Aqueous Synthesis of Mixed Yttrium−Barium Oxalates

The experimental domain for seeded precipitation of mixed (Y, Ba) oxalates has been investigated in the system [Y(OH) 3, Ba(OH) 2 ]−H 2 C 2 O 4 −[HNO 3, NaOH)]−H 2 O. A statistically designed series of experiments was performed in order to highlight the relative effects of various factors on the precipitate composition: reaction temperature (30−40 °C), rate of coreactant addition, volume of added seeding suspension, and aging time of the precipitate. The recently discovered Y 2 Ba 4 (C 2 O 4 ) 7 ·18H 2 O oxalate, in the form of octahedral crystals, has been detected in all the precipitates, together with another unknown mixed (Y, Ba) oxalate. Calculations based on elemental composition and thermogravimetric data, assuming residual amounts of BaC 2 O 4 ·0.5H 2 O, allowed the estimation of the probable stoichiometric formula of this new compound: Y 2 Ba 2 (C 2 O 4 ) 5 · w H 2 O. From SEM observations this compound precipitates in the form of pinacoidal crystals. The results of the statistical analysis have shown that the formation of Y 2 Ba 4 (C 2 O 4 ) 7 ·18H 2 O is favored by lower temperature, higher reactant addition rate, and lower volume of seeding suspension. The formation of Y 2 Ba 2 (C 2 O 4 ) 5 · w H 2 O occurs more readily at higher temperatures, for slower reactant addition. The two mixed (Y, Ba) oxalates and BaC 2 O 4 ·0.5H 2 O crystals were already present in the seeding suspension. Therefore, the seed suspension could not improve the selective formation of any mixed oxalate in the seeded, fed-batch system used. The most favorable experimental conditions were then successfully transferred to a new segmented flow tubular reactor, recently developed in our laboratory, allowing the selective precipitation of Y 2 Ba 4 (C 2 O 4 ) 7 ·18H 2 O for the first time.