1. Corrosion behavior of nickel–titanium continuous-casted alloysMinja Miličić Lazić, Dijana Mitić, Katarina Radović, Igor Djordjević, Peter Majerič, Rebeka Rudolf, Branimir Grgur, 2024, original scientific article Abstract: 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.
Keywords: nickel–titanium, corosion behaviour, electrochemical testing, NiTi biocompatibility
Published in DKUM: 30.06.2025; Views: 0; Downloads: 6
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2. 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, original scientific article Abstract: 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.
Keywords: PMMA, gold nanoparticles (AuNPs), biofilm, antibiofilm effect
Published in DKUM: 24.03.2025; Views: 0; Downloads: 6
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3. Experimental investigation of the biofunctional properties of nickel–titanium alloys depending on the type of productionMinja Miličić Lazić, Peter Majerič, Vojkan Lazić, Jelena Milašin, Milica Jakšić, Dijana Trišić, Katarina Radović, 2022, original scientific article Abstract: Nickel–titanium alloys used in dentistry have a variety of mechanical, chemical, and
biofunctional properties that are dependent on the manufacturing process. The aim of this study
was to compare the mechanical and biofunctional performances of a nickel–titanium alloy produced
by the continuous casting method (NiTi-2) with commercial nitinol (NiTi-1) manufactured by the
classical process, i.e., from remelting in a vacuum furnace with electro-resistive heating and final
casting into ingots. The chemical composition of the tested samples was analyzed using an energy
dispersive X-ray analysis (EDX) and X-ray fluorescence (XRF). Electron backscatter diffraction (EBSD)
quantitative microstructural analysis was performed to determine phase distribution in the samples.
As part of the mechanical properties, the hardness on the surface of samples was measured with
the static Vickers method. The release of metal ions (Ni, Ti) in artificial saliva (pH 6.5) and lactic
acid (pH 2.3) was measured using a static immersion test. Finally, the resulting corrosion layer was
revealed by means of a scanning electron microscope (SEM), which allows the detection and direct
measurement of the formatted oxide layer thickness. To assess the biocompatibility of the tested
nickel–titanium alloy samples, an MTT test of fibroblast cellular proliferation on direct contact with
the samples was performed. The obtained data were analyzed with the IBM SPSS Statistics v22
software. EDX and XRF analyses showed a higher presence of Ni in the NiTi-2 sample. The EBSD
analysis detected an additional NiTi2
-cubic phase in the NiTi-2 microstructure. Additionally, in the
NiTi-2 higher hardness was measured. An immersion test performed in artificial saliva after 7 days
did not induce significant ion release in either group of samples (NiTi-1 and NiTi-2). The acidic
environment significantly increased the release of toxic ions in both types of samples. However, Ni
ion release was two times lower, and Ti ion release was three times lower from NiTi-2 than from
NiTi-1. Comparison of the cells’ mitochondrial activity between the NiTi-1 and NiTi-2 groups did
not show a statistically significant difference. In conclusion, we obtained an alloy of small diameter
with an appropriate microstructure and better response compared to classic NiTi material. Thus, it
appears from the present study that the continuous cast technology offers new possibilities for the
production of NiTi material for usage in dentistry.
Keywords: nickel–titanium, continuous casting, characterization, biofunctional properties, biocompatibility
Published in DKUM: 24.03.2025; Views: 0; Downloads: 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, original scientific article Abstract: 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.
Keywords: Ni–Ti alloy, pitting corrosion, seawater, EDX analysis, nonlinear, probabilistic
Published in DKUM: 24.03.2025; Views: 0; Downloads: 9
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5. Development of a new AuCuZnGe alloy and determination of its corrosion propertiesRebeka Rudolf, Peter Majerič, Vojkan Lazić, Branimir Grgur, 2022, original scientific article Abstract: 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.
Keywords: gold alloy, germanium, production, characterization, corrosion properties
Published in DKUM: 24.03.2025; Views: 0; Downloads: 9
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6. 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, original scientific article Abstract: 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.
Keywords: complex concentrated noble alloy, high—entropy alloy, metastability
Published in DKUM: 20.03.2025; Views: 0; Downloads: 12
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7. Life cycle assessment (LCA) of the impact on the environment of a cosmetic cream with gold nanoparticles and hydroxylated fullerene ingredientsRebeka Rudolf, Peter Majerič, Zorka Novak-Pintarič, Andrej Horvat, Damjan Krajnc, 2024, original scientific article Abstract: This review provides a comprehensive Life Cycle Assessment (LCA) of a cosmetic cream to assess the environmental impacts throughout its entire life cycle, from raw material extraction to disposal, using the methodology according to international standards. The LCA was performed using the OpenLCA 2.0.1 software, with data from the Ecoinvent 3.8 database and relevant literature. The assessment focused on multiple impact categories, including climate change, acidification, eutrophication (freshwater, marine and terrestrial), ecotoxicity (freshwater), human toxicity (cancer and non-cancer), ionizing radiation, land use, ozone depletion, photochemical ozone formation, resource use (fossils, minerals and metals), and water use. The LCA of a cosmetic cream containing gold nanoparticles revealed significant environmental impacts across critical categories. The total climate change potential was 2596.95 kg CO2 eq., driven primarily by nanoparticle synthesis (60.7%) and electricity use (31.9%). Eutrophication of freshwater had the highest normalized result (3.000), with nanoparticle synthesis contributing heavily, indicating the need for improved wastewater treatment. The resource use (minerals and metals) scored 1.856, while the freshwater ecotoxicity reached 80,317.23 CTUe, both driven by the nanoparticle production. The human toxicity potentials were 1.39 × 10−6 CTUh (cancer) and 7.45 × 10−5 CTUh (non-cancer), linked to emissions from synthesis and energy use. The LCA of the cosmetic cream revealed several critical areas of environmental impact. The most significant impacts are associated with gold nanoparticle synthesis and electricity use. Addressing these impacts through optimized synthesis processes, improved energy efficiency, and alternative materials can enhance the product’s sustainability profile significantly.
Keywords: life cycle assessment, cosmetic cream, environmental impacts, gold nanoparticles
Published in DKUM: 17.12.2024; Views: 0; Downloads: 16
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8. The influence of the rolling direction on the mechanical properties of the Al-Alloy EN AW-5454-DMatjaž Balant, Tomaž Vuherer, Peter Majerič, Rebeka Rudolf, 2024, original scientific article Abstract: A complementary characterisation of the Al-alloy EN AW-5454 was carried out, intended for obtaining the laser hybrid welding parameters of subassemblies in the automotive industry. The investigation included a microstructural examination and the determination of the alloy’s properties using several analytical methods (HV5 hardness measurement, tensile test, Charpy impact toughness, fracture mechanics analysis). Samples were prepared in the longitudinal and transverse directions of a cold-rolled sheet of EN AW-5454 with thicknesses of 3.5 mm and 4 mm. The measured hardness on the thinner sheet was 5% higher than on the thicker sheet. The tensile and yield strength were nominal, while the elongations were smaller by 2.2–3.2% for the longitudinal samples and by 2.7–13.7% for the transverse samples. The smaller deviations from the nominal values are for the thinner sheet metal. A precise topographical analysis showed the brittle fractures of the samples. The Charpy impact toughness results on the thicker plate showed a 20% greater work needed to break it in the longitudinal direction than in the transverse direction. With the thinner sheet metal, 40% greater work was needed. SEM (scanning electron microscope) analysis has shown that the intermetallic Al6(Mn,Fe) particles in the longitudinal samples were mostly intact, with evidence of tough areas on the upper part of the fracture, indicating a better toughness than the specimens in the transverse direction. More crushed intermetallic particles were observed at the fractures of the transverse samples, and their distribution appeared to be more oriented in the direction of rolling. Fracture mechanics SENB (single edge notch bending) tests and their analysis showed that the resistance of the material to crack propagation in the longitudinal sample was about 50% greater than that in the transverse sample. SEM analysis of the fractures showed that the state of the intermetallic particles in the fracture mechanics testing and the fracture mechanism differed from the one in the Charpy fractures.
Keywords: Al-alloy EN AW-5454, characterisation, microstructure, properties
Published in DKUM: 02.12.2024; Views: 0; Downloads: 14
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9. Hybrid nanostructures of ▫$Fe_3O_4$▫ and Au prepared via coprecipitation and ultrasonic spray pyrolysisLan Kresnik, Peter Majerič, Darja Feizpour, Klementina Pušnik Črešnar, Rebeka Rudolf, 2024, original scientific article Abstract: The coupled processes of coprecipitation and ultrasonic spray pyrolysis (USP) were used to synthesize Fe3O4-Au hybrid nanostructures. The first coprecipitation method enabled the synthesis of Fe3O4 nanoparticles by mixing iron salts’ ions (Fe2+ and Fe3+) and ammonia as the base, and USP was used as the coating process of the Fe3O4 nanoparticles with Au. The formatted hybrid nanostructures consist of Fe3O4 nanoparticles that have Au on their surface in the form of gold nanoparticles (AuNPs). AuNPs have a crystalline structure and range in size from 10 to 200 nm. Additional characterization techniques, including ICP-OES, TEM, SEM, EDS, DLS, zeta potential, and room temperature magnetic hysteresis loops, were used to determine the chemical, physical, and magnetic properties of the Fe3O4 nanoparticles and hybrid nanostructures. It was found that USP produces separate AuNPs too (not just on the Fe3O4 surface), suggesting a bimodal formation of AuNPs. The zeta potential of the Fe3O4 nanoparticles showed poor stability (−15 mV), indicating a high tendency to aggregate, and the zeta potential of the hybrid nanostructures was also very low (≅0), which, comparatively means even worse stability. The saturation magnetization of the Fe3O4 nanoparticles was 35 emu/g, which is relatively lower than that of bulk Fe3O4, while the saturation magnetization of the hybrid nanostructures was significantly lower (0.1 emu/g) compared to the Fe3O4 nanoparticles.
Keywords: magnetic NPs, gold NPs, transmission electron microscopy, magnetic properties
Published in DKUM: 29.11.2024; Views: 0; Downloads: 14
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10. Contaminants in the soil and typical crops of the Pannonian region of SloveniaŽiga Jelen, Milan Svetec, Peter Majerič, Stanko Kapun, Lara Resman, Tatjana Čeh, Granit Hajra, Rebeka Rudolf, 2024, original scientific article Abstract: Soil contamination and the uptake of pollutants by food crops are widespread issues that vary greatly by region and are influenced by the mineral composition of the soil and local human activities. The Pannonian region, where agriculture has played a key role since Roman times, has been particularly impacted by the long-standing agricultural and industrial practices. While soil contamination with heavy metals is monitored by the Slovenian government, microplastic contamination and the uptake of pollutants into food crops have yet to become a regular component of monitoring efforts. In this study, we conducted a preliminary investigation into soil and crop contamination across the Pannonian region, focusing on identifying harmful contaminants and their potential uptake into food crops. Both soil and crop samples were analyzed for the presence of heavy metals with proven methods such as atomic absorption spectrometry (FASS), graphite furnace atomic absorption spectrometry (GF-AAS), atomic fluorescence spectrometry (AFS), and inductively coupled plasma–mass spectrometry (ICP-MS). Energy-dispersive X-ray spectroscopy (EDS) was found to be a potentially faster method of obtaining data on soil composition. Special attention was also given to the potential presence of microplastics in the region’s soils.
Keywords: soil contamination, Pannonia, soil, food crops, heavy metals, microplastics
Published in DKUM: 28.11.2024; Views: 0; Downloads: 7
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