Preparation and characterization of carbon nanotube reinforced aluminum composites

Introduction: Aluminium is widely used in a lot of applications due to his versatile properties; it has the electrical conductivity (37,7 × 106 S/m) and thermal conductivity (237 W/m·K) of a metal with a relative low density (2.7 g/cm3) and a good resistance to oxidation. For this reason it has been used for decades in structural application (aeronautic industry) and for electronic application (high tension cable). Unfortunately the mechanical properties are not so promising. In order to improve the mechanical properties of this metal, “Carbon nanotube (CNT) Reinforced Aluminum” are studied even if the number of papers in the literature is decidedly lower by comparing with “Carbon Reinforced Polymers”. This occurs because of the difficulty in the preparation of a composite with a good rate of dispersion of CNTs due, for example, to the low wettability between metal and carbon. Usually it is avoided the preparation of composites by melted metal because of the possibility of carbide formation with a consequent decreasing of several properties. The most used way to prepare CNTs aluminium composites is the powder metallurgy that allows the possibility to mix nanoparticles with aluminium powder to obtain a good rate of dispersion. In this work the composites, with different CNTs content, were prepared by a controlled melting, in inert gas,and a fast casting of a mix powder of aluminium and CNTs. Tensile strength and Young modulus were evaluated and correlated with the% of CNTs in the matrix. Materials and methods: MWCNTs were modified on the surface by autoclavation in alkaline aqueous solution of potassium peroxydisulfate according to the procedure reported in literature. After this treatment CNTs were mixed in a mortar and pressed into pellet with the aluminium powder. The pellets are, then, accommodated into the crucible of the furnace. After the heating the melted were fastly casted into a graphite mold attached to a centrifugal rotor. The specimens so obtained were tested with a tensile strength-testing machine (at different temperatures) and with a dynamic indenter. The microstructure was evaluated by SEM micrographies before and after the tests and the exact content of CNTs were evaluated by TGA in different atmosphere. Results: CNTs reinforced aluminium composites were prepared by melting aluminium with different concentrations of carbon. SEM micrographies show the rate of dispersion of carbon nanotube in the matrix. The results of mechanical characterization have demonstrated that exist a threshold of doping after which the carbon nanotube decrease the properties of the matrix. Discussion: The surface modification increases the repulsion between nanotubes and avoid their agglomeration. This involves a good dispersion in the matrix of aluminium. The mechanical properties have a trend with the carbon content: this proves that the change in terms of properties strongly depends on the rate of dispersion and on the preparation procedure