ASTM D874 Sulfated Ash from Lubricating Oils and Additives
Many lubricating oils contain metallic additives including zinc anti-wear compounds and magnesium detergents. The proper level of these additives is important for the lubricant to work properly. This method determines the concentration of metals (non-lead) in fully formulated lubricating oils and additive concentrates. It may be used as a quality control tool in new oils or as an indicator of additive depletion in used oils.
The sample is placed in a clean, dry crucible, heated and ignited to remove carbonaceous compounds. Sulfuric acid is added and the residue is heated to allow the sulfating reaction to occur. The crucible is ignited in a muffle furnace, cooled and weighed. The sulfuric acid/heat/muffle sequence is repeated until a constant weight is obtained. The percent sulfated ash is reported.