A new proposing model based on gene expression programming (GEP) to predict the microhardness of Ni/Al2O3 nanocomposite coating was the subject of the present study. Accordingly, a series of the laboratory experiments was designed by the factorial D-optimal array. This was accomplished by considering the most effecting practical electrodeposition parameters including the amount of Al2O3 nanoparticles in the bath, current density, temperature, magnetic stirring rate, time of stirring, and plating time as the input and the microhardness of the coating as the output of model. Various performance criteria including determination (R2) coefficient, the mean absolute error (MAE), and the root relative squared error (RRSE) were utilized to evaluate the developed models. Finally, the model with R2 = 0.9752, MAE = 0.030 and RRSE = 0.158 was developed as the optimum proposed function. Also, the results of the sensitivity analysis confirmed that the current density was the most effective parameter, while the amount of Al2O3 nanoparticles in the bath, plating time, magnetic stirring rate, time of stirring, and temperature had relatively lower effect. In conclusion, the exclusive features of the GEP simulation have been approved to determine Ni/Al2O3 nanocomposite coatings microhardness.
For more than a decade, there has been considerable interest in the fabrication of metal matrix composites by employing Friction Stir Processing (FSP). In this study a new model based on Zener-Hollomon (Z) parameter has been developed, which is believed to be the first of its kind, to accurately predict microstructural characteristics of Al-based composites Additionally, the processing window of composite fabrication determined and revealed that sound samples achieve within the range of 2.42 to 24.61 rev/mm for the ratio of rotation speed to travel speed (ω/ν). Recording the peak temperatures during processing beside the optical and Scanning Electron Microscopic (SEM) studies showed that increasing the number of FSP passes and the ratio of ω/ν have a remarkable influence on bolstering the role of nanoparticles in grain refinement. Results also indicated that the mean grain size of FSPed samples and matrix of nanocomposites decreases with an increase in the Z parameter. Finally, particular equations for various numbers of passes developed, which make a correlation between the grain size of Al-based composites and the FSP parameters via Z parameter.
The principles and magnetic properties of nanostructured high-entropy alloys (HEAs) processed by mechanical alloying are overviewed. Firstly, the general concepts of HEAs (multi-principal element alloys with ≥5 elements) and phase formation rules are briefly reviewed. Subsequently, the processing of nanocrystalline and amorphous HEAs by mechanical alloying and the effect of high-energy ball milling parameters are summarized. Finally, the magnetic properties of nanostructured HEAs are critically discussed to infer some general rules. In summary, a higher content of ferromagnetic elements (e.g. Fe, Co, and Ni) normally results in a higher saturation magnetization. The as-milled products with solid solution phases show better soft-magnetic properties compared to the fully amorphous phases, and increasing the amount of the amorphous phase decreases the saturation magnetization. The magnetic properties are also influenced by processing (such as sintering) and thermal history through the alteration of phases and crystallite size.
Highly ordered TiO2 nanotube arrays were synthesized by a two-step anodizing method. Although TiO2 nanotubes have excellent electrical and capacitive properties because they provide a unidirectional path for electron transfer. But these properties can be improved by effective methods such as non-metallic doping or by a conductive polymer. For this purpose, nitrogen and hydrogen doping methods and electrical deposition of polyaniline were used simultaneously to prepare the polyaniline-TiO2, polyaniline/N-TiO2, and polyaniline/H-TiO2 nanotube arrays samples. To evaluate the electrochemical and capacitive properties in more detail, cyclic voltammetry, electrochemical impedance spectroscopy, Matt-Schottky, and galvanostatic charge-discharge tests were performed. The results showed that the composite of TiO2 doped with hydrogen and deposited with polyaniline nanowires had the highest capacitance (5666 µF.Cm-2) at the current density of 100 µA/cm2, approximately 4.5 times more than polyaniline/TiO2 sample. It also has the lowest charge transfer resistance (0.008 Ωcm2) and the highest charge carrier density (1.63×1024cm-3). Increasing the density of charge carriers and decreasing the electrical resistance can be attributed to the fact that the hydrogen doping, the presence of oxygen vacancies, and conductive polymer increase the rate of separation of the charge carriers and decrease their recombination rate. Therefore, the electron transfer rate and the electric current increase.
The Ag/Co2O3/g-C3N4 as a novel nanocomposite was synthesized using a facile strategy by “one pot” method. The as-prepared nanocomposite was applied to improve the antibacterial effect against Escherichia coli and Staphylococcus aureus bacteria. The nanocomposite was characterized by Fourier transform infrared spectroscopy, X-ray Diffraction, and Scanning Electron Microscopy techniques. The strong interaction beetween the plans of graphitic carbon nitride (g-C3N4) and other particles can be resulted to stable nanocomposite. The zone inhibition of nanocomposite was determined for Gram-positive and Gram-negative bacteria. The findings showed the better activity of as-prepared nanocomposite against Gram negative bacteria rather to Gram positive bacteria. The Ag/Co2O3/g-C3N4 was shown good antibacterial effect compared to g-C3N4 and Ag patricles. Further, Colony Forming Unit was indicated the antibacterial behavior of as-prepared composite. The present study can explain insight into the synthesis of heterojunction composite for disinfection.
Magnesium alloys have received great attention for the medical applications due to their desired properties.But the main problem of magnesium alloys is the high rate of degradation which provides not enough time for healing.Therefore, in this study, it was tried to control the corrosion rate of Mg-Zn-Ca alloy by applying a nanofiber of polycaprolactone polymer coating and investigate the behaviors such as biocompatibility and rate of degradation. For this purpose, the polymer nanofibers were prepared by electrospinning method and applied on the surface of magnesium-zinc (4 wt. %) -calcium (2 wt. %) alloy, and the corrosion behavior and biological properties were compared with the uncoated alloy. corrosion behavior was measured with Tafel polarization test as well as hydrogen test in body fluid simulation solution, measurement of the pH of the solution after sample destruction, wettability angle test, cytotoxicity test and cell adhesion test.The Tafel polarization test showed that the applied coating increased the corrosion potential from -1.5 to -0.6 volts and corrosion rate reduced by about two order of magnitudes. The amount of hydrogen emitted by the corrosion reaction in the coated sample was much less than that of the uncoated sample. Biocompatibility test showed that the cytotoxicity of the coated sample was 8% lower than that of the uncoated sample. In the cell adhesion test, it was observed that far more cells adhered onto the surface of the coated sample compared to the uncoated sample. The wettability angle on the surface of the coated sample was 128° while that of the uncoated sample was 100°, due to the inherent hydrophobicity of this polymer. Despite the hydrophobicity of polycaprolactone polymer, which is not favorable for cell growth, due to the high biocompatibility of this polymer, coating Mg alloys with this method and material could have some advantages for future implants.
In this research, the dependence of CuFe2O4 particle size on the antibacterial properties was investigated. The morphology of the particles was controlled in the presence or lack of sucrose as a novel capping agent. Antibacterial properties of the CuFe2O4 nanoparticles were evaluated using the PVDF or silicon rubber matrices. The crystalline structures of the CuFe2O4 were confirmed by X-ray diffraction (XRD) patterns. The prepared nanostructures were more dissected using field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR), and vibrating sample magnetometer (VSM). Eventually, the copper ferrite particle size effect in PVDF and silicone rubber matrices on the antibacterial activity was investigated. The obtained results revealed significant antibacterial properties for the particles. It was found that decreasing particle size would improve antibacterial properties within both polymeric mediums. This research presents novel separable antibacterial magnetic nanostructure suspended in novel media.
Severe plastic deformation (SPD) has been one of promising routes to fabricate ultrafine-grained (UFG) materials, especially aluminum alloys. However, the SPD products often suffer from their small size. This issue implies the necessity of welding of UFG aluminum alloys for making them usable in complex, large forms in industries. Among various welding processes, those based on solid state welding seem to be more consistent with UFG materials. This is associated with the instability of UFG materials upon intense heating cycle that is common in fusion state welding processes. Friction stir welding (FSW) as a well-known process in the category of solid state welding is widely used for welding of aluminum alloys. This review paper provides an overview of the state-of-the-art of FSW of UFG aluminum alloys. To do so, specific attention is given to microstructural and textural evolutions, effect of secondary particles, and cooling medium. Applying cryogenic cooling medium as well as secondary nanoparticles could inhibit excessive grain growth in the stir zone, which were beneficial to improve the strength of the stir zone without remarkable decrease in the ductility. These processing routes did not affect the main recrystallization mechanism of the stir zone.
Development of biopolymers possessing both biodegradable and electrically conducting properties has attracted a huge interest in the biomedical field. These systems have some benefitials in wound healing and reducing the long-term health risks. In this study, the pectin-polycaprolactone (Pec-PCL) copolymers were synthesized by ring-opening polymerization. Subsequently, the solutions of the synthesized Pec-PCL and homopolyaniline (H-PANI) were blended in various ratios and their conductivity properties were measured by cyclic voltammetry and the composition of 80:20 was selected for electrospinning process because of the suitable electroactive behavior and biodegradability. The morphology, biocompatibility, hydrophilicity, and mechanical properties of the nanofibers were thoroughly investigated. Resulted scaffolds represented a porous structure with large surface area (110–130 nm) and Young’s modulus of 1615 ± 32 MPa, which imitated the natural microenvironment of extra cellular matrix (ECM) to regulate the cell attachment, proliferation and differentiation. The results demonstrated that these electrospun nanofibers could be potentially applied in biomedical such as tissue engineering.
Electrospinning, stabilization and carbonization are three steps of synthesizing electrospun carbon nanofibers (CNF), using polyacrylonitrile (PAN) precursor. In this study, the effect of the stabilization temperature was studied on the morphology and chemical state of the electrospun PAN fibers, which were later carbonized to produce carbon nanofibers. the stabilization was carried out on electrospun PAN fibers, at different temperatures of 230 °C, 240 °C, 250 °C and 280 °C for 2h with a heating rate of 2 °C/min. Fourier transform infrared spectroscopy was used to inspect the progress of stabilization reactions. The crystallinity and composition was studied by X ray diffraction and scanning electron microscopy was used to observe the morphology of the fibers. The results showed that 230 oC is the best stabilization temperature in which not only all expected reactions take place but also the fibrous morphology is preserved. Higher temperatures led to destruction of the fibrous morphology.
Titanium dioxide nanotubes (TNTs) were synthesized via an electrochemical anodization process. The influence of increasing the cathode surface area on the microstructure and order of the final product was investigated. To study the microstructure of the synthesized nanotubes, field emission scanning electron microscopy (FESEM) was employed. The degree of crystallinity and the characteristic of synthesized nanostructure was evaluated by X-ray diffraction (XRD). The porous initiation layer covering the tube-top became thinner and lost its’ integrity, as a consequence of employing a larger cathode. This is due to the enhanced reaction sites followed by intensifying the electrochemical reaction in the anodic oxidation processes. In contrast, a small surface area of the cathode made it possible to control the obtained nanostructure with no damages to the surface morphology. The average diameter of the surface nanopores increased from 60 to 67 nm by increasing the cathode surface area. Optical characterization demonstrates that the bandgap of the synthesized TiO2 nanotubes is about 3.2 eV. In the process of methylene blue (MB) degradation, the photocatalytic activity of the TNTs with an ordered initiation layer reaches 69% after 480 min irradiation.
Ex-situ and in-situ reinforced copper matrix composite samples containing 1.1 wt. % and 2 wt. % Al2O3 were produced by spark plasma sintering (SPS) at 830 °C and holding time of 30 min. In-situ reinforced sample was synthesized by a novel technique using the reaction between ball-milled copper oxide and Cu-10 wt. % Al filings as the additive and copper powder. The in-situ formation of alumina reinforcement was confirmed by SEM observation and EDS analysis. Morphology and distribution of reinforcement phase in different composite samples were studied. The in-situ reinforced composite sample showed superior flexural fracture strength and strain (349 MPa and 0.027, respectively). Different patterns of crack propagation were observed in the SEM images of fracture surfaces: the reinforcement’s interface path (due to the formation of undesired oxide phase) was dominant in the ex-situ samples, while the interface of in-situ reinforcements remained intact and the cracks originated in the agglomeration sites.
Hydrophobic and superhydrophobic coatings can be fabricated through the traditional two-step method, including fabrication of hierarchical micro and nanoscale roughness along with surface modification using low energy materials like fatty acids and fluoropolymers. Using a low energy material is not suitable due to its weak chemical bonding to the surface, and also, some of the used materials are toxic. Herein, a novel method has been introduced to fabricate the hydrophobic coating using the Wenzel wetting model. The aluminum substrate was chemically etched to create the nano-roughed surface structure and subsequent silane-based coatings can lead to increase the water contact angle without using any surface functionalization with low energy materials. In addition to that, two type of silane-based sol-gel coatings (TEOS and TEOS/GPTMS) have been used to investigate the benefits of hybrid organosilane sol-gel coating. The results indicated that the increasing in the surface roughness of silane-based coatings using chemical etching of the substrate leads to increase the water contact angle to hydrophobic state, which is supported by the Wenzel wetting model. The corrosion mitigation behavior of silane-based coatings on different substrate (bare and etched aluminum) has been studied in details.
The notable contributions of Iranian scientists in the field of formation and reversion of strain-induced martensite for grain refinement and enhanced mechanical properties of Fe-Cr-Ni austenitic stainless steels are reviewed. Accordingly, the processing of ultrafine grained (UFG) structure via cold rolling and reversion annealing is summarized for AISI 301, 304, 309Si, 316, and 321 stainless steels, as well as their variants. The repetitive and innovative thermomechanical processing routes are introduced as well. The understanding of the stages of annealing (reversion of strain-induced martensite to austenite, primary recrystallization of the retained austenite, and grain growth) and the underlying reversion mechanisms (diffusional-type and martensitic shear-type) constitute the subsequent part of this overview. Finally, the transformation-induced plasticity (TRIP) effect in the reversion-treated metastable austenitic stainless steels is discussed. The present review paper summarizes these achievements with the discussion on the future prospects in this research field.
CrN/Cu composite powders were synthesized by employing a novel two-step technique. Firstly, the Cr2O3+CuO precursors were prepared by the solution combustion synthesis (SCS) method using cupric nitrate, urea, and chromium nitrate as initial materials. Subsequently, the SCS precursors were calcined at 850 °C in NH3 for 6 h, and transformed to CrN/Cu composite powders. The composite powders consist of the uniform subsphaeroidal particles with the particle size ranging from 200 to 300 nm. After the friction-wear test, the removal volume of the sintered CrN/Cu composite specimen (0.0218 mm3) is almost 80 times smaller than that of the sintered pure copper specimen (1.6634 mm3). The addition of CrN can improve the tribological performance of sintered copper significantly. Moreover, the electrical conductivity of the sintered CrN/Cu composite specimen is high to 85.6% of IACS (International Annealed Copper Standard).
This work reports an ultrafast route for the preparation of hierarchical zeolite FAU by a combined templating-microwave heating method. An inexpensive and harmless cationic polymer polydiallyldimethylammonium chloride (PolyDADMAC) was used as a mesoporogen agent. Several characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and N2 sorption analysis confirmed the successful synthesis of hierarchical zeolite FAU with both inter and intra-crystalline mesopores. The effects of microwave heating times and polymer quantities on the structural properties of the final product were evaluated. A crystallization time of 180 minutes and microwave radiation at 90 C proved to be adequate to obtain the best product. Microwave heating resulted in the formation of nanozeolite crystallites with mesopores between them and polymer removal through calcination created mesopores inside the zeolite crystals.
The specific characteristics of silver nanoparticles (AgNPs), especially anticancer and antimicrobial properties, have led to their widespread usage in biology. The study looked at the anti-cancer activity of AgNPs, which were produced by a one-step green synthesis based on the use of Adonis vernalis leaf extract. Characterization of reducing agents in plant extracts was performed using (FT-IR) infrared spectroscopy. The presence of adsorption peak at 442 nm in UV-visible absorbance of bio-fabricated AgNPs indicates the effectiveness of proposed method. Transmission electron microscope (TEM) and field emission electron microscope (FESEM) were used to investigate the morphology and confirmed the spherical shape of products. Phase analysis and determination of the synthesized product crystal lattice was performed using X-ray diffraction (XRD) method. The stability of particles was determined using zeta potential analyze. Energy-dispersive X-ray (EDX) analysis confirmed the formation of high purity AgNPs. The MTT assay was used to determine the anti-toxic properties of produced products and the results demonstrated that silver nanoparticles biosynthesized by Adonis vernalis extract can be used to treat breast cancer.
In this paper, a facile method for preparing sub-micron spherical mesoporous silica by the sol-gel process and cationic surfactant cetyltrimethylammonium bromide (CTAB) as a soft template was reported. Moreover, the effect of surfactant concentration on the specific surface area and the total pore volume was investigated. The specific surface area, pore characteristic, morphology, chemical composition, and structure of mesoporous silica were studied using various methods. The N2 adsorption test showed that increasing the CTAB concentration from 4.6 mM to 7.2 mM increases the specific surface area from 416.48 to 564.07 m2g-1. However, the maximum pore volume was obtained at 5.9 mM CTAB. The spherical shape of the powders was confirmed by field emission scanning electron microscopy. Besides, X-ray diffraction, fourier transform infrared spectra, and energy dispersive spectrometry analysis indicated that the synthesized samples are SiO2, with an amorphous structure. Based on the structure and properties of obtained synthesized mesoporous silica, it is a good candidate for a drug reservoir and the carrier for new controlled drug delivery systems.
In the present work, the surface modification of Nitinol was carried out by a two-step process consisting of pretreatment and applying the bioactive composite coating to extend its biomedical applications. For pretreatment, we used a combination of chemical etching, boiling in distilled water and alkaline-heat treatment. According to the results of Raman and grazing-incidence X-ray analysis, the surface layer formed on the pretreated Nitinol was consisted of rutile phase and sodium titanate phases. The pretreatment significantly decreased the concentration of Ni ions released from Nitinol alloy into Ringer's solution during 10 days immersion from 126.6 ppb to 5.3 ppb. Moreover, this pretreatment process did not have the negative effect on the superelasticity of the Nitinol alloy. In the following, we used a composite coating of hydroxyapatite/chitosan on the pretreated Nitinol. This coating was applied using one-step cathodic electrophoretic deposition from suspension containing 5 g/L hydroxyapatite and 0.5 g/L chitosan at different voltages of 30, 40 and 50 V/cm2. A uniform coating with acceptable quality was obtained by electrophoretic deposition at 40 V/cm2 for 120 s. The morphology of this coating was studied using scanning electron microscope and Fourier transform infrared spectroscopy analysis. The findings confirmed fabrication of a crack free morphology, which was consisted of hydroxyapatite and chitosan. Finally, according to the results of potentiodynamic polarization test, the corrosion current density for bare, pretreated and pretreated/coated Nitinol were calculated about 2.63, 1.94 and 0.75 μA/cm2, indicating the effect of pretreatment and applying hydroxyapatite/chitosan coating on decreasing the corrosion rate of Nitinol.
A series of CuO-Cu2O/TiO2 nanocomposite samples were prepared by the sol-gel method. Before applying the sol-gel method, the Cu(OH)2 nanostructure on Cu powders were formed by in-situ solution treatment. The samples were characterized through some techniques and the photocatalytic performance of CuO-Cu2O/TiO2 nanocomposites for gas-phase 2-propanol photo-oxidation under UV and sunlight type illumination was evaluated. The effect of calcination process on the synthesis and photocatalytic activity of the samples was studied. The calcination process plays an important role in improving the properties of nanocomposite powders. The results showed that the nanocomposite formed successfully in desirable structure and morphology. The nanocomposite is composed by the mixture of TiO2 particle with an average particle size of about 300 nm and the copper oxide nanorods with a diameter of 50-100 nm. In this nanocomposite, the copper oxides nanostructures and TiO2 particles are the main components to form the heterojunction structure and provide enhanced photocatalytic performance compared to the TiO2 sample. The reaction rate of the most active nanocomposite sample prepared at the optimum conditions is almost 6 times larger than the TiO2 references.
