WO1996033954A2

WO1996033954A2 - Borosilicate glass

Info

Publication number: WO1996033954A2
Application number: PCT/DE1996/000610
Authority: WO
Inventors: Dietmar Stiebert; Hans-Georg Lich
Original assignee: Technische Glaswerke Ilmenau Gmbh
Priority date: 1995-04-28
Filing date: 1996-04-06
Publication date: 1996-10-31
Also published as: WO1996033954A3; MX9700022A; CA2193999A1; DE19515608C1; EP0767763A2

Abstract

The invention relates to a borosilicate glass with a linear thermal expansion between 20 and 300 °C of 3.9 to 4.5*10-6 K-1 for the production of laboratory, household, pharmaceutical container, lamp and flat glass and other special technical glasses which can be fully electrically melted and conditioned in cold-top conditions. For fixing the glass composition, this requires, besides the attainment of the desired glass properties, a consideration of the specifics of the fully electric melting process and therefore results in a limited range of variation of several glass oxides, the exclusion of the use of some raw materials, the choice of suitable refining agents, etc. The composition of the glass is SiO¿2? + ZrO2 77,0 to 81,0 % wt.; B2O3 + Na2O + K2O + CaO + MgO + BaO 16,0 to 18,5 % wt.; of which Na2O + K2O + CaO + MgO + BaO 5,4 to 7,0 % wt.; of which CaO + MgO + BaO to 0,9 % wt.; Al2O3 3,7 to 4,9 % wt.; Cl?-¿ 0,05 to 0,4 % wt.; CeO 0,0 to 1,0 % wt.; with the relations: ratio CaO + MgO + BaO / ZrO¿2? 0,0 to 1,5; ratio Na2O + K2O + CaO + MgO + BaO / B2O3 + SiO2 + Al2O3 + ZrO2 0,060 to 0,075. Only NaC1 or KC1 is used as a refining agent. A change between this glass and borosilicate glass 3.3 is reversible, repeatable as often as desired and possible within a short time.

Description

Borosilicate glass

The invention relates to a borosilicate glass with a linear thermal expansion between 20 ° C and 300 ° C of 3.9 to 4.5 x 10 ~ ⁶ K ^"1. It is used for the production of laboratory glass, household glass, pharmaceutical container glass, lamps ¬ glass, flat glass and other technically and optically high-quality glass products are used according to the invention when a borosilicate glass with the aforementioned property is to be produced in known fully electrically heated melting plants according to the cold-top principle.

Many borosilicate glasses are known in the prior art. Their properties determining the utility value are high chemical resistance, low thermal expansion, high resistance to temperature changes and high mechanical strength.

Borosilicate glass 3.3 according to DIN ISO 3585 is usually used for laboratory, housekeeping and apparatus glass. This type of glass contains only a little alkali (below 5%), SiO ₂ over 79% and B ₂ 0 ₃ to approx. 13%. It has a thermal expansion between 20 and 300 ° C of approx. 3.3 * 10 ~ ⁶ K ^"1. Furthermore, boron-containing melting glasses are known. They have higher alkali and / or alkaline earth contents, as well as sometimes additional oxides. The thermal expansion of these glasses is 3.6 to 5.2 * 10 ^-6 K ^"1 . Another well-known group is that of the so-called neutral pharmaceutical borosilicate glasses. In contrast to melt-down glasses, they achieve the highest chemical resistance values. Their alkali content is around 6.5 to 8.5% or alkaline earth with 3.2 to 5.0%, the thermal expansion is 4.8 to 5.1 * 10 ~ ⁶ K ^-1 . It is known, as described in the patent DE 37 22 130, to replace the large range of borosilicate glasses with a glass of thermal expansion of 4.0 to 5.0 * 10 ^-6 ^K_1 which meets most requirements. It is also known to perfect and specialize use-determining properties of the borosilicate glasses by means of an optimized composition and partial use of additional oxides such as ZnO, SrO, CsO, i ₂ 0 etc., as described, for example, in the patents DE 42 30 607, DE 40 12 288 or DE 43 25 656.

In the large-scale production of borosilicate glass 3.3, the fully electrical melt according to the cold-top method has become established because of improved energy efficiency, qualitative and ecological advantages. In this process, the heat of fusion in the interior of the melt pool is generated by the flow of electrical current, the surface of the melt pool being continuously coated with a new amount. A stable, well-insulating layer normally forms, which also retains volatile substances and feeds them back to the melt. Because of this superiority and its cost-reducing relevance, the known borosilicate glasses are tested for manufacturability using this method and its devices. Neutral pharmaceutical Borosilicatglaser can still do not melt all-electric, because the necessary refining agents As ₂ 0 ₃ and / or ^s - ° 2 ° 3 ^ i ^e destroy conventional molybdenum rod electrodes of the heating. The first approaches to a procedural problem solving are given in DE-PS 43 13 217.

Borosilicate glasses with a linear thermal expansion of 3.6 to 4.8 * 10 ~ ⁶ K ^_1 can only be melted fully electrically with strong qualitative restrictions. Due to higher flux contents (alkali, alkaline earth and boron oxide) they melt much faster than borosilicate glasses with a thermal expansion of 3.3 * 10 ^-6 K ^_1 . However, since approximately the same melting temperatures are required for complete glass formation, homogenization and refining despite higher flux contents, the well-insulating, cold batch mixture required for the fully electrical cold-top melting process cannot be produced in a stable manner, and the heat balance is disturbed. At worst, the process no longer allows the desired temperatures to be reached, so that blistered glass or unmelted particles leave the furnace.

If alkali and alkaline earth metal are added as usual as carbonate, which depending on its origin is contaminated with sulfate, the carbon and sulfur dioxide formed during the melting cannot be completely removed from the melt. On the one hand, the amounts of gas released for the tough borosili- cat glasses relatively high. On the other hand, the high solubility of C0 ₂ and S0 ₂ leads to high gas residues in the glass. It is known from other glasses that the solubility of C0 ₂ and S0 _{2 increases} with the basicity module (ratio of the network converters to the network formers). If this law is transferred to borosilicate glasses, the higher C0 ₂ or S0 ₂ solubility of the alkali and alkaline earth-rich borosilicate glasses compared to borosilicate glass 3.3 is obvious. At the latest as reboil glass, C0 ₂ and S0 _{2 are} released again and appear as gisps or bubbles in the finished glass. Suitable refining agents, such as As ₂ 0 ₃ and / or Sb ₂ O, can remove these gases in conjunction with other oxidizing agents, but because of their destructive effect on molybdenum electrodes, they cannot be used in fully electrically heated furnaces. As a result of their high alkaline earth contents, the glasses described in the patents DE 42 30 607, DE 37 22 130 and DE 43 25 656 have this decisive disadvantage.

Other partially used oxides such as PbO, SnO, CuO, NiO, CdO, FeO, Cr ₂ 0 ₃ and ZnO also have a corrosive effect on the Mo heating electrodes. Measures to protect the electrodes, such as the known methods for direct current passivation, are ruled out because of the use of known devices made of noble metal which is necessary in the feeder.

Furthermore, it is known that the fully electric cold-top melting process at the melting temperatures which are fixed for each type of glass and very high, especially in the case of borosilicate glass, only for a certain one Range of glass viscosity and electrical conductivity can be applied. An electrical conductivity of the glass which is too high at the usual melting temperature as a result of high alkali or alkaline earth contents leads to high current and energy densities, overheating, electrode wear and bubbles can occur. If the electrical conductivity is too low, an increasing part of the current flows through the stone material. Too high a glass viscosity requires unacceptably high temperatures for the refining or only enables them incompletely. In a glass that is too thin, often unmelted particles or uncleaned melt are mixed into the finished glass. The fully electrical cold-top process which has been tried and tested for borosilicate glass 3.3 is consequently not transferable to other glasses which have different viscosities and conductivities at comparable melting temperatures without significant consequences. Many of the known borosilicate glasses with a linear thermal expansion greater than 3.9 * 10 ~ ⁶ K ^-1 are, for example, over 7% in the sum of alkali plus alkaline earth metal content, including that of patent DE 37 22 130. They can be found in the do not melt the required melting temperatures above 1550 ° C with the proven fully electric cold-top process without bubbles.

The methods known in the prior art do not provide any information on fixing or controlling the redox potential of the borosilicate glasses. The invention is based on the object of specifying a soft borosilicate glass with a thermal expansion of 3.9 to 4.5 * 10 ^{~ 6} K ^"1 with a high chemical resistance, which, under the ecologically and energetically advantageous conditions of the known fully electric cold-top process can be produced.

According to the invention the object is achieved in that a processing temperature at 10 ⁴ dPa s of 1200 to 1270 ° C, a viscosity at 1550 ° C of 10 ² ' ⁶ to 10 ² ' ⁸ dPa s, a spec. electrical resistance at 1550 ° C from 20 to 33 .... cm or an electrical conductivity at 1550 ° C from 3.0 to 5.0 S / m, under cold-top conditions at about 1600 ° C melts at 0.3 to 0.5 mm / min and has the following basic composition:

Si0 ₂ + Zr0 ₂ 77.0 to 81.0% by weight ^B 2 ° 3 ^{+ Na} 2 ° ^{+ K} 2 ° ^{+ Ca0 + Mg0 + Ba0}

16.0 to 18.5% by weight thereof Na ₂ 0 + K ₂ 0 + CaO + MgO + BaO

5.4 to 7.0% by weight thereof CaO + MgO + BaO to 0.9% by weight ^Al 2 ° 3 ³ ' ^{7 to 4} ' ^{9% by weight} - ^~%

Cl 0.05 to 0.4% by weight

with the relations:

CaO + MgO + BaO

Ratio 0.0 to 1.5

Zr0 Ratio Na ₂ 0 + K ₂ 0 + CaO + MgO + BaO

0.060 to 0.075

^B 2 ° 3 + SiO-, + A1 ₂ 0 ₃ + ZrO-

Advantageous designs are specified in subclaims 2 to 5.

With the borosilicate glass according to the invention, specific experience with the specified method and its devices must be taken into account. Although the basic relationships between glass properties and composition for borosilicate glasses are known, the process-related restrictions lead to a new, contradictory and therefore hitherto unusual goal. The new glass belongs to the group of chemically resistant borosilicate glasses, which are characterized by the following properties:

- linear thermal expansion between 20 ° C and 300 ° C: 3.9 to 4.5 * 10 ~ ⁶ K ^"1

- Transformation temperature: over 540 ° C

- Hydrolytic resistance according to DIN 12111: 1st class

- Acid resistance according to DIN 12116:

1st Class

- Alkali resistance according to DIN 52322:

2nd Class

Because of its use as pharmaceutical and / or domestic glass, the glass is produced without toxic heavy metal oxides. It contains components to increase the brilliance and can be colored. So that it can be melted fully electrically in known furnaces, no PbO, SnO, CuO, NiO, CdO, FeO, Cr ₂ 0 ₃ , ZnO, As ₂ 0 ₃ and / or Sb ₂ 0 ₃ may be contained. For ecological reasons, no fluorides are used as refining agents.

In order to keep the gas content in the glass low, little or no carbon dioxide and no sulfur dioxide are released during melting. In order to avoid the failure of precious metal internals, the glass is not in a reduced state. The ability to be influenced by means of the usual oxidizing burner setting is not available in fully electrically heated melting plants. For ecological reasons, the customary addition of nitrates (O ₂ elimination and oxidation of polyvalent ions) is also ruled out because of their NO release.

The composition of the borosilicate glass which can be melted completely electrically under cold-top conditions takes into account not only chemical-physical glass properties but also process-related requirements. According to the invention, the fully electric cold-top method can be used with borosilicate glass with a thermal expansion of up to 4.5 * 10 ~ ⁶ ^K_1 and enables good glass quality if high-temperature material values such as viscosity and conductivity are close to them due to the process of a borosilicate glass 3.3. So that stable cold-top conditions prevail, the mixture is also melted at approximately the same speed as in borosilicate glass 3.3. The following of these values were demonstrated in melting tests:

- Processing temperature at 10 ⁴ dPa s: 1200 to 1270 ° C

- Viscosity at 1550 ° C: 10 ² ' ⁶ to 10 ² ' ⁸ dPa s

- spec. electrical resistance at 1550 ° C: 20 to 33 Ohm cm - melting rate of the batch without cullet: 0.35 to 0.45 mm / min.

Trial melting showed that the high processing temperature and the 1550 ° C. viscosity with a content of SiO ₂ plus ZrO _{2 of} over 77% and a content of A1 ₂ 0 ₃ of 3.5 to 5.0 % can be achieved. Over 81% Si0 ₂ plus Zr0 ₂ , however, the processing temperature and the viscosity at 1550 ° C. rise to uncontrollably high values and relics of these meltable components must also be expected. At 77% Si0 ₂ plus Zr0 ₂ , the linear thermal expansion rises above 4.5 * 10 ^-6 K ^~ with the Al ₂ 0 ₃ content according to the invention.

It was also found that the conductivity or the specific electrical resistance determined by the process, the ratio of the sum of the alkalis plus alkaline earths to the sum of Si0 ₂ + B ₂ 0 ₃ + A1 ₂ 0 ₃ + Zr0 ₂ at 0.060 to 0.075 fix. In addition, too high an electrical conductivity at 1550 ° C above 5 S / m leads to too high Current densities, below 3 S / m too much current flows through the stone material.

The sum of all oxides acting as fluxes (alkali + alkaline earth + B ₂ 0 ₃ ) accelerates the melting behavior. In order that the desired cold-top conditions prevail at the melting temperatures above 1550 ° C. required for the refining, ie that the batch cover required for the insulation does not melt, this amount of flux must not exceed 18.5%. In order to keep up to this value is comparable with Boro¬ silicate 3.3 mixture cover to er¬, at least 0.6% of the Si0 ₂ required to be replaced by the more schmelzverzögernd acting Zr0 _second At 16% flux, the glass melts more slowly than borosilicate glass 3.3, which would require impermissibly high temperatures and increase the risk of residual quartz relics occurring. Depending on the variable content of alkaline earth metal explained below, the melting behavior is stabilized by a defined increase in Zr0 ₂ by keeping the ratio of alkaline earth metal to Zr0 ₂ below 1.5.

As is known, the B ₂ 0 ₃ content influences the chemical resistance and is limited at the bottom by an excessively high processing temperature above 1300 ° C. and an excessively high 1550 ° C. viscosity. In connection with the alkali and alkaline earth content explained below, a range of 10.5 to 12.5% B ₂ 0 _{3 was} determined in order to achieve the required chemical resistance.

Experience has shown that the linear thermal expansion is strongly influenced by the content of alkali and alkaline earth. It was found that under Taking into account the limits of the alkaline earths for conductivity and carbonate addition, below, at least 5.4%, but at most 7.0% alkali plus alkaline earth may be used, so that the linear thermal expansion between 20 ° C and 300 ° C in the range of 3.9 to 4.5 * 10 ~ ⁶ K ^{-1 is} to be kept. Furthermore, it was found that the desired chemical resistance can be achieved by using the mixed alkali and additionally the mixer alkaline effect if, in addition to 5.0 to 5.8% Na ₂ 0, 0.3 to 1.5% K ₂ 0 or 0.6 to 0.9% alkaline earth or a combination of K ₂ 0 plus alkaline earth are added. Since BaO shows the most favorable effect from the alkaline earths, as well as from the advantages explained below, it is preferred. Since Li ₂ 0 would increase the tendency to devitrify, its use is dispensed with.

In addition to its melting retarding effect, Zr0 _{2 is} known to improve the chemical resistance, in particular to alkalis, the mechanical strength and in particular the grinding hardness of the glass, which has been shown to increase its use value, but also the effort required for mechanical processing. So that the glass can also be processed economically, the Zr0 ₂ content should be less than 2.4%. Surprisingly, when this glass was produced on an industrial scale, up to this value there was no risk of devitrification if A1 ₂ 0 _{3 was} 3.7 to 4.9%. To limit the processing temperature, the Al ₂ O ₃ content is preferably 4.1 to 4.5% and the ZrO ₂ content is preferably between 0.8 and 1.0%. In large-scale melting tests in fully electrically heated cold-top melting furnaces and subsequent determination of the gas content, it was also found that at a ratio of Na ₂ 0 + K ₂ 0 + CaO + MgO + BaO divided by Si0 ₂ + Al ₂ 0 ₃ + Zr0 ₂ + B ₂ 0 ₃ below 0.075 the contents of C0 ₂ and S0 ₂ in the glass decrease significantly. In order to keep the amount of carbon and sulfur dioxide introduced generally low, the use of alkaline earths is limited according to the invention to 0.9% and the use of carbonates is only permitted for these alkaline earths. Other carbonates or sulfates or carbonate-containing or sulfate-containing raw materials must not be used because of their carbon or sulfur dioxide release. MgO increases the tendency to devitrification and is therefore excluded as a raw material component. Compared to CaO, BaO increases the refractive index and promotes the brilliance of the glass, as is desirable when used as a household glass. Because of this property and its favorable influence on the acid class, only BaO is used as an alkaline earth component. This means that only impurities in CaO and MgO are permitted which, despite all precautions, can be brought into the glass up to 0.1%. The glass preferred according to the invention is alkaline earth-free to completely avoid the susceptibility to reboil except for the tolerated impurities. If it is necessary to decolorize the glass, the introduction of a defined amount of cerium-IV-oxide has proven to be advantageous for soda-lime glasses, since it oxidises polyvalent foreign ions. It has been found that the oxygen release occurs the cerium IV oxide does not destroy the molybdenum rod electrodes installed on the side or from below, since released oxygen no longer comes into contact with them. It was also found that the corrosive influence known from As ₂ 0 ₃ or Sb ₂ 0 ₃ does not occur with the amount of cerium oxide used according to the invention, despite the high melting temperature present in sulfate-free borosilicate glass. At the same time, the desired redox state can be set or controlled. However, the CeO content in the glass does not exceed 1%, since otherwise an increase in molybdenum wear would also adversely affect the chemical resistance. An inventive borosilicate glass with a linear thermal expansion between 20 ° C and 300 ° C of 3.9 to 4.5 * 10 ~ ⁶ K ^"1 , the transformation temperature of 540 to 575 ° C, a processing temperature at 10 ⁴ dPa s 1200 to 1270 ° C and 1550 ° C viscosity of ιo ² ^'65 dPa s, the cm and an electrical resistivity at 1550 ° C 20-33 Ohm an electrical conductivity at 1550 ° C from 3.0 to 5 .0 S / m and at the same time fulfills the first hydrolytic class according to DIN 12111, the first acid class according to DIN 12116 and the second alkali class according to DIN 52322, has the following composition: Si0 ₂ 76.6 to 78.0 wt.

B ₂ 0 ₃ 10.5 to 12.5 wt.

A1 ₂ 0 ₃ 3.7 to 4.9 wt. ^Na 2 ° ⁵ _' ° ^b: - ^{s 5} _' ^{8 wt} *

K ₂ 0 0.3 to 1.5 wt.

CaO and / or MgO (contamination) less than 0.1 wt.

BaO 0.0 to 0.9 wt.

CeO 0.0 to 1.0 wt. Zr0 ₂ 0.6 to 2.4 wt.

Cl 0.05 to 0.4 wt.

Only NaCl or KC1 is used as refining agent, As ₂ 0 ₃ or Sb ₂ 0 ₃ is excluded. The use of raw materials which contain CaO, MgO, sulfate or fluoride is only permitted with the exception of the smallest of impurities.

The borosilicate gel according to the invention dispenses with alkaline earth (apart from unavoidable impurities) and thus completely excludes the use of carbonates. This reduces the susceptibility to reboil. The alkalis are only introduced as borates, aluminum and / or silicates. This preferred glass according to the invention is characterized by the following composition: 76.6 to 77.7% by weight?

11.0 to 12.0% by weight

4.1 to 4.5% by weight

5.1 to 5.6% by weight

0.8 to 1.2% by weight

0.0 to 0.5% by weight

0.8 to 1.0% by weight

0.05 to 0.2% by weight

It is particularly advantageous that the borosilicate glass according to the invention, with its chemical composition and its physical properties, can be produced using the ecologically, energetically and economically highly efficient, fully electric cold-top melting process. In such a glass melting furnace, the glass according to the invention is used with the linear thermal expansion between 20 ° C. and 300 ° C. of 4.0 to 4.4 * 10 ^-6 K ^"1 , a transformation temperature of 550 to 575 ° C and one Processing temperature at 10 ⁴ dPa s from 1215 to 1260 ° C, the first hydrolytic class according to DIN 12111, the first acid class according to DIN 12116 and the second alkali class according to DIN 52322 melted and processed in good quality, with a temporary and reversible change with Borosili¬ catglas 3.3 is quick and easy.

The invention is explained in more detail below on the basis of an exemplary embodiment.

Glasses No. 5 to 19 shown in the table are examples of continuously working, fully electrically heated cold-top melting furnaces. Glass 9 to 11 was melted with 20 to 30% cullet.

Glasses 1 to 4 are used for comparison and can be melted fully electrically using the cold-top method.

Glass 1 is a borosilicate glass 3.3 according to DIN ISO 3585.

Glass 20 is used for comparison and cannot be produced with the fully electrical cold-top method without bubbles (alkali plus alkaline earth too high, specific electrical resistance too low, basicity module too high).

Notes on the table:

Glass oxide data in% by weight alpha: linear thermal expansion between 20 and 300 ° C in 10 ^"6 / K Tg: transformation temperature in ° C

Ep: sink point or processing temperature at

10 ⁴ dPa s in ° C Ew: softening point at 10 ⁷ ' ⁶ dPa s in ° CR: specific electrical resistance at 1550 ° C in ohm cm v: melting rate in mm / min visc. : Logarithm of viscosity at 1550 ° C in dPa s

Na ₂ 0 + K ₂ 0 + CaO + MgO + BaO

Basicity module =

B ₂ 0 ₃ + Si0 ₂ + A1 ₂ 0 ₃ + Zr0 ₂ Implementation examples (No. 1 to 4 and 20 for comparison)

No. 14 additionally 0.40% CeO. No. 20 additionally 0.33% CeO

Claims

PATENT CLAIMS

1. Borosiicatglas with a linear thermal expansion between 20 ° C and 300 ° C from 3.9 to 4.5 x 10 ^"6 K ^{" 1} , characterized in that it has a processing temperature at 10 ⁴ dPas from 1200 to 1270 ° C , a viscosity at 1550 ° C of 10 ² ' ⁶ to 10 ² ' ⁸ dPa s, a spec. electrical resistance at 1550 ° C from 20 to 33 Ohm cm or an electrical conductivity at 1550 ° C from 3.0 to 5.0 S / m, under cold-top conditions at approx. 1600 ° C with 0 , 3 to 0.5 mm / min melts and has the following basic composition:

^s i ° 2 ^{+ Zr0} 2 77.0 to 81.0 parts by weight

B ₂ 0 ₃ + Na ₂ 0 + K ₂ 0 + CaO + MgO + BaO

16.0 to 18.5% by weight thereof Na ₂ 0 + K ₂ 0 + CaO + MgO + BaO

5.4 to 7.0% by weight thereof CaO + MgO + BaO to 0.9% by weight

A1 ₂ 0 ₃ 3.7 to 4.9% by weight

Cl ~ 0.05 to 0.4% by weight

with the relations:

CaO + MgO + BaO

Ratio = 0.0 to 1.5

Zr0 ₂

Na ₂ 0 + K ₂ 0 + CaO + MgO + BaO

Ratio 0.060 to

0.075

B ₂ 0 ₃ + Si0 ₂ + A1 ₂ 0 ₃ + Zr0 ₂

2. borosilicate glass according to claim 1, characterized denotes ge _/ that it has a transformation temperature of 540-575 ° C, the first hydrolyti¬ rule rating according to DIN 12111, the first acid class according to DIN 12116 and the second lye class according to DIN 52322 equal and composition

Si0 ₂ 76.6 to 78.0% by weight

B ₂ 0 ₃ 10.5 to 12.5% by weight ^A1 2 ° 3 ³ ' ^{7 to 4} ' ^{9% by weight} - ^-%

Na ₂ 0 5.0 to 5.8% by weight

K ₂ 0 0.3 to 1.5% by weight

CaO and / or MgO (contamination) less than 0.1% by weight

BaO 0.0 to 0.9% by weight Zr0 ₂ 0.6 to 2.4% by weight

Cl ^" 0.05 to 0.4% by weight

having.

3. borosilicate glass according to claim 1 or 2, characterized in _/ that the batch is added as stabilizer and the redox state Entfärbungsmit¬ tel Ce-IV-oxide and 1.0 wt .-% is to Ce0 ₂ in the glass vor¬.

4. Borosilicate glass according to one of claims 1 to

3, characterized in that it is only produced using NaCl or KCl as a refining agent, As ₂ 0 ₃ or Sb ₂ 0 _{3 is} excluded and when adding NaCl or KCl the prescribed amount of Cl ^~ in the glass taking into account a possible present Chloride contamination in raw materials and cullet is set.

5. Borosilicate glass according to one of claims 1 to 4, characterized in that it has the following composition:

76.6 to 77.7% by weight 11.0 to 12.0% by weight

4.1 to 4.5% by weight 5.1 to 5.6% by weight 0.8 to 1.2% by weight 0.0 to 0.5% by weight

° ' ⁸ - ° is ¹ ' ° ^wt - ~%

Cl ^" 0.05 to 0.2% by weight

6. Use of the borosilicate glass according to one of claims 1 to 5 for the production of laboratory glass, household glass, pharmaceutical container glass, lamp glass, flat glass and other technically and optically high-quality glass products.