Formation of Copper–Neodymium Intermetallic Compounds by Carbothermic Reduction of Neodymium Oxide in the Presence of Copper

Abstract

Carbothermic reduction of neodymium(III) oxide (Nd 2 O 3 ) was performed by arc melting and in a graphite resistance furnace, using copper as a solvent metal. Successful carbothermic reduction was evident by formation of copper−neodymium intermetallics, where predominant phases were found to be Cu 6 Nd and Cu 5 Nd. The reduction reaction is proposed to be caused by thermal decomposition of neodymium oxide carbide (Nd 2 O 2 C 2 ) forming a molten mixture of neodymium(III) oxide and neodymium dicarbide (NdC 2 ) upon release of carbon monoxide (CO(g)), where subsequent decomposition of neodymium dicarbide was facilitated by a reduction in activity of formed elemental neodymium species solvated in molten copper. Addition of carbon in excess of neodymium oxide carbide stoichiometry was found to correlate with increased concentration of neodymium in copper, likely caused by an increase in concentration of neodymium dicarbide. 51 energy efficient, high productivity methods of producing and 52 recycling Nd are sought. 53 Due to the high affinity between rare earth elements and 54 carbon, forming a range of stable carbides and oxide carbides, 55 carbothermic reduction as a method of producing the 56 corresponding elemental compounds has been considered to 57 be difficult at best. 9 From available literature, several accounts 58 of carbothermic reduction with respect to elements that are 59 known to form stable carbides were found, among these, the 60 rare earths are represented. Some methods mentioned are 61 reduction by dissolving into suitable solvent metals, reaction 62 between carbides, and an element forming a more stable 63 carbide, formation of nitrides then vacuum decomposition of 64 said nitrides in solution with suitable solvent metals, etc. 10−18 65 Examples from literature reveals, among others, a patent by 66 Staggers that describes carbothermic reduction of rare earth 67 elements by formation of rare earth silicide alloys. 18 The 68 method apparently allows for the simultaneous carbothermic 69 reduction of rare earth oxides, especially cerium oxide (CeO 2 ) 70 along with alkaline earth oxides such as barium oxide (BaO), 71 calcium oxide (CaO), and strontium oxide (SrO) in the 72 presence of silica (SiO 2 ) and elemental iron (Fe) at elevated 73 temperatures, forming both rare earth and alkaline earth