dr Vit Prochazka
Katedra Fizyki Ciała Stałego WFiIS AGH
"Phase transormation in solid state followed by in-situ nuclear forward scattering."

11. 10. 2017


Zapraszamy na Środowiskowe Seminarium Fizyki Ciała Stałego które odbędzie się w dniu 8.11.2011 o godz. 9.15 w sali 224 C1 AGH, al. Mickiewicza 30

A core problem in material science is the understanding of process responsible for materials formation. It is essential for tailoring the efficiency of synthesis and material properties. However, investigation of such materials has become a challenging experimental task. To understand the process of material formation it is inevitable to study it in-situ, i.e. during the process. For this purpose we used in-situ nuclear forward scattering (NFS) of synchrotron radiation. NFS provides simultaneous information on changes in both structural and magnetic arrangements. Thus, the time dependent evolution of hyperfine interactions allows on fly inspection of structural changes. NFS time spectra were recorded during every minute over extended, approximately one hour, time periods. In this study we report on two examples of in-situ experiments, crystallization kinetics of metallic glasses and thermal decomposition of high valent iron compounds. We investigate metallic glasses exposed to elevating temperature and magnetic field. Their suitable chemical composition ensures formation of crystallites that are only several nanometers in size. Due to these dimensions, they provide beneficial magnetic properties of the so-called nanocrystalline alloys. NANOPERM alloy Fe90Zr7B3 was annealed and measured at constant temperatures up to 753 K without and with external magnetic field of 0.652 T. The presence of the magnetic field resulted in sufficient acceleration of the structural transformation. Crystallization of alloy with a composition of Fe81Mo8Cu1B10 was studied under dynamical changing temperature with and without external magnetic field. It was observed that the magnetic field causes one hundred Kelvin decrease in the onset of the crystallization temperature. In the second example of in-situ NFS experiments we follow the decomposition process of K2FeO4 . This compound was thermally treated under isothermal conditions at 200, 220, 235 and 250 o C. Intermediate phases with iron 5+ and 4+ were revealed during a transition from FeVI to FeIII. The application of in-situ NFS experiments appears to have a wide potential for observations of the evolution of phase transformations in real time performed on fly during short time intervals. Moreover, with increasing of photon source brilliancy also faster processes will be available for in-situ NFS experiments.