Electrical Properties of Some Carbon Black-Oil Suspensions

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Abstract
The dc conductivity and ac (1000 cps) properties of suspensions of R-40 carbon black in transformer, silicone, and linseed oils, and suspensions of Shawinigan black in linseed oil, were studied as functions of time, carbon black concentrations, and rotational speed of test cell. The dc conductivity was also studied as a function of voltage. Immediately after agitating the suspension, both ac and dc conductivities increase rapidly with time, then level off and approach a saturation value. For the dc conductivity, this value increases with increasing voltage in all suspensions studied except the highest concentrations (10 percent by weight), which obey Ohm's law. The rate of approach to saturation is independent of voltage but depends on carbon black concentration. Increasing the concentration increases the conductivity. Increasing the speed of rotation decreases the conductivity. Form factors for the carbon black particles are calculated from the dynamic values of the dielectric constant by Voet's method. Agglomeration factors are then determined. At low speeds the agglomeration factor decreases rapidly with increasing speed. At higher speeds it approaches unity asymptotically.