Preparations And Tribological Properties Of Novel Oil Soluble Organo-metal Compounds And Nano-metal Particles

Since sulfur/phosphorus-free organo-metal compounds own particular tribological properties, it is an increasing tendency for scientists to develop oil-soluble, environmentally friendly and high effective lubrication additives. The tribological behaviors of a series of oil soluble organo-metal salts, such as rare-earth naphthenate (REN), rare-earth alkylsalicylate (REA), stannous naphthenate (SN), stannous oleate (SO), zinc naphthenate, nickle naphthenate, manganese naphthenate, cobalt naphthenate, lead naphthenate and copper naphthenate, are invested in this paper. Analytical results show that most of them possess good tribological properties and there are synergistic effects between orgno rare-earth and orgno-tin compounds. Auger electron spectrum (AES) ans X-ray photoelectron spectrum (XPS) analyses are used to study the contributions of metal oxides and elementary metals produced on the rubbed surface. It is found that most of the decompounded products of organo metal additives are metal oxides during the friction and wear process. In order to improve the tribological effects of such additives and invest the contribution of elementary metals in the friction process, surface modified nano metal particles, such as nano rare-earth, nano-copper and nano-lead, are prepared through micro-emulsification chemical reduce method, and their tribological characteristics and mechanisms are studied in this paper. Furthermore, the foreground of nano rare-earth used as additive of novel environmentally acceptable engine oil are evaluated too.The diameters of surface-modified nano-metal particles are below 40 nm, and the sizes of elementary metal nucleus of the particles are less than 10 nm. They show excellent oil solubilities and good dispersibilities in organic solvents such as benzene and toluene.Surface modified nano rare-earth additive exhibits excellent tribological properties in white oil. When the concentration of the additive is 3.0%, its load-carrying capability (P_B= 647N) increases to 3.30 times that of base stock, and its wear scar diameter (WSD, D^294N_30min =0.29 mm) value and friction coefficient reduce to45.3% and 87.5% that of base stock respectively. It exhibits better anti-wear capability than that of zinc dialkyldithiophosphate (ZDDP) and REN. At the load of 196, 294, 392 and 490 N, the anti-wear capability of nano rare-earth additive is 1.24> 1.52> 1.37 and 1.15 times that of ZDDP respectively. Surface analysis of worn scar indicates that nano rare-earth can accelerate the oxydation of the metal surface during the friction process. It is found that there are not only nano rare-earth particles but also rare-earth oxides and ferreous oxides composed mainly by Fe3O4 and Fe2O3 on the rubbed surface. The main reason of the excellent tribological performance of nano rare-earth additive attributes to the formation of such a complicated protection film that is even more than 24 nanometers in depth.Novel environmentally friendly engine oil with sulfur and phosphorus free is trial manufactured by using nano rare-earth as anti-wear additive, and its tribological behavior and oxidation stability are also invested in this paper. The experimental results show that its anti-wear and firction-reducing capabilities and oxidation stablility in high temperature are better than those of commercial products.Surface modified nano-copper and nano-lead additives also show certain anti-wear and load-carrying capacities. Their anti-wear capabilities are as good as that of corresponding organo metal salts, while their load-carrying capabilities are better. Surface analysis finds that there is a deposit elementary metal film that is 10-13 nm in depth formed on the worn surface under the boundary lubrication condition, which is the main reason to their good tribological properties.Oil soluble rare-earth alkylsalicylate, stannous naphthenate and stannous oleate are synthesized for the first time, and their tribological performances and tribochemistry reaction mechanisms are also invested in this paper.Rare-earth alkylsalicylate exhibits excellent load-carrying and anti-wear capabilities and good friction-reducing capability. When its concentration is 4.0%, itsWSD value (D294N 30min =0.3 lmm) and friction coefficient reduce to 48.4% and 78.0%that of base oil respectively, and its load-carrying capability (j)u = 598N) increases to 3.05 times that of base oil. Compared with ZDDP, rare-earth alkylsalicylate showsbetter anti-wear effect under the selected range of loads. At the load of 196, 294, 392 and 490 N, the WSD value of rare-earth alkylsalicylate is 87.1%, 70.5%, 61.5% and 46.7% that of ZDDP respectively.Analyses of AES and XPS show that there is a boundary film formed by organo metals, ferrous oxides, rare-earth oxides and elementary rare-earth on the worn surface. But the concentration of oxygen in the friction surface lubricated by organo rare-earth is far less than that lubricated by nano rare-earth additive. Such a rare-earth enrichment lubrication film is the main reason of good tribological performance of organo rare-earth compound.Both stannous oleate and stannous naphthenate show good load-carrying, anti-wear and friction-reducing capabilities under moderate and low load. Analytical results of worn scar surfaces indicate that there is a boundary lubricating film containing Sn and Fe elements formed on the rubbed surface. And Sn element exists as SnO and SnC>2 while the Fe element exists as ferreous oxides and organo-ferreous in the boundary film. It is their combined effects that lead to the good performance of organo-tin compounds.Analytical results show that there are lubrication synergisms existed in the anti-wear and friction-reducing capabilities between stannous naphthenate and rare-earth naphthenate. In the load range of 196—549 N, the WSD value and friction coefficient of the complex of rare-earth naphthenate and stannous naphthenate are less than that of lubricant containing only rare-earth naphthenate or stannous naphthenate. Analytical results of AES and XPS indicate that there is a boundary lubricating film containing organo metal, ferreous oxides, rare-earth oxides, rare-earth and tin oxides formed on the friction surface. The alloy effect between rare-earth and tin may be the main reason of the synergistic effect of organo rare-earth and organo-tin compounds.There are good oil solubility and excellent tribological properties in the combined additive RES2 containing rare-earth and tin When the concentration ofRES2 is 3.0%, its WSD value (D^n = 0 31mm) and friction coefficient reduce to 516% and 74 1% that of base stock respectively, and load-carrying capability {/)? —...