1. Influence of isothermal annealing in the 600 to 750 °C range on the degradation of SAF 2205 duplex stainless steelJaka Burja, Borut Žužek, Barbara Šetina, 2024, original scientific article Abstract: We studied the effect of isothermal annealing (600–750 °C, 1 to 1000 min) on the microstructure
and mechanical properties of SAF 2205 duplex stainless steel. Impact toughness was found
to be significantly more affected than hardness by annealing. Annealing at 750 °C for 1000 min
resulted in a more than 90% decrease in impact toughness, while hardness only increased by 25%.
Tensile strength increased up to 100 MPa, but elongation decreased by more than 50% under the
same conditions. Sigma phase formation was minimal at lower temperatures (650 °C and below)
but increased significantly at higher temperatures. At 750 °C and 1000 min of annealing, the ferrite
content dropped from 50% to 16%. These findings suggest that annealing temperature and time need
to be carefully controlled to avoid a reduction in impact toughness and ductility caused by sigma
phase precipitation. The harmful effect of sigma phase precipitation on mechanical properties was
directly shown.
Keywords: duplex stainless steel, sigma phase, precipitation kinetics, mechanical properties, isothermal annealing
Published in DiRROS: 24.07.2024; Views: 225; Downloads: 180
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2. Adsorption efficiency of cadmium (II) by different alkali-activated materialsNataša Mladenović Nikolić, Ljiljana Kljajević, Snežana B. Nenadović, Jelena Potočnik, Sanja Knežević, Sabina Dolenec, Katarina Trivunac, 2024, original scientific article Abstract: The objective of this study was to demonstrate the potential utilization of fly ash (FA), wood ash (WA), and metakaolin (MK) in developing new alkali-activated materials (AAMs) for the removal of cadmium ions from waste water. The synthesis of AAMs involved the dissolution of solid precursors, FA, WA, and MK, by a liquid activator (Na2SiO3 and NaOH). In concentrated solutions of the activator, the formation of an aluminosilicate gel structure occurred. DRIFT spectroscopy of the AAMs indicated main vibration bands between 1036 cm−1 and 996 cm−1, corresponding to Si-O-Si/Si-O-Al bands. Shifting vibration bands were seen at 1028 cm−1 to 1021 cm−1, indicating that the Si-O-Si/Si-O-Al bond is elongating, and the bond angle is decreasing. Based on the X-ray diffraction results, alkali-activated samples consist of an amorphous phase and residual mineral phases. The characteristic “hump” of an amorphous phase in the range from 20 to 40◦ 2θ was observed in FA and in all AWAFA samples. By the XRD patterns of the AAMs obtained by the activation of a solid three-component system, a new crystalline phase, gehlenite, was identified. The efficiency of AAMs in removing cadmium ions from aqueous solutions was tested under various conditions. The highest values of adsorption capacity, 64.76 mg/g (AWAFA6), 67.02 mg/g (AWAFAMK6), and 72.84 mg/gmg/g (AWAMK6), were obtained for materials activated with a 6 M NaOH solution in the alkali activator. The Langmuir adsorption isotherm and pseudo-second kinetic order provided the best fit for all investigated AAMs.
Keywords: fly ash, metakaolin, wood ash, adsorption kinetics, cadmium (II)
Published in DiRROS: 23.05.2024; Views: 355; Downloads: 285
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3. High-temperature oxidation of boiler steels at 650 °CJaka Burja, Barbara Šetina, Borut Žužek, Tilen Balaško, 2023, original scientific article Abstract: This study presents a comprehensive investigation of the formation, composition and
behaviour of oxide layers during the high-temperature oxidation of four different steel alloys (16Mo3,
13Cr, T24 and P91) at a uniform temperature of 650 °C. The study is aimed at assessing the oxidation
damage due to short-term overheating. The research combines CALPHAD (CALculation of PHAse
Diagrams) calculations, thermogravimetric analysis (TGA) and advanced microscopy techniques, in-
cluding scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), to elucidate
the complex mechanisms controlling oxidation kinetics and oxide layer development. CALPHAD
calculations were used to determine the thermodynamically stable phases for each steel type at 650
◦C and different oxygen activities. The results showed different phase compositions, highlighting
the importance of the chromium content in steel for the formation of oxide layers. The different
oxidation kinetics and oxide layer compositions are presented and associated with the increased risk
of material degradation due to overheating. These results have significant implications for industrial
applications, mainly the susceptibility to oxidation of low-alloyed steels like 16Mo3 and 13 Cr and
contribute to a deeper understanding of oxidation processes in steels.
Keywords: high-temperature oxidation, thermogravimetric analysis, kinetics, CALPHAD, boiler steels, SEM, EBSD
Published in DiRROS: 26.01.2024; Views: 548; Downloads: 271
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4. Evolution of surface functional groups and aromatic ring degradation upon treatment of polystyrene with hydroxyl radicalsAlenka Vesel, Rok Zaplotnik, Gregor Primc, Miran Mozetič, 2023, original scientific article Abstract: The surface properties of hydrocarbon polymers are inadequate for numerous applications. Hence, they require alteration via functionalisation with desired functional groups. Hydroxyl groups are often preferred, since they enable appropriate polarity for the irreversible grafting of desired molecules. In this study, the surface kinetics resulting from the treatment of polystyrene with hydroxyl (OH) radicals from the gas phase was fundamentally investigated through a precisely-designed experiment. Polystyrene samples were exposed to various known fluences of OH radicals, and the evolution of surface functional groups versus the OH fluence was monitored using high-resolution X-ray photoelectron spectroscopy (XPS). The fluences of OH radicals varied between 1 × 1018 and 4 × 1023 m−2 in the process of finding a threshold fluence for the formation of specific groups. The surface concentration of carbonyl (C=O) groups could be measured using XPS at a fluence of approximately 5 × 1020 m−2. The C=O groups became measurable at a fluence of approximately 1.5 × 1021 m−2, and carboxyl (COOH)/ester groups at approximately 4 × 1021 m−2. As deduced from the XPS, a concentration of C=O groups at approximately 5 % occurred before the degradation of the aromatic ring. The formation of other oxygen-functional groups required opening of the aromatic ring. The results have been explained using a two-step process, considering available theories vis-a-vis initial stages in the functionalisation of PS with polar functional groups.
Keywords: polistiren, kinetika površinske funkcionalizacije, OH radikali, vpliv doze radikalov, časovni razvoj, polystyrene, surface functionalisation kinetics, OH radicals
Published in DiRROS: 09.11.2023; Views: 572; Downloads: 232
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5. Rotational dynamics of a protein under shear flow studied by the eckart frame formalismPetra Papež, Franci Merzel, Matej Praprotnik, 2023, original scientific article Keywords: energy, kinetics, molecules, protein structure, rotational dynamics, molecules, protein structure, rotational dynamics
Published in DiRROS: 06.09.2023; Views: 573; Downloads: 301
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7. Independent infuence of age on heart rate recovery after flywheel exercise in trained men and womenDamir Zubac, Nandu Goswami, Vladimir Ivančev, Zoran Valić, Boštjan Šimunič, 2021, original scientific article Abstract: The present study examined whether differences in the heart rate recovery following flywheel exercise cessation were associated with differences in maximal oxygen uptake (VO2 max.), age and sex in trained adults. Eleven men (age range 22-49 years, VO2 max.=43.6 +/- 7.6 mL kg min -1) and ten women (age range 20-53 years, VO2 max.=38.0 +/- 5.7 mL kg min%1) were randomly assigned to complete a squat-exercise on the flywheel ergometer set at three different moments of inertia, while their cardiovascular responses were continuously monitored. During the flywheel exercise the mean arterial pressure rose by ~35 to 40% (p=.001), and the increment was more robust in men than women. The cardiac index was two-fold greater across both sexes compared to the baseline (p=.001), while the rise in heart rate (~144 bpm) was more pronounced in women to compensate for their load-dependent stroke index decline (p=.001). The load-independent time-course changes in heart rate recovery markers were comparable between the sexes. When these indicators were pooled, a stepwise regression revealed age as the only relevant predictor of both fast and slow components of the heart rate recovery (~30 of the shared variance explained, p=.014). The present data suggest that the heart rate recovery declines with age, irrespective of sex, or well-preserved cardiorespiratory fitness in moderately-trained adults.
Keywords: training, exercise, Yo-Yo exercise, flywheel, heart rate variability, total peripheral conductance, oxygen uptake kinetics
Published in DiRROS: 11.06.2021; Views: 1242; Downloads: 1149
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8. A review of methane activation reactions by halogenation : catalysis, mechanism, kinetics, modeling, and reactorsDavid Bajec, Matic Grom, Damjan Lašič Jurković, Andrii Kostyniuk, Matej Huš, Miha Grilc, Blaž Likozar, Andrej Pohar, 2020, review article Keywords: methane, halogenation, catalysis, density functional theory, kinetics, mechanism
Published in DiRROS: 16.04.2020; Views: 2471; Downloads: 1539
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