Defect and Diffusion Forum Vols. 273-276

Abstract: It has been reported in the biocompatibility researches performed in-vivo and in-vitro that the electric signals produced by piezoelectric implants may induce accelerated healing of the injured tissue after implantation. Barium titanate (BaTiO3; BTO), as a well known piezoelectric ceramic, is a suitable candidate to be used in these kind of biomedical researches about the effect of the electrical polarity and piezoelectricity on tissues. The excellent biocompatibility and faster bone adaptation characteristics of hydroxylapatite (HA) have been well documented in the literature. Therefore, HA / BTO composites may be a suitable bioceramic material introducing both the piezo effect and biocompatibility at the same time. However, the main point to process such composites should be to keep HA and BTO phases as stable as possible not to loose the biocompatibility of HA and the piezoelectricity of BTO ceramics. In this research HA / BTO, piezo-composites were prepared with powder mixing method in various mixing ratios and sintered at the temperatures between 500 and 1300 oC. Sintering was carried out under different atmospheres to evaluate the effect of atmosphere on the phase stability of composites. Then composites are characterized with XRD, DTA, density measurements and d33 piezoelectricty coefficient measurements.

Abstract: The object of the present work is to study the spraying of poly-powders nickel bases containing Cr, Si, C and B elements addition with variable percentage of iron, deposited on a steel substrate by oxy fuel thermal spraying. The substrate surface was previously treated by Al–Ni bond coat and post–annealing at 650°C. The spraying powder and coating micro structure were investigated by combination of X-ray diffraction, electron microprobe and scanning electron microscope coupled to an analyzer energy dispersive x-ray. The adherence to substrate was determined by using shear test for adhesion. The result of this study was to investigate to compare potentials of HVOF sprayed NiCrBCSi and satellite 6 coating for a possible to replacement of hard chromium plating. A good adherence of coating NiCrBCSi (Fe) on steel substrate is explained by formation of large diffusion zone in interface after annealing and by the nature of the structure deposit duplexes.

Abstract: The precipitation of T1 phase during the ageing of an Al- Li- Cu -Zr alloy sheet was studied by DSC (Differential Scanning Calorimetric) technique. Results showed that precipitation of T1 phase occurred in temperature range of 250°C to 300°C whereas its dissolution occurred within the temperature of 450°C to 530°C. Furthermore, activation energies for precipitation and dissolution of T1 phase were determined 122.1 kJ/mol and 130.3 kJ/mol, respectively.

Abstract: To respond the need of industries to the new materials with higher specific modulus and lower density than those of the older Al alloys, aluminum- lithium alloys have been invented and improved. Aging process is one of the most important methods to improve the mechanical properties of aluminum- lithium alloys which are in the heat treatable category of aluminum alloys. Low temperature and natural aging processes cause the "short range diffusion" of Cu atoms in the aluminum and the formation of the GP zones. In this research, stability of GP zones and the effects of these areas on physical and mechanical properties of AA2090 alloy were investigated by hardness, electrical resistance, DSC (differential scanning calorimetric) and tensile tests. Results show that endothermic effect in the DSC diagrams of AA2090 alloy at 180°C to 240°C can be related to the enthalpy of GP zones dissolution. Formation of GP zones in the structure increases hardness, tensile strength and electrical resistance of Al- Li C u (2090) alloys.

Abstract: Magnetite (Fe3O4) nanoparticles were prepared simply by the reverse co-precipitation method from the solution of ferrous/ferric mixed salt in the presence of cationic surfactant (cetyl trimethyl ammonium bromide, CTAB) and nonionic surfactant (Polyethylene glycol, PEG) in two concentrations. Meanwhile, Fe3O4 nanoparticles without surfactant are also synthesized under the same condition for comparison. In addition via the reverse co-precipitation method, the pH which is an important factor in synthesis of magnetite was controlled at high values easily. The experimental results reveal that addition of surfactants affected on the size and morphology of the nanoparticles based on the X-ray diffraction (XRD) and scanning electron microscope (SEM) characterizations.

Abstract: The problem of unsteady natural convection heat transfer in a vertical opened porous cylinder submitted to a sinusoidal time variation temperature on the lateral wall has been investigated numerically. The widely used Darcy flow model without flow establishment at the cylinder exit has been used. In the case of constant wall temperature, two types of flows were obtained, with and without fluid recirculation, depending on the filtration Rayleigh number (Ra), the aspect ratio (A) and the Biot number (Bi) have been obtained. The obtained heat transfer, in case of low dimensionless oscillations amplitude (XA<0.5), shows a non significant enhancement (less than 5%) in comparison to the constant wall temperature case.

Abstract: Nanometer oxides e.g. SnO2, ZnO, TiO2, ZrO2, etc. have photocatalytic and gas sensing properties which can be different in nanometer range. They have been produced by several methods such as Chemical Bath Deposition (CBD), Pulsed-laser deposition, Chemical Vapor Deposition (CVD), screen printing and firing process, spray pyrolysis technique, magnetron sputtering, mechanical alloying, etc. It was found that the production method and its parameters would affect the size and morphology of these oxides. By using a composite of these oxides their properties would also be affected. In this paper the effects of sonication and reaction temperatures on SnO/ZnO coupled oxides' morphologies were investigated. These coupled oxides were characterized by X-Ray Diffraction (XRD), X-Ray Florescence (XRF), Scanning Electron Microscopy (SEM), and Differential Thermal Analysis (DTA). As a result of using the ultra sound source, the sizes of nano oxides decreased, which is one of the most important advantages of sonochemical synthesis in comparison with chemical bath deposition synthesis of these nano-composites.

Abstract: Constructing a new device we had to design some vapour-cooled current leads. This current leads are made of Low-Tc material connected with copper wires and some parts of High-Tc material. Its design is calculated keeping in mind the heat transfer by diffusion to a vapour-cooled stream that surrounds the conductive materials. The design and the calculations performed to achieve it, and also the background theory of the heat diffusion applied in this part of the device will be described.