Submitted to: Near Infrared Spectroscopy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/15/2001
Publication Date: 2/27/2001
Citation: Pasikatan, M. C., J. L. Steele, C. K. Spillman, and E. Haque. 2001. Near infrared reflectance spectroscopy for online particle size analysis of powders and ground materials. J. Near Infrared Spectrosc. 9: 153-164. Interpretive Summary: A finely-ground product reflects more near-infrared (NIR) energy than a coarser version of the same product. Hence, besides the conventional application of NIR reflectance spectrometry as a sensor for protein, starch, and other chemical constituents, it also has potential as a particle size sensor for ground product. As NIR beam penetrates through a powder it changes in direction and a portion is absorbed as it encounters the particles in the layer, until finally another portion returns to the surface. The portion that re-emerges from the surface is called diffuse reflectance and its properties are related to the product's particle size. We reviewed the basics of NIR reflectance spectroscopy related to particle size determination, the manner the ground product should be prepared, the method of presenting to the light beam, and calibration techniques. Integrating all theories and studies related to particle size determination by NIR reflectance could pave the way for industrial applications and identification of areas for further studies.
Technical Abstract: The cross-sensitivity of near-infrared (NIR) reflectance to the particle size of powders or ground materials has long been documented but not fully exploited for particle size estimation. Diffuse reflectance of a powder sample is dependent on light scattering within its layers, and a powder's absorption and scattering coefficient are related to its particle size. This is the basis of NIR reflectance-particle size calibrations. The availability of fiber optic probes and the speed of NIR spectrometers make them suitable for remote and online sensing of particle size, in addition to providing chemical information of a powder sample. The basics of NIR reflectance spectroscopy relevant to particle size determination and its relation to sample preparations, methods of presentation, reference methods, calibration development and validation were reviewed in this paper.