ANALYTICAL CHEMISTRY
1434 that the two methods check within 0.03%. The precision of the colorimetric method is somewhat better than the precision of the gravimetric method. There is no danger of silicon occurring in commercial titanium alloys as elemental silicon because of the high temperatures used in making titanium alloys and the great solubility of silicon in titanium. Titanium will dissolve up t o 8.5% silicon without the formation of elemental silicon. The fact that silicon is not present as elemental silicon in titanium alloys is an important point, as elemental silicon is not very soluble in hydrofluoric acid. Aluminum alloys frequently contain elemental silicon, because silicon has only a limited solubility in aluminum. S o trouble n as encountered in dissolving titanium alloys in the dilute hydrofluoric acid used, Most titanium alloys dissolve within 3 hours. However, the safe procedure is t o allow the samples t o dissolve overnight. Interferences that might be present in titanium alloys were studied. The amounts of the elements that did not interfere (in the presence of 0.5 gram of titanium) are shown in Table 111. The presence of more than 7.5% iron or more than 10% chromium leads t o low results, probably because some of the reducing agent is used t o reduce the ferric ion partially t o the ferrous state and the chromic ion t o the chromous state. Low results were ohtained when more than 0.75YOcopper was present. This could be due to the use of the reducing agent t o reduce the cupric ion t o the cuprous state. However, the interference of this relatively small amount of copper could be due t o some negative catalytic effect. Any copper present in a titanium alloy is reduced t o the metallic state by the titanous ion when the sample is dissolved. This metallic copper is subsequently dissolved on heating the solution with permanganate. The presence of more than 2.5% nickel or 2.5% cobalt leads t o low results for silicon. More than 0.5% phosphorus gives high results for silicon. All the above limit%for interferences in titanium alloys are greater than the nominal amounts of these elements that would be found in commerci:d titanium alloys.
Table 111. Amounts of Alloying Elements Not Interfering with Colorimetric Determination of Silicon in Titanium .4lloys Element Iron Chromium Copper rickel Cobalt Phosphorus Aluminum Manganese Tanadium Calcium Molybdenum Boron Tungsten Tin Carbon a
i?k,:?;
‘HdzCrzO;“
S i C l l ’6HzO CoClz’6Hz0 (?;H~)zHPOI .41z(S04)8~18HzO .\ZnSO,’ Hz0
Amount That Did Yot Interfere,
t=.
7 .5 (maximum amount permissibIe) 10 (maximum amount permissible) 0 . 7 5 (maximum amount permissible),
2 . 5 (maximum amount permissible). 2 . 5 (maximum amount permissible) 0 , 5 (maximum amount permissible!, 5
Jy,oc)l:c~h~o
?O ?
iisnoa
1
YHi)sMo;021.4HzO 10
Saz’lVO,. 2H10 p SnClz .2H?0 J Titanium alloy con- 0 . 5 taining 0.5% carbon Chromate ionis reduced to chromic atate in dissolving titanium metal.
Biabson. J. A , , lIattraw, H. C., ?iIaxmll, G. E., Darrow, A, and Xeedham, hl. F.,Zbid., 20,504 (1948). Bunting, U‘.E., Zbid., 16, 612 (1944). Cailson, A. B., and Banks, C. V., ANAL.CHEM.,24, 472 (1952). Case, 0. P., IXD.ENG.CHEM., AXAL.ED.,16,309 (1944). Clausen, D. F., and Roussopoulas, H. D., Anachem .$-CULS, 6 , 41 (1946).
Cox, H., Metallurgia, 33, 121 (1946). Davis, H. C., and Bacon, A . , J . SOC.Chem. Ind., 67, 316 11948). Ephraim, F., “Inorganic Chemistry,” p. 781, New York, Interscience Publishers, 1948. Gentry, C. H. R., and Sherrington, L. G., J . SOC.Chem. Ind., 65, 90 (1946).
Gettler, A. O., and Umberger, C. J., Am. J . Clin. Path., Tech. Sect., 9 , 1 (1945).
Guenther, R., and Gale, R. H., A x . 4 ~ CHEM., . 22, 1510 (1950). Hadley, W.H., Analyst, 70, 43 (1945). Hill, G. T., ANAL.CHEY.,21,589 (1949). Kahler, H. L., IND. ENG.CHEM.,-4x.4~. ED.,13, 536 (1941). Knudsen, H. W.,Juday, C., and lleloche, V. W., Ibid., 12, 270 (1940).
Kurtz, L. T., Ibid., 14,855 (1942). Lindsay, F. K., and Bielenberg, R. G., Ibid., 12, 460 (1940). Olsen, A. L., Gee, E. A., AIcLendon, V., and Blue, D. D., Zbid.,
LITERATURE CITED
(1) Abbey, S., r i s t ~CHEM., . 20, 630 (1948). (2) Adams, hl. F., IXD. E m . CHEM.,&%SAL.ED.,17, 542 (1945). (3) Alimarin, I . P., and Zveiev, V. S., Mzkrochemte, 22, 89 (1937). (4) Bergammi, C . , Anal. Cham Acta, 14,153 (1950). . 19. 873 11947). 15) Bolts. D. F.. and Alellon. -11. G.. A N ~ LCHEM.. (6) Boyle, A. J., and Hughey, V. V., IXD.ESG. CHEM.,ANAL. ED., 15,618 (1943). (7) Brabson, J. A,, Harvey, I. W., Maxwell, G. E., and Schaeffer, 0. A., Ibid., 16, 705 (1944).
Added as
16,462 (1944).
Potter, G. V., ANAL.CHEW,22, 927 (1950). Schwartz, At. C., IND.E m . CHEM.,Alx.4~.ED., 14, 893 (1942). Straub, F. G., and Grabowski, H. A., Zbid., 16, 574 (1944). Stroas, W., Analyst, 6 9 , 4 4 (1944). Tananaev, N. A., and Shapovelenko, A. M., J . A p p l . Chem. (U.S.S.R.), 11,352 (1938).
Titanium Metals Corp. of America, Kew York, “Handbook on Titanium Metal,” p. 50, 1952. RECEIVED for review -4pril 2, 1953. Accepted .4ugust 18, 1953.
(Methods for Analysis of Titanium Alloys)
Nephelometric and Gravimetric Determination of Small Amounts of Calcium in Titanium Alloys MAURICE CODELL, ALLEN CHERNEY,
AND
GEORGE NORWITZ
Pitman-Dunn Laboratories, Frankford Arsenal, Philadelphia, Pa.
C
ALCIUlI is sometimes present as an impurity in titanium alloys. Hitherto, no methods have been published for the determination of calcium in this type of alloy. The usual methods for the determination of calcium are not directly applicable to titanium alloys. The classical oxalate method (8, 14, 26), whereby the calcium is precipitated as the oxalate from a slightly ammoniacal solution containing a moderate excess of oxalate, is not applicable t o titanium alloys because of the coprecipitation of titanium. The precipitation of calcium oxalate from a slightly acidic solution (16) will provide a separation of calcium from small but not large
amounts of titanium. The use of a very large excess of oxalate ion will complex the titanium and prevent its precipitation from either an ammoniacal solution or an acidic solution. However, under these conditions the precipitation of the calcium oxalate is very incomplete. The separation of calcium as the sulfate from an alcoholic medium ( 1 , 9 ) is not directly applicable t o titanium alloys. It was found that a-ith a solution containing titaniumsulfate, calcium sulfate, and alcohol no precipitate a t all could be obtained, probably because of the formation of a titanium-calcium complex. The precipitation of the calcium a s calcium molybdate
V O L U M E 25, NO. 10, O C T O B E R 1 9 5 3 ( 2 1 , 29) or calcium tungstate (10, 2 5 ) cannot be used directly on titanium alloys because of the coprecipitation of the titanium. I n view of the failure of the above separations it was necessary to remove the titanium from solution containing the calcium before determining calcium. The ammoniacal separation of titanium from the calcium was found to give very poor recoveries of the calcium. The separation of the titanium by a cupferron precipitation and a chloroform extraction (4,20) was found to be very satisfactory. Having decided on the use of a cupferron precipitation and chloroform extraction, it was next necessary to find a means for determining the calcium. Two methods were consideied, the oxalate method and the sulfate method. Calcium oxalate has been used for the determination of small amounts of calcium ( I d , 19, 84). However, according to the experiments of the authors, the recoveries of less than 0.5 mg. of calcium as the oxalate left much to be desired. I t was, therefore, decided to investigate the sulfate method. Good results were obtained by the sulfate method, using either an ethanol (9) or a methanol medium ( I ) , but somewhat better results were obtained using the methanol medium. When more than 0.02% calcium was present the calcium could be accurately weighed as calcium sulfate. When less than 0.02% calcium was present, the most accurate means for determining the calcium was to dissolve the calcium sulfate precipitate in dilute nitric acid and determine the calcium nephelometrically as the stearate. I n the gravimetiic method for the determination of calcium as calcium sulfate, the precipitate is filtered through a filter paper and ignited as calcium sulfate. The ignition temperature mas not found to be critical. The temperature a t which the decomposition of calcium sulfate to calcium oxide starts to take place is 1200' C. (13). Duval ( 2 ) and Peltier and Duval ( 2 3 ) in their work with the Chevenard thermobalance found no evidence of decomposition of calcium sulfate at 1000D C. The Chevenard therniobalance is not applicable to temperatures greater than 1000" C. In this laboratory it was found that an ignition of the calcium sulfate for 5 t o 10 minutes with either a Tirrill or a Meker burner was satisfactory. In the nephelometric method for the determination of calcium it was decided to use the modified ammonium stearate reagent which contains some oleic acid (18, $92, W?). It was found that the best wave length for making the nephelometric readings was 415 mp. The readings follow Beer's law. Provision must be made for removing the many metals that can precipitate as sulfates in an alcoholic medium. It was decided to include an ammoniacal sulfide separation in the method in order to remove heavy metals not extracted by the chloroform. For alloys containing chromium, aluminum, manganese, or tungsten special separations must be made. As it was found that the ammoniacal sulfide separation method could not be safely relied on for removing the chromium quantitatively, it was decided to volatilize the chromium as chromyl chloride (88). I t was also found that the ammoniacal sulfide separation method was not reliable as a means for removing the aluminum. This is in keeping with the findings of others (6). To ensure the complete removal of aluminum, a careful ammoniacal separation ( 7 ) was made. The removal of manganese by precipitation from thc ammoniacal sulfide medium was found to be only partially complete. This was not surprising, as manganese sulfide i.; one of the most soluble of the precipitable sulfides. Possibly by allowing sulfide solution t o stand overnight (J),a more complete separation of the manganese could be obtained. However, it was decided that the safest procedure was t o separate the manganew as manganese dioxide after oxidation by persulfate (11, 16). I n keeping with the findings of other investigators (3, 4,I 7 ) , it was found t h a t tungsten was only partially removed by the cupferr on precipitation and chloroform estraction. I t was necessary, therefore, in alloys containing tungsten to remove any uneatracted tungsten as tungstic oxide. I n developing the procedures it was found that a surprisingly
1435 1argr blank could be obtairied from the use of C.P. ammoi~iunihj-dioxide or nitric acid. This was remedied by redistilling the minionium hydroxide and nitric acid used. APPARATUS AND REAGEYTS
A spectrophotometer having a nephelometric attachment was required. A Coleman Universal spectrophotometer, Model 14, with 20 X 40 mm. optically matched cuvettes was used in this laboratory. Gooch semimicro crucibles, about 5-ml. capacity. ,A 500-ml. suction filter flask with an adapter suitable for holding the semimicro Gooch crucible, and having a drawn-out stem which can fit into the neck of a IO-ml. volumetric flask. Nitric acid, c.P., redistilled. Ammonium hydroxide, c.P., redistilled. Hydrochloric acid, c.P.,specific gravity 1.19. Sulfuric acid, c.P., specific gravity 1.84. Perchloric acid, c.P., 70%. Nitric Acid, 0.05 .V. Dilute 1.4 ml. of redistilled nitric acid to 500 nil. with water. Sulfuric Acid (1 to 5 ) . llis 50 ml. of sulfuric acid and 250 nil. of water. Cupferron Solution, 9%. Dissolve 45 grams of cupferron in 500 nil. of water. Filter. Methanol, absolute. Chloroform, reagent grade. RIethvl Red Indicator. Dissolve 0.1 gram of methvl red powder in 100 ml. of 95% ethyl alcohol. Ammonium Chloride Wash Solution, 2 5 , . Dissolve 20 grams of C.P. ammonium chloride in 1 liter of water and make just alh:tline to methyl red with redistilled ammonium hydroxide. lmmonium Persulfate Wash Solution, 2y0. Dissolve 20 grams of C.P. ammonium persulfate in 1 liter of water. Ammoniacal Ammonium Sulfide Wash Solution A4dd20 nil. of redistilled ammonium hydroside to 1 liter of water and satutate with hydrogen sulfide. .Ammonium Stearate Reagent. Dissolve 4 grams of stearic acid and 0.5 ml. of oleic acid in 400 ml. of hot 9570 methanol. Add 20 grams of C.P. ammonium carbonate dissolved in 100 nil. of hot water. ll-hen cool, add 400 ml. of 95% methanol, 100 ml. of water, and 2 ml. of redistilled ammonium hydroxide. Filter. The solution should be water clear and colorless. Standard Calcium Solution 1 (I ml. = 0.045 mg. of calcium). Dissolve 0.1933 gram of C.P. calcium sulfate (CaSOc-2HzO) in water and dilute to 1 liter in a volumetric flask. Standard Calcium Solution 2 (1 ml. = 0.25 mg. of calcium). Dissolve 1.0739 grams of C.P. calcium sulfate (CaS04.2HzO) in water and dilute to 1 liter in a volumetiic flask. PROCEDURE
Gravimetric Procedure (for samples containing more than 0.02% calcium). Add 25 ml. of hydrochloric acid to a I-gram
sample contained in a 250-ml. beaker and warm on the hot plate until the sample is dissolved. Add 1 ml. of redistilled nitric acid, swirl, and remove immediately from the hot plate. Cool the solution to about 10' to 15" C. in an ice bath. At the same time cool the 9% cupferron solution and the chloroform. Transfer the sample to a 500-ml. separatory funnel, add 200 ml. of Yc', cupferron solution, and shake for 30 seconds to coagulate the precipitate. Add 100 ml. of chloroform and shake for 30 seconds. Open the stopcock occasionally to release the pressure. Allow 1 minute for the aqueous and chloroform layers to separate, then drain off and discard the chloroform layer. Add a second 100-ml. portion of chloroform to the separatoiv funnel and repeat the extraction and separation as above. =idd 5 ml. of cupferron solution. If a white flash of cupferron appears, enough cupferron has been added. If the precipitate formed is colored, add more cupferron solution and extract with a 50-ml. portion of chloroform. Test again with the cupferron solution to see whether the white flash occurs. If necessary, repeat the cupferron addition and extraction until the white flash 1s obtained. FVhen this occurs, extract with 50-ml. portions ot chloroform until both layers are water white. Transfer the aqueous phase to a 600-ml. beaker and evaporate the solution to d r \ ness on the hot plate. Add ahout 25 ml. of water and boll t o dissolve the salts. Cool, add 1 drop of methyl red indicator, add redistilled ammonium hydroxide until the solution is alkallne, and then add 10 drops in ewess. Pass a rapid stream of hydrogen sulfide through the solution for 10 minutes. Allow the preriprtate to settle for 30 minutes. Filter through a fine filter paper (Khatman KO. 42) into a 250-ml. beaker. Wash with ammoniacal ammonium sulfide Kash solution. Discard the precipitate. Eva orate the filtrate to a volume of about 20 ml. Remove from the got plate. .Add 10 rnl. of redistilled nitric acid and 1 1111 of
ANALYTICAL CHEMISTRY
1436
Table I. Calcium in Titanium Samples Not Containing Chromium, Tungsten, Aluminum, or Manganese Average Calcium Calcium Standard No. of Added, % Found, % Deviation, % Detns. Nephelometric 0,0045 0.0090 0.0135 0.0180
0.0045 0.0091 0.0135 0.0175
0.018
0.017 0.025 0,051 0.076 0.100 0.151 0.202 0.302
0.00000 0.00031 0.00000 0.00240
4 4
4 4
Gravimetric 0,027 0,050 0.075 0.100 0.150 0.200 0.300
0.001; 0.0012 0.0010 0.0000 0.0016 0.0016 0.0029 0.0035
3 3 5 4 5 6
4 3
Table 11. Calcium in Titanium Samples Containing Chromium, Tungsten, Aluminum, or Manganese Average Ca 1c i u m Calcium Standard x o . of Added, % Found, % Deviation, % Detns. Samples Containing 13% Manganese (Added as Manganese Metal) 0.040 0.060
0.039 0.0014 2 0,058 0.0022 2 Samples Containing 5% Aluminum (Added as Aluminum Metal) 0.090 0.092 0.0026 5
Samples Containing 5 % Tungsten (Added as Sodium 0.040
Tungstate) 2
0.040 0.0022 0.060 0.0000 2 Samples Containing 15% Chromium (Added as Chromic Oxide) 0.080 0.082 0,0000 3 Samples Containing 13’70 Manganese, 5% Aluminum, 5 % Tungsten, a n d 15% Chromium 0.135 0.136 0 0014 3 0,060
sulfuric acid. Evaporate to fumes of sulfuric acid. If the organic matter is not destroyed, add redistilled nitric acid dropwisr and repeat the evaporation to fumes of sulfuric acid. Allow to cool to room temperature. .4dd 2.5 ml. of water and mix thoroughly. Add 60 ml. of methanol and stir vigorously until a precipitate appears. Take care not to scratch the sides of the beaker. Allow to stand overnight. Filter through a fine filter paper (Whatman No. 42). Transfer the precipitate quantitatively to the filter paper, and wash with methanol. Place the filter paper and precipitate i n a tared platinum crucible, ignite at low heat until the paper is charred, and increase the heat until the carbon is burned off. Finallv. “ , ignite with a Tirrill burner a t red heat for 5 to 10 minUtes. Cool and weigh as CaS04. The factor for converting CaSO, to Ca is 0.2944. If tungsten, aluminum, or chromium is present, either individually or in combination, proceed as in the regular procedure to the point a t which the solution has been evaporated to dryness following the cupferron precipitation and chloroform extraction Add about 25 ml. of water and boil to dissolve soluble salts. If tungsten is present, filter through a fine filter paper (Whatman Yo. 42) and wash with hot water. Discard the precipitate and proceed with the ammoniacal sulfide separation as described If aluminum is present, make the solution just alkaline to methyl red with redistilled ammonium hydroxide and add 2 drops excess ammonium hydroxide. Heat to boiling. Filter through a medium texture filter paper (Whatman No. 4 0 ) and wash with hot ammonium chloride wash solution. Add a few drops of redistilled ammonium hydroxide to the filtrate and proceed with the ammoniacal sulfide separation. If chromium is present, wash the solution into a 250-ml. beaker, add 10 ml. of nitric acid and 10 ml. of perchloric acid, and evaporate to fumes of perchloric acid. Add hydrochloric acid dropwise to volatilize the chromium. Evaporate to dryness. Add :ibout 25 ml. of water, boil to dissolve the salts, and proceed with the ammoniacal mlfide separation. If manganese is present, proceed as in the regular method t o the point a t which the solution has been evaporated to a volunir of about 20 ml. following the ammoniacal sulfide separation. Then proceed as follows: Make the solution just acid to methyl red with dilute sulfuric acid (1 to 5) and add 2 drops of dilute sulfuric acid (1 to 5 ) in excess. Bring the solution to boiling and add 1 gram of ammonium persulfate. Boil 2 or 3 minutes to coagulate the manganese dioxide. Cool to room tempwnturr
-
Filter through a fine filter paper (Whatman No. 42) and wash with ammonium persulfate wash solution (27,). Add 10 drops of dilute sulfuric acid (1 to 5) and 10 ml. of redistilled nitric acid to the filtrate, and evaporate to fumes of sulfuric acid. .4dd the 2.5 ml. of water and 60 ml. of methanol and precipitate the calcium sulfate as in the regular procedure. Nephelometric Rocedure (for samples containing less than 0.02% calcium). Proceed as in the gravimetric procedure, but instead of filtering the calcium suHate through a filter aper, filter it through a semimicro Gooch crucible with an asgestos mat. Transfer the precipitate quantitatively to the Gooch crucible and waqh with methanol. Break the suction and discard the filtrate. Place a 10-ml. volumetric flask inside the filtering flask and insert the drawn-out stem of the adapter into the neck of the volumetric flask. Start the suction and dissolve the calcium sulfate into the 10-m1. volumetric flask with 10 ml. of hot 0.05 N nitric acid added in small portions from a wash bottle. Break the suction and remove the volumetric flask. Wash the contents of the 10-ml. volumetric flask into a 50-ml. volumetric flask with a little water, add 25 ml. of ammonium stearate reagent, and dilute to 50 ml. with water. Shake and allow to stand 15 minutes, Shake again. Compare nephelometrically a t 415 m,u with a reagent blank that has been carried through all steps of the procedure. Convert the readings t o per cent calcium by comparing the readings with the reading obtained with a standard sample. This standard sample is prepared by adding standard calcium solution I to calcium-free titanium metal and carrying the samplr tliioiigh :ill steps of the procedure. RESULTS
Z,i no stailtiat (1 w n p l e of titanium containing c~:111~1urn \vas .ivailable, the accuracy and precision of the procedures \vcrc vherked by adding qtandard calcium sulfate solution t o 1-pram portions of calcium-fre~titanium metal and carrying the samples through the procedurch. The r ~ s u l t obtained s for samples which (lid not contain rhroniiuni, tungsten, aluminum, or manganew are sho\\.ii in Table I. The r e p u b obtained for samples containing r.hroiiiium, tung~teii,:rluininum, or manganese are shown in Tahle 11 LITERATURE CITED
Caley, E. R., and Elrina. 1’. .J.. IKD.ENG.CHmf., . i s \ r , . En., 10,264 (1938).
Duval, C., AXAL.CHFX.,23, 1 2 i l (1951). Foster, M.D., Grinialdi. F. S., and Stevens, R. E.. Y. S.Gcological Survey, R c p l . 2 (1944). Furman, N. H., hlilson. K . A.,and Pekola, J. S., AKAI.. CHEM., 21,1328 (1949).
Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorgaiiic ilnalysis,” p. 59, S r n Y o r k , .John Wiley 6 Sons, 1929. Ibid., p. 391. Ibid., p. 397. Ibid., p. 497. Ibid., p. 503.
Katakousinos, TI., t’ruktirln ( d k t r d . Athenon), 4, 400 (1929). Knorre, G. von, Z . angczc. (‘hem., 16, 905 (1903). Kochakian, C. D., and Fox. R . P., IND. ESG. CHEM., ANAL.ED., 16,762 (1944).
Kolthoff, I. hl., and Sandell, E. B., “Textbook of Quantitative Inorganic Analysis.” p. 354, New York, Xacmillan Co., 1946. Ibid., p. 358. Lingane, J. J., IXD. ENG.CHEM.,ANAL.ED.,17, 39 (1945). Lundell, G. E. F., Hoffman, J. I., and Bright, H. A., “Chemical Analysis of Iron and Steel,” p, 206, Few Tork, John Wiley 6: Sons; 1931. Lundell, G. E. F., and Knowles, H. B., J . I n d Bng. Chc?n., 12, 344 (1920).
Lyman, H., J . Biol. Chem., 29, 169 (1917). Rllarsden,A. W.. J . SOC.Chem. Ind., 6 0 , 2 1 (1941). XIeunier, P., Compt. rend., 199, 1250 (1934). RIoser, R.,’and Robinson, R. J., IND. ENG.CHEM.,4 s \ r ED., 19,929 (1947).
Peech, AI., and English, L., Soil Sci., 57, 167 (1944). Peltier, S., and Duval, C., Anal. Chim. Acta, 1, 346 (1947). Rynasiewica, J., and Polley, M. E., ANAL.CHEM.,21, 1398 (1949). Saint-Sernin, A., Compt. rend., 156, 1019 (1913). Scott, W. W., “Standard Methods of Chemical Analysis,” 5th ed., Vol. 1, p. 210, New York, D. Van Nostrand Co., 1939. Snell, F. D., and Snell, C. T., “Colorimetric Methods of Analysis,” Vol. 1, p. 450, Kew York, D. Van Nostrand Co., 1936. U. S. Steel Corp., “Sampling and Analysis of Carbon and Alloy Steels,” p. 70, New York. Reinhold Publishing Corp., 1938. Wiley, R . C., IND. EBG.CHEM.,AXAL.ED.,3, 127 (1931). RECEIVED for reviea- April 2, 1953. Accepted August 18, 1953.
