Papers by Keyword: Crystallization

Abstract: Poly (lactic acid) (PLA) is a useful alternative to petrochemical commodity material used in such as in food packaging industries. Due to its inherent brittleness, low thermal stability, and poor crystallization, it needs to improve its properties, namely in terms of thermal and mechanical performance. The plasticized PLA composites reinforced with nanofiller were prepared by solvent casting and hot press methods. Thermal and mechanical properties, as well as the crystallinity study of these nanocomposites, were investigated to study the effect of tributyl citrate (TBC) and TiO₂ on the PLA composites. The addition of TBC improved the flexibility and crystallinity of the composites. Reinforcement of TiO₂ was found as a practical approach to improve the mechanical properties, thermal stability, and enhanced crystalline ability for plasticized PLA nanocomposites. Based on the results achieved in this study, the composite with 3.5% nanofiller (pPLATi3.5) presented the optimum set of mechanical properties and improved thermal stability.

Abstract: The article presents the results of an investigation of microstructural features and mechanical characteristics of Al-5.0Cu-0.5Mg alloy containing up to 0.4 wt. % Ag and up to 0.1 wt. % Ce. The experiment was conducted using optical microscopy, Scanning Electron Microscopy as well as an electron probe micro-analyzer and Differential Scanning Calorimetry. Samples in cast condition and after heat treatment were examined. The melting temperatures of non-equilibrium eutectics (non-equilibrium solidus), equilibrium solidus and liquidus were determined. The optimal temperature of the homogenizing heat treatment was determined, which was 500°C. Using this heat treatment mode resulted in the elimination of dendritic segregation and complete dissolution of silver in aluminum. Injection of cerium into the Al-Cu-Mg-Ag system during crystallization of the melt is accompanied by the formation of a coarse four-component phase, which has the morphology of polyhedrons, is on the grain boundaries. The estimation of the relation between microstructure characteristics and mechanical properties of the alloy has been made.

Abstract: The effect of milling time on the microstructure evolution and formation of amorphous phase of Ti₆₀Si₄₀ alloy produced by mechanical alloying (MA) has been investigated. Laser diffraction, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Differential Scanning Calorimetry (DSC) were employed to characterize the particle size, morphology and structure of mechanically alloyed Ti₆₀Si₄₀. When the milling time is increased to 20 h, the particle size decreases from 23.7 to 4.7 μm, the shape of the particles changes to spherical and the crystalline structure is transformed into an amorphous phase. The amorphous Ti₆₀Si₄₀ alloy is stable when heating up to 750oC. Above this temperature, the cold crystallization of the intermetallic compounds Ti₅Si₃ and/or Ti₅Si₄ begins.

Abstract: A synthesis of new di-and triblock polyurethane thermoplastic copolymers containing different mass ratio of two crystallizing blocks - poly (1,4-butylene glycol) adipate and poly-ε-caprolactone diols was developed. Using combination of danamometric analysis, IR-spectroscopy, differential scanning calorimetry and X-ray diffraction, the effect of the soft block composition and crystallization conditions on crystal structure and thermal behavior of the obtained polymers have been studied. For the triblock copolymers we have shown a possibility of control the kinetics of material hardening and final mechanical characteristics due to the mutual influence of polydiols during crystallization. In the result, the second crystallizing component allows to control amount, structure and quality of crystalline domains in polyurethanes by variation of crystallization conditions.

Abstract: This work investigates the microstructural and morphological changes on CIGS thin films submitted to a post-deposition heat treatment. The CIGS 1000 nm-thick films were deposited at room temperature by RF magnetron sputtering onto glass substrates covered with molybdenum films. After deposition, the samples were submitted to a heat treatment, with temperatures ranging from 450 to 575 oC. The treatment was also carried out under a selenium atmosphere (selenization), from 400 to 500 oC. Morphological analyzes showed that the as-deposited film was uniform and amorphous. When the treatment was carried out without selenization, the crystallization occurred at or above 450 oC, and the grains remained nanosized. However, high temperatures led to the formation of discontinuities on the film surface and the formation of extra phases, as confirmed by X-ray diffraction data. The crystallization of the films treated under selenium atmosphere took place at lower temperatures. However, above 450 °C the film surface was discontinuous, with a lot of holes, whose amount increased with the temperature, showing that the selenization process was very aggressive. X-ray diffraction analyses showed that the extra phases were eliminated during selenization and the films had a preferential orientation along [112] direction. The results indicate that in the manufacturing process of solar cells, CIGS films deposited at room temperature should be submitted to a heat treatment carried out at 450 °C (without selenization) or 400 °C (with selenization).

Abstract: A series of computer experiments using the molecular dynamics method, imitating the processes of the argon particles system cooling at different cooling rates, was carried out. As a result of modeling, solid phases of varying degrees of order were obtained, a comparative analysis of structures was performed using the calculation of the radial distribution functions of particles and using the author’s algorithm for recognizing clusters of a crystal structure.

Abstract: Several 2-substituted 4-nitrobenzoic acid (NBA) derivatives such as 2-chloro-4-nitrobenzoic acid (2C4NBA), 2-methyl-4-nitrobenzoic acid (2CH34NBA) and 2-hydroxy-4-nitrobenzoic acid (2OH4NBA) were selected as model compounds because of their availability and chemically similar structures, in which the different group/atom (R) does not significantly affect the dominant intermolecular interactions – hydrogen bonds formed by the carboxylic group [1]. Quantum chemical calculations of lattice and intermolecular interaction energy were carried out to identify possible factors, which could be, used in prediction of the formation of solid solutions (SS) in binary systems of chemically similar molecules, in this case - various nitrobenzoic acid derivatives. Meanwhile, crystallization experiments were used to determine the experimental information about formation of solid solutions. The obtained crystalline phases were characterized by combined use of powder X-ray diffraction (XRPD) and differential scanning calorimetry/thermogravimetry (DSC/TG) [2].

Abstract: The effect of shear stress on the viscosity and crystallization behavior of CaO-SiO₂-Al₂O₃ based mold fluxes were investigated, and the structure evolution of molten slag under shear stress were characterized by magic-angle spinning nuclear magnetic resonance technology (MAS-NMR). The results showed that with an increase of shear stress, the shear-thinning behavior of molten slag was found, and the strongest shear-thinning behavior was formed with an addition of 15% Al₂O₃. Correspondingly, the decrement of Q³(1Al) and Q²(1Al) species in molten slag were the largest from MAS-NMR results. In addition, under agitation, the crystallization fraction of sample increased from 71% to 88%, and the average grain size was reduced 23%. However, the shear stress has no influence on the crystal phase.

Abstract: In this work, we investigated the dynamics of nanocrystallization from the amorphous state of the Fe_72.5Cu₁Nb₂Mo_1.5Si₁₄B₉ alloy together with magnetic phase transformations. The thermomagnetic analysis was performed with the simultaneous recording of the temperature inside the core by a thermocouple and the inductance of the winding wound over the core. It was found that the permeability of the core after the crystallization peak first increases rapidly, and then decreases and stabilizes at some level. Permeability growth begins at a temperature that coincides with the Curie point of the Fe₈₀Si₂₀ solid solution. A decrease in permeability was associated with stabilization of the structure of the amorphous and crystalline phases upon cooling. With decreasing temperature, the active redistribution of chemical elements is suppressed, and silicon atoms occupy a stable position in the crystal lattice of iron. Nanocrystalline cores have different Curie temperatures in the state after the peak of crystallization and 300 seconds after the peak. This indicates the continuation of the diffusion of silicon from the amorphous matrix into Fe-Si nanocrystals for some time after the crystallization peak.

Abstract: Fe-Cu alloys are used as structural materials for manufacture of large machine parts subjected to shock loads. Fe-Cu alloys have a higher corrosion resistance in a humid atmosphere and in salt solutions than cast steel. Fe-Cu alloys have high enough damping characteristics. Upon cooling the Fe-Cu melts is stratified into two phases before crystallization which in field of gravity are separated by density. It is possible to suppress delamination and obtain a material with structure of a “frozen emulsion” by heating melt to the temperature T* determined for each composition by a specific way. In this paper, we studied surface tension of liquid alloys of Fe-1wt.% Cu, Fe-20wt.% Cu, and Fe-30wt.%Cu in order to determine the temperature T*. For the melt of Fe-20wt.% Cu value T*=1670°C is highest. It is confirmed by results of measuring temperature dependence of surface tension. Temperature dependence of the surface tension Fe-Cu melts is characterized by a positive value of the temperature coefficient of surface tension dσ/dT which is abnormal for metal melts. Experimental data on the density, the surface tension of Fe-Cu liquid alloys have of independent metrological importance for practical foundry.