Deformation of Al85Y8Ni5Co2 Metallic Glasses under Cyclic Mechanical Load and Uniform Heating

Modelling of the deformation process of Al85Y8Ni5Co2 amorphous alloys was carried out under simultaneous application of cyclic mechanical load (at 0.3 or 3 Hz frequencies) and continuously increasing temperature (heating rate 5 K/min). It is shown that deformation of the amorphous specimens occurs by the hyperbolic temporal dependence. It is analytically determined and experimentally proved that for non-isothermal cyclic deformation, the wave effects take place as a result of the superposition of thermal-activated and mechanical components. The behaviour of the material under thermo-mechanical action was described qualitatively within the framework of Spaepen’s model. The dependencies for the reaction force of the samples were obtained as two-parameter functions of the frequency and temperature. A reaction force surface of a specimen, as a function of the different forcing frequencies and time, has been plotted

Characterization and Dynamics of the Different Protonic Species in Hydrated 12-Tungstophosphoric Acid Studied by ²H NMR

Solid heteropolyacids (HPAs) are promising nonpolluting superacids used as catalysts and solid proton conductors. The catalytic and conducting properties of HPAs are very sensitive to the amount of hydration water present in the system, as water molecules tend to interact with the HPA acid protons to form [H₃O]⁺ and [H₅O₂]⁺ ions. These ions constitute active species that govern the catalytic reaction pathways and the proton migration mechanism. Establishing the structure and mobility of protonic species could yield important information concerning the functions of material based on HPA hydrates. In this work, we have performed the analysis of both ²H NMR line shape and the evolution of <i>T</i>₁, <i>T</i>₂ relaxation with temperature for the deuterated analogue of the solid 12-tungstophosphoric acid (TPA × <i>n</i>H₂O) at different hydration levels (0 < <i>n</i> < 6) in the wide temperature range of 103–503 K. This allowed us to characterize in detail the mobility of different protonic species, including acidic OH groups, water molecules, and hydroxonium ions. Kinetic parameters of internal and diffusional motions for different protonic species at different hydration levels <i>n</i> of TPA × <i>n</i>H₂O were derived

Methane Activation on Zn²⁺-Exchanged ZSM‑5 Zeolites. The Effect of Molecular Oxygen Addition

In relation to the reported methane activation on Zn-modified zeolite ZSM-5 at room temperature to afford the surface methoxy species by Xu et al. (<i>Chem. Sci.</i> <b>2012</b>, <i>3</i>, 2932), the activation of methane on Zn²⁺-exchanged H-ZSM-5 zeolite in the absence and the presence of molecular oxygen has been studied with ¹³C magic angle spinning (MAS) NMR spectroscopy. It has been established that the methane activation on zinc cationic sites under nonoxidative conditions occurs exclusively by an “alkyl” pathway to form the surface zinc-methyl species. The addition of the molecular oxygen (dioxygen) to methane adsorbed on the Zn²⁺-exchanged H-ZSM-5 zeolite results in the surface methoxy and other oxygen-containing species, such as formate, acetaldehyde, and acetic acid. The formation of the surface methoxy species occurs by the oxidation with molecular oxygen of zinc-methyl species primarily formed on the zeolite surface. The Zn²⁺/ZSM-5 zeolite with full substitution of Brønsted acid sites (BAS) by Zn²⁺ cations offers zinc-methyl species from methane at <i>T</i> ≥ 523 K, whereas Zn²⁺/H-ZSM-5 with partial substitution (60%) of BAS produces zinc-methyl at room temperature. BAS promotes the formation and decomposition (by the sample evacuation) of zinc-methyl species on Zn²⁺/H-ZSM-5 at room temperature. Zinc-methyl is readily oxidized by the dioxygen additive to offer methoxy species already at room temperature. Thus, it has been shown that pure methane forms only zinc-methyl species upon its interaction with zinc cationic sites of Zn²⁺-exchanged H-ZSM-5 zeolite, while the surface methoxide could be formed only by the interaction of zinc-methyl with dioxygen that might be contained in the reactive methane