Papers by Author: Ali Shokuhfar

Abstract: In this work, a flower-shaped ZnO/GO/Fe₃O₄ ternary nanocomposite was synthesized via the co-precipitation method. Two significant goals of the study were boosting the degradation efficiency of ZnO and achieving a fast and simple synthesis approach. The structure, properties, and morphology of the product were characterized, and the effect of the ZnO flower-shaped structure in combination with GO nanosheets and magnetite nanoparticles was investigated on the photocatalytic activity. The structure and quality of the prepared nanocomposite were assessed by X-ray diffraction pattern, UV-visible DRS spectroscopy, Field Emission Scanning Electron Microscopy (FE-SEM). The catalytic activity of the nanocomposite was assessed by spectrophotometric analysis. The developed nanocomposite offered high photodegradation efficiency in Rhodamine B degradation under UV-C light in comparison with pure ZnO. At a specific period, the efficiency of the synthesized sample was about two times greater than that of pristine ZnO particles. Our nanocomposite is anticipated to have practical benefits in wastewater treatment given its good performance, economic savings through reducing the amount of catalyst consumption and saving time, and being a facile and fast synthesis method.

Abstract: In this work the effects of volume fraction at different milling times and impact forces, defined as the ball-to-powder weight ratio (BPR), on the elemental diffusion during mechanical alloying process of Al-4.5wt%Mg/TiC composite were evaluated and compared with the TiC free samples (Al-4.5wt%Mg alloy). X-ray diffraction patterns of the monolithic and composite samples imply the fact that a higher level of mutual diffusion of constituents, Al and Mg, happened in the matrix in the presence of TiC particles. This effect of the reinforcing particles can be attributed to the increased densities of dislocation and vacancy caused by the presence of TiC particles within the matrix-giving rise to increasing the micro-strain, lattice parameter and decreasing the crystallite size. Scanning electron microscopy (SEM) was used not only to study the morphology of the powders but also to show the fact that the TiC powders were distributed during MA process. The TEM and HRTEM results showed that powder produced in this work has a nanosize.

Abstract: In this research, the formation mechanisms of a (NiCr)Al-Al2O3 nanocomposite were investigated. The structural changes of powder particles during mechanical alloying were studied by X-ray difractometry (XRD) and the morphology and cross sectional microstructure of powder particles were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The methodology involved mechanical alloying of NiO, Cr, and Al with molar ratios of 3:3:8. During mechanical alloying, NiO was first quickly reduced by aluminum atoms to produce NiAl nanocrystalline and Al2O3. Subsequently, and when a longer milling time was applied, chromium atoms diffused into the NiAl lattice. The heat treatment of this structure led to the formation of the (NiCr)Al intermetallic compound as well as Al2O3 with crystalline sizes of 23 nm and 58 nm, respectively.

Abstract: In this paper a novel L-shape microcantilever that is more sensitive in compare of traditional rectangular microcantilever is proposed. In traditional microcantilever surface stress sensor a slight momentum is induced by distributed area stress lead to a slight deformation. In contrast, the proposed sensor substitution the slight momentum with concentrated point force in lateral direction on the tip of the microcantilever. This lead to, mechanically amplifies of the influence of area stress and more displacement. In addition, it has been theoretically proved that proposed microcantilever sensor with same lateral area in compare with traditional microcantilever surface stress sensor can be 2 to 100 orders more sensitive. The proposed L-shape microcantilever configuration of sensor could be incorporated in most of the microfabrication processes. However in this paper we use a low cost fabrication method based on polymeric microcantilever with metal piezoresistive detection.

Abstract: Hydroxyapatite (HA) is a bioactive ceramic, employed mainly in bone tissue engineering since it exhibits superior biocompatibility and osteoconductivity. Attempts have been made to synthesize HA nanoparticles with chemical composition, morphology, crystallinity and Ca/P ratio similar to that of natural bone. While wet chemical methods are becoming more popular for synthesis of HA nanoparticles, ultrasound irradiation has shown to be an effective method to increase the rate of production and also to decrease particle size. However, process variables must be carefully selected. In the present study, HA nanoparticles with desirable characteristics have been synthesized by the aid of ultrasound irradiation and characterized by powder X-ray diffraction (XRD) and electron microscopy techniques.

Abstract: In this article the last findings of composites with polymer, metal and ceramic matrices containing carbon fibers and their applications in internal combustion engines in the world beside their advantages and superiorities in comparison with common industrial materials are investigated. Afterwards, the position of these materials in automotive engines in Iran is analyzed. Researches show that carbon fibers-reinforced composites due to unique properties (including high specific strength and specific modulus, low thermal expansion coefficient, high fatigue strength, and high thermal stability) can replace common structural materials in different engine parts (such as, casing, different components, cylinder lining, and etc.). Applying these composites will result in weight reduction and consequently fuel consumption reduction, less pollution, better function and efficiency, and more lifetimes. Of course one should consider that there is a vast potential for application and development of composites in automotive engine, which will become in practice by complementary researches through time. Due to novelty of this technology in the world and also the lack of carbon fibers production and insufficient knowledge of production and application of carbon fiber composites in Iran, this issue has not been seriously investigated.

Abstract: Nowadays, the nano-machining process is used to produce high quality finished surfaces with precise form accuracy. To understand and analyze the chip formation mechanism of nano-machining process on an atomistic scale, since the experimentation is not an easy task, numerical simulation such as molecular dynamic (MD) simulation is a very useful method. In this paper, MD simulation of the nano-metric cutting of single-crystal copper was performed with a single crystal diamond tool. The model was solved with both pair wise Morse potential function and embedded atom method (EAM) potential to simulate the inter-atomic force between the work-piece and a rigid tool. The chip formation mechanism, dislocation generation, tool forces and generated temperature were investigated. Results show that the Morse potential cannot perform an appropriate defect formation and plastic deformation in nano-metric cutting of metals. Also, tool forces in Morse potential are more than the forces in EAM potential. Furthermore, the fluctuations of resultant forces in Morse potential are greater than that of EAM. In addition, using many-body interaction potentials like EAM can lead to substantial changes in surface energies, elastic-plastic properties and atomic displacement, compared with the pair-wise potentials like Morse. Finally, the atomic displacement investigation shows that in EAM potential study, only the atoms in a local region near the cutting process are displaced, but in Morse potential a large portion of atoms has affected during cutting process. Subsequently, the chip temperature in EAM potential is more than that of Morse potential.

Abstract: Today, there is a need to understand the micro mechanism of material removal to achieve a better roughness in ultra precision machining (UPM). The conventional finite element method becomes impossible to use because the target region and grids are very tiny. In addition, FEM cannot consider the micro property of the material such as atomic defect and dislocation. As an alternative, molecular dynamics (MD) simulation is significantly implemented in the field of nano-machining and nano-tribological problems to investigate deformation mechanism like work hardening, stick-slip phenomenon, frictional resistance and surface roughness [1]. One of the machining parameters than can affect nano-cutting deformation and the machined surface quality is tool nose radius [2]. In this paper molecular dynamics simulations of the nano-metric cutting on single-crystal copper were performed with the embedded atom method (EAM). To investigate the effect of tool nose radius, a comparison was done between a sharp tool with no edge radius and tools with a variety of edge radii. Tool forces, coefficient of friction, specific energy and nature of material removal with distribution of dislocations were simulated. Results show that in the nano-machining process, the tool nose radius cannot be ignored compared with the depth of cut and the edge of tool can change micro mechanism of chip formation. It appears that a large edge radius (relative to the depth of cut) of the tool used in nano-metric cutting, provides a high hydrostatic pressure. Thus, the trust force and frictional force of the tool is raised. In addition, increasing the tool edge radius and the density of generated dislocation in work-piece is scaled up that is comparable with TEM photographs [6].

Abstract: In this work, the preparation of nanostructured Al-4.5wt%Mg powder through the mechanical alloying (MA) process was evaluated. The X-ray diffraction (XRD) technique was used to calculate the crystallite size and microstrain. Scanning electron microscopy (SEM) was used not only to study the morphology of the powders but also to show the fact that the Mg powders were distributed during the MA process. Transmission electron microscopy (TEM) was also used to demonstrate whether the produced powders are nanostructured or not. XRD results showed that microstrain and crystallite size of milled powder (after 10 h milling at the ball-to-powder weight ratio (BPR) of 20:1) were ≈-0.34% and ≈20nm respectively. XRD and TEM results showed that Al₁₂Mg₁₇ has been formed during MA process. This means that during this process, mutual diffusion of Al and Mg has occurred.

Abstract: Hydroxyapatite (HAp) is an important bioactive ceramic that possessing beneficial biocompatibility and osteoconductivity resulting in bonding to human bone tissues. The dry mechanochemical process is widely used to prepare nanometer HAp. However, little research has been carried out concerning the correlation between adding alumina and the structural changes during the mechanochemical process. In this research, special attention was paid to the effect of alumina additive on the crystallite size and lattice strain of nanocrystalline HAp. Characterization was accomplished by using powder X-ray diffraction (XRD). The obtained data demonstrated that the diffraction lines corresponding to the HAp phase became broad and weak with increasing alumina additive. In fact, the nanocrystalline HAp with high crystallinity degree can be synthesized in the proper amounts of alumina additive via mechanochemical method. Furthermore, an increase of alumina additive led to increase in lattice strain and decrease in size of the powder grain.