This International Standard describes the procedure for the determination of the mass percentage of sulfated ash from unused lubricating oils containing additives and from additive concentrates additives used in compounding. These additives usually contain one or more of the following metals: calcium, magnesium, zinc, sodium, potassium and tin. The elements sulphur, phosphorus and chlorine can also be present in combined form.
Application of this procedure to sulfated ash levels below 0,02 % (m/m). The lower limit of applicability of the proecdure is 0,005 % (m/m).
This International Standard is not intended for the analysis of used engine oils containing oils, nor is it recommended for the analysis of non-additive lubricating oils, for which ISO 6245:1993, Petroleum products - Determination of ash, is suitable.
NOTE 1 There is evidence that magnesium does not react in the same manner as alkali metals in this procedure. If magnesium additives are present, the data should be interpreteded with caution.
NOTE 2 There is evidence that samples containing molybdenum can give low results, since molybdenum compounds are not fully recovered at the temperature of ashing.
The sulfate ash may be used to indicate the concentration of known metal-containing additives in new lubricating oils. When phosphorus is absent, barium, calcium, magnesium, sodium and potassium are converted to their sulfates and tin(IV) and zinc to their oxides (see note 3). Sulfur and chlorine do not interfere, but when phosphorus is present with metals, it remains partially or wholly in the sulphated ash as metal phosphates.
NOTE 3 Since zinc sulfate slowly decomposes to its oxide at the ignition temperature specified in the procedure, samples containing zinc may give variable results unless unless the zinc sulfate is completely converted to the oxide.