The application of the droplet quartz crystal microbalance (QCM) to the measurement of viscosity for industrial oils is reported. In this approach a small-volume droplet of fluid is investigated via its influence on the resonant frequency of a quartz oscillator. The droplet QCM viscosity response is investigated for a selection of industrial oils, including commercial automotive lubricants, heavy fuel oils, calibration oils and used automotive lubricating oils. This approach shows significant analytical promise for distinguishing between heavy fuel oils dyed to indicate their duty status. It is also demonstrated that lubricating oils aged in engine tests exhibit an enhanced QCM viscosity response than accepted viscosity measurements would otherwise indicate. The locus at which the viscosity response saturates due to violation of the small loading approximation (extreme viscosities) is identified and found to be qualitatively consistent with established equivalent circuit models. The identification of commercial lubricating oils is observed to be unreliable on the basis of viscosity response alone.

We describe a dilatometer which is an improved version of the one previously used in this laboratory. It consists of a doubly twisted strip of beryllium copper with a mirror attached to its central region. This system is immersed in liquid helium II. Dilations of the sample are sensed by this system via a thin diaphragm, causing rotations of the mirror, which is detected by an external optical lever. The system has a sensitivity to relative length changes Δl/l of 10−11. Copper has been used as the test material to evaluate the performance of the instrument. It has been possible to make direct measurements of α, the coefficient of linear thermal expansion, down to 2 K for ΔT=0.2 deg. These results yield α=1.3×10−10 T+2.7×10−11 T3 deg−1. The ratio of these terms is much more accurately known than the absolute values because of uncertainty in the absolute calibration. The linear term leads to an electronic Grüneisen γ of 0.57. This value is compared with recent theoretical and experimental values.