Journal of Ultrafine Grained and Nanostructured Materials
Volume:55 Issue: 2, Dec 2022

Nanoporous BiVO4 thin films were deposited on fused silica substrate using reactive magnetron sputtering. The effect of annealing temperature on the microstructure, morphology and optical properties was evaluated. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), ultraviolet-visible spectroscopy (UV-Vis) and X-ray photoelectron spectroscopy (XPS). XPS demonstrated the Bi+3 and V+5 oxidation states, as well as the adsorbed and lattice oxygen on the film surface. The as-deposited films proved to be amorphous by the XRD results, while the pure monoclinic scheelite BiVO4 crystal structure was obtained after a post-annealing treatment at 300 and 450 ℃. FESEM images displayed a uniform surface with no grain boundaries for the as-deposited film, whereas nanopores with an average diameter of 20˗40 nm were observable in the film annealed at 450 ℃ as opposed to the film annealed at 300 ℃ with a dense and cracked surface. The association of nanoporosity with the efficiency of visible-light absorption was demonstrated by the UV-Vis spectrophotometry results with the narrowest bandgap (2.5 eV) concerning the film annealed at 450 ℃. The photocatalytic experiment under visible light showed an 80 % photodegradation of Rhodamine-B solution after 7 h, and the recycling experiment proved the stability of the thin films after three cycles. These results show the great potential of BiVO4 thin films deposited by reactive magnetron sputtering in photocatalytic wastewater treatment applications.

This paper presents an overview of the latest trends in the development of severe plastic deformation (SPD) using rolling methods. From many scientific works, it is known that severe plastic deformation provides intense grain grinding up to ultrafine and nanosized grains during multi-cycle deformation. It is also possible to obtain a uniform or gradient grain distribution over the cross-section of the workpiece. During SPD processes, the strength parameters can be increased several times. Of all the methods considered, asymmetric rolling has become the most widespread owing to its simple implementation in production conditions. Most of the known methods and devices for asymmetric rolling are designed for deformation in rolls with a smooth barrel, while the use of rolls with a relief surface allows the processing of metal to obtain a higher level of equivalent strain. Ensuring a high asymmetry level when rolling in relief rolls allows, in addition to the development of shear strain in two transverse directions (height and width), it also provides an additional level of shear strain in the longitudinal direction. In addition to the speed asymmetry, the rolling scheme in relief rolls is also suitable for the implementation of geometric asymmetry when one of the relief rolls has a reduced or increased diameter while maintaining the relief geometry on the roll surface.

In this work, the effects of ball-milling parameters on the structure of the Ti3AlC2 MAX-phase, the precursor of Ti3C2Tx MXene, is investigated. To clarify this effect, three approaches with different milling parameters were used to synthesize Ti3AlC2 MAX-phase. In all approaches, the initial elements with the proportion of 3Ti:1.3Al:1.9C were milled at different milling times, intervals, and rotating speeds. The resulting powders were sintered in a SPS furnace with the sintering temperature of 1000-1150 °C.  According to our observation, emerging intermediate Ti and Al compounds in the milling process is the key point for forming the final Ti3AlC2 since such compounds would assist the formation of MAX-phase in the SPS process. Moreover, the temperature increment during the milling process is necessary for the formation of such intermediate compounds. This condition can be achieved when the ratio of intervals to milling times in each milling step is low enough (5 min per 30 min) or the rotating speed is high enough (around 600 rpm). The Al layers in Ti3AlC2 MAX-phase obtained in each approach are etched by HF solution to reveal the difference between the resultant Ti3C2Tx MXene nanolayers. Our characterization suggests that ball-milling at 400 rpm for 18 hours with 5-minute intervals produces the highest quality MAX-phase and MXene.

This paper investigates the application of a mixture of three types of fuels, namely urea, glycine and hydrazine, for the synthesis of Ni-10 wt. % Al2O3 nanocomposite using the solution combustion method. Nickel and aluminum nitrates are used as an oxidizer. The fuels are used at two different fuel to oxidizer ratios. DSC-TGA diagrams prove hydrazine-nitrate reaction system can ignite before nitrate decomposition in contrary to urea-nitrate and glycine-nitrate systems. The results showed synthesized alumina at combustion temperatures less than 500 ºC is amorphous and the combustion temperatures more than 600 ºC made alumina crystalline. The measured surface area for the synthesized nanocomposite in air and less than 10 min was 207 m2 g-1. SEM and FESEM images prove the presence of small porosities in the synthesized nanocomposites. TEM image shows synthesized alumina in the nanocomposite has a mean particle size of less than 25 nm.

In the present study, four series of Al-6061/SiC composites synthesized via powder metallurgy technique were used to investigate the impact of the matrix grain size and/or the size of reinforcing particles on enhancing the compressibility of powder mixtures and hardness of the composites. In two series, the as-received Al powders have micron-sized grains mixed with either nano-sized or micron-sized SiC particles. For the other two series, the Al powders were initially milled to convert their grain size to nano-scale before mixing with either nano-sized or micron-sized SiC particles. The powder mixtures containing 1, 2, and 3 vol.% of SiC particles were cold pressed and hot extruded. The decreased compressibility in all of the four series of Al/SiC powder mixtures with increased SiC content attributed to the enhanced portion of the hard and non-deformable SiC particles in the powder mixtures resulting in a reduced degree of plastic deformation. Increment the SiCn content from 0% to 3% resulted in a significant increase in the microhardness of 20h planetary ball milled powders accompanied with decrease compressibility of powders. The composites were subjected to Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and X-ray diffraction (XRD) studies as well as density and hardness measurements. Metallographic studies and density measurements confirmed significant densification with no indication of voids in the samples’ microstructures after hot extrusion. The results revealed that matrix microstructure, as compared with the size of the reinforcing particles, was more influential in enhancing the powder compressibility and composite hardness.

Ultrafine-grained steels offer the prospect of high strength compared with traditional steel. In this article, the vibration responses of a beam as a function of the grain size of the material in HT-80 steel are investigated by an analytical approach. First, the relation between Young’s modulus and grain diameter in HT-80 steel is obtained based on the experimental results using curve fitting in the form of a mathematical equation. Then, governing equations of the cantilever beam and also associated boundary conditions are derived based on Hamilton’s principle using obtaining the total kinetic and potential energies of the system. After that, the natural frequencies of the system are determined using an analytical approach. Finally, numerical results of the natural frequencies of the system are presented concerning different values of the system parameters such as thickness, width, length, and grain size of the material. The obtained results show that the grain diameter of the material and also the dimensions of the beam such as thickness in the micro-scale have significant effects on the vibration response of the system. The presented approach can be used to estimate the vibration characteristics of ultrafine-grained steels and also microsystems such as piezoelectric cantilever-based MEMS sensors.

In this research, thermal stability, corrosion performance, hardness (H), and Young modulus (E) of Ni60Nb40, Ni60Nb20Zr20, and Ni60Zr40 amorphous ribbons were evaluated during the differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests, and nanoindentation technique, respectively. Results showed that the onset crystallization temperatures (To) of Ni60Nb40, Ni60Nb20Zr20, and Ni60Zr40 amorphous ribbons were 632 °C, 593 °C and 476 °C, respectively. It is determined that the higher Nb content increases the thermal stability against crystallization. Evaluation of corrosion resistance during potentiodynamic polarization test showed the polarization resistance value of 936 , 49, and 16 MΩ.cm2 for Ni60Nb40, Ni60Nb20Zr20, and Ni60Zr40 alloys, respectively. These results imply that the substitution of Zr with Nb enhances the thermal stability and corrosion resistance of Ni-Nb-Zr amorphous ribbons. Moreover, the H and E for Ni60Nb40, Ni60Nb20Zr20, and Ni60Zr40 amorphous ribbons were 171.3 and 15.01 GPa, 160.41 and 12.16 GPa, and, 188.52 and 14.13 GPa, respectively. It means complete substitution of Zr by Nb in Ni-Nb-Zr amorphous ribbons shows the highest hardness which is related to the Ni60Nb40 amorphous ribbon.

In this paper, a novel method of synthesis of zinc cobalt selenide (ZnCoSe) nanostructures via the hydrothermal method is introduced that is comprised of two stages as opposed to the direct method that could be done in a single stage. In the single-stage method, the consequent electrodes were covered by ZnCoSe that was directly and immediately synthesized while in the two-stage method, first, zinc cobalt oxide (ZnCoO) was hydrothermally produced then the oxygen atoms were replaced by selenium and the ZnCoSe* electrode was indirectly obtained. The structural and electrochemical evaluations showed boosted performance of the ZnCoSe* whose structure was found to be nanowire. In this paper, the specific capacitance values (Csp) of the ZnCoSe* , ZnCoO and ZnCoSe electrodes were measured to be 104, 64 and 62 F.g-1 at 20 mV/s scan-rate by Cyclic voltammetry (CV) which alongside the Galvanostatic Charge-Discharge (GCD) analysis, led us to conclude superior activity of the ZnCoSe* electrode. Electrochemical impedance spectroscopy (EIS) was also performed and its results were in accordance with those of the cyclic voltammetry. Based on the EIS results, ZnCoSe* showed the smallest charge transfer resistance (6.5 ohm/cm-2)  and consequently the supreme electrochemical behavior among the studied electrodes. Moreover, a better capacity retention value was recorded in the cyclability test of the ZnCoSe* electrode as the specific capacity value of this electrode reached 145% of its initial value after 2000 cycles.

This research deals with the preparation of Graphene Oxide (GO) from Graphite using Hummers method and then reduction of GO by three different methods (local olive leaf extract method, pure oleic acid method and sodium hypochlorite - urea in an alkaline medium method). The reduced Graphene Oxide (rGO) was analysed by infrared FTIR in the range of 400-4000 cm-1, and it was found that there are functional groups of oxygen such as epoxy group, and carbonyl group. Then rGO was analysed by UV-VIS spectroscopy in the range of 200-800 nm. Also, the structure and particle size of these sheets were studied by FESEM and EDX. It was revealed that the dimensions of the formed rGO by local olive leaf were within 500 nm-20 μm, while the reduction by chemical method in the presence of sodium hypochlorite and urea in an alkaline medium led in to a particle size in the range of 200 nm-2μm. Based on the EDX result, the GO composition is 53.22% carbon and 29.67% oxygen. The best method for synthesize of rGO was pure oleic acid method at temperature of 440 ℃ with a heating rate of 2.3 ℃/min. In this method, the particles were in the range of 200 nm-2 μm and based on EDX results, they were composed of 72.04% carbon and 24.32% oxygen.

Low resistance at high temperatures as well as low wear resistance are the limitations of polymer-based materials; therefore, to increase thermal stability and wear resistance of these materials, resistant coatings used to protect their surface in applications with good wear performance at high temperatures. The coating layer in this study includes epoxy resin mixed with polyvinyl chloride (PVC) as the organic phases, containing 5, 7.5, 10, 12.5, 15 and 17.5 %wt of the modified silica nanoparticles as inorganic phase are applied to polymeric substrates through dip-coating. Wear resistance, hardness and thermal gravimetry analysis (TGA) were used to evaluate the properties of applied hybrid coating. The results showed that the thermal stability of the substrate with Epoxy/PVC coating containing 12.5 %wt modified nanosilica had an increase up to 31.27% compared to the uncoated substrate. The hardness obtained in the uncoated substrate is 2H; While in substrates with coatings containing 12.5 and 15% wt of modified nanosilica increased to 6H. The wear rate of substrate with Epoxy/PVC hybrid coating containing 12.5 %wt of modified nanosilica had amount 75% reduce compared to the uncoated substrate. The results showed the potential ability of the formulated coating to enhance the working conditions of polymeric coating including high temperature and high wear conditions.

Airbrushing is a simple, cost-effective, and easy-to-use method for applying thin layer coatings. In this study, the fabrication of a graphite layer using airbrush spraying has been investigated, which requires stable graphite suspensions without any noticeable sedimentation before and while spraying. Aqueous suspensions with different ratios of Polyvinylpyrrolidone (PVP) to graphite were prepared. PVP was used as a surfactant that can disperse graphite particles in water, which also binds graphite particles to the substrate. For testing each suspension's stability, the turbidity of all samples was measured. The test demonstrated a specific ratio of PVP to graphite that makes the suspension most stable, which is 0.3g. A lower or higher amount of PVP was seen to make the stability worse. The sample with 0.3 grams PVP had the lowest sedimentation rate and thus was chosen for spraying. This optimum composition was sprayed on the substrate using an airbrush, and a graphite coat was obtained in the next step. The main application for the graphite-coated thin layer is in Li-ion batteries as a graphite-based anode.

Hierarchical titania with anatase/rutile crystalline phases were obtained by a hybrid hard/soft templating approach. Three sets of conditions were chosen including absolute ethanol, ethanol: water and absolute ethanol with the addition of microcrystalline cellulose as a hard template; in all of the experiments P123 three block co-polymer was utilized as the soft template. Crystallite sizes, porosity and surface acidity were found to change drastically by modifying the initial synthesis conditions. The obtained samples were characterized using powder XRD, FESEM, SEM, TEM, DRS, EDS, N2-physisorption, DLS and zeta potential meter. Methyl violet, methyl orange and malachite green were chosen as representative organic pollutants with different chemistries and a series of experiments were performed under a high-pressure mercury lamp equipped with UV filter. It was found that the hierarchical titania sample works best to remove methyl violet from aqueous media while simpler nanostructures obtained with soft templating work better for methyl orange and malachite green. Based on the characterization results, possible enhancement mechanisms were proposed to explain the drastic differences between the performance of different samples for removing different organic dyes.