Sulphur addition

Obviously the selection of an EP additive requires great care if it is too active it may give rise to excessive metal removal under normal operating conditions (see the section on corrosion by sulphur additives). Also, if a component is prone to fatigue pitting in service the presence of an overactive EP agent may result in corrosion fatigue. ... 

Corrosion by sulphur additives Sulphur compounds occur naturally in most lubricants and many oil additives contain sulphur. In a properly formulated lubricant these sulphur compounds should be inactive at ambient temperature. At elevated temperatures they may decompose to give more active materials which can stain and corrode metals, particularly silver and copper. However, these same sulphur compounds have many beneficial qualities this is why they are not removed com.pletely in refining and why they are used as additives. 

Presently the effective role of sulphur additive is not well explained because sometimes activation or deactivation phenomena are observed. Such a versatile behaviour is well-illustrated over noble metal-based catalysts particularly when they are dispersed on perovskite supports [111]. The catalytic performances of a prereduced Pt/LaCo03 in H2 at 450°C are illustrated in Figure 10.13a. After preactivation in H2 subsequent bulk and surface characterisation highlighted an extensive reduction of the perovskite... 

Various attempts have been made to improve the stability of amorphous sulphur. Addition of small amounts of halogens, i.e., chlorine, bromine, iodine, treatment with sulphur monochloride or the addition of a terpene have some effect on the rate of conversion. As far as is known, none of the modified materials are commercially available. 

D. Y. Lee, Modification of Asphalt and Asphalt Paving Mixtures by Sulphur Additives, Interim Report, Engineering Research Institute, Iowa State University, Ames, Iowa, 1971. 

When heated to a temperature above its melting point, picric acid can react with sulphur. Addition of sulphur lowers the ignition temperature of picric acid (see below). 

FOO, H.L., GR0NNING, L.M., GOODENOUGH, L., BONES, A.M., DANIELSEN, B-E., WHITING, D.A., ROSSITER J.T., Purification and characterisation of epithiospecifer protein from Brassica napus Enzymic intramolecular sulphur addition within alkenyl thiohydroximates derived from alkenyl glucosinolates, FEBS Letts., 2000,468,243-246. 

Sulphur additives function by the formation of layers of FeS and FeS04 at ferrous surfaces where these films have a lower energy of adhesion to the substrate than to each other. The reaction of sulphur additives involves a controlled corrosion process ... 

Similar to electrophilic sulphur additions, also electrophilic selenium additions to alkynes have been known for a long time. Some more recent examples will be mentioned. 

Method Continuous Crossing Continuous DroMing Precipitation ilphur Addition Precipitation Sulphur Addition Precipitation Sulphur Additlan... 

B.S. Terry, C.L. Harris and D.G.C. Robertson, The Decoppering of Liquid Lead Bullion by Elemental Sulphur Additions, Part 1 The Sulphidation of Lead by Elemental Sulphur. Trans. I.M.M.. 102,1993, C57-C62. 

The towns gas contained 460 mg of S/m. High sulphur addition was made in the form of H,S equivalent to 0 5 SO. in the 6 1 combustion products, i.c. about three times as much as from ordinary high-sulphur... 

In the present work it has been shown that FeS layers form within the oxide when ChlorOut is added to the system. It is proposed here that these FeS layers are themselves beneficial in that they reduce both ion and gas transport through the mixed oxide/sulphide layer. As a consequence, it seems that any sulphur addition that may form iron sulphide is beneficial. In the case of ChlorOut, the reactive compound is ammonium sulphate, which easily decomposes. Other sulphates, which are more thermodynamically stable, like calcium sulphate (gypsum), may not have any beneficial effect at all. 

With 2% of an EP sulphur additive (a di-mercapto-thiadiazole derivative). 

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