April 2005 Archives

Projects involving international collaboration are currently under way at the Stanford Linear Accelerator Center, in the U.S., using very bright pulses of X-ray light one thousand times shorter than those typically produced in conventional synchrotron rings. One of the topics studied very recently concerns melting- how solids transform into liquids on ultra fast time scales. In the experiment, laser light was used to melt a crystal of InSb, and then ultra-short X-ray pulses were sent to probe the material. The scattered X-rays provided a glimpse of the first step in the transition from solid to liquid. It was found that the transition state is governed by inertial dynamics, simply stated by Newton's First Law as: an object in motion continues in motion. For more information, see the paper, "Atomic-Scale Visualization of Inertial Dynamics", A. M. Lindenberg et al., Science, 308, 392-395 (2005).

At beamline ID18, ESRF, scientists studied pieces of hair and skin of Agnès Sorel, who was the beautiful mistress of 15th century French king, Charles VII. Very recently, from X-ray fluorescence spectra, they found that Sorel's remains contained abnormal levels of mercury. The manner of her death was previously unknown, but incredibly high levels of mercury have been found in her remains. This finding will give fresh impetus to the search to reveal the the truth behind this historical event. The source of this news is the web page of ESRF, http://www.esrf.fr/NewsAndEvents/PressReleases/sorel/

A team of scientists from the Technical University in Vienna, the Technical University in Berlin and the ESRF have combined tomography and diffraction using 80 keV X-rays to observe creep void evolution and the correlation to texture and microstructure development, which are important parameters for understanding the lifetime of components subjected to high temperature loading. The studies were carried out for a brass alloy, CuZn₄₀Pb₂, which contains three phases: -brass, s-brass, and Pb. They developed a specifically designed creep device in order to avoid artifacts during the tomography, and therefore the path of the incoming and the emerging X-rays over a complete 360 deg turn of the sample is identical. A tensile load of 25 MPa was applied by using a spring in order to avoid vibrations, and the sample was heated to 375 ºC by an induction-heated loop around the bottom of the sample. The results reveal that void growth versus time follows an exponential growth law and that the formation of large void volumes coincides with texture evolution and a steady state in the development of dislocation density. The in-situ determination of void evolution in bulk samples opens up new ways toward the assessment of creep damage to the strength of materials and subsequently towards lifetime predictions of samples and components subject to high temperature loading. For more information, see the paper, "Simultaneous Tomography and Diffraction Analysis of Creep Damage", A. Pyzalla et al., Science, 308, 92-95 (2005).