Effect of Pr3+/Pr4+ ratio on the oxygen ion transport and thermomechanical properties of the pyrochlore and fluorite phases in the ZrO2-Pr2O3 system

This paper examines the effect of the Pr3+/Pr4+ ratio on the mechanism of ionic and electronic transport in the (Pr2?xZrx)Zr2O7+x/2 (x = 0.15), Pr2Zr2O7, and Pr2(Zr2?xPrx)O7?x/2 (x = 0.1) pyrochlore phases and Pr3ZrOx with the fluorite structure and on the behavior of their thermal expansion coefficient (TEC). The solid solutions were prepared through coprecipitation followed by firing of the green compacts in air at a high temperature of 1550 ?C for 4 h. The Pr3+/Pr4+ ratio was shown to decrease in going from the (Pr2?xZrx)Zr2O7+x/2 (x = 0.15), Pr2Zr2O7, and Pr2(Zr2?xPrx)O7?x/2 (x = 0.1) pyrochlores to the Pr3ZrOx fluorite, leading to changes in the conductivity type from mixed (ionic?electronic) to electronic and in the color of the materials from beige to black and to an anomalous deviation of the TEC from linearity in fluorite Pr3ZrOx, i.e. at the highest Pr4+ content. According to impedance spectroscopy results, (Pr2?xZrx)Zr2O7+x/2 with x = 0.15 has purely oxide-ion conductivity (3 ? 10?3 S/cm at 1000 ?C) in a wide range of oxygen partial pressures: from 10?10 to 102 Pa. With increasing Pr content, p-type electronic conductivity becomes significant, reaching a maximum in fluorite Pr3ZrOx: ?0.5 S/cm at 1000 ?C. According to XPS data, all pyrochlore samples (Pr2?xZrx)Zr2O7+x/2 (x = 0.15), Pr2Zr2O7 and Pr2(Zr2?xPrx)O7?x/2 (x = 0.1) contain only Pr3+ at room temperature, whereas Pr3ZrOx contains both Pr3+ and Pr4+. The considerable deviation of the TEC of Pr3ZrOx from linearity above 500 ?C is due to partial reduction of Pr4+. The reduction process Pr4+ + e? ? Pr3+ followed by oxygen release in the range 500?1100 ?C has been identified in Pr3ZrOx by thermal analysis and mass spectrometry in a He atmosphere.371C-9F16-EBDE | Eduarda GomesN/

Titanium Complex Containing a Saligenin Ligand - New Universal Post-Metallocene Polymerization Catalyst: Copolymerization of Ethylene with Higher α-Olefins

Copolymerization reactions of ethylene with three α-olefins, 1-hexene, 1-octene and 1-decene, were carried out with a new post-metallocene catalyst based on Ti complex with a bidentate saligenin-type ligand I and two co catalysts, MAO and a combination of AlEt2Cl and MgBu2. Ability of the I - AlEt2Cl - MgBu2 system to copolymerize α-olefins with ethylene is far superior to that of the I - MAO system. Reactivity of α-olefins in copolymerization reactions with ethylene decreases in the sequence: 1-hexene>1-octene>1-decene. Both catalyst systems, I - MAO and I - AlEt2Cl - MgBu2, contain several populations of active centers that greatly differs both in the average molecular weights and in composition of the copolymer molecules they produce. Active centers in both catalytic systems show significant tendency to alternate monomer units in copolymer chains

Effect of Pr3+/Pr4+ ratio on the oxygen ion transport and thermomechanical properties of the pyrochlore and fluorite phases in the ZrO2-Pr2O3 system

This paper examines the effect of the Pr3+/Pr4+ ratio on the mechanism of ionic and electronic transport in the (Pr2-xZrx)Zr2O7+x/2 (x = 0.15), Pr2Zr2O7, and Pr-2(Zr2-xPrx)O7-x/2 (x = 0.1) pyrochlore phases and Pr3ZrOx with the fluorite structure and on the behavior of their thermal expansion coefficient (TEC). The solid solutions were prepared through coprecipitation followed by firing of the green compacts in air at a high temperature of 1550 degrees C for 4 h. The Pr3+/Pr4+ ratio was shown to decrease in going from the (Pr2-xZrx) Zr2O7+x/2 (x = 0.15), Pr2Zr2O7, and Pr-2(Zr2-xPrx)O7-x/2 (x = 0.1) pyrochlores to the Pr3ZrOx fluorite, leading to changes in the conductivity type from mixed (ionic electronic) to electronic and in the color of the materials from beige to black and to an anomalous deviation of the TEC from linearity in fluorite Pr3ZrOx i.e. at the highest Pr4+ content. According to impedance spectroscopy results, (Pr2-xZrx)Zr2O7+x/2 with x = 0.15 has purely oxide-ion conductivity (3 x 10(-3) S/cm at 1000 degrees C) in a wide range of oxygen partial pressures: from 10(-10) to 10(2) Pa. With increasing Pr content, p-type electronic conductivity becomes significant, reaching a maximum in fluorite Pr3ZrOx: similar to 0.5 S/cm at 1000 degrees C. According to XPS data, all pyrochlore samples (Pr2-xZrx)Zr2O7+1-x/2 (x = 0.15), Pr2Zr2O7 and Pr-2(Zr2-xPrx) O7-x/2 (x = 0.1) contain only Pr3+ at room temperature, whereas Pr3ZrOx contains both Pr3+ and Pr4+ The considerable deviation of the TEC of Pr3ZrOx from linearity above 500 degrees C is due to partial reduction of Pr4+ . The reduction process Pr4+ + e' -> Pr3+ followed by oxygen release in the range 500-1100 degrees C has been identified in Pr3ZrOx by thermal analysis and mass spectrometry in a He atmosphere. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved

A Novel Approach to Design Chitosan-Polyester Materials for Biomedical Applications

A novel approach to design chitosan-polyester materials is reported. The method is based on mechanical activation and effective intermixing of the substrates under high pressure and shear deformation in the course of solid-state reactive blending. The marked departure of this approach from previous practice resides on exploitation of a variety of chemical transformations of the solid polymers that become feasible under conditions of plastic flow. Low temperatures (above Tg but below the melting points of the crystalline polymers) are maintained throughout the process, minimizing mechanical and oxidative degradation of the polymers. Morphology as well as structural, mechanical, and relaxation properties of those prepared blends of chitosan with semicrystalline poly(L,L-lactide) and amorphous poly(D,L-lactide-co-glycolide) has been studied. Grafting of polyester moieties onto chitosan chains was found to occur under employed pressures and shear stresses. The prepared polymer blends have demonstrated an amphiphilic behavior with a propensity to disperse in organic solvents that widens possibilities to transform them into promising materials for various biomedical applications