Thiosulfate pitting

Photographic solutions, especially fixing solutions containing thiosulfates (pitting occurs). 

Garner. A., Newmann, R. C. (1991), Thiosulfate pitting of stainless steels, NACE Corrosion/91, Paper No. 186. 

In addition, from the analysis of the ac impedance spectra obtained from the previously pitted surfaces under open circuit conditions at room temperature in 0.5 M Na2S04 solution51 and from the in-situ pitted surfaces in Cl ion-containing thiosulfate solution at various applied potentials and solution temperatures,52 they verified that dr>ss is inversely proportional to the CPE exponent for capacitive charging process (Eq. 30)51 and the depression parameter for charge transfer process.52... 

E.G. Webb, R.C. AUdre, Pit initiation at single sulfide inclusions in stainless steel. II. Detection of local pH, sulfide, and thiosulfate, J. Electrochem. Soc. 149 (2002) B280-B285. 

W.T. Tsai, T.P. Wu, Pitting corrosion of AUoy 690 in thiosulfate-containing chloride solutions, J. Nucl. Mater. 277 (2000) 169-174. 

R.C. Newman, W.P. Wong, H. Ezuber, A. Gamer, Pitting of stainless steels by thiosulfate ions. Corrosion 45 (1989) 282-287. 

White waters can vary tremendously in composition among different paper machines, and may contain ions such as thiosulfate, chloride, and sulfate, plus additives to control pH, microbiological activity, drainage/retention, or other product qualities. Thiosulfate is a pitting agent that can be present from hydrosulfite brightening. Chloride is... 

Newman et al. [22-24] have aided the understanding of thiosulfate effects on the corrosion of Type 304 stainless steel in paper machine white water. One of their tests was the "scratch method [24] that was used to investigate pitting at various ratios of thiosulfate to sulfate, with chloride and bisulfite additions in simulated white water further defining the limits of corrosion resistance for stainless steels. 

Varjonen et al. [25] studied the pitting corrosion resistance of Type 316 stainless steel in white waters containing thiosulfate using an Avesta Cell, where the pitting breakdown could be studied without interference from crevice corrosion. Salonen et al. [26] and Laitinen et al. [27] used the contact electric resistance (CER) method to study the effect of thiosulfate on the films formed on Type 304 stainless steel. In the CER method, the resistance of the films formed on metal surfaces can be studied as a function of potential. Stable passive films have a high electrical resistance, whereas unstable (or absent) films have a low electrical resistance. 

Sulfide, sulfite, thiocyanate, thiosulfate — CE UV Direct Indirect Conductivity detection Amperometric detection Water sample of an open-pit Mining Lake [3]... 

Besides their possible role in pit initiation (see earlier), the dissolution of the MnS inclusions can generate thiosulfates [47, 67] or more likely sulfide [51, 52] ions, which are known to favor passivity breakdown. Indeed, Crolet et al. [54] observed higher depassivation pH on stainless steels with high sulfur content. According to Brossia and Kelly, the initiation involves a critical [Cl ]/[HS ] ratio. This efiect of MnS is unlikely in modem stainless alloys with very low sulfur contents. 

Sulfate-reducing bacteria have also been reported to be responsible for pitting corrosion on stainless steels in aqueous environments. The mechanisms proposed are mostly related to iron and steel. However, a different mechanism has been proposed in which the role of thiosulfate in the microbial pitting of stainless steel has been emphasized [137]. The same authors have also demonstrated clearly that SRB-induced pitting corrosion of stainless steel is unlikely to occur in a uniformly anaerobic SRB medium, whereas it will occur when the anaerobic sites are coupled to an oxygen cathode [136]. 

Generally, the most conducive environment for pitting is the marine environment. Ions, such as Cl , Br and I , in appreciable concentrations tend to cause pitting of steel. Thiosulfate ions also induce pitting of steels. 

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