US2243853A - Method of inhibiting corrosion - Google Patents

Description

Patented June 3, 1941 METHOD OF INHIBITING CORROSION James B. Castner, Woodbury, N. J assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application February 9, 1939, Serial No. 255,456

6 Claims.

This invention relates to a method of producing iron-containing bodies of improved stability, and more particularly to a method of preventing corrosion of said bodies.

In view of the fact that the corrosion of any apparatus containing iron is a serious economic problem to those engaged in industry, many experiments involving a great number of chemical compounds as well, as variations in their application have beenperformed, in order that this problem might be solved. Chieily, attention has centered about the inclusion of one or more chemical compounds in an aqueous liquid medium which is in direct contact with the iron structure over long intervals of time, as in internal combustion engines, for example. Several formulations have been satisfactory when employed in this manner, and consequently have found commercial application.

However, many instances prevail where corrosion of the iron-containing body is not due to its constant contact with a liquid, but instead occurs merely during its exposure to atmospheric conditions. Where permissible, the surfaces of such bodies are coated or painted wih materials capable of excluding the atmosphere, so that corrosion is prevented or at least retarded in this fashion. Obviously, many situations obtain where such procedure may not be employed because of the intended'use or subsequent treatment of the material. Among these may be mentioned those instances where a clean, bright metal surface is desired.

An object of the present invention is a novel method of inhibiting the corrosion of iron-containing bodies. Another object is a. method for inhibiting the corrosion of iron bodies under atmospheric conditions. A further obiect is the production of steel capable of resisting corrosion without protecting said steel with paint or other conventional coating. A still further object is the production of clean steel of enhanced corrosion-resistant properties. Other objects will become apparent as the invention is described further hereinafter. I have found that the foregoing objects are attained by treating the iron-containing body with a solution containing an inorganic nitrite and permitting a film of said solution to dry thereon.

The nltrites of alkali and alkaline earth metals have proved particularly emcacious. Moreover, because of economy and ease of handling, I prefer sodium nitrite, barium nitrite and calcium ment being accorded the material to be protected, but in general it may be effected in any convenient manner, such as clipping of the iron member into the nitrite solution, or by washing thoroughly with said solution. Quite surprisingly, this treatment imparts a very marked improvement in the corrosion-resistant properties of the material after it has been removed from contact with the nitrite solution.

I am aware that sodium nitrite has been added to various solutions in order to inhibit the corrosion of iron or steel with which said solutions are in contact, but heretofore it has been deemed necessary that said solution remain in direct contact with the material to be protected-against corrosion, merely subjecting the metal to a sodium nitrite solution being considered inefiective.

In order that my invention may be better understood. certain specific embodiments thereof are described in the following examples.

Example I Four pieces of mild steel, in the shape of a souare about 1 inch on the side and 1/10 inch thick, were tested to evaluate the eflicacy of the treatment with sodium nitrite. Two of the squares were submerged in a solution of sodium nitrite of 0.5% strength by weight. After several minutes, the squares were removed from the solution, and, together with the untreated steel squares, were placed in atmospheric storage, that is to say under atmospheric conditions of temperature and humidity. These samples were given a visual inspection at various intervals over a period of 6 months. At the'end of this storage period, the squares subjected to the sodium nitrite treatment exhibited no apparent signs of corrosion, whereas those not so treated gave positive signs of corrosion after 24 hours and were very badly corroded at the expiration of 6 months, practically their entire surfaces being covered with the typical reddish-brown color of corroded iron.

Example II A 0.5% by weight solution of calcium nitrite was substitiuted for water, which was normally used as the cooling agent in an operation involving the machining of steel to precise dimensions. Although the requisite control of temperature could be effected by means of water, the steel after machining tended to corrode very rapidly unless time-consuming and expensive precautions were exercised. The substitution of the aforementioned calcium nitrite as cooling agent permitted theproduction of a finished steel which did not corrode during the ordinary interval from the time of machining to the subsequent use of said steel.

It will be understood that my invention is not limited to the specific-embodiments set forth in the foregoing examples, but instead has application to any operation wherein it is desirable to prevent or retard the corrosion of iron-containing bodies. For example, it may be applied effectively to the pickling of steel, wherein steel is subjected to a pickling bath which usually contains sulfuric acid in order to cleanse and remove irregularities of the metal, the adhering acid being subsequently removed by washing with water. It is well lmown that steel treated in this manner has a tendency to corrode very quickly, a badlydiscolored surface often being apparent almost immediately after the steel becomes dry. The adoption of an inorganic nitrite solution as the wash solution, or as a separate bath following the water washing treatment, effects a marked improvement in the appearance of the steel after drying, as well as in its resistance to corrosion.

The strength of the sodium nitrite solution may be varied to suit the requirements of the particular application. However, I find a solution containing between 0.1 and 3.0% sodium nitrite tobe very eflicacious. Likewise, it is conceivable that in some cases said solution may be employed more advantageously if it is maintained at somewhat elevated temperatures. These variations, however, may be applied as conditions demand.

Thus, my invention renders possible iron-containing bodies of improved corrosion resistant properties without necessitating the application of a moisture-impervious coating thereon. Iron my invention permits of many modifications.

without varying from the spirit'or scope thereof. For example, certain compositions of steel may require longer contact with the nitrite solutions disclosed herein if the most advantageous results are to be obtained. For this reason, I intend to be limited only in accordance with the following claims.

I claim:

1. A steel body provided with a coating consisting of an inorganic nitrite.

2. The body of claim '1 wherein the nitrite employed is sodium nitrite.

3. The body of claim 1 wherein the nitrite employed is calcium nitrite.

4. The body of claim 1 wherein the nitrite employed as barium nitrite.

5. The method of imparting corrosion resistance to a steel body which comprises treating said body with an aqueous solution consisting of an inorganic nitrite and water and permitting the liquid to dry thereon to form a coating of said nitrite.

6. The method of producing steel free from discoloration and imparting corrosion resistance to the same, which comprises treating said steel with a mineral acid, removing said steel from said acid, washing the steel to remove adhering acid, and treating the steel with an aqueous solution consisting of an inorganic nitrite and water and permitting the liquid to dry thereon to form a coating of said nitrite. I

JAMES B. CASTNER.

CERTIFICATE OF CORRECTION Batent No. 2,215,855. June 5, 19LL1.

JAMES B. CASI'NER.

vIt is hereby certified that error appears in the printed sfzec-ification I of the above nuxpbered patent requiring correction as follows: Page 2, second colfimn, line 21, claim 1;, for "as" read --is--; and that the said Let' ters Patent should be read with this correction therein that the same mayconform t othe record of thecase in the Patent Office. si ned and sealed this 22nd day of July, A; D. 191 1.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.