Glass-ceramics are composite materials obtained from partial devitrification of a parent glass through a controlled heating treatment. The evolution of the glass structure under thermal treatment proceeds through thermodynamically metastable phases toward a final material made of microcrystalline phases finely dispersed into amorphous phases. The processes occurring during the devitrification and the physical properties of a glass-ceramic material basically depend on the composition, thermal treatments as well as on a number of factors, such as nucleation and crystallization phenomena, and chemical nature of the elements. An accurate knowledge of metastable phases and intermediate structures evolving during the thermal treatments are essential for a deep understanding the physical-chemistry processes giving rise to the final glass-ceramic material. One of the basic systems in glass ceramics technology belongs to the CaO-ZrO2-SiO2 (CZS) ternary system. In this work the structure of Zr atomic environment in a CaO-ZrO2-SiO2 glass-ceramic has been studied combining x-ray absorption spectroscopy (XAS), X-ray diffraction (XRD) and anomalous XRD (a-XRD) techniques as a function of thermal treatments. The analysis of XRD patterns demonstrates that the devitrification process, as a function of thermal treatment, proceeds through the partial segregation of Zr-depleted phases (Wollastonite-like) and Zr-rich phases (Zr-oxides). A detailed insight on the atomic structure around Zr ions was achieved combining a-XRD technique and the accurate analysis of XAS spectra both in the extended (EXAFS) and in near edge (XANES) regions. In the as quenched glass the Zr is 6-fold coordinated to Oxygen atoms in an amorphous environment rich of Ca and Si. Thermal treatment firstly (T=1000 - 1050 oC) determines the partial segregation of Zr in form of oxide which crystalline structure is that of tetragonal zirconia (t-ZrO2). Raising the temperature (T=1100oC) provokes the formation of ZrO2 crystallites in the monoclinic baddeleyite crystallographic phase (m-ZrO2). The analysis of XAS data demonstrates that a considerable amount of Zr still remains in an amorphous calcium-silicate phase.
Meneghini, C. (2004). The evolution of ZrO2 containing phases and devitrification processes in Ca-Zr-Si-O based glass ceramics: a comprehensive XRD and AS study.
The evolution of ZrO2 containing phases and devitrification processes in Ca-Zr-Si-O based glass ceramics: a comprehensive XRD and AS study
MENEGHINI, CARLO
2004-01-01
Abstract
Glass-ceramics are composite materials obtained from partial devitrification of a parent glass through a controlled heating treatment. The evolution of the glass structure under thermal treatment proceeds through thermodynamically metastable phases toward a final material made of microcrystalline phases finely dispersed into amorphous phases. The processes occurring during the devitrification and the physical properties of a glass-ceramic material basically depend on the composition, thermal treatments as well as on a number of factors, such as nucleation and crystallization phenomena, and chemical nature of the elements. An accurate knowledge of metastable phases and intermediate structures evolving during the thermal treatments are essential for a deep understanding the physical-chemistry processes giving rise to the final glass-ceramic material. One of the basic systems in glass ceramics technology belongs to the CaO-ZrO2-SiO2 (CZS) ternary system. In this work the structure of Zr atomic environment in a CaO-ZrO2-SiO2 glass-ceramic has been studied combining x-ray absorption spectroscopy (XAS), X-ray diffraction (XRD) and anomalous XRD (a-XRD) techniques as a function of thermal treatments. The analysis of XRD patterns demonstrates that the devitrification process, as a function of thermal treatment, proceeds through the partial segregation of Zr-depleted phases (Wollastonite-like) and Zr-rich phases (Zr-oxides). A detailed insight on the atomic structure around Zr ions was achieved combining a-XRD technique and the accurate analysis of XAS spectra both in the extended (EXAFS) and in near edge (XANES) regions. In the as quenched glass the Zr is 6-fold coordinated to Oxygen atoms in an amorphous environment rich of Ca and Si. Thermal treatment firstly (T=1000 - 1050 oC) determines the partial segregation of Zr in form of oxide which crystalline structure is that of tetragonal zirconia (t-ZrO2). Raising the temperature (T=1100oC) provokes the formation of ZrO2 crystallites in the monoclinic baddeleyite crystallographic phase (m-ZrO2). The analysis of XAS data demonstrates that a considerable amount of Zr still remains in an amorphous calcium-silicate phase.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
