نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 51 (زمستان 1398)

The goal of this study was to investigate the effect of sintering temperature on the synthesis and properties of B4C-TiB2 nanocomposites by sol gel and insitu method to obtain samples with 10 wt% TiB2 nanoparticles by pressureless sintering. Accordingly, raw materials of B4C and titanium tetraisopropoxide (TTIP) were used to synthesis of B4C-TiB2 by sol gel method and TiO2, Carbon and B4C powders used for synthesizing of B4C-TiB2 by insitu method. The samples were also sintered at 2100, 2175 and 2250 °C in argon atmosphere for 1.5 hours. After that, phase XRD and FESEM analysis, relative density and micro hardness tests were used. The results show that the relative density and microhardness of boron carbide have been improved by the formation of TiB2 by both methods of sol gel and in site synthesis, and the values obtained from the sol gel method are more than that of insitu synthesis. Relative density for B4C-TiB2 samples obtained from the sol gel method at 2100, 2175 and 2250°C was 73.63%, 81.67% and 92.03%, respectively, and for B4C-TiB2 specimens obtained from the in situ method was 71.49%, 78.66% and 90.07%. Also, increasing the temperature from 2100°C to 2250°C improves the compressibility and thus increases the relative density and microhardness of B4C-TiB2 nanocomposites in both methods.

The major aim of this study was to evaluate the effect of CaO content on in vitro hydroxyapatite formation, MC3T3cells cytotoxicity and proliferation as well as antibacterial efficiency of sol-gel derived SiO2–CaO–P2O5 ternary system. For this purpose, first two grades of bioactive glass (BG); BG-58s (mol%: 60%SiO2–36%CaO–4%P2O5) and BG-68s (mol%: 70%SiO2–26%CaO–4%P2O5)) with the fixed P2O5 content were synthesized by sol-gel method. Second, the effect of CaO content in their composition on in vitro bioactivity was investigated by soaking the BG-58s and BG-68s powders in simulated body fluid (SBF) for time periods up to 14 days. The evolution of the SBF composition was monitored by inductively coupled plasma atomic emission spectrometry (ICP-AES) analyses. Additionally, Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to characterize formed hydroxyapatite on BG's surface. On the other hand, Live/dead staining, 3-(4,5dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and alkaline phosphatase (ALP) activity assays were conducted respectively, as qualitatively and quantitatively assess for cell viability, proliferation and differentiations of MC3T3cells in presence of 58s and 68s BGs. Eventually, BG-58s with enhanced MC3T3 cells proliferation and ALP activity, acceptable bioactivity and significant high antibacterial effect against MRSA bacteria is suggested as a suitable candidate in comparison to BG-68S in order to further functionalizing for delivery of therapeutic ions and growth factors in bone tissue engineering.

ZnO (Zinc Oxide) is a whell-known semiconductor that widely used in many industries. In this research, photocatalytic activity of ZnO and nanocomposite resulting from it combination with ZnWO4 were investigated. The effect of adding ZnWO4 to ZnO nanoparticles was studied on the photocatalytic activity of ZnO-ZnWO4 nanocomposites. The water in oil microemulsion method was used to synthesize nanoparticles. and various stoichiometric ratios of this nanocomposite were synthesized to study photocatalytic properties. Characteristic were studied by X-ray diffraction, Field-scattering electron microscopy, Transmitted electron microscopy, and Ultraviolet-absorption spectroscopy. X-ray diffraction results show that ZnO-ZnWO4 nanocomposites with nanocrystals formed and the results of TEM showing the particle size distribution in the range of 40 to 60 nm. The results show that the photocatalytic degradation efficiency of methylene blue by ZnO nanoparticles has been significantly enhanced by the addition of ZnWO4 and the highest degradation efficiency is related to ZnO-30% ZnWO4 nanocomposite with 96.57%.

In this study, polyaniline (PA) accompanied by chitosan (CH) were used as effective and proper support for nanoparticles. LaFeO3 (LFO) nanoparticles were synthesized by sol-gel method and characterized by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) techniques. Pt-LFO/PA-CH nanocatalyst was prepared by chemical reduction of H2PtCl6 by NaBH4 on PA-CH support in the presence of LFO nanoparticles. The morphology and distribution of nanoparticles were determined by transmission electron microscopy (TEM) images. The catalytic activity of Pt-LFO/PA-CH nanocatalyst for methanol electro-oxidation was studied through cyclic voltammetry and electrochemical impedance spectroscopy. The effects of some experimental factors for methanol electro-oxidation, such as methanol concentration, scan rate and temperature were studied on the prepared catalyst. The activation energy of the anodic peak of methanol oxidation at Pt-LFO/PA-CH was also calculated and its value was obtained 14.17 kJ mol-1. The catalytic activity of Pt-LFO/PA-CH catalyst for methanol electro-oxidation was compared with Pt/PA-CH catalyst. The electrochemically active surface area of Pt-LFO/PA-CH catalyst (77.46 m2g-1Pt) was obtained more than Pt/PA-CH (54.69 m2g-1Pt). At methanol concentration of 1.76 M, the anodic peak current density of methanol oxidation at Pt-LFO/PA-CH (377.58 mA cm-2) was obtained more than Pt/PA-CH catalyst (203.67 mA cm-2). Higher electrochemically active surface area and current density of Pt-LFO/PA-CH for methanol oxidation indicating very improved catalytic activity of Pt-LFO/PA-CH for methanol electro-oxidation. Thus, the prepared catalyst can be utilized as effective catalyst for methanol electro-oxidation in direct methanol fuel cells.

In-situ synthesizing of Al/Cr was carried out to improve the strength of spot joining of Al plates. For this purpose, 0.03gr Cr powder with 10 μm particle size was inserted in the spot joining zone and the assembly was subjected to the Friction Stir Spot Welding Process (FSSW). Microstructure, formation of intermetallic compounds and mechanical properties of samples were investigated by optical microscopy (OM), scanning electron microscopy with spot and line EDS, tensile and microhardness measurements. Spot and line scan chemical analysis (Spot-EDS and Line-EDS) of joining area indicated that minimal tool rotation speed for formation of Al-Cr intermetallic compounds (Al13Cr2) is around 2500 rpm. Formation of Al-Cr rich intermetallic compounds in the joining area increased the hardness of joining zone more than two times of hardness of join without this components (140±5 HV and 60±5 HV). Furthermore, in-situ synthesis joining increase ultimate tensile strength of the joint from 40±5 Mpa to 130±10 Mpa

During last decade, the construction and application of various adsorbents of heavy metals have been interested by many researchers. Nanocomposites with high surface areaandporosity can remove large amount of these contaminants from aques media. In this research, nanocomposites of polyacrylamide-polystyrene/bentonite synthesized,and identified. The effective parameters effective on adsorption Cd+2,Pb+2 cations including pH, Bentonite / Polyacrylamide ratio, adsorption rate, time contact, cationic and cationic activity of adsorption activity were illustrated. The structure of nanocomposites was carried out by TEM, BET, FT-IR and XRD methods. The rates of lead and cadmium adsorption were measured by atomic absorption. The results of microstructural investigations showed that in polyacrylamide-polystyrene/bentonite nanocomposite the interlayer distance in crystal structure and specific surface increased significantly in comparison with the modified bentonite. Also, the results approved that the highest adsorption at pH = 6, the best ratio of bentonite to polyacramide 2. 5: 5, the optimum absorbance was 5 g / l, the duration of the call was 12 hours, and the highest metal adsorption at 150 mg /l concentration.

In this study, the synthesis of hollow mesoporous silicate particles was studied using TEOS precursor in the presence of a polystyrene template and CTAB surfactant micelles. The process was carried out in based on alcoholic system with pH control and adding CTAB surface activator at a suitable concentration. The results of the FTIR analysis showed that the pre-forming particles of TEOS formed surface boundaries during the synthesis process with CTAB surfactant agents. Also the presence of Si-O-Si bonds (range from 600 to 1320 cm-1) indicates the formation of silicate chains on polystyrene molds. Thermal analysis studies showed that using appropriate heat treatment and precise control, all organic compounds can be removed from the system and synthesized hollow mesoporous silica particle with the least structural defects at 380°C. The BET analysis showed that the specific surface of these synthesized mesoporous silicate particles is 1180 m2.g-1 X-ray diffraction results showed that the product obtained was amorphous silica and impurity phases are not formed in this system. The DLS analysis showed that the synthesized particles had dimensions ranging in size from 1 to 10 nm and the distribution of particle size has occurred in a narrow range. SEM images confirm the sphericality of nanoparticles with a mean size of 25-30 nm. Finally, the transmitted electron microscope images showed that the synthesized silicate particles were hollow, so that the diameter of the hollow cavity and its entire total diameter are about 30 and 80 nm, respectively.