Publication Date:
2012-09-13
Description:
The effect of the addition of NiO on the crystallization mechanisms has been studied for SiO 2 – Al 2 O 3 – MgO glass-ceramics. A detailed Rietveld analysis has been made to determine the chemical composition and the cation distribution in the spinel phase and the evolution of Ni 2+ coordination site using diffuse reflectance spectroscopy. Powder X-ray diffraction (XRD) results show the formation of β-quartz and spinel and the nickel fraction in the spinel phase decreasing as the plateau temperature increases. The determination of cation distribution in spinel using XRD reveals a preference of Ni 2+ and Al 3+ for octahedral sites and an increasing proportion of Ni 2+ in tetrahedral sites for heat treatments at high temperature (1100°C–1200°C). Diffuse reflectance spectroscopy shows that Ni 2+ is mainly fivefold coordinated in the starting glass, playing an important role in the crystallization of the spinel phase and it confirms the presence of tetrahedral and octahedral Ni 2+ in the glass-ceramics. The combination of these two techniques also indicates a chemical heterogeneity of spinel crystals with Ni 2+ -rich and Mg 2+ -rich zones.
Print ISSN:
0002-7820
Electronic ISSN:
1551-2916
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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