Electrical Relaxation Time Research Articles

Toner Charging Characteristics in the Rotation Mixing System of Toner and Carrier

Toner charge is very important in electrophotographic printing process. Many studies on toner charging mechanism have been carried out. However, understanding of toner charging characteristics is not yet sufficient. Toner charge distribution is measured by E-SPART (Electrical Single Particle Aerodynamic Relaxation Time) which can measure and analyze the size and the charge of respective toner. The measured toner is of a crushing type. Charging is carried out as follows: the toner is mixed with carriers in a bottle and mixed by the rotation of the bottle. Average toner charge of each channel of the toner diameter is estimated. It is found that the average toner charge is proportional to the square of toner diameter and shows a saturation as the diameter increases. The experiment of adding the toner after the toner is charged to nearly stationary is carried out. It is found that toner charge distribution becomes a new value due to charge exchange between the toner and the toner/carrier.

Electrostatic Effects on Dispersion, Transport, and Deposition of Fine Pharmaceutical Powders: Development of an Experimental Method for Quantitative Analysis

Currently, there is no standard method for testing the electrostatic properties of pharmaceutical powders. The objective of this study was to develop a method of characterizing the dispersion, charging, and transport properties of fine powder flowing through tubes of different materials. Powders of known composition and size distribution were dispersed pneumatically and transported through a short section of tubing containing spiral baffle inserts of the same material to simulate powder flow in long sections of horizontal and vertical tubes with bends. The test powder was dispersed using ring jet suction and passed through the baffled tube to a sampling chamber, from which the powder cloud was sampled for particle size and electrostatic charge distribution measurement using an Electrical Single Particle Aerodynamic Relaxation Time (E-SPART) analyzer. Experimental data on the tribocharging and transport properties of different powders are presented along with an explanation of the charging mechanisms. Analyses of particle size and electrostatic charge distributions in real time and on a single particle basis using the E-SPART analyzer coupled with surface structure analyses with XPS and UPS showed that: (1) most powders are charged bipolarly with relatively high charge-to-mass ratio (Q/M) values that would have a strong effect on transport and deposition of powders; and (2) surface structures, particularly adsorbates, influence the work function and tribocharging of powder. Different methods, including plasma treatment, with minimal changes or contamination of the bulk properties of the powders are also suggested. pharmaceutical powders tribocharging dispersion work function charge distributions charge decay plasma treatment

Electrical conductivity, speeds of sound, and viscosity of aqueous ammonium nitrate solutions

Density, electrical conductivity, speeds of sound, and viscosity of aqueous ammonium nitrate solutions were measured as functions of concentration (m, mol kg–1) (0.1599 [Formula: see text] m [Formula: see text] 20.42) and temperature (T, K) (273.15 [Formula: see text] T [Formula: see text] 323.15). Experimental values are consistent with the reported data. Variation of isotherms of electrical conductivity, isentropic compressibility, and structural relaxation time with concentration evoke structural information on the ion solvation in aqueous ammonium nitrate solution at different concentration regions. The primary hydration numbers of ammonium nitrate were estimated at a particular concentration at which the isentropic compressibility isotherms converge. The existence of free hydrated ions, resulting from strong ion solvent interactions in dilute to 9.1 mol kg–1, the solvent-separated ion-pairs resulting from the relative competition between the ion–solvent and the ion–ion interactions in 9.1 to 12.0 mol kg–1, and the solvent-shared ion-pairs beyond 12.0 mol kg–1 resulting from a decrease in the number of solvent molecules, govern the transport process.Key words: electrical conductivity, speeds of sound, viscosity, ammonium nitrate, hydration number.

BEHAVIOR IN ELECTRIC FIELDS OF SIMPLE BIOLOGICAL MEMBRANES

The latest studies in biophysics and biochemistry have revealed the major role that liquid crystals (LC) and related phenomena play in biological processes. To account for a number of membrane mechanisms in view of the theoretical model developed by S. J. Singer, studies were carried out on mixtures of fatty acids (arachidic, lauric, butyric) and cholesterol in different weight percentages. Such mixtures may help one understand some mechanisms on which the operation of biological membranes relies. To this end, the way these mixtures behave in an electric field was studied. Electric measurements were conducted from which the average time of electric relaxation (τ) and average electric permittivity (ε r ) were determined. Depending on cholesterol percentage, changes by more than one order of magnitude were found to occur in the electric relaxation time. The ratio between the various fatty acid components did not influence the average time τ in any significant manner. By contrast, the relative electric permittivity ε r was seen to decrease by at least one order of magnitude with raising the cholesterol percentage. The electric properties of such systems essentially depend on changing the amount of cholesterol in the system.

Li Mobility in the Orthorhombic Li0.18La0.61TiO3 Perovskite Studied by NMR and Impedance Spectroscopies

Electrical conductivity and NMR relaxation times (T 1 and T 2 ) have been determined in the Li 0.18 La 0.61 TiO 3 perovskite. At room temperature, the unit cell constants are a = 3.865-(1), b = 3.876(1), and c = 7.788(2) A and the space group Pmmm (orthorhombic). In this doubled perovskite, the Rietveld analysis of the X-ray powder pattern showed that La ions occupy preferentially one type of sites (z/c = 0), and Li and vacancies accommodate with the remaining La at the second site (z/c = 0.5). From this fact, Li motion should be favored in the plane ab; however, exchanges of Li between contiguous layers are detected above 200 K by NMR spectroscopy. From T 1 and T 2 NMR data, two main relaxation mechanisms have been detected, which have been ascribed to localized exchanges (200-273 K) and extended motions of Li (above 273 K). The dc conductivity shows a non-Arrhenius temperature dependence, and local activation energies of 0.41 and 0.26 eV were obtained in the low- and high-temperature ranges, respectively. Both NMR and electrical conductivity relaxations are described by stretched exponential functions, characteristic of correlated ion motions.

Theoretical and experimental characterization of self-heating in silicon integrated devices operating at low temperatures

The self-heating of Si devices operating in the 4 K<T<300 K range is discussed in this work. The temperature-dependent thermal time constant of a typical Si chip is calculated and compared to several electrical relaxation times. Thermal events may be indistinguishable from electrical events at low temperatures, and this makes the transient method an unreliable one for characterizing the cryogenic self-heating. A semi-analytical approach, which considers the temperature dependence of the thermal conductivity of Si, is used to calculate the steady-state thermal profile on the top surface of a Si IC where a device is dissipating power at different ambient temperatures. Theoretical results indicate that the temperature rises measured in earlier works cannot be due to the thermal properties of Si at low temperatures. A test chip containing several integrated Si devices is used to characterize experimentally the self-heating. The strong self-heating usually observed in Si devices operating at very low temperatures is dominated by the parasitic thermal resistance, of which the ceramic package is the main contributor. The dominance of this parasitic contribution decreases for an increasing ambient temperature and becomes similar to that of the Si device at 300 K.

Relating macroscopic electrical relaxation to microscopic movements of the ions in ionically conducting materials by theory and experiment

Whatever the preferred representation of the frequency dependence of electrical relaxation experimental data, complex conductivity ${\ensuremath{\sigma}}^{*}(\ensuremath{\omega}),$ complex permittivity ${\ensuremath{\varepsilon}}^{*}(\ensuremath{\omega}),$ or complex electric modulus ${M}^{*}(\ensuremath{\omega}),$ there is no escape from the fact that we are dealing with measurements which are macroscopic in nature. The question of how to relate the macroscopic measurement, which contains the high-frequency dielectric constant ${\ensuremath{\varepsilon}}_{\ensuremath{\infty}},$ to the microscopic movement of the ions remains to be answered. Comparing the results of a stochastic transport theory and of the electric modulus formalism, we find that the electric modulus faithfully reproduces the shape of the dispersion of the microscopic ionic movement. However, the electric modulus relaxation time is different from the microscopic relaxation time by a known and calculable factor that is proportional to the product of the high-frequency dielectric constant and temperature. Consequently, the entire electric modulus relaxation time spectrum is shifted uniformly away from the microscopic ion relaxation time spectrum by the same frequency-independent factor, and these two relaxation time spectra have effectively the same dependence on temperature, isotope mass, etc. In contrast to electrical conductivity relaxation, nuclear spin relaxation is a microscopic probe of ionic movement, and from its result we can directly infer the microscopic dynamics of the ions. A combined study of ionic motion using electrical relaxation and nuclear spin relaxation in a crystalline ionic conductor by Le\'on et al. provides the experimental data to enable us to verify the theoretical relation between the macroscopic electric modulus spectrum and the microscopic ionic hopping relaxation spectrum.

Recent advances in relating macroscopic electrical relaxation data to microscopic movements of the ions in ionically conducting materials

The question of how to relate the macroscopic conductivity relaxation measurement (ε∗(ω), σ∗(ω) or M∗(ω)) to the microscopic movement of the ions is a problem that must be resolved. Comparing with the results of a stochastic transport theory of charged carriers, we find that among the other choices the electric modulus, M∗(ω), is the most appropriate representation of the macroscopic data to describe the microscopic movement of the ions. It is found that M∗(ω) faithfully reproduces the shape of the dispersion of the microscopic ionic movement except that the entire electric modulus relaxation time spectrum is shifted uniformly away from the microscopic ionic hopping relaxation time spectrum by a calculable frequency-independent factor. Nuclear spin relaxation is a microscopic probe of ionic movement. A combined study of ionic motion using electrical relaxation and nuclear spin relaxation in a crystalline ionic conductor provides the means to verify the theoretical relation between the macroscopic electric modulus spectrum and the microscopic ionic hopping relaxation spectrum. Finally, we present some recent advances in our understanding of the experimental data that indicate the importance of ion– ion interactions in many ionically conducting crystals, glasses and melts.

ONE-DIMENSIONAL SIMULATION OF THE BREAKUP OF CAPILLARY JETS OF CONDUCTING LIQUIDS. APPLICATION TO E.H.D. SPRAYING

Nonlinear breakup of charged liquid jets is numerically analyzed in this work in the limit of a very small electrical Strouhal number T e/ T b≪1 (i.e. negligible charge relaxation effects, applicable to highly conducting liquids), where T e is the electric relaxation time of charges, and T b is the breakup time in a Lagrangian framework following the liquid jet at its average axial velocity. The influence of the electrical Bond’s number and viscosity on (i) the capillary Rayleigh’s most probable breakup length, (ii) the breakup time, (iii) the volume of the satellite, and (iv) the charge of both main drop and satellite, are analyzed. The model is related to the microjet break-up phenomena in the electrospraying of liquids in steady cone-jet mode, and its range of applicability to those particular problems discussed. Previous experimental results [Mutoh et al., 1979, Convergence and disintegration of liquid jets induced by an electrostatic field. J. Appl. Phys. 50, 3174–3179; Clopeau and Prunet-Foch, 1989, Electrostatic spraying of liquids in cone-jet mode. J. Electrostatics 22, 135–159.] support our numerical finding that the influence of the electrical Bond’s number on Rayleigh’s length is small within the usual parametrical limits of stability of a steady Taylor cone-jet at atmospheric pressure.

Pyroelectric hysteresis loop at ferroelectric phase transition

A theory of a nonlinear pyroelectric effect in a phase transition region of a ferroelectric thin film due to harmonic temperature changes with large amplitudes reaching tens of K has been developed. Polarization during the temperature cycle–pyroelectric hysteresis loop is obtained at various frequencies, amplitudes, thermal, and electric relaxation times. It is proved that ferroelectric film can be maintained in a monodomain state during the cycle. Applicability of a nonlinear pyroelectric cycle to solar energy conversion (ferroelectric solar cell) is discussed.

Electrohydrodynamic(ehd) enhancement of boiling heat transfer with a lo-fin tube

The effect of D. C electric field on nucleate boiling heat transfer for refrigerants of R-11, HCFC-123 and FC-72 was investigated experimentally by using a single lo-fin tube shell-and-tube heat exchanger. The lo-fin tube which brought two times increase in the heat transfer area provided about 150% of boiling heat transfer enhancement compared to that of smooth surface. This experimental study has revealed that the electrical charge relaxation time was an important parameter for the boiling heat transfer enhancement under electric field. Boiling heat transfer enhancement was obtained up to 40% for R-11 which had moderate relaxation time of 1.3s. However remarkable boiling heat transfer enhancement has been obtained up to three fold increase(300%) for HCFC-123 which has the electrical charge relaxation time of 0.89 x 10-3s. For FC-72 having longer relaxation time than the bubble detachment one, no appreciable effect on the nucleate boiling heat transfer was observed.

Electrical Conductivity, Viscosity, and Sound Velocity of Lithium Bromide + Lithium Nitrate + Acetamide Melt Systems

Densities, electrical conductivities, viscosities, and sound velocities of 0.22[xLiBr + (1 {minus} x)LiNO{sub 3}] + 0.78CH{sub 3}CONH{sub 2} were measured as functions of temperature (296.75 {le} T/K {le} 343.15) and composition (x = 0.0--1.0 mole fraction). Electrical conductivity, viscosity, and structural relaxation time were found to have non-Arrhenius temperature dependence and were analyzed by using the Vogel-Tamman-Fulcher equation. A significant mixed anion effect has been found in the electrical conductivity isotherms. Viscosity and structural relaxation time vary linearly with composition. The variation of electrical conductivity is governed by the mobility of Br{sup {minus}} and No{sub 3}{sup {minus}} ions and the competitive polarization exerted by anions on Li{sup +}, whereas the polymeric and rigid structure formed between Li{sup +} and acetamide primarily govern the viscosity process.

7Li NMR study of ionically conducting glasses

ABSTRACTTemperature dependence of 7Li NMR was measured in 50Li20-50B203 glasses. A new method for the analysis of motional narrowing of the line width (MNLW) incorporating Kohlrasuch-Williams-Watt (KWW) function, exp(-(t/τ)β) is presented. The obtained activation parameters are compared with that from conductivity. It was shown that MNLW can be explained by the same activation energy from conductivity. It was found that electrical relaxation time was an order of magnitude smaller than that from those from NMR line width. At high temperature region, where the line is well narrowed, a residual line width was observed. It is as large as 1 kHz, and gradually decreases with the increase in temperature. It was explained that there is a mobility difference in lithium ions in this glass. These results suggest that some fraction of ions are highly mobilized in the glass.

NMR at single crystal surfaces

Nuclear magnetic resonance has developed into a very powerful technique to study the structure and dynamics of atomic and molecular systems, in both the liquid and the solid phase. However, the investigation of single-crystal surfaces with the conventional NMR methods is essentially impossible due to the small sample size of less than 10 15 sites on 1 cm 2 . To overcome this for the important class of alkali adsorbates on metals and semiconductors, two methods are presented. Common to both is the preparation of a highly nuclear spin-polarized atomic beam of 6 Li in the one case and 8 Li in the other. The latter isotope is radioactive and undergoes a β-decay with a half-life of 0.84 s. Li adsorbed on the close-packed Ru(001) surface is investigated. The longitudinal relaxation time, T 1 , is the main observable and is used to deduce the local electronic density of states [LDOS(E F , r = 0)] and Li diffusion barriers. The second experiment uses 6 Li as an adsorbate, also studied on Ru(001). The nuclear polarization is measured by beam foil spectroscopy. A novel particle detected (photon counting) Fourier transform NMR technique is demonstrated. This is done by observing the time-dependent flux of circularly polarized light emitted behind the foil after a 90° pulse has been employed at the surface. Electric field gradients and transverse relaxation times, T 2 , are thus determined. A large difference between T 1 and T 2 is traced to the dimensionality of the system.

Analysis of exponential time-differencing for FDTD in lossy dielectrics

We determine the stability condition and analyze the accuracy of the exponential and centered time-differencing schemes for finite-difference time-domain (FDTD) in an isotropic, homogeneous lossy dielectric with electric and magnetic conductivities /spl sigma/ and /spl sigma/*, respectively. We show that these schemes are equivalent and determine that, for accuracy, both schemes must be used with a time step that finely resolves the electric and magnetic conduction current relaxation time scales. The implications of these results for perfectly matched layer (PML)-type absorbing boundary conditions are discussed.

On the Outcome of the Coulombic Fission of a Charged Isolated Drop

Observations on the Coulombic fission of isolated drops of diameterDcharged near the Rayleigh limit show that they often form a transient Taylor cone through which many droplets much smaller thanDare emitted. Sometimes, however, the products of the explosion are only a few, and their size is comparable toD. We argue that the “fine fission” mode takes place under the same conditions generally leading to the formation of a steady Taylor cone; namely,Dhas to be much larger than the charge relaxation lengthdm= (γτ2/ρ)1/3(τ = ϵϵ0/Kis the electrical relaxation time; ϵ0is the electrical permittivity of vacuum; ϵ,K, γ, and ρ are the dielectric constant, electrical conductivity, surface tension, and density of the liquid). Otherwise, no Taylor cone may form and the explosion must proceed through a “rough fission” mode. Consequently, although drops of low conductivity liquids may break up into a few large and probably unequal fragments, more conducting drops are bound to explode with little mass loss, producing many very small and relatively monodisperse daughter droplets. For the case of polar liquids for whichD >> dm, we reason that the emissions from the exploding drop must be quasi-steady, with characteristics similar to those of steady electrified cone-jets supported on a capillary tube. In addition, the liquid flow rateQthrough the cone-jet forming on the exploding drop must be near the threshold value, which is on the order ofQm= γτ/ρ. This fixes approximately the size and charge of the fission products to be on the order ofdmand of the Rayleigh limit, respectively. No quantitative data are available for the size of the daughters from exploding polar liquids. Furthermore, the electrical conductivityKhas not been reported for the polar liquids whose Coulombic explosions have been studied so far. But the present predictions agree qualitatively with available measurements on the relative charge over mass loss in Coulomb fissions.

Fluctuation Model for Structural Relaxation and the Glass Transition

ABSTRACTThe fluctuation or independently relaxing nanoregion model attributes the distribution of structural relaxation times in a glassforming melt to a physical distribution of nanoregions which vary in their properties. A quantitative test of this model is described, in which parameters derived from relaxational data on B2O3 glass are shown to be capable of predicting the anomalous light scattering in the glass transition region. It is also shown that the local inhomogenieties which lead to the distribution of structural relaxation times make only a very minor contribution to the distribution of electrical relaxation times in ionically conducting glasses and melts.

Enhancement of Evaporation of a Droplet Using EHD Effect. Onset of Instability of Gas-Liquid Interface under Electric Field Applied in a Stepwise Manner.

An experimental study is conducted to investigate the onset of instability of a liquid surface under an electric field applied in a stepwise manner. The critical voltages and the response times above which the liquid surface becomes unstable are measured under electric fields applied in two different ways. Instability criteria are derived theoretically using a modified Rayleigh-Taylor instability equation for the cases of a perfectly conducting liquid and a perfectly insulating liquid. According to the results of the experiment and theoretical analysis, consideration is made of the mechanism of the onset of EHD (electro-hydrodynamic) instability of the liquid surface having a long electrical relaxation time.

‘Window’ effect in the analysis of frequency dependence of ionic conductivity

Usually the frequency dependence of ionic conductivity of solids in analyzed in the form of a power law or as the deviation of imaginary part of electric modulus from ideal Debye peak. The power law formalism is shown to be sensitive to the choice of frequency window employs in the analysis. The results demonstrate the inadequacies of either formalism and a method is suggested of combining the two formalisms for parameterizing non-ideal electric response in the vicinity of the electrical conductivity relaxation time.

Analysis of electrical relaxation in glasses and melts with large concentrations of mobile ions

Various analyses of or fits to electrical relaxation data for a model Li 2OAl 2O 32SiO 2 glass s were tried. These included three-parameter fits using Kohlrausch-Williams-Watts (KWW) and Cole-Davidson (CD) distributions of electric field relaxation times, along with a four-parameter σ ′( ω n ) fit using the distribution implicitin the Jonscher expression for the frequency dependence of the real part of the complex conductivity, σ ′ = σ + Aω n . In the frequency range 10 −2 ≤ ω < τ> ≤10 2, where <τ> is the mean electric field relaxation time, the KWW firt was best, the σ ′( ω n ) fit second best and the CD fit the worst. Because the σ ′( ω n ) fit predicts qualitattively incorrect relaxation behavior at low frequencies, it is suggested that this method of data analysis not be used. It was noted that the dependence of σ ′ on ω 1 observed for ionically conducting solids at very high frequencies or very low temperatures make a nearly negligible contribution to the relaxation of the electric field.