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A scale formed by heat treatment of Ti in a nitrogen atmosphere containing oxygen at an extremely low partial pressure exhibited an exceptional degree of hydroxyapatite (HAp) formation in a simulated body fluid. Scanning transmission electron microscopy and electron energy loss spectroscopy indicated that the subsurface of this scale was composed of nitrogen doped rutile-type TiO2. The N-K edge energy-loss near edge structure spectrum of this layer in conjunction with the theoretical spectra of possible compounds obtained using the augmented plane wave plus local orbital band method suggested that oxygen sites were replaced by two nitrogens, resulting in an effective charge of +2. The enhanced HAp forming ability of this scale is likely related to the positively charged surface induced by the presence of N. Conversely, the subsurface scale formed by heat treatment in air, in which N is not found, leads to much slower HAp coverage, believed to be related to the lack of surface charge.
The effects of water vapor and oxygen on the cyclic fatigue behavior of oxygen-excess La0.8Sr0.2MnO3+δ (LSM) were investigated under three-point bending at 1273 K. Because the fatigue life did not obviously depend on the number of cycles, which also represented the effective time of the applied stress, the fracture was presumed to not be significantly controlled by stress-corrosion cracking. Under a low oxygen partial pressure (), however, wet exposure inhibited both fatigue fracture and permanent deformation, in which the LSM crystal lattice was distorted and the unit cell free volume was reduced. Under a high , on the contrary, the crystal symmetry was increased by the wet exposure. The inhibition of fatigue fracture and deformation at both high and low was probably caused by retardation of lanthanum diffusion through its vacancies.
A microstructural change during the formation reaction of aluminum titanate from a mixture of rutile and corundum powders has been studied. The characterization was carried out using a polarization microscope, a scanning electron microscope and a micro-focus X-ray diffractometer. The formation of aluminum titanate was controlled by a nucleation step. The formation reaction proceeded to form spherically oriented regions of aluminum titanate grains among the matrix of rutile and corundum. At the end of the reaction, the specimen was entirely filled with the oriented region of consisting several hundred micrometers. The oriented region was composed of primary aluminum titanate grains of several micrometers and pores. Large cracks due to a thermal expansion anisotropy were formed at the boundaries of the orientated regions. The formation of the oriented region was caused by a small change in free energy, increasing elastic energy, and the endothermic nature of the reaction.
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