[en] Novel core-shell-shell Fe@SiO₂@(MnZn)Fe₂O₄ soft magnetic composites (SMCs) with low core loss and high permeability were fabricated by a facile continuous chemical co-precipitation route and subsequent powder metallurgy technique. The typical double-shell structure for Fe@SiO₂@(MnZn)Fe₂O₄ powders was composed of a SiO₂−(MnZn)Fe₂O₄ mixed outer layer and an SiO₂ inner network embedded with trace amounts of (MnZn)Fe₂O₄. In comparison with Fe@SiO₂ SMCs, the Fe@SiO₂@(MnZn)Fe₂O₄ SMCs presented a notable flat high frequency characteristic up to 1 MHz, much higher permeability, and lower core loss which reduced with decreasing (MnZn)Fe₂O₄ layer thickness. Fe@SiO₂@(MnZn)Fe₂O₄ SMCs prepared with 4 mL (MnZn)Fe₂O₄ solution exhibited stable permeability of 64.0–63.5 up to 1 MHz and low core loss of 0.9–30.6 W/kg in 1–150 kHz. The strong magnetic coupling between the thin (MnZn)Fe₂O₄ layer and Fe cores effectively reduced the air-gap thickness and demagnetization field giving rise to a high permeability. The low core loss could be attributed to the full separation of Fe core by thin dielectric−electrically insulating magnetic coupled with a SiO₂/(MnZn)Fe₂O₄ insulating layer. Our findings might shed insight on the design of novel SMCs with low core loss and high permeability.

[en] Novel core@shell@shell structured carbonyl iron powder (CIP)@SiO₂@ Mn_0.6Zn_0.4Fe₂O₄ ferrite composites having great microwave absorption characteristics were successfully synthesized using chemical co-precipitation. The microstructure, morphology and microwave absorption performance of CIP@SiO₂@Mn_0.6Zn_0.4Fe₂O₄ ferrite composites were systematically investigated. The results show that both coating layers of SiO₂ and Mn_0.6Zn_0.4Fe₂O₄ are uniform and fine. The prepared CIP@SiO₂@Mn_0.6Zn_0.4Fe₂O₄ composites in this study display better dielectric loss and frequency characteristic at high frequency than CIP, CIP@SiO₂ and CIP@Mn_0.6Zn_0.4Fe₂O₄. The results of electromagnetic parameters also indicate that the enhanced microwave absorption performance primarily originates from the substantial contributions of magnetic loss to reflection loss. The optimal value of reflection loss of CIP@SiO₂@Mn_0.6Zn_0.4Fe₂O₄ having the thickness of 2 mm can reach up to −44.24 dB at 11.57 GHz as well as the bandwidth (RL ≤ −10 dB) from 9.04 to 16.16 GHz among the frequency range from 2 to 18 GHz. In addition, the greatly enhanced microwave absorption performance is attributed to good wave impedance matching, high attenuation constant, multi-relaxation processes and multiple interfacial polarization.

[en] The multi-wall carbon nanotube (MWCNT) reinforced alumina (Al₂O₃) matrix composites were fabricated by spray drying and vacuum hot-pressing sintering. The mechanical properties of the composites with different mass fractions of MWCNT were studied. The flexural strength and fracture toughness of the composite were 498.3 MPa and 5.69 MPa·m ^1/2, respectively, which were about 55.3% and 84.7% higher than that of pure Al₂O₃. With the increase in the content of MWCNT, the Vickers hardness and relative density of the composite decreased gradually. The correlation between the microstructure and the mechanical properties of the composite was analyzed. (paper)

[en] We study the moving and interaction of the compact-like pulses in the system of an anharmonic lattice with a double well on-site potential by a direct algebraic method and numerical experiments. It is found that the localization of the compact-like pulse is related to the nonlinear coupling parameter C_nl and the potential barrier height V₀ of the double well potential. The velocity of the moving compact-like pulse is determined by the linear coupling parameter C_l, the localization parameter q (the nonlinear coupling parameter C_nl) and the potential barrier height V₀ . Numerical experiments demonstrate that appropriate C_l is not detrimental to a stable moving of the compact-like pulse. However, the head on interaction of two compact-like pulses in the lattice system with comparatively small C_l leads to the appearance of a discrete stationary localized mode and small amplitude nonlinear oscillation background, while moderate C_l results in the emergence of two moving deformed pulses with damping amplitude and decay velocity and radiating oscillations, and biggish C_l brings on the appearing of four deformed kinks with radiating oscillations and different moving velocities.

[en] CNTs/Cu-Ti composites were fabricated successfully by spray pyrolysis, low energy ball milling and subsequent hot pressing (HP). Microstructure and mechanical properties of the composites were characterized by SEM, EDS, HRTEM, XRD, hardness and tensile tests. The results reveal that in situ generated nano-TiC particles, as a transition phase from CNTs to Cu-Ti matrix, which played a “rivet” role in enhancing the interfacial bonding between the CNTs and Cu-Ti matrix is formed in the composites. Consequently, mechanical properties of the CNTs/Cu-Ti composites are enhanced compared with alloy matrix, and an optimal balance between elevated ultimate tensile strength and impressively larger plastic deformation is achieved by adding 0.4 wt% CNTs in the composites. (ultimate tensile strength (UTS) 352 MPa, elongation 28.2%, the UTS is 39% higher than that of the Cu-Ti alloy, and the ductility increased significantly by 62%.) Finally, strengthening and toughening mechanisms are discussed. This study provides new insights into the interface structure and strength-ductility in metal-matrix composites.

[en] Highlights: • Anisotropic indexes, 3D graphs and projections of β-M₄AlN₃ are discussed. • Elastic anisotropy of β-M₄AlN₃ is in a sequence of β-Ta₄AlN₃ > β-Nb₄AlN₃ > β-V₄AlN₃. • The order of minimum thermal conductivity is β-V₄AlN₃ > β-Nb₄AlN₃ > β-Ta₄AlN₃. In this study, the first-principles calculations were employed to investigate the elastic, thermal properties, and the anisotropies in elastic modulus, Debye temperature and thermal conductivity of the ternary nitrides β-M₄AlN₃ (M = V, Nb, Ta). The results showed that they are brittle and not potentially superhard materials. The anisotropy indexes, 3D surface constructions and 2D planar projections were employed to characterize the anisotropies in elastic modulus and thermal conductivity. The sequences of anisotropies in both elastic modulus and thermal conductivity are β-V₄AlN₃ > β-Nb₄AlN₃ > β-Ta₄AlN₃. Besides, the sound velocities, Debye temperatures, and anisotropies were also discussed.

[en] Highlights: • CIP/SiO₂-RIP/SiO₂ SMCs with a high resistivity and low core loss were successfully fabricated. • The CIP surface is coated with a thick and stable amorphous insulating SiO₂-bond network. • The high resistivity is related to complete electrical intergranular isolation after the addition of CIP/SiO₂. • The SiO₂ amorphous layer grows with a high packing density and tightly adheres to the iron grains. Carbonyl iron powder (CIP) and reduced iron powder (RIP) were homogeneously coated with an SiO₂ insulating layer by a controlled in-suit chemical deposition procedure and used as raw materials to fabricate CIP/SiO₂-RIP/SiO₂ (C-R) soft magnetic composites (SMCs) by powder metallurgy techniques. Compared with RIP/SiO₂ powders, CIP/SiO₂ powders possess a higher SiO₂ content and more stable Si-O covalent network. The addition of CIP/SiO₂ to the C-R SMCs leads to a significantly increase in the resistivity due to the full electrical isolation of the RIP/SiO₂ particles. Transmission electron microscopy analysis confirms that a SiO₂ amorphous layer approximately 100–400 nm in thickness grows with a high packing density and adheres tightly to the iron grains, resulting in the effective constraint of electron transfer between the Si and O atoms. Annealed C-R SMCs containing 15–20 wt% CIP/SiO₂ have optimum properties with a high resistivity of 4980–6383 μΩ·m and a low core loss of 19.08–23.66 W/kg (50 mT, 100 kHz). The results of this present study provide a significant method to improve resistivity and reduce core loss.

[en] Amorphous-TiO₂/Cu₂Cl(OH)₃ (am-TiO₂/Cu₂Cl(OH)₃) composite photocatalyst was synthesized by a facile and novel spray pyrolysis method. The morphology, crystal structure, chemical composition, optical properties, and photocatalytic activity of the composite were characterized and investigated. It was noted that heating temperature played a fundamental role in determining the morphology of the composite photocatalyst as well as the crystallinity of TiO₂. Am-TiO₂ was firmly anchored on Cu₂Cl(OH)₃ with well dispersibility and served as the main sunlight absorber. Meanwhile, Cu₂Cl(OH)₃ acted as not only a carrier, but also a chemical catalyst of H₂O₂ to produce O₂ (electron acceptor). Compared with commercially available P25 specie, the composite with the addition of H₂O₂ exhibited higher photocatalytic performances for methyl orange (MO) degradation under simulated solar light irradiation. By considering the mechanism, the excellent performance was awarded to uniform dispersion of am-TiO₂ in the unique Cu₂Cl(OH)₃ and superfluous electron acceptor. (paper)

[en] Highlights: • CNT/Cu composites were fabricated by powder metallurgy routine. • CNT/Cu oxide powders were obtained by spraying pyrolysis method. • The interfacial shear stress (τ_y) was increased at elevated sintering temperature. • The simultaneous improvement of ductility and strength was achieved. Mono-dispersed and homogeneous carbon nanotube (CNT)/copper (Cu) composite powders were fabricated by spraying pyrolysis (SP) method successfully. Subsequently, CNT/Cu composites were obtained by spark plasma sintering (SPS) at sintering temperature ranged from 1023 to 1223 K (70–90% melting point of pure Cu). The mechanical properties, micro-morphology and interface microstructure of CNT/Cu composites were measured and characterized. The results reveal that Cu nano-particles (NPs) coated on the CNT surface are conducive to improving the wettability of CNT within matrix and reducing the interface energy between matrix and CNT, and finally stable interface structure is established. The traditional trade-off tendency between strength and ductility is balanced in the CNT/Cu composites, which are sintered at 1223 K. The ultimate tensile strength (UTS) shows 344 MPa and the elongation is 19.6%, which owing to the improvement of CNT–Cu interface bonding. At last, the role of interfacial bonding extent played in determining the load transfer efficiency of CNT is discussed.

[en] Unique architecture of reinforcement is explored for developing advanced metal matrix composites (MMCs). In the present study, Cu matrix composites reinforced by carbon nanofillers with reticulate structure were prepared by powder metallurgy. It was found that the high-efficiency strengthening effect was achieved by employing the hybrids of carbon nanotubes (CNTs) and reduced graphene oxide (RGO) as reinforcements in the Cu matrix. The tensile test results showed that the ultimate tensile strength of ~ 409 MPa was achieved in Cu matrix composite with 1.5 vol% of CNT-RGO hybrids, which is significantly higher than that reinforced with individual CNTs or RGO (~ 226 and ~ 259 MPa, respectively). Strengthening mechanisms including grain refinement, generation of dislocations by thermal mismatch, load transfer and Orowan looping system were discussed to understand the strengthening behaviors of CNT-RGO hybrids in MMCs. This work underscores the importance of interconnected architecture of reinforcements for improving mechanical properties of the composites and provides an insight to understand the strengthening behaviors of reticulate reinforcements in the composites.