Thermal and structural studies of sol-gel-derived yttria-doped ZrO2 nanoparticles

This investigation focuses on the role of different atmosphere conditions (air and vacuum) during annealing at different temperatures of sol-gel-derived zirconia ZrO2 (stabilised by yttria in 5 mol%) nanocrystals (5YSZ). Prepared samples were characterised by powder X-ray diffraction (PXRD), simultaneous differential thermal and thermogravimetric analysis, evolved gas analysis coupled with mass spectrometry (EGA-MS), Fourier transform infrared spectroscopy (FT-IR) and micro-Raman spectroscopy. The results of thermal analysis and PXRD analysis show the zirconia crystallisation onset at temperature not lower than 400 A degrees C, while EGA-MS analysis further identified gaseous thermal decomposition products. Average crystallite size of the 5YSZ annealed in air at 400, 600, 700 and 800 A degrees C was calculated to be 10, 15, 22 and 33 nm, respectively. On the other hand, crystallite size remains significantly lower when the heat treatment was conducted in vacuum, i.e. in the range 4-13 nm. Annealing atmosphere affects crystallisation, resulting in lower thermal treatment requirements and enabling controlled crystallite growth. PXRD, FT-IR and micro-Raman spectroscopy showed nanocrystalline 5YSZ samples were successfully stabilised in the tetragonal phase and preserved phase stability over the investigated wide thermal treatment range. Due to the yield of stable particle with small size at lower temperatures, the vacuum-prepared 5YSZ coatings are considered as highly applicable for steel corrosion protection.