Phase transition of elemental S in H2S-CO2-Cl- environment is observed and this behavior is indicated to be the same as physical properties of elemental S itself. Electrochemical behavior in S, H2S and S+H2S environment at high temperature is also investigated potentiodynamically by means of a pressure equilibrium type autoclave and it is clarified that elemental S accelerate cathodic reaction by the reaction of S → H2S, spontaneous potential (Esp) in S-H2O system become noble compared to Esp in nonsulfur-containing environment. Electrochemical reactivity of elemental S is related to increase of viscosity due to production of liquid μ sulfur over 160°C and reformation of sulfur at the corrosion site due to the reverse dissolution reaction of dissolved spec i es(SO42-, H2S, polysulfide). Furthermore, it is also clarified that critical pitting potential(Vc) of corrosion resistant alloy(CRA) of UNS No; N10276 alloy is less noble in order of S, H2S and S+H2S environment at 200°C. Mo content is important to improve Vc’. Solubilities of elemental S by self-oxidation-reduction reaction and production of polysulfide(Sx2-;x=2,3,4,5) are estimated by thermodynamic calculation. Calculated-solubility of elemental S is between 0.1g/l S and 1g/l S at 200°C in S-H2O system. It is discussed in relation with electrochemical behavior of elemental S. Finally, Corrosion mechanism at S-deposited portion in S-containing environment is discussed on the basis of those experimental results.

Subject
Sulfur, Corrosion resistant alloys, Molybdenum alloys, Autoclaves, Electrochemical reactions, Dissolution, Solubility, Corrosion reactions, Anodic reactions, Pitting, Environments, Electrodes, High temperature
© 1989 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
1989
Association for Materials Protection and Performance (AMPP)
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