Di-t-octyl disulfide

Most of the studies of the interaction between metallic iron and organic monosulfides or disulfides are based on the premise that the rate of formation of iron sulfides (FeS, FeS2) is a valid measure of additive reactivity. This was the premise used by Dorinson and Broman [24] in their comparison of the reactivities of di-t-octyl disulfide and di-n-octyl disulfide with iron powder. The kinetic data for 25% of additive in white oil fitted the following equations ... 

The value of Cfe for di-t-octyl disulfide and for di-n-octyl disulfide at a given temperature can be computed from Eqns 11-la and 11-1b. Because these equations were fitted to data for 25% additive in white oil, adjustment for concentration uses the fact that the rate of a pseudo-zero-order reaction is a linear function of concentration. Let us select 498 K (225 C) as the temperature the computed values of Ck are... 

X 10 gram-atom of sulfur from di-t-octyl disulfide will have 2... 

Figure 11-14 shows data obtained by Dorinson [38] in an investigation of the cooperative action of di-t-octyl disulfide and t-octyl chloride, two independently effective lubricant additives. The criteria for evaluation are the initial seizure load in the 10-second ASTM four-ball test and the magnitude and course of the post-seizure wear. With either 2% sulfur or 2% chlorine as the single active additive element in the lubricant, the post-seizure transition occurs in the load interval 80-100 kg, and the degree of seizure, as judged by the extent of wear, is not severe. With a combination of 1% sulfur and 1% chlorine in the... 

Figure 11-14. Cooperative additive action of t-octyl chloride and di-t-octyl disulfide. Four-ball test 10 seconds at 1750 rpm. Additives in white oil and wear/load index A. 9.1% Di-t-octyl disulfide, 2.08% S 48.0 kg. B. 8.52% t-Octyl chloride, 2.05% Cl 51.9 kg. C. 4.55% Di-t-octyl disulfide + 4.53% t-octyl chloride, 1.06% S, 1.00% Cl 81.0 kg. D. 9.1% Di-t-octyl disulfide + 8.52% t-octyl chloride, 2.1% S, 2.0% Cl 112.1 kg. Data by A. Dorinson [38].

TABLE 14-4. CONCENTRATION OF DI-t-OCTYL DISULFIDE AND WEAR RATE... 

The lubricated wear described above is squarely at odds with the behavior illustrated in Fig. 14-6 and with the wear-reducing action of 22% di-t-octyl disulfide in white oil reported by Dorinson and Broman [10] and shown in Table 11-6 (Chapter 11, Section 11.2.1). If Eqn 14-49 is a correct representation of additive action, it should be valid for both the reduction and the increase of wear by such action. To reduce wear, the first term on the right-hand side of the equation must control the overall rate and one way to do so is for the lump removal factor wear rate. But there is no physical necessity that q remains constant for all conditions of load, pressure, speed or state of lubrication. Since in physical terms the predominant effect of the lubricant is to inhibit the asperity adhesion process, it is not unanticipated that the average size of the transferred and detached particles as well as their number will be decreased by lubrication. It is to this latter type of mechanistic process that we must look for an explanation of why such parameters as contact pressure, rubbing speed and material properties affect the balance between the inhibition or promotion of wear by additive action and the transition from smooth lubricated wear to catastrophically damaging wear behavior such as scuffing. 

Fig. 21. Dependence of the induction period in the oxidation of polypropylene on the concentration of 2,6-di-tert-octyl-4-methylphenol (4) and with admixtures of disulfide in concentrations 1) 0.04 mole/kg 2) 0.08 mole/kg 3) 0.12 mole/kg. T = 200°C pog = 3 0 mm Hg.

---