Patented Dec. 12, 1950 2,534,030

UNITED STATES PATENT OFFICE 2,534,030 ANTSFREEZE COMPOSTON Edwin H. Keller, Wawa, Pa., assignor to E. I. du Pont de Nenours & Company, Winington, )e., a corporation of Relaware No Drawing. Application Februaary 27, 1948, Seria No. 1,829 2 Claims. (C. 252-4) 2 This invention relates to anti-corrosive anti pearance, which may lead to discarding the anti freeze Compositions Suitable for use as coolants in freeze Solution more frequently than would other internal combustion engines. It also relates to Wise be necessary. proceSSes or methods for preventing corrosion An object of this invention is to provide fur of metals which come in contact with such anti s ther improvements in antifreeze compositions. A freeze compositions. further object is to prepare a non-corrosive anti For many years it has been known that sodium freeze composition in which the corrosion in tetraborate is outstandingly effective as a cor hibitor does not tend to become converted to an rosion inhibitor in alcoholic antifreeze composi insoluble precipitate under any of the conditions tions (Kepfer, U. S. 1,911,195). Many attempts normally encountered in actual use. A further have been made to provide improved antifreeze object is to prepare an ethylene glycol antifreeze solutions containing inhibitors other than sodium which is Superior to previously known antifreeze tetraborate. Despite these numerous attempts, compositions from the standpoint of inhibition much of the antifreeze manufactured in this against corrosion, precipitate-formation, and Country at the present time contains the sodium foaming tendency. Other objects of the invention appear hereinafter. O tetraborate corrosion inhibitor disclosed by It has been discovered in accordance with this Kepfer. invention that alkali metal metaborates are far It has been discovered in recent years, how Superior to the previously employed alkali metal ever, that an improved corrosion inhibiting action tetraborates as antifreeze corrosion inhibitors. can be obtained by using paired inhibitors, e. g. Moreover, the alkali metal metaborates accord by pairing sodium tetraborate with mercaptoben ing to the invention, are efficient corrosion in zothiazole (Keller, 2,373,570) or by employing hibitors in alcoholic antifreeze compositions even an alkali metal tetraborate in combination with in the absence of added substances such as phos an alkali metal phosphate (Duus, U. S. applica phates which cause the development of precipi tion S. N. 337,207, filed May 25, 1940 now aban tates in antifreeze compositions under conditions doned; Canadian Patent 438,016; Kiffer, U. S. of actual use. In general, inhibitors which cause 2,384,553). The discovery of the synergistic ac rapid attack on Solder (e. g. inorganic nitrites, tion of the sodium tetraborate-mercaptobenzothi etc.) are avoided in accordance with this inven azole inhibitor has made possible the imanufac tion. ture of artificeeze compositions which remain The alcoholic antifreeze compositions which non-corrosive for prolonged periods of time. The are employed in the practice of the invention con pairing of an alkali metal tetraborate with an tain water-Soluble alcohols, e. g. methanol, alkali metal phosphate also has given rise to ethanol, isopropanol, ethylene glycol, propylene antifreeze compositions Superior to those ob glycols, butylene glycols, glycerol, etc., as freez tainable by the use of individual inhibitors. ing point depressants. The preferred freezing The tetraborate-phosphate inhibited antifreeze point depressant is ethylene glycol. The water coin positions, while virtually unsurpassed fron soluble alcohols having from 1 to 3 carbon atoms the standpoint of anti-corrosion properties, have per molecule are, in general, more efficient as certain disadvantages, viz., when admixed with freezing point depressants than are alcohols of tap water available in certain cities, these mix higher molecular weight. tures yield insoluble calcium phosphate which The quantity of alkali metal metaborate em separates out as a precipitate. The Sodium tetra ployed as corrosion inhibitor should be 0.5 to 7.5% borate - Inercaptobenzothiazole inhibited anti of the weight of the alcohol. Organic inhibitors, freeze compositions also tend to develop precipi Such as mercaptobenzothiazole compounds (e. g. tates after prolonged use, due to the conversion of the nercaptobenzothiazole compound to rela Enercaptobenzothiazole, alkali metal mercapto tively insoluble organic products, especially when benzothiazoles, etc.), di-isopropyl amine nitrite, the mixture has been subjected to the action of mono-, di- and triethanol amine and salts there actinic light. The developinent of precipitates of, etc. may be used in combination with the in alcoholic antifreeze compositions, even though 50 alkali metal metaborate inhibitor, if desired. The not necessarily affecting the anti-corrosion prop weight of organic inhibitor, when one is used, erties thereof is, nevertheless, highly undesirable should be from 0.0001 to 0.5%, based on the from a practical standpoint. Small passageways weight of alcohol. These organic inhibitors may in the cooling systern may become blocked with be omitted altogether, if desired, or they may solid. Also the coolant may take on a rusty ap be used in such extremely Small quantities that 2,534,030 4. any precipitate formed therefrom does not notice by a gain in weight of the metal, was observed. ably interfere with the inproved results obtained The corrosion rates not thus marked represent through the use of the metaborate as the inor loss of metal from the Surface of the test strips. Table I-Avoidance of formation of precipitate in antifreeae compositions 33% by volume of ethylene glycolin water

Inhibitor (weight percent Calcium Appearance of based on weight of ethyl- Source of water Cpt of Antifreeze ene glycol) P. P.M. Composition

2.2%borax.------Wilmington, Dell- 12 Clear. Do------Marion, O------70 D0. D0------Dayton, O--- 90 Do. Do------Galveston, Tex---- 18 DO. 2.5% sodium metaborate.--- Wilmington, De 2 Do. D - - - - Marion, O- 70 Do. Dayton, O. 90 Do. Galveston, Tex- 8 Do. Wilmington, De 2 Do. Marion, O.-- 70 Milky-precipitate

Settled out. Dayton, O.-- 90 Do. - Galveston, T 18, Clear.

not Theunusually Ca contents high. ofAccording Dayton and to Mariondata presented water, set by forth,Collins, above, Lamar are and Lohr, U. S. G. S. Water Supply Paper 658 (1932), the weighted average hardness of public water systems in 22 of the 48 States ex ceeds 120 l. P. M. Ca). Table II-Corrosion tests on metal strips sus 2}ended in 33 volume percent ethylene glycol. in water (160° F., 336 hours, stirring at 1750 R. P. M.)

Corrosion Rate, Inches Penetration per inhibitorb ((weight ht percent basedb on Year X 103 weight of ethylene glycol) Source of Water Aluni- Cast 50:50 Ull- 3S Copper Brass Sir 2.2 Marion, O. (450P. P.M. sulfate)- i6 28 0.5 --0.6 3. 6.3 Marion, O 0. O 1.5 O 2.5%2.7% NaBO2.2H2O.borax--0.7% - 1. 3 0.6 ... 3 i 0.20% Na mercaptobenzothiazole ------do - - 0 0.7 0. 1. 2.2%borax. ------Galvestor, Tex... (300 P. P. M. 30, .46 0.5 0.6 2 chloride). 5.0% borax. Galveston, Tex- 3 7 O 1. 6.3% NaBO2. 1, 7 2 0.9 1. 2.7% Na2EO2.2H2O.-- 8. 2 0.9 0.6 ------2.5%0.20% borax--0.70% Na mercaptobenzothiazole so 3 O 0.3 0 0.4 Wats,ibitor). only (no ethylene glycol, no in- Marig,ae O. (450 P. P. M. sul- 30 45 0.5 0.5 Water only (no ethylene glycol, no in- Galveston, Tex (300 P. P. M. 58 32 --1 --1 19 hibitor). chloride) ganic inhibitor. The inhibitors may be intro Table III.-Comparison of rusting tendency and duced into a previously used antifreeze mixture, foaming tendency of antifreeee compositions thus providing a reinhibiting effect, if desired. (33% by: volunie of ethylene glycol in water) The pH of the antifreeze Solution of this inven in circulating 2.72its assing automobile radiators tion is usually within the range of 8.5 to 9.5, as and engine blocks measured on a water Solution containing about 33% of the alcohol (plus inhibitor). In more dilute ethylene glycol solution, containing about Tinbefore dy"vageFoaming Ten 10% of the glycol, the pit is Sonewhat higher, Inhibitor- (weight.v. percent raised Rust, Volune Liquid viz. about 10. In general, the pH is within the on weight of ethylene glycol) if PE Carried over in range of 8.5 to 10. Aqueous solutions containing hours' Foamduring (c. test c.). about 10 to 60% of the freezing point depressant . generally have a sufficiently low melting point. 2.2%bora,X----...---- 520. 1,000 6.3% NaBO22H2O 1,120 800 Among the metals which are protected by the 2.5% borax--0.70% sodium phos herein... disclosed antifreeze Solutions are alumi phate-1-0.2% Na mercaptoben num, iron, Steel, copper, brass, solder, and the zothiazole------1,530 1,900 like. The most outstanding improvement in anti It is believed to be apparent from the data set Corrosive properties is noted when the water forth in the above tables that, in several respects, which is used as the diluent for the alcohol con the phosphate-free metaborate-containing anti tains SubStantial quantities of chloride. il’eeze is superior to the other antifreeze composi The following tables provide a comparison of tions, which heretofoie were considered to be the 2ntifreeze composition of this invention with a long the best of the heretofore known antifreeze previously disclosed antifreeze compositions con inixtures. taining sodium tetraborate or tetraborate-phos The term “antifreeze composition' as employed phate inhibitoi's. In the figures given in the in the Specification and claims includes the di tables a plus sign indicates that an increase in luted antifreeze in the form in which it is cir the thickness of the metal test strip as measured culated in the eiagiine, and also the undiluted, or 2,584,030 5 6 partially diluted, form, which is suitable for pack of Sodium metaborate and a quantity of mercap aging and shipping in accordance with the prac tobenzothiazole compound of the class consisting tice common in the trade. When the antifreeze of mercaptobenzothiazole and the alkali metal composition of this invention is shipped in cans salts thereof within the range of 0.0001 to 0.5% of (e. g. cans made of terneplate) there is no cor 5 the weight of the ethylene glycol, there being rosion of the metal container; even on prolonged present no other corrosion inhibitor, said com storage the composition, as shipped, generally position being characterized in that it has a pH contains not more than about 10% by weight of within the range of 8.5 to 9.5 when diluted with water. water until the ethylene glycol content is 33%. Since numerous modifications of the invention 0. EDWIN, H. KELER Will occur to those who are skilled in the art, it is to be understood that I do not limit myself except as set forth in the following claims. REFERENCES CITED I claim: The following references are of record in the 1. An antifreeze composition free of phosphate 15 file of this patent: and nitrite and containing from 10% to 60% by UNITED STATES PATENTS volume of ethylene glycol and from 0.5 to 7.5% by Weight of alkali metal metaborate corrosion in Number Name Date hibitor, based on the weight of the glycol, the 1964,808 Bottoms ------July 3, 1934 remainder of the composition being substantially 20 2,386,182 Balcar ------Oct. 9, 1945 all Water, said antifreeze composition being suit OTHER REFERENCES able for use in an internal combustion engine cooling System. Mellor's "Modern Inorganic Chemistry,' revised 2. An ethylene glycol anti-corrosive antifreeze edition (1939). Longmans, Green and Co., N.Y., composition containing from 0.5 to 7.5% by weight p. 662.