| Lubricants have been widely used in the field of machine manufacturing, automobile, architecture and light industry. As the resource of petrol was less and less and the pollution to the environment was worse increasingly, it was urgent to developt a reproducible and environment-friendly lubricant. This work investigates the effects of the nano-calcium carbonate, nano-carborundum and nano-ceria fillers on the rheological property and lubricating property of soybean oil.The rheological property of soybean oil was examined. It was showed by iodine- ethanol method that the iodine value of soybean oil was 147.06,, that was, soybean oil contained a lot of double-bonds and had a poor oxidation stability. The viscosity of soybean oil was tested with vertical viscometer. The result showed soybean oil was Bingham fluid and its viscosity had an increasing trend with shear rate but decreased with temperature. Soybean oil had a good property of viscosity-temperature. The viscosity-temperature coefficient of the soybean oil was 2.3 in the range of temperature 20-100 centigrade degrees. The freezing point and inclining point of soybean were subzero 20 centigrade degrees and subzero18 centigrade degrees, respectively.Nano-calcium carbonate, nano-carborundum and nano-ceria were taken as fillers to soybean oil. Tween-20,Tween-60 and Span-20 were used as surface modifier. These nano-particles were dispersed in soybean oil using ultrasonic shaking and mechanical blending methods. It was found that the best value of hydrophile-lipophile balance of mixing surface modifier was 11.The rheological property of soybean oil added nanoparticles was examined. The results showed that the nano-fillers had no effect on the fluid type of oil. The viscosity of soybean oil added with nano-particles had a decreasing trend with shear rate in the same temperature, but the decreasing rate in lower temperature was more obvious than that in higher temperature. The viscosity of soybean oil added with nano-particles had a decreasing trend with temperature. The content of surface modifier had a prominent effect on the property of viscosity-temperature of the oil, the higher content of modifier, the bigger variety of viscosity of oil was. The concentration of nano-fillers of the soybean oil had a light effect on oil viscosity in the testing condition.Lubricating property tests of the soybean oil were run on a universal micro-tribometer. The concentration and types of nano-particles had a great effect on friction coefficient and wear of sliding disc. The best concentrations of nano-calcium carbonate, nano-carborundum and nano-ceria added in the soybean oil were 0.5 % wt , 0.07 % wt and 0.7 % wt,respectively. Compared with nano-calcium carbonate, nano-carborundum, the nano-ceria paricles had the best lubricaiton property when the concentration of these three types of nano-particles was 0.1% in the soybean oil. The standard deviation of the friction coefficient was increasing with the concentration of nanoparticles in the soybean oil. The analysis results of instant friction coefficient curve showed that the curve of soybean oil with lower concentration of nano-particle had a similar trend with that of soybean oil. The instant friction coefficient curves of a higher concentration of nano-particles had a bigger wave than those of a lower one. The average friction coefficient of soybean oil with the concentration of 0.7% of nano-ceria was less than SAE5W-30 lubricant, but it had a poor frictional stability and lower wear resistance of the sliding disc compared with SAE5W-30 lubricant. Friction mechanism of soybean oil with nano-fillers was complicated. The nano-particles in soybean oil had both positive and negative effects on lubricating property. The analysis showed that nano-fjillers had several functions in lubricating , such as padding, friction transformation of particles, friction chemical action, polishing, destroying of oil film.
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