Co-authors​ :

 Ginevra LALLE (ITALY), Ilaria RAGO (ITALY), Ravi Prakash YADAV , Gianluca CAVOTO (ITALY), Francesco PANDOLFI , Maria Paola BRACCIALE (ITALY), Giovanni SOTGIU (ITALY), Irene BAVASSO (ITALY), Elisabetta PETRUCCI , Fabrizio SARASINI , Jacopo TIRILLÒ  

Hierarchical composite materials are gaining ever-growing attention thanks to the opportunities of combining high mechanical strength and multifunctionalities for a wide variety of applications. Significant research activity adopted chemical vapour deposition (CVD) to directly grow high loadings of carbon nanostructures, particularly carbon nanotubes (CNTs), on the surface of reinforcing fibres, thus enhancing the interfacial adhesion with the polymer matrix and providing additional functions, such as damage sensing, electromagnetic wave absorption, and electrochemical properties. The CVD method generally requires the presence of metal catalysts, commonly based on Fe, Ni and Co, which act as nucleation sites for the growing CNTs. While the addition of an external catalyst precursor is required for most fibre substrates, in-situ catalyst generation has been demonstrated for basalt fibres by promoting the microstructural segregation of iron oxides via basic or acidic pre-etching and the subsequent reduction in hydrogen atmosphere to nanocrystalline metallic iron. This approach, reported for the first time by Forster et al. [1], was employed for the growth of high density vertically aligned (VA)CNTs by Sarasini et al. [2]. However, the high temperatures used for the process (720-740 °C) caused a significant deterioration of the fibre mechanical properties, with a reported strength loss of 39%. In this context, a plasma-enhanced CVD (PECVD) technology is proposed herein as an alternative to thermal CVD. Thanks to a high energetic plasma, which supplies some of the energy for hydrocarbon decomposition and CNT formation, the PECVD method allows lower operating temperatures. The PECVD growth of a highly dense carpet of radially aligned CNTs was achieved on basalt fabrics at temperatures below 650 °C with in-situ catalyst generation, thus mitigating the fibre strength loss. Morphological characterization of the fibre surfaces was carried out by scanning electron microscopy (SEM), as shown in figure 1, while the quality of CNTs was investigated by Raman spectroscopy. The nature, structure, and growth modes of individual CNTs were investigated through transmission electron microscopy (TEM). To assess the effects of plasma and in-situ catalyst generation on CNT morphology, the results of all investigations were compared to the ones obtained via thermal CVD in previous works [2, 3]. Furthermore, electrochemical characterizations were performed on the CNT-decorated basalt fabrics suggesting possible new applications of the hierarchical fabric in the field of electrochemical sensors and supercapacitors.