Structural and oxygen content changes of hexagonal HoMnO manganite at the stability boundary in the perovskite phase have been studied by X-ray diffraction and thermogravimetry using in situ oxidation and reduction processes at elevated temperatures in oxygen and air. The oxygen storage properties during structural transformation between stoichiometric Hex0 and oxygen-loaded Hex1 phases, transition temperatures and kinetics of the oxygen incorporation and release are reported for materials prepared by the solid-state synthesis and high-impact mechanical milling. Long-term annealing experiments have shown that the Hex0 (δ = 0) → Hex1 (δ ≈ 0.28) phase transition is limited by the surface reaction and nucleation of the new phase for HoMnO 15MM. The temperatures of Hex0 ↔ Hex1 transitions have been established at 290 °C and 250 °C upon heating and cooling, respectively, at a rate of 0.1° min, also indicating that the temperature hysteresis of the transition could possibly be as small as 10 °C in the equilibrium. Ball-milling of HoMnO has only a small effect on improving the speed of the reduction/oxidation processes in oxygen, but importantly, allowed for considerable oxygen incorporation in air at a temperature range of 220-255 °C after prolonged heating. The Mn 2p XAS results of the Mn valence in oxygen loaded samples support the oxygen content determined by the TG method. The magnetic susceptibility data of the effective Mn valence gave inconclusive results due to dominating magnetism of the Ho ions. Comparison of HoMnO with previously studied DyMnO indicates that a tiny increase in the ionic size of lanthanide has a huge effect on the redox properties of hexagonal manganites and that practical properties could be significantly improved by synthesizing the larger average size (Y,Ln)MnO manganites.
Herein, we report on the hydrodynamic interfacial instability controlled by a thermodynamic parameter driving the liquid−liquid phase separation during fluid displacement in a Hele−Shaw cell. This instability remains even when the solution is guaranteed to be hydrodynamically stable. Adjusting the salt concentration helps control the miscibility of the solutions and change the pattern of the interface. We observe stable circular, fingering, and droplet formation patterns as the salt concentration is decreased from equilibrium. In addition, we analyze this interfacial instability using thermodynamic flux, which is determined from the growth rate of the interface, and provide a theoretical framework to quantitatively predict the transition points between the patterns. We find that the patterns transition to a state having higher entropy production.
Miscibility of both binary and ternary blends between poly(vinylidene fluoridehexafluoroacetone) P(VDF-HFA), Poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) was investigated by using dynamic mechanical and differential scanning calorimetric measurements. The interaction parameter in binary blends of P(VDF-HFA) and PMMA was-0.73 at 125°C and was largely affected by the existence of hexafluoroacetone units, compared with that of blends of poly(vinylidene fluoride) and PMMA. Phase separation behavior of this binary blends was elucidated by observing the change of transmittance on heating; the lower critical solution temperature (LCST) behavior was shown including both binodal and spinodal curves. Binary blends of P(VDF-HFA)/PVAc were also miscible and showed LCST behavior. Ternary blends of P(VDF-HFA)/PMMA/PVAc were miscible in spite of immiscible binary blends of PMMA/PV Ac and showed LCST phase diagram. After phase separation, ternary miscible blends were separated to two phases of P(VDF-HFA)/PMMA with very small domains of PVAc and P(VDF-HFA)/PVAc with also very small PMMA. At higher temperature, phase separation composed of P(VDF-HFA)/PMMA and P(VDF-HFA)/PVAc occurred.
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