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Research Objective The principal goals of this project are to develop advanced electrochemical emission spectroscopic (EES) methods for monitoring the corrosion of carbon steel in simulated DOE liquid waste and to develop a better understanding of the mechanisms of the corrosion of metals (e.g. iron, nickel, and chromium) and alloys (carbon steel, low alloy steels, stainless steels) in thes e environments. During the first two years of this project, significant advances have been made in developing a better understanding of the corrosion of iron in aqueous solutions as a function of pH, on developing a better understanding of the growth of passive films on metal surfaces, and on developing EES techniques for corrosion monitoring. This report summarizes work on beginning the third year of the 3-year project. Research Progress and Implications A new rate law for the growth of a passive film on a metal surface has been derived. The new law, which is based on the Point Defect Model (PDM) for the growth and breakdown of passive films [1], is found to account for the transient in thickness of the anodic film on tungsten in phosphate buffer, under voltage cycling, much more accurately than does the High Field Model. We have used tungsten, rather than iron, for this analysis, because the passive film on W is a pure oxygen vacancy conductor (for which the theory for thickness transients is currently developed) and because experimental data are available from our previous work [2]. The theory is currently being applied to iron, but the required experimental data were not available at the time of preparation of this report. The temporal change in thickness of the passive film on tungsten in phosphate buffer solution (pH = 1.5) as the potential is cycled from 10 V SCE to 6 V SCE and back to 10 V SCE is shown in Figure 1 [2]. The experimental data were calculated from measured capacitance data and by assuming that the film could be modeled as a parallel plate capacitor with a dielectric constant of 35 [2]. However, the parallel plate model is not entirely appropriate, because a sharp drop occurs in the calculated "thickness" as the potential is stepped from 10 V SCE in the negative direction. We previously [2] attributed this sudden decrease in apparent thickness to an artifact associated with a change in the space charge capacitance, an interpretation that was confirmed by also monitoring the change in thickness using optical reflectance measurements (no sudden change in thickness was detected using this latter technique). Excellent agreement is obtained between theory and experiment, which further supports the validity of the Point Defect Model. Finally, it is important to note that the High Field Model, which has been used for more than seventy years to describe the growth of anodic oxide films on metals, is unable to account for any of the data shown in Figure 1. Although the passive state of iron has been extensively studied in the past, considerable disagreement exists as to the nature and composition of the passive fil...