Papers by Keyword: Crystallite Size

Abstract: Silicon dioxide is the most common silicon compound and a major constituent of the Earth’s crust. Silicon dioxide, also known as silica, is a chemical compound that is an oxide of silicon with the chemical formula SiO₂. Silica is most commonly found in nature as quartz. Quartz exists in natural and synthetic forms. More specifically α-quartz is a widely known material, which is stable at low temperatures and pressures. The α-quartz is considered competent material because over the past many years it has attracted wide attention due to its unique characteristics. The article presents the research results from comparison between one of the morphological varieties of quartz – vein quartz of shungite rocks from Zazhogino deposit of Karelia – and a reference quartz sample. Via the Rietveld method, the values of the lattice parameters are determined. Apparent coherent length for vein quartz samples having contacts with various minerals are determined by the approximation method.

Abstract: Carbonated hydroxyapatite (CHAp) is an inorganic mineral that more closely resembles the main component of composing human hard tissue in 2-8 wt% carbonate content. CHAp powders have been synthesized from oyster shells using the precipitation method. Oyster shells are one type of shellfish from the bivalve class which is rich in calcium carbonate content. In this research, CaO from oyster shells obtained from the decomposition process of CaCO₃ was used as a source of calcium and diammonium hydrogen phosphate and ammonium bicarbonate as well as a precursor of phosphate and carbonate, respectively. In addition, carbonate content variations were x = 0, 0.3, 0.8 and 1.2 which were characterized by fourier transform infrared spectroscopy (FTIR), X-ray diffractometer (XRD), and scanning electron microscope-energy dispersive X-Ray (SEM-EDX) to determine the functional groups, crystallographic properties, morphology and Ca/P molar ratio, respectively. Carbonate ion substitution in the hydroxyapatite crystal structure is known to decrease crystallinity and crystallite size. The theory is in accordance with the results obtained in this study with the crystallite size is 74.322, 46.933, 37.727, and 31.499 nm for 0.95, 2.7, 5.7, and 9.35 wt.% carbonate content, respectively.

Abstract: The relationship between the microstructure and the conductivity of nanocrystallized oxygen ionic electrolytes has been received great interest since it provides guidelines for designing electrolytes with high performances which might find applications in fuel cells and oxygen sensors. Here, we present a strategy for controlling the calcination temperature to tune the crystallite size and ionic transport properties of solid electrolyte. Different crystallite sizes of Ce_0.8Gd_0.2O_2-δ (CGO) nanofiber electrolytes were prepared. As the average crystallite size decreased from 27 nm to 8 nm, the conductivity of the nanofibers increased by more than five times. An exceptionally high oxide ion conductivity of 0.023 S∙cm^-1 for the nanofibers was observed at 550°C. These insights into the effect of the crystallite size on the structure and the conductivity allow a better control of the electrical properties of solid electrolytes, which might foster their applications in electrochemical devices operable at lower temperatures.

Abstract: This study evaluated the effect of a heat treatment on the potential application of AlMg5Si2Mn die casting alloy as a substitute for wrought aluminium alloy products. The proposed heat treatment was intended to increase the workability of the AlMg5Si2Mn alloy, which is typically not malleable due to the presence of interconnected brittle phases. By disintegrating interconnected eutectic Mg2Si phases into fragmented particles and dissolving Mg-rich phases the workability was increased. Subsequently, heat treated samples were subjected to high-pressure torsion process. The microstructure of the heat treated and deformed samples were characterized using light and electron microscope. Hardness measurements were used to investigate the influence the number of HPT revolutions on mechanical properties.

Abstract: Variation of hardness and microstructure evolution in a solution treated AlMg3 aluminium processed by equal channel angular pressing and subjected to subsequent artificial ageing are investigated. The microstructure features of the UFG aluminium alloy are studied by light, electron microscopy and using X-ray diffraction analysis. Microstructural observations showed significant grain refinement. After four ECAP passes microstructure consist of elongated grains with average widths of shear bands of ∼100 nm. A significant increase in the microhardness was observed in the ECAPed samples due to the grain refinement and strain hardening. Prior ECAP solution treatment and a short time artificial ageing can additionally increase the strength of AlMg3 aluminium alloy.

Abstract: The carbides of refractory metals like tungsten carbide (WC), tantalum carbide (TaC) and niobium carbide (NbC), has been extensively studied due to their applications in several areas of industry, because of their specific properties; such as high melting point, high hardness, wear resistance, oxidation resistance and good electrical conductivity. The tungsten carbide, particularly, is generally used at hardmetal industries due to its high hardness and wear resistance. New synthesis techniques have been developed to reduce the synthesis temperature of refractory metal carbides using more reactive precursors and gas-solid reactions for carbon reduction. The result is producing pure carbides suitable properties for production of high quality cemented carbides and more selective catalysts. In this work, pure and nanostructured WC was obtained from the ammonium paratungstate hydrate (APT), at low temperature and short reaction time. Hydrogen (H₂) and methane (CH₄) were used as a reducing gas and carbon source, respectively. The precursor and obtained product were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results obtained by diffraction of X-rays showed that complete reduction and carburization of APT have been took place resulted in pure WC formation. The average crystallite size was in nanometer order reaching values of approximately 20.8 nm and a surface area (BET) of 26.9 m2/g.

Abstract: In this paper, we present the synthesis procedure and the results of an investigation of a novel silica xerogel (SX) glass ceramic developed from an amorphous SX derived from sago waste ash that incorporates TiO₂ as an additive. The studied compositions have been prepared by adding of either 20% or 80 wt% of TiO₂ into SX, respectively. The samples have been dry pressed and sintered in the temperature range between 900°C and 1500°C. Their properties have been characterized on the basis of the experimental data obtained using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and ultraviolet-visible (UV-Vis) spectroscopy. It has been found that an increase of the content of SX in the composition leads to an increase of the shift of the bandgap energy of TiO₂. The analysis based on the interpretation of both XRD patterns and FTIR spectrum allows one to explain the shift in the bandgap energy by an enlargement of the crystallite size of TiO₂ and by forming of more Si–O–Ti bonds in the samples with a smaller loading of TiO₂.

Abstract: The calcium carbonate was extracted from Pomacea Canaliculata Lamarck (Cherry shell) by using the hydrothermal method. Cherry shell was washed and crushed by DI water and mortar. The powder size was analyzed by particle (aperture Size 63 μm), added x HCl (x = 2, 3, 4) and y Na₂CO₃ (y = 1, 1.5, 2) mixed with fine powder from Cherry shell. The mixed power was filtered annealed by autoclave at controlled temperature at 333 K for 20 h. The crystal structure was characterized by X−ray diffraction method. The phase transformation of CaCO₃ was analyzed by Fourier transform infrared spectroscopy (FTIR). The morphology of Cherry shell and CaCO₃ powders were observed by using scanning electron microscope (SEM). It was found that the extracted CaCO₃ shows single phase of CaCO₃ crystal structure. Smallest crystallite size was found about of 0.54 μm.

Abstract: CaCu_2.8Co_0.2Ti₄O₁₂ ceramics were prepared by microwave-assisted sol gel method. The properties of materials can be highly dependent on crystallite size therefore measuring the crystallite size is among the important part in materials research work. In the present study, the crystallite size of the CaCu_2.8Co_0.2Ti₄O₁₂ ceramics sintered at temperature ranged from 975-1125°C were investigated. Different methods, approach and strategy of crystallite size measurement were demonstrated in this papers.Keywords: Crystallite size, CCTO

Abstract: This paper compares the effect of dispersants which are Sodium Laureth Sulfate (SLS) and distilled water (DW) on the crystallization, particle size distribution and morphological behavior of nanoalpha Alumina (α-Al₂O₃) synthesized from Aluminium (Al) dross waste. The synthesizing of nanoα-Al₂O₃ via wet milling method was performed using a planetary mill for 4 hours at a speed of 550 rpm. The nanoα-Al₂O₃ powders with dispersants were characterized with x-ray diffraction (XRD), particle size analyzer (PSA) and transmission electron microscopy (TEM). XRD analysis shows the broadening and shifting of peaks after the sample was calcined at 1300 °C, indicating high crystallinity. The crystallite size of α-Al₂O₃ milled with SLS is also smaller than the α-Al₂O₃ milled with DW. These results are consistent with the PSA analysis in which the graphs displayed a symmetrical trend. Then, the PSA analysis is validated with TEM observation up to 100000x magnification, particularly for α-Al₂O₃ milled with SLS.