Papers by Keyword: Mechanical Alloy

Abstract: Use of quicklime as a sole catalyst for transesterification is limited by poor chemical stability and post-reaction recovery. This study investigates the effect of dry milling time on the transesterification catalytic performance (activity and recovery) of mechanically alloyed MgO, Al₂O₃ and eggshell derived quicklime. Raw chicken eggshells were calcined at 900 °C. The resulting flaking eggshell ash was directly mixed and comminuted with MgO and Al₂O₃ in ball milling (BM) machine for 15, 30, 60, 90, 120 and 150 minutes. Each of the catalyst samples was analyzed for surface morphology and particle size distribution, and then utilized for biodiesel production. Analyses of catalyst samples showed that mean particle size reduced, while powder agglomeration advanced with milling time. Optimum catalytic performance was achieved with the composite alloyed for 120 minutes (Z120) and that resulted in fatty acid methyl ester (FAME) yield of 88.4% and catalyst recovery of 98.3%. Sample Z120 was further characterized by TEM, EDX, XRD and BET. Calcination of the composite catalyst enhanced its activity. Dry high energy BM of oxides can be utilized effectively for synthesis of composite catalysts.

Abstract: The Cu0.81Ni0.19 has been synthesized directly from elemental powder of nickel and copper by mechanical alloying. The alloyed Cu0.81Ni0.19 alloy powders are prepared by milling of 8h. The grain size calculated by Scherrer equation of the NiCu alloy decreased with the increasing of milling time. The end-product was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM)

Abstract: Direct hot extrusion of powder is the standard consolidation process to transform mechanically alloyed Oxide Dispersion Strengthened (ODS) steels into fully dense bars. It is a complex process including several steps. In this study, ODS steel bars were extruded and the material microstructure was characterized by TEM observations associated to SANS after each step. It was shown that the nano-cluster nucleation occurs during the powder pre-heating before hot-extrusion. During extrusion, the ferritic matrix undergoes a dynamic recovery but no further change of the nano-cluster distribution is observed.

Abstract: Elemental powders and carbon nanotubes (CNTs) were mixed and milled in a high energy shaker mill (SPEX-8000M), to produce 2024 aluminum (Al₂₀₂₄) matrix composites reinforced with CNTs. Milled products were consolidated by uniaxial load pressing followed by pressure-less sintering under argon atmosphere for 2 h at 773 K. The effect of CNTs concentration and milling time on Vickers microhardness (µHV) was studied. Scanning electron microscopy (SEM) micrographs show that by milling process it is possible to obtain a homogeneous dispersion of CNTs into the aluminum matrix. The mechanical properties of the composites show an important improvement with respect to reference samples. The possible strengthening mechanisms are discussed in the present work.

Abstract: Al-based hybrid composite reinforced by ultra-dispersed tungsten and B4C, was produced by mechanical alloying and hot extrusion. Structure of obtained composites was studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The compressive and tensile properties of these materials were investigated. Tribological tests showed high antifriction properties and wear resistance of composite containing B4C and tungsten. The dilatometric measurements showed that thermal expansion coefficient remains approximately constant up to 500 °C.