Kinetics Of Morphological Changes Research Articles

Thermal stability of refined Al6(Fe, Mn) phase formed in laser powder bed fusion process

The addition of Mn in Al–Fe alloys stabilizes the Al6Fe metastable phase (orthorhombic structure, oC28) owing to the partial occupation of Fe sublattice sites by Mn atoms (formation of Al6(Fe, Mn) phase), thereby achieving superior high-temperature strength of Al–Fe–Mn ternary alloys that are manufactured via laser powder bed fusion (L-PBF) process. This study aimed to fundamentally understand the thermal stability of the refined Al6(Fe, Mn) phase formed in the L-PBF fabricated Al–2.5%Fe–2%Mn alloy in terms of a thermodynamic approach and the kinetics of morphological changes in the Al6(Fe, Mn) phase at elevated temperatures ranging from 200 to 500 ℃. The L-PBF processed samples showed a high hardness of approximately 125 HV due to the formation of numerous dispersoids of the Al6(Fe, Mn) phase with sizes of several tens of nanometers in the α-Al matrix containing concentrated solute elements of Fe and Mn. The hardness and microstructure were almost unchanged even after exposure to a high temperature of 200 ℃ for an extended period of 1000 h. Upon exposure to 300 ℃, nucleation and growth of the Al6(Fe, Mn) phase occurred locally, particularly at grain boundaries in the α-Al matrix. Such a local growth contributed to a reduction in hardness upon thermal exposure. Simultaneously, numerous nanoscale precipitates were formed in the α-Al matrix, resulting in a suppressed reduction in hardness. Contrary to the result of the thermodynamic calculations, the θ-Al13Fe4 phase was scarcely found even after long-term exposure to 500 ℃. The θ-phase formation was accompanied by the dissolution of the refined Al6Fe metastable phase for strengthening, which significantly reduced the hardness during thermal exposure. The suppressed θ-phase formation could be associated with the thermodynamically stable Al6(Fe, Mn) phase developed during the L-PBF process, which predominantly contributed to the high microstructural stability of the L-PBF fabricated Al–Fe–Mn alloy at elevated temperatures.

Reversible small bowel obstruction in the chicken foetus

Background:Ligation of the embryonic gut is an established technique to induce intestinal obstruction and subsequently intestinal atresia in chicken embryos. In this study, we modified this established chicken model of prenatal intestinal obstruction to describe (1) the kinetics of morphological changes, (2) to test if removal of the ligature in ovo is possible in later embryonic development and (3) to describe morphological adaptations following removal of the ligature.Materials and Methods:On embryonic day (ED) 11, small intestines of chick embryos were ligated micro surgically in ovo. In Group 1 (n = 80) gut was harvested proximal and distal to the ligation on ED 12-19. In Group 2 (n = 20) the induced obstruction was released on day 15 and gut was harvested on ED 16-19. Acetyl choline esterase staining was used as to assess resulting morphological changes.Results:A marked intestinal dilatation of the proximal segment can be seen 4 days after the operation (ED 15). The dilatation increased in severity until ED 19 and intestinal atresia could be observed after ED 16. In the dilated proximal segments, signs of disturbed enteric nervous system morphology were obvious. In contrast to this, release of the obstruction on ED 15 in Group 2 resulted in almost normal gut morphology at ED 19.Conclusion:Our model not only allows the description of morphological changes caused by an induced obstruction on ED 11 but also-more important - of morphological signs of adaptation following the release of the obstruction on ED 15.

Transmission electron microscopy of Schistosoma mansoni cercariae treated with hinokitiol (beta-thujaplicin), a compound for potential skin application against cercarial penetration.

Since skin is the only route of entry of the parasite in schistosomiasis patients, intervention at the level of skin penetration should control the infection. Several compounds were screened for their ability to protect against cercarial penetration. Hinokitiol (beta-thujaplicin) was found to have a significant cercaricidal effect in vitro, although there is no information on its cercaricidal mechanisms. To study the kinetics of morphological changes in Schistosoma mansoni associated with exposure to hinokitiol in vitro, cercariae were incubated in media containing hinokitiol at different concentrations and examined by transmission electron microscopy (TEM). TEM revealed that ultrastructural changes occurred by 15 minutes post exposure, at a concentration of 25 microg/ml. Degenerative changes involving both tegument and deeper parenchymal structures were progressive with duration of exposure at the concentration of 50 microg/ml. These structural changes may account for the inability of hinokitiol-treated cercariae to infect the host.

Kinetics of morphological changes in surfactant systems

Equilibrium structures of surfactants have been studied in much more detail than morphological changes that can occur under non-equilibrium conditions. Recent experiments attempt to analyse pathways of such morphological transitions, in particular for micellar kinetics, solubilisation and formation/break-up of vesicles. Significant progress was made with respect to the achievable time-resolution in such structural investigations, which allows to identify intermediate structures. Understanding and control of the dynamics of surfactant systems is of fundamental importance for many applications of surfactants.

Kinetics of Morphological Changes in Nanoscale Metallic Films Followed by Auger Electron Spectroscopy

Kinetics of Morphological Changes in Nanoscale Metallic Films Followed by Auger Electron Spectroscopy

A correlation analysis of isothermal crystallization of long paraffins

The small-angle X-ray scattering (SAXS) curves for ultralongn-alkanes obtained by Ungar and Keller at different times after reaching the crystallization temperature have been Fourier analysed. The correlation curves so obtained at different temperatures and different annealing times reflect sensitively all those morphological features which are broadly characteristic of the scattering curves. In addition the correlation curves clearly show a transition from a non-integer-fraction length to extended chain structure. Crystalline and amorphous lengths, degree of order and half-widths which characterize kinetics of morphological changes are also reported.

Vapor sorption and liquid interactions with glassy polyblends of polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide)

AbstractPolystyrene, poly(phenylene oxide), and solution‐cast blends of the parent homopolymers were exposed to normal hexane in the liquid and vapor phase. The kinetics of absorption and desorption, the sorption equilibria, and the kinetics of morphological changes were studied as a function of temperature and blend composition.Absorption kinetics of n‐hexane vapor in all blends were largely controlled by polymer relaxations. The sorption rates from the vapor phase varied monotonically with blend composition and increased over a range of four orders of magnitude with increasing poly(phenylene oxide) content. The equilibrium n‐hexane content similarly increased monotonically with poly(phenylene oxide) content although the increase was only by a factor of two over the entire range of compositions. These results were interpreted in light of and were completely consistent with earlier findings with pure polystyrene homopolymer.Films immersed in liquid n‐hexane produced a white, opaque outer shell surrounding an essentially unaffected central core. The kinetics of this whitening process were much more rapid for each of the homopolymers than the kinetics characterizing morphological changes in the blends. These data suggest that film whitening is caused by crazing in the polystyrene‐rich samples and that solvent‐induced crystallization is involved in the whitening of the poly (phenylene oxide) rich material.