Advanced Ceramics Progress
Volume:1 Issue: 1, Spring 2015

The purpose of this research is to investigate the mechanical and electrical properties of nano structured cordierite. Nano grain size powders were synthesized through mechanical activation by high-energy ball milling of the starting powders containing 34.86 wt% Al2O3, 51.36 wt% SiO2, and 13.78 wt% MgO. Samples were prepared by conventional and microwave sintering at 1390°C. SEM observations illustrated the equiaxed nano-grains of cordierite with an average grain size of 40 nm for samples sintered in microwave. With the increase of milling time, samples sintered at 1390°C in microwave furnace obtained higher micro-hardness and density than those sintered at temperature in conventional furnace. Sample milled for 30 h and sintered in microwave furnace at 1390 C obtained the maximum dielectric constant of 5.5±0.1.

Oxyfluoride glass- ceramics containing CaF2 nano- crystals doped with Y3+ ions were prepared by onestep crystallization of SiO2- Al2O3- CaO- CaF2 glasses at different temperatures. X-ray diffraction (XRD) results have revealed that CaF2 was the only precipitated crystalline phase in glass- ceramic samples. According to the XRD results, a glass- ceramic was selected as the best sample in order to compare its optical properties with basic glass. Photoluminescence (PL) and UV-Vis spectra are utilized to check optical properties of glass and glass- ceramic samples. A broad emission band in the visible region was determined, which was stronger in the glassy sample. Scanning electron microscopy (SEM) observation and EDX (Energy-dispersive X-ray spectroscopy) results establish the doorway of Y3+ ions into just some of the crystals embedded in the glassy matrix, that was the rational reason of photoluminescence intensity decrease in glass-ceramic.

In this research, calcium titanate nano-particles were synthesized via mechanical alloying. To synthesize this compound, a mixture of calcium hydroxide and titanium dioxide, rotation speed of 250 rpm and differnet ball to powder weight ratio (10:1, 20:1, 30:1 and 50:1) were used. Phase investigation, morphology and structure of calcium titanate powder obtained were evaluated by X-ray diffraction, scanning electron microscopy and Energy-dispersive X-ray Spectroscopy respectively. The results of the X-ray diffraction analysis confirmed the formation of single-phase calcium titanate nanoparticles with cubic crystal structure. The agglomeration of powder has been shown in scanning electron microscope images. According to the results, the minimum of ball to powder weight ratio to synthesize this compound was 50:1 and milling time of 60 hs. The results of Zeta-sizer showed that the major part of the particle size distribution was in the range between 60 to 80 nm and this confirms the results of Williamson-Hall equation and scanning electron microscope images. Also, by using of Nelson-Riely and Cohen equations for calculating the lattice parameter, it was found that increasing milling time to 60 hs, leads to lattice parameter values to be closed to ideal values of calcium titanate phase.

Molecular dynamics simulations were applied to calculate self-diffusion coefficients (D i,self) and heats of adsorption for ethane, propane and n-butane. Simulations were done in temperature range of 300- 525 K for various concentrations inside the pores of silicalite type zeolite. Calculated values of selfdiffusion coefficients and heats of adsorption resulted from the current work, were in better agreement with experimental estimated values found in literature than those resulted from simulations reported by other authors. For instance, at temperature of 300K and loading of 5 molecules/unit cell, self-diffusion coefficients of 16.56×10-5, 7.62×10-5 and 5.81×10-5 cm2/s were calculated for C2H6, 3H8 and n-C4H10 respectively was compared to experimental reported values of 10×10-5, 9×10-5 and 6 10-5 cm2/s. At the same conditions, adsorption energies of 9.2, 11.48, and 13.66 kcal/mol. were calculated for ethane, propane, and n-butane respectively, while the experimental reported values found to b 6.93, 9.7 and 12.7 kcal/mol. Simulations showed that the diffusion decreases when loading increases and the heats of adsorptions were increase by molecular weight of hydrocarbons for all adsorbates studied.

In this study, Thermal expansion coefficient variation of Ln0.6Sr0.4Co0.2M0.8O3−δ (Ln=La,Nd,Sm and M= Fe,Ni,Mn) perovskite oxide were evalouated. Different compounds were prepared and thermal expansion coefficient were meseaured in different temperature by means of dilatometer analysis. Structural parameters of compounds were determined by X-ray diffraction and Field Emission Scanning Electron Microscopy (FE-SEM) was used for the morphological study. Using Nd + instead of La3+ led to tilting of the BO6 octahedra, phase transition from rhombohedral to the orthorhombic. Experimental results showed TEC decreases favorably with substitution of Nd3+ and Mn + ions in the lattice.

In this work, the result of additives on electrophoretically deposited patterns of ceramic nanoparticles with totally different chemical composition in the case of using AC electrical field are studied. For this purpose, by the assistance of coplanar electrodes with an interelectrode gap size of 150 μm, heterogeneous AC electrical field was applied to the suspensions of TiO2-acetone and WO3-acetone in the presence and absence of Polyethylenimine (PEI) as an additive at the frequency of Hz. The results verified that whereas WO3 nanoparticles tend to fill the gap once additive was not used, they show no tendency to enter it within the presence of PEI. However, TiO2 nanoparticles that leave the gap once additive was not applied, fill it in the presence of PEI.

In this study, the correlation between impurity content of reagents used (monetite and brushite both from Merck), soaking time and firing temperature in the solid state synthesis of α tricalcium phosphate (α -TCP) has been established. Mg impurity promoted formation of β-polymorph as a second phase in the resultant product. The extension of firing operation also led to an increase in the amount of α-TCP, higher firing temperature with an Equivalent soaking time resulted in a more purely synthesized α- TCP. The amount of α and β phases at each heating program were investigated through Match software system. The highest percentage of obtained α-TCP in the resultant product with the monetite precursor containing 0.43 wt.% magnesium impurity at 1350°C and 16 hours of soaking time was about 94%.

In this research, a numerical modeling method was utilized to calculate the stresses occurring during the thermal cycling in a functionally graded thermal barrier coating (FG - TBC). The temperature – dependent material response of this protective material was taken into account and the effects of the thermal cycle and interface morphology of the ceramic /metallic layer in a functionally graded coating system was investigated. Sinusoidal mode of asperity with specific wavelength and amplitude was used to model the two dimensional geometry of interface profile between layers. A finite element model was used to model the effect of the thermal loading imposed on the thermo mechanical response and stress distribution. In this regard, different observable facts were taken into account in the model such as: non- homogenous temperature distribution, periodic boundary condition and convective heat transfer. These phenomena depict the most real world situation in numerical simulation of multi-layer coating during cooling and thermal cycling, specifically near the ceramic/metal interface. In addition, regions which are potent to crack initiation and propagation in the system and the subsequent delamination places of the TBCs system were predicted.