Kinetics Of Solid-state Diffusion Research Articles

Interface characteristics and tensile fracture behavior of CoCrFeNi/6061Al matrix composites fabricated via spark plasma sintering and heat treatment

In this study, 3vol%CoCrFeNi high-entropy alloy (HEA) reinforced 6061Al matrix composites were prepared using spark plasma sintering (SPS), and a new strategy to regulate the interfacial structure of the diffusion layer by solid solution heat treatment was proposed. Based on the thermodynamics and kinetics of solid-state diffusion, the mechanism of the formation and growth of the diffusion layer and its influence on the mechanical properties of the composites were analyzed. At a solid solution temperature of 535 °C, a uniform diffusion layer forms between HEA and Al matrix, and the thickness of the diffusion layer increases with the extension of solid solution time. The diffusion layer is determined as a two-layer structure, with a columnar solid solution grain near HEA and an equiaxed crystal along with Al9Co2 solid solution layer near Al matrix. Optimal tensile strength and elongation of 211.5 MPa and 21.4% respectively are obtained at solid solution time of 60 min, with 12.8 μm in thickness. Superior interface bonding resulting from diffusion layer prevents the crack from expanding into the matrix, contributing to an enhanced ductility with the extension of solid solution time. This study provides valuable insights and theoretical guidance for developing HEA/Al composites with superior strength-ductility synergy.

Explosion Strategy Engineering Oxygen-Functionalized Groups and Enlarged Interlayer Spacing of the Carbon Anode for Enhanced Lithium Storage

Amorphous carbon monoliths with tunable microstructures are candidate anodes for future lithium-based energy storage. Enhancing lithium storage capability and solid-state diffusion kinetics are the precondition for practical applications. Transforming intrinsic oxygen-rich defects into active sites and engineering enlarged interlayer spacing are of great importance. Herein, a novel explosion strategy is designed based on oxalate pyrolysis producing CO and CO2 to successfully prepare lignin-derived carbon monolith (LSCM) with active carbonyl (C═O) groups and enlarged interlayer spacing. Explosion promotes the demethylation of methoxyl groups and cleavage of carboxyl groups to form C═O groups. CO2 etches carbon atoms in a short time to improve the heteroatom level, expanding the interlayer spacing. ZnC2O4 is decomposed at 400 °C, simultaneously producing CO and CO2, which constructs less C═O groups and large interlayer spacing. MgC2O4 is decomposed at 450 and 480 °C, staged-weakly producing CO and CO2, which constructs more C═O groups and larger interlayer spacing. CaC2O4 is decomposed at 480 and 700 °C, staged-uniformly producing CO and CO2, which constructs abundant C═O groups and largest interlayer spacing. The LSCM prepared by staged-uniform explosion exhibits high lithium storage capacity, superior rate capability, and cycling performance. The assembled lithium ion capacitor device achieves excellent energy/power densities of 78 Wh kg-1/100 W kg-1 and superior durability (capacitance retention of 8 4.6% after 20,000 cycles). This work gives a novel insight to engineer advanced oxygen-functionalized carbons for enhanced lithium storage.

Parameter Identification of Electrochemical Model for Vehicular Lithium-Ion Battery Based on Particle Swarm Optimization

The dynamic characteristics of power batteries directly affect the performance of electric vehicles, and the mathematical model is the basis for the design of a battery management system (BMS).Based on the electrode-averaged model of a lithium-ion battery, in view of the solid phase lithium-ion diffusion equation, the electrochemical model is simplified through the finite difference method. By analyzing the characteristics of the model and the type of parameters, the solid state diffusion kinetics are separated, and then the cascade parameter identifications are implemented with Particle Swarm Optimization. Eventually, the validity of the electrochemical model and the accuracy of model parameters are verified through 0.2–2 C multi-rates battery discharge tests of cell and road simulation tests of a micro pure electric vehicle under New European Driving Cycle (NEDC) conditions. The results show that the estimated parameters can guarantee the output accuracy. In the test of cell, the voltage deviation of discharge is generally less than 0.1 V except the end; in road simulation test, the output is close to the actual value at low speed with the error around ±0.03 V, and at high speed around ±0.08 V.

Thermodynamic assessment and applications of Ti-V-N system

Experimental Ti-V-N phase diagram data have been thermodynamically assessed and a consistent set of thermodynamic functions has been developed. Calculations have been performed to reveal some important features of the system. Problem areas in experimental data are indicated. The thermodynamic calculation is linked with limiting casesfor solid state diffusion kinetics. This is applied to a numerical simulation of ternary solidification processes of Ti-V-N alloys and to a discussion of the nitriding behaviour of Ti-V alloys.