Phase Transition Study of CaB6 under High Pressure

Phase transition of CaB6 sample under high pressure was studied by in situ electrical conductivity measurements and synchrotron X-ray diffraction up to 26GPa. Three anomalies in conductivity change were found respectively at 3.7, 12.4 and 21.9GPa. X-ray diffraction reveals that CaB6 transforms from Pm3m to orthogonal structure at 12.32GPa and hence the abnormal conductivity change at 12.4GPa can be attributed to the structural phase transition. The other two anomalies were considered as pressure-induced electronic phase transition in the pressure range of our measurements.

Fundamental Issues of Nanofluid Behavior

This paper will elucidate some of the behaviors of nanofluids other than the abnormal conductivity enhancement, which are of importance to the experimental and engineering use of nanofluids. Nanofluid is the common name of any sol colloid involving nanoscale (less than 100nm) sized particles dispersed within a base fluid. It has been shown previously that the dispersion of nano-particulate metallic oxides into water can increase thermal conductivity up to 30–40% over that of the base fluid and anomalously more than the mere weighed average of the colloid. There is a great potential for the use of nanofluids as a way to enhance fluid/thermal energy transfer systems. Due to the recentness of nanofluid science, there are still many issues which have not been fully investigated. This paper should act as a primer for the basic understanding of nanofluid behavior. Particle size and colloid stability are of key importance to the functionality of nanofluids. The pH and concentration/loading of nanofluids can alter the size of the nanoparticles and also the stability of the fluids. It will be shown through experiment and colloid theory the importance of these parameters. Furthermore, most of the existing literature uses volume percentage as the measure of particle loading, which can often be misleading. There will be discussion of this and other misleading ideas in nanofluid science.