基于冷冻胶凝反应强化机制的3D打印技术及应用研究

3D printing technology has become the focus of research for the integrated preparation of functional gradient ceramics. In present, the ceramics synthesized by 3D printing technology usually have low density and insufficient mechanical strength. In our earlier studies, freeze/gel-casting technique was employed in the production of ceramics with high mechanical strength, and it had small shrinkage in drying and sintering procedure. Besides, this technology has well controllability in production of ceramics and no need for rigid condition just like supercritical drying, which indicates it is a green and environmental technique. Hence, our group present a new mechanism for 3D printing which bases on freeze/gel-casting. However, the mechanism of freeze/gel-casting has not been revealed clearly, and it is insufficient in providing efficient theoretical helps in theory and basic science study is urgently needed. In order to have a overall grasp on 3D freeze/gel-casted printing technology and achieve the integrated preparation of functional SiO2 ceramics, this research will focus on the mechanism of freeze/gel-casting technique and crosslinking between the printed layers.

3D打印技术用于一体化制备功能梯度陶瓷材料已经成为研究的重点，目前可用于陶瓷3D打印的技术存在生坯密度低、产品强度不足的问题。申请者在前期研究中发现，冷冻胶凝成型不仅能够实现陶瓷高强度成型，且在陶瓷干燥、烧结阶段具有很小的收缩，工艺可控性极佳，同时无需超临界干燥等严苛的制备条件，是一种绿色环保、低成本的陶瓷成型技术。因此，本项目提出了基于冷冻胶凝反应的3D打印新途径。但是，冷冻胶凝反应的机理研究尚不充分，难以在3D冷冻打印技术研发中提供有效的理论支持，迫切需要基础科学攻关。本课题目标为突破冷冻胶凝机理和层间交联强化关键技术，全面掌握3D冷冻打印技术，并初步实现一体化制备复杂结构的熔石英陶瓷材料。

本项目针对复杂陶瓷构件难以一体化制备难题，开展了基于冷冻胶凝反应的3D打印新技术研究。首先，通过调控温度场控制了冰晶成核与生长的速率，研究了冰晶生长速率、尺寸等因素对溶胶颗粒之间Si-O-Si键生成的影响规律，并通过动力学研究计算了温度控制的凝胶反应活化能。研究发现，低温下形成的小冰晶具有更大的晶界面积，能够更有效的挤压溶胶颗粒，使得Si-O-Si反应更加充分，获得的凝胶强度越高。凝胶反应活化能高达24.1KJ/mol，高于常规方式引发的凝胶反应。然后，研究了陶瓷粉体粒度级配、纳米粉体掺杂量、球磨时间等因素对陶瓷浆料液相迁移现象的影响，获得稳定的陶瓷浆料，同时研究了有机塑化剂（聚乙二醇）和粘结剂（聚乙烯醇）掺杂及用量对陶瓷浆料塑性和粘性的影响，使浆料能够被3D打印成型设备在不同作用力下均匀挤出成型。随后，研究了3D打印层间冷冻交联方式及调控规律，发现层间先融合后逐步固化的方式为优选的层间结合方式，层间融合的时间间隔在10-20s范围内。其次，完成熔石英材料一体化打印成型和烧结制备，对陶瓷构件进行表征后认为，陶瓷件结构均匀、无缺陷，层间结合强度、陶瓷密度、物相组成均满足需求；最后，尝试打印氧化铝和氮化硅陶瓷材料，对技术应用进行了拓展。