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Niobium
5.3 Niobium
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. It is somewhat less corrosion resistant than tantalum, and like tantalum suffers from hydrogen embrittlement if it is made cathodic by a galvanic couple or an external e.m.f., or is exposed to hot hydrogen gas. The metal anodises in acid electrolytes to form an anodic oxide film which has a high dielectric constant, and a high anodic breakdown potential. This latter property coupled with good electrical conductivity has led to the use of niobium as a substrate for platinum-group metals in impressed-current cathodicprotection anodes. 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. Methods of Fabrication
Niobium possesses excellent room temperature fabrication characteristics compatible with all conventional production practices. Large reductions (up to 90%) of recrystallised material can be made without intermediate process annealing. Secondary fabrication operations such as stamping, drawing or forming into completed shapes can be performed cold. Intermediate anneals are dependent on the amount of work involved. In tube drawing or deep drawing, annealed niobium should be used. Reductions of 60 to 80% with multiple draws are customary before re-annealing, but the initial draw should have a depth not greater than 40 to 50% of the diameter. It machines in a similar manner to soft copper, and high-speed-steel tools with high cutting speeds are most satisfactory. Trichloroethane is recommended as a cutting medium and the work must be kept well flooded at all 5:24
517-1 034 at 20°C 241 at 500°C 89-117 at 1 O00"C
288 at 20°C 68 at 1050°C
UTS2*'
(MN/mZ)
' 9
8.57
(g/cm ')
Density
(MN/m2)
Yield stress
4 927
2 468
'
Boiling point ("C)
Melting point' ("C) 0.523 at 0°C 0.691 at 1873°C
0.268 at 15OC 0.320 at 1227°C
188 at 204°C 113 at 600°C 108 at 900°C
Modulus Of elasticity2+' (GN/m2) 0.38
ratio
Poisson's
17-173
Hardness (VPN)
t
Good
o
~
Resistance
15
-150 (based on rupture tests)
900-1 300°C
Recrystallisation temperature'
7 . 1 at 20°C 7 . 3 9 at 0-4Oo"C
2s
Coeflcient of thermal expansion (x10-6/"C)
Workability (ductile to ~brittle ~ trans. ~ l temp.) ("C)
Resistivity', (pWcm at 20°C)
Table 5.11 Mechanical properties of niobium
Thermal conductivity" (W/cm"C)
Specijic heat2 (J/g"C)
Table 5.10 Physical properties of niobium
800°C
temperature7
Stress relieving
1.16
thermal neutrons (barns/atom)
Cross section
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NIOBIUM
times. If it is not possible to use this coolant, satisfactory results can be obtained with water-soluble oil coolants. It can be welded by resistance, tungsten-inert gas (TIG), plasma arc and electron beam techniques. T o protect the metal from attack by air, resistance welding is carried out under water and the TIG method is best performed in a chamber of argon. The latter three methods produce ductile welds that equal the base metal in most of its characteristics. 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.
Corrosion Resistance Niobium like tantalum relies for its corrosion resistance on a highly adherent passive oxide film; it is however not as resistant as tantalum in the more aggressive media. In no case reported in the literature is niobium inert to corrosives that attack tantalum. Niobium has not therefore been used extensively for corrosion resistant applications and little information is available on its performance in service conditions. It is more susceptible than tantalum to embrittlement by hydrogen and to corrosion by many aqueous corrodants. Although it is possible to prevent hydrogen embrittlement of niobium under some conditions by contacting it with platinum the method does not seem to be broadly effective. Niobium is attacked at room temperature by hydrofluoric acid and at 100°C by concentrated hydrochloric, sulphuric and phosphoric acids. It is embrittled by sodium hydroxide presumably as the result of hydrogen absorption* and it is not suited for use with sodium sulphide. Atmospheric Niobium like several other refractory metals is extremely reactive with atmospheric oxygen. It will in fact react with air at temperatures as low as 200°C9 although reaction does not become rapid until temperatures above red heat (about 500°C) are reached; at 980°C the rate is 0.05 mm/h" and at 1200°C the rate is 300 mm/h". It is not attacked by oxygen at 100°C but the attack is catastrophic at 390°C. At lower temperatures a thin adherent oxide film is formed on the surface of the metal, but at higher temperatures, above red heat, the oxide diffuses rapidly throughout the metal with consequent embrittlement. At elevated temperatures the metal reacts with all the common gases including nitrogen (300-400"C), water vapour (300"C), carbon dioxide, carbon monoxide and hydrogen
(250°C). Protection of niobium and its alloys from oxidation in air is accomplished by coating, e.g. with zinc deposited by holding in zinc vapour at 865"Ct2or coating with a layer of chemically stable oxide, nitride or silicide. Silicide coatings applied by pack cementation, fused slurryt3 or by electrolytic methods have been found to be one of the most effective means of preventing oxidation of the metal. Water The corrosion resistance of pure niobium in water and steam at eievated temperatures is not sufficient to allow its use as a canning material in water-cooled nuclear reactors. Alloys of niobium with molybdenum, titanium, vanadium and zirconium however have improved resistance and have possibilities in this application. Whilst the Nb-10Ti-10Mo alloy offers
NIOBIUM
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the best corrosion resistance the Nb-7V alloy seems more practical on the basis of weldability. It also has good high-temperature strength properties. AcidsLo*'6'6Niobium is resistant to most organic acids and to mineral acids especially under oxidising conditions, Figs. 5.5 to 5.7 show the corrosion behaviour of niobium in laboratory tests in various concentrations of sulphuric and hydrochloric acids at the boiling point and at 190°C and 250"C, and in phosphoric acid at the boiling point. It has excellent resistance to nitric acid, the rate of attack in 70% acid at 250°C being only 0.25 mm/y. In dilute sulphurous acid at 100°C the corrosion rate is 0.0125 mm/y, but in concentrated acid at the same temperature it is greater than 0.25 mm/y.
Sulphurrc acid (%) Fig. 5 . 5
Niobium corrosion in sulphuric acid"
Alkalis's l 4 Though niobium is not attacked by most alkalis at room temperature it is seriously attacked at 9 8 ° C and severe embrittlement is obtained in concentrated alkali at room temperature and virtually all alkalis at 98°C. See Table 5.12 for detailed corrosion rates and embrittlement ratings. There is evidence to show that the corrosion product when niobium is attacked by sodium hydroxide is Na8Nb60,,. I 8H20. salt^'^^''^'^ Tests on niobium have only been carried out in a limited number of salt solutions; however, in the main niobium exhibited similar resistance to tantalum in most salt solutions, and like tantalum it is attacked by salts that hydrolyse to form alkalis. "3
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NIOBIUM
Fig. 5.6 Niobium corrosion in hydrochloric acid Is
0
IO 20 30 Hydrochloric acld (%I
LO
. E
E
I
ai
2
C
0 0
Fig. 5.7 Niobium corrosion in boiling phosphoric acid l 6
L L
0
V
0
20
LO
60
80
Concentration of H3P0, (%)
Gases9. 17. 19.20 It is unattacked by most common gases, e.g. nitrogen, hydrogen, oxygen, carbon dioxide, carbon monoxide and sulphur dioxide (wet or dry) up t o 100"C, and it is inert to chlorine and bromine (both wet and dry) to 100°C. It is, however, attacked by nitrogen at 300-400"C, hydrogen at 250"C, oxygen at 200"C, carbon and carbon-bearing gases at 1200-1 400°C and by chlorine at 200-250°C.
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NIOBIUM Table 5.12
Corrosion in alkalis8* ~~
Reagent
Concentration
NaOH
(@Jo)
1 5
Na, CO, K2C03
Na2PO, Na2S NaOH and Na, S NaOH
(W
Corrosion rate
(mm/y)
10 20 10 20 25 9
98 98 98 98 98 98 98 98 98 98 98
0.74 1.17 2.00 0.60 2.56 1.63 I .60 2.90 2.46 1.34 0.09
9
98
4.15
10
KOH
Temperature
1
5
KOH
Molten Molten
Embrittlement rating
B C C A
C B C C C B A
B Severe attack at 535°C Dissolves metal at 360°C
Nore. Embrittlement ratings were obtained by bending a wire corrosion-test-specimen and the following notations were used:
A wire unbroken when sharply bent.
B wire broken when sharply bent. C wire broken when handled or slightly bent.
Liquid Metals2'
Bismuth Niobium is resistant to bismuth at temperatures up to 56OoCz2 but is attacked at higher temperature^^^-^' and is therefore not considered a suitable container for handling liquid bismuth even under oxygen-free conditions26. Furthermore, the stress-rupture properties of niobium are significantly lowered when the metal is tested in molten bismuth at 8 1 5 ° C 2 4 * 2 7 . Gallium It is slightly less resistant than tantalum to gallium, showing good resistance at temperatures up t o 400°C but poor resistance above 450°Czs-30. Lead Although subject t o slight penetration at 980°C it shows no detrimental effects in stress rupture tests when tested in molten lead at this temperature*' or at 8 1 5 ° C 2 4 . It is highly resistant to mass transfer in liquid lead as indicated by data obtained in tests at 800°C with a thermal gradient
of 300°c31. Lithium Niobium has good resistance to molten lithium at temperatures up to 1 0 0 0 ° c 2 8 * 3 2 .
Mercury In static tests niobium shows good resistance to mercury at temperatures up to 6OOoCz8. Sodium, potassium and sodium-potassium alloys Liquid sodium, potassium or alloys of these elements have little effect on niobium at temperabut oxygen contamination of sodium causes an tures up t o 1 000°C28*33*34, increase in c ~ r r o s i o n ~Sodium ~ * ~ ~ .does not alloy with niobium3'. In mass transfer tests, niobium exposed t o sodium at 600°C exhibited a corrosion rate of approximately 1 mgcm-2d-1. However, in hot trapped sodium at 550°C no change of any kind was observed after 1 070 h38.
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NIOBIUM
Thorium-magnesium In static tests the thorium-magnesium eutectic had no appreciable effect on niobium at 850°C39. Uranium Short-term tests indicate that the practical upper limit for niobium as a container material for uranium is about 1 400°C40. Niobium is dissolved in a uranium-bismuth alloy in less than 100 h at a temperature of 800"C4'. Uranium eutectics with iron, manganese or nickel, corroded niobium at 800"C42and 1 000°C43.It is significantly attacked by uraniumchromium at 1 0oo"C". Zinc Molten zinc is reported to attack niobium at a significant rate at temperatures above 450°C45.It is attacked by zinc at 600°C and shows increasing solubility with temperature up to 850°C. Galvanic effects If niobium is cathodic in a galvanic couple the results can prove disastrous because of hydrogen embrittlement. If niobium is the anode in such a couple it anodises so readily that no damage occurs and the galvanic current drops to a very low value due to the formation of an anodic oxide film. Anodic oxide formation Lakhiani and S h r e i P have studied the anodic oxidation of niobium in various electrolytes, and have observed that temperature and current density have a marked effect on the anodising characteristics. The plateau on the voltage/time curve has been shown by electron microscopy to correspond with the crystallisation of the oxide and rupture of the previously formed oxide. It would appear that this is a further example of 'field recrystallisation'- a phenomenon which has been observed previously during anodisation of tantalum4'. No significant data on the galvanic behaviour of niobium are available; however, its behaviour can be expected to be similar to tantalum.
Alloys of Niobium Niobium-Tantalum Niobium and tantalum form solid-solution alloys which are resistant to many corrosive media and possess all the valuable properties of the pure metals. This could have great practical value since in a number of branches of technology it might permit the replacement of pure tantalum by a cheaper alloy of niobium and tantalum. Miller48 and Argent49reported data on the resistance of the niobium-tantalum system, but the tests were only carried out under mild conditions and the data have only limited significance. However, Gulyaev and Georgieva l6 and Kieffer, Bach and Slempkowski carried out tests at elevated temperatures and their work indicated that the corrosion rates of the alloys are substantially that of tantalum provided the niobium content does not exceed 50%. Niobium-Zirconium Nb-O.75Zr has excellent mechanical properties and similar corrosion resistance to pure niobium; higher zirconium concentrations reduce the corrosion resistance. Niobium-Titanium
Nb-8Ti exhibits unusual behaviour: although the
S:31 corrosion resistance is slightly lower than the pure metal it shows no sign of NIOBIUM
embrittlement in sulphuric and hydrochloric acids. The higher the titanium content the lower the corrosion resistance.
Niobium-Zirconium-Titanium Niobium alloys containing zirconium and titanium have improved resistance to high-temperature water 51 and have been evaluated for use in pressurised-water nuclear reactors. Niobium-Vanadium The presence of vanadium reduces niobium’s corrosion resistance to most media. The alloy containing 12.6 at. %V however has excellent resistance to high-temperature water and steam, and this property and the alloy’s relatively low neutron cross section give it considerable potential for nuclear applications. Niobium-Molybdenum The addition of molybdenum to niobium within the solid solution range gives improved corrosion resistance to hydrochloric and sulphuric acids.
Industrial Applications of Niobium Nuclear Niobium finds use in some nuclear reactors on account of its compatibility with uranium and liquid sodium/potassium at fast reactor temperatures. Impressed-current cathodic-protection anodes Niobium has, a high anodic breakdown potential (100V in sea water), a good electrical conductivity (13% that of Cu), good mechanical properties and anodises readily forming an adherent passive oxide film. These properties have led to it being used as a substrate for platinum in impressed-current cathodic-protection anodes for use in high-resistivity waters and other situations where high driving potentials are required to obtain good current spread. Niobium has the advantage over tantalum in that it is less costly, and its cost can be decreased by using a composite electrode with a copper core that also increases the conductivity of the anode5’. Capacitors Niobium’s electrical properties have also led to its investigation as a capacitor material; however, as far as is known there has been no significant commercial application of the material in this field. 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. Electrical Niobium is finding growing use in components for high-pressure sodium lamps. Miscellaneous Niobium also finds use in satellite launch vehicles and spacecraft and one of the principal applications for niobium-base alloys is in the production of super-conducting devices.
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NIOBIUM
Recent Developments Corrosion and other properties of niobium have been reviewed in Symposia held in 198lS3and 198254,and in updated suppliers' l i t e r a t ~ r e ~ ~ - ~ ~ . Wider application would result from improving the oxidation resistance of niobium and its alloys at elevated temperature. Oxidation kinetics are parabolic to paralinear over the range 400 to 600°C and linear from 700 to 900°C57,although oxidation rate is irregular in the range 600 to 81OoCs8. In contrast the kinetics of nitriding are parabolic over the range 400°C to 1100°Cs7.At room temperature the oxidation of niobium in oxygen is logarithmic and pressure dependents9. The oxidation rate of niobium in air from 800°C to above 1000°C can be decreased by alloying e.g. with hafnium, zirconium, tungsten, molybdenum, titanium or tantalumms6'.However, the preferred fabricable alloys still require further protection by coatingm. Ion implantation improves thermal oxidation resistance of niobium in oxygen below 500"C6*. In hydrochloric acid at temperatures up to lOO"C, the corrosion rate decreases with time and ferric iron c~ncentration~~. The presence of air does not affect the general corrosion rate but in 1 0 acid ~ it promotes pitting attack, which also arises in chloride-containing methanolic solutions in the absence of sufficient water to effect passivationu. Alloying niobium with 2.5% or more of tantalum significantly decreases corrosion rates in hydrochloric acid65. Niobium is resistant to pitting and general corrosion in hydrobromic acid up to the azeotropic concentration of 47 wt% and 124°C; the presence of free bromine enhances passivity@. Anodic oxide film properties depend upon ion concentration in acid chloride67and in alkaline6*solutions; films are more compact and crackfree in acid solution69.Alloying with more than 47% of nickel gives good resistance to hydrogen embrittlement in potassium hydroxide solution7'. Cathodic protection applications in fresh water include use of ferritecoated niobium7', and the more usual platinum-coated niobium72. Platinised niobium anodes have been used in seawater, ~nderground'~ and in deep wells73*74 and niobium connectors have been used for joining current leads". Excellent service has been reported in open-seawater , where anodic potentials of up to 120V are not deleterious, but crevice corrosion can occur at 20 to 40V due to local surface damage, impurities such as copper and iron, and under deposits or in mud7'. Recent information on the behaviour of niobium in molten salts is sparse and confined to a few specific, mixed-salt environment^^^. J. BENTLEY I.R. SCHOLES REFERENCES 1. Lyman, T., Metals Handbook, A.S.M. (1961)*
2. Hampel, C. A., Rare Metals Handbook, Reinhold, 2nd edn (1961)* 3. Quarrel, A. G., Niobium, Tantalum, Molybdenum and Tungsten, Report of Conference, University of Sheffield (1960)* These references can be found collectively in Properties of Refractory Metals, by S . J . Burnett, U.K.A.E.A. Research Report No. AERE R4 657. H . M . S . 0 (1969).
NIOBIUM
5:33
4. Krikorian, 0. H., ThermalExpansion of High TemperatureMaterials, UCRL 6 132, Sept. (1960). 5 . MacDonald, R. N. and Boucom, H. H., Nucleonics, 20 No. 8, Aug., 158 (1962)* 6. Mordike, B. L., J. Inst. Metals, 88 No. 6, 272 (1960)* 7. Chelius, J., Machine Design, March I (1962); 8. Tingley, I. 1. and Rogers, R. R., ‘Corrosion of Niobium and Tantalum in Alkaline Media’, Corrosion, 21 No. 2. 132 and 136, April (1965) 9. Balke, C. W., in Corrosion Handbook (Ed. H. H. Uhlig), 620-621 and 720-722, Wiley ( 1948) 10. Macleary, D. L., ‘Testing of Niobium and Niobium Alloys’, Corrosion, 18, 67t-69t. Feb. ( 1962) 1 I . Jaffee, R. J., Proceedings on an International Symposium on High Temperature Technology, Asilomar, California, 1959, McGraw Hill, New York, 61 (1960) 12. Wehrmann, Corrosionomics, Fansteel Metallurgical Corporation, Sept. (1956) 13. Priceman, C. and Soma, L., Development of Fused Slurry Silicide Coatings for the Elevated Temperature Oxidation Protection of Niobium and Tantalum Alloys, Report AFML-TR-68-210, Sylvania Electric Products Inc., Dec. (1968) 14. Cox, F. G., Niobium Welding and Metal Fabrication, 352-358, Oct. (1965) 15. Bishop, C. R., ‘Corrosion Tests at Elevated Temperatures and Pressures’, Corrosion, 19 No. 9, Sept., 308t-314t (1963) 16. Gulyaev, A. P. and Georgieva, I. Ya., Zashchita Metailov, 1 No. 6, 652-657, Nov.-Dec. ( 1965) 17. Technical Data on Fansteel Niobium, Bulletin TDB, Fansteel Metallurgical Corporation 18. Corrosion Tables of Special Materials and Rare Metals, Jacob and Korves GmbH 19. Meyll Shpeydel, Collection Nioby i Tafital (Nb and Ta), edited by 0. P . Kolchina (1960) 20. Gulbransen, E. A. and Andrew, K. F., Trans. A.I.M.E., 188, 586-599 (1950) 21. Barto, R. L. and Hurd, D. T., Research and Development, 26-30, Nov. (1966) 22. Stoughton, L. D. and Sheehan, T. V., Mechanical Eng., 78, 699-702 (1956)t 23. Lloyd, E. D. in Plansee Proceedings 1958-High Melting Metals, Metallwork Plansee AG, Reutte Tyrol, 249-256 (19S9)t 24. Parkman, R. and Shepard, 0. C., US Atomic Energy Commission Publication No. O R 0 45, June I 1 (1951)t 25. Frost, B. R. T. and Addison, C. C., et al., in Proceedings of Second United Nations International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1958, 7, Reactor Technology, 139-1657 26. Parr, G. W. and Graham, L. W., Bull. Inst. Metals, 4, 125-126, Dec. (1958)t 27. Grassi, R. C., Bainbridge, D. W. and Harman, J. W., US Atomic Energy Commission Publication No. AECU 2 201, July 31 (1952)t 28. Miller, E. C., Chapter 4 of Liquid Metals Handbook, US Atomic Energy Commission, Navy Dept., Washington, D.C., 144-183 (1952)t 29. Wilkinson, W. D., U S Atomic Energy Commission Publication No. ANL-5027, Aug. (1953) 30. Jaffee, R. I., Evans, R. M., Fromm, E.A. and Gonser, B. W., US Atomic Energy Commission, Publication No. AECD-3 317 (1949) and Metal Abstracts, 20, 241 (1952)t 31. Cathcart, J. V. and Manly, W. D., Corrosion, 12, 87t-91t (1956)t 32. Cunningham, J. E., US Atomic Energy Commission Publication No. ORNL-CF-51-7135, 78, July 23 (195l)t 33. Reed, E. L., J. A m . Ceram. SOC.,37, 146-153 (1954)t 34. Cottrell, W. B. and Mann, L. A., Nucleonics, 12, 22-25, Dec. (1954)t 35. Wyatt, L. M. and Dickinson, F. S., Welding and Metal Fabrication, 25, 378-385, 396 (1957)t 36. Raines, G. E., Weaver, C. V. and Stang, J. H., US Atomic Energy Commission, Publication No. BMI-I 284, Aug. (1958)t 37. Adams, R. M. and Sittig, M., in LiquidMetals Handbook, Sodium-NAKSupplement, U S Atomic Energy Commission, Navy Dept., Washington, D.C., 14 (1955)t 38. Eichelberger, R. L., U S Atomic Energy Commission Publication No. BNL-489; Proceedings of the French-American Conference on Graphite Reactors, 168-173, Nov. 12-13 (1957)t t These references can be found collectively Wilcy (1963).
In Colunibium and Tonlalum. edited by F . T. Sisco and E. Epremian. Chapt. 8.
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NIOBIUM
39. US Atomic Energy Commission Publication No. ISC-I 118, Semi-annual Summary, Research Report in Engineering for July-December, Ames Laboratory, Ames, Iowa (1958)t 40. McIntosh, A. B. and Bagley, K., J. Inst. Metals, 84, 251-270 (1955-1956)t 41. US Atomic Energy Commission Publication No. ISC-978, Semi-annual Research in Engineering for July-December, Ames Laboratory, Ames, Iowa (1957)t 42. US Atomic Energy Commission Publication No. ISC-607, Quarterly Summary Research Report in Metallurgy for January, February and March, Ames Laboratory, Ames, Iowa (1955)t 43. US Atomic Energy Commission Publication No. ISC-506, Quarterly Summary Research Report in Metallurgy for April, May and June, Ames Laboratory, Ames, Iowa (1954)t 44. US Atomic Energy Commission Publication No. ISC-423, Quarterly Research Report in Metallurgy for July, August and September, Ames Laboratory, Ames, Iowa (1953)t 45. Hodge, W., Evans, R. M. and Haskins, A. F., J. of Metals, 7 , 824-832 (1955)t 46. Lakhiani, D. M. and Shreir, L . L., Nature, Lond., 188, 4 744 (1960) 47. Vermilyea, D. A., J. Electrochem. SOC.,102, 207 (1955) 48. Miller, G. L., Tantalum and Niobium, Academic Press, 328 (1959) 49. Argent, B. B., J. Inst. Metals, 85, 547-551 (1957) 50. Kieffer, R. von, Bach, H. and Slempkowski, I., Werksto~eundKorrosion,No. 9,782-784, Sept. (1967) 51. Dayton, R. W. and Tipton, C. R., Battelle Memorial Inst. Progress Reports: BMI I 324, March I (1959), BMI 1 340, March 1 (1959) and Nuclear Science Abs., 13 Nos. 18 089 and 18 090 (1959)t 52. 'Niobond' and 'Tibond', Marston Excelsior, Wolverhampton, England (1974) 53. Lupton. D., Aldinger, F. and Schulze, K., Niobium in Corrosive Environments, Niobium 81, Proceedings of the International Symposium, San Francisco, edited by Harry Stuart, The Metallurgical Society of AIME, 533-560, (1981) 54. Refractory Metals and Their Industrial Applications. symposium sponsored by ASTM Committee B10 New Orleans, ASTM Special Technical Publication 849 (1982) 55. Columbium (Niobium), Teledyne Wah Chang Albany, P O Box 460,Albany, Oregon. 56. Columbium (Niobium), KBI Division of Cabot Corporation, PO Box 1462, Reading, PA. 57. Strafford, K. N., Corrosion Science, 19, 49-62 (1979) 58. Clenny, J. T. and Rosa, C. J., Met Trans, IIA, 1385-1389 (1980) 59. Crundner, M. and Halbritter, J. Surface Science, 136, 144-154 (1984) 60.Inouye, H., in Reference I, 615-636 61. Babitzke, H. R., Siemens, R. E., Asai, G. and Kato, H., Development of Columbium and Tantalum Alloys for Elevated-Temperature Service, Bureau of Mines Report of Investigations 6558, US Department of the Interior, (1964) 62. Pons, M., Caillet, M. and Galerie, A., Mater. Chem. Phys, 15, 45-60 (1986) 63. Covino, B. S. Jr, Carter, J. P. and Cramer, S. D., Corrosion, 36, 554-558 (1980) 64. Palit, G. C. and Elayaperumal, K., Corrosion Science, 18, 169-179 (1978) 65. Krehl, M., Schulze, K., Olzi, E. and Petzow. G., Z. Metallkde, 74, 358-363 (1983) 66. Uehara, I . , Sakai, T., Ishikawa. H., Ishii, E. and Nakane, M. Corrosion, 42, 492-499 ( 1986) 67. El-Basiouny, M. S., Bekheet, A. M. and Gad Allah, A. G. Corrosion, 40, 116-1 19 (1984) 68. Bulhks, L. 0. S. and D'Alkaine, C. V.. In Proceedings of the 8th International Congress on Metallic Corrosion (Mainz 1981) Frankfurt-am-Main; Dechema (1981) 69. Vijayan, C. P., Claessens, P. L. and Piron, D. L. Corrosion, 37, 170-174 (1981) 70. Sugimoto, K., Belanger, G. and Piron, D. L. Corrosion, 36, 437-441 (1980) 71. Kumar, A., Segan, E. G. and Bukowski, J. Materials Performance, 23, 24-28 (1984) 72. Baboian, R., Materials Performance, 22, 15-18 (1983) 73. Baboian, R., Materials Performance, 18, 9-15 (1979) 74. Toncre, A. C., Materials Performance, 19, 38-40 (1980) 75. Hayfield, P. C. S. Materials Performance, 20, 9-15 (1981) 76. Janz, G. J. and Tomkins, R. P. T., Corrosion in Molten Salts; An Annotated Bibliography, Corrosion, 35, 485-504 (1979)
NIOBIUM
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BIBLIOGRAPHY Meyll Shpeydel, Collection Niobi i Tantul, Ed. 0 . P. Kolchina, 565-571 (1960) Miller, G. L., Tantulum and Niobium, Butterworths. London (1959) Columbium and Tuntalum, Ed. F. T . Sisco and E. Epremian, Wiley, New York and London (1%3) Materials and Design, 74-78, Jan. (1968) Tantulum, Niobium and Zirconium, Murex Ltd., Rainham, Essex
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. It is somewhat less corrosion resistant than tantalum, and like tantalum suffers from hydrogen embrittlement if it is made cathodic by a galvanic couple or an external e.m.f., or is exposed to hot hydrogen gas. The metal anodises in acid electrolytes to form an anodic oxide film which has a high dielectric constant, and a high anodic breakdown potential. This latter property coupled with good electrical conductivity has led to the use of niobium as a substrate for platinum-group metals in impressed-current cathodicprotection anodes. 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. Methods of Fabrication
Niobium possesses excellent room temperature fabrication characteristics compatible with all conventional production practices. Large reductions (up to 90%) of recrystallised material can be made without intermediate process annealing. Secondary fabrication operations such as stamping, drawing or forming into completed shapes can be performed cold. Intermediate anneals are dependent on the amount of work involved. In tube drawing or deep drawing, annealed niobium should be used. Reductions of 60 to 80% with multiple draws are customary before re-annealing, but the initial draw should have a depth not greater than 40 to 50% of the diameter. It machines in a similar manner to soft copper, and high-speed-steel tools with high cutting speeds are most satisfactory. Trichloroethane is recommended as a cutting medium and the work must be kept well flooded at all 5:24
517-1 034 at 20°C 241 at 500°C 89-117 at 1 O00"C
288 at 20°C 68 at 1050°C
UTS2*'
(MN/mZ)
' 9
8.57
(g/cm ')
Density
(MN/m2)
Yield stress
4 927
2 468
'
Boiling point ("C)
Melting point' ("C) 0.523 at 0°C 0.691 at 1873°C
0.268 at 15OC 0.320 at 1227°C
188 at 204°C 113 at 600°C 108 at 900°C
Modulus Of elasticity2+' (GN/m2) 0.38
ratio
Poisson's
17-173
Hardness (VPN)
t
Good
o
~
Resistance
15
-150 (based on rupture tests)
900-1 300°C
Recrystallisation temperature'
7 . 1 at 20°C 7 . 3 9 at 0-4Oo"C
2s
Coeflcient of thermal expansion (x10-6/"C)
Workability (ductile to ~brittle ~ trans. ~ l temp.) ("C)
Resistivity', (pWcm at 20°C)
Table 5.11 Mechanical properties of niobium
Thermal conductivity" (W/cm"C)
Specijic heat2 (J/g"C)
Table 5.10 Physical properties of niobium
800°C
temperature7
Stress relieving
1.16
thermal neutrons (barns/atom)
Cross section
5:26
NIOBIUM
times. If it is not possible to use this coolant, satisfactory results can be obtained with water-soluble oil coolants. It can be welded by resistance, tungsten-inert gas (TIG), plasma arc and electron beam techniques. T o protect the metal from attack by air, resistance welding is carried out under water and the TIG method is best performed in a chamber of argon. The latter three methods produce ductile welds that equal the base metal in most of its characteristics. 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.
Corrosion Resistance Niobium like tantalum relies for its corrosion resistance on a highly adherent passive oxide film; it is however not as resistant as tantalum in the more aggressive media. In no case reported in the literature is niobium inert to corrosives that attack tantalum. Niobium has not therefore been used extensively for corrosion resistant applications and little information is available on its performance in service conditions. It is more susceptible than tantalum to embrittlement by hydrogen and to corrosion by many aqueous corrodants. Although it is possible to prevent hydrogen embrittlement of niobium under some conditions by contacting it with platinum the method does not seem to be broadly effective. Niobium is attacked at room temperature by hydrofluoric acid and at 100°C by concentrated hydrochloric, sulphuric and phosphoric acids. It is embrittled by sodium hydroxide presumably as the result of hydrogen absorption* and it is not suited for use with sodium sulphide. Atmospheric Niobium like several other refractory metals is extremely reactive with atmospheric oxygen. It will in fact react with air at temperatures as low as 200°C9 although reaction does not become rapid until temperatures above red heat (about 500°C) are reached; at 980°C the rate is 0.05 mm/h" and at 1200°C the rate is 300 mm/h". It is not attacked by oxygen at 100°C but the attack is catastrophic at 390°C. At lower temperatures a thin adherent oxide film is formed on the surface of the metal, but at higher temperatures, above red heat, the oxide diffuses rapidly throughout the metal with consequent embrittlement. At elevated temperatures the metal reacts with all the common gases including nitrogen (300-400"C), water vapour (300"C), carbon dioxide, carbon monoxide and hydrogen
(250°C). Protection of niobium and its alloys from oxidation in air is accomplished by coating, e.g. with zinc deposited by holding in zinc vapour at 865"Ct2or coating with a layer of chemically stable oxide, nitride or silicide. Silicide coatings applied by pack cementation, fused slurryt3 or by electrolytic methods have been found to be one of the most effective means of preventing oxidation of the metal. Water The corrosion resistance of pure niobium in water and steam at eievated temperatures is not sufficient to allow its use as a canning material in water-cooled nuclear reactors. Alloys of niobium with molybdenum, titanium, vanadium and zirconium however have improved resistance and have possibilities in this application. Whilst the Nb-10Ti-10Mo alloy offers
NIOBIUM
5:27
the best corrosion resistance the Nb-7V alloy seems more practical on the basis of weldability. It also has good high-temperature strength properties. AcidsLo*'6'6Niobium is resistant to most organic acids and to mineral acids especially under oxidising conditions, Figs. 5.5 to 5.7 show the corrosion behaviour of niobium in laboratory tests in various concentrations of sulphuric and hydrochloric acids at the boiling point and at 190°C and 250"C, and in phosphoric acid at the boiling point. It has excellent resistance to nitric acid, the rate of attack in 70% acid at 250°C being only 0.25 mm/y. In dilute sulphurous acid at 100°C the corrosion rate is 0.0125 mm/y, but in concentrated acid at the same temperature it is greater than 0.25 mm/y.
Sulphurrc acid (%) Fig. 5 . 5
Niobium corrosion in sulphuric acid"
Alkalis's l 4 Though niobium is not attacked by most alkalis at room temperature it is seriously attacked at 9 8 ° C and severe embrittlement is obtained in concentrated alkali at room temperature and virtually all alkalis at 98°C. See Table 5.12 for detailed corrosion rates and embrittlement ratings. There is evidence to show that the corrosion product when niobium is attacked by sodium hydroxide is Na8Nb60,,. I 8H20. salt^'^^''^'^ Tests on niobium have only been carried out in a limited number of salt solutions; however, in the main niobium exhibited similar resistance to tantalum in most salt solutions, and like tantalum it is attacked by salts that hydrolyse to form alkalis. "3
5:28
NIOBIUM
Fig. 5.6 Niobium corrosion in hydrochloric acid Is
0
IO 20 30 Hydrochloric acld (%I
LO
. E
E
I
ai
2
C
0 0
Fig. 5.7 Niobium corrosion in boiling phosphoric acid l 6
L L
0
V
0
20
LO
60
80
Concentration of H3P0, (%)
Gases9. 17. 19.20 It is unattacked by most common gases, e.g. nitrogen, hydrogen, oxygen, carbon dioxide, carbon monoxide and sulphur dioxide (wet or dry) up t o 100"C, and it is inert to chlorine and bromine (both wet and dry) to 100°C. It is, however, attacked by nitrogen at 300-400"C, hydrogen at 250"C, oxygen at 200"C, carbon and carbon-bearing gases at 1200-1 400°C and by chlorine at 200-250°C.
5:29
NIOBIUM Table 5.12
Corrosion in alkalis8* ~~
Reagent
Concentration
NaOH
(@Jo)
1 5
Na, CO, K2C03
Na2PO, Na2S NaOH and Na, S NaOH
(W
Corrosion rate
(mm/y)
10 20 10 20 25 9
98 98 98 98 98 98 98 98 98 98 98
0.74 1.17 2.00 0.60 2.56 1.63 I .60 2.90 2.46 1.34 0.09
9
98
4.15
10
KOH
Temperature
1
5
KOH
Molten Molten
Embrittlement rating
B C C A
C B C C C B A
B Severe attack at 535°C Dissolves metal at 360°C
Nore. Embrittlement ratings were obtained by bending a wire corrosion-test-specimen and the following notations were used:
A wire unbroken when sharply bent.
B wire broken when sharply bent. C wire broken when handled or slightly bent.
Liquid Metals2'
Bismuth Niobium is resistant to bismuth at temperatures up to 56OoCz2 but is attacked at higher temperature^^^-^' and is therefore not considered a suitable container for handling liquid bismuth even under oxygen-free conditions26. Furthermore, the stress-rupture properties of niobium are significantly lowered when the metal is tested in molten bismuth at 8 1 5 ° C 2 4 * 2 7 . Gallium It is slightly less resistant than tantalum to gallium, showing good resistance at temperatures up t o 400°C but poor resistance above 450°Czs-30. Lead Although subject t o slight penetration at 980°C it shows no detrimental effects in stress rupture tests when tested in molten lead at this temperature*' or at 8 1 5 ° C 2 4 . It is highly resistant to mass transfer in liquid lead as indicated by data obtained in tests at 800°C with a thermal gradient
of 300°c31. Lithium Niobium has good resistance to molten lithium at temperatures up to 1 0 0 0 ° c 2 8 * 3 2 .
Mercury In static tests niobium shows good resistance to mercury at temperatures up to 6OOoCz8. Sodium, potassium and sodium-potassium alloys Liquid sodium, potassium or alloys of these elements have little effect on niobium at temperabut oxygen contamination of sodium causes an tures up t o 1 000°C28*33*34, increase in c ~ r r o s i o n ~Sodium ~ * ~ ~ .does not alloy with niobium3'. In mass transfer tests, niobium exposed t o sodium at 600°C exhibited a corrosion rate of approximately 1 mgcm-2d-1. However, in hot trapped sodium at 550°C no change of any kind was observed after 1 070 h38.
5:30
NIOBIUM
Thorium-magnesium In static tests the thorium-magnesium eutectic had no appreciable effect on niobium at 850°C39. Uranium Short-term tests indicate that the practical upper limit for niobium as a container material for uranium is about 1 400°C40. Niobium is dissolved in a uranium-bismuth alloy in less than 100 h at a temperature of 800"C4'. Uranium eutectics with iron, manganese or nickel, corroded niobium at 800"C42and 1 000°C43.It is significantly attacked by uraniumchromium at 1 0oo"C". Zinc Molten zinc is reported to attack niobium at a significant rate at temperatures above 450°C45.It is attacked by zinc at 600°C and shows increasing solubility with temperature up to 850°C. Galvanic effects If niobium is cathodic in a galvanic couple the results can prove disastrous because of hydrogen embrittlement. If niobium is the anode in such a couple it anodises so readily that no damage occurs and the galvanic current drops to a very low value due to the formation of an anodic oxide film. Anodic oxide formation Lakhiani and S h r e i P have studied the anodic oxidation of niobium in various electrolytes, and have observed that temperature and current density have a marked effect on the anodising characteristics. The plateau on the voltage/time curve has been shown by electron microscopy to correspond with the crystallisation of the oxide and rupture of the previously formed oxide. It would appear that this is a further example of 'field recrystallisation'- a phenomenon which has been observed previously during anodisation of tantalum4'. No significant data on the galvanic behaviour of niobium are available; however, its behaviour can be expected to be similar to tantalum.
Alloys of Niobium Niobium-Tantalum Niobium and tantalum form solid-solution alloys which are resistant to many corrosive media and possess all the valuable properties of the pure metals. This could have great practical value since in a number of branches of technology it might permit the replacement of pure tantalum by a cheaper alloy of niobium and tantalum. Miller48 and Argent49reported data on the resistance of the niobium-tantalum system, but the tests were only carried out under mild conditions and the data have only limited significance. However, Gulyaev and Georgieva l6 and Kieffer, Bach and Slempkowski carried out tests at elevated temperatures and their work indicated that the corrosion rates of the alloys are substantially that of tantalum provided the niobium content does not exceed 50%. Niobium-Zirconium Nb-O.75Zr has excellent mechanical properties and similar corrosion resistance to pure niobium; higher zirconium concentrations reduce the corrosion resistance. Niobium-Titanium
Nb-8Ti exhibits unusual behaviour: although the
S:31 corrosion resistance is slightly lower than the pure metal it shows no sign of NIOBIUM
embrittlement in sulphuric and hydrochloric acids. The higher the titanium content the lower the corrosion resistance.
Niobium-Zirconium-Titanium Niobium alloys containing zirconium and titanium have improved resistance to high-temperature water 51 and have been evaluated for use in pressurised-water nuclear reactors. Niobium-Vanadium The presence of vanadium reduces niobium’s corrosion resistance to most media. The alloy containing 12.6 at. %V however has excellent resistance to high-temperature water and steam, and this property and the alloy’s relatively low neutron cross section give it considerable potential for nuclear applications. Niobium-Molybdenum The addition of molybdenum to niobium within the solid solution range gives improved corrosion resistance to hydrochloric and sulphuric acids.
Industrial Applications of Niobium Nuclear Niobium finds use in some nuclear reactors on account of its compatibility with uranium and liquid sodium/potassium at fast reactor temperatures. Impressed-current cathodic-protection anodes Niobium has, a high anodic breakdown potential (100V in sea water), a good electrical conductivity (13% that of Cu), good mechanical properties and anodises readily forming an adherent passive oxide film. These properties have led to it being used as a substrate for platinum in impressed-current cathodic-protection anodes for use in high-resistivity waters and other situations where high driving potentials are required to obtain good current spread. Niobium has the advantage over tantalum in that it is less costly, and its cost can be decreased by using a composite electrode with a copper core that also increases the conductivity of the anode5’. Capacitors Niobium’s electrical properties have also led to its investigation as a capacitor material; however, as far as is known there has been no significant commercial application of the material in this field. 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. Electrical Niobium is finding growing use in components for high-pressure sodium lamps. Miscellaneous Niobium also finds use in satellite launch vehicles and spacecraft and one of the principal applications for niobium-base alloys is in the production of super-conducting devices.
5:32
NIOBIUM
Recent Developments Corrosion and other properties of niobium have been reviewed in Symposia held in 198lS3and 198254,and in updated suppliers' l i t e r a t ~ r e ~ ~ - ~ ~ . Wider application would result from improving the oxidation resistance of niobium and its alloys at elevated temperature. Oxidation kinetics are parabolic to paralinear over the range 400 to 600°C and linear from 700 to 900°C57,although oxidation rate is irregular in the range 600 to 81OoCs8. In contrast the kinetics of nitriding are parabolic over the range 400°C to 1100°Cs7.At room temperature the oxidation of niobium in oxygen is logarithmic and pressure dependents9. The oxidation rate of niobium in air from 800°C to above 1000°C can be decreased by alloying e.g. with hafnium, zirconium, tungsten, molybdenum, titanium or tantalumms6'.However, the preferred fabricable alloys still require further protection by coatingm. Ion implantation improves thermal oxidation resistance of niobium in oxygen below 500"C6*. In hydrochloric acid at temperatures up to lOO"C, the corrosion rate decreases with time and ferric iron c~ncentration~~. The presence of air does not affect the general corrosion rate but in 1 0 acid ~ it promotes pitting attack, which also arises in chloride-containing methanolic solutions in the absence of sufficient water to effect passivationu. Alloying niobium with 2.5% or more of tantalum significantly decreases corrosion rates in hydrochloric acid65. Niobium is resistant to pitting and general corrosion in hydrobromic acid up to the azeotropic concentration of 47 wt% and 124°C; the presence of free bromine enhances passivity@. Anodic oxide film properties depend upon ion concentration in acid chloride67and in alkaline6*solutions; films are more compact and crackfree in acid solution69.Alloying with more than 47% of nickel gives good resistance to hydrogen embrittlement in potassium hydroxide solution7'. Cathodic protection applications in fresh water include use of ferritecoated niobium7', and the more usual platinum-coated niobium72. Platinised niobium anodes have been used in seawater, ~nderground'~ and in deep wells73*74 and niobium connectors have been used for joining current leads". Excellent service has been reported in open-seawater , where anodic potentials of up to 120V are not deleterious, but crevice corrosion can occur at 20 to 40V due to local surface damage, impurities such as copper and iron, and under deposits or in mud7'. Recent information on the behaviour of niobium in molten salts is sparse and confined to a few specific, mixed-salt environment^^^. J. BENTLEY I.R. SCHOLES REFERENCES 1. Lyman, T., Metals Handbook, A.S.M. (1961)*
2. Hampel, C. A., Rare Metals Handbook, Reinhold, 2nd edn (1961)* 3. Quarrel, A. G., Niobium, Tantalum, Molybdenum and Tungsten, Report of Conference, University of Sheffield (1960)* These references can be found collectively in Properties of Refractory Metals, by S . J . Burnett, U.K.A.E.A. Research Report No. AERE R4 657. H . M . S . 0 (1969).
NIOBIUM
5:33
4. Krikorian, 0. H., ThermalExpansion of High TemperatureMaterials, UCRL 6 132, Sept. (1960). 5 . MacDonald, R. N. and Boucom, H. H., Nucleonics, 20 No. 8, Aug., 158 (1962)* 6. Mordike, B. L., J. Inst. Metals, 88 No. 6, 272 (1960)* 7. Chelius, J., Machine Design, March I (1962); 8. Tingley, I. 1. and Rogers, R. R., ‘Corrosion of Niobium and Tantalum in Alkaline Media’, Corrosion, 21 No. 2. 132 and 136, April (1965) 9. Balke, C. W., in Corrosion Handbook (Ed. H. H. Uhlig), 620-621 and 720-722, Wiley ( 1948) 10. Macleary, D. L., ‘Testing of Niobium and Niobium Alloys’, Corrosion, 18, 67t-69t. Feb. ( 1962) 1 I . Jaffee, R. J., Proceedings on an International Symposium on High Temperature Technology, Asilomar, California, 1959, McGraw Hill, New York, 61 (1960) 12. Wehrmann, Corrosionomics, Fansteel Metallurgical Corporation, Sept. (1956) 13. Priceman, C. and Soma, L., Development of Fused Slurry Silicide Coatings for the Elevated Temperature Oxidation Protection of Niobium and Tantalum Alloys, Report AFML-TR-68-210, Sylvania Electric Products Inc., Dec. (1968) 14. Cox, F. G., Niobium Welding and Metal Fabrication, 352-358, Oct. (1965) 15. Bishop, C. R., ‘Corrosion Tests at Elevated Temperatures and Pressures’, Corrosion, 19 No. 9, Sept., 308t-314t (1963) 16. Gulyaev, A. P. and Georgieva, I. Ya., Zashchita Metailov, 1 No. 6, 652-657, Nov.-Dec. ( 1965) 17. Technical Data on Fansteel Niobium, Bulletin TDB, Fansteel Metallurgical Corporation 18. Corrosion Tables of Special Materials and Rare Metals, Jacob and Korves GmbH 19. Meyll Shpeydel, Collection Nioby i Tafital (Nb and Ta), edited by 0. P . Kolchina (1960) 20. Gulbransen, E. A. and Andrew, K. F., Trans. A.I.M.E., 188, 586-599 (1950) 21. Barto, R. L. and Hurd, D. T., Research and Development, 26-30, Nov. (1966) 22. Stoughton, L. D. and Sheehan, T. V., Mechanical Eng., 78, 699-702 (1956)t 23. Lloyd, E. D. in Plansee Proceedings 1958-High Melting Metals, Metallwork Plansee AG, Reutte Tyrol, 249-256 (19S9)t 24. Parkman, R. and Shepard, 0. C., US Atomic Energy Commission Publication No. O R 0 45, June I 1 (1951)t 25. Frost, B. R. T. and Addison, C. C., et al., in Proceedings of Second United Nations International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1958, 7, Reactor Technology, 139-1657 26. Parr, G. W. and Graham, L. W., Bull. Inst. Metals, 4, 125-126, Dec. (1958)t 27. Grassi, R. C., Bainbridge, D. W. and Harman, J. W., US Atomic Energy Commission Publication No. AECU 2 201, July 31 (1952)t 28. Miller, E. C., Chapter 4 of Liquid Metals Handbook, US Atomic Energy Commission, Navy Dept., Washington, D.C., 144-183 (1952)t 29. Wilkinson, W. D., U S Atomic Energy Commission Publication No. ANL-5027, Aug. (1953) 30. Jaffee, R. I., Evans, R. M., Fromm, E.A. and Gonser, B. W., US Atomic Energy Commission, Publication No. AECD-3 317 (1949) and Metal Abstracts, 20, 241 (1952)t 31. Cathcart, J. V. and Manly, W. D., Corrosion, 12, 87t-91t (1956)t 32. Cunningham, J. E., US Atomic Energy Commission Publication No. ORNL-CF-51-7135, 78, July 23 (195l)t 33. Reed, E. L., J. A m . Ceram. SOC.,37, 146-153 (1954)t 34. Cottrell, W. B. and Mann, L. A., Nucleonics, 12, 22-25, Dec. (1954)t 35. Wyatt, L. M. and Dickinson, F. S., Welding and Metal Fabrication, 25, 378-385, 396 (1957)t 36. Raines, G. E., Weaver, C. V. and Stang, J. H., US Atomic Energy Commission, Publication No. BMI-I 284, Aug. (1958)t 37. Adams, R. M. and Sittig, M., in LiquidMetals Handbook, Sodium-NAKSupplement, U S Atomic Energy Commission, Navy Dept., Washington, D.C., 14 (1955)t 38. Eichelberger, R. L., U S Atomic Energy Commission Publication No. BNL-489; Proceedings of the French-American Conference on Graphite Reactors, 168-173, Nov. 12-13 (1957)t t These references can be found collectively Wilcy (1963).
In Colunibium and Tonlalum. edited by F . T. Sisco and E. Epremian. Chapt. 8.
5:34
NIOBIUM
39. US Atomic Energy Commission Publication No. ISC-I 118, Semi-annual Summary, Research Report in Engineering for July-December, Ames Laboratory, Ames, Iowa (1958)t 40. McIntosh, A. B. and Bagley, K., J. Inst. Metals, 84, 251-270 (1955-1956)t 41. US Atomic Energy Commission Publication No. ISC-978, Semi-annual Research in Engineering for July-December, Ames Laboratory, Ames, Iowa (1957)t 42. US Atomic Energy Commission Publication No. ISC-607, Quarterly Summary Research Report in Metallurgy for January, February and March, Ames Laboratory, Ames, Iowa (1955)t 43. US Atomic Energy Commission Publication No. ISC-506, Quarterly Summary Research Report in Metallurgy for April, May and June, Ames Laboratory, Ames, Iowa (1954)t 44. US Atomic Energy Commission Publication No. ISC-423, Quarterly Research Report in Metallurgy for July, August and September, Ames Laboratory, Ames, Iowa (1953)t 45. Hodge, W., Evans, R. M. and Haskins, A. F., J. of Metals, 7 , 824-832 (1955)t 46. Lakhiani, D. M. and Shreir, L . L., Nature, Lond., 188, 4 744 (1960) 47. Vermilyea, D. A., J. Electrochem. SOC.,102, 207 (1955) 48. Miller, G. L., Tantalum and Niobium, Academic Press, 328 (1959) 49. Argent, B. B., J. Inst. Metals, 85, 547-551 (1957) 50. Kieffer, R. von, Bach, H. and Slempkowski, I., Werksto~eundKorrosion,No. 9,782-784, Sept. (1967) 51. Dayton, R. W. and Tipton, C. R., Battelle Memorial Inst. Progress Reports: BMI I 324, March I (1959), BMI 1 340, March 1 (1959) and Nuclear Science Abs., 13 Nos. 18 089 and 18 090 (1959)t 52. 'Niobond' and 'Tibond', Marston Excelsior, Wolverhampton, England (1974) 53. Lupton. D., Aldinger, F. and Schulze, K., Niobium in Corrosive Environments, Niobium 81, Proceedings of the International Symposium, San Francisco, edited by Harry Stuart, The Metallurgical Society of AIME, 533-560, (1981) 54. Refractory Metals and Their Industrial Applications. symposium sponsored by ASTM Committee B10 New Orleans, ASTM Special Technical Publication 849 (1982) 55. Columbium (Niobium), Teledyne Wah Chang Albany, P O Box 460,Albany, Oregon. 56. Columbium (Niobium), KBI Division of Cabot Corporation, PO Box 1462, Reading, PA. 57. Strafford, K. N., Corrosion Science, 19, 49-62 (1979) 58. Clenny, J. T. and Rosa, C. J., Met Trans, IIA, 1385-1389 (1980) 59. Crundner, M. and Halbritter, J. Surface Science, 136, 144-154 (1984) 60.Inouye, H., in Reference I, 615-636 61. Babitzke, H. R., Siemens, R. E., Asai, G. and Kato, H., Development of Columbium and Tantalum Alloys for Elevated-Temperature Service, Bureau of Mines Report of Investigations 6558, US Department of the Interior, (1964) 62. Pons, M., Caillet, M. and Galerie, A., Mater. Chem. Phys, 15, 45-60 (1986) 63. Covino, B. S. Jr, Carter, J. P. and Cramer, S. D., Corrosion, 36, 554-558 (1980) 64. Palit, G. C. and Elayaperumal, K., Corrosion Science, 18, 169-179 (1978) 65. Krehl, M., Schulze, K., Olzi, E. and Petzow. G., Z. Metallkde, 74, 358-363 (1983) 66. Uehara, I . , Sakai, T., Ishikawa. H., Ishii, E. and Nakane, M. Corrosion, 42, 492-499 ( 1986) 67. El-Basiouny, M. S., Bekheet, A. M. and Gad Allah, A. G. Corrosion, 40, 116-1 19 (1984) 68. Bulhks, L. 0. S. and D'Alkaine, C. V.. In Proceedings of the 8th International Congress on Metallic Corrosion (Mainz 1981) Frankfurt-am-Main; Dechema (1981) 69. Vijayan, C. P., Claessens, P. L. and Piron, D. L. Corrosion, 37, 170-174 (1981) 70. Sugimoto, K., Belanger, G. and Piron, D. L. Corrosion, 36, 437-441 (1980) 71. Kumar, A., Segan, E. G. and Bukowski, J. Materials Performance, 23, 24-28 (1984) 72. Baboian, R., Materials Performance, 22, 15-18 (1983) 73. Baboian, R., Materials Performance, 18, 9-15 (1979) 74. Toncre, A. C., Materials Performance, 19, 38-40 (1980) 75. Hayfield, P. C. S. Materials Performance, 20, 9-15 (1981) 76. Janz, G. J. and Tomkins, R. P. T., Corrosion in Molten Salts; An Annotated Bibliography, Corrosion, 35, 485-504 (1979)
NIOBIUM
5:35
BIBLIOGRAPHY Meyll Shpeydel, Collection Niobi i Tantul, Ed. 0 . P. Kolchina, 565-571 (1960) Miller, G. L., Tantulum and Niobium, Butterworths. London (1959) Columbium and Tuntalum, Ed. F. T . Sisco and E. Epremian, Wiley, New York and London (1%3) Materials and Design, 74-78, Jan. (1968) Tantulum, Niobium and Zirconium, Murex Ltd., Rainham, Essex