Nanocomposites and nanomaterials

Combined investigation of nanopores in MgO-Al2O3 ceramics 
H. Klym1, A. Ingram2, O. Shpotyuk3,4, I. Hadzaman5, 
I. Vasylchyshyn1
1 Lviv Polytechnic National University, Bandery str., 12, Lviv-79013, Ukraine 
E-mail: halyna..klym@lpnu.ua; klymha@yahoo.com  
2 Opole University of Technology, Ozimska str., 75, Opole- 45370, Poland
3 Vlokh Institute of Physical Optics, Dragomanova str., 23, Lviv-79005, Ukraine
4 Jan Dlugosz University in Czestochowa, 
13/15, Armii Krajowej Str., Czestochowa-,42200, Poland
5 Drohobych State Pedagogical University,
I. Franko str., 24, Drohobych-82100, Ukraine

Porous structure in functional humidity-sensitive MgO-Al2O3 spinel ceramics prepared at different sintering temperatures is studied. It is shown that the increase in sintering temperature (from 1100 to 1400 oC) results in the transformation of the pore size distribution in ceramics. It is established that porous ceramics with tri-modal pore size distribution including open macro-, meso- and micropores up to a few nm is humidity sensitive in the 25–95 % relative humidity range. It is demonstrated that positron annihilation lifetime spectroscopy supported by four-component fitting procedure is a promising tool for nanostructural characterization of MgO-Al2O3 spinel-type ceramics [1]. These phase extractions and free-volume entities in ceramic structure serve as specific trapping centers for positrons penetrating in ceramics. 
It is shown that the radius of free volumes of nanopores in MgO-Al2O3 ceramics was calculated using Tao-Eldrup model considering o-Ps “pick-off” lifetimes of the third and fourth components. With increasing of ceramics sintering temperature, the free volume radius R3 increases from 3.09 to 3.31 Ǻ and R4 decreases from ~18 Ǻ to 17 Ǻ. Thus, the MgO-Al2O3 ceramics with more perfect structure is characterized by larger nanopores needed for effective capillary condensation process.

1.	Klym H., Ingram A., Hadzaman I., Shpotyuk O. Evolution of porous structure and free-volume entities in magnesium aluminate spinel ceramics // Ceramics International, 2014, 40, pp. 8561–8567.