Method for the production of a cylindrical quartz glass body having a low oh content
According to a previously known method for producing a cylindrical quartz glass body having a low OH content, first an elongate, porous soot body is produced on a rotating support by flame-hydrolyzing a silicon-containing compound and removing layers of SiO 2 particles, whereupon said soot body is subjected to a dehydration treatment and is vitrified in a vitrification furnace. The aim of the invention is to create a simple method which is based on said method and makes it possible to produce a quartz glass cylinder having a low OH content while evenly distributing the OH concentration without additional technical complexity. Said aim is achieved by subjecting the soot body to a pretreatment in protective gas and/or a vacuum in the vitrification furnace following the dehydration treatment but prior to the vitrification thereof, the soot body being heated to a temperature ranging between 100° C. and 1350° C. in a heating area.
1 . A method for producing a cylindrical quartz glass body having a low OH content, said method comprising: producing an elongate porous soot body by flame-hydrolysis of a silicon-containing compound and layerwise deposition of SiO 2 particles on a rotating carrier, wherein said soot body is subjected to a dehydration treatment and then vitrified in a vitrification furnace, and wherein the dehydration treatment is carried out in a dehydration furnace, and, following the dehydration treatment, the soot body is introduced into the vitrification furnace and thereby contaminated with hydroxyl groups, and, prior to the vitrification, the soot body is subjected to a pretreatment in protective gas or a vacuum in the vitrification furnace, said pretreatment comprising a heating of the soot body in a heating zone to a temperature ranging between 100° C. and 1350° C.
2 . The method according to claim 1 , wherein, starting at an end thereof, the soot body is supplied to the heating zone and heated therein zonewise.
3 . The method according to claim 1 , wherein the soot body is heated in the heating zone to a temperature ranging from 800° C. to 1180° C. during said pretreatment.
4 . The method according to claim 1 , wherein an internal pressure of less than 100 mbar is maintained during said pretreatment.
5 . The method according to claim 3 , wherein an internal pressure of less than 1 mbar is maintained during said pretreatment.
6 . The method according to claim 2 , wherein the soot body is supplied to the heating zone at a speed of not more than 20 mm/min during said pretreatment.
7 . The method according to claim 1 , wherein the soot body is vitrified at a temperature of at least 1200° C. directly following the pretreatment, the internal pressure prevailing at the end of the pretreatment being maintained or reduced.
8 . The method according to claim 2 , wherein said end of the soot body is an upper end, and starting with said upper end the soot body is supplied to the heating zone during vitrification and is vitrified therein zonewise, the supply of the soot body to the heating zone taking place in a direction opposite to that during said pretreatment.
9 . The method according to claim 1 , wherein the cylindrical quartz glass body is used for producing a preform for optical fibers.
10 . The method according to claim 2 wherein the soot body is heated in the heating zone to a temperature ranging from 800° C. to 1180° C. during said pretreatment.
11 . The method according to claim 10 , wherein an internal pressure of less than 1 mbar is maintained during said pretreatment.
12 . The method according to claim 2 , wherein an internal pressure of less than 100 mbar is maintained during said pretreatment.
13 . The method according to claim 3 , wherein an internal pressure of less than 100 mbar is maintained during said pretreatment.
14 . The method according to claim 3 , wherein the soot body is supplied to the heating zone at a speed of not more than 20 mm/min during said pretreatment.
15 . The method according to claim 4 , wherein the soot body is supplied to the heating zone at a speed of not more than 20 mm/min during said pretreatment.
16 . The method according to claim 5 , wherein the soot body is supplied to the heating zone at a speed of not more than 20 mm/min during said pretreatment.
17 . The method according to claim 2 , wherein the soot body is vitrified at a temperature of at least 1200° C. directly following the pretreatment, the internal pressure prevailing at the end of the pretreatment being maintained or reduced.
18 . The method according to claim 3 , wherein the soot body is vitrified at a temperature of at least 1200° C. directly following the pretreatment, the internal pressure prevailing at the end of the pretreatment being maintained or reduced.
19 . The method according to claim 4 , wherein the soot body is vitrified at a temperature of at least 1200° C. directly following the pretreatment, the internal pressure prevailing at the end of the pretreatment being maintained or reduced.
20 . The method according to claim 5 , wherein the soot body is vitrified at a temperature of at least 1200° C. directly following the pretreatment, the internal pressure prevailing at the end of the pretreatment being maintained or reduced.
21 . The method according to claim 6 , wherein the soot body is vitrified at a temperature of at least 1200° C. directly following the pretreatment, the internal pressure prevailing at the end of the pretreatment being maintained or reduced.
22 . The method according to claim 16 , wherein the soot body is vitrified at a temperature of at least 1200° C. directly following the pretreatment, the internal pressure prevailing at the end of the pretreatment being maintained or reduced.
23 . The method according to claim 22 , wherein said end of the soot body is an upper end, and starting with said upper end the soot body is supplied to the heating zone during vitrification and is vitrified therein zonewise, the supply of the soot body to the heating zone taking place in a direction opposite to that during said pretreatment.