Volumetric Properties and Internal Pressure of Poly(α-olefin) Base Oils

Abstract

This paper describes the high-pressure volumetric properties of three commonly used poly(α-olefin) base oils—PAO 2, PAO 4, and PAO 8—with nominal 100 °C kinematic viscosities of 2, 4, and 8 cSt. Using a special variable-volume view cell that permits continuous pressure scan and volume measurements, densities were determined at 298, 323, 348, 373, and 398 K at pressures up to 40 MPa. Isothermal compressibilities, isobaric thermal expansivities, thermal pressure coefficients, and internal pressures were then evaluated. At each temperature, density–pressure correlations were developed for the range from 10 to 40 MPa. Density–temperature correlations were developed at 10, 20, 30, and 40 MPa. It is shown that the densities of PAO 2 (which were in the range from 0.7364 to 0.8214 g/cm3) are lower than those of PAO 4 (in the range from 0.7663 to 0.8470 g/cm3) or PAO 8 (in the range from 0.7664 to 0.8498 g/cm3). The densities of PAO 4 and 8 were essentially the same. Isothermal compressibilities of each base oil w...