摘要:

AbstractCarbon‐13 NMR spin‐lattice relaxation time (T1) data have been used to study the molecular dynamic aspects of base oils with different physical properties. Relaxation time measurements have been carried out on a few model compounds and a number of mineral base oils at various temperatures (273–373 K). Effective correlation time (°C) and rotational mobility data obtained for the model compounds and base oils have provided evidence of relationships between molecular flexibility and the temperature dependence of viscosity. It is possible to determine the average carbon alkyl chain lengths and the molecular weights of the base oils from the ratio of the T1values of Cβand Cintcarbons and the optimised value of the microviscosity factor (fr), respectively. A qualitative correlation between Arrhenius energies (Ea) for microscopic motion and macroscopic bulk properties such as viscosity and viscosity‐temperature characteristics has been observed. Base fluids having better viscosity‐temperature characteristics were also associated with lower values of Eafor micro‐ as well as macrosco

ISSN:0954-0075    

DOI:10.1002/ls.3010140302

出版商:John Wiley&Sons, Ltd    

年代:2002

数据来源: WILEY

摘要:

AbstractIn hydrodynamic lubrication theory, the oil film thickness build‐up increases with increasing sliding speed or oil viscosity, and the viscous resistance or shear stress also increases, both without limit. The entraining force forming the oil film is given by the moving surfaces, or by the adhesive force of the oil molecules on the rubbing surfaces and the interaction force between them. Therefore, the maximum friction force and maximum oil film thickness will be limited by the operating conditions, such as oil properties, rubbing materials, sliding speed, and load. In this study, friction tests were conducted using a plate‐on‐cylinder sliding contact apparatus. It was found that a critical shear stress existed, above which the friction force and oil thickness decreased from theoretical values. Slip in an oil film seems to occur when the theoretical shear stress exceeds the critical value of the oil, according to test conditions. The occurrence of slip in an oil film is responsible for the reduction in the oil film and friction force from theoretical values, leading to the lower‐viscosity components of the oil selectively passing through the conjuncti

ISSN:0954-0075    

DOI:10.1002/ls.3010140303

出版商:John Wiley&Sons, Ltd    

年代:2002

数据来源: WILEY

摘要:

AbstractThe frictional properties of lead‐tin thin films (thickness of 0.05–0.19 μm) with two types of copper interlayer were investigated. The thin film and the interlayer were formed on a silicon wafer surface by vacuum deposition. Friction tests were carried out using a ball‐on‐disc apparatus in a vacuum chamber. The thin copper interlayer reduced the friction coefficient and prolonged the film life. The effect of load on the friction coefficient is explained by an equation derived using the Hertzian contact area between a sphere and a plate. The thicker copper interlayer did not reduce the friction coefficient but markedly extended the life of the film. In this case, the dependence of the friction coefficient on the load is explained by an equation derived using the Hertzian contact area between a sphere with surface roughness of second order and

ISSN:0954-0075    

DOI:10.1002/ls.3010140304

出版商:John Wiley&Sons, Ltd    

年代:2002

数据来源: WILEY

摘要:

AbstractWear investigations concerning the different structures and metal atoms of metal dialkyldithiophosphates (MeDTPs) were conducted using a ball‐on‐disc apparatus. Steel ball bearings (3.175 mm in diameter) and counterface discs, made of hot pressed ZrO2partially stabilised by Y2O3, were used. The synthesised MeDTPs were made up of primary linear aliphatic alcohols with hydrocarbon lengths varying from 8 to 16 carbon atoms, and contained the following metals: zinc(II), iron(III), gallium(III), antimony(III), and copper(II). Tests were performed at room temperature. The sliding speed was set to a constant 0.03 m/s, and a constant 30 N load was used. The additives investigated were used as solutions in n‐hexadecane.The study also focused on the influence of additive concentration on wear. It was found that the effectiveness in reducing wear depends both on the metal atom and on the length of the hydrocarbon chain in the additive's molecules. The lowest wear volumes were observed for additives with n‐octyl and n‐tetradecyl hydrocarbon chains. The worst antiwear performance was observed for n‐dodecyl derivatives. For almost all additives, more concentrated solutions resulted in less wear. Some friction coefficient results are als

ISSN:0954-0075    

DOI:10.1002/ls.3010140305

出版商:John Wiley&Sons, Ltd    

年代:2002

数据来源: WILEY

摘要:

AbstractThe effect of the fibre structure of the grease on the frictional performance of lithium 12‐hydroxystearate greases with different fibre lengths was investigated in face, line, and point contact sliding tests. At high sliding speeds where the lubrication regime was practically hydrodynamic, the coefficient of friction of the base oil alone was lower than that of the greases. The coefficient of friction was roughly estimated as follows: base oil

ISSN:0954-0075    

DOI:10.1002/ls.3010140306

出版商:John Wiley&Sons, Ltd    

年代:2002

数据来源: WILEY

摘要:

AbstractIn recent years the role of laboratory methods in investigating the effectiveness of engine oil additives has dramatically increased, especially in predicting the performance of engine oils under field conditions. Some results of research under laboratory conditions on the ageing of engine oils with different performance levels are presented in this paper. The role of the action of antioxidant additives in engine oils for gasoline and diesel engines is described. The paper includes the results of experiments over time in laboratory testing of doped motor oils, use of IR spectroscopy, and reference oils. Single‐ and multi‐cylinder engine test results are also discussed. New, effective additive packages for different engine oils are conside

ISSN:0954-0075    

DOI:10.1002/ls.3010140307

出版商:John Wiley&Sons, Ltd    

年代:2002

数据来源: WILEY

摘要:

AbstractA four‐ball tester was used to evaluate the antiwear performance of an organotin compound, stannic stearate, plus a zinc dialkyldithiophospate (ZnDDP). The results indicate that stannic stearate combined with ZnDDP exhibits excellent antiwear properties in a paraffin‐based oil. The tin compound could also improve the antiwear performance of two commercial engine oils, SH/CD 15W‐50 and SE 15W‐40, which resulted in a reduction of the oil temperature and less oxidation of t

ISSN:0954-0075    

DOI:10.1002/ls.3010140308

出版商:John Wiley&Sons, Ltd    

年代:2002

数据来源: WILEY

ISSN:0954-0075    

DOI:10.1002/ls.3010140301

出版商:John Wiley&Sons, Ltd    

年代:2002

数据来源: WILEY