Papers by Keyword: Mechanochemical Processing

Abstract: Fine Al-Si3N4 composite particles were prepared via mechanochemical processing of the coarse aluminum powder and submicron silicon nitride powder in order to obtain the core-shell structure of composite powder particles. It was expected that soft aluminum particles could form a thin coat on hard silicon nitride particles. The resultant particles were characterized through scanning and transmission electron microscopy and electron spectroscopes. Their particle size distribution, specific surface area, nitrogen/oxygen content and phase composition were also determined. Chemical analysis showed that limited oxidation occurred during mechanochemical processing. It has been found that a thin Al-enriched layer (larger than 10 nm) formed at some Si3N4 particles apart from the opposite effect if Si3N4 particles were occluded in coarser Al items. Discussion of the results is also presented.

Abstract: This paper presents the characterization results of Zinc Oxide (ZnO) nanoparticles prepared by mechanochemical processing using different moles of diluents. ZnO nanoparticles of different crystallite size were synthesized by milling the precursor powders for 5 hours in a high energy ball mill with Zirconia media. NaCl was added as process control agent (PCA) to control the reaction kinetics, as final particle size of nanoZnO is influenced by the reaction rate. X-ray Diffraction (XRD) data was used to compute and analyze the crystallite size of nanoparticles and also to analyze the progress of reaction during milling process. Field Emission Scanning Electron Microscope was employed to analyze the particle morphology and size distribution of ZnO nanoparticles. Ultraviolet Visible (Uv-Vis) spectroscope was employed to analyze the optical absorption of ZnO nanoparticles. Tauc plots were used to determine the energy gap of the ZnO nanoparticles. Crystallite size values of ZnO nanoparticles are seen to be influenced by the amount of PCA and heat treatment. ZnO nanoparticles with a range of E_g (3.1 to 3.14 eV) were obtained depending on process parameters and an inverse relationship was observed between the crystallite size and the energy gap of the ZnO nanoparticles.

Abstract: Aluminium powder was milled under vacuum and/or ammonia atmospheres, in order to evaluate the effect of the order of the atmospheres on the amount of nitrides appearing in the powder after a subsequent heat treatment. All milling experiences were carried out at room temperature for 5 h. The XRD study of sintered powders showed that important amounts of AlN appeared after heating. The use of vacuum and ammonia flow allows controlling the percentage of N rich phases formed. Moreover, the capacity of incorporating nitrogen to the aluminium lattice is very influenced by the vacuum and ammonia flow atmospheres order during the milling process.

Abstract: Nanometer-scale protuberance and groove processing was performed on a silicon (Si) surface by diamond tip sliding using atomic force microscopy (AFM). The protuberances of 0-5 nm height were obtained the silicon surface by using the diamond tip of approximately 200 nm radius and the grooves of 0-2 nm depth were processed by the tip of about 50 nm radius. It was observed that both protuberance and groove were produced using the tip of about 100 nm radius. Indentation measurements show the hardness of processed parts was greater than that of unprocessed parts. Potassium hydroxide (KOH) solution etching was performed on the mechanochemically processed sample. The processed areas were prevented from etching due to the formation of a dense oxide layer. This may be because the processed parts were oxidized by tip sliding due to the effect of mechanochemical oxidation.

Abstract: Nano-crystalline CeO2 was synthesized by the mechanical milling and subsequent heat-treatment from the mixture of Ce(OH)4 as precursor, and NaCl as diluent. The diluent provided diffusion barrier during milling and heat-treatment, which was easily dissolved out by deionized water. The size of crystallite and the strain variance of CeO2 were depended on the temperature and heat-treatment time: increased with the temperature (400~700oC) and time (1~24 hours) increasing, and saturated near at 20nm in size owing to the densification of diluent. The synthesized nano-crystalline CeO2 powder was applied as an abrasive in CMP (Chemical Mechanical Planarization) slurry. When blanket-type SiO2 and Si3N4 wafers were polished with the slurries, the removal rates (RR) of SiO2 and Si3N4 wafers and selectivities (RRSiO2/RRSi3N4) were influenced by synthetic condition of abrasive, the suspension stability and the pHs of slurries.