HOMOGENEOUS QUARTZ GLASS FROM PYROGENIC SILICON DIOXIDE GRANULATE

Abstract

One aspect relates to a process for the preparation of a quartz glass body, including providing a silicon dioxide granulate composed of a pyrogenic silicon dioxide powder, making a glass melt out of the silicon dioxide granulate and making a quartz glass body out of at least part of the glass melt. The quartz glass body has an OH content of less than 10 ppm, a chlorine content of less than 60 ppm and an aluminium content of less than 200 ppb. One aspect also relates to a quartz glass body which is obtainable by this process. Furthermore, one aspect relates to a formed body and a structure, each of which is obtainable by further processing of the quartz glass body.

Claims

1-21. (canceled)

22. A process for the preparation of a quartz glass body comprising pyrogenic silicon dioxide, comprising: providing a silicon dioxide granulate comprising: providing a pyrogenic silicon dioxide powder; and processing the silicon dioxide powder to obtain a silicon dioxide granulate, wherein the silicon dioxide granulate has a greater particle diameter than the silicon dioxide powder; making a glass melt out of the silicon dioxide granulate in an oven; making a quartz glass body out of at least part of the glass melt; wherein the quartz glass body comprises: an OH content of less than 10 ppm; a chlorine content of less than 60 ppm; and an aluminium content of less than 200 ppb; wherein the ppb and ppm are each based on the total weight of the quartz glass body.

23. The process according to claim 22, wherein the pyrogenic silicon dioxide powder is present in the form of amorphous silicon dioxide particles, wherein the silicon dioxide powder comprises: a chlorine content of less than 200 ppm; and an aluminium content of less than 200 ppb; wherein the silicon dioxide granulate is treated with a reactant.

24. The process according to claim 22, wherein the warming of the silicon dioxide granulate takes place to obtain a glass melt by a mould melting process.

25. The process according to claim 22, wherein during the warming, for a period t.sub.T, a temperature T.sub.T is maintained which is below the melting point of silicon dioxide.

26. The process according to claim 25, further comprising at least one of: wherein the temperature T.sub.T is in a range from 1000 to 1700 C.; and wherein the period t.sub.T is in a range from 1 to 6 hours.

27. The process according to claim 25, wherein the period t.sub.T is before the making of the glass melt.

28. The process according to one claim 25, wherein the quartz glass body obtained is cooled at least to a temperature of 1000 C. at a rate of up to 5 K/min.

29. The process according to claim 25, wherein the cooling takes place in a temperature range from 1300 to 1000 C. at a rate of not more than 1 K/min.

30. The process according to claim 25, wherein the quartz glass body further comprises at least one of: a fictive temperature in a range from 1055 to 1200 C.; an ODC content of less than 510.sup.15/cm.sup.3; a metal content of metals different to aluminium of less than 300 ppb; a viscosity (p=1013 hPa) in a range from log.sub.10 ( (1200 C.)/dPas)=13.4 to log.sub.10 ( (1200 C.)/dPas)=13.9 or log.sub.10 ( (1300 C.)/dPas)=11.5 to log.sub.10 ( (1300 C.)/dPas)=12.1 or log.sub.10 ( (1350 C.)/dPas)=1.2 to log.sub.10 ((1350 C.)/dPas)=10.8; a standard deviation of the OH content of not more than 10%, based on the OH content of the quartz glass body; a standard deviation of the Cl content of not more than 10%, based on the Cl content of the quartz glass body; a standard deviation of the Al content of not more than 10%, based on the Al content of the quartz glass body; a refractive index homogeneity of less than 110.sup.4; and a transformation point Tg in a range from 1150 to 1250 C.; wherein the ppb and ppm are each based on the total weight of the quartz glass body.

31. The process according to claim 25, wherein the silicon dioxide powder comprises at least one of: a BET surface area in a range from 20 to 60 m.sup.2/g and; a bulk density in a range from 0.01 to 0.3 g/cm.sup.3; a carbon content of less than 50 ppm; a chlorine content of less than 200 ppm; an aluminium content of less than 200 ppb; a total content of metals different to aluminium of less than 5 ppm; at least 70 wt.-% of the powder particles have a primary particle size in a range from 10 to 100 nm; a tamped density in a range from 0.001 to 0.3 g/cm.sup.3; a residual moisture content of less than 5 wt.-%; a particle size distribution D.sub.10 in a range from 1 to 7 m; a particle size distribution D.sub.50 in a range from 6 to 15 m; and a particle size distribution D90 in a range from 10 to 40 m; wherein the ppm and ppb are each based on the total weight of the silicon dioxide powder.

32. The process according to claim 25, wherein the silicon dioxide powder is prepared from a compound selected from the group consisting of siloxanes, silicon alkoxides and silicon halides.

33. The process according to claim 25, wherein the processing of the silicon dioxide powder to a silicon dioxide granulate comprises: providing a liquid; mixing the pyrogenic silicon dioxide powder with the liquid to obtain a slurry; granulating the slurry to obtain a silicon dioxide granulate; and optionally treating the silicon dioxide granulate.

34. The process according to claim 25, wherein at least 90 wt. % of the silicon dioxide granulate is made from the pyrogenic silicon dioxide powder, based on the total weight of the silicon dioxide granulate.

35. The process according to claim 25, wherein the silicon dioxide granulate is characterised by at least one of: a chlorine content of less than 500 ppm; an aluminium content of less than 200 ppb; a BET surface area in a range from 20 to 50 m.sup.2/g; a pore volume in a range from 0.1 to 2.5 mL/g; a bulk density in a range from 0.5 to 1.2 g/cm.sup.3. a tamped density in a range from 0.7 to 1.2 g/cm.sup.3; a mean particle size in a range from 50 to 500 m; a carbon content of less than 5 ppm; an angle of repose in a range from 23 to 260, a particle size distribution D.sub.10 in a range from 50 to 150 m; a particle size distribution D.sub.50 in a range from 150 to 300 m; and a particle size distribution D.sub.90 in a range from 250 to 620 m, wherein the ppm and ppb are each based on the total weight of the silicon dioxide granulate II.

36. A quartz glass body obtainable by a process according to claim 25.

37. A quartz glass body containing pyrogenic silicon dioxide, wherein the quartz glass body comprises: an OH content of less than 10 ppm; a chlorine content of less than 60 ppm; and an aluminium content of less than 200 ppb; wherein the ppb and ppm are each based on the total weight of the quartz glass body.

38. The quartz glass body according to claim 37, wherein the quartz glass body comprises at least one of: a fictive temperature in a range from 1055 to 1200 C.; an ODC content of less than 510.sup.15/cm.sup.3; a metal content of metals different to aluminium of less than 300 ppb; a viscosity (p=1013 hPa) in a range from log.sub.10 ( (1200 C.)/dPas)=13.4 to log.sub.10 ( (1200 C.)/dPas)=13.9 and/or log.sub.10 ( (1300 C.)/dPas)=11.5 to log.sub.10 ( (1300 C.)/dPas)=12.1 or log.sub.10 ( (1350 C.)/dPas)=1.2 to log.sub.10 ( (1350 C.)/dPas)=10.8; a standard deviation of the OH content of not more than 10%, based on the OH content of the quartz glass body; a standard deviation of the Cl content of not more than 10%, based on the Cl content of the quartz glass body; a standard deviation of the Al content of not more than 10%, based on the Al content of the quartz glass body; a refractive index homogeneity of less than 110.sup.4; and a transformation point Tg in a range from 1150 to 1250 C.; wherein the ppb and ppm are each based on the total weight of the quartz glass body.

39. A process for the preparation of a formed body comprising: providing a quartz glass body according to claim 37, or a quartz glass body obtained by a process according to claim 22; and making a formed body out of the quartz glass body.

40. A formed body obtainable by a process according to claim 39.

41. A process for the preparation of a structure comprising: providing a formed body according to claim 40 and a part; and joining the formed body with the part to obtain the structure.

42. A structure obtainable by a process according to claim 41.

Description

FIGURES

[0581] FIG. 1 flow diagram (process for the preparation of a quartz glass body)

[0582] FIG. 2 flow diagram (process for the preparation of a silicon dioxide granulate I)

[0583] FIG. 3 flow diagram (process for the preparation of a silicon dioxide granulate II)

[0584] FIG. 4 schematic representation of a spray tower

[0585] FIG. 5 schematic representation of a gas pressure sinter oven (GDS oven)

[0586] FIG. 6 flow diagram (process for the preparation of a formed body)

DESCRIPTION OF THE FIGURES

[0587] FIG. 1 shows a flow diagram containing the steps 101 to 104 of a process 100 for the preparation of a quartz glass body according to the present invention. In a first step 101, a silicon dioxide granulate is provided. In a second step 102, a glass melt is made from the silicon dioxide granulate.

[0588] Preferably, moulds are used for the melting which can be introduced into and removed from an oven. Such moulds are often made of graphite. They provide a negative form for the cast item. The silicon dioxide granulate is filled into the mould and is first melted in the mould in step 103. Subsequently, the quartz glass body is formed in the same mould by cooling the melt. It is then freed from the mould and processed further, for example in an optional step 104. This procedure is discontinuous. The forming of the melt is preferably performed at reduced pressure, in particular in a vacuum. Further, it is possible during step 103 to charge the oven intermittently with a reducing, hydrogen containing atmosphere.

[0589] In another procedure, hanging or standing crucibles are preferably employed as the melting crucible. To this end, the silicon dioxide granulate is introduced into the melting crucible here and warmed therein until a glass melt forms. The melting preferably takes place in this case in a reducing, hydrogen-containing atmosphere. In a third step 103, a quartz glass body is formed. The formation of the quartz glass body is preferably performed by removing at least a part of the glass melt from the crucible and cooling, for example through a nozzle at the lower end of the crucible. In this case, the form of the quartz glass body can be determined partly by the design of the nozzle.

[0590] In this way, for example, solid bodies can be obtained. Hollow bodies are obtained for example if the nozzle additionally has a mandrel. This examplary representation of a process for the preparation of quartz glass bodies, and in particular step 103, is preferably performed continuously. In an optional step 104, a hollow body can be formed from a solid quartz glass body.

[0591] FIG. 2 shows a flow diagram containing the steps 201, 202 and 203 of a process 200 for the preparation of a silicon dioxide granulate I. In a first step 201, a silicon dioxide powder is provided. A silicon dioxide powder is preferably obtained from a synthetic process in which a silicon containing material, for example a siloxane, a silicon alkoxide or a silicon halide is converted into silicon dioxide in a pyrogenic process. In a second step 202, the silicon dioxide powder is mixed with a liquid, preferably with water, to obtain a slurry. In a third step 203, the silicon dioxide contained in the slurry is transformed into a silicon dioxide granulate. The granulation is performed by spray granulation. For this, the slurry is sprayed through a nozzle into a spray tower and dried to obtain granules, wherein the contact surface between the nozzle and the slurry comprises a glass or a plastic.

[0592] FIG. 3 shows a flow diagram containing the steps 301, 302, 303 and 304 of a process 300 for the preparation of a silicon dioxide granulate II. The steps 301, 302 and 303 proceed corresponding to the steps 201, 202 and 203 according to FIG. 2. In step 304, the silicon dioxide granulate I obtained in step 303 is processed to obtain a silicon dioxide granulate II. This is preferably performed by warming the silicon dioxide granulate I in a chlorine containing atmosphere.

[0593] In FIG. 4 is shown a preferred embodiment of a spray tower 1100 for spray granulating silicon dioxide. The spray tower 1100 comprises a feed 1101 through which a pressurised slurry containing silicon dioxide powder and a liquid are fed into the spray tower. At the end of the pipeline is a nozzle 1102 through which the slurry is introduced into the spray tower as a finely spread distribution. Preferably, the nozzle slopes upward, so that the slurry is sprayed into the spray tower as fine droplets in the nozzle direction and then falls down in an arc under the influence of gravity. At the upper end of the spray tower there is a gas inlet 1103. By introduction of a gas through the gas inlet 1103, a gas flow is created in the opposite direction to the exit direction of the slurry out of the nozzle 1102. The spray tower 1100 also comprises a screening device 1104 and a sieving device 1105. Particles which are smaller than a defined particle size are extracted by the screening device 1104 and removed through the discharge 1106. The extraction strength of the screening device 1104 can be configured to correspond to the particle size of the particles to be extracted. Particles above a defined particle size are sieved off by the sieving device 1105 and removed through the discharge 1107. The sieve permeability of the sieving device 1105 can be selected to correspond to the particle size to be sieved off. The remaining particles, a silicon dioxide granulate having the desired particle size, is removed through the outlet 1108.

[0594] FIG. 5 shows a preferred embodiment of the oven 1500 which is suitable for a vacuum sintering process, a gas pressure sinter process and in particular a combination thereof. The oven has from outside inward a pressure resistant jacket 1501 and a thermal insulating layer 1502. The space enclosed thereby, referred to as the oven interior, can be charged with a gas or a gas mixture via a gas feed 1504. Further, the oven interior has a gas outlet 1505 via which gas can be removed. According to the gas transport balance between gas feed 1504 and gas removal at 1505 an over pressure, a vacuum or also a gas flow can be produced in the interior of the oven 1500. Further, heating elements 1506 are present in the oven interior 1500. These are often mounted on the insulation layer 1502 (not shown here). For protecting the melt material from contamination, there is a so-called liner 1507 in the interior of the oven, which separates the oven chamber 1503 from the heating elements 1506. Moulds 1508 with material to be melted 1509 can be introduced into the oven chamber 1503. The mould 1508 can be open on a side (shown here) or can completely enclose the melt material 1509 (not shown).

[0595] FIG. 6 shows a flow diagram containing the steps 1601 and 1602 of a process for the preparation of a formed body. In the first step 1601, a quartz glass body is provided, preferably a quartz glass body prepared according to FIG. 100. Such a quartz glass body can be a solid or hollow body quartz glass body. In a second step 1602, a formed body is formed from a solid quartz glass body provided in step 1601.

Test Methods

[0596] a. Fictive Temperature

[0597] The fictive temperature is measured by Raman spectroscopy using the Raman scattering intensity at about 606 cm.sup.1. The procedure and analysis described in the contribution of Pfleiderer et. al.; The UV-induced 210 nm absorption band in fused Silica with different thermal history and stoichiometry; Journal of Non-Crystalline Solids, volume 159 (1993), pages 145-153.

b. OH Content

[0598] The OH content of the glass is measured by infrared spectroscopy. The method of D. M. Dodd & D. M. Fraser Optical Determinations of OH in Fused Silica (J.A.P. 37, 3991 (1966)) is employed. Instead of the device named therein, an FTIR-spectrometer (Fourier transform infrared spectrometer, current System 2000 of Perkin Elmer) is employed. The analysis of the spectra can in principle be performed on either the absorption band at ca. 3670 cm.sup.1 or on the absorption band at ca. 7200 cm.sup.1. The selection of the band is made on the basis that the transmission loss through OH absorption is between 10 and 90%.

c. Oxygen Deficiency Centers (ODCs)

[0599] For the quantitative detection, the ODC(I) absorption is measured at 165 nm by means of a transmission measurement at a probe with thickness between 1-2 mm using a vacuum UV spectrometer, model VUVAS 2000, of McPherson, Inc. (USA).

Then:

[0600]
N=/ [0601] with [0602] N=defect concentration [1/cm.sup.3] [0603] =optical absorption [1/cm, base e] of the ODC(I) band [0604] =effective cross section [cm.sup.2] [0605] wherein the effective cross section is set to =7.510.sup.17 cm.sup.2 (from L. Skuja, Color Centers and Their Transformations in Glassy SiO.sub.2, Lectures of the summer school Photosensitivity in optical Waveguides and glasses, July 13-18 1998, Vitznau, Switzerland).
d. Elemental Analysis

[0606] d-1) Solid samples are crushed. Then, ca. 20 g of the sample is cleaned by introducing it into a HF-resistant vessel fully, covering it with HF and thermally treating at 100 C. for an hour. After cooling, the acid is discarded and the sample cleaned several times with high purity water. Then, the vessel and the sample are dried in the drying cabinet.

[0607] Next, ca. 2 g of the solid sample (crushed material cleaned as above; dusts etc. without pre-treatment) is weighed into an HF resistant extraction vessel and dissolved in 15 ml HF (50 wt.-%). The extraction vessel is closed and thermally treated at 100 C. until the sample is completely dissolved. Then, the extraction vessel is opened and further thermally treated at 100 C., until the solution is completely evaporated. Meanwhile, the extraction vessel is filled 3x with 15 ml of high purity water. 1 ml HNO.sub.3 is introduced into the extraction vessel, in order to dissolve separated impurities and filled up to 15 ml with high purity water. The sample solution is then ready.

[0608] d-2) ICP-MS/ICP-OES Measurement

[0609] Whether OES or MS is employed depends on the expected elemental concentrations. Typically, measurements of MS are lppb, and for OES they are 10 ppb (in each case based on the weighed sample). The measurement of the elemental concentration with the measuring devices is performed according to the stipulations of the device manufacturer (ICP-MS: Agilent 7500ce; ICP-OES: Perkin Elmer 7300 DV) and using certified reference liquids for calibration. The elemental concentrations in the solution (15 ml) measured by the device are then converted based on the original weight of the probe (2 g).

[0610] Note: It is to be kept in mind that the acid, the vessels, the water and the devices must be sufficiently pure in order to measure the elemental concentrations in question. This is checked by extracting a blank sample without quartz glass.

[0611] The following elements are measured in this way: Li, Na, Mg, K, Ca, Fe, Ni, Cr, Hf, Zr, Ti, (Ta), V, Nb, W, Mo, Al.

[0612] d-3) The measurement of samples present as a liquid is carried out as described above, wherein the sample preparation according to step d-1) is skipped. 15 ml of the liquid sample are introduced into the extraction flask. No conversion based on the original sample weight is made.

e. Determination of Density of a Liquid

[0613] For measuring the density of a liquid, a precisely defined volume of the liquid is weighed into a measuring device which is inert to the liquid and its constituents, wherein the empty weight and the filled weight of the vessel are measured. The density is given as the difference between the two weight measurements divided by the volume of the liquid introduced.

f. Fluoride Determination

[0614] 15 g of a quartz glass sample is crushed and cleaned by treating in nitric acid at 70 C. The sample is then washed several times with high purity water and then dried. 2 g of the sample is weighed into a nickel crucible and covered with 10 g Na.sub.2CO.sub.3 and 0.5 g ZnO. The crucible is closed with a Ni-lid and roasted at 1000 C. for an hour. The nickel crucible is then filled with water and boiled up until the melt cake has dissolved entirely. The solution is transferred to a 200 ml measuring flask and filled up to 200 ml with high purity water. After sedimentation of undissolved constituents, 30 ml are taken and transferred to a 100 ml measuring flask, 0.75 ml of glacial acetic acid and 60 ml TISAB are added and filled up with high purity water. The sample solution is transferred to a 150 ml glass beaker.

[0615] The measurement of the fluoride content in the sample solution is performed by means of an ion sensitive (fluoride) electrode, suitable for the expected concentration range, and display device as stipulated by the manufacturer, here a fluoride ion selective electrode and reference electrode F-500 with R503/D connected to a pMX 3000/pH/ION from Wissenschaftlich-Technische Werkstatten GmbH. With the fluoride concentration in the solution, the dilution factor and the sample weight, the fluoride concentration in the quartz glass is calculated.

g. Determination of Chlorine (>=50 ppm)

[0616] 15 g of a quartz glass sample is crushed and cleaned by treating with nitric acid at ca. 70 C. Subsequently, the sample is rinsed several times with high purity water and then dried. 2 g of the sample are then filled into a PTFE-insert for a pressure container, dissolved with 15 ml NaOH (c=10 mol/l), closed with a PTFE lid and placed in the pressure container. It is closed and thermally treated at ca. 155 C. for 24 hours. After cooling, the PTFE insert is removed and the solution is transferred entirely to a 100 ml measuring flask. There, 10 ml HNO.sub.3 (65 wt.-%) and 15 ml acetate buffer and added, allowed to cool and filled to 100 ml with high purity water. The sample solution is transferred to a 150 ml glass beaker. The sample solution has a pH value in the range between 5 and 7.

[0617] The measurement of the chloride content in the sample solution is performed by means of an ion sensitive (Chloride) electrode which is suitable for the expected concentration range, and a display device as stipulated by the manufacturer, here an electrode of type Cl-500 and a reference electrode of type R-503/D attached to a pMX 3000/pH/ION from Wissenschaftlich-Technische Werkstitten GmbH.

h. Chlorine Content (<50 ppm)

[0618] Chlorine content <50 ppm up to 0.1 ppm in quartz glass is measured by neutron activation analysis (NAA). For this, 3 bores, each of 3 mm diameter and 1 cm long are taken from the quartz glass body under investigation. These are given to a research institute for analysis, in this case to the institute for nuclear chemistry of the Johannes-Gutenberg University in Mainz, Germany. In order to exclude contamination of the sample with chlorine, a thorough cleaning of the sample in an HF bath on location directly before the measurement was arranged. Each bore is measured several times. The results and the bores are then sent back by the research institute.

i. Optical Properties

[0619] The transmission of quartz glass samples is measured with the commercial grating- or FTIR-spectrometer from Perkin Elmer (Lambda 900 [190-3000 nm] or System 2000 [1000-5000 nm]). The selection is determined by the required measuring range.

[0620] For measuring the absolute transmission, the sample bodies are polished on parallel planes (surface roughness RMS <0.5 nm) and the surface is cleared off all residues by ultrasound treatment. The sample thickness is 1 cm. In the case of an expected strong transmission loss due to impurities, dopants etc., a thicker or thinner sample can be selected in order to stay within the measuring range of the device. A sample thickness (measuring length) is selected at which only slight artefacts are produced on account of the passage of the radiation through the sample and at the same time a sufficiently detectable effect is measured.

[0621] The measurement of the opacity, the sample is placed in front of an integrating sphere. The opacity is calculated using the measured transmission value T according to the formula: O=1/T=I.sub.0/I.

j. Refractive Index and Distribution of Refractive Index in a Tube or Rod

[0622] The distribution of refractive index of tubes/rods can be characterised by means of a York Technology Ltd. Preform Profiler P102 or P104. For this, the rod is placed lying in the measuring chamber the chamber is closed tight. The measuring chamber is then filled with an immersion oil which has a refractive index at the test wavelength of 633 nm which is very similar to that of the outermost glass layer at 633 nm. The laser beam then goes through the measuring chamber. Behind the measuring chamber (in the direction of the radiation) is mounted a detector which measures the angle of deviation (of the radiation entering the measuring chamber compared to the radiation exiting the measuring chamber). Under the assumption of radial symmetry of the distribution of refractive index of the rod, the diametral distribution of refractive index can be reconstructed by means of an inverse Abel transformation. These calculations are performed by the software of the device manufacturer York.

[0623] The refractive index of a sample is measured with the York Technology Ltd. Preform Profiler P104 analogue to the above description. In the case of isotropic samples, measurement of distribution of refractive index gives only one value, the refractive index.

k. Carbon Content

[0624] The quantitative measurement of the surface carbon content of silicon dioxide granulate and silicon dioxide powder is performed with a carbon analyser RC612 from Leco Corporation, USA, by the complete oxidation of all surface carbon contamination (apart from SiC) with oxygen to obtain carbon dioxide. For this, 4.0 g of a sample are weighed and introduced into the carbon analyser in a quartz glass boat. The sample is bathed in pure oxygen and heated for 180 seconds to 900 C. The CO.sub.2 which forms is measured by the infrared detector of the carbon analyser. Under these measuring conditions, the detection limit lies at <1 ppm (weight-ppm) carbon.

[0625] A quartz glass boat which is suitable for this analysis using the above named carbon analyser is obtainable as a consumable for the LECO analyser with LECO number 781-335 on the laboratory supplies market, in the present case from Deslis Laborhandel, Flurstrae 21, D-40235 Dusseldorf (Germany), Deslis-No. LQ-130XL. Such a boat has width/length/height dimensions of ca. 25 mm/60 mm/15 mm. The quartz glass boat is filled up to half its height with sample material. For silicon dioxide powder, a sample weight of 1.0 g sample material can be reached. The lower detection limit is then <1 weight ppm carbon. In the same boat, a sample weight of 4 g of a silicon dioxide granulate is reached for the same filling height (mean particle size in the range from 100 to 500 m). The lower detection limit is then about 0.1 weight ppm carbon. The lower detection limit is reached when the measurement surface integral of the sample is not greater than three times the measurement surface integral of an empty sample (empty sample=the above process but with an empty quartz glass boat).

l. Curl Parameter

[0626] The curl parameter (also called: Fibre Curl) is measured according to DIN EN 60793-1-34:2007-01 (German version of the standard IEC 60793-1-34:2006). The measurement is made according to the method described in Annex A in the sections A.2.1, A.3.2 and A.4.1 (extrema technique).

m. Attenuation

[0627] The attenuation is measured according to DIN EN 60793-1-40:2001 (German version of the standard IEC 60793-1-40:2001). The measurement is made according to the method described in the annex (cut-back method) at a wavelength of =1550 nm.

n. Viscosity of the Slurry

[0628] The slurry is set to a concentration of 30 weight-% solids content with demineralised water (Direct-Q 3UV, Millipore, Water quality: 18.2 Mcm). The viscosity is then measured with a MCR102 from Anton-Paar. For this, the viscosity is measured at 5 rpm. The measurement is made at a temperature of 23 C. and an air pressure of 1013 hPa.

o. Thixotropy

[0629] The concentration of the slurry is set to a concentration of 30 weight-% of solids with demineralised water (Direct-Q 3UV, Millipore, water quality: 18.2 Mcm). The thixotropy is then measured with an MCR102 from Anton-Paar with a cone and plate arrangement. The viscosity is measured at 5 rpm and at 50 rpm. The quotient of the first and the second value gives the thixotropic index. The measurement is made at a temperature of 23 C.

p. Zeta Potential of the Slurry

[0630] For zeta potential measurements, a zeta potential cell (Flow Cell, Beckman Coulter) is employed. The sample is dissolved in demineralised water (Direct-Q 3UV, Millipore, water quality: 18.2 Mcm) to obtain a 20 mL solution with a concentration of 1 g/L. The pH is set to 7 through addition of HNO.sub.3 solutions with concentrations of 0.1 mol/L and 1 mol/L and an NaOH solution with a concentration of 0.1 mol/L. The measurement is made at a temperature of 23 C.

q. Isoelectric Point of the Slurry

[0631] The isoelectric point, a zeta potential measurement cell (Flow Cell, Beckman Coulter) and an auto titrator (DelsaNano AT, Beckman Coulter) is employed. The sample is dissolved in demineralised water (Direct-Q 3UV, Millipore, water quality: 18.2 Mcm) to obtain a 20 mL solution with a concentration of 1 g/L. The pH is varied by adding HNO.sub.3 solutions with concentrations of 0.1 mol/L and 1 mol/L and an NaOH solution with a concentration of 0.1 mol/L. The isoelectric point is the pH value at which the zeta potential is equal to 0. The measurement is made at a temperature of 23 C.

r. pH Value of the Slurry

[0632] The pH value of the slurry is measured using a WTW 3210 from Wissenschaftlich-Technische-Werkstitten GmbH. The pH 3210 Set 3 from WTW is employed as electrode. The measurement is made at a temperature of 23 C.

s. Solids Content

[0633] A weighed portion m.sub.1 of a sample is heated for 4 hours to 500 C. reweighed after cooling (m.sub.2). The solids content w is given as m.sub.2/m.sub.1*100 [Wt. %].

t. Bulk Density

[0634] The bulk density is measured according to the standard DIN ISO 697:1984-01 with an SMG 697 from Powtec.

[0635] The bulk material (silicon dioxide powder or granulate) does not clump.

u. Tamped Density (Granulate)

[0636] The tamped density is measured according to the standard DIN ISO 787:1995-10.

v. Measurement of the Pore Size Distribution

[0637] The pore size distribution is measured according to DIN 66133 (with a surface tension of 480 mN/m and a contact angle of 140). For the measurement of pore sizes smaller than 3.7 nm, the Pascal 400 from Porotec is used. For the measurement of pore sizes from 3.7 nm to 100 m, the Pascal 140 from Porotec is used. The sample is subjected to a pressure treatment prior to the measurement. For this a manual hydraulic press is used (Order-No. 15011 from Specac Ltd., River House, 97 Cray Avenue, Orpington, Kent BR5 4HE, U.K.). 250 mg of sample material is weighed into a pellet die with 13 mm inner diameter from Specac Ltd. and loaded with 1 t, as per the display. This load is maintained for 5 s and readjusted if necessary. The load on the sample is then released and the sample is dried for 4 h at 1052 C. in a recirculating air drying cabinet.

[0638] The sample is weighed into the penetrometer of type 10 with an accuracy of 0.001 g and in order to give a good reproducibility of the measurement it is selected such that the stem volume used, i.e. the percentage of potentially used Hg volume for filling the penetrometer is in the range between 20% to 40% of the total Hg volume. The penetrometer is then slowly evacuated to 50 m Hg and left at this pressure for 5 min. The following parameters are provided directly by the software of the measuring device: total pore volume, total pore surface area (assuming cylindrical pores), average pore radius, modal pore radius (most frequently occurring pore radius), peak n. 2 pore radius (m).

w. Primary Particle Size

[0639] The primary particle size is measured using a scanning electron microscope (SEM) model Zeiss Ultra 55. The sample is suspended in demineralised water (Direct-Q 3UV, Millipore, water quality: 18.2 Mcm), to obtain an extremely dilute suspension. The suspension is treated for 1 min with the ultrasound probe (UW 2070, Bandelin electronic, 70 W, 20 kHz) and then applied to a carbon adhesive pad.

x. Mean Particle Size in Suspension

[0640] The mean particle size in suspension is measured using a Mastersizer 2000, available from Malvern Instruments Ltd., UK, according to the user manual, using the laser deflection method. The sample is suspended in demineralised water (Direct-Q 3UV, Millipore, water quality: 18.2 Mcm) to obtain a 20 mL suspension with a concentration of 1 g/L. The suspension is treated with the ultrasound probe (UW 2070, Bandelin electronic, 70 W, 20 kHz) for 1 min.

y. Particle Size and Core Size of the Solid

[0641] The particle size and core size of the solid are measured using a Camsizer XT, available from Retsch Technology GmbH, Germany according to the user manual. The software gives the D10, D50 and D90 values for a sample.

z. BET Measurement

[0642] For the measurement of the specific surface area, the static volumetric BET method according to DIN ISO 9277:2010 is used. For the BET measurement, a NOVA 3000 or a Quadrasorb (available from Quantachrome), which operate according to the SMART method (Sorption Method with Adaptive dosing Rate), is used. The micropore analysis is performed using the t-plot process (p/p0=0.1-0.3) and the mesopore analysis is performed using the MBET process (p/p0=0.0-0.3). As reference material, the standards alumina SARM-13 and SARM-214, available from Quantachrome are used. The tare weight of the measuring cell (clean and dry) is weighed. The type of measuring cell is selected such that the sample material which is introduced and the filler rod fill the measuring cell as much as possible and the dead space is reduced to a minimum. The sample material is introduced into the measuring cell. The amount of sample material is selected so that the expected value of the measurement value corresponds to 10-20 m.sup.2/g. The measuring cells are fixed in the baking positions of the BET measuring device (without filler rod) and evacuated to <200 mbar. The speed of the evacuation is set so that no material leaks from the measuring cell. Baking is performed in this state at 200 C. for 1 h. After cooling, the measuring cell filled with the sample is weighed (raw value). The tare weight is then subtracted from the raw value of the weight=nett weight=weight of the sample. The filling rod is then introduced into the measuring cell this is again fixed at the measuring location of the BET measuring device. Prior to the start of the measurement, the sample identifications and the sample weights are entered into the software. The measurement is started. The saturation pressure of nitrogen gas (N2 4.0) is measured. The measuring cell is evacuated and cooled down to 77 K using a nitrogen bath. The dead space is measured using helium gas (He 4.6). The measuring cell is evacuated again. A multi point analysis with at least 5 measuring points is performed. N2 4.0 is used as absorptive. The specific surface area is given in m.sup.2/g.

za. Viscosity of Glass Bodies

[0643] The viscosity of the glass is measured using the beam bending viscosimeter of type 401from TA Instruments with the manufacturer's software WinTA (current version 9.0) in Windows 10 according to the DIN ISO 7884-4:1998-02 standard. The support width between the supports is 45 mm. Sample rods with rectangular cross section are cut from regions of homogeneous material (top and bottom sides of the sample have a finish of at least 1000 grain). The sample surfaces after processing have a grain size=9 m & RA=0.15 m. The sample rods have the following dimensions: length=50 mm, width=5 mm & height=3 mm (ordered: length, width, height, as in the standards document). Three samples are measured and the mean is calculated. The sample temperature is measured using a thermocouple tight against the sample surface. The following parameters are used: heating rate=25 K up to a maximum of 1500 C., loading weight=100 g, maximum bending=3000 m (deviation from the standards document).

zc. Residual Moisture (Water Content)

[0644] The measurement of the residual moisture of a sample of silicon dioxide granulate is performed using a Moisture Analyzer HX204 from Mettler Toledo. The device functions using the principle of thermogravimetry. The HX204 is equipped with a halogen light source as heating element. The drying temperature is 220 C. The starting weight of the sample is 10 g10%. The Standard measuring method is selected. The drying is carried out until the weight change reaches not more than 1 mg/140 s. The residual moisture is given as the difference between the initial weight of the sample and the final weight of the sample, divided by the initial weight of the sample. The measurement of residual moisture of silicon dioxide powder is performed according to DIN EN ISO 787-2:1995 (2 h, 105 C.).

Examples

[0645] The example is further illustrated in the following through examples. The invention is not limited by the examples.

A. 1. Preparation of Silicon Dioxide Powder (OMCTS Route)

[0646] An aerosol formed by atomising a siloxane with air (A) is introduced under pressure into a flame which is formed by igniting a mixture of oxygen enriched air (B) and hydrogen. Furthermore, a gas flow (C) surrounding the flame is introduced and the process mixture is then cooled with process gas. The product is separated off at a filter. The process parameters are given in table 1 and the specifications of the resulting product are given in table 2. Experimental data for this example are indicated with A1-x.

2. Modification 1: Increased Carbon Content

[0647] A process was carried out as described in A.1., but the burning of the siloxane was performed in such a way that an amount of carbon was also formed. Experimental data for this example are indicated with A2-x.

TABLE-US-00003 TABLE 1 Example A1-1 A2-1 A2-2 Aerosol formation Siloxane OMCTS* OMCTS* OMCTS* Feed rate kg/h 10 10 10 (kmol/h) (0.0337) (0.0337) (0.0337) Feed rate of air (A) Nm.sup.3/h 14 10 12 Pressure barO 1.2 1.2 1.2 Burner feed Oxygen enriched air (B) Nm.sup.3/h 69 65 68 O.sub.2-content Vol. % 32 30 32 total O.sub.2 feed rate Nm.sup.3/h 25.3 21.6 24.3 kmol/h 1.130 0.964 1.083 Hydrogen feed rate Nm.sup.3/h 27 27 12 kmol/h 1.205 1.205 0.536 Feed Carbon compound Material methane Amount Nm.sup.3/h 5.5 Air flow (C) Nm.sup.3/h 60 60 60 Stoichiometric ratio V 2.099 1.789 2.011 X 0.938 0.80 2.023 Y 0.991 0.845 0.835 V = molar ratio of employed O.sub.2/O.sub.2 required for completed oxidation of the siloxane; X = molar ratio O.sub.2/H.sub.2; Y = (molar ratio of employed O.sub.2/O.sub.2 required for stoichiometric conversion OMCTS + fuel gas); barO = over pressure; *OMCTS = Octamethylcyclotetrasiloxane.

TABLE-US-00004 TABLE 2 Example A1-1 A2-1 A2-2 BET m.sup.2/g 30 33 34 Bulk density g/ml 0.114 + 0.011 0.105 + 0.011 0.103 + 0.011 tamped density g/ml 0.192 + 0.015 0.178 + 0.015 0.175 + 0.015 Primary particle size nm 94 82 78 particle size distribution D10 m 3.978 0.380 5.137 0.520 4.973 0.455 particle size distribution D50 m 9.383 0.686 9.561 0.690 9.423 0.662 particle size distribution D90 m 25.622 1.387 17.362 0.921 18.722 1.218 C content ppm 34 4 73 6 80 6 Cl content ppm <60 <60 <60 Al content ppb 20 20 20 Total content of metals other than Al ppb <700 <700 <700 residual moisture content wt.-% 0.02-1.0 0.02-1.0 0.02-1.0 pH value in water 4% (IEP) 4.8 4.6 4.5 Viscosity at 5 rpm, aqueous mPas 753 1262 1380 suspension 30 Wt-%, 23 C. Alkali earth metal content ppb 538 487 472
B. 1. Preparation of Silicon Dioxide Powder (Silicon Source: SiCl.sub.4) A portion of silicon tetrachloride (SiCl.sub.4) is evaporated at a temperature T and introduced with a pressure P into a flame of a burner which is formed by igniting a mixture of oxygen enriched air and hydrogen. The mean normalised gas flow to the outlet is held constant. The process mixture is then cooled with process gas. The product was separated off at a filter. The process parameters are given in table 3 and the specifications of the resulting products are given in table 4. They are indicated with B1-x.

2. Modification: Increased Carbon Content

[0648] A process was carried out as described in B.1., but the burning of the silicon tetrachloride was performed such that an amount of carbon was also formed. Experimental data for this example are indicated with B2-x.

TABLE-US-00005 TABLE 3 Example B1-1 B2-1 Aerosol formation Silicon tetrachloride feed kg/h 50 50 (kmol) (0.294) (0.294) Temperature T C. 90 90 Pressure p barO 1.2 1.2 Burner feed Oxygen enriched air, Nm.sup.3/h 145 115 O.sub.2 content therein Vol. % 45 30 Feed Carbon compound Material methane Amount Nm.sup.3/h 2.0 Hydrogen feed Nm.sup.3/h 115 60 kmol/h 5.13 2.678 Stoichiometric ratios X 0.567 0.575 Y 0.946 0.85 X = as molar ratio O.sub.2/H.sub.2; Y = molar ratio of employed O.sub.2/O.sub.2 required for stoichiometric reaction with SiCl.sub.4 + H.sub.2 + CH.sub.4); barO = Over pressure.

TABLE-US-00006 TABLE 4 Example B1-1 B2-1 BET m.sup.2/g 49 47 Bulk density g/ml 0.07 0.01 0.06 0.01 tamped density g/ml 0.11 0.01 0.10 0.01 Primary particle size nm 48 43 particle size distribution D10 m 5.0 0.5 4.5 0.5 particle size distribution D50 m 9.3 0.6 8.7 0.6 particle size distribution D90 m 16.4 0.5 15.8 0.7 C content ppm <4 76 Cl content ppm 280 330 Al content ppb 20 20 Total of the concentrations of ppb <1300 <1300 Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr residual moisture content wt.-% 0.02-1.0 0.02-1.0 pH value in water 4% (IEP) pH 3.8 3.8 Viscosity at 5 rpm, aqueous mPas 5653 6012 suspension 30 Wt-%, 23 C. Alkali earth metal content ppb 550 342

C. Steam Treatment

[0649] A particle flow of silicon dioxide powder is introduced via the top of a standing column. Steam at a temperature (A) and air are fed via the bottom of the column. The column is maintained at a temperature (B) at the top of the column and at a second temperature (C) at the bottom of the column by an internally situated heater. After leaving the column (holding time (D)) the silicon dioxide powder has in particular the properties shown in Table 6. The process parameters are given in Table 5.

TABLE-US-00007 TABLE 5 Example C-1 C-2 Educt: Product of B1-1 B2-1 Educt feed kg/h 100 100 Steam feed kg/h 5 5 Steam temperature (A) C. 120 120 Air feed Nm.sup.3/h 4.5 4.5 Column height m 2 2 Inner diameter mm 600 600 T (B) C. 260 260 T (C) C. 425 425 Holding time (D) silicon s 10 10 dioxide powder

TABLE-US-00008 TABLE 6 Example C-1 C-2 pH value in water 4% (IEP) 4.6 4.6 Cl content ppm <60 <60 C content ppm <4 36 Viscosity at 5 rpm, aqueous mPas 1523 1478 suspension 30 Wt-%, 23 C.

[0650] The silicon dioxide powders obtained in the examples C-1 and C-2 each have a low chlorine content as well as a moderate pH value in suspension. The carbon content of example C-2 is higher than for C-1.

D. Treatment with a Neutralising Agent

[0651] A particle flow of silicon dioxide powder is introduced via the top of a standing column. A neutralising agent and air are fed via the bottom of the column. The column is maintained at a temperature (B) at the top of the column and at a second temperature (C) at the bottom of the column by an internally situated heater. After leaving the column (holding time (D)) the silicon dioxide powder has in particular the properties shown in table 8. The process parameters are given in table 7.

TABLE-US-00009 TABLE 7 Example D-1 Educt: Product from B1-1 Educt feed kg/h 100 Neutralising agent Ammonia Neutralising agent feed kg/h 1.5 Neutralising agent Obtainable from Air Liquide: specifications Ammonia N38, purity 99.98 Vol. % Air feed Nm.sup.3/h 4.5 Column height m 2 inner diameter mm 600 T (B) C. 200 T (C) C. 250 Holding time (D) of s 10 silicon dioxide powder

TABLE-US-00010 TABLE 8 Example D-1 pH value in water 4% (IEP) 4.8 Cl content ppm 210 C content ppm <4 Viscosity at 5 rpm, aqueous mPas 821 suspension 30 Wt-%, 23 C.
E. 1. Preparation of Silicon Dioxide Granulate from Silicon Dioxide Powder

[0652] A silicon dioxide powder is dispersed in fully desalinated water. For this, an intensive mixer of type R from the Gustav Eirich machine factory is used. The resulting suspensions are pumped with a membrane pump and thereby pressurised and converted into droplets by a nozzle. These are dried in a spray tower and collect on the floor of the tower. The process parameters are given in Table 9 and the properties of the obtained granulate in Table 10. Experimental data for this example are indicated with E1-x. In E2-21 to E2-23, aluminium oxide is introduced as additive. In E2-31 and E2-32

2. Modification: Increased Carbon Content

[0653] The process is analogous to that described in E.1. Additionally, carbon powder is dispersed into the suspension as additive. Experimental data for these examples are indicated with E2-x.

TABLE-US-00011 TABLE 9 Example E1-1 E1-2 E1-3 E1-4 E1-5 E2-1 E2-21 E2-22 E2-23 Educt = Product A1-1 A2-1 B1-1 C-1 C-2 A1-1 A1-1 A1-1 A1-1 from Amount of educt Kg 10 10 10 10 10 10 1000 1000 1000 Additive Material C** Al.sub.2O.sub.3.sup.+ Al.sub.2O.sub.3.sup.+ Al.sub.2O.sub.3.sup.+ Max. Particle 75 m 65 m 65 m 65 m size Amount 1 g.sup. 0.32 g.sup. 0.47 g 0.94 g Water Rating* FD FD FD FD FD FD FD FD FD Litre 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 Dispersion Solids content Wt. % 65 65 65 65 65 65 65 65 65 Nozzle Diameter mm 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 Temperature C. 25 25 25 25 25 25 25 25 25 Pressure Bar 16 16 16 16 16 16 16 16 16 Installation m 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 height Spray tower Height m 18.20 18.20 18.20 18.20 18.20 18.20 18.20 18.20 18.20 Inner diameter m 6.30 6.30 6.30 6.30 6.30 6.30 6.30 6.30 6.30 T (introduced C. 380 380 380 380 380 380 380 380 380 gas) T (exhaust) C. 110 110 110 110 110 110 110 110 110 Air flow m.sup.3/h 6500 6500 6500 6500 6500 6500 6500 6500 6500 Installation height = distance between nozzle and lowest point of the spray tower interior in the direction of gravity. *FD = fully desalinated, conductance 0.1 S; **C 006011: Graphite powder, max. particle size: 75 m, high purity (available from Goodfellow GmbH, Bad Nauheim (Germany). .sup.+Aeroxide Alu 65: highly dispersed pyrogenic aluminium oxide, particle size 65 m (Evonik Industries AG, Essen (Germany)

TABLE-US-00012 TABLE 10 Example E1-1 E1-2 E1-3 E1-4 E1-5 E2-1 E2-21 E2-22 E2-23 BET m.sup.2/g 30 33 49 49 47 28 32 30 32 Bulk density g/ml 0.8 0.1 0.8 0.1 0.8 0.1 0.8 0.1 0.8 0.1 0.8 0.1 0.8 0.1 0.8 0.1 0.8 0.1 tamped density g/ml 0.9 0.1 0.9 0.1 0.9 0.1 0.9 0.1 0.9 0.1 0.9 0.1 0.9 0.1 0.9 0.1 0.9 0.1 mean particle m 255 255 255 255 255 255 255 255 255 size particle size m 110 110 110 110 110 110 110 110 110 distribution D10 particle size m 222 222 222 222 222 222 222 222 222 distribution D50 particle size m 390 390 390 390 390 390 390 390 390 distribution D90 SPHT3 Dimless 0.64-0.98 0.64-0.98 0.64-0.98 0.64-0.98 0.64-0.98 0.64-0.98 0.64-0.98 0.64-0.98 0.64-0.98 Aspect ratio Dimless 0.64-0.94 0.64-0.94 0.64-0.94 0.64-0.94 0.64-0.94 0.64-0.94 0.64-0.94 0.64-0.94 0.64-0.94 W/L (width to length) C content ppm <4 39 <4 <4 32 100 <4 <4 <4 Cl content ppm <60 <60 280 <60 <60 <60 <60 <60 <60 Al content ppb 20 20 20 20 20 20 190 270 520 Total of the ppb <700 <700 <1300 <1300 <1300 <700 <700 <700 <700 concentrations of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr residual moisture wt.-% <3 <3 <3 <3 <3 <3 <3 <3 <3 content Alkaline earth ppb 538 487 550 550 342 538 517 490 541 metal content pore volume ml/g 0.33 0.33 0.45 0.45 0.45 0.33 0.33 0.33 0.33 angle of repose 26 26 26 26 26 26 26 26 26

[0654] The granulates are all open pored, have a uniform and spherical shape (all by microscopic investigation). They tend not to stick together or cement.

F. Cleaning of Silicon Dioxide Granulate

[0655] Silicon dioxide granulate is first optionally treated with oxygen at a temperature T1 in a rotary kiln. Subsequently, the silicon dioxide granulate is treated with a co-flow of chlorine-containing components, wherein the temperature is raised to a temperature T2. The process parameters are given in Table 11 and the properties of the obtained treated granulate in Table 12.

TABLE-US-00013 TABLE 11 Example F1-1 F1-2 F2-1 F2-21 F2-22 F2-23 Educt = Product from E1-1 E1-2 E2-1 E2-21 E2-22 E2-23 Rotary kiln.sup.1) length cm 200 200 200 200 Inner diameter cm 10 10 10 10 Throughput kg/h 2 2 2 2 Rotational speed rpm 2 2 2 2 T1 C. 1100 NA NA 1100 1100 1100 Atmosphere O.sub.2 pur NA NA O.sub.2 pure O.sub.2 pure O.sub.2 pure Reactant O.sub.2 NA NA O.sub.2 O.sub.2 O.sub.2 Feed 300 l/h NA NA 300 l/h 300 l/h 300 l/h residual moisture content wt.-% <1 <3 <3 <1 <1 <1 T2 C. 1100 1100 1100 1100 1100 1100 Co-flow Component 1: HCl l/h 50 50 50 50 50 50 Component 2: Cl2 l/h 0 15 15 0 0 0 Component 3: N2 l/h 50 35 35 50 50 50 Total co-flow l/h 100 100 100 100 100 100 .sup.1)For the rotary kilns, the throughput is selected as the control variable. That means that during operation the mass flow exiting from the rotary kiln is weighed and then the rotational speed and/or the inclination of the rotary kiln is adapted accordingly. For example, an increase in the throughput can be achieved by a) increasing the rotational speed, or b) increasing the inclination of the rotary kiln away from horizontal, or a combination of a) and b).

TABLE-US-00014 TABLE 12 Example F1-1 F1-2 F2-1 F2-21 F2-22 F2-23 BET m.sup.2/g 25 27 23 26 26 23 C content ppm <4 <4 <4 <4 <4 <4 Cl content ppm 100-200 100-200 100-200 100-200 100-200 100-200 Al content ppb 20 20 20 190 270 520 Pore volume mm.sup.3/g 650 650 650 650 650 650 Total of the concentrations of ppb <200 <200 <200 <200 <200 <200 Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr Alkaline earth metal content ppb 115 55 35 124 110 116 tamped density g/cm.sup.3 0.95 0.05 0.95 0.05 0.95 0.05 0.95 0.05 0.95 0.05 0.95 0.05

[0656] In the case of F1-2 and F2-1, the granulates after the cleaning step show a significantly reduced carbon content (like low carbon granulates, e.g. F1-1) and a significantly reduced content of alkaline earth metals. SiC formation was not observed.

G. Making a Glass Body

[0657] Silicon dioxide granulate according to line 2 of Table 13 was used as raw material. A graphite mould was prepared with an annular hollow space and an outer diameter of the formed body of d.sub.a, an inner diameter of the formed body of d.sub.1 and a length l. A high-purity graphite foil having a thickness of 1 mm was applied on to the inner wall of the outer formed body and a graphite foil composed of the same high-purity graphite having a thickness of 1 mm was applied on to the outer wall of the inner formed body. A high-purity graphite web composed of a high-purity graphite having a bulk density of 1.2 g/cm.sup.3 and a thickness of 0.4 mm was applied on to the base of the annular hollow space of the mould (in the case of G-2: cylindrical hollow space). The high-purity graphite mould provided with the graphite foil was filled with the silicon dioxide granulate. The filled graphite mould was introduced into an oven to which a vacuum was applied. The filled silicon dioxide granulate was brought from the temperature T1 at a rate of heating R1 to a temperature T2 and held at this temperature for the period t2. Then, it was warmed at the rate of heating R2 to T3, and then, without any further tempering, brought at the rate of heating R3 to the temperature T4, and further at the rate of heating R4 to the temperature T5 and held at this temperature for the period t5. During the last 240 minutes, a pressure of 1.6*10.sup.6 Pa nitrogen is applied to the oven. Afterwards, the mould is gradually cooled. When a temperature of 1050 C. was reached, the mould was held at this temperature for a period of 240 min. Subsequently, it was further cooled gradually to T6. The process parameters are compiled in Table 13, the properties of the quartz glass body that was made in Table 14. Gradual cooling means that the mould is left to stand in the switched off oven without any cooling measures, i.e. is cooled only by emission of heat to the environment.

TABLE-US-00015 TABLE 13 Example G1-1 G1-2 G2-1 G2-21 G2-22 G2-23 Educt = F1-1 F1-2 F2-1 F2-21 F2-22 F2-23 Product from T1 C. 25 25 25 25 25 25 R1 C./min +2 +2 +2 +2 +2 +2 T2 C. 400 400 400 400 400 400 t2 min 60 60 60 60 60 60 R2 C./min +3 +3 +3 +3 +3 +3 T3 C. 1000 1000 1000 1000 1000 1000 R3 C./min +0.2 +0.2 +0.2 +0.2 +0.2 +0.2 T4 C. 1350 1350 1350 1350 1350 1350 R4 C./min +2 +2 +2 +2 +2 +2 T5 C. 1750 1750 1750 1750 1750 1750 t5 min 720 720 720 720 720 720 T6 C. 25 25 25 25 C. 25 C. 25 C.

TABLE-US-00016 TABLE 14 Example G1-1 G1-2 G2-1 G2-21 G2-22 G2-23 Length (quartz glass mm 2000 1000 2000 2000 2000 2000 body) Outer diameter (quartz mm 260 560 260 260 260 260 glass body) Inner diameter (quartz mm 45 45 45 45 45 glass body) (solid) OH content* ppm 0.3 0.2 0.4 0.2 0.4 0.2 0.3 0.2 0.3 0.2 0.3 0.2 C content ppm <4 <4 <4 <4 <4 <4 Cl content* ppm <60 <60 <60 <60 <60 <60 Al content* ppb 14 5 13 5 12 5 185 5 280 5 510 5 ODC content /cm3 0.8 * 10.sup.15 1.7 * 10.sup.15 1.1 * 10.sup.15x 0.8 * 10.sup.15 0.8 * 10.sup.15 0.8 * 10.sup.15 Sum of concentrations ppb 153 62 171 160 166 172 of Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr Refractive index homogeneity ppm 30 30 30 30 30 30 Fictive temperature C. 1109 1137 1148 1120 1113 1244 Viscosity Lg (/dpas) @1250 C. 12.6 12.4 12.7 12.6 12.6 12.7 @1300 C. 11.8 11.8 11.8 11.8 11.8 11.8 @1350 C. 11.1 11.1 11.1 11.1 11.1 11.2 data are the standard deviation All glass bodies show very good values for OH, catbon and aluminium content

H. Preparation of a Reactor

[0658] The quartz glass body produced in example G2-1 above is formed into a bell by glass blowing. Together with a lid (also composed of quartz glass, comprising feed-throughs), this forms a reaction chamber into which silicon wafers for semiconductor fabrication are introduced and then subjected to certain processes. The reaction chamber made out of the quartz glass prepared according to Example G had a significantly longer operating time (under comparable temperature conditions) than a conventional one. Moreover, better dimensional stability at high temperatures was observed.

J. Preparation of a Large Tube

[0659] The glass bodies from example G1-1 and G2-x were shaped in the warm in two steps at a temperature of 2100 C. Variations in the material homogeneity lead in such a treatment to variations in the geometry of the shaped glass body. The general procedure for such a two stage shaping step is known and for example is described in DE 10 2013 107 434 A1, paragraph [0051]-[0065]. The glass body from example G1-1 and G2-x is referred to there as a hollow cylinder. The properties of the glass body shaped in a first step from example J1-1 and J2-x are presented in table 17, and the properties after the second shaping step in table 18.

TABLE-US-00017 TABLE 17 Example J1-1 J2-21 J2-22 J2-23 Material = Product from G1-1 G2-21 G2-22 G2-23 1st shaping step: Intermediate cylinder Outer diameter mm 320 320 320 320 Wall thickness 15 15 15 15 Length 6200 6200 6200 6200 Al content ppb 14 5 185 5 280 5 510 5

TABLE-US-00018 TABLE 18 Example K1-1 K2-21 K2-22 K2-23 Material = Product from J1-1 J2-21 J2-22 J2-23 2nd Shaping step: Intermediate cylinder Outer diameter mm 960 960 960 960 Wall thickness 15 15 15 15 Length 2980 2980 2980 2980 Al content ppb 14 5 185 5 280 5 510 5 Wall thickness variation mm/m 0.31 0.39 0.56 1.1

[0660] The smaller the variation of the wall thickness, the better.

[0661] Measurement of the variation of the wall thickness: The sample body (Glass tube) is measured on a glass rotation bench. For this the sample body does not rotate. Parallel to the length axis of the sample body, an optical measuring head is run along the sample body and the wall thickness is recorded continuously as the separation of the measuring head from the outer surface of the sample body and captured as data. For the measuring head, a CHRocodile M4 from the company Precitec High Resolution was employed.