Magnesium aluminate MgAl2O4 ceramics with a spinel structure are known to be perspective materials for humidity sensors. It is established that functionality of these humidity-sensitive ceramics depends on their microstructural peculiarities concerning mainly phase composition. This work is aimed to investigate additional phases in the sintered magnesium aluminate ceramics using high-resolution X-ray photoelectron spectroscopy (XPS), taking into account the previous X-ray diffractometry (XRD) data.
The studied ceramics were prepared from initial powders of Al2O3 with specific surface area of 12.4 m2/g and MgO with specific surface area of 10.7 m2/g. The above oxides are weighed, mixed with a highly pure acetone, ball-milled during 96 h and dried. The obtained powder is mixed with an organic binder to prepare green body billets. Then, these pellets are sintered in a special technological regime with maximal temperatures of 1200 and 1400 oC during 2 and 9 h.
In respect to XRD analysis, the studied MgAl2O4 ceramics sintered at 1200 oC during 2 h contain three phases: main spinel phase and large amounts of additional MgO and Al2O3 phases (up to 12 %). In contrast, the ceramics sintered at 1400 oC during 2 and 9 h are two-phase ones with only small amounts of MgO phase (1.54 and 1.96 %, respectively).
It is shown that XPS core-level O 1s spectrum deconvoluting on two independent peaks corresponds to main spinel (biggest peak with position of binding energy 530.3 eV) and additional phases of MgO and/or Al2O3 (smaller peak with position of binding energy 531.1-531.9 eV). It is established that the full width at half maximum (FWHM) corresponds to quantity of main and additional phases in the sintered magnesium aluminate ceramics. These conclusions well agree with XRD data. The more perfect structure of ceramics (with smaller amount of additional phases) are obtained at higher sintering temperature and reflects decreasing of FWHM values in the deconvoluted core-level O 1s peaks.
Therefore, it should be concluded that high-resolution XPS method supported by conventional XTD technique can serve as quite informative tool to study interphase mass-transfer processes in the magnesium aluminate ceramics caused by their technological modification.
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