We present the mechanisms of formation of mesoporous scandia-stabilized zirconia using a surfactant-assisted process and the effects of solvent and thermal treatments on the resulting particle size of the powders. We determined that cleaning the powders with water resulted in better formation of a mesoporous structure because higher amounts of surfactant were preserved on the powders after washing. Nonetheless, this resulted in agglomerate sizes that were larger. The water-washed powders had particle sizes of >5 μm in the as-synthesized state. Calcination at 450 and 600 °C reduced the particle size to ∼1-2 and 0.5 μm, respectively. Cleaning with ethanol resulted in a mesoporous morphology that was less well-defined compared to the water-washed powders, but the agglomerate size was smaller and had an average size of ∼250 nm that did not vary with calcination temperature. Our analysis showed that surfactant-assisted formation of mesoporous structures can be a compromise between achieving a stable mesoporous architecture and material purity. We contend that removal of the surfactant in many mesoporous materials presented in the literature is not completely achieved, and the presence of these organics has to be considered during subsequent processing of the powders and/or for their use in industrial applications. The issue of material purity in mesoporous materials is one that has not been fully explored. In addition, knowledge of the particle (agglomerate) size is essential for powder handling during a variety of manufacturing techniques. Thus, the use of dynamic light scattering or any other technique that can elucidate particle size is essential if a full characterization of the powders is needed for achieving postprocessing effectiveness.
Generally, corrosion rates for sheet pile walls observed in nature and those obtained in the laboratory are different. In order to compare natural and laboratory corrosion rates, corrosion tests were carried out with an electrochemical corrosion cell. Various mild steel samples which were taken out from different sheet pile structures were examined with synthetic brackish water and synthetic seawater as immersion media. It was ensured that the electrical conductivity and the pH‐values were identical to those of the natural waters from which the sheet pile samples came from. The experimental results indicate that underwater corrosion rates in nature are only about one tenth to one eighth of the laboratory values. The corrosion rates in nature depend on the media and the corrosion zone. Furthermore, in laboratory test procedures, the initial corrosion is always tested whereas in nature a “protecting” layer of rust is formed, that lowers corrosion. Therefore, comparison of the values of the experiments with those from nature should be defined in accordance to age and zone of hydraulic steel structures. As a consequence, a corrosion coefficient with consideration of the age of structures was formed. The introduction of the coefficients's dependence on the lifetime of the construction allows improved corrosion rate predictions when the chemical composition of the immersion media is detected.
In a typical electrochemical cell, platinum wire is used as an anode for electrolytic reduction of UO2 spent LWR fuel in a molten salt system consisting of LiCl + 2-8 wt% Li2O. During the electrolysis, the metallic lithium migrates to the anode and attacks the platinum wire. Stability of the anode material is critical for sustained operation of the electrolytic UO2 reduction cell for reprocessing spent nuclear oxide fuels. This investigation aims at developing dimensionally stable anode materials for sustained operation under aggressive conditions. The investigated materials are: tungsten, molybdenum, hafnium, and tantalum, and stainless steels type 304 and 316. Corrosion properties of the candidate materials are compared with that of platinum using electrochemical polarization and impedance spectroscopy results. In order to simulate the lithium attack on the anode material, lithium was cathodically deposited and equilibrated for about one hour before starting the anodic polarization test in LiCl + 2 wt% Li2O molten salt at 650°C. Platinum samples showed an extensive surface cracking due to penetration of lithium. Type 316 stainless steel samples showed higher impedance and smaller passive current density than that of platinum at lower anodic potentials. Tungsten samples showed higher electrochemical impedance modulus and better passivity than any other materials tested in this study.
The W 0 -factor is a common metric to express the aggressivity of water against unalloyed iron. It accounts for multiple parameters, called rating numbers, which represent the concentration of chloride, sulfate and calcium ions, the pH-value and the acid capacity of the immersion medium. The use of ranges in the physical quantities metric rating number, however, allows for unaccounted variations in the immersion medium composition, i.e., slightly different immersion media may produce the same W 0 -factor. To verify the results, the experiments were also carried out with natural waters as immersion media and their W 0 -factors were determined. In addition, the DOC content, which is not included in the W 0 -factor, has an impact on the corrosive character of the immersion medium. In order to account for the influence of the DOC content in the measurements, multiple solutions with different DOC concentrations were investigated. The results show that a higher DOC content (based on humic substances) in the observed solutions causes a reduction in the corrosion rate. This result agrees with observations of nature.
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