Glasses oxynitride

Oxynitride glasses have been studied and some improvements claimed (Chapter 5.7). This includes the system Na-O-N-P where some substitution of N for O in the PO4 tetrahedra is believed to have been obtained. 

One common feature of all oxynitride glasses is that th are black. This blackness is not an intrinsic phenomenon of the materials themselves, but rather is consistent with the similar dark color of silicon nitride materials, especially those which have been produced at higher temperatures, and also in a carbon-rich environment It is now known that the dark color is due to a fine dispersion of metaDic particles within the glass [51], which form fundamentally as a result of trace metaDic impurities 

As with oxide glasses, heat treatment at temperatures above Tg but below the eutectic temperature in the system results in the formation of crystalline products. For most oxynitride glasses, the results of heat treatment will be a mixture of oxide and oxynitride crystalline products, with the exact phases produced differing significantly with the temperature(s) used. In oxide systems, where the aim of the heat treatment is to produce a single-phase crystalline product of controlled (small) grain size, it is 

A composition such as Ln2Si2A104N3 is dose to the limit of Al-substitution in the melilite structure, and in the low-Z rare earth systems. This composition is also close to the limit of nitrogen substitution in the liquid (and hence glass-forming) region in these systems. 

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Phosphorus oxynitride, PON, is a useful starting product, as a phosphorus and nitrogen source, to prepare various nitridooxophos-phates, in particular phosphorus oxynitride glass compositions (211). Moreover, it shows as a material excellent chemical stability with potential applications in several domains. In microelectronics, for example, PON has been used to form by evaporation insulating films for the passivation of III-V InP substrates and the elaboration of MIS (metal-insulator-semiconductor) structures (190, 212-215). PON could have also valuable properties in flame retardancy (176,191,216). 

Oxynitride glasses - glass ceramics composites S Hampshire, University of Limerick, Ireland 560... 

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. 

Crystallisation of oxynitride glasses to form multi-phase glass-ceramic composites... 

As with other silicate glasses, oxynitride glasses may be heat treated at appropriate temperatures to crystallise as glass-ceramics (Leng-Ward and Lewis, 1990 Thompson, 1992 Hampshire, 1993). The crystalline phases formed depend on both the composition of the parent glass and the heat-... 

Many studies of crystallisation of oxynitride glasses have concentrated on the Y-Si-Al-O-N system. Thompson (1989) outlined the various crystalline phases that exist in this system as shown in the Janecke prism in Fig. 21.2. 

Oxynitride glasses are silicate or alumino-silicate glasses in which oxygen atoms in the glass network are partially replaced by nitrogen atoms. As nitrogen increases, glass transition temperature, elastic modulus, viscosity and hardness increase while thermal expansion coefficient decreases. 

SiC particle reinforced oxynitride glass composites have been investigated and found to have higher values of mechanical properties which are related to the volume fraction of SiC inclusions, provided that SiC-glass reactions can be avoided. These composites have been shown to be suitable for viscoplastic forming. 

Hampshire, S. (1993), Oxynitride glasses and glass-ceramics , in Chen I.W., Becher, P.F., Mitomo, M., Petzow, G., Yen, T-S. (eds), Silicon Nitride Ceramics - Scientific and Technological Advances, Mater. Res. Soc. Symp. Proc., 287, 93-100. 

Hampshire, S., Pomeroy, M.J. (2004), Effect of composition on viscosities of rare earth oxynitride glasses , J. Non-Cryst. Sol., 344, 1-7. 

Hampshire, S., Flynn, R., Lonergan, J., O Riordan, A. (1992), Oxynitride glass systems and subsequent glass-ceramic heat treatments , in Carlsson, R. (ed.), Ceramic Materials and Components for Engines, Proc. 4th Int. Symp. Goteborg, June 1991, London, Elsevier Applied Science. 

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