When Bi1.8Pb0.4Ca2Sr2Cu3Oy powders were immersed into deionized water, a large quantity of Ca2+ and Sr2+ ions was detected in the aqueous solution, indicating the decomposition of the Bi1.8Pb0.4Ca2Sr2Cu3Oy superconductors in water. The pH of the solution was initially increased rapidly to 11.1 due to the formation of OH- ions. However, after 30 min, in the open system, the Ca2+ and Sr2+ ions would further react with CO2 in the atmosphere to form sparingly soluble carbonates and the pH of the solution was slowly decreased to 9.81 over 20 h. Only a small amount of Bi3+, Pb2+ and Cu2+ ions was detected in the aqueous solution. Non-soluble products, such as Bi2CuO4, CuO and Cu6PbO8, were observed in the reaction residue which might act as a barrier to prevent deterioration of the superconductor with water in the bulk sample. The chemical equation was given as Bi1.8PbxCa2Sr2Cu3Oy(s)+4H2O→2Ca2+(aq)+2Sr2+(aq) +8OH-(aq)+0.9Bi2CuO4(s)+xCu6PbO8(s)+(3−0.9−6x)CuO(s).
