| 1. |
- Naumovska, Elena, et al.
(författare)
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Local structure of hydrated nanocrystalline films of the proton conductor BaZr 1-x Sc x O 3-x/2 studied by infrared spectroscopy
- 2024
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Ingår i: Vibrational Spectroscopy. - 0924-2031. ; 130
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Tidskriftsartikel (refereegranskat)abstract
- We report results from a study of the local structure of hydrated nanocrystalline 2 μm films of the well known proton conductor BaZr1-xScxO3-x/2 with x = 0.45, 0.54 and 0.64, using infrared (IR) spectroscopy. The films were prepared by magnetron sputtering. Analysis of the IR spectra focused on the O–H stretching region (2000—3700 cm-1), which reveals the presence of several distinct O–H stretching bands for which the intensity and frequency of each band vary in an unsystematic manner with Sc concentration. The spectra for the two higher Sc concentrations, x = 0.54 and 0.64, exhibit a distinct, highly intense O–H stretching band centered at around 3400–3500 cm-1, which is assigned to relatively symmetric, weakly hydrogen-bonding, proton configurations. The spectrum for the lower Sc concentration, x = 0.45, does not feature such a band but a broader, weaker, O–H stretching band between approximately 2500 and 3700 cm-1, suggesting that the protons are more homogeneously distributed over a range of different local proton coordinations in this relatively weakly doped material. A comparison to the IR spectra of powder samples of similar compositions suggests that for x = 0.45, the spectra and proton coordination of films and powder samples are similar, whereas for x = 0.54 and 0.64, a larger fraction of protons seems to be located in weakly hydrogen-bonding proton configurations in the films compared to the respective powder samples.
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| 2. |
- Naumovska, Elena, 1995, et al.
(författare)
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Local structure of hydrated nanocrystalline films of the proton conductor BaZr1-xScxO3-x/2 studied by infrared spectroscopy
- 2024
-
Ingår i: Vibrational Spectroscopy. - : Elsevier. - 0924-2031 .- 1873-3697. ; 130
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Tidskriftsartikel (refereegranskat)abstract
- We report results from a study of the local structure of hydrated nanocrystalline 2 m films of the well known proton conductor BaZr1-xScxO3-x/2 with x = 0.45, 0.54 and 0.64, using infrared (IR) spectroscopy. The films were prepared by magnetron sputtering. Analysis of the IR spectra focused on the O–H stretching region (2000—3700 cm-1), which reveals the presence of several distinct O–H stretching bands for which the intensity and frequency of each band vary in an unsystematic manner with Sc concentration. The spectra for the two higher Sc concentrations, x = 0.54 and 0.64, exhibit a distinct, highly intense O–H stretching band centered at around 3400–3500 cm-1, which is assigned to relatively symmetric, weakly hydrogen-bonding, proton configurations. The spectrum for the lower Sc concentration, x = 0.45, does not feature such a band but a broader, weaker, O–H stretching band between approximately 2500 and 3700 cm-1, suggesting that the protons are more homogeneously distributed over a range of different local proton coordinations in this relatively weakly doped material. A comparison to the IR spectra of powder samples of similar compositions suggests that for x = 0.45, the spectra and proton coordination of films and powder samples are similar, whereas for x = 0.54 and 0.64, a larger fraction of protons seems to be located in weakly hydrogen-bonding proton configurations in the films compared to the respective powder samples.
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| 3. |
- Nzulu, Gabriel Kofi
(författare)
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Characterization of Gold Pathfinder Minerals
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this Thesis, I investigate the properties of artisanal small-scale gold mining concentrate samples from the Kubi Gold Project of the Asante Gold Corporation near Dunkwa-on-Offin in the Central Region of Ghana with a material science perspective.X-ray diffraction (XRD) is used to identify SiO2 (quartz), Fe3O4 (magnetite), and Fe2O3 (hematite) as the main indicator minerals in the mining site while contributions from pyrite, arsenopyrites, iridosmine, scheelite, tetradymite, garnet, gypsum, and other sulfate minerals were insignificant.Furthermore, the X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) results indicate elements like Fe, Ag, Al, N, O, Si, Hg, and Ti as the important host elements that either form alloy with Au or inherent elements in the soil at the site. The result also indicate that Si and Ag are in strong co-occurrence with Au due to their eutectic qualities, while N, C, and O follow alongside because of their attraction to Si. These findings indicate that primary geochemical dispersion evolving from crystallization of magma and hydrothermal liquids are the main attributes and this constitute a confirmative identification of Au indicator and pathfinding minerals in this mineralogical area. Furthermore, the findings suggest that XRD, XPS, and EDX could also be applied in other mineralogical laboratories to aid in identifying indicator minerals of Au and location of ore bodies at reduced environmental and exploration costs.
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| 4. |
- Nzulu, Gabriel Kofi, 1974-
(författare)
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Characterization of Pathfinders and Indicators of Gold
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Research on natural minerals and their chemical bonding to economically critical raw materials is a viable industrially relevant research area due to its increasing demand. Meeting demands requires fast, robust, and efficient techniques to explore new ore deposits and continuous operation of active mines as well as recycling. One of the most critical metals is gold which occurs in three main types of ore deposits: i) hydrothermal quartz veins and related deposits in metamorphic and igneous rocks; ii) volcanic-exhalative sulfide deposits, and iii) consolidated to unconsolidated placer deposits. Gold is commonly found as disseminated grains in quartz veins in pyrite and other sulfides or as rounded grains, flakes or nuggets in deposits in riverbanks, in contact with metamorphic or hypothermal deposits (e.g., skarns) or epithermal deposits such as volcanic fumaroles. Pathfinder elements and indicator minerals provide means to explore large areas for their potential mineral commodities such as gold, diamond, base metals, platinum group of elements, and rare earth elements by narrowing the search area to reduce exploration costs. The recent technological advancement in obtaining rapid geochemical results using field portable analytical devices as alternatives to the old approach where collected field samples are carried to the laboratory calls for further investigation to explore other techniques in mineral and metal exploration.In this Thesis, I investigate the properties of artisanal small-scale gold mining concentrate, outcrop, bulk Au, and drill hole samples from the Kubi Gold Project of the Asante Gold Corporation near Dunkwa-on-Offin in the Central Region of Ghana with a materials science perspective. X-ray diffraction (XRD) is used to identify SiO2 (quartz), Fe3O4 (magnetite), garnet, pyrite (FeS2), periclase (MgO), arsenopyrites, pyrrhotite, biotite, titanium oxide, and Fe2O3 (hematite) as the main indicator minerals in the mining site with less significant contributions from chalcopyrite, iridosmine, scheelite, tetradymite, gypsum, and a few other sulfates. X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) indicate that Fe, Ag, Al, N, O, Si, Hg, C, Ba, P, Ca, Mg, Na, Mn, Cl, S, K, and Ti are important host elements that form alloys with Au or are inherent in the sediment at the concession site. The results also indicate that Si and Ag are in strong co-occurrence with Au due to their eutectic qualities, while N, C, and O occur due to their attraction to Si. Also, the XPS results indicate that the relationship between Au and pathfinder elements or indicator minerals depends on the d-orbital of Au and other elements that possess octahedral or tetrahedral geometry to split into two states, eg and t2g that can acquire either higher or lower energy depending on the geometry and are responsible for the covalent, metallic, and ionic states of Au with other ligands. From the air anneal furnace (AAF) and differential scanning calorimetry (DSC), I investigated the transformations in quartz and pyrite minerals that alter to hematite minerals. The quartz samples are observed to transform from α-quartz to β-quartz and finally to cristobalite while the pyrite transforms to magnetite and later to hematite. These findings suggest that during the hydrothermal flow regime impurity materials are trapped by voids and faults and can be altered at different depositional stages by oxidation and reduction processes. Results from the scanning electron microscopy (SEM) revealed the presence of carbonates in fracture zones in the quartz, pyrite, and almandine-type garnet mineral in gabbroic rocks.The findings indicate that, from the top of the oxide zone, grains within sediments are seen to be controlled by quartz, and hematite, the bedrock consists of pyrite and pyrrhotite, and the orebody contains garnet, arsenopyrite, periclase, and biotite as pathfinder minerals within the concession area. Therefore, the Au mineralogy of the alluvial environment that is mined by artisanal small-scale miners is traced from the chemical weathering reaction of garnet minerals from the orebody that produces fractions of other indicator minerals as by-products in the Kubi mining area. These findings also indicate that primary geochemical dispersion evolving from the crystallization of magma and hydrothermal liquids are the main attributes and constitute the identification of indicator minerals and pathfinding elements in this mineralogical study area.Furthermore, the findings suggest that XRD, XPS, TEM, and EDX could be combined in other mineralogical laboratories to aid in identifying indicator minerals of Au and the location of ore bodies, to increase the knowledge in this field, and reduce environmental and exploration costs.
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| 5. |
- Nzulu, Gabriel Kofi, 1974-, et al.
(författare)
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Chemical Reactivity and Alteration of Pyrite Mineral in the Kubi Gold Concession in Ghana
- 2024
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Ingår i: Mining, Metallurgy & Exploration. - : Springer. - 2524-3462 .- 2524-3470.
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Tidskriftsartikel (refereegranskat)abstract
- Pyrite is the most common among the group of sulfide minerals in the Earth and abundant in most geological settings. This gangue mineral in association with garnet, hematite, magnetite, and other sulfide minerals acts as an indicator mineral in the Kubi concession of the Asante Gold corporation in Ghana. X-ray diffraction (XRD), air annealing in a furnace, energy-dispersive x-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) were applied to investigate the crystal structure, identify individual elements, permanence, transformation, and chemical/electronic properties of such pyrite. The study aims to identify individual elements and to gain an understanding of the surface reaction mechanisms, as well as the properties of precipitated pyrite particles observed during the hydrothermal formation of the ore deposit. XRD shows that pristine and annealed samples contain some hematite and quartz besides pyrite. Results from air annealing indicate that the relationship between pyrite and hematite-magnetite is controlled by temperature. EDX reveals that the sample has O and C as contaminants, while XPS in addition reveals Ba, Au, P, Al, and N. These elements are attributed to pyrite that bonds metallically or covalently to neighboring ligands/impurity minerals such as oxides, chalcogenide sulfides, as well as the gangue alteration minerals of magnetite and hematite in the pyrite sample.These findings suggest that during the hydrothermal flow regime, pyrite, pathfinder elements, and impurity minerals/metals were in contact with quartz minerals before undergoing hematite transformation, which thus becomes an indicator mineral in the Kubi gold concession.
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| 6. |
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| 7. |
- Nzulu, Gabriel Kofi, 1974-, et al.
(författare)
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Growth and thermal stability of Sc-doped BaZrO 3 thin films deposited on single crystal substrates
- 2023
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 772
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of BaZr1-xScxO3-x/2, (0 ≤ x ≤ 0.64), well known as proton conducting solid electrolytes for intermediate temperature solid oxide fuel cell, were deposited by magnetron sputtering. X-ray diffraction analysis of the as deposited films reveals the presence of single-phase perovskite structure. The films were deposited on four different substrates (c-Al2O3, LaAlO3〈100〉, LaAlO3〈110〉, LaAlO3〈111〉) yielding random, (110)- or (100)-oriented films. The stability of the as-deposited films was assessed by annealing in air at 600 °C for 2 h. The annealing treatment revealed instabilities of the perovskite structure for the (110) and randomly oriented films, but not for (100) oriented film. The instability of the coating under heat treatment was attributed to the low oxygen content in the film (understoichiometry) prior annealing combined with the surface energy and atomic layers stacking along the growth direction. An understoichiometric (100) oriented perovskite films showed higher stability of the structure under an annealing in air at 600 °C.
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| 8. |
- Nzulu, Gabriel Kofi, 1974-, et al.
(författare)
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Growth and thermal stability of Sc-doped BaZrO3 thin films deposited on single crystal substrates
- 2023
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 772
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of BaZr1-xScxO3-x/2, (0 ≤ x ≤ 0.64), well known as proton conducting solid electrolytes for intermediatetemperature solid oxide fuel cell, were deposited by magnetron sputtering. X-ray diffraction analysis of theas deposited films reveals the presence of single-phase perovskite structure. The films were deposited on fourdifferent substrates (c-Al2O3, LaAlO3〈100〉, LaAlO3〈110〉, LaAlO3〈111〉) yielding random, (110)- or (100)-orientedfilms. The stability of the as-deposited films was assessed by annealing in air at 600 ◦C for 2 h. Theannealing treatment revealed instabilities of the perovskite structure for the (110) and randomly oriented films,but not for (100) oriented film. The instability of the coating under heat treatment was attributed to the lowoxygen content in the film (understoichiometry) prior annealing combined with the surface energy and atomiclayers stacking along the growth direction. An understoichiometric (100) oriented perovskite films showedhigher stability of the structure under an annealing in air at 600 ◦C.
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| 9. |
- Nzulu, Gabriel Kofi, 1974-, et al.
(författare)
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Pathfinder elements and indicator minerals of Au from the Kubi Gold ore deposits in Ghana
- 2023
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Ingår i: Environmental Earth Sciences. - : Springer. - 1866-6280 .- 1866-6299. ; 82:16
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Tidskriftsartikel (refereegranskat)abstract
- The Au mineralization in the Kubi Gold Mining Area in the Birimian of Ghana is associated with garnet (about 85 vol.%), magnetite, pyrrhotite, arsenopyrite, and sulfide minerals, as well as quartz with gold and calcite. These minerals and the included elements can act as indicator minerals or pathfinder elements. For the present work, we collected samples from drill holes at different depths, from the alluvial zone (0–45 m) to the ore zone (75–100 m). The distributions of minerals and elements in the rocks that act as indicator minerals and pathfinder elements in the concession area were investigated along the drill hole cross sections. X-ray diffraction shows that the samples contain garnet, pyrite, periclase, and quartz as the main indicator minerals. By energy-dispersive X-ray spectroscopy, Fe, Mg, Al, S, O, Mn, Na, Cu, Si, and K are identified as corresponding pathfinder elements. The results indicate that the Au mineralization in the Kubi Mine area correlates mostly with the occurrence of garnet, pyrite, goethite, and kaolinite in the host rocks, which show towards the surface increasingly hematitic and limonitic alteration in form of Fe(oxy-)hydroxides.
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