Influência de Inibidores do Tipo Amina no Comportamento Eletroquímico de MnS Sintético e como Inclusão de Aço Carbono

The interaction between sulfur compounds and amines is well known and used for the removal of CS2 from hydrocarbides.1 Therefore, the existence of an interaction between amines added as corrosion inhibitors and MnS inclusions of steels is expected. In order to simulate the influence of amine-type inhibitors on the attack of MnS inclusions, pellets were manufactured by pressing (132 bar) MnS powder (Sigma Aldrich). After being electrically contacted by Au plating and Ag-glue on the back side, the pellets were embedded in epoxy and polished up to 1μm. Cyclic voltammetry (CV) of the so prepared samples were acquired in 0.1M Na2SO4, dearated or not and with additions of TEPA inhibitor (tetraethylenepentamine, Dorf-Ketal), aiming to study a system in which carbon steels are passivated and can suffer localized corrosion. For the simulation of galvanic pairs between MnS and steel, the synthetic inclusions embedded in epoxy and connected or not to AISI1006 carbon steel were studied in the same media using the scanning vibration electrode technique (SVET) under simultaneous polarization, as previously described [2]. Preliminary CV results of synthetic MnS are presented in Fig. 1 for additions of 0, 30 and 300 ppm TEPA, after stabilization of the voltammetric curves (10th cycle). Around the standard equilibrium potential of thiosulfate it is observed that 30 ppm TEPA additions promote MnS dissolution, while at 300 ppm TEPA the effect is reduced, evidencing the existence of competing factors in the dissolution process.