6 research outputs found
Effect of heat treatment on the structure and mechanical properties of zirconia crystals partially stabilized with samarium oxide
The effect of high-temperature treatment in different media on the phase composition, microhardness and fracture toughness of (ZrO2)1-х(Sm2O3)х crystals with x = 0.02÷0.06 has been studied. The crystals have been grown using direction melt crystallization in a cold skull. The crystals have been heat treated at 1600 °C for 2 h in air and in vacuum. The phase composition of the crystals has been studied using X-ray diffraction and Raman scattering. We show that samarium cations enter the ZrO2 lattice mainly in a trivalent charge state and do not change their charge after air or vacuum annealing. The as-annealed phase composition has changed in all the test crystals except for the (ZrO2)0.94(Sm2O3)0.06 composition. After air or vacuum annealing the (ZrO2)1-x(Sm2O3)x crystals with 0.002 ≤ x ≤ 0.05 contain a monoclinic phase. The (ZrO2)0.94(Sm2O3)0.06 crystals contain two tetragonal phases (t and t´) with different tetragonality degrees. After air or vacuum annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals the lattice parameters of the t and t´ phases change in opposite manners, suggesting that the tetragonality degree of the t phase increases whereas the tetragonality degree of the t´ phase decreases. The microhardness and fracture toughness of the as-annealed crystals depend on the Sm2O3 concentration in the solid solutions. The formation of the monoclinic phase in the (ZrO2)1-х(Sm2O3)х crystals with 0.037 ≤ x ≤ 0.05 significantly reduces the microhardness and fracture toughness of the crystals. Annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals triggers more efficient hardening mechanisms and thus increases the fracture toughness of the crystals. We show that air or vacuum annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals increases the fracture toughness of the crystals by 1.5 times as compared with that of the as-grown crystals
Synthesis of Iron Oxide Nanoclusters by Thermal Decomposition
Herein,
we report a novel one-step solvothermal synthesis of magnetite
nanoclusters (MNCs). In this report, we discuss the synthesis, structure,
and properties of MNCs and contrast enhancement in <i>T</i><sub>2</sub>-weighted MR images using magnetite nanoclusters. The
effect of different organic acids, used as surfactants, on the size
and shape of MNCs was investigated. The structure and properties of
samples were determined by magnetic measurements, TGA, TEM, HRTEM,
XRD, FTIR, and MRI. Magnetic measurements show that obtained MNCs
have relatively high saturation magnetization values (65.1–81.5
emu/g) and dependence of the coercive force on the average size of
MNCs was established. MNCs were transferred into an aqueous medium
by Pluronic F-127, and <i>T</i><sub>2</sub>-relaxivity values
were determined. <i>T</i><sub>2</sub>-Weighted MR phantom
images clearly demonstrated that such magnetite nanoclusters can be
used as contrast agents for MRI
Effect of heat treatment on the structure and mechanical properties of zirconia crystals partially stabilized with samarium oxide
The effect of high-temperature treatment in different media on the phase composition, microhardness and fracture toughness of (ZrO2)1-х(Sm2O3)х crystals with x = 0.02÷0.06 has been studied. The crystals have been grown using direction melt crystallization in a cold skull. The crystals have been heat treated at 1600 °C for 2 h in air and in vacuum. The phase composition of the crystals has been studied using X-ray diffraction and Raman scattering. We show that samarium cations enter the ZrO2 lattice mainly in a trivalent charge state and do not change their charge after air or vacuum annealing. The as-annealed phase composition has changed in all the test crystals except for the (ZrO2)0.94(Sm2O3)0.06 composition. After air or vacuum annealing the (ZrO2)1-x(Sm2O3)x crystals with 0.002 ≤ x ≤ 0.05 contain a monoclinic phase. The (ZrO2)0.94(Sm2O3)0.06 crystals contain two tetragonal phases (t and t´) with different tetragonality degrees. After air or vacuum annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals the lattice parameters of the t and t´ phases change in opposite manners, suggesting that the tetragonality degree of the t phase increases whereas the tetragonality degree of the t´ phase decreases. The microhardness and fracture toughness of the as-annealed crystals depend on the Sm2O3 concentration in the solid solutions. The formation of the monoclinic phase in the (ZrO2)1-х(Sm2O3)х crystals with 0.037 ≤ x ≤ 0.05 significantly reduces the microhardness and fracture toughness of the crystals. Annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals triggers more efficient hardening mechanisms and thus increases the fracture toughness of the crystals. We show that air or vacuum annealing of the (ZrO2)0.94(Sm2O3)0.06 crystals increases the fracture toughness of the crystals by 1.5 times as compared with that of the as-grown crystals
Reasons for the Differences in the Kinetics of Thermal Oxidation of the Support in Pt/C Electrocatalysts
High-temperature oxidation processes
of carbon microparticles Vulcan XC72 coated with platinum nanoparticles
(Pt/C) were studied by thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC). The presence of different specific temperature
ranges in the oxidation of carbon support was shown to be due to both
the peculiarities of granulometric composition of carbon black microparticles,
different size, and uneven spatial distribution of platinum nanoparticles
in the pores and on the surface of the carbon support. The correlation
between the length of a section in the thermograms and the fraction
of carbon microparticles poorly coated with platinum can be used to
analyze the uniformity of Pt nanoparticle spatial distribution in
the metal–carbon catalysts and therefore to select electrocatalysts
with optimal microstructure. This analysis is expected to be effectively
utilized in order to assess the uniformity of platinum distribution
on carbon microparticles and also to provide additional information
about granulometric composition of carbon supports
Comparison of the structure and physicochemical properties of ZrO2 based crystals partially stabilized with Y2O3, Gd2O3 and Sm2O3
The phase composition, density, microhardness and fracture toughness of (ZrO2)1-x(R2O3)х crystals (where R = Y, Sm and Gd) for x = 0.02–0.04 have been compared. The crystals have been grown using directional melt crystallization in a cold crucible. The phase composition of the crystals has been studied using X-ray diffraction and Raman spectroscopy. The microhardness and fracture toughness of the crystals have been evaluated by means of indentation. At stabilizing oxide concentrations of ≥ 2.8 mol.% for Y2O3 and Gd2O3 and ≥ 3.7 mol.% for Sm2O3 the crystals have densities close to the theoretical ones and contain two tetragonal phases. At lower stabilizing oxide concentrations the crystals contain the monoclinic phase. The fracture toughness of the tetragonal crystals increases with the ionic radius of the stabilizer. The highest fracture toughness values achieved when stabilized by a specific oxide are 11.0, 13.0 and 14.3 MPa·m1/2 for the 2.8YSZ, 2.8GdSZ and 3.7SmSZ crystals, respectively. The fracture toughness proves to depend on the crystallographic orientation of the crystals. The results of this work can be used in the design and fabrication of various structural components and devices