US2809138A - Bath solution and a process of treating metal surfaces - Google Patents

Description

2,809,138 Patented Oct. 8, 1957 ice BATH SOLUTION AND A PROCESS OF TREATING METAL SURFACES Ernst Wagner and August Moeller, Frankfurt am Main, Germany, assignors to Farbwerke Hoechst Aktiengeselb schaft vorrnals Meister Lucius & Briining, Frankfurt am Main, Germany, a corporation of Germany No Drawing. Application March 11, 1955, Serial No. 493,834

Claims priority, application Germany March 18, 1954 Claims. (Cl. 148--6.17)

The present invention relates to a bath solution and a process of treating metal surfaces.

It is known to be generally impossible to cover highalloy steels, for instance refined steels, by means of phosphatizing solutions with a layer of crystals intimately grown together. It has, therefore, already been proposed to use solutions of oxalic acid with addition of soluble, inorganic sulfides in order to obtain a well formed crystal layer facilitating the cold shaping of refined steels. Solutions of altered composition containing halogen ions, particularly chlorine ions, iron ions and sulfurous acid or oxalic acid have also been proposed already. Furthermore, in order to produce oxalate layers on refined steel containing 18% of chromium and 8% of nickel, solutions have been used which contain oxalic acid, ferric oxalate and bromide, ferric cyanide or thio-cyanide, the simultaneous use of sulfides, sulfites or thiosulfates also having been taken into consideration. Another known solution for preparing oxalate layers substantially consists of an oxygen containing sulfur compound developing sulfur dioxide under the conditions of the bath and a soluble alkali metal halide as activator. As oxygen containing sulfur compounds there are used, in this case, thiosulfate, hydrosulfite, tetrathionate or sulfite. When phosphate is added to the acid oxalate baths, the produced layers consist of oxalate and phosphate in varying composition.

It has proved a disadvantage of the known baths that the decomposition of the inorganic sulfur compounds takes place very rapidly, volatile compounds being split off, the partially contaminating effect of which, together with the annoyance caused by the disagreeable odor arising over the baths during the formation of the layers are extremely troublesome and require precautionary measures.

The common characteristic of all these substances is the production of a layer by means of inorganic sulfur compounds to which iron salts and halides are added in order to activate the surface of the refined steel.

Now, we have found a bath liquor for treating metal surfaces in order to produce surface layers, especially on low-alloy and higher alloy steels as well as on chromium-nickel alloys. When using this liquor, the disadvantages connected with the use of the known liquors are avoided. The bath liquor according to the invention has an acid degree corresponding to a pH range between about 1.0 and about 2.4 and contains, in aqueous solution, oxalic acid anions as well as organic sulfur compounds soluble in the bath liquor and characterized by the groups =C=S (thiourea (NH2)2=C=S); ECSH (thioglycolic acid HOOCH2C SH); i

of the oxalic acid can be produced in the bath liquor by.

adding oxalic acid or by using oxalates soluble in the acid bath liquor, especially alkali metal oxalates and ferric oxalates. Mixtures of various oxalates or mixtures of an oxalate with oxalic acid may likewise be used. The organic sulfur compounds characterized above may suitably be added to the solution in the form of the alkali metal compounds of such organic sulfur compounds. In particular, it is possible to operate with bath solutions which contain, either per se or in every desired mixture, the xanthates for instance methyl-, ethyl-, propyl-, butyl-, amylor hexyl-xanthate. Furthermore, solutions according to the inventioncan advantageously be used containing as organic sulfur compounds dithiophosphoric acid esters of the aliphatic or aromatic series. As a further example, solutions are mentioned which contain thiourea, eventually in mixture with other organic thio compounds of the aforementioned groups. Bath solutions containing thioglycolic acid can also be used.

The pH-value of the bath solutions can be adjusted in accordance with the amount of oxalic acid or in accordance with the added quantity of other acids, for instance also a corresponding quantity of sulfuric acid.

The bath solutions proposed according to the invention may, in addition, also contain P04 ions. There can, furthermore, also be present ions of heavy metals, for instance those of the trivalent iron and of manganese. The P04 ions can be produced by adding phosphoric acid and/or phosphates, especially phosphates of heavy metals. The bath solutions may, in addition, contain accelerators, for instance sodium sulfite, sodium bisulfite, alkali metal thiosulfate, alkali metal hydrosulfite, alkali metal thiocyanate.

The amount of oxalic acid and oxalates contained in the bath solution may vary within wide limits. They can, for instance, be present in such an amount that the oxalic acid anions contained in the bath solution amount to a quantity between about 0.5 gram and about grams per liter of bath solution. The quantity of organic sulfides proposed according to the invention may vary between about 0.025 gram and about 5 grams per liter.

When the solutions according to the invention are used for the treatment of metallic surfaces in order to produce surface layers, the operation at elevated temperature has proved advantageous, as it accelerates the development of the layer. Temperatures which have proved suitable range between about 20 C. and about 98 C. When proceeding in this way, the bath liquor proposed according to the invention and containing, in aqueous solution, oxalic acid anions and at least one of the afore-mentioned organic sulfur compounds and which, furthermore, has an acidity corresponding to a pH value between about 1.0 and about 2.4, is heated to a temperature within the afore-mentioned range, and the surface to be treated is contacted with this bath liquor by dipping it into the latter. If need be, it is also possible to vary the term perature during the treatment.

The temperature depends, to a large extent, upon the composition of the metal surfaces to be treated. For instance, low-alloy steels can be treated at temperatures of about 20 C. to about 60 C. and high-alloy steels at temperatures between about 60 C. and about 98 C. Of course, all other eventual additions proposed according to the invention can be added to the above mentioned bath solution which is cited as an example only, viz. phosphoric acid, phosphates, manganeseand ironions. The duration of the treatment when operating with the bath liquors proposed according to the invention is dependent, on the one hand, upon the shape and the composition of the metal surface to be covered with a layer, and, on the other hand, also upon the temperature of operation. The operation times generally coming into consideration vary between about 2 and about 40 minutes.

The bath solution is, for instance, prepared as follows: In a bath of 100 liters, 6 kilos of oxalic acid are dissolved, 3.1 liters of a solution are then added which contains 32.65% of primary manganese phosphate and 4.5% of phosphoric acid.

Finally, 0.2 kilo of a mixture consisting of 0.02 kilo of thio-urea and 0.18 kilo of sodium thiosulfate are added and the whole is well mixed. After heating the bath to 60 C.- 80 C. the refined steel par-ts are hung in and taken out of the bath when the reaction is finished, i. e. when no more gas is evolved. After rinsing, they are dried in a current of-hot air. If need be, they are dipped, before drying, into a neutral soap solution, then they are dried and submitted to cold shaping. The pH value of this bath solution is equal to l.

Solutions containing oxalic acid, oxalates, phosphoric acid and phosphates of heavy metals'as well as organic sulfur compounds as proposed according to the invention in quantities of about 0.025 gram up to grams perliter, are of particularly good use. These solutions are preferably suitable for the development of adhesive, tight coatings on refined steels. These coatings favour good deforming action. Such a bath solution, for instance, contains the following substances:

Crystallized oxalic acid in a quantity varying-between 1 gram to 200 grams per liter, preferably 40 grams to 60 grams, phosphoric acid or phosphates in aquantity varying between -2 grams and 35 grams per liter and calculated as P205, preferably 6 grams to 8.5 grams per liter, if desired iron in a quantity of 0.5 gram to '15 grams per liter, if desired manganese in a quantity of 0.05 gram to 3 grams per liter and organic sulfides as proposed by the invention in an amount between about 0.025 g. and about 5 grams per liter. The phosphates canbe added in the form of primary, secondary or tertiary alkali metal phosphates and'may, in this form, serve for'adjusting the pH value.

After the treatment, the coatings can be dried in the usual manner and then'also' be submitted to the cold tion are preferably used for the treatment of surfaces of iron, of alloy steels and unalloyed steels. However, they alsov allow the treatment of other metals or alloys, for

instance copper, zinc, aluminum, nickel and chromium. The metal surfaces can be in the form of sheets, Wires or in other shapes. 7

The. advantages ofrthe' bath solutions according to the invention especially consist in the factthat the organic sulfur compounds in solutions do not split off sulfur. Contrary to. inorganic sulfur compounds, their decomposition, and. therewith their use in the bath, takes place extraordinarily slowly, for instance when thiophosphates are used, and in many cases, forinstancein thecase of thiourea, it is not ascertainableat all. This means a much, reduced consumption of these substances in the bath.

Another advantage is'represented bythe fact that, when using some of the organic sulfur compounds proposedac cQrding-tothe invention, for instance 'thiourea, the annoyar ee causedby the disagreeable-odor above the-baths is. considerably reduced or even eliminated. According.-

to their chemical behavior it could not be expectedthat: theorganic sulfur compounds would develop the; same or, in several, cases, for instance, especially when thio;

phosphate is present, even a better efliciency than the inorganic sulfides. The esters of the thiophosphoric acid, which are suitably added to the baths in the form of alkali metal salts, as well as thiourea, remain as anions undecomposed on addition of an acid. Xanthic acid set free in acid solutions of alkali metal xanthates decomposes only after a certain time into the components, i. e. into carbon disulfide and alcohol. The decomposition takes place the more slowly, the longer the carbon chain is.

In the following examples sheets of refined steel of varying composition are treated with the bath solutions according to the invention. Previously, the sheets are freed from forge scales by pickling them in the usual acid pickling liquors. This preliminary treatment can also be eifected by means of alkaline pickling liquors or melts. According to Examples 1-12 the sheets of refined steel are dipped into a standard solution to which the substances mentioned for each case, according to the invention, are also added; in Examples 1353 variations in the composition of the standard solution are described which are within the above mentioned limits of the mixture. In each of the following Examples 1-12 the pH value of the bath solution amounts to about 1.

Example 1 A sheet of refined steel containing less than .15 of 0,03% of Si, 18.0% of Cr, 8.0% of Ni is dipped, for 10 minutes, into a solution of C.- C. This solution contains per liter 60 grams of crystallized oxalic acid, 3 grams of Mn, 9 grams of P205 and 0.25 gram of'potassium methylxanthate. A dark, crystallized layer is obtained. If instead of potassium methyl xanthate, the same quantity of potassium ethyl xanthate is used, while all other conditions remain the same, there is also obtained a dark, crystallized layer. When using solutions which, as an organic sulfide, contain per liter 0.25 gram of'potassium isopropylxanthate, dark gray crystallized layers are obtained. Solutions containing the same quantity of potassium butyl xanthate result under the same conditions in black-gray crystallized layers, whereas the use of solutions containing an equal quantity of potassium isobutyl xanthate as well as the use of an equal quantity of potassium amyl xanthate result in gray, crystallized layers. Light gray crystallized layers are obtained when. a solution according to the above characteristics is used which, instead of potassium methyl xanthate contains per liter 0.25 gram of potassium hexylxanthate and when the abovev mentioned operating conditions are maintained.

Example 2 A sheet of'refined steel containing less than 0.1% of C, 0.3% of Si and 18% of Cr is treated, at a temperature of 85 C., with a solution containing per liter 60 grams of crystallized oxalic acid, 3 grams of Mn, 9 grams of P205 as well as 0.25 gram of potassium hexylxanthate. The treatment is finished after 2 minutes. The sheet shows awell formed, uniform layer. When maintaining the same conditions, but working at a temperature of 60 C., the. treatment takes about 7' minutes.

Example 3 Example 4 A sheet of refined steel containing 18% of Cr and 8% of Ni is treated for 10-15 minutes at a temperature of 9,0. to, 95." C; withv a. solution containing'per' liter 60 gramsof'crystallized'oxalic acid, 3. grams-of Mn, 9 grams acce ed of P205 as well as 2 grams each of the following esters of the thiophosphoric acid: (a) Potassium salt of the diethyl ester, (b) Sodium salt of the dibutyl ester, (c) Potassium salt of the p-dicresyl ester, (d) Sodium salt of the diphenyl ester.

Well crystallized layers are obtained.

Example 5 A sheet of refined steel containing 18% of Cr is treated for 4 minutes at a temperature of 80 C. with a solution containing per liter 60 grams of crystallized oxalic acid, 3 grams of Mn, 9 grams of P205 as well as 2 grams of the potassium salt of the dibutyl ester of the dithiophosphoric acid. A light gray layer is developed.

Example 7 A sheet of refined steel containing 18% of Cr and 18% of Ni is treated for 3 minutes at a temperature of 80 C.

with a solution containing per liter 60 grams of crystal:

lized oxalic acid, 3 grams of Mn, 9 grams of P205 as well as 2 grams of the potassium salt of the dibutyl ester of thiophosphoric acid and 2 grams of sodium bisulfite. A well formed, gray, uniform layer is developed.

Example 8 A sheet of refined steel containing 18% of Cr and 8% of Ni is treated, for minutes, at a temperature of 90 C. to 95 C., with a solution containing per liter 60 grams of crystallized oxalic acid, 3 grams of Mn, 9 grams of P205 and 2 grams of thiourea. talline layer is developed.

Example 9 A sheet of refined steel containing 18% of Cr and 8% of Ni is treated, at a temperature of 60 C., with a solution containing per liter 60 grams of crystallized oxalic acid, 3 grams of Mn, 9 grams of P and 2 grams of thiourea as well as 3 grams of sodium bisulfite. After 3 minutes a uniform crystalline layer is obtained.

Example 10 A sheet of refined steel containing 18% of Cr, 10% of Ni and 2% of M0 is treated, for 10 minutes, at a temperature of 95 C., with a solution containing per liter 60 grams of crystallized oxalic acid, 3 grams of Mn, 9 grams of P205 as Well as 2 grams of thiourea and 3 grams of sodium bisulfite. The layer is uniformly crystalline Example 11 A sheet of refined steel containing 18% of Cr and 18% of Ni is treated, for 3-4 minutes, at a temperature of 60 C., with a solution containing per liter 60 grams of crystallized oxalic acid, 3 grams of Mn, 9 grams of P205 as well as 2 grams of thiourea and 0.2 gram of the potassium salt of the dibutyl ester of the thiophosphoric acid and 3 grams of sodium bisulfite. A uniform, dark layer is developed. When a temperature of 90 C. is applied, the reaction is already finished after 1 minute.

Example 12 A sheet of refined steel containing 18% of Cr and 8% of Ni is treated, for 3-4 minutes, at a temperature of 90 C., with a solution containing per liter 60 grams of crystallized oxalic acid, 3 grams of Mn, 9 grams of P205 as well as 2 grams of thioglycolic acid. A dark gray crystalline layer is obtained.

A thin, light gray crys-- 6 Examples 13-18 Additions to the bath per liter (vide table); chromiumnickel-steel containing 18% of Cr and 8% of Ni.

Examples oxalic Thiourea, sodium pH 1 acid, g. g. bisulfite, g.

NoTEs.-After about 5 minutes good development of the layer. Temperature: C. to 0.

Examples I9-31 Additions to the bath per liter (vide table); chromiumnickel-steel containing 18% of Cr and 8% of Ni.

Example oxalic P205, g. Thlourea,

acid, g.

sodium bisulfite, g.

t-nt-u- 9999995 95 999? NMMMMNNNNNNNN r vi w r-revi wer- OOOOOODOMOOOQDOOOWWMM r rr-z r-trr'r'm z- OQQOOQOOJCOQWQ No'rEs.After about 5 minutes good development of the layer; temperature: 90 0. to 95 0..

Examples 32-35 Additions to the bath per liter (vide table); chromium nickel-steel containing 18% of Cr and 8% of Ni.

Example oxalic P205, Fe thiourea, sodium pH acid, g. g. g g bisulfite, g.

No'rEs.-After about 5 minutes good development of the layer; temperature: 90 0. to 95 0.

Examples 36-38 Additions to the bath per liter (vide table); chromiumnickel-steel containing 18% of Cr and 8% of Ni.

Example oxalic, P205, Fe' thiourea, sodium pH acid, g. g. g g. bisulfite, g.

No'rEs.After about 5 minutes good development of the layer; temperature: 90 0. to 95 0.

Examples 39-46 Additions to the bath per liter (vide table); chromiumnickel-steel containing 18% of Cr and 8% of Ni.

oxalic P205, thiourea, sodium Example 8010., g. Mn, g g. bisulfite, pH

NOTES.AIlI8I' about 5 minutes good development of the layer; temperature: 90 0. to 95 0.

aseaias "I z ama es. .7751

, Additions to r ebath. p r iter. (videtabls).;chzemisa nickel-steelcontaining 18% of and of oxalic BzQr, ,Mn, Eef' thio sodium Example a oid, g. g, g, urea, bisuipH 200 6.6 2v 0.1a 0.2- 1.8 r 1 .0

perature: 90- O. to 95 0.

Ex mples. 52: 3

Addit on o. he-hath er i er iewabl chromiumel. ontain ng 8% o Cr. and. of N NOTESPAME bm S QJHQP 99 1.61164 91 3 9 3? 2 i -W 3. 5

Norms-After about 5' minutes good development of the layer;-te1n perature: 80C. to 85 Q We la m:

1. A bath liquor for treating metal; surfaces in order tg. prepare surface layers, said liquorconsisting essentiallyof an aqueous solution of oxalic acid; anions in an amount ranging from about 0.5, gram to. about 140. grams per liter, nd. an. am n ra g. rom about- 0.Q2 -.5 gram to about 5 grams per liter of at least one soluble'cofnpoundselected from the group consisting of xanthates, dithiophosphor c. ac d. e e s o the, lip a ic. ser s. di hiophq phoric ac e r of he roma ic. ie t iq lyq l c a id. and thiourea, said aqueous solution having an acidity corresponding to a pH value in the range from about 1.0 to about 2 .4.

2. A bath liquor as claimedin claim 1,.wl1erein said soluble compound isa xanthate.

3. A bath liquor; as cla med in claim 1, wherein said olubl compound is an organi este f. dimiq ho ph ric acid. a i

A bath q as cla medh 'Q ai l .whs' .ei a d soluble compound is hio lyeam acid.

A bath q or claimed n. laim 1, wherein. s id soluble compound is thiourea.

A bath q r asclia ued'ia cl im. .1 said liquo containing P04 ions.

7. A bath liquor as claimed in claim 1, said liquor containing ferric ions 1 8-. A ba h quor a cl med. in c aim I, sai liq oreo nin ions, of. m n anese;

A ba h. i uo as c aimed. in c a m. 1. sa d. iq o ont in ng, as n a ce erato a l a t subs an e e as e rom the group. con ist Qt so iumsulii e. iam. bi ii e. an alkal meta thib u at n. alkalime al hydrosulfite, and an alkali metal thiocyanate;

10. The process for the treatment of metal surfaces in order to prepare surface layers which comprises contacting-the metal surface at a temperature between about 20- C. and about 98* C. with a liquor consisting essen? tially of an aqueous solution of oxalic acid anions in an amount ranging from about 0.5 gram to about 140. grams per liter, and an amount rangingfrom about 0.025 gram to about 5 grams perliterof'at least one soluble com.- pound selected from the group, consisting of xanthates, dithiophosphoric acid esters o the aliphatic series, dithiophosphorie acid esters ofthe aromatic series, thioglycolic acid, and thiourea, said aqueous solution having an acidity corresponding to apH value in the range from about- 1.0; to about 2.4.

References Cited in. the file of this patent, UNITED STATES PATENTS

Claims (1)

1. A BATH LIQUOR FOR TREATING METAL SURFACES IN ORDER TO PREPARE SURFACE LAYERS, SAID LIQUOR CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF OXALIC ACID ANOINS IN AN AMOUNT RANGING FROM ABOUT 0.5 GRAM TO ABOUT 140 GRAMS PER LITER, AND AN AMOUNT RANGING FROM ABOUT 0.025 GRAM TO ABOUT 5 GRAMS PER LITER OF AT LEAST ONE SOLUBLE COMPOUND SELECTED FROM THE GROUP CONSISTING OF XANTHATES, DITHIOPHOSPHORIC ACID ESTERS OF THE ALIPHATIC SERIES, DITHIOPHOSPHORIC ACID ESTERS OF THE AROMATIC SERIES, THIOGLYCOLIC ACID, AND THIOUREA, SAID AQUEOUS SOLUTION HAVING AN ACIDITY CORRESPONDING TO A PH VALUE IN THE RANGE FROM ABOUT 1.0 TO ABOUT 2.4.