Nitrogen glasses

Abstract

Nitrogen glasses are prepared in various M-Si-O-N and M-Si-Al-O-N systems (M - Mg, Y, Ca & Nd) by fusing the appropriate metal oxide powders with Si0₂,A1₂0₃• Si₃N₄and AlN at 1600°-1700°C under a nitrogen atmosphere. The limits of glass formation in some of the nitrogen-containing systems are investigated and properties of the glasses are evaluated. Nitrogen is incorporated in M-Si-Al-0-N glasses up to 10-12.5 a/o, the highest being in the Y-Si-Al-0-N system. The nitrogen glass-forming regions are extensions of their appropriate M-Si-Al-O-N vitreous regions. Small homogeneous glass regions also form in some M-Si-O-N systems. Property measurements on both oxide and nitrogen glasses of the same cation composition show that viscosity, refractive index, dielectric constant, and a.c. conduotivity all increase with nitrogen incorporation these ohanges being due to the increased strength, directional charaoter and polarisabi1ity of the nitrogen bond compared with oxygen in the glass network. Grain-boundary vitreous phases, previously considered to b,e oxides, occurring in densified silicon nitride and β'-sialons have compositions within the nitrogen glass regions of their appropriate M-Si-O-N or M-Si-Al-O-N systems (where M - Mg or Y), and are therefore shown to be oxynitrides. A new Mg-Si-Al-O-N phase β" -magnesium sialon, isostructural with β-Si₃N₄and with a range of compositions near Mg₂₁Si₁₈Al₃0₄₈N₁₀, is obtained by devitrification of Mg-Si-Al-O-N glasses with a metal:non-metal atom ratio 3M:4X in the presence of undissolved β-Si₃N₄.