U.S. patent application number 10/845944 was filed with the patent office on 2004-10-21 for method and apparatus for oxygen refinement of a glass melt.
Invention is credited to Duch, Klaus-Dieter, Pfeiffer, Thomas, Roth, Gernot.
Application Number | 20040206126 10/845944 |
Document ID | / |
Family ID | 7632758 |
Filed Date | 2004-10-21 |
United States Patent
Application |
20040206126 |
Kind Code |
A1 |
Roth, Gernot ; et
al. |
October 21, 2004 |
Method and apparatus for oxygen refinement of a glass melt
Abstract
An apparatus for making glass in which a glass melt is refined
in a vessel with oxygen is described. It includes a melt-containing
vessel (10) having a refining region (3) for refinement of the
glass melt and a noble metal member for producing oxygen in the
melt. The noble metal member (40) has an outer side facing the
glass melt and an inner side facing away from the glass melt washed
with and acted on with oxygen. Oxygen-containing bubbles are
vigorously generated on the outer side of the noble metal member
facing the glass melt when the inner side is washed with the
oxygen.
Inventors: |
Roth, Gernot; (Dalheim,
DE) ; Pfeiffer, Thomas; (Ingelheim, DE) ;
Duch, Klaus-Dieter; (Bingen, DE) |
Correspondence
Address: |
STRIKER, STRIKER & STENBY
103 East Neck Road
Huntington
NY
11743
US
|
Family ID: |
7632758 |
Appl. No.: |
10/845944 |
Filed: |
May 14, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10845944 |
May 14, 2004 |
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09793041 |
Feb 26, 2001 |
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6769272 |
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Current U.S.
Class: |
65/346 ;
65/374.12 |
Current CPC
Class: |
C03B 5/187 20130101;
C03B 5/225 20130101; C03B 5/193 20130101; C03C 1/004 20130101 |
Class at
Publication: |
065/346 ;
065/374.12 |
International
Class: |
C03B 005/43 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2000 |
DE |
100 09 425.2 |
Claims
What is claimed is new and is set forth in the following appended
claims:
1-10. (canceled)
11. An apparatus for refining a glass melt, said apparatus
comprising a glass melt-containing vessel (10) including a refining
region (30) in which said glass melt is refined and a noble metal
member (40) arranged in the refining region (30) and wherein said
noble metal member has one side facing said glass melt and another
side acted on with oxygen facing away from the glass melt.
12. The apparatus as defined in claim 11, wherein at least a
portion of said one side of said noble metal member facing said
glass melt contacts said glass melt and said another side facing
away from the glass melt does not contact said glass melt.
13. The apparatus as defined in claim 11, wherein said vessel (10)
has a vessel bottom part and said noble metal member consists of
said vessel bottom part.
14. The apparatus as defined in claim 11, wherein said noble metal
member is a mechanical stirring device.
15. A glass for at least one of liquid crystal display devices,
thin film transistors, monitors, television picture tubes, optical
lenses, cooking units, microwave units, electrical devices, cooking
ranges, window glass, lamp glass and display glass, wherein said
glass is made by a method including refining a glass melt, said
refining comprising the steps of: a) arranging at least one noble
metal member in the glass melt, said at least one noble metal
member having an inner surface facing away from the glass melt and
an outer surface facing toward the glass melt; and b) bringing
oxygen or an oxygen-containing gas mixture into contact with the
inner surface of the at least one noble metal member facing away
from the glass melt so as to act on the inner surface with said
oxygen or said oxygen-containing gas.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to methods and processes for
oxygen refinement of water and/or liquids containing hydroxyl
groups, especially glass melts, to an apparatus for performing
these methods and to glass obtained using these methods as part of
the glass production process.
[0003] Liquids, in which gases are dissolved, which in part form
bubbles in the liquid, participate in many technical production
processes. Since these gases or gas bubbles interfere with further
processing and/or disadvantageously impair the properties and thus
the quality of the product, it is necessary to free the liquid of
these bubbles. This process is called bubble removal or
refinement.
[0004] In the following the problems of refinement of liquids are
described using the example of refinement of a glass melt, but the
invention should not be considered as limited to this example. The
same problem is present in other applications.
[0005] 2. Prior Art
[0006] During manufacture of glass from inorganic material raw
materials and of course silica or glass sand, soda, limestone,
marble or calcereous clay, are mixed and melted in a continuously
running process. The melting process takes place in different
stages, in which chemical reactions and physical processes occur
side-by-side. At higher temperatures solid state reactions occur at
the points of contact between neighboring grains. Moreover CO.sub.2
and H.sub.2O are released from the crystalline phase. The CO.sub.2
is generated by decomposition of the glass-forming salts. In so far
as sulfates are present also SO.sub.2 is released.
[0007] As a result of the decomposition of the starting materials
present in the reaction mixture a considerable quantity of gas is
generated during melting of glass. As a rough estimate, it is said
that about 1 kg of glass results from melting 1.2 kg of the
mixture, i.e. about 1/5 of the mixture weight is released in the
form of gas during the melting. Furthermore also other gases are
conducted through the mixture during the melting or introduced into
the melting glass by the combustion oven.
[0008] The release of the gases, especially of CO.sub.2, causes
good pre-mixing of the glass melt. The gas generation and thus the
pre-mixing are concluded at temperatures of about 800.degree. C. to
1100.degree. C.
[0009] The largest amount of gas escapes of course during the
initial melting of the glass, but a considerable portion of the gas
is captured by the melt. A portion of the captured gases is
dissolved in the glass melt, but another portion remains as local
gas inclusions, as so-called bubbles, in the glass melt. The
bubbles shrink or grow when the bubble internal pressure is lower
or higher than the equilibrium pressure of the dissolved gas. The
gas bubbles have different sizes.
[0010] The resulting melt is thus designated a raw melt. However it
has very distinct streaking or regions of varying index of
refraction and many bubbles, which impair the quality of a glass
and/or glass-ceramic body that is made from the glass melt. Because
of this reason the still strongly streaked and bubble containing
glass melt is heated further and homogenized by means of mechanical
stirring elements, by chopping with fine needles or by blowing
oxygen into it through fine nozzles. These methods refine the glass
melt of the gas bubbles.
[0011] The term "refinement" or "refining" of the glass means a
melting process comprising sequential melting process steps
performed in so-called refining chambers, which
[0012] removes gas bubbles of a predetermined size class; and
[0013] guarantees a certain adjustment of the gas content of the
glass melt and at the same time
[0014] is to be integrated in a complex sequence of melt processing
steps.
[0015] The refinement of the glass is thus of the greatest
significance for the quality of the end product of the melting
process.
[0016] Different methods have been formulated for the
refinement.
[0017] The gas bubbles have the tendency to rise in the melt due to
their buoyancy and to escape into the atmosphere from the vessel
containing the melt. Since this process however takes a
considerable time without other influences, it would make a
production process using it expensive because of its long dwell
time for the refinement. It is thus known however to produce higher
temperatures in the refining zone so that the viscosity of the melt
and thus the bubble rising speed is increased and so that the
bubble diameter also increases. These additional temperature
increases however require considerable energy, which similarly
greatly increases the process costs.
[0018] The chemical refinement of glass has been well tested and
further optimized. Chemical refining agents and of course oxides
are added to the melt in temperature-dependent oxidation stages.
Common refining agents include Sb(V) oxide, As(V) oxide and
Sn(IV)-oxide. An increased mixing of the melt and thus an improved
homogenization is obtained by oxygen released in situ by the
refining agents or by additional mechanical gas introduction.
Moreover the additional release of oxygen causes growth of small
gas bubbles present already in the glass melt.
[0019] Small bubbles are pumped up with the refining gas O.sub.2
arising from the refining agent during chemical refinement. The
resulting larger bubbles formed more rapidly rise in the glass
melt. The refinement thus leads to removal of the glass inclusions,
which leads to a higher quality product.
[0020] The chemical refinement also comprises a sequence of
elementary steps interlaced with each other spatially and
temporally. First the finely dispersed bubbles in the raw melt are
greatly inflated by the refining oxygen gas so that a drastic
shortening of the bubble rise time occurs. At the same time the
refining bubbles extract gas dissolved in the glass. As much as
possible, resorption of the unavoidably present residual bubbles
occurs in the subsequent cooling steps. Color, moisture content and
the so-called reboil conditions for O.sub.2 and SO.sub.2 are the
targeted parameters for a successful adjustment of the gas content
of the glass. Once a satisfactory bubble quality is obtained it is
not impaired in subsequent cool-down or casting processes.
[0021] Chemical refinement has several principal disadvantages.
First the methods. First these methods do not function well for
every glass system, especially during NaCl refinement, or only at
higher temperature, which also requires much time, since gas
diffusion in the melt takes too long. Thus the refining chambers
must be comparatively large, which further increases product costs.
Finally the chemical refining agents change the chemistry of the
glass and thus its properties. Moreover arsenic oxide is extremely
poisonous and the required purity is not reached without more work.
Major environmental problems are also connected both with its
manufacture and its use. They also occur for antimony oxide. Cerium
oxide itself is of course not poisonous, but it is extremely
expensive so that its use is limited to specialty glass.
[0022] So-called physical refining methods, which do not impair or
damage the chemistry of the glass, are also known because of these
disadvantages for chemical methods. The physical refinement of a
glass melt is based on the "forcing" of the bubbles to the surface
of the melt, where they are destroyed and their gas content
released or on their dissolution in the melt.
[0023] DE-A 3 022 091 described an apparatus for melting glass in a
melt oven with a refining device for refinement of the glass and at
least one receiver in which a direct current is applied to a heated
electrode formerly or usually operated with alternating
current.
[0024] A method and apparatus for melting of those glasses which
have a high reducing action in a melted state are described in DE-A
3 906 270. Especially in phosphate glass, whose reducing action is
even more pronounced in the melted state, erosion by immersion of
platinum parts should be avoided. The reducing action of phosphate
glass is so great that the glass reacts with platinum or a platinum
alloy of the melt-containing vessel to form a platinum-phosphorous
alloy. This platinum-phosphorous alloy however has a melting point
of 588.degree. C., which is below the glass melt temperature. This
alloy is dissolved in the melt, which leads to the dissolving of
the platinum glass melt-containing vessel. This is also the
situation for platinum stirring tools or elements. According to
this publication this is avoided by supplying the environment of
the glass melt container, i.e. its outer surface, with oxygen. The
interior surface, which is in contact with the glass melt, is
protected by an oxygen rich glass layer formed by the oxygen. Thus
the use of platinum containers is possible, which avoids the use of
ceramic melt-containing vessels, which impair the optical quality
of the glass. In this process however conditions must be selected
in which the oxygen permeability of the platinum container is
guarantied, which is achieved by raising the temperature.
[0025] U.S. Pat. No. 5,785,726 describes a method of making glasses
for flat display screens, especially LCDs (Liquid Crystal Displays)
and TFTs (Thin Film Transistors). In this method the production of
oxygen bubbles arising in the cool-down region, the so-called
"O.sub.2-reboil", is avoided by rinsing the platinum parts of the
cool-down region at least partially with hydrogen. The oxygen
present in the glass melt is reduced to water by the
hydrogen-permeable platinum vessel in this way, whereby oxygen gas
bubbles are dissolved.
SUMMARY OF THE INVENTION
[0026] It is an object of the present invention to provide an
improved method for refining and homogenizing a glass melt in which
the use of arsenic oxide, antimony oxide and cerium oxide can be
avoided.
[0027] It is also an object of the present invention to provide an
apparatus for performing the improved method.
[0028] These objects are attained by the method and apparatus
described in the appended claims.
[0029] Surprisingly it has been found that, although noble metals
are not oxygen permeable, conducting oxygen through a device having
a noble metal sleeve or casing, such as a noble metal pipe, which
is immersed or dipped in a liquid containing water and/or hydroxyl
groups, for example a glass melt, vigorously generates oxygen
bubbles in the liquid. This gas generation is so great, that the
liquid, which is the glass melt, is very thoroughly mixed by the
vigorous bubble generation. Because of this gas generation the
schlieren present is dissipated and the small bubbles present are
inflated, so that they rise faster. The conduction of oxygen
through a platinum pipe immersed or dipped in a glass melt thus
leads to very great oxygen bubble development in the melt and thus
to a removal of gas inclusions in the melt.
[0030] It is possible in this way to avoid the use of very
expensive and/or poisonous chemical refining agents. Glass of
higher purity may thus be prepared according to the methods of the
invention, which is free of gas inclusion and free of additional
impurities introduced by the refinement.
[0031] The method according to the invention is also suitable for
removal of water residues and/or hydroxyl residues.
[0032] Furthermore this method is very well controlled by adjusting
the oxygen content and/or partial pressure of oxygen in the gas
flow. The method is appropriately not limited to a definite
temperature as is required in many chemical and other physical
refining processes.
[0033] The noble metals which are suitable for use in this method
are principally all those noble metals, which are particularly
hydrogen permeable at the conditions occurring in the glass melt,
i.e. those which have a high hydrogen diffusion coefficient.
Platinum and all metals belonging to the platinum group metals,
gold, rhenium or alloys thereof, are suitable. According to the
invention other materials may be used for the noble metal member,
which are stable at the process temperatures and which have a
bridge or portion of the foregoing of noble metals. The bridge or
portion of the noble metals must extend between the outside surface
or outer side facing the glass melt and the inner or interior side
of the noble metal member. This type of bridge can be a network or
a number of fibers. A platinum vessel and/or platinum dish can be
used as the noble metal member. It is most important that the
oxygen acts only on those regions of the melt-containing vessel in
which the refining occurs. In a preferred embodiment of the method
of the invention, a noble metal pipe is arranged, especially in the
region in which the refining step occurs. Preferably the pipe runs
to the vessel bottom. This sort of pipe appropriately has a
meandering shape, which preferably passes through the entire
refining region. It some cases it has proven to be sufficient when
the oxygen-rinsed noble metal pipe is installed at a single place
in the refining region. In its simplest form the oxygen-rinsed
noble metal pipe is a U-shaped pipe, which is arranged in the melt
so that it is either dipped in the melt from above or is guided
through the melt from below. In both cases the horizontal portion
of the U-shaped pipe extends along the vessel bottom or is spaced a
short distance from it.
[0034] In an additional preferred embodiment the noble metal member
includes a stirrer rinsable with oxygen gas. In this way the
advantageous features may be combined with each other, which
produce mechanical stirring of the melt and thorough mixing. This
leads to a particularly efficient homogenizing and refining.
[0035] Air and oxygen-containing waste air from process gas, such
as exhaust gas from combustion, especially from gas and oil
burners. However it is also possible to use pure oxygen in the
method according to the invention.
[0036] In another preferred embodiment of the process the oxygen
input is controlled by means of a control element. This preferably
happens so that the oxygen partial pressure of the melt is
determined by means of a probe, such as the probe described by
Frey, Schaeffer and Baucke in Glasstechn. Ber. [Glass Engineering
Report] 53, pp. 116-123 (1980). The oxygen input to the noble metal
member can be exactly controlled by means of a control device
responding to the measured values from the probe. Since other
gases, such as CO.sub.2 or also SO.sub.2, are also removed by the
oxygen refining, the oxygen input can also be controlled by a
suitable SO.sub.2- or CO.sub.2-probe.
[0037] In an additional embodiment according to the invention the
oxygen introduced into the glass melt by the refining process
according to the invention is removed in a process step occurring
after the refining. This can occurs for example by working at low
pressure besides the known physical methods. The dissolved oxygen
and/or the minute, frequently invisible gas bubbles still present
expand under a low pressure, so that they rapidly rise to the
surface of the melt. In another possible embodiment the melt is
acted on by pressure in this process step so that a so-called
"forcing off" of the bubble formation occurs.
[0038] It is especially preferred however in a particularly
advantageous embodiment of the method to arrange an additional
hydrogen permeable noble metal member in the melt and to act on it
with hydrogen, hydrogen-containing gas or gases and/or vapors,
which split off hydrogen at higher temperatures, such as water
and/or ammonia. In this way oxygen still present in the melt is
reduced to water and/or to hydroxyl groups, which are dissolved in
the glass melt and in the finished glass. These latter products
have no noteworthy influence on the glass quality of the finished
glass. Preferably a control device or member controls the hydrogen
feed in this step. The control device or member itself receives its
control signals from an oxygen probe dipped in this region of the
glass melt.
[0039] The oxygen is preferably removed in the cool-down region.
This means that the appropriate additional noble metal member is
arranged in this region. The additional noble metal member can be
formed, as a whole, like the noble metal member described above for
generating oxygen in the melt. The so-called feeder trough is an
additional preferred location for removal of oxygen from the glass
melt.
[0040] The invention also includes an apparatus for performing the
foregoing method. The apparatus according to the invention includes
a region, in which the liquid, especially the glass melt, is in
contact with a noble metal member. The noble metal member has one
side facing the liquid and/or glass melt and another side acted on
with the oxygen that is facing away from the liquid and/or glass
melt. In a special embodiment of the apparatus this noble metal
member is the vessel base or bottom, in which the glass melt is
refined. In another preferred embodiment of the apparatus of the
invention the noble metal member is a mechanical stirrer, whose
interior side can be rinsed with the oxygen gas.
[0041] The glasses obtained by the method according to the
invention are especially suitable for making electronic tubes, such
as display screens, especially televisions and computer monitors,
as well as flat screen devices, such as LCDs and TFTs. Also the
glasses obtained by the method according to the invention are
especially suitable for optical lenses and units and devices
containing them. Lamp glass and glass for light sources are also
suitable applications. The glasses obtained by the method according
to the invention are also suitable for making cooking panels for
hearth, such as Ceran.RTM. panel, and for cooking-ware
(Jenaerglass.RTM.) and for microwave cooking units.
BRIEF DESCRIPTION OF THE DRAWING
[0042] The objects, features and advantages of the invention will
now be illustrated in more detail with the aid of the following
description of the preferred embodiments, with reference to the
accompanying figures in which the sole FIGURE is a flow chart for
the method of refining a glass melt according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] The sole FIGURE shows a glass melt vessel 10, in which the
minerals used to make glass, such as quartz, soda, lime, marble,
etc, are supplied in a finely divided or ground heap. Following
that these solids are melted in a melting region 20 and then flow
further into the refining region 30 of the vessel 10. A noble metal
pipe 40, which includes an oxygen inlet section 42 and an oxygen
outlet section 44, is arranged in the refining region 30 at the
bottom of the vessel 10. The oxygen inlet section 42 is controlled
by means of a first control device 50, which receives control
signals from a first oxygen probe 60 immersed or dipped in the
refining region 30. The melt region 20 and the refining region 30
of the glass melt vessel 10 are separated from a cool-down region
70 by means of a separating wall 80, which does not reach to the
surface of the glass melt. In the cool-down region 70 another noble
metal pipe 90, which is formed in a similar manner to the oxygen
supplying noble metal pipe 40, is arranged. This other noble metal
pipe 90 is washed or rinsed with hydrogen, water vapor or mixtures
of them with other gases. The hydrogen supply in the pipe 90 is
controlled by means of a second control device 100, which receives
its control signals from a second oxygen probe 110, which is
arranged in the cool-down region 70 or after it.
[0044] The disclosure in German Patent Application 100 09 425.2 of
Feb. 28, 2000 is incorporated here by reference. This German Patent
Application describes the invention described hereinabove and
claimed in the claims appended hereinbelow and provides the basis
for a claim of priority for the instant invention under 35 U.S.C.
119.
[0045] While the invention has been illustrated and described as
embodied in a method and apparatus for oxygen refining of a glass
melt and glasses manufactured by a process using this method and/or
apparatus, it is not intended to be limited to the details shown,
since various modifications and changes may be made without
departing in any way from the spirit of the present invention.
[0046] Without further analysis, the foregoing will so fully reveal
the gist of the present invention that others can, by applying
current knowledge, readily adapt it for various applications
without omitting features that, from the standpoint of prior art,
fairly constitute essential characteristics of the generic or
specific aspects of this invention.
* * * * *