Showing 8 results for Rajabi
S. M. Borghei and D. Rajabi Siahboomi,
Volume 19, Issue 1 (7-2000)
Abstract
This paper is about experimental results for partial reduction of vortex at vertical pipe intakes. One of the easiest and practical ways of reducing vortex effect is to use anti-vortex plates or baffles. These plates can be used to avoid the vortex completely or partially. This paper will concentrate on the latter case. Rectangular plates with different dimensions have been placed at different positions to the intake pipe. Three different pipe diameters (D), 50, 75 and 100 mm, have been used. Vortex reduction percentages have been measured for each case at a constant discharge in such a way that at a given discharge, three water heads on intake pipe, namely, the water head without plate (Hn.p.), water head with plate (H), and water head with complete vortex voidance (Hn.v.), have been measured and analyzed. Plate dimensions and positions have been chosen as a multiple of pipe diameter in order to analyze and introduce the results in nondimensional form. The results of more than 6000 data points show that a plate as small as DX1.5D at the right position can reduce the vortex effect and, hence, increase, the discharge for the same head by 80%. Finally the results are presented in graph and tables format for each plate, showing the effect at best plate positions.
M. Rajabi, R. A. Sedighi , S. M. Rabiee,
Volume 34, Issue 2 (Journal of Advanced Materials- Summer 2015)
Abstract
In this study, the effect of mechanical alloying on the microstructure and phase constituents of Mg-6Al-1Zn-1Si system was investigated. To understand the thermal behavior, isothermal annealing was performed at three different temperatures of 350, 400 and 450 °C for 1h. The results showed the grain size initially decreases with increasing the milling time up to 35h and then slightly increases. In contrast, the lattice strain increases sharply with increasing the milling time up to 35h and then decreases. Second-phase intermetallic particle Mg2Si was produced during annealing and the amount of this phase was increased with increasing annealing temperature. The mechanical alloying process decreased the formation temperature of Mg2Si.
D. Pezeshki, M. Rajabi, S.m. Rabiee, G. Khayati,
Volume 34, Issue 4 (Journal of Advanced Materials-winter 2016)
Abstract
In this study, the effect of Al2O3 addition as a diluent during mechanically activated self-propagating high temperature synthesis (MASHS) of Al2O3-ZrB2 composite was investigated. For this purpose, the thermite mixture of Al, ZrO2, H3BO3 and different amounts of Al2O3 (0, 3, 6, 9 wt.%) were used as the raw materials and mechanically activated for 5 h, then furnace sintering was performed at 650 °C. The results showed that by increasing the Al2O3 content up to 6 wt.%, the intensity of exothermic peak in the DSC curves increases, but for higher additive contents it decreases. In this case, more homogenous distribution of ZrB2 particles with finer grain size was observed.
F. Z. Akbarzadeh, M. Rajabi,
Volume 36, Issue 4 (Journal of Advanced Materials-Winter 2018)
Abstract
In this study, the composite material with composition of MgH2-10 wt% (25Ce-75Ni) has been prepared by co-milling of magnesium hydride powder with Ce-Ni alloy produced by vacuum arc remelting method. The effect of milling time and additive on magnesium hydride structure, i.e. crystallite size, lattice strain and particle size, and also hydrogen desorption properties of obtained composite were evaluated and compared with pure milled MgH2. It has been shown that the addition of 25Ce-75Ni alloy to magnesium hydride yielded a finer particle size. As a consequence, the desorption temperature of mechanically activated MgH2 decreased from 340 °C to 280 °C for composite 1(5 h mechanical alloying) and to 290 °C for composite 2 (15 h mechanical alloying). Further improvement in the hydrogen desorption tempreture of composite 1 can be related to finer particle size and higher Mg2NiH4 phase value, which corresponded with calculated enthalpy results.
M. Rajabi, M. Shahmiri, M. Ghanbari,
Volume 37, Issue 4 (Journal of Advanced Materials-winter 2019)
Abstract
In this study, the effects of boron (B) and zirconium (Zr) on the microstructure and mechanical properties of Fe3Al-based alloys were investigated. Cylindrical samples were produced using a vacuum induction melting furnace (VIM); consequently, the melt was cast into a metallic mold. The microstructure, phase identification, tensile and compressive mechanical properties and fractography of the samples were investigated. Upon microstructural observation, it was found that the alloys microstucture was denderitic and the precipitated phases were mostly present between interdendritic regions. Addition of B and Zr to the alloys resulted in the formation of boride precipitates and Laves phases. The results, therefore, showed that Zr had the most pronounced effect on the mechanical properties because of the formation of Laves phases. Fractographic studies of alloys also revealed that the brittle fracture was dominant between the samples.
T. Rajabi, M. Vahedi, S. K. Sadrnezhaad,
Volume 39, Issue 2 (Journal of Advanced Materials-Summer 2020)
Abstract
Zinc/zinc oxide nanoparticles are used in an increasing number of medical and industrial applications due to their attractive physical, chemical and antibacterial properties. Therefore, achieving a simple and beneficial way to produce them is an important aspect. In this study, zinc/zinc oxide nanopowders were synthesized by fast electric discharges between two electrodes of (a) a spark device in distilled water medium and (b) a handmade high-voltage ignition machine in argon gas medium. The resulting powders were characterized by x-ray diffraction (XRD), dynamic light scattering (DLS) and field emission electron microscopy (FESEM). Using the spark device in distilled water, a mixture of zinc crystals with an average diameter of 11.28 nm and zinc oxide crystals with an average diameter of 22.22 nm was produced. However, using the handmade device in argon, zinc crystals with an average diameter of 7.5 nm were obtained and subsequently oxidized due to their extremely high activity. The production rate of the high voltage discharge method was lower than other conventional methods. On the other hand, its ability in reducing the size and increasing the particle activity was higher than other methods.
E. Mohagheghpour, R. Gholamipour, M. Rajabi, M. Mojtahedzadeh Larijani,
Volume 40, Issue 3 (Journal of Advanced Materials-Fall 2021)
Abstract
In this study, the amorphous carbon thin films were deposited by ion beam sputtering deposition method on the glass and Ni–Cu alloy substrates. The structural evolution of amorphous carbon and its correlation with the kinetic energy of carbon atoms during the growth of thin film was investigated. The effect of substrate material, deposition temperature, and ion beam energy on the structural changes were examined. Raman spectroscopy indicated a structural transition from amorphous carbon to diamond-like amorphous carbon (DLC) due to an increase in deposition temperature up to 100°C and ion beam energy from 2 keV to 5 keV. The size of graphite crystallites with sp2 bonds (La) were smaller than 1 nm in the amorphous carbon layers deposited on Ni-Cu alloy. The results of residual stress calculation using X-ray diffractometer (XRD) analysis revealed a decreasing trend in the tensile residual stress values of the amorphous carbon thin films with increasing the ion beam energy.
F. Mofid Nakhae, M. Rajabi, H. R. Bakhsheshi-Rad,
Volume 40, Issue 3 (Journal of Advanced Materials-Fall 2021)
Abstract
Development of bioactive ceramic composite scaffold materials with enhanced mechanical strength has been a topic of great interest in bone tissue engineering. In the present study, β-tricalcium phosphate scaffolds with various amounts of bredigite and an interconnected pore network suitable for bone regeneration were fabricated by the space holder method. The effect of high concentrations of bredigite on the structure, mechanical properties (compressive strength), and in vitro bioactivity was investigated. According to the results, immersion in simulated body fluid (SBF) led to the apatite formation on the surface of the scaffold, but increasing the bredigite content caused the agglomeration of the bredigite phase at the grain boundaries and deteriorated the mechanical properties.
