Capillary suspension based additive manufacturing of highly porous, cellular ceramic structures with unprecedented mechanical strength/density ratio

多孔陶瓷的应用范围很广，包括过滤膜、催化剂载体、骨支架或轻质结构元件的复合材料。最近，我们在完善的单元操作的基础上，开发了一种新的高多孔烧结材料的加工路线。这个创新的概念使用所谓的毛细管悬浮液（三相系统固体/流体/流体）作为前置指针来制造高多孔烧结材料。因此，可以很容易地获得50%至80%的开孔率和0.5µm至50µm的孔径。在这里，我们希望推进这项技术，以制造具有迄今为止无与伦比的机械强度的高多孔陶瓷结构。将同时制定和评价两项战略：一种增材制造技术，即所谓的直接墨水书写（DIW）方法，有望创造出具有高多孔陶瓷支柱的细胞结构。这将导致陶瓷体的孔隙率达到90%，强度/密度比接近巴尔沙木。为这种印刷技术优化的浆料将被开发出来，毛细管悬浮液由于其高屈服应力和明显的剪切变薄行为而特别适合。初步实验表明，精心制备的毛细管悬浮液能够产生以前用DIW无法获得的精细特征尺寸（~ 50µm）。细胞结构将使用DIW制造，并测试其机械强度。毛细管悬浮液将用于在给定孔隙率下获得具有出色机械强度的陶瓷材料。这种方法的基本思想是使用三相毛细管悬浮液的二次液体作为载体，在大颗粒的接触区有针对性地沉积小的烧结活性颗粒。这将导致更高的孔圆度和增强的烧结颈，最终导致多孔陶瓷体的机械强度增加。例如，在初步实验中，通过添加细小的ZrO2分数，多孔Al2O3陶瓷的抗压强度可以提高三倍。精细颗粒的化学成分和大小将被系统地改变，所产生的结构将被仔细分析，以进一步提高机械强度。最后，将两个子项目的见解结合使用DIW和适当的材料组合来制造具有前所未有的比机械强度的多孔陶瓷结构。基于毛细管悬浮液的完全开放的多孔结构使得我们的新方法制备的材料在过滤和分离方面有很好的应用前景。因此，DIW将用于打印滤波器演示器，并评估其分离性能。

Porous ceramics are used in a broad range of applications including filtration membranes, catalyst carriers, bone scaffolds or composite materials for lightweight construction elements. Recently, we have developed a new processing route for highly porous sintering materials based on well-established unit operations. This innovative concept uses so-called capillary suspensions (three-phase systems solid/fluid/fluid) as pre-cursor to fabricate highly porous sintering materials. Thus open porosities between 50% and 80% and pore sizes ranging from 0.5 µm to 50 µm can be obtained easily. Here we want to advance this technology to fabricate highly porous ceramic structures with so far unmatched mechanical strength. Two strategies will be developed and evaluated in parallel:1. An additive manufacturing technique, the so-called Direct Ink Writing (DIW) method, shall be used to create cellular structures with highly porous ceramic struts. This is supposed to result in ceramic bodies with porosities > 90% and high strength/density ratio close to Balsa wood. Pastes optimized for this printing technique will be developed, and capillary suspensions are especially suited due to their high yield stress and pronounced shear-thinning behavior. Preliminary experiments suggest that carefully prepared capillary suspensions enable to create fine feature sizes (~ 50 µm) previously not accessible with DIW. Cellular structures will be fabricated using DIW and tested with respect to their mechanical strength.2. Capillary suspensions will be utilized to obtain ceramic materials with outstanding mechanical strength at a given porosity. The basic idea of this approach is to use the secondary liquid of the three-phase capillary suspension as a carrier for targeted deposition of small, sinter-active particles at the contact zones of the large particles. This should result in higher pore roundness and reinforced sintering necks finally resulting in an increased mechanical strength of the porous ceramic bodies. In preliminary experiments e.g. the compressive strength of porous Al2O3 ceramics could be tripled via addition of a fine ZrO2 fraction. Chemical composition and size of the fine particles will be varied systematically and the resulting structures will be carefully analyzed for a targeted further enhancement of mechanical strength. Finally, the insight from both subprojects shall be combined using DIW and appropriate material combinations for manufacturing porous ceramic structures with unprecedented specific mechanical strength. The fully open porous struts of capillary suspension based cellular structures makes the materials fabricated according to our new approach promising candidates for filtration and separation applications. Accordingly, DIW will be used to print a filter demonstrator and its separation properties will be evaluated.