NSF-Europe: SiC-Based Ceramics via Naturally Derived Scaffolds

碳化硅是已知的最硬、最难熔的材料之一，在自然界中不存在。碳化硅粉末合成和批量生产都是能源密集型过程，由于碳化硅的低扩散特性，通常在2000摄氏度以上进行。通过熔体渗透技术，在中等温度下可以使用的工艺数量有限，而且它们提供的微观结构控制很少。这里正在研究的另一种方法是依靠天然衍生的支架来生产碳化硅。这些所谓的“生物形态”碳化硅是通过热解木材来制造碳支架而产生的。然后将支架或模板用于硅渗透和反应，以产生多功能的碳化硅基微孔材料。这项工作的目标有三个方面：(A)了解由天然支架制备的胞状碳化硅的常温力学性能，并将这些材料与沥青合成的碳化硅泡沫进行比较；(B)测试这些材料在大的热瞬变中的抗热应力能力；以及(C)通过多次液态金属(铝和钛)的渗透，将碳化硅胞状材料用作混合材料的模板。这些方法可能提供具有独特结构和性能的新的碳化硅基复合材料家族。该项目将与西班牙的两所大学联合开展。用于研究的材料的生产将在塞维利亚大学完成，补充数值模拟将在马德里理工大学进行。这些拟研究的胞状碳化硅材料因其经济的生产手段、独特的胞状组织结构和性能以及用于碳化硅基复合材料的模板能力而显示出特殊的重要性。预计这种蜂窝状的微结构，再加上碳化硅的耐火性，将在极端温度下作为热交换器、高温过滤器、催化剂载体以及隔热和隔音材料提供潜在的用途。同样，与连续纤维增强材料相比，碳化硅基杂化材料提供了一种经济的复合材料生产方法。该NSF项目由多学科活动办公室、材料研究司(陶瓷)和国际办公室(西欧)共同资助，作为NSF和欧洲在材料研究方面的合作活动(NSF 02-135)。该项目是与西班牙的两个小组合作进行的，一个在塞维利亚大学，另一个在马德里理工大学。

Silicon carbide, one of the hardest and most refractory materials known, does not occur in nature. Both silicon carbide (SiC) powder synthesis and bulk production are energy intensive processes, often conducted in excess of 2000 degrees C due to low diffusivities characteristic of silicon carbide. A limited number of processes are available at moderate temperatures through melt infiltration techniques, and they offer little microstructural control. An alternative, under study here, relies on naturally derived scaffolds for SiC production. These so-called "biomorphic" silicon carbides are produced by pyrolyzing wood to create the carbon scaffold. The scaffold or template is then used for silicon infiltration and reaction to create versatile SiC-based cellular materials. The objectives of this work are three-fold: (a) to understand the ambient temperature mechanical properties of cellular SiC fabricated from naturally derived scaffolds, and to compare these materials with SiC foam synthesized from pitch, (b) to examine the thermal stress resistance of these materials in large thermal transients, and (c) to use the SiC cellular materials as templates for hybrid materials, through multiple liquid metal (aluminum and titanium) infiltrations. These methodologies may offer a new family of SiC-based composites with unique architectures, and hence, properties. This program will be conducted in conjunction with two universities in Spain. Production of the materials used for study will be accomplished at the University of Seville, and complementary numerical modeling will take place at the Polytechnic University of Madrid. These cellular SiC-based materials proposed for study show particular import for their economical means of production, their unique cellular microstructure and hence, properties, and their templating capability for SiC-based composites. It is anticipated that the cellular microstructure, coupled with the refractory nature of SiC, will provide potential uses as heat exchangers, high temperature filters, catalyst supports, and thermal and acoustic insulation in extreme temperatures. Likewise, the SiC-based hybrids offer strategies for economical means of composite production compared to continuous fiber-reinforced materials. This NSF project is co-funded by the Office of Multidisciplinary Activities, Division of Materials Research (Ceramics) and the International Office (Western Europe) as a Cooperative Activity in Materials Research between the NSF and Europe (NSF 02-135). This project is being carried out in collaboration with two groups in Spain, one at the University of Seville, and other at the Polytechnic University of Madrid.