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.
Towards accurate and reproducible metrology of manufactured ZnO nanoparticles
ZnO nanoparticles are a challenging material to disperse and stabilize due to their high density, tendency to aggregate and chemical properties. Manufactured ZnO nanoparticles often posses a high degree of size and shape dispersity, adding additional complexity to both sample preparation and subsequent characterization. In this paper, procedures for achieving stable and representative dispersions of ZnO nanoparticles from commercially available sources are discussed, and the average particle size determined from dynamic light scattering measurements is qualitatively evaluated against transmission electron microscopy images. The results highlight a number of important issues that need to be taken into consideration when performing a metrological assessment of particle sizes and size distributions in such systems.
Effects of the mineral phase and valence of vanadium on vanadium extraction from stone coal
The influence of roasting on the leaching rate and valence of vanadium was evaluated during vanadium extraction from stone coal. Vanadium in stone coal is hard to be leached and the leaching rate is less than 10% when the raw ore is leached by 4 mol/L H2SO4 at 90°C for 2 h. After the sample is roasted at 900°C for 2 h, the leaching rate of vanadium reaches the maximum, and more than 70% of vanadium can be leached. The crystal of vanadium-bearing mica minerals decomposes and the content of V(V) increases with the rise of roasting temperature from 600 to 900°C, therefore the leaching rate of vanadium increases significantly with the decomposition of the mica minerals. Some new phases, anorthite for example, form when the roasting temperature reaches 1000°C. A part of vanadium may be enwrapped in the sintered materials and newly formed phases, which may impede the oxidation of low valent vanadium and make the leaching rate of vanadium drop dramatically. The leaching rate of vanadium is not only determined by the valence state of vanadium but also controlled by the decomposition of vanadium-bearing minerals and the existence state of vanadium to a large extent.