Evolution of Structure and Free Volume in Nanoporous MgAl2O4 Spinel under Influence of Water

Structural properties and free-volume evolution were investigated in the humidity-sensitive MgAl
2
O
4
ceramics prepared at 1300
$^{\circ}\mathrm{C}$
for 2 h under the influence of water. It is shown that ceramics has a well-developed structure of pores with trimodal pore size distribution, grain boundaries and grains. It is determined that absorbed water in studied ceramics result in more intensive trapping of positrons near grain boundaries with extended defects. The presence of water in the inner structure of ceramics leads to specific fragmentation of free volume in the nanopores and ortho-positronium decaying in water.