針状ヘマタイト粒子からなる分散系の逆磁気粘性効果

概要

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We have investigated the negative magneto-rheological effect of a dispersion composed of spindle-like hematite (α-Fe2O3) particles by means of the experimental method. The spindle-like hematite particles were synthesized by aging a solution of FeCl3 and KH2PO4 for 72 hours at 373K. The particle size distribution was determined by a digital image analysis method from the electronic microscope observation of the particles. In the present study we have considered a glycerol-water-based dispersion in order to clarify the influences of the shear rate and the magnetic field strength on the negative magneto-rheological effect. The measurement of the viscosity was carried out using the rotational-type rheometer in an external magnetic field generated by the Helmholtz coils. The main results obtained here are summarized as follows. The viscosity of hematite/glycerol-water dispersions relative to that for no applied magnetic field case decreases with increasing magnetic field strength: that is, the negative viscosity certainly occurs, as theoretically predicted. Moreover, this negative magneto-rheological effect tends to decrease with increasing shear rate, which also qualitatively agrees with the theoretical prediction.