ritnms
Not a member yet
1551 research outputs found
Sort by
Refinement of waste phosphogypsum from Prahovo, Serbia: characterization and assessment of application in civil engineering
No full textTwo samples collected from the phosphogypsum deposits of the chemical products industry Elixir Prahovo (Serbia) were subjected to a recrystallization experiment performed over several repeated cycles. In these tests, phosphogypsum was separated into recrystallized (purified) gypsum, insoluble residue and supernatant. Both raw phosphogypsum and recrystallized gypsum were examined using inductively coupled plasma optical emission spectrometry, X-ray diffraction and scanning electron microscopy with energy-dispersive spectrometry. The activity concentrations of (238)u, (235)u, Ra-226, Pb-210,Th- 232 and 40 K were investigated using gamma-ray spectrometry. Based on the activity concentration results, a number of radiometric parameters were calculated for the original and recrystallized phosphogypsum (i.e. radium equivalent activity, y indices for construction materials, a index and external and internal hazard indices). Raw phosphogypsum samples showed greater mean activity concentration levels of U-238 and Ra-226 than the international recommended limits, while the recrystallized gypsum demonstrated notably lower activity concentrations for these two isotopes. The activity concentration of Ra-226 in recrystallized gypsum is similar to 6 times lower than in raw phosphogypsum. Therefore, recrystallized gypsum does not present a radiation hazard when used as a building material, while raw phosphogypsum meets the requirements only for road construction materials
Accumulation of trace elements in Tussilago farfara colonizing post-flotation tailing sites in Serbia
No full textThe purpose of this study was to examine the accumulation potential of spontaneously developed Tussilago farfara populations colonizing sites with different levels of anthropogenic pollution. Physical characteristics of the soil are presented, together with the concentrations of macroelements and microelements (Ca, Mg, Fe, S, Al, Pb, Zn, Cu, Cd, Mn, As, Sb, Ag, Ti, and Sr) in both soil and plants. The biological concentration, accumulation, and translocation factors were used to assess the potential for heavy metal accumulation. Considerable differences were found among assessions from unevenly contaminated habitats, particularly in comparison with an unpolluted site. In line with the ore's characteristics, substrate samples from polluted sites were heavily contaminated with Pb, Zn, As, and Sb. Increased levels of microelements were also detected in plant samples from flotation tailings. Despite active absorption of Zn, Cu, Cd, Mn, and Sr by the plants from mining sites, the detected quantities of these elements in all samples were below the hyperaccumulation threshold. However, the obtained results indicate that the use of T. farfara from such sites in traditional medicine could pose a risk to human health due to accumulation of several toxic elements in the plant's aboveground tissues. Additionally, as a successful primary colonizer and stabilizer of technogenic substrates, T. farfara has an important role in the initial phases of revegetation of highly contaminated sites
Electrophoretically Deposited Bioceramic Composite Coatings on Ti Substrate Intended for Medical Use
No full textBone implant materials are increasingly attracting attention in the biomaterials field. Among them, hydroxyapatite (HAP) has stood out as a prospective biomaterial due to excellent osseointegration ability, owing to its similarity with natural bone. However, due to the lack of adhesive and antibacterial properties, it is usually combined with polymers and antibacterial agents. Natural polymer chitosan (CS) was proven as an effective component of HAP-based composites, improving the adhesion and serving as a drug carrier.1 Inclusion of antibiotics into composite biomaterials has gained a lot of attention, as it is thus possible to achieve the desirable antibacterial activity. Gentamicin (Gent) was shown to be one of the most effective antibiotics in treating bone infections. In this work, bioceramic composite HAP/CS and HAP/CS/Gent coatings were successfully assembled on Ti plates by electrophoretic deposition technique (EPD).2 Deposition was carried out at a constant voltage of 5 V and for 12 min in a single step process from three-component aqueous suspension (Figure 1). Bioactive properties of deposited coatings were investigated in vitro, by immersion in simulated body fluid solution (SBF). After 7-day immersion in SBF, field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectroscopy (FTIR) were employed to investigate the coatings’ bioactivity, whereas electrochemical impedance spectroscopy (EIS) and polarization measurements were carried out during 28-day immersion in SBF in order to obtain valuable information about osseopromotive coatings’ nature. Biological testing included monitoring of alkaline phosphatase activity (ALP) that is associated with the coatings’ ability to promote new bone growth. The high increase in ALP activity (50 %) relative to the control pointed to the strong coatings’ aptitude for the osseointegration process and new bone growth. FTIR and FE-SEM analysis gave evidence of carbonate-substituted HAP, whose presence is desirable in bone implant applications. The formation of the new apatite layer was also confirmed by electrochemical measurements pointing to the high biomineralization potential of the coatings. Antibacterial activity kinetics in suspension against Staphylococcus aureus and Escherichia coli was also monitored to examine the potential coatings’ application. As expected, the gentamicin addition strongly improved the antibacterial activity of HAP/CS/Gent coating, and the effect was more pronounced against S. aureus.
All the obtained results potentially indicated a strong osseointegration ability of the HAP/CS/Gent coating classifying it as a promising material for bone tissue engineering
Valorization of Fly Ash from a Thermal Power Plant for Producing High-Performance Self-Compacting Concrete
No full textThis study analyzes the feasibility of valorizing industrial by-product, fly ash from a thermal power plant as a partial replacement of mineral filler-limestone for the production of self-compacting concrete (SCC). Three types of SCC mixtures with different portions of fly ash and the reference mixture with limestone were designed. The synthesized SCCs in the fresh state were examined for density, entrained air content, flowability (Slump flow, Slump flow time (t500), V-funnel time (tv)), passing ability (L-box), and segregation resistance, while hardened state testing included: density, compressive and flexural strength, static modulus of elasticity, water permeability, resistance against freezing in the presence of deicing salt, and SEM analysis. Taking into account the obtained results it can be concluded that the addition of fly ash has a positive impact on the concrete properties and that the optimal content of fly ash is 20 % with respect to the total filler mass
Antibacterialgraphene-basedhydroxyapatite/chitosan coating with gentamicin for potential applications in bone tissue engineering
No full textElectrophoretic deposition process (EPD) was successfully used for obtaining graphene (Gr)-reinforced composite coating based on hydroxyapatite (HAP), chitosan (CS), and antibiotic gentamicin (Gent), from aqueous suspension. The deposition process was performed as a single step process at a constant voltage (5 V, deposition time 12 min) on pure titanium foils. The influence of graphene was examined through detailed physicochemical and biological characterization. Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, X-ray diffraction, Raman, and X-ray photoelectron analyses confirmed the formation of composite HAP/CS/Gr and HAP/CS/Gr/Gent coatings on Ti. Obtained coatings had porous, uniform, fracture-free surfaces, suggesting strong interfacial interaction between HAP, CS, and Gr. Large specific area of graphene enabled strong bonding with chitosan, acting as nanofiller throughout the polymer matrix. Gentamicin addition strongly improved the antibacterial activity of HAP/CS/Gr/Gent coating that was confirmed by antibacterial activity kinetics in suspension and agar diffusion testing, while results indicated more pronounced antibacterial effect againstStaphylococcus aureus(bactericidal, viable cells number reduction >3 logarithmic units) compared toEscherichia coli(bacteriostatic, LT 3 logarithmic units).MTT assay indicated low cytotoxicity (75% cell viability) against MRC-5 and L929 (70% cell viability) tested cell lines, indicating good biocompatibility of HAP/CS/Gr/Gent coating. Therefore, electrodeposited HAP/CS/Gr/Gent coating on Ti can be considered as a prospective material for bone tissue engineering as a hard tissue implant
Theoretical analysis of hydromixture transport
No full textThis paper presents theoretical considerations and working parameters analyzes of hydrotransport during unstable flow. The variable flow of hydraulic mixture in installations causes unsteady operation and pipes spraying, pump damage, obturation in various sections of the pipeline, reduced capacity as well as higher operating costs. Using mathematical equations presented in this paper, such parameters of the hydraulic mixture, hydrotransport installation and control devices can be determined which protect system from possible clogging. Considering the fact that critical speed of hydraulic mixture depends on transported material grain size, mixture volume mass, diameter of pipeline and specific gravity of solid phase, it is possible to accurately analyze obturation in hydrotransport installations depending on those parameters. In order to prevent hydraulic impacts in hydrotransport installation pipelines, which value can be determined mathematically, it is necessary to adjust installation to hydromixture parameters and pump, or vice versa
Possibility of applying pyrophylite as filler in refractory coatings
No full textU radu su istraživani postupci pripreme punioca na bazi pirofilita za dobijanje vatrostalnih premaza sa kontrolisanim reološkim svojstvima. Polazni uzorci pirofilita dobijeni su iz ležišta Parsović-BiH. Istraživan je uticaj procesa mikronizirajućeg mlevenja na promenu svojstava vatrostalnog punioca, promenu veličine i oblika zrna punioca, disperznost i stabilnost suspenzije premaza. Za karakterizaciju dobijenih punioca korišćene su metode XRD, SEM i optička mikroskopija. U drugoj fazi istraživanja punioci su podvrgnuti procesu mikronizirajućeg mlevenja u mlinu sa keramičkim kuglama. Gornja granica krupnoće ulaznog materijala bila je 100% -2,00 mm. Vremena mikronizirajućeg mlevenja (min): 15; 20;25. Cilj je bio optimizacija svojstava punioca na bazi pirofilita, definisanje sastava premaza i postupaka njihove izrade. Kvalitet dobijenih premaza kontrolisan je u skladu sa standardom za ovu vrstu vatrostalnih proizvoda.The paper investigates the procedures for the preparation of fillers based on pyrophyllite for obtaining refractory coatings with controlled rheological properties. Starting samples of pyrophyllite were obtained from the Parsović-B&H deposit. The influence of the micronizing ginding process on the change in the properties of the refractory filler, the change in the size and shape of filler grain, the dispersion and stability of the coating suspension was investigation. To characterize the obtained fillers XRD, SEM and optical microscopy were used. In the second phase of the research, the fillers were subjected to the process of micronizing grinding in the mill with ceramic balls. The upper limit of the size of the input material was 100% -2,00 mm. Micronizing grinding time (min): 15; 20; 25. The aim was to optimize the properties of fillers based on pyrophyllite, to define the composition of coatings and the procedures for their production. The quality of the obtained coatings was controlled in accordance with the standard for this type of refractory products
Adsorpcija teških metala iz vodenih rastvora korišćenjem hidročađi istrošenog supstrata gljiva kao adsorbenta
No full textU ovom istraživanju je korišćena hidročađ istrošenog supstrata gljiva radi ispitivanje njegove
potencijalne primene kao sorbenta, u cilju uklanjanja Pb2+ i Zn2+ iz vodenih rastvora.
Hidročađ je pripremana u hidrotermalnom reaktoru na temperaturi od 200 °C pri reakcionom
vremenu od 1 h. Strukturna analiza istrošenog supstrata gljiva i hidročađi vršena je pomoću
SEM analize, na osnovu koje je uočeno povećanje poroznosti materijala nakon hidrotermalne
karbonizacije. Takođe, povećanje adsorpcionog kapaciteta hidročađi u odnosu na istrošeni
supstrat gljiva se može direktno dovesti u vezu sa formiranjem pora na površini ugljeničnog
materijala
Characterization of natural zeolite (clinoptilolite) as one of the high cation exchange capacity geopolymer material
No full textThe aim of this research is to subject one of the specific and locally used natural zeolite (clinoptilolite) from Vranjska Banja, Serbia with high cation exchange capacity. Mineralogical - X-Ray Diffraction Analysis (XRD), Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) and determination of cation exchange capacity (CEC) were investigated. Results showed homogenous structure with dominant clinoptilolite - heulandite type zeolites as most abundant minerals. The important aspect of this research is possibility of wider usage of natural zeolite-clinoptilolite due to cost-efficiency aspects of this natural material that can be exploited in large amount from several Serbian deposits e.g. “Zlatokop” (Vranjska Banja) and “Igroš Vidojević” (Brus), Serbia. The present of higher, but also extremely concentration of heavy metals in Pannonian, Internal Dinarides and wider European region lead us to boost novel high performance but economically viable techniques. The starting points are geochemical characterization of novel geo- materials before further water-treatment implementation
Efekti primene mikronizirajućeg mlevenja na kvalitet vatrostalnih punioca na bazi pirofilita, mulita, kordijerita i cirkona
No full textU radu je istraživano dobijanje vatrostalnih punioca na bazi različitih mineralnih sirovina, a pre svega pirofilita, mulita, kordijerita i cirkona. U cilju dobijanja vatrostalnih punioca visokih svojstava I primene u sintezi novih oblikovanih i neoblikovanih vatrostalnih materijala, vršena su sistematična istraživanja procesa pripreme mineralnih sirovina postupcima prečišćavanja, mlevenja i mehaničke aktivacije. Mlevenje i mehanička aktivacija punioca vršena je u visokoenergetskim mlinovima sa polazne veličine zrna 100μm do veličine zrna 15 μm. Posebna pažnja tokom istraživanja posvećena je ispitivanju uticaja mehaničke akrivacije punioca na reološka svojstva dobijenih vatrostalnih premaza za primenu u livarstvu. Karakterizacija dobijenih punioca vršena je primenom rendgenske difrakcione analize i skenirajuće elektronske mikroskopije, a kvalitativna mineraloška analiza i analiza oblika I veličine zrna punioca urađena je pod polarizacionim mikroskopom primenom imerzione metode I kompjuterskog programskog paketa Ozaria 2.5. Rezultati ispitivanja mogućnosti primene dobijenih vatrostalnih punioca za izradu livačkih premaza pokazali su da je veličina zrna punioca 15-20μm optimalana za postizanje zadovoljavajuće reologije primene premaza. Zadovoljavajuća svojstva premaza postignuta su primenom optimalnih sastava premaza i procesa njihove izrade