Papers by Keyword: Crystallization

Abstract: The paper presents the results of mathematical research of process of heat exchange between liquid metal coolant and molten steel. Research of process of heat exchange between liquid metal coolant and crystallizing the steel at temperatures above 1773 K allowed to determine parameters such as: the intensity of heat transfer for mutual parallel flow and counter flow, the minimum required length of heat exchange zone; the coolant that provides the best energy performance.

Abstract: The paper presents the investigation results of a metal plate re-melting process by a fiber laser beam using a high-speed video camera. The obtained video materials allow observing the transition process of molten metal to a solid state. The dependence of the molten metal transition to the solid state on the laser welding speed and on the focal distance (in the range of ± 20 mm) is analyzed. A quantitative analysis of the geometric dimensions of the microstructural components of the re-melted metal was carried out. When comparing the processed video material and microstructure elements of the molten pool, the similar trends are observed depending on the re-melting speed by a laser beam in a certain range of speeds from 20 to 45 mm/s. The obtained results can be used to develop a technique for estimating the presence of a key-hole depending on the laser focal distance.

Abstract: The article shows the results of multilayer laser cladding of heat-resistant single crystal nickel-based alloy ZhS32-VI (CSMX-4 analogue). The influence of the main technological parameters on geometry and microstructure formation of deposited beads was investigated. Based on obtained dependencies, the regression equations are compiled for describing the shape of bead and the ratio of directional and equiaxial crystallized sections. The obtained dependencies of regime parameters nomination allow restoring the gas-turbine blades by the method of laser cladding.

Abstract: The composite materials Fe₂O₃-ZrO₂ with different content of zirconium oxide have been obtained by thermochemical synthesis. The process of crystallization of zirconium dioxide and the effect of the amount of zirconium dioxide on the phase transformation have been studied by DTA and microscopy. The activation energy of the crystallization process was calculated by the Kissinger method to be in average 170 KJ/mol. It is shown that an increase of the ZrO₂ content leads to an increase of temperature of crystallization.

Abstract: The method of synthesis of new polyurethane urea thermoplastic elastomers with controlled physical network density by varying the crystallization rate of the soft block and the structure of the interphase has been developed. Fine-tuning of morphology and mechanical properties allows to desighn adaptive materials with shape memory. By combination of calorimetric and X-ray diffraction methods, the influence of chemical nature of diaisocyanates and the ratio of two types of crystallizable blocks, polybutylene glycol adipate diol (PBA) and poly-ε-caprolactone diol (PCL), on the structure and termal behavior of the thermoplastic elastomers has been studied.

Abstract: Nyamplung (Calophyllum inophyllum) is a multi-functional plant which is spread widely over the coast of Indonesia. Its seed produces a high content of oil, but its utilization is still limited. It is because C. inophyllum seed oil contains toxic compounds. Therefore, C. inophyllum seed oil has been used as a biodiesel raw material for many years. It was reported that C. inophyllum seed oil contains wax, but its percentage remains unknown. Wax has been used in cosmetics, pharmaceuticals, foods, and coatings industries as oil binder, water repellent, scratch resistance, and dispersion medium. In this work, wax was separated from C. inophyllum seed oil by solvent crystallization with and without separating non-polar lipid fraction (NPLF) from crude oil. Non-polar lipid fraction was separated by batch-wise solvent extraction using petroleum ether to methanol mass ratio of 3:1 (w/w) for eight stages. After eight stages, non-polar lipid fraction was collected for further separation by solvent crystallization method. The ratios of non-polar lipid fraction to acetone were 1:10, 1:20, and 1:40 (w/v). Then, the isolated wax was analyzed by gas chromatography. It was found that wax (purity of 40% and yield of 0.35%) was successfully isolated by separating non-polar lipid fraction from crude oil (batch wise solvent extraction for eight stages) and followed by solvent crystallization (non-polar lipid fraction to acetone ratio of 1:40 (w/v)).

Abstract: Very recently, crystallization of metallic glasses (MGs) has presented promising properties in the catalytic field. This work has investigated enhanced catalytic performance of crystallized Fe₇₈Si₉B₁₃ ribbons for fast activating persulfate (PS) with assistance of UV-vis light and heat. The ribbons were obtained by annealing at 750°C (Fe-A750) and cibacron brilliant yellow 3G-P (BY 3G-P) dye was used as pollutant. The results indicated that UV-vis light had limited capability to enhance PS activation efficiency by crystallized ribbons while the reaction rate using heat at 65°C was 7.5 times higher than at 25°C, suggesting an advanced performance with heat assistance of Fe-A750 ribbons. Activation energy ∆E for Fe-A750 was measured as 44.5 kJ mol^-1. In addition, 5 times reusability could be achieved for Fe-A750 ribbons under 45°C without catalytic decay. The surface morphologies of glassy ribbons, as-annealed Fe-A750 ribbons, HCl-treated Fe-A750 ribbons and after-reused Fe-A750 ribbons have also been systematically studied. This work provides a novel clue to promote applicability of novel crystallized ribbons from MGs.

Abstract: Recently, more attention has been paid to the development of gas hydrate deposits, the use of gas-hydrated technologies, suitable for energy-efficient transportation of natural gas, the separation of gas mixtures, production and storage of cold, desalinating of seawater, etc. Hydrate formation is one of the main processes of gas-hydrate technological installations. In the article a model is proposed that describes the kinetics of the formation of hydrate in disperse systems, which are characteristic for real conditions of operation of gas-hydrate installations, on the basis of a stochastic approach using Markov chains. An example of numerical calculations is presented on the basis of the proposed model of the dynamics of the total mass of gas hydrates, and changes in the velocity of their formation and size distribution at different values of the nucleation constants and growth rate of the gas hydrates, and results of these calculations are analyzed. It is shown that the rate of formation of hydrate has a maximum value in half the time period of the whole process. The obtained results of the calculations of the dynamics the total mass of gas hydrates are in good agreement with the results of calculations by the equation of kinetics Kolmogorov-Avrami. The proposed model can be applied to the inverse problem: the determination of the nucleation constants and the rate of growth of gas hydrates by the results of the dynamics of the formation of hydrate and the changes in the fractional composition of the generated gas hydrates.

Abstract: Nitrofurantoin was crystallized from multiple mixtures of water and organic solvents with and without additives to try to find and identify factors affecting phase obtained in crystallization and provide possible information on crystallization control. Obtained crystals were identified with powder X-ray diffractometry. Crystallization control possibilities were evaluated by using polymer additives and crystallization additives, by also using quantum chemical calculations to investigate the association of nitrofurantoin and additive molecules and calculate Gibbs energy of association.

Abstract: In this study, PP/clay nanocomposites have been fabricated at different nanoclay loadings, i.e. 0, 5, 10, and 5 wt% for the 1^st cycle and 2^nd cycle (re-processing). The prepared nanocomposites were then characterized by a Differential Scanning Calorimetry (DSC) to investigate the effects of nanoclay loadings and re-processing on the melting and crystallization of the nanocomposites. The DSC results showed that the melting temperature, T_m was not significantly affected by the nanoclay loadings and re-processing. In the other hand, the degree of crystallinity, X_c of the nanocomposites was higher than that of neat PP, but only reached a maximum at nanoclay loading of 5 wt% (i.e. 51.2% for NC-5-I and 48.3% for NC-5-II). Thereafter, the X_c decreased at higher nanoclay loadings. There was no significant difference in X_c between 1^st cycle and 2^nd cycle. Additionally, in all nanocomposites samples for both cycles, there were two crystallization temperatures, i.e. Tc₁ and Tc₂. In the overall crystallization process, the T_c of nanocomposites increased by 11-12°C compared to that of neat PP. Whereas, the onset crystallization temperature, T_oc also increased by approx. 13°C. Apparently, there was no significant effect of nanoclay loadings and re-processing on the T_c nd T_oc of the nanocomposites.