Growth Phenomena of Single Crystals of Naphthalene in Supercritical Carbon Dioxide

The growth behavior and growth rates of naphthalene single crystals in supercritical carbon dioxide were observed and measured at temperatures 307.7, 312.7, and 317.7 K and pressures 15, 17.5, and 20 MPa to highlight the behavior of crystal growth in the supercritical phase. The morphology of naphthalene crystals did not change during the steady growth in the supercritical phase. The crystal growth rates from the supercritical phase were almost independent of pressure and higher with increasing temperature or supersaturation and were approximately between 4 × 10-9 and 2.5 × 10-8 m s-1 as supersaturation varied from 0.018 to 0.073, values which were found to be intermediate between those from a liquid or vapor phase at the same supersaturation. The activation energy for crystal growth from the supercritical phase was determined as 70.9 kJ mol-1, which showed that the crystal growth mechanism in the supercritical phase is almost similar to that in the liquid or vapor phase and that the growth rates were governed by the surface integration step.