Nitrogen In Vanadium Research Articles

Behaviour of helium and hydrogen in vanadium alloys – innovative fusion reactor first wall materials: a review. Part 1. V – Ti and V – Fe alloys

This paper is the first part of a three-part review that looks at the effect of doping elements on the behaviour of helium, the development of gas porosity, as well as at the amount of retained hydrogen introduced into vanadium alloys with Ti, Cr, W and Ta (using different techniques) with a rapid decay of induced radioactivity. The same regularities have been identified regarding how the chemical composition of the alloys impacts the hydrogen entrapment and retention regardless of the way it is introduced: either through pressure saturation without defect formation or through ion implantation with radiation-induced defects entailed. It was established that when vanadium is doped with a chemically active element (V – Ti alloys), the concentration of the latter has a nonmonotonic effect on the helium porosity and the mass fraction of retained hydrogen. It can be attributed to the way titanium interacts with oxygen and nitrogen in vanadium, which dictates how much titanium hydride will form. The paper demonstrates that pre-irradiation of the alloy with helium ions results in a higher amount of retained hydrogen when it is introduced further, regardless of the temperature.

The diffusion of nitrogen in vanadium

A recent model for solute diffusion in solids, applied to nitrogen in vanadium, is discussed in terms of experimental evidence and thermodynamic considerations.

Calculation of diffusion coefficients of nitrogen in vanadium

In the 573–2098 K temperature region the diffusion coefficient of N in V varies by 10 orders of magnitude. In the present paper we show that this variation can be accounted for by the anharmonic properties of the bulk material, i.e. the temperature variations of the isothermal bulk modulus and the lattice parameter.

Quadrupolar effects in interstitial solid solutions of oxygen and nitrogen in vanadium

The51V NMR in dilute solid solutions of O and N in V was used to study quadrupolar effects due to alloying. The foils with the strong texture showed the discernible structure in the wings of the observed NMR spectra. The metallic site neighbour positions were selectively identified. Electric field gradients (EFG'S) and Knight shifts at these sites were measured. The origin of EFG's is discussed. The experimental data were used to construct the impurity potentials. The energy of O−O bonds in vanadium was estimated.

Diffusion of nitrogen in vanadium and niobium

The diffusion of N in the group VB metals V and Nb has been studied in the previously uninvestigated temperature range 300–500 °C using ion-beam techniques. Diffusion couples were created by ion implantation. The time-dependent diffusion profiles were monitored by the use of the Nuclear Resonance Broadening (NRB) technique. New values for the solubility of N in Nb were obtained. The diffusion rates presented support recent observations of the diffusivity of interstitial impurities in body-centered cubic metals in which positive deviations from Arrhenius behaviour have been seen at high temperatures.

Spectrophotometric determination of nitrogen in vanadium, titanium and uranium with thymol after alkali fusion

Vanadium metal packed into a nickel boat with potassium hydroxide, is fused at 500–600°C, and the volatilized ammonia is absorbed in dilute hydrochloric acid. The ammonia is converted to monochloramine with sodium hypochlorite at pH 9.8–10.3, and reacted with thymol at pH 11.5–11.9 for 1 h, and the absorbance is measured at 660 nm. The proposed method was also used for the determination of nitrogen in titanium and uranium. Nitrogen in some other metals such as Al, Be, In, Mg, Mn, Si, Sb, Sn, Ta, V, W and Zn which can be fused with potassium hydroxide and have melting points above 400°C may also be determined.

Solid solubility limit of nitrogen in vanadium at temperatures between 500 and 1500 °C. Precipitation phenomena in the system vanadium-nitrogen

The solid-solubility limit of nitrogen in vanadium has been determined in the temperature range 500–1500 °C using three different methods. The nitrogen saturation concentration, c s, increases from 2.6 at.% at 500 °C to 10.7 at.% at 1500 °C where it depends on the temperature, T, in °K according to the equation c s = 31.5 exp (− 3800 RT ) . At temperatures between 500 and 1500 °C the hexagonal β-nitride phase, V 3N, is in thermodynamic equilibrium with the α-vanadium-nitrogen solid solution: However, under certain conditions metastable nitride phases form. Ageing of vanadium-nitrogen alloys containing 8 and 10 at.% N at 500 °C results in the formation of an intermediate cubic nitride phase, which is probably also present in aged alloys with lower nitrogen concentrations. This cubic phase has a lattice parameter of 3.105 Å which is about 2% larger than the lattice parameter of the corresponding α-solid solution. During ageing of supersaturated α-vanadium-nitrogen solid solutions with nitrogen concentrations less than 6 at.% at temperatures below 500 °C, the V 3N phase is not formed, even on ageing for as long as 1000 h. However, at temperatures between 280 and 350 °C the precipitation of an interstitially-ordered phase is observed. This precipitation process is accompanied by age hardening at 300 °C.

Kinetics of solid vanadium-nitrogen reactions at high temperatures

Thermogravimetric studies were made to determine the kinetics of the reaction between 99.83 pct vanadium sheet and purified nitrogen gas in the temperature range of 1173 to 1723 K, at pressures of 9.3 × 104 to 9.3 Pa (700 to 7 × 10-2 torr) and times up to 160 h. Metallographic and X-ray diffraction techniques were used to examine the reaction products. The data followed either parabolic, cubic, or linear kinetics. In general it was observed that the initial kinetics were parabolic. At high temperatures and near atmospheric pressures, the reaction kinetics changed from parabolic to cubic at longer times. At the lowest pressure the preparabolic kinetics were linear. Weight gains in the parabolic region were mainly due to solution and diffusion of nitrogen in vanadium with the weight gain shown by the equation (ΔW/A)2 = 3.2 × 10-4 Te162-000/RTt. The cubic region was related to the formation of an outer layer of VN over an intermediate layer of V3N and a core of the saturated solution of nitrogen in vanadium with the approximate weight gain shown by the equation (ΔW/A)3 = 1.24 × 10-3Te-208,000/RTt Linear weight gains at low pressure were presumed to be controlled by the rate of nitrogen adsorption.

Vanadium nitrides: reactions of vanadium oxides with lithium in the presence of nitrogen

The reaction of vanadium oxides with liquid lithium containing dissolved nitrogen provides a method for the preparation of nitrides of vanadium. The oxides V2O5, VO2, V2O3, and VO are reduced by liquid lithium to the metal. Depending on the quantity of nitrogen available, further reaction then occurs to give the α phase solid solution of nitrogen in vanadium, the nitrides V3N and VN, or the ternary nitride Li7VN4.

Ordering of interstitial nitrogen in vanadium

The crystal structure of precipitates occurring in dilute solutions (0–6 at.%) of nitrogen in vanadium has been identified from electron diffraction patterns. The stoichiometry of the precipitate is approximately that of V 16N, this having been established by volume fraction measurements on aged samples. The structure consists of a base-centered orthorhombic array of nitrogen atoms which enclose a 4 × 4 × 1 array of b.c.t. vanadium atom unit cells, the complete assemblage constituting the superlattice unit cell. It is shown that the nitrogen atoms occupy the octahedral interstitial sites. A type of twinning in these alloys is identified, wherein the observed twin planes are twin planes for the nitrogen sublattice but are mirror planes, hence, not twin planes, for the vanadium atom sublattice. The twin planes of the vanadium sublattice, those across which the tetragonal axis changes orientation, were not observed in any of the precipitates.

Dosage de l'azote dans le vanadium par fusion reductrice sous vide

A study of the conditions for the determination of nitrogen in vanadium by vacuum fusion in a platinum bath has shown that ( a) the amount of nitrogen extracted depends on the ratio ( R) of the weights of platinum and vanadium, and ( b) the amount extracted passes through a maximum value for a particular R value depending on the temperature. With R values of ca. 2 and extraction temperatures above 1900°, results were in reasonable agreement with those obtained by the Kjeldahl method, the reproducibility being 2–3%.

Calculations of the energy and migration characteristics of carbon and nitrogen in α-iron and vanadium

Various properties of carbon and nitrogen in iron, and nitrogen in vanadium have been investigated with the aid of computer techniques. The metal-metal interaction, represented by a two-body central force which matches the elastic moduli, is sharply repulsive at close separation, and goes to zero midway between the second and third neighboring atoms. 531 atoms surrounding the defect were treated as individual particles, while the remainder of the crystal was treated as an elastic continuum with atoms imbedded in it. The iron-carbon interaction was represented by a cubic equation with the parameters chosen to yield the experimental value for the carbon migration energy, the activation volume (effectively zero), and the binding energy of a carbon atom to a vacancy. With this model the approximate experimental value of the energy of a carbon atom in solution in iron relative to Fe 3C was obtained. The model also gives the correct relaxation strength for internal friction, but does not reproduce closely the formation volume. The migration path for carbon, on the basis of this calculation, is a straight line from octahedral to octahedral position with the tetrahedral position as the saddle point. The behavior of nitrogen in iron is almost identical. The same method of calculation for nitrogen in vanadium reproduced closely the sizable experimental activation volume for this system. Some calculations of di-carbon formation and motion are also reported.

Strain-aging effects of nitrogen in vanadium

Specimens were strained in tension from room temperature to 550°C at strain rates in the range of 10 −3–10 −4/sec on iodide vanadium containing varying amounts of nitrogen in solid solution. Maxima in the tensile strength, yield strength, and strain-hardening coefficient, a minimum in the strain-rate sensitivity and the occurrence of serrated stress-strain curves were observed in the temperature range of 300° to 450°C. The activation energy for strain aging in vanadium was found to be 37.3 ± 3.7kcal/mole from the strain rate dependence of the strain-aging peak and 36.2 ± 4.5kcal/mole from a return-of-yield point method. These values agree well with those reported for the diffusion of nitrogen in vanadium as determined by other methods. Thus, the results of this investigation indicate that nitrogen is associated with many of the strain-aging effects observed in vanadium.

Effect of Pressure on the Mobility of Interstitial Oxygen and Nitrogen in Vanadium

Measurements of stress relaxation as a function of hydrostatic pressure up to 9000 kg/${\mathrm{cm}}^{2}$ have been made on a vanadium sample containing approximately 0.1 atomic percent dissolved oxygen and 0.2 atomic percent dissolved nitrogen. In the temperature range 83.0\ifmmode^\circ\else\textdegree\fi{} to 98.0\ifmmode^\circ\else\textdegree\fi{}C, the relaxation time due to dissolved oxygen is found to increase exponentially with pressure, the value at 9000 kg/${\mathrm{cm}}^{2}$ being about 1.7 times the value at 1 kg/${\mathrm{cm}}^{2}$. The pressure dependence of the stress relaxation can be interpreted in terms of an activation volume of 1.7 ${\mathrm{cm}}^{3}$/mole which is about equal to the molar volume of the diffusing oxygen atoms. The relaxation times due to the dissolved nitrogen have been measured at 156.8\ifmmode^\circ\else\textdegree\fi{}C and 163.0\ifmmode^\circ\else\textdegree\fi{}C. The values at 9000 kg/${\mathrm{cm}}^{2}$ are about 1.3 times the values at 1 kg/${\mathrm{cm}}^{2}$, the activation volume being about 1.1 ${\mathrm{cm}}^{3}$/mole.