Synthesis And Tribological Study Of Phosphonium-based Ionic Liquids In Water

At present,the traditional mineral oil resources are exhausting,and the synthetic oil is costly so that it is difficult to meet the increasing demand of industrial lubrication.Water-based lubricants are cheap,widely available,fire-resistant and biodegradable,making them ideal substitutes for mineral oil.However,they are confronted with the problem of poor tribological performance in practical industrial applications.Therefore,it is urgent to develop high-performance water-based lubrication additives.Ionic liquid additives(ILs)have drawn increasingly more attention since they were discovered.They have excellent film-forming ability and thermal stability.However,there are few studies on the application of ILs in water.In this paper,a series of water-soluble ILs based on phosphate anions and amine cations were prepared to combine the excellent film-forming property of ILs with the excellent tribological properties of P-N element.Firstly,four amines were screened to determine the optimal candidate for the cation of additives.Secondly,the relationship between alkyl chain length of ILs and tribological properties was investigated.Finally,based on stearic acid and palmitic acid,two kinds of water-soluble ILs were prepared to meet the requirements of alkyl chain length and economy.The structure of ILs was confirmed by infrared spectroscopy(IR).The thermal stability was tested by thermogravimetric analysis(TGA).The tribolgical performance was evaluated by four-ball tester.The wear scar surfaces were observed by scanning electron microscopy(SEM).The chemical composition of tribofilm was analyzed by X-ray photoelectron spectroscopy(XPS)and Xray absorption near-edge structure(XANES).The main conclusions can be drawn as follows:1.The four additives synthesized in Chapter 2 have excellent water solubility.The friction-reducing properties of water are respectively improved by four ILs with 73.21%,70.69%,69.06% and 76.60%,while the anti-wear properties of water are respectively improved by four ILs with 58.43%,66.37%,64.92% and 62.26%.2.Using diethanolamine as the cation,three kinds of water-soluble ILs with different alkyl chain length were prepared.Their water solubility,thermal stability and tribological properties are excellent.The longer the alkyl chain length is,the better the anti-wear and extreme pressure performance becomes.The longer the alkyl chain length is,the smoother the worn surface is.XPS result shows that the tribofilm of the worn surface is composed of iron oxide,iron phosphate and iron polyphosphate.XANES result shows that the tribofilm contains iron phosphate and iron pyrophosphate.3.Based on stearic acid and palmitic acid,two kinds of water-based ILs are prepared.Their thermal stability is excellent.When the addition amount is 0.5wt.%,ILs are able to improve the friction-reducing and anti-wear property of water by 70%.XANES result shows that the tribofilm contains iron phosphate and iron pyrophosphate.