Improvement the electrochemical performance of Cr doped layered-spinel composite cathode material Li1.1Ni0.235Mn0.735Cr0.03O2.3 with Li4Ti5O12 coating

The Cr doped layered-spinel composite cathode material Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 was synthesized and coated with different content of Li₄Ti₅O₁₂ by a sol–gel method. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The effect of Li₄Ti₅O₁₂ coatings on the electrochemical performance of the pristine material was evaluated from charge/discharge cycles, rate performance, and electrochemical impedance spectroscopy (EIS). The XRD results show that the lattice crystal and the content of spinel phase have been increased in the Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 materials after Li₄Ti₅O₁₂ coating. The results from TEM and selected area electron diffraction (SAED) indicate that the Li₄Ti₅O₁₂ coating assumes a spinel structure on the Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3. The discharge capacities, cycling and rate performances of the Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 materials in the first cycle are improved with the addition of Li₄Ti₅O₁₂. Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 coated with 3 wt% Li₄Ti₅O₁₂ shows the highest discharge capacity (271.7 mA h g⁻¹), highest capacity retention (99.4% for 100 cycles), and best rate capability (132 mA h g⁻¹ at 10 C). EIS result indicates that the resistance of Li_1.1Ni_0.235Mn_0.735Cr_0.03O_2.3 electrode decreases with the addition of Li₄Ti₅O₁₂. The enhanced electrochemical performance can be ascribed to the increased spinel content, lower resistance and the enhanced lithium-ion diffusion kinetics.     

Hard,tough and strong ZrO2–WC composites from nanosized powders

Yttria-stabilised zirconia (Y-TZP) based composites with a tungsten carbide (WC) content up to 50 vol.% were prepared from nanopowders by means of conventional hot pressing. The mechanical properties were investigated as a function of the WC content. The hardness increased from 12.3 GPa for pure Y-TZP up to 16.4 GPa for the composite with 50 vol.% WC, whereas the bending strength reached a maximum of 1551 MPa for the 20 vol.% WC composite. The toughness of the composites could be optimised by judicious adjustment of the overall yttria content by mixing monoclinic and 3 mol% Y₂O₃ co-precipitated ZrO₂ starting powders. An optimum fracture toughness of 9 MPa m^1/2 was obtained for a 40% WC composite with an overall yttria content of 2 mol%. The hardness, strength as well as fracture toughness of the ultrafine grained composites with a nanosized WC source was significantly higher than with micron-sized WC. The experimentally measured contribution of the different observed toughening mechanisms was evaluated as a function of the WC content. Transformation toughening was found to be the major toughening mechanism in ZrO₂–WC composites with up to 30 vol.% WC, whereas the contribution of crack deflection and bridging is significant at a secondary phase content above 30 vol.%.     

应变控制下水泥土动静力特性试验

为了研究循环荷载下水泥土的动静力特性,通过GDS振动三轴仪进行应变控制下的静力和逐级循环加载试验.静力试验表明:应变速率越大,水泥土强度越大,应变速率为5%时的峰值应力相对于being0.05%时提高了47.57%;掺入比决定水泥土应力-应变关系曲线的软化或硬化型式.通过逐级循环加载试验,进一步分析水泥土的应力-应变关系和动模量的发展规律,通过对双曲线模型的修正,建立描述水泥土应力-应变关系的经验模型.该模型共有3个参数,论述了各个参数的物理意义和确定方法,结果表明,本文模型简单实用,能够较好地反映水泥土的应力-应变关系.     

Magnetic properties enhancement of hot-deformed NdFeB magnets by two different methods of CeNdCu diffusion

Two different ways were used to control the distribution of cerium for the enhancement of coercivity. One was by coating CeNdCu in the prepared magnet and annealing to make CeNdCu diffuse into the grain boundary to increase the coercivity, the other was by mixing CeNdCu with initial magnetic powders and then preparing the hot-deformed magnet. The SEM-EDS result indicates that cerium diffuses more easily into the main phase by the mixing way, while cerium is mainly distributed in the grain boundary via the coating way. The heat-treatment process may be one of the dominant influencing factors for the distribution of Ce. Multi-steps heat treatment in the mixing way, consisting of hot-pressing, hot-deforming and post heat process, easily introduces Ce into the main phase Nd₂Fe₁₄B, which forms the Ce₂Fe₁₄B shell resulting in the decrease of H_A. But the coating way can ensure uniform dispersion of Ce in the grain boundary, which leads to the high coercivity.     

Electrical conductivity of REF_3-LiF(RE=La and Nd) molten salts

The electrical conductivity of REF3-LiF(RE=La and Nd) molten salts(xREF_3=5 mol%-40 mol%) was systematically measured over the temperature range from 1223 to 1423 K by using continuously varying cell constant(CVCC) method.Electrical conductivity values of LaF3-LiF and NdF_3-LiF molten salts within the studied ranges are 4.11-9.39 and 3.62-9.51 S/cm,respectively.The composition and temperature dependences of electrical conductivity and the factor of RE_2 O_3 on electrical conductivity were investigated.The electrical conductivity nonlinearly decreases with the increasing mole percent of REF_3 for the changing of structural ion in molten salts.A good linear relationship between the natural logarithm of electrical conductivity(lnκ) and the reciprocal of the absolute temperature(T~(-1)) can be interpreted by the trend that electrical conductivity linearly increases with increasing temperature.Although it is an important factor of RE_2 O_3 on electrical conductivity,the influence of RE_2 O_3 on conductivity is small for the very limited solubility of RE_2 O_3 in REF_3-LiF molten salts.The results of this work supplement the present electrical conductivity data of rare earth fluoride electrolyte.     

Compressive strength and impact resistance of Al2O3/Al composite structures fabricated by digital light processing

The combination of multi-materials is an alternative way to meet the diverse requirements for various applications. However, the processing difficulty especially in ceramic forming limited the structural innovations. In this paper, a combined methods of ceramic digital light processing (DLP) and metal infiltration is proposed to fabricate the Al₂O₃/Al composite structures with controllable ceramic skeletons. The interfacial, compressive and impact resistance properties were studied. The results showed that the Al₂O₃ grains were closely bonded, and no destructive defects occurred at the interface between Al₂O₃ and Al. The energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) results showed that the formation of protective phases contributed to the improvement of bonding strength. The compressive tests showed that the composite structures had better capabilities to absorb and resist the applied loads compared with Al structures. Finally, the impact resistance of the structures was discussed, the finite element analysis and the experimental results showed that the composite structures had advantages in dissipating the energy of incident objects and reducing the penetration depth. Based on these results, the damage model of Al₂O₃/Al structures was established, and the roles of different materials were revealed.     

Light-induced electron spin resonance study of galvinoxyl-doped P3HT/PCBM bulk heterojunctions

We report the effects of doping of P3HT/PCBM layers with spin 1/2 radicals of galvinoxyl (Gx) based on light-induced electron spin resonance (LESR), photoluminescence-detected magnetic resonance (PLDMR), and post-annealing experiments.LESR showed both a P3HT⁺ and PCBM⁻ signal for undoped P3HT/PCBM; however, as Gx doping increased (above ∼1 wt%), only the P3HT⁺ signal was evident in the LESR spectra, with no PCBM⁻ signal.The PLDMR exhibited a strong narrow signal at g = 2.002 that originates from nongeminate polaron pairs; no triplet PLDMR signal has been observed throughout the whole range of Gx concentrations (x = 0, 0.1, 1, 2, 4, 12 wt%). Adding Gx to ∼3 wt% led to a decrease of the PL-enhancement.There was big difference between the slow-dried P3HT/PCBM samples and the post-annealed samples. For the slow-dried samples, efficiency monotonously decreased with Gx additives. When post-annealed, however, an enhancement in η was observed at ∼2 wt% for P3HT/PCBM(1:2) samples.The LESR spectra for post-annealed samples revealed disappearance of Gx spin signals, and thus no spin interactions with PCBM⁻ spins. It is unlikely that the increase of efficiency after Gx doping of P3HT/PCBM solar cell is due to an increase of triplet states.     

Enhanced efficiency of organic solar cells by mixed orthogonal solvents

In this work, the effects of mixed solvents on donor–acceptor vertical phase separation and light absorption was investigated. By using mixed orthogonal solutions of 1,2 o-dichlorobenzene (o-DCB) and dichloromethane (DCM), a PCBM([6,6]-phenyl-C₆₁-butyric acid methyl ester)-rich top layer was induced in typical poly(3-hexylthiophene-2,5-diyl)(P3HT):PCBM bulk heterojunction structure. By carefully adjusting the o-DCB:DCM volume ratio, the contact between active layer and the Al cathode was significantly improved due to the precipitation of PCBM on the top surface, which resulting in an electron transport preferable interface between the active layer and cathode. Meanwhile, light absorption was also effectively improved due to the increased crystallinity of polymers under mixed solvents. Overall, the short circuit current was greatly increased, and the efficiency was improved from 3.07% in the control sample to 3.97% by adding 30% DCM. The detailed mechanism of the formation of PCBM-rich layer and enhanced light absorption with o-DCB:DCM solution was expatiated. Our findings suggest a facile spin coating method to fabricate efficient BHJ solar cells, which can pave the way for the large scale application of organic photovoltaic devices (OPVs) in the future.     

Combined action of crack closure and residual stress under periodic overloads: A fractographic analysis

The close relationship between sequence-sensitive near-tip residual stress and threshold stress intensity raises questions about load interaction models currently in use to estimate fatigue crack growth under variable amplitude loading. In an attempt to address them, experiments were performed on an Al–Cu alloy under specially designed load sequences with periodic overloads. Fractographic evidence from these tests confirms that fatigue crack closure, together with sequence sensitive variation in threshold stress intensity appear to explain all observed results. The fractographic data provide quantitative inputs for improved modeling of variable-amplitude fatigue, particularly at near-threshold crack growth rates. This study appears to suggest that conventional approaches based on the Wheeler and Willenborg residual stress models can provide reasonable estimates only by coincidence. They model the wrong parameter at lower fatigue crack growth rates and may simply not be valid at other growth rates.