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سال:1393 | دوره: | شماره: |تعداد مقالات:8

The aim of the present work is to study the effects of the nanostructured WC-20 wt. % (Fe, Co) with different iron to cobalt ratios on microstructure and hardness of the sintered samples.Furthermore, a sample with a cobalt binder was produced under the same conditions for comparison purposes. The nanocomposite development, after different milling times, was monitored by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A homogenous distribution of nanostructured WC (crystallite size less than 30 nm) in the binder matrix was formed after 25 h of milling. The hardness and the relative density of the WC-20wt. % (Fe, Co) composites consolidated by conventional sintering at 1350oC were investigated. In the sintered samples after 25 h of milling, tungsten carbide grains have a uniform distribution with a lower grain size.Densification and hardness improved after 25 h of milling and reached optimum levels for the 25 h milled powders with equal ratio of iron to cobalt.

The 70SiO2-15TiO2-15ZrO2 membrane was prepared by a sol-gel procedure. Corrosion behavior of the microporous top layer along with the membrane characterization in terms of pore size, surface area, pore volume and weight loss are described. The final ceramic membrane with a thickness of 400 nm and uniform surface was obtained. This membrane confirmed the fine microporous characteristic with mean pore size<2 nm. After corrosion test, the corroded membrane revealed a surface with non-uniform coverage of the top layer. The heated ceramic membrane was amorphous before and after corrosion test. Dissolution of ions increased in acid and basic solutions. The weight loss of samples increased when pH increased at 25oC. Porosity of samples increased after the corrosion test. The pore size increased as compared to that of the original membrane. Surface area of the membrane increased in basic solution, but decreased in acid solution.

The inhibition effect of N- (8-bromo-3H-phenoxazin-3-ylidene) -N, N’-dimethylaminium (DPhDMA) on the corrosion behavior of mild steel in 1.0 M HCl solution has been studied. Weight loss measurements, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and quantum chemical calculations were performed in this study. Electrochemical results revealed that DPhDMA is an effective mixed type inhibitor for mild steel in 1.0 M HCl solution, and its inhibition efficiency increased with increasing its concentration and with the immersion time of the samples in the corrosive media. The adsorption of DPhDMA also led to a reduction in electric double layer capacitance and an increase in charge transfer resistance confirming its inhibitive effect on the corrosion behavior of the mild steel samples. The thermodynamic parameters governing the adsorption process showed that DPhDMA was adsorbed spontaneously on mild steel surface through a combination of physical and chemical mechanisms following Langmuir adsorption isotherm. Quantum chemical calculations were used to correlate the performance of DPhDMA with its electronic structural parameters.

Using the Frobenius series method (FSM), an analytical solution is developed to obtain mechanical stresses of thick spherical pressure vessels made of functionally graded materials (FGMs). The cylinder pressure vessel is subjected to uniform internal pressure.The modulus of elasticity is graded along the radial direction according to power functions of the radial direction. It is assumed that Poisson’s ratio is constant across the cylinder thickness.Primarily, displacements and stresses have been obtained as closed-form solution. Next, the profiles are plotted for different values of inhomogeneity constant along the radial direction.Finally, the problem was solved by using the finite element method (FEM). The obtained results of finite element method were compared with those of the analytical method. The analytical solutions and the solutions carried out through the FEM showed good agreement. The values used in this study are arbitrarily chosen to demonstrate the effect of inhomogeneity on displacements, and stresses distributions.

Amorphous alloys have been taken into consideration because of their unique properties and are nominated as the future engineering materials. In this research, the effect of Ni and milling time on amorphization process and thermal stability of Ti50Cu50-xNix (x=10, 15, 25 at%) alloy system were investigated. The evolution of amorphization during mechanical alloying, thermal stability and subsequent heat treatment were evaluated by x-ray diffraction analysis (XRD) and differential scanning calorimetry (DSC). The results showed that alloys reached to the highest content of the amorphous phase in Ti50Cu40Ni10, Ti50Cu15Ni35 and Ti50Cu25Ni25 alloy compounds after 60, 40, and 10 hours, respectively.Differential scanning calorimetry showed thermal stability of the amorphous alloy, exhibiting a distinct glass transition and crystallization temperature and a wide supercooled liquid region for Ti50Cu25Ni25 powder alloy with a value about 45 k. Heating Ti50Cu25Ni25 amorphous alloy at 943 K for 10 min results in the formation of intermetallics such as CuTi and NiTi2 phases. In addition, mechanical properties of the amorphous powders were studied by Vickers microhardness test. The alloy with 25 percent Ni showed the high value of hardness about 884 Hv after 40 hours of mechanical alloying.

Application of Fe-TiO2 photocatalysis using sol-gel method by hot-dipping technique was investigated. The influences of fabrication parameters; molar ratios of Fe to TiO2, the sol temperature, poly ethylene glycol (PEG) content and the number of dipping cycles on the photocatalytic activity in visible light region were studied. Results revealed that a higher photocatalytic performance of Fe-TiO2 films could be achieved using the molar ratio of Fe to TiO2: 0.015, the sol temperature: 70oC, PEG content: 2 wt. % and 5 dipping cycles. The photodegradation efficiency of this sample after 2 h of visible light irradiation increased up to 80% and no crack was detected on the surface of the thin film. When the sol temperature increased from 25 to 70oC (the boiling point of the sol), its viscosity increased due to the presence of PEG via forming cross linkage. This phenomenon resulted in the change of the coating microstructure and the improvement the optical properties.

Nanocrystalline magnesium hydride powder was synthesized by mechanical milling of MgH2 in a planetary ball mill for various times. The effect of MgH2 structure, i.e. crystallite size, lattice strain, particle size, and specific surface area on the hydrogen desorption properties was investigated. A single peak of hydrogen desorption observed for as-received powder, exhibiting an average particle size of 30 mm. In contrast, all milled powders with much reduced particle size exhibited desorption peak doublet in DTA. It shown that the dehydrogenation temperature of MgH2 decreased from 421oC to 319oC after 30 h of mechanical milling. Here, the average crystallite size, specific surface area, and accumulated lattice strain were18 nm, 9.3 m2/g and 0.7%, respectively. There was no significant difference on the onset temperature of dehydrogenation between powders milled at different times.However, the amount of hydrogen release decreased, i.e. from 5.9 wt.% to 4 wt.% with increasing the milling time from 5 h to 30 h.

A considerable amount of mill scale is generated from steel making plants annually. Although some industries use it as raw material, since it contains iron in the form of FeO, Fe2O3, and Fe3O4, it can be considered as a valuable metallurgical raw material in iron and steel making industry as well. Thus, the aim of this study was to evaluate the possibility, efficiency, and consequences of the reduction of mill scale in the electric arc furnace. Accordingly, different portions of mill scale were charged into an electric arc furnace (with two different charging methods) and the results were compared with reference heats. Results revealed that charging mill scale into electric arc furnace decreases oxygen and carbon powder consumptions, while negatively influences on production time, energy and coke consumptions, and slag composition. Moreover, reducibility evaluations based on tapping weight and oxygen consumption showed that almost %14.9 of mill scale is reduced in electric arc furnace.