1. Why are the Early Gothic murals in St. Jacob’s Church in Ormož, Slovenia, almost entirely black?Anabelle Križnar, Katja Kavkler, Sabina Dolenec, 2024, original scientific article Abstract: In St. Jacob’s parish church in Ormož, Slovenia, mural paintings from around 1350–1370 are partially conserved in the northeastern corner of the main nave. They are almost completely black, indicating a large-scale pigment degradation. They were studied as a part of a larger research project aiming to identify materials applied and their possible degradation. First, they were studied in situ, and next, extracted samples of plaster, pigments, and colour layers were analysed by optical microscopy, Raman spectroscopy, FTIR spectroscopy, SEM-EDS, and XRD. Haematite, green earth, malachite, azurite, and tenorite were identified, showing that azurite and perhaps also malachite degraded to black tenorite, probably due to their fine grinding and their application directly on the fresh plaster. The plaster is made with small and large amounts of aggregate with mostly quartz with some impurities, which makes it fragile. The original appearance of these murals was of bright blue and green colours.
Keywords: mural painting, medieval painting, Gothic art, St. Jacob's Church, Ormož, Slovenia, pigments, chemical structure, colour degradation, optical microscopy, Raman microspectroscopy, FTIR, XRD
Published in DiRROS: 17.04.2024; Views: 32; Downloads: 8
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2. Potential of green ceramics waste for alkali activated foamsBarbara Horvat, Vilma Ducman, 2019, original scientific article Abstract: The aim of the paper is to research the influence of foaming and stabilization agents in the alkali activation process of waste green ceramics for future low cost up-cycling into lightweight porous thermal insulating material. Green waste ceramics, which is used in the present article, is a green body residue (non-successful intermediate-product) in the synthesis of technical ceramics for fuses. This residue was alkali activated with Na-water glass and NaOH in theoretically determined ratio based on data from X-ray fluorescence (XRF) and X-ray powder diffraction (XRD) that was set to maximise mechanical properties and to avoid efflorescence. Prepared mixtures were compared to alkali activated material prepared in theoretically less favourable ratios, and tested on the strength and density. Selected mixtures were further foamed with different foaming agents, that are Na-perborate (s), H2O2 (l), and Al (s), and supported by a stabilization agent, i.e., Na-dodecyl sulphate. The goal of the presented work was to prepare alkali activated foam based on green ceramics with density below 1 kg/l and compressive strength above 1 MPa.
Keywords: alkali activation, foaming, SEM, XRF, XRD, mechanical strength
Published in DiRROS: 14.09.2023; Views: 254; Downloads: 129
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3. Influence of particle size on compressive strength of alkali activated refractory materialsBarbara Horvat, Vilma Ducman, 2020, original scientific article Abstract: Influence of particle size on the mechanical strength of alkali activated material from waste refractory monolithic was investigated in this study. Precursor was chemically and mineralogically analysed, separated on 4 fractions and alkali activated with Na-water glass. Alkali activated materials were thoroughly investigated under SEM and XRD to evaluate the not predicted differences in mechanical strength. Influence of curing temperature and time dependence at curing temperatures on mechanical strength were investigated in the sample prepared from a fraction that caused the highest compressive strength.
Keywords: refractory materials, alkali activation, particle size, SEM, XRF, XRD, compressive strength
Published in DiRROS: 21.08.2023; Views: 339; Downloads: 241
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4. Preparation of façade panels based on alkali-activated waste mineral wool, their characterization and durability aspectsMajda Pavlin, Barbara Horvat, Vilma Ducman, 2022, original scientific article Abstract: Mineral wool is a widely used insulation material and one of the largest components of construction and demolition waste, yet it mainly ends up in landfills. In this work, we explored the potential recycling of waste stone wool in the pilot production of alkali-activated façade panels. The current work shows mechanical properties, SEM-EDS and mercury intrusion porosimetry analyses for three different mix designs used for the preparation of façade panels. They are all composed of waste stone wool and differ in the amount of co-binders (local slag, lime, metakaolin and/or fly ash) selected by the preliminary studies. In this study, co-binders were added to increase early strength and improve the mechanical properties and freeze-thaw resistance. The mechanical properties of each were measured up to 256 days, different durability tests were executed, and, by evaluating the mechanical properties, microstructure and workability of the mortar, the most suitable mix was selected to be used for pilot production. In addition, the leaching test of the selected mixture showed no exceeded toxic trace elements and therefore got classified as non-hazardous waste after its use.
Keywords: alkali activation, waste mineral wool, SEM, XRF, XRD, mechanical strength
Published in DiRROS: 19.06.2023; Views: 306; Downloads: 133
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5. The preparation and characterization of low-temperature foams based on the alkali activation of waste stone woolMajda Pavlin, Barbara Horvat, Mark Češnovar, Vilma Ducman, 2022, original scientific article Abstract: Waste mineral wool represents a huge amount of construction and demolition waste that is still not adequately returned into the value chain but needs to be landfilled. In the present study, waste stone wool (SW) was evaluated for the preparation of alkali-activated foams. For this purpose SW was milled and sieved below 63 μm, then the activator (sodium silicate) and different amounts of foaming agent (hydrogen peroxide, H2O2), varying between 1 wt% and 3 wt%, were added to the slurry and cured in moulds at an elevated temperature (70 ◦ C) for three days. In this way, foamed, highly porous materials were obtained whose density and mechanical properties were influenced by the amount of foaming agent used. The densities obtained ranged between 1.4 and 0.5 g/cm3, with corresponding mechanical properties of between 12.6 and 1.5 MPa and total porosities in the range 37.8–78.6%, respectively. In the most porous samples with the total porosity of 78.6%, a thermal conductivity of 0.092 W/(m∙K) was confirmed. The study confirmed the suitability of waste mineral wool (in our case SW) as a precursor for alkali-activated foams with potential use in the construction sector or other industrial applications.
Keywords: alkali activation, waste mineral wool, mechanical strength, open access, alkalijska aktivacija, odpadna volna, SEM, XRF, XRD, mehanska trdnost, odprti dostop
Published in DiRROS: 19.06.2023; Views: 243; Downloads: 191
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6. Effects of Zr doping into ceria for the dry reforming of methane over ▫$Ni/CeZrO_2$▫ catalysts ein situ studies with XRD, XAFS, and AP-XPS : in situ studies with XRD, XAFS, and AP-XPSFeng Zhang, Zenghui Liu, Xiaobo Chen, Ning Rui, Luis E. Betancourt, Lili Lin, Wenqian Xu, Cheng-jun Sun, A. M. Milinda Abeykoon, José A. Rodriguez, Janvit Teržan, Kristijan Lorber, Petar Djinović, Sanjaya D. Senanayake, 2020, original scientific article Keywords: nickel, ceria, zirconia, ▫$CeZrO_2$▫ solid solution, XRD, XAFS, AP-XPS, dry reforming of methane
Published in DiRROS: 13.03.2023; Views: 468; Downloads: 324
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7. Effects of a mixed O/F ligand in the Tavorite-type LiVPO[sub]4O structureSorour Semsari Parapari, Jean-Marcel Ateba Mba, Elena Tchernychova, Gregor Mali, Iztok Arčon, Gregor Kapun, Mehmet Ali Gülgün, Robert Dominko, 2020, original scientific article Keywords: XRD, SEM, V XANES, Tavorite-type, electrochemical properties
Published in DiRROS: 25.11.2020; Views: 1579; Downloads: 873
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