregates with an average particle size of 5 µm to 400 µm, alkali metal phosphates with an average particle size of 5 µm to 400 µm, alkali metal carbonates with an average particle size of 5 µm to 5000 µm, porous metal oxides with an average particle size of 5 µm to 5000 µm, or combinations thereof.

2. The salt bath system as described in claim 1, wherein, 90% or more of the regenerated media have a particle size greater than 5 µm.

3. The salt bath system as described in claim 1, wherein, Regeneration media include particles, rings, saddles, spheres, engineered monoliths, honeycombs, fibers, felts, active layers coated on or impregnated in an inert carrier, or combinations thereof.

4. The salt bath system as described in claim 1, wherein, The salt bath composition located in the first internal volume is essentially free of recycled materials.

5. The salt bath system as described in claim 1, wherein, The circulation device can be operated to circulate the salt bath composition through the retention device at a rate of 0.001 volume / hour to 10 volume / hour.

6. The salt bath system as claimed in claim 1, wherein: The inlet of the retention device is sealed by a sieve containing an opening, the effective diameter of which is less than or equal to 15% of the average particle size of the regeneration medium; or The outlet of the retention device is sealed by a screen containing an opening, the effective diameter of which is less than or equal to 15% of the average particle size of the regeneration medium; or Both the inlet and outlet of the retention device are enclosed by a screen containing openings, the effective diameter of which is less than or equal to 15% of the average particle size of the regeneration medium.

7. The salt bath system as claimed in claim 1, wherein, The second internal volume includes a first regeneration zone and a second regeneration zone located downstream of the first regeneration zone.

8. The salt bath system of claim 7, wherein: The first regeneration zone includes a first regeneration medium; and The second regeneration zone includes a second regeneration medium, which is different from the first regeneration medium.

9. The salt bath system as claimed in claim 8, wherein, The retention device includes a sieve located between a first regeneration zone and a second regeneration zone, wherein the sieve includes an opening with a diameter smaller than the average particle size of at least one of the first and second regeneration media.

10. A salt bath system for strengthening glass articles, the salt bath system comprising: A salt bath tank that defines a first internal volume, the first internal volume being enclosed by at least one sidewall; A salt bath composition located in a first internal volume, the salt bath composition comprising an alkali metal salt; A retention device, located outside and fluidly connected to a first internal volume, wherein the retention device defines a second internal volume enclosed by at least one sidewall and includes a regeneration medium located within the second internal volume; and A circulation device, located in the first internal volume and adjacent to the inlet of the retention device, is operable to circulate the molten salt bath through the retention device. The regeneration medium includes silica aggregates with an average particle size of 5 µm to 400 µm, alkali metal phosphates with an average particle size of 5 µm to 400 µm, alkali metal carbonates with an average particle size of 5 µm to 5000 µm, porous metal oxides with an average particle size of 5 µm to 5000 µm, or combinations thereof.

11. The salt bath system of claim 10, wherein, The temperature of the second internal volume is 3°C or more lower than the temperature of the first internal volume.

12. The salt bath system of claim 10, wherein, 90% or more of the regenerated media have a particle size greater than 5 µm.

13. The salt bath system of claim 10, wherein, Regeneration media include particles, rings, saddles, spheres, engineered monoliths, honeycombs, fibers, felts, active layers coated on or impregnated in an inert carrier, or combinations thereof.

14. The salt bath system of claim 10, wherein, The salt bath composition located in the first internal volume is essentially free of recycled materials.

15. The salt bath system of claim 10, wherein, The circulation device can be operated to circulate the salt bath composition through the retention device at a rate of 0.001 vol / hr to 10 vol / hr.

16. The salt bath system of claim 10, wherein: The inlet of the retention device is sealed by a sieve containing an opening, the effective diameter of which is less than or equal to 15% of the average particle size of the regeneration medium; or The outlet of the retention device is sealed by a screen containing an opening, the effective diameter of which is less than or equal to 15% of the average particle size of the regeneration medium; or Both the inlet and outlet of the retention device are enclosed by a screen containing openings, the effective diameter of which is less than or equal to 15% of the average particle size of the regeneration medium.

17. The salt bath system of claim 10, wherein, The second internal volume includes a first regeneration zone and a second regeneration zone located downstream of the first regeneration zone.

18. The salt bath system of claim 17, wherein: The first regeneration zone includes a first regeneration medium; and The second regeneration zone includes a second regeneration medium, which is different from the first regeneration medium.

19. The salt bath system of claim 18, wherein, The retention device includes a sieve located between a first regeneration zone and a second regeneration zone, wherein the sieve includes an opening with a diameter smaller than the average particle size of at least one of the first and second regeneration media.

20. A method for regenerating molten salt, the method comprising: Molten salt is circulated through a retention device located in a first internal volume of a salt bath, the molten salt including one or more impurities formed during the ion exchange process, and the retention device includes a regeneration medium located in a second internal volume defined by the retention device; and The molten salt is brought into contact with the regeneration medium in the retention device, wherein the contact reduces the concentration of one or more impurities in the molten salt. The regeneration medium includes silica aggregates with an average particle size of 5 µm to 400 µm, alkali metal phosphates with an average particle size of 5 µm to 400 µm, alkali metal carbonates with an average particle size of 5 µm to 5000 µm, porous metal oxides with an average particle size of 5 µm to 5000 µm, or combinations thereof.

21. The method of claim 20, wherein, The one or more impurities include: lithium nitrate, alkali metal nitrites, alkali metal oxides, alkaline earth metal nitrites, alkaline earth metal oxides, or combinations thereof.

22. The method of claim 20, wherein, 90% or more of the regenerated media have a particle size greater than 5 µm.

23. The method of claim 20, wherein, Regeneration media include particles, rings, saddles, spheres, engineered monoliths, honeycombs, fibers, felts, active layers coated on or impregnated in an inert carrier, or combinations thereof.

24. The method of claim 20, wherein, The salt bath composition located in the first internal volume is essentially free of recycled materials.

25. The method of claim 20, wherein, Molten salt is circulated through the retention device at a rate of 0.001 volume / hour to 10 volume / hour.

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