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.
Particle Size Distribution Measurement and Assessment of Agglomeration of Commercial Nanosized Ceramic Particles
ABSTRACT 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 (PCS, Malvern Zetasizer 4), and an x-ray disc centrifuge (XDC, 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 F AG 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's 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.
Thermodynamics on the Carbochlorination of Titanium-bearing Ores
The equilibrium compositions of the multi-component, multi-phase and multi-reaction system of carbochlorination of titanium-bearing ores are calculated with HSC, a computational chemistry software. The thermodynamic equilibrium calculation of the reaction system shows that a complete conversion of titanium-bearing ores is feasible at a temperature near 200oC. At temperatures ranging from 800 to 1600oC, the products of the reaction system are all in gaseous phase. Thermodynamic analysis accords with the industrial practice. The simulated results provide reasonable scientific basis for improving suitable technological conditions of the carbochlorination reduction.