Reflections on Early Stages of Environmentally Assisted Cracking from Corrosion Pits

A perspective is presented on the evolution of damage due to environmentally assisted cracking (EAC), from crack precursor development through to long crack growth. The variable nature of crack precursors is highlighted with an observation that uncontrolled chemistry excursions or fabrication defects could eliminate any significant delay associated with that step in the damage evolution process. Specimen preparation by machining and grinding can be critical in determining the apparent susceptibility of the metal to EAC and corrosion, and an example for 316L stainless steel is given to show how physical defects generated by the grinding wheel can become the dominant site for pitting attack relative to MnS inclusions. Corrosion pits are the most commonly observed precursor to cracks in aqueous chloride environments. The loci of sites of crack initiation around a pit are discussed and the inherent challenges in quantifying the growth of cracks smaller than the pit depth described with implications for modelling of the pit-to-crack transition. The remarkably enhanced stress corrosion crack growth rate data for short and small cracks in a 12Cr steam turbine blade in a simulated condensate environment are discussed in the context of crack electrochemistry modelling and the implications for engineering integrity.

New Polymer Inclusion Membranes in the Separation of Palladium, Zinc and Nickel Ions from Aqueous Solutions

The new polymer inclusion membrane (PIM) with a 1-alkyltriazole matrix was used to separate palladium(II) ions from aqueous chloride solutions containing a mixture of Zn-Pd-Ni ions. The effective conditions for transport studies by PIMs were determined based on solvent extraction (SX) studies. Furthermore, the values of the stability constants and partition coefficients of M(II)-alkyltriazole complexes were determined. The values of both constants increase with the growing hydrophobicity of the 1-alkyltriazole molecule and have the highest values for the Pd(II) complexes. The initial fluxes, selectivity coefficients, and recovery factors values of for Pd, Zn and Ni were determined on the basis of membrane transport studies. The transport selectivity of PIMs were: Pd(II) > Zn(II) > Ni(II). The initial metal ion fluxes for all the cations increased with the elongation of the alkyl chain in the 1-alkyltriazole, but the selectivity coefficients decreased. The highest values of the initial fluxes at pH = 4.0 were found for Pd(II) ions. The best selectivity coefficients Pd(II)/Zn(II) and Pd(II)/Ni(II) equal to 4.0 and 13.4, respectively, were found for 1-pentyl-triazole. It was shown that the microstructure of the polymer membrane surface influences the kinetics of metal ion transport. Based on the conducted research, it was shown that the new PIMs with 1-alkyltriazole can be successfully used in an acidic medium to separate a mixture containing Pd(II), Zn(II) and Ni(II) ions.

Influence of Aqueous Chloride and Bromide Anions on the Reactivity of ZnO on Bisphenol a Degradation

Zinc oxide (ZnO) nanoparticles have been widely investigated for applications in photocatalytic degradation of organic pollutants in wastewater. Despite the advantages of robust ZnO material, its photocatalytic activity is greatly affected by environmental factors. Halogen ions are commonly found in wastewater, which directly influence the pollutant aggregation and sedimentation, therefore it is necessary to discuss their effect on the photodegradation. The current study assesses the halogen ions effect on the photocatalytic degradation of BPA using different dosage of sodium chloride (NaCl) and sodium bromide (NaBr). The microstructural characterization of ZnO was conducted by transmission electron microscopy and hydrodynamic size was analyzed through dynamic light scattering. Degradation reactions of BPA with ZnO nanoparticles followed pseudo-first-order kinetics. The increase of ZnO dosage from 0.01 g/L to 0.1 g/L enhanced the degradation rate constant of BPA up to 0.089 min-1 (14.8 folds). In order to evaluate the the role halogen ions to degrade BPA, NaBr and NaCl were used. The degradation rate was reduced up to 26 folds (0.0034 min-1) after the addition of NaBr, which was attributed to the increase in hydrodynamic particle size leading, thereby restricting the light adsorption capacity. Noteworthy, upon addition of NaCl from 10 mM to 500 mM concentration, there was only a slight decrease (2.4 folds, 0.037 min-1) on the degradation rate of BPA. Therefore, this study unveils the role of chloride ions as an effective medium for BPA degradation by ZnO nanoparticles, without aggregation, and provides a novel platform for the treatment of organic pollutants in saline water.