Patent ID: 7178366

Claim:
A method for the production of a crack-free, internally vitrified SiO 2 crucible, comprising: sintering an amorphous, open-pored SiO 2 green-body crucible by means of exposure to a focal spot of a CO 2 laser beam, wherein the focal spot is moved relative to the inner surface of said crucible throughout the sintering, the sintering beginning at an upper inner edge of the SiO 2 green-body crucible by means of a focal spot of a first contact area, the focal spot sweeping over the upper inner edge of the SiO 2 green-body crucible and broadening during said sweeping to a second, larger contact area until the upper inner edge is fully vitrified, the focal spot then moving into the SiO 2 green-body crucible, an upper edge of said second contact area traversing the inner surface of said crucible proximate a lower edge of the prior path of said focal spot.