Best Practice in Laser Diffraction – A Robustness Study of the Optical Properties of Silica

This paper deals the determination of the particle size distribution of a material nominally (and inadequately) described as “0 – 10 silica”. First, we will outline the routes to obtaining a stable set of light scattering data via wet and dry laser diffraction determination. These stable data are a prerequisite for the deconvolution to a particle size distribution. Second, we will focus on the importance of using the correct optical constants (real and imaginary parts of the refractive index) in order that the derived particle size distribution is correctly stated.In particular this robustness study will show how incorrect optical properties can influence the form (shape) of the derived distribution, plus assignation of key points in the distribution (in particular, x10). Certain supplementary information is essential in confirming the correct optical properties
• Density via helium gas pycnometry
• X-ray diffraction (XRD) for polymorph confirmation
• Becke lines for bracketing the real part of the refractive index
• Volume concentration experiment for measurement of the imaginary/absorptive part of the refractive indexIn this manner we can then be confident of a stated particle size distribution and an awareness of the factors that can significantly affect this derived distribution.