FR2733511A1 - New anti-freeze compsns. and corrosion inhibition systems - Google Patents

Abstract

A new anti-freeze compsn. comprises a water-sol. liq. alcohol to lower the freezing pt. combined with a corrosion protection system. The latter is made up of: (a) at least one carboxylic acid or an alkali metal, ammonium or amine salt of the acid; (b) at least one 1,3-diazole chosen from imidazole, benzimidazole, imidazoline or their hydrocarbon derivs.; (c) at least one imide.

Description

 The present invention relates to a novel water-soluble antifreeze composition containing corrosion inhibiting additives, an aqueous heat transfer fluid containing the antifreeze composition, and a method of treating an aqueous heat transfer fluid in order to reduce corrosion of metals in contact with said fluid.

 It is known to use aqueous heat transfer fluids in heat exchangers such as central heating or cooling circuits of an internal combustion engine. Generally, the heat transfer fluid comes into contact with various metals or alloys constituting the different parts of these circuits, such as, for example, copper, brass, steel, cast iron, magnesium, aluminum and alloys tin and lead forming the solders. Corrosion problems thus become particularly difficult and complex, not only because of the need to protect each of the metals or alloys individually against corrosion, but also because of galvanic phenomena which may appear between the different metals or alloys present.

 In the case of certain heat exchanger circuits such as those for cooling internal combustion engines, in particular those operating on motor vehicles, the corrosion protection problems involve in particular aqueous heat transfer fluids containing compositions antifreeze. The antifreeze compositions essentially comprise a water-soluble organic compound lowering the freezing point of the heat transfer fluid, in particular a liquid alcohol such as a glycol, for example monoethylene glycol or monopropylene glycol. To these compositions, corrosion inhibitors are generally added in small proportion.

The antifreeze compositions thus obtained are then used in admixture with water to prepare the ready-to-use aqueous heat transfer fluid. The weight ratio of the amount of the antifreeze composition to that of water is determined by the desired freezing point of the fluid.

 Internal combustion engines, in particular those operating on motor vehicles, today comprise large parts of light metal, such as aluminum or its alloys, in order to lighten the weight of motor vehicles, and consequently to reduce the fuel consumption of vehicles.

 EP-AO 564 721 describes an antifreeze composition essentially based on glycol and on a corrosion inhibitor system comprising an aliphatic monocarboxylic acid from C5 to C16 or the salt of an alkali metal, ammonium or an amine of said acid, a triazole from a hydrocarbon group and an imidazole. It has been observed that when the antifreeze composition is used in cooling circuits of an internal combustion engine comprising significant parts of light metal such as aluminum or one of its alloys, the anticorrosive protection of this metal or of its alloys is not sufficiently assured, in particular over a long period.

 A new antifreeze composition has now been found which makes it possible to solve the above problems and in particular to improve the anticorrosive properties with respect to metals, in particular aluminum and its alloys, in a remarkable manner. compared to the old known compositions.

 The present invention therefore relates to an antifreeze composition comprising a liquid alcohol, soluble in water and lowering the freezing point and a corrosion inhibiting system, characterized in that the corrosion inhibiting system comprises (a) at least a carboxylic acid or the salt of an alkali metal, of ammonium or of amine of said acid, (b) at least one diazole-1, 3 chosen from imidazole, benzimidazole, imidazoline and their hydrocarbon derivatives, and (c) at least one imide.

 The corrosion inhibitor system of the present antifreeze composition preferably comprises the combination (a) of at least one carboxylic acid or at least one of the salts of an alkali metal, ammonium or a amine of said acid, (b) at least one 1,3-diazole chosen from limidazole, benzimidazole, limidazoline or their N- and / or C- substituted alkyl, aryl or aralkyl derivatives and (c) at least one cyclic or acyclic imide .

The corrosion inhibitor system can be used as
corrosion inhibitor in an aqueous heat transfer fluid, in particular in antifreeze compositions for cooling circuits
of an internal combustion engine, in particular of a motor vehicle comprising
large parts of a light metal, in particular aluminum or
one of its alloys. The present antifreeze composition is particularly suitable when used in circuits for
cooling of which at least 5%, preferably at least 10%, for example
10 to 60k of the internal surfaces are made of aluminum or one of its alloys, and therefore are in direct contact with said composition.
combination of corrosion inhibitors of the present antifreeze composition has a remarkable effect on the anticorrosive protection of aluminum and its alloys, while maintaining a high level of protection against other metals usually present in the motor vehicle engine cooling systems, such as copper, magnesium, steel, cast iron, brass or solder. The remarkable properties observed result from a synergistic effect between the main constituents of the combination of the corrosion inhibitor system of the present invention.

 More particularly, the antifreeze composition may contain from 0.1 to 10, preferably from 0.5 to 7%, in particular from 1 to 5 k by weight of one or more carboxylic acids or their corresponding salts mentioned above.

The carboxylic acid (s) can be chosen from monocarboxylic, aliphatic, alicyclic or aromatic acids, of
C5 to C10, in particular n-pentanoic acid, n-hexanoic acid, n-heptanoic acid, 2-ethyl hexanoic acid, n-octanoic acid, isoheptanoic acid, acid benzoic, ortho, meta and para ethyl benzoic acids or cinnamic acid. They can also be chosen from aromatic or aliphatic dicarboxylic acids (saturated or unsaturated carbon chain from C4 to C12, in particular succinic acid, adipic acid, sebacic acid, itaconic acid, azelaic acid, ortho-, meta- or para-phthalic acid, 2-methylene azelaic acid or muconic acid. It is preferred to use at least one acid from acids (A) and (B) mono- and di -aliphatic or alicyclic carboxyls.

 It is preferably possible to use a mixture of at least two of these acids or of the corresponding salts mentioned above, in particular at least two acids (A), or at least two acids (B), or even at least one acid (A) and at least one acid (B) which can preferably be used - in amounts such that the molar ratio between the acid (s) (B) or their corresponding salts and the acid (s) (A) or their corresponding salts is 0 , 1: 1 to 10: 1, preferably from 0.5: 1 to 5: 1, especially from 1: 1 to 4: 1. It is preferred to use at least two acids from among the aliphatic or alicyclic mono- and dicarboxylic acids (A) and (B).

 The antifreeze composition may also contain from 0.01 to 2, preferably from 0.05 to 1 k by weight of at least one diazole-1,3 mentioned above.

dans laquelle R1, R2 et R3 étant identiques ou différents représentent un atome d'hydrogène, ou un radical alcoyle, linéaire ou branché, notamment de C1 à C6, de préférence de C1 à C4 tel que le radical méthyle ou éthyle, ou un radical aryle notamment de C6 à C12, de préférence de C6 à
C10 tel que le radical phényle ou naphtyle, ou un radical aralcoyle notamment de C7 à C14, de préférence de C7 à C11 tel que le radical benzyle, et R4 représente un atome d'hydrogène de préférence, ou un radical hydrocarboné par exemple un radical alcoyle, aryle ou aralcoyle notamment de C1 à C14, tel que les radicaux méthyle, éthyle, phényle ou
benzyle et pouvant comporter notamment au moins une fonction amine, de
préférence tertiaire, et éventuellement au moins une fonction alcool, - le benzimidazole ou les dérivés alcoyle, aryle ou aralcoyle N- et/ou C
substitués du benzimidazole correspondant notamment à la formule

dans laquelle R3 et R4 ont les mêmes définitions que précédemment, R3 représentant par ailleurs le radical -SH, et R5, R6, R7, R8 étant identiques ou différents représentent un atome d'hydrogène ou un radical alcoyle, linéaire ou branché, notamment de C1 à C6, de préférence de C1 à C4 tel que le radical méthyle ou éthyle, et l'imidazoline ou les dérivés alcoyle, aryle ou aralcoyle N- et/ou Csubstitués de l'imidazoline correspondant notamment à la formule

More particularly, the 1,3-diazole can be chosen from - imidazole or the alkyl, aryl or aralkyl derivatives N- and / or C
substituted with the imidazole corresponding in particular to the formula

in which R1, R2 and R3 being identical or different represent a hydrogen atom, or an alkyl radical, linear or branched, in particular from C1 to C6, preferably from C1 to C4 such as the methyl or ethyl radical, or a radical aryl especially from C6 to C12, preferably from C6 to
C10 such as the phenyl or naphthyl radical, or an aralkyl radical in particular from C7 to C14, preferably from C7 to C11 such as the benzyl radical, and R4 preferably represents a hydrogen atom, or a hydrocarbon radical, for example a radical alkyl, aryl or aralkyl, in particular from C1 to C14, such as methyl, ethyl, phenyl or
benzyl and which may especially comprise at least one amine function,
preferably tertiary, and optionally at least one alcohol function, - benzimidazole or the alkyl, aryl or aralkyl derivatives N- and / or C
substituted benzimidazole corresponding in particular to the formula

in which R3 and R4 have the same definitions as above, R3 moreover representing the radical -SH, and R5, R6, R7, R8 being identical or different represent a hydrogen atom or an alkyl radical, linear or branched, in particular of C1 to C6, preferably from C1 to C4 such as the methyl or ethyl radical, and imidazoline or the N- and / or C-substituted alkyl, aryl or aralkyl derivatives of imidazoline corresponding in particular to the formula

in which R1, R2, R3 and R4 have the same definitions as above
dememnt, and R9 and R10 being identical or different have the same
definitions than those of R1 and R2. We prefer to use benzimi
dazole.

 The antifreeze composition can also contain from 0.01 to 2 X, preferably from 0.05 to 1 k by weight of at least one imide.

dans lesquelles R11 et R12 étant identiques ou différents représentent un radical alcoyle notamment de C1 à C11, de préférence de C1 à C5, tel que le radical méthyle ou éthyle, ou un radical aryle notamment de C6 à C14, de préférence de C6 à C12, tel que le radical phényle ou naphtyle, ou un radical aralcoyle notamment de C7 à C15, de préférence de C7 à C11, tel que le radical benzyle, R13 'représente un atome d'hydrogène, ou un radical alcoyle notamment de C1 à C6, de préférence de C1 à C4, tel que le radical méthyle ou éthyle, ou un radical aryle notamment de C6 à C14, de préférence de C6 à C12, tel que le radical phényle ou naphtyle, ou un radical aralcoyle notamment de C7 à C15, de préférence de C7 à C11 tel que le radical benzyle, et R14 représente un radical bivalent hydrocarboné en particulier un radical alcoylène, linéaire ou branché notamment de C2 à C8, de préférence de C2 à C4, tel que le radical éthylène de formule ( CH2-CH2 ) , ou un radical aryle bivalent notamment de C6 à C14, de préférence de C6 à C12, tel qu'un radical phénylène, par exemple le radical ortho-phénylène de formule:

ou un radical naphtylène, par exemple les radicaux naphtylène-1,2 ou -2,3 ou -3,4, ou un radical aralcoylène notamment de C8 à C16, de préférence de C8 à C12 tel que le radical de formule

More particularly the imide can be chosen from cyclic or acyclic imides corresponding in particular to the formulas

in which R11 and R12 being identical or different represent an alkyl radical in particular from C1 to C11, preferably from C1 to C5, such as the methyl or ethyl radical, or an aryl radical in particular from C6 to C14, preferably from C6 to C12 , such as the phenyl or naphthyl radical, or an aralkyl radical in particular from C7 to C15, preferably from C7 to C11, such as the benzyl radical, R13 ′ represents a hydrogen atom, or an alkyl radical in particular from C1 to C6 , preferably from C1 to C4, such as the methyl or ethyl radical, or an aryl radical in particular from C6 to C14, preferably from C6 to C12, such as the phenyl or naphthyl radical, or an aralkyl radical in particular from C7 to C15 , preferably from C7 to C11 such as the benzyl radical, and R14 represents a bivalent hydrocarbon radical, in particular an alkylene radical, linear or branched in particular from C2 to C8, preferably from C2 to C4, such as the ethylene radical of formula ( CH2-CH2), or a bivalent aryl radical, in particular from C6 to C14, preferably from C6 to C12, such as a phenylene radical, for example the ortho-phenylene radical of formula:

or a naphthylene radical, for example the 1,2-naphthylene radicals or -2,3 or -3,4, or an aralkylene radical in particular from C8 to C16, preferably from C8 to C12 such as the radical of formula

formules dans lesquelles R15 représente un radical alcoyle notamment de C1 à
C6, de préférence de C1 à C4 tel que le radical méthyle ou éthyle, ou un radical aryle notamment de C6 à C14, de préférence de C6 à C12 tel que le radical phényle ou naphtyle, ou un radical aralcoyle notamment de C7 à C15, de préférence de C7 à C11 tel que le radical benzyle, R16, R17 et R18 étant identiques ou différents représentent un atome d'hydrogène ou un radical alcoyle de C1 à C6, de préférence de C1 à C4 tel que le radical méthyle en éthyle, R19 représente un radical alcoyle notamment de C1 w C4, de préférence le radical méthyle ou éthyle, et R20, R21 et R22 étant identiques ou différents représentent un atome d'hydrogène ou un radical alcoyle notamment le radical méthyle ou éthyle. Parmi les imides, ou peut notamment utiliser l'acétylimide de formule

It is preferred to use an imide of formula (IV) or (V) in which R13 represents a hydrogen atom. More particularly, it is preferred to use a cyclic imide from the group consisting of succinimide, phthalimide, substituted hydrocarbon derivatives of succinimide and the substituted hydrocarbon derivatives of phthalimide corresponding respectively to the formulas

formulas in which R15 represents an alkyl radical, in particular from C1 to
C6, preferably from C1 to C4 such as the methyl or ethyl radical, or an aryl radical in particular from C6 to C14, preferably from C6 to C12 such as the phenyl or naphthyl radical, or an aralkyl radical in particular from C7 to C15, preferably from C7 to C11 such that the benzyl radical, R16, R17 and R18 being identical or different represent a hydrogen atom or an alkyl radical from C1 to C6, preferably from C1 to C4 such as the methyl to ethyl radical, R19 represents an alkyl radical in particular of C1 w C4, preferably the methyl or ethyl radical, and R20, R21 and R22 being identical or different represent a hydrogen atom or an alkyl radical in particular the methyl or ethyl radical. Among the imides, or may in particular use the acetylimide of formula

It is preferred to use succinimide or phthalimide.

 The weight percentages given above are based on the antifreeze composition, it being understood that the composition may also contain other additives.

 Thus a molybdate of an alkali metal such as sodium or potassium, or of ammonium can be advantageously used in the antifreeze composition and be associated with the combination of the corrosion inhibitor system of the present invention. The composition may in particular comprise from 0.01 to 1.5%, preferably from 0.05 to 0.5% by weight of such a molybdate, percentages expressed on the basis of the antifreeze composition.

 A polyol, in particular from C5 to C12 and which may contain from 5 to 12 alcohol functions having no reducing power, can also be advantageously used in the composition and thus be associated with the combination of the corrosion inhibitor system of the present invention. It is preferred to use sorbitol, xylitol, mannitol or sucrose. However, sorbitol is preferred. The composition may in particular comprise from 0.05 to 2.5%, preferably from 0.1 to 1.5 k by weight of polyol, percentages expressed on the basis of the antifreeze composition.

dans laquelle R23 représente un atome d'hydrogène ou un radical alcoyle, notamment de C1 à C4, tel que le radical méthyle ou éthyle, n = 1 à 6, de préférence n = 1 à 4, en particulier n = 1, et m = 1 à 4, en particulier m = 1 ou 2 ; on préfère le tolyltriazole ou un dérivé N-substitué du benzotriazole ou du tolyltriazole tel que celui vendu par CIBA sous la référence IRGAMET 42 ; le composé de triazole peut être utilisé
en une proportion allant de 0,02 à 0,6 % en poids par rapport à la
composition d'antigel, - un composé de thiazole, de benzothiazole ou de mercaptobenzothiazole ou
leurs sels d'un métal alcalin tel que le sodium ou le potassium,
notamment en une proportion allant de 0,01 à 015 % en poids par rapport à
la composition d'antigel, - au moins une base minérale telle que la soude ou la potasse, destinée à
neutraliser les acides et autres composés présents et à former les sels
correspondants, - des agents antimousse et antidépôt, des agents stabilisants, antitartre
et séquestrants des métaux alcalino-terreux et d'autres ions métalliques
bivalents, tels qu'un sel d'un acide poly(adéhydocarboxylique), et
notamment des agents stabilisants tels que des silanes notamment
fonctionnalisés.Other additives can also be used in the composition and thus be combined with the combination of the corrosion inhibitor system of the invention - a silicate of an alkali metal, such as sodium metasilicate,
in particular in a proportion of 0.01 to 0.3 k by weight relative to the
antifreeze composition, a borate of an alkali metal such as sodium tetraborate or
potassium, in particular in a proportion of 0.5 to 5% by weight relative to
to the antifreeze composition, a nitrate of an alkali or alkaline earth metal, such as nitrate of
sodium or magnesium, in particular in a proportion of 0.01 to 0.5 t in
weight relative to the antifreeze composition, - an alkali metal or amine phosphate, in particular in a proportion
from 0.5 to 5 k by weight relative to the antifreeze composition, - a triazole compound, in particular a C-substituted derivative and / or N
substituted for triazole, preferably an aromatic triazole such as
benzotriazole or tolyltriazole, preferably N-substituted by a
hydrocarbon radical which can in particular comprise at least one function
amine, in particular a tertiary amine function, and preferably at
at least one alcohol function, for example two alcohol functions, and which can
match the formula

in which R23 represents a hydrogen atom or an alkyl radical, in particular from C1 to C4, such as the methyl or ethyl radical, n = 1 to 6, preferably n = 1 to 4, in particular n = 1, and m = 1 to 4, in particular m = 1 or 2; tolyltriazole or an N-substituted derivative of benzotriazole or tolyltriazole such as that sold by CIBA under the reference IRGAMET 42 are preferred; the triazole compound can be used
in a proportion ranging from 0.02 to 0.6% by weight relative to the
antifreeze composition, - a compound of thiazole, benzothiazole or mercaptobenzothiazole or
their alkali metal salts such as sodium or potassium,
in particular in a proportion ranging from 0.01 to 015% by weight relative to
the antifreeze composition, - at least one mineral base such as soda or potash, intended for
neutralize the acids and other compounds present and form the salts
correspondents, - anti-foaming and anti-deposit agents, stabilizing agents, anti-scale
and sequestrants of alkaline earth metals and other metal ions
bivalent, such as a salt of a poly (adehydocarboxylic acid), and
in particular stabilizers such as silanes in particular
functionalized.

 The antifreeze composition contains as essential or majority component by weight a liquid alcohol soluble in water, making it possible to lower the freezing point. Liquid alcohol is usually a glycol or glycol ether. The glycol or glycol ether which can be used includes a glycol such as monoethylene glycol, diethylene glycol, monopropylene glycol or dipropylene glycol, or a glycol ether such as methyl, ethyl, propyl or butyl monoethylene glycol, diethylene glycol, monopropylene glycol or dipropylene glycol. Monoethylene glycol is particularly preferred.

 The present invention thus relates to an aqueous heat transfer fluid having a lower freezing point, comprising water and from 10 to 90%, preferably from 25 to 65% by weight of the antifreeze composition described above and comprising in particular the combination of the corrosion inhibitor system, the percentages by weight being based on the aqueous heat transfer fluid.

The present invention also relates to a process for treating an aqueous fluid, in particular heat transfer, containing a liquid alcohol soluble in water and lowering the freezing point, in order to reduce the corrosion of metals in contact with the fluid, by addition of a corrosion inhibitor system, characterized in that the corrosion inhibitor system comprises
(a) at least one carboxylic acid or a salt of an alkali metal,
ammonium or amine of said acid,
(b) at least one 1,3-diazole chosen from imidazole, the
benzimidazole imidazoline and their hydrocarbon derivatives,
and
(c) at least one imide
The corrosion inhibitor system used in the treatment of an aqueous fluid can moreover advantageously comprise other additives such as those mentioned above.

 The present invention is illustrated by the following examples.

Examples 1 and 2
According to the invention, various antifreeze compositions indicated in Table 1 are prepared.

 For each antifreeze composition, one or more aqueous fluids are prepared with which various measurements or different tests are carried out. Thus, the pH measured is measured according to the ASTM-D-1287/85 method for an aqueous fluid containing by volume 33% of antifreeze composition. The alkalinity reserve is also measured according to the ASTM-D-1121/88 method, as well as the corrosion rate of the aluminum according to the ASTM-D-4340/89 method.

An antifreeze composition NO 1 (example 1) is thus prepared based on monoethylene glycol which contains by weight
% Weight - monoethylene glycol 91.09 - water 1.50 - sebacic acid 2.60 - itaconic acid 2.00 - benzimidazole 0.05 - succinimide 0.10 - silane "GF 20" (2) (1) 0.05 - sodium nitrate 0.13 - "IRGAMET 42" {) (2) 0.18 - magnesium nitrate 0.04 - sodium hydroxide 2.26
(1) sold by WACKER (2) sold by CIBA and corresponding to the formula (XIII) in which R23
represents a methyl radical and n = 1.

The following measurements are carried out on this composition pH (according to ASTM D-1287/85) = 8.10
Alkalinity reserve (according to ASTM D-1121/88) = 12.6 ml 0.1 N HCl
Corrosion rate (according to ASTM D-4340/89) = 0.15 mg / cm1 / week
An antifreeze composition No. 2 (example 2) is also prepared based on monoethylene glycol which contains by weight
% Weight - monoethylene glycol 91.995 - water 1.70 - sebacic acid 2.00 - n-heptanoic acid 1 1.00 - sodium molybdate dihydrate 0.10 - sodium tetraborate decahydrate 1.20 - succinimide 0.05 - benzimidazole 0 , 08 - sodium metasilicate pentahydrate 0.17 - silane "GF 20") (1) 0.055 - "POC HS 2020" g) (2) 0.20 - soda 1.08 - sodium nitrate 0.20 - "IRGAMET 42 "# (3) 0.17
(1) sold by WACKER
(2) sold by DEGUSSA
(3) sold by CIBA and corresponding to formula (XIII) in which R23
represents a methyl radical and n = 1.

On this composition, the following measurements and tests are carried out pH (according to ASTM D-1287/85) = 7.80
Alkalinity reserve (according to ASTM D-1121/88) = 12.6 ml 0.1 N HCl
Corrosion rate (according to ASTM D-4340/89) = 0.00 mg / cm / week

Claims (14)

 (c) at least one imide.  and  benzimidazole, limidazoline and their hydrocarbon derivatives,  (b) at least one 1,3-diazole chosen from imidazole, the  ammonium or amine of said acid,  (a) at least one carboxylic acid or a salt of an alkali metal, CLAIMS 1. Antifreeze composition comprising a liquid alcohol soluble in water and lowering the freezing point, and a corrosion inhibiting system, characterized in that the corrosion inhibiting system comprises 2. antifreeze composition according to claim 1, characterized in that it comprises  (a) from 0.1 to 10% by weight of the carboxylic acid (s) or  or corresponding salts,  (b) from 0.01 to 2 a by weight of the 1,3-diazole (s), and  (c) from 0.01 to 2 a by weight of the imide (s) 3. antifreeze composition according to claim 1 or 2, characterized in that the carboxylic acid or acids are chosen from monocarboxylic, aliphatic, alicyclic or aromatic acids, from C5 to C10, and dicarboxylic acids (B) , aromatic or aliphatic with a saturated or unsaturated carbon chain from C4 to C12 4.An antifreeze composition according to claim 3, characterized in that at least two carboxylic acids are chosen from at least two acids (A), or at least two acids (s) or at least one acid (A) and at least an acid (B). 5. antifreeze composition according to any one of claims 1 to 4, characterized in that the 1,3-diazole is chosen from - imidazole or the alkyl, aryl or aralkyl derivatives N- and / or C  substituted with imidazole, - benzimidazole or the alkyl, aryl or aralkyl derivatives N- and / or C  substituted with benzimidazole, and - imidazoline or the alkyl, aryl or aralkyl derivatives N- and / or C  substituted with imidazoline. 6. antifreeze composition according to any one of claims 1 to 5, characterized in that the 1,3-diazole is benzimidazole. 7. antifreeze composition according to any one of claims 1 to 6, characterized in that the imide is a cyclic or acyclic imide corresponding to the formulas

 in which R11 and R12 being identical or different represent an alkyl, aryl or aralkyl radical, R13 represents a hydrogen atom or an alkyl, aryl or aralkyl radical, and R14 represents a bivalent hydrocarbon radical. 8. antifreeze composition according to claim 7, characterized in that the imide is chosen from succinimide, phthalimide and substituted hydrocarbon derivatives of succinimide and phthalimide. 9. antifreeze composition according to claim 7, characterized in that the imide is succinimide or phthalimide. 10. antifreeze composition according to any one of claims 1 to 9, characterized in that the corrosion inhibitor system further comprises a molybdate of an alkali metal or ammonium. 11. An antifreeze composition according to any one of claims 1 to 10, characterized in that the corrosion inhibitor system further comprises a silicate of an alkali metal. 12. An antifreeze composition according to any of claims 1 to 11, characterized in that the corrosion inhibitor system further comprises a silane. 13. An aqueous heat transfer fluid having a lower freezing point, comprising water and from 10 to 90 k by weight of the antifreeze composition according to any one of claims 1 to 12. 14. Process for the treatment of an aqueous fluid containing a liquid alcohol, soluble in water and lowering the freezing point, to reduce the corrosion of metals in contact with the fluid by adding a corrosion inhibiting system, characterized in what the corrosion inhibitor system includes  (a) at least one carboxylic acid or a salt of an alkali metal,  ammonium or amine of said acid,  (b) at least one 1,3-diazole chosen from imidazole, the  benzimidazole, imidazoline and their hydrocarbon derivatives,  and  (c) at least one imide.