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An effective synthesis method is reported for magnetic nickel ferrite (NiFe 2 O 4 ) nanoparticles involving planetary ball milling assisted solid-state reaction process. The precursors obtained by planetary ball milling the mixture of FeSO 4 · n 2 O, NiSO 4 ·, 2 O, NaOH and dispersant (NaCl) sufficiently at room temperature were calcined under different conditions to obtain pure NiFe 2 O 4 nanoparticles. The as-synthesized samples were characterized by thermogravimetry (TG) and differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) techniques. The results indicate that the calcination temperature for the precursor obtained by planetary ball milling can be lower to 750 °C to obtain impurity-free NiFe 2 O 4 nanoparticles with wide size distribution and double morphology, which is attributed to the higher reactivity of the precursor. The presence of defects and strains, derived from the continual ball collisions with high energy in the planetary ball milling process, is accounted primarily for the characteristics of magnetic properties. The solid-state reaction mechanism was proposed based on the analysis results of XRD, TEM and EDS. The planetary ball milling assisted solid-state reaction technique is considered to be a simple and effective synthesis method for NiFe 2 O 4 and other interesting nanomaterials. [ABSTRACT FROM AUTHOR]

Abstract: Short ZrO2 fibers (ZrO2(f)) reinforced NiFe2O4 ceramic composites were fabricated by cold pressing process. The phase composition, microstructure, mechanical properties and fiber/matrix interface of the composites were investigated by X-ray diffraction, scanning electron microscopy and mechanical testing machines. ZrO2(f) show good thermodynamic and chemical compatibility with NiFe2O4 ceramic matrix and effectively enhanced the mechanical properties. The toughening mechanisms are fiber bridging, interfacial debonding, fiber pullout, phase transformation and the matrix constraint effect. By incorporation of 3wt% fibers with the average length of 5∼6mm, the bending strength and fracture toughness of the composites reached 88.92MPa and 4.62MPam1/2, respectively, while the strength conservation ratio after thermal shock increased from 48.85% to 75.86%. The weak interface bonding built up between ZrO2(f) and NiFe2O4 facilitates the reinforcing effects of the fibers to operate. [Copyright &y& Elsevier]

Abstract: Samples with small amounts of V2O5 (0, 0.5, 1.0, 2.0, 2.5wt%, respectively) were prepared via ball-milling and two-step sintering from commercial powders (i.e., Fe2O3, NiO and V2O5). Micro-structural features, phase transformation, sintering behavior and magnetic properties of V2O5-doped NiFe2O4 composite ceramics have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermal dilatometer and vibrating sample magnetometer (VSM), respectively. Morphology and the detecting result of thermal dilatometer show that V2O5 can promote sintering process, the temperature for 2.5wt% V2O5-doped samples to reach the maximum shrinkage rate is 59°C lower than that of un-doped samples. With an increase of V2O5 from 0wt% to 2.5wt%, the apparent activation energy decreased from 813.919kJ/mol to 298.806kJ/mol. The early-stage synthesis process of un-doped ceramic samples and 2.5wt% V2O5-doped samples are mainly controlled by grain boundary diffusion and volume diffusion, respectively. Increasing V2O5 content, residual magnetization ratio (Mr/Ms) and coercivity (Hc) elevate, meanwhile, saturation magnetization decreases. [Copyright &y& Elsevier]

The compressive behavior of closed-cell copper-coated carbon fiber/aluminum composite foam with 1 and 5wt.% fibers was assessed under quasi-static and high-strain-rate loading conditions. The 5wt.% fiber/aluminum foam exhibits higher plastic collapse stress. The failure modes of fibers in the matrix were discussed. A strain-rate effect was demonstrated for fiber/aluminum foam. The strain-rate effect was more apparent at strain rates in the ∼ks−1 range and is attributed to the rate sensitivity of dense fiber/aluminum composite and to the foam structure. [ABSTRACT FROM AUTHOR]

Abstract: Aluminum foams containing 0.35, 1.0, 1.7vol.% copper-coated carbon fibers were fabricated by a melt route. The room temperature damping property of Al/C f foam was studied at different strain amplitude in two directions. The experimental results show that the critical strain amplitude decreases and the damping capacity of Al/C f foam increases with the copper-coated carbon fibers contents. It can be attributed to the interfacial micro-slip increasing with the C f contents and the microplasticity deformation arises from the micro-crack among the C f –Al interface. Moreover, the damping property in the transverse direction is higher than that in the longitudinal direction. The ratio of longitudinal loss factor to transverse loss factor is almost independent of the C f contents and strain amplitude. [Copyright &y& Elsevier]

Quasi-static compression tests for closed-cell aluminum foams manufactured by the melt route were conducted. Deformation mechanisms at the cell level are discussed. Cell shape and the inhomogeneity of the foam structure are considered the primary factors affecting the deformation modes. Four failure modes of closed-cell aluminum foam at the cell/membrane level reveal the mechanisms of energy absorption on the mesoscopic scale. Moreover, the friction between compacting cells helps to increase the energy absorption. [Copyright &y& Elsevier]

Abstract: Al–Si closed-cell aluminum foam sandwich panels (1240mm×1100mm) of different thicknesses and different densities were prepared by molten body transitional foaming process in Northeastern University. The experiments were carried out to investigate the sound insulation property of Al–Si closed-cell aluminum foam sandwich panels of different thicknesses and different densities under different frequencies (100–4000Hz). Results show that sound reduction index (R) is small under low frequencies, large under high frequencies; thickness affects the sound insulation property of material obviously: when the thicknesses of Al–Si closed-cell aluminum foam sandwich panels are 12, 22, and 32mm, the corresponding weighted sound reduction indices (R W ) are 26.3, 32.2, and 34.6dB, respectively, the rising trend tempered; the increase of density of Al–Si closed-cell aluminum foam can also increase the sound insulation property: when the densities of aluminum foam are 0.31, 0.51, and 0.67g/cm3, the corresponding weighted sound reduction indices (R W ) are 28.9, 34.3, and 34.6dB, the increasing value mitigating. [Copyright &y& Elsevier]

Abstract: The closed-cell Al–Si foams have been prepared by molten body transitional foaming process using TiH2 foaming agent. The cell shape anisotropy ratio of specimens with various relative densities was measured. The quasi-static compressive behavior of Al–Si foams in both longitudinal and transverse directions were investigated. The results show that Al–Si foam loaded in the transverse direction exhibits a lower stress drop ratio. The relationship between plastic collapse stress ratio and cell shape anisotropy is in accordance with Gibson and Ashby model. The plastic collapse stress and the energy absorption property of Al–Si foams increase following power law relationship with relative density. Moreover, Al–Si foams exhibit higher plastic collapse stress and the energy absorption property in the longitudinal direction than that in the transverse direction. [Copyright &y& Elsevier]

Abstract: Closed-cell aluminum alloy foams with 1.5, 3.0wt.% fly ash particles have been manufactured by molten body transitional foaming process. The room temperature damping properties of fly ash reinforced aluminum alloy foams were measured at different strain amplitude in two directions using the forced vibration mode. The results show that the damping properties of fly ash reinforced aluminum alloy foams increase with FA content. A critical strain amplitude εcrit was observed and εcrit decreases with increasing FA content. Moreover, the damping property in the transverse direction is higher than that in the longitudinal direction. The related mechanism has been discussed. [Copyright &y& Elsevier]

Abstract: Closed-cell aluminum foams were prepared by molten body transitional foaming process. The anisotropic damping property of closed-cell aluminum foam was measured in two directions using the forced vibration method. The measured results show that the loss factors of the TD specimens are higher than that of the LD specimens. The loss factors ratio βL /βT depends linearly on the shape-anisotropy ratio R. Anisotropic damping behavior is due to the variation of Young’s modulus resulting from anisotropic cell morphology. [Copyright &y& Elsevier]

Abstract The development of the "One Belt and One Road" strategy in China has resulted in the increased construction of high-speed railways in the country. Thus, the anti-seismic and shock absorption properties of a railway tunnel are very important when the high-speed railway crosses a seismic fault zone. Shock-absorbing materials currently used for tunnels have limited applications. Therefore, new shock-absorbing materials should be discovered. The closed-cell aluminum foam, which is a new shock-absorbing material, has not been applied for shock absorption in engineering. This study is the first to apply the closed-cell aluminum foam in designing a shock-absorbing layer for a high-speed railway tunnel. Closed-cell aluminum foam based on pure aluminum was used to design and manufacture the shock-absorbing layer for the tunnel lining. The feasibility of using closed-cell aluminum foam layer as damping design for tunnel lining was tested using a large-scale shaking table. Results showed that the closed-cell aluminum foam layer weakened the dynamic response of the tunnel lining. However, the shock absorption varied with the loading conditions. Highlights • A seismic simulation shaking table test was conducted to investigate the damping effect of the shock absorption layer. • The closed-cell aluminum foam layer reduced the acceleration response of the most measured points. • The effect of shock absorption varies with loading conditions. [ABSTRACT FROM AUTHOR]

Abstract: NiFe2O4 ceramics reinforced with ZrO2 particle was fabricated by conventional high-temperature solid state reaction. Effect of the sintering temperature (1100–1500°C) on the microstructure and mechanical properties of the ZrO2/NiFe2O4 composite ceramics was investigated in detail. The fracture surfaces of NiFe2O4 composite ceramics were observed by scanning electron microscopy (SEM). Elemental analysis of micro-structural phases was performed using energy dispersive spectroscopy (EDS), attached with SEM. Flexural strength by three-point bending techniques and fracture toughness were measured. It was indicated that when the sintering temperature was above 1400°C, phase transformation causing crack can directly lead to the strength degradation. The grain size of ZrO2 increases with increasing of the sintering temperature. The samples sintering at 1400°C had the highest flexural strength of 192±10MPa and fracture toughness of 3.38±0.05MPam1/2 due to densification, phase transformation. [Copyright &y& Elsevier]

Abstract: NiFe2O4 composite ceramics reinforced with carbon fibers (Cf), nickel-coated carbon fibers (NiCf) and ZrO2 fibers (ZrO2f) were fabricated by the conventional high-temperature solid state reaction at 1300°C for 6hs. The effects of the three kinds of fibers on microstructure and mechanical properties of NiFe2O4 composite ceramics were investigated. The fracture surfaces of NiFe2O4 composite ceramics were observed by scanning electron microscopy (SEM). Elemental analysis of micro-structural phases was performed using energy dispersive spectroscopy (EDS), attached with SEM. Flexural strength by three-point bending techniques and fracture toughness were measured. It was found that leaving holes after reactions between the carbon fiber and matrix led to decreased mechanical properties. The ZrO2f-doped composite had an improved fracture toughness of 3.05±0.1MPam1/2 compared to NiFe2O4 composite ceramics having 1.91±0.2MPam1/2 due to fiber debonding, fiber pull-out and fiber bridging as well as microcracking toughening. The results presented here show that ZrO2f can serve as a potential toughening agent for NiFe2O4 composite ceramics. [Copyright &y& Elsevier]

Abstract: Nickel ferrite (NiFe2O4) nanoparticles were synthesized via solid-state reaction. The precursors obtained by grinding the mixture of FeSO4·7H2O, NiSO4·6H2O, NaOH and dispersant (NaCl) sufficiently at room temperature were calcined under various synthetic conditions in order to get NiFe2O4 spinel nanoparticles. The effects of the synthetic parameters, namely preparation technique, dispersant content, calcination temperature and heat preservation time, on particle size and morphology have been investigated in detail to find the optimized parameters. X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) were employed to characterize the precursors and as-synthesized particles. The results indicate that structural morphology varies between needle and sphere with changing preparation technique. Proper content of NaCl as a dispersant is beneficial to obtain uniform particles with a narrow size distribution. The particle morphology changes gradually from sphere to polygon with the increase in calcination temperature. Grain growth is enhanced by prolonging heat preservation time. Room temperature magnetization results reveal a ferromagnetic behavior of the as-synthesized NiFe2O4 nanoparticles. The saturation magnetization is enhanced with the increase in grain size for less surface effect. The coercivity is decreased for larger grain size because of magnetization reversal. The solid-state reaction technique is considered to be a convenient, inexpensive and effective preparation method of NiFe2O4 in high yield. [Copyright &y& Elsevier]

Abstract: Two-step sintering (TSS) has been employed in the current study to suppress the accelerated grain growth of NiFe2O4 nanopowder compacts in the final sintering stage. Experiments are conducted to determine the appropriate temperatures for each step. The temperature range from 1200°C to 1300°C is effective for the first-step sintering (T 1) due to its highest densification rate. The second-step sintering temperature (T 2) should be within the kinetic window, where grain boundary diffusion is maintained but grain boundary migration is suppressed. The grain sizes of high density (≥98% theoretical density) NiFe2O4 compacts produced by TSS are smaller than 700nm, while that of those formed by CS are over 2.5μm. The evidence indicates that the saturation magnetization of nearly full NiFe2O4 ceramics is independent of grain size and likewise high, with the corresponding values of approximately 54emu/g. The Vickers hardness and fracture toughness both increase with the decrease of grain size and porosity. [Copyright &y& Elsevier]

Abstract: The impact of MnO2 as an additive on the properties of NiFe2O4-based cermets prepared by the two-steps sintering method has been investigated. The new material was characterized in terms of the crystal structure, microstructure, linear shrinkage, relative density and porosity. Moreover, the bending strength of NiFe2O4-based cermets was measured. Differential scanning calorimetry (DSC) and X-ray diffraction analysis (XRD) shows that the addition of MnO2 has no obvious influence on the crystal structure of the cermets. Scanning electron microscope (SEM) studies reveals that the grain sizes of cermets decreases slightly with doped MnO2. The results show that the linear shrinkage, relative density and bending strength increase at first and then decrease slightly. A high-density (99.56%) and high-strength (84.28MPa) NiFe2O4-based cermets has been obtained by adding 0.50wt% MnO2 into the matrix. [Copyright &y& Elsevier]

Mg-1.5Y alloy shows significantly enhanced room temperature impact toughness compared to pure Mg. Enhanced strength and ductility of Mg-1.5Y alloy are the principal contributors to the increased impact toughness. Under high deformation rate, pure Mg mainly deforms by basal slip and tensile twinning. In contrast, the fracture surface and profile analysis for Mg-1.5Y alloy indicated a blunt crack-tip, where the growth of tensile twinning is suppress and the deformation was dominated mainly by the dislocation slip. [ABSTRACT FROM AUTHOR]

Copper-coated carbon fibers were added to aluminum foam to stabilize metal films. Observation of the cell structure and the distribution of the fibers in the metal films shows that the stabilization is based not just on the presence of fibers but on both fibers and particles. The fibers act as mechanical barriers within the metal films, inducing a stronger stabilizing and disjoining pressure than particles. On the basis of these results, three stabilization models for aluminum/fibers are proposed. [ABSTRACT FROM AUTHOR]

Abstract: The wetting behavior of Al–Ge alloys on TiH2 substrates was investigated by an improved sessile drop method under high vacuum and in a temperature range of 773–818K. Results indicate that the equilibrium contact angles of Al–Ge/TiH2 increase linearly with temperature according to the following formula: θ =0.2882T −85.04, and decrease linearly as the Ge content increases from 25.2% to 36.2% according to the formula: θ =214−200Ge (wt.%). The worst wetting behavior was obtained for a pure Al/TiH2 system at its foaming temperature (973K). TiH2 particles were prone to aggregate and were thus difficult to disperse. This could be one of the reasons for closed-cell aluminum foam products having non-uniform pores. [Copyright &y& Elsevier]