J Fail. Anal. and Preven. (2011)11: 158-166 reactions(7) and(8), which would return to the above XRD Analysis and SEM Observation chain propagation again. As a result, thermal-oxidative he lubricating rease was repeatedly Figure 3a and b shows the XRD patterns of the fresh and decreased used grease sample, respectively. From the X-ray analysis, ROOH→→RO·+HO° (Eq 6)the patterns. The strongest diffraction peak from the fresh HO+RH→H2O+RO (Eq 7) sample, as shown in Fig. 3a, appeared at about 20=14 RO·+RH→ROH+R cq 8) corresponding planar spacing d=0.63 nm, another strong diffraction peak presents at about 20= 26, corresponding Thus, during the chain termination the content of the planar spacing d=0.34 nm. According to PDF cards, they arbonyl-containing oxidation products including acidic could be attributed to(100)and (101)crystalline planes of species and high-viscosity products increased in the the molybdenum disulfide(Mos2). In addition, some lubricating grease and heavily deteriorated the lubricating diffraction peaks of MoSz also appeared in thi properties of the grease profile. This means that the fresh grease was a According to Xue et al. [14], the intensiy egree of the observation and EDS analysis of the fresh grease confirmed of C=0 peaks lubricating grease containing MoS2. Actually, SEM was directly proportional to the degradation grease.As illustrated in Fig. 2b, the C=0 peak was sharp this fact as well. Figure 4a and b shows SEM and EDS and the peak intensity was high(compared with the fresh results of the fresh grease sample, respectively. As shown grease, see Fig. 2a). Consequently, it could be concluded in Fig. 4a, there were some even particulates(arrows)with that large amounts of compounds containing C=0 group a size of around 5 um dispersing in a fine microstructure of were produced in the used greases, i.e., the greases in the the greases. The EDS results indicated that those particu roller/raceway contacts were oxidized and degraded lates consisted of molybdenum (Mo) and sulfur (S) heavily. elements, namely MoS2. In comparison, the intensity of ig. 3 X-ray analysis of (a) fresh and (b)used grease 6000 0.000 40.000 4000 30 Springreactions (7) and (8), which would return to the above chain propagation again. As a result, thermal-oxidative stability of the lubricating grease was repeatedly decreased. ROOH
! D RO þ HO ðEq 6Þ HO þ RH ! H2O þ RO ðEq 7Þ RO þ RH ! ROH þ R ðEq 8Þ Thus, during the chain termination the content of the carbonyl-containing oxidation products including acidic species and high-viscosity products increased in the lubricating grease and heavily deteriorated the lubricating properties of the grease. According to Xue et al. [14], the intensity of C=O peaks was directly proportional to the degradation degree of the grease. As illustrated in Fig. 2b, the C=O peak was sharp and the peak intensity was high (compared with the fresh grease, see Fig. 2a). Consequently, it could be concluded that large amounts of compounds containing C=O group were produced in the used greases, i.e., the greases in the roller/raceway contacts were oxidized and degraded heavily. XRD Analysis and SEM Observation Figure 3a and b shows the XRD patterns of the fresh and used grease sample, respectively. From the X-ray analysis, it is clear that there were significant differences between the patterns. The strongest diffraction peak from the fresh sample, as shown in Fig. 3a, appeared at about 2θ = 14°, corresponding planar spacing d = 0.63 nm, another strong diffraction peak presents at about 2θ = 26°, corresponding planar spacing d = 0.34 nm. According to PDF cards, they could be attributed to (100) and (101) crystalline planes of the molybdenum disulfide (MoS2). In addition, some weak diffraction peaks of MoS2 also appeared in this XRD profile. This means that the fresh grease was a lithium lubricating grease containing MoS2. Actually, SEM observation and EDS analysis of the fresh grease confirmed this fact as well. Figure 4a and b shows SEM and EDS results of the fresh grease sample, respectively. As shown in Fig. 4a, there were some even particulates (arrows) with a size of around 5 μm dispersing in a fine microstructure of the greases. The EDS results indicated that those particu￾lates consisted of molybdenum (Mo) and sulfur (S) elements, namely MoS2. In comparison, the intensity of Fig. 3 X-ray analysis of (a) fresh and (b) used grease sample J Fail. Anal. and Preven. (2011) 11:158–166 161 123