RU2324766C2 - Corrosion metal inhibitor in dipping, chlorohydric and ortho - phosphoric acids - Google Patents

Abstract

FIELD: FIELD inorganic chemistry.

SUBSTANCE: invention refers to metal protection from oxygen corrosion by inhibitors. Inhibitor has the ratio, mass%: m-niterobensal - p-iodoaniline 14.8-17.9; 4.5 dichlor-2-threeflouromethylbenzimidazole 33.3-23.9; urotropine51.9-58.2. The technical result: inhibitor effectively protect from corrosion the steel, aluminium and titanium in dipping, chlorohydric and ortho-phosporic acids, don't let developing to hydrogen charging of the steel, besides inhibitor can be used for etching operation of steel, aluminium and titanium, and also for acid treatment of the devices of the mentioned metals.

EFFECT: it is achieved inhibitor for steel protection in acids and for etching operation of steel.

2 tbl, 3 ex

Description

The invention relates to the protection of metals from corrosion in acids by introducing inhibitors into the latter, and can be used for pickling steel, titanium and aluminum in mechanical engineering, as well as for acid cleaning of equipment from these metals.

The use of urotropin as an inhibitor of acid corrosion of steel is known. However, the protective effect of urotropine is not effective enough for steel and especially for titanium and aluminum. The disadvantage of urotropin is its high concentration, reaching 2% (Altsybeeva A.I., Levin SZ "Metal corrosion inhibitors". - L .: Chemistry, 1968, P.28-29).

The closest to the proposed solution in terms of technical nature and the result obtained is a well-known inhibitor - a condensation product of capric aldehyde and aniline (V.G. Turbina and N.G. Klyuchnikov "Protection of steel from corrosion of hydrochloric acid condensation products of amines and aldehydes", collection of articles "Metal Corrosion Inhibitors", Central Research Institute of Shipbuilding Technology, ed. Sudostroenie, 1965, p.124-129). A known inhibitor protects steel from corrosion better than urotropin. But even in this case, the corrosion protection is not large enough, amounting to 92.07 in terms of protection; 95.50 and 97.29%, respectively, in 3.5 and 7 normal hydrochloric acid solutions. For titanium and aluminum, the degree of protection is much lower. In addition, the inhibitor is not effective in the hydrogenation of steel.

The technical task is to develop an effective acid corrosion inhibitor not only for steel, but also for titanium and aluminum, which provides more reliable corrosion protection for the three metals and hydrogen resistance for steel.

The overall technical result is an increase in the effectiveness of the inhibitor due to the joint enhancement (synergism) of the protective effect of the mixture of components.

To achieve the technical result, a corrosion inhibitor of metals in sulfuric, hydrochloric and phosphoric acids is proposed based on the condensation product of an amine with an aldehyde, which is used as m-nitrobenzal-n-iodaniline, which additionally contains 4,5-dichloro-2-trifluoromethylbenzimidazole and urotropin.

Below are the structures of the inhibitor components

m-nitrobenzal-n-iodaniline

4,5-dichloro-2-trifluoromethylbenzimidazole

These components are part of the inhibitor in the following concentrations, wt.%:

m-nitrobenzal-n-iodaniline 14.8-17.9 4,5-dichloro-2-trifluoromethylbenzimidazole 33.3-23.9 urotropin 51.9-58.2

For the convenience of introducing the inhibitor into the solutions of the above acids, its composition is given, expressed in grams per liter, and the same sequence of components is preserved: 0.4-1.2, 1.6-0.9, 1.4-3.9.

Thus, the total concentration of inhibitor in g / l is 3.4 -5.9. An increase in concentration in excess of 5.9 g / l is impractical, since it does not practically lead to an increase in the effectiveness of corrosion protection.

When the components of the inhibitor are introduced into the acids, the condensation product is first dissolved (vigorous stirring is necessary), then the imidazole derivative and urotropin. The corrosion rate was measured by the volume of hydrogen released and by the gravimetric method. Hydrogen embrittlement (hydrogenation) was determined using a K-5 twisting machine by the number of revolutions before the specimen broke.

The test results are shown in tables and examples.

EXAMPLE I. For testing the proposed inhibitor was taken 3 N. hydrochloric acid solution containing 0.8 g / l of condensation product, 1.3 g / l of imidazole derivative and 2.7 g / l of urotropine (respectively wt.%: 16.5; 29.5 and 54.0), t .e. 4.8 g / l inhibitor. The experiments were carried out at 20 ± 1 ° С and 90 ± 1 ° С (the duration of the experiments was 48 and 0.5 h, respectively). The temperature was maintained using a liquid thermostat. Samples of steel with a size of 40 × 25 × 1 mm were cleaned with a fine emery cloth, degreased with acetone, kept for 2 hours in a desiccator over calcium chloride and weighed on an analytical balance. After the experiment, the samples were thoroughly washed with distilled water, wiped with a paper towel, kept in a desiccator and again weighed on an analytical balance. The corrosion rates calculated for changes in the masses of samples (in triplicate) were, for 20 ° С, without an inhibitor 9.45 · 10 ^-3 g / dm ² · h, with an inhibitor 2.2 · 10 ^-4 g / dm ² · h, at 90 ° C, respectively 29.58 g / dm ² · h and with an inhibitor of 0.1479 g / dm ² · h.

The found braking coefficients K amounted to:

From the values of the braking coefficients, the degrees of protection were calculated

In the second series of experiments, the corrosion rates of steel were measured for individual components that were taken at the above concentrations, and the braking coefficients were calculated:

for condensation product K ₂₀ = 2.6 for imidazole derivative K ₂₀ = 3.5 for urotropin K ₂₀ = 2.3

Thus, the theoretical inhibitory coefficient of the inhibitor, found from the values of the partial coefficients for the individual components, is only about 21, and the experimental value of the inhibitory coefficient of 43.5 is more than 2 times higher.

This result indicates a synergistic effect for the mixture of components.

The polarization measurements lead to the same conclusion: for individual components, the potentials change by 10-25 mV, for a mixture of components, i.e. for the proposed inhibitor, the anodic polarization is about 70 mV, the cathodic polarization is about 110 mV.

When determining the hydrogenation, the following results were obtained (average for 5-10 replicates) in terms of protection: without inhibitor 0, with an inhibitor of 37.5%.

For a known inhibitor, the degree of protection against hydrogenation is only 8%.

EXAMPLE II To protect against corrosion of aluminum by the proposed inhibitor (4.8 g / l) in 3 N. HCl, the value of the drag coefficient equal to 333 (temperature 20 ° С) was obtained. Braking factors for individual components were:

condensation product 5.8 imidazole derivative 4,5 urotropin 1.9

The theoretical drag coefficient is 49.6, i.e. more than 6 times less than the experimental value, which indicates a very significant synergistic effect.

For a known inhibitor under the same conditions, the drag coefficient is 65.5, i.e. significantly less than for the proposed inhibitor.

EXAMPLE III To suppress titanium corrosion in 5 n. phosphoric acid at 90 ° C, the proposed inhibitor was taken at the same concentration as in the previous examples. The drag coefficient for him was 2.4. The theoretical coefficient is equal to the product 1.2 × 1.0 × 1.3 = 1.56. Therefore, in this case, there is a synergistic action of the components, although to a lesser extent than in the previous examples. For a known inhibitor, the drag coefficient is 1.8.

A comparison of the results shown in the examples and tables 1 and 2, clearly indicates the superiority of the proposed inhibitor compared with the known corrosion of steel, aluminum and titanium in all tested acids. Quite significantly, the proposed inhibitor prevails over the known hydrogenation of steel.

In additional experiments, it was found that the proposed inhibitor significantly exceeds the PB-5 inhibitor widely used in industrial practice: the latter has a braking coefficient for steel equal to 41, and the proposed coefficient has a coefficient of more than 100. In addition, PB-5 coagulates under the influence of iron salts, accumulate in acidic solutions during corrosion of steels, and the proposed inhibitor under the same conditions is quite stable.

The proposed inhibitor can be recommended for the etching of tested metals in acids, as well as for acid cleaning of equipment in mechanical engineering, food industry and energy.

Claims (1)

Corrosion inhibitor of metals in sulfuric, hydrochloric and phosphoric acids, including the condensation product of an amine with an aldehyde and urotropin, characterized in that it additionally contains 4,5-dichloro-2-trifluoromethylbenzimidazole, and contains t-nitrobenzal-n-iodaniline as a condensation product in the following ratio of components, wt.%: m-nitrobenzal-n-iodaniline 14.8-17.9 4,5-dichloro-2-trifluoromethylbenzimidazole 33.3-23.9 urotropin 51.9-58.2