No abstract

Coccolithophores belong to the most abundant calcium carbonate mineralizing organisms. Coccolithophore biomineralization is a complex and highly regulated process, resulting in a product that strongly differs in its intricate morphology from the abiogenically produced mineral equivalent. Moreover, unlike extracellularly formed biological carbonate hard tissues, coccolith calcite is neither a hybrid composite, nor is it distinguished by a hierarchical microstructure. This is remarkable as the key to optimizing crystalline biomaterials for mechanical strength and toughness lies in the composite nature of the biological hard tissue and the utilization of specific microstructures.To obtain insight into the pathway of biomineralization of Emiliania huxleyi coccoliths, we examine intracrystalline nanostructural features of the coccolith calcite in combination with cell ultrastructural observations related to the formation of the calcite in the coccolith vesicle within the cell. With TEM diffraction and annular dark-field 1

No abstract

Liquid Silicon Infiltration (LSI) is a technique to manufacture non-oxide ceramic matrix composites such as C/C-SiC or SiC/SiC. In the beginning of this three-step process, fiber preforms are shaped and impregnated with phenolic resins. After curing, the preforms are pyrolyzed to convert the polymer matrix to a porous carbon matrix. This porosity is then used to infiltrate liquid silicon by capillary forces. Simultaneously, an exothermic reaction of silicon and carbon creates a silicon carbide matrix. Generally the liquid silicon reacts with any carbon and even with SiC present in the form of fibers, fiber coatings or matrix. Therefore, especially the fibers must be protected from Si attack effectively. The morphology of silicon carbide was observed to be heavily driven by Ostwald ripening. This can be suppressed by the addition of boron to the melt. The initially formed SiC crystals in C/C-SiC composites are hereby prevented from grain coarsening, resulting in almost completely preserved C/C blocks. For the manufacture of SiC/SiC composites, the silicon boron alloys allow an effective preservation of the nanocrystalline SiC-fibers. Thus, the use of Si based B containing alloys helps effectively to moderate and control the aggressive reaction during LSI process.

No abstract