S. Cottenier

Until now, several different chemical formulae are used to refer to the intermetallic theta-and eta-layers formed at the surface of hot-dip aluminized steel. To clear up the subsequent confusion, both layers were identified and characterized using several experimental techniques combined with DFT calculations.(1) EDX- and EBSD-mappings were performed on the cross section of a hot-dip aluminized steel and showed the presence of the two single phased intermetallic layers, theta and eta, just beneath the aluminum top-layer. The XRD-pattern of a sample of which the top aluminum layer was removed, confirmed the foregoing observations. The compositions of both layers were determined by APT and yield Fe4Al13 and Fe2Al5.6. DFT calculations showed the stability of the Fe4Al13 phase and predicted Fe4Al13 to be the only stable composition in that area of the Fe-Al phase diagram. Based on the DFT results, the ILEEMS spectrum of the theta-layer could be successfully analyzed and, for the first time, fully interpreted in accordance with the crystallographic structure of Fe4Al13. Fe4Al13 is suggested for referring to the composition of the theta-layer, instead of other formulae, e.g. FeAl3. The ILEEMSThlayer spectrum was best reproduced by a model-independent quadrupole splitting distribution, which supports the dis-ordered structure model for the eta-layer. An analysis based on the results of the DFT calculations, confirmed this finding. Because of the partially dis-ordered structure of the eta-layer and the width of the related region in Fe-Al phase diagrams, Fe2Al5-x is suggested for referring to the composition of the eta-layer.

Polonium isotopes are considered the most hazardous radionuclides produced during the operation of accelerator driven systems (ADS) when lead-bismuth eutectic (LBE) is used as the reactor coolant and as the spallation target material. In this work the use of gold surfaces for capturing polonium from the cover gas of the ADS reactor was studied by thermochromatography. The results show that gaseous monoatomic polonium, formed in dry hydrogen, is adsorbed on gold at 1058 K. Its adsorption enthalpy was calculated as -250 +/- 7 kJ mol(-1), using a Monte Carlo simulation code. Highly volatile polonium species that were observed in similar experiments in fused silica columns in the presence of moisture in both inert and reducing gas were not detected in the experiments studying adsorption on gold surfaces. PoO2 is formed in both dry and moist oxygen, and its interaction with gold is characterized by transport reactions. The interaction of bismuth, present in large amounts in the atmosphere of the ADS, with gold was also evaluated. It was found that bismuth has a higher affinity for gold, compared to polonium, in an inert, reducing, and oxidizing atmosphere. This fact must be considered when using gold as a material for filtering polonium in the cover gas of ADS.

We present ab initio calculated electric-field gradient tensors at Cd sites in a set of simple. yet diverse noncubic metals. By combining these predictions with carefully selected published experimental data, the nuclear quadrupole moment of the 245 keV 5/2(+) level of Cd-111 is determined to be 0.76(2) b. Knowing this quadrupole moment is important for time-differential perturbed angular correlation spectroscopy: decades of experimentally obtained nuclear quadrupole coupling constants for solids can now be more reliably converted into electronic structure information. For nuclear physics systematics, this is a rare opportunity to have reliable quadrupole moment information for a short-lived, level, that is not accessible to regular experimental methods. Much effort is spent on the determination of a meaningful error bar, which is an-aspect that gained only recently more attention in the context of density-functional theory predictions. This required assessing the numerical uncertainty in density functional theory predictions for electric-field gradient-tensors in solids. In contrast to quantum chemistry methods, these density functional theory predictions cannot detect systematic errors. By comparing our quadrupole moment value with an independent value Obtained from quantum chemistry calculations and experiment, we show that systematic errors are small for the systems studied here. Yet; there are indications that-density functional theory underestimates by a few percent the electric-field gradient, and therefore overestimates the quadrupole Moment by the saute amount. We point out which future work needs' to be done to characterize the possible deviations inherent to density functional theory.