50 research outputs found
Synthesis of zinc ferrite nanopowders in an RF thermal plasma
Nanosized zinc ferrite spinel powders of various compositions were produced in
an RF thermal plasma from oxide mixtures and from co-precipitated hydroxides. The
products were characterised for bulk chemical (ICP-AES), and phase composition
(XRD). In spite of the short residence time of the reagents in the plasma reactor
considerable extent of spinel formation was achieved. Magnetization and Curie point
measurements indicated that the spinel phases exhibited ferrimagnetic behaviour.
Ferrites synthetized in the RF plasma reactor were compared to that produced by the
conventional ceramic route
Atmospheric ageing of nanosized silicon nitride powders
Ambient oxidation of nanosized silicon nitride powder produced by the vapour phase reaction of silicon tetrachloride and ammonia has been studied in this work. Aliquots of the powder were stored in argon gas, in dry air and in air of 80% humidity, and changes in the bulk and surface properties were investigated against the ageing time. The powder samples were characterised by wet chemical analysis, XPS, TG-MS, FTIR, XRD and TEM methods. No significant changes were detected on storage in argon gas for 90 days. However, in samples stored in dry air and humid air, remarkable oxidation and formation of N-H species were found. The particulate powder tends to agglomerate in both dry and humid air, and this results in changes in the particle size and morphology. The nanosized silicon nitride powders therefore should be processed by excluding their contact with the oxygen and moisture containing ambient atmosphere
Torque Measurements and DEM Simulations in a Couette-type Device with Application to Particle Size Measurements
A continuously operating modified Cuette-type shearing device has been developed for
in-situ measurements to estimate the average particle size during size enlargement
processes in fluidized bed granulator. It was proven by experiments that well-defined
correlation exists between the mean torque and the average particle size being in the
device. DEM simulations revealed interesting aspects of this method
Synthesis of Spinel Ferrites in Radiofrequency Thermal Plasma Reactor
Formation of nanosized zinc-ferrites and nickel-zinc ferrites from iron- and
zinc oxide powders and corresponding nitrate solutions, respectively, was studied in RF
thermal plasma conditions. The products were characterized for chemical composition,
phase conditions, particle size distribution, morphologies and saturation magnetization.
Effects of synthesis conditions on properties of products were studied in details
Computer Tomograph Measurements in Shear and Gravity Particle Flows
The paper reports the recent results obtained on the applicability of cross-sectional digital
imaging method to study particle flow characteristics in 3D particle beds forced to move by
gravity or shear. X-ray CT imaging technique is widely used in medical diagnostics and, during
the last decades, its spatial and temporal resolution has been improved significantly. In this study,
an attempt was made to use this technique for engineering purposes. Two experimental set-ups
with different types of particle flows were investigated using Siemens Somatom Plus type CT
equipment. A series of trials were carried out in a small model hopper with flat bottom and
almost cylindrical side wall slightly deviating from verticality. Non steady-state flow was studied
during the outflow of particulate material from this vessel, through a central hole at the bottom.
Further investigation was fulfilled in a modified Cuette-type shearing device to study steady-state
shear flow. This equipment consisted of an almost cylindrical vessel identical to that used for
gravity flow measurements, and a smaller inner cylinder rotating within this vessel concentrically,
around its vertical axis. The surface of the inner cylinder was notched vertically, i.e.
perpendicularly to the direction of rotation to increase wall friction between the particles and the
cylinder. Almost spherical sucrose granules, also used for gravity flow measurements, were filled
into the gap between the rotating cylinder and the outer wall of the equipment. Movement of
particles took place due to shear, generated within the particle bed. By using X-ray CT technique,
cross-sectional digital images were obtained in every two seconds for both types of particle flows.
For this, the cross-sectional variation of the local Hounsfield density values were measured in a
matrix of 0.1x0.1x2.0 mm space elements. It was proved that the applied non-invasive crosssectional
imaging technique was suitable to distinguish the stationary and moving particle
regions, and by this, to estimate the location of the boundary zone between them
Theoretical and experimental aspects of carbon formation in thermal plasma
Formation of carbon black from Freons was studied in RF thermal plasma conditions. Equilibrium
compositions of the products were calculated by computer code ASTRA 4.0. The
experiments on thermal decomposition were performed in an RF thermal plasma reactor.
By comparing the calculated and experimental results a model was constructed on carbon
black formation in RF thermal plasma reactor
Synthesis of Zinc Ferrites in RF Thermal Plasma Reactor
Formation of nanosized zinc ferrite spinels was studied
from iron- and zinc oxide powders and corresponding
nitrate solutions, respectively in a radiofrequency thermal
plasma reactor. From the viewpoint of applications,
the research was motivated by the potential use of these
materials in advanced magnetic devices on the one
hand, and by their biomedical applications such as drug
carriers or agents for cancer treatment by hyperthermia
on the other. In this work effects of synthesis conditions
on properties of products were studied in details. The
products were characterised for chemical composition,
phase conditions, particle size distribution, morphologies
and saturation magnetisation. Most products exhibited
ferrimagnetic behaviour. Correlations among domain-
and particle sizes were also investigated. Conditions
for the synthesis of nanosized, inverse zinc ferrites
of high saturation magnetisation were established. It
was proved that in thermal plasma conditions normal
and inverse ferrites could be produced in a single step
process