Chord length characterization using focused beam reflectance measurement probe - methodologies and pitfalls

The impact of the solid concentration and refractive index of dispersing medium on the FBRM measurement of chord length and particle counts were investigated using the PVC (polyvinylchloride) particle systems. It was found that the chord length increased with the solid concentration in the diluted region, but decreased as the concentration became greater than 1.1%. The total particle counts were found to increase initially with the solid concentration, tapering off at high concentrations. The measured counts of small chords (1 μm–50 μm) were found to increase linearly with the solid concentration, those of the large chords increased with the concentration initially and leveled off (50 μm–200 μm) or decreased (200 μm–500 μm) with further increase of concentration. The impact of the refractive index of the dispersing medium on the FBRM measurement was also investigated, the result of which was corroborated by microscopy studies. Comparison between the FBRM and other sizing techniques revealed that when appropriate weighting factors were applied, good agreement could be achieved between the median average values of the chord length and particle size distributions.