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Povzetek: 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.
Ključne besede: polistiren, kinetika površinske funkcionalizacije, OH radikali, vpliv doze radikalov, časovni razvoj, polystyrene, surface functionalisation kinetics, OH radicals
Objavljeno v DiRROS: 09.11.2023; Ogledov: 85; Prenosov: 41
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Povzetek: In this paper, the effects of the sintering temperature on the pore evolution of the belite-sulfoaluminate cement clinker were evaluated. Belite-sulfoaluminate cement clinker with a targeted composition of 65 w/% b-belite, 20 w/% calcium sulfoaluminate and 10 w/% ferrite was sintered at three different temperatures: 1200 °C, 1250 °C and 1300 °C. To quantitatively evaluate the pore evolution during sintering, a 3D microstructure reconstruction by micro-CT was used. From the data, the pore volume frac- tion and pore number were extracted and compared, and the pore size distribution with the sintering temperature was obtained as well. Additionally, the pore shape and distribution were displayed in 3D based on actual microstructure data. Clinker samples were also characterized by Hg-intrusion porosimetry and gas sorption. The changes in the pore evolution occurred to a larger extent when sintering at 1300 °C. Apart from a significant porosity decrease, pore coarsening was evident at this temperature, reducing their connectivity and shrinkage of the clinker. Simultaneously, the bulk and apparent densities increased with the temperature due to densification, while the BET surface area of the studied clinkers decreased, indicating the rounding of pores and particle coalescence with an increasing grain growth.
Ključne besede: klinker, belit-sulfoaluminat, razvoj por, sintranje
Objavljeno v DiRROS: 04.08.2023; Ogledov: 169; Prenosov: 79
Celotno besedilo (2,27 MB)
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Ključne besede: gozdarstvo, lesna industrija, kmetijstvo, lovstvo, ribištvo, hudourniki, razvoj gozdarstva, premogovništvo, Slovenija, zborniki
Objavljeno v DiRROS: 12.01.2023; Ogledov: 451; Prenosov: 208
Celotno besedilo (142,40 MB)

Ključne besede: onkologija, zgodovina, razvoj medicine
Objavljeno v DiRROS: 23.12.2022; Ogledov: 257; Prenosov: 70
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Povzetek: Predšolski otroci preživijo velik del vsakdanjika v vrtcih, zato je treba umestiti obisk gozda, kot najobsežnejšega naravnega okolja v Sloveniji, v programe predšolskega varstva otrok. Na podlagi anket vzgojiteljev javnih vrtcev v Sloveniji (N = 133) smo analizirali navade, namene, ovire in skrbi pri obiskovanju gozda. V največji meri sta pogostost in dolžina obiska gozda odvisni od njegove oddaljenosti. Navade obiska gozda med gozdnimi vrtci, vključeni mi v Mrežo gozdnih vrtcev, ki jo organizira Inštitut za gozdno pedagogiko, se večinoma ne razlikujejo značilno od splošnih javnih vrtcev. Najpomembnejša razlika med njimi je pogostejši obisk v slabšem vremenu in sam namen obiska gozda. Glavne skrbi pri obisku gozda so klopi, strah pred poškodbami in neprimerna oprema otrok. Za manj pogostejši obisk gozda vzgojitelji navajajo med drugim tudi druge vzgojne prioritete vrtcev in premalo podpore s strani vodstva ter staršev, kar nakazuje potrebo po strateški promociji, izobraževanju in implementaciji preživljanja časa v gozdu v okviru predšolske vzgoje.
Ključne besede: gozdni vrtci, gozdna pedagogika, obisk gozda, razvoj otrok, klopi, predšolska vzgoja, okoljska vzgoja, naravna učna okolja
Objavljeno v DiRROS: 01.12.2021; Ogledov: 3079; Prenosov: 1846
Celotno besedilo (950,31 KB)
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