| Early in1992, an iron-nitride magnetic fluid was successfully synthesized by Nakatani et al. using vapour-liquid chemical reaction. Subsequently the iron-nitride ferrofluid has attracted wide interest due to its high saturation magnetization and relative stability. The iron-nitride ferrofluid had been mainly prepared by vapor-liquid chemical reaction method and plasma Chemical Vapor Deposition (CVD) technique. However, the reaction time was too long to apply in industrial production for vapor-liquid chemical reaction. The plasma CVD technique was operated at low pressure using needle-to-plate discharge to synthesize the iron-nitride ferroparticles. The inhomogeneous plasma environment may lead to the uneven ferroparticles, so that the iron-nitride ferrofluid was unstable.The atmospheric-pressure Dielectric Barrier Discharges (DBD) has been a hot point of plasma application research in recent years because of its various nice features, such as no requirement for vacuum system, low cost, and production line, and so on. The atmospheric-pressure DBD has been applied successfully in ozone synthesis, surface modification and new materials synthesis, et al. In this paper, ε-Fe3N-based ferrofluid has been synthesized by a homemade DBD device at atmospheric-pressure and the influence of discharge parameters on the properties of s-Fe3N-based ferrofluid has been investigated. The results are as follows:(1) The Atmospheric-Pressure DBD device has been developed in this paper. The atmospheric-pressure Ar/NH3/Fe(CO)5DBD plasma is produced under a carrier liquid by this device which may provide the experimental foundation for gas-liquid discharge plasma. The discharge characteristics and emission spectra have been studied for the atmospheric-pressure DBD plasma of Ar/NH3/Fe(CO)5.The research shows that two discharge modes, multi-pulse Atmospheric-Pressure Glow Discharge (APGD) and filamentary discharge, are coexistence in the atmospheric-pressure DBD plasma of Ar/NH3/Fe(CO)5in a discharge period. When Ar and NH3flow rates are respectively900and30ml/min, the Fe(CO)5pressure, the power supply frequency and applied voltage peak-peak value are respectively5.17×102Pa,20kHz and4600V, the single-pulse APGD and filamentary discharge are found in the discharge space, and the Lissajous figure is a quadrilateral with one step on the right-hand side. With increasing the applied voltage peak-peak value up to6400V, the discharge mode coverts to two-pulse APGD and filamentary discharge and Lissajous figure appears two steps. But when the applied voltage peak-peak value is up to7800V, filamentary discharge is the primary discharge mode.The main particles of Ar/NH3/Fe(CO)5DBD plasma are NH, N, N+, Fe, N2, Ar, Hα and CO, NH is decomposition products of NH3. When NH3flow rate is30ml/min, the emission spectra intensities of various particles reach the maximum at the same applied voltage. The emission spectra intensities of various particles increase with the increase of the applied voltage peak-peak value at the same NH3flow rate. Fe and N active radicals are two elementary species of synthesizing ε-Fe3N-based ferrofluid in atmospheric-pressure DBD plasma.(2) ε-Fe3N-based ferro fluid has been synthesized by a homemade DBD device at atmospheric-pressure. The synthesis period has been greatly shortened from30hours to2hours by the novel preparation technology. As a result of cost savings, the novel preparation technology of ε-Fe3N-based ferro fluid shows a good application in industry.NH3flow rate is the most important factor influencing on ferroparticle component of ε-Fe3N-based ferrofluid. When NH3flow rate is30ml/min, ferroparticle component is a single ε-Fe3N. Magnetic properties of ε-Fe3N-based ferrofluid are affected by the applied voltage peak-peak value. The The higher applied voltage peak-peak value rises, the stronger the saturation magnetization of ε-Fe3N-based ferrofluid become. When the applied voltage peak-peak value is up to7800V, the magnetic susceptibility decreases due to the influences of filamentary discharge. The surfactant is the key factor of influencing the stability of ε-Fe3N-based ferrofluid. When the mass ratio of surfactant and earrier liquid is2:11, the suspension percentage of ferroparticles in ε-Fe3N-based ferrofluid is still91.3%after12months sealing placed.(3) The first-order magnetic buoyancy formula of ferrofluid is researched based on Bernoulli’s equation. The influence of the applied voltage peak-peak value on first-order magnetic buoyancy has been investigated by the intelligent apparatus of nano-ferroparticles’ spatial distribution for ferrofluid.The higher the applied peak-peak value rises, the larger the apparent density and first-order magnetic buoyancy of ε-Fe3N-based ferrofluid increase. With weakening magnetic field intensity and magnetic field gradient, the ferrofluid’s apparent density decreases, This leads to the decrease of first-order magnetic buoyancy. When the applied voltage peak-peak value is7100V, six non-magnetic objects emerge under different currents. And Rosensweig peaks appear when the current is3.50A. The research can be applied to ferrofluid separation for different densities of non-magnetic objects. (4) The ferrofluid device for preparation TEM sample with the external magnetic field is developed in this paper (Invention patent:201210204709.4). Chained-alignment of suspended-ferroparticles in a carrier fluid exposed to the external magnetic field has been investigated experimentally and the influence mechanism of magnetic field on chained alignment has been interpreted theoretically.The ferroparticles are randomly distributed in the absence of an external magnetic field and turn out to be the chained-alignment patterns along the magnetic field orientation with the external magnetic field. When exposed to uniform magnetic field at intensity of11.1kA/m the ferroparticles form a chained-alignment pattern along the magnetic field orientation. With the external uniform magnetic field intensity up to28.6kA/m, more ferroparticles closely aggregate to chained-alignment patterns along the magnetic field direction.When the magnetic field intensity reaches28.7kA/m in the gradient magnetic field, a large number of ferroparticles gather around the coils and form complex clusters, while a small number of ferroparticles demonstrate a chain-alignment pattern along r direction with weaker magnetic field intensity. When the magnetic field gradient is gradually increasing from1.73kA/m2to5.11kA/m2, the cluster pattern of ferroparticles turn out to be dense along the axis. This research may enhance the applications of ε-Fe3N-based ferrofluid in the fields of mechanical engineering, bioengineering and thermodynamic engineering. |
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