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Switching elements are crucial components in electrical and electronic systems that undergo severe degradation due to the electrical arc that is generated during breaking. Understanding the behavior of the electrical arc and modifying its characteristics via proper electrode design can significantly improve durability while also promoting optimal performance, reliability, and safety in circuit breakers. This work evaluates the feasibility of carbon nanotube (CNT)-reinforced silver and copper metal matrix composites (MMCs) as switching electrodes and the influence of CNT concentration on the characteristics of the arcs generated. Accordingly, three different concentrations per MMC were manufactured via powder metallurgy. The MMCs and reference materials were subjected to a single break operation and the electrical arcs generated using 100 W and 200 W resistive loads were analyzed. The proposed MMCs displayed promising results for application in low-voltage switches. The addition of CNTs improved performance by maintaining the arc's energy in the silver MMCs and reducing the arc's energy in the copper MMCs. Moreover, a CNT concentration of at least 2 wt.% is required to prevent unstable arcs in both metallic matrices. Increased CNT content further promotes the splitting of the electrical arc due to a more complex phase distribution, thereby reducing the arc's spatial energy density. [ABSTRACT FROM AUTHOR]

The rise in electrification has considerably increased the demand for high-efficiency and durable electrical contact materials. Carbon nanoparticles (CNP) are a promising coating material due to their intrinsic transport properties (thus minimizing the impact on conductivity), their proven solid lubricity (potentially improving tribological performance), and their hydrophobic wetting behavior (potentially providing atmospheric protection). In this study, carbon nanotube and nanohorn coatings are produced via electrophoretic deposition on silver-plated surfaces, followed by tribo-electrical and wetting characterization. The proposed coatings do not negatively affect the conductivity of the substrate, showing resistance values on par with the uncoated reference. Tribo-electrical characterization revealed that the coatings reduce adhesive wear during fretting tests while maintaining stable and constant electrical contact resistance. Furthermore, CNP-coated surfaces show a hydrophobic wetting behavior toward water, with graphite and carbon nanotube (CNT) coatings approaching super-hydrophobicity. Prolonged exposure to water droplets during sessile drop tests caused a reduction in contact angle (CA) measurement; however, CNT coatings' CA reduction after five minutes was only approximately 5°. Accordingly, CNP (specifically CNT) coatings show auspicious results for their application as wear and atmospheric protective barriers in electrical contacts. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT)-reinforced silver and copper metal matrix composites—at three different reinforcement phase concentrations (0.5 wt.%, 0.75 wt.%, and 1 wt.%)—were produced via powder metallurgy and sintered via hot uniaxial pressing. Optical and electron microscopy techniques were used to characterize the powder mixtures and sintered composites. The latter were also electrically characterized via load-dependent electrical contact resistance (ECR) and surface fatigue tests. Particle size and morphology play a crucial role in CNT deposition onto the metallic powder. CNT were deposited exceptionally well onto the dendritic copper powder regardless of its larger size (compared with the silver flakes) due to the higher surface area caused by the grooves and edges of the dendritic structures. The addition of CNT to the metallic matrices improved their electrical performance, in general outperforming the reference material. Higher CNT concentrations produced consistently low ECR values. In addition, high CNT concentrations (i.e., 1 wt.%) show exceptional contact repeatability due to the elastic restitutive properties of the CNT. The reproducibility of the contact surface was further evaluated by the fatigue tests, where the composites also showed lower ECR than the reference material, rapidly reaching steady-state ECR within the 20 fatigue cycles analyzed. [ABSTRACT FROM AUTHOR]

Nickel matrix composites are produced with concentrations of 0.5-10 vol% of carbon nanotubes (CNT), onion-like carbon (OLC), or nanodiamonds (nD) as reinforcement phase by hot pressing. The effect of the carbon nanoparticle (CNP) type and concentration on the microstructure is analyzed. Grain sizes are measured and a model is adapted to predict the observed grain refinement for all CNP. The individual saturation concentration and maximum achievable grain refinement differs (for CNT: 3 vol%, OLC: 6.5 vol% and nD: 10 vol%), which is correlated to the agglomerate diameter distribution. This can be traced back to different hybridization states and different particle geometries, therefore providing valuable information for CNP-reinforced Metal matrix composites to a general extent. [ABSTRACT FROM AUTHOR]

Reinforcement distribution has a major influence on composite material behavior. This work presents a method to quantitatively analyze the reinforcement distribution homogeneity in metal matrix composites reinforced with carbon nanotubes. The method is based on the statistical two-dimensional analysis of the CNT cluster distribution within defined regions. A subsequent analysis of the material hardness allowed a correlation to the homogeneity, highlighting the influence of the CNT distribution. This analysis provides a straightforward and objective assessment of the reinforcement distribution, applicable to other types of composites. [ABSTRACT FROM AUTHOR]

The microstructural thermal stability and mechanical properties of carbon nanotube (CNT)-reinforced Ni matrix composites processed by high pressure torsion (HPT) are investigated. A structural assessment of the CNTs at the different processing steps was performed by means of Raman spectroscopy, not detecting any significant modification of the CNT structure throughout the whole procedure. After deformation, the composites showed a maximum fivefold increase in hardness, related to their microstructure and resembling a Hall–Petch behavior. In order to study the thermal stability, an annealing was made at a homologous temperature of 0.33, which exceeds the grain growth onset temperature for this type of composites. The presence of CNTs helped stabilize the microstructure by pinning the grain boundaries during HPT. This stabilization translated into a significant increase in hardness and remained, to a certain degree, after the thermal treatment. Our results highlight the feasibility of obtaining CNT-reinforced composites by this means, improving the properties without compromising the structural features of the reinforcement and increasing their distribution within the matrix. [ABSTRACT FROM AUTHOR]

Nickel (Ni) and carbon nanotube (CNT)-reinforced Ni-matrix composites were manufactured by solid state processing and severely deformed by high-pressure torsion (HPT). Micro-tribological testing was performed by reciprocating sliding and the frictional behavior was investigated. Tribo-chemical and microstructural changes were investigated using energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) and focused ion beam (FIB). The CNT lubricity was hindered due to the continuous formation of a stable oxide layer promoted by a large grain boundary area and by irreversible damage introduced to the reinforcement during HPT, which controlled the frictional behavior of the studied samples. The presence of CNT reduced, to some extent, the tribo-oxidation activity on the contact zone and reduced the wear by significant hardening and stabilization of the microstructure. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNT) have been recently proposed as stabilizers against grain growth that can happen even at low temperature inputs in nano-crystalline and ultrafine-grained materials obtained by severe plastic deformation. In this study, we analyzed the evolution of the structural defects on the nanotubes in CNT-reinforced nickel matrix composites with different reinforcement weight fractions. The composites were processed by high pressure torsion, and we used Raman spectroscopy as the main characterization technique. The results indicate that for CNT subjected to highly energetic processing, it is not sufficient to analyze only the I D /I G ratio (as proposed in the available literature), but it is also necessary to evaluate the shifting of the G band, which traces the amorphization trajectory undergone by the CNT. Furthermore, we observed that the deformation suffered by the CNT is related to the accumulated strain and varies with the partial CNT fractions of these composites. This is related to their capacity to withstand the plastic strain that occurs during deformation. In addition, the defective state reaches a saturation before achieving the saturation in the microstructural refinement. These results will help to efficiently optimize the processing of this type of engineering composites. [ABSTRACT FROM AUTHOR]