Ind. Eng. Chem. Prod. Res. Dev., Vol. 18, No. 1, 1979
(45) Seeboth, H., Leuecke, B., Ladwig, G., Kubias, E., Kreessig, J., Ulbricht.
13
(71) (72) (73) (74) (75)
Kerr, R. 0. (to Petro-Tex Chemical Corp.), U.S. Patent 3 156707 (1964). Nakamura, M., Kawai, K., Fujiwara, Y., J. Catal., 34, 345 (1974). Varma, R. L., Saraf, D. N., Ind. Chem. Eng., 20, T44 (1976). Ai, M., Bull. Chem. SOC. Jpn., 43(11), 3490 (1970). Ostroushko, V. I., Kernos, Yu. D., Khim. Prom. (Moscow), 48(2), 93 (1972); Chem. Absb., 76, 152942r (1972). (76) Kerr, R. 0. (to Petro-Tex Chemical Corp.), U.S. Patent 3288721 (1966). (77) Ai, M., Sekiya GakkaiShi, 14(5),324 (1971); Chem. Abstr., 75, 1 1 7 9 1 8 ~ (1 97 1). (78) Ken, R. 0. (to Petro-Tex Chemical Corp.), French Patent 1451 364 (1966); Belgian Patent 666 273 (1966);Neth. Appl. 6 507 591 (1966); British Patent 1 088 696 (1967). (79) Ohtaki, T., Koike, S., Hishida, T., Hatano, M. (to Mitsubishi Chemical Industries Co. Ltd.), Japanese Patent 7510714 (1975). (80)Ai, M., Suzuki, S., Bull. Chem. SOC. Jpn., 47(12), 3074 (1974). (81) Ai, M., Bull. Chem. SOC.Jpn., 44, 761 (1971). (82) Akimoto, M., Echigoya, E., J . Catal., 31, 278 (1973); 29, 191 (1973). (83) (a) Trifiro, F., Banfi, C., Caputo, G., Forzatti, P., Pasquon, I., J. Catal., 30(3),393 (1973); (b) Trifiro, I., Caputo, G., Villa, P. L., J. Less-Common Met., 36, 305 (1974); (c) Trifiro, F., Caputo, G., Forzatti, P.. Ind. Eng. Chem. Prod. Res. Dev., 14, 22 (1975). (84) Milberger, E. C., Dolhyj, S.R., Miko, S.J. (to Standard Oil Co., Ohio), U.S. Patent 3919257 (1975). (85) Milberger, E. C., Zagata, R. J. (to Standard Oil Co., Ohio), German Offen.
H., Lambros, A. (to Akademie der Wissenschaften der DDR), German Offen 2 255 394 (1973). (46) Ikawa, T., Yamamoto, H. (to Nippon Zeon Co., Ltd.)., Japanese Kokai
7 426 228 (1 974). (47) (a) Ueeda, R. (to Kuraray Co. Ltd.), Japanese Kokai 7 134313 (1972); (b) German Offen. 2 251 349 (1973); (c) Japanese Kokai 7 670 196 (1976). (48) Otaki, T., Hatano. M. (to Mitsubishi Chemical Industries Co. Ltd.: (a), Japanese Kokai 7 488 820 (1974); (b) Japanese Kokai 75 135022 (1975). (49) Umemura, S.. Sakai, F. (to Ube Irdustrks Ltd.), Japanese Kokai 7413 113 (1 974). (50) Milberger, E. C., Dolhyj, S. R., Hardman, H. F. (to Standard Oil Co.), German Offen. 2241 918 (1973). (51) Kawai, K., Nakamura, M. (to Kuraray Co. Ltd.), Japanese Kokai 739781 1
(1973). (52) Mizoguchi, J. (to TOYOSoda Mfg. Co. Ltd.), Japanese Patent 7 122 008 (1 97 1). (53) Ueeda, R., Maryuama, H. (to Kuraray Co. Ltd.), German Offen. 2359349 (1974). (54) Otaki, T., Hatano, M. (to Mitsubishi Chemical Industries Co. Ltd.), Japanese Kokai 7488821 (1974).
(55) Umemura, S.,Ohdan, K., Sakai, F., Bando, Y., Ikezawa. H. (to Ube Industries, Ltd.); (a) Japanese Kokai 7648615 (1976); (b) Japanese Kokai 7616612 (1976); (c) Japanese Kokai 7604 119 (1976). (56) Otaki, T., Wada, N., Hatano, M., (to Mitsubishi Chemical Industries Co., Ltd.; (a) Japanese Kokai 75 135021 (1975); (b) German Offen. 2516966 (1975); (c) Japanese Kokai 7680817 (1976). (57) Koike, S.,Akiyama, T., Kawakami, T., Iwanami, Y. (to Mitsubshi Chemical Industries Co., Ltd.), Japanese Kokai 7619 714 (1976). (58) Harrison, J. P. (to Chevron Research Co.), German Offen. 2 256 909 (1976); U.S. Patent 3985775 (1976); U S . Patent 3915892 (1975). (59) Raffeison, H., Lee, R., Dolan, T. J. (to Monsanto Co.). German Offen. 2412913 (1974): Freerks, M. C., Mount, R. A. (to Monsanto Co.), U.S. Patent 3977 998 (1976). (60) Stefani, G., Fontano, P. (to Lonza Ltd.), German Offen. 2 505 844 (1976). (61) Boghosian, E. M. (to Chem. Systems Inc.), German Offen. 2261 907
2603770 (1976). (86) Matsuura, K., Imai, H. (to Mitsubishi Chemical Industries Co., Ltd.), Japanese Patent 7 41 1 374 (1974). (87) Laguerie, C., Angelino, H., Chem. Eng. J,, 5, 33 (1973). (88) Matuura, R., Shimbo, T. (to Mitsubishi Chemical Industries Co. Ltd.), Japanese Patent 7301 372 (1973). (89) Ostroushko, V. I., Kernos, Yu. D., Ioffe, I.I., Nefiekhimiya, 12(3),362 (1972): Chem. Abstr.. 77, 100433b (1972). (90) Ai, M.; Harada, K., Suzuki, S., KogyoKagaku Zasshi. 73(3),524 (1970); Chem. Absrr., 73, 446311 (1970). (91) Ai, M., Bo@, P., Montarnal,R., Bull. Soc.Chim. h.,(8-9), 2775 (1970). (92) Ai, M., Boutry, P., Montarnal. R., Thomas, G., Bull. SOC. Chim. Fr., (8-9). 2783 119701. (93) Sunderland, P . , Ind. Eng. Chem., Prod. Res. Dev., 15, 90 (1976). (94) Varma, R. L., Ph.D. Thesis, Indian Institute of Technology, Kanpur, 1976. (95) Mars, P., van Kreveien, D. W., Special Supplement to Chem. Eng. Sci., 3, 41 (1954). (96) Akimoto, M., Echigoya, E., Bull. Jpn. Pet. Inst., l 6 ( l ) , 8 (1974). (97) Dente, M I Ranzi, E., Quiroza, 0. D., Biardi, G..Chem. Ind. (Mllan), 55(7), 563 (1973). (98) Escardino, A., Sola, C., Ruiz, F., A n . Ouim., 69(3),385 (1973);69(1 l ) , 1157 (1973). (99) Bissot, T. C., Benson, K. A.. Ind. f n g . Chem. Prod. Res. Dev., 2, 57 (1 963). (100) Agasiev, R. A., Shakhtakhtinskii,T. N., Azerb. Khim. Zh., (6), 14 (1969); Chem. Abstr.. 74, 3216p (1971).
(1973). (62) (a) Jurewicz, A. T., Young, L. B. (to Mobil Oil Corp.), German Offen. 2516229 (1975); 2550 119 (1976),(b) Burress, G. T. (to Mobil Oil Corp.), German Offen. 2 528 599 (1976). (63) Lemal, R., Vekemans, J. (to UCB, S.A.), German Offen. 2437 154 (1975). (64) Slinkard. W. E., Hughes, M. P. (to Celanese Corp.), U.S. Patent 3907833 (1975). (65) Freerks, M. C., Suda, M. (to Monsanto Co.), German Offen. 2 248 746 (1973). (66) Raffelson, H., Suda, M. (to Monsanto Co.): (a) German Offen. 2263 009 (1973); (b) German Offen. 2263010 (1973). (67) Freerks, M. C., Randle, S. (to Monsanto 13.): (a) German Offen. 2418281 (1974); (b) Belgian Patent 826647 (1975). (68) Kerr, R. O., Barone, B. J. (to Petro-Tex Chemical Corp.): (a) U.S. Patent 3960585 (1975); (b) German Offen. 2611 290 (1976). (69) Dolhyj, S. T. (to Std. Oil Co., Ohio), German Offen 2 453 677 (1975). (70) Cherry, W. E., Dickason. A. F., Hedge, J. A. (to Sun Ventures, Inc.), U.S. Patent 3 928 392 (1975); 3 968 054 (1976).
Received for re2ieu February 7, 1978 Accepted October 25, 1978
POLYMER COATINGS SECTION Electrochemical Techniques to Monitor Performance of Polymer Coatings in Corrosion Protection J6zsef DBvay, * Lajos Miszlros, and Ferenc Janlszik Electrochemistry Research Group, Hungarian Academy of Sciences, 8200 Veszprgm, Hungary
The determination of permittivity and activation energy of the dielectric relaxation of polymer coatings provides useful information on the effects of aging and deterioration. Measurement of polarization resistance was useful in studying the anticorrosive protection of steel.
Painting is the least expensive, the most frequently used, and a relatively durable corrosion preventive method; therefore it is of special importance to study the properties of paint coatings and the corrosion processes taking place under them. 0019-7890/79/1218-0013$01.00/0
Since results are obtained slowly in exposure tests, accelerated investigations utilizing electrochemical methods are desirable. Corrosion is an electrochemical phenomenon taking place at the interface of the metal in contact with the coating system. Thus all information 'C
1979 American Chemical Society
14
Ind. Eng. Chem. Prod. Res. Dev., Vol. 18, No. 1, 1979
related to these phenomena fosters the understanding of the protective mechanism of paints. In this field, empirical methods related to corrosion prevention of paint coatings are being replaced by conscious research and development. This question is extremely complicated, since the field is an interdisciplinary one, and moreover it is also complex with regard to electric and electrochemical methods. In this interdisciplinary endeavor we have chosen to treat the broad subject from the point of view of the electrochemist. There were several attempts to relate the anticorrosive properties of paint coatings to the penetration of oxygen (Guruviah, 19701, water (Brasher, 19561, or ions (Mayne, 1952). These theories really refer to possibilities of the electrochemical corrosion processes. The ion-exchange capacity (Boies et al., 1969; v. Fraunhofer et al., 1976) and the permselectivity (Wormwell e t al., 1950) of the paint coating are very important, especially with respect to concentration polarization due to the corrosion processes. I t is necessary to know which of these processes can be regarded as rate determining. According to many authors, interfacial corrosion is a function of specific coatings formulations (Wormwell et al., 1950; Yakubovitsch et al., 1964; Evans, 1968). With respect to conductivity, both the water and the dissolved ions must be taken into consideration (Kittleberger et al., 1952; Mayne, 1970). In this regard the osmotic effects between the solution within the paint coating and the corrosive electrolyte must also be considered. The determination of the electrode potential can be easily carried out, but it is usually not characteristic of corrosion in the case of an unknown corrosion mechanism (Brasher, 1956; Wormwell et al., 1950; Evans, 1960; Grubitsch et al., 1964; Whitby, 1938; Wormwell, 1949; Burns, 1936; Haring, 1939; Greenblatt, 1958; Crennell, 1950a,b; Jimeno, 1950; Bannister et al., 1930; Pourbaix, 1965). The anodic and cathodic polarization curves of the metal under the paint coating give far more information on the corrosion from an electrochemical point of view (Pourbaix e t al., 1965; Draley, 1959; Kargin e t al., 1958; Eisenfeld et al., 1964; Tomashov et al., 1964; Eisenfeld et al., 1968; Clay, 1969). In this case the ohmic resistance of the coatings causes difficulties as far as the measurement technique is concerned, and if one leaves this question out of consideration he might come to false conclusions. I t was suggested that the voltage drop due to measuring current on the resistance of the coating be estimated by measuring the resistance with alternating current, and that the latter value be used for the correction of the IR drop (Clay, 1965; Bureau, 1968a,b). However, the ac impedance of the paint applied to the metal also contains the faradaic impedance of the metal (Rosenfeld e t al., 1965). Corrections employing dc resistance of the films stripped off the metal were also reported (Bureau, 1968a,b). Model investigations cannot bring about reassuring solutions since only the study of polarization under the applied paint coatings gives meaningful indications. Such investigations were cairied out by Rosenfeld (1965) with galvanostatic polarization, the effect of the ohmic resistance being eliminated by a current interruption method. Several conclusions were drawn from these measurements. However, in the case of passivity, POtentiostatic and potentiodynamic measurements are needed for deeper understanding, not the galvanostatic or galvanodynamic ones. I t is well known that the permittivity of materials containing polar groups depends greatly upon the frequency used and on the temperature of the sample. This
fact led to the idea that structural changes in paint coatings which are brought about under various conditions could be followed by the measurement of the changes in permittivity. The polar groups of the coatings are in a state of random statistical motion caused by their thermal energy. The external electric field, however, tries to orient the dipoles by exercising a torque on them. Polarization and hence permittivity is greatly enhanced by the orientation of the polar groups. At a given frequency the increase of temperature first causes an increase in the orientation effect, but with further increase of the thermal motion a disorientation takes place. At a constant temperature, orientation becomes more difficult with increasing frequency because of the inertia of the polar groups. The ranges of frequency or temperature where the permittivity changes take place are known as dispersion ranges, and the points of inflexion on the curves of the corresponding functions are termed the relaxation temperature (T,) and the relaxation frequency (q), respectively. The structural changes due to aging or exposure (e.g., formation of cross-linked structure, oxidation, chain breaking) are accompanied by the formation or decomposition of polar groups or by the change of their environment. Therefore, they can be detected with good sensitivity using dielectric techniques. From the two possible experimental techniques the simpler thermal dielectric spectroscopy was chosen, as it can be easily carried out; i.e., the permittivity of coatings was measured a t constant frequency as a function of the temperature. In the measurements, the applied paint was the dielectric medium of the condenser which consisted of the base metal and a metal foil covering the paint. I t was possible to heat the condenser, and it was surrounded by an indifferent gas during the measurements to prevent oxidation. In Figure 1 the temperature dependence of the capacity (C), which is proportional to the permittivity and to the imaginary term of the admittance, and the temperature dependence of the real term of the admittance (G) is shown at different frequencies in the case of a control coating resin (identified as Epamin) selected to test the premise for the study. T h e temperature a t the absorption maximum of G practically corresponds to the inflexion point on the dispersion curve. Hence the relaxation temperature can be determined from both types of curves. We note that the large change with temperature occurs in the temperature range of 40 to 80 "C. The results of similar experiments carried out with Epamin coating exposed to heat treatment are shown in Figure 2; in this instance, however, the changes took place in the temperature range of 10 to 100 "C. The structural changes brought about by aging (e.g., further formation of cross-links) shift the relaxation temperature to higher values. These examples show that aging of coatings can be followed by dielectric measurement. This is also illustrated in Figure 3, where the dispersion spectra measured a t a frequency of 1000 Hz are shown after various heat treatments of colorless Epamin. I t was found once again that the effect of heat treatment is that the dispersion spectrum and the relaxation temperature are shifted toward higher values. In further experiments we studied the aging by atmospheric exposure of polyurethane lacquers cured by aliphatic or aromatic isocyanates. Both the colorless lacquers and the types pigmented with rutile or anatase were investigated with regard to the interaction of the
Ind. Eng. Chem. Prod. Res. Dev., Vol. 18, No. 1, 1979
+
I
o 0
A
100 200 500 IO00 ?Ox
i
Hz Hz HZ HZ
Hz
J
15
x mthoul Irealrrert A heat treatment 80°C 12 harE
* heat treatment BO’C 120hours f = 1000 HZ
IPF1~ ~
-~ _--*
25
’25
75
Figure 3. Dispersion spectra for unpigmented Epamin heat treated. Figure 1. Temperature dependence of capacity vs. frequency for unpigmented Epamin.
o
x
without exposure after 6 m t h s - s u r e
A
($1
[CPF,
300
lCIm
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0
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80
100 120 140
160
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40
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Figure 4. Pigmented aliphatic polyurethane Figure 2. Capacity vs. frequency for unpigmented Epamin treated 12 h at 80 “C.
pigment and the binder. The measurements were carried out a t various frequencies. For an illustration of the dielectric spectra obtained in this way, the permittivity (measured at 1000 Hz) of the polyurethane coatings cured by aliphatic isocyanates and pigmented by rutile or anatase, in their original condition and after atmospheric exposure for 6 months, are shown in Figure 4. It is apparent that the dispersion range was shifted toward higher temperatures upon exposure. In Figure 5 the change in the relaxation temperature of various polyurethane coatings cured with aliphatic isocyanate, namely the colorless and pigmented ones with anatase and rutile, respectively, is shown as a function of time in the case of storage without exposure and with atmospheric exposure started 2 weeks after the paint application. It was found that during storage without exposure the relaxation temperature of the coatings becomes stable after approximately 2 months and there were no further changes during the period of investigation. The increase in the first 2 months can be attributed to an increase of hardness owing to further slow formation of cross-links after drying.
In the case of atmospheric exposure the effect of pigmentation is striking for the colorless coating; the relaxation temperature begins to increase after exposure of 2 months which reflects changes in the structure of the coating, probably oxidation. Similar phenomena can be observed in the change in the relaxation temperature of coating pigmented with anatase with the difference that in this case the pigment delays the beginning of oxidation. On the other hand, the relaxation temperature of the coating pigmented with rutile becomes stable after hardening of approximately 1 month, similar to the case without exposure, and it does not change during further exposure. This fact indicates that the rutile pigment increases the stability and the weather resistance of the binder to a great extent. The relaxation temperature of coatings with polyurethane binders cured with aromatic isocyanate changes considerably even during storage without exposure (Figure 6), with the exception of the sample pigmented with rutile. The latter became stable and corresponds to the previous case. The stabilizing effect of rutile against atmospheric exposure, however, is effective only for a short period (approximately 1 month); neither rutile nor anatase can prevent the oxidation and the decomposition of the binder.
16
Ind. Eng. Chern. Prod. Res. Dev.. Vol. 18, No. 1, 1979
tr
1 tzar 2 pgms-t an3tase 3 pismen( rat le
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without exposure atmospherlc exposure
o
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Figure 5 . Aliphatic polyurethane. 4
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2 pigment anatase 3 plgrrant rutlle
$1 90
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2
3
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2
3
4
5
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Figure 7. .4ctivation energy changes with aliphatic polyurethane.
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.
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5
6
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atmospheric exposure
2
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Figure 6. Aromatic polyurethane.
The relaxation temperatures determined from the dielectric spectra measured a t various frequencies yiela a temperature-frequency relationship which can be described by an Arrhenius type equation o, = Ae-ea/RT
From this, one can determine pa,the energy of activation. The advantage of the calculation of the activation energy is that the results become independent of the frequency and temperature used in the measurement and of the geometry of the measuring cell. Figure 7 shows that the activation energy changed with time and exposure. The energies of activation of coatings stored without exposure became stable for the three types after approximately 2 months. With regard to the effect of atmospheric exposure, this characteristic value, however, remains unchanged only in the case of coatings pigmented with rutile, while the energies of activation of the two other types show a difference, indicating significant structural change. In Figure 8 the energies of activation of coatings with polyurethane binders cured with aromatic isocyanate are shown. During storage without exposure the energy of activation and simultaneously the structure of coating pigmented with rutile became stable, while the Bnergy of activation of the colorless coating and that of the coating pigmented with anatase shows a significant change even during storage. During atmospheric exposure, difference referring to oxidation or degradation can be observed in all three types. In the case of coatings pigmented with rutile, the energy of activation measured without exposure differs but
[mnthl
Figure 8. Activation energy changes wlth aromatic polyurethane.
slightly from that obtained after exposure, especially in the first 3 months. This fact also demonstrates the increased weather resistance due to the rutile content. On the basis of dielectric measurements it can be concluded that polyurethane binder cured with aliphatic isocyanate exhibits good weather resistance only if, pigmented with rutile, while the stability of polyurethane cured with aromatic isdcyanate was not improved permanently, even by iutile. This phenomenon calls attention to the fact that the applicability of a cuating under given circumstances, in this case its weather resistance, is not determined bxclusively by the binder, but the interaction between thk pigment and the binder is also important. These results ark in agreement with practical observations and this fact proves that the dielectric mecisuring technique reflects with good correlation to structural changes taking place in the coatings. Thus, it can be readily applied to follow the aging processes. I t was found in the case of other coatings, e.g., those drying by physical or oxidative ways or consisting of two components, that it takes 2 or 3 months for the coating to be stabilized, so the data of the beginning of the ex-
Ind. Eng. Chem. Prod.
posure have a great influence on the durability of the coating. It was also noted-in agreement with practical observations-that the laboratory tests should begin immediately after application, in the case of coatings exposed just after application, while the tests on coatings stored for longer periods before exposure should be tested after similar storage. In the case of baked coatings the optimum conditions for baking can be determined by dielectric investigations. The results of the measurements agreed well with practical observations. Epelboin (1973) measured the impedance of metals coated by paints using alternating current. On the basis of the change with the frequency of the real and imaginary part of the impedance this author could distinguish the role of the metal as an electrode and the role of the coating with respect to impedance. This method requires a sophisticated apparatus and computer calculations. It is apparent that a number of methods can be employed to examine the various coatings. We studied the effect of the surface layer on the rate of metal corrosion in the case of various coating types. An experimental technique was developed which is suitable for investigating the passivation by chemical processes occuring on the metal surface during application of the coating as well as for the study of changes in passivation during exposure. The method consists essentially of the electrochemical measurement of the rate of corrosion. The organic coating was dissolved from the metal surface by a suitable solvent mixture prior to the electrochemical investigation as its high electric resistance would have impeded the measurements and the structure of the surface layer would have been strongly altered by the reactions of the active component of the coating during the electrochemical test. However, the protective layer and the corrosion products firmly adhering to the metal surface were not removed by the solvent mixture composed of chlorinated hydrocarbons of low molecular weight, an ester and a ketone. The technique known as “linear polarization” was employed to determine the corrosion current density characteristic of the corrosion rate of metal plates prepared according to the above procedure. The measurement consisted of the determination of the polarization resistance of the electrode immersed in the corrosive medium. The polarization resistance is
Rp=(+?)
t=O
(dE/di)+, is the slope of the polarization curve of the electrode a t the potential where i = 0. This slope can be evaluated by graphical differentiation of the nearly linear polarization curve in the vicinity (within a few millivolts) of the corrosion potential where i = 0. The corrosion current density is given by the formula ,
1,
0.026
= RP
The polarization measurements were carried out in 0.1
m NaN03 as an electrolyte because this does not react with the surface layer and has only a weak corrosion effect. The polarization measurements were performed with a POtentiostat while the polarization curves were automatically recorded with an X-Y recorder. Experiments on model metals and paints proved the reliability of the method. Results of a series of experiments pertaining to a given problem will be discussed. We modeled the conditions encountered in the application of paint to steel surfaces
Res. Dev., Vol. 18, No. 1, 1979
17
Table I. Corrosion Current Density Measured o n Metal Plates of Varying Pretreatment History corrosion current density, MA/cmZ plates exposplates after plates expos- ed t o SUItreatremoval of ed t o salt phur dioxide ment metal coating mist chamber chamber be- withafter 300 h pre- fore o u t treat- coat- coat- Pro- Pelli- Pro- Pelli- Pro- Pelliment ing ing met kor met kor met kor
-
Aa Ib I1 I11
IV V VI VI1
B
I I1 I11
IV
v
VI VI1 C
I I1 I11 IV
V VI VI1
D
I I1 I11 IV
v
VI VI1
35.0 22.0 16.0 26.0 6.4 14.0 17.0
4.0 4.7 4.3 2.6 4.0 4.3 7.3
0.9 2.0 1.6 1.3 1.2 1.6 1.7
83 46 34 31 45 23 33
0.9 3.2 8.3 4.3 3.5 3.2 2.7
5.9 6.1 1.4 18.0 13.0 4.4 2.1
0.9 0.4 0.6 0.3 0.3 0.3 1.0
5.1 5.3 7.9 2.5 1.2 7.3 17.0
2.7 5.2 5.3 3.3 1.9 2.4 6.9
2.0 3.2 2.3 1.3 1.0 2.4 2.6
1010 1230 1450 1620 1230 1010 1140
0.4 0.4 0.4 0.2 0.1 0.4 0.9
2.4 2.5 2.6 1.9 1.8 2.7 2.9
0.4
59.0 18.0 38.0 7.8 6.7 9.8 20.0
3.9 4.1 6.4 4.8 3.0 5.6 8.8
7.6 14.0 25.0 16.0 22.0 23.0 22.0
6.5 19.0 13.0 4.8 5.6 7.5 6.5
0.8 0.4 2.2 0.8 0.5 1.7 1.9
25.0 50.0 53.0 44.0 11.0 37.0 42.0
10.0 14.0 32.0 60.0 4.7 3.5 31.0 29.0
36.0 80.0 1.8 8.4 17.8 10.3
7.9 5.6 27.0 9.6 18.0 12.2 9.8 1.7 12.4 0.3 14.9 1.9 24.0 1.9
0.7 1.5 0.4 0.5 0.3 0.5
3.2 6.6 5.4 10.0 14.4 15.0 5.1 3.0 4.8 0.8 6.3 4.6 7.1 5.4 4.2 3.5 2.1 1.9 4.7 5.3 3.9
0.4 3.5 5.8 1.0 0.8 1.9 5.4
a A, sand blasted surface; B, hand polished surface; C, surface treated with Ferrofixol; D, surface treated with Mavebit. I, without exposure; 11, exposure t o mixed industrial atmosphere for 168 h ; 111, exposure t o mixed industrial atmosphere for 236 h ; IV, exposure t o ammonia for 72 h; V, exposure t o ammonia for 168 h; VI, exposure to saturated water vapor for 24 h ; VII, exposure t o saturated water vapor for 72 h.
exposed to an atmosphere severely polluted by industrial gases. The variation of the rate of corrosion was measured on steel surfaces which were cleaned by a mechanical method or pretreated by a chemical procedure, and the metal was exposed to various corrosion effects for different periods of time between the cleaning procedure and the paint application. We intended to determine whether the quality and extent of contamination reached a critical value at which anodic metal dissolution exceeded the formation of a passive layer. The iron oxide layer was removed from the metal surface used in the experiments either by (A) sand blasting, or (B) manual polishing, or the iron oxide was chemically converted to an iron oxidephosphate layer by treatment with Ferrofixol C (an aqueous solution containing condensed amines and other organic compounds). After pretreatment, the plates were exposed for various lengths of time to an atmosphere containing either 3% ammonia or a mixture of corrosive gases, both saturated with water at 40 “C. Both adsorption and chemisorption could occur at the temperature of the gas chamber. After this treatment the plates were coated with either Promet (a paint of vinyl resin base containing a reactive component) or Pellikor (a synthetic alkyde resin paint
18
Ind. Eng. Chem. Prod. Res. Dev., Vol. 18, No. 1, 1979
containing a chromate pigment having an inhibitory effect). The coated surfaces were exposed to salt spray containing 0.05 mol/L of SO2 gas. The changes on the metal-paint boundary layer were examined by the above procedure after 300 h. The results are summarized in Table I. The corrosion current density values measured on iron plates which were not painted and not exposed to corrosion effects are also listed in order to facilitate the comparison of the data. It is apparent from the results that the metal surface was passivated simultaneously with the application of the coating in the case of the primers used in this investigation. The corrosion protective effects of the various pretreatments are clearly different. It is noteworthy that manual polishing considerably increases the metal surface as the latter is engraved by the hard granules of the polishing material. Thus the amount of active compounds present in the solution was not sufficient for passivating the surface of increased area. This fact accounts for the intense corrosion observed especially under the effect of highly aggressive chloride ions. The presence of contaminations affected the values of the corrosion current density to an identical extent, regardless of the pretreatment. A very small corrosion current density was observed on surfaces contaminated by ammonia. The results of these experiments led to the conclusion that the above method permits evaluation of the corrosion protection due to the chemical change occurring at the boundary layer of the metal and the paint coating without the determination of the structure and the composition of the boundary layer. Literature Cited
Cherry, B. W., Mayne, J. E. O., "Proceedings, 1st International Congress on Metallic Corrosion", p 539, Butterworths, London, 1962. Cherry, B. W., Mayne, J. E. O., "Proceedings, 2nd International Congress on Metallic Corrosion", p 680, NACE, Houston, Texas, 1966. Clay, H. F., J . Oil Coiour Chem. SOC.,52, 158 (1969). Clay, H. F., J . Oil Coiour Chem. Soc.. 48, 356 (1965). Crennell, J. T., J . SOC.Chem. Ind. London, 69, 371 (1950a). Crennell, J. T., J . SOC. Chem. Ind. London, 69, 536 (1950b). Draley, J. E., Ruther, W. E., De Boer, F . E., Youngdahl, C. A,. J . Nectrochem. Soc., 106, 490 (1959). Eisenfeld, Ch. B., Buybina. L. P., Skobeleva, I. A,, Krosilshikov, A. I., Zashch. Met., 4, 195 (1968). Eisenfeld. Ch. B.,Buybina, L. P., Levina. L. A,, Krosiishikov, A. I., Zh. Priki. Kbim., 35, 1759 (1962); 37, 1748 (1964). Epelboin, I., Metalio6erfkiche, 27, 113 (1973). Evans, U. R., "The Corrosion and Oxidation of Metals", p 899, E. Arnokl, London, 1960. Evans. U. R., "The Corrosion and Oxidation of Metals", 1st Supplement, p 207, E. Arnold, London, 1968. Greenblatt, J. H., J . Appi. Chem. Biotechnoi., 8, 229 (1958). Grubitsch. H.. Heckel, K., Monstad, O., Farbe Lack, 70, 167 (1964). Guruviah. S.,J . Oil Coiour Chem. ASSOC.,53, 669 (1970). Haring, H. E., Gibney, R. B., Trans. Electrochem. Soc., 76, 287 (1939). Jimeno, E., Medion-Costelianos, S.,Torre, J.. Boi. Inst. ESP. Oceanogr., 25, 33 (1950). Kargin, V. A., Karyakina, M. I., Berestneva, 2. Ya., Doki. AkadNauk SSSR. 120, 1065 (1958). Kittleberger, W. W., Elm, A. C., Ind. Eng. Chem., 44, 326 (1952) Mayne. J. E. O., Br. Corros. J . , 5 , 106 (1970). Mayne, J. E. O., Research(London),5 , 278 (1952). Pourbaix, M., Corr. Sci., 5 , 677 (1965). Pourbaix. M., Vandervelden, F., Corros. Sci., 5 , 81 (1965). Rosenfeld, I. L., Oshe, E. L., Akimov, A. G., Korroz. Met. Splavov, No. 2, 302 (1965). Tomashov. N. D., Mikhailovskii, Yu, N., Leonov, V. V., Corrosion, 20, 125 t, 218 t (1964). v. Fraunhofer, J. A.. Boxall, J., Surf. Technoi., 4(2), 187 (1976). Whitby, L., Paint Research Assoc. Tech. Rep. No. 96 (1938). Wormwell, F., Brasher, D. M., J . Iron Steel Inst., 164, 141 (1950). Wormwell, F., Brasher, D. M., J . Iron SteeiInst., 162, 129 (1949). Yakubovitsch, S. V., Nitsberg, L. V., Karyakina, M. I., "Proceedings, 6th International Conference on Electrodeposition", p 32 1, 1964.
Bannister, L. C., Evans, U. R., J . Chem. Soc., 1361 (1930). Boies, D. B., Northan, B. J., McDonald, W. P., Mater. Prot., 8, 30 (1969). Brasher, D. M., Nectropiat. Met. Finish., 9, 284 (1956). Bureau, M., Corros. Trait. Prot. Finition, 16, 235 (1968a). Bureau, M., Report of 41st Meeting of European Federation of Corrosion, p 481, Budapest, 1968b. Burns, R. M., Haring, H. B., Trans. Electrochem. Soc., 69, 169 (1936).
Received for revieu: August 28, 1978 Accepted September 22, 1978
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Presented at the 14th FATIPEC Congress, Budapest, Hungary, June 1978.
CATALYST SECTION Evaluation of Commercial Catalysts for the Fischer-Tropsch Reaction William G. Borghard and Carroll 0. Bennett" Department of Chemical Engineering, The University
of Connecticut, Storrs, Connecticut 06268
The hydrogenation of carbon monoxide was investigated at 20 atm (2.0 MPa) and 250 O C (523 K) in tubular reactors. Four commercial iron catalysts, one commercial cobalt catalyst, and an iron lathe turning catalyst were tested at three hydrogen to carbon monoxide feed ratios. At a relatively constant space velocity the overall rates of reaction gave a good indication of activity. The cobalt catalyst appeared to be the best. Its selectivity favored saturated hydrocarbons. A nitrided ammonia synthesis catalyst attained a similar activity. An optimal feed ratio of 2:l H,/CO was observed. The highest activities concurred with a 2:l feed ratio and the production of water.
Introduction The Fischer-Tropsch process continues to be studied as one of the possible methods for the conversion of coal to liquid fuel or chemical feedstock. The process can also 0019-7890/79/1218-0018$01.00/0
be considered as a means of peak-shaving by storing as a liquid the energy of gasified coal used as fuel to a combined-cycle power plant. This study was undertaken as part of the evaluation of readily available commercial-type catalysts for their suitability in such a process.
0 1979
American Chemical Society
