US2842461A - Lead coating process and material - Google Patents

Description

United States LEAD COATING PROCESS AND MATERIAL Henry A. Wagner, Cleveland, Paul Golar, South Euclid, and James R. Kusa, Maple Heights, Ohio, assignors to The E. F. I-lauserman Company, Cleveland, ()hio, a corporation of Ohio 7 Application December 2, 1955 Serial No. 550,759

4 Claims. (Cl. 117--13il)- No Drawing.

This invention relates as indicated to lead coatings,

more particularly to protective coatings for metal.

surfaces subject to corrosion, especially iron, steel and ferrous alloys.

The tendency of' the less noble metals to revert to their naturally occurring states has been recognized since their first employment, and many dilferent' methods have been adopted in an attempt to prevent, arrest or inhibit such corrosion or rust-ing. It has been. estimated that the annual monetary loss due to corrosion in. the United.

States alone is in excess of $5,5 00,000,0O0. Of course, indirect losses due to. escape of such materials .as oil, water, natural gas and other fluids from corroded pipe lines and losses due to down time in transportationfacil-F ties and manufacturing plants are difficult to appraise accurately. It should also be appreciated that construc- V ferrous metals: in use; any method of protecting the same even slightly more. efiectivelythan methods currently employedwould result in. at comparable extremely large annual dollar saving.

Each of the knownmet h'ods of protecting ferrous metal surfaces has certain inherent deficiencies and each such method will ordinarily be employed only in. certain selected fields of use. Protective organic coatings; which include the paints and lacquers; are reasonably effective as long as the protective film is not broken, but they tend to be rather expensive and often their cost is justified on the basis of their decorative qualities equally with their protective qualities. The applicationof metallic coatings both by hot dipping and electroplating is also an old cart. The'.les.s, noble metals-suchas'zinc are generally anodic with respect to ironin most environments and are classified as sacrificial. The protective coating gradually corrodes away and affords considerable protection as long as a continuous filin remains. There are situations, however, where: zinc: as: well as. lead, tin, cadmium and aluminum will reverse its potential with re spect to iron and consequently the position in the electromotive series cannot be wholly relied upon as an infallible index for predicting the glavanic behavior of metallic couples in all, environments. Coatings of nonsacrificial metals such as nickel and coppenmay also form galvanic cellswith. iron although-the current flow is in .the opposite directionr to that in. the case of the sacrificial metals, resulting in accelerated corrosion of the basemetal wherever the coating is broken or porous.

lacquers, phosgalvanizing, and other platatent ice Relatively thick coatings of such non-sacrificial metals are accordingly commonly employed.

Hot dip methods of applying protective metal coatings have certain advantages over similar coatings electrodeposited but also display certain inherent weaknesses. Thus, hot dip galvanized steel may develop cracks when flexed due to the formation of a hard zinc-iron alloy which is brittle and has poor adhesive properties. The hot dip method and: the electroplating method both tend to produce coatings rather non-uniform in thickness.

It is accordingly a principal object of the present invention to provide a protective lead coating for metal surfaces subjectto corrosion, particularly iron, steel and the ferrous alloys.

Another object is to provide such coating which. will be considerably less expensive than other coatings'commonly employed for a like purpose.

A further object is to provide such coating and methodof application of the same which will be adapted to sub stantially all sizes and shapes'of articles to be protected and will aiford a predictable uniform degree of protectron.

till another object is to provide such coating which will not interfere with subsequent working of the article or the application of other decorative coatings and the like but instead will facilitate the same.

Yet another object is to provide a method of lead coating by chemical: displacement and a bath suitable for such purpose which will be inexpensive and easy to" maintain with a minimum of supervision and adjustment.

Other objects of the invention will appear as the description proceeds.

To the accomplishment of the foregoing and relatedends, said invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following. description setting forth in detail" certain illustrative: embodiments" of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may beemployed.

Generally stated, our invention comprises the provision of a continuous lead coating on the metal surface to be protected by chemical displacement from a water bath containing the lead ion in solution, such bath having a lead ion concentration of at least about 1 gramer liter and awater soluble addition agent containing alkylene oxide condensation product, such bath als0-having an acid: pH'.

More particularly, we have discovered that ifi the proper type of addition agent (ordinarily a surfactant)- be selectedas indicated above, superior lead-deposits m'ay beobtained by chemical displacement from a bath" inwhich: the leadion concentration is relatively low, pre erably' from: about. 5 grams; per liter to about 8'5 grams p'er' liter. The bath should: desirably be heated to atem' perature of from about 150 F. to just below the boiling point of the bath for bestlresults.

Examples of water soluble lead salts which may be" utilized in. accordance with our invention, listed in theorder of. preferencehaving regard to the quality of the deposit formed, are as: follows:

Formate I Fluoborate Perchlorate Fluosilicate Acetate Citrate:

' Glycol'ate Tartrate- Lactate Malate Pr'opionate: Nitrate Sulphonate Chloride muchpreferred.

excellent deposit under the operating conditions of our invention, may nevertheless have explosive properties when improperly handled and it will accordingly probably not often be used in practice. Similarly, lead acetate, while producing a superior deposit, has a rather unpleasant odor which is likely to militate against its widespread use. The lead citrate and lead tartrate do not produce as refined deposits as most of the other salts listed, and furthermore require to be solubilized by additions of solubilizing agents such as sodium citrate and sodium tartrate. Lead chloride is not very soluble, and neither it nor lead nitrate are very satsfactory although deposits can be obtained at very low lead ion concentrations on the order of 1 gram per liter, for example.

- When the lead salt is a salt of an aliphatic mono-basic acid (preferred), e. g. lead formate and lead acetate, the water solution should contain from about 5 to about 130 grams per liter of the lead ion, and preferably from to 40grams per liter. It is a most unexpected feature of our invention that our new lead coating process operates especially well at such low lead concentrations. A pH of from 2.5 to 5.0 or slightly more is suitable but a pH of from 3.4 to 4.2 is preferred. An elevated temperature of from 170 to 210 F. considerably speeds the operation.

When the lead salt is a salt of an aliphatic mono-basic hydroxy acid, e. g. lead glycolate and lead lactate, the same rules and limitations apply as those given above for the lead salts of aliphatic mono-basic acids.

When the lead salt is a salt of an aliphatic poly-basic hydroxy acid, e. g lead tartrate and lead citrate, the water solution should contain from about 1 to 30 grams per liter of lead ion, and preferably from 5 to grams per liter. A pH of from 5 to 6 is best. Ordinarily a solubilizing agent such as the ammonium or alkali metal salts of these same acids will be employed to bring the desired amount of lead salt into solution.

. Among the inorganic lead salts, lead perchlorate is by far the most effective for our purpose. A pH of from 1.2 to 3.0 is suitable, but from 1.5 to 2.5 is preferred.

Lead ion concentrations for preferred specific examples of suitable lead salts are as follows:

In the case of lead formate and lead glycolate, noted above, the upper range of suitable lead ion concentration is limited merely by the maximum solubility of the salt.

While not preferred, lead gluconate, lead maleate, and lead di-glycolate may also be employed. W

In most cases the lead salt may be most conveniently prepared by reacting litharge with the proper acid. Thus 28 pounds of litharge (PbO, 91% Pb) may be added to 80 gallons of water at a temperature of l80-190 F. and agitated while 1.8 gallons of 90% formic acid is next added. When the litharge has entirely dissolved, water is added to bring the total volume to 100 gallons.

We have found that extraordinary improvement is obtained in the thickness, density, adhesion and corrosion resistance of the lead coating produced on ferrous articles by chemical displacement upon immersion in the solution of such lead salts if a small amount of an alkylene oxide condensation product with an organic compound containing an active hydrogen atom is incorporated in the bath. As a practical matter, these will ordinarily be ethylene oxide and propylene oxide condensation products with organic compounds. Their production is well understood by those skilled in the art.

These materials are generally useful as surfactants or wetting agents and should, of course, be stable at operating temperatures (ordinarily in excess of 170 F.). Likewise, it is much preferred that they be fully soluble in the relatively small quantities employed, although those forming cloudy or milky solutions perform satisfactorily. If the addition agent tends to remain at the surface of the bath, it is likely to be depleted by drag-out as coated articles are removed from the bath. It is apparently not merely the surfactant qualities of the addition agent which render it so effective for our purpose inasmuch as other types of surfactants produce little or no improvement. The non-ionic addition agents appear generally more suitable and effective in lower concentrations, but anionic and cationic agents may also be employed.

either saturated or unsaturated, x or x-l-y or x+y+z representing at least 3, normally 10 to 20, and up to moles of ethylene oxide:

(A) Substituted hydroxy compounds Alkyl phenols 30-0-4 onito .n

(2) Aliphatic alcohols R' o-(c 'H.0 ,,H (3) Partial esters of polyhydric alcohol and aliphatic acids (glycerol, sorbitol, or sorbitol anhydride):

RCOOCH2 CHO-(O:H4O):H

CHzO-(C:H4O),H

(4) Partial ethers of polyhydric alcohols and aliphatic alcohols:

RCH:O-CH:

H-O-(OzHiOhH HIO(CIH4O)1H (B) Substituted thio-alcohols (mercaptans) R'S-( 2 4 (C) Substituted acids (1) Aliphatic acids R'--COO (C l-I 0 H (2) Alkyl phosphates (3) Tertiary carbon fatty amine (F) Substituted ethylene oxinated alkyl phenols (1) Alkylated polyether sulfates R-O-0 oeHt0),-o-s-oNa o (2) Alkylaryl polyether sulfonates nO-ooenton-s-om (G) Condensation of ethylene oxidev with propylene oxide and propylene glycol 'noweHeo)nceHeonweHeoie (H) Condensarion with itself (solid high molecular In most of the above compounds, the ethylene oxide component will preferably constitute from about 60 to about 90% by weight, the extent of water solubility often being determined by the ethylene oxide content. Propylene oxide may be substituted for ethylene oxide in the above examples and often mixtures of ethylene oxide and propylene oxide condensation products may be employed. Ethylene oxide is, however, generally much preferred.

Some specific examples of suitable addition agents for use in accordance with our invention are condensation products of ethylene oxide with:

It will be seen that organic'compounds having an active hydrogen atom attached to an oxygen, sulphur, or nitrogen atom may thus be condensed with the alkylene oxide (ordinarily ethylene oxide or propylene oxide in order to obtain the desired water solubility) to produce the addition agents for use in our new baths from which lead is to be deposited on ferrous articles by chemical displacement. In most cases this addition agent will constitute only about 1% by weight of the coating bath or solution. From about 0.1 gram per liter to about grams per liter may be employed but there is seldom advantage in using over 1 gram per liter.

The following is given as a preferred illustrative example of the complete operation. approximately 170 F. and 33 grams per liter of litharge and 18 milliliters per liter of 90% formic acid are added and stirred until dissolved. Alternatively, 43 grams per liter of lead formate may be added. This will aiford a lead ion concentration of approximately 30 grams per.

liter. The pH may then be adjusted by slight additions Water is heated to h 6 of lithar'ge or formic acid to bring it within the 3.4-4.2 range. One gram per liter of an addition agent formed by condensing one mole of nonyl phenol with 15-30 mob of ethylene oxide is added to the bath. The temperature of the bath is raised to about 200 F. and the ferrous article immersed therein for a period of from about 4 to about 1.0 minutes, ordinarily about 7 minutes. The metal surface should, of course, be clean for best results' A lead deposit is obtained of from about 0.000075 to about 0.000150 inch in thickness. If immersed for a relatively long period at lower temperatures (e. g. F.) a heavier deposit may be obtained. The higher the temperature and the shorter the immersion pe riod, the thinner the deposit produced. As additional work is processed, the lead ion concentration is depleted and the amount of iron in solution increases. The lead ion concentration may conveniently be checked by measuring the specific gravity of the bath, titrating to determine the iron concentration, and then reading the lead ion concentration from a graph based on known concentrations. The pH should be checked periodically and adjusted as necessary. Oxidation of the iron from ferrous to ferric form occurs (air may be bubbled through the bath to hasten this) and the iron precipitates as ferric hydroxide. When the lead ion concentration drops to about 15-20 grams per liter, more lead formate may be added again to raise the concentration to 30 grams per literv Eventually the solution will become saturated with ferrous ion'(at about 35 grams per liter of ferrous ion) and thebath should be replaced. If the bath should be allowed to reach too low a temperature, lead formate may crystallize out but will redissolve on heating.

' Qne of the interesting features of the novel coating solution of this invention is its versatility in mode of application, Satisfactory deposits can be obtained by immersion, brushing on, flow coating, and spraying' The last-named method is often especially advantageous since much of industry is geared to spray coat various types of materials for chemical surface treatment of metals as in phosphating, chromating and the like. The mode of application will often be dictated by the facilities already available and the size and shape of the articles to be coated.

As might be expected, the rate of deposition is greatest at the start of the operation and gradually lessens with time. Sound deposits having a thickness of 0.0003 inch may be obtained and even more.

it will, of course, be appreciated that before the work is coated it should first be free of all oil, grease and dirt. Such prior cleaning operation may, for example, include vapor degreasing or preferably treatment with a chemical cleaner such as the commercially available alkali, emulsion or two-phase cleaners. Following such cleaning op eration, the work should be thoroughly rinsed in water, and if free of rust and scale it need not be acid pickled. If pickling should be required, however, the work will again be thoroughly water rinsed after completion of the pickling operation. It will then be conveyed to the processing tank or spray booth Where metallic lead is deposited thereon to the desired predetermined thickness. Subsequently, the work will be rinsed first in cold water and then in hot Water to facilitate drying, forced warm air drying being preferred.

The lead coated article may receive supplemental surface treatments such as chromat-ing, oxalating, sulphating and phosphating in dilute solutions. Under proper conditions, the lead may be bright flowed which further enhances its corrosion retarding ability. As a rule, hoW- ever, these various supplemental treatments will be found unnecessary. More frequently, the finished coated article will merely be painted or oiled, the surface being particu larly suited therefor.

Corrosion and Weathering tests have shown ferrous articles coated in accordance with the present invention to be exceptionally resistant to corrosion. Ferrous articles I? v lead. coated in accordance with this invention will withstand the conventional salt spray test for a period of time approximately equal to that achieved by an electroplated zinc coating.

The employment of lead coatings to facilitate deep drawing operations and the drawing of wire, and particularly the drawing of steel wire, has been suggested since it has been determined that lead is a lubricant in such drawing operations superior to the usual greases, oils, soaps, emulsions, etc., but such other methods have been generally adopted in the industry for the reason that no economical method of applying the lead coating has previously been available. Thin lead coatings may also serve efiiciently as a bearing metal in other applications.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed. 7

We therefore particularly point out and distinctly claim as our invention:

1. The method of forming a substantial sound adherent protective lead coating on ferrous articles which comprises subjecting such article to the action of a water solution of lead formate and the at least slightly water soluble condensation product of ethylene oxide and an organic compound, the solution having a pH of from 2.5 to 5.0 and a lead ion concentration of from 1 to 80 grams per liter, for a period of time sufficient to deposit a continuous corrosion-resistant lead coating on such article by chemical displacement.

2. The method of forming a substantial sound adherent protective lead coating on ferrous articles which comprises subjecting such article to the action of a water solution of lead formate and the at least slightly water soluble condensation product of ethylene oxide and an organic compound, the solution having a pH of from 3.4 to 4.2 and a lead ion concentration of from 10 to grams per liter, the temperature of the solution being above 170 F., per a period oftime sufficient to deposit a continuous corrosion-resistant lead coating on such article by chemical displacement.

3. A bath suitable for the coating of ferrous articles with lead by a chemical displacement reaction comprising a water solution of lead formate and the at least slightly water soluble condensation product of ethylene oxide with an organic compound having an active hydrogen attached to an O, S, or N atom, said solution having a pl-i of from 2.5 to 5.0 and a lead ion concentration of from 1 to grams per liter. 7

4. A bath suitable for the coating of ferrous articles with lead by a chemical displacement reaction comprising a water solution of lead formate and the at least slightly water soluble condensation product of ethylene oxide with an organic compound having an active hydrogen attached to an O, S, or N atom, said solution having a pH of from 3.4 to 4.2 and a lead ion concentration of from 10 to 40 grams per liter, the temperature of the bath being at least F.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Nov. 27,

Claims (1)

1. THE METHOD OF FORMING A SUBSTANTIAL SOUND ADHERENT PROTECTIVE LEAD COATING ON FERROUS ARTICLES WHICH COMPRISES SUBJECTING SUCH ARTICLE TO THE ACTION OF A WATER SOLUTION OF LEAD FORMATE AND THE AT LEAST SLIGHTLY WATER SOLUBLE CONDENSATION PRODUCT OF ETHYLENE OXIDE AND AN ORGANIC COMPOUND, THE SOLUTION HAVING A PH OF FROM 2.5 TO 5.0 AND A LEAD ION CONCENTRATION OF FROM 1 TO 80 GRAMS PER LITER, FOR A PERIOD OF TIME SUFFICIENT TO DEPOSIT A CONTINUOUS CORROSION-RESISTANT LEAD COATING ON SUCH ARTICLE BY CHEMICAL DISPLACEMENT.