Synthesis of Electromagnetic Wave-Absorbing Co–Ni Alloys and Co–Ni Core–Shell Structured Nanoparticles

Abstract

Co–Ni alloy nanoparticles, a potential candidate for microwave absorption material, were successfully synthesized by tuning the reduction timing of Co and Ni ions by introducing oleylamine as a complexing agent and 1-heptanol as a reducing solvent. The formation mechanism elucidated using time-resolved sampling and in situ X-ray absorption spectroscopy (XAS) and ultraviolet-visible (UV-vis) spectrophotometry measurements suggested that the delay in the reduction of Co ions via complexation with oleylamine facilitated the co-reduction of Co with Ni ions and led to the formation of Co–Ni alloys. The successful synthesis of Co–Ni alloys experimentally confirmed the differences in magnetic properties between alloy and core–shell structured Co50Ni50 particles. Further, the syntheses of Co–Ni alloys with different compositions were also possible using the above technique. In addition, the microwave absorption properties were measured using the free-space method utilizing a vector network analyzer of Co50Ni50polyethylene composite with different sheet thicknesses. A reflection loss (RL) value of −25.7 dB at 13.6 GHz for the alloy structure was more significant than the core–shell counterpart. The above values are high compared to results reported in the past. The validity of the measurements was confirmed by utilizing the parameter retrieval method to extract permittivity and permeability from the scattering parameter (S) and recalculation of the RL as a function of frequency.

Kinetically Controlled Direct Synthesis of B2- and A1-Structured Cu–Pd Nanoparticles

“…For the synthesis of Cu− Pd alloy NPs, reduction kinetics and reduction timing of the metallic cations have to be controlled. 37 But the standard reduction potentials of Cu and Pd are +0.34 and +0.984 V vs SHE, respectively, the Pd ion is easier to reduce to zerovalent Pd, and the reduction kinetics is high. Thus, it is necessary to consider a synthesis technique that could facilitate control over the reduction conditions and timing for the formation of bimetallic alloys.…”

“…Further, due to the difference in the initial reduction rates of metal, the internal structure of the metal particles could be tuned from a single crystal, singly twinned, multiply twinned, and further to stacking fault-lined, and the overall structure of the bimetals could be core–shell or alloy. The recent advances in the synthesis of metallic alloy nanostructures have proven that the use of the alcohol reduction method is a powerful choice to control the crystalline phase of metal/alloy NPs − such as Cu–Co and Co–Ni systems by tuning the reduction kinetics and timing. − In addition, the synthesis of transition–noble metallic NPs such as Ni–Pt, Co–Pt, and Ni–Pt–Pd was also reported. − …”

Composition sensitive selectivity and activity of electrochemical carbon dioxide reduction on Pd–Cu solid-solution alloy nanoparticles

“…In this study, we synthesized composition-controlled solid solution Pd-Cu alloy NPs by alcohol reduction method [43][44][45][46] and investigated the CO 2 RR properties. All the alloy NPs exhibited enhanced selectivity for the CO 2 RR compared with pure Pd and Cu particles.…”

Flexible Sandwich-Structured Co–Ni Alloy-Coated Basalt Fabrics via the Writing–Grafting–Activation–Deposition Process for Electromagnetic Interference Shielding and Electrothermal Conversion

“…Specifically, alloy nanoparticles have high potential for various applications (e.g., electromagnetic shielding, electronic inductors, magnetic separation) because the magnetic properties of alloy nanoparticles can be adapted to the applications by composition, structure, and size. 10 Metal coating techniques including sputtering, vacuum deposition, electroplating, and electroless deposition have been developed. 11 Electroless deposition technology has merits of easy operation and uniform coverage regardless of shape or size, which is extensively applied for nonconductive surface metallization.…”

“…Nanoparticles of iron group metals, i.e., Fe, Co, Ni, and their alloys, are attracting great interest because of their magnetic properties. Specifically, alloy nanoparticles have high potential for various applications (e.g., electromagnetic shielding, electronic inductors, magnetic separation) because the magnetic properties of alloy nanoparticles can be adapted to the applications by composition, structure, and size . Metal coating techniques including sputtering, vacuum deposition, electroplating, and electroless deposition have been developed .…”