Noncarnbonate mineral phases in marbles from Pohorje

Pohorski marmor je metamorfna kamnina, ki izdanja v obliki leč in manjših teles zlasti na vzhodnem in južnem delu pohorskega hribovja. Za razliko od ostalih metamorfnih kamnin na Pohorju za marmor še ne vemo natančno, pri kakšnih metamorfnih pogojih je nastajal. Delni vzrok za to je izjemna čistost pohorskih marmorjev z malo nekarbonatnimi minerali, ki pa so ključnega pomena za določitev metamorfnih pogojev v času nastajanja kamnin. Določitve teh nekarbonatnih mineralnih faz v pohorskem marmorju smo se lotili s pregledom poliranih zbruskov na optičnem mikroskopu pri polarizirani svetlobi. Bolj natančne preiskave nekarbonatnih mineralnih faz smo opravili z vrstično elektronsko mikroskopijo v kombinaciji z energijsko disperzijsko spektroskopijo rentgenskih žarkov (SEM/EDS) in z elektronsko mikrosondo v kombinaciji z valovnodolžinsko disperzijsko spektroskopijo rentgenskih žarkov (EPMA/WDS). Nekarbonatne mineralne faze, ki smo jih določili v marmorju, so: glinenci, pirokseni, amfiboli, olivini, kremen, epidot, muskovit, biotiti, flogopit, fengit, kloriti, serpentini, titanit, apatit, zoisit, cirkon, turmalini, skapolit, rutil, barit, ilmenit, hematit in pirit. Pirokseni so Ca-Mg sestave z 0,5 do 10,3 ut. % FeO in različnim deležem CaO in MgO, pri čemer smo določili predvsem različke endiopsid, diopsid, avgit in wollastonit.Glinenci so zelo različne sestave od skoraj popolnoma kalijevih glinencev s 93 mol. % ortoklazove komponente do povsem anortitovih razločkovnajdemo še plagioklaze s sestavo bytownita, labradorita, andezina in oligoklaza. Med amfiboli prevladujejo Ca amfiboli tremolit, aktinolit, edenit, fero-edenit in fero-pargasit, ki vsebujejo od 3,8 do 14,1 ut. % CaO, 4,5–24,1 ut. % MgO, 0,6–31,2 ut. % FeO ter do 0,2 ut. % MnO in do 1,5 ut. % Na2O. Od olivinov je prisoten forsterit s 85,2–97,4 mol. % forsteritove komponente. Glede na mineralno paragenezo kalcit + kremen + biotit + tremolit + forsterit + diopsid + plagioklaz ali kalcit + dolomit + kremen + biotit + tremolit + forsterit + diopsid + plagioklaz sklepamo, da so marmorji s Pohorja dosegli visoko stopnjo metamorfoze, ki sega v območje regionalne metamorfoze amfibolitnega faciesa.Pohorje marble is a metamorphic rock that forms lenses and smaller bodies and is outcropping predominantly on the eastern and southern parts of the Pohorje Mountains. Unlike for other metamorphic rocks from Pohorje, for marbles, we still do not know precisely what were the metamorphic conditions during the peak of the metamorphism. The partial reason for this is the exceptional purity of Pohorje marbles with very seldom non-carbonate minerals, which are crucial for determining metamorphic conditions at the time of rock formation. The determination of these non-carbonate mineral phases in the Pohorje marbles was carried out by examining the polished thin sections using the optical microscope under plain polarized light. More precise investigations of non-carbonate mineral phases were carried out using electron microscopy in combination with X-ray diffraction spectroscopy (SEM / EDS) and electron microprobe in combination with X-ray diffraction spectroscopy (EPMA / WDS). Recognized non-carbonate mineral phases in marbles are: feldspars, pyroxenes, amphiboles, olivines, quartz, epidot, muscite, biotites, phlogopite, fengite, chlorites, serpentines, titanite, apatite, zoisite, zircon, turmalins, scapolite, rutile, hematite and pyrite. Pyroxene are Ca-Mg pyroxenes with 0,5 do 10,3 wt % FeO and various proportions of Ca and Mg oxide, and are determined mainly as endiopside, diopside, augite, and wollastonite.The feldspars are very different in composition varying from almost pure potassium feldspar with 93 mol% of the orthoclase component to completely pure anorthite, and in addition there are plagioclases with the composition of bytownite, labradorite, andesite and oligoclase. Among the amphiboles, Ca amphibole tremolite, actinolite, edenite, ferro-edenite and ferro-pargasite are predominant, containing from 3.8 to 14.1 wt % CaO, 4.5-24.1 wt % MgO, 0.6-31.2 wt % FeO and up to 0.2 wt % MnO and up to 1.5 wt % Na2O. Forstite is present with 85.2–97.4 mol. % of forsterite component. Based on mineral paragenesis calcite + quartz + biotite + tremolite + forsterite + diopside + plagioclase or calcite + dolomite + quartz + biotite + tremolite + forsterite + diopside + plagioclase we conclude that marbles from Pohorje reached high matamorphic grade in the area of the regional metamorphism of the amphibolite facies

Oxidation of ilmenite for preparation of functional ceramics

Ilmenit se v naravi pojavlja kot akcesorni mineral v mnogih kamninah. Ker je zelo obstojen, se v procesih preperevanja pod vplivom vode in vetra kopiči v obliki težkih peskov, ki predstavljajo najpomembnejšo ekonomsko surovino za pridobivanje titana. Namen magistrske naloge je bil pokazati, da lahko naravne ilmenitne težke peske, ki so ekološko sprejemljivi ter na voljo v velikih količinah, uporabimo tudi za alternativne namene, na primer za pripravo keramike za termoelektrične aplikacije. V magistrski nalogi sem kot vhodni material uporabila ilmenitni pesek, ki ga v Cinkarni Celje uporabljajo za pridobivanje titanovega dioksida. Pesek sem najprej oksidirala pri temperaturah 600–800 °C in s tem sprožila nastanek rutilnih lamel. Peske sem sintrala v inertni atmosferi po dveh postopkih: s konvencionalnim sintranjem (na 1200 °C) ter s sintranjem v pulznem toku (SPSna 1100 °C). Na oba načina sem pripravila gosto keramiko. Prahove in sintrano keramiko sem analizirala z lasersko granulometrijo, TG, XRD, SEM/EDXS, MS, določila sem tudi gostoto sintranih vzorcev. V zadnjem koraku smo izmerili termoelektrične lastnosti sintranih vzorcev. Rezultati so pokazali, da so vzorci po sintranju sestavljeni iz matrice s sestavo psevdobrookit–feropsevdobrookit. Vzorci, ki so bili pripravljeni iz predoksidiranih prahov so vsebovali še vključke rutila. Konvencionalno sintrani vzorci so bili nekoliko bolj porozni in so imeli nižjo gostoto, kot vzorci pripravljeni po postopku SPS. Povprečna velikost zrn je pri vzorcih sintranih po SPS postopku manjša kot pri konvencionalno sintranih vzorcih. Meritve termoelektričnih lastnosti so pokazale, da imajo tako konvencionalno sintrani, kot tudi vzorci sintrani po SPS postopku nizko toplotno prevodnost, relativno visok Seebeckov koeficient ter nizko električno prevodnost, kar bi bilo potrebno izboljšati. Rezultati so pokazali, da so naravni ilmenitni peski primerni za pripravo funkcionalne keramike.Ilmenite is the most common accessory mineral in many rocks. During weathering, the primary rocks disintegrate and the ilmenite grains accumulate to heavy mineral fractions also known as heavy mineral sands. These sands today represent the main source of titanium. The aim of my master thesis was to show that natural ilmenite-rich heavy sands can also be used for advanced applications such as preparation of functional ceramics with thermoelectric properties. In my experimental work, I used ilmenite-rich sand provided by Cinkarna Celje as the starting powder. The starting (as received) powder was pre-oxidized at 600, 700 and up to 800 °C to trigger exsolution of rutile lamellae in ilmenite grains. The as-received powder and the pre-oxidized powders were sintered in an inert atmosphere using two procedures: pressureless conventional sintering (at 1200 °C) and pressure-assisted pulsed flow sintering (SPSat 1100°C). The powders were analyzed by laser granulometry, TG, XRD, SEM/EDXS and MS, we also determined absolute density of the sintered samples. In the last step, thermoelectric properties of the sintered samples were measured. The results have shown that all sintered samples consist of a matrix with the composition on the pseudobrookite–ferropseudobrookite tie-line, whereas the samples prepared from pre-oxidized powders contained rutile inclusions. The conventionally sintered samples were slightly more porous and had a lower density than the samples prepared by SPS. The average grain size was significantly smaller for the SPS sintered samples than for the conventionally sintered samples. Measurements of thermoelectric properties showed that both the conventionally sintered and SPS sintered samples have promising thermoelectric properties and show low thermal conductivity, relatively high Seebeck coefficient, but low electrical conductivity, which should be improved in the future. In my thesis, I have shown that natural ilmenite powder has great potential for the production of advanced functional ceramics

Enhanced Photocatalytic Activity of Hybrid rGO@TiO2/CN Nanocomposite for Organic Pollutant Degradation under Solar Light Irradiation

The three-component hybrid (rGO/TiO2/CN) nanocomposite was prepared in order to enhance the photocatalytic properties of anatase TiO2 nanoparticles (NPs) under solar-like irradiation. The rGO/TiO2/CN was prepared in a mixture of the reduced graphene oxide (rGO, 8 wt%), anatase TiO2 nanoparticles (NPs), and graphitic carbon nitride (g-C3N4, 16 wt%). It was self-assembled through the one-step hydrothermal method, followed by an annealing process. The photocatalyst was thoroughly characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), the Brunauer-Emmett-Teller (BET) nitrogen adsorption/desorption technique and UV-Vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the TiO2, TiO2/rGO, TiO2/CN and hybrid rGO/TiO2/CN nanocomposite was studied through the degradation of a rhodamine B (RhB) aqueous solution under solar-like irradiation. The results showed that the highest photocatalytic activity was achieved by the rGO/TiO2/CN mixture, which can be attributed to the synergistic effect of the incorporation of both rGO and g-C3N4 with TiO2. Further, the influence of the pH value of the RhB dye aqueous solution and different water matrix (Milli-Q, tap, and alkaline water) on the photocatalytic efficiency of the rGO/TiO2/CN nanocomposite was examined. In addition, a recycle test was performed for hybrid rGO@TiO2/CN to investigate the effectiveness of the photodegradation of RhB dye in three successive cycles. The conducted results indicate that the pH value of RhB dye aqueous solution and water matrices play an important role in the photocatalytic degradation rate

Photocatalytic Properties of Immobilised Graphitic Carbon Nitride on the Alumina Substrate

Textile industries significantly impact the contamination of wastewater. Conventional wastewater treatment methods consider the most common pollutants; however, they are very expensive and commonly produce toxic by-products. In the scientific community, advanced oxidation processes appear to be the most appealing, and a majority of the published work considers heterogeneous photocatalysis for the degradation of various toxic chemicals. For convenience, the reaction is performed directly in the water environment. In this work, a metal-free graphitic carbon nitride (g-C3N4) was prepared through a simple thermal method using urea as a precursor. Prepared g-C3N4 was deposited on the surface of the alumina ceramic ring by the dip-coating method using ethylene glycol as binder. The alumina ceramic ring, as substrate, was prepared by the slip casting method. Photocatalytic properties of immobilised graphitic carbon nitride were used for degradation of methylene blue as a model pollutant under simulated solar light irradiation. The photocatalyst was characterised by XRD, FTIR, UV-Vis DRS, TGA, BET and SEM/EDX analyses. The photocatalytic degradation of MB from an aqueous solution was found to increase with increasing irradiation time. It was found that the graphitic carbon nitride immobilised on alumina ceramic is convenient for largescale environmental applications because the whole setup is cheap, nontoxic, easy to operate and offers reusability with a high removal rate of MB after three consecutive cycles

Titanium doped yttrium manganite: improvement of microstructural properties and peculiarities of multiferroic properties

Yttrium manganite, YMnO3, was doped with different concentrations of titanium (x = 0, 0.04, 0.08, 0.10, 0.15, 0.20) in order to improve the microstructural and multiferroic properties. The powders were prepared using sol-gel polymerization complex method from citrate precursors. Depending on the titanium concentration, the hexagonal structure and/or the rhombohedral superstructure are present in the sintered samples. The YMn1–xTixO3+δ (x = 0.10, 0.15, 0.20) ceramic samples showed significantly reduced density of microcracks, and of inter- and intragranular pores, and relative densities greater than 90 %. The structural parameters for YMn1–xTixO3+δ (x = 0, 0.10, 0.15) were correlated with the results of magnetic and ferroelectric measurements. The most of titanium-doped samples showed a reduction of the leakage current density in comparison with undoped YMnO3, and their ferroelectric responses were slightly improved. The modifications in structural arrangement resulted in partial suppression of ideal antiferromagnetic ordering visible through decrease of the Néel temperature and Weiss parameter, as well as the appearance of weak ferromagnetism and increase of magnetization (especially, in samples x = 0.08, 0.10, 0.15). These changes in physical quantities most likely originated from incorporation of the uncompensated magnetic moments and possible spin canting induced by enhanced symmetry break of the superexchange bridges

Titanium doped yttrium manganite: improvement of microstructural properties and peculiarities of multiferroic properties

Yttrium manganite, YMnO3, was doped with different concentrations of titanium (x = 0, 0.04, 0.08, 0.10, 0.15, 0.20) in order to improve the microstructural and multiferroic properties. The powders were prepared using sol-gel polymerization complex method from citrate precursors. Depending on the titanium concentration, the hexagonal structure and/or the rhombohedral superstructure are present in the sintered samples. The YMn1–xTixO3+δ (x = 0.10, 0.15, 0.20) ceramic samples showed significantly reduced density of microcracks, and of inter- and intragranular pores, and relative densities greater than 90%. The structural parameters for YMn1–xTixO3+δ (x = 0, 0.10, 0.15) were correlated with the results of magnetic and ferroelectric measurements. The most of titanium-doped samples showed a reduction of the leakage current density in comparison with undoped YMnO3, and their ferroelectric responses were slightly improved. The modifications in structural arrangement resulted in partial suppression of ideal antiferromagnetic ordering visible through decrease of the Néel temperature and Weiss parameter, as well as the appearance of weak ferromagnetism and increase of magnetization (especially, in samples x = 0.08, 0.10, 0.15). These changes in physical quantities most likely originated from incorporation of the uncompensated magnetic moments and possible spin canting induced by enhanced symmetry break of the superexchange bridges

Immobilised rGO/TiO2 Nanocomposite for Multi-Cycle Removal of Methylene Blue Dye from an Aqueous Medium

This work presents the immobilisation of titanium dioxide (TiO2) nanoparticles (NPs) and reduced graphene oxide (rGO)-TiO2 nanocomposite on glass sheets for photocatalytic degradation of methylene blue (MB) under different radiation sources such as ultraviolet and simulated solar radiation. The TiO2 NPs and rGO-TiO2 nanocomposite were synthesised through a simple hydrothermal method of titanium isopropoxide precursor followed by calcination treatment. Deposition of prepared photocatalysts was performed by spin-coating method. Additionally, ethylene glycol was mixed with the prepared TiO2 NPs and rGO-TiO2 nanocomposite to enhance film adhesion on the glass surface. The photocatalytic activity under ultraviolet and simulated solar irradiation was examined. Further, the influence of different water matrices (milli-Q, river, lake, and seawater) and reactive species (h+, •OH, and e−) on the photocatalytic efficiency of the immobilised rGO/TiO2 nanocomposite was careful assessed. MB dye photocatalytic degradation was found to increase with increasing irradiation time for both irradiation sources. The immobilisation of prepared photocatalysts is very convenient for environment applications, due to easy separation and reusability, and the investigated rGO/TiO2-coated glass sheets demonstrated high efficiency in removing MB dye from an aqueous medium during five consecutive cycles

Immobilised rGO/TiO₂ Nanocomposite for Multi-Cycle Removal of Methylene Blue Dye from an Aqueous Medium

This work presents the immobilisation of titanium dioxide (TiO2) nanoparticles (NPs) and reduced graphene oxide (rGO)-TiO2 nanocomposite on glass sheets for photocatalytic degradation of methylene blue (MB) under different radiation sources such as ultraviolet and simulated solar radiation. The TiO2 NPs and rGO-TiO2 nanocomposite were synthesised through a simple hydrothermal method of titanium isopropoxide precursor followed by calcination treatment. Deposition of prepared photocatalysts was performed by spin-coating method. Additionally, ethylene glycol was mixed with the prepared TiO2 NPs and rGO-TiO2 nanocomposite to enhance film adhesion on the glass surface. The photocatalytic activity under ultraviolet and simulated solar irradiation was examined. Further, the influence of different water matrices (milli-Q, river, lake, and seawater) and reactive species (h+, •OH, and e−) on the photocatalytic efficiency of the immobilised rGO/TiO2 nanocomposite was careful assessed. MB dye photocatalytic degradation was found to increase with increasing irradiation time for both irradiation sources. The immobilisation of prepared photocatalysts is very convenient for environment applications, due to easy separation and reusability, and the investigated rGO/TiO2-coated glass sheets demonstrated high efficiency in removing MB dye from an aqueous medium during five consecutive cycles

Dissecting giant hailstones

The formation of giant hailstones is a rare weather event that has devastating consequences in inhabited areas. This hazard has been occurring more frequently and with greater size of hailstones in recent years, and thus needs to be better understood. While the generally accepted mechanism is thought to be a process similar to the formation of smaller hailstones but with exceptional duration and stronger updrafts, recent evidence suggests that biotic and abiotic factors also influence the growth of these unusually large ice chunks. In this study, we improved these findings by determining the distribution of a wide variety of these factors throughout the hail volume and expanding the search to include new particles that are common in the environment and are of anthropogenic origin. We melted the concentric layers of several giant hailstones that fell to the ground over a small region in Slovenia in 2019. The samples, up to 13 cm in diameter, were analyzed for biotic and abiotic constituents that could have influenced their formation. Using 16S rRNA-based metagenomics approaches, we identified a highly diverse bacterial community, and by using scanning electron microscopy and Raman spectroscopy, we found natural and synthetic fibers concentrated in the cores of the giant hailstones. For the first time, we were able to detect the existence of microplastic fibers in giant hailstones and determine the changes in the distribution of sand within the volume of the samples. Our results suggest that changes in the composition of hail layers and their great diversity are important factors that should be considered in research. It also appears that anthropogenic microfiber pollutants were a significant factor in the formation of the giant hailstones analyzed in this study