Carbonaceous powder to be dispersed in electrorheological fluid and

Abstract

An electrorheological fluid is constituted by using a dispersed phase of a carbonaceous powder having an oxygen content above 10% by weight but not more than 20% by weight and having an average particle diameter of 0.01-100 .mu.m, obtained by: heat-polymerizing a condensed polycyclic aromatic compound containing a main component of naphthalene by using HF/BF.sub.3 as a catalyst to obtain a 100% meso-phase pitch having a softening point within a range of 150.degree.-400.degree. C.; heat-treating and making the pitch infusible in an oxidizing atmosphere at a temperature not more than a fusing temperature of the pitch and not less than 50.degree. C. but not more than 400.degree. C. to allow the pitch to have an oxygen content of 12-25% by weight; and then heat-treating and carbonizing the pitch in an inert gas atmosphere at a temperature not less than 300.degree. C. but not more than 700.degree. C. It is thus possible to obtain an electrorheological fluid having low current consumption, a high electrorheological effect and excellent long-term durability, even when the carbonaceous powder having high oxidation resistance and a high oxygen content is used.