ABSTRACT
Aluminium is situated beneath boron in the same group of the periodic table. As the borate is a good antiwear agent of lubricating oils, it implies that aluminium compounds maybe possess similar antiwear property to borate. After testing seven alkoxy aluminium compounds, the results prove this assumption. The most efficient compound is triethoxy aluminium. When 2 mass % of triethoxy aluminium is added to ISO VG 68 oil, the load wear index of a fourball machine increases from 219 N to 519 N and the weld point from 1568 N to 4900 N. This compound also exhibits good corrosion protection property.
After the steel balls of the four-ball machine have been run in aluminium containing oil, its wear scars are analysed by scanning electron microscopy and X-ray energy dispersion analysis. The main compositions discovered on the scar surface are 5.7-48.3 atom % of iron, 4.4-11.2 atom % of aluminium, 37.1-59.1 atom % of oxygen, 8.7-23.5 atom % of carbon, and 0.3 - 1.1 atom % of chromium, under 3087 N -39 200 N of axial loads. When the loads are lower than 2450 N, the contents of oxygen are almost equal to zero and the contents of iron increase to 68.6-93.8 atom %. Based on the results of surface analysis and thermodynamic principles, the antiwear action mechanism of triethoxy aluminium is suggested, under low loads the weaker bond C-C (350 KJ/mol) is broken, the broken fragments may form polymer film during friction processes. As the loads increase, the stronger bond AI-0 (484.5 KJ/mol) is broken to create active aluminium and oxygen. The oxygen reacts with aluminium and iron to form a complicated solid solution containing AlxOY, FExOy on the surface. This complicated surface layer raises the weld point of the steel balls.
