Nano-sized SiO2 Research Articles

Nano-Sized SiO2 Sol-Gel for Structure-Controlled Optical Coatings

Sol-gel process of TEOS in the presence of amphiphilic polyethylene oxide (AEO) was investigated by the particle size distribution (SDP) and transmission electron microscopy (TEM). The results indicated that AEO influenced seriously both hydrolysis and polycondensation of TEOS, leading to the formation of the network in short order. With such kind of SiO2 sols, Two-layer SiO2 anti-reflective (AR) coatings were prepared by spin-coating, which showed high laser damage threshold.

The effect of magnetic interaction in barium hexaferrite particles

The effect of interactions on the magnetic relaxation of nanocrystalline hexagonal barium hexaferrite BaFe10.4Co0.8Ti0.8O19 is discussed. We had previously shown that according to the T ln(t/τ0) scaling, an enhancement of the lowest-energy barriers was detected when demagnetizing interactions were dominant. Also, the Henkel plots obtained for particles of about 10 nm of mean diameter showed that the overall interactions were demagnetizing. In the present work, we have modified the interactions by milling the particles with a nanosized SiO2 powder. Dipolar interactions are modified by breaking the particle aggregates. The observed overall interactions resulted to be also demagnetizing for the milled sample. The time dependence of the magnetization was analyzed according to two different procedures: the fluctuation field and activation volume analysis and the T ln(t/τ0) scaling. Activation volumes were found to increase with demagnetizing interactions and the leading demagnetizing mechanism appeared to shift from an individual particle mode for the unmilled sample to a collective one for the milled sample. The second approach showed larger relaxation rates at short times for the milled sample. The effective energy barrier distribution obtained from the scaling suggested that demagnetizing interactions increased in the milled sample, which led to an enhancement of the amount of the lowest-energy barriers.

Preparation and Formation Mechanism of Silica-Encapsulated Palladium Particles by Spray Pyrolysis

Silica-encapsulated palladium particles were formed from a palladium nitrate solution containing ultrafine SiO2 particles by ultrasonic spray pyrolysis. The mechanism of the formation of the encapsulated particles was investigated. A precursor particle formed below 700°C in the drying stage was composed of the homogeneous mixture of the nano-sized SiO2 and PdO⋅xH2O particles. When PdO is decomposed above 700°C, metallic palladium particles are formed in the matrix of silica. Because of the high surface free energy, the metallic palladium particles coagulate and condense to the composite particle interior. As a result of the relocation within the composite particle, SiO2 is forced out of the particle towards the surface to form a silica-encapsulated palladium particle.