Rutile Core Research Articles

Design of iso-material heterostructures of TiO2via seed mediated growth and arrested phase transitions.

Stabilization of different morphologies of iso-material native/non-native heterostructures is important for electron-hole separation in the context of photo-electrochemical and opto-electronic devices. In this regard, we explore the stabilities of different morphologies of rutile ("native", ground state phase) and anatase ("non-native" phase) TiO2 heterostructures through (1) seed-mediated growth and (2) a thermally induced arrested phase transition synthesis protocol. Furthermore, the experimental results are analyzed through a combination of Density Functional Tight Binding (DFTB) and Finite Element Model (FEM) methods. During the seed-mediated growth, anatase is grown over a polydispersed and polycrystalline rutile core through thermal treatment yielding core-shell, Janus and yolk-shell iso-material heterostructures as observed from HRTEM. The arrested phase transition of anatase to rutile at different annealing temperatures yields rutile crystals in the subsurface region of the anatase and rutile/core-thin anatase/shell heterostructures but does not yield a Janus structure. Small particles that can be modeled via DFTB computations suggest that: (1) a heterostructure of the rutile/core-anatase/shell is energetically more stable than the anatase/core-rutile/shell or any other Janus configuration, (2) the off-centered rutile/core-anatase shell is more favorable to the mid-centered rutile/core-anatase shell and (3) Janus heterostructures can be stabilized when the mass ratio of the rutile seed to anatase overgrowth is high. FEM simulations, performed to evaluate the importance of stress relaxation in bicrystalline materials without defects, suggest that Janus structures can be stabilized in larger particles. The present studies add to the heuristics available for synthesizing iso-material heterostructures.

Subduction channel fluid-rock interaction: Indications from rutile-quartz veins within eclogite from the Yuka terrane, North Qaidam orogen

High-pressure (HP) or ultrahigh-pressure (UHP) rutile-quartz veins that form at mantle depths due to fluid-rock interaction can be used to trace the properties and behavior of natural fluids in subduction zones. To explore the fluid flow and the associated element mobility during deep subduction and exhumation of the continental crust, we investigated the major and trace elements of Ti-rich minerals. Additionally, U–Pb dating, trace element contents, and Lu–Hf isotopic composition of zircon grains in the UHP eclogite and associated rutile-quartz veins were examined in the North Qaidam UHP metamorphic belt, Yuka terrane. The zircon grains in the rutile-quartz veins have unzoned or weak oscillatory zonings, and show low Th/U ratios, steep chondrite-normalized patterns of heavy rare earth elements (HREEs), and insignificant negative Eu anomalies, indicating their growth in metamorphic fluids. These zircon grains formed in 431 ​± ​3 ​Ma, which is consistent with the 432 ​± ​2 ​Ma age of the host eclogite. As for the zircons in the rutile-quartz veins, they showed steep HREE patterns on one hand, and were different from the zircons present in the host eclogite on the other. This demonstrates that their formation might have been related to the breakdown of the early stage of garnet, which corresponds to the abundance of fluids during the early exhumation stage. The core-rim profile analyses of rutile recorded a two-stage rutile growth across a large rutile grain; the rutile core has higher Nb, Ta, W, and Zr contents and lower Nb/Ta ratios than the rim, indicating that the rutile domains grew in different metamorphic fluids from the core towards the rim. The significant enrichment of high field strength elements (HFSEs) in the rutile core suggests that the peak fluids have high solubility and transportation capacity of these HFSEs. Furthermore, variations in the Nb vs. Cr trends in rutile indicate a connection of rutile to mafic protolith. The zircon grains from both the rutile-quartz veins and the host eclogite have similar Hf isotopic compositions, indicating that the vein-forming fluids are internally derived from the host eclogite. These fluids accumulated in the subduction channel and were triggered by local dehydration of the deeply subducted eclogite during the early exhumation conditions.

Characterisation of silicon, zirconium and aluminium coated titanium dioxide pigments recovered from paint waste

Titanium dioxide (TiO2) is the major white pigment used by the paint industry. However, the production of TiO2 is associated with a high carbon footprint. An alternative source of pigment could be created by developing a method to recover it from waste paint. In this paper two rutile pigments with different surface treatments were recovered from paint by a thermal recycling process. The pigments were analysed using powder x-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), surface area measurements (BET), laser diffraction for particle size analysis and zeta potential measurements before and after the recycling process. It was concluded that the rutile cores of both pigments were intact and there were no major changes in particle size distribution or surface charge for either pigment induced by the recycling process. However, XPS and zeta potential measurements showed that the surface coating of the pigments can be more or less degraded depending on the chemical nature, which might imply the need for further re-coating after-treatment. Another option would be to find another application for the pigment where the quality and function of the coating is of less importance.

Hierarchically structural TiO2 nanorods composed of rutile core and anatase shell as a durable anode material for lithium-ion intercalation

In the present work, hierarchically structural TiO2 nanorods composed of rutile core and anatase shell were successfully synthesized via a one-step hydrothermal route for the first time, and then were characterized by X-ray diffraction (XRD), Raman spectroscopy and scanning and transmission electron microscopy (SEM/TEM) measurements. It was found that the crystal phases of the same can be easily adjusted by changing the amount of the reactant during the reaction process. Furthermore, the sample was used as an anode for lithium-ion intercalation and exhibited high capacity and long-term cycling stability due to the synergistic effects of dual-phase TiO2. For instance, the capacities of 102.7 and 84.7mAhg−1 can be kept at 10 C for 1000cycles and 20 C for 5000cycles, respectively.

Formation and preservation of fresh lawsonite: Geothermobarometry of the North Makran Blueschists, southeast Iran

ABSTRACTA low‐grade metamorphic “Coloured Mélange” in North Makran (SE Iran) contains lenses and a large klippe of low temperature, lawsonite‐bearing blueschists formed during the Cretaceous closure of the Tethys Ocean. The largest blueschist outcrop is a >1,000 m thick coherent unit with metagabbros overlain by interlayered metabasalts and metavolcanoclastic rocks. Blueschist metamorphism is only incipient in coarse‐grained rocks, whereas finer grained, foliated samples show thorough metamorphic recrystallization. The low‐variance blueschist peak assemblage is glaucophane, lawsonite, titanite, jadeite±phengitic mica. Investigated phase diagram sections of three blueschists with different protoliths yield peak conditions of ~300–380°C at 9–14 kbar. Magnesio‐hornblende and rutile cores indicate early amphibolite facies metamorphism at >460°C and 2–4 kbar. Later conditions at slightly higher pressures of 6–9 kbar at 350–450°C are recorded by barroisite, omphacite and rutile assemblages before entering into the blueschist facies and finally following a retrograde path through the pumpellyite–actinolite facies across the lawsonite stability field. Assuming that metamorphic pressure is lithostatic pressure, the corresponding counterclockwise P–T path is explained by burial along a warm geothermal gradient (~15°C/km) in a young subduction system, followed by exhumation along a cold gradient (~8°C/km); a specific setting that allows preservation of fresh undecomposed lawsonite in glaucophane‐bearing rocks.

One-Step Microheterogeneous Formation of Rutile@Anatase Core–Shell Nanostructured Microspheres Discovered by Precise Phase Mapping

Nanostructured core–shell microspheres with a rough rutile core and a thin anatase shell are synthesized via a one-step heterogeneous templated hydrolysis process of TiCl4 vapor on the aerosol water–air interface. The rutile-in-anatase core–shell structure has been evidenced by different electron microscopy techniques, including electron energy-loss spectroscopy and 3D electron tomography. A new mechanism for the formation of a crystalline rutile core inside the anatase shell is proposed based on a statistical evaluation of a large number of electron microscopy data. We found that the control over the TiCl4 vapor pressure, the ratio between TiCl4 and H2O aerosol, and the reaction conditions plays a crucial role in the formation of the core–shell morphology and increases the yield of nanostructured microspheres.

Structure and Formation Mechanism of Black TiO2 Nanoparticles.

The remarkable properties of black TiO2 are due to its disordered surface shell surrounding a crystalline core. However, the chemical composition and the atomic and electronic structure of the disordered shell and its relationship to the core remain poorly understood. Using advanced transmission electron microscopy methods, we show that the outermost layer of black TiO2 nanoparticles consists of a disordered Ti2O3 shell. The measurements show a transition region that connects the disordered Ti2O3 shell to the perfect rutile core consisting first of four to five monolayers of defective rutile, containing clearly visible Ti interstitial atoms, followed by an ordered reconstruction layer of Ti interstitial atoms. Our data suggest that this reconstructed layer presents a template on which the disordered Ti2O3 layers form by interstitial diffusion of Ti ions. In contrast to recent reports that attribute TiO2 band-gap narrowing to the synergistic action of oxygen vacancies and surface disorder of nonspecific origin, our results point to Ti2O3, which is a narrow-band-gap semiconductor. As a stoichiometric compound of the lower oxidation state Ti(3+) it is expected to be a more robust atomic structure than oxygen-deficient TiO2 for preserving and stabilizing Ti(3+) surface species that are the key to the enhanced photocatalytic activity of black TiO2.

Effects of the physicochemical properties of titanium dioxide nanoparticles, commonly used as sun protection agents, on microvascular endothelial cells

Until now, the potential effects of titanium dioxide (TiO2) nanoparticles on endothelial cells are not well understood, despite their already wide usage. Therefore, the present work characterizes six TiO2 nanoparticle samples in the size range of 19 × 17 to 87 × 13 nm, which are commonly present in sun protection agents with respect to their physicochemical properties (size, shape, ζ-potential, agglomeration, sedimentation, surface coating, and surface area), their interactions with serum proteins and biological impact on human microvascular endothelial cells (relative cellular dehydrogenase activity, adenosine triphosphate content, and monocyte chemoattractant protein-1 release). We observed no association of nanoparticle morphology with the agglomeration and sedimentation behavior and no variations of the ζ-potential (−14 to −19 mV) in dependence on the surface coating. In general, the impact on endothelial cells was low and only detectable at concentrations of 100 μg/ml. Particles containing a rutile core and having rod-like shape had a stronger effect on cell metabolism than those with anatase core and elliptical shape (relative cellular dehydrogenase activity after 72 h: 60 vs. 90 %). Besides the morphology, the nanoparticle shell constitution was found to influence the metabolic activity of the cells. Upon cellular uptake, the nanoparticles were localized perinuclearly. Considering that in the in vivo situation endothelial cells would come in contact with considerably lower nanoparticle amounts than the lowest-observable adverse effects level (100 μg/ml), TiO2 nanoparticles can be considered as rather harmless to humans under the investigated conditions. Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-013-2130-3) contains supplementary material, which is available to authorized users.

Omphacite-bearing calcite marble and associated coesite-bearing pelitic schist from the meta-ophiolitic belt of Chinese western Tianshan

In the meta-ophiolitic belt of Chinese western Tianshan, marble (5–50cm thick) is found interlayered with pelitic schist. The marble is mainly composed of calcite (>90% in volume) and accessory phases include omphacite, quartz, dolomite, albite, phengite, clinozoisite and titanite with or without rutile core. This is the first omphacite (Jd35–50) reported from marble of Chinese western Tianshan. It mainly occurs in the calcite matrix, rarely as inclusion in albite. The presence of omphacite suggests that the layered marble was subjected to eclogite-facies metamorphism, consistent with the occurrence of high-Si phengite (Si a.p.f.u. up to 3.7) and aragonite relic in albite. The associated pelitic schist consists of quartz, white mica (phengite+paragonite), garnet, albite, amphibole (barroisite±glaucophane) and rutile/titanite, as well as minor amounts of dolomite, tourmaline and graphite. Coesite is optically recognized within porphyroblastic pelitic garnet and is further confirmed via Raman spectroscopy. Thermodynamic models support the UHP metamorphism of calcite marble, similar to the associated pelitic schist. Shared UHP-LT history of calcareous and pelitic rocks in Chinese western Tianshan suggests that the supracrustal carbon-rich sediments have been carried to depths of >90km during fast subduction and thus are potential sources for carbon recycled into arc crust.

Major Nb/Ta Fractionation Recorded in Garnet Amphibolite Facies Metagabbro

AbstractMobilities and fractionations of high-field-strength elements, especially Nb and Ta within a subducting slab, are important for deciphering the formation of the continental crust (CC). Here we report geochemical results on an epidote garnet amphibolite facies metagabbro body in the Tongbai-Dabie orogenic belt, central China. Our samples were hydrated during prograde metamorphism of the Triassic plate subduction. Major minerals such as amphibole, garnet, rutile, and ilmenite and garnet amphibolite bulk rocks show varied and overall lower Nb/Ta and/or Zr/Hf ratios than the continental crust. Magma differentiation might have contributed to variations of Zr/Hf but not those of Nb/Ta, suggesting major Nb/Ta fractionations during plate subduction. LA-ICPMS in situ trace element analyses of amphibole and especially rutile grains exhibit obvious chemical zonations. Typically, the rutile cores are usually small with higher Nb and Ta concentrations and lower Nb/Ta ratios compared to the thick rims. Chemical...

Root growth of TiO 2 nanorods by sputtering

The growth of TiO 2 nanorods by a simple sputtering method is reported. Here we show that by sputtering of Ti target in argon–oxygen plasma it is possible to grow rutile core and anatase shell heterostructure TiO 2 nanorods on gold (Au) coated Si(1 0 0) substrate without external heating. It seems that the nanorods grow because of the stress assisted diffusion of under-laying Au atoms into the TiO 2 film followed by catalytic growth of the nanorods at the root.

U-Pb ages and trace elements in metamorphic zircon and titanite from UHP eclogite in the Dabie orogen: constraints on P-T-t path

Laser ablation inductively coupled plasma mass spectrometry analyses of U–Pb isotopes and trace elements in zircon and titanite were carried out on epoxy mounts and thin sections for ultrahigh-pressure (UHP) eclogite in association with paragneiss in the Dabie orogen. The results provide a direct link between metamorphic ages and temperatures during continental subduction-zone metamorphism. Zircon U–Pb dating gives two groups of concordant ages at 242 ± 2 to 239 ± 5 Ma and 226 ± 2 to 224 ± 6 Ma, respectively. The Triassic zircon U–Pb ages are characterized by flat heavy rare earth element (HREE) patterns typical of metamorphic growth. Ti-in-zircon thermometry for the two generations of metamorphic zircon yields temperatures of 697 ± 27 to 721 ± 8 °C and 742 ± 19 to 778 ± 34 °C, respectively. We interpret that the first episode of zircon growth took place during subduction prior to the onset of UHP metamorphism, whereas the second episode in the stage of exhumation from UHP to HP eclogite facies regime. Thus, the continental subduction-zone metamorphism of sedimentary protolith is temporally associated with two episodes of fluid activity, respectively, predating and postdating the UHP metamorphic phase. The significantly high Ti-in-zircon temperatures for the younger zircon at lower pressures indicate the initial ‘hot’ exhumation after the peak UHP metamorphism. There are two types of titanite. One exhibits light rare earth element (LREE) enrichment, steep MREE–HREE patterns and no Eu anomalies, and yields Zr-in-titanite temperatures of 551 to 605 °C at 0.5 GPa, and the other shows LREE depletion and flat MREE–HREE patterns, and gives Zr-in-titanite temperatures of 782–788 °C at 2.0 GPa. The former is amenable for U–Pb dating, yielding a discordia lower intercept age of 252 ± 3 Ma. Thus, the first type of titanite is interpreted to have grown in the absence of garnet and plagioclase and thus in the early stage of subduction. In contrast, the second one occurs as rims surrounding rutile cores and thus grew in the presence of garnet during the ‘hot’ exhumation. Therefore, there is multistage growth of zircon and titanite during the continental subduction-zone metamorphism. The combined studies of chronometry and thermobarometry provide tight constraints on the P–T–t path of eclogites during the continental collision. It appears that the mid-T/UHP eclogite facies zone would not only form by subduction of the continental crust in a P–T path slightly below the wet granite solidus, but also experience decompression heating during the initial exhumation.

Synthesis of rutile–anatase core–shell structured TiO2 for photocatalysis

The crystal phases, surface states and hydroxyl groups of TiO(2) can intrinsically determine its performance in the applications of photocatalysis and dye-sensitized solar cells. Here we developed a unique rutile-anatase core-shell structured nanocrystalline TiO(2) with controlled surface states and hydroxyl groups for photocatalytic applications via a simple phase conversion method, where the semi-crystalline TiO2 embedded in the caramelized sucrose matrix following the hydrothermal process was first converted to a composite of TiO(x)C(y)/C by calcining in a nitrogen atmosphere, and this composite was subsequently converted to TiO(2) by calcining in an oxygen atmosphere. It was found that the rutile phase exists within anatase particles, and the depth of rutile core in the anatase shell particles can be tuned by adjusting the thickness of TiO(x)C(y) (x y) in the precursor composite TiO(x)C(y)/C simply through changing the calcination temperature. More interestingly, the amount of surface adsorbed water and hydroxyl groups and the abundance of surface states in such core-shell structured TiO(2) can be controlled by changing the size of the rutile and anatase phases. Finally, photocatalytic degradation reaction as an example clearly demonstrates the substantial role of the surface states in determining photocatalytic activity of the TiO(2) in desired applications.

HFSE systematics of rutile-bearing eclogites: New insights into subduction zone processes and implications for the earth’s HFSE budget

The depleted mantle and the continental crust are generally thought to balance the budget of refractory and lithophile elements of the Bulk Silicate Earth (BSE), resulting in complementary trace element patterns. However, the two high field strength elements (HFSE) niobium and tantalum appear to contradict this mass balance. All reservoirs of the silicate Earth exhibit subchondritic Nb/Ta ratios, possibly as a result of Nb depletion. In this study a series of nineteen orogenic MORB-type eclogites from different localities was analyzed to determine their HFSE concentrations and to contribute to the question of whether subducted oceanic crust could form a hidden reservoir to account for the mass imbalance of Nb/Ta between BSE and the chondritic reservoir. Concentrations of HFSE were analyzed with isotope dilution (ID) techniques. Additionally, LA-ICPMS analyses of clinopyroxene, garnet and rutile have been performed. Rutile is by far the major host for Nb and Ta in all analyzed eclogites. However, many rutiles revealed zoning in Nb/Ta ratios, with cores being higher than rims. Accordingly, in situ analyses of rutiles have to be evaluated carefully and rutile cores do not necessarily reflect a bulk rock Nb and Ta composition, although over 90% of these elements reside in rutile. The HFSE concentration data in bulk rocks show that the orogenic eclogites have subchondritic Nb/Ta ratios and near chondritic Zr/Hf ratios. The investigated eclogites show neither enrichment of Nb compared to similarly incompatible elements (e.g. La), nor fractionation of Nb/Ta ratios relative to MOR-basalts, the likely precursor of these rocks. This indicates that during the conversion of the oceanic crust to eclogites in most cases, (1) HFSE and REE have similar mobility on average, possibly because both element groups remain in the down going slab, and (2) no significant fractionation of Nb/Ta occurs in subducted oceanic crust. With an average Nb/Ta ratio of 14.2 ± 1.4 (2s.e.), the investigated eclogites cannot balance the differences between BSE and chondrite. Additionally, as their average Nb/Ta is indistinguishable from the Nb/Ta of MORB, they are also an unlikely candidate to balance the potentially small differences in Nb/Ta between the continental crust and the mantle.

The origin of rutile-ilmenite aggregates (“nigrine”) in alluvial-fluvial placers of the Hagendorf pegmatite province, NE Bavaria, Germany

Titanium placer deposits occur in alluvial-fluvial drainage systems which dissect Moldanubian gneisses intruded by Late Variscan pegmatites (Hagendorf province) in southern Germany. Based upon their texture (zonation, exsolution lamellae, intergrowth), microchemical data (Nb, Cr, Ta, V, Fe, W, Sn) and mineral inclusions, two major grain types of intergrown rutile and ilmenite have been established. Grains of type A are always zoned and consist of rutile cores enveloped by ilmenite containing small inclusions of wolframite. A core-rim transition zone is characterized by complex relations of rutile and ilmenite, with rutile lamellae being rich in Nb, V and Fe. Types B1 and B2 aggregates consist of ilmenite with lamellae of niobian rutile and/or ilmenorutile, and additionally have inclusions of ferrocolumbite, pyrochlore, betafite, sphalerite, pyrrhotite and Fe oxides. Such grain types featuring an intimate intergrowth of rutile and ilmenite were called nigrine. Type-C grains are quite similar in their morphological appearance but consist of W-enriched rutile devoid of mineral inclusions and reaction products. Pseudorutile and leucoxene replacing minerals of the nigrine aggregates are presumably caused by supergene alteration under fluctuating redox conditions. Phosphate and aluminum remobilized by supergene processes led to the formation of hydrous Ti-rich phases containing Al, P and Fe. High Nb and W concentrations in nigrine aggregates and in rutile type C may be taken as a marker for highly differentiated granites or pegmatites. This has implications for both, heavy-mineral-based provenance analysis and stream sediment exploration.

Methoxide of an Anderson‐Type Polyoxometalate and Its Conversion to a New Type of Species, [IMo9O32(OH)(OH2)3] 4‐.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Methoxide of an Anderson-Type Polyoxometalate and Its Conversion to a New Type of Species, [IMo9O32(OH)(OH2)3]4-

A totally new type of polyoxometalate, [IMo(9)O(32)(OH)(OH(2))(3)](4)(-), has been synthesized by reacting [IMo(6)O(22)(OMe)(2)](3)(-) with water. The [IMo(9)O(32)(OH)(OH(2))(3)](4)(-) anion further transforms into [(IMo(7)O(26))(2)](6)(-), a molecular oxide that has a rutile core, in dry acetonitrile, while it stays intact for several hours in wet acetonitrile.