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 the search for environmentally acceptable fluids for these purposes. A precision variable pathlength interferometer, incorporating some novel features, has been constructed and used to make sound speed measurements on a number of liquids with low speeds of sound. The measurements were made, with a precision of +/-0.05% and an uncertainty of +/-0.2%, at atmospheric pressure and at various temperatures in the range 273.15 to 303.15 K. The most promising low-sound speed liquid identified was n-perfluorohexane, which has a sound speed below 600 m . s(-1) in the temperature range of interest here. This liquid forms homogeneous mixtures over al least part of the temperature range with several alkanes including n-pentane, n-hexane, and 2,2-dimethylbutane. Experimental results for binary mixtures of perfluorohexane isomers with each of the aforementioned alkanes are reported.