Refining of Tantalum and Niobium Refining of Tantalum and Niobium Choudhury,, A. 19930101 00:00:00 LEY BOLD DURFERRIT Rückinger Str. 12 D6455 Erlensee, Germany CONTENTS Page INTRODUCTION CONSIDERATIONS FOR THE MELTING EQUIPMENT METALLURGY OF THE REMOVAL OF UNDESIRED IMPURITIES ECONOMICS OF ELECTRON BEAM MELTING