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 microwave-assisted (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 −0.03 × 10⁻⁶ K (0°C to 50°C).

中文翻译：

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微波混合热处理近零热膨胀透明铝硅酸锂玻璃陶瓷

需要极高尺寸稳定性的航天应用选择的材料是基于铝硅酸锂（LAS）的超低热膨胀玻璃陶瓷（ULEGC）。通常，推荐用于透明ULEGC加工的受控结晶过程涉及较长的浸泡时间，以实现所需的晶体数密度。本文提出了通过微波辅助（混合）结晶从常规加工的LAS玻璃中实现透明和纳米晶体ULEGC所采用的工艺优化程序。实验策略包括两个阶段（i）确定最佳结晶温度（T _c）在微波场下（ii）优化微波辅助结晶工艺以实现接近零的热膨胀系数（CTE）。发现微波环境下成核和结晶的最佳热处理时间表为720°C /分别为24小时和775°C / 0.3小时。优化的热处理条件通过产生热膨胀为-0.03×10 ^-6  K（0°C至50 ）的纳米晶体（35-50 nm）和透明（> 82％）ULEGC揭示了微波混合加热的功效°C）。