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.
Nanopowder metrology and nanoparticle size measurement - Towards the development and testing of protocols
There are many methods and instruments available for powder characterization and they are more or less well suited to powders in different size ranges. This report presents in more detail the relatively recent Centrifugal Particle Sizer (CPS) and its potential for particle size distribution measurement compared to more classical techniques (microscopy, laser diffraction, or photo correlation spectroscopy). To get reliable comparable data is of primary importance for new application developments. A series of protocols for nanosized powders - nanopowder metrology - was produced within the framework of a COST Action - COST 539 “Electroceramics from Nanopowders Produced by Non-conventional Methods”. The protocols have been tested using well-characterized commercial products, and for a series of powders produced in the COST Action 539. The results show that results between methods and or laboratories are often very good but some show significant deviations illustrating the need for a systematic approach and how the protocols can help us develop a Nanometrology for new functional powders.
Avian infectious bronchitis.
Avian infectious bronchitis (IB) is caused by the gammacoronavirus infectious bronchitis virus (IBV). The virus causes infections mainly in chickens and is a significant pathogen of commercial meat and egg type birds. IB is an acute, contagious disease characterised primarily by respiratory signs in growing chickens. In hens, decreased egg production and quality are often observed. Some strains of the virus are nephropathogenic and produce interstitial nephritis and mortality. The severity of IBV-induced respiratory disease is enhanced by the presence of other pathogens, including bacteria, leading to chronic complicated airsacculitis. Diagnosis of IB requires virus isolation or demonstration of viral nucleic acid from diseased flocks. Demonstration of a rising serum antibody response may also be useful. The widespread use of live and inactivated vaccines may complicate both the interpretation of virus isolation and serology findings. The occurrence of antigenic variant strains may overcome immunity induced by vaccination.