Glasses and composites: fundamentals and applications

Most commonly encountered classification of materials is based on their structure, namely the amorphous and crystalline phases. Both amorphous and crystalline materials (solids) can be either single phase or a combination of number of phases, the latter material is generally called as a composite material. There are many instances, wherein a synergistic mechanism operates and a composite material has many advantages over the corresponding single phase components. Composite materials find wide variety of applications and are commonly employed as catalysts, luminescent materials, glass ceramics, gas/hydrogen storage materials etc. In this lecture, composite materials such as glass ceramics, nanoparticles incorporated silica and multi component (phase) intermetallic alloys and their applications will be discussed. Glass ceramics made with certain annealing conditions are machineable. Typical example of a machineable glass ceramic is the one based on magnesium alumino silicate (MAS) glass. By addition of suitable nucleating agents, crystallization of a phase called potassium fluorophlogopite can be achieved in the glass matrix. This phase is having tile like structure and is responsible for the machine-able property of the composite material. Presence of such phases can be identified and their relative concentration can be evaluated based on solid state nuclear magnetic resonance technique, using ²⁹Si as the probe nuclei. Typical ²⁹Si Magic Angle Spinning Nuclear Magnetic Resonance (MASNMR) spectrum for MAS glass. ²⁹Si MAS NMR pattern of Magnesium Alumino Silicate glass ceramics prepared by adding 8 mol % Al₂O₃ ceramic prepared with addition of 8 mol% of Al₂O₃. The sharp peaks in the NMR pattern are characteristic of Potassium fluorophlogopite phase. Depending up on concentration of this phase, machine-ability of the material is found to change. In addition to this optical and energy storage properties of representative composite materials will also be discussed in detail in the present lecture