U.S. patent application number 15/612052 was filed with the patent office on 2017-09-21 for surface nitrided alkali-free glasses cross-reference to related applications.
The applicant listed for this patent is CORNING INCORPORATED. Invention is credited to Andrea Weiss Bookbinder, Dana Craig Bookbinder, Timothy Michael Gross, Pushkar Tandon.
Application Number | 20170267571 15/612052 |
Document ID | / |
Family ID | 53264815 |
Filed Date | 2017-09-21 |
United States Patent
Application |
20170267571 |
Kind Code |
A1 |
Bookbinder; Andrea Weiss ;
et al. |
September 21, 2017 |
SURFACE NITRIDED ALKALI-FREE GLASSES CROSS-REFERENCE TO RELATED
APPLICATIONS
Abstract
Alkali-free glasses are disclosed having (in weight %)
50.ltoreq.SiO.sub.2.ltoreq.80%,
2.ltoreq.Al.sub.2O.sub.3.ltoreq.17%,
8.ltoreq.B.sub.2O.sub.3.ltoreq.36%, and greater than or equal to 2%
and less than or equal to 25% of at least one of CaO, MgO, BaO, SrO
or ZnO. The alkali-free glasses can have a surface layer with
greater than 0.2 weight % N. Such alkali-free glasses are achieved
by nitriding processes and exhibit increased strength, scratch
resistance and chemical durability.
Inventors: |
Bookbinder; Andrea Weiss;
(Corning, NY) ; Bookbinder; Dana Craig; (Corning,
NY) ; Gross; Timothy Michael; (Corning, NY) ;
Tandon; Pushkar; (Painted Post, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNING INCORPORATED |
Corning |
NY |
US |
|
|
Family ID: |
53264815 |
Appl. No.: |
15/612052 |
Filed: |
June 2, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14710130 |
May 12, 2015 |
9695081 |
|
|
15612052 |
|
|
|
|
61993488 |
May 15, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03C 2201/02 20130101;
C03C 23/007 20130101; C03C 3/06 20130101; C03C 3/111 20130101; C03C
21/007 20130101; Y10T 428/315 20150115; C03C 3/091 20130101; C03C
3/045 20130101; C03C 2201/24 20130101 |
International
Class: |
C03C 3/04 20060101
C03C003/04; C03C 21/00 20060101 C03C021/00; C03C 23/00 20060101
C03C023/00; C03C 3/06 20060101 C03C003/06; C03C 3/091 20060101
C03C003/091; C03C 3/11 20060101 C03C003/11 |
Claims
1-30. (canceled)
31. A method of strengthening an alkali-free glass composition
comprising: subjecting a glass article comprising the alkali-free
glass composition to a heated gas mixture, wherein the gas mixture
comprises at least one nitrogen-containing compound, for a time and
at a temperature sufficient to create in at least one surface of
the glass article a nitrogen-containing layer comprising greater
than 0.2 weight % N, wherein the nitrogen-containing layer
increases the Young's modulus of the article.
32. The method according to claim 31 wherein the gas mixture
comprises NH3.
33. The method according to claim 31 wherein the time is from 24 to
240 hours and the temperature of the gas mixture is from
200.degree. C. and 1200.degree. C., and the gas pressure is between
0.2 to 20 atmospheres.
34. An article comprising an alkali-free glass composition
comprising a substrate comprising at least 99.9 wt % SiO2, the
alkali-free glass composition comprising a surface layer comprising
greater than 0.2 weight % N.
35. The article according to claim 34 wherein the surface layer
comprises a thickness of greater than 1 nm.
36. The article according to claim 34 wherein the surface layer
comprises greater than 1 weight % N.
37. An article comprising an alkali-free glass composition
comprising a molar volume greater than 26 cm3/mole, the composition
comprising a surface layer comprising greater than 0.2 weight %
N.
38. The article according to claim 37 wherein the molar volume is
greater than 27 cm3/mole.
39. The method according to claim 31, wherein the Young's modulus
increases by at least about 17%.
40. The method according to claim 31, wherein the Young's modulus
is at least about 72.7 GPa.
41. The method of according to claim 40, wherein the Young's
modulus is in a range from about 72.7 GPa to about 137.7 GPa.
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.
61/993,488 filed on May 15, 2014 the content of which is relied
upon and incorporated herein by reference in its entirety.
BACKGROUND
[0002] The present disclosure relates to surface nitrided
alkali-free glasses. The disclosure also relates to articles made
from such glasses, and methods for obtaining such glasses and
related articles.
[0003] Glass sheets or panels are finding increased use in devices
with "touch" capability. Glass sheets that are used in touch
devices can be formed by different methods, including fusion draw
process, float process, etc. The glass sheets made by the foregoing
processes inherently have only moderate intrinsic strength and
scratch resistance. Since the devices which employ touch
applications involve heavy handling and usage, the moderate
intrinsic strength and scratch resistance are not sufficient for
the glasses to be robust in these environments. Thus, there is an
immediate and critical need for glasses with higher strength and
scratch resistance.
SUMMARY
[0004] Compositions and articles disclosed herein provide
alkali-free glasses exhibiting improved strength (including edge
strength), scratch resistance and chemical durability properties.
"Alkali-free" as used herein means alkali metals were not
intentionally added although trace amounts may be present as
contaminants.
[0005] In accordance with one embodiment, articles including
alkali-free glass with improved strength, scratch resistance and
chemical durability are provided. Articles with the foregoing
characteristics may be formed by exposing post-formed alkali-free
glass sheets to a gas environment including at least one
nitrogen-containing compound at high temperatures to nitride the
glass sheet surface and edges. Surface nitriding solves the
problems of weak edge strength from exposed tension layer(s) on cut
strengthened glass, cut fusion laminate glass or thermally tempered
glass, as well as low strength flaws on unstrengthened glass.
Methods disclosed herein are compatible with low-cost, large-scale
manufacturing of glass sheets, which may be used in low-cost,
high-performance touch panel devices. For example, surface nitrided
alkali-free glass sheets (e.g., Eagle XG.RTM. glass and Lotus.TM.
glass) may be used for touch applications and made in thin film
transistor (TFT) fabrications. The presently disclosed glasses are
particularly well-suited to indium tin oxide (ITO) touch
application in TFT fabrications in which there is excess
manufacturing capacity, but alkali glass cannot be used due to
concerns of contaminating the fabrication.
[0006] Glass articles in accordance with the present disclosure may
be planar, such as sheets, or three-dimensional bodies, such as a
bottle, vial, etc. Glass sheets can be monoliths or may be employed
as one or more layers of a multi-layer glass laminate. The glass
sheets may also have 3D formats. Surface nitrided strengthened
glass that has been cut to expose unstrengthened edge(s) and fusion
laminated glass sheets are also disclosed.
[0007] The glass compositions may include phosphate and borate
glasses that have a tendency to incorporate higher amount of
nitride during the nitriding process.
[0008] In accordance with one embodiment, alkali-free glasses which
may be suitable for nitriding, or have been subjected to nitriding,
in accordance with the present disclosure may include in weight
percent 50.ltoreq.SiO.sub.2.ltoreq.80%,
2.ltoreq.Al.sub.2O.sub.3.ltoreq.17%,
8.ltoreq.B.sub.2O.sub.3.ltoreq.36%, and greater than or equal to 2%
and less than or equal to 25% of at least one of CaO, MgO, BaO, SrO
or ZnO. The alkali-free glasses can also include in weight percent
0-5% other minor components excluding alkali metals.
[0009] In accordance with another embodiment, alkali-free glasses
which may be suitable for nitriding, or have been subjected to
nitriding, in accordance with the present disclosure may include in
weight percent on an oxide basis 65.ltoreq.SiO.sub.2.ltoreq.75%,
7.ltoreq.Al.sub.2O.sub.3.ltoreq.13%,
5.ltoreq.B.sub.2O.sub.3.ltoreq.36%, 5.ltoreq.CaO.ltoreq.15%,
0.ltoreq.BaO.ltoreq.5%, 0.ltoreq.MgO.ltoreq.3% and
0.ltoreq.SrO.ltoreq.5%.
[0010] In yet a further embodiment, alkali-free glasses which may
be suitable for nitriding, or have been subjected to nitriding, in
accordance with the present disclosure may include P.sub.2O.sub.5,
which may provide more efficient nitriding. Such P.sub.2O.sub.5
containing alkali-free glasses may include in weight percent on an
oxide basis 40.ltoreq.SiO.sub.2.ltoreq.70%,
0.ltoreq.Al.sub.2O.sub.3.ltoreq.20%,
1.ltoreq.P.sub.2O.sub.5.ltoreq.15%,
0.ltoreq.B.sub.2O.sub.3.ltoreq.25%, and greater than or equal to 0%
and less than or equal to 25% of at least one of CaO, MgO, BaO, SrO
or ZnO.
[0011] In still another embodiment, alkali-free glass which may be
suitable for nitriding, or has been subjected to nitriding, in
accordance with the present disclosure is comprised essentially of
at least 99.9% (in weight %) pure silica (SiO.sub.2). "Pure silica"
as used herein means silicon dioxide to which other materials were
not intentionally added although trace amounts may be present as
contaminants.
[0012] Methods are disclosed for strengthening alkali-free glasses
disclosed herein. In one embodiment, a method of strengthening an
alkali-free glass composition includes nitriding the surface and/or
edges of a glass sheet in which the sheet is exposed to a plasma or
heated gas mixture, wherein the gas mixture includes of at least
one nitrogen containing compound such as N.sub.2, NH.sub.3, forming
gas (N.sub.2+H.sub.2) or mixture thereof.
[0013] Other aspects, features, and advantages will be apparent to
one skilled in the art from the description herein taken in
conjunction with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
[0014] For the purposes of illustration, one or more embodiments
are shown in the drawings, it being understood, however, that the
embodiments disclosed and described herein are not limited to the
precise arrangements and instrumentalities shown.
[0015] FIG. 1 is a schematic view of an alkali-free glass substrate
with a nitrogen-containing layer in accordance with one or more
embodiments disclosed herein;
[0016] FIG. 2 is a schematic, side view of the glass substrate of
FIG. 1 taken through cross-sectional line 2-2 indicating nitriding
of a surface;
[0017] FIG. 3 is a graphical depiction of the sensitivity of glass
Young's Modulus in the nitrided layer based on the N content;
[0018] FIG. 4 is a graphical depiction of weight percent nitrogen
(N) as a function of depth from the surface for a 1 mm thick silica
sheet (Glass A) treated with NH.sub.3, as measured by secondary ion
mass spectroscopy (SIMS);
[0019] FIG. 5 is a graphical depiction of weight percent nitrogen
(N) as a function of depth from the surface for a 0.7 mm thick
alkali-free sheet (Glass E) treated with NH.sub.3, as measured by
secondary ion mass spectroscopy (SIMS);
[0020] FIG. 6 is a graphical depiction of Young's modulus as a
function of depth for a non-alkali aluminosilicate sheet (Glass E)
treated with NH.sub.3; and
[0021] FIG. 7 is a graphical depiction of hardness as a function of
depth for a non-alkali aluminosilicate sheet (Glass E) treated with
NH.sub.3.
DETAILED DESCRIPTION
[0022] Various embodiments disclosed herein are directed to
alkali-free nitride strengthened glasses. In order to provide a
fuller understanding of how the discoveries herein were achieved,
and therefore the broad scope of the contemplated embodiments, a
discussion of certain experimentation and/or theory will be
provided. It is noted, however, that the embodiments herein are not
necessarily limited to any such experimentation and/or theory.
General Structure and Considerations
[0023] With reference to FIG. 1, a structure 100 may include an
alkali-free glass article 102 of interest in connection with the
development of novel processes and structures to improve the
strength, scratch resistance and chemical durability properties of
the alkali-free glass article 102.
[0024] With reference to FIG. 2, one or more embodiments herein
provide for a structure 100 having an alkali-free glass article 102
with a nitrogen-containing layer 104. In a broad aspect, the
structure 100 includes the alkaline-free glass article 102 and at
least one nitrogen-containing layer 104 substantially covering at
least a portion of a surface of the article 102. It is noted that
the phrase "substantially covering" herein means that the superior
layer (i.e., the layer 104) overlies the inferior layer (i.e., a
surface of the article 102). In one or more embodiments, the layer
104 may be disposed on any or all of the sides of the article
102.
[0025] In the illustrated examples, the alkali-free-glass article
102 is substantially planar, although other embodiments may employ
a curved or otherwise shaped or sculpted article 102 (e.g., a
three-dimensionally (3D) shaped glass article). Additionally or
alternatively, the thickness of the article 102 may vary, for
aesthetic and/or functional reasons, such as employing a higher
thickness at edges of the article 102 as compared with more central
regions.
Methods
[0026] Nitrided glass articles as described herein may be formed by
exposing post-formed alkali-free glass sheets to a heated gas
mixture including ammonia to nitride the article surface and edges.
The gas mixture including ammonia may include other gases such as
nitrogen, forming gas (N.sub.2+H.sub.2), etc. Nitriding of the
glass surfaces creates a diffusion layer of nitride into the
surface by exchanging O in the network for N, and unlike a
sputtered coating (e.g., sputtering SiON or AlN), without being
confined to a single theory, it is believed this nitride diffusion
layer does not create surface flaws and/or reduces existing flaws
in the glass surface by blunting them.
[0027] The mole fraction of ammonia in the gas mixture may be
between 0.02 and 1, in some embodiments between 0.05 and 0.8 and in
other embodiments between 0.1 and 0.6. In yet other embodiments, a
mixture of ammonia and nitrogen is used for nitriding, wherein the
ratio of ammonia to nitrogen is between about 10:1 to 1:20. In some
embodiments the gas composition flowed to the furnace is 100%
ammonia. In other embodiments, the gas composition flowed to the
furnace is 5% ammonia/95% N.sub.2. The composition of gas in the
furnace is typically in the range of 5-100% NH.sub.3. In some
cases, when flowing 100% NH.sub.3 to the furnace the NH.sub.3 may
partially decompose to N.sub.2+H.sub.2, so there may be between 30
to 90% NH.sub.3 in the furnace, with the remainder being
N.sub.2+H.sub.2 (1:3 ratio).
[0028] In general the flow rate of gas to the furnace in terms of
volumetric turnovers per hour is in the range of 0.2 to 10. The
furnace pressure in terms of atmospheres (absolute) is in the range
of 1 to 20. In one example, at a pressure of 1 atmosphere the flow
rate may be in the range of about 2-8 turnovers per hour. In
another example at a pressure of 100 psig the flow rate may be
about 1 turnover per hour.
[0029] In some embodiments, the nitriding temperature is between
the strain point and the anneal point of the glass. In some other
embodiments, the nitriding temperature is less than 100.degree. C.
above the anneal point of the glass and in yet other embodiments,
the nitriding temperature is less than 50.degree. C. above the
anneal point of the glass. In various embodiments the nitriding
temperature may fall within a range. For example, the nitriding
temperature may be from about 200.degree. C. to about 1200.degree.
C. In one embodiment the temperature is from about 300.degree. C.
to about 525.degree. C. In another embodiment the temperature is
from about 350.degree. C. to about 425.degree. C.
[0030] Exposure to nitriding gas may be for extended time periods.
The nitriding process exposure time may range from about 24 hours
to about 240 hours. For example in one embodiment the nitriding
process was conducted for 24 hours. In another embodiment, the
process was conducted for 168 hours. In yet another embodiment, the
process was conducted for 240 hours.
[0031] As a result of the nitriding process, the outer layer of the
glass surfaces and edges undergo a reaction to form SiON, SiN,
AlON, AlN, BON, BN, etc., i.e., Si--N, Al--N, B--N bonds are formed
wherein the Si, Al, B, may also be bonded to oxygen in the nitrided
layer. The top portion of the glass is transformed from an oxide
into a nitride or oxy-nitride layer.
[0032] It was surprisingly found that alkali-free glasses were
amenable to nitriding. As noted, nitriding by its nature involves
replacing at least some of the oxygen atoms of the workpiece with
nitrogen atoms. In alkali-free glasses, the oxygen atoms are held
more tightly than in alkali-containing glasses. One skilled in the
art would not expect that alkali-free glasses could be effectively
nitrided, let alone achieve improved strength and scratch
resistance. Now referring to FIG. 3, nitrided alkali-free glasses
made according to the disclosed methods exhibited an increase in
modulus as a function of N concentration in the nitrided glass,
which in turn improves the strength and scratch resistance
performance of the glass.
Glass Compositions and Examples
[0033] Alkali-free glasses 102 are disclosed having (in weight %)
50.ltoreq.SiO.sub.2.ltoreq.80%,
2.ltoreq.Al.sub.2O.sub.3.ltoreq.17%,
8.ltoreq.B.sub.2O.sub.3.ltoreq.36%, and greater than or equal to 2%
and less than or equal to 25% of at least one of CaO, MgO, BaO, SrO
or ZnO. In this embodiment the composition may further include 0-5%
other minor components excluding alkali metals. Other minor
components in the composition may include for example ZrO.sub.2,
Fe.sub.2O.sub.3, etc. These glass embodiments include alkali-free
borosilicate, alkali-free boroaluminosilicate, and alkali-free
aluminosilicate glasses.
[0034] In accordance with another embodiment, alkali-free glasses
include in weight percent on an oxide basis
65.ltoreq.SiO.sub.2.ltoreq.75%,
7.ltoreq.Al.sub.2O.sub.3.ltoreq.13%,
5.ltoreq.B.sub.2O.sub.3.ltoreq.36%, 5.ltoreq.CaO.ltoreq.15%,
0.ltoreq.BaO.ltoreq.5%, 0.ltoreq.MgO.ltoreq.3% and
0.ltoreq.SrO.ltoreq.5%.
[0035] In yet a further embodiment, alkali-free glasses include
P.sub.2O.sub.5, which may provide more efficient nitriding. Such
P.sub.2O.sub.5-containing alkali-free glasses may include in weight
percent on an oxide basis 40.ltoreq.SiO.sub.2.ltoreq.70%,
0.ltoreq.Al.sub.2O.sub.3.ltoreq.20%,
1.ltoreq.P.sub.2O.sub.5.ltoreq.15%,
0.ltoreq.B.sub.2O.sub.3.ltoreq.25%, and greater than or equal to 2%
and less than or equal to 25% of at least one of CaO, MgO, BaO, SrO
or ZnO.
[0036] In still other embodiment, alkali-free glass which may be
suitable for nitriding, or has been subjected to nitriding, in
accordance with the present disclosure is comprised essentially of
pure silica (SiO.sub.2). In other embodiments, alkali-free glasses
which may be suitable for nitriding, or have been subjected to
nitriding, in accordance with the present disclosure may include a
molar volume greater than 26 cm.sup.3/mole. In another embodiment,
such glasses may have a molar volume greater than 27
cm.sup.3/mole.
[0037] Non-limiting examples of some alkali-free glasses are shown
in Table 1 and are shown in both weight percent (wt. %) and mole
percent (mole %). The data in Table 1 also show the total amount of
RO (CaO, MgO, BaO, SrO and ZnO) and the molar volume of these
glasses (NA refers to "not available"). In some embodiments, the
summed of RO is in the range from 9 to 24 weight %. In addition,
examples of alkali-containing soda-lime silicate glass are shown
for comparison. The alkali-containing soda-lime silicate glass has
a molar volume of 23.3 cm.sup.3/mole, while the alkali-free glasses
shown have molar volumes greater than 26 cm.sup.3/mole.
TABLE-US-00001 TABLE 1 Glass B C D E Soda-lime silicate Component
wt. % mole % wt. % mole % wt. % mole % wt. % mole % wt. % mole %
SiO2 60 66 59 67 53 67 63 67 73 71.4 Al2O3 17 11 16 11 14 11 17 11
0 0 B2O3 8 8 11 10 9 10 11 10 0 0 CaO 4 5 6 7 0 0 7 9 9 9.4 MgO 3 5
0 0 0 0 1 2 4 5.8 SrO 8 5 3 2 0 0 1 1 0 0 BaO 0 0 5 2 24 12 0 0 0 0
ZnO 0 0 0 1 0 0 0 0 0 0 Na2O 0 0 0 0 0 0 0 0 14 13.3 RO sum 15 15
15 12 24 12 9 12 13 15.2 molar volume, 26.4 27.8 NA 27.3 23.3
cm.sup.3/mole
[0038] With reference to FIGS. 4-5, in some embodiments, upon being
subjected to nitriding processes described herein, the foregoing
alkali-free glass compositions include a nitrogen-containing layer
104 which includes greater than 0.2 wt % N.
[0039] In one embodiment the nitrogen-containing layer has a
thickness of greater than 1 nm. In another embodiment the thickness
of the nitrogen-containing layer is greater than 10 nm. In another
embodiment the thickness of the nitrogen-containing layer is
greater than 100 nm. In yet another embodiment the thickness is
greater than 1 micron. In still another embodiment the thickness is
greater than 10 microns. Thickness ranges may include at least one
of: (i) from 10-100 nm; (ii) from 100 nm-1 micron; (iii) from 1
micron-10 microns; and (iv) from 10-100 microns.
[0040] In one embodiment the nitrogen-containing layer 104 includes
greater than 0.2 wt % N. In another embodiment the
nitrogen-containing layer includes greater than 1 wt % N. In yet
another embodiment the nitrogen-containing layer includes at least
2 wt % N. In other embodiments, the nitrogen-containing layer
includes greater than at least 4 wt % N. In another embodiment, the
nitrogen-containing layer includes at least 8 wt % N. In still a
further embodiment the nitrogen-containing layer 104 includes at
least 14 wt % N.
[0041] The glass compositions described above may be in the form of
sheets, including but not limited to 3D sheets. The glass
compositions may be tempered/strengthened chemically and/or
thermally. The glass sheets can be monoliths or may be employed as
one or more layers of a multi-layer glass laminate. In some
embodiments the thickness of the glass sheet is less than 5 mm, in
other embodiments the thickness of the glass sheet is less than 2
mm, in other embodiments the thickness of the glass sheet is less
than 1 mm and in other embodiments the thickness of the glass sheet
is less than 1 mm and greater than 10 microns. In some embodiments
the area of each of the major surfaces of the glass sheet is
greater than 2 square centimeters, in other embodiments the area of
each of the major surfaces of the glass sheet is greater than 30
square centimeters, in other embodiments the area of each of the
major surfaces of the glass sheet is greater than 100 square
centimeters, and in other embodiments the area of each of the major
surfaces of the glass sheet is greater than 500 square centimeters.
In some embodiments thickness of the glass sheet is less than 1 mm
and the area of each of the major surfaces of the glass sheet is
greater than 30 square centimeters.
[0042] It may be advantageous to impart any number of functional
properties to a substrate, such as a glass substrate by applying a
layer to the substrate. Although the advantageous functional
properties achieved by adding a layer to a substrate are numerous,
examples of such functional properties include strengthening,
scratch resistance and chemical resistance. Accordingly, one or
more embodiments may involve providing a nitrided alkali-free glass
layer on a substrate such as another glass.
[0043] For example, an oxide glass, such as Gorilla.RTM. Glass,
which is available from Corning Incorporated, has been widely used
in consumer electronics products. Such glass is used in
applications where the strength of conventional glass is
insufficient to achieve desired performance levels. Gorilla.RTM.
Glass is manufactured by chemical strengthening (ion exchange) in
order to achieve high levels of strength while maintaining
desirable optical characteristics (such as high transmission, low
reflectivity, and suitable refractive index). Strengthened glass
through ion exchange (IX) techniques can produce high levels of
compressive stress in the treated glass, as high as about 400 to
1000 MPa at the surface. However, Gorilla.RTM. Glass is an alkali
glass, and processing of alkali glasses in certain fabrications,
such as ITO "touch" applications and displays, may not be
desirable. One or more layers of nitrided alkali-free glass may be
applied to a substrate such as Gorilla.RTM. Glass to provide a
device having increased strength, scratch resistance and chemical
durability.
Experimental Results
[0044] Samples of glass sheets (designated sample A and sample E)
having dimensions of 50 mm.times.50 mm.times.1 mm or 0.7 mm
thickness were placed in a 0.25 liter stainless steel vessel, the
vessel was sealed air tight, purged with ammonia gas (product code
AMAH35, Empire Airgas, Elmira, N.Y.), then heated to set
temperatures, pressures, ammonia flow rate (in standard cubic
centimeters per minute, sccm) and for times as described below in
Table 2. The glass compositions were as follows: glass A was pure
fused silica (100% SiO.sub.2); and glass E, a non-alkali
aluminosilicate, including approximately in weight percent
SiO.sub.2 (63%), Al.sub.2O.sub.3 (17%), B.sub.2O.sub.3 (11%), CaO
(7%), MgO (1%), SrO (1%).
TABLE-US-00002 TABLE 2 Flow Temperature, Pressure, rate, Time,
degrees C. psig sccm days 200 100 30-40 11 300 100 30-40 7 350 100
30-40 14 475 100 30-40 4 600 100 30-40 5
[0045] Samples of glass A and glass E before and after exposure to
ammonia (Table 2) were characterized by Secondary Ion Mass
Spectroscopy (SIMS). With reference to FIG. 4, the data for glass A
(pure silica) show that the silica glass was nitrided (i.e.,
contained nitrogen, N) from about 0.1 wt. % to about 2 wt. % N at
the near surface (first 20-50 nm), and 0.02 to about 0.16 wt. % N
at 500 nm depth, and the N was doped to greater than 3 microns,
depending on the conditions. Higher N incorporation and deeper
depth was found with higher temperatures (e.g., 600.degree. C. vs.
300.degree. C.). With reference to FIG. 5, the data for glass E (an
alkali-free glass) show that the alkali-free glass was nitrided
(i.e., contained nitrogen, N) from about 10 wt. % to about 14 wt. %
N at the near surface (first 10-100 nm), and 0.1 to about 1.4 wt. %
N at 500 nm depth, and the N was doped to greater than 2 microns,
depending on the conditions. Surprisingly, we found the non-alkali
glass to incorporate significantly more N (about ten fold) than the
silica glass treated under similar conditions. While not being
bound by a single theory, it is believed the higher N incorporation
could be due to high molar volume in the non-alkali glass. In some
embodiments, these glasses have molar volume greater than 25
cm.sup.3/mole, in some embodiments, these glasses have molar volume
greater than 26 cm.sup.3/mole. Also, surprisingly, higher maximum
weight percent N incorporation was found with lower temperature
(e.g., 475.degree. C. vs. 600.degree. C.), while deeper depth N
incorporation and was found with higher temperatures (e.g.,
600.degree. C. vs. 475.degree. C.). Increasing the temperature,
e.g., up to 800.degree. C., 1000.degree. C., 1200.degree. C. or
greater, would be expected to further increase the N incorporation
both in depth.
[0046] With reference to FIGS. 6 and 7, samples of glass E
(non-alkali aluminosilicate) before (sample E1) and after (samples
E2 and E3) exposure to ammonia according to the conditions in Table
2 were characterized at room temperature (about 20-25.degree. C.,
and 50% RH) using an Agilent Nano Indenter G200 (Agilent
Technologies, Inc. USA) for Young's modulus and hardness as a
function of depth from the surface. Variation in modulus and
hardness within about the first 50-80 nm from the surface are an
artifact from this measurement technique. The results show that the
modulus and hardness increased by about 17% and 19%, respectively
for the glass samples that were exposed to the ammonia treatment
(E2 and E3) as compared to the unexposed as-received glass sample
(E1).
[0047] Although the disclosure herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the embodiments herein. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
application.
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