TABLE OF CONTENTS Oxynitride glasses are special types of silicate or alumino-silicate glasses in which oxygen atoms in the glass network are partially replaced by nitrogen atoms (Hampshire, 2003a). They occur in M-Si-O-N, M 1-M 2-Si-O-N, M-Si-Al-O-N and M 1-M 2-Si-Al-O-N systems where M, M 1 and M 2 are modifying cations such as the alkali metals (Li, Na, K), the alkaline earths (Mg, Ca, Ba, Sr) or Y, La and the rare earth lanthanides. Oxynitride glasses exhibit higher refractoriness, elastic modulus, viscosity and hardness compared with the corresponding oxide glasses as a result of the extra cross-linking provided by nitrogen within the glass structure.
Oxynitride glasses may be heat treated to form glass-ceramics, effectively multi-phase composites. The process involves heat treatment at two different temperatures, firstly to induce nucleation, then to allow crystal growth of the nuclei. The crystalline phases formed depend on both the composition of the parent glass and the temperatures used for heat treatment. The extent of their formation and growth, the relative amounts and distributions of different phases (including residual glass) and their characteristics will determine the overall properties of the particular composite. The formation of these types of materials and their properties is outlined below.
Other investigations have incorporated SiC nano-phase inclusions into oxynitride glass matrices in order to form composites with improved mechanical properties.
Speciality or new glasses and glass-ceramics with novel functions are being used in modern industrial...
