Short-Range Nanoreaction Effect on the Hydrogen Desorption Behaviors of the MgH2-Ni@C Composite.

Doping a catalyst can efficiently improve the hydrogen reaction kinetics of MgH2. However, the hydrogen desorption behaviors are complicated in different MgH2-catalyst systems. Here, a carbon-encapsulated nickel (Ni@C) core-shell catalyst is synthesized to improve the hydrogen storage properties of MgH2. The complicated hydrogen desorption mechanism of the MgH2-Ni@C composite is elucidated. The experimental and theoretical calculation results indicate a short-range nanoreaction effect on the hydrogen desorption behaviors of the MgH2-Ni@C composite. The Ni@C catalysts and the adjacent MgH2 form nanoreaction sites along with preferential hydrogen desorption. The new interface between the in situ formed Mg and residual MgH2 contributes to the subsequent hydrogen desorption. With the nanoreaction sites increased via adding more catalyst, the short-range nanoreaction effect is more prominent; as a comparison, the interface effect becomes weaker or even disappears. In addition, the core-shell structure catalyst shows ultrahigh structural stability and catalytic activity, even after 50 hydrogen absorption and desorption cycles. Hence, this study provides new insights into the complicated hydrogen desorption behaviors and comes up with the short-range nanoreaction effect in the MgH2-catalyst system.

Corrosion behavior and mechanical degradation of as-extruded Mg-Gd-Zn-Zr alloys for orthopedic application.

The microstructures, corrosion behavior, and mechanical degradation of the as-extruded Mg-6.0Gd-0.5Zn-0.4Zr (wt %, GZ60K) and Mg-6.0Gd-1.0Zn-0.4Zr (wt %, GZ61K) alloys were investigated. In both alloys, stacking faults and precipitates are formed in the recrystallized microstructures. The corrosion rate of GZ61K calculated by the hydrogen evolution in simulated body fluid is 0.34 ± 0.13 mm/year, which is lower than that of GZ60K (0.45 ± 0.09 mm/year); and the current density of GZ61K (5.23 ± 1.41 µA cm-2 ) is much lower than that of GZ60K (11.95 ± 3.37 µA cm-2 ). The corrosion results indicate GZ61K is more resistant to corrosion than GZ60K, but GZ60K presents more uniform corrosion mode as compared to GZ61K. After immersion in simulated body fluid for 7, 14, and 21 days, a slight decrease in the strength of both alloys is observed. The yield strength half-life is assessed for mechanical degradation and determined to be 125 and 85 days for GZ60K and GZ61K, respectively. The as-extruded GZ60K alloy with more uniform corrosion and longer mechanical integrity shows promising potential for orthopedic application.