فصلنامه نانو مواد
پیاپی 18 (تابستان 1393)

In this paper, the crashworthiness of thin-walled columns made of epoxy/silica composite was investigated. Two size of silica nanoparticles, nominally 17 and 65 nm in diameter, were used. Nanosilica particles were dispersed almost homogenously in the epoxy resin up to 4.5 wt.% in three series of composite. First series of composites reinforced by particles with 17 nm in diameter, second series of composites reinforced by particles with 65 nm in diameter and finally, third series of composites reinforced by combination of both. All specimens were tested under quasi static loading using a servohydraulic instron machine. A scanning electron microscopy was used for fracture surface studies. The results show that the crash worthiness was decreased by the addition of the nanoparticles, and structures were collapsed under unstable and catastrophic mode. Also, it was observed that the particle size didn’t have remarkable effect on the energy absorption capability and use of both of these particles in a composite showed a little synergy effect.

In this study, the silica refractory brick containing nano-silica sol was prepared via gel casting method and then, the effect of firing temperature on the properties of this brick was investigated. The firing temperature and thermal behavior of composition were evaluated by use of STA. Besides, the physical properties, mechanical strength, phase composition and microstructure of these refractory bricks were evaluated after firing at 1150-1400 °C range. The results showed that the firing temperature has a great effect on the properties of these bricks. The nano silica sol transforms from amorphous to cristobalit phase at 1200 °C due to its high surface area. The formation of needle-like particles of cristobalit at 1200 °C leads to increasing of porosity. Microstructural evaluations revealed that cristobalit acts as bonding phase between silica particles which, leads to increasing of mechanical strength. The increasing of firing temperature above 1200 °C leads to improvement of sintering process, decreasing of porosity and then, improvement of mechanical strength. According to results, the suitable firing temperature was found at 1300 °C.

Considering the importance of nanostructured optical thin films of II-VI group of semiconductors, through simple and cost effective chemical methods, in the present research work, while using CBD method, influence of ammonium salt concentration as a complexing agent on the structural and optical properties of the thin films was investigated. The results indicated that, beyond a certain concentration, morphology, particle size, surface roughness, film thickness, and finally the optical properties of the prepared thin films undergo appreciable changes, which can help control of the film growth and consequently lead to optimization of the optical properties.

In this research, synthesizing zinc-oxide nanostructures performed with sol-gel method. Also influence of various parameters of this method in how to synthesizing this composition studied. Phase based and morphologic evaluations of powder performed sequentially by X-ray diffraction analysis (XRD) and scanning electron microscope (SEM). Starch film based sago starch and add plasticizers sorbitol/glycerol weight ratio of 3 to 1 by casting method was developed. Zinc oxide nanorod with density of 0, 1, 3 and 5% (w/w) addet to the films before casting and films were dried at controlled conditions. Physicochemical properties such as water absorption capacity (WAC), permeability to water vaper (WVP) and water solubility of the films were measured. Also the effects of addition of nanoparticles were measured on the antimicrobial properties of the films on the surface by Agar diffusion method. Results showed that by increasing concentration of ZnO nanorod, solubility in water, WAC and WVP of the film significantly (p

In this investigation micro and nano-structured ZrO2 coatings were plasma sprayed on Ni based substrates with a MCrAlY coating. Thermal shock was applied on samples by heating in a furnace to 1200 °C and quenching in 25 °C water. SEM and XRD techniques were used for evaluation of microstructure and phase transformations respectively. Resulted life times in thermal cycling test show that number of cycles to failure for nanostructured samples is 38% more than micro structured coatings. Moreover, investigation of samples cross section show that failure of nanostructured samples has occurred near interface of ceramic coating and MCrAlY layer while failure of micro-structured samples can be seen as deep vertical cracks in ceramic layer as well. Evaluation on phases shows no transformation after thermal shock test in any type of samples. Microscopic images show that porosity distribution of micro-structured coatings is more in homogeneous than nanostructured samples. Finite element modeling was used in order to verify experimental results and it shows that thermal stress in nanostructured coatings is 70 MPa less than micro-structured ones.

Nickel aluminids are compounds with good properties such as high melting point, high strength to weight ratio and high corrosion resistance especially at high temperatures. In this study, the effect of adding Mo with atomic percentages 1, 2.5 and 5 to the nanostructured alloy with chemical composition Ni50Al50 in a planetary mill were studied for times of 8 and 16 h. The structural changes of powder particles during mechanical alloying were investigated by X-ray diffractometery and scanning electron microscopy. The crystallite size and lattice strain milled powder particles was calculated using X-ray diffraction analysis and applying methods Williamson-Hall. The results showed that the addition of Mo in the NiAl alloy refined the NiAl grains obviously. Crystallite size decreased with increasing molybdenum content, so that in NiAl samples without Mo after 16 h milling, the crystallite size was more than 100 nm and with increasing molybdenum to 5 at.%, this value was reduced to 65 nm. Also the lattice strain has increased at first and then reached to a constant value with increasing molybdenum.

In this study, boron oxide reduction by silicon and magnesium was investigated and compared for synthesis SiC-B4C nanocomposite. The material in two groups, one consist of silicon, carbon and boron oxide and other magnesium oxide, boron, carbon and silicon were weighed. Weighed powders were milled by planetary mill under argon atmosphere. Pellets were prepared by uniaxial press from milled powder. The pellets were placed in tubal furnace with argon atmosphere control at 1000 °C temperature. For phase study and calculate the average of crystallite size, the samples were analyzed by XRD at any stage of process. The sample with the appropriate synthesis conditions was performed by SEM and TEM analysis. XRD analysis showed the inability of silicon for reduction of boron oxide at this process. These results also indicate success in reduction of boron oxide by magnesium and resulting in the synthesis of silicon carbide-boron carbide composite. Average crystallite size of SiC and B4C for sample with suitable synthesis conditions was calculated 11 and 10 nm respectively. The SEM micrograph indicated the composite consists of submicron sized particles. The image of TEM analysis confirmed the results of average crystallite size calculations and showed the composite composed from grains in nanoscale range.

Warm dynamic compaction is one of the powder metallurgical techniques for the production of composites and materials with high level of work hardening. In this paper, samples were produced using warm dynamic compaction method and statistical analysis was carried out to investigate the effects of temperature and volume fraction of nanoparticles on Al6061-SiC green samples. For this purpose, monolithic and composite samples containing various volume fractions of nanoparticles were compacted dynamically. The green cylindrical compacts with approximate diameter of 15 mm and the height of 10 mm were then ejected from the solid die and their properties such as density, ejection force, spring-back, micro hardness and hardness distribution within the compacts were evaluated. Nonlinear regression and response surface development was then carried out to analyze the influence of temperature and volume fraction of nanoparticles on properties of green samples. The results show that the compaction temperature has the greatest effect on green properties in comparison with nanoparticles content. Despite of hardness reduction, increasing compaction temperature leads to counterbalance the counteractive effects of adding nanoparticles on density reduction and increase of ejection force and heterogeneity.