نشریه علم و مهندسی سرامیک
سال پنجم شماره 3 (پیاپی 18، پاییز 1395)

The photocatalytic activity of mesoporous TiO2 modified by the carbon nanotubes (CNTs) and Ag is reported. The mesoporous TiO2 was synthesized by sol-gel method and mechanically mixed with functionalized multi-wall carbon nanotubes which was decorated by different amount of Ag. Mesoporous TiO2 and the nanocomposite were characterized by XRD¡ SEM¡ TEM¡ BET surface area analysis¡ FTIR¡ AAS¡ UV-Visible¡ DRS-UV and UV-Vis absorption spectroscopy. The photoactivity of nanocomposite containing mesoporous TiO2¡ MWCNT and Ag were evaluated by the degradation of methyl orange (MO) in aqueous solution under UV irradiation. Results showed that the CNT which was decorated with the 15.5% of Ag could facilitate the phocatalytic activity of mesoporous TiO2.

In this study Ti3SiC2 MAX phase synthesized by mixing of Ti, Si and C powders and mechanical alloying - heat treatment. The composition of 3Ti:1.3Si: 2C were used in order to evaluate the milling time and also heat treatment temperature in synthesis of Ti3SiC2 MAX phase. At first the initial powders were weighed and mechanical alloying was carried out using ball to the powder ratio of 50:1 for 30, 40 and 50 hours under argon atmosphere. Then the mixed powders were pressed in steel mold with the diameter of 1.2 cm to shape discs under the pressure of 200 MPa. After a complementary heat treatment of the samples at 1100, 1200 and 1300 °C for 1 hour, an X-ray diffraction analysis was used to examine phase composition while a field emission transmission electron microscope equipped with an EDS spectrometer was utilized to observe the microstructure. Finally, it was found that the maximum amount of the synthesized Ti3SiC2 MAX phase is totally equal to 75wt.% which is related to the sample with milling time of 40 hours and heat treated at the temperature of 1200°C. It was also observed that the weight percentage of the Ti3SiC2 MAX phase has decreased in the reaction products by increasing of the milling time from 40 to 50 hours.

The present study aimed to investigate the synthesis, microstructural and mechanical properties of alumina/zirconia-cobalt composite. The compositions containing 5, 10, 20 Vol.% of the sum of ZrO2 and Co were studied. The composite powders were prepared through mixing of alumina powder with partially stabilized zirconia and cobalt sulfate powders followed by calcination treatment at 1100 for 3h and reduction of cobalt by aluminum powder additive, in carbon bed at 950 for 3h. The XRD analysis showed the presence of Al2O3, t-ZrO2, Co and a little m-ZrO2. In order to investigate the properties of Al2O3/ZrO2-Co composite, composite powders were pressed uniaxial followed by Cold Isostatic Pressing (CIP) at 400MPa. The prepared discs were sintered in carbon bed at 1550 1600 , 1650 for 5h. The alumina specimen was also prepared with the same procedure. The final results showed that the highest relative density value was 83.9% obtained for the specimen with the composition containing 5vol.% ZrO2 and 5vol.% Co densified at 1650 for 5h. The bending strength and hardness of this specimen was 322MPa and 11.95MPa.m1/2 respectively. So 20.15% increment of bending strength and 15.96% decrease of hardness was observed compare to monolithic alumina. The decrease of hardness was due to the lower hardness of metallic phase and the increase of bending strength is occurred because of presence of zirconia and cobalt particles which prevent of alumina grains growth.

In this study, a nano-composite ceramic titania-alumina coating with different percentages of Benzotriazole include 1.2%, 3.6%, 4.8% was synthesed by sol-gel process and then applied by immersion technique on the surface of Al 2024. Phase behavior structural properties and surface morphology was investigated by using XRD, FESEM, AFM, respectively, and also corrosion behaviour were evaluated by using the polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution. The maximum inhibition at concentrations of 3.6% Benzotriazole can be cuased to decrease corrosion current density of 0.006797 mA to 0.002523 mA. The results show uniform and homogeneous coverage and increase the corrosion resistance of aluminum, due to release Benzotriazole inhibitors in the concentration of 3.6% Benzotriazol, particularly.

In this work, fractal dimensions and electrical conductivity of carbon–nickel films deposited at deposition times from 50 to 600 second were investigated. Because of the existence of fractal components in the surface topographies, the power spectra densities (PSDs) of all films show inverse power law variation at the high spatial frequency region. The fractal dimensions and the topography carbon-nickel films from 50 to 180 second are increased however; at 600 second these characteristics are decreased. It was observed that with increasing deposition time from 50 to 180 second, the room temperature electrical conductivity (σRT) of films increases from 2.87x10-9 to 2.3x10-8 Ω-1 cm-1 and then decreases to 6.62x10-9 Ω-1 cm-1 for films deposited at 600 second. Fractal dimensions and the room temperature electrical conductivity are in consistent with field emission scanning electronic microscopy (FESEM) images.

Oxide glasses have unique thermal properties. In the present work, it was investigated that how the thermal properties vary with composition. In this work, the ternary glasses of the form 40TeO2-(60-x)V2O5- xNiO with different molar percentage 0≤x≤20 have been prepared by standard rapid melt-quenching method. DSC curves of these ternary glasses have been investigated in the range (150- 500oC) at heating rates φ=3, 6, 9, 10 and 12K/min. Then, using their crystallization temperature (Tcr) and Avrami index (n), their crystallization activation energy (Ec) were calculated. Generally, results of this work show that the decreasing trend of crystallization activation energy, which can be attributed to the increasing of non-bridging oxygen's and increasing of fragility. The obtained values of (n) show that it fluctuates around n≈ 1, which can be attributed to surface or one-dimensional crystal growth of probably needle-like tellurium crystals.

Aluminum matrix composites due to low cost, high chemical stability, resistance to oxidation, resistance to abrasion and high mechanical strength at relatively high temperatures have a good status among advanced materials. This paper reports the synthesized Al(Zn)/Al2O3-AlxCuy composite by mechanical alloying and combustion synthesis in Al-ZnO-CuO system. A mixture of Al, ZnO, and CuO powders with different composition (Al-10-20wt.%ZnO with 6wt%CuO) are subjected to high-energy milling with different time of 0-60h. The compacted samples were sintered at different temperature (650-1150 ). X-ray diffraction results of ball-milled samples show that the Al2O3 phase is partially formed after sixty hours of ball-milling and the peaks of CuO are disappeared because of becoming amorphous state. By increasing milling time, the grain size is decreased and it is estimated that minimum grain size for sample (20 nanometer). Based on the model of RSM (Response surface methodology is used to optimize mechanical properties through box-behnken design), by increasing of ball-milling time in stationary conditions of sintering temperature and composition, the density of composite samples will be decreased while, the hardness will be increased to 295 Vickers that is accordance with experimental values. Increasing of ZnO content in stationary conditions of sintering temperature and ball-milling time causes increasing of density and hardness of composite samples. Thermal Analysis investigations show that with increasing milling time, due to mechanical activation and entrance of alloy elements into aluminum, melting point of aluminum (from 667 to 622 .) and starting temperature of alumio-thermic reaction (from 661 to 649 .) is reduced.