Directional solidification system and method
View Patent ↗The present invention relates to an apparatus and method for purifying materials using a rapid directional solidification. Devices and methods shown provide control over a temperature gradient and cooling rate during directional solidification, which results in a material of higher purity. The apparatus and methods of the present invention can be used to make silicon material for use in solar applications such as solar cells.
1. A system for directional solidification, comprising:
a mold, including:
an outer jacket;
a base positioned to directly contact molten material, the base lining a bottom of the outer jacket, the base including a heat conducting material of a higher thermal conductivity than a wall material positioned to directly contact molten material; and
a wall insulation structure positioned to directly contact molten material, the wall insulation structure lining a wall of the outer jacket, the wall insulation structure tapering in thickness from a rim of the mold, having a first thickness, to a bottom portion of the mold, having a second thickness that is thinner than the first thickness.
2. The system of claim 1 , wherein the wall insulation structure tapers in thickness from the rim of the mold to a bottom interface with the base.
3. The system of claim 2 , wherein the second thickness is approximately 25 percent thinner than the first thickness.
4. The system of claim 1 , wherein the wall insulation structure includes a layer of refractory bricks, and an exposed layer of substantially continuous refractory material.
5. The system of claim 1 , further including a top heater.
6. The system of claim 5 , wherein the top heater includes a number of silicon carbide heating elements.
7. The system of claim 5 , further including a vent hole in the top heater.
8. A mold for directional solidification, comprising:
a substantially rectangular shaped wall structure, including a long side and a short side;
a heat conducting base positioned to directly contact molten material, the base including a material of a higher thermal conductivity than a wall material, coupled to the substantially rectangular shaped wall structure;
wherein the substantially rectangular shaped wall is dimensioned to provide a wall contact area for a given quantity of molten silicon that is less than a wall contact area for a cylindrical mold having a diameter substantially equal to a length of the short side of the mold; and
wherein the substantially rectangular shaped wall structure is positioned to directly contact molten material, and the rectangular shaped wall structure tapers in thickness from a rim of the mold, having a first thickness, to a bottom interface with the heat conducting base, having a second thickness that is thinner than the first thickness.
9. The mold of claim 8 , wherein the rectangular shaped wall structure includes a rounded profile at wall intersections.