| As the rapid development of world economy, technology and culture, the main task of moderntribology is not only to decrease friction and wear, but also to protect the environment andincrease the quality of people’s life. Besides considering the request of practical using, how toimprove ecologic effect is also the significant issue of current lubricant research needed to bestudied and solved. In this article, four series of ashless and phosphorus-free mercaptothiadiazolederivatives are synthesized through methods meeting the demands of green chemistry, and thesederivatives are long-chain dithioether-type thiadiazole derivatives, long-chain polysulfurthiadiazole derivatives, thiadiazole derivatives containing hydroxyl and imidazoline-typethiadiazole derivatives. Their tribological characteristic is evaluated in biodegradable base stockand lithium grease by four-ball tester, including friction-reducing, antiwear and extreme pressureperformance. The lubrication mechanism of these mercaptothiadiazole derivatives is studiedthrough analysing relevant thermal films and tribofims generated by these derivatives by X-rayabsorption near edge structure spectroscopy (XANES). The main study and conclusions are asfollows.1. Long-chain dithioether-type thiadiazole derivatives have been synthesized.(1) Four derivatives are all effective in improving the tribological characteristic of colza oil, andunder high additive concentration, disubstitutes are superior to monosubstitutes. Onfriction-reducing performance, MTD with branched-chains is better than MDD without abranched-chain, and DTD with branched-chains is better than DDD without a branched-chain.Meanwhile, on antiwear performance, MTD with branched-chains is also better than MDDwithout a branched-chain, but DTD with branched-chains is similar to DDD without abranched-chain.(2) On enhancing the maximum non-seizure load, monosubstitutes are superior to disubstitutes. On enhancing the weld load, MTD with branched-chains is better than MDD without abranched-chain.(3) During the heating process, these derivatives easily undergo thermal-oxidation to generatehigh-valent sulfate. Furthermore, the adsorption capability of monosubstitutes is stronger than thatof disubstitutes; while the adsorption capability of the derivatives with branched-chains is weakerthan that of the derivatives without a branched-chain.(4) These derivatives tend to react with metal surface to generate low-valent sulfide underrubbing conditions.2. Long-chain polysulfur thiadiazole derivatives have been synthesized.(1) Two derivatives are not bad friction-reducing and antiwear lubricant additives, except theresults obtained at0.1wt%.(2) On enhancing the maximum non-seizure load, PDDD without a branched-chain is betterthan PDTD with branched-chains. On enhancing the weld load, PDTD with branched-chains isbetter than PDDD without a branched-chain.(3) Under the heating process, these derivatives easily undergo thermal-oxidation to generatehigh-valent sulfate, and the adsorption capability of PDTD with branched-chains is weaker thanthat of PDDD without a branched-chain.(4) These derivatives tend to react with metal surface to generate low-valent sulfide underrubbing conditions, and PDDD without a branched-chain is easier to be oxidized than PDTD withbranched-chains.3. Thiadiazole derivatives containing hydroxyl have been synthesized.(1) Four derivatives basically fail in improving the friction-reducing characteristic of baselithium grease, though they are effective in reducing wear, and on antiwear performance,long-chain derivatives are better than short-chain derivatives.(2) On enhancing the maximum non-seizure load, short-chain derivatives are better thanlong-chain derivatives. On enhancing the weld load, monosubstitutes are superior to disubstitutes,and short-chain derivatives are better than long-chain derivatives.(3) At various additive concentrations, thermal films generated by MEPD are similar to those generated by DEPD. These thermal films are composed of adsorbed organic sulfide and ferroussulfate at1.0wt%, and they consist of only organic sulfide at5.0wt%. Thermal films formed byMEDD at1.0wt%and5.0wt%are all composed of organic sulfide and ferrous sulfate. Thermalfilm formed by DEDD at1.0wt%consists of ferrous sulfate, and thermal film at5.0wt%is amixture of organic sulfide and ferrous sulfate.(4) Tribofilm formed by MEPD at1.0wt%consists of ferrous sulfide, and tribofilm at5.0wt%isa mixture of ferrous sulfide and ferrous disulfide. Tribofilms generated by MEDD at1.0wt%and5.0wt%are all composed of ferrous sulfide. Tribofilm generated by DEPD at1.0wt%is ferroussulfide, and tribofilm formed at5.0wt%consists of ferrous sulfide and ferrous disulfide. Tribofilmgenerated by DEDD at1.0wt%is composed of ferrous sulfate, a little organic sulfide and a littleferrous sulfide, and tribofilm formed at5.0wt%mainly consists of ferrous sulfide.4. Imidazoline-type thiadiazole derivatives have been synthesized.(1) Three derivatives are effective in reducing wear in synthetic diester, but they almost fail inimproving the tribological characteristic of colza oil. In biodegradable lithium grease, thesederivatives are effective in reducing wear. On friction-reducing performance, DIB is moreeffective than other derivatives at high additive concentration, and does well in reducing friction atlower loads but fails at higher loads.(2) Components of thermal films generated in synthetic diester and colza oil are similar to eachother. Thermal films generated at0.1wt%are mainly composed of ferrous sulfate, while thermalfilms consist of adsorbed organic sulfide and ferrous sulfate at1.0wt%. In biodegradable lithiumgrease, thermal films generated at1.0wt%all consist of adsorbed organic sulfide and ferroussulfide, but the main component of these thermal films turns into only ferrous sulfide at5.0wt%.(3) The main component of tribofilms generated in colza oil is ferrous sulfate, while tribofilmsgenerated in synthetic diester are mainly composed of ferrous sulfide. In biodegradable lithiumgrease, tribofilms generated by SIB and DIB at1.0wt%are composed of ferrous disulfide, ferroussulfide and ferrous sulfate, but for the tribofilm generated by OIB at the same additiveconcentration, the composition is ferrous sulfide and ferrous sulfate. Tribofilms generated by OIBand DIB at5.0wt%are similar to those generated at1.0wt%, and the tribofilm formed by SIB at5.0wt%is mainly composed of ferrous sulfide.5. Imidazoline-type thiadiazole derivatives are blended with T205in biodegradable base stock.(1) In synthetic diester, SIB blended with T205is superior to T205in reducing friction, butinferior to SIB; while other derivatives blended with T205are not as good as T205. In colza oil,three derivatives blended with T205are better than T205in reducing friction.(2) In synthetic diester, three derivatives blended with T205are better than T205in reducing wear. In colza oil, three derivatives blended with T205are also better than T205in reducing wear.(3) In synthetic diester, thermal films generated by three derivatives blended with T205arecomposed of ferrous sulfate and adsorbed organic sulfide. In colza oil, these thermal films consistof ferrous sulfate, organic sulfide and ferrous sulfide, and these derivatives are more easilyoxidized into high-valent sulfate in this base stock. On the other hand, components containingphosphorus in those thermal films generated in synthetic diester are polyphosphate, while thermalfilms formed in colza oil are composed of polyphosphate and phosphate.(4) In synthetic diester, tribofilm generated by SIB blended with T205is composed of ferroussulfate and a little organic sulfide, while tribofilms formed by other blended samples consist offerrous sulfide, organic sulfide and ferrous sulfate. In colza oil, relevant tribofilms are composedof ferrous sulfate and organic sulfide. In addition, components containing phosphorus in thosetribofilms generated in synthetic diester and colza oil are all polyphosphate, and additive T205hasplayed an important role. |
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