名古屋大学年代測定総合研究センターシンポジウム報告

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Hemihedrite from the Florence Lead-Silver mine in Pinal County, Arizona, USA was first described and assigned the ideal chemical formula Pb10Zn(CrO4)(6)(SiO4)(2)F-2, based upon a variety of chemical and crystal-structure analyses. The primary methods used to determine the fluorine content for hemihedrite were colorimetry, which resulted in values of F that were too high and inconsistent with the structural data, and infrared (IR) spectroscopic analysis that failed to detect OH or H2O. Our reinvestigation using electron microprobe analysis of the type material, and additional samples from the type locality, the Rat Tail claim, Arizona, and Nevada, reveals the absence of fluorine, while the presence of OH is confirmed by Raman spectroscopy. These findings suggest that the colorimetric determination of fluorine in the original description of hemihedrite probably misidentified F due to the interferences from PO4 and SO4, both found in our chemical analyses. As a consequence of these results, the study presented here proposes a redefinition of the chemical composition of hemihedrite to the ideal chemical formula Pb10Zn(CrO4)(6)(SiO4)(2)(OH)(2). Hemihedrite is isotypic with iranite with substitution of Zn for Cu, and raygrantite with substitution of Cr for S. Structural data from a sample from the Rat Tail claim, Arizona, indicate that hemihedrite is triclinic in space group P (1) over bar, a = 9.4891(7), b = 11.4242(8), c = 10.8155(7) angstrom, alpha = 120.368(2)degrees, ss = 92.017(3)degrees, gamma = 55.857(2)degrees, V = 784.88(9) angstrom(3), Z = 1, consistent with previous investigations. The structure was refined from single-crystal X-ray diffraction data to R-1 = 0.022 for 5705 unique observed reflections, and the ideal chemical formula Pb10Zn(CrO4)(6)(SiO4)(2)(OH)(2) was assumed during the refinement. Electron microprobe analyses of this sample yielded the empirical chemical formula Pb-10.05(Zn0.91Mg0.02)(Sigma) (= 0.93) (Cr5.98S0.01P0.01)(Sigma = 6.00) Si1.97O34 H-2.16 based on 34 O atoms and six (Cr + S + P) per unit cell.

A method of performing accurate oxygen analysis on cuprate based superconducting materials was established using electron probe micro analysis (EPMA). A range of YBa₂Cu₃O_δ ceramics with varying oxygen concentration were used to test the method. Using YBCO as a reference material, a suitable standard for oxygen analysis of Bi₂Sr₂CaCu₂O_δ (BiSCCO-2212) materials was obtained. This standard was used to perform full elemental analysis of a range of BiSCCO-2212 crystals, post annealed in pO₂'s between 10^-5-2atm. When the average Cu valence of each crystal was calculated and plotted as a function of the critical temperature (T_c) for each crystal, it was shown that BiSCCO-2212 materials conformed to the 'universal' trend illustrated by most other HTS and did not exhibit anomalous behaviour as had been previously believed. The phase assemblage and superconducting properties of BiSCCO-2212 Ag-clad multifilamental wires, prepared using the powder-in-tube (PIT) method by BICC, were studied as a function of a time/temperature profile. pO₂ of the processing atmosphere was found to be the predominant factor in determining the stoichiometry of the 2212 phase within wires. The phase assemblage is not simply a function of pO₂ as previously believed and can be controlled, in part, by the post annealing temperature. Homogenisation of the phase assemblage in BiSCCO-2212 Ag-clad wires can be achieved by prolonged heating (96hrs) at an appropriate temperature. An investigation into the 10K superconducting BiSCCO phase has shown the Sr-rich solid solution to extend towards the ideal stoichiometry of 2:2:1 (Bi:Sr:Cu) with increasing pO₂. Using a combination of high pO₂ (60atm) to achieve the appropriate Bi:Sr stoichiometry followed by post annealing in N₂ to adjust the oxygen content, it was possible to prepare single-phase ceramics of stoichiometry Bi_2.11(2)Sr_1.90(2)Cu_0.99(2)O_δ with a T_c=10.5K(5).

To provide an increased breadth in the knowledge of tephra dispersal, this pilot study examines a peat core from Lakselv in Finnmark County in northern Norway. Peat samples are exposed to burning, HCl, density separation and polarized light microscopy. One sample from a depth of 37.5-40 cm was analysed using an electron microprobe analyser (EMPA). At least two tephra horizons were identified, one at a depth of 12.5-17.5 cm and one at 37.5-40 cm. The lower horizon shows a chemical composition similar to eruptives from Jan Mayen and São Miguel, Azores while the origin of the upper horizon is unknown as no geochemical analysis was performed for that depth.

Extensive research has shown that electrochemistry is one of the factors that govern the flotation of sulfide minerals. Flotation is often adversely affected by uncontrolled oxidation, which is also an electrochemical process. The interest in pyrrhotite recovery arose after observing that there is a substantial loss of PGM due to the depression of pyrrhotite and the subsequent loss of any PGMs associated with it. The first part of this study focuses on the influence of chemical composition and crystal structure on the electrochemical behaviour of pyrrhotite in a 0.05 M Na2B4O7 solution. Rest potential and polarisation resistance measurements, as well as anodic polarisation diagrams, showed that the magnetic 4C type pyrrhotite is anodically more reactive than the non-magnetic 6C type pyrrhotite. It was also shown in cathodic polarisation diagrams that the non-magnetic 6C type pyrrhotite is a better substrate for oxygen reduction and is less susceptible to oxidation. ToF-SIMS showed the formation of an oxide layer on the pyrrhotite surface after oxidation. In the second part of this work, the influence of galvanic interactions on the electrochemical behaviour of pyrrhotite in contact with pentlandite was investigated. It was observed that, under oxygen-saturated conditions, as the amount of pentlandite increases, the reactivity towards oxidation of the mixed mineral system is reduced. Impedance measurements showed a decrease in capacitance values, indicating the formation of a continuous oxide layer on the surface and an increase in oxide layer thickness with decreasing pentlandite content. Anodic polarisation diagrams showed that under oxygen-deficient conditions and in the low potential region, pentlandite behaves as an inert material and does not have an influence on the oxidation behaviour of pyrrhotite. Hence, the anodic activities of the different magnetic 4C type pyrrhotites from Sudbury Gertrude, Phoenix and Russia were compared. It was shown that the oxidation reactivity decreased in the following order: Sudbury Gertrude magnetic 4C pyrrhotite > Phoenix magnetic 4C pyrrhotite > Russian magnetic 4C pyrrhotite; it also varied according to location. In the transpassive region, higher anodic currents were observed on the mixed samples because both pentlandite and pyrrhotite reacts. The reactivity increased in the order: pure pyrrhotite (Russia) < medium-pentlandite (Sudbury Gertrude) < high-pentlandite (Phoenix). In the presence of potassium ethyl xanthate, there was no change in the initial anodic reactivities of the different pyrrhotites. The anodic polarisation diagrams of the pure and mixed samples showed a reduction in the maximum anodic peak current, suggesting the presence of xanthate on the surface, which hinders oxidation of the mineral surface. In addition, the influence of cleaning of oxidised pyrrhotite with gaseous carbon dioxide was studied, using electrochemical and microflotation measurements. Electrochemical measurements indicated that CO2 treatment resulted in depassivation of the oxidised surfaces; this was supported by ToF-SIMS measurements that demonstrated a reduction in the oxide layer thickness after CO2 treatment. Anodic polarisation diagrams showed a higher anodic peak current, indicating that the surface is more reactive. Gaseous carbon dioxide conditioning of oxidised pyrrhotite resulted in improved flotation response of pyrrhotite with the aid of copper activation and higher air flow rate. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Materials Science and Metallurgical Engineering / unrestricted

[1] Four specimens of zoned tourmaline from granitic pegmatites are characterised in detail, each having unusual compositional and/or morphologic features: (1) a crystal from Black Rapids Glacier, Alaska, showing a central pink zone of elbaite mantled by a thin rim of green liddicoatite; (2) a large (~25 cm) slab of Madagascar liddicoatite cut along (001) showing complex patterns of oscillatory zoning; and (3) a wheatsheaf and (4) a mushroom elbaite from Mogok, Myanmar, both showing extensive bifurcation of fibrous crystals originating from a central core crystal, and showing pronounced discontinuous colour zoning. Crystal chemistry and crystal structure of these samples are characterised by SREF, EMPA, and 11B and 27Al MAS NMR and Mössbauer spectroscopies. For each sample, compositional change, as a function of crystal growth, is characterised by EMPA traverses, and the total chemical variation is reduced to a series of linear substitution mechanisms. Of particular interest are substitutions accommodating the variation in [4]B: (1) TB + YAl ↔ TSi + Y(Fe, Mn)2+, where transition metals are present, and (2) TB2 + YAl ↔ TSi2 + YLi, where transition metals are absent. Integration of all data sets delineates constraints on melt evolution and crystal growth mechanisms. [2] Uncertainty has surrounded the occurrence of [4]Al and [4]B at the T-site in tourmaline, because B is difficult to quantify by EMPA and Al is typically assigned to the octahedral Y- and Z-sites. Although both [4]Al and [4]B have been shown to occur in natural tourmalines, it is not currently known how common these substituents are. Using 11B and 27Al MAS NMR spectroscopy, the presence of [4]B and [4]Al is determined in fifty inclusion-free tourmalines of low transition-metal content with compositions corresponding to five different species. Chemical shifts of [4]B and [3]B in 11B spectra, and [4]Al and [6]Al in 27Al spectra, are well-resolved, allowing detection of very small (< ~0.1 apfu) amounts of T-site constituents. Results show that contents of 0.0 < [4]B, [4]Al < 0.5 apfu are common in tourmalines containing low amounts of paramagnetic species, and that all combinations of Si, Al and B occur in natural tourmalines.

[1] Four specimens of zoned tourmaline from granitic pegmatites are characterised in detail, each having unusual compositional and/or morphologic features: (1) a crystal from Black Rapids Glacier, Alaska, showing a central pink zone of elbaite mantled by a thin rim of green liddicoatite; (2) a large (~25 cm) slab of Madagascar liddicoatite cut along (001) showing complex patterns of oscillatory zoning; and (3) a wheatsheaf and (4) a mushroom elbaite from Mogok, Myanmar, both showing extensive bifurcation of fibrous crystals originating from a central core crystal, and showing pronounced discontinuous colour zoning. Crystal chemistry and crystal structure of these samples are characterised by SREF, EMPA, and 11B and 27Al MAS NMR and Mössbauer spectroscopies. For each sample, compositional change, as a function of crystal growth, is characterised by EMPA traverses, and the total chemical variation is reduced to a series of linear substitution mechanisms. Of particular interest are substitutions accommodating the variation in [4]B: (1) TB + YAl ↔ TSi + Y(Fe, Mn)2+, where transition metals are present, and (2) TB2 + YAl ↔ TSi2 + YLi, where transition metals are absent. Integration of all data sets delineates constraints on melt evolution and crystal growth mechanisms. [2] Uncertainty has surrounded the occurrence of [4]Al and [4]B at the T-site in tourmaline, because B is difficult to quantify by EMPA and Al is typically assigned to the octahedral Y- and Z-sites. Although both [4]Al and [4]B have been shown to occur in natural tourmalines, it is not currently known how common these substituents are. Using 11B and 27Al MAS NMR spectroscopy, the presence of [4]B and [4]Al is determined in fifty inclusion-free tourmalines of low transition-metal content with compositions corresponding to five different species. Chemical shifts of [4]B and [3]B in 11B spectra, and [4]Al and [6]Al in 27Al spectra, are well-resolved, allowing detection of very small (< ~0.1 apfu) amounts of T-site constituents. Results show that contents of 0.0 < [4]B, [4]Al < 0.5 apfu are common in tourmalines containing low amounts of paramagnetic species, and that all combinations of Si, Al and B occur in natural tourmalines.

Made available in DSpace on 2014-10-09T12:51:50Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:58Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP