1. Formation and corrosion-protective performance of zirconium conversion coating on aluminium heat exchanger componentsAna Kraš, Barbara Kapun, Nina Kovač, Matejka Podlogar, Sašo Šturm, Ingrid Milošev, Marko Kralj, Peter Rodič, 2026, izvirni znanstveni članek Povzetek: This study investigates the corrosion protection of aluminium heat exchangers used in freezers with a zirconium conversion coating (ZrCC). Tube and fins sections were subjected to a three-step surface treatment comprising (i) alkaline cleaning, (ii) acid desmutting, both with commercial SurTec® products, and (iii) deposition of conversion of Zr coating in a hexafluorozirconic acid (H2ZrF6) bath. The resulting surfaces were characterised for morphology, composition, and corrosion behaviour using scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, potentiodynamic polarisation, and neutral salt spray (NSS) testing. Zr formed a ∼70 nm oxide–hydroxide layer that preferentially nucleated and grew on cathodic Fe-containing intermetallic particles in tubes and fins. The coating improved passivity and delayed pit initiation in chloride-containing environments by broadening the passivity span ΔE up to 500 mV. Accelerated corrosion testing in NSS (ASTM B117) demonstrates that ZrCC can provide efficient protection for up to 90 h on tube-and-fin substrates, thereby supporting their implementation in industrial heat-exchanger production.
Ključne besede: zirconium conversion coating
Objavljeno v DiRROS: 29.07.2026; Ogledov: 127; Prenosov: 71
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2. Corrosion resistance of different commercial Zr, Zr/Ti and Zr/Cr(III) conversion coatings deposited on an Al alloy 3003Maja Mujdrica Kim, Ingrid Milošev, 2023, izvirni znanstveni članek Povzetek: Chromate-free conversion coatings are increasingly investigated as environmentally acceptable alternatives to conventional chromate conversion coatings for corrosion protection of aluminum alloys. In the present study, the electrochemical behaviour and long-term corrosion stability of several commercial conversion coating systems based on trivalent chromium (TCP), zirconium (ZrCC) and zirconium/titanium (Zr/TiCC) were systematically evaluated on AA3003 aluminum alloy and compared to chromate conversion coating (CCC) CR614. Three TCP coatings (ST650, MC1300 and B30002), two ZrCC (MC1700 and MC160/161), and one Zr/TiCC (B2040) were investigated. Coatings were prepared at pre-selected pH and concentration, but at varying conversion times. The protective performance of the coating was then tested across various exposure conditions using potentiodynamic polarization measurements: (i) after 24 h of exposure to air, (ii) after 24 h of immersion in 3.5 wt.% NaCl solution and (iii) simulated acid rain solution, and (iv) after exposure in a salt spray chamber for 500 h. The protective performance strongly depended on both the conversion conditions and the exposure environment. The optimal conversion times ranged between 40 s and 18 min, depending on the coating type. Differences between the investigated systems remained relatively limited when investigated after exposure to air and immersion in the simulated acid rain solution. However, in chloride-containing environments, substantially greater differentiation between the coatings was observed. Among the investigated systems, TCP coatings exhibited the most favourable overall corrosion performance, particularly after prolonged salt spray exposure, where ST650 and B30002 polarization resistance values were approximately 8800 and 5300 kΩ cm2, respectively, together with corrosion current densities as low as 0.0004 and 0.001 μA cm−2. ZrCC systems MC1700 and MC160/161 also provided significant corrosion protection, achieving polarization resistance values around 2700 and 2400 kΩ cm2 after 500 h of salt spray exposure, whereas the Zr/TiCC coating B2040 exhibited poorer long-term performance. The results further demonstrated that prolonged salt spray exposure provides considerably more realistic evaluation of long-term coating protectiveness than short-term electrochemical measurements alone. Overall, optimized TCP and ZrCC systems provided corrosion protection under chloride-containing conditions comparable to or superior to the investigated conventional chromate conversion coating CR614 deposited on AA3003 alloy.
Ključne besede: chromate-free conversion coatings
Objavljeno v DiRROS: 14.07.2026; Ogledov: 198; Prenosov: 117
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3. Corrosion behaviour of injection- and compression-moulded Nd–Fe–B and Sm–Fe–N magnets with different polymer bindersNikolina Lešić, Nataša Kovačević, Ingrid Milošev, 2026, izvirni znanstveni članek Povzetek: The corrosion behaviour and environmental durability of injection- and compression-moulded Nd–Fe–B and Sm–Fe–N magnets were investigated. For injection-moulded magnets, the effects of magnetic powder type (Nd–Fe–B and Sm–Fe–N), magnetic powder particle size (100 µm and 400 µm), and polymer binder (PPS and PA12) on corrosion resistance were studied. For compression-moulded magnets with an epoxy binder, the effects of powder type and size were examined. Corrosion resistance was investigated using potentiodynamic polarisation in electrolytes of varying pH (1.8–12.8). The Sm–Fe–N magnets exhibited slightly better corrosion resistance than the Nd–Fe–B magnets, irrespective of the polymer binder. The finer magnetic powders (100 µm) showed lower corrosion resistance due to their larger specific surface area, with a more pronounced effect in the compression-moulded magnets. The type of polymer binder had only a minor effect. The hygrothermal corrosion resistance and thermal stability were evaluated using bulk corrosion (BCT) and thermal shock tests, respectively. Surface corrosion was observed in all magnets after the BCT, with the compression-moulded magnets exhibiting a greater irreversible loss of magnetic properties. The thermal shock test caused a temporary reduction in magnetic properties, with recovery after remagnetisation, demonstrating the good thermal stability of both magnet types.
Ključne besede: magnetic powder, injection moulding, compression moulding, polymer-bonded magnets, bulk-corrosion test, thermal shock test, polymer binders
Objavljeno v DiRROS: 04.05.2026; Ogledov: 355; Prenosov: 250
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4. Influence of conversion time on polymeric speciation in zirconium conversion coatings deposited on aluminium alloy 5754 : a ToF-SIMS studyAna Kraš, Ingrid Milošev, Antoine Seyeux, Philippe Marcus, 2026, izvirni znanstveni članek Povzetek: The influence of conversion time on polymeric speciation and protective performance of zirconium conversion coatings (ZrCCs) on aluminium alloy AA5754 was investigated using samples treated in 150 ppm H2ZrF6 at pH 4.6 for 230 s and 480 s. Characterisation combined time-of-flight secondary ion mass spectrometry (ToF-SIMS) with region-of-interest analysis, electrochemical impedance spectroscopy in dilute Harrison’s solution after one hour, atomic force microscopy, and contact-angle measurements. ZrCC thickening is conversion-time-dependent, with a preference for growth above intermetallic particles. ToF-SIMS identified monomeric, dimeric, and trimeric zirconium hydroxide fragments, while tetrameric species were detected only at very low intensities, in contrast to previous observations on steel, possibly due to the lower overall pH increase during ZrCC formation. Despite the thicker layer obtained at 480 s, EIS indicated no improvement in corrosion protection compared with the 230 s. Morphological and wettability analyses further showed that the shorter treatment produced a rougher but more compact and uniform coating, which correlates with better short-term protective behaviour. These findings emphasise that compactness and uniformity, rather than thickness or wettability, govern the early protective function of ZrCCs and raise the question of whether tetrameric polymeric forms are required to establish a protective layer, as hypothesised for cold-rolled steel.
Ključne besede: polymeric speciation, zirconium conversion coatings
Objavljeno v DiRROS: 08.04.2026; Ogledov: 308; Prenosov: 222
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5. Review of coatings used for corrosion protection of aluminium alloysIngrid Milošev, Ana Koblar, 2026, pregledni znanstveni članek Povzetek: Aluminium and aluminium alloys are major technological metals, offering desirable mechanical properties, low density, thermal and electrical conductivity. Importantly, they exhibit high recyclability. While these materials are relatively stable and corrosion-resistant in most environments, they are often subjected to corrosion and wear in harsh environments. Coatings are the most common method of corrosion protection of aluminium and its alloys. Coatings can improve not only corrosion resistance but also wear resistance, and can add functional properties to the surface. In the present review, the coatings are summarised in five groups: (1) barrier aluminium oxide coatings, including anodised coatings, plasma electrolytic oxidised coatings, coatings deposited by atomic layer deposition, and by hydrothermal treatment, (2) conversion coatings including zirconium, chromate, titanium, trivalent chromium, and phosphate (3) metallic coatings comprising clad and electroplated metal coatings, (4) organic coatings comprising powder and liquids organic coatings, and sol–gel coatings, and (5) inhibition and wettability control coatings, comprising coatings incorporating inhibitors or nanoparticles and superhydrophobic coatings. The review focuses on production methodologies and the physical-chem-ical characteristics of coatings. Advantages and potential shortcomings of individual coatings are discussed in terms of their use and corrosion protection.
Objavljeno v DiRROS: 24.03.2026; Ogledov: 507; Prenosov: 313
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6. Influence of surface pretreatments on composition, structure and corrosion performance of zirconium conversion coating applied to AA7075-T6Gavrilo Šekularac, Janez Kovač, Ingrid Milošev, 2025, izvirni znanstveni članek Povzetek: The effect of chemical pretreatment of aluminium alloy 7075-T6 on the composition, morphology, and structure of zirconium conversion coatings (ZrCC) was investigated. Chemical pretreatments included: (i) alkaline etching and desmutting using commercial reagents, (ii) alkaline etching using sodium hydroxide, (iii) acidic etching using nitric acid, (iv) desmutting using a commercial reagent and boiling in deionised water, and (v) alkaline etching and desmutting using nitric acid. ZrCCs were deposited at room temperature from a 200 ppm H2ZrF6 solution of pH 4.8. A commercial SurTec® coating containing zirconium and trivalent chromium was used as a benchmark. The electrochemical behaviour was evaluated using potentiodynamic polarisation measurements and electrochemical impedance spectroscopy conducted over a minimum of 5 days and up to 15 days in 0.1 M NaCl. Corrosion resistance was further assessed through immersion testing. Microstructural characterisation was performed using scanning electron microscopy with energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. The SurTec® pretreatment of AA7075-T6 activated the self-sealing of the subsequently deposited ZrCC, about 40 nm thick, which exhibited the highest degree of compactness and uniformity. This study showed a significant impact of surface chemical pretreatment on the microstructural and protective properties of ZrCCs deposited on 7075 alloy.
Ključne besede: surface pretreatment, etching, desmutting
Objavljeno v DiRROS: 18.11.2025; Ogledov: 754; Prenosov: 386
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7. DED-LB manufactured Ti–6Al–4V–4Cu alloy : materials development, characterization, and in vivo biocompatibilityAndrej Jeromen, Anish Nair, Peter Rodič, Denis Sačer, Barbara Kapun, Maša Čater, Ana Brunčić, Katarina Kozlica, Radmila Milačič Ščančar, Andrej Cör, Edvard Govekar, Ingrid Milošev, Simon Horvat, 2025, izvirni znanstveni članek Ključne besede: Ti–6Al–4V–4Cu alloy, additive manufacturing, laser-based directed energy deposition (DED-LB), microstructure and phase analyses, corrosion, in vivo biocompatibility
Objavljeno v DiRROS: 10.11.2025; Ogledov: 633; Prenosov: 512
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9. The importance of chemical transformations of adsorbed molecules for corrosion inhibition : mercaptobenzimidazoles on copperAnton Kokalj, Erik Gregori, Barbara Kapun, Ingrid Milošev, 2025, izvirni znanstveni članek Povzetek: This study investigates whether mercaptobenzimidazoles act as thiolates in inhibiting copper corrosion. To this end, we examined three mercaptobenzimidazole derivatives — 2-mercaptobenzimidazole (SH-BimH), 2-mercapto-1-methylbenzimidazole (SH-BimMe), and 2-(methylthio)benzimidazole (Me-S-BimH) — as corrosion inhibitors for copper in 3 wt% NaCl solution using a combined experimental and computational approach. Me-S-BimH has a thiol group (single bondSH) replaced by a methylthio group (single bondSCH ), which should prevent the formation of surface thiolates. In contrast, SH-BimMe has the same molecular formula as Me-S-BimH, but its methyl group does not cap the thiol group. Corrosion experiments reveal that after 1 h of immersion, Me-S-BimH is considerably less effective than SH-BimH and SH-BimMe at inhibiting copper corrosion. However, after 100 h of immersion, Me-S-BimH performs comparably to SH-BimH and SH-BimMe. This delayed effectiveness suggests that a molecular transformation activates Me-S-BimH over time. To explore this phenomenon, we performed a detailed DFT study of potential chemical transformations of adsorbed Me-S-BimH. Most transformations are exothermic, but only molecular deprotonation and Csingle bondS bond cleavage between the azole ring and the methylthio group exhibit sufficiently low activation barriers to occur at room temperature. Similar deprotonation and Csingle bondS bond cleavage reactions occur also for SH-BimH and SH-BimMe, leading to more strongly bound species than their intact molecular forms. Due to these transformations, Me-S-BimH and SH-BimH eventually result in the same strongly bound species, while SH-BimMe forms an analogous species. These findings may explain why, over time, all three compounds exhibit similar corrosion inhibition characteristics, and highlight the importance of chemical transformations of adsorbed molecules in corrosion inhibition.
Ključne besede: copper, corrosion inhibition, electrochemical measurements
Objavljeno v DiRROS: 25.08.2025; Ogledov: 863; Prenosov: 545
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10. Alumina and hafnia thin films deposited by atomic layer deposition at different temperatures on biomedical stainless steel and titaniumIvan Spajić, Sandra Drev, Urška Trstenjak, Ingrid Milošev, 2025, izvirni znanstveni članek Povzetek: Alumina and hafnia films produced by the atomic layer deposition were applied to commercially pure Ti and stainless steel 316L specimens for protection under simulated human body conditions. The ALD films were deposited at 180 °C and 260 °C to determine how the deposition temperature affect the films' protective properties. Surface analysis of the ALD films included scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The barrier properties were tested electrochemically using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques in a simulated body solution at 37 °C. Alumina thin films showed substantial barrier properties, but after 30 days of immersion, the alumina dissolved regardless of the deposition temperature. EIS tests themselves promoted the dissolution of alumina. In contrast, the barrier properties of hafnia depended significantly on deposition temperature. Hafnia deposited at 180 °C exhibited substantial protective properties and remarkable stability over an extended immersion period. However, when deposited at 260 °C hafnia films showed strong protection at the outset, but after a few days of immersion, they lost their protective ability due to porosity. The key factors affecting the barrier properties of ALD hafnia films were the proportion of the crystalline phase and how crystallites formed.
Ključne besede: thin films, atomic layer deposition, titanium alloys, biomedical steel, medical implants
Objavljeno v DiRROS: 15.07.2025; Ogledov: 1287; Prenosov: 745
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