Spectrochemical Determination of Iron, Magnesium, and Manganese in Titanium Metal MAURICE J. PETERSON, Bureau of Mines, College Park, M d . A spectrochemical method for the determination of iron, manganese, and magnesium in titanium metal is described. A sulfuric acid solution of the metal is placed in a porous cup electrode, and excitation is by means of controlled Multisource unit. Average deviations from chemical values are approximately *S% for iron and manganese in the concentration rangee 0.08 to 0.5% and 0.02 to 0.2%, respectively. Average deviation for magnesium is 1 6 % in the range of 0.05 to 0.7%. The method has been useful for testing sample lots.
T
ITANIUM metal promises to become an important constructional and engineering material, owing to its unique combination of desirable properties, such as high strength, lightness, high melting point, and corrosion resistance. Moreover, there is an abundant supply of raw material. In conqection with the Bureau of Mines physical metallurgy program on the study of titanium and its alloys, a spectrochemical method of analysis of high-purity titanium has been applied to determination of iron, magnesium, and manganese. This investigation is part of a continuing program of development of new and improved methods of analysis and evaluation of minerals, mineral products, mehls, and alloys conducted by the Physical and Chemical Section of the Eastern Experiment Station, College Park, Md.
Table I. Sample
1064 1064-.4 1064-B 1064-C 1064-D 1001 1001-A
1001-B 1001-c
Data for Preparing Standard Samples
Per Cent Added Fe Mn Mg None None None None None 0.05 None None 0.15 None None 0.35 None None 0.70 None None None 0.05 0.05 None 0.15 0.15 None 0.35 0.35 None
Final Per Cent Mn Mg 0.10 ... 0.01 0.10 ... 0.06 0.10 ... 0.16 0.10 ,. 0.36
PREPARATION OF SAMPLES
Samples of the metal submitted for analysis were either in the form of powder (approximately 60 mesh) made by the reduction of titanic chloride with magnesium, or sheets made by consolidating this powder by the process of sheath rolling (8). Small turnings were cut from the flat surfaces of the sheath rolled samples, using a carbide-tipped cutter in the tool post of a lathe. Care was taken to discard the first 0.025 inch of metal removed from the surface, inasmuch as tests had shown that iron contaminates the surface as a result of the sheath rolling. Five hundred milligrams of powder or turnings were dissolved in 22 ml. of 25% sulfuric acid with the aid of heat. Boiling should be avoided, as it may cause precipitation of the titanium. When solution was complete, 10 drops of concentrated nitric acid were added to oxidize the titanium to the T i + + + +condition. The solution was again heated to remove excess 'oxides of nitrogen and allowed t o cool. Three grams of tartaric acid were then added to stabilize the titanium. Finally, the solutions were made up to a final volume of 25 ml. Solutions carefully prepared in this manner have shown no evidence of precipitation after several months.
Fe
0.10 0.098 0.148
0.248 0.448
.
0:023 0.073 0.173 0.373
0.71 0.42 0.42 0.42 0.42
PREPARATION O F STANDARDS
Two samples of chemically analyzed metal were used as start: ing material for the preparation of a series of standards. Standard sample 1064 contained 0.01% magnesium, a.value much less than that to be expected in bhe samples submitted for spectrochemical analysis. Standard sample 1001, containing 0.098% 1
Table 11. Lines Employed for Analyzing Titanium Element Element Line F e I1 2599.40 Iron M n I I 2593.73 Manganese Mg I1 2795.53 Magnesium a Index is concentration at which standard line are equal.
1
I-
Internal Concn. Standard Line Range Index" 0,084.5 0.42 Ti I1 2572,65 0.02-0.2 0.10 T i I1 2572.65 0.05-0.7 0.12 Ti I1 2811.94 intensities of analytical line and internal
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M e 2795.53 Ti
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2848.94
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0.1
LOG IN TENSITY
0.3
0.5
RAT10
Figure 1. Working Curve for Magnesium 1398
1
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w Essentially, the techniques are those recently described by Feldman (3,4 ) for the analysis of solutions by the porous cup electrode method. Gassman and O'Neill ( 5 ) have successfully applied the method to determination of phosphorus and metals in lubricating oils. Keirs and Englis (7) have described a similar procedure which utilizes a glass reservoir, one end of which is drawn to a pointed capillary. A carbon electrode is attached to the capillary, and liquid is fed into the spark through a small channel in the carbon. Recently Colin and Gardner (2)have adapted this procedure to determination of alumina in steel. Conventional methods of spectrographic analysis, such as the sparking of self-electrodes or Petrey disk samples, are not applicable because i t is not feasible to prepare a cast sample. At the temperature required for melting (3140' F.), titanium is very reactive; melting must be done under an inert atmosphere.
1
1
1399
V O L U M E 2 2 , N O . 11, N O V E M B E R 1 9 5 0 Tahlr 111.
"
Titanium Lines Used for Calibrating Emulsion
T i 1 2632.42 Ti I 2541.92 Ti I 2661.97 Ti I 255.5.99" Ti I1 2713.76 Ti 2572.65" T i 1 2727.42 Ti I1 2581.72 Ti I 2736.68 T i 1 2599.92 Ti I1 2 7 8 6 . 0 0 Ti I 2605.15 T i I1 2836.62 Ti I 2611 29 Ti I 2619.94 Classified by Riissell (9, 1 0 ) . BR lines of the spark spectriiin.of titanium.
Tahle 1V. Analyses of Different Solutions of Same Sample >I& % Fe, % 0.29 0.092 0.30 0.091 0.30 0.095 0.31 0.098 Each result is average of 2 determinations. Soliltion
%Inl % 0.029 0,029 0.030 0.028
iron :mil 0.023% nianganesc:, served as starting material for these t\vo elements. Five hundred milligram portions of each of these s:iniples were weighed and treated as described under sample preparation. Before making up to final volume, measured :tniounts of iron and manganese in 2570 sulfuric acid were added to three of the 1001 samples. In like manner, magnesium was :~tldedto four of the 1064 solutions. I n each instance, the amount :ttlded was calculated as per cent of the weight of t,itanium. The percentage? of the three elements added are summarized in T:lt)I? I . The line pairs used and the concentration ranges. are listed in T:tble 11. Chemical values of samples later suhmitted for analysis extended the ranges for iron arid manganese to 0.08 and 0.02%, respectively.
The equipment and opwnting c~~nditions used are lislrtl follows:
Spectrograph, grating, Eagle mounting (I ), 5.5 A. pel' nim. Slit width 100 microns. Grating aperture 1.25 inches. Region 2445 t o 3095 A,., second order. Condensing lens, quartz, spherical, ID = 25-cm. irna6e of discharge focused on grating. Upper electrode, high-purity graphite, 0.25 inch i n diameter, 1.125 inches long. Hole drilled with S o . 30 twist drill to within 1 mm. of flat bottom. Electrode held in spark stand with open end up. Lower electrode, high-purity graphite, 0.125 inch in diameter, pointed in p e n d sharpener. Gap, 2 mm. Spark stand, Bausch & Loinl) spring-clamp type. Tips wrapped with platinum foil. Power, Multisource unit ( 6 ) condenser discharge oscillating. Capacit>ance 2 pf. Inductance 50 ph. Resistance 0.4 ohm. Phase angle 95". Output potential 940 volts. Charge us. discharge 180". Exposure, 3 seconds for magnesium, 30 seconds for iron and manganese. Photographic plate, Eastman type 111-0. Development, 5 minutes itt 65' F., Eastman Forniuh IIK-50, continuois agitation. Densitometer, Baird noni,ecortling. PRECISION AND ACCURACY
As a check on the precision of the method, 29 single deterniinations using the same solution were made for iron arid manganese and 25 determinations for magnesium. Exposures were made on four plates and the per cent standard deviations were calculated. These were 7.6, G.7, and 6.8%, respectively, for iron, manganese, and magnesium.
PROCEDURE AND DISCUSSION
The sample electrodes are prearced at 5 amperes for 5 seconds with a direct current are before use. This makes them porous and a s s u m more uniform feeding of the liquid through the graphite. The upper electrode is filled by means of a glass pipet with a rubber bulb. Care must be taken to expel the liquid while the pipet tip is touching the bottom of the electrode cavity; otherwise, bubbles may form in the solution, causing- it to spatter during sparking. \Vith the type of discharrrr used. i t is neoessarv to connect the sample electidde to the negative 'terminal of {he hfultisource. Otherwise the porous cup electrode becomes too hot and the liquid boils over. After the electrode is filled and the gap adjusted the Multisource power is turned on for 5 seconds with the shutter closed. This is followed by a waiting period of approximately 15 seconds to allow the liquid to seep through the graphite. The lower electrode is replaced with one having a freshly prepared tip, and after a 8-second prespark, the shutter is opened for 3 seconds to record the spectrogram for the magnesium determination. The 3-src.ond prespark volatilizes any excess li,quid that may have seeped through the graphite. .4fter the plate holder is racked and the counter electrode replaced, the same sample electrode is presparked again for 3 seconds, followed 6y a 3Gsecond sparking to record the spectrogram for the iron and manganese determinations. It is important to replace the c'ounter electrode with one having a freshly prepared tip for each exposure, as the formation of titanium dioxide on the tip will cause erratic results. Each plate is cnlibiated by means of the group of titanium lines listed in Table 111, the relative intensities of which were determined from calibrations made with a direct current iron arc and step sector. Densitometer readings of the selected titanium lines are taken from one of the sample spectrograms exposed for 30 seconds. The data are treated in the usual manner by converting logintensity ratios to Concentration by means of the analytical curves shown in Figurea 1 and 2. S o background corrections are necessary. Averages of duplicate determinations are reported for each element. Two control standards are exposed in duplicate on each plate.
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0.501
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Mn 2 5 9 3 . 7 3 Ti 2572.65
.015
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L O G INTENSITY Figure 2.
0.1
0.3
RATIO
Working Curve'for Iron and Manganese
,To check for possible segrcgatiori, analyses were made on different solutions of the sitme sample. Results are as shown in Table IV. Deviations between the results of webchemical and spectrochemical determinat,ions are summarized in Table V.
1400
ANALYTICAL CHEMISTRY Table V. Accuracy of Results Element Iron Manganese Jlagnesium
No. of
Detns. 17 20 22
Conen. Range 0.080-0.13 0.020-0.040 0.27 -0.50
%.A?.
Deviation 7 8
8.2 5.6
The average deviations of approximately 8%’for iron and manganese and 5.6% for magnesium are considered adequate for routine testing of sample lots. Because there is considerable heating of the sample electrode nheii the Multisource is used, exposures must be of relatively short duration to avoid spattering of the solution. A spark stand equipped with water-cooled electrode holders would minimize heating of the sample electrode. The precision could probably be improved by using a conventional high voltage spark source, because this would allow one to use longer exposure periods, a slower optical system, and a slower emulsion. Use of a simple electrode with a truncated cone bottom similar t o that described by Scribner and Ballinger for the analysis of bronzes (11)would also probably improve the precision of the method. ACKNOWLEDGMENT
This investigation was conducted under the general direction of Paul M. Ambrose, chief, College Park Branch, Metallurgical
Division, and under the imniediate supervisioii of Howard F. Carl, chipf, Physical and Chemical Section. The author wishes to thank A. M. Sherwood and A. H. Macmillail for chemical analysis performed, Shirley Hodgson for preparation of many of the samples, and Charles E. White, of the rniversity of Maryland, for his many helpful suggestions LITER.4TURE CITED
(1) Baird, W. S.. “Proceedings of 6th Suniniei, Conference on Spectroscopy and Its Applications,” pp. 80--7. New York, John Wiley & Sons, 1939. (2) Colin, R. H., and Gardiier, D. .I..A S ~ L (’HEM.. 21, 7 0 1 4 (1949). (3) Feldman, C., I M . . 21, 1041-5 (1949). (4) Ihid., pp. 1211-15. (5) Gassman, A. G., and O’Neill, R. H.. Ihid., 21, 417-18 (1949). ( 6 ) Hasler, M. F., and Dietert, H. LV., J . Opticnl SOC.A m . , 33. 218-32 (1943). (7) Keirs, R. J.. and Englis, D. T.. IN). ENG.CHEM.,ANAL.ED.. 12, 275 (1940). (8) Office of Naval Research, Washington, D. C., “Titanium,” Report of Symposium on Titanium, 1949. (9) Russell, H. N., Astrophys. J., 66, 283-328 (1927). (10) Russell, H. N., Zbid., 66, 347-438 (1927). (11) Scribner, B. F., and Ballinger, J. C., J . Resmrch .Y,itl. H U T .
Standards (to be published).
RECEI\ E D June 7 ,
1950
Spectrochemical Analysis of Radioactive Solutions CYHUS FELDMAN, Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tenn., MYHON B. HAWKINS, Rudioisotope Applications Company, Berkeley, Calif., MARVIN MURRAY, Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tenn., AND DONALD R . WARD, Isotopes Division, U . S . Atomic Energy Commission, Oak Ridge, Tenn. A description is given of a chamber designed to permit electrodes for spectrochemical analysis to be loaded outside the spectrographic laboratory, excited with spark or other intermittent excitation, and disposed of with a minimum risk to personnel. If strippable films are used to protect the most heavily e;posed surfaces, residual radiation levels of -2 mr. per hour at contact on the chamber parts can easily be attained for samples customarily encountered. 7
I
S ASALYZING any type of material speckrochemically, one naturally attempts to attain the maximum accuracy, precision, sensitivity, and speed. In analyzing radioactive materials, however, the main consideration is safety, and the folloKiiig factors must be considered first:
Protection of operators from a, 0,and y radiation (shielding). Protection of operators from contact with radioactive materials, hlinimization of number of handling and transfer operations prior to excitation of sample. Prevention of air contamination, especially during excitation of sample. Safe and rapid disposal of used electrodes. Safe, rapid, and complete decontamination of auxiliary apparatus. The general interests of safety and efficiency are usually served best by standardizing techniques as much as possible. When the samples are tadioactive, safety and efficiency also affect the choice of excitation technique and sample form. CHOICE OF EXCITATION TECHNIQUE
Because the dischargm used in spectrochemical analysis are disruptive, they must be conducted within an enclosed chamber in order to provide shielding and prevent contamination of the air. It must be possible to decontaminate such a chamber quickly and safely, in order both to safeguard personnel and to have the chamber available for re-use BS soon as possible. The effectiveness and dispatch with which a surface can be
decontaminated tend to vary inversely with its area. The minimum permissible internal area of a chamber is dictated largely by the size and power rating of the discharge taking place within it. If the discharge continuously liberates large amounts of heat and vapor, as is the case 4 ith the direct current arc, the chamber must have a volume large enough to prevent overheating. This is a matter both of convenience of handling and of possiblr spectral line interferences from chamber materials which might be volatilized into the discharge if the chamber walls were too close to the arc. The use of spark techniques, however, lowers the temperature within the chamber, and makes it possible to adopt two measures which greatly simplify the decontamination problem: The size of the chamber caavity may be greatly reduced, thus decieasing the contaminated area. The area exposed to contamination may be coated before exposure with a strippable film. -4fter exposure, this film may be removed and the contarnination eliminated. This technique can be used only with spark excitation, because the film materials available cannot withstand the temperatures prevailing in an arc chamber. Almost all of the radioactive materials analyzed in the authors’ laboratory occur in solution form. Because this laboratory’s nonradioactive solutions are usually analyzed by either the copper spark method (1, 3 ) , or the porous cup method (e),
