Improvement of oxidation resistance of graphite by aluminosilicate coating with aluminum metaphosphate interlayer

M. Fekri,K. Jafarzadeh,S. A. Khalife Soltani,Z. Valefi,H. Mazhari Abbasi 한국탄소학회 2023 Carbon Letters Vol.33 No.7

In this research, in order to increase the oxidation resistance of graphite, kaolin and alumina powder with different ratios (26A-74S, 49A-51S, 72A-28S) and slurry method were used to create an aluminosilicate coating on the graphite substrate. In order to reduce the difference in the coefficients of thermal expansion of graphite with aluminosilicate coating, aluminum metaphosphate coating as an interlayer was prepared on the surface of graphite by cathodic electrochemical treatment. The isothermal oxidation test of the samples was carried out in air at a temperature of 1250 °C for 1, 3 and 5 h. The microstructure, chemical composition, and phase components of the coating were, respectively, analyzed by scanning electron microscope equipped with an energy-dispersive spectrometer and X-ray diffraction. The results indicated that, by increasing the withdrawal speed of the samples in slurry method, the amount of changes in the weight of the samples has increased and therefore had a direct effect on oxidation. In addition, it was approved that, at high-temperature oxidation, AlPO4 glass phase forms on aluminum metaphosphate interlayer which retards graphite oxidation. Along with aluminum metaphosphate, aluminosilicate coating also produces a glass phase which fills and seals the voids on the surface which prevents the oxygen to reach the surface of graphite. The created double-layer coating including an interlayer of aluminum metaphosphate + slurry coating prepared with the ratio of 26A-74S as the optimal coating in this research was able to increase the oxidation resistance of graphite by 73% at a temperature of 1250 °C.

Migration of Ca II H bright points in the internetwork

Jafarzadeh, S.,Cameron, R. H.,Solanki, S. K.,Pietarila, A.,Feller, A.,Lagg, A.,Gandorfer, A. EDP Sciences 2014 Astronomy and astrophysics Vol.563 No.-

Analysis of lateral extrusion of gear-like form parts

H. Jafarzadeh,G. Faraji,A. F. Dizaji 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.10

The analysis of lateral extrusion process was carried out. A three dimensional FE model was developed to analyze the effects of some important geometrical parameters such as initial billet dimensions, gap height and frictional condition on the required forging load, the material flow pattern and effective plastic strain distribution. The FE code of DEFORM-3D was employed. A series of experimental tests on commercial lead billets were carried out to verify the FE results. The simulation work has been performed by the rigid-plastic FE method. The results obtained using the numerical solutions have been compared with the experimental data for each case study in terms of required forming load and material flow pattern in different regions. Comparison between FE and experiment results showed good agreement. Both the simulation and experimental results highlight the major role of above mentioned parameters on the required forming load and material flow pattern. The results showed that the gap height has the greatest effect on the forming load and material flow. The results presented in this paper could be used as basic data in the design of the lateral extrusion process.

Numerical and experimental analyses of repetitive tube expansion and shrinking processed AZ91 magnesium alloy tubes

H. Jafarzadeh,K. Abrinia 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.2

A novel severe plastic deformation (SPD) technique entitled repetitive tube expansion and shrinking (RTES) has been developed tofabricate ultra-fine grained and nanostructured AZ91 tubular components. This method includes two different half-cycles and is based onpressing a tubular part through an angular channel die with two shear zones. In order to primarily demonstrate the deformation behaviorand refinement ability of RTES method, the FE simulations and experimental analyses were both done. Analytical calculations and FEsimulations of this method accompanied by Abaqus/explicit indicate that the large amount of equivalent plastic strain of 5.8 is imposed ineach cycle. In experimental investigations of a single-cycle of RTES, microstructural observations showed a significant grain refinementfrom the initial value of ~150 μm to ~700 nm. The distribution characteristic of refinement and hardness were consistent with that ofsimulated effective strain. This novel SPD method seems to be very promising for future commercial practice.

Accumulative radial-forward extrusion (ARFE) processing as a novel severe plastic deformation technique

H. Jafarzadeh,A. Babaei 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.6

A novel severe plastic deformation (SPD) technique entitled accumulative radial-forward extrusion (ARFE) is introduced for producingultra-fine grained bulk materials. This method is based on radial-forward extrusion process because of inherent capabilities for imposingextremely high plastic strains on material. ARFE was applied to AA1050 and the ability of this process in significant grain refinementis determined even after single cycle. Transmission electron microscopy (TEM) examination showed ultra-fine grains (UFGs) withthe average grain size of 450 nm after one cycle of ARFE. Furthermore, micro-hardness distribution through the part’s section indicatesthe hardness increase to ~52 Hv from the initial value of ~28 Hv after one cycle of ARFE. In order to further investigate of the accumulatedstrains, ARFE process was also numerically modelled by finite element method.

High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI

Jafarzadeh, S.,Solanki, S. K.,Stangalini, M.,Steiner, O.,Cameron, R. H.,Danilovic, S. American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.229 No.1

<P>We characterize waves in small magnetic elements and investigate their propagation in the lower solar atmosphere from observations at high spatial and temporal resolution. We use the wavelet transform to analyze oscillations of both horizontal displacement and intensity in magnetic bright points found in the 300. nm and the Ca II H 396.8 nm passbands of the filter imager on board the SUNRISE balloon-borne solar observatory. Phase differences between the oscillations at the two atmospheric layers corresponding to the two passbands reveal upward propagating waves at high frequencies (up to 30 mHz). Weak signatures of standing as well as downward propagating waves are also obtained. Both compressible and incompressible (kink) waves are found in the small-scale magnetic features. The two types of waves have different, though overlapping, period distributions. Two independent estimates give a height difference of approximately 450 +/- 100 km between the two atmospheric layers sampled by the employed spectral bands. This value, together with the determined short travel times of the transverse and longitudinal waves provide us with phase speeds of 29 +/- 2 km s(-1) and 31 +/- 2 km s(-1), respectively. We speculate that these phase speeds may not reflect the true propagation speeds of the waves. Thus, effects such as the refraction of fast longitudinal waves may contribute to an overestimate of the phase speed.</P>

Numerical and experimental investigation of the deformation behavior during the accumulative back extrusion of an AZ91 magnesium alloy

Faraji, G.,Jafarzadeh, H.,Jeong, H.J.,Mashhadi, M.M.,Kim, H.S. BUTTERWORTH - HEINEMANN 2012 MATERIALS AND DESIGN Vol.35 No.-

<P><B>Highlights</B></P><P>► The accumulative back extrusion (ABE) was introduced as a high straining method suitable for AZ91. ► The strain distribution and deformation behavior during the ABE process using the finite element simulation was investigated. ► The deformation ratio and die stroke led to better deformation homogeneity and more plastic strains.</P> <P><B>Abstract</B></P><P>In the present study, the finite element method (FEM) and an experimental investigation were performed during the accumulative back extrusion (ABE) processing of an AZ91 magnesium alloy in order to investigate the effects of the deformation ratio (= inner punch diameter/outer punch diameter) and die stroke (DS) on the plastic deformation behavior. The results showed that increasing the deformation ratio and DS led to better deformation homogeneity and more plastic strains. There are two distinct regions in the ABE processed samples containing low and high plastic strain areas and the metallurgical investigations showed that more grain refinement with a mean grain size of 1.5μm takes place in high strain regions while the grain sizes are larger in other regions. A comparison between the FEM and experimental results of the required loads and developed microstructures showed good agreement.</P>

Kinematics of Magnetic Bright Features in the Solar Photosphere

Jafarzadeh, S.,Solanki, S. K.,Cameron, R. H.,Barthol, P.,Rodrí,guez, J. Blanco,Iniesta, J. C. del Toro,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Knö,lker, M.,Pillet, V. Martí,nez,Su&aacut American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.229 No.1

<P>Convective flows are known as the prime means of transporting magnetic fields on the solar surface. Thus, small magnetic structures are good tracers of turbulent flows. We study the migration and dispersal of magnetic bright features (MBFs) in intergranular areas observed at high spatial resolution with SUNRISE/IMaX. We describe the flux dispersal of individual MBFs as a diffusion process whose parameters are computed for various areas in the quiet-Sun and the vicinity of active regions from seeing-free data. We find that magnetic concentrations are best described as random walkers close to network areas (diffusion index, gamma = 1.0), travelers with constant speeds over a supergranule (gamma = 1.9-2.0), and decelerating movers in the vicinity of flux emergence and/or within active regions (gamma = 1.4-1.5). The three types of regions host MBFs with mean diffusion coefficients of 130 km(2) s(-1), 80-90 km(2) s(-1), and 25-70 km(2) s(-1), respectively. The MBFs in these three types of regions are found to display a distinct kinematic behavior at a confidence level in excess of 95%.</P>

Educational Intervention Based on the Health Belief Model to Modify Risk Factors of Cardiovascular Disease in Police Officers in Iran: A Quasi-experimental Study

Mohsen Saffari,Hormoz Sanaeinasab,Hassan Jafarzadeh,Mojtaba Sepandi,Keisha-Gaye N. O’Garo,Harold G. Koenig,Amir H. Pakpour 대한예방의학회 2020 예방의학회지 Vol.53 No.4

Objectives: Police officers may be at a greater risk for cardiovascular disease (CVD) than the general population due to their high-stress occupation. This study evaluated how an educational program based on the health belief model (HBM) may protect police officers from developing CVD. Methods: In this single-group experimental study, 58 police officers in Iran participated in a 5-week intervention based on HBM principles. Outcomes included changes in scores on an HBM scale, time spent on moderate to vigorous physical activity (International Physical Activity Questionnaire), body mass index (BMI), blood lipid profile, blood glucose, and blood pressure. The intervention consisted of 5 HBM-based educational sessions. Follow-up was conducted at 3 months post-intervention. The paired t-test was used to examine differences between baseline and follow-up scores. Results: All aspects of the HBM scale improved between baseline and follow-up (p<0.05), except the cues to action subscale. Self-efficacy and preventive behaviors improved the most. BMI decreased from 26.7±2.9 kg/m2 at baseline to 25.8±2.4 kg/m2 at follow-up. All components of the lipid profile, including triglycerides, cholesterol, high-density lipoprotein, and low-density lipoprotein, showed significant improvements post-intervention. Blood glucose and blood pressure also decreased, but not significantly. Nearly 25% of participants who were not physically active at baseline increased their physical activity above or beyond the healthy threshold. Conclusions: A relatively brief educational intervention based on HBM principles led to a significant improvement in CVD risk factors among police officers. Further research is needed to corroborate the effectiveness of this intervention.