Aging and structural relaxation of hyper-quenched Mg65Cu25Y10 metallic glass

The structural relaxation, glass transition and crystallization processes of Mg65Cu25Y10 metallic glass are studied by Differential Scanning Calorimetry (DSC) and Mechanical spectroscopy. The relaxation model derived from the mechanical measurements is compared with the kinetics of these transformations obtained from the DSC curves. The structural relaxation kinetics is found to be controlled by the glassy dynamics following an Adams-Gibbs-Vogel function. The glass transition and crystallization kinetics are controlled by the dynamics of the supercooled melt following a Vogel-Fulcher-Tammann behaviour. The results suggest that the microscopic processes responsible of structural relaxation and aging below the glass transition correspond to the same processes generating the a-relaxation peak. (C) 2013 Elsevier B.V. All rights reserved.Peer ReviewedPostprint (author’s final draft

Enhanced hydrogen storage properties of LiAlH4 catalyzed by CoFe2O4 nanoparticles

The catalytic effects of CoFe2O4 nanoparticles on the hydrogen storage properties of LiAlH4 prepared by ball milling were investigated. The onset desorption temperature of the LiAlH4 + 2 mol% CoFe2O4 sample is 65 °C, which is 90 °C lower that of the as-received LiAlH4, with approximately 7.2 wt% hydrogen released at 250 °C. The isothermal desorption results show that for the 2 mol% CoFe2O4 doped sample dehydrogenated at 120 °C, 6.8 wt% of hydrogen can be released within 160 min, which is 6.1 wt% higher than that of the as-received LiAlH4 under the same conditions. Through the differential scanning calorimetry (DSC) and the Kissinger desorption kinetics analyses, the apparent activation energy, Ea, of the 2 mol% CoFe2O4 doped sample is calculated as 52.4 kJ mol -1 H2 and 86.5 kJ mol-1 H2 for the first two decomposition processes. This is 42.4 kJ mol-1 H 2 and 86.1 kJ mol-1 H2 lower compared with the pristine LiAlH4, respectively, indicating considerably improved dehydrogenation kinetics by doping the CoFe2O4 catalyst in the LiAlH4 matrix. From the Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses, a series of finely dispersed Fe and Co species with a range of valence states, produced from the reactions between LiAlH4 and CoFe2O4, play a synergistic role in remarkably improving LiAlH4 dehydrogenation properties. The rehydrogenation properties of the LiAlH4 + 2 mol% CoFe 2O4 sample have also been investigated at 140 °C under 6.5 MPa pressure held for 2.5 hPeer ReviewedPostprint (published version

The earthquake probabilities of the Liupanshan fault zone based on the Coulomb stress and friction constitutive law

AbstractAs the forefront of the northeastern margin of the Tibetan Plateau, the Liupanshan area is subjected to significant Cenozoic deformation. Considering the background of historical earthquakes and the current seismic activity, the Liupanshan fault poses a risk of strong earthquakes. This paper analyzes the evolution of Coulomb stress induced by the coseismic and postseismic viscoelastic deformation of six historical strong earthquakes that occurred around the Liupanshan area since the twentieth century. Additionally, based on the disturbance in Coulomb stress and the background seismicity rate, the probability of earthquake occurrence is quantitatively evaluated using the frictional constitutive law. The results indicate that northern section of the Liupanshan fault has higher earthquake potential than the southern section, warranting close attention. These findings serve as a reference for medium- and long-term earthquake forecast and risk assessment in the vicinity of the Liupanshan fault

Role of Nb in glass formation of Fe-Cr-Mo-C-B-Nb BMGs

A new Fe-based bulk metallic glass with superior glass-forming ability (GFA), Fe46Cr15Mo14C15B6Nb4, was developed based on the Fe-Cr-Mo-C-B alloy system by minor addition of Nb. The effects of Nb addition on glass formation of the Fe-50 xCr15Mo14C15B6Nbx (x = 0, 2, 4 and 6 at.%) alloys were investigated. The optimum addition content of Nb was determined as 4 at.% by X-ray diffraction and differential scanning calorimeter analysis. A fully amorphous rod sample with 3 mm in diameter was produced by using commercial-grade raw materials and a copper mold casting technique. This alloy shows an ultimate compressive strength of 1920 MPa and Vicker's hardness 1360 H-V, which is two to three times that of conventional high strength steel and suggests a promising potential for applications combining outstanding corrosion and wear resistance properties. The crystallization kinetics studies found that the activation energies for glass transition, onset of crystallization and crystallization peak were higher than those of other reported Fe-based bulk metallic glasses. The value of the fragility parameter m for the Fe46Cr15Mo14C15B6Nb4 alloy was calculated to be 34, indicating that the Fe-Cr-Mo-C-B-Nb alloy system is a strong glass former according to the Angell's classification scheme. It is inferred that the more sequential change in the atomic size, the generation of new atomic pairs with large negative heats of mixing and the amount of oxygen in the molten liquid neutralized into Nb oxides provide a synergetic effect for the remarkably improved GFA and thermal stability. (C) 2014 Elsevier B.V. All rights reserved.Peer Reviewe

Improved Hydrogen Storage Performance of MgH\u3csub\u3e2\u3c/sub\u3e–LiAlH\u3csub\u3e4\u3c/sub\u3e Composite by Addition of MnFe\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e4\u3c/sub\u3e

The catalytic effects of MnFe2O4 nanoparticles on the hydrogen storage properties of MgH2–LiAlH4, prepared by ball milling, are studied for the first time. The hydrogen storage properties and reaction mechanism are investigated by pressure–composition–temperature (PCT), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The nonisothermal desorption results show that MgH2–LiAlH4 + 5 mol % MnFe2O4 has a lower onset dehydrogenation temperature, 85, 50, and 40 °C lower than these of ball-milled MgH2–LiAlH4 sample for each stage in the dehydrogenation process. The isothermal dehydriding kinetics and isothermal rehydrogenation kinetics results indicate that adding MnFe2O4 to MgH2–LiAlH4 could significantly enhance the absorption/desorption kinetics of MgH2–LiAlH4. From the differential scanning calorimetry and Kissinger analysis, the apparent activation energy of the 5 mol % MnFe2O4-doped sample for the three decomposition stage is 55.8, 70.8, and 96.5 kJ/mol, resulting in a 45.7, 85.5, and 99.6 kJ/mol decrease, respectively, compared with the MgH2–LiAlH4 sample. These improvements are mainly attributed to in situ formed Fe0.872O phase and the amorphous Mn-containing phase during the dehydrogenation process, which act as the real catalyst in the MgH2–LiAlH4 + 5 mol % MnFe2O4 composite

Structural design of stainless steel

SIGLEAvailable from British Library Document Supply Centre-DSC:8127.922(P291) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Superior catalytic effect of nickel ferrite nanoparticles in improving hydrogen storage properties of MgH2

The catalysis of NiFe2O4 nanoparticles on the hydrogen storage performances of magnesium hydride synthesized by high-energy ball milling was studied for the first time. The H-2 storage performances and catalytic mechanism were studied by pressurecompositiontemperature (PCT), differential scanning calorimetry (DSC), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The nonisothermal dehydrogenation results display that the initial dehydrogenation temperature of 7 mol % NiFe2O4-doped MgH2 is 191 degrees C, which is 250 degrees C lower than that of pristine MgH2. The desorption kinetics displays that the MgH2+7 mol % NiFe2O4 sample could desorb 3.79 wt % H-2 within 1 h at 300 degrees C under H-2 pressure of 0.1 MPa. The absorption kinetics displays that the MgH2+7 mol % NiFe2O4 sample could absorb 2.06 wt % H-2 within 3 h near room temperature under H-2 pressure of 4 MPa. The desorption activation energy of the MgH2+7 mol % NiFe2O4 sample is 59.6 kJ/mol, decreasing 195.3 kJ/mol as compared with pristine magnesium hydride. The reaction enthalpy and entropy of the MgH2+7 mol % NiFe2O4 sample during the dehydrogenation process are improved. The enhancement in the H-2 storage performances of MgH2 by adding NiFe2O4 nanoparticles is primarily ascribed to intermetallic Fe7Ni3 and (Fe,Ni) phases during the desorption procedure, which act as the real catalyzer in the 7 mol % NiFe2O4-doped sample.Peer Reviewe

Ultralow lattice thermal conductivity and promising thermoelectric properties of a new 2D MoW3Te8 membrane

Assembling new van der Waals (vdW) materials is challenging for the development of two-dimensional (2D) function devices. The MoW3X8 membrane (X = Se, Te) is a new 2D TMDs membrane molecule composed of one WX2 monolayer and one WX2-MoX2-WX2 sandwich trilayer. The presence of Mo/W atoms endows the new structure with the bridges between X atoms that connect pairs of MoX2/WX2 monolayers and the terminal sites that produce the van der Waals gap in these layers. The mirror symmetry is broken and the phonon dispersion is suppressed by reducing the dimensionality of the MoW3X8 membrane. In this work, the phonon transport and thermoelectric properties of the MoW3X8 membrane are investigated using first-principles method combined with the semi-classical Boltzmann transport and relaxation time approximation (RTA) theories. It is found that the larger gap between low-frequency and high-frequency optical branches in the membrane prevents atomic vibrations and drastically reduces the phonon velocity in a mid-frequency range below the gap. The low-lying optical and acoustic phonon modes are closely linked in MoW3Te8 membranes, enhancing the phonon–phonon scattering and thereby shortening the phonon relaxation time. These characteristics allow the MoW3Te8 membrane to achieve an extremely low lattice thermal conductivity of 0.49 Wm-1K−1 relative to that of the MoW3Se8 membrane (3.25 Wm-1K−1), which also leads to the improvement in thermoelectric performance of the former one. Besides, the maximum ZT values of 4 (4.5) at 900 K and the carrier concentration of 4 × 1011 cm−2 in the n-type (p-type) MoW3Te8 membrane could be enriched because of the low lattice thermal conductivity

Silicon-hydrogen bond effects on aluminum-induced crystallization of hydrogenated amorphous silicon films

The effects of hydrogen dilution on aluminum-induced crystallization (ALE) of hydrogenated amorphous silicon (a-Si H) films have been studied. The Raman spectra showed that the short-range order (SRO) and the intermedium-range order (IRO) of the as-deposited a-Si films increased with the increase of the H2 dilution from 0% to 20%. The optical microscope (OM) and X-ray diffraction (XRD) observation revealed that, compared to the a-Si:H film deposited in pure Ar, the a-Si:H films deposited with H2 dilution in the range of 3-8% possessed a lower crystallization rate while the a-Si:H films deposited with high H2 dilution in the range of 15-20% possessed a faster crystallization rate. It was found that majority of the hydrogen existed in the form of monohydride (SiH) bond in the a-Si:H films with H2 dilution ratio of 3-8%, the bonding energy of which was higher than that of Si-Si bond, leading to a lower crystallization rate of a-Si:H films. While the dihydride (SiH2) bond became dominant in the a-Si:H films with high H-2 dilution of 15-20%, the bonding energy of which was lower than that of Si-Si bond, thus accelerating the crystallization rate. Therefore, it was illustrated that not the hydrogen concentration but the form of silicon-hydrogen bond determined the AlC process of a-Si:H films. (C) 2014 Elsevier B.V. All rights reserved