生物矿化与仿生材料Biomim04_Biomin2_Abal课件.pptVIP

From Biomineralization to Biomimetic Materials Chemistry:Abalone Shells Last lecture: repetition: proteins and protein structure mineralization of ferritin stages of biomineralization Today: structure and properties of abalone shells mechanism of formation stages of biomineralization Literature: ?Nacre: Properties,chrystallography, morphology and formation“ M.Sarikaya et al. In ?Biomimetics: Design and processing of materials“ (AIP Press, Woodbury, NY, 1995) 35. ?Ionotropic nucleation of calcium carbonate by molluscan matrix“ E.Greenfieldet al. Am.Zool. 24 (1984) 925. ?Control of crystal phase switching and orientation by soluble mollusc-shell proteins“ A.Belcher et al. Nature 381 (1996) 56. ?Control of aragonite or calcite polymorphism by mollusc shell macromolecules“ G.Falini et al. Science 271 (1996) 87. ?Does abalone nacre form by heteroepitaxial nucleation or by growth through mineral bridges?“ T.Sch?ffer et al. Chem.Mat. 9 (1997) 1731. Polymorphism of CaCO3 Calcite: most stable form from thermo-dynamic point of viewrhombohedral, large crystallites; easy cleavage ? brittle Aragonit:e fine, needle-like crystallites; no preferred cleavage planes Vaterite, hydrates and amorphous CaCO3 Mechanical Properties of Abalone Shells The mechanical properties of abalone shells are far better than synthetic CaCO3! comparable to modern engineering ceramics reason ? Microstructure of Nacre Widespread microstructure : outer “prismatic” layer (calcite) layered interior (aragonite) horizontal arrays of platelets with offset to each other 5 mass% organic material in interstitial space Fracture Mechanics of Nacre Cracks are often deflected within material branching of cracks sliding of adjacent platelets crack bridging Schematic IllustrationAbalone Shell Outer Layer: calcite; hard and brittle Inner Layer: Aragonite organic components; ?softer“ but high toughness Alternative Microstructures Observed in Abalone Shells Neopilina hyalina prisms of aragonite Form