颗粒悬浮液的凝固界面失稳机理研究

Ice-templated technology has become a novel method for manufacturing advanced porous materials. The solidification process of particle suspension is an important step of the ice-templated technology, and its solidification microstructure directly determines the porous structures and properties of materials. However, the lack of the inherent relationship between ice-templated process and microstructure and the failure of defect control lead to the dispersion of material properties. The development of ice-templated technology requires the theoretical study on the solidification microstructure formation in particle suspension. The solidification microstructure of particle suspension originates from the instability of the solidification interface. The lamellar ice crystal formation from planar interface instability is the important part of process - structure control. The ice bridge and ceramic bridge formation from the side and tip interface instability of lamellar ice crystal is the key to solve property dispersion of porous materials. Therefore, the instability mechanism of the solidification interface of particle suspension is a core scientific issue of ice-templated technology. This project plans to systematically investigate the unsteady evolution process of the solidification interface instability of particle suspension through real-time observation and in-situ comparison method. The quantitative relationship of the instability of planar interface, the formation of ice bridge and ceramic bridge and the ice-templated process is determined. The influence of solute and particle on the instability of the solidification interface is clarified. The instability mechanism of the planar interface and the formation mechanism of the ice bridge and the ceramic bridge are revealed. The accomplishment of this project can establish the theoretical foundation for the microstructure control and performance improvement of the aligned porous materials prepared by ice-templated technology.

冰模板技术已经成为制备先进多孔材料的重要方法之一。颗粒悬浮液凝固是冰模板法制备过程的重要环节，其凝固形态直接决定着多孔材料的组织特征与性能。然而冰模板技术工艺-组织内在共性规律的缺乏以及缺陷组织的不可控导致材料性能分散。冰模板技术的发展离不开对颗粒悬浮液凝固组织形成的理论研究。颗粒悬浮液凝固组织起源于凝固界面的失稳。悬浮液定向凝固平界面失稳形成层状冰晶是工艺-组织调控的核心，而后续层状冰晶侧面和尖端失稳形成的冰桥和陶瓷桥是解决性能分散的关键。因此，颗粒悬浮液凝固界面的失稳机理成为亟待解决的核心问题。本项目通过原位实时观察结合同步对比方法系统研究颗粒悬浮液凝固界面失稳的非稳态演化过程，获得平界面失稳和冰桥及陶瓷桥形成与工艺参数之间的定量关系，明晰颗粒和溶质对凝固界面失稳的影响规律，揭示颗粒悬浮液平界面失稳机理和冰桥及陶瓷桥形成机理，为冰模板法制备定向多孔材料的组织调控及性能提升奠定理论基础。

颗粒悬浮液凝固是冰模板法制备先进多孔材料的关键环节，其凝固形态直接决定多孔材料的孔隙特征与性能。冰模板多孔材料的组织调控目前主要依靠大量的工艺研究，且工艺-组织内在共性规律的缺乏以及缺陷组织的不可控导致材料性能分散。因此，冰模板技术的发展离不开对颗粒悬浮液凝固组织形成的理论研究。本项目采用独特的原位实时观察手段和同步对比方法，研究了离子型溶质、聚合物大分子溶质和纳米颗粒对水溶液定向凝固平界面失稳及后续微观组织形态的作用机制。首次采用视差法精确测量了颗粒悬浮液体系定向凝固中的颗粒过冷度和溶质过冷度，发现了两种不同的界面失稳机制——溶质主导失稳机制和颗粒主导失稳机制，并明晰颗粒-溶质相互作用对纳米颗粒悬浮液定向凝固微观组织演化的影响机制，最终建立了工艺及颗粒尺寸相关的微观组织选择图谱。首次实现了单晶冰晶的定向凝固研究，并由此发现了定向生长冰晶的V字形倾斜生长，以及溶质类型、浓度和抽拉速度等因素对倾斜生长的影响规律，从而揭示了定向冰晶片层组织中的冰搭桥形成的新机制。此外，获得了溶质浓度和抽拉速度对定向生长冰晶片层间距的影响规律，建立了工艺-成分-片层间距之间的标度率关系。本项目获得了颗粒悬浮液凝固界面微观组织演化中的一些关键基础科学问题的答案，其研究结果将为冰模板法制备定向多孔材料的组织调控及性能提升提供理论指导。