Interpretation of Focused Beam Reflectance Measurement (FBRM) Data via Simulated Crystallization

Focused beam reflectance measurement (FBRM) has gained much popularity as a tool for particle system characterization both in crystallization research and in manufacturing. The precise interpretation of FBRM data, however, still remains an issue of some conjecture and dispute. This study examines the relationship among total counts of chord lengths, statistics of chord length distribution, particle number and average particle size in simulated crystallization, which involves selective introduction of predetermined particle populations into a suspension so as to simulate the occurrence of nucleation and crystal growth as detected by the FBRM. The number of particles and particle size distribution were known precisely. It was found that a linear correlation existed between the counts of chord lengths and the number of particles for monosized populations, but not in the case of a dynamic process where there was a significant change in particle size. Square-weighted mean chord lengths were found to be able to track changes in average particle size qualitatively in some cases. Measured chord length distributions of monosized particle populations differed significantly from theoretically constructed distributions. These results have important implications for the interpretation of practical FBRM data, including the necessity to review the principles used in the restoration of particle size distribution from measured chord length distributions.