title: Water-Vapor Sorption Processes in Nanoporous MgO-Al2O3 Ceramics: the PAL Spectroscopy Study.
abstract: The water-vapor sorption processes in nanoporous MgO-Al2O3 ceramics are studied with positron annihilation lifetime (PAL) spectroscopy employing positron trapping and positronium (Ps)-decaying modes. It is demonstrated that the longest-lived components in the four-term reconstructed PAL spectra with characteristic lifetimes near 2 and 60-70 ns can be, respectively, attributed to ortho-positronium (o-Ps) traps in nanopores with 0.3- and 1.5-1.8-nm radii. The first o-Ps decaying process includes "pick-off" annihilation in the "bubbles" of liquid water, while the second is based on o-Ps interaction with physisorbed water molecules at the walls of the pores. In addition, the water vapor modifies structural defects located at the grain boundaries in a vicinity of pores, this process being accompanied by void fragmentation during water adsorption and agglomeration during water desorption after drying.
authors.affiliation: Lviv Polytechnic National University, 12 Bandera str., 79013, Lviv, Ukraine. klymha@yahoo.com.
authors.forename: Halyna
authors.initials: H
authors.lastname: Klym
authors.affiliation: Physics Faculty of Opole University of Technology, 75 Ozimska str., 45370, Opole, Poland.
authors.forename: Adam
authors.initials: A
authors.lastname: Ingram
authors.affiliation: Vlokh Institute of Physical Optics, 23 Dragoanova str., Lviv, 79005, Ukraine.|Institute of Physics of Jan Dlugosz University, 13/15 al. Armii Krajowej, Czestochowa, 42201, Poland.
authors.forename: Oleh
authors.initials: O
authors.lastname: Shpotyuk
authors.affiliation: Drohobych State Pedagogical University, I. Franko str., 24, Drohobych, 82100, Ukraine.
authors.forename: Ivan
authors.initials: I
authors.lastname: Hadzaman
authors.affiliation: V.E. Lashkaryov Institute of Semiconductor Physics of National Academy of Sciences of Ukraine, 41, Prospekt Nauki, 03680, Kiev, Ukraine.
authors.forename: Viacheslav
authors.initials: V
authors.lastname: Solntsev
keywords: Ceramics; Nanopores; Positron annihilation; Positronium; Trapping; Water sorption