U.S. patent application number 13/580810 was filed with the patent office on 2012-12-20 for chemically tempered glass.
This patent application is currently assigned to SCHOTT AG. Invention is credited to Stefan Meinhardt, Rolf Weitnauer.
Application Number | 20120321898 13/580810 |
Document ID | / |
Family ID | 44065881 |
Filed Date | 2012-12-20 |
United States Patent
Application |
20120321898 |
Kind Code |
A1 |
Meinhardt; Stefan ; et
al. |
December 20, 2012 |
CHEMICALLY TEMPERED GLASS
Abstract
Chemically tempered lithium aluminosilicate glasses and methods
of tempering are provided. The method allows fast tempering at
moderate temperatures, which leads to a deep zone of surface
tension with a high level of surface tension.
Inventors: |
Meinhardt; Stefan; (Neustadt
an der Orla, DE) ; Weitnauer; Rolf; (Rothenstein,
DE) |
Assignee: |
SCHOTT AG
Mainz
DE
|
Family ID: |
44065881 |
Appl. No.: |
13/580810 |
Filed: |
February 28, 2011 |
PCT Filed: |
February 28, 2011 |
PCT NO: |
PCT/EP2011/000954 |
371 Date: |
August 23, 2012 |
Current U.S.
Class: |
428/410 ;
65/30.1 |
Current CPC
Class: |
Y10T 428/315 20150115;
C03C 2204/00 20130101; C03C 21/002 20130101; C03C 3/093 20130101;
C03C 3/097 20130101; C03C 4/18 20130101 |
Class at
Publication: |
428/410 ;
65/30.1 |
International
Class: |
C03C 21/00 20060101
C03C021/00; C03C 15/00 20060101 C03C015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2010 |
DE |
10 2010 009 584.2 |
Claims
1-12. (canceled)
13. A chemically tempered glass article, comprising: a lithium
aluminosilicate glass comprising SiO.sub.2, Al.sub.2O.sub.3,
Li.sub.2O with 4.6 to 5.4% by weight, and Na.sub.2O with 8.1 to
9.7% by weight, wherein said glass has a chemical tempered zone of
compressive stress at a surface, said zone extending to a depth of
at least 50 micrometers into said glass, wherein, in said zone,
lithium ions are at least partially exchanged by alkali ions, and
wherein said zone exhibits a surface tension of at least 600
MPa.
14. The chemically tempered glass article of claim 13, wherein the
glass article is a glass sheet.
15. The chemically tempered glass article of claim 13, wherein said
depth is at least 80 micrometers and said surface tension is at
least 800 MPa.
16. The chemically tempered glass article of claim 13, wherein said
glass comprises: 58 to 65% by weight of SiO.sub.2; 16 to 20% by
weight of Al.sub.2O.sub.3; 0.1 to 1% by weight of B.sub.2O.sub.3;
4.6 to 5.4% by weight of Li.sub.2O; 8.1 to 9.7% by weight of
Na.sub.2O; 0.2 to 2.0% by weight of CaO; and 2.5 to 5.0% by weight
of ZrO.sub.2.
17. The chemically tempered glass article of claim 16, wherein said
glass further comprises 0.05 to 1.0% by weight of K.sub.2O.
18. The chemically tempered glass article of claim 16, wherein said
glass further comprises one or more of the components selected from
the group consisting of SnO.sub.2, CeO.sub.2, P.sub.2O.sub.5, and
ZnO in a total proportion from 0 to 2.5% by weight.
19. The chemically tempered glass article of claim 13, wherein said
glass comprises: 60 to 62% by weight of SiO.sub.2; 17.5 to 19.5% by
weight of Al.sub.2O.sub.3; 0.5 to 0.7% by weight of B.sub.2O.sub.3;
4.8 to 5.2% by weight of Li.sub.2O; 8.5 to 9.5% by weight of
Na.sub.2O; 0.2 to 0.5% by weight of K.sub.2O; 0.5 to 1.2% by weight
of CaO; 3.2 to 3.8% by weight of ZrO.sub.2; and one or more of the
components selected from the group consisting of SnO.sub.2,
CeO.sub.2, P.sub.2O.sub.5, and ZnO in a total proportion from 0.25
to 1.6% by weight.
20. The chemically tempered glass article of claim 13, wherein said
glass comprises: 61 to 62% by weight of SiO.sub.2; 17.5 to 18.5% by
weight of Al.sub.2O.sub.3; 0.5 to 0.7% by weight of B.sub.2O.sub.3;
4.9 to 5.1% by weight of Li.sub.2O; 8.8 to 9.3% by weight of
Na.sub.2O; 0.2 to 0.5% by weight of K.sub.2O; 0.5 to 1.2% by weight
of CaO; 3.2 to 3.8% by weight of ZrO.sub.2; and one or more of the
components selected from the group consisting of SnO.sub.2,
CeO.sub.2, P.sub.2O.sub.5, and ZnO in a total proportion from 0.5
to 1.0% by weight.
21. The chemically tempered glass article of claim 13, wherein the
glass article is suitable for as a cover glass for a device
selected from the group consisting of a mobile communication
device, a digital camera, a digital photo frame, a personal digital
assistant (PDA), a solar energy device, and a touch panel
display.
22. The chemically tempered glass article of claim 13, wherein the
glass article is suitable for as a bullet-proof glazing for ground
vehicle windows or high speed train windows.
23. A method for producing a chemically tempered glass article,
comprising: providing a glass is provided comprising SiO.sub.2,
Al.sub.2O.sub.3, Li.sub.2O with 4.6 to 5.4% by weight; and
Na.sub.2O with 8.1 to 9.7% by weight; storing said glass in an
alkali-containing salt melt for a period of not more than 8 hours
to exchange alkali ions of said glass with larger alkali ions of
said alkali-containing salt melt to build up a zone of compressive
stress at a surface of said glass; and ensuring said
alkali-containing salt melt does not exceed a temperature of
420.degree. C. during storing said glass, wherein said glass builds
a zone of compressive stress having a thickness of at least 50
micrometers and a surface tension of at least 600 MPa.
24. The method of claim 23, wherein said thickness is more than 50
.mu.m and said surface tension is more than 600 MPa.
25. The method of claim 23, wherein said alkali-containing salt
melt comprises a NaNO.sub.3 melt.
26. The method of claim 25, wherein said temperature is between
370.degree. C. and 420.degree. C.
27. The method of claim 23, wherein the step of storing said glass
in said alkali-containing salt melt comprises storing said glass in
one or more melts, wherein said melt or melts comprise at least two
alkali ion species with different ionic radii.
28. The method of claim 27, wherein said one or more melts
comprises a melt blend comprises salts of different alkali
metals.
29. The method of claim 28, wherein said melt blend has a content
of at least 15% by weight of NaNO.sub.3, said surface tension is
more than 800 MPa, and said thickness is deeper than 80
micrometers.
30. The method of claim 23, wherein the step of storing said glass
in said alkali-containing salt melt comprises storing said glass in
a melt blend having at least two different alkali ions, wherein
said melt blend includes at least 15% by weight of NaNO.sub.3and
said temperature is less than 400.degree. C., and wherein said
surface tension is more than 800 MPa, said thickness is deeper than
80 micrometers, and said period is less than 3 hours.
31. The method of claim 23, wherein storing said glass in said
alkali-containing salt melt comprises successively storing said
glass in at least two alkali salt melts having different alkali
metal species, and wherein said thickness is more than 80
micrometers and said surface tension is more than 800 MPa.
32. The method of claim 23, wherein the step of storing said glass
in said alkali-containing salt melt comprises storing said glass in
a first alkali salt melt before a second alkali salt melt, said
first and second alkali salt melts having different compositions,
said second salt melt comprising alkali ions that have a larger
ionic radius than alkali ions of said first salt melt, wherein said
temperature is less than 400.degree. C., said surface tension is
more than 750 MPa, said thickness is more than 80 micrometers, and
said period is not more than 3 hours.
Description
[0001] The invention generally relates to tempered glasses, in
particular the invention relates to the chemical tempering of
lithium aluminosilicate glasses. Chemical tempering or ion exchange
by immersing a glass substrate into a potassium nitrate melt below
the transformation temperature T.sub.G is generally known as a
method to increase the strength of thin and very thin silicate or
aluminosilicate glasses. Chemical tempering is preferably employed
for sheets of glass having a thickness smaller than 4 mm. For
special applications, thicker glass sheets may also be chemically
tempered. In silicate or aluminosilicate glasses, an ion exchange
typically only occurs between sodium ions in the glass and
potassium ions in the salt melt. By such an exchange, surface
compressive stresses with a depth of more than 80 .mu.m are only
achieved in very long exchange times of generally more than 12
hours.
[0002] Furthermore, it is generally known that the depth of ion
exchange depends on the time of immersion in the salt bath and the
temperature of the salt bath. Higher temperatures and longer
durations increase the exchange depth. However, the exchange depth
is not identical with the zone of surface compressive stress.
Depending on which and how many ions penetrate into the glass, a
different zone of surface compressive stress can result in function
of the Li content and sodium content and their proportion to each
other and to other components of the glass substrate. Typically,
however, the zone of surface compressive stress extends deeper into
the glass than the depth of the exchanged ions.
[0003] Commonly manufactured chemically tempered glasses in the
market, such as aluminosilicate glass, or common soda lime glass
usually have a Na.sub.2O content of more than 10% by weight, and by
default are tempered in potassium nitrate salt baths at
temperatures above 420.degree. C., preferably about 430.degree. C.,
and with tempering durations of more than 12 hours. The zone of
surface compressive stress thereby reaches a depth of 30 to 70
.mu.m. The amount of surface tension is between about 550 MPa in
tempered soda lime glass, or of about 750 MPa in aluminosilicate
glass.
[0004] For applications as cover glasses, however, there is the
problem that scratches may easily extend further into the glass
than the zone of surface tension, which results in a considerable
reduction of strength.
[0005] Also, for applications as front and side windows of railway
vehicles and bullet-proof glazing for vehicles, variably adjustable
penetration depths of more than 80 .mu.m and high strengths would
be interesting, provided that acceptable short process times are
feasible.
[0006] DE 196 16 633 C1 describes aluminosilicate glasses which,
due to the chemical tempering, are suitable as substrate glasses
for coating optical and magnetic storage media. Although deep
toughened zones and high strengths are achievable in these glasses,
long treatment durations of more than 12 hours in the salt melt and
high temperatures of above 420.degree. C. are required.
[0007] DE 196 16 679 C1 describes the chemical tempering of an
aluminosilicate glass using a potassium nitrate melt at
temperatures from 350.degree. C. to 500.degree. C. Although,
according to Table 3, the described glass after about 1.5 hours of
treatment exhibits a surface tension of 880 MPa, the thickness of
the zone of compressive stress is only about 15 .mu.m. To obtain a
zone of compressive stress of 105 .mu.m requires 15 hours of
treatment in the salt melt.
[0008] U.S. Pat. No. 4,156,755 A describes Li.sub.2O containing
aluminosilicate glasses for the ion exchange. Although it was
possible with this glass to obtain zones of compressive stress with
thicknesses of more than 80 .mu.m in short times, the surface
tension is not more than 600 MPa.
[0009] From EP 0 884 289 B1, a lithium aluminosilicate glass for
vehicles is known which also may be chemically tempered. The
Li.sub.2O content is from 3 to 4.5% by weight, and the Na.sub.2O
content is between 6 and 13% by weight. According to Table 7 this
glass, after 8 hours in a sodium nitrate melt of 380.degree. C.,
achieves a zone of compressive stress of 80 .mu.m thickness, but
the surface tension is only 2600 kg/cm.sup.2, which corresponds to
about 255 MPa. Even after 64 hours in the melt, the tension is only
3450 kg/cm.sup.2 corresponding to 339 MPa, with a thickness of
surface tension of 30 .mu.m, so that significantly thinner surface
tension zones must be assumed in case of shorter times.
[0010] US 2007/0060465 A1 describes the chemical tempering of
various lithium aluminosilicate glasses with a Li.sub.2O content
from 3 to 9% and an Na.sub.2O+K.sub.2O content of not more than 3%.
The described glasses are exposed to temperatures between
450.degree. C. and the annealing point.
[0011] WO 2010 005 578 A1 describes chemical tempering of
aluminosilicate glasses for multiple times to provide a maximum of
surface tension at a specific depth. Only the repeated tempering
(single or mixed melts) and durations of significantly more than 8
hours result in zones of compressive stress with depths of more
than 80 .mu.m. Moreover, the obtained compressive stress, according
to Table II, Example 13, with a depth of the zone of compressive
stress of 81 .mu.m is only 546 MPa. The process time to achieve
such a compressive stress is more than 23 hours.
[0012] While during chemical tempering, generally, high
inter-diffusion coefficients in the ion exchange of ions having
similar ionic radii result in deeper exchange depths in a
relatively short time, the exchange with ions whose radius is
significantly larger than the radius of the ion to be exchanged
results in a stronger influence on the short-range order and thus
to an increase of the surface compressive stress. This effect is
stronger, the greater the difference of the two radii. An
adjustment of the exchange depth with short process times is
therefore made through a lithium-sodium cation exchange. However,
if very high surface compressive stresses are required, the
exchange may be realized with the cations of the heavier alkali
metals. In this case, however, in function of the predetermined
exchange depth and the cation used, long processing times and high
process temperatures must be taken into account.
[0013] It will be evident from this discussion of the prior art
that the glasses and methods for chemical tempering known from
prior art do not permit quick tempering at moderate temperatures
leading to a deep surface tension zone with a high level of surface
tension.
[0014] Therefore, it is an object of the invention to provide such
glasses, or chemically tempered articles produced from such
glasses. This object is solved by the subject matter of the
independent claims. Advantageous embodiments and refinements of the
invention are set forth in the respective dependent claims. The
invention provides a material for future applications as cover
glasses and windows for vehicles, which is distinguished by a
reduction of the tempering time and tempering temperature and
simultaneously achieves an increase of the surface tension.
[0015] A chemically tempered glass article according to the
invention, preferably in form of a glass sheet, is made of a
lithium aluminosilicate glass, wherein the glass in addition to
SiO.sub.2 and Al.sub.2O.sub.3 which are characteristic for lithium
aluminosilicate glass comprises:
[0016] Li.sub.2O as a component with 4.6 to 5.4% by weight; and
[0017] Na.sub.2O as a component with 8.1 to 9.7% by weight; and
wherein
[0018] the glass due to the chemical tempering has a zone of
compressive stress at the surface; and
[0019] the zone of compressive stress extends to a depth of at
least 50 micrometers, preferably at least 80 micrometers into the
glass, and wherein in the zone of compressive stress lithium ions
are at least in part exchanged by other alkali ions; and
wherein
[0020] the zone of compressive stress exhibits a level of
compressive stress of at least 600 MPa, preferably at least 800
MPa.
[0021] The measurements of strength were performed and determined
using the double ring method according to EN 1288-5.
[0022] The surface tension or compressive stress in the zone of
compressive stress can be determined photoelastically. To this end
the glass samples are cut, and the surfaces are polished
perpendicular to the viewing direction. Then the compressive stress
in the surface can be determined by means of a microscope and
various compensating elements.
[0023] The thickness/depth of the zone of compressive stress may
also be determined photoelastically, at the cuts.
[0024] For the measurements of the exchange depth, Energy
Dispersive X-ray (EDX) depth profiles of the alkali ions can be
measured.
[0025] Glasses that have been found particularly suitable for the
purpose of the invention have the following composition:
[0026] 58 to 65% by weight of SiO.sub.2;
[0027] 16 to 20% by weight of Al.sub.2O.sub.3;
[0028] preferably 0.1 to 1% by weight of B.sub.2O.sub.3;
[0029] 4.6 to 5.4% by weight of Li.sub.2O;
[0030] 8.1 to 9.7% by weight of Na.sub.2O;
[0031] 0.05 to 1.0% by weight of K.sub.2O;
[0032] 0.2 to 2.0% by weight of CaO;
[0033] 2.5 to 5.0% by weight of ZrO.sub.2; and optionally one or
more of the components SnO.sub.2, CeO.sub.2, P.sub.2O.sub.5, and
ZnO in a total proportion from 0 to 2.5% by weight.
[0034] A preferred composition range is:
[0035] 60 to 62% by weight of SiO.sub.2;
[0036] 17.5 to 19.5% by weight of Al.sub.2O.sub.3;
[0037] 0.5 to 0.7% by weight of B.sub.2O.sub.3;
[0038] 4.8 to 5.2% by weight of Li.sub.2O;
[0039] 8.5 to 9.5% by weight of Na.sub.2O;
[0040] 0.2 to 0.5% by weight of K.sub.2O;
[0041] 0.5 to 1.2% by weight of CaO;
[0042] 3.2 to 3.8% by weight of ZrO.sub.2; and
[0043] SnO.sub.2, CeO.sub.2, P.sub.2O.sub.5, and ZnO in a total
proportion from 0.25 to 1.6% by weight.
[0044] Particularly preferable for obtaining a deep zone of
compressive stress with a high level of compressive stress already
at comparatively low temperatures of the salt melt is the following
composition:
[0045] 61 to 62% by weight of SiO.sub.2;
[0046] 17.5 to 18.5% by weight of Al.sub.2O.sub.3;
[0047] 0.5 to 0.7% by weight of B.sub.2O.sub.3;
[0048] 4.9 to 5.1% by weight of Li.sub.2O;
[0049] 8.8 to 9.3% by weight of Na.sub.2O;
[0050] 0.2 to 0.5% by weight of K.sub.2O;
[0051] 0.5 to 1.2% by weight of CaO;
[0052] 3.2 to 3.8% by weight of ZrO.sub.2; and
[0053] SnO.sub.2, CeO.sub.2, P.sub.2O.sub.5, and ZnO in a total
proportion from 0.5 to 1.0% by weight.
[0054] The invention especially allows to temper float glass panes
having the corresponding compositions. In this refinement the
tempered glass, accordingly, then has two non-polished surfaces. In
other words, the top and bottom sides are not mechanically
polished. Specifically, one surface is formed by fire polishing,
the other is formed by flowing onto a liquid tin bath. A float
glass pane may thus be identified by the fire-polished surface on
the one hand, and by the tin impurities of the opposite side.
[0055] With the glasses as mentioned above, it is now possible to
chemically temper the glass at temperatures below 420.degree. C.
and within a time of not more than 8 hours using one or more
alkali-containing salt melt(s), preferably alkali nitrate melt(s).
The obtained glasses may preferably be used as a cover glass for
mobile communication devices, digital cameras, digital photo
frames, personal digital assistants (PDAs), as a cover glass for
solar energy devices, or as substrates for touch panel displays.
Particularly preferred applications include bullet-proof glazing
for ground vehicles as well as front and side windows for high
speed trains. To achieve a thickness of the zone of compressive
stress of more than 50 .mu.m, preferably more than 80.mu.m, and
surface tensions, or compressive stresses in the zone of
compressive stress of more than 800 MPa, the process times in the
salt melt, if necessary, may be reduced to not more than 4 hours,
even to not more than 3 hours.
[0056] Accordingly, the invention also provides a method for
producing a chemically tempered glass article, wherein a glass is
provided which in addition to SiO.sub.2 and Al.sub.2O.sub.3
comprises
[0057] Li.sub.2O as a component with 4.6 to 5.4% by weight; and
[0058] Na.sub.2O as a component with 8.1 to 9.7% by weight; and
wherein
[0059] the glass article is stored in an alkali-containing salt
melt to exchange alkali ions of the glass with larger alkali ions
of the salt melt and so to build up a zone of compressive stress at
the surface of the glass article, so that a chemically tempered
glass is obtained; wherein
[0060] storing in the alkali-containing salt melt lasts for a time
of not more than 8 hours; and wherein
[0061] the temperature of the salt melt during storage of the glass
article does not exceed 420.degree. C.; and wherein
[0062] a zone of compressive stress having a depth of at least 50
micrometers; and
[0063] a compressive stress of at least 600 MPa is built up.
[0064] Several of the publications mentioned in the introductory
part specify a certain proportion of Li.sub.2O or Na.sub.2O for the
chemical tempering using alkali nitrates in order to achieve
appropriate surface tensions and zones of compressive stress.
Although previously surface tensions greater than 800 MPa have been
produced, this was not in conjunction with a zone of compressive
stress having a depth of more than 80 .mu.m, and not within 8 h and
below 430.degree. C. Though US 2007/60465 Al describes glasses with
high levels of surface tension and deep tension zones, these are
achieved at high temperatures of more than 450.degree. C. and with
Na.sub.2O contents of less than 3% by weight. However, at these
temperatures toxic nitrate vapors are already produced which impede
normal processing. Furthermore, the high temperatures incur higher
processing costs than temperatures of about 430.degree. C. or below
420.degree. C. Moreover, the process window gets very narrow, since
in this case the annealing point of the glass is near the treatment
temperature. Approaching the annealing temperature may result in a
stress relief. Thus there is a risk for the compressive stress to
become inhomogeneous.
[0065] In the study of lithium aluminosilicate glass substrates, a
correlation was observed between the depth of the zone of
compressive stress and the surface tension as well as the ions to
be exchanged in chemical tempering.
[0066] In order to achieve depths of the zone of compressive stress
of more than 80 .mu.m within not more than 8 hours of treatment
duration, the ionic radius of the penetrating ions should not
differ significantly from that of the ions to be exchanged to
ensure a fast exchange. Additionally, the ionic radius of the
penetrating ions should not be significantly larger than the ionic
radius of the compounds included in the glass substrate.
[0067] Ideal partners for an exchange with sodium ions or potassium
ions with a high penetration rate are the Li ion or the Na ion. The
Li ion has an ionic radius of about 1.45 10.sup.-10 m, the Na ion
has an ionic radius of about 1.8 10.sup.-10 m. Other constituents
of the glass have the following radii:
[0068] Si ion about 1.1 10.sup.-10 m,
[0069] Al ion 1.25 10.sup.-10 m,
[0070] K ion 2.2 10.sup.-10 m, and
[0071] Zr ion 1.55 10.sup.-10 m.
[0072] The larger inter-diffusion coefficient between lithium and
sodium compared to the inter-diffusion coefficient between sodium
and potassium, and the small difference between the ionic radii of
the sodium ion and the lithium ion as well as the other
constituents of the glass allows a high penetration rate. This
results in rapid penetration of the glass substrate. The sodium
ions fit better into the voids of a smaller volume, and due to
their small size their penetration is not affected so much as with
larger ionic radii of the other alkali metals.
[0073] If a potassium containing salt melt is used, there is not
only an exchange of lithium ions which reflects in a lower lithium
concentration in the zone of compressive stress. In this case,
additionally, there is found an elevated potassium concentration in
the zone of compressive stress, at least within portions thereof,
as compared to the interior of the glass.
[0074] In order to achieve depths of more than 80 .mu.m in an
appropriate time of not more than 8 hours, the glass according to
the invention should include at least a minimum proportion of
Li.sub.2O, preferably at least 4.6% by weight. More Li.sub.2O leads
to a faster exchange, however, a too high Li.sub.2O content
inhibits high surface tensions from building up. Therefore, on the
other hand, the Li.sub.2O content should not exceed 5.4% by weight.
It has been found that with glasses having such lithium contents,
surface tensions of more than 600 MPa or even more than 800 MPa can
be achieved in short process times of not more than 8 hours.
[0075] According to the invention, an adjustment of the depth is
preferably realized through the Li--Na exchange. An exchange only
with alkali ions larger than sodium results in an increase of
temperature to above 430.degree. C., or prolongs the time to more
than 8 hours in order to achieve the desired penetration
depths.
[0076] However, to achieve surface tensions of more than 800 MPa,
it is preferably suggested by the invention to involve further
alkali ions in the exchange. These suitably include, for example,
the Na ion in the glass and the K ion in the salt melt. Also, a
participation of Cs ions and Rb ions is possible. The significantly
larger ions from the salt melt lead to a significant increase of
stress at the surface, and thus to an increase of surface tension.
The various documents mentioned above describe Na.sub.2O contents
of up to 3%, or of more than 10%. However, Na.sub.2O contents of
less than 3% require temperatures of more than 450.degree. C. to
achieve surface tensions of about 800 MPa, as described, e.g., in
US 2007/0060465 A1. Though with Na.sub.2O contents of more than 10%
by weight, about 700 to 800 MPa can be achieved, however this is at
temperatures around 430.degree. C. and in times of more than 8
hours. Studies of the employed glasses have revealed that, in
contrast thereto, with Na.sub.2O contents from 8.1 to 9.6% by
weight, surface tensions of more than 800 MPa may result at
temperatures below 420.degree. C. and in times of not more than 8
hours.
[0077] Therefore, in order to obtain surface tensions of more than
600 MPa or even more than 800 MPa and zones of surface compressive
stress (also known as Depth of Layer--DoL) with depths of more than
50 .mu.m or even more than 80 .mu.m at temperatures of the salt
melt below 420.degree. C. and within a treatment duration of not
more than 8 hours, according to the invention the Li.sub.2O content
is selected between 4.6% and 5.4%, and the Na.sub.2O content is
selected between 8.1% and 9.7%.
[0078] It has been found that zones of compressive stress of more
than 50 .mu.m thickness and surface tensions of more than 600 MPa
can be achieved in not more than 8 hours of treatment in the salt
melt, when chemically tempering the above mentioned glasses
according to the invention for a single time in a preferably pure
(at least 95% purity) NaNO.sub.3 melt at temperatures from
370.degree. C. to 420.degree. C. The tempering times herein are
between 2h and 8h (see also Table 2 below; glasses 17 and 27). If,
on the other hand, the glass substrate is tempered using a pure (at
least 95% purity) KNO.sub.3 melt at temperatures from 380.degree.
C. to 400.degree. C., surface tensions of up to 1000 MPa are
produced, but only depths of the zone of compressive stress (DoL)
of 10 to 28 .mu.m.
[0079] Accordingly, besides the compositions of the glasses used in
chemical tempering, the choice of a respective melt and the process
parameters such as temperature and exchange time are crucial for
the desired material properties. As the above discussion
demonstrates, the prior art allows only a limited combination of
material properties, especially when short exchange times or low
process temperatures are desired.
[0080] The method according to the invention, in contrast, allows
to obtain both deep exchange depths and high levels of compressive
stress within a relatively short time and at low process
temperatures, in glasses with preferably the above mentioned
compositions. This is preferably realized by exchanging at least
two different alkali cation species, most preferably by a
sequential process in which the glass article is successively
chemically tempered in melts with different alkali cations. In this
case, the first step preferably comprises a lithium-sodium
exchange, while in the subsequent steps, preferably, melts with
larger alkali cations are used. The method according to the
invention thus provides an access to glasses with tailored
properties.
[0081] In order to achieve surface tensions of more than 800 MPa
and zones of compressive stress having a depth of more than 80
.mu.m within not more than 8 hours of treatment duration, it is
advantageous to perform a second (pure melt or melt blend), third
(pure melt or melt blend) or fourth (pure melt or melt blend) step
with one/several other alkali-NO.sub.3 melts, wherein in this case
the ionic radius of one of the alkali metals used in the second
step should be larger than that in the first melt.
[0082] In the third or fourth step, the alkali ions may again be
smaller than in the second step. Preferably in this case, potassium
nitrate (KNO.sub.3) should be used in the second step, but it is
also possible to use other alkali metal salts. The temperatures
employed in case of KNO.sub.3 are preferably between 380.degree. C.
and 420.degree. C. Advantageously, treatment durations of a maximum
of 6 hours suffice for step 1 in a NaNO.sub.3 melt. For step 2
using KNO.sub.3 or K.sub.2SO.sub.3, 2 hours or even less can be
scheduled according to a refinement of the invention. Steps 3 and 4
which are, optionally, additionally performed can be kept shorter
than one hour in total. Thus, the sum of all steps is less than 8
hours, as exemplified by glasses 17 and 27 described in Table
3.
[0083] In a refinement of the invention it is therefore
contemplated to successively perform the chemical tempering of the
glass article in at least two alkali salt melts of different
composition, which differ in particular in the contained alkali
metal species, wherein the glass article is stored in the melts for
a maximum of 8 hours in total, the temperature in each of the salt
melts during tempering is lower than 420.degree. C., and wherein a
zone of compressive stress with a depth of more than 80 .mu.m and a
compressive stress of more than 800 MPa are obtained.
[0084] Another possibility to obtain surface tensions of more than
800 MPa and zones of compressive stress deeper than 80 .mu.m within
a maximum of 8 hours of treatment duration is to use mixed melts.
These melt blends include salts of different alkali metals,
preferably different alkali metal nitrates. To ensure the high
penetration depths it is favorable to have a content of at least 15
wt.-%, preferably from 15 to 25 wt.-%, more preferably of about 20%
by weight of NaNO.sub.3 in the melt. The nitrate melt blend
includes at least two different alkali ions, for example Na and K,
or as well Na and Rb. But it is also possible that three or four
different alkali metals are included.
[0085] Preferred melt blends are a mixture of NaNO.sub.3 and
KNO.sub.3. The temperatures used with NaNO.sub.3/KNO.sub.3 are
between 380.degree. C. and 420.degree. C. In this case, the time
for the exchange process can also be kept at a maximum of 8 hours,
as exemplified in Table 4 for glasses 17 and 27.
[0086] To achieve surface tensions of more than 1000 MPa, Rb ions
or Cs ions may be used in chemical tempering. The method according
to the invention thus offers the possibility to effectively
incorporate alkali cations into the thus treated glass article,
whose radii are significantly larger than the radius of the lithium
cation, with short exchange times and relatively low process
temperatures.
[0087] In order to obtain penetration depths of 50 .mu.m or 80
.mu.m and more in a short time, in particular in not more than 4
hours, according to the invention the alkali ion to be exchanged in
the glass, Li.sub.2O and/or Na.sub.2O are present in sufficient
quantities. The amount of Li.sub.2O is preferably in a range from
4.8 wt.-% to 5.2 wt.-%, and the amount of Na.sub.2O is preferably
in a range from 8.5 wt.-% to 9,5 wt.-%.
[0088] These embodiments of the method according to the invention
have in common that the chemical tempering of the glass article is
performed in one or more melts, the melt(s) including at least two
alkali ion species with different ionic radii.
[0089] In order to achieve exchange depths of more than 50 .mu.m
and surface tensions of more than 600 MPa within a maximum of 4
hours, it is also possible to temper the glass articles according
to the invention for a single time in a pure (at least 95% purity)
NaNO.sub.3 melt at temperatures from 380.degree. C. to 390.degree.
C. (see Table 2; glasses 19 and 25). The tempering times for
obtaining such zones of compressive stress, in this case, are only
between 2 and 4 hours. If the glass substrate is tempered using a
pure (at least 95% purity) KNO.sub.3 melt at temperatures from
380.degree. C. to 400.degree. C., surface tensions of up to 1000
MPa are obtained, but only DoLs from 10 .mu.m to 28 .mu.m.
[0090] However, to achieve even a surface tension of more than 800
MPa with zones of compressive stress deeper than 80 .mu.in not more
than 4 hours, it is proposed to perform a second (pure melt or melt
blend), optionally yet a third (pure melt or melt blend),
optionally yet a fourth (pure melt or melt blend) step using
one/several other alkali-NO.sub.3 melts. It is advantageous in this
case if the ionic radius of one type of the alkali ions in the melt
employed in the second step is larger than in the first melt.
[0091] In the third or fourth step, the alkali ions may again be
smaller than in the second step. Preferably, KNO.sub.3 is used as a
constituent of the melt in the second step, but it is also possible
to use other alkali metal salts. The temperatures used with
KNO.sub.3 are preferably between 380.degree. C. and 400.degree.
C.
[0092] To achieve fast tempering and a deep reaching zone of
compressive stress, the following parameters are preferred:
[0093] The tempering duration in the first step in a NaNO.sub.3
melt is not more than 2 hours;
[0094] the tempering duration in the second step using a KNO.sub.3
melt is not more than 1.5 hours;
[0095] the duration of the third and fourth steps is less than 0.5
hours in total.
[0096] In Table 3, glass 19 and glass 25 are given as examples for
such a process.
[0097] Another possibility to obtain surface tensions>800 MPa
and penetration depths>80 .mu.m in less than 4 h is to use
so-called melt blends. These mixed melts are composed of different
alkali metal nitrates. To ensure the high penetration depths, an
alkali metal salt melt with at least 15 wt.-%, preferably from 15
to 25 wt.-%, more preferably about 20 wt.-% of NaNO.sub.3 is used.
The nitrate melt blend includes at least two different alkali ion
species, for example Na and K, or as well Na and Rb. However, it
may include 3 or 4 different alkali metals.
[0098] Preferred melt blends are mixtures of NaNO.sub.3 and
KNO.sub.3. The temperatures used for NaNO.sub.3/KNO.sub.3 are
between 380.degree. C. and 400.degree. C. The time required for the
exchange process is less than 4 h (see Table 4; glasses 19 and
25).
[0099] Particularly short treatment times of 4 hours or less may be
achieved as follows:
[0100] In order to achieve penetration depths of 50 .mu.m or 80
.mu.m and more in a short time of not more than 3 hours, again a
glass is used which comprises the alkali ion to be exchanged in the
glass, Li or Na, in a sufficient quantity. Therefore, the amount of
Li.sub.2O is preferably from 4.9 wt.-% to 5.1 wt.-%, and the amount
of Na.sub.2O is preferably between 8.8 wt.-% and 9,5 wt.-%.
[0101] In order to obtain exchange depths>50 .mu.m and surface
tensions >600 MPa in less than 3 hours, the above-mentioned
glass bodies may be chemically tempered in a pure (at least 95%
purity) NaNO.sub.3 melt for a single time, at temperatures from
380.degree. C. to 385.degree. C. The tempering time may even be
reduced to two to three hours. An example is given in Table 2 for
glass 22. When the glass substrate is tempered using a pure (at
least 95% purity) KNO.sub.3 melt at temperatures from 380.degree.
C. to 400.degree. C., surface tensions of up to 1000 MPa are
obtained, but only DoLs (depths of the zones of compressive stress)
from 10 .mu.m to 28 .mu.m.
[0102] To achieve even a surface tension of more than 750 MPa,
preferably more than 800 MPa, and zones of compressive stress of a
thickness or depth of more than 80 .mu.m in not more than 3 hours,
the invention in one embodiment thereof contemplates to perform of
the chemical tempering of the glass article in at least two steps
in alkali salt melts of different compositions, with a salt being
used in a second salt melt which includes alkali ions having a
larger ionic radius than the alkali ions of the melt used in the
first step, wherein the temperature of the melts during tempering
is less than 400.degree. C. In this case, the total storage time of
the glass article in all salt melts is not more than 3 hours.
[0103] Specifically, in a refinement of this embodiment of the
invention, the second step in a pure melt or melt blend is followed
by a third step in a pure melt or melt blend, and optionally by a
fourth step in a pure melt or melt blend. Preferably, alkali
nitrate melts are used, wherein the ionic radius of one species of
the alkali ions used in the second step, according to yet another
refinement of the invention, is larger than that of the first
melt.
[0104] In the third or fourth step, the alkali ions may again be
smaller than in the second step. Preferably, here, a potassium
salt, more preferably KNO.sub.3 may be used as a second step, but
it is also possible to use other alkali metal salts, alternatively
or additionally. The temperatures used with KNO.sub.3 are
preferably between 380.degree. C. and 390.degree. C. The following
parameters have been found to be advantageous in this embodiment of
the method according to the invention: In the first step in a
NaNO.sub.3 melt, the exchange time in the melt is not more than 1.5
hours. For the second step a KNO.sub.3 melt is used, in which case
the storage time in the melt is not more than 1.0 hours. The
duration of steps 3 and 4 is less than 0.5 hours in total. An
example for this method is given in Table 3 for glass 22.
[0105] Another possibility to obtain surface tensions or levels of
compressive stress in the zone of compressive stress of more than
800 MPa and penetration depths or zones of compressive stress
having a depth of more than 80 .mu.m within 3 hours or less is to
use so-called melt blends. These mixed melts are composed of
different alkali metal salts, preferably alkali metal nitrates. To
ensure the high penetration depths, preferably at least 15% by
weight of NaNO.sub.3 is used in the melt. The nitrate melt blend
includes at least two different alkali ions, for example Na and K,
or as well Na and Rb. However, it may include 3 or 4 different
alkali metals. A temperature of less than 400.degree. C. is
generally sufficient to establish a zone of compressive stress as
mentioned above.
[0106] Preferred melt blends for this purpose are mixtures of
NaNO.sub.3 and KNO.sub.3. The temperatures used with such a
NaNO.sub.3--KNO.sub.3 melt are preferably between 380.degree. C.
and 390.degree. C. The exchange process for obtaining a zone of
compressive stress with a level of more than 800 MPa of compressive
stress and a depth of the zone of compressive stress of more than
80 .mu.m requires a time of not more than 3 hours. An example for
this method is given in Table 4 for glass 22.
[0107] Now, the attached tables with the exemplary embodiments will
be explained in detail. Table 1 shows compositions for 16 glasses
which can be used for the invention. The compositions are given in
percent by weight. Furthermore given are the density p, the linear
thermal expansion coefficient .alpha., the glass transition
temperature Tg, and the temperatures at which the viscosity .eta.
of the glass is 10.sup.4 Pas, 10.sup.7.6 Pas, and 10.sup.13 Pas,
and the modulus of elasticity, shear modulus, and Knoop
hardness.
[0108] In addition, the ion-exchange conditions are indicated.
Specifically, potassium nitrate, sodium nitrate, or potassium
nitrate/sodium nitrate melt blends were used in these exemplary
embodiments. The proportions of KNO.sub.3 and NaNO.sub.3 in the
melt composition are each indicated in percent by weight.
Furthermore, the respective temperatures of the salt melts are
listed.
[0109] In all cases, the tempering duration was 8 hours.
[0110] Glasses 1 through 4 were tempered in pure sodium nitrate
melts. For glasses 5 through 8, a pure potassium nitrate melt was
used, and for glasses 9 through 16 a sodium nitrate/potassium
nitrate melt blend.
[0111] The highest compressive stresses were obtained in glasses 5
to 8, i.e. glasses that were tempered in a potassium nitrate melt.
Also the flexural strength ("Modulus of Rupture"--MOR) exhibits the
highest levels in these glasses. Surprisingly, however, the other
glasses exhibit advantageous mechanical properties that make them
particularly suitable for glazing of high-speed railway vehicles,
among other uses.
[0112] For the field of vehicle glazing, such as for high-speed
trains or glazing for bullet-proof vehicles, the glasses must pass
a variety of tests.
[0113] The windshield glass of high-speed trains must resist the
so-called Rock Strike test (RS942612). This test is intended to
simulate stone chipping at high speeds. A pointed aluminum profile
with a weight of 20 g is fired at the glass sheet with 400 km/h.
The glass must not break.
[0114] Table 1 indicates the maximum realized speed to which these
glasses resist in the above-described rock strike test, for glass
7, glass 11, and glass 15. Surprisingly, glasses 11 and 15, with
440 km/h and 540 km/h, respectively, resist to much higher speeds
than glass 7 with 290 km/h, although glass 7 exhibits a
significantly higher compressive stress (870 MPa, as compared to
730 MPa for glass 11, and 799 MPa for glass 15). The better
resistance of glasses 11 and 15 is due to the deep zone of
compressive stress according to the invention. While the exchange
depths in glasses 11 and 15 according to the invention exceed 80
.mu.m (92 .mu.m in glass 11, and 87 .mu.m in glass 15), the
exchange depth in glass 7 is only 16 .mu.m.
[0115] Table 2 shows the properties of glass articles according to
the invention after a single-step chemical tempering of different
durations in an NaNO.sub.3 melt. Glass 27 has the lowest contents
of Li.sub.2O and Na.sub.2O. In this glass, a compressive stress of
600 MPa is just reached after 8 hours in the melt. Even glass 17
with the highest contents of Li.sub.2O and Na.sub.2O requires a
tempering duration of about 8 hours in this melt to obtain a
compressive stress of 600 MPa.
[0116] The glasses having average contents of Li.sub.2O and
Na.sub.2O can even be tempered faster. For example in glass 22
having a Li.sub.2O content of 5 wt.-% and a Na.sub.2O content of
9.48 wt.-%, a high level of compressive stress of 650 MPa is
already achieved after 3 hours of storage in the salt melt. In each
of the glasses, accordingly, a single-step chemical tempering in
the NaNO.sub.3 melt at temperatures in a range from 370.degree. C.
to 420.degree. C. established a zone of compressive stress of more
than 50 .mu.m thickness with a surface tension of more than 600 MPa
within a maximum of 8 hours of treatment in the salt melt.
[0117] Table 3 shows the mechanical properties of the glasses also
listed in Table 2 after a two-step chemical tempering. The glasses
were tempered in a first step in a NaNO.sub.3 melt, and in a
subsequent, second step in a KNO.sub.3 melt. Accordingly, here,
chemical tempering of the glass articles was performed in a
plurality of melts, wherein the melts included at least two alkali
ion species with different ionic radii. Specifically, chemical
tempering of the glass article was performed successively in two
alkali salt melts of different compositions which differed in the
included alkali metal species, and the glass article was stored in
the melts for a maximum of 8 hours in total.
[0118] The durations of storage were varied as indicated in Table
3. As can be seen from Table 3, in all glasses a compressive stress
of more than 700 MPa, in particular also more than 800 MPa and a
depth of the zone of compressive stress of more than 80 .mu.m is
achieved by the two-step tempering which uses a salt in the second
salt melt that comprises alkali ions which have a larger ionic
radius than the alkali ions of the melt used in the first step (K
ions versus Na ion), at melt temperatures of less than 400.degree.
C., and within 8 hours.
[0119] In glass 22, even a surface tension of more than 800 MPa
(841 MPa) and a zone of compressive stress of a thickness of more
than 80 .mu.m (82 .mu.) could be built up at a temperature of the
salt melt of less than 400.degree. C. and within a total time of
storage of the glass article in all salt melts of not more than 3
hours.
[0120] Moreover, it can be seen that in the glasses according to
the invention the compressive stress even decreases again with
tempering times of more than 8 hours.
[0121] Table 4 lists exemplary embodiments of the invention, in
which a surface tension of more than 800 MPa and zones of
compressive stress deeper than 80 .mu.m are obtained in less than 8
hours of treatment duration by using a melt blend for chemical
tempering, wherein the melt blend comprises salts of different
alkali metals and has a content of at least 20 percent by weight of
NaNO.sub.3. The same glass compositions were used as in the
exemplary embodiments of Tables 2 and 3. For the salt melt, a
mixture of 20 wt.-% of sodium nitrate and 80 wt.-% of potassium
nitrate was used.
[0122] Specifically, in all glasses a zone of compressive stress of
more than 80.mu.m corresponding to the measured exchange depth and
a level of compressive stress of more than 800 MPa was achieved in
the melt blend within a maximum of 8 hours of tempering duration
and at temperatures of less than 400.degree. C. Here, similarly to
the exemplary embodiments listed in Table 3, it can be seen that
with longer treatment durations of 12 hours, although the zone of
compressive stress is somewhat deepening, the compressive stress
even decreases again.
[0123] Glasses 19, 22, and 25 achieve a level of surface tension of
more than 800 MPa with depths of the zone of compressive stress of
more than 80 .mu.m already after 4 hours of tempering duration. In
glass 22, these levels are even reached after 3 hours of storage in
the melt.
[0124] From the above examples it will be clear that glasses
according to the invention having contents of Li and Na according
to the invention can be tempered particularly quickly with deep
zones of compressive stress when using a sodium containing salt
melt, preferably a sodium nitrate containing salt melt for the
chemical tempering of the glass article.
TABLE-US-00001 TABLE 2 different glass compositions and properties
after single-step chemical tempering of different duration using
NaN0.sub.3 glass 17 glass 18 glass 19 glass 20 glass 21 glass 22
glass 23 glass 24 glass 25 glass 26 glass 27 glass composition
[wt.-%] Si0.sub.2 61.8 61.9 61.8 61.9 61.9 61.9 62.0 62.0 61.9 62.0
62.0 B.sub.20.sub.3 0.15 0.15 0.15 0.15 0.2 0.2 0.2 0.3 0.5 0.6 0.6
Al.sub.20.sub.3 17.9 17.8 17.9 17.8 17.9 17.9 17.8 17.8 17.8 17.8
17.8 Li.sub.20 5.4 5.3 5.2 5.1 5.05 5 4.95 4.9 4.8 4.7 4.6
Na.sub.20 9.7 9.6 9.6 9.5 9.5 9.48 9.45 8.85 8.5 8.1 8.1 K.sub.20
0.07 0.075 0.07 0.075 0.08 0.1 0.15 0.2 0.3 0.4 0.4 P.sub.20.sub.5
0.03 0.05 0.03 0.05 0.075 0.1 0.15 0.2 0.3 0.4 0.4 Mg0 -- -- -- --
-- -- -- -- 0.02 0.03 0.03 Ca0 0.6 0.7 0.6 0.7 0.75 0.8 0.85 0.09 1
1.2 1.3 Sr0 0.07 0.08 0.07 0.08 0.09 0.1 0.11 0.12 0.14 0.18 0.18
Zr0.sub.2 3.5 3.5 3.6 3.6 3.6 3.6 3.6 3.7 3.7 3.7 3.7 Zn0 0.07 0.08
0.07 0.08 0.08 0.08 0.09 0.11 0.13 0.16 0.16 Sn0.sub.2 0.05 0.05
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.15 Ce0.sub.2 0.05 0.05 0.1 0.1
0.1 0.1 0.1 0.1 0.12 0.16 0.2 Fe.sub.20.sub.3 0.1 0.1 0.1 0.1 0.1
0.1 0.095 0.09 0.08 0.07 0.07 chemical tempering: with 99%
NaNO.sub.3 380.degree. C. 3 h surface tension 570 MPa 587 MPa 650
MPa 610 MPa 560 MPa MOR 540 MPa 568 MPa 607 MPa 594 MPa 521 MPa
exchange depth 90 .mu.m.sup. 91 .mu.m.sup. 89 .mu.m.sup. 70
.mu.m.sup. 63 .mu.m.sup. with 99% NaNO.sub.3 380.degree. C. 4 h
surface tension 580 MPa 620 MPa 640 MPa 615 MPa 580 MPa MOR 546 MPa
571 MPa 604 MPa 578 MPa 536 MPa exchange depth 110 .mu.m .sup. 99
.mu.m.sup. 92 .mu.m.sup. 86 .mu.m.sup. 80 .mu.m.sup. with 99%
NaNO.sub.3 380.degree. C. 8 h surface tension 610 MPa 602 MPa 600
MPa 603 MPa 600 MPa MOR 579 MPa 562 MPa 576 MPa 553 MPa 514 MPa
exchange depth 140 .mu.m .sup. 132 .mu.m .sup. 119 .mu.m .sup. 112
.mu.m .sup. 110 .mu.m .sup. with 99% NaNO.sub.3 380.degree. C. 12 h
surface tension 540 MPa 550 MPa 550 MPa 540 MPa 530 MPa MOR 529 MPa
532 MPa 535 MPa 521 MPa 507 MPa exchange depth 170 .mu.m .sup. 159
.mu.m .sup. 150 .mu.m .sup. 142 .mu.m .sup. 135 .mu.m .sup.
TABLE-US-00002 TABLE 1 GLASSES (laboratory melts) 1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 composition wt.-% SiO.sub.2 61.8 61.9 62.0
61.9 61.8 61.9 62.0 61.9 61.8 61.9 62.0 61.9 61.8 61.9 62.0 61.9
B.sub.2O.sub.3 0.15 0.20 0.3 0.5 0.15 0.20 0.3 0.5 0.15 0.20 0.3
0.5 0.15 0.20 0.3 0.5 AL.sub.2O.sub.3 17.9 17.9 17.8 17.8 17.9 17.9
17.8 17.8 17.9 17.9 17.8 17.8 17.9 17.9 17.8 17.8 Li.sub.2O 5.15
5.05 4.90 4.90 5.15 5.05 4.90 4.90 5.15 5.05 4.90 4.90 5.15 5.05
4.90 4.90 Na.sub.2O 9.7 9.5 8.9 8.5 9.7 9.5 8.9 8.5 9.7 9.5 8.9 8.5
9.7 9.5 8.9 8.5 K.sub.2O 0.07 0.08 0.095 0.1 0.07 0.08 0.095 0.1
0.07 0.08 0.095 0.1 0.07 0.08 0.095 0.1 P.sub.2O.sub.5 0.03 0.075
0.2 0.3 0.03 0.075 0.2 0.3 0.03 0.075 0.2 0.3 0.03 0.075 0.2 0.3
MgO -- -- -- 0.02 -- -- -- 0.02 -- -- -- 0.02 -- -- -- 0.02 CaO 0.6
0.75 0.9 1 0.6 0.75 0.9 1 0.6 0.75 0.9 1 0.6 0.75 0.9 1 SrO 0.07
0.09 0.12 0.14 0.07 0.09 0.12 0.14 0.07 0.09 0.12 0.14 0.07 0.09
0.12 0.14 ZnO 0.07 0.08 0.11 0.13 0.07 0.08 0.11 0.13 0.07 0.08
0.11 0.13 0.07 0.08 0.11 0.13 ZrO.sub.2 3.60 3.60 3.70 3.80 3.60
3.60 3.70 3.80 3.60 3.60 3.70 3.80 3.60 3.60 3.70 3.80 CeO.sub.2
0.1 0.1 0.1 0.12 0.1 0.1 0.1 0.12 0.1 0.1 0.1 0.12 0.1 0.1 0.1 0.12
SnO.sub.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
0.1 0.1 Fe.sub.2O.sub.3 0.1 0.1 0.09 0.08 0.1 0.1 0.09 0.08 0.1 0.1
0.09 0.08 0.1 0.1 0.09 0.08 .rho. g cm.sup.-3 2.4880 2.4884 2.4805
2.4763 2.4880 2.4884 2.4805 2.4763 2.4880 2.4884 2.4805 2.4763
2.4880 2.4884 2.4805 2.4763 .alpha. 10.sup.-6 K.sup.-1 8.70 8.50
8.3 8.2 8.70 8.50 8.3 8.2 8.70 8.50 8.3 8.2 8.70 8.50 8.3 8.2 Tg
.degree. C. 502 505 520 525 502 505 520 525 5.02 505 520 525 5.02
505 520 525 Ig.eta. = 4 1060 1066 1074 1089 1060 1066 1074 1089
1060 1066 1074 1089 1060 1066 1074 1089 Ig.eta. = 7.6 715 718 726
737 715 718 726 737 715 718 726 737 715 718 726 737 Ig.eta. = 13
512 515 522 536 512 515 522 536 512 515 522 536 512 515 522 536
modulus of elasticity GPa 83.5 83.3 84.6 83.7 83.5 83.3 84.6 83.7
83.5 83.3 84.6 83.7 83.5 83.3 84.6 83.7 shear modulus GPa 64 34.1
34.1 33.8 64 34.1 34.1 33.8 64 34.1 34.1 33.8 64 34.1 34.1 33.8
Knoop hardness 640 650 640 630 640 650 640 630 640 650 640 630 640
650 640 630 ion-exchange conditions NaNO.sub.3 mol-% 100 100 100
100 50 50 50 50 20 20 20 20 KNO.sub.3 mol-% 100 100 100 100 50 50
50 50 80 80 80 80 temperature .degree. C. 380 380 380 380 390 390
390 390 385 385 385 385 390 390 390 390 compressive stress [MPa]
600 608 604 600 910 905 870 850 754 755 730 701 840 821 799 790
exchange depth .mu.m 132 115 109 100 21 18 16 14 110 99 92 87 101
94 87 81 MOR MPa 562 576 554 514 850 855 800 795 720 725 701 650
799 758 764 732 rock strike test 290 440 540 max. speed without
breaking km/h
TABLE-US-00003 TABLE 3 properties of different glasses after
two-step chemical tempering glass 17 glass 18 glass 19 glass 20
glass 21 glass 22 glass 23 glass 24 glass 25 glass 26 glass 27
glass composition Si0.sub.2 61.8 61.9 61.8 61.9 61.9 61.9 62.0 62.0
61.9 62.0 62.0 B.sub.20.sub.3 0.15 0.15 0.15 0.15 0.2 0.2 0.2 0.3
0.5 0.6 0.6 Al.sub.20.sub.3 17.9 17.8 17.9 17.8 17.9 17.9 17.8 17.8
17.8 17.8 17.8 Li.sub.20 5.4 5.3 5.2 5.1 5.05 5 4.95 4.9 4.8 4.7
4.6 Na.sub.20 9.7 9.6 9.6 9.5 9.5 9.48 9.45 8.85 8.5 8.1 8.1
K.sub.20 0.07 0.075 0.07 0.075 0.08 0.1 0.15 0.2 0.3 0.4 0.4
P.sub.20.sub.5 0.03 0.05 0.03 0.05 0.075 0.1 0.15 0.2 0.3 0.4 0.4
Mg0 -- -- -- -- -- -- -- -- 0.02 0.03 0.03 Ca0 0.6 0.7 0.6 0.7 0.75
0.8 0.85 0.09 1 1.2 1.3 Sr0 0.07 0.08 0.07 0.08 0.09 0.1 0.11 0.12
0.14 0.18 0.18 Zr0.sub.2 3.5 3.5 3.6 3.6 3.6 3.6 3.6 3.7 3.7 3.7
3.7 Zn0 0.07 0.08 0.07 0.08 0.08 0.08 0.09 0.11 0.13 0.16 0.16
Sn0.sub.2 0.05 0.05 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.15 Ce0.sub.2
0.05 0.05 0.1 0.1 0.1 0.1 0.1 0.1 0.12 0.16 0.2 Fe.sub.20.sub.3 0.1
0.1 0.1 0.1 0.1 0.1 0.095 0.09 0.08 0.07 0.07 with 99% NaNO.sub.3
390.degree. C. 2 h (1.sup.st step), and with 99% KNO.sub.3
390.degree. C. 1 h (2.sup.nd step) surface tension 764 MPa 788 MPa
841 MPa 743 MPa 732 MPa MOR 715 MPa 738 MPa 812 MPa 709 MPa 696 MPa
zone of compressive 88 .mu.m.sup. 85 .mu.m.sup. 82 .mu.m.sup. 80
.mu.m.sup. 63 .mu.m.sup. stress with 99% NaNO.sub.3 390.degree. C.
2 h (1.sup.st step), and with 99% KNO.sub.3 390.degree. C. 1.5 h
(2.sup.nd step) surface tension 784 MPa 811 MPa 823 MPa 804 MPa 761
MPa MOR 732 MPa 762 MPa 793 MPa 765 MPa 722 MPa zone of compressive
88 .mu.m.sup. 85 .mu.m.sup. 81 .mu.m.sup. 80 .mu.m.sup. 70
.mu.m.sup. stress with 99% NaNO.sub.3 390.degree. C. 4 h (1.sup.st
step), and with 99% KNO.sub.3 390.degree. C. 3 h (2.sup.nd step)
surface tension 808 MPa 803 MPa 811 MPa 804 MPa 803 MPa MOR 754 MPa
749 MPa 771 MPa 758 MPa 776 MPa zone of compressive 116 .mu.m .sup.
107 .mu.m .sup. 101 .mu.m .sup. 90 .mu.m.sup. 85 .mu.m.sup. stress
with 99% NaNO.sub.3 390.degree. C. 4 h (1.sup.st step), and with
99% KNO.sub.3 390.degree. C. 6 h (2.sup.nd step) surface tension
793 MPa 786 MPa 774 MPa 770 MPa 775 MPa MOR 743 MPa 748 MPa 753 MPa
734 MPa 742 MPa zone of compressive 115 .mu.m .sup. 107 .mu.m .sup.
103 .mu.m .sup. 90 .mu.m.sup. 85 .mu.m.sup. stress
TABLE-US-00004 TABLE 4 properties of different glasses after
two-step chemical tempering glass 17 glass 18 glass 19 glass 20
glass 21 glass 22 glass 23 glass 24 glass 25 glass 26 glass 27
chemical composition Si0.sub.2 61.8 61.9 61.8 61.9 61.9 61.9 62.0
62.0 61.9 62.0 62.0 B.sub.20.sub.3 0.15 0.15 0.15 0.15 0.2 0.2 0.2
0.3 0.5 0.6 0.6 Al.sub.20.sub.3 17.9 17.8 17.9 17.8 17.9 17.9 17.8
17.8 17.8 17.8 17.8 Li.sub.20 5.4 5.3 5.2 5.1 5.05 5 4.95 4.9 4.8
4.7 4.6 Na.sub.20 9.7 9.6 9.6 9.5 9.5 9.48 9.45 8.85 8.5 8.1 8.1
K.sub.20 0.07 0.075 0.07 0.075 0.08 0.1 0.15 0.2 0.3 0.4 0.4
P.sub.20.sub.5 0.03 0.05 0.03 0.05 0.075 0.1 0.15 0.2 0.3 0.4 0.4
Mg0 -- -- -- -- -- -- -- -- 0.02 0.03 0.03 Ca0 0.6 0.7 0.6 0.7 0.75
0.8 0.85 0.09 1 1.2 1.3 Sr0 0.07 0.08 0.07 0.08 0.09 0.1 0.11 0.12
0.14 0.18 0.18 Zr0.sub.2 3.5 3.5 3.6 3.6 3.6 3.6 3.6 3.7 3.7 3.7
3.7 Zn0 0.07 0.08 0.07 0.08 0.08 0.08 0.09 0.11 0.13 0.16 0.16
Sn0.sub.2 0.05 0.05 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.15 Ce0.sub.2
0.05 0.05 0.1 0.1 0.1 0.1 0.1 0.1 0.12 0.16 0.2 Fe.sub.20.sub.3 0.1
0.1 0.1 0.1 0.1 0.1 0.095 0.09 0.08 0.07 0.07 20% NaNO.sub.3 &
80% KNO.sub.3 390.degree. C. 3 h surface tension 763 MPa 787 MPa
836 MPa 770 MPa 761 MPa MOR 700 MPa 712 MPa 754 MPa 724 MPa 709 MPa
zone of compressive stress 82 .mu.m.sup. 80 .mu.m.sup. 80
.mu.m.sup. 63 .mu.m.sup. 50 .mu.m.sup. 20% NaNO.sub.3 & 80%
KNO.sub.3 390.degree. C. 4 h surface tension 785 MPa 803 MPa 822
MPa 805 MPa 783 MPa MOR 730 MPa 758 MPa 782 MPa 761 MPa 737 MPa
zone of compressive stress 100 .mu.m .sup. 91 .mu.m.sup. 87
.mu.m.sup. 81 .mu.m.sup. 65 .mu.m.sup. 20% NaNO.sub.3 & 80%
KNO.sub.3 390.degree. C. 8 h surface tension 814 MPa 810 MPa 815
MPa 784 MPa 803 MPa MOR 759 MPa 765 MPa 787 MPa 743 MPa 745 MPa
zone of compressive stress 120 .mu.m .sup. 118 .mu.m .sup. 102
.mu.m .sup. 99 .mu.m.sup. 82 .mu.m.sup. 20% NaNO.sub.3 & 80%
KNO.sub.3 390.degree. C. 12 h surface tension 799 MPa 783 MPa 768
MPa 741 MPa 729 MPa MOR 745 MPa 752 MPa 739 MPa 731 MPa 699 MPa
zone of compressive stress 150 .mu.m .sup. 142 .mu.m .sup. 120
.mu.m .sup. 109 .mu.m .sup. 105 .mu.m .sup.
* * * * *