ChemInform Abstract: Ionic Conductivity in Li2O‐Al2O3‐SiO2 Based Glasses and Glass Ceramics.

Lunkenheimer, P.; Gerhard, G.; Drexler, Franz; Boehmer, R.; Loidl, A.; Pannhorst, W.

doi:10.1002/chin.199624016

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“…This results in a higher dielectric loss which in turn is responsible for the microwave heating at elevated temperatures. Ionic conductivity studies on Zerodur precursor glass showed increasing conductivity with increasing temperature due to the drop in activation energy ( E ac ) required for electrical conduction at higher temperatures . Once phase separation, nucleation or crystal growth occur, the interfaces or structural discontinuity increase which act as resistance in series and play a role in the dielectric heating.…”

Section: Introductionmentioning

confidence: 99%

Near‐zero thermal expansion transparent lithium aluminosilicate glass‐ceramic by microwave hybrid heat treatment

et al. 2017

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The material of choice for space applications which demand very high dimensional stability is lithium aluminosilicate (LAS) based Ultra Low thermal Expansion Glass-Ceramic (ULEGC). Generally, the controlled crystallization process recommended for the processing of transparent ULEGC involves a long soaking duration to achieve the required crystal number density. This paper brings out the process optimization procedure adopted for realizing transparent and nanocrystalline ULEGC from conventionally processed LAS glass using microwaveassisted (hybrid) crystallization. The experimental strategy involves two stages (i) identification of the optimum crystallization temperature (T c ) under a microwave field (ii) optimization of a microwave-assisted crystallization process to achieve near zero Coefficient of Thermal Expansion (CTE).. Optimum heat-treatment schedules for nucleation and crystallization under a microwave environment were found to be 720°C/24 hours and 775°C/0.3 hours, respectively. The optimized heat-treatment condition revealed the efficacy of the microwave hybrid heating, by producing nanocrystalline (35-50 nm) and transparent (>82%) ULEGC having a thermal expansion of À0.03 9 10 À6 K (0°C to 50°C).

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Section: Introductionmentioning

confidence: 99%