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Hydraulic Fluids and Fluid-Handling Components
Published in Qin Zhang, Basics of Hydraulic Systems, 2019
Irrelevant to its viscosity, the lubricity of a hydraulic fluid is a special property used to measure the antiwear performance of the fluid. The pump is the critical dynamic element in any hydraulic system, and each pump type has different requirements for wear protection. Compared to piston pumps, vane and gear pumps require more antiwear protection because they operate with inherent metal-to-metal contact. As stated in Section 6.1.1, an ideal fluid should be able to form a full film between two facing surfaces of all motion pairs. Normally, most hydraulic fluids require use of some special additives to improve their antiwear performance, especially for the water-based fluids. The most frequently used antiwear additive is probably zinc dithiophosphate (ZDP). However, the ashless antiwear hydraulic fluids have become a popular means of reducing waste-treatment loads.
Lubricating Oils
Published in Don M. Pirro, Martin Webster, Ekkehard Daschner, Lubrication Fundamentals, 2017
Don M. Pirro, Martin Webster, Ekkehard Daschner
When the operating temperature exceeds about 200°F (93°C), the catalytic effects of metals become important factors in promoting oil oxidation. Under these conditions, inhibitors that reduce the catalytic effect of the metals must be used. These materials usually react with the surfaces of the metals to form protective coatings and, for this reason, are sometimes called metal deactivators. Typical of this type of additives are the dithiophosphates, primarily zinc dithiophosphate. The dithiophosphates also act to decompose hydroperoxides at temperatures above 200°F (93°C), so they inhibit oxidation by this mechanism as well.
Biocoatings and additives as promising candidates for ultralow friction systems
Published in Green Chemistry Letters and Reviews, 2021
Marcia Gabriely A. da Cruz, Tetyana M. Budnyak, Bruno V. M. Rodrigues, Serhiy Budnyk, Adam Slabon
Organophosphates (OP) are a well-known class of additives used in turbine oil lubricants. Despite the efficiency that organophosphorus compounds add to the lubrication systems, they represent a serious problem due to the generation of phosphorus emission and the toxicity of the degradation products (15). We have shown that in the case of lubricants containing functional additives, e.g. zinc dithiophosphate (ZDDP), detergents, dispersants, and antioxidants for engine and gear lubricants, the generated soot matrix particles contain 3–5 nm ZnO:P,S nanoparticles (16). Part of the issue caused by the use of OPs can be managed by substitution with thiazoles without efficiency losses. Another friction modifier widely applied in engine lubricants is the molybdenum di-thiocarbamate (Mo-DTC), which produces a tribofilm with MoS2 sheets that lead to low friction (17). However, this organic lubricant additive is a source of harmful emissions due to its toxicity (18).
Improving Hypoid Gear Oil Pitting Performance through Friction Reduction
Published in Tribology Transactions, 2020
Jens E. Johansson, Mark T. Devlin, Jeffrey M. Guevremont, Braham Prakash
The exact mechanism by which the AW/EP tribofilms affect thin-film friction is unclear. Previous studies have shown that the tribofilms formed by various AW/EP additives display different characteristics and morphologies (Topolovec-Miklozic, et al. (57); Najman, et al. (58)). For example, zinc dithiophosphate (ZDDP) AW additives are often found to have relatively high friction, which is often attributed to their unevenly distributed tribofilms (Taylor, et al. (8); Kapadia, et al. (9); Bennett (59)). Compared to ZDDP, ashless phosphorus-based AW additives form smoother and relatively thin films (Devlin, et al. (10)), and ball-on-disc tests have also shown that they tend to result in lower friction than those formed by ZDDP (Ribeaud (11)). However, a more recent study showed that ZDDP tribofilms can produce high friction even when the films formed are quite smooth (Taylor and Spikes (7)), implying that the exact mechanisms are not yet completely understood.
Tribological Behaviors of W/Mo Films under Lubrication of Zinc Dithiophosphates—Understanding Their Roles in Tribochemical Reactions
Published in Tribology Transactions, 2019
Xingliang Li, Wen Yue, Zhiqiang Fu, Haipeng Huang, Chengbiao Wang, Jiajun Liu
A lower viscosity lubricant and more effective additives are required to improve engine efficiency and durability in future engines (Zhou, et al. (7)). Ionic liquids (Qu, et al. (8); Berman, et al. (9)), graphene (Yadgarow, et al. (10)), and inorganic fullerene-like WS2/MoS2 nanoparticles (Tang and Li (11)) have been explored as potential lubricant additives in engine oils. However, zinc dithiophosphate (ZDDP) with a chemical formula of Zn[S2P(OR)2]2, where R is an alkyl or aryl group, is the most common antiwear additive and antioxidant used in commercially fully formulated engine oil. It has proved to be the most effective antiwear additive and cannot be fully replaced (Spikes (12); Nicholls, et al. (13)). Tribochemical reactions of ZDDP have been extensively published in the last decade (Mosey (14); Onodera, et al. (15)). Unfortunately, a ZDDP tribofilm formed on modified surfaces or coatings is not as fully understood as that on iron-based materials.