Line Start Methods of Sedimentation Fineparticle Size Characterization

If the fluid used to prepare the suspension is the same as that in the column, the layer of suspension will have a higher density than the column fluid. In this situation, as discussed earlier in this section, the assembled line start system in the column will be essentially unstable and tendrils of suspension will tend to bleed down the walls of the tube. Allen comments on the Werner instrument, 

Studies of the configuration of the injected cloud using high-speed photography showed that the cloud of fmeparticles moved down one seventh of the column before a stable cloud was obtained [41]. This failure of the initial cloud to remain in a narrow region at the top of the column would cause the real height of fall to be less than the column height. This factor would cause the measured size distribution to appear coarser than it should be. 

Sometimes the weight on the pan changed exponentially, and experimenters were tempted to take a short cut and extrapolate to the ultimate weight retained at infinite time by graphical techniques. If such an extrapolation was coupled with assumptions concerning the missing powder, the absolute accuracy of the ultimately derived Stokes diameter distribution of the powder was questionable. 

An operational disadvantage of the Micromerograph was that the sedimentation column was usually cleaned out at the end of a characterization study by a blast of gas. If the powder had any toxic attributes, it was very difficult to contain the emergent cloud. 

5 Sedimentation Studies of Fineparticles Moving in a Centrifugal Force Field 

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Line Start Methods of Sedimentation Fineparticle Size Characterization 105... 

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