Niobium mechanical properties

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. 

Niobium is used as a substrate for platinum in impressed-current cathodic protection anodes because of its high anodic breakdown potential (100 V in seawater), good mechanical properties, good electrical conductivity, and the formation of an adherent passive oxide film when it is anodized. Other uses for niobium metal are in vacuum tubes, high pressure sodium vapor lamps, and in the manufacture of catalysts. 

The basic corrosion behaviour of stainless steels is dependent upon the type and quantity of alloying. Chromium is the universally present element but nickel, molybdenum, copper, nitrogen, vanadium, tungsten, titanium and niobium are also used for a variety of reasons. However, all elements can affect metallurgy, and thus mechanical and physical properties, so sometimes desirable corrosion resisting aspects may involve acceptance of less than ideal mechanical properties and vice versa. 

Niobium is always found in nature associated with tantalum and it closely resembles tantalum in its chemical and mechanical properties. It is a soft ductile metal which, like tantalum, work hardens more slowly than most metals. It will in fact absorb over 90% cold work before annealing becomes necessary, and it is easily formed at room temperature. In addition, welds of high quality can be produced in the metal. In appearance the metal is somewhat similar to stainless steel it has a density slightly higher than stainless steel and a thermal conductivity similar to 1% carbon steel. 

The mechanical properties of niobium are dependent on the previous history of the material and the manufacturer should be consulted if these properties are likely to be critical. Physical and some typical mechanical properties are set out in Tables 5.10 and 5.11. 

Niobium closely resembles tantalum in its mechanical properties and for more detailed information relating to the fabrication of niobium see Section 5.5 on tantalum. 

Niobium-Zirconium Nb-0-75Zr has excellent mechanical properties and similar corrosion resistance to pure niobium higher zirconium concentrations reduce the corrosion resistance. 

Chemical plant It has been reported from some plants producing hydrochloric acid that tantalum condensers are being replaced by ones of niobium, and in certain petroleum plant niobium is being specified for its corrosion resistance and mechanical properties. 

The fast neutrons will cause atomic displacement and transmutation reactions in the wall material. For example after 20 years of operation, a niobium wall would contain 10 at % Zr, 0.06 at % Y, 0.28 at % He, and 0.5 at %H53h The impact on the mechanical properties of construction materials due to displacement damage and radioactive transformation is under intensive study but does not properly fall under the subject matter of this chapter. 

Because hafnium has a high absorption cross-section for thermal neutrons (almost 600 times that of zirconium), has excellent mechanical properties, and is extremely corrosion resistant, it is used to make the control rods of nuclear reactors. It is also applied in vacuum lines as a getter —a material that combines with and removes trace gases from vacuum tubes. Hafnium has been used as an alloying agent for iron, titanium, niobium, and other metals. Finely divided hafnium is pyrophoric and can ignite spontaneously in air. 

Table 2 presents mechanical properties of alloys with a matrix on the base of solid solution of niobium and molybdenum, dispersion-strengthened with chemical compounds, and also alloy with an additional frame strengthening owing to eutectoid TiFe. 

The presence of carbide and nitride precipitates in alloy steels can have a beneficial effect on the mechanical properties of the steels concerned. How-ever, the amounts, morphology and distribution of the precipitated phases must be carefully controlled in order to achieve the properties required. Because the presence of hard precipitates in a steel during hot-rolling operations can result in damage both to the rollers and to the steel, it is important that information be available on the ranges of temperature and composition in which precipitated phases are stable. For this reason, and also to achieve desired precipitation characteristics using the minimum amounts of expensive precipitating elements such as niobium, titanium, vanadium, etc., it is helpful to cany out prior calculations of the stability of precipitates in steels of different compositions. 

Zr-2.5 Nb [zirconium alloyed with 2.5 w/o (weight percent) niobium] has better mechanical properties than zircaloy, but is conoded more rapidly by water containing oxygen, such as is found in boiling-water reactors. It was the material prefened in 1971 [El] for pressure tubes in Canadian pressurized-water reactors. 

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. 

Pure niobium has relatively poor mechanical properties and readily oxidizes in air to niobium pentoxide (Nb205) at elevated temperatures. Various niobium-containing alloys such as Nb-lZr and C-103 have been successfully used in specific liquid-metal based nuclear applications and in the fabrication of various rocket components, see also Inorganic Chemistry. 

In Sweden there has been satisfactory experience of this steel for vessels, structures and piping. A fully killed niobium-treated steel is available in Belgium. These steels are normalized for pressure vessels and in this condition they have mechanical properties similar to those of the German St 52 type. 

The lattice of vanadium expands approximately linearly with the addition of aluminum [64]. The aluminum intermetallic compound, V3AI (V-25 atom% Al), expands the lattice by about 1% from 0.3025 nm in unalloyed vanadium to 0.3054 nm [64]. Molybdenum, cobalt and titanium also expand the lattice of vanadium, whereas elements such as chromium and iron cause the lattice to contract [83]. Addition of these elements can increase the mechanical strength of alloys relative to unalloyed vanadium [85]. For niobium and tantalum, mechanical properties can also be improved by alloying [86]. Buxbaum has patented a number of alloys of niobium, tantalum and vanadium for membrane use, including Ta-W, V-Co, V-Pd, V-Au, V-Cu, V-Al, Nb-Ag, Nb-Pt, Nb-Pd, V-Ni-Co, V-Ni-Pd, V-Nb-Pt, and V-Pd-Au [45]. 

Niobium, molybdenum tantalum and tungsten are refractory metals, i.e. the ones that show resistance against attack by liquid RE metals. These metals are usually listed in the literature in order of decreasing solubility in the liquid rare metals at high temperatures. Tungsten is the least soluble. However, tungsten is rather brittle and has poor mechanical properties compared to tantalum, which is the second best with respect to solubility. Tantalum containers are therefore used in purihcation of liquid rare element metals (Gupta and Krishnamurthy 2005). 

Corrosion of the plates not only detracts from their mechanical properties but also gives rise to undesirable corrosion products, namely, heavy-metal ions, which, when depositing on the catalysts, strongly depress their activity. The corrosion processes also give rise to superficial oxide films on the metal parts, and these cause contact resistance of the surfaces. For a lower contact resistance, metallic bipolar plates sometimes have a surface layer of a more stable metal. Thus, in the first polymer electrolyte membrane fuel cell, developed by General Electric for the Gemini spacecraft, the bipolar plates consisted of niobium and tantalum coated with a thin layer of gold. A bipolar plate could also be coated with a layer of carbide or nitride. 

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