Effect of the anionic composition of acidic solutions containing Fe(III) on the protection of low-carbon steel by a triazole inhibitor

The article summarizes the literature data and patents on the protection of steels and nonferrous metals in phosphoric acid solutions with various corrosion inhibitors. Some aspects of practical use of H 3 PO 4 solutions, their properties and corrosivity toward various metals are reviewed. It is shown that the overwhelming majority of individual organic and inorganic compounds, as well as composite inhibitors offered for the protection of metals in this medium are of low efficiency due to weak adsorption on metal surfaces. A promising method for the protection of steels in phosphoric acid media involves the use of formulations containing triazole derivatives and sulfur-containing additives. The components of these mixtures form polymolecular protective layers on the metal surface that are highly efficient in slowing down corrosion processes even at temperatures up to 100С. An important property of these protective layers is a strong chemical bond of the inhibitor molecules with the metal surface and with each other inside the layer. Inhibited H 3 PO 4 solutions resistant to the accumulation of corrosion stimulators-Fe(III) saltsmay become a new and promising field of use for this acid. The bibliographic list includes 170 sources.

Section: Ligandsmentioning

confidence: 99%

Protection of metals in phosphoric acid solutions by corrosion inhibitors. A review

2019

“…Fe(III) sulfate can considerably decrease the protective effect of metal corrosion inhibitors added to an etching solution [3].…”

Section: Introductionmentioning

confidence: 99%

A study of the H2SO4–H3PO4–H2O–Fe(III) system by cyclic voltammetry

2019

The electrochemical behavior of Fe(III) cations on a platinum electrode in the H 2 SO 4-H 3 PO 4-H 2 O, H 2 SO 4-H 2 O, and H 3 PO 4-H 2 O systems (25-95°C) has been studied by cyclic voltammetry. The oxidizing ability of the 2.0 M H 2 SO 4 + H 3 PO 4 system containing 0.10 М Fe(III) decreases as the molar fraction of H 3 PO 4 increases. The observed effect results from the formation of Fe(III) complexes with phosphate anions that are weaker oxidants than the corresponding hydrate and sulfate complexes. An increase in temperature causes an increase in the oxidizing ability of the H 2 SO 4-H 3 PO 4-H 2 O-Fe(III) system. This effect is most pronounced in the H 3 PO 4-H 2 O-Fe(III) system. Addition of H 3 PO 4 to H 2 SO 4 solutions converts Fe(III) cations from hydrate and sulfate complexes to phosphate complexes, which leads to a decrease in their diffusion rate in aqueous acid solutions. The decrease in the diffusion coefficient of Fe(III) cations is about 1/3 of the initial value. A probable reason for efficient protection of low-carbon steel by triazole-based composite inhibitors in H 3 PO 4 or its mixtures with H 2 SO 4 containing Fe(III), in comparison with similar solutions of H 2 SO 4 alone, is that phosphate complexes of Fe(III) are formed in these media. They have a lower oxidizing ability and diffusion rate in comparison with aqueous and sulfate complexes of Fe(III).

“…Corrosion of steel items in these media results not only from the reaction of the metal with the acid but also with Fe 2 (SO 4 ) 3 . The gain in corrosion losses due to the presence of Fe(III) cations, especially in cold solutions, may be considerable [1][2][3]. Reduction of Fe(III) cations with metallic iron that occurs in diffusion mode is usually poorly hindered by corrosion inhibitors, which makes steel protection by this method inefficient [4].…”

Section: Introductionmentioning

confidence: 99%

“…The oxidizing capability of the H 2 SO 4 -H 3 PO 4 -H2 O system containing Fe(III) and Fe(II) decreases as the relative content of H 3 PO 4 increases. The observed effect results from the formation of Fe(III) complexes with phosphate anions that are weaker oxidants than the corresponding hydrate and sulfate complexes.…”

mentioning

confidence: 98%

A potentiometric study of an H2SO4–H3PO4–H2O system containing Fe(III) and Fe(II) cations

2018

The potentiometric method was used to study an H 2 SO 4 -H 3 PO 4 -H 2 O system (20-95°C) containing Fe(III) and Fe(II) cations. The oxidizing ability of the 2 M H 2 SO 4 + H 3 PO 4 system containing Fe(III) and Fe(II) (1:1) decreases as the molar fraction of H 3 PO 4 increases. The observed effect results from the formation of Fe(III) complexes with phosphate anions that are weaker oxidants than the corresponding hydrate and sulfate complexes. Variation in the total content of the equimolar Fe(III) + Fe(II) mixture (C = 0.01-0.10 M) in 1 M H 2 SO 4 + 1 M H 3 PO 4 nearly does not affect its oxidizing ability. Conversely, an increase in the relative content of Fe(III) in the system considerably increases its oxidative potential. At a fixed concentration of the Fe(III) + Fe(II) mixture in the system (0.04 М), addition of an equimolar mixture of H 2 SO 4 and H 3 PO 4 (up to 6 M) somewhat decreases the oxidizing properties of the system.A probable reason of the efficient protection of low-carbon steel by triazole-based composite inhibitors in H 3 PO 4 or its mixtures with H 2 SO 4 containing Fe(III), in comparison with similar solutions of H 2 SO 4 alone, is that phosphate complexes of Fe(III) are formed in these media. They have lower oxidizing ability in comparison with aqueous and sulfate complexes of Fe(III).