Abstract
Chemical vapor deposition (CVD) is used as a method for the synthesis of carbon nanotubes (CNT) on substrates, most commonly pre-treated by a metal-catalyst. In this work, the capability of basalt fiber surfaces was investigated in order to stimulate catalyst-free growth of carbon nanotubes. We have carried out CVD experiments on unsized, sized, and NaOH-treated basalt fibers modified by growth temperature and a process gas mixture. Subsequently, we investigated the fiber surfaces by SEM, AFM, XPS and carried out single fiber tensile tests. Growth temperatures of 700 °C as well as 800 °C may induce CNT growth, but depending on the basalt fiber surface, the growth process was differently affected. The XPS results suggest surficial iron is not crucial for the CNT growth. We demonstrate that the formation of a corrosion shell is able to support CNT networks. However, our investigations do not expose distinctively the mechanisms by which unsized basalt fibers sometimes induce vertically aligned CNT carpets, isotropically arranged CNTs or no CNT growth. Considering data from the literature and our AFM results, it is assumed that the nano-roughness of surfaces could be a critical parameter for CNT growth. These findings will motivate the design of future experiments to discover the role of surface roughness as well as surface defects on the formation of hierarchical interphases.
Highlights
Effective surface treatment of reinforcement fibers is a key task in order to tailor composite interphases and to improve composite strength and toughness
After Chemical vapor deposition (CVD) Treatment adsorbed organic contaminations were identified by the C 1s peaks
On the CVD03 treated BAS11 fiber we found infrequent carbon nanotubes (CNT) in balled or elongated shapes (Figure 4a), whereas the corrosion shell of the NaOH treated fiber BAS16(A5) is more intensely overgrown by CNTs
Summary
Effective surface treatment of reinforcement fibers is a key task in order to tailor composite interphases and to improve composite strength and toughness. Recycling of fiber reinforced polymers is in the focus of several investigations. Chemical and thermal treatments of composites are the common way to separate the reinforcing fibers from the polymer matrices. A heat treatment might lead to sizing removal, a decrease of mechanical performance, and deterioration in the fiber-matrix adhesion. Thomason et al [1] highlighted thermal recycling as the most advanced recycling technology, but underline the drawback due to the cost competitiveness of recycled fibers. The poor performance to cost ratio as well as difficulties in the reprocessing of recycled fibers are itemized and considered as obstacles for the valuable reuse as reinforcement material. In the case of thermal recycled glass fibers, Thomason [1] pointed out that the regeneration of properties would have a major impact in all matters
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