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Isopiestic determination of the osmotic and activity coefficients of the {yKNO(3) + (1-y)K2HPO4}(aq) system at T=298.15 K
No full textThe osmotic coefficients of aqueous mixtures of KNO3 and K2HPO4 have been measured at T = (298.15 +/- 0.01) K by the isopiestic vapor pressure method at KNO3 ionic strength fractions y = (0.20581, 0.43631, 0.61099, and 0.83170), over the ionic strength range (2.4958 to 6.0801) mol.kg (1), using KCl(aq) and CaCl2(aq) as the reference standard solutions. These measurements include some new isopiestic results for the KNO3(aq) binary system extending slightly into the oversaturated (supersaturated) molality region from (2.1973 to 4.1295) mol.kg (1). Our new experimental results were modeled with an extended form of Pitzer's ion-interaction model equations, both with the usual Pitzer mixing terms and with Scatchard's neutral-electrolyte mixing terms, and with the Clegg-Pitzer-Brimblecombe equations based on the mole-fraction-composition scale. There are no previously published isopiestic measurements for the {yKNO(3) + (1 - y)K2HPO4}(aq) system. The present assessment yields NO3 - HPO42 mixing parameters for these models that are needed for modeling the thermodynamic activities of solute components of natural waters and other complex aqueous electrolyte mixtures. Model parameters for KNO3(aq) at T = (298.15 +/- 0.01) K were also evaluated using the present results along with critically-assessed osmotic coefficients taken from the published literature. Thermodynamic properties of the saturated solution were calculated using published solubilities of KNO3(cr) in water at T = 298.15 K and the evaluated ion-interaction model parameters for KNO3(aq)
Quantitative metallographic assessment of the electromagnetic casting influence on the microstructure of 7075 Al alloy
No full textThis study presents an attempt to obtain the better quality of an aluminum super-high strength alloy by application of electromagnetic field during the casting process. The conventional continuous casting process of aluminum alloys causes many defects, such as surface imperfections, grain boundary segregation, non-uniform grain size, and porosity. The better ingot surface along with the homogeneous fine-grained microstructure, and hence the better mechanical properties of the ingot, can be achieved by applying the electromagnetic casting process. The microstructure characterization, accompanied by quantitative metallographic assessment, reveals that it is possible to avoid or decrease many defects of as cast ingots during electromagnetic casting process. In this article, the microstructure of the samples of as cast 7075 aluminum alloy, obtained with and without electromagnetic field influence, was analyzed by optical microscope and the variation of key alloying elements content, i.e., Zn and Mg, through the ingot cross section was examined by chemical analysis. Besides, the microstructural parameters such as dendrite arm spacing, interdendritic space width, as well as eutecticum and intermetallic phases volume fraction, were measured using linear method. The electromagnetic field influence on the microstructure of the as cast 7075 Al alloy was evaluated based on measured quantitative metallographic data
Linear Polarization Study of the Corrosion of Iron in the Presence of Thiobacillus ferrooxidans Bacteria
No full textAn electrochemical investigation was conducted to evaluate the corrosion behavior of iron in deionized water (DIW) and medium salt in the pH range of 1 to 4. The times of immersion of the electrode in solutions were changed in the range of 0 to 120 hours. Corrosion currents were determined using the linear polarization technique. Tafel slopes, b(a) and b(c) were also determined by Tafel polarization measurements. The effect of Thiobacillus ferrooxidans on the iron corrosion behavior was noticed in both solutions at pH=1. However, a significant difference between DIW and medium salt existed. While in DIW the corrosion increased continuously with time (after first 24 hours) in medium salt it started to increase after five hours, showing the loss of inhibition properties of a protective layer. The increase in current in the presence of bacteria at pH of 1 was noticed: from 205 nA to 320 nA, and from 175 nA to 400 nA, for DIW and medium salt, respectively
A thermodynamic aspects of metallic secondary raw materials recycling possibility
No full textIndustrial products are made from different materials, therefore existing metallurgical plants are not always able to adequately process them. Knowing the thermodynamic parameters, possibility and degree of removal of contamininats from the base metal in the recycling process can be predicted. Such approach facilitates a decisions about products design, selection of recycling technology, reduces contamination and increases the system resources. In addition, recycling process becomes more profitable, reducing energy costs and increasing environmental protection. In this way, the use of resources becomes more sustainabl
Chemical processes occurring at contact surface liquid metal-mould
No full textDuring the casting of metals at the interface between metal and mould, or contact surface metal-mould, some chemical reactions occur. Reaction products penetrate or move toward the mould as well as toward the castings. In this work the chemistry at the contact surface between the metal and mould was studied. The objective of the work was better understanding of the chemical reactions that occur, at the interfaces, during the casting processes. All experiments were performed, both, on a laboratory and industrial scale, using the steel samples DIN G-X 120Mn 12, the steel samples came from the steel casting industrial plant production list. The moulds were made using the CO2 procedure. Some active components were added to the mould mixture. During the casting process, while liquid metal enter into the mould vacancy, a kind of intensive reaction of liquid metal with quartz sand and added active components occur thus forming a new chemical compounds. These Compounds have an important influence on the steel castings quality, and consequently on the production economy
Tobacco plant's capacity for uranium adoption
No full textThis paper presents the uranium adoption aptitude by the shoots Virginia and Burley, two varieties of a tobacco plant (Nicotiana tabacum L.), bred in natural conditions. Plants were grown on uranium mine tailings with an average uranium content of 15.3 mg kg-1. Each shoot sample was cross-sectioned into five uniform groups of leaves and stem segments. Statistical analysis of the results showed a substantial variance in uranium uptake subject to the section elderliness and origin of the parts. The highest concentrations of uranium values recorded in leaves of Burleys and Virginias nearest root shoot sections were 4.18 mg kg-1and 3.50 mg kg-1, respectively. These are 60 times higher rates than those previously published for leaves of cultivars grown under similar conditions. Taking into account the level of soil contamination, the content of accumulated uranium demonstrates prospective uranium hyperaccumulatory properties of tobacco plant and its potential utilization in phytoremediation of uranium contaminated mediums
Removal of lead from aqueous solutions by using the natural and Fe(III)-modified zeolite
No full textIn the present study, the sorption of lead by the natural and Fe(III)-modified zeolite (clinoptilolite) is described. The characterization of the natural zeolite-rich rock and the Fe(III)-modified form was performed by chemical analysis, point of the zero charge (pHpzc), X-ray powder diffraction, applying the Rietveld/RIR method for the quantitative phase analysis, and scanning electron microscopy. The effects of sorbents dose and the initial lead concentrations on its sorption by two sorbents were investigated. For both sorbents, it was determined that at lower initial concentrations of lead, ion exchange of inorganic cations in zeolites with lead, together with uptake of hydrogen dominated, while at higher initial lead concentrations beside these processes, chemisorption of lead occurred. Significantly higher sorption of lead was achieved with Fe(III)-modified zeolite. From sorption isotherms, maximum sorbed amounts of lead, under the applied experimental conditions, were 66 mg/g for the natural and 133 mg/g for Fe(III)modified zeolite. The best fit of experimental data was achieved with the Freundlich model (R-2 >= 0.94)
Application of phosphate glass in the production of pepper plants (Capsicum annuum L.)
No full textU radu su prikazani rezultati istraživanja primene fosfatnog stakla sa dodatkom Fe, Mn, Zn i Cu u proizvodnji biljaka-rasada paprike Capsicum annuum L. Ogled je izveden u stakleniku Poljoprivrednog fakulteta u Beogradu tokom 2011. godine a u okviru Projekta TR 34001 'Razvoj stakla sa kontrolisanim otpuštanjem jona za primene u poljoprivredi i medicini'. Biljke-rasada proizvedene su u polistirenskim kontejnerima i polipropilenskim saksijama. Ispitivan je uticaj doza fosfatnog stakla od: 0, 1, 2, 3, 4 i 5 g/l na sledeće osobine razvijenosti biljaka-rasada paprike: visinu, broj listova, nadzemnu masu, masu i dužinu korena. Rezultati istraživanja ukazuju da je najbolji efekat na ispitivane parametre razvijenosti biljaka-rasada paprike imala doza fosfatnog stakla od 1g/l supstrata. Dobijeni rezultati ukazuju i na potrebu daljeg istraživanja efekata fosfatnog stakla u proizvodnji drugih povrtarskih kultura, cveća, aromatičnog, začinskog i lekovitog bilja.This paper presents the results of the application of phosphate glass with the addition of Fe, Mn, Zn and Cu in the production of pepper plants of Capsicum annuum L. The experiment was conducted in the greenhouse of the Faculty of Agriculture in Belgrade during the year of 2011 within the Project TR 34001 'Development of the glass with the controlled release of ions for the applications in agriculture and medicine'. The plants were produced in polystyrene containers and polypropylene pots. The effect of the phosphate glass doses of: 0, 1, 2, 3, 4 and 5 g/l on the following properties of pepper plants development: height, leaf number, aboveground weight, weight and root length was examined. Research results indicate that the best effect on the examined parameters of the pepper plants development was found in the phosphate glass dose of 1g/l of substrate. The obtained results indicate a need for further research of the effect of the phosphate glass in the production of other vegetable crops, flowers, aromatic, spice and medicinal plants
Mechanical properties of polyvinyl chloride mixtures with the addition of modified calcite as filler
No full textU radu su prikazani rezultati ispitivanja mehaničkih osobina (zatezna čvrstoća, zatezno izduženje, prekidna čvrstoća i prekidno izduženje) na PVC mešavinama koje sadrže PVC (polivinil-hlorid), stabilizator, klizno sredstvo i punilac. Kao punilac korišćen je nemodifikovani kalcit i uzorci kalcita modifikovani stearinskom kiselinom suvim i mokrim postupkom. Rezultati ispitivanja su pokazali da PVC mešavina, koja sadrži kalcit modifikovan mokrim postupkom ima bolje mehaničke osobine od one mešavine koja sadrži kalcit modifikovan suvim postupkom. Tako je čvrstoća pri zatezanju PVC mešavine koja sadrži kalcit modifikovan sa 1,5% stearinske kiseline mokrim postupkom za 2,84% veća u odnosu na čvrstoću pri zatezanju PVC mešavine, koja sadrži kalcit modifikovan sa istim sadržajem stearinske kiseline, ali suvim postupkom.In this study, mechanical properties of PVC mixtures (PVC, stabilizer, lubricant and filler) such as tensile strength, tensile elongation, breaking strength and breaking elongation were investigated. Unmodified calcite, as well as calcite modified by stearic acid, were used as fillers in wet and dry processes. The PVC mixtures containing the calcite modified by wet procedure had better mechanical properties compared to those with the calcite modified by the dry process. Tensile and breaking strength of the PVC mixture containing the calcite modified with 1.5% stearic acid using the wet process were higher for 2.8 and 5.2%, respectively, compared to the PVC mixture containing the calcite modified with the same amount of acid used in the dry process. The tensile strength difference between the mixtures increased with the increase of the concentration of used stearic acid up to 3%. The strength of PVC mixture with the calcite modified by the wet process was 3.1% higher compared to the mixture containing calcite modified by dry process. The results showed that the bonding strength between calcite and the adsorbed organic component affected tensile strength, tensile elongation and breaking strength of the PVC mixtures. The best filler was obtained by wet modification using 1.5% stearic acid solution that provided the formation of a stearate monolayer chemisorbed on calcite. The PVC mixtures containing the calcite modified by wet process using 1.5% stearic acid solution exhibited the best mechanical properties. This calcite was completely hydrophobic with dominant chemically adsorbed surfactant, which means that stearate chemisorbed on calcite provided stronger interaction in the calcite-stearic acid-PVC system
Secondary measures for reduction of NOx emission in glass melting process
No full textU ovom radu su prikazani novi postupci smanjenja emisije NOx iz peći za topljenje stakla. Zbog visokih temperatura do kojih se zagreva vazduh neophodan za sagorevanje dolazi do visoke emisije oksida NOx iz staklarskih peći. Sekundarne mere usmerene su na razvoj postupaka za uklanjanje azotnih oksida iz dimnih gasova. Dat je prikaz selektivno nekatalitičkog, selektivno katalitičkog redukcionog i 3R postupka kao i njihove prednosti i nedostaci.In this paper the new methods for reduction of NOx emission from glass melting furnaces were presented. The secondary measures are focused on development of different methods for elimination of nitrogen oxide from the smoke gasses. The main characteristics of the selective catalytic reduction process (SCR), selective non catalytic reduction process (SNCR) and 3R process were presented and some advantages and limitations of these processes were analyzed