Inorganic Particle Size Measurement Below 100 nm - Where Life Gets Difficult
Several different methods, photon correlation spectroscopy (PCS), an X-ray disc centrifuge (XDC), X-ray powder diffraction (XRD) and high resolution scanning and transmission electron microscopy combined with image analysis have been used to characterise the particle size distributions of several inorganic powders ( Al2O3, FexOy, SiO2). The different powders cover the size range from 5 nm to around 100nm and have different shapes and degrees of agglomeration. The gamma alumina is highly agglomerated, the silicas are roughly spherical and the iron oxide slightly elongated but well dispersed (low agglomeration). The state of agglomeration and how different treatments such as milling and surface modification affect the state of agglomeration is often poorly described in most nanoparticle studies. We shall illustrate how agglomeration can described for an “as received” and attrition milled gamma alumina, both as a function of milling time and bead size. Results are presented after consideration of the hydrodynamic density in the sedimentation methods, and light scattering for the optical based methods. The results with model spherical silica powders (Dv50 of 12, 35 and 80 nm) show how the accuracy of the sedimentation methods depends strongly on a knowledge of the particle hydrodynamic density. This can be affected greatly by particle or agglomerate porosity, the thickness of the electrical double layer or strongly bound hydration layer often found for nanoparticles in the aqueous dispersions investigated. Precipitated iron oxide particles with sizes around 10 nm start pushing the limits of several of the methods. A careful protocol had to be developed using XRD and TEM to allow quick and reliable measurements to be made using PCS. This allowed the investigation of the effect of PVA adsorption on the size of the iron oxides important for biomedical applications.
Characterizing ASTM Carbon Black Reference Materials Using a Disc Centrifuge Photosedimentometer
ABSTRACT Cumulative and differential particle size distributions using disc centrifugation are presented for ASTM carbon black reference materials A4 through F4. The distributions for A4 through C4 form a group of relatively small-size particles. The distributions for D4 through F4 form a group of relatively large-size particles. The distributions for A4 and C4 are very nearly the same as are the distributions for F4 and E4. The results suggest that proper sample preparation can maintain size distribution stability for at least a year; only mild agitation is required to re-suspend the particles.
Effects of Solids Loading, pH, and Polyelectrolyte Addition on the Stabilization of Concentrated Aqueous BaTiO3 Suspensions
Colloidal stability of concentrated aqueous BaTiO3 suspensions with ammonium salts of poly(acrylic acid) (PAA-NH4) and poly(methacrylic acid) (PMAA-NH4) as a function of pH and solids loading is investigated. For suspensions with solids loading less than 40 vol%, the required polyelectrolyte concentration to stabilize aqueous BaTiO3 suspensions decreases with increasing pH, but remains relatively unchanged with increasing solids loading. As the solids loading continuously increases (e.g., >50 vol%), the required amount of polyelectrolyte increases, but exhibits a minimum at pH ∼ 9.2. The critical amount of polyelectrolyte needed to achieve colloidal stability of aqueous BaTiO3 suspensions as a function of pH and solids loading is summarized in a three-dimensional stability map.