V O L U M E 27, NO. 7, J U L Y 1 9 5 5 methyl hydroperoxide but not with the dihydroxydimethyl peroxide, and furthermore that the complex with hydroxymethyl hydroperoxide may have a slightly greater absorbancy than that formed with hydrogen peroxide. There are several reasons for this conclusion: The dilution of a test sample for analysis will cause Reaction 1 to reverse. However unless acid is also added, it can readily be shown from Zivailable kinetic data that the rate of this reverse reaction is so slow that,, for example, a t the end of 2 hours in neutral solution the amount of free hydrogen peroxide present will have increased only about 10%. The intensity of the color developed initially in the unmodified procedure corresponds t o slightly more than the amounts of hydrogen peroxide plus hydroxymethyl hydroperoxide calculated to be present a t equilibrium in the concentrated solution before dilution. I n the unmodified procedure the color intensity a t the end of 5 hours was about 105 to 110% of that expected if all the peroxide present were in the form of the titanium complex with hydrogen peroxide. Presumably practically all of the peroxide present is then in the form of hydrogen peroxide or hydroxymethyl hydroperoxide and is complexed. I n the case of acetaldehyde, the equilibrium data indicate that a far greater portion of the peroxide will be in the form of hydrogen peroxide or the monohydroxy hydroperoxide than is the case n-ith formaldehyde. Therefore no significant interference is noted in the unmodified procedure i n this case. One must be careful to distinguish between an ordinary organic hydroperoxide, RCH20011, and a hydroxyalkyl hydroperoxide, RCH(0H)OOH. The lat,t,er is a weak addition compound of an aldehyde and hydrogen peroxide which gives color formation
1175
with titanium. The former does not apparently complex with titanium to any appreciable extent as discussed previously. The titanium sulfate reagent is reported to hydrolyze to form a precipitate a t a p H over 0.8 (3). I n the unmodified procedure where the acidity in the colorimeter cell is approximately 0.55, it was observed that over the course of about 4 hours the absolute transmittance decreased by 5 to lo%, and a sIight opalescence appeared. However the rate of development of turbidity was unaffected by the presence of formaldehyde or hydrogen peroxide, so the use of a blank, as was done in all tests reported here, eliminated errors from this source. ACKNOWLEDGRlEhT
The authors wish to acknowledge the financial support of the Office of Saval Research, under Contract No. S5ori-OT819, SR-092-008. LITERATURE CITED
(1) .Illsopp, C. B., A n a l y s t , 66,371 (1941). (2) Bendig, AI., and Hirschmuller, H., 2. anal. Chem.. 120, 385 (1940). (3) BonBt-llaury, P., Compt. rend., 218, 117 (1944). (4) Egerton, A. C., Everett, A. J., Slinkoff, G. J., Rudrakanchana, S.,and Salooja, K. C.. Anal. Chim. A c t a , 10, 422 (1954). ( 5 ) Eisenberg, G. ll.,ISD. ENG.CHEM.,ASIL. ED., 15, 327 (1943). (6) Humpoletz, J. E., Australian J . Sci., 12, 111 (1949). (7) Klenk, Klepzig'a Texti2-Z., 42, 549 (1939). (8) l I a c S e v i n , W. SI., and Urone, P. F., ANAL. CHEM.,25, 1760 (1953). (9) Satterfield. C. S . ,Wilson. R. E., LeCiair, R. 11..and Reid, R. C . , Ibid.,26, 1792 (1964). R E C L I V Efor D review November 1 2 , 1954. -4ccepted February 1, 1955.
Determination of Titanium in Titanium Metal R O L A N D A. PAPUCCI F.
C. b o e m a n & Co.,
Cincinnati 70, O h i o
The development of new titanium-base alloys, containing iron, chromium, molybdenum, tin, manganese, aluminum, magnesium, nickel, cobalt, copper, silicon, tungsten, and vanadium has led to a search for faster, accurate methods for the direct determination of titanium. The method developed uses the Eberbach Dyna-Cath, high speed magnetic mercury cathode to separate titanium from the most common and interfering elements associated in high-purity titanium metal and titanium alloys. Titanium is then determined colorimetrically as the yellow- pertitanic acid. A significant saving in time has been accomplished with less care necessary to obtain the accuracy comparable to other methods.
T
0 MEET the need of the expanding titanium industry and new metallurgical advances, accurate and more rapid methods for the determination of impurities in titanium metal have been developed, especially since 1950. A method has been developed for the direct determination of titanium in highpurity titanium and titanium alloys, which combines speed with :tccuracv and without many painstaking conditions as in existing methods (1, 3, 7 , 8). While the theoretical bases for the method are not new, the adaptation of the procedure to titanium and titanium alloys compares favorshly n-ith other existing methods (f. 7 . 8,
RIethods for the determination of titanium in titanium metal have been reported. Knecht and Hibbert ( 4 ) first employed a method using a standard solution of ferric salt for the determination of titanium. I t was modified later to include the use of thiocyanate added directly to the test solution instead of an outside indicator (5, 6). Thompson (8) modified this method adapting it to the determination of titanium in high-purity titanium metal. The method offers satisfactory results and reproducibility, hut it possesses certain disadvantages in that an approuimate titration must be made before the actual determination in most cases, and the removal of impurities is tedious. The method described uses the Eberbach Dyna-Cath (a),high speed magnetic mercury cathode, to separate titanium from chromium, molybdenum, iron, tin, cobalt, nickel, copper, and manganese, the most common and interfering elements associated with titanium. Small amounts of aluminum, silicon, magnesium, oxygen, tungsten, and vanadium do not interfere with the colorimetric determination of titanium as the yellow or orange pertit a n k acid. For most allow, the amount of tungsten and vanadium present is usually under 0.04yo and no interference has been observed while working with relatively small samples. APPAR4TUS AND RE-IGENTS
Apparatus. Dyna-Cath, Eberbach Corp., high speed magnetic mercury cathode. Klett-Sdmmerson photoelectric colorimeter. Beckman quartz spectrophotometer, Model DL-. 1-olumetric flasks, 200-, loo-,
*
1176
ANALYTICAL CHEMISTRY
and 10-ml. capacity. Erlenmeyer flasks, 500-ml. capacity. Flask tongs. Beakers and covers. Reagents. Potassium bisulfate, fused, pure. Sulfuric acid (1 to 3), ( 1 to 5), and ( 1 to 9). Hydrogen peroxide, c.P., 3%. National Bureau of Standards standard samples, Kos. 154 and 121b. Standard titanium sulfate solution (1 ml. = 0.0001 gram of titanium). Preparation. Fuse 0.34 gram of titanium dioxide (sample 154) in a platinum dish with approximately 10 grams of potassium acid sulfate and dissolve the cold melt in 200 ml. of hot sulfuric acid (1 to 9). Cool to room temperature and dilute to 2 liters in a volumetric flask with sulfuric acid (1 to 9).
approximate volume. Cool, make up to volume in a 200-ml. volumetric flask, and pipet 2 ml. of the homogeneous solution in a 100-ml. volumetric flask. Add 20 ml. of sulfuric acid (1 to 3) and 50 ml. of distilled water. 4 d d 5 ml. of 3% hydrogen peroxide and make up to volume. Compare the color reading against known values of the standard titanium sulfate solution or compare reading, using blue filter No. 42 on the Klett-Summerson, to the calibration curve, Figure 1, determined by using Bureau of Standards standard samples 121b and 154. Percentage reading X 250 = % titanium in sample, when a 0.20-gram sample is taken.
Table I. PROCEDURE FOR DETERMINATION OF TITANIUM
Weigh accurately 0.20 gram of the sample and transfer to a 500ml. Erlenmeyer flask. Add 100 ml. of sulfuric acid 1 to 5) and heat over a hot plate until completely dissolved. his operation requires approximately 15 minutes. Remove from the hot plate and cool. Metallic tungsten is insoluble in the nonoxidizing acid ( 7 , 9) and minute black particles of metallic tungsten may separate in the solution. Since the amount of tungsten actually present in most titanium alloys is small, it may not be visible to the naked eye. If such a residue is present or suspected, remove by filtration on a KO.40 Whatman filter paper. Vanadium (1, 7 , 9), also in minute quantity if present, for the most part accompanie? the tungsten and is removed with it.
(I.
Determination of Titanium in Titanium Metal Titanium Determined, %
Nominal Compn. of Alloy, % Fe 0.50, N 0.03, C 0.04, 0 0.50, M n 0.05, W 0.03
Thompson’s method (8)
KlettSummerson
Beckman
Ti-15OA Fe 1.30, Cr 2.50, 0 0.30, C 0.02, N 0.025, W 0.04
95.89 95,92 95.86 95.86 95.84 95.86
95.89 95.96 95.89 95.91 95.89 95.87
95,94 95.94 95.90 95.92 95.92 95.89
Ti-175A Fe 1.75, Cr 3.00, 0 0.50,N & M n 0.04, C 0.03, W 0.02
94,03 94.02 93.96 93.98
94.01 94,05 93,98 93.98
94.04 94.06 94.02 94.02
Fe 2.00, Cr 2.00. h.10 2.00. C 0.04, 0 0.40, N & w 0.02
93.67 93.70 93,66
93.76 93.74 93.72
93.78 93.75 93.74
Fe 2.00, Cr 2.00, Mo 2.00, C 0.04, 0 0.40, N & W 0.02
92.80 92.76 92.72
92.80 92.81 92,75
92.82 92.80 92.80
RC-130B hfn 4.00, A1 4.00, 0 0.30, N 0.05. C 0.06
92.08 92.12 92.18 92.18 92.20
92 31 92.31 92.30 92.26 92.30
92.38 92.31 92.28 92.28 92.30
Ti-15OB C r 5.00, Mo 5.00. Fe 5.00, 0 0.30, N 0.03, C 0.04
85.80 85.84 85.78
85.87 85,87 8.5,88
85.90 85.92 85.90
A similar curve for the Beckman spectrophotometer may be determined using the same standards and measuring the percentage of absorbance or transmittance a t 425 mp on the Beckman. The results appear in Table I. DISCUSSION
50 1
0.5
030
035
P€ffC€NTAGGE
7/TAN/UM
Figure 1.
040
Titanium in titanium-base alloy*
The results obtained were found to be equally as accurate as those obtained by Thompson. The results obtained on the Beckman spectrophotometer can be considered more precise than the results obtained on the Klett-Summerson. The time involved in the two methods was in favor of the direct determination with an average time of 80 minutes. Less care is necessary to obtain the same accuracy. LITERATURE CITED
Add 50 ml. of 3% hydrogen peroxide to the filtrate; the solution changes from a greenish blue to a yellol\- orange. Evaporate the solution until the yellow color disappears, then to fumes of sulfur trioxide. Do not fume strongly. Cool, add 75 nil. of distilled water, and boil for 5 minutes. Cool, and place the solution, washing well the sides of the flask, in the Dyna-Cath cell beaker, containing approximately 1.5 pounds of clean mercury. Cover the cell beaker and electrolyze the electrolyte for approximately 15 minutes a t 10 to 15 amperes, to remove chromium, molybdenum, tin, cobalt, nickel, copper, zinc, iron, and most of the manganese from the electrolyte. For total alloy contents of less than lo%, the solution may assume the yellow color of pertitanic acid. Interrupt the electrolysis when this occurs and remove the electrolyte from the cell, washing well the inside of the cell and cathode Fvith small quantities of distilled water. The electrolyte may be clear or yellorvish in color. If the volume of the solution is more than 200 ml., place the contents on the hot plate in a 500-ml. heakrr and evaporate to
(1) Am. SOC.Testing Materials, “Methods for Chemical Analysis of Metals,” ASThl Designation E 30-45 (1945). (2) Center, E. J., Overbeck, R. C., and Chaxe, D. L., ANAL.CHEM., 23, 1134 (1951). (3) Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” Wiley, iYew York, 1929. (4) Knecht, E., and Hibbert, E., Ber., 36,1549 (1903). (5) Knecht, E., and Hibbert, E., “Xew Reduction Methods in Volumetric Analysis,” pp. 11, 51, Longinans, Green, London, 1918. ( 6 ) I b i d . , pp. 10, 70, 1925. (7) Scott, TV. W.,“Standard hlethods of Chemical Analysis,” 5th ed., Van Sostrand, New York. 1939. (8) Thompson, J. AI., A N ~ LCHEM., . 24, 1632 (1952). (9) Willard, H. H., and Diehl, H., “Advanced Quantitative bnalysis,” 5th ed., Van Nostrand, New York, 1950. RECEIVED for review July 12, 1954. Accepted January 28, 1955.
