Journal of Ultrafine Grained and Nanostructured Materials
Volume:53 Issue: 2, Dec 2020

Lanthanum nickelate with the chemical formula of La2NiO4+δ has attracted research interests during recent years, due to its hA high oxygen ion diffusivity for application as cathode material in solid oxide fuel cells (SOFCs). In this research, lanthanum nickelate with Ruddlesden–Popper (RP) crystal structure was synthesized via the co-precipitation method. The effects of OH-/NO3- molar ratio, La3+/Ni2+ molar ratio, co-precipitation temperature, and calcination temperature on the phase composition, thermal behavior, morphology, and electrochemical properties of the synthesized samples were investigated. Analysis of the X-ray diffractometry (XRD) patterns revealed that the optimum OH-/NO3- and La3+/Ni2+ molar ratios in the co-precipitation stage are 1.25 and 1.7, respectively. The formation of RP lanthanum nickelate is promoted by calcination of the co-precipitated powder at 1000 °C, while the calcination at lower temperatures may lead to the formation of perovskite (P) lanthanum nickelate. Scanning electron microscopy (SEM) studies showed that the mean particle size decreases from 428 to 332 nm by increasing the OH-/NO3- molar ratio from 1 to 1.5 while it increases from 67 to 183 nm by increasing the calcination temperature from 900 to 1000 °C. Simultaneous differential thermal analysis (DTA/TG) showed that the single RP lanthanum nickelate phase starts to form at 920 °C and fully formed at 960 °C. The electrochemical impedance spectroscopy data indicated that the cell with the electrode sintered at 1050 °C has the lowest polarization resistance. The polarization resistance reached 1 Ω cm2 at the testing temperature of 800 °C, for the electrode sintered at 1050 °C. Impedance curves of the electrode were fitted and simulated with two semicircles at high and low frequencies. The activation energy of 1.14 eV was calculated for the electrode polarization resistance of the lanthanum nickelate electrode.

In this study, the synthesis of the Ti2SC nano layer was investigated by ball milling of Ti, FeS2, and C powders. Formation of MAX phase powder after ball milling and after spark plasma sintered (SPSed) sample was characterized by X-ray diffraction (XRD). The morphology and the microstructure of powders were investigated by scanning electron microscopy (SEM) along with energy-dispersive spectroscopy (EDS). The results of the X-ray diffraction patterns showed the reaction between raw materials and the formation of Ti2SC and TiC phases as well as α-Fe, after 10 h ball milling. Iron in the product was removed by an acid washing with 0.5M HCl. Spark plasma sintering at 1450 °C was used to prepare a bulk Ti2SC sample. Archimedes' test results showed that the sample was consolidated to 98% of the theoretical density. To evaluate the wear behavior of the bulk sample, a pin-on-disk wear device was used. The results of the wear test showed a low wear rate. This low wear rate was attributed to the self-lubricating nature of the Ti2SC nano layer. The friction coefficient for the three forces was also uniform. As the wearing force increased, the wear rate also increased.

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.

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 present work was undertaken to characterize the wear behavior of nanostructured Al-Al3V and Al-(Al3V-Al2O3) compositesproduced by milling and hot extrusion. The samples were characterized by pin-on-disk wear test, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results of wear test showed the nanostructured composites, as compared with the base metal, exhibited higher wear resistance. Dominate wear mechanism of the composites was recognized to be formation of mechanically mixed layer (MML) on the worn surfaces. Comparison of wear behavior of the Al-10 wt. %Al3V and Al-10 wt. %(Al3V-Al2O3) composites showed that Al-10 wt. %Al3V composite at different temperatures and for different loads has less wear rate than the Al-10 wt. %(Al3V-Al2O3) composite due to the weaker bond strength between Al2O3 particles and Aluminum matrix.

In the present work, commercially pure Al powder and Al-B4C powder mixture including 5 to 20 wt. % B4C particles, were consolidated to disc shape samples through applying high pressure torsion process at room temperature. To study the microstructural characteristics and evaluating the mechanical properties of the fabricated samples SEM, microhardness and shear punch test experiments were performed, respectively. It has been found that, by applying high compression pressure and even without applying torsion, full density can be reached in consolidation of the composites including lower than 5 wt% of B4C particles. For the samples include more reinforcement, applying torsional strain (1 to 3 turns), plus high compression pressure although has a significant effect on redistribution of B4C particles in the Al matrix, but could not lead to full density. The results also showed that microhardness values increase by increasing B4C content, only if enough torsional strain were applied. The same trend was also recorded for the maximum shear strength, so that it is justified not only by the amount of used reinforcement but also by the degree of consolidation.

Rice husk-derived nanostructured silicon is synthesized using a cryogenic milling system. After calcination of rice husk at 700C, obtained silica was mixed with magnesium powder via cryomilling at -100°C for 1 to 6 hours, followed by a magnesiothermic reduction heat treatment. Electron microscopy results revealed the quality of mixing process with no chemical reaction occurred during milling as confirmed by X-ray diffraction analysis. Prolonged cryomilling not only improved the distribution of the powders but also provided a highly active magnesium powder inside the mixture. As a result, a final product with larger total pore volume and higher surface area was obtained. Finally, cryomilling for 6 hours combined with magnesiothermic in powder form (as compared to pelletized material) resulted in the highest total pore volume of 0.258 cm3.g-1 (corresponding to average pore diameter of 20.42 nm) and specific surface area of 50.44 m2.g-1. The average crystallite size of all samples is in the range of 45.57 to 53.28 nm,thus confirming formation of the nanostructured silicon.

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.

The impact of hot extrusion process on the grain refinement and tensile properties for the rare earth elements (RE) and strontium (Sr)-containing Mg-9Al-1Zn alloys was studied. Based on the microstructural analysis, the grain size values reduced after the hot extrusion process, compared to the cast alloys. Moreover, the tensile properties of the extruded alloys were remarkably higher than the cast alloys. These extraordinary results were related to the grain refinement by the dynamic recrystallization phenomenon, and fragmentation and distribution of the intermetallics. Moreover, the RE/Sr additions improved the grain size reduction, owing to the presence of fragmented Al11RE3 intermetallics.

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.

The effects of Al-5Ti-1B and Al-10Sr master alloys on the microstructure and tensile properties of extruded 6070 Al alloy have been investigated in current research. Different amounts of Al-5Ti-1B and Al-10Sr master alloys were added to provide 0.01-0.5 wt.% of each element (Ti/Sr) in the alloy before homogenization, extrusion and heat treatment process. After adding 0.03 wt.% Ti and 0.03 wt.% Sr to the alloy separately, reduction in the average grain size was found to be %83 and eutectic Si changed from needle shape to fine fibrous morphology. Although the combined addition of Al-5Ti-1B and Al-10Sr increased slightly the grain size of the alloy, there was a considerable improvement in tensile properties for the extruded and T6-heat treated specimens. Further improvement in tensile strength was achieved after T6 heat treatment for 0.1 wt% Sr + 0.03% Ti added specimens in which ultimate tensile strength (UTS) showed the highest value (410 MPa). Fracture surface examinations revealed that hot extrusion process changes the mode of fracture from brittle in the as-cast condition to a more ductile form.

In this paper, hydroxyapatite powder is produced via annealing of Bovine bone. The as received bovine bone was annealed at three different temperatures of 400 ℃, 700 ℃, and 1000 ℃ after a primary preparation stage. The powders obtained from annealed bovine bone were analyzed and characterized by Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), and Energy-Dispersive X-ray (EDX) spectroscopy. The XRD analysis showed that the annealed bone at 1000℃ is pure hydroxyapatite, at 700 ℃, it is mostly hydroxyapatite, and at 400℃, there are not enough hydroxyapatite crystals. The morphology of the samples was analyzed by SEM. It was observed that the bone annealed at 1000 ℃ exhibits human bone-like matrix particle shapes while at 400 ℃, and 700 ℃, the irregular shape exists. EDX analysis showed that Ca, P, C, and O were detected in the samples, while Ca and P were the major components. Also, the Ca/P ratios were more than 1.67, which is the ratio of stoichiometric hydroxyapatite.

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.