Effect of carbon black and thermal aging on the conduction mechanism of natural and styrene butadiene rubbers

Two types of carbon black namely fast extrusion furnace black (FEF) and high abrasion furnace black (HAF) were incorporated with a concentration of 50 phr into styrene butadiene rubber (SBR) and natural rubber (NR). The effect of the time of aging and temperature on the electrical conductivity was studied. It was found that a thermal aging at 95°C leads to the appearance of minimum in conductivity (σ) in both FEF/NR and HAF/NR. This was explained by a competition between two factors: degradation and increase of crosslinking density in the rubber matrix. In case of FEF/SBR and HAF/SBR it seems that these factors have comparable effects on the conductivity after 10 days of aging. From the current-voltage (I-V) characteristics the carrier concentration, trap density, and the drift mobility were calculated. The minimum found in the temperature dependence of σ for FEF/NR is discussed and found to be controlled by the relative dimension of carbon and rubber aggregates.     

Effect of preextension on electrical conductivity and physicomechanical properties of butyl rubber (IIR) loaded with different types of carbon black

The effect of preextension on the variation of the electrical conductivity (σ) of butyl rubber (IIR) loaded with high abrasion furance (HAF) and fast extrusion furance (FEF) carbon black with carbon concentration have been investigated. The change in σ has been explained as a result of the interaction between carbon and rubber and the effect of the occluded rubber. The effect of preextension on the electrical resistivity (ρ) variation with strain has also been studied. The changes have been interpreted as being due to either breakdown or reagglomeration, depending on the concentration of carbon black.     

Effect of ingredients on the electrical conductivity of styrene butadiene rubber

The effect of different ingredients, which are usually added during the preparation of rubber mixtures, on the electrical conductivity σ of styrene-butadiene rubber (SBR-1502) has been studied. It was found that processing oil (as softener) showed a marked increase in σ with respect to the pure sample. Stearic acid (as antioxidant), however, did not show a considerable effect on σ. The addition of constant concentration of 50 phr from different types of carbon black (filler) namely, ISAF, HAF, FEF and SRF to the rubber matrix resulted in different values of the initial conductivity of the vulcanized samples. The conduction mechanism through carbon black-loaded rubber vulcanizates has been discussed and rough estimation of the separation distance between carbon black particles (or aggregates) suggested. The carbon black-loaded rubber vulcanizates showed a reasonable stability and reproducibility of σ after pre-thermal-oxidative ageing at 365 K for 30 days.     

Magnetoresistance of CuxCo1-xFe2O4 Ferrites

Magnetoresistance measurements (Δ/R) were carried out on Cu _x Co_{1- x} Fe₂O₄ samples with x =1, 0.75, 0.50, 0.25 and cobalt ferrite in the range of magnetic intensity (H) from 1.0 to 4.5 kG. Linear plots were obtained between log (Δ/R) and log H for all compositions except that of cobalt ferrite. The values of n at x =0.5 do not agree with the results of some authors. The discrepancy may be attributed to the value of magnetic field intensity at which such measurements were carried out. The similarity of features of n and μ_D with composition leads us to believe that the magnetoresistance may arise from the scattering of conduction electrons by localized electrons involving the s-d exchange interaction.     

Effect of concentration and temperature on the electrical conductivity of butyl rubber loaded with different types of carbon black

In this study we are interested in the effect of concentration and temperature on the electrical resistivity of butyl rubber (IIR) loaded with two types of carbon black, (namely, high abrasion furnace black (HAF), and fast extrusion furnace black (FEF)). It was found that the conductivity at low carbon black concentrations is mainly achieved by thermal activation of carriers. Tunneling mechanism at low termperature followed by thermal activation at relatively high temperature is found to be predominant for moderate concentrations for both carbon blacks. The metal-like behaviour which was observed in highly loaded compounds was attributed to both, the thermal expansion of the tunneling paths between carbon-carbon agglomerates and the breakdown of carbon agglomerates with temperature.