Showing 4 results for Esfahani
A.r. Pishevar Esfahani and M.r.tavakoli Nejad,
Volume 23, Issue 2 (1-2005)
Abstract
In this paper, a numerical scheme is proposed for the multi-fluid compressible flows. This method is applied to the problem of underwater explosion. The proposed scheme is basically the extension of Godunov method in gas dynamic problems to the multifluid environments and is second-order accurate in space. In this method, also, the problem of artificial mixing of two different phases on Eulerian grids is prevented by a front tracking technique. The numerical results of this study are in very good agreement with previous numerical and exprimental results
M.h. Fathi, A. Hanifi, S.i. Roohani Esfahani,
Volume 30, Issue 2 (Dec 2011)
Abstract
Due to its biocompatibility, bioactivity and high durability properties, hydroxyapatite (HA) has a wide range of applications in medical cases such as bone defect treatment and bone tissue regeneration. Biological apatite as the most important integrity of the mineral part of hard tissues consists of tiny hydroxyapatite crystals in nanoregime. It seems that using the artificial hydroxyapatite with similar structure and chemical composition to biological apatite could increase its durability inside the natural hard tissues. The aim of the present work was the synthesis of nano structured hydroxyapatite via different routes, comparison of their characterization and enhancement of the bioactivity and bioresorbability of prepared hydroxyapatite by controlling its crystal size and chemical composition. Nano structured hydroxyapatite was prepared by mechanical activation and sol-gel routes. X-ray diffraction technique (XRD), Fourier transform infra red spectroscopy (FTIR) and transmission electron microscopy (TEM) were used to characterize the prepared hydroxyapatite powders. The synthesized powder was soaked in simulated body fluid (SBF) for various periods of time in order to evaluate its bioresorbability and bioactivity after immersion in SBF. Atomic absorption spectroscopy (AAS) was used to determine the dissolution rate of calcium ions in SBF media. Results showed that the mechanical activation prepared HA powder had nano scale structure with mean size of 29 nm and the sol gel prepared HA powder had nano scale structure with mean size of 25 nm. Ionic dissolution rate of prepared nano structured powders was higher than the conventional HA (with micron size) and were similar to biological apatite. It could be concluded that bioactivity behavior of hydroxyapatite powder is affected by its crystalline size. By using the nano structure HA powder with less than 50 nm crystalline size, the optimum bioactivity and bioresorbability would be achieved.
H. Esfahani, M. Rasouli Samar, F. Dabir, A. Abdollahzadeh,
Volume 38, Issue 1 (Journal of Advanced Materials-Spring 2019)
Abstract
In this study, mechanism and kinetic of formation of boride layer on In-738 superalloy were investigated via diffusion pack cementation method. Boriding was carried out at 900 °C for several short times (5, 15, 45 and 60 min). Phase study by means of X Ray defragtion (XRD) indicated that in addition to Ni3B, other phases such as Cr5B3, AlB2, and W2B were formed at the first period of process, and other compounds such as MoB2, VB, TiB, Ni6Si2B, and Mo2NiB2 were generated in the more prolonged time. SEM study also showed that not only the thickness of boride coating was increased, but also an interdiffusion zone (IDZ) was formed under the coating and it was grown by the upward diffusion of alloy elements. The kinetic study was good according to diffusion theory, confirming the two diffusion steps for IDZ. Thickness and hardness of the boride coating over 60 min process were 27.8 µm and 853 HV, respectively.
S. Borhani Esfahani, H. R. Salimi Jazi, M. H. Fathi, A. Ershad Langroudi, M. Khoshnam,
Volume 40, Issue 1 (Journal of Advanced Materials-Spring 2021)
Abstract
In this research, a kind of environmentally-friendly inorganic-organic hybrid nanocomposite coating based on silica containing titania/silica core/shell nanoparticles was synthesized and characterized for conservation of facade tiles in historical buildings. The matrix of the composite was prepared by sol-gel process via two methods of ultrasonic and reflux stirring. Tetraethyl orthosilicate (TEOS) and poly-dimethyl siloxane hydroxy-terminated (PDMS-OH) were used for the formation of silica network and creation of flexibility and hydrophobicity, respectively. Titania nanoparticles were used in the form of titania/silica core/shell as ultraviolet absorber. The synthesized nanocomposite was applied on the microscope slides and tiles by dip coating technique. The properties of nanoparticles and coatings were characterized by Fourier-transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM) and water contact angle measurement. The results revealed that formation of titania/silica core/shell structure was successful. The investigation of PDMS content effect on transparency, cohesion and hydrophobicity of the coating confirmed that the optimum content of this siloxane was around 20 wt.%. In general, the results showed that the silica-based hybrid nanocomposite reinforced with TiO2/SiO2 core/shell nanoparticles could produce a transparent and hydrophobic coating for tile and glass protection.
