This is SGER award in the Inorganic, Bioinorganic and Organometallic Chemistry Program to Professors Jay Switzer and Eric W. Bohannan at the University of Missouri at Rolla supports research on a current, urgent, public health problem involving lead in drinking water supplies from the perspective of materials science and electrochemistry. The passivation role of the formation and dissolution of oxide films, such as PbO2, PbO, CuO and Cu2O, on the inside of lead and copper pipes will be determined in the presence of commonly-used water disinfectants, hypochlorite and chloramines. The oxides on the inside of actual Pb service lines will be quantitatively analyzed and modeled with electrochemical studies of film growth and dissolution. Dr. Michael Schock of the Water Supply and Water Resources Division of the U.S. Environmental Protection Agency in Cincinnati, Ohio will provide pipes from affected water districts. The oxide films intact on the metal pipes will be analyzed by X-ray diffraction (XRD) in order to determine phases, crystallographic orientation, grain size and strain by Rietveld analysis. Cross-sectional transmission electron microscopy (TEM) will be used to determine the cross-sectional composition and grain size of the films. Due to the softness of Pb, focused ion beam techniques will be employed to prepare the thin cross-sections. Model systems will also be studied by standard electrochemical techniques, such as cyclic voltammetry, and the electrochemical quartz crystal microbalance (EQCM) to follow the growth and dissolution of oxide films in various water chemistries.
Both orthorhombic and tetragonal films of PbO2 will be deposited onto EQCM electrodes followed by studies of the dissolution of the films in the presence of hypochlorite, chloramines, carbonate, orthophosphate, and other species known to be present in municipal drinking water. Film growth by depositing Pb layers on Au or Pt EQCM electrodes will be followed to determine whether hypochlorite and chloramines can oxidize the surface to PbO2. These films will be analyzed by glancing angle XRD, and possibly XPS, to verify the film formation. Although the emphasis is on determining the cause of elevated lead levels in drinking water, the problem of Cu pipe dissolution will also be studied. These problems may be correlated, because Cu in contact with Pb may lead to a galvanic reaction whereby the Cu is oxidized (and dissolved) and the PbO2 passivating layers are reduced. This galvanic reaction might arise at the junctions of Pb and Cu pipes, at Pb solder joints on Cu pipes, and in "lead-free" brass fixtures.
This work may provide guidance from a chemical and materials science perspective to municipal water systems to assist in lowering lead levels in drinking water. The research team of chemists, chemical engineers, and materials scientists at the Materials Research Center at the University of Missouri at Rolla will provide interdisciplinary training for graduate students and postdoctoral associates.
