Tribological Performance And Wear-self-repairing Mechanism Of Silicate Particles As Lubricating Oil Additive

The silicate mineral particles as lubricating oil additive is a newly developed lubricating material of environmental protection in recent decade. They have shown excellent friction-reduction and anti-wear properties and special self-repairing function. However, the studies on the new lubricating additive, including their chemical composition, structure, preparation, properties, application and mechanism, especially the self-repairing function, are still at the infancy stage, it is still lacking in enough literature reports in this new field. Therefore, to carry out the research on the additive of silicate mineral particles is of important theoretical and practical meanings, the success of this research will promote the development of tribology and lubricating materials disciplines, will be helpful to realize the domestic industrialization of this technique, to enlarge the application fields and will make contribution to the energy-saving, and establishment of green engineering for the sustainable development..The present dissertation, for the first time, investigated the characteristics and necessary physical parameters of many kinds of layered silicate mineral particles as the lubricating oil additive, successfully prepared the oil-soluble and chemically synthetic silicate particles, emphatically studied the mechanism of self-repairing function, and finally, using the prepared lubricating additive conducted the running test of some practical mechanical equipment.The main contents and successes of this dissertation are as follows:(1) Evaluated 10 kinds of natural silicate mineral particles as the additive in lubricating oil, and proposed their necessary physical parametersEstablished the relationship between the composition, structure, particle size, concentration of the silicate particles and their tribological properties. It was found that the Muscovite, Palygorskite calcined at 8500 C, Sepiolite calcined at 8000 C, Chlorite calcined at 8250 C, Serpentinecalcined at at 8000 C, and Pyrophyllite calcined at 6000 C have better tribological properties. It was indicated that the crystalline structure of TO/TOT type, dioctahedron type, lamellar/fibrous type and at the amorphous transformation zone are the main standards of particles selection.(2)Prepared the oil-soluble silicate mineral particles with good tribological propertiesPrepared an oil-soluble natural silicate mineral particles (WK01), which was modified successfully by the organic long carbon chain molecules, they showed excellent oil solubility and dispersivity. The four-ball tribotest results exhibited that WK01 with concentration of 0.25% has the best wear-resistance, and that with concentration of 1.0% has the best friction-reduction property. The average friction coefficient of WK01 with concentration of 2.0% is 0.167, which is lower than 150SN base oil up to 44.8% in the SRV tribotest. The tribological properties of WK01 are better than that of the natural silicate particles CA01 in the pin-on-disc tribotest.(3)Successfully prepared the magnesium/ aluminum silicate particles, which are basically similar to the natural mineral particles, using the chemical synthetic method Eight magnesium/ aluminum silicate hydrate particles (HC/HL01, 02, 03, 04) were prepared by sol-gel method. The prepared silicate particles were characterized by FTIR, XRD, DTA, TGA and laser particle size analysis. The concentration of 0.25% HC01 and 0.125% HL04 showed the best tribological properties in four ball tribotest. Both HC04 and HL04 can improve the load-carrying capacity of the base oil 150SN, they exhibited excellent tribological properties in the pin-on-disc tribotest. A thick oxide and carbonized layer was formed on the friction surface, which might be the reason of“negative wear”effect.(4) Approached deeply the mechanism of self-repairing phenomenon and established the physical modelBased on the great quantity of micro-analyses, it was found that a layer of a certain thickness with characteristics of low roughness, high hardness, low friction coefficient and transparency was formed on the friction surface. The process and mechanism of wear-self-repairing phenomenon were proposed and described by the physical model. The chemical reaction equation and condition of self-repairing layer formation were deduced and calculated by the thermo-dynamical theory. The silicate particles can“bring”the metallic debri back to the friction surface during the friction process. A repaired layer with special structure was formed under high temperature and pressure condition. The metallic element in the repaired layer existed mainly in the form of substance, oxides and carbides. The carbon element existed in the form of metallic carbides and C substance with amorphous structure, which was quite complicated. The theoretical calculations figure out that graphite can be transformed to diamond at the condition with temperature of 800℃and pressure of 3.61GPa(5) Verified the positive effect of silicate mineral particle additive by running test of some practical mechanical equipmentA natural silicate particles lubricating oil additive was prepared and applied to air compressor, circulating water pump, gear box, diesel engine and gasoline engine, which all showed good antiwear property.