Key Engineering Materials Vols. 306-308

Abstract: A phase mixture model (PMM) was considered in which materials are treated as a mixture of grain interior phase, grain boundary phase and pores (if the material is porous) for the elasticity and plasticity of nanostructured materials (NSMs). In order to investigate the effects of grain size and porosity on the elastic modulus, a self-consistent method in conjunction with PMM was employed. The calculated results are compared with the experimental measurements in the literature. The elastic modulus of NSMs decreases with a decrease of the grain size and the decrement is relatively large at grain sizes below about 10 nm. The effect of porosity, however, is substantially greater than the grain size effect. For the plasticity of NSMs, grain size effects were introduced both via the dislocation glide mechanism and through the diffusion mechanisms providing mass transfer via grain boundaries. A good agreement between the calculated deformation behavior and experiment was found. The quality of the above predictions with regard to strength, strain hardening, strain sensitivity and ductility behavior testify the adequacy of the model. It is concluded that the model can be used as a convenient tool for simulating the deformation behavior of NSMs.

Abstract: Hollow polystyrene nanocapsules with sizes of ~100 nm have been prepared via a miniemulsion polymerization process by applying the encapsulation of a nonsolvent (i.e., isooctane). Divinylbenzene has been added to styrene as a cross-linking comonomer in order to improve a structural stability of the hollow polymer capsules. Morphology variation of nanocapsules with concentrations of divinylbenzene and also isooctane has been studied using transmission electron microscopy analysis. Kinetic study on the miniemulsion polymerization of styrene in the presence of divinylbenzene and isooctane has been carried out using fractional conversion data determined by the gravimetric analysis.

Abstract: Nanocrystalline CeO2 has been synthesized at room temperature using water-in-oil (w/o) microemulsion technique. The structure and properties of the nanocrystalline CeO2 were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and gas adsorption desorption measurement. XRD results showed the synthesized CeO2 has a face centered cubic structure with crystallite size of about 5.2 nm. TEM observation also indicated the presence of nanometer sized particles of CeO2. Coarser particles were also observed due to agglomeration. Gas adsorption desorption isotherms showed the behavior of fine particles with mesoporous structure.

Abstract: Nanocomposite Al2O3-Co was prepared by high-energy ball milling technique. Nanoscaled alumina particles (γ-Al2O3) of 5wt% with nominal size 39 nm were dispersed in cobalt matrix. The phase transformation of the element occurs in the powders mixture during the process was monitored by X-ray diffractometry (XRD). The results showed that cobalt exhibits phase transformation when subjected to ball milling. The phase formation of cobalt was found to depend on the milling intensity. As the milling time increased, the amount of the hexagonal close-packed (hcp) phase decreased.

Abstract: Magnetic iron oxides nanoparticles were synthesized at room temperature using water in oil microemulsion process. This microemulsion system was prepared using HTAB (surfactant), noctane (oil), 1-butanol (cosurfactant) and aqueous salt solution of Fe2+ and OH-. The microemulsions were used as microreactors for controlling the growth of the particles. The nanoparticles were characterized using TGA, XRD, TEM, BET, DLS and AGM. X-ray diffraction analysis revealed that the magnetic nanoparticles could be directly formed at room temperature. It also showed that the particles were either maghemite (γ-Fe2O3) or magnetite (Fe3O4). TGA thermogram showed two significant weight losses at around 100°C and 250° C, which were caused by dehydration and burn off of the surfactant. The surface area of the magnetic particles measured using gas absorption and desorption technique was 105.43m2/g, which indicated the presence of particles of 21nm in length. The size measured by TEM and DLS was 105nm and 107.9nm respectively due to the formation of large aggregated clusters. The sample also showed strong magnetic properties with the value of Ms of 11.2 emu/g.

Abstract: Stoichiometric nanocrystalline Ni3Al was prepared by mechanical alloying of elemental Ni and Al powders under argon gas atmosphere for different time (4-48h). The nanostructured Ni3Al powders were consolidated into bulk compacts and sintered in a small DTA furnace under flowing Argon to observe the exothermic reaction between the stoichiometric Ni and Al. The estimated crystallite size showed that the mechanically alloyed Ni3Al grain size decrease from 127 nm to 9.36nm with increasing mechanical alloying time from 4h to 48h. Agglomerations of the powder particles prevalently occurred as observed from the SEM micrographs. Saturation magnetization, Ms value of the mechanically alloyed powders decreases as milling time increases due to smaller amount of elemental nickel responding to the applied fields. Following reaction synthesis of the compacted powders, thermal profile analysis revealed the presence of exothermic peaks in the DTA curves at about 400oC. Relative densities of the sintered compact were measured and found to be from 77- 88% with the exception for the 48h mechanically alloyed sintered compact from milling balls contaminations. XRD results of the sintered compacts mechanically alloyed for 18h and above revealed the formation of pure nanocrystalline Ni3Al. Crystallites size estimations showed the occurrence of grain growth during sintering.

Abstract: Nanostructured silica and silica-iron composite particles were prepared using water-in-oil (w/o) reverse microemulsion. Double microemulsion technique is used for the synthesis of both types of nanostructured particles. X-ray Diffractometry (XRD), scanning electron microscopy (SEM), nitrogen gas adsorption-desorption isotherm technique, and differential scanning calorimetry (DSC) were used to characterize the synthesized particles. The gas adsorptiondesorption measurements revealed a mesoporous structure for the silica (SiO2) particles with a surface area of 300.49 m2/g. Upon the addition of an iron microemulsion to the silica microemulsion, silica-iron nanocomposite (Fe2O3-SiO2) was achieved which gave a surface area of 69.87 m2/g. This indicated a positive impregnation of the silica mesopores that was further confirmed by energy dispersive spectrometry (EDS). The XRD of bare SiO2 gave a single broad peak whereas SiO2-Fe2O3 demonstrated additional peaks confirming α-iron insertion in mesoporous silica. DSC curve with its characteristic peaks also indicated the presence of iron nanoparticles within silica. The product silica-iron nanocomposite has potential catalytic and semiconducting applications.

Abstract: The traditional finite element analysis method in conjunction with the atomic simulation technology was applied to study the mechanical properties of nanostructure materials. A phase mixture model in which nanocrystalline material is regarded as a mixture of crystalline phases and intercrystalline phases (grain-boundary, triple line junction and quadratic node) and pores is presented. The Morse potential function was used to simulate the nonlinear constitutive model of grain boundary phase of NC Fe. The effects of grain size and porosity were investigated in the literature. The calculated results are compared with previously published experimental data.

Abstract: The wave function expansion method is engaged for the theoretical derivations to study the effect of material parameters perturbations on the resonance acoustic scattering behavior of 1-3 piezoelectric composites. Numerical examples are provided to verify the effectiveness of the analysis. Results obtained are meaningful for the non-destructive evaluation of 1-3 piezoelectric composites.