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Rejuvenation has been considered to be an effective method for enhancing the mechanical properties of metallic glass. Herein, the effect of two rejuvenation methods, by enthalpy relaxation and through cryogenic thermal cycling (CTC) treatment, on the mechanical properties and energy state of a relaxed Cu49Hf42Al9 bulk metallic glass (BMG) is investigated. It is revealed that the method of rejuvenation by enthalpy relaxation is applicable to the present relaxed metallic glass system, where the energy state is lifted to a higher one from the relaxed state and the compressive plasticity surpasses that of the as-cast MG after rejuvenation. The CTC treatment can also recover the compressive plasticity of the relaxed MG even though only with a slight increase in the energy state. The combination of the above two methods, however, shows an unexpectedly stronger rejuvenation effect in the relaxed Cu49Hf42Al9 BMG, where the energy state of the optimally rejuvenated sample is comparable to that of the as-cast sample and the compressive plasticity of the optimally rejuvenated sample is more than twice and six times that of the as-cast sample and the relaxed sample, respectively. Our results show that a significant rejuvenation effect can be achieved by combining two or more rejuvenation methods, which opens a new route to tailor the properties of MGs. [ABSTRACT FROM AUTHOR]

Air pressure is one of the key factors affecting laser-induced breakdown spectroscopy (LIBS), and the mechanism of its influence on the spatial–temporal evolution of laser-induced plasma (LIP) is still not fully understood due to complex physical processes. In this study, the spatially and temporally resolved LIP's spectra at different pressures were collected from the direction of laser incidence, and the radial distribution characteristics of LIP along the target surface under the influence of air pressure were studied. Furthermore, the spatial–temporal evolution of the radial distribution of the electron density n e and electron temperature T e was studied using Stark broadening and a Boltzmann plot. Finally, the radial distribution of LIP satisfying the McWhirter criterion and the influence of air pressure on its spatial–temporal evolution were studied. It was found that air pressure has a significant effect on the radial distribution of LIP. The spectral intensity, electron density n e, and the electron temperature T e of the LIP decrease faster against distance r from the LIP core and slower with the delay time T d in a higher air-pressure environment. Furthermore, the LIP will gradually fail to satisfy the McWhirter criterion with the increase in the radius r and delay time T d; in addition, the lifetime of LIP, which satisfies the McWhirter criterion, is longer at higher pressure. This study is helpful in clarifying the influence of air pressure on the spatial–temporal evolution of LIP, optimizing the experimental parameters of LIBS, and providing a reference for application of LIBS. [ABSTRACT FROM AUTHOR]

The selective oxidation of tetrahydrofuran to γ-butyrolactone is an efficient method to convert biomass derivatives into high-value chemicals. In order to improve the efficacy of conversion of tetrahydrofuran to γ-butyrolactone, this study prepared an Ag–CeO2/α-Al2O3 catalyst via the impregnation method and used a solvent-free approach to convert tetrahydrofuran to γ-butyrolactone. And the conversion rate of 100% of raw material was achieved. The prepared catalyst was characterized by TEM, XRD, N2 adsorption-desorption and XPS, in order to better understand the performance of the catalysts. The results demonstrated that Ce3+ and Ce4+ coexist on the surface of the catalyst and verified the existence of metallic Ag (Ag0) in Ag–CeO2/α-Al2O3 catalyst. The reaction mechanism of the formation of γ-butyrolactone by γ-site switch (ring-opening and ring-closing) of tetrahydrofuran was deduced. This is attributed to the synergistic action of Ag and Ce. γ-Site switch effect (ring-opening and ring-closing) is proposed for the first time in this paper. [ABSTRACT FROM AUTHOR]

A polycrystalline TmNiAl2 compound with transition temperature near the liquid helium boiling point was successfully synthesized. Magnetic measurements show that FM (ferromagnetic) to FM and FM to PM (paramagnetic) transitions take place at 2.4 K and 4.0 K, respectively. Magnetic entropy change (–ΔSM) is calculated, and its maximal value [(–ΔSM)max] reaches as high as 20.7 J/kg K with the field change of 0–5 T. The low transition temperature together with large (–ΔSM)max at the liquid helium temperature zone originates from the weak spin-spin exchange interaction between Tm atoms. For a clear comparison, the magnetocaloric effect (MCE) of polycrystalline RNiAl2 (R = Tb and Gd) samples was also prepared and investigated. For the TbNiAl2 compound, FIM (ferrimagnetic) to AFM (antiferromagnetic) and AFM to PM transitions occur at 11.0 K and 21.5 K, respectively. As for the GdNiAl2 compound, an FM to PM transition occurs at 30.5 K. The value of (–ΔSM)max under the field change of 0–5 T is calculated to be 11.8 J/kg K and 17.3 J/kg K for TbNiAl2 and GdNiAl2, respectively. Compared with other RNiAl2-series MCE materials, TmNiAl2 exhibits the lowest working temperature and relatively larger (–ΔSM)max. The large MCE at low temperature indicates that TmNiAl2 is competitive among the MCE materials working at a liquid helium temperature zone. [ABSTRACT FROM AUTHOR]

The geochemical characteristics of melt inclusions and their host olivines provide important information on the processes that create magmas and the nature of their mantle and crustal source regions. We report chemical compositions of melt inclusions, their host olivines and bulk rocks of Xindian basalts in Chifeng area, North China Craton. Compositions of both bulk rocks and melt inclusions are tholeiitic. Based on petrographic observations and compositional variation of melt inclusions, the crystallizing sequence of Xindian basalts is as follows: olivine (at MgO > ~5.5 wt%), plagioclase (beginning at MgO = ~5.5 wt%), clinopyroxene and ilmenite (at MgO < 5.0 wt%). High Ni contents and Fe/Mn ratios, and low Ca and Mn contents in olivine phenocrysts, combining with low CaO contents of relatively high MgO melt inclusions (MgO > 6 wt%), indicate that Xindian basalts are possibly derived from a pyroxenite source rather than a peridotite source. In the CS-MS-A diagram, all the high MgO melt inclusions (MgO > 6.0 wt%) project in the field between garnet + clinopyroxene + liquid and garnet + clinopyroxene + orthopyroxene + liquid near 3.0 GPa, further suggesting that residual minerals are mainly garnet and clinopyroxene, with possible presence of orthopyroxene, but without olivine. Modeling calculations using MELTS show that the water content of Xindian basalts is 0.3-0.7 wt% at MgO = 8.13 wt%. Using 20-25% of partial melting estimated by moderately incompatible element ratios, the water content in the source of Xindian basalts is inferred to be ≥450 ppm, much higher than 6-85 ppm in dry lithospheric mantle. The melting depth is inferred to be ~3.0 GPa, much deeper than that of tholeiitic lavas (< 2.0 GPa), assuming a peridotite source with a normal mantle potential temperature. Such melting depth is virtually equal to the thickness of lithosphere beneath Chifeng area (~100 km), suggesting that Xindian basalts are derived from the asthenospheric mantle, if the lithospheric lid effect model is assumed. Keywords Melt inclusion * Olivine chemistry * Pyroxenite source * Water * Basalts * North China Craton, Introduction For years, it was thought that peridotite (olivine mode >40%), the predominant lithology in the upper mantle, is the source of mafic magmas (peridotite melts; e.g., Green and Ringwood [...]