Vitreous silica crucible with specific ratio of transparent layer and bubble-containing layer thicknesses
Provided is a vitreous silica crucible, which is resistant to deformation and corrosion even when heated at high temperature for a long time. There is provided a vitreous silica crucible of the present invention including a substantially cylindrical straight body portion, a curved bottom portion, and a corner portion smoothly connecting the straight body portion and the bottom portion, wherein a wall of the vitreous silica crucible includes, from an inner surface side, a transparent layer and a bubble-containing layer, and a ratio of a thickness of the bubble-containing layer with respect to a thickness of the transparent layer at an intermediate position between an upper end and a lower end of the straight body portion is 0.7 to 1.4.
1. A vitreous silica crucible comprising a substantially cylindrical straight body portion, a curved bottom portion, and a corner portion smoothly connecting the straight body portion and the bottom portion, wherein a wall of the vitreous silica crucible includes, from an inner surface side, a transparent layer and a bubble-containing layer, and a ratio of a thickness of the bubble-containing layer with respect to a thickness of the transparent layer at an intermediate position between an upper end and a lower end of the straight body portion is 0.7 to 1.4;
wherein the transparent layer is made of at least one of synthetic vitreous silica and natural vitreous silica, and the bubble-containing layer is made of natural vitreous silica;
wherein a ratio of a thickness of the transparent layer to a thickness of the bubble-containing layer at the corner portion is from 2.25 to 10;
wherein the thickness of the transparent layer is larger than that of the bubble-containing layer at the corner portion;
wherein the thickness of the transparent layer is 2 mm or more and 5 mm or less, and the thickness of the bubble-containing layer is 7 mm or more and 8.5 mm or less at the border between the bottom portion and the corner portion;
wherein the bubble-containing layer consists of two or more bubble-containing layers having different bubbles content rates from each other, without any other intervening layer, wherein the bubble content rate of each bubble-containing layer is 0.2% or more and 1% or less; and
wherein the bubble content rate of the transparent layer in the center of the bottom portion (B B ) is 0.01% or less, that at the border between the bottom portion and the corner portion (B BR ) is less than 0.2%, and that in the upper half of the straight body portion (B W ) is 0.1% or less, wherein B BR >B W >B B .
2. The vitreous silica crucible of claim 1 , wherein an average diameter of bubbles contained in the transparent layer is less than 100 μm.
3. The vitreous silica crucible of claim 1 , wherein an average diameter of bubbles contained in the bubble-containing layer is 20 μm or more and 200 μm or less.
4. The vitreous silica crucible of claim 1 , wherein the volume expansion rate, after 24-hour heat treatment at 1500 degrees C., at an intermediate position between the upper end and the lower end of the straight body portion of the vitreous silica crucible is 3% or less.
5. The vitreous silica crucible of claim 1 , wherein the transparent layer is thicker than the bubble-containing layer at the intermediate position of the crucible.