Advanced Ceramics Progress
Volume:3 Issue: 2, Spring 2017

The aim of this research is to investigate different X-ray based quantitative phase analysis methods for determination of cristobalite phase content in ceramic cores. For this purpose, four popular routes including peak absolute intensity method, relative intensity ratio method, direct or calibration method and internal standard (or Alexander-Klug) method have been chosen. Some control samples have been made using common raw materials used in the ceramic cores and characterized by X-ray diffraction (XRD) to measure the main peaks intensities. Using each quantitative method with their unique mathematical calculation procedures, the cristobalite phase contents have been calculated and compared to the real contents in the samples. The results showed that the presence of the amorphous fused silica phase could make drastic effects on the accuracy of the X-ray based quantitative phase analysis routes and the peak absolute intensity method showed the best results among the other routes.

The structural and optical characterization of Se-Ge alloys during melt quenching technique was the goal of this study. In this regards, five different samples of Se100-xGex (x= 10, 20, 30, 40, 50) were prepared by conventional melt quenching in quartz ampoule. The produced samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The results showed that the glass forming ability of Se70Ge30 and Se50Ge50 is so low and the structures of these alloys after quenching are combination of amorphous, GeSe2 and GeSe compounds. Although the structure of as-quenched Se90Ge10, Se80Ge20 and Se60Ge40 is fully amorphous, only Se60Ge40 shows IR transmittance (with higher 55% transmittance between 0.8-11 µm). The reflective index of this glass was in the range of 3.0 to 3.3 and decrease with increasing the wavelength. The Fermi energy, Urbach energy, indirect and direct band gaps values of Se60Ge40 glass were estimated about 0.2883, 0.1526, 1.345 and 1.28 e.V, respectively.

The effective shear and bulk viscosity, as well as dynamic viscosity, describe the rheological properties of the ceramic body during the liquid phase sintering process. The rheological parameters depend on the physical and thermo-mechanical characteristics of the material such as relative density, temperature, grain size, diffusion coefficient, and activation energy. Thermal behavior of the ceramic body during sintering process including the viscose flow deformation, anisotropic shrinkage, heterogeneous densification, as well as sintering stress, have significant influence on the both final body dimensional precision and densification process. In this paper, the numerical-experimental method has been developed to study both rheological and thermal behavior of hard porcelain ceramic body during liquid phase sintering process. After raw materials analysis, the standard hard porcelain mixture as a ceramic body was designed and prepared. The finite element method for the ceramic specimens during the liquid phase sintering process are implemented in the CREEP user subroutine code in ABAQUS. Densification results confirmed that the bulk viscosity was well-defined with relative density. It has been shown that the shrinkage along the normal axis of slip casting is about 1.5 times larger than that of casting direction. The stress analysis proved that the sintering stress is more than the hydrostatic stress during the entire sintering time so, the sintering process occurs completely. The inhomogeneity in Von-Misses, pressure, and principal stress intensifies the relative density non-uniformity. Dilatometry, SEM, XRD investigations as well as bulk viscosity simulation results confirmed that the “mullitisation plateau” was presented as a very little expansion at the final sintering stage, because of the highly amount of mullite formation.

Ilmenite, aluminum and graphite can be used to produce in-situ Al2O3/TiC–Fe composites which are used as cutting tools. Few publications can be found in the literature that discusse the effect of molar ratio of aluminum and graphite on the Al2O3/TiC–Fe formation mechanism. Therefore, the present research is designed to make the issue clear. To achieve this goal, at first, the mechanism of the Fe-TiC/Al2O3 composite formation from ilmenite, aluminum and graphite mixture with molar ratio of 1:2:1 was clarified. Then the samples with different molar ratios of aluminum and graphite were prepared. Both of aluminum and graphite ratios changed separately in this work. In the following, the samples were heat treated at 1300°C to be sure all reactions are completed. It was found that the optimum molar ratio of ilmenite, aluminum and graphite mixture is 1:2:1 because no undesired compound was detected in the products. Compared with the ratio of 1:2:1, increasing the aluminum content of the raw materials causes the TiAl3 formation while insufficient aluminum doesn’t allow the reactions to be completed. It also was found that using more graphite leads to form the Fe-C compounds and less graphite will cause the reaction not to be completed.

In this paper synthesis and characterization of a bioactive calcium phosphate glass-ceramic is presented, synthesized using a facile method. The glass-ceramic samples are synthesized with heat treating the parent glass at appropriate temperatures, where different calcium phosphate crystalline phases are grown in the parent glass samples during the heat treatment. The amounts of elements and oxides in the parent glass are determined by X-ray fluorescence analysis. Using differential scanning calorimetry method glass transition temperature of the parent glass, and the temperature range for heat treatments are determined. Several calcium phosphate crystalline phases are identified in the glass-ceramic samples. With the increase of heat treatment temperature from 540 ℃ to 560 ℃, β-Ca3(PO4)2 and β-Ca2P2O7 crystalline phases become the dominant crystalline phases among the other crystalline phases in the glass-ceramic samples. Bioactivity of the glass-ceramic samples are investigated by immersing the samples in Ringer's solution for 7, 21 and 28 days. By analyzing X-ray diffraction patterns, Fourier transform infrared spectra, and scanning electron microscopy images of the samples immersed in Ringer's solution, the formation of hydroxyapatite on the samples confirmed. The results show that the samples with β-Ca3(PO4)2 and β-Ca2P2O7 crystalline phases are more bioactive than the others.

The metal-assisted chemical etching (MACE) was used to synthesis silicon nanowires. The effect of etchant concentration, etching and chemical plating time and doping density on silicon nanowires length were investigated. It is held that the increasing of HF and H2O2 concentrations lead to etching rate increment and formation of wire-like structure. The results show that, the appropriate ratio of concentration to form the silicon nanowires obeyed the [HF]/[H2O2] = R equation when R= 2.5, 3 and 3.5 and any deviation of these ratio, cause to destruction of wire-like structure. Moreover, the critical etching rates to form the SiNWs are in the range of 4nm/s to 5nm/ s.

In this work, nanostructured TiO2 and Cr-doped TiO2 thin films were deposited on glass substrate through sonochemical-chemical vapor deposition (CVD) method. The resulting thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible absorption spectroscopy, and photoluminescence spectroscopy techniques. The TiO2 thin film has nanocubic morphology and the Cr-doped TiO2 thin film contains nanostructures with irregular shapes in its structures which these nanostructures themselves are composed from nanorods. Presence of Cr ions in the structure of TiO2 resulted in a decrease in the band gap energy of TiO2 and also in the reduction of photogenerated electron-hole recombination rate. The visible light photocatalytic activity of the prepared thin films were also investigated for degradation of paraoxon pesticide. According to the obtained results, the Cr-doped TiO2 thin film has higher photocatalytic activity than undoped TiO2 thin film. Moreover, in comparison with the undoped TiO2 thin film, the Cr-doped TiO2 thin film has higher stability.