Discussions on “Some Basic Concepts Regarding the Separation of Oily Water Mixtures”

Examination of adsorptive properties of graphite and MoS₂ revealed that their surfaces are composed of two distinct sites, i.e., basal plane and edge sites, having different affinities for polar compounds and paraffmic hydrocarbons.

It was therefore of interest to investigate the relationship between the proportions of the individual surface sites and the lubricating action of these solids.

This was done by preparing special graphite and MoS₂ powders having a high proportion of basal plane surface and comparing their lubricating properties to those of the powders having a relatively high ratio of edge to basal plane surface area.

It was found that the proportion of basal plane surface is an important factor in the lubricating performance of both graphite and MoS₂ and that the powders having predominantly basal plane surface have significantly better antiwear properties than the powders having a high ratio of polar to basal plane surface. The basal plane surface in MoS₂ plays an exceptionally important role in lubrication, and its contamination with strongly adsorbed paraffins reduces substantially the lubricating action of the powder.     

A study of the influence of steam treatment on the tribological behaviour of steel specimens

The influence of steam treatment (ST) on the tribological behaviour of steel was assessed by Falex, Schwingungsreibverschleiss (SRV) and Amsler tests performed either under dry conditions or using solid MoS₂, graphite, polytetrafluoroethylene (PTFE) or grease lubricants. ST produced a thin layer of magnetite containing small quantities of haematite. MoS₂ was found to be the best lubricant in Falex tests with normal test pieces. Only greaselubricated Amsler couples withstood the full testing cycle. The SRV tests were inconclusive because the endurance time was too short, only a few seconds with MoS₂ lubrication.The influence of ST varied in the Falex tests. No improvement was found with grease-lubricated journals and the load-carrying capacity of MoS₂-lubricated test pieces was decreased. However, it was beneficial for PTFE lubrication. In the Amsler tests the grease-lubricated disks were crazed and magnetite splinters were removed. The performance of the graphite lubricant was lowered by ST and the median lives of MoS₂- or PTFE-lubricated couples were increased although their reliability was impaired. In SRV tests, ST improved the performance of grease and MoS₂-lubricated test pieces. The test results do not confirm the reported improved behaviour of ST components, particularly cutting tools, in workshop practice.     

基于面接触的粉末润滑实验研究

利用石墨粉末颗粒,基于端面摩擦试验机对粉末润滑方式开展了摩擦学研究。试验了粉末冶金铜合金材料、粘结石墨润滑涂层、PTFE 3层自润滑复合材料3种试样在石墨粉末颗粒流润滑条件下的摩擦因数、温度及表面膜等特性,并与干摩擦和油润滑进行了对比。结果表明:粉末润滑可以实现与固体润滑膜、自润滑材料类似的无油固体润滑效果;利用它的持续补充性,可以实现动态补充和修复的固体润滑膜;但是,粉末润滑膜与基体附着能力较差。     

Material Study for Advanced Stern-Tube Bearings and Face Seals

The objective of the program was to evaluate improved materials for oil-lubricated stern-tube bearing and face-seal applications. Once good candidates were found for oil, they were then evaluated in seawater to show that if the seal fails and the bearing cavity is flooded with seawater, the bearing can still function at some reduced load and speed. The selected plastics were subjected to soak tests and friction and wear tests. Based on the tests, the following materials were recommended for bearing and face seals: polyimide, 15-percent graphite powder filled; polyamide-imide, 3-percent PTFE and 12-percent graphite powder filled; and phenolic, 15-percent graphite powder filled. The liner materials could be the same as those which are currently used: ABS Grade 2 and flame-sprayed Cr₂O₃ for bearings, and Niresist Type 2 for face seals. The selected plastic materials could also be successfully used in seawater lubrication.     

Traction Characteristics of High-Temperature Powder-Lubricated Ceramics (Si3N4/αSiC)

As part of a high-temperature, dry-lubricated bearing technology and lubricant system development program, a high-speed, high-temperature disk-on-disk tribometer was utilized and a matrix of traction data covering a range of load, speed and temperature was obtained. The influence of dry powder lubricants, TiO₂ and MoS₂, on the traction coefficients between two ceramic materials, Si₃N₄ and SiC, was investigated. The most important results of this investigation are characteristic curves for the traction coefficient vs. the slide/roll ratio with dry powders which are reminiscent of fluids, and the observation of dry powder lubricants' lower traction coefficients and wear. Measured tractions are found to be a strong function of powder lubricant type and values decrease moderately with slide-to-roll ratio and load. The data, show a weak sensitivity to temperature.     

The effect of lubricant additives on friction and wear studies of polyphenylene sulphide

Polyphenylene sulphide is a polymer with good thermal stability and high crystallinity. This paper summarizes the results of friction and wear studies of polyphenylene sulphide and its composites made with conventional solid lubricants to ascertain the suitability of the material as a matrix for solid lubricant additives. The polymer itself has a high coefficient of friction. Wear rate increases with load and speed. Addition of solid lubricant additives helps in improving the friction and wear of the polymer. Composites with MoS₂-Sb₂O₃ and PTFE gave better results than composites made by the addition of graphite and MoS₂ graphite. Wear rate of these composites increased with load and speed; but load and speed had little effect on friction.     

Measurement of Surface Areas of Basal Plane and Polar Sites in Graphite and MoS2 Powders

Recent work on graphite and MoS₂ powders revealed that the proportion of basal plane surface in the powder is an important factor in their anti wear properties and that the proportion of the polar “edge” surface may affect the abrasive properties of these solid lubricants. A method has been developed, therefore, for the independent measurements of the total basal plane and edge surfaces in the powders. The basal plane area is determined from the amount of adsorption of n-dotriacontane from solution in n-heptane. Similarly the edge area is determined from the adsorption of n-butanol.

A convenient and rapid method of estimating the proportions of basal plane and edge areas in the solid lubricants is to determine the integral heat of preferential adsorption of n-dotriacontane and n-butanol using the flow calorimeter.

The saturation of a sample of graphite or MoS₂ powder can be carried out by percolation with a succession of dilute solutions in n-heptane, and the total heats evolved are obtained in the form of peaks on the chart of a potentiometric recorder. The method can measure easily basal plane and edge surface areas down to 0.1 m²/g for graphites and can be used tentatively for MoS₂.     

On the Mechanisms of MoS2-Film Failure in Sliding Friction

The effect of oxygen on the life expectancy of a run-in molybdenum disulfide film under heavy load has been studied. Tested in argon, with only small quantities of oxygen present, the smooth running period is increased by at least two decades as compared to a test in oxygen.

Blister formation is an important phase in the gradual destruction of the lubricant film. Blisters of submicroscopic size can be traced with the electron microscope, and in the presence of oxygen macroscopic blisters are rapidly formed; their further history has been followed by cine-film. Oxygen promotes sintering of the individual particles 10 a continuous, smooth, and therefore highly reflective lubricant layer. This process is an essential condition for blistering.

No wear occurs during the smooth running period of MoS₂ lubrication. Graphite differs from MoS₂ in this respect and in its much lower load-carrying capacity. The cine-film of graphite-lubricated surfaces indicated a rougher surface and the formation of smaller blisters. On addition of graphite to MoS₂, a sudden change in surface features occurs within narrow limits of graphite concentration. It seems that the addition of 15% by weight of graphite increases the total life expectancy of the MoS₂ film, but reduces the length Of the smooth running period.     

Wear and friction behavior of alloyed gray cast iron with solid lubricants under boundary lubrication

Friction and wear behavior of MoS₂, boric acid, graphite and TiO₂ has been compared under extreme boundary lubrication condition. Boundary lubrication was simulated for the study. Results show that MoS₂ and graphite were 30-50% more effective than other two lubricants. Friction coefficient shows a decreasing trend with increase in sliding speed due to increasing temperature and higher shear force. High friction coefficient values were recorded for all the lubricants (0.2-0.5). This is due to predominating solid interactions during boundary lubrication condition. Boric acid and TiO₂ were not much effective in lubrication.     

Solid Film Lubrication of Worm Gears

A study was conducted to determine the feasibility of lubricating worm gears with bonded solid film lubricants. An apparatus for determining gear efficiency and lubrican film wear-life was fabricated. Several tests using conventional oil lubrication were conducted to establish baseline gear efficiency data. Efficiency and wear-life tests were made with four solid lubricant films, two of them incorporating MoS₂ and Sb₂O₃ in organic polyimide resin binders, and two using MoS₂, graphite and gold or bismuth in an aluminum phosphate or sodium silicate binder. Experimental data indicate that solid film lubrication of worm gears is feasible, without a serious loss of efficiency in situations where limited wear-life is acceptable.     

Study the Sensitivity of Solid Lubricating Additives to Attapulgite Clay Base Grease

The focus of this study was the development of a new lubricating grease, using surface-modified attapulgite clay as thickener and synthetic oil (PAO 40) as the base oil. The tribological sensitivity of the new grease was investigated by studying the effect of adding three solid additives [KB₃O₅, MoS₂, graphite and a graphite/MoS₂ mixture (mass ratio 3:2)]. Its tribological behavior was compared with that of traditional bentone grease by adding MoS₂. The dropping point and the cone penetration of the new grease were also investigated and analyzed. The wear scar diameter of the base grease was measured on an MRS-1 J (G) four-ball tester, and the tribological sensitivity of solid lubricating additives to attapulgite clay base grease was evaluated using an Optimol SRV reciprocating friction and wear tester. The addition of MoS₂ and the graphite/MoS₂ mixture to the new lubricating grease improved its friction-reducing ability, while the addition of KB₃O₅ improved its antiwear ability. The additives MoS₂ and the graphite/MoS₂ mixture also increased the load-carrying capacity of the base grease. The attapulgite clay grease containing MoS₂ had a better friction-reducing ability than the traditional bentone grease containing MoS_2.     

Erratum to: Study the Sensitivity of Solid Lubricating Additives to Attapulgite Clay Base Grease

The focus of this study was the development of a new lubricating grease, using surface-modified attapulgite clay as thickener and synthetic oil (PAO 40) as the base oil. The tribological sensitivity of the new grease was investigated by studying the effect of adding three solid additives [KB₃O₅, MoS₂, graphite and a graphite/MoS₂ mixture (mass ratio 3:2)]. Its tribological behavior was compared with that of traditional bentone grease by adding MoS₂. The dropping point and the cone penetration of the new grease were also investigated and analyzed. The wear scar diameter of the base grease was measured on an MRS-1 J (G) four-ball tester, and the tribological sensitivity of solid lubricating additives to attapulgite clay base grease was evaluated using an Optimol SRV reciprocating friction and wear tester. The addition of MoS₂ and the graphite/MoS₂ mixture to the new lubricating grease improved its friction-reducing ability, while the addition of KB₃O₅ improved its antiwear ability. The additives MoS₂ and the graphite/MoS₂ mixture also increased the load-carrying capacity of the base grease. The attapulgite clay grease containing MoS₂ had a better friction-reducing ability than the traditional bentone grease containing MoS_2.     

Multi-environmental lubrication performance and lubrication mechanism of MoS2/Sb2O3/C composite films

MoS₂–Sb₂O₃–C composite films exhibit adaptive behavior, where surface chemistry changes with environment to maintain the good friction and wear characteristics. In previous work on nanocomposite coatings grown by PVD, this type of material was called a “chameleon” coating. Coatings used in this report were applied by burnishing mixed powders of MoS₂, Sb₂O₃ and graphite. The solid lubricant MoS₂ and graphite were selected to lubricate over a wide and complementary range including vacuum, dry air and humid air. Sb₂O₃ was used as a dopant because it acts synergistically with MoS₂, improving friction and wear properties. The MoS₂–Sb₂O₃–C composite films showed lower friction and longer wear life than either single component MoS₂ or C film in humid air. Very or even super low friction and long wear-life were observed in dry nitrogen and vacuum. The excellent tribological performance was verified and repeated in cycles between humid air and dry nitrogen. The formation of tribo-films at rubbing contacts was studied to identify the lubricating chemistry and microstructure, which varied with environmental conditions. Micro-Raman spectroscopy and Auger electron spectroscopy (AES) were used to determine surface chemistry, while scanning electron microscopy and transmission electron microscopy were used for microstructural analysis. The tribological improvement and lubrication mechanism of MoS₂–Sb₂O₃–C composite films were caused by enrichment of the active lubricant at the contact surface, alignment of the crystal orientation of the lubricant grains, and enrichment of the non lubricant materials below the surface. Sb₂O₃, which is not lubricious, was covered by the active lubricants (MoS₂ – dry, C – humid air). Clearly, the dynamics of friction during environmental cycling cleaned some Sb₂O₃ particles of one lubricant and coated it with the active lubricant for the specific environment. Mechanisms of lubrication and the role of the different materials will be discussed.     

The mechanism of lubrication by molybdenum disulphide dispersed in oil and the effect of a zinc dialkyldithiophosphate additive

The effectiveness of the lubrication of hard smooth steel surfaces by molybdenum disulphide (MoS₂) dispersed in a mineral oil, both with and without a zinc dialkyldithiophosphate (ZDDP) additive, has been investigated using a four-ball extreme pressure lubricant test machine.Each oil, additive-oil or MoS₂ dispersion, exhibited a wear scar diameter-load curve with an abrupt transition from mild to severe wear at a characteristic load. When ZDDP was present in the oil, MoS₂ was effective at pre-transition but not post-transition loads, whereas in the absence of ZDDP the converse applied, with MoS₂ only beneficial above the transition load.These results are explained in terms of the adherence (or not) of MoS₂ particles to the films physically adsorbed on the steel surfaces at pre-transition loads. At the transition load the surface temperature reaches the desorption (or decomposition) temperature of the particular oil or additive film and MoS₂ then adheres to exposed metal, unless the latter chemically reacts with oil constituents to form a chemisorbed film.     

Ultralow Friction of Solids Exposed to Intensive Irradiation

Friction behavior of organic (polytetrafluoroethylene, polyethylene) and inorganic (molybdenum and tungsten disulfides, and graphite) lubricants sliding on steel in vacuum, with the friction surface simultaneously bombarded by an accelerated helium flux was studied. At a dose rate of about 10¹² erg/sec all the substances named except polytetrafluoroethylene (PTFE) showed a drastic decrease in friction coefficients to below 0.002, which is the sensitivity limit of the device used. In polyethylene (PE), MoS₂ and WS₂, the effect persisted through the whole period of exposure and gradually subsided after the irradiation was ceased. In graphite the effect was relatively short and disappeared abruptly during irradiation. It has been demonstrated that the phenomenon in question cannot be explained in terms of the known lubrication mechanisms, such as the “gas cushion” or electrostatic effects. Some preliminary suggestions as to the possible mechanism of the effect have been made.     

Lubrication at 750°C in a vacuum by a transfer film from self‐lubricating composites for roll/slide contact of Si3N4

Roll/slide friction tests were carried out at a temperature of 750°C in a vacuum. Disc specimens were made of Si₃N₄ with or without a sputtered MoS₂ film. A pin specimen was rubbed against one disc to supply a lubricating transfer film. With a pin made of an MoS₂‐based composite, the friction coefficient was around 0.3 and almost no wear of the discs was observed after 24 h of operation at a load of 50 N, a rotating speed of 0.5 m/s, and a slip ratio of 10%. Transferred patchy MoS₂ films were observed on the friction track. With a pin made of Ni‐based composite containing BN and graphite, the friction coefficient increased from 0.2 to 0.7 over a test time of about 8 h and severe disc wear was found. In an additional test using Si₃N₄ discs with a sputtered MoS₂ film without a pin, the friction coefficient was about 0.3, and no wear of the discs was found after 24 h of operation. The appearance of the friction track was similar to that in the test using the MoS₂‐based composite pin. It seems that the sputtered MoS₂ film wore, but wear particles reattached on the friction path to develop an effective lubricating film. These results demonstrate the effectiveness of transfer film lubrication for long‐term operation in a high‐temperature vacuum, and the superior ability of MoS₂ to develop an effective transfer film.     

Dry Sliding Friction and Wear Characteristics of Cu-Sn Alloy Containing Molybdenum Disulfide

The wear and sliding friction response of a hybrid copper metal matrix composite reinforced with 10 wt% of tin (Sn) and soft solid lubricant (1, 5, and 7 wt% of MoS₂) fabricated by a powder metallurgy route was investigated. The influence of the percentages of reinforcement, load, sliding speed, and sliding distance on both the wear and friction coefficient were studied. The wear test with an experimental plan of six loads (5–30 N) and five sliding speeds (0.5–2.5 m/s) was conducted on a pin-on-disc machine to record loss in mass due to wear for two total sliding distances of 1,000 and 2,000 m. The results showed that the specific wear rate of the composites increased at room temperature with sliding distance and decreased with load. The wear resistance of the hybrid composite containing 7 wt% MoS₂ was superior to that of the other composites. It was also observed that the specific wear rates of the composites decreased with the addition of MoS₂. The 7 wt% MoS₂ composites exhibited a very low coefficient of friction of 0.35. The hardness of the composite increased as the weight percentage of MoS₂ increased. The wear and friction coefficient were mainly influenced by both the percentage of reinforcement and the load applied. Wear morphology was also studied using scanning electron microscopy and energy-dispersive X-ray analysis.     

Effect of the Synergetic Action on Tribological Characteristics of Ni-Based Composites Containing Multiple-Lubricants

Ni-based self-lubricating composites with multiple-lubricants addition were prepared by a powder metallurgy technique, and the effect of multiple-lubricants on tribological properties was investigated from room temperature to 700?°C. The synergetic effects of graphite, MoS₂, and metallic silver lubricants on the tribological characteristics of composites were analyzed. XRD analysis showed that new Cr _x S _y and Mo₂C phase were formed in the composites containing graphite, MoS₂ and metallic Ag lubricants during the sintering process. The average friction coefficients (0.69?C0.22) and wear rates (11.90?C0.09?×?10^?5?mm³?N^?1?m^?1) were obtained when rubbing against Inconel 718 alloy from room temperature to 700?°C due to synergetic lubricating action of multiple-lubricants. A smooth lubricating was gradually generated on the worn surface, and the improving of tribological properties was attributed to the formation of lubricious glaze film on the worn surface and their partially transferred to the counterface. The graphite played the main role of lubrication at room temperature, while molybdate phase and graphite were responsible for low friction coefficients and wear rates at mid/high temperatures. The synergetic lubricating effect of molybdate (produced in the rubbing process at high temperatures) iron oxide (transfer from disk material to the pin) and remaining graphite multiple-lubricants play an important lubricating role during friction tests at a wide temperature range.     

Theoretical investigation of transient elastohydrodynamic lubrication with newtonian solid‐liquid lubricants

This paper reports a theoretical investigation of transient elastohydrodynamic lubrication of a line contact. A time‐dependent Reynolds equation and elasticity equations for compressible solid‐liquid lubricants were solved using finite volume and multigrid techniques. The lubricants used were mineral oils mixed with very small solid particles, MoS₂ and PTFE, which can be treated as Newtonian fluids. The two surfaces were initially at rest and in contact. The transient oil film pressure and oil film thickness were calculated numerically. This simulation showed the significant effects of solid particles on the lubrication characteristics.     

Influence of counterface roughness on the friction and wear of polytetrafluorethylene- and polyacetal-based composites

The friction of various composites is generally little dependent upon the roughness. When the composites contain glass or carbon fibres, their wear rates are also little dependent upon the roughness. However, the wear rates of PTFE incorporating MoS₂, graphite or bronze and polyacetal incorporating PTFE increase rapidly as the roughness increases beyond a certain critical value characteristic of each of these composites. The roughness-dependency of the wear rate is markedly affected by the transfer during sliding.