查看更多>>摘要：The paper aims to develop an excellent soft magnetic glassy alloy with a series of (Fe_(1-x)Ni_x)_(79)P_5B_(12)Si_3C_1 (x = 0, 0.2, 0.4, 0.5, 0.6). The annealing at (T_g-20) K for the 0.4Ni-0.5Ni alloys causes an extremely low coercivity below 1 A/m with very high effective permeability above 5-10~4 at 1 kHz in the maintenance of high saturation magnetic flux density of ≌ 1.2 T. Good effective permeability characteristics were recognized as is evidenced from high μ_e values above 6000 at 1 MHz. The core losses at induction of 100 mTare as low as 43 W/kg for 100 kHz and 1150 W/kg at 1 MHz for the annealed 0.6Ni alloy. Excellent soft magnetic properties are presumably due to the achievement of the fully relaxed glassy state which can be obtained only for the glass-type alloys with SCL region. This complex of magnetic properties is promising for future use as high-frequency type soft magnetic materials.
查看更多>>摘要：Solid electrolytes are critical in the development of solid-state batteries, which have advantages in terms of safety and stability. Lithium Lanthanum Titanate (Li_(3x)La_(2/3-x)TiO_3) is regarded as one of the most favored candidate solid electrolytes. However, the doping dependences of ionic conductivity and microstructure are still poorly understood. In this work, nominal Li_(0.5-x)La_(0.5)(Ti_(1-x)Nb_x)O_3 (LLTN, x = 0, 0.01, 0.03, 0.05 and 0.07, labelled as LLTNO, LLTN1, LLTN3, LLTN5, LLTN7, respectively) ceramics are synthesized to investigate the above doping effects. The bulk ionic conductivity of LLTN5 sample reaches as high as 0.71 × 10~(-3) S/cm, which is approximately two times higher than the bulk ionic conductivity of the undoped sample at room temperature. The XRD refinement and Raman results indicate that niobium doping increases the lattice cell along the c-axis and stretch the Ti-0 bond, which extends the tunnels for Li-ions diffusion. This work suggests that it is effective to enlarge the lattice cell for the improvement of the Li-ion conductivity in LLTO.
查看更多>>摘要：The crystal structure, pressure composition isotherms, and electrochemical properties of Zr_(0.2)Ti_(0.2)Ni_(0.2+x)Cr_(0.2)Mn_(0.2) (x = 0, 0.025, 0.05, 0.075, and 0.1) high-entropy alloys (HEAs) were investigated. The crystal structures of all the HEAs consisted of two phases: a primary phase with a C14-type (Zr_(0.5)Ti_(0.5))Mn_2 hexagonal structure and a secondary phase with a B2-type Ti_(0.6)Zr_(0.4)Ni cubic structure. Rietveld analysis revealed that the secondary phase increased with an increase in the x value. The hydrogen storage capacity of the HEAs was lower than that of the alloy with x = 0 because of an increase in the B2-type Ti_(0.6)Zr_(0.4)Ni phase, whereas the change in enthalpy of hydride formation (|ΔH|) decreased with increasing x, leading to the instability of hydrides. The alkaline treatment was performed by immersing HEA powders or electrode in a 6 M KOH aqueous solution at 378 K for 2 h. The Zr_(0.2)Ti_(0.2)Ni_(0.2)Cr_(0.2)Mn_(0.2) alloy surface changed to a porous and rough structure, and a ZrO_2 passive thin layer on their surface, which is replaced by NiO or Ni(OH)_2 after the alkaline treatment. The charge-discharge tests conducted using the HEA negative electrodes for Ni-MH batteries depict that the discharge capacity increased with an increase in x, and the highest discharge capacity was 368 mAh g~(-1) at x = 0.075 after the alkaline treatment. On increasing the x value, the high-rate dischargeability and cycle performance were also enhanced.
查看更多>>摘要：The synergistic effect of Zr addition and grain refinement on the corrosion resistance and pitting corrosion behavior of single α-phase Ti-Zr-based alloys was evaluated. The corrosion mechanisms of as-cast and hot-rolled Ti-xZr-4Al-0.005B alloys (x = 0,10, 20, 30, 40 wt%) in 5 M aqueous hydrochloric acid solution are investigated by analyzing their electrochemical and immersion corrosion behavior using scanning electron microscopy, electrochemical analyses, and X-ray photoelectron spectroscopy. Both Zr alloying and grain refinement improve the corrosion resistance; while grain refinement improves the stability of the passivation film, Zr addition increases the pitting sensitivity. Zr alloying and grain refinement greatly affects the pitting corrosion behavior in the alloy. In Ti or Ti-Zr alloys with low Zr content, grain refinement inhibits the appearance of corrosion pits inside the grains. For Ti-Zr alloys with higher Zr content, grain refinement induces small corrosion pits in the alloy. Grain refinement increases the frequency of corrosion pits in the Ti-Zr alloys with higher Zr content but inhibits the growth of the pits by improving the corrosion resistance and stability of the passivation film through the formation of more high-valence oxides and a thicker passivation film.
查看更多>>摘要：Effect of Mn content on the microstructure and corrosion resistance of Al-Cu-Mg-Mn alloys was examined by optical microscope (OM), scanning electron microscope (SEM), tensile tests, pitting corrosion and electrochemical tests. It is shown that increase of Mn content can accelerate the aging process of the Al-Cu-Mg-Mn alloys, which is beneficial to shorten heat treatment time. Polarization curves indicate that the corrosion current density and corrosion rate of Al-4Cu-2Mg-1.2Mn alloy are the lowest compared with Al-4Cu-2Mg-0.6Mn and Al-4Cu-2Mg-0.9Mn alloys for both the as-cast and heat-treated conditions. Electrochemical impedance spectroscopy (EIS) tests also demonstrate that Al-4Cu-2Mg-1.2Mn alloy displays the highest resistance. The maximum pitting corrosion depth of the as-aged Al-4Cu-2Mg-1.2Mn and Al-4Cu-2Mg-0.6Mn alloys is about 65 um and 110 um, respectively. Therefore, Mn addition can improve the mechanical properties and corrosion resistance of the Al-Cu-Mg alloys.
查看更多>>摘要：The CrCoNiSi_xAl_x(x = 0.1, 0.2) medium entropy alloys (MEAs) were designed to achieve significant improvement in strength and strain hardening via the minor addition of Si and Al elements to the CrCoNi MEA. The B2 + σ precipitation structure was formed on the CrCoNiSi_(0.2)Al_(0.2) MEA. Compared to CrCoNi MEA, the yield and ultimate tensile strengths of the CrCoNiSi_(0.2)Al_(0.2) MEA enhanced from 380 MPa to 850 MPa and 790-1287 MPa, respectively, while the uniform elongation was 23±5% that outperformed various advanced steels and Al-added MEAs/HEAs. The Orowan+shearing precipitation hardening mechanisms together with the deformation twins in a face-centered cubic (FCC) matrix were identified to improve the strength and strain hardening capacity. These findings provide guidance for the development of precipitation-hardened MEAs/HEAs with strength-ductility synergy.
查看更多>>摘要：Because of their multiple chemical valence states, multi-element transition metal oxides can undergo reversible redox reactions between the different valence states during charging and discharging. However, the low electrical conductivity of transition metal oxides limits the rate of electron transfer. The combination of transition metal oxides with three-dimensional carbon substrate is a promising but extremely challenging strategy to prepare high specific capacitance, stable and environmentally friendly supercapacitor electrode materials. Here we report a facile one-step vapor deposition synthesis of network-like FeNb_2O_6 nanostructures directly growing on flexible carbon cloth (CC). The as-prepared FeNb_2O_6/CC composite has good electrical conductivity, and the network-like structure also makes it have large specific surface area. Resultantly, the composite exhibits an high specific capacity of 365.9 mAh g~(-1) at a current density of 2.5 A g~(-1). And at the current density of 25 A g~(-1) a specific capacity of 75.9 mAh g~(-1) can still be maintained.
查看更多>>摘要：For the successful commercialization of Bi_2Te_3-based thermoelectric generator (TEG) devices, not only highly efficient TE materials, but also reliable bonding materials with high thermal stability are essential. In this study, we investigated the application of Cu nanoparticle paste (CNP) bonding for increasing the operating temperature of Bi_2Te_3-based TEG devices. Six-chip TEG devices were fabricated by joining surface-metalized Bi_2Te_3-based TE chips and Cu electrodes by CNP bonding. The optimal bonding was achieved when spark plasma sintering was carried out at 310-320 °C and 15 MPa. The 6-chip Bi_2Te_3-based TEG devices showed a maximum output power of 50-60 mW at the hot-side temperature of 400 °C (AT= 380 °C) and maintained almost the same output power after five thermal cycles. The scanning electron microscopy images of the thermally cycled electrodes further confirmed the robustness of the Cu nanoparticle joints. This work provides an effective method for joining TE chips and Cu electrodes for high-temperature TEG devices.
查看更多>>摘要：The Na-doped diopside (CaMg_(1-x)Na_(2x)Si_2O_6, x = 0-0.18) microwave dielectric ceramics were fabricated via solid-state reaction method. Three phases were identified through the XRD data that was refined with the Rietveld method to obtain structural information. The role of Na~+ substitution to promote the densification process could be corroborated by the SEM images and relative density. The P-V-L bond theory was used to explore the chemical bond characteristics and structure-performance relationships. Through discussion, the dielectric constant was determined by relative density rather than the bond ionicity. The Q× f value was dominated by the lattice energy, lattice vibration and was also related to the relative density and grain size. And the linear thermal expansion coefficient was closely correlated with the τf value. Excellent microwave dielectric properties, (εr = 7.573, Q× f = 35049 GHz, tan δ = 4.015 ×10~(-4),εr = -68.71 ppm/°C) and (εr = 7.646, Q× f = 37844 GHz, tan δ = 3.706 ×10~(-4), τf= -54.2 ppm/C) were achieved for the CaMg_(0.97)Na_(0.06)Si_2O_6 ceramics sintered at 1150 °C/3 h and 1200 °C/3 h, respectively.
查看更多>>摘要：The valence electron structures, thermal properties, hardness and magnetic moments of single-phase high entropy alloys with the face-centered cubic structure have been first investigated with the empirical electron theory of solids and molecules. The theoretical bond lengths agree with the experimental ones well. The calculated melting points of CrFeCoNi, CrMnFeCoNi and CrFeCoNiCu alloys are consistent with their differential thermal analysis (DTA) measured ones. The calculated magnetic moments of ferromagnetic FeCoNi and FeCoNiX_(0.25) (X=A1 or Si) alloys agree with the observed ones well. The physical properties of these alloys are strongly associated with their valence electron structures. It is suggested that the melting point, cohesive energy, hardness and magnetic moments of the face-centered cubic high entropy alloys are mainly modulated by bonding factor/, covalent electrons per atom n_c/atom, covalence electron pair n_A and 3d magnetic electron, respectively.
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Elsevier