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CORROSION IN AEROSOLS ( Reproduced by permission from SOAP AND CHEMICALS SPECIALTIES Vol. XLII, Nos. 7 & 8, July and August 1966 By Paul Sanders "Freon" Products Division E. I. du Pont de Nemours & Company Wilmington, Delaware 19898 co H a Ld rREON and COMBINATIONS OP FREON-- OR F -- WITH NUMERALS ARE DU PONT'S REGISTERED TRADEMARKS FOR ITS FLUOROCARBON PROPELLENTS Corrosion in Aerosols Corrosion pitfalls in aerosols cut by knowledge of electrochemical forces involved; extensive tests, and choice of right propellant, solvent, active in gredient, packaging medium, are key to stability. LTHQUGH there are hun\ dreds of successful aero- sol products, manv po tential aerosols never reach tne market and others fail after they are marketed. These products fail for a variety of reasons. Product instability, low market potential, lack of appeal, cost, and container corrosion are some of the factors that can be involved. There are many examples of container corro sion in aerosols and, in many in stances, this corrosion can be ex plained on the basis of the funda mental principles governing corro sion. It is the purpose of this pa per to discuss some of these corro sive aerosol systems along with some of the theory that applies to these systems. The possibility of container corrosion must be considered whenever anv aerosol product is packaged in a metal container. If an aerosol product leaks from the container, either before it reaches the consumer or during its use by the customer, the product was not tested sufficiently and should never have been placed on the market. Leakage is an extreme example of corrosion, but even very light container corrosion can mean failure in the case of a sen sitive product. There are a number of ways in which the possibility of packag ing a corrosive product in a metal container can be lessened. One is to carry out adequate storage sta bility tests. Another is to take ad- Paper presented at 52nd midyear meet ing. Chemical Specialties Manufacturers Assn.. Chicago. May lo. By Paul A. Sanders*, E. I. du Font de Nemours & Co., Freon Products Division, Wilmington, Del. vantage of the knowledge that is already available in the aerosol field. Aerosol loaders and suppli ers, such as the valve, container, and propellant manufacturers, have accumulated over the years a vast amount of information about the storage stability of many aero sol products. Quite often, the sta bility of an aerosol product can be predicted with considerable accur acy from the results already avail able with similar products. A third wav is to become familiar with the aerosol svstems known to cause cor rosion and to understand why these systems do cause corrosion. Most corrosion reactions are electrochemical in nature. Such a reaction involves the presence of an electrolyte, two electrodes, and a potential difference between the electrodes. An electrolyte is a liquid which contains ions and therefore is capable of conducting an electric current. Water is an ex ample of an electrolyte, and the more ions it contains, the better a conductor it is. The electrodes may be formed by two different metals, such as tin and iron in tinplate containers; or the electrodes may consist of two different locations on the same piece of metal. In either case, it is necessary to have a path, such as a piece of wire, for the electricity to flow between the electrodes in order to complete the circuit. (2) . In electrochemical corro sion, a number of reactions take place; positively charged metallic ions leave the anode and enter the electrolyte solution. This is the action that results in erosion and ultimate destruction of the metal that is the anode. At the same time, the electrons that are left as a result of the loss of the positively charged metallic ions to the solu tion, flow from the anode to the cathode through the path describ ed above. After the electrons reach the cathode, they meet and neutral ize positively charged hydrogen ions which travel through the elec trolyte tc> the cathode. The neu tralization of the hydrogen ions by the electrons in the cathode forms hydrogen molecules. All of these reactions occur simultaneously, but most of the corrosion in the svstem occurs at the anode where the metal ions go into solution. Common Corrosive Systems in Tinplate Many materials or combi nations of materials will cause cor rosion in tinplate containers. Some of these are so obviously corrosive to metal that they would never be considered for aerosol products. Others, however, cause corrosion only under certain conditions. The present discussion is concerned primarily with examples of the latter group. The particular ma terials or mixtures of materials which will be covered are: 1. Aerosol Propellants a. Propellant 11 and anhy drous ethyl alcohol; b. Propellant 11 and aque- EID 11437 ous ethyl alcohol; c. Propellant 11 and water; d. Propellant 21 and alkal ies; and e. Propellant 22 and alkalies: 2. Chlorinated solvents; 3. Surface active agents ; 4. Water; and 5. Acids, salts and alkalies Aerosol Propellants There is a wide variety of propellants available for the aero sol industry. These propellants differ considerably in their stab ility, and therefore their reactivity. Some of these materials, such as propellant 12 and propellant 114, are so stable that they can be used in almost any type of aerosol prod uct without fear of decomposition. Others, such as propellant 11, will react under specific circumstances to give corrosive reaction prod ucts. These specific circumstances are discussed in the paragraphs below. Propellant 11 Propellant 11 is one of the most useful of the propellants. Its low toxicity, nonflammabilitv, and high solvent power make it desir able for many aerosol products. Propellant 11 is particularly use ful as a vapor pressure depressant for propellant 12. However, pro pellant 11 can react in alcoholic, aqueous alcoholic, or aqueous sys tems to give products chat cause corrosion. Reaction of propellant 11 with anhydrous ethyl alcohol: Aerosol products such as hair sprays, room deodorants, colognes, etc. are generally formulated with combinations of propellant 11 and anhydrous ethyl alcohol. Since these products account for the major proportion of aerosols on the market, it is obvious that, in general, they h^ve not present ed much of a corrosion problem. However, under certain conditions, such as very low air concentration in the product, propellant 11 can react with ethyl alcohol via a free radical mechanism to give acetal dehyde. hydrogen chloride, and propellant 21 as the primary react ion products. tal variables that determines the polarity of the system and this is CCljF -f C:H5OH - CH,CHO -- HC1 -j- CHChF Secondary reactions form ace tal, ethyl chloride and water. The presence of acid, moisture, and dnplate establish the conditions ne cessary for electrochemical corro sion. When the concentration of hydrogen ions becomes sufficiently high, corrosion of the container occurs with the formation of hydro gen molecules and the evoluuon of hydrogen gas at the cathodic area. (2)- Oxygen has a profound effect upon the free radical re action between propellant 11 and ethyl alcohol. Low concentrations of oxygen catalyze the reaction be cause oxygen is a free radical cata lyst. However, high concentrations of oxygen have an opposite effect and inhibit the reaction as a result of the formation of inactive peroxy compounds which interrupt the chain reaction. (1). Besides its effect upon the free radical reaction, oxygen also is known to play a complex role in corrosive systems in general. For example, oxygen acts as a cathode depolarizer. Thus, when acids re act with metals, hydrogen accumu lates at the cathode and slows down the corrosion because the accumu lated hydrogen acts as a barrier and prevents other hydrogen ions from reaching the cathode. This process is called polarization. Oxvgen can react with the accumulated hydro gen to form water or hydrogen per oxide and hydroxyl ions (2) and the removal of the hydrogen from the cathode allows the corrosion reaction to continue. This effect of oxygen is called cathodic depolari zation. Due to these reactions, high concentrations of oxygen tend to promote corrosion. Tin and iron are very close in their electrochemical behavior and slight variations in the en vironment can determine which metal is the cathode and which is the anode. The concentration of oxygen is one of the environmen another important effect of oxv gen (8) . The reason that the polar ity of the tinplate system is so im portant is this: In tinplate con tainers, the area of tin exposed to the product is very large, compar ed with the area of the iron, which is available only as a result of im perfections or pinholes in the tin plate. When a cathode with a large area is coupled to an anode with a small area, severe electrochem ical corrosion can occur because the polarizing hydrogen which plates out on the cathode is spread out over a relatively large area and is easily removed by reaction with oxygen (2) . Corrosion is promoted when hydrogen is removed by de polarization. In electrochemical corro sion, the attack on the metal occurs primarily at the anode. Therefore, if the tin in a tinplate container is cathodic and the iron is anodic, the corrosive attack is concentrated on the relatively small areas of the iron. This results in pinholing. In addition, the unfavorable relation ship of the large cathodic area of the tin and the small anodic area of the iron increases the rate of corrosion so that pinholing can oc cur within a short time. However, if the tin is anodic and the iron is cathodic then the tin is attacked initially instead of the iron and generalized detinning occurs rather than pinholing. Also, the favorable relationship of the small area of the cathode (ohe iron) to the large area of the anode (the tin) pro motes a low rate of corrosion. At low concentrations of oxygen in tinplate containers, the tin is anodic and the iron is cathod ic. This is why tinplate containers have been so successful for pack aging food products. Low concen trations of oxygen tend to inhibit corrosion because of the effect upon polarity of the system. At higher concentrations of oxygen. E ID 1 1 4 3 8 the tin becomes cathodic aaid the iron anodic, which promotes corrosion. Thereiore, the effects of oxy gen upon the free radical reaction between propellant 11 and ethyl alcohol and upon the electrochem ical characteristics of the svstem tend to oppose each other as far as corrosion is concerned. The etfects are summarized in Table 1. Table 1. Effect of oxygen concentration Low Oxygon Concentration 1. Free radical reaction catalyzed -- promotes corrosion 2. Little cathodic depolarization -- retards corrosion 3. Tin anodic and iron cathodic -- retards corrosion High Oxygen Concentration 1. Free radical reaction inhibited -- retards corrosion 2. Cathodic depolarization -- promotes corrosion 3. Tin cafhodi< and iron anodic -- promotes corrosion The fact that considerablecorrosion occurs with propellant 11-ethvl alcohol combinations at low oxygen concentrations and very- little occurs at high oxygen concentrations shows that the most important factor is the free radical reaction. Apparently, the' polariz ing activitv of hydrogen at the cathode is not sufficient to prevent corrosion at low oxygen concentra tions. once the free radical reaction has been initiated. The corrosion is usually of the generalized detinning type which indicates that the tin is anodic. At high oxygen con centrations, the depolarizing effect of oxygen is of little consequence since the free radical reaction has been inhibited and there is no acid formed which will attack the tin plate. Therefore, there is no hydro gen for the oxygen to react with. Nitromerhane has been found to be an effective stabilizer for the free radical reaction and to prevent it, in most cases, regardless of the concentration of oxygen (9). Therefore, it is not necessary to attempt to control the oxygen con centration in an aerosol product in order to minimize the reaction be tween propellant 11 and alcohol. The combination of ethvl alcohol and propellant 11 is an excellent example of two compo nents that are noffcorrosive them selves but will react to form corro sive products. Aqueous Systems Oil - in - Water Emulsions and Three-phase Systems Many aerosol products, such as window cleaners, starch sprays, furniture polishes, etc., are formu lated either as oil-in-water emul sions, where the propellant is emul sified in die aqueous phase or as three-phase systems. Propellant 11 has never been used in these aque ous systems because it reacts with water to form salts and acidic prod ucts. The resultant high conduct ivity of the aqueous phase in con tact with the metals provides all the conditions necessary for electro chemical corrosion. Present evidence (10) indi cates that the reaction between pro pellant 11 anti water in tinplate containers is catalyzed by the metals present. The reaction prod ucts include propellant 21, fluoro carbon 112, and acidic materials. The reactions that have been pos tulated to account tor these prod ucts are (M = metal) : by adsorption on the metal sur faces. Actually, most inhibitors are considered to function as chem ically or physically adsorbed films which change the electrochemical nature of the system or act as barriers to corrosion processes (7) . Polar compounds are reported to work in this manner by acting as barriers to corrosion by water and it seems very likely that this is how nitromethane functions in this sys tem (7) . From another point of view, the decomposition of halo gen compounds by combinations of metal and moisture is considered to be free radical in nature (11) and nitromethane may also be functioning as a free radical in hibitor. Water-in-Oil Emulsions When products that require a fine spray, such as room deodor ants, are formulated as aqueous products, water-in-oil emulsions are used where the water is dispers ed in the propellant. In contrast to its instability in oil-in-water emul sions, propellant 11 is usually suf ficiently stable in water-in-oil sys tems. (12) There are several reasons for the increased stability of propel lant 11 in these systems. The water droplets in a water-in-oil emulsion are surrounded by an interfacial film of the oil soluble surfactant and this film prevents the water 2 CCLF A M -------- ----------- CCLF CCLF -- M CL 2 CCLF -- 2H..0 -- 2M -- CH CJ..F A M CL A M lOHL F \ CCLF A H .O--------------------- C = O A 2HCI .Cl-----------------------------* CO, -f HF + HC1 (H.,01 The propellant 11-water combination causes considerable corrosion in metallic containers; but water alone, without propel lant 11, also causes corrosion, al though less than the propellant 11water combination. Nitromethane is a fairly effective corrosion in hibitor for water alone or for the propellant 11-water combinadon. (10) This suggests that nitrome thane acts as a corrosion inhibitor from coming into contact with Che metal surface. As previously men tioned, the metal is the catalyst for the propellant 11-water reaction and the absence of contact un doubtedly prevents the reaction. Electrochemical reactions leading to corrosion are minimized in the water-in-oil emulsions also because the continuous phase of the emulsion is organic and is much less conductive than the E ID 1 1 4 3 9 aqueous phase of the oil-in-water emulsions. The surfactants used for the water-in-oil emulsions are nonionic and do not impart a charge to the dispersed water drop lets. The conditions in a water-inoil emulsion therefore are not favorable for the flow of electric current and this minimizes the tendency toward corrosion. In order for the water-in-oil emulsions to remain noncorrosive to metal, it is necessary for the emulsion itself to be stable as far as coalescence of the dispersed water droplets is concerned. If the water droplets coalesce during storage and form a separate, con tinuous water phase, this would be essentially the same as a threephase system and the separate water layer would be conducting. However, if the droplets main tain their individuality even though the emulsion creams, the conditions required for a noncor rosive system will remain. Aqueous Alcohol Systems The substitution of 95% ethyl alcohol for anhydrous ethyl alcohol in products such as hair sprays has been suggested in order to obtain a cost savings. Combi nations of 95% ethyl alcohol and propellant 11 are more corrosive than combinations with anhydrous alcohol because the propellant 11 can react with the ethyl alcohol and the water. However, nitromethane is a fairly effective inhibi tor for both of these reactions and combinations of 95% ethyl alco hol with propellant 11 containing nitromethane have been shown to have appreciable stability in metal containers. Combinations of 95% ethyl alcohol and propellant 11 with nitromethane as an inhibitor are al most as stable as combinations of anhydrous ethyl alcohol with un stabilized propellant 11 as far as corrosion in metal containers is concerned. The effect exerted bv the other components of the aero sol upon the reaction of propellant 11 with alcohol and water will usually determine whether or not a product with 95% ethyl alcohol can be marketed. During the study of the stabilization of anhydrous ethyl alcohol and propellant 11 by nitromethane, it was observed that in certain cases, the active ingredi ents in the aerosol products also inhibited the free radical reaction. In other instances, the ingredients had a catalytic effect. If the prod uct itself has an inhibiting effect, it may lend itself to be packaged in combination with propellant 11 containing nitromethane and 95% ethyl alcohol. Combinations of propellant 11 with 20% and 90% ethyl alco hol were found to be too corrosive to be packaged in metal contain ers, even with nitromethane pres ent. It is interesting that nitro methane is an effective inhibitor for propellant 11-ethyl alcohol systems or propellant J 1-water sysstems but is ineffective for aqueous ethyl alcohol combinations con taining appreciable concentrations of water. Aqueous alcohol solutions alone are probably fairly corrosive, even without propellant 11 pres ent. Aqueous ethvl alcohol foams, containing high proportions of alcohol, have received a consider able amount of attention during the last few years. In general, these products attack, metal con tainers, even when propellant 12/ propellant 114 combinations are used. Propellant 21 Propellant 21 has aroused considerable interest among aerosol fillers as a result of its excellent solvent properties. Stable in acidic and neutral aqueous systems, it decomposes rapidly under alkaline conditions. (13) The salts result ing from .the decomposition in alkaline systems undoubtedly would lead to increased corrosion, but this is academic since propel lant 21 would not be used in alka line conditions. There is no evi dence that propellant 21 will react with ethyl alcohol via a free radi cal reaction as does propellant 11. Propellant 22 Propellant 22 has found only limited application in aero sol products, partially as a result of its high pressure. Like propel lant 21, it is stable under acidic or neutral conditions but decomposes in alkaline systems. (14) Chlorinated Solvents As a general rule, chlori- nated compounds, such as methy lene chloride, methyl chloroform, and trichlorethylene, tend to be unstable in the presence of metals, water, and air. Many of these sol vents will decompose with forma tion of acidic products and this can cause corrosion problems dur ing bulk shipment or in nonaero sol applications that involve the cleaning of metal components. A wide variety of additives have been tested as potential stabilizers to prevent decomposition of the chlorinated solvents. A number of patents have been issued disclos ing stabilizers found to be effective in preventing the decomposition of the solvents. (15) Most of the common commercial chlorinated solvents now contain stabilizers. In aerosols, chlorinated com pounds serve as solvents for active ingredients and as vapor pressure depressants. Methylene chloride appears to be quite stable and has been used as a component of aero sols formulated both as oil-inwater and wa.ter-in-oil emulsions. Methyl chloroform is less stable and can cause corrosion in aqueous systems. EID 11440 AST unsuccessful attempts to P package aerosol shampoos based upon anionic detergents such as sodium laurvl sulfate, are well known. (16) Although these products appeared to have satisfac tory storage stability at elevated temperatures, they caused perfora tion of metal containers within a short time at room temperature. As a result, aerosols formulated with aqueous solutions of anionic de tergents are usually viewed with suspicion, as far as stability in metal aerosol containers is con cerned. Sodium alkyl sulfates ionize in solution and contain inorganic salts as impurities which also ionize. Solutions of sodium alkyl sulfates therefore are electrolytes with very high corrosive potentialties. Corrosion caused by these surfactants was of the pinholing type, and, as previously mentioned, it was comparatively rapid. The corrosive nature of the sodium laurvl sulfate systems at room temperature has been explained very effectively bv Root, who dem onstrated that in these systems, the tin is cathodic and the iron ano dic. (17) Therefore, corrosion was localized at the relatively minute areas where the iron was exposed and pinholing occurred rather than generalized detinning. This system is an excellent example of the severe corrosion that can occur when a cathode with a large area (the tin) is coupled with an anode with a small area (the iron) . The reason why the sodium laurvl sulfate shampoos appeared to be stable at elevated tempera tures may have been that the polarity of the system was reversed, at the higher temperatures, with tin becoming the anode and iron the cathode. As previously men tioned, iron and tin are close in their electrochemical properties, and it is very possible that varia tions in temperature might cause a reversal of polarity. If, at the higher temperatures, tin was the anode and iron the -cathode, the product would be expected to be much more stable. Root examined several other shampoo formula tions in which the tin was found to be anodic and the iron cathodic. These formulations were reported to have fairly good storage stabili ty at room temperature. There are many examples known where the storage stability results at ele vated temperature fail to correlate with room temperature tests. (23, 24, 25). Results of storage tests at elevated temperatures must there fore be viewed with a certain amount of caution. Again, it is possible, that in many of these cases, the lack of correlation be tween the room temperature tests and those at the accelerated tem peratures may be due to a reversal of polarity at the different tem peratures. Aerosol shaving lathers pro vide an interesting example of a stable svstem with surfactant pres ent. These products generally are formulated with triethanolamine salts of fattv adds as the emulsifving agents. Although these surfac tants are anionic, the rate of cor rosion of the shaving lathers is ac ceptably low and the products have been a tremendous success. There probably are a number of factors involved in the low corro sion rate of the triethanolamine salts. In these systems, the tin may be anodic and the iron cathodic, which would slow down corrosion considerably. Because triethanola mine salts are salts of a weak acid and a weak base, they tend to hy drolyze in solution rather than ionize. They do not contain inor ganic salts as impurities. There fore solutions of triethanolamine salts would be much weaker elec trolytes than solutions of sodium alkyl sulfates and corrosion would be correspondingly less. Still another factor may be that the tin and iron salts of fatty acids are insoluble in the aqueous phase. LaQue and Copson (4) have pointed out that corrosion is reduced when the corrosion prod ucts are insoluble. The salts of the alkyl sulfates would be expected to be soluble. West (18) has sug gested that fatty acid soaps should be considered as corrosion inhibi tors. Nonionic surfactants in general appear to cause much less corrosion than the anionic agents. This may be due to the decreased conductance of the aqueous solu tions, and possibly the system is anodic with respect to tin. Cationic agents, such as quaternary ammonium com pounds, have been used as germi cidal agents in aerosol products. These compounds have been re ported to cause corrosion in aque ous solutions. (19) Water In Aerosols The use of water as one of the major components in aerosol products has steadily increased during the past few years and water based aerosols now are com mon. Water has the advantages of being inexpensive, nontoxic, and a good solvent. Unfortunately, since water contains ions, it meets one of the first requirements for corrosion, which is the presence of an electrolyte. The corrosivity of water varies, depending upon the amount and type of dissolved solids and gases. (3) This, in turn, depends upon the source of the water. The corrosive activity of distilled water is low' compared with that of sea water with its high concentration of salts. The fact that dissolved gases influence the corrosive properties of water is shown by the attack on steel by water containing appreciable con centrations of carbon dioxide. E ID 1 1 4 4 1 If the storage stability of a water based product in a metal container is to be determined, it is important that the test pack is pre pared with the same type of water that will be used in production. The storage stability ot sumpiej prepared in the laboratory with distilled water may be quite dif ferent from that prepared with de ionized or tap water. Also, storage stability of a product prepared in one location may be entirely differ ent from that of samples prepared in a different location, as a result of the difference in the composi tion of the water. Acids, Salts, and Alkalies The hydrogen ion is one of the principal factors in causing corrosion as a result of its reaction at the cathode to form hydrogen. (4) Therefore, one would expect the rate of corrosion to be a func tion of the acidity of the solution. As far as iron is concerned, the dividing line between rapid and slow corrosion is reported to occur at a pH of 4.5, Free acids can attack metals in a number of ways. They can react with metals direct ly or they promote corrosion bv removing protective films from metals. The corrosiveness of salt solutions is well known, particu larly by those who have parked their cars by the seashore for ex tended periods. The solutions of most salts are good electrolytes and this provides an environment suit able for galvanic corrosion. The corrosiveness of a solution will vary considerably, depending upon the type of salts present. Acid, salts, such as some of the alumi num salts that have been used in andperspirant products, can be quite corrosive in aqueous solu tion. Generally alkalies are less corrosive than acids, but quite often they produce cathodic films which then cause anodic attack at localized areas. This results in a pitting type of corrosion. (3) Corrosivity in Aluminum Aluminum is a good ex ample of a metal that becomes pas sive as a result of the formation of a protective oxide film. This oxide film forms readily in the presence of oxygen or oxidizing agents and its thickness can be in creased by anodizing. Aluminum is quite resistant to many normal ly corrosive materials because of this protective oxide film. The film is reported to be stable under most conditions in the pH range of from 4.5 to 8.5. (5) Aluminum containers are used extensively in Europe and in some countries the majority of aerosol products is packaged in aluminum, indicating that many aerosol products have a satisfac tory storage life in this medium. In die United States, aluminum containers have been used to only a minor extent partially because they have been more expensive than tinplate containers. Con sequently, there is much less infor mation available in the United States on the compatibility of aero sol products in aluminum contain ers than there is for tinplate con tainers. However, aluminum con tainers offer a number of advan tages and storage stability tests with aluminum have therefore been carried out at intervals for a number of years. These studies have shown that combinations of propellants with alcohols can cause extensive corrosion of aluminum. This is unfortunate because a large pro portion of aerosol products are formulated with these combina tions. Thus, mixtures of anhy drous ethyl alcohol with propel lant 114 have been observed to cause perforation during storage at elevated temperatures. (17) In this case the attack is attributed to the formation of the aluminum alcoholate and hydrogen. The pos sibility of a rapid reaction in the presence of anhydrous alcohols and propellants with a build-up of pressure from the hydrogen was also noted in tests carried out in the presence of aluminum strips. (22) The addition of about 1.5% to 2.0% water had a strong inhi biting effect upon the corrosion; the water apparently inhibited the formation of the alcoholate, which is favored by anhydrous condi tions. (17, 20) Raising the con centration of water beyond the 2% level increased the rate of corro sion. Combinations of ethyl alco hol and propellant 11 caused very rapid corrosion of aluminum con tainers and there was no concen tration of water found which offer ed sufficient protection against the attack. Ethyl alcohol and propel lant 11 can react to form acidic materials and it was assumed that these attacked' the protective oxide film on the aluminum and exposed the metal itself to corrosive attack. Distilled water in alumi num containers causetl heavy cor rosion and build-up of pressure when the containers were pressur ized either with nitrogen or with nitrous oxide. The storage stabili ty appeared to be satisfactory, how ever, when the containers were pressurized with carbon dioxide. (21) Root studied the storage sta bility of three shaving lather for mulations in aluminum containers and reported that two of the form ulations had satisfactorv shelf life in the containers while the third caused considerable corrosion. 117) There seems to be little doubt that the use of aluminum containers for aerosol products will continue to increase as more in formation about the behavior of aerosol products in these contain ers becomes available. However, the studies that have been carried out indicate that some combina tions, such as mixtures of propel lant 11 anti alcohols, will have to be avoided.* E1D11442 References 1. Sanders, P. A., "Mechanism of the Reaction Between Trichloromouofluoromethane and Ethvi Alcohol/1 Proc. of the 46th Mid-Year Meet ing, CSMA, May 1960 ("Freon" Aerosol Report. A-51) 2. LaQue, F. L., Mav, T. P., Uhlie, H. H.. "Corrosion in ActionThe International Nickel Company. Inc.. 1955. 3. LaQue, F. L. and Copson, H. R.. "Corrosion Resistance of Metals and Alloys, 2nd Edition. Chapter 11, Reinhold Publishing Corporation. New York City, New York. 4. Ibid. Chapter 2 5. Ibid. Chapter 3 6. Ibid, Chapter 3 7. Ibid, Chapter 6 8. Ibid, Chapter 13 9. Bower, F. A. and Long, L. J. "Sta bilization of Alcohol-Based Aero sols, Proc. of the 47th Mid-Year Meeting, CSMA, May 10, 1961 ("Freon1' Aerosol Report, A-51 > 10. Sanders, P. A.. Soap and Chemical Specialties. Volume XLI, No. 12, December 1965. 11. Walling C., "Free Radicals m Solu tion" p. 294. John Wiiev and Sons, 1957. 12. Sanders. P. A.. J. Society of Cos metic Chemists. VqI. iX. No. 5 September 1953 / Freon'1 Aerosol Report, A-49 13. "Freon11 Aerosol Report. FA-23, " 'Freon-21,' Aerosol Solvent and Propellant" 14. "Freon" Technical Bulletin B-2, "Properties and Applications of the 'Freon' Fluorinated Hydrocarbons" 15. B. P. 773,187. L. S. Patent 2.135.238, U. S. Patent 3.391.639. U. S. Patent 2,567.621. U. 5. Patent 2.923,747, U. 5. Patent 3.159,532. 16. Foresman. R. A., Aerosol Age, September 1956. P. 34. 17. Root. M. J.. Aerosol Age, October 1958. P. 80. 18. West C. W., Aerosol Age, March 1961, P. 20. 19. Technical Bulletin BM-2108-2, "O. A.I.,'1 Hollingshead Corporation. 20. Geggard. E. D., Aerosol Age, Julv 1961, p. 20. " J( 21. Howe. R. M. and Languedoc. F. M.. Proc. 47th Mid-Year Meeting CSMA, May 17, 1961. 22. Downing, R. C. and Parmelee, H. M., Proc. CSMA, 37th Annual Meeting, New York, December 1950 ( rreon" Technical Bulletin. A-19) 23. Foresman. R. A.. "Oven Testing and Its Significance in Predicting Storage Life," Aerosol Age, Septem ber 1956, p. 34. 24. Glessner, A. S., "Water-Base In secticides in Tinplate Containers," Aerosol Age. October 1964. 25. Fulton. R. A., "Corrosive Studies of Aerosol Containers," Proc. of the 42nd Annual Meeting, CSMA, December, 1955, p. 80. FOR FURTHER INFORMATION Please contact one of the following district offices: 60 Glenwood Avenue East Orange, New Jersey 07018 Phone: 676-1112 (Area Code 201) 7 South Dearborn Street Chicago, Illinois 60603 Phone: 222-5000 (Area Code 312) 701 Welch Road Palo Alto, California 94304 Phone: 326-2840 (Area Code 415) 712 Main Street Suite 324 Gulf Building Houston, Texas 77002 Phone: 222-2468 (Area Code 713) 3503 North Hoyt Street El Monte, California 91734 Phone: 2S3-054S (Area Code 213) or: Wilmington. Delaware 19898 Phone: 999-3620 (Area Code 302) mm **. U. J. PAT. Off- Better Things for Better Living . . . through Chemistry E. I. DU PONT DE NEMOURS & COMPANY INCORPORATED "Freon" Products Division Wilmington, Delaware 19898 2M 10-46 MWNT6D IN U. S. A. E1D11443