Over the years, material science has opened doors to vistas of innovation. Designs like bullet-proof vests, heat resistant and water repelling suits and rust-deferring metals stand testimony to this fact. The conventional methods of improving material properties have been tried and tested for many years now. With the current generation riding high on the technological wave, the emphasis on novel avenues of research can’t be emphasised stronger. Carbon Nanotubes (CNTs) burst into the scene in the late twentieth century, creating a buzz in research circles. Of its numerous applications, its relevance to Strength of Materials is something that can hardly be overlooked. This aspect of CNTs was identified by M. Jagannatham, a PhD scholar of the Department of Metallurgical and Materials Engineering, whose project is to design Carbon Nanotube-reinforced composites .
Materials are best described by and used for the characteristic properties they exhibit. It has been observed that CNTs play a key role in amplifying select properties of metals and polymers. Jagan’s work deals with the reinforcement of purified CNTs in metal and polymer matrices, aiming to improve mechanical and electrical properties of the same.
Metal Matrix Composites
Metal Matrix Composites (MMCs), typically a mixture of powdered CNTs in a metal matrix, are manufactured either by Powder Metallurgy or Liquid Metallurgy. In Powder Metallurgy, the mixture of CNTs and the metal is blended by ball milling (grinding into an extremely f1ne powder) following which they are compacted with the help of a pressing machine to consolidate the powder and achieve uniform density. The resulting article is then subjected to elevated temperatures (sintered) to produce the f1nal composite with enhanced metal bonding .
Powder Metallurgy is generally preferred over Liquid Metallurgy (also called Casting) wherein a molten metal is poured into a mould containing CNTs with subsequent solidification needed to produce the f1nal composite.
CNTs suppress the electrical conductivity of metals and enhance their strength, making them ideal electronic packaging materials.
Jagan is quick to point out that every endeavour has its own share of hurdles and that his project is no different. Special care has to be taken to match the density of CNTs with that of the liquid metal, failing which the CNTs come out of the matrix. This can be achieved by depositing the CNTs with a coating of metals like Nickel or Copper. While compacting, the pressing machine should be handled properly lest gaps arise in the compacted mixture. Different metals require different levels of precaution. For instance, in the case of Aluminium, the formation of Aluminium Carbide renders the composite brittle and hence should be kept in check. Improper density and insufficient wettability of the CNT powder can lead to a non-uniform composition of the liquid mould.
Thus the required uniformity and strength of the composite warrants a careful examination of the manufacturing process.
Polymer Matrix Composites
Jagan also designs Polymer Matrix Composites which are produced in sealed vessels called autoclaves, where the pressure vessel supplies both heat and pressure to the workload placed inside it. “The fact that CNT-reinforced polymer composites can boast of enhanced electrical conductivity and mechanical properties is a boon to the aircraft and automobile industries,” he remarks .
CNTs seem to offer a conv1nc1ng solution to strengthen metals and polymers. Their presence has penetrated almost every branch of life today from packaging to automobiles, sports equipment to aircraft; the potential of CNTs to improve their durability follows suit.
M Jagannatham is pursuing his PhD at the Department of Metallurgical and Materials Engineering. He is a resident of Mahanadhi hostel.