Laigui Yu

Preparation of DDP-coated PbS nanoparticles and investigation of the antiwear ability of the prepared nanoparticles as additive in liquid paraffin

PbS nanoparticles of average diameter about 5 nm, which were surface-modified with dialkyldithiophosphate (DDP), were prepared by chemical synthesis. The synthesized DDP-coated PbS nanoparticles were characterized by infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electron diffraction (ED). The antiwear ability of the coated PbS nanoparticles as additive in liquid paraffin was investigated using a four-ball machine. The worn surfaces were analysed with XPS also. It was found that the dispersion capacity and oxidative stability of PbS nanoparticles could be improved effectively by surface modification with DDP. Meanwhile, DDP-coated PbS nanoparticles could improve the antiwear ability of liquid paraffin even at an extremely low concentration. This was attributed to the formation of a chemical reaction boundary film consisting of PbS, PbO, FeS, Fe2O3, SO4staggered2 and PO43.

An investigation of the friction and wear behaviors of Micrometer copper particle- and nanometer copper particle-filled polyoxymethylene composites

Micrometer and nanometer copper particle-filled polyoxymethylene composites (coded as POM-micro Cu and POM-nano Cu, respectively) were prepared by compression molding. The compression strength and tensile strength of the composites were evaluated with a DY35 universal materials tester. An RFT-III reciprocating friction and wear tester was used to examine the tribological properties of the composites. The elemental compositions in the transfer films and the chemical states of the elements in the composite-worn surfaces were analyzed with electron probe microanalysis and X-ray photoelectron spectroscopy, while the surface morphologies were observed with scanning electron microscopy. It was found that Cu(CH2O)n was produced in sliding of a POM-nano Cu pin against an AISI 1045 steel block and Cu2O was produced in sliding of a POM-micro Cu pin against the same counterface. POM-micro Cu exhibited higher copper concentration in the transfer film compared with POM-nano Cu, and the transfer film of the former was thick and patchy compared with that of the latter. It was also found that micrometer and nanometer copper particles as fillers in POM exhibit a distinctive size effect in modifying the wear mechanisms of the composites. In other words, the wear mechanism of POM-micro Cu is mainly scuffing and adhesion, while that of POM-nano Cu is mainly plastic deformation.

The tribological behaviors of copper-coated graphite filled PTFE composites

Abstract Polytetrafluoroethylene (PTFE) composites filled with different fillers and various filler proportions were made by compression molding. The powders of graphite, copper, copper-coated graphite (CCG), and copper-mixed graphite (CMG) were selected as the fillers. The tribological behaviors of composites in sliding against a stainless steel ring were evaluated on an MM-200 friction and wear tester. The morphologies and element chemical states of the worn composite surfaces were examined with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. It was found that the CCG particles prepared by chemical replacement method were characterized by loose and uniform covering of graphite particles by many tiny copper particles. The preferential transfer of graphite onto the surfaces of PTFE powders during the mixing process could be prevented by copper coating method, which was beneficial to further improving the wear resistance of composites. XPS analysis showed that no tribological reaction occurred during the friction process of PTFE sliding against stainless steel ring, but there was radical -CF 3 on the worn surfaces of PTFE composites, its generation mechanism and effect on the tribological behaviors of PTFE composites still need further study.

The effect of LaF3 nanocluster modified with succinimide on the lubricating performance of liquid paraffin for steel-on-steel system

Abstract LaF 3 nanocluster modified with succinimide was prepared. The effect of the modified LaF 3 nanocluster on the lubricating performance of liquid paraffin for steel-on-steel sliding system was investigated on a four-ball machine. The morphology of LaF 3 and its lubricating mechanisms as additive in liquid paraffin were studied by means of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was found that LaF 3 nanocluster modified with succinimide as an additive in liquid paraffin increased the load-carrying capacity and had good antiwear and friction-reduction behaviour. The XPS analysis of the worn steel surfaces indicated that a boundary lubricating film consisting of physically adsorbing film (succinimide) and tribochemically reacting film (lanthanum oxide and ferrous fluoride) was generated during the friction process. This contributed to improving the lubricating performance of liquid paraffin.

Study of the tribological behavior of sulfurized fatty acids as additives in rapeseed oil

Odorless sulfurized fatty acids, sulfurized octadecanoic acid (SOA) and sulfurized docosanoic acid (SDA), were synthesized. The tribological behavior of the synthesized compounds as additives in rapeseed oil was evaluated and compared with octadecanoic acid using four-ball friction and wear testers. The morphologies and elemental chemical states on the worn surfaces of the lubricated GCr15 steel were investigated by means of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). As the results, both SOA and SDA as additives in rapeseed oil show improved extreme pressure properties and friction-reducing behavior as compared with the rapeseed oil alone. They show better antiwear and extreme pressure properties than octadecanoic acid additive at relatively higher load. The differences in the tribological behavior of octadecanoic acid and SOA and SDA are attributed to their different action mechanisms therein. That is, octadecanoic acid functions by forming adsorption film alone while the two sulfurized fatty acids function by forming adsorption film and tribochemical reaction film during the friction process.

Friction and wear behaviors of a (Ca, Mg)-sialon/SAE 52100 steel pair under the lubrication of various polyols as water-based lubricating additives

The friction and wear behaviors of (Ca, Mg)-sialon/SAE 52100 steel pair under the lubrication of water or various polyol aqueous solutions were investigated with an SRV friction and wear tester in a ball-on-disc configuration. This was conducted to simulate the effect of polyols as aqueous additive in machining sialon ceramic. The morphologies of and elemental distributions in the worn surfaces of the lubricated sialon ceramics and counterpart steel were observed and determined with scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). All solutions of the tested polyols decreased the friction coefficient of (Ca, Mg)-sialon/SAE 52100 steel effectively and increased the wear volume loss of (Ca, Mg)-sialon to some extent as compared with dry sliding. The friction coefficients under the lubrication of distilled water and various polyols aqueous solutions of polyols showed almost no difference, and propanetriol was found to be the most effective for machining (Ca, Mg)-sialon with the concentration of polyols in water fixed as 5 wt%. The friction coefficients under the lubrication of propanetriol aqueous solutions in varied concentrations are closely related with the concentration, which came to the lowest value of 0.04 at a concentration of 75%. The friction-reducing performance of the polyols as additives in water was roughly correlated with their wetting behaviors on the sialon ceramic surface. In other words, the higher the wetting ability is, the lower the friction coefficients will be. Moreover, the wear volume losses of (Ca, Mg)-sialon also varied with the variation in the concentration of propanetriol in water. Accounting for the friction-reduction and wear behavior, 20% concentration of propanetriol in water could be recommended for machining (Ca, Mg)-sialon. Electron microscopic analysis indicates that polyols as additives in water enhanced the corrosive wear of sialon ceramic, which could be beneficial for increasing the machining efficiency. There existed interactions among water, polyols and sialon surfaces, which were dependent on the compositions of the lubricant solution. This accounts for the variations in the friction and wear behaviors with the concentration of polyols in water.

The tribological behaviors of some rare earth complexes as lubricating additives Part 2—The antiwear and extreme pressure properties in lithium grease

Abstract The antiwear and extreme pressure (EP) properties of rare earth 8-hydroxyquinolinates and of rate earth di-n-hexadecyldithiophosphates as additives in lithium grease were evaluated on an Optimol SRV friction and wear tester. The morphologies of the worn surfaces and the elemental distributions in the worn surfaces were observed and determined with an electron probe microanalyzer. Then the action mechanisms of these compounds as additives in lithium grease were discussed. It was found that rare earth di-n-hexadecyldithiophosphates in lithium grease exhibited better antiwear and extreme pressure properties than zinc di-n-butyldithiophosphate (ZDDP), while rare earth 8-hydroxyquinolinates registered antiwear and extreme pressure properties comparable to ZDDP. Moreover, the different tribological behaviors of the compounds as additives in lithium grease were closely related to different mechanisms. That is, rare earth 8-hydroxyquinolinates as additives in lithium grease exhibited physisorption action only, while copper 8-hydroxyquinolinate in lithium grease functioned by both physisorption and coordination ligand exchange reaction. The tribological behaviors of ReDDP was closely related to tribochemical reaction.

Investigation of the transfer film characteristics and tribochemical changes of Kevlar fiber reinforced polyphenylene sulfide composites in sliding against a tool steel counterface

Composites of polyphenylene sulfide reinforced with Kevlar 29 fiber were prepared by compression molding. The friction and wear behavior of the composites was examined with a pin-on-disc test rig. The morphologies and elemental composition of the transfer films on the counterface were analyzed with a scanning electron microscope equipped with an energy dispersive spectrometer. The tribochemical changes of polyphenylene sulfide composites during friction were examined by means of X-ray photoelectron spectroscopy. It has been found that the inclusion of Kevlar fiber increases the wear resistance of polyphenylene sulfide considerably. A discontinuous and thick transfer film forms on the counterface against unfilled polyphenylene sulfide, while a thin and uniform transfer film is generated on the counterface against the composite with 30% Kevlar fiber. The Kevlar fiber as a reinforcing agent promotes the decomposition and oxidation of the polymer matrix by way of increasing the frictional heating and the wear face temperature. This helps to increase the bonding strength of the transfer film on the counterface, and subsequently increases the wear resistance of the composites.

The tribological behaviors of some rare earth complexes as lubricating additives Part 1. An investigation of the friction-reducing behaviors and an XPS study of the tribochemical characteristics

Several rare earth coordination compounds of 8-hydroxyquinoline and of di-n-hexadecyldithiophosphate were synthesized. The burnished films of these coordination compounds on a GCr15 bearing steel (SAE 52100 steel) disc were prepared. The friction-reducing behaviors of the burnished films were evaluated on a DF-PM friction tester. The friction-reducing behaviors of these complexes as additives in a lithium grease were examined on an SRV fretting wear tester. The binding energies of some typical elements in the complexes before and after friction were determined on an X-ray photoelectron spectrometer. It was found that these coordination compounds could form a quite complete burnished film on a GCr15 bearing steel surface. The lowest friction coefficient was obtained with respect to the burnished film of neodymium di-n-hexadecyldithiophosphate (NdDDP), while a decreased friction coefficient was reached with respect to the burnished film of rare earth 8-hydroxyquinolinate, as compared with the non-burnished friction pairs. Besides, the SRV fretting wear test results revealed that NdDDP in lithium grease exhibited better antiwear and extreme pressure properties than zinc di-n-butyldithiophosphate (ZDDP), while the antiwear and extreme pressure performance of rare earth 8-hydroxyquinolinates is comparable to that of ZDDP. The related results will be published in a following part of this work. The XPS results indicated that tribochemical reactions were involved in the wear process of these coordination compounds as lubricants or as lubricating additives. Here in the first part of this work, the friction-reducing behaviors of the burnished films and of the additives in a lithium grease are dealt with, while the XPS study of the tribochemical characteristics of these complexes is also reported.

Tribological behaviors of (Ca, Mg)–Sialon under lubricating of polyols

Abstract The friction and wear behaviors of (Ca, Mg)–Sialon/GCr15 steel couple under dry sliding and lubrication of water and polyols (ethanediol, 1,3-butanediol, 1,4-butanediol and propanetriol) were investigated by an SRV tester in a ball-on-disk configuration. It was found that as compared with dry sliding, all the polyols not only reduced the friction coefficient of (Ca, Mg)–Sialon sliding against GCr15 steel significantly but also reduced the wear volume considerably (1–2 order). The lowest friction coefficient 0.06 was recorded as lubricated by ethanediol. The wear volume of (Ca, Mg)–Sialon sliding against a bearing steel under the lubrication of the tested polyols could be ranked as below: ethanediol>1,4-butanediol>1,3-butanediol>propanetiol. It was supposed that the performance of polyols was correlated with their molecular structures. Namely, the longer the chain length and/or the bigger the number of hydroxyl radicals, the smaller the wear volume of (Ca, Mg)–Sialon. Electron probe microanalysis (EPMA) of the worn surfaces indicated that the wear mechanisms of (Ca, Mg)–Sialon was dependent on the friction and wear test conditions. Fourier transform infrared spectroscopic (FT-IR) analysis of the worn ceramic surface showed that tribochemical reactions between (Ca, Mg)–Sialon and polyols was involved in the friction process, which led to the decrease in the wear volume and friction coefficient of (Ca, Mg)–Sialon sliding against GCr15 steel.