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Controlled vacuum environments as in space applications represent a challenge for the lubrication of tribological components. In addition to common space lubricant requirements like, e.g., low evaporation, a broad operational temperature range and a high stability during operation, long-term-storage (LTS) properties have gained increasing attention recently. The term addresses the time-dependent stability of a lubricant under static conditions, which can mean chemical degradation processes such as oxidation on the one hand, but also the physical separation of oil and thickener in heterogeneous lubricants like greases. Due to the extended storage periods of lubricated components on-ground but also during a space mission for several years, it has to be ensured that a lubricant is still functional after LTS. This article depicts the development of a space lubricant grease with LTS properties. Firstly, LTS requirements and methods for their assessment are discussed. In the following, a systematic approach towards the design of a grease formulation compatible with LTS is described. Finally, the manufacturing of prototype formulations and their broad characterization by means of LTS behaviour, outgassing, and tribological performance is presented. [ABSTRACT FROM AUTHOR]

Clathrate-I-based materials are promising for waste-heat recovering applications via thermoelectric (TE) effects. However, the lack of highly efficient p-type materials hampers the development of clathrate-based TE devices. In this work, the synthesis of the p-type semiconductor Ba7.8Au5.33Ge40.67 with clathrate-I structure is up-scaled by steel-quenching and spark plasma sintering treatment at 1073 K. A thermoelectric figure of merit ZT ≈ 0.9 at 670 K is reproducibly obtained, and 40 chemically homogeneous module legs of 5 × 5 × 7 mm3 are fabricated. By using a carbon layer as a diffusion barrier, electrical contacts are sustainable at elevated application temperatures. Eight couples with the clathrate-I compounds Ba7.8Au5.33Ge40.67 as p-type and Ba8Ga16Ge30 as n-type materials are integrated into a TE module with an output power of 0.2 W achieved under a temperature difference ΔT = 380 K (T1 = 673 K and T2 = 293 K). The thermoelectric performance of Ba7.8Au5.33Ge40.67 demonstrates the potential of type-I clathrates for waste heat recycling. [ABSTRACT FROM AUTHOR]

Clathrate-I-based materials are promising for waste-heat recovering applications via thermoelectric (TE) effects. However, the lack of highly efficient p-type materials hampers the development of clathrate-based TE devices. In this work, the synthesis of the p-type semiconductor Ba7.8Au5.33Ge40.67 with clathrate-I structure is up-scaled by steel-quenching and spark plasma sintering treatment at 1073 K. A thermoelectric figure of merit ZT ≈ 0.9 at 670 K is reproducibly obtained, and 40 chemically homogeneous module legs of 5 × 5 × 7 mm3 are fabricated. By using a carbon layer as a diffusion barrier, electrical contacts are sustainable at elevated application temperatures. Eight couples with the clathrate-I compounds Ba7.8Au5.33Ge40.67 as p-type and Ba8Ga16Ge30 as n-type materials are integrated into a TE module with an output power of 0.2 W achieved under a temperature difference ΔT = 380 K (T1 = 673 K and T2 = 293 K). The thermoelectric performance of Ba7.8Au5.33Ge40.67 demonstrates the potential of type-I clathrates for waste heat recycling. [ABSTRACT FROM AUTHOR]