US 3642652 A
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United States US. Cl. 252389 3 Claims ABSTRACT OF THE DISCLOSURE A mixture of boric esters of diethanolarnine having the formula (C H O BN),,, wherein n designates an integer of 1 to 6, used as a water-soluble rust preventing agent in media contacting ferrous metals, at a concentration of 0.8% to 5% by weight of said media.
BACKGROUND OF THE INVENTION This invention relates to novel water-soluble rust preventing agents to be used in aqueous media and polar media, liquids or pastes, contacting ferrous metals. It is also concerned with a method of protecting against rust ferrous metals kept in contact with such media.
Water, aqueous solutions, aqueous emulsions or moisture-containing air contacting ferrous metal promote the formation of rust.
At present are known as water-soluble rust inhibitors, inter alia, amines (Encyclopaedia of Chemical Technology, Raimond E. Kirk and Donald -F. Othmer, Interscience Encyclopaedia Inc., New York, vol. 2, p. 42, vol. 5, pp. 855, 857, Second supplement (1965) p. 260; US. Pat. No. 2,363,332) among which diethanolarnine, and salts of mineral acids and alkaline bases or amines such as phosphates, carbonates, borates, chromates, tungstates, molybdates, silicates, nitrites, these compounds being added for instance to anti-freeze products, to hydraulic fluids such as brake circuit fluids, to paints, etc. [Encyclopaedia of Chemical Technology, cf. supra, vol. 1, p. 851, vol. 2, pp. 42, 683, vol. 9, p. 214, vol. 11, pp. 192, 807, First supplement p. 283, Second supplement (1965) p. 260].
Among all these compounds, the most efficient and economical water-soluble rust preventers now in use are sodium chromate and sodium nitrate. Nitrite is active in aqueous media, at a relatively high concentration of the order of 3 to 4% by weight, and sodium nitrite solutions are objectionable in that they are unstable for example when used in metal grinding operations, and that they are destroyed by microorganisms. Among the other known rust inhibitors, some like sodium borate are stable in solution but all are objectionable because they are less active than sodium nitrite and must therefore be used at still higher concentrations. The use of chromate is strongly limited due to its toxicity and its high oxidizing power, and more particularly to the fact that it is the cause of very serious ulcerations when it contacts the human skin.
US. Pat. 3,227,739 relates to boric esters of dialkylolamines bearing a long chained radical on the nitrogen atom and which are for this reason insoluble in water but soluble in oils and are added as rust inhibitors to lubricating oils. These compounds cannot be used as water-soluble rust inhibitors to be added to aqueous and alcoholic media.
Morpholinopropyne (US. Pat. 3,345,299), an heterocyclic amine, acts as a corrosion inhibitor in aqueous acid solutions suitable for the treatment of metals (cleaning and pickling). Such a corrosion inhibitor prevents an excessive erosion of the metal surface by the acid, but does not prevent the metal from rusting.
atent O ice US. Pat. 2,993,007 recites other heterocyclic amines with a long chained hydrocarbon radical on the nitrogen atom, the fatty acid salts of which are used as corrosion inhibitors in static water and boiler water; these compounds are complex in structure and expensive.
DESCRIPTION OF THE INVENTION The applicant found that adding boric esters of diethanolarnine to aqueous media and polar media in low proportions, of the order of 0.8 to 5% by weight, will prevent ferrous metals from rusting.
The esters considered for this purpose are a mixture of esters having the formula:
The aforesaid ester mixture is prepared by heating together substantially stoichiometric proportions of diethanolarnine and boric acid at a temperature above 120 C. so that a condensation takes place between the boric acid and the hydroxyethyl groups of the diethanolarnine molecules, and preferably up to a temperature of about 120 C. to about 230 C., in order to obtain a rapid condensation reaction.
Preferably, the temperature should not exceed 230 C. to avoid a carbonization of the resulting esters.
The theoretical stoichiometric proportions of the initial ingredients are not critical and it is even advantageous to use an excess of diethanolarnine with respect to the boric acid in order to make up a slight loss of diethanolamine entrained by the water vapour released during the condensation.
The reaction yield is practically with respect to the initial boric acid.
By adhering to the above-described procedure the boric acid will fix itself not on the amine group of the diethanolarnine, but on the alcohol functions thereof.
The above-described method of preparation is the simplest and the most advantageous one, but any other conventional methods of preparing esters may be contemplated, although they are more expensive and frequently require subsequent purifications.
The product thus obtained has the appearance of a highly hygroscopic vitrous mass having a good transparency. It is odourless, soluble in Water, ethyl alcohol, alcohols as a rule, glycols, polyglycols, ethers and ketones, and substantially insoluble in nonpolar solvents.
This product is a very efficient rust inhibitor, its efficiency having been checked by applying the conventional Herber test. In an aqueous solution at a concentration rate of 0.8% to 1% by weight, its anti-rust action is equivalent to that of an aqueous solution containing 3 to 4% by weight of sodium nitrite. The rust inhibitor according to this invention is thus four times more efficient than one of the best presently known rust inhibitors, and its cost price is only twice that of sodium nitrite. It has also been checked that it is much more eflicient than diethanolamine and morpholine, which on the other hand have the disadvantage of an unpleasant smell, whereas the product of the invention is odourless. Morever, the product according to this invention is extremely stable in the solution form and another advantageous feature thereof is that it has antiseptic properties very useful when it is utilized for machining metals.
The rust-inhibiting action of the boric esters contemplated herein is higher than that of diethanolamine borate. This fact is probably due to the molecular structure of boric esters.
Witman W., 'Russel R., and Altieri, V. [Ind. Eng. Chem. 16, 445 (1924)] point out that the rate of corrosion of iron is independent of the pH in the pH range from 4 to 10, and that above pH=10 it decreases in proportion of the hydroxyl ion concentration. As the pH of solutions of boric esters of diethanolamine is about 8.4, the abovementioned effect cannot be accounted for explaining the action exerted by the product of this invention.
A typical example of a procedure for preparing this product is given hereinafter:
EXAMPLE 105 parts by weight of diethanolamine and 62 parts by weight of boric acid, i.e. stoichiometric proportions of these two initial substances, are gradually heated together up to 230 C. About 38 parts by weight of water in the form of steam are released and entrain a small fraction of diethanolamine. The yield of boric esters of diethanolamine has practically the theoretical value in relation to the initial boric acid.
In practice, the rust preventing agent according to this invention is preferably used by preparing concentrated solutions of this product in adequate solvents selected among those mentioned hereinabove. Before actually utilizing the rust preventing agent, the concentrated solution is added to the medium which is to contact ferrous metals by using adequate proportions of said solution, so that the concentration of the boric esters of diethanolamine in said medium lies in the range of 0.8% to by weight.
This invention is also concerned inter alia with the following applications:
(1) The anti-rust protection of water vessels, cooling towers, or water circuits, by incorporating said boric esters of diethanolamine in the liquid.
(2) The anti-rust protection of ferrous parts by impregnating same with an aqueous solution of boric esters of diethanolamine. To increase the wetting power of the solution, alcohols, soaps, or surface-tension products such as polyoxyethylenated octyl or nonyl-phenols may be associated therewith.
(3) The grinding of metals by using an aqueous solution of boric esters of diethanolamine. The following advantages are thus obtained: no foam is produced, the grinding wheels remain constantly clean and the workpieces, after drying, have a pleasant, varnish-like surface appearance and are efliciently protected against rust. As the boric esters of diethanolamine are antiseptic, the solutions are not exposed to destruction by microorganisms during their use.
.(4) The machining of metals, by associating with the boric esters of diethanolamine substances like soaps, lubricating emulsions, polyglycols, extreme-pressure additives, or wetting agents.
(5) The protection of vehicle radiators or cooling circuits containing anti-freeze solutions against rust, by incorporating in the anti-freeze solution a few percent units of boric esters of diethanolamine. Since the boric esters of diethanolamine slightly attack copper alloys, mercaptobenzothiazol is added to said esters to inhibit this attack. A typical anti-freeze solution composition may be as follows:
Parts by wt. Glycol 950 Boric esters of diethanolamine 30 Mercaptobenzothiazol in the form of an alkali metal salt or amine salt 20 (6) Hydraulic fluids for braking systems, or fluids for so-called incombustible hydraulic circuits, which do not comprise petroleum products, are rendered rust-proof by adding to these fluids a few percent units of boric esters of diethanolamine.
(7) For protecting against rust freshly degreased parts it is only necessary to add a few percent units of boric esters of diethanolamine to the degreasing agent utilized.
The applications of boric esters of diethanolamine as rust inhibitors are extremely numerous. The examples given hereinabove are only illustrative and should not be construed as limiting the scope of the invention.
What I claim is:
1. A water-soluble rust preventing agent for aqueous media and polar media which are to be put in contact with ferrous metals, consisting esesntially of a mixture of boric esters of diethanolamine having the formula CH2CH2O NH BOI-I wherein n designates an integer of 1 to 6, said mixture being a highly hygroscopic vitrous and odourless mass having a good transparency, soluble in water, alcohols, glycols, polyglycols, ethers, ketones, and substantially insoluble in nonpolar solvents.
2. A method of protecting against rust ferrous metals kept in contact with a medium promoting the formation of rust, comprising impregnating said ferrous metal with a product containing from 0.8% to 5% by weight of a water-soluble rust preventing agent of claim 1.
3. A method of protecting against rust ferrous metals kept in contact with a medium promoting the formation of rust, comprising adding to said medium 0.8% to 5% by weight of a water-soluble rust preventing agent of claim 1.
References Cited UNITED STATES PATENTS 3,015,629 1/1962 Truitt 252-389 3,227,739 l/l966 Verteeg 260462 3,429,909 2/1969 Schuster 260462 RICHARD D. LOVERING, Primary Examiner I. GLUCK, Assistant Examiner 'U.S. Cl. X.R. 2l2.7; 252; 260462