In situ electrodeposition of nickel cobalt selenides on FTO as an efficient counter electrode for dye-sensitized solar cells

Construction of transition metal selenides with high electrocatalytic performance is of significant importance, but it is still a challenge to develop the corresponding counter electrodes (CEs) by an electrodeposition technique. In the present work, nickel cobalt selenide (Ni_xCo_ySe) films are prepared in situ on fluorine-doped tin oxide (FTO) glasses through a potential reversal electrodeposition technique. The morphology and electronic structure of Ni_xCo_ySe films can be tuned by controlling the Ni/Co molar ratio in electroplating solution. Specially, Ni_xCo_ySe-6 film (the Ni/Co molar ratio of 1:1) with the optimized interaction between the Ni and Co elements displays numerous particles composed of sheets attached with nanocrystals, resulting in the more electrocatalytic active sites. Benefiting from the unique morphology and optimized synergistic effect, Ni_xCo_ySe-6 CE exhibits superior electrocatalytic activity for the triiodide reduction. Then, the dye-sensitized solar cell (DSC) fabricated by Ni_xCo_ySe-6 CE has demonstrated a power conversion efficiency (PCE) over 7.40%, which is higher than that of platinum (Pt)-based device (6.32%). Furthermore, Ni_xCo_ySe-6 array CE is also prepared by using polystyrene array as template. The PCE of the DSC with Ni_xCo_ySe-6 array CE reaches its maximum value of 7.64% and 20.9% larger than that of Pt-based device.     

Preparation and cupric ion release behavior of Cu/LDPE porous composites with tunable pore morphology for intrauterine devices

Copper/low-density polyethylene (Cu/LDPE) porous composites are novel materials for copper-containing intrauterine devices (Cu-IUDs). Here we report a method, i.e., by changing the mass ratio of two kinds of porogens that have different melting points through the combined techniques of injection molding and particulate leaching, to prepare the Cu/LDPE porous composites with tunable pore morphology. After these Cu/LDPE porous composites with different pore morphologies were obtained, the influences of pore morphologies on their cupric ion release behaviors were studied. The results show that the pore morphology has great influence on the cupric ion release behavior of Cu/LDPE porous composites. This phenomenon is caused by the different influences of different pore morphologies on the effective porosity and the surface hydrophilicity. And those results can be applied to guide the fabrication of Cu/LDPE porous composite Cu-IUDs with minimal weight at an appropriate cupric ion release rate.     

Comparative study of the microstructure of Ti-6Al-4V titanium alloy sheets under quasi-static and high-velocity bulging

Journal of Mechanical Science and Technology - In order to reveal the high-velocity deformation mechanisms of Ti-6Al-4V titanium alloy sheets, the dynamic deformation behavior and the...     

The effect of different methods to add nitrogen to titanium alloys on the properties of titanium nitride clad layers

In this investigation, titanium nitride (TiN) reinforcements are synthesized in situ on the surface of Ti–6Al–4V substrates with gas tungsten arc welding (GTAW) process by different methods to add nitrogen, nitrogen gas or TiN powder, to titanium alloys. The results showed that if nitrogen gas was added to titanium alloys, the TiN phase would be formed. But if TiN powder was added to titanium alloys, TiN + TiN_x dual phases would be presented. The results of the dry sliding wear test revealed that the wear performance of the Ti–6Al–4V alloy specimen coated with TiN or TiN + TiN_x clad layers were much better than that of the pure Ti–6Al–4V alloy specimen. Furthermore, the evolution of the microstructure during cooling was elucidated and the relationship among the wear behavior of the clad layer, microstructures, and microhardness was determined.     

Experimental study on the time change in fluidity and particle dispersion state of alumina slurries with and without sintering aid

The time change of the fluidity and particle dispersion state of alumina slurries with and without a sintering aid were investigated. The apparent viscosity of the slurry was measured at certain intervals. The hydrostatic pressure of the slurry, which represents the particle dispersion state, was also measured. We showed that the pH value, adsorbed amount of dispersant, and Mg ion concentration of the slurry hardly changed with time even though the apparent viscosity of the slurry increased with time. We suggest that the time change in the apparent viscosity, that is, the behaviour in which the apparent viscosity of the slurry increased with time, occurs when the electrostatic repulsion force is insufficient to maintain the particle dispersion state for a long time, such as shortage in the dispersant to its saturated amount.     

Effect of Mo addition on microstructure and mechanical properties of (Ti,W)C solid solution based cermets

(Ti,W)C solid solution was synthesized by milling a mixture of C and oxides and then reducing it at 1350 °C for 2 h. The microstructure and mechanical properties of (Ti,W)C solid solution based cermets with various Mo additions were systemically studied. The dark core–gray rim carbide grains and/or gray carbide grains embedded in black Ni based binder phase were observed. The grain size of the cermets decreased with increasing Mo addition, while excessive Mo addition would result in agglomeration and inhomogeneity of the grains. The dark core was transformed from (Ti,W)C into (Ti,W,Mo)C and Mo concentration in the dark core increased with increasing Mo content. The fracture toughness of the cermets decreased with the increase of Mo content, while the hardness and TRS reached a peak value at 10 wt.% and 15 wt.% Mo additions respectively, and declined with the further increase of Mo content.     

Electroactive shape memory polymer based on optimized multi-walled carbon nanotubes/polyvinyl alcohol nanocomposites

The development of shape memory polymers (SMPs) has gained remarkable attention due to their wide range of applications, from biomedical to electromechanical. In this work, we have developed and optimized an electroactive SMP based on polyvinyl alcohol/multi-walled carbon nanotubes (PVA/MWNTs) composites. When a constant voltage of 60 V was applied to the optimized sample, the polymer shape could be recovered to the original form within 35 s. Different weight fractions of MWNT/PVA composites were prepared by using a simple solution blending and transitional solution casting method, and their microstructures, electrical conductivities, thermal conductivities, and electroactive shape memory properties were investigated. According to our systematic analysis, the enhanced performance can be attributed to the reinforcement of MWNTs that led to the improved electrical and thermal conductivities of the PVA matrix.     

Fabrication and properties of diatomite ceramics with hierarchical pores based on direct stereolithography

Porous diatomite ceramics with hierarchical pores and high apparent porosity (50.29–56%) were successfully fabricated via direct stereolithography. The pre-ball-milling time, dispersant type and dispersant concentration were systematically investigated to prepare diatomite pastes with high solid loading, low viscosity and a self-supporting effect. The results showed that a pre-ball-milling time of 24 h was more suitable to prepare diatomite pastes with high solid loading, and Span80 at 2 wt% was the optimal dispersant to obtain 40 vol% diatomite paste with a low viscosity and a self-supporting effect. To restrain the formation of defects, a heating rate as low as 0.2 °C/min was allowed to control the pyrolysis rate in the multistage debinding process. At sintering temperatures ranging from 900 °C to 1000 °C, porous diatomite ceramics exhibited a typical bimodal porosity, high apparent porosity and great flexural strength.     

A comparative study on UV light activated porous TiO2 and ZnO film sensors for gas sensing at room temperature

In order to find a new approach for screening the photoactivated gas sensing materials with high sensitivity, a comparative study was carried out. With the simple technique of screen printing, TiO₂ and ZnO were used to fabricate the UV light activated gas sensors which were applied at room temperature. To facilitate the simultaneous measurements of the current transients of the two materials, they were printed on the same alumina substrate. Compared with ZnO, TiO₂ exhibited a superior performance to ethanol and formaldehyde gases. It was found that the responses of TiO₂ increased with the concentration of test gas and amounted to 224 and 1700 to 100 ppm ethanol and formaldehyde gases, respectively, while the responses of ZnO to 100 ppm ethanol and formaldehyde gases were 0.14 and 1.5, respectively. The mechanism of such a huge difference between TiO₂ and ZnO was discussed in detail. Furthermore, it is suggested that metal oxide semiconductor with lower photo-to-dark current ratio can achieve higher photoactivated gas sensitivity.     

Confidence limits for Weibull parameters estimated using linear least squares analysis

Confidence limits (at selected levels of 68.27%, 90%, 95% and 99%) for unbiased estimation of Weibull parameters obtained using linear least squares (LLS) analysis were investigated in this paper. A Monte Carlo procedure was used to obtain probability distributions for unbiased estimates of Weibull modulus, m, and Weibull scale parameter, S_o, as a function of total specimen number, N (10 ≤ N ≤ 200), and m (1 ≤ m ≤ 25). Inspection of the probability distributions indicated that confidence limits for m depended only on N whereas those for S_o depended on both N and m. Whilst the determination of confidence limits for m proved to be relatively straightforward, the respective values for S_o were obtained by fitting an empirical equation to the S_o probability distributions approximated by a Gaussian curve. Example values of m and S_o confidence limits for selected N have been presented in this work.