CERAMIC SCIENCE & ENGINEERING
Year:2016 | Volume:5 | Issue:1|Papers Count:7

One of drawbacks of solid oxide fuel cells (SOFCs) is high temperature ionic conductivity of their electrolytes. Several researches have been done to find a solution to overcome the problem. One method is to incorporate co-doped cerium oxide (Ceria) with metal salts such as carbonates. In the present work, nanopowders of calcium and samarium co-doped cerium oxide of Ca0.05Sm0.2-xCe0.75O1.9-d (CSDC 5) were prepared using citrate-nitrate auto combustion method. Phases and crystallite size of the sample were determined by X-ray diffraction (XRD). Field emission scanning electron microscope (FE-SEM) was used for morphological studies. The XRD pattern showed that a single-phase solid solution of calcium and samarium co-doped ceria was obtained. The crystallite size of the particles was 19 nm in diameter as calculated from data obtained through XRD result of (111) peak. FE-SEM images depicted that synthesized CSDC 5 powders were sphere-like and approximately 20 nm in size. Also, it was shown that the sintered CSDC 5 had a dense microstructure. The ionic conductivities of all samples were determined by AC impedance spectroscopy (EIS) in temperature range of 250 – 650ºC. EIS results demonstrated that Ca0.05Sm0.2Ce0.75O1.9- d had total conductivity of 0.015 S.cm-1 at 650 ºC. CSDC 5 – (Li, Na) 2CO3 (CSDC 5 – LN) nanocomposite electrolyte was synthesized by mixing the lithium and sodium carbonates with CSDC 5 nanopowders. XRD pattern of the composite sample was similar to the patterns of ceria and CSDC 5 which indicates that the carbonate phase was probably amorphous. TG/DTA thermal analysis results demonstrated that the carbonate phase was remained and undecomposed up to temperature of 730ºC. FE-SEM images of the composite powders depicted that CSDC 5 powders were covered by carbonate phase. In addition, the sintered composite showed a porous microstructure using FE-SEM. EIS data proved that above the temperature of 500ºC, total ionic conductivity of CSDC 5 – LN was 0.073 S.cm-1 which was nearly 5 times higher than that of CSDC 5. This implied that using carbonate phase would increase the total ionic conductivity due to multiple ions of Na+, Li+, and CO2-3 would be involved in ionic conduction at the mentioned temperature range. This makes it a serious candidate as electrolyte material for low temperature solid oxide fuel cell (LT-SOFC).

In the present research the nano- sized La0.8Sr0.2MnO3 (LSMO) powder was synthesized using a simple sol-gel method. Microwave absorbing materials consisting of 80wt% carbonyl iron (CI) particles and LSMO with different proportions of CI: LSMO being 80: 0, 79: 1, 77: 3, 74: 6, and 72: 8, respectively, and 20wt% molten wax are investigated in the frequency range of 8-12 GHz. The composite materials in the form of paints were applied on an aluminum substrate (22.8×10.1×0.8 mm3) with the thicknesses of 0.7, 0.9 and 1.1 mm, respectively. Phase analyses and crystallite size of the LSMO powder, morphology of particles, and the electro–magnetic (EM) absorption properties (8-12 GHz) of the paints were determined using X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM), and vector network analysis (VNA), respectively.The composite with a CI/LSMO ratio of 74: 6 showed an optimal reflection loss of–10.89 dB at 11.55 GHz with a matching thickness of 0.9 mm. By increasing the thickness of coating from 0.7 to 1.1 mm, the average absorption properties were increased. Therefore, CIP/LSMO composites were characterized as super-thin electromagnetic absorbers with a wider absorption bandwidth in GHz frequency bands.

In this paper, the effect of sodium phosphate salt concentration in the electrolyte on the electrochemical behavior and microstructure of plasma electrolytic oxidation coating formed on the 2024 aluminum alloy is studied. In order to evaluating the corrosion behavior, samples are immerged in 3.5 wt. % NaCl solution and then potentiodynamic polarization test and electrochemical impedance spectroscopy measurement are conducted. The microstructure of ceramic coating are investigated by X-ray diffraction (XRD) pattern and scanning electron microscopy (SEM) images. According to the results of corrosion tests can be found that increasing the concentration of sodium phosphate weaken the corrosion behavior of coating. Also, XRD pattern is shown the formation of ceramic compounds on the substrate. From SEM images can be concluded that increasing the sodium phosphate concentration in the electrolyte, leads to increasing the surface porosities and decreasing the thickness and quality of coating.

In this research the effect of polyethylene glycol and Polymethyl methacrylate surfactants were investigated on physical and radar absorption properties of barium hexaferrite synthesized via Sol-gel combustion method. In order to scrutiny investigate the phase, morphology and magnetic properties of final product X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) were used respectively. Also, electromagnetic parameters of synthesized samples were evaluated by using a vector network analyzer (VNA) device in the radar bands of X and Ku. As a result, the presence of polyethylene glycol as a surfactant has strongly influenced on the final phase purity. SEM represents the hexagonal particle morphology was prepared for all samples.According to the magnetic studies the greatest amount of saturation magnetization (56emu/g) and coercivity (5240 Oe) was achieved for the sample synthesis in the presence of Polyethylene Glycol. PEG sample X band in frequencies 11.5GHz and 10.6 GHz had the highest Reflection loss -1.5 dB and-1.8 dB. The width of the absorption of polyethylene glycol was better than the other two. In Ku Band the maximum absorbance value belonged to Poly (methyl methacrylate) sample which has Reflection loss -2.2 dB in frequency 17.1 GHz.Therefore, the absorption results have shown an increase in the broadband absorption in the case of using both surfactants in X and Ku bands.

Increasingly trend towards producing the larger tiles have been driving force of leading companies to develop the tile industry's technologies in order to meet needs and different tastes of end-users, architectures and building engineers. Apart from technological difficulties (pressing, handling of green and dried tile, applying the engobe, glaze and different decors, firing, surface treatments, sorting), the problems resulting from the being greater tile affect more on strength of tiles in green, dried and fired states. Therefore, designing the tile body formulations with sufficient green, dried and fired strengths having the ability to traverse from press to packaging phases is very important. On the other hand, the consecutive sampling from production line (including measuring the bending strength) is vital to ensure the process validity. Breaking the 20×20 cm2 tile is not a costly test but taking the same test on a large tile (for example 3.20×1.60 m2) is meant that a large area of a valuable product is rejected. The importance of nondestructive procedures is that we can evaluate the fired strengths of produced tile bodies reliably, without rejecting the product. In this paper is presented a nondestructive method based on Weibull statistical distribution model for evaluating the fired three point bending strength of unglazed tiles. Drop in fired strengths of samples tested by this method is negligible and it is possible to return those in production process for sorting and packaging.

The purpose of this research was to compare different reduction methods of alumina-cobalt composite from cobalt aluminate spinel. For this approach, the reduction of spinel with three methods of coke bed, reaction reduction with aluminum powder and reaction reduction with aluminum powder during sintering were investigated. The comparison of the results showed that the coke bed method was too time consuming which finally lead to excessive growth of the metal grains. The density of the sample which prepared from reaction reduction after sintering was 87% of theoretical density, while the density of the sample prepared from reaction reduction during sintering was 95%. The bending strengths of the reduced sample after sintering and during sintering were 227 and 354 Mpa respectively and The hardness of those samples were 7.2 and 9.1 Mpa.m1/2 respectively. With comparison of these results, it is clear that the reaction reduction during sintering method was a better way with no extra heat treatment and fines microstructure. Although this method can solve the wetting problem between metal and ceramic and leads to higher density which helps better mechanical properties.

Fused silica ceramics prepared by gel casting method. We studied the effect of temperature and time on the crystallization and microstructure of this ceramics at 1200, 1250, 1275, 1300 and 1350oC for 1, 2, 3, 4 and 5 hours. Results shows that to avoid the formation of crystalline phase in the bodies, these parts should be sintered at temperatures less than 1300oC. The best conditions for sintering this bodies is temperature at 1250oC for 5 hours, the density, porosity and water absorption of pieces that were obtained in this condition respectively were 1.95g/cm3, 10.47% and 5.83%.