Grain Porous Structure and Exploitation Properties of Humidity-Sensitive Magnesium Aluminate Spinel-Type Ceramics

Abstract

Grain porous structure in functional humidity-sensitive MgAl2O4 and modified MgO-Al2O3 ceramics prepared at 1200, 1300, and 1400 °C at 2 h is studied using combined X-ray diffraction, scanning electron microscopy, Hg-porosimetry, and positron annihilation lifetime spectroscopy. It is shown that the increase in sintering temperature from 1200 to 1400 °C results in the transformation of the pore size distribution in ceramics. Microstructure of these ceramics is improved with the increase of sintering temperature, which results in decreased amount of additional phases located near grain boundaries. These phase extractions serve as specific trapping centers for positrons penetrating the ceramics. The positron trapping and ortho-positronium decaying components are considered in the mathematical treatment of the measured spectra. Classic Tao-Eldrup model is used to draw the correlation between the ortho-positronium lifetime and the size of nanopores, which is complementary to porosimetry data. The studied ceramics with optimal nanoporous structure are highly sensitive to humidity changes with minimal hysteresis in adsorption-desorption cycles.