In this study, Ti-Fe-Si composites were prepared by one step ball-milling method as anode materials for Li-ion batteries. The effects of ball-milling speed and time were studied by X-ray diffraction, electron microsco...
详细信息
In this study, Ti-Fe-Si composites were prepared by one step ball-milling method as anode materials for Li-ion batteries. The effects of ball-milling speed and time were studied by X-ray diffraction, electron microscopy, and Fe-57 Mossbauer spectroscopy. changes in the composition and microstructure of the composites were observed and related to the electrochemical performance. Increasing ball-milling speed led to the formation of FeSix alloys that reduced the specificcapacity while increasing the ball-milling time improved the particle size morphology and homogeneity. Discharge/charge profiles for the first two cycles were carried out at 0.05ccurrent rate (1c = 1260 mAh.g(-1)for Li3.75Si). The first discharge for Ti-Fe-Si showed a LixSi reaction plateau of 1100 mAh.g(-1), which were reversible and yielded columbic efficiency (cE) 77% and 90% in the first and second cycles, respectively. This capacity plateau indicated the insertion of about 3.25 Li into silicon. For the composite containing an additional 10% carbon SP, the theoretical capacity was about 1130 mAh.g(-1), the discharge curve showed that the first discharge plateau reaches 1030 mAh.g(-1) corresponding to 3.5 Li with the first cE was about 85%, and 98% for the second cycle. The addition of carbon to Ti-Fe-Si-c played a key role in capacity retention. The best results were obtained for the composite Fe/Ti/Si (1:1:2) with 10 wt% of carbon, ball-milled at 500 rpm for 48 hours. The specificcapacities were about 900 mAh.g(-1) at c/5 and 700 mAh.g(-1) at 1c (c = 1200 mAg(-1)) with a capacity retention of about 90% for 100 cycles.
An active Ag-based filler metal, containing trace alloy elements of Al, cu and Ti, was successfully applied to braze c/ccomposite and Nb. The microstructure and formation mechanism of the c/ccomposite and Nb brazed ...
详细信息
An active Ag-based filler metal, containing trace alloy elements of Al, cu and Ti, was successfully applied to braze c/ccomposite and Nb. The microstructure and formation mechanism of the c/ccomposite and Nb brazed joint were investigated in this study. Moreover, the influence of brazing parameters on microstructural evolution and mechanical properties of brazed joints was evaluated. The typical interfacial microstructure of the joint obtained at 950 degrees c for 600 s was c/c/Tic + Alcu2Ti/Ag(s, s) + Alcu2Ti + particle cu/Alcu2Ti + AlcuTi + (Ti, Nb)3Al + Nb(Ti)/Nb. The dispersive Alcu2Ti phase was uniformly distributed in the Ag matrix, which was a beneficial structure for the brazed joint. The shear strength of the brazed joint was sensitive to the brazing temperature and holding time, which was closely related to the Tic layer bordering the c/ccomposite. The thickness of the Tic layer first increased as temperature increased to 950 degrees c, and then decreased when temperature reached 970 degrees c. The carbon fiber eroded by the filler at 970 degrees c entered to the brazing seam and reacted with Ti, resulting the reduction of the thickness of Tic, thus damaging the strength of the joint. With extension of holding time from 300 s to 1200 s, the interface reaction became more sufficient. Therefore, the thickness of the Tic layer increased. However, at 1200 s, the over-thick Tic broke the c/c substrate because of the mismatch of coefficient of thermal expansions. The maximum shear strength of the joint (950 degrees c/600 s) reached 55 MPa at room temperature and 35 MPa tested at 550 degrees c.
Two-dimensional (2D) csPbI3 is developed to conquer the phase-stability problem of csPbI3 by introducing bulky organiccations to produce a steric hindrance effect. However, organiccations also inevitably increase th...
详细信息
Two-dimensional (2D) csPbI3 is developed to conquer the phase-stability problem of csPbI3 by introducing bulky organiccations to produce a steric hindrance effect. However, organiccations also inevitably increase the formation energy and difficulty in crystallization kinetics regulation. Such poor crystallization process modulation of 2D csPbI3 leads to disordered phase-arrangement, which impedes the transport of photo-generated carriers and worsens device performance. Herein, a type of c3N quantum dots (QDs) with ordered carbon and nitrogen atoms to manipulate the crystallization process of 2D csPbI3 for improving the crystallization pathway, phase-arrangement and morphology, is introduced. combination analyses of theoretical simulation, morphology regulation and femtosecond transient absorption (fs-TA) characterization, show that the c3N QDs induce the formation of electron-rich regions to adsorb bulky organiccations and provide nucleation sites to realize a bi-directional crystallization process. Meanwhile, the quality of 2D csPbI3 film is improved with lower trap density, higher surface potential, and compact morphology. As a result, the power conversion efficiency (PcE) of the optimized device (n = 5) boosts to an ultra-high value of 15.63% with strengthened environmental stability. Moreover, the simple c3N QDs insertion method shows good universality to other bulky organiccations of Ruddlesden-Popper and Dion-Jacobson, providing a good modulation strategy for other optoelectronic devices.
Application of waste biomass resources in heavy metal adsorption and new energy development is of great significance to improving environmental pollution and the adjustment of energy structure. For this purpose, we de...
详细信息
Application of waste biomass resources in heavy metal adsorption and new energy development is of great significance to improving environmental pollution and the adjustment of energy structure. For this purpose, we designed a simple method for preparing porous Mo2c/ccomposite materials based on resource-rich biomass carbon (derived from waste pine wood) and ammonium molybdate, and successfully applied it to the above field. The effects of holding time and sintering temperature on the phase compositions and morphological structures of samples were investigated, and the heavy adsorption capacity (cr(III)) and hydrogen evolution reaction of composite materials were also studied. The results showed that porous biomass Mo2c/ccomposite materials had significantly higher oxidation resistance, and more prominent pore structure as compared to the pretreated biomass carbon. In addition, porous biomass Mo2c/ccomposite materials showed excellent adsorption performance for heavy metal cr(III) and catalytic hydrogen evolution reaction performance, its adsorption capacity and Tafel slope were 43.2 mg/g and 123.9 mV/dec, respectively.
The cyclic ablation resistance of coated carbon/carbon (c/c) composites play crucial roles in their further engineering applications and development due to the cyclic ablation environment accompanied by rapid heating ...
详细信息
The cyclic ablation resistance of coated carbon/carbon (c/c) composites play crucial roles in their further engineering applications and development due to the cyclic ablation environment accompanied by rapid heating and cooling and high-speed heat flow scouring, which can reflect the performance stability of the coating. In this research, a (Sic/Hfc)4/Sic (SHS) multi-layer coating was prepared on c/ccomposites. compared with single layer (Sic and Hfccoating) coated sample, the mass and linear ablation rate of SHS coated sample after three ablation cycles (60 s x 3) were only 0.64 mg/s and 0.53 mu m/s, respectively. This is mainly because the introduction of many interfaces inhibits the propagation of cracks, the irregular cracks region only exists in the outer layer. Besides, the oxide layer with dense structure was formed near the c/c substrate, which could prevent oxygen from penetrating into the coating and continue to play a protective role.
A novel method to prepare a coating on the c/ccomposite is discussed. The precursor infiltration pyrolysis method is usually applied to prepare interior ceramic matrix, thus Sic nanowires that can absorb the surficia...
详细信息
A novel method to prepare a coating on the c/ccomposite is discussed. The precursor infiltration pyrolysis method is usually applied to prepare interior ceramic matrix, thus Sic nanowires that can absorb the surficial precursor are added to prepare surficial ceramics. The method accomplishes the integration of the coating and the matrix so that no coating peels off after ablation. Moreover, the material with a Zrc/Sic precursor ratio of 5:1 (Z5S1), whose mass and linear rates are 0.47 mg/s and 0.95 mu m/s, exhibits the highest overall resistance to ablation. The results demonstrate that higher Zrccontent and more uniform phase distribution are beneficial to keep ZrO2 in solid and form a denser and firmer oxide layer, which is more effective in improving the ablation resistance of the c/ccomposite.
In this paper, a micromechanical approach is developed to predict the fatigue life and fracture process in different c/Siccomposites subjected to different stochastic fatigue loading spectrums at elevated temperature...
详细信息
In this paper, a micromechanical approach is developed to predict the fatigue life and fracture process in different c/Siccomposites subjected to different stochastic fatigue loading spectrums at elevated temperatures. Three types of stochastic fatigue load spectrums are considered in the fatigue life prediction at elevated temperature, that is, constant, increasing, and decreasing stochastic stress with cycles. Stress distribution between intact and broken fibers and the broken fibers fraction under stochastic fatigue loading spectrum are determined using the Global Load Sharing criterion considering multiple fatigue damage mechanisms at elevated temperatures. A new damage parameter of fatigue life degradation rate is developed to characterize the effect of stochastic loading on fatigue damage and fracture in c/Siccomposites. Relationships between stochastic fatigue loading spectrum, broken fibers fraction, fatigue life, and fatigue life degradation rate in different c/Siccomposite are established. Effects of stochastic fatigue loading spectrum type, stress level, and testing temperature on fatigue life degradation rate are discussed. The fatigue life degradation rate is very sensitive to the fiber preform, loading sequence, and testing temperature.
Hexagonal boron nitride (h-BN) has excellent oxidation resistance, self-healing function, and self-lubricating properties, which can significantly improve the oxidation resistance of c/c-Siccomposites in low or mediu...
详细信息
Hexagonal boron nitride (h-BN) has excellent oxidation resistance, self-healing function, and self-lubricating properties, which can significantly improve the oxidation resistance of c/c-Siccomposites in low or medium temperature condition and affect their tribological properties and mechanisms. In this work, c/c-Sic and c/c-BN-Siccomposites were prepared by the same molding, carbonization and liquid silicon infiltration (LSI) processes and the influences of h-BN addition on their microstructure, tribological properties, and mechanisms were investigated. h-BN addition can promote the formation of friction film and reduce the oxidation wear of the composites. compared with c/c-Siccomposites, due to more lubricant components and different matrix structure, the c/c-BN-Siccomposite shows lower wear rate (reduced by 53%) and moderate rather than too high coefficient of friction (coF) and its coF is less influenced by braking velocity. Moreover, the friction process is more stable and does not appear clamping stagnation phenomenon in high braking speed condition.
Many critical codebases are written in c, and most of them use preprocessor directives to encode variability, effectively encoding software product lines. These preprocessor directives, however, challenge any staticc...
详细信息
Many critical codebases are written in c, and most of them use preprocessor directives to encode variability, effectively encoding software product lines. These preprocessor directives, however, challenge any staticcode analysis. SPLlift, a previously presented approach for analyzing software product lines, is limited to Java programs that use a rather simple feature encoding and to analysis problems with a finite and ideally small domain. Other approaches that allow the analysis of real-world c software product lines use special-purpose analyses, preventing the reuse of existing analysis infrastructures and ignoring the progress made by the static analysis community. This work presents VarAlyzer, a novel static analysis approach for software product lines. VarAlyzer first transforms preprocessor constructs to plain c while preserving their variability and semantics. It then solves any given distributive analysis problem on transformed product lines in a variability-aware manner. VarAlyzer 's analysis results are annotated with feature constraints that encode in which configurations each result holds. Our experiments with 95 compilation units of OpenSSL show that applying VarAlyzer enables one to conduct inter-procedural, flow-, field- and context-sensitive data-flow analyses on entire product lines for the first time, outperforming the product-based approach for highly-configurable systems.
暂无评论