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
ANALYTICAL CHEMISTRY
152
The study of engine w-ear and corrosion by determination of several trace elements in the used crankcase oil is becoming increasingly popular, especially amomg operators of heavy Diesel-poweredequipment. The emission spectrograph offers a convenient and rapid means for this analysis. A spectrographic method for the quantitative determination of iron, lead, copper, silicon, aluminum, chromium, tin, and silver is described. The method is precise, sensitive, flexible, and relatively simple and rapid. A few grams of sample and a small volume of nonaqueous solution containing matrix and internal standard
amounts in detergent-type Diesel oils, are known t o have a considerable interelement or matrix effect in spectrochemical analysis ( 5 ) . I n the development work on this method, a number of matrix materials were tested, including magnesium carbonate, lithium carbonate, molybdenum trioxide, nickel oxide, barium carbonate and a 1 to 1 mixture of lithium carbonate and barium carbonate. Enhancement of the nickel internal standard lines was noted during the analysis of some detergenttype Diesel oils, especially those containing barium as an additive element, except when barium was also used in the matrix material. This is shown in Table I. It was concluded after considerable investigation that barium had the most pronounced matrix effect of the common additive elements, and was also effective in controlling the direct current arc emission. Therefore, it was chosen as the matrix element, and has been found satisfactory. Five grams of sample are sufficient for conducting an analysis on a typical used Diesel oil. APPARATUS
A Raird Associates 3-meter grating spectrograph and hpplied Research Laboratories bIultisource, densitometer, and calculating board were used. The electrodes used, shown in Figure 1, were made from regular grade carbon rods as furnished by the National Carbon Co. After shaping, the electrodes were purified by soaking for a t least 24 hours in hot 50% sulfuric acid. The electrodes were washed free of acid with distilled water and dried before use. This method of purification gave electrodes of sufficient purity for this analysis. The sulfuric acid wash was especially effective
are burned together in a crucible containing graphite powder. The residue, after thorough mixing, is subjected to direct current arc excitation. A procedure for preparing standards suitable for this analysis is described. By correlating engine wear and corrosion data with data obtained by spectrographic analysis of the used crankcase oil, such analyses may be used to judge the probable internal condition of engines. Such information could conceivably be used to avoid unnecessary and expensive overhauls of engines, or to predict impending engine failure before serious damage occurs.
in removing vanadium, which frequently occurs in varying amount in regular grade electrodes. While the presence of vanadium lines in the spectrograms did not interfere with the determination of any of the elements of interest, its removal from the electrodes not only simplified the spectrograms generally, but also rendered the electrodes sufficiently pure for vanadium drterminations using modifications of this procedure. REAGENTS AND CALIBRATION STANDARDS
Prepare a benzene solution containing 50 mg. of barium and 0.5 mg. of nickel per 5 ml. For this purpose organic barium and nickel compounds, such as naphthenates, sulfonates, phenolates, or salicylates, may be used. Care must be used in selecting the barium compounds because some contain quantities of silicon sufficient to cause serious contamination of samples. Add standard volumes of this solution to the samples in the subsequent analysis. Thebariumprovides aneffectivecommonmatrix and the nickel provides internal standard control for the determination of the trace elements. Standards for this method are prepared by contaminating pure mineral oil with small, known amounts of pure compounds of the elements of interest. h convenient procedure is to mix together compounds of these elements to form a master mixture. Such a mixture is: Grams 3.574 1.347 1.565 1.070 0.962 0.473 0.159 0.064
FesOa PbO CUO SiOn CrzOs Ah08 SnOz AgzCOs
Fe
Pb Cu Si Cr A1 Sn rig
= 27.2% = 13.6%
= 13.6‘3$ = 5.4370 = 5,434 = 2.719 = 1.369 = 0.54d
Diluting 1 gram of this mixture with 19 grams of powdered graphite yields a mixture with the following composition: Table I. Examples of Matrix Effect of Various Additive Elements, Matrix Materials, and Internal Standards Example No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
ildditive Matrix Internal Elements Material Standard Line None, standard hlgcos M g 2938.54 Ca, P , Z n Ba,P None, standard 10% hfoO3 hfo 2934.30 Ca, P, Zn 90% LixCOa Ba, P None, standard K O Ni 2821.29 C a , P , Zn None, standard 4% X i 0 Xi 2984.13 Ba,Ca.P 96% LizCOa Kone. standard 0 . 5 9 U ’ O Xi 2984.13 B a , P , Zn 99.5% IfizCOa Ca, P , Zn None, standard 0 5 4 X i 0 Ni 2821 29 49 7!’7 BaCOa Ca, P None 4b 7 5 d ~ i z ~ 0 3 Ba,P, K Kone, standard Residue from Ni 2821.29 Ba, P, K organic Ba None and Ni oomCa pounds Ba,Ca,P K,P Ca,P,Zn C3,P Ba, Ca
Trenst&anoe 35 1 , 3 0 5 , 3 7 . 0 31 6 , 3 4 . 7 , 3 5 . 1 20.2,22.5,21.3 31 0 , 2 8 . 9 , 3 2 . 0 30.3,27.8,32.3 19.2,21.5,18.2 16.8, 19.3.18.2 7 . 4 , 8.0, 6 . 9 22 3 , 2 4 . 2 . 2 0 . 9 1 2 . 2 , 14.7, 9 8 24.9. 2 4 . 3 , 2 3 . 6 18.3,16.2.17.7 23.2, 22.4, 2 5 . 6 33 1 . 3 2 3 , 3 1 34 8 , 3 1 7 , 2 9 33 0 , 3 7 6 , 3 2 29.1,31.5,32
9 7 0
8
18.1, 17.7, 16.6 1 7 . 8 . 18.4, 2 0 . 3 18.5,21.2,17.5 18.9, 19.7, 16.5 18.8, 1 7 . 2 , 1 6 . 8 17.5, 1 5 . 6 , 1 8 . 0 20.2,20.9, 16.2 2 0 . 1 , 19 2, 1 8 . 7 22.9, 17.8, 19.4
Although 5-gram samplings are specified in the analysis of samples, standards are prepared on a 25-gram basis to facilitate small weighings and to obtain sufficient material for continued use. Final concentrations pertaining to standards, however, are expressed on the basis of 5-gram samples. Weigh seven clean and ignited No. 4 tall-form porcelain crucibles each to the nearest 10 mg. Use one crucible to prepare a blank and prepare the series of standards in the other six. Add to each crucible 0.8 t o 1.0 gram of powdered graphite. Weigh carefully the amounts of diluted master mixture Ehown below and add each amount to its corresponding crucible: Standard
hIg.
1
9.2 18.4 36.8 73.5 147.0 294.0
2 3 4
;\
Add to each crucible, including the blank, about 25 grams of a white mineral oil, such as Nujol. Finally add by pipet to each
153
V O L U M E 2 5 , N O . 1, J A N U A R Y 1 9 5 3
bonaceous residue. Place in a muffle furnace a t temperatures not exceeding 1100' F., only long enough to burn away the soot which forms on the sides of the crucible. Cool and reweigh the crucible to the nearest 10 ing. Add sufficient powdered graphite to make the total weight of ash, coke, and graphite 300 5 10 mg. Mix thoroughly in the crucible itself with a spatula and rod. Sample by tamping the cratered ends of the electrodes into the mixture. Set the spectrograph to include the following: Wai e-length region Sllt Filteis
CAtHOS7
ANODE u;e 1.
Llec trodes
crucible, blank incliided, 25 nil. of the benzene solution containing the matrix and in'annl standard elements. Ignite the contents of the crucibles, and "JW the steps described in the procedure. After the excess carhiiaceous material has been removed, add sufficient additional pox dered graphite to make the total weight of each standard 1500 =k 10 mg. Mix the contents thoroughly, using a mortar and pestle if necessary to obtain a fine smooth powder. These standards now approximate the physical and chemical state of the samples, treated as described in the procedure, and are ready for use. The compositions of the standards based on 5 grams of sample are shown in Table 11. Concentrations of trace elements in the majority of used Diesel oils will fall within the ranges of concentrations provided by the standards. Should the range of concentrations not be applicable to a particular sample, a sample of more suitable size may be taken and appropriate corrections applied to thc results.
In addition, place two extra filters in the cassette of the s ectrograph a t the following wave-length positions. The first &ter is a 25 X 11 X 1.5 mm. piece of glass cut from a clean photographic plate and is placed in the cassette in the 3080 to 3110 A. region. The second filter is a 25 X 13 X 3.9 mm. piece of glass made up of three thicknesses of microscope slide, and is placed in the cassette to include the 3240 to 3290 A. region. These two filters are useful in reducing the densities of the A1 3092.71 .4. and Cu 3273.96 A. lines to useful quantities. Set the Multisource for direct current arc excitation to deliver 11 to 12 amperes with the arc burning. Adjust the analytical gap to 3 mm.; no further adjustment is made during the subsequent exposure. Arc the electrodes, without a pre-exposure period, until the material in the anode is consumed. This point, characterized by the fading of the red-green color from the arc gap, requires 80 to 90 seconds. Use Eastman Spectrum Analysis KO.1 plates and develop for 4 minutes in Eastman Kodak D-19 a t 70" F. The spectral lines shonn in Table I11 are free from interference,
Table IV.
Results of Analysis of Used Lubricating Oils
Sample X o ,
3
Additive Elements
Ca
PROCEDURE
\Veigh a clean, ignited S o . 1 tall-form porcelain crucible to the nearest 10 mg., neigh into the crucible 5 grams f 10 mg. of the well shaken sample, and add about 100 mg. of spectroscopic graphite. Add by pipet 5 ml. of the benzene solution containing matrix and internal standard. Ignite and permit the mixture to burn itself out, preferably on a hot plate, to a dry car-
Table 11.
2200-3600 A. 1 s t order 50 microns 3% transmittance
Trace Elements
Fe Pb cu Si Cr A1 Sn
Composition of Standards
31 ..
-
Standard Blank
Fe
1
5 10 20 40 80 160
2 3 4 5 6
(Basis 5-aram samde) Synthesis, Parts per Million Pb, Cu Si, Cr A1 Sn 2 5
5 10
20 40 80
Table 111. Element Ni
AI ~..
2 cu Fe Pb Si Sn
1
2 4 8 16 32
0 5 1
2 4 8 16
025 0 5 1
2 4 8
Ag 0 1 0 2 0 4 0.8 1 6 3 2
6
Ca, P, Zn
Pb cu Si AI Sn
8
Ba, Ca
Fe Pb cu Si Cr A1 Sn
Spectral Lines Wave Length, A. 2821.29 3042.71 3382.89 3014.76,3005.06 3273.96 2813.288 2802.00 2519.21 2839.99
Spectrographic Analysis, P.P.M. Run 1 R u n 2 R u n 3 47 44 45 15 14 16 22 18 21 6.8 5.3 6.1 4.0 4.1 3.9 1.2 1.1 1.1 1.4 1.5 1.4 0.82 0.84 0.85 9.2 8.4 8.6 1.5 1.6 1.4 3.0 2.4 3.0 3.2 2.0 2.8 1.1 0.75 0.80 6.9 7.4 7.8 2.2 1.8 2.1 9.2 7.8 9.4 2.1 2.3 3.5 4.6 4.7 4.6 0.92 0.93 1.2 1.3 1.3 1.4 16 16 1.5 5.1 4.7 4.3 8.4 9 0 9.4 20 20 19 5,l 4.8 4.9 6.0 5.9 6.1 0.70 0.70 0.64 34 24 25 19 21 18 37 ..
33 ..
1.4 1.8 2.1 3.1 3 2 3.1 1.6 1.5 1.6 5.6 5,2 5.0 3.7 3.7 3.8 2.5 2.3 2.3 3.9 3.2 3.2 0.52 0.40 0.50 1.9 1.9 1 9 25 25 24 4.5 4.4 4.3 5.0 4.8 4.8 1.7 1.9 1.9 6.5 6.7 6.6 I9 20 19 0.48 0.48 0.47 0 . 1 8 0 . 1 8 0.18 20 20 I9 11 12 14 5.3 5.8 6.2 1.9 2.1 1.8 5.7 5.5 5.6 0.93 0.98 0.89 0 . 3 5 0.41 0.41
ANALYTICAL CHEMISTRY
154
ACCURACY 4ND PRECIS103
Table \-, Analysis of Used Lubricating Oils Sample S o . 1 2 3
Element Fe
5
Pb Fe cu
Fe Pb
Sn
.4nalysis, P.P.M. Chemical Spectrographic 145 140 175 155 3.9 4.2 3.9 3.9
Precision of 3 ~ 1 0 %is generally obtained by this method. Typical results are shown in Table IV. Table V shows results obtained by both chemical and spectrographic analysis of six samples of used lubricating oils. It is expected that the same general procedure will be applicable to the analysis of oils, crude or processed, for trace quantities of other metals. ACKNOWLEDGMENT
27
12 0.5
34 13 0.6
6
The authors wish to express their appreciation to Harry Levin, L. L. Gent, and C. P. Miller for their assistance and suggestions during the development of this method and the preparation of the paper, and to Norma Bovino who prepared the manuscript. LITERA’TURE CITED
and may be used for photometry. Background density ie low and requires no correction. Obtain the per cent transmittance values of the spectral lines shown in Table 111 by means of a microphotometer. Calculate intensity ratios of the element lines, using the intensity of the Xi 2821.29 A. line as the internal standard. From the analytical curves, discussed under “Reagents and Calibration Standards,’, obtain the concentration of the trace elements directly in parts per million. Exposure of three spectrograms per sample and averaging intensity ratios are recommended where better precision is desired. However, reproducibility is generally good, and one G r two exposures per sample will provide adequate precision where time and sample load are factors.
(1)
Calkins, L. E., and White, M. If,,A’atl. Petroleum
Seus,
38,
R519 (1946).
Cassidy, W.A , , Mech. Eng., 72, S o . 10, 854 (1950). (3) Gambrill, C. M., Gassmann, A. G., and O’Nedl, W. R., A R ~ L . CKEM.,23,1365 (1951). (4) Gassmann, A. G., and O’Keill,W. R., Ibid., 21, 417 (1949). (5) Harvey, C. E., “Method of Semiquantitative Spectrographic Analysis,” Glendale, Calif., Applied Research Laboratories,
(2)
1947.
&Brian. R.. J . Pacific Ru.Club. 32. S o . 2. 6-12 (1948). (7) McBrian, R., and -itchison, L. C.,’S.A.E. J o t ~ m a l ,58, S o . 7, (6)
19-21 (1950). (8)
Pagliassotti, J. P., and Porsche, F. W,, ANAL.CHEM.,23, 1820
(9)
Sennstrom,H. R., Ry. Mech. Elec. Eng., 126, Issue 4, 65 (1952).
(1951).
RECEIYED for review May 21, 1952.
.4ccepted October 2, 1952.
Analysis of Sulfuric Acid Contact Plant Exit Gas Critical Review of Analytical Methods f o r Acid Mist and Sulfur Dioxide JOSEPH B. LOMBARD0 American Cyanamid Co., Calco Chemical Division, Bound Brook, S.J .
A
PRilCTIC.4L analytical method for the determination of SUI: furic acidmist and sulfur dioxide in sulfuric acidcontactplant exit gas M-asdeveloped after a comprehensive search of the literature disclosed the absence of such a method, which is essential for the proper control of the process and evaluation of air pollution. Its application has contributed materially to the intelligent control of a modern sulfuric acid contact plant.
REVIEW OF ANALYTICAL METHODS SULFURIC ACID MIST
The entire list of analytical methods for mist can be divided into two classes. Those of the first class separate and retain the mist, which is subsequently estimated by any of several methods. The other class depends upon various modifications of the Tyndall effect for a measure of mist concentration. Separation. FILTRATION. Cotton was employed by Alekseeva and Andronov (%),Gille (34), and Rabovskii and Shaposhnikova (69) both as a cotton fiber plugandimpregnatedinvarioussolutions. However, the use of cotton was criticized by Schmidt (86). Alekeeeva and Andronov ( 2 ) also combined cotton with either filter paper or alignin. Asbestos as an absorbent has found very extensive use. Weber studied its possibilities (110) and its use has been popularized, particularly by inclusion in two widely distributed industrial publications (12, 79). The inconvenience with asbestos absorption lies in the preparation of the asbestos
plug and the eventual washing of the acid from the asbestos. Goodeve (40) discusses in a general way the use of glass filters, while Flint (%8) directly uscs sintered glass as a filter for sulfuric acid mist in a power house flue gas installation. .41undum as a filtering agent is discussed by Weber (110) and was studied by Taylor and Johnstone (98). Although filter paper for filtration was tried by Weber ( I I O ) , its use has not been popular until very recently and then only for the determination of mist in air by Mader and others (56, 5 7 ) . Glass wool, rock wool, and other synthetic fibers have been found to be very efficient filters (9). ABSORPTION.The absorption of sulfuric acid mist in water or aqueous solutions has attracted considerable attention. Johnstone (47)proposed breaking up the large bubbles by means of sintered-glass porous membranes and thereby bringing about rapid absorption of the acid mist in water. Friedrich (31) investigated the effect of various types of laboratory gas washing bottles to determine the most efficient type for absorption. He found the screw type gave best results, especially when ground glass of the size of coarse sand was added to the bottles. Adadurov and Gernet ( I ) found that if the “fog” is allowed to re main in contact with steam for 3 to 6 seconds, reaction takes place and 99% of the sulfur trioxide is recovered. Remy and Vick ( 7 8 ) also investigated different types of gas washing bottles and, a t the same time, the use of alcohol and gelatin in the water to effect better absorption. They found that, whereas the type
