Indiana Oxidation Test for Motor Oils T. H. ROGERSAND B. H. SHOEMAKER, Standard Oil Company (Indiana), Whiting, Ind.
I
T S A PAPER (g) presented at the September, 1933, S. A. E.meeting it was shown that the oxidation stability
of motor oils is a n important characteristic, particularly in heavy-duty service. A comprehensive series of engine tests was made in which the changes taking place in a wide variety of oils were measured. Several types of oxidation tests were made on the same oils and it was found that a test using air a t 341 'F. (171.7' C.) gave the best correlation with the engine performance tests. In view of the rather general interest in this laboratory test (known as the Indiana oxidation test) it appears desirable to present in greater detail the procedure as well as the influence of various factors in the test. Upon oxidizing motor oils a t relatively high temperatures it is generally found that no insoluble oxidation products form during an initial period, after which asphaltene formation takes place a t an increasing rate, this behavior often being known as sludging. The Indiana oxidation test measures the length of time (sludging time) until rapid formation of asphaltenes begins, as indicated by an asphaltene content of 10 mg. per 10 grams of oil. In addition, as a measure of the rate of sludging, the time required to form a larger amount of sludge (100 mg. per 10 grams) is also determined. Motor oils vary widely in their oxidation stability-from 10 or 15 up to several hundred hours' sludging time-those of lighter grades having, in general, lower stabilities than the heavier grades. For oils of certain types which have little or no tendency to form asphaltenes, it becomes more desirable to measure the rate of viscosity increase for which the test procedure makes provision. I n general, on the basis of work previously described, for oils having a sludging time above about 100 hours, determination of the viscosity increase becomes more significant than sludging time and a sludging rate. The apparatus used for the Indiana oxidation test, with the exception of the glass flowmeters, is shown in Figure 1, and the test in standardized form as used by various laboratories of the Standard Oil Co. (Indiana) is described below.
METHOD APPARATUS.A thermostatically controlled oil bath suitable for immersion of the oil tubes to a depth of 30 cm. Bright stock of good stability is used for the bath, Temperature regulation at approximately 342" F. (172.2" C.) within *0.5' F. must be maintained. Oil tubes must be placed symmetrically with reference to stirrer and heater. Oil test tubes of heat-resistant glass of 40 to 44 mm. inside diameter, 450 t o 500 mm. long, provided with a slotted cork stopper into which is fitted an air delivery tube of glass, of 4 to 5 mm. inside diameter. Flowmeters, calibrated in liters of air per hour, through which air a t constant pressure is supplied. PROCEDURE. Determine the observed bath temperature which must be yaintained in order to keep the test oil at a temperature of 341 * 0.5" F. (171.7' C.), corrected. Take the temperature of the test oil with the tube in place, containing 300 cc. of oil, while passing through air at a rate of 10 liters per hour. Use a standardized thermometer, immersing it to the approximate center of the oil, and make appropriate stem correction. Having established this comparison of bath and test oil temperature, the observed bath temperature may be used for control so long as the rate of stirring of the bath is not markedly varied and the viscosity of the bath oil has not increased to more than 200 seconds Furol a t 210" F. (98.9" C.). Fill the oil tube to a depth of 23 cm. (approximately 300 cc. of oil.) Place the tube in the bath, the level of which must be at least 5 cm. above that of the test oil. The oil bath must be up to temperature and be so maintained that the temperature of the test oil is 341" * 0.5" F. The air delivery tube is placed so that
the end is within 6 mm. of the bottom of the oil tube. One-half hour after placing the oil in the bath, start the air at a rate of 10 * 1 liters per hour (as measured under laboratory conditions). The start of the test period is the time of starting the air. For determination of sludge values withdraw a 25-cc. sample of the test oil in a pipet. Weigh 10 grams ( * 0.1 gram) of this portion immediately into a 300-cc. Erlenmeyer flask, and dilute with 100 cc. of A. S. T. M. precipitation naphtha ( 1 ) . The naphtha used must, by comparative test on a sample of oxidized oil, give within 25 per cent of the sludge value obtained with a reference sample of A. S. T. M. precipitation naphtha. Stopper the flask and allow the solution to stand for 3 to 3.5 hours at room temwrature (70' to 85" F., 21.1' to 29.4" C.). Pkepare a G o o c h type c r u c i b l e (apy A L O L A G HEATERS proximately 35 mm. in diameter) with a m a t of 0.5 t o 0.65 g r a m of m e d i u m asbestos fiber. During preparat,ion of the mat, press it down before adding the last p o r t i o n . Dry the crucible at npproxim a t e l y 300" F. (148.9' C.) f o r a t least 2 h o u r s in an 53.3c M. o v e n a n d weigh. Filter the s a m p l e , wash with precipitaDIAMETRICAL SECTION tion naphtha, heat a t approximately 300" F. for 0.5 hour, and weigh. Express the sludge as milligrams per 10 grams of oil. Samples for sludge determination may be t a k e n e v e r y 24 TUBE hours before sludging HOLES begins. T a k e a t least three samples, giving sludge values bet,ween 5 and 125 COVER mg., including one beFIGURE 1. DIAGRAM OF APPARATUS tween 5 and 20 and one between 50 and 125. A plot of these values us. time on log paper is then used to determine the sludging time and the 100 mg. time. For tests made at barometric pressures differing by more than 5 per cent from one atmosphere, correct these times t o normal barometric pressure by multiplying the observed time by the ratio of the barometric pressure during the test to 760. For determination of viscosity increase, samples of approximately 75 cc. are withdrawn every 50 hours and used to run a Saybolt viscosity. This oil is then replaced in the test tube. -c
FACTORS AFFECTING THE OXIDATION TEST Significant factors in connection with the Indiana oxidation test are: TEMPERATURE CONTROL.I n view of the relatively steep temperature coefficient of the reaction, accurate temperature control is obviously necessary and it is important to use a standardized thermometer and make proper stem correction. Aside from faulty bath control, irregularities may be caused by the bath oil becoming too viscous, thus causing greater differential between bath and test oil temperature. AIR RATE. Under the conditions employed, a n excess of oxygen is provided and very precise measurement of air rate is not essential. However, marked variation from the standard air rate, particularly on the low side, will appreciably affect the sludging time.
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BAROMETRIC PRESSURE. As shown by Table I, the sludging time varies inversely with the partial pressure of oxygen.
FILTER.Variations in the mat thickness and area will affect the amount of asphaltenes obtained from a given sample. This appears to be due to adsorption as well as to TABLEI. INFLUENCE OF BAROMETRIC PRESSURE incomplete separation of the finely divided solids. For this ASPHALTENEB FORMEID reason the amount of asbestos and the area of the filter PRESSUREI OXYGEIN SUPPLY^ 10 Mg. 100 Mg. are kept constant. M m. Hours Hours
1 2 3
Atmospheric (750) Air 64.5 95.5 80% air,,20% N2 81 115 Atmospheric (750) 5s XX Air 840 -_ In each case the rate was 10 liters per hour at the pressure in question.
This relationship apparently holds only over relatively narrow limits, as the use o€ 100 per cent oxygen gives results which do not bear a constant relationship to those with air on a wide variety of oils. SETTLINGOF SLUDQEIN OIL TUBE. It is obviously necessary to obtain a homogeneous sample and the stirring afforded by the air delivery facilitates this. It is important that the air tube extend to the bottom of the tube as provided. PRECIPITATION NAPHTHA. Although the data are rather incomplete, it is indicated that variations within the A. S. T. M. specifications for precipitation naphtha may cause marked irregularity in asphaltene determinations. For example, with two naphthas, each of which met the requirements for gravity and distillation points, having aniline points of 59.0" and 57.6" C. (A. S. T. M. specification is 58" to 60" C.) differences of several fold in the asphaltene determination on the same sample of oxidized oil were obtained. This caused a difference of 5 hours (7 per cent) in the apparent sludging time as between the results obtained with the two naphthas. For this reason the standardization of the naphtha against a reference sample, arbitrarily adopted as a standard for one or more laboratories is recommended. TIMEOF STANDING.Variations in the time of standing of the naphtha solution before filtering may cause pronounced differences with stable oils, particularly a t low asphaltene concentrations. Observations show that the sludging time may be decreased by as much as 5 hours on increasing the time of standing from 3 to 18hours.
REPRODUCIBILITY Using the test as described above, agreement within a range of 10 per cent of the sludging time can be obtained by different operators. Duplicate determinations by the same operator show much closer agreement. Table I1 shows data obtained in different apparatus and by different operators. TABLE11. REPRODUCIBILITY OF THE INDIANA OXIDATION TEST OIL
I I I I I
ASPHALTB~NEB FORMED 10 Mg. 100 Mg. Hours Hours 62.5,63 93,93 64.5, 65,62.5 99, 99, 96
APPARATUS A
B
c
AR. RR
D
E4
0 0 . 0 . 00
Av.
I1
I1 I1 I1
A
C
ED-I
64.5 56 56 54 60
Aa
-
Av. 56.6 Observed values for oil I were 76.5 and 77; ?O hours for oil 11. These values were corrected for an observed barometrlc pressure of 650 mm. (I
LITERATURE CITED (1) Am. SOC. Testing Materials, Section 6(a), Method D91-33, A. S. T. M. Standards, Part 11, 1933. (2) Barnard, Barnard, Rogers, Shoemaker, and Wilkin, 8. A . E. Journal, 34,167 (1934). R ~ C E I V BJune22,1934. D Presented before the Division of Petroleum Chemistry a t the Kansas City Regional Meeting of the American Chemical Society, May, 1934.
Flame Determination of Copper by Carbon Tetrachloride PETERGABRIEL,1393 St. Marks Ave., Brooklyn, N. Y.
THE
qua1 method of determining copper compounds and carbon tetrachloride placed in a small receptacle attached alloys uL is to place the substance to be tested on a clean to the Bunsen burner. The flame always turns blue when copper is present, but platinum wire and insert it in the inner part of the flame. If with a minute amount of copper it i's sometimes copper is present, the outer flame is colored green, necessary to moisten the substance with water but this is not a definite test for copper because and juggle it in the flame, to find the best part many other elements burn with a green flame. for that particular substance-usually the tip of The test is more delicate if the s u b s t a n c e is the flame. soaked with hydrochloric acid, when copper colors The amount of copper present and the other the outer flame azure-blue with tinges of green. elements with which the copper is united deterHowever, this test is subject to interference of mine the length of time the substance should reother elements, it is inconvenient and not clean, main in the flame. The flame usually turns blue and the receptacle which contains the hydroimmediately, even with minute amounts. In chloric acid must be cleaned after every test to the case of copper telluride, nearly a minute is reavoid impurities which may spoil further tests. quired before the appearance of the blue color, If a copper compound or alloy is placed in the and even when the blue color appears traces of flame, the whole flame is1 colored b l u e when green can be seen in the flame, caused by the chlorine is passed through the draft of the Bunsen FIGURE 1. APPARATUS FOR FLAME presence of tellurium. burner. Other elements which burn with a green DETERMINATION The same test can be applied to calcium, and flame are not affected by the c h l o r i n e . The A , wire twisted around is even more delicate because in this case the chlorine method is much more effective than the burner for grip flame turns from reddish orange to red. The acid method, but is more troublesome. B small receptacle C , ' ootton soaked with change of color in the flame must be carefully C a r b o n tetrachloride has the same effect as carbon tetrsahloride noted when dealing with compounds of calcium. chlorine upon the color of the flame, and the D ,d r a f t of B u n s e n R ~ C ~ I VAugust ED 26, 1934. burner test requires only a piece of cotton soaked with
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