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8495919 
Journal Article 
Anti-wear Chemistry of ZDDP and Calcium Borate Nano-additive. Coupling Experiments, Chemical Hardness Predictions, and MD Calculations 
Martin, JM; Onodera, T; Bouchet, M; Hatakeyama, N; Miyamoto, A; , 
2013 
1 
Tribology Letters
ISSN: 1023-8883
EISSN: 1573-2711 
SPRINGER/PLENUM PUBLISHERS 
NEW YORK 
50 
1 
95-104 
WOS:000316364100010 
Zinc dialkyl dithiophosphate (ZDDP) is an anti-wear additive for steel surfaces currently used in engine oils. Its anti-wear performance (against abrasion) is due to tribochemical reaction of zinc polyphosphate with abrasive metal oxides nanoparticles, under the combined effect of pressure and shear. However, phosphorous and sulfur are nocuous for environmental issues. Borates are possible candidates to replace phosphates in engine oils. Friction reduction with borates is found to be better than ZDDP but the anti-wear efficiency of borates is lower. In this work, we show how chemical hardness model and computer simulation can explain these different behaviors. Also we show that molecular dynamics is able to predict accurately behavior of mixtures of phosphates and borate. Results show that mixtures of additives with a P:B ratio slightly above unity can be a good compromise to have both good tribological performance and low content of phosphorous and sulfur in the lubricant. 
MD calculation; Borate additives; XPS analysis