US1639694A

US1639694A - Process of rust proofing and articles produced thereby

Info

Publication number: US1639694A
Application number: US108162A
Authority: US
Inventors: Green Matthew; Hobart H Willard
Original assignee: Parker Rust Proof Co
Current assignee: Parker Rust Proof Co
Priority date: 1926-05-10
Filing date: 1926-05-10
Publication date: 1927-08-23
Anticipated expiration: 1944-08-23
Also published as: FR632342A; GB270679A; DE508785C; NL25645C; BE341226A

Description

?atented Aug. 23, 1927.

UNITED STATES PATENT OFFICE.

MATTHEW GREEN, 0F DETROITL AND HOBART H. WILLARD, OF A NN' ARBOR, MICHI- GAN, ASSIGNORS TO PARKER.RUST-PROOF COMPANY, 01 DETROIT, MICHIGAN, A,

CORPORATION OF MICHIGAN.

PROCESS OF RUST P ROOFING AND ARTICLES PRODUCED THEBEBY.

No Drawing. Application filed May 1b,

This invention relatesto a process of rustprooting iron articles and to the articles rustproofcd in this manner.

More particularly, the invention relates to producing on the surface of iron articles a coating of phosphates which are insoluble in Water, and to the articles coated in this manner.

The process of rust-proofing iron articles by producing thereon a coating of insoluble phosphates is well-known. While other materials have been used to some extent, the coatings Which have been produced have been essentially phosphates of iron. Analysis shows that, While other phosphates are present to some extent, .the major portion of the coating consists of ferrous monohydrogen phosphate. This particular phosphate is slightly soluble and, therefore, does not furnish complete protection against rusting.

it has been discovered that, when mangunese dihydrogen phosphate is'present in the rust-proofing bath in considerable proportions relatively to the other materials in the bath, aconsiderable portion of the coating consists of phosphate of manganese. The exact composition of the different phosphates in such a coating is very difiicult to determine, but it has been discovered that, when a considerable percentage of manganese is present in such a coating, the proportion of phosphorus to metal in the coating more nearly approaches that present in r the normal phosphate than thatpresent in the monohydro'gen phosphate. The exact proportion may be varied by many conditions, but the following examples may be mentioned in order to bring out clearly the intended distinction. When the coating contains iron and manganese atoms in about the ratio of two to one, the ratio of the metal to phosphorus is a trifle greater than that which would result from the coating being one-half monohydrogen phosphate and one-half nor- With manganese forming about one-half of the metal in the coating, the proportion of metal in the coatingto phosphorus in the coating was found to mdicate a proportion of approximately 6/? normal phosphate and 1/7 monohydrogen phosphate. In the monohydrogenphosphate these atoms of metal and phosphorus are in 1926. semi No. 108,162.

the ratio of 1 to 1, while in the normal phosphate the ratio is 3 to 2. Analyses of coatings containing-iron and manganese in the proportion of 2 to l have shown an atomic proportion .of 5 to 4 of metal to phosphorus, and similarly a proportion of 1 to 1 in the metals has shown a proportion of 1.4+ to 1 of metal to phosphorus.

Normal phosphate is much less soluble than monohydrogen phosphate, and corrosion tests corroborate the analyses described above. That is, coatings comparatively high in manganese and apparently high in normal phosphate are found to be much more resistant to rusting than coatings. consisting largely of monohydrogen phosphate.

' While this eflect is gradually increased with the increase of manganese in the coating, it appears that the proportion of normal phosphate is increased more rapidly than the proportion of manganese, and that a proportion of manganese amounting to onehalf as'much as the iron in the coating is decidedly effective in increasing the quality of the coating, but that a percentage of manganese equaling that of the iron in the coating produces a very much more resistant coating. WVhile beneficial results may be obtained from our invention by having present in the coating an amount of manganese equal to one-half ofthe iron in the coating, it is preferable to have at least as much manganese as iron in the coating in order to obtain a protective layer which is substantially normal phosphate.

'It has been found that, where manganese dihydrogen phosphate and ferrous dillydrogen phosphate are present in a rustproofing solution, the manganese phosphate being less than the ferrous phosphate, there is a selective action Which'results in producing in the coating a larger proportion of manganese than there is in solution in the bath. For example, one-third as much manga'nese. as iron in a bath may result in onehalf as much manganese as iron in the coating, while approximately one-half as' much manganese as iron in the bath will produce approximately as much manganese as iron inthe coating. It will be understood that many conditions alter these. proportions to some extent, and that the proportions given above are for purposes o illustration and are not. given as being fixed ratios under all circumstances.

. gen phosphate.

There are several ways in which a bath of the desired composition may be obtained.

Some of these ways will be described If manganous dihydrogen orthophosphate is dissolved in water, and the water boiled for some time, a portion of the phosphate is precipitated as an insoluble phosphate and some free acid is liberated. We have found that from seven to seventy pounds of the said phosphate dissolved in one hundred twenty-five gallons of water and boiled as described will produce a satisfactory rustsludge, and

proofing solution, twenty to twenty-five pounds being the preferred amount. When an iron article, or an article havlng asurface containing iron, is immersed in such a solution, the formation of a, rust-proofing coating begins at once. There is no preliminary pickling of the work to bring the solution into balance, such as necessarily results where free acid is added to the bath and where iron must be dissolved from the work to bring the solution into balance, and the articles do not lose appreciably in weight or measurably in size. Nevertheless, in the process of forming the coating, a certain amount of the iron is dissolved in the bath. Some of this .is fixed as insoluble phosphates in coating, some of it forms insoluble phosphates which are deposited as art of it remains as ferrous dihydrogen p osphate dissolved in the bath. It will be readily understood that more of the phosphate radicals are in combination with a given amount of manganese in the dihydrogen phosphate than there are in the insoluble coating and, therefore, the phosphate introduced into the bath introduces sufficient phosphate radicals to form the phosphates of iron mentioned above.

If the bath is used continuously for rustproofing purposes for a considerable time, it constantly becomes less rich in manganese and richer in iron, reference being had to these materials dissolved in the bath in the form of dihydrogen phosphate. When the bath is replenished by an additional amount of manganese phosphate, the proportion of manganese to 1ron is increased, but is not brought back to the proportion which it had originally. The proportion of iron in the bath continues'to increase until it reaches a certain percentage in proportion to the maximum acidity. Thereafter the iron in the bath seems to remain approximately constant, whereas the manganese and acid are increased when constant iron content is replenished with manganese phosphate, it maybe easily brought up to a point where the manganese 4 will be more than half as much as the iron in the bath, but as this bath is used for" rust-proofing purposes the manganesemay be almost completely exhausted from the bath before the deposition of a coatingwill cease. In such a case, the'coating last formed is principally ferrous monohydrogen phosphate. By replenishing at comparatively short intervals, the amount of.

manganese in the bath may be kept above one-third as much as the iron, with a result of producing more normal phosphate than monohydrogen phosphate in the coating. The strength of the rust-proofing solution may be varied considerably and still rustproofeffectively. However, as the amount of iron in the bath seems to be approximately relative to the maximum acidity of the bath, it is preferable to replenish the bath to bring it each time to approximately the same strength. In this way the proportion of'manganese to iron is increased to the highest practicable amount at. each replenishment.

Theoretically, the best results would be obtained by replenishing the bath constantly so as to keep itat a substantially constant strength, as that would maintain the proportion of manganese in thebath at its highest point continuously. However, there are some objections to replenishing during the time of rust-proofing in the same bath, and the next best results are obtained by replenishing after each load. As it is desirable to allow some time for the bath to, become uniform after each replenishment,- there is some delay due to replenishing after each load. Satisfactory results may be ob,- ta'ined by replenishing after every other load. In general, it may be stated that the manner and frequency of replenishment will depend to some extent upon the quality of the coating desired. For the highest quality of coating, the bath should be kept as nearly as is practicable to the highest available proportion of manganese. Sometimes the coating produced with a less percentage of manganese is entirely suflicient for the desired purposes, and in such cases less care is required in maintaining the bath with a uniformly high manganese content.

III

While the preferred method of replenishing the bath is by adding a material consisting essentially of manganese dihydrogen phosphate, it will be understood that other methods may be used for obtaining the desired bath. This invention relates more especially to. the bath which is desired, to the manner of replenishment, and to the coating produced. Various modifications may be made within the scope of the appended claims. 1

What we claim is:

1. Iron or steel or articles com osed or having asurface of iron or steel urnished with a coating or deposit of hosphates of iron and of manganese, there eing at least one-half as much manganese as iron in the coating.

2. Iron or steel or articles com osed or having a surface of iron or steel rnished with a coating or deposit of phosphates of iron and of manganese, there being in the coating more than six atoms of the metal to five atoms of phosphorus.

3. A method of rust-proofin articles of iron or having a surface of iron or steel which consists in forming a dilute solution of phosphoric acid and dihydrogen phosphates of iron and manganese, there being at least one-third as much manganese as iron in the solution and there being sufficient dihydrogen phosphates in the solution in proportion to the free acid to rustroof articles without reducing the weight thereof, placing iron or steel articles in the solution and maintaining the solution hot until {the articles are rust-proofed.

4. The method of rust-proofing articlesof iron or having a surface of iron or steel which consists in forming a dilute solution of phosphoric acid and dihydrogen phosphates of iron and manganese, there being at least one-third as much manganese as iron in the solution and there being sufiicient dihydrogen phosphates in the solution in proportion to the free acid to rust-proof articles without reducing the weight thereof, placing iron or'steel articles in the solution and maintaining the solution hot until the articles are rust-proofed, introducing other articles into the bath and repeating the process and adding tothe solution from time to time materials which maintain the amount of manganese in the solution above one-third the iron in the solution.

5. A solution for rust-proofing purposes containing dihydrogen phosphates of manganse and iron and free acid, the phosphates being in sufiicient amounts so as to rustproof an immersed iron article without significant loss of-weight and the manganese in the dissolved phosphates being more than one-third as much as the iron in the dissolved phosphates.

In testimony whereof we have hereunto signed our names to this specification. HOBART H. WILLARD. MATTHEW GREEN.