The wear behaviour of steel lubricated by some oxygen‐containing derivatives of heterocyclic nitrogen‐containing compounds (HNCC) under boundary lubrication conditions

Abstract

AbstractThe effect of an oxygen‐containing group on the wear behaviour of heterocyclic nitrogen‐containing compounds (HNCC) have been investigated on a four‐ball machine and a SRV tester. The preliminary results show that the substitution of the hydroxyl group and aldo‐group significantly increases the antiwear effectiveness of the parent compounds. However, the alkyloxyl group involved in some HNCC does not improve the wear performance of HNCC.In order to get a better understanding of the role of oxygen‐containing groups in wear chemistry, a pair of compounds, quinoline and 8‐hydroxyquinoline, were chosen for further study. The analytical results of worn surfaces, wear debris and deposits showed that the difference in sliding behaviour between quinoline and 8‐hydroxyquinoline can be related to chemical reaction at the rubbing surfaces involving metal, HNCC and a hydroxyl group in HNCC or oxygen dissolved in the base stock. Under the same test conditions, these compounds, which are similar in chemical structure, give quite different reaction products. Quinoline is decomposed and oxidised by oxygen dissolving in the base stock to form a carboxylate function (soap). In the case of 8‐hydroxyquinoline, partial surface products are converted to higher molecular species, probably due to the catalytic action of fresh metal surface being exposed by rubbing. The new species, with higher molecular weight, probably belong to a kind of friction polymer, function as a boundary lubricant, and dramatically increase the antiwear effectiveness of the compound. The antiwear mechanisms of oxygen‐containing derivatives of HNCC are also discussed.