Spectrographic Method for Analyzing Lubricating Greases C. W. KEY
and
G . D. HOGGAN
Richfield O i l Corp., Wilmington, Calif.
Metallic soaps are cdmmonly included in greases to impart superior performance characteristics. Precise analyses during the compounding of such greases are highly desirable. This spectrographic method was developed to provide a rapid and accurate means of determining the concentrations of aluminum, calcium, lithium, sodium, and barium in lubricating greases. Investigations disclosed that 2-ethyl hexoic acid, strontium 2-ethyl hexoate, cobalt 2-ethyl hexoate, heavy naphtha, amyl acetate, and lubricating greases could Be blended to produce a homogeneous mixture with a Mid-Continent solvent-treated mineral oil. The liquid so produced was transferred from a porcelain boat by a rotating disk to the discharge gap of a high voltage spark in an inert atmosphere. Spectral lines produced by the excitation of a high precision case are recorded on No. 2 spectrum analysis roll film for analysis. A complete analysis by this method may be completed in approximately 50 to 60 minutes, as compared to as much as 40 hours by conventional chemical methods. More frequent analyses by this direct spectrographic method provide better control over the processing and blending of lubricating greases.
T
HE addition of metal organic soaps to lubricating oils to produce grease and gear oils was for many years classified as an art rather than a science. However, recently with the advent of hypoid gears, higher speeds, greater work loads, and more severe operating conditions, it has become necessary to compound these materials with more scientific knon ledge and control. The type and concentration of metallic additive or other compounding ingredients used depends to a great extent upon the performance level desired, severity of operating conditions, and the characteristic which is to be improved. These materials may be added to lubricating oil.. to yield greases with waterproof, extreme preseure, high temperature, antifoam, anticorrosion, or other characteristics. Such compounds may contain aluminum, calcium, copper, iron, potassium, lithium, magnesium, sodium, phosphorus, lead, dicon, titanium, zinc, and barium. During the compounding of lubricating greases, it is highly desirable to have rapid and accurate methods of determining the metal concentration. Only by precise analyses can optimum product quality be maintained. Ashing, followed by chemical or ipectrographic analysis, consumes too much time to be of much kwiiefit. In the authors' laboratory, it was desirable to have a rapid and precise method for the determinations of aluminum, calcium, lithium, sodium, and barium in greases. Spectrographic methods for analyzing lubricating oils have 1 een reported by several investigators. Calkins and White (2) impregnated the electrode with oil; Gambrill, Gassmann, and O'Neill(3) used both a porous cup and a rotating disk. Barney and Kimball ( I ) , Hansen, Skiba, and Hodgkin (4), and Meeker and Pomatti ( 7 ) used modifications of a crater or cup electrode. Pagliassotti and Porsche (8) used a rotating electrode partially immersed in the oil. Since many of the metallic constituents normally present in heavy duty lubricating oil additives are also present in greases, it was believed that the spectrographic rotating disk electrode principle could be applied t o the latter if a homogeneous solution could be prepared and maintained. Such a method would eliminate the problems and inaccuracies inherent in chemical or spectrographic methods performed upon the ash.
I t would also provide a more rapid means of determining concentrations of these metallic additives. EQUIPMENT
The Applied Research Laboratories' 2-meter spectrograph, high precision source unit, film developing and drying machines, and projection comparator-densitometer were used. A Dunn-Lowry calculator was used for the calculations. Xo. 6.4 porcelain boats with a notch cut in the right side, approximately 1.75 inches from the handle end, mere used to hold the sample during discharge. Spectrum analysis No. 2 roll film was used in the spectrographic camera. INVESTIGATION
The authors (6) have found that homogeneous blends of residual fuel oil and naphtha containing barium, nickel, sodium, calcium, and cobalt 2-ethyl hexoates could be prepared, and it was, therefore, believed that similar techniques might be used for greases. Investigations of numerous solvents disclosed that a Mid-Continent solvent-treated mineral oil with a viscosity of approximately 200 S.S.V. a t 100" F., heavy naphtha, amyl acetate, strontium 2-ethyl hesoate, cobalt 2-ethyl hexoate, and lubricating greases produced a homogeneous liquid that was transferred from a porcelain boat by a rotating disk to the discharge gap in optimum concentrations and uniformity. The strontium hexoate served as both an internal standard and buffer, whereas the cobalt served as an internal standard. The strontium and cobalt hexoates were added to a blend of the lfid-Continent solvent-treated mineral oil, heavy naphtha, and amyl acetate, hereinafter referred to as grease diluent. The volume per cent of each constituent is shown in Table I. Prespark and exposure times were established by time-intensity ratio curves. The selected periods are shown in Table 11. Reproducibility series established the optimum disk size and speed. A disk electrode, 0.25 inch thick by 0.5 inch in diameter, rotating at 14 r.p.m. gave the best results; these same electrode dimensions had previously been found to be optimum for lubricating oils. The disk was cut from 0.5-inch special purity graphite rod.
Table I. Composition of Grease Diluent Yol. Compound Mineral oil Heavy naphtha Sr 2-ethyl hexoate (10% Sr) Co 2-ethyl hexoate (1% Co) Amyl acetate
%
28 10
ti0
1
1 -
100
Table 11. Discharge and Exposure Conditions High precision case Capacity. microfarad Inductance, microhenrys Current, amperes Intensity control stand position Transmittance, % Grating shutter setting Prespark, seconds Exposure, seconds Disk
s. P. graphite
0.007 360 8.5 '11
100
0.3 48 12 14
0.5 0.25
0.25 120
3
1900
1901
V O L U M E 26, NO. 1 2 , D E C E M B E R 1 9 5 4 The arc-spark stand on the spectrograph was modified, as previously reported ( 6 ) , to permit the discharge to take place in an inert atmosphere of nitrogen. -1suction tube through the door was also employed to remove vapors as soon as they formed. This with the nitrogen atmosphere gave a more uniform discharge, reduced self-absorption, and prevented ignition of the sample.
the notch. A typical boat is shown in Figure 1. The boat is positioned in the arc-spark stand so that the stainless steel shaft, which holds thc rotating disk, fits into the groove without binding. Figure 1 also shows the arc-spark stand assembly without the door and suction system. These have been omitted from the dran-ing for the sake of clarity. I
70 I
STANDARDS, INTERNAL ST4VD4RDS. 4 N D BIJFFER
The standards for calcium, lithium, sodium, and barium were prepared by adding known concentrations of these metals as the 2-ethyl hexoates to lubricating oils. The aluminum standard was prepared from a commercially prepared aluminum stearate grease which had been cheniicnally analyzed. The 2-ethyl hexoate of aluminum had such a low solubility in the mineral oil-internal standard-buffer solution that it could not be used. Chemical analyses Tvere performed on :tll standards to confirni their metal concentration.
30
25 20
I5
in 0.9 08 07 0.6
1
i
Ne
\I
w
0.5
4
a4
ROTATING DISC ELECTROD
LI c;,Bo} No
AI
Figure 2.
INLET
i
1
i
~-
Figure 1. Arc-Spark Stand Assembly
Strontium %ethyl hexoate was used as the buffer. It also served as the internal standard for calcium and barium. Cobalt 2-ethyl hexoate was used as the internal standard for lithium, sodium, and aluminum. In preparing these standards, a 1 0 0 ~ o ewew of the theoretical amount of %ethyl hexoic acid was used. A liruvy naphtha with a boiling range of 355' to 385" F. was adclrd to the hexoates t o yield a concentration of 0.95% cobalt and 9.6670 strontium, by weight. The naphtha was composed primarily of paraffinic type hydrocarbons. In the case of the strontium, the naphtha had the added benefit of preventing recrystallization of the metallic salt. The above hexoate solutions are also used in the authors' laboratory for other spectrographic methods, thereby reducing the number of standards that must be prepared and maintained. They were added to the Mid-Continent solvent-treated mineral oil, heavy naphtha, and amyl acetate to give the volume per cent shown in Table I. PROCEDURE
The grease sample is heated in an electric oven to a temperature which renders it sufficiently fluid to be stirred. Four grams of the grease are dissolved in 16 grams of the grease diluent. Heating and stirring are continued until a homogeneous solution is obtained. ilfter the grease is completely dissolved in the diluent, a sufficient volume is transferred to a 6.4 porcelain boat to fill it to
1
B 910
16 15
10 25 3
4
8
6 7 0 9 IO
3
4
5
6 7 8 9
2
25
Working Curves for Direct Grease \lethod
A 0.25-inch spectrographic graphite rod with a 120' cone is used as the counter electiodr. .4 :I-mm. gap between this and the rotating disk electrode is ubed. Electrical discharge and exposure controls are adjusted t o produce the conditions shown in Table 11. Just prior to the initiation of the discharge, thr nitrogen flow from the 0.25-inch copper tubes (6) is adjusted to permit 0.7 cubic foot per minute to enter the electrode housing along the optical axis and 2.6 from the base. The suction system is then opened. ExpoQuresare completed and the film developed. FILM DEVELOPMENT
The exposed film is developed in Eastman D-8 developer for 2 minutes a t 65" F. I t is submersed in the short-stop solution for 0.5 minute and in Kodak liquid x-ray fixer for 2 minutes, then washed for 5 minutes and dried. The film calibration was made in accordance with procedures reported hy Harvey ( 5 ) . WORKIYG CURVES AND CALCULATIOhS
Working curves are prepared from exposure' data ohtaineti with the previously described standards. Typical B orhi r i g r u ves ~ are shown in Figure 2 in which logarithmic coordinates were used to plot the intensity ratios us. weight per cent metal. The intensity ratio scale used for aluminum is one tenth of that used for other metals The data from the working curves are transferred to the Dunn-Lowry calculator from which the weight pel cent metal in the grease is read directly. I n practice, ekposures from one or more suitable standards are recorded on the same film as the sample. This practice provides a check on the results obtained and gives a meawie of the day to day instrument variations if they occui . DISCUSSIOIV AND R E S U L T S
The chemical determinations of metallic elements compounded in greases are extremely tedious and time-consuming. Estimates given by chemists doing greme analyses indicate a variation from S to 40 hours to complete an analysis of some greases. Such delays in obtaining results are not conducive to proper control of grease manufacture. Data so obtained can only serve as a guide to indicate what has been done instead of what is being or should be done during processing. The direct spectrographic method described here requires
1902
ANALYTICAL CHEMISTRY
Table 111. Reproducibility Series, Grease Method Element
Wt.
%
No. of Analyses
Coefficient of Variation
Max. Dev. of Element,
%
- 19 Li
0.20
10
9.2
Ca
0.60
10
4.1
Ka
0.30
10
3.3
Ba
0.40
10
5.0
AI
0.25
10
3.3
who are working in this direction may benefit by the work done in the authors’ laboratory.
4-13
+-- 844 .. 78 +- 4.0 5.0
ACKNOWLEDGMENT
The authors wish to express their gratitude to Eskil Gross and C. E. Marquart for the spectrographic analyses, and to the Richfield Oil Corp. for permission to report these results.
fl0.l
+- 45 .. 87
about 50 to 60 minutes for the analysis of a single sample. A considerable economy in processing and analyses can thus be obtained by this method. Table I11 shows a statistical evaluation obtained from the analyses of several synthetic greases of known composition. These so-called greases were prepared from chemically analyzed metal salts of organic acids and suitable solvents including lubricating oil. The coefficient of variations obtained show that acceptable results may be obtained by this method. Additional data will be required to completely evaluate the method on all types of greases; however, the procedure has given sufficient promise that it is being submitted to the industry so that others
LITERATURE CITED
(1) Barney, J. E.,11, and Kimball. W. -4..ANAL. CHEM.,24, 154850 (1952). (2) Calkins, L. E.,and White, M. >I., YuV. Petroleum News, 38, R519-30 (1946). (3) Gambrill, C. M., Gassmann, A. G., and O’Neill, W. R , . i ~ 4 ~ CHEW,23, 1365-9 (1951). (4) Hansen, J., Skiba, P., and Hodgkin, C. R., Ibid., 23, 1362-5 (1951). (5) Harvey, C. E.,“Spectrochemical Procedures,” Glendale, Calif., Applied Research Laboratories, 1950. (6) Key, C. W., and Hoggan, G. D., - 4 ~ 4CHEW, ~. 25, 1673-6 (1953). (7) Meeker, R. F., and Pomatti, R. C., Ibad., 25, 151-4 (1953). (8) Pagliassotti, J. P., and Porsche, F. W., Ibid., 23, 1820-3 (1951). R E C E I V E for D review M a y 26, 1954 Accepted September 13, 1964 Presented before t h e Division of Refining. American Petroleum Institute, Houston Tex , M a y 1954
Separation of Titanium Combined with Spectrophotometric Determination of Titanium in Steel JOSEPH R. SIMMLER, K A R L H. ROBERTS, and S A M U E L M. TUTHILL Department o f Chemical Control, Mallinckrodt Chemical Works, St. Louis 7, M o .
A new quantitative separation of titanium from titanium-bearing steels (0.05 to 1.0% titanium) has been utilized as the basis of the procedure described. The titanium is coprecipitated with added zirconium when the zirconium is precipitated as the arsenate from a strongly acid (1N) solution. This technique separates titanium from the usual elements in steel, and particularly from vanadium, molybdenum, and chromium. The titanium is then determined spectrophotometrically in the presence of zirconium as the peroxytitanium complex.
T
1TANIUP.I in steel is often determined by the colorimetric method based on the yellow color that develops when hydrogen peroxide is added to an acid solution containing titanium. This procedure is subject to serious interferences from elements which form colored ions in solution, such as iron, nickel, and chromium, or colored peroxy compounds, such as vanadium (8), molybdenum ( 9 ) , and columbium ( a ) ; and from ions which bleach the color of the peroxy-titanium compound, such as fluoride (i‘), phosphate (IO), and large amounts of alkali salts ( 4 ) . Some of these interferences may be overcome by the addition of the interfering species to the standard solution, but such a technique is not satisfactory in practical analysis, because it requires previous knowledge of the kind and amount of interfering elements. The usual separation procedures are discussed by Lundell, Bright, and Hoffman (3). Pribil and Schneider (6) showed that titanium may be quantitatively precipitated as the hydroxide in the presence of iron, mercury, copper, lead. bismuth, and nickel, provided the disodium salt of ethylenediaminetetraacetic acid is used as a complexing
agent. Pickering ( 5 ) recently adapted this techpique of separating titanium to the rapid determination of titanium in titaniferous ores. Feigl and Rajmann ( I ) , in developing a specific qualitative test for titanium, showed that titanium is coprecipitatcd with zirconium arsenate from a strongly acid solution, and they used this phenomenon as a means of separating small amounts of titanium from large amounts of iron, vanadium, and chromium. This suggested the possibility of quantitatively determining titanium in titanium-bearing steels by combining this separation with a spectrophotometric method for the final determination. Such a procedure would combine the advantages of a simpler means of separating titanium from steel components and an over-all shortening of the elapsed time for the analysis. The present paper describes the development of such a procedure. APPARATUS AND REAGENTS
Spectrophotometer. Beckman Epectrophotometer, Model DU; 1-cm. Corex cells. Titanium Standard Solution, about 1 mg. of titanium per ml. Add 0.85 gram of titanium dioxide to 5 grams of ammonium sulfate and 25 ml. of sulfuric acid in a 500-ml. Erlenmeyer flask and heat until solution is effected. Cool, dilute to approximately 400 ml., filter into a 500-ml. volumetric flask, and dilute to volume. Standardize the solution by precipitating the titanium in 25.00-ml. aliquots with dilute ammonium hydroxide and finally igniting and weighing as TiOn. Zirconium Solution, 1%. Dissolve 2.78 grams of zirconium sulfate in 100 ml. of 20 volume yo hydrochloric acid. Arsenic Acid Solution,. 20%. .~ Dissolve 20.0 g - r a m of arsenic acid in 100 mi. of water. Wash Solution. Place 1.0 ml. of the 20% arsenic acid solution in a 100-ml. volumetric flask and dilute to volume with 10 volume % hydrochloric acid.
.
