Table IX.
Sample Niobium metal (Yokosawa Chem.)
Niobium metal (Johnson) Ferroniobium Ta (Nb 61%) _.
+
Analysis of Niobium Metal and Ferroniobium
Amount of Sample Taken, Grams 0,0590 0.0500 0.0500 0.0500 0.0500 0.0500 0.0500 0.1000 0.1000 0.0593 0.0.593 0.0226 0.0226
Amount Ta Found of T a Added, fig, Micrograms Per cent 0 138.8 0.235 0 117.5 0,235 0 118.8 0.238 75.0 ... 192.5 75.0 191.3 ... 125.0 241.3 ... 125.0 242.5 ... 0 300.0 0.30 0 300.0 0.30 0 3025 5.10 0 3040 5.15 0 1160 5.13 0 1150 5.09
Amount Obtained by Subtraction of T a in Sample, fig.
... ...
75.0 73.8 123.8 125.0
... ...
as shon-n in the analysis of niobium metal with a known amount of tantalum added, and also that this procedure gives accurate results. As noted earlier, boron is the only element usually present in iron, steel, and niobium metal, n-hich undergoes a similar color reaction. Tantalum and other elements have no effect on this method. Since a simple method for removal of boron has been found, the present procedure is satisfactory, as the analytical results indicate. From 0.005 to 0.5% of tantalum can be determined without any preliminary separation of tantalum, and the author suggests that this method will also be applicable to a somewhat wider range of tantalum (from 0.001 to 54&) than that described above. LITERATURE CITED
RESULTS AND DISCUSSION
A known amount of tantalum was added to steel of various compositions not containing tantalum, and the determination was carried out by the method mentioned above. Satisfactory results were obtained as listed in Table VII. As indicated by the results in Table VII, a satisfactory determination can also be carried out b y heating the sample containing boron with an excess of hydrofluoric acid to form boron trifluoride, and further by heating with sulfuric acid until white fumes evolve to evaporate boron.
Tantalum was determined in stainless steels containing a known amount of tantalum, and the result of the present analytical procedure was approximately the same as that of spectrophotometric determination using pyrogallol, as indicated in Table VIII. Results of the determination of tantalum in niobium metal, ferroniobium, and niobium metal with a h o l m amount of tantalum added are given in Table TX. It is clear from the results in Table IX that the presence of a comparatively large quantity of niobium does not affect the determination of tantalum
(1) Ikenbery, L., Martin, J. L., Boyer, R. J., AXAL.CHEW25, 1340 (1953). (2) Ishibe, I., Hosoda, K., Higashide, H., Rept. 4846, 19th Committee of Japan Society for Promotion of Science, 1957. (3) Kindman, L., Darn-vert, C. L., White, G., Metallurgia 62, 125 (1960). (4) Palilla, F. C., hdler, N., Hiskey, C. P., ANAL.CHEM.25, 926 (1953). (5) Poluetkov, N . S., Kononenko, L. Z., Lauer, R. S.,J . Anal. Chem. U.S.S.R. 13, 449 (1958). (6) Yana, N., Mochizuki, H., Kajiyama, R., Misaki, T., Rept. 3274, 19th Committee of Japan Society for Promotion of Science, 1954. RECEIVEDfor review July 11, 1961. Accepted February 1, 1962.
Analysis of High-Purity Chromium R.
E. HEFFELFINGER,
E. R. BLOSSER, 0. E. PERKINS, and W. M. HENRY
Analytical Spectroscopy Division, Battelle Memorial Institute, Columbus, Ohio
b A combination chemical-spectrographic method for determining metallic impurities in high-purity chromium i s described. Chromium i s removed from the metallic impurities b y volatilization as chromyl chloride. The remaining solution i s examined spectrographically for elements such as iron, nickel, aluminum, manganese, titanium, vanadium, magnesium, and copper in the 0.1to 30-p.p.m. range. Direct arcing of chromic sulfate i s used for the determination of silicon.
C
a metal used for modern high-temperature applications, has good oxidation resistance. cold workability, high-temperature toughness, and availability. Brittleness, one of its less desirable properties, appears to be related to the impurities present. HROhIIUM,
K h e n the importance of the purity of chromium was first learned, the only satisfactory method for the determination of metallic impurities was the spectrographic analysis by d.c. arc excitation of chromic sulfate which permitted detections in the order of 10 to 50 p.p.ni. Hon-ever, it soon heedme necessary to improve both the detectability and the accuracy of the determination of the impurity elements. To accomplish this, we selected a chemical separation step-volatilization of chromium as the chromyl chlorideprior to spectrographic analysis. The impurities were thus concentrated from a large amount of sample into a small volume of solution free of the matrix material. Then the highly reproducible spark excitation could be used with solution standards to determine these concentrated impurities. Others have
added the separated impurity elements to a powder matrix such as calcium carbonate to handle the very small amount of impurity and then completed the analysis by d.c. arc spectrographic technique ( 2 ) . The solution spark offers greater precision and accuracy because of the inherently higher Irecision of spark and>.sis and because of less handling of thc impurities PROCEDURE
Dissolve 5.lb5.5 grams of chromium in 80 ml. of &I7 hydrochloric acid and dilute in a 100-nil. graduated cylinder to give a chromium concentration of 0.1 gram per ml. The excess above 50 ml.-i.e., 1-5 ml. -may then be tapped off and put into a crucible with 2 nil. of concentrated sulfuric acid, dried, and ignited a t 800°C. to obtain chromic sulfate which is analyzed by ordinary d.c. arc techniques to deVOL. 34, NO. 6, M A Y 1962
621
~~
Table I.
Table II.
Spectrographic Conditions"
ELECTRICAL PAR.4METERS Discharge voltage 15,000 Capacitance 0.007 pf. Inductance 50 ph. Resistance residual Discharges per 240 second Radio-frequency 8 amp. current
Typical Standard Compositions Used with Solution-Spark Spectrographic Analysis (Assuming impurities from 5 grams of Cr are in 5-ml. total volume)
P.P.iM. Each Impurity, Based on Cr 30.0
Standard
10.0
Upper electrode
0.0015 0.0005
50 seconds 50%
SA-1 5 mm. Lucite cup, porous cup or rotating disk '/r-inch diameter pointed electrode with '/&nch radius a t point
Dilute the acid solution with pure water to 5 ml. The sample is now ready for spectrographic examination. The samples are compared with standards by a solution-spark technique (1). The spectrographic conditions are s h o m in Table I. STANDARDS
Typical compositions for standards for impurity elements found in chromium are shown in Table 11. The standards are taken through the same procedure, using the same quantities of reagents as for the samples.
termiiie silicon and other impurities present in detectablp amounts. To the 50 ml. of chromium solution which contains 5 grams of chromium, add 40 ml. of 60Yc pcrchloric acid and 0.13 m g . of cobalt (thc cobalt is added as a 5 m I . tap from 3 ma. of pure cobalt metal dissolved in 5 nil. of concentrated HXOa and diluted to 100 ml.). Heat thc solution gently to fumes of perchloric and until the chromium is oxidized to the scsivalent oxidation state ( d e q red color). Continue heating the solution strongly and add concentrated hydrochloric acid, specific gravity 1.19, a few milliliters a t a time, until the chromium is evolved. This nil1 require about 40 to 60 nil. of hydrochloric acid. Fume off any perchloric acid remaining. Remaining in the beaker from which the chromium was removed are the impurities and a trace of chromium. To the cooled beaker, add 1 ml. each of concentrated sulfuric acid, hydrochloric acid, and nitric acid, and allow to stand for a few hours or overnight to ensure that the impurities dissolve completely.
622
Mn
Fe
0.2
19. 3. 22.
1. 1.2
ACCURACY
-111indication of the accuracy of this method IS given in Table IT' nhich shon s amounts of various elcments rec o i ~ r e dafter addition to a chromium specimen of known purity. -1few elements such as =is, B,and Sn aw partially or completely yolatile a t
1.1 3. 3.2 3.2
ANALYTICAL CHEMISTRY
21.
10.
29. 29.
