Iranian Journal of Materials Science and Engineering

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In this study different volume fractions of SiC particles of various sizes were introduced into the semisolid A356 aluminum alloy by a mechanical stirrer. Then the slurry was poured into a permanent die of certain dimensions either when the metal alloy was partially solid (semisolid-semisolid or SS route) or after reheating to above the liquidus temperature of the alloy (semisolid-liquid or SL route). Both the SS and SL composite samples were solution-treated at 520°C for 8 hours followed by quenching in water at room temperature. Microstructural characterization studies have been conducted on both the SL and SS samples to quantify the effects of the size andcontent of the SiC particles as well as the solutionizing treatment on the morphology and size ofthe eutectic silicon particles and the matrix grain (globule) size. The results were rationalized in terms of the different nucleation, fragmentation, spherodization and coarsening events, which had taken place during the processing of these composites. Finally the impact of these microstructural features in improving the wear properties of the composites has been discussed.

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Abstract: Multiwalled carbon nanotubes (MWCNTs) were coated with MgO nano particles using simple precipitationmethod. The growth of Mg(OH)2particles was controlled by adjusting the alkaline concentration, salt concentrationand feed rate in simple precipitation method. The nanometer-sized Mg(OH)2particles were precipitated on the surfaceof functionalized MWCNTs by reaction between MgSO4 solution and NH4OH. The samples have been characterizedby scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction and thermal gravimetricanalysis. The results showed a nominally complete MgO coating over the entire outer surface of MWCNTs resulting inimprovement of their oxidation durability.

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Kinetic models are the most important instruments for predicting and evaluating the performance of flotation circuits. To determine the kinetic order and rate of flotation of a gilsonite sample, flotation experiments were carried out in both rougher and cleaner stages. Experiments conducted using the combinations of petroleum-MIBC, gas oil-pine oil, and one test without any collector and frother. Five first order kinetic models were applied to the data obtained from the flotation tests by using the Matrix Laboratory software. Statistical analysis showed that the classic first order model perfectly matched the rougher and cleaner results performed using petroleum-MIBC combination. The kinetic constants (k) were calculated as 0.04 (s^-1) and 0.01 (s^-1) for the rougher and cleaner, respectively. Rougher and cleaner tests without collector and frother also matched with the modified gas/solid adsorption and rectangular models with the k values of 0.05 (s^-1), and 0.01 (s^-1), respectively. The relationship between flotation rate constant, maximum combustible recovery and particle size were also studied. The results showed that the maximum flotation combustible recovery and flotation rate were obtained with an intermediate particle size both in the rougher and cleaner flotation processes. The combustible recovery and flotation rate in the rougher flotation process were higher than that in the cleaner flotation process.

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Li₇La₃Zr₂O₁₂ (LLZO) garnets are one of the promising materials as electrolytes for solid-state batteries. In this study, Li_7-3xAl_xLa₃Zr₂O₁₂ (x= 0.22, 0.25, and 0.28) garnet is synthesized using the combustion sol-gel method to stabilize the cubic phase for higher ionic conductivity. The X-ray diffraction (XRD) results of as-synthesized powders reveal that by addition of 0.22 and 0.25 mole Al, the tetragonal phase still co-exist, whereas 0.28 mole Al addition resulted in a single cubic phase. Afterward, the as-synthesized powders are pressed and sintered at 1180°C for 10h. The hardness evaluation revealed that Al addition increases the hardness that shows better resistance against Li dendrite formation. Besides, the secondary electron microscopy results demonstrate that the dopant has not a huge impact on particle size and grain growth whereas the porosity content has been changed. Finally, the investigation of samples' electrochemical behavior reveals that the addition of Al increases the ionic conductivity of samples by increasing the density and stability of the cubic phase as well. The results declare that the 0.25 Al sample has the highest ionic conductivity. This behavior is thought to be due to the promotion of sintering and increment of bulk ionic conductivity by doping Al.

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The coated β-tricalcium phosphate (β-TCP) with dicalcium phosphate dihydrate (DCPD) has attracted much attention in the biomaterials field due to the increase in its osteoconductivity. Besides, the porous bioceramic scaffolds with controlled pore sizes are significant in stimulating bone-like cell activity. In this study, the effect of the setting-time process and acidic-calcium phosphate (CaP) concentrations on the fabrication and properties of porous DCPD/ β-TCP scaffolds were studied. Subsequently, the specimens were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), compression strength and Fourier transforms infrared (FTIR). The study results revealed that the porous DCPD/ β-TCP scaffolds with macro- and micropore sizes were successfully obtained after the 300-600 µm of porous β-TCP granules were exposed to an acidic-CaP solution. Furthermore, the setting-time process and acidic-CaP concentrations increased the DCPD interlocking between granules, and the mechanical strengths of scaffolds increased up to 0.5 MPa. Meanwhile, the porosity levels were changed based on the formation of DCPD crystals. This study was expected to provide novel insights to researchers in the field of bioceramics through its investigation on the creation of porous DCPD/ β-TCP scaffolds.

 

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The sensitivity of lead dioxide coating properties to the deposition conditions and electrolyte composition has allowed the preparation of coatings with different properties for different applications. In this study, the effects of electrolyte additives on the electrodeposition process were investigated using electrochemical measurements such as cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The results showed that the presence of fluoride ions significantly reduce the possibility of TiO₂ formation. The addition of copper ions not only prevents lead loss at the cathode, but also leads to the formation of copper oxide on the surface at initial stages, which hinders nucleation of PbO₂. The presence of sodium dodecyl sulfate (SDS) also interferes with the nucleation process as it occupies active nucleation sites. The α-PbO₂ interlayer prevents copper oxidation and solves the problem of lead dioxide nucleation. Finally, it was found that the simultaneous use of all additives together with the α-PbO₂ interlayer has a positive effect on the coating process.