1. Corrosion behavior of nickel–titanium continuous-casted alloysMinja Miličić Lazić, Dijana Mitić, Katarina Radović, Igor Djordjević, Peter Majerič, Rebeka Rudolf, Branimir Grgur, 2024, izvirni znanstveni članek Opis: Variations in the corrosion behavior of biomedical NiTi alloys in Cl− containing and acidic
environments present a problem with their biological implantation. The objective of this research
was to evaluate the synergy of the microstructure, the corrosion behavior, and the biocompatibility of
novel continuous-cast NiTi alloys and to compare them with commercial NiTi alloys. The two alloys
have a practically identical nominal chemical composition, but they differ in production technology.
The continuous casting technology involved vacuum induction melting of the basic components
and vertical continuous casting, while the commercial NiTi alloy was produced through a process of
casting, hot rolling, and forming into square shapes. The microstructure was revealed to determine
the surface area and size of grains. The corrosion of a commercial nickel–titanium alloy and one
prepared by a novel continuous casting method in acidic and chloride-containing solutions was
studied via analytical and electrochemical tests. Localized corrosion characteristics related to oxide
properties, when exposed to 9 g L−1 NaCl solution, were examined with focused ion beam analysis
and subsequent microchemical analysis of the formed corrosive products. Corrosion potential over
time and the oxide film resistance were analyzed using linear polarization measurements. To obtain
a preliminary estimate of biocompatibility, human fibroblast cells were used in indirect contact,
i.e., alloy conditioning medium. The continuous casting method resulted in a reduction in the
average grain size in comparison to the commercial sample and better corrosion stability of the
sample in an acidic environment. Also, in a solution of 9 g L−1 NaCl the commercial sample showed
high values for the corrosion current density (jcorr = 6 µA cm−2), which indicated low corrosion
resistance, while the continuous casting sample possessed much better corrosion stability and lower
values for the corrosion current density (jcorr = 0.2 µA cm−2). In line with that, elemental analysis of
the corroded surfaces showed higher Cl− ion deposition over the surface layer of the commercial
sample, suggesting local oxide breakdown. Moreover, NiTicc reached a value three times higher
for polarization resistance (Rp = 270 kΩ cm2) over time in comparison to the commercial sample
(Rp~100 kΩ cm2). Biocompatibility evaluation showed that human fibroblast cells exhibited altered
metabolic activity. An MTT assay showed that cells’ mitochondrial activity dropped below that of
control cells in the presence of both materials’ supernatants.
Ključne besede: nickel–titanium, corosion behaviour, electrochemical testing, NiTi biocompatibility
Objavljeno v DKUM: 30.06.2025; Ogledov: 0; Prenosov: 4
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2. Comparison study of four commercial SARS-CoV-2-rapid antigen tests : characterisation of the individual componentsŽiga Jelen, Ivan Anžel, Rebeka Rudolf, 2022, izvirni znanstveni članek Opis: During the corona virus (COVID-19) pandemic, there was a sharp increase in the need for diagnostic tests that could detect the presence of SARS-CoV-2 virus or its antibodies quickly and reliably. An important type in the group of diagnostic tests are rapid antigen lateral flow immuno-assay (LFIA) tests, which operate on the immuno-chromatographic principle with the lateral flow of analyte. Clinical practice in the last year has shown that such diagnostic tests can be effective in preventing the spread of the SARS-CoV-2 virus.The development, and, thus, the production of the rapid antigen LFIA tests, is influenced by a number of factors that determine their sensitivity and accuracy indirectly. These factors are directly dependent on the type of antibody produced, which is formed as an immune response when infected with the virus. The production of the rapid antigen LFIA tests is associated with the appropriate selection of basic components that determine the type and quality of these tests. The basic components include: substrates and membranes, antigens, antibody labels and compatible buffers. The correct choice of membranes and their materials is crucial to compiling an effective rapid antigen LFIA test. This study therefore presents a comparative analysis of four commercially available SARS-CoV-2-rapid LFIA tests using state-of-the-art characterisation techniques scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectrometry (ICP-OES), environmental scanning electron microscope / energy-dispersive X-ray spectroscopy (ESEM/EDX), Fourier-transform infrared spectroscopy / attenuated total reflection (FTIR/ATR) for the individual components. The obtained results were the starting point for the development and assembling of our own rapid antigen LFIA test based on gold nanoparticles as antibody labels.
Ključne besede: hitri antigenski testi, komponente, karakterizacija, analize, rapid antigen test, components, characterisation, analysis
Objavljeno v DKUM: 26.03.2025; Ogledov: 0; Prenosov: 5
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3. Unraveling the antibiofilm activity of a new nanogold resin for dentures and epithesisVera Ivanović, Danica Popović Antić, Sanja Petrović, Rebeka Rudolf, Peter Majerič, Miloš Lazarević, Igor Djordjević, Vojkan Lazić, Milena Radunović, 2022, izvirni znanstveni članek Opis: Dentures and epitheses are mostly made from poly(methyl methacrylate) (PMMA), which
does not show antimicrobial properties. They present reservoirs of microorganisms grown in
biofilms. The aim of this study is to prepare a PMMA enriched with gold nanoparticles (AuNPs)-
PMMA/AuNPs and the examination of its physical, mechanical and antimicrobial properties. The
AuNPS were synthetized from HAuCl4 using the ultrasonic spray pyrolysis method with lyophilization. The PMMA/AuNP samples were compared to PMMA samples. Density was measured by
pycnometer. Microhardness was evaluated using the Vickers hardness test. Monomicrobial biofilm
formation (Streptococcus mitis, Candida albicans, Staphylococcus aureus and Escherichia coli) was measured by colony-forming units (CFUs) and MTT test and visualized by SEM. AuNP release was
measured indirectly (the CFUs of the medium around the sample). The density and microhardness
of the PMMA/AuNPs were similar to those of the PMMA. CFU and MTT values for the biofilms
formed on the PMMA for each of the tested species were higher than those of the biofilms formed on
the PMMA/AuNPs. The CFUs of the medium around the sample were similar for both materials.
PMMA/AuNPs showed a significant reduction in the monomicrobial biofilms of all tested species.
AuNPs are not released from PMMA/AuNPs. Density, indirect measurement of residual monomer
and dentures weight were similar between PMMA and PMMA/AuNPs. Microhardness, as a measure
of the wear resistance, was also similar between tested discs.
Ključne besede: PMMA, gold nanoparticles (AuNPs), biofilm, antibiofilm effect
Objavljeno v DKUM: 24.03.2025; Ogledov: 0; Prenosov: 2
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4. A nonlinear probabilistic pitting corrosion model of Ni–Ti alloy immersed in shallow seawaterŠpiro Ivošević, Gyöngyi Vastag, Nataša Kovač, Peter Majerič, Rebeka Rudolf, 2022, izvirni znanstveni članek Opis: The degradation of metal materials in a marine environment represents the consequence
of the electrochemical corrosion of metals under the influence of the environment. The application
of new materials in the maritime industry requires experimental, real-world research on the form
of corrosive damage and the intensity of the corrosion. This paper analyses the pitting corrosion of
a rod-shaped nickel–titanium (Ni–Ti) alloy that was produced by means of the continuous casting
method. In total, three samples were posted in a real seawater environment and analysed after 6,
12, and 18 months. Pits were detected on the Ni–Ti alloy after 18 months of exposure to the marine
environment. The database on pitting corrosion was created by measuring depth in mm, which was
performed by means of a nonlinear method, and by the generation of an artificial database of a total
of 120, gauged in critical pit areas. The data were obtained by the application of a nonlinear model,
and under the assumption that corrosion starts after 12 months of exposure in the corrosive marine
environment. The EDX analysis of the Ni–Ti alloy composition inside the pits and on the edges of the
pits indicated that the corrosion process in the hole of the pit occurs due to the degradation of the Ni.
Ključne besede: Ni–Ti alloy, pitting corrosion, seawater, EDX analysis, nonlinear, probabilistic
Objavljeno v DKUM: 24.03.2025; Ogledov: 0; Prenosov: 5
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5. Synthesis of complex concentrated nanoparticles by Ultrasonic Spray Pyrolysis and lyophilisationLidija Simić, Srečko Stopić, Bernd Friedrich, Matej Zadravec, Žiga Jelen, Rajko Bobovnik, Ivan Anžel, Rebeka Rudolf, 2022, izvirni znanstveni članek Opis: The development of new multicomponent nanoparticles is gaining increasing importance
due to their specific functional properties, i.e., synthesised new complex concentrated nanoparticles
(CCNPs) in the form of powder using ultrasonic spray pyrolysis (USP) and lyophilisation from the
initial cast Ag20Pd20Pt20Cu20Ni20 alloy, which was in the function of the material after its catalytic
abilities had been exhausted. Hydrometallurgical treatment was used to dissolve the cast alloy,
from which the USP precursor was prepared. As a consequence of the incomplete dissolution of
the cast alloy and the formation of Pt and Ni complexes, it was found that the complete recycling
of the alloy is not possible. A microstructural examination of the synthesised CCNPs showed that
round and mostly spherical (not 100%) nanoparticles were formed, with an average diameter of
200 nm. Research has shown that CCNPs belong to the group with medium entropy characteristics.
A mechanism for the formation of CCNPs is proposed, based on the thermochemical analysis of
element reduction with the help of H2 and based on the mixing enthalpy of binary systems.
Ključne besede: complex concentrated nanoparticles, ultrasonic spray pyrolysis, lyophilisation, characterization, formation mechanism
Objavljeno v DKUM: 24.03.2025; Ogledov: 0; Prenosov: 2
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6. Development of a new AuCuZnGe alloy and determination of its corrosion propertiesRebeka Rudolf, Peter Majerič, Vojkan Lazić, Branimir Grgur, 2022, izvirni znanstveni članek Opis: In this paper, we present the idea and development of a new gold-copper-zinc-germanium
(AuCuZnGe) alloy, which is related to the method of production and research of its key properties, so
that the new Au alloy could be used for jewelry production and in dental technology. The research
design was associated with the determination of appropriate chemical composition, manufacturing
technology, and performing the characterization. Melting and casting technologies were used to cast
the AuCuZnGe alloy while rolling was used to prepare the cylinders and cutting to make square
plates with a = 10 mm and thickness of 1 mm. Such plates were provided for corrosion testing.
Observation of the plate0
s microstructure was performed with Scanning Electron Microscopy (SEM)
equipped by Energy-Dispersive X-ray spectrometry (EDS) and X-ray diffraction (XRD). Corrosion
testing involved performing the following measurements: Polarization, the open circuit potentials,
and linear polarization resistance. Based on the SEM, EDS, XRD, and results of corrosion testing it can
be concluded that the new AuCuZnGe alloy possesses high corrosion stability and can be classified
as a high noble alloy.
Ključne besede: gold alloy, germanium, production, characterization, corrosion properties
Objavljeno v DKUM: 24.03.2025; Ogledov: 0; Prenosov: 5
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7. Cast microstructure of a complex concentrated noble alloy ▫$Ag_{20}Pd_{20}Pt_{20}Cu_{20}Ni_{20}▫$Lidija Simić, Rebeka Rudolf, Peter Majerič, Ivan Anžel, 2022, izvirni znanstveni članek Opis: A complex concentrated noble alloy (CCNA) of equiatomic composition (Ag20Pd20Pt20Cu20Ni20
–20 at. %) was studied as a potential high—performance material. The equiatomic composition
was used so that this alloy could be classified in the subgroup of high—entropy alloys (HEA). The
alloy was prepared by induction melting at atmospheric pressure, using high purity elements. The
degree of metastability of the cast state was estimated on the basis of changes in the microstructure
during annealing at high temperatures in a protective atmosphere of argon. Characterisation of the
metallographically prepared samples was performed using a scanning electron microscope (SEM)
equipped with an energy dispersive spectrometer (EDS), differential scanning calorimetry (DSC),
and X–ray diffraction (XRD). Observation shows that the microstructure of the CCNA is in a very
metastable state and multiphase, consisting of a continuous base of dendritic solidification—a matrix
with an interdendritic region without other microstructural components and complex spheres. A
model of the probable flow of metastable solidification of the studied alloy was proposed, based on
the separation of L—melts into L1
(rich in Ni) and L2
(rich in Ag). The phenomenon of liquid phase
separation in the considered CCNA is based on the monotectic reaction in the Ag−Ni system.
Ključne besede: complex concentrated noble alloy, high—entropy alloy, metastability
Objavljeno v DKUM: 20.03.2025; Ogledov: 0; Prenosov: 7
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8. Synthesis of Ni/Y2O3 nanocomposite through USP and lyophilisation for possible use as coatingTilen Švarc, Srečko Stopić, Žiga Jelen, Matej Zadravec, Bernd Friedrich, Rebeka Rudolf, 2022, izvirni znanstveni članek Opis: The Ni/Y2O3 catalyst showed high catalytic activity. Based on this, the aim of this study
was to create Ni/Y2O3 nanocomposites powder with two innovative technologies, Ultrasonic Spray
Pyrolysis (USP) and lyophilisation. In the USP process, thermal decomposition of the generated
aerosols in an N2/H2 reduction atmosphere caused a complete decomposition of the nickel (II) nitrate
to elemental Ni, which became trapped on the formed Y2O3 nanoparticles. The Ni/Y2O3 nanocomposite particles were captured via gas washing in an aqueous solution of polyvinylpyrrolidone (PVP)
in collection bottles. PVP was chosen for its ability to stabilise nano-suspensions and as an effective
cryoprotectant. Consequently, there was no loss or agglomeration of Ni/Y2O3 nanocomposite material during the lyophilisation process. The Ni/Y2O3 nanocomposite powder was analysed using
ICP-MS, SEM-EDX, and XPS, which showed the impact of different precursor concentrations on the
final Ni/Y2O3 nanocomposite particle composition. In a final step, highly concentrated Ni/Y2O3
nanocomposite ink (Ni/Y2O3 > 0.140 g/mL) and test coatings from this ink were prepared by applying them on a white matte photo paper sheet. The reflection curve of the prepared Ni/Y2O3
nanocomposite coating showed a local maximum at 440 nm with a value of 39% reflection. Given that
Ni is located on the surface of the Ni/Y2O3 nanocomposite in the elemental state and according to the
identified properties, tests of the catalytic properties of this coating will be performed in the future.
Ključne besede: Ultrasonic Spray Pyrolysis (USP), lyophilisation, Ni/Y2O3 nanocomposite, characterisation, coatings
Objavljeno v DKUM: 20.03.2025; Ogledov: 0; Prenosov: 7
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9. Corrosion of NiTiDiscs in different seawater environmentsJelena Pješčić-Šćepanović, Gyöngyi Vastag, Špiro Ivošević, Nataša Kovač, Rebeka Rudolf, 2022, izvirni znanstveni članek Opis: This paper gives an approach to the corrosion resistance analysis and changes in the
chemical composition of anNiTi alloy in the shape of a disc, depending on different real seawater
environments. The NiTi discs were analysed after 6 months of exposure in real seawater environments:
the atmosphere, a tidal zone, and seawater. The corrosion tests showed that the highest corrosion rate
for the discs is in seawater because this had the highest value of current density, and the initial disc
had the most negative potential. Measuring the chemical composition of the discs using inductively
coupled plasma and X-ray fluorescence before the experiment and semiquantitative analysis after
the experiment showed the chemical composition after 6 months of exposure. Furthermore, the
applied principal component analysis and cluster analysis revealed the influence of the different
environments on the changes in the chemical composition of the discs. Cluster analysis detected small
differences between the similar corrosive influences of the analysed types of environments during the
period of exposure. The obtained results confirm that PCA can detect subtle quantitative differences
among the corrosive influences of the types of marine environments, although the examined corrosive
influences are quite similar. The applied chemometric methods (CA and PCA) are, therefore, sensitive
enough to register the existence of slight differences among corrosive environmental influences on
the analysed NiTi SMA.
Ključne besede: NiTi discs, corrosion rate, real seawater environment, cluster analysis (CA), principal component analysis (PCA)
Objavljeno v DKUM: 20.03.2025; Ogledov: 0; Prenosov: 6
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10. Oxidation behaviour of microstructurally highly metastable Ag-La alloyAndraž Jug, Mihael Brunčko, Rebeka Rudolf, Ivan Anžel, 2022, izvirni znanstveni članek Opis: A new silver-based alloy with 2 wt.% of lanthanum (La) was studied as a potential candidate
for electric contact material. The alloy was prepared by rapid solidification, performed by the melt
spinning technique. Microstructural examination of the rapidly solidified ribbons revealed very fine
grains of αAg and intermetallic Ag5La particles, which appear in the volume of the grains, as well as
on the grain boundaries. Rapid solidification enabled high microstructural refinement and provided
a suitable starting microstructure for the subsequent internal oxidation, resulting in fine submicronsized La2O3 oxide nanoparticle formation throughout the volume of the silver matrix (αAg). The
resulting nanostructured Ag-La2O3 microstructure was characterised by high-resolution FESEM
and STEM, both equipped with EDX. High-temperature internal oxidation of the rapidly solidified
ribbons essentially changed the microstructure. Mostly homogeneously dispersed nano-sized La2O3
were formed within the grains, as well as on the grain boundaries. Three mechanisms of internal
oxidation were identified: (i) the oxidation of La from the solid solution; (ii) partial dissolution of
finer Ag5La particles before the internal oxidation front and oxidation of La from the solid solution;
and (iii) direct oxidation of coarser Ag5La intermetallic particles.
Ključne besede: Ag-La alloy, rapid solidification, metastable microstructure, internal oxidation, characterisation, formation mechanism
Objavljeno v DKUM: 20.03.2025; Ogledov: 0; Prenosov: 1
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