148
ANALYTICAL CHEMISTRY
by the silica content. If the silica in the original weighed samples was in the range 0 to 1.0 mg. of Sios, a 50-ml. aliquot of the neutralized solution was taken and for the range 1.0 to 20 mg. of SiOza 5-ml. aliquot was used. The adjusted solution was transferred to a 100-ml. mixing cylinder and made u p to 75 ml. and 2 ml. of 5% ammonium molybdate added. After 5 minutes, 10% tartaric acid was added, dependent on the salt concentration.
0,201 0.15
A blank for all reagents used was prepared and measured in the same manner. Molybdenum Yellow Method. When samples containing more than 400 micrograms of silica per sample aliquot were regularly encountered, the absorbancy measurements were made on the yellow molybdisilicic acid complex a t 410 m p . To the pH adjusted solution a t 75 ml., 7.5 ml. of 5% ammonium molybdate were added and mixed. After 5 minutes, 2 ml. of 10% citric acid were added, the solution was made up to 100 ml. and mixed, and the absorbancy measurements were made 2 to 10 minutes following the addition of the citric acid. Four calibration curves for standard solutions were usually made a t the concentrations 0.585 and 5.85 grams of sodium chloride and 0.746 and 7.46 grams of potassium chloride per 100 ml. These curves are illustrated in Figures 2 t o 5 . ACKNOWLEDGMENT
0
2 0.10 U
0.051
0
The authors express their appreciation to G. L. Murphy and George Oplinger for helpful advice.
/
LITERATURE CITED
400 600 800 MICROGRAMS S I L I C A
200
1000
Figure 5. Calibration Curve Yellow complex, IO-mm. cells, 410 mo 0.58 g r a m of sodium chloride
When the salt concentration was greater than 2 grams of sodium chloride per 100 ml. or 3 grams of potassium chloride per 100 ml., 2 ml. of 10% tartaric acid were used; otherwise 4 ml. of 10% tartaric acid. After the addition of tartaric acid the solution was allowed to stand 5 minutes, 5 ml. of reductant solution were added, and the solution was u p to 100 ml. The solution was mixed after the addition of each reagent. After 10 minutes the absorbancy was measured in a 1-cm. cell a t 660 mp. Very small amounts of silica may be measured more accurately a t 825 mp.
(1) Adams, M. F., IND.ENG.CHEM.,ANAL.ED.,17, 542 (1945). (2) Am. SOC. Testing Materials, ASTM Designation 859-50T, Referee Method B. (3) Barnes, H., Clayton, H. R., Irving, H., and Leyton, L., Ann. Repts. Progress Chem. (Chem. SOC.London), 21, 341 (1949). (4) Bunting, W.E., IND.ESG. CHEM.,ANAL.ED.,16, 612 (1944). (5) Dienert, F., and Wandenbulcke, F., Cornpl. rend., 176, 1478 (1923). (6) Hiskey, C. F., ANAL.CHEM.., 21, 1440 (1949). (7) Jolles, A , , and Keurath, F., 2. angew. Chem., 11, 315 (1898). (8) Kahler, H. L., IND.ERG.CHEM.,ANAL.ED., 13, 536 (1941). Zbid., 12, 270 (9) Knudson, H. W.,Juday, C.. and bleloche, V. W., (1940). (10) Robinson, J., and Spoor, H. R., Ibid., 8, 455 (1936). (11) Schwartz, M. C., Ibid., 14, 893 (1942). (12) Stoloff, L. S., Ibid., 14, 636 (1942). (13) Straub, F. G., and Grabowski, H. -4,, Ibid., 16, 574 (1944). (14) Strickland, J. D. H., J . Am. Chem. Soc., 74, 862-76 (1952). (15) Thayer, L., IND.ENG.CHEM.,ANAL.ED., 2, 276 (1930). (16) Thompson, T. G., and Houlton, H., Ibid., 5 , 417 (1933). RECEIVED for review July 7, 1952. l c c e p t e d October 3, 1952.
Photometric Determination of Silicon in Ferrous, Ferromagnetic, Nickel, and Copper Alloys A Molybdenum Blue Method C. L. LUKE Bell Telephone Laboratories, Inc., Murray Hill,N . J.
T
HE purpose of the present investigation was the development
of a simple photometric method for the determination of silicon in all types of ferrous, ferromagnetic, nickel, and copper alloys. A few qualitative experiments and a study of the recent literature on photometric silicon analysis ( 2 , 4,7 ) indicated that it would be virtually impossible to develop such a widely applicable method without resorting to separations before the photometric determination was made. From the work of Guenther and Gale (3) it appeared probable that the interfering constituents could be separated by one of the new precipitation-extraction techniques. Serfass and his associates (8)used a sodium diethyldithiocarbamate-chloroform extraction to remove nickel from nickel plating baths prior to the determination of aluminum. This extraction method proved to be satisfactory for the removal of the metals which interfere in the silicon determination.
As a result, a method has been developed which is rapid, convenient, and widely applicable. The method is not applicable to alloys where solution of the silicon is incomplete-e.g., National Bureau of Standards aluminum base alloy, No. 86-e-but almost all ferrous, ferromagnetic, nickel, or copper alloys can be successfully analyzed. The method consists of solution of the sample in a mixture of hydrochloric and nitric acids, destruction of the nitrio acid by heating with formic acid, removal of all interfering metals by a carbamate-chloroform extraction, and finally, determination of silicon by the usual photometric molybdenum blue method using, essentially, the technique described by Minster ( 5 , 6 ) . The time of analysis is approximately 2 hours. The method is applicable in the range of 0.01 to 2% of silicon if the rather poor precision and accuracy in the upper ranges, which result from the limitations of photometric technique, can be
V O L U M E 2 5 , N O . 1, J A N U A R Y 1 9 5 3
149
A simple, rapid photometric method for the determination of silicon in ferrous, ferromagnetic, nickel, and copper alloys has been developed. Wide applicability is its most unique and important feature. Interfering elements are removed by a carbamate-chloroform extraction and silicon is then determined by the photometric molybdenum blue method. Confirmatory data on a wide variety of samples of known silicon content are presented.
tolerated. The results of analysis of various metals and alloys of known silicon content by the recommended method are given in Table I. APPARATUS
Photoelectric Photometer. An Evelyn photometer with a 765 mp filter and 2-cm. absorption cells was used in the present invedigation. REAGENTS
Redistilled Water. I n order to obtain a low blank it will usually be necessary to redistill the ordinary distilled water, condensing the steam in a block tin pipe and catching and storing the distillate in polyethylene bottles equipped with polyethylene screw caps. Alternatively, deionized water obtained from a monobed resin ion exchange column may be used. Standard Silicon Solution (0.01 mg: of silicon per ml.). Transfer 0.1000 gram of powdered silicon dioxide to a platinum crucible and heat to constant weight a t l l O O o C. to remove water. Treat. t,he dry residue with hydrofluoric and sulfuric acids, evaporate to dryness, reignite, and weigh. The weight of the original sample minus the weight of water plus residual oxides represents the silica content. Transfer an accurately weighed portion of t'he undrieti powdered silicon dioxide, which is equivalent to 0.107 gram of silicon dioxide, to a platinum dish. ;Idd 10 ml. of redistilled water and about, 0.5 gram of potassium hydroxide. Warm until complete solution of the sample occurs. (If the particular sample available is not soluble in potassium hydroxide, it may be necessary, inst'ead, to resort to a fusion with 1 gram of anhydrous sodium carbonate followed by solution of the cooled melt in water.) \Torking quickly, pour the solution into 350 ml. of redistilled water in a 400-ml. beaker and wash out the dish into the beaker. Transfer the solution from the beaker to a 500-ml. volumetric flask, dilute to the mark with redistilled water, and transfer to a clean dry polyethylene bottle. Working quickly, pipet .50 ml. of this solution to a 500-ml. volumetric flask, dilute to the mark with redistilled water, mix, and transfer to a clean dry polyethylene bottle. Sulfuric Acid Solution (1 to 3 ) . Pour. 100 ml. of sulfuric acid into 300 ml. of redistilled water. Cool and transfer to a polyet'hylene bottle. Ammonium Molybdate Solution. Dissolve 10 grams of the !arger cryst,als of ammonium molybdate. ( NH4)6M07024.4H20, in 200 ml. of redistilled water by sivirling. Store in a polyethylene bottle. Stannous Chloride Solution. Transfer 1 gram of the larger crystals of stannous chloride, SnClz, 2H20, to a 100-ml. volumetric flask and add 2 ml. of hydrochloric acid. Warm gently until a clear solution is obtained. Cool, dilute to the mark with redistilled water, and mix. Prepare fresh each dav as required. Hydrochloric Acid-Nitric Acid Mixture. Rhx 40 ml. of hydrochloric acid plus 40 nil. of redistilled water plus 20 ml. of nitric acid. Prepare fresh each day as required. Carbamate Solution. Dissolve 5 grams of Eastman's C.P. sodium diethyldithiocarbamate in 100 ml. of redistilled water. Filter if the solution is cloudy. Store in a polyethylene bottle. Prepare fresh each day as required. PROCEDURE
Preparation of Calibration Curve. Transfer 0, 1,2, 3 , 4,5 , and 6 ml. of standard silicon solution (0.01 mg. of silicon per ml.) from a good quality buret to 100-ml. volumetric or Bates sugar flasks and add 1 ml. of 1 to 3 sulfuric acid. Dilute to 55-ml. volume with redistilled water and mix. Add 10 ml. of ammonium molybdate solution, mix, and allow to stand 5 minutes. Add 30 ml. of 1 to 3 sulfuric acid, stopper the flask, and invert once or twice to mix the solution. (The stannous chloride that is added subsequently must not he allowed to come in contact with nonacidified ammonium molybdate solution on the walls of the flasks; otherwise some reduction of the molybdate r\ ill result.) -4dd 1 ml. of
stannous chloride solution and s\l-irl to mix. Immediately dilute to the mark and mix well by inverting the flask four or five times. Transfcr a portion of the eolut'ion to 2-cm. absorption cells and read thp per cent transmittnncy of the solutions a t 765 n i p 5 minutes after the addition of the stannous chloride. (\\-hen using the 765 me filter provided with the Evelyn photometer there appears to be a slight time lag before a steady reading is obtained after the absorpt,ion cell is inserted in the photometer.) Distilled wat,er should be used as the reference solution. Prepare a calibration curve by plotting per cent transmittancy values on the logarithmic scale of semilog paper against milligrams of silicon added to the flasks. If distilled water and reagents of sufficient purity have been employed, the transmittancy of the sample to which no silicon has been added should be in the neighborhood of IOOY,. Analysis of Sample. Transfer u p to 0.2000 gram of the milled sample to a 125-niI. conical flask. The sample taken should contpin not mor(, than about 0.5 mg. of silicon; or, if the expected silicon c~ontentis over 1%, not more than about 0.3 mg. of silicon. Carry a rcvigent blank through the entire analysis. Add 10 nil. of hydrochloric acid-nitric acid mixture, cover, and warm gently to dissolve the sample. ( I n the w e n t that nickel metal is being analyzed, dissolve the sample in 4 nil. of 1 to 1 nitric? acid by heating gently and then add 6 nil. of 2 to 1 hydrochloric acid.) Avoid, as much as possible, loss of acid by volatilization. Ignore insoluble carbides or other material surh as tungsten. \\-hen solution is complete, remove the cover and add about 1 nil. of formic acid from a medicine dropper. When decomposition of the nitric acid starts, remove the sample to a cooler place and alloil- the reaction t,o proceed. Add further 1-ml. portions of formic acid from time to time, rsarming occasionally, if necessary, to maint,ain the decomposition. About 3 or 4 ml. of forinic acid will be required to destroy the nitric acid. Finally, \\.hen the gassing subsides,, return the flask to the low temperature hot
Table I.
Determination of Silicon in Various Rletals and Alloys
Sainple Aliquot slae, Taken, Micon, %Mg. MI. Found Present Sample 0 173 200 0.16 1 NBS steel, No. 19-e 10 0 173 200 0 17 2 NBS steel, No. 19-e 10 0.58 100 5 0 589 3 NBS Cr-Ki (18-9) steel, KO.101-c 0 . 6 0 5 0 S89 4 NBS Cr-h'i (18-9) steel, No. 101-c 100 0.33 200 0 323 5 NBS Mo-W-Cr-V steel, No. 134 5 0 . 3 3 0 323 200 5 6 NBS Mo-W-Cr-V steel, No. 134 7 NBS casting alloy (64 Xi-17 Cr1 56 25 1.45 10 15 F e ) , No. 161 8 KBS casting alloy (64 h-i-17 Cr1 36 25 1 . 5 0 10 15 F e ) , KO.161 9 S B S electrical-heating alloy (77 1 420 25 1 . 4 3 10 Xi-20 Cr), No. 169 10 S B S electrical-heating alloy (77 1 42'J 1 . 3 7 25 Ni-20 C r j , No. 169 10 11 NBS electrical-heating alloy (77 1 42a 1 . 4 1 25 10 Ni-20 Cr), KO.169 0 16 200 10 0.16 12 Permalloy (45 Ni-55 Fej 0 16 200 0.16 10 13 Permalloy (45 Ni-55 Fe) 0 11 200 0.12 10 14 Permalloy (80 Ni-15 Fe-5 AIo) 0 02 25 200 0.02 15 Reinalloy (70 Fe-20 Xfo-IO Co) 16 Vanadium Perrnendiir (50 Fe-48 0 11 0.11 200 10 c o - 2 V) 17 Yanadiurn Perrnendur (50 Fe-48 0 11 200 0.12 10 c o - 2 V) 0 10 0.12 200 10 18 Vicalloy ( 5 5 c o - 3 0 Fe-15 Y) 0 10 0.11 200 10 19 Vicalloy (55 Co-30 Fe-15 Vj 0 67 0.65 J0 10 20 KBS monel, No. 162 0 67 0.66 21 NBB monel, KO.162 50 10 0 019 0 019 '00 25 22 APThI standard nickel S o . 6166 0 20 200 10 0.19 23 ASTM standard nickel 40. 2555 0 LO 0.20 10 200 24 ASTM standard nickel S o . 2553 0 075b 200 25 0.072 25 S B S ounce metal, KO.124 0 048 200 25 0.046 26 KBP manganese bronze, KO.R2-b n 048 0 050 200 25 27 S B S manganese bronze. X o . 62-b 0 12 200 0 13 10 28 KBS phosphor bronze, S o . f.3-b 0 12 0 13 10 200 29 KBS phosphor bronze, S o . 63-b Value obtained gravimetrically b y ,J. 1'. Jensen of these laboratririw. h .Iverage value for silicon reported by various cooperating analysts W&8 0.071%:.
150 plate, rinse down the walls with about 0.25 ml. of formic acid, and heat to gentle boiling to expel brown fumes completely. Avoid the addition of an unnecessary excess of formic acid and avoid loss of too much hydrochloric acid by boiling. Cool the sample to room temperature. Transfer without delay to a 100-nil. volunietric flask, filtering through a fine-textured paper if necessary. Dilute without delay to the mark with redistilled water and mix. Transfer a 5-, lo-, or 25-m1. aliquot portion of the solution, containing preferably 0.01 to 0.06 mg. of silicon, to a 150-ml. Squibb-type separatory funnel. .4dd 1 ml. of 1 to 3 sulfuric acid to the 5-ml. aliquot or 0.5 nil. of the same acid to the 10- or 25-ml. aliquot. Add 35, 25, or 0 ml. of redistilled water, respectively, to the 5-> lo-, or 25-ml. aliquot and swirl to mix. Add a 5, lo-, or 25-ml. portion of the carbamate solution, respectively, to the 5-, lo-, or 25-nil. portion of the sample solution. Stopper and shake once or twice to mix the sample thoroughly. Add 35 ml. of chloroform, stopper, and shake vigorously for 30 seconds. Remove the stopper and allow the layers to separate. When separation has occurred, swirl the solution to loosen the floating drop of chloroform and then drain o f f and discard as much as posqible of the lower layer. (Avoid too rapid drain off; otherwise some of the aqueous layer may be sucked down into the stem of the funnel.) Repeat the extraction two or more times with 10- to 15-ml. portions of chloroform to remove traces of extractable carbamates. In the wash extractions a 10-second shaking is adequate. 'When the chloroform layer remains colorless after the second or subsequent wash extraction, drain off the chloroform as completely as possible. Transfer the aqueous solution back to the 125-nil. conical flask with the minimum amount of washing. Heat just to gentle boiling to expel most of the chloroform. (If large drops of chloroform persist, they can be removed by touching with a glass stirring rod. Small drops of chloroform remaining in the solution will do no harm.) Cool to room temperature. Transfer the solution to a 100-ml. volumetric or Bates flask with the minimum amount of washing. Add 10 ml. of ammonium molybdate solution and proceed as directed for preparation of calibration curve, With the aid of the calibration curve, determine the weight of silicon present in the sample and the reagent blank. Alternative Method of Analysis of Nickel. As the method described above is not applicable to samples containing less than about 0.01% of silicon, an alternative method, in which larger samples are employed, must often be used in the analysis of electronic nickel. Minster's method (6) cannot be used because severe fading of the molybdenum blue color occurs on those samples which have undergone electrolysis. Spparently oxidation of the stannous chloride occurs, catalyzed by traces of mercury salts, peroxide, or reduction products of nitric acid. As electronic nickel is relatively free of elements which would cause interference in a silicon determination, the mercury cathode separation can be omitted, providing suitable correction for the background color of the nickel is made. The follo\\ing method is used in these laboratories for the determination of silicon in electronic nickel. Dissolve 0.2 to 0.5 gram of the sample in 5 ml. of 1 to 1 nitric acid, cool, add 5 ml. of sulfamic acid (10 per cent), dilute to 45 ml. with redistilled water, and neutralize to Congo paper with approximately 6 N ammonium hydroxide which has been prepared by bubbling ammonia gas for 10 minutes into 200 ml. of redistilled water in a polyethylene bottle resting in an ice bath. 911 accessories which come in contact with the ammonium hydroxide, such as bubblers and medicine droppers should be of polyethylene. Add 1 ml. of 1 to 3 sulfuric acjd, develop the color, and complete the analysis as directed above, using an appropriate calibration curve. Correct for reagent blank and for background color. Make the latter correction by carrying a duplicate sample through the entire analysis, but omitting the addition of the ammonium molybdate and stannous chloride. With the higher ranges of silicon, transfer suitable aliquots of the sample solution to beakers, add 5-ml. portions of sulfamic acid (lOa/o), and sufficient 1 to 1 nitric acid to compensate for the loss of acid incurred by the aliquoting, and then proceed to the neutralization. Mix the aliquots of standard silicon solution used for the preparation of the calibration curve with 5 ml. of 1 to 1 nitric acid plus 5 ml. of sulfamic acid solution (10%) before the neutralization.
ANALYTICAL CHEMISTRY No difficulty with fading has been encountered with this method and the results obtained have been very satisfactory, as can be seen from Table 11. DISCUSSION
The colored metal ions manganese, chromium(III), iron(III), cobalt, molybdenum(V), and molybdenum(V1) exhibit little or no absorption a t 765 mp. On the other hand, vanadium(IV), vanadium(V), copper(II), and to a lesser extent nickel show absorption in this region and will therefore interfere in the silicon determination unless removed or compensated for. In addition, iron( 111), vanadium(V), molybdenum( VI), and copper(11) interfere by oxidizing the stannous chloride which is added to reduce the silicomolybdate complex. Under the conditions of the method described above, not much more than about 2 or 3 mg. of iron(111) can be present a t the time of the addition of the stannous chloride; otherwise low results for silicon are obtained. The iron interference can be virtually eliminated by reducing the metal to the ferrous state with the aid of a silver reductor before the addition of ammonium molybdate. The iron(I1) partially reduces any silicomolybdate complex to molybdenum blue but does not appear to reduce any of the ammonium molybdate itself. Unfortunately, the same cannot be said for molybdenum(V) and copper(1). When molybdenum(T~1)and copper(I1) are separately reduced to molybdenum(V) and copper( I ) in a silver reductor and treated with ammonium molybdate, the solutions turn dark blue. Because of these difficulties, attempts to use the silver reductor were abandoned and the removal of interfering metals by carbamatechloroform extraction was investigated.
Table 11. Analysis of Electronic Nickel Sample 1 ASTM standard nickel KO.2565 2 ASTM standard nickel No. 6166 3 Nickel metal, A 4 Nickel metal B 5 Nickel metal: C
Silicon, % Found Present 0.20 0.20 0.019 0.019 0.0093 0.0095° 0.0037 0.0038" 0.00080 0.00076a
a Samples were mixtures of 250, 100, and 20 rng. of A S T M etandard nickel 6166 plus, respectively, 250, 400, and 480 rng. of very pure nickel. Correction was made for slight traces of silicon in the latter, analysis of pure nickel for silicon being made b y t h e method being tested.
Aluminum, chromium(III), and lead are not extracted by carbamate under the conditions recommended in the above method. Extraction of manganese is very incomplete. Iron(111), vanadium(V), nickel, cobalt, molybdenum(VI), copper(11)) zinc, and tin(1V) are all extracted, although the completeness varies with the metal and is probably not quantitative in any instance. Fortunately, however, the amounts remaining cause little or no error in the silicon analysis. Of the commonly encountered elements, only vanadium may cause trouble. The unextracted vanadium usually has an absorption which is equivalent t o about 1 microgram of silicon. This error can usually be ignored. ,4n unusual phenomenon was encountered in the analysis of high-iron high cobalt alloys such as Vicalloy or Vanadium Permendur. When ammonium molybdate is added to the extracted aliquots of these samples, the solutions turn light blue in color suggesting that partial reduction of the silicon heteropoly complex is taking place. Fortunately, as can be seen in Table I, this premature reduction does not appear to affect the silicon results. Experiments on synthetic mixtures of iron and cobalt show that, whereas the blue color is obtained with 50-50 mixtures of the two metals when silicon is present, no blue color is obtained in its absence. Nor is any color encountered in the presence or absence of silicon, when each of the two metals is analyzed individually. Vanadium does not appear to play any role in the reaction. No hlue color is encountered in the analysis of a
151
V O L U M E 2 5 , NO. 1, J A N U A R Y 1 9 5 3 Remalloy (70 iron-20 molybdenxm-10 cobalt) or in any of the other alloys tested. According to Case ( I ) , the silicon in some copper alloys is not completely soluble unless hydrofluoric acid is used. This does not appear to be true of the copper alioys tested in the present investigation. In fact, complete solution of the silicon has been obtained in all ferrous, ferromagnetic, nickel, and copper samples tested by the method to date, with one exception, provided the ratio of acid to silicon a t the time of the solution of the sample is sufficiently high. In the analysis of NBS nickel casting alloy 161 an insoluble residue remains and the results for silicon are somewhat low (see Table I j. ,4higher ratio of acid to silicon is required for complete solution of high-silicon samples than for lowsilicon samples. Because of the need for high initial acidity it is best, whenever possible, to dissolve the sample in the 10 ml. of hydrochloric acid-nitric acid mixture rather than to dissolve it in 4 in!. of 1 to 1 nitric acid and then add 6 ml. of 2 to 1 hydrochloric acid. After complete solution has been accomplished, there is no harm in lowering the acidity by dilution of the sample. The acidity of the solution a t the time of the carbamate extraction must be high enough to permit efficient extraction by the chloroform and yet not so high as to prevent the formation of the heteropoly complex in the subsequent color development. If the acidity is too low a t the time of extraction, the carbamates may tend to remain in the aqueous layer. Even under the recommended condition, a clean-cut extraction is not obtained with certain alloys. Thus in the analysis of NBS steel sample 134. three chloroform washes are required to remove the carbamates completely from the aqueous laver.
When sample 134 is dissolved, a blackish insoluble residue of tungsten and carbon is obtained. No loss of silicon occurs, however, when this residue is removed by filtration. To date no loss of silicon has been noted as a result of a carbide residue. Once an analysis is started it should be carried through to completion the same day, in order to keep the blanks from the glassware as low as possible. Carbamate solutions diwolve glassware fairly rapidly and should always be stored in polyethylene. If reagents and distilled water of sufficient purity have been used, the reagent blank should not amount to more than about 3 micrograms of silicon. The Vaughan method of eliminating intei ference from phosphorus used by Minster ( 5 ) has proved to be very satisfactory, as can be seen from the fact that NBR phosphor bronze sample 63-b is succrssfully analyzed by the method described above. LITERATURE CITED (1) Case, 0. P., IND.ENG.CHEM., ANAL.ED., 16, 309 (1944). (2) Gentry, C. H. R., and Sherrington, L. G., J . SOC.Chem. Znd., 65, 90 (1946). (3) Guenther, R., and Gale, R. H., . ~ N A L . CHEX.22, 1510 (1950). (4) Hill, U. T., Ibid., 21, 589 (1949). ( 5 ) Minster, J. T., Analyst, 71, 428 (1946). (6) Zbid., 73, 507 (1948). (7) Rosental, D., and Campbell, H. C., IND. ENG.CHEM.,ANAL.ED., 17, 222 (1945). (8) Serfaas, E. J., and associates, “A.E.S. Research Report, Serial No. 6, Determination of Impurities in Electroplating Solutions,” pp. 33-40, rlmerican Electroplateis’ Society, P.O. Box 168, Jenkintown, Pa.
RECEIVED for review May 22, 1952. Accepted September 25, 1952.
Spectrographic Determination of Trace Elements in lubricating Oils -
R. F. 3IEEKER AND R. C. PO31ATTI Beacon Laboratories, The Texas Co., Beacon, N. Y .
l-
THE use of the emission spectrograph, by operators and
builders of heavy Diesel-powered equipment and oil companies, to study engine wear and corrosion by analysis of the used oil is becoming increasingly popular. This applies particularly to railroads in connection with maintenance of Diesel locomotives (8, 6, 7 , 9). Because the determination of several elements, usually occurring in the order of a few parts per million or less, is required in studies of this type, the spectrograph provides a convenient, relatively rapid, and often the only economically practical means of analysis. The quantities of iron, lead, copper, aluminum, tin, and silver present in a used Diesel oil are commonly considered to be indicative of the extent of wear or corrosion which has occurred in various parts of the engine. The quantity of chromium may indicate wear and corrosion, amount of cooling system leakage, or both. The amount of silicon present may indicate the quantity of road dust and dirt which has found its way into the engine, thereby providing an indication of the condition of the filters. While additional elements may be of interest to some operators, it is believed that the determination of the eight elements discussed above provides a fairly complete picture. However, if the determination of other trace elements is desired, this method can be extended to include them. 4ddjtive elements are more conveniently determined in lubricating oils by procedures invohing direct analysis of the oil (1,4, 8). Iron and lead, as well as additive elements, may be determined by direct analysis ( 3 ) .
DISCUSSION
A number of important general points concerning spectrographic analysis of used oil for trace elements, t o study and predict engine wear, should be emphasized. Careless or improper sampling of such oils could easily lead to erroneous interpretations and conclusions. Analysis of an individual sample of ubed lubricating oil Itill, by itself, yield information of little value. Such analyses must be correlated with the service records of the equipment and oils involved, and actual engine wear data. Only then can such analyses be used to judge the probable internal condition of engines, or to establish operating limits. To be of value, a method for the deterniination of trace elements in oils should meet the following requirements: 1. Be applicable to the elements indicative of wear, corrosion, and contamination. 2. Be unaffected by variations in types of additives present in heavy-duty oils. 3. Be applicable to low and high ranges of concentrations of trace elements. 4. Be capable ol’ analysis on small amounts of sample. 5. Be sufficiently precise to detect significant differences between samples.
The eight elements of interest are included, in known amounts, in a series of synthetic standards which cover a 32-fold range. The additive elements, frequently present in relatively large
