No abstract

No abstract

Transparent α‐alumina ceramics are fabricated using spark plasma sintering. Paramagnetic defects related to the optical properties of the ceramics have been investigated using electron spin resonance (ESR) analyses. An isotropic ESR signal at g = 2.003 (S = 1/2) with a linewidth of 0.5 mT is formed during sintering. The g = 2.003 signal intensity has a weak correlation with the absorbance in the visible region but does not correlate with the real in‐line transmission (RIT) at 650 nm. An ESR signal with a fine structure attributed to Fe3+ was detected in both the α‐Al2O3 starting powder and the sintered ceramic samples. The degree of c‐axis orientation of the grains has been determined using the Fe3+ signal intensity, which depends on the angle between the directions of the c‐axis and the applied magnetic field. The ESR analysis indicated that the c‐axis tends to be oriented in the direction of the sintering pressure. The degree of c‐axis orientation was found to correlate with the RIT in highly densified ceramics.

Synopsis:Slush nitrogen is a mixture of liquid and solid nitrogen. Fine solid particles are included and dispersed in the liquid phase. It enables the utilization of latent heat and make it possible to increase the quantity of refrigeration supply. Therefore, it is expected that it will be applied as a refrigerant for high-temperature super conductivity devices. This study deals with the pipe flow characteristics of slush nitrogen. The relationship between pressure loss and velocity is investigated experimentally. Flow velocity and mass solid fraction are made to be control parameters. As a result, on the condition that the solid proportion is less than 0.2, pressure loss in the pipe flow increases as the solid proportion increases. However, this increasing rate decreases with increasing flow velocity, and it is found that the pressure loss does not increase even if the solid proportion is increased under the condition of very high flow velocity. Furthermore, observation and classification of the flow pattern by visualization was carried out. The result of the visualization indicates that the flow pattern of the slush nitrogen can be classified into four patterns: uniform flow, layer flow, slide flow and separation flow. In addition, the relationship between the Reynolds number and tube friction coefficient was deduced and an empirical formula was derived.

No abstract