Application of the Texas quartz spiral gauge to the measurement of interaction second virial coefficients Rev. Sci. Instrum. 53, 83 (1982); 10.1063/1.1136797 Erratum: Experimental technique for direct measurement of interaction second virial coefficients J. Chem. Phys. 59, 6691 (1973); 10.1063/1.1680060 Experimental technique for direct measurement of interaction second virial coefficientsInteraction second virial coefficients have been measured from -125° to 50°C in 25° increments for the following systems: N2-Ar, Ar--H2, Ar-He, Ne-Ar, N2-H2, N2-He, Ne-N2, Hz-He, Ne--H2, and Ne-He. The excess second virial coefficients were reproduced usually within 0.1 cc/mole by measuring the pressure change of mixing two pure gases at constant temperature and volume. With these excess quantities and literature values of Bu , the interaction second virial coefficients were calculated. The comparison between experimental interaction second virial coefficients and those calculated by the Kihara potential waE considered good at the higher temperatures and fair to poor at the lower temperatures where the deviation was sometimes as much as 8 cc/mole. This deviation is probably mainly due to the assumption of the geometric-mean mixing rule for the characteristic energy between the dissimilar molecules. In the temperature range of -125 0 -50°C, the excess quantity E was empirically correlated to the absolute temperature by the relation, E=aTfI where the value of f' J was essentially the same for most of the binary mixtures studied.

In contrast to graphite, MoS2 retains its lubrication properties in vacuum. The coefficient of friction of MoS2 powder, compressed into pellets, has been measured under high vacuum conditions. Well run-in surfaces, which have been stationary for a period of time, show higher friction initially upon resumption of sliding. Presence of an amorphous layer of sulfur during sliding is postulated.

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A friction test apparatus has been developed which permits accurate measurements under high vacuum. Sliding motion inside the vacuum chamber is accomplished by magnetic coupling through the chamber wall. The lag angle between the magnets, observed by means of stroboscopic illumination, measures the friction. Calibration of the magnetic coupling is obtained from the period of oscillation of the driven magnet with respect to the driving magnet.