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Carbon Nanotubes Reinforced Cement Composites - Applications & Performances

Carbon nanotubes (CNT) , discovered by S. Iijima in 1991, are an allotropic form of the carbon as well as graphite and diamond. CNT can be seen as graphite sheets rolled up on themselves forming a cylinder with closed extremities. Two types of carbon nanotubes are known: Single Wall NanoTubes (SWNT), formed by one graphite sheet rolled up, and Multi Wall NanoTubes (MWNT) similar in appearance to a number of graphite sheets rolled together.
CNTs have unique mechanical properties that make them close to ideal reinforcing materials (modulus of elasticity higher than 1 TPa, yield tensile strength between 20 and 60 GPa). In addiction to mechanical properties, CNTs are also highly electrically and thermally conducting. CNTs have several distinct advantages as a reinforcing material for cements: greater strength, high energies request for crack propagation and the smaller diameters of CNT means that they can be more widely distributed in the cement matrix. About electrical properties, it showed that the addition of CNT to cement paste leads to a notable decrease in volume electrical resistivity and a distinct enhancement in compressive sensitivity. Particularly, the electric conductivity of CNT/cement composites varies with stress: the number of contact points of CNTs increase with increase of loading, and the more the contact points are the lower electric resistivity will be. The present paper concludes describing the proposal research to evaluate mechanical and pressure-sensitive properties of CNT/cement composites. In detail, the purpose is to analyze variations in terms of electrical resistivity by changing stress condition are obtained by adding a minimum amount of CNT and by treating preliminary CNT by immersion in acid solutions.

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7 Chapter I CARBON NANOTUBES 1 THE DISCOVERY OF CARBON NANOTUBES In 1985 the American chemist Richard E. Smalley discovered that, in particular situations, the atoms of carbon compose some orderly structures of spherical form: the fullerenes. The structure, after a following loosening, tends to roll up on itself, getting a typical cylindrical form: the carbon nanotubes (CNT). They can likewise be seen to the fullerene as one of the carbon allotropic forms. In the 1991 Sumio Iijima, at the NEC Fundamental Research Laboratory of Tsukuba (Japan), used a high resolution transmission electron microscope (TEM) in order to study the particulate created in an electric discharge between two carbon electrodes. He discovered this particulate contained structures consisting of a lot concentric carbon tubes. One year later, Thomas Ebbesen and Pulickel Ajayan, also they at the NEC in Tsukuba, developed an efficient method to manufacture great quantities of these so-called Multi Wall NanoTubes (MWNTs). Subsequently, in 1993, the Iijima group, at the NEC, and the Donald Bethune, at the IBM Almaden Research Center in California, independently discovered the Single Wall NanoTubes (SWNTs). In the last decade, a lot of researches about carbon nanotubes began. In the few years from their discovery innumerable interesting characteristics and many potential applications are individualized. 1.1 FULLERENES Among the most promising substances for the possible nano-technological implications must surely be remembered the crystalline carbon in its various forms. Till 1985 only

Laurea liv.I

Facoltà: Ingegneria

Autore: Lorenzo Milesi Contatta »

Composta da 123 pagine.

 

Questa tesi ha raggiunto 409 click dal 23/05/2011.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.