US1388325A - Treatment of iron or steel for the prevention of oxidation or rusting - Google Patents

Description

UNITED STATES PATENT OFFICE.

mm s. crrmwrcx, or nasr CLEVELAND, AND mane Rnsnx, or crumm moms, 011110, assrenons no THE CLEVELAND METAL rnonuo'rs com. rm, or omvnnm, orrro, A coarona'rron or one.

TREATMENT OI OB STEEL FOR THE PREVENTION OI OXIDATION OR RUS'IING.

llo Drawing.

To all whom it may concern:

Be it known that we, (1) LEE S. CHAD- WIGK and (2) MARC .Rnsnx, citizens of the United States, residing at 1) East Cleveland and (2) Cleveland e1ghts, 1n the county of Cuyahoga and State of OhlO, have invented a certain new and useful Improvement in the Treatment of Iron or Steel for the Prevention of Oxidation or Rusting, of which the following is a full, clear, and exact description.

This invention relates to improvements in the art of treating iron or steel articles, or articles having a coating of iron or steel, for the purpose of preventing oxidatlon or rusting thereof, and wherein such artlcles are provided with a protectlve covering adapted to render the surfaces thereof ca able of resisting, or of being unaffected y, the action of moisture and other oxidlzing influences.

It has heretofore been proposed to treat iron or steel or articles composed of or having a surface of iron or steel with a dilute solution of ordinary phosphoric acid (H POQ and preferably in the presence of iron filings or other compound lntended to control or regulate the rapidity or strength of the chemical action upon the metal or articles undergoing th treatment.

It has also been proposed to treat such articles by boiling them in solutions of soluble phosphate of iron, manganese or zinc.

The foregoing processes are more or less unsatisfactory for the following reasons:

The coating formed consists essentiallv of normal or basic phos hates, which are insoluble in water but so uble in even very weak 7 acid solutions. Hence, if any free phosphoric or other acid be present, the coatin will dissolve in part at least in such aci causing the final coating to be thin or uneven and subject to removal, as by rubbin vigorously, especially while wet. If, on t e other hand, the solutions employed contain only soluble phosphates of iron, manganese or zinc,- without any free acid, the solutions are of themselves so very faintly acid that they will act only on chemically clean iron, free from scale, grease and dirtand, even then, will act only very slowly; hence, articles to be treated in such soluble phosphates require sand-blasting or some similar treatment be- Speciflcation of Letters Patent.

Patented Aug. 23, 1921.

Application filed October 1, 1917. Serial 110. 194,117.

fore immersion in the solution and then requlre that they be kept in the solution usually from two to three hours before the treatment is completed.

By our methodoftreatment, we are enabled to produce a rust-proof coating on llOIl or steel parts in which the coating can be obtained in a much shorter time than is requ red by any previous process, with less preliminary treatment of the metal and at a material saving of expense; furthermore, the resultant coating i denser, harder, and more unlform, and hence superior in its rust-resistlng qualities to the coatings produced by any of the previously proposed processes with which we are familiar.

It is well known that if iron i immersed in certainmetallic salts, the iron will be dissolved and the metal of that salt deposited. This is because the metal in the salt is less basic than iron; that is, less electro positive;

hence iron tends to re lace itin the solution to form a more stab e compound with the acid radical than the other metal did. The speed with which this action goes on, however, depends on the relative strengthpf the acid radical and the basic radical, therchange being rather rapid in solutions having an acid reaction and proceeding more slowly in nearly neutral solutions. 4

The common metals which iron willv replace "in this manner in the solutions of their salts are lead bismuth, tin, copper, mercury, silver and gold. Now the di-hydrogen phosphates of most of these metals are soluble and have an acid reaction when dissolved in water. Hence, if iron or steel articles are placed in solutions containing soluble dihydrogen phosphates of any of these metals, two reactions 0 on simultaneously. In one, iron replaces t e metal in the phosphate. In the other, iron combines with the soluble di-hydrogen phosphate to form an insoluble normal phosphate. When the work is first placed'in the bath, the first reaction predominates; but, as the phosphate coating row heavier, or builds up, less of the metal is deposited. Th final coating consists of a mixture, or com ound, of normal hosphates of iron and of t e metal in the sa t, together with some of the metal itself deposited in with the phosphates. While other reactions may proceed to a slight extent between the metals and the phosphates, they do not progress to an extent to affect the resultant coating.

As the action of the salt in dissolving the iron proceeds rather rapidly when the work is first placed in the bath, the work is cleaned of scale or dirt and of thin films of oil within the first few minutes following the insertion of the work in the bath, which results in a very uniform coating being produced in a very short time and without preliminar treatment. In case the work contains muc grease, the only treatment needed is to wash it in naphtha, or some similar solvent.

It will be noted that this action is entirely different from any that can take place with salts of any of the metals previously used for rust proof work, for these metals are not less electro-positiv than iron and, consequently, they will not be deposited along with the phosphates.

While this process may be carried out by the use of any soluble phosphate of the metals less basic than iron, in practice we ordinarily employ mixtures of copper dihydrogen phosphate and copper mono-hydrogen phosphate, the presence of the monohydrogen phosphate insuring the absence of all free acid. hese copper hosphates may be made in a number of di erent ways, as, for instance:

30 pounds of blue vitriol or cop er sulfate crystals are dissolved in ten ga lons of boiling water. Phosphate of soda is dissolved in hot water and added to the foregoing solution in such proportion as to turn red litmus paper slight y blue; this usually requires from 50 to 90 pounds of phos hate of soda, dependin on its strength. en take about one-ha f as much phosphate of soda as has been used before, place in a copper can and add to it about 14 pounds of sulfuric acid testing 66 Baum, adding enough water to cause thev hosphate to dissolve in the acid. Then a d the second solution to the first solution in a mixing tank and add enough water to make a total of about 60 gallons, stirring very thorou hly. The phosphate of soda referred to a is diso ium mono-hydrogen phosphate Na,HPO,. As the amount of moisture contained in the phosphate of soda varies, the amount to be used must be judged by its chemical effect and this amount will vary from time to time for reasons'stated.

The products formed are copper di-hydrogen phosphate, copper mono-hydrogen phosphate, and sodium sulfate. As the sodium sulfate formed is inert, it is not necessary to remove it from the solution. By varying these proportions the various quantities of di-hydrogen and mono-h drogen phoflphates present can be change as desire The work to be treated is hung in a tank .hard, dense and uniform and contains a sufficient quantity of metallic copper so that it may be plated. After being taken from the bath, the parts may be oiled or otherwise treated as desired.

Instead of using a phosphate or hosphates of copper, we may use the so uble phosphates of one or more metals one of which at least should be less basic than iron.

Still another method is' to add to bone ashconsisting principally of Ca (PO two-thirds of its weight of sulfuric acid and two-thirds of its wei ht of blue vitriol. This will precipitate ca cium sulfate and leave in solution copper-di-hydrogen phosphate, which can be drawn off. Sodium phosphate may then be added to the solution until the desired quantity of mono-hydrogen phosphate is formed.

A further and important advantage of our process is that it enables us to employ a relatively cheap acid (sulfuric aci thereby cheapenin the cost of the rust-proofing op.- eration. urthermore, as pointed out hereinbefore, this low cost of ingredients is attended with a shorter period of treatment and with the production of a coatin superior to that secured by the practice 0 any other process with which we are familiar. In our patent #1,320,734, we have described compounds and a rocess for coating metal wherein the ingredients of the compounds include an alkali phosphate, copper sulfate, and sulfuric acid, and wherein certain features disclosed therein are covered broadly by the claims. In this application, we disc ose compounds which ave the advantage, over those disclosed in said patent, of producing both the di-hydro en phosphate and the mono-hydrogen phosp ate of metals less basic than iron, also the use of soluble prosphates of a lurality of metals, at least one of which is es basic than iron.

Having thus described our invention, what we claim is 1. The process of treating iron or steel, or articles com osed of or having a surface of iron or stee which includes subjecting the said articles to the action of a bath containing a mixture of di-hydrogen and monohydrogen phosphates of a. metal less basic than iron.

2 The process of treating iron or steel, or articles composed of or having a surface of iron or steel, which includes subjecting the said articles to the action of a bath containing a mixture of copper di-hydrogen phosphate and copper mono-hydrogen phosphate.

3.: A compound for treating iron or steel containing mixtures of di-hydrogen and mono-hydrogen phosphates of a metal less basic than iron.

4. A compound for treating iron or steel containing a mixture of copper di-hydrogen phosphate and copper mono-hydrogen phosphate. I

5. The process of treating iron or steel, or articles composedof or having a surface of iron or steel, which includes subjecting the said articles to the action of a bath containing phosphates of a metal less basic than iron.

6. The process of treating iron or steel or articles composed of or having a surface of iron or steel which includes subjecting the said articles to the action of a bath containing a mixture of metallic phosphates at least one of which phosphates is of a metal less basic than iron. 7

7. The process of treating iron or steel or articles composed of or having a surface of iron or steel which includes subjecting the said articles to the action of a bath containing a metallic di-hydrogen phosphate and a metallic mono-hydrogen phosphate, the dihydrogen phosphate being of a metal less basic than iron.

In testimony whereof we hereunto aflix our signatures.

LEE S. CHADWICK. MARC RESEK.