Papers by Keyword: Crystallite

Abstract: This work investigates the properties of copper thin films deposited by magnetron sputtering. The substrate is biased by a negative voltage (V_s), which controls the energy ions bombardment during the deposition of the thin films. In order to focus solely on the ions energy contribution, the power supply was fixed and the working pressure was selected at 5 Pa. This ensures energetic sputtered particles completely thermalized, by a sufficient number of collisions with the Argon gas. X-ray diffraction analysis revealed that substrate voltage V_s affects essentially the structure and size of the formed crystallites. The preferred orientation (111) and the larger crystallite size (30 nm) were achieved at V_s = - 60 V. The Cu (111)/(200) peak intensity ratio is maximal (12.55) at - 60 V, corresponding to the lowest resistivity value (6.33 mW.cm). Optimum corrosion resistance of the deposited thin film was achieved at -60 V. At high crystallite sizes, nanoindentation analysis showed a thin film that is more elastic (133 GPa) and less hard (1.96 GPa).

Abstract: Modification of nanometer size order in anode material of hematite nanoparticles is believed to be one of the keys to increasing the specific capacity of Li-ion batteries application. So that, the synthesis temperature dependence of nanocrystallite size properties in co-precipitated hematite nanoparticles is studied. Sample of Hematite nanoparticles is modified the physical properties by synthesis temperature and then annealed of 700°C for 4 hours. The crystallite size increase with the increase of the synthesis temperature i.e., 23.06 to 29.64 nm. It is indicated that the synthesis temperature affects crystallite formation. Furthermore, the magnetic properties show that the coercive field decrease from 869 to 211 Oe with the increase of the temperature synthesis. It is related to the change in the nanosize-order of the sample crystallite.

Abstract: In this study, the process of decomposition of CaCO₃ and crystallization of CaO has been analyzed. The aim of this work is to compare behavior and changes in microstructure between different limestone samples (as geological age and origin, total porosity, hardness category). Studied samples were analyzed in high temperature chamber during the firing process by XRD analysis. With the increasing temperature, the growth of crystallites was measured and computed. In multiple samples a different behavior in these properties was observed. Further analysis studied different temperatures of the end of decomposition of CaCO₃ and the beginning of formation of CaO in soft-porous and hard-recrystallized limestones.

Abstract: This work is focused on the effect and properties of input material on speed of decarbonation. Various types of limestones were used from quarries all around the world and their different properties and behavior were studied. The aim of this research is to find the influence of chemical composition, petrography, porosity and microstructure of limestones on speed .and profile of decarbonation. Process of decarbonation of calcite is subsequently evaluated for the crystallinity of the newly formed product.

Abstract: High performance nanostructured light metals and alloys are very interesting for replacing conventional heavier materials in many industrial components. High Energy Ball Milling and Cryomilling are useful techniques to obtain nanocrystalline powders. In this work the effect of several milling conditions such as rotation speed, time, ball to powder ratio and temperature on the crystallite and particle size and morphology in pure aluminum are presented. X-Ray Diffraction, Laser Diffraction and Scanning Electron Microscopy are used. High energy ball milling at ambient and cryogenic temperature of Al powders rapidly leads to a nanometer size down to about 35 nm. High ball to powder ratio promotes both low crystallite and particle size. Small crystallite size like 18 nm and particle size as 4 μm were achieved in the most energetic conditions at ambient temperature. Isopropyl alcohol used as liquid media and protective atmosphere has a strong influence on the results depending on the milling temperature of Al.

Abstract: Sintered glass-ceramics have been successfully prepared using glass particles derived from a waste water flocculate. Influence of heat treatment conditions (sintering temperature and soaking time, heating rate) and size of the glass particles on the microstructure and density, hardness of the obtained glass-ceramics has been studied. The results show that the prepared glass-ceramics have gehlenite and anorthite as main crystalline phases. SEM analysis indicates that the size and morphology of the crystallites vary with the preparation conditions. A dense glass-ceramic with a high hardness can be obtained by sintering glass powder sized smaller than 0.075mm with a relatively slow ramping rate (3°C/min) to a temperature higher than the crystallization peak temperature of the parent glass for a short period of 30min to 1h.

Abstract: β-SiC particles were synthesized using silicon powder and carbon black at 1300°C. The effect of grinding the silicon powder raw material into smaller particles on the synthesis and crystallinity of the SiC particles was investigated. The size of the silicon particles decreased and the surface of the silicon particles increasingly oxidized into silicon oxide with increasing grinding time, thus decreasing the yield of SiC because of the higher SiO₂ content in the ground silicon powder, since SiO₂ transforms into SiC at a higher temperature than does silicon. Although the sizes of the silicon particles in the raw materials were different, all the synthesized SiC crystallites showed similar size. Transmission electron microscopy-energy dispersive X-ray spectroscopy analysis showed that although most of the synthesized SiC particles were smaller than 100 nm, the primary SiC particles had aggregated, and some unreacted silicon was observed inside the large aggregated SiC particles.

Abstract: The influence of the degree of crystallinity of polymers on the glass transition temperature T_g of their amorphous domains is quantitatively analyzed. The analysis is made based on the Mandelkerns ideas [ concerning the restrictive effect of crystallization on the mobility of macromolecules within the amorphous domains. At low degrees of crystallinity, T_g of amorphous domains slowly increases, and then increases much faster at high degrees of crystallinity.

Abstract: The influence of the degree of crystallinity of polymers on their elasticity modulus has been analyzed. Consideration was made of the situation when the amorphous parts of the polymers were in the rubbery state. A semi-crystalline polymer was considered in the form of a polymeric network in which the crystallites played the role of physical cross-links. Generalized equation of the rubber elasticity was applied to the analysis; this equation contained the Van-der-Waals volume of the cross-links and also the volume of a repeat unit of linear fragments. It was found that reduction of the crystallites size down to nanosize essentially increased the elasticity modulus at their fixed concentration.

Abstract: The motion of impurity ions affects the electrical properties of polymer solid. The ions move through free spaces which exist in the non-crystalline part between polymer crystallites. The free spaces have inhomogeneous size distribution depending on a property of polymers or crystallization conditions. The homogeneity or inhomogeneity of the size of the free space affects the ionic motion, and consequently it also affects the electrical properties of polymer solids. In order to study the electrical properties of polymer solids in relation with such motion of impurity ions, the conductivity relaxation time was calculated for isotactic poly (propylene) (iPP), low density poly (ethylene) (LDPE) and plasticized poly (vinyl chloride) with dioctyl phthalate (p-PVC) from the electric modulus as a function of frequency which was observed by means of the Broadband Dielectric Spectroscopy (BDS). The value of the conductivity relaxation time reflects the non-crystalline structure of these polymers.