Stabilization of low-valence transition metal towards advanced catalytic effects on the hydrogen storage performance of magnesium hydride

Magnesium hydride(MgH_(2))has been widely regarded as a potential hydrogen storage material owing to its high gravimetric and volumetric capacity.Its sluggish kinetics and high activation energy barrier,however,severely limit its practical application.Transition metal oxides(TMOs)have been extensively used as catalysts to improve the hydrogen storage performance of MgH_(2),but the low-valence transition metal(TM)ions,resulting from the reduction of TMOs accompanied by the formation of inactive Mg O,have been demonstrated to be the most effective components.Herein,we theoretically and experimentally confirm that the doping of low-valence TMs into Mg O could effectively weaken the Mg-H bonds and decrease the energy required for hydrogen desorption from MgH_(2),leading to superior catalytic activity compared to both TMOs and Mg O.In particular,the apparent activation energy for the dehydrogenation of Mg(Nb)O-catalyzed MgH_(2)could be reduced to only 84.1 kJ mol^(-1),and the reversible capacity could reach around 7 wt.%after 5 cycles with a capacity retention of 96%.Detailed theoretical calculations confirm that the remarkable orbital hybridization between Mg(Nb)O and MgH_(2)promotes charge transfer from MgO to the MgH_(2)monomer,resulting in significantly weakened stability of MgH_(2),which could effectively enhance its hydrogen storage performance.

The effect of LPSO on the deformation mechanism of Mg-Gd-Y-Zn-Zr magnesium alloy

The tensile deformation behavior and corresponding microstructure evolution of the Mg-4.7Gd-3.4Y-1.2Zn-0.5Zr(at.%)magnesium alloy with long period stacking structure(LPSO)are studied by electron backscatter diffraction(EBSD)and slip lines methods.The results show that less and very small size of twins is observed in the grains with high value of Schmid factor for twinning,which indicates that the growth of the{10–12}twinning deformation is prevented by the LPSO phase.The prismatic lines present in grains of which the prismatic slip Schmid factor is above 0.4.The favorable orientation and LPSO phase synergistically promote the activation of prismatic slip.The inhomogeneous rotation of the grains during deformation is the reason for the microcrack at grain boundary.

Effects of heat treatment on mechanical properties of an extruded Mg-4.3Gd-3.2Y-1.2Zn-0.5Zr alloy and establishment of its Hall–Petch relation

The effects of T4,T5,and T6 treatment on the microstructure and mechanical properties of the extruded Mg-4.3Gd-3.2Y-1.2Zn-0.5Zr(wt.%)alloy with a relatively low RE content(7.5 wt.%)were investigated.T4 treatment at 450–500°C induces a gradual grain growth ofα-Mg but an obvious transition of texture component from<0001>⊥ED to<0001>∥ED.Interdendritic LPSO phases are highly stable against annealing while intragranular ones experience dissolution and re-precipitation.After peak-ageing at 200°C,the elongation of as-extruded and T4 samples is just slightly reduced or even increased due to the weak ageing hardening response.T5 sample exhibits an attractive combination of strength and ductility,with a tensile yield strength(TYS)of 303 MPa and elongation of 20.0%.The Hall–Petch relation for the alloys with or without ageing treatment has been estimated.Grain boundary strengthening rather than precipitation strengthening has the dominant contribution to TYS,and a modified equation is developed to predict grain boundary strengthening values for Mg-Gd-Y-Zn-Zr alloys which contain different Schmid factors for basal slip.

Water-Mediated Spontaneously Dynamic Oxygen Migration on Graphene Oxide with Structural Adaptivity for Biomolecule Adsorption

We theoretically and experimentally show that,with water being adsorbed,the graphene oxide(GO)is converted to a spontaneously dynamic covalent material under ambient conditions,where the dominated epoxy and hydroxyl groups are mediated by water molecules to spontaneously break/reform their C–O bonds to achieve dynamic oxygen migration.This dynamic material presents structural adaptivity for response to biomolecule adsorption.Both density functional theory calculations and ab initio molecular dynamics simulations demonstrate that this spontaneously dynamic characteristics is attributed to the adsorption of water molecules,which sharply reduces the barriers of these oxygen migration reactions on GO to the level less than or comparable to the hydrogen bonding energy in liquid water.

A high-performance Mg-4.9Gd-3.2Y-1.1Zn-0.5Zr alloy via multidirectional forging after analyzing its compression behavior

A high-performance Mg-4.9Gd-3.2Y-1.1Zn-0.5Zr alloy has been fabricated by multidirectional forging(MDF)after analyzing its compression behavior.The as-homogenized alloy exhibits a high activation energy Q of deformation(~285 kJ/mol).The size of DRXed grains after compression tends to decrease as the Z-H parameter(Z)increases,showing a grain size exponent m of~4.0.Lamellar LPSO phases,kinking deformation,and bimodal microstructure are detected at the relatively low compression temperature of 350 and 400℃,while sufficient DRX can be achieved at 500℃,accompanied by the dissolution of lamellar LPSO.According to the processing maps,MDF was successfully conducted under an appropriate condition.After peak-aged at 200℃for 78 h,the MDFed billet exhibits a tensile yield strength(TYS)of 331 and 305 MPa at room temperature and 200℃,respectively.The high strength mainly results from the combination of fine grains,low Schmid factor for basal slip,sufficientβ’ageing precipitates,and directionally arranged interdendritic LPSO phases,etc.This paper provides a feasible way for the fabrication of high-performance,low-RE-content,and large-scale Mg components for industrial production.

Formulation of lyotropic liquid crystal emulsion based on natural sucrose ester and its tribological behavior as novel lubricant

The tribological behavior of oil-in-water emulsions formulated with natural lyotropic liquid crystal(LLC)emulsifiers based on natural sucrose ester was studied for the first time.Polarized optical microscopy,synchrotron radiation small-angle X-ray scattering,wide-angle X-ray scattering,and synchrotron radiation infrared microspectroscopy demonstrated that LLC emulsifiers were tightly ordered at the oil–water interface with a distinct nematic texture.The viscosity of emulsion was observed to change over time.Moreover,the zeta potential and laser particle size distribution verified the emulsion’s satisfactory stability.The frictional shearing test proved that the coefficient of friction of the emulsion versus pure oil decreased by 34.2%.The coefficient of friction of the emulsion with liquid crystal decreased 10.1%versus that without liquid crystal.Although liquid crystal emulsion did not exhibit outstanding anti-wear performance compared with pure oil,its wear volume was 29.4%less than the emulsion without liquid crystal.X-ray photoelectron spectroscopy and scanning electron microscope–energy dispersive X-ray spectroscopy(SEM–EDS)proved that the tribo-film of the emulsion with liquid crystal was formed synergistically by the liquid crystal phase with the base oil.The formulation affecting the lubricant quality was further studied by orthogonal experiments.The resulting Stribeck curve behavior suggested that proper composition with a slightly higher viscosity can better reduce friction in both boundary lubrication and mixed lubrication regimes.The lubrication mechanism indicated that the periodically ordered liquid crystal was transported to the sliding asperity in the form of emulsion droplets,which bored the pressure and released the oil to form a tribo-film.This LLC emulsion is environmentally friendly and potentially non-irritant to the skin.Thus,it has promising application prospects as novel water-based and biological lubricants.