Advanced Ceramics Progress
Volume:3 Issue: 1, Winter 2017

Mechanical alloying and vacuum sintering have been used to produce bulk nanostructured Ti5Si3 and Ti5Si3-15Wt.% Al2O3 nanocomposite. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used to study the microstructural characteristics of the samples. Indentation method was used to calculate hardness, elastic modulus and fracture toughness of bulk samples. The results showed that the nanometric grains were obtained through mechanical alloying and remained in nanometric scale after subsequent sintering. It was also observed that the in-situ produced Al2O3 through mechanochemical reaction has amorphous structure which crystallized during sintering process. Nanohardness, elastic modulus and fracture toughness of Ti5Si3-15Wt.% Al2O3 nanocomposite were calculated as 1660 HV, 238 GPa and 5.5 MPa.m1/2 that is higher than monolithic Ti5Si3 and other Ti5Si3-based nanocomposites. Toughening mechanisms based on crack deflection and crack bridging were suggested as responsible factors for fracture toughness increase Ti5Si3/Al2O3 nanocomposite.

Transparent polycrystalline spinel ceramic was fabricated without any sintering aids by spark plasma sintering method of a mixture of Al2O3 and MgO powders for only 10min soak at 1250°C. Densification, microstructure and optical transparency of spinel were examined. The spinel exhibits an in-line transmission of 55% for a visible-wavelength of 470nm and high hardness value of 2040 HV.

This current study reports preparation of Nickel-Gadolinium doped Ceria (Ni-GDC) composite via controlled unidirectional freeze casting of aqueous-based GDC slurry completed with nickel infiltrated into the porous GDC samples. Gadolinium doped ceria powder prepared by gel-combustion synthesis method. The oxide powder was confirmed to be the fluorite-structured of Ce0.8Gd0.2O1.9 solid solution by X-ray diffraction. The synthesized powder with dolapix as a dispersant, ammoniac as an agent pH, poly vinyl alcohol (PVA) as a binder and water as a solvent were used to prepare stable GDC slurries. Freeze casting process was done in different solid loading of GDC at 35, 45 and 44 wt. %, and two different rates of 1 and 3 ̊C/min to obtain desirable pore structure. After removing the frozen ice at -58 ̊C the green samples were sintered for 2 h in air at 1300 °C. The pore structure and final microstructure were studied by scanning electron microscopy. The porosity of the sintered samples was in a range of 60-70% , and were depended on solid content and freeze casting rate. Finally nickel solution was infiltrated into hierarchically porous GDC samples, after reduction at 800 ̊C, Ni-GDC composite was attained.

An experimental setup has been developed for successive photo-electrochemical etch and EIS measurement of semiconductor samples. Furthermore an algorithm based on electrochemical capacitance-voltage (ECV) has been developed for calculating dopant profile based on the measurements by developed setup. Phosphorous diffusion profile in p-type silicon was estimated by employing developed setup and algorithm. Obtained results were compared with the results of calibrated ECV instrument and dopant profile-resistivity correspondence method. Cross-sectional imaging was used for confirming the estimated dopant diffusion depth.

Zirconium and its alloys have many applications in orthopedic medicine and compared to stainless steel, titanium and other metals used in the manufacture of implants has higher strength and corrosion resistance. Research shows that the method of preparation and surface modification before coating process has a significant impact on improving the metal implants among which include the sandblasting operation. In this glass ceramic is coated on zirconium by sol-gel method and the impact of surface modification procedure on the grip is assessed. First the chemical composition was determined by the quantometric test and then the surface roughness and morphology was analyzed before and after the coating in two sandblasted and non- sandblasted modes was studied by AFM. Coating morphology and structure and creating a structure without separation at the interface was investigated by Scanning Electron Microscope (SEM). Fuzzy analysis was conducted on the samples prepared before and after immersion in SBF solution by X-ray diffraction (XRD) and infrared spectroscopy (FTIR) techniques. The results showed better coating of the surface after the sandblasting and biocompatibility of the coating after placement in the SBF solution.

In this study various yttria doped zirconia based thin films were prepared by the aqueous tape casting method. The rheological property of the paste was studies. The phase content and microstructure of the samples was investigated by X-ray diffraction and scanning electron microscope, respectively. The mechanical properties of thin films were studied by Vickers microhardness and nanoindentation methods. It was found that microhardness, nanohardness and Young’s modulus of thin films are not dependent on yttria content, but toughness of the samples improved by increasing tetragonal phase content of the samples.

The reverse co-precipitation method was used for synthesis of the pure phase multiferroic BiFeO3 (BFO) nanoparticles. Influence of different pH values on the microstructure and magnetic properties of the BFO nanopowders was investigated. Thermogravimetric-differential thermal analysis (TG-DTA) technique indicated that the optimal temperature for calcination is 550°C. The phase formation and the existence of transient phases (like Bi25FeO39 and Bi2Fe4O9) has been studied using X-ray diffractometry (XRD). The morphological features of the nanopowders were characterized by field emission scanning electron microscopy (FESEM) and the presence of absorption bands at 400 to 3600 was investigated by Fourier transformed infrared (FTIR) spectroscopy. The magnetic properties of the synthesized powders were measured using vibrating sample magnetometery (VSM). The results showed that the BFO powders have R3c crystal structure. The FESEM micrographs showed pseudo-cubic shape and particles size in the range of 25-236 nm. The magnetic hysteresis loops were indicated a weak ferromagnetic behavior of the samples at room temperature. Whereas the particles size of as-prepared powders were lower than the spiral spin cycloid (62 nm) and because of high surface-to-volume ratio of nanoparticles, which causes more uncompensated surface spins, the weak ferromagnetic behavior has been seen.