Permeability and additive sorption and extraction in lubricating greases

The effect of the area and type of surface of ten silica thickeners and aluminum oxide on grease permeability, on the sorption of PAN [Phenyl-α-naphthylamine] by the grease, and on subsequent extraction were studied. For grease containing 6% per cent of thickener, permeability coefficients varied from 20.1 x 10⁻¹¹ cm² to 168 x 10⁻¹¹ cm². For each silica type they decreased with increase in surface area of the thickener. The level of the permeability coefficient is generally related to the worked penetration. In sorption measurements using permeating oils of varying PAN concentration, the amount of PAN associated with the thickener surface increased with PAN concentration. PAN concentration after equilibrium was reached was independent of the thickness of the grease cake. For each type of the silica thickener studied, the equilibrium PAN concentration increased with thickener surface area. Extraction experiments were performed with oil containing no additive on the same grease samples on which sorption experiments were run. The final PAN concentrations were small. The differences among the final equilibrium concentrations of additive in the greases were a function of the type of silica thickener. No significant surface area trend was observed. Initial rate constants for the additive exchange were the same for both sorption and extraction suggesting that the rate limiting step for replacement of the oil in the grease or for additive transfer between permeating oil and the oil in the grease is the same for the sorption and extraction experiments --Abstract, page x-xi

Study of the atmospheric turbulence in free space optical communications

Abstract-In this paper the effect of atmospheric turbulence on free space optical (FSO) communications is investigated experimentally by designing a turbulence simulation chamber. The distributions of bits ‘0 ’ and ‘1 ’ levels are measured with and without turbulence. The bit error rate (BER) is then obtained from the distributions. The temperature gradient within the channel is less than 6 °C resulting in turbulence of log irradiance variance of 0.002. The received average signal is measured and used to characterise the simulated turbulence strength. We then evaluated the BER with turbulence and found that from an error free link in the absence of turbulence, the BER increased significantly to about 10-4 due to the turbulence effect. I