Particle Size by Sedimentation SediGraph III 5120
3-4 Mar 2010
Particle Size by Sedimentation
As the sample particles fall, they absorb some of the X-rays
and prevent them from reaching the detector. The X-ray
intensity is recorded at each step in the cell movement. The
analysis program collects data at up to 220 sedimentation
heights based on the operator-specified starting and ending
diameters for the particle analysis. The analysis program
determines the target sedimentation heights and times based
on the run type (High speed, Standard or High Resolution)
and calculation of the particles’ terminal velocities. The rate
at which particles fall through the liquid is described by
Stokes’ Law. The largest particles fall at the fastest rate,
while the smallest particles fall at the slowest rates, until all
of the particles have settled and the liquid is clear.
Each collected intensity value is compared to the X-ray intensities at the corresponding
heights for both the baseline and full-scale concentrations for the sample. The resulting per-
centage is used to determine the total particle mass at each point in the cell. The analysis
program uses the percentage of particle mass and calculated particle falling rates to determine
the maximum particle size for each point in the cell (particle distribution).
The analysis data is stored in the control module and can be displayed or printed in a variety of
graphic and standard report formats. Because particles rarely exhibit a uniform shape, each
particle is reported as an Equivalent Spherical Diameter (the diameter of a sphere of the same
material with the same terminal velocity).
The SediGraph III 5120 is designed to provide analysis results which vary by no more than 2
mass percent among samples from a homogenous lot.
When the analysis is complete, the sample and fluid mixture is drained from the cell into the
mixing chamber, and then the mixing chamber is drained into a waster reservoir. If the opera-
tor has selected the rinse option, a rinsing liquid is then drawn into the analyzer and the entire
system is rinsed and drained. The rinse operation may be set to a specific number of cycles or
to continue until the previously obtained baseline concentration is achieved. Rinsing always
occurs when a MasterTech is used with the SediGraph III 5120.
To Next Page
Loading...
Need help?
General
