Conductivity Of Composite System Research Articles

Effects of temperature and humidity on electrical properties of proton conducting KH2PO4 / SiO2 composites

In the present work the temperature and humidity effects on electrical properties of KH2PO4/SiO2 composites have been studied. Composite nature of the system has been confirmed by the XRD patterns. Wagner’s polarization method confirms the ionic conduction in the prepared systems. Temperature and humidity dependent ac conductivity was measured by using complex impedance spectroscopy in the frequency range 10 Hz to 105 Hz. In pure KH2PO4 the conductivity is influenced by the hopping of the proton through defects while in KH2PO4/SiO2 composite systems, the conductivity of composite system is governed by hydrophilicity below 130 0C. In the present composite systems, absorption of KH2PO4 takes place at the surface of silica which produce defects near the salt KH2PO4/oxide Sio2 interface. The transition temperature of composite was found to be decreased in comparison to the pure KDP.

Electric heating property from butyl rubber-loaded boron carbide composites

We researched the electric heating property from butyl rubber-loaded boron carbide composite. The effects of boron carbide content on bulk resistivity, voltage-current characteristic, thermal conductivity and thermal stability of boron carbide / butyl rubber (IIR) polymer composite were introduced. The analysis results indicated that the bulk resistivity decreased greatly with increasing boron carbide content, and when boron carbide content reached to 60%, the bulk resistivity achieved the minimum. Accordingly, electric heating behavior of the composite is strongly dependent on boron carbide content as well as applied voltage. The content of boron carbide was found to be effective in achieving high thermal conductivity in composite systems. The thermal conductivity of the composite material with added boron carbide was improved nearly 20 times than that of the pure IIR. The thermal stability test showed that, compared with pure IIR, the thermal stable time of composites was markedly extended, which indicated that the boron carbide can significantly improve the thermal stability of boron carbide / IIR composite.

Nonlinear behavior and universal scaling of ac conductivity in (100 − x) BaTiO3/(x) La0.7A0.3MnO3 (A = Pb/Ca) composites

We have measured the ac conductance σ (x,f) of the ferroelectric–ferromagnetic (100 − x) BaTiO3/(x) La0.7A0.3MnO3 (A = Pb/Ca) composites as a function of frequency (f) by varying x in wt% (20, 30, 40 and 50%) at a constant temperature T (300 K). σ (x,f) of the sample with fixed x remains at an almost constant dc value σ 0 at a lower frequency at a fixed temperature T. With the increase of f, σ (x,f) increases slowly from σ 0. Finally, σ (x,f) increases rapidly with ffollowing a power law with an exponent n in the high frequency regime. In the scaled coordinate, the data for σ(x, f) fall on the same universal master curve, indicating the existence of a general scaling formalism for the ac conductivity in composite systems. The characteristic frequency fc scales with σ 0 as fc ∼ σ (0,x)xf , where xf is the onset exponent. We have also shown that fc, scaling formalism of ac conductivity data can be successfully applied in insulating/conducting composite systems irrespective of the conducting phase.

Dielectric behaviour of the composite system: multiwall carbon nanotubes dispersed in ferroelectric liquid crystal

Ferroelectric liquid crystal–multiwall carbon nanotube (FLC-MWCNTs) composite systems have been prepared by dispersing low (0.03 and 0.10 wt.%) concentration of MWCNTs in the liquid crystal matrix. Relaxation behaviours of pure and composite systems have been investigated. Thermo-optic studies infer a small shift (∼5 K) in the clearing temperature of the dispersed systems. Dielectric measurements reveal that the MWCNTs influenced the permittivity. The relaxation time, relaxation frequency and dielectric strength have been evaluated and discussed. The influence of MWCNTs concentration on the conductivity of composite systems has been investigated.

Transport and structural properties of compounds (1 − x)CsHSO4-xKH2PO4

The homogeneous substitution of cations (K+) and anions (H2PO 4 − ) for CsHSO4 is performed. The dependences of protonic conductivity and structure of (1 − x)CsHSO4-xKH2PO4 (x = 0.05–0.9) compounds on the composition are studied. It is found that the introduction of KH2PO4 leads to the formation of a new highly conductive phase. At small amounts of introduced KH2PO4 (x = 0.05), a mixed salt forms; its low-temperature conductivity is by more than two orders of magnitude higher than that of the source salts. The thermal behavior of mixed salt (1 − x)CsHSO4-xKH2PO4 of various compositions and the peculiarities of crystal structure are studied. The structural parameters of the salt at x = 0.05–0.5 are close to those of Cs3(HSO4)2(H2PO4). At higher x, another phase forms, whose structure has yet to be determined. The thermal stability of the salt decreases with increasing fraction of KH2PO4 introduced. The conductivity of the composites based on the mixed salt and silicon dioxide (1 − y){xKH2PO4-(1 − x)CsHSO4}-ySiO2 (x = 0.05, 0.1; y = 0.1–0.7) is studied. It is shown that, in the low-temperature range, the conductivity of composite systems increases within an order of magnitude, passes through a maximum, and, then, decreases at y > 0.5 due to the percolation effect.

Properties of thermally conductive micro and nano size boron nitride reinforced silicon rubber composites

In the current study, the effects of loading level of micro or nano size BN particles on the thermal, mechanical, and morphological properties of silicone rubber are investigated. Three micron size and two nano size BNs with different particle sizes and shapes are used. All five types of BNs are found to be well-dispersed in silicone rubber matrix despite some local agglomerates. In general, the addition of BN particles in silicone matrix decreases the tensile strength and strain at break, coefficient of thermal expansion (CTE) values, on the other hand increases modulus, hardness and thermal conductivity. Nano size fillers have more pronounced effect on tensile properties of composites in comparison to micron size BNs at any given loading level. The aspect ratio of the filler is found to be very effective in achieving high thermal conductivity in composite systems. Dielectric constants of composites vary between dielectric constant of silicone and BN.

Thermal characteristics of defective carbon nanotube-polymer nanocomposites

The interfacial thermal resistance of pristine and defective carbon nanotubes (CNTs) embedded in low-density polyethylene matrix is studied in this paper. Interface thermal resistance in nanosystems is one of the most important factors that lead to the large variation in thermal conductivities in literature and the novelty of this paper lies in the estimation of the interfacial thermal resistance for defective nanotubes-systems. Thermal properties of CNT nanostructures are estimated using molecular dynamics (MD) simulations and the simulations were carried out for various temperatures by rescaling the velocities of carbon atoms in the nanotube. This paper also deals with the mesoscale thermal conductivities of composite systems, using effective medium theories by considering the size effect in the form of interfacial thermal resistance and also using the conventional micromechanical methods like Hashin-Shtrikman bounds and Wakashima-Tsukamoto estimates.

Effective medium theory in studies of conductivity of composite polymeric electrolytes

The application of effective medium theory to a description of a temperature and composition dependence of conductivity of composite polymeric electrolytes is presented. Conductivities of several composite systems containing conducting (NASICON) or nonconducting (Θ-Al 2O 3, polyacrylamide) additives are analyzed in terms of effective medium theory approaches. All of the systems studied are based on polyether matrices. The influence of grain size distribution, concentration and type of additives on conductivity of composite systems is discussed. The model presented assumes that an increase in the conductivity in comparison to polyether based electrolytes is due to the formation of highly conductive layers at the polyether matrix-filler interface. Variation of the conductivity of this layer with grain sizes, and the concentration of a filler is assumed and discussed. The theoretical assumptions are confirmed by experimental data obtained by several techniques, such as impedance spectroscopy, DSC, NMR and energy dispersive X-ray diffractometry.

Core–shell morphology as a model for the study of gas permeation in composite systems

AbstractStructured latex particles prepared by emulsion polymerization were used as a model to simulate the interphase region between two phases. Multiphase polymer films comprised of high and low permeability polymers of various compositions were used. The model system consisted of a poly(n‐butyl methacrylate) (PBMA) matrix and a discontinuous phase with core and shell morphology. The structured particle had a PBMA core and a vinylidene chloride – n‐butyl methacrylate (VDC–BMA) copolymer shell. The shell transport characteristics wer altered by changing the (VDC–BMA) copolymer molar ratio. The physical and transport properties for each individual component were measured. Nitrogen was the probe gas. Films used for permeation experiments were prepared by latex casting. The results showed that the morphology of a heterogeneous polymeric system and the transport characteristics of their components had a considerable effect on the magnitude of the transport properties. Experimental data also showed the dependence of the gas global permeability coefficient on the nature of the simulated interphase region, the shell, and the weight percentage of such interphase in the heterogeneous polymeric films. Upon increasing the VDC content in the VDC–BMA copolymer, the gas permeability decreased. The data were fitted to the electrical analogs of conductivity in composite systems. For the matrix filled with structured particles the overall permeability coefficient could best be described when the individual permeabilities were considered as the inverse resistances in parallel.