نشریه علم و مهندسی سرامیک
سال پنجم شماره 2 (پیاپی 16، تابستان 1395)

In this study, nanoporous anodic aluminium oxide (NAAO) layers were synthesized by mild and mild-hard anodization two methods in a solution of oxalic acid and NAAO-Sm3 nanocomposite were synthesized by boiling the (NAAO) layers in a solution of samarium nitrate. Then, the samples were annealed at different temperatures under argon atmosphere. For characterization of the morphology, phase structure, energy levels, and emission wavelengths of the NAAO-Sm3 nanocomposite layers from a field emission scanning electron microscope (FE-SEM), x-ray diffraction (XRD), and photoluminescence (PL) spectroscopy were respectively used. The results indicate that increasing annealing temperature leads to decreasing the PL spectra intensity at wavelengths of 397 and 433 nm that related to (oxygen vacancies) but the PL intensity of the NAAO-Sm3 nanocomposite layer is increased at 400 nm wavelength. With the excitation of the NAAO-Sm3 nanocomposite layer at 400 nm wavelength, four main emission bands of the 4F-4F intra-configuration transitions of ions Sm3 were clearly observed. These transitions include 4G5/2 → 6H5/2 (556 nm, green) and 4G5 2 → 6H7/2 (601nm, orange), 4G5/2 → 6H9/2 (647 nm, reddish), and 4G5/2→ 6H11/2 (709nm, red), respectively

Self-propagation high-temperature synthesis due to good properties such as low equipment and the economy is a suitable route for the synthesis of engineering materials. In this study effect of activation on SHS synthesis of TiB2-TiC-Ni cermet with 15 wt% Ni content was investigated. Starting materials were activated 3h and under Ar atmosphere. After activation, green powders pressed to cylindrical shape. Synthesis process was done in the tube furnace at the temperature of 1000°C under Ar flow. XRD pattern shows that nanocrystalline TiB2 and TiC were synthesized. The crystallite size of synthesized samples has been calculated by Rietveld method. The average crystallite size of TiB2 and TiC phase in the sample with 15 wt % Nickel was 68 nm and 30 nm, respectively. Also, SEM images show that activated sample have finer and more uniform microstructure.

Stabilized zirconia has desirable properties including high hardness, high chemical stability and a thermal expansion coefficient close to metals. Therefore, in this study, zirconia-yttria-Benzotriazole hybrid based coatings were applied on the surface of AA2024 by sol-gel method. To this aim, zirconia and zirconia-yttria-Benzotriazole solutions synthesized by alkoxide precursors were applied on the surface by immersion process, and then heat treated at 150°C. Phase analysis, morphology and the chemical bond properties were investigated by GIXRD, FESEM and FTIR, respectively. Furthermore, corrosion properties were evaluated by electrochemical methods such as polarization and electrochemical impedance techniques in 3.5% NaCl solution. Results showed a homogeneous and crack free zirconia-yttria-Benzotriazole hybrid coating, which exhibited proper corrosion resistance.

Considering the importance of magnetic nanoparticles in applications such as magnetic storage, bio, high frequency materials, catalysts and petroleum industries, the nickel ferrite nanoparticles (NiFe2O4) by coprecipitation method were created on the surface of carbon nanotubes that are covered with polyaniline. Seeding polymerization were selected for the polymerization process. This polymer contain many suitable places for germination of ferrite nanoparticles. Structural analysis of materials by X-ray diffraction (XRD) was performed . Using the Scherrer equation, average crystallite size were obtained 11.6 nm. infrared spectroscopy Testing (FTIR) were done in the range of 300 cm-1 to 4000 cm-1. Two absorption bands were seen in 416 cm-1 and 594 cm-1 that relate to the vibration of metal ions in the spinel structure and peaks relate to carbon nanotubes and conductive polyaniline were detected. Furthermore the results of UV-Vis curves confirms that polymerized nanotubes are made. According to the pictures obtained from scanning electron microscopy (SEM) and transmission electron microscopy (TEM), This nanocomposite contains carbon nanotubes with uniform coating of polyaniline and spherical ferrite nanoparticles with average diameter of 8.31 nm.

The mechanical milling method was used in this study to investigate the effect of adding Cr2O3, ZrO2, and Nb2O5 on the sintering behavior and microscopic structure of alumina ceramics. To this end, alumina powder was used as raw material and Cr2O3, ZrO2, and Nb2O5 powders as additives in weight proportions of approximately 0.6%, 10%, and 1 wt% respectively. Composite powders were pressurized at 300 MPa inside a metallic forming mold. The samples were then sintered at 1300 to 1500ºC for 2 hours in the furnace. The x-ray diffraction method was used for identifying the resulting phases and a scanning electro-microscope (SEM) for examining the resulting microstructures. The results showed that adding the above oxides caused an increase in the density and hardness of the sintered sample, which reached their respective maxima at 1500°C. The greatest density and hardness were obtained for the alumina-Nb2O5 sample as 3.78 g/cm3 and 1292 HV respectively. On the other hand, the grain size of the matrix in the alumina sample increased after the process of sintering in the presence of the above oxides was completed, reaching a maximum value of 3.68 mμ.

In this study, zirconium carbide (ZrC) coatings are electrodeposited on zirconium substrate by electrolysis from molten salt at 772 oC. Electrodeposition is carry out at 120 and 380 mA/cm2 as electrolysis current densities. The coatings have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR) methods. Corrosion resistance of coatings are investigated using potentiodynamic polarization test in a solution containing boric acid (H3BO3) and lithium hydroxide (LiOH) at pH= 6.85. The production of zirconium carbide coatings has been confirmed by XRD, FTIR and EDX analysis methods. The results show that zirconium carbide coatings improve the corrosion resistance of zirconium. Moreover, the passivation zone has been expanded by ZrC coatings. The electrodeposition current density shows incredible effect on electrocrystallization, nanostructure and consequently corrosion resistance of ZrC coatings. As the coating electrodeposited at 120 mA/cm2 shows lower corrosion rate. Nanostructure, coherency of ZrC particles, and absence of cracks in the coating are affected this behavior of zirconium carbide coatings.

The purpose of this research is to improve the thermomechanical properties of yttria stabilized zirconia (YSZ) thermal barrier coating through replacing ceria stabilized zirconia (CSZ) were applied by thermal spray technique on IN738LC base metal. In the present investigation the thermal expansion behaviors of the IN738LC, NiCrAlY, YSZ and CSZ coatings were tested. Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) were used to determine the crystallographic structure and phase transformation. The experimental results indicate that the thermal expansion within the CSZ is higher than of the YSZ. Also experimental results showed that CSZ layer formed has a porous structure whereas porosities were smaller than YSZ layer