@inproceedings{AckerDuckeRietigetal., author = {Acker, J{\"o}rg and Ducke, Jana and Rietig, Anja and M{\"u}ller, Tim and Eisert, Stefan and Reichenbach, Birk and L{\"o}ser, Wolfgang}, title = {Segregation, grain boundary milling, and chemical leaching for the refinement of metallurgical-grade silicon for photovoltaic application}, series = {Silicon for the Chemical and Solar Industry XII, Trondheim, 2014}, booktitle = {Silicon for the Chemical and Solar Industry XII, Trondheim, 2014}, editor = {Oye, Harald A. and Brekken, Harald and Rong, Harry and Tangstad, Merete and Tveit, Halvard}, publisher = {Department of Materials Science and Engineering, Norwegian University of Science and Technology}, address = {Trondheim}, isbn = {978-82-997357-8-0}, pages = {177 -- 188}, abstract = {The present work describes a completely new approach to the solidification refinement of metallurgical-grade silicon. The new process comprises the following steps: (i) The first step involves adding auxiliary metals to the molten silicon in order to segregate the metallic and non-metallic impurities in the secondary phase after cooling. (ii) The melt is rapidly cooled in the cellular solidification regime. This generates a Si microstructure with a defined cell size in which all cell boundaries are surrounded by the secondary phase. Furthermore, the secondary phase should form an interconnected three-dimensional network. (iii) The solids are crushed by shockwaves using electrohydraulic fragmentation techniques. The shockwaves lead to preferential crushing at the interface between the silicon and the secondary phase. (iv) The secondary phases are fast and effectively removed by microwave-assisted high-pressure leaching that was newly developed for this process. The potential of the new refinement procedure is demonstrated with auxiliary metals Ca, Al, and Ti. This new procedure yields a significant decrease in phosphorous and metal impurities.}, language = {en} } @misc{GrafeLoeserSchmitzetal., author = {Grafe, Hans-Joachim and L{\"o}ser, Wolfgang and Schmitz, Steffen and Sakaliyska, Miroslava and Wurmehl, Sabine and Eisert, Stefan and Reichenbach, Birk and Acker, J{\"o}rg and Rietig, Anja and Ducke, Jana}, title = {NMR investigation of boron impurities in refined metallurgical grade silicon}, series = {Physica status solidi. A, Applications and Materials Science}, volume = {212}, journal = {Physica status solidi. A, Applications and Materials Science}, number = {9}, issn = {1862-6319}, doi = {10.1002/pssa.201431908}, pages = {2031 -- 2036}, abstract = {The nuclear magnetic resonance (NMR) method was applied for tracking boron impurities in the refining process of metallurgical grade (MG) silicon. From the NMR signal of the 11B isotope at an operating temperature 4.2 K, the boron concentration can be estimated down to the order of 110 wppm B. After melting and resolidification of MG-Si alloyed with Ca and Ti, a major fraction of B impurities remains in the Si solid solution as inferred from the characteristic NMR frequency. The alloying element Ti does not form substantial fractions of TiB2. Acid leaching of crushed powders of MG-Si alloyed with Ca and Ti can diminish the initial impurity content of B suggesting its accumulation in the grain boundary phases.}, language = {en} }