EXPLANATION
This test method covers the voltammetric determination of hindered phenol and aromatic amine antioxidants in new or used type non-zinc turbine oils in concentrations from 0.0075 mass % up to concentrations found in new oils by measuring the amount of current flow at a specified voltage in the produced voltammogram. This test method is not designed or intended to detect all of the antioxidant intermediates formed during the thermal and oxidative stressing of the oils, which are recognized as having some contribution to the remaining useful life of the used or in-service oil. Nor does it measure the overall stability of an oil, which is determined by the total contribution of all species present. Before making final judgment on the remaining useful life of the used oil, which might result in the replacement of the oil reservoir, it is advised to perform additional analytical techniques as in accordance with Test Methods ASTM D6224, ASTM D4378, and ASTM D2272, having the capability of measuring remaining oxidative life of the used oil.
This test method is applicable to non-zinc type of turbine oils as defined by ISO 6743 Part 4, Table 1. These are refined mineral oils containing rust and oxidation inhibitors but not antiwear additives. The test is also suitable for manufacturing control and specification accceptance.
TEST SUMMARY
A measured quantity of sample is dispensed into a vial containing a measured quantity of acetone based electrolyte solution and a layer of sand. When the vial is shaken, the hindered phenol and aromatic amine antioxidants and other solution soluble oil components in the sample are extracted into the solution, and the remaining droplets suspended in the solution are agglomerated by the sand. The sand/droplet suspension is allowed to settle out and the hindered phenol and aromatic amine antioxidants dissolved in the solution are quantified by voltammetric analysis. The results are calculated and reported as mass % of antioxidant or as mmol of antioxidant per litre of sample for prepared and fresh oils, and as a % remaining antioxidant for used oils.
TEST PRECISION
No information on bias can be presented since the result of this test is defined only in terms of this test method.