Recycling FAST-sliced SILICON swarf, F. Schmid and D. B. Joyce, 24th EU PVSEC, Hamburg, Germany, September, 2009.
Abstract: A major waste of silicon (Si) occurs during photovoltaic (PV) production at the wafering stage, where up to 50% of the Si ends up in the swarf as a disposal problem. The purpose of this work is to demonstrate that the Fixed Abrasive Slicing Technique (FAST) for slicing wafers can be used to allow much of this swarf to be recycled thereby reducing the cost and environmental impact of PV. Unlike conventional multi-wire slurry (MWS) saws, in FAST, the diamond abrasive is fixed to the wires, and does not mix with and contaminate the swarf. The diamonds also protect the wire from wear and limit the contamination of the Si swarf by the metal wire. We have sliced Si by FAST, recovered and characterized the swarf. Based on these results, large amounts of swarf simulant were made from high purity Si powders. This swarf simulant was then processed pyrometallurgically to produce Si feedstock. The feedstock was analyzed, and is shown to have average resistivity of 1.9 Ohm*cm. The highest level of impurity was Al at 0.58 ppmw. All other impurities were below 0.1 ppmw.

RECENT ADVANCES IN UPGRADING METALLURGICAL GRADE (MG) SILICON, F. Schmid and D. B. Joyce, 24th EU PVSEC, Hamburg, Germany, September, 2009.
Abstract: As the price of photovoltaic (PV) electricity approaches grid parity, the potential explosion in demand for PV means that the solar grade silicon (SoG Si) industry will need a rapidly scaleable, inexpensive and less capital-intensive source of silicon. A recent advance in the refining of metallurgical grade silicon (MG Si) into SoG Si by a slagging/gettering technique promises such a rapidly scaleable process. We have demonstrated reduction of phosphorus (P) in MG Si from 26 ppm to 0.51 ppm and a reduction of boron (B) from 19 ppm to 7 ppm using just such a process.

Correlation of Sapphire Quality with Uniformity and Optical Properties, Chandra P. Khattak, Frederick Schmid and Maynard B. Smith, SPIE Proc. 3060 (1997), Window and Dome Technologies and Materials V, Orlando, FL 21-22 April 1997.
Abstract: Large sapphire boules, up to 34cm diameter, 65kg, are being grown by the Heat Exchanger Method (HEM) and even larger sizes are sought to meet future requirements of advanced optical systems. These boules, especially in large sizes, exhibit lattice distortion and light scatter in a very narrow range. A qualitative grading system has been developed to characterize sapphire. Windows of five grades and different orientations were prepared and measured for refractive index homogeneity to evaluate transmitted wavefront distortion. The data showed that the refractive index homogeneity for all samples was in the 10^-7 (0.1 ppm) range. The fact that lattice distortion does not affect the transmitted wavefront allows fabrication of large sapphire windows in production mode at low cost.