IDENTIFICATION OF ENVIRONMENTALLY ACCEPTABLE LOW-SOUND SPEED LIQUIDS

Liquids with unusually low sound speeds are required as filling fluids for sonar targets and acoustic lenses. In this paper, we report on th e search for environmentally acceptable fluids for these purposes. A p recision variable pathlength interferometer, incorporating some novel features, has been constructed and used to make sound speed measuremen ts on a number of liquids with low speeds of sound. The measurements w ere made, with a precision of +/-0.05% and an uncertainty of +/-0.2%, at atmospheric pressure and at various temperatures in the range 273.1 5 to 303.15 K. The most promising low-sound speed liquid identified wa s n-perfluorohexane, which has a sound speed below 600 m . s(-1) in th e temperature range of interest here. This liquid forms homogeneous mi xtures over al least part of the temperature range with several alkane s including n-pentane, n-hexane, and 2,2-dimethylbutane. Experimental results for binary mixtures of perfluorohexane isomers with each of th e aforementioned alkanes are reported.