High Zr Content Research Articles

MAGMA COMPOSITION AND FORMATION CONDITIONS OF ALKALI-SALIC ROCKS OF THE EARLY MESOZOIC ADAATSAG BIMODAL ASSOCIATION OF THE KHARKHORIN RIFT ZONE OF CENTRAL ASIA (DATA FROM THE STUDY OF MELT INCLUSIONS IN MINERALS)

Based on the method of investigation of melt inclusions using electron and ion microprobe, the magma composition and formation conditions of comendites of the Early Mesozoic Adaatsag volcanic association (Mongolia) were studied. The mechanisms leading to the accumulation of rare and rare earth elements in them were determined. Melt and fluid inclusions are found in quartz from the comendites, collected from different parts of the volcanic sequence. The melt inclusions consist of glass, a gas bubble and daughter minerals represented by fluorite, polylithionite and potassium feldspar. The use of the Raman spectroscopy method made it possible to study the composition of the gas phase in melt inclusions. It is determined that the predominant components of the gas phase are water and hydrogen. Fluid inclusions are represented by aqueous solutions that correspond to KF in composition. The concentration of KF in the solution reach up to 4.0–4.1 wt. %. Thermometric experiments with melt inclusions and analysis of the composition of glasses of homogenized melt inclusions in quartz of the comendites showed that the crystallization of magmas of these rocks occurred from water-saturated rare-metal melts with high contents of Li, Zr, F, Rb, Nb, Y and Th at temperatures of 880–930°C and at a pressure of 1000 bar at a depth of ~3.5 km and was accompanied by degassing processes. Comparison of the obtained data on the study of melt inclusions in the phenocrysts of the alkali-salic rocks of the same age volcanic associations Adaatsag, Dzarta-Кhuduk and Sant, developed within the Kharkhorin rift zone, revealed general patterns of their magma evolution. This allowed us to propose a similar mechanism of their formation, involving the accumulation of many rare and rare-earth elements, as well as volatile components (F, H2O) in the process of crystallization differentiation. Subsequently, a salt melt rich in Li, F and water could be separated from such comendite magmas. The detection of fluoride aqueous inclusions in quartz allows us to suppose the further evolution of the salt melt leading to the appearance of a concentrated aqueous fluid and the possible participation of the latter in metasomatic processes.

Mechanical and Anticorrosive Properties of TiNbTa and TiNbTaZr Films on Ti-6Al-4V Alloy

In this study, TiNbTa and TiNbTaZr films were utilized as protective coatings on a Ti-6Al-4V alloy to inhibit corrosive attacks from NaCl aqueous solution and simulated body fluid. The structural and mechanical properties of multicomponent TiNbTa(Zr) films were investigated. The corrosion resistance of the TiNbTa(Zr)-film-modified Ti-6Al-4V alloy was evaluated using potentiodynamic polarization tests in a NaCl aqueous solution. The results indicate that the TiNbTa(Zr) films with high Ti and Zr contents exhibited inferior corrosive resistance related to the films with high Ta and Nb contents. Moreover, the TiNbTa(Zr)-coated Ti-6Al-4V plates were immersed in Ringer’s solution for eight weeks; this solution was widely used as a simulated body fluid. The formation of surficial oxide layers above the TiNbTa(Zr) films was examined using transmission electron microscopy and X-ray photoelectron spectroscopy, which prevented the elution of Al and V from the Ti-6Al-4V alloy. Ti33Nb19Ta21Zr27, Ti15Nb68Ta8Zr9, and Ti8Nb8Ta79Zr5 films are suggested as preferential candidates for TiNbTa(Zr)/Ti-6Al-4V assemblies applied as biocompatible materials.

Facile Surface Modification of MgMn2O4 Positive-Electrode Material for Improving Cycle Performance of Magnesium Rechargeable Batteries.

MgMn2O4 with a tetragonal spinel structure shows promise as a positive-electrode material in magnesium rechargeable batteries (MRBs), which have drawn considerable attention as post lithium-ion batteries. However, the material currently suffers from poor cycle performance. In this study, we attempt to improve the cycle performance of MgMn2O4 via the Zr modification of its particle surface. X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy demonstrate that the surface modification is successfully performed by immersing MgMn2O4 powder into a Zr-containing aqueous solution, followed by heat treatment. However, Zr segregation is observed at high Zr concentration. Furthermore, structural analyses using synchrotron X-rays indicate that the Zr modification has an influence on the bulk structure of the MgMn2O4 powder. The positive-electrode properties of the powders are investigated using discharge/charge cycle tests, which show that Zr modification can drastically improve the cycle performance and coulombic efficiency. These improvements are supposed to be due to suppression of an unexpected reaction by the Zr-surface modification and lower structural distortion after the modification. These findings clearly demonstrate the significant potential of surface modification as a method for obtaining high-performance MRBs.

A RECENTLY DISCOVERED TRACHYTE-HOSTED RARE EARTH ELEMENT-NIOBIUM-ZIRCONIUM OCCURRENCE IN NORTHERN MAINE, USA

AbstractReported here are geological, geophysical, mineralogical, and geochemical data on a previously unknown trachyte-hosted rare earth element (REE)-Nb-Zr occurrence at Pennington Mountain in northern Maine, USA. This occurrence was newly discovered by a regional multiparameter, airborne radiometric survey that revealed anomalously high equivalent Th (eTh) and U (eU), confirmed by a detailed ground radiometric survey and by portable X-Ray fluorescence (pXRF) and whole-rock analyses of representative rock samples. The mineralized area occurs within an elongate trachyte body (~1.2 km2) that intrudes Ordovician volcanic rocks. Geologic constraints suggest that the trachyte is also Ordovician in age. The eastern lobe (~900 × ~400 m) of the trachyte is pervasively brecciated with a matrix containing seams, lenses, and veinlets composed mainly of potassium feldspar, albite, and fine-grained zircon and monazite. Barite is locally abundant. Minor minerals within the matrix include columbite, bastnäsite, euxenite, chlorite, pyrite, sphalerite, and magnetite. The pXRF analyses of 22 samples (App. Table A1) collected from the eastern lobe demonstrate that this entire part of the trachyte is highly mineralized. Whole-rock geochemical analyses for samples from the eastern lobe document high average contents of Zr (1.17 wt %), Nb (1,656 ppm), Ba (3,132 ppm), Y (1,140 ppm), Hf (324 ppm), Ta (122 ppm), Th (124 ppm), U (36.5 ppm), Zn (689 ppm), and Sn (106 ppm). Among light REE, the highest average concentrations are shown by La (763 ppm) and Ce (1,479 ppm). For heavy REE (HREE), Dy and Er are the most abundant on average (167 and 114 ppm, respectively). No HREE-rich minerals such as xenotime have been identified; the HREE may reside chiefly in monazite and bastnäsite, and within the fine-grained zircon. Very strong positive correlations (R2) of 0.92 to 0.98 exist between Th and Zr, Nb, Y, Ce, Yb, and Sn, indicating that the radiometric data for eTh are valid proxies for concentrations of these metals in the mineralized rocks.Trachyte-hosted REE-Nb-Zr deposits like the occurrence at Pennington Mountain also are known in eastern Australia and in the south Qinling belt of Central China. Based on comparisons with these deposits, and the lack of detailed geologic mapping in the Pennington Mountain region, we suggest that other rare-metal occurrences contained in trachyte may exist elsewhere in northern Maine, and more widely in the Appalachian-Caledonian orogen where volcanic and subvolcanic trachytes have been recognized.

Generation of aluminous A-type granite by partial melting of felsic restite: Evidence from Mesozoic granitoids in the southern margin of the North China Craton

Aluminous A-type granites generally show high SiO 2 contents of >70 wt%, and their petrogenesis is still hotly debated with respect to source nature, magmatic processes and tectonic setting . This paper presents a comparison of petrography , geochronology and geochemistry between a Mesozoic syenogranite and its adjacently contemporaneous granitoids in the Xiong'ershan area, the hanging wall of the Paleozoic continental collision zone between the North China Craton and the North Qinling microcontinent. Syenogranites at Taishanmiao are metaluminous to weakly peraluminous, and belong to high-K calc-alkaline to shoshonitic series. They contain embayed bipyramidal quartz crystals , quartz-feldspar intergrowths and high Fe biotite species as well as accessory fluorite , magnetite and ilmenite . They exhibit significantly negative Ba, Sr and Eu anomalies with most δEu values of <0.5, and relatively high contents of Nb, Ta and Zr. They are weakly magnesian to ferroan in lithochemistry and mostly fall into the field of aluminous A-type granite in terms of their high Zr contents and 10,000 × Ga/Al ratios. Furthermore, they have low Y/Nb ratios of <1.20, falling into the A1-type field of the Nb-Y-Ce ternary diagram. The geochronological results indicate that the Taishanmiao syenogranites were emplaced into the late Paleoproterozoic Xiong'er Group volcanics at 119 ± 1 Ma, consistent with emplacement ages of the late stage non-adakitic granitoids at Funiushan in the same area. Whole-rock Nd and zircon Hf O isotope compositions are similar between the two types of granitoids, indicating that they share a common magma source that is composed of the ancient crustal basement in the southern margin of the North China Craton and the juvenile crust of the North Qinling microcontinent. According to their petrographic and geochemical features, the syenogranites are categorized into aluminous A-type whereas the non-adakitic granitoids belong to I-type. Therefore, they were produced by partial melting of felsic restites after extraction of hydrous granitic melts to form the Funiushan I-type granites. As such, the composition of these granitoids is primarily dictated by both source composition and magmatic processes at the ancient convergent plate margin. Although the granitic magmatism would take place in the post-collisional period, the aluminous A-type granite was formed in the terminal stage of post-collisional magmatism. In addition, the post-collisional granites record reactivation of the hanging wall in the continental collision zone. • The Taishanmiao syenogranites belong to aluminous A1-type granite. • The syenogranites were derived from partial melting of the felsic restite. • The felsic restite was produced by extraction of hydrous granitic melts. • The syenogranites are petrogenetically associated with calc-alkaline granitoids. • Granite composition is also dictated by crustal anataxis and melt extraction.

Geochemical Constraints on Petrogenesis and Tectonics of the Middle Devonian Granitic and Coeval Mafic Magmatism from the Tannuola Terrane (Northern Central Asian Orogenic Belt)

The Tannuola terrane, located in the northern Central Asian Orogenic Belt, comprises magmatic rocks, attributed to island-arc and collisional settings during the Early Cambrian to the Late Ordovician. However, zircon U-Pb age, geochemical, and Sr-Nd isotopic constraints demonstrate that there was a short episode of peralkaline A-type granite magmatism in the northeast border area of the Tannuola terrane. The obtained zircon U-Pb age of 387.7 ± 3.3 Ma indicates emplacement of the peralkaline A-type granitic rocks in the Middle Devonian (Eifelian–Givetian period boundary). Petrologically, these rocks are mainly composed of riebeckite granites and aplites, which are approximately synchronous with augite-rich dolerites. The granitic rocks are ferroan and calc-alkalic to alkali-calcic in composition. They are characterized by a high content of SiO2, total alkali, Zr, and total REE. Significant depletion of Ba, Sr, P, Ti, and Eu indicates fractionation of plagioclase and/or K-feldspar. The values of εNd(t) in riebeckite granites range from +5.61 to +6.55, and the calculated two-stage model age ranges between 610 and 520 Ma. Coeval dolerites on the chondrite-normalized REE pattern, (Th/Yb)pm–(Nb/Yb)pm, and Th/Yb–Nb/Yb diagrams show compositional affinity between E-MORB and OIB. They are rich in incompatible elements with high HFSE/LREE ratios (Nb/La &gt; 1), indicating that the primary magma originated from the lithospheric mantle metasomatized by asthenosphere-derived melt. Based on these geochemical characteristics, it can be reasonably inferred that the peralkaline A-type granitic rocks, and the coeval mafic rocks, are anorogenic and were emplaced in an extensional tectonic environment despite slightly higher Y/Nb values, which might be caused by a crustal contamination effect. The geochemistry of mafic rocks suggests that the magma originated from the enriched mantle sources. The results of a zircon-saturation thermometer show high initial magma temperatures between 923 and 1184 °C, with an average of 1030 °C, indicating this rock association might be related to a mantle plume beneath the northern Central Asian Orogenic Belt.

Facile synthesis of lattice-defective and recyclable zirconium hydroxide coated nanoscale zero-valent iron for robust arsenite removal

A novel core-shell structured adsorbent, zirconium hydroxide coated nanoscale zerovalent iron (NZVI@Zr(OH)4), was developed for aqueous arsenite (As(III)) removal. The effects of water content and Zr dose for the coating process on the coating efficiency, anti-corrosion stability, and As(III) removal were investigated to optimize the performance of NZVI@Zr(OH)4. The Zr(OH)4 shell with a coating ratio of 200 wt% (Zr/Fe) was demonstrated to completely cover the NZVI surface, which can protect the NZVI core from aqueous corrosion in aerobic conditions and maintain its ferromagnetism. Due to the strong ferromagnetism of NZVI, a magnetism saturation value of 32.3 emu/g could be obtained with a high Zr content of 44.5 wt%, which could concurrently guarantee the quick magnetic separation for recycling and the high As(III) adsorption capacity. The Zr(OH)4 shell synthesized at room temperature possesses a weak crystalline and mesoporous structure. Abundant oxygen lattice defects with the uncoordinated Zr(IV) on the surface of Zr(OH)4 shell could be utilized for the As(III) removal via chemisorption. As a result, the NZVI@Zr(OH)4 performed a much higher capacity (380.0 mg-As·g−1 or 853.2 mg-As·g-Zr−1) than commercial Zr(OH)4 and other magnetic Zr-based materials, which was not affected by the pH variation and the co-existed environmental anions and natural organic matters. Therefore, NZVI@Zr(OH)4 is a promising material that can be applied and recycled to remove As(III) under diverse aqueous conditions.

Lithostratigraphy, Lithogeochemistry, and Tectono-Magmatic Framework of the ABM Replacement-Style Volcanogenic Massive Sulfide (VMS) Deposit, Finlayson Lake District, Yukon, Canada

Abstract The Upper Devonian ABM deposit is a bimodal-felsic, replacement-style volcanogenic massive sulfide (VMS) deposit within the Finlayson Lake district in Yukon, Canada. The deposit is hosted by predominantly felsic volcanic rocks of the upper Kudz Ze Kayah formation that were deposited in an active back-arc basin in three sequences consisting of interbedded felsic volcaniclastic rocks and argillites, and felsic lava flows and domes, and felsic and mafic sills. The felsic rocks fall into two groups, Felsic A and Felsic B (FA and FB), based on immobile elements and their ratios. Relative to the FB group, the FA group has high Zr concentrations (&amp;gt;550 ppm) and generally higher contents of high field strength elements. The FA/FB chemostratigraphy roughly coincides with the lithostratigraphic sequences. Sequence 2 hosting the mineralization consists of FB felsic rocks; the hanging-wall Sequence 3 and footwall Sequence 1 felsic rocks have FA signatures. An argillite lens, recording a period of volcanic quiescence, occurs at the upper contact of Sequence 2. From reconstruction of the basin architecture, two sets of synvolcanic faults are inferred. The synvolcanic faults were interpreted based on thickness changes of volcanosedimentary units and the distribution of coherent rocks. During breaks in volcanism, synvolcanic faults acted as conduits for upwelling hydrothermal fluids, which were diverted laterally into unconsolidated volcaniclastic rocks and formed the replacement-style VMS mineralization. Although the mineralized lenses are hosted by FB felsic rocks, their replacement-style nature implies that the mineralizing processes occurred during the break in volcanism and were genetically associated with the overlying FA felsic volcanic rocks.

Cellular microstructure modification and high temperature performance enhancement for Sm2Co17-based magnets with different Zr contents

• Sm(Co bal Fe 0.09 Cu 0.09 Zr x ) 7.2 magnets were prepared with x ranging from 0.025 to 0.04. • It was investigated that the high temperature magnetic properties changing regulation as Zr content changes, and the intrinsic coercivity at 773 K up to 667 kA . m −1 was achieved. • The Cu-lean characteristic at cell boundary phase is the reason that gives rise to higher magnetic properties at elevated temperatures for magnets with higher Zr content. Influence of Zr contents on high-temperature magnetic performance of Sm(Co bal Fe 0.09 Cu 0.09 Zr x ) 7.2 ( x = 0.025, 0.03, 0.035, 0.04) magnets were investigated. As x increases from 0.025 to 0.04, the temperature coefficient of intrinsic coercivity ( H cj ) is optimized from -0.1673% K −1 to -0.1382% K −1 and the H cj at 773 K gradually increases from 556.32 kA m −1 to 667 kA m −1 . The microstructure and microchemistry of different Zr-content magnets were revealed by a transmission electron microscope equipped with EDS. The increasing Zr content induces that the average size of cells decreases from ∼ 76 nm to ∼ 56 nm and the weight fraction of 1:5H cell boundary phase increases from ∼ 25% to ∼ 37% as well, resulting decreasing of the average Cu content at cell boundaries from 13.59 at% to ∼ 8.52 at%. It is found that the Cu-lean characteristic at cell boundary phase is the reason that gives rise to higher magnetic properties at elevated temperatures for x = 0.04 magnet.

Natural aging of metallic glasses

Metallic glasses (MGs) are intrinsically metastable, and tend to relax and crystallize at elevated temperatures. However, it is generally believed that their amorphous nature at room temperature can be retained for a sufficiently long time. Herein, we report the long-term stability of a series of Cu-Zr MGs in natural environment after twelve years. Surprisingly, the Cu-Zr MGs with a low Zr content (i.e., below 66.7 at%) encountered severe instability, which was induced by room-temperature oxidation. Although those with a high Zr content preserve the shiny surfaces due to the formation of a dense ZrO2 layer, their thermal properties (e.g., glass transition temperature Tg and onset crystallization temperature Tx) are appreciably changed due to oxygen permeation. Our findings not only shed light on the understanding of the thermal stability of MGs in general, but also have important implications for engineering applications of these disordered solids.

Tailoring the composition of the functional Cu–Cr–Zr–La/Ce alloys for electromechanical applications

Tailoring the compositions of the functional Cu–Cr–Zr–La/Ce alloys involve producing alloys with dilute (0.05%), low (0.16–0.2%), medium (0.41–0.44%), and high (0.66–0.91%) Cr content at dilute (0.06%), medium (0.5%), and high (0.98%) Zr content with (0.23–0.4%) La or (0.03–0.12%) Ce. The effect of these compositional differences on the microstructure, hardness, and electrical properties was studied for different aging times (0, 1, and 1.5 h). The best combination of hardness and electrical properties was achieved after 1.5 h of aging for all studied alloys. The effect of the chemical composition on tensile properties and wear resistance was studied after 1.5 h of aging. Unlike Zr, high Cr content has a negative influence on the tensile strength and wear resistance.

Structural, chemical, optical and photocatalytic properties of Zr co-doped anatase-rutile mixed phase TiO2: Ag nanoparticles

Zr co-doped TiO2:Ag nanoparticles were synthesized by the co-precipitation method and the influence of Zr co-dopant with varying content on the structural, optical and photocatalytic properties of TiO2:Ag photocatalysts was investigated. X-ray diffraction and Raman spectroscopy confirmed the anatase-rutile mixed phase of TiO2 and Zr content eased the anatase-rutile phase transformation. X-ray diffraction peak shift with Zr content indicated the substitutional doping of Zr4+ ions into TiO2 lattice. The optical properties of the nanoparticles were investigated with diffuse reflectance spectroscopy, photoluminescence and Fourier transform infrared spectroscopy. Zr dopants induced the Burstein-Moss effect, resulting in the broader bandgap and photoluminescence shift. X-ray photoelectron spectroscopy was utilized to reveal the surface chemical environment of the Zr co-doped TiO2:Ag nanoparticles and found the presence of Zr4+ ions on the photocatalyst surface, which act as electron traps. The dependence of operational parameters such as photocatalytic load, dye concentration and pH on Zr co-doped TiO2:Ag nanocatalyst was also monitored. The photocatalysts demonstrate improved photocatalytic activity toward methylene blue degradation with maximum efficiency achieved by the photocatalyst having the highest Zr content. 20 mg and 10.35 μM were found to be the optimum values for photocatalytic load and initial methylene blue concentration, respectively. Further, at alkaline pH, complete decolorization of the reaction mixture was observed in only 60 min with 92.6% efficiency by highest co-doped photocatalyst. The effect of Zr content on degradation rate with different parameters was also explored with a possible mechanism to understand the effect of dopants on photocatalytic activity of the photocatalysts.

Geology, Geochemistry, and Geochronology of the Giant Rio Tinto VMS Deposit, Iberian Pyrite Belt, Spain

Abstract The Rio Tinto deposit is a giant volcanogenic massive sulfide deposit (VMS) that contains more than 500 Mt of pyrite-rich massive sulfides and more than 2 Gt of mineralized stockwork. Three broad lithostratigraphic groups occur in the regional stratigraphy: the phyllite-quartzite group, the volcano-sedimentary complex, and the Baixo Alentejo Flysch Group. These three major packages reflect the evolution of a depositional environment from a stable platform to deposition in pull-apart continental basins during oblique subduction and collision and coeval synorogenic flysch sequence. The volcano-sedimentary complex, which hosts massive sulfide mineralization at Rio Tinto, can be divided into four major units: (1) the Mafic Siliciclastic Unit, (2) the Lower Sedimentary Unit, (3) the Felsic Unit, and (4) the Upper Sedimentary Unit. The Felsic Unit is further subdivided based on new U-Pb zircon geochronology into three distinct subunits. Felsic Unit I (ca. 356 Ma) includes dome complexes dominated by rhyodacite and reflects the onset of felsic magmatism in the region. Felsic Unit II (ca. 352–348 Ma) represents the main interval of volcanic activity, also dominated by rhyodacite domes and related aprons, and is associated with widespread VMS mineralization. Felsic Unit III (ca. 340 Ma) reflects a late pulse of rhyolitic volcanism. Massive sulfides occur as two different styles of mineralization: (1) replacive ores as discordant pipes hosted by glass-rich felsic rocks and enclosed by a large zone of stockwork-like mineralization and (2) overlying shale-hosted exhalative mineralization in small anoxic basins, probably formed during the collapse of the volcanic domes of Felsic Unit II in the Middle-Late Tournaisian. New lithogeochemical data illustrate two types of mafic rocks in the Mafic Siliciclastic Unit: a basaltic andesite and a high–Ti-Zr basalt, both of tholeiitic affinity. Using immobile element ratios (heavy rare earth elements [HREEs], Al, Y, Zr, and Ti) of the Felsic Unit, fundamental differences have been recognized between the subunits. The unmineralized Felsic Unit I is characterized by high Zr content (225–300 ppm) and a pronounced Eu negative anomaly, and probably represents the most fractionated rocks. Felsic Unit II is characterized by Zr values between 50 and 200 ppm. The low Zr values of the mineralized unit contrast with the typically high Zr values of the felsic rocks related to volcanogenic massive sulfides elsewhere and, at a regional scale, can help to discriminate potentially fertile domes from barren volcanism.

Geology, geochemistry, and apatite/titanite U–Pb geochronology of ca. 1.88 Ga alkaline ultrabasic dykes in the Southern Province near Sudbury, Ontario

The area northeast of Sudbury, Ontario, is well known for hosting one of the largest unexplained geophysical anomalies in the Canadian Shield, the Temagami Anomaly. In search of a geological explanation for this anomaly, low-grade metamorphic ultrabasic dykes have been discovered in the overlying Huronian Supergroup sedimentary rocks, both in outcrop and in a deep drill core. Here, we report on the first geochemical and geochronological data obtained on these dykes and compare these data with known magmatic units in and around the 1850 Ma impact-generated Sudbury Igneous Complex (SIC). The NW-striking dykes, which cut across sedimentary rocks of the ca. 2.3 Ga Cobalt Group, and which are, in turn, crosscut by pseudotachylitic breccia, are characterized by distinctively high concentrations of Ti, P, Nb, and Zr, highly fractionated rare earth element patterns (La/YbN 7.6–15.5), and a lack of crustal contamination (Nb/Th &gt; 10). Such features are typical of modern ocean island basalts but very different from Palaeoproterozoic rocks previously documented in the wider region. Multigrain U–Pb laser ablation inductively coupled plasma mass spectrometry analyses performed on magmatic titanite and apatite with high Th/U ratios yielded 1876.0 ± 8.7 and 1880.9 ± 8.3 Ma, respectively, which we interpret as the intrusion age of the dykes. This interpretation is supported by similar whole-rock Sm-Nd model ages of 1890–2000 Ma (initial εNd +2.5). This magmatic event in the footwall of the SIC shortly before the impact was coeval with, and likely genetically related to, the 1.88–1.87 Ga Circum-Superior Large Igneous Province.

Crystal nucleation and growth processes in Cu-rich glass-forming Cu-Zr alloys.

The glass formation ability of an alloy depends on two competing processes: glass-transition, on one hand, and crystal nucleation and growth, on the other hand. While these phenomena have been widely studied before in nearly equiatomic Cu-Zr alloys, studies are lacking for solute/solvent-rich ones. In the present work, molecular dynamics simulations show that the addition of a small amount of Zr (1-10 at. %) to Cu drastically increases the incubation time and slows down crystal growth, thus, leading to an improved glass forming ability. The crystal nucleation and growth processes of a competing face-centered cubic (FCC) Cu crystalline phase are analyzed in detail. In particular, the values of the critical cooling rate, incubation period for crystallization, and growth rate of FCC Cu crystals in these Cu-rich alloys are obtained. The growth of a supersaturated FCC Cu solid solution is found to be polymorphic at the interface (except for alloys with 9 and 10 at. % Zr) though a Zr concentration gradient is observed within growing crystals at high enough Zr content. The crystal growth rate before crystal impingement is nearly constant in all alloys, though it decreases exponentially with the Zr content. Crystallization kinetics are also analyzed within the existing theories and compared with the experimental values available in the literature.

Efficient Dry Impregnation of Zirconium into H‐ZSM‐5 Zeolites

AbstractThere is considerable interest in adjusting the acidity and pore architecture of zeolites. Herein, we present solventless incorporation of zirconium (∼2–10 wt.%) in a precursor and desilicated (0.2 and 0.4 mol L−1 NaOH) H‐ZSM‐5 zeolite. Infrared and UV‐vis‐DR spectroscopy confirmed the grafting of highly dispersed Zr in all the zeolites. XRD indicated the presence of ZrO2 in zeolites with higher Zr contents. The micropore volume of the precursor zeolite decreased by ∼10 %, suggesting the presence of Zr mainly on the external surface, while it decreased more than 20 % for the desilicated sample, suggesting Zr had access to the micropores at higher Zr contents. Infrared spectroscopy after pyridine adsorption provided evidence for the Brønsted and Lewis acid sites in all zeolites, but the Brønsted acid‐to‐Lewis acid site ratio decreased by &gt;50 % depending on the Zr and NaOH concentrations. The presence of Zr critically changed the predominant nature of the acid sites of the desilicated zeolites.

Petrogenesis and Tectonics of Eocene–Oligocene Phonolites of Mecejana, Ceará, NE Brazil: the Role of the Fernando de Noronha Fracture Zone, Equatorial Atlantic

Abstract Located on the western continental tip of the Fernando de Noronha transform fracture (FNTF), northeastern Brazil, the Eocene–Oligocene Mecejana Phonolitic Province (MPP) was subjected to a multi-methodological study, comprising field and microscopic characterization, mineral and whole-rock chemistry, and Sr-Nd isotopes. These rocks intrude the Precambrian crystalline basement, forming mainly plugs oriented in the NE–SW direction. They are composed of alkali basalt, phono-tephrite, tephri-phonolite, and phonolite with phenocrysts of nepheline and sanidine, and minor diopside, aegirine-augite, aegirine, kaersutite, biotite and titanite. Chemically, they are sodic (Na2O/K2O &amp;gt; 1) and display Light Rare Earth Elements (LREE) enrichment, concave upward or flat Heavy Rare Earth Elements (HREE) patterns, weak to strong Eu anomaly, and high contents of Nb, Ta and Zr. They delineate two chemical groups, the less-evolved one comprising basalt to tephri-phonolites and the more evolved constituted by phonolites. Oxide and trace element modeling points out to an evolution by fractional crystallization, leaving olivine-rich gabbro and foidolite/nepheline syenite cumulates, respectively. The analyzed samples have Sr-Nd isotopic ratios akin to ocean island basalt (OIB) rocks (positive εNd of +3.0 to +0.9 at 30 Ma) and low to high 87Sr/86Sri (at 30 Ma) of 0.70264–0.70955. The data suggest a three-stage evolution model for the MPP: (1) &amp;lt;5% partial melting of a metasomatized phlogopite-amphibole-garnet peridotite generates an alkali basalt melt, (2) polybaric differentiation of this melt at crustal level (~570–220 MPa, 1040–645°C) leads firstly to phono-tephrites and tephri-phonolites and then to (3) foidolite and nepheline syenite. Petrographic, chemical, and isotopic characteristics of the MPP and similar rocks of the Fernando de Noronha islands suggest the control by the FNTF and reactivation of NE–SW trending deep-rooted Precambrian faults allowing channeling and emplacement of the alkaline magmas.

Unconventional Highly Active and Stable Oxygen Reduction Catalysts Informed by Computational Design Strategies

AbstractDiscovering and engineering new materials with fast oxygen surface exchange kinetics and robust long‐term stability is essential for the large‐scale, economically viable commercialization of solid oxide fuel cell (SOFC) technology. The perovskite catalyst material BaFe0.125Co0.125Zr0.75O3 (BFCZ75), predicted to be promising from recent density functional theory (DFT) calculations and unconventional due to its extremely high Zr content and low electronic conductivity, exhibits oxygen reduction reaction surface exchange rates on par with Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) and excellent stability at typical operating temperatures. New composite electrodes are engineered by integrating BFCZ75 with commercial electrode materials La1–xSrxMnO3 (LSM) and La1–xSrxCoyFe1–yO3 (LSCF) and achieve high performance as measured by low area specific resistance (ASR) values, with the LSCF/BFCZ75 ASR values comparable to top performing noncomposite electrode materials such as SrCo0.8Sc0.2O3–δ, BaNb0.05Fe0.95O3–δ and BaCo0.7Fe0.22Y0.08O3–δ. The use of BFCZ75 as a composite with LSCF achieving low ASR values shows that BFCZ75 is highly active and can easily integrate into existing SOFC material supply chains, lowering the barrier for potential commercial application of new electrode materials. Finally, these findings point to a broader unexplored class of perovskite materials with high fractions of redox inactive species (e.g., Zr, Nb, and Ta) that may unlock new pathways to realizing improved commercial SOFCs.

Microstructure and mechanical properties of Nb[sbnd]16Si alloys with Zr additions

To optimize the microstructure and fracture toughness of NbSi based alloys, the effect of Zr addition on the microstructure and mechanical properties was investigated in Nb16Si alloy. The results show that Zr element promotes the sluggish eutectoid reaction of (Nb, Zr)3Si → Nbss + α-(Nb, Zr)5Si3, and Nb-16Si-8Zr alloy only contains Nbss and α-(Nb, Zr)5Si3 phases. From the energy point of view, as the Zr content reaches 4 at.%, (Nb,X)5Si3 phase is more stable than (Nb, X)3Si phase. With the increase of Zr content, the fracture toughness increases since high Zr content refines eutectic structure and increases the content of primary Nbss. The thickness of primary Nbss has a strong influence on crack propagation. Most of the cracks can destroy primary Nbss phase with the thickness of (20 ± 2) μm and continue to propagate in the original direction. However, it will deflect when it intersects primary Nbss phase with a thickness of about (30 ± 2) μm. The improvement of compressive properties was caused by solid solution of Zr.

Modified copper zinc ferrite nanoparticles doped with Zr ions for hyperthermia applications

The problem of the present work is to synthesize a nanomagnetic material with low TC below 45 °C and its particle size below 30 nm to be appropriate material for convert magnetic loss into heat energy. A series of Cu0.4Zn0.6+yZryFe2–2yO4 nanoparticles compositions where y = (0.05, 0.1) were synthesized via citrate sol–gel method. The prepared samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The grains were observed from SEM confirming the crystalline structure of the ferrite which was detected by X-ray diffraction. Magnetic hysteresis loop measurements illustrate that materials exhibit soft magnetic properties at low Zr content, while at higher Zr content all materials behave as superparamagnetically without any saturation magnetization Ms. The initial magnetic permeability ({mu }_{i}) at frequency 10 kHz as a function of temperature was measured. A sudden change in {mu }_{i} appears around Curie temperature, making our samples good candidates for magnetic temperature transducer (MTT) devices. The DC resistivity for sample at y = 0.05, 0.1 was studied. The resistivity decreases linearly with increasing temperature within the given range of temperature up to 666 K for all samples. The dielectric constant of all samples is nearly independent on temperature through the range of 450 to 600 K which is a common character of ferrites. The dielectric loss was found to increase by increasing temperature, which may be related to the increase in AC conductivity. Hyperthermia measurements show the maximum specific power loss and temperature increase were 26 w/gr and 43 °C, respectively, for sample containing Zr = 0.05, after 2 min of measurements. One of the real applications of the material is that it is used as an effective method in tumor treatment by exposing the patient to external magnetic field.