Method for producing a tube consisting of quartz glass, tubular semi-finished product consisting of porous quartz glass, and the use of the same
In a known method for producing a quartz glass tube by means of flame hydrolysis of a silicon-containing start component, SiO 2 -containing particles are produced, said particles are deposited on a carrier, forming a soot tube having a porous soot wall with a predetermined radial soot density profile, and the soot tube is treated in a chlorine-containing atmosphere and is then vitrified. To modify said method in such a way that a predetermined radial refractive index distribution is obtained also after dehydration treatment in a chlorine-containing atmosphere, it is suggested according to the invention that the density should be adjusted in such a way that in an inner region of the soot wall it is increased to at least 25% of the density of quartz glass, in an outer region of the soot wall the density is reduced, and in a transition region adjoining the inner region, the density decreases towards the outer region, with the proviso that the transition region extends over at least 75% of the thickness of the soot wall. The inventive tubular semi-finished product is characterized by a soot wall having, in an inner region, a density which is increased to at least 25% of the density of the quartz glass, a reduced density in an outer region, and, in a transition region adjoining the inner region, a density which decreases towards the outer region, said transition region extending over at least 75% of the thickness of the soot wall
1 . A method for producing a quartz glass tube by flame hydrolysis of a silicon-containing start component, said method comprising: supplying the start component to a deposition burner by which SiO 2 -containing particles are produced, wherein said particles are deposited on a carrier rotating about a longitudinal axis thereof, so as to form a soot tube having a porous soot wall with a predetermined radial soot density profile, treating the soot tube is in a chlorine-containing atmosphere, and vitrifying the treated soot tube, wherein the soot wall has an inner region having an increased density of at least 25% of the density of quartz glass, an outer region of the soot wall having a reduced density such that there is a difference in density between the increased density in the inner region and the reduced density in the outer region ranging between 4% and 12%, and a transition region adjoining the inner region and having a density that decreases towards the outer region, wherein the transition region extends over at least 75% of the thickness of the soot wall.
2 . The method according to claim 1 , wherein in the inner region the increased density is between 25% and 35% of the density of quartz glass.
3 . The method according to claim 1 , wherein the soot tube is vitrified by being heated from the outside so as to form an inwardly migrating melt front.
4 . The method according to claim 1 , wherein the density in the transition region decreases continuously toward the outer region of the soot wall.
5 . The method according to claim 4 , wherein the density in the transition region decreases substantially linearly toward the outer region of the soot wall.
6 . The method according to claim 1 , wherein the density decreasing in the transition region from the inner region to the outer region is obtained by reducing a surface temperature of the soot tube as said soot tube is formed.
7 . The method according to claim 1 , wherein the inner region is not more than 30 mm away from an inner wall of the soot tube.
8 . The method according to claim 7 , wherein the inner region is not more than 20 mm away from the inner wall of the soot tube.
9 . The method according to claim 2 , wherein in the inner region the increased density is between 28% and 32% of the density of quartz glass.
10 . The method according to claim 2 , wherein in the outer region the reduced density is between 20% and 27% of the density of quartz glass.
11 . The method according to claim 9 , wherein in the outer region the reduced density is between 20% and 27% of the density of quartz glass.
12 . The method according to claim 2 , wherein in the outer region the reduced density is between 20% and 24% of the density of quartz glass.
13 . The method according to claim 9 , wherein in the outer region the reduced density is between 20% and 24% of the density of quartz glass.
14 . The method according to claim 2 , wherein the density in the transition region decreases continuously toward the outer region of the soot wall.
15 . The method according to claim 14 , wherein the density in the transition region decreases substantially linearly toward the outer region of the soot wall.
16 . The method according to claim 9 , wherein the density in the transition region decreases continuously toward the outer region of the soot wall.
17 . The method according to claim 16 , wherein the density in the transition region decreases substantially linearly toward the outer region of the soot wall.
18 . The method according to claim 10 , wherein the density in the transition region decreases continuously toward the outer region of the soot wall.
19 . The method according to claim 18 , wherein the density in the transition region decreases substantially linearly toward the outer region of the soot wall.
20 . The method according to claim 11 , wherein the density in the transition region decreases continuously toward the outer region of the soot wall.
21 . The method according to claim 20 , wherein the density in the transition region decreases substantially linearly toward the outer region of the soot wall.
22 . The method according to claim 12 , wherein the density in the transition region decreases continuously toward the outer region of the soot wall.
23 . The method according to claim 22 , wherein the density in the transition region decreases substantially linearly toward the outer region of the soot wall.
24 . The method according to claim 13 , wherein the density in the transition region decreases continuously toward the outer region of the soot wall.
25 . The method according to claim 24 , wherein the density in the transition region decreases substantially linearly toward the outer region of the soot wall.