Influence of oxide films on primary water stress corrosion cracking initiation of alloy 600

In the present study alloy 600 was tested in simulated pressurised water reactor (PWR) primary water, at 360 °C, under an hydrogen partial pressure of 30 kPa. These testing conditions correspond to the maximum sensitivity of alloy 600 to crack initiation. The resulting oxidised structures (corrosion scale and underlying metal) were characterised. A chromium rich oxide layer was revealed, the underlying metal being chromium depleted. In addition, analysis of the chemical composition of the metal close to the oxide scale had allowed to detect oxygen under the oxide scale and particularly in a triple grain boundary. Implication of such a finding on the crack initiation of alloy 600 is discussed. Significant diminution of the crack initiation time was observed for sample oxidised before stress corrosion tests. In view of these results, a mechanism for stress corrosion crack initiation of alloy 600 in PWR primary water was proposed

Size effect on magnetism of Fe thin films in Fe/Ir superlattices

In ferromagnetic thin films, the Curie temperature variation with the thickness is always considered as continuous when the thickness is varied from $n$ to $n+1$ atomic planes. We show that it is not the case for Fe in Fe/Ir superlattices. For an integer number of atomic planes, a unique magnetic transition is observed by susceptibility measurements, whereas two magnetic transitions are observed for fractional numbers of planes. This behavior is attributed to successive transitions of areas with $n$ and $n+1$ atomic planes, for which the $T_c$'s are not the same. Indeed, the magnetic correlation length is presumably shorter than the average size of the terraces. Monte carlo simulations are performed to support this explanation.Comment: LaTeX file with Revtex, 5 pages, 5 eps figures, to appear in Phys. Rev. Let

Dynamics Of Internode And Stem Elongation In Three Cultivars Of Maize

The kinetics of elongation of individual internodes, the peduncle and panicle of maize were studied in field experiments in Gatton (Australia) using two tropical cultivars, and compared to similar data previously collected in Grignon (France) on a temperate cultivar. Data for phytomer initiation and organ extension and appearance were related to thermal time calculated from the temperature in the growing zone. Extension of internodes was analysed using a four stage framework:- an initial exponential stage, transition to rapid extension, rapid (linear) extension and transition to final length. The kinetics of internode extension were similar in Gatton and Grignon, though the rates of processes differed. Transition from stage 1 to stage 2 coincided with collar emergence. The commencement of rapid extension of the peduncle coincided with a transient reduction in the rates of extension of vegetative internodes. Further work is needed to assess whether they are effects of genotype only, or genotype and environment