Burner for chemical vapour deposition of glass

1. A burner for a vapour deposition process, comprising:

a front face;

a precursor exit port defined in said front face for ejecting a glass precursor material, the precursor exit port having a center centrally-located on said front face, said precursor exit port having a concave shape at said front face comprising a circular central region and a plurality of radial regions extending from the central region and each radial region is defined by a pair of walls converging toward the axis and an end wall, respectively; and

an annular orifice defined in said front face for ejecting a gas, said annular orifice surrounding said central orifice.

2. The burner according to claim 1 , wherein said precursor exit port has a symmetry about an axial plane.

3. The burner according to claim 1 , further comprising a ring of nozzles, each nozzle in the ring of nozzles being defined by a respective surface, the ring of nozzles surrounding said precursor exit port for ejecting a flame reactant.

4. The burner according to claim 3 , wherein the annular orifice is located between said precursor exit port and said ring of nozzles.

5. The burner according to claim 4 , wherein said precursor exit port has first angular sectors of minimum radial dimensions and second angular sectors of maximum radial dimensions.

6. The burner according to claim 5 , wherein said ring of nozzles comprises a first set of nozzles in the same angular positions of said second angular sectors and a second set of nozzles in the same angular positions of said first angular sectors.

7. The burner according to claim 6 , further comprising a first set of ducts terminating in said first set of nozzles and a second set of ducts terminating in said second set of nozzles, the ducts of the first set being inclined at a first angle with respect to a central axis of said burner and the ducts of the second set being inclined at a second angle with respect to said central axis, said second angle being greater than said first angle.

8. The burner according to claim 1 , having a central duct terminating in said percursor exit port for the passage of said glass precursor material, and comprising a central member positioned inside the central duct for forcing the glass precursor material toward an external boundary of said central orifice.

9. The burner according to claim 8 , wherein the central member has at least an enlarged portion that substantially fits with external walls of said central duct.

10. The burner according to claim 1 , wherein the plurality of radial regions extending from the central region of the precursor exit port are evenly-spaced with respect to one another.

11. The burner according to claim 1 , wherein the plurality of radial regions extending from the central region of the precursor exit port are triangular in shape.

12. A burner for a vapour deposition process, comprising:

a face block having a front face;

a central duct for the passage of a glass precursor material, the central duct exiting in a precursor exit port on said front surface;

a circular duct for the passage of a gas reactant, said circular duct extends around said central duct and terminates in a circular reactant exit port on said front surface;

wherein said precursor exit port has a concave shape at said front face increasing contact surface between the precursor and the reactant, said concave shape comprising a circular central region and a plurality of radial regions extending from the central region and each radial region is defined by a pair of walls converging toward the axis and an end wall, respectively.

13. The burner according to claim 12 , wherein the radial regions are evenly-spaced around the circular central region so as to define non-contiguous radial regions.

14. The burner according to claim 12 , wherein the end wall of each radial region lays on a same circumference as the end walls of the other radial regions.

15. The burner according to claim 12 , wherein the end walls of the radial regions lays close to the internal boundary of the circular reactant exit port.

16. The burner according to claim 12 , wherein the radial regions have a triangular shape.

17. The burner according to claim 12 , further comprising a first passage and a second passage terminating each in two rings of orifices.

18. The burner according to claim 17 , wherein the circular reactant exit port is located between said precursor exit port and said rings of orifices.

19. The burner according to claim 17 , wherein the orifices of the inner ring of orifices are in a number that is twice the number of the radial regions of the circular reactant exit port.