Particle size distribution measurement and assessment of agglomeration of commercial nanosized ceramic particles

Commercially available powders with primary particle sizes of 10-100 nm (transition aluminas, Boehmites, and a commercially available silica dispersion) have been studied using three different instruments, a photocentrifuge (Horiba CAPA 700), photon correlation spectroscopy (PC, Malvern Zetasizer 4), and an x-ray disc centrifuge (ADC, Brookhaven X-ray Disc Centrifuge BI-XDC). Particle size distributions for five powders were collected with each instrument and in conjunction with nitrogen adsorption measurements an agglomeration factor calculated. An example is given to show the importance. of using a light scattering correction when measuring particle size distributions with a Photocentrifuge for a gamma alumina powder where the uncorrected data can overestimate the D(V50) by up to a factor of 10 depending on the powder. The importance of the assessment of agglomeration and how different treatments such as milling modifies the, agglomeration factor FAG is illustrated for an "as received" and attrition milled gamma alumina. Results are discussed with respect to the assumptions and limitations of the different instruments. Results are presented after consideration of the hydrodynamic density in the sedimentation methods, and light scattering for the optical based methods. For narrow size distributions in the 15-25 nm range all three instruments show very a good correlation. When the size range approaches the 40-100 nm regime PCS is very sensitivity to. small populations of agglomerates. The instrument giving, the best resolution in the 10-100 nm range was found to be the XDC. The speed of measurement should also be born in mind and varies enormously from several minutes for the PCS to several hours for the sedimentation techniques. To assess the accuracy of the measured sizes a model spherical silica powder was analyzed on all the instruments as well as by image analysis. The results with the silica powder showed how the accuracy of the sedimentation methods depends strongly on a knowledge of the suspended particles hydrodynamic density. This can be effected greatly by particle or agglomerate porosity and the thickness of the electrical double layer in the aqueous dispersions investigated. The results with the silica suggest accuracy on the size better than +/-20% is difficult without an accurate hydrodynamic density whereas consistency between methods for narrow size distributions can be better than 5% for median volume diameters.