Yttrium Enrichment Research Articles

Grain Size Analyses and Mineral Compositions of Core Sediments in the Western North Pacific Ocean: Implications for the Rare Earth Element and Yttrium Enrichment and Deposition Environment

Rare earth element and Yttrium (REY)-rich deep-sea sediments have been identified as significant potential resources. Although grain size analysis is important for the study of deposition environment and the future exploration of REY, related research is limited. Here, we have investigated the grain size and mineral composition of bulk pelagic sediments from Western North Pacific to indicate the evolutions of deposition environment. Grain size analysis results reveal that silt contents are dominant, and the grain size ranges between 20 and 40 μm and can be an additional grain characteristic indicator for REY-rich sediments. Furthermore, the better sorting coefficient of REY-rich sediments reflects the scouring action of bottom currents, which allows the preservation of coarse-grained bioapatite and the removal of clay fraction particles. ΣREY is negatively correlated with clay fractions but positively correlated with sand and silt fractions for the REY-rich sediments, and this is consistent with the dominant distribution of silt-sized biogenic apatite. In addition, grain size distribution (GSD) varies significantly after HCl treatment in the REY-rich sediment. Therefore, for deep-sea sediments collected below the carbonate compensation depth (CCD), an additional presence of a grain size peak at ~20–40 μm and distinct differences in GSD after HCl treatment can serve as important indicators for REY enrichment sediments.

Factors controlling rare earth element plus yttrium enrichment in Fe[sbnd]Mn crusts from Canary Islands Seamounts (NE Central Atlantic)

Marine minerals are important because concentrate in their structure high contents of strategic and critical elements as rare earth elements. Forty-two samples from eight seamounts of Canary Islands Seamount Province (CISP) have been analyzed in order to evaluate their rare earth elements plus yttrium contents (REY). Highest contents of REY are related to hydrogenetic minerals and essentially Fe-vernadite (on average 3000 μg/g). Diagenetic minerals, on the other hand, show the lowest REY contents with an average content of 260 μg/g. These differences also depend on the growth rates, hydrogenetic minerals with growth rates between 0.5 and 5 mm/Ma allow the incorporation of more REY in their structure. REY contents in studied samples varies depending several factors associated with depth and location, shallowest samples presumably growth near or within the oxygen minimum zone are the most enriched with up to 3800 μg/g due to local enrichment of these elements and the slowest growth rate promoted by the reduced ambient conditions while deeper samples around 3000 m water depth show 2800 μg/g. Location also has a role in REY contents essentially due to the presence of different currents. Samples faced to north are exposed to the more oxygenated waters of the North Atlantic Deep Water and are depleted in REY if compared with deeper samples facing to south to the more oxic Antarctic Bottom Water. Finally, the case of study made on three different seamounts of the CISP show that FeMn crusts from this area could provide on average 130 tons of hydrometallurgical recovered REY (based on 1 km2 areal crust coverage) together with interesting quantity of several other strategic and base elements as Mn, Co, Ni, Cu, V, Mo between others.

X‐ray computed tomography of deep‐sea clay as tools to detect rare earth elements and yttrium enrichment

AbstractPelagic clay that contains rare‐earth elements and yttrium (REY) at over 2000 ppm (termed “highly REY‐rich mud”) has been reported from a few areas in the western North Pacific Ocean through focused geochemical analyses. Those REY are carried by biogenic calcium phosphate, suggesting that the formation of highly REY‐rich mud involves enhanced biological productivity. However, detecting REY enrichment in sediment is time‐consuming, and the global significance of the formation of REY‐rich mud is still under debate. Here we perform x‐ray computed tomography (CT) analyses on cores recovered around Minamitorishima Island and demonstrate the positive correlation with highly REY‐rich mud and high CT numbers of the sediment. The variation of the CT number matches the wet bulk density. Further quantitative analyses using direct measurements of density and geochemistry suggest that a grain density increase and a porosity decrease due to the REY‐carrying biogenic apatite are essential to explain the high CT numbers in the REY‐enriched layer. While the chemical composition itself is of minor importance to elevate the CT numbers, our results suggest that x‐ray CT can be a proxy for highly REY‐rich mud.

Characterization of a Cr2O3 scale formed on chromium with implanted yttrium ions by advanced electron microscopy

Although the advantageous effect of reactive elements on the oxidation resistance of alloys that form protective Cr2O3 scales was discovered 80 years ago, the underlying mechanism has still not been fully explained. One of its aspects, which was investigated in depth in the presented paper, is the structure of grain boundaries in the oxidation product. Atomic-resolution scanning transmission electron microscopy ((S)TEM) was used to examine the micro- and nanostructures of Cr2O3 formed on chromium implanted with yttrium ions. Oxidation was performed in air at either 1073 K or 1273 K. A FEI (S)TEM Titan Cubed G2 60–300 equipped with a ChemiSTEM was used to examine scale's nanostructure at a resolution down to 70 picometres. Lamellae were cut using a ZEISS NEON 40 EsBCrossBeam, a scanning electron microscope with focused ion beam (FIB). Phase composition was identified via selected area diffraction (SAED), and the chemical composition was determined via energy-dispersive X-ray spectroscopy (STEM-EDS). For both oxidation temperatures, chromium was found in the interior of the Cr2O3 scale in the form of the YCrO3 perovskite. The STEM-HAADF atomic-resolution microscopic image was found to be fully consistent with a computer-simulated crystal structure of the perovskite structure obtained by means of the JEMS software. If the layer containing yttrium is treated as a marker, then it may be assumed that the thinner outer layer grew due to the outward diffusion of metal via point defects in the cation sublattice, while the thicker inner layer formed as a result of the inward diffusion of oxygen via point defects in the anion sublattice. For the higher oxidation temperature, yttrium enrichment was also observed in the grain boundary area in chromia. However, STEM observations did not reveal the presence of an intermediate layer with a perovskite structure between Cr2O3 grains. Sulfur segregation at the chromia/metal interface was observed.

Ediacaran–Cambrian phosphorites from the western margins of Gondwana and Baltica

AbstractThe late Ediacaran–mid Cambrian occurrences of phosphorites in the western Mediterranean region (West Gondwana) and southern Sweden (north‐west Baltica) are related to the poleward drift of West Gondwana and the northern drift of Baltica. As a result, these regions crossed subtropical and temperate palaeolatitudes of the Southern Hemisphere, in which oceanic upwelling and high organic productivity were the probable sources of phosphorus along their western margins. A parallel south‐west/north‐east migration trend of evaporites and delayed, time transgressive phosphorites point to distal upwelling environments associated with shallower arid conditions. Concentration of hardground‐derived phosphate accumulations took place by repeated alternations of low sedimentation rates and condensation,in situearly diagenetic and microbially mediated precipitation of amorphous and cryptocrystalline, carbonate‐bearing francolite, winnowing and polyphase reworking of previously phosphatized skeletons and hardground‐derived clasts. Thicker phosphorites of economic importance display a spiculate sponge‐thromboid consortium that points to a distinct benthic community developed on suboxic, slope to basinal substrates. For most phosphorite samples an up to ten‐fold enrichment in rare earth element concentration relative to post‐Archaean average Australian shale reflects significant incorporation of rare earth elements and yttrium after deposition. Considerable scavenging took place from anoxic pore waters, following reductive dissolution of iron oxides as evidenced from the medium rare earth element enrichment in most samples. This contrasts with the rare preservation of primary sea water features, such as cerium depletion and yttrium enrichment, in phosphatized thrombolites from the shallower realms (for example, Montagne Noire). The data are consistent with phosphogenesis after upwelling and transgression of nutrient‐rich, suboxic–anoxic, ferruginous waters over more oxygenated, rifting settings and inland portions of an evolving passive margin.

Inductively coupled reactive ion etching studies on sputtered yttria stabilized zirconia thin films in SF6, Cl2, and BCl3 chemistries

Downscaling of yttria stabilized zirconia (YSZ) based electrochemical devices and gate oxide layers requires successful pattern transfer on YSZ thin films. Among a number of techniques available to transfer patterns to a material, reactive ion etching has the capability to offer high resolution, easily controllable, tunable anisotropic/isotropic pattern transfer for batch processing. This work reports inductively coupled reactive ion etching studies on sputtered YSZ thin films in fluorine and chlorine based plasmas and their etch chemistry analyses using x-ray photoelectron spectroscopy. Etching in SF6 plasma gives an etch rate of 7 nm/min chiefly through physical etching process. For same process parameters, in Cl2 and BCl3 plasmas, YSZ etch rate is 17 nm/min and 45 nm/min, respectively. Increased etch rate in BCl3 plasma is attributed to its oxygen scavenging property synergetic with other chemical and physical etch pathways. BCl3 etched YSZ films show residue-free and smooth surface. The surface atomic concentration ratio of Zr/Y in BCl3 etched films is closer to as-annealed YSZ thin films. On the other hand, Cl2 etched films show surface yttrium enrichment. Selectivity ratio of YSZ over silicon (Si), silicon dioxide (SiO2) and silicon nitride (Si3N4) are 1:2.7, 1:1, and 1:0.75, respectively, in BCl3 plasma. YSZ etch rate increases to 53 nm/min when nonoxygen supplying carrier wafer like Si3N4 is used.

Effect of Segregation on Surface and Near-Surface Chemistry of Yttria-Stabilized Zirconia

The present work reports the effect of segregation on surface and near-surface composition of yttria-stabilized zirconia, YSZ. The study included the determination of the effect of both temperature (1073–1673 K) and oxygen activity (10–10 Pa < p(O2) < 75 kPa) on segregation-induced concentration profiles of yttrium. The secondary ion mass spectrometry, SIMS, was applied to determine the chemical composition of the outermost surface layer as well as the layers beneath the surface. It is shown that the effect of oxygen activity on the segregation-induced enrichment of yttrium is substantial in the temperature range 1073–1473 K. The maximum of enrichment in yttrium is observed at 1273 K. The segregation-induced enrichment of YSZ is considered in terms of a low-dimensional surface structure that is formed due to surface enrichment in both yttrium (dopant) and silicon (impurity). The effect of the surface and near-surface chemistry on the performance of YSZ-based energy conversion devices is discussed.

Effects of carbothermal reduction on the thermal and electrical conductivities of aluminum nitride ceramics

This study attempts to control the oxygen content by adding various amounts of yttria sintering additives or by introducing an in situ carbothermal reduction using a carbon addition during the Power processing step. While both yttria and the carbon addition increased the thermal conductivity and electrical resistivity, carbon addition was more effective in increasing the DC volume resistivity for specimens that had 3 or 5 wt% Y 2O 3. Among several elements of the electrical conductivities of the grains and grain boundaries, the conductivity of the grains appeared to be more relevant to the thermal conductivities of AlN ceramics. In addition, yttrium enrichment was observed in the grain boundary region. We also found that an in situ carbothermal reduction resulted in a small amount of yttrium-aluminate second phases, which are beneficial to the plasma resistance of the AlN ceramics.

Analysis of the demixing of yttria-stabilized zirconia in an electric field for different diffusion mechanisms

Steady-state demixing of the cations in yttria-stabilized zirconia in an electric field is analyzed for diffusion via independent vacancies, by vacancy pairs and by vacancy triplets. We analyze two conditions, one (open system) where the vacancies are everywhere close to an internal surface, which allows the Schottky defect reaction to permit the equilibration of the concentration of the vacancies, the other (closed system) where such equilibration is only possible at the external surface. For diffusion via independent vacancies and vacancy pairs, critical values of the ratio of the yttrium to zirconium vacancy exchange frequencies causing yttrium enrichment at the cathode are determined. It is also shown that diffusion via the vacancy-triplet mechanism always leads to yttrium enrichment at the anode end. Using Monte Carlo simulation, we also verify the analysis of the situation where demixing occurs by independent cation vacancies in a closed system.

Enrichment of yttrium from rare earth concentrate by ammonium carbonate leaching and peroxide precipitation

The rare earth elements (REE) solubility with ammonium carbonate vary progressively from element to element, the heavy rare earth elements (HRE) being more soluble than the light rare earth elements (LRE). Their solubility is function of the carbonate concentration and the kind of carbonate as sodium, potassium and ammonium. In this work, it is explored this ability of the carbonate for the dissolution of the REE and an easy separation of yttrium was achieved using the precipitation of the peroxide from complex yttrium carbonate. For this work is used a REE concentrate containing (%) Y 2O 3 2.4, Dy 2O 3 0.6, Gd 2O 3 2.7, CeO 2 2.5, Nd 2O 3 33.2, La 2O 3 40.3, Sm 2O 3 4.1 and Pr 6O 11 7.5. The mentioned concentrate was produced industrially from the chemical treatment of monazite sand by NUCLEMON in São Paulo. The yttrium concentrate was treated with 200 g L −1 ammonium carbonate during 10 and 30 min at room temperature. The experiments indicated that a single leaching operation was sufficient to get a rich yttrium solution with about 60.3% Y 2O 3. In a second step, this yttrium solution was treated with an excess of hydrogen peroxide (130 volumes), cerium, praseodymium and neodymium peroxides being completely precipitated and separated from yttrium. Yttrium was recovered from the carbonate solution as the oxalate and finally as oxide. The final product is an 81% Y 2O 3. This separation envisages an industrial application. The work discussed the solubility of the REE using ammonium carbonate and the subsequent precipitation of the correspondent peroxides.

Effect of yttrium on the performances of zirconia based catalysts for the decomposition of N2O at high temperature

Abatement processes for the reduction of N2O emissions from acid nitric plants can be implemented in different positions. Among the different possibilities, a catalytic process set up between the ammonia converter and the absorber could be a practicable solution. In those running conditions, at high temperature, in the presence of NO, O2 and water, the catalytic decomposition of N2O (in the absence of a reducing agent) can take place. However, catalysts usually suffer from a strong deactivation owing to the occurrence of thermal sintering which significantly lowers their specific surface area. Catalytic testing performed at laboratory scale showed that zirconia based catalysts stabilised by yttrium incorporation could be of potential interest. However, the mode of yttrium incorporation seems to be a key factor. According to the preparation procedure, surface yttrium enrichment may occur and then strongly inhibit the catalytic decomposition of N2O. Co-precipitation methods can be profitably used for the preparation of modified-ZrO2 catalysts in order to obtain yttrium homogeneously distributed in the bulk material. According to this preparation method, a synergy effect on the catalytic activity and also on the stability has been observed on ZrO2 containing low amount of yttrium whereas an inhibiting effect prevails on highly loaded yttrium based catalysts irrespective of the mode of yttrium incorporation.

Effect of cooling rate on the location and chemistry of glassy phases in silica-doped 3Y-TZP ceramics

The morphology and the composition of glassy phases in silica-doped 3Y-TZP ceramics are studied for two extreme conditions of cooling. On the one hand, materials quenched after sintering exhibit silica-rich glassy phases both at grain boundaries and multiple junctions, with an enrichment of yttrium and zirconium. These observations are related to equilibrium at high temperature. On the other hand, materials slowly cooled exhibit glassy phases only at multiple junctions. During specific conditions of cooling, it is thus shown that dewetting can occur, giving rise to a low temperature equilibrium without glassy phase.

Space-charge concepts on grain boundary impedance of a high-purity yttria-stabilized tetragonal zirconia polycrystal

A detailed impedance analysis using the brick-layer model is performed on a high-purity yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). Space-charge impedance is generally formulated and expressions for the respective space-charge models are therefrom derived depending on whether dopant ions are mobile or immobile. Pronounced yttrium segregation in Y-TZP is also considered in the analysis in that the dopant profile is assumed to be frozen from a high-temperature equilibrium distribution. Comparison with experimental observations shows that the electrically measured grain-boundary thickness corresponds to the Schottky-barrier width, slightly modified by the dopant segregation. The grain-boundary resistance is not consistent with any space-charge models and the strong defect interaction due to the yttrium enrichment is suggested to be mainly responsible.

Examination of Y2Cu2O5 additions on microstructural development in YBa2Cu3O7 − δ superconductors

The role of Y2Cu2O5 on liquid phase flux and microstructure evolution were examined in two series of experiments. The first series of experiments dealt with a low temperature processing ( 1020 dgC) melt powder melt growth process (MPMG). Differential thermal analysis measurements were used to study the impact on liquidus formation reactions, solidification temperatures and kinetics. Microstructural evaluations via SEM, EDS along with TEM and microdiffraction techniques reveal some unique aspects of Y2Cu2O5 additions on the liquid phase matrix and microstructural refinement during processing. The yttrium enrichment of the Pt-Ba-Cu-O phase for MPMG samples was shown along with significant coalescence of such a phase not seen in similar samples with Y2Cu2O5. Extensive liquidus formation occurs allowing for texturing via diffusive couple oxide liquid phase intrusion below the peritecticecomposition.

Interface and grain boundary structures in YBa2Cu3O7-x and YBa2Cu4O8 materials

Y2BaCuO5YBa2Cu3O7-x (Y211/Y123) interfaces in melt-processed YBa2Cu3O7-x were studied by high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. Yttrium enrichment and barium depletion were observed locally at the Y211/Y123 interfaces where Y123 (001) facets were present. This effect may be interpreted as the result of lattice substitution of Ba by Y near these interfaces. Cation nonstoichiometry was found near Y211/Y123 interfaces where liquid phases (Cu-Ba-O) were present. This chemical disorder introduces numerous point defects in the Y123, and these defects may act as additional pinning sites alongwith stacking faults. A comparison of grain boundary (GB) chemical composition in polycrystalline YBa2Cu3O7-x and YBa2Cu4O8(Y124), studied using nanoprobe parallel-detection electron energy-loss spectroscopy (EELS), is presented. The studies of Y124 show that stoichiometric grain boundaries can also form weak links between superconducting grains. It is suggested that weak-link behavior is determined largely by misorientation at grain boundaries.

Surface analytical study of hydrothermally treated zirconia ceramics

The hydrothermal instability of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) imposes serious problems on their range of applications as ceramic materials. It is well known that a generally uniform distribution of yttrium cations prevents the transformation of the metastable tetragonal into the monoclinic crystallographic modification. The induced crack propagation is widely considered to be a major source of mechanical failure in zirconia ceramics. The segregation was investigated of yttrium and other cations on the surface of hydrothermally treated ceramic samples with angle resolved XPS (X-ray photoelectron spectroscopy). The combination of this method with the high lateral resolution of SAM (scanning Auger microprobe) yields three dimensional distribution profiles of Y3+, Al3+ and Si4+. The relative content of the two crystallographic modifications of zirconia at the surface has been determined with XRD (X-ray diffraction). Additional Raman spectroscopic measurements partially confirm these results but suffer from quantification problems. A possible mechanism for the enrichment of yttrium in the surface layer and its promotive function for the phase transformation of zirconia is proposed. Preliminary results from experiments with temperature variable XPS measurements also indicate the formation of either yttrium- or zirconium hydroxide which are both suspected to contribute to crack propagation along the grain boundaries.

Surface and grain boundary analysis of doped zirconia ceramics studied by AES and XPS

The surface- and grain boundary composition of Y, Ce and Ti doped zirconia were studied by X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy/Scanning Auger Microscopy. The grain boundaries and free surfaces showed the same enrichment levels. After heat treatment ≥ 1000 ‡C all yttria doped samples showed yttrium enrichment. In the ZrO2-Y2O3 system the yttrium enrichment did not depend on the bulk concentration and amounted 30–34 mol% YO1.5 in all cases. As a consequence the segregation factor increases with decreasing solute concentration in the bulk. The thickness of the segregation layer was about 2–4 nm. In the ternary Y doped systems yttrium is the main segregant. In ceria-doped tetragonal zirconia polycrystals (Ce-TZP) systems significant segregation of cerium starts atT≥1300‡C and is mainly attributed to Ce3+. In Y,Ti-TZP systems also strong segregation of Ti4+ occurs. The absolute value of the increase of the surface concentration in fine grained material is smaller than in coarse grained material. This is mainly due to depletion of the bulk.

Yttrium enrichment and improved magnetic properties in partially melted Y-Ba-Cu-O materials

Samples of Y-Ba-Cu-O materials with the formulation Y:Ba:Cu = x:2:3 and values of x ranging between 1 and 3 were prepared by partial melting at a maximum temperature of 1045 °C. Measurements of magnetic susceptibility and maximum (low-field) as well as remanent magnetization show highest values for x = 2. XRD and SEM/EDX analyses show that the corresponding structure involves numerous small crystals of Y2BaCuO5 (211) embedded in highly ordered assemblages of continuous YBa2Cu3O7−y (123) layers. The presence of these impurity sites is correlated with flux pinning capacity. Other impurity phases include CuO, a minor phase which shows an increase in amount when x increases, BaCuO3, a possibly detrimental minor phase which vanishes when x is raised from 1 to 2, and zones of intermediate composition between the 211 grains and the 123 layers, which are formed from the residual liquid upon cooling. These intermediate regions, like the 211 grains themselves, become gradually more important when x is increased from 1 to 3.

Microstructural and compositional variations in laser-deposited superconducting thin films

We have investigated thickness and composition variations in laser-deposited superconducting thin films and their effects on the microstructure development after subsequent annealing to recover the superconducting properties. Superconducting thin films were deposited on magnesium oxide substrates using a pulsed excimer laser (λ=308 nm, τ=45×10−9 s). These films were annealed at about 900 °C in helium and oxygen atmospheres followed by slow cooling to room temperature. The forward directed nature of the laser-induced deposition process in controlling the spatial variation in thickness of the film was examined using gas dynamics of the laser generated plasma. The compositional variation as a function of spatial distance was determined by Rutherford backscattering spectrometry. Correlation of the presence of different phases with the average composition in the film was done using transmission electron microscopy combined with x-ray microanalysis techniques. The slight enrichment of yttrium in the film resulted in yttrium-rich phases in the microstructure.