U.S. patent application number 16/576049 was filed with the patent office on 2020-01-09 for glasses having improved ion exchangeability and thermal expansion.
This patent application is currently assigned to Schott AG. The applicant listed for this patent is Schott AG. Invention is credited to Ulrich Fotheringham, Martun Hovhannisyan, Miriam Kunze, Ulrich Peuchert, Michael Schwall, Holger Wegener.
Application Number | 20200010358 16/576049 |
Document ID | / |
Family ID | 62910029 |
Filed Date | 2020-01-09 |
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United States Patent
Application |
20200010358 |
Kind Code |
A1 |
Fotheringham; Ulrich ; et
al. |
January 9, 2020 |
GLASSES HAVING IMPROVED ION EXCHANGEABILITY AND THERMAL
EXPANSION
Abstract
The present invention relates to glasses having a composition
made up of base glasses. The glasses have a good chemical
toughenability in combination with an advantageous coefficient of
thermal expansion. Owing to their composition and the production
process, the homogeneity of the properties of the glasses at their
surface is high compared to the bulk glass. Furthermore, the
fragility of the glasses is low, so that they can be processed to
produce very thin glass articles.
Inventors: |
Fotheringham; Ulrich;
(Wiesbaden, DE) ; Schwall; Michael; (Mainz,
DE) ; Peuchert; Ulrich; (Bondenheim, DE) ;
Kunze; Miriam; (Neustadt am Rubenberge, DE) ;
Hovhannisyan; Martun; (Frankfurt am Main, DE) ;
Wegener; Holger; (Alfeld, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schott AG |
Mainz |
|
DE |
|
|
Assignee: |
Schott AG
Mainz
DE
|
Family ID: |
62910029 |
Appl. No.: |
16/576049 |
Filed: |
September 19, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15891723 |
Feb 8, 2018 |
|
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16576049 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03C 3/091 20130101;
C03C 2203/10 20130101; C03C 2203/50 20130101; C03C 3/093 20130101;
C03C 10/0054 20130101 |
International
Class: |
C03C 3/093 20060101
C03C003/093 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 8, 2017 |
DE |
10 2017 102 482.4 |
Claims
1. A glass, comprising: TABLE-US-00017 A constituent phase min.
max. Albite 10 mol % 40 mol % Reedmergnerite 10 mol % 65 mol %
Potassium reedmergnerite 0 mol % 20 mol % Grossular 0 mol % 10 mol
% Cordierite 0 mol % 10 mol % Willemite 0 mol % 15 mol % Silicon
dioxide 0 mol % 50 mol % Diboron trioxide 0 mol % 15 mol % Titanium
wadeite 0 mol % 24 mol % Strontium feldspar 0 mol % 20 mol %
Celsian 0 mol % 20 mol %
wherein a number of degrees of angular freedom per atom is
calculated according to a formula: f = i = 1 n c i z i f i i = 1 n
c i z i , ( 1 ) ##EQU00008## wherein f is a number of degrees of
angular freedom per atom, c.sub.i is a mole fraction of the i-th
constituent phase, z.sub.i is a number of atoms per structural unit
in the i-th constituent phase, f.sub.i is a number of degrees of
angular freedom per atom in the i-th constituent phase, and "n" is
a number of constituent phases, such that said number of degrees of
angular freedom per atom is not more than 0.24.
2. The glass according to claim 1, wherein said glass has an
average thickness of not more than 2 mm.
3. The glass according to claim 1, wherein said glass has a
composition which includes the following constituent phases:
TABLE-US-00018 Constituent phase min. max. Albite 15 mol % 40 mol %
Reedmergnerite 10 mol % 40 mol % Potassium 1 mol % 15 mol %
reedmergnerite Grossular 0 mol % 9 mol % Cordierite 0 mol % 8.5 mol
% Willemite 0 mol % 8.5 mol % Silicon dioxide 1 mol % 40 mol %
Diboron trioxide 1 mol % 15 mol % Titanium wadeite 0 mol % 20 mol %
Strontium feldspar 0 mol % 10 mol % Cel sian 0 mol % 10 mol %
4. The glass according to claim 1, wherein said glass has a
composition which includes the following constituent phases:
TABLE-US-00019 Constituent phase min. max. Albite 20 mol % 40 mol %
Reedmergnerite 10 mol % 35 mol % Potassium 1 mol % 15 mol %
reedmergnerite Grossular 0 mol % 8.5 mol % Cordierite 0 mol % 8.5
mol % Willemite 0 mol % 7.5 mol % Silicon dioxide 3 mol % 40 mol %
Diboron trioxide 1 mol % 12 mol % Titanium wadeite 0 mol % 18 mol %
Strontium feldspar 0 mol % 5 mol % Celsian 0 mol % 5 mol %
5. The glass according to claim 1, wherein the glass is free of
grossular, willemite, strontium feldspar and/or celsian.
6. The glass according to claim 1, wherein a sum of the proportions
of silicon dioxide and diboron trioxide is not more than 50 mol
%.
7. The glass according to claim 1, wherein the glass further
includes a balance of further constituents which does not exceed a
proportion of 5 mol %, and said balance does not contain the
following oxides: SiO.sub.2, TiO.sub.2, B.sub.2O.sub.3,
Al.sub.2O.sub.3, ZnO, MgO, CaO, BaO, SrO, Na.sub.2O and
K.sub.2O.
8. The glass according to claim 7, wherein said proportion of said
balance is not more than 2 mol % of said glass.
9. The glass according to claim 1, wherein a proportion of
potassium reedmergnerite is not more than 15 mol %.
10. The glass according to claim 1, wherein a coefficient of
thermal expansion is calculated according to formulae: E pot _ = i
= 1 n c i j = 1 m z i , j E pot , j i = 1 n c i j = 1 m z i , j , (
2 ) ##EQU00009## wherein E.sub.pot is an average potential well
depth, m is a number of cation types present, E.sub.pot,j is a
potential well depth for a j-th cation type, and z.sub.j,i is a
number of cations of the j-th type in an i-th constituent phase;
and CTE = ( 51815 ( kJ Mol ) E pot _ - 27.205 ) ppm / K , ( 3 )
##EQU00010## wherein CTE is the thermal coefficient of thermal
expansion, such that said coefficient of thermal expansion is
between 4.5 ppm/K and 6.5 ppm/K.
11. The glass according to claim 10, wherein the coefficient of
thermal expansion calculated according to formulae (2) and (3) in a
surface glass corresponds to at least 50% of the coefficient of
thermal expansion calculated according to formulae (2) and (3) in a
bulk glass.
12. The glass according to claim 10, wherein the coefficient of
thermal expansion calculated according to formulae (2) and (3) in a
surface glass corresponds to not more than 99% of the coefficient
of thermal expansion calculated according to formulae (2) and (3)
in a bulk glass.
13. A method for producing a glass, comprising the steps of:
melting a plurality of glass raw materials to produce a glass melt
having a composition which includes: TABLE-US-00020 A constituent
phase min. max. Albite 10 mol % 40 mol % Reedmergnerite 10 mol % 65
mol % Potassium reedmergnerite 0 mol % 20 mol % Grossular 0 mol %
10 mol % Cordierite 0 mol % 10 mol % Willemite 0 mol % 15 mol %
Silicon dioxide 0 mol % 50 mol % Diboron trioxide 0 mol % 15 mol %
Titanium wadeite 0 mol % 24 mol % Strontium feldspar 0 mol % 20 mol
% Celsian 0 mol % 20 mol %
wherein a number of degrees of angular freedom per atom is
calculated according to a formula: f = i = 1 n c i z i f i i = 1 n
c i z i , ( 1 ) ##EQU00011## wherein f is a number of degrees of
angular freedom per atom, c.sub.i is a mole fraction of the i-th
constituent phase, z.sub.i is a number of atoms per structural unit
in the i-th constituent phase, f.sub.i is a number of degrees of
angular freedom per atom in the i-th constituent phase, and "n" is
a number of constituent phases, such that said number of degrees of
angular freedom per atom is not more than 0.24; moulding a flat
glass article from the glass melt; and cooling the flat glass
article.
14. The method according to claim 13, wherein the moulding of the
flat glass article is carried out in one of a down draw, an
overflow fusion, and a redrawing process.
15. The method according to claim 13, wherein the step of cooling
is carried out by an active cooling step using a coolant or by
allowing the flat glass article to cool passively.
16. A method, comprising the steps of: providing a glass having a
composition including: TABLE-US-00021 A constituent phase min. max.
Albite 10 mol % 40 mol % Reedmergnerite 10 mol % 65 mol % Potassium
reedmergnerite 0 mol % 20 mol % Grossular 0 mol % 10 mol %
Cordierite 0 mol % 10 mol % Willemite 0 mol % 15 mol % Silicon
dioxide 0 mol % 50 mol % Diboron trioxide 0 mol % 15 mol % Titanium
wadeite 0 mol % 24 mol % Strontium feldspar 0 mol % 20 mol %
Celsian 0 mol % 20 mol %
wherein a number of degrees of angular freedom per atom is
calculated according to a formula: f = i = 1 n c i z i f i i = 1 n
c i z i , ( 1 ) ##EQU00012## wherein f is a number of degrees of
angular freedom per atom, c.sub.i is a mole fraction of the i-th
constituent phase, z.sub.i is a number of atoms per structural unit
in the i-th constituent phase, f.sub.i is a number of degrees of
angular freedom per atom in the i-th constituent phase, and "n" is
a number of constituent phases, such that said number of degrees of
angular freedom per atom is not more than 0.24; using said glass as
one of a covering glass, a display glass, a substrate glass, an
electrically insulating dielectric intermediate layer, and a
polymer replacement in a finishing of surfaces.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
15/891,723, entitled "GLASSES HAVING IMPROVED ION EXCHANGEABILITY
AND THERMAL EXPANSION", filed Feb. 8, 2018, which is incorporated
herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to glasses and glass products
which combine good chemical toughenability with low fragility and
desired thermal expansion properties. The low fragility may serve
to give a very substantial independence of the chemical toughening
result from the thermal history, which, in the case of glasses
which have been subjected to forming before prestressing, can
differ significantly.
[0003] In one embodiment, the invention relates to ultra-thin
glasses, which term refers to glasses having a thickness of 400 m
and below, down to 20 m and less.
[0004] Production processes for such glasses and uses thereof are
also provided by the present invention.
[0005] The present invention also relates to glasses having a
composition made up of base glasses. The glasses are characterized
by good chemical toughenability in combination with a desired
coefficient of thermal expansion. Owing to their composition and
the production process, the homogeneity of the properties of the
glasses on their surface can be high compared to the bulk glass.
Furthermore, the fragility of the glasses can be low, so that they
can be processed to produce very thin glass articles.
2. Description of the Related Art
[0006] Glasses having good ion exchangeability, i.e. good chemical
toughenability, and a low fragility and advantageous thermal
expansion may be required for many applications. The importance of
the fragility introduced by C.A. Angell as derivative of the
decadic logarithm of the viscosity with respect to the variable
(T.sub.G/T) is its relationship to the number of configurational
degrees of freedom in the glass, see, for example, R. Bohmer, K. L.
Ngai, C.A. Angell, D. J. Plazek, J. Chem. Phys., 99 (1993)
4201-4209. The greater the fragility, the greater is the number of
configurational degrees of freedom and the more different are the
various configurations due to different thermal histories in which
the glass can be present. TG is the glass transition temperature;
i.e. in a definition via the viscosity curve, the temperature at
which the viscosity is 10.sup.12 pascal seconds.
[0007] These different configurations in turn have an influence on
the stress relaxation, i.e. the unavoidable antagonistic effect
occurring when the stress is built up by ion exchange. This means
that glass samples having one and the same composition but a
different thermal history will build up different stresses in the
same ion-exchange process. This is of particular importance for
glass which is subjected to different forming processes, which
naturally imply different thermal histories, before toughening.
[0008] The process of chemical toughening may also be referred to
as chemical prestressing, chemical tempering, chemical
strengthening, ion-exchange strengthening, ion-exchange tempering,
ion-exchange toughening, or ion-exchange prestressing. All of these
terms refer to a process wherein a smaller ion in a glass is
replaced by a larger one, e.g. sodium is resplaced by potassium, or
lithium is replaced by sodium or potassium, thereby forming a
compressive stress layer on the surface of the glass.
[0009] The thermoviscoelastic models which describe the stress
relaxation are described, for example, in George W. Scherer:
Relaxation in Glass and Composites. Krieger Publishing Company
Malabar (1992); the relationship which the nonlinearity parameter
"x" describing the influence of the configuration on the thermal
activation of stress relaxation has with the fragility is
discussed, for example, in Roland Bohmer, Non-linearity and
non-exponentiality of primary relaxations, Journal of
Non-Crystalline Solids, 172-174 (1994), 628-634.
[0010] Since the glass may also be used in the non-toughened state,
it is still important that a low fragility means a high dimensional
stability of the glass at all possible thermal stresses below the
glass transition temperature, which correlates with the
configurational proportion of the coefficient of thermal expansion,
see Raphael M. C. V. Reis, John C. Mauro, Karen L. Geisingera,
Marcel Potuzak, Morten M. Smedskjaer, Xiaoju Guo, Douglas C. Allan,
Relationship between viscous dynamics and the configurational
thermal expansion coefficient of glass-forming liquids, Journal of
Non-Crystalline Solids 358 (2012) 648-651, and via this
configurational proportion of the coefficient of thermal expansion
with, in turn, the number of configurational proportions (see
above).
[0011] Ultra-thin glass can be affected by the fragility and the
configurational proportion of the coefficient of thermal expansion.
The thickness, which as described above spans a wide range, is
determined by the mass throughput and drawing speed. If ultra-thin
glass of one and the same glass type is to be produced using one
and the same drawing facility, a constant mass throughput and
uniform width of the sheet being drawn, the drawing speed firstly
has to be selected proportionally to the reciprocal thickness to
achieve the constant mass throughput and the uniform drawn sheet
width. The differences in the drawing speeds are considerable owing
to the abovementioned typical range of the glass thicknesses.
Independently thereof, the glass runs through one and the same
cooling section generally configured as cooling shaft after exit
from the drawing nozzle, since the drawing facility is one and the
same drawing facility and the temperatures at the beginning and end
of the cooling section are the same. The temperature at the
beginning is the same as the temperature in the drawing tank, and
the temperature at the end is the temperature from which the glass
can be handled freely. This means that the cooling rate also has to
be proportional to the reciprocal thickness. The glass thus runs
through the cooling shaft with significantly different cooling
rates, and it is difficult, especially for high cooling rates, to
realize a homogeneous temperature over the width of the sheet cross
section. However, different temperature histories over the width of
the glass sheet lead to distortions whose magnitude depends on
these differences in the temperature history but also on the
abovementioned configurational proportion of the coefficient of
thermal expansion and thus the fragility. A low fragility thus
ensures a certain robustness of the ultra-thin glass against
adverse influences in the production process.
[0012] The use of such glasses as covering glasses for displays of
electronic appliances can be of economic relevance. Here, measures
which lead to a higher ion exchangeability often also lead to a
higher fragility, and vice versa.
[0013] US 2013/0165312 A1 discloses covering glasses for
semiconductor manufacture, which display a particular thermal
expansion, low alpha radiation and a high elastic modulus. The
glasses described there contain very high proportions of alkali
metal oxides and alkaline earth metal oxides, by which means a high
thermal expansion is said to be made possible. However, the glasses
cannot be described by the base glass system of this invention
because they differ in stoichiometric terms from the glasses of
this invention. In addition, the glasses described there have very
high proportions of Al.sub.2O.sub.3 and at the same time
comparatively little MgO, so that a high proportion of albite would
be expected, which increases the fragility. Furthermore, because of
the very low B.sub.2O.sub.3 content the glasses described there
lack the proportion of reedmergnerite desired according to the
invention, which would again reduce the fragility. The
abovementioned very high proportion of alkali metal oxides and
alkaline earth metal oxides results in a high value of the
coefficient of thermal expansion, which is at least
99.2.times.10.sup.-7/K in the examples, and thus in fact very
high.
[0014] DE 20 2012 012 876 U1 is concerned with the ion
exchangeability of glasses. In the case of the glasses described
there, the main focus is on the hydrolytic and mechanical
resistance in order to avoid firstly fracture and splintering and
secondly leaching of glass constituents. Most of the glasses in the
document do not contain any B.sub.2O.sub.3. In many of the claimed
compositions described there no boron is present at all. The
proportion of boron is not quantified in the description. In the
examples, there is a boron content of not more than 4.6%; however,
at the same time a measurement rule according to which the boron
content in mol % should be smaller than 0.3 times the difference
between the sum of the proportions of alkali metal oxides and the
proportion of aluminium oxide is presented. This measurement rule
serves to achieve a very high ion mobility. The compositions
described in the present invention do not overlap this measurement
rule.
[0015] What is needed in the art is glasses which combine good
chemical toughenability with low fragility and desired thermal
expansion properties. In addition, the glasses should be able to be
produced in modern sheet glass manufacturing processes.
SUMMARY OF THE INVENTION
[0016] The present invention provides a targeted combination of
stoichiometric glasses, i.e. glasses which also exist as crystals
in the same stoichiometry and whose properties can be assumed to be
very similar in each case for glass and crystal because of the
identical topology of the structural components, as has been
examined in the literature in many examples by way of NMR
measurements or the like. For this purpose, stoichiometric glasses
are selected which can be combined to obtain a behaviour which can
achieve the object of the invention. In the present patent
application, these stoichiometric glasses are also referred to as
"base glasses" or "constituent phases".
[0017] In the present invention, a high but not very high ion
mobility is sought in order to achieve desired values for the
fragility and the coefficient of thermal expansion. Why and how
this is contradictory is explained in the description of the
present invention.
[0018] It is not a new concept to describe glasses in terms of the
constituent phases to be assigned thereto. Specification of the
base glasses makes it possible to draw conclusions as to the
chemical structure of a glass (cf. Conradt R: "Chemical structure,
medium range order, and crystalline reference state of
multicomponent oxide liquids and glasses", in Journal of
Non-Crystalline Solids, Volumes 345-346, 15 Oct. 2004, Pages
16-23).
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention provides a glass having a combination
of base glasses, which can be characterized by the following phases
constituting the glass:
TABLE-US-00001 TABLE 1 Constituent phase min. max. Albite 10 mol %
40 mol % Reedmergnerite 10 mol % 65 mol % Potassium reedmergnerite
0 mol % 32 mol % Grossular 0 mol % 10 mol % Cordierite 0 mol % 10
mol % Willemite 0 mol % 15 mol % Silicon dioxide 0 mol % 50 mol %
Diboron trioxide 0 mol % 15 mol % Titanium wadeite 0 mol % 24 mol %
Strontium feldspar 0 mol % 20 mol % Celsian 0 mol % 20 mol %
Optional balance 0 mol % 5 mol %
[0020] The glasses of the present invention can be characterized by
their composition and their constitution. The composition is
selected in terms of the phases constituting the glass within the
limits described herein.
[0021] The phases constituting the glass are of course not present
in crystalline form but in amorphous form in the glass product.
However, this does not mean that the constituent phases have
completely different structural components in the amorphous state
than in the crystalline state. As stated above, the topology of the
structural components, i.e., for example, the coordination of the
participating cations to surrounding oxygen atoms or the
interatomic distance resulting from the coordination and strength
of the bond between these cations and surrounding oxygen atoms, is
comparable. For this reason, many properties of the glass of the
invention can be described well in terms of the constituent phases,
in particular in order to indicate the inventive achievement and
the problems overcome by the invention (cf. Conradt R., loc. cit.).
Here, the glass can naturally be produced not only using the
corresponding crystals but also using conventional glass raw
materials as long as the stoichiometric ratios permit the formation
of the appropriate structural components of the base glasses.
[0022] The chemical toughenability by replacement of sodium by
potassium in a suitable salt melt, e.g. potassium nitrate, is
achieved in the case of the inventive glasses by a substantial
proportion of structural components which contain sodium and have a
high sodium mobility. An example of a constituent phase which
positively influences the chemical toughenability is albite. The
glasses and glass articles according to the present invention can
be chemically toughened.
[0023] The desired value of the fragility can be mapped onto a
condition for the parameter actually addressed, namely the number
of configurational degrees of freedom, and an appropriate
calculation method. According to the studies by C.A. Angell (see,
for example, R. Bohmer, K. L. Ngai, C.A. Angell, D. J. Plazek, J.
Chem. Phys., 99 (1993) 4201-4209), the fragility is equal to a
minimum value which would be obtained for a course of the viscosity
curve following the Arrhenius law and which is achieved
approximately by uncontaminated, in particular OH-free, fused
silica plus a further contribution which correlates with the number
of configurational degrees of freedom which "thaw" at T.sub.G and
there show up as c.sub.p jump in a dynamic calorimetric
measurement.
[0024] This number can be determined by topology methods and
comparison with calorimetric measurements. Since each
configurational change is a nonsimilarity image and therefore
includes changes of atomic angles, the number of configurational
degrees of freedom per mol follows the number of degrees of angular
freedom per atom. The latter are calculated by the method described
in DE 10 2014 119 594 A1, using the relationship reported in
Alberto Garcia, Marvon Cohen, First Principles Ionicity Scales,
Phys. Rev. B 1993, 4215-4220, for the degree of ionization of a
cation-oxygen bond, which is incorporated herein by reference. The
comparison of the result multiplied by the gas constant R with the
c.sub.p jump at T.sub.G carried out on the example of various
commercial glasses such as Borofloat33, Borofloat40, LF5, LLF1, K7,
AF45, etc., justifies this procedure.
[0025] Since the glasses of the invention represent a combination
of the constituent phases indicated above, it is sufficient for
setting up the calculation method that the number of degrees of
angular freedom per atom be indicated numerically for each
constituent phase. The following may apply here:
TABLE-US-00002 TABLE 2 Formula Number of Number of degrees
Constituent (normalized to atoms per of angular freedom phase a
simple oxide) structural unit per atom Albite (Na.sub.2O .cndot.
Al.sub.2O.sub.3 .cndot. 26/8 0.318898019 6SiO.sub.2)/8 Reed-
(Na.sub.2O .cndot. B.sub.2O.sub.3 .cndot. 26/8 0.235470229
mergnerite 6SiO.sub.2)/8 Potassium (K.sub.2O .cndot. B.sub.2O.sub.3
.cndot. 26/8 0.238787725 reed- 6SiO.sub.2)/8 mergnerite Grossular
(3CaO .cndot. Al.sub.2O.sub.3 .cndot. 20/7 0.666147023
3SiO.sub.2)/7 Cordierite (2MgO .cndot. 2Al.sub.2O.sub.3 .cndot.
29/9 0.427525473 5SiO.sub.2)/9 Willemite (2ZnO .cndot. SiO.sub.2)/3
7/3 0.725827911 Silicon SiO.sub.2 3 0 dioxide Diboron
B.sub.2O.sub.3 5 0.170590747 trioxide Titanium (K.sub.2O .cndot.
TiO.sub.2 .cndot. 3 0.459052018 wadeite 3SiO.sub.2)/5 Strontium
(SrO .cndot. Al.sub.2O.sub.3 .cndot. 13/4 0.501247171 feldspar
2SiO.sub.2)/4 Celsian (BaO .cndot. Al.sub.2O.sub.3 .cndot. 13/4
0.508110848 2SiO.sub.2)/4
[0026] The calculation method for determining the degrees of
angular freedom f per atom in the finished glass is therefore:
f = i = 1 n c i z i f i i = 1 n c i z i , ( 1 ) ##EQU00001##
where c.sub.i is the mole fraction of the i-th constituent phase in
the glass composition concerned, z.sub.i is the number of atoms per
structural unit in the i-th constituent phase and f.sub.i is the
number of degrees of angular freedom per atom in the i-th
constituent phase. "n" is the number of constituent phases.
[0027] The position of the coefficient of thermal expansion in the
desired range is likewise ensured by way of a calculation method.
This is determined with reference to the average bond strength.
[0028] The coefficient of thermal expansion is inversely
proportional to this (or to the "depth of the interatomic potential
wells"). In a simple picture of oxidic glasses, the cations are in
each case placed in a potential well formed by the surrounding
oxygen atoms, and the depth of the potential well is considered to
be the sum of the bond strengths of the various single bonds to the
surrounding oxygen atoms, i.e. the total interaction energy is
concentrated in potential wells with the cations in the centre and
the oxygen atoms in the periphery. Thus, the reverse case no longer
has to be considered; it would also be more difficult to analyse
since an oxygen atom can be located between a number of different
cations, which conversely cannot occur in purely oxidic glasses.
These values have been tabulated, e.g. in DE 10 2014 119 594
A1:
TABLE-US-00003 TABLE 3 Potential well Cation depth/(kJ/mol) Si 1864
B 1572.5 Al 1537 Li 585 Na 440.5 K 395 Mg 999 Ca 1063 Sr 1005 Ba
976 Zn 728 Ti 1913
[0029] The values for Sr, Ba, Zn and Ti do not originate from DE 10
2014 119 594 A1, but have been calculated by precisely the same
method described there using the sources cited there.
[0030] An average potential well depth can be calculated from the
composition of a glass composed of the abovementioned constituent
phases, the numbers of various cations present in the respective
phase and the potential well depths per cation tabulated above:
E pot _ = i = 1 n c i j = 1 m z i , j E pot , j i = 1 n c i j = 1 m
z i , j , ( 2 ) ##EQU00002##
[0031] Here, m is the number of cation types present, E.sub.pot,j
is the potential well depth tabulated above for the j-th cation
type and z.sub.j,i is the number of cations of the j-th type in the
i-th constituent phase. The sums overj are tabulated below:
TABLE-US-00004 TABLE 4 Constituent phase j = 1 m z i , j
##EQU00003## j = 1 m z i , j E pot , j ##EQU00004## Albite 1.25
1892.38 Reedmergnerite 1.25 1901.25 Potassium reedmergnerite 1.25
1889.88 Grossular 1.14 1693.57 Cordierite 1.22 1940.67 Willemite
1.00 1106.67 Silicon dioxide 1.00 1864.00 Diboron trioxide 2.00
3145.00 Titanium wadeite 1.20 1659.00 Strontium feldspar 1.25
1951.75 Celsian 1.25 1944.50
[0032] This average bond strength is related, as a comparison with
various commercial glasses such as Borofloat33, Borofloat40, AF45,
AF32, etc. showed, to the coefficient of thermal expansion
according to the following formula:
CTE = ( 51815 ( kJ Mol ) E pot _ - 27.205 ) ppm / K , ( 3 )
##EQU00005##
[0033] The selection of the constituent phases has been made since
combinations of them display the desired ion exchange behaviour and
the desired values for fragility and coefficient of expansion. The
role of the individual constituent phases is once again presented
in detail below.
[0034] Albite
[0035] A base glass which is representative of a constituent phase
in the glass according to the present invention is albite glass. It
is known that albite (NaAlSi.sub.3O.sub.8) has a high sodium
diffusivity because of its structure made up of a framework of
SiO.sub.4 and A10.sub.4 tetrahedra with mobile sodium ions in the
framework, see Geochimica and Cosmochimica Acta, 1963, Vol. 27,
pages 107-120. A proportion of albite glass therefore contributes
to a high sodium mobility, which promotes ion exchange and thus the
chemical toughenability of the glasses. Compared to nepheline
(synthetic variant without potassium: NaAlSiO.sub.4) which has an
even higher sodium diffusivity, albite has the advantage of a
significantly lower melting point (1100-1120.degree. C.), which
improves the fusibility of the glass.
[0036] The arithmetic proportion of albite in the glasses of the
present invention may be at least 10 mol % and not more than 40 mol
%. An amount of albite which is too small impairs the ion
exchangeability and chemical toughenability in respect of the
replacement of sodium by potassium. The glass may contain albite in
a proportion of at least 15 mol %, for example at least 18 mol %
and for example at least 20 mol %. Pure albite glass would have an
optimal chemical toughenability, but would not achieve the
objective in respect of the required fragility. The number of
degrees of angular freedom per atom in albite is 0.318898019 and
thus more than the value desired for the glass of the present
invention. Thus, albite can be used in a proportion of not more
than 35 mol %, for example not more than 32 mol %, for example not
more than 30 mol % and for example not more than 25 mol %. For the
purposes of the invention, one mole of albite is one mole of
(Na.sub.2O.Al.sub.2O.sub.3.6SiO.sub.2)/8.
[0037] Reedmergnerite
[0038] The boron analogue reedmergnerite has a significantly
smaller number of degrees of angular freedom per atom than albite,
namely 0.235470229. The glass of the invention therefore contains
reedmergnerite glass as further base glass, for example, the glass
contains more reedmergnerite than albite. This base glass is made
up of SiO.sub.4 and BO.sub.4 tetrahedra in a manner analogous to
albite glass, but with a more close-meshed structure because of the
greater bond strength of the B--O bond compared to the Al--O bond.
In addition, the B--O bond is more covalent than the Al--O bond.
Both these facts result in firstly a smaller contribution to the
fragility, but the mobile sodium atoms in the framework have,
according to Anderson and Stuart (Journal of the American Ceramic
Society, Vol. 37, No. 12, 573-580), a higher thermal enthalpy of
activation than in albite glass, so that the contribution to sodium
ion mobility at one and the same temperature is lower in
reedmergnerite glass than in albite glass. According to the present
invention, the glass described here may include at least 10 mol %
of reedmergnerite, such as at least 15 mol % or at least 18 mol %,
for example at least 20.5 mol % or at least 25 mol % and for
example at least 30 mol % of reedmergnerite. To ensure a
satisfactory toughenability, the amount of reedmergnerite is,
however, restricted to not more than 65 mol %, for example not more
than 60 mol %, for example not more than 45 mol %, for example not
more than 40 mol % and for example not more than 35 mol %. For the
purposes of the invention, one mole of reedmergnerite may one mole
of (Na2O.B2O3.6SiO2)/8.
[0039] Potassium Reedmergnerite
[0040] To increase the devitrification stability, the potassium
analogue of reedmergnerite can additionally also be added to the
glass. In the case of such an addition, the finished glass contains
not only sodium but also potassium as alkali and is therefore more
stable to devitrification. As regards the number of degrees of
angular freedom per atom, it behaves similarly to reedmergnerite;
this number can be 0.238787725. This base glass will hereinafter be
referred to as "potassium reedmergnerite" since it can be
considered to be the potassium analogue of reedmergnerite having
the danburite structure.
[0041] The glasses of the present invention can contain potassium
reedmergnerite in a proportion of from 0 to 32 mol % or up to 30
mol %. With a view to the devitrification stability, some
embodiments contain at least 1 mol % potassium reedmergnerite, for
example at least 5 mol % or at least 8 mol %. In order not to
impair the chemical toughenability, the amount of potassium
reedmergnerite in the glass of the present invention may be
restricted to not more than 25 mol %, for example not more than 20
mol % and for example not more than 15 mol %. For the purposes of
the present invention, one mole of potassium reedmergnerite is one
mole of (K.sub.2O.B.sub.2O.sub.3.6SiO.sub.2)/8.
[0042] Some embodiments according to the present invention, the
proportion of reedmergnerite in the glass can be greater than the
proportion of potassium reedmergnerite, for example at least twice
as high.
[0043] The total proportion of the abovementioned base glasses
albite, reedmergnerite and potassium reedmergnerite in the glass of
the present invention can be at least 50 mol %, for example at
least 60 mol %. However, the proportion may be restricted to not
more than 90 mol % and for example not more than 80 mol %. All
three constituent phases presented above (albite, reedmergnerite,
potassium reedmergnerite) contain alkali metals in an appreciable
amount, and these lead to a high thermal expansion. For this
reason, further constituent phases in which alkaline earth metals
or zinc, i.e. cations which lead to a moderate coefficient of
expansion, are present instead of alkali metals are introduced.
[0044] Grossular, Cordierite and Willemite
[0045] The three further constituent phases grossular
(Ca.sub.3Al.sub.2Si.sub.3O.sub.12), cordierite
(Mg.sub.2Al.sub.4Si.sub.5O.sub.18) and willemite
(Zn.sub.2SiO.sub.4) which are optionally present each have a high
proportion of alkaline earth metals or zinc, so that their
influence on the coefficient of expansion is considerable.
Conversely, the respective number of angular conditions per atom
can be very high (grossular: 0.666147023, cordierite: 0.427525473,
willemite: 0.725827911).
[0046] The glasses of the present invention can therefore contain
grossular in proportions of from 0 to 10 mol %, for example in
amounts of up to 9 mol % or up to 8.5 mol %. In some embodiments,
at least 1 mol %, for example at least 3 mol % and for example at
least 5 mol %, of grossular is used. Some embodiments of the
glasses of the present invention are free of grossular. For the
purposes of the present invention, one mole of grossular can be one
mole of (3 CaO.Al.sub.2O.sub.3.3SiO.sub.2)/7.
[0047] The glasses of the present invention can contain cordierite
in proportions of from 0 to 10 mol %, for example in amounts of up
to 8.5 mol % or not more than 5 mol %. In some embodiments, at
least 1 mol %, for example at least 3 mol % and for example at
least 4 mol %, of cordierite is used. Some embodiments of the
glasses of the present invention are free of cordierite. For the
purposes of the present invention, one mole of cordierite can be
one mole of (2MgO.2Al.sub.2O.sub.3.5SiO.sub.2)/9.
[0048] The glasses of the present invention can therefore contain
willemite in proportions of from 0 to 15 mol %, for example in
amounts of up to 10 mol %, for example up to 8.5 mol % or up to 7.5
mol %. In some embodiments, at least 0.5 mol %, for example at
least 3 mol % and for example at least 5 mol %, of willemite is
used. For the purposes of the present invention, one mole of
willemite can be one mole of (2ZnO--SiO.sub.2)/3.
[0049] In another embodiment, the sum of the proportions of
grossular, cordierite and willemite in the glass of the invention
can be at least 3 mol %, for example at least 4 mol % or at least 5
mol %, in order to influence the coefficient of expansion in the
desired way. However, a total of not more than 25 mol %, for
example not more than 20 mol %, not more than 15 mol % or not more
than 10 mol %, of these base glasses can be used.
[0050] When it is said in the present description that the glasses
are free of a component or of a constituent phase or do not contain
a certain component or constituent phase, this is intended to mean
that this component or constituent phase may be present at most as
impurity in the glasses. This means that it is not added in
significant amounts. Amounts which are not significant are,
according to the present invention, amounts of less than 300 ppm
(molar), such as less than 10 ppm (molar), less than 50 ppm
(molar), or less than 10 ppm (molar). The glasses of the present
invention can be free of lithium, lead, arsenic, antimony, bismuth
and/or cadmium.
[0051] Silicon Dioxide and Diboron Trioxide
[0052] Finally, a proportion of a base glass composed of pure
SiO.sub.2 is also possible in order to set a low fragility. The
glasses of the present invention can comprise SiO.sub.2 as base
glass in a proportion of at least 0 mol % and not more than 50 mol
%, not more than 40 mol %, not more than 30 mol %, not more than 25
mol % or not more than 20 mol %. However, its content can be
restricted to not more than 18 mol %, not more than 16 mol %, not
more than 14 mol % or not more than 12 mol %. An excessively high
proportion of silicon dioxide impairs the fusibility, so that some
embodiments can contain less than 10 mol % of this component. It
has been found that SiO.sub.2 in amounts of at least 1 mol %, for
example at least 3 mol % or at least 5 mol % can be used.
[0053] The proportion of silicon dioxide can be smaller than the
respective proportion of reedmergnerite and/or albite. The molar
ratio of the proportion of silicon dioxide to reedmergnerite and/or
albite is even not more than 1:2, not more than 1:3, for example
not more than 1:4. The limitation of the proportion of silicon
dioxide is, for example, to be considered as due to the fact that
the properties of the significant base glasses reedmergnerite and
albite should predominate in the glass of the present
invention.
[0054] A proportion of diboron trioxide also leads to a low
fragility, although to a smaller degree than silicon dioxide but
without influencing the fusibility. A proportion of from 0 mol % to
15 mol %, up to 12 mol % or up to 10 mol %, of diboron trioxide can
therefore be provided. In some embodiments, the proportion of
diboron trioxide is at least 1 mol % and for example not more than
5 mol % or not more than 3 mol %.
[0055] The sum of the proportions of silicon dioxide and diboron
trioxide can be, according to the present invention, not more than
50 mol %, not more than 40 mol %, not more than 35 mol % or not
more than 30 mol %, not more than 20 mol %, not more than 15 mol %
and not more than 12.5 mol %.
[0056] Components which Increase the Index of Refraction
[0057] In order to replace window glass as optical cover glass, it
may be necessary to set the index of refraction to a value of from
1.5 to 1.6, for example 1.523 (typical index of refraction of
window glass at the sodium D line, see M. Rubin, Optical properties
of soda lime silica glasses, Solar Energy Materials 12 (1985),
275-288). For this reason, up to three components containing heavy
ions which increase the index of refraction are provided according
to the invention: titanium wadeite (contains titanium), strontium
feldspar (contains strontium), celsian (contains barium).
[0058] The proportion of titanium wadeite in the glass of the
present invention can be from 0 mol % to 24 mol %. The content can
be not more than 20 mol %, for example not more than 18 mol %. Some
embodiments of the glasses of the present invention are free of
titanium wadeite. However, other embodiments, the content of this
component can be at least 1 mol %, at least 5 mol %, at least 10
mol % or even at least 13 mol %. For the purposes of the present
invention, one mole of titanium wadeite is one mole of
(K.sub.2O.TiO.sub.2.3SiO.sub.2)/5. TiO.sub.2 present in the glass
increases the solarization resistance, which is particularly
relevant in applications in which longevity is advantageous.
[0059] The proportion of strontium feldspar in the glass of the
present invention can be from 0 mol % to 20 mol %. The content can
be not more than 10 mol %, for example not more than 5 mol %. Some
embodiments of the glasses of the present invention are free of
strontium feldspar. However, in other embodiments, the content of
this component can be at least 0.5 mol %, at least 1 mol %, at
least 2 mol % or even at least 3 mol %. For the purposes of the
present invention, one mole of strontium feldspar can be one mole
of (SrO.Al.sub.2O.sub.3.2SiO.sub.2)/4.
[0060] The proportion of celsian in the glass of the present
invention can be from 0 mol % to 20 mol %. The proportion may be
not more than 10 mol %, for example not more than 5 mol %. Some
embodiments of the glasses of the present invention are free of
celsian. However, in other embodiments, the content of this
component can be at least 0.5 mol %, at least 1 mol %, at least 2
mol % or even at least 3 mol %. For the purposes of the present
invention, one mole of celsian can be one mole of
(BaO.Al.sub.2O.sub.3.2SiO.sub.2)/4.
[0061] As a general rule for selection of an index of refraction in
the range from 1.45 to 1.6, the method of Appen presented
comprehensively in H. Bach, N. Neuroth, Properties of Optical
Glass, second corrected printing, Schott-Series on Glass,
Springer-Verlag Berlin Heidelberg New York (1998), pp. 73-76,
including a precise description of the calculation method and the
necessary parameters, is used. The abovementioned document of the
Schott document series is incorporated in full into the disclosure
of the present patent application. The original literature of Appen
is cited in this document of the Schott document series.
[0062] Further Components
[0063] In addition to the abovementioned components, the glass can
contain further constituents which are referred to as "balance"
herein. The proportion of the balance in the glass of the invention
can be not more than 5 mol %, in order not to disturb the glass
properties set by careful selection of suitable base glasses. In
some embodiments, the proportion of the balance in the glass is not
more than 4 mol % or not more than 3 mol %, for example not more
than 2 mol % or not more than 1 mol %. The balance may contain,
oxides which are not present in the base glasses mentioned here.
Thus, the balance may not contain any SiO.sub.2, TiO.sub.2,
B.sub.2O.sub.3, Al.sub.2O.sub.3, ZnO, MgO, CaO, BaO, SrO, Na.sub.2O
or K.sub.2O. According to the invention, as balance, use is
optionally made of additions of further simple oxides of
"intermediates", i.e. oxides which are between the network formers
such as SiO.sub.2 and the network modifiers such as Na.sub.2O (see
K. H. Sun, Journal of The American Ceramic Society Vol. 30, No. 9
(1947), pp. 277-281). Although these oxides alone do not form any
glasses, they can be incorporated in the abovementioned percentage
range into the network. Thus, the balance can contain, in
particular, oxides such as ZrO.sub.2. According to the theory of A.
Dietzel, Die Kationenfeldstarken und ihre Beziehungen zu
Entglasungsvorgangen, zur Verbindungsbildung und zu den
Schmelzpunkten von Silicaten, Berichte der Bunsengesellschaft fiir
physikalische Chemie Vol. 48 No 0.1 (1942), 9-23, Nb.sub.2O.sub.5
and Ta.sub.2O.sub.5 also count as "intermediates", as can be
calculated using the ionic radii according to R. Shannon, Revised
Effective Ionic Radii and Systematic Studies of Interatomic
Distances in Halides and Chalcogenides, Acta Cryst. (1976) A32,
751-767.
[0064] In another embodiment, the glass of the invention can be
characterized by the following proportions of constituent phases in
the base glass composition. The ranges of proportions indicated
above and below and further features in respect of the glass of the
invention also apply to the embodiment outlined below:
TABLE-US-00005 TABLE 5 Desired Particularly Desired Constituent
phase min. max. min. max. Albite 15 mol % 27 mol % 18 mol % 24 mol
% Reedmergnerite 25 mol % 38 mol % 30 mol % 35 mol % Potassium 5
mol % 20 mol % 9 mol % 13 mol % reedmergnerite Grossular 0 mol % 10
mol % 0 mol % 3 mol % Cordierite 0 mol % 10 mol % 0 mol % 3 mol %
Willemite 0 mol % 10 mol % 4 mol % 9 mol % Silicon dioxide 0 mol %
12 mol % 7 mol % 10 mol % Diboron trioxide 0 mol % 8 mol % >0
mol % 5 mol % Titanium wadeite 5 mol % 24 mol % 12 mol % 20 mol %
Strontium feldspar 0 mol % 10 mol % 0 mol % 3 mol % Celsian 0 mol %
10 mol % 0 mol % 3 mol % Optional balance 0 mol % 5 mol % 0 mol % 5
mol %
[0065] In another embodiment, the glass of the invention can be
characterized by the following proportions of constituent phases in
the base glass composition. The ranges of proportions indicated
above and below and further features in respect of the glass of the
invention also apply to the embodiment outlined below:
TABLE-US-00006 TABLE 6 Desired Particularly Desired Constituent
phase min. max. min. max. Albite 15 mol % 27 mol % 18 mol % 24 mol
% Reedmergnerite 40 mol % 65 mol % 50 mol % 62 mol % Potassium 0
mol % 15 mol % 0 mol % 5 mol % reedmergnerite Grossular 1 mol % 10
mol % 5 mol % 9 mol % Cordierite 0 mol % 10 mol % 0 mol % 3 mol %
Willemite 0 mol % 10 mol % >0 mol % 3 mol % Silicon dioxide 0
mol % 20 mol % 6 mol % 14 mol % Diboron trioxide 0 mol % 10 mol %
>0 mol % 5 mol % Titanium wadeite 0 mol % 10 mol % 0 mol % 3 mol
% Strontium feldspar 0 mol % 10 mol % 0 mol % 3 mol % Celsian 0 mol
% 10 mol % 0 mol % 3 mol % Optional balance 0 mol % 5 mol % 0 mol %
5 mol %
[0066] Other Glass Properties
[0067] The glass of the present invention can be present as glass
product, for example glass sheet or glass plate, having a thickness
of not more than 2 mm, for example not more than 1 mm, not more
than 500 .mu.m, not more than 250 .mu.m, not more than 150 .mu.m or
not more than 100 .mu.m. The glass of the present invention can be
processed to produce a thin glass or ultra-thin glass. Particularly
thin glasses are sometimes chemically toughenable only with
difficulty, so that the high hardness which the glasses of the
invention have even without toughening can be desired in the case
of thin glasses.
[0068] Owing to the combination of the phases constituting the
glass, the glasses of the present invention display a thermal
expansion (also: CTE) of not more than 8 ppm/K, for example not
more than 7.5 ppm/K, which is advantageous for many applications.
The abovementioned coefficient of expansion can be an, in
embodiment, at least 4 ppm/K or at least 5 ppm/K. The thermal
expansion can be calculated as described above in formula (3).
[0069] Owing to its substantial proportion of albite glass, the
glass may have a chemical toughenability characterized by a
threshold diffusivity of at least 15 .mu.m.sup.2/h or at least 20
.mu.m.sup.2/h at a temperature of 450.degree. C. in KNO.sub.3. The
threshold diffusivity is a measure of the rate at which potassium
ions are incorporated into the glass during chemical toughening.
The threshold diffusivity is calculated from the depth of the
compressive stress layer (DoL) and the time (t), as explained in DE
20 2012 012 876 U1.
Embodiment 1: 6.5 ppm/K<CTE<8 ppm/K
[0070] In one embodiment, the glass of the invention has a CTE in
the range from 6.5 ppm/K to 8 ppm/K. The conformity of a glass to
this embodiment is ensured by fulfillment of the above inequation
and application of the abovementioned formula (3). In this
embodiment, the glass is especially, but not exclusively, provided
for a combination with aluminium oxide ceramics. An example of such
a structure is described in U.S. Pat. No. 6,109,994. There, a glass
covering sheet closes off a field emission display structure to
which a column construction composed of aluminium oxide belongs.
The high CTE cannot be combined with a very low fragility, but the
number of degrees of angular freedom per atom calculated according
to the abovementioned formula (1) should be <0.30, for example
<0.29, <0.28, <0.27, <0.26, or <0.25. In particular,
the number of degrees of angular freedom per atom can be at least
0.1.
Embodiment 2: 4.5 ppm/K<CTE<6.5 ppm/K
[0071] In one embodiment, the glass of the invention has a CTE in
the range from 4.5 ppm/K to 6.5 ppm/K. The conformity of a glass to
this embodiment is ensured by the fulfillment of the above
inequation and application of the abovementioned formula (3). In
this embodiment, the glass is especially, but not exclusively,
provided for a combination with aluminium nitride, see, for
example, C. K. Lee, S. Cochran, A. Abrar, K. J. Kirk, F. Placido,
Thick aluminium nitride films deposited by room-temperature
sputtering for ultrasonic applications, Ultrasonics 42 (2004)
485-490. The number of degrees of angular freedom per atom
calculated according to the abovementioned formula (1) should be
<0.30, for example <0.29, <0.28, <0.27, <0.26,
<0.25, <0.24, <0.23, <0.22, <0.21, or <0.20. In
particular, the number of degrees of angular freedom per atom can
be at least 0.1.
Embodiment 3: 3.5 ppm/K<CTE<4.5 ppm/K
[0072] In one embodiment, the glass of the invention has a CTE in
the range from 3.5 ppm/K to 4.5 ppm/K. The conformity of a glass to
this embodiment is ensured by the fulfillment of the above
inequation and application of the abovementioned formula (3). In
this embodiment, the glass is especially, but not exclusively,
provided for a combination with silicon or silicon-based
components. Glasses having a thermal expansion in this range are
often bonded to silicon or silicon-based components, see, for
example, F. Saharil, R. V. Wright, P. Rantakari, P. B. Kirby, T.
Vaha-Heikkila, F. Niklaus, G. Stemme, J. Oberhammer,
"Low-temperature CMOS-compatible 3D-integration of
monocrystalline-silicon based PZT RF MEMS switch actuators on rf
substrates", 2010 IEEE 23rd International Conference on Micro
Electro Mechanical Systems (MEMS), 2010, pp. 47-50. The number of
degrees of angular freedom per atom calculated according to the
abovementioned formula (1) should be <0.30, for example
<0.29, <0.28, <0.27, <0.26, <0.25, <0.24,
<0.23, <0.22, <0.21, <0.20, <0.19, <0.18,
<0.17, <0.16, or <0.15. In particular, the number of
degrees of angular freedom per atom can be at least 0.1.
[0073] In the case of the glasses of the present invention, the
number of degrees of angular freedom per atom in the bulk glass is,
for example, less than 0.30, less than 0.29, less than 0.28, less
than 0.27, less than 0.26, less than 0.25, less than 0.24, than
0.23, than 0.22, than 0.21, than 0.20, less than 0.19, less than
0.18, less than 0.17, less than 0.16, or less than 0.15. If it is
ensured that the number of degrees of angular freedom per atom does
not exceed this value, the fragility remains in a desired range. In
particular, this value can be advantageous in order to make it
possible to produce ultra-thin glass articles, too. In particular,
the number of degrees of angular freedom per atom can be at least
0.1.
[0074] Production Process
[0075] The present invention also provides a process for producing
a glass according to the present invention, including the steps:
[0076] melting of the glass raw materials, [0077] moulding of a
glass article, in particular a glass sheet or a glass plate, from
the glass melt, [0078] cooling of the glass.
[0079] Cooling can be carried out by active cooling using a
coolant, e.g. a cooling fluid, or by allowing the glass to cool
passively.
[0080] In one embodiment, the moulding of the glass article takes
place in a down draw, overflow fusion or redrawing process. In
these sheet glass processes, glasses having the desired very small
thickness can be produced. Furthermore, these processes may have
the advantage that high cooling rates can be achieved.
[0081] The choice of raw materials is not restricted to particular
raw materials. In particular, it is not necessary to use the
abovementioned base glasses as raw materials for these glasses,
even though this would be possible in principle. Rather, the
critical factor is that the raw materials be used in the suitable
stoichiometric composition so that the base glasses are present
stoichiometrically in the glass.
[0082] Surface Properties
[0083] The glasses of the present invention may have a property
gradient between the bulk glass and the surface of a glass article
produced from the glass. A glass article made of the glass
described herein is likewise part of the present invention.
[0084] For the purposes of the invention, a "surface" can be a
proportion of the glass which is close to the glass/air interface.
The glass forming the surface will here be referred to as "surface
glass"; the remaining glass located further in the interior will
here be referred to as "bulk glass". A precise demarcation between
surface and bulk is difficult; therefore, it is specified for the
purposes of the present invention that the surface glass is present
in a depth of about 6 nm. The properties of the surface glass are
consequently determined at a depth of about 6 nm. The properties of
the bulk glass are determined by calculation since the glass
composition at a greater depth does not experience any change as a
result of production. Bulk glass is in any case present at a depth
of 500 nm. The surface can be advantageously influenced by
particular measures during glass production. The properties of the
surface glass are critical for particular properties of the glass
which are measured on the surface. These include, for example, the
base resistance and the hydrolytic resistance. The composition of
the surface glass at a depth of about 6 nm can be measured by
Cs-TOF-SIMS at 1000 eV.
[0085] It has been found that the loss of surface material
occurring during production of the glasses of the invention relates
mostly to sodium and boron. In the glass of the invention, sodium
can be assigned to the reedmergnerite and the albite. Boron in the
glass of the invention can be assigned either to reedmergnerite or
potassium reedmergnerite or is present as separate constituent
phase B.sub.2O.sub.3. It has also been found that, in contrast to
the loss of sodium, boron and other constituents, a relative
enrichment of the surface in silicon takes place. However, this is
desirable only within limits.
[0086] According to DE 10 2014 101 756 B4, the surface depletion of
sodium ions can be advantageous for the hydrolytic stability. At
the same time, this depletion also has an effect on the fragility
and the number of degrees of angular freedom and the coefficient of
thermal expansion. The latter becomes particularly clear when the
abovementioned formula (2) for the average potential well depth is
reformulated so that the relationship to the normalized proportions
d.sub.j/.SIGMA.d.sub.j of the individual cations is made clear:
E pot _ = i = 1 n c i j = 1 m z i , j E pot , j i = 1 n c i i = 1 m
z i , j = j = 1 m ( i = 1 n c i z i , j ) E pot , j i = 1 m ( i = 1
n c i z i , j ) .ident. j = 1 m d j E pot , j i = 1 m d j where d j
= ( i = 1 m c i z i , j ) , ( 4 ) ##EQU00006##
[0087] The calculation of the average potential well depth
obviously leads to a higher value in the surface region when the
proportion of cations having a low potential well depth as per
Table 3 decreases there. This means a lower coefficient of thermal
expansion at the surface and thus different coefficients of
expansion in the interior and at the surface.
[0088] Due to the hot forming to which the glass of the present
invention can be subjected, changes in the glass composition occur
at the surface. This change leads to a deviation of the thermal
expansion in the surface glass from that of the bulk glass. As a
result of the composition and in combination with aspects of the
production process, it is possible according to the invention for
the glass of the invention to have a thermal expansion (CTE)
calculated according to formula (4) from the composition measured
by Cs-TOF-SIMS at the surface, at a depth of about 6 nm, which is
at least 50%, at least 60%, at least 70% or at least 80%, of the
thermal expansion in the bulk glass. From the standpoint of the
hydrolytic stability, the thermal expansion calculated according to
formula (4) at the surface, at a depth of about 6 nm, can be not
more than 99%, for example not more than 98% or not more than 95%,
compared to that in the bulk glass. The values can, be measured
immediately after production of the glass.
[0089] The loss of particular glass components at the surface of
the glass and thus also the thermal expansion is dependent not only
on the glass composition but also on the production process. In
particular, the loss of free B.sub.2O.sub.3 can be set by setting
the partial pressure of water vapour during moulding of a glass
article. More diboron trioxide vaporizes in the form of metaboric
acid at a higher partial pressure of water vapour. Likewise, the
thermal expansion in the surface glass can also be influenced by
increasing the drawing speed and reducing the partial pressure of
water vapour. A person skilled in the art is therefore able to set
the desired properties.
[0090] The glass of the present invention can be present in the
form of a glass article, for example in the form of a sheet glass
or a glass plate, and have at least one fire-polished surface, for
example two fire-polished surfaces. A "fire-polished surface" is a
surface which has a particularly low roughness. The production
processes of the invention make it possible to produce glass
products which have particular surface qualities. The glass
products have at least one fire-polished surface, for example two
fire-polished surfaces, due to the production processes by which
they can be obtained. In contrast to mechanical polishing, a
surface is not ground in the case of fire polishing, but instead
the material to be polished is heated to such a temperature that it
flows and becomes smooth. The costs of producing a smooth surface
by fire polishing are therefore significantly lower than for
producing a mechanically polished surface. The roughness of a
fire-polished surface is lower than that of a mechanically polished
surface. In relation to a shaped glass article, "surfaces" mean the
upper side or underside, i.e. the two sides which are largest
compared to the remaining sides.
[0091] The fire-polished surface(s) of the glasses of the present
invention can have a quadratic roughness (Rq or also RMS) of not
more than 5 nm, for example not more than 3 nm or not more than 1
nm. The peak-to-valley height Rt of the glasses can be not more
than 6 nm, not more than 4 nm, and not more than 2 nm. The
peak-to-valley height is determined in accordance with DIN EN ISO
4287. The roughness Ra can be less than 1 nm according to the
invention.
[0092] In the case of mechanically polished surfaces, the roughness
values are poorer. In addition, polishing tracks can be discerned
under an atomic force microscope (AFM) in the case of mechanically
polished surfaces. Furthermore, residues of the mechanical
polishing agent, e.g. diamond powder, iron oxide and/or CeO.sub.2,
can likewise be discerned under the AFM. Since mechanically
polished surfaces always have to be cleaned after polishing,
particular ions are leached from the surface of the glass. This
depletion in particular ions can be confirmed by secondary ion mass
spectrometry (ToF-SIMS). Such ions are, for example, Ca, Zn, Ba and
alkali metals.
[0093] Use
[0094] The invention also provides for the use of a glass according
to the present invention as covering glass or display glass,
substrate glass, especially for metallic conduits, or as
electrically insulating dielectric intermediate layer, especially
as interposer, e.g. in an electronic or optoelectronic appliance,
or as polymer replacement in the finishing of surfaces.
EXAMPLES
[0095] A composition indicated in terms of base glasses can easily
be converted into a composition in mol % by a matrix. The
composition in terms of base glasses can be, as above, reported in
the following normalized form:
TABLE-US-00007 TABLE 7 Formula (normalized to Constituent phase a
simple oxide) Albite
(Na.sub.2O.cndot.Al.sub.2O.sub.3.cndot.6SiO.sub.2)/8 Reedmergnerite
(Na.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8 Potassium
reedmergnerite (K.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8
Grossular (3CaO.cndot.Al.sub.2O.sub.3.cndot.3SiO.sub.2)/7
Cordierite (2MgO.cndot.2Al.sub.2O.sub.3.cndot.5SiO.sub.2)/9
Willemite (2ZnO.cndot.SiO.sub.2)/3 Silicon dioxide SiO.sub.2
Diboron trioxide B.sub.2O.sub.3 Titanium wadeite
(K.sub.2O.cndot.TiO.sub.2.cndot.3SiO.sub.2)/5 Strontium feldspar
(SrO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 Celsian
(BaO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4
[0096] The conversion of these compositions into a composition in
mol % of the following simple oxides
TABLE-US-00008 TABLE 8 # Oxide 1. SiO.sub.2 2. TiO.sub.2 3.
B.sub.2O.sub.3 4. Al.sub.2O.sub.3 5. ZnO 6. MgO 7. CaO 8. SrO 9.
BaO 10. Na.sub.2O 11. K.sub.2O
can be carried out with the aid of the matrix indicated below.
Here, the composition in mol % of the base glasses is multiplied as
column vector from the right onto the matrix:
6 / 8 6 / 8 6 / 8 3 / 7 5 / 9 1 / 3 1 0 3 / 5 2 / 4 2 / 4 0 0 0 0 0
0 0 0 1 / 5 0 0 0 1 / 8 1 / 8 0 0 0 0 1 0 0 0 1 / 8 0 0 1 / 7 2 / 9
0 0 0 0 1 / 4 1 / 4 0 0 0 0 0 2 / 3 0 0 0 0 0 0 0 0 0 2 / 9 0 0 0 0
0 0 0 0 0 3 / 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 / 4 0 0 0 0 0 0 0
0 0 0 0 1 / 4 1 / 8 1 / 8 0 0 0 0 0 0 0 0 0 0 0 1 / 8 0 0 0 0 0 1 /
5 0 0 .times. ( Na 2 O Al 2 O 3 6 SiO 2 ) / 8 ( Na 2 O B 2 O 3 6
SiO 2 ) / 8 ( K 2 O B 2 O 3 6 SiO 2 ) / 8 ( 3 CaO Al 2 O 3 3 SiO 2
) / 7 ( 2 MgO 2 Al 2 O 3 5 SiO 2 ) / 9 ( 2 ZnO SiO 2 ) / 3 SiO 2 B
2 O 3 ( K 2 O TiO 2 3 SiO 2 ) / 5 ( SrO Al 2 O 3 2 SiO 2 ) / 4 (
BaO Al 2 O 3 2 SiO 2 ) / 4 ##EQU00007##
[0097] The result of the multiplication of the column vector onto
the matrix gives the composition of the glass in mol %.
[0098] Conversely, a composition in mol % can be converted simply
into a base glass composition via the respective inverse matrix.
Here, naturally only those base glass compositions which on
conversion do not give any negative values for the base glasses are
according to the invention.
[0099] Glasses According to the Present Invention
[0100] As a first example, a glass having the following composition
will be examined:
Example 1
TABLE-US-00009 [0101] TABLE 9 Formula (normalized Proportion/
Constituent phase to a simple oxide) mol % Albite
(Na.sub.2O.cndot.Al.sub.2O.sub.3.cndot.6SiO.sub.2)/8 21.5719
Reedmergnerite (Na.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8
32.9332 Potassium reedmergnerite
(K.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8 11.9446
Grossular (3CaO.cndot.Al.sub.2O.sub.3.cndot.3SiO.sub.2)/7 0
Cordierite (2MgO.cndot.2Al.sub.2O.sub.3.cndot.5SiO.sub.2)/9 0
Willemite (2ZnO.cndot.SiO.sub.2)/3 6.52253 Silicon dioxide
SiO.sub.2 8.28669 Diboron trioxide B.sub.2O.sub.3 2.28438 Titanium
wadeite (K.sub.2O.cndot.TiO.sub.2.cndot.3SiO.sub.2)/5 16.4505
Strontium feldspar (SrO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0
Celsian (BaO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0
[0102] This glass has the following properties: [0103] 1. The
number of degrees of angular freedom per atom calculated according
to (1) is thus 0.291. [0104] 2. The average potential well depth
calculated according to (2) is 1499 kJ/mol, which in turn leads
according to (3) to a thermal expansion of 7.4 ppm/K.
[0105] Replacing 8 percent of potassium reedmergnerite by albite
gives a second illustrative glass. This may increase the chemical
toughenability.
Example 2
TABLE-US-00010 [0106] TABLE 10 Formula (normalized to a Proportion/
Constituent phase simple oxide) mol % Albite
(Na.sub.2O.cndot.Al.sub.2O.sub.3.cndot.6SiO.sub.2)/8 29.5719
Reedmergnerite (Na.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8
32.9332 Potassium reedmergnerite
(K.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8 3.9446 Grossular
(3CaO.cndot.Al.sub.2O.sub.3.cndot.3SiO.sub.2)/7 0 Cordierite
(2MgO.cndot.2Al.sub.2O.sub.3.cndot.5SiO.sub.2)/9 0 Willemite
(2ZnO.cndot.SiO.sub.2)/3 6.52253 Silicon dioxide SiO.sub.2 8.28669
Diboron trioxide B.sub.2O.sub.3 2.28438 Titanium wadeite
(K.sub.2O.cndot.TiO.sub.2.cndot.3SiO.sub.2)/5 16.4505 Strontium
feldspar (SrO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0 Celsian
(BaO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0
[0107] This glass has the following properties: [0108] 1. The
number of degrees of angular freedom per atom calculated according
to (1) is thus 0.298. [0109] 2. The average potential well depth
calculated according to (2) has, as in Example 1, a value of 1499
kJ/mol, which in turn leads according to (3) to a thermal expansion
of 7.4 ppm/K.
[0110] Example 1 and Example 2 have been produced as experimental
melts. It was to be determined how the glass can be chemically
toughened. The samples were toughened once at 440.degree. C. and
once at 450.degree. C. for 9 hours in KNO.sub.3.
[0111] Glass plates (30 mm.times.30 mm.times.1 mm) were produced
from the experimental melts. To homogenize the surfaces, the
samples were precleaned for 3 minutes in 1% 12PA (mild alkaline
cleaner) in an ultrasonic bath at 37 kHz. The samples were treated
at 440.degree. C. and 450.degree. C. for 9 hours in KNO.sub.3.
After ion exchange, the samples have to be freed of the potassium
nitrate salt. For this purpose, the samples were cleaned for 5
minutes in 1% 12PA at 130 kHz and subsequently rinsed with DI
water.
[0112] The compressive stress (CS) and the depth of the compressive
stress layer (DoL) were measured on the plates. The measurement of
the compressive strength and the depth of layer were carried out on
a surface stress meter.
[0113] On each sample, CS and DoL were measured three times at the
middle on each side. The tables show mean and standard deviation
for the experimental melts measured.
440.degree. C., 9 h:
TABLE-US-00011 [0114] Mean Standard deviation CS DoL CS DoL [MPa]
[.mu.m] [MPa] [.mu.m] Example 1 Sample 1 496.5 24.8 6.8 0.5 Sample
2 492.7 25.3 6.5 1.0 Example 2 Sample 1 556.7 25.8 7.9 0.6 Sample 2
558.7 26.0 5.9 0.2
450.degree. C., 9 h:
TABLE-US-00012 [0115] Mean Standard deviation CS DoL CS DoL [MPa]
[.mu.m] [MPa] [.mu.m] Example 1 Sample 1 476.3 28.4 4.2 1.4 Sample
2 476.5 29.4 3.2 0.3 Example 2 Sample 1 535.2 28.9 3.7 0.5 Sample 2
536.6 29.3 2.7 0.8
[0116] The examples were configured as cast blocks. In the case of
production by drawing, the partial pressure of water vapour is set
so that the total boron content at the surface is not less than 80%
of the boron content in the interior of the glass.
Example 3
TABLE-US-00013 [0117] TABLE 11 Formula (normalized to a Proportion/
Constituent phase simple oxide) mol % Albite
(Na.sub.2O.cndot.Al.sub.2O.sub.3.cndot.6SiO.sub.2)/8 30
Reedmergnerite (Na.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8
30 Potassium reedmergnerite
(K.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8 20 Grossular
(3CaO.cndot.Al.sub.2O.sub.3.cndot.3SiO.sub.2)/7 0 Cordierite
(2MgO.cndot.2Al.sub.2O.sub.3.cndot.5SiO.sub.2)/9 0 Willemite
(2ZnO.cndot.SiO.sub.2)/3 0 Silicon dioxide SiO.sub.2 5 Diboron
trioxide B.sub.2O.sub.3 10 Titanium wadeite
(K.sub.2O.cndot.TiO.sub.2.cndot.3SiO.sub.2)/5 5 Strontium feldspar
(SrO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0 Celsian
(BaO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0
[0118] This glass has the following properties: [0119] 1. The
number of degrees of angular freedom per atom calculated according
to (1) is thus 0.25. [0120] 2. The thermal expansion calculated
according to (2) and (3) is 6.62 ppm/K.
Example 4
TABLE-US-00014 [0121] TABLE 12 Formula (normalized to a Proportion/
Constituent phase simple oxide) mol % Albite
(Na.sub.2O.cndot.Al.sub.2O.sub.3.cndot.6SiO.sub.2)/8 30
Reedmergnerite (Na.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8
10 Potassium reedmergnerite
(K.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8 5 Grossular
(3CaO.cndot.Al.sub.2O.sub.3.cndot.3SiO.sub.2)/7 0 Cordierite
(2MgO.cndot.2Al.sub.2O.sub.3.cndot.5SiO.sub.2)/9 0 Willemite
(2ZnO.cndot.SiO.sub.2)/3 0 Silicon dioxide SiO.sub.2 35 Diboron
trioxide B.sub.2O.sub.3 10 Titanium wadeite
(K.sub.2O.cndot.TiO.sub.2.cndot.3SiO.sub.2)/5 10 Strontium feldspar
(SrO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0 Celsian
(BaO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0
[0122] This glass has the following properties: [0123] 1. The
number of degrees of angular freedom per atom calculated according
to (1) is thus 0.196. [0124] 2. The thermal expansion calculated
according to (2) and (3) is 4.96 ppm/K.
Example 5
TABLE-US-00015 [0125] TABLE 13 Formula (normalized to a Proportion/
Constituent phase simple oxide) mol % Albite
(Na.sub.2O.cndot.Al.sub.2O.sub.3.cndot.6SiO.sub.2)/8 35
Reedmergnerite (Na.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8
10 Potassium reedmergnerite
(K.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8 10 Grossular
(3CaO.cndot.Al.sub.2O.sub.3.cndot.3SiO.sub.2)/7 0 Cordierite
(2MgO.cndot.2Al.sub.2O.sub.3.cndot.5SiO.sub.2)/9 5 Willemite
(2ZnO.cndot.SiO.sub.2)/3 0 Silicon dioxide SiO.sub.2 35 Diboron
trioxide B.sub.2O.sub.3 5 Titanium wadeite
(K.sub.2O.cndot.TiO.sub.2.cndot.3SiO.sub.2)/5 0 Strontium feldspar
(SrO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0 Celsian
(BaO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0
[0126] This glass has the following properties: [0127] 1. The
number of degrees of angular freedom per atom calculated according
to (1) is thus 0.193. [0128] 2. The thermal expansion calculated
according to (2) and (3) is 4.67 ppm/K.
Example 6
TABLE-US-00016 [0129] TABLE 14 Formula (normalized to a Proportion/
Constituent phase simple oxide) mol % Albite
(Na.sub.2O.cndot.Al.sub.2O.sub.3.cndot.6SiO.sub.2)/8 30
Reedmergnerite (Na.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8
30 Potassium reedmergnerite
(K.sub.2O.cndot.B.sub.2O.sub.3.cndot.6SiO.sub.2)/8 5 Grossular
(3CaO.cndot.Al.sub.2O.sub.3.cndot.3SiO.sub.2)/7 0 Cordierite
(2MgO.cndot.2Al.sub.2O.sub.3.cndot.5SiO.sub.2)/9 0 Willemite
(2ZnO.cndot.SiO.sub.2)/3 10 Silicon dioxide SiO.sub.2 10 Diboron
trioxide B.sub.2O.sub.3 10 Titanium wadeite
(K.sub.2O.cndot.TiO.sub.2.cndot.3SiO.sub.2)/5 5 Strontium feldspar
(SrO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0 Celsian
(BaO.cndot.Al.sub.2O.sub.3.cndot.2SiO.sub.2)/4 0
[0130] This glass has the following properties: [0131] 1. The
number of degrees of angular freedom per atom calculated according
to (1) is thus 0.274. [0132] 2. The thermal expansion calculated
according to (2) and (3) is 7.01 ppm/K.
[0133] While this invention has been described with respect to at
least one embodiment, the present invention can be further modified
within the spirit and scope of this disclosure. This application is
therefore intended to cover any variations, uses, or adaptations of
the invention using its general principles. Further, this
application is intended to cover such departures from the present
disclosure as come within known or customary practice in the art to
which this invention pertains and which fall within the limits of
the appended claims.
* * * * *