Spectrophotometric Determination of Titanium in Steels ALFRED WEISSLER, Naval Research Laboratory, Washington, D. C. Absorption spectra have been determined for the hydrogen peroxide complexes of titanium and vanadium in the presence of 1 gram of iron, in perchloric-phosphoric acid solution. These spectra furnish the basis for improved rapid, accurate methods for the determination of from 0.5 to 6 my. of titanium in iron, steel, vanadium steel, and stainless steel, without separating the titanium or using hydrofluoric acid; accuracy approaching one part per hundred may be obtained. Details are given for a method of determining metallic and combined titanium in steel, which has given good reproducibility.
T
H E desirability of a mure rapid method of accurate analysis for titanium in steels has been emphasized by recent interest in the effects of metallic versus combined titanium on hardenability, in titanium-stabilized stainless steels, and in Tvelding steels containing small amounts of vanadium and titanium. Spectrophotometric analysis appeared to offer an opportunity to eliminate time-consuming separations. The standard procedure for titanium analysis in steel includes a cupferron separation from the bulk of the iron, prior to the addition of hydrogen peroxide and comparison of the intensity of the yellow color (1, 8 ) . However, some recent methods omit such a separation (6, 8, 9 ) and, for example, decolorize the iron by the addition of phosphoric acid. In the presence of much of colored ions such as chromium, nickel, or iron, the visual colorimetric determination of titanium is difficult. The large amounts of chromium in stainless steels may be separated by sodium carbonate plus sodium peroxide ( I $ ) , mercury cathode electrolysis (6), boiling perchloric acid and sodium chloride ( I J ) , or filtration of chromic acid out of 70% perchloric acid solution (16). If the interfering element vanadium is present in the steel, it may be separated by sodium carbonate fusion (4). Some popularity has been achieved by other colorimetric reagents for titanium, such as gallic acid (16), thymol (IO), and chromotropic acid, 1,8-dihydroxynaphthalene-3,6disulfonicacid
(6). I n general, these require preliminary separation of titanium. Considerable interest has been evinced in the ratio of metallic to combined titanium in steel ( 7 , 11), and methods for separating the two have suggested the use of various dilutions of hydrochloric acid (3,14, 17). EXPERIMENTAL WORK
The apparatus and reagents have been described (18). A series of synthetic standard titanium steels n'as prepared by adding varying amounts of titanium solution to 1 gram of K.B.S. iron 55a. These were then treated as described in Method A, below, and the absorption spectra measured from 360 to 600 mp Figure 1 shoirs that the peak absorption is at 400 mp, and it is narrower than in the absence of phosphoric acid, where the peak is at 410 mp. Figure 2 indicates that even in the presence of 1 gram of iron, a linear relation exists between titanium concentration and optical density at 400 and at 460 mp. To investigate interference by vanadium, a series of synthetic standard vanadium steels was prepared by adding varying amounts of vanadium solution to 1 gram of iron 55a. These were then treated as described in Method A, and the absorption spectra measured from 360 to 620 mp, as shown in Figure 3. Even in the presence of 1 gram of iron, Beer's law is valid at 400 and 460 mp, as shown in Figure 4. SIWJLTANEOUS DETERMINATION OF TITAXIUM AND \'ANAD i u M IN STEEL. It was observed that when 1 gram of steel is treated as in Method A, the presence of 1 mg. of titanium gives a density of 0.269at 400 mp, and 0.134 at 460 mp. Under similar conditions, 1 mg. of vanadium gives an optical density of 0.057 at 400 mp, and 0.091 at 460 mp. If z represents the number of milligrams of titanium, y the number of milligrams of vanadium,
/
/'
0
Figure 1.
Absorption Spectra of Titanium-Peroxide Complex
In phosphoric-perchloric acid solullon containing 1 gram of iron
60
Figure 9 .
2.0
3.0 4 0 50 6.0 my. T/TAN/OM /ff SOmL
ZO
Linearity of Titanium Concentration-Denrity Relation In presence of 1 gram of iron
INDUSTRIAL A N D ENGINEERING CHEMISTRY
776
my.VANADIUM I N 50ml.
WAVELENGTH -Inp
Figure
3.
Absorption Spectra of Peroxide Complex
Vol. 17, No. 12
Figure 4.
Vanadium-
Linearity of Vanadium Concentration-Density Relation In presence of 1 gram of iron
In phoaphorls-perchloric acid rolutlon containing 1 gram of iron
and the two absorb independently of each other, the following sfmultaneous equations can be set up:
0.269 x 0.134 x
++ 0.057 2/ = Dwo 0.091 y = Dim
These can be solved to give:
x = 5.40 Dlou y 15.9 Ddw
- 3.38 D m - 7.54 D m
It can be seen that small errors in reading density will affect the vanadium result more than the titanium. As a test of the above equations, several synthetic vanadiumtitanium standard steels were prepared and analyzed by Method A, measuring the density of each solution at 400 and at 460 mp. Table I s h o w the accuracy of the results; as was expected, the vanadium errors are the greater. As a further test, several standard cast irons of kn0m.n titanium and vanadium content n-ere analyzed by Method A. Table I1 shows the extremely accurate
Table
111.
Determination of Titanium in Synthetic Standards of Stainless Steel withput Separating Titanium (0.5gram of Std. 1Olb plus varying amounts of titanium) Ti Added D 4 0 0 Ti Recovered Error
Table
%
%
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
0.040 0.180 0.320 0.453 0.580 0.722 0.855 0.997
0.80
1.132
0 : ib3
0.206 0.304' 0.397 0.501 0.600 0.704 0.803
% 0:003 0.006 0.004 -0,003 0.001 0.001 0.004 0.003 Av. 0.003
1.
Simultaneous Determination of Titanium and Vanadium in Synthetic Standard Steels (1 gram of standard 55a plus varying amounts of V and Ti, with 10 ml. of HCIOi and 4 ml. of 1:1 HsPO4, diluted to 50 ml.) Sample Ti Added V Added D408 Dao Ti Found V Found % % % % 1 0,050 0.050 0.172 0.116 0.054 0.052 2 0.050 0.400 0.366 0.430 0.052 0.406 3 0.100 0.200 0.370 0.298 0.100 0.195 0.389 0.311 0.104 0.200 4 0.200 0.200 0.640 0.436 0.201 0.210 0.649 0.440 0.200 0.211 5 0.300 0.200 0.902 0.570 0.295 0.228 6 0.100 0.600 0.600 0.660 0.101 0.598
Table
results obtained for titanium; however, the vanadium results proved to be rather high. This subject was not pursued further, since the major interest was in titanium. Although the molybdenum-peroxide complex shows an intense peak at 330 mp it is impossible to make measurements in that region, in the presence of 1 gram of iron, because of the strong absorption of ferric perchlorate in the ultraviolet.
It. Analysis of Standard Cast Irons Containing Titanium and Vanadium Sample
Std. 6d, 0.139% Ti and 0.209% V Std. 7c, 0.067% Ti and 0.042% V 8td. 74,0.114% Ti and 0.018% V Std. 82,0.048% Ti and 0.011% V
Dloo
0.393 0.392 0.206 0.207 0.323 0.322 0.142 0.143
Duo 0.215 0.215 0.130 0.130 0.177 0.177 0.078 0.078
Ti Found
Error
%
%
0.139 0.000 0.139 0.000 0.067 0.000 0.068 +0.001 0.114 0.000 0.114 0.000 0.049 +0.001 0.049 +0.001 Av. 0.0004
DETERMINATIOX OF TITANIUM IN STAINLESS STEELS. In view of the great monochromaticity available, the possibility pre-
sented itself of an accurate determination of titanium in stainless steel, without separation from the nickel, chromium, iron, etc. A series of synthetic standard titanium stainless steels was prepared by adding varying amounts of titanium solution to 0.500gram samples of N.B.S. standard 18-8 steel 101b. These were then analyzed by Method B, described below. Table I11 shows the high accuracy of the results obtained, using the experimental finding that under these conditions 1 mg. gives an optical density of 0.272 at 400 mp, and subtracting as a blank the density 0.040 given by lOlb itself, To investigate possible interference by columbium and tungsten, a similar series waa prepared from standard 123a (0.002% Ti, 0.75% Cb, 0.11% W) and analyzed by Method B; Table IV shows that the results are accurate even in this case. Further, adding up to 0.5% of columbium to standard steel 121 caused an error of less than 0.01% of titanium. Three standard stainless steels of known titanium content were analyzed by Method B. Table V shows that the corrected results for 121 and 121a are good, but those for 123a indicate a rather high relative error, with absolute error only 0.004%.
ANALYTICAL EDITION
December, 1945
IV.
Determination of Titanium in Synthetic Standards of 0.75% Columbium, 0.11% Tungsten Stainless Steel, without Separating Titanium (0.5gram of Std. 1238 plus varying amounta of titanium) Ti Present Dm Ti Found Error Table
%
% 0.036 0.312 0.582 0.862 1.135
0.002 0.202 0.402 0.602 0.802
Table Steel
V.
Analysis Certified Titanium
% 0.005
0.007 0.210 0.409 0.614 0.815
0.008 0.007 0.012 0.013 Av. 0.009
of Standard Titanium Sbinless.Steelr Dtw
Ti Found Ti Corrected Uncorrected for M o and V
%
%
Std. 121
0.394
Std. 121a
0.361
Std. 123s
0.002
%
0.547 0.542 0.489 0.492
DETERMINATION OF METALLIC AND COMBINED TITANIUM IN STEEL. Reproducible results for metallic and combined titanium in steel were obtained by Method C, as shown in Table VI, even \Then 2 to 1 hydrochloric acid was substituted for the 1 to 1 acid. I t was found important to use close-textured filter paper for the separation; medium-textured paper allows some of the finer particles to pass through. Since most of the combined titanium in steel is present as titanium carbonitride, the validity of the method was tested by adding 30 and 40 mg. of titanium carbonitride to 1-gram samples of iron 55a, and analyzing for metallic (or soluble) titanium as in Method C. Only a negligibly small fraction of the carbonitride was soluble in the dilute hydrochloric acid under these conditions. Method C omits use of phosphoric acid to decolorize iron. Although not necessarily advantageous this is a permissible variation, since ferric perchlorate is nearly colorless. However, in this case, titanium-free steels give a blank of density 0.026 at 410 mp for the acid-soluble portion, and this blank must be subtracted from all such readings. Optical density at 410 mp resulting from 1 mg. of titanium under these conditions is 0.304, so that slightly greater sensitivity is attained. METHODS IN DETAIL
METHOD A, FOR LOW-ALLOY IRON AND STEEL. Dissolve 1.000 gram of sample in 10 ml. of 1 to 1 nitric acid plus 10 ml. of 70% perchloric acid, by warming in a 125-rnl. Phillips beaker. Evaporate to fumes of perchloric acid, and continue heating vigorously until the fumes become transparent two thirds of the way up the beaker. Cool rapidly in water, in order to minimize peroxide formation. Add 25 ml. of water to dissolve the salts, then 4 ml. of 1 to 1 phosphoric acid. Destroy any yellow color due to chromate by adding 3 or 4 drops of sulfurous acid, or more if necessary. To remove silica and graphite, filter through a 9cm. Whatman KO. 40 paper into a 50-ml. volumetric flask. Wash thoroughly ~ i t several h small portions of water, dilute to
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the mark, and mix thoroughly. Measure the optical density at 400 and 460 mp of a 3-ml. portion to which one drop of 30% hydrogen peroxide has been added, using as a blank a similar portion to which one drop of water hss been added. Even in the presence of varying amounts of vanadium, the percentage of titanium in the steel is equal to 0.540 D m 0.388 D d M . If vanadium and molybdenum are known to be absent, then the percentage of titanium is simply Dm/2.69. If the vanadium and molybdenum percentages are known, the titanium percentage is equal to Dm/2.69 minus one tenth of the molybdenum percentage minus one fifth of the vanadium percentage. These correction factors are calculated from the optical densities at 400 mp. METHODB, FOR STAINLESSSTEEL. Dissolve a 0.500-gram sample in 15 ml. of 1 to 1 hydrochloric acid plus 2 ml. of nitric acid in a 125-ml. Phillips beaker. Add 10 ml. of 70% perchloric acid; evaporate, fume, and cool as in Method A. Add 20 ml. of water to dissolve the salts, 4 ml. of 1 to 1 phosphoric acid, and 5.0 ml. of saturated sulfurous acid, to reduce the chromium completely. Warm gently 10 or 15 minutes to expel excess sulfurous acid, filter through a 9-cm. No,40 paper into a 50-ml. volumetric flask, wash thoroughly with several small portions of water, and dilute to the mark. Measure the optical density a t 400 mp of a peroxidized portion against an unperoxidized portion. Then the percentage of titanium is Dc&.36 minus one tenth of the molybdenum percentage minus one fifth of the vanadium percentage. METHODC, FOR METALLIC AND COMBINED TITANIUM IN STEEL. Transfer a 1.000-gram sample to a 125-ml. Phillips beaker, add 25 ml. of 1 to 1 hydrochloric acid, and dissolve by moderate heating. After one hour (by which time action has ceased) filter through a 9-cm. No. 42 paper, and wash carefully with 5 to 95 hydrochloric acid. Catch filtrate and washings in a 250-ml. Phillips beaker, and add 10 ml. of perchloric acid and about 5 ml. of nitric acid. Evaporate, fume strongly, and continue as in Method A, except for omitting the phosphoric acid, and measuring the optical density at 410 mp. Then in the absence of much vanadium or molybdenum, the percentage of metallic titanium in the steel is (Ddl0 0.26)/3.04. A density of 0.026 is obtained when 1gram of a titanium-free steel is analyzed by this procedure. The combined titanium is determined as follops: Return the insoluble residue and paper from the first filtration to the ori inal 125-ml. Phillips beaker. Add 7 ml. of perchloric acid and a%out 30 ml. of nitric acid, and digest at moderate heat until all organic matter is destroyed. Then evaporate to fumes of perchloric acid and fume vigorously for 3 minutes. Cool in water, add 25 ml. of water and 3 drops of sulfurous acid, and filter through a 9-cm. No. 40 paper into a 50-ml. volumetric flask. Wash thoroughly with several small portions of water, dilute to the mark, mix well, and determine the optical density at 410 mp. Then D410/3.04 gives the percentage of combined titanium in the steel.
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ACKNOWLEDGMENT
Grateful acknowledgment is made to Louis Singer, who in-‘ spired the author’s interest in this problem. LITERATURE CITED
(1) Am. SOC. Testing Materials, Methods of Chemical Analysis of Metals, p. 74 (1943). (2) Cunningham, T. R., IND. EXG.CHEX.,ANAL.ED.,5, 305 (1933). (3) Dieckmann, T., Z. anal. Chem., 60, 230 (1921). (4) Dymov, A. M.,and Volodina, 0. A., Zavodskaya Lab., 5, 1047 (1936). (5) Endredy, A. V., and Brugger, Fr., Z . anorg. allgem. Chem., 249, 263 (1942). (6) Gutnian, S. AI., Zarogatskaya, E. Ii.,and Vyrapaeva, Z. A., Zavodskaya Lab., 9, 101-2 (1940). (7) Hume-Rothery, W., Raynor, G. V., and Little, 9.T., J . Iron Steel Inst. (Mar., 1942, preprint). Table VI. Determination of Metallic and Combined Titanium in Steel (8) Johnson, C. M., Iron Age, 132, 16 (Aug. 24, 1933). (9) Kenigstuhl, M. D., Zavodskaya Lnt., 9,1203 (1940). A. Solution in 1: 1 HCl B. Solution in 2: 1 HC1 Sum of (10) Lenher, V., and Crawford, W. G., J . Am. Chem. Sum of metallic metallic Soc., 35, 141 (1913). (11) Leve, N. F., and Gurevich, -4. B., Zavodskaya Lab., Total Metallic Combined combined and ?Tetallic Combined combined and Sample Titanium 9, 957 (1940). titanium titanium titanium titanmm titanium titanium (12) Mathesius, H., Chem.-Ztg., 54, 131 (1930). % % % % % % % (13) Mukhina, 2. S..Zavodskaya Lab., 8 , 162 (1939). Std. 82 0.048 0.000 0.048 0.048 0.000 0.049 0.049 (0.048% Ti) 0.047 (14) “Scott’s Standard Methods of Chemical Analysis”, 0.000 0.048 0.048 0.000 0.049 0.049 pp. 992-4, New York, D. Van Nostrand Co., GMO 0.059 0.000 0.059 0.059 0.001 0.059 0.060 0.060 0.000 0.057 0.057 0.001 0.057 0.058 1939. (15) Shemyakin, F. M.,and Neumolotova, A , , J . Gen. GMP 0.101 0.003 0.095 0.097 0.001 0.097 0,098 0.102 0.003 0.095 0.098 0.001 0.097 0.098 Chem. (U.S.S.R.), 5 , 491 (1935). . 14, (16) Silverman, L., IND.ENG.CHEM.,A N ~ LED., GMR 0.189 0.002 0.183 0.185 0.005 0.184 0.189 0.189 0.003 0.182 0.185 0.004 0.182 0.186 791 (1942) GMS 0.350 0.010 0.335 0.345 0.011 0.341 0.352 (17) Tsinberg, S.L., Zavodskaya Lab., 6, 358 (1937). 0.352 0.012 0.339 0.351 0.011 0.342 0.353 (18) Weissler, Alfred, IND. ENG.CHEM.,ANAL.ED.,17, 695 (1945). . \_.__,_
