1038
ANALYTICAL CHEMISTRY
were plotted to obtain the aiialytical curve. Using this curve, the results obtained from duplicate analysis are shown in Table VI. From the collected data, using the per cent mean deviation a8 a measure of the reproducibility of the analytical procedure, an average mean deviation of 7.5% was obtained. As stated in the beginning, the primary purpose of this investigation was to establish the practicality of working with the 2497.733-boron line. Since for some time analyses of 0.0006% boron and lower have been reported using a conventional prism spectrograph with alternating current arc or pulsating unidirectional arc excitation (18),it is therefore assumed, from consideration of the high degree to which the interference is resolved, that the use of these forins of excitation with echelle spectrographs should result in increased sensitivity. ACKNOWLEDGMENT
The authors are indebted to C. F. Montione for assistance in the experimental work reported in this paper. LITERATURE CITED
(1) Buyanov, X. I-., Lutsenko, -4.V.,and Sorokina, N. S . , Zarodskaya Lab., 13, 447-51 (1947). (2) Corbett, R. B., and Williams, -4.J., Iron Age, 156, 54-7 (1945). (3) corliss, c. H.. and Scribner, B. F,, J . ~~~~~~~h-wdl, B ~
S t a n A r d s , 36, 351-64 (1946).
(4) Dean, R. S., and Silkes, B.. 7363 (1946).
U. S. Bur. Mines Inform. Circ.
( 5 ) Digges, T. G., and Reinhart. F. AI., J . Research Natl. Bur.
Standards, 39,67-I31 (1947). (6) Falkova, 0. B., Compt. rend. acad. sci. U.R.S.S., 48, l i 9 - 8 1 (1945). (7) Gegechkori, N. h l . , and Fal’kova, 0. B., ZacodsknUiz Lab., 1 1 , NO.1 , 71-4 (1945). 31., (8) Grange, R. A , Siens, W. B., Holt, W. S., and Garvey Am. SOC.Metals, Preprint KO.5 (1949). (9) Harrison, G. R., J . O p t . Soc. Amer., 39, 522-8 (1949). (10) Harvey, C. E., “Spectrochemical Procedures,” Chap. 111, Pasadena, Calif., ;\pplied Research Laboratories, 1950. (11) Irish, P. R., J . O p t . Soc. Ainer.. 35, 226-33 (1945). (12) Kirchgessner, W. G., Reo. Sci. Znstr., 22, 289-92 (1951). Zaaodskaya Lab., 12, 574(13) Lutsenko, A . V . , and Sorokina, K.N., 6 (1946). (14) Masi, O., Spectrochim. Acta, 1, 462-70 (1940). (15) Metallurgical Advisory Board, Metal Progr., 81-92 (1951). (16) Pretorius, P. J. C., J . S . A f r i c a n Chem. Inst., 1, 81-3 (1948). (17) Prokof’ev, V. K., Dolzladg A k a d . Nauh S.S.S.R., 50, 185-7 (1945). (18) Rozsa, J. T., and Zeeb, L. E.. Steel, 131, 92, 94, 97 (1952). (19) Shurkus. A A . . and Kirchnessner. W. G.. ANAL.CHEW..23. 685 (1951) . (20) Soc. Automotive Engrs., Inc., 29 West 39th St., Yew York, I-. Y . , 1947. (21) Washburn, T. S . , Proc. Conf. Natl. Open Hearth Comm.. I r o n Steel D i c . , Ani. Inst. X n i n g AIet. Engrs., 26, 153-4 (1943). ~ ! a ,) \f”oodruff,J . F.9 J . O p t . SoC. Amel.., 40, 192-6 (1950).
’r.
RECEIVED f o r review January 8 , 1933. Acceiited ;\pril 10, 19.53.
Spectrochemical Determination of Magnesium, Iron, Silicon, and Manganese in Titanium Metal H. 4.HELLER AND R. W. LEWIS Bureau of Mines, U . S. Department of the Interior, Boulder City, A-ei.. During an extensive research program involving the production of high-purity titanium metal, the need arose for reasonably rapid and accurate methods for the determination of the major impurity elements in this material. “Wet” chemical methods were time-consuming and often inaccurate in the concentration ranges encountered. A search of the literature did not disclose suitable spectrochemical methods. The spectrochemical methods reported
T
HE production of high-purity ductile titanium by methods proposed by Kroll ( 7 ) and developed by the U. S. Bureau of
Mines ( 3 , 4,10) is rapidly expanding in commercial output. The Electrometallurgical Experiment Station, Boulder City, Sevada, is conducting an extensive research program in an effort to improve the process and to lower the cost, of the metal. In connection \Titti this work. efforts are continually being directed to the development of improved methods of analysis. Chemical determinations of the main impurit,y elements in titanium metal are very time-consuming and unreliable for the low range in which these inpurities are generally found. Spectrographic determinations of these impurities made directly on samples of metal are subject to wide variation, because the impurit,ies generally tend to segregate, so that the very small portion of the metal actually excited may not be an “average” sample. By dissolving a comparatively large sample, the sampling error is diminished, and considerat,ions of variation of matrix or metallurgical history are avoided by excitation of such a solution. .-i spectrochemical procedure \Tap then developed which made
here permit the determination of the four major impurity elements found in ductile titanium: magnesium, 0.04 to 0.17q0; iron, 0.03 to 0.20%; silicon, 0.02 to 0.12%; manganese, 0.01 to 0.05%. These methods should be of value to any laboratory engaged in the analysis of high-purity titanium and having similar equipment. The same techniques, w-i th appropriate modifications, should also find application in the analysis of titanium alloys.
possible the determination of the four major impurity eleniriits in a single sequence of operations. These methods were deyeloped t o provide accurate, reasonably rapid analyses and are based on excitation of a dilute hydrochloric acid solution of the metal using a c*ommercially available solution-escitation apparatus ( 1 ). For some time, magnesium, iron. arid manganese determinatiom were made on samples dissolved in dilute sulfuric acid, employing a sample preparation similar to that used by Peterson (9). Attempts to determine silicon in thwe solutions met xvith little success because of poor reproducihility. It was later found that much better results were ohtairied n-hen hydrochloric acid solutions were used, and that iron could be determined to a l o ~ e r limit of about, 0.03yo in chloride solutions as compared xith a lower limit of 0.075yo when sulfate solutions were used. This increased sensitivity also permitted the use of spectrum analysis S o . 1 plates for the iron determination, whereas it had previously been necessary to use Type 111-0 plates for greater sensitivity despite the inherent superiority of spect,rum analysis Fo. 1 in quantitative work. Finally, working curves for hydrochloric
V O L U M E 2 5 , NO. 7, J U L Y 1 9 5 3 acid sample preparations were also established for the magnesium and manganese determinations because of t'he economies in time and materials that mould result from the use of a single sample preparation. APPARATUS
The spectrograph used for this work was a Baird 3-meter grating instrument with modified Eagle mounting ( 2 ) ,the grating having an average reciprocal linear dispersion of 5.5 A. per mm. in the first order. A slit n-idth of 25 microns was used and the spectral region for all determinations was 1870 to 3290 .$., first order. The spark stand was the Cniversal type manufactured by Applied Research Laboratories. The upper electrode was of Special grade high-purity graphite, 0.25 inch in diameter by 2 inches long, tapered t o a hemispherical point having a '/ls-inch radius. These electrodes were reshaped after each exposure until too short for further use. The lower electrode, or excitation surface, consist,ed of a disk of "Special" grade high-purity graphite, 0.5 inch in diameter and l / g inch thick, with a '/S-inch hole in the center. Disks of t>hesedimensions and quality are availalde commercially. In this laboratory they are cut from 0.5inch-diameter graphite rods 10 inches long. The machining operations are performed on a small lathe, using a very thin cut-off tool to minimize waste. During excitation, a disk is mounted on a Zraphite spindle and nd with approsimately onein the sample solution which tion boat. The spindles are 0.25-iricli-diameter graphite rods to dimensions shown in Figure I . The "necked" portion of the spindle provides clearance for the edge of the combustion boat. To ensure a friction fit with the drilled disks, the ends of these spindles are turned to exactly 0.125-inch diameter, as measured with a micrometer calipcr. The machined ends of these spindles are then immersed for :t few minutes in a bath of high-melting-point wax to make them acid-repellent. This prevents the ordinarily porous graphite from carrying acid t o the metal chuck of the solut.ion excitation apparatus, and the spindles can be used repeatedly by wiping clean between samples. A fresh disk is used for earh exposure. The wax-impregnated spindles are fitted with spatter shields. as illustrated in Figure 1, cut from '/ginch neoprene stock with laboratory cork borere. These shields protect, the metal chuck from spattered acid solution. The original panel of the solution-escitation apparatus, through which the spindle protrudes, \vas altered by lathe-boring a 1-inch-diameter opening, concentric Kith the original aperture, to a depth of 0.25 inch to accommodate the spatter shields.
1039 form, and the platform is raised until the solution level alinost reaches the graphite spindle. Other equipment includes: a spherical quartz condensing lens, positioned to focus the spark-discharge on the grating. Power, Multisource (6) with variable settings for the various determinations as discussed below. Polarity of the sample is positive. Analytical gap, 4.5 mm. Photographic plates, Eastman, spectrum analysis KO.1, Photographic processing, 5-minute development in Eastman formula D-19 a t 20' C. with continuous agitation. Plates are then treated in stop bath, Eastman formula SB-5, for 1 minute, followed by Lxation in Eastman formula F-5, with occasional agitation for approximately twice time to clear. Plates are washed in running tap water at pevailing temperature for 15 minutes. Forced drying in warm air is used after exress a a t e r has been removed with viscose sponge.
PYREX G L A S S
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ET COMBUSTION BOAT
7
Figure 2. Analytical Gap, Showing Placement of Mist-Removal Tube
GRAPHITE, 0 . 5 0 " O.D.
Densitometer, Leeds & Sorthrup I
