Cb 340

The surface morphology of all samples was determined by scanning electron microscopy (Zeiss CB 340, Oberkochen, Germany) and atomic force microscopy (Nanosurf FlexAFM, Nanosurf GmbH, Langen, Germany). The average values of the inner diameters obtained by analysis of scanning electron microscopy (SEM) images of the different nanotube surfaces are arithmetic mean values of 20 nanotubes per specimen. For the analysis and quantification of surface roughness, the standard atomic force microscopy (AFM) instrument software Nanosurf Easyscan 2 was applied. The line roughness values of three different positions on each sample were analyzed with scan field sizes of approximately 5 µm × 5 µm. The measurements were performed in air under tapping mode, using a scan speed of 0.3 s/line, and a silicon cantilever Tap190-Al G (Innovative Solutions Bulgaria Ltd, Sofia, Bulgaria) with a tip radius of about 10 nm or smaller [36 ].

The prefabricated laminates were cut into bars with a size of 4 × 45 mm² using two parallel cutter blades (n = 10), stored for 24 h at 37 °C and >90% humidity and finally cured in water for another 24 h at 37 °C.
Force-displacement curves were recorded in a 4-point-bending test setup according to ISO 6872 on a universal testing machine with a crosshead speed of 1 mm/min and a 2.5 kN load cell and used to calculate bending strength σ_b (MPa) and bending modulus E (MPa) as follows (Equations (1) and (2)): ${\sigma }_b=\frac{3\times l_A\times F_{max}}{b\times a^2}$
$E=\frac{3\times l_A\times l_B^2\times \left(F_H-F_L\right)}{4\times X\times b\times a^3}$
where l_A = 10 mm is the span length, l_B = 20 mm is the length of the reference bar, F_max (N) is the maximum occurring force, F_H (N) is the end and F_L (N) the starting force of the bending modulus calculation, X (mm) is the bar bending, b (mm) is the bar width and a (mm) is the bar height. The areas under the stress-displacement-curves were calculated up to σ_b as a measure for fracture energy.
Scanning electron microscopy (SEM) of the fiber mats and the cement laminates was performed with a crossbeam scanning electron microscope (SEM, CB 340, Carl Zeiss Microscopy GmbH, Oberkochen, Germany) with an acceleration voltage of 2 kV. Before analysis, the samples were sputtered with a 4 nm platinum layer.

In order to observe the topography of the TiN coating inside of the stainless steel tubes they were first cut to quarters. The pieces were washed with acetone (Carl Roth, Karlsruhe, Germany) and finally coated with a 2 nm layer of platinum in a sputter coater (EM ACE600; Leica, Vienna, Austria). The image of the TiN coating inside of the stainless steel tube was then taken on a scanning electrode microscope (SEM; CB 340; Zeiss, Oberkochen, Germany), (Figure 3f).