Reexamination of Superconductive Homopolar Motors for Propusion

ACS Appl. Mater. Interfaces

Kotvis³

et al. 2011

The frictional properties of a sliding copper-copper interface exposed to dimethyl disulfide (DMDS) are measured in UHV under conditions at which the interfacial temperature rise is <1 K. A significant reduction in friction is found from the clean-surface values and sulfur is found on the surface and below the surface in the wear scar region by Auger spectroscopy. Because the interfacial temperature rise under the experimental conditions used to measure friction is very small, tribofilm formation is not thermally induced. The novel, low-temperature tribofilm formation observed here is ascribed to a shear-induced intermixing of the surface layer(s) with the subsurface region as suggested using previous molecular dynamics simulations. Although the tribofilm contains predominantly sulfur, a small amount of carbon is also found in the film.

Section: Introductionmentioning

confidence: 99%

Low-Temperature, Shear-Induced Tribofilm Formation from Dimethyl Disulfide on Copper

ACS Appl. Mater. Interfaces

Kotvis³

et al. 2011

“…However, the tribological chemistry can depend critically on the nature of the substrate so that a good lubricant additive for one type of surface may not be applicable to another. In particular, the lubrication of sliding copper−copper interfaces in electrical motors − provides a particular challenge. Gas-phase lubricants based on water vapor have been used to reduce friction and wear, − but they tend to lead to asymmetric wear rates and failure at higher temperatures. , The following explores the chemistry of dimethyl disulfide (DMDS) on copper surfaces to establish whether it is sufficiently reactive to potentially form a tribofilm near room temperature as required for lubrication of the sliding copper−copper contact in an electric motor.…”

Section: Introductionmentioning

confidence: 99%

The Surface Chemistry of Dimethyl Disulfide on Copper

et al. 2010

Langmuir

The surface chemistry of dimethyl disulfide (DMDS) is studied on a Cu(111) single crystal and a polished copper foil in ultrahigh vacuum as a basis for understanding its tribological chemistry using a combination of temperature-programmed desorption (TPD), reflection-absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS). Low-energy electron diffraction reveals that the polished foil becomes ordered on heating in vacuo and displays identical surface chemistry to that found on the Cu(111) surface. Dimethyl disulfide reacts with the copper surface at 80 K to form thiolate species. Heating the surface to ∼230 K causes a small portion of the thiolate species to decompose to form methyl groups adsorbed on the surface. Further heating results in methane and C(2) hydrocarbon desorption at ∼426 K, due to a reaction of adsorbed methyl species, to completely remove carbon from the surface and to deposit atomic sulfur.

“…The tribological chemistry of a particular lubricant additive depends critically on the nature of the substrate so that a good lubricant additive for one type of surface may not be applicable to another. The lubrication of sliding copper–copper interfaces in electrical motors − provides a particular challenge due to the requirement for a lubricious, yet conductive, tribofilm. Gas-phase lubricants based on water vapor have been used to reduce friction and wear, but they tend to lead to asymmetric wear rates and failure at higher temperatures. , Because of their low toxicity, boron-containing molecules have been proposed as potential lubricants.…”

Section: Introductionmentioning

confidence: 99%

Surface Chemistry of Isopropoxy Tetramethyl Dioxaborolane on Cu(111)

2012

Langmuir

The surface chemistry of isopropoxy tetramethyl dioxaborolane (ITDB), tetramethyl dioxaborolane (TDB), and 2-propanol is studied on a clean Cu(111) single crystal using temperature-programmed desorption (TPD). 2-Propanol is found to have two competing reactions on the copper surface. Dehydration results in water and propene formation, and dehydrogenation results in the formation of acetone and hydrogen. ITDB directly adsorbed on the surface reacts completely and does not molecularly desorb. TDB and 2-propanol decompose desorbing mainly 2,3-dimethyl 2-butene and acetone, respectively. Both of those products desorb above room temperature and are present in TPDs of ITDB. An additional acetone desorption peak was observed for ITDB at higher temperatures than acetone desorption from 2-propanol. This higher temperature peak at ∼391 K was attributed to two acetone molecules forming from the tetramethyl end group resulting from a stronger bound surface species in ITDB compared to TDB despite their identical end groups. The copper surface seems to be reactive enough toward ITDB at room temperature that a potential boron-containing tribofilm could be produced for copper-copper sliding contacts. Despite their similarities, ITDB and TDB have different surface species present at room temperature, so their tribological properties will be investigated in the future.