U.S. patent number RE30,883 [Application Number 06/121,078] was granted by the patent office on 1982-03-16 for method of producing synthetic quartz glass.
This patent grant is currently assigned to Heraeus Quarzscmelze GmbH. Invention is credited to Albert Muhlich, Karlheinz Rau, Fritz Simmat, Norbert Treber.
United States Patent |
RE30,883 |
Rau , et al. |
March 16, 1982 |
**Please see images for:
( Certificate of Correction ) ** |
Method of producing synthetic quartz glass
Abstract
An improvement in a method for producing a synthetic hydroxyl
ion-free quartz glass wherein a hydrogen free silicon compound is
heated in a hydrogen-free gas stream while the gas stream is passed
through an induction coupled plasma burner, the gas stream
containing elemental and/or bound oxygen and the oxidation product
is deposited on a refractory support as a vitreous mass, the
improvement lying in including in the gas stream a gaseous
hydrogen-free, thermally decomposable compound which yields
fluorine in an amount of at least 500 gms. per kilogram of silica
to be produced; an apparatus for producing a synthetic OH ion-free
quartz glass comprising an induction coupled plasma burner which
burner has disposed thereabout 3 concentric quartz glass tubes
disposed in stepped configuration of which the outermost tube is
the longest and the innermost tube is the shortest. The apparatus
includes means for passing through the innermost tube a
hydrogen-free gas stream containing elemental oxygen and/or bound
oxygen together with a gaseous hydrogen free thermally decomposable
compound which yields fluorine. The apparatus further contains
means for passing a separating gas such as oxygen through the space
defined by the innermost tube and the middle tube and the middle
tube and the outermost tube.
Inventors: |
Rau; Karlheinz (Hanau,
DE), Simmat; Fritz (Gelnhausen, DE),
Muhlich; Albert (Frankfurt, DE), Treber; Norbert
(Kriftel, DE) |
Assignee: |
Heraeus Quarzscmelze GmbH
(Hanau, DE)
|
Family
ID: |
5954072 |
Appl.
No.: |
06/121,078 |
Filed: |
February 13, 1980 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
713541 |
Aug 11, 1976 |
|
|
|
Reissue of: |
874965 |
Feb 3, 1978 |
04162908 |
Jul 31, 1979 |
|
|
Foreign Application Priority Data
|
|
|
|
|
Aug 16, 1975 [DE] |
|
|
2536457 |
Aug 16, 1975 [DE] |
|
|
2536572 |
|
Current U.S.
Class: |
65/60.51;
385/123; 427/167; 427/452; 65/397 |
Current CPC
Class: |
C03B
37/01413 (20130101); C03B 37/01426 (20130101); C03B
37/01823 (20130101); C03C 3/06 (20130101); C03B
2201/075 (20130101); C03B 2207/85 (20130101); C03C
2201/12 (20130101); C03C 2203/40 (20130101); C03B
2201/12 (20130101) |
Current International
Class: |
C03B
37/018 (20060101); C03B 37/014 (20060101); C03C
3/06 (20060101); C03C 017/00 (); C03C 017/02 ();
C03C 025/02 () |
Field of
Search: |
;65/3A,18,3R,6D,32,157,111 ;427/167,34 ;350/96.30 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2247307 |
|
Mar 1974 |
|
DE |
|
2253723 |
|
Jul 1975 |
|
FR |
|
5156641 |
|
Nov 1974 |
|
JP |
|
Primary Examiner: Lindsay, Jr.; Robert L.
Attorney, Agent or Firm: Sprung, Felfe, Horn, Lynch &
Kramer
Parent Case Text
This is a continuation of application Ser. No. 713,541, filed Aug.
11, 1976 and now abandoned.
Claims
What is claimed is:
1. A method for forming a coating of a fluorine containing
synthetic OH ion-free quartz glass on a refractory support which
comprises passing a hydrogen-free silicon compound, gaseous oxygen
and vaporous CCl.sub.2 F.sub.2, CClF.sub.3 or CF.sub.4 in a
hydrogen free gas stream through an induction coupled plasma burner
whereby said hydrogen-free silicon compound reacts with said oxygen
to form synthetic OH ion-free quartz glass, the amount of said
CCl.sub.2 F.sub.2, CClF.sub.3 or CF.sub.4, passed through said
burner, being sufficient to yield .[.a.]. fluorine .[.content in
the quartz glass.]. in an amount of at least 500 grams per kg of
quartz to be produced whereby there is formed a fluorine-doped
synthetic OH ion-free quartz glass and depositing said
fluorine-doped synthetic OH ion-free quartz glass as a coating on a
refractory support.
2. A method according to claim 1 wherein said refractory support is
quartz glass having a rod shape and said synthetic OH ion-free
quartz glass formed by reaction of said hydrogen-free silicon
compound and said oxygen is deposited thereon, the refractive index
of the refractory support being increased by refractive index
raising metal ions, the refractive index of said support decreasing
with the distance from its axes.
3. A process according to claim 1 wherein a sufficient amount of
fluorine is passed through said plasma burner together with said
hydrogen-free silicon compound and elemental and/or bound oxygen,
that the fluorine containing synthetic OH ion-free quartz glass has
a refractory index n.sub.D of 1.457 to 1.435.
4. A method according to claim 1 wherein said refractory support is
in the form of a rod shape and the resultant synthetic OH ion-free
quartz glass is deposited in the form of a sleeve on said
rod-shaped support.
5. A method according to claim 1 wherein CCl.sub.2 F.sub.2 is
admixed in vapor form with said oxygen.
6. A method according to claim 1 wherein said CClF.sub.3 is admixed
in vapor form with said oxygen.
7. A method according to claim 1 wherein said CF.sub.4 is admixed
in vapor form with said oxygen.
8. A method according to claim 1 wherein the amount of said
CCl.sub.2 F.sub.2, CClF.sub.3 or CF.sub.4 is increased as the
synthetic OH ion-free quartz glass increases in thickness.
9. A method according to claim 1 wherein said hydrogen-free silicon
compound is selected from the group consisting of SiCl.sub.4,
SiCl.sub.3 F, SiCl.sub.2 F.sub.2 and SiClF.sub.3.
10. A method according to claim 9 wherein said vaporous CCl.sub.2
F.sub.2, CClF.sub.3 or CF.sub.4 is thermally decomposed in said
plasma burner at a temperature in the range of 1800.degree. to
2600.degree. C.
11. A method according to claim 10 wherein said CCl.sub.2 F.sub.2,
CClF.sub.3 or CF.sub.4 is thermally decomposed in said plasma
burner at a temperature between 1850.degree. and 2000.degree.
C.
12. A method according to claim 9 wherein the weight relationship
of the fluorine in said vapor CClF.sub.2, CClF.sub.3 or CF.sub.4 to
silicon in said hydrogen-free silicon compound is in the range of
50 to 800 grams fluorine per kg of silicon.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for the production of synthetic
quartz glass, to an apparatus for the practice of the method, and
to the use of the synthetic quartz glass.
2. Discussion of the Prior Art
For the manufacture of light-conductive fibers having a core and a
jacket, it is desirable, especially when high-purity quartz glass
is used, to have available a jacket material which has a lower
refractive index than the core material. To this end it was
proposed in French Patent Application No. 2,208,127 to use as the
jacket material a quartz glass doped either with boron oxide or
with fluorine. The fluorine-doped quartz glass is obtained by
oxidizing silicon tetrafluoride in accordance with the equation
SiF.sub.4 +2H.sub.2 O+O.sub.2 .fwdarw.SiO.sub.2 +4HF, whereby small
amounts of fluorine are to be incorporated into SiO.sub.2. However,
the oxidation can also be brought about by reactive methods in
which no hydrogen or H.sub.2 O is present, such as for example in
the high-frequency plasma, so that no hydrofluoric acid will
form.
It is clear that it is not possible by the disclosed method to
produce a fluorine-doped quartz glass in which the fluorine doping
will result in a predetermined reduction of the refractive index
below that of high-purity quartz glass. It is in this light that
one must also interpret the statement made in U.S. Pat. No.
3,869,194, that the differences achieved in the refractive indexes
of core material and fluorine-doped jacket material in a
light-conductive fiber are so slight that such fibers are not
suitable for optical signal transmission.
The production of synthetic quartz glass which is substantially
free of "water" and thus free of absorption bands at wavelengths of
1.4, 2.2 and 2.7 .mu.m--hereinafter referred to as
"hydroxyl-ion-free"--is known from German Pat. No. 1,208,740. The
hydroxyl-ion-free quartz glass is obtained by oxidizing a
hydrogen-free silicon compound in a hydrogen-free gas stream
containing elemental and/or bound oxygen, and depositing the
oxidation product as a vitreous mass on a refractory support, the
gas stream being passed through an induction-coupled plasma
burner.
Accordingly, it is an object of this invention to provide a
repeatable process for the production of a synthetic,
hydroxyl-ion-free quartz glass especially such a quartz glass
having a refractive index of n.sub.D .ltoreq.1.4570. It is
especially an object of this invention to provide such a process
for the production of synthetic hydroxyl-free quartz glass having a
fluorine content of at least 4 g per kg of synthesized
SiO.sub.2.
SUMMARY OF THE INVENTION
Broadly, this invention contemplates an improvement in a process
for producing a synthetic hydroxyl ion-free quartz glass wherein a
hydrogen-free silicon compound is heated in a hydrogen-free gas
stream, the gas stream being passed through an induction coupled
plasma burner and containing elemental and/or bound oxygen and the
oxidation product is deposited on the refractory support as a
vitreous mass, the improvement comprising including in said gas
stream a gaseous hydrogen-free thermally decomposable compound
which yields fluorine in an amount of at least 500 gms per kg of
silica to be produced.
Accordingly, the objects of the present invention are achieved in a
process for the production of synthetic, hydroxyl-ion-free quartz
glass by oxidizing a hydrogen-free silicon compound in a
hydrogen-free gas stream containing elemental and/or bound oxygen
and depositing the oxidation product as a vitreous mass on a
refractory support, the gas stream being passed through an
induction-coupled plasma burner, by the fact that, in accordance
with the invention, for the achievement of a prescribed reduction
of the refractive index of synthetic quartz glass, a hydrogen-free,
heat-decomposable fluorine compound in vapor form, especially
dichlorodifluoromethane (CCl.sub.2 F.sub.2), is introduced into the
flame of the plasma burner in the amount of at least 500 g per kg
of synthesized SiO.sub.2.
At the same time it has been found advantageous to add the fluorine
compound in vapor form to the oxygen being supplied for maintaining
the flame in the plasma burner. To obtain a deposition product
whose refractive index is to vary in a prescribed manner, it is
advantageous to increase or decrease the amount of fluorine
compound added during the depositing procedure. In such a manner
there is produced a glass whose refractive index n.sub.D is 1.457
to 1.435. If, in the case of increasing the amount of fluorine
compound, a rod of synthetic, hydroxyl-ion-free quartz glass is
used as the refractory support and is set in motion relative to the
plasma burner, by rotating it for example, during the depositing of
the fluorine-doped, synthetic, hydroxyl-ion-free quartz glass, one
obtains a foreproduct for the manufacture of light conducting
fibers, which consists of a core of the refractory support material
and a covering of fluorine-doped synthetic quartz glass.
A parabolic decrease of the refractive index in the covering is
obtained if the amount of fluorine compound added is increased as
the thickness of the covering increases. A light conducting fiber
is then produced by drawing a foreproduct of this kind.
Instead of the rod of synthetic, hydroxyl-ion-free quartz glass, a
rod of synthetic quartz glass can advantageously be used whose
refractive index is increased by the addition of refractive index
increasing metal ions. It is advantageous to use a doped rod of
synthetic quartz glass whose refractive index decreases with
distance from the rod axis. Thermally decomposable
hydrogen-free-fluorine compounds which can be used according to the
invention include the following: CClF.sub.3, CF.sub.4.
As sources of hydrogen-free silicon compound which can be used in
accordance with this invention to provide hydroxyl-ion-free quartz
glass one can employ the following: SiCl.sub.4, SiCl.sub.3 F,
SiCl.sub.2 F.sub.2, SiClF.sub.3.
Generally speaking the amount of hydrogen-free thermally
decomposable fluorine compound relative to the hydrogen-free
silicon compound would depend upon the nature of the glass desired
and in particular the relative amount of the fluorine in the
compound. Broadly speaking, however, the weight relationship of the
fluorine in the thermally decomposable fluorine compound to the
silicon in the hydrogen free silicon compound will be in the range
of 50 to 800 gms. fluorine per kg of silicon, preferably between
150 and 300 gms. fluorine per kg of silicon.
The process is conducted by heating the hydrogen free silicon
compound in the presence of the hydrogen-free gas stream containing
elemental and/or bound oxygen and thermally decomposable fluorine
compound at temperatures generally in the range of 1800.degree. to
2600.degree. C., preferably between 1850.degree. and 2000.degree.
C. The temperatures are employed in an amount sufficient to deposit
the so-heated mass upon a refractory support as a vitreous mass.
The fluorine is present together with the silicon compound for a
residence time of between 0.02 and 0.3 seconds, preferably between
0.04 and 0.15 seconds.
It has been found advantageous to use a burner having three quartz
glass tubes disposed concentrically at some distance from one
another, the outer tube overreaching the middle and innermost tube
and the middle tube overreaching the innermost tube. The working
gas and the silicon compound including the fluorine compound
present in vapor form are fed through the innermost tube, and a
separating gas, preferably oxygen, is fed through the interstice
between the innermost and the middle tube and between the middle
tube and outermost tube. The process of the invention differs from
the state of the art particularly in that the fluorine doping of
the synthetic quartz glass is no longer subject to caprice, but
takes place at a specific, predetermined rate. Reductions of the
index of refraction to values of 1.4532 can easily be achieved in
the synthetic quartz glass produced by the process of the
invention, thereby providing the assurance that this quartz glass
will be suitable also for the manufacture of light-conducting
fibers, especially also for those light conducting fibers whose
core consists of quartz glass of high purity.
BRIEF DESCRIPTION OF DRAWINGS
Referring to the drawings herein:
FIG. 1 is a side elevational view of an apparatus which can be
employed to carry out the claimed process; and
FIG. 2 is a view similar to FIG. 1 showing a further apparatus for
carrying out the claimed process.
DESCRIPTION OF SPECIFIC EMBODIMENTS
Referring to the drawings herein with the understanding that they
serve to diagramatically illustrate the process of the invention,
reference numeral 1 indicates a silicon tetrachloride reservoir
from which the silicon tetrachloride is pumped by a proportioning
pump 2 through the feed line 2 into a heated vaporizing dish 4, via
line 3. Oxygen is fed into the vessel 5 containing the vaporizing
dish through the line 6. The mixture of oxygen and silicon
tetrachloride formed in vessel 5 is delivered through the
ground-glass connection 7-8 made of quartz glass, into the plasma
burner. The plasma burner is composed of a metal base 9 and the
three quartz glass tubes 10, 11 and 12 which are sealed from one
another and from the outside atmosphere within the metal base. The
induction coil 13, which is supplied by the high-frequency electric
power generator 14 is disposed about the free end of the outermost
tube 12. The working gas and the two separating gases T-1 and T-2
are delivered through tangentially disposed lines 15, 16 and 17.
Into the housing 18 which contains the plasma burner there extends
a quartz glass piece 19, which serves as the substrate on which the
fluorine-doped synthetic quartz glass is deposited. The piece of
quartz glass 19 is held on a mandrel 20 in a device 21 which makes
it possible to rotate and slowly draw back the piece during the
depositing process, as indicated by the arrows 22 and 23. By means
of the positioning system 24 it is possible to orientate the quartz
glass piece 19 in all three directions with respect to the plasma
flame.
The igniting of the plasma burner is performed in a conventional
manner. Argon gas is introduced through the lines 15 and "ignited"
by means of a tungsten rod in the vicinity of the coil 13 which is
supplied with high-frequency energy. After this ignition, oxygen is
slowly fed to the argon, and the argon content of the mixture is
reduced until finally only oxygen is being fed. In like manner,
oxygen is fed through lines 16 and 17 as separating gases T-1 and
T-2.
As soon as the plasma burner is burning properly, the quartz glass
piece 19 is advanced into the flame and heated with simultaneous
rotation. When a temperature of about 1900.degree. C. is reached,
the vaporous mixture of silicon chloride and oxygen is fed from
vessel 5 into the plasma burner and then dichlorodifluoromethane
(CCl.sub.2 F.sub.2) is admixed, at a rate, for example, of 0.7
kg/h, with the oxygen being introduced through line 15. Due to the
high temperature of the plasma flame the SiCl.sub.4 decomposes and
reacts with the oxygen to form SiO.sub.2, which deposits itself on
the quartz glass piece 19 and vitrifies. The
dichlorodifluoromethane is also decomposed by the high temperature
of the plasma flame and fluorine is incorporated into the vitreous
SiO.sub.2 in a proportion of, for example, 5000 parts per
million.
Since only gases or vapors which are free of hydrogen are used in
the process of the invention, the product, fluorine-doped synthetic
quartz glass, is free of hydroxyl ions.
Instead of the quartz glass piece 19, a rod 19' of
hydroxyl-ion-free synthetic quartz glass can be used, as
represented diagrammatically in FIG. 2, which is held in end mounts
26 which are longitudinally displaceable and contain machinery for
the rotation of the rod 19' (arrows 27 and 28). The fluorine-doped
synthetic quartz glass is then deposited as a covering 29 on the
rod 19'. The product thus obtained is a foreproduct which can then
be drawn directly to form a light-conductive fiber.
The use of a plasma burner having three concentric quartz glass
tubes in a stepped configuration with the outermost tube
overreaching the middle and innermost tubes and the middle tube
overreaching the innermost tube, and blanketing the innermost and
middle tubes with a separating gas, preferably oxygen, has the
advantage that no silica can collect on the burner.
* * * * *