Nanocomposites and nanomaterials

Modification of free volume in the nanostructured
MgAl2O4 ceramics caused by water molecules 
H. Klym1, A. Ingram2, I. Hadzaman3, I. Karbovnyk4

1 Lviv Polytechnic National University, Bandery str., 12, Lviv-79013, Ukraine 
E-mail: halyna..klym@lpnu.ua; klymha@yahoo.com 
2Opole University of Technology, Ozimska str., 75, Opole- 45370, Poland
3 Drohobych State Pedagogical University,
I. Franko str., 24, Drohobych-82100, Ukraine
4 Department of Electronics and Computer Technologies, Ivan Franko National University of Lviv, 107, Tarnavskogo Str., Lviv-79000, Ukraine
In this work transformation of free volumes in the nanoporous humidity-sensitive MgAl2O4 ceramics was studied using positron annihilation lifetime spectroscopy. It was shown that positron annihilation processes in MgAl2O4 ceramics are adequately described by multichannel model that combines positron trapping and ortho-positronium o-Ps decaying channels [1]. The first component of the PAL spectra reflects the basic microstructural features of spinel ceramics, the second one corresponds to voids and defects localized near grain boundaries, and the third one describes the “pick-off” annihilation of o-Ps in nanopores [2]. 
To reveal the most significant changes in positron trapping parameters due to influence of adsorbed water molecules, a methodological approach to the processing of PAL spectra, which takes into account the specificity of microstructure of the MgAl2O4 ceramics, is proposed. In the framework of this approach, the effects of catalytic influence are represented by positron trapping rate in defects d, which is calculated on the assumption that the positron lifetimes 1, 2 and 3 remain unchanged. The processes of adsorption-desorption of water in MgAl2O4 ceramics are fully described by observed changes in the parameter d.

1.	Klym H., Ingram A., Shpotyuk O., Hadzaman I., HotraO., Kostiv Y. Nanostructural free-volume effects in humidity-sensitive MgO-Al2O3 ceramics for sensor applications // Journal of Materials Engineering and Performance, 2016, 25(3), pp. 866-873.
2.	Klym H., Ingram A., Shpotyuk O., Hadzaman I., Solntsev V. Water-vapor sorption processes in nanoporous MgO-Al2O3 ceramics: the PAL spectroscopy study // Nanoscale research letters, 2016, 11(1), pp.1-7.