Amorphization of cristobalite at high temperature in vacuum
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W. Wang,a) X.X. Huang, and J.K. Guo Structural Ceramics Center, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, People’s Republic of China (Received 27 December 2004; accepted 12 May 2005)
Amorphous transition behavior of silica polymorphs under high pressure has been extensively studied by using diamond-anvil cells or shock wave technologies at ambient temperature. Here, we report the amorphization of crystalline silica fiber in cristobalite polymorph in the temperature range of 1050–1350 °C without pressure applied in vacuum. X-ray diffraction, infrared spectra, and Raman spectra illustrated the transition. Raman spectra revealed that no significant changes had happened to the SiO4 unit during the transition. It is suggested that the driven-off of interstitial oxygen attributed to the transition and the reaction between the diffusing hydrogen and interstitial oxygen promoted the process.
Silica is a very important substance for its specific functional and structural properties. It has been widely used in numerous technological fields, such as semiconductors, catalyst carriers, optical devices, aircraft materials, etc. The amorphization behavior of silica polymorphs has been observed in the diamond-anvil cell (DAC) under high pressure (usually higher than about 10 GPa) and shock wave experiments. It has attracted extensive attention from geology, condensed-state physics, and materials science.1–7 Cristobalite is one of the silica polymorphs usually found in lithosphere rocks formed from high-temperature melts spouted from the Earth’s centrosphere. The study of cristobalite phase transition is helpful for the further understanding of many natural phenomena.3 In this communication, we report an amorphization behavior from cristobalite to amorphous phase in the crystalline silica fiber when heat-treated at moderate temperature without pressure applied in vacuum (艋10 Pa). In the present experiment, the vitreous silica fiber (VSF) with commercial high purity (艌99.95 wt% SiO2, d ∼ 5 m; Feilihua Quartz Glass Co. Ltd., Jingzhou, People’s Republic of China) was heat-treated at 1350 °C for 0.5 h in air. Crystalline silica fiber (CSF) in cristobalite polymorph was produced (1350 °C × 0.5 h–air). It
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0266 J. Mater. Res., Vol. 20, No. 8, Aug 2005
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can be seen from the x-ray diffraction (XRD) pattern that cristobalite was the main crystalline phase in the CSF [Fig.1(a)]. Further, the CSF was re-treated at different temperature for 0.5 h in vacuum (艋10 Pa), noted as [temperature]-CSFH (for example, 850 °C-CSFH). When the temperature was 850 °C, no significant difference was found in the XRD patterns between CSF and 850 °C-CSFH [Figs. 1(a) and 1(b)]. However, the peak disappeared completely when the CSF was heat-treated at 1050–1250 °C [Figs. 1(c) and 1(d)]. For the 1350 °CCSFH, the peak remained, though sharply weakened. For the 1550 °C-CSFH,
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