Distinctive properties of rock-forming blue quartz: inferences from a multi-analytical study of submicron mineral inclusions
Wolfgang SeifertDieter RhedeRainer ThomasHans‐Jürgen FörsterFriedrich LucassenPeter DulskiRichard Wirth
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Abstract The study discusses the mineralogical, geochemical and thermometric properties of rock-forming blue quartz from eight worldwide occurrences. Compared to non-blue quartz, blue quartz contains significant amounts of submicron-sized (1 μm—100 nm) and nanometre-sized (<100 nm) inclusions. Mica, ilmenite and rutile constitute the most abundant submicron-sized inclusions, and are formed probably by syngenetic precipitation in the boundary layer between quartz and melt (entrapment model). Nanometre-sized rutile possibly originated by epigenetic exsolution of Ti from the quartz structure (exsolution model). Rayleigh scattering of light by nano-particulate inclusions best explains the origin of the blue colour. Blue quartz is generally Ti-rich (∼100—300 ppm) and formed at high temperatures (∼700°C—900°C). The large number, and high spatial density, of tiny xenocrystic inclusions of Ti-bearing minerals make calculations of crystallization temperatures using the Ti-in-quartz thermometer unreliable. The geological significance of blue quartz remains obscure.Keywords:
Rutile
Nanometre
Ilmenite
A chemical inducing process was developed to synthesize rutile titania mica pearlescent pigment.Using SnCl 4 and its complex as the chemical inducing promoters, complete rutile titania mica pearlescent pigment was prepared by calcining at 850 ℃ for 0 5 h.By orthogonal design the optimal dosage of the chemical inducing promoters making rutile TiO 2 crystal was determined as m (mica)∶ m (SnCl 4)∶ m (ZnO)∶ m (C additive)=100∶3∶2∶4. It makes the calcination time shorter and the phase transition temperature of TiO 2 which covered mica drop about 100 ℃.The prepared rutile titania mica pearlescent pigment has good optical properties like pearl.
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The micro-structure of natural rutile heated and annealed under argon atmosphere was studied by means of X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The results indicate that the lattice of heated rutile specimens was expanded,and ilmenite appeared when the heating temperature reached 900℃ and 1 000℃. Like rutile,ilmenite is a kind of natural semiconductor mineral. It grew in the direction at a 31°angle with rutile's (010) planes and formed dual coupled semiconductor with rutile. The results of the UV-vis test indicate that the appearance of ilmenite in the rutile sample can effectively enhance the photocatalytic activity of the specimens.
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Titanium Dioxide
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The present work is devoted to the influence of combined microwave heating at a frequency of 2.45 GHz on the oxidation process of Vietnamese ilmenite ore. In oxidation by this method, the heating rate is high for the first 0.5 h and decreases during subsequent treatment. In this case, in the whole volume of each ilmenite ore particle, equilibrium pseudobrookite and rutile phases form. It is shown that, under the influence of microwave irradiation, the growth rate of the pseudobrookite phase is higher than that of the rutile phase. To reduce iron contained in the obtained pseudobrookite-rutile mixture, sucrose was added to it. However, the X-ray diffraction analysis data indicate that iron is not reduced under the action of sucrose, and reverse transformation of pseudobrookite into ilmenite occurs.
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Analysis on beach ilmenite placer was conducted by X-ray diffraction(XRD) and chemical analysis.Results indicated that the beach ilmenite placer was comprised of 18.1% ilmenite and 77.4% nigrine,and Fe(Ⅱ) in the ilmenite was mostly oxidized to Fe(Ⅲ).The synthetic rutile was prepared from beach ilmenite placer by reduction-fluidization leaching method.Analysis on the synthetic rutile was conducted by XRD,optical microscope,chemical analysis and grain size screening method.The results showed that the synthetic rutile was a rutile type TiO2,in which the content(mass fraction) of TiO2 was 96.12%,the content of CaO and MgO was 0.21% and particle size of +150 μm accounted for 96.5% with perforated hollow structure.It was a high-end product of synthetic rutile and an ideal material for producing chloride titanium dioxide and sponge titanium.
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The synthetic rutile is prepared by directly leaching ilmenite from Panzhihua area with hydrochloric acid.The results show that the grain size of ilmenite ore and the concentration of hydrochloric acid are the most remarkable influencing factors on the TiO2 grade in synthetic rutile.The TiO2 grade of 94.39% in the synthetic rutile is achieved under the conditions of ilmenite ore 4h grounding,leaching with 30% HCl solution,4:1 for liquid/solid ratio at 95℃ for 4h.While for the unground ilmenite ore,it needs 10h to obtain synthetic rutile of only 91.38% TiO2 with the same leaching parameters as for 4h ground ore.
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