Nanocomposites, a high performance material exhibit unusual property combinations and unique design possibilities. With an estimated annual growth rate of about 25% and fastest demand to be in engineering plastics and elastomers, their potential is so striking that they are useful in several areas ranging from packaging to biomedical applications. In this unified overview the three types of matrix nanocomposites are presented underlining the need for these materials, their processing methods and some recent results on structure, properties and potential applications, perspectives including need for such materials in future space mission and other interesting applications together with market and safety aspects. Possible uses of natural materials such as clay based minerals, chrysotile and lignocellulosic fibers are highlighted. Being environmentally friendly, applications of nanocomposites offer new technology and business opportunities for several sectors of the aerospace, automotive, electronics and biotechnology industries.

Nanocomposites are composites in which at least one of the phases shows dimensions in the nanometre range (1 nm = 10^-9 m)¹. Nanocomposite materials have emerged as suitable alternatives to overcome limitations of microcomposites and monolithics, while posing preparation challenges related to the control of elemental composition and stoichiometry in the nanocluster phase. They are reported to be the materials of 21^st century in the view of possessing design uniqueness and property combinations that are not found in conventional composites. The general understanding of these properties is yet to be reached², even though the first inference on them was reported as early as 1992³.

Before going into details regarding processing, structure, properties and applications of the three types of nanocomposites, let us look at the potentials of these systems and the general opportunities they provide. Ceramics have good wear resistance and high thermal and chemical stability. However, they are brittle. In this context, the low toughness of ceramics has remained a stumbling block for their wider use in industry. In order to overcome this limitation, ceramic-matrix nanocomposites have been receiving attention, primarily due to the significant enhancement on mechanical properties which can be achieved. For example, the incorporation of energy-dissipating components such as whiskers, fibres, platelets or particles in the ceramic matrix may lead to increased fracture toughness.The reinforcements deflect the crack and/or provide bridging elements, hindering further opening of the crack. In addition, the incorporated phase undergoes phase transition in conjunction with the volume expansion initiated by the stress field of a propagating crack, contributing for the toughening and strengthening processes, even in nanocomposites³⁶.

The potential of ceramic matrix nanocomposites (CMNC), mainly the Al₂O₃/SiC system, was revealed by the pioneering work of Niihara. Most studies reported so far have confirmed the noticeable strengthening of the Al₂O₃ matrix after addition of a low (i.e. ~10%) volume fraction of SiC particles of suitable size and hot pressing of the resulting mixture. Some studies have explained this toughening mechanism based on the crack-bridging role of the nanosized reinforcements³⁹. Consequently, the incorporation of high strength nanofibres into ceramic matrices has allowed the preparation of advanced nanocomposites with high toughness and superior failure characteristics compared to the sudden failures of ceramic materials⁴⁰.