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

碳化硅是已知的最硬和最难熔的材料之一，在自然界中并不存在。 碳化硅（SiC）粉末合成和批量生产都是能源密集型工艺，由于碳化硅的低扩散率特性，通常在超过2000摄氏度的温度下进行。 有限数量的工艺可在中等温度下通过熔体渗透技术获得，并且它们提供很少的微观结构控制。 另一种选择，在这里研究，依赖于自然衍生的支架碳化硅生产。 这些所谓的“生物形态”碳化硅是通过热解木材来产生碳支架的。 然后将支架或模板用于硅渗透和反应，以产生通用的SiC基蜂窝材料。 这项工作有三个目标：（a）了解由天然衍生支架制造的多孔SiC的环境温度机械性能，并将这些材料与由沥青合成的SiC泡沫进行比较，（B）检查这些材料在大的热瞬变中的耐热应力性，以及（c）使用SiC多孔材料作为混合材料的模板，通过多次液态金属（铝和钛）渗透。 这些方法可以提供一个新的家庭的SiC基复合材料具有独特的架构，因此，属性。 该计划将与西班牙的两所大学合作进行。 塞维利亚大学将完成研究所用材料的制作，马德里理工大学将进行补充数值建模。 这些蜂窝状SiC基材料的研究表明，其经济的生产手段，其独特的蜂窝状微观结构，因此，性能，和他们的SiC基复合材料的模板能力特别重要。 预计蜂窝状微观结构与SiC的耐火性质相结合，将提供作为热交换器、高温过滤器、催化剂载体以及极端温度下的隔热和隔音的潜在用途。同样，与连续纤维增强材料相比，SiC基混合物提供了经济的复合材料生产方法。该NSF项目由多学科活动办公室、材料研究部（陶瓷）和国际办公室（西欧）共同资助，是NSF和欧洲之间材料研究的合作活动（NSF 02-135）。这个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.