内含高压气体的仿植物细胞结构多孔材料的制备及其力学特性研究

Porous ceramics with ultra-low density are of great interest as potential engineering material in various industrial fields such as high temperature environment, et.al. However, their poor specific mechanical properties restrict their potential applications. Improving the specific strength is a complex and technological problem in the processing of ultra-low density ceramics materials around the world. There is an effective way to improve the specific mechanical properties of porous materials with ultra-low density by obtaining imitation plant cells with pressurized gas. The enclosed plasma liquid pressure in plant cells contributed to the excellent mechanical properties such as the high compressive strength. In this research, imitation plant cell structure cellular borosilicate glasses with pressurized gas filled closed pores were prepared by capsule-free hot isostatic pressing and subsequent isothermal heat treatment. During the sintering process, the argon gas was dissolved in the glass under high pressure, and then, argon gas released to form pressurized nano- to micro- size Ar-filled closed pores under low pressure at elevated temperatures. Based on the inert gas atom diffusion behavior study during inert gas dissolving and releasing process, the effect of gas dissolve rate on the porosity, pore structure and enclosed gas pressure of porous glass will be revealed, and the mechanism of pore formation by inert gas nucleation-growth process will be clarified. The influence of process parameters (dissolve rate, melting temperature, gas pressure, and heating rate) on the microstructure and mechanical properties of porous borosilicate glass will be investigated. Combined with analysis of micromechanics behavior of closed pore with enclosed gas pressure and the numerical simulation, the theory model between the enclosed gas pressure and mechanical behavior of porous materials will be built, and the strengthening mechanism by enclosed gas pressure will be clarified. This research is expected to be a direction for the preparation of ultrahigh specific strength porous materials with ultra-low density.

超轻多孔陶瓷材料在轻质耐热承载等领域可发挥重要作用，比强度的提高是超轻多孔材料的重点和难点。获得仿植物细胞结构的充填高压气体的闭气孔是减重增强的有效手段。本研究结合植物细胞"原生质内压增强补韧"思想，拟采用"高压惰性气体原子固溶-降压气体释放"成孔技术，将惰性气体原子固溶的Pyrex玻璃体通过降压热处理释放气体，制备纳米至微米级闭孔内填充高压气体的仿植物细胞结构多孔Pyrex玻璃材料。通过对惰性气体的固溶与释放过程的扩散行为研究，揭示固溶率对气孔率、气孔结构和内压的调控作用，阐明气孔的成核-长大规律和多孔玻璃的成孔机制。研究固溶及热处理的温度、压力、升温速率对材料微观结构及力学性能的影响规律，进而实现材料组织和性能优化。结合高压气孔胞元孔壁的微观力学性能测试及数值模拟，揭示气孔内压的增强机理，建立多孔材料的气孔内压与尺度相关联的力学行为的理论模型，为超轻高比强多孔材料的创新设计提供新思路。

超轻多孔陶瓷材比强度的提高是超轻多孔材料的重点和难点。获得仿植物细胞结构的充填高压气体的闭气孔是减重增强的有效手段。本研究以超轻高比强多孔玻璃材料为背景，通过对惰性气体“高压固溶-降压释放成孔”工艺过程的优化，实现了高气孔率、高比强多孔Pyrex材料的制备。通过在多孔玻璃材料的闭气孔内填充高压气体，实现了材料的高性能化。通过热力学计算建立了高压气氛条件下碳的氧化反应相图。确立了内含高压气体的仿植物细胞结构多孔Pyrex玻璃材料的制备工艺，获得性能优异的超轻高比强多孔Pyrex玻璃材料；材料的压缩强度、抗弯强度远高于同类型多孔玻璃材料，这是由于气孔内压远高于0.1 MPa，内部压力显著地提高了孔的坍塌应力。相同气孔率条件下，增加气孔内压力，多孔玻璃的比抗弯强度和比压缩强度增加。 H100A10试样的气孔内压力为~15.7 MPa，由于内部压力较高，在周围玻璃基体内形成压应力，抗弯强度达到71.6 MPa，高于致密Pyrex玻璃的抗弯强度69 MPa，比抗弯强度为其2倍。获得了气体原子固溶及热处理的温度、压力、升温速率对材料微观结构及力学性能的影响规律。阐明了惰性气体原子在Pyrex玻璃中的高压固溶、降压释放行为规律，阐明了气孔的成核-长大规律和多孔玻璃的成孔机制，明确气孔内压的控制参数，在常压条件下800 ºC低温热处理时，孔的形成包含两个来源：a）高压气孔膨胀形成大气孔；b）固溶的Ar原子低压下释放后“释放-聚集”成小孔。热处理气氛压力和玻璃黏度决定了闭气孔内部的气体压力。通过单个气孔微观力学行为与多孔材料宏观力学行为分析，揭示了气孔内压对超轻多孔材料的强化机理。由于气孔内高压气体作用，在气孔周围的玻璃存在压应力，对压痕过程起阻碍作用。随着气孔内压增加，残余压应力增大，所需要的压入载荷也明显增大。本项目的研究结果为超轻高比强多孔材料的创新设计提供了新方法和新思路。