SAID SHEHATA

The electrical properties measurements were carried out for the complex (CH2)2(NH3)2Mn1-xCdxCl4, 0.0 ≤ x ≤ 1.0 at different temperatures as a function of frequency (100-1000 kHz). Four transition points were obtained for x = 0.5, which are assigned as thermochromism, interlayer exchange interaction, order-disorder and chain melting. The presence of more than one straight line in the conductivity data clarifies the presence of more than one conduction mechanism, and the calculated values of the activation energy indicate the semiconducting characteristics of the investigated complexes. The values of the calculated relaxation time indicate its dependence on Cd content as well as the heating temperature. The expected critical concentration at x = 0.5 agree well with the percolation theory of Mont-Carlo group. The IR spectra indicate that the force constant of the bonds and the atomic mass vibration are affected by Cd content. © 2005 Elsevier B.V. All rights reserved.

The electrical properties measurements were carried out for the complex (CH2)2(NH3)2Mn1-xCdxCl4, 0.0 ≤ x ≤ 1.0 at different temperatures as a function of frequency (100-1000 kHz). Four transition points were obtained for x = 0.5, which are assigned as thermochromism, interlayer exchange interaction, order-disorder and chain melting. The presence of more than one straight line in the conductivity data clarifies the presence of more than one conduction mechanism, and the calculated values of the activation energy indicate the semiconducting characteristics of the investigated complexes. The values of the calculated relaxation time indicate its dependence on Cd content as well as the heating temperature. The expected critical concentration at x = 0.5 agree well with the percolation theory of Mont-Carlo group. The IR spectra indicate that the force constant of the bonds and the atomic mass vibration are affected by Cd content. © 2005 Elsevier B.V. All rights reserved.

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The electrical conductivity of a range of ordinary Portland cement based mortars was studied over a period of 6h hydration. The influence of water/cement (w/c) ratio (0.20, 0.25 , up to 0.40), thermal cycling curing temperature (20, 30 and 40°C ), and the pozzolanic additions [35% fly ash, 35% slag and (35% fly ash+ 35% slag) to the OPC separately] on conductivity was investigated, and the activation energy E g established for conduction processes. E g was found to be system specific and was in the range -0.12 up to -0.212 eV at w/c = 0.20. Results indicate that the changes in the electrical conductivity and the activation energy of each system mainly depend on the microstructural changes, occurring during the hydration mechanism. These changes are not constant with the curing time and the w/c ratios. The proper consideration in the change of the pore microstructure leads to the optimization of the finer pores microstructure which occurs at the w/c ratios 0.30 and 0.35 in all various cementitious systems. Those ratios are considered to be the optimum ratios for reducing the porosity.

The electrical conductivity of a range of ordinary Portland cement based mortars was studied over a period of 6h hydration. The influence of water/cement (w/c) ratio (0.20, 0.25 , up to 0.40), thermal cycling curing temperature (20, 30 and 40°C ), and the pozzolanic additions [35% fly ash, 35% slag and (35% fly ash+ 35% slag) to the OPC separately] on conductivity was investigated, and the activation energy E g established for conduction processes. E g was found to be system specific and was in the range -0.12 up to -0.212 eV at w/c = 0.20. Results indicate that the changes in the electrical conductivity and the activation energy of each system mainly depend on the microstructural changes, occurring during the hydration mechanism. These changes are not constant with the curing time and the w/c ratios. The proper consideration in the change of the pore microstructure leads to the optimization of the finer pores microstructure which occurs at the w/c ratios 0.30 and 0.35 in all various cementitious systems. Those ratios are considered to be the optimum ratios for reducing the porosity.

The electrical conductivity of a range of ordinary Portland cement based mortars was studied over a period of 6h hydration. The influence of water/cement (w/c) ratio (0.20, 0.25 , up to 0.40), thermal cycling curing temperature (20, 30 and 40°C ), and the pozzolanic additions [35% fly ash, 35% slag and (35% fly ash+ 35% slag) to the OPC separately] on conductivity was investigated, and the activation energy E g established for conduction processes. E g was found to be system specific and was in the range -0.12 up to -0.212 eV at w/c = 0.20. Results indicate that the changes in the electrical conductivity and the activation energy of each system mainly depend on the microstructural changes, occurring during the hydration mechanism. These changes are not constant with the curing time and the w/c ratios. The proper consideration in the change of the pore microstructure leads to the optimization of the finer pores microstructure which occurs at the w/c ratios 0.30 and 0.35 in all various cementitious systems. Those ratios are considered to be the optimum ratios for reducing the porosity.