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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A new rapid volumetric method for the determination of niobium in the presence of tantalum and it application to the analysis of niobium minerals

Taylor, Charles Edward. January 1909 (has links)
Thesis (Ph. D.)--Columbia University. / Biographical.
2

A new rapid volumetric method for the determination of niobium in the presence of tantalum and it application to the analysis of niobium minerals

Taylor, Charles Edward. January 1909 (has links)
Thesis (PH. D.)--Columbia University. / Biographical.
3

A magnetic and structural investigation of CoCrPt, Nb alloy thin films

Almasi-Kashi, Mohammad January 2002 (has links)
No description available.
4

Estudo comparativo entre a recristalização do nióbio puro e da liga Nb-1%Zr. / Sem título em inglês

Siciliano Junior, Fulvio 26 February 1993 (has links)
Este trabalho aborda de forma comparativa o encruamento, a recuperação, a recristalização e o crescimento de grão do nióbio puro e da liga \'NB\'-1%\'ZR\'. Os dois materiais foram produzidos pelo mesmo processo - refusão em forno de feixe eletrônico - e no mesmo equipamento. O processo de conformação - forjamento rotativo - e os graus de deformação escolhidos também foram os mesmos para os dois materiais. Foram escolhidos graus elevados de deformação: 60, 80, 90 e 99% de redução em área. Os recozimentos foram realizados em ampolas de quartzo previamente evacuadas. Foram realizados recozimentos por 2, 4 e 6 horas numa ampla faixa de temperaturas: 700 a 1300°C para o nióbio puro e 800 a 1300 °C para a liga. Um total de mais de 150 amostras foi pesquisado. Todo o zircônio da liga encontrava-se em solução sólida e teve os seguintes efeitos principais em relação ao nióbio puro: endurecimento por solução sólida sem significativa alteração da taxa de encruamento, aumento de cerca de 100 \'GRAUS\'c nas temperaturas de início e fim da recristalização e forte inibição do crescimento de grão. Os dois materiais amoleceram consideravelmente por processos de recuperação. / This work is a comparative study on work hardening, recovery, recrystallization and grain growth of purê niobium and Nb-1%Zr alloy. Both materials were produced by the same process - electron beam melting - in the same equipment. The deformation process swaging - and the chosen degrees of deformation were the same for both materials. The degress of deformation (60, 80, 90 and 99%) were calculated referred to the reduction in area. The annealing was performed in evacuated quartz capsules for 2, 4 and 6 hours in a wide range of temperatures: 700 to 1300°C for purê niobium and 800 to 1300°C for the alloy. About 150 specimens were tested. All the zirconium in the alloy was in solid solution, and the main influences of the zirconium addition were: solid solution hardening with no change in work hardening rate, increase about 100°C in the temperature of beginning and ending of recrystallization and strong inhibition of grain growth. Both materials have shown considerable softening by recovery processes.
5

Grain refinement of cast niobium via equal channel angular extrusion/annealing

Bryant, Don O. 25 April 2007 (has links)
This research investigated the effectiveness of equal channel angular extrusion (ECAE) and annealing to improve the grain morphology and mechanical properties of electron-beam remelted pure niobium. Extrusions were performed at room temperature with a 90o die. Routes 1A, 2C, 4E and 8E were investigated with duplicate billets undergoing routes 1A, 2C and 4E to determine reproducibility. Niobium proved to be very workable during the ECAE process. Hardness increased most dramatically after the first pass and leveled off thereafter. Recrystallization temperatures for the Reference Metals material ranged from a low of 800o C for routes 2C, 4E and 8E to a high of 1000o C for route 1A. For the Wah Chang material, the recrystallization temperatures ranged from a low of 800o C for the 4E ECAE processed material to a high of 950o C for the asreceived material. The initial grain size and orientation have been hypothesized to be influential on recrystallized grain morphology for ECAE/annealing processed niobium. Smaller initial grains produce a smaller and more homogeneous recrystallized grain microstructure. The average grain diameters for the recrystallized 4E ECAE processed Wah Chang material are 13 ± 6.3 mm for the 1000o C annealed state (no banding) and are 21 ± 9.5 mm for the 1100o C annealed state (no banding). Reference Metals material that underwent route 4E and annealed at 1000o C resulted in an average grain diameter of 28 mm for billet 2 (banding) and an average grain diameter of 32 mm for billet 19 (slight banding). Reference Metals material that underwent route 8E (no banding) annealed at 1000o C resulted in an average grain diameter of 36 mm. Reference Metals material that underwent route 4E samples annealed at 1100o C resulted in an average grain diameter of 26 mm for billet 2 (banding) and an average grain diameter of 43 mm for billet 19 (slight banding). Route 8E (significant banding) annealed at 1100o C resulted in an average grain diameter of 29 mm. Strain failure decreases from the as-cast material to the worked/recrystallized material while the 0.2% yield stress and ultimate tensile strength increase from the as-cast material to the worked/recrystallized material. Long sub-grains are created in the as-worked material after one and two passes and become more broken up after four passes. Sub-grain boundary angles increase with increasing strain. To produce a fine and homogeneous microstructure from large grained niobium, intermediate annealing should be employed.
6

On the specific gravities of niobium and tantalum pentoxides ...

Lamme, Maurice Allison. January 1909 (has links)
Thesis (Ph. D.)--Columbia University.
7

Extraction of tantalum and columbium from their ores ...

Jenness, Leslie George, January 1930 (has links)
Thesis (Ph. D.)--Columbia University, 1930. / Vita.
8

On the specific gravities of niobium and tantalum pentoxides ...

Lamme, Maurice Allison. January 1909 (has links)
Thesis (Ph. D.)--Columbia University.
9

The electrical resistance of niobium and vanadium single crystals at low temperatures

Clayton, John Frederick January 1963 (has links)
An investigation into the variation of electrical resistance with temperature for high purity niobium and vanadium single crystals has been carried out. Niobium was studied over the temperature range -30°C to -146°C. It was found that in its highest purity there was little or no anomaly. At lower purities an anomaly in the region of -120°C was discovered which was attributed to oxygen or nitrogen or both changing their position on the lattice to one of higher strain energy because of changes in energy associated with the bonding between interstitials and the lattice. Hydrogen doping of niobium produced an overall increase in resistivity. A drop in the resistance curve was noted at -100°C which was thought to be due to hydrogen, being mobile and non-bonded, moving off the high strain energy sites under the influence of thermal contraction. Hydrogen embrittlement was attributed to hydrogen occupation of high strain energy-sites. Vanadium was found to have a slope change at.-170° when tested between -130°C and -196°C. No definite explanation of this is suggested. Ultrasonic testing of vanadium showed attenuation minima at -100°C and -170°C. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate
10

Some properties of vanadium and niobium pentafluorides

Cavell, Ronald George January 1960 (has links)
The reactions of various amines with vanadium and niobium pentafluoride have been studied. Pyridine and ammonia reacted with vanadium pentafluoride reducing vanadium from the pentavalent to the tetravalent state and forming monosolvated complexes of vanadium tetrafluoride. The products isolated were pyridinetetrafluorovanadium IV, (Py) VF₄, and amminotetrafluorovanadium IV, (NH₃) VF₄. Ethylenediamine also reduced vanadium pentafluoride to the tetravalent state but formed a more highly solvated denvative of vanadium tetrafluoride. The product was identified as tris (ethylenediamine) tetrafluorovanadium IV and has been formulated as the octahedral complex [V(en)₃] F₄. Niobium pentafluoride reacted with ammonia to form a 2:1 adduct of niobium pentafluoride, diammonopentafluoroniobium V, (NH₃) ₂NbF₅. The product formed on reaction of ethylenediamine with niobium pentafluoride had the composition NbF₅ (en)₁.₆. It has been considered as a highly solvated 1:1 adduct ethylenediaminepentafluoroniobium V. No reduction of niobium has been observed in amine reactions. The infrared spectra and magnetic suceptibilities of the complexes have been measured and the dissociation pressure of diamminopentafluoroniobium V has been determined. The solubilities and melting points of the complexes were also investigated. The pentafluorides of vanadium and niobium, in contrast to the highest chlorides of the same metals, are not solvolysed by the amines studied here. This common behaviour of fluorides, coupled with an apparent maximum coordination number of six for vanadium has been used to explain the reduction of vanadium pentafluoride by the amines. The reduction of vanadium occurs because the association of vanadium pentafluoride in the liquid state has saturated the coordination number of vanadium, so that any solvated product formed by the amines has an unstable coordination number which must be lowered. The fact that solvolysis, which provides a method of reducing the coordination of the central atom without reducing its valence state, cannot occur with fluorides, requires that the reduction in coordination number of vanadium must proceed through an alternate mechanism with concomitant reduction of the valence of vanadium. This interpretation is consistent with the behaviour of niobium pentafluoride which forms solvated derivatives in which niobium has increased its coordination number to seven or eight, the probable maximum coordination number of niobium. Structures have been suggested for the products of the amine reactions. The properties of the pyridine and ammonia derivatives of vanadium pentafluoride, (Py)VF₄ and (NH₃) VF₄, plus the improbable coordination of five for vanadium in the monomer suggests that the compounds are polymers. The most probable structure is a long chain of VF₄. Base units linked by fluorine bridge bonds such as have been proposed to explain association of vanadium pentafluoride. The ethylenediamine derivative of vanadium pentafluoride, [V(en)₃] F₄, is probably a monomeric compound, for there is no need to postulate association to increase the coordination number of vanadium to six. The many complex ions formed by ethylenediamine suggest that it is reasonable to postulate the formation of the [V(en)₃]⁺⁴ ion. This is the first hexacoordinate cationic complex of tetravalent vanadium, with the exception of vanadyl complexes, to be reported. The niobium pentafluoride complexes (NH₃) ₂NbF₅, (en)NbF₅ may be septacoordinate monomers, isostructural with iodine heptafluoride, or octacoordinate fluorine bridged polymers. The proposed structures are based only on the few qualitative properties that are available for the compounds. Complete structure determinations are required for verification of the structures proposed. A nuclear magnetic resonance study of vanadium pentafluoride has yielded only the F¹⁹ chemical shift of vanadium pentafluoride of -335 ppm relative to trifluoroacetic acid. The broad nuclear resonance absorption obtained has been explained in terms of rapid fluorine exchange occuring in conjunction with quadrupole broadening due to the electric quadrupole moment of vanadium. / Science, Faculty of / Chemistry, Department of / Graduate

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