High-temperature nitridation of Ni-Cr alloys

The nitriding behavior of nickel-chromium alloys was investigated at 1398 K over the range 1 to 6000 bar of external nitrogen pressure. The morphology of the nitrided zone depends on the concentration of chromium in the initial alloy and the N2 pressure (fugacity) applied upon the system. The transition from CrN to Cr2N precipitation was observed within the reaction zone after nitriding at 100 to 6000 bar of N2 when the chromium content in the initial alloys was 28.0 at. pct or higher. It is shown that the ternary phase p (Cr10Ni7N3) is formed in this system at 1273 K. through a peritectoid reaction between Cr2N and nickel solid solution and becomes unstable above 1373 K. The thermodynamic evaluation of the Ni-Cr-N system was performed and phase equilibria calculated. Evidence for "up hill" diffusion of nitrogen near the reaction front during the internal nitridation of Ni-Cr alloys at 1398 K was found. It was attributed to the relative instability of chromium nitrides and strong Cr-N interaction in the matrix of the Ni-based solid solution within the nitrided zone

Perylene toxicity in the estuarine environment of Ria de Aveiro (Portugal)

Perylene, a 5-ring polycyclic aromatic hydrocarbon is common in estuarine sediments and its toxicity in the benthic and planktonic compartments is not yet clarified. The objectives of this work were: (1) to follow the toxicity of high concentrations of perylene (110 mg l−1) on benthic bacteria and macrofauna (amphipod Corophium multisetosum); (2) to determine the effects of a low load of perylene (2 μg l−1) on the metabolism of suspended bacteriobenthos after 9-day exposure, mimicking the effects of tidal erosion; (3) to contrast the effects of this low perylene load on the particle-free bacterioplankton and on the suspended and particle-adhered bacteriobenthos. No impact was detected in bacterial abundance exposed to 110 mg perylene l−1 for 9 days. This concentration of perylene evoked no acute effects in C. multisetosum but, chronic toxicity assays revealed statistically significant negative effects on survival, growth and number of pregnant females. The bacterioplankton and the suspended bacteriobenthos, exposed to 2 μg perylene l−1 during 2 weeks, responded with altered profiles of activity when compared to the control suspension. These values ranged, respectively, for bacterial biomass production from 134 to 210 and from 24 to 184 μg C l−1 h−1, for aminopeptidase from 1824 to 11,127 and from 1464 to 15,488 nmol l−1 h−1, and for β-glucosidase from 87 to 400 and from 57 to 1278 nmol l−1 h−1. The rate of oxygen consumption in the perylene-exposed suspension (0.04–2.85 mmol O2 kg−1 dw sed h−1) exhibited a clearly distinct profile in relation to the control (0.57–1.60 mmol O2 kg−1 dw sed h−1). The overall reactivity of the bacteriobenthos to perylene was interpreted as the result of toxic pressure followed by evolution of a diverse bacterial community