Probabilistic Assessment of Reinforcing Steel Depassivation in Concrete under Aggressive Chloride Environments Based on Natural Exposure Data

The probability distributions of the critical threshold chloride concentration Ccr, the chloride diffusion coefficient D, and the surface chloride concentration Cs are determined based on the collected natural exposure data, and the probability estimation of reinforcement depassivation in concrete is presented using Monte-Carlo simulation. From sensitivity analysis of mean value for ccr, cs, and D on the depassivation probability of reinforcement, it is found that ccr, cs, and D respectively has the greatest, smaller, and the lowest effect on the probability of depassivation. Finally the effect of stress state of concrete on the reinforcement depassivation probability is analyzed. It is found that the influence of stress state becomes apparent as exposure time increases.

First-principles calculations of the hole-induced depassivation of SiO2/Si interface defects

The holes induced by ionizing radiation or carrier injection can depassivate saturated interface defects.The depassivation of these defects suggests that the deep levels associated with the defects are reactivated,affecting the performance of devices.This work simulates the depassivation reactions between holes and passivated amorphous-SiO_(2)/Si interface defects(HP_(b)+h→P_(b)+H^(+)).The climbing image nudged elastic band method is used to calculate the reaction curves and the barriers.In addition,the atomic charges of the initial and final structures are analyzed by the Bader charge method.It is shown that more than one hole is trapped by the defects,which is implied by the reduction in the total number of valence electrons on the active atoms.The results indicate that the depassivation of the defects by the holes actually occurs in three steps.In the first step,a hole is captured by the passivated defect,resulting in the stretching of the Si-H bond.In the second step,the defect captures one more hole,which may contribute to the breaking of the Si-H bond.The H atom is released as a proton and the Si atom is three-coordinated and positively charged.In the third step,an electron is captured by the Si atom,and the Si atom becomes neutral.In this step,a Pb-type defect is reactivated.

Application of electrochemical depassivation in PRB systems to recovery Fe^0 reactivity

Permeable reactive barriers （PRBs） show remarkable Cr（VI） removal performance. However, the diminished removal rate because of mineral fouling over time is the bottleneck for application of PRBs. The present study demonstrated that electrochemical depassivation was effective for recovering the Fe^0 reactivity, and minerals can be cleaned layer by layer with no secondary ion contamination and no transformation from Cr（III） to Cr（VI）. The removal recovery rate increased with increasing electrolysis voltage before reaching the optimal electrolysis voltage, and then decreased as the electrolysis voltage further increased. The recovery effect at electrolysis voltages of 5, 10, and 15 V show the same trend as a function of electrolysis time, where recovery rate first increased and then decreased after reaching the optimal electrolysis time. The Cr（VI） removal rate significantly decreased with increasing electrolysis distance. Furthermore, Fe^0 brush meshes electrode, Fe^0 fillings, and polyvinyl chloride （PVC） meshes separators were combined to create an Electro-PRB configuration for the caisson excavation construction technique, which lays the foundation for establishment of promising Electro-PRB systems to treat Cr（VI）-contaminated groundwater.

Interaction of the Linear-Connected Pittings

In this work, the mechanism of interaction of pittings, occurring on the heterogeneous surface of the passivated metal at presence in an aqueous electrolyte solution the activating (halide) anions is developed. A mathematical scheme describing this mechanism is presented. The equations for the currents density of the anodic dissolution of pitting as a function of concentration of activating anions and free water are obtained. The closed system of the equations representing a basis theory of an interaction of pittings is obtained.

Cl-induced passivity breakdown in α-Fe_(2)O_(3)(0001), α-Cr_(2)O_(3)(0001),and their interface: A DFT study

The presence of chloride ions is the critical factor of passivity breakdown of the protective film and eventually leads to localized corrosion. However, the mechanism and the role of chlorides in these processes are still controversial. Hematite and chromia are generally believed to be the major components of outer and inner oxide layers on stainless steels. In the present paper, a comparative study of Cl ingress into pristine and defective α-Fe_(2)O_(3)(0001) surface, α-Cr_(2)O_(3)(0001) surface, along with their interface, was conducted using density functional theory. Vacancy formation energy calculation confirms good stability of α-Cr_(2)O_(3)and high reactive activity of the interface region. Cl inserts into an O vacancy is energetically more favorable than Fe vacancy and interstitial site, demonstrating Cl-induced degradation complies with the ion exchange model. Transition state search for Cl diffusion through O vacancies shows α-Cr_(2)O_(3)is more protective than α-Fe_(2)O_(3), while the interface region is the weak point of the duplex passive film.

Ligand-mediated contaminant degradation by bare and carboxymethyl cellulose-coated bimetallic palladium-zero valent iron nanoparticles in high salinity environments

The application of nanoscale zero-valent iron(nZVI) for the degradation of contaminants has been extensively investigated, however, few studies have focused on degradation in high salinity environments. In this study, the ability of bare and carboxymethyl cellulose(CMC)-coated bimetallic Pd-nZVI particles to degrade 33′44′-tetrachlorobiphenyl in high saline water(SW) is examined with particular attention given to the effects of ethylenediaminetetraacetic acid(EDTA) on the rate of degradation. EDTA enhances the reactivity of Pd-nZVI in SW, with evidence provided to link this to the removal of the passivating layer. Additionally, a conceptual model is proposed which provides a quantitative description of the removal of these iron oxide layers in the presence of EDTA. An optimum EDTA to bare Pd-nZVI molar ratio of 0.1 exists, with insufficient EDTA unable to remove the passivating layer whilst excess EDTA results in Fe loss and enhanced agglomeration due to magnetic attraction of the bare Fe(0) particles. In contrast, CMCcoating of Pd-nZVI assemblages actually impedes degradation, despite the coated particles displaying a smaller average size compared to uncoated particles, with even the presence of EDTA in this case not significantly improving degradation. The reduced reactivity in the presence of CMC is primarily attributed to the effect of CMC on the association of Pd with nZVI particles. In particular, the presence of CMC reduced the total amount of Pd incorporated with the stabilized particles compared to the non-stabilized particles.Additionally, the presence of CMC results in less Pd present in its reactive zero-valent oxidation state.