An effort was conducted to study and characterize the effects of nanodiamond particles as an additive to lubricating mineral oil. The tests were run for varying concentrations ranging from pure mineral oil to 0.01% weight-concentration of nanodiamonds. The friction was measured throughout the tests, and the resulting wear was measured with optical profilometry. It was observed that both the average friction coefficient and the wear would decrease proportionally to the concentration of nanodiamond particles, and the 0.01% nanodiamond weight concentration was observed to improve the tribological performance of lubricating mineral oil. Chemical analysis of contacting surfaces showed no significant distinction from the nanodiamond mixture versus the pure mineral oil, while particle size analysis demonstrated that the nanoparticles themselves remained intact (i.e., no breakup) in the contact interface. This helps to conclude that a mechanical and not a chemical effect of the nanodiamond particles helped to protect the metallic surface from wear and improve the lubricating ability of the mineral oil.
An effort was made to study and characterize the tribological characteristics of diamond nanoparticles as compared to neat mineral oil in the presence of sliding contact typically observed in the standard ASTM D4172 four-ball test. Four-ball tests were conducted with a solution of diamond nanoparticles and mineral oil, both at varying run times and bulk oil temperatures, and a consistent reduction in wear rates was observed. Numerical simulations were performed; it was observed that by enhancing the thermal conductivity of the lubricant, the wear reduction rate was observed to match the diamond nanoparticles solution results remarkably. This effort provides evidence that this additive wear reduction is in part caused by reduced lubricant temperatures due to the enhanced conductivity of the diamond.
We demonstrate the evolution of picosecond pulses in silicon nanowire waveguides by sum frequency generation cross-correlation frequency-resolved optical gating (SFG-XFROG) and nonlinear Schrödinger equation (NLSE) modeling. Due to the unambiguous temporal direction and ultrahigh sensitivity of the SFG-XFROG, which enable observation of the pulse accelerations, the captured pulses' temporal and spectral characteristics showed remarkable agreement with NLSE predictions. The temporal intensity redistribution of the pulses through the silicon nanowire waveguide for various input pulse energies is analyzed experimentally and numerically to demonstrate the nonlinear contributions of self-phase modulation, two-photon absorption, and free carriers. It indicates that free carrier absorption dominates the pulse acceleration. The model for pulse evolution during propagation through arbitrary lengths of silicon nanowire waveguides is established by NLSE, in support of chip-scale optical interconnects and signal processing.
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