Showing 10 results for A. Saidi
N. Zarrinfar and A. Saidi,
Volume 21, Issue 2 (1-2003)
Abstract
Titanium carbide is used as an attractive reinforcement to produce particulate metal matrix composites. One of the problems to use this carbide as a reinforcement in copper-based composites is the lack of wetability in Cu-TiC system. This property improves as the C/Ti ratio in carbide decreases.
Problems to use this carbide as a reinforcement in copper-based composites is the lack of wetabiity in Cu-TiC system. This property improves as the C/Ti ratio in carbide decreases.
A practical method is presented in this paper to improve the dispersion of titanium carbide into liquid copper and emphasis is placed on the C/Ti ratio in the carbide. It was observed that the C/Ti ratio in a raw mixture containing only Ti and C was equal to C/Ti ratio in the carbide after synthesis but when copper powder was added to the raw materials, this ratio was higher than the starting value. Regarding the relationship between the titanium carbide lattice parameter and the C/Ti ratio in the carbide and this ratio in the raw mixture, a graph was drawn that related the C/Ti=1, a network of agglomerated TiC particles with the same C/Ti ratio is formed which cannot be dispersed into liquid copper. When this ratio is decreased to 0.3, particulate titanium carbide with C/Ti=0.5 can be easily dispersed into liquid copper.
Keywords: SHS reaction, titanium carbide
M. Shamanian and A. Saidi,
Volume 24, Issue 1 (7-2005)
Abstract
The 25Cr-35Ni heat resistant steel has been widely used when resistance to oxidation and creep rapture at elevated temperatures is required. In this paper, the microstructural effect on the weldability of this alloy is investigated. The results of this study indicate that this steel has a perfect weldability in the as cast condition but does not possess good weldability in the aged condition. The as cast microstructure of 25Cr-35Ni steel consists of austenite matrix and a network of primary carbides, while the aged condition consists of austenite matrix and y primary and secondary carbides. The morphological change of primary
carbides and the secondary carbides precipitate formation, reducing the elongation and ductility of aged steel, should have enhanced the steel susceptibility to cracking, particularly in the area of the eutectic carbides, and hence, the reduced weldability of the steel. The cracking observed was of the intergranular type and spread along the eutectic carbides. It was found that the carbides in the as cast steel consisted of NbC and M23C6, whereas that of the aged steel also exhibited Ni16Nb6Si7 and M23C6 carbides
J. Safarian-Dastjerdi and A. Saidi, ,
Volume 24, Issue 1 (7-2005)
Abstract
A higher bustle temperature in midrex direct reduction process is always desirable due to its positive effect on the productivity and DRI quality. The limit of the bustle temperature is related to the sticking or clustering behaviour of oxide pellets during the reduction in the reactor. It has been well estabilished that coating of oxide pellets by a refractory material decreases its
tendency to clustering. In this study, the clustering behaviour of oxide pellets (produced from Golegohar-Chadormalu iron ore) during redution at different temperatures was investigated. The effect of coating with different amounts of hydrated lime on the clustering behaviour was also examined. Microscopic examination of coated pellets shows a porous, non-continious layer of Ca(OH)2 being fromed on the surface of the pellets. The clustering tendency of coated pellets, measured by the standard sticking test at pilot scale, was much lower, compared with normal (uncoated) pellets, while their reducibility was the same.
N. Setoudeh, A. Saidi, A. Shafyei and N. J. Welham,
Volume 25, Issue 1 (7-2006)
Abstract
Anatase-to-rutile phase transformation was studied in milled and unmilled samples. Ball milling was carried out in two types of ball mills, planetary and tumbler, with a ball-to-powder ratio of 40:1 over 2-48 hours. First, the unmilled samples
were heated in the furnace at various temperatures for different periods of time. The results revealed that the anatase-to-rutile transformation completed at 980 after 48 hours. The rate of transformation in milled samples was greatly higher than that of unmilled ones. Activation energy in unmilled samples was about 440 kj/mol. The rate of transformation in the planetary ball mill was higher than that in tumbler mill. In the former, transformation almost finished after 16 hours of milling while in the lattar, it did not finish even after 48 hours. XRD results revealed that the transformation proceeds through an intermediate srilankite phase in all milled samples. However, srilankite was not observed in the unmilled samples.
M. Karbasi, A. Saidi, and Gh. Ariyanpour,
Volume 26, Issue 1 (7-2007)
Abstract
Production of nickel-silver by mechanical alloying was investigated. Effects of parameters such as milling duration, ball to powder weight ratio, and chemical composition on mechanical alloying process, and alloy's color and microstructure were studied. The milled powders were characterized, using XRD and SEM. Results showed that nickel-silvers could be produced by mechanical alloying in a wide range of compositions. Alloyed powder with a bright silvery contrast and less than 15 nm grain size could be obtained by optimization of milling parameters. Zinc content of the powder mixture had a significant effect on the minimum alloying time. Ball to powder ratio up to 25 also reduced minimum alloying time but it had no significant effect above this value.
N. Setoudeh, A. Saidi, A. Shafyei and N.j. Welham,
Volume 27, Issue 2 (1-2009)
Abstract
M. Kasiri Asgarani, A. Saidi, M. H. Abbasi,
Volume 28, Issue 1 (Jun 2009)
Abstract
The effects of mechanochemical treatment of monoclinic zirconia in high energy planetary ball mill on its phase transformation were investigated. The mechanical treatment in ball mill reduces the grain size, increases microstrain, and causes phase transition to metastable nanostructured tetragonal and cubic phases. XRD and TEM results show considerable amounts of amorphous phase during ball milling. Surface area measurements by BET method over long milling times reveal that ZrO2 particles are agglomerated with an amorphous phase as a binder. The mechanical treatment increases the reactivity of zirconia in chlorine gas. Annealing of ball milled zirconia in the chlorine atmosphere produces oxygen vacancy in zirconia (ZrO2-x) and causes the amorphous phase to be crystallized and to change into cubic and tetragonal phases. The chlorine atmosphere increases the stability temperatures of cubic and tetragonal phases to 800°C and 1000°C, respectively. In this situation, the energy of grain boundary and oxygen vacancy play important roles in the stability of tetragonal and cubic phases.
M. Godarzi , A. Saidi,
Volume 30, Issue 2 (Dec 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.
Kh. Biralvand, M.h. Abbasi, A. Saidi,
Volume 31, Issue 1 (Jun 2012)
Abstract
Carbothermic reduction of Molybdenite in the presence of Magnesium oxide was thermodynamically studied. The stability diagrams for MoS2-MgO and MoS2-MgO-C Systems was prepared. The reduction of MoS2 with Carbon in the presence of Magnesium oxide proceeded through the direct oxidation of MoS2 by MgO to form intermediate molybdenum oxidized Species, MoO2 and MgMoO4. The results showed that the gaseous phase is mainly composed of CO. Stability diagrams for Mo-O-C (Reduction of MoO2 with carbon) and Mo-Mg-C-S-O (Reduction of MgMoO4 with carbon) were also investigated. The results showed that the Reduction of oxidized species leads to the formation of Mo, Mo2C, MoC or MgO products.
M.godarzi, A. Saidi,
Volume 33, Issue 2 (Journal of Advanced Materials-fall 2015)
Abstract
In recent years, much research has been performed in the field of nanomaterials synthesis using mechanochemical process. In this research, TixAly/Al2O3 ceramic matrix nanocomposite was produced by the mechanochemical method. Aluminum and inexpensive titanium oxide powders were used as raw materials, and milling was performed under N2 atmosphere. The results showed that reduction of TiO2 by Al is the first step of synthesis process, and then Ti reacts with residual Al. The synthesis after 10 hours of milling resulted in titanium aluminide and aluminium oxide. With the increase of milling time to 80 hours, titanium aluminide quantity was increased. Also, the results showed that the heating of samples containing titanium aluminide in the argon and nitrogen atmospheres does not lead to complete decomposition of aluminides.
