Технолошки факултет [Научни радови] / Faculty of Technology [Scientific papers]
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- СтавкаQuantification of Modifiers Fading during Melt Holding in the Aluminum Casting Furnace(MDPI, 2023) Djurdjevic, Mile; Manasijevic, Srecko; Smiljanic, Slavko; Ristic, MarkoStrontium (Sr) and sodium (Na) are the most used modifiers in the aluminum casting industry. Both lose their concentration (fade) during holding in the melting furnace. Three types of chemical reactions in the melt may cause modifier fading: vaporizing, oxidizing, or reacting with some other elements from the melt. Due to Na and Sr’s very low vapor pressure, their vaporization from the aluminum melt was excluded as a reason for the modifiers’ fading. Oxidation looks like the major chemical reaction that causes the fading of Na and Sr from an aluminum melt. The present paper aimed to quantify the fading of Na and Sr in an Al–Si–Cu–Mg alloy. The loss of modifiers (Na and Sr) during melt holding in a furnace can be analytically quantified using equations taken from the literature. The calculated surface reaction rate constant (ks) can estimate the modifier’s loss during melt holding in industrial and laboratory furnaces.
- СтавкаInfluence of Process Parameters in Three-Stage Purification of Aluminate Solution and Aluminum Hydroxide(MDPI, 2023) Damjanovic, Vladimir; Filipovic, Radislav; Obrenovic, Zoran; Perusic, Mitar; Kostic, Dusko; Smiljanic, Slavko; Stopic, SreckoThe influence of process parameters in the three-stage purification of aluminate solution from the Bayer process and aluminum hydroxide was considered in this paper. One of the ways of purification is treating the aluminate solution in order to reduce the concentrations in the starting raw material (solution) and then treating the aluminum hydroxide at a certain temperature and time in order to obtain an alumina precursor of adequate quality. The purification process itself is divided into three phases. The first phase involves the treatment of sodium aluminate with lime in order to primarily remove Ca2+ and (SiO3)2 impurities. Phase II aims to remove impurities of Zn2+, Fe2+, and Cu2+ by treatment with controlled precipitation using specially prepared crystallization centers. In Phase III, Na+ is removed by the process of hydrothermal washing of Al2O3 3H2O. In this work, parameters such as temperature (T), reaction time (t), and concentration of lime (c) were studied in order to remove the mentioned impurities and obtain the purest possible product that would be an adequate precursor for special types of alumina.
- СтавкаAge-related changes in antioxidant defenses of the Mediterranean centipede Scolopendra cingulata (Chilopoda)(2023) Mitić, Bojan M.; Borković-Mitić, Slavica S.; Vranković, Jelena S.; Stojanovića, Dalibor Z.; Pavlović, Slađan Z.Antioxidant enzymes play an important role in protective mechanisms against reactive oxygen species (ROS) and their effectiveness changes with age. Herein the effect of development/aging on the activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR) and glutathione S-transferase (GST), as well as concentrations of sulfhydryl (SH) groups and the total glutathione (GSH) were analyzed in five age classes of the Mediterranean centipede Scolopendra cingulata as follows: embryo, adolescens, maturus junior, maturus and maturus senior. The results presented here revealed low activities of SOD, CAT, GSH-Px, GR and GST in eggs (i.e. embryos), probably because of the degree of their development. The transition from embryos to juveniles was accompanied by a sudden increase in the levels of antioxidant enzyme activities; such changes are likely to make free-living and feeding individuals more suited for conditions that promote the increased generation of ROS. Our results also demonstrate that the trends of antioxidant enzyme activities during the transition from juveniles to adults of S. cingulata were not uniform; their activities increased or decreased with age, suggesting that the enzymes were being regulated differentially. Discriminant analysis was also performed and the variables that separated the examined age classes were GR, GST, SH groups and, most importantly, body length. Body length is in direct proportion to the age of the individuals, which clearly indicates that development has a great influence on the antioxidant defense regulation in this centipede.
- СтавкаInfluence of suspension heating rate on properties of zeolite 13X(Association of the Chemical Engineers of Serbia, 2023) Janković, Mladen B.; Perušić, Mitar D.; Damjanović, Vladimir M.; Filipović, Radislav Lj.; Obrenović, Zoran B.; Tadić, Goran S.; Kostić, Duško D.It is known that the temperature of crystallization during the synthesis of zeolite is one of the most important process parameters. However, during the research work on the synthesis of zeolite 13X and the introduction of this material into regular industrial production, it was noticed that the heating rate of the starting reaction suspension can have an equally important influence. This influence can be so pronounced that a difference of just a few minutes in reaching the crystallization temperature can make a significant difference in product quality, affect the presence of other phases in the crystal, or even determine the direction of zeolite crystallization. Therefore, the aim of this work was to show the influence of the heating rate on the quality of the obtained 13X zeolite powders. The obtained samples were analysed in terms of crystallinity (by X-ray diffraction), chemical composition, granulometry and specific surface area (by Brunauer-Emmett-Teller analysis), and regarding water and CO2 adsorption capacities. Additionally, scanning electron microscopy analysis of the samples showed the morphological characteristics of different 13X zeolite powders. The analysis results of the obtained powders confirmed the influence of the heating rate and helped to define the optimal synthesis parameters i.e. the initial temperature and heating time, that resulted in stable product quality.
- СтавкаComparison of the Bacterial Inactivation Efficiency ofWater Activated by a Plasma Jet Source and a Pin-to-Pin Electrode Configuration Source(MDPI, 2023) Čobanović, Radovan; Maletić, Dejan; Kocić-Tanackov, Sunčica; Čabarkapa, Ivana; Kokić, Bojana; Kojić, Predrag; Milošević, Slobodan; Stulić, Višnja; Vukušić Pavičić, Tomislava; Vukić, MilanIn this comparative study, the bacterial inactivation efficiency of plasma-activated water (PAW) generated by two distinct plasma reactors, one utilizing a nitrogen plasma jet electrode and the other a hybrid argon plasma reactor, was explored. The present study involved the assessment of antimicrobial activity against suspensions of three Gram-positive and three Gram-negative bacterial strains in their planktonic cell state. Bacterial suspensions were introduced into PAW five days after generation. Subsequently, the viability of the bacteria was assessed at various time intervals, specifically at 0.5, 1, 3, 5, 10, and 24 h, in order to evaluate the effect of inactivation. Structural changes in bacteria after PAW treatment were assessed using a scanning electron microscope (SEM). The physicochemical properties of PAW, including pH, conductivity, and concentrations of H2O2, NO2 -, and NO3 - during aging were measured. The present study demonstrated the effective inactivation of the tested bacterial strains by PAW. Gram-positive bacteria displayed greater resistance compared to Gram-negative species, with the lowest reductions in bacterial counts observed for B. cereus, and the highest for Escherichia coli O157:H7. Morphological damage was evident across all bacterial species examined. Physicochemical measurements showed slow decay of the reactive species in the aging process. This study illustrated the potential utility of PAW as an alternative disinfectant.