No abstract

Magnesium alloys have been widely used in recent years as lightweight structural materials in the manufacturing of automobiles, airplanes, and portable computers. Magnesium alloys have extremely low density (as low as 1738 kg · m −3 ) and high rigidity, which makes them suitable for such applications. In this study, the thermal conductivity of two different magnesium alloys made by twin-roll casting was investigated using the laser-flash technique and differential scanning calorimetry for thermal diffusivity and specific heat capacity measurements, respectively. The thermal diffusivity of the magnesium alloys, AZ31 and AZ61, was measured over the temperature range from −125 • C to 400 • C. The alloys AZ31 and AZ61 are composed of magnesium, aluminum, and zinc. The thermal conductivity gradually increased with temperature. The densities of AZ31 and AZ61 were 1754 kg · m −3 and 1777 kg · m −3 , respectively. The thermal conductivity of AZ31 was about 25 % higher than that of AZ61, and this is attributed to the amount of precipitation.

Eutectic cells of Co/C and Ni/C for use in thermocouple calibration were manufactured and tested to investigate their melting and freezing characteristics using type B thermocouples. It was observed that the melting and freezing behaviour of Co/C and Ni/C systems are very similar. The freezing plateaus were found to be flatter than those of melting, but the melting points were closer to the ideal transition temperatures, which is an extrapolated value to zero temperature difference from the set temperature to induce melting/freezing, than the freezing points. Based on the observed results, the melting process is recommended for use when calibrating thermocouples.

We have studied the effects of a phospholipid (dl-α-phosphatidylcholine dimyristoyl:  DMPC), which forms an extended flat bilayer aggregate (nearly zero spontaneous curvature), on the spherical−cylindrical shape of nonionic surfactant micelles (pentaethylene glycol mono-n-dodecyl ether:  C12E5) in terms of an aggregation number, critical micellization concentration (cmc), second virial coefficient (A 2), and hydrodynamic diameter (D H) by laser light scattering. The aggregation number and critical micellization concentration increase as the amount of DMPC is increased. On the basis of the cmc values, the total free energy per micelle of C12E5/DMPC mixtures is estimated. The free energy per micelle of C12E5/DMPC mixtures decreases as DMPC is added. This is consistent with the decrease of A 2 and the strong hydrophobicity of DMPC compared with that of C12E5. The average contour length, the diffusion coefficient, and the end-cap energy of mixed micelles are estimated on the basis of the cmc and molecular specific volumes of the moiety. The end-cap energy of the mixed micelles and the average contour length increase as DMPC is added, which is also reasonable considering the molecular structure of DMPC. Furthermore, the diffusion coefficients obtained from dynamic laser light scattering are in excellent agreement with the estimated diffusion coefficients obtained from a one-dimensional growth model based on static light scattering measurements.