Microstructural evolution of Al-20Si-5Fe alloy during rapid solidification and hot consolidation

Al-20Si-5Fe melt was rapidly solidified into particles and ribbons and then consolidated to near full density by hot pressing at 400°C/250 MPa/1 h. According to the eutectic-growth and dendritic-growth velocity models, the solidification front velocity and the amount of undercooling were estimated for the particles with different sizes. Values of 0.43−1.2 cm/s and 15–28 K were obtained. The secondary dendrite arm spacing revealed a cooling rate of 6 × 10⁵ K/s for the particles with an average size of 20 μm. Solidification models for the ribbons yielded a cooling rate of 5 × 10⁷ K/s. As a result of the higher cooling rate, the melt-spun ribbons exhibited considerable microstructural refinement and modification. The size of the primary silicon decreased from approximately 1 μm to 30 nm while the formation of iron-containing intermetallic compounds was suppressed. Supersaturation of the aluminum matrix in an amount of ∼7 at.% Si was noticed from the XRD patterns. During the hot consolidation process, coarsening of the primary silicon particles and precipitation of β-Al₅FeSi phase were observed. Evaluation of the compressive strength and hardness of the alloy indicated an improvement in mechanical properties due to the microstructural modification.     

Bacterial foraging solution based fuzzy logic decision for optimal capacitor allocation in radial distribution system

This paper proposes a novel methodology for the optimal location and sizing of shunt capacitors in radial distribution systems. This method is based on a fuzzy decision making which using a new evolutionary method. The capacitor placement optimization problem includes: minimizing the cost of peak power, reducing energy loss and improving voltage profile. The installation node is selected by the fuzzy reasoning supported by the fuzzy set theory in a step by step procedure. Also an evolutionary algorithm known as bacteria foraging algorithm (BFA) is utilized in solving the objective multivariable optimization problem and the optimal node for capacitor placement is determined. The proposed approach is applied to 34-bus distribution system as a test study and the results are compared with previous method. The results show that this method provides more economic solution by reducing power losses, energy loss, total required capacitive compensation and show a good improvement in nodes voltage to be in the requested range. Comparison between the proposed method in this paper and similar methods in other research works shows the effectiveness of the proposed method for solving optimum capacitor planning problem.     

Large-scale precipitation synthesis of α-alumina with poly aluminum chloride: Optimization of synthesis parameters

α-Alumina production has been industrialized since many years ago. Nevertheless, there are still challenges in the efficient synthesis of α-alumina with subtle specifications for high-tech applications, specifically on large scales. So, here, we investigated the large-scale synthesis of α-alumina by the precipitation method and with industrial grade poly aluminum chloride (PAC) as the aluminum precursor, for the first time. The synthesis procedure was optimized in terms of synthesis yield and facilitation of α-alumina formation by adjusting the concentration of the precursor (PAC) and precipitant (NaOH) solutions. The samples were characterized by conducting several analyses, including X-ray diffraction, X-ray fluorescence, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, dynamic light scattering, and gas adsorption. The results indicated the significant effects of PAC and NaOH concentrations on the synthesis yield and facilitation of the α-alumina formation. According to the results and process considerations, working at higher levels of PAC (.75 g/ml) and NaOH (1.0 M) concentrations was found to be the optimum synthesis conditions. Moreover, the potential of the optimized sample as the abrasive material and the catalyst support was evaluated. The results confirmed the high potential of the optimized sample in these applications. This study therefore introduces a promising and cost-effective method for the large-scale synthesis of versatile α-alumina.