Адхезија епоксидних катафоретских превлака на легурама цинка

One of the most important factors in corrosion prevention by protective coatings is the loss of coating adhesion under environmental influence. In this work, the adhesion of epoxy cataphoretic coatings was examined on steel and steel modified by Zn-Fe and Zn-Co alloys. The dry and wet adhesions of epoxy primers were measured by the direct pull-off standardized procedure, as well as indirectly by the NMP test. The corrosion stability of the coated samples was investigated by electrochemical impedance spectroscopy. It was shown that under dry testing conditions all the samples exhibited very good adhesion. However, different trends of adhesion loss of different protective systems during exposure to a corrosive agent (3 % NaCl solution) were observed. The lowest adhesion values were obtained for epoxy coating on the steel substrate. The change in adhesion of the epoxy coating on steel modified by Zn-Co alloy during immersion in 3 % NaCl solution for 24 days was the smallest of all the investigated samples. Electrochemical impedance measurements in 3 % NaCl solution confirmed the good protective properties of this protective system, i.e., greater values of pore resistance were obtained.Један од најважнијих фактора у заштити од корозије органским превлакама је губитак адхезије органских превлака под утицајем корозионе средине. У овом раду проучавана је ад- хезија епоксидних катафоретских превлака на челику и челику модификованом легурама Zn–Fe и Zn–Co. Испитиване су тзв. сува и мокра адхезија стандардним pull-off поступком, као и NMP тестом. Корозиона стабилност свих узорака је испитивана спектроскопијом елек- трохемијске импеданције. Сви узорци су имали добру почетну адхезију, међутим током де- ловања корозионог агенса (3 % NaCl) промена адхезије се значајно разликовала код различи- тих заштитних система. Најмање вредности адхезије су добијене у случају епоксидне пре- влаке на челику. Укупно смањење адхезије током 24 дана испитивања је најмање за епок- сидну превлаку на челику модификованом Zn–Co легуром. Највеће вредности отпорности у порама епоксидне превлаке током целокупног испитиваног периода деловања корозионог аг- енса код превлаке на челику модификованом Zn–Co легуром такође указују на велику ста- билност овог заштитног система

Otpornost prema koroziji aluminijumske legure serije 7000 posle novog dvostepenog termičkog taloženja

Corrosion properties of an aluminium alloy 7000 series were investigated by different electrochemical methods. The alloy was subjected to the one-step and to a new two-step precipitation hardening. Polarization measurements in the 3.5 wt. % NaCl solution have shown a more positive value of the pitting potential (Epit) and a higher corrosion resistance for the two-step aged alloy. The electrochemical impedance spectroscopy (EIS) has also shown that the two-step aged alloy has better corrosion properties (higher value of polarization resistance, Rp, and lower value of double-layer capacitance, Cdl) comparing to the one-step aged alloy.Otpornost prema koroziji aluminijumske legure serije 7000 ispitivana je primenom različitih elektrohemijskih metoda. Legura je bila podvrgnuta jednostepenom i novom dvostepenom termičkom taloženju. Polarizaciona merenja u 3,5 mas.% NaCl su pokazala da legura posle dvostepenog termičkog taloženja ima pozitivniju vrednost potencijala pitinga (Epit) i veću otpornost prema koroziji. Spektroskopija elektrohemijske impedancije (SEI) je takođe pokazala da legura posle dvostepenog termičkog taloženja ima bolju otpornost prema koroziji (veću vrednost polarizacione otpornosti, Rp i manju vrednost kapacitivnosti dvojnog sloja, Cdl) u poređenju sa legurom posle jednostepenog termičkog taloženja

Impedansni odgovor aluminijuma sa zaštitnom prevlakom oksida cerijuma tokom izlaganja hloridnoj korozionoj sredini

Electrochemical impedance characteristics of bare Al and Al with CeO2 coating prepared sol-gel procedure from the ceria sol are investigated. The corrosion behavior is monitored during the exposure to 3 wt. % NaCl aqueous solution. Experimental data are fitted to various equivalent electrical circuits with special attention to inductive features. Equivalent electrical circuits involving inductivity represent impedance response equally well as the ones without inductivity, although the parameter values gained from the former correspond better to the proposed model of physicochemical changes during corrosion of investigated samples.Korozione karakteristike aluminijuma i aluminijuma na koji je naneta prevlaka oksida cerijuma sol-gel postupkom ispitivane su primenom spektroskopije elektrohemijske impedancije tokom izlaganja u vodenom rastvoru 3 mas. % NaCl. Dobijeni podaci analizirani su ekvivalentnim električnim kolima različite konfiguracije uz posebnu diskusiju koja se odnosi na pojavu induktivnog ponašanja. Ekvivalentna kola sa induktivnim elementom i bez njega podjednako dobro opisuju impedansne odgovore, mada vrednosti parametara kola u kojima je uključena induktivnost više odgovaraju predloženom modelu fizičko-hemijskih promena tokom procesa korozije ispitivanih sistema

Cyclic voltammetry study of electrochemically synthesized Ag/PVP nanocomposite

Hydrogel nanocomposites of silver nanoparticles (AgNPs) and crosslinked poly(N-vinyl-2- pyrrolidone) (PVP) were synthesized in situ by a novel electrochemical method. PVP hydrogels, crosslinked by gamma-irradiation, were swollen in the solution containing 0.1 M KNO3 and 3.9 mM AgNO3. PVP polymer matrix nanocavities were used as nanoreactors for AgNPs synthesis. The reduction of silver cations was performed using two-Pt-electrode electrochemical cell. The polarity of the electrodes was changed on the half of the implementation time, enabling the Ag+ ions reduction in the bulk. Cyclic voltammetry (CV) was performed in a three-electrode electrochemical cell, using the saturated calomel electrode (SCE) as a reference. Ag/PVP nanocomposites were scanned by CV immediately after the synthesis and after drying followed by reswelling in 0.1 M KNO3. Ag/PVP was compared with CVs of the following systems: Pt electrode in 0.1 M KNO3; Pt/PVP system in 0.1 M KNO3; Ag/Pt system in 0.1 M KNO3 + 3.9 mM AgNO3 solution.Belgrade, Serbia, June 6-10, 2010Related to the published paper in the Proceedings of the Second Regional Symposium on Electrochemistry South-East Europe, [http://cer.ihtm.bg.ac.rs/handle/123456789/3523

Corrosion Testing of an Al-Zn-Mg-Cu Alloy After Different Heat Treatment Regimes by the Application of Electrochemical Methods

Abstract: The corrosion tendency in the 7000 series aluminium alloys changes depending on the content of alloying elements, thermal and thermo-mechanical treatments, etc. An alloy of this type applied in the production of weapons and military equipment has been investigated by applying different electrochemical methods. A degree of the precipitation hardening (aging) of the alloy has been evaluated by measuring its electrical resistivity. The corrosion potential measurements (Ecorr.) gave information about the distribution of the alloying elements between the solid solution and the precipitation phases. The polarization measurements, performed in the 0.5 M NaCl solution, have shown a more positive value of the pitting potential (Epit.) and a greater corrosion resistance for the two-step aged alloy. The electrochemical impedance spectroscopy (EIS) has also shown that the two-step aged alloy has better corrosion properties (a higher value of polarization resistance, Rp, and a lower value of capacitance, Cdl) comparing to the one-step aged alloy. These results enable a deeper insight into the effects of both heat treatment and alloying elements, primarily copper, on the corrosion resistance of the tested alloy

Određivanje pokrivenosti površine čelika gvožđe-fosfatnim prevlakama anodnim rastvaranjem primenom linearne voltametrije

In this study, the effect of deposition time and concentration of NaNO2 in the phosphate bath on the surface morphology of iron-phosphate coatings on low carbon steel was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The composition of ironphosphate coatings was determined using energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), while surface coverage was evaluated by the voltammetric anodic dissolution (VAD) technique in the borate solution. The addition of NaNO2 to the phosphate bath significantly increased the surface coverage since better packed crystals of smaller size, which favour the phosphate nucleation, were obtained. It was also shown that prolonged deposition time increased the surface coverage, coating roughness and crystal size in the lateral direction, altering also the crystal shape from large platelets non-uniformly distributed on the steel surface during the initial time to better packed laminated and needle-like structures during prolonged exposure.U ovom radu je, primenom skenirajuće elektronske mikroskopije (SEM) i mikro- skopije međuatomskih sila (AFM), ispitivan uticaj vremena taloženja i koncentracije NaNO2 u rastvoru za fosfatiranje na morfologiju gvožđe-fosfatnih prevlaka na nisko-ugljeničnom čeliku. Sastav gvožđe–fosfatnih prevlaka je određen primenom energetske disperzione atomske analize (EDS) i difrakcijom H-zraka (XRD), dok je pokrivenost površine određivana anodnim rastvaranjem u boratnom rastvoru primenom linearne voltametrije (VAD). Pokazano je da dodatak NaNO2 u rastvoru za fosfatiranje značajno povećava pokrivenost površine čelika, jer se formiraju bolje pakovani kristali, manje veličine. Duže vreme taloženja takođe povećava pokrivenost površine, kao i hrapavost prevlake i širinu kristala. Oblik kristala se tokom dužeg vremena taloženja menja od kristala u obliku većih ploča neuniformno raspoređenih na površini čelika, ka bolje pakovanim laminarnim i igličastim kristalima

Multifunkcionalni kompoziti na bazi alginatnih hidrogelova za potencijalnu primenu u oblogama za rane

Alginate hydrogels are widely used in wound dressings due to hydrophilicity, biocompatibility, flexibility, and high sorption capacity, providing effective moisture regulation in wounds and inducing rapid granulation and reepithelization of the damaged tissue. However, these dressings are not bioactive so that different methodologies have been investigated to extend functionality of alginate hydrogels. In the present work, we show several approaches to achieve this aim by addition of different biologically active components. These include incorporation of silver nanoparticles as potent antimicrobial agents (1), bioactive honey components (2), activated charcoal (AC) particles as carriers of therapeutically active agents (3) as well as the use of Zn-alginate hydrogels that release zinc ions (4). The obtained composites were comprehensively characterized regarding composition, cytotoxicity, antibacterial activity, release kinetics of active agents and wound treatment in a rat model. Ag/alginate nanocomposite hydrogels releasing silver ions and/or nanoparticles exhibited high bactericidal activity against a broad spectrum of standard and multi-drug resistant clinical bacterial strains (Escherichia coli, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus – MRSA, Acinetobacter baumannii and Pseudomonas aeruginosa). Especially interesting results were obtained against 13 clinical isolates of A. baumannii, which were completely extinguished over 48 h in 6 cases (2). However, in 3 clinical isolates, antibacterial effects were not noticed implying possibility for development of bacterial resistance to silver. In the treatment of 2nd degree burns in rats Ag/alginate nanocomposites exhibited the same efficiency as commercial medical products (5). Composite alginate hydrogels with immobilized AC particles impregnated with povidone iodine (PVP-I) as a model therapeutically active agent, were developed with the aim to provide controlled particle release in the wound without actually releasing the adsorbed substance, thus achieving the desired activity without adverse effects by systemic absorption. The composite Ca-alginate hydrogels induced strong bactericidal effects against two standard bacterial strains and clinical multi-resistant wound isolates (MRSA, E. coli, P. aeruginosa, Еnterococcus faecalis and Proteus mirabilis) without releasing PVP-I in the environment (3). Furthermore, composite Zn-alginate hydrogels released zinc ions in addition to AC particles with adsorbed PVP-I, which induced additional microbicidal effects on one wild yeast strain (Candida albicans). The obtained bactericidal effects were ascribed to effective adsorption of bacteria onto AC particles and further direct contact with the adsorbed iodine, while the antifungal activity against C. albicans was assigned to released Zn 2+. Overall, the developed composite alginate hydrogels have shown high potentials for utilization in variety of multifunctional wound dressings according to the specific needs.Alginatni hidrogelovi se široko koriste u oblogama za rane zbog svoje hidrofilnosti, biokompatibilnosti, fleksibilnosti i velikog sorpcionog kapaciteta čime obezbeđuju efikasnu regulaciju vlažnosti rane i podstiču brzu granulaciju i reepitelizaciju oštećenog tkiva. Međutim, ove obloge nisu bioaktivne tako da su istraživane različite metodologije kako bi se proširila funkcionalnost alginatnih hidrogelova. U ovom radu je prikazano nekoliko pristupa ostvarivanju tog cilja dodatkom različitih biološki aktivnih komponenata. Ovi pristupi uključuju inkorporaciju nanočestica srebra kao potentnog antimikrobnog agensa (1), bioaktivnih komponenata meda (2), čestica aktivnog uglja (AU) kao nosača terapeutski aktivnih agenasa (3), kao i primenu hidrogelova Zn-alginata koji otpuštaju jone cinka. Dobijeni kompoziti su sveobuhvatno karakterisani u pogledu sastava, citotoksičnosti, antibakterijske aktivnosti, kinetike otpuštanja aktivnih agenasa i tretmana rana u eksperimentalnom modelu opekotina na pacovima. Ag/alginatni nanokompozitni hydrogelovi su usled otpuštanja jona i/ili nanočestica srebra, pokazali izraženu baktericidnu aktivnost prema širokom spektru standardnih i kliničkih multi- rezistentnih bakterijskih sojeva (Escherichia coli, Staphylococcus aureus, meticilin-resistentni Staphylococcus aureus – MRSA, Acinetobacter baumannii i Pseudomonas aeruginosa). Posebno interesantni rezultati su dobijeni u kulturama 13 kliničkih izolata A. baumannii, gde je u 6 slučajeva postignut potpun baktericidan efekat u toku 48 h (2). Ipak, kod 3 klinička izolata nije postignuto antibakterijsko dejstvo što ukazuje na mogućnost razvoja bakterijske rezistencije na srebro. U tretmanu opekotina drugog stepena na pacovima, Ag/alginatni nanokompoziti su pokazali istu efikasnost kao komercijalni medicinski proizvodi. Kompozitni alginatni hidrogelovi sa imobilisanim česticama AU impregniranih povidon-jodom kao model terapeutski aktivnom komponentom, su razvijeni sa ciljem da obezbede kontrolisano otpuštanje čestica AU u rani bez otpuštanja adsorbovane supstance kako bi se na taj način postiglo željeno dejstvo bez neželjenih efekata sistemske apsorpcije. Kompozitni Ca-alginatni hidrogelovi su pokazali jake baktericidne efekte na dva standardna bakterijska soja i nekoliko kliničkih multi- rezistentnih izolata iz rana (MRSA, E. coli, P. aeruginosa, Еnterococcus faecalis i Proteus mirabilis) bez otpuštanja povidon-joda u okolinu (3). Isto tako, kompozitni Zn-alginatni hidrogelovi su otpuštali jone cinka uz otpuštanje AU čestica sa adsorbovanim povidon-jodom što je prouzrokovalo dodatno mikrobicidno dejstvo na jedan divlji soj gljivice Candida albicans. Dobijeni baktericidni efekti su pripisani efikasnoj adsorpciji bakterija na čestice AU i daljem direktnom kontaktu adsorbovanog joda sa ćelijskom membranom bakterija, dok je antifungalna aktivnost u odnosu na C. albicans pripisana otpuštenim Zn 2+ jonima. Može se zaključiti da su razvijeni kompozitni alginatni hdrogelovi pokazali veliki potencijal za primenu u raznovrsnim multifunkcionalnim oblogama za rane prilagođenim specifičnim potrebama.Drugi naučni simpozijum Saveza farmaceutskih udruženja Srbije sa međunarodnim učešćem, 28. 10. 2021. Beogra

Macrophages, the main marker in biocompatibility evaluation of new hydrogels after subcutaneous implantation in rats

Biocompatibility of materials is one of the most important conditions for their successful application in tissue regeneration and repair. Cell-surface interactions stimulate adhesion and activation of macrophages whose acquaintance can assist in designing novel biomaterials that promote favorable macrophage–biomaterial surface interactions for clinical application. This study is designed to determine the distribution and number of macrophages as a means of biocompatibility evaluation of two newly synthesized materials [silver/poly(vinyl alcohol) (Ag/PVA) and silver/poly(vinyl alcohol)/graphene (Ag/PVA/ Gr) nanocomposite hydrogels] in vivo, with approval of the Ethics Committee of the Faculty of Veterinary Medicine, University of Belgrade. Macrophages and giant cells were analyzed in tissue sections stained by routine H&E and im munohistochemical methods (CD68+ ). Statistical relevance was determined in the statistical software package SPSS 20 (IBM corp). The results of the study in terms of the number of giant cells localized around the implant showed that their number was highest on the seventh postoperative day (p.o.d.) in the group implanted with Ag/PVA hydrogels, and on the 30th p.o.d. in the group implanted with Ag/PVA/Gr. Interestingly, the number of macrophages measured in the capsular and pericapsular space was highest in the group implanted with the commercial Suprasorb© material. The increased mac rophage number, registered around the Ag/PVA/Gr implant on 60th p.o.d. indicates that the addition of graphene can, in a specific way, modulate different biological responses of tissues in the process of wound healing, regeneration, and integration

Electrophoretic deposition of alumina and boehmite coatings on metal surfaces

Electrophoretic deposition (EDP) is gaining increasing attention both in science and industry, due to novel applications in the processing of advanced ceramic materials and ceramic coatings. Electrophoretic deposition has become very interesting because this method has allowed the formation of thin films or multilayer films of controlled thickness and morphology, enabling the formation of films on substrates of complex geometry, aimed for different applications. This review paper represents the mechanism of electrodeposition of ceramic coatings (alumina and boehmite coatings) on metal surfaces, as well as the determination of the optimal deposition parameters (applied voltage, deposition time, electrodeposition bath temperature, suspension concentration) in order to control the thickness and morphology of deposited films. It was shown that coatings of maximum thickness, low porosity and good adhesion were obtained at lower deposition voltages and for longer deposition times

Određivanje zaštitnih svojstava polimernih prevlaka dobijenih postupkom elektroforetskog taloženja

Using electrochemical impedance spectroscopy, thermogravimetric analysis, gravimetric liquid sorption experiments, differential scanning calorimetry and optical microscopy, the corrosion stability of organic coatings was investigated. It was suggested that electrolyte penetration through an organic coating occurs in two steps. The first step is related to water uptake, when molecules of pure water diffuse in the micropores of the polymer network according to Ficks law, and it is independent of the type and dimensions of ion in the corrosive electrolyte. The second step is related to water and ions penetration through the macropores which leads to contact between the electrolyte and the metal surface and the beginning of electrochemical processes at the metallic interface. Statistical analysis of different layers of the coating through its thickness using optical microscopy and image analysis enabled determination of the pore number, pore size distribution, mean pore diameter, mean pore area and mean percentage of the surface covered by pores. These results suggested the dimensions of the pores through the coating and, knowing the number of the pores on each layer, the quantity of electrolyte inside the macropores was calculated. It was shown that conduction through the coating depends only on conduction through the macropores, although the quantity of electrolyte in the micropores of the polymer network is about one order of magnitude greater than that inside the conductinq macropores.Na osnovu rezultata dobijenih iz spektroskopije elektrohemijske impedancije, termogravimetrijske analize, diferencijalne skenirajuće kalorimetrije, sorpcionih merenja i optičke mikroskopije, ispitivana je koroziona stabilnost polimernih prevlaka i pretpostavljen je mehanizam prodiranja elektrolita kroz njih. U prvom stupnju dolazi do absorpcije molekula vode koji difunduju u mikropore polimerne mreže prema Fikovom zakonu difuzije. U drugom stupnju molekuli vode i joni prodiru kroz makropore u prevlaci do metalne osnove, što dovodi do degradacije prevlake i procesa korozije na supstratu. Takođe su određeni oblik i dimenzije provodnih makropora i izračunat je sadržaj elektrolita u prevlaci