مجله مواد و فناوری های پیشرفته
سال نهم شماره 4 (زمستان 1399)

In this study, the properties of Al2O3-B4C synthesized nanocomposite components were investigated. The Al2O3-B4C nanocomposite powder was synthesized from aluminum, boron oxide, and graphite powders via mechanical alloying route, followed by self-propagation high-temperature synthesis (SHS). In order to produce bulk parts, the nanocomposite powder was sintered by hot pressing at 1400, 1500, and 1600 °C. Characterization of powder samples and bulk parts was performed using X-ray diffraction and scanning electron microscopy. The results of the X-ray diffraction analysis showed that no phase change occurs in the mechanochemical process, instead, the reduction of particle size and proper mixing of the powders encourages the SHS process and product formation. The best results were obtained to the bulk part that sintered at a temperature of 1500 °C with a hardness of 19.6 GPa, 99.4 % relative density, and 6.7 MPa.m1/2 toughness. Also, as the sintering temperature rises to 1600 °C and the density increases, the hardness of the part decreases due to grain growth.

The purpose of this investigation is to find a new coating method to reduce economic costs, meet the needs of the marine industry to high-strength ship propellers and increase the lifetime of these pieces during the operation in seawater. For this purpose, milled TM mineral powder (containing a combination of iron and titanium) was coated on the surface of a Nibral alloy substrate by high-speed oxygen fuel (HVOF) thermal spraying process. The coating properties were evaluated using X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), microhardness, and roughness analysis. Also, the tribological behaviour of the substrate and the coating was evaluated using the pin on disk wear test under a 10 N load and a distance of 1000 m at ambient temperature. The results of powder characterization indicate the suitable particle size distribution and the presence of phases containing iron and titanium elements in the powder. Accordingly, the crystallinity and phase stability of the powder in the coating were enhanced by the presence of CuFe2O4, Fe3O4, and Fe2.6O4Ti0.52 phases. The results showed that the high velocity of throwing particles during spraying and the density of the coating structure caused the increase of the coating adhesion to the substrate, the decrease of porosity and the increase of hardness of the coating. This coating, with a lower wear rate than the substrate, significantly increased the wear resistance of the specimen.

In the last decade, many cases of modified chemical processes for the green synthesis of nanomaterials have been reported. Considering the remarkable properties of nanomaterials and environmental issues, a rapid and biocompatible approach as a new option for the synthesis of copper oxide nanoparticles (CuO-NPs) using Chenopodium album )C.album(leaf extract, as a renewable and non-toxic reducing agent and an effective stabilizer, was presented in this study. It is noteworthy that the current synthesis process can provide the possibility of rapid, cheap, and high efficiency production of CuO nanoparticles with a spherical morphology (135 nm) at ambient temperature and pressure. Optimization of important parameters in the formation of CuO-NPs, such as pH, copper ion concentration, the quantity of leaf extract, and incubation time and temperature was examined. The formation of CuO-NPs was confirmed by UltraViolet-Visible (UV–Vis) spectroscopy, X-Ray Diffraction (XRD), Fourier Transform InfraRed (FT-IR) spectroscopy, and Transmission Electron Microscopy (TEM). Owing to the good stability and superior catalytic activity of the synthesized CuO-NPs, they were used to degrade methylene blue (MB) and rhodamine B (RhB) dyes as water colour contaminants in the presence of NaBH4 at room temperature. The reaction process was monitored using UV-visible measurements at regular intervals. According to the reaction conditions, reduction of MB and RhB occurred at 8 min and 52 min, respectively.

The purpose of this study was to prepare and compare a hydroxyethyl cellulose/hyaluronic acid (HEC/HA)-based scaffold with and without gelatin for the treatment of second-degree partial-thickness burns. The scaffolds were prepared by freeze-drying method from the aqueous solutions of the mentioned polymers. Microstructural examination by scanning electron microscopy (SEM) indicated the average pore size of 120 and 98 µm for the gelatin-free and gelatin-containing scaffolds, respectively. According to the dynamic rheology measurements (DMA), all the solutions were flowable in which, the loss modulus was higher than the storage one. Moreover, the solutions revealed shear-thinning behaviour at low frequencies, which changed to shear thickening at frequencies higher than 100 s-1. Both loss and storage modulus increased by adding gelatin to the polymer solutions. The scaffolds water uptake was up to 3,000%. The addition of gelatin to the HA/HEC solution increased the polymer network collapse up to 2 hours and led to reducing the scaffolds degradation rate. Cytotoxicity assay in the presence of the scaffolds showed that more than 80 % of the fibroblast cells were viable (compared to the control group), meanwhile, the presence of  gelatin had a positive effect on the metabolic activity of the cells and increased the rate of cell proliferation.  Scratch test results showed the ability of scaffolds to increase the cell migration rate compared to the control sample. The hydroxyethyl cellulose/hyaluronic acid/gelatin scaffold due to the presence of gelatin and improved the cell migration, which indicating the rapid re-epithelialization, reduced wound contraction to   73 % within 24 hours.

In this research, the electrodeposition of antimony was studied in alkaline sulfide solution. The effect of time and temperature of electrowinning step on antimony recovery, current efficiency and specific energy in the temperature range of 45-65 °C for 0-6 h was investigated. Furthermore, the kinetics of electrodeposition was studied, and the results were used in developing mathematical model. Results show that increasing the temperature of electrowinning decreases antimony recovery, current efficiency and increases energy consumption. Hydrogen evolution at the cathode at low concentration of antimony in the solution and occurrence of harmful reactions at the electrodes lead to energy consumption and decrease current efficiency and antimony recovery. Maximum antimony recovery was 70 % after 6 h electrodeposition at 45 °C and maximum current efficiency was 90 % after one hour electrodeposition at the same temperature. The energy consumed per one kilogram of deposited antimony in the temperature range of the experiments was in the range of 1.35-2.28 kWh. Minimum value of consumed energy was achieved at 45 °C. The kinetic investigation shows that Avrami- Erofeyev equation can be used for prediction of antimony recovery with high accuracy.

Abstract     In this research work, electrospun TiO2/PVP nanofibers were prepared by using two different collectors, i.e., flat stationary plate and rotating drum. The effects of these collectors in conjunction with polymer concentration in TIP/PVP sol solutions (i.e., 3, 5, and 7 wt. %) were investigated on morphologies of the as-spun TiO2/PVP composite nanofibers. SEM micrographs were used for determination of the average  nanofiber diameters and their standard deviations (SDs). Rotating speed of the collecting drum was set at 500 rpm for all samples prepared by it, while other electrospinning parameters (i.e., applied voltage, flow rate, tip-to-collector distance, and needle gage) were the same for the counterpart samples prepared from each of sol solutions by two types of collectors, throughout the experiment. It was observed that TiO2/PVP nanofibers electrospun by rotating drum have average diameters and SD of 144 ± 58 nm (from sol solution with 3 wt. % PVP at applied voltage of 10 kV) and 122 ± 71 nm (from sol solution with 5 wt. % PVP at applied voltage of 15 kV). These magnitudes were pretty much lower than the average diameters of TiO2/PVP nanofiber prepared by a flat stationary plate. The average diameters of TiO2/PVP nanofiber prepared by flat stationary plate and rotating drum were 258 ± 122 and 292 ± 135 nm, respectively when polymer concentration in TIP/PVP sol solution increased to 7 wt. %. It is clearly shown that by increasing polymer concentration in electrospinning solution, the average diameter of the electrospun TiO2/PVP nanofibers increased, afterward. Therefore, rotational speed of collecting drum should be increased rationally if there is a need for preparation of finer electrospun nanofibers.

Nickel-based catalysts are used in refining and petrochemical processes. After being regenerated and reused several times, these catalysts are released as used catalysts in nature, which, in addition to environmental risks, are not economically viable due to the presence of the precious metal nickel. Hydrometallurgical methods are commonly used to extract nickel, which is difficult and expensive. Due to the significant shortage of nickel mines, the use of these secondary resources is quite important. In this study, the possibility of nickel recovery from used catalysts has been investigated. Initially, the cokes were removed, and then the effects of three different acids on nickel leaching were investigated. Various parameters such as temperature, mixing speed, liquid to solid ratio, particle size, and acid concentration were investigated. After the complete leaching of nickel, nickel purification was performed by selective nickel hydroxide precipitation.