ADVANCED MATERIALS IN ENGINEERING (ESTEGHLAL)
Year:2020 | Volume:38 | Issue:4 |Papers Count:11

In this study, seven-layer nanofiber structures consisting of polycaprolactone/ chitosan polymers loaded with methotrexate and 5-fluorouracil anti-cancer drugs, for controlled drug delivery, were produced and evaluated. For this purpose, the second, fourth and sixth layers were loaded with drug and placed between the drug-free layers. The surface morphology of drug-free and drug-loaded nanofibers was investigated by scanning electron microscopy (SEM) and Fourier transform infrared spectrometry (FTIR) was used to study their chemical structure. The drug release rate in phosphate buffered saline (pH=7. 4) and the released drug concentration were measured by spectrophotometry. Mechanical properties of single-and multi-layered samples were also investigated. SEM images showed formation of uniform and beadless fibers. FTIR spectrum confirmed presence of the drugs in the polymer mixture with no interaction. It was found that by increasing the chitosan content, a brittle structure with decreased elongation is formed. The release behavior of methotrexate and 5-Fluoracil drugs in neutral pH environment for 26 days was evaluated and the results exhibited a slow and sustained release.

In this study, joining of Ni3Al intermetallic compounds using the transient liquid phase (TLP) process with Cu interlayer was investigated. The binding process was carried out in a vacuum furnace at a temperature of 1050 ° C for different times of 30, 60, 90 and 120 minutes. The effect of time variation on microstructure and mechanical properties of the joint zone was investigated. The EDS analysis results of the joints proved formation of the athermally solidified zone (ASZ), isothermally solidified zone (ISZ) and diffusion affected zone (DAZ) at different times. After 90 minutes, brittle eutectic phases still exist in the joint line. However, by increasing the process time to 120 minutes, a copper-rich solid solution was formed in the joint line. Maximum hardness was attained in DAZ region and due to formation of more brittle compounds. By increasing the process time to 90 min, the hardness in the joint center-line increased. After 120 min, the hardness in the joint center-line decreased to about 224 HV. Maximum shear strength was achieved to be about 60 MPa at a process time of 30 minutes and due to formation of Nirich matrix at the joint. With increasing time to 90 min, the shear strength decreased to about 34 MPa. After 120 minutes and due to formation of copper-rich solid solution as well as disappearance of eutectic compounds, shear strength again increased to about 44 MPa. Investigation of fracture surfaces showed that until 90 minutes, fracture mode was mainly brittle whereas by increasing time to 120 minutes, a more ductile fracture occurred.

The purpose of this study was to evaluate the effect of glycyrol (tri-dentate, GLY) and ethylenediamine (double-dentate clay, en) chelating agents on phase and morphology changes of spinel nanoparticles synthesized by sol-gel method. Characterization of samples was performed by X-ray diffraction (XRD) and field-emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray spectrometer (EDX). The results showed that both samples synthesized with GLY and en contain cubic spinel phase. The sample synthesized with ethylenediamine has a pyramidal morphology with particle size in the range of 20-25 nm whereas the specimen prepared with glycerol is spherical with particle size in the range of 20-25 nm. Finally, suggested mechanism for morphological changes of spniel nanoparticles was discussed.

In this research, the optical properties of tungsten disulfide including dielectric function, the static refractive index, the imaginary part of the dielectric function, optical band gap, energy loss spectrum and its magnetic properties have been studied. Calculations have been done by using Quantum Espresso package which is based on density functional theory and pseudo-potential technique. The static refractive indices of this compound at diffrent x and z directions were calculated 3. 66 and 2. 55, respectively. The amount of optical band gap, obtained from the imaginary part of dielectric function, was estimated to be 1. 45 eV. In addition, bulk plasmon energy, obtained from energy loss spectrum at x and z directions, were obtained to be 17. 95 eV and 17. 25 eV, respectively.

Amorphous steel slag was blended with different concentrations of waste glass (20, 40, 50, 60, 70 wt. %) and SiC to obtain a composite. According to Hot Stage Microscopy images, slag-glass composite contractions started at 1050 º C. scanning electron microscope micrographs of slag-SiC (foaming agent) composite revealed tunnel-like porosities of 500 to 1000 microns. Gaseous products of carbide decomposition led to the formation of these tunnel-like porosities. By adding up to 50 wt. % of waste glass to this composite and sintering at 1200 ° C, the size of cavities decreased by 10 times and achieved 50 microns to form spherical cavities. By increasing glass content, the total porosity of slag-glass-SiC increased to 80 wt. % followed by a decrease in the strength to 3. 2 MPa. Having an overall density of 0. 8 g/cm 3, the slag-glass composite could be classified as a porous foam material. Pseudo Waltonite phase was also detected in this composite after sintering.

Due to special properties such as low density, high strength and high corrosion resistance Ti-6Al-4V alloy has been used extensively in various industries, especially in the aerospace aspects. However the major problem of this alloy is its poor tribological properties under relatively high loads. In the present study, in order to improve the tribological properties of mentioned alloy, chromium particles were added to Ti-6Al-4V layers in the nitrogen-containing atmosphere during the Tungsten Inert Gas (TIG) welding process. Microstructural investigations using optical microscopy, X-ray diffraction analysis and scanning electron microscopy, proved the formation of TiN, TiCr2 and Cr2N particles in the matrix of hard titanium phase. The hardness of TIG alloyed layer increased to 1000 HV0. 3 which was 4 times higher than that of the base alloy. Moreover, the wear rate of TIG alloyed samples with chromium and nitrogen under 30N load and distance of 1000 m was 5. 9 times lower than that of the bare Ti-6Al-4V alloy.

In this research, solid state carbothermal synthesis of HfB2 Nano powders was investigated. For this purpose, HfO2, H3BO3, carbon active or phenolic resin were used as raw materials for carbothermal reaction. After 2-4 hours of milling the raw materials by a planetary ball in an ethanol media, the mixture was heat dried and pressed in to disks under pressure of 20-30 bar. The disks were then placed in a graphite crucible and heat-treated at 1500– 1600 ° C for 1 hour under flowing Ar atmosphere. The powder product was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and backscattered electron (BSE) imaging. The heat treatment temperature, amount of boric acid, milling and heat treatment time were recognized as four factors influencing synthesis and size of HfB2 powder particles. SEM images reported irregular morphologies with a particle size of about 2-4 µ m for HfB2 powder. The best sample was obtained at a molar ratio of HfO2: phenolic resin carbon: boric acid = 1: 5: 5 at 1600 ° C after 1 hour of heat treatment. XRD results confirmed synthesis of pure HfB2 with a crystallite size of about 60 nm.

The concentrated solar power (CSP) is one of the renewable energy sources in which solar irradiation heat energy will be used in a steam turbine to generate electrical grid. Solar radiation is absorbed by a solar receiver reactor on the surface of a porous solar absorber. In this survey, synthesis and mechanical/thermal characterization of micro-porous silicon carbide (SiC) absorber to be used in solar reactor is carried out. SiC foams were synthesized and categorized based on three different pore sizes i. e. 5, 12 and 75 ppi. Mechanical behavior and thermal shock resistance of porous foams in the working temperature range for absorber (25-1200 ° C) were evaluated. Results revealed that the specific compressive strength (σ c/ρ ) of foams increase exponentially by a decrement in the porosity percentage and the average pore size. Moreover, for foams with smaller pore size, a considerable decrease in mechanical strength due to thermal shock was observed. This could be due to increase in the number of struts per unit volume i. e. more weak struts to withstand the mechanical loading. So, porous foams with coarser pore sizes were distinguished to be more capable of tolerating thermal shock while serving as solar absorbers.