| This work was to prepare the ultrafine particles of Acyclovir (ACV) by using RESS (the rapid expansion of supercritical solution) and to prepare the ultrafine particles of titanocene dichloride (Cp2TiCl2) using GAS (gas antisolvent recrystallization) process.The solubility of ACV in supercritical CO2 was measured within a large range of pressure and temperature. The effects of temperature and pressure on the solubility were investigated. It was found that ACV has poor solubility in SCF-CC^ and its solubility increases with the increasing of pressure and temperature. No retrograde area was found as reported in some literatures. P-R equation can correlate the experiment data of ACV solubility with reasonable greetment.In the RESS experiment, particles prepared are generally smaller, more uniform and better morphology than the starting material. Size of particles decreases with the increasing of pre-expansion temperature, and increases with the increasing of collection distance and pre-expansion pressure. Extraction temperature has no obvious effect on the size of the particles.Cp2TiCl2 particles can be prepared with smaller size and narrower size distribution than the starting material in the GAS experiment. With increasing the rising rate of the pressure, both size and size distribution of particles both decrease rapidly at the initial stage, and then decrease slowly when the rate of rising pressure reaches a certain value. Results also show that the particle size decreases with the increasing of Cp2TiCl2 concentration in chloroform. Pressure in precipitator offers almost no effect on the size of particles.The dissolution rate of the Cp2TiCb particles of starting material and the ultrafine particles prepared in GAS process was measured. It was found that the dissolution rate of the ultrafine particles is much greater than that of the particles of starting material. This is an imposing demonstration that ultrafine particles effectively improve the dissolution rate.
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