Independent Effects of Nitrogen Substitution for Oxygen and Yttrium Substitution for Magnesium on the Properties of Mg‐Y‐Si‐Al‐O‐N Glasses

Abstract

Glasses of composition (in equivalent percent) (28 −x)Mg:xY:56Si:16Al:(100 −y)O:yN, with x= 0, 14, or 28 for y= 0 and 15 and with x= 0, 7, 14, 21, or 28 for y= 10, were prepared by melting and casting. For glasses where the nitrogen content was varied for a constant cationic ratio, the glass molar volume (MV), compactness (C), Young's modulus (E), glass‐transition temperature (Tg), and dilatometric‐softening temperature (Tds) varied linearly as the nitrogen content increased, with MV decreasing and the other properties increasing. From the incremental changes in these properties with nitrogen content, for glasses with x= 0, 14, and 28, good linear fits (R2 > 0.99) were obtained, and best‐fit slopes are reported here. The property changes and their linearity were consistent with the increased cross‐linking of the glass network by tricoordinated nitrogen. The replacement of magnesium by yttrium led to a nonlinear decrease in glass compactness and to nonlinear increases in MV, Tg, and Tds. However, linear correlations were found for MV and ionic volume and for Tg, Tds, and the coordination of (Si,Al)(O,N) tetrahedra of the glass structural units to the modifier cations not involved in charge compensating aluminum ions in fourfold coordination. The replacement of magnesium by yttrium had little effect on Young's modulus, and this result was related to similar changes in the compactness, C. The present results showed that the effects of substituting nitrogen for oxygen and yttrium for magnesium are independent and additive; thus, no synergistic effects of anion and cation substitutions were observed.

SiAlON glasses: Effects of nitrogen on structure and properties

“…Figure 6 shows a plot of molar volume and compactness data as a function of nitrogen substitution for a 37Y:42Si:21Al (eq.%) glass 33) and clearly shows a good linear correlation. Such linearity has previously been presented by Pomeroy et al 6) and analysis of the data of Lofaj et al 26) also shows that molar volume and fractional glass compactness as a function of nitrogen content of the glasses are reasonably linear. The changes in compactness indicate that the replacement of oxygen by nitrogen induces a contraction of the glass structure, which is linked to the increased coordination of nitrogen compared to oxygen.…”

“…With respect to modifier cation type, evidence shows 16),17),21) that as the cation field strength (charge/square of ionic radius) of the modifier increases then so do elastic modulus, hardness, glass transition temperature and viscosity. For mixed modifier systems, the same effects are seen in terms of atomic concentration averaged field strengths, 6) but only if the cations have the same valency. The data and analyses reviewed here, whilst not exhaustive, clearly illustrate that the effects of nitrogen substitution are very similar for different glass systems.…”

“…Rouxel 40) has conclusively shown that, for a wide variety of different types of glasses, Young's modulus is controlled by the compactness of the glass structure. Thus, the linear trend shown by Pomeroy et al 6) between Young's modulus and fractional glass compactness is wholly expected. Figure 7 shows additional data 33) for a 37Y:42Si:21Al (eq.%) glass which exemplifies the linear dependence of Young's modulus on glass compactness.…”

“…The data of Hampshire et al 32) first showed linearity for plots of hardness v. nitrogen content and subsequent detailed analysis by Pomeroy et al 6) showed that for a glass containing 56 eq.% Si, 16 eq.% Al and 28 eq.% of the mixed modifiers Mg and Y, the slopes of plots of Young's modulus v. nitrogen content were the same for each of three different modifier compositions used (in eq.%: 28Mg:0Y; 14Mg: 14Y; 0Mg:28Y). Other work 33) with glasses of cation composition (in eq.%) 37M:42Si:21Al (M = either Y or Er) showed that linear correlations between both microhardness and nitrogen content and Young's modulus and nitrogen content were again observed.…”

Structural characterisation of Er–Si–Al–O–N glasses by Raman spectroscopy

“…It is seen from Table 1 that density increases with increasing nitrogen content and this is solely attributable to the fact that nitrogen causes increases in glass compactness as noted previously. 30 From Table 1 it is also clear that microhardness, glass transition temperature and dilatometric softening temperature increase with increasing nitrogen content. Figs.…”