CAREER: Complex Lead Oxides as Corrosion Films and Extended Inorganic Hybrids

Oberlin College, Oberlin OH

Investigators

Abstract

TECHNICAL SUMMARY: Carboxylic acid corrosion of lead and its alloys is a major cause of degradation of historic cultural objects such as organ pipes. Complex lead oxide carboxylates form as products of this corrosion process and constitute a structurally rich yet understudied family of compounds. This project, supported by the Solid State and Materials Chemistry program, pairs analysis of the growth and composition of corrosion films with advanced structural characterization of lead oxide carboxylate corrosion products and their related synthesized phases. Laboratory exposure studies will establish how susceptibility of lead-tin alloys to carboxylic acid attack depends on alloy composition and humidity. Phase identification, elemental mapping, and high-resolution oxidation state identification in oxide corrosion films will provide insight into the role of each metal in the corrosion process. The project aims to move understanding of carboxylic acid attack of lead-tin alloys from the phenomenological to the mechanistic. Model studies will be linked to artifact deterioration through analysis of authentic organ pipe samples and use of environmental data from organ cases. Hydrothermal methods will be employed to synthesize a family of lead oxide carboxylates, for which observed corrosion products form the basis. These hybrid materials contain infinite components based on edge-sharing Pb4O tetrahedra. The partial charge model will provide insight into the solution influences governing formation of diverse 0-, 1-, and 2-D Pb4O-based architectures. 207Pb NMR will complement X-ray diffraction in characterization of Pb2+ lone pair stereoactivity. This project takes place at a primarily undergraduate institution and is centered on the participation of undergraduate researchers. Applications of the research to the field of art conservation will be used as the basis for an integrated program of education of undergraduate non-science majors and interdisciplinary K-12 outreach. NON-TECHNICAL SUMMARY: Corrosion of lead and its alloys leads to loss of performance in objects as varied as lead acid batteries and historic organ pipes. Particularly in light of its toxicity, full understanding of the interactions of lead with its environment and the chemistry of its corrosion products is critical. This project, supported by the Solid State and Materials Chemistry program, will use laboratory exposure experiments, as well as characterization of authentic samples, to elucidate the causes and mechanisms of corrosion of lead-tin alloy organ pipes. Compounds that form as corrosion products, as well as related synthesized phases, will be subjected to detailed structural analysis. Outcomes will have applications to the conservation of culturally important organs that are enjoyed in concerts and recordings, treasured by musicologists for their ties to notable composers, and valued as physical documents of pre-industrial handcraft and technology. This project will take place at Oberlin College, a primarily undergraduate institution with a strong tradition of preparing students for graduate study and careers in science. Undergraduate students will be the primary participants in all phases of the project research. They will receive training in techniques of materials characterization that are not always encountered in the canonical chemistry curriculum. The PI will use the link between the project research and art conservation as the starting point for an undergraduate course for non-science majors on the chemistry of art materials. Through partnership with Oberlin?s nationally recognized Allen Memorial Art Museum (AMAM), students in the course will produce written, audio, and hands-on tools to create a materials tour of the museum. These media will be implemented in the AMAM?s established K-12 outreach program.