Tantalum-based alloys

Hallowell, J.B., Maykuth, D.J. and Ogden, H.R., Silicide Coatings for Tantalum and Tantalum-Base Alloys, in Refractory Metals and Alloys III Applied Aspects, 30, Part 2, American Institute of Mining, Metallurgical and Petroleum Engineers, Dec. (1963)... 

Gypen, L.A. and A. Demytiere New Tantalum Base Alloys for Chemical Industry Applications, 9 Metal Progress, 127(2), 27 3d (Febmaty 1985). 

After deformation both niobium- and tantalum-based alloys are usually heat treated in high vacuum before delivering in order to achieve a fine grained primarily recrystallized microstructure. 

For comparison, the high-temperature strength of stress-relieved 1-mm sheets made of Mo- and W-hased materials is shown in Fig. 3.1-166. For short-term appUcation under high stresses, the precipitation-strengthened Mo alloys TZM and MHC offer the hest performance up to a service temperature of 1500 °C. For higher temperatures, W-hased materials should he applied. Tantalum-based alloys are used only if additional high ductility is required after cooling to room temperature. 

L.A. Gypen, M. Brabers, and A. Deruyttere. 1984. Corrosion resistance of tantalum base alloys. Elimination of hydrogen embrittlement in tantalum by substitutional alloying, Werkstoffe Corrosion, 35 37-46. 

Pla.tinum, Platinum plating has found appHcation in the production of platinised titanium, niobium, or tantalum anodes which are used as insoluble anodes in many other plating solutions (see Metalanodes). Plating solutions were often based on platinum "P" salt, which is diamminedinitroplatiniim (IT). A dinitroplatinite sulfate—sulfuric acid bath has been used to plate direcdy onto titanium (129). This bath contains 5 g/L of the platinum salt, pH adjusted to 2.0 with sulfuric acid. The bath is operated at 40°C at 10—100 A/m. Other baths based on chloroplatinic acid have been used in both acid and alkaline formulations the acid bath uses 20 g/L of the platinum salt and 300 g/L hydrochloric acid at 65° C and 10—200 A/m. The alkaline bath uses 10 g/L of the platinum salt, 60 g/L of ammonium phosphate and ammonium hydroxide to give a pH of 2.5—9.0. The alkaline bath can be plated directly onto nickel-base alloys acid baths require a gold strike on most metals. 

In the time since 1994 a lot of materials, Stainless steel [6], Ni-base alloys [6-9], numerous high performance ceramic materials [7, 9-12] and metals like Titanium [13-14], Tantalum [15], Niobium [16], Gold [6] and Platinum [6] have been tested under SCWO typical conditions in the Institute for Technical Chemistry) laboratories. 

The first commercial metal membranes for hydrogen separation and purification were made of palladium alloyed with 23-25 wt % silver. These membrane were of the unsupported type and tubular in shape. Nevertheless, the wall thickness was substantial by current standards—typically at least 100- an thick. Advances in drawing thin-walled metal tubes has allowed for palladium-silver tubular membranes to be made with much thinner walls, about 20- an thick. Composite membranes are also usually at least 25-/an thick. REB Research and Consulting (Oak Park, MI) provides tubular composite metal membranes consisting of a palladium coating over a tantalum base metal, although other group 4 or 5 base metals may be used. 

The DSA-type anodes are inert , coated anodes made of a valve metal (titanium, niobium, or tantalum) base coated with an electrochemically active coating. The active coating is made either of noble metals or of mixed metal oxides. Noble metals in active coatings are usually platinum or platinum alloys. Mixed metal-oxide coatings contain active oxides and inert oxides the active components are usually ruthenium dioxide (R.UO2) and iridium dioxide (IrC>2) and the inert components are mostly titanium dioxide (TiC>2) and other oxides such as tantalum... 

Molybdenum, niobium, and tantalum (bcc crystal structure) form a continuous series of solid solutions with tungsten, but only Nb and Ta additions lead to a strong straining effect. Higher additions of Nb and Ta raise the recrystallization temperature but also increase the DBTT and thus decrease the workability. Therefore, none of these binary or ternary tungsten base alloys developed in the past [6.2] has attained commercial importance. The only important tungsten-base solid-solution alloy today is tungsten-rhenium. 

The corrosion resistance of various metals and alloys in high-temperature liquid lithium is shown in Figure 11. Unfortunately, lithium is much more corrosive than sodium. Consequently, it will be impossible to take full advantage of its many attractive heat-transfer properties until a satisfactory container material is found. The most corrosion-resistant pure metals in a static isothermal system are molybdenum, niobium, tantalum, tungsten, and iron. Of the commercially available structural materials, no alloys tested to date have had satisfacto corrosion resistance at a temperature above 1400 F. for extended time periods in systems where temperature differentials exist. Even though iron has good resistance in static isothermal lithium, iron and iron-base alloys suffer from mass trans-... 

The metals commonly used in medical devices are stainless steel (Types 316 and 316 L), cobalt-chromium-based alloys, titanium, and titanium-based alloys. Metals are used extensively in orthopedic surgery for load-bearing devices, such as artificial joints and fixation devices (wires, pins, screws fracture plates, etc.). Other metals include tantalum, gold, and mercury alloys the latter two are used predominantly in dentistry. 

Metals are utilized for applications requiring high strength and/or endurance, such as structural components of heart valves, endovascular stents, and stent-graft combinations. Commonly used alloys include austenitic stainless steels (SS), cobalt-chrome (Co-Cr) alloys including molybdenum-based alloys, tantalum (Ta), and titanium (Ti) and its alloys. Elgiloy, a cobalt-nickel-chrome-iron... 

In the methods used for the investigation of corrosion resistance, biocompatibility and bioadhesion the researchers try to simulate and imitate the natural in vivo condition of the implant. Only in the near past have efforts been made to standardize these tests. Because of a longtime decline of standardization the tests described up until now in literature differ and the results of such diversified tests are not comparable. Corrosion measurements, for example, are performed in different solutions with changing pH values and atmospheres (aerated or de-aerated). Only if different materials have been investigated in one test and under the same conditions does a comparison of their behaviour for this test seem possible. Nevertheless, regarding the differing test results, the most corrosion resistant materials seem to be the special metals (titanium, niobium, tantalum and their alloys), followed by wrought CoCr-based, cast CoCr-based alloys and stainless steel. 

Vanadium, niobium, tantalum and molybdenum and their alloys have demonstrated good corrosion resistance in liquid Pb-Li [8]. These materials have dissolution rates in the range 0.001 to 0.004 g/m /day at 645 C [8], which is far superior to the performance of Fe-based alloys. However, the cost associated with many of these materials would make their application impractical for a full-scale reactor. 

Nickel-based alloys, which form the bulk of alloys produced, are basically nickel-chrome alloys with a face-centered cubic solid-solution matrix containing carbides and the coherent intermetallic precipitate y-NijlAfTi). This latter precipitate provides most of the alloy strengthening and results in useful operating temperatures up to 90% of the start of melting. Further additions of aluminum, titanium, niobium, and tantalum are made to combine with nickel in the y phase, and additions of molybdenum, tungsten, and chromium strengthen the solid solution matrix. 

As stated in the introduction, Ta coating may be used as substrate in the preparation of DSA oxygen electrodes it consists of a thin and porous layer of Iridium oxide, which acts as catalyst, obtained by thermal oxidation of an iridium compound on a valve metal. The lifetime of the anode in water electrolysis in extreme conditions of polarization (anodic current = 50 A/m ), acid concentration (30% m/m) and temperature (T = 80°C) is sensitive to the corrosion resistance of the valve metal This is shown on table I [24], which standardized life time (lifetime reported for the mass surface density of the catalyst Ir02) for some varieties of titanium base alloys and a tantalum coating as substrate ... 

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