Papers by Keyword: Phase Formation

Abstract: Pelletising, i.e. transformation of fine dusty materials into lump materials (pellets, briquettes, pellets), is an important technical task solved in many sectors of the national economy - ferrous and non-ferrous metallurgy, chemical industry and in a number of other industries. The process of pelletising ores and ore concentrates is of the greatest importance for the production of iron and steel, i.e. for ferrous metallurgy. The most common method of pelletising is pelletising - granulation of iron ore concentrates in special granulation plants, usually with the use of binders. As a result of pelletising, so-called pellets are produced, which are subjected to hardening firing (roasting pellets) or achieve the required level of properties without high-temperature treatment (non-roasting pellets) through the use of special binders. The current trend is the transition from firing methods of pellet hardening to non-firing (low-temperature) methods.

Abstract: A high entropy Ni-Al-Ti-Mn-Co-Fe-Cr alloy (HEA) system was fabricated using spark plasma sintering (SPS). The alloys at different elemental compositions were developed at a sintering temperature of 850 °C, a heating rate of 90 °C/min, a pressure of 50 MPa, and a dwelling time of 5 min. The sintered alloys' mechanical characteristics, microstructure, phase evolution, and density were assessed. The evolved microstructure of the sintered HEAs shows a homogenous dispersion of the alloying metals. The sintered microstructures showed a mixture of simple and complex phases. The phase refinement shows that the sintered HEAs exhibited a lower and the least grain size of 2.28 µm compared to the Ni₅₀Al₅₀ alloy having 8.26 µm. Likewise, a higher micro-strain value of 1.25E-1 was attained by the non-equal atomic HEA, while the unalloyed has 1.87E-3. The microhardness value of the sintered alloys varied from 103.5 HV to 139.2 HV, while their measured density varied from 5.23 g/cm³ to 6.44 g/cm³.

Abstract: In this article in order to verify the probability of the formation of the compound CaBaAl₄O₈, a thermodynamic analysis of the following possible solid-phase reactions of its formation was carried out: formation of CaBaAl₄O₈ from the initial components - calcium carbon dioxide, barium carbon dioxide and aluminum oxide; the probability of formation of dual compounds CaAl₂O₄ and BaAl₂O₄ from the same raw materials (since the compound CaBaAl₄O₈ is located on the BaAl₂O₄-CaAl₂O₄ conjugate) and the possibility of formation of the compound CaBaAl₄O₈ from binary compounds CaAl₂O₄ and BaAl₂O₄. As a result of our experimental studies, the existence of ternary compounds Вa₃CaAl₂O₇ and ВaCa₂Al₈O₁₅ was confirmed, and it was found that the Вa₃CaAl₂O₇ compound exists in the system at least up to a temperature of 1400 °C. Thus, our studies have determined an increase in the temperature limits of its existence, in contrast to the data of previous researchers, who indicated 1250 °C as the upper temperature of existence of Вa₃CaAl₂O₇.

Abstract: The paper describes the process of obtaining a high-density ceramic material based on magnesium aluminate spinel - material, which feature-wise will be lighter by mass of the used bullet-proof glass, and less resource-proof compared to modern ceramic armored. The sintering was carried out in a vacuum using a modifying gallium oxide additive to intensify the process. The effect of the additive concentration on the phase formation in the magnesium aluminate spinel-oxide gallium system, as well as the density and ceramics light transmission, is considered.

Abstract: Ti-6Al-4V alloy ribbons were successfully prepared by rapid solidification at different roller speeds. The morphology and microstructure of Ti-6Al-4V alloy ribbons were studied by X-ray diffractometer, scanning electron microscope and energy spectrum analysis. The effect of SiO₂ on the microstructure and properties of Ti-6Al-4V alloy ribbons were discussed. It is found that the Ti-6Al-4V alloy ribbons consist of β phase with alternated distribution of α' phase and α'' phase. And quicker roller speed promotes the formation of α' phase for the higher rapid solidificationg cooling rate. According to the analysis of energy spectrum data, it is found that there is chemical reactions between the Ti-6Al-4V material and the quartz tube wall during electromagnetic induction melting at high temperature, and the Si elements are segregated at the embossment induced by quick solidification and the phase interfaces between α′ phase and β phase.

Abstract: Bulk metallic glass matrix composites have emerged as new potential material for structural engineering applications owing to their superior strength, hardness and high elastic strain limit. However, their behaviour is dubious. They manifest brittleness and inferior ductility which limit their applications. Various methods have been proposed to overcome this problem. Out of these, introduction of foreign particles (inoculants) during solidification have been proposed as most effective. In this study, an effort has been made to delimit this drawback. A systematic tale has been presented which explain the evolution of microstructure in Zr_47.5Cu_45.5Al₅Co₂ and Zr₆₅Cu₁₅Al₁₀Ni₁₀ bulk metallic glass matrix composites with varying percentage of ZrC inoculant as analysed by secondary electron and back scatter electron imaging of as cast unetched samples. A support is provided to hypothesis that inoculation remain successful in promoting phase formation and crystallinity and improve toughness.

Abstract: The effect of Li and Sr impurities on the kinetics and structure formation of alloys in the Sn - Pb, In - Zn, Sn - Zn systems used in the soldering of instrument nodes in electronics has been investigated. The XPS method showed that under the given experimental conditions and the indicated concentrations of lithium impurities in lead and strontium in zinc, there are no prerequisites for the formation of chemical compounds, which is explained by an insignificant impurity content, although a significant amount of chemical compounds is formed according to state diagrams. It was also established that impurities affect the kinetics of phase growth in the junction zone.

Abstract: Reactive sintering is a process where synthesis reaction of the ceramic phases is combined with sintering (densification) of the composite. Dense lightweight titanium oxycarbide-aluminium oxide ceramic-ceramic composites were produced from titanium dioxide, carbon black as graphite source and aluminium precursors by high energy attritor milling, followed by reactive sintering. Titanium oxycarbide and aluminium oxide phases were synthesized during reactive sintering in situ. To investigate the microstructure evolution and phase formation, the specimens were sintered at different temperatures (600-1725 °C) in vacuum. Scanning electron microscopy and X-ray diffraction were used to analyze the microstructure and phase formation. Mechanical performance (hardness and fracture toughness) was evaluated.

Abstract: The subject of this study was an experimental confirmation of stability of composite nanostructured gypsum silicate binder (CNGSB) system under high-temperature exposure (up to 1000 °C). The hypothesis of the heat-resistance performance of gypsum-based binder was crystallization process in CNGSB system involving a silicate constituent as a reactive component in NB. XRD and DTA analyses demonstrated that thermal exposure of CNGSB to wide range of temperatures of 20–1000 °C leads to α-quartz to β-quartz phase transformation in the binder; amorphous alkali-aluminosilicate (gel) changes to crystal phase of Са-albite. The calculation of cell volumes characteristics for low-temperature (before thermal exposure) and high-temperature (after thermal exposure) phases was performed. The calculated ratios of unit cell volumes were close to 1 which ensures a structural stability of the GNB under thermal exposure and confirms its heat-resistant performance.

Abstract: Many synthesis methods are available to obtain a set of specific characteristics for lead zirconate titanate (PZT) piezoelectric ceramic powders. In this work, we have successfully prepared PZT powder samples through the Polymeric Precursor Method with x = 0.6, according the general formula Pb (Zr_xTi_1-x)O₃. The powders were thermally treated from 380 to 550 oC and characterized by Raman spectroscopy and X-ray diffraction (DRX) in order to evaluate the effects of thermal treatment on the phase formation and the crystallization processes. The results obtained by Raman spectroscopy were compared to refined crystal data obtained by Rietveld method, leading to coherent conclusions about the structural effects occurring along the temperature of calcination. It was possible to characterize the tetragonal perovskite phase as predominant phase occurs only after 500 oC, but its crystallinity is already determined by synthesis method. Thus, no ordering process is verified for perovskite as a function of the temperature increasing during thermal treatment, in spite of the continuous pyrochlore-to-perovskite phase transition. The pyrochlore secondary phase starts to vanish before its proper crystallization process, changing the tetragonality of previously formed perovskite phase.