1. SEM images_Manuscript

2. Al2O3 fibers with radially aligned CNT networks inside the composite (Control)

3. High contrast SEM images of crack propagation in Al2O3 and CNT-Al2O3 flexure specimens after exposure experimentation. The top and bottom of each SEM image represents the top and the bottom loading surfaces of the composite specimens where the crack propagates from the bottom to the top surface upon fracture.
(a)
(b)
(c)
(d)
(e)
(f)
Al2O3 (Ctrl)
Al2O3 (Hy)
Al2O3 (HT-S)
CNT (Ctrl)
CNT (Hy)
CNT (HT-S)

4. (a)
(c)
(b)
(d)
Al2O3 (Ctrl)
Al2O3 (HT-L)
CNT (Ctrl)
CNT (HT-L)
Cross sectional SEM images of fractured surfaces before and after long term hydrothermal exposures. The yellow arrows point to the hackle patterns observable on fiber surfaces when the composites undergo brittle fracture.

5. (a)
(b)
Fiber
Polymer
Ctrl
HT-L
SEM images of fractured CNT-Al2O3 cross sections, before and after long term hydrothermal exposure. The highlighted sections show the dominance of CNT pullouts and fractures due to the secondary reinforcement mechanisms observed in CNT composites. These reinforcements remain intact even after the long-term hydrothermal exposure.

6. SEM image of a typical tensile fracture observed on short specimens during 3-point bend tests. The crack originates at the bottom surface and traverses to the top surface (loading surface) beneath the loading pin, as observed in flexure specimens. The fractography presented here is of a CNT-Al2O3 (Ctrl) sample.

7. SEM images of crack propagation in flexure specimens
SEM images of crack propagation in flexure specimens. (a) Al2O3 (Ctrl), (b) CNT-Al2O3 (Ctrl), (c) Al2O3 (Hy), (d) CNT-Al2O3 (Hy), (e) Al2O3 (HT-S), (f) CNT-Al2O3 (HT-S).
(a)
(b)
(c)
(d)
(e)

8. SEM images of fractured sample surfaces showing fiber cross sections directly in contact with environmental conditions (a) Al2O3 (Ctrl), (b) CNT-Al2O3 (Ctrl), (c) Al2O3 (Hy), (d) CNT-Al2O3 (Hy), (e) Al2O3 (HT-S) and (f) CNT-Al2O3 (HT-S). Deposits of bayerite (Al(OH)3) and boehmite (AlOOH) were observed on fiber surfaces of hydro and hydrothermal specimens respectively (highlighted). The control specimens have relatively clean outer fiber surfaces.
(a)
(b)
(c)
(d)
(e)

9. High magnification images of precipitates found on exposed fiber toes of the composites. (a) bayerite deposits on hydro specimens, (b) boehmite deposits on hydrothermal specimens.