GLASS, METHOD FOR PRODUCING A GLASS, AND GLASS MELTING APPARATUS

Abstract

A glass element has, per kg of glass, 50 or fewer inclusions having a size of 2 μm to 10 μm. The glass element can be made of borosilicate glass.

Claims

1. A glass element made of borosilicate glass, wherein the glass element has, per kg of glass, 50 inclusions or fewer having a size from 2 μm to 10 μm.

2. The glass element according to claim 1, wherein the glass element has, per kg of glass, 2000 inclusions or fewer having a size of 10 μm or less.

3. The glass element according to claim 1, wherein the glass element has, per kg of glass, 50 inclusions or fewer having a size 50 μm or less, and/or a size of 50 nm or more.

4. The glass element according to claim 1, wherein the glass element has, per kg of glass, 40 inclusions or fewer.

5. The glass element according to claim 1, wherein the inclusions comprise metallic inclusions, and wherein the glass element has, per kg of glass, 40 metallic inclusions or fewer having a size of 50 μm or less.

6. The glass element according to claim 1, wherein the inclusions comprise nonmetallic inclusions, and wherein the glass element has, per kg of glass 25 nonmetallic inclusions or fewer having a size of 2 μm to 50 μm.

7. The glass element according to claim 1, wherein the inclusions comprise bubbles, wherein the glass element has, per kg of glass, 25 bubbles or fewer having a size of 50 μm or less, and/or 50 nm or more.

8. The glass element according to claim 1, wherein the glass element has a composition that comprises, in wt %: SiO.sub.2 60 to 90%, preferably 76% to 90%; B.sub.2O.sub.3 0 to 20%; Al.sub.2O.sub.3 0 to 20%; Li.sub.2O 0 to 10%; Na.sub.2O 0 to 10%; K.sub.2O 0 to 10 %; MgO 0 to 10 %; CaO 0 to 10 %; SrO 0 to 10 %; and BaO 0 to 10%.

9. The glass element according to claim 1, wherein the glass element has at least one feature selected from the group consisting of: i) a weight of the glass element is 0.01 kg to 350 kg; ii) a glass plate form with a thickness from 0.01 cm to 10 cm; iii) a glass plate form with a length and width from 1 cm to 500 cm; iv) a transmission of the glass element, normalized to a glass element in the form of a glass plate with a thickness of 6.5 mm at a wavelength of 400 nm to 800 nm, that is 70% or more; and v) no inclusions having a size greater than 50 μm.

10. The glass element according to claim 1, wherein the glass element is a glass plate or a glass tube.

11. The glass element according to claim 1, wherein the glass element has, per kg of glass, 2000 inclusions or fewer having a size of 50 nm to 500 nm.

12. The glass element according to claim 1, wherein the glass element has, per kg of glass, 2000 inclusions or fewer having a size of 500 nm to 2 μm.

13. A method for producing a glass element made of borosilicate glass comprising the steps: i) providing a batch, comprising, in wt %: SiO.sub.2 60 to 90%, preferably 76% to 90%; B.sub.2O.sub.3 0 to 20%; Al.sub.2O.sub.3 0 to 20%; Li.sub.2O 0 to 10%; Na.sub.2O 0 to 10%; K.sub.2O 0 to 10%; MgO 0 to 10 %; CaO 0 to 10 %; SrO 0 to 10 %; and BaO 0 to 10 %; ii) heating the batch to form a glass melt, iii) conditioning the glass melt, and iv) cooling the glass melt to provide the glass element, wherein, during step ii) and/or iii): a) the glass melt is heated at least in part with an electric resistance heater by subjecting electrodes to a heating current, wherein, as heating current, an alternating current with a frequency from 1 kHz and 200 kHz is used; b) a contact surface with which the glass melt is in contact comprises 30% or more contact material in the form of melt-cast zirconium oxide material with a proportion of over 70 wt % ZrO.sub.2; and c) from 1% to 50% of a volumetric flow is withdrawn from a bottom material of the glass melt in a bottom region of the glass melt.

14. The method according to claim 13, further comprising during step ii) and/or iii), a viscosity of the glass melt is brought to and/or maintained at from 30 Pas and 450 Pas.

15. The method according to claim 13, wherein the alternating current has a frequency from 1 kHz to 100 kHz.

16. The method according to claim 13, further comprising a contact surface with which the glass melt is in contact comprises 60% or more contact material in the form of melt-cast zirconium oxide material with a proportion of 75 wt % or more ZrO.sub.2.

17. The method according to claim 13, wherein5% to 40% of a volumetric flow is withdrawn from a bottom material of the glass melt in a bottom region of the glass melt.

18. A glass melting apparatus comprising: a first heating device for heating a batch to form a glass melt, a conditioning device for conditioning the glass melt, and a bottom withdrawal device for withdrawing bottom material of the glass melt, wherein the first heating device and/or the conditioning device comprises a second heating device that has at least two electrodes for resistance heating; and wherein A) the second heating device is configured so that the at least two electrodes are subjected to a heating current in the form of an alternating current with a frequency from 1 kHz to 200 kHz; and/or B) a contact surface with which the glass melt is in contact comprises 30% or more contact material in the form of melt-cast zirconium oxide material with a proportion of over 70 wt % ZrO.sub.2; and/or C) the bottom withdrawal device is configured to withdraw from 1% to 50% of a volumetric flow from the bottom material of the glass melt in a bottom region of the first heating device and/or the conditioning device.

19. A method for operating a glass melting apparatus that comprises a first heating device for heating a batch to form a glass melt, a conditioning device for conditioning the glass melt, and a bottom withdrawal device for withdrawing bottom material of the glass melt, wherein the first heating device and/or the conditioning device comprises a second heating device that has at least two electrodes for resistance heating, the method comprising: I) operating the second heating device by subjecting the electrodes to a heating current that is an alternating current with a frequency from 1 kHz to 200 kHz, II) bringing the glass melt into contact with a contact surface that comprises 30% or more melt-cast zirconium oxide material with a proportion of over 70 wt % ZrO.sub.2; and III) operating the bottom withdrawal device so that from 1% to 50% of the volumetric flow is withdrawn from a bottom material of the glass melt in a bottom region of the glass melt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0144] FIG. 1 is a glass melting apparatus in accordance with an embodiment of the present disclosure.

[0145] FIG. 2 is a method for producing a glass element in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0146] FIG. 1 shows a glass melting apparatus in accordance with an embodiment of the present disclosure.

[0147] A glass melting apparatus 1 is shown in detail in FIG. 1. The glass melting apparatus 1 comprises a heating device 2 in which the heating and melting of the starting material, that is, of the so-called batch, takes place. For this purpose, the heating device 2 has a tank 2a, which is furnished with a bottom withdrawal device 6a for withdrawing bottom material 11 of the glass melt 10.

[0148] In order to ensure an adequate homogeneity and the absence of bubbles, the melting here is followed by the refining of the glass melt 10 in a downstream situated refining device 23, which can also be employed at the same time as a transport region for transporting the glass melt 10 to a subsequent section. A key goal of the refining of the glass melt 10 is represented by the removal of physically and chemically bound gases in the glass melt 10 from the glass melt 10. After conclusion of the refining, a renewed formation of bubbles in the melt should be at least reduced or even prevented. The refining can fundamentally take place inside the same tank 2a or else in a separate tank. The refining device 23 is followed by a conditioning device 3, in which the glass melt 10 is further conditioned and/or homogenized. Situated on the bottom of the conditioning device 3 is another bottom withdrawal device 6b.

[0149] The walls 20 of the aforementioned devices 2, 23, 3 of the glass melting apparatus 1 comprise of a refractory material, such as, for example, the above-described melt-cast zirconium oxide material. In accordance with FIG. 1, the heating device 2 is separated from the refining device 23 by means of a flow-influencing element 15 that extends transverse to the flow direction over the entire width of the glass melting apparatus 1 in this region and blocks this region essentially completely, with the exception of a slight overhang to the line of position of the glass. The flow-influencing element 15 can also be arranged in an alternative or supplemental manner in the transition region between the refining device 23 and the conditioning device 3.

[0150] Furthermore, the glass melting apparatus 1 has a heating device 4 with electrodes 5 for resistance heating, which are connected to an alternating current source 8, which supplies the alternating current having a frequency of between 1 kHz and 200 kHz as heating current. In addition, the glass melt can be heated with gas burners, for example (not shown). A control device 30 controls the conditioning device 3, the heating device 2, the alternating current source 8, and, if need be, the refining device 23 as well as the bottom withdrawal devices 6a, 6b in such a way that, on the one hand, between 1% and 50% of the volumetric flow of the glass melt 10, such as, for example, 25%, of the bottom material of the glass melt is withdrawn and, if need be, can be fed back to the heating device 2 and in such a way that, on the other hand, a resistance heating of the glass melt 10 occurs at least in the conditioning device 3. Furthermore, the contact surfaces 7 that are in contact with the glass melt 10 comprise contact material 7a in the form of melt-cast zirconium oxide material with a proportion of over 70 wt % ZrO.sub.2. preferably melt-cast zirconium oxide material with a proportion of over 85 wt % ZrO.sub.2.

[0151] FIG. 2 shows steps of a method for producing a glass element in accordance with an embodiment of the present disclosure.

[0152] The method comprises the following steps:

[0153] In a first step S1, a batch is provided in accordance with an embodiment of the present disclosure. In a further step S2, the batch is heated to form a glass melt. In a further step S3, the glass melt is conditioned and, in a further step S4, the glass melt is cooled to provide the glass element.

[0154] In a preferred embodiment in a method for producing a glass element, preferably in the form of a glass plate, preferably of a borosilicate glass plate, the following steps S1 to S4—preferably first S1, then S2, then S3, and lastly S4—are carried out.

EXAMPLES

[0155] Shown in the following table is the total number of inclusions of a comparative example and of examples in accordance with embodiments of the disclosure, divided into various categories, namely, bubbles, nonmetallic inclusions, and metallic inclusions:

TABLE-US-00001 Nonmetallic Metallic Example Bubbles inclusions inclusions [Unit] Number/kg Number/kg Number/kg 1.sup.a 4.7 33.5 66.8 2.sup.b 0.3 0.2 53.2 3.sup.b 0 0 52.4 4.sup.b 0 0 8.8 5.sup.b 0 0 7.7 6.sup.b 0 0 6.4 .sup.aComparative Example .sup.bExample in accordance with embodiments of the disclosure

[0156] The size distribution of the metallic inclusions per kg of glass of Examples 3 to 6 in the range of 0 to 50 μm is presented in the following table, in which only inclusions with a size of 2 μm or more are taken into consideration in the given size interval of 0 μm to 5 μm of the following table:

TABLE-US-00002 Size in μm Example 0 to 5 5 to 10 10 to 20 20 to 30 30 to 40 40 to 50 [Unit] Number/kg Number/kg Number/kg Number/kg Number/kg Number/kg 3.sup.b 10.5 10.5 10.5 7.0 3.5 3.5 4.sup.b 6.9 1.9 0 0 0 0 5.sup.b 7.0 0.7 0 0 0 0 6.sup.b 5.1 1.3 0 0 0 0 .sup.bExample in accordance with embodiments of the disclosure

[0157] In Comparative Example 1 and Example 2, the size distribution of the inclusions was not determined exactly. In Examples 2 and 3, although the total number of inclusions was just over 50 (for example, Example 2: 0.3+0.2+53.2=53.7 per kg) per kg of glass, the size of some inclusions was over 50 μm, so that the number of inclusions with a size of 50 μm or less and thus also the number of inclusions with a size of 10 μm or less was under 50 inclusions per kg of glass (see second table; Example 3: 10.5+10.5+10.5+7.0+3.5+3.5=45.5 per kg). Besides the inclusions given in the second table, inclusions with a size over 100 μm were additionally found in Example 3. In Examples 3 to 6, the number of inclusions with a size of 50 μm or less was under 50 inclusions per kg (see second table) and, in Examples 4 to 6, even under 10 inclusions per kg. In addition, the glass plates of Examples 4 to 6 had no further inclusions with a size over 50 μm (as seen by comparison of the first and second tables).

[0158] Comparative Example 1 is an example of a glass element in the form of a glass plate, for which none of the herein described improvements were used on the glass melting apparatus. In other words, a hitherto known glass melting apparatus or a hitherto known production method was used. The total number of inclusions here was markedly over 50 and the number of inclusions in the particular category was also very high. Even through the exact size of each individual inclusion was not determined in Comparative Example 1, it may be assumed that, on account of the high number of inclusions also in the range under 50 μm, the number of the inclusions must lie markedly over 50 inclusions per kg. Proceeding therefrom, a test glass melting apparatus was successively continuously improved.

[0159] First of all, in an experiment in the glass melting apparatus, a portion of the contact surface (about 70% or more) with which the glass melt was in contact was furnished with contact material made of melt-cast zirconium oxide material with a proportion of over 70 wt % ZrO.sub.2. At the same time, the glass melting apparatus was operated in such a way that between 1% and 50% of the volumetric flow was withdrawn from the bottom material of the glass melt in a bottom region of the glass melt. This led to a significant reduction of the bubbles and nonmetallic inclusions (see, for example, Example 2). The number of metallic inclusions lies in Example 2 at over 50 (number=53.2), of which, as already described above, although a large part of the inclusions had a size of 50 μm or less, some inclusions also had a size over 50 μm. Accordingly, a glass plate produced in such a way has, per kg of glass, 50 inclusions or fewer with a size of 10 μm or less. Furnishing a smaller portion of the contact surface with the special contact material (30% of contact surface or more) led to a reduction of the bubbles and nonmetallic inclusions. Zero bubbles and nonmetallic inclusions per kg having a size of 50 μm or less were found for glass plates that were produced by use of a glass melting apparatus in which a large part of the contact surface (90% or more or even 95% or more) with which the glass melt was in contact was melt-cast zirconium oxide material with a high proportion (85 wt % or more or even 95 wt % or more) of ZrO.sub.2, and, in addition, a large proportion (between 25 vol. % and 35 vol. %) was withdrawn from the bottom material of the glass melt in a bottom region of the glass melt (see Examples 3 to 6).

[0160] The electric resistance heating was also optimized. To this end, for test purposes, a new electric resistance heater in accordance with an embodiment of the present disclosure was installed in the glass melting apparatus. In Comparative Example 1, a conventional resistance heater was used and a large number of metallic inclusions was determined in the glass plate produced thereby. In Examples 2 to 6, the glass melt was heated and/or warmed at least in part by means of an electric resistance heater by subjecting electrodes to a heating current, wherein, as heating current, an alternating current having a frequency of between 1 kHz and 200 kHz was used, whereby the number of metallic inclusions could be reduced. The number of metallic inclusions could be further markedly reduced by adjusting the frequency between 1 kHz and 100 kHz until, finally, especially few metallic inclusions were found at a frequency of between 8 kHz and 15 kHz (see Examples 4 to 6).

[0161] It is additionally evident from the examples that the best result is achieved when all three improvement steps described herein are employed.

[0162] In summary, at least one of the embodiments of the disclosure has at least one of the following advantages: [0163] reduction of inclusions, preferably of inclusions of metallic particles, with a size of 50 μm or less; [0164] increase of the flexibility of the glass in regard to various applications, [0165] higher quality of the glass; [0166] fewer rejects; and [0167] reduced number of bulk defects or lower bulk defect densities.

[0168] The glass element produced by means of embodiments of the disclosure can preferably be employed or used for the following applications: [0169] laser applications with high energy density; [0170] large-format, homogeneous and/or low-defect photomasks for lithographic applications; [0171] nanoimprint lithography, imprint molds for imprinting of precision lenses or nanostructures down to the nm range, such as, for example, hard-drive magnetic layers or the like; [0172] substrates for flat metal lens designs and optics; [0173] superglass wafers; and [0174] precision windows in displays, preferably for OLEDs.

[0175] Although the present disclosure was described on the basis of preferred exemplary embodiments, it is not restricted to these, but can be modified in diverse ways.