Papers by Keyword: Mechanochemical

Abstract: The present work is aimed at the synthesis of fluorine substituted and carbonate substituted hydroxyapatites (FHA, CHA) by the mechanochemical method. The shortest milling time required for the synthesis of FHA and CHA using calcium hydroxide and diammonium hydrogen phosphate as precursors was estimated. In addition to the Ca and P precursors, ammonium carbonate and ammonium fluoride were used for carbonate and fluorine substitutions, respectively. Thermal stability of the synthesized FHA and CHA was evaluated. The phase composition and crystallite size were evaluated by the X-Ray Diffraction (XRD). Fourier Transform Infrared Spectroscopy (FTIR) technique was employed to confirm the functional groups corresponding to the FHA and CHA. Thermal stability of the FHA and CHA was determined by the XRD and FTIR studies on the FHA and CHA powders annealed at 900 ^°C. From the XRD and FTIR results, it is observed that the 30 min milling time is the shortest time for the complete formation of FHA and CHA. The powders synthesized with a minimum milling time of 30 min exhibited better thermal stability.

Abstract: Mechanochemical synthesis is a simple and effective method to prepare ceramic compounds with nanosize. The present work was aimed at investigating the application of the mechanochemical method to synthesize nanocrystalline hydroxyapatite (HA). The shortest milling time required for synthesizing HA, using Ca (OH)₂ and (NH₄)₂HPO₄ as precursor materials was also established. The synthesized samples were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) to determine the phases evolved, functional groups present and to assess the size and morphology of the particles, respectively. Further, the thermal stability of the synthesized powders was investigated by heating to a temperature of 900 °C with a dwell time of 2 h. The broadening of the XRD peaks was used to find out the crystallite size and Williamson-Hall plots were used to estimate the lattice strain. The XRD and FTIR results demonstrated that the complete formation of the HA phase by mechanochemical method has started within a milling time of 30 min using Ca (OH)₂ and (NH₄)₂HPO₄ as precursors and the Ca/P ratio of the HA increased with increasing milling time. The TEM micrographs demonstrated that the HA particles are nanosized, non-spherical and highly agglomerated.

Abstract: Structure evolution and morphology of La_0.7Sr_0.3Co_0.8Fe_0.2O_3-δ (LSCF 7328) were investigated during two different preparation methods namely mechanochemical and combination of mechanochemical-solid state. The result shows that no characteristic peak of perovskite oxide was found on the diffractogram of the product of sole mechanochemical method at 600 rpm and up to 12 h of high energy milling process. On the other hand, the manual grinding method that was followed by solid state calcination produces irregular particle size. Due to the result, the combination of both methods was proposed to obtain the fine structure formation and particle size distribution. Rietveld refinement was used to investigate the lattice distortion. It was found that unit cell remains unchanged at increasing milling time. Moreover, the combination method produces regular particle size at milling time of 0.5 h. At longer milling time, the more regular particle size is formed which comes from highly energy transfer of milling.

Abstract: Polycrystalline diamond (PCD) has excellent properties such as high hardness, high chemical inertness, high wear resistance and a low friction coefficient. Thus, it has been expected to be applied to used in various mechanical parts such as sliding parts. However, diamond is difficult to machine owing to its high hardness and chemical inertness. Therefore, a highly efficient and high-quality machining process is required for PCD. In this study, the authors developed fixed abrasive polishing tools for the mirror-like surface finishing of PCD that contain mechanochemical abrasive grains with diamond grains. As a result of fixed abrasive polishing experiments, it was clarified that a mirror-like surface can be obtained by fixed abrasive polishing using a tool containing SiO₂ and diamond abrasives. Moreover, it was found that the removal efficiency can be increased under a high-temperature condition.

Abstract: Mechanochemical destruction (MCD), a novel non-combustion technology based on the high energy ball milling, has proven to be promising in the destruction of these chemicals in various wastes, and cannot product secondary pollution such as dioxin. So far, the areas that MCD research carried on can be categorized in metal oxide/hydroxide and salt, and elemental metals and hydrogen donor. This paper reviews the effects of the reaction conditions on the destruction efficiency of MCD, such as dehalogenation, milling time, rotation speed, and charge ratio. Based on the requirements of industrial application for Halogenated Organic Wastes removal, the research trends of MCD for the future are brought up in order to further improve destruction efficiency and cost saving.

Abstract: The mechanochemical synthesis method was employed to synthesis hydroxyapatite (HA) and magnesium (Mg) doped hydroxyapatite (HA) powders. The effects of Mg²⁺ into the synthesized HA powder properties were investigated. Characterization of the synthesized HA (Mg-free HA) and Mg–doped HA at various concentrations (1% - 9% MgHA) were accomplished through X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses. The nano size powder of HA and Mg-doped HA were successfully synthesized through the present method and the influenced of Mg²⁺ in the HA was also indicated by the different peaks intensity and the crystal sizes obtained.

Abstract: In this study, the mechanochemical method was employed to synthesize hydroxyapatite (HA) and magnesium (Mg) doped hydroxyapatite (HA) powders. The effect of Mg²⁺ into the synthesized HA powder properties were investigated. Characterization of the synthesized HA and Mg doped HA at various concentrations (1% - 5% MgHA) were accomplished through X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses. nanosize of HA and Mg doped HA powders were successfully synthesized through the present method as indicated from the different peaks intensity and adsorption bands obtained in XRD pattern and FTIR respectively.

Abstract: In the present work, we have prepared ZnO nanoparticles by a two-step mechanochemical synthesis method. The reaction was carried out in a paste state at room temperature with a short grinding time of 20 min. The prepared ZnO nanoparticles were characterized by using x-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis-differential thermal analysis (TGA/DTA). XRD and TEM results demonstrated that ZnO have a single phase nature with wurtzite structure with high crystallinity. The lattice parameters calculated from XRD pattern are a= 3.25 Å and c= 5.248 Å and the average grain size of the ZnO nanoparticles was found to be ~ 20 nm (TEM) or ~22 nm (XRD). FTIR spectra demonstrated the peak at ~455 cm^-1 which correspond to stretching mode of ZnO.

Abstract: Activated carbon can be the best selection for the solid media of hydrogen storage materials because of cheap, good availability, high quantity of pore on its surface and good adsorption capacity. To obtain optimal handling of coconut charcoal-based (CSAC) without reducing its property on hydrogen adsorption capacity, the effect of mechanochemical and pelletizing process to CSAC was examined. Mechanical milling by using planetary ball mill was conducted to reduce particle size distribution and to mechanochemically process CSAC with KOH. CSAC particles reduce its particle size distribution to nano and sub micron size due to mechanical milling. After mechanochemical and pelletizing process, the surface area and pore volume of CSAC decrease to 68.5% and 61% compared with those of as received sample. However, hydrogen adsorption capacity of CSAC pellet only decrease 5 and 9% at measurement pressure and temperature of 4000 kPa, -5oC and 4000 kPa, 25oC, respectively.

Abstract: The property of raw kaolinite-coal-gangue is very stable, and reactivity of kaolinite-coal-gangue is enhanced by mechanical force. The SEM, XRD and IR were used to analyze mechanochemical changes during kaolinite-type-coal gangue grinding. The results showed that mechanical force plays a dominant role in the enhanced reactivity, by inducing dehydration reactions the lattice OH grouping decreased with the extension of grinding time. The separation of tetrahedral and octahedral layers combined with the increasing disorder of the kaolinite crystal structure, resulting in kaolinite-type-coal gangue particles become "loose" aggregates. Moreover, due to destroy to tight Si-O and Al-O bond, the mechanical force increases the solubility of SiO2 and Al2O3, which enhanced the reactivity of coal gangue.