Thermochemical Behavior of Nickel-Coated Nanoaluminum Particles

Abstract

Thermochemical behavior of nickel-coated aluminum particles in the size range of 4−18 nm is studied using molecular dynamics simulations. The analysis is carried out in isothermal− isobaric and isochoric-isoenergetic ensembles using an embedded atom method. Emphasis is placed on analyzing the melting points of the core and shell, diffusion of atoms, and intermetallic reactions. The aluminum core melts at a temperature greater than the melting point of a nascent aluminum particle due to the cage-like mechanical constraint imposed by the nickel shell. The melting point of the aluminum core increases from 775 to 1000 K when the core diameter increases from 3 to 12 nm. The melting point of the core is not significantly affected by variations in the shell thickness in the range of 1−3 nm, although the melting point of the shell increases with increasing thickness from a value as low as 1100 K at 1 nm to 1580 K at 3 nm. Melting is followed by diffusion of atoms and energy release due to intermetallic reactions, which result in ignition of the particle in vacuum. For a core diameter of 3 nm, the ignition temperature increases from 800 to 1600 K when the shell thickness increases from 0.5 to 3.0 nm. The diffusion coefficient of aluminum atoms in the nickel shell exhibits an exponential dependence on temperature, with activation energy of 34.7 kJ/mol. The adiabatic reaction temperature of the particle increases from 1650 to 2338 K when the core diameter increases from 3 to 8 nm. The calculated values agree reasonably well with those obtained via thermodynamic energy balance analysis.

SHS in Ni/Al Nanofoils: A Review of Experiments and Molecular Dynamics Simulations

“…The thermochemical behavior associated with alloying and reactivity of nickel‐coated aluminum and aluminum‐coated nickel nanoparticles have also been well investigated. Sundaram et al determined the diffusion coefficient of Ni atoms in the Al shell as a function of the temperature and shell thickness.…”

Multicomponent Shale Oil Flow in Real Kerogen Structures via Molecular Dynamic Simulation

“…The NEMD simulations were conducted in the NVT ensemble at 300 K for 18 ns, and we collected the last 6 ns of trajectories for analysis. The temperature was maintained by a Nosé-Hoover thermostat perpendicular to the flow direction [41,42], which reduced the effect of thermal motion on the velocity in the flow direction. During the simulation, as shown in Figure 2, we froze the kerogen matrix layer (KML) and controlled the temperature (300 K) of the rough adsorption layer (RAL) [29,43], which made the kerogen interface flexible [44].…”

Bimodal NdNiAl and NdFeB hybrid catalytic and magnetic nanoparticles laminated on Fe foam: catalytic conversion of CO + 3H2 to CH4

“…Although the main phase of NdNiAl was Ni 3 Al, the residual phases of the NdNiAl nanoparticles were completely transformed into intermetallic Ni 3 Al compound by heat treatment at high temperature. This is shown by the exothermic peak at 684.0 C. 44,49 Meanwhile, due to the amorphous structure of the NdFeB nanoparticles, the magnetic nanoparticles had a signicantly broader melting point than those of the bulk materials. Furthermore, the magnetic nanoparticles, being considerably bigger (93.1 nm) than the NiAl (21.1 nm) or NdNiAl nanoparticles (21.8 nm), presented the melting range at much higher temperature, close to 740 C. Thus, there might be sintering and necking between the NdFeB nanoparticles at the stabilization (lower) temperature of 700 C. Because Fe foam existed in a bulk state, no signicant transformation of the inert structure was noticed; thus, the TGA of the Fe foam indicated slight oxidation until at least 1000 C. As a result, both the catalytic and magnetic nanoparticles were likely to be completely consolidated with the Fe foam through heat treatment at 700 C, although increasing the temperature might improve this consolidation to some extent.…”