Compositions – Heat-exchange – low-freezing or pour point – or high boiling... – Organic components
Reexamination Certificate
1999-10-21
2001-05-08
Ogden, Necholus (Department: 1751)
Compositions
Heat-exchange, low-freezing or pour point, or high boiling...
Organic components
C252S073000, C252S075000, C252S079000
Reexamination Certificate
active
06228283
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to aqueous corrosion inhibitors for extending diesel engine coolant lifetime through polymeric polycarboxylate secondary silicate stabilization. More particularly, this invention relates to an antifreeze formulation for inhibition and prevention erosion and corrosion of aluminum and the corrosion of other metals exposed to an aqueous liquid in automotive coolant systems. The formulation further inhibits mineral scale.
The novel antifreeze formulation comprises a mixture of polymeric polycarboxylates, azoles, nitrate and nitrite salts, phosphates, siloxane stabilized silicates and transition metal compounds which provide protection against the cavitation corrosion of aluminum in aqueous liquids reducing the corrosion rate and is effective at relatively low concentrations and varying pH ranges. The addition of selected polymeric polycarboxylates not only significantly reduces glycol based coolant cavitation erosion-corrosion, heat rejecting aluminum corrosion, and hard water precipitates and scale, it has been discovered that selected polymeric polycarboxylates in combination with siloxane stabilized silicates enhance secondary silicate stabilization leading to improvement in aluminum corrosion protection and coolant life when utilized with selected amounts of the above-identified additives. The formulations are particularly suitable for diesel engine applications.
DESCRIPTION OF THE PRIOR ART
Antifreeze/coolant technology traditionally use silicate as a corrosion inhibitor. Silicates are particularly useful in protecting aluminum automotive cooling system components. The silicate corrosion inhibitors generally also use a phosphate, usually in the form of an alkali metal salt, to help protect metal cooling system parts and also as a buffer to control the pH of the coolant. Often phosphate salts are used to help maintain a stable alkaline environment from which multiple corrosion inhibitors can most effectively function.
Traditionally antifreeze/coolant is sold at nearly one-hundred percent glycol content. This concentrated packaging allows for flexibility so that the user can dilute the antifreeze/coolant, as needed, with available water to obtain the required freeze/boil protection. However, corrosion protection is needed over the entire dilution range.
In modern automotive engineering, many engine components are fabricated from aluminum. Engine coolants, primarily ethylene glycol or propylene glycol based solutions, must transfer heat from operating aluminum engines while inhibiting corrosion. Older automotive engines did not have aluminum components and thus, the traditional antifreeze/coolant compositions may produce corrosion in heat rejecting aluminum or aluminum alloy components. The cavitation erosion-corrosion of aluminum water pumps upon exposure to aqueous systems such as water-cooled internal combustion engine coolants is a relatively new development.
U.S. Pat. No. 4,717,495 by Hercamp et al., hereby incorporated by reference, teaches a sodium-free buffer solution. U.S. Pat. No. 4,548,787 discloses the use of a combination water soluble phosphate with tungstae, selenate and molybdate for protection against cavitation erosion-corrosion on aluminum. U.S. Pat. No. 4,404,113 discloses the use of polyhydric alcohols as corrosion inhibiting and cavitation reducing additives for coolants.
Certain polycarboxylate type materials have been disclosed for prevention of precipitates in antifreeze/coolant compositions. for example, U.S. Pat. No. 3,663,448 discloses scale inhibition for industrial cooling waters using amino phosphonate and polyacrylic acid compounds, U.S. Pat. No. 3,948,792 discloses an aqueous additive mixture to reduce and modify the amount of silicate scale formed in automotive cooling systems.
U.S. Pat. No. 4,487,712 discloses the use of polyacrylic acid as a silicate stabilizer to inhibit gelation which is a silicate depletion mechanism which can occur separately from hard water precipitates.
The addition of polymeric polycarboxylates has been shown to significantly reduce glycol based coolant cavitation erosion-corrosion as set forth in U.S. Pat. Nos. 5,288,419 and 5,290,469; to reduce heat rejecting aluminum corrosion as set forth in U.S. Pat. Nos. 5,320,670 and 5,290,467; and to reduce hard water precipitates and scale as set forth in U.S. Pat. Nos. 5,330,670 and 5,290,468.
U.S. Pat. No. 4,440,721, discloses the combination of a water-soluble phosphate with a water soluble molybdate, tungstate, or selenate for providing a protective effect against the cavitation corrosion of aluminum in aqueous liquids. While alkali metal molybdates and the soluble salts of tungstic and selenic acids have been used in antifreeze compositions to prevent the corrosion of metals, particularly cast iron, soluble salts of molybdic, tungstic and selenic acids act to retard the corrosion of aluminum, particularly the cavitation erosion-corrosion of aluminum water pumps.
None of the above references provide a means for obtaining a long life silicate based antifreeze composition as does Applicant's present invention. The combination of a selected polymeric polycarboxylates, azoles, preferably hydrocarbyl azole compounds, nitrate and nitrite salts, molybdates, phosphates, stabilized silicates and transition metal compounds provide protection against the cavitation corrosion of aluminum in aqueous liquids reducing the corrosion rate and is effective at relatively low concentrations and varying pH ranges. The addition of selected polymeric polycarboxylates not only significantly reduces glycol based coolant cavitation erosion-corrosion, heat rejecting aluminum corrosion, and hard water precipitates and scale, it has been discovered that utilization of selected polymeric polycarboxylates in combination with certain additives enhance secondary silicate stabilization leading to improvement in aluminum corrosion protection and coolant life.
Moreover, such a formulation would be designed for modern aluminum engine based passenger car cooling systems. The formulation must be liquid, easily miscible with diluted antifreeze in the cooling system, protect all cooling system metals, have a useful shelf life, not harm automotive finishes or paint and not promote excessive cooling system foam.
SUMMARY OF THE INVENTION
The present invention has met the above-described need by providing an antifreeze/coolant composition using selected polymeric polycarboxylate additives which reduce corrosion over the entire dilution range without creating precipitates. This composition is soluble in water, alcohol, and alcohol/water mixtures, is compatible with other commonly used antifreeze/coolant components, does not corrode or damage automotive cooling systems and is effective at relatively low concentrations. In addition, the present corrosion inhibition formulations are effective in reducing corrosion in the entire range of cooling system metals, including heat rejecting aluminum, aluminum alloys, copper, steel, cast iron, brass, solder and the like.
It his been found that water-soluble salts of an acid elected from the group consisting or molybdic, tungstic and selenic acids or salts thereof, in combination with a water-soluble phosphate and a polymeric polycarboxylate provide a synergistic improvement in the retardation or the cavitation erosion-corrosion of aluminum water pumps and other metal engine components when used in contact with aqueous liquids, particularly aqueous antifreeze compositions containing a water-soluble alcohol freezing point depressant.
It is an object of the present invention to provide corrosion inhibition formulations for antifreeze/coolant compositions with selected polymeric polycarboxylate additives for reducing glycol based coolant cavitation erosion-corrosion.
It is another object of the present invention to provide corrosion inhibition formulations for antifreeze/coolant compositions with selected polymeric polycarboxylate additives for enhancing silicate stability providing an improvement in coolant life.
It is another obje
Lockwood Frances E.
Turcotte David E.
Ashland Inc.
Carrithers David W.
Carrithers Law Office
Ogden Necholus
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