Large-sized hollow porous quartz glass preform and method of manufacturing the same

1 . A large-sized hollow porous quartz glass preform of a cylindrical shape having an outer diameter of more than 300 mm and a length of 2 m or more,

wherein the preform has an average density of 0.56 g/cm 3 or more and 0.77 g/cm 3 or less as a whole,

wherein a density fluctuation amount per unit length among four points, each located at a distance of 105 mm from an inner surface in a radial direction in four directions at 90° intervals in a cylindrical cross-section is 10%/cm or less with respect to an average value of the four points, and

wherein the preform is free of any crack.

2 . The large-sized hollow porous quartz glass preform according to claim 1 , wherein the large-sized hollow porous quartz glass preform is obtained by a method comprising the steps of:

arranging a plurality of burners for synthesizing glass fine particles at predetermined intervals and subjecting the burners to reciprocating movement to deposit glass fine particles on a rotating target, to thereby grow a soot body; and

extracting the target from the soot body, to thereby manufacture a hollow porous quartz glass preform,

wherein a rotation peripheral speed of the soot body is controlled so as to be practically constant by fluctuating a rotation number of the soot body on the basis of a fluctuating outer diameter of the soot body during growth, and

wherein a frequency factor γ calculated by the following equation (1) is set so as to fall within a range of the following expression (2) in a range in which the outer diameter of the soot body is more than 250 mm:

γ= S /( L·N m )  (1)

0.13≤γ< 1 . 0   (2)

in the equation (1), S represents a moving speed (mm/min) of the burners, L represents a moving distance (mm) of the burners, and N m represents a lowest value (rpm) of the rotation number of the soot body, which is fluctuated.

3 . The large-sized hollow porous quartz glass preform according to claim 2 , wherein the method to obtain the large-sized hollow porous quartz glass preform further comprises moving a turning position in the reciprocating movement of the burners by a predetermined distance, wherein a movement amount of the turning position in one to-and-fro cycle of the burners is ⅓ or less of a flame diameter of each of the burners applied to the soot body.

4 . The large-sized hollow porous quartz glass preform according to claim 2 , wherein the frequency factor γ is 0.13 or more and 0.3 or less.

5 . The large-sized hollow porous quartz glass preform according to claim 2 , wherein the method uses the obtained large-sized hollow porous quartz glass preform to obtain a synthetic quartz glass cylinder.

6 . A hollow synthetic quartz glass cylinder, which is obtained by dehydrating and vitrifying the hollow porous quartz glass preform of claim 1 , has an outer diameter of from 200 mm to 500 mm, a length of from 0.7 m to 3.5 m, an OH group concentration of less than 5 ppm, and a chlorine content concentration of 500 ppm or more and 3,000 ppm or less, and is free of any appearance failure portion resulting from a crack of a porous member.

7 . The hollow synthetic quartz glass cylinder according to claim 6 , wherein a “maximum-minimum difference” of chlorine concentrations at four positions at 90° intervals in a peripheral direction at equal distances from an inner surface in a cylindrical cross-section of the hollow synthetic quartz glass cylinder is within 15% with respect to an average value of the four positions.

8 . A hollow synthetic quartz glass cylinder, which is obtained by pre-sintering and vitrifying the hollow porous quartz glass preform of claim 5 , has an outer diameter of from 200 mm to 500 mm, a length of from 0.7 m to 3.5 m, and an OH group concentration of 50 ppm or more and 500 ppm or less, and is free of any appearance failure portion resulting from a crack of a porous member.

9 . The hollow synthetic quartz glass cylinder according to claim 8 , wherein a “maximum-minimum difference” of OH group concentrations at four positions at 90° intervals in a peripheral direction at equal distances from an inner surface in a cylindrical cross-section of the hollow synthetic quartz glass cylinder is within 15% with respect to an average value of the four positions.

10 . The large-sized hollow porous quartz glass preform according to claim 1 , wherein the cylindrical cross-section is 2%/cm or less with respect to an average value of the four points.

11 . A large-sized hollow porous quartz glass preform of a cylindrical shape having an outer diameter of 500 mm or more and a length of 1.0 m or more,

wherein the preform has an average density of 0.56 g/cm 3 or more and 0.77 g/cm 3 or less as a whole,

wherein a density fluctuation amount per unit length among four points, each located at a distance of 105 mm from an inner surface in a radial direction in four directions at 90° intervals in a cylindrical cross-section is 10%/cm or less with respect to an average value of the four points, and

wherein the preform is free of any crack.

12 . The large-sized hollow porous quartz glass preform according to claim 11 , wherein the large-sized hollow porous quartz glass preform is obtained by a method comprising the steps of:

arranging a plurality of burners for synthesizing glass fine particles at predetermined intervals and subjecting the burners to reciprocating movement to deposit glass fine particles on a rotating target, to thereby grow a soot body; and

extracting the target from the soot body, to thereby manufacture a hollow porous quartz glass preform,

wherein a rotation peripheral speed of the soot body is controlled so as to be practically constant by fluctuating a rotation number of the soot body on the basis of a fluctuating outer diameter of the soot body during growth, and

wherein a frequency factor γ calculated by the following equation (1) is set so as to fall within a range of the following expression (2) in a range in which the outer diameter of the soot body is more than 250 mm:

γ= S /( L·N m )  (1)

0.13≤γ<1.0  (2)

in the equation (1), S represents a moving speed (mm/min) of the burners, L represents a moving distance (mm) of the burners, and N m represents a lowest value (rpm) of the rotation number of the soot body, which is fluctuated.

13 . The large-sized hollow porous quartz glass preform according to claim 12 , wherein the method to obtain the large-sized hollow porous quartz glass preform further comprises moving a turning position in the reciprocating movement of the burners by a predetermined distance, wherein a movement amount of the turning position in one to-and-fro cycle of the burners is ⅓ or less of a flame diameter of each of the burners applied to the soot body.

14 . The large-sized hollow porous quartz glass preform according to claim 12 , wherein the frequency factor γ is 0.13 or more and 0.3 or less.

15 . The large-sized hollow porous quartz glass preform according to claim 12 , wherein the uses the obtained large-sized hollow porous quartz glass preform to obtain a synthetic quartz glass cylinder.

16 . The large-sized hollow porous quartz glass preform according to claim 11 , wherein the cylindrical cross-section is 2%/cm or less with respect to an average value of the four points.