Chemical unstabilities in La0.25Ce0.52Nd0.17Pr0.06O2 induced by mechanical milling

M. R. ESQUIVEL

Ciudad de Buenos Aires-Argentina

Congreso; CONGRESO SAM/CONAMET 2009; 2009

Asociación Argentina de Materiales

La0,25Ce0,52Nd0,17Pr0,06O2 was synthesized from the oxidation of a La0,25Ce0,52Nd0,17Pr0,06 alloy in air. The structure was refined with space group Fm3m with lanthanides in Wyckoff positions (4a) and oxygen in (8c), respectively. The cell parameter found was a = 5,512(7) Å. The oxide was mechanically milled in a low energy mill during 150 h. Unlike regular milling processes, no successive control of fracture and cold welding was observed and no extensive changes in microstructural properties were achieved. Instead, the structure resists damage and amorphization and processing leads to the formation of a highly reactive structure. It reacts with oxygen and humidity at room temperature leading to the formation of La0,25Ce0,52Nd0,17Pr0,06(OH)3 after 150 h of milling. The hydroxide produced was assigned to space group P63/m with Lanthanides randomly distributed in Wyckoff positions (2c) and Oxygen in (6h). Cell parameters found were a = 6,375 Å and c = 3,753 Å.  The formation of the hydroxide and the thermal stability of the oxide were also analyzed by Differential Scanning Calorimetry (DSC). The oxide is unstable under milling.  La0,25Ce0,52Nd0,17Pr0,06(OH)3 evolves under heating by releasing water and producing exothermal events. The results are discussed along with the stabilities of CeO2 and La(OH)3.