Thermal Resistance of Alkali Activated Binders Synthesized Using the Fly Ash and Steel Slag

The thermal resistance of alkali-activated binders based on fly ash (FA), electric arc furnace slag (EAFS) and their FA/EAFS blends was assessed. Compressive strengths of samples before and after firing were measured. The samples were characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energydispersive X-ray spectra (EDS), thermal (TG/DTA) analysis. Besides, the sintering shrinkage were recorded by thermomechanical analyzer (TMA) during non-isothermal sintering up to 900 ºC with heating rate of 15 º/min, in an air atmosphere. The main reaction products in FA and EAFS based alkali activated binders are the sodiumalumino-silicate-hydrate (N–A–S–H) and calcium-alumino-silicate-hydrate (C-A-S-H) type gels, respectively. FA/EAFS based binders are characterized by the presence of N-A-S-H gel with the high content of Ca. The EAFS based binders exhibited superior performances in terms of compressive strength than FA based binders. Thermal resistance of FA based binders was improved by the slag addition. This research was supported by a Ministry of Science of Montenegro under the contract No. 01-460

Transparentni nanokompozitni filmovi za primenu u plastičnoj elektronici

As solar cell technology gains more and more attraction every year, research keeps up with trends by an exponential number of published papers every year. These papers cover a wide range of topics regarding solar cells and the individual components of which they are comprised, which is the subject of this thesis. Different topics of research have been addressed in order to better understand and optimize individual solar cell components (layers) such as silver nanowires (AgNWs), AgNW based nanocomposite and Ag dendrites for the application as transparent electrodes, polymer nanocomposites (PNC) for the possible application as protective layers (encapsulants) as well as organic tandem solar cells as a whole device, utilizing AgNWs as the transparent electrode. The first part of the thesis concentrates on AgNWs and an AgNW based nanocomposite. These AgNWs were synthesized by a simple polyol reduction process. The main focus of this research was elucidating the solid-state wetting and subsequently welding mechanisms that occur during annealing of AgNWs before a layer of aluminum doped zinc oxide (AZO) is deposited on them, for the enhancement of properties essential for an electrode in a solar cell. Microstructural characterization using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that solid-state wetting and subsequent welding occurred only between nanowires whose contact geometry is characterized by an enormous difference in radii of curvature. Results also indicated that, for two AgNWs in contact, during annealing, the AgNW in contact through a smaller radius of curvature dissolves, Ag atoms diffuse and are incorporated in a welded zone between the AgNWs whose crystallographic orientation is inherent from the AgNW in contact through a large radius of curvature. Wetting angle between two welded AgNWs was measured to be below 4.8°, indicating almost complete wetting. Direct atomic column measurements were performed in order to elucidate crystal lattice distortion. Tomography was employed to better understand the morphology of the welded zone and confirmed the welding mechanism based on cross sectional transmission electron microscopy imaging. Electron diffraction orientation and strain mapping were performed in order to elucidate possible strain fluctuation across the AgNWs as well as confirm crystallographic orientation of the welded zone. Crystal lattice distortion, directly measured by atomic column displacements in drift corrected cross-sectional atomic resolution scanning transmission electron microscopy images of an AgNW, prepared by focused ion beam (FIB), demonstrated non-uniform distribution of strain in five twin segments of the nanowire...S obzirom na porast interesovanja za solarnim tehnologijama, istraživanja idu u korak sa takvim trendovima što se manifestuje eksponencijalnim rastom broja objavljenih naučnih radova svake godine. Ovi radovi pokrivaju širok spektar tema vezanih za solarne ćelije i individualne slojeve od kojih su one sačinjene, što je i predmet proučavanja ove teze. Istraživanja su se odvijala u nekoliko pravaca kako bi se bolje razumeli i optimizovali individualni slojevi (komponente) solarnih ćelija kao što su nano-žice srebra, nanokompoziti na bazi nano-žica srebra i dendriti srebra, za primenu kao transparentne elektrode, polimerni nanokompoziti za primenu kao zaštitni slojevi (enkapsulanati) kao i kompletne organske tandem solarne ćelije koje koriste nano-žice srebra kao transparentne elektrode. Prvi deo teze fokusiran je na nano-žice srebra i nanokompozite na bazi nanožica srebra. Nano-žice su sintetisane jednostavnom metodom poliol redukcije. Osnova ovog istraživanja bila je razumevanje mehanizama kvašenja u čvrstom stanju i zavarivanja do kojih dolazi prilikom zagrevanja nano-žica, pre nego što je sloj cink oksida dopiran aluminijumom nanešen radi poboljšanja svojstava, od suštinskog značaja za elektrodu u solarnoj ćeliji. Mikrostrukturna karakterizacija korišćenjem skenirajuće elektronske mikroskopije (SEM) i transmisione elektronske mikroskopije (TEM) otkrila je da se kvašenje i zavarivanje odvijaju samo između nano-žica čiji su poluprečnici zakrivljenja u tački dodira veoma različiti. Rezultati su takođe pokazali da, kod dve nano-žice u kontaktu, prilikom zagrevanja, atomi srebra iz područja nano-žice u kontaktu malog poluprečnika zakrivljenja difunduju i ugrađuju se u zonu zavarenog spoja, koja povezuje dve nano-žice. Kristalografska orijentacija zavarenog spoja nasleđena je od nano-žice u velikog poluprečnika zakrivljenja u tački dodira. Ugao kvašenja između dve nano-žice manji je od 4.8°, što je indikator potpunog kvašenja. Tomografija je korišćena kako bi se bolje razumela morfologija zavarenog spoja i potvrdio mehanizam zavarivanja, ustanovljen na osnovu rezultata transmisione elektronske mikroskopije poprečnih preseka nano-žica. Mapiranje orientacije i naprezanja elektroskom difrakcijom urađeno je kako bi se utvrdila raspodela naprezanja u nano-žicama i potvrdila kristalografska orijentacija zavarene zone. Distorzija kristalne rešetke direktno je merena mapiranjem pomeranja atomskih kolona na slikama skenirajuće transmisione elektronske mikroskopije poprečnih preseka nano-žica, pripremljenih fokusiranim jonskim snopom (FIB metodom). Ustanovljena je neravnomerna raspodela naprezanja u dvojnikovanim segmentima nano-žica..

Geopolymer materials based on the electric arc furnace slag

The remelting of iron and steel scrap in the electric arc furnaces generates the non-hazardous waste – electric arc furnace slag (EAFS), which can be disposed of to appropriate landfills. Currently, this slag found its application in conventional concrete production to improve its mechanical, chemical and physical properties, as an additive to asphalt base mixture and in cement production. In this study we have investigated the effect of alkaline dosage on the strength and thermal resistance of EAFS based geopolymers. The results have shown that these materials are mainly amorphous with some crystal phases remained from the undisolved EAFS such as larnite, gehlenite, wuestite, monticellite, calcite. Compressive strength of these materials is strongly influenced by the alkaline dosage. An increase of NaOH concentration in the interval of 7-10 M leads to the increase of geopolymer’s strength. The maximal compressive strength of EAFS based geopolymer was obtained using the 10 M NaOH. Further increase of alkaline dosage to the value of 13 M NaOH results in the slight decrease of the geopolymer strength. Additionally, depending on the synthesis parameters, EAFS based geopolymers exhibit improved durability in high temperature environments in comparison with conventional cement based materials. All investigated samples exhibit a shrinkage which is attributed to the change of porosity. The mass loss due to the loss of water was also observed. This research was supported by a Ministry of Science of Montenegro under the contract No 01-460

Alkali Activated Slag as Adsorbents for Cu2+ Removal from Wastewaters

The removal of heavy metals from wastewaters is presently a global imperative primarily due to their well-known toxic nature and detrimental effects on the environment, and more importantly, on human health. Currently, special attention is paid to the use of novel slag based materials – alkali activated slag (AAS) as potential novel adsorbents. Our previous studies have shown that electric arc furnace slag (EAFS) can be successfully used as a precursor for the production of AAS. Generally, alkaline activation involves a chemical reaction between solid aluminosilicate materials and a highly alkaline activator. The alkali activation mechanism of slag involves the dissolution of slag in a highly alkaline, which is followed by the condensation and hardening processes. Dependent on the pH and type of alkaline activator, calcium (alumina) silicate hydrate or C–(A)–S–H gel has been identified as a reaction product of slag alkali activation. The objective of this research was to investigate the removal of Cu2+ from aquatic solution using alkali activated slag (AAS) obtained by alkaline activation of EAFS

A novel type of building material derived from the by-products of steel making industry

Electric arc furnace slag (EAFS) and electric arc furnace dust (EAFD) are the waste materials generated during the iron and steel scrap remelting in electric arc furnace. EAFS is non-hazardous material which has found its application in different field of civil engineering. On the other hand, EAFD is classified as hazardous matreials due to the presence of heavy metals (Zn, Pb, Cu Cr and Cd) and their potential leaching into environment. Stabilization/solidification (S/S) of toxic waste is a widely investigated as simply method for production of stable product. Cement binder was mainly used for this purpose but important shift in the use of different waste materials as a cement replacement was observed. The aim of this study was to investigate the possibility of S/S of heavy metals from EAFD using the alkali activated binders based on EAFS. The alkali activated slag with a different content of EAFS was synthesised and characterized using the SEM/EDS, XRDP, FTIR. The binding of Zn into the reaction product of slag alkali activation was founded. The immobilization efficacy was evaluated using TCLP Method No. 1311 (USEPA) and EN 12457-2 (EULFD) leaching tests

Uticaj strukture čestica na nasipnu masu elektrolitički dobijenog bakarnog praha

The quantitative microstructural analysis and the sieve analysis of copper powder as well as the scanning electron microscopy analysis of the copper powders particles were performed. It was found that the structure of the copper powder particles determines the apparent density of copper powder. The powder particles from the same fractions of different powders occupy approximately the same volume, but the structure of metallic copper is very different. This causes the difference in apparent densities of copper powder obtained under different conditions. The more dendritic is the structure of powder particles the smaller is the apparent density of copper powder.Izvršena je kvalitativna mikrostrukturna i granulometrijska analiza bakarnih prahova kao i analiza morfologije i strukture čestica praha pomoću skenirajuće elektronske mikroskopije (SEM). Ustanovljeno je da struktura čestica praha određuje nasipnu masu bakarnog praha. Čestice iste frakcije različitih prahova zauzimaju otprilike istu zapreminu, ali je struktura metalnog bakra različita. Ovo uzrokuje razlike u nasipnoj masi bakarnog praha dobijenog pod različitim uslovima. Što je struktura čestica više dendritična to je manja nasipna masa bakarnog praha

Poster presentation: "Palladium-copper bimetallic nanocatalyst for electrochemical ethanol oxidation and oxygen reduction in alkaline media"

The necessity of replacement of traditional energy sources with renewable and green alternatives has initiated vast research of direct alcohol fuel cells (DAFC). Ethanol is non-toxic and its crossover through a membrane is lower than methanol due to its larger molecule size. However, the splitting of C–C bond in ethanol is energetically difficult and much effort in electrocatalysts’ improvement is still needed to take the advantage of the high mass energy density of ethanol [1,2]. Electrochemical oxidation of alcohols in requires a noble metal, Pt or Pd, to adsorb the molecule, but also some other oxophilic metal to facilitate further reaction of the adsorbed intermediates Their promoted oxidative desorption can be achieved by introducing oxygen-containing species at the surface, which may also modify the electronic structure of the noble metal centers and thus weaken the strong adsorbate–noble metal bond. Copper is inactive for alcohol oxidation but its addition to palladium enhances the ethanol oxidation reaction (EOR) rate [3,4]. Various forms of Pd-Cu electrocatalysts exhibited improved mass activity for the EOR and oxygen reduction reaction (ORR), but the effect of Cu addition on the specific activity is not so clear. Therefore, in the present work, specific activity for EOR and ORR of synthesized Pd-Cu nanoparticles [5] supported on high area carbon was examined. As reference catalysts, synthesized Pd/C and commercial Pt/C were used.For the electrochemical characterization the nanocatalysts were applied on a glassy carbon (GC) substrate in the form of a thin–film. Pd/C and Pt/C were characterized by cyclic voltammetry, Cuupd, and COads stripping in an acid and an alkaline solution. Electrochemically active surface area (ECSA) of the Pd-Cu nanocatalyst was calculated from the charge of desorption of CO in the alkaline solution. Cyclic voltammetry showed that in the presence of Cu atoms on the Pd surface, the onsets of CO desorption were negatively shifted. This indicates that Cu atoms provide oxygen-containing species at adjacent Pd sites at a lower potential than that achieved on pure metals. Nanocatalyst’s activity for EOR was investigated under potentiodynamic and potentiostatic conditions. Adding of Cu to Pd enhances the intrinsic activity of Pd for the EOR, with the greatest effect achieved for one Cu atom to 2-4 Pd atoms. Bimetallic catalysts surpassed Pd/C by mass activity, as well. The activity of Pt/C for EOR was higher compared with Pd-based catalysts, both as specific and mass activity, but with a significant decline over 30 min potentiostatic stability test. Therefore, the bifunctional and electronic effect contributed to the good performance of the nanoalloy for EOR. For ORR, Pd-Cu/C showed a negative half-wave potential shift compared to Pd/C and Pt/C of 11 and 30 mV, respectively. However, it was found that the specific ORR activities of Pd-Cu/C and Pd/C are the same at low current densities, i.e. up to a potential of 0.90 V, but higher than the specific activity of Pt/C by a factor of 5.The poster presented at: 74th Annual Meeting of the International Society of Electrochemistry, "Bridging Scientific Disciplines to Address the World’s Challenges," 3 - 8 September 2023 Lyon, FranceAbstract: [https://cer.ihtm.bg.ac.rs/handle/123456789/6623

Alkali activated slag based on steelmaking slag: application and properties

Alkali activated slag (AAS) is an environmentally friendly material which were extensively investigated in a pass two decade. Currently, these materials are considering as an effective alternative for cement binder. Process of slag alkali activation involves a chemical reaction between solid calcium aluminosilicate materials and a highly alkaline activator. The alkali activation mechanism of slag consists of the slag dissolution in a highly alkaline which is followed by the condensation and hardening processes yielding formation of calcium (alumina) silicate hydrate C– (A)–S–H gel as a reaction product of slag alkali activation. Properties of these materials primarily depends on the choice of solid row materials. Primarily, granulated blast furnace slag, by product of iron production) is considering as a precursor for AAS synthesis. However, an important shift towards the use of steelmaking slag is also observed. Although electric arc furnace slag has already found its application mainly in civil engineering, this investigation has aimed to investigate properties of AAS prepared using the electric arc furnace slag (EAFS) with an emphasize with different possibilities of its application. Characterization of AAS involved XRDP, SEM/EDS and pore size analysis with the aim to build up a detailed illustration of AAS from the stand point of different application

New environmentally acceptable materials based on fly ash, steelmaking slag and Zn-reach electric arc furnace dust

The newer methods of electric arc furnace dust (EAFD) valorisation include its stabilization into materials which potentially can be used in construction. This is the most promising method because of the low costs and waste reduction. The purpose of these study was to investigate the properties of alkali activated cement (AAC) based on fly ash (FA) or steelmaking electric arc furnace slag (EAFS) as an agent fora stabilization/solidification of EAFD. The control type of AAC samples were prepared by mixing of solid precursor (FA or EAFS) with a mixture of 10 M NaOH and Na2SiO3 solutions followed by curing at in the oven for 48 h at 65 C. The samples of AAC doped with EAFD were prepared at the same conditions but the EAFD was added to the starting mixtures with FA in quantities of 10, 20 and 30% of total solid phase and 1, 2, 5 and 7 % of total EAFS solid phase. The results have shown that both, FA and EAFS can be successfully used as an agent for EAFD stabilization. AAC samples based of FA and EAFS exhibited strength which is suitable for both, landfill and construction applications. Stabilization of EAFD into the AAC matrix occurred by chemical and physical immobilization. Chemical immobilization of Zn into the reaction product of FA and EAFS alkali activation was confirmed by SEM/EDS investigations. The leaching of Zn from both, AAC matrix based on FA and EAFS is inferior in comparison to pristine EAFD and met the criteria for granular waste disposal at landfills for non-hazardous waste according the EN 12457-2 test

Study of microstructure and magnetic properties of optimally annealed R/Q Nd4.5Fe77B18.5 alloy

The rapid-quenched (R/Q) and subsequently optimally annealed Nd-Fe-B alloy with 12 wt% Nd was characterized using the X-Ray diffractometry (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HREM) and superconducting quantum interference device (SQUID) magnetometer. It was found that microstructure of the investigated alloy mainly consist of Fe3B, Nd2Fe14B phases and minor content of α-Fe phase, with mean crystal grain sizes being below 30 nm. The ferromagnetic exchange coupling between the grains of identified hard and soft magnetic phases has direct influence on the magnetic properties as it is illustrated by SQUID hysteresis loop. Correlation of the measured magnetic properties with results of microstructure analysis indicates that the investigated rapid-quenched Nd-Fe-B alloy has the nanocomposite structure in optimal magnetic state