Patent Description:
Glass-ceramics are nominally produced by a thermal process in which the as-made glass is thermally treated to produce a controlled crystalline phase. Cerium and silver photosensitizers have been used in glass systems, such as FOTOFORM™ and FOTA-LITE™, to produce photosensitive materials in which the crystal content is well below the <NUM>% level that typically defines a glass ceramic. In such glass systems, an opal (i.e., opaque, optically dense, white, light scattering) phase containing NaF is formed in regions of the glass that are exposed to short wavelength light followed by heat treatment, while unexposed regions of the glass remain clear. Photosensitive glasses and composite articles comprise glass and glass ceramics obtained therefrom are, for example, known from <CIT>, <CIT> and <CIT>.

Photosensitive lithium zinc aluminosilicate glasses that can be selectively cerammed to provide patterned regions of glass and glass ceramic, and composite glass articles made from such glasses and glass ceramics are provided. When these glasses are exposed to ultraviolet (UV) radiation and thermally treated (cerammed), a lithium-based glass ceramic having a β-quartz crystal structure is formed in selected regions of the glass. The lithium zinc aluminosilicate glass is "positively" photosensitive; i.e., a lithium-based glass ceramic is formed in the portion of the glass that is exposed to the UV radiation while the transparent lithium zinc aluminosilicate glass remains in those regions that are not exposed to the UV radiation. In some embodiments, the lithium-based glass ceramic is "opalized"; i.e., opaque or translucent, or in some embodiments opalescent. Compressive and tensile stress at the interface of the lithium-based glass-ceramic and lithium zinc aluminosilicate glass may be used to frustrate to crack propagation in such a composite glass/glass ceramic article. Methods of making composite glass articles comprising such lithium-based glass ceramics and lithium zinc aluminosilicate glasses are also provided.

Accordingly, the invention relates to a composite glass article comprising a first region and a second region in contact with the first region at an interface. The first region comprises a lithium-based glass ceramic. The lithium-based glass ceramic comprises a residual glass phase and a ceramic phase comprising a lithium aluminosilicate phase having a lithium aluminosilicate stuffed β-quartz structure. The second region comprises a transparent lithium zinc aluminosilicate glass comprising at least one sensitizing agent and at least one nucleating agent. The lithium zinc aluminosilicate glass is positively photosensitive to ultraviolet radiation and comprises: from <NUM> wt% to <NUM> wt % SiO<NUM>; up to <NUM> wt% K<NUM>O; from <NUM> wt% to <NUM> wt% ZnO; up to <NUM> wt% Br-; from <NUM> wt% to <NUM> wt% Al<NUM>O<NUM>; from <NUM> wt% to <NUM> wt% CeO<NUM>; from <NUM> wt% to <NUM> wt% Ag; from <NUM> wt% to <NUM> wt% LizO; up to <NUM> wt% Na<NUM>O; from <NUM> wt% to <NUM> wt% F-; and up to <NUM> wt% ZrO<NUM>.

The invention further relates to a method of making a composite glass article comprising a lithium zinc aluminosilicate glass and a lithium-based glass ceramic. The lithium-based glass ceramic comprises a residual glass phase and a ceramic phase, wherein the ceramic phase comprises a lithium aluminosilicate phase having a lithium aluminosilicate β-quartz structure, and a residual glass phase. The method comprises: providing a lithium zinc aluminosilicate precursor glass comprising from <NUM> wt% to <NUM> wt % SiO<NUM>; up to <NUM> wt% K<NUM>O; from <NUM> wt% to <NUM> wt% ZnO; up to <NUM> wt% Br-; from <NUM> wt% to <NUM> wt% Al<NUM>O<NUM>; from <NUM> wt% to <NUM> wt% CeO<NUM>; from <NUM> wt% to <NUM> wt% Ag; from <NUM> wt% to <NUM> wt% Li<NUM>O; up to <NUM> wt% Na<NUM>O; from <NUM> wt% to <NUM> wt% F-; and up to <NUM> wt% ZrO<NUM>; at least one sensitizing agent and at least one nucleating agent, wherein the lithium zinc aluminosilicate glass is positively photosensitive; exposing a first region of the lithium zinc aluminosilicate precursor glass to ultraviolet radiation having a wavelength in a range from about <NUM> to about <NUM>, wherein a second region of the lithium zinc aluminosilicate precursor glass is unexposed to the ultraviolet radiation; heating the lithium zinc aluminosilicate precursor glass at a first temperature for a first time period, wherein the first temperature is in a range from <NUM> to <NUM> and the first time period is in a range from <NUM> hours to <NUM> hours; and heating the lithium zinc aluminosilicate precursor glass at a second temperature for a second time period to form the lithium-based glass ceramic in the first region, wherein the second temperature is in a range from <NUM> to <NUM> and the second time period is in a range from <NUM> hours to <NUM> hours.

These and other aspects, advantages, and salient features will become apparent from the following detailed description, the accompanying drawings, and the appended claims.

In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures. It is also understood that, unless otherwise specified, terms such as "top," "bottom," "outward," "inward," and the like are words of convenience and are not to be construed as limiting terms. In addition, whenever a group is described as comprising at least one of a group of elements and combinations thereof, it is understood that the group may comprise, consist essentially of, or consist of any number of those elements recited, either individually or in combination with each other. Similarly, whenever a group is described as consisting of at least one of a group of elements or combinations thereof, it is understood that the group may consist of any number of those elements recited, either individually or in combination with each other. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range as well as any ranges therebetween. As used herein, the indefinite articles "a," "an," and the corresponding definite article "the" mean "at least one" or "one or more," unless otherwise specified. It also is understood that the various features disclosed in the specification and the drawings can be used in any and all combinations.

As used herein, the terms "composite glass article" and "composite glass ceramic articles" are used in their broadest sense to include any object made wholly or partly of glass and glass ceramic. Unless otherwise specified, all compositions are expressed in terms of weight percent (wt%). As used herein, the terms "ceram" and "ceramming" refer to a heat treatment (or heat treatments) or process in which a precursor glass is converted to a glass-ceramic.

As used herein, the term "glass ceramic" refers to a material comprising a glass phase and a crystalline ceramic phase, wherein the ceramic phase accounts for or comprises at least <NUM> volume percent of the material. The terms "glass ceramic" and "crystalline" are equivalent terms and may be used interchangeably herein.

As used herein, the term "opal" refers to an opaque, optically dense, white, and/or light scattering glass, ceramic, or glass ceramic material that may, but does not have to, have opalescent properties. The term "opalizing" refers to a process of transforming a glass, ceramic, or glass ceramic material into an opal material. An opal or opalized material comprises at least one crystalline or ceramic phase in which the crystalline particles have a mean particle size that is within or greater than the wavelength range of visible light (<NUM>-<NUM>). As used herein, the term "translucent" refers to a material that transmits and diffuses light such that objects beyond the material cannot be seen clearly with the unaided eye.

As used herein, the terms "reverse photosensitive," "negative photosensitive," and "negatively photosensitive" refer to a material and process whereby a region of the material exposed to electromagnetic radiation remains clear, while an unexposed remainder of the material becomes opalized or translucent when the material is subsequently heated at a temperature greater than room temperature. Conversely, the terms "positive photosensitive" and "positively photosensitive" refer to a material and process whereby a region of the material exposed to electromagnetic radiation becomes opalized or translucent, while the unexposed remainder of the material remains clear.

It is noted that the terms "substantially" and "about" may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. Thus, a glass that is, for example, referred to as being "substantially free of TiO<NUM>" or "free of TiO<NUM>" is one in which TiO<NUM> is not actively added or batched into the glass, but may be present in very small amounts (e.g., ≤ <NUM> ppm or, in some embodiments, ≤ <NUM> ppm) as a contaminant.

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

The invention relates to composite glass articles comprising a positively photosensitive lithium zinc aluminosilicate glass. The positively photosensitive lithium zinc aluminosilicate glass comprises: from about <NUM> wt% to about <NUM> wt % SiO<NUM> (<NUM> wt% ≤ SiO<NUM> ≤ <NUM> wt%); up to about <NUM> wt% K<NUM>O (<NUM> wt% ≤ K<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% ZnO (<NUM> wt% ≤ ZnO ≤ <NUM> wt%); up to about <NUM> wt% Br- (<NUM> wt% ≤ Br- ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Al<NUM>O<NUM> (<NUM> wt% ≤ Al<NUM>O<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% CeO<NUM> (<NUM> wt% ≤ CeO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Ag (<NUM> wt% ≤ Ag ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Li<NUM>O (<NUM> wt% ≤ Li<NUM>O ≤ <NUM> wt%); up to about <NUM> wt% Na<NUM>O (<NUM> wt% ≤ Na<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% F- (<NUM> wt% ≤ F- ≤ <NUM> wt%); and up to about <NUM> wt% ZrO<NUM> (<NUM> wt% ≤ ZrO<NUM> ≤ <NUM> wt%).

In some embodiments, the positively photosensitive lithium zinc aluminosilicate precursor glass may be produced by adding ZrO<NUM> to the negatively photosensitive lithium zinc aluminosilicate composition. Non-limiting examples of these glasses are listed in Table <NUM> below. Example <NUM> in Table <NUM> is an exemplary composition of the photonegative glass ceramic and glass. In these embodiments, the positively photosensitive lithium zinc aluminosilicate glass comprises: from about <NUM> wt% to about <NUM> wt % SiO<NUM> (<NUM> wt% ≤ SiO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% K<NUM>O (<NUM> wt% ≤ K<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% ZnO (<NUM> wt% ≤ ZnO ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Br- (<NUM> wt% ≤ Br- ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Al<NUM>O<NUM> (<NUM> wt% ≤ Al<NUM>O<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% CeO<NUM> (<NUM> wt% ≤ CeO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Ag (<NUM> wt% ≤ Ag ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Li<NUM>O (<NUM> wt% ≤ Li<NUM>O ≤ <NUM> wt%); up to about <NUM> wt% Na<NUM>O (<NUM> wt% ≤ Na<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% F- (<NUM> wt% ≤ F- ≤ <NUM> wt%); and from about <NUM> wt% to about <NUM> wt% ZrO<NUM> (<NUM> wt% ≤ ZrO<NUM> ≤ <NUM> wt%).

<FIG> is a photograph of samples in which ZrO<NUM> was added to the negatively photosensitive lithium zinc aluminosilicate precursor glass composition. The resulting glasses are positively photosensitive, with the opalized ceramic phase present in those portions of the samples that were exposed to UV radiation and a lithium zinc aluminosilicate glass phase present in those portions of the samples that were not exposed to UV radiation. Samples A and B each have composition <NUM> (containing <NUM> wt% ZrO<NUM>) and samples C, D, and E each have composition <NUM> (containing <NUM> wt% ZrO<NUM>) listed in Table <NUM>. Heat treatment times and temperatures that were used to form the lithium-based glass ceramics in examples <NUM> and <NUM> are listed in Table 2A. Exposed portions <NUM> of samples A-E in <FIG> are opalized while unexposed portions <NUM> remain clear. X-Ray diffraction (XRD) analysis of the opalized material indicates the presence of a virgilite Li-aluminosilicate phase. <FIG> is a XRD pattern obtained for an opalized portion of a sample having composition <NUM> that was exposed to UV radiation, subsequently heat treated first at <NUM> for two hours, cooled to room temperature, and then heat treated again at <NUM> for two hours. The XRD pattern shows that the dominant phase has the stuffed β-quartz Li-aluminosilicate (virgilite LixAlxSi<NUM>-xO<NUM>) crystal structure.

In other embodiments, the positively photosensitive lithium zinc aluminosilicate precursor glass is produced by increasing the alumina content relative to that of SiO<NUM> in the negatively photosensitive lithium aluminosilicate composition. In these embodiments, the positively photosensitive precursor glass comprises: from about <NUM> wt% to about <NUM> wt % SiO<NUM> (<NUM> wt% ≤ SiO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% K<NUM>O (<NUM> wt% ≤ K<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% ZnO (<NUM> wt% ≤ ZnO ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Br- (<NUM> wt% ≤ Br- ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Al<NUM>O<NUM> (<NUM> wt% ≤ Al<NUM>O<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% CeO<NUM> (<NUM> wt% ≤ CeO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Ag (<NUM> wt% ≤ Ag ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Li<NUM>O (<NUM> wt% ≤ Li<NUM>O ≤ <NUM> wt%); up to about <NUM> wt% Na<NUM>O (<NUM> wt% ≤ Na<NUM>O ≤ <NUM> wt%); and from about <NUM> wt% to about <NUM> wt% F- (<NUM> wt% ≤ F- ≤ <NUM> wt%). Non-limiting examples of these glasses and glass-ceramics are listed in Table <NUM> below. The alumina content in examples <NUM> and <NUM> were increased by <NUM> wt% and <NUM> wt%, respectively, relative to the composition of reference example <NUM>, listed in Table <NUM>. Example <NUM> was first heated at <NUM> for two hours and then cooled to room temperature (about <NUM>) and later heated at <NUM> for two hours, whereas example <NUM> was first heated at <NUM> for two hours and then cooled to room temperature and later heated at <NUM> for two hours. <FIG> is a photograph of samples of examples <NUM> (F in <FIG>) and <NUM> (G in <FIG>) following irradiation and heat treatments. Both samples have opalized regions <NUM> - and, in sample G, <NUM> and <NUM> - where exposed to UV radiation. The XRD pattern obtained for example <NUM>/sample G indicates that the major phase in the opalized regions has the "stuffed β-quartz" lithium-aluminosilicate (virgilite) LixAlxSi<NUM>-xO<NUM> crystal structure.

While ZnO is a constituent of the negatively photosensitive glass-ceramic and precursor glasses, a positively photosensitive glass-ceramic and precursor glass may be obtained by increasing the ZnO concentration relative to the alumina and silica content in the negatively photosensitive lithium aluminosilicate composition. In these embodiments, the positively photosensitive glass precursor glass comprises: from about <NUM> wt% to about <NUM> wt % SiO<NUM> (<NUM> wt% ≤ SiO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% K<NUM>O (<NUM> wt% ≤ K<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% ZnO (<NUM> wt% ≤ ZnO ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Br- (<NUM> wt% ≤ Br- ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Al<NUM>O<NUM> (<NUM> wt% ≤ Al<NUM>O<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% CeO<NUM> (<NUM> wt% ≤ CeO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Ag (<NUM> wt% ≤ Ag ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Li<NUM>O (<NUM> wt% ≤ Li<NUM>O ≤ <NUM> wt%); up to about <NUM> wt% Na<NUM>O (<NUM> wt% ≤ Na<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% F- (<NUM> wt% ≤ F- ≤ <NUM> wt%), and up to about <NUM> wt% ZrO<NUM> (<NUM> wt% ≤ ZrO<NUM> ≤ <NUM> wt%). Compositions of non-limiting examples of these positively photosensitive lithium zinc aluminosilicate glasses are listed in Table <NUM> below. The glass-ceramic may, in some embodiments, be obtained by first exposing the positively photosensitive precursor glass to ultraviolet light followed by a first heat treatment at about <NUM> for two hours, then cooling the precursor glass to room temperature (about <NUM>) and later heating the precursor glass at about <NUM> for two hours to form the glass ceramic. <FIG> is a photograph of samples of examples <NUM> (H in <FIG>) and <NUM> (I in <FIG>) following irradiation and heat treatments. Both samples have opalized region <NUM> - and, in sample H, <NUM>, and in sample I, <NUM> - where the material was exposed to UV radiation. The XRD pattern obtained for examples <NUM>/sample I (<FIG>) indicates that the major phase in the opalized regions has the "stuffed β-quartz" lithium-aluminosilicate (virgilite) LixAlxSi<NUM>-xO<NUM> crystal structure.

In other embodiments, the positively photosensitive lithium zinc aluminosilicate precursor glasses may be obtained by replacing fluorine with bromine. In such embodiments, the precursor glass may comprise up to about <NUM> wt% or, in some embodiments, up to about <NUM> wt% Br. In these embodiments, the positively photosensitive lithium zinc aluminosilicate precursor glass may comprise: from about <NUM> wt% to about <NUM> wt % SiO<NUM> (<NUM> wt% ≤ SiO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% K<NUM>O (<NUM> wt% ≤ K<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% ZnO (<NUM> wt% ≤ ZnO ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Br- (<NUM> wt% ≤ Br- ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Al<NUM>O<NUM> (<NUM> wt% ≤ Al<NUM>O<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% CeO<NUM> (<NUM> wt% ≤ CeO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Ag (<NUM> wt% ≤ Ag ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Li<NUM>O (<NUM> wt% ≤ Li<NUM>O ≤ <NUM> wt%); up to about <NUM> wt% Na<NUM>O (<NUM> wt% ≤ Na<NUM>O ≤ <NUM> wt%); and from <NUM> wt% to about <NUM> wt% F- (<NUM> wt% ≤ F- ≤ <NUM> wt%). Non-limiting examples of these glasses and glass-ceramics are listed in Table <NUM> below. The XRD patterns obtained for samples having the composition listed for example <NUM> indicate that the major phase in the opalized regions has the "stuffed β-quartz" lithium-aluminosilicate (virgilite) LixAlxSi<NUM>-xO<NUM> crystal structure. Although these samples were heat treated at different temperatures, no discernable difference in the XRD data was observed.

The invention relates to a composite glass article comprising a lithium-based glass ceramic and a photosensitive lithium zinc aluminosilicate glass as described above. The composite glass article comprises a first region and a second region. The first region comprises a lithium-based glass ceramic comprising a ceramic phase and a residual glass phase. The ceramic phase comprises a lithium aluminosilicate (LAS) phase having a lithium aluminosilicate stuffed β-quartz structure, such as described hereinabove. In some embodiments, the lithium-based glass ceramic is free of at least one of Na<NUM>O, MgO, P<NUM>O<NUM>, TiO<NUM>, ZrO<NUM>, or bromine. In some embodiments, the LAS phase comprises at least about <NUM> volume percent of the glass ceramic region.

The second region comprises a lithium zinc aluminosilicate glass that is photosensitive to ultraviolet radiation having a wavelength in a range from about <NUM> to about <NUM>, such as those described hereinabove. The lithium zinc aluminosilicate glass comprises at least one sensitizing agent and at least one nucleating agent. In some embodiments, the at least one sensitizing agent may include, but is not limited to, at least one of silver or cerium. The at least one nucleating agent may include, but is not limited to, silver and/or at least one halogen or halide. In some embodiments, the at least one nucleating agent comprises at least one of fluorine, chlorine, or bromine. In particular embodiments, the at least one nucleating agent comprises fluorine or bromine.

In some embodiments, the first region is opaque or translucent. In some embodiments, the lithium zinc aluminosilicate glass is transparent.

The second region comprises a positively photosensitive lithium zinc aluminosilicate glass; i.e., a region of the glass, exposed to ultraviolet radiation having a wavelength in a range from about <NUM> to about <NUM> becomes opalized or translucent when later heat treated separately at a first temperature and at a second temperature, while the unexposed remainder of the material remains clear following such heat treatments. These positively photosensitive glasses have been previously described hereinabove, and comprise: from about <NUM> wt% to about <NUM> wt % SiO<NUM> (<NUM> wt% ≤ SiO<NUM> ≤ <NUM> wt%); up to about <NUM> wt% K<NUM>O (<NUM> wt% ≤ K<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% ZnO (<NUM> wt% ≤ ZnO ≤ <NUM> wt%); up to about <NUM> wt% Br- (<NUM> wt% ≤ Br- ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Al<NUM>O<NUM> (<NUM> wt% ≤ Al<NUM>O<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% CeO<NUM> (<NUM> wt% ≤ CeO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Ag (<NUM> wt% ≤ Ag ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Li<NUM>O (<NUM> wt% ≤ Li<NUM>O ≤ <NUM> wt%); up to about <NUM> wt% Na<NUM>O (<NUM> wt% ≤ Na<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% F- (<NUM> wt% ≤ F- ≤ <NUM> wt%); and up to about <NUM> wt% ZrO<NUM> (<NUM> wt% ≤ ZrO<NUM> ≤ <NUM> wt%).

In some embodiments, the positively photosensitive lithium zinc aluminosilicate glass comprises: from about <NUM> wt% to about <NUM> wt % SiO<NUM> (<NUM> wt% ≤ SiO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% K<NUM>O (<NUM> wt% ≤ K<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% ZnO (<NUM> wt% ≤ ZnO ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Br- (<NUM> wt% ≤ Br- ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Al<NUM>O<NUM> (<NUM> wt% ≤ Al<NUM>O<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% CeO<NUM> (<NUM> wt% ≤ CeO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Ag (<NUM> wt% ≤ Ag ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Li<NUM>O (<NUM> wt% ≤ Li<NUM>O ≤ <NUM> wt%); up to about <NUM> wt% Na<NUM>O (<NUM> wt% ≤ Na<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% F- (<NUM> wt% ≤ F- ≤ <NUM> wt%); and from about <NUM> wt% to about <NUM> wt% ZrO<NUM> (<NUM> wt% ≤ ZrO<NUM> ≤ <NUM> wt%).

In some embodiments, the positively photosensitive lithium zinc aluminosilicate glass comprises: from about <NUM> wt% to about <NUM> wt % SiO<NUM> (<NUM> wt% ≤ SiO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% K<NUM>O (<NUM> wt% ≤ K<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% ZnO (<NUM> wt% ≤ ZnO ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Br- (<NUM> wt% ≤ Br- ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Al<NUM>O<NUM> (<NUM> wt% ≤ Al<NUM>O<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% CeO<NUM> (<NUM> wt% ≤ CeO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Ag (<NUM> wt% ≤ Ag ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Li<NUM>O (<NUM> wt% ≤ Li<NUM>O ≤ <NUM> wt%); up to about <NUM> wt% Na<NUM>O (<NUM> wt% ≤ Na<NUM>O ≤ <NUM> wt%); and from about <NUM> wt% to about <NUM> wt% F- (<NUM> wt% ≤ F- ≤ <NUM> wt%).

In some embodiments, the positively photosensitive lithium zinc aluminosilicate glass comprises: from about <NUM> wt% to about <NUM> wt % SiO<NUM> (<NUM> wt% ≤ SiO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% K<NUM>O (<NUM> wt% ≤ K<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% ZnO (<NUM> wt% ≤ ZnO ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Br- (<NUM> wt% ≤ Br- ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Al<NUM>O<NUM> (<NUM> wt% ≤ Al<NUM>O<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% CeO<NUM> (<NUM> wt% ≤ CeO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Ag (<NUM> wt% ≤ Ag ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Li<NUM>O (<NUM> wt% ≤ Li<NUM>O ≤ <NUM> wt%); up to about <NUM> wt% Na<NUM>O (<NUM> wt% ≤ Na<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% F- (<NUM> wt% ≤ F- ≤ <NUM> wt%), and up to about <NUM> wt% ZrO<NUM> (<NUM> wt% ≤ ZrO<NUM> ≤ <NUM> wt%).

In some embodiments, the positively photosensitive lithium zinc aluminosilicate glass comprises: from about <NUM> wt% to about <NUM> wt % SiO<NUM> (<NUM> wt% ≤ SiO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% K<NUM>O (<NUM> wt% ≤ K<NUM>O ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% ZnO (<NUM> wt% ≤ ZnO ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Br- (<NUM> wt% ≤ Br- ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Al<NUM>O<NUM> (<NUM> wt% ≤ Al<NUM>O<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% CeO<NUM> (<NUM> wt% ≤ CeO<NUM> ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Ag (<NUM> wt% ≤ Ag ≤ <NUM> wt%); from about <NUM> wt% to about <NUM> wt% Li<NUM>O (<NUM> wt% ≤ Li<NUM>O ≤ <NUM> wt%); up to about <NUM> wt% Na<NUM>O (<NUM> wt% ≤ Na<NUM>O ≤ <NUM> wt%); and from <NUM> wt% to about <NUM> wt% F- (<NUM> wt% ≤ F- ≤ <NUM> wt%).

In some embodiments, the first region (the lithium-based glass ceramic) and the second region (the lithium zinc aluminosilicate glass) of the composite glass articles described herein may be randomly dispersed throughout the composite glass article. In other embodiments, the first region and second region are spatially separate from each other.

In some embodiments, the first region (the lithium-based glass ceramic) and the second region (the lithium zinc aluminosilicate glass) of the composite glass articles described herein may be arranged in an array. The array may, in some embodiments, be a regular, repeated pattern, which may be either short range (i.e., having/extending in a dimension of up to about <NUM> or less) or long range (i.e., having a dimension/extending in a dimension of greater than <NUM>). Such an array may be formed by selectively irradiating portions of the precursor glass with UV light in a predetermined pattern, or by shielding a portion of the precursor glass from the UV light.

In some embodiments, the lithium-based glass ceramic has a thermal expansion ΔL<NUM>/L<NUM> and the lithium zinc aluminosilicate glass has a thermal expansion ΔL<NUM>/L<NUM> measured between room temperature and a second temperature T, wherein <NUM> ≤ T ≤ <NUM>, where ΔLi is the change in dimension Li of the lithium-based glass ceramic and the lithium zinc aluminosilicate glass over the temperature range measured. This thermal expansion differential places the lithium zinc aluminosilicate glass in tension and the lithium-based glass ceramic in compression at the boundary between the glass and ceramic phases, thereby increasing the mechanical strength of the composite glass article.

Thermal expansion of the lithium-based glass ceramic and the lithium zinc aluminosilicate glass of the composite glass article are plotted as function of temperature in <FIG> and <FIG>, respectively. As seen in <FIG> and <FIG>, the lithium-based glass ceramic undergoes a <NUM>% decrease in volume as it cools from the thermal development temperature of <NUM>, whereas the lithium zinc aluminosilicate glass undergoes a <NUM>% decrease in volume upon cooling from the thermal development temperature. Thus volume of the lithium-based glass ceramic experiences a <NUM>% greater volume decrease relative to the lithium zinc aluminosilicate glass, which results in a build-up of compressive stress in the lithium-based glass ceramic and tensile stress in the lithium zinc aluminosilicate glass at the boundary of the glass ceramic/glass interface. The nature of the compressive and tensile stresses that develop under this condition provides a stress region that is capable of deflecting a propagating crack.

The induced stress between the lithium-based glass ceramic and the lithium zinc aluminosilicate glass may be observed in the resulting optical birefringence and on the microscopic level as well. <FIG> are microscopic images of a composite glass article under non-polarized light and polarized light, respectively. Composite glass article <NUM> comprises a lithium-based glass ceramic <NUM> and a lithium zinc aluminosilicate glass <NUM>. Stress <NUM> at the interface between the lithium-based glass ceramic <NUM> and the lithium zinc aluminosilicate glass <NUM>, which is induced by the photo-elastic effect, is visible under polarized light (<FIG>).

<FIG> is a photograph showing the internal stress produced by the patterned composite glass article comprising the negatively photosensitive lithium zinc aluminosilicate glass and the lithium-based glass ceramic described herein. The sample is viewed between crossed polarizers, and the magnitude of the stress is seen through the photo-elastic effect (i.e., stress-induced birefringence). The composite glass article comprises lithium zinc aluminosilicate glass <NUM> surrounded by the lithium-based glass ceramic <NUM>. The negatively photosensitive lithium zinc aluminosilicate glass in composite glass article <NUM> has the composition of example <NUM> (Table <NUM>). When viewed between crossed polarizers, stress patterns <NUM> appear in the glass regions <NUM> surrounded by the glass ceramic region <NUM>.

By introducing compressive and tensile stress at the boundary interface of the glass-ceramic and lithium zinc aluminosilicate glass, the patterned composite glass articles described herein may be used to frustrate crack propagation from the edges of such an article. Such an article is schematically shown in <FIG>. Composite glass article <NUM> comprises a first region <NUM> comprising a lithium zinc aluminosilicate glass and a second region comprising a lithium-based glass ceramic <NUM>. Both the lithium zinc aluminosilicate glass and the lithium-base glass ceramic are described herein. If the lithium zinc aluminosilicate glass is positively photosensitive, a central portion <NUM> of the precursor glass <NUM> is not exposed to UV radiation, while a peripheral portion <NUM> of the precursor glass <NUM> is exposed to UV radiation. Following exposure to the UV radiation (<NUM> in <FIG>), the precursor lithium zinc aluminosilicate glass is then heated to and held at a first temperature for a predetermined period of time and cooled to room temperature (<NUM>), and then heated to and held at a second temperature for a predetermined period of time and cooled to room temperature (<NUM>) to form the lithium-based glass ceramic and composite glass article <NUM>. A glass-ceramic is formed in the exposed peripheral portion <NUM>, wherein a compressive stress (<NUM> in <FIG>) exists within the lithium-based glass ceramic and a tensile stress is created in the lithium zinc aluminosilicate glass at the interface between the lithium zinc aluminosilicate glass and lithium-based glass ceramic. This interfacial stress frustrates the propagation of cracks from the edges of the composite glass article <NUM>.

In those instances in which the lithium zinc aluminosilicate glass is negatively photosensitive, central portion <NUM> of the precursor glass <NUM> is exposed to UV radiation, while peripheral portion <NUM> of the precursor glass <NUM> is not exposed to UV radiation. Following exposure to the UV radiation (<NUM> in <FIG>), the precursor lithium zinc aluminosilicate glass is then heated to and held at a first temperature for a predetermined period of time and cooled to room temperature (<NUM>) to form the lithium-based glass ceramic and composite glass article <NUM>.

A flow chart describing a reference method for making a composite glass article using a negatively photosensitive lithium zinc aluminosilicate glass is shown in <FIG>. In a first step <NUM> of method <NUM>, a negatively photosensitive lithium zinc aluminosilicate precursor glass comprising at least one sensitizing agent and at least one nucleating agent is provided. The precursor glass may be formed by those means known in the art including down-draw (fusion- or slot-draw), up draw, float methods, casting, molding, or the like.

In a second step <NUM>, a first region of the negatively photosensitive lithium zinc aluminosilicate precursor glass is exposed to ultraviolet radiation having a wavelength in a range from about <NUM> to about <NUM>, while a second region of the negatively photosensitive lithium zinc aluminosilicate precursor glass is unexposed to the ultraviolet radiation. In some aspects, the first region is irradiated with a UV laser such as, for example, a <NUM> pulsed laser or the like, or a beam of continuous UV light such as, for example, a <NUM> Hg arc lamp; while a second region of the precursor glass is not irradiated with (i.e., unexposed to) the UV radiation. In other aspects, the second region of the precursor glass may be shielded from the UV radiation. Such shielding may include an opaque or reflective film, such as those known in the art, which is applied to the surface of the second region. As previously described hereinabove, the UV radiation may, in some aspects, have a wavelength of <NUM>, <NUM> frequency, and a fluence of <NUM> W/cm<NUM>. In some aspects, the UV laser or beam is rastered across at least the portion of the negatively photosensitive lithium zinc aluminosilicate precursor glass. For example, the precursor glass may be irradiated for <NUM> seconds with UV light rastered across the material at a rate of <NUM>/sec. In other aspects, the negatively photosensitive lithium zinc aluminosilicate precursor glass may be continuously irradiated with UV light for a fixed time period (e.g., for about <NUM> minute, or for times ranging from about <NUM> to about <NUM> seconds).

The UV-exposed negatively photosensitive lithium zinc aluminosilicate precursor glass is then heated to form the lithium-based glass ceramic in the second region, thereby forming the composite glass article (step <NUM>). In some aspects, the exposed lithium zinc aluminosilicate precursor glass is heated at a temperature in a range from about <NUM> to about <NUM> for at least about <NUM> hours. In some aspects, the crystalline lithium-aluminosilicate and LiF phases (when present) in the second region, which was not exposed to the UV radiation, have crystal sizes of at least as large as the wavelength of visible light (≥ <NUM>) and thus scatter light and are opalized, rendering the ceramic phase opaque or translucent. In some aspects, however, the crystal sizes in the second region are sufficiently small so as to not scatter or appreciably refract light, thus rendering the ceramic phase transparent.

The invention also provides a method of making the composite glass article described hereinabove from a positively photosensitive lithium zinc aluminosilicate precursor glass (precursor glass). The composite glass article comprises a lithium zinc aluminosilicate glass and a lithium-based glass ceramic. The lithium-based glass ceramic comprises a residual glass phase and a ceramic phase comprising a stuffed β-quartz lithium-aluminosilicate (virgilite, or LixAlxSi<NUM>-xO<NUM>) crystal structure and, in some embodiments, a crystalline LiF phase. The lithium-based glass ceramic, in some embodiments, may be opalized or translucent.

A flow chart describing the method is shown in <FIG>. In a first step <NUM> of method <NUM>, a positively photosensitive lithium zinc aluminosilicate precursor glass comprising at least one sensitizing agent and at least one nucleating agent is provided. The precursor glass may be formed by those means known in the art including down-draw (fusion- or slot-draw), up draw, float methods, casting, molding, or the like.

In a second step <NUM>, a first region of the positively photosensitive lithium zinc aluminosilicate precursor glass is exposed to ultraviolet radiation having a wavelength in a range from about <NUM> to about <NUM> while a second region of the lithium zinc aluminosilicate glass is unexposed (i.e., not exposed) to the ultraviolet radiation. In some embodiments, the first region is irradiated with a UV laser such as, for example, a <NUM> pulsed laser or the like, or a beam of continuous UV light such as, for example, a <NUM> Hg arc lamp; while a second region of the precursor glass is not irradiated with UV radiation. In other embodiments, the second region of the precursor glass may be shielded from the UV radiation. Such shielding may include an opaque or reflective film, such as those known in the art, which is applied to the surface of the second region. As previously described hereinabove, the UV radiation may, in some embodiments, have a wavelength of <NUM>, <NUM> frequency, and <NUM> W/cm<NUM> energy. In some embodiments, the UV laser or focused beam is rastered across at least the portion of the negatively photosensitive lithium zinc aluminosilicate precursor glass. For example, the precursor glass may be irradiated for <NUM> seconds with UV light rastered across the material at a rate of <NUM>/sec. In other embodiments, the positively photosensitive lithium zinc aluminosilicate precursor glass may be continuously irradiated with UV light for a fixed time period (e.g., for about <NUM> minute, or for times ranging from about <NUM> to about <NUM> seconds, or, in some embodiments, for up to two hours).

Claim 1:
A composite glass article comprising a first region and a second region in contact with the first region at an interface, the first region comprising a lithium-based glass ceramic, the lithium-based glass ceramic comprising a ceramic phase and a residual glass phase, wherein the ceramic phase comprises a lithium aluminosilicate phase having a lithium aluminosilicate stuffed β-quartz structure, and the second region comprising a lithium zinc aluminosilicate glass, wherein the lithium zinc aluminosilicate glass is transparent, comprises at least one sensitizing agent and at least one nucleating agent and is positively photosensitive to ultraviolet radiation; wherein the lithium zinc aluminosilicate glass comprises: from <NUM> wt% to <NUM> wt % SiO<NUM>; up to <NUM> wt% K<NUM>O; from <NUM> wt% to <NUM> wt% ZnO; up to <NUM> wt% Br-; from <NUM> wt% to <NUM> wt% Al<NUM>O<NUM>; from <NUM> wt% to <NUM> wt% CeO<NUM>; from <NUM> wt% to <NUM> wt% Ag; from <NUM> wt% to <NUM> wt% Li<NUM>O; up to <NUM> wt% Na<NUM>O; from <NUM> wt% to <NUM> wt% F-; and up to <NUM> wt% ZrO<NUM>.