Search

The effect of a galia (Ga2O3) addition on the crystallographic phase evolution and the crystal growth behavior of zirconia (ZrO2) rich powder were investigated. Binary compositions of galia-zirconia powder (on the zirconia-rich side of the quasi-binary phase diagram) were obtained by the sol-gel method and calcined at different temperatures for 2 h. Rietveld refinement (FullProf program) was used to determine the crystallographic phase composition. Crystal size was approximated based on X-ray diffractions analysis combined with estimates of average crystal size obtained by processing high-resolution scanning electron microscopy images. The surface area of the powders obtained was measured via the Brunauer-Emmett-Teller method. Zirconia-galia sol-gel powders were found to form tetragonal or mixed tetragonal-monoclinic solid solution phases depending on both composition and calcination temperature. It was shown that galia suppressed crystal growth process in zirconia, producing finer nano-powders with higher surface area compared to pure zirconia. [ABSTRACT FROM AUTHOR]

The effect of a galia (Ga2O3) addition on the crystallographic phase evolution and the crystal growth behavior of zirconia (ZrO2) rich powder were investigated. Binary compositions of galia-zirconia powder (on the zirconia-rich side of the quasi-binary phase diagram) were obtained by the sol-gel method and calcined at different temperatures for 2 h. Rietveld refinement (FullProf program) was used to determine the crystallographic phase composition. Crystal size was approximated based on X-ray diffractions analysis combined with estimates of average crystal size obtained by processing high-resolution scanning electron microscopy images. The surface area of the powders obtained was measured via the Brunauer-Emmett-Teller method. Zirconia-galia sol-gel powders were found to form tetragonal or mixed tetragonal-monoclinic solid solution phases depending on both composition and calcination temperature. It was shown that galia suppressed crystal growth process in zirconia, producing finer nano-powders with higher surface area compared to pure zirconia. [ABSTRACT FROM AUTHOR]

Abstract: The dissolution enthalpy, ΔHDS, and the formation enthalpy, ΔHf,ox, of bulk lutetium‐doped cerium oxide (LuDC) were studied at 701°C in molten sodium molybdate. For the composition range of Ce1−XLuXO2−X/2, studied 0 ≤ X ≤ 0.3, the ΔHDS decreases linearly and smoothly with lutetium content according to ΔHDS, kJ/mol = 73.5(1.0)−165.1(5.5)·x). The enthalpy of formation, ΔHf,ox, becomes more exothermic linearly with lutetium content. No anomaly in ΔHf,ox is observed at low Lu2O3 concentration as reported previously for several other rare‐earth‐doped ceria systems, suggesting possible differences in clustering and microstructure, which may also be related to difference in processing conditions. [ABSTRACT FROM AUTHOR]

Industrially relevant nanopowder was synthesised by microwave hydrothermal synthesis to obtain well-controlled composition (ZrO2–AlO(OH) system) which was found to determine a number of physical and thermal characteristics. This study reports variation of particle size, density, specific surface area (SSABET), as well as thermal behaviour of nanopowder mixtures of ZrO2–AlO(OH) in the whole range of compositions. It was found that the onset temperature (Ton) of physically and chemically bounded water desorption depends on the Al3+/or AlO(OH) content. The lower content of Al3+ in the ZrO2–AlO(OH) system, the higher Ton of physically bound water desorption. There are three distinct temperature regions for water decomposition for nanomaterials investigated in air (at approximately 50, 250 and 450 °C). These temperature ranges depend on particle size and chemical composition of ZrO2–AlO(OH) nanopowders. Materials were divided into three groups characterised by different properties: (1) ZrO2 with 2–12% of Al3+, where particle sizes are from 4 to 8 nm, (2) ZrO2 with 30–67% of AlO(OH), where particle sizes are from 10 to 13 nm, and (3) ZrO2 with 80–99% of AlO(OH), where particle sizes are from 13 to 23 nm. AlO(OH) content determines thermal and physico-chemical properties of synthesised ZrO2–AlO(OH) nanopowders. [ABSTRACT FROM AUTHOR]