Nanocomposites and nanomaterials

Multicomponent positron-positronium trapping models to study of internal nanovoids in ceramic solids
H. Klym1, A. Ingram2, I. Hadzaman3

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 Ivan Franko Drohobych State Pedagogical University,
I. Franko str., 24, Drohobych-82100, Ukraine
Positron annihilation lifetime spectroscopy (PALS) is one of the most sensitive method to studying of internal nanovoids in solids. However, in relation to glassy and ceramic powder and fine-dispersed materials with functional properties, this method was rarely used due to complications in the interpretation of the obtained results and the absence of a model that would describe the annihilation processes in these materials. The aim of this work is study of free nanovolumes in humidity-sensitive ceramics using multicomponent positron-positronium trapping models.
It is shown that to humidity-sensitive ceramics the first component with parameters (1, I1) reflects the microstructural properties of material and the second one with parameters (2, I2) describes the volume defects near intergranular boundaries formed by additional phases. The second channel contained only one component with parameters (3, I3) and reflected the process of “pick-off” annihilation of ortho-positronium o-Ps in nanopores. After performance of PALS investigation in dry and wet modified MgO-Al2O3 ceramics using high-statistical measurements, it was possible to fix the schedule for the four components. Thus, the second channel contained two components with parameters (3, I3) and (4, I4) that reflected decay of o-Ps atoms in nanopores. The second o-Ps-related channel contains two components, the first of which with the parameters (3, I3) reflects the annihilation of o-Ps through the “pick-off process in nanopores with ~ 0.2-0.3 nm in size and in water by “bubble” mechanism, which leads to an increase in the intensity I3. The second component of this channel with parameters (4, I4) describes the annihilation of o-Ps also through the “pick-off” process, but in an empty pore volume with radius of 1.8-2 nm. Water molecules are formed in layer on the walls of the pore.
Thus, multicomponent positron-positronium model is more acceptable to describe transformation of free volumes in materials with developed porous structure and study adsorption-desorption processes in such ceramics as MgO-Al2O3 spinel’s.