Behavior Of Niobium Research Articles

Effects of martensite-austenite constituents on mechanical properties of heat affected zone in high strength pipeline steels-review

To improve oil and gas pipelines reliability through the minimization of defects in the welded joint, many researches were conducted to control local brittle zones in weld joints, mainly Martensite-Austenite constituents (M-A). The latter may present toughness problems for the Heat Affected Zone (HAZ) in American Petroleum Institute (API) grade steels. Given the complexity of this problem due to several parameters involved in the behavior of M-A constituents and consequently the performance of the HAZ, the recent literature was reviewed. The formation, quantity and morphology of M-A in the HAZ of multi-pass welds were elucidated. The inherent potency of M-A constituents in deteriorating toughness and initiating fracture was highlighted. The purpose is to give a state of the art and extract the points not treated yet, related to the interaction between M-A constituents, metallurgical design, welding thermal cycle and toughness in HAZ of pipeline steels. In this article, a particular attention was given to the yet not clarified behavior of Niobium (Nb) and Titanium (Ti) carbonitride, in the case of two pass welding and their ability to control Austenite grain growth.

Behaviour of niobium during early Earth’s differentiation: insights from its local structure and oxidation state in silicate melts at high pressure

Niobium (Nb) is one of the key trace elements used to understand Earth’s formation and differentiation, and is remarkable for its deficiency relative to tantalum in terrestrial rocks compared to the building chondritic blocks. In this context, the local environment of Nb in silica-rich melts and glasses is studied by in situ x-ray absorption spectroscopy (XAS) at high pressure (P) up to 9.3 GPa and 1350 K using resistive-heating diamond-anvil cells. Nb is slightly less oxidized in the melt (intermediate valence between +4 and +5) than in the glass (+5), an effect evidenced from the shift of the Nb-edge towards lower energies. Changes in the pre-edge features are also observed between melt and glass states, consistently with the observed changes in oxidation state although likely enhanced by temperature (T) effects. The oxidation state of Nb is not affected by pressure neither in the molten nor glassy states, and remains constant in the investigated P-range. The Nb–O coordination number is constant and equal to below 5 GPa, and only progressively increases up to at 9.3 GPa, the maximum P investigated. If these findings were to similarly apply to basaltic melts, that would rule out the hypothesis of Nb/Ta fractionation during early silicate Earth’s differentiation, thus reinforcing the alternative hypothesis of fractionation during core formation on reduced pre-planetary bodies.

Nanostructured Anodic Oxide Films of Niobium: Features of Electrochemical Formation, Functional Properties and Applications (Review)

The review summarizes data on the anodic behavior of niobium in aqueous solutions. Features of electrochemical formation nanostructured oxide coatings on niobium by anodic oxidation are systematized. The article deals with theoretical aspects formation of the porous anodic oxide layers. The influence of process parameters and the characteristics of the electrolyte on layer of niobium oxide were analyzed. The functional properties of porous coating on niobium are considered and promising areas of practical application identified.

Electrochemical behavior of niobium electrodeposited 316 stainless steel bipolar plate for PEMFC in choline chloride based ionic liquids

Niobium was electrodeposited on 316 stainless steel bipolar plates of a fuel cell in water and air-stable choline chloride based ionic liquids. The electrochemical corruption property of bipolar plates in simulated PEMFC environment was investigated. It was showed that the plating film was distributed on the surface of 316 stainless steel like isolated islands with height less than 50 nm. The XPS, XRD results showed that a smooth and strong chemical inert film of NbO and Nb2O5 was formed on the surface of 316 stainless steel. In simulated cathodic condition, the corrosion potential of Nb coated stainless steel was improved by 244 mV, whilst in an anodic condition, it was improved by 105 mV. The current densities for the coated 316 stainless steel were decreased to 2.479 4 μA•cm-2 from 14.810 μA•cm-2 at -0.1 V and to 0.576 μA•cm-2 from 13.417 μA/•cm-2 at 0.6 V, respectively. It was implied that the niobium coating effectively decreased the corrosion rate. The results of the electrochemical tests indicated that the corrosion resistance of stainless steel was greatly improved after coated with niobium.

The Origin of Niobium and Tantalum Mineralization in the Nechalacho REE Deposit, NWT, Canada

The behavior of niobium and tantalum is poorly understood in rocks that have undergone significant hydrothermal alteration, and niobium-tantalum minerals of hydrothermal origin are rarely mentioned in the literature. Consequently, the mobility of these critical metals, although widely considered to be negligible, has not been evaluated. In this paper, we present the results of a study of the genesis of niobium and tantalum mineralization in the Nechalacho rare metal deposit, Northwest Territories, Canada, which contains one of the largest known resources of these metals in rocks that have undergone intense hydrothermal alteration. Analyses and examination of samples using the electron microprobe has led to the identification of a variety of niobium- and tantalum-bearing minerals in the Nechalacho deposit. Niobium-bearing zircon, columbite-(Fe), fergusonite-(Y), and samarskite-(Y) were identified in the ore zones of the deposit, uranopyrochlore, and columbite-(Fe) were found outside the ore zones, and magmatic fluornatropyrochlore was shown to be the sole niobium-tantalum mineral in relatively unaltered syenites below the Basal ore zone. Based on the paragenetic relationships among the above minerals, variations in the composition of the columbite group minerals as a function of location in the Nechalacho Layered Suite and the distribution of niobium, tantalum, zirconium, and uranium in the bulk rocks, we have developed a model to explain the occurrence of niobium and tantalum in the Nechalacho deposit. The first step in the concentration of these elements was the crystallization of niobium- and tantalum-bearing zircon and eudialyte in the subhorizontal Upper and Basal ore zones, respectively. This was accompanied by the crystallization of magmatic columbite-(Fe) in the Upper ore zone. Fergusonite-(Y) crystallized in the Basal ore zone and also formed due to the breakdown of eudialyte. Outside the ore zones, there was crystallization of pyrochlore and to a lesser extent magmatic columbite-(Fe). This step led to the development of strong spatial associations among niobium, zirconium, and uranium that are evident as strong positive correlations in the bulk-rock concentrations of these elements at the meter scale. During the ensuing intense and widespread hydrothermal alteration, niobium was locally remobilized. Hydrothermal columbite-(Fe) and fergusonite-(Y) formed at the cores of altered zircon grains. Wholesale replacement of magmatic columbite-(Fe) and fergusonite-(Y) by hydrothermal anhedral crystals occurred in the two ore zones. The estimated relative proportions of the sources of these minerals in the ore zones, although varying to some extent because of a dependence on the amount of niobium mobilized from zircon, is ~40/60. Outside the ore zones, columbite-(Fe) and uranopyrochlore are the present manifestations of the former pyrochlore. With the exception of magmatic fluornatropyrochlore in the fresher syenites below the Basal ore zone and a single example of magmatic columbite-(Fe) in an Upper ore zone sample, all niobium and tantalum minerals have a hydrothermal origin as a result of this pervasive alteration.

Phase Transformation Behavior of Niobium Containing Microalloyed Steel with Predeformation and Continuous Cooling

The continuous cooling phase transformation behavior of niobium microalloyed steel was studied by Thermecmastor-Z thermomechanical simulator; the continuous cooling transformation curves (CCT) were established. The change of microstructure under different cooling rates was observed, and the influence of deformation in austenite non-recrystallization region on transformation was discussed. Based on these work, it was possible to know that the phase transformation is retarded and the ferritic grain is refined dramatically as the cooling rate increasing. The deformation in austenite non-recrystallization region caused deformation stored-energy, which improved the grain refinement of transformation to some extent, but not significant.

Cyclic Oxidation Behaviour of Heat Resistance Cast Steel

The oxidation behaviour of niobium and titanium enriched, heat resistant cast steel 30Ni-18Cr has been evaluated under cyclic conditions. Cyclic testing was carried out in the air, at temperature of 800, 900 and 1000°C. The alloys underwent oxidation in 5 cycle tests. Characterization of the corrosion products was performed using SEM and X-ray examinations. The cross section and the surface of tested alloys were examined. It has been found that the oxidation resistance of cast steel 30Ni-18Cr in thermal cycling is higher when niobium or especially titanium are added to chemical composition of the alloy. The formation of scale rich in titanium oxides TiO2 was contributed to better oxidation behaviour.

The behaviour of niobium and molybdenum during uni-axial strain loading

The mechanical response of niobium and molybdenum during one dimensional shock loading in the weak shock regime is investigated in terms of the Hugoniot elastic limit (dynamic yield) and spall (tensile) strengths. Results indicate that although both metals have high elastic limits of ca. 2 GPa, their responses are very different. Deformation in the weak shock regime in niobium is controlled by both the motion and generation of dislocations, resulting in high spall (dynamic tensile) strengths and ductility. In contrast, molybdenum has low spall strength and ductility, which suggests lower dislocation mobility in this metal. We have also shown that the strain-rate in the rising part of the shock front is related to the stress amplitude by the fourth power, as first shown by Swegle and Grady. Although we have not been able to elucidate further on the power relation, we believe that the scaling factor A is related to a materials ability to accommodate shock imposed plasticity via slip and dislocation generation. Overall, we have used arguments about the Peierls stress in body centred cubic metals to explain these results, with niobium (low Peierls stress) having a high dislocation mobility, resulting in behaviour showing some similarities to face centred cubic metals. Molybdenum, with its much higher Peierls stress has a much lower dislocation mobility, and hence lower spall strengths and ductility.

Influence of Niobium on the Beginning of the Plastic Flow of Material during Cold Deformation

Investigations were conducted on low-carbon steel and the steel with same chemical composition with addition of microalloying element niobium. While tensile testing was carried out, the thermographic measurement was tacking place simultaneously. A specific behavior of niobium microalloyed steel was noticed. Test results have shown that, in the elastic deformation region, thermoelastic effect occurs, which is more pronounced in niobium microalloyed steel. Start of plastic flow in steel which is not microalloyed with niobium begins later in comparison to the microalloyed steel, and it is conducted so that, at the point of maximum stress, deformation zone is formed within which stresses grow. In steel microalloyed with niobium after proportionality limit, comes the occurrence of the localized increase in temperature and the occurrence of Lüders band, which propagate along the sample forming a deformation zone.

Model Study on Behavior of Niobium in High Carbon Rare Earth Steel

Abstract A coupling thermodynamic model which quantificationally described elements segregation and inclusions precipitation during solidification process of high carbon RE steel was proposed. According to the SEM and energy spectrum analysis, the model could completely consist with experiment results. Effects of mass fraction of niobium on the state of rare earth and niobium and constituents of inclusions during the solidification process of high carbon rare earth steel were studied. The results as follows:(1) Niobium carbide is gradually precipitated during solidification process. The content of solid niobium solution is rapidly increased at the late stage of solidification. With increasing mass fraction of carbon, concentration distribution of solid niobium solution is decreased at first and then increased.(2) With increasing mass fraction of niobium, both the temperature and content of niobium carbide precipitation are increased; the average precipitation content of solid niobium solution is gradually increased.(3) With increasing mass fraction of niobium, the content of solid RE solution. RE oxysulfide and nitride are increased, and the content of RES inclusion and RE aluminate are decreased.

Viscosity of niobium-containing oxide-fluoride melts

Influence of Nb2O5 on viscosity of the CaF2-based and CaF2-30% Al2O3-based melts was investigated using a vibration viscosimetry method in the range 1523–1873 K. It is found that viscosity of the melts rise and the crystallization range shifts to lower temperatures as the Nb2O5 concentration increases from 0 to 25 wt %. The activation energy of viscous flow increases from 34 to 110 kJ mol−1 and from 56 to 148 kJ mol−1 for the CaF2-based and CaF2-30% Al2O3-based melts, respectively. The obtained data indicate the complexing behavior of niobium in the oxide-fluoride melts.

Fracture behavior of niobium by hydrogenation and its application for fine powder fabrication

Fracture behavior of pure niobium (Nb) by several hydrogenation procedures has been investigated to elucidate the fundamental mechanisms of hydrogen pulverization, which can then be used to produce fine Nb powders with high purity. Concentric cracks and microcracks were introduced in recrystallized Nb specimens, leading to pulverization, when they absorb hydrogen enough to form a large volume of the face-centered orthorhombic β-NbH phase. This hydride phase exhibits anisotropic expansion of Nb lattice and embrittlement. Thus, the fracture of Nb plates occurs in the following sequence: hydrogen absorption, the formation of the ordered hydride phase, strain generation arising from the phase transformation, and crack nucleation and propagation. The authors also show that Nb powders less than 1 µm were prepared by hydrogenation and ball-milling at a temperature below 203 K, in which hydrogen was removed by dehydrogenation at above 724 K. Thus, fine and contamination-free Nb powders can be effectively fabricated by using hydrogenation, ball-milling, and dehydrogenation procedures.

Retention and phytoavailability of radioniobium in soils

Radioniobium is present in long-lived nuclear waste as a result of the activation of zirconium pellets associated with the nuclear fuel. The behaviour of niobium (Nb) in the environment and especially its fate in the soil–plant system has not been thoroughly investigated so far. In safety assessment of French long-lived nuclear waste disposal, data concerning the mobility and the bioavailability of Nb in soils are needed as well as general trends of its fate in the specific environment around the site of French underground research laboratory. Therefore, we investigated the mobility of 95Nb in three different soils typical of the area of north-eastern France and its uptake by two plants, rye grass ( Lolium perenne L.) and winter wheat ( Triticum æstivum L.). Soil:solution distribution of 95Nb was observed in 1:10 batch experiments with deionized water for a 3-day period. Results showed that K d values were high (in the order of 10 3 L kg −1) and were still significantly increasing after 3 days. A mathematical model, fitted to describe the decrease of the radioactivity after 3 days, is proposed to calculate sorption ratios—SR—(rather than K d values as equilibrium was not reached) over longer periods. Soil-to-plant concentration ratios (CR) were measured in shoots and roots of the two plants after cultivation on two soils spiked with 95Nb (406 kBq kg −1). Soil-to-root dry weight CR were high (0.30–1.52) and could probably be due to efficient uptake into the roots. However, no transfer of Nb to plant shoots was detected in any of the soils. Nb is thus a rather immobile element in soils and its transfer to plants seems limited to underground parts. It would therefore tend to accumulate in surface horizons of soils in case of long-term continuous surface release.

Electrochemical Behavior of Niobium and Aluminum in Chloride Melts

Electrochemical Behavior of Niobium and Aluminum in Chloride Melts

Behavior of Niobium, Tantalum and other high field strength elements in adakites and related lavas from The Philippines

Abstract Pliocene–Quaternary adakites and spatially and temporally associated niobium‐enriched basalts (the latter thought to be derived by melting of slab melt‐metasomatized mantle) from the Philippine island arcs have been selected for analysis of high field strength elements (HFSE). All these samples have nearly constant and chondritic Zr/Hf ratio (36.5) and slightly infrachondritic Nb/Ta ratio (14.7). We interpret adakitic magmas to be derived from the partial melting at approximately 900°C of subducted mid‐ocean ridge basalts (MORB) crust, with rutile and/or ilmenite as residual minerals. Melting calculations show that, under these conditions, slab melts should have suprachondritic Nb/Ta ratios. The obvious discrepancy with our data is attributed to insufficient knowledge of rutile‐melt partition coefficients for HFSE. Consequently, abnormal Nb/Ta or Zr/Hf ratios cannot be considered as potential markers of slab melting processes in island arcs.

Behavior of Niobium, Tantalum and other high field strength elements in adakites and related lavas from The Philippines

Behavior of Niobium, Tantalum and other high field strength elements in adakites and related lavas from The Philippines

Catalytic Behavior of Niobium(v)–Tetraphenylporphyrin in the Oxidation of Cyclohexene with Hydrogen Peroxide Evaluated by 1H NMR Spectroscopy

The catalytic efficiency of the niobium(V)–tetraphenylporphyrin complex in the oxidation reaction of cyclohexene with aqueous hydrogen peroxide was evaluated using 1H NMR spectroscopy.

Columbite solubility in granitic melts: consequences for the enrichment and fractionation of Nb and Ta in the Earth's crust

The behaviour of niobium and tantalum in magmatic processes has been investigated by conducting MnNb2O6 and MnTa2O6 solubility experiments in nominally dry to water-saturated peralkaline (aluminium saturation index, A.S.I. 0.64) to peraluminous (A.S.I. 1.22) granitic melts at 800 to 1035 °C and 800 to 5000 bars. The attainment of equilibrium is demonstrated by the concurrence of the solubility products from dissolution, crystallization, Mn-doped and Nb- or Ta-doped experiments at the same pressure and temperature. The solubility products of MnNb2O6 (Ksp Nb) and MnTa2O6 (Ksp Ta) at 800 °C and 2 kbar both increase dramatically with alkali contents in water-saturated peralkaline melts. They range from 1.2 × 10−4 and 2.6 × 10−4 mol2/kg2, respectively, in subaluminous melt (A.S.I. 1.02) to 202 × 10−4 and 255 × 10−4 mol2/kg2, respectively, in peralkaline melt (A.S.I. 0.64). This increase from the subaluminous composition can be explained by five non-bridging oxygens being required for each excess atom of Nb5+ or Ta5+ that is dissolved into the melt. The Ksp Nb and Ksp Ta also increase weakly with Al content in peraluminous melts, ranging up to 1.7 × 10−4 and 4.6 × 10−4 mol2/kg2, respectively, in the A.S.I. 1.22 composition. Columbite-tantalite solubilities in subaluminous and peraluminous melts (A.S.I. 1.02 and 1.22) are strongly temperature dependent, increasing by a factor of 10 to 20 from 800 to 1035 °C. By contrast columbite-tantalite solubility in the peralkaline composition (A.S.I. 0.64) is only weakly temperature dependent, increasing by a factor of less than 3 over the same temperature range. Similarly, Ksp Nb and Ksp Ta increase by more than two orders of magnitude with the first 3 wt% H2O added to the A.S.I. 1.02 and 1.22 compositions, whereas there is no detectable change in solubility for the A.S.I. 0.64 composition over the same range of water contents. Solubilities are only slightly dependent on pressure over the range 800 to 5000 bars. The data for water-saturated sub- and peraluminous granites have been extrapolated to 600 °C, conditions at which pegmatites and highly evolved granites may crystallize. Using a melt concentration of 0.05 wt% MnO, 70 to 100 ppm Nb or 500 to 1400 ppm Ta are required for manganocolumbite and manganotantalite saturation, respectively. The solubility data are also used to model the fractionation of Nb and Ta between rutile and silicate melts. Predicted rutile/melt partition coefficients increase by about two orders of magnitude from peralkaline to peraluminous granitic compositions. It is demonstrated that the γNb2O5/γTa2O5 activity coefficient ratio in the melt phase depends on melt composition. This ratio is estimated to decrease by a factor of 4 to 5 from andesitic to peraluminous granitic melt compositions. Accordingly, all the relevant accessory phases in subaluminous to peraluminous granites are predicted to incorporate Nb preferentially over Ta. This explains the enrichment of Ta over Nb observed in highly fractionated granitic rocks, and in the continental crust in general.

Creep of niobium and solid solution strengthened Nb-1wt.%Zr

The search for new materials for advanced aerospace structural applications at elevated temperatures has renewed an interest in niobium and its alloys due to its high melting point (2741 K), low thermal neutron cross section, good corrosion resistance against liquid lithium, and low density (8. 58 gm/cc) compared to other refractory metals. However, the diffusivity of bcc niobium is high and, as a result, the creep strength of niobium is inherently weak. Solid solution strengthening is one approach to improve the creep strength of metallic materials. Solid solution strengthening of class M (pure metal type) materials changes the creep response and rate controlling deformation mechanism. Class M materials show a normal transient during the primary stage in a semilogarithmic plot of [dot [Epsilon]] versus [Epsilon] and the rate controlling mechanism is dislocation climb. Class A (alloy type) materials show an inverse transient during the primary stage in a [dot [Epsilon]] versus [Epsilon] semilogarithmic plot, and the rate controlling mechanism is viscous glide. The objective of this paper is to study and compare the creep behavior of niobium and Nb-1wt. %Zr.

Influence of intercritical annealing on strength and impact behaviour of niobium containing steels

AbstractThe influence of inter critical annealing at 730°C on the impact properties and strength of C–Mn–Al–Nb steels has been examined. For low Mn (0·56%), Nb steels, intercritical annealing resulted in improved impact performance and the impact transition temperature (ITT) was reduced by as much as 35 K with no change in strength. The improvement in impact performance is considered to be due to Mn segregating to the α/γ boundaries leading to refinement of the grain boundary carbides. This refinement increased with holding time at 730°C in accordance with an increased grain boundary segregation of Mn. Strength was not influenced because grain size remained unchanged on intercritical annealing. The improvement in impact behaviour was greater the longer the holding time at 730°C but was significant even after 15 min. Improvements occurred both on cooling from the austenitising temperature (9·20°C) to 730°C and on heating from room temperature to 730°C, the latter heat treatment being the more beneficial. F...