Single crystal samples of the alloy Fe-20%Cr-5%Al with and without Y-doping were used to study the "reactive element" (RE) effect, which causes improved oxidation behaviour and formation of a protective Al2O3 layer on this alloy. The oxidation was followed by AES at 10-7 mbar O2 up to about 1000 °C. Most observations were peculiar for this low pO2 environment, but yttrium clearly favors the formation of Al-oxide and stabilizes it also under these conditions, probably by favoring its nucleation. The oxides formed are surface compounds of about monolayer thickness, not clearly related to bulk oxides.
Furthermore, the morphologies of oxide scales were investigated by SEM, after oxidation at 1000°C for 100 h at 133 mbar O2. On Fe-Cr-Al the scale is strongly convoluted and tends to spalling, whereas the presence of Y leads to flat scales which are well adherent. This difference is explained by a change in growth mechanism. The tendency for separation of oxide and metal was highest for the samples with low energy metal surface, i.e. (100) and (110), the scale was better adherent on the (111) oriented surface and on the polycrystalline specimen, since in the latter cases the overall energy for scale/metal separation is higher.
All observations, from the low and from the high pO2 experiments, are discussed in relation to the approximately ten mechanisms proposed in the literature for explanation of the RE effects.
We determined the elements Cu, Fe, K, and Zn in normal human platelets by neutron activation analysis. The platelets were obtained from seven donors and treated as described in Part I. The elemental composition is expressed on a wet-weight basis for plasma-free platelets. The following results were obtained (+/- values are 1 SD); "Pure" platelets: trapped plasma = 378 +/- 35 mg/g, water content = 715 +/- 15 mg/g, mean weight of the single platelet (by two different methods) = 9.9 +/- 1.1 pg and 11.2 +/- 1.7 pg, K = 4.39 +/- 1.06 mg/g, Zn = 49.23 +/- 10.97 microgram/g, Fe = 12.28 +/- 2.94 microgram/g, and Cu = 1.39 +/- 0.25 microgram/g. "Impure" platelets: trapped plasma = 349 +/- 31 mg/g, water content = 736 +/- 12 mg/g, K = 3.26 +/- 0.78 mg/g, Zn = 35.71 +/- 7.99 microgram/g, Fe = 17.11 +/- 5.10 microgram/g, and Cu = 1.39 +/- 0.21 microgram/g. To our knowledge, no data on Fe and Cu in platelets have hitherto been reported.
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