Nb Wt Research Articles

Electrochemical studies on zirconium and its biocompatible alloys Ti‐50Zr at.% and Zr‐2.5Nb wt.% in simulated physiologic media

Different electrochemical studies were carried out for Zr and its biocompatible alloys Ti-50Zr at.% and Zr-2.5Nb wt.% in solutions simulating physiologic media, Ringer and PBS (phosphate buffered saline) solutions. The results from rest-potential measurements showed that the three materials are spontaneously passivated in both solutions and that the Ti-50Zr alloy has the greatest tendency for spontaneous oxide formation. Some corrosion parameters (such as the pitting and repassivation potentials) were obtained via cyclic voltammetry in both solutions, revealing that the Ti-50Zr has the best corrosion protection while Zr has the worst. On the other hand, the pre-anodization (up to 8 V vs. SCE) of the alloys in a 0.15 mol/L Na2SO4 solution led to a significant improvement in their protection against pitting corrosion when exposed to the Ringer solution. Elemental analyses by EDX showed that during pitting corrosion, there is no preferential corrosion of any of the alloying elements (Zr, Ti, Nb).

Effect of isothermal annealing on the corrosion behavior of Zr– xNb alloys

To study the effect of isothermal annealing on the corrosion behavior of Zr– xNb alloys, several systematic studies on corrosion and oxide characteristics were performed for the Zr– xNb alloys ( x=0.1∼2.0 wt%). The samples were annealed at 570 °C for 0–1000 h after β-quenching. The corrosion resistance of the 0.1 and 0.2 wt% Nb alloys where Nb existed in the equilibrium soluble state in the matrix was excellent in the quenched and annealed conditions. For the high Nb-containing alloys, the corrosion rates were very sensitive to the annealing condition, and it took about 50 h at 570 °C to reach corrosion rates comparable to the low Nb wt% alloys. The corrosion resistance is correlated to the stabilization of the tetragonal ZrO 2 and columnar oxide structure when the Nb concentration in the matrix is reduced to the equilibrium soluble limit.

Mutual effects of hydrogenation and deformation in Ti-Nb alloys

Alloying of Ti-based alloys with hydrogen is used to modify the microstructure and improve mechanical properties. In this study, hydrogen charging was performed electrochemically in a 2:1 glycerin-phosphoric acid electrolyte at high fugacities. This research investigated in detail, by means of X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal desorption spectroscopy (TDS), and microhardness tests, the influence of hydrogen at high fugacities on the phase stability, desorption behavior, and microhardness in Ti-Nb (20 to 45 wt pct Nb) alloys before and after deformation. Hydrogenation of Ti-Nb was found to exhibit a significant effect on the phase stability as well as the microhardness of Ti-Nb alloys. Hydrogenation of Ti-20 wt pct Nb led to precipitation of (Ti,Nb)H x in the metastable a" matrix. In Ti-Nb alloys with 40 or 45 wt pct niobium, hydrogen stabilized the bcc β phase, but destabilized the hcp w phase. With increasing hydrogen content, an expansion of the lattice constant of the β phase occurred, followed by the formation of (Ti,Nb)H x . The influence of hydrogen on the microhardness of Ti-40 wt pct Nb and Ti-45 wt pct Nb shows only a minor effect, whereas Ti-20 wt pct Nb exhibits significant softening in response to hydrogen charging up to 3000 ppm. The TDS showed that deuterium desorption strongly depends on the niobium content and the deformation treatment prior to or after charging. The observed results should provide further insight on the mutual effects and the resulting micromechanism of hydrogenation and deformation in Ti-Nb alloys.

Studies on the stability of anodic oxides on zirconium biocompatible alloys

Studies on the stability of anodic oxides grown on zirconium and its biocompatible alloys Ti-50Zr at.% and Zr-2.5Nb wt.%, in aerated Ringer physiological solution, at 25 and 37 °C, were carried out by comparing their formation charge and their reconstruction charge after dissolution at open circuit in the physiological solution. The stability of oxides grown in the Ringer solution and in a 0.15 mol L-1 Na2SO4 solution was compared. The obtained results show that the stability of these oxides is increased by aging under potentiostatic conditions and can be decreased by the presence of chloride ions in the electrolyte during the anodization process.

Failure behaviour of an ultra high strength low alloy steel

An ultra high strength low alloy steel having the composition Fe - 0.3C - 1.35Cr - 0.9Mo - 0.25V - 0.1Nb (wt-%), has been developed using the electroslag refining process. In order to understand the failure behaviour of the material, tensile coupons, surface crack tension (SCT) specimens, compact tension (CT) specimens, and pressure chambers were fabricated and tested. The fracture parameters of the material were evaluated from the test data. Using these parameters a failure assessment diagram was generated to quantify the effects of the presence of cracks on material strength. Fracture strength estimates on SCT and CT specimens compare well with test results. The effects on fracture properties owing to weld/heat treatment processes have also been examined. To select a suitable failure theory for this material, failure assessment has been carried out on pressure chambers and verified with test results. Fracture analysis has also been carried out on the cylindrical vessels containing axial surface cracks and it was found that failure pressure decreases with increasing in crack size.

A study on preparation of copper–niobium composite by aluminothermic reduction of mixed oxides

Cu–Nb composites have come into prominence because of their high strength and high electrical conductivity. A number of preparative techniques have received attention among the investigators due to difference in melting point, density and crystal structure of the constituents. In the present paper a simple, easy to scale up, non-furnace process involving co-reduction of mixed oxides (CuO, Nb2O5) with aluminium in the presence of slag fluidizer CaO has been attempted to prepare a Cu–2.5Nb (wt%) composite. A typical charge composition of about 58.2% CuO, 3.5% Nb2O5, 23.3% CaO and 15% Al (specific heat 715 kcal/kg) resulted in a Cu–Nb product with 83% yield of nearly targeted composition. As reduced composite was homogenized by arc melting. Remelted and consolidated composite was drawn into wires of <0.5 mm diameter to convert the dendritic niobium phase into the filamentary form. Property evaluation studies such as optical metallography, hardness, electrical resistivity measurements etc. have been carried out.

Niobium sulfide as a dopant for hydrotreating NiMo catalysts

Niobium sulfide has been recently found to be an interesting new active phase for hydrodesulfurization. In this work, niobium was used as a dopant for a conventional hydrotreating catalyst. A NiMo hydrotreating catalyst in the oxide form was doped with various contents of Nb precursor salt (0<Nb wt.%<7). After drying, the activation of the catalyst was performed with CS 2 sulfiding agent in a high pressure vessel. The use of this new dopant increased the catalytic activity in both HDS and HYD model reactions. Highest activities were obtained with an optimum Nb content of 5 wt.%. The selectivity of the products was also modified since more isomerized compounds where produced. Various techniques were used to determine structural and morphological characteristics of the materials. TEM pictures only showed the presence of lamellar particles similar to MoS 2. EDX analysis demonstrated the homogeneous distribution of the transition metal elements (Ni, Mo, Nb) even with small electron probes at high magnification. EXAFS was used to determine the local environment of Nb atoms and showed that Nb was present in the form of “NbS 2” entities similar to the bulk phase.

Hot working characteristics of Zr-2.5Nb using processing maps

A simple condition for metallurgical stability in processing maps is proposed. The applicability of the stability criterion has been verified using test data ofZr-2.5Nb (wt-%) alloy with an equiaxed (α + β) preform microstructure.

Interaction between oxidation and mechanical properties of 20Cr–25Ni–Nb stabilised stainless steel

The influence of oxidation in carbon dioxide and of heat treatment in an inert gas (argon) for up to 2000 h at 1000°C on the metallurgical structure of a 20Cr–25Ni–Nb (wt-%) stabilised stainless steel, annealed before these exposures at 930°C, has been investigated. The effect of oxidation for varying periods and of the corresponding argon heat treatments on the subsequent creep rupture properties of the steel at 750°C has also been studied. The influence of concurrent strain, from a constant applied load, on the oxidation behaviour of the same type of steel has also been examined during 100 h oxidation, in carbon dioxide at 1000°C.MST/1176

Positron annihilation study of radiation damage in neutron-irradiated zirconium and its alloys

Nominally pure zirconium and its alloys Zr1wt.%Nb and Zrwt.% Cu0.40wt.% Fe0.55wt.% Mo-0.20wt.% V irradiated at 60, 300 and 450°C to fast neutron fluences of 10 21, 10 22 and 10 23 m −2 (E >1 MEV) were studied by the angular correlation positron annihilation (PA) method. A pronounced dependence of PA parameters on the irradiation temperature indicates that there is a decrease in the amount of defects of an open-volume nature which are sampled by the positron at higher irradiation temperatures. At lower temperatures there is a particularly strong increase in the parabolic (free electron) annihilation component of the multicomponent alloy: this is tentatively associated with self-interstitial trapping at undersized solute atoms. High dislocation densities present in pure zirconium and the Zr1 wt.%b alloy before irradiation seem to have little effect on positron trapping at irradiation defects in these materials and on the irradiation damage processes.

Niobium-Alloyed high speed steel by powder metallurgy

A philosophy for the use of strong carbide formers like niobium in high speed steels is described. It follows the concept of independently optimizing the compositions of the matrix (for maximum secondary hardening potential) and the volume fraction of the blocky carbides (for protection against abrasive wear). Normally, the two are interdependent through the action of the solidification equilibria, but separate control becomes possible when the blocky carbides are formed by a strong carbide former such as niobium. During normal ingot solidification, such strong carbide formers would produce very large primary carbides. This can be avoided by atomization and powder metallurgical processing. In this way, a steel has been produced whose matrix composition is similar to that of AISI M2, and whose primary carbides are all of NbC type. Its composition is 1.3C, 2W, 3Mo, 1.6V, 3.2Nb (wt pct). Because of its high stability, NbC is a much more effective obstacle to grain growth than the normal high speed steel carbides, and this allows substantially higher austenitization temperatures to be used. Despite its leaner composition, the Nb-alloyed steel matches the cutting performance of AISI M2, and its secondary hardening seems to be more persistent at high temperatures.

Petrology of the Carbonatites and Associated Rocks of Sung Valley, Jaintia Hills District, Meghalaya, India

Abstract In Sung Valley, (Lat : 25°31' -25°36'N : Long; 92°05' -92°10'E) the Shillong Series rocks comprising mainly quartzites and phyllites are intruded by a N-S trending, roughly oval shaped body of pyroxenite covering an area of about 35 km2 and into which the following genetically related rock types have been emplaced in order of decreasing age and abundance. Peridotites (stock-like bodies), ijolites (ring dyke and plug like), carbonatites (incomplete cone sheets) and syenites (sheets, dykes and veins). Minor dykes and veins of magnetite-serpentine rock, ijolite and melilite-bearing types with a rough radial disposition are also present. Fenitization, due to both ijolites and carbonatites, has affected older rocks resulting in wollastonite-rich aegirine-augite bearing rocks, K-feldspar-aegirine-augite veins and oversaturated potassic syenites. Carbonatites are mainly sovites with minor beforsite and types rich in magnetite and apatite are present. Average abundances of trace elements (values in ppm) characterizing carbonatites such as Bu (549), Sr (3134), La (50-100), Ce (489), Y (50), Nb (372), Zr (179) and P2O5 (5.7) wt% are comparable to those found in reported intrusive carbonatites. The weathered mantle of the carbonatites and the contact zones between carbonatites and pyroxenites have resulted in soils rich in pyrochlore, apatite and magnetite. It is postulated that the carbonatites may be differentiates of an ijolitic magma, in turn derived (liquid immiscibility?) from a parental mela-nephelinite or alkali picritic magma. The ultramafic suite could represent the cumulates from such a picritic source.

49 SOURCE OF ERRORS IN WT.DISCREPANCIES BETWEEN BIRTH CERTIFICATE TAPES &amp; NEWBORN HOSP.RECORD

In order to obtain NB hosp.charts for auditing purposes,birth tapes of all neonates medical records < 2500g. in ′79 were presented to indiv. hosp.to match c 1494 NB charts from 14 hosp.All wts.on birth tapes are in gms.while several hosp.normally use lbs.There was an overall birth wt.discrepancy of 37%(557out of 1494).Significance testing was done by the paired t-test & X2. RESULTS:The sources of error included:transcribing wrong digits; inaccurate conversion of lbs.to gms; reversing digits;recording birth wt.at different times on birth certif. & neonatal chart.2)III ctrs.had signif. fewer errors compared to I (X2=13.2;P < .001) & to II ctrs. (X2=20.8;P <.001).3)Of the 14 hosp.most of the errors had lower NB wt. listed on the birth certif.4)Highly signif.diff.(P < .001)in wt. were noted in 2 hosp.while an addit.two had borderline signif. diff. (P < .1).In performing survey chart research,a reliability wt.check c the NB chart needs to be done when using birth certif.Supported by: NCHSR Grant HPA-R18HS03832.