compounds has negligible effect on the ECT of oil, which is
less than 50 pC/ml. However, the significant increases in ECT
are detected by the thermal aging test [7]. BTA is commonly
used in Japan at the concentrations of 10 ppm and 34 ppm, the
latter of which is used in this experiment. DBPC is added at a
commonly used concentration of 3,000 ppm. The ECT of oil
is also less than 50 pC/ml when adding either of these
additives. The effects of two types of additives on two types
of sulfur compounds, which increase the ECT of oil, can be
investigated in this experiment.
Oil, copper catalyst and oxygen are placed together inside a
500 ml stainless-steel test receptacle and heated inside an oven
with a temperature deviation of 1 °C. The copper catalyst is a
1-mm-diameter hard drawn copper wire whose surface area is
298 cm2. 50 ml of air is added to the oil so that the oxygen
concentration in oil is 20,000 ppm. After the thermal aging
test, the ECT of oil is measured by the mini-static-tester
method [11] at room temperature. The structure of mini-static
tester is shown in Figure 2. An Oil sample is flowed to a paper
filter, which is placed in a filter holder and leakage current
from paper filter is measured by a electrometer. Table 1
summarizes the test conditions.