Reaction of superconducting Y(Ba1.5Sr0.5)Cu3Oy (abbreviated as YS-123) powder with water in a closed system at pH 7 and 25 °C, after 150 h, the concentration ratio of Y:Ba:Sr:Cu ion in the solution is 0.0025:1:0.33:0.0003. Mass equation of the reaction is similar to that of YBa2Cu3Oy (abbreviated as Y-123). Leaching rate of the Ba ion is higher than that of the Sr ion at the beginning of the reaction, which reflects the basicity difference between these two alkaline earth elements. The initial rate equation is expressed as Ro = k [S]oa [H3O+]ob. [S]o is the initial surface area of YS-123 powder and H3O+ a catalyst. A and b are found to be 0.99 ± 0.02 and 0.58 ± 0.02, respectively. The initial rate, Ro, for 100.1 mg powder with a mean radius of 0.025 mm at pH 7 and 25 °C is 1.35 ’ 10-6 mol·min-1. Rate constant, k, is (0.54 ± 0.03), (1.1 ± 0.1) and (1.90 ± 0.08) ’ 10-3 mol·min-1·cm-2·M-0.6 for the reaction at 10, 25 and 40 °C, respectively, by using a = 1 and b = 0.6 for calculation. Activation energy (Ea) and pre-exponential factor (A) calculated from the Arrhenius equation are 31.2 ± 0.4 kJ·mol-1 and (3.0 ± 0.4) ’ 102 mol·min-1·cm-2·M-0.6. Although the amount of Sr substitution to Ba is only 25%, initial reaction rate of YS-123 in water is 2 orders magnitude smaller than that of Y-123 at pH 7.
Relation:
Journal of the Chinese Chemical Society=中國化學會會誌 49(5), pp.867-873
