An automated apparatus for measuring sound speeds in hazardous gases

Abstract

Our laboratory has developed an automated apparatus for measuring the sound speed in hazardous gases such as those used in processing semiconductors. The sound speed is deduced from measurements of the acoustic resonance frequencies of a gas-filled, cylindrical cavity. After the cavity is calibrated with argon, the uncertainty in the sound speed is less than 0.01%. The u(P,T) data span the temperature and pressure ranges 200–475 K and 100–1500 kPa. From the measured sound speeds we derive the ideal gas heat capacities from the zero-pressure intercepts with a typical uncertainty of only 0.1%. The virial equation of state is also deduced from u(P,T) providing the temperature-dependent density virial coefficients. In comparisons with Burnett measurements, we find that the densities calculated with the derived virial equation of state have uncertainties of less than 0.1% in density. Some recent measurements in SF6, CF6, and C2F6 will be used to illustrate the systems capabilities. Work in progress on BCl3 will also be discussed.