Composition for reducing the removal of material by pickling in the pickling of metal surfaces that contain galvanized and/or ungalvanized steel

Abstract

An aqueous composition for reducing corrosive removal of material in pickling of metallic surfaces comprising bare and/or galvanized steel. The composition includes a mixture of a compound of the formula R.sup.1O—(CH.sub.2).sub.x—C≡C—(CH.sub.2).sub.y—OR.sup.2 in which R.sup.1 and R.sup.2 are both H, and a compound of the formula R.sup.1O—(CH.sub.2).sub.x—C≡C—(CH.sub.2).sub.y—OR.sup.2 in which R.sup.1 and R.sup.2 are each, independently of one another, an HO—(CH.sub.2).sub.w— group with w≥2. X and y are each, independently of one another, from 1 to 4 in each of the two compounds of the formula R.sup.1O—(CH.sub.2).sub.x—C≡C—(CH.sub.2).sub.y—OR.sup.2. A process for pickling a metallic surface with reduced corrosive removal of material is disclosed.

Claims

1. An aqueous composition for reducing corrosive removal of material in pickling of metallic surfaces comprising bare and/or galvanized steel, wherein the composition comprises a mixture of a compound of formula I
R.sup.1O—(CH.sub.2).sub.x—C≡C—(CH.sub.2).sub.y—OR.sup.2  (I), in which R.sup.1 and R.sup.2 are both H and a compound of the formula I in which R.sup.1 and R.sup.2 are each, independently of one another, an HO—(CH.sub.2).sub.w— group with w≥2, wherein x and y are each, independently of one another, from 1 to 4 in each of the two compounds of the formula I, wherein a mixing ratio in % by weight of the compound of the formula I in which R.sup.1 and R.sup.2 are both H and the compound of the formula I in which R.sup.1 and R.sup.2 are each, independently of one another an HO—(CH.sub.2).sub.w— group with w≥2 is in a range from 0.5:1 to 2:1 (calculated as 2-butyne-1,4-diol and 2-butyne-1,4-diol bis(2-hydroxyethyl) ether), wherein the composition additionally comprises at least one compound of formula II
R.sup.1O—(CH.sub.2).sub.x—S—(CH.sub.2).sub.y—OR.sup.2  (II), in which R.sup.1 and R.sup.2 are each, independently of one another, an HO—(CH.sub.2).sub.w— grows with w≥2 and x and y are each, independently of one another, from 1 to 4.

2. The composition according to claim 1, wherein a sum of x and y is from 2 to 5 in each of the two compounds of the formula I.

3. The composition according to claim 2, wherein the composition comprises a mixture of 2 butyne-1,4-diol and 2-butyne-1,4-diol bis(2-hydroxyethyl) ether.

4. A concentrate from which a composition according to claim 1 is obtainable by dilution with a suitable solvent and/or dispersion medium and optionally a pH adjustment.

5. A process for pickling a metallic surface comprising bare and/or galvanized steel, wherein the surface is, in successive process steps i) optionally cleaned and/or rinsed, ii) brought into contact with an aqueous pickling composition and iii) brought into contact with an aqueous rinsing composition, where the pickling composition in step ii) and/or the rinsing composition in step iii) is a composition according to claim 1.

6. The process according to claim 5, wherein the pickling composition in step ii) is a composition comprising a mixture of a compound of formula I
R.sup.1O—(CH.sub.2).sub.x—C≡C—(CH.sub.2).sub.y—OR.sup.2  (I), in which R.sup.1 and R.sup.2 are both H and a compound of the formula I in which R.sup.1 and R.sup.2 are each, independently of one another, an HO—(CH.sub.2).sub.w— group with w≥2, where x and y are each, independently of one another, from 1 to 4 in each of the two compounds of the formula I, wherein a mixing ratio in % by weight of the compound of the formula I in which R.sup.1 and R.sup.2 are both H and the compound of the formula I in which R.sup.1 and R.sup.2 are each, independently of one another an HO—(CH.sub.2).sub.w— group with w≥2 is in a range from 0.5:1 to 2:1 (calculated as 2-butyne-1,4-diol and 2-butyne-1,4-diol bis(2-hydroxyethyl) ether), wherein the composition additionally comprises at least one compound of formula II
R.sup.1O—(CH.sub.2).sub.x—S—(CH.sub.2).sub.y—OR.sup.2  (II), in which R.sup.1 and R.sup.2 are each, independently of one another, an HO—(CH.sub.2).sub.w— group with w≥2 and x and y are each, independently of one another, from 1 to 4.

7. The process according to claim 6, wherein a total concentration of the two compounds of the formula I is in a range from 31 to 620 mg/l (calculated as 2-butyne-1,4-diol).

8. The process according to claim 5, wherein the rinsing composition in step iii) is a composition comprising a mixture of a compound of formula I
R.sup.1O—(CH.sub.2).sub.x—C≡C—(CH.sub.2).sub.y—OR.sup.2  (I), in which R.sup.1 and R.sup.2 are both H and a compound of the formula I in which R.sup.1 and R.sup.2 are each, independently of one another, an HO—(CH.sub.2).sub.w— group with w≥2, where x and y are each, independently of one another, from 1 to 4 in each of the two compounds of the formula I, wherein a mixing ratio in % by weight of the compound of the formula I in which R.sup.1 and R.sup.2 are both H and the compound of the formula I in which R.sup.1 and R.sup.2 are each, independently of one another an HO—(CH.sub.2).sub.w— group with w≥2 is in a range from 0.5:1 to 2:1 (calculated as 2-butyne-1,4-diol and 2-butyne-1,4-diol bis(2-hydroxyethyl) ether), wherein the composition additionally comprises at least one compound of formula II
R.sup.1O—(CH.sub.2).sub.x—S—(CH.sub.2).sub.y—OR.sup.2  (II), in which R.sup.1 and R.sup.2 are each, independently of one another, an HO—(CH.sub.2).sub.w— group with w≥2 and x and y are each, independently of one another, from 1 to 4.

9. The process according to claim 8, wherein a total concentration of the two compounds of the formula I is in a range from 3 to 62 mg/l (calculated as 2-butyne-1,4-diol).

10. The process according to claim 8, wherein the pickling composition in step ii) comprises sulfuric acid.

11. The process according to claim 5, wherein a pH of the rinsing composition in step iii) is in a range from 2 to 8.

12. The use of a metallic surface pickled by means of the process according to claim 5 in a field of treatment of parts.

13. The composition according to claim 1, wherein the mixing ratio in % by weight of the compound of the formula I in which R.sup.1 and R.sup.2 are both H and the compound of the formula I in which R.sup.1 and R.sup.2 are each, independently of one another an HO—(CH.sub.2).sub.w— group with w≥2 is in a range from 0.75:1 to 1.75:1 (calculated as 2-butyne-1,4-diol and 2-butyne-1,4-diol bis(2-hydroxyethyl) ether).

14. The composition according to claim 13, wherein the mixing ratio in % by weight of the compound of the formula I in which R.sup.1 and R.sup.2 are both H and the compound of the formula I in which R.sup.1 and R.sup.2 are each, independently of one another an HO—(CH.sub.2).sub.w— group with w≥2 is in a range from 1:1 to 1.5:1 (calculated as 2-butyne-1,4-diol and 2-butyne-1,4-diol bis(2-hydroxyethyl) ether).

15. The process according to claim 7, wherein the total concentration of the two compounds of the formula I is in a range from 31 to 310 mg/l (calculated as 2-butyne-1,4-diol).

16. The process according to claim 9, wherein the total concentration of the two compounds of the formula I is in a range from 3 to 31 mg/l (calculated as 2-butyne-1,4-diol).

Description

EXAMPLES

(1) Aqueous pickling solutions A to E each comprising 20% by weight of H.sub.2SO.sub.4, 50 g/l of Fe.sup.2+ and optionally one or two corrosion inhibitors were made up.

(2) The composition of the solutions is shown in Tab. 1 below:

(3) TABLE-US-00001 TABLE 1 Pickling Content of corrosion solution Corrosion inhibitor(s) inhibitor(s) A — — B N,N′-diethylthiourea 150 mg/l C N,N′-di(o-toly)thiourea + total of 100 mg/l N,N′-dibutylthiourea + hexamethylenetetraamine D but-2-yne-1,4-diol 100 mg/l E 2-butyne-1,4-diol  50 mg/l bis(2-hydroxyethyl) ether F but-2-yne-1,4-diol + 50 mg/l and 25 mg/l 2-butyne-1,4-diol bis(2-hydroxyethyl) ether)

(4) Test plates made of CRS (cold-rolled steel) were in each case weighed before treatment with one of the pickling solutions.

(5) Three plates in each case were then immersed for 5 minutes in a bath comprising one of the pickling solutions B to F (with corrosion inhibitor(s)) and one plate was immersed for the same time in a bath comprising pickling solution A (without corrosion inhibitor). The baths had a temperature of 60° C. The plates were rotated at a speed of 400 rpm.

(6) All plates were subsequently rinsed with deionized water, dried and weighed. The weight loss caused by the treatment with pickling solution in each case represents the corrosive removal of material.

(7) For each of the sets of three plates which had been treated with one of the pickling solutions B to F, the average of the corrosive removal of material was in each case calculated and this was divided by the value for the one plate treated with pickling solution A. The result in percent was subtracted from 100 percent and the respective inhibition index of the corrosion inhibitors(s) was thus determined (see Tab. 2 below).

(8) TABLE-US-00002 TABLE 2 Pickling solution Inhibition index A  0% B 96% C 96% D 85% E 92% F 97%

(9) The corrosion inhibitors of the pickling solutions B and C, which are to be avoided from both toxicological and environmental points of view, thus each displayed an excellent inhibition index of 96%. The inhibition indices of the individual inhibitors but-2-yne-1,4-diol (pickling solution D) and 2-butyne-1,4-diol bis(2-hydroxyethyl) ether (pickling solution E) remain significantly behind at 85% and 92%, respectively. The inhibition index of the mixture according to the invention of the two latter corrosion inhibitors (pickling solution F) was, however, surprisingly high at 97% and was even superior to the abovementioned corrosion inhibitors which are to be avoided.

(10) The plates were then additionally zinc phosphated. The pickling solutions B and F were added in increasing amounts to the phosphating bath. The appearance of the plates was firstly evaluated. Secondly, the layer weight in g/m.sup.2 calculated as P.sub.2O.sub.5 were determined by means of XRF analysis.

(11) The results for the pickling solutions B according to the prior art, comprising various amounts of N,N′-diethylthiourea, are reported in Tab. 3 and those for the pickling solutions F according to the invention, comprising various amounts of the mixture of but-2-yne-1,4-diol and 2-butyne-1,4-diol bis(2-hydroxyethyl) ether, are reported in Tab. 4.

(12) TABLE-US-00003 TABLE 3 Appearance of the plates Layer weight Content of (school grades of in g/m.sup.2 corrosion 1 = very good to (calculated inhibitor 6 = unsatisfactory) as P.sub.2O.sub.5) — 1 2.864  10 mg/l 5 2.272  25 mg/l  6+ 0.320 100 mg/l 6 0.144 200 mg/l 6 0.192

(13) TABLE-US-00004 TABLE 4 Appearance of the plates Layer weight Content of (school grades of in g/m.sup.2 corrosion 1 = very good to (calculated inhibitors 6 = unsatisfactory) as P.sub.2O.sub.5) — 1 3.264 25 and 12.5 mg/l 2 3.264 50 and 25 mg/l  2− 3.264 100 and 50 mg/l 4-5 3.008

(14) It can thus clearly be seen from Tab. 3 that a dramatic decrease in the layer thickness and thus an ever more unsatisfactory formation of the phosphate layer occurs on steel with an increasing content of N,N′-diethylthiourea.

(15) As can be seen from Tab. 4, only a significantly higher content of but-2-yne-1,4-diol and 2-butyne-1,4-diol bis(2-hydroxyethyl) ether has, in comparison, a significant adverse effect on the layer formation.

(16) Accordingly, the mixture of the invention not only reduces the corrosive removal of material but also leads to no interference in the layer formation, for example as a result of carrying-over of the pickling solution, in a subsequent phosphating step.