U.S. patent application number 17/688277 was filed with the patent office on 2022-06-16 for ultra-thin, non-frangible glass and methods of making.
The applicant listed for this patent is CORNING INCORPORATED. Invention is credited to Pascale Oram, Rostislav Vatchev Roussev, Vitor Marino Schneider.
Application Number | 20220185727 17/688277 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-16 |
United States Patent
Application |
20220185727 |
Kind Code |
A1 |
Oram; Pascale ; et
al. |
June 16, 2022 |
ULTRA-THIN, NON-FRANGIBLE GLASS AND METHODS OF MAKING
Abstract
Glasses having a thickness tin a range from about 0.1 mm to less
than 0.4 mm which, when chemically strengthened, is non-frangible
and has a physical center tension CT (also referred to herein as
"physical CT"), wherein
CT>|-1.956.times.10.sup.-16.times.t.sup.6+1.24274.times.10.sup-
.-12.times.t.sup.5-3.09196.times.10.sup.-9.times.t.sup.4+3.80391.times.10.-
sup.-6.times.t.sup.3-2.35207.times.10.sup.-3.times.t.sup.2+5.96241.times.1-
0.sup.-1.times.t+36.5994|, where t is expressed in microns.
Inventors: |
Oram; Pascale;
(Hammondsport, NY) ; Roussev; Rostislav Vatchev;
(Painted Post, NY) ; Schneider; Vitor Marino;
(Painted Post, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNING INCORPORATED |
Corning |
NY |
US |
|
|
Appl. No.: |
17/688277 |
Filed: |
March 7, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15403817 |
Jan 11, 2017 |
11286203 |
|
|
17688277 |
|
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62278125 |
Jan 13, 2016 |
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International
Class: |
C03C 21/00 20060101
C03C021/00; C03C 3/097 20060101 C03C003/097; C03C 4/18 20060101
C03C004/18; H05K 5/00 20060101 H05K005/00 |
Claims
1-38. (canceled)
39. A method of ion exchanging a glass article having a thickness
t, wherein 0.1 mm.ltoreq.t<0.4 mm, the method comprising: a. ion
exchanging the glass article in a first ion exchange bath at a
temperature in a range from about 300.degree. C. to about
500.degree. C., the first ion exchange bath comprising from about
25% to about 100% KNO.sub.3 by weight and up to about 75%
NaNO.sub.3 by weight; b. forming a compressive stress layer, the
compressive stress layer extending from a surface of the glass
article to a depth of compression DOC, wherein
0.05t.ltoreq.DOC.ltoreq.0.22t; and c. forming a tensile region in a
center portion of the glass article, the tensile region extending
from the depth of compression DOC to a center region of the glass
article, the tensile region having a physical center tension CT,
wherein
CT>|-1.956.times.10.sup.-16.times.t.sup.6+1.24274.times.10.sup.-12.tim-
es.t.sup.53.09196.times.10.sup.-9.times.t.sup.4+3.80391.times.10.sup.-6t.s-
up.3-2.35207.times.10.sup.-3.times.t.sup.2+5.96241.times.10.sup.-1.times.t-
+36.59941, where t is expressed in microns.
40. The method of claim 39, wherein forming the compressive layer
comprises forming a stress profile, wherein at least a portion of
the stress profile is linear and has a slope m1, and wherein 200
MPa/.mu.m.gtoreq.|m1|.gtoreq.1 MPa/.mu.m.
41. The method of claim 40, wherein 20
MPa/.mu.m.gtoreq.|m1|.gtoreq.1.2 MPa/.mu.m.
42. The method of claim 39, further comprising: a. ion exchanging
the glass article in a second ion exchange bath after ion
exchanging the glass article in the first ion exchange bath, the
second ion exchange bath comprising; and b. forming a second region
of the stress profile, the second region extending from the surface
to a first depth D1, the second region having a linear portion
extending from the surface to a depth of up to about 5.mu.m, the
linear portion having a slope m2, wherein 200
MPa/.mu.m.gtoreq.|m2|.gtoreq.30 MPa/.mu.m.
43. The method of claim 42, wherein
0.08t.ltoreq.DOC.ltoreq.0.22t.
44. The method of claim 42, wherein the compressive layer has a
compressive stress CS at the surface, and wherein 500
MPa.ltoreq.CS.ltoreq.950 MPa.
45. The method of claim 39, wherein the glass article is
non-frangible.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn. 119 of U.S. Provisional Application Ser. No.
62/278,125, filed Jan. 13, 2016, the contents of which are relied
upon and incorporated herein by reference in their entirety.
BACKGROUND
[0002] The disclosure relates to an ion exchangeable glass. More
particularly, the disclosure relates to an ion exchangeable glass
having a thickness of less than 0.4 mm. Even more particularly, the
disclosure relates to a glass which, when ion exchanged, is
non-frangible.
[0003] In an ion exchange process diffusion of the larger cations
(e.g., K+) into a glass is guided by a classical complementary
error function. The shape and value of the stress profile resulting
from ion exchange was previously determined by the physical center
tension limit, which is the tensile stress or physical center
tension value above which undesirable behavior, such as
frangibility, was expected to occur when the glass suffered an
impact or insult.
SUMMARY
[0004] The present disclosure provides glasses having a thickness t
in a range from about 0.1 mm to less than 0.4 mm which, when
chemically strengthened, is non-frangible and has a physical center
tension CT (also referred to herein as "physical CT") that exceeds
a frangibility limit; i.e.,
CT>|-1.956.times.10.sup.-16.times.t.sup.6+1.24274.times.10.sup.--
12.times.t.sup.5-3.09196.times.10.sup.-9.times.t.sup.4+3.80391.times.10.su-
p.-6.times.t.sup.3-2.35207.times.10.sup.-3.times.t.sup.2++5.96241.times.10-
.sup.-1.times.t+36.5994|, where t is expressed in microns.
[0005] Accordingly, one aspect of the disclosure is to provide a
glass article having a thickness t, wherein 0.1 mm.ltoreq.t<0.4
mm, a compressive layer extending from a surface of the glass
article to a depth of compression DOC and a tensile region
extending from the depth of compression to a center region of the
glass article. The tensile region under a physical center tension
CT, wherein
CT>|-1.956.times.10.sup.-16.times.t.sup.6+1.24274.times.10.sup.-12.tim-
es.t.sup.5-3.09196.times.10.sup.-9.times.t.sup.4+3.80391.times.10.sup.-6.t-
imes.t.sup.3-2.35207.times.10.sup.-3.times.t.sup.2+5.96241.times.10.sup.-1-
.times.t+36.5994|, where t is expressed in microns, and wherein the
glass is non-frangible.
[0006] Another aspect of the disclosure is to provide a glass
article having a thickness t, wherein 0.1 mm.ltoreq.t<0.4 mm,
and comprising: a compressive layer extending from a surface of the
glass article to a depth of compression DOC and a tensile region
extending from the depth of compression to a center region of the
glass article, the tensile region under a physical center tension
CT, wherein
CT>|-1.956.times.10.sup.-16.times.t.sup.6+1.24274.times.10.sup.-12.tim-
es.t.sup.5-3.09196.times.10.sup.-9.times.t.sup.4+3.80391.times.10.sup.-6.t-
imes.t.sup.3-23.35207.times.10.sup.-3.times.t.sup.2+5.96241.times.10.sup.--
1.times.t+36.5994|, where t is expressed in microns. The
compressive layer has a stress profile comprising: a first region
extending from at least a first depth D1 to the depth of
compression DOC, wherein at least a portion of the first region is
linear and has a slope m1, wherein 20
MPa/.mu.m.gtoreq.|m1|.gtoreq.1.2 MPa/.mu.m and where 9
.mu.m.ltoreq.D1.ltoreq.17 .mu.m; and a second region extending from
the surface to a depth of up to the first depth D1, the second
region having a linear portion extending from the surface to a
depth of up to about 5 .mu.m or less and having a slope m2, wherein
200 MPa/.mu.m.gtoreq.|m2|.gtoreq.30 MPa/.mu.m; and wherein the
glass article is non-frangible.
[0007] Another aspect of the disclosure is to provide a method of
ion exchanging a glass article having a thickness t, wherein 0.1
mm.ltoreq.t<0.4 mm. The method comprises: ion exchanging the
glass article in a first ion exchange bath at a temperature in a
range from about 300.degree. C. to about 500.degree. C., the first
ion exchange bath comprising from about 25% to about 100% KNO.sub.3
by weight and up to about 75% NaNO.sub.3 by weight; forming a
compressive stress layer, the compressive stress layer extending
from a surface of the glass article to a depth of compression DOC,
wherein 0.05t.ltoreq.DOC.ltoreq.0.22t; and forming a tensile region
in a center portion of the glass article, the tensile region
extending from the depth of compression DOC to a center region of
the glass article, the tensile region having a physical center
tension CT, wherein
CT>|-1.956.times.10.sup.-16.times.t.sup.6+1.24274.times.10.sup.-12.tim-
es.t.sup.5-3.09196.times.10.sup.-9t.sup.4+3.80391.times.10.sup.-6.times.t.-
sup.3-2.35207.times.10.sup.-3.times.t.sup.2+5.96241.times.10.sup.-1.times.-
t+36.5994|, where t is expressed in microns, and wherein the glass
is non-frangible.
[0008] According to aspect 1 of the disclosure a glass article is
provided. The glass article has a thickness t, wherein 0.1
mm=t<0.4 mm, a compressive layer extending from a surface of the
glass article to a depth of compression DOC and a tensile region
extending from the depth of compression to a center region of the
glass article, the tensile region is under a physical center
tension CT, wherein
CT>|-956.times.10.sup.-16.times.t.sup.6+1.24274.times.10.sup.-12.times-
.t.sup.5-3.09196.times.10.sup.-9.times.t.sup.4+3.80391.times.10.sup.-6.tim-
es.t.sup.3-2.35207.times.10.sup.-3.times.t.sup.2+5.96241.times.10.sup.-1.t-
imes.t+36.59941, where t is expressed in microns.
[0009] According to aspect 2 of the disclosure, the glass article
of aspect 1 is provided wherein 0.05t.ltoreq.DOC.ltoreq.0.22t.
[0010] According to aspect 3 of the disclosure, the glass article
of aspects 1 or 2 is provided wherein the compressive layer has a
compressive stress CS1 at the surface, and wherein 200
MPa.ltoreq.CS1.ltoreq.950 MPa.
[0011] According to aspect 4 of the disclosure, the glass article
of any of aspects 1 to 3 is provided wherein the glass article is
ion exchanged.
[0012] According to aspect 5 of the disclosure, the glass article
of any of aspects 1 to 4 is provided wherein the compressive layer
has a stress profile, wherein at least a portion of the stress
profile is linear and has a slope m1, and wherein 200
MPa/.mu.m.gtoreq.|m1|.gtoreq.1 MPa/.mu.m.
[0013] According to aspect 6 of the disclosure, the glass article
of aspect 5 is provided wherein 20 MPa/.mu.m.gtoreq.|m1|.gtoreq.1.2
MPa/.mu.m.
[0014] According to aspect 7 of the disclosure, the glass article
of aspect 6 is provided wherein 1.5 MPa/.mu.m.ltoreq.|m1|.ltoreq.15
MPa/.mu.m.
[0015] According to aspect 8 of the disclosure, the glass article
of aspect 6 is provided wherein the stress profile further
comprises a second region extending from the surface to a depth up
to a depth D1, where 9 .mu.m.ltoreq.D1.ltoreq.17 .mu.m, the second
region having a linear portion extending from the surface to a
depth of up to about 5 .mu.m and having a slope m2, wherein 200
MPa/.mu.m.gtoreq.|m2|.gtoreq.30 MPa/.mu.m.
[0016] According to aspect 9 of the disclosure, the glass article
of aspect 8 is provided wherein 160 MPa/.mu.m.gtoreq.|m2|.gtoreq.40
MPa/.mu.m.
[0017] According to aspect 10 of the disclosure, the glass article
of aspect 9 is provided wherein 120 MPa/.mu.m.gtoreq.|m2|.gtoreq.45
MPa/.mu.m.
[0018] According to aspect 11 of the disclosure, the glass article
of any of aspects 1 to 10 is provided wherein the glass article
comprises an alkali aluminosilicate glass.
[0019] According to aspect 12 of the disclosure, the glass article
of aspect 11 is provided wherein the alkali aluminosilicate glass
comprises up to about 10 mol % Li.sub.2O.
[0020] According to aspect 13 of the disclosure, the glass article
of aspect 11 is provided wherein the alkali aluminosilicate glass
is lithium-free.
[0021] According to aspect 14 of the disclosure, the glass article
of aspect 11 is provided wherein the alkali aluminosilicate glass
comprises at least about 4 mol % P.sub.2O.sub.5 and from 0 mol % to
about 5 mol % B.sub.2O.sub.3, wherein
1.3<[(P.sub.2O.sub.5+R.sub.2O)/M.sub.2O.sub.3].ltoreq.2.3, where
M.sub.2O.sub.3=Al.sub.2O.sub.3+B.sub.2O.sub.3, and R.sub.2O is the
sum of monovalent cation oxides present in the alkali
aluminosilicate glass.
[0022] According to aspect 15 of the disclosure, the glass article
of aspect 14 is provided wherein 11 mol
%.ltoreq.M.sub.2O.sub.3.ltoreq.30 mol %.
[0023] According to aspect 16 of the disclosure, the glass article
of aspect 14 is provided wherein the alkali aluminosilicate glass
comprises from about 40 mol % to about 70 mol % SiO.sub.2; from
about 11 mol % to about 25 mol % Al.sub.2O.sub.3; from 0 mol % to
about 5 mol % B.sub.2O.sub.3; from about 4 mol % to about 15 mol %
P.sub.2O.sub.5; from about 13 mol % to about 25 mol % Na.sub.2O;
and from 0 mol % to about 1 mol % K.sub.2O.
[0024] According to aspect 17 of the disclosure, the glass article
of aspect 14 is provided wherein R.sub.xO is the sum of alkali
metal oxides, alkaline earth metal oxides, and transition metal
monoxides present in the glass, and wherein 13 mol
%.ltoreq.R.sub.xO.ltoreq.30 mol %.
[0025] According to aspect 18 of the disclosure, the glass article
of any of aspects 1 to 16 is provided wherein the physical center
tension CT is less than or equal to about 200 MPa.
[0026] According to aspect 19 of the disclosure, the glass article
of aspect 18 is provided wherein the center tension CT is less than
or equal to about 135 MPa.
[0027] According to aspect 20 of the disclosure, the glass article
of aspect 19 is provided wherein the center tension CT is less than
or equal to about 98 MPa.
[0028] According to aspect 21 of the disclosure, the glass article
of any of aspects 1 to 20 is provided wherein DOC>0.15t, wherein
CT(MPa).ltoreq.(85/ t(mm)).
[0029] According to aspect 22 of the disclosure, the glass article
of aspect 21 is provided wherein 0.18t<DOC<0.22t, wherein
CT(MPa).ltoreq.(79/ t(mm)).
[0030] According to aspect 23 of the disclosure, the glass article
of aspect 22 is provided wherein 0.16t<DOC<0.19t, wherein
CT(MPa).ltoreq.(73/ t(mm)).
[0031] According to aspect 24 of the disclosure, the glass article
of any of aspects 1 to 23 is provided wherein the glass article is
non-frangible.
[0032] According to aspect 25 of the disclosure a consumer
electronic product is provided. The consumer electronic product
comprises: a housing having a front surface, a back surface and
side surfaces; electrical components provided at least partially
within the housing, the electrical components including at least a
controller, a memory, and a display, the display being provided at
or adjacent the front surface of the housing; and the glass article
of any of aspects 1 to 24 disposed over the display. According to
aspect 26 of the disclosure a glass article is provided. The glass
article has a thickness t, wherein 0.1 mm.ltoreq.t<0.4 mm, and
comprises: a compressive layer extending from a surface of the
glass article to a depth of compression DOC, the compressive layer
having a stress profile. The stress profile comprises: a first
region extending from at least a first depth D1 to the depth of
compression DOC, wherein at least a portion of the first region is
linear and has a slope ml, wherein 20
MPa/.mu.m.gtoreq.|m1|.gtoreq.1.2 MPa/.mu.m and where 9
.mu.m.ltoreq.D1.ltoreq.17 .mu.m; and a second region extending from
the surface to a depth of up to the first depth D1, the second
region having a linear portion extending from the surface to a
depth of up to about 5 .mu.m or less and having a slope m2, wherein
200 MPa/.mu.m.gtoreq.|m2|.gtoreq.30 MPa/.mu.m; and a tensile region
extending from the depth of compression to a center region of the
glass article, the tensile region under a physical center tension
CT, wherein
CT>|-1.956.times.10.sup.-16.times.t.sup.6+1.24274.times.10.sup.-12.tim-
es.t.sup.5-3.09196.times.10.sup.-9.times.t.sup.4+3.80391.times.10.sup.-6.t-
imes.t.sup.3-2.35207.times.10.sup.-3.times.t.sup.2+5.96241.times.10.sup.-1-
.times.t+36.59941, where t is expressed in microns.
[0033] According to aspect 27 of the disclosure, the glass article
of aspect 26 is provided wherein 0.08t.ltoreq.DOC.ltoreq.0.22t.
[0034] According to aspect 28 of the disclosure, the glass article
of aspect 27 is provided wherein 0.1t.ltoreq.DOC.ltoreq.0.20t.
[0035] According to aspect 29 of the disclosure, the glass article
of any of aspects 26 to 28 is provided wherein the compressive
layer has a compressive stress CS at the surface, and wherein 200
MPa.ltoreq.CS.ltoreq.950 MPa.
[0036] According to aspect 30 of the disclosure, the glass article
of any of aspects 26 to 29 is provided wherein the glass article is
ion exchanged.
[0037] According to aspect 31 of the disclosure, the glass article
of any of aspects 26 to 30 is provided wherein the glass article
comprises an alkali aluminosilicate glass.
[0038] According to aspect 32 of the disclosure, the glass article
of aspect 31 is provided wherein the alkali aluminosilicate glass
comprises up to about 10 mol % Li.sub.2O.
[0039] According to aspect 33 of the disclosure, the glass article
of aspect 31 is provided wherein the glass is lithium-free.
[0040] According to aspect 34 of the disclosure, the glass article
of aspect 31 is provided wherein the alkali aluminosilicate glass
comprises at least about 4 mol % P.sub.2O.sub.5 and from 0 mol % to
about 5 mol % B.sub.2O.sub.3, wherein
1.3<[(P.sub.2O.sub.5+R.sub.2O)/M.sub.2O.sub.3]<2.3, where
M.sub.2O.sub.3=Al.sub.2O.sub.3+B.sub.2O.sub.3, and R.sub.2O is the
sum of monovalent cation oxides present in the alkali
aluminosilicate glass.
[0041] According to aspect 35 of the disclosure, the glass article
of aspect 31 is provided wherein the glass comprises from about 40
mol % to about 70 mol % SiO.sub.2; from about 11 mol % to about 25
mol % Al.sub.2O.sub.3; from 0 mol % to about 5 mol %
B.sub.2O.sub.3; from about 4 mol % to about 15 mol %
P.sub.2O.sub.5; from about 13 mol % to about 25 mol % Na.sub.2O;
and from 0 mol % to about 1 mol % K.sub.2O.
[0042] According to aspect 36 of the disclosure, the glass article
of aspect 31 is provided wherein 11 mol
%.ltoreq.M.sub.2O.sub.3.ltoreq.30 mol %.
[0043] According to aspect 37 of the disclosure, the glass article
of aspect 31 is provided wherein R.sub.xO is the sum of alkali
metal oxides, alkaline earth metal oxides, and transition metal
monoxides present in the glass, and wherein 13 mol
%.ltoreq.R.sub.xO.ltoreq.30 mol %.
[0044] According to aspect 38 of the disclosure, the glass article
of any of aspects 26 to 37 is provided wherein the center tension
CT is less than or equal to about 200 MPa.
[0045] According to aspect 39 of the disclosure, the glass article
of any of aspects 26 to 38 is provided wherein the center tension
CT is less than or equal to about 135 MPa
[0046] According to aspect 40 of the disclosure, the glass article
of any of aspects 26 to 39 is provided wherein the center tension
CT is less than or equal to about 98 MPa.
[0047] According to aspect 41 of the disclosure, the glass article
of any of aspects 26 to 40 is provided wherein DOC>0.15t,
wherein CT(MPa).ltoreq.(85/ t(mm)).
[0048] According to aspect 42 of the disclosure, the glass article
of aspect 41 is provided wherein 0.18t<DOC<0.22t, wherein
CT(MPa).ltoreq.(79/ t(mm)).
[0049] According to aspect 43 of the disclosure, the glass article
of aspect 42 is provided wherein 0.16t<DOC<0.19t, wherein
CT(MPa).ltoreq.(73/ t(mm)).
[0050] According to aspect 44 of the disclosure, the glass article
of any of aspects 26 to 43 is provided wherein the glass article is
non-frangible.
[0051] According to aspect 45 of the disclosure a consumer
electronic product is provided. The consumer electronic product
comprises: a housing having a front surface, a back surface and
side surfaces; electrical components provided at least partially
within the housing, the electrical components including at least a
controller, a memory, and a display, the display being provided at
or adjacent the front surface of the housing; and the glass article
of any of aspects 26 to 44 disposed over the display.
[0052] According to aspect 46 of the disclosure a method of ion
exchanging a glass article having a thickness t, wherein 0.1
mm.ltoreq.t<0.4 mm is provided. The method comprises: ion
exchanging the glass article in a first ion exchange bath at a
temperature in a range from about 300.degree. C. to about
500.degree. C., the first ion exchange bath comprising from about
25% to about 100% KNO.sub.3 by weight and up to about 75%
NaNO.sub.3 by weight; forming a compressive stress layer, the
compressive stress layer extending from a surface of the glass
article to a depth of compression DOC, wherein
0.05t.ltoreq.DOC.ltoreq.0.22t; and forming a tensile region in a
center portion of the glass article, the tensile region extending
from the depth of compression DOC to a center region of the glass
article, the tensile region having a physical center tension CT,
wherein
CT>|-1.956.times.10.sup.-16.times.t.sup.6+1.24274.times.10.sup.-12.tim-
es.t.sup.5-3.09196.times.10.sup.-9.times.t.sup.4+3.80391.times.10.sup.-6.t-
imes.t.sup.3-2.35207.times.10.sup.-3.times.t.sup.2+5.96241.times.10.sup.-1-
.times.t+36.5994|, where t is expressed in microns.
[0053] According to aspect 47 of the disclosure, the method of
aspect 46 is provided wherein forming the compressive layer
comprises forming a stress profile, wherein at least a portion of
the stress profile is linear and has a slope ml, and wherein 200
MPa/.mu.m.gtoreq.|m1|.gtoreq.1 MPa/.mu.m.
[0054] According to aspect 48 of the disclosure, the method of
aspect 46 is provided wherein 20 MPa/.mu.m.gtoreq.|m1|.gtoreq.1.2
MPa/.mu.m.
[0055] According to aspect 49 of the disclosure, the method of
aspect 46 is provided wherein 15 MPa/.mu.m.gtoreq.|m1|.gtoreq.1.5
MPa/.mu.m.
[0056] According to aspect 50 of the disclosure, the method of any
of aspects 46 to 49 is provided further comprising: ion exchanging
the glass article in a second ion exchange bath after ion
exchanging the glass article in the first ion exchange bath, the
second ion exchange bath comprising; and forming a second region of
the stress profile, the second region extending from the surface to
a first depth D1, the second region having a linear portion
extending from the surface to a depth of up to about 5 pm, the
linear portion having a slope m2, wherein 200
MPa/.mu.m.gtoreq.|m2|.gtoreq.30 MPa/.mu.m.
[0057] According to aspect 51 of the disclosure, the method of
aspect 50 is provided wherein 0.08t.ltoreq.DOC.ltoreq.0.22t.
[0058] According to aspect 52 of the disclosure, the method of
aspect 51 is provided wherein 0.1t.ltoreq.DOC.ltoreq.0.20t.
[0059] According to aspect 53 of the disclosure, the method of any
of aspects 46 to 52 is provided wherein the compressive layer has a
compressive stress CS at the surface, and wherein 500
MPa.ltoreq.CS.ltoreq.950 MPa.
[0060] According to aspect 54 of the disclosure, the method of any
of aspects 46 to 53 is provided wherein the glass article is
non-frangible.
[0061] These and other aspects, advantages, and salient features
will become apparent from the following detailed description, the
accompanying drawings, and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] FIG. 1 is a cross-sectional schematic view of an ion
exchanged glass article;
[0063] FIG. 2 is a schematic representation of a compressive stress
profile obtained for a single ion exchange process;
[0064] FIG. 3 is a schematic representation of a compressive stress
profile obtained for a double ion exchange process;
[0065] FIG. 4 is a plot the physical center tension as a function
of the sample thickness for a single ion exchange process;
[0066] FIG. 5 is a plot of stress profiles generated in 200 .mu.m
glass samples by a double ion exchange process;
[0067] FIG. 6 is a is a detail of the stress profiles shown in FIG.
5;
[0068] FIG. 7 is a plot of the physical center tension (CT) limit
and minimum level of NaNO.sub.3 poisoning of the ion exchange bath
as functions of glass thickness for a single ion exchange process;
and
[0069] FIG. 8 is a plot of the physical center tension (CT) limit
and minimum level of NaNO.sub.3 poisoning of the ion exchange bath
as functions of glass thickness for a double ion exchange
process.
[0070] FIG. 9 is a representation of a non-frangible sample after a
frangibility test.
[0071] FIG. 10 is a representation of a frangible sample after a
frangibility test.
[0072] FIG. 11A is a plan view of an exemplary electronic device
incorporating any of the strengthened articles disclosed
herein.
[0073] FIG. 11B is a perspective view of the exemplary electronic
device of FIG. 11A.
DETAILED DESCRIPTION
[0074] 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.
[0075] Referring to the drawings in general and to FIG. 1 in
particular, 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.
[0076] As used herein, the terms "glass article" and "glass
articles" are used in their broadest sense to include any object
made wholly or partly of glass. Unless otherwise specified, all
glass compositions are expressed in terms of mole percent (mol %)
and all ion exchange bath compositions are expressed in terms of
weight percent (wt %).
[0077] 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 "substantially free of Li.sub.2O," for
example, is one in which Li.sub.2O is not actively added or batched
into the glass, but may be present in very small amounts as a
contaminant; i.e., less than 0.1 mol %. "Free of Li.sub.2O" means
that the glass contains 0 mol % Li.sub.2O.
[0078] As used herein, the terms "depth of layer" and "DOL" refer
to the depth of the compressive layer as determined by surface
stress meter (FSM) measurements using commercially available
instruments such as the FSM-6000 stress meter or the like.
[0079] As used herein, the terms "depth of compression" and "DOC"
refer to the depth at which the stress within the glass changes
from compressive to tensile stress. At the DOC, the stress crosses
from a positive (compressive) stress to a negative (tensile) stress
and thus has a value of zero. The depth of compression DOC and
stress profile are determined from the spectra of bound optical
modes for TM and TE polarization by using the inverse
Wentzel-Kramers-Brillouin (IWKB) method, which is described in U.S.
Pat. No. 9,140,543, entitled "Systems And Methods for Measuring the
Stress Profile of Ion-Exchanged Glass (hereinafter referred to as
"Roussev I")," filed by Rostislav V. Roussev et al. on May 3, 2012,
and claiming priority to U.S. Provisional Patent Application No.
61/489,800, having the same title and filed on May 25, 2011. The
contents of the above patent applications are incorporated herein
by reference in their entirety. Other methods known in the art,
including, but not limited to, refractive near filed (RNF),
polarimetric (e.g., scattering linear polarimetry (SCALP)), and
etching and polishing techniques may be used to determine DOC and
the stress profile of the strengthened glass article.
[0080] As use herein, the terms "physical central tension" and
"physical CT" refer to the tensile stress at the center or midpoint
(i.e., t/2, where t is the thickness of the glass article) of the
glass article.
[0081] As described herein, compressive stress (CS) and central
tension or physical center tension (CT) are expressed in terms of
megaPascals (MPa), depth of layer (DOL) and depth of compression
(DOC) are expressed in terms of microns (pm), where 1 .mu.m=0.001
mm, and thickness t is expressed herein in terms of millimeters,
where 1 mm=1,000 .mu.m, unless otherwise specified.
[0082] According to the scientific convention normally used in the
art, compression is expressed as a negative (<0) stress and
tension is expressed as a positive (>0) stress. Throughout the
instant description, however, compressive stress CS is expressed as
a positive or absolute value--i.e., as recited herein, CS=|CS| and
central tension or tensile stress is expressed as a negative value
in order to better visualize the compressive stress profiles
described herein.
[0083] As used herein, the "slope (m)" refers to the slope of a
segment or portion of the stress profile that closely approximates
a straight line. The predominant slope is defined as the average
slope for regions that are well approximated as straight segments.
These are regions in which the absolute value of the second
derivative of the stress profile is smaller than the ratio of the
absolute value of the first derivative at approximately half the
depth of the region. For a steep, shallow segment of the stress
profile near the surface of the strengthened glass article, for
example, the essentially straight segment is the portion for each
point of which the absolute value of the second derivative of the
stress profile is smaller than the absolute value of the local
slope of the stress profile divided by the depth at which the
absolute value of the stress changes by a factor of 2. Similarly,
for a segment of the profile deeper within the glass, the straight
portion of the segment is the region for which the local second
derivative of the stress profile has an absolute value that is
smaller than the absolute value of the local slope of the stress
profile divided by half the DOC.
[0084] For typical stress profiles, this limit on the second
derivative guarantees that the slope changes relatively slowly with
depth, and is therefore reasonably well defined and can be used to
define regions of slope that are important for the stress profiles
that are considered advantageous for drop performance.
[0085] Let the stress profile as a function of depth "x" be given
by the function
.sigma.=.sigma.(x) (1)
and let the first derivative of the stress profile with respect to
depth be
.sigma. ' = d .times. .sigma. dx , ( 2 ) ##EQU00001##
and the second derivative be
.sigma. '' = d 2 .times. .sigma. dx 2 . ( 3 ) ##EQU00002##
[0086] If a shallow segment extends approximately to a depth
d.sub.s, then for the purposes of defining a predominant slope, a
straight portion of the profile is a region where
.sigma. '' .function. ( x ) < 2 .times. .sigma. ' .function. ( x
) d s . ( 4 ) ##EQU00003##
[0087] If a deep segment extends approximately to a larger depth
DOC, or to a larger depth d.sub.d, or to a depth DOL in traditional
terms, then a straight portion of the profile is a region where
.sigma. '' .function. ( x ) < 2 .times. .sigma. ' .function. ( x
) d d .apprxeq. 2 .times. .sigma. ' .function. ( x ) DOC .apprxeq.
2 .times. .sigma. ' .function. ( x ) DOL . ( 5 ) ##EQU00004##
[0088] The latter equation is also valid for a 1-segment stress
profile obtained by a single ion exchange in a salt containing only
a single alkali ion other than the ion being replaced in the glass
for chemical strengthening.
[0089] Preferably, the straight segments are selected as regions
where
.sigma. '' .function. ( x ) < .sigma. ' .function. ( .tau. ) d ,
( 6 ) ##EQU00005##
where d stands for the relevant depth for the region, shallow or
deep.
[0090] The slope m of linear segments of the compressive stress
profiles described herein are given as absolute values of the
slope
d .times. .times. .sigma. dx ##EQU00006##
--i.e., m, as recited herein, is equal to
d .times. .times. .sigma. dx . ##EQU00007##
More specifically, the slope m represents the absolute value of the
slope of a profile for which the compressive stress generally
decreases as a function of increasing depth.
[0091] Compressive stress CS and depth of layer DOL are stress
profile parameters that have been used to enable quality control of
chemical strengthening. Compressive stress CS provides an estimate
of the surface compression, which correlates well with the amount
of stress needed to cause a failure of a glass article,
particularly when the glass is free of deep mechanical flaws. Depth
of layer DOL is used as an approximate measure of the depth of
penetration of the larger (strengthening) cation (e.g., K.sup.+
during K.sup.+ for Na.sup.+ exchange), with larger DOL values
correlating well with greater depths of the compression layer,
protecting the glass by arresting deeper flaws, and preventing
flaws from causing failure under conditions of relatively low
externally applied stress.
[0092] Even with minor to moderate bending of a glass article, the
bending moment induces a stress distribution that is generally
linear with depth from the surface, having a maximum tensile stress
on the outer side of bending, a maximum compressive stress on the
inner side of the bending, and zero stress at the so-called neutral
surface, which is usually in the interior. For tempered glass
parts, this bending-induced constant-slope stress distribution is
added to the tempering stress profile to result in the net stress
profile in the presence of external (bending) stress.
[0093] The net stress profile in the presence of bending-induced
stress within the glass article generally has a depth of
compression DOC that differs from the stress profile without such
bending. In particular, the depth of compression DOC is reduced on
the outer side of the glass article during bending. If the stress
profile has a relatively small stress slope at depths in the
vicinity of and smaller than the DOC, the DOC can substantially
decrease in the presence of bending. In the net stress profile, the
tips of moderately deep flaws could be exposed to tension, while
the same flaw tips would normally be arrested in the compression
region of the stress profile without bending. These moderately deep
flaws can thus grow and lead to fracture during bending.
[0094] As used herein, the terms "error function" and "Erf" refer
to the function which is twice the integral of a normalized
Gaussian function between 0 and x/.sigma. 2, and the terms
"complementary error function"and "Erfc" are equal to 1 minus the
error function; i.e., Erfc=1-Erf(x).
[0095] Frangible behavior refers to specific fracture behavior when
a glass article is subjected to an impact or insult. As utilized
herein, a glass is considered non-frangible when it exhibits at
least one of the following in a test area as the result of a
frangibility test: (1) four or less fragments with a largest
dimension of at least 1 mm, and/or (2) the number of bifurcations
is less than or equal to the number of crack branches. The
fragments, bifurcations, and crack branches are counted based on
any 2 inch by 2 inch square centered on the impact point. Thus a
glass is considered non-frangible if it meets one or both of tests
(1) and (2) for any 2 inch by 2 inch square centered on the impact
point where the breakage is created according to the procedure
described below. In a frangibility test, an impact probe is brought
in to contact with the glass, with the depth to which the impact
probe extends into the glass increasing in successive contact
iterations. The step-wise increase in depth of the impact probe
allows the flaw produced by the impact probe to reach the tension
region while preventing the application of excessive external force
that would prevent the accurate determination of the frangible
behavior of the glass. In one embodiment, the depth of the impact
probe in the glass may increase by about 5 .mu.m in each iteration,
with the impact probe being removed from contact with the glass
between each iteration. The test area is any 2 inch by 2 inch
square centered at the impact point. FIG. 9 depicts a non-frangible
test result. As shown in FIG. 9, the test area is a square that is
centered at the impact point 130, where the length of a side of the
square a is 2 inches. The non-frangible sample shown in FIG. 9
includes three fragments 142, and two crack branches 140 and a
single bifurcation 150. Thus, the non-frangible sample shown in
FIG. 9 contains less than 4 fragments having a largest dimension of
at least 1 mm and the number of bifurcations is less than or equal
to the number of crack branches. As utilized herein, a crack branch
originates at the impact point, and a fragment is considered to be
within the test area if any part of the fragment extends into the
test area. While coatings, adhesive layers, and the like may be
used in conjunction with the strengthened glass articles described
herein, such external restraints are not used in determining the
frangibility or frangible behavior of the glass articles. In some
embodiments, a film that does not impact the fracture behavior of
the glass article may be applied to the glass article prior to the
frangibility test to prevent the ejection of fragments from the
glass article, increasing safety for the person performing the
test.
[0096] A frangible sample is depicted in FIG. 10. The frangible
sample includes 5 fragments 142 having a largest dimension of at
least 1 mm. The sample depicted in FIG. 10 includes 2 crack
branches 140 and 3 bifurcations 150, producing more bifurcations
than crack branches. Thus, the sample depicted in FIG. 10 does not
exhibit either four or less fragments or the number of bifurcations
being less than or equal to the number of crack branches.
[0097] In the frangibility test described herein, the impact is
delivered to the surface of the glass article with a force that is
just sufficient to release the internally stored energy present
within the strengthened glass article. That is, the point impact
force is sufficient to create at least one new crack at the surface
of the strengthened glass sheet and extend the crack through the
compressive stress CS region (i.e., depth of layer) into the region
that is under central tension CT.
[0098] Accordingly, the chemically strengthened glasses described
herein are "non-frangible"--i.e., they do not exhibit frangible
behavior as described hereinabove when subjected to impact by a
sharp object.
[0099] Described herein are glasses having a thickness t, wherein
0.1 mm.ltoreq.t.ltoreq.0.4 mm (100 .mu.m.ltoreq.t.ltoreq.400
.mu.m); such as 0.1 mm.ltoreq.t<0.4 mm (100
.mu.m.ltoreq.t<400 .mu.m); 0.1 mm .ltoreq.t.ltoreq.0.38 mm (100
.mu.m.ltoreq.t.ltoreq.380 .mu.m); 0.1 mm.ltoreq.t.ltoreq.0.35 mm
(100 .mu.m.ltoreq.t.ltoreq.350 .mu.m); and any sub-ranges contained
therein. The glasses are chemically strengthened, having a
compressive layer extending from a surface of the glass article to
a depth of compression DOC (also referred to herein as "DOC") and a
tensile region extending from the depth of compression to a center
region of the glass article. The tensile region is under a physical
center tension CT (also referred to herein as "physical CT"),
wherein
CT>|-1.956.times.10.sup.-16.times.t.sup.6+1.24274.times.10.sup.-12.tim-
es.t.sup.5-3.09196.times.10.sup.-9.times.t.sup.4+3.80391.times.10.sup.-6.t-
imes.t.sup.3-2.35207.times.10.sup.-3.times.t.sup.2+5.96241.times.10.sup.-1-
.times.t+36.59941, where t is expressed in microns. The glasses do
not exhibit undesirable behavior, such as frangibility, when
subjected to a sharp, fracture-inducing impact; i.e., the glasses
are non-frangible.
[0100] A cross-sectional schematic view of an ion exchanged glass
article is shown in FIG. 1. Glass article 100 has a thickness t,
first surface 110, and second surface 112. Glass article 100, in
some embodiments, has a thickness t of up to about 1 mm. While the
embodiment shown in FIG. 1 depicts glass article 100 as a flat
planar sheet or plate, glass article may have other configurations,
such as three dimensional shapes or non-planar configurations.
Glass article 100 has a first compressive layer 120 extending from
first surface 110 to a depth of compression (DOC) d.sub.1 into the
bulk of the glass article 100In the embodiment shown in FIG. 1,
glass article 100 also has a second compressive layer 122 extending
from second surface 112 to a second depth of compression d.sub.z.
First and second compressive layers 120, 122 are each under a
compressive stress CS. In some embodiments, first and second
compressive layers 120, 122 each have a maximum compressive stress
at the first and second surfaces 110, 112, respectively. Glass
article also has a central region 130 that extends from d.sub.1 to
d.sub.z. Central region 130 is under a tensile stress or physical
center tension (CT), which balances or counteracts the compressive
stresses of layers 120 and 122. The depths of compression d.sub.1,
d.sub.2 of first and second compressive layers 120, 122 protect the
glass article 100 l from the propagation of flaws introduced by
sharp impact to first and second surfaces 110, 112 of glass article
100, while the compressive stress minimizes the likelihood of a
flaw penetrating through the depth d.sub.1, d.sub.2 of first and
second compressive layers 120, 122.
[0101] In some embodiments, the depth of compression "DOC" is
greater than 0.05t; such as at least 0.1t; at least 0.15t; and any
sub-ranges contained therein. The depth of compression DOC, in some
embodiments, has a maximum value of about 0.22t (i.e.,
DOC.ltoreq.0.22t).
[0102] The glass, in some embodiments, is ion exchanged, and has a
maximum compressive stress "CS1" in a range from about 200 MPa to
about 950 MPa at the surface of the glass. In some embodiments, the
compressive layer of the strengthened glass has a compressive
stress profile--i.e., the compressive stress varies as a function
of depth beneath the surface of the glass. At least a portion of
the compressive stress profile is linear, the linear portion having
a slope "m1" wherein -200 MPa/.mu.m.ltoreq.m1.ltoreq.1 MPa/.mu.m
or, when expressed in terms of the absolute value of the slope
"|m1|," 200 MPa/.mu.m.gtoreq.|m1|.gtoreq.1 MPa/.mu.m. In some
embodiments, -20 MPa/.mu.m.ltoreq.m1.ltoreq.-1.2 MPa/.mu.m, or 20
MPa/.mu.m.gtoreq.|m1|.gtoreq.1.2 MPa/.mu.m; such as 20
MPa/.mu.m.ltoreq.m1.ltoreq.-1.2 MPa/.mu.m, or 20
MPa/.mu.m.gtoreq.|m1|.gtoreq.1.2 MPa/.mu.m; -15
MPa/.mu.m.ltoreq.m1.ltoreq.-1.5 MPa/.mu.m, or 15
MPa/.mu.m.gtoreq.|m1|.gtoreq.1.5 MPa/.mu.m; and any sub-ranges
contained therein.
[0103] The stress profile, in some embodiments, further includes a
second region extending from the surface to a depth "D1." D1 is in
a range from at least at least about 5 .mu.m up to about 17 .mu.m.
In some embodiments, D1 is at least about 7 .mu.m; such as at least
about 9 .mu.m. In some embodiments, D1 is less than or equal to
about 15 .mu.m; such as less than or equal to about 13 .mu.m. The
second region includes a linear portion extending from the surface
to a depth of up to about 5 .mu.m. The linear portion has a slope
"m2," wherein -200 MPa/.mu.m.ltoreq.m2.ltoreq.-30 MPa/.mu.m or,
expressed in terms of the absolute value of the slope "|m2|," 200
MPa/.mu.m.gtoreq.|m2|.gtoreq.30 MPa/.mu.m. In some embodiments,
-160 MPa/.mu.m.ltoreq.m2.ltoreq.-40 MPa/.mu.m, or 160
MPa/.mu.m.gtoreq.|m2|.gtoreq.40 MPa/.mu.m; such as -120
MPa/.mu.m.ltoreq.m2.ltoreq.-45 MPa/.mu.m, or 120
MPa/.mu.m.gtoreq.|m2|.gtoreq.45 MPa/.mu.m; and any sub-ranges
contained therein.
[0104] In some embodiments, the glass is strengthened by a
single-step ion exchange (SIOX) process in which the glass is
immersed in an ion exchange bath comprising from about 25 wt % to
100 wt % potassium nitrate (KNO.sub.3) and from 0 wt % to about 75
wt % sodium nitrate (NaNO.sub.3). The ion exchange is carried out
at a temperature in a range from about 300.degree. C. to about
500.degree. C. Additional materials such as silicic acid may be
added to the ion exchange bath to improve bath performance.
[0105] In some embodiments, the compressive stress profile obtained
via the SIOX process is substantially linear within the compression
region, as schematically shown in FIG. 2, which is a plot of
compressive stress (CS) as a function of depth within the glass. In
FIG. 2, the compressive stress exhibits substantially linear
behavior, resulting in a straight line compressive stress profile
"a" having a slope "m.sub.a," expressed in MPa/.mu.m, that
intercepts the vertical y-axis at "CS.sub.s." CS profile a
intercepts the x-axis at point "d.sub.a," which is the depth of
compression DOC. At this point, the total stress is zero. Below
DOC, the glass article is in tension, reaching a central physical
center tension approximately midway through the glass
article--i.e., at about t/2.
[0106] In some embodiments, the compressive stress profile a of the
glass article described herein has a slope m.sub.a following the
SIOX step that is within a specified range. The slope m.sub.a, in
some embodiments, is taken as the ratio of the compressive stress
at the surface CS to the depth of compression DOC (i.e., CS/DOC).
In FIG. 2, for example, slope m.sub.a of line a lies between upper
boundary .delta..sub.2 and lower boundary .delta..sub.1. As
described herein, the slope m.sub.a, upper boundary .delta..sub.2,
and lower boundary .delta..sub.1 are expressed in terms of their
absolute values; thus,
.delta..sub.2.gtoreq.m.sub.a.gtoreq..delta..sub.1 is equivalent to
|.delta..sub.2|.gtoreq.|m.sub.a.gtoreq.|.delta..sub.1|. In some
embodiments, the single step ion exchange produces a compressive
stress profile having a slope m.sub.a having an absolute value
"|m.sub.a|" in a range from 1 MPa/.mu.m to about 200 MPa/.mu.m (1
MPa/.mu.m.ltoreq.|m.sub.a|.ltoreq.200 MPa/.mu.m; such as 2
MPa/.mu.m.ltoreq.|m.sub.a|.ltoreq.8 MPa/.mu.m; 3
MPa/.mu.m.ltoreq.|m.sub.a|.ltoreq.6 MPa/.mu.m; 2
MPa/.mu.m.ltoreq.|m.sub.a|.ltoreq.4.5 MPa/.mu.m; and any sub-ranges
contained therein.
[0107] Alternatively, the slope m.sub.a may be expressed in terms
of depth of layer (DOL) as determined by surface stress meter
measurements, and calculated as the ratio of the compressive stress
at the surface CS.sub.s to the DOL (i.e., CS.sub.s/DOL). The
absolute value |m.sub.a| of the slope m.sub.a when expressed in
terms of DOL is in a range from about 0.6 MPa/.mu.m to about 200
MPa/.mu.m; such as from about 0.6 MPa/.mu.m to about 15 MPa/.mu.m;
from about 0.8 MPa/.mu.m to about 10 MPa/.mu.m; from about 1.5
MPa/.mu.m to about 10 MPa/.mu.m; and any sub-ranges contained
therein.
[0108] In some embodiments, the glass is strengthened by a two-step
ion exchange (DIOX) process. Here, the glass is first subjected to
the SIOX process to achieve a deep depth of compression DOC or
depth of layer DOL. The glass is then subjected to a second ion
exchange in a bath comprising at least 95% KNO.sub.3 by weight, in
some embodiments, at least 97% KNO.sub.3 by weight, and, in still
other embodiments, 100% KNO.sub.3 by weight. The second ion
exchange step is typically carried out at temperatures ranging from
about 370.degree. C. to about 410.degree. C. for times ranging from
about 5 minutes to about 30 minutes. In a particular embodiment,
the second ion exchange is carried out at about 390.degree. C. for
about 12 minutes. The depth of compression DOC following the DIOX
process is in a range from about 0.05t to about 0.22t; such as from
about 0.1t to about 0.20t; and any sub-ranges contained
therein.
[0109] The compressive stress profile resulting from the DIOX
process is a combination of more than one substantially linear
function, as schematically shown in FIG. 3. As seen in FIG. 3, the
compressive stress profile has a first segment or portion "a'" and
a second segment or portion "b." At least part of first portion a'
exhibits substantially linear behavior from the strengthened
surface of the glass article to a depth "d.sub.a'." Portion a' has
a slope "m.sub.a'," and y-intercept "CS.sub.s," which is the
compressive stress at the surface of the glass. In some
embodiments, depth d.sub.a' is in a range from about 10 .mu.m to
about 13 .mu.m. The second portion b of the compressive stress
profile is the result of the first ion exchange, or SIOX, step and
extends from approximately depth da.sub.a' to the depth of
compression DOC, and has a slope "m.sub.b." Following the second
ion exchange experiment, the slope m.sub.b of the SIOX portion of
the profile, expressed in terms of the absolute value of m.sub.b
"|m.sub.b|" is in a range from about 1 MPa/.mu.m to about 30
MPa/.mu.m; such as from about 1.2 MPa/.mu.m to about 20 MPa/.mu.m;
from about 1.5 MPa/.mu.m to about 15 MPa/.mu.m; and any sub-ranges
contained therein. The slope m.sub.a' of the DIOX portion of the
profile, expressed in terms of the absolute value of m.sub.a'
(i.e., |m.sub.a'|) is in a range from about 30 MPa/.mu.m to about
200 MPa/.mu.m; such as from about 40 MPa/.mu.m to about 160
MPa/.mu.m; from about 45 MPa.mu./m to about 120 MPa/.mu.m; and any
sub-ranges contained therein. Alternatively, the slope m.sub.a' of
the DIOX portion of the stress profile may be expressed in terms of
depth of layer (DOL) as determined by surface stress meter
measurements, and calculated as the ratio of the compressive stress
at the surface CS.sub.s to the depth of layer DOL (i.e.,
CS.sub.s/DOL). The slope m.sub.a' of the DIOX portion of the stress
profile expressed in terms of DOL is in a range from about 40
MPa/.mu.m to about 200 MPa/.mu.m; such as from about 40 MPa/.mu.m
to about 160 MPa/.mu.m; from about 45 MPa/.mu.m to about 120
MPa/.mu.m; and any sub-ranges contained therein.
[0110] The compressive stress at depth d.sub.a' "CS(d.sub.a')" is
given by the expression
CS(d.sub.a').apprxeq.CS.sub.s-d.sub.a'(m.sub.a' (7).
[0111] In non-limiting examples, the physical center tension "CT"
is about 200 MPa, when the thickness "t" is about 100 .mu.m; the
physical CT is about 135 MPa when the thickness is 200 .mu.m; and
the physical CT is about 96.7 MPa when the thickness is 300
.mu.m.
[0112] In some embodiments, the DOC is in a range from 0.05t to
about 0.22t (0.05t.ltoreq.DOC.ltoreq.0.22.t), where t is the
thickness of the glass.
[0113] The compressive layer has a maximum compressive stress
CS.sub.s in a range from about 200 MPa to about 950 MPa (200
MPa.ltoreq.CS.ltoreq.950 MPa) at the surface of the glass; such as
from about 500 MPa to about 950 MPa (500 MPa.ltoreq.CS.ltoreq.950
MPa); and any sub-ranges contained therein.
[0114] The glasses described herein are ion exchangeable alkali
aluminosilicate glasses, which, in some embodiments, are formable
by down-draw processes, such as slot-draw or fusion-draw processes,
that are known in the art. In particular embodiments, such glasses
may have a liquidus viscosity of at least about 100 kiloPoise (kP);
such as at least about 130 kP. In one embodiment, the alkali
aluminosilicate glass comprises SiO.sub.2, Al.sub.2O.sub.3,
P.sub.2O.sub.5, and at least one alkali metal oxide (R.sub.2O),
wherein 0.75.ltoreq.[(P.sub.2O.sub.5 (mol %)+R.sub.2O (mol
%))/M.sub.2O.sub.3 (mol %)]<1.2, where
M.sub.2O.sub.3=Al.sub.2O.sub.3+B.sub.2O.sub.3. In some embodiments,
the alkali aluminosilicate glass comprises or consists essentially
of: from about 40 mol % to about 70 mol % SiO.sub.2; from 0 mol %
to about 28 mol % B.sub.2O.sub.3; from 0 mol % to about 28 mol %
Al.sub.2O.sub.3; from about 1 mol % to about 14 mol %
P.sub.2O.sub.5; and from about 12 mol % to about 16 mol % R.sub.2O
and, in certain embodiments, from about 40 to about 64 mol %
SiO.sub.2; from 0 mol % to about 8 mol % B.sub.2O.sub.3; from about
16 mol % to about 28 mol % Al.sub.2O.sub.3; from about 2 mol % to
about 12 mol % P.sub.2O.sub.5; and from about 12 mol % to about 16
mol % R.sub.2O. In some embodiments, 11 mol
%.ltoreq.M.sub.2O.sub.3.ltoreq.30 mol %; in some embodiments,13 mol
%.ltoreq.R.sub.xO.ltoreq.30 mol %, where R.sub.xO is the sum of
alkali metal oxides, alkaline earth metal oxides, and transition
metal monoxides present in the glass; and in still other
embodiments, the glass is lithium-free. These glasses are described
in U.S. Pat. No. 9,346,703, entitled "Ion Exchangeable Glass with
Deep Compressive Layer and High Damage Threshold," filed Nov. 28,
2011, by Dana Craig Bookbinder et al. and claiming priority from
U.S. Provisional Patent Application No. 61/417,941, filed on Nov.
30, 2010, and having the same title, the contents of which are
incorporated herein by reference in their entirety.
[0115] In certain embodiments, the alkali aluminosilicate glass
comprises at least about 4 mol % P.sub.2O.sub.5, wherein
(M.sub.2O.sub.3 (mol %)/R.sub.xO (mol %)).ltoreq.1,
M.sub.2O.sub.3=Al.sub.2O.sub.3+B.sub.2O.sub.3, and R.sub.xO is the
the alkali metal oxides, alkaline earth metal oxides, and
transition metal monoxides present in the glass. In some
embodiments, the alkali metal oxides, alkaline earth metal oxides,
and transition metal monoxides are selected from the group
consisting of Li.sub.2O, Na.sub.2O, K.sub.2O, Rb.sub.2O, Cs.sub.2O,
MgO, CaO, SrO, BaO, and ZnO. In some embodiments, the glass is
lithium-free and consists essentially of from about 40 mol % to
about 70 mol % SiO.sub.2; from about 11 mol % to about 25 mol %
Al.sub.2O.sub.3, from about 4 mol % to about 15 mol %
P.sub.2O.sub.5; from about 13 mol % to about 25 mol % Na.sub.2O;
from about 13 to about 30 mol % R.sub.xO, where R.sub.xO is the sum
of the alkali metal oxides, alkaline earth metal oxides, and
transition metal monoxides present in the glass; from about 11 to
about 30 mol % M.sub.2O.sub.3, where
M.sub.2O.sub.3=Al.sub.2O.sub.3+B.sub.2O.sub.3; from 0 mol % to
about 1 mol % K.sub.2O; from 0 mol % to about 4 mol %
B.sub.2O.sub.3, and 3 mol % or less of one or more of TiO.sub.2,
MnO, Nb.sub.2O.sub.5, MoO.sub.3, Ta.sub.2O.sub.5, WO.sub.3,
ZrO.sub.2, Y.sub.2O.sub.3, La.sub.2O.sub.3, HfO.sub.2, CdO,
SnO.sub.2, Fe.sub.2O.sub.3, CeO.sub.2, As.sub.2O.sub.3,
Sb.sub.2O.sub.3, Cl, and Br; and where
1.3<[(P.sub.2O.sub.5+R.sub.2O)/M.sub.2O.sub.3].ltoreq.2.3, where
R.sub.2O is the sum of monovalent cation oxides present in the
glass. In some embodiments, the glass is lithium-free. The glass is
described in U.S. Pat. No. 9,156,724 by Timothy M. Gross, entitled
"Ion Exchangeable Glass with High Crack Initiation Threshold,"
filed Nov. 15, 2012, and U.S. Pat. No. 8,756,262 by Timothy M.
Gross, entitled "Ion Exchangeable Glass with High Crack Initiation
Threshold," filed Nov. 15, 2012, both claiming priority to U.S.
Provisional Patent Application No. 61/560,434 filed Nov. 16, 2011.
The contents of the above patent and applications are incorporated
herein by reference in their entirety.
[0116] The shape and values of the stress profile in an ion
exchanged glass were previously thought to be limited by the center
tension limit--i.e., the center tension above which frangible
behavior was expected to be observed when the glass suffered an
impact sufficient to penetrate the compressive surface layer. This
limit is was usually expressed in terms of the center tension CT,
the value of the tensile stress in the center of the glass at the
position where x=t/2. This center tension occurs naturally due to
the force balance of the compressive stress induced in the sample
during the ion exchange process. The integral or sum of the stress
at each point in the compressive portion of the stress profile must
equal the integral or sum of the stress at each point in the
tensile portion of the profile, so that the glass article is not
curved or warped by the ion exchange process.
[0117] It is assumed that in the stress profile obtained by the
single ion exchange process, ion diffusion is guided by a classical
complementary error function. It was experimentally shown that this
limits the physical center tension CT limit, and that the CT limit
varied with thickness, as shown in FIG. 4, which is a plot of the
physical center tension CT limit as a function of glass thickness.
In FIG. 4, the center tension limit data are given for single ion
exchange (SIOX) and follow an approximated complementary error
function (erfc) shape (line B). The CT limit is given by the
expression
CT=-1.956.times.10.sup.16t.sup.6+1.24274.times.10.sup.-12t.sup.5-3.09196-
.times.10.sup.-9t.sup.4+3.80391.times.10.sup.-6t.sup.3-2.35207.times.10.su-
p.-3t.sup.2+5.96241.times.10.sup.-1t+36.5994 (8),
where t is expressed in microns.
[0118] A curve (line A in FIG. 4) may be used to determine other
physical center tension limit values for glass thicknesses ranging
from 100 .mu.m to 1,200 .mu.m. Based on curve A, the physical CT
limit for an ion exchanged glass article having a thickness of 300
.mu.m is approximately 97 MPa; for 200 .mu.m glass thickness, the
CT limit is approximately 135 MPa; and for 100 .mu.m glass
thickness, the CT limit is approximately 200 MPa.
[0119] Examples of stress profiles generated in glass samples
having a thickness of 200 .mu.m by a double ion exchange (DIOX)
process are shown in FIG. 5. FIG. 6, shows a portion of FIG. 5 in
more detail. The stress profiles were determined from the spectra
of bound optical modes for TM and TE polarization by using the
inverse Wentzel-Kramers-Brillouin (IWKB) method, previously
described hereinabove. The first ion exchange step was carried out
in a "poisoned" (i.e., comprising greater than 30 wt % NaNO.sub.3)
bath that is a mix of NaNO.sub.3 and KNO.sub.3. The second ion
exchange step is carried out in an ion exchange bath containing
mostly (i.e., .gtoreq.96 wt %) KNO.sub.3 with little poisoning,
creating a "spike" (i.e. a steep increase in compressive stress at
the surface of the glass) in the stress profile. For the glass
thicknesses (0.1-0.4 mm) described herein, ions diffusing into the
glass from opposite surfaces may meet at the center t/2 of the
glass in reasonably short ion exchange times. Before the diffusing
ions reach the center t/2, the stress profile produced by the first
ion exchange step takes the form of a complementary error-function
(Erfc). After the diffusing ions reach the center of the glass, the
overall stress profile obtained by the first ion exchange step
resembles a parabolic function. The spike creates a change in the
slope of the stress profile, leading to a higher compressive stress
at the surface. The depth of compression (DOC) is the point where
the compressive stress is zero (i.e., the point at which the stress
transitions from compressive to tensile stress). The center tension
is the value of the stress in the center or midpoint between the
opposing major surfaces of the glass (i.e., t/2).
[0120] A series of experiments were conducted on ion exchanged
glass having an initial thickness of 200 .mu.m. The samples were
first ion exchanged in a poisoned ion exchange bath (49 wt %
NaNO.sub.3//51 wt % KNO.sub.3) at about 450.degree. C. for 1.5
hours, 2 hours, 4 hours, 8 hours, 12 hours, 14 hours, and 16 hours,
followed by ion exchange at about 390.degree. C. for 12 min (0.2
hour) in a second bath of pure (100 wt %) KNO.sub.3. None of these
ion exchanged glass samples exhibited frangible behavior when
impact tested, indicating that that there is a region where ions
from the ion exchange bath may diffuse for any period of time
without resulting in frangible behavior of the glass. This may be
attributed to the level of poisoning of the ion exchange bath (or
baths) that is used to obtain the compressive stress spike. This
minimum level of poisoning should correlate with or correspond to
the maximum allowable CT for a given thickness as described in FIG.
5. When the ion exchange bath poisoning exceeds the minimum level,
the physical central tension CT for the glasses described herein
may exceed the CT limit (i.e., CT exceeds the frangibility limit
given in equation (8)) without exhibiting frangible behavior. Thus,
the lower limit of the maximum physical tension CT in the glass may
be given by the expression:
CT>|-1.956.times.10.sup.-16t.sup.6+1.24274.times.10.sup.-12t.sup.5-3.-
09196.times.10.sup.-9.sup.4+3.80391.times.10.sup.-6t.sup.3-2.35207.times.1-
0.sup.-3t.sup.2+5.96241.times.10.sup.-1t+36.5994| (9),
where t is expressed in microns.
[0121] The level of ion exchange bath poisoning required to reach a
condition in which ions may diffuse indefinitely without producing
frangible behavior has been estimated and experimentally confirmed.
FIG. 7 is a plot of the CT limit (line A) and minimum level of
NaNO.sub.3 poisoning (line B) of the ion exchange bath as functions
of glass thickness for a single ion exchange (SIOX) process. At
poisoning levels above line B, ions can diffuse indefinitely
without producing frangible behavior.
[0122] When the glass is subjected to a second ion exchange to
provide a sharp increase or "spike" in compressive stress at the
surface of the glass, the minimum bath poisoning levels at which
indefinite diffusion of ions without producing frangibility will
shift. The CT limit (line A) and minimum level of NaNO.sub.3
poisoning (line B) of the ion exchange bath as functions of glass
thickness are plotted for a two-step or double ion exchange (DIOX)
process in FIG. 8. As with single-step ion exchange (FIG. 2), ions
may diffuse indefinitely without achieving frangibility when
poisoning levels exceed the lower limit of line B. With two-step
ion exchange, the ion diffusion resulting from ion exchange in a
bath of 100 wt % KNO.sub.3 for 12 minutes at 390.degree. C. induces
additional stress in the sample, which shifts the minimum poisoning
limit in order to compensate for the additional stress induced in
the sample. The two-step ion exchange process increases the minimum
poisoning level needed to achieve the diffusion effect described
above by about 10%.
[0123] The shape of the stress profile, depth of compressive layer
DOL, physical center tension CT, and the threshold for frangible
behavior for glasses with substantially nonlinear diffusion may be
obtained from an empirical model, summarized in Table 1. Based on
modeling, frangible behavior is expected in an alkali
aluminosilicate glass having a thickness of 200 .mu.m (0.2 mm) when
the glass is subjected to single ion exchange in a molten salt bath
of essentially pure KNO.sub.3 to achieve a depth of layer DOL of
about 27 .mu.m, a maximum compressive stress CS at the surface of
about 820 MPa, and a physical CT of about 107.+-.5 MPa. The depth
of compression DOC of this glass is estimated to be about 21.5
.mu.m. While the high CS is desirable for strength in applications
such as of thin glass covers, the low depth of compression DOC of
21.5 .mu.m is a concern for fracture caused by flaw introduction.
In another example, the CS is reduced, the DOL is increased by ion
exchange (SIOX) in a single bath containing about 5 wt % NaNO.sub.3
with the balance being essentially KNO.sub.3. The onset of
frangible behavior now occurs at a DOL of about 36.5 .mu.m, with a
CS of about 610 MPa, a DOC of about 26.8 .mu.m, and a physical CT
of about 113.+-.5 MPa. In another example, in an ion exchange
mixture having about 10 wt % NaNO.sub.3 with the balance being
essentially KNO.sub.3, the frangible behavior is approached when
the DOL is about 47 .mu.m, the CS is about 490 MPa, the DOC is
about 31.5 .mu.m, and the physical CT is about 120.+-.5 MPa. The
DOC is almost 50% greater than that of a sample prepared in a pure
KNO.sub.3 bath, and may provide substantially better protection
against flaw introduction, and may therefore be preferred in
applications where the glass is less protected against flaw
introduction by the overall system design.
TABLE-US-00001 TABLE 1 Summary of properties calculated for ion
exchanged alkali aluminosilicate glass having a thickness of 200
.mu.m (0.2 mm). Bath CS (MPa) DOL (.mu.m) DOC (.mu.m) CT (MPa) SIOX
100 wt % KNO.sub.3 820 27 21.5 107 .+-. 5 SIOX 5 wt % NaNO.sub.3
610 36.5 26.8 113 .+-. 5 SIOX 10 wt % NaNO.sub.3 490 47 31.5 120
.+-. 5
[0124] In one example of the empirical model, an alkali
aluminosilicate glass having a nominal composition of about 57 mol
% SiO.sub.2, 0 mol % B.sub.2O.sub.3, about 17 mol %
Al.sub.2O.sub.3, about 7% P.sub.2O.sub.5, about 17 mol % Na.sub.2O,
about 0.02 mol % K.sub.2O, and about 3 mol % MgO and a thickness of
200 .mu.m is subjected to a two-step ion exchange process. A first
ion exchange is performed at about 450.degree. C. for about 5.5
hours in a molten ion exchange bath containing about 51 wt %
KNO.sub.3 and about 49 wt % NaNO.sub.3, resulting in in a
compressive stress at the largest DOL of about 87 .mu.m, and a
physical CT of up to about 114 MPa. The depth of layer DOL
following the first ion exchange step is in a range from about 0.3t
to about 0.44t, where t is the thickness. The glass is then
subjected to a second ion exchange step in a bath containing about
0.5 wt % NaNO.sub.3 and about 99.5 wt % KNO.sub.3 for 15 minutes at
390.degree. C. Following the second ion exchange step, the CS is
about 796 MPa at the surface, and the shallow, steep "spike" region
produced by the second ion exchange step extended from the surface
of the glass to a depth of about 12-13 .mu.m. The physical CT after
the second step is about 154 MPa and is estimated to be near the
onset of frangibility in this regime of deep ion exchange with a
sharp CS spike at the surface. The depth of compression is about 44
.mu.m before the addition of the spike in the second ion exchange
step, and about 34.5 .mu.m after the spike. The slope of the deep
(i.e., the segment of the stress profile extending from a depth of
about 13 .mu.m to the DOL or DOC) portion of the profile within the
compression region is about 4.5 MPa/.mu.m. In this example the DOL
is about 0.435t, where t is the thickness of the glass, and the
K.sup.+ concentration profiles from the two ends of the substrate
barely reach the center of the glass (t/2). In some embodiments,
the absolute value of the slope of the deep portion of the
compression region is a range from about 2 MPa/.mu.m to about 15
MPa/.mu.m.
[0125] In another example of the empirical model, an alkali
aluminosilicate glass having a nominal composition of about 57 mol
% SiO.sub.2, 0 mol % B.sub.2O.sub.3, about 17 mol %
Al.sub.2O.sub.3, about 7% P.sub.2O.sub.5, about 17 mol % Na.sub.2O,
about 0.02 mol % K.sub.2O, and about 3 mol % MgO and a thickness of
200 .mu.m is subjected to a two-step ion exchange process. A first
ion exchange is performed at about 450.degree. C. for about 4.8
hours in a molten ion exchange bath containing about 57 wt %
KNO.sub.3 and about 43 wt % NaNO.sub.3. After the first ion
exchange step, the maximum compressive stress at the surface of the
glass was 218 MPa, the depth of layer DOL was about 87 .mu.m, and
the physical CT was about 129 MPa. The following the first ion
exchange step, the DOL is preferably in a range from about 0.3t to
about 0.44t. A second ion exchange step was performed for 12
minutes at 390.degree. C. in a bath containing about 2.5 wt %
NaNO.sub.3 and about 95 wt % KNO.sub.3. The CS after the second
step is about 720 MPa, and the shallow, steep "spike" region
produced by the second step extended from the surface of the glass
to a depth of about 11 .mu.m. The physical CT after the second step
is about 158 MPa, and is estimated to be near the onset of
frangibility in this regime of deep ion exchange with a sharp CS
spike at the surface. The depth of compression DOC is about 44
.mu.m before the addition of the spike in the second ion exchange
step, and about 38 .mu.m after formation of the spike. The absolute
value of the slope of the deep portion of the profile within the
compression region is about 5 MPa/.mu.m. In this example the DOL is
about 0.435t, and the K.sup.+ concentration profiles from the two
ends of the substrates barely reach the center of the thickness
(t/2).
[0126] In another example of the empirical model, an alkali
aluminosilicate glass having a thickness of 200 .mu.m and nominal
composition of about 57 mol % SiO.sub.2, 0 mol % B.sub.2O.sub.3,
about 17 mol % Al.sub.2O.sub.3, about 7% P.sub.2O.sub.5, about 17
mol % Na.sub.2O, about 0.02 mol % K.sub.2O, and about 3 mol % MgO
is subjected to a two-step ion exchange process. A first ion
exchange is performed at about 450.degree. C. for about 4.25 hours
in a molten ion exchange bath containing about 58 wt % KNO.sub.3
and about 42 wt % NaNO.sub.3. After the first ion exchange step,
the maximum compressive stress at the surface of the glass was 229
MPa, the depth of layer DOL was about 82 .mu.m, and the physical CT
was about 123 MPa. A second ion exchange step was performed for 12
minutes at 390.degree. C. in a bath containing about 2.5 wt %
NaNO.sub.3 and about 95 wt % KNO.sub.3. The CS after the second
step is about 730 MPa, and the shallow, steep "spike" region
produced by the second step extended from the surface of the glass
to a depth of about 11 .mu.m. The physical CT after the second step
is about 153 MPa, and is estimated to be near the onset of
frangibility in this regime of deep ion exchange with a sharp CS
spike at the surface. The depth of compression DOC is about 43
.mu.m before the addition of the spike in the second ion exchange
step, and about 37 .mu.m after formation of the spike. The slope of
the deep portion of the profile within the compression region is
about 5.3 MPa/.mu.m. In this particular embodiment, the depth of
layer after the first step should be between about 0.3t and about
0.43t and, in some embodiments, between about 0.35t and about
0.42t.
[0127] The experimental physical center tension CT limits shown in
FIG. 4 have been obtained for stress profiles generally having a
ratio of DOC to thickness t of 0.15 or less. Based on observations
of non-frangible and frangible samples having higher DOC/t ratios,
the upper (i.e., frangibility) limit for the physical center
tension as a function of thickness is greater when the depth of
compression and stress profile are relatively deep, e.g., when
DOC>0.12t, and, in some embodiments, DOC>0.15t. In order to
be non-frangible, the physical center tension CT of the ion
exchanged glasses described herein should not exceed this upper
limit. In some embodiments, the upper physical CT limit
"CT.sup.upper" is given by the expression
CT.sup.upper(MPa)=(85/ t(mm)) (10),
and, in certain embodiments,
CT.sup.upper(MPa)=(79/ t(mm)) (11).
[0128] The CT limit given in equation (11) is particularly
recommended when the depth of compression DOC achieved by single
(SIOX) or double (DIOX) ion exchange processes is less than about
0.22t and greater than about 0.18t (i.e., 0.18t<DOC<0.22t).
For example, in order to avoid undesired behavior, such as
frangible behavior, an ion exchanged 0.2 mm thick glass sample
having a DOL of 87 .mu.m and a DOC of 38 um following the second
step of the DIOX process should have a physical CT that is less
than or equal to the CT.sup.upper value provided by equation (11).
Equation (11) may also be used for stress profiles achieved by a
SIOX process when the concentration of the ions from the ion
exchange bath in the center of the substrate begins to increase
measurably as a result of the ion exchange.
[0129] In those embodiments in which in which
0.16t<DOC<0.19t, the physical CT should not exceed a reduced
upper limit:
CT.sup.upper(MPa)=(73/ t(mm)) (12),
which was imposed on a 0.2 mm thick example in which the DOL was
about 82 .mu.m and the DOC was about 37 .mu.m after the second step
of the DIOX process.
[0130] The strengthened articles disclosed herein may be
incorporated into another article such as an article with a display
(or display articles) (e.g., consumer electronics, including mobile
phones, tablets, computers, navigation systems, and the like),
architectural articles, transportation articles (e.g., automotive,
trains, aircraft, sea craft, etc.), appliance articles, or any
article that requires some transparency, scratch-resistance,
abrasion resistance or a combination thereof. An exemplary article
incorporating any of the strengthened articles disclosed herein is
shown in FIGS. 11A and 11B. Specifically, FIGS. 11A and 11B show a
consumer electronic device 200 including a housing 202 having front
204, back 206, and side surfaces 208; electrical components (not
shown) that are at least partially inside or entirely within the
housing and including at least a controller, a memory, and a
display 210 at or adjacent to the front surface of the housing; and
a cover substrate 212 at or over the front surface of the housing
such that it is over the display. In some embodiments, the cover
substrate 212 may include any of the strengthened articles
disclosed herein.
[0131] While typical embodiments have been set forth for the
purpose of illustration, the foregoing description should not be
deemed to be a limitation on the scope of the disclosure or
appended claims. Accordingly, various modifications, adaptations,
and alternatives may occur to one skilled in the art without
departing from the spirit and scope of the present disclosure or
appended claims.
* * * * *