Glass-Induced Lead Corrosion of Heritage Objects: Structural Characterization of K(OH)·2PbCO₃

The investigation of the corrosion of a lid made from a tin-lead alloy of a 200 years old beer jug induced by the degradation of the potash based glass revealed SnO, Cerussite (PbCO₃) and K(OH)·2PbCO₃ as main corrosion product. A model experiment, simulating the corrosion of lead at room temperature confirmed the formation of K(OH)·2PbCO₃ as a corrosion product in alkaline, potassium containing medium. For detailed characterization K(OH)·2PbCO₃ was prepared by hydrothermal synthesis, as well. K(OH)·2PbCO₃ crystallizes in space group P6₃/mmc with lattice parameters of a = 5.3389(1) Å and c = 13.9295(5) Å. The structure consists of Pb(OH)_1/2(CO₃)_6/9[CO₃]_3/9^1/2- layers and intercalated K⁺ and exhibits a close relationship to the crystal structure of hydrocerussite (Pb(OH)₂·2PbCO₃), also known as "lead white". A novel structure family, Mⁿ⁺(OH)_n·2PbCO₃ (with n = 1,2), was identified by structure solution of K(OH)·2PbCO₃, which can be assigned to a 2H-type subspecies and detailed comparison to Pb(OH)₂·2PbCO₃, which represents a 3R-type subspecies.