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

Randomly oriented twin domains in electrodeposited silver dendrites

Silver dendrites were prepared by electrochemical deposition. The structures of the Ag dendrites, the type of twins and their distribution were investigated by scanning electron microscopy (SEM), Z-contrast high angle annular dark field transmission electron microscopy (HAADF), and crystallographically sensitive orientation imaging microscopy (OIM). The results revealed that the silver dendrites were characterized by the presence of randomly distributed 180 degrees rotational twin domains. The broad surface of dendrites was of the {111} type. The directions of growth of the main dendrite stem and all branches were of the lt 112> type

Zeolit NaX kao templat za dobijanje monoatomski dispergovane platine impregnacijom sa rastvorom Pt(II)-acetilacetonata u acetonu

The incorporation of platinum into the cavities of NaX zeolite was realized by impregnation and thermal decomposition of the organometallic compound Pt(II)-acetylacetonate dissolved in acetone. A high dispersion of platinum to predominantly mono-atomic particles was achieved thanks to the tight fit of the Pt(II)-acetylacetonate molecules in the aperture of the zeolite supercage. Using the high angle annular dark field imaging technique of HRTEM, individual Pt particles situated within the zeolite crystals were, for the first time, clearly visible. This offers new possibilities of studying the distribution of incorporated metal particles along the crystal depth.Platina je ugrađena u kaveze zeolita NaX impregnacijom i termalnim razlaganjem organometalnog jedinjenja Pt(II)-acetilacetonata, rastvrenog u acetonu. Visoka disperznost platine pretežno u vidu jednoatomnih čestica, postignuta je zahvaljujući bliskosti dimenzija molekule Pt(II)-acetilacetonata i prečnika ulaznog otvora supekaveza zeolita. Tehnikom širokougaone difrakcije i tamnog polja ultravisokorezolutivne elektronske mikroskopije, prvi put su učinjene vidljivim individualne čestice platine smeštene unutar kristala zeolita, što otvara nove mogućnosti u proučavanju raspodele ugrađenih metalnih čestica po dubini kristala

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

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

Kinetics of the Hydrogen Oxidation on Pt Modified Moox Nano-Sized Catalyst in the Presence of Carbon Monoxide

Poster presented at the 11th Conference of the Materials Research Society of Serbia - YUCOMAT 2009, Herceg Novi, Montenegro, August 31 – September 4, 2009

Kinetics of the hydrogen oxidation on pt modified MoOx nano-sized catalyst in the presence of carbon monoxide

Due to the importance of the HOR in fuel-cells technology, various Pt-based catalysts have been examined from the viewpoint of immunity of the electrocatalysis of the HOR from CO-poisoning of the anode catalysts. An appreciable improvement of the CO tolerance has been found at Pt with adatoms such as Ru, Sn [1,2], Pt-M (M=Ru, Rh, Os, W Sn) [3-5] based alloys, and Pt with oxides (RuOxHy) [6]. In the present work, the electrocatalytic of home made highly dispersed nano-sized MoOx-Pt/C catalysts prepared by the polyole method combined by MoOx post-deposition was investigated in the presence of CO, in 0.5 moldm-3 HClO4 solution. The partial pressure of CO in CO/H2 gas mixture was 100 ppm. Carbon monoxide was adsorbed on the RDE for various time interval with keeping the potential at 0.05 V (RHE). The coverage of CO was determined by applying the first potential sweep (from 0.04 to 1.20 V), in N2 saturated solution at potential scan rate of 0.1 Vs-1 and compared it with the sweep on the clean electrode, by measuring the decrease in the hydrogen desorption charge, ΔQH. MoOx(20%)Pt/C catalyst exhibits an excellent CO tolerance, as it was found that the reduction in kinetic current, Ik, is negligible even at ΘCO = 0.46. It was found for this catalyst too, that the CO adsorption rate was much slower than that of Pt and the Pt sites for HOR were not so rigidly blocked by adsorbed CO partially due to its enhanced mobility, resulting from their modified electronic structure of surface Pt sites. Voltammetric studies suggest that an excellent CO tolerance of this catalyst could be also result of the oxidation of adsorbed CO to CO2 by oxophilic MoOx species at low overpotentials by a redox-mediated mechanism.Poster: [https://hdl.handle.net/21.15107/rcub_dais_266

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

Uticaj reversne struje na nasipnu masu pri elektrolitičkom taloženju bakarnog praha

The possibility of depositing copper powders with different apparent density by changing the shape of reversing current wave is shown. The morphology and crystallinity of powder particles can be varied considerably by changing shape of the reversing current wave and, hence, the apparent density of powders. The relation of apparent density with particle morphology and structure was illustrated.U radu je pokazana mogućnost dobijanja bakarnih prahova različitih nasipnih masa promenom oblika talasa reversne struje. Uspostavljena je zadovoljavajuća veza između morfologije i strukture čestica praha bakra i nasipne mase praha

Platinum Nanocatalysts at Titanium Oxide Based Supports for Low Temperature Fuel Cell Applications

A comparative study on catalytic activity of platinum nanoparticles on different titanium oxide supports for proton exchange membrane fuel cells reactions was performed. Non stoichiometric titanium oxides – Ebonex, niobium doped titanium oxide and ruthenium doped titanium oxide were applied as the supporting materials. Platinum nanocatalysts (20% Pt) on different support were synthesized by impregnation or borohydride reduction method. Synthesized supports and catalyst were characterized by BET (Brunauer, Emmett, Teller), X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Homogenous Pt nanoparticles distribution over the niobium and ruthenium doped TiO2 support, without pronounced particle agglomeration was confirmed by HRTEM technique. The average Pt particle size was 3 nm and 5.4 nm for Pt at niobium doped TiO2 and ruthenium doped TiO2, respectively. However, it was not possible to determine accurately average Pt particle size at Ebonex support, due to the non-uniform distribution of the Pt nanoparticles. Electrochemically active Pt surface area of the catalysts was determined by integration of the cyclic voltammetry curve in the potential region of underpotential deposition of hydrogen, after double layer charge correction, taking into account the reference value of 210 μC cm-2 for full monolayer coverage. Kinetics of the oxygen reduction reaction at Pt nanocatalysts on different titanium based supports was studied by cyclic voltammetry and linear sweep voltammetry at rotating gold disc electrode. Two different Tafel slopes at Pt catalysts on niobium and ruthenium doped supports were observed: one close to 60 mV dec-1 in low current density region, and other ~120 mV dec-1 in higher current densities region. Only at Ebonex based support one single Tafel slope (~ 106 mV dec-1) was observed. The specific activities for oxygen reduction, expressed in terms of kinetic current densities per electrochemically Pt active surface area, as well as per mass of Pt loaded, at the constant potential of practical interest (0.85 V and 0.90 V vs RHE, where the mass transport contribution current can be neglected), were compared to carbon supported one, with the same Pt loading. Stability tests, by repetitive cycling from 0.03V to high anodic potentials (up to 1.4 V vs RHE) were performed. The advantages of carbon free supports application in terms of stability, durability and life time of the catalysts were discussed