Repository of Faculty of Chemical Engineering and Technology University of Zagreb
Not a member yet
2768 research outputs found
Sort by
Synthesis and structural characterization of novel benzothiazole derivatives
No full textU ovom radu opisana je sinteza novih derivata benzotiazola primjenom mikrovalovima potpomognutih, mehanokemijskih i klik reakcija. Za sintezu derivata benzotiazola pripravljen je 4-O-propargilbenzaldehid (1) SN2 reakcijom 4-hidroksibenzaldehida i propargil-bromida uz K2CO3 kao bazu. 2-(4-(prop-2-in-1-iloksi)fenil)benzotiazol (2) priređen je ciklizacijom
4-O-propargilbenzaldehida (1) i 2-aminotiofenola u dimetilformamidu uz Na2S2O5 kao oksidacijsko sredstvo. Huisgenovom 1,3-dipolarnom cikloadicijom
2-(4-(prop-2-in-1-iloksi)fenil)benzotiazola (2) i odgovarajućih azida uz bakrov(II) acetat kao katalizator sintetizirani su 1,2,3-triazolni derivati benzotiazola (3-9). Mehanokemijske reakcije ciljanih derivata benzotiazola (3-9) provedene su u kugličnom mlinu. 1H i 13C-NMR spektroskopijom potvrđene su strukture svih novopripravljenih derivata benzotiazola.This paper describes the synthesis of new benzothiazole derivatives using microwaveassisted, mechanochemical and click reactions. For the synthesis of benzothiazole derivatives, 4-O-propargylated benzaldehyde (1) was prepared by SN2 reaction of 4-hydroxybenzaldehyde and propargyl bromide using K2CO3 as a base.
2-(4-(prop-2-yn-1-yloxy)phenyl) benzothiazole (2) was prepared by cyclization reaction of 4-O-propargyl benzaldehyde (1) and 2-aminothiophenol in dimethylformamide with Na2S2O5 as oxidizing agent. 1,2,3-triazolyl derivatives of benzothiazole (3-9) were prepared by Huisgen 1,3-dipolar cycloaddition of 2-4-(prop-2-yn-1-yloxy)phenyl benzothiazole (2) and the corresponding azides using copper(II) acetate as catalyst. Mechanochemical reactions of the desired compounds (3-9) were performed in a ball mill. The structures of all newly prepared benzothiazole derivatives were confirmed by 1H and 13C-NMR spectroscopy
Synthesis and spectroscopic characterization of novel hydroxyl substituted benzoxazole derivatives as potential sensors for metal cations in solutions
No full textCilj ovog rada bila je sinteza akrilonitrilnih i 2-fenil supstituiranih derivata benzoksazola. Spoj 6 priređen je iz sintetiziranog spoja 4 reakcijom Knoevenagelove kondenzacije. Navedeni spojevi 4 i 6 uspješno su izolirani. Također su sintetizirani spojevi 10, 16 i 17, međutim, no oni su dobiveni kao smjese željenih produkata i preostalih neizreagiranih reaktanata. Preostali spojevi koje je bilo u cilju sintetizirani u sklopu ovog rada nisu uspješno sintetizirani. Provedena je mikrovalovima potpomognuta redukcija spoja 6 uz NH4HCO2 kao redukcijsko sredstvo. Strukture priređenih čistih spojeva potvrđene su 1H i 13C NMR spektroskopijom, te MS spektrometrijom. UV/Vis spektroskopska karakterizacija spoja 6 provedena je u 5 otapala različite polarnosti koja uključuju MQ vodu, metanol, etanol, etil-acetat i acetonitril. Spektroskopskim titracijama je ispitana mogućnost spoja 6 kao optičkog senzora za detekciju kationa (Hg2+, Fe3+, Co2+ te Zn2+) u otopinama pri različitim koncentracijama kationa.The main goal of this work was a synthesis of acrylonitrile and 2-phenyl substituted benzoxazole derivatives. Compound 6 was prepared from synthesized compound 4 by the reaction of Knoevenagel condensation. The specified compounds 4 and 6 have been successfully isolated. Compounds 10, 16, and 17 were also synthesized; however, they were obtained as mixtures of desired products and remaining unreacted reactants. The remaining compounds synthesized as part of this paper have not been synthesized successfully.
A microwave assisted reduction of compound 6 was with NH4HCO2 as a reducing agent.
The structures of the prepared pure compounds were confirmed by 1H and 13C NMR spectroscopy and MS spectrometry. UV/VIS spectroscopic characterization of compound 6 was performed in 5 solvents of different polarity including MQ water, methanol, ethanol, ethyl acetate and acetonitrile. The possibility of the compound 6 for the detection of cations (Hg2+, Fe3+, Co2+ and Zn2+) in solutions at different cation concentrations has been investigated by spectroscopic titrations
Effect of multiple mechanical recycling process on release of additives from polypropylene microplastics
No full textPolimeri su temeljni materijali modernog društva, s polipropilenom (PP) kao jednim od najčešće korištenih termoplastičnih polimera zbog svoje fleksibilnosti, izdržljivosti i prilagodljivosti različitim primjenama. Dodavanje aditiva ključno je za poboljšanje mehaničkih svojstava polimernih materijala. Međutim, s porastom svjetske proizvodnje i upotrebe polimera raste i količina plastičnog otpada, što predstavlja veliki ekološki izazov. Mehaničko recikliranje često se promovira kao održivo rješenje za smanjenje plastičnog otpada. Iako termoplasti teoretski mogu izdržati više ciklusa recikliranja bez značajnog gubitka svojstava, malo je istraživanja posvećeno proučavanju utjecaja ovih procesa na otpuštanje aditiva, koji u obliku mikroplastike mogu dospjeti u okoliš. Cilj ovog rada je bio analizirati utjecaj višestrukog mehaničkog recikliranja na otpuštanje aditiva iz polipropilenske mikroplastike.
U tu svrhu pripremljena su dva uzorka. Prvi uzorak je se sastojao od polipropilena (PP) s dodanim antioksidansima i plastifikatorom, dok su drugom uzorku polipropilena (PP) dodani antioksidansi. Nakon pripreme, provedena je simulacija pet ciklusa mehaničkog recikliranja u laboratorijskom ekstruderu. Nakon svakog ciklusa recikliranja, uzorci su usitnjeni na veličinu mikroplastike. Karakterizacija uzoraka provedena je nakon 1., 3. i 5. ciklusa, kako bi se odredile promjene svojstava polipropilena uzrokovane migracijom aditiva. Metode karakterizacije uključivale su infracrvenu spektroskopiju s Fourierovom transformacijom (FTIR), termogravimetrijsku analizu (TGA) i diferencijalnu pretražnu kalorimetriju (DSC).
Ove metode omogućile su praćenje promjena u kemijskoj strukturi, toplinskim svojstvima i stupnju kristalnosti uzoraka polipropilena. Također praćene su i migracije aditiva iz mikroplastike u vodu, te je određena toksičnost vodenih uzoraka prema bakterijskoj kulturi Vibrio fischeri, omjer biorazgradivosti i sadržaj ukupnog organskog ugljika.Polymers are fundamental materials in modern society, with polypropylene (PP) being one of the most widely used thermoplastic polymers due to its flexibility, durability and adaptability to various applications. The addition of additives is essential for improving the mechanical properties of polymer materials. However, with the increasing global production and use of polymers, the amount of plastic waste is also increasing, which represents a major environmental challenge. Mechanical recycling is often promoted as a sustainable solution to reducing plastic waste. Although thermoplastics can theoretically withstand multiple recycling cycles without significant loss of properties, little research has been devoted to studying the impact of these processes on the release of additives, which can end up in the environment in the form as microplastics. The aim of this work was to analyze the effects of multiple mechanical recycling processes on release of additives from polypropylene microplastic.
Two samples were prepared for this purpose. The first sample consisted of polypropylene with added antioxidants and plasticizer, while the second sample contained polypropylene with only antioxidant. After preparation, a simulation of five cycles of mechanical recycling were simulated in a laboratory extruder. After each recycling cycle, the samples were ground to microplastic size. Characterization of the samples was conducted after the 1st. 3rd and 5th cycles to determine changes in the properties of polypropylene caused by the migration of additives. Characterization methods included Fourier-Transform Infrared Spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC). These methods allowed monitoring changes in the chemical structure, thermal properties, and crystallinity of the polypropylene samples. The migration od additives from microplastics into water was also monitored, and the toxicity of water samples according to Vibrio fischeri bacterial culture, biodegradability ratio and total organic carbon content were determined
Razvoj mjernog postupka za detekciju mikro i nanoplastičnih čestica u uzorcima tkiva
No full textWith the mass accumulation of plastic pollution in the environment, problems are present even on the micro and nano scale. Micro and nanoplastic (MNP) particles with a diameter of less than one millimeter, mostly generated by the degradation and wearing down of larger plastic parts, are accumulating in the ecosystem and reaching the human body in different ways. The potential of the particles to adsorb harmful substances poses a big threat to ecosystems and human health. Analytical chemistry offers essential tools for the detection, quantification, and characterization of small particles, enabling researchers to study their distribution, composition, and impact. The most used methods are different types of microscopy and spectroscopy. This work provides the process of preparing and analyzing different tissue samples for MNP research. A review of the most common tissue digestion methods was made, along with two analytical methods that were used to detect, quantify, and characterize MNPs: optical microscopy and spectroscopy. MNP particles were found and identified in the tissue samples, along with present contaminants.Sve većim rastom plastičnog onečišćenja u okolišu javljaju se problemi čak i u mikro i nano razmjerima. Plastične čestice promjera manjeg od milimetra koje uglavnom nastaju razgradnjom i trošenjem većih dijelova plastike, nakupljaju se u ekosustavu te različitim putevima dolaze i do organizma čovjeka. S potencijalom adsorpcije štetnih tvari, mikro- i nano plastika predstavlja veliku prijetnju ekosustavima i ljudskom zdravlju. Analitička kemija nudi bitne alate za detekciju, kvantifikaciju i karakterizaciju malih čestica, omogućujući istraživačima proučavanje njihovog sastava, distribucije i utjecaja. Najčešće metode koje se koriste su razni oblici mikroskopije i spektroskopije. Ovaj rad sadrži proces pripreme i analize različitih uzoraka tkiva za istraživanje mikro- i nano plastike. Napravljen je pregled najčešćih metoda digestije tkiva te dvije analitičke metode koje su korištene za detekciju, kvantifikaciju i karakterizaciju mikro- i nano plastike: optička mikroskopija i spektroskopija. U uzorcima tkiva pronađene su i identificirane mikro- i nanoplastične čestice, uz prisutna onečišćenja u obliku fragmenata i vlakana
Graphene-encapsulated V2O5 for application in aqueous Zn-ion battery
No full textU ovom radu provedena je ugradnja V2O5 u reducirani grafenov oksid (rGO) te karakterizacija dobivenog materijala u troelektrodnom sustavu. Osim toga provedena je sinteza i karakterizacija rGO papira u koji je ugrađen V2O5. Cilj rada bio je dobiti stabilan, savitljiv i samostojeći materijal koji će biti pogodan kao katoda u Zn-ionskim vodenim baterijama. Ispitivanje različitih rGO/V2O5 elektroda je pokazalo da se u 2 mol dm^-3 otopini ZnSO4 dobivaju veći kapaciteti u odnosu na 3 mol dm^-3 otopina ZnSO4. Isto tako pokazano je da su veći kapaciteti dobiveni kod elektroda s 50 % V2O5 nego kod elektroda s 70% V2O5 te da je materijal bolje iskorišten kad je manja masa aktivnog materijala nanesena na elektrodu. U ovom istraživanju pripravljen je GO papir s 70 % V2O5 koji je reduciran elektrokemijskim putem pri -1.4 V, pri čemu je grafenov oksid (GO) preveden u rGO.
U priređenoj bateriji Zn je imao ulogu anode dok je rGO/V2O5 korišten kao katoda. Svojstva Zn//rGO/V2O5 baterije su ispitana metodama kronoamperometrije (CA) i cikličke voltametrije (CV). U cikličkim voltamogramima zabilježeni su anodni i katodni strujni vrhovi koji odgovaraju redoks reakciji V2O5. Vrijednosti kapaciteta baterije, dobiveni metodom CV kreću se u rasponu od 41.06 mAh g^-1 do 311.85 mAh g^-1 pri brzinama promjene potencijala od 50 do 1 mV s^-1 Proveden je i galvanostatski proces punjenja i pražnjenja baterije. Vrijednosti kapaciteta baterije, zabilježeni tijekom galvanostatskog ispitivanja, kreću se u rasponu od 77.78 mAh g^-1 pri najvećoj struji (4.3 mA, 5.0 A g^-1 ), do 306.07 mAh g^-1 pri najmanjoj struji (0.7 mA, 0.8 A g^-1).In this work, the incorporation of V2O5 into reduced graphene oxide (rGO) and the characterization of the obtained material in a three-electrode system were carried out.
In addition, the synthesis and characterization of rGO paper in which V2O5 was incorporated was carried out. The goal of the work was to obtain a stable, flexible and free-standing material that will be suitable as a cathode material in Zn-ion water based batteries. Examination of different rGO/ V2O5 electrodes showed that higher capacities are obtained in 2 mol dm^-3 ZnSO4 solution compared to 3 mol dm^-3 ZnSO4 solution. It was also shown that highercapacities were obtained with electrodes with 50% V2O5 than with electrodes with 70% V2O5 and that the material was better utilised when a smaller mass of active material was applied to the electrode. In this research, GO paper with 70% V2O5 was prepared and it was reduced electrochemically at -1.4 V, in order to convert graphene oxide (GO to rGO. In the prepared battery, Zn played the role of the anode while rGO/ V2O5 was used as the cathode. The properties of the Zn//rGO/ V2O5 battery were tested by chronoamperometry (CA) and cyclic voltammetry (CV) methods. In the cyclic voltammograms, anodic and cathodic current peaks corresponding to the V2O5 redox reaction were recorded. The battery capacity values, obtained by the CV method, range from 41.06 mAh g^-1 to 311.85 mAh g^-1 at scan rates from 50 to 1 mV s^-1. The galvanostatic process of charging and discharging the battery was also carried out. The battery capacity values, recorded during the galvanostatic test, range from 77.78 mAh g^-1 at the highest current (4.3 mA, 5.0 A g^-1 ),
to 306.07 mAh g^-1 at the lowest current (0 .7 mA, 0.8 A g^-1 )
Synthesis of methacrylate tert-polymer additives with functional 2-(diisopropylamino)ethyl methacrylate for improvement of low-temperature diesel properties
No full textDizelsko gorivo je naftna prerađevina kojemu se smanjenjem određenih komponenata čuva okoliš, ali gubi puni sjaj tog istog goriva. Svrha ovog rada je sinteza polimernih aditiva kojima je funkcija poboljšanje niskotemperaturnih svojstava dizelskog goriva. Sintetizirano je ukupno šest polimernih aditiva radikalnom polimerizacijom. Reakcija se odvijala izotermno pri 95 °C uz 70% inicijator Peroxan PO 70 tijekom 4 sata. Polimeri imaju različite udjele dugolančanih komonomera, oktadecil-metakrilat i dodecil-metakrilat: 1:1, 1:3, 3:1 i različite udjele metilmetakrilata (35%, 45%). Pripremljenje su i formulacije polimernih aditiva koncentracije 2000 ppm s neaditiviranim dizelom kako bi se ispitalo djelovanje polimernih aditiva pri niskotemperaturnim svojstvima. Metodom infracrvene spektrosktroskopije s Fourierovom transformacijom i metodom 1H nuklearnom magnetskom rezonancijom provjerena je čistoća sintetiziranih polimera u vidu zaostalih monomera te potvrđena stuktura sintetiziranih polimera. Prema FTIR ATR i 1H NMR analizi polimerni aditivi su zadovoljavajuće čistoće, točnije početni sastav smjese monomera približno odgovara sastavu sintetiziranog polimernog aditiva s 0,81% zaostalih monomera. Diferencijalnom pretražnom kalorimetrijom određene su temperature kristalizacije i entalpije kristalizacije čistih polimernih aditiva i formulacija u dizelu. Spektri analize prikazuju kako porastom udjela oktadecil-metakrilat komonomera temperatura kristalizacije se povećava, dok kod formulacija aditiva s dizelom temperatura kristalizacije se snižava porastom udjela oktadecilmetakrilat komonomera. Morfologija kristalizacije n-parafina u dizelu praćena je optičkim mikroskopom s polarizacijom opremljenim hladnim postoljem. Uočena je promjena kristala formulacija polimernog aditiva MDO35-D5-31 koncentracije 2000 ppm u dizelu, kristali su manji i sferičnog oblika. Formulacija dizelskog goriva s dodatkom 2000 ppm aditiva provedena je po ASTM D5950 metodi koje je pokazalo poboljšanje točke tečenja dizelskog goriva dodatkom sintetiziranih polimernih aditiva.Diesel fuel is a petroleum product that, by reducing certain amounts of components, helps preserve the environment but loses the full potential of the fuel. The purpose of this study is to synthesize polymeric additives that improve the low-temperature properties of diesel fuel. A total of six polymeric additives were synthesized through radical polymerization. The reaction was carried out isothermally at 95 °C using 70% Peroxan PO 70 initiator for 4 hours. The polymers have different ratios of long-chain comonomers, octadecyl methacrylate, and dodecyl methacrylate: 1:1, 1:3, 3:1, and different ratios of methyl methacrylate (35%, 45%). Formulations of polymeric additives were prepared at a concentration of 2000 ppm with untreated diesel to investigate the effect of polymeric additives on the low-temperature properties. The purity of synthesized polymers in terms of residual monomers and the confirmed structure of the synthesized polymers were verified using Fourier-transform infrared spectroscopy and proton nuclear magnetic resonance method. According to the FTIR ATR and 1H NMR analyses, the polymer additives exhibit satisfactory purity. More specifically, the initial composition of the monomer mixture approximately corresponds to the composition of the synthesized polymer additive with 0.81% residual monomers. Differential scanning calorimetry was used to determine the crystallization temperatures and enthalpies of crystallization for pure polymeric additives and formulations with diesel. The analysis spectra showed that as the ratio of octadecyl methacrylate comonomer increased, the crystallization temperature also increased, while in the additive formulations with diesel, the crystallization temperature decreased with the increase in the ratio of octadecyl methacrylate comonomer. The morphology of n-paraffin crystallization in diesel was observed using a polarizing optical microscope equipped with a cold stage. A change in the crystals of the 2000 ppm concentration formulation of the polymeric additive MDO35-D5-31 in diesel was observed, with smaller and spherical-shaped crystals. A formulation of diesel fuel with the addition of 2000 ppm additive was performed using the ASTM D5950 method, which showed an improvement in the pour point of diesel fuel with the addition of the synthesized polymeric additives
Removal of micropollutants from water using ferrate(VI)
No full textVoda kao izvor života je neprocjenjivo blago koje u današnje vrijeme dobiva na velikom značaju zbog rasta gospodarstva koje ga crpi sve više, populacije koja također eksponencijalno raste te klimatskih promjena koje djeluju na cjelokupni život na planeti. Mikroonečišćivala samo su od jednih u nizu onečišćivala koji predstavljaju prijetnju vodenom ekosustavu. U ovom radu ispitana je mogućnost uklanjanja postojanih organskih onečišćivala kao što su pesticidi alaklor, atrazin i diuron iz vodene otopine primjenom ferata(VI). U sklopu rada ispitan je utjecaj procesnih parametara, pH vrijednosti (5, 7, 9) te koncentracija ferata (2,50 mM, 5,00 mM, 7,50 mM), na učinkovitost uklanjanja predmetnih onečišćivala. Promjena koncentracije pesticida praćena je tekućinskom kromatografijom visoke djelotvornosti. U svim slučajevima najveći doseg uklanjanja postignut je s najvišom ispitanom koncentracija ferata. Kiseli uvjeti pogodovali su razgradnji alaklora i atrazina, dok su neutralni uvjeti pogodovali razgradnji diurona.Water as a source of life is a priceless treasure that is becoming increasingly important nowadays due to the growth of the economy that draws more and more of it, the population that is also growing exponentially, and climate changes that affect all life on the planet. Micropollutants are only one of a series of pollutants that pose a threat to the aquatic ecosystem. In this work, the possibility of removing persistent organic pollutants such as the pesticides alachlor, atrazine and diuron from an aqueous solution using ferrate(VI) was examined. As part of the work, the influence of process parameters, pH values (5, 7, 9) and ferrate concentration (2.50 mM, 5.00 mM, 7.50 mM) on the effectiveness of removing the pollutants in question was examined. The change in pesticide concentration was monitored by high-performance liquid chromatography. In all cases, the highest removal reach was achieved with the highest tested ferrate concentration. Acidic conditions favored the degradation of alachlor and atrazine, while neutral conditions favored the degradation of diuron
Thermal properties and microstructure of implant material for hip endoprosthesis
No full textTitanijeva legura Ti-6Al-4V već se dugi niz godina koristi u komercijalne svrhe kao biomedicinski materijal, odnosno materijal za izradu implantata, zahvaljujući svojim pogodnim karakteristikama za ljudsko tijelo kao što su dobra mehanička svojstva, biokompatibilnost, otpornost na koroziju i sposobnost dobre oseointegracije. S druge strane, površina legure može poslužiti kao podloga za stvaranje bakterijskog biofilma, što može uzrokovati infekcije te ozbiljne komplikacije nakon ugradnje implantata. Eksperimentalni dio rada obuhvaća lasersku modifikaciju površine titanijeve legure Ti-6Al-4V nanošenjem sloja bakra pri različitim uvjetima rada lasera s ciljem dobivanja intermetalne Ti2Cu faze, poznate po svojim antibakterijskim svojstvima. Tri dobivena uzorka karakterizirana su mikroskopskim tehnikama optičkog i pretražnog elektronskog mikroskopa u svrhu promatranja prisutnosti intermetalne faze, udjela elemenata i mikrostrukture dobivenog sloja. Osim toga, provedeno je ispitivanje mikrotvrdoće metodom po Vickersu za sva tri uzorka.Titanium alloy Ti-6Al-4V has been used commercially for many years as a biomedical material, i.e. a material for making implants, thanks to its favorable characteristics for the human body, such as appropriate mechanical properties, biocompatibility, corrosion resistance and the ability for good osseointegration. On the other hand, the surface of the alloy can be a substrate for the formation of bacterial biofilm, which can cause infections and serious complications after implant placement. The experimental part of the work includes laser modification of the surface of titanium alloy Ti-6Al-4V by depositing a layer of copper under different laser operating conditions with the aim of obtaining an intermetallic Ti2Cu phase, known for its antibacterial properties. All three obtained samples were characterized by microscopic techniques of optical and scanning electron microscopy in order to observe the presence of the intermetallic phase, the ratio of elements and the microstructure of the obtained layer. In addition, microhardness testing was performed using the Vickers method for all three samples
Impedance determination of the corrosion resistance of steel protected by hard anodic coatings
No full textKorozija metala predstavlja konstantan izazov u industriji, uzrokujući značajne ekonomske, sigurnosne i ekološke posljedice. S druge strane, čelik se ističe kao jedan od najvažnijih industrijskih materijala, zahvaljujući izvrsnim mehaničkim svojstvima, dostupnosti i mogućnostima termomehaničke obrade. Usprkos mnogim poželjnim svojstvima, čelik u agresivnim korozivnim uvjetima pokazuje ograničenu otpornost ukoliko nije odgovarajuće zaštićen. Ovaj rad istražuje korozijsku otpornost čelika zaštićenog tvrdim anodnim prevlakama korištenjem elektrokemijske impedancijske spektroskopije (EIS), elektronske pretražne mikroskopije (SEM) i mjerenja hrapavosti površine. Ispitivane su dvije različite prevlake (1 i 2) titanijeva nitrida (TiN) s različitim elementarnim omjerima titanija i dušika na dvije različite podloge (A i B), u ukupno četiri kombinacije označene sa TiN-1A, TiN-1B, TiN-2A i TiN-2B. Također, ispitivane su prevlake bestrujnog nikla (EN-A) i tvrdog kroma (TK-A). Elektrokemijskom impedancijskom spektroskopijom (EIS) primjenom ćelije s elektrolitskom paste, snimljeni su impedancijski spektri koji su interpretirani analizom oblik te modula impedancije i faznog kuta pri frekvenciji od 0,01 Hz. SEM mikroskopija omogućila je analizu mikrostrukture i elementarnog sastava, dok je ispitivanje hrapavosti površine pružilo uvid u topografske karakteristike prevlaka.Corrosion of metals remains a persistent challenge in industry, leading to considerable economic, safety, and environmental consequences. On the other hand, steel stands out as one of the most important industrial materials due to its excellent mechanical properties, availability, and suitability for thermomechanical processing. Despite these favorable characteristics, steel exhibits limited resistance in aggressive corrosive environments unless adequately protected. This study investigates the corrosion resistance of steel protected with hard anodic coatings using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and surface roughness measurements. Two different titanium nitride (TiN) coatings (1 and 2), with varying elemental ratios of titanium and nitrogen, were examined on two different substrates (A and B), resulting in four combinations labelled TiN-1A, TiN-1B, TiN-2A, and TiN-2B. Additionally, electroless nickel (EN-A) and hard chrome (HC-A) coatings were also investigated. Electrochemical impedance spectroscopy (EIS) using a paste electrolyte cell was employed to record impedance spectra, which were interpreted based on the shape and magnitude of the impedance modulus and phase angle at a frequency of 0.01 Hz. Scanning electron microscopy (SEM) enabled analysis of the microstructure and elemental composition, while surface roughness measurements provided insight into the topographical characteristics of the coatings
Coprecipitation synthesis of tungsten-based high-entropy oxide
No full textCilj ovog rada bila je sinteza visoko-entropijskog oksida (HEO) s volframom primjenom koprecipitacijskog postupka. U prvoj sintezi su kao polazni reaktanti korišteni kloridi metala: volframa (WCl6), tantala (TaCl5), vanadija (VCl3), kroma (CrCl3) i hafnija (HfCl4). U iduće tri sinteze kromov klorid zamijenjen je željezovim kloridom (FeCl3), dok je u zadnjoj sintezi kao izvor titanijevih kationa korišten titanijev butoksid (Ti(C4H9O)4) umjesto željezovog klorida. Svi sintetizirani uzorci analizirani su infracrvenom spektroskopijom s Fourierovom transformacijom (FTIR) i energijski razlučujućom rendgenskom spektroskopijom (SEM/EDS). FTIR analiza potvrdila je transformaciju miješanih metalnih hidroksida u visoko-entropijske okside tijekom termičke obrade. Jedan uzorak dodatno je analiziran termogravimetrijskom analizom (TGA) kako bi se odredila temperatura na kojoj dolazi do najvećeg gubitka mase tijekom žarenja, odnosno optimalni uvjeti toplinske obrade. Rezultati SEM/EDS analize ukazuju na homogenu raspodjelu metalnih kationa na molekularnoj razini u prekursorskim materijalima, a u termički obrađenim materijalima žarenjem je došlo do separacije faza, te je u samo dva uzorka postignuta zadovoljavajuća homogenost. Uočen je dobar stupanj podudaranja stvarnih množinskih udjela elemenata s teorijskim vrijednostima, što potvrđuje učinkovitost koprecipitacije u sintezi ovakvih kompleksnih oksidnih sustava. Dva uzorka s najhomogenijom distribucijom elemenata dodatno su karakterizirana rendgenskom difrakcijskom analizom (XRD) radi određivanja faznog sastava. Dobiveni difraktogrami ukazuju na prisutnost višefazne strukture, zbog čega nije moguće sa sigurnošću utvrditi je li došlo do ugradnje svih pet kationa u jedinstvenu kristanu rešetku. Međutim, indikacije djelomične ugradnje svih pet kamiona prisutne su u jednoj od faza. U drugom uzorku uočeno je razdvajanje faza unatoč prethodno potvrđenoj homogenosti prekursora.The aim of this study was the synthesis of high-entropy oxide (HEO) with tungsten using the coprecipitation synthesis. In the first synthesis, metal chlorides of tungsten (WCl6), tantalum (TaCl5), vanadium (VCl3), chromium (CrCl3) and hafnium (HfCl4) were used as starting precursors. In the next tree syntheses, chromium chloride was replaced with iron chloride (FeCl3), while in the last synthesis, titanium butoxide (Ti(C4H9O)4) as used as a source of titanium cations instead of iron chloride. All synthesized samples were characterized by Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS). FTIR analysis confirmed the transformation of mixed metal hydroxides into high-entropy oxides during thermal treatment. One of the samples was additionally analyzed using thermogravimetric analysis (TGA) to determine the temperature at which the greatest mass loss occurs during calcination, thereby identifying the optimal thermal treatment conditions. The results of SEM/EDS analysis indicate a homogeneous distribution of metal cations at the molecular level in the precursor materials, while in the thermally treated materials, phase separation occurred, with only two samples achieving satisfactory homogeneity. A good correlation between the experimental and theoretical amount fractions was observed, confirming the effectiveness of the coprecipitation method in synthesizing compositionally uniform multicomponent oxide systems. Two samples with the most homogeneous elemental distribution were further analyzed by Xray diffraction (XRD) to determine their phase composition. The obtained diffractograms indicate the presence of a multiphase structure, which is why it is not possible to determine with certainty whether all five cations have been incorporated into a single crystal lattice. However, indications of partial incorporation of all five cations are present in one of the phases. In the other sample, phase separation was observed despite the homogeneous precursor composition