I
MILTON LEVY Coating and Chemical Laboratory, Aberdeen Proving Ground, Md.
Corrosion Inhibitors in Automotive Coolant Media Action on Polarization Characferistics of Steel Needed background is presented on the action of inhibitors in ethylene glycol solutions used as automotive antifreeze. Materials that meet the conditions of the suggested corrosion test operate 2000 hours in a simulated vehicle cooling system and should be satisfactory in field service
Tm
ultimate test of an antifreeze is satisfactory service in the field. Therefore an antifreeze program is needed which will ensure that a given material will meet this requirement. As no single completely reliable laboratory corrosion test for predicting the value of an antifreeze is known, this installation had adopted an integrated test program of laboratory, dynamometer type (simulated vehicle cooling system, SVCS), and field service procedures. The accelerated laboratory glassware corrosion test (Florence flask stationary corrosion test, FFSCT) developed a t this laboratory will generally distinguish between coolants that are definitely deleterious from the corrosion standpoint and those suitable for further evaluation. The test unit is a simple, static type using a wide mouthed Florence-type flask with coupled metal specimens (aluminum, copper, solder, brass, steel, and iron) totally immersed in the test solution aerated at 0.03 cu. foot per minute, while held at 180" F. for 192 hours, To evaluate the corrosion of metal specimens, corrosion ratings are assigned, based on weight loss per unit area and appearance of each specimen. Data obtained at this laboratory indicated that materials having corrosion ratings of 21 or less in the Florence flask stationary corrosion test generally will operate approximately 2000 hours in a simulated vehicle cooling system and will probably prove satisfactory in field service. The dynamometer type or simulated vehicle cooling system unit consists of an arrangement of mechanical units, black iron tank, automobile radiator, and coolant pump, to permit the test solution to be circulated in a closed system in which circulation rate and solution temperature (180" f 5" F.) can be controlled. The system is periodically shut down to simulate actual operational conditions. Application of the polarization technique with externally applied e.m.f. as an accelerated test has been proposed. This technique also yields basic and significant information about the proc-
esses associated with corrosion inhibitors. The magnitude of the current flow produced between dissimilar metals in a corrosive medium is a measure of the galvanic attack. The formation of protective films is readily followed through current flow-time measurements and permits subsequent polarization measurements. This investigation deals with the action of some corrosion inhibitors in automotive coolant media, on the polarization characteristics of steel, and with possible use of the polarization technique with externally applied e.m.f. as a test for the evaluation and screening of inhibitors. The effect of concentration change of inhibitor on the polarization characteristics of steel and the effect of inhibitor addition on the galvanic attack produced by the coupling of dissimilar metals in coolant media have also been studied. Both Mears (70) and Gatos (6)have reviewed the electrochemistry of inhibitor action. Important work on polarization studies of inhibitors is to be found in the investigations of Hoar and Holliday (8), Wormwell and Mercer ( 7 I ) , and Elze and Fischer ( 3 ) . Apparatus and Experimental Procedures
The anodic and cathodic behavior of corroding metals was studied by making the metal (steel) anodic or cathodic against an auxiliary electrode (copper) in the corrosive medium by means of an externally applied e.m.f. In this manner the entire metal is made the anode or cathode of an electrolytic cell. The current densi>y of the metal usually encountered in the corrosion process ranges from 1 to 100 ma. per sq. cm. The potential of the metal under the external e.m.f. is measured against a reference electrode. Plots of this potential us. current density represent the polarization characteristics of the metal in the desired environment. By using this technique and the apparatus described by Hatch (7), the following inhibitor materials were studied in Aberdeen tap water and 30% ethylene
glycol-tap water media : borax, sodium nitrite, mercaptobenzothiazole, sodium citrate, triethanolamine, hydroquinone, sodium chromate, sodium silicate, and sodium benzoate. Government specification (5) prescribes antifreeze of the permanent type (ethylene glycol) ; consequently alcohol mixtures were not considered in this study. The test specimens are metal strips, steel and copper, 3 X '/2 inch, held parallel to and a t a fixed distance of l / 2 inch from each other by a micarta spacer. Connections are made with '/z inch wide metal strips of the same composition as the strip to which it is connected. Steel surface area exposed to electrolyte is 14.26 sq. cm.; copper, .15.36 sq. cm. The metal strips were cleaned by belt sanding with 120 paper, scrubbed with 00 steel wool, rinsed with 9570 boiling ethyl alcohol, and air-dried. Polarization measurements were made after 48 hours of immersion of test strips in the desired medium, so that any protective film formed would become well established. In the interim current-flow measurements were made between the steelcopper couple in the media enumerated above. A zero resistance ammeter circuit was utilized. The test cell was connected to either of the circuits as desired, by means of a suitable switch arrangement. The current generated by the metallic couple was measured with a milliammeter, ranges 0 to 0.03, 0 to 1, and 0 to 15 ma. The meter was inserted in the circuit only when current measurements were taken; a t all other times the cells were short-circuited, Potential measurements were made with a Beckman Model G meter in conjunction with a Beckman saturated calomel electrode. The current magnitude was adjusted during polarization tests by means of variable resistances in series (1000, 5000, and 50,000 ohms) with the cell and meter. These resistances were short-circuited a t all times except during polarization measurements. The electrolytic test cells were maintained a t 25" z t 0.2' C. throughout the entire VOL. 50, NO. 4
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Figure 1 . With steel-copper couples the curve for uninhibited tap water is in a relatively high current range
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z c
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0 Untreated tap water N 0.25% MBT-tap water A 0.50% MBT-tap water
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0 01
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Figure 2. With steel-copper couples borax decreases galvanic attack of the steel A
1.0% borax-tap water 1 .O% borax-0.1 % MET-tap water
test, with no aeration of solution. The tap water used in the test solutions had a conductivity of 1.09 X low4mho and chloride ion concentration of 6 p.p.m.
Results Because of similarity, all polarization and current flow curves are not graphically represented. Borax. The current flow-time curve for uninhibited tap water (Figure 1) is in a relatively high current range, an indication of considerable acceleration of the anodic member of the steelcopper couple as a result of the couple. Initially it dropped sharply, indicative of oxide film formation, followed by a sharp rise as destruction of the oxide film proceeded on the steel anode. The current flow decreases for the couple in tap water treated with 1.Oy0 borax, then levels off to a low value (Figure 2). Borax considerably decreases the galvanic attack of the anodic member of the couple (steel). Figure 3 shows the results of polarization measurements of steel as anode and cathode after 48-hour immersion in
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Figure 3 . Influence of borax on polarization characteristics of. steel in untreated tap water and untreated 30% ethylene glycol
untreated tap water, tap water inhibited with 1.0% borax, and 2.0% borax. These data are from the same series of tests as the current-flow data. The upper arms of the curves represent the potential of steel as cathode and as a function of current; the lower arms, those of steel as anode. The intersection of the anodic and cathodic potentials represents the open circuit potential of steel. The current that corresponds to the intersection is the local action corrosion current for steel. The addition of 1.0% borax to tap water causes no change in the slope of the cathodic polarization curve, but does change the slope of the polarization curve of the anode. Thus the inhibition of current flow a t this concentration appears to be due to a marked increase in the polarization of the anode. I n concentration of 2.070 borax the polarization curves are qualitatively similar to that of the 1.0% borax, except that the anodic slope is steeper in the 1.0% borax. Again the chief cause for the low current flow is anodic polarization. The current corresponding to the open circuit potential of steel at 2.0y0 borax concentration is greater than that of the l.Oyo. The greater anodic polarization (steeper anodic slope) and smaller local action corrosion current of the 1.O% borax indicate its superiority
INDUSTRIAL AND ENGINEERING CHEMISTRY
over the 2.0% as an anodic polarizer. The current-time curve for untreated 30% ethylene glycol (Figure 4) is in a lower current range than that of untreated tap water, but high relative to the level of curves obtained with borax added. Comparing the current flow curves of tap water treated with 1.0% borax (Figure 2) and 30% ethylene glycol treated with 1.0% borax (Figure 4), the galvanic current at a steady state condition for the former is eight times that of the latter. The addition of 1.070 borax to 307, ethylene glycol effects little change in the slope of the cathodic polarization curve (Figure 3), but a marked change in the slope of the anodic polarization curve. The polarization curves for the 2.0% borax concentration are almost identical with those of the 1.07,. The 2.0% borax concentration appears to be no more effective than the 1.O% as an anodic polarizer. Considrring the polarization curves of 1.0% borax-tap rvater and 1.0% borax-30% ethylene glycol (Figure 3), the current corresponding to the open circuit potential of steel or the intersection of anodic and cathodic polarization curves is approximately the same for both. Comparing the local action corrosion current difference, between untreated and treated tap water and untreated and treated 3oy0 ethylene glycol (Figure 3), the difference
CORROSION INHIBITORS
8
0
Figure 4. Galvanic current a t steady state is eight times higher for untreated than for borax-treated ethylene glycol 0 Untreated 30% ethylene glycol A 1.0% borax-30% ethylene glycol
of the former is approximately twice that of the latter. This is due to the difference in the local action corrosion current for steel of the untreated system. The inhibitive action of borax in tap water and 30% ethylene glycol is primarily due to the increase in the polarization of the anode. Evans (4) classified inhibitors inducing anodic polarization as anodic inhibitors. Sodium Nitrite. Figure 5 represents the current-flow characteristics of tap water inhibited with 1.0% sodium nitrite and 1.5Oj, sodium nitrite. The addition of sodium nitrite caused a marked inhibitive action on the galvanic attack. The current dropped sharply to a very low value initially, rose slightly, and leveled off at a low value. At 24 hours there was a reversal of polarity, which continued with rising current values to 48 hours. The low steady current toward the end of the test represents light galvanic attack. Sodium nitrite does not entirely prevent film breakdown. Although there is little difference in the curves generally, the initial current measurement of the 1.0% sodium nitrite material was approximately twice that of the 1.5% sodium nitrite material. Treatment of tap water with 1.0% sodium nitrite causes a slight change in the slope of the cathodic arm but a marked change in the slope of the anodic polarization curve. The addi-
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Figure attack
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Addition of sodium nitrite inhibits galvanic 0 1.0% sodium nitrite-tap water A 1.5% sodium nitrite-tap water
tion of sodium nitrite in concentration of 1.5% causes little change in the polarization curves of the 1.0% inhibited material. I t would appear the 1.5% concentration is no more effective as an anodic polarizer than the 1.0%. The current-flow curve for 30% ethylene glycol treated with 1.5% sodium nitrite indicates a sharp initial decrease, followed by a leveling off and a subsequent steady rise from 5 to 24 hours, and a final leveling off. There was a reversal of polarity from 5 to 48 hours. The current flow rise occurred with the reversal of polarity. This was also true of tap water treated with 1.5% sodium hitrite. Addition of sodium nitrite to 3070 ethylene glycol did not affect the slope of the cathodic arm, but markedly affected the slope of the anodic polarization curve. The local action corrosion current, or current corresponding to the open circuit potential of steel, showed little inhibition, apparently because of the much higher level of the potential of steel as cathode. As sodium nitrite in tap water and 30% ethylene glycol retards or arrests the anodic reactiou, it is classified as an anodic inhibitor. Sodium Citrate. The current-flow curve for tap water treated with 1.5% sodium citrate (Figure 6) rises sharply as destruction of the oxide film on the steel anode proceeds, falls sharply, and levels off at a relatively high value.
The curve is characterized by a rather high current-flow level. The final current is 11/2 times that of the initial. Figure 7 represents the polarization characteristics of tap water treated with 1.5% sodium citrate. There is no change in the slope of the cathodic polarization curve; however, the slope of the anodic arm decreases. Conditions which decrease the slopes of polarization curves-Le., shift the convergence point of anodic and cathodic potential to higher current values-accelerate corrosion. If polarization of the anode is prevented, convergence occurs at a higher current value and corrosion is increased (Figure 7). The current-flow curve for 30y0 ethylene glycol treated with 1.5% sodium citrate is similar to that of tap water treated with 1.5% sodium citrate, but its current level is considerably lower. In Figure 7 the polarization characteristics are similar to those of tap water treated with 1.5% sodium citrate. Sodium citrate in concentration of 1.57, behaves as a corrosion accelerator by preventing polarization of the anode in both tap water and 30% glycol media. Triethanolamine. The current flow for tap water treated with 1.5% triethanolamine is a series of initial rises and falls, followed by a gradual decrease and a final leveling off. A low currentflow level is obtained. Triethanolamine VOL. 50, NO. 4
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Figure 6. Relation of current flow to time between steelcopper couples 0 1.5% sodium citrate-tap water
A 0 5% hydroquinone-taa water
exerts an inhibitive action on the galvanic attack. I t was expected that with a steel-copper couple, steel would behave as the anodic member, copper the cathodic. However, there was a reversal of polarity throughout the entire current-flow test. Polarization data for this medium are shown in Figure 8. The inhibitor does not affect the cathodic polarization, but decidedly increases the anodic polarization. Amines according to Mann and others ( 7 , 9) are effective because they adsorb a t cathodic areas and interfere with the processes there. This theory of cathodic inhibition has been disputed. Cross and Hackerman (2) have shown that the slopes of both anodic and cathodic polarization curves are influenced by isopropylamine, isobutylamine, and di-nbutylamine, the former to a larger extent. Figure 8 indicates the inhibitive action of triethanolamine is due to a marked increase in the anodic polarization. In a 30y0ethylene glycol medium the addition of 1.5y0 triethanolamine causes the current flow to rise rather sharply and level off at a low value. As in the case of 1.5% triethanolamineinhibited tap water, there is a reversal of polarity throughout the current-flow test. The anodic and cathodic polarization curves are similar to those of the triethanolamine-inhibited tap water (Figure 8). The inhibition appears to be due to a marked increase in anodic polarization. The local action corrosion current is smaller for the 30% ethylene glycolwater-triethanolamine material. Hydroquinone. Figure 6 represents the current flow of tap water treated with 0.5% hydroquinone. There is an initial rise. followed by a leveling off
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Figure 7. Influence of sodium citrate on polarization characteristics of steel in untreated t a p water and untreated 3070 ethylene glycol solution
at a relatively high current value. Hydroquinone in 0.5y0 concentration does not appear to inhibit the galvanic attack effectively. There is no change in the cathodic polarization characteristics due to the addition of 0.5% hydroquinone. However, the anodic slope decreases, indicating acceleration of corrosion. The current flow for 30% ethylene glycol treated with 0.57G hydroquinone rises sharply, falls, and finally levels off a t a current value more than twice that of the initial measurement. Hydroquinone does not exert an inhibitive action. The addition of 0.5% hydroquinone does not affect the cathodic polarization curve; however, the slope of the anodic polarization curve decreares, resulting in a shift of convergence point of anodic and cathodic potential to higher current values. In concentration of 0.5% in both tap water and 3oy0 ethylene glycol, hydroquinone behaves as a corrosion accelerator. Sodium Chromate. The current-flow curves for the tap water system treated with 0.1 and 0.25% sodium chromate drop sharply and level off at a low value. The chromate apparently delays but does not entirely prevent the film breakdown. The low constant level at the end of the test repre-ents slight galvanic attack of steel and destruction of the initial oxide film. The final level of the 0.25% sodium chromate material is that of the 0.10% sodium chromate. Sodium chromate exerts a marked inhibitive action on the galvanic attack.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Addition of 0.10% sodium chromate to tap water effected little change in the slope of the cathodic arm but markedly increased the slope of the anodic polarization curve. Sodium chromate also reduces the open circuit potential difference between the local anodes and cathodes. The slope of the anodic polarization curve for 0.257, sodium chromate is slightly steeper. However, this greater inhibition is not reflected in the local action corrosion value, probably because of the higher potential level of steel as cathode in 0.257, sodium chromate. The current flow for the steelcopper couple in 30% ethylene glycol treated with 0.2570 sodium chromate falls sharply to a very low value and gradually decreases to zero. It appears that sodium chromate almost entirely prevents the oxide film breakdown in a 30% ethylene glycol medium. A slight increase in the slope of the cathodic polarization curve is caused by addition of 0.2570sodium chromate to 3070 ethylene glycol. However. there is a marked increase in the slope of the anodic polarization curve. In tap water and 3070 ethylene glycol media, sodium chromate in concentrations of 0.1 and 0.25% behaves as an anodic polarizer. Sodium Silicate. The current-flow curve for tap water treated with 2 7 , of 40y0 sodium silicate drops to zero initially, rises slightly, levels off at a very low value. and finally drops to zero. The slight rise occurs coincidental with a reversal of polarity, which con-
CORROSION INHlBl TORS 12
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Figure 8. Influence of triethanolamine on polarization characteristics of steel in untreated tap water and untreated 30% ethylene glycol
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tinues until the current drops to zero again. At zero the polarity reverses to its original state at the start of the testi.e., steel anode, copper cathode. The curve is characterized by a very low current level. Addition of 0.8y0sodium silicate caused a slight increase in the slope of the cathodic polarization curve but a marked increase in the anodic polarization curve. The initial current generated by the couple in 0.8% sodium silicate-inhibited 30% ethylene glycol is low, probably because of the low potential difference due to an initially present film or coating. The current decreases slightly, rises rather sharply, indicative of partial film breakdown and gradually drops to a very low value. The anodic and cathodic polarization curves of the 0.8y0 sodium silicate-3070 ethylene glycol are similar to those of 0.8% sodium silicate-tap water. There is a marked increase in the anodic polarization curve. In both tap water and 30% ethylene glycol, O.8yOsodium silicate functions as an anodic polarizer. Sodium Benzoate. The current flow for the treated system drops to a low value initially, and gradually decreases to a very low level. Sodium benzoate in 1.5y0concentration markedly inhibited the galvanic attack of steel. Polarization measurements with steel after exposure to tap water treated with 1.5%
Figure 9. Influence of mercaptobenzothiazole on polarization characteristics of steel in untreated tap water and tap water treated with 1.070 borax
sodium benzoate indicated little change in the cathodic polarization curve, but a marked increase in the slope of the anodic polarization curve. The current flow curve for 3oy0 ethylene glycol inhibited with 1.5% sodium benzoate drops rapidly until there is a reversal of polarity and it subsequently increases. The anodic and cathodic polarization curves are almost identical to those in tap water-1 .5y0sodium benzoate. Sodium benzoate in 1.5% concentration behaves as an anodic polarizer in both tap water and 30% ethylene glycol media. Mercaptobenzothiazole. Figure 1 represents the current flow between steel and copper in tap water to which mercaptobenzothiazole (MBT) in concentration of 0.25 and 0.5070 has been added. The addition of mercaptobenzothiazole considerably lowered the initial current level and the subsequent current flow varies little from the initial value. The o.50y0 mercaptobenzothiazole current flow is at a lower level than the 0.25%. Mercaptobenzothiazole is insoluble in tap water at room temperature. The anodic and cathodic polarization curves do not differ from those of untreated tap water, which reflects its insolubility in this medium at room temperature (Figure 9). Mercaptobenzothiazole is somewhat soluble in an alka-
line medium; therefore 0.1% mercaptobenzothiazole was added to a 1.0% borax solution. Figure 2 represents the current-flow characteristics of this material. The curve is characterized by a very low level flow a t both initial and final points. The current level is lower than that of mercaptobenzothiazole in a tap water medium. The addition of 0.1% mercaptobenzothiazole to the 1.O% borax-tap water solution causes little change in the anodic polarization curve but a more pronounced change in the cathodic polarization curve (Figure 9). These data indicated 0.1% mercaptobenzothiazole functions as a cathodic polarizer in an alkaline 1.O% borax medium.
Discussion The data reported here indicate that the following materials act primarily as anodic polarizers in both tap water and 3Oy0 ethylene glycol media: borax (1.0, 2.0%), sodium nitrite (l.O! 1.5%), triethanolamine (1.5%), sodium chromate (O.l! 0.25%), sodium silicate (0.8y0),and sodium benzoate (l.5yo). This increased anodic polarization caused a marked reduction in the current flow between the anodic and cathodic members. Although amines are generally considered to adsorb a t cathodic areas and interfere with the reactions there, the data obtained indicate triethanolamine (1.5y0 concentration) functions priVOL. 50, NO. 4
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Table I.
Anodic and Cathodic Polarization
Polarization Local Action Current Values, 1 , Ma.
Material 1.0% borax-water 2.0% borax-water 1.0% borax-30% ethylene glycol 2.0% borax-30% ethylene glycol 1.0% sodium nitrite-water 1.57, sodium nitrite-water 1.0% sodium nitrite-30% ethylene glycol 1.5% sodium nitrite-30% ethylene glycol 1.5% sodium citrate-water 1.5% sodium citrate-JO% ethylene glycol 0.1% sodium chromate-water 0.25% sodium chromate-water 0.2570 sodium chromate-307, ethylene glycol 0.8% sodium silicate-water 0.8% sodium silicate-30% ethylene glycol 1.5% triethanolamine-water 1.5% triethanolamine+30% ethylene glycol 1.57* sodium hen-oate-water 1.5% sodium benzoate-307, ethyle n e glycol 0.5% hydroquinone-water 0.5% hydroquinone-30% ethylene glycol 0.1% mercautobenzothiazole in 1.0% boraxlwater Untreated water Untreated 30% ethylene glycol ’
Anodic Anodic Anodic Anodic Anodic Anodic
19 30 19 18 16
svcs
Performance, Hours 2000 2000
8
17 Anodic Accelerator
0.25 0.54
Accelerator Anodic Anodic
0.51 0.13 0.13
34
Anodic Anodic
0.21 0.175
10 13
2000
Anodic Anodic
0.16 0.21
7 24
2000 Failure 1032
Anodic Anodic
0.13 0.25
30 14
2000
Anodic Accelerator
0.235 0.52
25 41
Accelerator
0.35
35
Cathodic
0.10 0.48 0.29
16 34 39
marily as an anodic polarizer in tap water and 30y0 ethylene glycol environments. Mercaptobenzothiazole behaves as a cathodic polarizer in a 1.0% borax-water medium. Sodium citrate and hydroquinone in the concentrations considered behave as corrosion accelerators in tap water and 30% ethylene glycol media because of anode depolarization. Anodic and cathodic polarization data on varying concentrations of borax (1.0, 2.0’7i0) and sodium nitrate (1.0, 1.5y0)indicate that the higher concentration of borax is less effective; the higher concentration of sodium nitrite is no more effective than the lower concentration (Table I), The evidence that sodium citrate behaves as a corrosion accelerator in a water medium is enhanced by data reported in Table I-Le., 1.5% sodium citrate-water failed in simulated vehicle cooling system testing after only 609 hours of operation. An acceptable material normally operates 2000 hours successfully. The accelerated corrosion test rating is much in excess of the acceptable 21. The results in Table I indicate corrosion ratings of 41 and 35, which corroborates the evidence of hydroquinone behavior as a corrosion accelerator in these media. The increased inhibition offered by rnercaptobenzothiazole to a 1.O% borax-water solution is reflected in both polarization data and results of accelerated laboratory corrosion test-Le., the local action corrosion current I , de-
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0.14 0.2 0.15 0.16 0.27 0.27
FFSCT Rating
17 40
Failure 1081 Failure 609
9
2000
Failure 1392 Failure 1428
creases from 0.14 to 0.10 ma. as the accelerated laboratory corrosion test rating decreases from 19 to 1 6 (Table I). To date simulated vehicle cooling system data are not available for all the materials considered in this investigation, because of the relatively great length of time required for each test. The action of triethanolamine and sodium nitrite on the polarization characteristics of steel did not correlate with results of the simulated vehicle cooling system test. Prior investigations a t this laboratory (data recorded in government technical report not available for public dissemination) and data reported by Worm~vell and Mercer ( 7 7 ) have indicated the deleterious effect of sodium nitrite on solder and of triethanolamine on copper. The action of the inhibitors studied on the polarization characteristics of steel was essentially the same in tap water and 30% ethylene glycol media. Conclusions
Generally, results of the polarization tests correlated with those obtained in the Florence flask stationary corrosion test and simulated vehicle cooling system test-i.e., materials exhibiting anodic or cathodic inhibitive action had Florence flask stationary corrosion test ratings below 21 and successfully completed 2000 hours of simulated vehicle cooling system operation. Materials behaving as corrosion accelerators had corrosion test
INDUSTRIAL AND ENGINEERING CHEMISTRY
ratings above 21 and failed in simulated vehicle cooling system testing. Materials found from polarization tests to be either anodic or cathodic inhibitors for local action corrosion of steel reduced galvanic corrosion of the steel-copper couple. Similarly, materials causing increased galvanic current flow were anodic depolarizers of steel. This investigation indicates the possible use of the polarization technique with externally applied e.m.f. as a screening test for inhibitors in coolant media, with a substantial saving in time. Polarization tests lasted 48 hours; the corrosion test requires 192 hours. However, the anomalous nature of the results of the triethanolamine and sodium nitrite materials (noncorrelation with test results in the simulated vehicle cooling system) reflects the need for further investigation of the action of the inhibitors on the polarization characteristics of copper, solder. brass, and iron (other metals comprising the automotive cooling system) at both room and elevated temperatures before such an electrochemical test could be adopted as a screening test for inhibitor materials. This will be the subject of future investigations. The application of the polarization technique might be extended to include combinations of inhibitors as well as those used singly. The effect of additional selected inhibitors on the polarization characteristics of metals in coolant media could be readily followed with each successive addition, to indicate a combination of inhibitors producing the most effective corrosion inhibition. Acknowledgment
The author wishepto express his appreciation to C. F. Pickett and H. K. Ross for reading the manuscript and making suggestions. literature Cited
Ch’iao, S.-S., Mann, C. A , , IND. ENG.CHEM.39, 910 (1947). Cross, B. L., Hackerman. N., CorroJzon 1 0 , 4 1 1 (1954).
Elze, J., Fischer, H.. J . Electrochem. Soc. 99, 259 (19521.‘
Evans, U. R., “Metallic Corrosion, Passivity and Protection,:’ p. 535, Longmms, Green, London, 1948. Federal Specification 0-E-771.4, “Ethylene Glycol Inhibited,” 1953. Gatos, H. C., Corrosion 12, 39-47 (1956).
Hatch, G. B., IND.EXG. CHEM.44, 1781 (1952).
Hoar, T. P., Holliday, R. D., J . APPl. Chem. 3,502 (1953).
Mann, C. A , , Lauer, B. E.. Hultin, C. T., IND. EKG. CHEM.28, 159 (1 936),
Mears, R. B., Corrosion 11, 50-2 (1955).
Wormwell, F., Mercer, A. D., J. A$@. Chem. 3, 22, 133 (1953).
RECEIVED for review March 22, 1957 ACCEPTED August 17, 1957
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