Evaluation of Some Analytical Procedures for Niobium-Base Alloys J. P. McKAVENEY Central Research laboratory, Crucible Steel Co. of America, Pittsburgh 13, Pa. Analytical data for three commercial niobium-base alloys were used to evaluate conventional chemical and vacuum fusion procedures for carbon, hydrogen, and oxygen. Chemical and optical spectrographic: solution procedures developed a t this laboratory are discussed regarding the determination of alloying amounts ( I to 25%) of molybdenurn, tungsten, titanium, and zirconium. Various chemical, optical, and x-ray spectrographic procedures currently used by industry were compared by round-robin analyses of samples from the three niobium alloys. Examination 3f the roundrobin data enables conclusions to b e drawn concerning the elements that will require additicnal analytical method development.
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HE investigation of analytical methods for niobium-base alloys, first begun in this laboratory in November 1959, was necessitated by work under a U. S. Air Force contract to develop manufacturing methods for three commercial alloys (F48-General Electric, D31 and D41-Du Poct). The initial literature survey uncoirered references to methods ( 1 , L) developed a t the Westinghouse Atomic Poww Laboratories, mostly dealing with the determination of trace impurities in high purity niobium. Reed (14) outlined a procedure for the determination of alloying amounts of molybdenum, titanium, tungsten, and zirconium based on the classical separation method of Powell and Schoeller (12). Correspondence with General Electric Co. (7) revealed that an ion-exchange technique based on the work of Hague ( 5 ) coild be used to separate titanium, molybdenum, tungsten, and zirconium in a hydrofluorichydrochloric wid medium. The Union Carbide Xetals Co. (11‘1supplied x-ray methods on the determination of the desired alloying elemer ts. The x-ray method, based on the earlier work of Mitchell (IO).used chemical dissolution, cupferron and cinchonir e precipitation, ignition of the mixed oxides, and fluorescent analyses of a briquet prepared from the ignited residue. In April 1960, Battelle Memorial Institute reported on the determination 0:’ oxygen, nitro-
gen, hydrogen, and carbon in niobium (9). The report was essentially a review, but it contained good reference material for application to the interstitial elements. After the completion of this investigation in July 1961, Elwell and Wood (3) briefly outlined chemical methods for the determination of carbon, oxygen, nitrogen, chromium, iron, molybdenum, nickel, silicon, titanium, tungsten, and zirconium. Because of the close similarity of the methods to those for titanium- and zirconium-base alloys, “only brief notes on the methods applied to niobium are recorded.” The literature survey indicated that the determination of the desired metallic elements in the niobium-base alloys was difficult because of their chemical similarity (Table I). Table I1 contains a summary of atomic properties of the elements which further emphasizes their similar chemical and physical properties. These elements are transition elements. Their two outer principal quantum shells are incomplete and they are characterized specifically by their inThe elements complete d subshell. are members of transition series corresponding t o unfilled 3d, 4d, and 5d orbitals. The transition elements show pronounced resemblance t o each other, particularly in their physical properties. Their oxidation states are very numerous and their compounds are
often highly colored. Furthermore, coordination compounds are the rule and simple compounds are the exception. The (n)d, (n l)s, and (n 1)p orbitals of the transition metals are responsible for the chemical bonding of the various ligands used in compound formation. Ligands such as thiocyanate,.peroxide, or fluoride are used in chemical analysis of niobium-base alloys. The principal emission lines shown in Table I1 result from electronic transitions also involving the (n)d, (n l)s, and (n l)p outer orbitals. However, the x-ray l i e s of columns 6 and 7 result from electronic transitions involving only the innermost or R, L, and M shells of the atom. Many secondary emission lines not shown in Table I1 can be used for analytical
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Table I. Periodic Relationship and Percentage Composition of Alloying Elements in Niobium Alloys
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PA
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Table II.
Element Ti Zr
Atomic Properties of Alloying Elements in Niobium Atpmic Principal X-ray linea, Electronic size, Ionic size, emission lines, A. configuration A. A. A. K L 18 [Ar]3d%2 1 46 0.68(+ 4 ) 3349, 3999, 3361 2 . 7 4 8 ~ ~ 1 3653, 3234, 3642 2.51481 36 [Iir]4d%* 1.57 0.80(+4) 3392, 3438, 3496 O.784ai 6.057 3601, 3557, 3572 0.70oPi 36 ..
Kb
[I
