Electrorheological fluid compositions

Claim 1

An electrorheological fluid composition consisting essentially of an electrically nonconducting liquid and 10 to 50 vol. % silica particles dispersed therein, wherein the nonconducting liquid being at least one member selected from the group consisting of petroleum-derived lubricants, transformer oils, silicone oils, dibutyl sebacate, chlorinated paraffins, alkyl bromides, aromatic polycarboxylic acid alkyl esters, aromatic polycarboxylic acid halophenylalkyl esters, halophenyl alkyl ethers, and fluorine-containing oils and the silica particles being spherical particles formed by hydrolyzing a silicon alkoxide in a reaction mother liquor, the silicon alkoxide being of the following general formula (1) Si(OR).sub.4 ( 1) in which R is an alkyl group in the presence of an alkali catalyst, and drying at or below 500° C. and the silica particles: have an average diameter of 0.1-2.0 μm, have a BET nitrogen specific absorption area of ≦100 m 2 /g, have a carbon content of ≦3% and have a weight lose of 2-12% when heated up to 200° C. in thermogravimetric analysis and a weight lose of 2-10% when heated to 200° C. to 1000° C. in thermogravimetric analysis.