Glass with high proportion of zirconium-oxide and its uses

Details Glass with high proportion of zirconium-oxide and its uses Glass with high proportion of zirconium-oxide and its uses

2001-07-05

2003-09-30

Sample, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S071000, C501S038000

Reexamination Certificate

active

06627569

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a glass having a high zirconium oxide content, and to uses thereof.
2. Description of the Related Art
Glasses having a high zirconium oxide content have mainly been described in connection with alkali-resistant glass fibers for concrete reinforcement. Compared with E-glass, a substantially alkali-free aluminoborosilicate glass, fibers made from known ZrO
2
-containing glasses do have higher alkali resistance, but, in particular, their resistance in cement over a long period is inadequate. The alkali resistance of concrete-reinforcing fibers is of importance and is therefore usually to the fore during glass development, since the cement sets under highly alkaline conditions (pH values up to about 12.5). Besides the alkali resistance, however, the other chemical resistance, in particular the hydrolytic resistance, is clearly also of importance for long-term use as a reinforcing agent in concrete since it improves the long-term resistance.
Glasses which exhibit high resistance both to water, acids and caustic lyes are interesting for a wide variety of applications, for example for pharmaceutical packaging or for inspection windows in process tanks, in particular if they additionally have high heat resistance.
A feature for high heat resistance is a high glass transition temperature T
g
. In glasses having a high T
g
, experience has shown that the so-called compaction (shrinkage) is low. This is shrinkage of glass parts during temperature treatment below the T
g
, a property which can only be determined with sufficient accuracy with great experimental complexity and is of importance, for example, for applications in which very strict standards are set for the shape fidelity of the glass parts, for example for applications in display technology.
For optical applications, glasses having high negative anomalous partial dispersion in the blue spectral region (&Dgr;P
g,F
) are extremely interesting for correction of image aberrations. A disadvantage of the glasses in this series that have been disclosed hitherto is that they either have large amounts of PbO, which is undesired from environmental points of view, and have poor chemical resistance or that large amounts of the very expensive raw materials Nb
2
O
5
and in particular Ta
2
O
5
have to be used for lead-free substitution products, which makes economical manufacture much more difficult. Lead-free glasses of this type are disclosed in DE-A 27 29 706.
SUMMARY OF THE INVENTION
A wide variety of specifications in the patent literature which describe alkali-resistant glasses having high ZrO
2
contents are also already known, but these still have disadvantages.
British Patent Specification GB 1,290,528 describes glass compositions for the production of glass fibers which comprise from 13 to 23 mol % of R
2
O (0-2% of Li
2
O, remainder Na
2
O). Glasses having such a high alkali metal content, as also occur in European Patent Specification EP 0 446 064 B1, which describes glass fiber materials for components of exhaust systems for internal-combustion engines (13-18% by weight of Na
2
O+K
2
O), exhibit poor hydrolytic resistance.
The same applies to the glass fibers in accordance with DE 17 96 339 C3 based on a glass comprising 11% by weight of Na
2
O and 1% by weight of Li
2
O and to the glasses converted into fibers in DE 40 32 460 A1, comprising 10-15% by weight of Na
2
O and 0.1-2% by weight of K
2
O.
The glass compositions from German Laid-Open Specification DE-A 2 406 888, which likewise have a high alkali metal content (10-25% by weight of R
2
O), comprise up to 20% by weight of oxides of the rare earth metals, for example cerium oxide or also naturally occurring mixtures of these oxides.
Rare-earth metal oxides, to be precise together with TiO
2
in an amount of 0.5-16% by weight, where the TiO
2
content is at most 10% by weight of the glass, are also present in the glasses from German Laid-Open Specification DE 31 07 600 A1. They furthermore comprise 0.1-1% by weight of Cr
2
O
3
. An essential aspect here is that the chromium is substantially in the trivalent state.
German Laid-Open Specification DE-A 26 14 395 describes Al
2
O
3
-free glasses, which have to comprise 0.5-10% by weight of Cr
2
O
3
+SnO
2
for their alkali resistance, components which have the following disadvantages: Cr
2
O
3
only dissolves in the glass flux with difficulty, and problems can also occur on use of chromium salts due to “chromium knots”. SnO
2
is a good nucleating agent and therefore promotes crystallization. The glasses furthermore require 0.05-1% by weight of SO
3
as melt assistant, which can result in interfering foam and blow-hole formation.
DE-A 30 09 953 describes glass fibers which, besides ZrO
2
, must contain ThO
2
. This component is necessary in order to achieve alkali resistance. Owing to its radio-activity, however, it is desirable to be able to omit this component.
EP 0 500 325 A1 discloses glass fibers containing 5-18 mol % of TiO
2
. Their resultant chemical resistance is achieved at the expense of very high susceptibility to crystallization, which is particularly disadvantageous with respect to the spinnability of the glass melt to give fibers.
The Patent Specification DD 293 105 A5 describes a process for the production of highly alkali-resistant glass fibers and products produced therefrom, in which the glass melt to be spun, besides SiO
2
, R
2
O
3
, ZrO
2
, RO and R
2
O (K
2
O, Na
2
O and/or Li
2
O), also contains fluoride. This fluxing agent can only be omitted if Li
2
O is present.
JP 62/13293 B2 describes glass compositions containing at least 5% by weight of B
2
O
3
for the core glass and cladding of glass fibers. ZrO
2
is merely an optional component. Although these glasses have high water resistance, this cannot, however, be guaranteed over the entire composition range owing to the high B
2
O
3
contents at the same time as relatively high alkali metal contents, since water-soluble alkali metal borate phases can easily form.
DE-A 2 323 932 describes glass fibers which contain both P
2
O
5
and also B
2
O
3
in addition to very high contents of ZrO
2
(8-16 mol %). The alkali metal content can vary within a broad range (1.5-25 mol %). Although such a high ZrO
2
content greatly increases the alkali resistance, P
2
O
5
reduces it again however. In addition, the hydrolytic resistance cannot be adequate over the entire composition range.
GB 2 232 988 A describes ZrO
2
-containing glass fibers which are coated with a thermoplastic resin in order to improve their alkali resistance. Owing to this additional process step, fibers of this type can only be produced expensively and in a complex manner. Fiber materials which can be used are glass fibers from the SiO
2
—ZrO
2
—R
2
O system with a fairly large variation latitude of the components and with further merely optional components, since, owing to the coating, the corresponding properties of the glass lose importance.
DE-A 29 27 445 describes glass compositions having high ZrO
2
contents, namely 18-24% by weight. Although the glasses consequently have high alkali resistance, a high content has, however, an adverse effect on the processing properties and devitrification stability.
By contrast, CZ 236 744 describes glass fibers made from mineral raw materials for cement reinforcement which contain only from 5 to 10% by weight of ZrO
2
, a content with which high alkali resistance can only be achieved with difficulty.
It is an object of the invention to provide a glass which has not only high caustic lye resistance, but also high hydrolytic resistance and good acid resistance and which has high heat resistance and good processing properties.
This object is achieved by the glass having a high zirconium oxide content which is described in the main claim.
The glass according to the invention comprises from 54 to 72% by weight of SiO
2
. At higher contents, the meltability would be impaired, while at lower contents, glass formation would be more difficult. At least 55% by weight are pa

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