Nickel nanoparticles (NPs) are widely used in many fields, but contact with oxygen leads to structural damage and degradation of their properties, so a comprehensive understanding of their oxidation mechanism is of great importance. In this work, we performed reactive molecular dynamics simulations to investigate the oxidation mechanism of Ni NPs. The results show that the oxidation of Ni NPs mainly includes the formation of surface oxide nuclei, oxide extension to form oxide layers covering the surface, and the inward growth of oxide layers. We have investigated the structure of the oxidation products and found that it consists of Ni–O tetrahedra interconnected by sharing one Ni atom. In addition, the effects of initial oxygen concentration, temperature, and humid environment on oxidation behavior are discussed. This work contributes to the understanding of the oxidation of Ni NPs at the atomic scale, which helps in the design of anti-corrosion of Ni NPs and the preparation of novel nickel oxides.

Understanding on oxidation is critical for the improvement of aluminum melt quality which determines the properties of the aluminum alloy processed by casting. However, the oxidation mechanism of aluminum melt is still unclear in atomistic scale. In this work, we performed reactive molecular dynamics simulation to investigate the oxidation mechanism of aluminum melt on an atomic scale. Our results focus on the island-like nucleation on the melt surface and the following growth of the oxide film. The oxide grows via ion diffusion and the diffusion of O anions plays a greater effect. The evolution of the diffusion coefficient indicates an island-by-layer growth on the aluminum melt. Kinetically, the oxide growth obeys a linear law during the nucleation stage and switches to a logarithmic law after a closed oxide film forms. Besides, we emphasize the effect of oxygen content and ambient temperature on the formation of oxides. Our research can provide insights into the atomic-scale oxidation mechanism of aluminum melt which contributes to the better design for anti-oxidation methods during casting and the oxide-based functional materials.

In this paper, the solidification behavior of Al-Ti alloy in confined nanoslits is studied by molecular dynamics simulation. Results show that the solidification structure of Al-Ti alloy is determined by the synergistic effect of slit sizes and cooling rate. The slower the cooling rate and the smaller the slit sizes the stronger the crystal forming ability. During the solidification process, Al-Ti alloy tends to solidify layer by layer from the position near the confined walls. With the decrease of the slit size, the system is layered along the dimension of confinement, and in the unrestricted plane, the atoms of the system are arranged regularly, which is due to the geometric constraint effect of the confined walls and the interaction between the confined walls and Al-Ti atoms. Our findings provide insight into the solidification behavior of liquid metal in the confined space.

We report the layering and liquid–liquid phase transition of liquid titanium confined between two parallel panel walls. Abnormal changes in the volume and the potential energy confirm the existence of the liquid–liquid phase transition of the liquid titanium. The typical feature of the liquid–liquid phase transition is layering, which is induced by the slit size, pressure and temperature. We highlight the fact that the slit size and pressure will determine the number of layers. In addition, with the change in the slit size, the density of the confined liquid expresses a fluctuating law. The phase diagram of the layering transition is drawn to clearly understand the layering. This study provides insights into the liquid–liquid phase transition of liquid metal in a confined space.

Ab initio molecular dynamics calculations have been carried out to search for the ground state structure of Fe n Ti 13-n clusters and measure the thermal expansion of Fe n Ti 13-n .The volume of Fe n Ti 13-n clusters during thermal expansion is jointly determined by anharmonic interaction and magneto-volume effect.It has been found that Fe 6 Ti 7 ,Fe 9 Ti 4 ,Fe 11 Ti 2 ,and Fe 13 clusters can exhibit the remarkable magneto-volume effect with abnormal volume behaviors and magnetic moment behaviors during thermal expansion.A prerequisite for the magneto-volume effect of Fe n Ti 13-n clusters during thermal expansion has been revealed and the magnitude of the magneto-volume is also approximately determined.Furthermore,the magneto-volume behaviors of Fe n Ti 13-n clusters are qualitatively characterized by the energy contour map.Our results shed light on the mechanism of the magneto-volume effect in Fe n Ti 13-n clusters during thermal expansion,which can guide the design of nanomaterials with zero expansion or even controllable expansion properties.

In this work, we perform molecular dynamics simulations with the reactive force-field to systematically unravel the oxidation mechanism of Ni groove defects. We show that Ni atoms at the edge of groove are preferentially oxidized, and then diffuse outward with cation vacancies left. The oxidation spreads to both sides directionally by vacancies expansion. The effects of groove defect type, temperature, and oxidizing medium on oxidation kinetics are evaluated. We reveal that the oxidation degree of Ni {1 1 0} system is greater than that of Ni {1 1 1} system, owing to the different atomic arrangement. The high temperature can effectively promote oxidation. Under the oxygen environment, the oxidation directionally spread layer by layer, while the introduction of water vapor can change this mechanism, leading to the inward spreading of oxidation. We expect this work would provide theoretical guidance for the improvement of anti-corrosion measures of Ni-based superalloys.

We report theoretical evidence of the substrate-induced liquid-liquid phase transition (LLPT) behaviors in a single Al droplet and Ti-Al droplets. The Al droplet can produce an LLPT induced by substrates in part, forming a special three-layer structure. However, the introduction of a Ti droplet can promote the LLPT in an Al droplet. Al and Ti droplets do not coalesce into a homogeneously mixed droplet but produce the ordered liquid films. The substrate-induced LLPT in the Al droplet is characterized by the transition from the disordered to ordered structure. Results indicate that the substrate and the Ti droplet are the driving forces to promote the LLPT. The LLPT of the Ti-Al droplets in the wedge-shaped substrate is also observed, indicating that the confined Ti-Al droplets are more likely to undergo an LLPT.

Nanostructured black TiO2 materials prepared through a hydrogenation process have evoked significant interest in solar energy harvesting and conversion technologies due to their strong light absorption and utilization performances.