Patent Publication Number: US-11648549-B2

Title: Ion exchange systems and methods for ion exchanging glass articles

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application claims the benefit of priority under 35 U.S.C § 120 of U.S. Provisional Application Ser. No. 62/772,842 filed on Nov. 29, 2018, the content of which is relied upon and incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present disclosure generally relates to ion exchange systems and methods for ion exchanging glass articles and, more specifically, to ion exchange systems having a plurality of chambers. 
     BACKGROUND 
     Historically, glass has been used as a preferred material for many applications, including food and beverage packaging, pharmaceutical packaging, kitchen and laboratory glassware, and windows or other architectural features, because of its hermeticity, optical clarity and excellent chemical durability relative to other materials. 
     However, use of glass for many applications is limited by the mechanical performance of the glass. In particular, glass breakage is a concern, particularly in the packaging of food, beverages, and pharmaceuticals. Breakage can be costly in the food, beverage, and pharmaceutical packaging industries because, for example, breakage within a pharmaceutical filling line may require that neighboring unbroken containers be discarded as the containers may contain fragments from the broken container. Breakage may also require that the filling line be slowed or stopped, lowering production yields. Further, non-catastrophic breakage (i.e., when the glass cracks but does not break) may cause the contents of the glass package or container to lose their sterility which, in turn, may result in costly product recalls. 
     One root cause of glass breakage is the introduction of flaws in the surface of the glass as the glass is processed and/or during subsequent filling. These flaws may be introduced in the surface of the glass from a variety of sources including contact between adjacent pieces of glassware and contact between the glass and equipment, such as handling and/or filling equipment. Regardless of the source, the presence of these flaws may ultimately lead to glass breakage. 
     Ion exchange processing is a process used to strengthen glass articles. Ion exchange imparts a compression (i.e., compressive stress) onto the surface of a glass article by chemically replacing smaller ions within the glass article with larger ions from a molten salt bath. The compression on the surface of the glass article raises the mechanical stress threshold to propagate cracks; thereby, improving the overall strength of the glass article. Surface compression and depth of layer are dependent on the ion exchange processing time and temperature. The center tension evolves in the center of the glass thickness to counteract the surface compression. While time and temperature are increased to increase depth of layer, the surface compression decreases over time due to stress relaxation and due to force balance which reduces the strength of the glass article. The combination of the center tension, depth of layer and surface compression can all contribute to the functional performance of the parts. 
     Generally, a conventional ion exchange process is performed in an ion exchange bath that includes a large tank configured to contain as much as about 30 metric tons of molten salt. During the ion exchange process, solids may be introduced into the bath either as additives that remove impurities present in the bath, that control the bath chemistry (such as the pH of the bath), or that capture byproducts of the ion exchange process to extend the useful life of the salt in the bath. Such solids tend to settle to the bottom of the salt bath and may form regions of the molten salt having an increased concentration of solids. Additionally, the concentration of smaller ions in the ion exchange bath increases while the concentration of larger ions in the ion exchange bath decreases, eventually reaching a condition in which the concentration of larger ions is too low to maintain a high enough concentration in equilibrium with the glass surface, causing the surface compressive stress to fall below a target value. Prior to reaching such concentrations, it is conventional to drain the salt from the ion exchange bath and refill the entire bath with fresh salt. However, the concentration of solids at the bottom of the bath tends to slow the flow of salt, which reduces the ease with which salt may be removed from the bath. This in turn increases the amount of downtime required to refill the bath, which leads to increased costs associated with conventional ion exchange processing. 
     SUMMARY 
     According to embodiments of the present disclosure, an ion exchanging tank is provided. The ion exchange tank includes a processing chamber and an additive chamber separated by a weir system, the weir system having a flow channel between two partitions and fluidly connecting the processing chamber to the additive chamber, wherein the flow channel is divided from the additive chamber by a first partition and divided from the processing chamber by a second partition, i.e., the first partition separates the additive chamber from the flow channel and the second partition separates the flow channel from the processing chamber, wherein the additive chamber comprises a solids-absorbing material disposed therein. 
     According to embodiments of the present disclosure, a method for ion exchanging glass articles is provided. The method includes adding fresh salt and solid additives to an additive chamber of an ion exchange tank, applying heat to the additive chamber to form molten salt, flowing the molten salt out of the additive chamber, through a flow channel of a weir system of the ion exchange tank, and into a processing chamber of the ion exchange tank, and ion exchange processing at least one glass article in the processing chamber, wherein the additive chamber comprises a solids-absorbing material disposed therein. 
     Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be understood more clearly from the following description and from the accompanying figures, given purely by way of non-limiting example, in which: 
         FIG.  1    schematically illustrates an ion exchange tank in accordance with embodiments of the present disclosure; 
         FIG.  2    schematically illustrates an ion exchange tank in accordance with embodiments of the present disclosure; 
         FIG.  3    schematically illustrates an ion exchange tank in accordance with embodiments of the present disclosure; 
         FIG.  4    schematically illustrates a cross-sectional view of a cassette assembly in accordance with embodiments of the present disclosure; 
         FIG.  5    illustrates a robotic lift system with a rotation tool in accordance with embodiments of the present disclosure; 
         FIG.  6    schematically illustrates a cross-sectional view of an additive chamber of an ion exchange tank in accordance with embodiments of the present disclosure; and 
         FIG.  7    schematically illustrates a cross-sectional view of an additive chamber of an ion exchange tank in accordance with embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein, “have,” “having,” “include,” “including,” “comprise,” “comprising” or the like are used in their open ended sense, and generally mean “including, but not limited to.” 
     All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure. 
     The present disclosure is described below, at first generally, then in detail on the basis of several exemplary embodiments. The features shown in combination with one another in the individual exemplary embodiments do not all have to be realized. In particular, individual features may also be omitted or combined in some other way with other features shown of the same exemplary embodiment or else of other exemplary embodiments. 
     Embodiments of the present disclosure relate to an ion exchange tank having a processing chamber and an additive chamber separated by a weir system. The additive chamber includes a solids-absorbing material and at least one glass article is at least partially immersed in a salt bath within the processing chamber where an ion exchange process is performed. Embodiments of the present disclosure advantageously reduce the concentration of solid additives in the processing chamber where ion exchange processing is performed on glass articles. As such, as compared to tanks used in conventional ion exchange processing, ion exchange tanks as described herein facilitate faster draining and refilling of the processing chamber. Embodiments of the present disclosure also advantageously allow for ion exchange processing to be performed in the processing chamber at the same time that fresh salt is added to the additive chamber and that heat is applied to the additive chamber  106   b  melt the fresh salt to form molten salt. As compared to tanks used in conventional ion exchange processing where the fresh salt added to the tank must first be heated to form molten salt prior to beginning ion exchange processing, ion exchange tanks as described herein allow for the processing chamber to be filled with molten salt and for the ion exchange process to begin in the processing chamber once the filling of the chamber is complete. 
     As used herein, the term “conventional ion exchange process” refers to an ion exchange process in which smaller alkali metal ions in a glass article are exchanged for larger alkali metal ions to impart a compressive stress in the glass article, wherein the ion exchange process is carried out for a sequence of glass articles or a sequence of batches of pluralities of glass articles, in the same salt bath. 
     With reference to  FIG.  1   , a cross section of an ion exchange tank in accordance with embodiments of the present disclosure is shown. The ion exchange tank  100  includes a bottom  102  and sidewalls  104  which define an interior space  106  configured to hold a molten salt bath. The interior space  106  of the ion exchange tank includes a processing chamber  106   a  and an additive chamber  106   b  separated by a weir system  110 . As shown, the weir system  110  includes a first partition  112  extending from the top of the tank  100  toward the bottom  102  of the tank  100  and a second partition  114  extending from the bottom  102  of the tank  100  toward the top the tank  100 . A flow channel  116  is disposed between the first partition  112  and the second partition  114 . The first partition  112  divides the additive chamber  106   b  from the flow channel  116  and the second partition  114  divides the processing chamber  106   a  from the flow channel  116 . An opening  118  between the second partition  114  and the bottom of the first partition  112  fluidly connects the additive chamber  106   b  to the flow channel  116  of the weir system  110 . 
       FIG.  1    illustrates an ion exchange tank  100  including a second partition  114  of the weir system  110  having a height that is substantially similar to the height of the sidewalls  104  of the ion exchange tank  100 . However, it should be appreciated that the second partition  114  may have any height such as, for example, any height that is less than the height of the sidewalls  104  of the ion exchange tank  100 .  FIG.  2    illustrates an ion exchange tank  100  including a second partition  114  of the weir system  110  having a height that is less than the height of the sidewalls  104  of the ion exchange tank  100 . 
     The ion exchange tank  100  may further include an inlet  122  through which fresh salt and/or solid additives may be introduced into the additive chamber  106   b . The ion exchange tank  100  may further include a processing chamber outlet  120   a  through which molten salt may be removed from the processing chamber  106   a . The processing chamber outlet  120   a  may be fluidly connected to the processing chamber  106   a  via an opening disposed in the bottom  102  of the ion exchange tank  100  within the processing chamber  106   a . Alternatively, the opening may be disposed in a sidewall  104  of the ion exchange tank  100  within the processing chamber  106   a . Additionally, the system may also include an additive chamber outlet  120   b  through which the contents of the additive chamber  106   b , including solid additives, may be removed from the additive chamber  106   b . The additive chamber outlet  120   b  may be fluidly connected to the additive chamber  106   b  via an opening disposed in the bottom  102  of the ion exchange tank  100  within the additive chamber  106   b . Alternatively, the opening may be disposed in a sidewall  104  of the ion exchange  100  within the additive chamber  106   b.    
     As further shown in  FIG.  1   , the ion exchange tank  100  as described herein may include a plurality of heating apparatuses  130   a ,  130   b  configured to heat the salt bath to an ion exchange temperature, the ion exchange temperature generally being a temperature in which both the first and second metal salts are molten. The ion exchange temperature may be, for example but without limitation, between about 380° C. to about 570° C.; however, it will be appreciated by those skilled in the art that other temperatures may be used. According to embodiments of the present disclosure, first heating apparatus  130   a  may be positioned and configured to heat the processing chamber  106   a  and second heating apparatus  130   b  may be positioned and configured to heat the additive chamber  106   b . It is contemplated herein that each of the first heating apparatus  130   a  and second heating apparatus  130   b  may include a plurality of heating apparatuses. The first and second heating apparatuses  130   a ,  130   b  may have the same operating power or heating apparatus  130   a  may have a different operating power than heating apparatus  130   b . As one non-limiting example, the second heating apparatus  130   b  may heat the additive chamber  106   b  to a temperature at which molten salt is formed. In contrast, the first heating apparatus  130   a  maintain an ion exchange temperature in the processing chamber  106   a  where the ion exchange temperature is less than the temperature at which molten salt is formed. In such an example, because less energy would be required to maintain the ion exchange temperature, the first heating apparatus  130   a , as compared to the second heating apparatus  130   b , may be a smaller, less expensive apparatus having a lower operating power. This effectively reduces the overall costs of the ion exchange tank  100  and also leads to a reduction in ion exchange processing costs as compared to a conventional ion exchange process. 
     The ion exchange tank  100  may further include a solids-absorbing material  140  disposed within the additive chamber  106   b . The solids-absorbing material  140  selectively absorbs solids or reduces the concentration of the solids in the additive chamber  106   b . In particular, the solids-absorbing material  140  may selectively absorb the solid additives as a result of, for example, reaction of the solids-absorbing material  140  with the solid additives being thermodynamically and/or kinetically more favorable than reaction of the solids-absorbing material with the other salt ions in the additive chamber  106   b . The solids-absorbing material  140  may be disposed at or near the bottom of the additive chamber  106   b . As the contents of the additive chamber  106   b  move over the solids-absorbing material  140  and toward the flow channel  116  of the weir system  110 , solids are separated from the molten salt and prevented from traveling through the flow channel  116  and into the processing chamber  106   a . Optionally, at least a portion of the solids-absorbing material  140  may be disposed in the flow channel  116  of the weir system  110 . 
     As shown in  FIG.  1   , the solids-absorbing material  140  may be disposed at or near the bottom of the additive chamber  106   b .  FIG.  6    illustrates an alternative configuration of the additive chamber  106   b  where the solids-absorbing material  140  is positioned in the opening  118  between the bottom  102  of the ion exchange tank  100  and the first partition  112 . As shown in  FIG.  7   , the additive chamber  106   b  may further include a porous container  160  where the solids-absorbing material  140  is disposed in the porous container  160 . In operation, the contents of the additive chamber  106   b  may flow through the pores of the porous container  160  to contact the solids-absorbing material  140 . 
     Optionally, the ion exchange system may further include a stirring apparatus  150  disposed in the additive chamber  106   b  and configured to stir the contents of the additive chamber  106   b . The stirring apparatus  150  may advantageously aid in the formation of molten salt and reaction of the molten salt with the solid additives within the additive chamber. The stirring apparatus  150  may also reduce or eliminate stratification, or concentration non-uniformity, of the components of the contents of the additive chamber. 
       FIG.  1    further illustrates a glass article  302  that may be at least partially immersed in the salt bath within the tank  100 . For example, the glass article  302  may be a glass container and, as shown in  FIG.  1   , may be a plurality of glass containers. Merely for purposes of illustrating the ion exchange tank  100 , the glass containers are shown contained in a magazine apparatus  400  which will be described in more detail below. The glass article  302  includes a plurality of substrate metal ions which are alkali metal ions (e.g., Li + , Na + , K + ). The salt bath  304  includes a plurality of first metal cations (e.g., K + ) at a first metal ion concentration, and a plurality of second metal cations (e.g., Na + ) at a second metal ion concentration. The first metal cations and second metal cations may be introduced into the salt bath as first and second metal salts (e.g., KNO 3  and NaNO 3  respectively). 
     In operation of the ion exchange tank  100  described herein, fresh salt is introduced into the additive chamber  106   b  either through the inlet  122  or by being introduced through an opening at the top of the ion exchange tank  100 . Similarly, additives as described herein may also be added to the additive chamber either through the inlet  122  or by being introduced through an opening at the top of the ion exchange tank  100 . Heat is applied to the additive chamber  106   b  by heating apparatus  130   b  to melt the fresh salt and form molten salt. Optionally, a stirring apparatus  150  is operated to stir the contents of the additive chamber  106   b.    
     Due to hydrostatic pressure present in the additive chamber  106   b , molten salt is driven from the additive chamber  106   b , through opening  118  and along the flow channel  116  of the weir system  110 , over the top of the second partition  114  of the weir system  110  and into the processing chamber  106   a . In the processing chamber  106   a , an ion exchange process is performed in the molten salt bath with at least one glass article  302  in the processing chamber  106   b . Due to the solids-absorbing material  140  in the additive chamber  106   b , solid additives are retained in the additive chamber  106   b  and substantially all of the solid additive is prevented from passing through opening  118  and along the flow channel  116  of the weir system  110 , over the top of the second partition  114  of the weir system  110  and into the processing chamber  106   a.    
     Generally during ion exchange processing, a glass article  302  is placed in the processing chamber  106   a  of the ion exchange tank at an ion exchange temperature, for a predetermined period of time, for example, in the range of about 1 hour to about 10 hours. The entire glass article  302 , or only a portion of the glass article  302 , may be immersed in the molten salt during the ion exchange process. Optionally, a single glass article  302  may be immersed in the molten salt during the ion exchange process, or a plurality of glass articles  302  may be immersed in the molten salt at the same time. Where a plurality of glass articles  302  are processed, the plurality of glass articles  302  may be subdivided into smaller groups, “runs,” or lots, which undergo ion exchange in the molten salt in succession. 
     Glass articles  302  as described herein may be formed from alkali aluminosilicate glass compositions which are amenable to strengthening by ion exchange. Such composition generally includes a combination of SiO 2 , Al 2 O 3 , at least one alkaline earth oxide, and one or more alkali oxides, such as Na 2 O and/or K 2 O. The glass composition may be free from boron and compounds containing boron. The glass compositions may further comprise minor amounts of one or more additional oxides such as, for example, SnO 2 , ZrO 2 , ZnO, TiO 2 , As 2 O 3 , or the like. These components may be added as fining agents and/or to further enhance the chemical durability of the glass composition. For example, glass articles as described herein my be formed from the ion exchangeable glass composition described in granted U.S. Pat. No. 8,980,777 filed Oct. 25, 2012 entitled “Glass Compositions with Improved Chemical and Mechanical Durability” the contents of which are incorporated herein by reference in their entirety. 
     Exemplarily glass compositions that glass articles  302  as described herein may be formed from include glass compositions which meet the criteria for pharmaceutical glasses described by regulatory agencies such as the USP (United States Pharmacopoeia), the EP (European Pharmacopeia), and the JP (Japanese Pharmacopeia) based on their hydrolytic resistance. Per USP 660 and EP 7, borosilicate glasses meet the Type I criteria and are routinely used for parenteral packaging. Examples of borosilicate glass include, but are not limited to Corning® Pyrex® 7740, 7800 and Wheaton 180, 200, and 400, Schott Duran, Schott Fiolax, KIMAX® N-51A, Gerrescheimer GX-51 Flint and others. Soda-lime glass meets the Type III criteria and is acceptable in packaging of dry powders which are subsequently dissolved to make solutions or buffers. Type III glasses are also suitable for packaging liquid formulations that prove to be insensitive to alkali. Examples of Type III soda lime glass include Wheaton 800 and 900. De-alkalized soda-lime glasses have higher levels of sodium hydroxide and calcium oxide and meet the Type II criteria. These glasses are less resistant to leaching than Type I glasses, but more resistant than Type III glasses. Type II glasses can be used for products that remain below a pH of 7 for their shelf life. Examples include ammonium sulfate treated soda lime glasses. These pharmaceutical glasses have varied chemical compositions and have a coefficient of linear thermal expansion (CTE) in the range of 20-85×10 −7 ° C. −1 . 
     Generally, the molten salt bath may include a first cation and a second cation wherein the first cation is larger than the second cation. At the beginning of the ion exchange process, the bath may include only the first cation. Optionally, the second cation may be intentionally included in the bath at the beginning of the ion exchange process. In either case, the second cation is introduced into the bath during the ion exchange process. The ion exchange bath may include, for example, a potassium salt such as potassium nitrate (KNO 3 ) and a small amount of the corresponding sodium salt (NaNO 3 ), which may be present as a contaminant or intentionally added to the bath, with the K+ ion being the first cation and the Na+ ion being the second cation. After the ion exchange is considered to be complete the glass article  302  is removed and washed to remove excess salt from the ion exchange bath. This process is repeated for additional glass articles in the same ion exchange bath until the salt in the ion exchange bath no longer provides a high enough surface concentration to achieve a CS above a targeted CS, a CT above a targeted CT, or a DOL above the targeted DOL. As ion exchange processing is performed on each glass article  302 , the concentration of smaller cations in the ion exchange bath increases while the concentration of larger cations in the ion exchange bath decreases, eventually reaching a concentration in which too few larger cations are available to be exchanged for the smaller cations in the glass article. This phenomenon is referred to as “poisoning” of the bath. As used herein, the terms “poisoning ions” and “poisoning cations” refer to the smaller cations that leave the glass and enter the ion exchange/salt bath during the ion exchange process and “poisoning salt” refers to the salts of such cations. The increase in concentration of poisoning cations as ion exchange progresses causes gradual deterioration of the CS, CT and DOL over time for glass articles that are subsequently ion exchanged in the same salt bath. Prior to reaching a concentration in which too few larger cations are available to be exchanged for the smaller ions in the glass article, the entire contents of the ion exchange bath may be replaced. 
     As described above,  FIG.  4   , schematically depicts a cross-sectional view of a cassette assembly  410  which may include a plurality of magazine apparatuses  400  stacked adjacently and secured together in a cassette  608 . The magazine apparatuses  400  are configured to retain glass articles  302 , such as glass vials, during ion exchange processing while allowing for acceptable levels of fluid contact by the molten salt in the processing chamber  106   a  with all areas (interior and exterior) of the glass articles  302  when the magazine apparatus  400  is partially or fully submerged in the molten salt. Each magazine apparatus  400  generally includes a bottom support floor  500 , a plurality of glassware-securing members  420 , a cover plate  440  and vertical supports  430  that securely connect the bottom support floor  500 , the glassware-securing members  420 , and may removably secure the cover plate  440 . 
     According to embodiments of the present disclosure, the operation of the ion exchange tank  100  described herein may further include recirculating salt from the processing chamber  106   a  of the ion exchange tank  100 . Dragout, or salt which adheres to the surface of the glass article  302 , or to the surface of any fixture or carrier which contacts the glass article  302  in the ion exchange tank  100 , exits the molten salt bath when the glass article  302  and/or the fixture or carrier is removed from the ion exchange tank  100 . Dragout is conventionally washed off the glass article  302  and/or the fixtures without being recirculated. 
     However, according to embodiments of the present disclosure, a robotic lift system  210  including a rotation tool  215  may be configured to move the glass article  302  and/or the fixture or carrier out of the processing chamber  106   a  to a position over the additive chamber  106   b . The rotation tool  215  may include engagement features, such as a plurality of prongs  219  as shown in  FIG.  5   , which are configured to engage with a portion of the magazine apparatus  400  so that the magazine apparatus  400  can be rotated. Thus, in operation, the robotic lift system  210  may be controlled to mount the magazine apparatus  400  onto the rotation tool  215 . The rotation tool  215  may be motorized such that the rotation tool  215  can perform a rotation sequence to substantially drain the magazine apparatus  400  of molten salt into the additive chamber  106   b.    
       FIG.  3    illustrates an ion exchange tank  100  in accordance with embodiments of the present disclosure. As shown in  FIG.  3   , the ion exchange tank  100  may include a pump device  250  configured to transfer molten salt from the processing chamber  106   a  to the additive chamber  106   b . In operation, molten salt is recirculated from the processing chamber  106   a  by way of the pump device  250 . According to embodiments of the present disclosure, the molten salt may be circulated continuously. Alternatively, the molten salt may be circulated at predetermined intervals for predetermined periods of time. As shown in  FIG.  3   , molten salt is pumped by way of the pump device  250  out of the processing chamber  106   a , over the top of the weir system  110 , and into the additive chamber  106   b . As an alternative, the processing chamber  106   a  may be fluidly connected via a pipe to the additive chamber  106   b  and the pump device  250  may be configured to pump molten salt from a recirculation outlet (not shown) in the processing chamber  106   a , through the pipe, and into the additive chamber  106   b.    
     According to the embodiments of the present disclosure, ion exchange processing may be performed in the processing chamber  106   a  at the same time that fresh salt is added to the additive chamber  106   b  and that heat is applied to the additive chamber  106   b  melt the fresh salt and form molten salt. As compared to tanks used in conventional ion exchange processing where the fresh salt added to the tank must first be heated to form molten salt prior to beginning ion exchange processing, ion exchange tanks as described herein allow for the processing chamber  106   a  to be filled with molten salt and for the ion exchange process to begin once the filling of the chamber  106   a  is complete. 
     According to embodiments of the present disclosure, molten salt in the processing chamber  106   a  may be drained through processing chamber outlet  120   a  while the contents of the additive chamber  106   b  remain unaltered. Because solid additives are confined to the additive chamber  106   b  of the ion exchange tank described herein, embodiments of the present disclosure prevent a concentration of solids forming at the bottom of the tank, such as frequently occurs in conventional ion exchange processing, which in turn facilitates faster draining and refilling of the processing chamber  106   a  than in tanks used in conventional ion exchange processing. The additive chamber  106   b  may also be drained through additive chamber outlet  120   b . Because the processing chamber  106   a  and the additive chamber  106   b  are drained through separate outlets, the chambers may be drained with different frequencies and at different times. 
     While the present disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the present disclosure.