Volumen II - SAM

Microstructure is elucidated from the analysis of SEM backscattered electron (BEI) images – which have
compositional contrast (brightness increases with atomic number) – and elemental mapping of carbon (C)
and molybdenum (Mo):
- at low contents of filler, even though there are PE rich zones and MoS2 rich zones, there is a good
dispersion of filler, and PE matrix seems to be continue (Figure 2a);
- at high contents of filler, dispersion of MoS2 is poor, giving place to zones without MoS2 and lack of PE
matrix continuity (Figure 2b).
Sliding abraded surfaces show different features under SEM examination depending on MoS2 content (figure
3). PE exhibit many microscopic undulations that may arise from friction heat softening of the polymer
matrix [8], while worn surface of PE/10 composite only exhibits fine scratches related with mild adhesion
wear. If MoS2 content is increased, signs of agglomerated abrasion and severe deformation (micro-ductility)
appear in abraded surface. Surface fracture is also seen in PE/25 abraded surface, which accounts for
increased wear.
(a)
(b)
Figure 2. BES + EPMA images for PE/07 (up) and PE/25 (down) composites: BEI (left), C map (middle)
and Mo map (right).
Figure 3. SEM of composite’s abraded surfaces under sliding wear.
Wear contact of materials results in heat generation with an increase of temperature at the interface. The
wear resistance of materials depends upon the quantity of the heat generated and the way this heat is
dissipated [6]. Due to its nature, MoS2 seems capable of increasing thermal conductivity of materials,
enhancing heat dissipation with a concomitant reduction of melting wear. Moreover, a modest increase in
friction coefficient with sliding distance was observed during tests (it was attributed before to adhesive wear
1048