Papers by Keyword: Crystallization

Abstract: O₂ plasma treatment induces a transformation in the structure of WO₃ thin films, converting them into a crystalline structure. Amorphous WO₃ thin films were deposited on silicon produced by pulsed DC reactive magnetron sputtering at room temperature. The as-deposited films were treated with oxygen plasma powered by an RF generator. During the plasma treatment, the pressures were set at 1 x 10^-1 to 1x 10^-2 mbar, while the RF supplied powers at 100 W and 200 W. The effects of plasma treatment induced modifications of structure and physical properties of WO₃ thin films. Several techniques were used to characterize microstructure, phase composition and surface morphology of the films including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM). An RF generator powered the O₂ plasma treatment on the as-deposited films. During the plasma treatment, the pressures were set at 1.0x10^-1and 1.0x10^-2 while the RF powers was supplied at 100 and 200 watt, respectively. The film's crystal structure changed at 200W plasma power and 1 x 10^-2 mbar operating pressure. The O₂ plasma treatment significantly changed the thickness of the films, probably as a result of changes in the packing density and surface etching. The experimental results suggest that the plasma treatment excitation process after crystallization can transform the films' amorphous structure into a crystalline structure.

Abstract: Analysis of literature sources and empirical data indicate a variety and a large volume of experimental material, which often characterizes the uncertainty and contradiction of information regarding the effect of sulphur and manganese on the corrosion behaviour of steels obtained using traditional methods. This leads to the need to search for new, alternative methods for its effective analysis. The task of assessing and predicting the corrosion properties of structural steels is a key one in the general problem of managing the operational reliability of welded metal structures and equipment for the chemical, metallurgical, oil and gas, mining and other industries. The possibilities of its solution consist of using new information technologies, a component of which is intelligent means of information processing, such as artificial neural networks (ANN). The use of ANN makes it possible to create qualitatively new hardware and software that significantly expand the classes of emerging problems and increase the efficiency of analysis and forecasting. In the process of long-term operation of metal structures in many industrial industries, the metal is in direct contact with sulfur-containing agents at high temperatures. This leads to the saturation of the surface layer of the metal with sulfur with a concentration of up to 0.6%, which further makes it impossible to carry out repair and welding operations due to the formation of hot cracks. It was found that adding metallic manganese into the electrode coating in an amount of 20-25% significantly increases (4-5 times) the resistance against the formation of hot cracks. Sulfur content in the deposited metal has the opposite effect on the appearance of hot cracks. So, with a sulfur content of 0.042% and more, the resistance of the metal against the formation of hot cracks decreases sharply. It is shown that an increase in the content of metallic manganese in the electrode coating significantly reduces the content of dissolved sulfur in the deposited metal. Moreover, this tendency is typical for steels with different sulfur content in the surface layers and with different service life. For example, for steel with a service life of 20 years, the initial sulfur content in the surface layer of the metal (up to 1 mm) was about 0.52%. Adding metallic manganese in the coating of electrodes in an amount of 20-25% made it possible to reduce the sulfur content in the deposited metal to 0.03-0.045%, i.e. 12.6-17.3 times. In addition, the corrosion rate decreases with an increase in the content of metallic manganese in the electrode coating. The lowest corrosion rate for all steels involved in the research was established at 20-25% manganese content in the coating.

Abstract: Currently, native starch as a binder and sizing component is used extremely rarely due to its inherent disadvantages. It has been replaced everywhere with modified starches of various kinds. Studies have shown that polyelectrolyte flocculants can be created on the basis of starch if ionizable groups are introduced into the macromolecules of amylose and amylopectin. At the same time, it was found that the treatment of starch with oxidizing agents (of various natures and activities) can significantly improve the functional properties of native starch when gluing, used for surface sizing, and as a binder for corrugated cardboard. In this work, we also obtained oxidized starch in order to create an adhesive binder on its basis, and only local raw materials were used. It is shown that this method makes it possible to regulate the number of functional groups (oxidizing effect, or OE) in oxidized starch and its paste viscosity within a wide range. This is achieved by changing the molar ratio of the catalyst and oxidizer. During the oxidation process, it is possible to vary the concentration ratios of the oxidizer, catalyst, and conditions. Using FeSO₄ as a catalyzer, the oxidized starch pastes show a less pronounced pseudoplasticity and are characterized by reduced viscosity. The analysis showed that during the oxidation of corn starch with hydrogen peroxide, changes in the supramolecular structure of starch are insignificant: a certain repeated decrease in the level of crystallinity takes place, which leads to a decrease in the gelatinization temperature and also the viscosity of starch pastes.

Abstract: Crystal size disribution is a parameter used to indicate the quality of sugar crystals obtained from the crystallization process. The better the crystal size distribution, the better the quality of the sugar crystals produced. The good quality of sugar crystals has an impact on the easier separation process that will occur in the centrifugal machine and can reduce sugar loss both in the centrifugal machine and in the sugar grader. The purpose of this study is to determine the effect of the number of sugar seeds, the quality of the mother liquor and the length of time used in the crystallization process on the quality of white sugar crystals produced in the Batch Vacuum Pan and to obtain the best interaction from several levels used for each factor, which can be used as a reference for producing sugar products that have crystal size distribution values according to the desired standard. Each treatment was carried out twice. Observations were made on material characteristics (brix, pol, and purity) and product sugar characteristics (average crystal size and coefficient of variation of crystal size). Measurement of the characteristics of sugar using a sieving (granulometer) which is then calculated using the ICUMSA GS2-37 method. The influence of factor’s main effect and interaction were analyzed using analysis of variance at the level of p value ≤ 0.05. Further tests for each factor’s main effect and interaction with p values ≤ 0.05 were carried out using the Duncan Multiple Range Test (DMRT). The best distribution of sugar crystal size was obtained from the interaction of sugar seed factors with levels of 3 m³, 5 m³, or 10 m³ which interacted with the quality factor of mother liquor (fine liquor + 0 m3 molasses), and 2 hours of cooking time, Where the results of the interaction of this factor produce a percentage of sugar with a size larger than 0.8 mm as much as 80%.

Abstract: In this paper, BaO-ZnO-TiO₂-SiO₂ is used as the research system of high refractive index glass, and IR, XRD and DTA are used to study the structure, thermal behavior, crystallization and chemical stability of different glasses when B₂O₃ gradually replaces SiO₂. The results show that when B₂O₃ replaces SiO₂, glass still has an amorphous structure, and the density of glass shows a decreasing trend with the increase of B₂O₃ content. With the increase of B₂O₃ content, the boron-oxygen tetrahedron gradually transforms into the boron-oxygen triangle, which makes the overall crystallization of the glass structure weaken. The results show that the density, refractive index and water resistance of glass beads without B₂O₃ are the best. With the increase of B₂O₃ content, the activation energy of crystallization decreases, the potential barrier to be overcome for crystallization decreases, as the same time the phenomenon of glass crystallization is obvious. Keywords:High refractive index glass; BaO-ZnO-TiO₂-SiO₂; Crystallization; Chemical stability

Abstract: Magnesium phosphate cements (MPCs) find application as alternative inorganic binders in construction, for crack repair and recycling of hazardous wastes. For the most common formulation, setting occurs through the reaction in water between magnesium oxide and potassium dihydrogen phosphate. The products include MgKPO₄·6H₂O (MKP) and an amorphous phase. Their use is somehow limited by the short working time and excessive release of heat. In this work, glucose has been introduced in the formulation of MPC to extend the setting time and modulate the rate of heat evolution. This can be considered an inexpensive and sustainable solution. The mechanism of action of the additive has been studied by investigating the reaction with isothermal conduction calorimetry, whereas the microstructure and phase composition of the obtained cements have been studied with scanning electron microscopy and X-ray powder diffraction, respectively. Results indicated that the additive influenced the reaction path thanks to the interaction at the molecular level with the dissolution process of magnesium oxide, as well as with the nucleation and growth of MKP. This has been confirmed by the changes induced in the size and shape of MKP crystals observed after the experiments conducted on diluted systems.

Abstract: In this paper, BaO-ZnO-TiO₂-SiO₂ is used as the research system of high refractive index glass, and IR, XRD and DTA are used to study the structure, thermal behavior, crystallization and chemical stability of different glasses when Al₂O₃ gradually replaces CaO. The results show that when Al₂O₃ replaces CaO, the glass still has an amorphous structure. With the increase of Al₂O₃ content, the glass structure first becomes tight, and then due to the formation of [AlO₆], the glass network becomes loose, and the glass density peaks with the increase of Al₂O₃ content. DTA analysis showed that with the increase of Al₂O₃ content, the devitrification trend of the glass increased during the cooling process, the crystallization peak moved to the low temperature direction, and the exothermic effect weakened, indicating that the surface crystallization trend of the glass increased and the overall crystallization became weaker. The results show that the density, refractive index and water resistance of glass microspheres containing only CaO are the best, but the crystallization of glass is obvious during heat treatment.

Abstract: A numerical model is presented to simulate the crystallization kinetics in fiber-based composite with thermoplastic semicrystalline matrix. The proposed model, based on Schneider's formalism, considers the specificity of crystalline entities growing in confined medium such as fibrous composite. Indeed, transcrystallization has been experimentally observed many times and its effects on both kinetics and mechanical properties have been largely demonstrated. As an application, this paper aims at illustrating this former effect with a finite element (FE) simulation of the cooling down of a plate. The simulated materials are polypropylene alone and a fiber-based composite with a polypropylene matrix. Information on the temperature, the rate of transformation and the microstructure are obtained from both materials and compared to emphasize the contribution of transcrystallization.

Abstract: Yttria stabilized tetragonal zirconia (Y_0.08Zr_0.94O₂, YSZ) nanopowders were successfully synthesized by microwave solvothermal method (MSM). The synthesizing temperature, holding time and mineralizer concentration were optimized. The crystallization and particle distribution of as-prepared YSZ nanopowders were identified by DSC/TG, XRD, FESEM, TEM, FTIR, DLS, and BET. The dispersion of YSZ nanopowders dried by different methods and modified by polyethyleneimine (PEI) was analyzed and discussed. The results show that the PEI modified samples have the best dispersion, and the dispersion of freeze-dried samples is better than that of traditional dried ones. The particle size of the PEI modified samples calculated from the surface area determined by BET is 15.7 nm, which is consistent with that determined by TEM (16.5 nm), but slightly smaller than that calculated by the Scherrer formula according to XRD (22.3 nm). This may be attributed to the different testing principles in these methods.

Abstract: 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 Ti₅₀Al₃₀Ni₂₀ alloy. Cyclic amorphous-crystalline-amorphous phase transformations were investigated during mechanical alloying, using high-energy ball milling technique. After 20 h of milling, an amorphous/nanocrystalline phase was obtained. This amorphous/nanocrystalline phase tended to transform into crystalline grains after 50 h of milling. In a cyclic phase transformation, the obtained crystalline phase is transformed into the amorphous phase after 70 h of milling. This amorphous phase crystallized through a single sharp exothermic peak at 590°C. On the basis of our results, the destabilizing effect of the defects created by the milling media (balls), which leads to the cyclic transformations, depends on the input energy and milling time.