CRYSTAL PULLING FROM A HIGHLY IMPURE GROWTH MELT
A method and system for crystal pulling from a growth melt that is produced by molten oxide electrolysis are presented. The method may be used as a purification step in processing raw feedstock such as lunar regolith. The Czochralski technique is a similar, but substantially different, process of crystal pulling from a growth melt. In the Czochralski technique, the growth melt is a very pure liquid of the element that is to be formed into a single crystal. In embodiments described herein, the growth melt is substantially impure and may be a combination of two or more elements having similar concentrations, even though only one of the elements is to be formed into a single crystal.
1 . A method for crystal pulling from a growth melt that is produced by molten oxide electrolysis, the method comprising:
via electrolysis in a first vessel containing a melted oxide material, producing an iron- and oxygen-depleted electrolyte;
receiving a portion of the iron- and oxygen-depleted electrolyte into a second vessel;
crystal pulling an element from the iron- and oxygen-depleted electrolyte in the second vessel; and
at least during the crystal pulling, controlling temperatures of the iron- and oxygen-depleted electrolyte in the second vessel based, at least in part, on a melt profile that represents a melt temperature of the iron- and oxygen-depleted electrolyte as a function of the concentration of the element.
2 . The method of claim 1 , wherein the element is silicon.
3 . The method of claim 1 , wherein the oxide material is a mixture of two or more metallic oxides.
4 . The method of claim 1 , wherein the second vessel is separated from the first vessel via a conduit that conveys the portion of the iron- and oxygen-depleted electrolyte from the first vessel.
5 . The method of claim 4 , wherein controlling temperatures of the iron- and oxygen-depleted electrolyte in the second vessel comprises at least partially controlling heat transfer of a flow of the portion of the iron- and oxygen-depleted electrolyte in the conduit.
6 . The method of claim 1 , wherein crystal pulling the element in the second vessel is performed while simultaneously performing the electrolysis in a first vessel.
7 . The method of claim 1 , wherein the electrolysis in the first vessel involves a liquid cathode that, based on density of the liquid cathode compared to density of the melted oxide material, collects at a bottom portion of the first vessel and is in contact with a cathodic electrode of the electrolysis.
8 . The method of claim 1 , further comprising collecting oxygen gas from the first vessel while simultaneously crystal pulling the element in the second vessel.
9 . A method for purifying an iron- and oxygen-depleted melt, the method comprising:
crystal pulling an element from the iron- and oxygen-depleted melt; and
based, at least in part, on a melt profile that represents a melt temperature of the iron- and oxygen-depleted electrolyte as a function of the concentration of the element, changing the temperature of the iron- and oxygen-depleted melt as the concentration of the element decreases.
10 . The method of claim 9 wherein the element is silicon.
11 . The method of claim 9 , wherein the iron- and oxygen-depleted melt is produced by electrolysis.
12 . A molten oxide electrolysis (MOE) system comprising:
a first vessel that includes i) an anode and ii) a cathodic electrode in a bottom region of the first vessel, wherein
the cathodic electrode is configured to be in electrical communication with a melted oxide material in the first vessel,
the anode and the cathodic electrode are configured to provide an electrical current therebetween for a process of electrolysis of the melted oxide material, and
the process of electrolysis of the melted oxide material produces a liquid cathode in contact with the cathodic electrode;
a second vessel that is separated from the first vessel by a conduit for carrying, from the first vessel to the second vessel, a portion of the melted oxide material that is iron- and oxygen-depleted, wherein the portion of the melted oxide material that is iron- and oxygen-depleted is a growth melt;
a rod-mounted seed crystal of an element in or above the second vessel and configured to be immersed in the growth melt; and
temperature-control electronics configured to control the temperature of the growth melt based, at least in part, on a melt profile that represents a melt temperature of the growth melt as a function of the concentration of the element.
13 . The MOE system of claim 12 , wherein the element is silicon.
14 . The MOE system of claim 13 , wherein the temperature-control electronics are further configured to decrease the temperature of the portion of the growth melt as the concentration of the silicon decreases.
15 . The MOE system of claim 13 , wherein the temperature-control electronics are further configured to increase the temperature of the growth melt as the concentration of the silicon decreases.
16 . The MOE system of claim 12 , wherein the melted oxide material is a mixture of two or more metallic oxides.
17 . The MOE system of claim 12 , wherein the melted oxide material is derived from lunar regolith.
18 . The MOE system of claim 12 , further comprising an oxygen gas collecting port in the first vessel.
19 . The MOE system of claim 12 , wherein the rod-mounted seed crystal of the element is configured to produce a crystal of the element via a crystal pulling process.
20 . The MOE system of claim 12 , wherein the liquid cathode, based on density of the liquid cathode compared to density of the melted oxide material, collects in the bottom region of the first vessel.