US2787565A - Treatment of metal surfaces - Google Patents

Description

nitrate salts.

United States Patent-O ice TREATMENT OF METAL SURFACES Claims priority, application Italy May 8, 1950 8 Claims. (Cl. 148-6.15)

The present invention relates to new and useful compositions in the treatment of metals such as iron and iron alloys, zinc and cadmium, particularly by coating the metals with a phosphate layer, and to a process of treating the metals.

The present invention is a continuation-in-part of my copending application Serial No. 223,166 filed April 26, 1951, now abandoned for Process for the Preparation of Nitrophosphate Salts or Multi-Acid and Multimetallic Salts for the Nitrophosphatization of Iron, Its Derivatives and Alloys as Also of Cadmiumand Zinc.

The formation of phosphate coatings on iron, zinc and cadmium substances by the use of free phosphoric acid and acidic phosphate compounds has been well known. An oxidizing agent is also employed'in conjunction with the phosphoric acid and acid phosplate compounds for the formation of the phosphate coating. The most suitable oxidizing agent was found to be nitric acid plus- I-Iowever, compositions containing phosphoric acid, nitric acid, phosphates and nitrates, although the same are effective in the treatment of the metal have been found to be disadvantageous in that the solutions have to be prepared fresh.

The use of nitrates in combination with phosphates for the formation of phosphate layers .on metals shall herein be referred to as nitrophosphating" and the solutions used for this purpose shall be referred to as nitrophosphating solutions. Nitrophosphating has become well regarded and is used to a much greater extent at the present time than is simple phosphating because of the much greater speed of production of phosphate layers obtained by this method. For example, whereas simple phosphating requires a treatment time of from 60-90 minutes, the time required by the use of a nitrophosphating solution is reduced to from /i-4 minutes.

However, the lack of chemical stability of nitrophosphating solutions hitherto known has been a great disadvantage. The lack of stability is primarily due to a loss in total acidity which is apparently caused by a dis placement of the nitric acid and is more pronounced, the greater the concentration of nitric acid. Due to the instability of the previously known solutions, it was impossible to obtain consistent efficiency and after standing a few days it required a great deal more of the solution to achieve the same eifectiveness as with fresh solutions.

Many attempts have been made to overcome this difficulty. It was first attempted to overcome this difl'iculty by'the addition of alkaline nitrates to the solution. However, this was unsuccessful. It was then attempted to overcome the difliculty by the addition of many different substances to the solutions, including glycerin, lanolin,'ethylene oxide derivatives, and thiourea, all of which have proved to be unsuccessful for one reason or another.

It is therefore an object of the present invention to provide for the formation of nitrophosphating solutions containing free phosphoric acid, free nitric acid and phosphates and nitrates, which solutions are stable over long periods of time.

the present invention.

2,787,565 Patented Apr. 2, 1957 It is an additional object of the present invention to provide stable nitrophosphating solutions which retain maximum efiiciency without substantial loss of acidity over long periods of time.

It is a further object of the present invention to provide a process of producing stable nitrophosphating solutions.

It is another object of the present invention to provide a process for the coating of metals with a phosphate layer.

With the above objects in view, the present invention mainly comprises an aqueous solution of at least one metallic phosphate, at least one metallic nitrate, phosphoric acid and nitric acid and at least one phosphoprotein. It has been found that the phosphoproteins which are the albumins derived from milk, eggs and plants in low concentration in the nitrophosphate solution give the desired stability to the solution so that the same has substantially constant activity over prolonged periods of time. The amount of the phosphoprotein is preferably less than the amount of the nitric acid and the phosphoric acid.

The present invention which comprises the utilization of milk, egg and plant albumins in combination with solutions for the production of phosphate layers on metals and particularly ferrous metals is mainly applicable to multi-acid and multi-metallic solutions which are used for the production of phosphate layers and which, as explained above are herein designated as nitrophosphating solutions. These solutions are designated as multi-acid because they contain more than one acid, namely both phosphoric acid and nitric acid. Preferably the solutions are also multi-metallic in that the phosphates and nitrates in the solution are of more than one metal, such as zinc, manganese, copper, nickel, etc.

The nitrophosphating solutions with the phosphoprotein added thereto are preferably prepared as liquid salt concentrates which are diluted before use with water so that the liquid salt concentrate is between 120% by weight of the final diluted solution. The liquid salt concentrate contains the phosphoprotein in an amount less than the amount of either the free nitric or the free phophoric acid and preferably between 03-25% by weight. Although greater amounts of phosphoprotein may be utilized, it has been found that as little as 0.3% by weight of the phosphoprotein will have a sufiicient stability action and therefore greater amounts than 2.5% by weight are unnecessary. The preferred amount of phosphoprotein is between 0.5-1.0% by weight of the concentrate.

The amount of phosphate in the liquid salt concentrate, including both the metallic phosphates and the free phosphoric acid, may vary between 4075% by weight of the concentrate. The amount of nitrate in the liquid salt concentrate, including both the metallic nitrates and the free nitric acid, may vary between 20-50% by Weight of the concentrate. The amount of water in the liquid salt concentrate may vary between 348% by weight of metallic nitrate to free nitric acid may vary within extremely wide limits without in any way departing from It is only essential that the solution contain nitric acid partially combined with a metal and partially in the form of free nitric acid and that it contain phosphoric acid partially combined with a metal and partially in the form of free phosphoric a-cid.t The only limiting feature in this respect is that preferably the amount of total acidity of the solution is between 3*?- Although the scope of the present invention is not meant to be limited by any theory as to how 1 e stabiliu ing action of the phosphoprotein operates, it is believed that the same is partly due to a buffering efiect. Neverthelessyit is mainly of interest to note, that the phosphoprotein according to' the present invention maintains a constantand unvaried ratio between the undissociated and dissociated nitric acid.

The phosphoproteins, namely the milk; egg and plant albumins are well known: and may be utilized according t'othe resent invention nomattcr what'process'is utilized for the production of the phosphoprotein'. Thefolloirin'g'; however, illustrates a process of obtaining the phosphoproteih milk albumin or laetalbumin from milk. 1

The milk is skimmed and centrifuged. The milk residue thus obtained is treated with' sulfuric acid in" an amount of 430-440 g. sulfuric acid per each 1000 liters of milk, thus forming a precipitate labile calcium phosphoprotein. instead of sulfuric acid it is' possible to utilize hydrochloric acid, however in the ratio of 665-670 g. hydrochloric acid per each 1000 liters of milk;

The obtained precipitate is washed With-water, dried in-hot air at a temperature greater than 47 C., and then pressed and ground to powder form. The resulting product is a white amorphous powder which is tasteless and has a density of about 1.25-'l.2 6, is" insoluble in water, alcohol and ether; soluble in alkaline solutions, partly soluble in concentrated-acid solutions and compietely soluble in diluteacidsolutions: Thereforeup'on dilution of the liquid salt concentrate containing the phosphop'rotcin, a's'above described, and'heatin'gat the hydrolysis temperature, i. 50 90 Czit is easily possible to completely dissolve the phosphoprotein contained in'the concentrate.

Egg albumin and plant albuminmay' be prepared by substantially the same method above describedfor'the preparation of milkalbumin; and thee'gg albumin and plant albumin are even more soluble in dilute a'eid solutions than is the milk albumin. Althou'gh eg'g,plantand ni'iik'albumin are all suitable according to the present invention for the stabilization of nitrophos'phatingsoliitions, the best results have been obtained 'with millt'al'bu min. Although no exact chemical formula can be given for'the milk albumin, it is known to consist of "the following:

Percent by'w eight" Animal fats 0.5-1' Protein substances (i. e. labile calcium phospho protein) 80-82 Moisture 10-1-2 Ash 5-7 The present invention mainly comprises the addition to a concentrated nitropho'sphating solution' which" is diluted before use with water in an amount such that the concentrate is' between- 120% by weight of theffinal' diluted-solution; of'a phosphoprotein namely milk, egg

and plant albumin: in an-amount of. 0.345% by weight of the concentrate. The proportionsofm'efal'li'c -phos phates phosphori'c acid, metallic nitrat'esandnitric acid niay. be varied within-very wide limits'in the solutionsso long' as the proportions are suitable to givethedesir'ed nitrophosphating properties. concerned mainly with the addition of the pliosphopro tein to -the solution: rather than with: the/"specific properdens ehother components ofi'th'e solutions? r The present invention is 4' tl te tltelsss thet lqw nsstamples. eaver; to. i strate preferred liquid salt concentrates according to the present invention, the scope of said invention not however 'being limited to the specific examples given.

EXAMPLE I A liqu id salt concentrate prepared containing the followingcomponen'ts:

Percent by weight Zn(HaPOXlzTZHgG43121 04 70 ZntfNOaM-l- HNO; 24 Milk albumin 0.5 Water 5.5

The ratio" of total 'aciditytto free acidity of the above is 3:1. The \veightof'the' free nitric .acid'is about 34% of the weight of the free phosphoric acid.

EXAMPLE ii A liquid salt concentrate is prepared containing the following components in the proportions indicated:

Pe'rcentjby weight Zn (NQaDiFMMNOElz-FHNO? 23 Egg aibuinin's; 1 Water 6 The ratio of total acidity tofree'acidity of the above is 75]. and the weight of thefree' nitric acid is about 33% or the f'ree-phosphoric acid.

EXAMPLE In A coneenttate for .nitr'ophosphating solutions is preparcd'containing the following components in the proportions indicated:

I i v Percent by Weight ZnHdRO l IMnG U' 68 ZntNQ); (PQ3) 2'-1''Ni( N O3)2F C1''(NQ3')?+HNOQ3 Plant-protein (from soy'abe'ans) 013 Water 4.7

Theratio of total aciditytofree acidity of the above is 4:1 and the, weight of'f -reenitric acid is about 40% of the weightof freephosphoric acid.

EXAMPLE iv A concentrate: for nitrophosphating solutions is prepared containing the following components in the proportions indicated:

Percent by weight angst to free acidity of the above is 5.511; and the weight-ofthe free nitricacid is about equal to the weight ofgtheifr'ee phosphoric acid The following is-illustrat'ive of tiieprefe'rre'cl process of preparing a-liquid' salt concentrate according to the present invention 7 Into an acid; resistant vessel is placed concentrated -nitric-facid and concentrated phosphoric acid in a predetermined-ratioas'in any-of the above examples, for example inn ratio of-70 parts phosphoric acid to 24 parts nitric acid-asin E tampleL- and the acids are'b'eate'd to a temperature of 70 89? and a predetermined-quantity of the phosph'opr'otein, suchasmilk, egg-or plant albumin is added,--i. e. 0.5 part byweight-of the final concentrate as in Example-I. Then the particular metals such as zinc, manganese,nick el= or' the like" are added in a quantity SuchEthatth'eratiocf total acidity to free acidity of the r final fconcent'rate'zis between 3-7.

In Example I the ratio of total acidity to free acidity is adjusted to 3:1"

The liquid salt concentrates of the present invention generally have a density which varies between 1.45-1.6 and have in suspension a reddish substance of colloidal consistency. The particles forming the suspension are the albumin. Upon dilution, these particles are dissolved and the clear solutions formed. The product is sold commercially in the form of the liquid salt concentrate which is diluted by the user in an amount such that the final solution contains the liquid salt concentrate in an amount of l20% by weight.

The liquid salt concentrate is preferably diluted in the proportion of 7-15% concentrate to 93-85% water. The solutions are used for the treatment of metals in an amount of about 1000 cc. per each square meter of surface to be nitrophosphated, requiring about eight hours of working time. It is not sufficient industrially if the solution remains in good condition for 1-2 days, but it is indispensable that the solution remain effective for the production of phosphate layers on the metal in accordance with a standard for 30 or more consecutive or alternate work days. This was impossible prior to the present invention. However, according to the present invention the solutions remain effective over extended periods of time and even for 1000 days or more.

There are various methods of measuring the efliciency of nitrophosphating solutions which allow for the determination of the eificiency of the stabilizing action of the phosphoprotein added to the nitrophosphating solutions according to the present invention. One method of measurement is based upon the measurement of the total acidity of the solution when fresh and after a certain time period. According to this method the total acidity of the diluted solution is determined by a standard acidimetric measurement in accordance with which the solution is titrated with 0.1 N NaOH using phenolphthalein as an indicator. For example, cc. of the diluted solution are taken and 3 drops of phenolphthalien are added thereto. 0.1 N NaOH is then added until the color change of the phenolphthalien indicator. The number of cc. of NaOH required corresponds to the number of cc. of total acidity of the solution and is expressed as points of acidity. So, for example solution I diluted in a ratio of 7% concentrate to 93% water will have 45-46 points of total acidity and the same solution diluted in a ratio of concentrate to 85% water will have a total acidity of 92-94 points.

The following tests illustrate the stabilizing action of the phosphoproteins according to the present invention.

Test A A concentrate is prepared according to any one of Examples I, II, III or IV without the addition of the phosphoprotein thereto. The concentrate is diluted with water to form a 10% solution. The total acidity immediately after preparation is taken as 100%. After 48 hours it is found that the total acidity of the solution is between 92-95% of the original total acidity. After 10 days, heating the solution at 80 C. for 8 hours a day (a total of 80 hours of heating) the remaining total acidity is found to be 75-78% of the initial. The loss in total acidity is apparently due to the elimination of nitric acid.

Test B A concentrate is prepared as in Test A with the addition of a phosphoprotein such as milk, egg or plant albumin in an amount of 0.5% by weight of the concentrate. The'concentrate is diluted with water to form a 10% solution. The total acidity immediately after preparation is the same as in Test A and is taken as 100%. After 48 hours the solution is found to have no loss of total acidity, the total acidity still being at 100%. After 10 days, heating the solution at 80 C. for 8 hours a day (a total of 80 hours heating) the remaining total acid-ity'is found to be between 95-97% of the initial total acidity.

greases Here too, the loss of total acidity is due to the elimination of nitric acid. However, as may be seen, the phosphoprotein achieves a'profound stabilization of the solution.

Another method of determining the efficiency'of the nitrophosphating solution is based upon the number of square meters of metal that is coated by a specified quan tity of the solution.

In order for the phosphate layer on the surface of the metal resulting from treatments with the nitrophosphating solution to be satisfactory, it must meet certain requisites, as for example:

1. The thickness of the layer must be between 3-10 microns, the thinner the better;

2. The resistance to corrosion must be at least of the resistance achieved by the same layer'produced by a freshly prepared solution, namely on the first day of preparation.

3. The amount of iron must not be above a certain limit, and for example it should not exceed 1-2.5 g. per- 1000 cc. of solution.

The more closely the solutions correspond to requisites 1, 2 and 3 mentioned above, the better the quality of the phosphate layer produced. It is an accepted principle in this field that a freshly prepared nitrophosphate solution has the property of generating nitrophosphate layers of optimum quality but that the quality becomes progressively worse as the solution becomes older and is 75-80% of the initial efficiency after a few days and is only 20-25% of the initial efii-ciency after 1000 days. The progressive lessening of efficiency becomes more pronounced after the second day of use of the solution and is probably due to a series of secondary chemical reactions to which the solution is subjected, for example the following: v

a. Variation of the oxidimetric state which generally is constantly reduced as time passes. This is generally referred to as the RedOx potential;

b. Variation of the initial pH curve, the initial pH which may for example be between 2.1-3 depending upon the salt used and upon the relationship between the quantity of acid and the quantity of metals. The value fluctuates as the solution is used due to changes-in the pH and the relationship between the nitric acid and the phosphoric acid as well as between free acidity and total acidity and the increase of iron content in the: solution.

The addition of a phosphoprotein to the solution according to the present invention stabilizes both a and b above so that the solution retains its effectiveness for 1000 days or more and even after 1000 days the solution still maintains 80-85% of its initial effectiveness.

An additional means of determining the efiiciency-of the nitrophosphating solution which clearly establishes the stabilizing effect of the addition of the phosphoprotein to the solution is as follows: 1

Test C A salt concentrate is prepared according to any one of Examples 1, II, III and IV without any addition of phosphoprotein. The concentrate is diluted'with water the initial value. After the 10 days, the following checking determinations are made:

(1) The consumption of salt expressed as 'g./sq. m. is determined and for this solution is given an arbitrary value of 100.

(2) The protective value of the nitrophosphating layer obtained by this solution is determined from the 5th day on and for this solution is given the arbitrary value of This solution is used for the nitrophos-i arses-as A salt concentrate isyprepared as in TestC however with the addition of 1% of milk albumin. The concentrate is diluted in water in an amount such that the concentrate is of the final solution. This solution therefore the same as in Test C abovetexcept for the phosphoprotein content. This solution is used for the nitrophosphating of 1 square meter of a metallic surface for each 1000 cc. of solution for 8 hours a day during 10 days and with daily replenishment of the consumed salt to theinitial value. The following checkingdeterminations are made and compared to the values obtained utilizing the solutionsof Test C2,

(.1) The consumption of saltexpressed-es. g./sq..m. undetermined and compared with that of Test C: above. Compared to the arbitrary value of Test C the amount ofsaltis 60. It .is therefore aparent that by the addition of the phosphoprotein, .thejsame, amount of metal may be treated utilizing only slightly more than'one half the amount required. without the. phosphoprotein.

(2) T he protective value of the layeiaobtained, by this solution is determined from the 5th ,day on andcompared to that obtained in. Test C. .The value isfouhd to be 250 as compared to the arbitrary value of '100 from Test C. It may therefore be seen that .the protective layer obtained by the addition of phosphoprotein to the solution is about 2 /2 times that obtained without the phosphoprotein.

,While theinvention has been illustrated. and described as embodied in treatment ofmetals,.itis. not intended to be limited to the details shown, since various niodifica tions and structural changes maybe made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention. that others can by applying current knowledge readily adapt it for various applications without omittin'gifeatures that, from the standpoint of prior art, fairly constituteessential characteristics of the generic or specific aspects of this invention-and, therefore, such adaptations should .and are intended to be comprehended within-the meaningand range of equivalence of the followingclaims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A liquid salt composition adapted tobe diluted: with water in an amount such that said composition is between 1-20% by weight of the diluted solution which is adapted to be used for the treatment of metallic surfaces, said liquid salt composition essentially consisting ofat-least one metallic phosphate, at least one metallic nitrate, free phosphoric acid, free nitric acid and at least onephosphoprotein, said phosphoprotein being present in an amount less than the amount of said free acids and at least in an amount of 0.3% by Weight of said liquid salt composition, the totalacidity of said liquid salt composition being between 3-7 times the free acidity thereof.

2. A liquid s'alt'compositiorl adapted tobe'diluted' with water in an aniountfs'uch' that said composition, is be twee'r'i" 140% by weight of thediluted solution which is adapted to be used for" the treatment ofm'etallic. surfaces, said liquid salt composition essentially consisting of jat least one metallic phosphate, at least one metallic nitrate, free, phosphoric acid, free nitric-acidaa'nd at least ofn'e phosph'op'rotein, said phosphoprotein being present in an amount between 0.3-2.5 by ,weight of said liquid salt composition, the total acidityof saidliquid saltcomposition being between 3-7 times the free acidity thereof.

3. A liquid salt composition adapted to be diluted with water in an amount such that said composition is between l% by weight of the diluted solution which is adapted to be'used for the treatment of metallic surfaces, said liquid salt composition essentially consisting of3=l8 water by weight, at least one metallic phosphate, at least 8 one mastitis-aerate; fiee' phosphoric acid, free nitric acid and at least 'one phosphop'rotein,:said phosphoprotein being present-in an amount between 0.3-2.5 by weight of said liquid salt composition, the total; acidity of said liquid salt composition being between 3-7 times the free acidity thereof. w g

4. A liquid salt composition adapted to be diluted with water in an amount such that said composition is between l20% by weight of the diluted solution which is adapted to be used for the treatmentof metallic surfaces, said liquid salt compositioness entially consisting of 3-18% water by weight, at least one metallic phosphate, at least one metallic nitrate, free phosphoric acid, free nitric acid and at least one phosphoprot ein, said phosphoprotein being present'in an amount between 05-10% by weight of said liquid salt composition, the total acidity of said liquid salt composition being between 3-7 times the free acidity thereof. V

5. A liquid salt composition adapted to be diluted with water in an amount such that said composition is between l-20% by weight of the diluted solution which is adapted to be used for the treatment of metallicsurfaces, said liquid salt composition essentially consisting of at least one metallic phosphate, at least one metallic nitrate, free phosphoric acid," free nitric acid and at least one phosphoprotein selected from the group consistingof milk, egg and plant albumins, said phosphoprotein being present in an amount less than the amount of said free acids and at least in an amount of 0.3% by weight of said liquid salt composition, the total acidity of said liquid salt composition being between 3-7 timesthe free acidity thereof.

6. A liquid salt composition adapted to be diluted with water inan amount such that said composition is between l-20% by weight of the diluted solution which is adapted to be used for the treatment of metallic surfaces, said liquid salt composition essentially consisting of at least one metallic phosphate,- at least one metallic nitrate, free phosphoric acid, free nitric acid and at least one phosphoprotein selected from the group consisting of milk, egg

and plant albumins, saidphosphoprotein being'present in an amount between 0.3-'2.5% by weight of said liquid salt composition, the total acidity of said liquidsalt composition being between 3-7 times the free acidity thereof.

7. A liquid salt composition adapted to be diluted with water in an amount such that said composition is between l-20% by weight of the diluted solution which is adapted to be used for the treatment of metallic surfaces, said liquid salt composition essentially consisting of 31-8% water by weight, at least one metallic phosphate, at least one metallic nitrate, free phosphoric acid, free nitric acid andat least one phosphoprotein selected from the group consisting of milk, egg and-plant albumins, said phosphoprotein being present in an amount between 03-25% by weight of said liquid salt composition, the total acidity of said liquid salt composition being the free acidity thereof. i

8. A process of producing a liquid salt composition adapted to be dil ut ed' with water in an amount such that between 3-7 times said composition isgbetween 1-20% .by. weight of the diluted solution which is adapted to be used for the treatment of metallic surfaces, comprising the steps of mixing concentrated nitric acid with concentrated phosphoric acid in an amount such that said nitric acid is between 3/10 to equal the amount of said phosphoric acid; adding" apowde red phosphop'rotein to the thus formed mixture in a predetermined quantity adjusted to be between 03-25% by weight of the final composition; and dissolving inj'said mixture having said phosphoprotein added thereto atleastone metal selected from the group consisting of zinc, manganese, nickel and copper in an amount such that the. total acidity of the resulting mixture is between 3 7 times the free acidity thereof.

(References on '1 following page) References Cited in the file of this patent UNITED STATES PATENTS Williams Nov. 4, 1924 Gravell Aug. 11, 1925 5 Wallace Feb. 3, 1931 10 Darsey Aug. 25, 1942 Tanner et a1. Nov. 17, 1942 McBride Mar. 22, 1949 Shawcross Apr. 12, 1949

Claims (1)

1. A LIQUID SALT COMPOSITION ADAPTED TO BE DILUTED WITH WATER IN AN AMOUNT SUCH THAT SAID COMPOSITION IS BETWEEN 1-20% BY WEIGHT OF THE DILUTED SOLUTION WHICH IS ADAPTED TO BE USED FOR THE TREATMENT OF METALLIC SURFACES, SAID LIQUID SALT COMPOSITION ESSENTIALLY CONSISTING OF AT LEAST ONE METALLIC PHOSPHATE, AT LEAST ONE METALLIC NITRATE, FREE PHOSPHORIC ACCID, FREE NITRIC ACID AND AT LEAST ONE PHOSPHOPROTEIN, SAID PHOSPHORPROTEIN BEING PRESENT IN AN AMOUNT LESS THAN THE AMOUNT OF SAID FREE ACIDS AND AT LEAST IN AN AMOUNT OF 0.3% BY WEIGHT OF SAID LIQUID SALT COMPOSITION, THE TOTAL ACIDITY OF SAID LIQUID SALT COMPOSITION BEING BETWEEN 3-7 TIMES THE FREE ACIDITY THEREOF.