Silicon purification mold and method
View Patent ↗The present invention relates to an apparatus and method for purifying materials using a fractional solidification. Devices and methods shown provide control over a temperature gradient and cooling rate during fractional 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 method, comprising:
forming a molten metal alloy in a crucible, wherein the alloy forms a binary eutectic system with silicon;
cooling at least a portion of the molten metal alloy to a temperature below a liquidus temperature and above a eutectic temperature to precipitate silicon from the molten metal alloy;
controlling temperature within the crucible to maintain a minimum temperature above the eutectic temperature within the crucible;
actively heating at least a top surface of the crucible to maintain a minimum temperature above the eutectic temperature within the crucible;
preferentially cooling the crucible from a bottom surface that includes a heat conducting material having a higher thermal conductivity than walls of the crucible; and
separating the precipitated silicon from the molten metal alloy.
2. The method of claim 1 , wherein forming a molten metal alloy in a crucible includes forming a silicon-aluminum alloy in a crucible.
3. The method of claim 2 , wherein forming a molten metal alloy in a crucible includes forming silicon-aluminum alloy in a starting composition between approximately 60 wt. % silicon and 22 wt. % silicon, with a balance being substantially aluminum.
4. The method of claim 2 , wherein forming a molten metal alloy in a crucible includes forming silicon-aluminum alloy in a starting composition between approximately 50 wt. % silicon and 30 wt. % silicon, with a balance being substantially aluminum.
5. The method of claim 2 , wherein cooling includes maintaining a temperature within the crucible in a range between approximately 577° C.-1100° C.
6. The method of claim 2 , wherein cooling includes maintaining a temperature within the crucible in a range between approximately 720° C.-1100° C.
7. The method of claim 2 , wherein cooling includes maintaining a temperature within the crucible in a range between approximately 650° C.-960° C.
8. The method of claim 1 , wherein controlling temperature within the crucible includes covering a top of the crucible.
9. A method, comprising:
forming a molten metal alloy in a crucible, wherein the alloy forms a binary eutectic system with silicon;
cooling the molten metal alloy to a temperature below a liquidus temperature and above a eutectic temperature to precipitate silicon from the molten metal alloy;
actively heating the crucible to maintain a minimum temperature above the eutectic temperature within the crucible, wherein actively heating the crucible includes heating a top surface of the crucible;
preferentially cooling the crucible from a bottom surface that includes a heat conducting material having a higher thermal conductivity than walls of the crucible; and
separating the precipitated silicon from the molten metal alloy.
10. The method of claim 9 , wherein forming a molten metal alloy in a crucible includes forming a silicon-aluminum alloy in a crucible.
11. The method of claim 9 , wherein actively heating the crucible includes heating sides of the crucible.