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Vapor Pressure of Octafluorocyclobutane (RC-318) from 234 K to 387 K Measured with a Variable-Volume View Cell

Year: 2026
Type: preprint
Abstract: Saturated vapor pressures of octafluorocyclobutane (c-C4F8, RC-318) were measured at 32 temperatures from 234.33 K to 387.01 K, corresponding to pressures from 20.62 kPa to 2.698 MPa. Measurements were performed in a variable-volume cell with sapphire windows, enabling direct observation of the vapor–liquid meniscus and visual confirmation of the two-phase state at each point. The highest measurement was obtained 1.36 K below the reported critical temperature (Tc = 388.37 K). Temperature was measured with a platinum resistance thermometer traceable to the ITS-90, and pressure was measured with a calibrated transducer. The combined expanded uncertainty in the saturation pressure, U(ps) (k = 2), was estimated to be 0.2–0.6% over the measured range. The data were correlated with a four-term Wagner equation constrained to the critical parameters of Douslin et al.,[3] giving an average absolute relative deviation (AARD) of 0.23%, a root-mean-square relative deviation of 0.34%, and a maximum absolute relative deviation of 0.82%. The measurements agree with the reference equation of state of Platzer et al.[28] with an AARD of 0.27%. Combined with saturated-phase molar volumes from the reference equation of state, the correlation gives an enthalpy of vaporization that decreases from about 25.4 kJ·mol−1 at 234 K, through 23.3 kJ·mol−1 at the normal boiling point, and approaches zero at the critical point. These measurements provide a modern, internally consistent vapor-pressure data set for a high-GWP fluorinated gas that is widely used in semiconductor processing and has also been investigated for dielectric applications.
Source: ChemRxiv
DOI: 10.26434/chemrxiv.15009592/v1
Language: English
Field: Chemistry
Open Access status: green
OpenAlex ID: W7214720130
Cites: 11
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Related to: 10