复合莫来石纤维前驱体结晶行为研究

Crystallization Behavior of Hybrid Mullite Fiber Precursors

无玻璃相微晶结构是莫来石纤维获得良好高温力学性能的关键,采用单/双相莫来石复合前驱体可在不添加玻璃相物质前提下,调控莫来石纤维结晶结构。在复合前驱体中,单相莫来石组分在~980℃原位生成的莫来石晶粒可作为晶核,诱导双相莫来石组分在较低的温度下形成莫来石晶相,使前驱体具有较好的结晶特性及致密化特性,并获得微晶、均匀、致密的结构。采用单、双相莫来石前驱体混合的方法制备了一系列可纺复合莫来石前驱体,通过XRD、DSC及SEM对其高温莫来石结晶行为进行了研究,并据此确定了最佳的复合前驱体组成。研究发现,含70wt%单相组分的复合前驱体具有最好的结晶及致密化特性,与双相莫来石前驱体相比,经1400℃热处理20 h后,其晶核密度从8×10^(12)/cm^3提高到1×10^(15)/cm^3,平均粒径从~360 nm降至~120 nm。

Glass free fine-grained microstructure is ideal for preparing mullite fibers with good high temperature mechanical properties. Single phase/diphasic mullite hybrid precursor was adopted to adjust crystalline microstructure of mullite fibers without adding any glass formers. The single phase precursor crystallized in situ to form mullite at 980℃ acting as seed crystals for diphasic components in hybrid precursors to induce the formation of mullite crystals at low temperatures. A series of spinnable hybrid mullite precursors were prepared by mixing single phase and diphasic mullite precursors, and their high temperature crystallization behaviors were investigated by XRD, DSC and SEM, with which optimum formulation of hybrid precursor was determined. The results reveal that hybrid precursor containing 70wt% single phase component has ideal crystalline properties and densification characteristics, with fine grain, uniform, and dense structure. Compared with the pure diphasic mullite precursor, the introduction of 70wt% single phase precursor resulted in an increase in apparent nucleation from 8×10^12/cm^3 to 1×10^15/cm^3, and a reduction in grain size from 360 nm to 120 nm after heat-treatment at 1400℃ for 20 h.