Showing 7 results for Alumina
M. Godarzi , A. Saidi,
Volume 30, Issue 2 (12-2011)
Abstract
In recent years, much research in the field of advanced materials synthesis using the mechanochemical process has been performed. In this study, Al2O3-TiN nanocomposite was produced by the mechanochemical method and using inexpensive material TiO2 (instead of pure titanium which is too expensive). Also, aluminum and titanium oxide powders were used as raw materials. Milling under N2 atmosphere with 5 atmospheric pressure was performed and the products were evaluated by the SEM and XRD. Milling results showed that in the first stage of the synthesis process, titanium oxide is reduced by aluminum and the process continues, producing titanium reaction with nitrogen. When the Al/TiO2 ratio molar is equal to 1.2 and 1.3, after 20 hours of milling, TiN peaks in the XRD appears. Moreover, the results showed that milling leads to the formation of fine and spherical particles.
S. Otroj, F. Mohammadi, M.r. Nilforushan,
Volume 33, Issue 1 (7-2014)
Abstract
In this paper, the effect of MgCl2 addition on the kinetics of MA spinel formation was investigated. For this purpose, the stoichiometric mixture of MgCO3 and calcined aluminum was calcined at 1100 °C for 1 hr. Then, the calcined composition was wet-milled and after addition of 6% MgCl2 the compositions were pressed and fired at 1300 and 1500 °C for different times. Spinel phase content was determined using semi-quantitative phase analysis. With regard to Jander's equation, the rate constant was calculated, and the activation energy was obtained from Arrhenius equation. The results showed that the addition of MgCl2 leads to the acceleration of the spinel formation reaction. Besides, 55.71 Kcal/mol as the activation energy was calculated for the composition containing 6 wt.% MgCl2 compared with 93.06 Kcal/mol for the composition without MgCl2.
P. Seifollahzadeh, M. Kalantar, A. Mashreghi, S.s. Ghasemi,
Volume 34, Issue 3 (12-2015)
Abstract
Mullite and alumina are common in high-temperature applications because of their low thermal expansion coefficient and good thermal shock resistance. Evolution of SiC in the matrix and using it as reinforcing phase can improve thermo-mechanical properties of these materials. Also, in-situ formation of the reinforcing phases by using inorganic materials is an economical process. In this work, crystallization of SiC as reinforcing phase in the matrix of mullite-alumina by carbothermal reaction processes of inorganic materials (andalusite and kaolinite) was studied. According to the ratio of C/SiO2 and process conditions, some properties of the composite such as phase transformation, microstructure and physical and mechanical properties were investigated. The results showed that optimal ratio of C/SiO2 and firing temperature of densification to form SiC crystals were 3.5 and 1600°C for andalusite and 5.5 and 1500°C for kaolinite.
N. Zakeri, S. Otroj, M.r. Saeri,
Volume 34, Issue 3 (12-2015)
Abstract
In this study, the effect of nano-titania addition on the mechanical strength of mullite-bonded alumina-siliconcarbide nano-composites was investigated. To this end, the gel-casting process via nano-silica sol was used for shaping the nano-composite.The firing temperature of composition was determined by use of STA. The compressive and bending strengths of samples were measured after firing at 1300 °C. Besides, the physical properties, phase composition and microstructure of the composites were evaluated after firing. The results showed that the use of nano-titania up to 1 wt.% had a higher effect on improvement of nano-composite mechanical strength. The nano-titania addition led to increasing of mullite phase and higher growth of its needle-like grains. Enhancing of ceramic bonds between grains and the improvement of mechanical strength were obtained by increasing the mullite phase.
P. Radmehr, A. Zakeri, S. Alamolhoda,
Volume 34, Issue 4 (3-2016)
Abstract
In this research, TiAl/Al2O3 composite was synthesized from mechanically activated TiO2-Al powder mixtures using microwave heating.The initial powder mixtures were mechanically activated and pressed into cylindrical tablets and then heated in a microwave oven. The effect of different amounts of excess Al and microwave susceptor material (SiC or graphite) on the ignition time and the resultant reaction products were evaluated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used for characterization of the synthesized samples. XRD patterns revealed that when there was no excess Al in the initial powder mixture, the main resulting intermetallic phase would be Ti3Al with negligible amounts of TiAl, while with 10 wt% excess Al, TiAl phase could be formed in the composite product.The results also showed that microwave synthesis took place faster and more reproducible when samples were packed in the graphite powder than when placed between two SiC blocks.
S. Safi, Dr G. H. Akbari,
Volume 36, Issue 1 (6-2017)
Abstract
Strengthening of copper matrix by dispersion of metallic oxides particles as an efficient way to increase strength without losing thermal and electrical conductivities has been recognized for many years. Such a composite can withstand high temperatures and keep its properties. Such copper alloys have many applications especially in high temperature including resistance welding electrodes, electrical motors and switches. In the present work, at first, the Cu-1%Al solid solution was prepared by the mechanical alloying process via 48 hours of milling. Subsequently, 0.66 gr of copper oxide was added to Cu-1%Al solid solution and mechanically milled for different milling times of 0,16, 32, 48 hours. The milled powder mixtures were investigated by X-Ray Diffraction and scanning electron microscopy techniques. The lattice parameter of Cu increased at first, but then decreased at longer milling times. The internal strain increased and the average Cu crystal size decreased during milling process.The particle size decreased during the whole process. With increasing annealing temprature from 450°C to 750°C, the microhardness values of samples decreased at the beginning but then increased. From these results, it can be concluded that nanosize aluminaparticles are formed in the copper matrix.
F. Ebrahimi, F. Ashrafizade, S. R. Bakhshi,
Volume 36, Issue 3 (11-2017)
Abstract
In this research, ordered porous anodic templates with 30 nm diameter and 15 µm thickness were prepared by using double anodization process. Dip coating method was employed to synthesize strontium ferrite in the form of nanowires in sol dilution. Ferrite nanopowders were also synthesized using sol gel method. The characterization of the nanostructures were examined by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive Spectroscopy (EDS). Hysteresis loops of nanopowders and nanowires, parallel and perpendicular to the wires axes, were measured by Superconducting Quantom Interference Device (SQUID). The results showed that double anodization in 0.3 M oxalic acid at 4 oC with a single anodization for 12 hours could produce ordered template. Dip coating in 80 oC for two hours could form fine and uniform strontium ferrite nanowires. The produced material showed parallel anisotropy.
