Ionic liquids composed of phosphonium cations and organophosphate, carboxylate, and sulfonate anions as lubricant antiwear additives.

Oil-soluble phosphonium-based ionic liquids (ILs) have recently been reported as potential ashless lubricant additives. This study is to expand the IL chemistry envelope and to achieve fundamental correlations between the ion structures and ILs' physiochemical and tribological properties. Here we present eight ILs containing two different phosphonium cations and seven different anions from three groups: organophosphate, carboxylate, and sulfonate. The oil solubility of ILs seems largely governed by the IL molecule size and structure complexity. When used as oil additives, the ranking of effectiveness in wear protection for the anions are organophosphate > carboxylate > sulfonate. All selected ILs outperformed a commercial ashless antiwear additive. Surface characterization from the top and the cross-section revealed the nanostructures and compositions of the tribo-films formed by the ILs. Some fundamental insights were achieved: branched and long alkyls improve the IL's oil solubility, anions of a phosphonium-phosphate IL contribute most phosphorus in the tribo-film, and carboxylate anions, though free of P, S, N, or halogen, can promote the formation of an antiwear tribo-film.

Enhancing thermoelectric performance of ternary nanocrystals through adjusting carrier concentration.

The carrier concentration of chemically synthesized Bi(2)Te(3)-based nanocrystals (NCs) is for the first time reported to be adjusted by forming ternary Bi(2-x)Sb(x)Te(3) NCs (x = 0.02, 0.05, 0.10, 0.20, 0.50, and 1.50) through partial substitution of Bi with Sb. Carrier concentrations of ternary Bi(2-x)Sb(x)Te(3) NCs were successfully adjusted by a factor of more than 10 controlled by the stoichiometric partial Sb/Bi substitution level. The power factors of the stoichiometric ternary Bi(2-x)Sb(x)Te(3) NCs improved three times compared to the parent Bi(2)Te(3) due to the carrier concentration adjustment.

Improvement of the thermoelectric power factor through anisotropic growth of nanostructured PbSe thin films.

Nanostructured PbSe films with different (200)/(111) grain size ratios were prepared by anisotropic growth on glass substrates. Although face centered cubic bulk PbSe is an isotropic material, the thermopower (S), electrical conductivity (sigma) and hole mobility of the prepared nanostructured PbSe films show an obvious dependence on the anisotropic parameter, (200)/(111) grain size ratio. The thermoelectric power factor (S(2)sigma) of the nanostructured films is improved with higher (200)/(111) grain size ratio. Temperature-dependent transport measurements suggest that grain boundary scattering dominates in these nanostructured films. Subtle changes in the microstructure are discussed in the light of the effect on grain boundary activation energy (barrier height). A 20% enhancement of the room temperature thermopower (S) at given carrier concentrations is demonstrated for the CBD-grown nanostructured PbSe films compared to single crystal bulk PbSe.

Cubic AgPb(m)SbTe(2+m): bulk thermoelectric materials with high figure of merit.

The conversion of heat to electricity by thermoelectric devices may play a key role in the future for energy production and utilization. However, in order to meet that role, more efficient thermoelectric materials are needed that are suitable for high-temperature applications. We show that the material system AgPb(m)SbTe(2+m) may be suitable for this purpose. With m = 10 and 18 and doped appropriately, n-type semiconductors can be produced that exhibit a high thermoelectric figure of merit material ZTmax of approximately 2.2 at 800 kelvin. In the temperature range 600 to 900 kelvin, the AgPb(m)SbTe(2+m) material is expected to outperform all reported bulk thermoelectrics, thereby earmarking it as a material system for potential use in efficient thermoelectric power generation from heat sources.