| A high fidelity in situ technique for measuring electrochemical noise data on carbon steel in alkaline solutions, referred to as Electrochemical Emission Spectroscopy (EES), or Electrochemical Noise Measurement (ENM), has been developed in this thesis as a means of monitoring general corrosion and pitting corrosion on carbon steel in simulated DOE nuclear waste storage systems and to develop a better understanding of the corrosion processes of carbon steel in these environments. The data acquisition system is essential to the accuracy of voltage and current measurements and the validity of experimental data for further analysis. Time and frequency domain analyses display different characteristics for general corrosion and pitting corrosion. DOE raw noise data analysis shows that the penetration corrosion rate in liquid/sludge phases is in the order of 10−2–10−3 mm/year for the carbon steel-lined tanks in the DOE waste environments. In addition, good correlation has been observed between EES and traditional Linear Polarization Resistance (LPR) method in detecting the corrosion rates of carbon steel.; The passive state on iron in EDTA (ethylene diammine tetra acetic acid, disodium salt, C10H14N2Na2O 8)-containing borate buffer solutions of pH ranging from 8.15 to 12.87 at ambient temperature has been explored using Electrochemical Impedance Spectroscopy (EIS), another powerful in situ electrochemical method for investigating steady-state electrochemical and corrosion systems. It has been found that frequency sweep range, perturbation voltage amplitude, solution pH, and film formation voltage are important factors to influence the impedance of passive iron. The steady-state passive films formed on iron have been shown to satisfy the conditions of linearity, causality, stability and finiteness, on the basis of the good agreement observed between the experimental impedance data and the Kramers-Kronig transforms calculated data over most of the frequency range employed.; The Point Defect Model (PDM) has been tested as a valid means of accounting for the passivity of iron, and most of its predictions have been experimentally observed. An impedance model for passive iron based on the PDM has been developed to interpret the impedance of this metal in borate buffer solutions as a function of applied film formation voltage and solution pH. Nonlinear curve fitting to the experimental data derives kinetic parameters (transfer coefficients and standard rate constants) for the interfacial reactions occurring in the barrier oxide layer on passive iron. This thesis concludes that the dominant defects for passive iron must be oxygen vacancies, or cation (Fe2+ or possibly Fe3+) interstitials, or both, due to the electronic character of the passive film. |
