Showing 9 results for Zakeri
Y. Zakeri, M. R. Aref,
Volume 9, Issue 1 (1-1991)
Abstract
J. A. Zakeri and F. J. Jie,
Volume 24, Issue 1 (7-2005)
Abstract
Continuous welded turnouts are important for CWR track through the railway station. According to equivalent resistance and non-linear theories and the principle of force diagram, a new method of theoretical calculation for continuous welded turnouts was developed. The continuous welded turnouts designed and installed according to the new theory behaved fairly well. The data collected on sites basically agreed with those of theoretical calculation. It was proved that the calculation theory is correct and values of calculation parameters are reasonable.
J. A. Zakeri,
Volume 27, Issue 1 (7-2008)
Abstract
Investigation of vertical vibrations of a railway turnout is important in designing track components under moving loads of trains. In this paper, the turnout is simulated by a linear finite element model with modal damping. A section of the turnout has a length of 36 sleeper spans surrounding the crossing. Rails and sleepers are modeled with uniform Rayleigh-
Timoshenko beam elements. The rails are connected via railpads (linear springs) to the sleepers, which rest on an elastic foundation. The rolling stocks are discrete systems of masses, springs, and dampers. By passing the trains at a constant speed, only vertical dynamics (including roll and pitch motions) is studied. The wheel-rail contact is modeled using a non-linear Hertzian spring. The train-track interaction problem is solved numerically by using an extended state space vector approach in conjunction with modal superposition for the turnout. The results show that the rail discontinuity at the frog leads to an increase in the wheel-rail contact force. Both smooth and irregular transitions of the wheels from the wing rail to the crossing nose have been examined for varying speeds of the vehicle. Under perfect conditions, the wheels will change quite smoothly from rolling on the wing rail to rolling on the nose. The impact at the crossing will then be small, giving a maximum wheel-rail contact force which is only 30--50 per cent larger than the static contact force. For uneven transitions, the severity of the impact loading at the crossing depends strongly on the train speed. The increase in the contact force, as compared with the static force, is in the order of 100 per cent at 70 km/h and 200 per cent at 150 km/h.
N. Zakeri, S. Otroj, M.r. Saeri,
Volume 34, Issue 3 (Journal of Advanced Materials-fall 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 (Journal of Advanced Materials-winter 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.
M. Asadrokht, A. R. Zakeri,
Volume 36, Issue 1 (Journal of Advanced Materials-Spring 2017)
Abstract
Despite a great thermodynamic driving force, copper cementation by aluminum from sulfate solutions involves a relatively slow kinetics due to the presence of the passive oxide film on the surface of aluminum. The previous studies have confirmed the positive effect of the presence of small amounts of chloride ion on reducing the scale of this problem. In this paper, the effect of concurrent ball milling on the kinetics of this process has been investigated. The cementation experiments were carried out in a polyamide jar with alumina balls inside by planetary ball milling. The studied parameters were ball number (0, 4), temperature (25-55 °C) and time (0-240 s). All experiments were conducted at constant condition of [Cu2+] = 6 g/L, [Cl−] = 75 mg/L, rotation speed of 160 rpm, average aluminum particle size of 279 µm and [H+] = 1.94×10-3. The results showed that concurrent ball milling reduces the induction period of the cementation process to less than 120 s. The apparent rate constant of cementation showed the positive influence of simultaneous milling on the kinetics of the studied cementation process. Moreover, activation energies of the induction and main periods were calculated to be respectively 86 and 26 kJ.mol-1, indicating the shift of the reaction mechanism from chemical control to mass transfer control.
M. H. Bakhshi, A. Zakeri,
Volume 36, Issue 4 (Journal of Advanced Materials-Winter 2018)
Abstract
Electrowinning is one of the methods for recovery of nickel metal from pregnant leach solutions. In industrial practice, the Ni content in electrolytes is usually above 80 g/L. However, many nickel solutions obtained from processing of secondary nickel resources are much less concentrated and this makes the electrowinning of such solutions difficult. In the present study, Nickel electrowinning from 30 g/L sulfate solutions has been investigated and the effect of the parameters such as current density (CD), temperature (T) and boric acid concentration (BA) on the current efficiency and nickel deposit quality has been determined using a central composite design methodology. The statistical analysis of experimental results revealed the significant factors and a proper model was obtained for each response variable. The results revealed two important negative interaction effects of T´BA and CD´BA which means that increasing temperature and current density could result in a higher current efficiency and satisfactory Ni deposit quality only at lower boric acid concentrations. By using overlaid contour plot method for multiple response optimization, the optimum condition for attaining current efficiencies of >95% and a smooth and compact Ni deposit quality was determined as CD = 2-2.5 A/dm2, T = 25-30 °C, and BA = 10 g/L.
H. Mirzaaei Ghasabe, A. Zakeri, Sh. Mirdamadi, M. Ghorbanzadeh,
Volume 37, Issue 3 (Journal of Advanced Materials-Fall 2018)
Abstract
In this study, the recovery of lithium from the cathode of the spent Li-ion batteries of the LiNixMnyCozO2 type was investigated. After complete discharging and dismantling, the cathodic section was cut and its aluminum content was selectively dissolved in 2.5 M NaOH solution at room temperature for 2 hr. In the next step, selective dissolution of lithium by oxalic acid from the de-aluminized cathode material was investigated and optimized using the response surface methodology of the central composite design. The effect of three parameters of time (35-100 min), temperature (40-70 °C), and oxalic acid concentration (0.5-1.2 M) on the lithium recovery percentage and manganese concentration was studied as the response variables. According to the statistical analysis of the results and the developed models, an optimum condition (T = 70 °C, t = 122 min and oxalic acid concentration of 1.1 M) was suggested and verified experimentally, resulting in the lithium recovery of about 95% and Mn2+ concentration of about 110 mg/L.
N. Zakeri, H.r. Rezaie, J. Javadpour, M. Kharaziha,
Volume 39, Issue 4 (Journal of Advanced Materials-Winter 2021)
Abstract
In recent years, nanoceramics have been used in scaffolds to emulate the nanocomposite with a three-dimensional structure of natural bone tissue. In this regard, polycaprolactone biopolymer is widely used as a scaffold in bone tissue engineering. The goal of this research is to produce porous scaffolds of polycaprolactone - zeolite biocomposite with suitable mechanical, bioactive and biological properties for bone tissue engineering applications. The nanocomposite scaffolds were synthesized by solvent casting/particulate leaching and freeze-drying approaches. Microscopic investigations showed generation of pores with an average size of 200-400μm after addition of ceramic phase. Energy dispersive X-ray analysis confirmed uniform distribution of ceramic phase in polycaprolactone matrix. FTIR results determined the binding type of zeolite nanoparticles to the polycaprolactone matrix as physical bonding. The results of mechanical tests showed the increase in young’s modulus after addition of ceramic phase (from 0.04 to 0.3 and 3 to 7 MPa, respectively). The hydrophilicity of polycaprolactone increased after adding nanozeolite and more weight loss was observed for scaffold containing 20% zeolite (53.52 6 1.6%) with an increase in the rate of hydroxyapatite formation. The results showed that the prepared scaffolds have potential for cancellous bone tissue engineering application.
