The invention provides a refrigerating machine oil comprising as a base oil at least one oxygen-containing oil having a carbon/oxygen molar ratio of 2.5 or more and 5.8 or less, and being used in combination with a (Z)-1,1,1,4,4,4-hexafluoro-2-butene refrigerant.

A trunk piston marine engine lubricant comprises in respective minor amounts (A) an overbased metal hydrocarbyl-substituted hydroxybenzoate detergent system, and (B) a hydrocarbyl-substituted succinic acid anhydride, preferably made by halogen- or radical-assisted fractionalization processes, where the ratio of succinic anhydride to hydrocarbyl chains is in the range of 1.4 to 4. The lubricant, when used to lubricate such an engine fuelled by heavy fuel oil, exhibits improved control of asphaltene precipitation and deposition on engine surfaces.

A low-friction coating includes: an aliphatic hydrocarbon group showing a peak in a region of 2,900 cm.sup.1 to 3000 cm.sup.1 in an infrared absorption spectrum; a carbonyl group showing a peak in a region of 1,650 cm.sup.1 to 1,800 cm.sup.1 in an infrared absorption spectrum; an aromatic component (C.sub.7H.sub.7.sup.+) showing a peak at mass 91.1 in a positive ion spectrum obtained by TOF-SIMS; and a condensed ring based component (C.sub.9H.sub.7.sup.+) showing a peak at mass 115.2 in the positive ion spectrum obtained by TOF-SIMS.

A low-friction coating includes: an aliphatic hydrocarbon group showing a peak in a region of 2,900 cm.sup.1 to 3000 cm.sup.1 in an infrared absorption spectrum; a carbonyl group showing a peak in a region of 1,650 cm.sup.1 to 1,800 cm.sup.1 in an infrared absorption spectrum; an aromatic component (C.sub.7H.sub.7.sup.+) showing a peak at mass 91.1 in a positive ion spectrum obtained by TOF-SIMS; and a condensed ring based component (C.sub.9H.sub.7.sup.+) showing a peak at mass 115.2 in the positive ion spectrum obtained by TOF-SIMS.

The invention relates to the use of one or more M-methyl-N-acylglucamines of the formula (I) wherein R.sup.1 represents a linear or branched, saturated or unsaturated hydrocarbon group having 7 to 21 carbon atoms, as a corrosion inhibitor.

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