When a reactive and miscible less-viscous liquid displaces a more-viscous liquid in a Hele-Shaw cell, reactive miscible viscous fingering takes place. We succeed in showing experimentally how a reactive miscible viscous fingering pattern in a radial Hele-Shaw cell changes when the viscosity of the more-viscous liquid is varied owing to variation in chemical species concentration induced by an instantaneous chemical reaction. This is done by making use of a polymer solution's dependence of viscosity on pH. When the viscosity is increased by the chemical reaction, the shielding effect is suppressed and the fingers are widened. As a result, the ratio of the area occupied by the fingering pattern in a circle whose radius is the length of the longest finger is larger in the reactive case than in the non-reactive case. When the viscosity is decreased by the chemical reaction, in contrast, the shielding effect is enhanced and the fingers are narrowed. These lead to the area ratio being smaller in the reactive case than in the non-reactive case. A physical model to explain this change in the fingering pattern caused by the chemical reaction is proposed.
A total of 7.4 wt % of hydrogen was released from the mixture of magnesium amide and magnesium hydride at a molar ratio of 1:2 by mechanical ball milling. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD) characterizations along with the amount of hydrogen released at different stages of ball milling reveal that magnesium imide was first formed in the reaction. The imide then reacted continuously with magnesium hydride and was converted to magnesium nitride and hydrogen. Thermodynamic calculation shows that the hydrogen desorption is a mild endothermic reaction with the standard enthalpy change of about 3.5 kJ/mol of H2.
KENJI MATSUDA, YASUHIRO UETANI, TATSUO SATO, and SUSUMU IKENOThe QЈ phase in an Al-1.0 mass pct Mg 2 Si-0.5 mass pct Cu alloy at a peak-aged condition of 523 K was observed by a high-resolution transmission electron microscope (HRTEM), in order to identify its structure and chemical composition, and was compared with the type-C precipitate in an Al-1.0 mass pct Mg 2 Si-0.4 mass pct Si alloy (the excess-Si alloy). The QЈ phase has similar features to the type-C precipitate, according to results of electron diffraction patterns and images taken by the HRTEM, that is, they have similar hexagonal crystal lattices (a ϭ 1.04 nm and c ϭ 0.405 nm) to each other. The type-C precipitate in the excess-Si alloy was the ternary Al-Mg-Si phase, and the QЈ phase was the quaternary Al-Mg-Si-Cu phase in the Al-Mg-Si-Cu alloy, as determined by energydispersive X-ray spectroscopic (EDS) analysis. KENJI MATSUDA, Associate Professor, and SUSUMU IKENO, Professor, are with the Faculty of Engineering, Toyama University, Toyama, chosen to obtain the peak-aged condition at 523 K for each 930-8555 Japan. YASUHIRO UETANI, Associate Professor, is with the alloy. The TEM samples were made by a twin-jet electrical Research Institute of Technology, Toyama Prefectural University, Toyama, polishing technique using a nitric acid-methanol solution. 939-0398 Japan. TATSUO SATO, Professor, is with the Faculty of Engi-The micro Vickers hardness of each alloy was also measured,
In a previous paper the authors showed that when the surface velocity of a body having lower elastic modulus is faster than that of a body having higher elastic modulus, and when the radius of curvature of the former is larger than that of the latter, a deep conical depression (dimple) is produced in the contact surface. This dimple occurs in place of the flat plateau predicted by the point contact elastohydrodynamic lubrication (EHL) theory. In this paper, the effects of surface kinematic conditions on the formation of such abnormal phenomena, which cannot be predicted by the present EHL theory, are investigated under rolling/sliding conditions using the optical interferometry technique. Transient behavior of the dimple caused by a groove passing through the EHL conjunction is also discussed based on direct observations. It has been found that the dimple occurs when the lubricating oil in the contact area is composed of solidified and unsolidified parts, and the dimple itself corresponds to the solidified part. On the basis of this finding, it has been asserted that the establishment of a new EHL theory is needed.
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