Residual thermal stresses in a Fe3Al/Al2O3 gradient coating system

To combine the merits of both metals and ceramics into one material, many researchers have been studying the deposition of alumina coating using plasma spray on metal substrates. However, as the coatings are deposited at a high temperature, residual thermal stresses develop due to the mismatch of thermal expansion coefficients of the coating and substrate and these are responsible for the initiation and expansion of cracks, which induce the possible failure of the entire material. In this paper, the residual thermal-structural analysis of a Fe3Al/Al2O3 gradient coating on carbon steel substrate is performed using finite element modelling to simulate the plasma spray. The residual thermal stress fields are obtained and analyzed on the basis of temperature fields in gradient coatings during fabrication. The distribution of residual thermal stresses including radial, axial and shear stresses shows stress concentration at the interface between the coatings and substrate. The mismatch between steel substrate and composite coating is still the dominant factor for the residual stresses

Direct synthesis and strong cathodoluminescence of Al2O3 nanotubes

α-Al₂O₃ nanotubes were synthesized in bulk quantity by using simple physical evaporation of pure aluminum powders at 1000 °C. Field emission scanning electron microscopy and transmission electron microscopy observations show that the nanotubes have diameters smaller than 100 nm and lengths up to several microns. Cathodoluminescence measurements revealed a strong luminescence band in the wavelength range of 280–380 nm centered at 330 nm, which could be attributed to the oxygen vacancies in the α-Al₂O₃ nanotubes. Sacrificial template model is regarded as the possible formation mechanism of the nanotubes.

Controlled synthesis and characterization of 10 nm thick Al2O3 nanowires

α-Al₂O₃ nanowires, with diameter around 10 nm, were synthesized in bulk quantity by heating the mixture of pure aluminum and graphite powders at 900 °C. Scarcity of oxygen is regarded as the reason for the growth of the small diameter α-Al₂O₃ nanowires at relatively low temperature. The product was characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence. The Oxygen vacancies in the nanowires lead to the strong photoluminescence in the wavelength range of 400–700 nm with its peak at 527 nm.

Effect of nano-Al2O3 addition on the densification of YSZ electrolytes

This work investigates the effect of nanosized Al2O3 addition on the sinterability of YSZ electrolyte. (1-x)YSZ + Al2O3 ceramics with compositions x = 0 to 0.01 were prepared by the conventional mixed oxide route from a commercial powder suspension (particle size <50 nm), and sintered at 1200 to 1500 degrees C for 2 hours in air. Densification, phase evolution, and microstructure were characterized by SEM/EDS and XRD. An improvement in sintered density was observed for the samples with 0.2 to 0.5 mol% Al2O3, though depending on the sintering temperature. Only cubic zirconia was detected as crystalline phase, although XRD features suggested chemical interactions depending upon the amount of Al2O3. The grain size of YSZ was homogeneous and no second phase segregation was detected in the tested range of incorporated nano-Al2O3 and sintering temperatures.

A resonance tunable and durable LSPR nano-particle sensor : AL2O3 capped silver nano-disks

Localized surface plasmon resonance (LSPR) biosensors are employed to detect target biomolecules which have particular resonance wavelengths. Accordingly, tunability of the LSPR wavelength is essential in designing LSPR devices. LSPR devices employing silver nano-particles present better efficiencies than those using other noble metals such as gold; however, silver nano-particles are easily oxidized when they come in contact with liquids, which is inevitable in biosensing applications. To attain both durability and tunabilty in a LSPR biosensor, this paper proposes alumina (AL₂O₃) capped silver nano-disks. It is shown that through controlling the thickness of the cap, the LSPR resonance frequency can be finely tuned over a wide range; and moreover, the cap protects silver nano-particles from oxidation and high temperature.