Food containers, metals exposed to the atmosphere, and structural metals exposed to corrosive environ-* Electrochemical Society Active Member.ments are often protected by polymeric coatings, simple or complex in formulation. The rate of corrosion at the metal-polymer interface in the earliest stages is difficult to determine, particularly when the coating ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 150.214.146.47 Downloaded on 2015-04-13 to IP

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A neutron powder diffraction study of α‐normaland β‐PbO2 , both chemically prepared and electrochemically formed in cycled battery plates, was carried out to correlate the electrochemical activity of the lead‐acid battery with the atomic arrangement of the electrode constituents. Our results are consistent with the presence of hydrogen in the structure of β‐PbO2 , but the departure of the occupancy factors from stoichiometric values are not large enough to unambiguously establish whether there are lead or oxygen deficiencies. If the Pb:O ratio corresponds to exact stoichiometry, any hydrogen which is present must be accompanied by a reduction of Pb+4. There is a significant increase in the lattice parameter a of β‐PbO2 in cycled battery electrodes relative to the value found in chemically prepared β‐PbO2 . No change in the c parameter, however, was detected. These dimensional changes are consistent with a configuration for hydrogen similar to that observed in the rutile‐type structure of SnO2 , in which there are OH− ions oriented perpendicular to the c axis. The profile parameters obtained in this analysis show that the crystallites of β‐PbO2 in the positive plate material of a battery cycled three times (Y3) are smaller than those in the chemically prepared compound (∼450Å vs. 800Å), while there are no significant differences between the latter and β‐PbO2 in the positive plate material of a battery cycled 36 times (Y36). The average structure of α‐PbO2 cannot be accurately determined by profile analysis, at the present time. The difficulties encountered in the refinement may be due to extensive defects, nonspherical crystallites of small size, and/or small departures of the structure from orthorhombic symmetry.