Effects of nitrogen and lanthanum on the preparation and properties of La–Ca–Si–Al–O–N oxynitride glasses

Three series (La-15, N-18 and N-30 series) of oxynitride glasses were prepared by melting batches at 1550–1650 °C for 2 h under N2 atmosphere in a Si–Mo-heated resistance furnace. Nominal compositions of the three series glasses in equivalent percent (eq.%) are La15Ca12Al15Si58O(100 − x)Nx (x = 0, 6, 12, 18, 24, 30, 36), LaxCa(27 − x)Al15Si58O82N18 (x = 0, 4.5, 9, 15, 21, 27) and LaxCa(27 − x)Al15Si58O70N30 (x = 0, 4.5, 9, 15, 21, 27), respectively. The homogeneity of these samples was determined by scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS). The amorphous nature of these samples was verified by an X-ray diffractometer with Cu/Kα radiation. Fourier-transform IR spectroscopy was done to find out the basic structural units in some of these glasses. The effects of N/O ratios (eq.%) and La/Ca ratios (eq.%) on the properties such as density (ρ), thermal expansion coefficient (α), glass transition temperature (Tg), the crystallization temperature (Tc), Vickers hardness (HV), bending strength (σ) and leaching rate (L.R.) were investigated. The effects of nitrogen and lanthanum on the properties are independent and additive. At the same time, the relationship between these properties and the structures of the glasses were discussed. Note that nitrogen seems to enhance the beneficial effects of lanthanum on these properties.