Sedimentation
Sedimentation analysis is based on the determination of the stationary velocity of the descent of particles in a fluid phase. Conditions for the method are a thorough preparation of the sample and selection of a suitable sedimentation liquid. In particular, the dispersion of the sample requires extensive experiences with the method.
In the simplest case sedimentation is carried out in the field of gravity. The method can be realized differentially (incrementally) or integrally (cumulatively). The individual measuring procedures differ substantially in the way of determination of the particle quantity. The actual sedimentation process, however, always goes after the same physical laws.
Depending on particle density, grain size analyses in the range of 2 - 100 µm can be carried out using force of gravity sedimentation. Application of the measuring method will be problematic, if the particles are not chemically uniform and thus have a different density. In this case an error occurs during the calculation of particle size. This, however, will not arise, if the velocity of descent is used as dispersion size, which is often the case for example for the investigation of technical sedimentation processes.
The measuring range could be expanded towards smaller particles, if sedimentation was carried out in the centrifugal field. Centrifugal sedimentation is, however, a substantially more complex measuring method.
Sedimentation is especially suitable for all samples already available in a wet state, as for example sludges and suspensions. The method should be used in each case, if the measuring task resulted in the determination of sedimentation speeds.
Approximately 500 to more as 1000 ml sedimentation liquid with a solid content lesser than 0.5% are needed for an analysis depending on the method.
In-house sedimentation methods:
- pipette method
- sedimentation balance
- pipette centrifuge
- drop plate centrifuge