Preparation and sintering of nano Fe coated Si_3N_4 composite powders

Fe/Si3N4 composite powder was synthesized by the heterogeneous precipitation-thermal reduction process,and then pressed into flakes under a pressure of 10 MPa.Flakes were sintered by pressureless and hot-pressing at 1 600℃under 0.1 MPa N2. The chemical composition,phases and microstructure of composite powder and sintered flakes were investigated by energy dispersive spectroscopy(EDS),X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscopy (TEM).The results show that the structure of composite powders is Si3N4 coated by nano Fe.The crystal phases of sintered flakes by pressureless are Fe(Si)compound,SiC and Si3N4.The crystal phases of the sintered samples by hot-pressing are Fe,Fe(Si) compound and Si3N4.It is found that crystal phases flakes obtained by pressureless and hot-pressing are very different.

Elastic-plastic properties of thin film on elastic-plastic substrates characterized by nanoindentation test

To characterize the elastic-plastic properties of thin film materials on elastic-plastic substrates,a simple theory model was proposed,which included three steps:dimensionless analysis,finite element modeling and data fitting.The dimensionless analysis was applied to deriving two preliminary nondimensional relationships of the material properties,and finite element modeling and data fitting were carried out to establish their explicit forms.Numerical indentation tests were carried out to examine the effectiveness of the proposed model and the good agreement shows that the proposed theory model can be applied in practice.

Phosphorous-doped carbon nanotube/reduced graphene oxide aerogel cathode enabled by pseudocapacitance for high energy and power zinc-ion hybrid capacitors

The design and development of energy storage device with high energy/power density has become a research hotspot.Zinc-ion hybrid capacitors(ZHCs)are considered as one of the most promising candidates.However,the application of ZHCs is hindered by their low energy density at high power density due to the unsatisfactory cathode material.In this study,a novel 3D phosphorus-doped carbon nanotube/reduced graphene oxide(P-CNT/rGO)aerogel cathode is synthesized through a synergistic modification strategy of CNT insertion and P doping modification combined with 3D porous design.The as-obtained P-CNT/rGO aerogel cathode manifests significantly increased surface aera,expanded interlayer spacing,and enhanced pseudocapacitance behavior,thus leading to significantly enhanced specific capacitance and superb ions transport performance.The as-assembled ZHC based on P-CNT/rGO cathode delivers a superior energy density of 42.2 Wh/kg at an extreme-high power density of 80 kW/kg and excellent cycle life.In-depth kinetic analyses are undertaken to prove the enhanced pseudocapacitance behavior and exceptional power output capability of ZHCs.Furthermore,the reaction mechanism of physical and chemical adsorption/desorption of electrolyte ions on the P-CNT/rGO cathode is revealed by systematic ex-situ characterizations.This work can provide a valuable reference for developing advanced graphene-based cathode for high energy/power density ZHCs.

Optimization of Al^(3+) Doping on the Microstructure and Electrochemical Performance of Spinel LiMn_(2)O_(4)

A series of spinel Li Al_(x)Mn_(2-x)O_(4) (x≤0.1) cathode materials was synthesized by controlled crystallization and solid state route with micro-spherical Mn_(3)O_(4) as the precursor.X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyze the crystal structure of the synthetic material and the microscopic morphology of the particles.It was found that Al^(3+)doping did not change the spinel structure of the synthesized materials,and the particles had better crystallinity.In the charge and discharge test of the synthesized materials,we found that Al^(3+)doping would slightly reduce the discharge capacity,but it could effectively improve the cyclic stability of the material.The initial capacity of Li Al_(0.04)Mn_(1.96)O_(4) is 121.6 m Ah/g.After 100 cycles at a rate of 1 C (1 C=148 m A/g),the capacity can still reach 112.9 m Ah/g,and the capacity retention rate is 96.4%.Electrochemical impedance spectroscopy (EIS) suggests that Al^(3+)doping can effectively enhance the diffusion capacity of lithium ions in the material.