Observation of in-plane oriented Guinier-Preston zones in Al-Cu.

Known for a long time, the first metastable precipitate which forms in Al-Cu alloys during natural ageing are the so-called Guinier-Preston zones (GPZ), platelets of Cu on {100} planes of only one atomic layer thickness. Only with the development of aberration corrected transmission electron microscopes (TEM), direct observation and imaging of these platelets was possible, but with the restriction, that only edge view was possible. Here we show that under appropriate conditions an observation in a plan-view is possible and allows further insight into the shape and arrangement of the GP-zones. Furthermore, this demonstrates that single atom detection of one Cu atom in a column of Al atoms is possible.

L12 ordering and δ' precipitation in Al-Cu-Li.

The precipitation mechanism of the δ' (Al3Li) phase in Al-Li alloys has been controversially discussed in recent decades, specifically with respect to a conjectured congruent ordering process. However, kinetics in the Al-Li system does not allow to resolve the intermediate stages of precipitation and hence to experimentally clarify this issue. In this paper, we are revisiting the subject in ternary Al-Cu-Li alloys with pronouncedly slower kinetics, employing Transmission Electron Microscopy, High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy, Differential Scanning Calorimetry and Atom Probe Tomography. The results show clear evidence for congruent ordering in a selected compositional range, revealing an already strongly L12 ordered microstructure after natural aging with a chemically homogeneous Li distribution and a decomposition of the alloy upon annealing at elevated temperatures. The presented study of the δ' precipitation evaluates the reaction pathway of this process and compares it to the predictions of the Bragg-Williams-Gorsky model with respect to decomposition and ordering in this alloy system.

Immunization with soot from a non-combustion process provokes formation of antibodies against polycyclic aromatic hydrocarbons.

The emission of soot during combustion processes used in transportation, manufacturing, and power generation is of increasing concern because of its serious adverse health effects. In particular, the ability to modulate the immune system has recently been established. In the present investigation, an artificial soot sample that was prepared by fragmentation of acetylene in a laser-induced plasma was used as an antigen for the immunization of a rabbit. A highly sensitive competition curve in an indirect competitive ELISA using a benzo[a]pyrene-BSA conjugate as a coating antigen could be constructed for benzo[a]pyrene with an IC50 of 2.94 mug/l (11.65 nmol/l). In contrast to the high affinity, the soot antiserum dilution (antibody titer) of 1:750 was rather low. The cross-reactivity was tested with 16 parent polycyclic aromatic hydrocarbons, 7 nitrated polycyclic aromatics, and 3 methylated, hydroxylated or butyric acid derivatives. The results obtained suggest that the vertebrate immune system can respond to an immunization with soot by the generation of high affinity IgG class antibodies against polycyclic aromatics. It is likely that antibodies are raised against the molecular structures which form the framework of the soot particles and not against adsorbed and extractable polyaromatic compounds. The experiments suggest that if soot is considered a T-independent antigen, the isotype switch, essentially from IgM to IgG, could have been caused by co-inoculation with a T-dependent antigen, i.e., mycobacteria contained in Freunds complete adjuvant. However, at the cellular level the mechanism remains to be uncovered.