The extraordinary combination of strength and toughness attained by nature's highly sophisticated structural design in nacre has inspired the synthesis of novel nanocomposites. In this context, the organic-inorganic hierarchical design of nacre has been mimicked. However, two key features of nacre, namely the scaling of the structural components and the low content of the organic phase, have not been replicated yet. Here, we present thin nanocomposite films with properly adjusted thicknesses of the organic and inorganic layers, as well as a microstructure that closely resembles that of nacre. These films, which are obtained by the combination of low-temperature chemical bath deposition of titania with layer-by-layer assembly of polyelectrolytes, exhibit enhancement in a fracture toughness by a factor of 4, combined with notable increase in hardness, while the Young's modulus is largely preserved in comparison to the single titania layer. Our findings highlight the significance of the 10:1 inorganic/organic layer thickness ratio evolved by nature, and provide novel perspectives for the future development of efficient bioinspired thin films.
Deposition experiments from aqueous solutions of zinc nitrate were performed in a bio-inspired way using biomolecules as directing agents. A global overview of the effect of various amino acids 8 and dipeptides 21 was done in term of structure and morphology of the obtained coating. The selection of certain biomolecules leads to the formation of smooth ZnO thin films. Variations of the amino acid chemical function and the sequence used within the peptides combination give rise to a wide variety of morphologies ranging from films to three dimensional nets. The data obtained from scanning electron microscopy and X-ray diffraction are discussed and correlated to the chemical properties of the biomolecules.
Bond coats play a crucial role in the performance of thermal barrier coating systems. Ru alloys have been identified as promising candidates; therefore, systematic studies were performed on the oxidation behavior of bulk RuAl (50–50 at.%). Isothermal oxidation and thermogravimetric analyses were performed at 1100 °C for different times ranging from 0.1 h to 500 h. Microstructural characterization was performed by scanning and transmission electron microscopy. The results showed the formation of an α–Al2O3 layer on top of a δ–Ru layer. Interface instability between these layers and evaporation of gaseous Ru-oxides lead to the formation of large elongated cavities and alternating α–Al2O3/δ–Ru layers.
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