Observations on the Rheological Behaviors of Magnetic Paint

Abstract

Some rheological behaviors of paints containing magnetic powders (γ-Fe2O3) were investigated from the view point of interfacial phenomena, compared with the paints containing non-magnetic powder (α-Fe2O3), and the following results were obtained:Both α-and γ-Fe2O3 paints without dispersing agent, show the structural viscosity, and its tendency is more remarkable in the former paint.By the addition of the dispersing agents, the structure forming action of particles in α-Fe2O3 paints is weakened and its flow character is altered to a Newtonian pattern. On the other hand, in the γ-Fe2O3 paints, the structure still remains and Bingham-type flow is maintained.These behaviors were considered to be caused by the formation of different structures in each paints. In the α-Fe2O3 paints, the particles form three-dimensional honey-comb structures as shown in Fig. 10 (b), only with the interparticular attractive forces. In the case of the γ-Fe2O3 paints, particles were arranged as chains or closed chains shown in Fig. 10 (a), by magnetic attractive force.The applicability of Casson's equation, the appearence of 2nd Newtonian region and the thixotropic behaviors for the γ-Fe2O3 paints will mean the degradation of the chain to smaller units by shearing force, together with the rearrangement and orientation.