We measured the speed of sound in the process gases Cl2, HBr, BCl3, and in the surrogate gases SF6, CF4, and C2F6. The data range up to 475 K (200 C) and from 25 kPa to 1500 kPa (or to 80% of the vapor pressure for condensable gases). The data were analyzed to obtain ideal-gas heat capacities Cp0(T) with uncertainties of 0.001 Cp0. The data were also used to parametrize model pair and three-body intermolecular potentials which were used to estimate the properties of the gases up 800 K, temperatures well above the range of the data. From the model potentials, we deduced the nist-equation of state P(V,T) and the viscosity Η(T). For gases where other data exist, we find the errors in the estimates are less than 0.001 V and 0.1 Η (The thermal conductivity κ(T), can be estimated from Η(T) with an uncertainty of 10%.) Plans include measuring the speed of sound in WF6, direct acoustic measurements of the transport properties, and dissemination of the results as a user-friendly data base for PCs and in publications in archival journals.
Proceedings of SEMICON West '99, Workshop on Gas Distribution Systems