By‐products including unwanted phase formation and/or unreacted starting materials are normally seen in the outcome of solid‐state synthesis approaches used in the literature for powder processing of ...advanced materials; this drawback requires critical attention and must be addressed in the new synthesis pathways in order to obtain quality powder products. A high energy mechanical milling approach was developed in this work. Addressing the drawback, the starting materials were mechanically activated by a high energy ball mill before their mixing step. It was found that highly pure barium titanate nanopowders with high tetragonality character are obtained using the approach developed here. The work also characterized tetragonality, role of the mechanical activation and postmilling thermal treatment on structure, phase formation and morphology of the obtained powder products. It was found that the mechanical activation accelerates the kinetic of formation of barium titanate and enhances the purity and tetragonality of the final products. The mechanism behind this achievement and the related reaction pattern are disclosed in this work. In order to obtain highly pure tetragonal barium titanate, a calcination temperature of 1173 K (900°C) after 30 hours mechanical activation is necessary; if these requirements are not satisfied, the final powder product contains impure phases and/or unreacted starting materials. The results also indicated that the processing conditions result in enhancement of tetragonality character of the final powder products. It seems that the method developed here can be used as a generalized methodology for obtaining the quality highly pure monosized nanocrystals of the mixed oxides for assembling in nanotechnology.
•Aluminum 6061-T6 plates were joined with low-carbon galvanized steel by FSSW.•Due to the low process temperature, the steel microstructure did not change.•The intermetallic layer has a direct effect ...on the quality and strength of the joint.•By increasing the length of pins the tensile strength was improved.
Friction stir welding is an efficient method for joining steel and aluminum plates at a point of disturbance. In many studies, the tool is only introduced into the aluminum plate, avoiding penetration into the steel plate due to its high strength and the need for a robust tool. Under such conditions, the created connection usually possesses low mechanical properties. In this research, by increasing the strength of the H13 steel tool through thermal operations, the possibility of penetration and bonding of aluminum 6061 with galvanized low-carbon steel has been provided. Moreover, by penetrating the steel plate, the integration of galvanized layers in the disturbance region has been facilitated. The examined variable parameters include pin length, rotational speed, and tool dwell time. Mechanical properties such as tensile strength, fracture force, and Vickers hardness were investigated. Furthermore, the weld microstructure and intermetallic layers were examined using scanning electron microscopy (SEM) and EDS analysis. Tensile and shear strength increase with an increase in pin length, rotational speed, and tool dwell time. Shear fracture loading showed a decrease with increasing pin length, then reached its maximum value when using long pins, while continuously increased with higher rotational speed and longer tool dwell time. As we approach the center of the weld in both the steel and aluminum parts, smaller grain sizes are observed due to increased plastic deformation, more material mixing, and increased mechanical tool pressure, while in the heat-affected zone, a coarse grain structure forms. Hardness in the aluminum plate decreased in the heat-affected zone and reached its minimum value in the thermo-mechanical-affected zone, then increased to the maximum value in the nugget zone, while hardness changes in the steel plate were uncertain. The most influential parameter on mechanical and microstructural properties was pin length, followed by rotational speed and tool dwell time.
Purity and synthesis temperature of nanocrystals are key challenges facing the scientific community. Herein a novel solid-state approach to synthesize fine BaTiO3 nanocrystals with narrow size ...distribution using a high-speed ball-milling process is reported. In order to improve the kinetics of this reaction, the starting materials, BaCO3 and TiO2, were milled for 10 h before mixing and initiating the synthesis reaction. The contribution of this step to the BaTiO3 formation is analyzed by XRD diffractometry and FE-SEM techniques. It was found that the use of the mechanically activated starting materials favors the decomposition of BaCO3 at low temperatures and improves the Ba2+ diffusion through the formed BaTiO3 layer. In consequence, very fine BaTiO3 nanocrystals free from the secondary phases were obtained at a lower temperature in contrast to the previous works.
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•Very fine BaTiO3 nanocrystals were obtained at a lower temperature.•Method is able to obtain highly-pure BTO nanocrystals.•The approach is simple, and useful for large-scale production purposes.
Synthesis of nanocrystalline hydroxyapatite with high degree of crystallinity results in improved bioactivity responses due to its high specific surface area and low ion release. Therefore, the ...innovative methods resulting in these qualities are of significant importance especially for 3D printing of biomaterials and biocomponents made by hydroxyapatite. Addressing the qualities essential for bioperformance of hydroxyapatite, a new method was developed in this work, which is able to prepare impurity-free hydroxyapatite nanocrystals at ambient conditions. Characterization of role of processing conditions and their successive optimization resulted in a facile cost-effective process in contrast to the literature. Stoichiometric nanoscale hydroxyapatite free from by-products, unwanted materials (unwanted phase formation) and impurities was obtained by the approach. It was found that the longer drying time increases the crystallinity of the as-washed precipitate; however, to reach a high degree of crystallinity, application of a heat treatment process is essential. The designed short time heat treatment was able to enhance the crystallinity of the dried precipitate while its structure remained nanoscale after heat treatment. Keeping the nanoscale structure of the samples even after heat treatment allows using its benefits for improvement of biocompatibility, osteoconductivity and tissue in-growth of the biomaterials made by these nanoscale hydroxyapatite powder products. The results showed that the amino acid (glycine) has a significant effect on the crystallinity of the hydroxyapatite due to its effect on kinetic of hydroxyapatite crystallization (nucleation of new crystals) by enhancing the surface diffusion mechanism in the precipitate. In contrast, the glycine also controlled the growth process of the nucleated crystals by its adsorption on the growing surfaces and/or by introducing the strain to the growing crystals. These stresses controlled the growth of the nanocrystals and induced directional growth and morphological changes in the hydroxyapatite powder products.
The present study was tested how Oncorhynchus mykiss can respond to dietary supplementations of autochthonous probiotics, including Lactobacillus delbrukei subsp. bulgaricus and Lactobacillus ...acidophilus and Citrobacter farmeri by measuring different parameters. To address that, 300 fish weighing 19.08–32.9 g were fed by probiotics-enriched diets, containing 5 × 107 CFU g−1 for 60 days. Our results indicated that probiotics, especially L. acidophilus and L. bulgaricus are involved in enhancing the growth performance of this species as compared with the control group. Blood profile (Hemoglobin and Hematocrit) showed significant (P < 0.05) increases in probiotic fed groups compared with the control. Serum lysozyme and complement activities were higher in probiotic-fed fish while similar changes were not observed in the case of bactericidal activity and Nitroblue Tetrazolium (NBT) reduction. Better colonization of lactic acid bacteria in fish intestine was observed following L. acidophilus and L. bulgaricus administrations (P < 0.001). Digestive enzyme activities of intestine, including amylase, trypsin, lipase and alkaline phosphatase were elevated either significant or insignificant while protease activity did not act the same. All probiotic treatments led to mild or strong (P < 0.001) up-regulation of cytokine and growth gene expressions of intestine in comparison with the control group. Higher in vitro antagonist activities of L. acidophilus and L. bulgaricus against the Lactococcus garvieae were coincident with in vivo challenge test. The relative percentage of survival (RPS) was obtained 63.71 and 51.56 for L. bulgaricus and L. acidophilus, respectively, which were higher in those treated fish as compared to control fish. Our results may suggest that the probiotics, applied here, can promote growth performance by improving digestive enzyme activity, gut micro flora and growth gene expression. Up-regulation of immune regulatory proteins may increase the non-specific immune responses and bacterial resistance in this species as well.
•Fish responses or even adjustment to different autochthonous probiotics might be different from molecular to organism.•L. acidophilus and L. bulgaricus can promote growth performance by improving digestive enzyme activity, gut micro flora.•Up-regulation of immune regulatory proteins may increase the non-specific immune responses and bacterial resistance.
In this study, aluminum 6061-T6 plates were joined with low-carbon galvanized steel using friction stir spot welding. Three conical pins with varying lengths (short, medium, and long) were utilized, ...along with different dwell times and rotation speeds of the tool. The objective of this research was to compare the simultaneous effects of several important process parameters on mechanical and welding properties. The results indicate that the use of short conical pins significantly increased the microhardness in the upper aluminum plate. Conversely, increasing the pin length led to higher microhardness in the lower steel plate. Tensile shear loading was greater for short pins compared to medium pins, attributed to the influence of the tool shoulder. However, with increasing pin length, failure loading reached its highest value due to the dispersion of particles in the weld. The failure mode for short pins exhibited a mixed pattern, which transitioned to a ductile shape in all conditions as pin length increased. Overall, the most influential parameter was the tool penetration depth, which positively affected the obtained properties. The rotational speed of the tool was the second most significant parameter, followed by the dwell time.
•One of the influential parameters in this process, which has received less attention, is the tool shoulder diameter.•Predominant element in Aluminum 2024 alloy, after aluminum, is copper. Copper has ...excellent thermal conductivity, quickly transferring the frictional heat produced to the plates and rapidly heating the parts. Meanwhile, in the Aluminum 7075 alloy plates, the predominant element after aluminum is zinc.•Additionally, the melting temperature of the Aluminum 2024 alloy is around 510 degrees Celsius, which is lower than that of the Aluminum 7075 alloy (approximately 600 degrees Celsius).•The fracture mode of all produced joints was nugget pull-out, which, under optimal conditions, resulted in a wider and more separated nugget zone.•Increasing the tool shoulder diameter led to an increase in tensile-shear strength due to the greater length of the bonded region.
In most studies conducted on friction stir spot welding, the focus has been on process parameters and the tool pin geometry. One of the influential parameters in this process, which has received less attention, is the tool shoulder diameter. The spread or concentration of the weld can significantly affect the weld strength and mechanical properties of the joint. In this research, two tools made of H13 hot-work steel with different shoulder diameters of 20 and 25 mm were prepared. Three rotation speeds of 1000, 1600, and 2400 rpm were considered for the welding process. The arrangement of aluminum plates on top of each other was varied in two configurations, parallel and overlapped. Mechanical properties, including tensile shear strength and Vickers micro-hardness, were investigated. The microstructure of different weld zones was also examined using an optical microscope. The results showed that increasing the tool shoulder diameter could enhance the breaking force and tensile shear strength of the joints. Meanwhile, the rotation speed had an optimal value, and with its increase, the breaking force initially increased and then decreased. Placing the 2024-T3 aluminum plate on top of the stack also increased the tensile shear strength of the samples. The fracture mode of the broken specimens was entirely nugget pull-out, which became more pronounced during the use of optimal parameters. Micro-hardness in the region influenced by heat decreased, reaching a minimum in the thermo-mechanically affected zone. In the stir zone, micro-hardness increased significantly due to intense plastic deformation and material compression. The microstructure in the nugget region appeared fine-grained and compact, while the region affected by coarse grain experienced significant heat effects. Increasing the tool shoulder diameter led to an increase in the nugget zone and the length of the bonded region. However, it did not have a significant effect on grain size in the nugget region.
In this study, welding a Ni-Mo-based superalloy (Hastelloy B-2) was examined in order to characterize the microstructure and mechanical performance of joints along with assessing the effects of ...current intensity on the microstructure and mechanical responses of different weld zones. The gas tungsten arc welding (GTAW) process was used to weld the samples using ERNiCrMo-2 filler metal. The pulsed current GTAW process was used to weld the superalloy sheets of thickness of 1 mm with background current (Ib) of 20 A and 40 A and peak current (Ip) of 80 A and 60 A. Tensile and Vickers microhardness tests were conducted to evaluate the effect of pulsed current on mechanical properties of the welds along with chemistry and microstructure characterizations. Finally, the fracture surfaces after the tensile test were studied using SEM fractography analysis. The results indicated that increasing Ib and decreasing Ip led to low heat input and high cooling rate resulting in a high thermal gradient. This caused microstructure transition from the columnar dendrites to the coaxial ones in the weld zone; molten metal convection in the fusion zone led to fine grains in the weld zone during welding time. Moreover, a significant decrease in the amount of molybdenum carbides at the interdendritic regions of the weld metal was observed under these conditions. The tensile strength of the weld metal was higher than that of the base metal resulting in the fracture of all welds from the base metal. Additionally, the microhardness results indicated a significant increase for the weld metal compared to both heat-affected zone (HAZ) and base metal. The higher mechanical properties of the weld metal is attributed to the increase in background current and decrease in peak current leading to a fine grain microstructure. Fractography following the tensile test showed a completely ductile fracture.
•Pool boiling experiments were conducted to study the effect of pitch, width, and depth of parallel channels in bi-conductive surfaces.•The optimal channel pitch reduced the bubble departure diameter ...by about 21%.•Increasing the channel width up to the optimum value can cause thermal concentration and enhance heat transfer at low heat fluxes.•The highest value of HTC with 58% improvement was achieved in the lowest value of the channel depth.
Since pool boiling is widely used in many modern industries, the need to improve it has led to the development of new methods. One of the new methods studied much less so far, is creating bi-conductive surfaces. In our study, in three separate series, the effect of pitch, width, and depth of low-conductive channels are investigated. Copper samples were grooved by wire electrical discharge machining (WEDM) and filled with a mixture of epoxy and hydrophilic silica aerogel. Pool boiling experiments were conducted with deionized water at atmospheric pressure. In addition, the samples' images were obtained by scanning electron microscopy (SEM), and visualization of bubble formation was provided by a high-speed camera. According to the results, sample 4 with 2.5 mm channel pitch, 0.5 mm width, and 0.3 mm depth reached a heat flux of 103.9 W/cm2 and heat transfer coefficient (HTC) of 7.6 W/cm2 K. This shows 62 % and 58 % improvement respectively, compared to the plain surface. Channel pitch best selection resulted in 21 % reduction in bubble departure diameter. Increasing the channel width to an optimal value of 1.5 mm leads to thermal concentration and improving HTC up to 146 % in low heat fluxes. In depth variation series, the lowest value of 0.3 mm led to the best performance in improving heat transfer. The present study provides a good understanding of dimensional characteristics' impact of low-conductive channels on pool boiling heat transfer.
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•An experimental study was conducted to improve pool boiling by combining electrodeposition and bi-conductive surfaces.•Wickability, porosity, thickness and maximum HTC were evaluated using RSM ...method.•HTC of the best sample improved by 2.61 times compared to the plain sample.•Experimental correlations were established for the objective parameters.•Porosity maximized in the middle range of current density and time while HTC reduced.
This study investigated the effect of simultaneously changing influential parameters of the electrodeposition method, with proposing an intensified approach for promoting the pool boiling process by creating hybrid bi-conductive surfaces. With the help of surface response methodology (RSM), current density, time, and the number of electrodeposition steps were varied to experimentally study the wickability, porosity, thickness, and maximum heat transfer coefficient (HTC) of fifteen coated samples. Boiling experiments were performed with deionized water at atmospheric pressure. The characteristics of surfaces were studied by conducting scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and profilometry tests. The results of three-dimensional graphs showed that with increasing the number of steps, the wickability became independent of time and current density of the electrodeposition process, while the thickness of the porous layer increased. Also, when the porosity peaked, the HTC plummeted, which can be due to the water replenishment obstacles. In addition, experimental correlations for the desired parameters were extracted using the regression model. Finally, by combining electrodeposition and bi-conductive methods in the electrodeposited sample with low-conductive channels of 1.5 mm width and 2.5 mm pitch, heat flux and HTC improved by 62% and 260% compared to the plain sample, respectively.
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