Study on antiwear and reducing friction additive of nanometer ferric oxide

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Abstract

Amorphous ferric oxide with a particle size of about 20–50 nm was prepared using the ethanol supercritical fluid drying technique. The tribological properties of 500 SN oil containing nanometer particles were measured using four-ball and block-on-ring tribotesters. Results indicated that the wear resistance and load-carrying capacity of the oil was raised and its friction coefficient was decreased. Excessive nanometer additive was disadvantageous for the load-carrying capacity of lubricating oil. The dispersing agent played an important role in the improvement of the tribological properties, and copper stearate was markedly superior to sorbitol monostearate. Nanometer ferric oxide took effect by its deposition on the rubbing surface.

Introduction

Since Kubo1, 2predicted and found the energy level discretion, and the change in the electric, magnetic and thermal properties of nanometer particles resulting from this discretion, much attention has being paid to the preparation3, 4, 5and application[6]of nanometer particles. The above characteristics of nanometer particles are known as the “Kubo effect”. For example, nanometer material has been used as an absorbent and gas sensory material[7]due to its high surface area as well as its heterogeneous properties as catalysts8, 9. In tribology studies, oil-soluble additives to reduce wear and friction have been studied extensively, but there have been few investigations on the application of nanometer particles. One example was the research on nanometer graphite[10]as a lubricating oil additive. The extreme pressure properties of some inorganic additives have, in fact, been found to be superior to some organic additives. For example, boric ester has generally been used as an additive to reduce friction or oxidation of lubricating oil11, 12, 13. Potassium borate was, however, used as qan extreme pressure additive due to its high load-carrying capacity14, 15, 16. Unfortunately, the insolubility and dispersion difficulties of inorganic powders restrain their application in lubricating oil. It is a reasonable deduction that the dispersion stability of nanometer particles has an advantage over micron particles. On the other hand, the roughness of the friction surface is often several microns thick, so that micron particles of a certain hardness can be used as a grinding material. An example of this was the investigation by Knapp and Nitta[17], in which zirconium oxide with a particle diameter of less than 3 μm was used as an abrasive. Nanometer particles can, however, deposit on the rubbing surface. Oh et al.[18]studied the tribology properties of over-based calcium sulphate, which was suspended in dodecane in the form of colloid. The colloid was thought to act as an antiwear “mattress” on the rubbing surface. Moreover, Georges et al.[19]also researched the effect of the compaction of worn material on friction as well as the dependence of shear behavior on the pressure and volume fraction of wear particles. Georges et al.[20]thought that the third body, constituted by the wear debris, generally acted as a dynamic screen between ceramic and metallic surfaces that limited the wear of the ceramic material they studied. Therefore, it is important to study nanometer additives of lubricating oil.

Nanometer titanium oxide has been studied as a lubricating oil antiwear additive in our previous investigations[21]. The results indicated that although there was an additive element on the wear scar, cleaned by ultrasonic bath in ligroin and water, the additive element did not seem to be able to permeate into the substrate, with the exception of nanometer borate. In other words, the nanometer materials probably took effect only by their deposition on the wear scar, i.e. by the formation of the third body as a dynamic film. To demonstrate this, nanometer ferric oxide particles were prepared using the ethanol supercritical fluid drying (BSFD) technique, and the tribological properties of lubricating oil were studied in this research. It did not seem possible that the element of nanometer ferric oxide permeated into the substrate and improved its tribological properties.

Section snippets

Chemicals

Analytical reagent grade ferric sulphate, copper nitrate, aqueous ammonia, absolute ethyl alcohol; and chemically pure grade ligroin (333–393 K), sorbitol monostearate and stearic acid were all manufactured in China.

Preparation of nanometer ferric oxide

Ferric sulphate 43.3 g was dissolved in 100 ml distilled water, and 36.6 ml aqueous ammonia were added to the solution dropwise and stirred. It was then filtered with suction. The precipitate was washed with 30 ml distilled water, which was repeated two times, and it was then washed

Characterization of nanometer ferric oxide

The sol–gel method is a universal preparation technique for powder material. However, sol particles are liable to coagulate with each other because of the surface tension effect of aqueous solutions in drying[28], and the coagulation was often irreversible because of contact recrystallization between particles[29]. In the supercritical fluid drying preparation procedure, advent is removed in the supercritical condition. Particles will not coagulate with each other without the gas-fluid

Conclusion

Nanometer ferric oxide with a particle size of about 20–50 nm was prepared using the ethanol supercritical fluid drying technique. The ferric oxide was almost amorphous. The tribological properties of the ferric oxide, used as an antiwear and friction reduction additive in lubricating oil, was measured. Results indicated that wear resistance and load-carrying capacity of 500 SN basic oil were improved and the friction coefficient was decreased by the ferric oxide. Excessive nanometer particle

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