فصلنامه نانو مواد
پیاپی 3 (پاییز 1388)

In this research, electrodeposition of nanocrystalline Ni–Co alloys thin films was studied by electrochemical techniques. Cyclic voltammetry and current transient measurements were used to characterize the Co–Ni system in order to obtain the nucleation and growth mechanism. The cyclic voltammetry results clearly showed that electrodeposition of cobalt, nickel and Co–Ni alloy is diffusion-controlled process with a typical nucleation mechanism. The redox potentials of the Co and Ni are shifted to more cathodic potentials in the Co–Ni alloy system. In addition, the current transients revealed that nucleation mechanism is instantaneous with a typical three dimensional (3D) nucleation and growth process. The number of nucleation sites is increased with the overpotential and nickel or cobalt concentration. It was found that addition of nickel sulfate to cobalt solution, resulted in increasing the number of nucleation sites and therefore the nucleation rate of the Co–Ni alloy system is increased. However, AFM analysis showed that alloying cobalt thin films with nickel changed the microstructure. In this condition, a large number of equally sized spherical grains are observed in single cobalt deposits, while the rectangular particles are deposited in the Co–Ni alloy system as layer-by-layer deposition.

In present work, three different methods were used for conducting the anodes. First, a thin layer of graphite was coated on the surface of NiO-YSZ composites by painting. In the second method, NiO-YSZ composites were reduced at 850 °C in hydrogen/argon atmosphere and the Ni YSZ cermets were produced. In the third method, although no methods were used for electrical conducting, only substrates with more than 50% open porosity could use. A uniform and stable YSZ suspension was applied for electrophoretic deposition in mixed acetone-ethanol medium. Afterwards, sintering was done at high temperature. Then, the current of circuit was recorded and weight of deposition and film density were calculated. Finally, microstructure of coating and its thickness were observed by SEM for green and sintered samples. By increasing electrical resistivity of the substrate, the current of circuit, weight of deposition and film density reduced. It was also detected that the size of deposited particles decreased less than 100 nm by decreasing electrical conductivity. The smallest particle size that was achieved by using the saturated substrate was 59 nm. By using substrates with high electrical conductivity, the quality of the deposited film was improved.

The objective of this study is investigation of particle size of nucleation agent effect on morphology, types of crystalline phases and microstructure of lithium aluminum silicate glassceramic. In order to achieve this aim, the Li2O-CaO-Al2O3-SiO2 system was investigated by incorporation of Nb2O5 as nucleation agent. So, glass-ceramic with spoduman as main crystalline phase, lithium metasilicate (Li2SiO3) and wollastonite (CaSiO3) as secondary phases were created. The size of Nb2O5 particles was changed into nanoscale. Crystalline phases, crystallization behavior and microstructure of the glass-ceramic were analyzed by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Changing of nucleation agent particle size to nanometric scale lead to decreasing of nucleation temperature, increasing of spoduman as major crystalline phase volume fraction, decreasing of secondary phases volume fraction and improvement of mechanical properties.

The development of new products which are abundant in nature, low in cost and have minimal environmental impact for restoration or remediation of natural resources is an important area of material sciences. The use of hydroxyapatite materials as potential sorbents for the removal of heavy metals has been emphasized in recently decade. Nanocrystalline hydroxyapatite powder was synthesized by calcium nitrate hydrated and di-ammonium hydrogen phosphate via the solutionprecipitation method followed by heat treatment. Phase evolution, were studied by XRD. TEM technique was used for estimate crystal size and morphology. Moreover, a simple kinetic growth investigation was performed on the nanocrystalline growth process during heat treatment. Results have shown nanocrystalline hydroxyapatite with hexagonal system can be successfully prepared from raw materials by the precipitation technique to 1200 °C and growth rate to increase exponentially with temperature and also the growth rate constants to increase with time.

Composite fibers (YAG/Al2O3) were prepared by sol-gel method using water as the solvent. They were synthesized from aluminium salt, aluminium metal and yttrium oxide. Transparent fibrous gels were obtained by immersing a thin wire into the viscous solution, then pulling it up by hand. Effect of yttria on crystallization and microstructure of fibers were also investigated. When yttria content was increased, the crystallization of YAG shifted to a lower temperature, whereas the transformation temperature to α-Al2O3 shifted to a higher temperature. However, the same temperature (1400 ºC) was required to obtain the fibers containing α-Al2O3 and YAG. The composite fibers were denser than alumina fibers. As the yttria content increased, the fiber diameter increased but grain size and densification of fibers decreased.

The aim of this research is synthesis of bioglass-58S nanopowders by sol-gel method. Also, effect of aging time on morphology, structure and particle size of powders for biomedical applications was investigated. Bioglass-58S powders were analyzed by X-ray diffraction pattern (XRD), Fourier transform infrared spectroscopy (FTIR), zetasizer instrument, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD result showed the powder is amorphous and glassy. According to FTIR spectroscopy, silicates bonds were formed in all powders. Zetasizer results proved that the particle sizes of powders and agglomerates were increased by aging time. The SEM images confirmed these results, too. As well, TEMobservations showed the increasing of aging time caused the growth of grain sizes between 50-200 nm. Since, these powders synthesized in nanometric scale, the reaction of materials and body can accelerate, whereupon improve bone formation process.

In this study¡ zinc silicate (Zn2SiO4) nanostructured particles have been synthesized by sol-gel process using zinc nitrate and tetra ethyl oxysilane (TEOS) precursors. Results have been shown information of amorphous and crystalline structures during increasing of calcination temperature. Structural evolutions of gel and calcined gel in different temperatures have been investigated using DTA and XRD analyses¡ respectively. Due to XRD analysis of calcined samples in 800 and 900 oC¡ and Scherrer equation has been obtained grain size 13 and 27 nm¡ respectively. Also¡ DTA analysis of precursors has been shown endothermic reaction of solvents evaporation and decomposition organic phases¡ and exothermic reaction of Zn2SiO4 composition. Furthermore¡ SEM observations showed negligible difference between powder size of amorphous precursors and crystalline Zn2SiO4 were between 50 and 400 nm. Moreover¡ UV-visible spectroscopy analysis for photocatalyst properties has been shown acceptable results.