Effect of Nitrogen on Properties of Na₂O–CaO–SrO–ZnO–SiO₂ Glasses

Abstract

Glasses in the Na 2 O-CaO-SrO-ZnO-SiO 2 system have previously been investigated for suitability as a reagent in Al-free glass polyalkenoate cements (GPCs). These materials have many properties that offer potential in orthopedics. However, their applicability has been limited, to date, because of their poor strength. This study was undertaken with the aim of increasing the mechanical properties of a series of these Zn-based GPC glasses by doping with nitrogen to give overall compositions of: 10Na 2 O-10CaO-20SrO-20ZnO-(40 -3x) SiO 2 -xSi 3 N 4 (x is the no. of moles of Si 3 N 4 ). The density, glass-transition temperature, hardness, and elastic modulus of each glass were found to increase fairly linearly with nitrogen content. Indentation fracture resistance also increases with nitrogen content according to a power law relationship. These increases are consistent with the incorporation of N into the glass structure in threefold coordination with silicon resulting in extra cross-linking of the glass network. This was confirmed using 29 Si MAS-NMR which showed that an increasing number of Q 2 units and some Q 3 units with extra bridging anions are formed as nitrogen content increases at the expense of Q 1 units. A small proportion of Zn ions are found to be in tetrahedral coordination in the base oxide glass and the proportion of these increases with the presence of nitrogen.

Mechanical properties, structure, bioactivity and cytotoxicity of bioactive Na-Ca-Si-P-O-(N) glasses

“…The increase in Tg with N is consistent with previous studies of oxynitride glasses [12][13][14][15][16][17][18] which have shown that N creates extra cross-linkages and stiffens the glass network [33].…”

“…For oxynitride glasses (without fluorine), the slope is somewhat lower but this was thought to be due to the presence of bubbles in the glass. The benefit of nitrogen seems to be similar for the glasses studied here and bioactive glasses containing nitrogen which have been previously reported [14,17,18,22,23].…”

“…One solution to the challenge of low strength glasses is to incorporate nitrogen into the silicate network [12][13][14]. When nitrogen replaces oxygen in alumino-silicate glasses, glass transition temperature, elastic modulus and hardness increase linearly with nitrogen content [12][13][14][15][16][17][18]. In a study of substitution of N for O in a potentially bioactive glass composition in the SiO 2 -CaO-Na 2 O system, it was shown that nitrogen increases mechanical properties [14,17] and this can be explained by the fact that N may be viewed as a network forming anion [19].…”

Review: Elaboration, structure, and mechanical properties of oxynitride glasses

“…For example, the reduction of oxides such as Li 2 O, Al 2 O 3 , MgO, CaO, and BaO by Si 3 N 4 is not thermodynamically feasible in the usual temperature range of syntheses, in opposition to Na 2 O, P 2 O 5 , K 2 O, Cs 2 O, and ZnO. 5,88,72,108,109 Nevertheless, this reduction is sometimes observed via an exothermic reaction in the form of vapors. 37 However, let us recall that such a tool brings no information about the kinetics.…”

Bioactivity and Cytotoxicity of Oxynitride Glasses

“…However, the low mechanical strength and inherent brittleness of these bioglasses have restricted their use to non-load-bearing applications [15] such as ossicles in the middle ear. The incorporation of nitrogen into the silicate network has been proposed as solution to resolve the problem of low strength in glasses [16,17] .…”