Compositions – Preservative agents – Anti-corrosion
Reexamination Certificate
1999-10-13
2002-06-04
Gupta, Yogendra N. (Department: 1751)
Compositions
Preservative agents
Anti-corrosion
C252S389100, C252S396000, C252S076000, C252S079000, C422S007000
Reexamination Certificate
active
06398984
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to compositions which assist in the corrosion protection of magnesium, magnesium-aluminum, aluminum-magnesium and aluminum alloys in engine coolants and heat-exchange fluids. Aliphatic mono- or di-basic acids or aromatic carboxylate acids, or the alkali metal, ammonium or amine salts thereof, have been found to provide corrosion protection to magnesium, in addition to the protection that these acids already provide to other metals, such as aluminum, iron, copper and solder, when combined with a fluoride or a fluorocarboxylic acid or a salt thereof. Specific combinations of such acids or salts with fluoro compounds have been found to provide synergistic corrosion protection for magnesium. The optional addition of a hydrocarbyl triazole and/or a thiazole to these combinations provides improved corrosion protection, particularly to copper alloys but also to other metals such as aluminum. The presence of the fluoride and/or a fluorocarboxylate has been found to significantly improve the high temperature magnesium corrosion protection properties for individual carboxylates, for combinations of carboxylates, and for combinations of carboxylates and hydrocarbyl triazoles and/or thiazoles.
Automobile engine cooling systems contain a variety of metals, including copper, solder, brass, steel, cast iron, aluminum, magnesium, and their alloys. The possibility of corrosive attack on such metals is high, due to the presence of various ions as well as the high temperatures, pressures, and flow rates found in such cooling systems. The presence of corrosion products within the cooling system can interfere with heat transfer from the engine combustion chambers, which may subsequently cause engine overheating and engine component failure due to excess metal temperatures. See generally Fay, “Antifreezes and Deicing Fluids,”
Kirk
-
Othmer Encyclopaedia of Chemical Technology
(1978) ed, vol 3, pp 79-95. It would therefore be generally advantageous if the formation of corrosion products within automobile cooling systems could be controlled or eliminated. It is one object of the instant invention to provide a corrosion inhibitor useful in the prevention and control of corrosion in automobile engine cooling systems containing various metals, particularly magnesium.
The trend towards improved fuel economy for automobiles has led to the increased use of lightweight materials such as aluminum and magnesium alloys for engine and cooling system components. However, it has been found that pitting and crevice corrosion are particularly prevalent in aluminum and magnesium-containing cooling systems. Pitting of thin-walled automobile radiator tubes may lead to tube perforation. Crevice corrosion at cylinder head packings or coolant hose connections may also occur. Both types of corrosion may lead to eventual coolant loss, with subsequent engine overheating and component failure. Other forms of localized corrosion such as deposit attack from deposition of corrosion products may also result.
Many conventional corrosion inhibitor additives used in automobile cooling systems do not provide adequate protection against the pitting, crevice, and deposit attack corrosion phenomena found with magnesium, aluminum and various other metal alloys. It would therefore be particularly advantageous if such localized corrosion phenomena could be controlled or eliminated. It is another object of the instant invention to provide a corrosion inhibitor for use in automobile cooling systems, which prevents or controls localized corrosion of magnesium.
All corrosion inhibitors employed in automobile antifreeze/coolant formulations are gradually depleted by use and the build-up of corrosion products in the cooling system. It would thus be advantageous if the build-up of corrosion products within the system and subsequent corrosion inhibitor depletion or degradation could be controlled or eliminated. It is a further object of the instant invention to provide a corrosion inhibitor which is less prone to depletion or degradation than traditional corrosion Inhibitors used in antifreeze/coolant formulations.
2. Description of Related Information
Organic Acid Technology (OAT) coolants and heat exchange fluids have been introduced, providing improved corrosion protection and having a long life. OAT corrosion-inhibitor packages in aqueous and glycol concentrates are used in automotive, heavy duty, marine and industrial applications. OAT corrosion-inhibitors are also used in secondary cooling systems and in a variety of industrial heat exchange fluids. Several U.S. and foreign patent references disclose the use of carboxylic acids, or the salts of such acids as corrosion inhibitors in antifreeze/coolant and heat-exchange fluid compositions. These compositions are optimized for the protection of aluminum and other materials currently used in the above applications.
Various corrosion inhibitors have been added to heat transfer fluids to reduce corrosion of metallic systems. For example, U.S. Pat. No. 4,587,028 (Darden) discloses non-silicate antifreeze formulations containing alkali metal salts of benzoic acid, dicarboxylic acid and nitrate. Additional ingredients including alkali metal hydroxides, alkali metal nitrates and aromatic triazoles, such as tolyltriazole or benzotriazole are preferably provided. U.S. Pat. No. 4,647,392 (Darden et al) discloses corrosion inhibitors using aliphatic monobasic acids or salts, hydrocarbyl dibasic acids or salts and hydrocarbonyl triazole. U.S. Pat. No. 4,657,689 (Darden) discloses corrosion inhibitors containing aliphatic monobasic acids or salts, hydrocarbyl dibasic acids or salts, hydrocarbyl azoles and specific hydrocarbyl alkali metal sulfonates. U.S. Pat. No. 5,085,791 (Burns) discloses antifreeze compositions containing cyclohexane acid corrosion inhibitor alone or in combination with other corrosion inhibitors, particularly sebacic acid and tolyltriazole. The cyclohexane acid includes cyclohexyl carboxylic (formic) acid, cyclohexyl acetic acid and cyclohexyl propionic acid. The cyclohexane acid is targeted to inhibit lead solder and/or aluminum corrosion. U.S. Pat. No. 4,105,405 (Wehle et al) discloses the use of cyclohexane hexacarboxylic acid corrosion inhibitors.
JP-A-08 020763 (Seiken Kogaku Kogyo KK) describes a fluid for use as a coolant in internal combustion engines comprising glycol, water, a magnesium compound, an alkyl benzoic acid (e.g. p-tert-butylbenzoic acid) or a salt, a do-decane diacid or a salt and a triazole or thiazole.
JP-A-08 085782 (Nippon Chem Kogyo KK) describes a glycol based antifreeze composition containing a dodecanedioic acid or a salt, p-tert-butylbenzoic acid or a salt and a triazole, together with a silicate, molybdate, benzoate or thiazole. The composition is free from amines, phosphates, borates and nitrites.
Engine manufacturers are now evaluating the use of magnesium as a material for engine and heat-transfer systems. Traditional inhibitor packages do not give adequate corrosion protection to magnesium components. In general, currently used OAT coolants are only mildly aggressive, but the protection levels for magnesium are not sufficient, particularly at the high temperatures found in working engines. Previous research has indicated that a combination of an alkylbenzoic acid (4-tert-butylbenzoic acid), an aliphatic monoacid (octanoic acid) and a hydrocarbyl triazole (tolyltriazole), provides improved corrosion protection for magnesium, in comparison with traditional and OAT coolant formulations (Table I in U.S. Pat. No. 4,851,145 (van Neste)). EP-A-0229254 (Asahi Glass Co Ltd) describes an electrolytic capacitor comprising a capacitor element and an electrolyte impregnated into the element, wherein the electrolyte contains a fluorocarboxylic acid or salt dissolved in an organic solvent.
There is need for a coolant system which provides high levels of corrosion protection to magnesium components.
SUMMARY OF THE INVENTION
The present invention relates to an antifreeze concentrat
Lievens Serge Stefan
Maes Jean-Pierre Leopold
Gupta Yogendra N.
Hamlin Derrick G.
Howrey Simon Arnold & White
Reinisch Morris N.
Texaco Inc.
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