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Herein, we report a simple, versatile, defect-engineered method to fabricate Ru quantum dots (Ru QDs) uniformly anchored on a nitrogen-doped holey graphene (NHG) monolith. It uses in situ pyrolysis of mixed glucose, dicyandiamide (DCDA), and RuCl3, followed by an acid treatment, and a final heat treatment to introduce in-plane holes of various sizes. A novel transmission method in scanning electron microscopy was successfully implemented to directly visualize the holes with color contrast. A low accelerating voltage of 5 kV enabled prolonged observation without significant electron beam damage. The mechanisms of hole creation were examined in detail using various characterization techniques as well as control experiments. The Ru QDs had significant catalytic activity and resulted in larger in-plane holes through the graphene sheets. The mechanical strain and the chemical reactivity of Ru QDs significantly diminished the activation energy barrier for the oxidation of C=C bonds in the graphene structure. The Ru QD/NHG hybrid material was utilized as an electrocatalyst for the oxygen evolution reaction in Li–O2 batteries, showing much lower charge overpotentials compared to the bare NHG counterpart. The defect-laden holey graphene counterpart can be highly functionalized for multiple applications, leading to a new method of nanoengineering based on atomic scale defects. [ABSTRACT FROM AUTHOR]

In this study, the structural evolution of two nanostructured Cu-22 wt pct Ge (Cu-20 at. pct Ge) and Cu-26 wt pct Ge (Cu-24 at. pct Ge) alloys upon mechanical alloying (MA) with subsequent heat treatment was investigated, and the phase transitions were monitored by means of various characterization methods. The findings indicated that, when the MA process continued for some time, a nanocrystalline α-Cu(Ge) solid solution was formed, which partially transformed into an amorphous phase. Further MA processing for 20 hours led to the formation of a disordered nanometric ε-CuGe intermetallic compound with a monoclinic crystal structure. Increased milling time subsequently led to the diminishing of the content of the amorphous phase which transformed into ε-CuGe nanocrystals. Clearly, a nanocrystallization transformation occurred upon ball milling principally on account of the accumulated energy due to the heavy mechanical deformation. Crystallization was also seen to occur at 473 K (200 °C) after annealing the MA-ed powders, leading to the formation of an ordered ε-CuGe intermetallic phase with an orthorhombic structure. The crystallographic relationships between the two disordered and ordered intermetallic phases were also discussed. [ABSTRACT FROM AUTHOR]

The structural evolution of Cu-12 wt·%Ge (∼Cu-11 at·%Ge) alloy processed by means of mechanical alloying (MA) with subsequent heat treatment was studied using X-ray diffraction profiles, scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM observations as well as differential thermal analysis(DTA). The fcc Cu(Ge) solid solution ( α) was produced at early stages of MA and amorphised upon further milling. This was followed by the formation of ζ−Cu5Ge intermetallic nanocrystals after 40 h of milling. The subsequent annealing process led to the nanocrystallisation of the amorphous powder. The X-ray crystallite size data showed the exceptional thermal stability of the alloy prepared. The mechanism of the stability was also investigated. In addition, a thermodynamic analysis based on Miedema's semiempirical model was carried out for the evaluation of the experimental results and a good agreement was found between them. [ABSTRACT FROM AUTHOR]

In the current study, the two alloys, Ni-20 at. pct W and Ni-35 at. pct W, were mechanically alloyed and subsequently heat treated to evaluate their structural variations using X-ray diffraction, scanning, and transmission electron microscopy, and differential thermal analysis. In addition, the effect of Fe contamination on the progress of mechanical alloying was investigated. The results showed that the Ni-20 at. pct W contained only Ni(W) solid solution even after prolonged milling times, while the Ni-35 at. pct W was amorphized after 40 hours of milling. The composition of the amorphized alloy was estimated to be Ni-31 at. pct W. Furthermore, it was demonstrated that the nanocrystalline NiW intermetallic compound was stable at temperatures greater than 1303 K (1030 °C) and did not completely vanish upon peritectoid reaction. Consequently, an exceptional grain coarsening resistance was observed at high temperatures near the melting points. The mechanisms involved in this outstanding thermal stability were also probed. [ABSTRACT FROM AUTHOR]