Core-shell structured MoS2@S spherical cathode with improved electrochemical performance for lithium-sulfur batteries

To suppress shuttling effect and improve electrochemical performance of the sulfur cathode for lithium-sulfur batteries, core-shell structured MoS₂@S spherical cathode has been synthesized through a chemical route using MnCO₃ as template. The MoS₂ shells consist of MoS₂ nanosheets. For comparison, MoS₂/S cathode has also been synthesized through melting and diffusion of sulfur to commercial MoS₂ powders. The electrochemical performance of the MoS₂@S and MoS₂/S cathodes have been evaluated using cyclic voltammetry, discharge/charge cycling, electrochemical impedance spectroscopy coupled with impedance fitting. The electrochemical performance of the MoS₂@S spherical cathode has been much improved compared with that of MoS₂/S. The capacity of the MoS₂@S spheres can reach 1185.7 mA h g^?1 at 0.2 C and 955.1 mA h g^?1 at 1 C with initial-cycle coulombic efficiency of 90%. The capacity fading of each cycle is 0.1% during 200 lithiation/delithiation cycles. The MoS₂@S spherical cathode with high cyclic capacity and stability is promising cathode candidate for lithium-sulfur batteries.     

Influence of temperature and thickness on the off-axis behaviour of short glass fibre reinforced polyamide 6.6 – Quasi-static loading

This paper investigates the anisotropic behaviour of mechanical properties of a short glass fibre reinforced polyamide 6.6 (PA66-GF35) under quasi-static loading. For this purpose tensile tests were carried out on dog-bone specimens, machined out from injection moulded plates 80 × 80 mm, of three different thicknesses t (1–3 mm) at eight different orientation angles. The tests were performed at room temperature as well as at 130 °C. Material elastic constants were estimated from fitting experimental tensile moduli according to the theory of elasticity for orthotropic materials. A fit on geometrical tensile strengths with the Tsai–Hill failure criterion provided instead the material strength parameters. Both specimen thickness and temperature appear to have a strong influence on mechanical properties and degree of anisotropy.     

Effects of Zr/Ce molar ratio and water content on thermal stability and structure of ZrO2–CeO2 mixed oxides prepared via sol–gel process

ZrO₂–CeO₂ mixed oxides were synthesized via sol–gel process. Thermal stability, structure and morphology of samples were investigated by powder X-ray diffraction, FT-Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. In this approach, the solvent composition and Zr/Ce molar ratio have great influences on the structure and morphology of final products. With decreasing water content in the mixed solvent, specific surface area of powders increased and the single tetragonal phase was obtained. Only when the volume ratio of water and ethanol and the Zr/Ce molar ratio were 1:1, tetragonal t″-Zr_0.5Ce_0.5O₂ could be stabilized in powders at temperature as high as 1000 °C. Meanwhile, tetragonal (t′) and (t″) phases coexisted in Zr_0.5Ce_0.5O₂ solid solution without peak splitting after calcination at 1100 °C, further transforming into cubic and tetragonal (t′) phases at 1200 °C. The effective activation energy for Zr_0.5Ce_0.5O₂ nanocrystallite growth during annealing is about 5.24 ± 0.15 kJ/mol.     

Ferromagnetic element microalloying and clustering effects in high Bs Fe-based amorphous alloys

Fe_(83)(Co_x,Ni_y)(B_(11)Si_2P_3C_1)_(1-x,y/17)(x,y=1–3)amorphous alloys with high saturation magnetic flux density(B_s)and excellent soft-magnetic properties were developed and then the microalloying and clustering effects were explored.The microalloying of Co and Ni improves the B_sfrom 1.65 T to 1.67–1.72 T and 1.66–1.68 T,respectively.The Ni-doped alloys exhibit better soft-magnetic properties,containing a low coercivity(H_c) of about 5.0 A/m and a high Effective permeability(μ_e)of(8–10)×10~3,whereas the microalloying of Co leads to a deteriorative H_c of 5.0–13.0 A/m and a μ_eof(5–8)×10~3.Moreover,microalloying of Ni can increase the ductile-brittle transition(DBT)temperature of the ribbons,while a totally opposite effect is found in the Co-doped alloys.The formation of dense α-Fe(Co,Ni)clusters during annealing process is used to explain the distinct effects of Co and Ni microalloying on the magnetic properties and bending toughness.     

Synthesis of dispersed PrBaCo0.9Cu0.1O5+δ cathode nanopowders with layered perovskite structure for intermediate temperature solid oxide fuel cells

PrBaCo_1.9Cu_0.1O_5+δ (PBCCO) nanopowders were synthesized by an EDTA-citrate complexing process using water and ethanol as solvents, and their structures and electrochemical properties were characterized. PBCCO precursor gels were highly oxidized at 450 °C, using either water (PBCCO-W) or ethanol (PBCCO-E) as the solvent. PBCCO powders calcined at 450 °C had a second phase, while those calcined at 850 °C for 4 h were obtained as single phase PBCCO with a layered perovskite structure in the P4mm space group. PBCCO-E primary particles were approximately 5–10 nm in size and were well-dispersed compared with those of the PBCCO-W powder. We hypothesized that the enhanced dispersibility of the PBCCO-E powder was caused by a decrease in bridging hydrogen bonds on the chelate surface, which prevents chelate agglomeration in sol state. It causes the larger specific surface area of PBCCO-E powders and thus a lower polarization resistance (R_p) than that of PBCCO-W powders at the measured temperature. The R_p value of PBCCO-E powder was 0.041 Ω cm² at 750 °C, which is about 1.5 times lower than that of PBCCO-W at the same temperature.     

Exploration of structural,thermal, vibrational and spectroscopic properties of new noncentrosymmetric double borate Rb3NdB6O12

New noncentrosymmetric rare earth borate Rb₃NdB₆O₁₂ is found in the ternary system Rb₂O–Nd₂O₃–B₂O₃. The Rb₃NdB₆O₁₂ powder was fabricated by solid state synthesis at 1050 K for 72 h and the crystal structure was obtained by the Rietveld method. Rb₃NdB₆O₁₂ crystallized in space group R32 with unit cell parameters a = 13.5236(4), c = 31.162(1) Å, Z = 3. From DSC measurements, the reversible phase transition (I type) in Rb₃NdB₆O₁₂ is observed at 852–936 K. The 200 μm thick tablet is transparent over the spectral range of 0.3–6.5 μm and the band gap is found as E_g ～ 6.29 eV. Nonlinear optical response of Rb₃NdB₆O₁₂ tested via SHG is estimated to be higher than that of K₃YB₆O₁₂. Blue shift of Nd luminescent lines is found in comparison with other borates. The vibrational parameters of Rb₃NdB₆O₁₂ are evaluated by experimental methods.     

Influence of temperature and thickness on the off-axis behaviour of short glass fibre reinforced polyamide 6.6 – cyclic loading

This paper investigates the anisotropic properties of short glass fibre reinforced polyamide 6.6 (PA66-GF35) under tension–tension and tension–compression cyclic loading. Tensile fatigue tests were carried out on dog-bone specimens, machined out from injection-moulded plates 80 × 80 mm, of three different thicknesses t (1 and 3 mm) at three different nominal fibre orientation angles θ (0°, 30° and 90°). The tests were carried out at RT as well as at 130 °C.The Tsai–Hill failure criterion, modified to account for cyclic loading, is applied to the fatigue data for estimating the fatigue strength parameters of the material under investigation. Results are compared to the strength parameters obtained under quasi-static loading in a previous part of this work [De Monte M, Moosbrugger E, Quaresimin M. Influence of temperature and thickness on the off-axis behaviour of short glass fibre reinforced polyamide 6.6 – quasi-static loading. Composites: Part A, 2010;41(10):1368–79]. The experimental results highlight how specimen thickness remarkably affects mechanical properties: the thinner the specimen the higher will be the degree of anisotropy. Also temperature strongly reduces the fatigue strength under cyclic loading. The Tsai–Hill criterion allows for an adequate fitting of experimental data at the investigated temperatures and load ratios.     

Electrochemical characterization of LaBaCuCoO5+δ–Sm0.2Ce0.8O1.9 composite cathode for intermediate-temperature solid oxide fuel cells

In order to improve the electrochemical performance of the LaBaCuCoO_5+δ (LBCC) electrode, LaBaCuCoO_5+δ–Ce_0.8Sm_0.2O_1.9 (LBCC–SDC) are prepared and characterized for potential application as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on an SDC electrolyte. Electrical conductivity, thermal expansion and electrochemical properties are investigated by four probing DC technique, dilatometry, AC impedance and polarization techniques, respectively. It is found that the thermal expansion coefficient (TEC) and electrical conductivity decrease with the increase of SDC content in LBCC–SDC composites. AC impedance spectra based on SDC electrolyte measured at intermediate temperatures show that the addition of SDC to LBCC improves the electrochemical performance of a LBCC cathode, and that a LBCC–SDC20 cathode exhibits superior electrochemical performance in the LBCC–SDCx composite cathodes. Moreover, even when the content of SDC is up to 40 wt%, the area specific resistance of the LBCC–SDC40 composite cathode on SDC electrolyte is lower than the corresponding interfacial resistance for pure LBCC at 650–800 °C. The power density of the Ni–SDC/SDC/LBCC–SDC20 cell is 615 mW cm^?2 at 800 °C. These results indicate that LBCC–SDCx is a potential cathode material for application in IT-SOFCs.     

Entropy generation in a heat exchanger working with a biological nanofluid considering heterogeneous particle distribution

Entropy generation rates considering particle migration are evaluated for a biologically produced nanofluid flow in a mini double-pipe heat exchanger. The nanofluid is used in tube side and hot water flows in annulus side. Silver nanoparticles synthesized through plant extract method from green tea leaves are utilized. Particle migration causes non-uniform concentration distribution, and non-uniformity intensifies by increase in Reynolds number and concentration. The results indicate that at high concentrations and Reynolds numbers, particle migration can have a great effect on entropy generation rates. For water inlet temperature of 308 K, the contribution of friction in nanofluid entropy generation is much more than that of heat transfer. However, as the water inlet temperature increases to 360 K, the heat transfer contribution increases such that at low Reynolds numbers, the thermal contribution exceeds the frictional one. For total heat exchanger, Bejan number is smaller than 0.2 at water inlet temperature of 308 K, while Bejan number has a large value at water inlet temperature of 360 K. Furthermore, entropy generation at the wall has an insignificant contribution, such that for Re = 1000 and φ_m = 1%, the total entropy generation rates for the nanofluid, wall, and water are 0.098810, 0.000133, and 0.041851 W/K, respectively.     

Study on dynamic strain aging phenomenon of 3004 aluminum alloy

3004 Aluminum alloy has been subjected to tension test at a range of strain rates (5.56 × 10⁻⁵ to 5.56 × 10⁻³ s⁻¹) and temperatures (233–573 K) to investigate the effect of temperature and strain rate on its mechanical properties. The serrated flow phenomenon is associated with dynamic strain aging (DSA) and yield a negative strain rate dependence of the flow stress. In the serrated yielding temperature region a critical transition temperature, T_t, was found. The critical plastic strain for the onset of serrations has a negative or positive temperature coefficient within the temperature region lower or higher than T_t. According to the activation energy, it is believed that the process at the temperature region lower than T_t is controlled by the interaction between Mg solute atom atmosphere and the moving dislocation. In the positive coefficient region, however, the aggregation of Mg atoms and precipitation of second phase decrease the effective amount of Mg atoms in solid solution and lead to the appearance of a positive temperature coefficient of the critical plastic strain for the onset of serrations.     

Porous structure to improve microwave absorption properties of lamellar ZnO

The novel porous ZnO nanoflakes were fabricated by a facile two-step method containing preparation of precursor ZnCO₃ and subsequently calcination of ZnCO₃. The as-prepared products were analyzed by X-ray diffraction, scanning electron microscopy, and thermalgravimetric analysis. The results reveal that the porous ZnO nanoflakes were in the diameter and thickness of several to tens micrometers and 100–500 nm, respectively. The microwave absorption properties of porous ZnO nanoflakes were investigated by the network analyzer, which exhibit the minimal reflection loss of ?34.5 dB at 10.7 GHz with only thickness of 1.5 mm. The effective absorption (below ?10 dB) bandwidth can be tuned between 7.0 GHz and 17.1 GHz by tuning absorber thickness of 1.0–2.2 mm. Thus, the porous lamellar ZnO could be used as a promising absorbing material with the features of high efficiency absorption, wide-band and light weight.     

Low temperature synthesis of Co3O4 and (Co1−xMnx)3O4 spinels nanoparticles

The (Co_1?xMn_x)₃O₄ solid solution have been synthesized in water at 60 °C by soda addition to a cationic solution. XRD patterns show that spinel oxide has been obtained except for pure cobalt composition which exhibits also the presence of hydroxide and oxy-hydroxide. Therefore, to reach this composition, a different synthesis route has been developed: the cationic solution is added to the soda and for the first time Co₃O₄ nanoparticles have been synthesized by a direct precipitation in aqueous solution at low temperature. For each composition, the particles are well crystallized and exhibit a size close to 50 nm. Each particle is composed by several crystallographic domains of about 10 nm. The cubic to tetragonal transition reported in the literature for x = 0.46 is observed in between x = 0.33 and x = 0.50. Raman spectra show that substitution of Co by Mn, in the cubic phase, introduces a random high disorder. In the tetragonal phase, occupation of the octahedral site remains a random occupation, while the tetrahedral site seems to be preferentially occupied by Co ions. All these results show that the precipitation is a simple, fast and safe process to synthesize pure phase of (Co_1?xMn_x)₃O₄ spinel solid solution in aqueous media at low temperature.     

Electrochemical performance of (La,Sr)(Co,Fe)O3−δ–(Ce,Sm)O2−θ–CuO composite cathodes for intermediate temperature solid oxide fuel cells

La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ–CuO composite cathodes were studied for the potential application in intermediate temperature solid oxide fuel cells. Ce_0.8Sm_0.2O_2?θ electrolyte with porous Ce_0.8Sm_0.2O_2?θ interlayer was successfully prepared by one-step sintering process. The effect of interlayer between cathode and electrolyte and CuO on the electrochemical performance of the composite cathodes was investigated by AC impedance spectroscopy. The application of interlayer decreased the area specific resistance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ cathode. The addition of CuO to La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ reduced the phase formation temperature of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ by 150 °C and the addition of CuO to La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ cathode reduced the optimal calcination temperature of the cathode to 800 °C. The composite cathode with 2 mol% CuO calcined at 800 °C exhibited the lowest area specific resistance of 0.05 Ω cm² at 700 °C in air, which was reduced by 67% compared with that of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ–Ce_0.8Sm_0.2O_2?θ cathode. The studies of the corresponding single cell performance, thermal expansion and thermal cycling behaviors further indicated that the composite cathode with 2 mol% CuO could be a promising cathode material.     

Effect of Ni on reactive diffusion between Au and Sn at solid-state temperatures

Influence of Ni on the kinetics of the reactive diffusion between Au and Sn was experimentally studied at solid-state temperatures. Binary Sn–Ni alloys with Ni concentrations of 1, 3 and 5 mass% were used to prepare sandwich (Sn–Ni)/Au/(Sn–Ni) diffusion couples by a diffusion bonding technique. The diffusion couples were isothermally annealed at temperatures of T = 433, 453 and 473 K for various times in an oil bath with silicone oil. After annealing, AuNiSn₈, AuSn₄, AuSn₂ and AuSn compound layers were observed to form at the (Sn–Ni)/Au interface in the diffusion couple. The total thickness l of the compound layers monotonically increases with increasing annealing time t according to the equation l = k(t/t₀)ⁿ, where t₀ is unit time, 1 s. The exponent takes values between n = 0.29 and 0.37 under the present annealing conditions. Such values of n < 0.5 indicate that the grain boundary diffusion contributes to the rate-controlling process and the grain growth occurs at certain rates. The higher the Ni concentration of the Sn–Ni alloy is, the faster the overall growth of the compound layers occurs. This means that Ni is an accelerator for the reactive diffusion between Au and Sn at solid-state temperatures. The acceleration effect of Ni becomes more remarkable at higher annealing temperatures. Such influence of Ni on the kinetics is mainly attributed to the dependencies of the growth rate of the AuNiSn₈ layer on the composition of the Sn–Ni alloy and the annealing temperature.     

Oxygen adsorption and desorption characteristics of LSCF5582 membranes for oxygen separation applications

This study examines the oxygen adsorption and desorption characteristics of La_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ (LSCF5582) membranes prepared at sintering temperatures of 1200–1300 °C, with the aim of gaining an insight into their performance in the surface reaction limited regime for oxygen separation applications. The findings of this work are then compared with our experimental data on Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ (BSCF5582) membranes. It is demonstrated that the adsorption rate constants of both membranes are two orders of magnitude greater than their respective oxygen desorption rate constants as the oxygen adsorption occurs in less than 24 s whilst the oxygen desorption takes approximately one hour to reach equilibrium. The activation energy for oxygen adsorption of LSCF5582 reduced to a quarter of its value with increasing the sintering temperature from 1200 °C to 1300 °C. This is attributed to the oxygen exchange occurring more rapidly along the grain boundaries resulting in a lower activation energy. The LSCF5582 grain sintered at 1200 °C is the optimum selection for oxygen separation applications at an operating temperature of 850 °C and oxygen partial pressure of 0.21 bar.     

Improved mechanical properties of biomedical ZrNbHf alloy induced by oxidation treatment

The effects of air oxidation upon the kinetics and mechanical properties of ZrNbHf alloy were studied in the temperature range of 550–650 °C. The oxidation kinetics derived from the weight gain measurements showed a parabolic rate law and an oxidation breakdown behavior transforming from a parabolic to linear rate law observed at 650 °C. The microstructure analysis indicates that the oxide layer consists of both monoclinic and tetragonal ZrO₂ and undergoes a transformation between t-ZrO₂ and m-ZrO₂ with increasing oxidation time, which is an important reason for kinetics transition. The mechanical property examination presents that the oxidation treatment brings about a nearly fourfold increase in the surface hardness with a protective thickness limit of 4–6 μm. Most interestingly, the hardened surface oxide layer brings about a nearly 70 MPa increase in yield strength and a slight decrease in tensile elongation under true stress–strain conditions. The present study reports on an optimized oxidation process designed to obtain a protective and hardened ZrO₂ film for biomedical ZrNbHf alloy with higher performance.     

Synergistic anticancer effect of green synthesized nickel nanoparticles and quercetin extracted from Ocimum sanctum leaf extract

Leaf extract of medicinally important plant Ocimum sanctum(O. sanctum) has been used for the synthesis of nickel nanoparticles(Ni Gs) and extraction of quercetin(Qu). Qu has been conjugated with Ni Gs for enhanced anticancer effect on human breast cancer MCF–7 cells. Extracted Qu was conjugated with polyethylene glycol(PEG) coated Ni Gs(Qu–PEG–Ni Gs) which was used as carriers for breast cancer treatment. Anticancer activity of Qu–PEG–Ni Gs was evaluated by assessing cell viability, reactive oxygen species(ROS) production, caspase activity, mitochondrial membrane potential(MMP) and changes in nuclear morphology(staining methods). 0.85 mg of quercetin was extracted from 1 g of leaves with retention time(R_t) of 2.914 min. Loading and encapsulation efficiency of quercetin onto PEG–Ni Gs was 15.04% and 82% respectively and Qu–PEG–Ni Gs has shown a sustained release of Qu of about 84% after 48 h. Qu and Qu–PEG–Ni Gs showed dose dependent(1.56–50 μg/m L) anticancer effect against MCF–7 cells with IC50 values of 50 and 6.25 μg/m L respectively which was mediated by oxidative stress due to ROS over-production that induced loss of mitochondrial membrane potential, capsase-9,-7 activities leading to apoptosis. The present study validates that Qu–PEG–Ni Gs can be used as a potential anticancer agent for cancer therapy.     

High energy-storage properties of Bi0.5Na0.5TiO3-BaTiO3-SrTi0.875Nb0.1O3 lead-free relaxor ferroelectrics

New lead-free ferroelectric (0.94-x)Bi_0.5Na_0.5TiO₃-0.06BaTiO₃-xSrTi_0.875Nb_0.1O₃ (BNBT-STN, x = 0 and 0.2) are synthesized by using a solid state reaction process. In this work, an obvious evolution of dielectric relaxation behavior and slim P–E hysteresis loops with high P_max and low P_r is observed for BNBT-0.2STN, indicating the dominant of ergodic relaxor phase with dynamic polar nano-regions (PNRs). A relatively large recoverable energy density (W_rec = 1.17 J/cm³) with high energy efficiency (η = 91%) is obtained. Furthermore, it shows small variation (9%) in the temperature range of 30–150 °C and fatigue-free behavior, which can be attributed to the absence of ferroelectric domain in the relaxor phase. The achievement of these characteristics provides that tailoring by B-site vacancies is a potential route when designing a new energy-storage system for BNT-based relaxor ferroelectric materials.     

Synthesis and characteristics of nature-superlattice-structured Bi3TiNbO9–Bi4Ti3O12 ferroelectric thin films by MOD

Natural-superlattice-structured ferroelectric thin films, Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT), have been synthesized on Pt/Ti/SiO₂/Si by metal organic decomposition (MOD) using BTN–BIT (1 mol:1 mol) solution. BTN–BIT films show natural-superlattice peaks below 2θ = 20° in X-ray diffraction patterns, which indicate that the BTN–BIT films annealed at 700–800 °C in O₂ ambient are consisted of iteration of two unit cells of Bi₃TiNbO₉ and one unit cell of Bi₄Ti₃O₁₂. As the annealing temperature increases from 600 to 750 °C, uniform and crack-free films, better crystallinity and ferroelectric properties can be obtained, but the pyrochlore phase in BTN–BIT films annealed over 800 °C would impair the ferroelectric properties. With the increase of O₂ flow rate from 0.5 to 1.5 L/min, both remanent polarization P_r and coercive electric field E_C increase, which are mainly attributed to reduction of the vacanvies of Bi and oxide ions in the films. Natural-superlattice-structured BTN–BIT thin films having 2–1 superlattice annealed at 750 °C in O₂ ambient with a flow rate of 1.5 L/min exhibit superior ferroelectric properties of P_r = 23.5 μC/cm² and E_C = 135 kV/cm.