Study On Tribological Properties And Mechanisms Of Series Of Novel Organic Boric Acid Esters As Additives

The developmental trends of industrial lubricants are to enhance the thermal oxidative stability, to prolong the using period of oil and to save energy. Based on the above trends, some new demands to additives for industrial lubricants come forth, for example, employing some new types of additives containing boron. In this dissertation, the active elements, such as S, P and N, were introduced into the organic borate esters for different purposes, and eight kinds of boric acid esters as lubricant additives were designed and prepared. Their tribological properties were explored in different base oils using four-ball machine, and their tribological action mechanisms were studied by virtue of SEM, EDS, XPS, three-dimensional non-contact surface profilometer and ACPI/MS, etc. The antioxidation properties, corrosion-inhibiting properties and thermal stability of some additives were also investigated. The main conclusions of the dissertation are shown as follows:1. In order to improve the tribological properties of two additives used widespreadly, boron was introduced into their structures. Two additives (BDDP and BDTC) were synthesized and their tribological behaviors were compared with ZDDP and MoDTC in synthetic diester and rapeseed oil, respectively. Compared with ZDDP, BDDP in synthetic diester shows better load-carrying and friction-reducing property. Meanwhile, BDDP can improve the antiwear performance of the base oil evidently. But its antiwear property is slightly worse than that of ZDDP. It possesses better thermal stability than ZDDP, and has high efficiency in controlling the oxidation of Esterex A51. Compared with MoDTC, BDTC possesses extraordinary EP property in rapeseed oil, and its antiwear property is better under relatively higher load. Moreover, its friction-reducing property is almost equivalent to that of MoDTC, and exhibits dramatically high thermal stability and antioxidation property.2. Introduce the S element into borate ester and design new type of B-S load-carrying additive for replacing sulfurized olefins.Compared with sulfurized olefins, DSB and BXT have no noticeable odor and little corrosion to copper, and exhibits better thermal stability and excellent antioxidant performance. The load-carrying properties of BXT and sulfurized olefins make a great difference. The former has higher pB value, and yet the latter has higher pD value. Moreover, the antiwear and friction-reducing capacity of DSB is better than that of sulfurized olefins under higher load. The load-carrying properties of BXT as additive in RSO are equivalent to sulfurized olefins (even better than the latter under lower concentration). Moreover, BXT possesses better friction-reducing and antiwear ability at relatively lower concentration.3. Introduce heterocyclic groups into borate ester and seek the substitute for ZDDP. BTSB possesses comprehensive tribological property and probably partially replaces ZDDP. Its EP property is dramatically better than that of ZDDP, and exhibits better friction-reducing property compared with ZDDP, but its antiwear property is slightly worse than that of ZDDP. It is effective in protecting copper from corrosion and its antioxidant property is almost equivalent to that of ZDDP. BTBM in RSO has very high PB value, but its antiweld property is bad. Compared with ZDDP, the antiwear performance of BTBM is worse, but possesses extreme excellent friction-reducing property. As corrosion inhibitor, BTBM can control the copper corrosion markedly.4. Based on electronic conjugation theory, design and prepare borate esters additive with high hydrolytic stability.Compared common borate ester, the two additives possesses higher hydrolytic stability. PBDDP in Esterex A51 possess better load-carrying and friction-reducing property compared with ZDDP. Its antiwear performance is equivalent to that of ZDDP, and exhibits better thermal stability and remarkable antioxidation performance. PBDTC as additive in RSO possess better load-carrying and friction-reducing property compared with MoDTC. Its antiwear performance excels that of MoDTC under high load. PBDDP exhibits rather better thermal stability and extreme excellent antioxidation performance, compared with MoDTC and ZDDP, respectively.5. Study the effect of adding into amine on the tribological properties and hydrolytic stability of borate ester. The loading-carry capability of borate ester containing no active element is relatively weak. When amine and borate ester form BN coordination bond, the loading-carry performance of the complexes become worse compared base oil. However, BN ammonium complex can improve the loading-carry performance of base oil. Under relatively low load, borate ester containing no active element has slightly antiwear property, and its antiwear performance can be improved when BN coordination bond or BN ammonium formed.6. The antioxidation performance of phenyl-borate derivative and its synergistic effects with hydroxybenzene type antioxidant.The phenyl-borate contain no active element in RSO has a few antioxidation properties. The phenyl-borate contain S, P possesses extreme excellent antioxidation property, even excel T501. Phenyl-borate derivatives have synergistic antioxidation effects with T501, especially for PBDDP and T501. Phenyl-borate derivatives can not remarkably rid the radical, which shows it do not accord with the antioxidation mechanism of"capture radical". When the oxidation reaction occurs initially, Phenyl-borate derivatives can decrease the depletion of T501 greatly, which can answer for their synergistic effects.7. When studying the tribological action mechanisms of some borate containing active element, it can be found that the organic borate ester can be decomposed when sliding, and the decomposed borate ester or B2O3 adsorbed on worn surface. The adsorption layer can prevent the direct contact between friction pairs, thereby reducing wear. When the additive contains active element, such as N, S and P, these element can react with metal surface to form inorganic reaction layer composed of FeSO4,FeS,FePO4, etc. Both of which contribute to the formation of complex boundary lubricating film and present better antiwear effects.