Abstract
The kinetics of the crystallization of cristobalite in the amorphous silica glass were studied for samples prepared by gel-casting and sintering in air. Avrami and rate equations were used to calculate the rate constants and the activation energy. The results showed that the crystallization obeys the first order and occurs mainly on the surface with activation energy of 543-546kJ/mol. The fewer amounts of OH-groups and the high amount of oxygen vacancies are expected to stand behind the increase in the activation energy as compared with that reported in literatures. Keywords: Devitrification, Gel-Casting, Silica Glass, Cristobalite, Crystallization.
Highlights
Transparent silica glass is widely used in many applications due to its unique electronic characteristics such as low dielectric constant, low dielectric loss, high melting point, high thermal shock resistance, and high transparency for wide range of light spectrum [1]
It has been noticed that surface devitrification occurs at 1100oC which is well below that reported by LI, et al [2], they clearly reported that silica glass crystallizes heterogeneously to form cristobalite when the temperature approaches 1300oC and the crystallization is controlled by nucleation and diffusion at the same time
The broad peak at 22.3o is the characteristic peak observed for amorphous silica with nanosize
Summary
Transparent silica glass is widely used in many applications due to its unique electronic characteristics such as low dielectric constant, low dielectric loss, high melting point, high thermal shock resistance, and high transparency for wide range of light spectrum [1]. Many techniques have been used to prepare transparent silica glass; these include spark plasma sintering (SPS) [3,4,5], pressure less sintering [4], vapor-phase axial deposition [6,7], solid phase sintering [8, 9], slip casting [10], and sol gel method [11,12,13,14,15,16]. Transparent silica glass was successfully prepared by gel casting method followed by sintering in air [18]. It has been noticed that surface devitrification occurs at 1100oC which is well below that reported by LI, et al [2], they clearly reported that silica glass crystallizes heterogeneously to form cristobalite when the temperature approaches 1300oC and the crystallization is controlled by nucleation and diffusion at the same time
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