فصلنامه نانو مواد
پیاپی 25 (بهار 1395)

In this research surface composite layers containing nano sized TiB2, Al2O3-TiB2, ZrO2 and CNTs particles have been fabricated on Al alloy substrate by friction stir processing. Effect of different processing variables such as number of passes and strengthening particle on distribution of particles, hardness and tribological properties of surface nanocomposite layer have been evaluated by electron microscopy, hardness and wear test. Results showed that surface properties of aluminum alloy will be enhanced and the optimum conditions of properties which can be determined by comparing the effects of different parameters will be obtained. An increase in the number of passes up to four modifies microstructure and accordingly mechanical and tribological properties were enhanced. Maximum hardness of 210 HV was measured for specimens FSPed with Al2O3-TiB2 powder after four passes. Surface composite produced by FSP significantly improved the dry sliding wear resistance of the Al6061 alloy by changing the wear mechanism. The FSPed sample with Al2O3-TiB2 particles had higher wear resistance in comparison with others. This enhancement is a consequent of better bonding between particles and aluminum matrix and higher microhardness.

Preparation of ion stable ferrofluid with water liquid carrier is presented in this paper. Iron oxide nanoparticles and tetramethyl ammonium hydroxide (TMAH) were used as solid phase and stable agent respectively. Magnetic properties of nanoparticles and ferrofluid were investigated by VSM. Particle size was calculated by Sherrer formula and magnetic data and compared with the sizes estimated by TEM micrograph. The size of particles were about 10 nm and their saturation magnetization were between 65.5 and 84 emu/g. Saturation magnetization of ferrofluid, its density and the density of suspended particles were calculated using magnetic data and compared with those calculated by direct measurement and a simple method for estimating magnetization of ferrofluid was proposed. Results showed that the extent of stirring the fluid during preparation affect its quality. Also the content of magnetic phase in the fluid directly affects its saturation magnetization and initial susceptibility.

In this paper, nanotechnology advantages are used to improve oxidation resistance of graphite. The elementary SiC coating has been developed on graphite substrate using a pack cementation method and the secondary coating has been produced using a slurry painting method at 1600 °C during 2 hours. The oxidation resistance of coating have been tested has been performance at 1500 °C. The phase composition and surface microstructures of the coating were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The variations of Gibbs free energy of reactions were calculated using by HSC Chemistry software. The results showed that the coating obtained by the pack cementation is a dense graded structure consisting β-SiC. There were lots of SiC nanofibers on the secondary coating with 50-70 nm diameters. The SiC nanofibers coated samples exhibit good oxidation resistance at high temperature. The graphite was fully destroyed during 1 hour however the mass loss of the SiC nanofibers coated samples after 10 h of oxidation at 1500 °C was 6%.

In this study, barium hexa ferrite M type nanopowders doped via Mg2, Zn2, Ti4 have been prepared by mechanical activation process under various Fe/Ba molar ratios of 10, 11 and 12. The ratios Fe/Ba, 10 and 12 as interphase Fe phase was observed more in the ratio of 11 as the optimum ratio of barium hexa ferrite single-phase synthesis is seen to be. The combination of synthesis and doped barium hexa ferrite with the values 0.9, 0.7, 0.5 investigated magnetic and morphological analysis by using XRD, SEM and VSM was investigated. Williamson-Hall calculations and charts are indicative of strain in the structure of the strain and increase the dopants increases the strain on the combined network. SEM images showed distinct hexagonal nanoparticles to the grain boundary. Dopants preferred an increase in the growth of particles in directions a and b structures was created. dopants and succession ions increase in Mg2, Zn2, Ti4 and Fe3 in all samples of these elements in a crystallography position yielded reduced saturation magnetization and coercivity. The coercivity, for example, doped with x=0.7 was 50 Oe, respectively. Finally, the study barium hexa ferrite conversion as a magnetic hard material to a soft magnetic behavior happened.

In this study, the effect of water-based titanium oxide nanofluid on total heat transfer coefficient heat transfer rate, mean heat transfer, pressure drop and entropy generation for double tubed heat exchanger equipped with snake tubes has been investigated. Our results reveal that with the use of nanofluid, the heat transfer coefficient is increased about 18.10 to 18.22 percent and this will also lead to an increase in heat transfer rate. The entropy generation has been increased about 24 percent compared to water-based fluid. In addition, using both nanofluid with particle volume fraction of 0.3 percent and snake tube as a flow turbulent simultaneously results in 24.3 and 38 percent increase in effective heat transfer. Therefore, the efficiency of heat exchanger is increased.

In this study, alumina-zirconia stabilized with yttria nanocomposites providing by sol-gel method were studied. After preparing the nanocomposite, sintered using spark plasma sintering process was conducted. Al2O3-30wt.% YSZ nanocomposites were prepared using sol-gel method sintered by spark plasma sintering at temperature of 1300-1400 °C with 50-degree increments. Phase changes with X-ray diffraction, microstructure with scanning and transmission electron microscopy, mechanical properties of hardness and fracture toughness was measured. The results showed that all Al2O3-YSZ nanocomposite containing 30wt.% YSZ reached over 95% theoretical density at 1350 °C and nearly full density at 1400 °C. The Vickers hardness and fracture toughness of Al2O3-30wt.% YSZ nanocomposites were prepared using sol-gel method sintered by spark plasma sintering at 1400 °C reached a maximum value of 1975 HV and 6.2 MPa.m1/2, respectively that highest mechanical properties achieved in this research and compared to conventional sintering methods with better mechanical properties.