Guangzhi Song

Up-scalable synthesis, structure and charge storage properties of porous microspheres of LiFePO4@C nanocomposites

Novel porous micro-spherical aggregates of LiFePO4@C nanocomposites have been synthesized in large quantities via an improved sol–gel method combined with spray drying technology (sol–gel-SD method), which required no surfactants or templates. With this new procedure, a precursor was prepared through the process of sol–gel and subsequent spray drying. A series of analyses, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and a combined system focused ion beam (FIB)/SEM were performed after the as-obtained LiFePO4@C was heat-treated at 700 °C for 12 h. The as-obtained LiFePO4@C had a large specific surface area (20.2 m2g−1), with an average nano-size of 32 nm and a main pore diameter of 45 nm. Contact with electrolyte occurred easily, which facilitated the electrical and lithium ion diffusion. In comparison with nano-sized LiFePO4@C particles prepared by a sol–gel method, the current product presented a high coulombic efficiency of 97.2%, a large reversible capacity of 133.8 mAh/g and an excellent capacity retention rate close to 100% after 50 cycles. The sol–gel-SD method provides an additional strategy to easily deal with gelatin and shows potential for use in the preparation of similar superstructures of other composites.

Interdiffusion Behavior of Ni–Cr–Al–Y Coatings Deposited by Arc-Ion Plating

Ni–Cr–Al–Y coatings were deposited on the Ni3Al–base superalloys IC-6 and K17 by arc-ion plating. The results indicated that a small amount of substrate atoms, such as Co, Ti, Mo, etc., existed in the Ni–Cr–Al–Y coatings near the substrates, probably due to “sputter” and “antisputter.” For the alloy K17, the impeding effect of Al was not obvious, because the temperatures of the substrate and the coating were high (420–480°C) during the deposition process and interdiffusion was accelerated. However, for alloy IC-6 which contains Al, as well as a high concentration of Mo, the diffusion of Cr was impeded. Vacuum heat treatment at 1050°C drastically increased diffusivities and the presence of Al and Mo was not enough to prevent some Cr diffusion. Thus, the coating became more uniform and close to the desired composition.

Influence of quantity and energy of the particles in gas phase on nucleation of the HFCVD of diamond films

In this paper, the nucleation of diamond films was studied with the varied bias value and mass current density by adjusting the gas flow rate through the chamber. Results showed that the two parameters above greatly influenced the nucleation density and the morphology of diamond films. Both bias value and mass current density had an optimum value in which the nucleation density reached the maximum. The nucleation of diamond films by hot filament chemical vapor deposition (HFCVD) is a competitive process of deposition and etches (sputtered) due to particle impact on the substrate. The magnitude of the particle energy in gas plasma and mass current density of gas controlled the competitive process and determined whose process was primary. The deposition process was gradually strengthened and the nucleation density increased due to the increment of the energy and quantity of the adatoms and reached a maximum at optimization with the increment of the two parameters mentioned above. The deposition process is suppressed by strengthened particle impact on substrate and the etch (sputtered) process was primary with the further increment of the two parameters above.