Characterization of the degree of dispersion of constituents in cement paste or mortar by DC electrical resistivity measurement was demonstrated for the constituent being much more conducting than cement (i.e., short carbon fibers) and much less conducting than cement (i.e., latex particles). The fiber dispersion is described by the ratio of the measured conductivity to the calculated value. The latex particle dispersion is described by a factor in an electrical conduction model.

Corrosion of potential candidate electrode materials, molybdenum and tantalum, in a simulated nuclear waste glass melt was investigated using electrochemical (dc-powered) and non-powered tests. Electrochemical corrosion data showed that tantalum was more corrosion-resistant than molybdenum in this melt. Tantalum also showed passivation. The non-powered test data showed that tantalum corroded more than molybdenum. This was attributed to penetration of protective passivation layer at the tantalum-glass interface by the glass melt. Microstructural features and chemistry across selected electrode-glass interfacial regions supported these results.

D.C. electrical transport measurements have been done over the temperature range 200 K. to 450 K on the mixed conductor Cu3.0CS2 This work extends the original work done on CuxCS2 over the temperature range 260 K to 350 K. Above 220 K, the voltage versus time curves follow the Yokota model for mixed conductors. Below 220K, the voltage versus time curves were practically constant, suggesting very little ionic transport below this temperature, and an electronic conductivity of the order of 10−5 (Ω cm)−1 at 200 K. At ambient temperatures, the ionic conductivity and electronic conductivity were both of the order of 10−3 (Ω cm)−1, and the chemical diffusion coefficient found to be of the order of 10−6 cm2s−1, in agreement with earlier work on Cu3CS2. Above 220 K, the ionic conductivity versus temperature plots were of the Arrhenius form with an activation energy of about 0.36 eV. The jump time and residence time were estimated to be of the order of 10−12s and 10−6s respectively, confirming hopping as the mode of ionic transport. The electronic conductivity versus temperature plot confirmed thermal activation as the mode of electronic transport. The results suggest CuxCS2 to be very stable and the Yokota model, with very little modification, to be very reliable for the analysis of these mixed conductors.

A composite solid state electrochemical device, with (Gd1-xCax)2Ti2O7 serving as the electrolyte and Gd2(Ti1-xMox)2O7 (GT-Mo) as the anode has recently been proposed. The latter exhibits high levels of mixed conduction under reducing atmospheres, but decomposes at high Po2. We have recently succeeded in extending the stability limits of the GT-Mo to higher Po2 with the addition of Mn. In this study, we report on the conductivity and stability of Gd2((Mo13Mn2/3)xTi1-x)207 (GMMT) as a function of Po2, T, and composition utilizing impedance spectroscopy and x-ray diffraction. The addition of Mn extends the stability region of the material to Po2 = 1 atm with little change in the magnitude of the conductivity. Defect models explaining the dependence of the conductivity on oxygen partial pressure are presented. Preliminary results from the use of an electronic blocking sandwich cell used to isolate the ionic conductivity of GMMT are also presented.

Composition. dependence of electrical conductivity of ionic-electronic composite was camined using yttria(8mol%) stabilized zirconia-NiO composites. The contributions of ectronic and ionic charge carriers to the electrical conductivity were determined by Hebb-Vagner polarization technique and electromotive force measurement of galvanic cell. Up to 6 sol% NiO addition, the conductivity decreased since the electronic NiO acted as an insulator in onic matrix. However the ionic transport was dominant until NiO content reaches 26 vol%. Mixed conduction was observed between 26 and 68 vol% of NiO. The effects of composition on he electrical properties were explained by the microstructure and thus by the distribution of two hases.

The measured microwave effective dielectric properties of metal-dielectric composites show discrepancies when data from free space, resonant cavity or transmission line measurements are compared. Discrepancies are especially evident for materials where the metallic concentration is near the percolation threshold. This paper presents theory and measured data which highlight and resolve these discrepancies. Electrical correlation length is the relevant parameter which must be considered in choice of measurement technique. Agreement between effective medium models and measurement are best when focussed beam measurement techniques are utilized so as to produce planar wave-fronts whose extent is 3–4 freespace wavelengths when incident on the sample.

The dielectric properties of composites are affected in different ways by a number of parameters. These include the electrical properties of both the filler and matrix, the wetting properties of the matrix on the filler, the size and shape of the filler, and the amount of the filler. Most composite systems have been studied via dc resistivity measurements which clearly show the effect of the addition of a second phase to an insulating matrix. However, frequency dependent measurements can provide additional insight into the mechanisms controlling the electrical response. The frequency dependence of the dielectric properties of composites will be shown. The permittivity and admittance plots of BN/B4C composites will be given and the relevance of the trends seen in them will be discussed.

Using a computer simulation, impedance spectra of mixtures of conducting and insulating hard spheres which have random or regular arrangements of the components are studied. These simulations can be used to calculate the a.c. electrical properties of a multi-component composite using a personal computer. It is shown in this study that a.c. impedance spectra are sensitive functions of the filling fraction and the geometrical arrangement of the components, and especially, the impedance spectra of the composite show the abnormal arc originated from the isolated clusters in the composite.

Measurements of both components of the complex AC conductivity σ*m of continuum percolation systems, based on Graphite and hexagonal Boron Nitride, over a large frequency range, for samples near the conductor insulator composition, are reported. The results of the real part of σ*m (σmr) above the critical volume fraction (φc) and the imaginary component (σmi = iωεoεmr) below φo are shown to have the correct power law dispersion behavior, but only if the non-universal exponents measured in previously described DC experiments are used. It is also shown that all the results can be scaled, as is predicted by percolation theory, so as to lie on two continuous curves, one below and one above φc. Unfortunately the actual ωc values used to scale the experimental results are found not to be in good agreement with theoretical predictions.

Conductivity results and 1/f noise (Sav) measurements from some systems with a cellular structure (composites in which small conductor particles embed on the surface of larger and regular insulator particles) are given. The usual DC percolation parameters (φc,t & s) were obtained from fitting the results to the Percolation equations. φc values for the systems have been found to lie in the range 0.01 – 0.07, while both non-universal and close to universal values have been measured for the exponents s and t. In addition, 1/f or flicker noise results on the systems give an additional exponent ω from the relationship Sav/Vdc2 = KRω. For the systems measured so far, the exponent ω is observed to take different values ω1 close to and ω2 further away from the conductor-insulator transition, but on the conducting side (ω > ωc). The very different values (s, t & ω), obtained for the various conducting powders, in the same macroscopic structure, indicates that the way the powders distribute themselves on the insulating particles is a major factor in determining the exponents.