Nb Fraction Research Articles

Soluble fraction of stabilising elements in ferritic stainless steel

The addition of stabilising elements such as Nb or Ti to ferritic stainless steel has gained in importance in recent years. These elements are added to the steel mainly to stabilise C and N, i.e. to remove C and N from the solid solution, owing to their strong tendency to form carbide and nitride precipitates. However, when added in excess, stabilising elements also provide different mechanical properties and corrosion behaviour to the steel. In order to understand the benefits of these additions, it is essential to know the fraction of these elements dissolved in the steel matrix. In this work, electron probe microanalysis (EPMA) results of different Ti-stabilised and Nb-stabilised ferritic stainless steel grades are reported, with the aim of determining the soluble fraction of Ti and Nb and elucidate its relationship with the bulk content of these elements.

Optical properties and degradation mechanism of magnesium-niobium thin film switchable mirrors

Magnesium-niobium (Mg-Nb) thin films with a palladium (Pd) top layer were prepared on glass substrates by means of DC magnetron sputtering deposition, at room temperature. A Mg-Nb thin film with a Pd top layer can be switched to a transparent state from a mirror-like state by loading with 4% hydrogen gas. The optical properties of Mg(1-x)Nbx thin film switchable mirrors, with x ranging from 0.13 to 0.37, coated with a Pd layer were investigated using a UV-Vis-NIR optical photometer. The optical transmittance of the hydride states decreased with an increasing Nb fraction. Mg-Nb thin film switchable mirrors show color-neutral characteristics in the hydride state. The degradation mechanism of Mg-Nb thin films when loading hydrogen (H) gas was studied using X-ray photoelectroscopy (XPS) and scanning electron microscope (SEM) methods. We showed that Mg-Nb-H thin films are transparent, color-neutral semiconductors with a band cap of 2.2 ± 0.2 eV.

Structural and Dielectric Characteristics in a Ca(Mg1/3Nb2/3)O3–CaZrO3 System

This study investigates the effect of CaZrO3 (CZ) substitution on the evolution of an ordered structure in a Ca(Mg1/3Nb2/3)O3 (CMN) system using Raman spectroscopy, X‐ray diffractometry, and transmission electron microscopy. It indicates that a (1−x) CMN−(x)CZ solid solution has the 1:2 and 1:1 ordered structure distorted by the antiphase, the inphase tilting of oxygen octahedra, and the antiparallel shift of A‐site cation. A distinct correlation is noted between the transition of the ordered structure and microwave dielectric properties. The differences in ɛr and τf are attributed exclusively to the differences in the type of cation arrangement. The structure with the 1:2 ordering exhibits a lower relative permittivity and a more negative τf than the structure with the 1:1 ordering. The increased fraction of compressed Nb–O bond in the 1:2 ordered structure associated with a large NbO6 octahedral distortion is correlated with a decrease in relative permittivity and change of τf toward more negative values. Simultaneously, the substitution of the Zr4+ ion causes a linear increase in polarizability, and it also results in an increase in the relative permittivity.

Dispersion Strengthened Nb$_{3}$Sn Wire

Dispersion strengthened Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and regular Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn composites were fabricated. Their mechanical and superconducting properties were measured and compared. An increase in strength up to 10% and J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (18 T, 4.2 K) up to 28% was achieved. The nanoparticle strengthened Cu, as a replacement of Cu, could be co-deformed with Nb to make Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wire without changing the volume fractions of Nb and Sn and heat treatment conditions. The paper argues that nanoparticle pining effects play a major role in improvement of the properties.

Making continental crust through slab melting: Constraints from niobium–tantalum fractionation in UHP metamorphic rutile

The formation of the continental crust (CC) is one of the most important processes in the evolution of the silicate Earth. Exactly how the CC formed is the subject of ongoing debate that focuses on its subchondritic Nb/Ta ratio. Nb and Ta are “geochemical identical twins,” so they usually do not fractionate from each other. Here, we show that rutile grains from hydrous rutile-bearing eclogitic layers recovered from drillcores in the Dabie-Sulu ultrahigh pressure terrain have highly variable Nb/Ta values (ranging from 5.4 to 29.1, with an average of 9.8 ± 0.6), indicating major fractionation of Nb and Ta most likely occurred during blueschist to amphibole–eclogite transformation in the absence of rutile. It is suggested that the released fluids with subchondritic Nb/Ta were transported to, and retained by, hydrous rutile-bearing eclogite in colder regions, resulting in suprachondritic Nb/Ta ratios for drier eclogite in hotter regions. Further dehydration of hydrous rutile-bearing eclogites cannot transfer the fractionated Nb/Ta values to the CC due to the low solubility of Nb and Ta in fluids in the presence of rutile, while dehydration-melting results in a major component of the CC, the tonalite–trondhjemite–granodiorite (TTG) component, which is responsible for the low Nb/Ta of the CC. Consequently, residual eclogites have variable but overall suprachondritic Nb/Ta.

Superconducting Properties of&lt;tex&gt;$rm Nb_3rm Sn$&lt;/tex&gt;Wires With Radially Arranged Filaments

An internal-tin route Nb3Sn superconducting wire that has both remarkably low hysteresis loss (Qh) and high critical current density (Jc) was developed according to a new design idea. The wire was constructed by arranging the filaments in a radial layout, enlarging the outer filaments along the radial direction, intentionally narrowing the filament spacing in the radial direction, and enlarging the filament spacing in the tangential direction. Thus, the electromagnetic coupling among the filaments in the tangential direction due to the bridging and/or proximity effect was suppressed without decreasing the volume fraction of Nb. As a result, excellent properties such as Jc(12 T)=1.15times103 A/mm2 Qh=301 mJ/cm3 (for 1 cycle of B=plusmn3 T), Tc=17.3 K, and Bc2=24.1 T were obtained. Scanning electron microscope observations confirmed that the cause of experimental Qh values being lower than expected is that the majority of the filaments in the second and outermost rows were not completely combined. Electron probe micro-analyses confirmed that the good Tc and Bc2 values resulted from the qualitative improvement of the Nb3Sn compound. This wire is promising for use with conduction-cooled high-field magnets and for the strands of fusion coils

Superconducting properties of internal-tin route Nb 3Sn wires with radially arranged filaments : Development that realizes high Jc and low hysteresis loss

An internal-tin route Nb 3Sn superconducting wire that has both remarkably low hysteresis loss ( Q h) and high critical current density ( J c) was developed according to a new design idea. The wire was constructed by arranging the filaments in a radial layout, enlarging the outer filaments along the radial direction, narrowing the filament spacing in the radial direction intentionally and enlarging the filament spacing in tangential direction. Thus, the electromagnetic coupling among the filaments in tangential direction due to the bridging and/or proximity effect was suppressed without decreasing the volume fraction of Nb. As a result, excellent properties such as J c(12 T) = 1.15 × 10 3 A/mm 2 and Q h = 301 mJ/cm 3 (for 1 cycle of B = ±3 T) were obtained. We also evaluated the transition temperature ( T c) and upper critical field ( B c2) of the wire. The values for T c and B c2 were 17.3 K and 24.1 T, respectively, which were much better than those of usual internal-tin route wires. Moreover, electron probe micro-analyses confirmed that the good T c and B c2 were the result of the qualitative improvement of the Nb 3Sn compound based on the effects of arranging the Nb filaments radially, increasing the ratio of Sn-to-Nb and shortening the diffusion length for Sn. This wire is promising for use with conduction-cooled high-field magnets, in which there is a need to decrease the load of the cryocooler, and also for the strands of fusion coils.

The evolution of primary and secondary niobium carbonitrides in AISI 347 stainless steel during manufacturing and long-term ageing

Nb(C,N) precipitates were studied in a niobium-stabilised stainless steel (AISI 347) statically aged at 700 °C. Scanning electron microscopy and energy filtered transmission electron microscopy were used to determine the volume fraction and precipitate size of primary and secondary Nb(C,N) after ageing times between 0 and 70,000 h. The experimental data were correlated with simulations of Nb(C,N) formation based on the assumption that the process is controlled by diffusion. These simulations provide a rationale for the existence of two sets of niobium carbonitrides in commercial tubes of AISI 347. Growth of primary Nb(C,N) occurred essentially during manufacturing, with no significant growth at 700 °C. Rapid dissolution and re-precipitation of secondary Nb(C,N) occurred during manufacturing. Coarsening at 700 °C of secondary particles was modelled using the Lifshitz–Slyozov–Wagner theory, which overestimated the coarsening rate. These problems were overcome with a model developed by the authors. This model takes both growth and coarsening into account.

Strain-Induced Precipitation of Nb(CN) during Deformation of Undercooled Austenite in Nb-Microalloyed HSLA Steels

By using TEM strain-induced precipitation of Nb(CN) during deformation of undercooled austenite was investigated in Nb-microalloyed steel. The results showed that at 1200°C all of Nb were dissolved and there were no Nb(CN) precipitates formed during cooling until down to 760°C; During deformation enhanced ferrite transformation Nb(CN) of dynamic precipitation required an incubation period, but compared with isothermal transformation it reduced significantly. Only when the strain increased to 0.69, Nb(CN) began to precipitate on dislocation nodes and grain boundaries. Furthermore the volume fraction of Nb(CN) precipitation increased with increasing strain but their coarsening wasn’t significant. Results showed that the measured grain size is in good agreement with the calculated value.

Ｎｂ３Ｓｎ線材の現状と将来展望―発見から５０年を記念して―内部拡散法によるＮｂ３Ｓｎ超電導線材の開発

The development of high performance Nb3Sn wires with an internal-tin route was reviewed. The internal-tin wires have excellent productivity and low production cost because the drawing process does not require intermediate annealing. This process has the advantage of producing several types of wires with wide superconducting properties for practical applications. We have been producing wires with high critical current density (Jc) and low hysteresis loss for fusion applications such as the ITER and KSTAR. We have also developed internal-tin wires with Jc>1600 A/mm2 at 12 T, 4.2 K for general high field magnets. Recently, we have been developing a new wire configuration for next generation high energy accelerators in collaboration with the KEK High Energy Accelerator Research Organization. The wire, called a distributed-tin (DT) wire, has an original structure in which the multi-Nb filament modules and Sn rods are uniformly distributed in a Cu matrix. The values of Jc of the DT wire are 2120 A/mm2 at 12 T, 4.2 K, which was obtained by increasing the Nb and Sn fractions of the wires, and 207 A/mm2 at 20 T, 4.2 K, because of the improvements in Bc2 and Tc. It is anticipated that the DT wires will be applied to not only next generation accelerators, but also high resolution NMRs.

Compositional variability in lavas from the Ontong Java Plateau: results from basalt clasts within the volcaniclastic succession at Ocean Drilling Program Site 1184

Abstract Tholeiitic basalts have been recovered from drill sites in different locations on the Ontong Java Plateau (OJP) and are remarkably homogeneous across this large igneous province. The most abundant basalt type is represented by the Kwaimbaita Formation on Malaita in the Solomon Islands, where it is capped by the isotopically distinct and slightly more incompatible-element-enriched basalt of the Singgalo Formation. Ocean Drilling Program (ODP) Leg 192 drilled five sites on the OJP, four of which penetrated basement lava successions. All basalt recovered during Leg 192 is chemically and isotopically indistinguishable from Kwaimbaita-type lavas. Site 1184 of ODP Leg 192 is situated on the eastern salient of the OJP, and is unique because the recovered volcaniclastic succession contains the first conclusive evidence for emergence of part of the OJP above sea level. Within this succession are clasts of basaltic material. We report the major element-, trace-element and isotopic compositions of 14 moderately to highly altered basalt clasts. On the basis of incompatible-element concentrations, specifically high field strength elements (HFSE) and rare earth elements (REE), four groups of clasts are defined. Group 1 clasts are similar to basalt from the Kwaimbaita Formation. Group 2 clasts show variable composition, but the heavy rare earth element (HREE) concentrations are similar to those of basalts from the Kwaimbaita Formation. Group 3 clasts have compositions similar to the high-MgO Kroenke-type basalt recovered during ODP Leg 192. Group 4 clasts are more evolved than the Kwaimbaita or Singgalo lavas, and contain deep negative Eu and Sr anomalies on primitive-mantle (PM)-normalized diagrams, as well as high concentrations of Nb, Ta and Th. Group 4 clasts also show a large fractionation of Nb from La and have (Nb/La) PM ratios of approximately 2. Sr-, Nd- and Pb-isotope ratios were measured on five clasts covering all four groups. Although the Sr- and Pb-isotope ratios exhibit some variability, which we attribute to alteration, the Nd-isotope ratios are within the field defined for Kwaimbaita-type lavas. We conclude that most of the compositional variability displayed by these clasts is a result of alteration and that Ta appears to be the most immobile incompatible trace element. All of the clasts were derived from the mantle source that produced the Kwaimbaita-type and Kroenke-type basalts. Our data emphasize the widespread nature of Kwaimbaita-type basalt and show that the source region was active under both the eastern salient and the high plateau of the OJP.

High field Nb/sub 3/ Sn conductor development at oxford superconducting technology

Oxford Instruments, Superconducting Technology (OI-ST) produces Nb/sub 3/Sn wire via several "internal Sn" routes. Recently, 12 T, 4.2 K non-Cu critical current density (J/sub c/) values of /spl sim/2900 A/mm/sup 2/ have been achieved by increasing the Nb and Sn fractions of the filament subelements. Similar conductors for high field use have shown engineering current density (J/sub e/) values of 170 A/mm/sup 2/ at 23.5 T, 1.8 K. OI-ST is also involved with research for the High Energy Physics (HEP) National Conductor Program. Results on composites made entirely by hot extrusion are described. Finally, the present status of Ta-Sn powder-in-tube (PIT) and Nb/sub 3/Al precursor strand development are presented. PIT strands have irreversibility fields over 26 T at 4.2 K, while Nb/sub 3/Al precursor strand has been produced by a route that promotes bonding of the billet components.

Mg substitutions for Zn in 0.8Pb[Zn 1/3(Ta,Nb) 2/3]O 3–0.2PbTiO 3 ceramics and dielectric properties

Systematic substitutions of Mg for Zn in 20 mol% PbTiO 3-added Pb[Zn 1/3(Ta,Nb) 2/3]O 3 (with different fractions of Ta and Nb) were attempted. The perovskite developments turned out to be promoted significantly by the Mg replacement. Values of the maximum dielectric constant and corresponding temperature were higher at higher Nb concentration. Frequency-dependent dielectric dispersion (with diffuse modes in the phase transition) was observed in the entire ceramics, except for the compositions without any Mg substitution. Microstructure observation results were generally consistent with the perovskite formation yields (determined by X-ray analysis).

Amorphization and phase evolution in Fe–Nb films prepared by ion beam assisted deposition

The ion beam assisted deposition (IBAD) technique is utilized to study amorphization in Fe–Nb binary metal systems. The amorphous range covers a Nb fraction of approximately 34–60 at.%. The Fe-rich and Nb-rich supersaturated solid solutions of the bcc phase were obtained in Fe 66Nb 34 and Fe 31Nb 69 films, respectively. In the Fe 66Nb 34 films, the ‘amorphous→amorphous+bcc→bcc’ evolution with increased ion beam energy from 2 to 8 keV is observed accompanying changes of film morphology. The phase formation in the IBAD process is determined by both thermodynamic and kinetic factors.

A natural shock-induced dense polymorph of rutile with α-PbO 2 structure in the suevite from the Ries crater in Germany

A dense post-rutile titanium dioxide (TiO 2) phase was discovered in shocked garnet gneisses from the Ries crater by reflected-light microscopy, laser microRaman spectroscopy and micro-beam X-ray diffraction. The Raman spectrum consists of nine bands at wave numbers: 152, 175, 285, 315, 340, 358, 428, 532 and 575 cm −1. These bands are identical to those of the α-PbO 2-structured polymorph of TiO 2 synthesized in a dynamic laboratory experiment. The diffraction pattern of the natural mineral revealed an orthorhombic lattice, similar to the α-PbO 2 polymorph with the cell parameters a=4.535(2) Å; b=5.499(2) Å; c=4.900(2) Å (space group Pbcn; columbite-type structure), density ρ=4.34 g/cm 2, where the numbers in parentheses are standard deviations in the last significant digits. This new polymorph is 2% denser than rutile. The rutile/α-PbO 2 polymorph phase transformation occurs exclusively at the grain boundaries between rutile and the shock-compacted host biotite and advances inwards in rutile. This textural relation establishes phase boundaries as the preferable fabric settings for dynamic-induced high-pressure phase transitions. Ab initio calculations negates the formation of the α-PbO 2 polymorph by inversion of a parental fluorite-structured polymorph during decompression. Heating of the experimentally produced α-PbO 2 polymorph above 500°C shows that it inverts back in a laboratory time scale to rutile. Hence, the survival of the α-PbO 2-structured polymorph in naturally shocked rocks constrains the post-shock temperature of the TiO 2-bearing assemblage at an upper bound of 500°C. The presence of this dense phase is expected in the Earth’s upper mantle below 123 km. The rutile/α-PbO 2-structured polymorph phase transition in subducted crustal limbs in the upper mantle should then be accompanied by considerable changes in the partitioning and fractionation of Nb and Ta between this TiO 2 polymorph and the coexisting dense silicates.

Metastable phases formation in Cu–Nb films by ion-beam-assisted deposition

The Cu–Nb alloy films with positive heat of mixing were prepared by ion-beam-assisted deposition (IBAD) technique. A new Nb-rich fcc phase and an amorphous phase, with composition range around 65–75% Nb fraction, were obtained in Cu–Nb films deposited under Ar + ion bombardments with energy below 7 keV. The supersaturated bcc phase was also formed in Cu 20Nb 80 films by IBAD. The formation mechanism of metastable phases in Cu–Nb system is discussed in terms of the procedure far from equilibrium and compared with that in Fe–Zr system by IBAD.

Normal zone propagation and quench characteristics of Nb/sub 3/Sn wires with jelly-roll and in-situ processed CuNb reinforcements

The stability of three types of CuNb reinforced Nb/sub 3/Sn wires has been experimentally studied in order to clarify effects of critical current density, J/sub c/, and Nb fraction in CuNb reinforcements. The stabilities, i.e., minimum quench energy, MQE, and normal zone propagation velocity, "/sub p/, were evaluated for sample wires having low J/sub c/ and low Nb fraction (A) and high J/sub c/ and low Nb fraction (B) with in-situ processed CuNb reinforcement and high J/sub c/ and high Nb fraction with jelly roll processed CuNb reinforcement (C). The MQE decreased with increase in transport current density normalized by J/sub c/, critical generation density, and Nb fraction, on the other hand, /spl nu//sub p/ increased with increasing the transport current density, regardless of Nb fraction. We obtained basic data for the design of magnets having both a high stability and mechanical strength.

Strain-induced precipitation behaviour in hot rolled strip steel

The strain-induced precipitation of Nb(C,N) into the austenite in a Nb-microalloyed steel was investigated both experimentally and using a predictive model. The precipitation of Nb(C,N) was measured indirectly from the hardness at room temperature after thermomechanical treatment. The predictive model combined the precipitation start model of Dutta and Sellars with the Avrami equation and the additivity principle to allow prediction of the volume fraction of Nb(C,N) precipitated. The effects of several thermomechanical schedules were studied. These were (i) the effect of isothermal hold temperature and duration; (ii) the effect of deformation temperature at high and low cooling rates; (iii) the effect of cooling rate prior to the austenite to ferrite transformation; and (iv) the effect of multiple pancaking deformations. The fit between the experimental data and calculated results was found to be good in all cases with the exception of the slow cooling rate results of schedule (ii). It was concluded that the model could, once calibrated, successfully predict the hardness and strength of thermomechanically processed Nb-microalloyed steels.

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

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

Niobium and tantalum in carbonaceous chondrites: Constraints on the solar system and primitive mantle niobium/tantalum, zirconium/niobium, and niobium/uranium ratio

Abstract— We have determined Nb, Y, and Zr abundances in the carbonaceous chondrites Orgueil (CI), Murray (CM2), Murchison (CM2), Allende (CV3), and Karoonda (CK4), and in the eucrites, Pasamonte and Juvinas, by a recently developed spark source mass spectrometric technique using multiple ion counting (MIC‐SSMS). The abundance of Ta was determined in the same meteorites by radiochemical neutron activation analysis (RNAA). Precision of the MIC‐SSMS and RNAA techniques is ∼3% and ≤ 5%, respectively.The new abundances for CI chondrites are: Nb = 0.247, Ta = 0.0142, Zr = 3.86, Y = 1.56 μg/g; or 0.699, 0.0202, 11.2, and 4.64 atoms/106 Si atoms, respectively. The values agree with earlier compilations, but they are a factor of 2 more precise than earlier analyses. Trace element concentrations in the CM, CV, and CK chondrites are higher than in the CI chondrite Orgueil by about 37, 86, and 120%, respectively, in agreement with the variable absolute contents of refractory lithophile elements in different groups of carbonaceous chondrites.Of particular interest are the chondritic Nb/Ta, Zr/Nb, and Nb/U ratios, because these ratios are important tools for interpreting the chemical evolution of planetary bodies. We obtained Nb/Ta = 17.4 ± 0.5 for the carbonaceous chondrites and the Juvinas‐type eucrites investigated. Though this value is similar to previous estimates, it is much more precise. The same is true for Zr/Nb (15.5 ± 0.2) and Zr/Y (2.32 ± 0.12). In combination with recently published MIC‐SSMS U data for carbonaceous chondrites, we obtained a chondritic Nb/U ratio of 29 ± 2.Because Nb, Ta, Zr, Y, and U are refractory lithophile elements and presumably partitioned into the silicate phase of the Earth during core formation, the elemental ratios may also be used to constrain evolution of the Earth's primitive mantle and, with the more precise determinations fractionation of Nb and Ta during magmatic processes and mantle‐crust interactions, can now be interpreted with greater confidence.