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•A water-based ferrofluid was irradiated with photons and electrons.•The dose was that usually involved in radiation therapy of human subjects (50 Gy).•Electron irradiation induced ...minor change in the colloidal stability of ferrofluid.•Magnetic heating of ferrofluid at 100 kHz is not affected by irradiation.•Magnetic hyperthermia can be applied in the same time period as radiation therapy.
The paper reports on the effect of therapeutic-like irradiation of a water based magnetic fluid with magnetite particles double-surfacted with oleic acid on its magnetic heating characteristics. To assess the effect of irradiation, a quantity of the initial sample was retained as the reference sample. The other part of the ferrofluid was irradiated with a photon beam (with the energy of 10 MeV and the dose of 50 Gy) and with an electron beam (of the energy of 9 MeV and the dose of 50 Gy).
The frequency dependence of the complex magnetic permeability, μ(ω) = μ′(ω)-i μ″(ω), was affected only in the case of the electron irradiated sample and over the approximate range of 10–100 kHz.
The dynamic light scattering investigation revealed a small increase of the average of the size of light scattering entities and of the polydispersity index of the sample irradiated with electrons compared to the reference sample.
Magnetic heating experiments, performed at the frequency of 100 kHz and with various amplitudes of magnetic field, H, (of 25, 50, 75 and 100 Oe) did not reveal significant difference in the heating rate values of the reference sample and of the irradiated samples. Therefore, magnetic hyperthermia can be involved in the therapy plan, in the same period of time as the radiation therapy, provided at the frequency of the alternating magnetic field larger than the frequency corresponding to the Brownian relaxation peak.
The paper reports on the frequency (
f
) and static magnetic field (
H
) dependencies of the microwave propagation parameters, in the ranges 0.1–6 GHz and 0–90.7 kA/m, of a kerosene-based ferrofluid ...with magnetite particles, filtered in magnetic field gradient. In the investigated range, the sample exhibits ferromagnetic resonance phenomenon and Maxwell–Wagner dielectric relaxation. Unlike the usual way of studying the propagation of microwaves through different media, in this paper we have defined an overall reflection coefficient,
Rw(f, H)
, of a material with thickness,
w
, deposited on a total reflective support, which takes into account both the attenuation of wave within the material and the reflection at the air–material interface. Based on the measured relative magnetic permeability,
μ
r
, and relative dielectric permittivity,
ε
r
, a comprehensive and meaningful set of microwave propagation parameters are determined. Apart from
Rw(f, H)
, this set of parameters of ferrofluid includes the attenuation constant of the electromagnetic wave,
α
(f, H)
, the phase constant
β
(f, H)
, the real,
n’(f, H)
, and imaginary,
n”(f, H)
, components of the refractive index, the reflection coefficient at the interface air–material,
R(f, H)
, and the quarter wavelength in material,
λ
1
/
4
(f, H).
Based on the theoretical considerations and characteristics of ferrofluid, simplified and practical formulas of the propagation parameters are given and also possible applications of the results are suggested (such as electromagnetic absorber, phase shifter, microwave lenses and vibration sensor). This connection between theory and experimental results offers an example for the preliminary design of microwave applications of ferrofluids and, by extension, for any material consisting of magnetic nanoparticles dispersed in a dielectric matrix.
Graphic abstract
Results of experiments on small-angle scattering of neutrons and X-rays on colloidal suspensions with anisometric barium hexaferrite nanoparticles in an aqueous solvent are reported. It has been ...shown that the preparation according to a new method produces fairly stable colloids with two types of particles of reproducible morphology and size: large lamellar-shaped particles (~100 nm) with a thickness of ~7 nm and small isometric particles with a size of ~6 nm.
Gas bubbles in shaped sapphire Bunoiu, O.M.; Duffar, Th; Nicoara, I.
Progress in crystal growth and characterization of materials,
01/2010, Letnik:
56, Številka:
3
Journal Article
Recenzirano
Shaped sapphire single crystals almost always contain a typical defect: small bubbles also known as “micro-voids”. The goal of this paper is to review the existing literature and give a survey of our ...recent work on this specific defect. As a conclusion to our review we propose a mechanism for bubble formation and its occurrence and distribution in shaped sapphire.
The bubbles contain CO which originates as a result of complex reactions between the molten alumina, Mo crucible and graphite pieces. The CO dissolves in the molten alumina and is probably present as a saturated solution whatever the growth conditions. Then the dissolved gas is rejected at the solid–liquid interface and bubble nucleation occurs where the concentration of CO is highest. Therefore, the location of the bubbles in the crystal is governed by the hydrodynamics in the meniscus, which include Marangoni convection. The bubble is finally incorporated in the crystal when it reaches a critical size which depends only on the growth rate.
When a central capillary channel is used, the bubbles are located in a layer close to the surface of the crystal from where they can be easily removed by polishing. Also, all the literature agrees on the fact that interface destabilization at high velocity results in the presence of bubbles throughout the entire crystal and should be avoided.
Voids engulfment in shaped sapphire crystals Nicoara, Irina; Bunoiu, O.M.; Vizman, D.
Journal of crystal growth,
01/2006, Letnik:
287, Številka:
2
Journal Article, Conference Proceeding
Recenzirano
In shaped crystals besides the usual structural defects, such as dislocations, faceting, and grain boundaries, so-called “voids” have been observed almost always; this defect affects especially the ...optical quality of the crystals. The influence of growth conditions on size and distribution of trapped gas bubbles in shaped sapphire crystals has been studied both experimentally and by numerical simulation of the fluid flow in the meniscus. The influence of the pulling rate, of the ambient temperature and of the shaper design has been taken into account.
High-density polyethylene (HDPE) composites with different amounts of ZrO2 nanoparticles (1–20 vol%) were prepared by high-pressure thermal pressing. The effect of γ-irradiation on their structural ...and thermal properties was investigated using small-angle neutron scattering (SANS), X-ray diffraction (XRD), Raman spectroscopy, infrared spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). SANS analysis confirmed good dispersion of the nanoparticles in HDPE matrix. Upon exposure to γ-radiation only small changes in the lattice parameters and the crystalinity degree occurred for both HDPE and the nanocomposities. More significant changes for irradiated HDPE were observed in DSC-derived parameters, including the decrease in the melting point, and increase in crystalinity degree. This trend was even more pronounced for the nanocomposities. A possible explanation assuming resonant enchantment of polymer chain scission in the presence of ZrO2 nanoparticles is discussed. The extent of radiation-induced oxidation was essentially the same for pure HDPE and the nanocomposities, suggesting that the process is diffusion controlled. The thermal stability of the irradiated composites was somehow higher than that pure HDPE.
•HDPE composites with different amounts of ZrO2 nanofiller prepared by high-pressure thermal pressing.•Good dispersion of the ZrO2 nanoparticles obtained while preserving the crystalline structure of the HDPE matrix.•Absence of a diffusion region between the filler particles and the polymer matrix confirmed by SANS.•Influence of γ-irradiation on the structural and thermal properties of HDPE and HDPE+%ZrO2 nanocomposites was investigated.•HDPE+%ZrO2 nanocomposite exhibited excellent thermal and thermo-oxidative stabilities.
The manipulation of nanoparticles is becoming an important issue as they are massively generated in combustion or material synthesis processes and are highly toxic to human health. Therefore, a ...considerable interest is shown to their separation in accordance with their physical or chemical characteristics using dielectrophoresis. Dielectrophoretic (DEP) force is exerted when a neutral particle is polarized in a non-uniform electric field, and depends on the dielectric properties of the particle and the suspending medium. This paper investigates the behavior of a suspension of nanometric particles under the action of DEP force. A theoretical model is proposed and a set of numerical results is provided. In particular, the particles' trajectories are computed for a planar electrode array configuration. PUBLICATION ABSTRACT
