The impedance properties of the oxide film on the Ni–Cr–Mo Alloy-22 in neutral concentrated sodium chloride solution

The oxide film properties on Alloy-22 in the applied potential (E) range −600 mV to 600 mV (vs. saturated KCl, Ag/AgCl reference electrode) were characterized by Electrochemical Impedance Spectroscopy (EIS) in near neutral pH, 5 M NaCl solutions, at 30 °C. The impedance properties of the film were compared to the chromium content of the film determined by X-ray photoelectron spectroscopy (XPS). The oxide film properties on Alloy-22 may be divided into three applied potential (E) ranges: −600 mV ≤ E < −300 mV, −300 mV ≤ E ≤ 300 mV, and E > 300 mV. For the range −600 mV ≤ E < −300 mV the film resistance (R_film) increases with potential accompanied by an increase in Cr₂O₃ content; in the range −300 mV ≤ E ≤ 300 mV, R_film values and the Cr₂O₃ content of the oxide film achieve their maximum values; for E > 300 mV, a decrease in both R_film and Cr₂O₃ is observed accompanied by a significant increase in Cr(OH)₃. Comparison of the impedance properties for Alloy-22 to those of Ni–Cr alloys indicate that the barrier layer oxide on Alloy-22 contains a lower number of less mobile defects, most likely Cr interstitials. Destruction of the barrier layer for E > 300 mV leads to the formation of a thicker, less protective bilayer, which is high in Mo content.     

Crevice corrosion initiation and propagation on Alloy-22 under galvanically-coupled and galvanostatic conditions

The initiation and propagation of crevice corrosion on the Ni–Cr–Mo Alloy-22 has been studied in concentrated chloride solutions under galvanically-coupled and galvanostatic conditions. Under galvanically-coupled natural corrosion conditions crevice corrosion initiated but propagation was limited by repassivation. This was attributed to the slow kinetics of oxygen reduction on passive surfaces external to the crevice. Under galvanostatic conditions a potential more positive than 200 mV_Ag/AgCl and an applied current greater than 5 μA were required to stabilize propagation. A minimum critical current density to establish active sites within the crevice was estimated to be around 250 μA cm⁻².     

Corrosion product analysis on crevice corroded Alloy-22 specimens

Surface analytical techniques were applied to characterize corrosion products formed during the crevice corrosion of the Ni–Cr–Mo(W) Alloy-22 in 5 mol/L NaCl at 120 °C. Micro-Raman spectroscopy demonstrated the formation of polymeric molybdates within the crevice corroded region where intergranular corrosion dominated. The location and chemical speciation of the Mo and W species formed was investigated by Raman mapping. Crevice corrosion was found to propagate preferentially across the alloy surface rather than to penetrate deeply at localized sites, a feature which appears to be linked to the formation and build-up of polymeric molybdates.     

The evolution of crevice corrosion damage on the Ni–Cr–Mo–W alloy-22 determined by confocal laser scanning microscopy

Crevice corrosion of alloy-22 was studied galvanostatically (10–200 μA) at 120 °C in 5 M NaCl. Corrosion damage was analyzed by confocal laser scanning microscopy to obtain penetration profiles. Three-dimensional images demonstrate that damage morphologies varied with applied current. At low applied currents (?70 μA), propagation predominantly leads to penetration into the alloy, whereas at higher applied currents (>70 μA) corrosion damage spreads across the alloy. Limited penetration depths at higher currents are attributed to metal dissolution inhibition by the rapid formation of insoluble molybdates, which force propagation to shift to areas unprotected by molybdate layers.     

Evidence of a Time-Dependent Long-Term Stage of Memory for a Spatial Learning Task in the Chick (Callus gallus).

The generalizability of temporal parameters of memory formation previously observed for a passive avoidance task was investigated in a spatial task with day-old chicks (Callus gallus). The percentage improvement in completion time over 2 separate trials was measured, and chicks were found to complete the second trial faster at all times tested up to 2 hr, except at 55 min posttraining. In addition, retention at 120 min, but not at 30 min, posttraining was found to be impaired by protein synthesis inhibition. These findings are consistent with the timing of a long-term stage of memory formation following passive avoidance training, implying that there may be some hardwiring to the temporal characteristics of memory formation in this species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Collaborative investigations on thoron and radon in some rural communities of Balkans

This paper deals with the results of the first-field use in the Balkans, i.e. Serbia and Republic of Srpska (Bosnia and Hercegovina), of a passive polycarbonate Mark II type and poliallyldiglycol carbonate (Cr-39) alpha track detectors sensitive to thoron as well as to radon. Both types of solid state nuclear track detectors were designed and supplied by National Institute of Radiological Sciences (NIRS), Chiba, Japan. The commercial names for these detectors which all have been field tested in Balkan rural communities are known as: UFO and RADUET passive discriminative radon/thoron detectors. No database of thoron and thoron progeny concentrations in dwellings in Serbia or Balkans region exist, and as a result, the level of exposure of the Serbian population to thoron and its progeny is unknown so far.