Study on the hydrogen absorption properties of a YGdTbDyHo rare-earth high-entropy alloy

This study investigated the microstructure and hydrogen absorption properties of a rare-earth high-entropy alloy(HEA),YGdTbDyHo.Results indicated that the YGdTbDyHo alloy had a microstructure of equiaxed grains,with the alloy elements distributed homogeneously.Upon hydrogen absorption,the phase structure of the HEA changed from a solid solution with an hexagonal-close-packed(HCP)structure to a high-entropy hydride with an faced-centered-cubic(FCC)structure without any secondary phase precipitated.The alloy demonstrated a maximum hydrogen storage capacity of 2.33 H/M(hydrogen atom/metal atom)at 723 K,with an enthalpy change(ΔH)of-141.09 kJ·mol^(-1)and an entropy change(ΔS)of-119.14 J·mol^(-1)·K^(-1).The kinetic mechanism of hydrogen absorption was hydride nucleation and growth,with an apparent activation energy(E_(a))of 20.90 kJ·mol^(-1).Without any activation,the YGdTbDyHo alloy could absorb hydrogen quickly(180 s at 923 K)with nearly no incubation period observed.The reason for the obtained value of 2.33 H/M was that the hydrogen atoms occupied both tetrahedral and octahedral interstices.These results demonstrate the potential application of HEAs as a high-capacity hydrogen storage material with a large H/M ratio,which can be used in the deuterium storage field.

A novel nanoporous Mg-Li material for efficient hydrogen generation

Hydrogen generation material is a new kind of energy material that can supply hydrogen by reacting with water and is drawing more and more attention with the development of hydrogen economy. In this study, a novel nanoporous magnesium-lithium material prepared by a physical vapor deposition method exhibits an excellent hydrogen generation property. It generates hydrogen efficiently and quickly with saltwater, reaching a hydrogen generation amount of 962 mL g^(-1) and hydrogen generation rates of 60 mL g^(-1)min^(-1), 109 mL g^(-1)min^(-1),256 mL g^(-1)min^(-1) and 367 mL g^(-1)min^(-1) at 0 ℃, 25 ℃, 35 ℃ and 50 ℃, respectively. The nanoporous magnesium-lithium material is composed of a solid solution phase with a magnesium-lithium atomic ratio of 17:3. By synchrotron radiation analysis, the sizes of the nanopores are in the range of 100 nm ~ 600 nm with an average size of 280 nm, and the porosity is calculated to be ~42.4%. The improved hydrogen generation property is attributed to the nanoporous structure with a high specific surface area, and the addition of lithium element which acts as active sites in hydrogen generation process.

Microstructure evolution and solidification behaviour of ZrB_(2)-SiC composite ceramics fabricated by laser surface zone-melting

Microstructure evolution and solidification behaviour of ZrB_(2)-SiC composite ceramics fabricated by laser surface zone-melting were investigated.Microstructure coarsening at high scanning speed and mi-crostructure refining after turning off the laser was observed due to the changes in the solidification rate.The solidification behaviour from bottom to top of the molten pool was studied,where there are some coarsen eutectic bands caused by the secondary heating of the melting pool on the solidified eu-tectic zone in the molten pool.The deviation of melt composition from the eutectic ratio due to the volatilization of SiC can form a coarse primary ZrB_(2) phase among fine eutectic structure(single-phase instability),and the constitutional supercooling due to the accumulation of impurity elements can form coarse eutectic dendrites among fine eutectic structure(two-phase instability).Both single-phase insta-bility and two-phase instability are adverse to the mechanical properties,which should be prevented by adjusting the composition of raw materials and the solidification process.