Solid Nb Research Articles

Creation of ultrathin niobium nitride films at temperatures less than 100 °C

Thin NbN films were synthesized by a method of magnetron sputtering of solid Nb targets by nitrogen ions at temperatures less than 100 °C on substrates of the sapphire. The dependences of electrical resistance of films on the temperature in range 4.2 K – 300 K were measured. Volt-ampere characteristics and critical current density vs film thickness of films were made at a temperature of 4.2 K. The microstructure and film-depth chemical composition of thin films were investigated by analytical methods of the transmission electronic microscopy (HRTEM, EELS) on a cross-section samples made by the FIB technique. HRTEM and EELS study showed the Nb0.84N phase and poly-crystal structure of niobium nitride films. It was found that the critical current density falls down by an order of magnitude when the film thickness was less than 4 nanometers.

Antibacterial Test from Ekstract of Kirinyuh Leaves to Inhibit Vibrio sp. Bacteria Growth which Caused Ice-ice Diseases in Seaweed (Eucheuma cottoni)

Indonesia is the largest archipelagic country so it has enormous coastal potential as well. One of the coastal potential that has great benefits for the community is seaweed cultivation. Production of seaweed cultivation in NTB province in 2012 reaches 657,700 tons and increase every year. But in fact, the development of seaweed cultivation business have several obstacles, one of them is the presence of ice-ice disease that infects the seaweed Eucheuma cottoni species. This ice-ice disease causes a decrease in the quality and quantity of seaweed causing crop failure. This ice-ice disease attacks the thallus in the seaweed and causes the seaweed thallus to become brittle and breaks easily due to the lysis of epidermal cells and chloroplasts. The ice-ice disease is caused by a bacterial infection of Vibrio sp. which occurs when seaweed become stress due to adverse environmental conditions such as rising temperatures and salinity. The ice-ice disease can be threat using antibacterial compounds which found in plants such as tannins, flavonoids, and saponins. One of the plants that contain antibacterial is kirinyuh (Chromolaena ordorata). The antibacterial content on kirinuyuh leaves is extracted using a simple maceration method with aquadest as a solvent, and yields of extraction was diluted into concentrations of 20%, 40%, 60%, 80%, and 100%. Leaf extract of kirinyuh with variation of concentration was tested in vitro condition by using diffusion agar method with paper disk on solid NB media which has been overgrown with Vibrio sp. The result of in vitro test using diffusion agar method with paper disk was obtained that kirinyuh extract is able to inhibit the growth of Vibrio sp. bacteria with the widest inhibit zone is 10.315 mm at 100% concentration.

Burning rate of solid homogeneous energetic materials with a curved burning surface

We study experimentally the combustion of a double-based solid propellant NB at a pressure of p = 1 bar, and show that combustion occurs in the cellular-oscillating mode: combustion occurs in the form of separate cells that periodically appear on the burning surface, move along it and disappear. We show that in this mode, a carbonized skeleton is formed on the burning surface, consisting of products of incomplete decomposition of propellant. This skeleton is associated with the burning surface and plays an important role in maintaining the cellular-oscillating mode of combustion of the double-based propellant. To explain the experimental data, we consider a combustion model with a curved burning surface. We show that the burning rate depends on the curvature of the burning surface: with increasing curvature of the burning surface, the local burning rate decreases and combustion becomes impossible if the nondimensional radius of curvature (Michelson-Markstein criterion) of the burning surface becomes less than some critical value. The calculated critical value of the Michelson-Markstein criterion is in good agreement with that obtained in experiments. Using the developed model of combustion of solid homogeneous energetic materials (SHEMs) with a curved burning surface, we calculate the critical combustion diameter of various SHEMs and the shape of stationary cells on the burning surface. The critical combustion diameters of various SHEMs calculated in this way we compare with the available experimental data. A good agreement between the theory and experiments was obtained.

On the partial enthalpy of mixing of Nb in liquid Al

The heat of dissolution at infinite dilution of solid Nb in liquid Al was determined indirectly by dissolving small pieces of solid NbAl3 in liquid aluminum in an isothermal calorimeter at 1126 ± 0.5 K. A value of ∞Qdiss(NbAl3,298 K,1126 K) = 75.3 ± 3.0 kJ mol−1 was measured. The derived partial enthalpy of mixing at infinite dilution for Nb in Al is ΔmixH∞ = -243.2 kJ mol−1. A lower limit for the solubility of solid Nb in liquid Al is also obtained from these measurements. The observed limit is 10 times higher than the accepted experimental value in the literature. In addition, heat content measurements for NbAl3 were performed at three different temperatures using drop calorimetry with empty crucibles. The measured heat contents are compared to values obtained from phonon calculations in the quasi-harmonic approximation.The quality of the determined heat of dissolution was checked by measuring the enthalpy of formation of solid NbFe2 and NbNi3. Values of -17.5 ± 2.9 kJ (mol of atoms)−1 and -30.7 ± 3.5 kJ (mol of atoms)−1 were found. These values agree with available experimental and theoretical data from the literature which confirms the validity of our experimental approach. A new, unknown and metastable magnetic configuration was discovered for NbFe2 in ab-initio simulations and will be discussed.

Electronic transition in solid Nb at high pressure and temperature

The electrical resistivity of high purity solid Nb has been measured at fixed pressures up to 5 GPa in a large volume press and temperatures up to ∼1900 K. The expected resistivity decrease with pressure and increase with temperature were found. A transition was observed in the temperature dependence of resistivity at high temperature. The transition is discussed in terms of the effects of pressure and temperature on the electronic band structure of Nb causing a resistivity behavior characteristic of a change from the “minus group” to the “plus group.” Extrapolation of the pressure dependence of the transition temperature suggests that Nb would show plus group behavior at room T at an estimated pressure of ∼27 ± 7 GPa. The electronic thermal conductivity was calculated using the Wiedemann-Franz law and was in very good agreement with 1 atm data. We show that the temperature dependence of the calculated electronic thermal conductivity increases with a steep slope from room temperature up to the electronic transition temperature for all fixed pressures. Above the transition temperature, the T-dependence of electronic thermal conductivity remained constant at 2 GPa and exhibited an increasingly negative slope at higher pressures. The isothermal pressure-dependence of electronic thermal conductivity is positive.

Dendritic solidification and thermal expansion of refractory Nb–Zr alloys investigated by electrostatic levitation

The dendritic growth and thermal expansion of isomorphous refractory Nb–5%Zr, Nb–10%Zr, and Nb–15%Zr alloys were studied by electrostatic levitation technique. The obtained maximum undercoolings for the three alloys were 534 (0.2TL), 498 (0.19TL), and 483 K (0.18TL), respectively. Within these undercooling ranges, the dendritic growth velocities of the three alloys all exhibited power laws, and achieved 38.5, 34.0, and 27.1 m s−1 at each maximum undercooling. The microstructures were characterized by coarse dendrites at small undercooling, while they transformed into refined dendrites under large undercooling condition. In addition, the measured thermal expansion coefficients of solid Nb–Zr alloys increased linearly with temperature. The values at liquid state were more than double of those at solid state, which also displayed linear dependence on temperature.

The Electrochemical Synthesis of LiNbO2 in Molten Salts and its Application for Lithium Ion Batteries with High Rate Capability

ABSTRACT Herein, we report an effective, fast and controllable electrochemical synthesis of layered structure LiNbO 2 by electrolysis of solid Nb 2 O 5 in molten LiF-LiCl salt. For the first time, the electrochemical performance of LiNbO 2 as an anode for lithium ion battery is investigated. Such a material shows a high reversible capacity of ∼190 mAh g −1 at 0.25C (1C = 200 mA g −1 ), superior rate capability (52 mA h g −1 at 80C) and excellent long-term cycle stability (75 mAh g −1 after 1000 cycles at 50C), due to the favorable kinetics benefiting from the high electronic conductivity and fast lithium diffusion in layered crystal structure of LiNbO 2 . It indicates that LiNbO 2 is a promising anode candidate. Moreover, this work may provide a facile and controllable way to synthesize electrode materials for lithium ion batteries and other electrochemical energy storage applications.

<i>In Situ</i> Al<sub>3</sub>Nb Formation in Liquid Al by Nb Particle Addition

Master alloys are used in the metals industry to control chemical composition and to help to achieve a particular microstructure or promote growth of desired phases. This study reports on making a Al3Nb containing aluminium (Al) - niobium (Nb) master alloy by solid-liquid reaction processing, where solid Nb particles are added to the liquid Al. Nb react with Al to form in-situ Al3Nb. The in-situ formed Al3Nb particles were facet and polygonal in shape. The three dimensional analysis revealed that the outer surface of the partially reacted Nb was covered with faceted Al3Nb particles. The different nature and morphologies of the in-situ phases that were produced were determined using SEM, EDX, XRD and extraction techniques. A mechanism for the observed microstructural difference is discussed.

<i>In Situ</i> Al<sub>3</sub>Nb Formation in Liquid Al by Nb Particle Addition

Master alloys are used in the metals industry to control chemical composition and to help to achieve a particular microstructure or promote growth of desired phases. This study reports on making a Al3Nb containing aluminium (Al) - niobium (Nb) master alloy by solid-liquid reaction processing, where solid Nb particles are added to the liquid Al. Nb react with Al to form in-situ Al3Nb. The in-situ formed Al3Nb particles were facet and polygonal in shape. The three dimensional analysis revealed that the outer surface of the partially reacted Nb was covered with faceted Al3Nb particles. The different nature and morphologies of the in-situ phases that were produced were determined using SEM, EDX, XRD and extraction techniques. A mechanism for the observed microstructural difference is discussed.

Effect of Ti Concentration on the Growth of Nb3Sn Between Solid Nb(Ti) and Liquid Sn

The change in the growth rate of the Nb3Sn product phase because of Ti addition is studied for solid Nb(Ti)–liquid Sn interactions. The growth rate increased from no Ti to 1 at.% and 2 at.% of Ti in Nb, and the activation energy decreased from 221 kJ/mol to 146 kJ/mol. Based on the estimated values, the role of grain boundary and lattice diffusion is discussed in light of the possibility of increased grain boundary area and point defects such as antisites and vacancies.

Investigation on electrochemical reduction process of Nb 2O 5 powder in molten CaCl 2 with metallic cavity electrode

The direct electrochemical reduction process of Nb 2O 5 powder was investigated by cyclic voltammetry and constant potential electrolysis with a novel metallic cavity electrode in molten calcium chloride at 850 °C. The products of both constant potential and constant voltage electrolysis were characterized by XRD, SEM and EDX. CaNb 2O 6 was formed upon addition of solid Nb 2O 5 into molten CaCl 2 when CaO was present. During the electrolysis solid Nb 2O 5 was reduced to various niobium oxides of lower oxidation states, including some composite oxides, and then was converted completely to metallic niobium near −0.35 V ( vs. Ag/AgCl), which was more positive than the reduction potential of Ca 2+. Constant potential electrolysis was applied at the potentials near the reduction current peaks derived from the cyclic voltammetry curves, and cell voltages were monitored. The voltage was near 2.4 V when the oxide was metallized at −0.35 V ( vs. Ag/AgCl). Nb 2O 5 pellet could be used to prepared metallic niobium at cell voltage 2.4 V in a larger electrolysis bath filled with calcium chloride at 850 °C. The experiment results further demonstrated the direct electrochemical reduction mechanism of Nb 2O 5 powder in a molten system.

A study of cathode improvement for electro-deoxidation of Nb 2O 5 in a eutectic CaCl 2–NaCl melt at 1073 K

Significant improvement of cathode in the electro-deoxidation of solid Nb 2O 5 in a eutectic CaCl 2–NaCl melt at 1073 K has been achieved by addition of carbon, calcium carbonate or calcium oxide powder to Nb 2O 5 powder. The powder mixtures were compacted into pellets and sintered, and then applied as the cathode. The results showed that the additives increased the oxygen vacancies and had an effect on particle size and surface area of the sintered solid Nb 2O 5 cathode. It was possible to accomplish the direct electrochemical reduction of solid Nb 2O 5 to metallic Nb rapidly by optimizing the amounts of carbon, calcium carbonate or calcium oxide added.

Nb/Alバルク複合体中での1873-2073 K におけるA15型Nb3Alの生成と成長 : 第1報. 層状A15相の平面状成長

Formation of A15 type Nb3Al phase at the interface between solid Nb and liquid Al in a bulky Nb/Al composite has been studied at as high temperatures as from 1873 to 2073 K. The A15-phase layer grows keeping the interfaces planar when heated at 2023 K or lower, whereas the interface adjacent to Nb solid solution, Nbs.s, becomes “nonplanar” when heated at 2073 K. It is suggested that the formation process of A15 phase consists of three stages; the rapid dissolution of Nb into liquid Al until nucleation of A15 phase at the Nb/Al interface, and the following two stages (1st and 2nd ones) for growth of A15 phase. The planar growth rate of A15-phase on the 1st stage is considerably faster than that on the 2nd one. A model for the planar growth rate of A15-lphase on the 2nd stage has been presented. The model is based on the unidirectional inter-diffusion fluxes of Nb and Al atoms in the three sequential regions of Nbs.s, A15 and σ-phases. The “nonplanar” growth of A15-phase will be detailed in Part II of the present study.

Formation and Growth of A15 Type Nb<SUB>3</SUB>Al in a Nb/Al Composite at 1873-2073 K: Part II. Nonplanar Growth of the A15-Phase Layers

Formation of A15 type Nb 3 Al phase at the interface between solid Nb and liquid Al in a bulky Nb/Al composite has been studied at as high temperatures as from 1873 to 2073 K. The A15-phase layer grows keeping the interfaces planar when heated at 2023 K or lower, whereas the interface adjacent to Nb solid solution, Nb S.S , becomes nonplanar when heated at 2073 K. It is suggested that the formation process of A15 phase consists of three stages; the rapid dissolution of Nb into liquid Al until nucleation of A15 phase at the Nb/Al interface, and the following two stages (1st and 2nd ones) for growth of A15 phase. The planar growth rate of A15-phase on the 1st stage is considerably faster than that on the 2nd one. A model for the planar growth rate of A15-1phase on the 2nd stage has been presented. The model is based on the unidirectional inter-diffusion fluxes of Nb and Al atoms in the three sequential regions of Nb S.S , A15 and σ-phases. The nonplanar growth of A15-phase will be detailed in Part II of the present study.

Pore structure of sintered niobium after reaction with hydrogen and nitrogen

Compact structures obtained by vacuum sintering of niobium powder are widely used in electronic engineering as metal plates in oxide semiconductor capacitors, which realise electrical capacity in an Nb anodic, Nb2O5 solid state MnO2 electrolyte metal dielectric semiconductor Nb–MDS system. This paper presents the method for stabilising porosity in these structures by using both Nb powder hydrogenation and nitriding of niobium hydride sintered pellets for their production. The effect obtained is explained in terms of the sintered powder porous structure.

Power modulation technique for noncontact high-temperature calorimetry

A new noncontact calorimetric method has been developed based on inductive heating of a metallic spherical bulk sample by a power-modulated radio-frequency field under ultrahigh vacuum conditions. From the pyrometrically measured temperature response the specimen’s external (due to radiative heat loss) and internal relaxation time (due to thermal conductivity) are found to differ by more than two orders of magnitude allowing the specific heat as well as thermal conductivity of the sample to be determined as a function of temperature. The agreement between the measured and predicted temperature response for solid Nb demonstrates the applicability and accuracy of the method which is particularly useful for metastable or chemically reactive samples at high temperature.

Intermetallic compound layer growth at the interface of solid refractory metals molybdenum and niobium with molten aluminum

The growth mechanisms and growth kinetics of intermetallic phases formed between the solid refractory metals Mo and Nb and molten aluminum have been studied for contact times ranging from 1 to 180 minutes at various temperatures in the range from 700 to 1100°C. The growth of the layers of the resulting intermetallic phases has been investigated under static conditions in a saturated melt and under dynamic conditions using forced convection in unsatured aluminum melts. The Nb/Al interfacial microstructure consisted of a single intermetallic phase layer, Al3Nb, whereas two to four different phase layers were observed in the Mo/Al interface region, depending upon the operating temperature. It was found that, in a satured melt, the intermetallic phase growth process was diffusion-controlled. The parabolic growth constants of the first and second kind and integral values of the chemical diffusion coefficients over the widths of the phases were calculated for both Mo/Al and Nb/Al systems. It also was found that the AlNb2 phase grew between the Nb and Al3Nb phases after consumption of the saturated Al phase. Similarly, the AlMo3 phase grew between the Mo and Al8Mo3 phases with diminishing of all the other existing compound phases. In an unsaturated melt, the intermetallic phase layer grows at the solid surface while, simultaneously, dissolution occurs at the solid/liquid interface. This behavior is compared to the growth mechanisms proposed in existing theories, taking into consideration that interaction occurs between neighboring phases. It was found that the intermetallic phase, Al8Mo3, adjoining the base metal, was not bonded strongly to the base metal Mo and was brittle; its hardness also was larger than that of the layer near the adhering aluminum and the adjacent phases.

SO 3 adducts of hexameric oxoniobate cluster in nonintegral subnormal oxidation states: Formation, properties and formulation

Niobium(V) in 9 M H 2SO 4 has been reduced by metallic zinc to a red-brown solution from which a series of salts containing the cluster anion, [Nb 6O 7(O·SO 3) 12] 16− have been isolated. The compounds have been characterized from analytical, IR spectral and magnetic data and the structure of the cluster and its formation are proposed. The anion is a 12-sulphur trioxide adduct of the ‘Nb 6O 19’ cluster and contains Nb 6(22+) with the average valency of 3.67 for each Nb. Nb 6(20+) corresponding to Nb(3.33) and Nb 6(26+) corresponding to Nb(4.33) have been potentiometrically shown to be formed as redox derivatives of Nb 6(22+) in different aqueous conditions. Isolation of solid Nb(3.33) has been attempted.

Secondary electron yield and Auger electron spectroscopy measurements on oxides, carbide, and nitride of niobium

Secondary electron yield measurements before and after Ar ion sputter cleaning were made on Nb and Nb compounds of interest for rf superconducting cavities. Total secondary electron yields (σ) for primary energies 20–1500 eV were measured for solid Nb (σmax=1.3 at 300 eV), anodized Nb2O5 (σmax=1.2 at 300 eV), and powders of Nb(σmax=1.0 at 400 eV), NbO (σmax=0.9 at 400 eV), NbO2 (σmax=1.0 at 400 eV), Nb2O5 (σmax=0.95 at 400 eV), NbC(σmax=0.8 at 400 eV), and NbN (σmax=0.8 at 500 eV). Determinations were made for Auger elemental sensitivities, and the relationship between Auger peak heights and oxide stoichiometry is discussed. The sputter etch rate of anodized Nb2O5 was measured by depth profiling anodic coatings of known thickness.

Further investigations of the solid-liquid reaction and high-field critical current density in liquid-infiltrated Nb-Sn superconductors

Superior superconducting properties, such as high J c 's and T c 's, have been obtained from reacted liquid-infiltrated Nb-Sn composite wires. These excellent properties are attributed to the chemistry and structure of the material, which is prepared by a unique solid (Nb) - liquid (Sn) reaction. From heat capacity measurements, sharp bulk superconducting transitions of the Al5 phase occur at 17.2-18 K and the weight fraction of Al5 in the composite wire is ~23%. Analytical electron microscopy techniques have shown that: the microstructure of these conductors consists of alternating large-grain and small-grain filaments; these two types of filaments correspond to BCC Nb(Sn) and cubic Al5 Nb_{75\pm{x}}Sn_{25\mp{x}} phases, respectively; the Al5 filaments ( \leq0.5 \mu m) are chemically homogeneous in terms of measured X-ray intensity ratios to within ±7%, which implies that x\sim1.5 ; and the Al5 grains are essentially free of extended lattice disorder down to a resolution of ∼0.34nm. Recent work in which Nb is alloyed with Ta has shown that these superconducting properties can be improved upon; e.g. high overall J c 's of \sim1.8 \times 10^{4} A/cm2at 20 T and 4.2 K have been measured. Also, the liquid-infiltrated Nb(Ta)-Sn composites have a damage strain tolerance nearly double that of commercial bronze-processed Nb-Sn conductors.