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(11) | EP 1 266 981 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 158(3) EPC |
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| (54) | ANTICORROSIVE AGENT FOR STAINLESS STEEL AND METHOD OF ANTICORROSIVE TREATMENT OF STAINLESS STEEL |
(57) An anticorrosive agent for a stainless steel surface comprising a hydroxylamine salt;
a method of anticorrosive treatment of a stainless steel surface which comprises contacting
the stainless steel surface with an aqueous solution of a hydroxylamine salt and heating
it. The method can be employed for significantly improving the corrosion resistance
of stainless steel under severe circumstances.
[Technical Field]
[0001] The present invention relates to an anticorrosive agent for a surface of a stainless steel article and an anticorrosive treatment using the same. Particularly, the invention relates to an anticorrosive agent for a surface of a stainless steel article and an anticorrosive treatment using the same which are effectively utilizable under severe conditions.
[0002] It is known that a surface of metal article can be converted to have a corrosion-resistant coating or increased corrosion resistance by treating the surface with an inorganic or organic corrosion inhibitor.
[0003] It is known that among metals a stainless steel containing chromium shows high resistance to corrosion. However, even such stainless steel is gradually corroded on its surface when it is kept under strong acidic or alkaline condition, or when it is placed under weak acidic or alkaline condition for a long period of time. The corrosion causes damage of the stainless steel. Further, if stainless steel is employed as material for making a reaction vessel (to be used for performing chemical reaction) or storage vessel, the corrosion products migrate into the material in the vessel as impurities.
[0004] A hydroxylamine salt (NH2OH·A, in which A is an acid such as H2SO4, H3PO4, or HCl) can be prepared, for example, by reacting sodium hydrogensulfite and sodium nitrate in an aqueous solution to obtain an aqueous sodium hydroxylamine disulfonate solution, and hydrolyzing the sodium hydroxylamine disulfonate. The hydroxylamine salt is stable in the solid form or in an aqueous solution. The hydroxylamine salt per se is generally employed as a starting material in chemical reactions. It is also used for leaving or preparing a highly chemically unstable free hydroxylamine which is of value as a chemical compound or for processing or washing electronic materials, when it is required.
[0005] As an anticorrosive treatment of iron or the like, there is known a phosphate treatment which is performed by treating a metal surface with an aqueous acidic phosphate solution. For instance, United States Patents No. 4,149,909, No. 4,865,653, and No. 5,597,465; Published EP Applications No. 0 695 817 A1 and No. 0 315 059 A1; WO 93/03198; and WO 93/20259 teach that a metal such as iron or zinc can be made to have improved corrosion resistance by placing the metal in contact with an aqueous iron phosphate or zinc phosphate solution, respectively, and forming on the metal surface a phosphate coat and that the formation of phosphate coat is enhanced by addition of several weight % of a hydroxylamine salt such as hydroxylamine sulfate into the aqueous phosphate solution.
[0006] The present invention provides an anticorrosive agent and an anticorrosive treating method which are effective to enhance corrosive resistance of stainless steel under severe conditions.
[Disclosure of Invention]
[0007] The present inventors have studied for discovering an anticorrosive agent and anticorrosive treating method which does not cause corrosion of stainless steel under severe acidic or alkaline conditions for long period of time. As a result, they have discovered that a surface of stainless steel is converted into a highly anticorrosive surface when it is heated in an aqueous hydroxylamine solution. The present invention has been made upon the discovery.
[0008] The present invention resides in an anticorrosive agent for stainless steel surface which comprises a hydroxylamine salt.
[0009] The invention further resides in a method for anti-corrosive treatment which comprises heating a stainless steel surface to a temperature of 50°C or higher in contact with the above-mentioned hydroxylamine salt anticorrosive agent.
[0010] Preferred embodiments of the hydroxylamine salt anticorrosive agent for stainless steel surface according to the invention are described below.
(1) The hydroxylamine salt is hydroxylamine sulfate or hydroxylamine phosphate.
(2) The anticorrosive agent comprising 0.2 to 50 wt.% of a hydroxylamine salt.
[Preferred Embodiments for Performing Invention]
[0011] The hydroxylamine salt anticorrosive agent of the invention generally is in the form of an aqueous solution. The concentration is in the range of 0.2 to 50 wt.%, preferably in the range of 5 to 20 wt.%. Examples of the hydroxylamine salts include hydroxylamine sulfate, hydroxylamine phosphate, and hydroxylamine hydrochloride. Particularly preferred are hydroxylamine sulfate and hydroxylamine phosphate. These hydroxylamine salts can be prepared by known methods, as described hereinbefore.
[0012] In the method, an article of stainless steel can be prevented from corrosion by keeping the article in contact with a heated aqueous solution of a hydroxylamine salt. The aqueous hydroxylamine salt solution is preferably heated to a temperature of 50°C or higher. If the article of stainless steel is kept into contact with an heated hydroxylamine salt solution in an pressure-resistant reaction vessel such as an autoclave, the temperature can be 100°C or higher. Generally, the temperature is kept in the range of 60 to 160°C. The stainless steel article is kept in contact with the heated hydroxylamine salt solution, preferably for a period of 3 minutes or longer, more preferably 1 to 20 hours.
[0013] There are no limitations with respect to stainless steel which can be treated by the method of the invention. But, the method of the present invention is preferably applied to anticorrosive treatment of stainless steel containing chromium element and nickel element.
[0014] The anticorrosive treatment of the invention can effectively prevent corrosion of stainless steel under severe conditions and obviate migration of impurities of corrosion products. For instance, if a distillation apparatus made of stainless steel (employed for obtaining an aqueous hydroxylamine solution of increased purity, which is of value for preparing pharmaceutically active compound or of value as a detergent for washing electronic parts) is previously treated by the above-mentioned anticorrosive treatment, the corrosion of the apparatus by the highly corrosive hydroxylamine is effectively obviated, and migration of the impurities from the apparatus is effectively avoided.
[Example 1]
[0015] In a glass-made flask equipped with a reflux condenser, an aqueous hydroxylamine phosphate solution (concentration: 20 wt.%) was placed. A specimen of stainless steel having the below-mentioned alloy composition was placed in the aqueous hydroxylamine phosphate solution.
[0016] The flask was then placed on an oil bath heated to approx. 100°C, for 8 hours or 24 hours, for performing anti-corrosive treatment.
(1) SUS 304L Stainless steel (composition: Fe approx. 73%, Ni approx. 9%, Cr approx. 18%)
(2) SUS 316L Stainless steel (composition: Fe approx. 70%, Ni approx. 12%, Cr approx. 16%, Mo approx. 2%)
(3) SUS 310S Stainless steel (composition: Fe approx. 57%, Ni approx. 19%, Cr approx. 24%)
[0017] Thus treated specimen was weighed, and placed in an aqueous 10 wt.% sulfuric acid solution in a heat-resistant glass bottle. The glass bottle was placed in a thermostat heated to 80°C and kept for certain periods. Then, the glass bottle was taken out from the thermostat. The specimen was recovered from the sulfuric acid solution, washed with water, dried, and weighed. Both weights were compared for determining weight loss which was caused by corrosion of the stainless steel specimen.
[0018] For comparison, the equivalent stainless steel specimen having no corrosion-inhibiting treatment was subjected to the above-mentioned test for evaluating the resistance in the sulfuric acid solution.
[0019] The results are set forth in Tables 1 to 3.
Table 1
| (for SUS 304L) | |||
| Time (hr.) in aq. H2SO4 | Specimen of 8 hrs. treatment (weight g) | Specimen of 24 hrs. treatment (weight g) | Specimen of no treatment (weight g) |
| 0 | 16.4526 | 17.9558 | 18.5543 |
| 1 | -- | -- | 18.2378 |
| 24 | 16.4523 | 17.9557 | -- |
| 44 | 16.4521 | 17.9556 | -- |
| 68 | 16.4518 | 17.9554 | -- |
| 116 | 16.4517 | 17.9553 | -- |
| 164 | 16.4513 | 17.9548 | -- |
| 188 | 16.4513 | 17.9548 | -- |
| 236 | 16.4514 | 17.9554 | -- |
| 284 | 16.4516 | 17.9554 | -- |
| 380 | -- | 17.9546 | -- |
| 529 | -- | 17.9544 | -- |
Table 2
| (for SUS 316L) | ||
| Time (hr.) in aq. H2SO4 | Specimen of 8 hrs. treatment (weight g) | Specimen of no treatment (weight g) |
| 0 | 18.2641 | 18.2103 |
| 24 | 18.1244 | 17.6733 |
| 44 | 18.0132 | -- |
Table 3
| (for SUS 310S) | ||
| Time (hr.) in aq. H2SO4 | Specimen of 8 hrs. treatment (weight g) | Specimen of no treatment (weight g) |
| 0 | 17.3690 | 17.5489 |
| 1 | -- | 17.4191 |
| 8 | 17.3690 | -- |
| 23 | 17.3686 | -- |
| 47 | 17.3687 | -- |
| 71 | 17.3685 | -- |
| 95 | 17.3688 | -- |
| 119 | 17.3686 | -- |
| 161 | 17.3684 | -- |
| 209 | 17.3683 | -- |
| 281 | 17.3685 | -- |
| 329 | 17.3681 | -- |
| 455 | 17.3679 | -- |
[Example 2]
[0020] The procedures of Example 1 were repeated except for replacing the aqueous hydroxylamine phosphate solution with an aqueous hydroxylamine sulfate solution (concentration: 20 wt.%).
[0021] In the corrosion resistance-enhancing treatment, the treatment was additionally performed for 8 hours, 24 hours, or 72 hours.
[0022] The specimens having been subjected to anticorrosive treatment were examined in their anticorrosive performance in the same manner as in Example 1. The results are set forth in Tables 4 to 6.
Table 4
| (for SUS 304L) | ||
| Time (hr.) in aq. H2SO4 | Specimen of 8 hrs. treatment (weight g) | Specimen of no treatment (weight g) |
| 0 | 15.5943 | 18.5543 |
| 1 | -- | 18.2378 |
| 24 | 15.5944 | -- |
| 44 | 15.5940 | -- |
| 68 | 15.5937 | -- |
| 116 | 15.5935 | -- |
| 164 | 15.5931 | -- |
| 188 | 15.5931 | -- |
| 236 | 15.5935 | -- |
| 284 | 15.5937 | -- |
| 380 | 15.5930 | -- |
| 529 | 15.5929 | -- |
Table 5
| (for SUS 316L) | ||
| Time (hr.) in aq. H2SO4 | Specimen of 8 hrs. treatment (weight g) | Specimen of no treatment (weight g) |
| 0 | 18.2045 | 18.2103 |
| 24 | 18.0672 | 17.6733 |
| 44 | 17.9577 | -- |
Table 6-1
| (for SUS 310S) | ||
| Time (hr.) in aq. H2SO4 | Specimen of 8 hrs. treatment (weight g) | Specimen of no treatment (weight g) |
| 0 | 17.7900 | 17.5489 |
| 1 | -- | 17.4191 |
| 8 | 17.7901 | -- |
| 24 | 17.7897 | -- |
| 47 | 17.7897 | -- |
| 71 | 17.7895 | -- |
| 95 | 17.7898 | -- |
| 119 | 17.7896 | -- |
| 167 | 17.7892 | -- |
| 215 | 17.7894 | -- |
| 287 | 17.7895 | -- |
| 335 | 17.7888 | -- |
| 455 | 17.7889 | -- |
| 628 | 17.7887 | -- |
Table 6-2
| (for SUS 310S) | ||
| Time (hr.) in aq. H2SO4 | Specimen of 24 hrs. treatment (weight g) | Specimen of no treatment (weight g) |
| 0 | 17.9786 | 17.5489 |
| 1 | -- | 17.4191 |
| 24 | 17.9787 | -- |
| 44 | 17.9788 | -- |
| 68 | 17.9785 | -- |
| 116 | 17.9782 | -- |
| 164 | 17.9784 | -- |
| 236 | 17.9784 | -- |
| 284 | 17.9779 | -- |
| 335 | 17.9777 | -- |
Table 6-3
| (for SUS 310S) | ||
| Time (hr.) in aq. H2SO4 | Specimen of 72 hrs. treatment (weight g) | Specimen of no treatment (weight g) |
| 0 | 17.5712 | 17.5489 |
| 1 | -- | 17.4191 |
| 19 | 17.5713 | -- |
| 67 | 17.5710 | -- |
| 115 | 17.5711 | -- |
| 187 | 17.5711 | -- |
| 235 | 17.5707 | -- |
| 355 | 17.5707 | -- |
| 528 | 17.5706 | -- |
[Example 3]
[0023] In an autoclave, an aqueous hydroxylamine sulfate solution (concentration: 20 wt.%) was placed. A specimen of stainless steel (3) described in Example 1 was placed in the autoclave.
[0024] The autoclave was then placed on an oil bath heated to approx. 160°C, for 3 hours, for performing anti-corrosive treatment of the specimen.
[0025] The specimen was then placed in the aqueous sulfuric acid solution in the manner described in Example 1, to examine the corrosion resistance of thus treated specimen. The results are set forth in Table 7.
Table 7
| (for SUS 310S) | ||
| Time (hr.) in aq. H2SO4 | Specimen of 3 hrs. treatment (weight g) | Specimen of no treatment (weight g) |
| 0 | 17.1045 | 17.5489 |
| 1 | -- | 17.4191 |
| 124 | 17.1041 | -- |
[Example 4]
[0026] In an autoclave, an aqueous hydroxylamine sulfate solution (concentration: 5 wt.%) was placed. A specimen of stainless steel (1) or (3) described in Example 1 was placed in the autoclave.
[0027] The autoclave was then placed on an oil bath heated to approx. 160°C, for 8 hours, for performing anti-corrosive treatment of the specimen.
[0028] The specimen was then placed in the aqueous sulfuric acid solution in the manner described in Example 1, to examine the corrosion resistance of thus treated specimen. The results are set forth in Tables 8 to 9.
Table 8
| (for SUS 304L) | ||
| Time (hr.) in aq. H2SO4 | Specimen of 8 hrs. treatment (weight g) | Specimen of no treatment (weight g) |
| 0 | 17.9588 | 18.5543 |
| 1 | -- | 18.2378 |
| 124 | 17.9583 | -- |
Table 9
| (for SUS 310S) | ||
| Time (hr.) in aq. H2SO4 | Specimen of 8 hrs. treatment (weight g) | Specimen of no treatment (weight g) |
| 0 | 35.5074 | 17.5489 |
| 1 | -- | 17.4191 |
| 124 | 35.5066 | -- |
[0029] As is apparent from the results shown in Tables 1 to 9, the specimens of stainless steel having been treated with an aqueous hydroxylamine salt solution according to the present invention keep their weights even after they are placed in a heated aqueous sulfuric acid solution for several ten hours or several hundred hours. In contrast, the equivalent specimens of stainless steel having been subjected to no anti-corrosive treatment loss their weights within one to 24 hrs. In the aqueous sulfuric acid solution, the untreated specimens show blacken surface or give bubble formation within a short period of time.
[0030] Accordingly, it is clear that the anticorrosive agent and anticorrosive treatment of the invention are effective for keeping stainless steel from corrosion.
[Industrial Utility]
[0031] The anticorrosive agent of the invention which comprises a hydroxylamine salt is of value to prominently enhance resistance to corrosion of stainless steel, particularly chromium-containing stainless steel. Further, the method of anticorrosive treatment according to the invention keeps stainless steel placed under severe conditions such as acidic or alkaline conditions for a long period of time from corrosion. This means that migration of impurities of corrosion products and their contamination is effectively avoided.
1. An anticorrosive agent for stainless steel surface which comprises a hydroxylamine
salt.
2. The anticorrosive agent of claim 1, in which the hydroxylamine salt is hydroxylamine
sulfate or hydroxylamine phosphate.
3. The anticorrosive agent for stainless steel surface which comprises an aqueous solution
of 0.2 to 50 weight % of a hydroxylamine salt.
4. A method of anticorrosive treatment of stainless steel surface which comprises heating
the stainless steel surface to a temperature of 50°C or higher in contact with the
anticorrosive agent of any one of claims 1 to 3.
5. The method of anticorrosive treatment of stainless steel surface, in which the heating
is performed at 50 to 200°C.