The Experts below are selected from a list of 23097 Experts worldwide ranked by ideXlab platform
Johannes Lutzenkirchen - One of the best experts on this subject based on the ideXlab platform.
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cloud history can change water ice surface interactions of Oxide Mineral aerosols a case study on silica
Atmospheric Chemistry and Physics, 2020Co-Authors: Ahmed Abdelmonem, Sanduni Ratnayake, J D Toner, Johannes LutzenkirchenAbstract:Abstract. Mineral aerosol particles nucleate ice, and many insights have been obtained on water freezing as a function of Mineral surface properties such as charge or morphology. Previous studies have mainly focused on pristine samples despite the fact that aerosol particles age under natural atmospheric conditions. For example, an aerosol-containing cloud droplet can go through freeze–melt or evaporation–condensation cycles that change the surface structure, the ionic strength, and pH. Variations in the surface properties of ice-nucleating particles in the atmosphere have been largely overlooked. Here, we use an environmental cell in conjunction with nonlinear spectroscopy (second-harmonic generation) to study the effect of freeze–melt processes on the aqueous chemistry at silica surfaces at low pH. We found that successive freeze–melt cycles disrupt the dissolution equilibrium, substantially changing the surface properties and giving rise to marked variations in the interfacial water structure and the ice nucleation ability of the surface. The degree of order of water molecules, next to the surface, at any temperature during cooling decreases and then increases again with sample aging. Along the aging process, the water ordering–cooling dependence and ice nucleation ability improve continuously.
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cloud history changes water ice surface interactions of Oxide Mineral aerosols e g silica
Atmospheric Chemistry and Physics, 2019Co-Authors: Ahmed Abdelmonem, Sanduni Ratnayake, J D Toner, Johannes LutzenkirchenAbstract:Abstract. Abstract. Mineral aerosol particles can act as ice nucleators, and many insights have been obtained on water freezing as a function of Mineral surface properties such as the charge or morphology. Previous studies have mainly focused on pristine samples, despite the fact that under natural atmospheric conditions, aerosol particles age. For example, an aerosol-containing cloud droplet can go through different freeze-melt cycles, so that not only the aerosol surface structure may change, but also the ionic strength and pH of the cloud droplet. The potential variation of the surface properties of an ice nucleating particle during its residence in the atmosphere has been largely overlooked. Here, we use an environmental cell in conjunction with nonlinear spectroscopy (second-harmonic generation) to study the effect of freeze-melt processes on aqueous chemistry at silica surface at low pH. We found that the successive freeze-melt cycles disrupt the dissolution equilibrium, substantially changing the surface properties, giving rise to marked variations in the interfacial water structure and the ice nucleation ability of the surface. The degree-of-order of water molecules, next to the surface at a specific temperature, decreases and then increases again with sample aging. The water ordering–cooling dependence and ice nucleation ability improve continuously.
Patrick Olivier - One of the best experts on this subject based on the ideXlab platform.
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nb ta ti sn Oxide Mineral chemistry as tracer of rare element granitic pegmatite fractionation in the borborema province northeastern brazil
Mineralium Deposita, 2008Co-Authors: Hartmut Beurlen, Marcelo R R Da Silva, Rainer Thomas, Dwight Rodrigues Soares, Patrick OlivierAbstract:The Borborema Pegmatitic Province (BPP), northeastern Brazil, is historically important for tantalum mining and also famous for top-quality specimens of exotic Nb–Ta Oxides and, more recently, for the production of gem quality, turquoise blue, ‘Paraiba Elbaite.’ With more than 750 registered Mineralized rare-element granitic pegmatites, the BPP extends over an area of about 75 by 150 km in the eastern part of the Neoproterozoic Serido Belt. The Late Cambrian pegmatites are mostly hosted by a sequence of Neoproterozoic cordierite–sillimanite biotite schists of the Serido Formation and quartzites and metaconglomerates of the Equador Formation. The trace-element ratios in feldspar and micas allow to classify most pegmatites as belonging to the beryl–columbite phosphate subtype. Electron microprobe analyses (EMPA) of columbite, tapiolite, niobian–tantalian rutile, ixiolite and wodginite group Minerals from 28 pegmatites in the BPP are used to evaluate the effectiveness of Nb–Ta Oxide chemistry as a possible exploration tool, to trace the degree of pegmatite fractionation and to classify the pegmatites. The columbite group Mineral composition allows to establish a compositional trend from manganoan ferrocolumbite to manganocolumbite and on to manganotantalite. This trend is typical of complex spodumene- and/or lepidolite-subtype pegmatites. It clearly contrasts with another trend, from ferrocolumbite through ferrotantalite to ferrowodginite and ferrotapiolite compositions, typical of pegmatites of the beryl–columbite phosphate subtype. Large scatter and anomalous trends in zoned crystals partially overlap and conceal the two main evolution patterns. This indicates that a large representative data set of heavy Mineral concentrate samples, collected systematically along cross-sections, would be necessary to predict the metallogenetic potential of individual pegmatites. Other Mineral species, e.g. garnets and/or tourmaline, with a more regular distribution than Nb–Ta Oxides, would be more appropriate and less expensive for routine exploration purposes. The currently available Nb–Ta Oxide chemistry data suggest the potential for highly fractionated Ta–Li–Cs pegmatites in the BPP, so far undiscovered, and encourages further, more detailed research.
Ahmed Abdelmonem - One of the best experts on this subject based on the ideXlab platform.
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cloud history can change water ice surface interactions of Oxide Mineral aerosols a case study on silica
Atmospheric Chemistry and Physics, 2020Co-Authors: Ahmed Abdelmonem, Sanduni Ratnayake, J D Toner, Johannes LutzenkirchenAbstract:Abstract. Mineral aerosol particles nucleate ice, and many insights have been obtained on water freezing as a function of Mineral surface properties such as charge or morphology. Previous studies have mainly focused on pristine samples despite the fact that aerosol particles age under natural atmospheric conditions. For example, an aerosol-containing cloud droplet can go through freeze–melt or evaporation–condensation cycles that change the surface structure, the ionic strength, and pH. Variations in the surface properties of ice-nucleating particles in the atmosphere have been largely overlooked. Here, we use an environmental cell in conjunction with nonlinear spectroscopy (second-harmonic generation) to study the effect of freeze–melt processes on the aqueous chemistry at silica surfaces at low pH. We found that successive freeze–melt cycles disrupt the dissolution equilibrium, substantially changing the surface properties and giving rise to marked variations in the interfacial water structure and the ice nucleation ability of the surface. The degree of order of water molecules, next to the surface, at any temperature during cooling decreases and then increases again with sample aging. Along the aging process, the water ordering–cooling dependence and ice nucleation ability improve continuously.
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cloud history changes water ice surface interactions of Oxide Mineral aerosols e g silica
Atmospheric Chemistry and Physics, 2019Co-Authors: Ahmed Abdelmonem, Sanduni Ratnayake, J D Toner, Johannes LutzenkirchenAbstract:Abstract. Abstract. Mineral aerosol particles can act as ice nucleators, and many insights have been obtained on water freezing as a function of Mineral surface properties such as the charge or morphology. Previous studies have mainly focused on pristine samples, despite the fact that under natural atmospheric conditions, aerosol particles age. For example, an aerosol-containing cloud droplet can go through different freeze-melt cycles, so that not only the aerosol surface structure may change, but also the ionic strength and pH of the cloud droplet. The potential variation of the surface properties of an ice nucleating particle during its residence in the atmosphere has been largely overlooked. Here, we use an environmental cell in conjunction with nonlinear spectroscopy (second-harmonic generation) to study the effect of freeze-melt processes on aqueous chemistry at silica surface at low pH. We found that the successive freeze-melt cycles disrupt the dissolution equilibrium, substantially changing the surface properties, giving rise to marked variations in the interfacial water structure and the ice nucleation ability of the surface. The degree-of-order of water molecules, next to the surface at a specific temperature, decreases and then increases again with sample aging. The water ordering–cooling dependence and ice nucleation ability improve continuously.
John R Beckett - One of the best experts on this subject based on the ideXlab platform.
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kaitianite ti 3 2 ti 4 o 5 a new titanium Oxide Mineral from allende
Meteoritics & Planetary Science, 2021Co-Authors: John R BeckettAbstract:Kaitianite, Ti³⁺₂Ti⁴⁺O₅, is a new titanium Oxide Mineral discovered in the Allende CV3 carbonaceous chondrite. The type grain coexists with tistarite (Ti₂O₃) and rutile. Corundum, xifengite, mullite, osbornite, and a new Ti,Al,Zr‐Oxide Mineral are also present, although not in contact. The chemical composition of type kaitianite is (wt%) Ti₂O₃ 56.55, TiO₂ 39.29, Al₂O₃ 1.18, MgO 1.39, FeO 0.59, V₂O₃ 0.08 (sum 99.07), yielding an empirical formula of (Ti³⁺_(1.75)Al_(0.05)Ti⁴⁺_(0.10)Mg_(0.08)Fe_(0.02))(Ti⁴⁺_(1.00))O₅, with Ti³⁺ and Ti⁴⁺ partitioned, assuming a stoichiometry of three cations and five oxygen anions pfu. The end‐member formula is Ti³⁺₂Ti⁴⁺O₅. Kaitianite is the natural form of γ‐Ti₃O₅ with space group C2/c and cell parameters a = 10.115 A, b = 5.074 A, c = 7.182 A, β = 112o, V = 341.77 A³, and Z = 4. Both the type kaitianite and associated rutile likely formed as oxidation products of tistarite at temperatures below 1200 K, but this oxidation event could have been in a very reducing environment, even more reducing than a gas of solar composition. Based on experimental data on the solubility of Ti³⁺ in equilibrium with corundum from the literature, the absence of tistarite in or on Ti³⁺‐rich corundum (0.27–1.45 mol% Ti₂O₃) suggests that these grains formed at higher temperatures than the kaitianite (>1579–1696 K, depending on the Ti concentration). The absence of rutile or kaitianite in or on corundum suggests that any exposure to the oxidizing environment producing kaitianite in tistarite was too short to cause the precipitation of Ti‐Oxides in or on associated corundum.
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kaitianite ti3 2ti4 o5 a new titanium Oxide Mineral from allende
Meteoritics & Planetary Science, 2020Co-Authors: John R BeckettAbstract:Kaitianite, Ti³⁺₂Ti⁴⁺O₅, is a new titanium Oxide Mineral discovered in the Allende CV3 carbonaceous chondrite. The type grain coexists with tistarite (Ti₂O₃) and rutile. Corundum, xifengite, mullite, osbornite, and a new Ti,Al,Zr‐Oxide Mineral are also present, although not in contact. The chemical composition of type kaitianite is (wt%) Ti₂O₃ 56.55, TiO₂ 39.29, Al₂O₃ 1.18, MgO 1.39, FeO 0.59, V₂O₃ 0.08 (sum 99.07), yielding an empirical formula of (Ti³⁺_(1.75)Al_(0.05)Ti⁴⁺_(0.10)Mg_(0.08)Fe_(0.02))(Ti⁴⁺_(1.00))O₅, with Ti³⁺ and Ti⁴⁺ partitioned, assuming a stoichiometry of three cations and five oxygen anions pfu. The end‐member formula is Ti³⁺₂Ti⁴⁺O₅. Kaitianite is the natural form of γ‐Ti₃O₅ with space group C2/c and cell parameters a = 10.115 A, b = 5.074 A, c = 7.182 A, β = 112o, V = 341.77 A³, and Z = 4. Both the type kaitianite and associated rutile likely formed as oxidation products of tistarite at temperatures below 1200 K, but this oxidation event could have been in a very reducing environment, even more reducing than a gas of solar composition. Based on experimental data on the solubility of Ti³⁺ in equilibrium with corundum from the literature, the absence of tistarite in or on Ti³⁺‐rich corundum (0.27–1.45 mol% Ti₂O₃) suggests that these grains formed at higher temperatures than the kaitianite (>1579–1696 K, depending on the Ti concentration). The absence of rutile or kaitianite in or on corundum suggests that any exposure to the oxidizing environment producing kaitianite in tistarite was too short to cause the precipitation of Ti‐Oxides in or on associated corundum.
Hartmut Beurlen - One of the best experts on this subject based on the ideXlab platform.
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nb ta ti sn Oxide Mineral chemistry as tracer of rare element granitic pegmatite fractionation in the borborema province northeastern brazil
Mineralium Deposita, 2008Co-Authors: Hartmut Beurlen, Marcelo R R Da Silva, Rainer Thomas, Dwight Rodrigues Soares, Patrick OlivierAbstract:The Borborema Pegmatitic Province (BPP), northeastern Brazil, is historically important for tantalum mining and also famous for top-quality specimens of exotic Nb–Ta Oxides and, more recently, for the production of gem quality, turquoise blue, ‘Paraiba Elbaite.’ With more than 750 registered Mineralized rare-element granitic pegmatites, the BPP extends over an area of about 75 by 150 km in the eastern part of the Neoproterozoic Serido Belt. The Late Cambrian pegmatites are mostly hosted by a sequence of Neoproterozoic cordierite–sillimanite biotite schists of the Serido Formation and quartzites and metaconglomerates of the Equador Formation. The trace-element ratios in feldspar and micas allow to classify most pegmatites as belonging to the beryl–columbite phosphate subtype. Electron microprobe analyses (EMPA) of columbite, tapiolite, niobian–tantalian rutile, ixiolite and wodginite group Minerals from 28 pegmatites in the BPP are used to evaluate the effectiveness of Nb–Ta Oxide chemistry as a possible exploration tool, to trace the degree of pegmatite fractionation and to classify the pegmatites. The columbite group Mineral composition allows to establish a compositional trend from manganoan ferrocolumbite to manganocolumbite and on to manganotantalite. This trend is typical of complex spodumene- and/or lepidolite-subtype pegmatites. It clearly contrasts with another trend, from ferrocolumbite through ferrotantalite to ferrowodginite and ferrotapiolite compositions, typical of pegmatites of the beryl–columbite phosphate subtype. Large scatter and anomalous trends in zoned crystals partially overlap and conceal the two main evolution patterns. This indicates that a large representative data set of heavy Mineral concentrate samples, collected systematically along cross-sections, would be necessary to predict the metallogenetic potential of individual pegmatites. Other Mineral species, e.g. garnets and/or tourmaline, with a more regular distribution than Nb–Ta Oxides, would be more appropriate and less expensive for routine exploration purposes. The currently available Nb–Ta Oxide chemistry data suggest the potential for highly fractionated Ta–Li–Cs pegmatites in the BPP, so far undiscovered, and encourages further, more detailed research.
