From FAST to FLASH: Field assisted sintering of oxide ceramics with controlled electric field and current density

闪速烧结是一种陶瓷材料致密化的新工艺。这一过程是基于通过施加电场和外部加热相结合来迫使陶瓷体内的电流流动。在与材料电阻率有关的起始温度下，样品变得足够导电，高电流开始通过样品，并伴随着明亮的光发射和非常快的致密化在几秒钟内。由于样品几乎完全耗散了电能，闪速烧结被认为是一种非常节能和经济的方法。到目前为止，闪速烧结只在实验室规模上进行了示范，使用的是小狗骨形或条形样品。大多数影响闪速烧结的因素在文献中都是在非常基本的水平上描述的，但据我们所知，闪速烧结与工艺参数之间的相互作用尚缺乏系统的研究。提出了一种研究思路，旨在通过可靠地避免热点形成、控制致密化和调整显微组织来稳定闪光事件。实现这些目标的主要关键将是开发电流速率或功率速率控制的闪速烧结模式，这种模式到目前为止在文献中很少被描述。基于数值模拟的温度分布计算将为实验工作提供有力的支持。这一概念的成功前景得到了SPP1959第一阶段所取得的成果的支持，该成果展示了Gd掺杂CeO2的电流控制闪速烧结。与闪速烧结领域的领先科学家的合作工作已经开始，这将在1959年SPP的第二阶段继续进行。此外，在SPP1959第一阶段建立的预测致密化和晶粒长大的模型将通过考虑闪速烧结的特定效应而得到扩展，例如高压电场的影响。

Flash sintering is a novel process for densification of ceramic materials. The process is based on forcing a current flow within a ceramic body by applying an electric field in combination with external heating. At an onset temperature, which is - amongst others - related to the material resistivity, the sample becomes sufficiently conductive and high electric current starts to pass through the sample accompanied by bright light emission and very fast densification in few seconds. Due to the fact that the electric power is almost completely dissipated by the sample, flash sintering is discussed to be very energy efficient and economic.Up to now, flash sintering has been only demonstrated on lab-scale using small dog-bone or bar shaped samples. Most influence factors of flash sintering are described on a very fundamental level in literature, but a systematic study how flash sintering and processing parameters interact is – to best of our knowledge – still lacking. A research concept is proposed, which aims on stabilizing the flash event by reliably avoiding hot spot formation, controlling the densification and tuning the microstructure. Main key for achieving these goals will be the development of current rate or power rate controlled flash sintering mode, which has been only rarely described in literature so far. Experimental work will be strongly supported by calculating the temperature distribution based on numerical simulations. Prospect of success of this concept is supported by results achieved during the first period of SPP 1959 by demonstrating current rate controlled flash sintering of Gadolinium doped ceria. Collaboration work with leading scientists in the field of flash sintering was initiated, which will be continued in the second period of SPP 1959. Furthermore, the model developed in the first period of SPP 1959 to predict densification and grain growth will be amplified by including specific effects of flash sintering, e.g. influence of high electric field.