(Methods f o r Analysis of Titanium Alloys)
Colorimetric Determination of Small Amounts of Aluminum in Titanium Alloys 3lAUKICE CODELL AND GEORGE NORWITZ Pitmuir-Dtcnn Laboratories, Frankford Arsenal, Philadelphia, Pa. 0 SATISFACTORY method has been proposed for the determination of small amounts of aluminum in titanium alloys. The “Handbook on Titanium lIetal,” 1952 edition (12), describes a gravimetric method for the determination of aluminum in titanium alloys. The method, hoxever, is applicable only to nlloys containing more than 0.2q;b aluminum (12). In view of the need of an accurate method for determining small amounts of aluminum in titanium alloys, an investigation R R S undertaken to develop such a procedure. A colorimetric n i d i o d seemed advisable. It was decided t o use aluminon as the caolorimetric reagent. The use of aluminon for the colorimetric determination of aluminum was first proposed by Hammett and Sottery in 1925 (2). Since that time many papers have appeared regarding its use (1,3,4,6-8, 10, 1 1 , l S ) . I t has been the experience of the authors that the pII of 5.3 proposed by Craft and lhkepeace ( 1 ) is to be preferred for the alunlinon color. Therefore, it was decided t o use the composite aluminon reagent desc:id~edby Craft and llakepeare. This reagent is made from alununon, acetic acid, ammonium liytlroxide, gelatin, and benzoic acid (added as a preservative), The direct application of aluminoil to t lie colorimetric deterniinntion of aluminum in titanium alloys without any separations was not possible because of the marked interference from the titanium. The best means for removing the titanium seemed to be t o precipitate the titanium with cupferron on a small-size aliquot (0.02 gram). The cupferron in the filtrate was then destroyed I)?evaporating t o fumes of perchloric acid, the perchloric acid driven off, and t,he aluminon color developed. In addition t o removing titanium, the cupferron precGpitatiou also serves t o remove iron, tungsten, and vanadium (5, Q), all of which would intwfere with the aluminon color. Moderate amounts of chromium as chromate do not interfere with the aluminon color ( 2 ) . However, if more than 1% chromium is present, the chromiuni should be volatilized as chromyl chloride nddirig hydrochloric avic! t o the fuming perchloric acid solution.
Cupferron Solution, 5%. Dissolve 5 grams of cupferron i n water and dilute to 100 ml. with water. Cupferron Wash Solution. ildd 15 ml. of cupferron solution (5y0)and 50 ml. of hydrochloric acid to 435 ml. of water. PROCEDURE
Preparation of Calibration Curve. Pipet I-, 2-, 3-, 5, 6-, and 8-ml. aliquots of standard aluminum solution into 250ml. beakers which are covered with borosilicate glass watch glasses. Adjust the volumes to 5 1 ml. by boiling or by adding water. Add 15.0 ml. of composite aluminon reagent and heat on the steam bath (high steam) for 30 minutes. Allow the solutions to cool to room temperature, transfer to 100-mi. volumetric flasks, and dilute to the mark. Compare colorimetrically with the reagent blank a t 540 mp. Plot the per cent transmittance against per cent aluminum. The calihration curve obtained by the authors followed Beer’s law up to about 0.257, aluminum, then deviated very slightly from Beer’s law in the range of 0.25 to 0.40yGaluminum. Method. Transfer a 1-gram sample to a 250-ml. beaker covered with a borosilicate glass watch glass. Add 20-ml. of hydrochloric acid and warm on the hot plate until the sample is dissolved. Add 1 ml. of nitric acid and boil for a minute. Cool, and dilute t o 500 ml. in a volumetric flask. Pipet a 10-ml. aliquot into a 250-ml. beaker, add 6 ml. of hydrochloric acid, and dilute to 50 ml. with water. Add 6 ml. of 5% cupferron solution from a buret while stirring. Allow to stand 5 minutes (no longer), Filter through a medium texture filter paper (FThatman No. 40). Collect the filtrate in a 250-ml. beaker. Test for complete precipitation by adding a drop or two of cupferron solution to the filtrate. A white flash indicates complete precipitation. Wash the beaker and precipitate with cupferron wash solution. .4dd 5 ml. of nitric acid and 3 ml. of perchloric acid to the filtrate and evaporate to fumes of perchloric acid. If more than 1%
*
‘I’ahle I.
Aluminum .Idded, o/c 0 010 0 050 0 100 0 250 0 400
APPARATCS A A U K&:iGb,Y‘I’S
h Colenian Universal spectiophotoiiieter , Model 14, Kit11 optically matched 13 X 13 X 105 mm. cuvettes A Beckman pH meter equipped with glass and calomel electrodes. Standard Aluminum Solution. Dissolve 0.1235 gram of A12(S04),.18 HzO in water, add 5 ml. of hydrochloric acid, and dilute to 1 liter with water in a volumetric flask. One milliliter of this solution contains 0.010 mg. of aluminum. On an 0.02gram sample 1 ml. of the solution is equivalent to 0.0570 aluminum. Benzoic Acid Solution, 10%. Dissolve 50 grams of benzoic acid in 500 ml. of methanol. Buffer Solution. Mix 950 ml. of nmnionium hydroxide and 860 ml. of glacial acetic acid. Cool to room temperature and add more acid or base as necessary to adjust the pH from 5.25 to 5.35 when diluted 1 to 20 (5 to 100). Dilute to 2 liters with water. Gelatin Solution, lyG. Dissolve i grams of gelatin by adding hot water and stirring. Cool and dilute to i o 0 ml. with water. Composite Aluminon Reagent. Dissolve 0.7 gram of aluminon (obtained by the authors from Eastman Kodak Co., Rochester, N. Y.) in about 400 ml. of water and add 140 ml. of benzoic acid solution (10%). Dilute to 700 ml. x i t h water. Add in order 700 ml. of buffer solution and ‘700ml. of gelatin solution (1%) and shake. The composite reagent should starid 3 days before using. It is stable for several months if stored i n the dark
Aluminum in Synthetic Samples of Titanium -4lloys Average .iluminum r o u n d , 70 0 011 0 050 0 098 0 254 0 398
Standard Deviation, 70 0 003 0 005 0 006 0 022 0 016
s o . of Detns 5
5 5
5
Table 11. Aluminuni in the Presence of Possible Interferences Amount Added,
Element % Added a s Chromium 1 0’ Chromiuiii 10.0b Iron 10.0 Molybdenum 10.0 Tungsten 5,O Vanadium 5.0 Manganese 10.0 Silicon 8.0 Copper 5.0 Cobalt 5.0 Nickel 5.0 Tin 5.0 Manganese 5.0 Calcium 5.0 Boron 1.0 Phosphorus 0.05 Phosphorus 0.10 Phosphorus 0.20 Phosphorus 0.30 Phosphorus 0.50 Phosphorus 1.00 Phosphorus 1.50 a Witt.out rhroniyl chloride separation. b With cl8ru:nyl chioride separation.
1437
Aluminum Added,
Aluminum Found,
0.100
0.098
0.100
0,097 0.104 0.100 0.105 0.097 0.106 0.096
%
0.100 0.100
0.100 0.100
0,100 0,100 0.100 0.100 0.100 0.100
0.100 0.100 0.100 0.25 0.28 0.25 0.25 0.25
0.25 0.25
R
0.096
0.101 0.097 0,100
0.103 0,095 0.097 0.25
0.26 0.23 0.20 0.19 0.15
0.10
ANALYTICAL CHEMISTRY
1438 chromium is present, add hydrochloric acid dropwise to the fuming perchloric acid solution to volatilize the chromium as chromyl chloride. With the cover lid ajar evaporate to dryness but do not bake. Bllow to cool, and wash down the sides of the beaker and the cover lid. Remove the cover lid. Evaporate to dryness once more but do not bake. Allow to cool. Wash down the sides of the beaker with about 20 ml. of water. Boil down to a volume of 5 f 1 ml. Allow ta cool somewhat, and add 15.0 ml. of composite aluminon reagent. Cover with the watch glass and heat on the steam bath (high steam) for 30 minutes. .411ow to cool to room temperature, transfer to a 100-ml. volumetric flask, and dilute to the mark. Compare colorimetrically with the reagent blank a t 540 mp. Convert the readings to per cent aluminum by consulting the calibration curve. PRECAUTION. Do not use beakers that have been used for the analysis of steels, as the iron becomes absorbed in the glass and cannot be removed even with cleaning solution. RESULTS
The results obtained for aluminum in synthetic samples prepared by adding standard aluminum solution to I-gram samples of sponge titanium are shown in Table I. The results obtained for aluminum in the presence of possible interferences are shown in Table 11. None of the metals found in commercial titanium alloys interferes with the method. The
presence of more than 0.10% phosphorus causes low results. Fortunately, phosphorus is rarely present in commercial titanium alloys except in traces. LITERATURE CITED (1) Craft, C. H., and iMakepeace, G. R., IXD. ENG.CHEM.,A 3 . 4 ~ . ED.,1 7 , 2 0 6 (1945). (2) Hammett, L. P., and Sottery. C. T., J . Am. Chem. SOC.,47, 142 (1925). (3) Luke, C. L., Ax.4~.CHEM.,24, 1122 (1952). (4) Luke, C . L., and Braun, K. C., Ibid., 24, 1120 (1952). (5) Lundell, G. E. F., and Hoffman, J. I., “Outlines of Methods of Chemical Analysis,” p. 117, Kew York, John Wiley B: Sons, 1938. (6) Olsen, A. L., Gee, E. A., and McLendon, V., IND.ENG.CHEM., ANAL.ED.,16, 169 (1944). (7) Roller, P. S.,J . Am. Chem. SOC.,55, 2437 (1933). (8) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” p. 116, Kew T o r k , Interscience Publishers, 1944. (9) Smith Chemical Co., G. F., Columbus, Ohio, “Cupferron and Neo-Cupferron,” p. 14, 1938. (10) Strafford, N., and Wyatt, P. F., A n a l y s t , 68, 319 (1943). (11) Ibid., 72, 54 (1947). (12) Titanium Metals Corp. of ;Imerica, S e w York, “Handbook on Titanium Metal,” 5th ed., p. 56, 1952. (13) Yoe, J. H., and Hill, W. L., J . Am. Chem. SOC.,49, 2395 (1927).
RECEIVED for reriea February
10, :%3.
Accepted August 18, 1953.
(Methods for Analysis of Titanium Alloys)
Determination of Molybdenum in Molybdenum-Titanium Alloys by Precipitation as the Sulfide GEORGE NORWITZ AND &MAURICECODELL Pitman-Dunn Laboratories, Frankford Arsenal, Philadelphia, Pa.
T
HERE is little information in the literature concerning the
determination of molybdenum in titanium alloys, although molybdenum-titanium alloys are important. The “Handbook of Titanium Metal,” 1952 edition (25), states that no satisfactory method has been proposed for the determination of molybdenum in titanium alloys. Various procedures that are used for the determination of molybdenum in other types of materials are not very satisfactory when applied to titanium alloys. The thiocyanate-stannous chloride extraction method (3,18) leaves much to be drsired on account of the instability of the color. There are no volumetric methods for molj bdrnum that can be used in the presence of large amounts of titanium. The m-benzoinoxime precipitation method (1,9) is not very reliable for the determination of molybdenum in titanium alloys. I t was decided to investigate the possible application of the sulfide method to the determination of molybdenum in titanium alloys. Quantitative precipitation of molybdenum as the sulfide has always bren considered a difficult matter (6, 10). In the usual procedure the molybdenum sulfide is precipitated from a hot solution, digested for about 2 hours, filtered, and ignited to the oxide ( 2 , 7 ) . Two precipitations u i t h intervening oxidation of the molybdenum are usually made ( 7 ) . Even with two precipitations only about 2 to 10 mg. of moljbdenum can be precipitated (8). Some investigators have recommended the use of a pressure flask for the precipitation of molybdenum sulfide. However, according to Hillebrand and Lundell (6) this does not help to any appreciable extent. Another disadvantage of the methods that have been proposed for the precipitation of molybdenum as the sulfide is the incomplete separation of the molybdenum in the 3resence of such elements as vanadium (6) and the contamination i f the precipitate by such elements as titanium which hydrolyze, especially when the solutions are heated. From the above it would seem that hefore a wccevful method for the determination of molybdenuni in molybdenum-titanium alloys could be devel-
oped, the proper conditions for the precipitation of molybdenum sulfide would have to be studied. Such a study was undertaken. REAGENTS
Standard Molybdenum Solution (1 ml. = 0.0050 gram of molybdenum). Dissolve 7.500 grams of pure molybdenum trioxide in a minimum amount of 15y0 sodium hydroxide and dilute to I liter in a volumetric flask. Hydrochloric acid, specific gravity 1.19. Sitric acid, specific gravity 1.42. Sulfuric acid, specific gravity 1.84. Perchloric acid, 70%. Phosphoric acid, 85%. Hydrofluoric acid, 48%. Tartaric Bcid Solution, 2070. Dissolve 200 grams of C.P. tartaric acid in water and dilute to 1 liter Kith water. Hydrogen peroxide, C.P. 30%. Sulfuric Acid-Hydrogen Sulfide R a s h Solution. Add 15 ml. of sulfuric acid to 1 liter of water and saturate with hydrogen sulfide. Sulfuric Acid-Tartaric Acid-Hydrogen Sulfide Wash Solution. Add 15 ml. of sulfuric acid and 20 ml. of 20% tartaric acid solution to 1 liter of water and saturate with hydrogen sulfide. F4CTORS INVOLVED IN IIOLYBDENUM SULFIDE PRECIPITATION
Necessity of Allowing Sulfide Solutions to Stand. Overnight. Aliquots of standard molybdrnum solution were pipetted into 250-ml. beakers and 5 ml. of sulfuric acid were added. The solutions were diluted with water to 175 nil., and hydrogen sulfide was passed through the solutions for 15 minutes a t room temperature. One set of solutions was allowed to stand 2 hours and then filtered; a second set was allowed to stand overnight before filtering. The precipitates werr washed with sulfuric acidhydrogen sulfide wash solution and ignited a t 500” C. The results obtained, shown in Table I, indicate that the solutions must stand overnight. S o experiments were conducted with hot solutions because heating a dilute sulfuric acid solution containing 1 gram of titanium leads to hydrolysis of the titanium.
