Preparation and electrochemical properties of some (Sc1−xTix)Ni alloys

A series of (Sc_1−xTi_x)Ni alloys and their hydrides (Sc_1−xTi_x)NiH_y, where x=0, 0.1, 0.3, 0.5, and y=2.9, 2.58, 2.23 and 1.55, have been prepared. The ability to store hydrogen gradually decreases with increasing Ti content in line with the reduction of the unit cell volume from 32.16 ų for ScNi to 29.68 ų for (Sc_0.5Ti_0.5)Ni. The electrochemical discharge capacity, however, varies in a more complex manner with (Sc_0.7Ti_0.3)Ni composition displaying the highest value of 231 mAh/g. The discharge capacity losses after 10 electrochemical charge–discharge cycles also vary non-linearly between 46% for (Sc_0.9Ti_0.1)Ni and 5% for (Sc_0.5Ti_0.5)Ni.     

Electronic structure of SnO2 (110) surface

The electronic structure of the stoichiometric and reduced SnO₂ (110) surfaces is studied with first-principles calculations. Calculations are carried out with two complementary self-consistent ab initio–DFT–GGA methods. Surface relaxation is considered, where the most prominent feature turns out to be the surface layer in-plane oxygen displacement of the reduced surface outwards, about 0.4 Å with respect to the surface layer tin atoms. The electronic structure of the relaxed surfaces is considered in terms of atomic orbitals and rehybridization, and the surface band structure. The bands are flat at the stoichiometric surface, but strong dispersion occurs at the reduced surface. The dispersion results in electronic levels into the band gap, which have also been experimentally observed.     

采用响度控制改进算法的封闭车厢主动消声

以响度为噪声主动控制目标,提出逆模型结构和延迟补偿结构相结合的LFLMS改进算法。以轿车封闭车厢为载体构建双通道主动消声系统。以发动机噪声为噪声源,用三种控制算法进行试验,结果表明LFLMS改进算法与LFLMS算法的控制效果相近,且收敛速度快;响度控制声压减小不及声压控制,但响度减小量更大,主观听觉效果更好。     

Efficient and scalable preparation of MoS2 nanosheet/carbon nanotube composites for hydrogen evolution reaction

An efficient and scalable method combining ball-milling and liquid-phase exfoliation was used to prepare MoS₂ nanosheets. Ammonium bicarbonate as an exfoliation aid could accelerate the delamination and pulverization of bulk MoS₂ during preparation. The ball-milled MoS₂ was further exfoliated by sonication (S–MoS₂NS) or high-speed shear-exfoliation (H–MoS₂NS) to obtain MoS₂ nanosheets dispersion with high concentration. Moreover, MoS₂ quantum dots were also obtained by prolonging sonication time (S–MoS₂QS). Most of S–MoS₂NS and H–MoS₂NS have lateral dimensions less than 150 nm. The S–MoS₂QS size concentrates at around 5 nm. The H–MoS₂NS mixed with aminated multi-walled carbon nanotubes (MWCNT) could form H–MoS₂NS/MWCNT composites with a good conductive network, and was used as a hydrogen evolution reaction (HER) catalyst. The H–MoS₂NS/MWCNT composites containing 56 wt% H–MoS₂NS exhibited a favorable HER activity with a low overpotential of 284 mV at 10 mA/cm², a Tafel slope of 97 mV/dec and good stability in acid medium.     

Roughness effects of gas diffusion layers on droplet dynamics in PEMFC flow channels

Water management remains one of the major challenges in optimising the performance of PEMFCs, in which liquid accumulation and removal in gas diffusion layers (GDLs) and flow channels should be addressed. Here, effects of GDL surface roughness on the water droplet removal inside a PEMFC flow channel have been investigated using the Volume of Fluid method. Rough surfaces are generated according to realistic GDL properties by incorporating RMS roughness and roughness wavelength as the main characteristic parameters. Droplet dynamics including emergence, growth, detachment, and removal in flow channels with various airflow rates are simulated on rough substrates. The influences of airflow rate on droplet dynamics are also discussed by comparing the detachment time and droplet morphology. The liquid removal efficiency subject to different surface roughness parameters is evaluated by droplet detachment time and elongation, and regimes of detachment modes are identified based on the droplet breakup location and detachment ratio. The results suggest that rough surfaces with higher RMS roughness can facilitate the removal of liquid inside flow channel. Whilst surface roughness wavelength is found less significant to the liquid removal efficiency. The results here provide qualitative assessments on identifying the key surface characteristics controlling droplet motion in PEMFC channels.     

Mesoscale modelling of the yield point properties of silicon crystals

The yield point properties that characterize silicon crystals in the temperature domain where Peierls forces govern the dislocation mobility have been investigated in easy glide conditions with the help of a three-dimensional mesoscopic simulation of dislocation dynamics. The influence of temperature, applied strain rate and initial dislocation microstructure, the latter consisting of a random initial distribution of dislocation sources, were examined in detail and globally found in fair agreement with the available experimental results. A critical examination of a well-known model by Alexander and Haasen has been performed, leading to a discussion and reformulation of the law accounting for the multiplication rate of dislocations. The present lack of knowledge on the mechanisms by which new dislocation sources are formed during the plastic deformation of silicon crystals is emphasized.     

Evolution of the physicochemical properties of oil-free sweet potato chips during microwave vacuum drying

The demand for healthy and convenient foods is a worldwide trend. Sweet potato attracted great attention due to its carbohydrates with a low glycemic index. Dehydrated sweet potatoes can be an excellent alternative for using and adding value to this raw material. The objective of this study was to evaluate the physicochemical properties of sliced sweet potato during the microwave vacuum drying (MWVD) for producing crispy oil-free chips. Fresh sweet potato samples were selected, peeled, sliced, blanched, and then dehydrated using a microwave oven adapted with a vacuum chamber and a rotation system to operate under vacuum. It was measured the evolution of moisture, water activity, temperature, color, apparent specific mass, porosity, and acoustic/mechanical analysis of the texture during the MWVD. Crispy sweet potato chips were obtained in <30 min, presenting low moisture (0.028 g g⁻¹ db) and water activity (0.262). The dehydrated samples showed high porosity (67.5%) and a low apparent density (0.456 g cm⁻³). Optical micrographs and acoustic/mechanical properties showed an expanded (puffed) product structure with large pores, which resulted in irregular acoustic/mechanical signals, characteristics of a crispy food matrix. Colorimetric analyses indicated a little change between fresh and dried samples, with an absence of burnt spots. In conclusion, MWVD is a suitable process to produce highly porous sweet potato chips, adding value, and extending the vegetable's shelf life.     

Predicting electrical and thermal abuse behaviours of practical lithium-ion cells from accelerating rate calorimeter studies on small samples in electrolyte

An accelerating rate calorimeter (ARC) is used to measure the thermal stability of de-intercalated Li_1+xMn_2−xO₄ in LiPF₆ EC:DEC (33:67) electrolyte. Self-heating is detected well after the 80°C onset of self-heating measured for lithium intercalated mesocarbon microbead (MCMB) electrodes in LiPF₆ EC:DEC (33:67) electrolyte. As a result, the initial self-heating measured in a practical carbon/Li_1+xMn_2−xO₄ lithium-ion cell is caused by reactions at the anode. In previous work, we have proposed a model for the reactions that cause self-heating in MCMB electrodes in electrolyte. By assuming that a cell self-heats only because reactions occur at the anode, the model can be used to predict the power generated by the amount of MCMB in practical cells with an inert cathode. The calculated chemically generated power can be combined with power loss measurements, due to the transfer of heat to the environment, to predict the short-circuit behaviour and the oven exposure behaviour for a cell containing an MCMB anode and an inert cathode. The results agree qualitatively with short-circuit and oven exposure results measured on NEC Moli energy 18650 cells containing an Li_1+xMn_2−xO₄ cathode.     

On the composite characteristics of small binary granules formed in a continuous rotating conical vessel with grinding media

In order to produce small composite granules having binary components of CaCO₃ and SiC powders, experiments were carried out by the simultaneous operation of granulation, grinding, and separation in a single continuous rotating conical vessel with grinding media. To characterize these composite granules, SiC agglomerates contained in a granule were separated by chemical methods, and the size distributions of granules and SiC agglomerates were measured by an image analyzer through a microscope. The structure of a composite granule was characterized by comparing the size of a composite granule with that of SiC agglomerates in the granule. It was found that composite structures of the granules could be classified into six kinds of structural models, and that the composite structure depended on the size of the granules and the volume fraction of the SiC component in the granule.     

A combined study of nanocrystalline aluminium by X-ray diffraction and mechanical spectroscopy

Nanocrystalline aluminium was prepared by ball milling in different conditions. The milled powders were characterized by X-ray diffraction in order to determine accurately the crystal size and the internal strains. Mechanical spectroscopy measurements in the 300–700 K temperature range were performed with a torsion pendulum on consolidated nanocrystalline powders. The anelastic spectrum is characterized by a broad internal friction peak and an exponential background. These data are compared with those obtained on a coarse grained sample and correlated with the information derived from X-ray diffraction analysis.