Rotating high-gravity field

Reactive crystallization/precipitation can also be conducted in high-gravity (Higee) fields using rotating equipment. In China this technique has been used successfully for the production of nano-size particles of CaC03. Ultraline particles... 

In general, the retention of the stationary phase in the coil rotated in the unit gravity field entirely relies on relatively weak Archimedean screw force. In this situation, application of a high flow rate of the mobile phase would cause a depletion of the stationary phase from the column. This problem can be solved by the utilization of synchronous planetary centrifuges, free of rotary seals, which enable one to increase the rotational speed and, consequently, enhance the Archimedean screw force. The seal-free principle can be applied to various types of synchronous planetary motion. In all cases, the holder revolves around the centrifuge axis and simultaneously rotates about its own axis at the same angular velocity w. 

Iodine vapor is characterized by the familiar violet color and by its unusually high specific gravity, approximately nine times that of air. The vapor is made up of diatomic molecules at low temperatures at moderately elevated temperatures, dissociation becomes appreciable. The concentration of monoatomic molecules, for example, is 1.4% at 600°C and 101.3 kPa (1 atm) total pressure. Iodine is fluorescent at low pressures and rotates the plane of polarized light when placed in a magnetic field. It is also thermoluminescent, emitting visible light when heated at 500°C or higher. 

One way to remove these particles from air is to subject them to high centrifugal forces. If an aerosol particle is caused to move in a circular path, it will have a radial acceleration given by Eq. 7.1. This radial acceleration can be likened to the acceleration due to gravity in a gravitational field. By rotating the aerosol, accelerations many times that of gravity can be achieved. 

All hydrodynamic CCC systems utilize an Archimedean screw force that is created by coil rotation in the force field some use low-speed rotation of the coil in vmit gravity while others subject the coil to a high-speed planetary motion. An Archimedean force drives all objects in the coil toward one end of the coil, which is called the head the other end is called the tail. 

Sedimentation is normally very slow, but it can be accelerated by ultracentrifugation, a technique that replaces the gravitational field with a centrifugal field. The effect can be achieved in an ultracentrifuge, which is essentially a cylinder that can be rotated at high speed about its axis with a sample in a cell near its periphery (Fig. 11.1). Modern ultracentrifuges can produce accelerations equivalent to about 10 that of gravity (TO g ). Initially the sample is uniform, but the top (innermost) boundary of the solute moves outward as sedimentation proceeds. 

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