This paper presents a comprehensive study on thermal, structural and optical properties of novel willemite glass-ceramics. The precursor glass in the ZnO-SLS glass system was successfully prepared using conventional meltquenching technique and willemite (Zn 2 SiO 4 ) glass-ceramics were derived from this precursor glass by a control crystallization process. The effect of heat-treatment temperature on the phase transformation, morphology and size of Zn 2 SiO 4 crystal phase was examined using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) techniques. Furthermore, fourier transform infrared reflection (FTIR) spectroscopy was used to evaluate the Zn 2 SiO 4 crystal structural evolution. The average size of Zn 2 SiO 4 crystallite obtained from calculation of XRD is found to be in the range 30-60 nm, whereas the grain size observed in FESEM is in range of 200-400 nm. The appearance of SiO 2 , ZnO 4 and Zn-O-Si bands detected from FTIR indicate the formation of Zn 2 SiO 4 crystal phase. Besides, the study of the optical band gap has found that optical band gap of the glass-ceramics decreased as the heat treatment temperature increased. The photoluminescence spectra of willemite glass-ceramics exhibit two different emissions around 525 nm (green) and 585 nm (yellow); exhibit a characteristic of broad absorption band around 260 nm. These two different spectra reveal that the luminescence performance of the willemite glass-ceramics was enhanced with the progression of heat treatment temperature due to different located energy levels of the b-Zn 2 SiO 4 and a-Zn 2 SiO 4 crystalline phase. Such luminescent glass-ceramics was expected to find potential applications in phosphors and opto-electronic devices.

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Willemite glass-ceramics were successfully derived from conventional melt-quench ZnO-SLS precursor glass by an isothermal heat treatment process. The effect of heat treatment temperatures on the physical properties was investigated by Archimedes principle and linear shrinkage. The generation of willemite crystal phase and morphology with increase in heat treatment temperature was examined by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and field emission scanning electron microscopy (FESEM) techniques. X-ray diffraction revealed that the metastableβ-Zn2SiO4and thermodynamically stable zinc orthosilicateα-Zn2SiO4phases can be observed at temperatures above 700°C. The experimental results indicated that the density and shrinkage of the glass-ceramic vary with increasing the sintering temperature. FTIR studies showed that the structure of glass-ceramic consists of SiO2and ZnO4units and exhibits the structural evolution of willemite glass-ceramics. The characteristic of strong vibrational bands can be related to theSiO44-tetrahedron corresponding to reference spectra of willemite.

Binary zinc phosphate glass system with composition of (ZnO)x(P2O5)1−x, (x= 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 mol%) was successfully prepared using a conventional melt-quenching method. Composition dependence of physical properties and elastic properties in the (ZnO)x(P2O5)1−xwere discussed in association with the effects of adding zinc oxide (ZnO) as a modifier. The addition of ZnO modifier was expected to produce substantial changes on physical properties of the phosphate glasses. An increase in density values of the phosphate glasses was observed. Elastic moduli were studied by measuring ultrasonic longitudinal and shear velocities (VlandVt) of the glasses at room. Longitudinal modulus, shear modulus, bulk modulus, Young’s modulus, Poisson’s ratio, and Debye temperature(θD)were derived from both data of velocities and respective density of all of the samples. Findings from present work showed dependence of density and elastic moduli of each ZnO-P2O5series on glass composition.

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