An experimental study of the degradation of particles in complex plasma

Changes of melamine–formaldehyde resin (MF-R) particles occurring in complex dusty plasma have been investigated. Using a specially developed method, plasma-modified MF-R particles have been extracted from a dust trap after levitation for various periods of time and studied by electron microscopy techniques. Changes in the surface structure of MF-R particles are determined, and quantitative data on the variation in particle dimensions depending on the time of occurrence in plasma are obtained.     

The interaction between charged dust particles in a plasma

A solution to the Poisson-Boltzmann equation for a cloud of charges surrounding two charged dust particles, considered as Debye atoms forming a Debye molecule, is studied by numerical methods. It is demonstrated that attractive forces between the particles arise when two conditions are satisfied. First, the Debye screening radius, corresponding to the electron density at a half average spacing between particles, must be equal to approximately half of this distance. In this case, the attraction arises at a distance equal approximately to the average spacing between particles. Second, charges of one sign must be concentrated predominantly on the particles. Should the particles possess only a small fraction of charges of one sign, they will repulse at any distance. Estimates of the electrostatic pressure and surface tension in a gas of dust particles are obtained.     

The effect of humid and dusty atmosphere on shock wave destruction in a glow-discharge plasma

The influence of air humidity and the dust present in air and nitrogen on the structure of a pressure momentum distribution behind a shock wave propagating across the positive column of glow discharge in these gases has been experimentally studied. Analysis of the experimental data provides information concerning the mechanism of shock wave degradation under such conditions.     

The distribution functions of charged particles in the vicinity of a cylindrical body in a flow of collisionless plasma in magnetic field

The distribution functions are investigated of charged particles in the wall region in the vicinity of a cylindrical body placed in a flow of collisionless plasma. For comparison with the studies by other authors, the calculation is first performed for the case of quiescent plasma in the absence of magnetic field. Subsequent calculations consistently include the directional velocity of plasma and external magnetic field. The basic features of obtained distribution functions are revealed and explained.     

Reconstruction of the mass distribution of charged particles in a periodic electric field

A method is proposed for determining the mass spectrum of a monochromatic precisely directed source by means of a plane-parallel capacitor with a sinusoidally time-dependent voltage on the plates. The mass spectrum is reconstructed from an integral equation that relates the current to the collector with the amplitude of the ac part of the voltage. Pis’ma Zh. Tekh. Fiz. 23, 1–7 (January 26, 1997)     

Energy loss distribution of charged particles in thin absorbers

Conclusions 1. For thin absorbers, the Landau theory incorporating certain above-listed corrections is a general-purpose one and is in good agreement with experiment both for heavy and light charged particles 0.01. 2. For intermediate layers (0.01 1 and 1), exact solutions are provided by the Vavilov theory [11]. 3. The numerical-analytic method of plotting the energy loss distribution function proposed in [13] is suitable for very thin ( 0.01) absorbers.Translated from Izmeritel'naya Tekhnika, No. 3, pp. 60–62, March, 1970.     

An experimental study on the influence of particles on grain boundary migration

The pinning effect of particles on grain boundary migration was studied in a Fe–20 mass% Cr alloy deoxidised with Ti and Zr. The different nitrogen contents (65, 248 and 490 ppm) were used to vary the number of precipitated inclusions. The specimens from equiaxed zones of metal samples with different particle densities were examined by in situ observations during a 60-min holding time at 1200 and 1400 °C in a Confocal Scanning Laser Microscope. The change of particles pinning effect on the grain growth was described by an average grain size, [`(D)]_textA bar{D}_{text{A}} , and the ratio between the perimeter and area of grains, P _GB/A _G. It was found that the pinning effect of particles (mostly complex Ti–Zr oxynitrides) on grain growth decreased with a decreased nitrogen content in the metal. Furthermore, the effect of particles decreased with an increased temperature of treatment, due to the reduction of the number of particles on the grain boundaries.     

An experimental study of the dynamics of formation of plasma in a vacuum-arc discharge

An experimental study is made of the dynamics of formation of plasma in a vacuum-arc discharge (VAD) at different currents and different transverse dimensions of CuCr50 electrodes. High-speed multipleframe photography is used to obtain the time dependence of the current channel diameter and determine the rate of plasma expansion. It is demonstrated that the rate of expansion under the experimental conditions is independent of the discharge current, as well as of the presence or absence of external axial magnetic field. Two modes are identified, which differ from one another by the rate of expansion. Experiments are performed with anodes and cathodes of different diameters in the range of currents from 2 to 15 kA. It is demonstrated that, with electrodes of different sizes, a discharge initiated at the cathode center expands with time to the size of the smaller electrode while retaining the cylindrical shape. The anode temperature is calculated for two modes in view of the variation of the source power and of the transverse dimension of the zone of heating. It is demonstrated that the anode spot in the mode of rapid expansion is formed under insignificant heating of the anode. In the case of slow expansion, a strong heating of the anode is possible, under which its intense evaporation occurs. The anode temperature is calculated in view of the evaporation losses for modes with different numbers of jumpers arising as a result of the breaking of vacuum switch contacts.     

An experimental study of moisture uptake and transport in a bed of urea particles

Urea, a widely used nitrogen fertilizer, is susceptible to moisture adsorption from ambient air which leads to caking and handling problems. Scanning Electron Microscopy (SEM) images of a nearly spherical urea particle and a fractured cross-sectional area of a urea particle show internal porosity and external surface roughness. BET test analysis indicates that the internal surface area available for water vapour adsorption is comparable to, or larger than, the external surface area of urea particles. In this research, experiments were undertaken to obtain the transient response of a packed and initially dry porous urea bed after humid air starts to flow slowly through the bed. The experimental data for local and total bed moisture content shows that the internal moisture diffusion inside the porous urea particles is a very slow process which limits the rate of moisture accumulation in the bed.     

An experimental study of ash particles adhesion force in flue gas

In this study, experiments and analyses have been carried out to investigate the influences of denitrification and flue gas Waste Heat Recovery Systems (WHRS) on ash particles adhesion force. With use of a denitrification system, it is found that the ash particles adhesion force is strongly influenced by the mass ratio, R, of (NH₄)HSO₄ to ash. Three influencing zones are identified, i.e., little effect zone (R < 1:150), intermediate effect zone (1:150 < R < 1:60), and huge effect zone (R > 1:60). It is necessary to operate in the little effect zone in order to avoid ash deposition in the air preheater. With use of a WHRS, it is found that the ash adhesion force is strongly affected by the flue gas temperature in comparison with the Engineering Acid Dew Temperature (EADT). With decreasing temperature below the EADT, both the collected ash amount and ash adhesion force rise, and the detected particles size increases, indicating particle accumulation that improves ash collection efficiency.     

An experimental study on the effect of chloride penetration on moisture diffusion in concrete

Chloride penetration and moisture diffusion are two important transport processes for studying the long-term durability of concrete. The chloride penetration and moisture transfer in concrete are considered as two coupled transport processes. An experimental study was conducted for determining the related material parameters in the coupled transport processes. For the coupled moisture diffusion, we consider that the total moisture fluxJ _H ^t is resulted from two driving forces: the gradient of moistureH, and the gradient of free chlorideC _f , that is,J _H ^t =?D _H-H grad(H)?D _H-Cl grad(C _f′ ). In this formulation, two transport parameters are involved: the moisture diffusion coefficientD _H-H and the coupled moisture diffusion coefficient due to chloride diffusionD _H-Cl . A seepage test was designed specifically for determining the two transport parameters. The test data showed that the chloride penetration accelerates the moisture diffusion significantly. The two transport parameters were determined using the present test data. The result showed thatD _H-Cl is not a constant, but depends linearly on the free chloride concentration.     

Motions of charged particles in plasmas

The motion of a single charged particle in magnetic and electric fields B and E is described by the basic non-relativistic equation of motion in which radiation damping is neglected.

With emphasis on vector methods, data are obtained for the drift-free reference case of motion in a circular helix, and then the drift velocity perpendicular to B due to electric field perturbation of the circular case is used to obtain the familiar gravitational and curved magnetic line drifts. Application of the gravitational drift to the plasma physics Rayleigh-Taylor instability is examined critically in the light of information which can be obtained from the macroscopic equation of motion for a plasma in a magnetic field.

For a spatially perturbed magnetic field a guiding centre treatment using the standard orthogonal curvilinear co-ordinate system of differential geometry yields, after time averaging, the first-order Alfvén and curvature drifts, the latter being in agreement with the result obtained less rigorously from the electric drift velocity. The magnetic field geometry is described in terms of an extended set of Frenet-Serret partial derivatives which involve six scalar quantities, five of which are independent when a scalar magnetic potential exists. After time averaging there also exists a first order velocity component of unusual form parallel to B. For the usually encountered case of B irrotational, this component vanishes.

The three equations of motion for the components of the particle velocity are also obtained in terms of this curvilinear co-ordinate system, and when time averaged the equation of motion for the particle velocity component parallel to B enables the spatial adiabatic invariance of a spiralling particle's magnetic moment to be rapidly established.

The case of B dependent on the time, which can lead to radial compression of a plasma, is discussed from drift and non-drift view points, and the difference between Larmor's frequency and the gyrofrequency is emphasized. A simple microscopic treatment of the polarization drift is also included.

Finally the historical and mathematical significance of adiabatic invariance is discussed, with particular reference to the magnetic moment in plasma physics.     

An experimental method for measurement of strain distribution between wood the flour particles and polymer matrix on micro-mechanical level

Wood plastic composites (WPCs) are comprised of wood flour and thermoplastic polymer. The matrix is typically high-density polyethylene, poly (vinyl chloride), or polypropylene. The effect of morphology and micromechanics of wood flour particles on the mechanical performance of the bulk composite is a relatively unexplored area. The knowledge about the in situ properties of wood particles and the interfacial properties between the wood particles and the polymer matrix in the bio-composites is very limited. The objective of this work is to characterize the full-field deformation and strain distribution in and around wood particles embedded in polymer matrix. The mechanical tests are performed in small-scale tensile loading stage on thin composite samples containing 1-3 wood particles orientated at various angles. The deformations and strains is measured using optical measurement system based on Digital Image Correlation (DIC) principle.     

Influence of charged particles on the fullerene formation process

The influence of charged particles on the process of fullerene formation is determined. Systematic experiments are used to show that the presence of carbon ions in the fullerene formation zone substantially increases the fullerene content in the soot. Pis’ma Zh. Tekh. Fiz. 25, 35–40 (March 12, 1999)