فصلنامه مواد پیشرفته در مهندسی
سال چهل و یکم شماره 4 (زمستان 1401)

In this study, a 3D bioactive glass composite scaffold containing 2 mol% silver/polycaprolactone (PCL) was synthesized by a 3D printer with the advantages of reproducibility and high flexibility in shape and size. The effective parameters (printer parameters, ratio of glass-phase, polymer phase, and solvent in printer ink) were determined for printing of nanocomposite scaffold by Taguchi method. Characterization of printed scaffolds was performed using X-ray diffraction, scanning electron microscope, infrared spectroscopy, bioactivity test, atomic emission spectroscopy, toxicity test, and cell proliferation. The results related to the synthesis of silver-containing bioglass by sol-gel method and heat treated at 550°C offered nanoparticles with an average diameter of less than 15 nm and a homogeneous distribution of silver in the matrix. Ratio of polymer phase to glass powder equivalent to 0.5, concentration of polymer in solvent of 50%, retraction of 1.5, and drive gear of 1200 are obtained as the optimum conditions for scaffold printing with acceptable quality (percentage, size and distribution of holes, regular structure of layers, and repeatability). The fabricated scaffold in optimal conditions revealed significant antibacterial properties, good bioactivity, acceptable cell viability, and high ALP activity. 3D printed BG/PCL nanocomposite scaffolds with macro (up to 500 µm) and micro size of holes and porosity percentage up to 64% in the structure can be a promising candidate for bone tissue engineering.

In the present research, alumina-ceria particles were synthesized by a sol-gel method. The produced particles were characterized by X-ray diffraction and scanning electron microscopy. Then, alumina matrix composites containing 15 wt.% of ceria were densified under 80 MPa pressure at different temperatures by spark plasma sintering process. X-ray diffraction results showed that the powder produced before heat treatment has an amorphous structure, while alumina and ceria phases are formed after calcination at 800 °C. The produced particles have an average particle size of 250 nm. The effect of sintering temperature on the density of samples, grain size, and hardness of composites was investigated. The samples were densified at about 1400 °C, reaching a density of about 97% of the theoretical density. The microstructure analysis revealed that the composite grains have grown with increasing sintering temperature. The results declared that increasing the temperature and pressure in the sintering process enhances the density of the samples. The Vickers hardness of the composites increased with increasing sintering temperature, as the composite samples sintered at 1400 °C for 20 minutes at a pressure of 80 MPa had the highest Vickers hardness of about 15.3 GPa.

In this research, using the manual shielded metal arc welding (SMAW) process, a wear-resistant layer was created by AMA1600v, AMA1622v, and AMA1623v hard coating electrodes on the St37 carbon mild steel, and the effect of the number of welding passes on the microstructure and corrosion resistance of the coatings was evaluated. For this purpose, optical microscope, scanning electron microscope (SEM) equipped with Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were used. The results showed a distribution of different carbide deposits in the microstructure of the coating metals. The deposits were complexs of the carbides of chromium, molybdenum, and vanadium. The results of the XRD demostrated the presence of martensite, austenite, chromium carbide, and molybdenum carbide phases in all three coating metals. Tungsten carbide (W2C) was observed only in the AMA1623v sample. The results of the Tafel polarization test showed that the bare and the 1622v samples had the highest corrosion current density (15.23 µA/cm2 and 7.06 µA/cm2, rspectively) among the under-studied samples, and therefore had the highest corrosion rate and the lowest corrosion resistance. Also, the results of the test showed that the corrosion current density of the 1600v sample (6.29 µA/cm2) was higher than that obtained for the 1623v sample (4.80 µA/cm2), which revealed the lower corrosion resistance of the 1600v sample. In addition, according to the results of the electrochemical impedance spectroscopy (EIS) analysis, the highest charge transfer resistance and coating resistance with the values of 6.3 kOhm.cm2 and 68.5 Ohm.cm2, respectively, belonged to the 1623v sample, which was also proven by the polarization test. Moreover, the lowest charge transfer resistance and coating resistance among the coated samples with the values of 2.73 kOhm.cm2 and 42.5 Ohm.cm2, respectively, belonged to the 1622v sample.

Tracking military structures and equipment is one of the parameters to create superiority in military battles. Camouflage has long been used to reduce the possibility of detection of military structures and equipment. Development of knowledge in the field of tracking and discovering military structures and equipment followed by the necessity of using the concealment in order to reduce vulnerability in war, has enhanced the importance of using new camouflage and radar evasion methods. The use of nanotechnology in the field of radar evasion of military facilities was developed by introducing graphene as a very strong absorber of electromagnetic waves. Graphene coating on the military installations causes the absorption of electromagnetic waves and as a result, these installations are not detected by the enemy's radar.  Referring to the fact that there is a functional relationship between the diameter of the graphene oxide used and the radar evasion of the equipment, an attempt has been made in this article for the first time to find a solution to control and monitor the radar evasion quality using graphene oxide (with the scientific name of RGO/NiFe2O4) in the microwave spectrum of 7GHZ by the profile approach and presentation of a regression relationship. This model can be used to monitor the quality of radar evasion products (cheaper and faster than existing methods). Finally, sensitivity analysis of the model showed that the ability to detect non-conformity in the manufactured products can be detected quickly (between 1 and 20 samples) with the change in the parameters of the regression model.

In this research, coal tar and soft bitumen were used as raw materials and the low-cost liquid phase carbonization (LCP) method was employed to synthesize mesophase carbon microbeads. First, the effect of temperature, time, and various pressures on the synthesis of mesophase bitumen was investigated. Also, the effect of various solvents on the synthesis efficiency of mesophase carbon microbeads was evaluated. The structural and chemical characteristics of the mesophase carbon microbeads were evaluated using field emission scanning electron Microscopy (FESEM), X-ray energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The results showed that the pressure of 7 bar and extraction with solvent of pyridine had a great effect on the morphology, removal of impurities in raw materials, and production efficiency. Also, the results of XRD and SEM revealed that mesophase carbon microbeads were not always spherical in shape.

In this research, the effect of adding SiC nanoparticles on the hardness and wear behavior of A380 aluminum alloy was investigated. A380 aluminum powder and SiC nanoparticles with values of 0, 0.5, 1, and 2 wt.% were ground in a planetary ball mill in argon atmosphere for 10 hours. The weight ratio of ball to powder and the rotation speed was adjusted at 1:10 and 250 rpm, respectively. After the milling process, a hot press was used to produce the samples. The products were produced through a graphite mold with a diameter of 15 mm at a heating rate of 10 °C/min to a final sintering temperature of 520 °C and a holding time of 30 minutes in vacuum under pressure of 50 MPa and were placed in the hot press machine. The microstructure and hardness of the samples were examined using an optical microscope and Vickers hardness tester apparatus, respectively. The wear resistance was evaluated by pin-on-disk method. The greatest hardness of the samples was related to the aluminum alloy containing 0.5 wt.% SiC nanoparticles. AlA380-2 wt.% SiC nanocomposite represented the highest wear resistance compared to the other experimented samples.