A novel approach to composite preparation by direct synthesis of carbon nanomaterial on matrix or filler particles
Introduction
It is hardly possible to imagine progress in the construction, aerospace, automotive, energy and medical fields without the creation and development of new composite materials with improved mechanical and tuned electrical and thermal properties. Carbon nanomaterials, such as carbon nanotubes (CNTs), nanofibers (CNFs) and graphene, have recently attracted tremendous scientific interest due to their remarkable and useful properties, such as exceptional tensile strength, elastic modulus, and electrical and thermal conductivity [1], [2], [3], [4]. These materials are considered to be promising candidates for next-generation high-performance structural and multifunctional composite materials [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18].
One of the largest obstacles to creating strong, electrically or thermally conductive carbon-based composites is the difficulty of obtaining a good dispersion of the carbon nanomaterials in a matrix, because carbon nanomaterials tend to agglomerate and form bundles [14], [19], [20], [21]. Although many papers have recently been devoted to achieving a good dispersion, the problems of obtaining enhanced composite properties still exist [22], [23], [24], [25]. There are a few different approaches to dispersing carbon nanomaterials in a matrix [23]. The most common one is based on a simple mixing of the materials in a powder form by ball or rotor milling. Even though this approach is very simple and straightforward, it does not necessarily lead to good mixing and usually shortens and damages the carbon nanomaterials, which subsequently results in a less efficient reinforcement and insufficient effect on the composite material properties. Another widely used approach relies on preparation of a water dispersion of the carbon nanomaterials and subsequent mixing with the matrix particles. The carbon nanomaterials first need to be carefully purified and dispersed in water either by functionalization or by adding surfactants [11], [22], [23], [25], [26], [27], [28]. However, strong acid functionalization and ultrasonication treatment can also undesirably affect the properties of carbon nanomaterials, i.e. shorten the tubes and fibers and introduce defects in the structure.
We have recently proposed an approach based on direct synthesis of carbon nanomaterials on the surface of the matrix particles [29], [30]. Usually the matrix, which needs to be modified, might contain a certain amount of catalyst suitable for the synthesis of CNTs and CNFs or could provide a surface for graphene growth. For instance, most commercially available cements naturally contain up to 10 wt.% iron oxide. This amount of the catalyst is sufficient for the growth of CNTs and CNFs on the surface of cement particles without adding catalytic material [29], [31]. Micron-sized copper particles at certain conditions can be used either for the synthesis of CNFs [30] or graphene layers [32].
In this paper we summarize our knowledge and also present new results on the preparation of a good dispersion of CNTs, CNFs and graphene in a matrix, with the intention of improving the mechanical or electrical properties of carbon-based composite nanomaterials. Here, for the first time, in addition to traditional cementations and copper composites mentioned above, we have utilized fly ash, sand and soil as matrix (or filler) materials to grow CNFs and CNTs for further composite modification. Therefore, we propose new kinds of cheap precursors for the growth of carbon nanomaterials.
Section snippets
Materials
For the experiments, Portland sulfate-resistant cement and ground sulfate-resistant clinker, containing about 4 wt.% Fe2O3, were utilized. We used standard construction sand with an iron concentration of about 5 wt.%. Fly ash particles with a mean size of 3–5 μm and 10% iron oxide content were utilized without any additional pretreatment. All these materials were purchased from FinnCementti.
Natural soil, containing about 5 wt.% Fe2O3, was taken from Finnish coniferous forest without organic and
Cement-based materials
Cement is one of the most commonly used construction materials due to its low cost and high workability. The world consumption of the cement is constantly growing due to rising construction engineering needs. Thus, an improvement in the basic mechanical properties and durability of materials based on cement is very important. Fig. 1 shows the general concept of achieving an even dispersion of carbon nanomaterials in the cement (or clinker) matrix, or more precisely, a matrix precursor. After
Conclusions
We have proposed a novel approach to create well-dispersed carbon nanomaterials by directly growing these on the surface of matrix particles, resulting in further improvements of the mechanical and electrical properties of the composite materials.
Utilizing cement (clinker) particles as a catalyst and a support material, we obtained a hardened paste which exhibited a 2–2.5× increase in compressive strength and a 40× increase in electrical conductivity after curing for 28 days in water.
Acknowledgments
This work was supported by the Federal Agency for Science and Innovations of the Russian Federation and by the Academy of Finland.
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