Stabilization of tetragonal phase of nanostructured Fex/ZrO2 system (0 ≤ x ≤ 25) prepared by modified sol-gel method

In the present study, Fex/ZrO2 (0 ≤ x ≤ 25) nanoparticles were synthesized by a facile modified Sol-Gel method. Stabilization of the tetragonal phase of ZrO2 is studied as a function of both the Fe incorporation ratios and thermal treatment. The Fe incorporation ratios are tested up to the extreme just before FeO and Fe2O3 phases are formed separately. The prepared Fex/ZrO2 nanoparticles XRD analysis depicts the formation of zirconium oxide at different Fe ratios in the nanoscale with an excellent degree of crystallinity in the tetragonal phase. The effect of thermal treatment on stabilizing the tetragonal phase of Fex/ZrO2 nanoparticles is extensively studied. The phase transition to the monoclinic phase is determined as function of Fe incorporation ratios and annealing temperatures. The optical absorbance spectra showed that the optical band gap decreased with increasing Fe ratios without the formation of doping bands which confirms the formation of Fex/ZrO2 single matrix.

Phenomena Occurring upon the Sintering of a Mixture of Yttria–Zirconia Nanometric Powder and Sub-Micrometric Pure Zirconia Powder

Mixtures of powders essentially differing in their particle morphology and size were applied to prepare polycrystals in a Y2O3-ZrO2 system. An yttria–zirconia solid solution nanometric powder with a Y2O3 concentration of 3.5% was prepared by subjecting co-precipitated gels to hydrothermal treatment at 240 °C. The crystallization occurred in distilled water. The pure zirconia powders composed of elongated and sub-micrometer size particles were also manufactured through the hydrothermal treatment of pure zirconia gel, although in this case, the process took place in the NaOH solution. Mixtures of the two kinds of powder were prepared so as to produce a mean composition corresponding to an yttria concentration of 3 mol%. Compacts of this powder mixture were sintered, and changes in phase composition vs. temperature were studied using X-ray diffraction. The dilatometry measurements revealed the behavior of the powder compact during sintering. The polished surfaces revealed the microstructure of the resulting polycrystal. Additionally, the electron back scattering diffraction technique (EBSD) allowed us to identify symmetry between the observed grains. Hardness, fracture toughness, and mechanical strength measurements were also performed.

Bimetallic Cu/Fe Catalysts for Ibuprofen Mineralization

At present, the use of conventional wastewater processes is becoming increasingly challenging, mainly due to the presence of biorecalcitrant organic matter. Advanced oxidation processes such as Fenton, Fenton-like and hybrid processes have been successfully employed for the treatment of highly concentrated and toxic non-biodegradable pollutants. Here, a series of bimetallic catalysts, based on Cu/Fe supported over ZrO2, were investigated for the mineralization of ibuprofen with a heterogeneous Fenton-like reaction. The materials were prepared by incipient wetness impregnation and characterized by standard techniques. Temperature-programmed experiments highlighted the promotion of the reduction in CuO due to the synergistic effects of the coupled redox cycles of copper (Cu2+/Cu+) and iron (Fe+3/Fe+2). 5%Cu-5%Fe/ZrO2 not only displays the highest ibuprofen mineralization (83%) under optimum conditions but also exploits its activity in a wider range of pH (3–5) with extremely low metal leaching. The recycling of bimetallic catalysts reveals that only the 5%Cu-5%Fe/ZrO2 system is able to provide sustainable activity in heterogeneous Fenton process.

The Preparation of Dense Materials in the MgO–ZrO2 System by the Application of Nanometric Powders

Crystallization under hydrothermal conditions allowed us to prepare nanometric powders in the MgO–ZrO2 system of different magnesia concentrations. Sintering runs of these powder compacts studied using dilatometry measurements during heating and cooling revealed essential differences in their behavior. The microstructure of the resulting polycrystal is strongly related to the magnesia content in the starting powder, which strongly influences the phase composition of the resulting material and its mechanical properties. It should be emphasized that the novel processing method of such materials differs from the usual applied technology and leads to magnesia–zirconia materials of a different microstructure than that of “classical” materials of this kind.

К 125-летию со дня рождения лауреата Нобелевской премии академика Николая Николаевича Семенова Полуэмпирические методы расчета температур ликвидуса в оксидных системах

In the present study, two semi-empirical methods (geometric and polynomial) were proposed to calculate liquidus temperatures in ternary and quaternary systems using the data on the equilibria in the corresponding binary systems. Advantages, limitations, and peculiarities of application of the semi-empirical methods proposed were considered. The reliability of the results of calculating the liquidus temperature values in the Gd2O3-Y2O3-ZrO2 system was illustrated by comparison with the available data on the phase equilibria. The capacity to evaluate the eutectic line position in the temperature-composition coordinates was shown in multicomponent oxide systems. It was mentioned that the semi-empirical approaches proposed may find a further use to evaluate the liquidus temperature values in multicomponent systems with the aim of reducing the amount of experimental investigations of phase equilibria at high temperatures.

Al2O3 AND ZrO2 CERAMIC MATERIALS OBTAINED BY SOL-GEL METHOD

The rheological properties, processes of structure and phase formation of the Al2O3–ZrO2 system compositions obtained by the sol-gel method have been investigated. The temperature range of crystallization of the compositions is 900–1100 °C. With an increase in the concentration of zirconium dioxide in the system, the temperature of the transition from the tetragonal to the monoclinic phase decreases. The effect of the ratio of the components in the initial solutions and the temperature regime of heat treatment of gels on the physicochemical properties of nanopowders and sintered materials has been studied. Ceramic materials of eutectic composition give the highest density and lower values of porosity and water absorption.