TY - BOOK

T1 - Mechanisms of fixed contamination of commonly engineered surfaces

AU - Williamson, Becky

PY - 2018

Y1 - 2018

N2 - This project is concerned with developing a greater understanding of the deposition of radioactive solids,colloids, or ions suspended in aqueous liquid onto the surface of stainless steel. Fixed contamination oncontaminated metallic surfaces is commonly removed using (electro) chemical methods. The mostcommon methods employed are the use of mineral acids or MEDOC (Metal Decontamination byOxidation with Cerium). However, these result in dissolution of the passive oxide layer formed at themetal surface. This increases the level of secondary waste which, in turn, increases the burden of effluenttreatment plants. The passivation of steels in HNO3 is complicated by the autocatalytic reduction ofHNO3 to aqueous HNO2 which attacks the steel surface. We describe the effect of this behaviour onprocess steels in stagnant and/or flowing conditions. Rotating Disk Electrode (RDE) studies indicate thatat HNO3 concentrations ≤20% wt. the reaction is surface based. At HNO3 concentration ≥20% wt. thereaction occurs in the bulk solution. We established a series of corrosion potentials for varyingconcentrations of nitric acid. These corrosion potentials allowed us to age steel in a controlled fashion.Thus, we describe work carried out on electrochemically accelerated oxide growth on 316L SS andSS2343 in HNO3 media and HNO3 media with radionuclide surrogates (depleted U, Ce and Eu).Characterisation was performed using combined Linear Sweep Voltammetry (LSV), ElectrochemicalImpedance Spectroscopy (EIS) and Electrochemical Quartz Crystal Microgravimetry (EQCM)measurements. Areas of active, passive, high voltage passive, transpassive and secondary passivationregimes in the associated current voltage were identified. Further, we have directly measured the growthof that layer by using in situ microgravimetry. X-Ray Photoelectron Spectroscopy (XPS) was used todetermine film composition and presence of contaminant uptake. The passive film on 316L SS is formedof a passive film consisting of Cr(III) hydroxide rich layer and Cr(III) oxide layers at lower potentials.With increasing HNO3 and potential the layer becomes more Cr(III) oxide rich before oxidising to Cr(VI).No radionuclide surrogate contaminants were detected within passive films formed in this study.

AB - This project is concerned with developing a greater understanding of the deposition of radioactive solids,colloids, or ions suspended in aqueous liquid onto the surface of stainless steel. Fixed contamination oncontaminated metallic surfaces is commonly removed using (electro) chemical methods. The mostcommon methods employed are the use of mineral acids or MEDOC (Metal Decontamination byOxidation with Cerium). However, these result in dissolution of the passive oxide layer formed at themetal surface. This increases the level of secondary waste which, in turn, increases the burden of effluenttreatment plants. The passivation of steels in HNO3 is complicated by the autocatalytic reduction ofHNO3 to aqueous HNO2 which attacks the steel surface. We describe the effect of this behaviour onprocess steels in stagnant and/or flowing conditions. Rotating Disk Electrode (RDE) studies indicate thatat HNO3 concentrations ≤20% wt. the reaction is surface based. At HNO3 concentration ≥20% wt. thereaction occurs in the bulk solution. We established a series of corrosion potentials for varyingconcentrations of nitric acid. These corrosion potentials allowed us to age steel in a controlled fashion.Thus, we describe work carried out on electrochemically accelerated oxide growth on 316L SS andSS2343 in HNO3 media and HNO3 media with radionuclide surrogates (depleted U, Ce and Eu).Characterisation was performed using combined Linear Sweep Voltammetry (LSV), ElectrochemicalImpedance Spectroscopy (EIS) and Electrochemical Quartz Crystal Microgravimetry (EQCM)measurements. Areas of active, passive, high voltage passive, transpassive and secondary passivationregimes in the associated current voltage were identified. Further, we have directly measured the growthof that layer by using in situ microgravimetry. X-Ray Photoelectron Spectroscopy (XPS) was used todetermine film composition and presence of contaminant uptake. The passive film on 316L SS is formedof a passive film consisting of Cr(III) hydroxide rich layer and Cr(III) oxide layers at lower potentials.With increasing HNO3 and potential the layer becomes more Cr(III) oxide rich before oxidising to Cr(VI).No radionuclide surrogate contaminants were detected within passive films formed in this study.

U2 - 10.17635/lancaster/thesis/416

DO - 10.17635/lancaster/thesis/416

M3 - Doctoral Thesis

PB - Lancaster University

ER -