Niobium addition

Addition of niobium to austenitic stainless steels inhibits intergranular corrosion by forming niobium carbide with the carbon that is present in the steel. Without the niobium addition, chromium precipitates as a chromium carbide film at the grain boundaries and thus depletes the adjacent areas of chromium and reduces the corrosion resistance. An amount of niobium equal to 10 times the carbon content is necessary to prevent precipitation of the chromium carbide. 

C-M bond addition, for C-C bond formation, 10, 403-491 iridium additions, 10, 456 nickel additions, 10, 463 niobium additions, 10, 427 osmium additions, 10, 445 palladium additions, 10, 468 rhodium additions, 10, 455 ruthenium additions, 10, 444 Sc and Y additions, 10, 405 tantalum additions, 10, 429 titanium additions, 10, 421 vanadium additions, 10, 426 zirconium additions, 10, 424 Carbon-oxygen bond formation via alkyne hydration, 10, 678 for aryl and alkenyl ethers, 10, 650 via cobalt-mediated propargylic etherification, 10, 665 Cu-mediated, with borons, 9, 219 cycloetherification, 10, 673 etherification, 10, 669, 10, 685 via hydro- and alkylative alkoxylation, 10, 683 via inter- andd intramolecular hydroalkoxylation, 10, 672 via metal vinylidenes, 10, 676 via SnI and S Z processes, 10, 684 via transition metal rc-arene complexes, 10, 685 via transition metal-mediated etherification, overview,... 

The striking features after oxidation of Ti35A15Nb for 4h at 900°C are the slight enrichment of aluminium in the metal subsurface zone instead of aluminium depletion, the preferred formation of AlON in wide parts of the metal/oxide interface and the development of a rather dense, coarse-grained partial layer consisting of titania in the oxide scale. Several reasons for the beneficial effect of niobium addition on the oxidation behaviour are discussed in the literature [5,10,11]. Beside the influence of niobium on the aTl/aAI ratio and expansion of the 7-TiAl phase field the effect of doping of titania by niobium is often discussed. By doping of titania with niobium the concentra-... 

The present contribution focuses on the effect of various elements added by ion implantation on the isothermal and cyclic oxidation behaviour of the 7-Ti A1 based inter-metallic alloys Ti-48Al-2Cr and Ti-48Al-2Cr-2Nb at 800°C in air.These particular materials were selected since the ternary chromium addition improves the mechanical properties especially room temperature ductility [9-11] and the quaternary niobium addition improves the oxidation resistance [8, 14, 15]. Comparison will be made between materials modified by ion implantation and alloys in which elements were added by alloying techniques. 

Niobium additions, it was stated, behaved similarly, and only heat treatment, as described previously, was effective in conferring immunity to nitric acid. It was reported [37], however, that columbium additions (8x C + N content), but not titanium additions, minimize the observed intergranular corrosion of welds exposed to boiling 65% HNO3. This behavior may be explained by the observed marked reactivity of titanium carbides, but not niobium carbides, with HNO3 along grain boundaries where such carbides are concentrated [38]. 

Trigueiro, R, Ferreira, C., Volta, J., et al. (2006). Effect of Niobium Addition to Co/y-Al203 Catalyst on Methane Combustion, Catal. Today, 118, pp. 425-432. 

Titaruum and niobium additions equal to five or ten times the carbon content, respectively, permit the carbon to precipitate as titanium or niobium carbides during a sensitizing heat treatment. The carbon precipitation does not reduce the chromium content of the grain boundaries. 

The idea of this work was to obtain Sb, V and Nb containing catalysts supported on mesoporous materials. The previous study [8] indicated that MCM-41 mesoporous structure is promising for VSbOx loading. In this woik the effects of different preparation methods and conditions are studied in detail. The applied strategy is based on the introdnction of different amounts of Sb and V oxide species on NbMCM-41 material, application of different sequences of step by step impregnation, post synthesis one pot adsorption and different temperature treatment. To explain the influence of niobium additive on the properties of the SbVOx phases, the supports without Nb (sihcate - MCM-41 and aluminosilicate - AlMCM-41) are also used. 

Niobium additions were furthermore said to markedly inerease hardness and tensile strength of B-Fe alloys air-cooled from 950 or 1100°C and water quenehed duetility and toughness of the alloy, however, decreased with Nb additions [1966Has]. A general survey of the effect of concentration and transition metals on crystallization of Fe based amorphous alloys was given by [1987She]. [1980Che] evaluated some key physico-mechanieal properties of iron-boride materials alloyed with Nb, Mo, and W. 

Gauer L, Alperine S, Steinmetz P and Vassel A (1994), Influence of niobium additions on high-temperature oxidation behavior of Ti3Al alloys and coatings , Oxid Met, 42 (1/2), 49-74. 

In addition, the following ASTM Standard Specifications are for the Nb—lOHf—ITi—IZr alloy known commercially as C103 B652-92 Niobium—Hafnium AHoy Ingots B654-92 Niobium—Hafnium AHoy Foil, Sheet, Strip, and Plate B655-92 Niobium—Hafnium AHoy Bar, Rod, and Wine. 

In addition to oxidation itself, gas diffusion into the base metal can be more damaging than the actual loss of metal from the surface. Thus the loss in mechanical properties owing to diffusion of oxygen into niobium makes it more difficult to protect niobium against oxidation damage than molybdenum, even though molybdenum has less resistance to normal oxidation effects than niobium. 

A large deposit of loparite occurs ia the Kola Peninsula, Russia. The production of REO reaches 6500 t/yr. Loparite contains over 30% of rare-earth oxides from the cerium group. In addition, loparite contains up to 40% titanium oxide and up to 12% niobium and tantalum oxides. 

Other Metals. AH the sodium metal produced comes from electrolysis of sodium chloride melts in Downs ceUs. The ceU consists of a cylindrical steel cathode separated from the graphite anode by a perforated steel diaphragm. Lithium is also produced by electrolysis of the chloride in a process similar to that used for sodium. The other alkaH and alkaHne-earth metals can be electrowon from molten chlorides, but thermochemical reduction is preferred commercially. The rare earths can also be electrowon but only the mixture known as mischmetal is prepared in tonnage quantity by electrochemical means. In addition, beryIHum and boron are produced by electrolysis on a commercial scale in the order of a few hundred t/yr. Processes have been developed for electrowinning titanium, tantalum, and niobium from molten salts. These metals, however, are obtained as a powdery deposit which is not easily separated from the electrolyte so that further purification is required. 

Tungsten with the addition of as much as 5% thoria is used for thermionic emission cathode wires and as filaments for vibration-resistant incandescent lamps. Tungsten—rhenium alloys are employed as heating elements and thermocouples. Tantalum and niobium form continuous soHd solutions with tungsten. Iron and nickel are used as ahoy agents for specialized appHcations. 

Niobium is important as an alloy addition in steels (see Steel). This use consumes over 90% of the niobium produced. Niobium is also vital as an alloying element in superalloys for aircraft turbine engines. Other uses, mainly in aerospace appHcations, take advantage of its heat resistance when alloyed singly or with groups of elements such as titanium, tirconium, hafnium, or tungsten. Niobium alloyed with titanium or with tin is also important in the superconductor industry (see High temperature alloys Refractories). 

Another method of purifying niobium is by distillation of the anhydrous mixed chlorides (29). Niobium and tantalum pentachlorides boil within about 15°C of one another which makes control of the process difficult. Additionally, process materials must withstand the corrosion effects of the chloride. The system must be kept meticulously anhydrous and air-free to avoid plugging resulting from the formation of niobium oxide trichloride, NbOQ. Distillation has been used commercially in the past. 

Niobium is also important in nonferrous metallurgy. Addition of niobium to tirconium reduces the corrosion resistance somewhat but increases the mechanical strength. Because niobium has a low thermal-neutron cross section, it can be alloyed with tirconium for use in the cladding of nuclear fuel rods. A Zr—l%Nb [11107-78-1] alloy has been used as primary cladding in the countries of the former USSR and in Canada. A Zr—2.5 wt % Nb alloy has been used to replace Zircaloy-2 as the cladding in Candu-PHW (pressurized hot water) reactors and has resulted in a 20% reduction in wall thickness of cladding (63) (see Nuclear reactors). 

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