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Magneli phase titanium sub-oxide conductive ceramic TiO was used as the support for Pt due to its excellent resistance to electrochemical oxidation, and Pt/TiO composites were prepared by the impregnation-reduction method. The electrochemical stability of TiO was investigated and the results show almost no change in the redox region after oxidation for 20 h at 1.2 V (vs NHE) in 0.5 mol/L HSO aqueous solution. The catalytic activity and stability of the Pt/TiO toward the oxygen reduction reaction (ORR) in 0.5 mol/L HSO solution were investigated through the accelerated aging tests (AAT), and the morphology of the catalysts before and after the AAT was observed by transmission electron microscopy. At the potential of 0.55 V (vs SCE), the specific kinetic current density of the ORR on the Pt/TiO is about 1.5 times that of the Pt/C. The LSV curves for the Pt/C shift negatively obviously with the half-wave potential shifting about 0.02 V after 8000 cycles AAT, while no obvious change takes place for the LSV curves for the Pt/TiO. The Pt particles supported on the carbon aggregate obviously, while the morphology of the Pt supported on TiO remains almost unchanged, which contributes to the electrochemical surface area loss of Pt/C being about 2 times that of the Pt/TiO. The superior catalytic stability of Pt/TiO toward the ORR could be attributed to the excellent stability of the TiO and the electronic interaction between the metals and the support. [ABSTRACT FROM AUTHOR]

The shear thinning and shear thickening rheological properties of PCC/PEG suspension were investigated with the increase of oscillatory amplitude stress at different constant frequencies. The results show that the complex viscosity was initially independent of stress amplitude and obvious shear thinning occurred, then dramatic shear thickening took place after reaching the minimum viscosity. Typically, in a constant frequency of 5 rad/s, the elastic modulus, viscous modulus, and tanδ (δ is the out-of-phase angle) vs. the stress amplitude was investigated. It is found that the elastic modulus initially appeared to be independent of stress amplitude and then exhibited a rapid decrease, but the viscous modulus was independent of amplitude stress at lower amplitude stress. After reaching the minimum value the viscous modulus showed a rapid increase. On the other hand, tanδ increased from 0.6 to 92, which indicates that the transition from elastic to viscous had taken place and tanδ showed a steep increase when shear thickening occurred. Lissajous plots are shown for the dissipated energy vs. different maximum stress amplitude in the shear thinning and shear thickening regions. The relationship of dissipated energy vs. maximum stress amplitude was determined, which follows a power law. In the shear thinning region the exponent was 1.91, but it steeply increases to 3.97 in the shear thickening region. [ABSTRACT FROM AUTHOR]

The influence of non-isothermal melt crystallization on thermal behavior and isothermal melt crystallization kinetics of poly-L-lactide (PLLA) were investigated by differential scanning calorimetry (DSC), polarizing micrograph (POM) and x-ray diffraction (XRD). Crystallization performed at lower cooling rates (2°C·min-1) is accompanied by a variation of the kinetics around 118°C. The glass transition temperature of PLLA decreases with increase of cooling rate, and the crystallinity at the end of crystallization increases with decreasing cooling rate. The size of PLLA spherulites increases with a decrease in the cooling rate, and PLLA becomes almost amorphous cooled at rapid rate (>10°C·min-1). PLLA exhibits an Avrami crystallization exponent n = 3.01±0.13 in isothermal crystallization in the range from 90°C to 140°C. According to Hoffman-Lauritzen theory, two crystallization regime are identified with a transition temperature occurring at 118°C, and the value of Kg(II)/Kg(III) is 2.17 [Kg(II) = 6.025 × 105K2, Kg(III) = 1.307 × 106 K2]. [ABSTRACT FROM AUTHOR]