Papers by Keyword: Mechanochemical Process

Abstract: Hydroxyapatite (HAp), with chemical formula of Ca₁₀(PO₄)₆(OH)₂,is one of the most popular biomaterials applied as a scaffold or a scaffold component in bone tissue engineering. Synthesis of this material using calcium from a natural sourcewill be a good strategy for cost reduction. Waste cockle shells containing abundance of nearly pure calcium carbonate (CaCO₃) are ideal sources of calcium. In this study, the waste cockle shells were turned to CaO nanoparticles using a simple chemical route. The CaO nanoparticle was used as a starting material to react with hydrous and anhydrous calcium hydrogen phosphate (CaHPO₄) with calcium-to-phosphate (Ca/P) ratios in the range of1.5-1.67 under a mechanochemical process. The synthesized products were characterized by X-ray diffraction technique and scanning electron microscope.The experimental results revealed that under the same reaction timethe reaction using the dehydrated CaHPO₄yielded a mixture ofHApand residual CaHPO₄whereas the reaction using hydratedCaHPO₄(CaHPO₄.2H₂O) yieldeda mixture of HApand beta tricalcium phosphate (β-TCP). The HAp yields of the reactions using dehydrated and hydratedCaHPO₄were 71% and 51 %, respectively.

Abstract: Lithium niobate powders were prepared by mechanochemical treatments using Li2CO3 and Nb2O5 as raw materials. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) were employed to evaluate the morphologies and structures of samples. The mechanism of LiNbO3 formation of the ground mixture samples was discussed. The crystal structure of mixture was collapsed into a disordered structure, which increased with increasing grinding time. At the same time, the specific surface area increase and the bond energy reduction of the mixture occurred. Consequently, high energy ball milling enables increase of the internal energy, reduction of the activation energy, and improvement of the uniform mixing stage, which resulted in direct formation of singal phase LiNbO3 at a low temperature (500°C). However, the temperature must reach 1200°C for the traditional method.

Abstract: Sr-ferrite powders were preparated by mechanochemical treatments using SrCO3 and Fe2O3 as raw materials. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM) were employed to evaluated the morphologies, structures and magnetic properties of samples. The results indicated that the starting mixture became amorphous stage after ball-milled for 30h, and single phase SrFe12O19 could be obtained after annealed at 900°C for 2h. And the saturation magnetization was 58.2Am2/kg, and coercivity was 281.2 kA/m at room temperature. In comparison with the traditional firing method , the mechanochemical method benefited achieving the higher coercivity, which indicated that the samples had a better magnetic properties.

Abstract: Mn-ferrite powders were prepared by mechanochemical treatments using MnO₂ and Fe₂O₃ as raw materials. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM) were employed to evaluated the morphologies and structures of samples. The results indicated that the starting mixture became amorphous stage after ball-milled for 40h, and single phase MnFe₂O₄ could be obtained after annealed at 1200°C for 2h. In comparison with the traditional firing method , the mechanochemical method benefited achieving the higher saturation magnetization, which indicated that the samples had a better magnetic properties.

Abstract: Mechanochemical processing of zirconium oxychloride and yttrium chloride precursors with lithium carbonate has been used to synthesis ultrafine powders of yttria-stabilized zirconia. The purposes of this work are to synthesis 8% mol yttria-stabilized zirconia powder via a mechanochemical process and to study the effect of LiCl as an inert diluent on agglomerate size of ultrafine powders. 8% mol yttria-stabilized zirconia powder was prepared from zirconium oxychloride and 8 %mol yttrium chloride precursors with lithium carbonate by using planetary ball mill and heat treatment. Chemical reaction between reactant mixtures occurs during post-milling heat treatment at low temperature to form composite powder. The products of this reaction consist of ultrafine powders embedded within LiCl as soluble salt by-product. The ultrafine powder is then recovered by removing the salt through a washing procedure. The powders were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and particle size analysis. The results indicated that 8% mol yttria-stabilized zirconia crystal structure depends on post-milling heat treatment temperatures. The structure of yttria-stabilized zirconia is transformed to a tetragonal form at 400 oC and 500 oC. Furthermore, it tends to form a cubic structure at 600 oC. However, agglomerate size of ultrafine powders also depends on the concentration of lithium chloride as an inert diluent and the washing procedure. Primary particle size of ultrafine powders is 30 nm.

Abstract: Mechanochemical process was applied for brass alloy production using chemical grade oxide powders. Alpha brass was produced when CuO, ZnO and PbO were milled under argon atmosphere in the presence of graphite (as reducing agent). Concurrent reduction of zinc, copper and lead oxides took place in the argon atmosphere, whereas the reactions of the reduction did not proceed well in the closed chamber that filled with air. These reactions were promoted by milling time up to 100 hours. The amount of reduction tends to decrease for longer times.

Abstract: A special kind of surface modified copper nanoparticles was selected as the auto-reconditioning materials to in situ generate a copperized protective film on iron-base metal surfaces under designed tribological conditions. The morphologies and element distributions of the formed film were observed and determined by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The micro mechanical properties and tribological behaviors were investigated by nano test system and ball-on-disc tribotester. The results show that the morphology of the protective film is smooth, the nano-hardness decreases by 46% and the friction coefficient of the copperized protective film is about 0.10. The forming mechanism of the auto-reconditioning film can be described that the copper nanoparticles deposit on the worn surfaces and form iron-copper alloy film with lower hardness and shear strength, which has better friction-reducing, antiwear and surface-optimizing behaviors.

Abstract: As the electrodes of secondary battery are made with sulfide composite powders, excellent electrode system of environmental non-toxicity and with high specific energy density and low material cost can be obtained. In this study, the (Fe, M)S2 composite powders was synthesized by mechanochemical processes (MCP) in order to improve of the cycle life in bettery. The formation of pyrite phase appreared at the case which adds nickel, but it was not observed in the case where the transition metal was does not add but the transition metal such as cobalt, molybdenum was added in stead. From charge-discharge test results, the initial discharge capasity of (Fe, Ni)S2 electrode was 845 mAh/g. The initial discharge capasity of (Fe, Co)S2 electrode was 500mAh/g, but it showed a better cycle perfoemance than the case where the diffrent transition metal was added.

Abstract: Mechanochemical process was employed to prepare Fe/MgO and Fe/NaCl nanocomposites. The carbon nanostructures (nanotubes and carbon-encapsulated Fe nanoparticles) were successfully synthesized using two nanocomposites as the catalyst. Our wok revealed that the morphology of Fe nanoparticles in the Fe/MgO nanocomposites depended on the distribution and particle size of iron oxides in the precursors. The size of Fe nanoparticles greatly affected their catalytic properties and the morphologies of carbon nanotubes. The successful carbon encapsulation of Fe nanoparticles was achieved by using the mechanochemically derived Fe/NaCl catalyst.