Amounts Of Zr Research Articles

The phase and morphology evolution of Y-Zr-O complex oxide dispersion-strengthened (ODS) Mo powders during mechanical alloying and annealing

Nanostructural Y-Zr-O complex oxide dispersion-strengthened (ODS) Mo alloys are designed for accident-tolerant fuel cladding. The phase and morphology evolution of ODS Mo powders during mechanical alloying (MA) and annealing were studied. The dissolution and reprecipitation mechanisms were revealed by quantitative calculation of dissolved Y and Zr amounts, thermodynamics and dynamics analysis, and phase analysis. The results reveal MA induces Mo grain refinement and a high density of dislocations in powders, facilitating the dissolution of Y2O3 and Mo2Zr and the formation of Mo supersaturated solid solution, rather than the negative mixing heat. By subtracting vacancies and oxygen effects, the dissolved amount is estimated as 2.2 at.% Y and 1.8 at.% Zr after 96 h-milling. During annealing, the Y-Zr-O complex oxide is precipitated in Mo-10 wt%Y2O3 powders above 900 °C since the introduced ZrO2 contamination during MA, and then cubic-Y2O3 beyond 1100 °C. The findings provide a scientific basis for controlling Y-Zr-O complex oxide nanoprecipitates and optimizing the service performance of Mo alloys.

Petrology and Geochemistry of Lamprophyres from Tirthal Area, in Eastern Margin of the Eastern Dharwar Craton, Khammam, Telangana, India

The presence of lamprophyre dykes is very common in the Eastern Dharwar Craton (EDC), southern India. The present paper reports five new lamprophyre bodies from the Tirthal area near the bank of the Muneru River (80°08ʹ 13.00ʹʹ:17°19ʹ 9.0ʹʹ), north of Khammam, Telangana.Petrography and geochemistry of the lamprophyre dykes are also discussed in this paper. The study area mainly consists of granitoids of Peninsular Gneissic Complex-II (PGC-II) of the EDC. The lamprophyre intrudes the granitoids of the EDC.Petrographic studies revealed the presence of panidiomorphic texture. Euhedral crystals of clinopyroxene, biotite and amphibole are present as phenocryst in the lamprophyre,while k-feldspar, plagioclase feldspar, biotite and apatite are present in the groundmass.The lamprophyre is characterized by SiO2 (40.03%-45.23%), Fe2O3(9.09%-13.45%), MgO (9.78%-11.96%), CaO (8.25%-14.78%), K2O (0.69%-2.37%), TiO2 (1.3%-1.53%) and Al2O3 (9.76%-12.02%) contents. Similarly trace elements analysis gavehigher amounts of Ba (2030-10498ppm), Sr (438-925 ppm), Ni (156-225 ppm), Zr (417-590 ppm), V (141-169 ppm) and Cr(388-482 ppm). All the samples gave higher LREE values as compared to HREE with a total REE content within the range of 1108.50-2004.49 ppm. The lamprophyre is classified as minette belonging to Calc Alkaline Group based on geochemical and petrological studies.

Catalytic Activity and Electrochemical Stability of Ru1-xMxO2 (M = Zr, Nb, Ta): Computational and Experimental Study of the Oxygen Evolution Reaction.

We use computations and experiments to determine the effect of substituting zirconium, niobium, and tantalum within rutile RuO2 on the structure, oxygen evolution reaction (OER) mechanism and activity, and electrochemical stability. Calculated electronic structures altered by Zr, Nb, and Ta show surface regions of electron density depletion and accumulation, along with anisotropic lattice parameter shifts dependent on the substitution site, substituent, and concentration. Consistent with theory, X-ray photoelectron spectroscopy experiments show shifts in binding energies of O-2s, O-2p, and Ru-4d peaks due to the substituents. Experimentally, the substituted materials showed the presence of two phases with a majority phase that contains the metal substituent within the rutile phase and a second, smaller-percentage RuO2 phase. Our experimental analysis of OER activity shows Zr, Nb, and Ta substituents at 12.5 atom % induce lower activity relative to RuO2, which agrees with computing the average of all sites; however, Zr and Ta substitution at specific sites yields higher theoretical OER activity than RuO2, with Zr substitution suggesting an alternative OER mechanism. Metal dissolution predictions show the involvement of cooperative interactions among multiple surface sites and the electrolyte. Zr substitution at specific sites increases activation barriers for Ru dissolution, however, with Zr surface dissolution rates comparable to those of Ru. Experimental OER stability analysis shows lower Ru dissolution from synthesized RuO2 and Zr-substituted RuO2 compared to commercial RuO2 and comparable amounts of Zr and Ru dissolved from Zr-substituted RuO2, aligned with our calculations.

Role of Cr in Mn-rich precipitates for Al–Mn–Cr–Zr-based alloys tailored for additive manufacturing

Novel alloy concepts enabled via additive manufacturing processes have opened up the possibility of tailoring properties beyond the scope of conventional casting and powder metallurgy processes. The authors have previously presented a novel Al–Mn–Cr–Zr-based alloy system containing three times the equilibrium amounts of Mn and Zr. The alloys were produced via a powder bed fusion-laser beam (PBF-LB) process taking advantage of rapid cooling and solidification characteristics of the process. This supersaturation can then be leveraged to provide high precipitation hardening via direct ageing heat treatments. The hardening is enabled with Zr-rich and Mn-rich precipitates. Literature study confirms that Mn-rich precipitates have a notable solubility of Cr, for example, the Al12Mn precipitate. This study aims to clarify the effect of Cr solubility in the thermodynamics and kinetics simulation and compare the precipitation simulations with samples subject to >1000 h isothermal heat treatment, thus creating an equilibrium-like state. The results show that Cr addition to the precipitates stabilizes the Al12Mn precipitate while slowing the precipitation kinetics thus producing a favourable hardening response. Such observations could be insightful while designing such alloys and optimising heat treatments of the current or even a future alloy system.

Magnetron Sputtering as a Microstructural Screening Tool for Laser Additive Manufacturing: Study on Ni Superalloys

In this work, magnetron sputtering coupled with a heat treatment is demonstrated as a route to obtain surrogate microstructures comparable to those achieved by laser‐based additive manufacturing (AM) for Ni superalloys. Furthermore, this technique is shown to be a novel and efficient way of screening elemental additions with high compositional resolution for AM, without the need for designing and characterizing custom‐atomized powders. Herein, Inconel 718 films are sputtered from both arc‐melted and AM targets to capture any compositional changes and to develop a comprehensive methodology. Films are characterized via electron microscopy techniques to establish similarities between sputtered plus heat‐treated films and bulk AM Inconel 718 microstructures reported in literature. Since Inconel 718 is susceptible to high‐temperature S embrittlement, films were then co‐sputtered with small amounts of Zr or Hf, which are found to facilitate sulfur segregation via nano secondary ion mass spectrometry analysis. Overall, this work highlights how magnetron sputtering plus heat treatment can be leveraged to rapidly screen novel AM microstructures, thereby accelerating the development and deployment of AM materials.

Conversion of CO2 to higher alcohols on K-CuZnAl/Zr-CuFe composite

Direct conversion of CO2 into higher alcohols (C2+OH) is highly desirable, but rather challenging due to requiring the synergetic action of C-C coupling and CO insertion. Here, we developed a new K-CuZnAl/Zr-CuFe composite, which gave CO2 conversion and C2+OH selectivity of 40.6% and 22.4% respectively, while CO selectivity is only 10.3% at 320 °C, 4 MPa and 6000 mL gcat−1 h−1. The C2+OH STY can reach 195.1 mg gcat–1 h–1, and is well maintained within 200 h at higher GHSV of 24000 mL gcat−1 h−1. Introduction of K-CuZnAl and decrease of the contact distance of K-CuZnAl and Zr-CuFe boost the formation and subsequent conversion of CO* intermediate. In addition, doping small amounts of Zr into CuFe catalyst hinders the phase separation of Cu and Fe species by enhancing their interface interaction. As a result, the CHx * species generated on iron carbide through CO* dissociative activation quickly reacts with the non-dissociative adsorbed CO* on adjacent Cu to produce more C2+OH.

Fabrication and Characterization of Colorant-Doped Glass Produced with Local Sand of Nong Phok Site

It is well-known that silica sand is a special type of quartz sand that is suitable for glass fabrication due to its high silica content and low content of iron oxide. In this work, chemical analysis has been carried out on a sand sample from the Nong Phok site, Roi Et province, northeastern Thailand. The geological resources show that this site possesses a surface-to-near surface sand deposit. The grain of fine white sand consists of clear crystals. The grain shape is mainly angular-to-round. Chemical analysis shows that the sand contains more than 99 wt% silica and small amounts of Al, Ca, Ti, and Zr which is in agreement with international standards for glass production. The sand has been used as raw material for the fabrication of soda-lime, lead crystal, and lead-free high refractive index glasses. The colorless and various colored glass products have been satisfactorily used in domestic art and glass manufacturers which promotes local employment and economics.

Superior Energy Storage Capability and Fluorescence Negative Thermal Expansion of NaNbO3-Based Transparent Ceramics by Synergistic Optimization.

Transparent dielectric ceramics are splendid candidates for transparent pulse capacitors (TPCs) due to splendid cycle stability and large power density. However, the performance and service life of TPCs at present are threatened by overheating damage caused by dielectric loss. Here, a cooperative optimization strategy of microstructure control and superparaelectric regional regulation is proposed to simultaneously achieve excellent energy storage performance and real-time temperature monitoring function in NaNbO3-based ceramics. By introducing aliovalent ions and oxides with large bandgap energy, the size of polar nanoregions is continuously reduced. Due to the combined effect of increased relaxor behavior and fine grains, excellent comprehensive performances are obtained through doping appropriate amounts of Bi, Yb, Tm, and Zr, Ta, Hf in A- and B-sites of the NaNbO3 matrix, including recoverable energy storage density (5.39Jcm-3), extremely high energy storage efficiency (91.97%), ultra-fast discharge time (29ns), and superior optical transmittance (≈47.5% at 736nm). Additionally, the phenomenon of abnormal fluorescent negative thermal expansion is realized due to activation mechanism of surface phonon at high temperatures that can promote the formation of [Yb···O]-Tm3+ pairs, showing great potential in real-time temperature monitoring of TPCs. This research provides ideas for developing electronic devices with multiple functionalities.

Effect of Zr4+ doping on the electrochemical properties of Na3MnTi(PO4)3/C cathode materials

NASICON structural materials have the advantages of structural stability, high ion conductivity, and high working potential, which have attracted widespread attention as cathode for sodium-ion batteries. Although the three-electron reaction in the NASICON structure Na3MnTi(PO4)3 increases the specific capacity of the material, poor electronic conductivity remains a key factor restricting its practical application. Herein, Na3Mn1-xZrxTi(PO4)3/C (x = 0, 0.01, 0.03, 0.05, 0.07 and 0.1), a typical three-dimensional NASICON structure cathode material for sodium-ion batteries, was synthesized by the sol-gel method. Through powder X-ray diffraction, the Zr4+ doping in the Na3MnTi(PO4)3 (NMTP) structure was verified. It was found that doping trace amounts of Zr at the Mn site can not only reduce the Jahn-Teller effect caused by Mn3+, but also strengthen the Zr-O bond compared to the Mn-O bond, making the crystal structure more stable by reducing the proportion of Mn. According to the findings of the EIS test, a suitable amount of Zr doping can enhance the electronic conductivity and Na ion diffusion coefficient of NMTP/C electrode materials, weaken polarization phenomena, increase electrode reaction rate, and significantly improve the rate performance and cycling performance of Na3Mn1-xZrxTi(PO4)3 material. The Na3Mn1-xZrxTi(PO4)3/C sample prepared has high initial capacity of 124mAh/g, a capacity retention rate of 86 % after 200 cycles at 0.2C, and a capacity retention rate of 84 % after 500 cycles at 1C. This proves that the material still exhibits excellent cycling stability and structural stability after high current cycling. More importantly, the Na3Mn0.95Zr0.05Ti(PO4)3 (Zr5-NMTP)//Hard carbon full battery also exhibits ideal electrochemical performance.

Mineral and crystal chemical study of pseudo-C2/mnon-metamict chevkinite-(Ce): An investigation into the intracrystalline distribution of LREE, HREE, and octahedral cations in samples from the Azores and Pakistan

AbstractThe cation distribution among the A, B, C, and D sites of 13 crystals of chevkinite-(Ce) by X-ray single-crystal diffraction and electron microprobe analyses is reported in this article. The general formula of chevkinite-(Ce) is A4BC2D2O8(Si2O7)2, where A = REE, Ca, Th, Sr; B = Fe, Mn, Mg; C = Fe, Ti, Nb, Zr, Mg, Al; and D = Ti. Ten crystals come from quartz-bearing syenite samples of Agua de Pau (Azores Islands), and three are euhedral chevkinite crystals of a quartz-bearing pegmatite from Tangir Valley, northwestern Pakistan. The real space group for these samples is P21/a, but the average structure in space group C2/m was used for structural refinement and further interpretation. Cation distribution was determined by minimization of the function fΣNσ2 that represents the sum of the squared numbers of standard deviation by which each expected quantity differs from the calculated one. Both X-ray diffraction and electron microprobe data were considered in minimization. Our results show that the two non-equivalent A sites are occupied dominantly by REE and Ca, distributed mainly as a function of their ionic size. Lanthanum enters only the 10-coordinated A2 site, whereas heavier and smaller REE enter only the 8-coordinated A1. Furthermore, comparison between bond valence sum and formal charge revealed highly stretched bonds for the A1 polyhedron, suggesting that bond lengths are too long for HREE. These findings can help better characterize the well-known ability of chevkinite to fractionate LREE from HREE. The Azores chevkinite is particularly enriched in Nb relative to its host rock. Our results show that Ti occupancy in the D sites can be as low as ca. 50% due to the presence of significant amounts of Nb, besides Fe and Zr. For two Azores crystals showing patchy zoning, a complex history of late-stage crystallization is inferred, with multiple events of Ca and REE enrichments. One of these crystals showed the best structure refinement, implying that late-magmatic to deuteric alteration stages did not affect its crystallinity. The CaO content of Azores chevkinites practically spans the entire chevkinite field in the chevkinite/perrierite CaO vs. FeO discrimination diagram. In addition, we identified possible structural stability limits that can be linked to the occupancy of the B site at high CaO, and of the C sites at high-FeO contents. The Pakistan chevkinites were also analyzed by Mössbauer spectroscopy. Only one Fe3+ component was identified, which occupies the C sites. Among the two ferrous doublets, the component with the highest isomeric shift value is Fe2+ entering the most distorted crystallographic site B, while the other, representative of a less distorted octahedral site, corresponds to Fe2+ entering the D sites.

Metals Contained in Various Formulations of Mineral Nitrogen Fertilizers Determined Using Portable X-ray Fluorescence

According to the Scopus database, over the last five years, 91 scientific papers with the keyword “pXRF” (portable X-ray fluorescence) were published in indexed journals in the domain of environmental science and agricultural science, which indicates more frequent applications of this technique in scientific research. The pXRF method is characterized by speed, precision, accuracy, and the possibility of a simultaneous analysis of a large number of elements, albeit with higher limits of detection (LODs) as a major disadvantage. The presence of metals in certain phosphate fertilizers is well established, though not to the same extent as in mineral nitrogen fertilizers. The aim of this research was to determine the metal content (As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Si, Sr, Th, U, Zn, Zr, and Y) in thirteen commercial mineral nitrogen fertilizers via the pXRF method. Six straight fertilizers (ammonium nitrate, ammonium sulphate nitrate, limestone ammonium, nitrate, and urea) and seven complex fertilizers (various NPK formulations), which are different even according to their production technology, produced in Croatia were analyzed using the handheld Vanta C (Olympus) XRF analyzer according to the loose powder method and “point and shoot” technique. Data quality control was performed by analyzing the reference fertilizer samples and certified and reference soil samples. The results revealed that the determined contents of Cd, Mn, and Th were relatively higher in the single-component fertilizers, while the contents of As, Cr, Fe, Ni, Si, Sr, Zn, Zr, Y, and U were relatively higher in the complex fertilizers. Due to the higher LODs of Co and Pb (3 mg/kg) and Mo (2 mg/kg), the pXRF method was not appropriate for the determination of these metals in the analyzed fertilizers. The quantified metal content in the analyzed fertilizers varied as follows: 2.0–8.0 mg As/kg; 11.5–31.3 mg Cd/kg; 29.8–118.5 mg Cr/kg; 7.8–26.3 mg Cu/kg; 16.5–2209 mg Fe/kg; 20.3–5290 mg Mn/kg; 6.2–27.8 mg Ni/kg; 1156–4581 mg Si/kg; 2.0–469.8 mg Sr/kg; 3.0–35.3 mg Th/kg; 2.0–82.8 mg U/kg; 1.4–166 mg Zn/kg; 9.7–15.3 mg Zr/kg; and 16.5–128.0 mg Y/kg. The results indicated that the pXRF method is particularly suitable for measurement and metal detection in complex nitrogen mineral fertilizers with higher amounts of metals, but it is not suitable for the detection and quantification of the lower amounts of As, Zr, Y, Cu, Ni, and Cr in single-component nitrogen fertilizers. Compared to all of the investigated fertilizers, the highest amounts of As, Cr, Cu, Fe, Ni, U, Zn, and Zr were quantified in the NPK 7-20-30 formulation.

Fluid-fluxed partial melting of the Buncheon granitic gneiss in the Yeongnam Massif, Korea: Protracted (ca. 1.86–1.84 Ga) reworking of the Paleoproterozoic Korean arc

The fluid-fluxed melting of igneous protoliths provides an opportunity to assess the role of fluid for the formation and modification of continental crust during high-temperature metamorphism. In order to investigate such an anatexis in the Buncheon granitic gneiss, Yeongnam Massif, we combined field, microstructural, and geochemical studies with the U-Pb and oxygen isotopic analyses of zircon and monazite. The granitic gneisses comprise metatexitic migmatites containing leucosomes, although neither melanosomes nor peritectic phases are associated with neosomes. These migmatites underwent syn-kinematic wet melting in the presence of ca. 0.9–1.4 wt% H2O (estimated from the pseudosection modeling) via the reaction, plagioclase + K-feldspar + quartz + H2O = melt, that took place at ∼650–750 °C and 4–6 kbar. The leucosomes differ in the degree of Eu anomalies and have variable amounts of rare earth elements, Zr, Y, and Th. Such variations are attributed to the segregation and migration of melts as well as the entrainment of residual phases. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages of zircon and monazite were determined from two granitic gneisses and three leucosomes together with an adjacent, undeformed Hongjesa granite. Zircon grains are oscillatory-zoned, except for homogeneous overgrowth rims rarely present in two leucosomes. Both zircon domains were dated at ca. 1.98–1.97 Ga and ca. 1.86 Ga, respectively, suggesting that igneous protoliths were partly recrystallized during the late Orosirian. Monazites from two gneiss samples contain submicroscopic polycrystalline inclusions of K-feldspar + quartz + apatite, reflecting the presence of former melts, and yielded a pooled 207Pb/206Pb age of 1859 ± 6 Ma (n = 30). In contrast, monazites from a leucosome are inclusion-free, and yielded the youngest age of 1840 ± 16 Ma (n = 6). This result is interpreted to represent the melt crystallization at ca. 1.84 Ga following the ca. 1.86 Ga anatexis. On the other hand, monazite from the Hongjesa granite, yielded a weighted mean 207Pb/206Pb age of 1878 ± 5 Ma (n = 11), most likely reflecting a prograde metamorphic growth. The δ18O values of ca. 1.98–1.97 Ga igneous zircon in granitic gneisses are 7.1–7.2 ‰, but those from the leucosome are reduced at 5.9–6.7 ‰. The latter is largely identical to 5.7–6.7 ‰ estimated from ca. 1.86 Ga domains of zircon in the leucosome and monazite in the granitic gneiss; in contrast, a slightly lower δ18O value of 5.46 ± 0.61 ‰ is recorded in the ca. 1.84 Ga monazite of leucosome. The relatively low δ18O values are most likely accounted for by an influx of fluid that has apparently triggered partial melting in the granitic gneiss, and the fluid itself is possibly linked to the crystallization of mafic magmas in an arc complex. Taken together, in contrast to the majority of zircons preserving the crystallization age of igneous protoliths, monazites are more susceptible to recrystallization during the fluid-present melting and permit us to decode a protracted (∼20 m.yr.) episode from partial melting to melt crystallization in the Yeongnam Massif. Such a longevity of melt-present system typifies the prolonged crustal reworking of Paleoproterozoic Korean arc situated at the eastern margin of the North China Craton.

Effect of Zr on microstructure and hot cracking susceptibility of ZGH451 superalloy fabricated by direct energy deposition

Four groups of newly developed Ni-based superalloy samples with different Zr contents were manufactured by Direct energy deposition (DED). This study focuses on the influence of Zr element concentration on microstructure and cracking formation mechanism in DED-processed Ni-based superalloy ZGH451. Although Zr content is low, it strongly affects the formation of the precipitated phase and hot tearing tendency. Measurement of the crack area showed that the crack density value increases with the Zr concentration. According to thermodynamic simulation results and microstructures observed, Zr microsegregation in the interdendritic regions and considerable amounts of Zr is present in oxides or carbides. Zr contributes to forming large-size carbides mainly due to zirconia providing nucleation sites and the dissolution of Zr. Simultaneously, the solidification has been retarded due to the continuous accumulation of large Zr atoms, which increases the γ-γ′ eutectic fraction. Moreover, Zr addition could effectively decrease the solidus temperature of ZGH451 alloys, leading to the critical liquid film at the end of solidification. Based on these results, staying below 0.05 wt% of Zr content to reduce the risk of hot tearing in additive manufacturing superalloy was proposed.

High-Concentration Self-Assembly of Zirconium- and Hafnium-Based Metal-Organic Materials.

Metal-organic frameworks (MOFs) are crystalline, porous solids constructed from organic linkers and inorganic nodes that are promising for applications in chemical separations, gas storage, and catalysis, among many others. However, a major roadblock to the widespread implementation of MOFs, including highly tunable and hydrolytically stable Zr- and Hf-based frameworks, is their benchtop-scalable synthesis, as MOFs are typically prepared under highly dilute (≤0.01 M) solvothermal conditions. This necessitates the use of liters of organic solvent to prepare only a few grams of MOF. Herein, we demonstrate that Zr- and Hf-based frameworks (eight examples) can self-assemble at much higher reaction concentrations than are typically utilized, up to 1.00 M in many cases. Combining stoichiometric amounts of Zr or Hf precursors with organic linkers at high concentrations yields highly crystalline and porous MOFs, as confirmed by powder X-ray diffraction (PXRD) and 77 K N2 surface area measurements. Furthermore, the use of well-defined pivalate-capped cluster precursors avoids the formation of ordered defects and impurities that arise from standard metal chloride salts. These clusters also introduce pivalate defects that increase the exterior hydrophobicity of several MOFs, as confirmed by water contact angle measurements. Overall, our findings challenge the standard assumption that MOFs must be prepared under highly dilute solvothermal conditions for optimal results, paving the way for their scalable and user-friendly synthesis in the laboratory.

Effect of Zirconia on Pd–Pt Supported SBA-15 Catalysts for the Oxidation of Methane

A series of methane oxidation catalysts were prepared by doping Santa Barbara Amorphous-15 (SBA-15), a highly mesoporous silica sieve, with varying amounts of Zr (5, 10, and 15 wt%) and loading with 2 wt% Pd and 4 wt% Pt. The catalysts were characterized using various techniques, including BET, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR). Fresh and aged catalysts were evaluated for methane oxidation. Aging was performed using a simulated lean burn natural gas (NG) engine exhaust containing water vapor (10% vol) and sulfur (10 ppm). It was found that the catalyst with 15 wt% zirconia was the most active and stable of the series, exhibiting the lowest T50 of 481 °C after 40 h of aging. The Pd–Pt catalyst loaded on pure SBA-15 had a T50 of 583 °C after aging, which was 102 °C higher than that of the Pd–Pt catalyst with 15 wt% Zr. The results suggest that the increased performance was due to the higher amount of reducible PtOx species in the proximity of ZrO2 and the sulfur scavenging effect of zirconia, which protected the active metals from forming inactive sulfur complexes. Overall, the Pd–Pt catalyst with 15 wt% Zr loaded on SBA-15 demonstrated excellent methane oxidation activity, hydrothermal stability, and sulfur resistance and can be considered a viable candidate for reducing the methane slip from a lean burn NG engine exhaust.

Genetic implications, composition, and structure of trioctahedral micas in xenoliths related to Plinian eruptions from the Somma-Vesuvius volcano (Italy)

Abstract The present work is part of a systematic mineralogical and petrographic characterization of mica-bearing xenoliths from Somma-Vesuvius volcano (Roman Magmatic Province, southern Italy). Skarns, composite skarns-marbles and cumulates from Pompeii Plinian eruption (AD 79), and skarns and syenite from Avellino eruption (3945 ± 10 cal yr BP) were investigated to define the crystal chemistry of the Somma-Vesuvius trioctahedral micas and to draw inferences on petrogenetic processes to which they were subjected. Xenoliths were characterized by means of polarized optical microscopy, scanning electron microscopy (SEM-EDS), X-ray powder diffraction (XRPD), and bulk-rock geochemical analyses. Mica crystals were studied using electron microprobe analysis (EMPA) and single-crystal X-ray diffraction (SCXRD). Micas from skarns are variably associated with Mg ± Ca silicates (clinopyroxene, vesuvianite, humite, clinohumite, chondrodite, forsterite, and garnet), other sporadic silicates (anorthite, sodalite, titanite, and britholite), apatite, calcite, various types of oxides, as well as rare sulfides and halides. In composite skarn-marble rocks, the mineral assemblages show some differences compared to skarns, as a lack of clinopyroxene and the presence of dolomite. Cumulate samples consist of mica and clinopyroxene, whereas syenite is mainly composed of mica, K-feldspar, feldspathoids, and clinopyroxene. Together with mica, apatite occurs in all the lithotypes. Trace element arrays are scattered for skarn and composite skarn-marble samples. The REE patterns have a general enrichment in light (La, Ce, Pr, Nd) and medium (Sm, Eu, Gd, Tb, Dy) rare earth elements, in some cases with slight positive Gd anomaly. Cumulate samples generally have low amounts of Ba, Sr, Zr, and Th, while syenite exhibits low concentrations of trace elements, except for Rb, Cs, and Tl. Mica crystals occurring in the studied xenoliths are phlogopite with different Al and Mg contents at the octahedral site, a negligible tetraferriphlogopite component and variable dehydrogenation degree. All samples belong to the 1M polytype (C2/m and C2 space group) and have a wide range of unit-cell parameters, especially of the c axis [5.3055(1) ≤ a ≤ 5.3218(1) Å, 9.1893(1) ≤ b ≤ 9.2188(4) Å, 10.1803(2) ≤ c ≤ 10.2951(2) Å]. The shortest c-cell parameter pertains to de-hydrogenated phlogopite from Avellino skarn, whereas OH-rich phlogopite from Pompeii composite skarns-marbles has a c-cell parameter that approximates that of the end-member phlogopite. Overall, it is observed that the crystal chemistry of the micas studied here extends the known range of the other Vesuvian micas from the literature. The Ti-depletion and the wide degree of dehydrogenation of phlogopites from skarns and composite skarns-marbles suggest that the studied samples originated under variable pressure conditions. In addition, the presence of humite in the mineral assemblage seems to indicate the occurrence of devolatilization reactions. The scarce mica occurrence in cumulate and mainly in syenite, instead, may depend on pressure conditions in the magma storage system exceeding the mica stability.

Eutectic, precipitation-strengthened alloy via laser fusion of blends of Al-7Ce-10Mg (wt.%), Zr, and Sc powders

Laser powder-bed fusion was used to create an Al-7Ce-10Mg-0.71Zr-0.23Sc (wt.%) alloy, using hypoeutectic Al-7Ce-10Mg (wt.%) pre-alloyed powder blended with either elemental Zr and Sc powders (∼20 µm in size), or pre-alloyed, concentrated Al-10Zr and Al-10Sc (wt.%) powders (comprised of 1-5 µm Al3Zr or Al3Sc particles embedded in a <45 μm Al-rich matrix). The effects of process parameters and powder selection on the homogeneity of the as-fabricated microstructure were investigated via metallography and compared to predictions from a simple numerical model describing the dissolution of Zr powders in the melt pool during printing. Both experiments and model show that decreasing scan speed leads to greater dissolution of Zr and Sc, but remelting has no significant effect. The samples produced with Al-10Zr and Al-10Sc powder additions show greater amounts of Zr and Sc dissolution than those produced with elemental Zr and Sc additions, because of the smaller size (5 µm for prealloyed vs. 20 µm for elemental) and lower melting point (1580 and 1320°C for Al3Zr, Al3Sc vs. 1850 and 1541°C for Zr, Sc) of the dissolving species. The alloys fabricated with prealloyed powders display larger amounts of very fine grains (1-2 µm) nucleated by primary L12 Al3(Zr,Sc) precipitates, and a clear hardening response during aging, consistent with supersaturated Zr and Sc forming a high number density of secondary L12 Al3(Zr,Sc) nanoprecipitates.

Doping low amount of Zirconium in Rh-LTO to prepare durable catalysts for dry reforming of methane

Zr doped Rh-La2Ti2O7 with different amounts of Zr were prepared with a sol-gel process and used as catalysts for dry reforming of methane. The samples as prepared were characterized by a series of methods including powder X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), and temperature-programmed reduction (TPR). The XPS and XAS spectra revealed the effect of doped Zr in the electronic environment of catalysts. The results showed that when the doping amount of Zr was at a low level, the activity and stability of the DRM catalyst were significantly improved. Tests of catalytic activity showed that the reforming performance of Rh-LTZO-x catalysts was affected by the Zr/Ti loading ratio. It was favored when Zr/Ti ratio was low and incomplete methane conversion was observed when Zr/Ti=1. Compared to Rh-LTO, the optimized catalyst Rh-LTZO-10 enhanced conversion of methane and carbon dioxide from 77% to 86%, 83% to 90%, respectively. The optimized catalyst Rh-LTZO-10 exhibited long stability life over 200 h of the reaction and there was only a small amount of carbon deposition. The low amount of Zr doping may accelerate the transfer rate or number of electrons during the reaction, enhance the interaction between the active component Rh and the support, so that Rh can stably exist in the structure and achieve long stability in DRM reaction.

Monte Carlo simulations of surface segregation to discover new hydrogen separation membranes

Surface compositions play a predominant role in the efficiency and lifetime of membranes and catalysts. The surface composition can change during operation due to segregation, thus controlling and predicting the surface composition is essential. Computational modelling can aid in predicting alloy stability, along with designing surface alloys and near-surface alloys that can outperform existing materials. In this work, a computational model to predict surface segregation in ternary alloys is developed. The model, based on Miedema's semi-empirical model and Monte Carlo simulations, enables to predict long- and short-range ordering in the surface and subsurface layers. It is used to screen a vast range of alloy compositions to design a novel ternary Pd-based material for H2 separation membranes. The addition of specific amounts of Cu and Zr to Pd is expected to reduce poisoning and enhance the permeability as compared to pure Pd.

Multiphase Alloy Nuclear Waste Forms Developed for Pyrochemical U-10Mo Scrap Recovery Waste Streams

The US High Performance Research Reactor (USHPRR) Conversion program is developing an Al-clad Zr-bonded U-10Mo nuclear fuel foil to enable the conversion of research reactors to high-assay low-enriched uranium (HALEU) alloy fuel. Fabrication scrap from the fuel manufacturing will be electrorefined to recover the HALEU, which will generate waste streams consisting of Zr, Mo, and residual U retained in the stainless steel anode basket used in the electrorefiner. Four alloys were formulated with different relative amounts of Zr, Mo, and 316L-SS to represent the expected range of waste compositions. Laboratory-scale ingots were made and metallurgically characterized to assess differences in the microstructures and distributions of the surrogate waste metals. Different amounts of the same dominant phases with similar compositions were formed in most materials: a γ-austenite based matrix, two ZrFe2 intermetallic phases that could host residual uranium, an FeCrMo sigma (σ) intermetallic phase, a chi (χ) phase, and a secondary austenite (γ2) phase. Electrochemical tests were conducted to compare the corrosion behaviors in acidic and alkaline brine solutions for a range of simulated environmental redox conditions. Corrosion of the Mo-rich γ and γ2 solid solutions and the σ and χ intermetallic phases occurred. The multiphase alloy waste form formulated with the lowest molybdenum and highest zirconium contents showed the highest corrosion resistance and has sufficient amounts of ZrFe2 to immobilize trace amounts of residual uranium in the waste stream. The alloy formulation strategy and testing approach will be presented with key results.Work conducted at Argonne National Laboratory is operated for the U.S. Department of Energy, Office of Science under contact DE-AC02-06CH11357.