1. Vakuumsko litje stelitne zlitine : magistrsko deloKatja Križovnik, 2025, master's thesis Abstract: Magistrsko delo obravnava razvoj postopka izdelave stelitne zlitine v laboratorijskem okolju, ki se uporablja v zobni protetiki za kovinska ogrodja zobnih protez. Predstavljeni so postopki vakuumskega indukcijskega litja in termo-mehanske obdelave (visokotemperaturno homogenizacijsko žarjenje, mehko žarjenje in kovanje). Obrazložene so mehanske in fizikalne lastnosti ter mikrostruktura stelitnih zlitin v odvisnosti od pogojev, načina litja in termo-mehanske obdelave. Pojasnjena je prednost vakuumskega indukcijskega litja v kovinske kokile v primerjavi z litjem v enkratne peščene forme. Magistersko delo obravnava tudi okoljski vidik vakuumskega indukcijskega taljenja in ulivanje stelitnih zlitin v forme. S svetlobnim in vrstičnim elektronskim mikroskopom je bila v okviru raziskav opravljenih v tem magistrskem delu okarkterizirana mikrostruktura sletitne zlitine. Določene so bile tudi fizikalne in mehanske lastnosti te stelitne zlitine. V sklepnem delu smo dokazali, da je lahko z uporabo vakuumskega indukcijskega litja in naknadne termo-mehanske obdelave zmanjšana prisotnost livarskih napak. To so lunkerji, kristalne in blokovne izceje, razpoke, vključki, plinska in krčilna poroznost. Tako izdelamo stelitno zlitino, ki ustreza lastnostim, ki so za ta tip zlitin podane v standardu ASTM F75
Keywords: Stelitne zlitine, vakuumsko indukcijsko litje, kovinska kokila, poroznost, karbidi, mikrostruktura
Published in DKUM: 05.05.2025; Views: 0; Downloads: 7
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2. Functional coatings with ethyl cellulose-calcium carbonate alkaline nanoparticles for deacidification and mechanical reinforcement of paper artifactsMatej Bračič, Jasna Malešič, Mihael Brunčko, Doris Bračič, Alenka Ojstršek, Tea Kapun, Sašo Gyergyek, Karin Stana-Kleinschek, Tamilselvan Mohan, 2025, original scientific article Abstract: Paper artifacts susceptible to acid hydrolysis and mechanical stress require effective conservation methods to ensure their longevity. In this study, a novel approach for the deacidification of acidic paper using calcium carbonate (CaCO3) [1,2]-ethylcellulose nanoparticles (CaCO3-EC NPs) dispersed in a non-aqueous ethyl acetate solution is presented. The dispersions were carefully prepared and applied to model acidic paper samples using a dipcoating method and then analyzed for their effectiveness. Transmission electron microscopy showed the formation of agglomerates containing quadrangular alkaline nanoparticles with diameters of 40 to 100 nm and a total agglomerate size of 250 nm. Hydrodynamic analyzes indicate the presence of a swollen ethyl cellulose coating on these agglomerates, which facilitates their dispersion. The results show the effectiveness of the CaCO3-EC NPs system in neutralizing acidic components (change of paper pH from 4.3 to 7) due to the homogeneous distribution within the paper substrates, effectively arresting the degradation processes. Acid-base titration showed a linear correlation between the concentration of alkaline nanoparticles and the alkaline reserve, emphasizing the role of ethylcellulose in facilitating particle transport within the paper matrix. In addition, ethylcellulose was found to improve the mechanical properties of the treated paper, as demonstrated by the standard mechanical tests. Importantly, the optical properties remained unchanged after treatment, as no adverse changes in color were observed. These results underline the effectiveness of the developed deacidification dispersions for the treatment of acidic paper and potentially other cellulose-based cultural heritage documents prone to acidic degradation. This approach offers promising implications for preserving and restoring valuable historical materials.
Keywords: ethylcellulose, calcium carbonate, functional coating, deacidification, strengthening, cultural heritage
Published in DKUM: 20.03.2025; Views: 0; Downloads: 1
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3. Oxidation behaviour of microstructurally highly metastable Ag-La alloyAndraž Jug, Mihael Brunčko, Rebeka Rudolf, Ivan Anžel, 2022, original scientific article Abstract: 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.
Keywords: Ag-La alloy, rapid solidification, metastable microstructure, internal oxidation, characterisation, formation mechanism
Published in DKUM: 20.03.2025; Views: 0; Downloads: 1
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4. Sodobni inženirski materialiIvan Anžel, Franc Zupanič, Mihael Brunčko, 2025, other educational material Abstract: Skripta, Sodobni inženirski materiali je kot temeljno študijsko gradivo namenjeno pervenstveno študentom 2. stopnje študijskih programov Strojništva, Gospodarskega inženirstva, Mehatronike in študentom Inženirsko oblikovanja izdelkov. Skripta je sestavljena iz treh poglavij: (i) Zgradba in izbira inženirskih materialov; (ii) Lastnosti inženirskih materialov; (iii) Primeri sodobnih inženirskih materialov. V prvem poglavju je obravnavana zgradba kovinskih, keramičnih, polimernih in kompozitnih materialov ter predstavljeni so kriteriji, ki omogočajo inženirjem glede na želeno kombinacijo lastnosti materialov, njihovo ustrezno izbiro za določeno aplikacijo. Drugo poglavje obravnava lastnosti sodobnih inženirskih materialov s poudarkom na poglobljenem študiju razlage korelacij med zgradbo, mikrostrukturo in lastnostmi. V zadnjem najobsežnejšem poglavju so predstavljeni izbrani primeri sodobnih inženirskih materialov, katerih uporaba e v industrijski praksi dandanes zelo aktualna. Če naštejemo samo najbolj zanimive: disperzijsko utrjeni materiali, spominske zlitine, konstrukcijska keramika, materiali za shranjevanje vodika, hitrostrjeni kovinski materiali, sodobne aluminijeve zlitine, biopolimeri in še mnogi drugi.
Keywords: sodobni inženirski materiali, zgradba, izbira materialov, mikrostruktura, lastnosti
Published in DKUM: 27.02.2025; Views: 0; Downloads: 752
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5. Comparative analysis of a 3D printed polymer bonded magnet composed of a TPU-PA12 matrix and Nd-Fe-B atomised powder and melt spun flakes respectivelyGranit Hajra, Mihael Brunčko, Leo Gusel, Ivan Anžel, 2025, original scientific article Abstract: The present study reports the development of new polymer bonded magnet containing a Thermoplastic Polyurethane (TPU) – Nylon (PA12) blend as the matrix material and Nd-Fe-B magnetic particles. Two composite materials were explored: one using Nd-Fe-B atomised spherical powder (ASP) and another incorporating Nd-Fe-B melt-spun flakes (MSF). The filaments were formulated by blending TPU, PA12, and one of selected type of Nd-Fe-B particles using a mixing device. The ASP and the MSF were integrated into the matrix via a precise compounding process and 3D printing was used to produce the testing specimens. The preliminary findings indicate that both formulations exhibited promising magnetic properties while maintaining the mechanical characteristics of TPU and PA12. The atomised spherical powder formulation demonstrated worse magnetic behaviour compared to the melt-spun flake formulation. ASP particles enable better fluidity of the composite material during 3D printing. However, the close-packed arrangement of these particles is the cause of much higher porosity and consequently the poorer mechanical and magnetic properties. Optimization of the processing parameters showed significant influence on the final magnetic performance and structural integrity of the printed specimens.
Keywords: bonded magnets, Nd-Fe-B melt spun flakes, Nd-Fe-B atomised powders, material extrusion, additive manufacturing, fused specimen fabrication
Published in DKUM: 08.01.2025; Views: 0; Downloads: 9
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6. Predelava odpadnih zaščitnih kirurških mask v nov funkcionalen polimerni material : doktorska disertacijaAlen Erjavec, 2024, doctoral dissertation Abstract: Proizvodnja osebne varovalne opreme (OVO) v zadnjih letih izredno hitro narašča. K tej rasti je zagotovo prispevala pandemija bolezni COVID-19, ki pa ni edini razlog za izredno hitro rast tega sektorja. Po podatkih številnih analitičnih hiš bo trg OVO do leta 2028 imel več kot 60 % rast v primerjavi z letom 2020. Z večanjem proizvodnje OVO, pa se večajo tudi količine tega tipa odpadka in s tem pritisk na prevzemnike odpadkov. Glede na to, da gre pri zaščitnih kirurških maskah (ZKM), za enega najbolj razširjenih kosov OVO, ki ima izredno kratek čas uporabe in je njegova življenjska pot izredno linearno naravnana, so v tej doktorski disertaciji bili analizirani vplivi tega kosa OVO na okolje in predstavljene možnosti recikliranja tega materiala v večvrednostne materiale. Opravljena je bila raziskava rokovanja Slovencev z ZKM v kateri je bilo ugotovljeno, da je v prvem letu pandemije v Sloveniji bilo uporabljenih več kot 344 milijonov kosov ZKM. Prav tako je bila opravljena ocena odpadka in ocena vpliva ZKM na okolje, kadar so te nepravilno odložene. Dokazano je bilo, da so materiali zastopani v ZKM izredno primerni za postopke mehanskega recikliranja. Z namenom zagotavljanja večvrednosti končnega reciklata, so reciklatu ZKM bila dodana naravna polnila. Izbrana so bila polnila na osnovi celuloze in hitozana, saj gre za najbolj razširjena naravna polimera. Med polnili na osnovi celuloze so bili uporabljeni celulozni nanokristali, celulozne nanofibrile in kvaternizirane celulozne nanofibrile, med tem ko sta med hitozani bila uporabljena hitozan z nizko molekulsko maso in kvaterniziran hitozan. Večina polnil, je izkazala pozitiven vpliv na mehanske lastnosti reciklata, saj so nekatera povečala elastičnost reciklata tudi do 100%. Izvedene so bile številne analize površine. Te analize so med drugim pokazale, da prisotnost vseh polnil izkazuje dvig hidrofobnosti materiala, obe kvaternizirani polnili, pa v prisotnosti več kot 10 % izkazujeta tudi zelo dobro antibakterijsko delovanje reciklata, na gram + bakterije Staphylococcus aureus.
Keywords: zaščitne kirurške maske, mehansko recikliranje, večvrednostno recikliranje, naravna polnila, polimerni kompozit
Published in DKUM: 29.11.2024; Views: 0; Downloads: 58
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7. Advance analysis of the obtained recycled materials from used disposable surgical masksAlen Erjavec, Julija Volmajer Valh, Silvo Hribernik, Tjaša Kraševac Glaser, Lidija Fras Zemljič, Tomaž Vuherer, Branko Neral, Mihael Brunčko, 2024, original scientific article Abstract: The production of personal protective equipment (PPE) has increased dramatically in recent years, not only because of the pandemic, but also because of stricter legislation in the field of Employee Protection. The increasing use of PPE, including disposable surgical masks (DSMs), is putting additional pressure on waste collectors. For this reason, it is necessary to find high-quality solutions for this type of waste. Mechanical recycling is still the most common type of recycling, but the recyclates are often classified as low-grade materials. For this reason, a detailed analysis of the recyclates is necessary. These data will help us to improve the properties and find the right end application that will increase the value of the materials. This work represents an extended analysis of the recyclates obtained from DSMs, manufactured from different polymers. Using surface and morphology tests, we have gained insights into the distribution of different polymers in polymer blends and their effects on mechanical and surface properties. It was found that the addition of ear loop material to the PP melt makes the material tougher. In the polymer blends obtained, PP and PA 6 form the surface (affects surface properties), while PU and PET are distributed mainly inside the injection-molded samples.
Keywords: mechanical recycling, disposable surgical mask, morphology, surface properties, mechanical properties, nonwoven materials, PPE
Published in DKUM: 09.04.2024; Views: 232; Downloads: 22
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8. Determination of shear bond strength between PEEK composites and veneering composites for the production of dental restorationsAnamarija Kuchler, Klementina Pušnik Črešnar, Iztok Švab, Tomaž Vuherer, Majda Žigon, Mihael Brunčko, 2023, original scientific article Abstract: We studied the shear bond strength (SBS) of two PEEK composites (BioHPP, BioHPP plus) with three veneering composites: Visio.lign, SR Nexco and VITA VM LC, depending on the surface treatment: untreated, sandblasted with 110 μm Al2O3, sandblasted and cleaned ultrasonically in 80% ethanol, with or without adhesive Visio.link, with applied Visio.link and MKZ primer. For the BioHPP plus, differential scanning calorimetry (DSC) revealed a slightly lower glass transition temperature (Tg 150.4 ± 0.4 °C) and higher melting temperature (Tm 339.4 ± 0.6 °C) than those of BioHPP (Tg 151.3 ± 1.3 °C, Tm 338.7 ± 0.2 °C). The dynamical mechanical analysis (DMA) revealed a slightly higher storage modulus of BioHPP (E’ 4.258 ± 0.093 GPa) than of BioHPP plus (E′ 4.193 ± 0.09 GPa). The roughness was the highest for the untreated BioHPP plus, and the lowest for the polished BioHPP. The highest hydrophobicity was achieved on the sandblasted BioHPP plus, whereas the highest hydrophilicity was found on the untreated BioHPP. The highest SBSs were determined for BioHPP and Visio.lign, adhesive Visio.link (26.31 ± 4.17 MPa) or MKZ primer (25.59 ± 3.17 MPa), with VITA VM LC, MKZ primer and Visio.link (25.51 ± 1.94 MPa), and ultrasonically cleaned, with Visio.link (26.28 ± 2.94 MPa). For BioHPP plus, the highest SBS was determined for a sandblasted surface, cleaned ultrasonically, with the SR Nexco and Visio.link (23.39 ± 2.80 MPa).
Keywords: BioHPP, CAD/CAM milling, BioHPP plus, pressing, veneering composites, roughness, wettability, shear bond strength
Published in DKUM: 05.04.2024; Views: 213; Downloads: 21
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9. Evaluation of the impact and fracture toughness of a nanostructured bainitic steel with low retained austenite contentMihael Brunčko, Peter Kirbiš, Ivan Anžel, Leo Gusel, Darja Feizpour, Tomaž Irgolič, Tomaž Vuherer, 2023, original scientific article Abstract: The impact and fracture toughness of a nanostructured, kinetically activated bainitic steel was determined using Standard methods. Prior to testing, the steel was quenched in oil and aged naturally for a period of 10 days in order to obtain a fully bainitic microstructure with a retained austenite content below 1%, resulting in a high hardness of 62HRC. The high hardness originated from the very fine microstructure of bainitic ferrite plates formed at low temperatures. It was determined that the impact toughness of the steel in the fully aged condition improved remarkably, whereas the fracture toughness was in line with expectations based on the extrapolated data available in the literature. This suggests that a very fine microstructure is most beneficial to rapid loading conditions, whereas material flaws such as coarse nitrides and non-metallic inclusions are the major limitation for obtaining a high fracture toughness.
Keywords: evaluation of fracture toughness, impact toughness, nanostructured bainite, natural aging, low retained austenite content, kinetically activated bainite KAB
Published in DKUM: 16.02.2024; Views: 390; Downloads: 29
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10. Mehanizem hitre tvorbe bainita pri nizkih temperaturah : doktorska disertacijaPeter Kirbiš, 2022, doctoral dissertation Abstract: V okviru doktorske disertacije je bil razvit nov postopek hitre tvorbe bainita v jeklih ter posledično nova skupina bainitnih jekel, ki imajo izjemno hitro kinetiko tvorbe bainita pri nizkih temperaturah, običajno pod 250°C. Za ta jekla je značilen razvoj izjemno fine bainitne mikrostrukture med kontinuirnim ohlajanjem/kaljenjem iz temperature avstenitizacije, ne da bi pri tem potrebovali izotermne toplotne obdelave. Udarna žilavost in druge mehanske lastnosti ostajajo v skladu z najpogostejšimi zahtevami glede žilavosti in standardnimi specifikacijami, hkrati pa ohranjajo zadostno prekaljivost za zagotovitev homogenih lastnosti znotraj velikih presekov. Ta jekla imajo visoko trdoto do 65HRC in majhno geometrijsko popačenje oz. distorzijo med toplotno obdelavo.
Zaradi teh lastnosti so novo razvita jekla še posebej primerna za izdelavo orodij za delo v hladnem, nožev, balistične zaščite ter strojnih delov visoke trdnosti.
Ključna značilnost teh jekel je tvorba bainitnih nukleusov pri visoki temperaturi in hitra rast bainitnega ferita pri nizki temperaturi. To je v nasprotju z običajnimi oz. splošno poznanimi jekli in železovimi zlitinami, znotraj katerih se ta dva koraka izvajata sočasno. Metoda, s katero smo to dosegli, se je poimenovala kinetična aktivacija bainita -KAB in skupine zlitin KAB jekla.
Keywords: Jeklo, Bainit v jeklih, nanostrukturni bainit, mehanizmi utrjanja, kinetika tvorbe bainita
Published in DKUM: 08.06.2023; Views: 581; Downloads: 71
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