1841. Particle size manipulation as an influential parameter in the development of mechanical properties in electric arc furnace slag-based AAMKatja Traven, Mark Češnovar, Vilma Ducman, 2019, original scientific article Abstract: Alkali-activated materials (AAM) have gained recognition as a promising alternative to technical ceramic and building materials owing to the lower energy demands for production and the potential to use slag as a precursor. In the present study, five sets of slag-based AAM pastes were prepared with different particle sizes (fractions d < 63, 63 < d < 90, and 90 < d < 125 μm in different mass ratios) under the same curing regime and using a fixed precursor to activator (water) mass ratio. Precursors and the hardened AAM are evaluated using BET, XRD, XRF, SEM, FTIR, reactivity of precursors by leaching, and mercury intrusion porosimetry (MIP). Chemical analysis indicated only marginal differences among the different-sized fractions of input materials, whereas the BET surface area and reactivity among the precursors differed significantly-smaller particles had the largest surface area, and thus, higher reactivity. The mineralogical differences between the precursors and hardened AAM were negligible. The results revealed that compressive strength was significantly influenced by particle size, i.e., a threefold increase in strength when the particle size was halved. Microstructural evaluation using MIP confirmed that the porosity was the lowest in AAM with the smallest particle size. The low porosity and high reactivity of the fine fractions led to the highest compressive strength, confirming that manipulation of particle size can significantly influence the mechanical properties.
Keywords: alkalijsko aktivirani materiali, žlindra iz obločne peči, mehanska aktivacija, mehanske lastnosti, poroznost, alkali-activated materials (AAM), electric arc furnace steel slag, mechanical activation, mechanical properties, porosity
Published in DiRROS: 22.11.2023; Views: 420; Downloads: 175
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1842. The role of relative humidity on crystallization of calcium carbonate from calcium acetoacetate precursorAndreja Pondelak, Francesca Rosi, Celeste Maurich, Costanza Miliani, Srečo D. Škapin, Andrijana Sever Škapin, 2019, original scientific article Abstract: Calcium acetoacetate, Ca(OAcAc)2, was exposed 7, 30 and 365 days to different values of relative humidity (33%, 48%, 75% and 96%) at 40 °C in order to study its transformation to CaCO3. The resulting Ca(OAcAc)2 decomposition and the time dependence of the phase transformations were monitored and critically evaluated by Fourier transform infrared spectroscopy, field emission scanning electron microscopy and X-ray powder diffraction. The impact of relative humidity on CaCO3 polymorph formation was thoroughly assessed. In all of the conditions used and for all ageing periods, the formed crystal structure is found to be vaterite. At the lowest relative humidity (33%), the amorphous CaCO3 remains more or less almost untransformed even after one year of exposure. It is proposed that the reason for the stability of amorphous CaCO3 is due to the limited amount of physisorbed water on the surfaces of the particles, which is considered the driving force for its transformation. However, the carbonation process is faster in the case of the highest humidity (96%). The findings are not only important for better solutions in the field of cultural heritage, but also shed new light on the fundamental mechanism of CaCO3 crystallization.
Keywords: calcium acetoacetate, relative humidity, carbonation, amorphous carbonate, vaterite, mechanism
Published in DiRROS: 22.11.2023; Views: 505; Downloads: 207
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1843. Epidemiologija raka dojk in presejanjeMaja Primic-Žakelj, Vera Pompe-Kirn, 1998, review article Abstract: Rak dojk je v Sloveniji najpogostejši rak pri ženskah. Leta 1995 je za njim zbolelo 784 žensk (76,7/100.000), pričakujemo pa , da se bo v prihodnjih desetih letih incidenca še večala. Delež rakov, odkritih v omejenem stadiju se povečuje; leta 1995 je bilo takih 44% vseh primerov. Čeprav se je preživetjolnic izboljšalo (67-odstotno 5-letno relativno preživetje bolnic z rakritim v letih 1988-92), ostaja rak dojk pri ženskah na prvem mestu med vzroki smrti zaradi raka. Med dikazane nevarnostne dejavnike sodijo poleg spola in starosti še poprejšnji rak dojk , nekatere benigne bolezni dojk, družinska obremenitev, ionizirajoče sevanje, nekateri reproduktivni dejavniki in debelost. V primarni preventivi zaenkrat ni posebnih priporočil, so le splošna: vzdrževanje normalne telesne teže, pravilna prehrana, telesna dejavnost in zmernost pri pitju alkoholnih pijač. Ocenjujejo, da presejanje, redno mamografsko pregledovannje žensk po 50. letu starosti z dodatnim kliničnim pregledom ali brez njega, zmanjša umrljivost za rakom dojk med pregledanimi za okrog 30%. Populacijsko presejanje priporočajo večinoma po 50.letu starosti. Problem raka dojk je mogoče reševati celostno, s primarno preventivo, zgodnjim odkrivanjem in dostopnostjo do užinkovitega zdravljenja, predvsem pa z vlaganjem sredstev tja, kjer je razmerje med stroški in koristjonajugodnejše.
Published in DiRROS: 21.11.2023; Views: 323; Downloads: 126
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1846. Stanje slovenskih gozdov : poročilo o rezultatih nacionalne gozdne inventure 2022Mitja Skudnik, Luka Krajnc, Gal Kušar, Anže Martin Pintar, 2023, treatise, preliminary study, study Keywords: monitoring, nacionalna gozdna inventura, odmrla lesna biomasa, temeljnica, površina gozda, lesna zaloga, vzorčne ploskve, poročila
Published in DiRROS: 21.11.2023; Views: 451; Downloads: 0 |
1847. Discretionary capitalization of development expendituresPrimož Petek, Mateja Jerman, Sandra Janković, 2023, original scientific article Abstract: The paper examines the discretionary nature of (non)capitalizing development expenditures in financial statements. A review of the literature shows that companies may have different motives and factors for (non)capitalizing development expenditures. This study analyzes a sample of 547 companies from the information and communications technology (ICT) sector listed on the Frankfurt Stock Exchange in the period 2009-2018. The ICT sector was selected because it represents an industry with high R&D (research and development) expenditures. The results of the probit regression analysis made on 3,718 observations show that the capitalization of development expenditures is significantly positively related to the size and return on assets of the firm and negatively related to the age of the firm. Larger and more profitable firms are more likely to capitalize development expenditures, while older firms are less likely to capitalize development expenditures. Our results contribute to the literature in the field of positive accounting theory providing additional insights into factors associated with decisions to (non)capitalize development expenditures.
Keywords: capitalization, development expenditures, discretion, incentives, intangible assets
Published in DiRROS: 21.11.2023; Views: 358; Downloads: 227
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1849. Efficiency of novel photocatalytic coating and consolidants for protection of valuable mineral substratesAndreja Pondelak, Sabina Dolenec, Jonjaua Ranogajec, Luka Škrlep, Snezana B. Vučetić, Vilma Ducman, Andrijana Sever Škapin, 2019, original scientific article Abstract: In the process of protection and consolidation of valuable materials, the efficiency is the crucial property that needs to be considered. TiO2/ZnAl layered double hydroxide (LDH) coating and silicate- and carbonate-based consolidants were synthesized and proposed to be used for protection and consolidation of four porous mineral substrates: brick, stone, render and mortar. The photocatalytic efficiency of TiO2/ZnAl LDH coating, as well as consolidation efficiency of two consolidants, both applied on model substrates, were studied. The photocatalytic coating showed significant activity and performed well after the durability tests involving rinsing and freezing/thawing procedures. After treatment with both consolidants, a serious enhancement of consolidation of the used substrates was found. On the other hand, the application of TiO2/ZnAl LDH, as well as consolidants, caused negligible changes in the water vapour permeability values and in appearance of the porous mineral substrates, indicating a high level of compatibility.
Keywords: photocatalytic coating, consolidant, protection, conservation, porous substrate, cultural heritage
Published in DiRROS: 21.11.2023; Views: 366; Downloads: 224
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1850. Activation and repassivation of stainless steels in artificial brines as a function of pHEmir Mujanović, Bojan Zajec, Tadeja Kosec, Andraž Legat, Stefan Hönig, Gerald Zehethofer, Gregor Mori, 2019, original scientific article Abstract: When planning oil wells with stainless steel components, two possible reasons for depassivation have to be considered-chemical depassivation caused by acidizing jobs and mechanical depassivation caused by various tools and hard particles. The study explores conditions causing chemical activation of investigated steels and circumstances under which repassivation occurs after activation. The main focus of the study is to determine, how quickly various steels can repassivate under different conditions and to find pH values where repassivation will occur after depassivation. The investigated steels were ferritic (martensitic or bainitic) in the cases of 13Cr, 13Cr6Ni2Mo, and 17Cr4Ni2Mo, austenitic in the case of 17Cr12Ni2Mo, and duplex (austenitic and ferritic) in the case of 22Cr5Ni3Mo. Potentiodynamic experiments were employed to obtain electrochemical properties of investigated steels, followed by immersion tests to find ultimate conditions, where the steels still retain their passivity. After obtaining this information, scratch tests were performed to study the repassivation kinetics. It was found that repassivation times are similar for nearly all investigated steels independent of their chemical composition and microstructure.
Keywords: stainless steels, activation, repassivation
Published in DiRROS: 21.11.2023; Views: 352; Downloads: 161
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