Ultrasonic attenuation spectroscopy for multivariate statistical process control in nanomaterial processing

Ultrasonic attenuation spectroscopy (UAS) is an attractive process analytical technology (PAT) for on-line real-time characterisation of slurries for particle size distribution (PSD) estimation. It is however only applicable to relatively low solid concentrations since existing instrument process models still cannot fully take into account the phenomena of particle–particle interaction and multiple scattering, leading to errors in PSD estimation. This paper investigates an alternative use of the raw attenuation spectra for direct multivariate statistical process control (MSPC). The UAS raw spectra were processed using principal component analysis. The selected principal components were used to derive two MSPC statistics, the Hotelling's T2 and square prediction error (SPE). The method is illustrated and demonstrated by reference to a wet milling process for processing nanoparticles.

Measured UAS spectra and SPE chart during the milling operation.Figure optionsDownload as PowerPoint slideHighlights
► Ultrasound attenuation spectroscopy (UAS) is used on-line for direct product quality control in nanomaterials processing.
► UAS raw spectra are used to derive multivariate statistical process control (MSPC) charts for monitoring nanoparticle quality.
► It avoids the difficulty associated with errors in estimating particle size distribution at high solid concentrations.
► The method is demonstrated using a wet milling process for size reduction of aluminum oxide particles.