Evolution of ZDDP-derived reaction layer morphology with rubbing time

Functional additives, particularly extreme pressure and antiwear additives, in formulated oil will compete to adsorb and function in tribological contacts. A low-polarity commercial base oil, poly-α-olefin (PAO), blended with zinc dialkyl dithiophosphates (ZDDP) has been studied. The tribological performance was evaluated using a ball-on-disk test rig under mixed rolling-sliding conditions in the boundary lubrication regime at 90°C. An adapted in situ interferometry technique was used to monitor the additive-derived reaction layer formation. The thickness of the reaction layer evolves with rubbing until reaching a limiting thickness value of approximately 70 nm. The evolution of the topography and mechanical properties of the ZDDP-derived reaction layer with rubbing time were studied using Atomic Force Microscopy. A constant roughening and hardening of the additive-derived layer with rubbing time is observed and related to the different tribological performance of the layer at different rubbing times.     

Biodiesel production from castor oil in Brazil: A difficult reality

The Brazilian National Program for Production and Use of Biodiesel (PNPB in Portuguese) has created a huge demand for biodiesel in Brazil. The PNPB is strongly based on social development through the inclusion of family farmers in projects integrated with biodiesel power plants. Among the various oilseeds, castor bean (Ricinus communis L.) was identified as the ideal one to promote social development in the semi-arid region. However, although promising, the mechanisms of the federal program are still insufficient to promote the effective participation of family farmers. This research shows that companies are facing huge problems in implementing contracts with family farmers. It describes and analyzes the functioning dynamics of this agro-production chain. This paper addresses the identification and the discussion of these obstacles, in order to increase the competitiveness of the biodiesel agribusiness chain, based on castor oil social projects in Brazil.     

Behaviour of Corrosion Inhibitors Under Different Tribological Contact

Additives in lubrication technology perform by physically or chemically adsorbed films on tribological surfaces. In water lubricated tribosystems when the environment is very corrosive the additives effect is especially important. Typically applied corrosion inhibitors neutralize pH of contaminants in the fluid. Ethanolamines and ethylamines are known as ligands which can form chelate bonds with metals via their amino, hydroxyl and deprotonated hydroxyl groups. In tribology they are widely accepted, as corrosion inhibitors and detergents especially for water-based lubricants. This study inquires static corrosion behaviour of the solution as well as tribological performance in two types of tribotesters which represent different contact situations. Understanding the performance of the first chemisorbed layers of additives on the work piece yields important information for the optimization of lubrication in aqueous solutions. The structure of the adsorbed compounds based on amines on the tribological surfaces was studied with usage of angle-resolved X-ray photoelectron spectroscopy (ARXPS). Analysis of the ARXPS results was performed using stratification method, which provides information of the depth and relative amount of each element in each layer. The experimental results were compared with simulations performed with simulation of electron spectra for surface analysis software. The objective was to confirm the accuracy of the performed analysis.     

Effect of ZDDP on friction in fretting contacts

The effect of ZDDP on fretting wear was investigated in a ball on flat machine. The results confirm previous work that anti-wear agents may reduce friction and wear in fretting contacts. It was further found that temperature, adsorption time, base oil polarity as well as the presence of other surface active additives in the oil were all important parameters affecting the ability of ZDDP to protect the surfaces against fretting wear.