Claims
- 1. In a method of purifying metallurgical grade silicon, the steps comprising:
- A. charging a quartz tube with chunks of metallurgical grade silicon containing impurities consisting essentially of aluminum and boron;
- B. heating the silicon to a temperature within a range of 800.degree. C. to 1350.degree. C. in vacuo;
- C. continuously passing through said chunks a stream of reactant gas at 0.1 torr to one atmosphere consisting essentially of silicon tetrafluoride to effect a metathetical reaction of aluminum and boron impurities of the silicon with the silicon tetrafluoride with AlF.sub.3 and BF.sub.3 being formed and leaving a residue of silicon of improved impurity; and wherein the AlF.sub.3 formed reacts
- with the surface of the quartz tube to form silicon tetrafluoride and aluminum oxide which deposits as a coating on said surface.
- 2. The method of claim 1 wherein the chunks are of a size within a range of 0.1-10 mm, and the reactant gas is passed through said chunks for a period of four to twenty hours.
- 3. The method of claim 2 wherein the quartz tube is characterized by an inside diameter of 1-4 inches and a length of 24-36 inches.
- 4. The method of claim 2 wherein the impurities further contain nickel and the reactant gas further contains carbon monoxide and wherein the carbon monoxide reacts with the nickel to form volatile Ni(CO).sub.4.
ORIGIN OF THE INVENTION
The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 USC 2457).
US Referenced Citations (6)
Foreign Referenced Citations (2)
Number |
Date |
Country |
625027 |
Aug 1961 |
CAX |
1039752 |
Sep 1958 |
DEX |