Frictional Characteristics of IF-WS2 Nanoparticles in Simulated Engine Conditions

The efficacy of inorganic fullerene-like (IF) tungsten disulfide (WS₂) nanoparticles as engine oil friction modifier additive was investigated using a high-stroke reciprocating piston ring–cylinder bore bench test system. Frictional characteristics of various IF-WS₂ nanoparticle concentrations in mineral oil were experimentally analyzed in simulated engine conditions controlling oil temperature, speed, and normal load. Though the effect of IF-WS₂ nanoparticles on piston ring and cylinder bore friction was minor in low concentrations, after a running period in a mixed lubrication regime with 10% additive, a considerable reduction in friction coefficient was observed when the IF-WS₂ formulated oil was used. This reduction remains to some extent with reference mineral oil after solvent cleaning of the mating components. The results show that a thin tribofilm gradually forms on the piston ring and the cylinder bore surfaces, reducing the friction coefficient in a mixed lubrication regime. However, in order to obtain the friction reduction there seems to be a threshold in the concentration of IF-WS₂ in mineral oil and film development period. The effects of lubrication regime, contact load, speed, and surface roughness on tribofilm formation are also discussed. The presence of WS₂ tribofilm formed on the piston ring and the cylinder bore surfaces was further verified using Raman spectroscopy.     

RAPID HIGH PERFORMANCE LIQUID CHROMATOGRAPHIC DETECTION OF FUROSINE (ε‐N‐2‐FUROYLMETHYL‐L‐LYSINE) IN YOGURT AND CHEESE MARKETED IN TURKEY*

Furosine (ε‐N‐2‐furoylmethyl‐L‐lysine) content determination in the yogurt and different cheese types (pickled white, kasar, processed, canned tulum, blue‐veined and mozzarella cheeses) marketed in Turkey was performed using ion‐pair reversed‐phase high performance liquid chromatography (RP‐HPLC). Calibration study (R² = 0.9999), analytical method validation and recovery studies gave satisfactory results. The lowest furosine values were observed in pickled white cheeses (5.35 ± 0.01 to 7.28 ± 0.02 mg/100 g protein). All cheeses except pickled white showed furosine values between 182.16 ± 0.12 (canned tulum) and 261.32 ± 0.10 mg/100 g protein (ripened kasar). The highest content of furosine was observed in whole yogurt (316.47 ± 0.17 mg/100 g protein) which could be because of severe heat treatment and the addition of milk powder during the manufacturing process. The method provides a rapid, reproducible and accurate determination of this Amadori compound (ε‐deoxy‐fructosyl‐lysine) in yogurt and cheese samples.