Nano-sized SiO2 Particles Research Articles

The formation of nano-size SiO2 thin film on an aluminum plate with hexamethyldisilazane (HMDSA) and hexamethyldisiloxane (HMDSO)

This study is using HMDSA (C6H19NSi2) or HMDSO (C6H18OSi2) vapor into C3H8/air premixed flames to form SiO2 thin film on the surface of an aluminum plate. With the addition of HMDSO or HMDSA to premixed flames, an orange secondary flame or a flame brush appeared and was contributed to the formation of SiO2 particles. Based upon the EDS, XPS and FTIR analysis, it is believed that the synthesized products consist of mainly SiO2 and a small amount of SiO. The pure SiO2 crystal structure, was proved by XRD analysis, which may form from the SiO2 amorphous structure after high temperature (1300°C) thermal treatment. The nano-size SiO2 particles, which ranged from 2.5–25 nm, are proved by analysis of the BET and TEM. A 2-D CFD-RC code with 12 reduced chemical reaction mechanism, based upon the SIMPLER procedure, was successfully employed to predict the flame temperature and both of the SiO2 and SiO concentration profiles. Compared with the experimental results, the calculated temperature profiles in the post-flame region are in good agreement with the measured data and observation phenomena.

T⋅ln(t/τ) scaling approach and fluctuation field analysis in interacting particulate systems

The time dependence of the magnetization in samples having a different degree of interparticle interactions is analyzed. The selected compound was a nanocrystalline powder of the composition BaFe10.4Co0.8Ti0.8O19 with and without an admixture of nanosized SiO2 particles. Two different approaches were considered for the analysis of the thermally activated demagnetization: the T⋅ln(t/τ0) scaling of the thermomagnetic relaxation in zero applied field, and the classical fluctuation field and activation volume analysis. The energy barrier distribution obtained from the former approach shows that the occurrence of larger demagnetizing interactions leads to a relative enhancement of the lowest energy barriers with respect to the largest barriers. Activation volumes are found to increase with demagnetizing interactions and the leading demagnetizing mechanism appears to shift from an individual particle mode (coherent or nucleation) to a collective one. Both analyses are suggested to be taken into account in order to ascertain the influence of interactions on the magnetic properties of nanocrystalline particles.