Minor Ti Research Articles

Carrier-microencapsulation for preventing pyrite oxidation

The oxidation of pyrite causes the formation of acid mine drainage polluted by heavy metals. This paper proposes carrier-microencapsulation (CME) for preventing pyrite oxidation. In CME, an organic agent is used as an in-situ carrier for transporting Ti from Ti minerals to the pyrite surface through an aqueous phase. Then, the organic carrier is decomposed and Ti(OH)4 or TiO2 film is formed on the pyrite surface as a protective coating against oxidation.To demonstrate the effect of CME on pyrite oxidation, shaking-flask leaching experiments of ground pyrite were performed at 298 K in air for 25 days, with or without anatase (TiO2) and catechol (1,2-dihydroxybenzene) as the organic carrier. The amounts of Fe and S extracted from the pyrite were lower with TiO2 and catechol than without TiO2 or catechol, indicating that CME using TiO2 and catechol is effective in suppressing pyrite oxidation. When TiO2 and catechol coexist, the Ti concentration in the solution phase increased initially and then decreased. SEM-EDX analysis of the CME-treated pyrite showed that Ti and O are present on the pyrite surface. Cyclic voltammogram of catechol showed that catechol was oxidized on pyrite electrode. These results indicate that Ti is extracted from TiO2 by catechol as a Ti-catechol complex and that the complex is adsorbed and oxidized on pyrite to form a Ti(OH)4 or TiO2 coating suppressing pyrite oxidation.

Elemental geochemistry of river sediments from the Deccan Traps, India: Implications to sources of elements and their mobility during basalt–water interaction

The abundances of several major (Na, Ca, Mg, K, Al, Ti, Fe) and minor elements (Sr, Ba, Mn, P, V, Cr, Ni, Cu and Zn) have been measured in twenty-eight sediment samples from seventeen rivers belonging to the Krishna headwaters and west flowing Western Ghat rivers, all of which drain the Deccan Trap basalts. These results, particularly those of Na, Ca, Mg and Sr coupled with those reported for these elements in the dissolved phase of the same rivers, provide an assessment of their relative mobility and insight into the nature of chemical weathering of Deccan basalts. The sediments are heavily depleted in Na, Ca, Mg and Sr relative to parent basalts (by ∼ 60%). The abundance ratios of these elements in sediments are roughly the same as those in basalts and in dissolved phases of these rivers [Das, A., Krishnaswami S., Sarin M. M., Pande K., 2005a. Chemical weathering in the Krishna basin and the Western Ghats of the Deccan Traps: Rates of basalt weathering and their controls. Geochim. Cosmochim. Acta 69, 2067–2084.], suggesting their near congruent release from basalts to water during chemical weathering, both at present and over the residence time of particles in the basin. K and Ba show limited mobility relative to the above four elements. The abundances of K and Ba are strongly correlated, most likely due to their association in rock forming minerals. Al, Fe and Ti, are generally enriched in the sediments, resulting from the loss of more mobile elements from basalts and their association with secondary minerals formed during weathering. The data also provide evidence for the fractionation of Fe and Al during chemical weathering and erosion. Fe and Ti exhibit significant correlation, attributable either to their co-occurrence in weathering resistant minerals and/or due to scavenging of Ti by Fe oxy-hydroxides formed during weathering of basalts. The abundance of minor elements (Mn, P, V, Cr, Ni, Cu and Zn) and their ratios with Al show significant scatter, by and large bracketing the range reported for Deccan basalts. The wide and overlapping ranges in the concentration of these elements and their ratios relative to Al, between sediments and basalts place severe constraints in assessing their mobility during weathering and erosion, and in judging the role of anthropogenic sources in contributing to their abundances. Among the minor elements, there is a hint that Zn concentration may have been influenced by anthropogenic inputs. Mn, V and Ni, analogous to Ti, show significant correlation with Fe, either due to their association with Fe–Ti minerals or their sequestration by Fe oxy-hydroxides. The mobility of elements during weathering and erosion of Deccan basalts follows the trend (Na ≈ Ca ≥ Mg ≈ Sr) > (K ≥ Ba) > (Al ≥ Fe ≈ Ti). There is considerable spatial variability in the intensity of chemical weathering of Deccan basalts. The CIA (Chemical Index of Alteration) values for the sediment range between 42 and 92, compared to ∼ 37 for the Deccan basalts. The lower CIA values are in sediments richer in CaCO 3. This may be a result of semi-arid climate of the region which facilitate CaCO 3 precipitation and restrict chemical weathering/erosion. Higher CIA values are generally associated with sediments from basins with higher runoff. Modeling the major element composition of sediment and water yields estimates of particulate abundances in water. These estimates agree with the measured values within a factor of ∼ 2 for some of the rivers whereas in some others they differ by more than a factor of 3–4. The use of sediment composition instead of that of the suspended matter, spatial and temporal variations in sediment flux and non-steady state erosion all can contribute to this discrepancy. These factors also seem to be contributing to difference in CO 2 consumption estimated from sediment composition and that reported based on dissolved phase data.

EPR evidence for maghemitization of magnetite in a tropical soil

Electron paramagnetic spectroscopy (EPR) was used in combination with standard rock magnetic methods to study magnetic minerals in a tropical soil. The susceptibility and hysteresis measurements showed magnetite grains with a Curie temperature near 850 K as the dominant magnetic remanence carriers in the soil. A minor Ti content in the magnetite was found by energy dispersive X-ray analysis. In order to get insight into the weathering status of the magnetite, different chemical treatments, including oxalate and citrate—bicarbonate—dithionite (CBD) extraction, were applied to the soil samples. The hysteretic properties exhibited no significant differences between the untreated and the CBD or oxalate treated samples. By contrast, the comparison of the EPR spectra revealed a significant broadening of the linewidth (δB) and a shift of the g-values (geff) to lower fields after the CBD treatment. Furthermore, the spectral parameters geff and δB exhibited an angular dependence. At low temperature, the CBD treated samples showed a jump in δB between 120 and 100 K, the temperature range characteristic for the Verwey transition in magnetite. The changes in the spectral properties after the CBD treatment, which dissolves ferric oxides, were attributed to the removal of maghemite formed by the oxidation of magnetite, that is, during the maghemitization of the magnetite grains.

Mesozoic monazite in Neoproterozoic metasediments: Evidence for low-grade metamorphism of Sinian sediments during Triassic continental collision, Liaodong Peninsula, NE China

Sericite phyllite from the Sinian Shisanlitai Formation, Dalian area, Liaodong Peninsula, NE China, contains an assemblage of newly-formed lower-greenschist facies minerals (sericite, chlorite, Fe minerals and Ti minerals) plus aggregates of fine-grained monazite. The texture of the monazite, its mineral inclusions, and its close association with Fe oxide minerals show that it is not detrital or diagenetic, but a product of the low-grade metamorphism. SHRIMP U-Th-Pb dating of the monazite at 217 ± 15 Ma shows that the metamorphism, and associated regional deformation and fluid flow, occurred in the Late Triassic, coeval with the waning stages of the Dabie-Sulu orogeny. The Dabie-Sulu tectonothermal event has produced both deformation and metamorphism in rocks of the eastern North China Block at least up to ∼200 km north of the main continent-continent collision zone.

A New Occurrence and New Data on Akdalaite, a Retrograde Mineral from UHP Whiteschist, Kokchetav Massif, Northern Kazakhstan

Akdalaite (5Al2O3·H2O), as well as hogbomite, kyanite, Zn-bearing staurolite, Mg-chlorite, gahnite, hercynite, quartz, apatite, and zircon, are present as submicrometer-size minerals associated with rutile aggregates occurring as inclusions in garnet porphyroblasts of whiteschist from the Kulet Kol region, Kokchetav Massif, northern Kazakhstan. The akdalaite crystals, ∼0.5 to 1 μm in size, are subhedral to euhedral, and are bounded by (0001), (0001), {1100}, {1101} facets. EDX analyses show minor Si, Ti, Cr, Fe, Mg, Zn, and Ga, in addition to the major component Al. Electron diffraction data yield the following crystal structural information: space group P63mc, and a = 5.58(1) Å, c = 8.86(2) Å, which are similar to those of synthetic tohdite, but are distinctly differentfrom those reported for the type specimen of akdalaite (P612 or P61 , a = 14.97 Å, c = 2.87 Å). The akdalaite type specimen, stored in the museum of the All-Russian Institute of Mineral Resources (VIMS) in Moscow, had also been re-examined; it has crystallographic parameters similar to tohdite. It is therefore concluded that crystallographic data of the akdalaite type specimen derived from powder X-ray experiments are in error, and that akdalaite is the natural counterpart of tohdite.

Lu–Hf apatite geochronology of mafic cumulates: An example from a Fe–Ti mineralization at Smålands Taberg, southern Sweden

We have employed Lu–Hf apatite chronology to determine the age of a magnetite-rich melatroctolite in southern Sweden, known as the Smålands Taberg Fe–Ti ore deposit. The melatroctolite is poor in incompatible elements and minerals forming at more advanced stages of differentiation, which precludes the use of minerals (baddeleyite, zircon, titanite or apatite) commonly used for dating the emplacement of igneous rocks. Enclaves of leucogabbro in the melatroctolite have REE patterns parallel with the host melatroctolite and identical initial Hf and Nd isotope compositions. These characteristics are conclusive evidence for a common parental magma. The leucogabbro is a slightly more evolved facies that underwent limited fractionation of olivine and titanomagnetite; the two major mineral phases in the melatroctolite. Apatite and plagioclase, separated from the leucogabbro, plus a whole-rock sample define a Lu–Hf isochron with a slope corresponding to an age of 1204.3 ± 1.8 Ma. This result is close to the lower age boundary previously reported for this magmatic event comprising dolerites, syenites and granites. The Lu–Hf apatite chronometer merits attention as a new tool in generating accurate and precise ages for igneous, silica-undersaturated rocks that may be difficult to date with traditional techniques.

Transmission electron microscopy and atomic force microscopy characterisation of titanium-base alloys nitrided under glow discharge

The microstructure of titanium alloys (Ti–1Al–1Mn, Ti–6Al–4V) nitrided under glow discharge was characterised using light microscopy , X-ray diffraction and analytical electron microscopy. The investigations revealed a complex multilayered microstructure produced by diffusion at 850 and 900 °C at the surface. The layers formed on the Ti–1Al–1Mn alloy were identified as δ-TiN (face-centred cubic NaCl type), δ′-Ti 2N (tetragonal body-centred), ε-Ti 2N (tetragonal primitive) phases and α (N) solid solution containing up to 19 at.% nitrogen. The layers formed on the Ti–6Al–4V alloy also contained, besides the phases mentioned above, Ti 2AlN and other minor Ti–Al–N ternary phases. The layer topography of both nitrided alloys, examined by atomic force microscopy, exhibited pronounced surface development. A relationship between the microstructure of the alloys and their micromechanical and tribological properties has been established. It shows that the improved properties are related to the presence of nanocrystalline δ-TiN in the outermost sublayer on the top of the layers composed of δ′ + ε-Ti 2N and Ti 2AlN crystals.

Crystal chemistry and paragenesis of compositionally unique (Al-, Fe-, Nb-, and Zr-rich) titanite from Afrikanda, Russia

Titanite is a common accessory mineral in silicocarbonatite from the Afrikanda alkaline-ultramafic complex, Kola Peninsula, Russia. In addition to large crystals (described elsewhere), this rock contains microscopic crystals and aggregates of titanite intimately associated with, or mantling, primary Ti minerals (perovskite, ilmenite, magnetite, and garnets). The microcrysts commonly exhibit complex zoning patterns that represent a combination of oscillatory, core-rim, and/or sectorial zoning. Eight varieties of microcrystic titanite, differing in chemical composition, mode of occurrence, and style of zoning, can be distinguished. Most of the compositions have >20% of the Ti site occupied by Al, Fe, Nb, Zr, or a combination thereof, whereas substitutions at the Ca site are limited to <2%. Analysis of element correlations and Raman spectra suggests that the compositional diversity of the titanite arises from the following substitutions: (Al,Fe3+)(OH)Ti-1O-1, (Al,Fe3+)NbTi-2, Al(OH)Zr-1O-1, and ZrTi-1. Using the end-member notation, different varieties of the microcrysts contain up to 20 mol% CaFeSiO4(OH), 37 mol% CaAlSiO4(OH), 35 mol% Ca(Al0.5Nb0.5)SiO5, and 26 mol% CaZrSiO5. This compositional diversity is unparalleled by titanite from any other locality or rock type, including material from three other Kola carbonatites examined in the present work (Kovdor, Turiy Mys, and Seblyavr). All compositional varieties of the microcrystic titanite crystallized at late evolutionary stages as products of reaction between the primary Ti minerals and a deuteric aqueous fluid at temperatures near 200 °C, weakly acidic pH, and a(H4SiO40) >10.4. Under these conditions, the earlier-formed Zr minerals zirconolite and zircon were unstable and underwent extensive re-equilibration with the fluid, involving partial removal of Zr. Implications of these data for the safe disposal of nuclear waste are discussed. The structure of zirconian titanite was examined using a synthetic sample of analogous composition (25 mol% CaZrSiO5). Its structure was refined by the Rietveld method from X-ray powder diffraction data in space group A2/a [a 7.1119(7), b 8.7724(8), and c 6.6007(6) Å, β 113.569(4)°]. Reflections violating A centering and/or indicative of Ti-Zr ordering were not observed, and attempts to refine the structure in two alternative space groups (P21/a and P21) were unsuccessful.

Lithium in nigerite-group minerals

Nigerite-group minerals (polysomatic tin-bearing oxides) from the type locality Egbe District, Kabba Province (Nigeria) and from the abandoned tin mine of Tsomtsaub, between Omaruru and Uis in Namibia have been reinvestigated chemically and by single-crystal X-ray diffraction. At both localities nigerite occurs in quartz-sillimanite rocks associated with pegmatites. Both nigerites can be classified as ‘zinconigerite-6 N 6 S ’, space group R 3M m , a = 5.71, c = 55.4 A. In both structures the octahedral M2 site in the T1-layer of the nolanite module is completely occupied by Sn with minor Ti. Charge balance for the tetravalent cations is achieved by partial Li substitution for Al in adjacent octahedral sites (O-layer) sandwiched between two Trlayers. For the first time the presence of essential Li in nigerite-group minerals has been demonstrated by Secondary Ion Mass Spectrometry (SIMS) yielding 0.61 (6) and 0.70(7) wt.% Li2O for nigerite from Nigeria and Namibia, respectively. Associated gahnite in the Nigerian sample is free of Li2O. Both investigated nigerite-group minerals have tetrahedral Zn: Fe > 1 in the spinel module and are therefore assigned to the zinconigerite subgroup. It is suggested that Sn-rich nigerite-group minerals (6 N 6 S and 2 N 1 S polysomes) from rare-element pegmatites or skarns possess essential Li for charge balance whereas low Sn, Ti-bearing nigerites, displaying an extended solid solution with hogbomite, do not require Li for charge balance.

Baddeleyite, zirconolite and calzirtite in lateritic rocks from Ryoke and Chichibu Terranes, Japan

Baddeleyite, zirconolite and calzirtite were found in lateritic rocks from Ryoke and Chichibu Terranes in southwestern Japan. This is a new type of natural occurrence of the minerals. The lateritic rocks are associated with limestone widely distributed into Ryoke metamorphic and Chichibu non-metamorphic complexes. Baddeleyite, zirconolite and calzirtite are associated with Ti minerals such as anatase, ilmenite, perovskite and titanite. Calzirtite occurs simultaneously with perovskite. Rhabdophane-(Ce) like minerals also occurs in the lateritic rocks such as in emeries from Ko-Oge Island. Baddeleyite and calzirtite have compositions close to the ideal compositions, ZrO2 and Ca2Zr5Ti2O16. Zirconolite, CaZrTi2O7, accommodates significant amounts of Fe, Nb, Ta, and small amounts of Al and REE. Minor amounts of ACT are also found in the mineral. The chemical substitution in zirconolite is controlled by the reaction: REE3+ + 2(Al + Fe)3+ + (Nb + Ta)5+ ⇔ Ca2+ + 3Ti4+. Baddeleyite is a relict of the lateritization stage, or formed by the decomposition of zircon. Zirconolite formed during the prograde stage of metamorphism by the reaction; calcite + 2anatase + baddeleyite ⇔ zirconolite + CO2. The formation of calzirtite in Ca-metasomatic emery is independent from the deformation of zirconolite during the prograde stage of metamorphism.

Major and trace element geochemistry and 40Ar/ 39Ar geochronology of Laramide plutonic rocks associated with gold-bearing Fe skarn deposits in Guerrero state, southern Mexico

Fe–Au skarn deposits related to intrusive centers, mostly of granodioritic composition, are widespread in southern Mexico's Guerrero state. These intrusive rocks are largely associated with the NW–SE-oriented Laramide magmatic belt that extends across most of western Mexico. The geochemical composition and ages of representative rocks from the Mezcala mining district in central Guerrero are studied to evaluate the petrogenetic aspects of the ore-related magmas. Some major and trace elements display nearly linear silica variation trends, which suggest a possible comagmatic origin. However, other elements have scattered distributions, possibly due to irregular mantle-to-crust magma mixing ratios, heterogeneities in the composition of the assimilated crustal material, or modifications during the emplacement or postemplacement processes. Major element chemistry indicates calc-alkalic metaluminous compositions, whereas trace element data suggest a volcanic arc tectonic setting, confirming that these rocks evolved from magmas generated above a subduction zone. Compared with the Laramide granites from the northern part of the belt in northwestern Mexico, which intruded a crust underlain by Proterozoic North American rocks, the studied samples are similar but relatively low in Nb and high in Sr, the middle rare earth elements (REE), P, and Zr. They also display minor Ti enrichments and a moderate depletion in the heavy REE. These characteristics may indicate a source of basaltic composition. New 40Ar/ 39Ar dating of granodiorites and dacite porphyries shows a north-to-south age progression from 66.2±0.8 Ma in the northern part of the belt to 62.2±0.7 Ma in the south. Moreover, the argon dates identify a younger postorogenic igneous event 35–30 Ma ago. This event is poorly documented and may have occurred after the extinction of the Laramide arc and prior to the mid-Tertiary Sierra Madre Occidental ignimbrite flare-up. On the basis of limited geochemical data, these rocks appear to be depleted in P 2O 5 and Sr and enriched in U relative to the studied Laramide granites. A Fe skarn deposit located in Buena Vista de Cuéllar, in the north central part of Guerrero, suggests that this magmatic pulse took place after the ore development of the Mezcala district.

Preparation of calibration materials for microanalysis of Ti minerals by direct fusion of synthetic and natural materials: experience with LA-ICP-MS analysis of some important minor and trace elements in ilmenite and rutile.

Calibration materials for microanalysis of Ti minerals have been prepared by direct fusion of synthetic and natural materials by resistance heating in high-purity graphite electrodes. Synthetic materials were FeTiO3 and TiO2 reagents doped with minor and trace elements; CRMs for ilmenite, rutile, and a Ti-rich magnetite were used as natural materials. Problems occurred during fusion of Fe2O3-rich materials, because at atmospheric pressure Fe2O3 decomposes into Fe3O4 and O2 at 1462 degrees C. An alternative fusion technique under pressure was tested, but the resulting materials were characterized by extensive segregation and development of separate phases. Fe2O3-rich materials were therefore fused below this temperature, resulting in a form of sintering, without conversion of the materials into amorphous glasses. The fused materials were studied by optical microscopy and EPMA, and tested as calibration materials by inductively coupled plasma mass spectrometry, equipped with laser ablation for sample introduction (LA-ICP-MS). It was demonstrated that calibration curves based on materials of rutile composition, within normal analytical uncertainty, generally coincide with calibration curves based on materials of ilmenite composition. It is, therefore, concluded that LA-ICP-MS analysis of Ti minerals can with advantage be based exclusively on calibration materials prepared for rutile, thereby avoiding the special fusion problems related to oxide mixtures of ilmenite composition. It is documented that sintered materials were in good overall agreement with homogeneous glass materials, an observation that indicates that in other situations also sintered mineral concentrates might be a useful alternative for instrument calibration, e.g. as alternative to pressed powders.

Accessory mineral record of magma-fluid interaction in the Laoshan I- and A-type granitic complex, Eastern China

The Laoshan granitic complex (LGC) in East China is composed of many intrusive units which can be divided into two distinct suites, I-type and A-type. There exist different assemblages of accessory minerals between the two units. In the I-type suite, the quartz monzonite contains the accessory mineral assemblage of titanite + magnetite + zircon, the biotite monzogranite is titanite + magnetite + ilmenite + zircon, whereas the accessory mineral assemblage in the quartz syenite is rutile + magnetite + zircon. In the alkali granite of the A-type suite, accessory mineral assemblage consists of Fe-Ti minerals including titanite, magnetite, ilmenite and rutile in addition to frequently-observed zircon and sparse pyrochlore. In the arfvedsonite granite, however, magnetite, titanite and rutile disappear, Nb-rich pyrophanite-dominant ilmenite becomes the only Ti mineral. In addition, large amounts of mineral containing REE and HFSE were crystallized. Zircon is also present in the all two facies of the A-type suite, but with different compositions. Especially, zircon in the arfvedsonite granite is enriched in Hf but poor in U and Th relative to the alkali granite. The change in accessory mineral assemblage in the different facies of both I-type and A-type suites reflects variation in temperature and/or fO2 during crystallization of every magma chamber. Particularly, presence of the large amount of HFSE- and REE-bearing minerals in the arfvedsonite granite may be attributed to the accumulation of fluids at the end of evolution of A-type magma. Geochemically, the fluid is enriched, on one hand, in REE and HFSE, and on other hand, in volatiles (F, P and CO2).

Fractionation of Nb and Ta from Zr and Hf at Mantle Depths: the Role of Titanian Pargasite and Kaersutite

Selective enrichment or depletion in either Zr and Hf (HFSE) INTRODUCTION or Nb and Ta (HFSE) is a feature commonly observed in many Because of their similar crystal-chemical properties (i.e. mantle-derived melts and amphiboles occurring as either disseminated high charge and ionic radius), high field strength elements minerals in mantle xenoliths and peridotite massifs or in vein (HFSE: Ti, Zr, Hf, Nb and Ta) are considered to behave assemblages cutting these rocks. The fractionation of Nb from Zr as a coherent group of substituents in rock-forming silicate seen in natural mantle amphiboles suggests that their incorporation minerals, and thus are not expected to fractionate greatly is governed by different crystal-chemical mechanisms. An extensive during partial melting and crystallization processes (Sun set of new partitioning experiments between pargasite–kaersutite and & McDonough, 1989). Nevertheless, fractionation of melt under upper-mantle conditions shows that HFSE incorporation HFSE from HFSE is a common feature in many and fractionation depends on amphibole major-element composition primitive mantle melts such as island-arc volcanics and and the presence or absence of dehydrogenation. Multiple regression intra-plate alkaline melts, suggesting either the presence analysis shows that DNb/Zr is strongly dependent on the mgof a solid phase with DNb,Ta significantly different from number of the amphibole as a result of a combination of amphibole DZr,Hf, or of two distinct phases controlling these element and melt structure effects, so that the following generalizations pairs. Experimental investigations of HFSE decoupling apply: (1) high-mg-number amphiboles crystallized from unmodified have been so far focused on Ti minerals (rutile and mantle melts more easily incorporate Zr relative to Nb leading to ilmenite), because of their high compatibility for HFSE an increase of the Nb/Zr ratio in the residual melt; (2) low-mgand their consequent capability of altering HFSE signumber amphiboles, such as those found in veins cutting peridotites, natures of equilibrium melts. Rutile has been shown to may strongly deplete the residual melt in Nb and cause very low have partition coefficients for Ta and Nb exceeding that Nb/Zr in residual melts. Implications and applications to mantle for Zr by one to two orders of magnitude, with Zr a environments are discussed. further one to two orders higher than other trace elements ( Jenner et al., 1993; Foley et al., 2000). Rutile could thus cause significant decoupling between Nb and Zr, and has the potential to produce the pattern typical of islandarc basalts (Foley & Wheller, 1990; Foley et al., 2000), in

Al and Ti secondary neutral and secondary ion emission from oxide samples in the high-frequency sputtering mode of HF-plasma SNMS

A strong Al+ and a minor Ti+ peak without a proportional increase of the O+ signal in SNMS high-frequency sputtering mode (HFM) time profiles of an insulating µm-thick oxide layer on Ti-48Al-2Cr-2Nb led us to check for a possible contribution of positive secondary ions (SI+). SI+ and SI– (negative secondary ions) can be detected in ion energy spectra. This is shown using Al+, O–, AlO–, and AlO2– ions sputtered from massive Al2O3. Similarly, and depending on stoichiometry, also Ti+ from mixed sintered, microscopically inhomogeneous Al2O3-TiO2-SiO2 pellets has been identified to be partly SI+. The subtraction of an assumed contribution of ionized secondary neutrals (SN+) suggests that SI+ may form several 10% of the detected ions obtained in the HFM sputtering and plasma processes. However, the positive surface potential of some 10 V being necessary to cause detectable SI+ contributions does not build up on µm-thin insulating layers. Therefore, we have to conclude that the Al+ and Ti+ peaks in the sputter time profiles of the µm-thick oxide layer on Ti-48Al-2Cr-2Nb which are accompanied by an O+ deficiency cannot have been caused by SI+. Instead, their more probable origin is the inhomogeneous Al2O3 interlayer itself. Together with the residues of a topmost TiO2 layer which has strongly been depleted in O by preferential sputtering, the relative O+ deficiency may be explained without assuming SI+ contributions.

Evidence of titanium mobility in soil profiles, Manaus, central Amazonia

Titanium minerals are classically considered to be very resistant to weathering in soils. Consequently, variations of titanium concentrations within the soils were used to estimate rates of weathering of parent material. Mobility of Ti was studied in an Amazonian ferralsol using a large set of techniques. Chemical and mineralogical studies of Ti distribution in the soil profile showed that weathering of Ti minerals follows the mineral sequence: ilmenite, pseudorutile, rutile and anatase. This weathering leads to absolute Ti losses on the profile scale. Mineral bags were located at different depths within the top soil, and removed after 6, 12, 18 months in the soil. In all bags the presence of newly generated anatase was recorded after the exposure periods, showing the rapidity of the processes. The vegetation recycles a significant quantity of Ti, increasing Ti mobility in soils. These results indicate that Ti can be mobile under certain conditions and thus should not always be used to estimate weathering rates.

The effect of processing on the microstructure and texture of slab cast C415 alloy variants

Alloy C415 is a candidate material for high speed civil transport application. The alloy is essentially a modification of alloy 2519 and contains Al-Cu-Mg with Ag, Mn and Zr addition. The excellent mechanical properties associated with the alloy has been attributed to the presence of Ag and Mg, which promotes the precipitation of hexagonal shaped plates of {Omega} phase on {l_brace}111{r_brace} planes. In this study, two C415 alloy variants were produced via slab casting, and thermomechanical processed into sheets. This investigation is focused on understanding the effects of (a) homogenization and (b) minor Ti addition on the development of microstructure and texture in two slab cast C415 alloy variants. The difference between the alloy variants was a minor Ti (0.15 wt %) addition in one variant. Although, there are numerous reports on deformation and recrystallization, the combined effects of processing and alloy composition on microstructure and texture is not very clear. For instance, there is evidence that minor addition of Mg, and Zn in Al alloys decrease the temperature for recrystallization, but the corresponding information on the effect on texture is sketchy. Varying the amount of alloying elements may influence the deformation texture through the lowering of the stacking faultmore » energy or result in the development of totally new (recrystallization) texture components.« less

Geochemistry and provenance of the Altendorf feldspathic sandstone in the Middle Bunter of the Thuringian basin (Germany)

An integrated mineralogical and geochemical study of the Altendorf feldspathic sandstone in the Middle Bunter of the Thuringian basin (Germany) was carried out to obtain more information on its provenance, sedimentological history and geochemistry. The fine- to coarse-grained sandstone has an average composition of 66% (63–71%) quartz, 30% (27–35%) feldspar, and a fine-grained illitic matrix. The heavy-mineral assemblage consists mainly of tourmaline, zircon, rutile, apatite and opaque Fe–Ti minerals. It is inferred that this terrigenous material was laid down at the margin of the Bunter basin. High abundances of igneous quartz grains determined by cathodoluminescence (CL), the lack of metamorphic heavy minerals as well as alkali feldspar with an average K 2O/Na 2O ratio of 14.9 point to material of mostly granitic origin. Regional geologic and paleogeographic observations suggest that granites of the Older and Younger Intrusive Complex of the western Erzgebirge are possible source rocks of the feldspathic sandstone. The geochemical signature of the alkali feldspar (K 2O/Na 2O ratio, BaO content) points to the Bergen and Kirchberg Granites as possible parent rocks. Comparing the mineralogical and geochemical data of the presumed source granites with those of the Altendorf sandstone provides information on the sedimentation processes. Weathering, fluvial transport and sedimentation under arid climatic conditions have caused complete decomposition and removal of plagioclase and biotite, lowered the bulk REE content and led to the development of a positive Eu anomaly. The immobile trace elements (e.g., Ta, Th, Zr, Sc, Co, Ti) are best suited for provenance determination because of their relatively low mobility during sedimentary processes. Elemental ratios such as La/Sc, Th/Sc, Co/Th and Th/Ta have inherited the signature of the parent rocks and thus, may be particularly useful for provenance studies. To evaluate the control of specific minerals and grain-size fractions on the distribution of trace elements in the sandstone, separated fractions of quartz, feldspar, the <20-μm fraction and heavy minerals were additionally analyzed. The concentration densities (elemental concentration in the fraction/fraction weight) reveal that, with exception of Hf, the influence of the heavy-mineral fraction on the whole-rock geochemistry is insignificant although this fraction generally plays the most important role as carrier of trace elements. Quartz, feldspar and the <20-μm fraction have similar concentration densities (between 20 and 40%) for the REE with exception of Eu, which is mainly hosted in feldspar (strong positive Eu anomaly). The influence of the <20-μm fraction on the distribution of the REE and the elements U, Th, Sc, Ta strongly depends on the abundance of this fraction in the sediment. Alkali feldspar contains most of the Ba, Sr, Rb and Cs in the samples (concentration densities of up to 97%). Thus, differences in the abundances of these elements in whole-rock samples can be related to changes in the mineralogical composition (quartz/feldspar ratio) of the sediment.

TEM and SNMS studies on the oxidation behaviour of NiCrAlY-based coatings

The effect of minor Ti additions content (0% Ti, 0.4% Ti, 1% Ti, 2% Ti) on the oxidation behaviour of Ni-20Cr-10Al-0.4Y (in weight-%) model alloys was investigated in the temperature range 950°C to 1100°C up to 200 h in Ar - 20% O 2 . Alloy microstructure, oxide scale morphology and microstructure of the scale were characterized by SEM/EDX and TEM. The growth mechanisms of the alumina scales formed on the model alloys were studied by two-stage oxidation experiments with 18 O 2 -tracer and subsequent SNMS-analyses. The microstructural observations were correlated with the oxide scale properties in respect to growth rates and spalling resistance. which was tested during cyclic oxidation.

Mechanical response, chemical variation, and volume change in the Brookneal and Hylas shear zones, Virginia

Changes in volume and chemical composition were compared with strain indicators measured in two Alleghanian shear zones in granitoid plutons within the Virginia Piedmont. Both shear zones have measurable kinematic indicators that consistently record dextral strike-slip movement. The Brookneal zone, in the Melrose Granite, exhibits one ductile deformation event whereas the Hylas zone, in the Petersburg Granite, records both brittle and ductile events. Comparison of the chemical variation and volume change for each of the shear zones yields several surprising similarities given the differences in deformational history and structural style of the two zones. Overall, both zones experienced volume decreases during deformation from undeformed to ultramylonitic. Silica, K, and U increased in both zones with decreases in Fe, Mg, Sr, Ti, Mn, Y, Nb, Zr. Changes in element behavior with incremental changes in strain are different in each zone and appear to be directly related to the style of deformation and strain processes operating at each deformational stage. Chemical data from the Brookneal shear zone clusters into three groups corresponding to weak deformation, moderate strain, and ultramylonite. Deformation in the Hylas shear zone is more complex and abrupt changes in volume and element behavior may be related to brittle events late in the deformation history. The choice of immobile elements for mass balance and volume calculations was based on the petrography of the samples. The concentration of titanite in the Melrose Granite changes from several percent in the undeformed rock to absent with very minor Ti oxides in the ultramylonite. A similar decrease in most accessory minerals takes place in the Hylas zone; however monazite increases significantly. Titanium mobility is implied in the results of the chemical analyses and volume calculations. Further, it is postulated that the fluid source for the shear zones includes dehydration reactions in the granites themselves and may include other sources, especially in the case of the Hylas zone. Pressure driven fluid movement and mechanical response of the deforming rocks may be responsible for some of the observed variations in the chemistry and volume of the zones.