Die Entstehungs‐ und Ausbreitungskinetik von Sulfatnestern bei der atmosphärischen Korrosion von Stahl

Abstract

Kurzfassung Die atmospharische Korrosion von Stahl beginnt an einzelnen Punkten, deren Zahl langsam ansteigt, bis die Stahloberjlache mit einer Rostschicht bedeckt ist. Die anfangliche Verteilung der Korrosionspunkte scheint mit aktiven Sulfideinschliissen zusammenzuhangen (vor allem MnS). Die dabei entstehenden Mangansulfate werden hydrolysiert, wodurch Sch wefelsaure entsteht, die zur Bildung von Sulfatnestern fuhrt. Das darin entstehende Eisensulfat wird hydrolysiert, und diese Reaktion bestimmt die Ceschwindigkeit der Ausbreitung der Sulfatnester. Voraussetzung fur einen ein wandfreien Rostschutz ist die Beseitigung derartiger Sulfatnester, was nur durch Entfernen der Rostschicht (mechanisch oder durch Beizen) moglich ist; blo$es Abwaschen oder die Verwendung von Roststabilisatoren reichen dazu nich t aus.

On the Involvement of H 2 O 2 and SO 2 in the Atmospheric Corrosion of Steel

“…It has been proposed (19)(20)(21) that the nests are regions of the corroding surface at which active surface sites develop high concentrations of corrosion products and electrolyte which subsequently seed adjacent surface regions. It has been proposed (19)(20)(21) that the nests are regions of the corroding surface at which active surface sites develop high concentrations of corrosion products and electrolyte which subsequently seed adjacent surface regions.…”

“…The mechanism proposed here for the involvement of SO2 and H202 in the atmospheric rusting of steel is not inconsistent with earlier concepts of "sulfate nests" on steel surfaces. It has been proposed (19)(20)(21) that the nests are regions of the corroding surface at which active surface sites develop high concentrations of corrosion products and electrolyte which subsequently seed adjacent surface regions. The active sites are thought to be produced by the adsorption of active species beneath hygroscopic particles, and it has been proposed that the sulfur originates in manganese sulfide inclusions (20).…”

“…It has been proposed (19)(20)(21) that the nests are regions of the corroding surface at which active surface sites develop high concentrations of corrosion products and electrolyte which subsequently seed adjacent surface regions. The active sites are thought to be produced by the adsorption of active species beneath hygroscopic particles, and it has been proposed that the sulfur originates in manganese sulfide inclusions (20). The present work modifies this picture in two ways: the supply of sulfur already in the S(IV) or S(VI) valence state comes from the atmosphere rather than from the metal matrix, and atmospheric hydrogen peroxide significantly modifies the iron and sulfur chemistry in some seasons of the year.…”