Aluminum powders are known to provide outstanding volumetric exothermic enthalpy energy during thermal oxidation. However, the amount of energy released tends to be limited by the dense surface oxide (Al₂O₃) layer of the powder. Hence, a prerequisite for improving the reactivity of passivated Al particles is to remove the Al₂O₃ film from the surface. Considering that the self-propagating high-temperature synthesis (SHS) reaction of Ni and Al can generate additional exothermic heat in Al powder, Ni can be considered as a promising alternative to the surface oxide layer. Here, we report oxide-layer-free fine Al particles with a characteristic Ni/Al interface, where a Ni layer replaces the Al₂O₃ film. The microstructure of the synthesized powder consists of a 200-nm-thick Ni layer homogeneously coated on the Al surface, which has nanosized craters caused by the geometrical removal of Al₂O₃. Thermal analysis and in-situ heating transmission electron microscopy (TEM) results clearly show that active interdiffusion of atoms through the Ni/Al interface results in the formation of intermetallic compounds to provide additional exothermic energy, compared to the result for simply mixing Ni and Al powders. Hence, these findings provide new routes for the design and application of reactive metallic particles using the SHS reaction.

In this study, electroless-plating of a nickel-phosphor (Ni–P) thin film on surface-controlled thermoelectric elements was developed to significantly increase the bonding strength between Bi–Te materials and copper (Cu) electrodes in thermoelectric modules. Without electroless Ni–P plating, the effect of surface roughness on the bonding strength was negligible. Brittle SnTe intermetallic compounds were formed at the bonding interface of the thermoelectric elements and defects such as pores were generated at the bonding interface owing to poor wettability with the solder. However, defects were not present at the bonding interface of the specimen subjected to electroless Ni–P plating, and the electroless Ni–P plating layer acted as a diffusion barrier toward Sn and Te. The bonding strength was higher when the specimen was subjected to Ni–P plating compared with that without Ni–P plating, and it improved with increasing surface roughness. As electroless Ni–P plating improved the wettability with molten solder, the increase in bonding strength was attributed to the formation of a thicker solder reaction layer below the bonding interface owing to an increase in the bonding interface with the solder at higher surface roughness.

In the present study, we have demonstrated a facile and robust way for the fabrication of Cu-graphite composites (CGCs) with spatially-aligned graphite layers. The graphite layers bonded to the copper matrix and the resulting composite structure were entirely characterized. The preferential orientation and angular displacement of the nano-sized graphite fiber reinforcements in the copper matrix were clarified by polarized Raman scattering. Close investigation on the change of the Raman G-peak frequency with the laser excitation power provided us with a manifestation of the structural and electronic properties of the Cu-graphite composites (CGCs) with spatially-distributed graphite phases. High resolution transmission electron microscopy (TEM) observation and Raman analysis revealed that reduced graphite oxide (rGO) phase existed at the CGC interface. This work is highly expected to provide a fundamental way of understanding how a rGO phase can be formed at the Cu-graphite interface, thus finally envisioning usefulness of the CGCs for thermal management materials in electronic applications.

In this study, we examined the thermal stability, bonding strength, and interfacial characteristic of a Ni–W–P coating applied for solder joint of Bi₂Te₃ thermoelectric modules. This layer had uniform thickness and was confirmed to be amorphous even after annealing at 200°C for 150 h, demonstrating its thermal stability. Moreover, the barrier layer hindered the interdiffusion between Sn and Te, eliminating the formation of brittle intermetallic at the solder joint. Thus, the bonding strengths of p- and n-type thermoelectric units were improved approximately 1.3- and 2.8-fold, respectively, compared to the bonding strengths obtained without a Ni–W–P layer. In addition, the bonding strength was not affected by heating at 200°C for 150 h. The reliability of bonding strength was caused by the excellent thermal stability, and solder wettability of the barrier layer, which resulted in a bonding interface without brittle intermetallic and defects.